Unravelling and enhancing the power recovery and nitrogen removal mechanism from wastewater by isolating input nitrogen in a coupled microbial fuel cell system

Abstract

Poor recovery energy of microbial fuel cells (MFCs) persists and is considerably lower when dealing with nitrogen, a substantial challenge of this technology. This study investigated power generation from treating different COD/N ratio wastewater by isolating the input nitrogen using the coupled MFC system, including nitrification-MFC (N-MFC) and denitrification-MFC (D-MFC). Energy from wastewater was predominantly recovered in the N-MFC due to the system's configuration, which allowed for the oxidation of over 75% of organic matter input while simultaneously isolating nitrogen input. The nitrogen isolation was affected by the electricity generation of the N-MFC. The complete nitrification was done in the first mode under dissolved oxygen (DO) of 4 mg L−1 in the cathode chamber of the N-MFC. When the DO was decreased to 0.6 mg L−1 in the second mode, over 95% of the ammonium was oxidized to nitrite and nitrate in a 2:1 ratio. The N-MFC's power density of 6.16–6.3 W m−3 was achieved in the first mode, while a power generation of 0.82 W m−3 was obtained in the second mode. The principal mechanism for nitrogen removal at the D-MFC was autotrophic denitrification. The first mode nitrogen removal efficiency was 56.9%, 72.7%, and 80.2% for COD/N input of 5.5, 7.1, and 10.3, respectively. The second mode utilized the short-cut nitrification-denitrification process, superior to the first mode with regards to energy efficiency and nitrogen removal. However, the usage of CEM as separator and aeration requirement makes this technology expensive. Results indicated that nitrogen removal and effective utilization of organic matter for energy recovery could be achieved with a proper configuration for a coupled MFC and in future the cost can be reduced.