Study on enhancing sludge methanogenesis by adding acetylene black and effect on the characteristics & microbial community of anaerobic granular sludge

The effect of acetylene black (ACET) as additives on methane production, extracellular polymeric substances (EPS), microbial community structure and methanogenesis pathway during sludge anaerobic digestion (AD) was investigated in this study. The results indicated that the addition of 2 g L-1 ACET resulted in a 44.36% increase in methane accumulation. ACET, which resulted in the increase of EPS and VSS/TSS by 4.71-50.64%, effectively improved the physicochemical properties of anaerobic granular sludge (AnGS). During anaerobic digestion, the high throughput sequencing presented direct evidence that the ACET increased microbial diversity and enriched functional microorganisms such as norank_f__Synergistaceae, norank_f__Anaerolineaceae, and unclassified_f__Clostridiaceae_3, which can improve the hydrolysis acidification process and the acetotrophic pathway. These results were reaffirmed by applying metagenome inference and gene content inference (16S function prediction). Microscopically, significant enhancement in the AD efficiency can be due to the methanogenesis promoted by the ACET that can construct direct interspecies electron transfer (DIET) between the unclassified_f__Clostridiaceae_3, norank_f__Anaerolineaceae, and Methanosaeta. These results were expected to provide primary research data for improving the performance of anaerobic reactors and the development of microbial fuel cells.