Mechanistic Insights into Biochar-Enhanced Two-Stage Anaerobic Digestion of Food Waste: Significance of Microbial Community Dynamics

High Resolution Image Download MS PowerPoint Slide Adding biochar in anaerobic digestion (AD) has been widely investigated recently in single-stage AD rather than in two-stage AD. Despite a few reports suggesting improved performance of two-stage AD with biochar addition, the existing reports provide limited insights into the role of biochar in microbial dynamics and its mechanisms of enhancement. This study investigated the impact of different biochar dosages (5, 15, and 25 g/L) on the two-stage mesophilic AD of food waste, focusing on biogas production, dynamics of volatile fatty acids (VFAs), organic removal, and microbial community diversity and structure. During the first stage, cumulative hydrogen (H 2 ) production increased by 23−30% in biochar-amended reactors, while in the methanogenesis stage, cumulative methane (CH 4 ) yields increased by 31−41%. However, no statisticallly significant differences ( p > 0.05) were obeserved among the different biochar dosages, suggesting that 5 g/L would be the optimum dosage for both stages. Biochar promoted the accumulation of VFAs during the first stage while enhancing VFA conversion to methane in the second stage, with 5 g/L of biochar exhibiting the lowest VFA accumulation. In addition to increased microbial diversity and richness, 5 g/L of biochar also selectively enriched various fast-growing hydrolytic/fermentative taxa in the first stage while significantly stimulating syntrophic fatty-acid degraders ( Syntrophomonas ) and metabolically versatile methanogens ( Methanosarcina ) in the second stage, indicating improved syntrophic cooperation and potential facilitation of direct interspecies electron transfer (DIET). These findings highlight biochar as a promising functional additive for improving two-stage AD of food waste.