EPA 910-R-07-002 Alaska 

United States 

Environmental Protection 

Agency 

Region 10 

1200 Sixth Avenue 

Seattle WA 98101 

Idaho 

Oregon 

Washington 

Office of Water and Watersheds April 2007 

Advanced Wastewater 

Treatment to Achieve Low 

Concentration of Phosphorus 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

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Acknowledgements

EPA is very grateful to the operators and managers of the wastewater treatment plants included 

in this evaluation. Without their time and assistance this project would not have been possible. 

A special thank you goes to Magali Prevost who donated her time to help EPA Region 10 staff 

conduct the evaluation and complete this report. EPA also expresses appreciation to the 

following individuals who assisted by providing facility information or review of the project 

report: 

Dave Pincumbe, EPA-Region I 

Ken Merrill, Washington Department of Ecology 

Laurie Mann, EPA-Region 10 

Ken Kosinski and Robert Wither, New York Department of Environmental Conservation 

Jon Gasik and Tim McFetridge, Oregon Department of Environment Quality 

Dr. Remy Newcome, University of Idaho, Moscow and Bluewater Technologies Inc. 

Bonnie Beavers, Center for Justice 

Kathleen Suozzo, Delaware Engineering 

Project Manager And Report Writer 

David Ragsdale, Engineer 

EPA Region 10, Office of Water & Watersheds 

Web Posting 

Jeff Philip, Webmaster 

EPA, Region 10 

Cover Page 

Christopher Moffett, Graphic Designer 

EPA Region 10 

Photos 

All photos by report writer unless otherwise noted 

For Additional Information About This Report: 

David Ragsdale, Engineer 

EPA Region 10, Office of Water & Watersheds 

(360) 407-6589 

Email: ragsdale.dave@epa.gov
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

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Abstract 

In this report, EPA Region 10 presents observations of advanced wastewater treatment installed 

at 23 municipalities in the United States. These facilities employ chemical addition and a range 

of filtration technologies which have proven to be very effective at producing an effluent 

containing low levels of phosphorus. 

Observations from this evaluation include: 

• Chemical addition to wastewater with aluminum- or iron-based coagulants followed by 

tertiary filtration can reduce total phosphorus concentrations in the final effluent to very low 

levels. The total phosphorus concentrations achieved by some of these WWTPs are consistently 

near or below 0.01 mg/l. 

• The cost of applying tertiary treatment for phosphorus removal is affordable, when 

measured by the monthly residential sewer fees charged by the municipalities that operate these 

exemplary facilities. The monthly residential sewer rates charged to maintain and operate the 

entire treatment facility ranged from as low as $18 to the highest fee of $46. 

• There appeared to be no technical or economic reason that precludes other dischargers 

from using any of the tertiary treatment technologies that are employed at these WWTPs. Any 

of these technologies may be scaled as necessary to fulfill treatment capacity needs after 

consideration of site specific conditions. 

• Other pollutants that commonly affect water quality such as biochemical oxygen demand, 

total suspended solids, and fecal coliform bacteria are also significantly reduced through these 

advanced treatment processes. 

• WWTPs which utilize enhanced biological nutrient removal (EBNR) in the secondary 

treatment process can often reduce total phosphorus concentrations to 0.3 mg/l or less prior to 

tertiary filtration. While employing EBNR is not essential to achieving high phosphorus removal 

rates, EBNR enhances the performance and reduces operating costs (especially chemical use) of 

the subsequent tertiary filtration process. Recently published studies report that the longer solids 

retention times used in BNR processes also removes a significant amount of other pollutants 

contained in municipal wastewater, including toxics, pharmaceuticals, and personal care 

products. 

• The low effluent turbidity produced by tertiary filtration allows for efficient disinfection of

final effluent without chlorination through the use of ultraviolet treatment. 

• The treatment processes and quality of the final effluent produced by tertiary filtration for 

phosphorus removal typically meet state criteria for wastewater reclamation. Reuse of this high 

quality effluent can be an attractive alternative to direct discharge into surface waters in 

situations where restrictive NPDES permit limitations apply. 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

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Table of Contents

Acknowledgements......................................................................................................................... 2 

Abstract........................................................................................................................................... 3 

Nutrients and Water Quality Problems........................................................................................... 5 

Evaluation considerations............................................................................................................... 6 

Summary of Observations............................................................................................................... 6 

City of Aurora, Sand Creek Wastewater Reuse Plant................................................................... 11 

Breckenridge Sanitation District, Iowa Hill Wastewater Reclamation Plant .............................. 13 

Breckenridge Sanitation District, Farmers Korner Wastewater Treatment Plant......................... 17 

Snake River Wastewater Treatment Plant .................................................................................... 19 

Pinery Wastewater Reclamation Facility...................................................................................... 22 

Clean Water Services, Rock Creek Advanced Wastewater Treatment Plant ............................... 26 

Clean Water Services, Durham Advanced Wastewater Treatment Plant..................................... 30 

Stamford Wastewater Treatment Plant......................................................................................... 34 

Walton Wastewater Treatment Plant ............................................................................................ 39 

Milford Wastewater Treatment Plant............................................................................................ 44 

Alexandria Sanitation Authority (ASA) Advanced Wastewater Treatment Plant........................ 47 

Upper Occoquan Sewage Authority (UOSA)............................................................................... 51 

Fairfax County Wastewater Management, Noman M. Cole Jr. Pollution Control Plant.............. 57 

Blue Water Technologies, Inc – Pilot facility at the Hayden Wastewater Treatment Plant........ 62 

CoMagTM Technology – Pilot testing at the Concord Wastewater Treatment Plant .................... 66 

LOTT Budd Inlet Wastewater Treatment Plant............................................................................ 69 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

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Nutrients and Water Quality Problems 

Phosphorus and nitrogen are nutrients that are essential for aquatic plant and algae growth. Most 

waters naturally contain enough of these nutrients to support native aquatic life. However, an 

over-abundance of these nutrients can over-stimulate plant and algae growth such that they 

create water quality problems. Over 1,000 waterbodies in Idaho, Oregon and Washington are 

identified as being impaired due to excessive nutrient loading and are included on state Clean 

Water Act 2004 §303(d) lists for water quality problems. The problems caused by nutrient 

enrichment of lakes, stream, and rivers are not unique to the Northwest states as many other 

waterbodies across the United States have also been identified as impaired by nutrients. Nutrient 

impairments affect the survival of many aquatic species such as salmon; affect the safety of 

drinking water supplies; affect the aesthetics of recreational areas, and the ability to navigate 

through rivers and lakes. 

In freshwater systems, phosphorus is typically the nutrient that is in short supply relative to 

biological needs, which means that the productivity of aquatic plans and algae can be controlled 

by limiting the amount of phosphorus entering the water. Many streams and lakes in the 

Northwest are documented to have very little capacity to assimilate phosphorus loading during 

the “critical” warm and dry summer period without significant water quality degradation. Large 

diurnal swings in pH and dissolved oxygen may occur as excessive amounts of nutrients are 

metabolized by aquatic plants and algae. The range of these swings is often measured to exceed 

the state water quality criteria established to protect fish and other aquatic organisms in their 

various life stages. Therefore, the amount of phosphorus currently entering these waters exceeds 

the seasonal loading capacity and must be reduced if these water quality problems are to be 

resolved. 

The sources of phosphorus loading vary depending on the human activities and conditions in a 

specific watershed. In the Northwest, phosphorus loading into streams and lakes from nonpoint 

sources (e.g. agriculture, pet waste) is often minimal during the summer months because there is 

typically very little rainfall runoff to flush pollutants into receiving waters. The discharges of 

treated wastewater can be the most significant source of phosphorus loading during these critical 

summer months. To address these water quality problems, state environmental agencies and the 

Environmental Protection Agency (EPA) are requiring dischargers to reduce the amount of 

phosphorus in their effluent. 

Achieving very low phosphorus levels in treated wastewater will require the installation of 

additional treatment. A number of water quality studies in Northwest states have determined 

waste load allocations which will require dischargers to achieve total phosphorus effluent 

concentrations that range from as low as 0.009 to 0.05 mg/l. Even as WWTP operators in the 

Northwest consider installing additional treatments to address water quality problem, they are 

also planning to upgrade capacity of their plants to accommodate rapid population growth. With 

many other interests competing for limited public and private resources, resolving water quality 

problems is often contentious and slow. Implementation of water quality improvement plans 

(called Total Maximum Daily Loads (TMDLs)) have been significantly delayed by arguments 

about the availability and cost of treatment technologies capable of achieving very low 

phosphorus targets. 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

In response to these discussions, EPA – Region 10 initiated a project to evaluate municipal 

wastewater treatment plants which have demonstrated exemplary phosphorus removal through 

their treatment processes. The primary goal of this project was to obtain and share information 

about the technology, performance and costs of applying advanced wastewater treatment for 

phosphorus removal. 

Evaluation Considerations 

The WWTPs included in this project were selected because monitoring results have 

demonstrated their treatment to be very effective at removing phosphorus. The reported 

performance at each of these facilities has been well documented by monitoring conducted over 

periods of several years. EPA attempted to include a variety of treatment technologies and 

facilities of different sizes in this evaluation. However, not all facilities that achieve exemplary 

phosphorus removal nor all filtration technologies could be presented in this report. A number of 

the WWTPs that are currently achieving good phosphorus removal are planning treatment 

upgrades that will allow them to also meet a total nitrogen limitation of 3 mg/l. Some 

information about treatment to remove nitrogen is presented in the description of the LOTT, 

Budd Inlet WWTP. 

Treatment performance is characterized by discharge monitoring information required by the 

National Pollutant Discharge Elimination System (NPDES) permits which authorize these 

facilities to discharge treated wastewater. Monitoring of the final effluent per NPDES permit 

requirements is conducted and reported in accordance with EPA approved analytical methods 

and quality control procedures. This monitoring information provides the best readily available 

information with which to characterize WWTP performance. EPA presents the average and 

range of reported monthly average phosphorus concentrations to indicate long term treatment 

performance. These monthly average values may not be representative of daily fluctuations in 

effluent quality experience by these WWTPs. Effluent concentrations are sometimes reported as 

zero or less-than values on discharge monitoring reports when the monitored concentrations are 

well below permit limitations or laboratory reporting limits for phosphorus. The actual effluent 

phosphorus concentration in the final effluent of these facilities may be significantly better than 

characterized in discharge monitoring reports. 

Although each of the WWTPs are very well maintained and operated, very few are being pressed 

by stringent NPDES limitations to optimize treatment to achieve the best phosphorus removal 

possible. The table under Summary of Observations lists the applicable NPDES permit 

phosphorus limitations for each of the facilities evaluated. The lowest phosphorus limitation 

established for any of these WWTPs was a monthly average limitation of 0.05 mg/l. Operators 

at many of these WWTPs conveyed that if necessary, even better phosphorus removal 

performance could be achieved through operational changes to the existing treatment system. 

This is a consideration that should not be overlooked by dischargers, consultants and regulators 

as they consider treatment options. 

Summary of Observations 

Information about treatment technology, performance and residential sewer treatment fees for 

each of the 23 WWTPs evaluated is summarized in the following table. 

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Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10

Facility Name 

and Location

NPDES 

Permit 

Number 

Capacity Advanced Phosphorus Treatment Technology NPDES Permit Limitation for Phosphorus *Average Effluent Phosphorus Concentration Range o

Av

Phos

Concen

Sand Creek WWRP Aurora, CO CO0026611 5 mgd BNR,filtration None 0.1 to 0.2 mg/l N/A Breckenridge S.D., Iowa Hill WWRP, CO 

CO0045420 1.5 mgd BNR, chemical addition, tertiary settlers and filtration 0.5 mg/l daily max & 225 lbs/year 0.055 mg/l 0.017 to 0

Breckenridge S.D., Farmers KornerWWTP, CO 

CO0021539 3 mgd BNR, chemical addition, tertiary settlers and filtration 0.5 mg/l daily max & 225 lbs/year 0.007 mg/l 0.002 to 0

Summit CountySnake River WWTP, CO 

CO0029955 2.6 mgd BNR, chemical addition, tertiary settlers and filtration 0.5 mg/l daily max & 340 lbs/year 0.015 mg/l <0.01 to 0

Pinery WWRFParker, CO CO0041092 2 mgd BNR, chemical addition, two- stage filtration 0.05 mg/l & 304 lbs/year 0.029 mg/l 0.021 to 0

Clean Water Services, Rock Creek WWTP, OR 

OR0029777 39 mgd Chemical addition, filtration 0.1 mg/l (monthly median limitation) 0.07 mg/l 0.04 to 0.

Clean Water Services, Durham WWTP, OR OR0028118 24 mgd BNR, chemical addition, filtration 0.11 mg/l (monthly median limitation) 0.07 mg/l 0.05 to 0.

Stamford WWTP Stamford, NY NY0021555 0.5 mgd Chemical addition, two-stage filtration 0.2 mg/l <0.011 mg/l <0.005 to 

mg/l

Walton WWTP Walton, NY NY0027154 1.55 mgd Chemical addition, two-stage filtration 0.2 mg/l <0.01 mg/l <0.005 to 

Milford WWTP Milford, MA MA0100579 4.8 mgd Multi-point chemical addition, filtration 0.2 mg/l 0.07 mg/l 0.04 to 0.Alexandria SanitationAuthority AWWTP, Alexandria, VA

VA0025160 54 mgd 

BNR, Multi-point chemical addition, tertiary settling andfiltration

0.18 mg/l 0.065 mg/l 0.04 to 0.

