A new Anti-inhibition strategy to overcome high ammonia stress for anaerobic co-digestion of food waste and sewage sludge by applying a domesticated anaerobic electrocatalytic cathodic-membrane bioreactor (AnEC-MBR)

Anaerobic membrane bioreactor (AnMBR) is recognized as an advanced technology for the anaerobic digestion (AD) of food waste and sewage sludge. However, the elevated ammonia concentration in the anaerobic co-digestion of food waste and sewage sludge poses a significant challenge by inhibiting methane production. In this study, an electrochemical anaerobic membrane bioreactor equipped with a stainless steel‑carbon felt (CF)-Ti/RuO₂-membrane cathode (composite cathodic membrane) was constructed (anaerobic electrocatalytic cathodic-membrane bioreactor, AnEC-MBR). The long-term performance and the underlying working principles were investigated to illuminate how the bio-electrocatalytic system mitigates ammonia inhibition over 340 days of operation. Bio-electrocatalytic system successfully restored the system's methane production capacity at a high ammonia concentration of 4.5 g/L. Methane production nearly dropped to 0 mL without the electrical stimulation, it recovered and stabilized at 112.9 ± 5.2 mL-CH₄/g COD when applying electrical stimulation. Further investigations employing enzyme activity analysis, microbiological analysis, and metagenomics explored the mechanisms underlying ammonia tolerance in the AnEC-MBR. Bio-electrocatalytic process reshaped the microbial community, enriching hydrogenotrophic methanogens (Methanobacterium and Methanoculleus) and Methanosarcina-dominated methanogenic archaea. Key metabolic pathways, including butyrate/propionate degradation, and hydrogenotrophic/methylotrophic methanogenesis, were significantly enhanced. Genes involved in energy metabolisms were significantly upregulated, likely providing the sufficient energy necessary for microbial resistance to high-strength ammonia stress. The activities of relevant enzymes and the electron transfer activities in the anaerobic system were enhanced as well. This study provides novel insights into and practical guidance for understanding the mechanisms of mitigating high-strength ammonia inhibition in anaerobic digestion through bio-electrocatalytic process during the long-term operation of AnMBR.