Enhancement of volatile fatty acids degradation and rapid methanogenesis in a biochar-assisted anaerobic membrane bioreactor via enhancing direct interspecies electron transfer

In this investigation, we assessed the efficacy of a biochar-supported anaerobic membrane bioreactor (BC-AnMBR) for continuously treating swine wastewater (SWW) under varying NH₄⁺-N stress levels. Our findings revealed that as the NH₄⁺-N concentration escalated from 440 mg/L to 1400 mg/L, the BC-AnMBR exhibited a notable 14.5 % improvement in NH₄⁺-N removal under heightened ammonia pressure compared to the conventional AnMBR (CG-AnMBR). This enhancement primarily stemmed from ion-exchange interactions between the functional groups (hydroxyl, carboxyl, ester, and aldehyde groups) on the biochar surface and NH₄⁺-N, serving as the primary mechanism of action. Moreover, concerning resource recovery, the BC-AnMBR sustained a standard methane yield of 0.184 LCH₄/gCOD, surpassing that of the CG-AnMBR by more than threefold. Microbial community analysis unveiled that the BC-AnMBR fostered the enrichment of ammonia-tolerant electroactive methanogenic archaea, notably from the genera Methanosarcina and Methanolinea. Notably, up-regulation of functional genes associated with key enzymes involved in propionic and butyric acid degradation and the autotrophic methanogenic pathway was observed in the BC-AnMBR, consequently accelerating methane production rates. Ultimately, the incorporation of biochar amplified the activity of the microbial electron transport system by 41.77 % and boosted the concentration of c-type cytochrome by 50.6 %. These enhancements facilitated the establishment of direct interspecies electron transfer, ensuring the stability of the anaerobic digestion process under ammonia-inhibited conditions.