Upper OccoquanSewerage Authority WWTP, VA

VA0024988 42 mgd Chemical (high lime) and tertiary filtration 0.10 mg/l <0.088 mg/l 0.023 to <

Fairfax County, Noman Cole WWTP,VA 

VA0025364 67 mgd 

BNR, chemical addition,tertiary clarification and filtration

0.18 mg/l <0.061 mg/l <0.02 to <

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Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Facility Name 

and Location 

NPDES 

Permit 

Number 

Capacity Advanced Phosphorus Treatment Technology NPDES Permit Limitation for Phosphorus *Average Effluent Phosphorus Concentration Range o

Av

Phos

Concen

BluePro Treatment Pilot results at Hayden WWTP, ID 

N/A N/A Iron coated sand in two-stage Centra-Flo Filters. N/A 0.013 mg/l N/A 

CoMag Treatment Pilot results at Concord WWTP, MA 

N/A N/A 

Chemical addition, ballast sedimentation, magnetic polishing 

N/A 0.04 mg/l N/A 

WWTPs not visited for this evaluation : Delhi, NY NY0020265 0.82 mgd Activated sludge, chemical addition, filtration 0.11 mg/l 0.04 mg/l <0.02 to 0

Pine Hill WWTP, NY NY0026557 0.5 mgd RBC, sand filters, chemical addition, microfiltration 0.2 mg/l 0.06 mg/l 0 to 0.12 

NYC DEP-Grand Gorge STP, NY NY0026565 0.5 mgd RBC, sand filters, chemical addition, microfiltration 0.2 mg/l < 0.04 mg/l 0 to 0.05 Hobart – V PCF, NY NY0029254 0.18 mgd 

Activated sludge, sand filters, chemical addition, microfiltration 

0.5 mg/l < 0.05 mg/l 0.026 to 0

Snyderville Basin Water Reclaimation District, UT 

UT0020001 4 mgd BNR, chemical addition, filtration 0.1 mg/l 0.04 mg/l 0.03 to 0.

Ashland WWTP Ashland, OR OR0026255 2.3 mgd ADWF Oxidation Ditch, chemical addition, membrane filtration 1.6 lb/day (= 0.083 mg/l) 0.07 mg/l 0.05 to 0.McMinneville WWTP McMinneville, OR 

OR0034002 5.6 mgd ADWF Oxidation Ditch (BNR), Chemical addition, multi-media traveling bed filtration 0.07 mg/l 0.058 mg/l 0.036 to 0

Facility Name 

and Location 

NPDES 

Permit 

Number 

Capacity Advanced Nitrogen Treatment Technology 

NPDES Permit 

Limitation for 

Total Inorganic 

Nitrogen (TIN) 

*Average 

Effluent TIN 

Concentration 

Range o

Avera

Concen

LOTT WWTP Olympia, WA WA0037061 28 mgd Biological Nutrient Removal 3 mg/l 2.2 mg/l 1.23 to 2.

* This is the average of monthly average measurements achieved as reported by the facility on NPDES discharge monitoring reports. The per

averages were determined is identified in the discussion about each facility. Many facilities have seasonal water quality-based limitations for 

** The costs of construction, operation and maintenance of WWTPs discharging into the Delaware River watershed are partially subsidized b

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Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

- 9 - 

Summary of Observations (continued)

• Tertiary filtration aided by chemical addition can reduce total phosphorus concentrations in 

the final effluent to very low levels. This treatment is employed at all but one of the 

WWTPs included in this evaluation. To achieve very low phosphorus concentrations, 

chemicals must be added to wastewater to associate phosphorus with solids that can then be 

successfully removed through filtration. Aluminum- or iron-based coagulants and polymer 

are the chemicals most commonly used for this purpose. 

• Traveling sand bed filters, mixed- media gravity filters, Dynasand filters and variations of

these filtration technologies are used by all of the WWTPs evaluated. Filtration has been 

employed for many years to treat drinking water and more recently applied to treat 

wastewater. Filtration technologies for treating wastewater are rapidly evolving as water 

quality agencies and dischargers strive to protect sensitive receiving waters from potential 

impacts of pollutants in the treated effluent. With proper design, there are no apparent 

reasons why any of these filtration technologies may not be installed in either small or large 

scale applications. Selection of a filtration technology includes the usual considerations 

such as: desired effluent quality; reliability of treatment equipment; capital, operating and 

maintenance costs; equipment footprint, and future expandability. 

• Application of two-stage filtration processes produced the lowest phosphorus levels 

observed in this evaluation. Two-stage treatment may be achieved through use of a first 

and second stage filter or by providing tertiary clarification prior to filtration. The Walton 

and Stamford WWTPs achieved the lowest measured phosphorus concentration in their 

effluent (about 0.01 mg/l or less) by utilizing two-stage Dynasand filters from Parkson 

Corporation. Excellent treatment results were also obtained by Breckenridge WWTPs, 

the Snake River WWTP and the Alexandria AWWTP using a two-stage treatment process 

consisting of chemical addition with tertiary settling in advance of their sand bed filters. 

Modular two-stage filters from US Filter Corporation installed at the Pinery WWTP 

employs a synthetic media in the first stage and sand media in the second stage. The 

Fairfax County, Noman Cole WWTP utilizes large tertiary clarifiers followed by filtration 

through sand beds. 

• Table 1 identifies which of the WWTPs include in this evaluation have also incorporated 

enhanced biological nutrient removal (EBNR) into their secondary treatment processes to 

remove phosphorus. An EBNR treatment system promotes the production of phosphorus 

accumulating organisms which utilize more phosphorus in their metabolic processes than a 

conventional secondary biological treatment process. The average total phosphorus 

concentrations in raw domestic wastewater is usually between 6 to 8 mg/l and the total 

phosphorus concentration in municipal wastewater after conventional secondary treatment 

is routinely reduced to 3 or 4 mg/l. Whereas, EBNR incorporated into the secondary 

treatment system can often reduce total phosphorus concentrations to 0.3 mg/l and less. 

Facilities using EBNR significantly reduced the amount of phosphorus to be removed 

through the subsequent chemical addition and tertiary filtration process. This improves the 

efficiency of the tertiary process and can significantly reduce the costs of chemicals used to 

remove phosphorus. Staff at the Fairfax County WWTPs reported that their chemical 

dosing was cut in half after EBNR was installed to remove phosphorus. 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

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• The treatment provided by these WWTP also removes other pollutants which commonly 

affect water quality to very low levels. Biochemical oxygen demand (BOD) and total 

suspended solids are routinely less than 2 mg/l and fecal coliform bacteria less than 10

fcu/100 ml. Turbidity of the final effluent is very low which allows for effective 

disinfection using ultraviolet light, rather than chlorination. Recent studies report finding 

that WWTPs using EBNR also significantly reduce the amount of pharmaceuticals and 

health care products from municipal wastewater, as compared to the removal accomplished 

by conventional secondary treatment. 

• Only four of the WWTPs included in this evaluation utilize anaerobic digesters to stabilize 

removed solids. Facilities which utilize anaerobic digesters need to consider the potential 

that a significant phosphorus load might be released from the removed solids and thereafter 

returned to the wastewater being treated. The Clean Water Services WWTPs manages the 

phosphorus loading associated with the use of anaerobic digesters by equalizing the flow of 

these return streams (supernatant and centrate) over time. Other studies indicate that

phosphorus removed with alum does not resolubilize in anaerobic digesters, whereas 

phosphorus removed with iron salts may solubilize in the absence of adequate iron. 

Operators have identified the amount of alum or iron necessary to control resolubilization 

of phosphorus in anaerobic digesters to be a cost consideration. 

• Applying advanced water treatment to remove phosphorus is affordable for most 

municipalities as demonstrated by the monthly residential sewer fees charged by the 

WWTPs included in this evaluation. These fees are listed in the Summary of Observations 

Table and are typically less than $30. EPA intended to identify in more detail the costs 

incurred by these WWTPs to install and operate tertiary treatment for phosphorus removal. 

However, it was soon determined that separating the costs of the tertiary treatment from 

overall facility operating costs was beyond the resources and time available to complete 

this project. EPA instead presents the monthly residential sewer fees charged by each of 

these WWTPs as an indicator of the costs to construct, maintain and operate these facilities, 

including the tertiary treatment for phosphorus removal. 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

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City of Aurora - Sand Creek Wastewater Reuse Plant

Contact Information:

Mailing address: 

18301 EAST QUINCY AVENUE 

Aurora, Colorado 80010 

303-326-8807 

NPDES permit No. CO0026611, expiration date December 31, 2002 

Receiving water: Sand Creek or reclaimed for irrigation use 

Sand Creek WWRP Treatment:

Raw Primary Biological Secondary Effluent Filtration UV 

Wastewater Æ Clarification Æ Nutrient Æ Clarification Æ (Parkson Dynasand Æ Disinfection 

 Removal Filters) 

Treatment capacity: 5 mgd average daily flow

Aurora WWRP Performance Information:

Parameter Limitation 

Avg of

monthly 

averages 

Range of monthly 

averages 

Maximum

individual 

measurement 

TSS 30/45 mg/l 1.0 mg/l 0.5 to 1.84 (6/04) 7.0 mg/l

N-NH3 None *<0.14 mg/l *<0.1 to <0.33 mg/l 1.7 mg/l

BOD 30/45 mg/l * <2.3 mg/l <2.2 to <4.0 mg/l 6.1 mg/l (6/05)

Phosphorus none **0.1 to 0.2 mg/l

Reporting 

period 

4/01 to 5/06 

8/03 to 5/06 

4/01 to 5/06 

4/01 to 5/06 

* Most of these measurements were reported as less than (<) values 

Monthly Sewage Service Charge: $2.16 plus a usage fee of $1.99 per 1,000 Gallons water 

used. 

Facility description:

The City of Aurora is east of the City of Denver in Colorado. This facility began operation in 

2001 and either discharges treated effluent to Sand Creek or the wastewater is reused for 

irrigation on public lands, such as parks and golf courses. Some of the irrigation sites are as far 

as 17 miles away from the WWTP. Although this is a long distance to pump water, the high 

demand for the water in this arid area causes the value of reclaimed wastewater to be nearly the 

price of potable water! 

Treatment at this WWTP involves screening and grinding; primary clarification; biological 

nutrient removal (BNR) in the contact basins; secondary clarification; filtration through single 

pass Dynasand filters (four cells with 4 filters per each cell); UV disinfection. Solids removed 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

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during the course of treatment are routed back into the sewer main where they are ultimately 

treated at the Denver, Metro WWTP. BNR is accomplished by exposing wastewater through 

sequential anoxic, anaerobic and aerobic zones maintained in the contact basins. 

Direct discharge from this WWTP is into the Cherry Creek watershed. The Cherry Creek 

watershed includes a reservoir that is currently impaired due to excessive loading of nutrients. 

The Aurora WWTP currently does not have any effluent limitation for phosphorus. At the time 

of this visit, the NPDES permit for this facility was expired and WWTP operators expected that 

phosphorus limitations might be included in the proposed permit reissuance. Monitoring for 

total phosphorus is conducted weekly and analyses achieve an analytic reporting level of 0.05 

mg/l. 

No chemicals are currently used at the plant to enhance phosphorus removal. Nevertheless, the 

final effluent typically contains between only 0.1 to 0.2 mg/l total phosphorus. Influent BOD 

and ammonia nitrogen were reported to be approximately 200 to 300 mg/l and 30 mg/l, 

respectively. Effluent BOD concentrations average about 2.2 mg/l and ammonia nitrogen is less 

than 0.1 mg/l. 

Operational considerations:

• The single pass Dynasand filters used as tertiary treatment at the Aurora WWTP include 

four cells, each with four continuous backwashing upflow sand media filters. The 

surface area of each filter measures seven by seven feet and the filters are 16 feet deep. 

• Plant operators state they had encountered no serious maintenance or operational 

problems with the DynaSand filters. WWTP operators also responded that they were 

unaware of any reason why application of these filters could not be “scaled-up” to 

accommodate a much larger treatment capacity than the 5 mgd currently being treated 

through the Aurora facility. Additional filters will likely be added in the future to 

accommodate increasing treatment capacity needs in the service area. 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

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Breckenridge Sanitation District - Iowa Hill Wastewater Reclamation Plant

Contact Information:

District Office: 

1605 Airport Road 

Breckenridge, CO 80424 

Phone: 970-453-2723 

Fax: 970-453-2013 

Mailing Address: 

PO Box 1216 

Breckenridge, CO 80424 

NPDES Permit No. CO0045420, expiration date 31 December 2004 

Receiving water: Blue River (tributary to Dillon Reservoir) 

Iowa Hill WWTP Performance Information: 

Parameter NPDES 

Limitation

Avg of

monthly 

averages 

Range of 

monthly 

averages 

Maximum

individual 

measurement 

(date)

BOD 30 mg/l 1.55 mg/l 0.64 to 3.02 mg/l 12.6 mg/l (4/00)

TSS 30 mg/l 2.07 mg/l 0.49 to 6.2 mg/l 18.1 mg/l (4/00) 

N-NH3 10 mg/l 0.41 mg/l 0.16 to 1.8 mg/l 8.2 mg/l (4/00) 

Phosphorus 

0.5 mg/l daily

max & 225 

lb/year 

0.55 mg/l 0.017 to 0.13 mg/l 0.13 mg/l (6/00)

Reporting 

period 

4/00 to 12/02

4/00 to 12/02 

4/00 to 12/02 

5/00 to 12/02 

Iowa Hill WWTP Process: 

InfluentÆ ScreeningÆ ActivatedÆ Biological Æ ChemicalÆMixing Æ FiltrationÆ Disinfection 

(Scalping & Grit Sludge Aerated Addition & Settling (Parkson

Plant) Removal Biological Filter (Alum) (Densadeg) DynaSand 

Treatment (IDI “BioFor”) Filter) 

Design Treatment Capacity: 1.5 MGD average dry weather flow 

Monthly household sewer use fee: $19/month 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Facility description:

The Breckenridge Sanitation District collects wastewater from the town of Breckenridge and the 

surrounding area. The District operates three (3) wastewater treatment facilities including the 

Iowa Hill WWTP and the Farmers Korner WWTP which were visited as part of this evaluation. 

