Microbial fuel cells for simultaneous carbon and nitrogen removal

The recent demonstration of cathodic nitrate reduction in a microbial fuel cell (MFC) creates opportunities for a new technology for nitrogen removal from wastewater. A novel process configuration that achieves both carbon and nitrogen removal using MFC is designed and demonstrated. The process involves feeding the ammonium-containing effluent from the carbon-utilising anode to an external biofilm-based aerobic reactor for nitrification, and then feeding the nitrified liquor to the MFC cathode for nitrate reduction. Removal rates up to 2 kg COD m−3 NCC d−1 (chemical oxygen demand: COD, net cathodic compartment: NCC) and 0.41 kg NO3−-N m−3 NCC d−1 were continuously achieved in the anodic and cathodic compartment, respectively, while the MFC was producing a maximum power output of 34.6±1.1 W m−3 NCC and a maximum current of 133.3±1.0 A m−3 NCC. In comparison to conventional activated sludge systems, this MFC-based process achieves nitrogen removal with a decreased carbon requirement. A COD/N ratio of approximately 4.5 g COD g−1 N was achieved, compared to the conventionally required ratio of above 7. We have demonstrated that also nitrite can be used as cathodic electron acceptor. Hence, upon creating a loop concept based on nitrite, a further reduction of the COD/N ratio would be possible. The process is also more energy effective not only due to the energy production coupled with denitrification, but also because of the reduced aeration costs due to minimised aerobic consumption of organic carbon.