## Municipal Nutrient Removal Technologies Reference Document

EPA 832-R-08-006, September 2008

This document was prepared by the following staff from the Ann Arbor, Michigan, and Fairfax, Virginia, offices of Tetra Tech, Inc ., under U.S. Environmental Protection Agency (EPA) Contract EP-C-05-046.

Shin Joh Kang, Ph.D., P.E., Principal Author Kevin Olmstead, Ph.D., P.E., Author Krista Takacs, P.E., Author James Collins, Author and Project Manager



### Acknowledgements

EPA Office of Wastewater Mana gement staff and the authors would like to acknowledge the efforts of the following EPA-st ate project workgroup members:

Dan Murray

─ EPA

, ORD
Da vid Pin cumb e ─ EPA Region 1
Dav e Ragsdale

─ EPA Region 10 Denny Rowland

─ CT

, DEP Gary Johnson

─ CT

, DEP (formerly) Dr. Ta-Shan Yu

─ M D, MDE

The authors appreciate the revi ew and feedback on an early dr aft of the document that was conducted by the EPA Regions and also by se veral state permitti ng and water quality agencies, as coordinated by the Association of State and Inte rstate Water Pollution Control Agencies.

In addition, a formal technical review of the draft documen t was conducted by professionals with experience in wastewater treatment in accordance with EPA Peer Review Guidelines. While every effort was made to accommodate a ll of the Peer Review comments, the results and conclusions do not indicate consensus a nd may not represent the views of all the reviewers. The technical reviewers of this document included the following:Ms. Jeanette Brown, Executive Director, Wate r Pollution Control Authority, Stamford, CT

Sudhir Murthy, Ph.D., P.E., Manager for Pro cess Development, D.C. Water and Sewer Authority (DCWASA), Washington, DC

J.B. Neethling, Ph.D., PE, BECC, Senior Vice president, HDR, Inc., Folsom, CA

Amit Pramanik, Ph.D., BCEEM, Senior Program Director, Water Environment Research Foundation, Alexandria, VA

Clifford W. Randall, Ph.D., Professor, Virginia Polytechnic Institute and State University, Blacksburg, VA

H. David Stensel, Ph.D., PE, Professor, University of Washington, Seattle, WA

Printed copies of this document are printed w ith vegetable-based ink on paper that contains a minimum of 50 percent post-consumer fi ber content and is chlorine free.

Electronic copies of this document can be downloaded from EPA’s Office of Wastewater Management web site at: www.epa.gov/owm

Cover photo credits: Photo (lower left) courtesy of Enviroquip, Inc., Austin. Texas. Photo (upper right) courtesy of Natural Resources Conservation Service Photo inserts credit: Tetra Tech, Inc.

## Preface

The U.S. Environmental Protection Agency (E PA) is charged by Congress with protecting the nation’s land, air, and water resources. U nder a mandate of environmental laws, the Agency strives to formulate and implement actions leading to a balance between human activities and the ability of ecosystems to support and sustai n life. To meet this mandate, the Office of Wastewater Management (OWM) provi des information and technical support to solve environmental problems today and to build a knowledge base necessary to protect public health and the environment well into th e future. This publication was prepared under contract to EPA, by Tetra Tech, Inc. The docum ent provides current state of development as of the publication date; however, it is expected that this document will be revised periodically to reflec t advances in this rapidly evolvi ng area. Except as noted, information, interviews, and data development were conduc ted by the contractor. While there are many proven, cost-effective nutrient removal tec hnologies and numerous new technologies or modifications of existing technologies availabl e to detailed study, the case studies in this document were selected on the basi s of specific criteria. The crit eria included the ability to provide as least one year of full-scale operating and perf ormance data, capability of providing detailed capital and operation and main tenance cost breakdowns, and the ability to provide the data within the time frame esta blished for completing the document. It is anticipated that as the document is update d, additional case studie s on new technologies could be included. Some of the information, especially related to emer ging technologies, was provided by the manufacturer or vendor of th e equipment or technology and could not be verified or supported by a full-scale case study. In some cases , cost data were based on estimated savings without actual field data. Wh en evaluating technologies, estimated costs, and stated performance, efforts should be ma de to collect current and more up-to-date information.

The mention of trade names, specific vendors, or products does not represent an actual or presumed endorsement, preference, or acceptanc e by EPA or the federal government. Stated results, conclusions, usage, or practices do not necessarily represent th e views or policies of
EPA.

## How to use this document

EPA is providing this reference document to make information available on recent advances in nutrient removal technology and practices. The goal of this document is straightforward – to provide information that will assist local decision makers and regiona l and state regulators plan cost-effective nutrient removal projects for municipal wastewater treatment facilities. Volume 1 provides key information on technol ogies, case studies, and capital and O&M costs for retrofitting or expanding existing facilities.

Chapter 1 provides a brief history of nutrient removal in the United States which sets the stage for the detailed presentation of the curr ent status of nutrient removal practices and

costs.
Chapter 2 includes detailed information on commonly used biological and physiochemical nutrient removal technologies and preliminar y information on emerging phosphorus removal and side stream nitrogen removal processes. It presents detailed technical and cost information about both biological and physiochem ical treatment technologies. The technical information includes detailed process descriptions and operating factors for more than 40 different treatment alternatives for removi ng nitrogen, phosphorus, or both from municipal wastewater streams. The information also includes data on process performance and reliability that were developed from full-scal e operating data obtained voluntarily from 30 wastewater treatment plants throughout the Un ited States and in Ca nada. This extensive analysis allows decision makers to evaluate full-scale performance data obtained from specific facilities.

Chapter 3 provides a synthesis of the information generated from the nine fully scale case studies. The case studies facili ties represented a variety of technologies in both cold- and warm-weather locations were the subject of in-d epth discussion of the factors involved in successful process design and operation, as well as a detailed process cost analysis. The full case study reports are provided in Volume 2 of this document.

Chapter 4 contains information on general cost estimates for many of the available nutrient removal technologies for both retrofits and expans ion of existing faciliti es. The accuracy of the cost estimate will vary depending on the level of detail provided in the evaluation. If the cost estimate is based on cost curves or costs fr om similar facilities or technologies with very little consideration of local conditions, the co st estimate might be accurate to within only approximately 50 percent. If more detailed studies such as soil borings, preliminary engineering design drawings, and draft specifications are prepared, the estimate will be more

accurate.

Chapter 5 presents a set of cons iderations and an approach fo r planning for process upgrades that includes projecting future loads, assessi ng existing capabilities, preparing a mass balance that includes all return and recycle flows and loads, developing the needed expansion and upgrade that should incorporate flex ibility into the opera tion of the plant to account for futureuncertainties, evaluating feasible alternatives, and selecting the recommended plan. Chapter 5 also presents a list of technologies capable of meeting the selected ta rget effluent range for nitrogen, phosphorus, or both and technology selection factors to be considered in identifying and evaluating feasible technologi es on the basis of design and operational and cost factors.

Volume 2, Appendix A contains detailed case st udy reports for each of the nine facilities evaluated as part of this proj ect. The objective of the case st udies was to present the data from selected technologies for a one-year period; to identify the factors th at contribute to the reliability of nitrogen and phosphorus removal; to identify the factors that contribute to the costs of various removal technologies; and to evaluate the reliability of nutrient removal through a simple, yet sound statistical method by which performance data could be presented and compared.

Volume 2, Appendix B provides th e technical and statistical ba sis of using coefficient of variation to describe performance reliability.September 2008 Municipal Nutrient Remo val Technologies Reference Document

i 

## Contents

Volume 1 – Technical Report Executive Summary

Chapter 1. Introduction and Histor y 1.1 Overview ......................................................................................................1-1 1.2 Background of Nitrogen and Phosphorus Removal in the United States.....1-2 1.2.1 Lake Tahoe .....................................................................................1-3 1.2.2 Great Lakes.....................................................................................1-4 1.2.3 The Occoquan Reservoir and the Chesapeake Bay.......................1-6 1.3 NPDES Permitting........................................................................................1-8 1.3.1 Watershed-based Permitting and Water Quality Trading................1-8 1.4 References .................................................................................................1-10

Chapter 2. Treatment Technologies and Technology Matrix 2.1 Overview ......................................................................................................2-1 2.2 Nitrogen Removal Processes.......................................................................2-1 2.2.1 Nitrogen Species in Wastewater .....................................................2-1 2.2.2 Nitrogen Removal Factors ..............................................................2-3 2.2.3 Nitrogen Removal Technologies .....................................................2-9 2.3 Phosphorus Removal Processes ...............................................................2-27 2.3.1 Biological Phosphorus Removal ...................................................2-27 2.3.2 Chemical Phosphorus Removal....................................................2-31 2.3.3 Phosphorus Removal Technologies .............................................2-35 2.4 Nitrogen and Phosphorus Removal Processes..........................................2-48 2.4.1 Nitrogen and Phosphorus Removal Factors .................................2-48 2.4.2 Nitrogen and Phosphorus Removal Technologies........................2-50 2.5 Full-Scale Nutrient Removal Process Cases..............................................2-57 2.5.1 Nitrogen Removal Matrix and Variability Data...............................2-57 2.5.2 Phosphorus Removal Matrix and Variability Data.........................2-66 2.5.3 Combined Nitrogen and Phosphorus Removal Matrix and Variability Data ..............................................................................2-74 2.6 Summary ....................................................................................................2-77 2.6.1 Performance and Variability ..........................................................2-77 2.6.2 Nitrogen Removal Technologies ...................................................2-80 2.6.3 Phosphorus Removal Technologies .............................................2-80 2.6.4 Combined Nitrogen and Phosphorus Removal Technologies.......2-80 2.7 References .................................................................................................2-81 Attachment 1: Locations Providing Data .............................................................2-91

Chapter 3. Case Studies and Reliability Factors 3.1 Introduction and Overview............................................................................3-1 3.1.1 Permit Limits for the Case Study Facilities......................................3-1 3.2 Summary of Case Studies............................................................................3-4 3.2.1 Total Nitrogen and Phosphorus Removal at Low Concentration Limits (3 mg/L or less in TN) ...........................................................3-4Municipal Nutrient Removal Technologies Reference Document September 2008

ii 3.2.2 Total Nitrogen and Phosphorus Removal at Mid-Level Concentration Limits (3 to 6 mg/L)................................................ 3-15 3.2.3 Phosphorus Removal Low Level (less than 0.1 mg/L).................. 3-24 3.3 Reliability Factors....................................................................................... 3-29 3.3.1 Wastewater Characteristics .......................................................... 3-29 3.3.2 Fermenter and VFA Generation.................................................... 3-30 3.3.3 Bioreactor Design and Process Parameters................................. 3-31 3.3.4 Secondary Sludge Thickening ...................................................... 3-32 3.3.5 Sludge Digestion........................................................................... 3-32 3.3.6 Recycle Flows and Loads ............................................................. 3-32 3.3.7 Wet-Weather Flow Management .................................................. 3-33 3.3.8 Tertiary Filters ............................................................................... 3-34 3.3.9 Tertiary Clarifier............................................................................. 3-34 3.4 Cost Factors............................................................................................... 3-37 3.4.1 Capital Costs................................................................................. 3-37 3.4.2 Operation and Maintenance Costs................................................ 3-40 3.4.3 Unit Costs...................................................................................... 3-41 3.5 Summary.................................................................................................... 3-43 3.5.1 Discharge Permits......................................................................... 3-43 3.5.2 Phosphorus Removal.................................................................... 3-44 3.5.3 Nitrogen Removal ......................................................................... 3-46 3.5.4 Costs for Capital and O&M ........................................................... 3-48 3.6 References................................................................................................. 3-49

Chapter 4. Cost Factors 4.1 Modifying Existing Facilities ......................................................................... 4-1 4.1.1 Literature Review ............................................................................ 4-1 4.1.2 Case Studies................................................................................... 4-3 4.2 Retrofit Process Cost Models....................................................................... 4-4 4.2.1 CAPDETWorks ............................................................................... 4-5 4.2.2 Retrofit Phosphorus Removal Technologies................................... 4-8 4.2.3 Retrofit Nitrogen Removal Technologies ...................................... 4-12 4.2.4 Combined Nitrogen and Phosphorus Scenarios........................... 4-16 4.3 Expansion Process Cost Models................................................................ 4-19 4.3.1 Phosphorus Removal Technologies ............................................. 4-19 4.3.2 Nitrogen Removal Technologies................................................... 4-24 4.3.3 Combined Nitrogen and Phosphorus Scenarios........................... 4-29 4.4 Discussion of Cost Factors......................................................................... 4-33 4.5 Summary.................................................................................................... 4-34 4.6 References................................................................................................. 4-35

Chapter 5. Upgrading Existing Facilites 5.1 General Approach to Upgrading................................................................... 5-1 5.1.1 Success Criteria.............................................................................. 5-1 5.1.2 Facility Planning.............................................................................. 5-2 5.2 Available Technologies ................................................................................ 5-2 5.3 Technology Selection Criteria ...................................................................... 5-6 5.3.1 Nitrogen Removal ......................................................................... 5-11 5.3.2 Phosphorus Removal Plant Factors.............................................. 5-14September 2008 Municipal Nutrient Remo val Technologies Reference Document

iii 5.3.3 Nitrogen and Phosphorus Removal Plant Factors ........................5-18 5.4 Design and Operational Factors in Nutrient Removal ................................5-18 5.4.1 Influent Wastewater Characteristics..............................................5-21 5.4.2 Sources of Biodegradable Carbon ................................................5-23 5.4.3 Impact of Wet-Weather Flows.......................................................5-24 5.4.4 Managing Sludge-Handling Processes .........................................5-25 5.4.5 Recycle Flows ...............................................................................5-26 5.4.6 SCADA Requirements and Sensors .............................................5-29 5.4.7 Staffing Requirements...................................................................5-29 5.4.8 Training Needs..............................................................................5-29 5.4.9 Pilot Testing ..................................................................................5-30 5.5 Finalizing Process Selection ......................................................................5-30 5.6 Summary ....................................................................................................5-32 5.7 References .................................................................................................5-34

Volume 2 - Appendices

Appendix A – Case Studies Denitrification Central Johnston County, NC Lee County, FL Phosphorus removal Kalispell, MT Clark County, NV Nitrogen and phosphorus removal Kelowna, BC Marshall Street in Clearwater, FL Noman Cole in Fairfax County, VA North Cary, NC Western Branch in Upper Marlboro, MD

Appendix B – Reliability and Coefficient of Variation



### Figures
Figure 2-1. Denitrifying filter process. ................................................................................2-10 Figure 2-2. Biological upflow filter. .....................................................................................2-11 Figure 2-3. Modified Ludzack-Ettinger process..................................................................2-12 Figure 2-4. Cyclically aerated activated-sludge process....................................................2-12 Figure 2-5. Four-stage Bardenpho process. ......................................................................2-13 Figure 2-6. Oxidation ditch process. ..................................................................................2-14 Figure 2-7. Integrated fixed-film activated sludge process.................................................2-16 Figure 2-8. Moving-bed biofilm reactor process.................................................................2-17 Figure 2-9. MBR process. (a) External filter in lieu of clarifier;...........................................2-18 Figure 2-9. MBR process. (b) In-tank filter.........................................................................2-19 Figure 2-10. Step-feed activated sludge process...............................................................2-20 Figure 2-11. Biodenitro process.........................................................................................2-21 Figure 2-12. Schreiber countercurrent aeration process....................................................2-22Municipal Nutrient Removal Technologies Reference Document September 2008

iv Figure 2-13. Sequencing batch reactor..............................................................................2-23 Figure 2-13A. InNitri process. ............................................................................................2-24 Figure 2-13B. BABE process. ............................................................................................2-25 Figure 2-13C. SHARON process .......................................................................................2-26 Figure 2-13D. ANAMMOX process....................................................................................2-27 Figure 2-14. Fermentation process....................................................................................2-35 Figure 2-15. A/O (Phoredox) process. ...............................................................................2-36 Figure 2-16. Oxidation ditch with anaerobic zone..............................................................2-37 Figure 2-17. Phosphorus chemical/filter process...............................................................2-38 Figure 2-18. Parkson Dynasand D2 advanced filter system..............................................2-44 Figure 2-19. CoMag process. ............................................................................................2-46 Figure 2-20. Blue-PRO process.........................................................................................2-47 Figure 2-21. U.S. Filter Trident process.............................................................................2-47 Figure 2-22. A2O process..................................................................................................2-50 Figure 2-23. Five-stage modified Bardenpho process. ......................................................2-51 Figure 2-24. University of Cape Town process..................................................................2-52 Figure 2-25. Modified University of Cape Town process. ..................................................2-53 Figure 2-26. Virginia Initiative process...............................................................................2-54 Figure 2-27. Johannesburg process. .................................................................................2-54 Figure 2-28. Biodenipho (phased isolation ditch) process. ................................................2-55 Figure 2-29. Blue Plains process. ......................................................................................2-56 Figure 2-30. Westbank process (Kelowna, British Columbia)............................................2-57 Figure 2-31. Monthly average frequency curves for TN: low-range removal. ....................2-60 Figure 2-32. Concentric oxidation ditch. ............................................................................2-63 Figure 2-33. Monthly average frequency curves for TN—mid-range removal. ..................2-65 Figure 2-34. Monthly average frequency curves for ammonia nitrogen.............................2-66 Figure 2-35. Monthly average frequency curves for TP—low-end removal.......................2-70 Figure 2-36. Monthly frequency curves for TP removal—mid-range removal....................2-73 Figure 3-1. Western Branch WWTP: Monthly frequency curves for TP...............................3-5 Figure 3-2. Western Branch WWTP: Monthly frequency curves for ammonia nitrogen.......3-6 Figure 3-3. Western Branch WWTP: Monthly frequency curves for TN...............................3-7 Figure 3-4. Lee County, Florida: Monthly frequency curves for TP. ....................................3-8 Figure 3-5. Lee County, Florida: Monthly frequency curves for TN. ....................................3-8 Figure 3-6. Johnston County, North Carolina: Monthly average frequency curves for TP............................................................................................................................. ....3-10 Figure 3-7. Johnston County, North Carolina: Monthly average frequency curves for ammonia nitrogen. .......................................................................................................3-10 Figure 3-8. Johnston County, North Carolina: Monthly average frequency curves for TN. ............................................................................................................................ ...3-11 Figure 3-9. Marshall Street Advanced WWTP, Clearwater, Florida: Monthly average frequency curves for TP...............................................................................................3-13 Figure 3-10. Marshall Street Advanced WWTP, Clearwater, Florida: Monthly average frequency curves for ammonia nitrogen.......................................................................3-13 Figure 3-11. Marshall Street Advanced WWTP, Clearwater, Florida: Monthly average frequency curves for TN...............................................................................................3-14 Figure 3-12. North Cary, North Carolina: Monthly average frequency curves for TP. .......3-15 Figure 3-13. North Cary, North Carolina: Monthly average frequency curves for ammonia nitrogen. .......................................................................................................3-16 Figure 3-14. North Cary, North Carolina: Monthly average frequency curves for TN. .......3-16September 2008 Municipal Nutrient Remo val Technologies Reference Document

v Figure 3-15. Kelowna, British Columbia: Monthly average frequency curves for TP. ........3-18 Figure 3-16. Kelowna, British Columbia: Monthly average frequency curves for ammonia nitrogen. .......................................................................................................3-19 Figure 3-17. Kelowna, British Columbia: Monthly average frequency curves for TN.........3-19 Figure 3-18. Noman M. Cole Pollution Contro l Plant, Fairfax County, Virginia: Monthly average frequency curve for TP...................................................................................3-21 Figure 3-19. Noman M. Cole Pollution Contro l Plant, Fairfax County, Virginia: Monthly average frequency curve for ammonia nitrogen...........................................................3-22 Figure 3-20. Noman M. Cole Pollution Contro l Plant, Fairfax County, Virginia: Monthly average frequency curve for TN...................................................................................3-22 Figure 3-21. Clark County Water Reclamation Plant, Las Vegas, Nevada: Monthly average frequency curve for TP...................................................................................3-25 Figure 3-22. Clark County Water Reclamation Plant, Las Vegas, Nevada: Monthly average frequency curve for TN...................................................................................3-26 Figure 3-23. Clark County Water Reclamation Plant, Las Vegas, Nevada: Monthly average frequency curve for ammonia nitrogen...........................................................3-26 Figure 3-24. Kalispell, Montana: Monthly average frequency curve for TP. ......................3-28 Figure 3-25. Kalispell, Montana: Monthly average frequency curve for ammonia nitrogen. ...................................................................................................................... .3-28 Figure 3-26. Kalispell, Montana: Monthly average frequency curve for TN. ......................3-29 Figure 4-1. O&M costs for retrofit phosphorus removal technologies ($/MG treated)........4-11 Figure 4-2. Capital costs for retrofit phosphorus technologies ($ per gpd capacity). .........4-11 Figure 4-3. Life-cycle costs for retrofit phosphorus removal technologies ($/MG treated)....................................................................................................................... ..4-12 Figure 4-4. Capital costs for retrofit nitrogen removal scenarios........................................4-14 Figure 4-5. O&M costs for retrofit nitrogen removal scenarios...........................................4-15 Figure 4-6. Life-cycle costs for retrofit nitrogen removal scenarios....................................4-15 Figure 4-7. Capital costs for retrofit nitrogen plus phosphorus removal technologies. ......4-17 Figure 4-8. O&M costs for retrofit nitrogen plus phosphorus removal technologies. .........4-18 Figure 4-9. Life-cycle costs for retrofit nitrogen plus phosphorus removal technologies. ..4-18 Figure 4-10. O&M costs for expansion phosphorus removal technologies ($/MG treated)....................................................................................................................... ..4-22 Figure 4-11. Capital costs for expansion phosphorus removal technologies.....................4-22 Figure 4-12. Life-cycle costs for expansion phosphorus removal technologies.................4-23 Figure 4-13. Component percentages of total O&M costs for 1 MGD expansion phosphorus removal technologies. ..............................................................................4-23 Figure 4-14. Component percentages of total O&M costs for 10 MGD expansion phosphorus removal technologies. ..............................................................................4-24 Figure 4-15. Capital costs for expansion nitrogen removal scenarios. ..............................4-26 Figure 4-16. O&M costs for expansion nitrogen removal scenarios. .................................4-27 Figure 4-17. Life-cycle costs for expansion nitrogen removal scenarios. ..........................4-27 Figure 4-18. Component percentages of total O&M costs for 1 MGD expansion nitrogen removal technologies. ....................................................................................4-28 Figure 4-19. Life-cycle costs for expansion nitrogen plus phosphorus removal technologies. ................................................................................................................4- 28 Figure 4-20. Component percentages of total O&M costs for 10 MGD expansion nitrogen removal technologies. ....................................................................................4-29 Figure 4-21. Capital costs for expansion nitrogen plus phosphorus removal technologies. ................................................................................................................4- 31Municipal Nutrient Removal Technologies Reference Document September 2008

vi Figure 4-22. O&M costs for expansion nitrogen plus phosphorus removal technologies. .4-31 Figure 4-23. Life-cycle costs for expansion nitrogen plus phosphorus removal technologies.................................................................................................................4- 32 Figure 4-24. Component percentages of total O&M costs for 1 MGD expansion nitrogen plus phosphorus removal technologies..........................................................4-32 Figure 4-25. Component percentages of total O&M costs for 10 MGD expansion nitrogen plus phosphorus removal technologies..........................................................4-33



### Tables
Table ES-1. Cost estimates for retrofit technologies.............................................................14 Table ES-2. Cost estimates for expansion technologies for 10 MGD...................................20 Table 2-1. Process Performance Data: Nitrogen Removal—Plant Effluent.......................2-58 Table 2-2. Detailed curve information for Case Study Facilities in Figure 2-31 .................2-61 Table 2-3. Detailed curve information for Case Study Facilities in Figure 2-33 .................2-65 Table 2-4. Detailed curve information for Case Study Facilities in Figure 2-34 .................2-66 Table 2-5. Process Performance Data: Phosphorus Removal—Plant Effluent .................2-67 Table 2-6. Detailed curve information for Case Study Facility in Figure 2-35....................2-70 Table 2-7. Detailed curve information for Case Study Facilities in Figure 2-36 .................2-73 Table 2-8. Process Performance Data: Nitrogen and Phosphorus Removal— Plant Effluent................................................................................................................2 -78 Table 3-1. Discharge permit limits and performance data summary ...................................3-2 Table 3-2. Statistical comparison of Canadian and U.S. permit limits .................................3-4 Table 3-3. Monthly variation of wastewater characteristics at Fairfax County, Virginia .....3-30 Table 3-4. Case study facilities’ treatment processes........................................................3-35 Table 3-5. Case study facilities’ capital costs .......................................................................38 Table 4-1. Upgrade costs for Maryland, Connecticut, and others........................................4-2 Table 4-2. Upgrade costs for case studies ..........................................................................4-3 Table 4-3. Cost factors used in CAPDETWorks estimates..................................................4-6 Table 4-4. Comparison of CAPDETWorks and actual costs for Clearwater, Florida, and Kalispell, Montana..........................................................................................................4-7 Table 4-5. Cost model influent wastewater parameters.......................................................4-8 Table 4-6. Process parameters for phosphorus removal scenarios ..................................4-10 Table 4-7. Process parameters for nitrogen removal scenarios ........................................4-13 Table 4-8. Process parameters for nitrogen removal scenarios ........................................4-16 Table 4-9. Process parameters for phosphorus removal scenarios ..................................4-20 Table 4-10. Process parameters for nitrogen removal scenarios ......................................4-25 Table 4-11. Process parameters for combined nitrogen and phosphorus removal scenarios...................................................................................................................... 4-30 Table 5-1. Process list: TP...................................................................................................5 -3 Table 5-2. Process list: TN...................................................................................................5 -4 Table 5-3. Process list: ammonia nitrogen...........................................................................5-4 Table 5-4. Process list: TN plus TP .....................................................................................5-5 Table 5-5. Technology selection matrix: nitrogen removal ..................................................5-7 Table 5-6. Technology selection matrix: phosphorus removal.............................................5-8 Table 5-7. Technology selection matrix: nitrogen and phosphorus removal........................5-9 Table 5-8. Decision matrix example 1................................................................................5-31 Table 5-9. Decision matrix example 2................................................................................5-32September 2008 Municipal Nutrient Remo val Technologies Reference Document

vii 

## Acronyms/Abbreviations

Al 3 Aluminum sulfate (or Alum)

ANAMMOX anaerobic ammonia oxidation

ASCE American Society of Civil Engineers

A/O anoxic/oxic

A2/O anaerobic/anaerobic/oxic

AS activated sludge

AT 3 Aeration Tank 3 process

BABE bio-augmentation batch enhanced

BAF biological aerated filter
BAR bioaugmentation reaeration

BASIN biofilm activated sl udge innovative nitrifiation

BNR biological nutrient removal

BOD biochemical oxygen demand
BOD-to-TKN biochemical oxygen demand-to -total Kjeldahl nitrogen ratio

BOD-to-TP biochemical oxygen demand-to-total phosphorus ratio

BPR biological phosphorus removal
CANON completely autotrophic n itrogen removal over nitrite

CAS cyclic activated sludge

CBOD carbonaceous biochemical oxygen demand

COD chemical oxygen demand

COV coefficient of variation

CP central plant

CWSRF Clean Water State Revolving Fund

DAF dissolved-air flotation unit

DO dissolved oxygen

DON dissolved organic nitrogen

EBPR enhanced biological phosphorus removal

ENR Engineering News-RecordMunicipal Nutrient Removal Technologies Reference Document September 2008

viii EPA Environmental Protection Agency

FeCl 3 ferric chloride

FFS fixed-film systems

GAO glycogen accumulating organism
GPD gallons per day

HDWK headworks

HCO 3 - bicarbonate

H 2 CO 3 carbonic acid
HRT hydraulic retention time

IFAS integrated fixed-film activated sludge

I&C instrumentation and control
kWh/year kilowatt-hours per year

MAUREEN mainstream autotrophic recycled enhanced N-removal
MBBR moving-bed biofilm reactor

MBR membrane bioreactor

MG million gallons

MGD million gallons per day
mg/L milligrams per liter (equivalent to parts per million)

LE modified Ludzack-Ettinger

MLSS mixed liquor suspended solids

MW molecular weight
N nitrogen

NH 4 ammonium

NH4-N ammonia nitrogen

NL no limit

NPDES National Pollutant Discharge Elimination System

OLAND oxygen limited aerobic nitr ification-denitrification

ORP oxidation-reduction potential

O&M operation and maintenance

PAO phosphate accumulating organismsSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

ix PID phased isolation ditch

PLC programmable logic controller

PO 4 3- phosphate

POTWs publicly owned treatment works

RAS return-activated sludge

rbCOD readily biodegradable carbonaceous oxygen demand
rDON refractory dissolv ed organic nitrogen

SCADA supervisory control and data acquisition
SBR sequencing batch reactor SE secondary effluent

SND simultaneous nitrifica tion and denitrification

SF subsurface flow
SHARON single reactor high-activi ty ammonia removal over nitrate

SRT solids retention time

TMDL total maximum daily load

TKN total Kjeldahl nitrogen

TN total nitrogen

TP total phosphorus

TRPA Tahoe Regional Planning Agency

TSS total suspended solids

UCT University of Cape Town

UV ultraviolet

VFA volatile fatty acids

VIP Virginia Initiative process

VSS volatile suspended solids

WAS waste activated sludge

WEF Water Environment Federation

WERF Water Environment Research Foundation
WQBEL water quality-based effluent limit

WWTP wastewater treatment plantSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Executive Summary ES-1 

## Executive Summary

One of the major concerns regarding constituen ts in municipal wastewater treatment plant discharges is the concentrati on of nutrient compounds, in part icular nitrogen and phosphorus. Nutrients stimulate the growth of microorganisms (includi ng algae) and other aquatic vegetation in receiving waters, leading to d ecreased oxygen levels. Excess nutrients are a significant water quality concern in many of the nation’s wate rs and a leading cause of impairment of designated uses. Wastewater treatment plants that employ conventional biological treatment processes designed to m eet secondary treatment effluent standards typically do not remove total nitr ogen (TN) or total phosphorus (TP) to an extent sufficient to protect certain receiving waters. Wastewater treatment facilities are increasingly being required to address this issue by implementi ng treatment processes that reduce effluent nutrient concentrations to levels that regul ators deem sufficiently protective of the environment. Such implementation usually i nvolves retrofitting the plant to enhance the biological treatment processes or to include chemical tr eatment to effect phosphate precipitation. The challenge for those faciliti es, however, is to determine which treatment alternatives will best meet their needs, both technically and financially, and to make the decision that is most sustainable.



### Purpose of this Document

This reference document includes technical in formation developed to assist municipal decisionmakers and regional and state regulat ors in planning for nutrient removal from municipal wastewater streams. Consequently, it is not intended to be a design manual for use by engineers in generating design parameter values or drawings. It presen ts detailed technical and cost information about bot h biological and physiochemical treatment technologies. The technical information includes detailed proce ss descriptions and opera ting factors for more than 40 different treatment al ternatives for removing nitr ogen, phosphorus, or both from municipal wastewater streams. The informati on also includes data on process performance and reliability that were de veloped from full-scale operating data obtained voluntarily from 30 wastewater treatment plants throughout the United States and in Canada. This extensive analysis allows decisionmakers to evaluate full-scale performance data obtained from specific facilities. Nine of the f acilities were the subject of in-d epth case studies that further examined the factors involved in successful process design a nd operation, as well as process cost analysis. Case study summaries ar e provided in Volume II, Appendix A.

Cost information for various technologies was al so developed from literature sources, as well as from the facilities contacted for the case studies for this document. Capital and operation and maintenance (O&M) cost estimates in 2007 dollars were determined for the nine case study facilities. In addition, capital , O&M, and life-cycle costs we re estimated for 12 retrofitMunicipal Nutrient Removal Technologies Reference Document September 2008

ES-2 Executive Summary and 20 expansion alternatives using CAPDET Works software (Hydromantis Corporation, Ontario, Canada).



### Content of Document

The document has five chapters. Chapter 1 pr ovides a brief introduc tion and history of nutrient removal at wastewater treatment plan ts. Chapter 2 provides an overview of more than 40 alternative technologies that are av ailable for providing nitrogen and phosphorus removal in municipal wastewater treatment. Nitrogen removal technologies are based on biological nitrification-denitrif ication because that is the generally preferred method for removing nitrogen. Both chemical and biol ogical methods for phosphorus removal are described. The technologies disc ussed range in complexity from one-point chemical addition for phosphorus precipitation to a 5-stage Ba rdenpho system for combined biological phosphorus and nitrogen removal. The descriptions include pro cess configurations, factors important in design and operation, and observed ra nges of effluent con centrations. Chapter 3 of the document summarizes important findi ngs of the case studies and associated technologies. Information on capital operations, maintenance, and life-cycle costs is provided in Chapter 4. Finally, Chapter 5 presents info rmation about upgrading existing faci lities for those who are evaluating the use of nutrient removal technologies.



### Technologies, Performance, and Reliability

Chapter 2 provides operating results from 30 full-scale treatment facilities. Full-scale operating data were obtained from these facili ties on a voluntary basis and analyzed for the reliability of nitrogen and phosphorus removal, as applicable under the facility’s National Pollutant Discharge Elimination System (NPDES) permit or, in some cases, where facilities voluntarily achieved removal results above and beyond the NPDES requirements. Most of the facilities are throughout the United States; on e is in Canada. It should be emphasized that the performance data for these facilities re flect differences in operating philosophy, permit limitations, temperature, influent conditions, fl ow conditions, and the relative plant load compared to design. Thus, the documented performance does not necessarily represent optimum operation of the technologies presented.



### Common Statistical Base

Performance data from the fac ilities are presented in Tables 2-1, 2-5, and 2-8 for nitrogen removal, phosphorus removal, and combin ed nitrogen plus phosphorus removal, respectively. In general, performance was a ffected by both the sele cted technology and the permit limit for each substance. The data pres ented include the range of monthly average effluent concentrations observed at the facili ty, as well as concentr ations corresponding to the statistically derived values for the annua l average, maximum month, maximum week, and maximum day, as data were available. These concentrations were de rived by plotting the monthly average effluent concentrations for a year in ascending order on probability paper.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Executive Summary ES-3 The annual average corresponded to the average, or the 50 percent probability, while the monthly maximum corresponded to the 92 percent pr obability. The sl opes of these reliability

curves corresponded to the reliability, or variability as defined statistically: lower slopes meant that the process as implemented at that facility would produce more consistent effluent parameter values compared to processes impl emented elsewhere with higher slopes. These slopes are related to the coefficient of variati on (COV) for the data set, which is defined as one standard deviation divided by the mean. To a ttain the same target effluent concentrations (e.g., meet the same NPDES limits), treatment processes with a lo w (e.g., 20 percent) COV are considered more reliable , whereas those with a hi gh (e.g., 60 percent) COV are considered less reliable, because they are more variable . Appendix B, in Volume II of this document, presents detailed information a bout this technique. C OV alone might not be sufficient to evaluate the perfor mance of treatment processes.



### Performance of Technologies Technologies are available to reliably attain an annual average of 0.1 milligram per liter (mg/L) or less for TP and 3 mg/L or less for TN . Reliability curves were developed for the 9 case studies and for 21 other faci lities for which suitable data were acquired from plants that removed TN, TP, and both TN and TP. The reliab ility of the plants that were required to remove ammonia nitrogen is also included.

Nitrogen Removal The nitrogen removal processes evaluate d for this document all employ biological nitrification of ammonia nitr ogen and organic nitrogen under aerobic conditions. Most of the systems also employ biological denitrificati on under anoxic conditions. Table 2-1 presents effluent TN concentrations re ported by 19 facilities. The perf ormances were grouped into three categories: (1) high effl uent nitrogen (annual average concentrations above 5 mg/L TN); (2) medium effluent nitrogen (annual aver age concentrations between 3 and 5 mg/L); and (3) low effluent nitrogen (annual average co ncentrations below 3 mg/L TN). Reliability curves are presented in Chapter 2, Figures 2- 31 and 2-33, for low and medium effluent TN, respectively.

The following seven systems reported annual average concentrations above 5 mg/L:

• Johannesburg process, Hagerstown, Ma ryland, full-year data, 7.86 mg/L, COV 21 percent

• Virginia initiative process (VIP), lite rature report, 6.12 mg/L, no COV available

• Step-feed activated-sludge (AS) process, Cumberland, Maryland, full-year data, 6.7 mg/L, COV 27 percent

• Anerobic/anox/oxic (A 2 O) process, literature report , 7.3 to 9.0 mg/L, no location or COV availableMunicipal Nutrient Removal Technologies Reference Document September 2008

ES-4 Executive Summary • Schreiber process, litera ture report, 8 mg/L, no location or COV available

• Blue Plains process, as d one at the Blue Plains facility in Washington, D.C., 7.5 mg/L, no COV available

• Step-feed AS, Fairfax County, Virginia , case study, 5.25 mg/L , 12 percent COV

Six processes were found to generate annual average effluent TN between 3 and 5 mg/L:

• Cyclic on-off (operational air adjustment ), Ridgefield, Connecticut, full-year data, 4.59 mg/L, COV 25 percent

• Sequencing batch reactor, Thomaston, Connecticut, full-year data, 4.59 mg/L, 50 percent COV

• Modified Ludzack-Ettinger (MLE), West minster, Maryland, full-year data, 4.35 mg/L, 23 percent COV

• Westbank process, Kelowna, British Columbia (Canada), case study, 4.38 mg/L, 12 percent COV

• Phased isolation ditches (PIDs), Jewett Ci ty, Connecticut, full-year data, 4.2 mg/L, 42 percent COV

• Biological anoxic filters, Cheshire, Connecticut, two-thirds-year data, 3.6 mg/L, 62 percent COV

Seven processes were found to produce annual av erage effluent TN levels below 3 mg/L:

• Integrated fixed-film activ ated sludge (IFAS), literatu re, 2.8 mg/L (low observed value), no location or COV available

• Concentric ring oxidation ditch, Hammonton, New Jersey, full-year data, 3 mg/L, 32 percent COV

• Step-feed AS, Piscataway, Maryland, full-year data, 2.58 mg/L, 57 percent COV

• 5-stage Bardenpho, Clearwater, Florida– Marshall Street facility, case study, 2.32 mg/L, 16 percent COV

• 5-stage Bardenpho, Clearwater, Florida–Nort heast facility, full -year data, 2.04 mg/L, 42 percent COV

• Denitrification filter, Ce ntral Johnston County, North Carolina, case study, 2.14 mg/L, 16 percent COV

• Denitrification filter, Le e County, Florida, case study, 1.71 mg/L, 28 percent COVSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Executive Summary ES-5 • 3-sludge process including denitrifying AS , Western Branch, Maryland, case study, 1.6 mg/L, 36 percent COV

Phosphorus Removal Table 2-5 in Chapter 2 presents effluent TP concentration reported by 17 facilities. Most systems employed chemical treatmen t to effect part or all of th e TP removal, except as noted. The performances were grouped into two cat egories––low effluent phosphorus (annual average concentrations between 0.1 and 0.5 mg /L TP) and very low effluent phosphorus (annual average concentrations below 0.1 mg/L TP). The corresponding groups of reliability curves are presented in Chapter 2, Figures 2- 35 and 2-36, for very low and low effluent TP, respectively.

The following six systems reported producing an annual average effluent TP between 0.1 and 0.5 mg/L:

• VIP, literature report, 0.4 mg/L, no COV available

• University of Cape Town (UCT) process with filter, Penticton, British Columbia, literature report, 0.3 mg/L, no COV available

• Anoxic/oxic (A/O) process (no chemical and no filter), Genesee County, Michigan, full-year data, 0.24 mg/L, 50 percent COV

• The Westbank process with fermenter and filter, Kelowna, British Columbia, case study, 0.139 mg/L, 12 percent COV

• A 2 O with volatile fatty acid (VFA), chemical , tertiary clarifier, and filter, Durham, Oregon, full-year data, 0.132 mg/L, 33 percent COV

• Modified UCT with fermenter and filter, Kalispell, Montana, case study, 0.12 mg/L, 19 percent COV

Eleven systems reported producing an annual av erage effluent TP at or below 0.1 mg/L:

• A/O with filter, Clark County, Nevada , case study, 0.1 mg/L, 30 percent COV

• PhoStrip with filter, Truckee Meadows, Nevada, literature report, < 0.1 mg/L, no COV available

• Oxidation ditch with denitrif ication filter with alum, L ee County, Florida, case study, 0.098 mg/L, 47 percent COV

• Chemical addition with flocculating clarif ier, Chelsea, Michigan, full-year data, 0.09 mg/L, 14 percent COVMunicipal Nutrient Removal Technologies Reference Document September 2008

ES-6 Executive Summary • Step-feed AS with fermen ter and filter, Fairfax County, Virginia, case study, 0.09 mg/L, 21 percent COV

• Membrane bioreactor, Hyrum, Utah, fu ll-year data, 0.07 mg/L, 107 percent COV

• Chemical addition with tertiary clarifie r and filter, McMinnville, Oregon, seasonal (6 months) data, 0.058 mg/L, 63 percent COV

• 5-Stage Bardenpho with chemical and filter, Pinery, Colorado, 0.031 mg/L, 34 percent COV

• Membrane bioreactor, Lone Tree Cree k, Colorado, 0.027 mg/L, 27 percent COV

• Enhanced biological phosphorus removal with chemical addition and filter, Breckenridge, Colorado, literature report, 0.01 mg/L, no COV available

• Chemical addition with tertiary filter a nd infiltration basin, Brighton, Michigan, full year data, 0.01 mg /L, 0 percent COV

Combined Nitrogen and Phosphorus Removal Table 2-8 in the document presents effluent TN and TP concentrations reported by 12 facilities. Most systems employed chemical treatment to effect pa rt or all of the TP removal, except as noted. The facilities we re divided into three groups: t hose with TN greater than 5 mg/L; those with TN less than 5 mg/L a nd TP between 0.1 mg/L and 0.5 mg/L; and those with TN less that 5 mg/L and TP less than 0.1 mg/L. The reliability curves for nitrogen removal for these facilities are included in Chapter 2, Figures 2-31 and 2-33; the reliability curves for phosphorus removal for these facili ties are included in Figures 2-35 and 2-36.

The following five systems reported an annual average TN over 5 mg /L and variable TP:

• UCT, literature report, 8.9 to 10 mg/L TN, TP and location unspecified, COV not available

• IFAS, literature report, Broomfield, Colorado, 5.6 to 11.3 mg/L TN, 0.2 to 1.7 mg/L TP, COV not available

• VIP, literature report, 3 to 10 mg/L TN , 0.19 to 5.75 mg/L TP, location unspecified, COV not available

• VIP with VFA addition, literature report, 5 to 10 mg/L TN, 0.6 to 0.8 mg/L TP, COV not available

• Modified UCT with VFA addition, McDowe ll Creek, North Caro lina, literature report, 5 to 6 mg/L TN, 0.1 to 2.7 mg/L TP, COV not availableSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Executive Summary ES-7 Five systems reported annual average TN leve ls less than 5 mg/L and annual average TP levels between 0.1 and 0.5 mg/L:

• Biodenipho/PID, North Cary, North Carolin a, case study, 3.55 mg/L TN, 0.31 mg/L TP, 26 percent COV (TN), 87 percent COV (TP)

• Three-stage AS system with denitrif ying sludge and filter, Western Branch, Maryland, case study, 1.63 mg/L TN, 0.43 mg/L TP, 36 percent COV (TN), 62 percent COV (TP)

• 5-Stage Bardenpho with chemical addition a nd filter, Clearwater, Florida, Marshall Street facility, case study, 2.32 mg/L TN , 0.11 mg/L TP, 16 percent COV (TN), 64 percent COV (TP)

• 5-Stage Bardenpho with chemical addition a nd filter, Clearwater, Florida, Northeast facility, full-year data , 2.04 mg/L TN, 0.20 mg/L TP, 42 percent COV (TN), 82 percent COV (TP)

• Denitrification filter with chemical addition, Central Johnston County, North Carolina, case study, 2.14 mg /L TN, 0.26 mg/L TP, 16 per cent COV (TN), 60 percent COV (TP)

Two systems reported an annual average TN less than 5 mg/L and an annual average TP less than 0.1 mg/L:

• Step-feed AS with fermente r and filter, Piscataway, Maryland, full-year data, 2.59 mg/L TN, 0.09 mg/L TP, 57 percent COV (TN), 89 percent COV (TP)

• Denitrification filter with chemical add ition, Lee County, Florida, Fiesta Village facility, case study, 1.38 mg/L TN, 0.098 mg/L TP, 40 percent COV (TN), 47 percent COV (TP)



### Performance Factors for Design and Operation Key factors found to affect the performance of nutrient removal processes are discussed in Chapters 2 and 3.

Nitrogen Removal For nitrogen removal, key factors are presented in Section 2.2.2. They include an adequate supply of carbon from internal or external so urces, the number of anoxic zones, favorable temperature, sufficient alkalinit y, the sludge age and ma intenance of a deep sludge blanket in the secondary clarifier, and proper management of the recycle flows.

An adequate supply of carbon is needed to meet one of the following: chemical oxygen demand (COD)-to-total Kjeldahl nitrogen (TKN) ratio, readily biodegradable COD-to-TKNMunicipal Nutrient Removal Technologies Reference Document September 2008

ES-8 Executive Summary ratio, biochemical oxygen demand (BOD)-to-T KN ratio, or VFAs. A fermenter is a good source of internal carbon at a f acility. If an insufficient amount of carbon is present inside the facility, however, extern al carbon sources are needed. Typica lly, methanol or another locally available material is selected.

The number of anoxic zone is a function of the target concentration a nd the existing facility. For facilities with a target c oncentration of 3 mg/L or less, typically two anoxic zones are required for a single-sludge system. Having a number of swing zones provides significant protection against changing wast ewater characteristics and ot her conditions. In addition, the size of the anoxic zone depends on the carbon source: smaller zones are designed with a readily biodegradable carbon like VFAs, whereas larger zones are designed with a lessbiodegradable carbon sour ce in the wastewater. A separate de nitrifying filter, however, is not affected by these factors.

Alkalinity is an essential requirement for nitrification, and its stoichiometry is well established. Denitrification in the same sludge system enables recovery of approximately 30 percent of the alkalinity in accordance with th e stoichiometry. Supplementary alkalinity, in the form of caustic or lime, can be used in soft-water regions.

The sludge age is an operating parameter that varies from region to region, reflecting the temperature and changing characteristics of wast ewater during the year. It varied from 10 to 50 days in the case studies.

Operationally, many facilitie s reported a strategy by whic h a significant amount of denitrification was accomplished by maintainin g 3 to 4 feet of sludge blanket in the secondary clarifier.

Recycle flows contributed to a significant amount of nutrient and affect ed the performance of the technologies. Ammonia nitrogen from anaerobi c digestion and dewatering are significant, and flow equalization reduces shock e ffects on the biological processes.

Phosphorus Removal For phosphorus removal, the key factors are presented in Section 2.3. They are based on a system that consists of multiple processes conducted in series to reach an extremely low target concentration. This proven practice cons ists of a biological process, followed by a chemical process, and eventually by a physical process in which solids are separated from the effluent water. The key factors included, for bi ological removal, an adeq uate supply of VFAs in the wastewater (and the use of a fermenter to generate additional VFAs where needed), the size of the anaerobic and aerobic zones, the number of swing zones, the sludge age, the control of secondary release, a nd the depth of the sludge blanke t in the secondary clarifier. For chemical removal, the key factors include d the number of chemical application points,September 2008 Municipal Nutrient Remo val Technologies Reference Document

Executive Summary ES-9 the dosage, the need for a ter tiary clarifier, and the type of filters for final polishing. Management of recycle flows is anothe r key factor for reliable operations.

The recommended carbon supply is expressed in many ways, which include a VFA-to-TP ratio of 4 or higher, a BOD-to-TP ratio of greater than 20, and a readily biodegradable COD-to-TP ratio of 15 or greater. If insuffici ent VFAs are present in the wastewater yearround, a fermenter is a necessity for reliable performance. The typical design includes a sludge age of 4 days or longer and a hydrau lic retention time of longer than 6 hours, depending on the temperature and location. The sizes of the anaerobic and aerobic zones, along with the swing zone, are im portant factors for ensuring re liable performance. Because of varying wastewater charac teristics during the year, th e swing zone provides added assurance of reliable performance.

Maintaining 2 to 4 feet of sludge blanket in the secondary clarifie r was reported to be beneficial to many facilities, including thos e described in the Ke lowna, Lee County, and Central Johnston County case st udies. Clark County, on the ot her hand, reported use of a no-blanket policy to prevent the secondary release of phosphorus.

Tertiary clarifiers were effective in reducing th e load to the tertiary filter, where the target concentration was low. Fairfax County; Clar k County; and Brighton, Michigan, have shown added flexibility and reliability.

Special filters were effectiv e in reaching a phosphorus conc entration below 0.1 mg/L. They included a membrane filter at Hyrum, Utah, and at Lone Tree Creek, Colorado, a Dynasand filter at Breckenbridge, Colorado, and a Trident filter at Pinery, Colorado. Land application of tertiary clarifier effluent through 6 feet of soil layer in Brighton produced an effluent concentration of 0.01 mg/L at a ll times, making it the most relia ble of all the technologies.

The management of recycle flows is necessary to avoid high phosphorus concentrations from building up in the wastewater remaining in the facility (phosphorus that is not disposed of with the biosolids). Therefore, opportunities for sludge to be anaerobic for long periods should be minimized. This is done by avoiding th e use of long-term sludge storage as well as avoiding the use of an anaerobic di gester or thickener. The use of lime or ferric chloride to chemically remove phosphorus from the recycle stream might be needed in such instances.

Combined Nitrogen and Phosphorus Removal For combined removal of nitrogen and phosphorus , the key factors presented above apply. In addition, a careful approach is necessary to ba lance the needs for each process in a singlesludge system (see Section 2.2 for details). Th ese needs include optimal allocation of carbon sources, the size of the anoxic z one, control of dissolved oxygen and nitrate nitrogen, and the number and placement of chemical application points.Municipal Nutrient Removal Technologies Reference Document September 2008

ES-10 Executive Summary The VFA from the same sources can be allocat ed between the anaerobic zone and the anoxic zone, depending on the needs and the contro l philosophy. Both the step-feed AS and the Westbank processes use this principle with a varying split formula to produce reliable performance. Under this appro ach, the size of anoxic zone can be reduced in comparison with the normal-mode AS.

Good control of dissolved oxygen and nitrate nitrogen is achieved with online sensors and automation of control functions, as is the case in Clark County and Clearwater.

For two-sludge and three-sludge systems, the cont rols are separated, and thus less effort is required to balance the needs for nitrogen removal versus phosphorus removal. These systems include the denitrification filters at Lee County and Central Johnston County and the three-sludge system in Western Branch. A simpler control and good performance are advantages at these facilities; the disadvantages include the new facilities––with their larger footprint and high cost for carbon––required.

Wet-Weather Flow The reliability of technologies also depends in part on how the facili ty manages wet-weather flows. The key factors are the size and locat ion of the equalization basin, selection of treatment processes, and operational flexibility available.

The size of the equalization basin depends on th e sewer system in place. The peaking factors and the ability to bypass upstream treatment pr ocess are site-specific constraints. The reliability of the overall technologies is ensured with a large-enough basin, as is the case in North Cary, which has 58 percent of the aver age daily flow rate; Fa irfax County, which has 11.5 percent of the average daily flow rate in the raw wastewater and 20 percent in the secondary effluent; and Kelowna, with 7.5 percent of the daily average flow rate.

Step-feed AS offers a distinct advantage in maintaining a higher sl udge inventory in the aeration basin while maintaining a low solids loading rate on the secondary clarifiers, as shown in Fairfax County and Kelowna.

To address extreme storm conditions, many f acilities have developed storm modes of operation, under which aeration is suspended in a section of the ae ration basin during the high-flow period. The size and duration depend strictly on the size of the storm and the layout of the facility.

The PID at North Cary has a storm mode of ope ration, which allows quick adjustment of the cycle time and thus affords protection of the sludge inventory from washouts.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Executive Summary ES-11 Case Study Locations Kelowna, British Columbia (Canada) Clearwater, Florida (Mar shall Street Plant) Lee County, Florida Upper Marlboro, Maryland (Western Branch Plant) Kalispell, Montana Clark County, Nevada Central Johnston County, North Carolina North Cary, North Carolina Fairfax County, Virginia (Noman Cole Plant) 

### Emerging Technologies Chapter 2 also includes presents emerging t echnologies that show promise for effective nutrient removal but have not yet had extensive full-scale operation so that their performance and reliability could be assessed. These include the Co-Mag process, which entails ballasted flocculation with magnetic separation of the ba llast; the Blue PRO process, which involves ferric chloride-aided adsorption of phosphorus on ferric oxide; and the Trident HS process, which employs metal precipitation of phosphorus , two-stage clarificat ion, and filtration.



### Case Studies Involving Nine Municipalities

Chapter 3 provides a synthesis of the informa tion generated from the ni ne case studies that were developed for this document. Most of the case study facilities are throughout the United States; one plant is in Canada. Facilities in both cold and warm weather locations were included in the study. The facilities varied wi th respect to whether phosphorus removal, nitrogen removal, or both were required under the NPDES perm it. All the facilities exhibited outstanding performance. The objective of the case studies was four-fold:

• To present the data from selected technologies for a one-year period

• To identify the factors that contribute to the reliability of nitrogen and phosphorus removal

• To identify the factors that contribute to the costs of various re moval technologies

• To evaluate the reliability of nutrient re moval through a simple, yet sound statistical method by which performance data c ould be presented and compared

The performance of the technologies in use at the case study facilities is summarized below.

For biological phosphorus removal, efficient an d reliable performance was shown at four facilities, two of which had dedicated fermente rs. The annual average effluent concentration was 0.12 mg/L in Kalispell (modified UCT process with fermenter) and 0.14 mg/L in Kelowna (3-stage Westbank process with fermenter), with corresponding COVs of only 19 percent and 21 percent, respectively. North Cary (PID process) had an average concentration of 0.38 mg/L with a COV of 64 percent, and Central Johnston County (MLE with long anoxic detention time and high internal recirculatio n) had an average concentration of 0.26 mg/L with a COV of 62 percent. Key factors included favorableMunicipal Nutrient Removal Technologies Reference Document September 2008

ES-12 Executive Summary wastewater characteristics, an on-site fermenter, and a good design that included flexible features like swing zones, multiple points of carbon feed, safeguards against secondary release and minimal return of recycle fl ows from sludge handli ng, and good controls developed and practiced based on key process parameters. Operationa l factors included sludge blankets (also referred to as denitrification blankets) in the secondary clarifiers, maintained at Central Johnston County and Kelowna; optimization of fermenter parameters throughout the year; and control strategies based on nitrate concentration, blanket monitoring, dissolved oxygen, and oxidation-redu ction potential measurements at some facilities.

Three facilities practiced a combination of biological phosphorus removal and chemical addition. The average annual effluent concentr ations were lowered down to 0.09 mg/L with COVs of 30 percent in Clark County (A/O process) and 21 pe rcent in Fairfax County (stepfeed AS process with fermenter). Clearwate r (5-stage Bardenpho process) achieved an average concentration of 0.132 mg/L with a CO V of 40 percent. Key factors for increased removal included the added flexibility of having a tertiary clarifier, multiple feed points for chemical addition, a good filter system, and prevention of secondary release.

Two facilities––Lee County and Western Branch ––relied on adding chemicals to their AS processes for phosphorus removal. The average annual concentrations for the two facilities were 0.1 mg/L and 0.47 mg/L, with COVs of 56 and 62 percent, respectively.

For ammonia nitrogen removal, two facilities were studied. The Kalispell and Clark County facilities removed ammonia w ith the highest efficiency and reliability––0.07 mg/L and 0.12 mg/L as an annual average with COVs of 0 percent in Kalispell an d 14 percent in Clark County. Contributing factors included adequate sludge age and a sufficient supply of oxygen.

Six facilities were required to remove TN, and they all met their respective permit limits efficiently and reliably. The average annual e ffluent concentrations were 2.32 mg/L with a COV of 16 percent in Clearwate r (5-Stage Bardenpho), 3.7 mg/L with a COV of 14 percent in North Cary (PID), and 4.38 mg/L with a COV of only 12 percent at Kelowna (Westbank process). Denitrification filters were installed to remove n itrogen at Central Johnston County and Lee County; their performance was good and reliable. The average concentrations were 2.14 mg/L and 1.57 mg/L with COVs of 16 and 34 percent, respectively.

To achieve low effluent nitrogen concentra tions, Western Branch a dded a denitrifying AS process with a methanol feed system to its existing two-stage AS-nitr ifying sludge system. This created a three-sludge system, the pe rformance of which was good and reliable. The average concentration was 1.7 mg/L with a COV of 36 percent. The key factors for this high reliability included favorable wastewater charac teristics, an adequate supply of carbon, a flexible design with swing zones, separate control of mixing and aeration, multiple carbon feed points, minimization of recycle loads, and proper design of the sludge-handlingSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Executive Summary ES-13 processes. Operating factors included a denitr ification blanket at some locations; proper sludge age; online monitoring; and automation of process control based on nitrate, dissolved oxygen, and oxidation-reduction pote ntial at some locations.



### Costs

Chapter 4 presents comprehensive cost info rmation for nutrient removal technologies at municipal facilities. The information is based on the literature reviewed, the data collected specifically for the case studies prepared for this document, and the use of the CAPDETWorks software.

The literature from which cost information wa s obtained includes studie s surveying facilities in Maryland, Connecticut and Colorado. The Maryland studies include the costs for capital and O&M (except labor). The Connecticut study had capital and O&M costs (including labor costs) for one facility and capital and O&M costs (excluding labor costs) for the other facility. The Colorado study includes only capital costs. These literature data were assumed to be accurate. The U.S. Environmental Protection Agency (EPA) does not assume responsibility for the reported data.

Additional cost information was obtained in conjunction with devel oping the case studies prepared for this report. The costs reported fr om these sources includ ed capital costs updated to 2007 dollars using the Engineering News-Record Index, and O&M costs for energy and chemicals but not for labor or maintenance. Th ese cost data were pr ovided and verified by the study facilities and were assumed to be accurate. EPA does not assume responsibility for the reported data.

In addition, cost estimates were developed fo r all cost items using CAPDETWorks software for 12 retrofit and 20 expansion alternatives. The cost estimates are based on unit costs updated to 2007 using published cost index va lues. CAPDETWorks was run for three flow rates: 1 million gallons per day (MGD), 5 MGD, and 10 MGD. These rates were selected to represent the majority of facilities in the c ountry. On the basis of information from EPA’s Clean Watersheds Needs Survey database, near ly 80 percent of existi ng facilities are less than 1 MGD, and about 97 percent of t hose facilities are 10 MGD or less. The CAPDETWorks cost database was assumed to be accurate. Capital costs were automatically updated to 2007 dollars. EPA does not a ssume responsibility for the data.



### Capital, O&M, and Life-Cycle Costs for Retrofits Table ES-1 presents the incremental costs of retrofit technologi es obtained from the literature, case studies, and projections us ing CapdetWorks arranged by the amount of treatment achieved by the various systems. The sources of the data are shown on the table, and the flow rate in each system is noted. CAPDETWorks results are presented below for 1- and 10-MGD flow; more complete cost cu rves are presented in Chapter 4. For allMunicipal Nutrient Removal Technologies Reference Document September 2008

ES-14 Executive Summary technologies, costs vary substant ially, which reflects the selected technologies, chemical use, power use, and for CAPDETWorks estimates, projected labor requirement s. The size of the system is a significant cost f actor: Higher unit costs are associ ated with smaller facilities compared to larger facilities b ecause of economies of scale.

Table ES-1. Cost estimates for retrofit technologies

Target concentration (annual average) Initial concentration (annual average) Technologies (conversion or add-on indicated by

footnote) Location Flow rate (MGD) Capital $/gpd capacity O&M $/MG treated Life-cycle $/MG treated Total N target only TN, 5.1 mg/L 9.6 mg/L TN Cyclic on/off aeration a Ridgefield, CT 1 $0.20 $111 ---

TN, 5.0 mg/L 7 mg/L TN Denitrification filter b Cheshire, CT 3.5 $1.65 $136 ---

8 mg/L TN MLE Æ 4-stage Bardenpho a Seneca, MD 20 $0.21 $63 ---

8 mg/L TN MLE Æ 4-stage Bardenpho a Freedom, MD 3.5 $0.99 --- ---

8 mg/L TN MLE Æ 4-stage Bardenpho a Cumberland, MD 15 $1.10 $122 ---

15 mg/L TN Lagoon Æ 4- stage Bardenpho a Hurlock, MD 1.5 $4.12 --- ---

8 mg/L TN Denitrification filter b Baltimore, MD 180 $1.39 --- ---

8 mg/L TN Denitrification filter b Cox Creek, MD 15 $1.74 $104 ---

6.5 mg/L TN 5-stage Bardenpho + denitrification filter b Frederick, MD 7 $1.41 --- ---

40 mg/L TN d Phased oxidation ditch a CW 10 $0.47 $44 $157

40 mg/L TN d MLE retrofit a CW 10 $0.71 $82 $164 40 mg/L TN d Step-feed retrofit a CW 10 $0.65 $91 $245 TN, 3 mg/L or less

40 mg/L TN d Denitrification filter b CW 10 $0.71 $156 $324

TN, 1 mg/L 42 mg/L TN e 5-stage Bardenpho with MBR and

reverse osmosis b Las Virgenes, Calabasas, CA 16 $5.20 --- ---September 2008 Municipal Nutrient Remo val Technologies Reference Document

Executive Summary ES-15 Table ES-1. Cost estimates for retrofit technologies (continued)

Target concentration (annual average) Initial concentration (annual average) Technologies (conversion or add-on indicated by

footnote) Location Flow rate (MGD) Capital $/gpd capacity O&M $/MG treated Life-cycle $/MG treated Total P Target Only 5 mg/L TP Fermenter retrofit, no filter b CW 10 $0.18 $7 $50

5 mg/L TP 1-point chemical addition, no filter b CW 10 $0.03 $91 $98 TP, 0.5 mg/L 5 mg/L TP Fermenter + sand filter retrofit b CW 10 $0.44 $25 $130

5 mg/L TP Fermenter + sand filter + 1-point chemical addition b CW 10 $0.47 $106 $218

TP, 0.1 mg/L 5 mg/L TP 2-point chemical addition + filter b CW 10 $0.29 $215 $283

Ammonia-N + TP limitsAmmoniaN+TP, 1.5 mg/L & 1 mg/L 37 mg/L Ammonia-N, 10 mg/L TP Cyclic on/off aeration a for ammonia-N Broomfield , CO 8 $1.00 --- ---

AmmoniaN+TP, 1.5 mg/L & 1 mg/L 37 mg/L Ammonia-N, 10 mg/L TP IFAS a for ammonia-N Broomfield , CO 8 $0.85 --- ---

AmmoniaN+TP, 1.5 mg/L & 1 mg/L 37 mg/L Ammonia-N, 10 mg/L TP MBBR b for nitrification/ denitrification Broomfield , CO 8 $1.70 --- ---

AmmoniaN+TP, 1.4 mg/L & 1 mg/L 24 mg/L Ammonia-N, 4 mg/L TP Modified UCT with fermenter and sand filter c Kalispell, MT, case study 3 $3.03 $108 ---

AmmoniaN+TP, 1 mg/L & 0.18 mg/L 18.9 mg/L Ammonia-N, 6.4 mg/L TP Step-feed AS with dual-media and deep-bed filter + 1-point chemical addition c Fairfax, VA, case study 67 $1.07 $106 ---

AmmoniaN+TP, 0.6 mg/L & 0.2 mg/L 27 mg/L Ammonia-N, 5.8 mg/L TP A/O with VFA and dual mediafilters and chemical addition a Clark Co., NV, case study 100 $2.01 $183 ---

TN+TP limits TN+TP, 6 mg/L & 0.25 mg/L 28.8 mg/L TN, 6 mg/L TP 3-stage Westbank with fermenters a Kelowna, BC, case study 10.5 $3.25 $77 ---Municipal Nutrient Removal Technologies Reference Document September 2008

ES-16 Executive Summary Table ES-1. Cost estimates for retrofit technologies (continued)

Target concentration (annual average) Initial concentration (annual average) Technologies (conversion or add-on indicated by

footnote) Location Flow rate (MGD) Capital $/gpd capacity O&M $/MG treated Life-cycle $/MG treated TN+TP, 3.9 mg/L & 2 mg/L 56 mg/L TN
, 7.7 mg/L TP Oxidation ditch with sand filter a North Cary, NC, case study 12 $2.84 $60 ---

TN+TP, 3.7 mg/L & 1 mg/L 31.2 mg/L TN, 5.8 mg/L TP Plug flow AS with denitrification filter c Central Johnston Co., NC case study 7 $0.58 $221 ---

TN+TP, 3 mg/L & 1 mg/L 24 mg/L TN, 3.7 mg/L TP 3-stage activated sludge with chemical addition b Western Branch, MD, case study 30 $1.73 $165 ---

TN+TP, 3 mg/L & 1 mg/L 28 mg/L TN, 5 mg/L TP 5-stage Bardenpho with sand filter + chemical addition a Clearwater , FL (Marshall Street) case study 10 $2.95 $242 ---

TN+TP, 3 mg/L & 0.5 mg/L 33.2 mg/L TN, 3.8 mg/L TP Denitrification filter + chemical addition b Lee Co., FL (Fiesta Village) case study 5 $2.79 $265 ---

40 mg/L TN, 5 mg/L TP PID retrofit with 1-point chemical addition, clarifier, and filter a CW 10 $0.89 $199 $411

40 mg/L TN, 5 mg/L TP 5-stage Bardenpho retrofit with chemical addition a CW 10 $1.30 $256 $566
TN+TP, 3 mg/L & 0.1 mg/L

40 mg/L TN, 5 mg/L TP Nitrification/ chemical addition/ denitrification filter retrofit b CW 10 $0.75 $448 $626

Notes: Case = case study as described in Chapter 3; O&M does not include labor. CW = cost from CAPDETWorks A/O with VFA = anoxic/oxic enriched with volatile fatty acids AS = activated sludge CT = Connecticut Study. CT-1 plant incl uded labor in the O&M cost; CT-2 did not. IFAS = integrated fixed-film activated sludge MD = Maryland Study. Incremental cost for retrofitting from 8 mg/L TN to 3 mg/L TN does not include labor in O&M. MLE = modified Ludzack-Ettinger process MBBR = moving-bed biofilm reactor MBR = membrane bioreactor PID = phased isolation ditch Other = other literature sources TN = total nitrogen as N TP = total phosphorus as PSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Executive Summary ES-17 UCT = University of Cape Town process For combined TN and TP technologies (TN+TP), fi rst target number is for TN, second for TP

a Conversion
b Add-on

c Combination conversion and add-on
d Secondary effluent (as influent for add on processes)

e 5-stage Bardenpho with MBR and reverse osmosis removes both TN and TP but the study reported only on TN

Life-cycle costs were calculated for the CAPDETWorks results by first annualizing the capital cost at 20 years at 6 percent interest. The annualized capital cost was then added to the annual O&M cost to obtain a total annual cost. This cost was then divided by the annual flow to get the life-cycle cost per million gallons (MG) treated.