A small package plant is also operated by the district. The Iowa Hill WWTP was newly 

constructed in 1999 and has since been widely cited for its quality of effluent, especially its low 

effluent total phosphorus. Influent flow to the plant is “scalped” from the main District 

interceptor in the Blue River Valley. Solids removed during treatment at the Iowa Hill WWTTP 

are routed back into the interceptor for treatment at the Farmers Korner WWTP. 

Discharge from both of these facilities enters Dillon reservoir which is used to supply drinking 

water to the Metropolitan Denver area. To prevent eutrophication of Dillon reservoir, an annual 

maximum mass loading limitation of 225 pounds per year and daily maximum concentration of 

0.5 mg/l for total phosphorus were established. Facility operators target achieving an effluent 

concentration of 0.01 to 0.02 mg/l total phosphorus to meet the annual loading limitation. 

Treatment at this WWTP is accomplished by screening and grit removal in the headworks; 

activated sludge biological treatment; biological aerated filter (IDI “BioFor” for nitrification); 

chemical coagulation using alum; flocculation and clarification using tube settler (IDI

“Densadeg”); filtration (single stage Parkson “Dynasand” filters); disinfection and 

dechlorination. The Dynasand filter reject rate is reported to be about 15 to 20%. The Dynasand 

filters are configured in four, two-cell units for a total of 8 filters beds which are each 8 feet 

deep. 

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Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Influent concentrations of total phosphorus were measured to be about 6 mg/l during the time of 

this visit (winter) which is very a typical value for untreated domestic wastewater. The aeration 

basins are operated with an anoxic zone to provide for biological removal of phosphorus. About 

sixty percent of the influent phosphorus was reported to be removed through the biological 

treatment process. 

Sodium sulfate is added to maintain alkalinity through the treatment process for phosphorus 

removal. Approximately 100 to 120 mg/l sodium sulfate is applied to the wastewater just 

upstream of where alum is added. Alum is used to precipitate phosphorus. The alum dose at the 

time of this visit was approximately 135 mg/l and is used with 0.5 to 1.0 mg/l cationic polymer. 

Operational considerations:

• The District representative indicated that construction to double the current 1.5 mgd 

treatment capacity at this plant is being considered to accommodate growth in the service 

area. 

• It was reported that the airlift tube in the Parkson (Dynasand) filters had to be replaced 

because of wear caused by sand abrasion. 

• Backwashing of the BioFor unit and improved hydraulic controls in the Densadeg unit 

presented some operational difficulties. 

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Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

- 16 - 

• Fecal coliform levels in the final effluent are so low (0 to 10 colonies/100 ml) that they

typically meet permit limitations without disinfection. Accordingly, the use of chlorine 

and sodium bisulfite (for dechlorination) are minimal. 

• Facility operators prefer the more conventional flocculation-clarification units with tube 

settlers and bed filters that are installed at the Breckenridge Sanitation District, Farmers 

Korner WWTP. The Farmers Corner WWTP effluent quality is reported to be as good as 

that produced by the Iowa Hill WWTP with less operational attention. 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Breckenridge Sanitation District - Farmers Korner Wastewater Treatment 

Plant

Contact Information:

District Office: 

1605 Airport Road 

Breckenridge, CO 80424 

Phone: 970-453-2723 

Fax: 970-453-2013 

Mailing Address: 

PO Box 1216 

Breckenridge, CO 80424 

NPDES permit No. CO0021539 expiration date 31 July 2008 

Receiving water: Blue River (tributary to Dillon Reservoir) 

Design Treatment Capacity: 3.0 MGD average dry weather flow 

Farmers Korner Treatment Processes: 

InfluentÆScreeningÆActivatedÆSecondaryÆChemicalÆ TertiaryÆ FiltrationÆ Disinfection 

 & Grit Sludge Clarification Addition Clarification 

 Removal (with BNR) (tube settlers) 

Residential sewer use fee: $19/month 

Farmers Korner WWTP Performance Information:

Parameter NPDES 

Limitation

Avg of

monthly

averages

Range of

monthly

averages

Maximum 

individual

measurement

Reporting

period 

BOD5 30 mg/l 1.0 mg/l 0.57 to 2.40 mg/l 5.78 (Dec 03) Aug 03 thru

Apr 06

TSS 30 mg/l 1.07 mg/l 0.3 to 3.10 mg/l 5.2 (Dec 05) Same

NH3-N 10 mg/l 3.36 mg/l 0.31 to 16.66 

mg/l 21.88 (May 05) Same

Total 

Phosphorus

 225 lb/yr &

0.5 mg/l daily

max

0.007 mg/l 0.002 to 0.036

mg/l 0.06 (Dec 05) Same

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Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

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Facility Description:

The Breckenridge Sanitation District collects wastewater from the town of Breckenridge, 

Colorado and the surrounding area. The District operates three wastewater treatment facilities 

including the Iowa Hill and Farmers Korner WWTPs which were visited as part of this 

evaluation. Facilities at the Farmers Korner WWTP were upgraded in 1999 to the present 

treatment configuration. Influent flow to this plant includes municipal wastewater from the 

service area and removed solids from the District’s Iowa Hill WWTP. 

Discharge from the Farmers Korner WWTP enters Dillon reservoir which is used to supply 

drinking water to the Metropolitan Denver area. To prevent eutrophication of Dillon reservoir, 

the NPDES permit established an annual maximum mass loading limitation of 225 pound/day 

and a daily maximum concentration of 0.5 mg/l for total phosphorus. Facility operators target 

achieving an effluent concentration of 0.01 to 0.02 mg/l total phosphorus to ensure meeting the 

annual loading limitation. 

Treatment at Farmer Korner WWTP consists of screening and grit removal; biological nutrient 

removal; chemical coagulation and flocculation using polymer and alum; clarification via tube 

settlers; filtration though mixed media bed filters; disinfection with chlorine and dechlorination 

(using sodium bisulfite). Solids removed during treatment are routed to an aerated storage tank, 

dewatered by centrifuge; and the solids utilized at a mine reclamation site. Caustic soda is added 

to maintain alkalinity though the treatment process. 

Operational Considerations:

• Ten operators are employed to run the three Breckenridge District wastewater treatment 

plants and also maintain 20 pump stations in the collection system. 

• Fecal coliform levels in the final effluent are so low (0 to 10 colonies/100 ml) that they 

typically meet permit limitations without disinfection. Accordingly, the amount of 

chemicals used for disinfection are minimal. 

• The alum dose applied at the time of this visit was approximately 135 mg/l and is used 

with 0.5 to 1.0 mg/l cationic polymer. 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Snake River Wastewater Treatment Plant

Contact information:

Summit County Board of Commissioners 

Snake River Wastewater Treatment Plant 

4344 Swan Mountain Road 

Dillon, Colorado 80435-8474 

970-468-5794 

Chuck Clause, Utility Director 

Stoner Turner, Chief Operator

NPDES Permit No. CO0029955, expiration date JanAN-31-2008 

Receiving water: Dillon Reservoir

Snake River WWTP Process: 

Influent ÆScreening ÆAeration Æ Secondary Æ Chemical Æ Flocculation ÆClarification Æ

 Basins Clarifiers Coagulation 

ÆFiltrationÆ Disinfection 

Snake River WWTP Performance Information: 

Parameter NPDES 

Limitation

Avg of

monthly

averages

Range of monthly

averages

Maximum individual

measurement (date)

Reporting

period 

BOD 30/45 mg/l 0.7 mg/l 0.3 to 2 mg/l 3 mg/l (8/03) 2/03 to 5/06 

TSS 30/45 mg/l 0.6 mg/l 0.2 to 2 mg/l 4 mg/l (8/04) 2/03 to 5/06 

N-NH3 5.8 mg/l 0.25 mg/l <0.01 to 1.82 mg/l 9.85 mg/l (7/04) 

Phosphorus

340 lb/year total

& 0.5 mg/l daily

max 

0.015 mg/l <0.01 to 0.04 mg/l 0.08 (2/84) 2/03 to 5/06 

Design Treatment Capacity: 2.6 MGD 

Residential sewer use fee: $36/month ($108 quarterly) 

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Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

- 20 - 

Facility Description:

The Snake River WWTP treats domestic wastewater collected from a service area that is south 

and east of the Dillon Reservoir. Treated effluent is discharged into Dillon Reservoir which is 

used as a drinking water supply for the Denver Metropolitan area. Water quality-based effluent 

limitations for phosphorus have been established in the NPDES permit issued to this WWTP and 

other dischargers into the reservoir to prevent eutrophication. Construction to upgrade treatment 

and capacity of the plant was completed in 2002. 

Treatment at the Snake River WWTP includes screening and grit removal; aeration basins; 

secondary clarification; chemical coagulation and flocculation using with alum and polymer; 

tertiary clarification (rectangular conventional with inclined plate settlers); mixed media bed 

filters (5 feet deep); and disinfection (the filtration process removes enough fecal coliform so that 

conventional disinfection is not normally required). The average alum dose is 70 mg/l in the 

wastewater and is reported to vary from 50 to 180 mg/l. A greater dose of alum is applied during 

the winter period. The operator reported the polymer dose concentration to be about 0.1 mg/l. 

Removed solids are routed to an aerobic digester from which waste solids are dewatered by 

centrifuge and utilized for mine site reclamation. 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Empty rectangular clarifier with inclined plate settlers at Snake River WWTP 

Operational considerations:

• Air supplied to the aerobic digesters is turned off for 2 hours three times a day to raise the 

pH. 

• Recycle streams that are routed to the headworks make up about 40 percent of the total 

plant flow, including grit screenings wash water, WAS thickener decant mixed-media 

filter backwash waste water, aerobic digester decant and centrate. 

• Plant operators are very pleased with operation of the upgraded plant. Good phosphorus 

removal is achieved through the aeration basins without EBPR. Total phosphorus 

concentrations measured in the secondary effluent range from 0.5 to 3.0 mg/l. Facility 

operators speculated the variability of phosphorus in the secondary effluent is possibly 

because chemical sludge that is recycled to head of plant aids removal of phosphorus 

through the biological process and secondary clarification. Return streams include WAS 

thickener decant, aerobic digester decant and centrate. 

• Essentially complete nitrification of wastewater is achieved in the aeration basins. 

• The filtration process removes enough fecal coliform so that conventional disinfection is 

not normally required. 

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Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

- 22 - 

Pinery Wastewater Reclamation Facility

Contact Information:

Pinery Water and Wastewater District 

6516 North State Highway 83 

Parker, Colorado 80134 

Mailing address: 

P.O. Box 1660 

Parker, Colorado 80134 

Telephone: 303-841-2797 

NPDES Permit No. CO0041092, expiration date Sept 30, 2010 

Receiving water: Groundwater in Cherry Creek Reservoir subbasin 

Design Treatment Capacity: 2.0 MGD 

Treatment Processes:

Influent ÆScreening Æ EBNR Æ Secondary Æ Chemical ÆFiltration Æ UV 

 & Grit (BardenPho Clarification Addition “Memcor” Disinfection 

 Removal 5 stage) 

Pinery WWTP Treatment Performance: 

Parameter 

NPDES 

Limitation

(monthly average) 

Average of 

monthly 

averages 

Range of monthly 

averages 

Maximum

measurement 

(date)

BOD 30 mg/l 1.1 mg/l 0.36 to 5.2 mg/l 6.4 mg/l (8/05) 

TSS 30 mg/l 2.2 mg/l 0.6 to 13.3 mg/l 33.3 mg/l (4/04) 

Phosphorus 0.05 mg/l & 

304 lbs/year 0.029 mg/l 0.021 to 0.074 mg/l 0.234 mg/l (11/05) 

Reporting 

period 

1/03 to 9/05 

1/03 to 9/05 

1/03 to 9/05 

Monthly residential sewer use fee: $18 month ($36 bimonthly, plus additional fee for water 

usage over 6,000 gallons) 

Facility Description:

The Pinery Wastewater Treatment Plant was originally constructed in 1990 and upgraded in 

2005. The plant treats domestic wastewater from a service area located south of Parker 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

- 23 - 

Colorado. Discharge from the treatment plant is directed into Cherry Creek. Water quality-based 

limitations for phosphorus and other pollutants have been established in the NPDES permit to 

protect the shallow Cherry Creek aquifer and the reservoir. The enhanced biological nutrient 

removal process utilized at the Pinery Plant is recognized as being very well operated and has 

been studied and cited numerous times as an example of exemplary application of this 

technology. 

Treatment consists of screening and grit removal; BNR Activated Sludge (BardenPho 5 Stage 

[Anaerobic Basin, Anoxic Basin, Oxidation Ditch Aeration Basin, Anoxic Basin, Reaeration 

Basin]); Clarifiers [2 parallel rectangular]; Chemical addition using alum and polymer; Effluent 

Polishing and filtration [using 4 US Filter Memcor filter modules] ; and UV disinfection. The 

US Filter units utilize two-stage filtration in which the first stage is upflow through a plastic 

media with air scour. The second stage filtration is through a downflow, mixed media with 

backwash cleaning. The concentration of alum used for coagulation was reported to be 95 mg/l. 

Residuals solids removed during treatment are routed to aerobic digester tanks. These solids are 

dewatered on a belt filter press and dried/composted for land application. 

Operational Considerations:

• The concentration of total phosphorus in the plant influent is high (8 to 10 mg/l) because 

phosphoric acid is used in the District’s water supply for corrosion control. 

• Ortho-P is monitored by on-line instrumentation (Hach series 5000 Low-Range) in the 

influent to the chemical treatment system and the final filter effluent. This equipment is 

capable of measuring phosphorus to concentrations as low as 0.01 mg/l. 

• The Memcor filters used for effluent polishing are upflow through plastic media 

(adsorption) and downflow through an anthracite sand media filter. Backwash of the 

filter unit components is automatically initiated when a preset head loss is measured. The 

total flow of backwash water used to clean the filters is about 15%. Flushing and 

backwash water is equalized and introduced to the reaeration basin ahead of the 

secondary clarifiers. 

