Sustainable Technologies for Achieving Very Low

Nitrogen and Phosphorus Effluent Levels

I

n 2001 the U.S. Environmental Protection 

Agency published new criteria for nutrients 

in receiving waters, driving wastewater 

treatment plants (WWTPs) to significantly lower 

total nitrogen (TN) and total phosphorus (TP) in 

treated effluents. Although existing technology 

produces effluents containing either low 

TN and TP levels (5 mg/L and 0.5 mg/L, 

respectively) or very low TN and TP levels 

(3 mg/L and 0.1 mg/L, respectively), there 

has not been a comprehensive assessment 

of efficiency and long-term sustainability of 

the technologies. This WERF project fills the 

gap with a cost-benefit analysis of the various 

nutrient removal technologies. WWTPs can 

use this information to compare capital and 

operating costs of nutrient removal schemes, 

and regulatory agencies can use it to better 

assess the technology constraints and economics of nutrient removal. 

Current Technologies Have Limitations

The team surveyed WWTPs and conducted an extensive literature search. They also 

summarized case studies on design, operating and performance data, and regulatory 

compliance with low TN and/or TP effluent requirements. 

The researchers found several state-of-the-art technologies currently in vogue to achieve 

low TN and TP. They also found, however, that most nutrient removal plants can remove 

either TP or TN to very low levels, but not both. The various modes for N and P removal 

include tertiary treatment systems such as chemical precipitation and effluent filtration 

for P reduction, and denitrification filters and/or methanol addition in secondary or tertiary 

systems to enhance N removal. 

The study also noted that upgrading the treatment plants to achieve very low N and P 

levels would add significant costs. Factors driving the cost increases include the use 

of chemicals, effluent filtration, increased energy needs, provisions for redundancy and 

reliability, and increased sludge processing. 

The study underscored several other challenges to achieving very low TN and TP levels. 

One problem is the lack of organic carbon (or another electron donor) for biological 

nutrient removal (BNR). Others include the presence (in the influent) of hard-to-remove or 

recalcitrant forms of dissolved organic nitrogen (DON), and the presence of byproducts of 

the BNR process.

Project Team Evaluated Nutrient Removal Alternatives

The project team developed a technology threshold matrix (for plant capacity up to 100 

MGD) that would guide selection of treatment alternatives. 

Benefits

n Evaluates technologies to achieve low 

levels of total nitrogen (TN) and total phosphorus (TP) in wastewater effluent.

n Identifies key challenges and knowledge 

gaps in achieving very low TN and TP levels.

n Discusses potential constraints in achieving 

very low TN and TP levels attributable to the 

speciation of TN and TP – in influent and effluent and in the BNR process – that are not 

efficiently removed in current processes.

n Informs regulators of the feasibility and 

cost benefits of nutrient reduction to very 

low effluent levels of reactive and non-reactive nutrients.

Related Products

Technology Assessments: Nitrogen Removal 

Using Oxidation Ditches (96CTS1)

Characterizing Mechanisms of Simultaneous 

Biological Nutrient Removal During 

Wastewater Treatment (00CTS17UR)

Factors Influencing the Reliability of 

Enhanced Biological Phosphorus Removal

(01CTS3)

Dissolved Organic Nitrogen Characterization 

and Bioavailability in Wastewater Effluents

(02CTS1a)

On-Line Nitrogen Monitoring and Control 

Strategies (03CTS8)

WERF Workshop on Nutrient Removal:

How Low Can We Go? (05CTS1W)

Related Ongoing Research

Nutrient Challenge Program (NUT1R06)

Available Format

Online PDF.

Wat e r En v i r o n m e n t Re s e a r c h F o u n d at i o n wa s t ewat e r t r e at m e n t a n d r e u s e

EXECUTIVE SUMMARY

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As effluent limits become more stringent, 

better characterization of influent wastewater 

and source tracking of pollutants into the 

collection system is needed.
One of the main criteria in comparing the various N and P removal technologies is achieving 

effluent quality on a sustainable basis. The technology assessment entailed a two-tier 

system for nutrient removal: Tier I effluents (TN and TP levels of less than 5.0 mg/L and 

0.5 mg/L, respectively) and Tier II effluents (TN and TP levels of less than 3.0 mg/L and 

0.1 mg/L, respectively). Economic criteria included the cost of implementing the technologies. 