For nitrogen removal technologies, the capit al costs ranged between $0.99 and $1.74 per gallon per day (gpd) capacity. The low cost repr esents converting AS facilities from meeting 8 mg/L to meeting 3 mg/L, while the high cost represents adding new denitrification filters.

For nitrogen removal, the O&M cost reported in the Maryland study ranged from $63 to $122 and did not include labor in the O&M co st. The Connecticut plant at $111 per MG treated included labor in the O&M cost, but the Connecticut pl ant at $136 per MG treated did not include labor in the O&M cost.

For chemical phosphorus removal, the capital costs ranged between $0.03 and $0.29 per gpd capacity. The low cost was for chemical feed equipment and storage tanks for one chemical addition point, while the higher cost was for two chemical a ddition points. For biological phosphorus removal, the costs ranged between $0.44 and $0.47 per gpd capacity. The costs were from conversion of the AS proce ss and the addition of new fermenters.

For chemical phosphorus removal, the O&M cost range was $91 to $215 per MG treated. This cost included the cost of chemicals, pow er, labor, and the handling of the additional sludge caused by chemical addition. The low cost represents single-point chemical addition without filtration. The high cost re presents two-point chemical feed with tertiary filtration to achieve a lower target limit, 0.1 mg/L.

The rest of the costs presented in Table ES-1 are for combined processes that remove phosphorus and a nitrogen species. The following rules were applied to rationally allocate costs between nitrogen and phosphorus removal during preparation of the case studies described in Chapter 3:

• Electrical power was propor tional to oxygen demand (e.g., nitrification versus BOD removal).

• The external carbon source (e.g., methanol) was entirely for nitrogen removal.

• Fermenters were assumed to be entirely for phosphorus removal.Municipal Nutrient Removal Technologies Reference Document September 2008

ES-18 Executive Summary • The tertiary filter was assumed to be entirely for phosphorus removal.

• The denitrification filter (capital and O&M) was assumed to be 95 percent for nitrogen removal and 5 percent fo r phosphorus removal via filtration.

• The coagulation chemicals were assumed to be entirely for phosphorus removal.

• Other costs were allocated in proportion to the hydraulic retention times for nitrogen and phosphorus removal.

Although the focus of this document is the remo val of both nitrogen and phosphorus, some of the study facilities have limits for only phosphor us and ammonia nitrogen. The capital cost estimates for these facilities ranged from $0.85 per gpd capacity (Broomfield, Colorado, for IFAS installation) to $3.03 per gpd capacity (K alispell). O&M costs were available for only three case study facilities––Ka lispell, Clark County, and Fairfax County. They ranged from $106 to $183 per MG treated; the lo wer numbers resulted from use of a fermenter, rather than chemical addition, to obtain TP removal.

For combined nitrogen and phosphorus remova l technologies, capital costs ranged between $0.58 and $3.25 per gpd capacity. The high-cost fac ilities typically included a fermenter, additional piping for the anoxic zone, swing zones, and filters. The factors that most affected O&M costs were the use of an external carbon source, power fo r the equipment installed, the use of chemical coagulants and polym ers, and increased sludge production.

The combined nitrogen and phosphorus rem oval O&M costs ranged from $60 to $265 per MG treated for the case study facilities. Thos e costs did not include labor estimates. The lower costs were associated with systems that use fermenters to aid in biological phosphorus removal (with no chemical addition), while the higher costs were associated with chemical addition for phosphorus or nitrogen removal.

The O&M cost estimates generated using CA PDETWorks ranged from $199 to $448 per MG treated. The CAPDETWorks estimates included la bor costs. The low costs reflect one-point chemical feed, while the high cost represen ts methanol feed, chemicals for phosphorus removal, and filtration. The life-cycle cost ra nge was from $411 to more than $1,000 per MG treated. The wide range of life- cycle costs reflects the selected unit operations, chemical use, power use, and projected labor requirements. De tails of the costs are provided in Chapter 4.

For nitrogen removal, nitrifica tion/denitrification a ttained 5–8 mg/L without extra chemicals, using a single anoxic zone; the capital cost ranged from $0.63 to $2.17 per gpd capacity. The low cost was for a PID, and the high cost was for a 4-stage Bardenpho. The range of O&M costs was from $122 to $453 per MG treated, re presenting all cost items, including chemicals, labor, sludge handling, and power.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Executive Summary ES-19 

### Capital, O&M, and Life-Cycle Costs for Expansion Table ES-2 presents the CAPDETWorks-gene rated cost estimates for 20 expansion technologies for a 10-MGD average flow for the indicated target nutrien t concentrations. The

term expansion , as used here, is defined as a paralle l train and no increase in design flow. Chapter 4 presents a full set of cost curves , including values for 1 and 5 MGD. For all technologies, costs vary; higher unit costs are associated with smaller facilities compared to larger facilities because of ec onomies of scale. In general, costs are higher for the expansion processes compared to correspond ing retrofit processes because there is no opportunity to use the existing facilities. Chapter 4 also includes bar graphs th at show the breakdown of O&M for the expansion technologies into labor, energy, material, a nd chemical/sludge costs. The graphs show that the percentage of the O& M cost devoted to labor was higher for 1-MGD plants (labor at 40 to 50 percent of total O&M) than for 10-MGD facilities (labor at 15 to 25 percent of total O&M). The percentages devoted to energy and chemical costs remained proportional to the flow.

For chemical phosphorus removal, the cost ra nged from $0.03 to $0.29 for chemical feed equipment and storage tanks. The O&M cost range was $91 to $215 per MG treated, based on one or two chemical feed points.

For biological phosphorus removal to reach 1 mg /L without extra chemicals, the cost was estimated at $1.21 per gpd capacity. With a fermente r and tertiary filter, the cost went up to $1.52 per gpd capacity, and the O&M cost wentup from $280 to $308 per MG treated.

For combined nitrogen and phosphorus remova l, the capital cost range was $1.36 to $2.48 per gpd capacity. The lower costs were for target TN concentrations of 5 mg/L and target TP concentrations of 1 mg/L, while the high costs we re for target concentr ations of 3 mg/L TN and 0.1 mg/L TP. The higher costs also reflect the use of two chemical addition points and methanol feed. The O&M costs ranged from $259 to $477. The low cost represents high target TN and TP, while the high cost represen ts low target TN and TP limits, as shown in Table ES-2.

To achieve a TP level of 0.1 mg/L or belo w, two-point chemical addition followed by a clarifier and high-performance filters might be needed. High-performance filters that can remove phosphorus to this level include the Dynasand D2, DensaDeg, membrane filters, and Trident. Emerging technologies include CoMag and Blue PRO. Cost information for these processes should be obtained from th e manufacturers of the technologies.Municipal Nutrient Removal Technologies Reference Document September 2008

ES-20 Executive Summary Table ES-2. Cost estimates for expansion technologies for 10 MGD

Nutrient/ target concentration Initial concentration Technology Capital $/gpd capacity O&M $/MG treated Life-cycle $/MG treated 40 mg/L TN PID $0.63 $122 $273 40 mg/L TN MLE $1.61 $309 $695 40 mg/L TN 4-stage Bardenpho $2.17 $453 $971 TN, 5 mg/L

40 mg/L TN Denitrification filter $0.71 $156 $324 TP, 1 mg/L 5 mg/L TP A/O, no additional equipment $1.21 $280 $568

5 mg/L TP 1-point chemical addition $0.03 $91 $98 5 mg/L TP A/O with fermenter $1.26 $290 $590 TP, 0.5 mg/L 5 mg/L TP A/O with fermenter and sand filter $1.52 $308 $670

5 mg/L TP 2-point chemical addition with filter $0.29 $215 $283
TP, 0.1 mg/L 5 mg/L TP A/O with fermenter, filter, and chemical addition $1.55 $389 $758

40 mg/L TN, 5 mg/L TP Step-feed $1.36 $299 $625

40 mg/L TN, 5 mg/L TP SBR $1.94 $302 $766 TN+TP, 5 mg/L & 1 mg/L 40 mg/L TN, 5 mg/L TP 3-stage processes (e.g., UCT, VIP) $2.05 $436 $925

40 mg/L TN, 5 mg/L TP 5-stage Bardenpho, no filter $2.19 $452 $975

40 mg/L TN, 5 mg/L TP Modified UCT with fermenter and filter $2.33 $456 $1014 TN+TP, 5 mg/L & 0.5 mg/L 40 mg/L TN, 5 mg/L TP 5-stage Bardenpho with filter $2.45 $455 $1040

40 mg/L TN, 5 mg/L TP PID with chemical addition, clarifier, and filter $0.83 $259 $456 TN+TP, 5 mg/L & 0.1 mg/L 40 mg/L TN, 5 mg/L TP SBR with chemical addition and filter $1.87 $387 $834

40 mg/L TN, 5 mg/L TP Nitrification with 1-point chemical addition and denitrificiation filter $0.75 $448 $626
TN+TP, 3 mg/L & 0.1 mg/L 40 mg/L TN, 5 mg/L TP 5-stage Bardenpho with chemical addition and filter $2.48 $477 $1070

Notes: A/O = anoxic/oxic PID = phased isolation ditch SBR = sequencing batch reactor TN = total nitrogen as N TP = total phosphorus as P UCT = University of Cape Town process VIP = Virginia Initiative process For combined TN and TP technologies (TN+TP), fi rst target number is for TN, second for TP.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Executive Summary ES-21 

### Technology Selection and Permit Limits

Chapter 5 of the document describes how to ev aluate options for nutrient removal retrofits. The technologies are summarized in Tables 5- 1 through 5-4. The first consideration is to determine what the candidate processes should be, which depends on the target concentration of the nutrient and the existing facility.

The review of data sources performed in prep aring this document identified six technologies that meet low (less than 3 mg/L) TN concentration limits with good reliability. These are the 4-stage Bardenpho process with a conventional filter; the step-feed AS process with a conventional filter; concentric (phased) oxidation ditches; and two types of denitrification filters, one downflow and the other upflow.

The technologies identified for achieving mid-le vel TN removal concentrations (between 3 and 8 mg/L) are the A 2 /O, biological aerated filter, th e MLE process, sequencing batch reactors, cyclic AS, biological aerated filters, IFAS, moving bed biofilm reactor, 3-stage Westbank, 4-stage Bardenpho and post-aeration a noxic with methanol (known as the Blue Plains process). The nitrogen removal technol ogies mentioned in the preceding paragraph were also identified as being able to reliably meet TN concentrations of 8 mg/L or higher without the use of filters.

The technologies that meet low (less than 0.1 mg/L) TP concentra tion limits with good reliability are membrane filters, proprietary high-performance filters (Trident, Dual Sand D2, Advanced Filtration System, and land applic ation through infiltration bed. The emerging technologies include the prioprieta ry Blue PRO and CoMag process.

The additional technologies id entified for meeting mid-level TP removal concentrations (between 0.1 and 0.5 mg/L) are chemical preci pitation with conventio nal filter, 3-stage Westbank with conventional filter, chemical precipitation with tertiary clarifier and conventional filter, modified UCT process with conventional filter, PI Ds with conventional filter, 5-stage Bardenpho with chemical and conventional filter, and step-feed AS with conventional filter. The conventiona l filters include sand filters, deep bed anthracite filters, dual-media filters, and other traditional filters.

The technologies that meet TP concentra tions between 1.0 and 0.5 mg/L are chemical precipitation, A/O with conve ntional filter preferred, 5-st age Bardenpho, the proprietary PhoStrip process with conve ntional filter pref erred, and sequencing batch reactors.

The technologies that meet concen trations of 3 mg/L or less of TN and 0.1 mg/L or less of TP are step-feed AS plus a tertiary clarifie r with chemical addition and a high-performance filter, denitrification filter with chemical addition and a high-performance filter, membrane bioreactors with chemical additi on, and the use of land applicati on associated with any of the three technologies listed above.Municipal Nutrient Removal Technologies Reference Document September 2008

ES-22 Executive Summary Additional technologies that meet TN concentrations of less than 3 mg/L and achieve TP concentrations between 0.1 and 0.5 mg/L were identified. These are st ep-feed AS with a conventional filter, 5-stage Bardenpho with a conventional filter, PID with a conventional filter, denitrification filters plus chemical phosphorus removal and conventional filtration, 4- stage Bardenpho process plus ch emical phosphorus removal with conventional filtration and denitrification, and AS plus chemical phos phorus removal with c onventional filtration.

The technologies identified as meeting TN concentrations between 3 and 8 mg/L and meeting TP concentrations between 0.5 and 1 mg/L are sequencing batch reactors with conventional filtration, the modified UCT process, the A/O process, the PhoStrip II process, 3-stage Westbank, step-feed AS, PIDs, and 5- stage Bardenpho, as we ll as the following technologies with chemical phosphorus removal added: A 2 /O, biological aerated filter, the MLE process, cyclic AS, biological aerated filters, IFAS, moving bed biofilm reactor, 4- stage Bardenpho, and post-aerati on anoxic with methanol ( known as the Blue Plains process). Sequencing batch reactor s and the 3-stage Westbank process can also achieve these limits if accompanied by chemical phosphorus removal.



### Factors in Upgrading Existing F acilities, Decision Matrix, and Sensitivity Analysis

Factors to be considered in upgrading existing facilities incl ude wastewater characteristics, site constraints, existing solids-handling f acilities, wet-weather flows, automation and sensors, and sustainability. These factors are listed in Chapter 5, Tables 5-5 through 5-7. Among other factors, the wastewat er characteristics determine the need for fermenters for VFA production for use in biol ogical nutrient removal. Fe rmenters can produce enough carbon to supplement the wastewater for both biological phosphorus removal and denitrification. An external carbon supply s hould be avoided for long-term sustainability, where feasible.

Site constraints could determine whether it is feasible to add new processes or whether there is only enough space to modify the existing facili ties. Thus, such constraints are a key factor in making decisions regarding upgrades.

Existing on-site sludge-handling f acilities have a significant imp act on selecting technologies and eventually sizing the selected technologi es. One needs to determine whether a sidestream treatment is needed or whether ther e is a need to oversize the main treatment processes to handle recycle loadings from so lids thickening, digestion, and dewatering. For biological phosphorus removal processes, aerobic thickening and digestion are recommended. For facilities with anaerobic digestion, proper recycle loads should be incorporated into pro cess sizing and selection.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Executive Summary ES-23 Wet-weather flows are a significant factor in selecting technologi es, as well as in incorporating an equalization ba sin. The size of the basin and its location are usually based on the site-specific flow conditions.

Automation and the use of onlin e sensors are significant fact ors in managing energy, labor, and chemicals. Cost savings from reduced energy use is a key ju stification for the investment, as well as a reliab le process control measure. On line sensors monitor dissolved oxygen, ammonia nitrogen and nitrate nitroge n, ortho-phosphate, oxidation reduction potential, and some specific parameters of local interest. Supervisory control and data acquisition (SCADA) systems are usually recomm ended for monitoring and, in some cases, for process control and optimization.

Regulators and municipalities evaluating nutrient removal te chnologies should consider sustainability as a key criterion in selecting a technology. One of the great challenges in the wastewater sector is to provide reasonable cost treatment that will enable reuse of the effluent, as well as recovery of the nutrient s, and thereby reduce the overall demand on water resources. The costs of nutrient removal are affected significantly by the selection of a technology. Each technology requires a certainlevel of energy consumption, requires a particular amount of treatment chemicals, and has implications for the potential reuse of effluent and biosolids.

The process evaluation tables (decision matrices) in Chapter 5 show specific criteria that project proponents can develop on the basis of stakeholder input. Th ese criteria and the weighting factors are based on the site-specific conditions of the facility and the priority of the project. Typical criteria include site requirements and the room for future plant expansion, costs (capital and life- cycle costs), the efficiency and sustainability of treatment, and flexibility for accommodating future changes in wastewater characteristics. Sustainability factors include the energy (electrical) consump tion, the external carbon source (e.g., methanol) requirement, the potential fo r methane gas recovery and power generation, the sludge reuse potential, odors, and public perc eptions. It is recommended that a sensitivity analysis be conducted in anticip ation of increased costs associated with rising energy costs, increased biosolids management costs, uncertain ties in waste characteristics, uncertainties in regulations, and other costs, assuming increase s of 50 percent or 100 pe rcent. Alternatives should be compared with respec t to these factors in making the final technology selection.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 1: Introduction and History 1-1 

## CHAPTER 1: Introduction and History

1.1 Overview

Wastewater treatment plants (WWTPs) that us e conventional biological treatment processes designed to meet secondary treat ment effluent levels do not re move nitrogen or phosphorus to any substantial extent. Retrofitting the conventional secondary biological treatment processes is an increasingly popular way to achieve nitrogen and phosphorus reductions. This approach typically relies on m odifications to biological trea tment processes so that the bacteria in these systems also convert nitr ate nitrogen to inert nitrogen gas and trap phosphorus in the biosolids that are removed from the effluent.

This document presents information about availa ble technologies that can be used to remove nitrogen and phosphorus from municipal wastew ater. Descriptions of the technologies are presented, along with data that show the cost and reliability of the performance that was achieved for specific applications of the tec hnology. One of the purpos es of the resources presented in this document is to help regulat ors develop appropriate discharge permit limits with a full understanding of available technologies, the reli ability of the technologies, and the ability of plants that are retrofitted with su ch technologies to meet their permit limits in a sustainable way. Another key objective of th e document is for this information to be available for assimilation by the regulated co mmunity so that plant operators and other decisionmakers, including rate payers, can be better informed about this topic.

Information about many of the technologies described in this document was obtained by developing a series of nine case studies. A dditional information about these and other technologies was gathered from the litera ture, including publications of the Water Environment Federation, Wate r Environment Research Found ation, other organizations, recent reports from Maryland and Connecticut, and data from about 20 municipalities that participated voluntarily by provi ding data during the case study development process. One of the unique aspects of this document is that fu ll-scale plant performance data were collected, and this information is expressed on the same statistical basis for easy comparison. The data are accompanied by a discussion of the key f actors that contribute to the performance reliability of various process systems. These factors include wastewater characteristics; process parameters; environmental parameters such as temperature, chemistry, and biology; and operating parameters. Cost information is presented, as are factors that should be considered when selecting a retrofit or new upgrade process technology for removing nitrogen, phosphorus, or both.Municipal Nutrient Removal Technologies Reference Document September 2008

1-2 Chapter 1: Introduction and History 

### 1.2 Background of Nitrogen and Phosphorus Removal in the United States

The Federal Water Pollution Control Act of 1965 be gan a series of envi ronmental legislative reforms that initiated a consistent approach to pollution control ba sed on water quality and beneficial use goals (USEPA 1993). During the late 1960s and throughout the 1970s, much effort was devoted to reducing phosphorus in wastewater effluents (Rast and Thornton 1996). For example, the implementation of phosphorus removal at the Blue Plains WWTP in Washington, D.C, resulted in dramatic water quality improvement in the Potomac River.

The 1972 Amendments to the Federal Water Po llution Control Act, known as the Clean Water Act (CWA), established the foundation for wastewater di scharge control in the United States. With respect to nonpoint source pollu tion, section 208 of th e CWA Amendments of 1972 stipulated that “substate watersheds in which nonpoint source pollution control, along with the control of point source discharges by required technologies, was to be addressed by a watershed water quality plan” (National Academy of Sciences 1999). Since 1972, the U.S. Environmental Protection Agency (EPA ) has awarded $44.6 billion under the sewagetreatment construction gran ts program. The 1987 CWA Am endments authorized an additional $18 billion, total, for the constr uction grants program through 1990 and the State Revolving Fund (SRF) program through 1994. Of this amount, $9.6 billion is authorized for continuation of construction grants , and at least $8.4 billion is fo r use as capitalization grants to set up the SRFs (USEPA 1998).

Although nearly all WWTPs provide a minimu m of secondary treatment, conventional secondary biological treatment processes do not remove the phosphorus and nitrogen to any substantial extent. Tertiary treatment can re move nitrogen and phosphorous through carefully designed chemical reactions that generate easily isolated products su ch as precipitates and gases, though it is considered a costly technology (Carberry 1990).

Advanced treatment technologies can be extensions of conve ntional secondary biological treatment to remove nitrogen and phosphorus . Biological treatment processes called biological nutrient removal (BNR) can al so achieve nutrient reduction, removing both nitrogen and phosphorus. Most of the BNR pro cesses involve modifications of suspendedgrowth treatment systems so that the bacteria in these systems also convert nitrate nitrogen to inert nitrogen gas and trap phosphorus in the solids that are remove d from the effluent (USEPA 2004b).

In addition to conventional tert iary treatment, there are half-t ertiary treatment methods that remove some minerals and organic material , such as the method used by the WWTP in Orange County, California. In addition, constr ucted wetlands are now being looked at as a cost-effective and technically f easible approach to treating wastewater. In 2004 there were approximately 1,000 constructed wetlands in op eration in the United States. ConstructingSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 1: Introduction and History 1-3 wetlands is often less expensive than building traditional wastewater treatment facilities. In addition, wetlands have low operation and maintenance (O&M) costs and can handle fluctuating water levels (USEPA 2004a).

The following discussion provides some examples of nutrient removal technologies that have been used or are currently in use in the United States. The discussion is not intended to be an exhaustive history of nutrient removal from municipal wastewater. EPA recognizes the substantial efforts being undert aken in many parts of the country to reduce nutrients, including many mid-continent locations, Long Island Sound, Puget Sound, and numerous other estuaries on the Atlantic, Gulf of Mexico, and Pacific coasts.



### 1.2.1 Lake Tahoe One of the earliest tertiary treatment plants was introduced by South Lake Tahoe, California, and Stateline, Nevada, to protect Lake Tahoe. Th e threat to the lake became serious in the late 1950s when the population along the sout h shore of the 21-mile -long lake increased sixfold in addition to an increas e in the number of tourists. Se ptic tanks were used for many years before the construction of WWTPs in th e 1960s (Lake Tahoe Environmental Education Coalition 2005).

The South Tahoe Public Utility District was formed in 1950 with the intention of treating sewage from the south shore, including Nevada ’s casinos. Later in that decade, the Nevada side formed its own district, and the South Tahoe Public Util ity District took responsibility for sewage from the city of South Lake Tahoe and from Eldorado County (Lake Tahoe Environmental Education Coalition 2005).

By 1965 an innovative advanced te rtiary treatment plant, whic h treated sewage to drinking water standards, was installed. Effluent from the plant is not discharged to Lake Tahoe; instead, it is pumped through a 27- mile pipeline over Luther Pass into a storage reservoir in Alpine County. All effluent from the city of South Lake Tahoe and Eldorado County areas has been exported through this system since April 1968 (Lake Tahoe Environmental Education Coalition 2005).

Once the export system was completed, the treatm ent plant reduced its treatment to advanced secondary treatment, which disinfected the treate d effluent water but le ft trace amounts of nitrogen and phosphorus. This effl uent water is stored in a re servoir near Woodfords during the winter and released for use by ranchers to ir rigate their pastures a nd alfalfa crops in the summer (Lake Tahoe Environmental Education Coalition 2005).

On California’s northern and west ern shores, two local jurisdictions collect all the sewage in the sanitary sewers and pump it to Truckee. Th e Tahoe City Public Ut ility District and the North Tahoe Public Utility District cooperated under a Joint Powers Agreement to build aMunicipal Nutrient Removal Technologies Reference Document September 2008

1-4 Chapter 1: Introduction and History joint sewerage facility in 1968 to treat the sewage of both districts (Lake Tahoe Environmental Education Coalition 2005).

The Tahoe Regional Planning Compact was ad opted in 1969 when the California and Nevada legislatures agreed to create the Tahoe Regional Planning Agency (TRPA) to protect Lake Tahoe (Tahoe Regional Planning Agen cy 1980). The compact, as amended in 1980, defines the purpose of the TRPA:

To enhance governmental efficiency a nd effectiveness of the Region, it is imperative there be established a Tahoe Regional Planning Agency with the powers conferred by this compact including the power to establish environmental threshold carrying capacities and to adopt and enforce a regional plan and implementing ordinances which will achieve and maintain such capacities while providing opportunities for orderly growth and development consistent with such capacities (Tahoe Regional Planning Agency 1980).

In 1978 the Tahoe-Truckee Sanitation Agency built a state-of-the-art tertiary treatment plant in Truckee. Since then, the Tahoe City and North Tahoe Public Utility Districts have collected all sewage between D.L. Bliss Stat e Park at Emerald Bay and Kings Beach and have transported it to the Tahoe-Truckee Sani tation Agency plant through pipelines. The tertiary-treated effluent from this plan t is injected into the ground (Lake Tahoe Environmental Education Coalition 2005).



### 1.2.2 Great Lakes The Great Lakes region led the nation in developing successful nutrient control and contaminant cleanup strategies during the 1970s. Th e deterioration of Lake Erie in the 1960s due to eutrophication prompted bilateral actions by Canada and the United States to sign the first Great Lakes Water Quality Agreement in 1972. The Agreement outlined abatement goals for reducing phosphorus loads primarily from laundry detergents and municipal sewage effluent. In response to this commitment, Canada and Ontario en acted legislation and programs for controlling point sources. Between 1972 and 1987, Canada and Ontario invested more than $2 billion in sewage trea tment plant construction and upgrading in the Great Lakes Basin (Environment Canada 2006).September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 1: Introduction and History 1-5 The 1978 Agreement between the United States and Canada on Great Lakes Water Quality, which followed the original 1972 Agreem ent, contains the following text:

3. Nutrients
(a) Phosphorus

The concentration should be limite d to the extent necessary to prevent nuisance growths of algae, weeds and slimes that are or may become injurious to any be neficial water use. (Specific phosphorus control requirements are set out in Annex 3.)

ANNEX 3
Control of Phosphorus
1. The purpose of the following programs is to minimize eutrophication problems and to prev ent degradation with regard to phosphorus in the boundary waters of the Great Lakes System. The goals of phosphorus control are:

(a) Restoration of year-round aer obic conditions in the bottom waters of the Central Basin of Lake Erie;
(b) Substantial reduction in the pr esent levels of algal bio-mass to a level below that of a nuisa nce condition in Lake Erie;
(c) Reduction in present levels of algal biomass to below that of a nuisance condition in Lake Ontari o including the International Section of the St. Lawrence River;
(d) Maintenance of the oligot rophic state and relative algal biomass of Lakes Superior and Huron;
(e) Substantial elimination of algal nuisance growths in Lake Michigan to restore it to an oligotrophic state; and
(f) The elimination of algal nuisance in bays and in other areas wherever they occur.
2. The following programs shall be developed and implemented to reduce input of phosphorus to the Great Lakes:

(a) Construction and operation of municipal waste treatment facilities in all plants discharging more than one million gallons per day to achieve, wh ere necessary to meet the loading allocations to be deve loped pursuant to paragraph 3 below, or to meet local c onditions, whichever is more stringent, effluent concentrations of 1 milligram per liter totalMunicipal Nutrient Removal Technologies Reference Document September 2008

1-6 Chapter 1: Introduction and History phosphorus maximum for plants in the basins of Lake Superior, Michigan, and Huron, and of 0.5 milligram per liter total phosphorus maximum for plants in the basins of Lakes Ontario and Erie.
(b) Regulation of phosphorus in troduction from industrial discharges to the maximum practicable extent.
(c) Reduction to the maximum ex tent practicable of phosphorus introduced from diffuse sour ces into Lakes Superior, Michigan, and Huron; and a substantial reduction of phosphorus introduced from di ffuse sources into Lakes Ontario and Eric, where necessary to meet the loading allocations to be developed pursu ant to paragraph 3 below, or to meet local conditions, whichever is more stringent.
(d) Reduction of phosphorus in household detergents to 0.507 percent by weight where necessary to meet the loading allocations to be developed pursu ant to paragraph 3 below, or to meet local conditions, whichever is more stringent.
(e) Maintenance of a viable research program to seek maximum efficiency and effectiveness in the control of phosphorus introductions into the Great Lakes (CIESIN 1995).

As reported in the 1995 biennial progress repor t, all the U.S. and Canadian open-water phosphorus target levels have been achieved through combined efforts to improve the performance of sewage treatment plants, to re duce levels of phosphorus in detergents, and to implement agricultural best management practices . Current loads are clearly below the target loads of the 1978 Agreement for Lakes Superior , Huron, and Michigan and are at or near target limits for Lakes Erie and Ontario. Lake Er ie still experiences brief periods of anoxia in some areas of its central basin. The 1997 State of the Great Lakes Report reviewed nutrient data since 1994 and concluded that no appreciable change had occu rred in the nutrient status of the lakes and that the lake s continued to meet the target s for phosphorus reduction in the agreement. Continuing success is attributed to implementing a number of programs to control soil erosion and sedimentation, as well as ot her forms of nonpoint source control (USEPA 2006).



### 1.2.3 The Occoquan Reservoi r and the Chesapeake Bay The Occoquan Reservoir serves as a drinking wa ter supply for a service area of more than 1 million people in the northern Virginia suburbs of Washington, D.C. The Occoquan Policy was adopted by the Virginia State Water Cont rol Board in 1971. This Policy commissioned the development of a regional treatment pl ant, the Upper Occoquan Sewage AuthoritySeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 1: Introduction and History 1-7 (UOSA) Advanced Wastewater Treatment (AWT ) Plant. When it went online in 1978, the UOSA AWT Plant replaced 11 conventional secondary treatment plants in Fairfax and Prince William counties. The quality of effluent from these plants was variable, and no provisions were made for the removal of nutrients from th e discharges. In contra st, the regional UOSA AWT Plant included monthly average nutrient li mits of 0.1 milligrams per liter (mg/L) for Phosphorus and 1.0 mg/L for unoxidized nitrogen m easured as total Kjeldahl nitrogen (TKN) (Occoquan Monitoring Lab 2008 and Randall 2008). Developed to protect the drinking water supply (Occoquan Reservoir) for the Virginia suburbs of Washington, D.C., this plant currently treats 50 MGD and is the largest indi rect sewage-to-drinking water system in the world. It is unique in that, although originally designed to remove nitrogen by ion exchange removal of NH4-N, most of the nitr ogen is discharged in the form of nitrates to a stream that enters the reservoir to reduce the release of phosphorus from the sediments, thereby helping control algae blooms and protec ting water quality (Randall 2008).

In the late 1970s and early 1980s, Congress funde d scientific and estuar ine research in the Chesapeake Bay, pinpointing three areas, incl uding nutrient enrichment, as requiring immediate attention. The Chesapeake Bay Progr am was created in 1983 after the signing of The Chesapeake Bay Agreement of 1983 (Chesapeake Bay Program 1983). The Chesapeake Bay Program is a unique regional partnership between the states of Maryland, Pennsylvania, and Virginia; the District of Columbia; the Chesapeake Bay Commission; EPA; a tristate legislative body; and citizen a dvisory groups. It has led and di rected the restoration of the Chesapeake Bay since 1983 (Chesapeak e Bay Program 2005). However, the Chesapeake Bay 2006 Health and Restoration Assessment reports show that the ba y’s overall health remains degraded, despite significant advances in rest oration efforts by progr am partners through newly focused programs, legislation, and funding (Chesapeake Bay Program 2007).

Since the signing of the Chesapeake Bay Agreement of 1983, program partners have adopted two additional bay agreements, the 1987 Chesapeake Bay Agreement and Chesapeake 2000 (Chesapeake Bay Program 2000). The main goals of Chesapeake 2000 are to continue efforts to achieve and maintain the 40 percent nutrien t reduction goal agreed to in 1987; to adopt goals for tributaries south of the Potomac Rive r; and to “correct the nutrient and sediment related problems in the Chesapeake Bay and its tidal tributaries sufficiently to remove the Bay and the tidal portions of its tributaries fr om the list of impaired waters under the CWA” (Chesapeake Bay Program 2000).

EPA has calculated that nitrogen and phosphorus discharges from all sources must be drastically reduced beyond current levels and th at municipal WWTPs, in particular, will have to reduce nitrogen discharges by 72 per cent (Chesapeake Bay Foundation 2002). On March 21, 2003, the program partners agreed to reduce nutrient pollution by more than twice as much as was accomplished since coordinated ba y restoration efforts began nearly 20 years ago. The District of Columbia and states that border the bay have agreed to reduce the amount of nitrogen discharged from the current 275 million pounds to no more thanMunicipal Nutrient Removal Technologies Reference Document September 2008

1-8 Chapter 1: Introduction and History 175 million pounds per year and to reduce the am ount of phosphorus discharged from the current 18.8 million pounds to no more than 12.8 million pounds per year (Chesapeake Bay Program 2003). EPA Region 3 has established a nutrient criteria team to implement the National Nutrient Strategy issued by EPA fo r the Mid-Atlantic region (Chesapeake Bay Program 2003).



### 1.3 NPDES Permitting

The National Pollutant Discharge Elimination Sy stem (NPDES) aids in the attainment of water quality standards by regulating point sources that discharge into the surface waterbodies. Effluent limitations are the primary mechanism in NPDES permits for controlling discharges of pollutant s to receiving waters. When de veloping effluent limitations for an NPDES permit, a permit writer must consider limits based on both the technology available to control the polluta nts (i.e., technology-based efflue nt limits) and limits that are protective of the water quality standards of the receiving water (i.e ., water quality-based effluent limits, or WQBELs). A permit writer may find that a discharge causes, has the reasonable potential to cause, or contributes to an exceedance of a water quality standard and that technology-based effluent lim its are not adequate to ensure that water quality standards will be attained in the receiving water. In such cases, CWA section 303(b)(1)(c) and the NPDES regulations at 40 CFR 122.44(d) requ ire that the permit writer develop more stringent WQBELs designed to ensure that wa ter quality standards are attained. Developing appropriate effluent limits in NPDES permits is a vital component of the water quality standards-to-permits process.

For more information about the permitting pr ocess, see the following documents and Web sites:

EPA’s National Pollutant Discharge Elim ination System (NPDES) Web site at http://www.epa.gov/npdes

EPA’s NPDES Permit Writers’ Manual http://cfpub.epa.gov/npdes/wri termanual.cfm?program_id=45



### 1.3.1 Watershed-based Permitti ng and Water Quality Trading To assist in determining how various permitted di scharges affect attainment of water quality criteria on a watershed basis, EPA has deve loped watershed-based permitting and water quality trading as innovative tools that use a watershed approach. EPA expects that watershed-based permitting and water quality tr ading will be useful tools for implementing WQBELs for nitrogen and phos phorus in NPDES permits.

Watershed-based permitting is an approach to NPDES permitting in which permits are designed to attain watershed goa ls that reflect consideration of all sources/stressors in aSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 1: Introduction and History 1-9 watershed or basin. These permits are devel oped through a watershed planning framework to communicate with stakeholders and to integrat e permit development with monitoring, water quality standards, total maximum daily load (TMDL), nonpoint source, source water protection, and other programs. The ultimate goal of watershed-based permitting is to develop and issue NPDES permits that consider the entire watershed, no t just an individual point source discharger.

Water quality trading is a vol untary market-based approach that, if used in certain watersheds, might achieve water quality standard s more efficiently and at lower cost than traditional approaches. For a given pollutant, costs for controlling point source discharges compared to costs for controlling nonpoint s ource runoff often vary significantly in a watershed, creating the impetus for water qua lity trading. Through water quality trading, facilities that face higher polluta nt control costs to meet th eir regulatory obligations can purchase pollutant reducti on credits from other sources that can generate the reductions at a lower cost, thus achieving the same or better overall water quality improvement. Trading also can provide ancillary environmental benefits like flood control, riparian improvement, and habitat.

For more information on new tools developed by EPA that can assist with meeting water quality goals, see the following documents and Web sites:

Watershed-based Permi tting Policy Statement and related information http://www.epa.gov/npdes/pubs/wat ershed-permitting-policy.pdf

Watershed-Based National Pollutant Discharge Elimination System (NPDES) Permitting Implementation Guidance http://www.epa.gov/npdes/pubs/wat ershedpermitting_finalguidance.pdf

Watershed-based National Pollutant Dischar ge Elimination System (NPDES) Permitting Technical Guidance http://www.epa.gov/npdes/pubs/water shed_techguidance_entire.pdf

Water quality based permitting and related information http://cfpub.epa.gov/npdes/wqbasedpermitting/wspermitting.cfm

EPA’s Water Quality Trading Web site http://www.epa.gov/owow/watershed/trading.htm

Trading policy statement http://www.epa.gov/owow/watersh ed/trading/tradingpolicy.html

Water Quality Trading Assessment Handbook http://www.epa.gov/owow/watershed/trading/handbook

Water Quality Trading Toolkit for Permit Writers http://www.epa.gov/waterqualitytrading/WQTToolkit.htmlMunicipal Nutrient Removal Technologies Reference Document September 2008

1-10 Chapter 1: Introduction and History 

### 1.4 References

Carberry, J.B. 1990. Environmental System s and Engineering . Saunders College Publishing, Orlando, FL.

Chesapeake Bay Foundation. 2002. Reducing Nitrogen and Phosphorus from Wastewater Treatment Facilities. http://www.cbf.org/site/PageServer?pagename= resources_facts_nutrient_red_ww . July 2002. Accessed October 3, 2007.

Chesapeake Bay Program. 1983. The Chesapeake Bay Agreement of 1983

. http://www.chesapeakebay.net/pubs/1983ChesapeakeBayAgreement.pdf . Revised March 4, 1996. Accessed October 3, 2007.

Chesapeake Bay Program. 1987. 1987 Chesapeake Bay Agreement

. http://www.chesap eakebay.net/pubs/199.pdf . December 15, 1987. Accessed October 3, 2007.

Chesapeake Bay Program. 2000. Chesapeake 2000

. http://www.chesapeakebay.net/ pubs/chesapeake2000agreement.pdf . June 28, 2000. Accessed October 3, 2007.

Chesapeake Bay Program. 2003. Bay Criteria: Defining Rest ored Bay Water Quality

. http://meso.spawar.navy.mil/Newsltr /Refs/AWQC_DO_WC_CA_Chesapeake.pdf

. June 4, 2003. Accessed October 3, 2007.

Chesapeake Bay Program. 2005. Overview of the Bay Program. http://www.chesapeakebay.net/overview.htm . Revised February 20, 2008. Accessed October 3, 2007.

Chesapeake Bay Program. 2007. 2006 Bay Health & Restoration Assessment Details Bay’s Degraded Water Quality, Restoration Efforts Throughout Watershed

. http://www.chesapeakeba y.net/newsassessment041807.htm . Revised February 14, 2008. Accessed October 3, 2007.

CIESIN (Center for International Eart h Science Information Network). 1995. Environmental Treaties and Resource Indicators (ENTRI ): 1978 Agreement Between the United States and Canada on Great Lakes Water Quality

. http://sedac.ciesin.org/en tri/texts/bi-lateral/2.6X -USXCan-Gt.Lks-H2O.html

. Amended October 16, 1983. Accessed October 3, 2007.

Environment Canada. 2006. Great Lakes Water Quality Agreement

. http://www.on.ec.gc.ca/greatlakes/de fault.asp?lang=En&n=FD65DFE5-1

. December 12, 2006. Accessed October 3, 2007.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 1: Introduction and History 1-11 Lake Tahoe Environmenta l Education Coalition. 2005. Lake Tahoe Report #87: Export of Tahoe’s Treated Sewage Protects the Lake

. http://4swep.org/resource s/LakeTahoeReport/087.html . Revised February 3, 2005. Accessed May 13, 2008.

National Academy of Sciences. 1999. New Strategies for America’s Watersheds

. National Academy of Sciences, Washington, DC.

Occoquan Watershed Monitoring Lab. 2008. Information on the Occoquan Policy. http://www.owml.vt.edu/aboutowml.htm . Accessed August 5, 2008.

Randall, C.W. 2008. Personal communication through peer review comments on draft document. Received May 2008.

Rast, W., and J.A. Thornton. 1996. Trends in Eutrophication Resear ch and Control. Hydrological Processes 10:295–313.

Tahoe Regional Planning Agency. 1980. Tahoe Regional Planning Compact (Public Law 96- 551-Dec. 19, 1980)

. http://www.trpa.org/documents/about_trpa/Bistate_Compact.pdf

. December 19, 1980. Accessed October 3, 2007.

USEPA (U.S. Environmental Protection Agency). 1993. Nitrogen Control Manual

. EPA/625/R-93/010. U.S. Environmental Pr otection Agency, Washington, DC.

USEPA (U.S. Environmental Protection Agency). 1998. EPA Announces Guidance on State Revolving Funds for Sewage Treatment

. http://www.epa.gov/history/topics/cwa/02.htm . Revised September 21, 2007. Accessed October 3, 2007.

USEPA (U.S. Environmental Protection Agency). 2004a. Constructed Treatment Wetlands

. EPA 843-F-03-013. U.S. Environmental Prot ection Agency, Office of Water. http://www.epa.gov/owow/wetlands/pdf/ConstructedW.pdf . August 2004. Accessed October 3, 2007.

USEPA (U.S. Environmental Protection Agency). 2004b. Primer for Municipal Wastewater Treatment Systems . EPA 832-R-04-001. http://www.epa.gov/OWM/primer.pdf

. September 2004. Accessed October 3, 2007.

USEPA (U.S. Environmental Protection Agency). 2006. United States Great Lakes Program Report on the Great Lakes Water Quality Agreement

. http://www.epa.gov/glnpo/ glwqa/usreport/part4.html# EXCESSIVE%20NUTRIENT%20LOADINGS. March 9, 2006. Accessed October 3, 2007.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-1 

## CHAPTER 2: Treatment Technologies

2.1 Overview

This chapter presents information about availabl e technologies that can be used to remove nitrogen and phosphorus from municipal wast ewater. The technologies are presented along with performance data that show the variability of the effluent concentrations. The purpose of this chapter is to help permit writers devel op appropriate discharge permit limits with a full understanding of available tec hnologies, their variability, an d their ability to meet the proposed limits in the most sustainable way. Th e same information is made available to municipal planners and engineer s to assist in their prepara tion of compliance plans for new discharge permits.

The information in this document was obtaine d from many sources, incl uding publications of the Water Environment Federation (WEF), Water Environment Research Foundation (WERF), and other organizations ; reports from the states of Maryland and Connecticut; and data from 30 municipal treatment facilities that participated voluntarily in 2006 and 2007.

The full-scale performance data are expre ssed on the same statistical basis for easy comparison. The data are accompanied by a discussi on of the key factors that contribute to the performance variability and reliability of various systems. These factors are wastewater characteristics; process parameters; environmental parameters such as temperature, chemistry, and biology; and operating paramete rs. It should be emphasized that the performance data for these facilities refl ect differences in operating philosophy, permit limitations, temperature, influent conditions, fl ow conditions, and the relative plant load compared to design. Thus, the documented performance does not necessarily represent optimum operation of the technologies presented.

Following this chapter, Chapter 3 provides a detailed discussion about the case studies on nine facilities. Cost information is presented in Chapter 4, and design f actors that should be considered when selecting a retrofit or a ne w upgrade process technology are discussed in Chapter 5.



### 2.2 Nitrogen Removal Processes

2.2.1 Nitrogen Species in Wastewater For the purposes of this document, only biol ogical nitrogen removal is considered, along with physical removal by filtration of solid s containing incorporated nitrogen. Other physical-chemical processes, such as breakpoint chlorination, ion exchange, and air stripping, are not included because they ar e not usually feasible for municipalities because of technical, regulatory, and cost considerations.Municipal Nutrient Removal Technologies Reference Document September 2008

2-2 Chapter 2: Treatment Technologies The biological removal of nitrogen is carried out through a three-st ep process: (1) the conversion of ammonia from or ganic nitrogen by hydrolysis a nd microbial activities, called ammonification ; (2) the aerobic conversi on of ammonia to nitrat e by reacting the ammonia with oxygen in a process called nitrification ; and (3) the conversion of nitrate to nitrogen gas by reacting the nitrate with organic carbon under anoxic conditions in a process called denitrification . The nitrification process is accomp anied by the destruct ion of alkalinity (e.g., bicarbonate, HCO 3 - , is neutralized to carbonic acid, H 2 CO 3 ). Alkalinity is recovered as part of the denitrification proce ss with the generation of hydroxide.

The chemical equations involved in the biolog ical conversion of nitr ogen are as follows:

1. Formation of ammonia from organic nitr ogen by microorganisms (ammonification):

Organic nitrogen Æ NH 4 +
2. Nitrification to nitrite by Nitrosomonas species and other autotrophic bacteria genera:

NH 4 + + 3/2 O 2 + 2HCO 3 - Æ NO 2 - + 2H 2 CO 3 + H 2 O
3. Nitrification to nitrate by Nitrobacter species and other autotr ophic bacteria genera:

NO 2 - + 1⁄2 O 2 Æ NO 3 -
4. Denitrification by denitrifying mi croorganisms with no oxygen present:

NO 3 - + organic carbon Æ N 2 (g) + CO 2 (g) + H 2 O + OH The stoichiometry for nitrif ication shows 4.57 grams of oxyg en per gram of ammonia nitrogen and consumption of 7.14 grams of al kalinity as measured as calcium carbonate (CaCO 3 ) per gram of ammonia nitrogen. The stoich iometry for denitrification shows at least 2.86 grams of chemical oxygen demand (COD) requi red per gram of nitrate nitrogen or 1.91 grams of methanol per gram of nitrate nitr ogen. This includes car bon incorporated into biomass production (Metcalfe & Eddy, 2003, p 621) . Alkalinity is generated as 3.57 grams per gram of nitrate nitrogen denitrified (WEF and ASCE, 2006, pp. 39 and 71, respectively).

Nitrification operates on ammoni a nitrogen and most of the to tal Kjeldahl nitrogen (TKN). Dissolved organic nitrogen (DON) compounds are typically complex nitrogen-containing molecules that constitute a portion of TKN but ar e difficult to break down. In most localities, the average DON concentration rang es from 0.5 to 2 milligrams per liter (mg/L) (Demirtas et al. 2008); however, higher DON concentrations can occur in some locations because of industrial sources or natural components in the background. High DON concentrations negatively affect the ability of a plant to achieve a low final total nitrogen (TN) level, even with installation of the processes described in this chapter.

A reasonable solution to address the presen ce of DON that is based on science and technology is needed. Pagilla (WERF 2007) char acterized DON in wastewater and reportedSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-3 that it could be grouped by molecular wei ght (MW). The DON co mpound group with an MW of less than 1,000 Dalton (Da) includes ur ea, amino acids, DNA, peptides, and various synthetic compounds. The DON group with an MW ranging between 1,000 and 1,000,000 Da includes fulvic acids. Hi gh-MW DON includes humic substa nces. Biological wastewater treatment has been considered effective in removing low-MW DON, while high-MW DON is considered refractory to this kind of tr eatment. Sedlak and Pehlivanoglu-Mantas (2006) indicated that a portion of the recalcitrant DON could have a slow degradation rate, and thus the effect on the receiving stream water w ould be low. Pagilla (WERF 2007) proposed a short-term test protocol to a ssess the bioavailability of DON using algae and bacteria. More research is needed to determine the sources and fate of DON in wastewater treatment processes and the method by which bioa vailability can be demonstrated.



### 2.2.2 Nitrogen Removal Factors

Carbon Source Many have reported from their research the quan tity of carbon, in proportion to the nitrogen present in the wastewater, necessary to reduc e the amount of nitrogen. They have included the COD-to-TKN ratio, the readily biodegradab le COD (rbCOD)-to-TKN ratio, and volatile fatty acids (VFAs). A biochemical oxygen dema nd (BOD)-to-TKN ratio of 4 or greater is sufficient for biological nitrog en removal to occur (Neethli ng et al. 2005; WEF and ASCE 1998; Lindeke et al. 2005). Norm al domestic wastewater cont ains a sufficient COD-to-TKN ratio to remove 65 to 85 percent of the nitr ogen in a single-pass process like the modified Ludzack-Ettinger (MLE) (Barnard 2006) or in attached-growth systems like biological aerated filters (BAFs) (Stephenson et al. 2004) and moving-bed biofilm reactors (MBBRs) (Rusten et al. 2002). Simultane ous nitrification a nd denitrification (SND) in oxidation ditches, such as the Orbal oxidation ditch system, has shown up to 90 percent nitrogen removal in the extended-aeration mode. When combined with a pre-anoxic zone, the oxidation ditch can produce an average TN con centration of less than 3.1 mg/L with an 85 th percentile value of 4 mg/L (B arnard 2006). The 4-stage Bard enpho process using a carousel aeration basin produced an aver age TN concentration of 1.9 mg/L, where plant sludge was hauled away to another plant for processing (d eBarbadillo et al. 2003). Processes such as the 4-stage Bardenpho can fully utilize influent carb on and meet most limits except for very low targets. This means that they will have cost savings via reduced energy use and no need for supplemental carbon, which results in no additional sludge production.

When it is determined that an additional carbon source is needed to achieve the desired level of nitrogen removal, there are two types of sources—in-plant and external. In-plant sources include primary effluent, which can be step -fed to the activated -sludge process, and fermentation of primary sludge to obtain VF As and other readily used carbon compounds. Step-feeding reduces the needed tank footprint due to lower hydraulic and sludge detention times; reduces or eliminates the need for an additional carbon sour ce; and, as an extra advantage, provides the wastewat er treatment plant (WWTP) operators the ability to betterMunicipal Nutrient Removal Technologies Reference Document September 2008

2-4 Chapter 2: Treatment Technologies handle wet-weather flows. Successful operation, however, requires oxygen control, an alkalinity supply, and good instrumentat ion incorporated into the system.

In New York, Chandran et al. (2004) were able to achieve 4 mg/L in a four-pass system with additional carbon in a limited anoxic zone vol ume. McGrath et al. (2005b) reported threeway split feed with anoxic, swing, and aeration zones that were 35 percent, 15 percent, and 50 percent of the activated sludge tank volume, respectively. Duri ng the last 12 months of the study, effluent TN ranged from 3 to 7.25 mg/L, with an annual average of 5 mg/L. Tang et al. (2004) developed a model to obtain the optimal step-feed pattern to use in four plants in the Los Angeles County Sanitation Districts. They found that for a system with two anoxic stages, feeding approximately two- thirds of the flow to the fi rst stage and one-third of the flow to the second stage provide d the best overall removal. As the number of anoxic stages increases, less is put into the first stage, but the first stage still rece ives 40 to 50 percent of the total flow. In general, use of more than four anoxic stages provides minimal benefits. Less primary effluent and return activated sl udge (RAS) should be fed to the last stage because any ammonia or nitrate that is not treated in the last stage passes through the secondary clarifiers and increases the TN concentration in the overall discharge. If the BODto-TKN ratio is low, however, a higher percenta ge of the flow (compared to typical BOD-toTKN ratios) should be fed to the later stages. Alternatively, equal dist ribution of flow among the splits, with no flow to the last section, ha s also been found to wo rk well (Metcalf & Eddy 2003).

An in-plant alternative to st ep-feeding is fermentation. Fermen ters are usually associated with plants that perform biological phosphorus re moval. It is also not ed, however, that when high nitrate concentrations are returned to the anaerobic zone, de nitrification occurs, consuming some of the VFAs that the fermenter produced. Fermenters can therefore be used to provide a source of carbon for plants that perform denitrification. Stinson et al. (2002) reported on a pilot study performed by the New York City Department of Environmental Protection that compared denitrification rate s achieved by feeding methanol, acetate, and fermentate. The results from the pilot plants operating in the step-feed activated-sludge mode indicate that denitrification rates for fermenta te and acetate were similar at 0.15 to 0.30 mg of nitrate nitrogen per milligram of volatile suspended solids (VSS) per day (mg N/mg VSSday), whereas denitrification rates using metha nol were significantly lower at 0.04 to 0.08 mg N/mg VSS-day. Higher denitrification rates re sulted in less carbon source addition and therefore less sludge production.

Methanol is most often used as an external carbon source because of its relatively low cost. Methanol, however, is corrosive and combustible and therefore requires special handling to meet Occupational Safety and Health Admini stration (OSHA) regula tions and NFPA-820: Standard for Fire Protection in Wastewat er Treatment and Co llection Facilities . Some plants are considering alternatives to methanol because of these flammability and explosion concerns. Other chemicals, such as MicroC (distributed by Environmental OperatingSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-5 Solutions, Inc.) can be used. The company th at manufactures MicroC recently introduced MicroCG, which replaces the 5 to 6 percent of methanol in MicroC with glycerin.

Communities with a nearby supplemental carbon s ource, such as molasses or brewery waste, can consider the opportunity to use such sources. The advantage of using an external carbon source is that the operation is independent of the nature and volume of the influent wastewater, giving the operators much more flexibility. The disadvantage is that the additional carbon source will increase capital costs due to the construction of chemical storage, feed pumps, and piping and will requi re substantial operating costs for purchasing the chemicals and handling the extra sludge ge nerated because of the addition. The carbon source is typically added to the separate-stage anoxic zone or denitrification filters. A study by deBarbadillo et al. (2005) presented exte rnal carbon source doses for denitrification filters. Typical methanol doses are between 2.5 and 3 times the amount of nitrate nitrogen to be removed on a mass basis (WEF and ASCE 2006, p. 75).

Number of Anoxic Zones A single anoxic basin with an internal recycl e stream can achieve re asonable rates of TN removal in the range of 6 to 8 mg/L. An ex ample of such a process is the MLE process (described in more detail later). The internal recycle returns nitrates produced by nitrification in the aeration basin to the anoxic zone for de nitrification. With the anoxic zone at the beginning of the process, carbon source addition is not usually necessary because domestic wastewater typically provides enough carbon to achieve 65 to 85 percent removal (Barnard 2006).

In general, the denitrification rate increases with increasing internal recirculation, up to a maximum of 500 percent (WEF and ASCE 2006). Denitrification in wa stewaters with BODto-TKN ratios less than 4-to-1 or COD-to-TKN ratios less than 10-to -1 typically is not benefited by high internal recirculation. This is because such wastewater has insufficient carbon to support an elevated denitrification rate.

Having two anoxic zones allows lower TN efflue nt concentrations to be achieved because more of the nitrates produced after nitrifica tion in the aeration basi n can be treated by an internal recycle to the firs t anoxic zone or by flowing th rough the second anoxic zone. Aeration is usually recommended after the seco nd anoxic zone to both strip nitrogen gas formed in the anoxic zone and to decrease the po ssibility of denitrific ation in the secondary clarifiers. This has the effect of reducing nitrogen gas releas e in the secondary clarifier, which could result in rising sludge. In addi tion, maintaining aerobic conditions prevents phosphorus release in the seconda ry clarifiers. Adding a carb on source to the second anoxic zone can further increase denitrification by ensu ring that sufficient carbon is available for the process to occur. Barnard (2006) has reporte d that processes involving two anoxic zones, such as the 4- or 5-stage Bardenpho process, can achieve TN concentrations between 2.5 and 3.5 mg/L. Clearwater, Florida, operates the Marshall Street and Northeast AdvancedMunicipal Nutrient Removal Technologies Reference Document September 2008

2-6 Chapter 2: Treatment Technologies Pollution Control Facilities. Both plants ar e achieving annual average TN levels below 3 mg/L––2.32 and 2.04 mg/L, respectively––with out a supplementary carbon source.

Temperature Temperature affects the rate of both nitrificat ion and denitrification. At lower temperatures, the nitrification and denitrification rates decr ease, leading to poorer performance in the winter if operational changes ar e not made to compensate for the decreased kinetic rates. Nitrification can occur in wastewater te mperatures of 4 to 35 degrees Celsius ( o C). Typical wastewater temperatures range between 10 and 25 °C (WEF and ASCE 2006, p. 41). The nitrification rate doubles for every 8 to 10 °C rise in temper ature, meaning that in areas that experience a wide range of temperatures betw een winter and summer , nitrification rates could differ by a factor of 4 over the cour se of a year (WEF and ASCE 2006, p. 42). Denitrification is also subject to temperature, although to a lesse r extent than nitrification. On the basis of a wastewater temperature range of 10 to 25 °C, the denitrification rate would be expected to vary by a factor of only 1.5 (W EF and ASCE 2006, p. 73). Alternative carbon sources should be explored to determine if an additional carbon supply could provide better denitrification performance in cold weather than others. Alte rnatively, external carbon might not be needed at all during warm weather cond itions, because the process might be able to meet the treatment objectives with th e available carbon in the wastewater.

Alkalinity Alkalinity is consumed as part of the nitrification process because hydrogen ions are created when ammonia nitrogen is converted to nitrate nitrogen. Denitrification restores a portion of the alkalinity during the convers ion of nitrate nitrogen to n itrogen gas. The nitrification process consumes 7.14 grams of alkalinity as calcium carbonate (CaCO 3 ) per gram of ammonia nitrogen removed (WEF and ASCE 2006, p. 39). Denitrification produces 3.57 grams of alkalinity as CaCO 3 per gram of nitrate nitrogen removed (WEF and ASCE 2006, p. 71). Therefore, to convert 1 gram of a mmonia nitrogen to 1 gram of nitrogen gas, approximately 3.6 grams of alkalinity as CaCO 3 is consumed. Nitrification can generally occur at pH values between 6.5 and 8.0 sta ndard units (s.u.). The recommended minimum alkalinity in the secondary effluent is 50 mg/L as CaCO 3 , although as much as 100 mg/L is suggested by standard design manuals (WEF an d ASCE 2006, p. 43). If the alkalinity will be below the recommended levels, chemical additi on might be necessary. Sodium hydroxide or lime is added at some plants to mainta in acceptable alkalinity and pH levels.

Solids Retention Time The solids retention time (SRT) must be long enough to maintain nitrification. The microorganisms responsible for nitrification ha ve a much slower growth rate than other heterotrophic bacteria. Therefore, doubling of the nitrification microorganism population requires 10 to 20 times longer than for other heterotrophic bacteria (WEF and ASCE 2006, p. 40). Maintaining longer SRTs can also reduce the amount of energy required for mixing ifSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-7 tank sizes and liquid volumes can be redu ced. In addition, energy can be saved if denitrification can be achieved in an SND app lication (Barnard et al . 2004; Kang et al. 2006). Some plants with mechanical aerators and/or concentric ditches operating with the same SRTs have a lower aerator energy-to-volume ra tio. The lower energy requirement is because of SND, which results in reduced oxygen needs. For example, Barnard (2004) reported that the aerator energy density was decreased by more than half when the SRT was increased from 8 days to 24 days. Concurrently, the SND rate increased from 30 percent at an 8-day SRT to 70 percent at a 24-day SRT. The optimum SRT for a given WWTP depends on several factors, including wast ewater temperature, dissolved oxygen (DO) concentration in the aerobic zone, pH, alkalinity, inhibition from chemicals, and variations in hydraulic flow and organic load. In general, denitrifying mi croorganisms are relatively slow growing and can be subject to washout at high flows in the bioreactor or clarifier. Therefore, secondary clarifier design that assures maximum retenti on of the slower grow ing microorganisms can be critical to maintaining reliable nitrogen removal performance.

Hydraulic Retention Time Hydraulic retention time (HRT) affects both ni trification and denitr ification. The aerobic zone(s) of single nitrification/denitrification processes must be large enough to allow most of the carbonaceous BOD (CBOD) to be consumed before nitrification can begin. The size of the anoxic zone(s) must be sufficient to allow denitrification to occur without consuming the entire carbon source that might be needed for biological phosphorus removal. Anoxic zones are typically 35 to 50 percent of the secondary treatment process by volume. Because of the uncertainty in the required volume, some plants are designed with sw ing zones that can be operated in an anoxic or aerobic mode. Generall y, swing zones can be operated as aerobic during the summer and anoxic during the wi nter, when low temperatures lower the denitrification rates. However, sufficient aerob ic detention time must be maintained for adequate nitrification. To test whether the HRT is limiting, two samples can be collected at the same time from the end of the anoxic zone. One sample can be filtered and analyzed for nitrates immediately, while the second sample can be filtered and analyzed for nitrates after 30 minutes. If the second sample has a lower n itrate concentration than the first, the HRT limits denitrification. If there is little difference between the tw o samples, it is more likely that lack of an adequate carbon source is lim iting the denitrification (Tang et al. 2004).

Dissolved Oxygen Nitrification requires the presence of sufficien t DO, and the rate of nitrification can be limited when the DO concentration is too low to support a sufficiently high oxygen transfer rate. In municipal activated sludg e systems with HRTs of 6 to 8 hours, the nitrific ation rate is maximized when the DO concentration is 2 mg/L or greater (WEF and ASCE 2006, p 42). Fixed-film systems, such as the MBBR or the integrated fixed-film activated sludge (IFAS) system, might need higher DO concentrations to prevent the biomass attached to the media from becoming anaerobic, which could lead to poor system performance.Municipal Nutrient Removal Technologies Reference Document September 2008

2-8 Chapter 2: Treatment Technologies The presence of DO inhibits some desirable biol ogical processes, partic ularly denitrification. DO concentrations of 0.2 mg/L or greater decrease the denitrificat ion rate in the anoxic zone (WEF and ASCE 2006, p 183). This is because the energy expended breaking NO 3 to obtain oxygen is greater than that from using molecular oxygen, so most microorganisms preferentially use DO when it is available rather than NO 3 . Denitrification is made most efficient when DO is kept low throughout th e anoxic zone. Thus, low DO levels in the internal recycle or RAS lines can effectively reduce the require d HRT of the anoxic zone. It is recommended that DO concentrations in re turn flows be limited to about 1 mg/L (WEF and ASCE 2006, p.182).

Additional Design Considerations to Enhance Nitrogen Removal Additional design considerations that can help make pl ant operation easier include accounting for return flow and loads as well as external loads in the basis of the design, incorporating a supervisory c ontrol and data acquisition (SC ADA) system and other online monitoring for process control, and including allo wances for flexibility in the design. If the return flow and loadings from side-streams such as filter backwash or sludge handling are included in the basis of the design, the plant wi ll be able to treat th e loadings that the processes receive, rather than requiring a portion of the standa rd design safety factor to account for these return streams. In addition, if the plant receives septage, landfill leachate, or similar hauled or direct waste streams, thos e loads should be accounted for in the basis of design. Accounting for all these loadings might lead to larger tank sizes, blowers, or chemical storage facilities.

Online monitoring allows the reco rding of real-time process information that can be used to make operating decisions. SCADA allows automa tic control of the pr ocess in conjunction with online monitoring. The SC ADA system can help in process optimization, and it can result in operational savings in situations wher e too much air is being added by automatically adjusting the amount of air delivered to the process.

Operational flexibility is gained by installing swing zones in anticipation of uncertainties in the future wastewater charac teristics and operating conditions . The swing zone should be equipped with both mixers and aerators, which ca n be operated as either an anoxic or aerobic zone, depending on conditions at the plant (which might vary s easonally as well as diurnally between the day and night hours). The swing zo ne is known as a performance enhancer as well as an electricity saver when mixers are us ed instead of aerators during low-flow periods. This flexibility in design increases costs but can contribute to the long-term compliance and sustainability of biological nutrien t removal as the wastewater a nd flow characteristics at the facility will change in the future.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-9 

### 2.2.3 Nitrogen Removal Technologies

Nitrification/Denitrification Some facilities are required to remove only ammonia-N or TKN, with no current requirements to remove nitrate or nitrite. In such instances, the bi ological conversion of ammonia (or TKN) to nitrate is readily accomp lished by increasing the SRT in the biological system, increasing the HRT, and ensuring that there is sufficient oxygenation to accomplish the conversion. System designs in the past incorporated a two-sludge strategy: first, BOD was removed in an activated-sl udge reactor with a clarifier, and then a second activatedsludge system was run in series to accomplis h nitrification. Current practice is to do both BOD removal and nitrification in a single sludge system, especi ally in retrofit situations, thereby saving land requirements by avoiding a new set of clarifiers and making the operation simpler. Significant energy savings is also anticipated in a single sludge system due to a reduced volume requiring aeration. McClintock et al. (1988, 1992) and Randall et al. (1992) report a reduction of 20 percent in volume requiring aeration, with a 40 percent or greater reduction in sludge production in single sludge systems compared to separate systems.

All the technologies described below except the denitrifying filters can be used to accomplish nitrification; if nitrate rem oval is not required, that portion need not be implemented. This could result in savings of capital or operat ion and maintenance (O&M) costs. During the planning and design of a nitrifica tion retrofit, it would be logi cal to leave space for future denitrification in case future permits require it. In addition, there are advantages to accomplishing some denitrification, if it is supported by influent BOD, because doing so results in reduced overall sludge generation.