• Sulfuric acid is used for pH control in the treatment process as optimum AlPO4 

precipitation occurs when the pH = 6.0. 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Modular Memcor Filter (US Filter Company) at Pinery WWRP. Each of these modules has a 

treatment capacity of approximately 0.5 mgd. 

Metering equipment used for chemical addition at Pinery WWRP 

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Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Memcor filter module at Pinery WWRP undergoing backwash 

• The laboratory TP and Ortho-P procedures use a Hach DR4000 colorimeter with 1” 

cuvettes which can achieve total phosphorus detection levels to less than 0.01 mg/l. 

• Chemical sludge does not settle well in the secondary clarifiers at the Pinery WWTP, so 

a portion goes over the weirs and is removed again in effluent filter system. 

• Water conservation measures and the progressive water and sewer use fee are working in 

the District. The result is that water consumption is decreasing and the concentration of 

influent wastewater is increasing. 

• Operators have found measuring the oxidation-reduction potential (ORP) of wastewater 

in the plant to be an effective parameter for managing the biological treatment system. 

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Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Clean Water Services, Rock Creek Advanced Wastewater Treatment Plant

Contact Information:

Clean Water Services 

Rock Creek Advanced Wastewater Treatment Plant 

3235 SW River Road 

Hillsboro, OR 97123 

503-648-8774 

NPDES Permit No. OR0029777, expires 31-JAN-2009 

Design capacity: 39 mgd dry weather treatment 

Receiving water: Tualatin River 

Clean Water Services, Rock Creek AWWTP Performance Information:

Parameter 

NPDES 

Limitation

(monthly avg) 

1Avg of

monthly 

averages 

1Range of monthly 

averages 

1Maximum

individual 

measurement 

(date)

CBOD 8 mg/l (seasonal) 1.4 mg/l 1.3 to 1.5 mg/l 1.6 mg/l (5/05) 

TSS 8 mg/l (seasonal) 1.2 mg/l 0.9 to 1.8 mg/l 1.8 mg/l (8/05) 

Phosphorus *0.10 mg/l 0.07 mg/l 0.04 to 0.09 mg/l 0.09 mg/l (9/05) 

Reporting 

period 

5/05 to 10/05

5/05 to 10/05

5/05 to 10/05 

* Limitation established as a monthly median concentration 

1 Monitoring information from dry season when nutrient limitations apply (May through October 

Rock Creek AWWTP Treatment Processes:

- 26 - 

Wastewater

Influent 

45 MGD 

headwork

Primary 

clarifier Aeration basin 

Secondary

clarifier 

alum lime polymer

Tertiary 

claricone 

Mixed media filter 

alum polymer Sodium

hypochlorite

Sodium

bisulfite

Final effluent 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Monthly residential sewer use fee: $16.07 plus $1.11/ccf/month. The average monthly 

residential fee is $27. 

Facility Description:

Clean Water Services Rock Creek AWWTP (from CWS informational publication)

Clean Water Services operates four wastewater treatment plants with a service area that includes 

over 800 miles of collection system piping in Washington County, Oregon. The largest of these 

WWTPs is the Rock Creek facility which discharges into the Tualatin River. These Clean 

Water Services plants are staffed by well trained operators with support from knowledgeable 

operations analysts. Numerous upgrades to treatment have been installed at the Rock Creek 

WWTP over time. The most recent upgrade to improve phosphorus removal was installed in 

1993. The Tualatin River contains natural background levels of phosphorus that are 

significantly higher than observed in many other northwest watersheds. Because the water 

quality of the Tualatin River was impaired by excessive nutrient loading from various sources in 

the watershed, a TMDL was established which includes a wasteload allocation for phosphorus 

loading from the Rock Creek AWWTP. The wasteload allocation is equivalent to the natural 

background concentration of phosphorus in the River at the point of discharge. This wasteload 

allocation is expressed in the NPDES permit as a monthly median limitation of 0.1 mg/l which 

applies seasonally from May through October. 

Primary, secondary

And tertiary sludge 

Anaerobic digester centrifuge 

landfill 

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Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

- 28 - 

Wastewater flow is divided for treatment through the east and west side treatment trains. 

Treatment at the Rock Creek WWTP consists of screening and grit removal; alum addition;

primary clarification; extended aeration; secondary clarification; flocculation using alum and 

polymer; tertiary clarification; filtration; disinfection (with chlorine) and dechlorination. Four 60 

foot diameter ClariCone tertiary clarifiers are used on the east treatment train to provide contact 

time and settling after addition of polymer and alum. Filtration on the east train is accomplished 

with six monomedia anthracite gravity flow bed filters. The west treatment train uses 

conventional clarifiers for tertiary settling followed by filtration through four dual media gravity 

flow bed filters. 

Phosphorus is removed in four locations within the Rock Creek treatment system: alum 

enhanced removal in the primary clarifiers; biological removal in the aeration basins; chemical 

flocculation and removal in the tertiary clarifiers; and removal through filtration. Treatment 

upgrades to install enhanced biological nutrient removal of phosphorus are being considered as a 

means for reducing the current cost of chemicals used for phosphorus removal. Clean Water 

Services maintains an informative website 

(http://www.cleanwaterservices.org/AboutUs/Wastewater/TreatmentProcess.aspx) which 

provides additional information about current treatment and planned upgrades of this facility. 

Operational Considerations:

• The average concentration of total phosphorus in the raw plant influent is 6 mg/l. 

• Lime is added to maintain pH and alkalinity through the treatment process. The cost of 

lime used for treatment is about $150,000 per year. 

• System analysts have determined that the phosphorus limitation will usually be met if the 

total suspended solids concentration is 1.5 mg/l or less in the final effluent. A strong 

empirical relationship has also been observed that when the aluminum to total 

phosphorus ratio is 5:1 to 7:1 in the secondary effluent, that the total phosphorus 

concentration in the final effluent will be less than 0.1 mg/l. 

• A ratio (not stoichametric) of about 50:1 dry alum to phosphorus is the target dose rate in 

the tertiary clarifiers. Alum use during May through October (when phosphorus 

limitations apply) costs about $250,000, based on acquiring alum at $172 per dry ton. 

This usage of alum equates to a cost of approximately $1,500 per day, or about $50 per 

mgd of wastewater treated. 

• The formation of struvites (ammonium, magnesium, phosphorus crystals) has been an 

operational problem in some of the slow velocity piping, such as in the heat exchanger 

recirculation.

• Resolubization of phosphorus in return streams from anaerobic handling of removed 

solids represents about 20 percent of the phosphorus and ammonia-nitrogen loading to 

the plant. The loading from these return streams is managed by storage and flow 

equalization back into the treatment system. 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

• The secondary effluent that goes to tertiary treatment typically has the following 

characteristics: total phosphorus < 0.5 mg/l; orthophosphorus <0.1 mg/l; TSS < 10 mg/l; 

COD < 50 mg/l and N-NH3 <0.01 mg/l. 

• Performance records kept by Clean Water Services staff document that the 50th percentile 

of monthly average total phosphorus concentrations achieved over the previous eight 

years is 0.071 mg/l. Concentration of total phosphorus in the final effluent have been 

reduced to as low as 0.032 mg/l. CWS systems analysts expect that better phosphorus 

removal could be achieved if more effective final filtration equipment were installed.

They estimate that if a final effluent TSS concentration of 0.5 mg/l were achieved, the 

total phosphorus concentration would be about 0.03 mg/l. 

Aeration basin at Clean Water Services, Durham AWWTP. The basins at the Rock Creek 

WWTP may be modified in the future to also provide enhanced biological phosphorus removal. 

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Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Clean Water Services, Durham Advanced Wastewater Treatment Plant

Contact Information:

Clean Water Services 

Durham Advanced Wastewater Treatment Plant 

16580 SW 85th Street 

Tigard. OR 97224 

Phone No. 503.831.3600 

NPDES Permit No. OR0028118, expiration date JAN-31-2009

Design capacity: 24 mgd average dry weather treatment flow 

Receiving water: Tualatin River 

Durham AWWTP Treatment Process: 

Wastewater

Influent 

24 MGD 

headwork 

Primary 

clarifier 

Aerated zone 

(alum) lime VFA 

Anaerobic 

zone Anoxic 

zone 

Secondary

clarifier 

Tertiary 

clarifier Mixed media filter 

alum (polymer)

Sodium

hypochlorite 

Sodium

bisulfite

Final effluent 

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Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Clean Water Services, Durham AWWTP DMR information: 

Parameter 

NPDES 

Limitation

(monthly avg) 

1Avg of

monthly 

averages 

1Range of monthly 

averages 

1Maximum

individual 

measurement 

(date)

CBOD 8 mg/l (seasonal) 2.2 mg/l 1.7 to 2.6 mg/l 4.2 mg/l (6/05)

TSS 8 mg/l (seasonal) 1.8 mg/l 1.7 to 2.8 mg/l 2.8 mg/l (5/05)

Phosphorus *0.11 mg/l 0.07 mg/l 0.05 to 0.1 mg/l 0.1 mg/l (9/05)

Reporting 

period 

5/05 to 10/05

5/05 to 10/05

5/05 to 10/05 

* Limitation establishes as a monthly median concentration 

1 Monitoring information from period when seasonal nutrient limitations apply (May through October)

Monthly sewer use fee: $16.07 plus $1.11/ccf/month. The average monthly residential fee is 

$27. 

Facility Description:

Clean Water Services operates four wastewater treatment plants with a service area that includes 

over 800 miles of collection system piping in Washington County, Oregon. These Clean Water 

Services plants are staffed by well trained operators with support from knowledgeable operations 

analysts. The Durham Advanced Wastewater Treatment Plant is the second largest of the four 

WWTPs and discharges treated effluent into the Tualatin River. This plant was constructed in 

1976 and upgraded to the existing treatment configuration in 1989. Maximum daily wet weather 

treatment capacity is about 80 mgd. 

The Tualatin River reportedly contains natural background levels of phosphorus that are 

significantly higher than observed in many other northwest watersheds. Because the water 

quality of the Tualatin River was impaired by excessive nutrient loading from various sources in 

the watershed, a TMDL was established which includes a wasteload allocation for phosphorus 

loading from the Durham AWWTP. The wasteload allocation is equivalent to the estimated 

natural background concentration of phosphorus in the River. This wasteload allocation is 

expressed in the NPDES permit for this facility as a monthly median limitation of 0.11 mg/l 

which applies seasonally from May through October. 

Treatment at the Durham AWWTP consists of screening and grit removal; primary clarification; 

biological treatment with enhanced biological nutrient removal; secondary clarification: 

Primary 

sludge 

Anaerobic digester 

landfill 

Secondary and 

Tertiary sludge 

Gravity 

thickener

- 31 - 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

- 32 - 

chemical addition of alum and polymer for phosphorus removal; tertiary clarification; filtration 

through dual media gravity bed filters and disinfection. Lime is added to the biological process 

to maintain pH and alkalinity. Removed solids are anaerobically digested, dewatered by

centrifuge, and utilized as fertilizer. A two-stage fermenter is operated to produce volatile fatty 

acids which are added to the biological contact basins. The enhanced biological nutrient removal 

process at times reduces total phosphorus to levels that are less than the 0.11 mg/l permit 

limitation. However, this performance is not achieved during the entire period when the seasonal 

phosphorus limitations are in effect. The tertiary treatment with chemical addition and filtration 

provides assurance that the final effluent is of consistently good quality. Some of the treated 

effluent is reclaimed for irrigation. 

Operational considerations: 

• Nitrate-nitrogen may interfere with biological phosphorus removal if sufficient volatile 

fatty acids (VFAs) are not maintained. Therefore, creation of volatile fatty acids (VFAs) 

is necessary for the enhanced biological phosphorus removal process to work properly.

Operators route solids from the primary clarifier to a two-stage fermenter system. The 

fermenter produces 500 mg/l VFAs when provided a two and one half day solids 

retention time. For good biological removal of phosphorus, the optimal relationship for 

VFAs to phosphorus in the contact basins is about 5:1. 

• Operators have determined that orthophosphorus comprises about 75 to 80 percent of the 

total phosphorus. Automatic sampling equipment provides continuous, low level 

orthophosphorus information that can be used to adjust treatment as necessary. A target 

of 0.02 mg/l orthophosphorus was identified as representing optimal treatment 

performance by the current treatment configuration. 

• Secondary effluent quality information is used to operate the biological phosphorus 

removal process. Operators target achieving a final effluent concentration of 0.07 mg/l 

by reducing total phosphorus in the secondary effluent to 0.50 mg/l or less. 

• The amount of biosolids generated by biological phosphorus removal is somewhat more 

than would be produced by using only chemical treatment for phosphorus removal. 

