Extractive Nutrient Recovery for Sustainably Managing Phosphorus in Sidestreams and Biosolids

Authors:

  • Joe Rohrbacher, Wendell O. Khunjar, Ronald Latimer, Katya Bilyk - Hazen and Sawyer

Solids processing operations at wastewater treatment plants often produce sidestreams from thickening, decanting and dewatering. These sidestream flows can contribute significant soluble nitrogen and phosphorus loads back to the liquid stream process, particularly if digestion processes are employed. For instance, sidestream nitrogen and phosphorus loads from wastewater treatment plants that perform biological nutrient removal and have anaerobic digestion typically account for 15-20 percent of influent nitrogen, and 20-30 percent of influent phosphorus even though the sidestream flow may only account for 1% of the total plant flow. Nutrient loads from sidestreams can make compliance with effluent nitrogen and phosphorus limits significantly more costly.

Sidestream treatment is often considered to reduce the impact of sidestreams on the liquid stream process. Sidestream treatment also provides an opportunity to recovery resources from wastewater, particularly phosphorus. Nutrient recovery from sidestreams and biosolids also provides an opportunity to reduce the nutrient loading associated with land application of biosolids. An example of a sidestream nutrient recovery is struvite precipitation technology, which simultaneously recover both phosphorus and nitrogen by adding magnesium chloride and sodium hydroxide to precipitate out struvite pellets. The pellets are a sustainable end-product that can be marketed as a slow-release fertilizer. Recovery of finite resources such as phosphorus will likely play a major role in wastewater treatment plants of the future.

The presentation will include a review of several case studies where nutrient recovery was determined to be the most effective nutrient treatment option that can be integrated with biosolids management strategies geared towards maximizing resource recovery. The case studies demonstrated that nutrient recovery can be an economical alternative for simultaneously controlling nuisance struvite precipitation as well as reducing phosphorus loads in the sidestream. Additionally, nutrient recovery can provide utilities with another option for manipulating the nutrient content of biosolids to match land application requirements.

The case studies indicate that successful adoption of recovery systems is dependent on the amount of nutrient that must be removed and that payback periods are shorter when the sidestream load and biosolids phosphorus content represent a significant portion of the overall nutrient load that the plant treats. Barriers that could limit a shift towards embracing nutrient recovery at wastewater treatment facilities will also be discussed. Special emphasis will be placed on outlining how extractive nutrient recovery can be integrated into biosolids management plans of the future that target maximizing resource recovery.

For more informatiom, please contact the author at jrohrbacher@hazenandsawyer.com.

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Horizons Fall 2017 (pdf)

Horizons showcases significant water, wastewater, reuse, and stormwater projects and innovations that help our clients to achieve their goals, and can help you achieve yours. Articles are written by top engineers and process group leaders, demonstrating and explaining the beneficial application of a variety of technologies and tools.

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