METHANOGENESIS MECHANISMS AND MICROBIAL ECOLOGY IN THE ANAEROBIC CO-DIGESTION OF SLUDGE AND GREASE

Abstract

To elucidate the inhibition mechanisms of sludge-grease anaerobic co-digestion (ACoD) and the microbial community succession patterns, this study systematically investigated the process through an enzyme addition strategy. Results demonstrated that compared with sludge mono-digestion, sludge-grease ACoD significantly enhanced methane yield, with the 1.5% mixed fatty acids group achieving a cumulative methane yield of (666.40±30.71) mL/g VS, representing a 179.4% increase over the control group. An addition of 3% unsaturated long-chain fatty acids (LCFAs) was identified as the inhibitory threshold for anaerobic digestion (AD). Both lipase and PECI (Peroxisomal 3,2-trans-enoyl-CoA isomerase) enzyme addition restored methanogenic activity, with the 1% PECI enzyme treatment group achieving a cumulative methane yield of up to 1627.76 mL/g VS, exhibiting the most effective mitigation. However, the addition of both enzymes showed limited improvement in reducing the lag phase of AD. Microbial community analysis revealed that low concentrations of lipase enriched Synergistetes, thereby facilitating the recovery of methanogenic functions, whereas high concentrations suppressed Synergistetes activity. Low concentrations of PECI enzyme promoted Bacteroidetes to dominate the late-stage degradation, while high concentrations maintained stable Synergistetes metabolic activity, thereby effectively circumventing LCFAs toxicity and acid accumulation risks. These findings provide a theoretical basis and technical reference for the engineering application of AD treating lipid-containing organic wastes.