Evaluation of the Process and Economic Benefits of Sidestream Nutrient Removal and Recovery
- Jacob Porter - Hazen and Sawyer
This paper will present sidestream treatment alternatives for nitrogen and phosphorus removal and results of recent sidestream treatment evaluations and projects. For nitrogen removal, three biological processes were evaluated: bioaugmentation nitritation/denitritation, and nitritation/deammonification. For phosphorus removal, struvite precipitation was considered and compared with the cost of traditional chemical removal.
A sidestream is any process flow resulting from the treatment of biosolids that flows back into the liquid treatment train. Sidestream treatment therefore, refers to the interception and manipulation of the sidestream with a treatment removal objective, typically nutrients.
Sidestream treatment is often economical due to the relatively low volume and high concentration of nutrients present. In a plant implementing biological nutrient removal and anaerobic digestion, sidestreams can account for 15-20 percent of influent nitrogen, and 20-30 percent of influent phosphorus. Benefits to sidestream treatment include, increasing the factor of safety on nitrification and biological phosphorus removal and allowing lower nutrient standards to be achieved with conventional technology.
Economic evaluations of sidestream nitrogen removal for two different treatment plants will be presented. Nitritation/deammonification had higher capital costs but in all both cases had the lowest net present cost and a fast payback period (0 – 3 years) because supplemental carbon is not needed.
Several cost evaluations have demonstrated that a struvite recovery process is less expensive than chemical precipitation on a net present cost basis, has a payback of between 5 and 15 years, and recovers a finite resource. A process called WASSTRIP® was developed which releases phosphate and magnesium from waste activated sludge prior to digestion, controlling struvite precipitation in digesters and solids handing equipment, and increasing product yield. This process appears to improve the payback period by 3 years. Results from a full-scale Ostara installation; and Multiform Harvest and Ostara pilots including the WASSTRIP®-type process will be presented as well.
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