Digestion of waste activated sludge received from mainstream wastewater treatment produces an effluent stream commonly called a “sidestream,” that contains high concentrations of nitrogen. Removal of nitrogen from the sidestream is desirable if the sidestream is recycled, but nitrogen removal often requires input of energy. It has recently been proposed that a microbial fuel cell (MFC) may be a viable technology to remove nitrogen from sidestreams while also producing electricity (rather than requiring energy input). Therefore, the overall objective of this presentation is to evaluate the performance of an MFC to remove nitrogen from the sidestream of aerobic digestion at a municipal wastewater treatment facility in Hillsborough County, Florida. In order to achieve this goal, the specific objectives were to quantify (1) nitrogen removal from the sidestream using an MFC and (2) power generation by the MFC. The MFC consisted of two 700-mL glass chambers, connected with a glass bridge with a proton-exchange membrane. The MFC was initially operated with synthetic solutions for 90 days until bacterial populations were established and stable conditions were achieved. During this start-up period, the influent to the anodic chamber was soybean-casein digest medium (ATCC medium 1065), and the influent to the cathodic chamber was Geobacter metallireducens medium (ATCC medium 1768). Sodium nitrate was added to the cathodic medium to achieve an initial total nitrogen concentration of 255 mg/L as N; subsequently, sodium nitrate was added as needed. Carbon paper electrodes were used and anoxic conditions were maintained by gently bubbling nitrogen gas in both chambers. The anode of the MFC was inoculated with Shewanella putrefaciens, and the cathode was inoculated with Geobacter metallireducens. Voltage was measured and treated liquid samples from both chambers were analyzed twice per week for concentrations of nitrogen and chemical oxygen demand (COD). Removed samples were replaced with fresh solution. The maximum power output recorded at this stage was 13 mW/m2 of anodic electrode surface area. The maximum and average nitrate removal achieved over 3 days period were 100% and 50% respectively. Following the initial start-up period, the anode influent was switched to municipal raw wastewater, and the cathode influent was switched to an aerobically digested sidestream. Voltage and nitrogen removal will be recorded for a period of 120 days and results will be reported.

Microbial Fuel Cell for Removal of Nitrate from the Effluent (Sidestream) of Aerobic Digestion

2019 Spring National Meeting

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