The presence of nitrogen encourages the growth of organic matter and algae, which leads to eutrophication of marine and freshwater ecosystems. In conventional wastewater treatment facilities the removal of nitrogen is achieved through simultaneous nitrification and denitrification of the wastewater. Microbial fuel cells (MFC) present an alternative technology to conventional methods for nitrate removal. The MFC is a bioelectrochemical device capable of harvesting electrons from organic sources. Bacteria in the anode compartment oxidize organic compounds, and the electrons are transferred across an external load to a terminal electron acceptor at the cathode. A typical MFC has an abiotic cathode and biotic anode. Recently more attention has been given toward the utilization of biological cathodes for the reduction of sulfate, nitrate, carbon dioxide, fumarate, and other electron acceptors. Previous studies have demonstrated an MFC’s capacity for biological denitrification at the cathode¹ where bacteria can reduce nitrate to nitrite to nitrogen gas. In this study we monitored the performance and taxonomic dynamics of two denitrifying MFCs with different cathode materials.

            A two-chamber reactor configuration (600mL total volume) was used with alternative cathode catalysts. Acetate was provided at the anode as the electron donor and sodium nitrate was introduced at the cathode as the electron acceptor. Denitrification efficiency of the MFC was evaluated as a function of the different cathode materials and the taxonomic communities. One of the reactors had carbon cloth cathode with activated carbon/carbon black mixture (AC-MFC); the other reactor had carbon cloth cathode with carbon black layer (CB-MFC). Nitrate was periodically added to cathode chamber and the concentration of nitrate and nitrite was periodically monitored. Initial results show a removal rate of 2.02 mg/L/d and 5.31 mg/d [NO₃^-] for the AC-MFC and CB-MFC after 230 days of operation. Biofilm and planktonic samples were periodically extracted from the anode, cathode, solution, and membranes of each system and were used to estimate the phylogenetic composition of each community based on 16S rRNA gene sequences. The presence of Geobacteraceae at the anode supports the observed acetate consumption and current production of both systems. Additionally, denitrifying and nitrifying bacteria were identified in the cathode compartment and support the simultaneous nitrification and denitrification observed in the cathode chamber. Further studies will be conducted to evaluate functional roles of dominant species in the community.