Feasibility of In Situ Bioelectrocatalytic Computation to Implement Simultaneous Nitrogen Removal of Anaerobic Digestate and Biogas Upgrading

Abstract

A two-chamber bioelectrochemical system was constructed to investigate the feasibility of bioelectrocatalysis regulation to enhance simultaneous nitrogen removal from anaerobic digestate and biogas upgrading. The key mechanisms of the bioelectrocatalytic process in inducing the cathode/anode biofilm development and the multiroutes of carbon/nitrogen metabolisms were elucidated. The results showed that increasing the cathode potential led to a higher CH₄ production rate. In particular, when the cathode potential was adjusted to −0.8 V vs Ag/AgCl, the CH₄ production rate increased rapidly to 14.5 ± 2.9 mL/L/day. Under these conditions, the NH₄⁺-N removal in the anode chamber reached 90%, and the total nitrogen removal was 79.5 ± 1.8%. These findings confirmed the effective simultaneous achievement of CO₂ electromethanogenesis and anode denitrogenation. Moreover, Methanobacterium was continuously enriched in the cathode biofilm, with an abundance of 13.9%. Similarly, the abundance of Candidatus_Brocadia (anaerobic ammonia oxidation bacteria genus) in the anode biofilm was increased from 2.9 to 10.9%. Applying bioelectrocatalysis can target functional microorganism enrichment, stabilize the system operation, and realize efficient nitrogen removal and CO₂ electromethanogenesis. This study provides a beneficial supplement to the conventional anaerobic digestion technology for further enhancing simultaneous nitrogen removal of anaerobic digestate and biogas upgrading.