Carbon-negative wastewater treatment via CO2-to-acetate microbial electrosynthesis coupled with biological nitrogen removal.

This study presents a renewable electricity-driven microbial electrosynthesis (MES) system integrated with biological nitrogen removal (BNR) to achieve carbon-negative wastewater treatment. The MES system converts CO₂ into acetate, which is directly utilized as an internal carbon source for denitrification. Incorporation of biochar-derived conductive materials enhanced electron transfer, increasing acetate productivity to 1.98 g/L·d with a Coulombic efficiency of 75 %. Coupling MES with BNR achieved a TN removal efficiency exceeding 97 %, while maintaining system stability during intermittent solar power supply through microbial energy storage mechanisms. Life cycle assessment showed a net CO₂ uptake of 0.22 g CO₂/g N removed, with a 61 % reduction in environmental impact when solar-driven compared to traditional BNR. Moreover, acetate production costs ($1.22/kg) were competitive with industrial benchmarks. This work demonstrates a scalable approach to transform wastewater treatment plants into carbon-negative biorefineries, advancing sustainable water management and resource recovery.