Biochar application in anaerobic digestion: Performances, mechanisms, environmental assessment and circular economy

Understanding on effectiveness of biochar application in anaerobic digestion while attaching importance to impact of this process on environment and circular economy have been gaining more and more attention. In this review the influences of biochar application in anaerobic digestion on methane production, system stability, lag period, and in-situ biogas purification and upgradation are systematically identified and discussed. Notably, the underlying mechanisms of buffering effect, direct interspecies electron transfer, microbial immobilization, disinhibition effect, and quorum sensing are analyzed. Meanwhile, the impacts of biochar application in anaerobic digestion on pollutant removal, waste management, and greenhouse gas emission reduction are comprehensively evaluated. Furthermore, a specific attention is paid to the roles of biochar in promoting anaerobic digestion circular economy. Finally, based on current challenges, future perspectives are proposed for engineering practice. The aim of this review is to gain insight into biochar application in anaerobic digestion from the perspective of performance improvement, environmental friendliness and economic sustainability.