• Return streams from anaerobic handling of removed solids (supernatant from digesters 

and centrate from centrifuges) comprises about 20 percent of the total phosphorus loading 

to the plant. The loading from these return streams is managed by storage and 

equalizing its flow back into the treatment system. 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Empty tertiary clarifier at Clean Water Services, Durham AWWTP 

Empty gravity flow bed filter at Clean Water Services, Durham AWWTP

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Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Stamford Wastewater Treatment Plant

Contact Information:

Village of Stamford Wastewater Treatment Plant 

Railroad Avenue 

Stamford, New York 12167 

Telephone: 607-652-3172 

Operated by: Delaware Operations 

NPDES Permit No. NY0021555, expiration date JUL-01-2009 

Receiving water: West Branch Delaware River Watershed 

Stamford WWTP Treatment Process: 

Stamford WWTP Performance Information: 

Parameter NPDES 

Limitation

Average of 

monthly 

averages 

Range of monthly 

averages 

Maximum

individual 

measurement 

Phosphorus 0.2 mg/l *<0.011 mg/l <0.005 to < 0.06 mg/l 0.06 (11/05) 

N-NH3 2.5 mg/l *<0.98 mg/l <0.03 to 0.63 mg/l 0.63 (7/05) 

TSS 30 mg/l *<3.3 mg/l < 2 to 8 mg/l 8 (3/03) 

CBOD 25 mg/l *<4.5 mg/l <3.5 to 8 mg/l 8.5 (8/04) 

Reporting 

period 

2/03 to 5/06 

7/04 to 5/06 

2/03 to 5/06 

7/04 to 5/06 

Plant 

Effluent

Two-stage 

DynaSand Æ

Filters 

Aerated tank / 

secondary clarifier 

Reject water clarifier 

Coagulant 

(PASS)

chlorine Dechlorination 

headwork 

Wastewater 

Influent 

Secondary sludge 

Dual Sand sludge 

Aerated sludge 

digester Belt filter press Solids to

landfill 

polymer

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Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

- 35 - 

* Almost all measurements were reported as less than (<) values 

Design Treatment Capacity: 0.5 MGD (requested certification for 0.7 mgd pending @ New 

York State Department of Environmental Conservation (NYSDEC) 

Monthly household sewer use fee: $10 /month 

Note about sewer fees: The costs of construction, operation and maintenance of any and all unit 

processes (which are in excess of New York State standards at this and other WWTPs 

discharging into the Delaware River watershed) are subsidized by the City of New York. The 

Stamford WWTP unit processes funded by the City of New York include the chemicallyenhanced tertiary filtration, redundant disinfection, dechlorination systems, emergency stand-by 

power generation, telemetry and alarm systems, and sludge dewatering. The incremental O&M 

cost increase of these unit processes, as well as additional operations staffing and accounting 

personnel, are funded annually by the City of New York. 

Facility Description:

The Village of Stamford wastewater treatment plant (Stamford) receives municipal wastewater

from residences and a number of businesses in this community. Delaware Operations is 

contracted to operate this facility for Stamford. Discharge of treated effluent from Stamford is 

into the 2,000 square mile New York City Watershed, including the Delaware River watershed, 

which is a primary drinking water supply for the City of New York. To protect the quality of 

this receiving water, the City of New York provides funding for municipal dischargers in the 

watershed to construct and operate advanced wastewater treatment. In return for this financial 

assistance, these municipalities must maintain and operate their facilities to produce high quality 

effluent. Design criteria for tertiary treatment and NPDES permit limitations are established by 

the New York State Department of Environmental Conservation. 

Wastewater treatment at the existing Stamford WWTP was upgraded and became fully 

operational in 2003. Treatment consists of grit removal and screening; extended aeration and 

secondary clarification (in combined aeration basin/clarifier); chemical addition for flocculation 

using PASS and filtration through two-stage Dynasand filters. Removed solids are routed to an 

aerobic digester. Waste solids are dewatered in a belt press and sent to a landfill. There are also 

large equalization basins available to which raw wastewater may be routed for storage during 

times of high influent flow. 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Combined aeration basin and clarifier (in center of unit) at Stamford WWTP 

The DynaSand filters installed at Stamford were obtained from the Parkson Corporation. Both 

the first stage and the second stage filters operate as continuous backwashing, upflow, sand 

media filters. There are nine sets of first and second stage filters, each with an approximate 

surface area of fifty square feet. The sand media in the two meter deep first stage filter has an 

average diameter of 1.3 millimeters. The second stage sand media is 0.9 millimeters. Secondary 

treated wastewater is pumped to a distribution header from which it flows by gravity through the 

first and then the second stage filters. Influent to the first stage filters is chlorinated to inhibit 

biological growth. Because PASS hydrolyzes so quickly, this flocculant is added to the influent 

of each first stage filter, rather than being mixed in the distribution header. The reject stream

from the filters is routed to a small clarifier and the overflow is returned mixed with influent to 

the first stage filter. Solids removed in the reject clarifier are routed to a new aerobic digester, 

into which secondary solids are also mixed, and then dewatered in a newly installed 1.0 meter 

belt press. 

- 36 - 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Generic diagram of two stage DynaSand filtration system (courtesy of Parkson Corporation). 

Note: the Stamford WWTP uses a concrete clarifier in lieu of a lamella settler. 

Operational Considerations:

• Analyses for phosphorus, BOD and TSS in the final effluent are conducted using EPAapproved testing methodologies by a NYS-certified laboratory. For data quality control 

purposes, samples of final effluent are routinely split and sent to a state certified contract 

laboratory which specializes in achieving extremely low reporting levels for phosphorus. 

Nevertheless, most of the sample results are reported as less than values (<) on the 

monthly discharge monitoring. These results routinely demonstrate the effluent as being 

significantly below permit limitations but do not necessarily accurately characterize the 

very low phosphorus concentrations in the effluent. 

• A correlation between pathogens and turbidity in the effluent was established for 

municipal dischargers in the watershed. Continuous monitoring of turbidity is a closely 

watched NPDES permit requirement. Treatment plant operation is optimized to achieve 

very low effluent turbidity. The excellent removal of other pollutants such as 

phosphorus, is primarily a by-product of WWTP operation focused on maintaining low 

turbidity in the final effluent. 

• The design hydraulic loading rate specified by New York City for the Parkson Dynasand 

filters is 3.36 gallon/square foot/minute (g/ft2/min). Operators report the best 

performance has been achieved at Stamford with a filter loading rate of between 4.0 and 

- 37 - 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

4.5 gpm/sq. ft. but stated that the filters continue to perform very well up to loading rates 

of over 5.0 gpm/sq.ft. 

• The filters in use are routinely rotated based on the amount of time they have been in

service. There are nine (9) filter trains at the Stamford WWTP; under typical operating 

conditions, only 2 filters are running.

• PASS is obtained from the Eaglebrook Company (phone number 450.652.0665) at an 

approximate cost of $4/gallon. Stamford operators say the addition of PASS is flow 

paced at a rate of about 30 gallons per one half mgd of wastewater treated. This equates 

to a cost of approximately $240/day/per mgd for flocculant. 

• There is essentially no sand lost from the DynaSand filters during operation. 

• The reject rate from the filters is designed and operated to be about 10 percent of the total 

flow. The percent reject decreases at higher loading rates. 

• The overflow rate from each DynaSand filter can easily be adjusted by inserting different 

size plastic weirs. 

Plastic weirs used for adjusting overflow rate from DynaSand Filters 

• The turbidity of the effluent was 0.053 NTU at the time of EPA’s site visit. Turbidity is 

closely monitored as it has been determined to be a good surrogate for measuring 

pathogens potentially present in the discharge. The NPDES permit limit for turbidity is 

0.5 NTU. 

- 38 - 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Walton Wastewater Treatment Plant

Contact Information:

Walton Wastewater Treatment Plant 

54 South Street 

Walton, New York 13856 

Phone Number (607) 865-6993

Operated by: Delaware Operations 

NPDES Permit No. NY0027154, expiration date Feb 2008 

Receiving water: Delaware River Watershed 

Design Treatment Capacity: 1.55 mgd (average daily flow) 

Treatment Process Diagram: 

Headwork 

DualSand 

filters 

Coagulant 

 AlCl 

Chlorine 

Dechlorination 

Aerated 

equalization tank 

Aerobic tank 

Secondary clarifier 

Plant 

Effluent 

Influent 

Gravity thickener 

Secondary sludge 

Aerobic digester Belt filter press 

Landfill 

- 39 - 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

- 40 - 

Walton WWTP Performance Information:

Parameter NPDES 

Limitation

Average of 

monthly 

averages

Range of monthly 

averages

Maximum

individual 

measurement

Total P 1 0.2 mg/l <0.01 mg/l <0.005 to < 0.06 mg/l <0.06 mg/l (3/06) 

N-NH3 2 8.8 mg/l 0.24 mg/l <0.05 to 1.4 mg/l 1.4 mg/l (6/05)

TSS 30 mg/l <3.5 mg/l <2.6 to <4.9 mg/l <4.9 mg/l (12/05) 

CBOD 25 mg/l <3.7 mg/l <2.5 to <4.5 mg/l <21 mg/l (7/04) 

Reporting 

period

2/03 to 3/06

6/03 to 6/06 

2/03 to 3/06

2/3 to 3/06

1 Almost all phosphorus measurements were reported as less than (<) a specified detection value. 

The reported detection value was used for summarizing performance, although the actual 

concentration is lower. 

2 There are seasonal limitations for ammonia nitrogen and performance is summarized for the 

period when this limitation applies. 

Monthly household sewer use fee: $10 month plus charges based on water usage. 

(Note: the costs of construction, operation and maintenance of this and other WWTPs

discharging into the Delaware River watershed are subsidized by the City of New York.) 

Facility Description:

The Walton Wastewater Treatment Plant (WWTP) receives municipal wastewater from

residence and a number of businesses in this community plus a significant amount of wastewater 

from a nearby dairy creamery. Wastewater from the creamery constitutes about 80 percent of the 

organic loading and 40 percent of the flow into the WWTP. The influent to the WWTP would 

be characterized as high strength with an average BOD concentration of 350 mg/l. Discharge of 

treated effluent from Walton is into the 2,000 square mile Delaware River watershed, which is a 

primary drinking water supply for the City of New York. To protect the quality of this receiving 

water, the City of New York provides funding for municipal dischargers in the watershed to 

construct and operate advanced wastewater treatment. In return for this financial assistance, 

these municipalities must maintain and operate their facilities to produce high quality effluent. 

Design criteria for tertiary treatment and NPDES permit limitations are established by the New 

York Department of Environmental Conservation. 

Wastewater treatment at the existing Walton WWTP was upgraded and became fully operational 

in 2003. Treatment consists of grit removal and screening; extended aeration and secondary 

clarification; chemical addition for flocculation using aluminum chloride (added to the 

wastewater at both the secondary clarifiers and the distribution header for the DynaSand filters); 

and filtration through two-stage Dynasand filters; disinfection with chlorine and dechlorination 

with sulfur dioxide. Chlorine is added to the filter influent to control biological growth in the 

filters. Removed solids are routed to an aerobic digester. Waste solids are dewatered in a belt 

press and sent to a land fill. 

The DynaSand filters installed at the Walton WWTP were obtained from the Parkson 

Corporation. Both the first stage and the second stage filters operate as continuous backwashing, 

upflow, sand media filters. There are five sets of first stage and second stage filter modules. 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Each module contains four DynaSand filters which have an approximate surface area of two 

hundred square feet (or eight hundred square feet per module). So, there is total of 40,000 square 

feet surface area of primary filters and the same amount of secondary filter surface area. The 

sand media in the two meter deep first stage filters has an average diameter of 1.3 millimeters. 

The second stage filters are one meter deep and contain sand media of 0.9 millimeter average 

diameter. The number of filters in use is adjusted as needed to accommodate flow through the 

plant. The filter modules in use are routinely rotated according to time in service. 

Secondary treated wastewater is pumped to a distribution header where aluminum chloride and 

chlorine is added and from which it flows by gravity through the first and then the second stage 

filters. The reject stream from the filters is routed to the headworks of the plant. 

DynaSand Filters at 

Walton WWTP 

The above picture shows a side view of the distribution header (far right), first stage and second 

stage DynaSand filters installed at the Walton WWTP. Flow through the filters is by gravity 

from the distribution header. The people shown in this picture are standing on grating above the 

second stage filters. This building houses twenty (2 meter deep) first stage and twenty (1 meter 

deep) second stage DynaSand filters which have a combined total surface area of about 80,000 

square feet. The installation is configured to create five banks of filters which are rotated into 

Mixing tank 

1st stage filter

2nd stage filter

- 41 - 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

use on a time basis. At the time of this visit, two of the five filter banks were being used to treat 

the entire wastewater flow at this plant. 

View into top of DynaSand filter at Walton WWTP. This picture shows sand being returned 

from washer at top of lift tube in a second stage filter. These filters are designed to wash sand 

continuously (without any backwash cycle). 

Operational Considerations: 

• About 80 percent of the loading and 40 percent of the wastewater flow into the Walton 

WWTP comes from the Kraft Dairy operation. 

• Analyses for phosphorus, BOD and TSS in the final effluent are conducted using EPA 

approved testing methodologies. For data quality control purposes, samples of final 

effluent are routinely split and sent to a state certified contract laboratory which 

specializes in achieving extremely low reporting levels for phosphorus. Nevertheless, 

most of the sample results are reported as less than values (<) on the monthly discharge 

monitoring. These results routinely demonstrate the effluent as being significantly below 

permit limitations but do not necessarily characterize the excellent quality of the effluent. 

- 42 - 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

- 43 - 

• The turbidity of the effluent was 0.062 NTU at the time of EPA’s site visit. Turbidity is 

closely monitored as it has been determined to be a good surrogate pollutant for 

measuring the pathogens potentially present in the effluent. The NPDES permit limit for 

turbidity is 0.5 NTU. 

• The maximum treatment capacity of the plant is 3 mgd. The DynaSand filters are not the 

limiting factor as this flow can be treated by using only 3 of the 5 filter modules. 

• Total phosphorus concentrations in the secondary effluent typically range between 1 to 2 

mg/l. 

• The cost of aluminum chloride to the Walton WWTP was reported to be $4.64/gallon. A 

streaming current meter (which measures the negative charge of particles in the water) is 

used to control aluminum chloride dosing. Approximately 50 to 60 gallons of aluminum

chloride are used each day which equates to a daily cost of about $250/day at this 1.5 

mgd facility.

• The filter press is operated 3 times a week to dewater solids from the aerobic digester.

Solids are sent to a landfill and removed liquid is returned to the plant headworks. 

Operators reported observing no changes in treatment plant performance caused by the 

solids handling return streams. 

• The design hydraulic loading rate specified by New York City for the Parkson DynaSand 

filters is 3.36 gallon/square foot/minute (g/ft2/min). Operators report they typically run 

filters at hydraulic loading rate of between 4.0 and 4.5 g/ft2/min but stated the filters 

would continue to perform very well up to loading rate of 5.0 g/ft2/min. 

• The filters in use are routinely rotated based on the amount of time they have been in

service. 

• There is essentially no sand lost from the DynaSand filters during operation. 

• The reject rate from the filters is designed and operated to be about 10 percent of the total 

flow. 

