Biochar-induced quorum sensing enhances methane production by strengthening direct interspecies electron transfer.

Biochar addition promotes direct interspecies electron transfer (DIET) between syntrophic bacteria and methanogens and increases the secretion of N-acyl homoserine lactones (AHLs); however, the specific role of AHLs in biochar-promoted DIET remains unclear. In this study, biochar accelerated the degradation of volatile fatty acids, increasing the maximum methanation rate by 24.97 ± 0.23 %. Compared to the control system, biochar significantly enhanced the secretion of AHLs, resulting in an approximate 2.7-fold increase. The increase in AHLs subsequently promoted the synthesis of c-type cytochromes and humic acid-like substances, improving the electron exchange capability of extracellular polymeric substances (EPS), thereby promoting DIET. Additionally, increasing the proportion of polysaccharides in EPS improved the structure of sludge flocculants, thereby improving microbial enrichment. Microbial community analysis revealed that biochar-induced AHLs enriched potential DIET partners, with the relative abundance of Geobacter and Methanosaeta increasing from 2.88 % and 54.69 % to 4.91 % and 55.60 %, respectively. These findings demonstrate that biochar-induced AHLs enhance DIET by improving EPS electron transfer capacity and enriching electroactive microorganisms, thereby enhancing methane production.