Removal of nitrate from agricultural runoff in biochar electrode based biofilm reactor: Performance and enhancement mechanisms

A biochar electrode based biofilm reactor was developed for advanced removal of nitrate from agricultural runoff. The corn-straw (Zea mays L.) biochar formed at 500 C has an adsorption capacity of NO3--N up to 2.659 mg g(-1). After 45-day start-up phase, the removal efficiency of nitrate reached 93.4% when impressed current was 20 mA, hydraulic retention time was 12 h and chemical oxygen demand/total nitrogen (C/N) ratio was 0.56 without additional carbon source. In comparison, neither electrochemical reduction alone nor microbial denitrification alone could obtain the ideal nitrate removal efficiency. The results implied that bio-electrochemical reduction was the main way of nitrate removal in the biofilm electrode reactor (BER). The denitrification efficiency of 88.9% could still be obtained when C/N = 0. It is because biochar can significantly promote the utilization efficiency of cathode electrons by microorganisms. Thus, biochar is a promising electrode material, which provides a new idea for the optimization of BER.

Automated summary

A biochar electrode based biofilm reactor was developed for advanced removal of nitrate from agricultural runoff. By optimizing operation conditions and utilizing bio-electrochemical reduction, high nitrate removal efficiency could be achieved. The biochar electrode material significantly promotes the utilization efficiency of cathode electrons by microorganisms, thereby improving the denitrification capacity.