Denitrification Filters Denitrification filters are usually placed after the secondary tr eatment process. One of their advantages is that in addition to providing nitr ogen removal, they act as an effluent filter. Denitrification filters have a more compact area compared to other add-on denitrification processes. The filters can be operated in downflow or upflow configurations. As the process is performing denitrification after most of the BOD has been removed from the wastewater, a carbon source, such as methanol, must be supplied.

There are two general types of denitrifying filter. One is an adaptation of conventional deepbed filters, as provided by Leopold Co. a nd Severn-Trent. These employ sand, gravel, anthracite, or other filter media in some comb ination, at a depth of 8 to 12 feet (WEF and ASCE 2006). They are typically operated in a downflow mode (with water directed down from the top of the bed); this means that ni trogen gas generated with in the bed could be trapped between the grains. Thus, the beds require periodic bumping , whereby the flow of water or air is directed upward in the bed. This releases the tra pped nitrogen gas. Less frequently, a full backwash is performed to remove accumulated solids. The backwash isMunicipal Nutrient Removal Technologies Reference Document September 2008

2-10 Chapter 2: Treatment Technologies usually returned to the head of the plant or to the secondary treatment process. Existing sand filters can be retrofitted to become denitrificatio n filters if there is sufficient space to increase the bed depth. Conventional denitrification filters are typically loaded at 2 to 3 gallons/min/ft 2 , with removal to 1 to 2 mg/L nitrate nitrogen.

The second general type of de nitrifying filter is exemplifie d by the Biofor system from Infilco/Degremont and the Biostyr system fr om Kruger/Veolia. They are operated in an upflow configuration and use plastic media for microbial attachment. These types of filters are often paired with biologi cal activated filters (BAFs) , which accomplish BOD removal and nitrification. Because they are operated in upflow mode, pumping is required, which increases operating costs. The plastic media can be hydraulically loaded at 8 to 9 gallons/min/ft 2 , with removal to 1 to 1.5 mg/L nitrat e nitrogen. However, the plastic media are not as efficient at capturing solids as the conventional granular media. A biological upflow filter is illustrated in Figure 2-1.

Secondary Treatment Process Secondary Clarifier (if used)

Effluent Influent

RAS (if used)

WAS Methanol or other carbon source

Denitrifying Filter Filter Backwash

Figure 2-1. Denitrifying filter process.

The advantage of both types of denitrifying f ilters is that they can accomplish complete nitrate removal with a very sm all footprint in a bu ilding, and possibly no additional footprint if an older conventional filter can be retrofitted. A disadvant age of this system is that an additional carbon source (typical ly methanol) is usually requir ed, with associated increased sludge generation. In certain cases, additiona l pumping and electrical costs might be required. The denitrifying filter process is illustrated in Figure 2-2.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-11 Effluent Influent

Recirculation

Anaerobic Zone Aerobic Zone

Main flow direction

Figure 2-2. Biological upflow filter.

Modified Ludzack-Ettinger Process The MLE consists of an anoxic basin upstream of an aerobic zone. An in ternal recycle carries nitrates created during th e nitrification process in the aerobic zone al ong with mixed liquor to the anoxic zone for denitrification. RAS is mixe d with the influent to the anoxic zone. The extent of denitrificati on is tied to the mixed liquor recycle flow; higher recycle rates increase denitrification. Because only recycled nitrate has the opportunity to be denitrified, the MLE alone cannot achieve extremely low fina l nitrogen concentrations. The maximum denitrification potential is a pproximately 82 percent at a 500 percent recycle rate (WEF and ASCE 2006). TN effluent concentrations typi cally range from 5 to 8 mg/L (Barnard 2006). Actual denitrification might be limited by othe r factors, such as carbon source availability, process kinetics, and anoxic or aerobic zone sizes. Furthermore, oxygen recycled from the aerobic zone can negatively affect the denitr ification rate in the anoxic zone (WEF and ASCE 2006). Performance factor s include limitations due to the single anoxic zone and the internal recycle rate that returns nitrates to the anoxic zone. Selection factors include the possibility of constructing walls in existing basins to create an anoxic zone; additional pumping, piping, and electricity to accommodate the internal r ecycle; and the possible need for an additional carbon source to promote de nitrification. The modified Ludzack-Ettinger process is illustrated in Figure 2-3.Municipal Nutrient Removal Technologies Reference Document September 2008

2-12 Chapter 2: Treatment Technologies Anoxic Tank Aerobic Tank Secondary Clarifier Effluent Influent

RAS Nitrified Recycle

WAS Figure 2-3. Modified Ludzack-Ettinger process.

Cyclically Aerated Activated Sludge In a cyclically aerated activated-sludge system, the aeration system is programmed to turn off periodically, allowing denitrif ication and nitrification to occur in the same tank. This conversion is thus easy to achieve, with lit tle or no capital expenditure required. The cyclically aerated activat ed-sludge system can be used to re trofit existing plants if sufficient SRTs can be maintained to allow nitrification to occur. The length of the cycle time depends on the loading rate and the target limit, with the HRT being 2 to 4 times the cycle time (Ip et al. 1987). If the aerobic SRT time is sufficient to achieve nitrif ication, the cyclic process can reduce TN in the effluent. Aeration can be provided by diffusers or surface aerators. Sequencing batch reactors (SBRs) and oxidation ditches can be designed to operate as cyclically aerated act ivated-sludge systems (WEF and AS CE 1998). The cyclically aerated activated-sludge process is illustrated in Figure 2-4. The range of TN effluent concentrations found at the case study facilities for this study was 3.1 mg/L to 10.4 mg/L (see Table 2-1 in Section 2.5).

Anoxic/Aerobic Tank (Aeration on Timer) Secondary Clarifier Effluent Influent

RAS

WAS Figure 2-4. Cyclically aerated activated-sludge process.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-13 Four-Stage Bardenpho Process The 4-stage Bardenpho process involves an anox ic zone, followed by an aerobic zone (with an internal recycle to the firs t anoxic zone), which is followed by a second anoxic zone and a small aerobic zone. The first two tanks are simila r to the MLE process. With pumps and zone sizes typically set large enough to accommodate a 400 percent inte rnal recycle rate, the first anoxic zone accomplishes the bulk of the denitr ification. The second anoxic zone removes nitrates from the first aerobic zone that are not recycled to the first anoxic zone. A carbon source, such as methanol, might need to be added to the second anoxic zone to achieve good denitrification. The second aerobic zone rem oves the nitrogen gas from the wastewater before the wastewater enters the secondary clarifiers. By aerating, the possibility of denitrification in the clarifier is removed. Th e sludge tends to settle better, and overall operation of the secondary clarifie r is improved (WEF and ASCE 2006).

The Bardenpho process has been used in numer ous underlying configurations, including plug flow, complete mix, and oxidation ditch reactors; some configurations have used existing oxidation ditches for the first two basins and additional constructed tanks for the secondary basins (WEF and ASCE 2006). Selection factors include a large proce ss footprint involving several large basins; re trofit of existing basins is possi ble but unlikely. Additional piping, pumping, and electricity are need ed for the internal recycle streams. Although the available carbon source might be adequate, it is likely that the second anoxic zone will require supplemental carbon, with the associated generation of additional sludge and increased O&M costs. Performance factors incl ude the presence of two anoxic z ones and the internal recycle rate, which runs as high as five times of th e influent flow rate. The 4-stage Bardenpho process is illustrated in Figure 2-5. The range of TN effluent concen trations found in the literature evaluated for this study was 3.5 mg/L to 12.1 mg/L (see Table 2-1 in Section 2.5).

Anoxic Tank Aerobic Tank Secondary Clarifier Effluent Influent

RAS Nitrified Recycle

Anoxic Tank Aeration Tank (Optional) Methanol Addition

WAS
Figure 2-5. Four-stage Bardenpho process.Municipal Nutrient Removal Technologies Reference Document September 2008

2-14 Chapter 2: Treatment Technologies Oxidation Ditch Processes Oxidation ditch processes use channels in a loop to provide con tinuous circulation of wastewater and activated sludge. Surface or su bmerged aerators provide aeration, and anoxic zones are made possible by judicious placement of the aerators. As mentioned earlier, oxidation ditches can also be operated as cyclic ally aerated activated-sludge systems. As an alternative to internal anoxic zones, anoxic basins can be constructed before or after an existing ditch. If there are aerob ic zones downstream of anoxic zones, provision should be made for an internal recycle or an external anoxic basin to allow denitrification of any additional nitrates. Selection f actors include a potentially larg e footprint. Compared to an existing system that is not denitrifying, electricity usage could be reduced because some aerators would be turned off to create anoxic zones. With ditches, no additional piping and pumping are needed unless external basins are us ed. Such basins might be needed to achieve very low nitrogen levels. In such cases, an additional carbon source would likely be needed for the denitrification reactor. Performance can be increased by using automatic DO controls that are capable of turning blowers on or off as necessary to maintain the desired set points. The oxidation ditch process is illustrated in Figure 2-6. The range of TN effluent concentrations for processes evaluated for this study were 6 to 10 mg/L as TN. Sen et al. (1990) reported less than 4 mg/L TN after optim izing aeration.

Secondary Clarifier Effluent Influent Aerators Flow

WAS RAS

Figure 2-6. Oxidation ditch process.

Fixed Film Processes Fixed-film, or attached growth systems are possi ble alternatives to su spended growth systems for nutrient removal. The medium can either be in a packed configuration, such as in a trickling filter, or suspended, such as in an IFAS or MBBR system. Fixed films provide an advantage for slow-growing bacteria, such as those involved in nitrification and denitrification processes, because the attach ment gives those organisms longer residence times in the reactor. Fixed-f ilm systems are also less prone to washout or toxic upsets.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-15 Trickling filters can be used as an add-on process to provide n itrification. Additional information on trickling filters can be found in Wastewater Engineering: Treatment and
Reuse (Metcalf & Eddy 2003). Use of a fixed-film carrier media allows the growth of additional biomass compared to a similarly size d activated sludge system, which can result in increased nitrification and denitrification in the given volume. Carrier media can be retrofitted into existing susp ended-growth systems, provide d that sufficient volume is available in the reactors. Separate aerobic and anoxic zones could be required if both nitrification and denitr ification are desired.

Integrated Fixed-Film Activated Sludge IFAS systems are hybrids that have attached growth media included in an activated-sludge basin. The media for attached growth can be a fixed type or a floa ting type. Fixed media include rope or some other stranded material (example brand names include Ringlace® and Bioweb®). Floating media can include sponges (Captor®, Linpor®), packing material, such as the saddles that would be used in packed towers for air stripping or gas absorption; or plastic media similar to those used in an MBBR (Kaldnes®, Hydroxyl®, or Bioprotz®) (Copithorn 2007; Welander and Johnson 2007). Floating media can be free-floating or retained in the basin by enclosing th em in cages or installing screens.

IFAS systems usually have higher treatment ra tes and generate sludges with better settling characteristics and lower mass than activated-slu dge systems. Because the media can be held in zones within the overall basin, there is the possibility of ha ving nitrification and denitrification occur in the same basin, in se parate anoxic and aerobic zones. To obtain very low nitrogen concentrations in the effluent, two distinct anoxic zones s hould be provided so that one can be used for final polishing. Alternativel y, separate zones can be eliminated with tight control of DO. Selecti on factors include a medium footprint using the existing activated-sludge system, with construction within the aeration basin to install the selected method of media retention. No additional piping and pumping ar e typically needed, as long as the flow pattern is set to obtain sequen tial aerobic/anoxic conditions. If no additional pumping is needed, electrical co sts are likely to be reduced for zones no longer being aerated. If a carbon source needs to be fe d to secondary anoxic zones to maintain denitrifying activity, some additional sludge will be gene rated, and O&M costs will increase.

The IFAS system reduces the footprint signifi cantly by providing additional surface area for attached growth to occur within the same basin area as a comparable activated-sludge process. As such, a retrofit IFAS is frequently an alternative to adding tank capacity to an activated-sludge system (Johnson et al. 2005). A fine screen (3 to 6 mm) is recommended upstream of the secondary proce ss to prevent material like ha ir from interfering with the surface area of the medium. To promote nitrification and denitrification, a higher DO concentration might be required in the aerobic zone when compared to an extended-aeration process. The extra oxygen could be required to penetrate the biomass growth on the medium so that it does not become anaerobic. Aeration is often done by diffused air (fine or coarseMunicipal Nutrient Removal Technologies Reference Document September 2008

2-16 Chapter 2: Treatment Technologies bubble), as mechanical aeration could interfer e with the fixed-film media (Johnson et al. 2005). Higher RAS rates tend to promote better TN removal. The IFAS pr ocess is illustrated in Figure 2-7. The range of TN effluent concentr ations at plants with IFAS technologies in the literature evaluated as pa rt of this study was 2.8 mg/L to 17.0 mg/L (see Table 2-1 in Section 2.5).

Anoxic Tank Aerobic Tank Secondary Clar ifier Effluent Influent Tanks contain f ixed or floating media for a ttached growth

Waste Sludge Medi a re tention sieves (if necess ary) RAS

Figure 2-7. Integrated fixed-film activated sludge process.

Moving-Bed Biofilm Reactor An MBBR consists of small plastic media (carrier elements) in an anoxic or aerobic zone that allow attached growth to occur. The plastic is typically polyethylene with a specific gravity slightly less than 1.0. The carrier elements from most manufacturers are shaped like cylinders or wheels with internal and external fins. Th ese shapes provide a high surface area per unit volume that is protected from shear forces , allowing better biofilm growth. The MBBR process can be retrofitted into an existing ac tivated-sludge basin. This process combines the technologies of activated sludge and biofilm processes and is frequently used for upgrading an existing plant, especially when space is limited. Such high-rate biofilm processes are highly efficient in removing organic and nitrogen loads.

MBBRs can be used within separate aerobic and anoxic zones. Slow-speed, submersible mixers are used in anoxic zones; air is s upplied in aerobic zones by coarse bubble diffusers because fine bubbles tend to coalesce in the plas tic media. A sieve is used to retain the media in the designated basin. MBBR technology does not involve any return flows and does not rely on suspended growth to provide additi onal treatment. Selection factors include a medium footprint (however, including a recycle stream would increase the footprint), withSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-17 construction of only screens for retaining th e carrier elements needed in the basins. Depending on how the system is being operated and the target limit, there might or might not be a need for an additional carbon source or pos t-reactor treatment; if no additional carbon is needed, no additional sludge will be generate d, reducing O&M costs. The MBBR process is illustrated in Figure 2-8. The range of TN ef fluent concentrations for MBBR found in the literature evaluated as part of this study wa s 2.8 mg/L to17 mg/L (see Table 2-1 in Section 2.5).

Figure 2-8. Moving-bed biofilm reactor process.

Membrane Bioreactor The membrane bioreactor (MBR) consists of anoxic and aerobic zones followed by a membrane that filters the so lids from the mixed liquor, ta king the place of secondary clarifiers. The membranes can be immersed in th e final activated-sludge basin, or they can be set up in a separate vessel. The membranes ca n function in an inside -out mode, where only clean water exits the membranes, or in an outside-in manner, where only clean wastewater can enter the membranes. Usually wastewater must be pumped through the membranes, but in certain circumstances gravity feed can be used. By removing the need for settling, MBRs can operate at higher mixed liquor suspende d solids (MLSS) concentrations (8,000 to 18,000 mg/L) than a comparable activ ated-sludge system (2,000 to 5,000 mg/L). The membranes are typically configured as hollow fiber tubes or flat plates. The membranes can either be immersed in the final tank, or they can be opera ted as a separate, stand- alone unit. If they are operated as a separate unit, an internal recycle returns a portion of the solids retained by the membranes to the anoxic zone. Anoxic

Tank Aerobic Tank Secondary Clarifier Effluent Influent Tanks contain suspended plastic media for attached growth

Waste Sludge Media retention sievesMunicipal Nutrient Removal Technologies Reference Document September 2008

2-18 Chapter 2: Treatment Technologies Biofouling of the membranes is typically th e most significant operational issue. Some manufacturers schedule a relax period or a back pulse to re duce the growth. The membranes must be cleaned periodically (quarterly to semiannually) us ing citric acid or sodium hypochlorite, depending on the type of f ouling and the system manufacturer’s recommendations. In addition, reducing the slud ge age tends to reduc e the formation of extracellular polymers, which tend to be the major cause of fouling. MBR system selection factors include a smaller foot print than conventional activ ated-sludge systems, with construction in existing basins or clarifiers. Lower effluent nitr ogen is obtained with second anoxic zones, potentially accompanied by carbon source addition. As mentioned earlier, additional pumping is likely to be required to get water thro ugh the membrane, thus requiring additional electricity. The addi tional chemicals result in mo re sludge formation, but MBR systems overall provide less sludge formation than conventional systems because of their higher SRTs and higher sludge concentrations. New facilities are being designed and built to meet limits of 3 mg/L TN. The MBR process is illustrated in Figure 2-9.

Anoxic Tank Aerobic Tank Membrane Filter

Effluent Influent

Retained Biomass

Waste Sludge Membrane

Pump

RAS Aerobic

Tank Anoxic Tank

(a)

Figure 2-9. MBR process. (a) Extern al filter in lieu of clarifierSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-19 Anoxic

Tank Aerobic Tank Membrane Filter Effluent

Influent

Waste Sludge Membrane Pump

Aerobic

Tank Anoxic

Tank

(b)

Figure 2-9. MBR process. (b) In-tank filter

Step-Feed Activated Sludge The difficulty with carrying out full nitrificat ion/denitrification with a sequence of aerobic and anoxic reactors is that little carbon is ava ilable to maintain microbial populations in the secondary reactors. As described earlier, this problem can be overcome by feeding supplemental carbon. Alternatively, feed can be provided directly to each anoxic zone to ensure that sufficient carbon is available. This step-feed strategy has the additional advantage of providing a means for the pl ant to better handle wet-weathe r events by reducing the solids loading to the clarifiers. The bi omass inventory is maintained preferentially more in the first section and then less in the second section a nd the succeeding sections in proportion to the flow split going into each section. The last sect ion maintains the least amount of biomass in inverse proportion to the flow and thus the MLSS concentration is the lowest. The solids loading rate to the clarifiers thus will be th e lowest for the flow. The microorganisms in the later stages treat not just the fresh feed but also anything coming from upstream zones. The selection factors are a relativel y large footprint for the basins , with in-basin retrofit of additional piping and possibly pumping. Extra head could be required, depending on the hydraulic configuration of the system. If additio nal pumping is required, electrical costs will be increased. However, no additional chemicals should be required because the food needs of the secondary microorganisms ar e accounted for. The step-fee d activated sludge process is illustrated in Figure 2-10. The range of TN efflue nt found in the literatu re evaluated as part of this study was 1.0 mg/L to 14.0 mg /L (see Table 2-1 in Section 2.5).Municipal Nutrient Removal Technologies Reference Document September 2008

2-20 Chapter 2: Treatment Technologies Secondary Clarifier Effluent Influent

RAS

WAS Aerobic

Tank Anoxic Tank Aerobic Tank Anoxic Tank Aerobic Tank Anoxic Tank

Figure 2-10. Step-feed activated sludge process.

Biodenitro Process The Biodenitro process, a variation of the oxi dation ditch, consists of two oxidation ditches side by side. Influent is fed alternately to the ditches, allowing anoxic and aerobic zones to form for nitrification and denitrification. The ditches are alternately aerated and not aerated, and mixing is maintained by the flow in the ditches. The ditches periodically switch modes, and the overall result is th at the water passes through mu ltiple aerobic and anoxic zones before discharge. Because oxidation ditches re quire large footprints, having multiple ditches requires a great deal of land. Some pumping might be requir ed, depending on the hydraulic profile. Because the influent is continually swit ched, the need for additional food is typically reduced or eliminated. To accomplish low effluent nitrogen concentrations, an external anoxic zone following the oxidation ditches mi ght be needed. The Biodenitro process is illustrated in Figure 2-11. The range of TN effl uent concentrations for a phased isolation ditch (PID) found at the case study facilities fo r this study was 1.8 mg/L to 7.0 mg/L and in the literature evaluated as pa rt of this study was 1.6 mg/L to 5.4 mg/L (see Table 2-1 in Section 2.5).September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-21 Secondary Clarifier Effluent Influent

RAS

WAS Alternating Aerobic/Anoxic Tanks

Flows switch when tanks alternate Tank 1-Anoxic

Tank 2-Aerobic

Figure 2-11. Biodenitro process.

Schreiber Process The patented Schreiber count ercurrent aeration process ca n provide nitrification and denitrification in one basin. The wastewater ente rs a circular basin equipped with a rotating bridge that provides mixing. Aeration is provi ded by fine-bubble diffusers attached to the bridge. Should sequencing betw een aerobic and anoxic conditions be required, the aeration can be turned off while the bridge continues to keep the tank mixed. The system footprint is approximately that of a conventional activated -sludge system but with additional equipment built in. Because it includes alternating aer obic/anoxic conditions in one tank, very low effluent TN concentrations are possible, when optimized. The performance could be further enhanced with additional anoxic zones downstrea m of the primary reactor. In the standard Schreiber configuration, the n eed for additional food is typi cally reduced or eliminated because everything is done in one tank. The Schreiber countercurren t aeration process is illustrated in Figure 2-12. The TN effluent concentrations for the Schreiber process in the literature evaluated as part of this study was 8.0 mg/L (see Table 2-1 in Section 2.5).Municipal Nutrient Removal Technologies Reference Document September 2008

2-22 Chapter 2: Treatment Technologies Secondary Clarifier Effluent Influent

Waste Sludge RAS Rotating Bridge

Aeration/Anoxic/ (Anaerobic) Tank

Aeration on timer

Figure 2-12. Schreiber countercurrent aeration process.

Sequencing Batch Reactor Facilities with small or intermittent flows might benefit from using an SBR. Such reactors are filled over the course of time, and then the contents ar e processed under the conditions deemed necessary to achieve th e required treatment. In the case of nitrogen removal, the conditions would include both aerobic and a noxic time. Multiple SBR units allow for continuous feeding of wastewater and batch pr ocessing. SBRs typically have four phases: a fill phase, during which mixing is maintained; a react phase with alternating aerobic and anoxic cycles; a settle phase, during which mi xing is turned off so the microorganisms can settle; and a decant phase, when the effluent is drained. Depending on the length of time needed for filling, reacting, and decant, multiple SBR units allow for receiving wastewater continuously. The footprint for SBRs can be small, depending on the required number of reaction vessels. The need for additional food is typically low because everything is done in one vessel. Very low effluent nitrogen can be obtained through the use of multiple aeration and anoxic steps, with food added if needed. An SBR is illustrated in Figure 2-13. The range of TN effluent concentrations for the SBR found in th e literature evaluate d as part of this study was 1.6 mg/L to 13.6 mg/L (s ee Table 2-1 in Section 2.5).September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-23 Effluent Influent

Waste Sludge SBR under aerobic/anoxic

conditions
Cycle times determined based

on conditions

Figure 2-13. Sequencing batch reactor.

Sidestream Processes One issue that needs to be decided at plants where low TN is required in the effluent is whether and how to treat recycle nitrogen lo ads coming from sludge processing and other activities and deciding whether to include a separate treatme nt of those streams. These streams typically contain high concentrati ons of ammonia nitrogen and would make treatment in the main biological treatment system difficult to manage when the sludge handling processes send large loads.

Typical solutions for high sidestream loads w ould be equalization; di urnal control of the sidestream flow so that it is fed during lo wer mainstream load periods; or dedicating one mainstream train to handle the sidestream. Often, a be tter solution is to treat the sidestream before recycle. The following systems have been proposed for such sidestream nitrogen treatment and have been implemented at so me places in the United States and Europe.

InNitri Process—Nitrification The ammonia-laden water is treated in a separate nitrification reactor be fore recycling to the plant headworks. This therefore reduces the am monia-nitrogen load in the recycle stream. The recycle stream then provides a seed of nitr ifying bacteria to the main reactor. Such a supply would often not be available in the main stream because of having to maintain too low a SRT so that the nitrifiers would wash out of the system (Philips and Kobylinski 2007). This constant feed of nitrifiers is thus beneficial for facilities that must nitrify or achieve low effluent concentrations year-round. The sidestre am reactor size can be small, and it can be operated at an elevated temper ature compared to the main reactor. By seeding that mainMunicipal Nutrient Removal Technologies Reference Document September 2008

2-24 Chapter 2: Treatment Technologies system with nitrifiers, the main SRT can be reduced, which can t hus reduce overall capital and O&M costs. The process has been piloted in the United States in Arizona (Warakomski et al. 2007). The process is illustrated in Figure 2-13A.

Figure 2-13A. InNitri process.

Bio-Augmentation Batch Enha nced (BABE)—Nitrification The BABE process is a variati on on the InNitri process. In BABE, the reactor is a batch system that is fed batches of return sludge fr om the main activated sludge system along with the sidestream. This batch reactor is operate d both aerobically and anoxically and therefore both nitrifies and denitrifies the sidestream. This means that alkali nity lost during the nitrification process will be pa rtially recovered during denitrif ication, and the sidestream will not require neutralization before reintroduction to the mainstream. The effluent of the batch reactor contains nitrifiers, which will enhan ce the population in the main system. Full-scale testing has been done in the Netherlands (P hilips and Kobylinski 2007). The process is illustrated in Figure 2-13B.

There are a number of other bio-augmentation pr ocesses that have been developed in Europe and elsewhere. Examples include the Mainst ream Autotrophic Recycle Enabling Enhanced N-removal (MAUREEN), the Bio-augmentati on R (regeneration) (BAR) process, the Aeration Tank 3 (AT-3) Process, and the biof ilm activated sludge innovative nitrification (BASIN) process (Parker and Wanner 2007). The BAR and AT-3 processes have been proven in demonstration scale, while others show promise for the future. Activated Sludge Tank Secondary Clarifier Effluent Influent

RAS

WAS

Recycled Sidestream Nitrification

ReactorSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-25 Figure 2-13B. BABE process.

Nitritation–Denitritation A recently developed alternative to conventional nitrification/denitrficat ion is the process of nitritation, where only nitrite is produced aerobically. This process is sold under the proprietary name SHARON, or Single-reactor High-activity A mmonia Removal over Nitrite. The process is run at elevated temperatures (30–35 °C) at lower SRTs to favor growth of ammonia oxidizers (such as Nitrosomonas sp

. ) over nitrite oxidizers (such as Nitrobacter sp.). Denitrifiers are then encouraged to convert the nitrite to nitrogen gas. By not oxidizing all the way to nitrate, oxygen and energy us age is reduced (Wara komski et al. 2007). Methanol can be used for dentrification, if neces sary. The process is used at several locations in Europe and, as of 2007, was being installe d at the New York City Ward Island Water Pollution Control Facility. The SHARON pr ocess is illustrated in Figure 2-13C. Activated Sludge Tank Secondary Clarifier Effluent Influent

RAS

WAS

Recycled Sidestream BABE Reactor Bio-augmentationMunicipal Nutrient Removal Technologies Reference Document September 2008

2-26 Chapter 2: Treatment Technologies Figure 2-13C. SHARON process

Another process for converting ammonia to nitrite uses a newly discovered group of autotrophic microorganisms that can anaerobical ly oxidize ammonia using nitrite. This is called the ANAMMOX process, for Anaerobic Ammonia Oxidation. These microorganisms are favored by elevated temperat ures (above 35 °C), and grow ve ry slowly. In this case, a strategy for obtaining nitrite is to use the first step of the SHARON process to produce nitrite, then oxidizing a bypassed ammonia st ream with the nitrite. ANAMMOX systems have been implemented in Europe, in particul ar in Rotterdam (Warakomski et al. 2007). The ANAMMOX process is presented in Figure 2-13D. Two fixed-film processes using similar strategies to SHARON and ANAMMOX—the Oxygen Limited Aerobic NitrificationDenitrification (OLAND) and Completely Au totrophic Nitrogen Removal Over Nitrite (CANON)—are under devel opment (Stensel 2006). Activated Sludge Tank Secondary Clarifier Effluent Influent

RAS

WAS

Recycled Sidestream Nitritation Reactor (Aerobic) Denitritation Reactor (Anoxic)

Heat ExchangerSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-27 Figure 2-13D. ANAMMOX process.



### 2.3 Phosphorus Removal Processes

Phosphorus can be removed from wastewater by biological uptake by microorganisms and by chemical precipitation with a metal cation. De pending on the target c oncentration, a plant process might employ both technologies. Such a combined approach might be of particular benefit if the target concentration is very low and the starting concentrat ion is high. In such a case, biological removal is used to remove the bulk of the phosphorus, and chemical polishing follows to achieve the final concentra tion; such an approach tends to reduce sludge formation.



### 2.3.1 Biological Phosphorus Removal
Biological Phosphorus Species
The reactions involved in bi ological phosphorus removal are as follows (Pattarkine and Randall 1999):

1. Anaerobic biological phosphorus release by Phosphate Accumulating Organisms (PAOs):

PAOs + stored polyphosphate + Mg ++ + K + + glycogen + VFA Æ
PAOs + stored biopolymers + Mg ++ + K + +_CO 2 + H 2 O + PO 4 3- (released) Activated Sludge Tank Secondary Clarifier Effluent Influent

RAS

WAS

Recycled Sidestream Nitritation Reactor (Aerobic) Denitritation Reactor (Anoxic)

Ammonia BypassMunicipal Nutrient Removal Technologies Reference Document September 2008

2-28 Chapter 2: Treatment Technologies 2. Aerobic biological phosphorus uptake by PAOs:

PAOs + stored biopolymers + Mg ++ + K + + O 2 (or NO 3 ) + PO 4 3- Æ

PAOs + stored polyphosphate + Mg ++ + K + +glycogen + CO 2 + H 2 O

Biological phosphorus removal works by encour aging the growth of phosphate-accumulating organisms (PAOs), which are then subjected firs t to anaerobic conditions and then to aerobic conditions. Under anaerobic conditions, the microbes break the high-energy bonds in internally accumulated polyphosphate, resu lting in the release of phosphate (PO 4 3- ) and the consumption of organic matter in the form of volatile fatty acids (V FAs) or other easily biodegraded organic compounds. VFAs include short-ch ained carboxylic acids such as acetic, proprionic, butyric, and valeric, among others. When the microbes are then put under aerobic conditions, they take up phosphate, form ing internal polyphosphate molecules. This luxury uptake results in more phosphate being included in the cells than was released in the anaerobic zone, so the total phos phate concentration in solutio n is reduced. When the microorganisms are wasted, the contai ned phosphate is also removed.

Beyond the luxury uptake of phosphate, microorgani sms also remove phosphate as part of their normal BOD removal. A small amount of phosphorus is removed in the conventional activated-sludge process during B OD removal. This amount is typically 1.5 to 2 percent on a dry weight basis (WEF and ASCE 1998).

When these organisms enriched in polyphosphate are wasted, the contained phosphate is also removed. PAOs that are exposed to an anaerob ic environment followed by an aerobic zone can exhibit phosphorus removal levels 2.5 to 4 times higher than those for conventional activated-sludge system s (WEF and ASCE 1998). Thus, the fraction of phosphorus in wasted dry solids could be at le ast 8 percent or more.

A sufficient supply of VFAs is the key to removing phosphorus biologically. Barnard et al. (2005) reported that when using a mixture of acetic and propionic acids produced by on-site fermentation, the COD-to-TP ratio in the plan t influent could be as low as 8. As the phosphorus permit limits have been lowered in recent years, chem ical polishing, often combined with better filtration processes, has become necessar y. A discussion of significant factors that affect the phos phorus removal process follows.

Biological Phosphorus Removal Factors Volatile Fatty Acid Availability in Wastewater A key factor in determining the cost-effectiv eness of biological phosphorus removal is the relative amount of organic material that can be used by the PAOs. That is because if VFAs or rbCOD is not present in a sufficient ratio to ortho-phosphorus, the process becomes less reliable and phosphorus removal can be reduced.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-29 For facilities where retrofitting is being consid ered, the data most likely available are COD and BOD. Literature indicates that a COD-to-T P ratio of 45 and a BOD-to-TP ratio of 20 are the minimum values needed to meet a 1 mg/L TP limit (McGrath 2005a; WEF and ASCE 2006). If data are available about rbCOD, lite rature shows that good biological phosphorus removal was observed at rbCOD-to-TP ratios of about 15 (Barnard et al. 2005). The rbCOD can be converted to short-chain VFAs in the anaerobic zone and then used by PAOs (Lindecke et al. 2005). Finally, if VFAs have been determined, it has been found that a minimum VFA-to-TP ratio of at least 4 is recommended to obtain good biological phosphorus removal (Neethling et al. 2005).

In-plant generation of VFAs is made possible in many different ways at existing facilities–– adding a new fermenter (for either primary or RAS), converting a sludge thickener, or returning supernatant from an existing anaerobic digester. Fermenters can be single-stage or two-stage. They are optimized by adding a mixer that allows VFAs in the solids to enter the anaerobic zone directly. A sour ce of elutriating water, either primary effluent or final effluent, is fed to the fermenter to flush out the VFAs produced and sent to the anaerobic zone. The VFA production from fermenting primary sludge typically yields 0.066 to 0.15 g VFA/g total solids (both expressed as COD), although values up to 0.3 g VFA/g solids have been reported (Barnard et al. 2005). Complete-mix fermen ters are typically designed with an HRT of 6 to 12 hours, an SRT of 4 to 8 days, and a solids concentration between 1 and 2 percent (WEF and ASCE 2006, p 326).

Temperature Although the biological phosphorus removal process is not significantly affected by temperature, the fermentation process is slower at low temperatures (Lindeke et al. 2005). Therefore, lower phosphorus removal might occu r in the winter because of reduced VFA production in the plants that use fermenters. Th e temperature effect was reported as directly influencing the sludge age needed for adequate generation of VFAs (Baur et al. 2002). At 24 °C, a 1-day sludge age was sufficient. A 4-day sludge age was required to generate sufficient
VFAs at 14 °C.

At the upper end of the temperature range, the performance of PAOs showed reduced phosphorus uptake activity above 30 °C and seriously inhibited act ivity at 40 °C (Panswad et al. 2003; Rabinowitz et al. 2004). At temper atures above 30 °C, glycogen-accumulating organisms (GAOs) were reported as a detrimen t to enhanced biological phosphorus removal (EBPR) (Barnard 2006).

Solids Retention Time Very good biological phosphorus removal perfor mance was reported when SRT values of 16 and 12 days were provided for wastewater at 5 °C and 10 °C, respectively. The system performance was not affected when the SRT was varied between 16 and 24 days at 5 °C.Municipal Nutrient Removal Technologies Reference Document September 2008

2-30 Chapter 2: Treatment Technologies Similarly, varying the SRT between 12 and 17 days at 10 °C did not affect the biological phosphorus removal (Erdal et al. 2002).

Secondary Phosphorus Release Secondary release is of concer n in EBPR plants. Biological p hosphorus removal occurs in a two-step process, in which phosphorus is releas ed in the anaerobic zone by PAOs and then taken up by the same PAOs in the aerobic zone. The microorganisms favored in the anaerobic zone are capable of absorbing more phosphorus in the aerobic zone than was released in the anaerobic z one, leading to a net reducti on in phosphorus when these microorganisms are removed from the process through settling and wasting. However, if the PAOs are put under anaerobic conditions following phosphorus update, there will be unintended secondary release of phosphorus. An aerobic conditions can arise in secondary clarifiers with long SRTs, inside the tertiary filters, and in some sludge-handling operations. In addition, anaerobic conditions can arise in the activated sludge unit if aeration is not maintained at a sufficiently high level or if th e extent of oxygen tape ring through a plug flow system is too great. The released phosphorus is often returned to the head of the secondary process, via the RAS from the secondary clar ifiers or supernatant/ filtrate from sludgehandling operations. This reci rculated phosphorus thus increa ses the load on the secondary process and decreases the ove rall biological phosphorus remova l that can be achieved. Secondary phosphorus release can be reduced by minimizing the amount of time that mixed liquor or return sludge is held before recirculation, reduc ing return flows from sludgehandling operations, and treati ng the sludge-handling return st reams before introduction to the secondary process. In some cases, a small dose of alum is added to the tertiary filter to minimize the secondary release (see the Clark County, Nevada, Case Study in Chapter 3). Sidestream treatment has been proposed for some large facilities, incl uding facilities in New York (Constantine 2006) and Wash ington, D.C. (Constantine 2005).

Nitrates in Return Streams Nitrates in the return streams, such as RAS or internal recycle lines , can negatively affect biological phosphorus removal. The nitrates cause consumption of the VFAs needed for biological phosphorus removal and introduce a source of oxygen that is used before phosphorus release, minimizing the amount of biological phosphorus that can be removed. Because 1 mg/L nitrate-N is the equivalent of 2.86 mg/L DO, and nitrate does not have a maximum concentration like DO, nitrate has the potential to cause even more disruption to biological phosphorus removal than DO. In a step-feed system, McGrath et al. (2005) determined that 6 mg/L of nitrate nitrogen wa s the upper limit tolerabl e for successful EBPR in one particular full-scale ope ration. If sufficient rbCOD is ava ilable, higher concentrations of return stream nitrate could possibly be tolerated with adequa te phosphorus removal.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-31 Dissolved Oxygen in Return Streams Similar to nitrates, DO entering the anaerobic zone negatively affects biological phosphorus removal. The recycled DO essentially reduces the anaerobic HRT, because it needs to be reduced to zero before anaerobic metabolic ac tivities for biological phosphorus removal can occur. Because the PAOs are facultative aerobe s, they will use any available oxygen present in the anaerobic zone to aerobi cally metabolize VFAs. This re sults in a reduced anaerobic phosphorus release and, thus, reduced phosphorus uptake in the aerobic zone. In addition, heterotrophic aerobic organisms present in the anaerobic zone will compete for the VFAs, further reducing PAO anaerobic metabolism. If DO sources in the return stream cannot be minimized, additional VFAs might be required (Benisch 2004).



### 2.3.2 Chemical Phosphorus Removal
Chemical Phosphorus Species Current chemical phosphorus removal design is based on equilibrium precipitation theory (WEF 1997, 1998; USEPA 1987a, 1987b). The chemi cal precipitate of ortho-phosphorus is carried by treatment with a trivalent metal cation, typically ferric ion (Fe 3+ ) or aluminum (Al 3+ ). Ferric ion is typica lly supplied in the form of ferric chloride (FeCl 3 ). Aluminum is supplied as alum (aluminum sulfate). When a sour ce like waste pickle liq uor is available, the ferrous ion (Fe 2+ ) can be used as the metal cation. The precipitation reaction depends on the various phosphate species (e.g., H 2 PO 4 1-, , HPO 4 2- ) being converted to PO 4 3- , with the consumption of alkalinity (or OH - , hydroxide ion). This means th at sufficient alkalinity must be present for the chemical precipitation reaction to be completed.

1. Conversion of phosphate sp ecies to phosphate ion:

H n PO 4 (3-n)- + nOH - Æ PO 4 3- + n H 2 O

2. Chemical phosphorus removal by alum (aluminum sulfate):

Al 2 (SO 4 ) 3 Æ 2 Al 3+ + 3 (SO 4 2- )

Al 3+ + PO 4 3- Æ AlPO 4 (s)
3. Chemical phosphorus removal by ferric chloride:

FeCl 3 Æ Fe 3+ + 3 Cl -

Fe 3+ + PO 4 3- Æ FePO 4 (s)

4. Ferrous ion conversion to ferric ion:

2Fe 2+ + 1⁄2 O 2 + 2H + Æ 2Fe 3+ + H 2 OMunicipal Nutrient Removal Technologies Reference Document September 2008

2-32 Chapter 2: Treatment Technologies Chemical addition occurs in prim ary clarifiers (when pr esent) or in the secondary process, in the aeration basin or upstream of the secondary clarifiers, or in tertiary clarifiers or other treatment processes. Feeding chemicals to the primary clarifiers usually requires less chemical use than feeding to the secondary or tertiary process. Feedi ng chemicals at both the primary and secondary clarifiers results in le ss chemical use than feeding to the secondary process alone, allowing some phosphorus to be removed in the prim ary clarifiers and polishing to occur in the secondary process.

Recent research shows that in addition to e quilibrium precipitation, sorption is a predominant phenomenon. The factors that promote sorption, such as sorbent characteristics, variable stoichiometry, alkalinity, mixing at point of dosage, diffusion, and time-based kinetics, are processes that must be considered in designing systems to achieve a low total phosphorus (TP) concentration (Smith et al. 2007).

Chemical Phosphorus Removal Factors Phosphorus Species at Application Point Phosphorus in the raw wastewater is found in three forms—organically bound phosphorus, polyphosphate, and orthophosphate. Organically bound phosphorus can be settled in the primary clarifiers or tran sformed into orthophosphates by the microorganisms in the secondary process. Polyphosphates are soluble a nd pass through the primary clarifiers. In the secondary process, the polyphosphates are c onverted biologically into orthophosphates. Orthophosphates are also soluble and will pass into the final effluent if they are not removed biologically or chemically. Orthophosphates readily form a precipitate following the addition of metal salts, forming a floc that can then be settled or filtered from the wastewater.

Metal-to-Phosphorus Ratio In general, the molar ratio of the metal to infl uent phosphorus concentratio n (Al to P or Fe to P) increases as the target phosphor us effluent concentration decrea ses. The curve is flatter at higher effluent phosphorus concentrations, but it becomes particularly steep as the target concentration decreases below 0.5 mg/L (WEF and ASCE 1998). For a given amount of phosphorus to be removed, the amount of chemical th at needs to be fed is less for plants that employ tertiary chemical treatment following bi ological phosphorus removal, as compared to plants that use one- or tw o-point chemical phosphorus removal. When simultaneous precipitation is practiced, the MLSSs will co ntain a high phosphorus concentration, and it could easily exceed the concen tration for an EBPR sludge.

Choice of Chemical
Alum and ferric chloride are often used for chemical phospho rus removal. The choice of which chemical to use should be made on the ba sis of jar testing and chemical costs. The impact on downstream processes is another fact or to consider. Alum sludge can be more difficult to thicken and dewater than sludge from ferric chlori de. Ferric chloride is moreSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-33 corrosive and requires special piping. In addi tion, ferric chloride can cause problems with ultraviolet disinfection if the chemical is bake d onto the quartz sleeves . Ferrous sulfate is a viable alternative if a source is available. The presence of other metals or species that react with phosphate can cause simultaneous preci pitation of multiple metal phosphates or complexation effects that would thus require higher aluminum or ferri c doses than expected.

Feed Point Location Chemicals for phosphorus removal can be added to the primary clarifiers, the secondary treatment system (either to the aeration basin or upstream of the secondar y clarifiers), or the tertiary treatment process. Th e chemical should be well mixed with the wastewater at the feed location to form a good floc . If the chemical is not fed to a well-mixed location, an inline static mixer might be needed.

Phosphorus is a micronutrient and is needed by the microorganisms in the aeration basin to remove BOD and nitrogen. Care must be taken not to remove too much phosphorus in the primary clarifiers. A general rule of thumb is that the phosphorus in the influent to the activated-sludge basin sh ould be 1 to 1.5 percent of the BOD to be removed. For example, if 200 mg/L of BOD is to be removed in the aera tion basin, at least 2 to 3 mg/L of phosphorus is required in the primary effluent. This ru le-of-thumb ratio, however, can vary according to sludge age and the chemical do sage. If too much phosphorus is removed in the primary clarifiers, the operation of the aeration basin might be negatively affected.

Number of Feed Points
Alum or ferric chloride can be fed at one, two, or more locatio ns in the plant. Single-point application works well for plants that n eed to achieve moderate phosphorus removal concentrations (approximately 0.5 mg/L). Two f eed points, which might be either primary and secondary clarifiers or s econdary clarifiers a nd tertiary treatment, can achieve lower phosphorus concentrations and can use less chemi cals than dosing in one location. Several of the tertiary treatment processe s operate more efficiently if the TP concentration in the secondary effluent is less than 1 mg/L. For pl ants that do not have the ability to remove phosphorus biologically, two chemical feed point s might be required because the tertiary treatment process typically requires alum or ferri c chloride to form a floc before removal. Three feeding locations might be appropriate fo r plants that have a relatively high TP raw influent concentration (greater than 6 mg/L ), which might occur in communities with significant commercial a nd industrial discharges.

Mixing Requirements Rapid mixing is required when the chemical is added to the wastewater to allow the molecules to react. In addition, the density and viscosity of th e metal salts are larger than that of the wastewater, which allows the chemical to settle to the bottom. If rapid mixingMunicipal Nutrient Removal Technologies Reference Document September 2008

2-34 Chapter 2: Treatment Technologies conditions do not exist at the chemical inject ion location, an in-line static mixer might be required.

After the initial rapid mixing, gent le mixing is required to allow larger flocs to form. Usually, the movement of the wastewater through the treatment plant is sufficient for the floc formation. However, turbid areas of the plant might break up the floc, which would decrease phosphorus removal through se ttling or filtration.

pH Phosphorus solubility varies between iron and aluminum ions. Theoretically, the lowest effluent phosphorus concentration achievable with iron salts is 0.07 mg/L at a pH of approximately 6.9 to 7.0 s.u. Recent laboratory re sults indicate that uniformly high removal may occur at pH values between 5.5 and 7 (S mith 2007). Aluminum sa lts are theoretically capable of achieving effluent phosphorus concen trations down to 0.01 mg/L in a pH range of 6.6 to 7.2 s.u. (Kang et al. 2001; WEF and AS CE 1998). The actual effluent phosphorus concentration achieved and the optimum pH range will be site-dependent because of other chemical reactions that occur in the wastewat er. Recent research indi cates that the highest phosphorus removal efficiency occurs at a pH of between 5.5 and 7.0 s.u. However, the pH of the wastewater does not have a significan t effect on chemical phosphorus removal (Smith et al. 2007). Alum and ferric chloride are acidic and therefore capable of lowering the effluent pH. If sufficient alkali nity is not available to adequa tely buffer the wastewater, pH adjustment might be needed.

Suspended Solids Removal Capturing the floc formed dur ing chemical precipitation plays an important role in phosphorus removal. Sludge at WWTPs that us e biological phosphorus removal contains 4.5 percent phosphorus on a dry weight basis compared to 1.5 percent phosphorus for plants that use chemicals (USEPA 1987a). The phosphorus in the suspended solids in the effluent will require additional removal of the total suspended solids (TSS) in the final effluent in meeting low phosphorus limits. Tertiary processes like clar ifiers or filters are more efficient at capturing solids. Feeding metal salts in conj unction with the tertia ry process improves phosphorus removal.

Sludge Handling Chemical phosphorus removal generates addition al sludge. Phosphorus can be released from the chemical sludge if the sludge is exposed to or stored in an anaerobic environment. Return flows, such as supernatant or water from dewatered sludge, can contain high levels of phosphorus. Maintaining aerobic conditions in th e sludge is recommended. If this is not feasible, treatment of the sludge re turn flows should be considered.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-35 Recent analysis of phosphorus precipitation (Smith et al. 2007) suggests possible thermodynamic and kinetic factors in achieving extremely low (less than 0.01 mg/L) effluent phosphate concentrations. These factors include pH, metal (aluminum or iron) used for precipitation, the presence of additional me tals, materials that can complex with the phosphate such as COD and TSS, alkalinity, degree of mixing, and process time.



### 2.3.3 Phosphorus Removal Technologies
Enhanced Biological Phosphorus Removal Technologies

Fermentation If biological phosphorus removal is desired, the process is carried out under anaerobic conditions with VFAs providing the carbon source for the microorganisms. If the influent has too low a VFA concentration for adequate phosp horus removal (greater than approximately 4-to-1 mass of VFAs to mass of phosphorus in th e influent to be removed) the concentration must be increased. The VFAs can be supplied from an outside source or can be formed by on-site fermentation of primary sludge or RAS. Fermenting sludge to generate VFAs has the additional advantage of reduci ng the amount of sludge to be disposed of. Fermenting the primary sludge is preferred to using seconda ry sludge because doing so reduces the amount of phosphate released from the sludge. Fermentation is particularly helpful for large plants in cold climates and for plants where the strength of the wastewater tends to be low. In some situations, fermentation also occurs in the coll ection system, as well as in the anaerobic zone. Fermentation is illustrated in Figure 2-14.

Anaerobic Aerobic Tank Secondary Clarifier Effluent Influent

RAS

WAS RAS + VFA

Fermentation

of Primary Sludge or RAS RAS to Fermenter (optional)

Primary Sludge to Fermenter (optional)

Figure 2-14. Fermentation process.

Anaerobic/Oxic (A/O), or Phoredox, Process The anaerobic/oxic (A/O) process consists of an anaerobic zone upstrea m of an aerobic zone. The RAS enters the head of the anaerobic zone with the influent. In the anaerobic zone,Municipal Nutrient Removal Technologies Reference Document September 2008

2-36 Chapter 2: Treatment Technologies PAOs release phosphorus, which is subsequently taken up in the aerobic zone. One potential problem for A/O operation is that any nitrates re cycled from the aerobic zone of side streams can inhibit anaerobic growth (selection) of PAOs. To reduce this effect, the anaerobic zone is often split into an anoxic chamber for nitrate denitrification and a seri es of anaerobic zones for phosphorus release. The process has a medium -sized footprint and is relatively easy to retrofit into an existing basin by installing ba ffle walls and mixers to produce an anaerobic zone. If sufficient VFAs are available, an additional carbon source is not needed. Because there is some additional pumping, there are so me additional electrical costs; however, less sludge is generated under anaerobic conditi ons. To obtain extremely low phosphorus (less than 0.1 mg/L), chemical addition should be examined. The A/O (Phoredox) process is illustrated in Figure 2-15. The range of TP efflue nt concentrations evaluated in the literature reviewed for this study was 0.025 mg/L to 2.3 mg/L (see Table 2-5 in Section 2.5 for details).

Anaerobic Aerobic Tank Secondary Clarifier Effluent Influent

RAS

WAS
Figure 2-15. A/O (Phoredox) process.

Oxidation Ditch
Oxidation ditches were di scussed earlier in the Nitrogen Removal section. The design and operation of an oxidation ditch for phosphor us removal is much the same, with the requirement that an anaerobic zone be establis hed. The anaerobic zone (sometimes called a selector ) can be set up within the ditch or as an external tank upstream of the ditch. The oxidation ditch does not necessarily need to be operated with anoxic zones, although doing so can aid in the partial recove ry of alkalinity. As with the A/O process, additional carbon in the form of VFAs is needed only if sufficient rb COD is not already present in the influent. To obtain very low phosphorus (under 0.1 mg/L), additional carbon is required. The carbon should be added upstream of the secondary clarif ier to avoid depleting that nutrient from the biological process. Lower TP concentrations can be achieved by close monitoring and regulation of the anaerobic zone flow and DO levels. An oxidation ditc h with an anaerobic zone is illustrated in Figure 2-16. TP effluent concentrations range between 1 and 2 mg/L with the anaerobic zone. See Concentric Oxidation Ditch elsewhere in this chapter for its performance.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-37 Secondary
Clarifier Effluent Influent Aerators Flow Anaerobic

Zone (Selector)

WAS RAS

Figure 2-16. Oxidation ditch with anaerobic zone.

Physical-Chemical Technologies

Chemical Addition Aluminum or iron salts––most commonly alum (aluminum sulfate) and ferric chloride––can be added to precipitate phosphorus in the sec ondary clarifiers or te rtiary filters. Adding chemicals results in a limited capital investment initially, but chemical costs and the additional sludge generated incr ease the O&M costs of the process. Chemicals can be added at a number of locations in the wastewater treatment process; th e most common are the primary clarifiers, the secondary basins just before the second ary clarifiers, and upstream of the tertiary filters. Care must be taken in the fi rst two cases not to add so much chemical as to take the phosphorus below the concentration needed to sustain the secondary treatment microorganisms.

Chemical addition allows the facility to obtain extremely low effluent concentrations because more chemical can always be used with no significant impact on the microorganisms. However, using more chemicals creates a greater volume of sludge. Filtration can be used to remove fine precipitate part icles and achieve lower concen trations. The footprint for chemical addition is small, and only limite d piping and pumping are required (see Chapter 5 for more details). This means the capital costs are low, but the operating costs can be high for chemicals and sludge disposal. The phosphorus chem ical/filter process is illustrated in Figure 2-17. The range of TP effluent concentrations from combined chemical addition followed by filtration from the case studies and evaluated in the literature reviewed for this study was 0.1 mg/L to 2.3 mg/L (see Table 2- 5 in Section 2.5 for details).Municipal Nutrient Removal Technologies Reference Document September 2008

2-38 Chapter 2: Treatment Technologies Aerobic Tank Secondary Clarifier

Effluent Secondary Influent

RAS

WAS Filter Chemical Addition (Alum or Ferric)

(optional) Chemical Addition (Alum or Ferric)

(optional) Filter Backwash

Primary Clarifier Chemical Addition (Alum or Ferric)

(optional)

Figure 2-17. Phosphorus chemical/filter process.

Chemical Removal with Conventional Filtration Technologies Sand filters are used to polish effluents by re moving suspended solids. To the extent that phosphate is associated with suspended solids, sand filters can provide effective removal. Rapid mixing should occur before entering the filter to ensure that the chemicals are distributed throughout the secondary effluent, al lowing floc to form. Descriptions of the some of the filtration alternatives are provided below. They have particular application downstream of chemical addition and when the discharge standard is below 0.1 mg/L.

Filters can be used to capture phosphorus in the solid phase. Adding chemicals can increase the effectiveness of the filters by precipitating the soluble phosphorus in to a solid form that can be captured by the filters. Several varieties of filters can be used in multiple configurations. Filter media can range from mono-media, such as sand, to multimedia, such as sand with anthracite or gravel. Standard and deep-bed filters are avai lable. Cloth filters, which use cloth to capture the solids rather than sand, can also be used. Filters can be operated in series to improve removal. For example, a deep-bed filter could be operated in series with a standard bed filter. A clarifier is used to remove solids from the filter backwash before the treated backwash is returned to the head of the plant.

Filter Media Media within the filters trap particles between the pores. The smaller the pore spaces, the smaller the particles that can be removed. De scriptions of the most common filter media follow.

Sand Filters Sand is typically used in single-medium filters. The size and uniformity of the sand depend on the application and characteri stics of the secondary effluent at the individual plant. The uniformity of the sand is important because varying sizes can provide smaller pores forSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-39 greater filtration; however, during backwashi ng the media can become stratified, with the smaller particles toward the top of the filter. Large solids particles in the secondary effluent might fill the pores between the small particles, decreasing the amount of water that can pass through the filter, increasing h ead loss, and leading to more frequent backwash cycles.

Dual-Media Filters Dual-media filters typically us e anthracite in combination with the sand. Anthracite can adsorb organic compounds in addition to filtering solid s. It is softer than sand, and abrasion during backwashing can decrease the size of the anthracite particles. These smaller particles could cause blinding of the filter by trapping larg er solids on the surface of the media, which would block the passage of the water if the an thracite is not remove d during the backwash cycle. Other media combinations in dual-me dia filters include ac tivated carbon and sand, resin beds and sand, and resin beds and anthracite.

Multimedia Bed Filters Multimedia beds can contain anthracite, sand, and garnet or ilmenite. Garnet and ilmenite have a higher density than sand, allowing them to settle to the bottom of the filter after backwashing. In addition, garn et and ilmenite can have a smaller pore size than sand, allowing the smallest solids to be trapped by th e garnet before the wastewater exits the filter when operated in a downflow mode.

Backwash Methods Filters can be backwashed using water, air, or a combination of air and water. Filters can be backwashed using water alone. Air backwashing can be used as part of the backwashing process, but it is usually not effective in rem oving solids particles wit hout the use of water. Descriptions of various backwash protocols are provided below.

The water acts to fluidize the bed, thereby rele asing the particles trapped between the pores. The most effective way to backwash a bed is to force the filter media to rub together. This assists in removing the secondary effluent particles, which ca n adhere to media because of the biological nature of the solids, which can be sticky . Backwashing the filter using air before or during the water backwash cycle allows scouring of the media.

Air and water can be used simultaneously to backwash the filter. This process reduces the amount of water required to backwash the filt er and also requires less time, reducing the volume of backwash water generated per cycl e. Simultaneous air and water backwash can produce a cleaner filter, which will extend the ru n time of the filter compared to water alone or air scour followed by water. In addition, stratification does not occur with simultaneous air and water backwashing, so the smaller media gr ains do not accumulate at the surface of the filter bed. The smaller grains at the filter su rface can become clogged by large particles in the wastewater, which reduces the filt er run time. In an unstratifie d bed, the media grain sizes areMunicipal Nutrient Removal Technologies Reference Document September 2008

2-40 Chapter 2: Treatment Technologies distributed uniformly throughout the filter, a llowing the suspended solids to be trapped throughout the filter depth, further incr easing the run time of the filter.

Filtered effluent can be used to backwash and re move the solids trapped in the filter media. The filter typically needs to be backwashed at a high rate, approximately 15 to 20 gpm/ft 2

, for at least 15 to 20 minutes. Backwashing gene rates a large volume of reject water to be returned to the head of the plant. The slug of backwash water, which contains solids and phosphorus, can negatively affect the operation of the treatment plant. To minimize the impact of the filter backwash, the water can be stored in an equalization basin and slowly fed back to the head of the plant; treatment with chemicals to remove some of the solids is also possible.

Bed Depth The media depth can vary with the type of filter selected. Traveling bridge and pulse bed filters have relatively shallow bed depths of 10 to 12 inches. Standard beds typically contain approximately 2 feet of filter media, while d eep beds contain approximately 4 to 6 feet of media. The deeper the bed, the longer the fi lter can operate before backwashing. However, deeper beds require a higher backwash rate to release the solids trapped in the media.

Gravity Filters Wastewater is applied to the top of the media bed, allowing the water to flow downward by gravity. The wastewater is then collected in underdrains that allow the wastewater to enter but retain the filter media. Once a set amount of time passes or a predetermined head loss is measured in the filter, a backwash cycle is in itiated. The filter is backwashed by either water or an air/water combination that removes the trapped solids from the media. The solids are directed to the head of the plant, while the f ilter media are retained. After the backwash cycle is complete, the filter is placed back into servi ce. (Usually, the entire filter must be taken out of service to be backwashed.) A supply of f iltered effluent (stored in a clear well) to backwash the filter might be required. If the production rate of the filters that remain in service is greater than the required backwash rate, the clear well might not be needed. Alternatively, some filters are divided into two to four cells, which allows only one cell to be taken out of service at a time while the remain ing cells continue to produce water that can be used to backwash the out-of-service cell.

If the sand or alternate medium contains a variet y of particle sizes, th e smaller grains might accumulate at the top of the filter. The smaller grains have smaller pore sizes, which might be filled or blinded by the wastewater at a faster rate than the larger grains. This accumulation might lead to more frequent backwashing of the filters. Using an air/water backwash system, rather than water alone, might minimize this problem by not fully fluidizing the bed.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-41 Moving-Bed Filter A moving-bed filter cleans a portion of the gra nular media continuously so that operation does not need to stop to perform a backwash cy cle. The filter can operate in a downflow or upflow mode. In the downflow mode, wastewater enters the top of the filter and flows downward through the media. The solids filtered from the wastewater are drawn downward with the sand. An airlift pump transfers the solids and sand to the top of the filter, where a filter washbox is located. The sand is separated from the solids by gravity. The cleaned sand is returned to the top of the filter, and the solids are returned to the plant headworks or directed to disposal.

In an upflow moving-bed filter, the wastewater enters through the bottom of the filter and is pumped upward through the sand. Solids captured in the sand move downward and are airlifted to a reject compartm ent through the center of the f ilter. The turbulence created by the air lift pumps separates the solids from the sand. The clean sand is separated from the solids by gravity. The solids are directed to the headworks of the plant, and the clean sand is deposited on top of the filter. The advantage of an upflow filter is that the wastewater encounters the sand containing the most solids first and passes through the cleanest sand before it exits the filter over a weir.

Pulsed-Bed Filters Pulsed-bed filters have a relatively shallow be d containing approximately 10 inches of sand or alternate medium. Secondary effluent is a pplied to the top of the filter. Diffusers are located on the top of the bed surface. Once the water level reaches the air mix probe, air is supplied to the diffusers, suspending the larger particles above the bed; filtration continues during this process. As operation continues, solids might settle onto the surface of the bed, causing a rise in the water level to the pulse mix probe. When the bed is pulsed, effluent is not discharged from the filters. Air that is trapped in the underdrains is released by backwash pumps and travels upward through the clogged media. The solids ar e released at the top of the bed and suspended by the diffusers on the media surface. The effluent valve is then reopened, and operation of the filters can cont inue. After a set number of pulses, a full backwash of the filter occurs to remove th e trapped solids from the filter. The pulses are designed to extend the operation of the filter a nd decrease the number of backwash cycles required compared to a conventional filter.

Traveling Bridge/Automatic Backwash Filter The automatic backwash filter or traveling bridge filter has a relatively shallow sand depth of 12 inches. The width of the unit is typically fi xed at approximately 16 feet. The length of the traveling bridge filter is determined by the amount of surface area required for a given application. Wastewater is a pplied to the top of the sand and filters downward through the filter. The head loss across the filter is relati vely low at less than 4.9 feet (WEF and ASCE 1998, pp. 16–19). A traveling bridge and backwash hood move along the filter to backwashMunicipal Nutrient Removal Technologies Reference Document September 2008

2-42 Chapter 2: Treatment Technologies one cell of the filter at a time. This allows the remaining filter cells to stay in operation while a portion of the filter is backwashed. The rate of backwash water generated is less because of the shallow sand bed and smaller area backwashed when compared to a conventional sand filter. In a conventional f ilter, the backwash might need to be stored to allow the solids to be fed slowly back to the head of the process to avoid slug loads. A filter then removes solids that pass through the tertiary cl arifier. The traveling bridge filter produces a relatively constant amount of backwash wh en the filter is in operation.

Cloth Filters Cloth filters, as the name implies, use specially designed cloth to filter the wastewater, rather than sand or other granular media. The cloth pane ls are installed vertical ly inside a steel or concrete tank. The wastewater submerges the cloth panels and travels horizontally through them. Solids accumulate on the outside of the clot h panels, while filtered water is collected on the inside of the panels and directed to the effluent chamber. The solids on the outside of the cloth form a mat, and the water level in the filter rises. When the water reaches a preset level, the filter is backwashed by liquid suct ion. The cloth filters are rotated during the backwash process. Two cloth filter panels are backwashed at a time, allowing the other panels to continue filtering wa ter, thereby eliminating the need to have a tank to store flows for backwashing the filter. The backwashed solids are directed to the headworks of the plant. Larger solids settle to the bottom of the basi n, from which they are periodically pumped out and directed to the head works of the plant or th e solids-handling process.

Cloth filters can operate at a higher hydrauli c loading rate than granular media filters, resulting in a smaller footprint. The backwash rate is also redu ced because there is no need to fluidize the bed as required with granular medi a filters. Cloth filters are usually installed in small plants (average flows less than 5 to 10 MGD); however, the Orange County, Florida, WWTP uses cloth filters at an average a nnual flow of 29.5 MGD and plans to expand to accommodate 43 MGD.

Tertiary Clarification with Filtration The practice of adding tertiary clarifiers upstream of filters can further achieve low solids concentrations and thus low phosphorus effl uent levels. Scott and Laurence (2007) performed a pilot study using the combination of tertiary clarification followed by filtration to obtain effluent concentrati ons in a municipal wastewater consistently below 0.05 mg/L, and sometimes below 0.01 mg/L, when using al um doses of 75 mg/L with polymer addition. Tertiary clarifiers that coul d be used include solids contac t clarifiers, upflow buoyant-media clarifiers, tube clarifiers, plat e clarifiers, and a second set of secondary clarifiers. To improve performance through the ter tiary clarifiers, a coagulant, such as alum or ferric chloride, and a polymer can be added upstream of the unit.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-43 Solids contact clarifiers mix the secondary effl uent with coagulants and previously settled solids, forming larger floc. After mixing in the center of the clarifier, the wastewater moves outward to the settling zone, where the solids move downward to the bottom and the treated water exits the unit over a weir. Periodicall y, solids are removed from the clarifier for treatment and disposal. A filter then removes so lids that pass through the tertiary clarifier.

The upflow buoyant-media clarif ier mixes the coagulant and polymer with the secondary effluent, allows flocculation to occur, and provi des clarification. A tube clarifier has inclined tubes in a portion of the clar ifier. The water flows up through the tubes, and solids flow downward to the bottom of the clarifier, from which they are pumped out. Similarly, a plate clarifier has inclined plates installed in a portion of th e clarifier. The water flows upward between the plates, and solids settle onto the plates and slide down to the bottom of the clarifier. For the tertiary clar ification process to be successf ul, the velocity through the unit must be low enough to allow the solids in the secondary effluent to settle.

Membrane Filtration Technologies Membrane filters can be used externally to re move suspended solids or can be incorporated into the activated-sludge process as an M BR. MBR systems employ a suspended-growth biological reactor, from which effluent is passed through a membrane filter. By so doing, suspended solids are effectively removed from the effluent. Phosphate is retained in the reactor as polyphosphate taken up by the microor ganisms (if biological phosphate removal is operating) or as chemically generated suspe nded solids. Crawford et al. (2006) examined phosphorus removal at several U.S. plants, includ ing one in Traverse City, Michigan. In all configurations, the membrane is associated with the final ae robic step, and microorganisms are recirculated with a portion of the membra ne concentrate. If chemicals are needed to achieve low effluent phosphorus, they can be added before the membrane to precipitate whatever the microorganisms have not take n up. At the Hyrum WWTP in Utah, an MBR produced effluent concentrations of 0.07 mg/L for the annual av erage. The facility uses an aluminum salt for coagulation and chemical phosphorus removal. Another MBR facility at Lone Tree Creek, Colorado, achieves an annual average of 0.027 mg/L.