• The overflow rate from each DynaSand filter can easily be adjusted by inserting different 

size plastic weirs (pictured in Stamford WWTP description). 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Milford Wastewater Treatment Plant

Contact information:

Mailing address: 

Milford Wastewater Treatment Plant 

P.O. Box 644 

Milford, MA 01757 

Phone Number: 508-478-0059 

NPDES Permit No. MA0100579, expiration date 31-MAR-2010 

Receiving water: Headwaters of Charles River 

Permitted flow: 4.8 mgd (monthly average) 

Milford WWTP Process Diagram: 

Wastewater 

Influent 

Polymer

Headwork 

Primary 

clarifier 

Trickling filters

Intermediate 

clarifier 

lime

Gravity 

filters 

Rotating

biological

contactor 

Final 

clarifier 

PACL 

UV disinfection 

Final 

Effluent

- 44 - 

Primary, 

secondary and 

tertiary sludge

To incineration 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Gravity thickener

Milford WWTP Performance Information:

Parameter NPDES 

Limitation

Avg of

monthly 

averages 

Range of 

monthly 

averages 

Maximum

individual 

measurement(date) 

BOD 30/45 mg/l 3.7 mg/l 1.3 to 7.4 mg/l 9.1 mg/l (4/05)

TSS 30/45 mg/l 1.7 mg/l 0.48 to 8.0 mg/l 13.6 (2/03) 

N-NH3* 1.0 mg/l 0.26 mg/l 0.05 to 0.48 mg/l 0.19 mg/l (6/03) 

Phosphorus* 0.2 mg/l 0.07 mg/l 0.04 to 0.16 mg/l 0.16 mg/l (6/04) 

Reporting 

period 

7/03 to 4/06 

1/03 to 4/06 

 6/03 to10/05 

 6/03 to10/05 

* NPDES limitations for phosphorus and ammonia are seasonal. The 0.2 limit for phosphorus 

applies April 1 - October 31. The ammonia limitation for the month of May is 5.0 mg/l only and 

is 1.0 mg/l for the period from June 1 - October 31. The performance information shown is for 

the periods of each year when these seasonal water quality-based limitations apply. 

Monthly residential sewer use fees: $27.50 ($330/year) 

Facility Description:

Wastewater treatment facilities were originally constructed to serve the local community in 

1902. Remnants of that original facility and some of the subsequent treatment upgrades may still 

be observed. The current treatment facility was constructed in 1985 and treats domestic 

wastewater from the surrounding service area. Discharge is into the headwaters of the Charles 

River. During the dry period of the year, the discharged effluent constitutes the entire flow at 

this point of the river. The collection system suffers from inflow and infiltration problems which 

cause influent flow to the WWTP to be quite high in response to significant rain events. As a 

result, influent BOD concentrations are sometimes diluted to below 80 mg/l. Severe rainfall 

during the preceding week resulted in influent flows being greater than 8 mgd at the time of the 

site visit. Although the permit limitation for flow is 4.8 mgd, the plant has demonstrated the 

ability to treat these high flows and still produce an excellent quality effluent. 

Treatment at the Milford WWTP consists of screening and grit removal; primary clarification;

trickling filters; intermediate clarification (with polymer addition to aid settling); rotating 

biological contactors; secondary clarification; chemical addition using poly-aluminum chloride; 

filtration through mixed media traveling bed filters; ultraviolet disinfection. The final effluent is 

discharged down a cascading outfall to achieve reaeration prior to mixing in the receiving water. 

Approximately 1 mgd per day of the final effluent is utilized by the local power company for 

cooling water. 

- 45 - 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Operational considerations:

• A colorimetric method is used for analyzing total phosphorus. The reportable level 

achieved in the Milford laboratory using this testing methodology is typically about 0.02 

mg/l total phosphorus. 

• Approximately 17 to 20 gallons of polymer are added prior to the intermediate clarifiers. 

• Approximately 300 to 400 gallons per day of PACl are used to flocculate phosphorus. 

Facility representatives stated the cost of PACl to be $1.50/gallon. So, the total daily cost 

of PACl ranges from about $450 to $600. 

• Removed solids are routed to an aerobic thickener. The concentration of thickened solids 

coming out of the thickener is only about 3%. Having to haul so much water with these 

solids represents the largest single cost ($350,000/year) of operating this WWTP. 

• The trickling filters and rotating biological contactors appear to be very resilient to 

increase flows caused by inflow and infiltration. However, the record setting rainfall 

during the winter months of 2006 had affected treatment removal of ammonia-nitrogen. 

Trickling filters at Milford WWTP 

Cascading discharge structure into Charles River at Milford WWTP 

Rotating Biological Contactors at Milford WWTP 

- 46 - 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Alexandria Sanitation Authority (ASA) Advanced Wastewater Treatment 

Plant

Contact Information:

Alexandria Sanitation Authority 

1500 Eisenhower Avenue 

Alexandria, VA 22314 1987 

Phone: 703-549-3381 

Aerial View on ASA Advanced Wastewater Treatment Facility (from ASA staff) 

NPDES Permit: No. VA0025160 , expires 20-JAN-2009 

Receiving water: Hunting Creek (a tributary to the Potomac River) 

Design Treatment Capacity: 54 mgd (average dry weather) 

Phosphorus treatment technology: Triple point chemical addition in which ferric chloride is 

added to primary and secondary settling tank influents and alum is added to the tertiary settling 

tank influent. 

- 47 - 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Alexandria AWWTP (provided by ASA staff)

Alexandria Advanced WWTP Performance Information: 

Parameter 

1

NPDES

Limitation

(monthly avg) 

Average of 

monthly 

averages

Range of monthly 

averages

Maximum

individual 

measurement 

Phosphorus 0.18 mg/l 0.065 mg/l 0.04 to 0.1 mg/l 0.15 mg/l (4/05) 

N-NH3 8.4 mg/l *<0.1 mg/l 0 to 0.2 mg/l 0.6 mg/l (1/06)

TSS 6 mg/l 1.5 mg/l <0.1 to 5.4 mg/l 9.2 mg/l (2/04)

CBOD 5 mg/l *<0.1 mg/l 0 to 0.5 mg/l 1.0 mg/l (12/05) 

1

Reporting 

period

9/04 to 5/06 

9/04 to 5/06 

9/04 to 5/06 

9/04 to 5/06 

* Monitoring results during this period were typically reported as zero or less than detection 

1 The summarized monitoring data is inclusive of all values submitted during the reporting period regardless of

when seasonal water quality based effluent limitations apply 

Monthly household sewer use fee: $4.17 plus $4.49 per 1,000 gallons water used 

Facility Description:

The ASA Advanced WWTP treats wastewater with combined storm sewers from a service area 

of approximately 51 square miles including the City of Alexandria and portions of Fairfax 

County. The population served is approximately 400,000 people. ASA began construction to 

upgrade the 54 mgd design flow facilities in 1999 to meet the water quality requirements of the 

Potomac Embayment Standards and the Chesapeake Bay Agreement. Initial operation of the new 

Biological Nutrient Removal (BNR) system was achieved in December 2002. 

- 48 - 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

- 49 - 

Treatment consists of screening; grit removal; primary settling with possible addition of ferric 

chloride and polymer; methanol or volatile fatty acid added to biological reactor basins to aid 

BNR; ferric chloride and polymer addition prior to secondary settling; alum addition and 

mixing; tertiary clarification with inclined plate settlers; dual media gravity bed filtration; UV 

disinfection and post aeration. Removed solids are dewatered in centrifuges and the centrate is 

returned to the primary clarifiers. Then sludge is pre-pasteurized; anaerobically digested; 

centrifuged again and sent to land application as Class A biosolids. The moisture content of the 

biosolids after treatment is about 70 percent. 

Operational Considerations: 

• High influent flows during rain events often exceed 80 mgd. The plant has treated peak 

influent flows of 108 mgd during extreme storm events. 

• The average influent concentration of total phosphorus was reported to be about 4.5 mg/l. 

• Operators reported an observed trend of increasing influent concentrations while influent 

flow has remained steady. Speculation about the cause of these phenomena is that the 

ASA progressive sewer rates (which are based in part on water usage) have promoted 

water conservation. 

• The facility is currently considering treatment upgrades necessary to achieve a required 

monthly average effluent target for total nitrogen of 3.0 mg/l. 

• Multiple point chemical addition is utilized for phosphorus removal. Ferric chloride is 

added to primary and secondary settling tank effluents. Alum is mixed into the influent 

to the tertiary settling tanks. The alum contained in the return stream was reported to aid 

in phosphorus removal through the plant processes. 

• Sodium hydroxide is added to the primary effluent, the secondary effluent and after the 

gravity filters to increase pH and maintain alkalinity. 

• The concentration of total phosphorus in the secondary effluent is typically about 0.4 to 

0.5 mg/l. Facility representatives reported that the average concentration of phosphorus 

in the final effluent during 2005 was approximately 0.05 mg/l. 

• The approximate annual cost for chemicals used in treatment is $2.4 million. This 

includes $1.4 million for sodium hydroxide, $300,000 each for alum and polymer, and 

$300,000 for ferric chloride and methanol. 

• The plant is equipped with custom-made computerized controls (supervisory control data 

acquisition system) to enhance the efficiency of operation. 

• Biological treatment at ASA includes methanol fed to sequential anoxic and aerobic 

zones in the secondary process. Primary wastewater is ‘step fed’ into the secondary 

basins. A portion of the wastewater from each aerobic zone is recycled back to the 

preceding anoxic zone. 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Chemical mixing paddles in front portion of sedimentation tanks at Alexandria AWWTP 

Bed filter undergoing backwash at Alexandria AWWTP

- 50 - 
Ad

EPA

vanced Treatment to Achieve Low Concentration of Phosphorus April 2007

 Region 10

- 51 - 

Upper Occoquan Sewage Authority (UOSA)

Millard H. Robbins Regional Wastewater Reclamation Facility

Contact information:

Upper Occoquan Sewage Authority 

Millard H. Robbins Regional Water Reclamation Plant 

14631 Compton Road 

Centreville, VA 20121-2506 

Phone No. 703-830-2200 

NPDES Permit: No. VA0024988, expiration date FEB-19-2007 

Treatment capacity: 42 mgd annual average flow, 128 mgd instantaneous peak flow 

Receiving water: Unnamed Tributary of Bull Run Creek (Bull Run is a major tributary of the 

Occoquan Reservoir) 

UOSA WRF Treatment Performance Information:

Parameter NPDES 

Limitation

Average of 

monthly**

averages

Range of monthly**

averages

Maximum

individual 

measurement

Total 

Phosphorus 0.10 mg/l *<0.088 mg/l 0.023 to <0.282 mg/l 0.580 mg/l (2/03) 

TSS 1 mg/l *<0.549 mg/l 0 to 2 mg/l NA 3/02 to 9/03 

Reporting 

period

3/02 to 12/04 

2/05 to 6/06 

* estimated average because many measurements were reported as less than (<) values or below 

detection limit 

** Weekly averages for Total Phosphorus 

Monthly residential sewer use fees: (of the 4 four UOSA member jurisdictions): 

- Fairfax County sewer rates: $3.03/1000 gallons (FY 2004) 

- Prince William County sewer rates: $3.75/1000 gallons (FY 2003) 

- City of Manassas sewer rates: $4.09/1000 gallons (FY 2004) 

- City of Manassas Park sewer rates: $35.00 as monthly Water and Sewer Service Charge 

(FY 96 through FY 2004) 
vanced Treatment to Achieve Low Concentration of Phosphorus April 2007

 Region 10

- 52 - 

UOSA Treatment plant schematic (provided by UOSA):AdEPA
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

- 53 - 

Facility Description: 

For nearly 30 years, the Upper Occoquan Sewage Authority (UOSA) has provided advanced 

wastewater treatment water reclamation for a service area in Virginia that includes portions of 

Fairfax County, Prince William County, and the cities of City of Manassas, and the City of 

Manassas Park. Nineteen miles downstream from the UOSA discharge is a drinking water 

withdrawal from the Occoquan Reservoir that serves approximately 1.3 million people. Around 

1972 UOSA selected a biological, physical, chemical treatment process (high lime treatment 

system) that could reliably produce a high quality reclaimed wastewater that would both protect 

the quality and augment the amount of water in the reservoir. 

The 10 mgd treatment capacity of the original plant has been upgraded in several stages to about 

54 mgd since it began operation in 1978. Continuing rapid development and population growth 

in the service area is again prompting consideration of treatment plant expansion to 

accommodate the need for additional wastewater treatment capacity. In 1972, the high lime 

treatment process represented the best technology for consistently achieving the necessary high 

quality effluent. However, since that time other treatment technologies have evolved that also 

produce high quality effluent. The next plant expansion may include use of a technology other 

than high lime treatment. 

UOSA maintains and operates this facility with well- qualified staff that routinely provides 

educational tours of their treatment facility. EPA greatly appreciates that UOSA allowed use of 

their educational materials for describing the treatment process in this report. 

UOSA liquid treatment process is composed of: 

- A conventional treatment that removes 90% of most incoming pollutants: screening; grit 

removal; primary clarification; aerobic biological selectors; activated sludge aeration

basins with nitrification/denitrification processes; secondary clarification. 

- A chemical advanced treatment – high-lime process – to reduce phosphorus to below 

0.10 mg/l, to capture organics from secondary treatment, to precipitate heavy metals and 

to serve as a barrier to viruses : lime slurry added to rapid mix basins (to achieve pH of 

11); anionic polymer added in flocculation basins; chemical clarification; first stage 

recarbonation to lower pH to 10; recarbonation clarifiers to collect precipitated calcium 

carbonate; second stage recarbonation to lower pH to 7; storage in ballast ponds. 

- Physical advanced treatment to meet stringent limits for TSS (1 mg/l) and COD (10 mg/l) 

including alum and/or polymer addition; multimedia filters; activated carbon contactors. 

