Denitrification in perspective of carbon neutralization: CO2 emission reduction and electricity generation by Fe-anode and bio-cathode MFC

In order to solve the problem of insufficient carbon source for denitrification in sewage treatment plants (STPs), iron-dependent autotrophic denitrification was investigated. Combining the iron-dependent autotrophic denitrification and the microbial fuel cell (MFC) would not only be economical to remove nitrate in wastewater but also be environmentally friendly. With iron as anode and denitrification biofilm on the cathode, the Fe-MFC is operated continuously for 42 days (in total 6 cycles). With removal efficiency of 92% and volumetric removal rate of 0.0055 kg-N·m−3·d−1, nitrate is successfully removed with no CO2 emission. The output voltage of the MFC maintained at 540 mV for 80 h, and then it decreases linearly to below 15 mV with the consumption of substrate (nitrate) under sequencing batch operation. Along with the consumption/passivation of iron-anode and the adaption of microbes to the new environment, the electric power and the Volt-ampere charge (q*) of bio-cathode dropped from cycle 1 to cycle 6 by 39% and 44% respectively. The microbial community analysis showed that the dominant genus in the biofilm was Thauera which could use electrode electrons as electron donor directly. With Fe-MFC both CO2 emission reduction and electricity generation came true for denitrification. The Fe-MFC technology is feasible to treat nitrogen pollution in low C/N wastewater. It also provides new thought for denitrification under carbon neutralization policy.