Treatment of an Aerobic Digester Sidestream in a Microbial Fuel Cell: Nitrate Removal and Electricity Generation

Abstract

Aerobic digestion of waste activated sludge is a common practice at water reclamation facilities. Dewatering of digester effluent produces a liquid stream, commonly referred to as a sidestream, that is rich in nitrogen and phosphorus. Removal of nitrogen from the sidestream improves mainstream treatment, but usually requires input of energy and/or chemicals. The purpose of this study was to evaluate the microbial fuel cell (MFC) as a candidate technology to remove nitrogen from the sidestream of aerobic digestion while simultaneously producing electricity, without requiring input of energy or chemicals. Toward this goal, a bench-scale MFC was constructed and operated for a period of 125 days to remove nitrogen (nitrate) from an aerobic digester sidestream from a treatment facility in Hillsborough County, Florida. The average removal rate of nitrogen was 14 mg/(L·day), the average power production was 0.38 mW/m2 of electrode surface area, and the apparent efficiency of electron transfer from anode to cathode was 41%. The nitrogen removal rate and apparent electron transfer efficiency are similar to those observed in previous MFC studies treating other nitrate-containing streams via cathodic denitrification. The low power generation may be due partly to the two-chamber configuration of the MFC employed, which was appropriate for the goals of this study but is not the most advanced MFC configuration. Therefore, we conclude that the MFC remains a promising candidate for nitrate removal from aerobic digester sidestreams, but that MFC configurations more advanced than the one employed here will be required for the technology to be viable at a larger scale.