Humic metal complexes as dominant anaerobic digestion inhibitor Multidimensional diagnostic framework from full scale sludge treatment plant

This study investigates a 16,200 ton full-scale anaerobic digestion (AD) plant facing poor organics reduction and limited biogas recovery. Biochemical methane potential tests using active exogenous sludge confirmed that the inefficiency stemmed from the intrinsic properties of the waste activated sludge, not insufficient microbial activity. Alkaline thermal hydrolysis increased methane yield by 69%, yet the maximum output remained low (76 mL CH4/g VS), suggesting deeper inhibition. Further diagnostic based on the detection of physical properties, biological structures, material composition, and microbial communities are applied to localize root causes.