Specialty Filter Descriptions Dynasand D2 Advanced Filtration System The Dynasand D2 advanced filtration system c onsists of deep bed and standard bed upflow filters in series. The deep bed filter contains coarse sand and uses a proprietary process called continuous contact filtration, wh ich allows coagulation, floccu lation, and separation to occur in the filter. The standard bed filter is f illed with a finer sand mix. Both filters are continuously backwashed. The backwash water from the filters is treated in a lamella gravity settler, a high-rate gravity plate settler, to remove solids before being returned to the head of the plant. Alum is added upstream of both filte rs. The process is depicted in Figure 2-18.Municipal Nutrient Removal Technologies Reference Document September 2008

2-44 Chapter 2: Treatment Technologies Figure 2-18. Parkson Dynasand D2 advanced filter system.

Actiflo Actiflo is a sand-ballasted flocculation proce ss. Metal salt and polymer are added upstream of the coagulation tank. The pH is adjusted to optimize phosphorus removal on the basis of the wastewater characteristic s at the specific site and th e type of polymer used. The wastewater is then mixed with fine sand and polymer. The fine sand, referred to as microsand, provides a large surface area to which th e formed floc can attach; it also increases the sedimentation rate by acting as ballast. The solids are settled in a clarifier equipped with lamellar tubes. The microsand is recovered in a cyclonic separator and returned to the process. A sand filter can follow the Actiflo process to capture additional solids and further reduce the effluent phosphorus concentration.

DensaDeg DensaDeg is a high-rate solids contact clarifica tion process that consists of a reactor zone, a presettling/thickening zone, and a clarification zone. Metal salts are mixed with the influent to the process, and the pH is adjusted to optimize phosphorus removal based on the wastewater characteristics at th e specific site. The wastewater then enters the base of the reactor and is mixed with sludge returned from the solids contact clar ifier. The reactor tank contains a turbine and draft tube that promote floc formation and separate the solids. Polymer is added to increase the sludge density. In the presettling/thickening z one, the sludge settles to the bottom because of the increased density a nd continues to thicken. Sludge is returned to the reactor zone or removed from the process fo r further treatment. In the clarification zone, Dynasand Deep Bed Filter Dynasand Standard Bed Filter Final Effluent

Lamella Filter Alum Alum

Reject Water Secondary Effluent 2 n d filter

scour water 1 s t
filter

scour wate rSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-45 the supernatant flows up through the settling tubes as the e ffluent from the process. Additional phosphorus can be removed by following the process with filtration.

Enhanced Biological Phosphorus Removal with Filtration Technologies Chemical addition, filtration, or both can be used to polish effluent from biological phosphorus removal processes. Drury et al. ( 2005) reported chemical polishing of EBPR effluent ahead of the tertiary filter at Clark County, Nevada. An upper feed limit was established at 10 mg/L alum to prevent plugging in the filter, while th e effluent phosphorus concentration was regularly as low as 0.1 mg/L. At Durham, Oregon, Stephens (2004) reported effluent concentrations as low as 0.07 mg/L with chemical polishing and filtration. Any of the biological phosphorus removal technologies described previously could be combined with chemical addition, conventional filtration, membrane filtration (external to the activated-sludge process), or the specia lty filtration processes mentioned earlier.

Emerging Technologies The following processes have undergone testing, treating a portion of the flow at a minimum of one plant. Full-scale data are not availabl e for these processes, although the processes are being considered for upgrade s at several facilities.

CoMag Process The CoMag process consists of ballasted flo cculation, solids contact clarification, and highgradient magnetic separation. The flocculation tank has three compartments. In the first compartment, wastewater is mixed with a me tal salt and the pH is adjusted to optimize phosphorus removal on the basis of the wastewater characteristics at the specific site. Then fine magnetic particles are added to increase the density of the floc. In the third compartment, polymer is added to increase flocculation. The wa stewater enters a soli ds contact clarifier. Most of the solids are returned to the floccula tion tank. The remaining solids are wasted from the system. A magnet separator captures solids that passed th rough the clarifier by attracting the magnetic particles that were added in the second compartment of the flocculation tank. The effluent is then sent to the disinfection process for the treatment plant. The backwash from the magnet separator is mixed with the wasted sludge, which passes through a magnetic ballast recovery system to minimize the loss of the magnetic ballast. The remaining sludge is sent to the sludge-handling system for the plan t. The recovered magnetic ballast is returned to the flocculation tank (Tozer 2007). The Co Mag process is illustrated in Figure 2-19.Municipal Nutrient Removal Technologies Reference Document September 2008

2-46 Chapter 2: Treatment Technologies Figure 2-19. CoMag process.

Blue PRO Process The Blue PRO process consists of addition of a chemical, typically ferric chloride to form ferric phosphate precipitate. This step is fo llowed by a proprietary pre-reactor zone and moving-bed filter. The process uses a Centra-flo continuous backwashing filter. Unlike most filters, which rely on trapping solids between the media par ticles to remove phosphorus, the Blue PRO filtration system contains a bed of hydrous ferric oxide-coated media, in which ferric phosphate and other pollutant s are filtered. The abrasion of the sand particles against one another in the moving bed filter exposes new adsorption s ites on the media. The process can be operated in a dual-stage mode with two Blue PRO filtration systems in series. In the Blue PRO-CEPT system, the reject from the filters is returned to the head of the plant. The process is illustrated in Figure 2-20. Magnetic Separator Clarifier

Separator Water Magnetic Ballast Recovery Fresh Magnetic Ballast

Sludge Processing Chemical Treatment To Disinfection Polymer Metal Salt + pH Control

FeedSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-47 Figure 2-20. Blue-PRO process.

Trident HS The Trident HS system consists of two clar ification processes follo wed by filtration. Metal salts and polymer are added upstream of the tube clarifier, which contains a recycle flow of precipitated solids to decrease the variation of the influent qual ity entering the unit. From the tube clarifier, additi onal polymer is added before the wastewater enters an adsorption clarifier. The adsorption clarifier consists of a buoyant-media bed to remove additional solids before filtration. The media in the clarifier do not have any ad sorption properties. The unit is an upflow filter containing coarse media. Th e accumulated solids are flushed from the clarifier using air and water from the tube clarifier. A mixed-media gravity filter follows the two-stage clarification process for applications designed to meet phosphorus concentrations of less than 0.1 mg/L. The filter is backwash ed using air and water simultaneously. The process is depicted in Figure 2-21.

Figure 2-21. U.S. Filter Trident process. Tube Clarifier Adsorption Clarifier Mixed Media Filter Final Effluent Influent Al/Fe

Polymer Polymer Fe 3+ Moving Bed Filter 1

Pre-reactor 1 Secondary Effluent

Fe 3+ Pre-reactor 2 Moving Bed Filter 2

Reject Effluent

RejectMunicipal Nutrient Removal Technologies Reference Document September 2008

2-48 Chapter 2: Treatment Technologies Infiltration Basin/Land Application Use of an infiltration basin or land applica tion is the state of the science in phosphorus removal technology. Phosphorus is further removed through land application, before discharge to surface water. In addition, some soils are capable of adsorbing phosphorus, thereby extending the limit of technology for phosphorus removal. Land application requires a large amount of available space. A syst em designed for the Brighton, Michigan, plant employs approximately 25 acres/MGD treated. In th at system, after biological treatment in an oxidation ditch, chemical treatment to 0.2 mg/L, a nd tertiary clarificati on, the wastewater is sprayed onto the land and collected through a system of underdr ains. The treated water is then discharged to a surface water. The treate d water has a phosphorus concentration of less than 0.01 mg/L at all times. The soil should be tested before construc ting a land application system to verify the adsorption capacity of the soil and predict the length of time that the field can be used. In the case of Brighton, the design flowrate for the infiltration basin is 2.54 gal/day/ft 2 . As designed, the soil had a cation ex change capacity of 2.0 milliequivalents/100 g; with the initial phosphorus content in the soil, the mini-colum n test results presented in the engineering report indicate an estimated usef ul life of the soil of at least 40 years.



### 2.4 Nitrogen and Phosphorus Removal Processes

2.4.1 Nitrogen and Phos phorus Removal Factors The removal factors for proce sses that achieve both nitroge n and phosphorus removal are a combination of the removal factors for processe s that target removal of only one of the nutrients.

Balancing the various factors might be necessary to achieve adequate TN and TP removal. For instance, nitrates in the RAS stream might need to be minimized to promote biological phosphorus removal in the anaerobic zone. This is more likely to be an issue at plants with a single anoxic zone because the n itrates created after nitrificat ion in the aeration zone do not have an opportunity to denitrify. To avoid this problem, the RAS could be held in an equalization tank before return to the anaerob ic zone. The equaliza tion zone might also reduce the DO in the RAS, which would furthe r improve the performance of the anaerobic zone. The retention time, however, would have to be limited to prevent secondary release of phosphorus. Alternatively, the RAS c ould be diverted to the anoxi c zone rather than to the anaerobic zone.

Plants achieving both nitrogen and phosphorus removal must be designed and operated to avoid the release of phosphate w ithout either VFAs or nitrates present. Anaerobic or anoxic zones that are too big remove carbon and nitrates , resulting in the releas e of phosphate that is not taken up in the aerobic zone. Similarly, if nitrate removal has been enhanced, there might not be any way to prevent phosphorus release in the lower portions or deep in the sludge blanket of the secondary clarifier. If that happens in the sludge, the release might notSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-49 immediately affect the effluent directly, but it could result in a buildup of phosphorus in the secondary treatment system that would eventually raise the final phosphorus concentration. This trade-off between nitrat e and biological phosphorus re moval requires well-considered design, analysis, and process cont rol. As an alternative, nitrat e removal can be made extremely efficient in the secondary proc ess, and chemical precipitati on and filtration can be used subsequently to remove phosphorus to an extremely low level.

There are several other factors to be aware of in a combined system. In general, the COD-toTKN ratio determines which zones need to be large and which shou ld be small. Oxygen in the feed to anaerobic or anoxic zone s should be minimized because it will inhibit those reactions. Temperature can also affect the processes: under cold co nditions, fermentation might not provide sufficient VFAs for the less temper ature-sensitive phosphate uptake reaction, and denitrification can be slowed. The result woul d be reduced phosphorus and nitrogen removal. Because phosphate removal and nitrification co nsume alkalinity while denitrification supplies alkalinity, it could be that some alkalinity will have to be suppl ied to allow all processes to proceed normally. In addition, phosp horus is a necessary nutrient fo r microbial growth. If TP is reduced too low before a biological process like denitrification, the growth of the microorganisms could be inhibited, thereby requiring the addition of supplemental phosphorus.

The biological removal of phosphorus and of nitrogen compete for available carbon at certain plants with two anoxic zones, such as those in the 5-stage Bardenpho process. The available carbon in the influent or return side streams can be used fo r biological phosphorus removal and nitrification. However, some plants might require methanol or an alternative carbon source to be added to the second anoxic zone. Pl ants that are required to meet low effluent phosphorus limits (less than 0.1 mg/L) will likely require an alternative carbon source and tertiary filtration.

An evaluation comparing the 5-stage Barde npho process and the 4-stage Bardenpho process might be warranted in situations that would require methanol to be fed for nitrogen removal, as well as alum or ferric chloride for a dditional phosphorus removal. In the 4-stage Bardenpho process, phosphorus could be removed only chemically. Depending on the operation of the aerobic zones, sufficient carbon could be available at the second anoxic zone to eliminate the need to feed methanol. The 4-stage Bardenpho process would have no additional sludge from the nitrogen removal pro cess because methanol would not be added; however, there would be more sludge from the chemical phosphorus removal. By using chemical phosphorus removal only, some of the balancing act described previously between biological phosphorus and nitrogen removal wo uld not be necessary, making operation of the plant easier. If methanol addi tion can be avoided, it can save some costs and O&M problems associated with its handling.Municipal Nutrient Removal Technologies Reference Document September 2008

2-50 Chapter 2: Treatment Technologies 

### 2.4.2 Nitrogen and Phosph orus Removal Technologies

Anaerobic/Anoxic/Oxic The anaerobic/anoxic/oxic (A 2 O) process consists of an anaerobic zone, an anoxic zone, and an aerobic zone. An internal recycl e stream returns nitrates from the aerobic zone to the anoxic zone, as in the MLE process. RAS is recycled to the head of th e anaerobic zone along with the secondary influent. This process thus allows fo r simultaneous nitrogen and phosphorus removal. With the inclusion of the anoxic zone, the concentrat ion of nitrates in the re turn sludge is reduced (compared to the A/O process), meaning that the anaerobic proc ess is more efficient. The existing activated-sludge basin can be modified to include the anaerobic and anoxic zones, assuming sufficient volume rema ins in the aerobic zone to pe rform nitrification. With two recycle streams, some piping and pumping are needed, but extr a head might not be required depending on the hydraulics of the plant. With on ly one anoxic z one and if VFAs are sufficient, there might not be a need to supplement the carbon. With A 2 O, as with all combined nitrogenphosphorus biological systems, some phosphorus is taken up in the anoxic zone by the PAOs, and the sludge residence time in each zone must be sufficien t to allow complete phosphate release or uptake. The clarifier al so must be operated to regularly waste solids to avoid release of phosphate by the en dogenous respirati on of PAOs. The A 2 O process is illustra ted in Figure 2-22. The ranges for TN and TP removal technologies ev aluated in this study are 7.3 mg/L to 9.0 mg/L and 0.025 mg/L to 0.98 mg/L, respectively (see Tables 2-1 and 2-5). These results are for effluent from a system such as th at shown in Figure 2-22. Another facility using A 2 O followed by chemical addition and f iltration achieved TP co ncentrations of 0.13 mg/L annual average (see Table 2-2 in Section 2.5).

Anoxic Tank Aerobic Tank Secondary Clarifier Effluent Influent

RAS Nitrified Recycle

Anaerobic

Tank

WAS

Figure 2-22. A 2 O process.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-51 Five-Stage Bardenpho Process The 5-stage Bardenpho process is similar to the 4-stage Barde npho process with the exception that an anaerobic zone is added ahead of the 4-stage system . The internal recycle from the first aerobic zone to the first anoxic zone remains in place. RAS is returned to the head of the anaerobic zone and is fed with the secondary infl uent (or primary effluent if primary settling is implemented). Methanol might need to be fed to the second anoxic zone to provide a carbon source for denitr ification. As with the 4-stag e Bardenpho, the footprint is large and internal construction is needed during retrofits to define the zones. Extra head is not typically needed; however, nitr ate recycle between the first aerobic zone and anoxic zone might require additional pumpi ng. The second anoxic zone could require additional carbon in the form of methanol or as VFAs if such are being added to support phosphorus uptake. For extremely low phosphorus concentrations, chemi cal addition, preferably in a downstream system so as to not remove all phosphate fr om the biological system, could be used. The 5-stage Bardenpho process is illustrated in Fi gure 2-23. The ranges of TN and TP effluent concentrations from the case studies that used 5-stage Ba rdenpho with chemical addition were 0.87 mg/L to 5.59 mg/L in TN and 0.06 mg/L to 1.09 mg/L in TP (see Table 2-3 in Section 2.5 for details).

Anoxic Tank Aerobic Tank Secondary Clarifier Effluent Influent

RAS Nitrified Recycle

Anoxic Tank Aerobic Tank (Optional) Methanol Addition

WAS Anaerobic Tank

Figure 2-23. Five-stage modified Bardenpho process.

University of Cape Town Process The University of Cape Town (UCT) process, a variation of the Phoredox process, consists of anaerobic, anoxic, and aerobic zones. An inte rnal recycle returns nitrates from the aerobic zone to the head of the anoxic zone. A second internal recycle return s wastewater from the anoxic zone to the head of the anaerobic zone. RA S is directed to the head of the anoxic zone to minimize the amount of nitrates entering the anaerobic zone. The intent of the design is to keep the concentration of VFAs and the phosphate-accumulating reactions high, without competition from denitrification reactions usi ng the VFAs. This process has a medium-sizedMunicipal Nutrient Removal Technologies Reference Document September 2008

2-52 Chapter 2: Treatment Technologies footprint and could be set up in existing basins , depending on the volume available. As with other processes in this section, no additional head would be needed, but there would be extensive piping and pumping for the recycle st reams. If sufficient VFAs are present, no supplemental carbon sources are required. Achi eving a very low phosphate concentration requires downstream chemical precipitation and filtration. The UCT process is illustrated in Figure 2-24. The TN and TP effluent concentr ations found in the li terature for the UCT process with filtration were 8.9 mg/L to 10.0 mg/L in TN and 0.3 mg/L in TP (see Tables 2-5 and 2-8 in Section 2.5 for details).

Anoxic Tank Aerobic Tank Secondary Clarifier Effluent Influent

RAS Nitrified Recycle

Anaerobic

Tank

WAS Mixed Liquor

Recycle

Figure 2-24. University of Cape Town process.

Modified University of Cape Town Process The modified UCT process, another variation of the Phoredox process, has an anaerobic zone followed by two anoxic zones and an aerobic zone upstream of the secondary clarifiers. The two anoxic zones in series are designed to operate such that no nitrates are returned to the anaerobic zone. The nitrates from the aerobic z one are returned to the head of the second anoxic zone, while a second internal recycle retu rns flow from the end of the first anoxic zone to the head of the anaerobic zone. RAS is directed to the head of the first anoxic zone. This process has a medium-sized footprint and co uld be set up in existi ng basins if sufficient volume is available. As with other processes in this section, no additional head is needed, but extensive piping and pumping are needed for the recycle streams. If sufficient VFAs are present, no supplemental carbon sources are required. Achieving a very low phosphate concentration requires downstream chemical pr ecipitation and filtration. The modified UCT process is illustrated in Figure 2-25. The ranges of TN and TP effluent concentrations found in the literature for the modifi ed UCT process with VFA add ition were 5.0 mg/L to 6.0 mg/L in TN and 0.1 mg/L to 2.7 mg/L in TP (s ee Table 2-8 in Section 2.5 for details).September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-53 Aerobic Tank Secondary Clarifier Effluent Influent

RAS Nitrified Recycle

Anaerobic

Tank

WAS Mixed Liquor

Recycle Anoxic Tank Anoxic Tank

Figure 2-25. Modified University of Cape Town process.

Virginia Initiative Process The Virginia Initiative process (VIP) is simila r to the modified UCT process and is another variation of the Phoredox process. The nitrates from the aerobic zone are returned to the head of the first anoxic zone, instead of the second anoxic zone as is done with the modified UCT process. The second return is from the end of the second anoxic zone to the head of the anaerobic zone. RAS continues to enter the h ead of the first anoxic zone. The VIP process allows for additional denitrifi cation and thus minimizes the introduction of nitrate to the anaerobic zone. Nitrate in the an aerobic zone would interfere w ith phosphorus release, and so would reduce the opportunity for subsequent pho sphorus uptake in the aerobic zone. The VIP process is operated in a high-rate mode, allo wing for small tank volumes, which require less space than other similar processes. This proce ss has a medium-sized footprint and could be set up in existing basins. As with other proce sses in this section, no additional head is needed, but extensive piping and pumping are needed for the recycle streams. As with the other processes, if sufficient VFAs are pres ent, no supplemental carbon sources are required. Achieving a very low phosphate concentration requires downstream chemical precipitation and filtration. The VIP is illustrated in Figure 2-26. The ranges of TN and phosphorus effluent concentrations found in the lite rature for the VIP were 3.0 mg/L to 10.0 mg/L in TN and 0.19 mg/L to 5.75 mg/L in TP; for the VIP with VFA addition the ranges were 5.0 mg/L to 10.0 mg/L in TN and 0.6 mg/L to 0.8 mg/L in TP (s ee Tables 2-1, 2-2, and 2-3 in Section 2.5 for details).Municipal Nutrient Removal Technologies Reference Document September 2008

2-54 Chapter 2: Treatment Technologies Aerobic Tank Secondary Clarifier Effluent Influent

RAS Nitrified Recycle

Anaerobic

Tank

WAS Mixed Liquor

Recycle Anoxic Tank Anoxic Tank

Figure 2-26. Virginia Initiative process.

Johannesburg Process The Johannesburg process, another variation of the Phoredox process, consists of anaerobic, anoxic, and aerobic tanks in series. An internal recycle returns nitrates from the end of the aerobic zone to the head of the anoxic zone. An anoxic zone on the RAS line allows denitrification to occur, reducing the amount of nitrates that ente r the anaerobic zone. Denitrification in the anoxic tank on the RAS line can be li mited by a lack of carbon, which can be overcome by bringing sludge from the end of the anaerobic z one to the RAS-line anoxic zone. The dedicated anoxic zone allows a smaller footprint than some other systems. As with other processes in th is section, no additional head is needed, but extensive piping and pumping are needed for the recycle streams. If sufficient VFAs are present, no supplemental carbon sources are required. Achi eving a very low phosphate concentration requires downstream chemical precipitation. The Johannesburg process is illustrated in Figure 2-27. The range of TN for one applica tion of the Johannesburg process was 2.03 mg/L to 11.44 mg/L TN (see Table 2-1 in Section 2.5 for details).

Anoxic Tank Aerobic Tank Secondary Clarifier Effluent Influent

RAS Nitrified Recycle

Anaerobic

Tank

WAS Anoxic Tank

Figure 2-27. Johannesburg process.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-55 Biodenipho Process The PID, or Biodenipho, process is similar to the Biodenitro process, with the exception that an anaerobic tank is placed ups tream of the two oxidation ditc hes, which are operated in a cyclical manner to promote denitrification and n itrification. The result of phasing (or cycling) is that organic carbon in the wastewater is used for both denitrification and biological phosphorus removal. If sufficient carbon is pres ent, no supplemental source is required. The RAS is directed to the anaerobi c zone. As with the Biodenitro process, the footprint of the system can be large. Achieving a very low phosphate concentration might require downstream chemical precipitati on and filtration. The Biodenipho process is illustrated in Figure 2-24. The ranges of TN and TP effluent concentrations found in the literature for the Biodenipho process were 1.78 mg/L to 7.02 mg/L in TN and 0.09 mg/L to 1.99 mg/L in TP (see Table 2-3 in Section 2.5 for details).

Secondary Clarifier Effluent Influent

RAS Anaerobic

Tank

WAS Alternating Aerobic/Anoxic Tanks

Flows switch when tanks alternate Tank 1-Anoxic

Tank 2-Aerobic

Figure 2-28. Biodenipho (phase d isolation ditch) process.

Blue Plains Process The Blue Plains process was a re trofit to the existing nitrificat ion activated-sludge process at the Washington, DC, facility. A new anoxic zone was created inside the aeration tank with an HRT of 0.8 hour from the nominal 3.3 hours in th e total basin. The design sludge age was 13 days. The existing return activ ated-sludge system remained unchanged in this retrofit. Methanol was fed directly into this new anoxic zone for a target nitr ogen concentration of 7.5 mg/L (Kang et al. 1992; Sadi ck et al. 1998). Phosphorus is removed by ferric chloride addition and tertiary filtration. The Blue Plains process is depicted in Figure 2-29. The TN and TP effluent concentrations found in the literature for the Blue Plains process were 7.5 mg/L in TN and 0.12 mg/L in TP (see Table 2-1 in Section 2.5 for details).Municipal Nutrient Removal Technologies Reference Document September 2008

2-56 Chapter 2: Treatment Technologies Aerobic Zone Nitrification

Secondary Clarifier Effluent

to Tertiary Fitler Effluent from First Stage---

High Rate Activated Sludge

RAS

WAS Methanol Feed Aerobic Zone Nitrification Anoxic Zone Denitrification FeCl 3 addition

Figure 2-29. Blue Plains process.

Westbank Process The Westbank process is a modification of a fi ve-stage Bardenpho, with elimination of both the second anoxic zone and the re aeration zone. The process uses a step-feed arrangement for distributing primary effluent a nd fermenter supernatant (VFA-e nriched) to the anaerobic and anoxic zones, as shown in Figure 2-30. The pr ocess consists of a small pre-anoxic zone, followed by an anaerobic zone, an anoxic zone, and an aerobic zone. The pre-anoxic zone minimizes the DO and nitrates entering the an aerobic zone, thereby maximizing the release of phosphorus. RAS is fed to the anoxic zone. Pr imary effluent is divided between the preanoxic zone (to denitrify the RAS), anaerobic zone (to stim ulate phosphorus release), and anoxic zone (to stimulate denitrification). The direct feeding of the primary effluent to the anoxic zone increases the denitrif ication rate, thereby reducing th e required size of the anoxic zone compared to that in a 5-stage Barde npho system. The fermenter supernate, containing VFAs, is fed directly to the anaerobic zone. An internal recycle at a flow ratio of up to 600 percent directs the nitrates from the aerobic zone to the anoxic zone for denitrification. In the specific case of Kelowna, British Columbia, the effluent from the Westbank process is gravity filtered. The TN and TP effluent con centrations found during the case study period for the Westbank process with filtration ranged from 2.7 mg/L to 5.8 mg/L in TN, with an average of 4.4 mg/L in TN, a nd were 0.05 mg/L to 1.88 mg/L in TP, with an average of 0.14 mg/L TP (see Tables 2-1 and 2-2 in Section 2.5 for details).September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-57 Figure 2-30. Westbank process (Kelowna, British Columbia).



### 2.5 Full-Scale Nutrient Removal Process Cases

2.5.1 Nitrogen Removal Matr ix and Variability Data The variability or reliability of nitrogen control technologies is summarized in Table 2-1. For plants for which a full year of daily nitrog en removal data were obtained, a statistical summary is presented for the annual av erage, maximum month, maximum week, and maximum day. These correspond to the points at 50, 92, 98, and 99.7 percent, respectively, when plotted on probability paper (based on the nu mber of data points). This summary is the first known in the literature to compare full- scale technologies on an equal basis. Monthly, weekly, and daily maximums may be set by regulato ry authorities for facilities that discharge to particularly sensitive waters. If TN effluent data were collected weekly because that was all that the permit required, the daily maximu m value was not available. The performance levels shown from reported sources are documen ted in descending order for the technologies reported. It should be emphasized that, for this table as well as Ta bles 2-5 and 2-8, the performance results reflect specific operating philosophy, permit limitations, temperature, influent conditions, flow conditi ons, and the relative plant load compared to design. Thus, they do not necessarily repres ent optimum operation of the te chnologies presented. Most of the selected periods appeared to be typical; however, climate and weat her variations could significantly affect performance. Similarly, the performance results reflected in the curves in Figures 2-31, 2-33, 2-34, 2-35, and 2-36 reflect si te-specfic situations and do not necessarily represent optimum operation of the technologies. To Secondary ClarifierMunicipal Nutrient Removal Technologies Reference Document September 2008

2-58 Chapter 2: Treatment TechnologiesTable 2-1. Process Performance Data: Nitrogen Removal—Plant EffluentNitrogen removalVariability (mg/L)ReferenceTN(ppm)TechnologyPlant effluentobserved valueor range(mg/L)Std dev./COV %Annualaverage(50%)Max.month(92%)Max.week(98%)Max.day(99.7%)Johannesburg2.03 to 11.44 1.66/21 7.8610.41 11.57 13.28 Hagerstown, MarylandA2O7.3 to 9.0a-- -- -- -- -- Maryland ReportbVIP 6.12a-- 6.12 -- -- -- Neethling 200510Step-feed AS1.80/27 6.70 8.62 9.82 13.05 Cumberland, MarylandIFAS4.9 to 11.3a-- -- -- -- -- Masterson 2004McQuarrie 2004MBBR5.8 to 6.8a-- -- -- -- -- Täljemark et al. 2004MLE2.2 to 15a1.00/234.355.546.137.76LeesburgWestminster, Maryland4-stage Bardenpho3.5 to 12.1a-- -- -- -- -- Maryland ReportSchreiber system8a-- -- -- -- -- Maryland ReportBlue Plains process7.5a-- -- -- -- -- Washington DCc(Kang et al. 1992)(Sadick et al. 1998)PIDs, clarifiers, aerobicdigestion1.8 to 7.0 0.51/14 3.67 4.46 5.87 --North Cary, NorthCarolinadPIDs1.4 to 11.3 1.81/42 4.2 7.311.3 -- Jewett City, ConnecticutcSBR1.6 to 13.6 2.31/50 4.59 6.84 10.68 14.35 Thomaston, ConnecticutcCyclic on-off3.1 to 10.4 1.17/25 4.596.15 7.62 8.64 Ridgefield, ConnecticutcWestbank2.7 to 5.80.51/12 4.38 4.9 5.84 --Kelowna, BritishColumbiac,d5Step-feed AS3.7 to 7.4 0.63/12 5.25 6.15 8.01 -- Fairfax, Virginiac,dSeptember 2008 Municipal Nutrient Removal Technologies Document

Chapter 2: Treatment Technologies 2-59Table 2-1. Process Performance Data: Nitrogen Removal—Plant Effluent(continued)Nitrogen removalVariability (mg/L)ReferenceTN(ppm)TechnologyPlant effluentobserved valueor range(mg/L)Std dev./COV %Annualaverage(50%)Max.month(92%)Max.week(98%)Max.day(99.7%)Biological aerated filters 1.4 to 6.8 2.24/62 3.61e7.13e9.80a13.91aCheshire, ConnecticutcConcentric oxidation ditch 1.6 to 5.4 0.95/32 3.0 4.24 5.29 6.46 Hammonton, New JerseyStep-feed AS1 to 14 1.48/57 2.58 4.30 5.89 9.16 Piscataway, Marylandc5-stage Bardenpho1.24 to 4.29 0.35/160.86/422.322.043.103.103.753.904.365.44Clearwater, Florida-MSd,fClearwater, Florida-NEf3Denitrification filters 0.47 to3.76 0.36/16 2.14 2.77 3.13 4.25Johnston County, NorthCarolinac,dDenitrification filter0.13 to 6.500.56/28 1.71 2.61 3.90 --Lee County, FloridadDenitrifying activatedsludge0.4 to 10.4 0.59/36 1.63 2.46 4.22 --Western Branch,MarylanddNotes:A2O = anaerobic/anoxic/oxicAS = activated sludgeCOV = coefficient of variationIFAS = integrated fixed-film activated sludgeMBBR = moving-bed biofilm reactorMLE = modified Ludzak-EttingerPID = phased isolation ditchSBR = sequencing batch reactorVIP = Virginia Initiative processPerformance periods are listed in Attachment at end of References section.aData obtained from literature; data were not reviewed as part of project.bGeorge Miles & Buhr, LLC, and Gannett Fleming 2004.cRetrofit application.dCase study plant is explained in more detail in Chapter 3.eValues are based on 8 months of data, rather than 12 months.fClearwater, Florida, has two facilities––Marshall Street (MS) and Northeast (NE)The data reflect specific operating philosophy, permit limitations, influent conditions, flow conditions and the relative plantloadings compared to their design at these facilities. Thus,they do not necessarily represent optimumoperation of the technologies presented.Source: Table format adapted from WEF and ASCE 1998.Municipal Nutrient Removal Technologies Reference Document September 2008

2-60 Chapter 2: Treatment Technologies Figure 2-31 shows nitrogen removal technologies that have been demonstrated to produce low-range TN average results. Four technologies are shown in this group: denitrification filter, 5-stage Bardenpho, concentric oxidation di tch with a high recirculation rate, and stepfeed activated sludge. All of these technologies produced effluent that was under 3 mg/L TN for an annual average, and each facility exhib ited low variability. In addition, the monthly maxima (92 percent) points for all five techno logies were under 5 mg/L; therefore, it is conceivable that all of thes e technologies could meet that value for a monthly maximum limit.

Table 2-2, as well as Tables 2-3, 2-4, 2-6 and 2-7, presents information about the case study facilities included in Figures 2-31, 2-33, 2-34, 2-35, and 2-36, respectively. These tables show the number of data points used in deve loping the referenced curves, temperature information, and average flow compared to desi gn load. This number of data points show that the curve is based on a full year. The load ing shows what fraction of the overall capacity was in use during the selected year. The temperature shows the range over which the plant was operated during the year. Th e reader is cautioned that th ese curves represent actual performance but not necessarily the optimal performance level for the given treatment technologies. This also means that the coeffi cient of variation (COV) could be higher or lower for different actual applications. Add itional details, includi ng permitted discharge limits, are presented in Chapter 3.

1 6

2

3 7

5

4

0.1

1 10

Percent Less Than or Equal ToNitrogen, mg/L

1---Denitrifying AS---Western Branch, MD 6- Step Feed AS -Piscataway, MD 2 - Five-stage Bardenpho - Northeast Clearwater, FL 3 - Denitrification Filter-Johnston Co. NC 7 - Oxidation Ditch w/ IR-Hammonton, NJ 5 - Five-stage Bardenpho - Marshall St.,Clearwater, FL 4-Denite Filter-Lee County, FL 0.1 50 40 3020 10 5 1 2 0.5 0.05 60 70 80 90 95 98 99 99.5 99.95 99.9

Figure 2-31. Monthly average frequency curves for TN: low-range removal.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-61 Table 2-2. Detailed curve information for Case Study Facilities in Figure 2-31

Plant # Data points Min temp Max temp Ave. temp Ave. flow MGD Design flow MGD Western Branch, MD 236 51 °F 76 °F 64 °F 19.3 30

Lee Co., FL 261 -- -- 30.4 °C* 3.2 5.0
Central Johnston Co., NC 249 13.1 °C 27.9 °C 20.4 °C 4.1 7.0

Marshall St., Clearwater, FL 260 22.1 °C 31.1 °C 27.5 °C 5.5 10.0

* Only one available in July 2006.

The annual average and the maximum month c oncentrations, respectively, are shown for each facility:

1 = Denitrifying activated sl udge: 1.63 mg/L and 2.46 mg/L with a COV of 36 percent at Western Branch, Maryland
2 = 5-stage Bardenpho: 2.04 mg/L and 3.10 mg /L with a COV of 42 percent at the Clearwater, Florida, northeast plant
3 = Denitrification filter: 2.14 mg/L and 2.77 mg/L with a COV of 16 percent at the Central Johnston County, North Carolina, plant
4= Denitrification filter: 1.71 mg/L and 2.61 mg/L with a COV of 28 percent at the Lee County, Florida, plant
5 = 5-stage Bardenpho: 2.32 mg/L and 3.1 mg/L with a COV of 16 percent at the Clearwater, Florida, Marshall Street plant
6 = Step-feed activated sludge (AS): 2.5 8 mg/L and 4.30 mg/L with a COV of 57 percent at the Piscat away, Maryland, plant

7 = Concentric oxidation ditch with intern al recycle: 3.0 mg/L and 4.24 mg/L with a COV of 32 percent at the Hammonton, New Jersey, plant

A brief summary of the selected facilities that meet the low annual ni trogen limit of 3 mg/L is presented below. The 4-stage and 5-stage Bardenpho processes can achieve low effluent nitrogen concentrations because of the pres ence of two anoxic zones, allowing nitrates created in the first aeration basin to be denitrif ied. A review of literature results suggests that a 4-stage Bardenpho should do as well as or be tter than a 5-stage Bardenpho in nitrogen removal (deBarbadillo et al. 2003), but no facil ity was available for this investigation. A high internal recycle rate (four times the average flow ) is also important with this process. A stepfeed activated sludge process has proven reli able in nitrogen removal because of a new understanding of increased deni trification at the anoxic zone in the presence of primary effluent as a natural carbon source. Denitrification filters can also be used to achieve lowMunicipal Nutrient Removal Technologies Reference Document September 2008

2-62 Chapter 2: Treatment Technologies effluent nitrogen levels. The process requires th at methanol or an alternative carbon source be provided because the secondary treatment pr ocess usually has removed most of the BOD, which is needed to convert nitrates to nitrog en gas. In a concentric oxidation ditch, SND has been successful.

Clearwater, Florida Clearwater, Florida, operates two 5-stage (one anaerobic z one followed by two anoxic and two aerobic zones) Bardenpho WWTPs, the Marshall Street and Northeast advanced pollution control facilities. Th e second anoxic zone provides an opportunity to denitrify the nitrates created in the aerati on zone, allowing lower TN effl uent concentrations to be achieved when compared to a plant with only one anoxic zo ne. Some 5-stage Bardenpho plants require that a carbon source, such as me thanol, be fed to the second anoxic zone (the fourth reactor zone). However, neither of the plants in Clearwater re quires methanol addition to achieve average TN concentrations below 3 mg/L. This is because of high internal recirculation, which aids efficient use of th e carbon source in accomp lishing denitrification (WEF 1998). The internal recycle rate is 400 pe rcent of the average flow (4Q), which is relatively high. The RAS rate is approximately 90 percent at the Mars hall Street plant and 110 percent at the Northeast plant. The food- to-microorganism ratios are relatively low–– 0.024 and 0.04––at the Northeast and Marsha ll Street plants, respectively.

Johnston County, North Carolina The Central Johnston County Regional WWTP in North Carolina employs biological nitrogen removal through an MLE configuration followed by de nitrification filters supplied by F.B. Leopold to achieve an annual averag e TN effluent concentration of 2.06 mg/L. The biological treatment consists of an anoxic z one followed by an aerobic zone. An internal recycle returns some of the nitrates from the aerobic zone to the anoxic zone for denitrification, as in the MLE process. Methanol is fed upstream of the denitrification filters at a methanol-to-nitrate ratio of 4.5 lb to 1 lb.

Piscataway, Maryland The Piscataway Advanced Wastewater Treat ment Plant in Accokeek, Maryland, has two step-feed activated sludge treatment trains to rem ove TN. The first train consists of five sets of anoxic and aerobic basins in series, with the capability to feed primary effluent to the first four anoxic zones. There are four sets of anoxi c and aerobic zones in series. Primary effluent can be fed to the first three a noxic zones. RAS enters the firs t anoxic zone in both trains. The annual average TN concentration in the efflue nt from the Piscataway plant is 2.58 mg/L. Methanol or an alternative carbon source is not needed because primary effluent can be fed to each anoxic zone, with the exception of the last zone in each train. In addition, internal recycles are not necessary because of the mu ltiple anoxic/aerobic zones in series. Sodium hydroxide is added upstream of the step-feed activated sludge pro cess to increase theSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-63 alkalinity of the wastewater. This is necessary since alkalinity is cons umed as part of the nitrification process but only a portion is returned following denitrification.

Hammonton, New Jersey The Hammonton WWTP has a concentric oxidation ditch consisting of three channels (Figure 2-32). The outer and middle channels are operated at a lo w DO concentration to promote anoxic conditions. Surface aerators provide aeration and mixing to limit anaerobic conditions. The inner channel is operated at a DO concentration of 2 to 2.5 mg/L to promote nitrification. The plant uses automatic DO c ontrol. If the DO is outside the programmed range, the number of aerators operating in each channel is automatically adjusted. If the DO is too high, an aerator is shut down; if the DO in the channel is too low, an aerator turns on. As with other oxidation ditches, the operating level of the tanks can be adjusted to provide additional HRT, as needed, within the operating li mits of the aerators. The external RAS rate is 100 percent of the average flow (1Q). The unique aspect of the oxidation ditch is the internal recycle that di rects mixed liquor from the inner chan nel to the outer channel. In the summer the internal recycle is 400 percent of the average flow (4Q). Because of lower temperatures in the winter, which affect the ki netics of the nitrifica tion and denitrification processes, the internal recycl e is increased to 500 percent of the average flow (5Q).

Figure 2-32. Concentric oxidation ditch.Municipal Nutrient Removal Technologies Reference Document September 2008

2-64 Chapter 2: Treatment Technologies Lee County, Florida The Fiesta Village Advanced Treatment Facility employs oxidation ditches followed denitrification filters to achie ve an annual average concentra tion of 1.38 mg/L with a COV of 40 percent. Methanol is fed upstr eam of the denitrification filters at a dosage of 3 lb methanol per lb of nitrate.

Western Branch, Maryland This facility employs a unique denitrifying activated-sludge stage following two upstream activated-sludge stages, making a three-stage syst em overall. Methanol is fed upstream of the denitrifying stage. The annual average efflue nt concentration was 2.52 mg/L, with COV of 36 percent.

The next group of technologies is shown in Figure 2-33. These facilitie s have different TN permit limits, and some provide TN removal on a voluntary basis; thus, a wide variation is shown in their performance. These technologi es could be extended to achieve effluent concentrations in the range of 3 to 8 mg/L on an annual average basis. Annual averages and the maximum month concentrations were as follows:

1 = Phased isolation ditch (Biodenipho or PID): 3.67 mg/L and 4.46 mg/L, COV of 14 percent, at North Cary, North Carolina
2 = Biological aerated filter (BAF): 3.61 mg/L and 7.13 mg/L , COV of 62 percent, at Cheshire, Connecticut
3 = Phased isolation ditch: 4.2 mg/L and 7.3 mg/L, COV of 42 percent, at Jewett City, Connecticut
4 = Westbank: 4.38 and 4.9, COV of 12 percent, at Kelowna, British Columbia
5 = Modified Ludzak-Ettinge r (MLE): 4.35 mg/L and 5.54 mg/L , COV of 23 percent, at Westminster, Maryland
6 = Cyclic on-off activated sludge (AS): 4.59 mg/L and 6.15 mg/L, COV of 25 percent, at Ridgefield, Connecticut
7 = Sequencing batch reactor (SBR): 4.59 mg /L and 6.84 mg/L, COV of 50 percent, at Thomaston, Connecticut
8 = Step-feed activated sludge (AS): 6.70 mg/L and 8.62 mg/L, COV of 27 percent, at Cumberland, Maryland
9 =Johannesburg: 7.86 mg/L and 10.41 mg/L, COV of 21 percent, at Hagerstown, MarylandSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-65 1 6 2

7

3

8

4 9

5

1 10 100

Percent Less Than or Equal ToNitrogen, mg/L 1 - Phased Isolation Ditch--North Cary, NC 6 - Cyclic On-Off-Ridgefield, CT 2 - BAF-Cheshire, CT 7 - SBR-Thomaston, CT 3 - Phased Isolation Ditch - Jewett City, CT 8 - Step Feed AS-Cumberland, MD 4 - Westbank - Kelowna, BC 9 - Johannesburg--Hagerstown, MD 5 - MLE-Westiminster, MD

0.1 50 4030 20 10 5 1 2 0.5 0.05 60 70 80 90 95 98 99 99.5 99.95 99.9

Figure 2-33. Monthly average frequency curves for TN—mid-range removal.

Table 2-3. Detailed curve information for Case Study Facilities in Figure 2-33

Plant # Data points Min temp Max temp Ave. temp Ave. flow MGD Design flow MGD North Cary, NC 155 16 °C 27 °C 21 °C 7.0 12.0 Kelowna, BC 52 13 °C 22 °C 17.3 °C 8.5 10.6

Low variability was shown by the North Cary PID and the Westbank process, with COVs of 14 percent and 12 percent, respectively. Common elements of these two facilities were two anoxic zones and a good carbon supply for denitrif ication, preceded by an anaerobic zone for phosphorus removal. Although the other systems would meet an annual average limit of 5 mg/L, they would not meet a monthly maximu m limit of 5 mg/L because of higher annual averages or higher COVs.

Some facilities have to meet ammonia nitrogen limitations wit hout meeting a TN limit. In general, removal of ammonia nitrogen invol ves ensuring enough sludge residence time and hydraulic residence time to allow nitrification to occur in all seasons covered by the permit. Figure 2-30 reflects facilities that have been used to meet ammonia limitations, all of which are discussed further in the case studies in Chap ter 3. The figure shows that all the facilities met their ammonia limits, ranging between 0.5 and 2.0 mg/L at all times, with relatively low
COVs.Municipal Nutrient Removal Technologies Reference Document September 2008

2-66 Chapter 2: Treatment Technologies Monthly Average Frequency Curves for Ammonia-Nitrogen

1

4 2

5

3.

0.01 0.1

1 10

Percent Less Than or Equal ToNitrogen, mg/L

1 - Step Feed AS-Noman Cole, VA 4 - Modified UCT-Kalispell, MT 2 - Plug Flow A.S.-Central Johnston Co., NC 5 - Phased Isolation Ditch-North Cary, NC 3 - A/O - Clark Co, NV 0.1 50403020 10 5 1 2 0.5 0.05 60 70 80 90 95 98 99 99.5 99.95 99.9

Figure 2-34. Monthly average frequency curves for ammonia nitrogen.

Table 2-4. Detailed curve information for Case Study Facilities in Figure 2-34

Plant # Data points Min temp Max temp Ave. temp Ave. flow MGD Design flow MGD Clark Co., NV 365 17 °C 30 °C 25 °C 98 110 North Cary, NC 249 16 °C 27 °C 21 °C 7.0 12.0 Noman Cole, Fairfax Co., VA 365 14 °C 28 °C 21 °C 47.4 67

Central Johnston Co., NC 249 13.1 °C 27.9 °C 20.4 °C 4.1 7.0

Kalispell, MT 12 8.5 °C 19.6 °C 14.3 °C 2.9 3.1 * Only one available in July 2006.



### 2.5.2 Phosphorus Removal Ma trix and Variability Data Table 2-5 shows variability data for phosphor us removal technologies from 14 selected facilities. The figures following the table show variability data from well-operated full-scale facilities for a full year’s operation. The results are shown in the order of descending effluent phosphorus concentration.Chapter 2: Treatment Technologies 2-6 7 September 2008 Municipal Nutrient Removal Technologies DocumentTable 2-5. Process Performance Data: Phosphorus Removal—Plant EffluentPhosphorus removalVariability (mg/L)P(ppm)TechnologyRange of valuesobserved(mg/L)Std dev./COV %Annualaverage(50%)Max.month(92%)Max.week(98%)Max.day(99.7%)Reference21A2O with VFA addition,chemical addition, tertiaryclarifier, and filtrationa0.025 to 0.980.044/330.132 0.18 0.646 0.98 Durham, OregondVIP0.19 to 5.0c-- 0.40 1.75 3.6 7.5 VIP, Neethling 2005A/O0.03 to 0.430.12/500.24 0.36 0.44 0.75 Genesee County, MichigandUCT with filter0.3c-- -- -- -- --Penticton, British ColumbiaBarnard, 20060.5Westbank with fermenter andfilters0.05 to 1.880.03/210.14 0.20 0.25 -- Kelowna, British Columbiab,dChemical addition andflocculating clarifiers0.07 to 0.230.01/140.09 0.11 -- -- Chelsea, MichiganPhoStrip< 0.1 Ortho-Pc-- -- -- -- --Truckee Meadows, NevadaBarnard et al. 2006Modified UCT with fermenter 0.03 to 0.370.023/190.12 0.15 0.31 0.36 Kalispell, MontanabTertiary clarifier with chemicaladdition and filtersa0.026 to 0.240.036/630.058 0.12 0.17 0.23 McMinnville, OregonaA/O with chemical addition tofilters0.03 to 2.30.03/300.10 0.17 0.41 0.56 Clark County, NevadabStep-feed AS with fermenterand filter0.02 to 0.260.02/210.09 0.12 0.16 0.26 Fairfax, Virginiab,d0.1MBR0.011 to 0.5540.075/1070.070 0.17 0.29 0.54 Hyrum, UtahDenitrification filter with alum 0.02 to 1.340.05/350.102 0.19 0.39 -- Lee County, FloridabMunicipal Nutrient Removal Technologies Reference Document September 20087

2-68 Chapter 2: Treatment TechnologiesTable 2-5. Process Performance Data: Phosphorus Removal—Plant Effluent(continued)Phosphorus removalVariability (mg/L)P(ppm)TechnologyRange of valuesobserved(mg/L)Std dev./COV %Annualaverage(50%)Max.month(92%)Max.week(98%)Max.day(99.7%)Reference5-stage Bardenpho oxidationditch with chemical additionand filters0.02 to 0.0780.011/340.031 0.061 0.078 -- Pinery Water, ColoradoMBR0.01 to 0.0830.0074/270.027 0.038 0.053 -- Lone Tree Creek, ColoradoEBPR with high rate solidscontact clarifier, chemicaladdition, and filtersto 0.02c--0.01 0.02 -- -- Breckenridge, ColoradoChemical addition, tertiaryclarifiers, filter, infiltration basin0.01(monthlyaverages)0/00.01 0.01 0.01 0.01 Brighton, MichiganNotes:A2O = anaerobic/anoxic/oxicA/O = anoxic/oxicAS = activated sludgeEBPR = enhanced biological phosphorus removalMBR = membrane reactorUCT = University of Cape Town processVFA = volatile fatty acidVIP = Virginia Initiative processPerformance periods are listed in Attachment at end of References section.aSeasonal permit limit of 0.07 mg/L; results based on only seasonal data.bSubject of case study described in Chapter 3.cData obtained from literature; data were not reviewed as part of report.dRetrofit applications.The data reflect specific operating philosophy, permit limitations, influent conditions, flow conditions and the relative plantloadings compared to their design at these facilities. Thus,they do not necessarily represent optimumoperation of the technologies presented.Source: Table format adapted from WEF and ASCE 1998.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-69 Figure 2-35 shows the best-performing TP remo val processes, with the lowest phosphorus concentration in the effluent. All of these plan ts added chemicals to achieve their respective effluent phosphorus concentrations. Beginning with the lowest, the land application of tertiary effluent in Brighton, Michigan, had a flat line at 0.01 mg/L. The next lowest used MBR in Lone Tree Creek, Colorado, which had an annual average concentration of 0.027 mg/L, and a 5-stage Bardenpho with tertiary clar ifier and Trident filter in Pinery, Colorado, which had an annual average of 0.031 mg/L. The annual average and maximum month concentrations are shown below with COVs.

1 = Land application: 0.01 mg/L for annual average and maximum month with COV of 0 percent, in Brighton, Michigan
2 = Biofor, DensaDeg, and MBR: 0.01 mg/L annual average and 0.02 mg/L monthly maximum, in Breckenridge, Colorado
3 = MBR: 0.027 mg/L and 0.038 mg/L, COV of 27 percent, in Lone Tree Creek, Colorado
4 = Five-stage Bardenpho, tertiary clarif ier, Trident filter: 0.031 mg/L and 0.061 mg/L, COV of 34 percent, in Pinery, Colorado
5 = Tertiary clarifier/f ilter: 0.058 mg/L and 0.12 mg/L, COV of 63 percent, in McMinnville, Oregon (seasonal limit)
6 = MBR: 0.07 mg/L and 0.17 mg/L, COV of 107 percent, in Hyrum, Utah

7 = Denite filter: 0.10 mg/L and 0.19 mg/L, COV of 35 percent, in Lee County, Florida

Note that COV did increase to 107 percent and 63 percent for Hyrum and McMinnville. This was caused by changing conditions, especially temperature and water chemistry, through the year, which affected the precipitation/membrane filtration process in Hyrum and the effects of the seasonal limit for McMinnville. Although these two facilities can meet the 0.1 mg/L TP limit on an annual average basis, they might not meet the monthly maximum.

The second group of TP removal processes in cluded EBPR with chemical addition and tertiary filters––Fai rfax County, Virginia, and Clark C ounty, Nevada. The annual average concentrations were 0.09 mg/L at both, and both were very re liable with the maximum month concentration below 0.2 mg/L. More descrip tion of selected facilities follows.

Achieving TP concentrations of less than 0.1 mg/L usually requires the use of chemicals (alum or ferric chloride) and filtration. Alum has a lower solubility limit than ferric chloride and is usually used in low-effluent phosphorus applications. Filtrat ion can be provided by sand filters, denitrification f ilters, or membranes. For the phosphorus to be captured byMunicipal Nutrient Removal Technologies Reference Document September 2008

2-70 Chapter 2: Treatment Technologies 1 2

3 4 5 6

7

0.001 0.01 0.1

1 10

Percent Less Than or Equal ToTotal Phosphorus, mg/L

1 - Chem Addn + Tert Clarifiers + Land Application-Brighton, MI 2 - Biofor, DensaDeg, and MBR-Breckenridge, CO (only Ann. Ave. and Max Month available) 3 - MBR-Lone Treek Creek, CO 4 - 5 Stage Bardenpho w chemical and filter, Pinery, CO 5 - Tert Clarifier + Chem Addn + Filter-McMinnville, OR 6 - MBR + Chem Addn-Hyrum, UT 7-Denite filter Lee County, FL 0.1 50 40 30 2010 5 1 2 0.5 0.05 60 70 80 90 95 98 99 99.5 99.95 99.9

Figure 2-35. Monthly average frequency curves for TP—low-end removal.

Table 2-6. Detailed curve information for Case Study Facility in Figure 2-35

Plant # Data points Min temp Max temp Ave. temp Ave. flow MGD Design flow MGD Lee Co., FL 261 -- -- 30.4 °C* 3.2 5.0 * Only one available in July 2006

either filtration method, a suffici ently sized floc must be formed through coagulation with alum or other chemicals. To achieve effluent concentrations below 0.03 mg/L, more than one filtration step is required. For example, the Iowa Hill Reclamation Facility in Breckenridge, Colorado, has a DensaDeg high-rate solids clar ifier (manufactured by Infilco Degremont) that uses sand particles to remove phosphorus floc, followed by additional chemical addition and a deep-bed sand filter. The lowest phosphor us concentrations were observed at the Brighton Environmental Control Facility in Brighton, Michigan, which uses chemical addition, claricones, and land application to an infiltration bed. The mechanism for phosphorus removal in the infiltration bed is adsorption to the soil particles. The water is collected from the infiltration beds by underdra ins before discharge to the surface water. The process is very reliable, with a COV of 0 percent. It requir es a large area, however, which might not be available in most places, pa rticularly for retrofit applications.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-71 McMinnville, Oregon Phosphorus is removed through one-point chem ical addition using alum and aluminum chlorohydrate upstream of the ter tiary clarification, which is then followed by filtration. The seasonal average effluent concentration ach ieved is 0.058 mg/L. The permit limit applies from May through October. During the rest of the year, no phosphorus limit is in place and effluent concentrations are significantly high er. TP is not measured from November through April. Orthophosphorus concentrations as high as 3 mg/L have been recorded during this period.

Hyrum, Utah The Hyrum WWTP has an MBR manufactured by Enviroquip/Kubota. Phosphorus is removed by adding alum to the activated-sludge tank. The floc that is formed does not pass through the flat-plate membranes, which take th e place of the clarifiers and filtration in a conventional plant. The annual average efflue nt phosphorus concentration is 0.07 mg/L. The COV is relatively high at 107 percent.

Pinery Water, Colorado The Pinery Water plant removes phosphorus biologically in the fi ve-stage Bardenpho process, which is followed by a clarifica tion and filtration process called Trident, manufactured by U.S. Filter. The Trident pr ocess involves tube clarification, adsorption clarification, and multimedia filt ration. Alum is fed upstream of the tube clarifier to promote flocculation. The plant meets a mont hly average permit limit of 0.05 mg/L.

Breckenridge, Colorado The Iowa Hill Water Reclamation Facility achieves low effluent phosphorus concentrations, beginning with an anaerobic selector upstream of the activated-sludge process. A BAF follows. Then the wastewater enters a high- rate solids contact clarifier known as the Densadeg process, manufactured by Infilco- Degremont. The process involves flocculation and plate settling. The sand is recycled and reused in the flocculation process. The wastewater then passes through a Dynasand filt er, manufactured by Park son. The plant has a daily phosphorus limit of 0.05 mg/L and has re ported effluent values below 0.01 mg/L.

Brighton, Michigan The Brighton Environmental Control Facility’s process consists of secondary treatment, claricones, and infiltration ba sins. The secondary treatment pr ocess is an oxidation ditch, which provides little biological phosphorus remova l. Ferric chloride is added to provide some chemical removal. Additional ferric chloride and a polymer are added to remove phosphorus in the claricones. The wastewater is then applied to a rapid infiltration bed. The phosphorus is adsorbed to the soil particles in the infiltration bed. The wastewater is then collected in underdrains for disc harge to the surface water. Soil adsorption provides a very reliable treatment system, as long as the cap acity of the soil is not exceeded. Although theMunicipal Nutrient Removal Technologies Reference Document September 2008

2-72 Chapter 2: Treatment Technologies process is capable of meeting a 0.01 mg/L TP effluent concentrati on, it requires a large amount of space, which might not be available in most areas. Furthermore, the soil in the vicinity of the treatment plant needs to allow water infiltratio n (sandy soils are needed; clay is not suitable). The land requirement for this facility was 25 acres per million gallons of capacity, which was sufficient to provide treatment for 40 years.

Figure 2-36 shows the mid-level phosphorus rem oval processes. The Piscataway Advanced Wastewater Treatment Plant (1) in Accok eek, Maryland, feeds alum and polymer to secondary clarification followed by a gravity mixed-media filter to remove phosphorus. The secondary treatment process is a step-feed activ ated sludge process. The annual average final effluent phosphorus concentration was 0.09 mg /L, and the maximum month was 0.20 mg/L. Lee County, Florida, achieved an annual aver age concentration of 0.102 mg/L with alum addition through a denitrificati on filter acting as a filter.

Treatment plants in Kalispell, Montana (2) and Kelowna, British Columbia (5) use EBPR with fermenters, producing annual average concentrations of 0.12 mg/L and 0.139 mg/L, respectively. Neither facility used chemicals, and yet both were very reliable in their performance, with maximum month concentrat ions of 0.15 mg/L and 0.2 mg/L, respectively. The COVs for Kalispell and Kelowna were ve ry low at 19 percen t and 12 percent, respectively.

The next facility removed phosphorus by using EBPR without fermenters with some alum addition. Clearwater, Florida (numbers 3 and 6 in Figure 2-36) added alum to the 5-stage Bardenpho facility and achieved effluent con centrations of 0.132 mg/L and 0.21 mg/L as the annual average and the maximum month, respectively.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-73 1 6

2 7

3

8 4 9

5

10

0.01 0.1

1 10

Percent Less Than or Equal ToTotal Phosphorus, mg/L

1 - Step Feed w/ Fermenter-Piscataway, MD 6- Five-stage Bardenpho-Northeast, Clearwater, FL 2 - EBPR w/ VFA Addn + Filters-Kalispell, MT 7 - Denitrification Filters + Chem Addn-Johnston Co., NC 3 - Five-stage Bardenpho-Marshall St., Clearwater, FL 8 - A/O--Genesee Co., MI 4 - A2O with VFA, chemical, and filter-Durham, OR 9 - Phased Isolation Ditch-North Cary, NC 5 - Westbank--Kelowna, BC 10 - Triple sludges---Western Branch, MD. 0.1 5040 302010 5 1 2 0.5 0.05 60 70 80 90 95 98 99 99.5 99.95 99.9

Figure 2-36. Monthly frequency curves for TP removal—mid-range removal.

Table 2-7. Detailed curve information for Case Study Facilities in Figure 2-36

Plant # Data points Min temp Max temp Ave. temp Ave. flow MGD Design flow MGD Western Branch, MD 285 51 °F 76 °F 64 °F 19.3 30 Central Johnston Co., NC 52 13. 1 °C 27.9 °C 20.4 °C 4.1 7.0 Marshall St, Clearwater, FL 260 22.1 °C 31.1 °C 27.5 °C 5.5 10.0 Kalispell, MT 104 8.5 °C 19.6 °C 14.3 °C 2.9 3.1 Kelowna, BC 51 13 °C 22 °C 17.3 °C 8.5 10.6 North Cary, NC 155 16 °C 27 °C 21 °C 7.0 12.0 * Only one available in July 2006

The next group of TP removal processes incl uded EBPR without fermenters or chemical addition––Genesee County, Michig an; North Cary, North Carolin a; Central Johnston County, North Carolina, and Western Branch, Maryland. Th eir annual average effluent concentrations were 0.24 mg/L, 0.38 mg/L, and 0.26 mg/L, respectiv ely. The variability increased to varying degrees without fermenters at these facilities , and thus the maximum month concentrations were 0.36 mg/L, 1.0 mg/L, and 0.64 mg/L, respectiv ely. No chemicals were added at these facilities, and the results we re therefore more variable.Municipal Nutrient Removal Technologies Reference Document September 2008

2-74 Chapter 2: Treatment Technologies In summary, chemical precipitation with alum or ferric chloride has been proven to produce effluent concentrations below 1 mg/L in TP since the 1970s in the Great Lakes region based on the International Joint Commission agreem ent between the United States and Canada. Chemical precipitation followed by filtration li kewise has been prove d to produce effluent concentration between 0.5 and 0.1 mg/L in TP. If the permittee desires the lowest possible concentration with low variability, the fo llowing processes appear suitable––MBR, land application using infiltration beds , or step-feed activated sludge with fermenters. In addition, chemical addition with special filters is a t echnology that is emerging, and it is anticipated that full-scale data could be available in th e near future. These special filters include the Dynasand D2 advanced filtration process, the Trident process, the Blue PRO filtration system, and the CoMag process. The second gr oup, EBPR with chemical addition, appears suitable for compliance with a 0.5 mg/L limit. If the permittee desires EBPR only, EBPR with fermenters appears to be most suita ble. EBPRs without fermenters offer higher variability but will meet the 1.0 mg/L permit limit.



### 2.5.3 Combined Nitrogen and Phosphorus Removal Matrix and Variability Data To achieve TN concentrations below 3 mg/L a nd TP concentrations of less than 0.3 mg/L usually requires chemical addition and filtra tion for phosphorus removal because few plants are able to achieve effluent concentrations be low 0.3 to 0.4 mg/L biologically. Therefore, the options for meeting simultaneous nitrogen and p hosphorus removal are the same as those for TN removal, as long as chemical addition and filtration are added for phosphorus removal. In the extreme cases where the phosphorus limit is near 0.01 mg/L, Husband et al. (2005) reported the need to supplement phosphorus in support of full denitrification. A study by deBarbadillo et al. (2006) also recommended a phosphoric acid feed system if the growth rate of denitrifying heterotrophic organisms might be limited during high-nitrate loading periods. During the pilot testing, they observe d that a filter infl uent orthophosphorus-tonitrate nitrogen ratio of 0.02 or higher is safe.

North Cary, North Carolina The North Cary WWTP in North Carolina is a PID. The Biodenipho process from Veolia Water/Krueger has two oxidation di tches, which are automatically controlled to operate in alternating aerobic and anoxic modes. An exte rnal anaerobic tank for phosphorus removal is configured upstream of the ditches. When aerat ion is not required, mixers are available to keep the mixed liquor in suspension. The anaer obic tank upstream of the ditch has a 2-hour detention time. The isolation ditch is operated in a 240-minute cycle. Fo r the first 30 minutes, both ditches operate in an aerobic mode. For the next 90 minutes, ditch 1 operates in an anoxic mode while ditch 2 continues in an aerobic zone. A second 30-minute cycle follows with both ditches operating in an aerobic zone. In the last 90 minutes, ditch 1 continues to operate in an aerobic mode, while ditch 2 opera tes in an anoxic mode. This alternating strategy allows nitrifi cation to occur, followed by denitrification while in the anoxic mode.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-75 The low TN concentrations are achieved with a final anoxic tank that follows the PIDs; it is the second anoxic tank, as in th e 5-stage Bardenpho process. The wastewater is then reaerated before the secondary clarifiers to prevent denitrification, ca using rising sludge. The RAS rate is 55 percent of the average flow (0.55Q). The RAS enters a holding tank with a 30-minute detention time to minimize the amount of nitrates that enter the anaerobic tank. The sludge age is approximately 16 to 18 days . The secondary effluent passes through a deep-bed sand filter. Methanol can be fed to aid in denitrification, if needed; however, methanol has never been fed. The plant has the ability to add alum or ferric chloride to aid in phosphorus removal, but this has not been n ecessary for the past 2 years. The annual averages were 3.55 mg/L in TN and 0.38 mg/L in TP in the case study. The maximum month averages were 4.46 mg/L in TN and 1.06 mg/L in TP, without any chemical addition.

McDowell Creek, North Carolina
The McDowell Creek WWTP in North Carolina us es a modified UCT process. Sugar waste is added upstream of the anaerobic zone to provide an additional source of carbon for phosphorus removal. To supplement the influent al kalinity, lime is also added to ensure that nitrification rates will not be limited. The pro cess has two internal r ecycle streams––from the second anoxic zone to the anaerob ic zone and from the aeration z one to the first anoxic zone. The internal recycle from the end of the anoxic zone to the head of the anaerobic zone minimizes the nitrates that are returned. This eliminates competition of the nitrates with the PAOs for the VFAs, thereby improving biol ogical phosphorus removal. The anoxic-toanaerobic recycle is retu rned at a rate of 70 percent of the average flow (0.7Q), while the aerobic-to-anoxic recycle has a return rate of 320 percent of average flow (3.2Q). The RAS is returned to the first anoxic zone at a rate of 90 percent of average flow (0.9Q). The RAS enters at the head of the anoxic zone to mini mize the presence of nitr ates in the anaerobic

zone.

A deep-bed sand filter follows the secondary clarifiers; it is designed to provide an opportunity for additional deni trification by microorganisms under anoxic conditions. The water passes through the filter, but no chemicals are added because of the ability to meet the loading limits biologically. Alum is fed to the belt filter press filtrate, which returns to the plant headworks. If the primary influent phos phorus concentration is elevated, additional alum can be fed to the primary clarifiers. A s econd feed point is av ailable upstream of the secondary clarifiers, but it is not used. The McDowell Creek WWTP is achieving an annual average TP concentration of 0.1 mg/L biologically through VFA addition, with minimal chemical addition. The secondary effluent and final effluent TP values are approximately equal (the filter has little effect on the phos phorus concentration).

Clearwater, Florida Clearwater, Florida, operat es two 5-stage Bardenpho WWTPs , the Marshall Street and Northeast advanced pollution control facil ities. The second anoxic zone provides anMunicipal Nutrient Removal Technologies Reference Document September 2008

2-76 Chapter 2: Treatment Technologies opportunity to denitrify the nitrates created in the aeration zone, allowi ng lower TN effluent concentrations to be achieved when compared to a plant with only one anoxic zone. Some 5- stage Bardenpho plants require th at a carbon source, such as me thanol, be fed to the second anoxic zone (the fourth reactor zone). However, neither of the plants in Clearwater requires methanol addition to achieve average TN concen trations below 3 mg/L. The internal recycle rate is 400 percent of the average flow (4Q) , which is relatively high. The RAS rate is approximately 90 percent at the Marshall Street plant and 110 per cent at the Nort heast plant. The food-to-microorganism ratios for these plan ts were relatively low––0.024 and 0.04 at the Northeast and Marshall Stre et plants, respectively.

