Advancing autotrophic nitrogen removal in low C/N ratio wastewater: Innovative application of supercapacitor to enhance microbial electrolysis cells

This study presents a novel approach, the Supercapacitor Microbial Electrolysis Cell (SC-MEC), which utilizes a supercapacitor as an external power source to enhance the efficiency of autotrophic nitrogen removal in low C/N ratio wastewater. The results demonstrated that the SC-MEC system, operating under anaerobic conditions and devoid of any organic carbon source, exhibited exceptional performance in ammonia oxidation and total nitrogen (TN) removal when solely relying on ammonia nitrogen as the electron donor. Operating at a voltage of 1.8 V with a capacitance capacity of 30 F, ammonium oxidation rated up to 56.51 mg/L/day and TN removal rated up to 54.64 mg/L/day, in which 97% of ammonium nitrogen was converted to gaseous nitrogen. Furthermore, the charging and discharging process of supercapacitors autonomously regulated the bipolar potentials. Cyclic voltammetry (CV) analysis showed the significantly enhanced electrochemical activity of the SC-MEC system during the reaction process. Based on in-situ CV test results, it was inferred that this enhancement was associated with extracellular electron transfer mediators. The microbial community analysis revealed a process of synchronous nitrification and denitrification (SND) coupled with anammox, involving multiple genera, such as Candidatus Kuenenia, Nitrosomonas, Truepera, and Bosea. In conclusion, this study highlights the tremendous potential of SC-MEC in achieving efficient autotrophic nitrogen removal, offering more feasible and economical solutions for addressing low C/N water pollution issues.