The Water Research Foundation

Guidelines for Optimizing Nutrient Removal Plant Performance

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Path to Optimization

Water Resource Recovery Facility

Water Resource Recovery Facilities (WRRF) can be divided into five types. The type is typically reflective of the size of the WRRF and the permit requirements. Review WRRF definitions.

Water Resources Recovery Facility Definitions

Secondary treatment

Secondary treatment refers to WRRFs designed to meet secondary treatment standards as defined in the Clean Water Act (CWA). These standards are reflected in terms of five-day biochemical oxygen demand (BOD), total suspended solids (TSS) removal, and pH. No nutrient removal is achieved.

Conventional nutrient removal (CNR)

Nutrient removal achieved by conventional treatment processes. Biological nutrient removal (BNR) is achieved by modifying the aeration basin configuration for nitrogen (N) and/or phosphorus (P) removal without external carbon (C) addition. Chemical addition to a primary clarifier or secondary process for P removal are examples of CNR processes.

Tertiary nutrient removal (TNR)

Nutrient removal with a combination of modified secondary and tertiary treatment processes. These processes include enhanced particle removal (using processes such as granular, media, or microfiltration) and chemical addition (such as carbon for denitrification or metal salts for P removal). TNR typically requires more than one anoxic zone for enhanced denitrification, either in the secondary treatment process or in a combined denitrification and tertiary filtration process.

Small non-mechanical process

Small-system WRRFs serving small or transient communities with space available for low-rate treatment processes (e.g., septic systems, lagoons), which require minimal mechanical equipment (e.g., screening, pumping).

Small mechanical process

Small communities such as towns, new residential developments, transient communities, and other communities with limited space available can use mechanical treatment facilities to meet permit requirements. These facilities are typically smaller versions of secondary, CNR, or even TNR WRRFs. The optimization strategies for small mechanical processes will therefore be similar to those for large WRRFs.

Please select the existing treatment process (secondary, conventional nutrient removal, or tertiary nutrient removal). Review definitions for more information. Select one of the options below.

Not sure where to start?

Your selections:

Potential Strategies

Biological Nutrient Removal

Chemical Use

Small Mechanical

Small Non-Mechanical

Strategy References for Decision Trees

Albertson, O.E. 1989. Slow down that trickling filter. WPCF Operations Forum, January and August.

Albertson, O.E. 1995. Excess biofilm control by distributor speed modulation. J. Env. Eng. Am. Soc. Civil Eng., 121 (4).

Boelee, N.C., H. Temmink, M. Janssen, C.J.N. Buisman, and R.H. Wijffels. 2012. Scenario Analysis of Nutrient Removal from Municipal Wastewater by MicroAlgal Biofilms. Water. 4:460-473.

Bounds, J., J. Ye, F.M. Kulick, and J.P. Boltz. 2010. Nitrifying Trickling Filter Provides Reliable, Low-Energy and Cost- Effective Tertiary Municipal Wastewater Treatment of a Lagoon Effluent. WEFTEC 2010.

Chan, R., R. Gray, D. Rich, and S. McDonald. 2000. “Rerating Nitrifying Trickling Filter Capacity Through Field Testing and Process Modeling.” WEF’s 73rd Annual Technical Exhibition and Conference. Anaheim, California: WEFTEC.

Collison, R.S. and M.E. Grismer. 2018. Upscaling the Zeolite-Anammox Process: Treatment of Secondary Effluent. Water 2018, 10, 236; doi:10.3390/w10030236.

Crites, R., E.J. Middlebrooks, R. Bastian, and S. Reed. 2014. Natural Wastewater Treatment Systems, 2nd ed. CRC Press: Boca Raton, Florida.

Grismer, M.E. and R.S. Collison. 2017. The Zeolite-Anammox Treatment Process for Nitrogen Removal from Wastewater—A Review. Water 2017, 9, 901; doi:10.3390/w9110901.

Gross, M., W. Henry, C. Michael, and Z. Wen. 2013. “Development of a Rotating Algal Biofilm Growth System for Attached Microalgae Growth with In Situ Biomass Harvest.” Bioresource Technology. 150:195–201.

Hu, Z. and G.G. Gagnon. 2005. “Re-examining recirculating filters.” Water Environment Technology. 17(1):64–68.

Iowa DNR. 2016. Lagoon Based ammonia removal – OPTAER™ Submerged Attached Growth Reactor (SAGR ™). Iowa DNR New Wastewater Technology Assessment No. 11-1, https://www.iowadnr.gov/Portals/idnr/uploads/water/wastewater/techassessments/tech_assessment_111_sagr.pdf. Accessed May 18, 2022.

Mattson, R.R., M. Wildman, and C. Just. 2018. Submerged attached-growth reactors as lagoon retrofits for cold-weather ammonia removal: performance and sizing. Wat. Sci. Technol. 78.8 2018. doi: 10.2166/wst.2018.399.

Merufinia, E., H. Rezaei, J. Ghaderi, A. Shamsaei. 2014. "Considerable Reduction in Sewage Pollutants of Urmia City from Modernist view of Biolac Process." J. Civil Eng. Urban., 4 (4): 353-363.

Neethling, J., M. Falk, and E. Evans. 2023. Guidelines for Optimizing Nutrient Removal Plant Performance. Project 4973. Denver, CO: The Water Research Foundation.

Nurdogan, Y. and W.J. Oswald. 1995. Enhanced nutrient removal in high-rate ponds. Wat. Sci. Technol. 31(12):33-43.

Pano, A., and E.J. Middlebrooks. 1982. Ammonia Nitrogen Removal in Facultative Wastewater Stabilization Ponds. Journal Water Pollution Control Federation 54 (4) 344-351. https://www.jstor.org/stable/25041312.

U.S. EPA. 2021. Types of Septic Systems. Accessed May 6, 2022. https://www.epa.gov/septic/types-septic-systems.

Wall, D., D. Frodsham, and D. Robinson. 2002. Design of Nitrifying Trickling Filters. Alexandria, WEFTEC 2002.

WEF 2010. Nutrient Removal. WEF Manual of Practice No. 34. Prepared by the Nutrient Removal Task Force of the Water Environment Federation. Published by Water Environment Federation, Alexandria, Virginia.

WRF 4973 Guide - Chapter 5. See Neethling et al. 2023 above.