Phosphorus is removed biologically in the anaer obic zone. Alum is fed to the second anoxic zone (the fourth reaction basin) for the dua l purpose of phosphorus polishing and meeting the state’s additional requirement to meet low-leve l trihalomethane concentrations in the reuse water. In addition, a gravity sand filter is used to remove phos phorus tied to suspended solids in the final effluent. The annual average concen trations were 2.32 mg/L in TN and 0.11 mg/L in TP at the Marshall Street plant and 2.04 mg/L in TN and 0.20 mg/L in TP at the Northeast plant. Both plants operated with high efficiency and low variability.

Central Johnston County, North Carolina The Central Johnston County Regional WWTP in North Carolina employs biological nitrogen removal followed by F.B. Leopold den itrification filters to achieve an annual average TN effluent concentration of 2.14 mg/L . The biological treatment consists of an MLE, with an anoxic zone followed by an aerobic zone. An internal re cycle returns some of the nitrates from the aerobic zone to the a noxic zone for denitrification, as in the MLE process. Methanol is fed upstream of the denitr ification filters using a methanol-to-nitrates ratio of 4.5 to 1.

No chemicals are added for phosphorus removal, although it is likely th at some phosphorus is removed through the denitrification filters . The annual average concentrations were 2.14 mg/L in TN and 0.26 mg/L in TP. The maxi mum month concentrati ons were 2.77 mg/L in TN and 0.64 mg/L in TP, a very reliable nitrogen removal but less for TP.

Table 2-3 summarizes technologies to achieve both TN and TP removal. The results are shown in the order of descending effluent phos phorus concentration. COVs for TN and TP removal displayed similar patterns to plants th at perform only TN or TP removal. That is, COVs were lower for TN and higher for TP removal. Nitrogen removal performance was efficient and reliable. COVs were below 50 pe rcent for the 5-stage Ba rdenpho, denitrification filters, and the PID with anoxic tank. COVs fo r phosphorus, however, went high as the target concentration approached the critic al level of 0.1 mg/L or below.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-77 Research Needs
More research is needed to identify the cause of high variability when phosphorus concentrations are low and to develop strategies to improve performance. The solubility products of phosphorus compounds are known to be dependent on other chemical species and the pH in the wastewater. In addition, Banisch et al. (2007) reported nonreactive phosphorus in the effluent in the range of 0.01 to 0.12 mg/L. More res earch is needed to determine the minimal level of phosphorus need ed to support healthy growth of nitrogenremoval organisms in facilities where remova l of both nitrogen and phosphorus is required.



### 2.6 Summary

On the basis of an extensive review of the literature and actual data from 30 full-scale facilities, this chapter has presented a compilation of full plant performance on the same statistical basis. The following paragraphs summarize major findings on nutrient removal technologies.



### 2.6.1 Performance and Variability A probability plot of actual data from fu ll-scale operation is a good representation of performance and allows easy comparison of one technology against another on a consistent basis. Full-scale data generally follow a normal distribution. The coeffici ent of variation, or COV, is a good measure of statis tical variability. The lower the COV, the more reliable the performance; conversely, higher COV values indicate more variability in performance.Municipal Nutrient Removal Technologies Reference Document September 2008

2-78 Chapter 2: Treatment TechnologiesTable 2-8. Process Performance Data: Nitrogen and Phosphorus Removal—Plant EffluentNitrogen and phosphorus removalVariability (mg/L)N(ppm)TechnologyRange of valuesobserved(mg/L)Std dev./COV %Annualaverage(50%)Max.month(92%)Max.week(98%)Max. day(99.7%)ReferenceP(ppm)Johannesburg TN: 2.03 to 11.44TP: 0.19 to 8.31.66/210.96/1457.860.6610.412.4911.573.913.288.3Hagerstown,Maryland210UCTTN: 8.9 to 10aTP: 0.3WEF and ASCE19981IFASTIN: 5.6 to 11.3aTP: 0.2 to 1.7aBroomfield, COMcQuarrie 2004VIPTN: 3 to 10TP: 0.19 to 5.75Rabinowitz 2004VIP with VFA addition TN: 5 to 10TP: 0.6 to 0.8Neethling2005Step-feed withfermenterTN: < 5.0; 3 to 13TP: < 0.3; 0.1 to 51.48/570.08/892.590.094.300.205.890.319.160.52Piscataway, MDBiodenipho/PID TN: 1.78 to 7.02TP: 0.09 to 1.990.93/140.27/643.670.384.461.065.871.456.791.78North Cary, NCb0.55Modified UCT with VFAadditionTN: 5 to 6aTP: 0.1 to 2.7a0.100.250.753.75McDowell Creek,NCNeethling 20050.1Chapter 2: Treatment Technologies 2-79 September 2008 Municipal Nutrient Removal Technologies DocumentTable 2-8. Process Performance Data: Nitrogen and Phosphorus Removal—Plant Effluent(continued)Nitrogen and phosphorus removalVariability (mg/L)N(ppm)TechnologyRange of valuesobserved(mg/L)Std dev./COV %Annualaverage(50%)Max.month(92%)Max.week(98%)Max. day(99.7%)ReferenceP(ppm)High rate, nitrification,and denitrificationactivated sludgeTN: 0.4 to 10.4TP: 0.05 to 1.880.59/360.27/621.630.432.460.894.220.99Western BranchbHyattsville, MDTN: 1.24 to 4.29TP: 0.06 to 0.370.36/160.07/402.320.133.10.213.750.264.290.46Clearwater, FL-MSb5-stage Bardenpho withchemical addition for PremovalTN: 0.87 to 5.59TP: 0.06 to 1.090.86/420.16/822.040.203.100.443.900.635.441.07Clearwater, FL-NEDenitrification filterswith chemical additionTN: 0.13 to 6.50TP: 0.02 to 1.340.56/280.05/351.710.1022.610.193.700.39Fiesta VillagebLee County, FLDenitrification filterswith chemical additionTN: 0.84 to 3.13TP: 0.1 to 1.010.36/160.09/622.140.262.770.643.131.01----Johnston Co., NCb,cNotes:IFAS = integrated fixed-film activated sludgePID = phased isolation ditchUCT = University of Cape Town processVFA = volatile fatty acidsVIP = Virginia Initiative processPerformance periods are listed in table at end of References sectionaData obtained from literature; data were not reviewed as part of report.bSubject of case study described in Chapter 3.cRetrofit application.The data reflect specific operating philosophy, permit limitations, influent conditions, flow conditions and the relative plantloadings compared to their design at these facilities. Thus,they do not necessarily represent optimumoperation of the technologies presented.Source: Table format adapted from WEF and ASCE 1998.Municipal Nutrient Removal Technologies Reference Document September 2008

2-80 Chapter 2: Treatment Technologies 

### 2.6.2 Nitrogen Removal Technologies Four technologies were identif ied to meet the low concentration limit with low variability. These are the 4- and 5-stage Bardenpho proce sses, the step-feed activated sludge process, concentric oxidation ditches, and denitrification filte rs with carbon sources. COVs for these processes are below 50 percent, and the technologies achieve annual average TN effluent concentrations below 3 mg/L. Seven technolog ies were identified for mid-level nitrogen removal between concentrations of 3 and 8 mg/L. The key factors that c ontribute to efficient and reliable nitrogen removal are an ade quate supply of a carbon source (internal or external), flexibility in desi gn (such as the number of anoxic/ aerobic zones), temperature, alkalinity balance, and sludge age. DON has b een reported in varying concentrations. The DON is a critical variable for determining TN standards because the chemicals have limited availability for biological removal.



### 2.6.3 Phosphorus Removal Technologies Biological phosphorus removal (without filters or chemical addition) achieved an annual average effluent concentration of 0.26 mg/L with a COV of 35 percent. Excellent performance with low variability was reported for biological phosphorus removal processes, which achieved mean effluent concentrations down to 0.12 mg/L with a COV of 19 percent and 0.14 mg/L with a COV of 12 percent in a nother plant. The key performance factors included a sufficient supply of VFAs from an on-site fermenter, temperature, control of secondary phosphorus release, and good filtrat ion. The practical TP limit of 0.1 mg/L is reached consistently with chemical addition and filtration. However, variability increases significantly at the targ et limit of 0.1 mg/L and below. The COVs increase to 93 percent for a plant achieving an annual average of 0.058 mg/L and to 107 percent for a facility meeting an annual average mean 0.07 mg/L. Special filters have proved effective in achieving low concentrations below 0.03 mg/L. They include the Trident filter fr om U.S. Filter, the Dynasand D2 advanced filtration system from Parkson, and membrane filtration processes from various manufacturers. The only tec hnology evaluated that meets a TP effluent concentration of 0.01 mg/L at a ll times is land application of tertiary effluent through soil. The COV at the Brighton, Michigan, plant em ploying this technology is 0 percent in this

case.



### 2.6.4 Combined Nitrogen and Ph osphorus Removal Technologies

The TN and TP removal data show the same tre nds as the plants that performed only TN or TP removal. The nitrogen removal is as reli able as that described earlier, whereas the phosphorus removal shows higher COVs, indi cating potential inter action between the solubility product at pH and ot her chemical species that o ccur throughout the year. Another factor is the nonreactive form of phosphorus in the wastewater , which might vary during the year. More research is needed to determine thes e chemical interactions. More research is alsoSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-81 needed to establish the minimum phosphorus concentration needed to support nitrogen removal in the same process.



### 2.7 References

Barnard, J. 2006. Biological Nutrient Rem oval: Where We Have Been, Where We Are Going. In Proceedings of the Water Environment Federation’s 79th Annual Technical and Educational Conference , Dallas, TX, October 21–25, 2006.

Barnard, J., M. Steichen, and C. deBarbadill o. 2004. Interaction Between Aerator Type and Simultaneous Nitrificatio n and Denitrification. In Proceedings of the Water Environment Federation’s 77th Annual Technical and Educational Conference , New Orleans, LA, October 2–6, 2004.

Barnard, J., A. Shaw, and D. Lindeke. 2005. Usi ng Alternative Parameters to Predict Success for Phosphorus Removal in WWTPs. In Proceedings of the Water Environment Federation’s 78th Annual Technical and Educational Conference , Washington, DC, October 29–November 2, 2005.

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Benisch, M., R. Baur, and J.B. Neeth ling. 2004. Decision Tree for Troubleshooting Biological Phosphorus Removal. In Proceedings of the Water Environment Federation’s 77th Annual Technical and Educational Conference , New Orleans, LA, October 2–6, 2004.

Benisch, M., D. Clark, J.B. Neethling, H.S. Fredrickson, and A. Gu. 2007. Can Tertiary Phosphorus Removal Reliably Produce 10 ug/l? In Proceedings of Nutrient Removal
2007 , Baltimore, MD, 2007.

Brandão, D., G.T. Daigger, M. O’Shaughnessy, and T.E. Sadick. 2005. Comprehensive Assessment of Performance Capabilities of Biological Nutrient Removal Plants Operating in the Chesapeake Bay Region. In Proceedings of the Water Environment Federation’s 78th Annual Technical and Educational Conference , Washington, DC, October 29–November 2, 2005.Municipal Nutrient Removal Technologies Reference Document September 2008

2-82 Chapter 2: Treatment Technologies Carroll, J.R., P. Pitt, and A. van Niekerk. 2005. Optimization of Nitrifi cation/Denitrification Process Performance and Reliability at the Blue Plains Advanced Wastewater Treatment Plant. In Proceedings of the Water Envi ronment Federation’s 78th Annual Technical and Educational Conference , Washington, DC, October 29–November 2,
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deBarbadillo, C., V. Bates, C. Cauley, S. Holcomb, B. Ebron, S. Rexrode, and J. Barnard. 2003. Pushing the Limits of Technology: Perf ormance and Operations Considerations for Plants Operating High Level Nitrogen Removal. In Proceedings of the Water Environment Federation’s 76th Annual Technical and Educational Conference , Los Angeles, CA, October 10–11, 2003.

deBarbadillo C., M. Lambert, D. Parker, W. Wells, and R. Willet. 2004. Denitrification Filters: A Comparison of Manufacturers and Review of Performance, Patent and Bidding Issues. In Proceedings of the Water Envi ronment Federation’s 77th Annual Technical and Educational Conference , New Orleans, LA, October 2–6, 2004.

deBarbadillo, C., A.R. Shaw, and C.L. Wallis-Lage. 2005. Evaluation and Design of DeepBed Denitrification Filters: Empirical Design Parameters vs. Process Modeling. In Proceedings of the Water Environment Federation’s 78th Annual Technical and Educational Conference , Washington, DC, October 29–November 2, 2005.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-83 deBarbadillo, C., R. Rectanus, R. Canham, and P. Schauer. 2006. Tertiary Denitrification and Very Low Phosphorus Limits: A Practic al Look at Phosphorus Limitations on Denitrification Filters. In Proceedings of the Water Environment Federation’s 79th Annual Technical and Educational Conference , Dallas, TX, October 21–25, 2006.

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Demirtas, M.U., C. Sattayatewa, and K.R. Pagilla. 2008. Bioavailability of Dissolved Organic Nitrogen in Treated Effluents. Water Environment Research, 80 :397-406.

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Erdal, U.G., Z.K. Erdal, and C.W. Randall. 2002. Effect of Temper ature on EBPR System Performance and Bacterial Community. In Proceedings of the Water Environment Federation’s 75th Annual Technical and Educational Conference , Chicago, IL, September 29–October 2, 2002.

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Friedrich, T.W., J.K. McLellan, T. Deniz, a nd J. Milligan. 2005 .Biological Nutrient Removal Process Enhancement Analysis of the Marshall Street Advanced Pollution Control Facility, Clearwater, Florida. In Proceedings of the Water Environment Federation’s 78th Annual Technical and Educational Conference , Washington, DC, October 29–November 2, 2005.

George Miles & Buhr, LLC, and Gannett Fleming. 2004. Refinement of Nitrogen Removal from Municipal Wastewater Treatment Plants

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Ip, S.Y., J.S. Bridger, and N.F. Mills. 1987. Effect of Alternating Aerobic and Anaerobic Conditions on the Economics of the Activated Sludge Systems. Water Science and Technology, 19 :911-918.

Johnson, T.L., C.L. Wallis-Lage, A.R. Shaw, and J.P. McQuarrie. 2005. IFAS Options— Which One is Right for Your Project? In Proceedings of the Annual Conference, Water Environment Federation, 2005.

Kang, S.J., W.F. Bailey, and D. Jenkins. 1992. Bi ological Nutrient Removal at the Blue Plains Wastewater Treatment Plant in Washington, D.C. Water Science Technology,
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Kang, S., K. Hoversten, and D. Lund. 2001. Th e Highest Level of Phosphorus Removal Practical from Municipal Wastewater Treatment Plants. In Proceedings of Annual Conference, Water Environmental Federation, Arlington,VA, 2001.

Kang, S., K. Olmstead, T. Nobinger, C. Pa tel, and G. Hill. 2006. Time vs. Space: Two Successful Biological Nutrient Removal Strategies. In Proceedings of the Annual Conference , Water Environment Federation, 2006.

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Katehis, D, S. Murthy, B. Wett, E. Locke, and W. Bailey. 2006. Nutrient Removal from Anaerobic Digester Side-Stream at the Blue Plains AWTP. In Proceedings of the Water Environment Federation’s 79th Annual Technical and Educational Conference , Dallas, TX, October 21–25, 2006.

Kiiskinen, S., and F. Tommi. 2005. Advanced N itrogen Removal: Experi ences and Operation Results of 80 MGD Postdenitrification Filters, Viikinmäki WWTP, City of Helsinki.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 2: Treatment Technologies 2-85 In Proceedings of the Water Environment Federation’s 78th Annual Technical and Educational Conference , Washington, DC, October 29–November 2, 2005.

Lindeke, D., and J. Barnard. 2005. The Role a nd Production of VFA’s in a Highly Flexible BNR Plant. In Proceedings of the Water Environment Federation’s 78th Annual Technical and Educational Conference , Washington, DC, October 29–November 2,
2005.

Liubicich, J., P. Pitt, E. Psaltakis, A. Zabi nski, and T. Lauro. 2004. Bench Scale Testing of the IFAS Technology at the Mamaroneck WWTP. In Proceedings of the Water Environment Federation’s 77th Annual Technical and Educational Conference , New Orleans, LA, October 2–6, 2004.

Masterson, T., J. Federico, G. Hedman, and S. Duerr. 2004. Upgrading for Total Nitrogen Removal With a Porous Media IFAS System. In Proceedings of the Water Environment Federation’s 77th Annual Technical and Educational Conference , New Orleans, LA, October 2–6, 2004.

McBean, E., and F. Rovers. 1998. Statistical Procedures for Analysis of Environmental Monitoring & Risk Assessment . Prentice Hall, New York.

McClintock, S.A., J.A. SHerrard, J.T. N ovak, and C.W. Randall. 1988. Nitrate Versus Oxygen Respiration in the Activated Sludge Process. Journal WPCF, 60(3):342-350.

McClintock, S.A., V.M. Patterkine, and C. W. Randall. 1992. Comparison of Yields and Decay Rate for a Biological Nutrient Rem oval Process and a Conventional Activated Sludge Process. Water Science and Technology 26(9-11):2195-98.

McGrath, M., G. Shero, and J. Welton. 2005a. Fe rmentation for Improving Nutrient Removal at a Virginia Wastewater Treatment Facility. In Proceedings of the Water Environment Federation’s 78th Annual Technical and Educational Conference

, Washington, DC, October 29–November 2, 2005.

McGrath, M, K. Gupta, and G.T. Daigger. 2005b. Operation of a Step-Feed BNR Process for both Biological Phosphorus and Nitrogen Removal. In Proceedings of the Water Environment Federation’s 78th Annual Technical and Educational Conference

, Washington, DC, October 29–November 2, 2005.

McQuarrie, J., K. Rutt, J. Seda, and M. H aegh. 2004. Observations from the First Year of Full-scale Operation—The IFAS/BNR Process at the Broomfield Wastewater Reclamation Facility, Broomfield, CO. In Proceedings of the Water Environment Federation’s 77th Annual Technical and Educational Conference , New Orleans, LA, October 2–6, 2004.Municipal Nutrient Removal Technologies Reference Document September 2008

2-86 Chapter 2: Treatment Technologies Metcalf & Eddy. 2003. Wastewater Engineering: Treatment and Reuse, McGraw-Hill, New York.

Narayanan, B., H.O. Buhr, R. Chan, J. Demir, R. Gray, D. Howell, S. Jones, and S. Shumaker. 2002. Fermentation of Return Ac tivated Sludge to Enhance Biological Phosphorus Removal. In Proceedings of the Water Environment Federation’s 75th Annual Technical and Educational Conference , Chicago, IL, September 29–October 2, 2002.

Neethling, J.B., B. Bakke, M. Benisch, A. Go, H. Stephens, H.D. Stensel, and R. Moore.
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Pai, P., D. Dielmann, W. Shepherd, E. Leveque , S. Semenza, M. Clyburn, and B. Narayanan. 2004. Operational Strategies and Treatmen t Technologies for Meeting Very Low Total Phosphorus Limits. In Proceedings of the Water Environment Federation’s 77th Annual Technical and Educational Conference , New Orleans, LA, October 2–6,
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Pape, R., K. Chandran, I. Ezenekwe, B. S tinson, J. Anderson, L.A. Carrio, J. Sexton, V. Sapienza, and K. Gopalakrishnan. 2004. H ybrid Step-Feed BNR Configuration for Enhanced Nutrient Removal at NYC WPCPs. In Proceedings of the Water Environment Federation’s 77th Annual Technical and Educational Conference , New Orleans, LA, October 2–6, 2004.

Parker, D.S., and J. Wanner. 2007. Improving N itrification through Bioaugmentation. In Proceedings of Nutrient Removal 2007 , Baltimore, MD, 2007.

Pattarkine, V.M., and C.W. Randall. 1999. The Re quirement of Metal Cations for Enhanced Biological Phosphorus Removal by Activated Sludge. Water Science and Technology 40(2):159-165.

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Chapter 2: Treatment Technologies 2-91 

### Attachment 1: Locations Providing Data

Location Data performance period Brighton, Michigan January through December 2005 Chelsea, Michigan October 2005 through September 2006 Clark County, Nevada January through December 2006
Clearwater, Florida: Northeast October 2005 through September 2006
Clearwater, Florida: Marshall Street October 2005 through September 2006 Cumberland, Maryland January through December 2005
Cheshire, Connecticut April through November 2006 Durham, Oregon January through December 2004
Enfield, Connecticut September 2005 through August 2006 Jewett City, Connecticut Sept ember 2005 through August 2006
New Haven, Connecticut Sept ember 2005 through August 2006 Ridgefield, Connecticut Sept ember 2005 through August 2006
Thomaston, Connecticut Sept ember 2005 through August 2006 Hagerstown, Maryland January through December 2005 Genesee County, Michigan October 1999 through September 2000
Hammonton, New Jersey January through December 2005 Hyrum, Utah November 2005 through September 2006 Central Johnston County, Smithfield,
North Carolina October 2005 through September 2006

Kalispell, Montana July 2005 through June 2006 Fairfax County, Virginia January through December 2006 Piscataway, Maryland January through December 2005 McMinnville, Oregon January 2005 through October 2006
Kelowna, British Columbia January 2005 through December 2005 North Cary, North Carolina October 2005 through September 2006 Pinery Water, Colorado January through December 2004 Western Branch, Marlboro, Maryland January through December 2006 Westminster, Maryland Octobe r 2005 through September 2006 Lee County, Florida January through December 2006 Breckenridge, Colorado January through December 2003
Lone Pine Tree, Colorado January through December 2006September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 3 - Case Studies and Reliability Factors 3-1 

## CHAPTER 3: Case Studies and Reliability Factors

3.1 Introduction and Overview

The objective of the case studies was threefold: to study selected techno logies that remove nitrogen, phosphorus, or both to low concentrations; to identify factors that contribute to reliability; and to identify factors that contribute to costs. Nine facilities were selected as case studies, and the results are summarized in th is chapter. (The complete case studies are presented in Volume II, Appendix A).

In selecting the case study locat ions, consideration was given to ensuring that there was a variety of technologies that ach ieved low effluent concentrati on in either ammonia nitrogen and phosphorus or both total nitr ogen (TN) and total phosphorus (TP), a variety of locations in cold- and warm-weather regi ons, and a variety of sludge-ha ndling processes. The chapter is organized to present the specific nutrient removal tec hnologies selected, followed by factors that influence the reliability of performance and costs, in both capital and operation and maintenance (O&M), at these facilities.

To establish a simple and ye t sound statistical method by whic h plant performance and data can be presented and compared, the coefficien t of variation (COV) was used in this study. The statistical background is included in Volume II, Appendix B.



### 3.1.1 Permit Limits for the Case Study Facilities Table 3-1 summarizes the nutrient permit require ments for all the case study facilities. For the U.S. facilities, these values come from the National Pollutant Discharge Elimination System (NPDES) permits issued by the facility’s state regulatory aut hority, and they were current as of the writing of this manual in summer 2007. For the facility in Kelowna, British Columbia, the relevant limits were as given by Environment Canada.

Table 3-1 demonstrates that there was a wide variety in discharge seasons and numeric limits for the case study facilities. The facilities have standards ranging from annual averages to daily maximums. Total maximum daily loads (T MDLs) were used in some locations to develop load limits, while straight concentration limits were used as the basis for technologies in Florida. It is notable that limits for maximum w eek and maximum month were specified in one case, while the limits for maximum day and maximum month were specified in another. In another case, limits were set for maximu m week, maximum month, and entire quarter. Clearwater, Florida, ha s limits for maximum w eek and maximum month and an annual limit.Municipal Nutrient Removal Technologies Reference Document September 2008

3-2 Chapter 3 - Case Studies and Reliability FactorsTable 3-1. Discharge permit limits and performance data summaryPermit limits and performance results( mg/L)Quarterly or annualMonthWeekMax dayPlant andlocationNutrientremovalprocessesAnnualaverageCOV forannualaverageAvgpermitlimitsMax (q)Avg (a)resultAvgpermitlimitsMaxmonthresultAvgpermitlimitsMaxweekresultPermitlimitMax dayNoman M. ColePollutionControl Plant;Fairfax County,VirginiaStep-feed ASwith dual media& deep bed filter+ ferric chlorideTP = 0.09NH4-N =0.12TN = 5.25TP: 21%NH4-N:14%TN: 12%Noquarterly orannuallimits-- TP = 0.18Sum NH4-N = 1.0Win NH4-N= 2.2TN =reportTP = 0.12NH4-N =0.135TN = 6.0TP = 0.27Sum NH4-N = 1.5Win NH4-N= 2.7TN = reportTP = 0.16NH4-N=0.29TN = 8.01No dailylimits--KalispellAdvancedWastewaterTreatment,Kalispell,MontanaMod. UTC withfermenter andup flow sandfilter (nochemical for P)TP = 0.121NH4-N =0.07TP: 19 %NH4-N: 0%Noquarterly orannuallimits-- TP=1.0NH4-N=1.4TP=0.15NH4-N =0.07No weeklylimits-- No dailylimits--Clark CountyWaterReclamationDistrict, NevadaA/O process withactive primaryfor VFA withdual media filters+ alumTP = <0.09NH4-N =0.12TP: 30%NH4-N:14%Noquarterly orannuallimits-- NomonthlyaveragelimitsTP = 0.12NH4-N =0.15No weeklylimits-- TP= 0.22aNH4-N =0.64aTP = 0.22NH4-N =0.57CentralJohnstonCountySmithfield,North CarolinaPlug flow AS(anoxic,aeration) withdenitrificationfilter andmethanol (Nochem. for P)TP = 0.26NH4-N =0.44TN = 2.14TP: 62%NH4-N:12%TN: 16 %TP = 2.0(Q)TN = 3.7**TP = 0.47(Q Max)TN = 2.14(Av)TP=1.0Sum NH4-N = 2.0Win NH4-N= 4.0TP = 0.64NH4-N =0.54Sum NH4-N = 6.0Win NH4-N= 12.0NH4-N =0.86No dailylimits--North Cary,North CarolinaOxidation ditch(Biodenipho)with upflow sandfilter(No chemicalfor P)TP=0.38AmmoniaN = 0.08TN=3.7TP: 64%AmmoniaN: 102%TN: 14 %TP = 2.0(Q)TN = 3.94b(A)TP = 0.57(Q max)TN = 3.7(Av)Sum NH4-N = 0.5Win NH4-N= 1.0NH4-N =0.34No weeklylimits-- No dailylimits--September 2008 Municipal Nutrient Removal Technologies Reference Document

Chapter 3 - Case Studies and Reliability Factors 3-3Table 3-1. Discharge permit limits and performance data summary(continued)Permit limits and performance results( mg/L)Quarterly or annualMonthWeekMax dayPlant andlocationNutrientremovalprocessesAnnualaverageCOV forannualaverageAvgpermitlimitsMax (q)Avg (a)resultAvgpermitlimitsMaxmonthresultAvgpermitlimitsMaxweekresultPermitlimitMax dayKelowna, BritishColumbia,Canada3-stageWestbank withfermenters(No chemicalfor P)TP=0.139TN=4.38TP: 21%TN: 12%TP = 0.25(A)TP = 0.139(Av)NomonthlyaveragelimitTP = 0.20NH4-N=1.01TN = 4.9No weeklylimits-- TP = 2.0TN =6.0(daily max)TP = 0.25TN = 5.8Marshall StreetWaterReclamationFacility,Clearwater,Florida5-stageBardenpho withsand filter +alumTP=0.132NH4-N=0.038TN=2.32TP: 40%NH4-N:18%TN: 16%TP = 1.0(A)TN = 3.0(A)TP = 0.132(Av)TN = 2.32(Av)TP = 1.25TN = 3.75TP = 0.21TN = 3.1TP = 1.5TN = 4.5TP = 0.26TN = 3.75TP = 2.0TN = 6(daily max)TP = 0.37TN = 4.29Lee County,FloridaAS withdenitrificationfilter andmethanoladdition + alumTP=0.102TN=1.57TP: 35%TN: 28%TP = 0.5(A)TN = 3.0(A)TP = 0.08(Av)TN = 1.57(Av)TP = 0.5TN=3TP = 0.19TN = 2.61TP = 0.75TN=4.5TP = 0.39TN = 3.70TP = 1.0TN=6(daily max)TP = 0.27TN = 5.98WesternBranch,Upper Marlboro,MarylandThree AS withmethanoladdition + alumTP = 0.47NH4-N =0.22TN = 1.70TP: 62%NH4-N:163%TN: 36%TP = 0.3c(A)TN = 4.0c(A)--TP = 1.0TN = 3.0(Apr-Oct)NH4-N =1.5(Apr-Oct),NH4-N =5.5(Nov-Mar)-- TN = 4.5(Apr-Oct)-- -- --Notes:A/O = anoxic/oxicAS = activated sludgeCOV = coefficient of variation: onestandard deviation divided by the meanNH4-N = ammonia nitrogenNL = No limitTP = total phosphorusTN = total nitrogenSum = SummerWin = WinterChem. = chemicala Daily maximum permit limits were derived from a wasteload allocation on the basis of dailymaxima at design flowb Annual average permit limit derived from a wasteload allocation on the basis of annual averageat design flowc Annual average limits based on 30 MGD annual load following installation of Maryland-fundedupgradesMunicipal Nutrient Removal Technologies Reference Document September 2008

3-4 Chapter 3 - Case Studies and Reliability Factors The permit for Kelowna, British Columbia, also includes reliability cr iteria for phosphorus removal, which specified limits for the maximum day, 99 th percentile, 90 th percentile, and annual average, as follows:

Maximum day 2.0 mg/L TP
99 th percentile 1.5 mg/L
90 th percentile 1.0 mg/L Annual average 0.25 mg/L

These Canadian limits are comparable to statisti cs as applied at U.S. facilities, as shown in Table 3-2. For example, the Canadian 90 th percentile limit is slightly less stringent than the U.S. maximum month limit for data collected on a daily basis.

Table 3-2. Statistical comparison of Canadian and U.S. permit limits

Statistical percentile U.S. term––averaging or maximum period Canadian term––percent less than value 50 Annual average 50th percentile 80 Maximum quarter --
90 -- 90th percentile
92.3 Maximum month --
98.1 Maximum week --
99 -- 99th percentile 99.7 Maximum day --



### 3.2 Summary of Case Studies

Table 3-1 above shows the loca tion of and technologies used in each of the case studies.

The highlights of each case study are presented in order, from facilities with the lowest permit limit to those with the highest permit limit. All facilities were required to remove varying levels of phosphorus. Tw o facilities had ammonia nitr ogen permit limits but no TN limits, while the other seven fac ilities had TN limits, as show n in Table 3-1. This chapter presents the nitrogen and phosphorus removal facilities first, followed by the facilities required to remove ammonia nitrogen and phosphorus.



### 3.2.1 Total Nitrogen an d Phosphorus Removal at Low Concentration Limits (3 mg/L or less in TN) Four case studies fell into this group, and they are characterized as having multiple, distinct, anoxic zones with sufficient carbon supply.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 3 - Case Studies and Reliability Factors 3-5 Case Study No. 1: Western Branch, WSSC, Maryland This facility has a three-stag e activated-sludge system followed by tertiary filtration. The third activated-sludge stage was added to prov ide denitrification us ing methanol as the carbon source. The permit includes a monthly average ammonia limit of 1.5 milligrams per liter (mg/L) in summer (April–October) and 5.5 mg/L in winter (November–March). The TN limits are 3 mg/L as a monthly average and 4.5 mg/L as a weekly average, which both apply during the summer (April–October). An annual average TN limit of 4.0 mg/L is expected to go into effect in the future. The phosphorus limit for the future is 0.3 mg/L at the design flow of 30 million gallons per day (MGD).

The Western Branch Wastewater Treatment Pl ant (WWTP) is part of the Washington Suburban Sanitary Commission (WSSC) system, and it is in Upper Marlboro, Maryland. The plant employs three separate activated-sludge systems in series to accomplish biochemical oxygen demand (BOD) removal (high-rate activ ated sludge, or HRAS), nitrification (nitrification activated sludge, or NAS), and de nitrification (denitrifi cation activated sludge, or DNAS). The return activated sludges (RAS) are kept separate to facilitate the growth of specific types of microorganisms in each syst em by allowing for differing sludge residence times. After grit removal and screening, the wa stewater goes directly to the HRAS. The effluent is filtered prior to ultraviolet ( UV) disinfection. Waste activated sludges (WASs) from the three systems are combined, thickene d by dissolved air flotation (DAF), dewatered by centrifuge, and burned in two multiple-hearth incinerators.

The plant does not have primary settling. Alum was added to remove phosphorus. The process recycle water from the DAF, cent rifuge, and incinerator is return ed to the headworks. The plant treated an annual average flow of 23.0 MGD, and the maxi mum month flow was 26.6 MGD.

Western Branch WWTP, WSSC Monthly Average Frequency Curves for Total Phosphorus

0.001 0.01 0.1

1 10 100

Percent Less Than or Equal ToTotal Phosphorus, mg/L

Plant Influent HRAS Influent HRAS Effluent NAS Effluent DNAS Effluent Final Effluent 0.1 5040302010 5 1 2 0.5 0.05 60 70 80 90 95 98 99 99.5 99.9599.9 Mean = 0.43 mg/L Std. Dev. = 0.27 mg/L C.O.V. = 62%

Figure 3-1. Western Branch WWTP: Monthly frequency curves for TP.Municipal Nutrient Removal Technologies Reference Document September 2008

3-6 Chapter 3 - Case Studies and Reliability Factors Western Branch WWTP, WSSC Monthly Average Frequency Curves for Ammonia-Nitrogen

0.001

0.01

0.1

1 10 100

Percent Less Than or Equal ToAmmonia-Nitrogen, mg/L

Combined Raw Influent HRAS Influent HRAS Effluent

NAS Effluent DNAS Effluent Final Effluent 0.1 50 40 302010 5 1 2 0.5 0.05 60 70 80 90 95 98 99 99.5 99.9599.9 Mean = 0.13 mg/L Std. Dev. = 0.22 mg/L C.O.V. = 163%

Figure 3-2. Western Branch WWTP: Monthly frequency curves for ammonia nitrogen.

The performance was efficient and reliable durin g the evaluation period for TN but moderate for ammonia nitrogen and TP. The average concentrations were 1.63 mg/L in TN with a COV of 36 percent, 0.2 2 mg/L in ammonia nitrogen with a COV of 163 percent, and 0.43 mg/L in TP with a COV of 62 percent.

Several factors contributed to this performance at Western Br anch, including the following:

1. Wastewater characteristics. Because th is facility uses a separate stage for denitrification with methanol and alum for phosphorus removal, the wastewater characteristics were not a concern.

2. Three activated-sludge systems in se ries provided redundancy and thus added reliability for TN removal, but a large footprint was required for the bioreactors and clarifiers.

3. The first two stages provided BOD removal and nitrification in two separate stages in series. The nitrate in the effluent from the second stage (NAS) averaged 16.5 mg/L with a COV of 12 percent. Note that this is high because denitrification was not designed to occur in this stage. The meth anol dosage averaged 2.5 lb/nitrate nitrogen entering the DNAS tank.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 3 - Case Studies and Reliability Factors 3-7 Western Branch WWTP, WSSC Monthly Average Frequency Curves for Total Nitrogen

0.1

1 10 100

Percent Less Than or Equal ToNitrogen, mg/L

Combined Raw Influent HRAS Influent NAS Effluent

DNAS Effluent Final Effluent 0.1 50 4030 2010 5 1 2 0.5 0.05 60 70 80 90 95 98 99 99.5 99.9599.9 Mean = 1.63 mg/L Std. Dev. = 0.59 mg/L C.O.V. = 36%

Figure 3-3. Western Branch WWTP: Monthly frequency curves for TN.

4. The control strategy included daily testing of key para meters and adjustment of the methanol dosage, when needed.

5. Alum was fed to the DNAS tanks for phosphor us removal at an average dosage of 10 mg/L with good results.

6. Dissolved oxygen (DO) probes were insta lled for continuous monitoring in the first two stages. The signals from the probes were used to control the air valves and thus control the air flow to the basins. The pl ant also has online sensors for suspended solids and sludge blanket levels in the secondary clarifiers.

7. Recycling of phosphorus has been minimized at the facility. The sludge is thickened under aerobic conditions, which reduces phospho rus release. In addition, the biosolids are incinerated rather than digested, which also redu ces phosphorus recycle because most of it stays with the ash.

8. No special procedures are in pl ace for managing wet-weather flows.

Case Study No. 2: Fiesta Village WWTP in Lee County, Florida This facility has an oxidation ditch followed by denitrification filters with a methanol feed system. The permit contains an annual average TN limit of 3 mg/L and TP limit of 0.5 mg/L, with higher values for monthly and weekly averages. In additi on, the permit specifies a daily limit of 5 mg/L in total suspended solids (TSS) for water reuse.Municipal Nutrient Removal Technologies Reference Document September 2008

3-8 Chapter 3 - Case Studies and Reliability Factors The facility was an extended-aeration oxidation ditch, and four denitrif ication filters were added along with three screw pumps. Alum was used for the TSS control required for water reuse, which aided phosphorus removal at the same time. The sludge was digested aerobically, stored, and hauled away fo r processing at another county facility.

Fiesta Village WWTP, Lee Co., FL Monthly Average Frequency Curves for Total Phosphorus

0.01 0.1

1 10 100

Percent Less Than or Equal ToTotal Phosphorus, mg/L

Raw Influent Final Effluent 0.1 5040 302010 5 1 2 0.5 0.05 60 70 80 90 95 98 99 99.5 99.9599.9 Mean = 0.102 mg/L Std. Dev. = 0.035 mg/L C.O.V. = 35%

Figure 3-4. Lee County, Florida: Monthly frequency curves for TP.

Fiesta Village WWTP Lee Co., FL Monthly Average Frequency Curves for Nitrogen

0.100 1.000 10.000 100.000

Percent Less Than or Equal ToNitrogen, mg/L

Raw Influent - Total N Final Effluent - Total N Secondary Effluent NO3-N 0.1 50 40 3020 10 5 1 2 0.5 0.05 60 70 80 90 95 98 99 99.5 99.9599.9 Mean = 1.71 mg/L Std. Dev. = 0.48 mg/L C.O.V. = 28%

Figure 3-5. Lee County, Florida: Monthly frequency curves for TN.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 3 - Case Studies and Reliability Factors 3-9 The performance was efficient and reliable. Th e plant achieved a TN concentration of 1.71 mg/L with a COV of 28 percent and TP concentration of 0.1 mg/L with a COV of 35 percent.

A number of key factors contribut ed to this high performance:

1. Denitrification is accomplished in two processe s in series: first in the oxidation ditch, which has a target nitrate nitrogen con centration of 3 to 3.5 mg/L, followed by the denitrification filter, with a minimal dose of methanol feed to remove additional nitrate nitrogen.

2. The high level of denitrification in the oxi dation ditch is a unique accomplishment at this plant, achieved by carefully contro lling the brush aerators. The standard procedure calls for turning off one brush aerator during the day and two during the night, which provides anoxic zone(s) within the ditch comprising approximately 25 to 50 percent of the tank volume. The location of these aerators varies, depending on the season. In addition, the clarif iers operate with a denitr ifying sludge blanket depth between 2.5 ft and 3.5 ft.

3. The denitrifying filters then bring the nitr ate nitrogen below 3 mg/L with a methanol feed rate of 1.9 lb/lb nitrat e nitrogen, which is low. The dosage is determined on the basis of daily performance. This process is compact with a small footprint and, thus, is preferred at a locat ion with limited space.

4. Alum was fed at an average dosage of 8.9 mg/L at a mass basin Al/TP ratio of 2.32 to reach an effluent concentration of 0.1 mg/L

5. Recycle loads are minimal primarily due to the fact that aerobically digested sludge is hauled off-site for proces sing at another facility.

6. During wet-weather periods, a normal mode of operation is maintained. Under extreme peak flow conditions, however, th e biomass inventory is protected from surges by shutting off a number of aerators.

Case Study No. 3: Central Johnston County, North Carolina This facility has a plug-flow ac tivated-sludge system followed by a denitrification filter with a methanol feed. The permit includes a monthl y ammonia limit of 2 mg/L in summer and 4 mg/L in winter, and an annual average TP limit of 1 mg/L. In addition, the TN limit is set on the basis of a load limit of 56,200 lb per year, which is equivalent to 3.7 mg/L on an annual average basis at the design flow of 7 MGD.

This facility was retrofitted from conventiona l activated sludge to enhanced biological phosphorus removal (EBPR), followed by a separate -stage denitrification filter for nitrogen removal. The plant treated 5.17 MGD during th e maximum month and had an annual average of 4.12 MGD during the evaluation period. Ther e is no primary settling, and the WAS isMunicipal Nutrient Removal Technologies Reference Document September 2008

3-10 Chapter 3 - Case Studies and Reliability Factors aerobically digested before de watering by a belt filter press o ff-site. After UV disinfection, the reclaimed water is stored for reuse.

Johnston County, NC Monthly Average Frequency Curves for Total Phosphorus

0.01 0.1

1 10 100

Percent Less Than or Equal ToTotal Phosphorus, mg/L

Raw Influent Final Effluent 0.1 504030 2010 5 1 2 0.5 0.05 60 70 80 90 95 98 99 99.5 99.95 99.9 Mean = 0.26 mg/L Std. Dev. = 0.164 mg/L C.O.V. = 62%

Figure 3-6. Johnston County, North Carolina: Monthly average frequency curves for TP.

Johnston County, NC Monthly Average Frequency Curves for Ammonia-N

0.1

1 10 100

Percent Less Than or Equal ToNitrogen, mg/L

Raw Influent Ammonia-N Final Effluent Ammonia-N 0.1 50 40 30 2010 5 1 2 0.5 0.05 60 70 80 90 95 98 99 99.5 99.95 99.9 Mean = 0.44 mg/L Std. Dev. = 0.055 mg/L C.O.V. =12%

Figure 3-7. Johnston County, North Carolina: Monthly average frequency curves for ammonia nitrogen.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 3 - Case Studies and Reliability Factors 3-11 Johnston County, NC Monthly Average Frequency Curves for Total Nitrogen

0.1

1 10 100

Percent Less Than or Equal ToNitrogen, mg/L

Raw Influent TN Final Effluent TN 0.1 50 40 302010 5 1 2 0.5 0.05 60 70 80 90 95 98 99 99.5 99.95 99.9 Mean = 2.14 mg/L Std. Dev. = 0.36 mg/L C.O.V. =16%

Figure 3-8. Johnston County, North Carolina: Monthly average frequency curves for TN.

The performance was highly efficient and reliable for nitrogen removal and biological phosphorus removal. The TN COV for the monthly average was very reliable at 16 percent at a mean concentration of 2.14 mg/L. The COV for am monia nitrogen was also very reliable at 12 percent at a mean concentration of 0.44 mg /L. The COV for TP was 62 percent at an average of 0.26 mg/L on a monthly basis. TP during the maximum month was 0.64 mg/L at this COV, meeting the pe rmitted limit of 1 mg/L.

Several distinct factors were noted at this facility:

1. The wastewater characteristics are favor able for nutrient removal. The BOD-to-TP ratio and BOD-to-total Kjel dahl nitrogen (TKN) ratio were 55.1 and 10, respectively, where 25 and 4 are reported as adequate in the literature (Lindeke et al. 2005; Neethling et al. 2005; WEF and ASCE 1998).

2. A significant amount of denitrification was accomplished in the clar ifier, with a deep sludge blanket of 3 to 4 feet. (T his can be referred to as a denitrification blanket .) As a result, the RAS flow rate was reduced si gnificantly. Note that all these procedures were developed and optimized by plant personnel.

3. Biological phosphorus removal was successfu lly achieved in the re trofitted activated sludge without any chemical addition.

4. Methanol was added before the denitrification filters. The methanol was fed at a controlled dosage with online monitoring of nitrate, by a Hach probe. The average dosage of methanol for the year was relatively low at 14 mg/L.Municipal Nutrient Removal Technologies Reference Document September 2008

3-12 Chapter 3 - Case Studies and Reliability Factors 5. This process is compact with a small footprint and, thus, is preferred at a location with limited space.

6. The recycle loads are minimized because only aerobic digestion is available on-site. The sludge is dewatered off-site, so ther e is no return flow from the dewatering

process.
7. Wet-weather flows are managed without major difficulties. Even during Tropical Storm Alberto in June 2006, the plant opera ted normally. As a result of Alberto, flow increased from 3.4 to 10.5 MGD, following 10 inches of precip itation in a 24-hour period. Under extreme weather conditions like a hurricane, the plant would shut down part of the aeration basins and protect the sludge inventory. This c ould last for up to a day without causing adverse effect s on the biomass at the plant.

Case Study No. 4: Marshall Street Advanced WWTP, Clearwater, Florida The Clearwater, Florida, facility uses a 5- stage Bardenpho process fo llowed by a sand filter with alum feed. This facility was retrofitted fr om conventional activated sludge to the 5-stage Bardenpho process and tertiary filtration.

The NPDES permit includes annual limits of 3 mg/L for TN and 1 mg/L for TP. Monthly average limits are 3.75 mg/L for TN and 1.25 mg/L for TP. In addition, dichlorobromomethane and dibromochlor omethane are limited to 24 and 46 μg/L, respectively, on an a nnual average basis.

The plant was designed to treat 10 MGD. It treated 6.85 MGD during the maximum month with an annual average of 5.45 MGD for the eval uation year. The wastewat er is settled in the primary tanks, treated at the Bardenpho proce ss, and filtered through ra pid sand filters before chlorination. The WAS is thickened by rotary-dru m thickeners and then digested along with the primary sludge in anaerobic digesters befo re dewatering by a belt filter press. The biological treatment process selected is a classic 5-stage Bardenpho design with a long hydraulic retention time (HRT, 20 hours) and a long sludge retention time (SRT, 25 days) with an anaerobic zone for denitrification fo llowed by two separate al ternative aerobic and anoxic zones for nitrification and phosphorus removal. No ex ternal carbon source is used.

The performance was highly efficient and relia ble for nitrogen and phosphorus removal. The COVs were 16 percent for the monthly averages at a mean concentration of 2.32 mg/L TN. The COV for phosphorus was 40 percent at an average concentration of 0.13 mg/L. This process has a large f ootprint and thus requires a large site.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 3 - Case Studies and Reliability Factors 3-13 Marshall Street Advanced WWTP Clearwater, FL Monthly Average Frequency Curves for Total Phosphorus

0.01

0.1

1 10 100

Percent Less Than or Equal ToTotal Phosphorus, mg/L

Raw Influent Final Effluent 0.1 5040302010 5 1 2 0.5 0.05 60 70 80 90 95 98 99 99.5 99.9599.9 Mean = 0.132 mg/L Std. Dev. = 0.052 mg/L C.O.V. = 40%

Figure 3-9. Marshall Street Advanced WWTP, Clearwater, Florida: Monthly average frequency curves for TP.

Marshall Street Advanced WWTP Clearwater, FL Monthly Average Frequency Curves for Ammonia Nitrogen

0.01

0.1

1 10 100

Percent Less Than or Equal ToAmmonia Nitrogen, mg/L

Raw Influent - Ammonia-N Final Effluent - Ammonia N 0.1 50403020 10 5 1 2 0.5 0.05 60 70 80 90 95 98 99 99.5 99.9599.9 Mean = 0.038mg/L Std. Dev. = 0.007 mg/L C.O.V. = 18%

Figure 3-10. Marshall Street Advanced WWTP, Clearwater, Florida: Monthly average frequency curves for ammonia nitrogen.Municipal Nutrient Removal Technologies Reference Document September 2008

3-14 Chapter 3 - Case Studies and Reliability Factors Marshall Street Advanced WWTP Clearwater, FL Monthly Average Frequency Curves for Nitrogen

0.1

1 10 100

Percent Less Than or Equal ToNitrogen, mg/L

Raw Influent - Ammonia-N Final Effluent - Total N 0.1 50403020 10 5 1 2 0.5 0.05 60 70 80 90 95 98 9999.5 99.9599.9 Mean = 2.32 mg/L Std. Dev. = 0.38 mg/L C.O.V. = 16%

Figure 3-11. Marshall Street Advanced WWTP, Clearwater, Florida: Monthly average frequency curves for TN.

Contributing factors at this f acility include the following:

1. Thorough operating guidelines were devel oped and followed by the plant personnel.

2. This facility had favorable wastewater characteristics in BOD, TKN, and TP. The BOD-to-TP ratio was 37.5 and the BOD-to-TKN ratio was 6.7. Both ratios are higher than what is considered ad equate, 25 and 4, respectively.

3. Process controls were automated with on line probes for DO, nitrate, ortho-phosphate, and oxidation-reduction potential (ORP). The controls were based on readings in the second anoxic zone for nitrate, DO, a nd ORP. The strategy developed by plant personnel includes a minimum target ORP at –60 millivolts and nitrate nitrogen at 0.5 mg/L. DO levels are then adjusted by automa tic controls to stay in this region. In addition, plant personnel use turbidity and conductivity meters for effluent monitoring. Turbidity is for reuse mo nitoring, as required by Florida, and conductivity is used as an ear ly warning indicator for poten tial seawater intrusion to the sewer system to protect the water reuse customers.

4. Alum is added to meet the trihalomehthan e requirements of Florida for water reuse. The average dosage was 27 mg/L as alum, or at the aluminum-to-phosphorus ratio of 1.6 on a molar basis.

5. Recycle flows from dewatering are mixed with the plant influent and treated together. The recycle loadings from dewatering we re moderate at 30 percent for phosphorusSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 3 - Case Studies and Reliability Factors 3-15 and 14 percent for nitrogen. Thickening by mechanical equipment helped in minimizing recycle loads in nitrogen and phosphorus. Anaerobic digestion also contributed to the increase in recycle load s of these nutrients to moderate levels.

6. Wet-weather flows are handled w ith the normal mode of operation.



### 3.2.2 Total Nitrogen and Phosphorus Removal at Mid-Level Concentration Limits (3 to 6 mg/L) Three case studies fell into this group, and they are characterized as having one anoxic zone with or without ex ternal carbon sources.

Case Study No. 5: North Cary, North Carolina The North Cary, North Carolina, facility us es a phased isolatio n oxidation ditch (PID) (Biodenipho) with an upflow sand filter. The NPDES permit requires ammonia limits of 0.5 mg/L for summer and 1.0 mg/L in winter, 3.9 4 mg/L for TN on an annual average, and 2 mg/L on a quarterly basis.

This facility was expanded, replacing the Schr eiber process with a PID, in 1997. The design flow was 12 MGD and treated 8.7 MGD in th e maximum month and 7 MGD as the annual average of this evaluation period. The wastewater is treated at this PID, filtered by an upflow Dynasand filter, and disinfected by UV irradiation before discharge. The facility has a 2– million-gallon (MG) equalization basin online and has additional storage capacity of 7 MG in the old facility on-site. The sludge is aerobically digested and sh ipped to another facility for dewatering and drying.

North Cary, NC Monthly Average Frequency Curves for Total Phosphorus

0.01 0.1

1 10 100

Percent Less Than or Equal ToTotal Phosphorus, mg/L

Raw Influent Final Effluent 0.1 5040 302010 5 1 2 0.5 0.05 60 70 80 90 95 98 99 99.5 99.9599.9 Mean = 0.379 mg/L Std. Dev. = 0.241 mg/L C.O.V. = 64%

Figure 3-12. North Cary, North Carolina: Monthly average frequency curves for TP.Municipal Nutrient Removal Technologies Reference Document September 2008

3-16 Chapter 3 - Case Studies and Reliability Factors North Cary, NC Monthly Average Frequency Curves for Ammonia Nitrogen

0.01 0.1

1 10 100

Percent Less Than or Equal ToNitrogen, mg/L

Raw Influent - Ammonia-N Final Effluent - Ammonia-N 0.1 5040 30 20 10 5 1 2 0.5 0.05 60 70 80 90 95 98 9999.5 99.9599.9 Mean = 0.081 mg/L Std. Dev. = 0.082 mg/L C.O.V. = 102%

Figure 3-13. North Cary, North Carolina: Monthly average frequency curves for ammonia nitrogen.

North Cary, NC Monthly Average Frequency Curves for Total Nitrogen

0.01 0.1

1 10 100

Percent Less Than or Equal ToNitrogen, mg/L

Raw Influent - Total Nitrogen Final Effluent - Total Nitrogen 0.1 50403020 10 5 1 2 0.5 0.05 60 70 80 90 95 98 99 99.5 99.9599.9 Mean = 3.67 mg/L Std. Dev. = 0.512 mg/L C.O.V. = 14%

Figure 3-14. North Cary, North Carolina: Monthly average frequency curves for TN.

The performance was efficient and reliable. The COVs were 102 percent for ammonia at a mean concentration of 0.08 mg/L, 64 percent fo r TP at a mean concentration of 0.38 mg/L, and 14 percent for TN at a mean concentrati on of 3.67 mg/L. This was achieved without any chemical addition. The quarterly average TP wa s 0.57 mg/L at this C OV and met the limit ofSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 3 - Case Studies and Reliability Factors 3-17 2 mg/L. The maximum month ammonia nitroge n concentration was 0.34 mg/L, well within the permit limit of 0.5 mg/L in summer.

This process provides two anaer obic selector zones ahead of the oxidation ditch, which alternate between anoxic and aer obic cycles to maximize nitr ification and denitrification using the carbon present in the wastewater. Th e oxidation ditch is followed by two anoxic zones and one reaeration zone.

Several key factors were noted at this facility:

1. Wastewater characteristics were favor able. The BOD-to-TP ratio and BOD-to-TKN ratio were 31.6 and 4.3, respectively. Both were adequate in accordance with the literature.

2. Reliability is ensured with two anaerobi c zones ahead of and two anoxic zones after the ditch. The automatic pro cess logic control of cycle times is based on online DO

measurements.
3. Separate means of providing aeration and mi xing in the ditch allow optimal control of aerobic and anoxic cycles for best performance.

4. Recycle loads are minimized by having onl y aerobic digestion on-site; there are no anaerobic processes. The digested sludge is transported off-site for processing, and therefore no recycled loads go back to the facility.

5. Wet-weather operation follows the normal mode of operation. The PID process design allows the cycle time to be adjusted based on incoming flow. When the system is in storm mode the plant is switched to sedimentation, thereby preventing solids washout.

6. Equalization basins with a total volume of 9 MG are available. During Tropical Storm Alberto in June 2006, all the equalization basins were filled, the PID operated in storm mode for a short duration, and the faci lity was still able to comply with all NPDES permit limits.

Case Study No. 6: Kelowna, British Columbia The Kelowna, British Columbia, facility uses a 3-stage Westbank process with a fermenter and a dual-media filter. The Canadian Ministry of Environment permit requires a TN limit of 6 mg/L and 2.0 mg/L on a daily basis, or 1.5 mg/L on the 99 th percentile, or 1 mg/L on the
90 th percentile, and 0.25 mg/L on an annual basis for TP.

This facility was retrofitted from the exis ting 5-stage Bardenpho to the 3-stage Westbank process. The design capacity is 10.5 MGD, and the facility treated 7 MGD as the annual average for the evaluation year. The wastewater is settled in primary tanks, treated at theMunicipal Nutrient Removal Technologies Reference Document September 2008

3-18 Chapter 3 - Case Studies and Reliability Factors bioreactor, filtered through dua l-media filters, and disinfected by UV. The primary sludge is fermented and stored before dewatering and composting off-site. The secondary sludge is thickened by DAF and stored. Combined primar y and secondary sludge is then dewatered by centrifuge for off-site composting. The primary e ffluent can be sent to the equalization basin, which has a capacity equivalent to approxima tely 7.5 percent of th e average design flow.

The performance was efficient and reliable. The COV was 12 percent for the monthly average data at a mean concentration of 4.38 mg/L TN. The COV for TP was 21 percent at the mean concentration of 0.139 mg/L. The ma ximum month average was 0.20 mg/L TP and 4.9 mg/L TN at these low COVs.

Some of the unique features of this facility are as follows:

1. The wastewater characteristics were fa vorable but not sufficient year-round. The BOD-to-TP ratio was 26.6 and found to be somewhat low for a cold-region facility. The BOD-to-TKN ratio was 5.3, which was adeq uate for what is recommended in the literature.

2. The unique features of this facility include the fermente r for volatile fatty acid (VFA) production, which ensured a reliable and effi cient operation of th e EBPR. The design and operation of fermenter te chnology evolved from this f acility. Current operation is based on 5-day sludge age year-round, and th e predominant VFA species were acetic acid and propionic acid, both of wh ich are desirable for a good EBPR.

Kelowna, BC Monthly Average Frequency Curves for Total Phosphorus

0.01

0.1

1 10 100

Percent Less Than or Equal ToTotal Phosphorus, mg/L

Raw Influent Final Effluent 0.1 50 40 302010 5 1 2 0.5 0.05 60 70 80 90 95 98 99 99.5 99.95 99.9 Mean = 0.139 mg/L Std. Dev. = 0.03 mg/L C.O.V. = 21%

Figure 3-15. Kelowna, British Columbia: Monthly average frequency curves for TP.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 3 - Case Studies and Reliability Factors 3-19 Kelowna, BC Monthly Average Frequency Curves for Ammonia-N

0.1

1 10 100

Percent Less Than or Equal ToNitrogen, mg/L

Raw Influent Ammonia-N Final Effluent Ammonia-N 0.1 5040302010 5 1 2 0.5 0.05 60 70 80 90 95 98 99 99.5 99.9599.9 Mean = 0.575 mg/L Std. Dev. = 0.26 mg/L C.O.V. =45%

Figure 3-16. Kelowna, British Columbia: Monthly average frequency curves for ammonia nitrogen.

Kelowna, BC Monthly Average Frequency Curves for Total Nitrogen

0.1

1 10 100

Percent Less Than or Equal ToNitrogen, mg/L

Raw Influent TN Final Effluent TN 0.1 50403020 10 5 1 2 0.5 0.05 60 70 80 90 95 98 99 99.5 99.9599.9 Mean = 4.38 mg/L Std. Dev. = 0.51 mg/L C.O.V. =12%

Figure 3-17. Kelowna, British Columbia: Monthly average frequency curves for TN.Municipal Nutrient Removal Technologies Reference Document September 2008

3-20 Chapter 3 - Case Studies and Reliability Factors The annual production of VFA is equivalent to 10 mg/L in the influent to the bioreactor from the fermenters. Other source s of VFA in the plant included centrate from dewatering, primary effluent, and in fluent, all of which added up to the equivalent of 7 mg/L as an average. Th e target VFA was 4–8 mg VFA/mg for soluble phosphorus removed. The VFA-rich fermente r supernatant (17 mg /L) was directly discharged to the anaerobi c zone, ensuring a steady feed of VFA to the phosphorusaccumulating organisms (PAOs).

3. A step-feed of influent is split equally fo r both the anaerobic and anoxic zones. This process has evolved from the 5-stage Barde npho, with the modificat ions resulting in shorter HRT (10 hours) and SRT (10 days). The HRT of the an aerobic zones was reduced from 3 hours to 1 hour with the dir ect addition of VFA and primary effluent.

4. Like the Central Johnston County, North Caro lina, and Lee County, Florida, facilities, this facility used a denitrif ication blanket in the clarif ier. The average depth ranged between 2 and 3 feet. Nitrat e reduction in the RAS blanket up to 6 mg/L did not create rising sludge concerns. This allowed minimal potential for nitrate return to the anaerobic zone.

5. The denitrification was controlled by con tinuously monitoring ORP at the end of the anoxic zone. These data were fed into the co mputer system to ensure that a sufficient amount of primary effluent was diverted to the anoxic zone to m eet the nitrate load from the nitrified internal recycle flow. Th e average was approximately 50 percent of the primary effluent.

6. The Kelowna plant operates under extremely low temperatures. A monthly average low temperature of 13 degrees Celsius (° C) was observed during the months of January and February. A high temperatur e of 22 °C was recorded in August.

7. The facility has an especially flexible de sign. Of the 21 bioreactor cells, 17 have dual equipment––mixers and diffusers. This allows each cell to have the ability to be operated as a swing zone, which was expensiv e but offers great fl exibility for changes in wastewater and permit requirements.

8. Recycle loads from dewatering were minimi zed by maintaining sepa rate processes for secondary sludge and primary sludge. No sl udge digestion was practiced. The total recycle loads from dewatering were only 13 percent in TP and 0.1 percent in TN.

9. Wet-weather flows were managed under th e normal mode of operation, using the equalization basin. The collection system was separated, and the seasonal variation was not very significant. The maximum m onth flow was 10 percent higher than the average flow. The total basin capacity was e quivalent to 7.5 percent of the influent design flow rate.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 3 - Case Studies and Reliability Factors 3-21 Case Study No. 7: Fairfax County, Virginia The Noman M. Cole facility in Fairfax County, Virginia, uses a step-feed activated-sludge process with a tertiary filt er with ferric chloride addition. The NPDES permit limits are 1.0 mg/L for ammonia nitrogen in summer and 2.2 mg/L in winter, and 0.18 mg/L for TP on a monthly basis. The facility is not required to report TN, but it started a voluntary program in anticipation of the future limit as a part of the Chesapeake Bay Initiative.

This facility was expanded from the existi ng step-feed activated-s ludge plant in 2002. The new design capacity of the plant is 67 M GD, and the annual average flow was 47 MGD during the evaluation year. The wastewater is settled in the prim ary tanks, treated by activated sludge with three to four feed points, settled again in the tertiary clarifier, and filtered before disinfection by chlorination and dechlorination. The secondary effluent is equalized up to 13.2 MG. The tertiary filters co nsist of the old, dual-media units and the new, deep mono-media filters. The headworks area also has retention basins with a capacity of 5.7 MG and an equalization basin with 4 MG, which together are equivalent to 15 percent of the average flow. The secondary sludge is thicke ned by DAF. The primary sludge is fermented in the gravity thickeners, which operate at an HRT of less than a day and a sludge age of 3 days. The fermented primary sludge and thickened secondary sludge were mixed together for dewatering by centrifuge, followed by incineration.

Noman M. Cole Pollution Control Plant - Fairfax County, VA Monthly Average Frequency Curves for Total Phosphorus

0.01 0.1

1 10 100

Percent Less Than or Equal ToTotal Phosphorus, mg/L

Raw Influent Primary Influent Primary Effluent Secondary Effluent Tertiary Clarifier Influent Tertiary Clarifier Effluent Final Effluent 0.1 504030 20 10 5 1 2 0.5 0.05 60 70 80 90 95 98 99 99.5 99.95 99.9 Mean = 0.086 mg/L Std. Dev. = 0.018 mg/L COV = 21%

Figure 3-18. Noman M. Cole Pollution Control Plan t, Fairfax County, Virginia: Monthly average frequency curve for TP.Municipal Nutrient Removal Technologies Reference Document September 2008

3-22 Chapter 3 - Case Studies and Reliability Factors Noman M. Cole Pollution Control Plant - Fairfax County, VA Monthly Average Frequency Curves for Ammonia Nitrogen

0.01 0.1

1 10 100

Percent Less Than or Equal ToNitrogen, mg/L

Raw Influent - Ammonia N Final Effluent - Ammonia N 0.1 50 4030 20 10 5 1 2 0.5 0.05 60 70 80 90 95 98 99 99.5 99.95 99.9 Mean = 0.12 mg/L Std. Dev. = 0.016 mg/L COV = 14%

Figure 3-19. Noman M. Cole Pollution Control Plan t, Fairfax County, Virginia: Monthly average frequency curve for ammonia nitrogen.

Noman M. Cole Pollution Control Plant - Fairfax County, VA Monthly Average Frequency Curves for Nitrogen

0.1

1 10 100

Percent Less Than or Equal ToNitrogen, mg/L

Raw Influent - TKN Final Effluent - Total N 0.1 50403020 10 5 1 2 0.5 0.05 60 70 80 90 95 98 99 99.5 99.95 99.9 Mean = 5.25 mg/L Std. Dev. = 0.63 mg/L COV = 12%

Figure 3-20. Noman M. Cole Pollution Control Plan t, Fairfax County, Virginia: Monthly average frequency curve for TN.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 3 - Case Studies and Reliability Factors 3-23 The plant performed well with good reliabi lity. The COV was 21 percent for TP on a monthly basis at a mean concentration of 0.09 mg/L. The COV for ammonia nitrogen was 14 percent at a mean concentration of 0.12 mg/L N. The COV was 12 percent for TN on a monthly average at a mean concentration of 5.25 mg/L. This facility included three feed locations with a 40, 40, and 20 percent flow split in the old plant and four feed points with a 25 percent split in the new plant, with an anoxi c zone in each feed point, which provides an opportunity to denitrify rapidly wi th carbon present in wastewater.

Contributing factors for this group of facilities include the following:

1. The wastewater characteristics were fa vorable. The BOD-to-TP ratio and BOD-toTKN ratio were 29.5 and 5.4, respectively.

2. The step feed is unique in providing a dedicated carbon supp ly and three anoxic cycles for better nitrogen removal. Caustic soda is fed to supplement the alkalinity deficiency in the wastewater.

3. Phosphorus removal is achieved in three st eps: biological removal in activated sludge, chemical removal in tertiary clarifier, and then tertiary filters.