The team learned that emerging technologies – such as sidestream N removal by 

SHARON/Anammox (anaerobic ammonium oxidation), and implementation of membrane 

bioreactor systems – can achieve lower nutrient levels. 

The following processes consistently received high scores in the evaluation process. 

Bardenpho process employs a series of aerobic and anoxic tanks; Johannesburg process 

is a modification of the Bardenpho process.

Bardenpho + chem-P + sand filtration

Modified Bardenpho + chem-P + sand filtration

Modified Bardenpho with fermenter + sand filtration

Johannesburg high IR + chem-P + sand filtration

The team evaluated selected technologies at lab-scale, pilot-scale, and full-scale. Labscale MBR studies included: 1) treatment of highly concentrated ammonium rich centrate 

wastewater (sidestreams in WWTPs) to obtain low TN values in the effluent; and 2) 

investigation of simultaneous nitrification and denitrification of dilute wastewater without 

compromising the COD removal under low DO conditions. They also used a pilot-scale 

MBR system to achieve simultaneous low TN and TP in the wastewater effluent on a 

sustainable basis at the Flagg Creek WWTP (Hinsdale, IL). In a demonstration study, the 

team investigated chemically enhanced P removal in the anaerobic zone of the EBPR 

process and chemical usage minimization. The research also describes the full-scale 

technology demonstration at John Egan Wastewater Reclamation Plant at the Metropolitan 

Water Reclamation District of Greater Chicago, using step-feed BNR and chemical P 

removal to achieve low TN and TP levels, respectively. The report discusses N and P 

speciation projects at participating WWTPs, including selected Illinois plants, and the 

District of Columbia Water and Sewer Authority Blue Plains advanced treatment plant. 

Future Research Needs

Additional research efforts are warranted in several related areas: 1) identification of 

alternative carbon sources for N and P removal; 2) source control of N and P to minimize 

their loads on the treatment plants; 3) ways to deal with the composition and calcitrant 

constituents of DON in influent wastewater; 4) impact of BNR processes in the generation 

of DON products; and 5) integrated strategies to balance point and non-point source 

control of N and P in a watershed approach.

Related Research

WERF project, Dissolved Organic Nitrogen Characterization and Bioavailability in Wastewater 

Effluents (02CTS1a), investigated the speciation of the TN in the treated effluent and 

suggested that the dissolved organic nitrogen (DON) formed a major part of the total 

nitrogen in the effluent that was derived from incoming wastewater sources and from 

the biological treatment processes (products of cell metabolism and lysis) employed to 

reduce nitrogen levels. DON’s bioavailability for bacteria and algae growth – triggering 

eutrophication in the receiving waters – has sparked considerable interest among 

researchers seeking a rational regulatory approach to setting nitrogen levels in the 

discharge permits, particularly in regard to DON. WERF is actively pursuing this effort. 

WERF research is also assessing the limits of technology (LOT) of the biological processes 

and inherent constraints to removal of total nitrogen to very low levels (less than 3 mg/L).

Sustainable Technologies for Achieving Very Low Nitrogen and Phosphorus Effluent Levels

Contractors

Krishna R. Pagilla, Ph.D., P.E.

Illinois Institute of Technology

Meltem Urgun-Demirtas, Ph.D.

Illinois Institute of Technology

Project Subcommittee

James L. Barnard, Ph.D., P. Eng.

Black and Veatch

Rajendra P. Bhattarai, P.E.

City of Austin

John T. Novak, Ph.D., P.E.

Virginia Tech

Andrea C. Rex, Ph.D.

Massachusetts Water Resources Authority

Rao Y. Surampalli, Ph.D., P.E.

U.S. Environmental Protection Agency

Kenneth N. Wood, P.E.

DuPont

Water Environment Research Foundation n 635 Slaters Lane, Suite 300 Alexandria n VA 22314-1177

EXECUTIVE SUMMARY

The research on which this report is based 

was funded in part by the U.S. Environmental 

Protection Agency (U.S. EPA) through 

Cooperative Agreement No. CR-83155901 

with the Water Environment Research 

Foundation (WERF). Unless an U.S. EPA logo 

appears on the cover, this report is a publication of WERF, not U.S. EPA. Funds awarded 

under the agreement cited above were not 

used for editorial services, reproduction,

printing, or distribution.

6/09