- Disinfection by chlorination/dechlorination process. 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

UOSA Water Reclamation Facility (WRF) – in the forefront are fine bubble diffuse aeration 

basins constructed during the plant expansion to 27 mgd which are off-line in this picture. 

Secondary Clarifiers with lime handling buildings in background at UOSA WRF 

- 54 - 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Removed solids processing at UOSA WRF: 

- Primary sludge and waste activated sludge are screened, digested, blended, dewatered by 

centrifuge and ultimately dried to produce fertilizer pellets. 

- Chemical and recarbonation sludge are concentrated by gravity thickeners, filter press 

and then transported to a UOSA owned captive landfill. 

Lime slurry being mixed into wastewater at UOSA WRF 

Operational Considerations:

• The UOSA WRF experiences significant increased influent flows as the result of inflow 

and infiltration into the collection system. Although the annual average design flow into 

the plant is approximately 42 mgd, peak hourly influent flows of 120 mgd have been 

experienced during extreme storm conditions. 

• Handling and mixing (slaking) lime is “messy”. Scaling in the treatment system after 

lime addition also presents a maintenance problem.

• Operators believe the existing treatment system could achieve even lower levels of 

phosphorus in the final effluent with additional chemical addition. 

• The 2006 operating budget was $21,227,800 to operate and maintain this facility. 

Over half of this cost is for UOSA staff wages. Electrical power and chemical costs are 

approximately $2,691,000 and $1,562,000, respectively. 

- 55 - 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Lime scaling on chemical clarifier weirs at the UOSA WRF 

- 56 - 
Adva

EPA

nced Treatment to Achieve Low Concentration of Phosphorus April 2007

 Region 10

- 57 - 

Fairfax County Wastewater Management, Noman M. Cole Jr. Pollution 

Control Plant

Contact Information:

Wastewater Treatment Division 

Noman M. Cole Jr. Pollution Control Plant 

9399 Richmond Highway 

Lorton, VA 22079 

Phone No. 703.550.9740 

NPDES Permit: No. VA0025364, expiration date APR-13-2008 

Design capacity: 67 mgd 

Receiving water: Pohick Creek, tributary of Potomac River and Chesapeake Bay 

Noman Cole WWTP Performance Information: 

Parameter NPDES 

Limitation

Average of

monthly averages

Range of monthly

averages

Maximum 

individual

measurement

Total 

Phosphorus 0.18 mg/l *<0.061 mg/l <0.02 to <0.13 mg/l 0.20 mg/l (10/05) 

Orthophosphorus none *<0.057 mg/l <0.05 to <0.11 mg/l 0.20 mg/l (10/05) 

NH3 - N **1 mg/l *<0.040 mg/l 0 to 0.20 mg/l 0.64 mg/l (10/05) 

BOD 5 mg/l below detection

limit 

Non detectable to <2

mg/l 2 mg/l (4/03) 

TSS 6 mg/l *<1.21 mg/l 0 to 3.5 mg/l 4.1 mg/l (12/04) 

Reporting 

period

4/03 to 6/06 

4/03 to 6/06 

4/03 to 6/06 

4/03 to 6/06 

4/03 to 6/06 

* Many measurements were reported as less than (<) values or below detection limit 

** Seasonal limitation : from April to October (2.2 mg/l from November to March) 

Monthly sewer use fee: $ 3.28/1000 gallons used. The average monthly residential fee is $21. 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

 PROCESS FLOW DIAGRAM 

B3 NOMAN M. COLE,JR., POLLUTION CONTROL PLANT , COUNTY OF FAIRFAX , VIR

RP1

PROCESS LEGEND 

PRELIMINARY/PRIMARY TREATMENT BNR AWT SOLIDS HANDLING INCINERATION ODOR CONTROL SUPPORT & ANCILLARY 

RAW 

SEWAGE BAR 

SCREENS 

(3) 

FLASH MIX 

TANKS (2) AERATION 

TANKS (9) 

EQUALIZATION

 BASINS (2) 

DEGRITTERS 

(6) 

POLYMER 

LIME 

CHEMICAL SLUDGE RECYCLED 

TO HEAD OF PLANT 

Centrifuges (6) 

NaOCl 

SECONDARY 

CLARIFIERS 

(10) 

DUAL-MEDIA 

GRAVITY 

FILTERS (10) TERTIARY 

CLARIFIERS 

(5) 

MONO-MEDIA 

GRAVITY 

FILTERS (8) 

SLUDGE 

STORAGE TANKS (2) 

BACKWASH TANK EFFLUENT 

R.A.S 

PRIMARY

SLUDGE 

SCRUBBER WASTEWATER 

W.A.S. 

POLYMER 

FILTRATE 

WATER 

OVER 

FLOW 

BACKWASH 

TANK 

(3) 

PRIMARY TANKS (8) 

GRAVITY 

THICKENERS 

(4) 

FLOTATION 

THICKENERS 

(3) 

A.S.E. 

PUMP 

STATION 

TERTIARY 

CLARIFIER 

EFFLUENT 

P.S. 

BACKWASH NaOCl P.S. 

POLYMER 

 SCREENINGS 

TO I - 95 

CO-DISPOSAL 

POLYMER 

FERRIC CHLORIDE 

6 

2 

2 

4 

3 

2 

2 1 

C B1 C D/D1 F/F1 QQ

H1

Q1/Q2

J1/J2

R1/R2

K3

K1/K2

CC

EE

DD

FF

BB

MULTIPLE -

HEARTH 

INCINERATORS (6) 

POLYMER 

SRF

SEPTAGE 

RECEIVING 

FACILITY 

EQUALIZATION 

TANKS 

RAW 

WASTEWATER 

P.S. 

B

B2

EQUALIZATION 

TANKS PUMPS 

RWW PUMPS 

RWW 

SW

SW 

NaOH 

RETENTION 

POND #1 

RP PUMPS 

S KK1 G

GFE 

P.S. 

1 

NaOCl 

KK2

FOREIGN 

SLUDGE 

RECEIVING 

FACILITY 

(Diagram provided by Fairfax County WWTP staff) 

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Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Facility Description:

Fairfax County is one of 15 counties and cities in Virginia and Maryland that comprise the 

Washington D.C. Metropolitan Statistical Area. Fairfax County owns and operates the Noman M. 

Cole Jr. Pollution Control Plant. This facility receives mostly domestic wastewater from over 

3,200 miles of sewer lines in the service area and currently treats an average influent flow of 45 

mgd. This and other municipal dischargers to the Potomac River and Chesapeake Bay are 

required to achieve monthly and weekly average permit limitations for total phosphorus of 0.18 

and 0.27 mg/l, respectively. A monthly average limitation of 3 mg/l for total nitrogen will 

become effective in the year 2010. 

Treatment at the Noman Cole Plant consists of screening; primary clarification (covered for odor 

control); biological treatment with enhanced biological nutrient removal (BNR); polymer 

addition as needed; secondary clarification; equalization and storage in retention ponds; tertiary 

clarification with ferric chloride addition to remove phosphorus; disinfection with sodium

hypochlorite; filtration through dual/mono media gravity bed filters. Tertiary sludge is routed to a 

gravity thickener to create volatile fatty acids (VFAs) which are added to aid the biological 

phosphorus removal process. Removed solids from the primary and secondary clarifiers are 

dewatered by lime addition, filter presses and centrifuge, and then incinerated in multiple hearth 

incinerators. The inert ash is hauled by truck to a landfill. 

Baffles installed in wastewater contact basin (empty) to achieve anoxic and aerobic conditions for 

enhanced biological nutrient removal at Noman Cole PCP. 

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Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Wastewater contact basin in operation at Noman Cole PCP 

Operational considerations: 

• The combination of biological nutrient removal, chemical addition with tertiary clarification 

and filtration effectively reduces total phosphorus concentrations to well below the 0.18 mg/l 

permit limitation. Other pollutants such as BOD, TSS and fecal coliform are also reduced to 

very low levels through these treatment processes. 

• The amount of ferric chloride added in the tertiary clarifier to remove phosphorus has been 

reduced since biological phosphorus removal was implemented. The ferric chloride dosage 

before installation of biological nutrient removal was 18 to 20 mg/l. The concentration used 

now is down to 9 to 10 mg/l. 

• The treatment processes are continuously being evaluated and optimized by staff with the goal 

of consistently meeting permit limitations in the most cost effective manner. 

• Treatment upgrades necessary to meet the new nitrogen limitation are currently being 

considered. It is likely that methanol addition and other changes to the biological treatment 

train will be made to enhance nitrogen removal from wastewater. 

• Opportunities to reuse the high quality final effluent for irrigation or as cooling water are 

being considered. 

• The Noman Cole annual operating budget is reported to be approximately $18 to $20 million. 

• Ferric chloride costs in 2005 were about $180,000. 

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Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Empty tertiary clarifier at Noman Cole PCP 

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Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

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Blue Water Technologies, Inc– Full scale pilot facility installed at the Hayden 

Area Regional Wastewater Treatment Plant

Contact Information:

Hayden Area Regional Wastewater Treatment Plant 

10108 North Atlas Road 

Hayden, ID 83835 

Blue Water Technologies, Inc: 

10108 10450 North Atlas Airport Road 

Hayden, ID 83835 

Phone No 208-209-0391 

Website: www.blueh2o.net 

NPDES Permit: No. ID0026590, expiration date 02-NOV-2004 

Design capacity of Hayden WWTP: 1.65 mgd 

Receiving water: Spokane River 

Monthly sewer use fee: Company representatives estimate that were the Blue PRO phosphorus 

removal system added to the existing Hayden WWTP as tertiary treatment, the residential sewer 

use fee would increase by only $1.20 / month to cover all costs of construction and operation. 

Company representatives estimate the capital cost for the Blue PRO phosphorus removal system

as tertiary treatment is $178,000 for a 1-mgd treatment plant and $494,000 for a 3-mgd treatment 

plant. 

Facility Description:

The Hayden WWTP is operated by the Hayden Area Regional Sewer Board, serving the greater 

Hayden, Idaho, area. The permitted plant flow is 1.65 mgd. All of the treated wastewater is 

utilized for silvacultural irrigation during the warm, dry summer period. During the other times 

of the year, WWTP effluent is discharged into the Spokane River. The quality of the Spokane 

River and Long Lake are documented as being impaired by excessive loading of nutrients during 

the summer period. An intensive water quality evaluation effort by the State of Washington 

determined that phosphorus loading from the point source dischargers must be significantly 

reduced to restore water quality. A TMDL is currently being developed by the state which will 

specify very low wasteload allocations for discharges into the river. 

Treatment at the Hayden WWTP consists of screening and grit removal; oxidation ditches (2) 

with mechanical mixers; secondary clarification (3); and chlorine disinfection. Removed solids 

are aerobically stabilized and dewatered by a belt filter press. Although the Hayden WWTP is 

capable of providing treatment to nitrify ammonia, it is typically not operated in a nitrification 

mode during the summer months when the effluent is land applied. 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Blue Pro filtration at the Hayden Wastewater Research Facility:

In 2004, Blue Water Technologies, Inc and the University of Idaho, in conjunction with the 

Hayden Area Regional Sewer Board constructed a full scale wastewater research facility to 

develop and test their treatment system. This installation is called the Hayden Wastewater 

Research Facility (HWRF). HWRF uses secondary effluent from the WWTP prior to chlorine 

addition and has the capacity to treat about one fourth of the total plant discharge. 

Concentrations of phosphorus in the Hayden WWTP influent are typically about 7 to 9 mg/l. 

After secondary treatment the concentration of total phosphorus in the Hayden secondary effluent 

(without Blue PRO in operation) is typically about 4 mg/l. Since one purpose for testing this 

technology was to demonstrate how well it would perform as an add-on tertiary treatment to a 

secondary WWTP, the Hayden facility represented a good choice to test this technology. 

Cutaway diagram of Centra-Flo filter at Blue PRO installation at Hayden HWRF 

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Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

- 64 - 

The Blue PRO technology combines co-precipitation and sorption to remove both particulate and 

soluble phosphorus. Through these processes, some phosphorus is precipitated and removed from 

water as it moves upward though the sand media. At the same time, some phosphorus is adsorbed 

onto the hydrous ferric oxide coated sand. This adsorption mechanism allows the process to 

achieve very low concentrations of phosphorus in the effluent. The phosphorus is then removed 

from the sand through abrasion and separated in the sand washer at the top of the filter. The 

treatment process installed at the HWRF is composed of: 

- a pre-reactor where coagulant (ferric sulfate) is added and mixed with the secondary 

effluent; 

- two continuous backwashing, upflow sand bed filters. The size of each filter is 14 feet 

deep, with a surface area of 50 square feet. The filters can be operated as single-pass or 

sequentially as a two-stage filtration system. The reject stream (around 7-8% of the flow 

to the filters) is recycled to the headworks of the Hayden WWTP. 

A long-term, steady-state study was conducted from December 2005 through February 2006 

using 0.25 mgd of the Hayden secondary effluent. Blue PRO was operated as a two-single-pass 

stage filtration system in December and as a two-stage filtration system in January and February 

during the study, although the second stage was not optimized until halfway through December. 

The reject stream (containing phosphorus and solids removed in the filters) returned to the 

WWTP headworks were observed to cause the phosphorus removal efficiency through the 

secondary process to improve significantly. This is likely the result of dosing the WWTP influent 

with the ferric compound used in the Blue PRO process. Concentrations of total phosphorus in 

the secondary effluent were observed to drop from 4 mg/l to about 1 mg/l during the steady state 

study. The monthly averages of total phosphorus in the Blue PRO effluent obtained during this 

steady-state study are: 

- 0.036 mg/l in December (second stage filtration not optimized) 

- 0.009 mg/l in January 

- 0.016 mg/l in February 

-

The average effluent TSS concentration using two-stage filtration during the study was about 1 

mg/l. Considering all data from 2005 through 2007, the average phosphorus result was 0.014 

mg/L TP, with a standard deviation of 0.006 mg/L. Based on the results of long term testing, 

Blue Water representatives state their phosphorus removal system can consistently achieve an 

effluent quality of less than 0.030 mg/l total phosphorus. This performance may vary when 

applied to the effluent of a different WWTP. Mobile pilot treatment facilities have been 

constructed and deployed to test the Blue PRO treatment process at other WWTPs. Results 

similar to those demonstrated at the HWRF have been achieved in these pilot studies. 