4. Primary sludge is fermented in gravity thickeners with an SRT of 3 days and HRT of approximately 1 day. The units are operated between the hours of 8 a.m. and 2 p.m., when the greatest amount of ammonia re aches the plant. The VFA production was equivalent to 10 mg/L by chemical oxyge n demand in the primary effluent. The VFAs consist of 33 percen t acetic acid, 49 percent pr opionic acid, and 18 percent others. VFAs produced in this way are fed to the anoxic zones of the activated-sludge

process.
5. Secondary sludge is thickened by DAF, t hus minimizing the release of phosphorus and ammonia.

6. The plant design already includes recy cle flows and loadings. They include 10 percent in BOD, 19 percent in TSS and 23 percent in TP. All tanks and processes are sized to include these loadings, which is a conservative approach. Lime is added to the cake up to 13 percent by weight to minimize these recycle loads back to the plant.

7. Wet-weather operation follows the normal mode of operation. Th e facility manages the wet-weather flow in four distinct steps: at the retention basins first, then equalization at the headworks, step-feed ac tivated sludge, and finally equalization of the secondary effluent. Because the facility is a step-feed f acility, the process is more stable than that at other plants. The equali zation basins were desi gned to divert flow at 1.6 times the average flow and then agai n in the secondary effluent before the tertiary clarifiers.Municipal Nutrient Removal Technologies Reference Document September 2008

3-24 Chapter 3 - Case Studies and Reliability Factors 

### 3.2.3 Phosphorus Removal Low Level (less than 0.1 mg/L) There are two case studies for this level of pe rformance, one with bot h biological phosphorus removal and chemical phosphorus removal (Clark County, Nevada) and the other characterized as having bi ological phosphorus removal (Kalispell, Montana).

Case Study No. 8: Clark County, Nevada The Clark County, Nevada, facility uses an anoxic and then oxygenated (anoxic/oxic, or A/O) process with primary sludge thickening for VFA production and tertiary filters with alum feed. This facility was expanded from 88 MGD to 110 MGD in 1995 for the A/O process to meet daily load lim its on nutrients. The limits are equivalent to an ammonia limit of 0.56 mg/L and a phosphorus limit of 0.19 mg/L at 110 MGD. The facility treated 95 MGD during the evaluation period. Clark County made these vo luntary efforts to reduce phosphorus during the evaluation period to the lowest possible concentration.

The facility has two plants––the Central Plant (CP) and the Advanced Waste Treatment Plant (AWT). The wastewater is settle d at primary tanks, treated in the A/O process, filtered, and disinfected by UV irradiation and sent either to reclaimed-wate r users or to Las Vegas Wash and eventually to Lake Meade. The AWT has tert iary clarifier ahead of its filter, whereas the CP does not. The tertiary filter at the AWT does not have air scour, whereas the CP filter has air scour capability. Ferric chloride is added into the primary clarifiers for odor control, while alum is added to both the tertiary clarifiers and tertiary filters. The secondary sludge is thickened by DAF, stored together with primar y sludge, and dewatered by a belt filter press. The cake is sent to a landfill.

The facility produced low concentration phosph orus and ammonia in the effluent with good reliability. The COV was 30 percent on the aver age concentration of 0.099 mg/L in TP and 14 percent on the average ammonia concentratio n of 0.12 mg/L. The daily limits were met in accordance with the permit, at 0.22 mg/L fo r TP and 0.57 mg/L for ammonia nitrogen.

Contributing factors for this facility include the following:

1. The wastewater characteri stics were favorable. The BOD-to-TP ratio was 29.8 for the year and ranged from 26.5 to 34.2 on a monthly basis.

2. VFA generation was achieved in the prim ary settling tanks. The practice was based on thickening the sludge up to 5 percent total solids (TS). The upper limit was 6 percent; and higher percen tages should be avoided.

3. The A/O process parameters were optim ized for the SRT and RAS flow rate seasonally. The clarifier operated with a mi nimal sludge blanket—less than 6 inches. The automation and computer controls incl ude DO control at 0.5 mg/L using multiple probes on all nine basins with WAS management on a daily basis. The critical time ofSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 3 - Case Studies and Reliability Factors 3-25 the year is when the temperature rises above 110 degrees Fahre nheit (°F) and oxygen transfer becomes less efficient.

4. Biological phosphorus removal by the A/O process followed by chemical addition reduced overall chemical sludge generation.

5. Waste secondary sludge was thickened in the DAF unit, thereby minimizing phosphorus release because of anaerobic conditions.

6. Alum was added to the tertiary clarifier in the AWT and alum was added again to the tertiary filter to minimize secondary release of phosphorus in the filters.

7. Recycle loads were minimized by daily pro cessing of all sludge (a no storage policy), ferric addition to the filtrate from dewate ring, DAF thickening of the WAS, and not digesting sludge on-site.

8. The plant follows the normal operating pr ocedures during wet-weather events in August and September.

Clark Co. Water Reclamation Plant - Las Vegas, NV Monthly Average Frequency Curves for Total Phosphorus

0.01

0.1

1 10 100

Percent Less Than or Equal ToTotal Phosphorus, mg/L

0.1 504030 20 10 5 1 2 0.5 0.05 60 70 80 90 95 98 99 99.5 99.95 99.9 Mean = 0.0995 mg/L Std. Dev. = 0.0297 mg/L COV = 30%

Figure 3-21. Clark County Water Reclamation Plant, Las Vegas, Nevada: Monthly average frequency curve for TP.Municipal Nutrient Removal Technologies Reference Document September 2008

3-26 Chapter 3 - Case Studies and Reliability Factors Clark Co. Water Reclamation Facility Monthly Average Frequency Curves for Nitrogen

0.1

1 10 100

Percent Less Than or Equal ToNitrogen, mg/L

Raw Influent - TKN Final Effluent - Total N 0.1 50403020 10 5 1 2 0.5 0.05 60 70 80 90 95 98 9999.5 99.9599.9 CP Mean =15.4 mg/L Std. Dev. = 0.54 mg/L COV = 3.5%

Figure 3-22. Clark County Water Reclamation Plant, Las Vegas, Nevada: Monthly average frequency curve for TN.

Clark Co. Water Reclamation Facility Monthly Average Frequency Curves for Ammonia Nitrogen

0.01

0.1

1 10 100

Percent Less Than or Equal ToNitrogen, mg/L

Raw Influent - TKN Final Effluent - Total N 0.1 50403020 10 5 1 2 0.5 0.05 60 70 80 90 95 98 99 99.5 99.9599.9 CP Mean =0.12 mg/L Std. Dev. = 0.0116 mg/L COV = 14%

Figure 3-23. Clark County Water Reclamation Plant, Las Vegas, Nevada: Monthly average frequency curve for ammonia nitrogen.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 3 - Case Studies and Reliability Factors 3-27 Case Study No. 9: Kalispell, Montana The Kalispell, Montana, facility uses a modified University Cape Town (UCT) process with a fermenter and an upflow sand filter. The NPDES permit specifies a monthly limit of 1 mg/L in TP and an ammonia limit of 0.14 mg/L N. The facility was designed for 3 MGD and treated 2.8 MGD during this evaluation year. The wastewater is settled in the primary tanks, treated in the modified UCT process, filtered, a nd then disinfected using ultraviolet radiation before discharge. The primary sludge is ferm ented before anaerobic digestion. The secondary sludge is thickened by DAF. The thickened seco ndary sludge and digest ed primary sludge are dewatered together by a belt filter pre ss and then trucked o ff-site for composting.

The plant operated very efficiently and re liably. The COV was 19 percent on a monthly average basis at the mean concentration of 0.12 mg/L TP. The COV for ammonia nitrogen was 0 percent, below detection at all periods. The effluent co ncentrations in the maximum month were 0.15 mg/L for TP a nd 0.07 mg/L for ammonia nitrogen.

The unique features of this facility are as follows:

1. The wastewater characteri stics were favorable. The BOD-to-TP ratio was 55, much higher than the value of 25 reported favorable in the literature. No nitrogen removal is required at this facility.

2. A 2-stage fermenter was installed to ensure a definite supply of VFAs in anticipation of low winter temperatures and increa sed flows during the spring snowmelts and rainfalls. The fermenter took the primary sl udge and operated at an SRT of 5 days and an HRT of 7 to 21 hours. The unique system allows independent control of HRT and SRT. The HRT is controlled by adjusti ng fermenter volume, while the SRT is controlled by a function of th e mass of solids lost from th e primary clarifier and the volume of fermented sludge wasted daily from the fermenter. The VFA production was estimated to be equivalent to 18 mg/L at 20 °C and 13 mg/L at 13 °C.

3. The bioreactor has been optimized for SRT and HRT, and the RAS is now designed to maintain a target mixed liquor suspende d solids level in the aeration basin. A noblanket policy has been applie d to the clarif ier operation.

4. The WAS is thickened in DAF units and t hus kept aerobic to minimize release of phosphorus, before it is dewatered by belt filter press. Although this facility nitrified fully down to the detection limit (at 0.07 mg/L ), denitrification was not required and thus was not practiced. The COV for amm onia nitrogen was 0 percent at the mean concentration of 0.07 mg/L as nitrogen. The COV was 31 percent at the mean concentration of TN of 10.6 mg/L.

5. Both digester supernatant and filtrate from dewatering returned to the plant’s headworks. The ortho-phosphorus in these st reams averaged 6 percent of the plant’s influent TP.Municipal Nutrient Removal Technologies Reference Document September 2008

3-28 Chapter 3 - Case Studies and Reliability Factors 6. The equalization basin was sized to stor e 12.5 percent of the plant influent. The normal mode of operation is mainta ined during wet-weather periods.

Figure 3-24. Kalispell, Montana: Monthly average frequency curve for TP.

Figure 3-25. Kalispell, Montana: Monthly aver age frequency curve for ammonia nitrogen. 0. 01 0.1

1 10 100

Raw Influent Fi na l Ef f l uent 0.1 50 40 30 2010 5 1 2 0.5 0. 0 5 6 0 7 0 8 0 9 0 9 5 98 99 99.5 99. 95 99.9 Mean = 0.121 mg/ L Std. De v . = 0.023 mg/L C.O.V. = 19% Kalispell, MT M on t h ly A v e r a g e Fr e qu ency Cu r v es f or To tal P ho s phorus

Percent Less Than or Equal To T otal Phosphorus, mg/ L

Kalispell, MT Monthly Average Frequency Curves for Ammonia Nitrogen

0.0 0.1 1.0 10.0 100.0

Percent Less Than or Equal To Ammonia Nitrogen, mg/L

Raw Influent Final Effluent 0.1 50 40302010 5 1 2 0.5 0.05 60 70 80 90 95 98 99 99.5 99.9599.9 Mean < 0.07 mg/L Std. Dev. = 0.00 mg/L C.O.V. = 0%September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 3 - Case Studies and Reliability Factors 3-29 Figure 3-26. Kalispell, Montana: Monthly average frequency curve for TN.



### 3.3 Reliability Factors

3.3.1 Wastewater Characteristics

BOD-to-TP and BOD-to-TN Ratios The BOD-to-TP ratios ranged between a low of 26.6 at Kelowna and a high of more than 50 at Kalispell on average for the year. There were monthly variat ions in these ratios at each facility because of weather conditions and the sewer system. The monthly variations in Fairfax County, Virginia, are shown in Table 3-3. To make the extent of variations clearer, the BOD-to-TP (or BOD-to-TKN) ratios were no rmalized by dividing the monthly values by the average of those values. This shows that the relative variation in values was small, between 90 percent and 110 percen t of the average. The BOD-to-TP ratio remained between 28 and 33.5 in the plant influent and 24.4 and 33.8 in the primary effluent.

The BOD-to-TKN ratios ranged between a low of 4.3 at North Cary to a high of 10 at the Central Johnston County, North Carolina. Th e BOD-to-TKN ratio varied between 4.6 and 6.1 at Fairfax, Virginia, as shown below.

Table 3-3 shows that the BOD-to-T P ratio in the primary effluent went down as low as 24 in some months at the Fairfax, Virginia. The Nort h Cary and Central Johnston plants, as well as the Fairfax County plant, decided to use EBPR and installed fermenters to ensure reliable operation. At the Clark County, Nevada, facility , the BOD-to-TP ratio was noted as a low 29 for the annual average and the primary settling tanks were converted to a thickener/fermenter for VFA generation. Kalispell, MT Monthly Average Frequency Curves for Total Nitrogen (Goal)

0.01 0.1

1 10 100

Percent Less Than or Equal To Ammonia Nitrogen, mg/L

Raw Influent Final Effluen t 0.1 50403020 10 5 1 2 0.5 0.05 60 70 80 90 95 98 99 99.5 99.95 99.9 Mean = 10.6 mg/L Std. Dev. = 3.31 mg/L C.O.V. = 31%Municipal Nutrient Removal Technologies Reference Document September 2008

3-30 Chapter 3 - Case Studies and Reliability Factors Table 3-3. Monthly variation of wastewater characteristics at Fairfax County, Virginia

Date INF BOD-to-TP Normalized by avg PE BOD-to-TP Normalized by avg INF BOD/TKN Normalized by avg Jan-06 33.1 1.1 29.8 1.0 6.1 1.1
Feb-06 33.7 1.1 29.5 1.0 5.4 1.0
Mar-06 28.3 0.9 27.4 1.0 5.3 1.0 Apr-06 28.2 0.9 27.1 0.9 5.5 1.0 May-06 27.2 0.9 26.8 0.9 4.7 0.9
Jun-06 28.9 1.0 24.4 0.9 5.5 1.0
Jul-06 28.8 1.0 26.1 0.9 5.9 1.1 Aug-06 29.4 1.0 28.1 1.0 4.6 0.9 Sep-06 31.5 1.0 32.4 1.1 5.0 0.9 Oct-06 33.5 1.1 33.8 1.2 4.9 0.9
Nov-06 32.2 1.1 32.0 1.1 5.4 1.0
Dec-06 28.2 0.9 26.3 0.9 5.4 1.0 Avg 30.3 28.7 5.3

The low temperatures encountered by the cas e study facilities during the study period were 10 °C and 13 °C at the Kalispell, Montana, and Kelowna, British Columbia, facilities, respectively. Much warmer conditions occurred at plants in Florida.

At those facilities that depend on methanol feed for nitrogen removal or chemical feed for phosphorus removal, however, these characteri stics in BOD (i.e., BOD-to-TP or BOD-toTKN ratio) were not as critical in design or operation as at th e other facilities for reliable performance.



### 3.3.2 Fermenter and VFA Generation

Three facilities had dedicated fermenters ; one used primary settling tanks for VFA generation. The reliability of EBPR was ensu red by having a fermenter in the facility.

• Kalispell, Montana, had a 2-stage fermente r with a variable SRT and HRT up to an SRT of 3–5 days with an HRT of 24 hours or less.

• Kelowna, British Columbia, and Fairfax C ounty, Virginia, had gravity thickeners converted with an SRT of 3 to 5 days. The HRT averaged approximately 1 day (a 24-hour period).

• Clark County, Nevada, had primary settling ta nks successfully serving as thickeners and fermenters at total solids concentrations of 5 percent.

The other facilities relied on VFAs found in the influent or generated fr om in-plant recycles.

The goal was to produce VFA of 18 mg/L in the influent to bioreactors so that a VFA-tophosphorus ratio of 4 or higher could be main tained. Among these facilities, Kalispell andSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 3 - Case Studies and Reliability Factors 3-31 Kelowna had biological phosphorus removal (no chemicals) and produced an annual average of 0.12 and 0.13 mg/L with COVs of 19 and 21 percent, respectiv ely. Other facilities achieved lower concentrations but require d chemical addition, filtration, or both.



### 3.3.3 Bioreactor Design and Process Parameters The case studies demonstrated a range of pr ocess parameters that were designed in accordance with industry standards or were uniquely developed by plant personnel. These parameters are summarized below.

1. SRT and HRT : The bioreactor systems for the case study plants have a wide range of SRTs, from 5 days and more than 40 days in warm months to between 9 and 60 days in cold months. The Kelowna system was optimized for nutrient removal through the use of a denitrifying sludge blanket; when the system was operated in step-feed mode, shorter SRTs and HRTs were possible than in other systems. The HRTs ranged from 10 hours in Kelowna to 20 hours in Clearwater, Florida.

2. Denitrifying sludge blanket in secondary clarifier : A denitrifying blanket is maintained in three facilities. Den itrifying blankets ensured good phosphorus removal, alkalinity recovery, and shorteni ng the anoxic zone in the bioreactor. Two facilities, however, maintain a no-blanket policy; the conc ern is secondary release of phosphorus (Kalispell and Clark County).

3. Step-feed mode : For both nitrogen and phosphorus removal, primary effluent was a good source of carbon, and thus the step-feedi ng of primary effluent accelerated the biological activities and reduced the size of the anoxic z one requirement. The feed locations varied from two at Kelo wna to four at Fairfax, Virginia.

4. Flexible design/swing zones : The reliability of the biological process increases significantly in facilities with built-in swing zones. Kelowna and Clearwater have swing zones, and they allow adjustment on the basis of changing wastewater characteristics as well as the treatment obj ective. Kelowna evolved from the classic 5-stage Bardenpho to a 3-stage Westbank process using flexible design. It treats 70 percent more flow in the same original tanks. Clearwater has the flexibility to operate in either 5-stage Bardenpho mode for nitrogen and phosphorus removal or 4-stage Bardenpho mode for nitrogen remova l. North Cary has the flexibility of separate mixing and aeration in the oxid ation channel and thus can operate in accordance with wastewater flow and dema nd (summer vs. winter, or wet vs. dry days).

5. Carbon source : All the facilities us e the internal carbon pres ent in the wastewater, although some facilities have fermenters to increase VFA production. Three facilities use external carbon sources to support den itrification: two (Cen tral Johnston CountyMunicipal Nutrient Removal Technologies Reference Document September 2008

3-32 Chapter 3 - Case Studies and Reliability Factors and Lee County) use denitrif ying filters and one (Western Branch) uses denitrifying activated sludge.

6. Automatic controls and sensors : In all facilities, DO contro l is universally practiced. All activated sludge plants have a network of DO probes and use the resulting data in making daily decisions on operation and contro l. Nitrate and ORP se nsors are used in the facilities that remove nitrogen. Nitrate probes are in used in Central Johnston County, Clearwater, and Kelowna. An OR P probe is used in Clearwater and Kelowna. Standard procedures include targ et values for ORP, nitrate nitrogen, and DO for best nitrogen removal in these facilities.

7. WAS management : Sludge blanket meters are used in Clearwater, Florida, and Clark County, Nevada. At the Clark County facili ty, the plant comput er (following preprogrammed operating criteria) makes daily WAS decisions for each of the nine activated-sludge units. At other facilities, samples are analyzed and operating decisions are made accordingly, with excellent results.

8. Denitrification filter : Central Johnston County, North Carolina, and Lee County, Florida, both employ downflow denitrific ation filters with supplemental carbon supplied by an automated methanol feed system. Both facilities pump the filter effluent to the next treatment process. Both systems have good reliability for both nitrogen removal and phosphorus rem oval to low levels via filtration.



### 3.3.4 Secondary Sludge Thickening Secondary sludge thickening is one of the key factors in maintaining EBPR and minimizing the negative effect of recycle lo ads on the facility. For those facilities with EBPR, all but one uses DAF or a rotary-drum thicke ner and avoid phosphorus release.



### 3.3.5 Sludge Digestion Sludge digestion is a critical element in reduc ing the recycle loads to the facility. Three facilities digest sludge aerobi cally: Central Johnston County, North Carolina; Lee County, Florida; and North Cary, No rth Carolina. The plants thereby minimize phosphorus and nitrogen release that would otherwise o ccur under anaerobic conditions. The Kalispell, Montana, facility digests primary sludge, but not secondary sludge, anaerobically. The remaining facilities digest sl udge anaerobically and thus incr ease the recycle loads to the main plant. Two of these fac ilities, Kelowna and Fairfax County, have the capability to add lime to the cake and thus reduce the recycle of phosphorus. Kelowna eventually ceased lime addition when the recycle loads become low enough to manage.



### 3.3.6 Recycle Fl ows and Loads All facilities with tertiary f ilters have provisions to equalize backwash water through existing or new tanks. The filtrate from dewatering is se nt back to the main plant and could imposeSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 3 - Case Studies and Reliability Factors 3-33 significant nutrient loads. Recycle loads were observed to range be tween 13 and 30 percent of TP and TKN, respectively.

The best cases for recycle loads were found at the Central Johnston County, North Carolina, and Lee County, Florida, facilities, where the secondary sludge is aerobically digested and sent away for off-site processing. These facilities do not prac tice primary settling.

The next-best case was found at the Kelown a, British Columbia, facility, where the secondary sludge is thickened aerobically with DAF and stored separately from the primary sludge. The primary sludge is fermented and st ored for joint dewatering with the thickened secondary sludge. The final cake is sent away for composting. The recycle loads at Kelowna were the lowest of all the case study facilitie s at 13 percent of the influent TP load and 0.1 percent of the influent TN load.

The next best case was Western Branch, Ma ryland, where all the sludge is thickened aerobically by DAF, dewatered by centrifuge, and bur ned in incinerators. It is notable that recycle loads are received from dewatering back to the main plant but not from secondary sludge handling.

The next best case was found at the North Cary, North Carolina, facility, where the secondary sludge is digested aerobically and dewatered.

The next best case was found at Fairfax Count y, Virginia, where the secondary sludge is thickened aerobically while th e primary sludge is fermented; the fermented primary sludge and the thickened secondary sludge are combin ed for dewatering. Lime can be added to reduce the phosphorus recycle lo ad. The plant was designed to handle recycle loads of 13 percent of influent TP and BOD and 30 percent of influent TSS.

The next best case was found at the Clark C ounty, Nevada, facility, where the secondary sludge is thickened aerobically and stored wi th the fermented primary sludge; they are subsequently dewatered together. Ferric chloride is added to the sludge feed.

Two facilities operate anaerobic sludge dige stion and thus increase the opportunity for recycling ammonia nitrogen and phosphorous to the plant headwork s. The Kalispell, Montana, facility digests primary sludge only before dewatering, and th e Clearwater, Florida, facility digests both primary a nd thickened secondary sludge.



### 3.3.7 Wet-Weather Flow Management
Equalization Basin
Three facilities have some form of flow equalization. Fairfax County, Virginia, has two basins: one at the headworks ar ea and one at the secondary e ffluent. They have capacities representing 11 percent and 20 pe rcent of influent daily flow, respectively. North Cary, NorthMunicipal Nutrient Removal Technologies Reference Document September 2008

3-34 Chapter 3 - Case Studies and Reliability Factors Carolina, has a large-capacity basin at the headworks. All told, the plant could equalize 28 percent of the influent daily flow by using the basin and existing unused tanks. Kelowna, British Columbia, has a basin with a capacity of 7.5 percent of the daily primary effluent flow. These basins ensure steady operation of the facility under high-flow conditions by reducing hydraulic surges in the settling tanks, providing stable chemical feed, and maintaining reliable process controls, where automated.

Process Design Three plants have processes that have inhere nt advantages during hi gh-flow periods. Fairfax County, Virginia, and Kelowna, British Colu mbia, both have step-feed activated-sludge systems, which means that high flows can be distributed through the aeration basins better than with a conventional feed plant. North Car y, North Carolina, has a PID, which offers the operators the ability to adjust the cycl e time during wet-weather flow conditions.

Mode of Operation Under emergency conditions, plan t personnel can shut down porti ons of the aeration basins and thereby prevent solids fr om overloading the clarifiers, potentially causing a loss of biomass. The recovery back to normal operation is thereby ensured with the secured biomass inventory. The shutdown can be accomplished manually or by preprogrammed modes of operation.



### 3.3.8 Tertiary Filters All facilities have tertiary filters, which help the facilities meet low TP concentration limits. Central Johnston County and Lee C ounty, Florida, have denitrific ation filters, which differ from the traditional filters used at other locatio ns. The filters at the other locations include rapid sand filters (two locations); dual-media f ilters with anthracite and sand (four locations); a deep mono-media filter (one location), and a dual sand filter (one location). More details can be found in Chapter 2 of this manual.



### 3.3.9 Tertiary Clarifier Two facilities have tertiary clarifiers. Fairfax County, Virginia, has a tert iary clarifier before the tertiary filters. Ferric chlori de is added to the clarifier to aid settling. The sludge from this process is recycled to the plant headwork s. At Clark County, Nevada, the AWT plant operates a tertiary clarifier ahead of the sand filt er. Alum is fed to the clarifier to aid settling. The sludge from this clarifier is thickened befo re being recycled to the headworks. For both facilities, the use of tertiary clarification provi des added reliability for the subsequent tertiary filter operations.

Table 3-4 presents the wastewat er characteristics and treatm ent processes of the case study facilities.September 2008 Municipal Nutrient Removal Technologies Reference Document

Chapter 3 - Case Studies and Reliability Factors 3-3 5Table 3-4. Case study facilities’ treatment processesFacilityFairfax,VAKalispell,MTClarkCo., NVCentralJohnston, NCN. Cary,NCKelowna,BCClearwater,FLLee Co.FLWesternBranch, MDWastewater characteristicsBOD-to-TP ratio29.5 54.9 29. 55.1 31.6 26.637.5 34.8 89.7 (COD/TP)BOD-to-TKN ratio5.4 5.7 5.5 10. 4.35.36.74.0 13.9 (COD/TN)Temperature inoC15–25 10–20 20–29 14–27 16–27 13–22 23–31 30 13–23Equalization basin– percent of influentflow11.5–20 58 7.5Equalizationbasinlocation Raw/SE Raw RawBioreactorsBioreactor typeStep-feedASMod.UCTA/OASdenit. filterOxid. ditch Westbank BardenphoAS/denit. filterTriple ASSRT in bioreactor, days16–19 8–12 5–9 7-9 11–14 6–9 25–44 24–59 6–60Fermenter SRT, days34–5 primary No No 3–6NoNoSwing zonesyes yesyesyesyesMixing/aeration separated inbioreactoryes yesDenitrificationblanket yes yes yes yes yesDenitrificationfilteryes yesExternal carbon sourceMethanolMethanol MethanolAlkalinity supplementNaOHOnline DO probeyes yes yes yes yes yesyesyesyesOnline NO3probeyesyesyesOnline ORP probeyesyesOnline ortho-P probeyesyesTertiary TreatmentTertiaryclarifier yes yesTertiary filtersTertiary conventional sand filteryesyesTertiary dual-media filteryesyesyesyesTertiary deep mono-media filteryesTertiary dual sand filteryesMunicipal Nutrient Removal Technologies Reference Document September 2008

3-36 Chapter 3 - Case Studies and Reliability FactorsTable 3-4. Case study facilities’ treatment processes(continued)FacilityFairfax,VAKalispell,MTClarkCo., NVCentralJohnston, NCN. Cary,NCKelowna,BCClearwater,FLLee Co.,FLWesternBranch, MDSludge HandlingPrimary settling / yes or noyesyes yes NO NO yesyesNONOSecondary sludge thickening –aerobicDAF DAF DAF DAF Rotary drum DAFSec sludge gravitythickening/holdingyesSeparate secondary/primary sludgestorageyesNo dewatering on-siteyesOn-site aerobic sludge digestionyes yesYesOn-site anaerobic primary sludgedigestionYesOn-site anaerobic prim+sec. sludgedig.Yes YesNo on-site sludge digestionyes yesyesyesRecycle Streamschemical treatment offiltrate/centratelime FeCl3limeFiltrate/centrate recycle pointHDWKFilter Backwash recycle point primaryHDWK HDWKHDWK HDWKNotes:BOD-to-TP = biochemical oxygendemand-to-total phosphorus ratioBOD-to-TKN = biochemical oxygendemand-to-total Kjeldahl nitrogen ratioDAF = dissolved-air flotation unitDO = dissolved oxygenHDWK = headworksORP = oxidation-reduction potentialSE = Secondary effluentSRT = solids retention timeSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 3 - Case Studies and Reliability Factors 3-37 

### 3.4 Cost Factors

The costs incurred for the st udied facilities were analy zed to allow comparison on a consistent basis. Both capital and O&M costs were considered.



### 3.4.1 Capital Costs Capital costs incurred for nutri ent removal upgrades were provided by plant personnel at the studied facilities. If the upgrades were part of an overall program of upgrades at the plant (e.g., expansion, installation of UV disinfection), the best estimates were obtained of what was done for secondary treatment, tertiary filtration, and applicable sludge handling. The costs incurred in the past we re updated on the basis of the Engineering News-Record ’s Construction Cost Index, as provided in the U. S. Department of Agriculture Web site (USDA 2007). The capital costs for the plants are show n in Table 3-5. The land cost was not included in this evaluation.

The capital costs incurred for the biological nut rient removal (BNR) projects were allocated among phosphorus removal, nitrogen removal, and BOD removal. The allocation was done as follows:

1. If costs for particular pieces of equi pment specifically for one nutrient could be obtained, that cost was allocated entirely to that nutrient. For example, the cost of the fermenter used at Kalispell was known and attributed entirely to phosphorus removal. Another example is denitrificaiton f ilters entirely for nitrogen removal.

2. If particular pieces of equipment could be allocated to two nutrients, that was done with an even split. For example, the mixers used at Kalispell were just for anoxic tanks, where nitrogen and BOD would be re moved. In other cases, the installation was clearly for both phosphorus and nitrogen removal.

3. For all instances where no equipment brea kout was available or the equipment would go toward all treatment, the costs were allocated by the percentages 12 percent to phosphorus, 48 percent to nitrogen, and 40 perc ent to BOD. This allocation was based on an estimate-of-cost breakdown for Kelowna and provided a consistent basis for comparing relative costs. For denitrifying filte rs, all the BOD percentage was attributed to nitrogen, making the sp lit 12 percent phosphorus and 88 percent nitrogen.

4. For Clearwater (Marshall St reet), the cost fractions were 17, 63, and 20 percent for phosphorus, nitrogen, and BOD, respectively. In that instan ce, the total cost of the BNR upgrades was known, as were the vol umes of the various vessels. Those volumes were attributed to phosphorus or nitrogen removal (fermenter to phosphorus, anoxic basins to nitrogen), while the aeration basin wa s apportioned 10 percent for phosphorus, 50 percent for nitrogen, and 40 perc ent for BOD. The fraction of the total volume for each nutrient was used for the cost apportionment.Municipal Nutrient Removal Technologies Reference Document September 2008

3-38 Chapter 3 - Case Studies and Reliability FactorsTable 3-5. Case study facilities’ capital costsFacilityFairfax, VAKalispell, MTClarkCounty, NVCentralJohnston,NCNorth Cary,NCKelowna, BCClearwater,FLLee County,FLWesternBranch, MDDesignflowMGD 67 3 110 7 12 10.5 10 5 30InfluentP(mg/L) 6.4 4.1 5.8 5.8 7.7 6.0 5 3.85 3.7InfluentN(mg/L) 34.6 39.6 30.3 31.2 56.4 28.8 44.8 33.2 23.9Influent NH3-N(mg/L) 24.3 26.8 28 45.5 21.3 28 27.2 19.6Capital attributed to P(2007 dollars)$0 $1,190,000 $65,450,000 $889,000 $4,089,600 $6,818,000 $5,019,000 $480,000 $2,464,000Capital attributed to N(2007 dollars)$71,600,000 $4,310,000 $56,980,000 $2,400,000 $16,358,000 $27,273,000 $18,600,000 $13,460,000 $49,583,000Capital attributed toother (2007 dollars)$0 $3,600,000 $98,570,000 $0 $13,632,000 $22,728,000 $5,905,000 $11,630,000 $84,906,000Electrical attributed to P(kWh/yr)3,360,000 389,000 * 1,843,000 377,400 884,000 931,000 62,700 262,400Electrical attributed to P(dollars/yr)$185,000 $17,500 * $103,200 $17,400 $41,500 $102,400 $7,500 $26,200Electrical attributed to N(kWh/yr)18,060,000 1,077,000 * 4,169,000 2,558,000 4,100,000 4,623,000 1,911,500 8,865,000Electrical attributed to N(dollars/yr)$993,000 $48,500 * $233,500 $118,000 $193,000 $509,000 $192,000 $886,500Electrical attributed toother (kWh/yr)0 1,045,600 * 588,000 0 919,000 2,075,000 2,162,000 16,066,000Electrical attributed toother (dollars/yr)$0 $47,100 * $33,000 $0 $43,200 $230,000 $259,000 $1,607,000Chemical attributed to P(dollars/yr) (alum, ferric)$393,000 $5400 * $0 $0 $0 $7,400 $34,600 $107,000Chemical attributed to N(dollars/yr) (Methanol,pH control caustic asneeded)$250,000 $0 * $53,100 $0 $0 $0 $83,900 $425,000Sludge attributed to P(tons/yr) (alum/ferric orbiological uptake sludge)730 0 * 0 90 0 5.8 37.5 72.9September 2008 Municipal Nutrient Removal Technologies Reference Document

Chapter 3 - Case Studies and Reliability Factors 3-39Table 3-5. Case study facilities’ capital costs(continued)FacilityFairfax, VAKalispell, MTClarkCounty, NVCentralJohnston,NCNorth Cary,NCKelowna, BCClearwater,FLLee County,FLWesternBranch, MDSludge attributed to P(dollars/yr)$393,000 $0 * $0 $17,900 $0 $1,500 $21,900 $32,400Sludge attributed to N(methanol conversion)(tons/yr)0 0 * 60 1702 0 0 14.1 839Sludge attributed to N(dollars/yr)$0 $0 * $15,100 $341,000 $0 $0 $8,300 $372,000Total O&M attributed toP (dollars/yr)$970,000 $17,500 $3,004,000 $103,200 $35,300 $40,300 $109,800 $64,000 $165,000Total O&M attributed toN (dollars/yr)$1,243,000 $57,800 $3,852,000 $301,700 $230,000 $109,000 $509,000 $284,200 $1,311,000Annualized capital for P(6%, 20 years)$0 $168,100 $5,710,000 $51,000 $357,000 $595,000 $438,000 $41,900 $215,000Annualized capital for N(6%, 20 years)$6,240,000 $323,600 $4,970,000 $302,700 $1,426,000 $2,378,000 $1,620,000 $1,174,000 $4,324,000Unit O&M for TP ($/lb) $1.07 $0.49 $1.81 $1.48 $0.23 $0.27 $1.37 $1.77 $0.78Unit capital For TP ($/lb) $0.00 $2.84 $3.43 $0.73 $2.28 $3.97 $5.38 $1.16 $1.01Unit total for TP ($/lb) $1.07 $3.33 $5.24 $2.21 $2.51 $4.24 $6.76 $2.93 $1.79Unit O&M for TN ($/lb) $0.29 $0.19 $0.43 $0.49 $0.41 $0.14 $0.75 $0.91 $0.99Unit capital for TN ($/lb) $1.47 $1.46 $0.55 $0.49 $2.54 $3.05 $2.40 $3.87 $3.27Unit total for TN ($/lb) $1.76 $1.65 $0.98 $0.98 $3.36 $3.19 $3.15 $4.78 $4.26Unit capital cost($/gal/day)$1.07 $3.03 $2.01 $0.58 $2.84 $3.25 $2.95 $2.79 $1.73Note: Cost data available per unit operation;boldface type indicates actual dollar amounts.Municipal Nutrient Removal Technologies Reference Document September 2008

3-40 Chapter 3 - Case Studies and Reliability Factors The apportioned costs are detailed in each cas e study and summarized in Table 3-5. Table 3- 5 also presents the annualized capital cost for phosphorus and nitrogen, which was done at a 6 percent interest rate for 20 years.



### 3.4.2 Operation and Maintenance Costs The case studies considered only three categor ies of O&M costs: pow er/electrical usage, chemical usage, and the cost of disposing of extra sludge generated by the nutrient removal processes. All other costs, including labor, were excluded from c onsideration. Labor was excluded for three reasons:

1. Labor and energy costs are highly sensitive to local conditions, such as the prevailing wage rate, the relative strength of the local economy, the presence of unions, and so on; thus, they would only confound comparison of the inherent cost of various technologies.

2. For most processes, the incremental ex tra labor involved in carrying out nutrient removal is recognized but not significant, in view of the automatic controls and supervisory control and data acquisiti on (SCADA) system that came with the upgrades. For example, if an activated-sludge system is now to be operated to remove nutrients, the amount of monitoring, checking of basins, and making process decisions is very similar. Adding an entirely new process could require additional labor hours per week, but that is very s ite-specific and difficult to determine and compare. With nutrient removal upgrades, ma ny facilities added automation features along with SCADA system and thus the n eed for additional labor is minimal.

3. Additional labor-hour determination is di fficult because the plants were largely unable to break down which extra personne l were employed because of nutrient removal and related overtime costs.

Electrical costs were estimated on the basis of direct plant data or the power draw of the blowers/aerators, mixers, and pumps used for treatment. The power draw, in kilowatt-hours per year (kWh/year), was allocated among phosphorus, nitrogen, and BOD removal. The allocation was done in the same manner as capital allocation:

1. If the piece of equipment was for one nutri ent, those kWh/yr were allocated entirely to that nutrient. That was the case for mixers in an anaerobic tank or a fermenter.

2. For aeration blowers, the allocation of kWh was based on the oxygen demand by PAOs, nitrifiers, and standard heterotrophic organisms. In this manner, the allocation 10 percent for phosphorus, 50 percent for nitrogen, and 40 percent for BOD was developed.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 3 - Case Studies and Reliability Factors 3-41 For other pieces of equipment, the distributi on of kWh was the same as the main capital distribution: 12 percent for phosphorus, 48 perc ent for nitrogen, and 40 percent for BOD.

The electrical cost for each nutrient was determined by multiplying the kWh/year by the average electrical cost, as supplied by plant pe rsonnel. This average co st covers the actual consumption charge (kWh) and the peak dema nd charge imposed by the local utility.

If a plant had to add chemicals for nutrient re moval, the cost and amount of the chemicals were supplied for the case study. The chemicals used by these municipa lities were alum and ferric chloride for phosphorus removal and meth anol for denitrification. One plant (Noman M. Cole in Fairfax County, Virginia) also used sodium hydroxide as needed to control the pH following nitrification.

If a plant generated additional sludge because of nutrient removal, the cost of disposing of that additional sludge was included. In general, if an anaerobic or anoxic process is used for nutrient removal, the overall amount of sludge should go down compared to a fully aerobic process, and those processes inherently ge nerate less sludge. Add itional sludge would be generated if phosphorus was removed chemically or if methanol (or other external carbon source) was added for denitrif ication. The sludge yield of 0.2 lb/lb BOD was used for methanol feed, where applicable.

Table 3-5 presents the annual O&M estimates for nutrient removal at the case study facilities.



### 3.4.3 Unit Costs The annualized capital costs and annual O& M costs were normalized by dividing by the mass of nutrient removed during the study peri od. These normalized costs became the Unit O&M and Unit capital costs presented in Table 3- 5, with the cost expressed as dollars per pound of nutrient removed. The calculation was done for TP and TN. As a comparison, the unit capital cost for the BNR expansion was cal culated as the dollars per gallon per day capacity. The following observations can be made about the results in the table:

1. The unit O&M cost for TP ranged from $0.23 per pound for North Cary, $0.27 per pound in Kelowna, and $0.49 per pound in Kalis pell to $1.81 for Clark County at the high end. The low cost in North Cary is because of fully functioning biological phosphorus removal. The low costs for Kelo wna and Kalispell are because of those plants having fully functioning biological phosphorus removal aided by a fermenter (so chemicals are not needed). The trade-off for the low operating costs was higher capital costs ($3.05 per pound phosphorus and $1.48 per pound phosphorus for Kelowna and Kalispell, respectively). The capit al cost at North Ca ry was moderate at $2.35 per pound.

2. The capital cost range for TP was $0 for the Noman M. Cole plant in Fairfax County to high-end costs of $3.05 per pound for Kelowna, $3.27 per pound in WesternMunicipal Nutrient Removal Technologies Reference Document September 2008

3-42 Chapter 3 - Case Studies and Reliability Factors Branch, and $3.87 per pound in Lee Count y. The costs for installing phosphorus removal processes at Noman M. Cole, an olde r plant, were fully depreciated and were not available.

3. The unit O&M for nitrogen removal is low, with costs ranging from $0.14 to $0.99 per pound removed. Higher costs are associated with having to add chemical, while the plants with the lowest costs for nitroge n removal (Kelowna a nd Kalispell) are able to effect total nitrification and deni trification without chemical addition.

4. The capital cost for nitrogen removal is low, ranging from $0.49 to $3.87 per pound, with the lowest capital cost for TN removal at Central Johnston County, where the retrofit was based substantia lly on existing facilities with addition of denitrification filters. High-value locations involved major additions, a nd they included Lee County, Western Branch, and Kelowna, at $3.87, $3.27, and $3.05, respectively.

5. The overall unit capital cost for these plants on a flow basis ranged from $0.58/gallon per day (gpd) for Central Johnston County to $3.25/gpd for Kelowna.

The factors affecting cap ital costs are as follows:

1. The treatment to be added : The major factor is the availabi lity of existing facilities. In those facilities with available site and tanks, much can be retrofitted without significant cost. If a new bi ological treatment is added, however, it adds to higher capital cost. Chemical treat ment requires less capital.

2. Built-in flexibility in the design : Some plants include fermenters for EBPR or swing zones with two types of equipment and two modes of operation for nitrogen removal, such as the 4-stage and 5-stage Bardenpho process. The added flexibility increases capital costs but allows operators to poten tially reduce O&M costs through reductions in energy or chemical usage.

3. Equalization basin : Basins are expensive capital items but could reduce O&M costs because of lower peak demands for power and chemical.

4. Treatment of recycle flows : Equipment and buildings for lime or ferric addition are expensive.

5. The amount of automation : Depending on the size of the facility, this expense could be expensive but could be bene ficial in saving O&M costs.

6. Separate storage tanks for the seco ndary sludge from the primary sludge : This is an added cost at EBPR facilities to cons ider for control of recycle loads.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 3 - Case Studies and Reliability Factors 3-43 The factors affecting the O&M costs are the following:

1. Use of external supplemental carbon : If methanol must be purchased, that will tend to push the costs up, compared to use of in-stream carbon generated by a fermenter or fed to the anoxic zone by a step-feed mechanism.

2. Use of chemical for phosphorus removal : As with methanol a ddition, if the plant has to use chemical phosphorus removal to meet the discharge limit, it will tend to have a higher cost than if biological phosphorus removal can be used. Ideally, the biological phosphorus removal will use site-generat ed VFAs for the carbon source in the anaerobic zone; if such are not availabl e, chemical addition will be required, at greater cost.

3. Alkalinity Addition for nitrification . Caustic soda is added to supplement alkalinity in those areas with soft water (low alkalinity).

4. Use of a fermenter : In some cases, sufficient VFAs ex ist in the influent and in-plant recycle stream so that the EBPR does not need additional VFAs. If some must be added, they are typically generated by fe rmenting primary solids. This fermentation can take place in a dedicated unit that, theref ore, has associated operating costs, or in some cases, the fermentation can occur in a sludge thickener, with less electrical use than a dedicated unit.

5. Automation : Automation adds cost but could save O&M costs by optimizing power usage and chemical usage.



### 3.5 Summary

The performance and costs of the treatment pr ocesses at the nine case study facilities are summarized in the sections that follow.



### 3.5.1 Discharge Permits The discharge permits are diverse in the num ber of discharge seasons, allowable nutrient discharge limits, and averaging period. Some of these diverse permit requirements are based on TMDLs; others are based on a state policy for water reuse (such as Florida’s), or a regional goal (such as the goals for the Chesapeake Bay and the Long Island Sound).

An in-depth evaluation was made of full-scal e plant performance, and the performance was presented using a simple statistical basis for co mparison and interpretati on. The coefficient of variation, or COV, represents one standard deviation divided by the mean. With this, all performance data for one year were pr esented for these selected facilities.

All nine facilities provided one year of data, a nd the monthly average values were used in the summary as the base. Weekly averages were also used where a permit limit was specified.Municipal Nutrient Removal Technologies Reference Document September 2008

3-44 Chapter 3 - Case Studies and Reliability Factors 

### 3.5.2 Phosphorus Removal The discussion below summarizes the highlights of efficiency and reliability related to phosphorus removal that was accomplished at th e facilities. Four facilities removed phosphorus biologically, without chemical addition. Three faci lities used chemicals to supplement biological phosphorus removal. Tw o facilities removed phosphorus primarily with chemical addition. The first four facil ities relied on biological phosphorus removal followed by tertiary filters. They met the perm it limits and performed efficiently and reliably.

• Kalispell, Montana: 0.12 mg/L TP at a COV of 19 percent

• Kelowna, British Columbia: 0.14 mg/L TP at a COV of 21 percent

• Central Johnston County, North Carolina : 0.26 mg/L TP at a COV of 62 percent

• North Cary, North Carolina: 0.38 mg/L TP at a COV of 64 percent

Both Kalispell and Kelowna have fermente rs, operate year-round, and show very high reliability. Two facilities without fermenters produced good effluent but at an increased COV, or reduced reliability compared to those with fermenters.

With small amounts of chemical addition, biological phosphorus removal was taken to even lower effluent concentrations and increased reliability, as follows:

• Clark County, Nevada: 0.09 mg/L TP at a COV of 30 percent

• Fairfax, Virginia: 0.09 mg/L TP at a COV of 21 percent

• Clearwater, Florida, Marshall Street: 0.13 mg/L TP at a COV of 40 percent

Clark County, Nevada, used primary settling ta nks as VFA generators, and Fairfax County, Virginia, had a fermenter online. Both showed lower COVs than the others at varying chemical dosages. Clearwater, Florida, fed alum to remove trihalomethanes for water reuse purposes, and Clark County, Nevada, added alum to push the limit of the existing facility.

Two facilities used chemicals for phosphorus removal:

• Lee County, Florida: 0.10 mg/L TP at a COV of 35 percent

• Western Branch, Maryland: 0.43 mg/L TP at a COV of 62 percent

These facilities remove nitrogen in an add-on process with methanol, and thus a decision had been made to remove phosphorus with chemical addition instead of retrofitting the existing processes for biologic al phosphorus removal.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 3 - Case Studies and Reliability Factors 3-45 The factors for reliable oper ation include the following:

1. Favorable wastewater characteristics : The BOD-to-TP ratio in the influent and primary effluent.

2. Fermenters that ensured an adequate supply of carbon : Ensured reliability during cold months and wet-weather periods. Kalispell, Montana, and Kelowna, British Columbia, achieved the highest reliabilit y, followed by Fairfax County, Virginia, and Clark County, Nevada, which use active pr imary settling for sludge thickening and VFA production, both with chemical addition.

3. Flexible design : Flexible design with swing z ones in anticipation of changing conditions in weather and wastew ater characteristics, including

− Equipping aeration tanks with both mixers a nd aerators for separate control, like North Cary, North Carolina

− Compartmentalizing the basin and crea ting swing zones, like Kalispell, Montana, and Kelowna, British Columbia

− Adding multiple feed points for carbon f eed, like Fairfax County, Virginia, for step-feed

− Placing a tertiary clarifie r ahead of the tertiary filter to reach a low concentration limit

− Having multiple chemical feed points

4. Flow equalization for stable operation : The facilities have equalization available, with the amount of storage varying based on their sewer systems. Kelowna has an equalization basin with volume 7.5 percent of the design flow, based on a relatively tight sewer system that has low infiltration. Fairfax County, Virgin ia, has two basins with a total volume of 31 percent of the design flow.

5. Wet weather : Storm flows were handled favorably with step-feed activated sludge at Fairfax County, Virginia, and the PID at North Cary, North Carolina. In addition, North Cary had the largest basins to st ore wet-weather flows––a 7-MG retention basin and a 2-MG equalization basin for the 12-MGD facility). The operational controls in many facilities in cluded shutting off a section of the aeration tanks during peak flow periods and protecting the biom ass inventory to prevent solids washout. This emergency shutoff mode of operati on lasted up to 24 hours but was followed by a successful restart, meeting all permit limits.

6. Recycle loads were minimized by

− Keeping secondary sludge aerobic un til dewatering; thickening, storing, and aerobic digestion—Central Johnston County, North Carolina; Lee County, Florida; North Cary, North Caro lina; and Kalispell, Montana.Municipal Nutrient Removal Technologies Reference Document September 2008

3-46 Chapter 3 - Case Studies and Reliability Factors − Treating filtrate with lime or ferric chloride—Fairfax County, Virginia, and Clark County, Nevada. Kelowna, British Columbia, no longer adds lime.

− No sludge digestion on-site—Kelowna, British Columbia, and Clark County, Nevada.

7. Operating denitrification bl anket in secondary clarifiers : Four facilities have developed operating procedures to maxi mize the denitrification of RAS in the clarifier and have made it a permanent pr actice for successful biological phosphorus removal: Kelowna, British Columbia; Central Johnston County, North Carolina; Lee County, Florida; and Clearwater, Florida.

8. Automation of process controls with sensors : Some facilities have multiple sensors, with automated process controls using the resulting signals . Commonly monitored parameters were DO, ORP, and nitrat e in the wastewater and the sludge blanket. Clark County, Nevada, used the dail y results to control the blowers and the sludge age. Other facilities rely on a daily check of critical parame ters and take steps to optimize the operation with efficiency and achieve a high degree of reliability.



### 3.5.3 Nitrogen Removal For nitrogen removal, the following paragraphs summarize the efficiency and reliability accomplished at the case study facilities.

Two facilities that are required to remove only ammonia nitrogen met the permit limits and performed efficiently and reliably:

• Kalispell, Montana: 0.07 mg/L ammonia nitrogen at a COV of 0 percent

• Clark County, Nevada: 0.12 mg/L ammoni a nitrogen at a COV of 14 percent

Seven facilities are required to remove TN. These facilities met the permit limits and performed efficiently and very reliably:

• Central Johnston County, North Carolina : 2.14 mg/L TN at a COV of 16 percent

• Lee County, Florida: 1.71 mg/L TN at a COV of 28 percent

• Clearwater, Florida, Marshall Street: 2.32 mg/L TN at a COV of 16 percent

• North Cary, North Carolina: 3.7 mg/L TN at a COV of 14 percent

• Kelowna, British Columbia: 4.38 mg/L TN at a COV of 12 percent

• Western Branch, Maryland: 1.63 mg/L TN at a COV of 36 percent

• Noman Cole, Fairfax County, Virginia: 5.25 mg/L TN at a COV of 12 percentSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 3 - Case Studies and Reliability Factors 3-47 Reliability factors for these perf ormances included the following:

1. Favorable wastewater characteristics : BOD-to-TKN ratios of above 4 in all cases. For add-on processes with methanol additi on, however, this ratio was not a concern. Methanol dosage at three such facilities depended directly on the nitrate nitrogen coming into the add-on process.

2 Adequate supply of carbon : Central Johnston County, North Carolina; Western Branch, Maryland; and Lee County, Florida, ne ed a separate stage for denitrification and all feed methanol. Other plants use carbon present in their wastewater.

3. Flexible design : This ensures added reliability in anticipation of variations in the weather and in wastewater characteristics.

− Swing zones at Kelowna, British Columbia

− Separate control of mixing and aerat ion at North Cary, North Carolina

− Multiple carbon feed points (step-feed) at Fairfax County, Virginia; Kelowna, British Columbia; and Clearwater, Florida

4. Flow equalization : The same principles that apply to phosphorus removal also apply to nitrogen removal. The backwash water from the denitrification fi lter is sent to a basin for equalization. In Central Johnston County, Nort h Carolina, the backwash water is stored in filter backwash reclaim tanks before it is pumped to the headworks. In Lee County, the backwash goes to a m ud well before it is returned to the headworks.

5. Recycle loads : The best strategy is to minimize recycle loads:

− Keep sludge handling aerobic in thic kening, storing, and stabilization

− Process all sludge each day: Clark County, Nevada

− Provide no sludge digestion on-site: Ke lowna, British Columbia; Clark County, Nevada; and Western Branch, Maryland

− Treat the recycle loads: lime addition at Fairfax County, Virginia, and Kelowna, British Columbia, and ferric chloride at Clark County, Nevada

− It is important to note that Fairfax County, Virginia, accounted for the recycle loads in their retrofit or expansion design

6. Wet-weather flows : The step-feed and PID offer the best process protection against wet-weather flows. North Cary, North Carolin a, has the largest storage capability, as described above. The operational controls in many facilities included shutting off a section of aeration tanks dur ing the peak flow periods and protecting the biomass inventory to prevent solids washout. This emergency shutoff mode of operation lasted up to 24 hours but was followed by a successful restart in meeting all permit limits.Municipal Nutrient Removal Technologies Reference Document September 2008

3-48 Chapter 3 - Case Studies and Reliability Factors 7. Denitrification blanket in secondary clarifier : A denitrification blanket ensures good nitrate removal and alkalinity recovery; it also optimizes the anoxic zone in the bioreactor, allowing the anoxi c basin size to be reduced.

8. Automatic controls with multiple sensors : Some facilities have multiple sensors, and process controls were based on them. They include DO, ORP, and nitrate in the wastewater and sludge blanket. Clark County, Nevada, uses these data to control the blowers and the sludge age. Clearwater, Fl orida, uses these data on DO, ORP, and nitrate. The target limits are set for these three parame ters at the anoxic zone for reliable nitrogen removal.



### 3.5.4 Costs for Capital and O&M
Capital Cost The capital cost at the case study facilities fo r nutrient removal was estimated on the basis of consultation with the owners because all the upgr ades were a part of an overall expansion. The estimate was obtained for secondary treatment, tertiary clarification and filtration, and applicable sludge handling. The capital cost s incurred for nutrient removal were then allocated among phosphorus removal, nitrogen rem oval, and BOD removal. There is a wide variation in costs because of the t ype and age of the existing facility.

1. Unit cost for treatment capacity : This cost varied from a low of $0.58 to a high of $3.25/gpd capacity according to the existing f acility and the age of construction. The variation was based on the capability of the existing facility, the desired level of treatment, and when the plant modifications were carried out.

2. Unit cost for TP removal : This cost varied from zero to a high of $5.38 per pound of TP removed.

3. Unit cost for TN removed : This cost varied from a low of $0.49 to a high of $387 per pound TN removed.

O&M Costs This study included three categorie s of O&M costs: power/electri cal usage, chemical usage, and cost of disposing of extra sludge genera ted by nutrient removal processes. Labor was excluded because of the high va riation in geographic location, difficulty in allocating the fraction for nutrient removal, and an understand ing that the staff size did not change after upgrade.

1. Unit cost for phosphorus : This cost ranged from a low of $0.23 to $0.1.81 per pound TP removed.

2. Unit cost for TN removal : This cost ranged from a low of $0.14 to a high of $0.99 per pound TN removed.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 3 - Case Studies and Reliability Factors 3-49 Contributing factors include the following:

1. The biological phosphorus removal facilities added capital cost, especially where fermenters were installed, but ensured a high degree of reliability in performance. The O&M cost was lower than that for the other processes.

2. Flexibility in design, such as the swing zone and alternate mode of operation, added costs (and redundant equipment and structur es) but provided added capability to handle changing wastewater charac teristics and new regulations.

3. Equalization basins added costs but pr ovided a higher degree of treatment for captured flows in the basin.

4. Separate storage tanks for secondary sl udge and primary sludge added costs but ensured more reliable performance, especially at EBPR facilities.

5. Treatment of recycle flows with lime or fe rric chloride added costs but resulted in more reliable performance.

Total Annual Cost
The annual costs were estimated on the basis of a 6 percent interest rate for 20 years.

1. The unit cost for phosphorus removal ranged from a low of $1.07 to a high of $6.76 per pound TP removed.

2. The unit cost for TN removed ranged from a low of $0.98 to a high of $4.78 per pound TN removed.

The contributing factors described in the above section on Capital and O&M costs all apply to the total cost.



### 3.6 References

Lindeke, D., and B, James. 2005. The Role and Production of VFAs in a Highly Flexible BNR Plant. In Proceedings of WEFTEC , 2005.

McBean, E., and F. Rovers. 1998. Statistical Procedures for Analysis of Environmental Monitoring Data & Risk Assessment. Prentice Hall, Upper Saddle River, NJ.

Neethling, J.B., B. Bakke, M. Benisch, A. Go, H. Stephens, H.D. Stensel, and R. Moore.
2005. Factors Influencing the Reliability of Enhanced Biological Phosphorus Removal. Water Environmental Research Fe deration (WERF) Report 01-CTS-3. IWA Publishing, London.Municipal Nutrient Removal Technologies Reference Document September 2008

3-50 Chapter 3 - Case Studies and Reliability Factors USDA (U.S. Department of Agriculture). 2007. Price Indexes and Discount Rates

. U.S. Department of Agriculture, Na tural Resources Conservation Service. http://www.economics.nrcs.usda.gov /cost/priceindexes/index.html . Accessed May 15,
2007.

USEPA (U.S. Environmental Protection Agency). 1988. Retrofitting POTWs for Phosphorus Removal in the Chesapeake Bay Drainage Basin . U.S. Environmental Protection Agency, Washington, DC.

USEPA (U.S. Environmental Protection Agency). 1993. Manual: Nitrogen Control

. EPA-625-R-93-010. U.S. Environmental Pr otection Agency, Washington, DC.

WEF and ASCE (Water Environment Federation and American Society of Civil Engineers).
1998. Design of Municipal Wastewater Treatment Plants. WEF Manual of Practice No. 8, Volume II, 4th ed. American So ciety of Civil Engineers, Reston, VA.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 4: Cost Factors 4-1 

## CHAPTER 4: Cost Factors

This chapter summarizes the cost factors to be considered in evaluating alternative technologies for upgrades at ex isting facilities and, more broa dly, provides context on cost for the entire document. Costs vary widely, de pending on a number of factors, including the target concentrations for nitrogen and phosphorus, as well as the existing facilities’ suitability to be used for upgrades.

As also discussed in Chapter 5, there are three general types of possible plant upgrades to be considered for costs: retrofitting existing facilities with additional piping and equipment; adding a new process or technology to an existin g treatment train; or expanding the existing plant, possibly with an entirely different te chnology. Section 4.1 descri bes costs reported at selected facilities in the United States, as well as costs incurred by facilities included in the cases studies provided in Chapter 3. Section 4.2 describes the results of estimating costs for 12 retrofit alternatives for nutrient rem oval, with the estimates generated using CAPDETWorks software. Finally, Section 4.3 desc ribes the estimated co sts for 20 expansion alternatives for nutrient removal, again with the estimates generate d using CAPDETWorks. In all cases, capital and operation and maintena nce (O&M) costs are provided as available. In addition, Section 4.3 provides a breakdown of the relative fraction of various components of O&M costs, i.e., labor, chemical, and energy costs.



### 4.1 Modifying Existing Facilities

4.1.1 Literature Review
Modifying or retrofitting existing facilities is often the least costly and most environmentally favorable approach for wastewater treatment fac ilities that are required to implement nutrient removal. Maryland (MDE 2004) and Connecticut (CTDEP 2006) have both implemented programs to assist treatment plants in upgrading processes for nutrient removal. Note that the construction industry indices of Engineering News-Record were 7,298.25 for September 2004 and 7,700 for July 2006 for comparative purposes. Table 4-1 shows the costs for various technologies used in the upgrades. Fo r each technology, the fo llowing are shown: the size of the facility (in milli on gallons per day [MGD]), the cap ital cost (in dollars per gallon per day [gpd] capacity), the O&M cost per MGD day treated, and the O&M unit cost for removal of 1 pound of nitrogen. The upgrad es cost between $0.22 and $5.20 per gpd capacity. The Maryland data consis t of projected costs to upgrade from the current treatment process. The O&M costs from Maryland, where available, are based on only the projected increase in electricity and chemical usage. Specifically, labor cost s and any anticipated increases in sludge-handling or disposal costs are not in cluded in the Maryland data.Municipal Nutrient Removal Technologies Reference Document September 2008

4-2 Chapter 4: Cost Factors Table 4-1. Upgrade costs for Maryland, Connecticut, and others

Treatment
processes Location Actual effl. TN (ppm) Initial TN

conc. (ppm) New TN goal (ppm) Flow (MGD) Capital Cost $/gpd capacity O&M Cost $/MG treated O&M Cost $/lb TN removed Cyclic on/off Ridgefield, CT -- 9.6 5.1 1 $0.20 $111 $0.60 Added upflow denitrification filter Cheshire, CT 6 7 5 3.5 $1.65 $136 $1.05

MLE Æ 4-stage Bardenpho Seneca, MD 16 8 3 20 $0.21 $63 $1.51

MLE Æ 4-stage Bardenpho Freedom, MD 8 8 3 3.5 $0.99 -- --

Step-feed AS Æ 4-stage Bardenpho Cumberland, MD 7.3 8 3 15 $1.10 $122 $2.94

MLE Æ added denite. filter Baltimore, MD 9 8 3 180 $1.39 -- --

MLE Æ added denitrification filter Cox Creek, MD 16 8 3 15 $1.74 $104 $2.50

A 2 O Æ 5-stage Bardenpho + denitification filter Frederick, MD
23 6.5 3 7 $1.41 -- --

Post-MBBR for TN removal a Broomfield, CO 8 8 3 8 $1.70 -- --

On/off aeration a Broomfield, CO -- 8 3 8 $1.00 -- --

IFAS a Broomfield, CO -- 8 3 8 $0.85 -- --

Lagoon Æ 4-stage Bardenpho Hurlock, MD -- 15 3 1.5 $4.12 -- --

MLE Æ MBR/5- stage Bardenpho a Las Virgenes Calabasas, CA -- 42 1 16 $5.20 -- --

Notes: A 2 O = anaerobic/anoxic/oxic MBBR = moving-bed biofilm reactor AS = activated sludge MBR = membrane biological reactor IFAS = integrated fixed-film activated sludge MLE = modified Ludzack-Ettinger MG = million gallons TN = total nitrogen

a Stephenson and Mohr 2005

O&M cost data are presented for facilities that had such information included in the studies reviewed.

The Broomfield, Colorado, and Las Virgenes Munici pal Water District (i n California) capital costs are also based on projections. The Connectic ut data are based on actual costs to upgrade the plant. The O&M costs for the Connecticut plants are an estimate of the actual costs associated with nitrogen removal. The O&M cost s represent the total O&M costs for nitrogenSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 4: Cost Factors 4-3 removal, not the incremental increase from the upgrades. Specifically, the Ridgefield, Connecticut, O&M costs include electric ity, sludge-handling and disposal, labor, maintenance, and administrative costs associat ed with nitrogen removal at the plant. No chemicals are added at this facility. O&M cost s for Cheshire, Connectic ut, include electricity, chemicals, and laboratory costs associated with nitrogen removal at the plant.



### 4.1.2 Case Studies
Table 4-2 presents the cost results for the upgrad es done at the facilitie s examined in the case studies found in Chapter 3 and Appendix A (in Volume II) of this document. The table shows the flow, the capital cost in dollars per gallon of treatment capacity, th e O&M cost in dollars per million gallons (MG) treated, and the unit O&M costs for removal of a pound of nitrogen, phosphorus, or ammonia nitrogen, as applicable. The ca pital costs were determined by totaling the capital expenditures for nutri ent removal technologies (costs brought to present worth by using cost indices) and then dividing that total by th e gpd capacity of the plant. The construction index of the Engineering News-Record was 7,959.17 in July 2007. The O&M costs for the case studies included powe r/electricity usage, chemical usage, and sludge disposal costs associated with the nutri ent being removed (total nitrogen [TN], total phosphorus [TP], or ammonia nitrogen). Labor costs were not included in the O&M costs. The O&M costs for nitrogen, ammonia, and phosphorus for a year were divided by the pounds of those substances removed over the year to obtain the unit costs. Similarly, the total O&M dollars expended over the ye ar were divided by the total flow processed at the plant over the year to obtain th e dollars per MG treated.

Table 4-2. Upgrade costs for case studies

Process Location Design flow (MGD) TargetConcentration (annual average) InitialConcentration (annual average) $/gpd
capacity $/MG O&M $/lb TN O&M $/lb TP O&M $/lb NH 3 Step-feed AS with tertiary clarifier and filter Fairfax County, VA 67 AmmoniaN+TP, 1 mg/L & 0.18 mg/L (TN 5.2 mg/L voluntary) 18.9 mg/LammoniaN, 6.4 mg/L TP $1.07 $106 $0.46 $1.07 --

Modified UCT with fermenter + tertiary filter Kalispell, MT 3 AmmoniaN+TP, 1.4 mg/L & 1 mg/L 24 mg/LammoniaN, 4 mg/L TP $3.03 $108 -- $0.49 $0.22

A/O with tertiary clarifier + tertiary filter Clark County, NV 100 AmmoniaN+TP, 0.6 mg/L & 0.2 mg/L 27 mg/LAmmoniaN, 5.8 mg/L TP $2.01 $183 -- $1.81 $0.50Municipal Nutrient Removal Technologies Reference Document September 2008

4-4 Chapter 4: Cost Factors Table 4-2. Upgrade costs for case studies (continued)

Process Location Design flow (MGD) TargetConcentration (annual average) InitialConcentration (annual average) $/gpd
capacity $/MG O&M $/lb TN O&M $/lb TP O&M $/lb NH 3 Plug flow AS with denitrification filter Johnston County, NC 7 TN+TP, 3.7 mg/L & 1 mg/L 31.2 mg/L TN, 5.8 mg/L TP $0.58 $221 $0.48 $1.48 --

Key factors affecting the costs presented in Tables 4-1 and 4-2 are summarized below. Capital costs depend largely on the facilities available to meet the new requirements. Making a simple change in mode of operation from continuous aeration to the cyclic on-off mode of activated sludge was the lowest-cost conversi on (Ridgefield, Connecticut ). Conversion of the Freedom, Maryland, modified Ludzack-Ettinge r (MLE) to a 4-stage Bardenpho required a mid-level expense of approximately $1.00/gpd capacity. Adding denitrific ation filters at Cox Creek, Maryland, was more expensive at $1.30 to $1.74/gpd capacity, but the upgrade had a small footprint. Adding fixed-film media at Broomfield, Colorado (Stephenson and Mohr 2005) was an option at a similar cost, also w ith a small footprint. Adding a fermenter for biological phosphorus removal at Kalispell, Montana, brought the cost above $3.00/gpd capacity, but the benefits were reliable operation and low O&M costs. Flexible design also tended to increase the capital costs. An exampl e of this is the Marshall Street plant in Clearwater, Florida, which included having the flexibility of two modes of operation–– operating as a 4-stage or a 5- stage Bardenpho––at the same facility. Another example of designed flexibility is North Cary, North Carolina, where mixers and aerators are in the same basin for better control in th e phased isolation ditch (PID).

