Landfill leachate promotes synergistic effects in anaerobic digestion of municipal wastewater treatment sludge and scum: Modeling and mix ratio optimization

Abstract This study investigated the anaerobic co-digestion (Aco-D) of landfill leachate (LL), waste activated sludge (WAS), and sewage scum (SS) to optimize methane (CH 4 ) production and soluble chemical oxygen demand (sCOD) removal. This research aims to address the challenges of sludge management and landfill leachate treatment while exploring sustainable energy recovery through biogas. A batch biogas production test (BMP) was performed in reactors containing various volumetric mixtures of LL, WAS, and SS, with a focus on optimizing the mixing ratio to improve the CH 4 yield and sCOD removal. A modified Gompertz model was applied to analyze CH 4 production, and desirability analysis was used to determine the optimal co-substrate proportions. The results showed that the highest CH 4 yield of 435.4 ± 13.2 mL per gram of volatile solids (VS) was achieved with equal proportions of each substrate (1/3 LL, 1/3 WAS, 1/3 SS). Maximum sCOD removal (74.9%) occurred with a mixture containing 1/6 LL, 1/6 WAS, and 2/3 SS. The co-digestion impact factor (CIF) revealed a significant synergy (CIF = 1.73) in the 1/3 mixture. The study concluded that the inclusion of LL in Aco-D not only enhanced the solubilization of WAS and SS but also provided a buffering effect, improving overall biogas production and reducing the lag phase duration in SS digestion, which justified the synergy found between the co-substrates. These findings highlight the potential of using Municipal Wastewater Treatment Plant (MWWTP) effluents and landfill leachate for efficient waste-to-energy applications, offering a sustainable solution for sludge management and renewable energy generation. Graphical abstract