A next-generation technology termed “Blue CAT” is currently in operation at HWRF. This 

patent-pending process adds an advanced oxidation component to the base Blue PRO process, 

achieving oxidation potentials up to 875 mV. In addition to improving phosphorus and solids 

removal over Blue PRO, this new technology adds disinfection to <2 cfu/100 mL and destructive 

removal of emerging micropollutants, such as endocrine disruptors, pharmaceuticals, and 

pathogens. The Blue PRO long-term, steady-state study report and other information about the 

Blue PRO phosphorus removal system are available from the Blue Water Technologies, Inc. 

website: www.blueh2o.net. Attributes claimed by this treatment system include: 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

- 65 - 

- high efficiency, removing 99%+ of TP from municipal wastewater, 

- low chemical dose, typically 6-10 mg/L Fe 

- continuously flowing filtrate – no interruption for backwashing, 

- low capital, operating, and maintenance costs (total for 1 MGD and 1 pass : less than 

$34.7300/lb of P removed), 

- minimal sludge production, may improve sludge quality and reduce handling costs, 

- works effectively without pH adjustment, 

- highly tolerant of interfering water chemistry – wide usage 

- significantly lowers turbidity and BOD (40% BOD removal and 80% TSS removal during 

the steady-state study), 

- does not affect transmissivity for UV disinfection, 

- mobile treatment units available, 

- arsenic, selenium, and heavy metals such as zinc may also be removed. 

- the Blue PRO tertiary treatment may also be adapted to denitrify through the filter(s).); 

installations achieve <3 mg/L total nitrogen. 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

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CoMagTM Technology – Concord Wastewater Treatment Plant

Contact Information:

Concord Public Works Water/Sewer Division 

135 Keyes Road 

Concord, MA 01742 

CoMag Process 

Ray Pepin, Senior Engineer 

Cambridge Water Technology (CWT) 

Suite 100 

41 Hutchins Drive 

Portland, Maine 04102 

207-774-2112 x3349 

NPDES Permit: No. MA0100668, expiration date 28-FEB-2011

Design capacity: 1.2 MGD as average daily flow and 4.0 maximum daily flow 

Receiving water: Concord River 

Facility Description:

The existing Concord WWTP was built in 1986 and has a 1.2 mgd monthly average annual 

permitted discharge flow and discharges to the Concord River. Treatment through this WWTP 

currently consists of headworks, primary settling; trickling filters; secondary clarification; sand 

filters; and chlorine disinfection. Water quality of the Concord River is impaired, partially 

because of excessive amounts of nutrients entering the river. The seasonal total phosphorus 

effluent limitation which applies from April to October was lowered from 0.75 to 0.2 mg/l. The 

existing facility could only produce an effluent with a TP concentration of 0.6 to 0.7 mg/l by 

adding alum in advance of the secondary clarifiers. Therefore, a plant upgrade was needed to 

meet the proposed phosphorus limit and restore the quality of the receiving water. 

The Concord WWTP is currently undergoing upgrade construction which, in addition to installing 

tertiary treatment for phosphorus removal (CoMagTM), will improve the headworks, provide a 

new sludge dewatering process and switch from chlorine to UV disinfection. The tertiary process 

specification also required that the process be capable of meeting permit limits with one 

CoMagTM clarifier off line at maximum daily flow. The budget cost for the entire upgrade is $9.7 

million, of which the CoMagTM process itself is less than 1/3 of the installed cost. The CoMagTM 

process supplier has certified that its treatment process will be capable of consistently achieving 

an effluent total phosphorus concentration of <0.05 mg/l. 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

CoMagTM Treatment Process: 

CoMag is a “magneto-chemical” wastewater treatment process that incorporates the use of finely 

divided magnetic ballast to bind precipitated phosphorus and other fine particulates. The 

technology evolved from the minerals processing industry and all unit operations have been 

utilized for many years. Magnetite provides a “magnetic ballast seed” that when mixed with alum

and polymer increases both flocculation and settling rates. These properties reduce the tank sizes 

necessary to remove the floc from wastewater. Since the floc particles are attracted to a magnet, 

High Gradient Magnetic Separation (HGMS) is used for final effluent “polishing filtration” rather 

than traditional sand filtration or membrane systems. The unit area flow rates that can be treated 

through the HGMS are claimed to be 50 times greater than those of traditional filters. The ballast 

seed is recovered from removed solids and from the effluent. 

The CoMagTM process was selected for installation at the City of Concord because long-term pilot 

testing demonstrated its ability to achieve high phosphorus removal efficiencies at comparatively 

low costs. Other factors that prompted the Concord WWTP decision to install CoMagTM 

included: 

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Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

- 68 - 

- Reduced chemical doses are required to achieve low effluent total phosphorus 

concentrations, resulting in lower operational costs. 

- CoMagTM utilizes simple clarifiers that are one-tenth the size of conventional clarifiers and 

does not require lamella style tubes which can plug or foul, thereby reducing capital costs 

and footprint requirements. 

- The magnetic separator has a footprint 2 to 5 percent of the size required for conventional 

filtration processes. 

- Ballasted sludge is very dense and cohesive, with little carry over of pin floc from the 

clarifier, even at high overflow rates, thereby allowing CoMag to handle wide variations 

in flows and loads. 

- Ballasted sludge settleability is dependable and predictable. 

- Ballast recycling and recovery is highly efficient and minimize ballast usage. 

- The CoMagTM process has proven to be effective in removing TSS, metals, color, 

turbidity, pathogens and other pollutants. 

- The process is simple and robust. All maintenance items are easily accessible and readily 

available. No specialized tools or training are required to operate or maintain the process. 

* Information about CoMagTM was provided by company representatives at the Concord WWTP 

or extracted from the article “CoMagTM Process Achieves Low Effluent Total Phosphorus Levels 

While Reducing Footprint and Cost” by Steve Woodard. 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

LOTT Budd Inlet Wastewater Treatment Plant

Contact Information:

LOTT Budd Inlet Treatment Plant 

500 Adams Street N.E. 

Olympia Washington 98501-6911 

NPDES Permit No. WA0037061, expiration date SEP-30-2010 

Design capacity: 28 mgd 

Receiving water: Budd Inlet (South Puget Sound) 

LOTT Budd Inlet Treatment Performance Summary: 

Parameter NPDES 

Limitation

Average of 

monthly 

averages

Range of monthly 

averages**

Maximum reported 

measurement (date)**

Total Inorganic 

Nitrogen * 3 mg/l 2.2 mg/l 1.23 to 2.81 mg/l 2.81 mg/l (4/04) 

BOD * 9 mg/l 4.17 mg/l 2.14 to 8.66 mg/l 16.5 mg/l (5/06) 

TSS 30 mg/l 7.15 mg/l 2.75 to 12.3 mg/l 21.3 mg/l (3/06) 

Reporting 

period

4/03 to 9/06 

4/03 to 9/06 

1/03 to 9/06 

* Seasonal limitation 

** Data from period when seasonal limitations apply 

Monthly residential sewer fee: $25.50

LOTT Budd Inlet WWTP Treatment Schematic: 

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Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

- 70 - 

Facility Description:

The LOTT Budd Inlet Treatment Plant provides advanced treatment of wastewater collected from

a service area that includes the cities of Lacey, Olympia and Tumwater plus portions of Thurston 

County. These entities form the LOTT Alliance which operates the regional WWTP. Treated 

effluent is discharged into the marine waters of Budd Inlet which is located at the southern end of 

Puget Sound. This part of Puget Sound is poorly flushed and is very sensitive to nutrient loading, 

especially during the late spring through fall period. Excessive nutrient loading is blamed for 

low dissolved oxygen and excessive aquatic plant and algae growth in these waters. A TMDL is 

currently under development by Washington State for this water body which is expected to 

establish wasteload allocations (WLAs) for the Budd Inlet Treatment Plant as well as for other 

sources of nutrient loading. Although these WLAs have not yet been determined, it is a fact that 

Budd Inlet does not have any capacity for additional nutrient loading during the critical warm

weather season. 

The LOTT facility has undergone many changes since it was upgraded to provide secondary 

treatment in 1982. During this time most of the storm water collection systems have been 

separated from the sewage collection system, although a small portion in the downtown Olympia 

sewer is still a combined system. The original UNOX wastewater treatment basins were 

converted and additional tankage built to provide anoxic, aerobic; second anoxic and final aerobic 

wastewater contact areas necessary to accomplish enhanced biological nutrient removal (EBNR) 

of nitrogen. A high internal recycle rate of about 4:1 is maintained to provide adequate contact 

time for wastewater treatment through EBNR. This recycle rate means that for every 10 mgd of 

wastewater influent treated about 50 mgd is routed through the treatment system. The mixed 

liquor suspended solids concentration is maintained at about 1800 mg/l in the contact basins. 

This represents a solids retention time of about 20 days. Many other improvements to improve 

treatment efficiency at the LOTT plant are currently under construction or are being planned. 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

Secondary clarifiers undergoing upgrade construction at LOTT’s Budd Inlet Treatment Plant 

(2006) 

In addition to primarily domestic wastewater, LOTT received high strength wastewater from the 

Olympia brewery until that facility closed about three years ago. The resulting changes to the 

character of the influent wastewater required significant adjustment in operation of the WWTP. 

One associated change was that LOTT began adding methanol to provide food for the bacteria 

necessary to accomplish denitrification of the wastewater. Additional adjustments to wastewater

recycling within the treatment system and to operation of the aeration basins have maintained 

excellent nitrogen removal efficiency. With the operation experience gained over time, these 

adjustments have significantly reduced the need to add methanol. At the time of the EPA visit to 

the LOTT WWTP, continuous monitors indicated that the total inorganic nitrogen level of the 

final effluent was less than 1 mg/l (0.1 mg/l NH3-N + 0.59 mg/l NO3-N + 0.1 mg/l NO2-N = 0.79 

mg/l TIN). 

Treatment at LOTT consists of: flow into an influent equalization basin (2.25 mgd); screening; 

grit removal; primary clarification; EBNR (methanol is added to the second anoxic basin); 

secondary clarification and ultraviolet disinfection. Removed solids are routed to dissolved air 

flotation thickeners, stabilized in anaerobic digesters, and dewatered by centrifuge before being 

disposed by land application. Centrate from the centrifuge is metered back into the primary 

effluent. 

A portion of the LOTT effluent is reclaimed and utilized for irrigation of public lands. The final 

effluent destined for reuse is provided filtration through single-stage, continuous back-washing 

Parkson sand filters. These filters are each 14 feet deep and configured in three banks of two 

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Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

- 72 - 

filters. Polyaluminum chloride (PACl) is added to aid filtration effectiveness. Additional 

disinfection is provided by chlorination. 

Planning for the Future:

The rapid development and population growth in the South Puget Sound service area required the 

LOTT partners to carefully plan to meet future wastewater treatment needs. The marine waters of

Budd Inlet are already impaired by excessive loading of nutrients and this situation precludes the 

option of simply increasing treatment capacity and discharge at the main plant. Although the 

existing LOTT plant already achieves about the best nitrogen removal that current biological 

treatment technology can accomplish, there is simply no assimilative capacity in South Puget 

Sound for additional nutrient loading during the critical period. 

LOTT implemented numerous water conservation programs in the service area and began 

promoting use of reclaimed wastewater for irrigation and groundwater recharge. LOTT also 

decided to meet the need for additional wastewater treatment capacity by constructing ‘satellite’ 

facilities. These satellite wastewater treatment plants are located in areas needing sewer service 

where land is still available to accommodate reuse of the effluent. Advanced treatment is 

provided at the satellite WWTPs to meet state requirements for reclaimed wastewater such that it 

may be utilized for groundwater recharge and/or irrigation during the dry summer months. The 

first of the planned satellite treatment plants is a two mgd membrane bioreactor treatment plant 

that was placed in operation in 2006. The membranes are hollow fiber filaments produced by 

U.S. Filter Corporation. Treated effluent from this satellite WWTP is reclaimed and used for 

groundwater recharge. Solids removed during treatment at the satellite plant are returned to the 

sewer main for handling at the Budd Inlet WWTP. Land was recently purchased by LOTT for 

construction of a second satellite plant. 

Operational Considerations:

• The five trains of aeration basins have excess capacity and only two of the five basins are 

typically needed to treat wastewater flows during normal dry weather. The aeration 

delivery system installed in these basins is somewhat limiting to operational control. 

• Adjusting aeration (DO setpoints) has significantly reduced the need to add methanol as 

supplemental feed for bacteria necessary for nitrogen removal. Methanol is only fed 

during nighttime hours. Methanol currently costs about $1.60 per gallon (delivered to the 

plant). 

• Nitrate concentration measured in the aeration basin effluent is used for process control 

for determining how much food additive (methanol) to use. 

• Oxidation/reduction meters are installed and connect to the SCADA system to assist with 

operational control. 

• A high internal recycle rate (4 gallons recycled: 1 gallon treated) is necessary to achieve 

the desired effluent quality. The electricity and maintenance costs associated with internal 

recycle pumping are quite expensive. 
Advanced Treatment to Achieve Low Concentration of Phosphorus April 2007 

EPA Region 10 

24 inch internal recycle piping at LOTT’s Budd Inlet WWTP 

• There have been some problems with filamentous bacteria (Microthrix parvicella). 

Operators are experimenting with polyaluminumchloride (PAX) to control this organism. 

• Sludge collectors in the secondary clarifiers are being upgraded. 

• An operational goal is to keep total inorganic nitrogen levels in the final effluent under 2 

mg/l to insure that the 3 mg/l permit limitation is met consistently.

- 73 -