Costs for flow equalization basins were incl uded for Fairfax, North Cary, and Kelowna, and could not readily be separated from other plant costs. Typi cally, equalizati on basins add $1.00 to $2.00 per gallon capacity in capital co sts, depending on location, hydraulics, and control devices. Equalization basi ns give the plant operators cap abilities to better manage and treat recycle flow streams, as we ll as to handle wet-weather flows.



### 4.2 Retrofit Process Cost Models

As discussed in detail in Chap ter 5, readers of this document seeking to select a retrofit process technology to achieve nutrient remova l requirements should first determine which processes are technically suited for the specific objectives at their f acility. After candidate technologies have been identified, the readers should assess the estimated capital and O&M costs. They should use this cost information as a factor in selecting th e process, along with other factors such as reliability, sustainability, and environmental considerations discussed in Chapter 5.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 4: Cost Factors 4-5 This section provides planning- level cost estimates for 12 re trofit treatment alternatives, including several alternatives involving the anoxic/oxic (A/O) process, also known as the Phoredox process. These alternatives were deemed the most likely retrof it options to be used at existing plants because of footprint size, ease of installation in an operating facility, ability to meet treatment objectives, and overall cost s. Each alternative was evaluated at three different flow rates––1 MGD, 5 MGD, and 10 MGD. This range was deemed to cover the flow rate range of most readers of this manual. Note that the cost rankings represented in the cost curves will likely hold for larger and sm aller flows. Ultimately, readers should find the process scenarios that best matc h their candidate technologies to obtain a cost estimate. Three alternatives not included in these estimat es are membrane biological reactors, land application for nutrient removal, and special filters like the Blue PRO; these technologies are new and thus have no software-based model fo r estimating costs. A reader seeking cost estimates for these processes shoul d contact the process vendors.



### 4.2.1 CAPDETWorks

The cost estimates for the scenarios were de veloped using CAPDETWo rks software, version 2.1. The U.S. Environmental Protection Agency (EPA) and U.S. Army Corps of Engineers originally developed this software as a planning tool; Hydromantis Corporation now maintains and updates (2006). The software work s as follows. The user generates a process layout involving a number of unit operations. Th e user can also define input variables, including wastewater flow rate, wastewater infl uent quality, and desire d effluent quality or other performance coefficients . Alternatively, the user can choose to use default values developed by Hydromantis. The software then calculates the required sizes of the unit operations and uses cost-curve models from the software’s database to estimate the capital, labor, chemical, and energy co sts that would be incurred.

The cost functions included in software ve rsion 2.1 (the most recent available during document preparation) were updated in 2000. The model uses several standard indices to update costs to current dollars: the Engineering News-Record (ENR) Construction Cost Index, the Marshall & Swift Inde x, and the Pipe Index. Values were obtained from a U.S. Department of Agriculture Web site (USDA 2007) that transcribes historical values of these indices. The values used for the indices are shown in Table 4-3, along w ith other cost factors used in all CAPDETWorks runs.

A number of authors have used the CAPDET model to provide pl anning-level costs. Wright et al. (1988) found that the progr am provides construction cost es timates that are within plus or minus 20 percent of the actual co sts. Overall, they showed that feasible alternatives can be compared using estimations from CAPDETWorks because the software includes all the items needed for process assessment except land and bu ilding costs. In general, the rankings of alternatives by cost will not change significantly for pl ants of different sizes.Municipal Nutrient Removal Technologies Reference Document September 2008

4-6 Chapter 4: Cost Factors To further verify the validity of CAPDETWorks, examples were run with the model to match what was installed at two of the case study lo cations discussed in Chapter 3, the Marshall Street facility in Clearwater, Florida, a nd the Kalispell Advanced Wastewater Treatment facility in Kalispell, Montana. The model was us ed to cost the biological treatment systems, tertiary filters, and any ferm enters/digesters used to provide volatile acids for phosphorus treatment. Primary treatment, preliminary trea tment, and sludge handling were not included in the costing. Because CAPDETWorks does not include a fermenter unit operation, two thickeners were used as an approximation.

Table 4-3. Cost factors used in CAPDETWorks estimates

Indices used to

update costs Value Date

ENR 7,940 May 2007
Marshall & Swift 1,360 2007 Pipe Index 732 2007
Cost factors Value Unit Electricity $0.08 kW-hr Labor $25.00 Person-hour
Alum $0.41 lb as Al2(SO4)3-14H 2 O

The design and actual influent flow rate, influent constituents, and other basic plant parameters were inputs for the software, along with the known plant la youts. The model was then run to obtain estimates of capital cost fo r installing the plant, as well as O&M estimates for power consumption, chemical usage (if any) , and additional sludg e generation (if any). Those were the only components of O&M included in the case studies. In the event that current operating flow was well below the desi gn flow, as was the case for Clearwater, a second run was done with the current flow to obtain operating costs.

Life-cycle costs were calculated for the CAPDETWorks results by first annualizing the capital cost at 20 years at 6 percent interest. The annualized capital cost was then added to the annual O&M cost to obtain a total annual cost. This cost was then divided by the annual flow to get the life-cycle cost per MG treate d. The model results were then compared with the results presented in the case studies develo ped for this manual. All capital costs for both the software estimates and the actual capital costs were updated to 2007 dollars.

For electrical costs, the total electricity used in the unit operations cite d was used rather than the breakdowns for phosphorus and nitrogen used in the case studies; this is because the CAPDETWorks software provides to tal electricity, including that attributable to biochemical oxygen demand (BOD) removal. Chemical costs in such cases were both nil.

Table 4-4 presents the results of the modeling versus case st udy results comparison for both Clearwater and Kalispell.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 4: Cost Factors 4-7 For Clearwater, the estimated capital cost from CAPDETWorks was close to the actual capital cost, within 17 percent. The O&M cost s are similarly close, within 6 percent.

For Kalispell, the estimated capital cost is within 2 percent of the actual cost. The O&M costs are 29 percent off. The difference here might be that CAPDETWorks designed a smaller anoxic zone relative to the rest of the system than Kalispell actually uses ; that would account for higher blower usage and, thus , the higher elec trical costs.

Overall, these results indicate that CAPDET Works would provide reasonably accurate cost estimates for comparative purposes during planning.

Table 4-4. Comparison of CAPDETWorks and actual costs for Clearwater, Florida, and Kalispell, Montana

Cost Clearwater: 5-stage Bardenpho Kalispell: University of Cape Town

CAPDETWorks Actual % Difference CAPDETWorks Actual % Difference
Total capital $35,541,000 $29,500,000 17 $8,903,000 $9,100,000 2

O&M electrical $640,000 $610,000 5 $159,000 $113,000 29

O&M chemical $0 $74,000 -- $0 $0 --

O&M sludge $0 $0 -- $0 $0 --

Total O&M $640,000 $684,000 6 $159,000 $113,000 29

Certain input assumptions were common to all model runs, and they are presented in Table 4-5. Beyond these values, various model components had default parameters, which are shown as the scenarios are discu ssed below. All capital cost results include a percentage of total unit costs to accoun t for engineering, site preparation, electrical and c ontrol installation, and building costs. O&M results include operations labor, maintenance labor (both costed at $25/hour), maintenance materials, chemical s (alum for selected phosphorus removal processes, methanol for selected nitrogen rem oval processes), and energy. This is in contrast to the Maryland study, the Connecticut study, and the case studies, in which labor and maintenance material costs were exclude d. This means that the CAPDETWorks O&M estimates will be higher than those for similar systems in those studies.Municipal Nutrient Removal Technologies Reference Document September 2008

4-8 Chapter 4: Cost Factors 

### 4.2.2 Retrofit Phosphorus Removal Technologies
Five retrofit plans for implementing phosphorus removal were evaluated. All five involved modifying or making additions around an existin g biological treatment system that was not accomplishing phosphorus removal.

1. Alum addition at one point upstream of an existing conventional activated-sludge process, 0.5 parts per million (ppm) TP target, no filter

2. Alum addition at two points, both up stream and downstream of an existing conventional activated-sludge process, 0.1 ppm TP target, sand filter downstream

Table 4-5. Cost model influent wastewater parameters

Parameter Value Average flow (MGD) 1, 5, 10 TSS (mg/L) 220
% volatile solids 75% BOD (mg/L) 220 Soluble BOD (mg/L) 80 COD (mg/L) 500 Soluble COD (mg/L) 300 TKN (mg/L) 40 Soluble TKN (mg/L) 25 Ammonia nitrogen (mg/L) 22 TP (mg/L) 5 pH (standard units) 7.6 Nitrite/nitrate (mg/L) 0.0 Temperature, summer 23 oC Temperature, winter 10 oC

Notes: BOD = biochemical oxygen demand COD = chemical oxygen demand TKN = total Kjeldahl nitrogen TP = total phosphorus TSS = total suspended solids

3. Refitting an existing conventional activated -sludge system to an A/O (Phoredox) or University of Cape Town (UCT) process, w ith a fermenter added to generate volatile fatty acids to support biological phosphorus uptake, with a target of 0.5 mg/L. The A/O CAPDET model was used to re present all such processes.

4. Refitting an existing conventional activated -sludge system to an A/O configuration, with a fermenter added to generate volatile fatty acids and a sand filter added to aid removal of phosphorus-containing solid s, with a target of 0.5 mg/LSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 4: Cost Factors 4-9 5. Refitting an existing conventional activated -sludge system to an A/O configuration, with a fermenter and sand filter added, as well as alum addition, with a target of 0.1 mg/L

In these calculations, the following assumptions were made with respect to planning cost estimates:

1. The cost to convert an existing activ ated-sludge process to A/O would incur 25 percent of the cost of a new A/O unit with the same capacity; this allows for the addition of walls and baffles to set off anaerobic zones.

2. As a fermenter module has yet to be esta blished for CAPDETWorks, the capital and operating costs of a gravity thickener, adjusted upward by 50 percent, were used instead. A thickener operated anaerobically is a good approximation of a fermenter; the 50 percent allowance includes the pipes a nd mixers that would be required for a fermenter.

3. Post-secondary chemical treatment was assu med to require an alum dose four times the dose that would be suggested by stoichiome try; for example, if the stoichiometric dose was 0.5 mg/L, a dose of 2 mg/L of alum as Al was used.

4. A sand filter was assumed for tertiary filtration used in retrofits 4 and 5.

5. It was assumed that no additional aeration capacity would be needed for retrofitting an existing activated-sludge reactor to A/O.

Table 4-6 presents the alum doses used in the costing for retrofits 1, 2, and 5.

Figures 4-1 through 4-3 are gra phs of the O&M costs (in dolla rs per MG treated), capital costs (in dollars per gpd capacity), and life-cycle costs (in dollars per MG treated) for these scenarios. The costs were estimated at 1 M GD, 5 MGD, and 10 MGD average influent flow. The life-cycle costs were determined by summ ing the O&M dollars per MG treated and the capital costs annualized to 20 years at 6 percent per MG treated.

From these figures, the following observations can be made:

1. The overall lowest cost option for O&M, as well as for life-cycle, is installation of a fermenter with a retrofit of the existing pr ocess to A/O. The lowest capital cost alternative is one-point chemical addition, bu t the retrofit/fermenter alternative is the second-lowest capital alternat ive. The estimated O&M for A/O plus fermentation is $5 to $25 per MG treated, wh ile the capital ranges between $0.19 and $0.32 per gpd capacity.

2. The lowest operating costs are associat ed with not using chemical, i.e., the alternatives of A/O with a fermenter a nd A/O with a fermenter and filter. TheseMunicipal Nutrient Removal Technologies Reference Document September 2008

4-10 Chapter 4: Cost Factors alternatives are two of the three lowest-life-cycle-cost alternatives, with the low capital cost for one-point chemical addition also resulting in a low life-cycle cost. The highest operating cost was associated with doing two chemical additions because both have elevated doses. These high operating cost s result in that alternative’s having the highest life-cycle costs as well.

Table 4-6. Process parameters for phosphorus removal scenarios

Process Costed items Alum dose (mg/L as Al)
1 Alum feed 2.4 2 Alum feed (2 points) with sand filter 2.6; 2.4 3 A/O conversion, fermenter N/A 4 A/O conversion, ferment er, Sand filter N/A

5 A/O conversion, fermenter, sand filter, alum feed (post-secondary treatment) 1.3

Notes: A/O = anoxic/oxic N/A = not available

3. If a TP level of 0.1 mg/L or lower in th e effluent is required, use of post-secondary chemical treatment with a filter might be needed. In that instance, these results indicate that using biological phosphoru s removal with a fermenter to get the concentration down to between 0.5 and 1 mg/L can save resources because doing so reduces the required post-secondary chemical dose.

4. The cost for using alum in the second f eed point was conservative, because regular biological uptake was not excluded in the dosage estimation. This means that actual costs for post-secondary chemical phosphorus removal will be lower.

5. A tertiary clarifier might be applicable to aid the tertiary filtra tion process, but it was not included in these retrofit cost curves.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 4: Cost Factors 4-11 0 50 100 150 200 250 300

0 2 4 6 81 0 1 2 Flow (MGD)O&M Costs ($/MG treated)

Fermenter Retrofit, 0.5 ppm TP target, no filter Fermenter+Sand Filter Retrofit, 0.5 ppm target 1 point addition alum addition , 0.5 ppm TP target, no filter Fermenter+Filter+1 point Alum addition, 2 ppm dose, 0.1 ppm TP target 2 pt alum addition, 0.1 ppm TP target, filter
Figure 4-1. O&M costs for retrofit phosphorus removal technologies ($/MG treated).

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00

0 2 4 6 81 0 1 2
Flow (MGD)Capital costs ($/gpd capacity)

1 point addition alum addition , 0.5 ppm TP target, no filter Fermenter Retrofit, 0.5 ppm TP target, no filter 2 pt alum addition, 0.1 ppm TP target, filter Fermenter+Sand Filter Retrofit, 0.5 ppm target Fermenter+Filter+1 point Alum addition, 2 ppm dose, 0.1 ppm TP target
Figure 4-2. Capital costs for retrofit phosphorus removal technologies ($ per gpd capacity).Municipal Nutrient Removal Technologies Reference Document September 2008

4-12 Chapter 4: Cost Factors $0.00 $50.00 $100.00 $150.00 $200.00 $250.00 $300.00 $350.00 $400.00 $450.00 $500.00

0 2 4 6 81 0 1 2
Flow (MGD)Life-cycle Costs ($/MG treated)

Fermenter Retrofit, 0.5 ppm TP target, no filter 1 point addition alum addition , 0.5 ppm TP target, no filter Fermenter+Sand Filter Retrofit, 0.5 ppm target Fermenter+Filter+1 point Alum addition, 2 ppm dose, 0.1 ppm TP target 2 pt alum addition, 0.1 ppm TP target, filter
Figure 4-3. Life-cycle costs for retrofit phosphorus removal technologies ($/MG treated).



### 4.2.3 Retrofit Nitrogen Removal Technologies
Four retrofit plans for implementing nitrogen removal were evaluate d. All four involved modifying or making additions around an existin g biological treatment system that was not accomplishing phosphorus removal.

1. Installation of additional tank capacity for an oxidation ditch to allow sufficient residence time in an anoxic zone for denitrific ation to occur

2. Retrofitting an existing activated-sludge system as a modified Lutzak-Ettinger (MLE), with anoxic and aerobic zone s and internal recirculation

3. Retrofitting an existing activ ated-sludge system to be a step-feed system to provide sufficient biochemical oxygen demand (B OD) to the anoxic zones to allow denitrification to occur

4. Installation of a den itrifying filter, along with a methanol systemSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 4: Cost Factors 4-13 In these calculations, the following assumptions were made with respect to planning cost estimates:

1. The cost to convert an existing activated -sludge process to M LE or step-feed would incur 33 percent of the cost of a new such unit with the same capacity; this allows for the addition of walls and baffles to set o ff anoxic zones, along with additional piping and recirculation pumping. The same ratio wa s applied to install additional secondary clarification and blower capacity.

2. Methanol was assumed to be needed only for the denitrifying filter, at a dose of 3 mg methanol per mg nitrate nitrogen.

3. The target TN concentration was assumed to be 3 mg/L.

Table 4-7 presents the items costed for thes e plans, as well as the methanol dosage if applicable.

Table 4-7. Process parameters for nitrogen removal scenarios

Process Costed items Methanol dose (lb/lb NO 3 ) 1 Tanks, mixers N/A 2 MLE conversion, filter N/A 3 Step-feed AS conversion, filter N/A 4 Denitrifying filter 3

Notes: AS = activated sludge MLE = modified Ludzack-Ettinger N/A = not available

Figures 4-4 through 4-6 are gra phs of the capital costs (in dollars per gpd capacity), O&M costs (in dollars per MG treate d), and life-cycle costs (in dolla rs per MG treated) for these nitrogen treatment plants. The costs were estimated at 1 MGD, 5 MGD, and 10 MGD average influent flow. The life-cycle costs were determined by summing the O&M dollars per MG treated and the capita l costs annualized to 20 years at 6 percent per MG treated.

From these figures, the following observations can be made:

1. The lowest-cost option is the installation of additional tank capacity for an existing oxidation ditch because this had both the lowest capital and O&M costs and therefore the lowest life-cycle cost. It should be not ed, however, that a gr eat deal of land area could be required for this alternative.

2. The denitrifying filter had clearly the highest operating cost, because of the methanol requirement. The other processes use orga nic matter in the wastewater to support denitrification, which gives a large cost savings. The high operating cost forMunicipal Nutrient Removal Technologies Reference Document September 2008

4-14 Chapter 4: Cost Factors denitrifying filters led to that alternativ e’s having the highest life-cycle cost. The advantage of denitrifying filters, however, is that they have very small footprints.

3. The step-feed and MLE alternatives had si milar capital, O&M, a nd life-cycle costs. Technically, each has advantages and disadva ntages, as described elsewhere in this manual.

4. None of these alternatives employed a post-secondary filter. Such a filter could be useful in achieving low TN concentrations through removal of solids containing nitrogen. For example, an effluent with a total suspended solids (TSS) at 10 mg/L could contain 0.5 mg/L (i.e., 5 percent) TN in a filterable form. Therefore, in meeting an overall effluent limit of 3 mg/L TN, a tertiary filter could be helpful.

$0.00 $0.20 $0.40 $0.60 $0.80 $1.00 $1.20 $1.40 $1.60

0 2 4 6 81 0 1 2 Flow (MGD)Capital Cost per gpd

Denit Filter 3 ppm TN Step Feed Retro--1/3 of Step Feed/PFR on reactor MLE Retro--1/3 of MLE Extra basins for PID

Figure 4-4. Capital costs for retrofit nitrogen removal scenarios.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 4: Cost Factors 4-15 $0.00 $50.00 $100.00 $150.00 $200.00 $250.00 $300.00 $350.00 $400.00 $450.00 $500.00

0 2 4 6 8 10 12
Flow (MGD)O&M Costs per MG treated

Denit Filter 3 ppm TN Step Feed Retro--1/3 of Step Feed/PFR on reactor Extra basins for PID MLE Retro--1/3 of MLE
Figure 4-5. O&M costs for retrofit nitrogen removal scenarios.

$0.00 $100.00 $200.00 $300.00 $400.00 $500.00 $600.00 $700.00 $800.00 $900.00

0 2 4 6 81 0 1 2
Flow (MGD)Life Cycle Costs ($/MG treated)

Denit Filter 3 ppm TN Extra basins for PID Step Feed Retro--1/3 of Step Feed/PFR on reactor MLE Retro--1/3 of MLE
Figure 4-6. Life-cycle costs for retrofit nitrogen removal scenarios.Municipal Nutrient Removal Technologies Reference Document September 2008

4-16 Chapter 4: Cost Factors 

### 4.2.4 Combined Nitrogen and Phosphorus Scenarios
The following three retrofit alternatives fo r achieving combined nitrogen and phosphorus removal to very low levels (3 ppm TN, 0.1 ppm TP) were evaluated. All the technologies used a combination of biological nutrient remova l to achieve nitrification/denitrification and some phosphorus removal, plus chemical phos phorus removal to polish the effluent to 0.1 ppm TP. All scenarios included a tertiary filter (or denitrification filter).

1. Oxidation ditch retrofitted with additional tanks (as was done above for nitrogen removal), with one-point alum addition for phosphorus removal, plus a tertiary clarifier and a tertiary sand filter.

2. A nitrifying activated-sludge reactor retr ofitted with two-point alum addition for phosphorus removal plus a denitrification filter.

3. Conversion of an activated-sludge system to a 5-stage Bardenpho with chemical addition for polishing phosphorus and a tertiary filter

In these calculations, the following assumptions were made with respect to planning cost estimates:

1. The cost to convert an existing activat ed-sludge process to a 5-stage Bardenpho would incur 50 percent of the cost of a new such unit with the same capacity. This allows for the addition of walls and baffles to set off anoxic zones, installation of additional tank capacity, and a dditional piping and recirc ulation pumping. The same ratio was applied to install additional sec ondary clarification a nd blower capacity, as well as material and energy costs.

2. Methanol was assumed to be needed only for the denitrifying filter, at a dose of 3 mg methanol per mg nitrate-nitrogen.

3. The target TN concentration was assumed to be 3 mg/L; the target TP concentration, 0.1 mg/L.

Table 4-8 presents the items costed for thes e plans, as well as the methanol dosage if applicable.

Table 4-8. Process parameters for nitrogen removal scenarios

Process Costed items Methanol dose (lb/lb NO 3 )

1 Basins, mixers, alum addition, tertiary clarifier, tertiary filter N/A

2 Alum addition, denitrifying filter 3 mg/mg NO 3 -N

3 5-stage Bardenpho conversion, alum addition, tertiary filter N/A

Note: N/A = not availableSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 4: Cost Factors 4-17 Figures 4-7 through 4-9 are gra phs of the capital costs (in dollars per gpd capacity), O&M costs (in dollars per MG treate d), and life-cycle costs (in dolla rs per MG treated) for these alternatives. The costs were estimated at 1 MGD, 5 MGD, and 10 MGD average influent flow. The life-cycle costs were determined by summing the O&M dollars per MG treated and the capital costs annualized to 20 ye ars at 6 percent per MG treated.

From these figures, the following observation can be made:

1. The lowest-cost alternative on a life-cycle basis is the oxidation ditch modifications. This is so because it has the best combination of reduced operating costs (because of accomplishing biological nutrient removal) and capital costs. The lowest-capital-cost option was the use of chemical phosphorus re moval and a denitrifying filter, but that alternative has the highest operating costs; th e lowest operating costs were attached to the ditch additions.

$0.00 $0.50 $1.00 $1.50 $2.00 $2.50

0 2 4 6 81 0 1 2 Flow (MGD)Capital Cost ($/gpd capacity)

5-Stage/Chem P Retro = 1/2 old 5 Stage ---3 NO3/0.3 P Nitrification/Chem P/Denite Filter--3 NO3/0.1 P N&P PID Retro Figure 4-7. Capital costs for retrofit ni trogen plus phosphorus removal technologies.Municipal Nutrient Removal Technologies Reference Document September 2008

4-18 Chapter 4: Cost Factors $0.00 $100.00 $200.00 $300.00 $400.00 $500.00 $600.00 $700.00 $800.00 $900.00

0 2 4 6 81 0 1 2
Flow (MGD)O&M Costs ($/MG treated)

5-Stage/Chem P Retro = 1/2 old 5 Stage ---3 NO3/0.3 P Nitrification/Chem P/Denite Filter--3 NO3/0.1 P N&P PID Retro
Figure 4-8. O&M costs for retrofit nitrogen plus phosphorus removal technologies.

$0.00 $200.00 $400.00 $600.00 $800.00 $1,000.00 $1,200.00 $1,400.00

0 2 4 6 81 0 1 2
Flow (MGD)Life-Cycle Costs ($/MG treated)

5-Stage/Chem P Retro = 1/2 old 5 Stage ---3 NO3/0.3 P Nitrification/Chem P/Denite Filter--3 NO3/0.1 P N&P PID Retro
Figure 4-9. Life-cycle costs for retrofit nitrogen plus phosphorus removal technologies.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 4: Cost Factors 4-19 

### 4.3 Expansion Process Cost Models

There are situations where a retr ofit might not be adequate and the owners of the wastewater treatment operation must consider a plant expa nsion. As discussed in detail in Chapter 5, project teams seeking to select a new pr ocess technology to meet nutrient removal requirements should first determine which proce sses are technically suited for the specific objectives at their facility. Once candidate technologies have b een identified, the project team members should assess the estimated capital and O&M costs. They should use this cost information as a factor in making the process selection, along with ot her factors such as reliability, sustainability, and environmental considerations.

This section provides planning-le vel cost estimates for 20 treatment scenarios. The scenarios were selected because they are most representa tive of the likely treatment process candidates to be considered, on the basis of what has been observed from the case studies and other evaluations conducted for this document. As was done for the retrofit cases above, each scenario was evaluated using CAPDETWorks at three different flow rates––1 MGD, 5 MGD, and 10 MGD. This range was deemed to cover th e flow rate range of most readers of this manual. All basic process assumptions used in the retrofit section also apply for these expansion cases.



### 4.3.1 Phosphorus Removal Technologies
Eight scenarios for implementing phosphorus removal were evaluated:

1. Alum addition at one point upstream of an existing conventional activated-sludge process, 0.5 ppm TP target, no filter

2. Alum addition at two points, both up stream and downstream of an existing conventional activated-sludge process, 0.1 ppm TP target, sand filter downstream

3. A/O process with biological treatm ent to 1 ppm TP, no extra equipment

4. A/O process with biological treatment to 0.5 ppm TP, fermenter included to supply volatile fatty acids

5. A/O process with biological treatmen t to 0.5 ppm TP, fermenter and sand filter included

6. A/O process with biological treatment to 0.1 ppm TP, fermenter, chemical addition downstream of bioreactor, and sand filter included

7. Modified UCT (3-stage) process with bi ological treatment to 0.5 ppm TP, fermenter and sand filter included

8. Five-stage Bardenpho process with biol ogical treatment to 0.5 ppm TP, sand filter includedMunicipal Nutrient Removal Technologies Reference Document September 2008

4-20 Chapter 4: Cost Factors Table 4-9 presents process parameters for thes e scenarios, including the hydraulic residence time (HRT) in the bioreactor, if appli cable, and the chemical dosage of alum.

Figures 4-10 through 4-12 are graphs of the O& M costs (in dollars per MG treated), capital costs (in dollars per gpd capacity), and life-cycle costs (in dollars per MG treated) for these scenarios. The costs were estimated at 1 M GD, 5 MGD, and 10 MGD average influent flow. The life-cycle costs were determined by summ ing the O&M dollars per MG treated and the capital costs annualized to 20 years at 6 pe rcent per MG treated. Figures 4-13 and 4-14 present the percentage breakdow n of the total O&M costs for the eight technologies for 1 MGD and 10 MGD, respectively.

Table 4-9. Process parameters for phosphorus removal scenarios

Process Costed items HRT (hr) Alum dose (mg/L as Al)
1 Alum feed N/A 2.4 2 Alum feed (2 points) N/A 2.6; 2.4 3 A/O, clarifier, blower 12.6 N/A 4 A/O, clarifier, fermenter, Blower 13.1 N/A 5 A/O, clarifier, fermenter , filter, blower 13.1 N/A 6 A/O, clarifier, fermenter, f ilter, blower, alum feed 13.1 2.4 7 UCT, clarifier, filter, fermenter, blower 12.0 N/A 8 5-stage Bardenpho, clarifie r, filter, blower 15.1 N/A

Notes: A/O = anoxic/oxic N/A = not available UCT = University of Cape Town process

From these figures, the following observations can be made:

1. The lowest-cost options are to implement one-point and two-point alum addition for an existing biological treatment system. Th is can be done if no additional nitrogen removal is required.

2. The A/O costs are fairly close together , with higher overa ll costs incurred as additional units are added, as well as when chemical addition is included. These costs include installation of a new A/O biological treatment system (reactor plus clarifier). If an existing reactor/clarif ier can be modified to an A/ O system by installing walls in the basin, adding an anaerobic tank, and so forth, the capital costs for these alternatives would be substantially reduced.

3. The costs for including post-secondary chemical phosphorus removal are conservative, because regular biological phosphorus uptake was not accounted for. This means the required dose would be lo wer, thereby reducing chemical costs.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 4: Cost Factors 4-21 4. The 3-stage modified UCT process and 5- stage Bardenpho process have the highest overall costs because of process complexit y, as well as conservative inclusion of a number of recycle pumps (4 Q for internal recirculation and 3 Q for return-activated sludge and other back-up design elements). These processes sh ould be considered when substantial nitrogen re moval is also required.

5. As shown by processes 5 and 6, all biologi cal removal processes, whether new or existing, can be enhanced for phosphorus re moval by installing a sand filter, alum addition, or both. As discussed elsewhere in this document, including a sand filter or alum addition might have overall treatm ent benefits beyond nutrient removal, including enhanced wastewater reuse pot ential, TSS control, and reduction of trihalomethane formation.

6. The UCT process costs can be assumed to be representative of other 3-stage processes, such as the Virginia Initia tive process (VIP), an aerobic/anoxic/oxic process (A 2 O), and Westbank bioreactor because a ll involve three stages with varying amounts of mixing and aeration in the different stages.

7. Figures 4-13 and 4-14 indicate that the frac tion of the total cost attached to labor expenses decreases with larger facilities; associated increases in the fraction of the cost are attached to energy and other components. In particular, the 1 MGD labor costs range from 40 to 50 percent of the total except for the two simple chemical addition technologies, while the 10 MGD labor costs range from 15 to 25percent of the total.Municipal Nutrient Removal Technologies Reference Document September 2008

4-22 Chapter 4: Cost Factors $0.00 $100.00 $200.00 $300.00 $400.00 $500.00 $600.00 $700.00 $800.00 $900.00

0 2 4 6 8 10 12 Flow (MGD)O&M Costs ($/MG treated)

5 Stage Bardenpho to 0.5 ppm TP w filter Mod UCT to 0.5 ppmTP w ferm+filt A/O w fermenter, filter, and alum addition to 0.1 ppm TP A/O to 0.5 ppm TP w fermenter+filter A/O to 0.5 ppm TP w Fermenter A/O to 1 ppm TP No ferm, no chem, no filter 1 point addition alum addition , 0.5 ppm TP target, no filter 2 pt alum addition, 0.1 ppm TP target, filter
Figure 4-10. O&M costs for expansion phosphorus removal technologies ($/MG treated).

$0.00 $0.50 $1.00 $1.50 $2.00 $2.50 $3.00 $3.50 $4.00 $4.50

0 2 4 6 81 0 1 2 Flow (MGD)Capital costs ($/gpd capacity)

5 Stage Bardenpho to 0.5 ppm TP w filter Mod UCT to 0.5 ppmTP w ferm+filt A/O w fermenter, filter, and alum addition to 0.1 ppm TP A/O to 0.5 ppm TP w fermenter+filter A/O to 0.5 ppm TP w Fermenter A/O to 1 ppm TP No ferm, no chem, no filter 2 pt alum addition, 0.1 ppm TP target, filter 1 point addition alum addition , 0.5 ppm TP target, no filter
Figure 4-11. Capital costs for expansion phosphorus removal technologies.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 4: Cost Factors 4-23 $0.00 $200.00 $400.00 $600.00 $800.00 $1,000.00 $1,200.00 $1,400.00 $1,600.00 $1,800.00 $2,000.00

0 2 4 6 81 0 1 2 Flow (MGD)Life-cycle Costs ($/MG treated)

5 Stage Bardenpho to 0.5 ppm TP w filter Mod UCT to 0.5 ppmTP w ferm+filt A/O w fermenter, filter, and alum addition to 0.1 ppm TP A/O to 0.5 ppm TP w fermenter+filter A/O to 0.5 ppm TP w Fermenter A/O to 1 ppm TP No ferm, no chem, no filter 2 pt alum addition, 0.1 ppm TP target, filter 1 point addition alum addition , 0.5 ppm TP target, no filter
Figure 4-12. Life-cycle costs for expansion phosphorus removal technologies.

1 MGD P Technologies

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

5 Stage Bardenpho Westbank A/O with Chem P A/O with Fermenter and Filter A/O with Fermenter A/O no ferm, chem, or

filter Plain AS, 2 alum feed, .1 ppm out, filter 1 alum feed, .5 ppm out, no filter Energy
Chemical
O&M Materials

Labor

Figure 4-13. Component percentages of total O&M costs for 1 MGD expansion phosphorus removal technologies.Municipal Nutrient Removal Technologies Reference Document September 2008

4-24 Chapter 4: Cost Factors 10 MGD P Technologies

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

5 Stage Bardenpho Westbank A/O with Chem P A/O with Fermenter and Filter A/O with Fermenter A/O no ferm, chem, or

filter Plain AS, 2 alum feed, .1 ppm out, filter 1 alum feed, .5 ppm out, no filter Energy
Chemical

Materials

Labor

Figure 4-14. Component percentages of tota l O&M costs for 10 MGD expansion phosphorus removal technologies.



### 4.3.2 Nitrogen Removal Technologies
The following eight scenarios for implementing nitrogen removal were evaluated. All the technologies were selected specifically for TN removal, i.e., including denitrification. If a facility is required to remove only ammonia or total Kj eldahl nitrogen (TKN), all systems outlined below except the denitrifying filter will accomplish that task. In that case, the denitification system need not be operated. Th e project team might, how ever, wish to design the implementation to allow for future denitr ification should the permit eventually change.

1. PID, 5 ppm TN target

2. Denitrifying filter, 3 ppm TN target

3. Step-feed, 5 ppm TN target (1 ppm TP)

4. MLE, 5 ppm TN target, without sand filter

5. Sequencing batch reactor (SBR), 5 ppm TN target

6. Three-stage UCT 5 ppm TN target (1 ppm TP)

7. Four-stage Bardenpho, 5 ppm TN target (biological phosphorus removal not supported)September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 4: Cost Factors 4-25 8. Five-stage Bardenpho process, 5 ppm TN targ et with biological treatment to 0.5 ppm
TP

Table 4-10 presents process assumptions for these scenarios, including the HRT in the bioreactor (if applicable) and me thanol dosage (if applicable).

Figures 4-15 through 4-17 are graphs of the O& M costs (in dollars per MG treated), capital costs (in dollars per gpd capacity), and life-cycle costs (in dollars per MG treated) for these nitrogen scenarios. The costs were estimat ed at 1 MGD, 5 MGD, and 10 MGD average influent flow. The life-cycle costs were de termined by summing the O&M dollars per MG treated and the capital costs a nnualized to 20 years at 6 percen t per MG treated. Figures 4-18 and 4-19 present the percentage breakdown of th e total O&M costs for the eight technologies for 1 MGD and 10 MGD, respectively.

Table 4-10. Process parameters for nitrogen removal scenarios

Process Costed items HRT (hr) Methanol dose (lb/lb NO 3 )
1 PID, clarifier, sand filter 8.8 N/A

2 Denitrification filter N/A 3 3 Step-feed AS, clarifier, filter, blower 12.4 N/A
4 MLE reactor, clarifier, blower 16.8 N/A
5 SBR, sand filter, blower 9 (total cycle time) N/A
6 UCT, clarifier, blower 12.1 N/A 7 4-stage Bardenpho, clarifier, blower 14.5 N/A 8 5-stage Bardenpho, clarifier, blower 15.1 N/A

Notes: AS = activated sludge MLE = modified Ludzack-Ettinger N/A = not available PID = phased isolation ditch SBR = sequencing batch reactor UCT = University of Cape Town process

From these figures, the following observations can be made:

1. The lowest-cost options are the oxidation ditch and the denitrification filter. The denitrification filter has the advantage of a very small footprint for inclusion within an existing system.

2. Step feed also has major advantages as a retrofit technol ogy with an existing activated-sludge system because it can be accomplished largely by redirecting flows without needing to build subs tantial additional tank capacity.Municipal Nutrient Removal Technologies Reference Document September 2008

4-26 Chapter 4: Cost Factors 3. The 3-, 4-, and 5-stage processes had the highest overall costs because of the number of tanks and process complexity. The 3-st age process costs can be assumed to be representative of all 3- stage processes––UCT, A 2 O, VIP, Westbank, or others.

4. Figures 4-18 and 4-20 indicate that the frac tion of the total cost attached to labor expenses decreases with larger facilities; th e associated increases in the fraction of the cost are attached to energy and other components. In particular, the 1 MGD labor costs range from 40 to 50 percent of the total for all technologies except for the denitrification filter that has comparatively low other costs, so that labor is a large fraction of the total, while the 10 MGD labor costs range from 15 to 25 percent of the total.

$0.00 $0.50 $1.00 $1.50 $2.00 $2.50 $3.00 $3.50 $4.00

0 2 4 6 81 0 1 2 Flow (MGD)Capital Cost per gpd

5 Stage 5N 0.5 P 4 Stage Bardenpho 5 N 5 P 3 Stage generic - 5 N 1 P SBR 5 N 1 P MLE to 5 ppm TN, no filter Step Feed 5 N 1 P Denit Filter 3 ppm TN PID 5 ppm TN target
Figure 4-15. Capital costs for expansion nitrogen removal scenarios.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 4: Cost Factors 4-27 $0.00 $100.00 $200.00 $300.00 $400.00 $500.00 $600.00 $700.00 $800.00 $900.00

0 2 4 6 8 10 12 Flow (MGD)O&M Costs per MG treated

5 Stage 5N 0.5 P 4 Stage Bardenpho 5 N 5 P 3 Stage generic - 5 N 1 P SBR 5 N 1 P MLE to 5 ppm TN, no filter Step Feed 5 N 1 P Denit Filter 3 ppm TN PID 5 ppm TN target
Figure 4-16. O&M costs for expansion nitrogen removal scenarios.

$0.00 $200.00 $400.00 $600.00 $800.00 $1,000.00 $1,200.00 $1,400.00 $1,600.00 $1,800.00

0 2 4 6 8 10 12 Flow (MGD)Life Cycle Costs ($/MG treated)

5 Stage 5N 0.5 P 4 Stage Bardenpho 5 N 5 P 3 Stage generic - 5 N 1 P SBR 5 N 1 P MLE to 5 ppm TN, no filter Step Feed 5 N 1 P Denit Filter 3 ppm TN PID 5 ppm TN target
Figure 4-17. Life-cycle costs for expansion nitrogen removal scenarios.Municipal Nutrient Removal Technologies Reference Document September 2008

4-28 Chapter 4: Cost Factors 1 MGD N Technologies

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

5 Stage Bardenpho--
N 4 Stage Bardenpho-- 5stage with Anaerobic zeroed out MLE SBR I (with Anaerobic

phase) Step Feed/PFR Denite Filter (alone) PID 3 Stage generic Energy

Chemical

O&M Materials

Labor

Figure 4-18. Component percentages of total O&M costs for 1 MGD expansion nitrogen removal technologies.

$0.00 $200.00 $400.00 $600.00 $800.00 $1,000.00 $1,200.00 $1,400.00 $1,600.00 $1,800.00

0 2 4 6 8 10 12 Flow (MGD)Life Cycle Costs ($/MG treated)

5 Stage 5N 0.5 P 4 Stage Bardenpho 5 N 5 P 3 Stage generic - 5 N 1 P SBR 5 N 1 P MLE to 5 ppm TN, no filter Step Feed 5 N 1 P Denit Filter 3 ppm TN PID 5 ppm TN target
Figure 4-19. Life-cycle costs for expansion ni trogen plus phosphorus removal technologies.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 4: Cost Factors 4-29 10 MGD N Technologies

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

5 Stage Bardenpho- -N 4 Stage Bardenpho-

-5stage

with Anaerobic zeroed out MLE SBR I (with Anaerobic

phase) Step Feed/PFR Denite Filter (alone) PID 3 Stage generic Energy
Chemical

Materials

Labor

Figure 4-20. Component percentages of tota l O&M costs for 10 MGD expansion nitrogen removal technologies.



### 4.3.3 Combined Nitrogen and Phosphorus Scenarios
The following four scenarios for implementing combined nitrogen and phosphorus removal to very low levels (3 ppm TN, 0.1 ppm TP) were evaluated. All th e technologies used a combination of biological nutrien t removal to achieve nitrifica tion/denitrification and some phosphorus removal, plus chemical phosphorus re moval to polish the effluent to 0.1 ppm TP. All scenarios included a tertiary filter (or denitrification filter), and all except the SBR included a tertiary clarifier to help ge t solids (and thus TN and TP) lower.

1. PID with dual (two-point) chem ical addition plus tertiary cl arifier plus tertiary filter

2. SBR with chemical plus tertiary filter

3. Nitrification with chemical plus denitrification filter

4. Five-stage Bardenpho with ch emical plus tertiary filter

Table 4-11 presents process assumptions for these scenarios, including the HRT in the bioreactor and alum dose for th e chemical phosphorus removal.Municipal Nutrient Removal Technologies Reference Document September 2008

4-30 Chapter 4: Cost Factors Table 4-11. Process parameters for combined nitrogen and phosphorus removal
scenarios

Process Costed items HRT (hr) Alum dose (mg/L as Al)

1 PID, clarifier, dual alum additions, tertiary clarifier, sand filter, blower 13 2.0; 1.0

2 SBR, alum addition, sand filter, blower 15 (total cycle time) 2.08

3 Nitrifying AS, clarifier, dual alum addition, denitrification filter, blower 11.8 2.6, 4.8

4 5-stage Bardenpho, clarifier, alum addition, sand filter, blower 15.5 2.1

Notes: AS = activated sludge PID = phased isolation ditch SBR = sequencing batch reactor

Figures 4-21 through 4-23 are graphs of the O& M costs (in dollars per MG treated), capital costs (in dollars per gpd capacity), and life-cycle costs (in dollars per MG treated) for these nitrogen scenarios. The costs were estimat ed at 1 MGD, 5 MGD, and 10 MGD average influent flow. The life-cycle costs were de termined by summing the O&M dollar per MG treated and the capital costs a nnualized to 20 years at 6 percen t per MG treated. Figures 4-24 and 4-25 present the percentage breakdown of th e total O&M costs for the four technologies for 1 MGD and 10 MGD, respectively.

From these figures, the following observations can be made:

1. The lowest-cost option was the oxidation d itch, with the other technologies close in

cost.
2. In comparing the nitrification with dual alum additions and denitrifcation filter (which is very dependent on chemicals) w ith the 5-stage Barde npho, the capital costs for the Bardenpho are greater than those for the nitrification system, but the operating costs are much lower, with the result that the total costs (as reflected in the life-cycle graph) are similar.

3. Overall, if chemical phosphorus removal is to be used to attain 0.1 ppm or lower, either early chemical phosphorus remova l or an efficient biological phosphorus removal system should be employed so that th e dose in the final stage is reasonable.

4. As Figures 4-24 and 4-25 indicate, the frac tion of the total cost attached to labor expenses decreases with larger facilities, wi th the associated increases in the fraction of the cost attached to energy and other components. In particular, the 1 MGD labor costs range from 40 to 50 percent of the total for all technologies, while the 10 MGD labor costs range from 15 to 25 percent of the total.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 4: Cost Factors 4-31 $0.00 $0.50 $1.00 $1.50 $2.00 $2.50 $3.00 $3.50 $4.00 $4.50 $5.00

0 2 4 6 8 10 12
Flow (MGD)Capital Cost ($/gpd capacity)

5Stage Barden- 3 NO3 0.1 P Nitrification/Chem P/Denite Filter--3 NO3/0.1 P PID w chemical + tert clar + tert filt SBR w chem+filt
Figure 4-21. Capital costs for expansion nitr ogen plus phosphorus removal technologies.

$0.00 $200.00 $400.00 $600.00 $800.00 $1,000.00 $1,200.00 $1,400.00

0 2 4 6 81 0 1 2 Flow (MGD)O&M Costs ($/MG treated)

5Stage Barden- 3 NO3 0.1 P Nitrification/Chem P/Denite Filter--3 NO3/0.1 P PID w chemical + tert clar + tert filt SBR w chem+filt
Figure 4-22. O&M costs for expansion nitrogen plus phosphorus removal technologies.Municipal Nutrient Removal Technologies Reference Document September 2008

4-32 Chapter 4: Cost Factors $0.00 $500.00 $1,000.00 $1,500.00 $2,000.00 $2,500.00

0 2 4 6 81 0 1 2
Flow (MGD)Life-Cycle Costs ($/MG treated)

5Stage Barden- 3 NO3 0.1 P Nitrification/Chem P/Denite Filter--3 NO3/0.1 P PID w chemical + tert clar + tert filt SBR w chem+filt
Figure 4-23. Life-cycle costs for expansion ni trogen plus phosphorus removal technologies.

1 MGD N+P Technologies

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Nitrification/Chem P/Denite Filter--3 NO3/0.1 P 5-Stage Barden/Chem P--3 NO3/0.1 P PID with chemical + tert clar + tert filter SBR w chem + filt Energy

Chemical

Materials

Labor

Figure 4-24. Component percentages of total O& M costs for 1 MGD expansion nitrogen plus phosphorus removal technologies.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 4: Cost Factors 4-33 10 MGD N+P

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Nitrification/Chem P/Denite Filter--3 NO3/0.1 P 5-Stage Barden w Chem P---3 NO3/0.1 P PID w chemical + tert clar + tert filt SBR w chem + filt Energy

Chemical

Materials

Labor

Figure 4-25. Component percentages of total O&M costs for 10 MGD expansion nitrogen plus phosphorus removal technologies.



### 4.4 Discussion of Cost Factors

For a project team trying to estimate costs for upgr ading existing facilities, the first step is to obtain site-specific data. On th e basis of the data, the project team can determine what modifications are available and their associated costs.

The cost estimates given in this chapter are for only the technologies directly involved in nutrient removal; however, an overall program to upgrade a plant to allow for nutrient removal will likely include other costs not reflecte d in this analysis. The ability of a plant to adequately handle nutrients will be enhanced by flow equalization, proper management of recycle flows, wise selection of sludge-handl ing processes, and a llowance for variable conditions in the influent wastewater and the weat her. To the extent that these considerations are included in a plant’s pro cess design, the overall costs coul d be substantially affected. However, most of these plant-wide processes will be the same for all nutrient removal technologies, so inclusion is not an is sue for planning-level process selection.

In addition, site-specific sludge-h andling practices affect the ove rall costs. Decisions about sludge handling could be made on the basis of more than the process upgrades for nutrient removal in some instances, or they could be a part of the nutrien t removal project. In particular, the cost of thickening, stabilization (digestion), and dewate ring might favor one alternative over another. Aer obic digestion of secondary slud ge would be desired for theMunicipal Nutrient Removal Technologies Reference Document September 2008

4-34 Chapter 4: Cost Factors biological phosphorus removal alternative, whereas it would not be crit ical for the chemical phosphorus removal alternative. Anaerobic di gestion might not be favored for nitrogen removal if another alternative exists.

O&M costs are dependent on the nutrient removal technology selected, the flexibility of the operating mode, and whether the systems for controlling power and chemical feed are automated or manual. Operating the exact num ber of aerobic zones at optimal dissolved oxygen control levels would be critical in pow er management. Chemical dosage for methanol or coagulating chemical is a key factor at su ch facilities. The labor cost included in this section uses the national averag e rate of $25 per hour. Regional labor cost variations can be expected.

As shown in Figures 4-13, 4-14, 4-18, 4-19, 4-24, and 4-25, the distribution of the O&M costs among the various components will vary depending on facility size, in addition to natural variations based on th e selected technology, the char acteristics of the influent wastewater, and the required level of treatment. In general, smaller facilities will have a larger fraction of the total O&M costs devoted to labor compared to that fraction for larger facilities. This is because, essentially, a 10-MGD facility will not require 10 times the staffing of a 1-MGD facility but will require 10 times the energy and chemical expenditure. Thus, the overall fraction devoted to staffing decreases, and th e relative fraction devoted to other components increases. For the technologies examined in this study, the labor costs for 1-MGD facilities are generally around 40 to 50 percent of the total, while the costs for 10- MGD facilities are generally ar ound 15 to 25 percent of the tota l. These are general trends, and local conditions could greatly affect the final fractions.



### 4.5 Summary

In upgrading existing facilities, re aders are encouraged to evaluate all feasible alternatives and determine the best plan in accordance withthe success criteria established early in the planning phase. Key factors in the decisionm aking include the proposed permit limits, the availability of an existing facility for modi fication, site requirements, costs in capital and O&M, sustainability in energy, chemical and sl udge management, and potential odor or other environmental factors. For analyzing costs, the reader can examine what has happened at potentially similar facilities, as described in Section 4.1. From the case studies developed for this manual, as well as surveys carried out in Maryland and Connecticut, it was found that costs could vary greatly, depending on the natu re of the existing facility, the required upgrade, and other site-specifi c factors. The costs for modification ranged from a low of $0.20 to a high of $5.25 per gpd capacity.

Planning-level capital, O&M, and life-cycle co st curves for 12 retrofit and 20 expansion alternatives were developed using CAPDETWorks. These curves provide an estimate of the costs; exact costs will likely be different because of local conditions. In general, unit costsSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 4: Cost Factors 4-35 are higher for smaller facilities than for larger facilities because of economies of scale. The relative fraction of the O&M costs for the expansion alternatives were also determined for 1-and 10-MGD plants. In general, labor repres ents 40 to 50 percent of the O&M costs for 1-MGD facilities and 15 to 25 percent of the O&M costs for 10-MGD facilities.

The cost curves were developed so that project teams can directly comp are costs of selected alternatives. Project teams following the selecti on matrix process described in Chapter 5 can use the curves for capital, O&M, or life-cycle costs in their evalua tion of alternatives.



### 4.6 References

CTDEP (Connecticut Department of Environmental Protection). 2006. Annual Report of the Nitrogen Credit Advisory Board, 2006

Hydromantis Corporation. 2004. CAPDETWorks User’s Manual , v 2.1. Hydramantis Corporation, Hamilton, Ontario.

MDE (Maryland Department of the Environment). 2004. Refinement of Nitrogen Removal from Municipal Wastewater Treatment Plants . Maryland Department of the Environment, Baltimore, MD.

Stephenson, R., and J. Mohr. 2005. Nutrient Removal in an Uncertain Regulatory Environment. In Proceedings of the Water Envi ronment Federation’s 78th Annual Technical and Educational Conference , Washington, DC, October 29–November 2, 2005, pp. 518–532.

USDA (U.S. Department of Agriculture). 2007. Price Indexes and Discount Rates

. U.S. Department of Agriculture, Na tural Resources Conservation Service. http://www.economics.nrcs.usda.gov /cost/priceindexes/index.html . Accessed May 15,
2007.

Wright, D.G., G.G. Patry, C.E. Letman, and D.R. Woods. 1988. A Procedures for Estimating the Capital Cost of Ontario Wastew ater Treatment Plant Using CAPDET. Canadian Journal of Civil Engineering 15:799–806.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 5: Upgrading Existing Facilities 5-1 

## CHAPTER 5: Upgrading Existing Facilities

The topic of upgrading existing facilities has become increasingly important because many publicly owned treatment works (POTWs) in th e United States are considering the addition of nutrient removal technologies. Th is chapter presents important issues to be considered in upgrading existing facilities, incl uding evaluation of av ailable technologies, general selection factors, design and operational factors, and finally selection of the appropriate technology using a decision matrix methodology.



### 5.1 General Approach to Upgrading

In addition to the important topics presented in this chapter for assessi ng appropriate nutrient removal technologies, readers are encouraged to review relevant technical references on the subject of upgrading wastewater treatment pl ants, such as WEF Manual of Practice No. 28, Upgrading and Retrofitting Water and Wastewater Treatment Plants (WEF 2004); EPA’s Handbook: Retrofitting POTWs for Phosphorus Removal in the Chesapeake Bay Drainage
Basin (1987); EPA’s Nitrogen Control Manual (1993) and, specifically on nutrient removal, WEF Manual of Practice No. 30, Biological Nutrient Removal Operation in Wastewater Treatment Plants (WEF 2005).



### 5.1.1 Success Criteria One of the key tasks of the project team eval uating a facility upgrade is to establish success criteria for the project early in the planning st age. In doing so, the te am should seek input from all stakeholders in the permittee’s organi zation. The stakeholders might include elected officials; utility administrators; and repr esentatives from operation, maintenance, and technical services at the facility. They might also include representatives from environmental organizations, citizens groups, and the public . The selection criteria might include sustainability, cost-effectiveness, ease of operation and maintenance (O&M), project schedule, and site requirements. Sustainability implies a simultaneous focus on economic, social, and environmental performance. A techno logy selected on the basis of sustainability has reliably lower energy use, lower production of sludge, lower use of added chemicals, and generally lower use of resources compared to other technologie s. Another selection criterion to be considered is the potential to use the treated wastewater for reuse applications. For nutrient removal technologies, se lection considerations incl ude energy usage, chemical usage, and generation of biosolids. The projec t team can establish a rating formula by which each topic is assigned a weighting factor. A fi nal score can thereby be obtained for each alternative evaluated.Municipal Nutrient Removal Technologies Reference Document September 2008

5-2 Chapter 5: Upgrading Existing Facilities 

### 5.1.2 Facility Planning The project team has three main tasks to carry out:

1. Assess the existing facility and its ab ility to meet permit requirements.

2. Identify needed upgrades.

3. Develop and evaluate feasible alternatives.

Choices in upgrading the plant might include modifying existing facilities, adding new processes in parallel or in series, or replacing existing pro cesses with new ones. Critical issues to be considered by the project team include agreement on design loadings for the planning period based on mass bala nce and energy balances (where applicable), the degree of flexibility for future uncertainties in regulat ion or influent wastew ater characteristics (or both), operation during construc tion, interim permit compliance, and the phasing of the construction in the future. Related project issues include the schedule, safety, site requirements, the potential for odor, and the costs of the alternatives.

The project team typically presents a recomm ended implementation plan, from previously agreed-upon selection criteria, to the approval authority. The t eam can invite the public to participate in the evaluation.



### 5.2 Available Technologies

WEF Manual of Practice No. 8, Design of Municipal Wastewater Treatment Plants (WEF and ASCE 1988), Volume II, Chapter 15, defines an integrated process as a method that combines biological and chemical or physic al unit operations and processes to reduce concentrations of nitrogen and phosphorus in plan t effluent to below levels that would be attainable solely by synthesis in a typical s econdary treatment facility. The manual, referred to as MOP 8, includes design guidelines. It also identifies inherent limitations in biological processes, which stem from vari ables such as influent wastewater characteristics, methods of solids handling, and the biological population dynamics of mixed cultures within a given treatment facility. For example, an insufficien t supply of volatile fatty acids (VFAs) during the year can decrease denitrif ication and phosphorus removal.

Decreased VFAs are expected with cold wast ewater temperatures and wet-weather events. Nutrients, particularly ammonia and phosphor us, can be released because of prolonged sludge storage and digestion. High nutrient concentrations can al so be found in return flows from the other sludge-handling processes. S econdary release of nut rients in secondary clarifiers and tertiary filter s can occur, and the nutrients are capable of overloading the biological process when returned upstream of the sensitive unit process. Upsets from slug discharges from industries can also negatively affect the treatment plant by organically or hydraulically overloading the biol ogical process or introducing pollu tants that are toxic to theSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 5: Upgrading Existing Facilities 5-3 microorganisms. Because of thes e biological limitations, the biol ogical system often needs to be supplemented by a physical process, such as final filtration, to remove additional phosphorus and nitrogen-bearing solids; chem ical addition, to precipitate additional phosphorus; or an external carbon source for denitrification. Chemical coagulants and flocculants are added to wastew ater to remove phosphorus sepa rately or concurrently with nitrogen removal.

The project team can consider t echnologies on the basis of target concentrations, as shown in Tables 5-1 through 5-4, which ar e adapted from similar tables in Chapter 2. These tables show the levels of treatment possible by using various technologies for the removal of total nitrogen (TN), total phosphorus (TP), or both. While the lists are reasonably comprehensive, a number of technologies, partic ularly emerging technologies, are not included in the tables. Such technologies might be available and a ppropriate for a given application and should therefore be considered, where applicable.

Table 5-1. Process list: TP

Concentration Technology
Up to 1 mg/L All
1.0 to 0.5 mg/L Chemical precipitation A/O; filter preferred 5-stage Bardenpho PhoStrip; filter preferred
SBR
0.1 to 0.5 mg/L Chemical precipitation with filter 3-stage Westbank with filter Chemical precipitation with tertiary clarifier and filter
Modified UCT with filter
PID with filter 5-stage Bardenpho with chemical and filter Step-feed AS with filter
0.1 mg/L and below Membrane filter High-performance filter: Trident Dynasand D2 Advanced Filtration System Blue PRO CoMag Land application/infiltration bed

Notes: A/O = anoxic/oxic AS = activated sludge PID = phased isolation ditch SBR = sequencing batch reactor UCT = University of Cape Town process “filter” = conventional filter, such as a sand filter, deep bed anthracite filter, dual-media filter, or one of the other tradi tional filters described in Chapter 2Municipal Nutrient Removal Technologies Reference Document September 2008

5-4 Chapter 5: Upgrading Existing Facilities Table 5-2. Process list: TN

Concentration Technology 8 mg/L or higher All; no filter required
3 to 8 mg/L A 2 O; filter preferred
MLE
SBR Cyclic activated sludge
BAF
IFAS
MBBR 3-stage Westbank 4-stage Bardenpho Post-aeration anoxic with methanol (Blue Plains process)
3 mg/L and below 4-stage Bardenpho; filter required
PID with filter
Denitrification AS with filter Step-feed AS with filter
Denitrification filter: Tetra filter Leopold filter Biostyr filter

Notes: A 2 O = anaerobic/anaerobic/oxic AS = activated sludge BAF = biological aerated filter IFAS = integrated fixed-film activated sludge MBBR = moving-bed biofilm reactor MLE =modified Ludzack-Ettinger PID = phased isolation ditch “filter” = conventional filter, such as sand filter, deep bed ant hracite filter, dual-media filter, or one of the other traditi onal filters described in Chapter 2

Table 5-3. Process list: ammonia nitrogen

Concentration Technology
All Add aeration and clarifier
IFAS
MBBR
A/O
MLE
Oxidation ditch
SBR 3-stage Westbank

Notes: IFAS/MBBR = integrated fixed-film ac tivated sludge/moving-bed biofilm reactor A /O = anoxic/oxic MLE = Modified Ludzack-Ettinger SBR = sequencing batch reactorSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 5: Upgrading Existing Facilities 5-5 Table 5-4. Process list: TN plus TP

TN concentration TP concentration Technology 3 to 8 mg/L > 1 mg/L SBR; filter preferred
Modified UCT
A/O PhoStrip II 3-stage Westbank Step-feed AS
PID 5-stage Bardenpho Table 5-2 alternatives for TN 3 to 8 mg/L plus chemical phosphorus removal 3 to 8 mg/L 0.5 to 1 mg/L SBR; filter required
Modified UCT
A/O PhoStrip II 3-stage Westbank Step-feed AS
PID 5-stage Bardenpho Table 5-2 alternatives for TN 3 to 8 mg/L plus chemical phosphorus removal 3 mg/L or less 0.1 to 0.5 mg/L Step-feed AS; filter required 5-stage Bardenpho; filter required PID; filter required
Denitrification filter Table 5-2 alternatives for TN 3 mg/L or below plus chemical phosphorus removal and filtration

3 mg/L or less 0.1 mg/L or less Step-feed AS + tertiary clarifier with chemical and filter
Denitrification filter with chemical and additional filter Ammonia removal process Phospshorus process Upstream process
MBR with chemical Land application from above three

Notes: A/O = anoxic/oxic AS = activated sludge PID = phased isolation ditch MBR = membrane bioreactor SBR= sequencing batch reactor UCT = University of Cape Town process “filter” = conventional filter, such as a sand filter, deep bed anthracite filter, dual-media filter, or one of the other tradi tional filters described in Chapter 2Municipal Nutrient Removal Technologies Reference Document September 2008

5-6 Chapter 5: Upgrading Existing Facilities After the project team identifies the processes th at are capable of meeting the desired target levels for nitrogen, phosphorus, or both, they can review the descriptio ns of the processes and schematics in Chapter 2. Capital and O&M costs can be found in Chapter 4. Section 5.3, Technology Selection Criteria, and Section 5.4, De sign and Operational Factors in Nutrient Removal, can then be reviewed. Using all this information and the in dividual conditions at the plant, the project team can narrow down the list of processes to be evaluated for implementation and then conduct an evaluation as described in Section 5.5, Finalizing Process Selection, to select the process th at will be used to upgrade the plant.



### 5.3 Technology Selection Criteria

In developing technology alternatives, the proj ect team should consider appropriate factors for design and operation. These include site cons traints; reliability of the technology; capital and O&M costs; and sustainabi lity, including energy usage, chemical usage, and additional sludge protection. A detailed discu ssion on reliability and contribu ting factors is presented in Chapter 2 of this document, and cost considerat ions are provided in Chapter 4. This chapter presents process selection factors for the project team to consider.

Tables 5-5 and 5-6 contain fact ors that affect the selection of feasible technologies for nitrogen and phosphorus removal, respectively. Table 5-7 summarizes the selection factors for technologies that remove both TN and TP. Thes e tables present key factors, arranged in a matrix that should be considered in selecti ng the best technology for a given location. The factors in the tables represent general trends . However, some of the factors might not be applicable in specific situations. For exampl e, in warm-weather locations, a building might not be required, despite a Yes for that technology.

For the same discharge limit, the constraints could favor one technology over another. Some of the processes can be used in series. For example, to achieve low TN levels, a denitrification filter might be used following th e 4-stage Bardenpho process. Both the 4-stage Bardenpho and filtration lines woul d need to be reviewed in Ta ble 5-5 to determine the site, wastewater, and operational factor s that apply to these processe s. Similarly, to achieve low TP effluent concentrations, a 5-stage Bardenpho process could be used in combination with chemical precipitation and filtration. All three lines for these processes would need to be reviewed in Table 5-6 to determ ine the applicable selection factor values. Descriptions of the columns under each factor category are provided below.

The following three sections (5.3.1, 5.3.2, and 5.3.3) discuss selection factors to be considered for achieving nitrogen and phos phorus removal, as well as nitrogen plus phosphorus removal.

