Towards Circularity in Anaerobic Digestion: Methane Yield Enhancement Using Biochar from Co-Pyrolysis of Anaerobic Sludge and Residual Lignocellulosic Biomass

Improper management of anaerobic pig sludge poses significant environmental and health risks. Converting this waste into biochar to enhance methane production during anaerobic digestion (AD) presents an environmentally sound and circular solution, especially when the biochar is produced through co-pyrolysis with lignocellulosic biomass residues. This study first determined the co-pyrolysis biomass ratio (anaerobic sludge to lignocellulosic biomass) that caused the highest increase on methane yield. Subsequently, the effects of biochar dosage (6, 12, 18, 24, and 30 g/L) and particle size (0.5–1 cm, 212–355 µm, and <53 µm) on methane production were assessed. Biochar derived from up to 25 % anaerobic pig sludge increased methane yield by 74.49 ± 1.25 % without compromising its catalytic effect. Methane yield was significantly affected by both biochar dosage and particle size, with best results observed at dosages of 12–18 g/L. These findings highlight the feasibility of the co-pyrolysis of anaerobic pig sludge and lignocellulosic residues as an attractive circular solution for integrated waste management and energy production.