Selective acetate production with CO₂ sequestration through acetogen-enriched sludge inoculums in anaerobic digestion

In order to investigate the role of acetogens in anaerobic digestion, acetogens-enriched sludge was used as inoculum for anaerobic digestion. Acetogens were successfully enriched from raw sludge with sodium formate and the fhs gene copy number was up to 6.08 × 10⁹copies/mL. By using acetogens-enriched sludge as inoculum, the substrate utilization rate and acetate percentage in volatile fatty acids (VFAs) were significantly improved. The yield of acetate was 1.77 times higher than the yield in the control fermentation study without addition of acetogens-enriched sludge. With CO₂sparging in the headspace of the reactors, the acetate yields were greatly enhanced due to the acetogenesis reaction. The microbial community structure shifted significantly after three batches of anaerobic fermentation with acetogens-enriched inoculums. The dominated terminated restriction fragment shifted from 519 bp (71.81%) to 483 bp (21.2%), and 519 bp probably represents Granulicatella genus while 483 bp represents Clostridium, Eubacterium, Methylophilus, Nannocystis, respectively. The findings in this study provide a sound basis for development of a potential enhanced anaerobic digestion process to increase acetate yield while mitigating greenhouse gas (CO₂) emission.