• Footprint. The Footprint column refers to the relative amount of space that a process requires, which depends on the number of tanks and the required size of each process. General size indications of small, medi um, and large are provided in the tables.September 2008 Municipal Nutrient Removal Technologies Reference Document

Chapter 5: Upgrading Existing Facilities 5- 7Table 5-5. Technology selection matrix: nitrogen removalSite factorsWastewaterfactorsOperation factorsProcessFootprintBuildingneededConstructionin existingaerationbasinPipingandpumpingExtraheadneededSecondaryprocessrecyclestreamsAdditionalcarbonsourceneededExtraelectricityChemicalsneededAdd’lsludgeDenitrificationfiltersSmall Yes No Yes Yes No Yes Yes Yes YesMBBR Medium No Maybe1No No No Maybe No Maybe MaybeSBR/cyclicactivatedsludgeMedium No Yes No Maybe No Maybe Yes Maybe MaybeMLE/3-stageWestbankMedium No Maybe Yes No Yes Maybe Yes Maybe MaybePhasedisolation ditchLarge No Maybe No No No Maybe Yes Maybe Maybe4-stageBardenphoLarge No Maybe Yes No Yes Maybe Yes Maybe MaybeA2O Medium No Maybe Yes No Yes Maybe Yes Maybe MaybeAnoxic zonefollowingaeration(BluePlains)Medium No Maybe No Maybe No Yes Yes Yes YesBiologicalaeratedfiltrationMedium Maybe No Yes Yes Yes Maybe Maybe Maybe MaybeStep-feed AS Large No Yes Yes No Yes No No No NoIFAS Medium No Maybe1No No Yes Maybe Maybe Maybe MaybeNotes:1Installation of media retention screens, as needed.Additional carbon source and chemical needs: Toobtain sufficient carbon for anoxic reaction, use either external source (methanol) or step-feed activated sludge.Construction needs: External filters require extraspace and could require abuilding depending on conditions.Adjustments in basins include walls to section off anoxic basins and, potentially, piping to accommodate step-feed activated sludge.Additional sludge generation is partially dependenton the need for addition of a carbon source.Selection factor designations are general guidelinesand may not apply for allsite-specific conditions.Municipal Nutrient Removal Technologies Reference Document September 2008

5-8 Chapter 5: Upgrading Existing FacilitiesTable 5-6. Technology selection matrix: phosphorus removalSite factorsWastewaterfactorsOperation factorsChemicalsneededProcessFootprintBuildingneededConstructionin existingaerationbasinPipingandpumpingExtraheadneededSecondaryprocessrecyclestreamsAdditionalcarbonsourceneededExtraelectricityC add’nChemP remAdd’lSludgeA/O Medium No Yes No No No Maybe Yes MaybeMaybe NoSBR/CAS Medium No Yes No Maybe No No Yes No Maybe NoVIP/modifiedUCTMedium No Maybe Yes No Yes Maybe Yes Maybe Maybe NoChemicalprecipitationSmall Yes No Yes No No No Minimal No Yes YesTertiaryclarifier/tertiaryfilterMedium Maybe No Maybe Yes Yes No Yes No Yes YesPhoStrip Small No No Yes No Yes No Yes No Yes Yes5-stageBardenphoLarge No Maybe Yes No Yes Maybe Yes Maybe Maybe Maybe3-stageWestbankMedium No Maybe Yes No Yes Maybe Yes Maybe Maybe MaybeEBPR with VFAaddition andfiltersMediumMaybe(Filters)Maybe Yes Yes Yes Yes Yes Yes Maybe MaybeMBR Small Yes Yes Yes Yes No Maybe Yes Maybe Yes YesPhasedisolation ditchLarge No Maybe No No No No Yes No Maybe MaybeMembrane filter Small Maybe No Yes Yes Yes No Yes No Yes YesCoMag Medium Maybe Maybe Yes Yes Yes No Yes No Yes YesInfiltration basin Large No No No Yes No No Minimal No Yes YesNotes: CAS = cyclic activated sludge; VIP = Virginia Initiative process; EBPR = enhanced biological phosphorus removal; VFA = volatile fatty acidsSee “Tertiary clarifier/tertiary filter” row for information that applies to specialty filters.Selection factor designations are general guidelinesand may not apply for allsite-specific conditions.September 2008 Municipal Nutrient Removal Technologies Reference Document

Chapter 5: Upgrading Existing Facilities 5-9Table 5-7. Technology selection matrix: nitrogen and phosphorus removalSite factorsWastewaterfactorsOperation factorsChemicalsneededProcessFootprintBuildingneededConstructionin existingaerationbasinPipingandpumpingExtraheadneededSecondaryprocessrecyclestreamsAdditionalcarbonsourceneededExtraelectricityCAdd’nChem PRemAdd’lsludgeStep-feed withselectorMedium No Yes Yes No No No No No Maybe MaybeIFAS withselectorMedium No Maybe1No No Maybe Maybe Maybe Maybe Maybe MaybeA2O Medium No Yes Yes No Yes Maybe Yes Maybe Maybe MaybeSBR/CAS Medium No Yes No Maybe No Maybe Maybe Maybe Maybe MaybeVIP/modifiedUCTMedium No Maybe Yes No Yes Maybe Yes Maybe Maybe MaybePhostrip II Medium No No Yes No Yes No Yes No Yes Yes3-stageWestbankMedium No Maybe Yes No Yes Maybe Yes Maybe Maybe Maybe5-stageBardenphoLarge No Maybe Yes No Yes Maybe Yes Maybe Maybe MaybeEBPR withVFA additionMedium No Maybe Yes Maybe No Yes Yes Yes Maybe MaybeMBR Small Yes Yes Yes Yes Yes Maybe Yes Maybe Yes YesChemicalprecipitationSmall Yes No Yes No No No Minimal No Yes YesFiltration Medium Maybe No Maybe Yes Yes No Yes No Yes YesDenitrificationfilterSmall Yes No Yes Yes No Yes Yes Yes Maybe YesPhasedisolation ditchLarge No Maybe No No No No Yes No Maybe MaybeNotes:1Installation of media retention screens, as needed.Additional carbon source: To obtain sufficientcarbon for anoxic reaction, use externalsource (methanol) or step-feed activated sludge.Construction needs: Adjustments in basins include walls to section off anoxic basins and, potentially, piping to accommodate step-feed activated sludge.Selection factor designations are general guidelinesand may not apply for all site-specific conditionsMunicipal Nutrient Removal Technologies Reference Document September 2008

5-10 Chapter 5: Upgrading Existing Facilities • Building Needed. This column indicates whether the process should be placed in a building to prevent opera tional problems at low temperatures. An entry of Maybe in the tables indicates that for plants in th e north (with low winter temperatures) the equipment probably needs to be placed in a building, while for plants in more moderate climates it might not.

• Construction in Exis ting Aeration Basin. The existing aeration basin might require modifications (construction) to implement the process. Processes that are external to the secondary treatment process, such as filters, would not involve construction in the existing aeration basin. Several of the pr ocesses require a pa rticular ratio of anaerobic, anoxic, and aerobic zones to function properly. Construction within the existing aeration basin would involve buildi ng walls, baffles, or both to create such zones. Replacement of the aeration devices wi th mixers would also be needed in the anaerobic and anoxic zones. A table entry of Maybe indicates that modifications might be needed, depending on the size of the existing aeration basins. For example, if there is space to create an anoxic z one within the existing aeration basin and sufficient volume remains to perform nitrifi cation in the aerobic zone, the answer is
Yes . Conversely, if insufficient volume rema ins for the aerobic zone, the anoxic zone would be constructed ahead of the existi ng aeration basin and mi nimal changes would be made, with the exception of allowing fl ow to enter the aeration basin from the newly constructed anoxic zone.

• Piping and Pumping. The term piping and pumping refers to whether the process involves return lines, requires more than one feed line (in th e case of step-feed applications), or requires additional pumping equipmen t, or both. In the case of processes that use filters (for nitrogen or phosphorus removal), the column entry is
Yes because the filter backwash is returned upstream of the secondary process. Piping and pumping are needed for all processes that involve new internal recycle lines. An entry of Maybe indicates that internal recycles might be needed, depending on the existing process. For example, an existing modified Ludzack-Ettinger (MLE) process that is being upgraded to a 4-stage Barde npho might not need a new internal recycle, depending on the existing capacity, whereas an existing extended-aeration plant would require the installation of a new internal recycle line.

• Extra Head Needed. The hydraulics for the proposed process should always be reviewed to verify that the wastewater flows through the plant as designed. Certain processes require additional head, which li kely needs to be provided by pumps, for the wastewater to enter and pass through the process, and th erefore additional land is required. Processes that require additiona l biological tanks likely require little additional head, whereas add-on processes might require pumping.

• Secondary Process Recycle Streams. This column identifies the processes that have internal recycle lines that require additional land. To achie ve low effluent nitrogenSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 5: Upgrading Existing Facilities 5-11 limits, internal recycle lines are usually re quired to denitrify th e nitrates created during nitrification. Phosphorus removal te chnologies, unless paired with nitrogen removal processes, usually have only a return activated sludge (RAS) line.

• Additional Carbon Source Needed. Some processes require an additional carbon source to function. For example, denitrifi cation filters requir e methanol or an alternative carbon source, such as MicroC , for the process to function correctly because most of the biochemical oxygen demand (BOD) has been removed from the wastewater after secondary treatment. Ad equate carbon is needed for biological nutrient removal (BNR) (USEPA 1993). A table entry of Maybe indicates that whether additional carbon is needed de pends on the available carbon source (in the form of BOD or VFAs) in the influent to the process at the plant where the upgrades are being evaluated. Some plants might re quire additional car bon sources, whereas others might not.

• Additional Electricity. An increase in electricity usage is expected in cases where the upgrade requires the addition of pumps because of increased hydraulic head, additional reactor volume (to aerate or provide mixing), or new or increased return rates. A table entry of Maybe indicates that electricity usage depends on the existing process at the plant and the t ype of upgrade be ing evaluated.

• Chemicals Needed. This column is included under Operation Factors to emphasize the cost associated with chemical addition. If VFAs are generated by using an on-site fermenter, no additional chemical cost would be expected at the plant, although electricity usage might increase somewhat because of the power required to operate the mixer. Other chemicals that might need to be added include caustic soda or lime for alkalinity control and me tal salts, such as alum or ferric chloride, for phosphorus removal.

• Additional Sludge. Additional sludge generation is typi cally associated with chemical addition. If the process or the site-specifi c conditions at the plant being retrofitted require chemical addition, additional sludge will be generated compared to the amount generated by the existing process. Pl ants that do not need chemical addition are unlikely to generate significant additional sludge, unless an expansion is being performed in conjunction with the pl ant upgrades. All additional sludges will typically incur additi onal disposal costs.



### 5.3.1 Nitrogen Removal

Site Factors Footprint The footprint of the selected process is importa nt in any retrofit because space is typically limited. For retrofitting an existing activated-slu dge system, an additional footprint could beMunicipal Nutrient Removal Technologies Reference Document September 2008

5-12 Chapter 5: Upgrading Existing Facilities avoided with the MLE process. MLE is a single -stage, two-basin system in which the anoxic zone precedes the aerobic zone , with recycling of aerobic mixe d liquor to allow the nitrate arising in the aerobic zone to be denitrifie d. This configuration ha s the advantage of not requiring an additional carbon source for the anoxic process because the anoxic microorganisms are mixed with the full-strengt h waste from the primary clarifier. The disadvantages of the process are twofold: the overall nitrogen removal is limited by the mixed-liquor recycling rate, and the oxygen included in the recycle stream reduces denitrification (WEF 2006). Thus, MLE is suitabl e where the site is limited and the level of treatment required is in the mid-ra nge between 7.5 and 8 mg/L for TN.

The 3-stage Westbank process is similar to the 5-stage Bardenpho without the last two zones. In addition, the 3-stage Westbank process has th e capability to feed a portion of the primary effluent to the head of the process, the anaerob ic zone, and/or the anoxic zone. This step-feed approach results in a smaller anoxic zone co mpared to prior practi ce because of a steady supply of readily biodegradable carbon for denitrification.

Denitrification filters provide the smallest foot print for a newly installed process, and they are a proven option for achieving low nitroge n concentrations. The technology involves passing secondary effluent through a deep-bed fi lter that contains denitrifying organisms. The process has the additional advantage of actin g as a filter for removing suspended solids. Implementation requires capital expenditures fo r equipment, building, and costs associated with a pumping station where av ailable hydraulic head is limited. In addition, denitrification filters require an external carbon source, typically methanol, wh ich results in a significant chemical cost. The effluent TN concentrations can be below 3 mg/L; they are less than 2 mg/L at some facilities.

For ammonia removal, using an integrated fixed-film activated sludge (IFAS) technology or a moving-bed biofilm reactor (M BBR) technology offers a small footprint as a retrofit into aeration basins or as an add-on process at existing facili ties (Copithorn 2007).

Building Needed Most of the retrofit systems for nitrogen re moval do not need additional buildings because the systems use existing aeration basins or construction of exte rnal anoxic zones. Filters, such as denitrifying filters and upflow biological aerated filters, could be housed in buildings in cold-weather locations. Certain manufacturers use biological upflow filters in integrated systems designed to achieve nitrification and denitrification in a single unit. In addition, upflow filters can be operated aerobically to achieve nitrification (WEF and ASCE 2006).

Construction in Existing Aeration Basin Most of the retrofit technologi es make use of existing aeration basins because of site limitations and the need to increase capacity in existing tanks. Where n eeded, partitions are installed to create zones, and sc reens are installed to hold microbi al carrier media, if required.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 5: Upgrading Existing Facilities 5-13 Such media are used in both the MBBR and IFAS systems (Johnson et al. 2005; McQuarrie et al. 2004). Example installations include de nitrification by IFAS using sponge media in Fairfield, Connecticut; ringlace in Annapolis, Maryland; and BioWeb in Windsor Locks, Connecticut. Nitrification examples include Kaldnes media in Broomfield, Colorado, and Cheyenne, Wyoming (Loader 2007). Readers are encouraged to review the process descriptions for MBBR and IFAS in Chapter 2.

The phased isolation ditch (PID) is appropriate only if an oxi dation ditch is already present but would require construction in the existi ng aeration basin. Filtration units, such as denitrification filters and biological aerated f ilters, are usually not constructed in existing aeration basins. The MLE, 3-stage Westbank, and 4-stage Bardenpho processes would likely require construction in the aerati on basin to install baffle walls a nd internal recycle lines. If sufficient volume is available, anoxic and anaerobic zones (in the case of the 3-stage Westbank and 4-stage Bardenpho process) could be constructed in the existing aerobic tank. The step-feed activated-s ludge system would require constr ucting anoxic basins and feed points within the aeration basin. If sufficient vol ume is not available, some of the alternating anoxic and aerobic basins could be constr ucted outside the ex isting aeration basin.

Piping and Pumping/Extra Head Need ed/Secondary Process Recycle Streams Most of the nitrogen removal technologies involve sec ondary recycles. Exceptions include the MBBR, denitrifying filters, sequencing batc h reactor (SBR), cyclic activated sludge (CAS), anoxic zone following aeration, and PID. The piping and pump size for the secondary recycle depend on the design flow, but they mu st be sufficient to maintain the needed nutrient concentrations in each zone so that ni trate is removed to the target level (WEF and ASCE 2006). The step-feed activated-sludge and 3-stage Westbank processes would also require piping for the multiple feed points to the anoxic zones.

Pumping would be required in plants with denitrifying filters because sufficient head following the aeration basins is not usually available. The filt ers could be constructed as a new add-on process such as the Tetra Filter or Leopold filter or as a retrofit of existing granular media filters into bi ological anoxic filters (BAFs).

Wastewater Factors

Additional Carbon Source Needed With the exception of the step-feed activated-s ludge process, any of the biological nitrogen removal processes could need additional carbon, depending on the primary effluent characteristics at the specific plant. The carbon source could be methanol or a VFA source inside or outside the plant. VFAs can be adde d directly in the form of acetic acid, brewery waste, molasses, or other sugar forms. A fermen ter could also be used to generate VFAs onsite from primary sludge, RAS, or the supernatant from the anaerobic digesters. Additional discussion is presented in Section 5.4 of this chapter, Design and Operational Factors inMunicipal Nutrient Removal Technologies Reference Document September 2008

5-14 Chapter 5: Upgrading Existing Facilities Biological Nutrient Removal. Methanol or MicroC would need to be added for the denitrification filter to function properly.

Operational Factors Additional Electricity If internal recycle lines are not included in the existing proces s, electricity costs would likely increase when implementing biological nitrogen removal. Electricity costs would also increase with the use of a denitrification f ilter or biological aerate d filter because of the pumping that would be required.

Chemicals Needed All TN removal applications require adequate influent al kalinity concentrations for nitrification to occur. The denitrification process restores some of the alkalinity consumed during nitrification, but there is a net loss of alkalin ity through the TN removal process. In soft-water regions, nitrifica tion consumes alkalinity, lowers pH, and impairs biological processes. Adequate alkalinity is maintain ed by adding lime or caustic when influent alkalinity levels are low. Maintaining a target pH between 6.2 and 6.5 standard units (s.u.) will minimize the cost of adding lime or caustic soda in nitrifying facilities. Chapter 2 presents more details on alkalinity.

As mentioned previously, a carbon source in the form of methanol or VFAs might also be required for biological nitrogen removal. The filt er options would also require the addition of methanol or an alternative carbon source for nitrogen removal.

Additional Sludge Upgrades that require the addition of methanol would pr oduce additional sludge compared to the existing process. If chemical addition is not needed, the sludge yield would not be expected to change significantly.



### 5.3.2 Phosphorus Removal Plant Factors

Site Factors Footprint Chemical addition of metal salts, such as ferri c chloride or alum, requires a minimal footprint for installing chemical feed pumps and a stor age tank. The capital cost is low, but O&M costs are high because of ongoing chemical costs. Chemical feed doses increase exponentially as the phosphorus effluent goal approaches 0 mg/L; th e feed dose curve is particularly steep in the range of 0 to 0.3 mg/L. The minimu m phosphorus concentration that can be achieved economically through chemical addition is dependent on the wastewater characteristics and the effectiveness of the cl arifiers. Polymer addition is practiced in many plants to aid settling, with minimal site re quirements. Chemical addition can increase theSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 5: Upgrading Existing Facilities 5-15 effectiveness of other phosphorus removal technol ogies, such as tertiary clarifiers and filters. Therefore, chemical addition is rarely used as the sole phosphorus removal technology to achieve low-level phosphorus lim its (less than 0.2 mg/L).

Membrane bioreactors (MBRs) have a relatively small footprint because of the higher mixedliquor suspended solids (MLSS) concentration in the aeration basin when compared to conventional plants that rely on clarifiers to remove solids. The pores in the membranes form a physical barrier to particles/fl oc that is larger than the por e size (and any biological growth that forms on the membrane). Clarifiers require floc of sufficient size a nd density to settle so the floc can be removed from the flow str eam. The higher MLSS concentration in the MBR system allows more biomass to be treated in a smaller tank.

The SBR and CAS systems have smaller foot prints than the other activated-sludge alternatives because clarifiers ar e not needed to settle the mixed liquor. The settling occurs in the same tank as the reaction phase.

The anaerobic/oxic (A/O) process consists of three anaerobic cells upstream of an aerated zone. This process might require little additional footprint in a retrofit application if sufficient volume capacity is available in the existing aeration basin. Otherwise, additional tankage would need to be constructed for the anaerob ic cells. A fermenter might be required if additional VFAs are needed to meet biological phosphorus removal requirements.

Alternatives that include th e 5-stage Bardenpho process woul d require a large footprint because two anoxic zones would be needed in addition to the anaerobic zone. The 5-stage Bardenpho process is usually ge ared more toward removal of both phosphorus and nitrogen, rather than phosphorus removal alone. However, the process denitrifies the nitrates produced during nitrification, reducing th e amount of nitrates in th e RAS, which increases the effectiveness of the anaerobic zone. The 5-st age Bardenpho process with chemical addition and filtration would require a very large footprint. The PID also has a relatively large footprint because two oxidation ditch tanks w ould need to be constr ucted. The infiltration bed would require the largest footprint among a ll the technologies, but it also provides the highest level of removal with low O&M costs.

Buildings Buildings are usually required for chemical feed equipment and filtration processes in areas of the country that experience low winter temp eratures. The chemical needs to be protected to avoid freezing, which can decrease the efficien cy or make feeding the chemicals difficult. Blowers that provide air to the aeration tanks w ould need to be installed in a building for ease of maintenance as well as for noise control. The fermenter, anaerobic, anoxic, and aerobic tanks typically would not need to be c overed or constructe d inside a building.Municipal Nutrient Removal Technologies Reference Document September 2008

5-16 Chapter 5: Upgrading Existing Facilities Construction within Aeration Basins
Anaerobic zones could be constructed in existin g aeration basins if sufficient capacity would remain for the removal of BOD and ammoni a nitrogen (if needed). SBRs are usually constructed at new plants rather than as a retrofit alternat ive because the tank is usually deeper than a typical aeration basin and extensive piping changes would be required.

Chemical feed equipment, fermenters, and fi lters would all be c onstructed outside the aeration basin. Piping to connect any of the chem ical feed pumps, fermenter tank, or filter backwash system to the aeration basins would be needed, but construction within the aeration basins would be minimal. The PhoStrip proc ess treats a portion of th e settled mixed liquor from the secondary clarifier. Therefore, cons truction within the aera tion basin would not be necessary, but modifications to th e RAS system would be needed.

Conversion to an MBR system could involve significant constructi on within the aeration basins. In addition to installing the membrane s, a portion of the aeration basin might be converted to anaerobic and anoxic zones to promote biological phosphorus removal and alkalinity recovery. If sufficient aerobic capacity is not available at the existing plant, the anaerobic and anoxic zones, as well as the me mbrane tank, could be constructed outside the aeration basins.

Piping and Pumping/Extra Head/Secondary Recycle Streams The 5-stage Bardenpho process, MBRs, and filters all have return stream s. Internal return streams are part of the 5-stage Bardenpho and MBR processes, and backwash is returned during cleaning of the filters. Filter backwash can be returned to the he ad of the plant or to the secondary process. Phosphorus concentratio ns in the filter backwash could be high. Returning the backwash to an e qualization basin to allow the flow to be slowly blended with the raw influent might improve the phosphorus removal efficiency by not introducing a slug of phosphorus all at once. Alternatively, sidest ream treatment of the filter backwash, which could involve settling the solids before retu rning the flow, could also improve phosphorus removal at the plant.

Under most circumstances MBRs require additi onal head to draw wastewater through the membranes at the end of the process. Certai n manufacturers might be able to provide a gravity-fed system in special situations, dependi ng on the hydraulics of th e rest of the plant. Pumping is generally required at plants that select filtration to achie ve phosphorus removal.

Wastewater Factors

Additional Carbon Source Needed In biological phosphorus removal, a sufficient concentration of VFAs is required. VFAs are present in sufficient quantity in the wastew ater in many locations but need to be supplemented in other locations. Where neede d, VFAs can be added directly from anSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 5: Upgrading Existing Facilities 5-17 external source in the form of acetic acid, brew ery waste, molasses, or other sugar forms. A fermenter could also be installed to generate VFAs on-site from primary sludge, RAS, or the supernatant from the anaerobic digesters. Carbon sources would not be necessary for process options that rely on chemical phosphorus rem oval or filtration, unle ss they are used in conjunction with biological phosphorus remova l. Additional discussion is presented in Section 5.4 of this chapter, Design and Operatio nal Factors in Biological Nutrient Removal.

Operational Factors Additional Electricity Anaerobic zones and fermenters require mixe rs that use a relatively small amount of electricity. Electricity usage increases would be e xpected with processes that have an internal recycle, such as the Virginia Initiative process (VIP) and 5-stage Bardenpho, whereas a significant decrease would be expected from a reduced aeration volume in the tank. The MBR process requires additional electricity for aeration and pumping. Chemical phosphorus removal would require the additi on of pumps; however, the pump s would be relatively small, and electricity usage would be expected to be minimal.

Chemicals Needed Phosphorus removal technologies could require adding metal salts like alum or ferric chloride, particularly in plants required to meet low phosphorus limits. Because of the possibility of an upset in the biological phosphorus process, many plants incorporate chemical phosphorus removal as a back-up system to ensure that permit limits can be met. At facilities that must meet an extremely low phosphorus limit, two or more feed points for coagulants and polymer a ddition would be expected.

The PhoStrip process treats only a porti on of the RAS. Following the anaerobic tank, chemical precipitation, using lime, removes th e phosphorus from the stripper overflow before returning the rest of the flow to the prim ary clarifier. Because only a portion of the wastewater is treated through the PhoStrip process, the amount of chemical needed is significantly less than what would be required in a secondary treatment process.

Additional Sludge Upgrades that incorporate chemical phosphorus removal would be expected to generate additional sludge, especially at facilities that ar e required to feed a high dose of chemicals to reach a low level of phosphorus, such as below 0.5 mg/L and especially below 0.2 mg/L. Biological phosphorus removal, however, woul d not generate additional sludge. In some circumstances, less sludge might be generate d if the coagulant was fed to the primary clarifiers, thereby reducing th e BOD and total suspended soli ds (TSS) loadings to the secondary process.Municipal Nutrient Removal Technologies Reference Document September 2008

5-18 Chapter 5: Upgrading Existing Facilities 

### 5.3.3 Nitrogen and Phosphor us Removal Plant Factors Most of the processes listed in Table 5-7 we re included in Table 5- 5 or 5-6 but without certain minor modifications (e.g., step-feed and IFAS include selectors in Table 5-7, but not those in Table 5-5). The select or would consist of an anaerob ic tank to promote biological phosphorus removal. As with the A/O process, th e anaerobic tank could be constructed in the aeration tank if sufficient capacity was avai lable to accommodate the anoxic and aerobic zones needed for treatment. No building would be required for the anaerobic tank. No internal recycles are as sociated with the selector beyond the RAS line.

The PhoStrip II process is similar to the P hoStrip process, except a pre-stripper tank is upstream of the stripper tank to remove nitrat es before they enter the anaerobic zone.

As noted in Table 5-4, chemical precipitation, tertiary filtra tion, or both could be used to provide phosphorus removal at the end of any of the processes designe d solely for nitrogen removal. Therefore, readers should consult Table 5-5 in co njunction with Table 5-7 to identify other feasible upgrade alternatives for plants attempti ng to achieve both nitrogen and phosphorus removal. Adding chemical and phys ical phosphorus removal technologies, as opposed to biological removal, mi ght be particularly attractive at a plant that already is removing nitrogen.



### 5.4 Design and Operational Factors in Nutrient Removal

The following factors are critic al in assessing existing faci lities and developing feasible alternatives:

• Influent wastewater characteristics

• Sources of biodegradable carbon

• Impact of wet-weather flows

• Managing sludge-handling processes

• Recycle flows

• Supervisory control and data acquis ition (SCADA) requirements and sensors

• Staffing requirements

• Training needs

• Pilot testing

The project team members are en couraged to consider all thes e factors and incorporate them in developing feasible technology alternatives.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 5: Upgrading Existing Facilities 5-19 Influent wastewater characteristics are importa nt to consider because the technology being considered might not operate properly if the pl ant cannot provide the conditions required. For example, if the BOD-to-TP ratio is too low in the primary effluent, biological phosphorus removal will not occur consiste ntly at the plant without a su pplemental carbon source. For plants that need to increase biodegradable carbon, considering possible sources is important. Such sources could include chemical addi tion or in-plant generation by constructing fermenters.

Permit limits for nitrogen, phosphorus, or both mu st be met during dr y- and wet-weather conditions. Wet-weather flows can be significantly higher than average dry-weather conditions for plants with combined collection systems or separated sewers that have high rates of inflow and infiltration. Biological systems can lose solids during elevated flow periods at the plant. Biological processes re ly on sufficient biomass to remove nitrogen, phosphorus, or both. Chemical and physical processes are also less efficient under elevated hydraulic conditions. Considering alternative operation strategies will minimize the possibility of exceeding permit limits because of wet-weather events. For example, the North Cary Water Reclamation Facility in North Cary, North Carolina, was able to comply with all permit limits when 8 inches of rain fell du ring Tropical Storm Alberto in 2006 by diverting water to equalization and operating the BioDen ipho process in the storm mode. For more information on this plant, see the North Cary Case Study in Volume II, Appendix A.

The return flows from sludge handling can contain significant amounts of nitrogen and phosphorus, which can organically overload the removal process and cause poor performance and the possibility that the plant’s permit lim its will be exceeded. Reviewing methods to minimize or treat the return of nitrogen and phosphorus and incor porating them into the plant design will improve the operation of the select ed process. In additi on, recycle flows from other processes, such as internal recycles, RAS, and filter backwash, can also affect the nitrogen and phosphorus removal process, part icularly if biological removal has been selected. For example, high concentrations of dissolved oxygen in the RAS can negatively affect anaerobic and anoxic zones. It takes tim e for the microorganisms to use the dissolved oxygen, turning part of an anaerob ic tank into an anoxic zone or a portion of the anoxic tank into an aeration zone. The smaller effective volume could decrease the efficiency of the

process.

Operation of the selected process coul d be optimized by incorporating SCADA and operational sensors that can be programmed to make change s using real-time analyses. Optimization could include diur nal variations in the incomi ng wastewater or occasional changes in the influent wastewater characte ristics. If the operational strategies are programmed, the plant can react to changes much more quickly, instead of waiting for results from the laboratory, which could be hours or days old. For example, online monitoring can automatically adjust the feed rate of coagulan t to be fed for chemical phosphorus removal or the methanol dose in denitrification filters. The alternative would be to wait for theMunicipal Nutrient Removal Technologies Reference Document September 2008

5-20 Chapter 5: Upgrading Existing Facilities laboratory results to show that the effluent concentrations were elevated for several days and then have to feed more chemicals to en sure that the monthly permit limit was met.

A plant upgraded to provide nut rient removal cannot function properly without enough staff to operate the processes and perform maintenanc e activities. In additi on, it is important that the staff be trained to operate the upgraded processes properly.

Pilot testing of a limited number of upgrade process alternativ es is highly recommended to verify that the process will operate as antici pated on the wastewater at a given location. Many of the processes depend on the proper influe nt wastewater characteristics and water chemistry to provide the predicted nitrogen or phosphorus concentratio ns. By incorporating pilot testing into the selection or design pha se, accommodations can be made to amend the influent wastewater, if required. For example, if it is found during pilot testing that VFAs are deficient upstream of a biological nitrogen remo val process, a fermenter can be incorporated into the design and constructed as part of th e upgrade instead of incorporating it as an expensive retrofit afte r most of construction has been completed.

A key issue is to understand the interrelati onship among the liquid treatment and solidshandling processes and to quantify and size a ll unit processes properly. The mass balance and energy balance should include a ll recycle loads for the select ed technology. Preparing a mass balance during the planning stage can contribute greatly to a successful upgrade project. The mass balance needs to include all the nutrient inputs and outputs for each unit process. The return flows from sludge-handling processes and filter backwashes that are quantified as part of the mass balance can then be incorporated into the basis of design for the upgraded plant. This approach will ensure that the processes are designed to handle the nutrient loadings from these sources.

Another key question is how to manage the un certainty in the future––changing regulations and the need for more stringent nutrient rem oval, variable wastewater characteristics, and phasing of future population growth in the servic e area. Design flexibility might be needed in anticipation of future uncertainties. It can be incorporated by constructing additional process tanks or swing zones in the secondary pro cess. The swing zone could be between the anaerobic and anoxic zones, the anaerobic and aerobic zones, or th e anoxic and aerobic zones, depending on the secondary process select ed. For example, a swing zone between the anoxic and aerobic zones would c ontain both mixers and diffusers. If it was determined that additional residence time was needed in the anoxic zone for denitrification, the mixers in the swing zone could be operated. If additional aeration was needed fo r nitrification, the diffusers could be operated. Depending on the season and influent wastewater characteristics, the swing zone could be opera ted in either mode. Switching between modes on the basis of the wastewater characteristic s would be relatively easy to do through the use of automated controls. The following sections provide addi tional information on the critical factors in design, operation, or in many cases both.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 5: Upgrading Existing Facilities 5-21 

### 5.4.1 Influent Wastewater Characteristics The evaluation begins with a review of the wastew ater data described below, if available. If few or no data are available, data should be collected, especially at the influent, primary effluent, other in-plant sources , and secondary effluent if tertiary processes are being considered. It is recommended that at least a full year of data be collected to quantify seasonal variations.

Biological Phosphorus Removal Data needed include the BOD-to-TP, VFA-to -TP, and readily biodegradable chemical oxygen demand (rbCOD)-to-P ratios in the plant influent and primary effluent. A BOD-to-TP ratio of 25 or higher at the bior eactor influent is de sirable as a general guide when there are no data for the influent to the bioreactor. At the wastewater treatme nt plant in Durham, Oregon, the performance of the enhanced biological phosphorus removal (EBPR) was unstable at a BOD-to-TP ratio of 20 or below at the aeration influent (Neethling et al. 2005). A VFA-to-P ratio of 4.3 was observed. At the McDowell Creek, North Carolina, facility, the BOD-to-TP ratio remained above 30 and had fa vorable EBPR performance. The COD-to-TP ratio should exceed 8 in the plant influent (Tre mblay et al. 2005), while the rbCOD-to-P ratio should exceed 11 (Barnard et al. 2005) or 18 with a fermenter (Barnard 2006). The important point to monitor is at the influe nt to the bioreactor, not at th e plant influent. An assessment should be made to determine whether the supply of VFAs is sufficient year-round, especially in cold months when VFA production is lowest in the sewer system and incidental sources at the wastewater treatment plant. The decision to install a fermenter s hould be based on this assessment. As Chapter 3 of this document notes , the benefits of having a fermenter on-site were documented in Kalispell, Montana, and Kelowna, British Columbia. The phosphorus removal at those plants was ach ieved strictly by a biological process using the modified University of Cape Town (UCT) process a nd 3-stage Westbank process, respectively. The reliability graphs indicate low coefficient of variation (COV) values at both plants.

Chemical Phosphorus Removal Jar testing is recommended to determine the design parameters for chemical phosphorus removal. Jar tests can be conducted to compare coagulants, such as lime, ferric chloride, and alum, to determine which one provides the most efficient and cost-effective removal. The tests should be conducted on the wastewater fr om the location where the chemical will be added. Mixing, flocculation, and settling times th at approximate the conditions that will be found at the chemical feed point and settling location should be select ed. Several doses of each coagulant should be tested, and the quantity of sludge produced from each should be compared before selecting which one will be used at the plant. Analyzing the clear liquid for TP will aid in determining which coagulant provides the best removal. Polymer can be combined with the coagulant testing to de termine whether performance can be improved. The jar tests can also be used to determine the recommended chemical feed dose by focusing on the value that provided the best result. For ex ample, if alum was selected as the coagulantMunicipal Nutrient Removal Technologies Reference Document September 2008

5-22 Chapter 5: Upgrading Existing Facilities and a dose of 10 mg/L as aluminum produced th e clearest effluent dur ing the comparison of coagulants, performing additional jar tests at 6, 8, 10, 12, and 14 mg/L as aluminum would help to identify the best feed dose for use in the design.

Titrations can be conducted to determine the alkalinity of th e solids produced during the jar testing. The pH, TSS, and volatile suspended solids in the settled precipitate can also be analyzed to estimate the amount of chemical sludge that will be pr oduced in the upgraded plant. This information can be used to ensu re that sufficient sludge-handling capacity is included in the design for the upgraded plant.

Chemical addition can also be used to remove phosphorus from recycle flows, such as RAS, filter backwash, or return from sludge-handli ng processes. Lime, alum, or ferric chloride could be used in this application. Jar tests for these chemical could be performed. Sludge quantities produced from chemical addition coul d be estimated by analyz ing the settled solids for alkalinity, pH, ortho-phosphorus , ammonia nitrogen, and TSS.

Nitrogen Removal
Useful data include the BOD- to-total Kjeldahl nitrogen (T KN) and COD-to-TKN ratios in the plant influent and primary effluent. Both ra tios are important factors to achieve low TN effluents. Low ratios might limit the nitrogen removal efficiency. Grady et al. (1999) reported a BOD-to-TKN ratio in the range of 6.8 to 9.5 for near-complete nitrogen removal. Most wastewater has a COD-to -TKN ratio of 8 to 10 after primary sedimentation. At low ratios, more reliance on endogenous respiration is needed to denitrify. When the COD-toTKN ratio falls below 9 and high nitrogen remo val is required, providi ng some form of methanol, acetate, or other carbon source is necessary. Alternatively, fermentation would produce supplemental carbon to increase th e BOD-to-TKN ratio to promote nitrogen removal. When the ratio is expected to be low consistently throughout the year or periodically (from cold weathe r, for example), decisions need to be made regarding the source, feed equipment, and storage tanks that will be us ed to supply carbon.

Temperature Impacts The impact of temperature on biological rem oval processes varies depending on the location of the plant in the country. Usually, areas that experience cold winter s need to incorporate operational flexibility to successfully treat wastewater at low temperatures. On the other hand, areas of the country that experience wastewater temperatures greater than 30 o C could experience inhibition of the biological phosphor us removal process and might need to consider using chemical phosphorus removal dur ing such periods. For nitrifying organisms, the upper limit is 33 o C, beyond which the nitrification ra te falls off quickly (USEPA 1993).

The most critical low-temperature impact occurs during spring wet-weather events when the snow and ice melts increase the TSS and BOD in the influent wastewater and at the same time lower the water temperature. Lower wastewat er temperatures result in a reduction of theSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 5: Upgrading Existing Facilities 5-23 VFAs from the sewer system and in-plant pr ocess sources. With fermenters on-site, both Kalispell, Montana, and Kelowna, British Columbia, reported full EBPR operation at temperatures as low as 8 o C, as shown in Chapter 3 of this document. Other plants experienced poor biological performance and used chemical addition as a standard procedure when low wastewater temperatures were recorded.

Generally, biological processes operate with a longer sludge age at low temperatures, especially when nitrification and denitrification are required as part of the treatment process. If the process cannot be operated at a long enough sludge age to s upport nitrification and denitrification, alternative processes should be considered, such as converting the existing process to IFAS or MBBR. Generally, low te mperatures do not adversely affect EBPR.



### 5.4.2 Sources of Biodegradable Carbon

This section discusses how to use wastewater characteristics in selecting a carbon source.

Maximize In-plant Sources Using primary settling tanks, an anaerobic digest er, a thickener, or sludge storage tanks can produce a significant amount of VFAs. A primary se ttling tank has been used successfully as a VFA generator in many locations. At the Clark County, Nevada, facility, the primary sludge is thickened up to 5 pe rcent to produce VFAs in the range of 35 to 45 mg/L. The upper solids limit was established at 6 percent. However, the VFA production from primary tanks varies from plant to plant. Thickeners and sludge storage tanks are rich sources of VFAs. The Genesee County, Michigan, facility relies on these two sources for a year-round supply of VFAs.

Find Local Commercial or Industrial Sources Local and industrial sources can provide a good supply of readily biodegradable waste materials. At the McDowell Creek plant owne d by Charlotte-Mecklenburg Utility in North Carolina, high-level BOD water from a soft drin k manufacturer is delive red directly to an anaerobic zone. The waste has a B OD of 40,000 to 130,000 mg/L (Neethling 2005).

Install Fermenters Installing fermenters by converting existing th ickeners or by adding a new fermenter can ensure an adequate supply of VFAs for cold months and wet periods. The reliability of EBPR depends on a continuous supply of VFAs. The Kelo wna, British Columbia, facility converted its existing thickeners. The Kalispell, Montana, facility designed a two-stage fermenter system. A new generation of fermenters provi des improved mixing and effective controls. The minimal solids retention time was 2.5 days to generate sufficient VFAs at the McDowell Creek Plant (Tremblay 2005). The fermenters we re also an additional carbon source for nitrogen removal. The feed points can be prioritized between phosphorus removal and nitrogen removal on the basis of the performance of both. For example, the VFAs from theMunicipal Nutrient Removal Technologies Reference Document September 2008

5-24 Chapter 5: Upgrading Existing Facilities fermenter can be sent to either the anaerobic zone or the anoxic zone, depending on the need at the time. In Kelowna, British Columbia, VFAs are sent to both zones, thereby reducing the size of the anoxic zone significantly. While th e fermenter requires land to build on, the reduction in the anoxic zone can result in an overall de creased land requirem ent. The critical factor to note is the improved reliability of the BNR process when operated in conjunction with a fermenter.

Temperature Impacts The impact of temperature on biodegradable car bon sources varies depending on the location of the plant in the country. Temperature has a greater effect on areas that experience cold winter temperatures. Lower wastewater temperat ures result in a reduction of the VFAs from the sewer system and in-plant process sources . Fermenters in the northern portions of the country need to be sized such that sufficien t VFAs are produced to support BNR at the lowest wastewater temperatures anticipated.



### 5.4.3 Impact of Wet-Weather Flows This section describes how the management of wet-weather flows can affect process selection. Although this issue is not usually severe in municipalities with separate storm sewers, it is an important issue in communitie s with combined sewer systems or collection systems that have high inflow and infiltration rates. The peaking factor and permit conditions are usually established for th e critical discharge season.

Two factors are noteworthy in selecting technolog ies. First, certain technologies handle wetweather flows better than those based on activat ed sludge and clarification. They include denitrification filters, fixed-film processes such as MBBR, and step-feed activated sludge. Second, off-line storage of peak fl ows can be a critical requirement.

During wet-weather events, equalization basins can be used to store as much water as possible, if they are available. If equalization basins are not part of the ex isting plant, it is recommended that they be included as part of the upgrade project. Th e equalization basin can be operated as an on-line process in that all wastewater flow s through the basin as part of normal operation. Alternatively, the equalization basi n could be an off-line process, such that flow would be diverted to the equalization basins only when needed during wet-weather events. The equalization basin could be located in the sewer system, at the headworks, or following the primary clarifiers or secondary clarifiers. Pl acement after the secondary clarifiers would be reco mmended only if the nutrient remova l processes to be protected from elevated hydraulic flow rates are tertiary clarifiers or filters. The size of the equalization basin should be based on the flow patterns that the plant expe riences (including diurnal flow variations and wet-weather volum es received). The permit limits also should be considered when sizing the equalization basins: more equa lization volume would be required at plantsSeptember 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 5: Upgrading Existing Facilities 5-25 that need to meet a daily nitr ogen or phosphorus limit, while pl ants with monthly or yearly limits might be able to use smaller equalization basins.

How the plant is operated during wet-weather ev ents depends on the specific unit processes available. For plants that would like to c ontinue the normal mode of operation during wetweather events, converting the existing facilities to a step-f eed activated-sludge or IFAS system is a possible alternative. Both processe s protect the MLSS, so they are designed to maintain the biomass inventory in the proce ss train during elevated hydraulic flow periods.

Another alternative would be to construct new facilities to ad dress wet-weather flows. For example, additional secondary clarifiers c ould be constructed to decrease the surface overflow rates during wet-weather events. Step -feed activated-sludge, CAS, PID, or IFAS systems could be constructed as new facilitie s to handle wet-weather flows. The PID would need to be operated in storm mode, which can be controlled by a SCADA system, similar to the operating mode used at the North Cary Wate r Reclamation Facility in North Cary, North Carolina. Storm mode operation includes allowing flow to enter and leave only the outer ring of the ditch. Wastewater within the middle and inner ch annels continues to circulate, but it is not discharged to the clarifier until after the wet-weather event has ended, thereby retaining the MLSS, which are then available to repopulate the outer cha nnel. New storage tanks could also be used to store recycle flows during wet-weather events.

The existing or upgraded facili ties could also be operated us ing a wet-weather mode specific to the plant. For example, the return of recy cle flows could be tem porarily suspended during wet-weather events, or the aeration zone(s) co uld be shut down for up to 24 hours. These are common practices used to protect secondary cl arifiers from solids overloading. In addition, temporarily shutting down the sludge-handli ng processes is an option, if feasible.



### 5.4.4 Managing Sludge-Handling Processes Managing sludge-handling processes is one of th e key factors to cons ider in selecting a nutrient removal process and making the upgr ade successful. As described below, both quantity and quality are of concern in sludge management and recycle flows in a nutrient removal process.

• Quantity. Upgrading from the normal secondary process to the advanced treatment level might increase the sludge quantity (and alter the quality) significantly. Adequate capacity should be incorporated into the design. Chemical phosphorus removal increases the quantity of sludge. The quant ity could double if th e target phosphorus concentration falls below 0.5 mg /L and could triple if the target falls below 0.2 mg/L because of the increased capture of fine pa rticles through tertiary filtration (USEPA 1987). No increases in sludge, however, were reported from conversion to biological phosphorus removal when operated at a l ong sludge age. Similarly, no additional increase in sludge production was reported for conversion to nitrogen removal, exceptMunicipal Nutrient Removal Technologies Reference Document September 2008

5-26 Chapter 5: Upgrading Existing Facilities in the case where methanol or another carbon source was added. In both examples, the sludge age was a key parameter. The biological sludge quantity is inversely proportional to the design sludge age (W EF and ASCE 1998). The sludge-handling processes might need to be sized up to ha ndle the increased quantity of sludge from the upgrades.

• Quality. In terms of quality of sludge and recycle, significant changes can be expected. They include changes in thicke ning and dewatering due to changes in the composition of the sludge from the new technology. For example, the chemical sludge produced from phosphorus removal from iron salts is easier to settle, thicken, and dewater (USEPA 1987) than from tradit ional activated sludge processes. Tertiary filters, however, capture fine particles and make sludge thickening, dewatering, and digestion more challenging. BNR sludge with a long sludge age te nds to digest well but results in significant recycle loads to the main treatment train (see the next section). In some BNR facilities, prim ary settling and anaerobic digestion are eliminated, and thus the sludge quality is changed drasti cally; aerobic thickening and aerobic digestion reduce the recycle loadings back to the main train, and the digested sludge might require differen t chemicals for dewatering.



### 5.4.5 Recycle Flows Recycle flows can introduce significant variability in the treatment plant flows and loads. It has been reported that a total of 15 per cent to 50 percent of the phosphorus removed originates in the recycle fl ows (WERF 2005). The recycle flow s to be evaluated are flows from sludge-handling facilities a nd backwash water from tertiary filters and tertia ry clarifiers because those flows can carry nutrients that ar e not removed with the sludge back upstream in the treatment process.

Anaerobic digestion releases high concentrations of ammonia. High levels of phosphorus can also be released at an EBPR plant. Return flows can upset the carbon-to -nitrogen ratio or the carbon-to-phosphorus ratio required for effective BNR processes. This is particularly true at regional facilities that handle sludge from multiple plants or at facilities that receive large volumes of septage.

In many cases, the magnitude of loadings from recycle flows can be minimized. Following are recommendations for properl y handling recycle flows.

The first recommendation to minimize the recycle impact is to keep the sludge aerobic for EBPR upgrades. This means keeping the sludge ae robic at each step and all the way through the sludge-handling processes––digestion, thicke ning, and storage. Two examples are noted in Chapter 3. All waste-activated secondary sludge (WAS) is kept ae robic at the Kelowna, British Columbia, facility, while the primary sludge is separately fermented and stored before dewatering. No digestion is provided at the Ke lowna plant because the sludge is shipped off-September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 5: Upgrading Existing Facilities 5-27 site for composting. The recycle loads contai ned 13 percent TP and 0.1 percent TKN. When lime was added before dewatering, the phosphorus load to the EBPR process was further reduced to 6 percent. When sludge is digested, the recycle load s increase. At the Kalispell, Montana, facility, the secondary sludge is thickened using di ssolved air flotation, while the primary sludge is anaerobically digested. The primary and secondary sludges are kept separate until the time of dewatering. This ope ration is noteworthy in avoiding a potential increase in recycled phosphorus loads if these two sludges were to be combined and stored for any time.

The second recommendation is to plan for recycle loading from anaerobic digestion and dewatering, especially from BNR facilities. Th e recycle phosphorus loads were reported to be high in the faciliti es with anaerobic processes––25 per cent of the total influent phosphorus loading at the Durham, Oregon, facility and th e McDowell Creek, North Carolina, facility and 50 percent at the Lower Reedy Creek, Flor ida, facility (WEF 2005). Jones and Takacs (2004) reported a modeling technique that can be used to estimate recycle loads in such cases. They reported recycle loadings of 35 percent to 50 percent in phosphorus and 20 percent to 30 percent in ammonia nitrogen from the anaerobic digester operating at a 20-day sludge age in their modeling when th e volatile suspended solids destruction was assumed to be 35 percent. These authors used the General Activated Sludge–Digestion Model (ASDM), which was developed and implemented in BioWin 2.1. They also identified the variables that can reduce recycle loads on the basis of the dige stion detention time, equilibrium chemistry, and formation of struvite in the system. Tang et al. (2004) reported recycle loads of 50 percent for ammonia nitrogen in comparison to the plant influent loads at the Valencia Water Reclamati on Plant in the Los Angeles C ounty Sanitation District, where both primary and secondary sludge were anaerobically digested.

At non-EBPR plants, the recycle loads are le ss than those from EBPR plants; they are typically less than 15 percent. Anaerobic di gestion is the main source of ammonia and phosphorus recycle back to the main plant. U nder a normal operating schedule, this load can be managed successfully by car efully controlling the operatin g schedule and implementing certain strategies. These include flow equalization to avoid shock loadings, filter backwash to an equalization basin with su fficient storage capacity, and pr oper controls. At nitrogen removal plants, it was not suggested that th e nitrogen in recycle be removed. Ammonia nitrogen is high in anaerobic digester supern atant and in the liquid from dewatering such sludge.

For EBPR plants, it is suggested that WAS be kept separate from primary sludge and be kept aerobic, as described earlier. The following gui delines are suggested for biosolids thickening, stabilization, and storage facilities:

• For sludge thickened by dissolved air flotati on or other mechanical thickeners (rotary belt thickeners), aerobic digestion is preferred.Municipal Nutrient Removal Technologies Reference Document September 2008

5-28 Chapter 5: Upgrading Existing Facilities • Storage tanks that have aeration capability and are large enough to hold biosolids are recommended.

• An equalization basin for recy cle flows might be needed.

• The dewatering schedule might need to be modified to alter when the recycle loads are returned from the day shift to a later shift.

• Rerouting the feed point to the bioreactor to maximize VFAs and other beneficial ingredients, that is, step f eed to the anaerobic and anoxic zones, or to one of them, depending on the priority at the time, should be considered.

• Adding lime to the centrifuge to minimize the amount of recycle load should be considered.

The centrifuge at the Noman Cole plant in Fairfax County, Virginia , was designed to add lime to reduce recycle lo ads at the dosage of up to 13 pe rcent of the solids loading. To remove most of the soluble phosphorus, the Kelowna, British Columbia, facility fed lime to centrifuges to a pH of 9. This practice ended in 2006. The ne t increase of phosphorus in recycle loads was dramatic, while the TSS loads were reduced as illustrated below:

• Soluble COD : 417 to 700 mg/L, a 67 percent gain

• Soluble P : 34 to 137 mg/L, a 405 percent gain

• Total P : 109 to 200 mg/L, an 82 percent gain

• Ammonia nitrogen : 15 to 21 mg/L, a 39 percent gain

• TKN : 52 to 68 mg/L, a 30 percent gain

• TSS : 1,031 to 765 mg/L, a 24 percent decrease

The Kelowna plant determined that the increase in recycle loads in both nitrogen and phosphorus was manageable because of the avai lability of VFAs from the fermenter, wastewater characteristic s, and other process control parameters in place.

The third recommendation is that facilities should consid er converting anaer obic digestion to aerobic digestion as part of l ong-term planning, where it is found to be cost-effective. Consideration should also be gi ven to the potential loss of green energy when deciding how to act on this recommendation.

For drying, composting, or other Class A pr oducts, additional guide lines might apply.

In addition, the following guidelines apply for cer tain facilities with te rtiary clarifiers and tertiary filters:September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 5: Upgrading Existing Facilities 5-29 • Consider adding an equalization basin for f ilter backwash water so that the flow can be distributed evenly throughout the 24- hour period, thereby controlling the power usage and chemical feed rate evenly. Most facilities send this water to the headworks or equalization basin, thereby reducing s hock loads to the re st of the plant.

• Add thickener for tertiary clarifier sludge. Because the waste sludge is dilute with a low solids concentration, thickening of the tertiary sludge is recommended.

All the above should be incorporated into the design basis (flo w and loadings), and each unit process should be evaluated for e fficient and reliable performance.



### 5.4.6 SCADA Requirements and Sensors Most BNR facilities have adopted automate d control systems, which include dissolved oxygen controllers operating with a programmable logic contro ller (PLC) and associated SCADA. In other facilities more specific c ontrols, based on other sensors for nitrate, oxidation-reduction potential (ORP), and flow have been adopted. Each facility has developed specific programs on the basis of its permit limits, the skill levels of personnel, and the technology employed at the facility. In other f acilities, more specifi c controls using a combination of sensors have been installed. Available sensors incl uded ammonia nitrogen, nitrate and nitrite nitrogen, ortho-phosphorus, and ORP (Weerapperuma and De Silva 2004; Demko et al. 2007). New tools included the sl udge blanket monitor, TSS and turbidity meters, and total organic carbon analyzers. Some of these tools have be en installed at BNR facilities for accurate monitoring of performance and also as an early warning system for toxic shocks that might be entering the plant. No facility has employed these data in actual control of treatment processes, however. At the North Cary, Nort h Carolina, plant, the oxidation ditch operates in anoxic and aerobic cycles in alternating phases. The exact decision on phasing is made on the basis of preset control logic, which is site-specific and fully automated. Most facilities install PLCs with a human-machine interface and multiple screens connected to the main computer system , flow meters, level sw itches, online sensors, and system alarms.



### 5.4.7 Staffing Requirements Most facilities maintained the same level of staffing after the BNR processes were installed. No new hires were reported for the BNR upgrades. The existing staff was trained on the operation of the BNR process and related new equipment and instrumentation.



### 5.4.8 Training Needs In the upgrade projects and case studies included in this document, training in new process operation and monitoring was provided by the proj ect consultant or the manufacturer of the process, when applicable, during the design and construction period. During startup, more detailed training was provided as a part of the construction contra ct. Follow-up trainingMunicipal Nutrient Removal Technologies Reference Document September 2008

5-30 Chapter 5: Upgrading Existing Facilities included seminars and workshops offered by stat e agencies and professional organizations like the Water Environment Federation (WEF), it s local affiliates, and other organizations. Training in process controls and informa tion technology was provided mostly in-house. Laboratory personnel received training from equipment suppliers, where applicable. Additional training could be obtained by atte nding specialty cour ses on the subject.



### 5.4.9 Pilot Testing In many of the upgrade projects, before selecting a technology, the project team went through a preliminary engineering evaluation and conducted pilot testing of the fa vored alternative to verify the concept with the actua l wastewater to be treated and to develop sizing data for the process. The duration of the pilot testing de pended on the seasonal changes in wastewater characteristics, the technologies selecte d, whether the facility was new versus well established, the number of parameters to operate under, and the specific objectives established. The typical duration ra nged from 6 months to 1 year for a biological process. At the Blue Plains facility in Washington, D.C., p ilot testing of the process lasted 6 months. For physical and chemical processes, however, pilot testing requires far less time.

This pilot testing can be carried out at the planning stage or delayed until the design phase of the project to accommodate the overall schedule.



### 5.5 Finalizing Process Selection

The project team’s final step is to evalua te feasible alternatives and determine the recommended plan. The project team can compar e the potential alternatives and select the best process in accordance with the success cr iteria established at the beginning of the project.

The reader can obtain information on genera l cost estimation from Chapter 4 of this document for appropriate technologies being co nsidered. Alternatively, a cost estimate based on upgrading the individual plant to the proces ses being considered co uld be performed as part of the evaluation.

The accuracy of the cost estimate will vary de pending on the level of detail provided in the evaluation. If the cost estimate is based on cost curves or costs from similar facilities or technologies with very little c onsideration of local conditions , the cost estimate might be accurate to only within approximately 50 percen t. If more detailed studies such as soil borings, preliminary engineering design drawi ngs, and outline specifications are prepared, the estimate will be more accurate. Non-cost criteria should include those items of most concern to the public. At a minimum, odor, tra ffic, noise, air emissions, dust, water quality, wetland infringement, and other environmental impacts need to be assessed.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 5: Upgrading Existing Facilities 5-31 Two examples are shown below. Both examples include a weighting factor to indicate the relative importance of each crite rion being considered. In Ta ble 5-8, the alternatives are assigned values from 1 to 4 (there are four alte rnatives), with 1 the most favored alternative for the given criteria. Therefore, the most fa vored alternative is the one with the lowest number at the bottom of the table. Once this ba sic rating is complete, a sensitivity analysis can be carried out by changing the weighting f actors for one or more criteria items, e.g., increasing the cost of energy by a factor of 50 percent or 100 percent. The process can be repeated for another parameter, such as th e future regulatory requi rements or biosolids handling. The new ranking can be comp ared among these alternatives.

Table 5-8. Decision matrix example 1

Alternatives Criteria for comparison Weighting factor A B C D Costs (capital and O&M) 1 2 1 4 3 Reliability 1 3 1 2 4 Efficiency 1 1 2 4 3 Expandability 1 2 3 1 4
Ease of O&M 2 3 1 4 2 Environmental impacts—chemical use 3 4 1 3 2
Efficient land use 1 2 1 4 3 Energy use 2 2 1 4 3 Future regulatory requirements 1 4 3 2 1 Employee and public health and safety 2 2 3 4 1 Market stability for biosolids reuse/disposal 1 1 4 2 3
TOTAL -- 41 28 52 39

Note : The rating scale is 1 to 4. Smaller numbers represent a more favorable alternative. No two alternatives may have the same score for the same category. Totals are determined by su mming the score for each criterion times the weighting factor, which should be adjusted for the local situati on. The alternative with the lowest tota l is the best overall alternative by this

measure.
In the second example, an altern ate scale is used to evaluate the alternatives. It is based on assigning a number from 1 to 10 for each criterion, with 1 bei ng the least favored and 10 the most favored. The weighting factor is multiplied by the score to determine the total points. Table 5-9 shows an example from another case (WEF 2004). The bottom line figures are then compared to select the recommended alternative. The highest scorer is th e best alternative in this method. The same sensitivity analysis de scribed under the first ex ample can be carried out for the cost of energy, or other pa rameters of choice, and compared again.Municipal Nutrient Removal Technologies Reference Document September 2008

5-32 Chapter 5: Upgrading Existing Facilities Table 5-9. Decision matrix example 2
Option 1 Option 2 Option 3 Criteria Weight Score Points Score Points Score Points Site requirement 8 5 40 5 40 4 32 Capital cost 6 3 18 5 30 4 24
O&M cost 6 3 18 4 24 4 24 Reliability 8 4 32 5 40 5 40 Flexibility 10 3 30 4 40 3 30 Use of existing facilities 6 3 18 4 24 4 24 Sludge production 8 2 16 3 24 3 24 Public perception 7 3 21 3 21 3 21 Total points 193 243 219
Rank 3 1 2

The project team can choose which method to em ploy and the criteria to be included in making the final technology selection.

Once a technology is selected, th e next step is to prepare a conceptual design. The design should include a demolition plan, a site plan with major pipes and facilities, a hydraulic profile, process flow and mass balances, ge neral drawings with building and major equipment footprints, one-line electrical drawings, a basic instrumentation and control philosophy and block diagram, and architectu ral renderings. A constr uction schedule should also be developed to ensure that the existing plant can continue to operate and meet permit limits until the upgrades are placed on-line. Th e recommended plan is then presented for public approval and implementation.



### 5.6 Summary

As more municipalities are required to meet stringent nutrient load limitations to protect receiving waterbodies, upgrading existing facilities with sust ainable technologies is an important challenge, as well as an opportunity. This chapter pr esented the general approaches to upgrading existing facilities, explained how to set success criteria for the upgrade, and provided tables that can be used to screen feasible alternatives, along with selection factors and design and operational factor s that can assist in identifying the right technology for the municipality.

Planning for process upgrades includes proj ecting future loads, assessing existing capabilities, preparing a mass ba lance that includes all return and recycle flows and loads, developing the needed expansion and upgrade th at should incorporate flexibility into the operation of the plant to account for future uncer tainties, evaluating feasible alternatives, and selecting the recommended plan. The success cr iteria might include sustainability, cost-September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 5: Upgrading Existing Facilities 5-33 effectiveness, ease of O&M, project schedule, and site requirements. The sustainability factors could include energy usage, chemical usage, and the recycling of biosolids.

A list of technologies capable of meeting the selected target effluent range for nitrogen and/or phosphorus can be developed. Technology selection factors, including the following, should then be reviewed for each alternative:

• Site factors – Footprint – Need for a building – Possibility of construction in the existing aeration basin – Piping and pumping requirements – Need for additional head – Presence of secondary process recycle streams

• Wastewater factors – Need for additional carbon source

• Operation factors – Extra electricity usage – Need for chemical addition – Generation of additional sludge

The next step is to identify and evaluate f easible technologies on th e basis of design and operational factors and cost factors like the following:

• Wastewater characteristics in the influe nt, primary effluent, and recycle streams

• Carbon source management, internal and external

• How to manage wet-weather flows

• How to manage recycle flows

• How to design and operate sludge-handling processes

• How much automation and control is needed

• Staffing and training needs

Important considerations include how to incorporate flexibility in anticipation of uncertainties and changing conditions in wast ewater characteristics and regulations. Factors considered might include flow equalization, the number of swing zones, alternative modes of operation, and safety factors.Municipal Nutrient Removal Technologies Reference Document September 2008

5-34 Chapter 5: Upgrading Existing Facilities The project team should select the recommended process in accordance with the established success criteria. The final process might include a combination of the following, in parallel or in series:

• Replace the existing process with a new process.

• Convert the existing process to a new process.

• Add a new process to the existing process.

The recommended process option should accompany an implementation plan that includes an overall schedule, funding, a construction and ope rational plan, costs, and startup procedures. The success of the upgrades will ensure fu ll compliance with the new permit with good reliability in the most sustainable way (in en ergy usage, chemical usage, and recycle of biosolids).



### 5.7 References

Barnard, J. 2006. Biological Nutrient Rem oval: Where We Have Been, Where We Are Going. In Proceedings of the Water Environment Federation’s 79th Annual Technical and Educational Conference , Dallas, TX, October 21–25, 2006.

Barnard, J., A. Shaw, and D. Lindeke, 2005. Usi ng Alternative Parameters to Predict Success for Phosphorus Removal in WWTPs. In Proceedings of the Water Environment Federation’s 78th Annual Technical and Educational Conference , Washington, DC, October 29–November 2, 2005.

Copithorn, R. 2007. Design and Operational Issues Associated with Integrated Fixed Film Activated Sludge (IFAS) . Nutrient Removal Workshop: Doing More with Less, Water Environment Federation/IWA, Baltimore, MD.

deBarbadillo, D., A. Shaw, and C.L. Wallis-L age. 2005. Evaluation and Design of Deep Bed Denitrification Filters: Empirical Design parameters vs. Process Modeling. In Proceedings of the Water Environment Federation’s 78th Annual Technical and Educational Conference , Washington, DC, October 29–November 2, 2005.

Demko, M., F. Coughehenour, A. Santos, and S. Jeyannayagam. 2007. An alyzing Analyzers: An Evaluation of On0line Nutrient Analyzer s at the City of Plant City Wastewater Reclamation Facility. In Proceedings, Specialty Conference on Nutrient 2007 , Water Environment Federation and Interna tional water Associ ation, PP 298-310, 2007.

Grady, C.P.L., G.T. Daigger, and H.C. Lim. 1999. Biological Wastewater Treatment . Marcel Dekker, Inc., New York.September 2008 Municipal Nutrient Remo val Technologies Reference Document

Chapter 5: Upgrading Existing Facilities 5-35 Johnson, T., C. Wallis-Lage, A. Shaw, and J. McQuarrie. 2005. IFAS Options––Which One Is Right for Your Project? In Proceedings of the Water Environment Federation’s 78th Annual Technical and Educational Conference , Washington, DC, October 29– November 2, 2005.

Jones, R., and I. Takacs. 2004. Modeling the Im pact of Anaerobic Digestion on the Overall Performance of Biological Nutrient Re moval Wastewater Treatment Plants. In Proceedings of the Water Environment Federation’s 77th Annual Technical and Educational Conference , New Orleans, LA, October 2–6, 2004.

Kang, S.J., P. Horvatin, and L. Briscoe. 1985. Full Scale Biological Phosphorus Removal Using A/O Process in a Cold Climate. In Proceedings of the Inte rnational Conference on Management Strategies for Phosphorus in the Environment , July 1985.

Loader, K. 2007. IFAS and MBBR Solutions to Plant Upgrade Problems: Cheyenne, Wyoming Case Studies. In Proceedings, Workshop B: Nutrient 2007 , Water Environment Federation and Internati onal Water Association, March 2007.

McQuarrie, J., K. Rutt, and J. Seda. 2004. Obse rvations from the First Year of Full Scale Operation––The IFAS/BNR Process at th e Broomfield Wastewater Reclamation Facility in Broomfield, CO. In Proceedings of the Water Environment Federation’s 77th Annual Technical and Educational Conference , New Orleans, LA, October 2–6,
2004.

Neethling, J.B., and A. Gu. 2007. Phosphorus Sp eciation Provides Direction to Produce 10 ug/l. 2007. Nutrient Removal Specia lty Conference, Baltimore, 2007.

Neethling, J.B., B. Bakke, M. Benisch, A. Go, H. Stephens, H.D. Stensel, and R. Moore.
2005. Factors Influencing the Reliability of Enhanced Biological Phosphorus Removal. Water Environmental Research Fe deration (WERF) Report 01-CTS-3. IWA Publishing, London.

Pehlivanoglu, D., and D. Sedlak. 2004. Bioava ilability of Wastewater Derived Organic Nitrogen to the Alga Selenastrum Capricornutum. Water Research 38:3189–3196.

Pehlivanoglue, D., and D. Sedlak. 2006. Wastew ater Derived Dissolved Organic Nitrogen: Analytical Methods, Characteri zation, and Effects—A Review. Critical Reviews in Environmental Science and Technology 36(3):261–285.

Tang, C.-C., P. Prestia, R. Kettle, D. Chu., B. Mansell, J. Kuo, R. Horvatin, and J. Stahl. 2004. Start-up of a Nitrification/Denitrificat ion Activated Sludge Process with a High Ammonia Side-Stream. In Proceedings, Water Environment Federation, WEFTEC

, 2004.Municipal Nutrient Removal Technologies Reference Document September 2008

5-36 Chapter 5: Upgrading Existing Facilities Tremblay, S., H. Hilger, J. Barnard, C. deBarbadillo, and P. Goins. 2005. Phosphorus Accumulating Organisms Utilization of Volatile Fatty Acids Produced by Fermentation of Anaerobic Mixed Liquor. In Proceedings of the Water Environment Federation’s 78th Annual Technical and Educational Conference , Washington, DC, October 29–November 2, 2005.

USEPA (U.S. Environmental Protection Agency). 1989. Retrofitting POTWs for Phosphorus Removal in the Chesapeake Bay Drainage Basin . EPA/625/6-89/020. U.S. Environmental Protection Agency, Washington, DC.

USEPA (U.S. Environmental Protection Agency). 1993. Nitrogen Control . EPA/625/R93/010. U.S. Environmental Protection Agen cy, Office of Water, Washington, DC.

Weerapperuma, D., and V. De Silva. 2004. On-l ine Analyzer Applications for BNR Process Control. In Proceedings of the Water Envir onment Federation’s 77th Annual Technical and Educational Conference , New Orleans, LA, October 2–6, 2004.

WEF (Water Environment Federation). 2004. Upgrading and Retrofitting Water and Wastewater Treatment Plants . WEF Manual of Practice No. 28. WEFPress, Alexandria, VA.

WEF (Water Environment Federation). 2005. Biological Nutrient Removal Operation in Wastewater Treatment Plants. WEF Manual of Practice No. 30.

WEF (Water Environment Federation) and ASCE (American Society of Civil Engineers).
1998. Design of Municipal Wastewater Treatment Plants. WEF Manual of Practice No. 8, Volume II, 4th ed. pp 15-1 through 15-114. American Society of Civil Engineers, Reston, VA.

WEF (Water Environment Federation) and ASCE (American Society of Civil Engineers) Environmental and Water Resources Institute. 2006. Biological Nutrient Removal (BNR) Operation in Wastewater Treatment Plants. WEF Manual of Practice No. 29. WEFPress, Alexandria, VA.

Welander, T., and C. Johnson. 2007. Upgrading Activated Sludge Plants for Enhanced Nitrogen Removal Using MBBR-based Technology. In Proceedings, Workshop B: Doing More with Less . Nutrient Removal 2007, Water Environment Federation/International Wa ter Association, March 2007.