Anaerobic digestion of fat, oil, and grease (FOG) under combined additives: Enhanced digestibility, biogas production, and microbiome

Addition of a single additive (such as biochar or calcium) in anaerobic digestion has been studied previously. However, the effect of combined additives in anaerobic digestion (including fat, oil, and grease) has not been well-investigated yet. In this study, the biogas/biomethane, lipid degradation, and volatile fatty acids were investigated under various concentrations of combined additives. The effect on principal reactions, microbial community, and functional enzymes was also analyzed under different concentrations of calcium-modified biochar. The fat, oil, and grease was degraded up to 81.91 % resulting in 9.03-fold higher biomethane production. Acidogenesis and methanogenesis efficiencies were induced up to 53.31 % and 67.91 %, respectively, due to the enrichment of bacteria (such as Clostridium >50 %, Sporosarcina >18 %, Cellulosilyticum >8 %) and archaea (such as Methanosphaera >49 %). Increased abundance of Co-A ligase, short-chain acyl-CoA dehydrogenase, acetate kinase, and formylmethanofuran dehydrogenase, represented mixed hydrogenotrophic and acetoclastic methanogenesis. The current study demonstrated that co-additives can be added to overcome microbial inhibition and facilitate biomethanation at high fat, oil, and grease concentrations.