The Biochar Pretreatment Addition Coupled with Codigestion for Facilitating Methane Production from Anaerobic Digestion: Performance and Mechanisms

A new technology using biochar pretreatment coupled with codigestion (BPC) to increase methane production of waste-activated sludge (WAS) in anaerobic digestion (AD) was introduced in this study. The findings indicated that BPC dramatically increased methane production with a maximum cumulative methane production of 74.34 L CH4/kg VS at 2.0 g biochar/g VS pretreatment, which increased by 57.6% compared to the control. Model fitting analysis revealed that BPC significantly promoted both the reaction rate and the biochemical methane potential (BMP). In the pretreatment process, the high alkalinity and stable pH buffer ability of biochar further enhance the release of organics, facilitating subsequent methanogenic fermentation. In the AD process, oxygen-containing functional groups such as C═O and C–OH, related to redox properties, play an essential role in augmenting methane generation. This might be attributed to the biochar improving the direct interspecies electron transfer from methanogenic bacteria through conductive material. Microbial community analysis demonstrated that the functional microorganisms that participated in the AD process were enriched from 28.16% in the control to 35.15 and 35.45% in traditional biochar addition and BPC group, respectively. It will be clear for the application of BPC technology to enhance methane yield.