Energy Recovery and Nitrogen Management from Struvite Precipitation Effluent via Microbial Fuel Cells

Engineered struvite precipitation (ESP) is now a common procedure to recover phosphorus and nitrogen from waste streams such as wastewater-treatment-plant sidestreams, urine, landfill leachate, and agricultural waste. Depending on the waste stream, the liquid effluent from ESP is likely to still contain either nitrogen or phosphorus. In the case of wastewater-treatment-plant sidestreams, the liquid recycled back to the head of the plant still contains high concentrations of nitrogen, which can cause instability in mainstream treatment processes and additional energy and chemical costs. Therefore, a need exists to remove the nitrogen before it reaches the mainstream. For this research, nitrogen removal and energy recovery from the effluent of ESP were achieved using a proof-of-concept fixed-film nitrification and microbial fuel cell (MFC) process. Fixed-film nitrification and MFC together removed 52% of nitrogen from the liquid effluent of ESP, while the MFC generated 0.3-mW power per ${\mathrm{m}}^2$ of anodic surface area. This process was not energy neutral, as energy input for aeration was greater than the energy output from the MFC. However, the goal of energy neutrality may be advanced beyond this proof-of-concept study by reducing the energy input for aeration and increasing energy output through further improvement of MFC performance. This is the first study to demonstrate how fixed-film nitrification and MFCs can be used to treat the liquid effluent from ESP to recover energy and remove nitrogen, while simultaneously reducing the undesirable recycling of nutrients from sidestreams back to mainstream treatment. The process is aimed to transform wastewater-treatment plants into resource recovery facilities of the future, and to reduce operational costs through nutrient removal, energy generation, and decreased nutrient load to mainstream treatment.