Understanding the role of biochar in different stages of anaerobic digestion and its feasibility of reuse

This study explores the role and recycling feasibility of pig manure biochar (PB) in anaerobic digestion (AD), with particular emphasis on alterations in PB surface functional groups, with a reduction of acidic groups on PB by approximately 30 % during the acidogenic phase; however, microbial aggregation appeared to buffer this dissolution effect. In the methanogenic phase, increased PB oxidation was observed, marked by a reduction in lactone groups and an increase in phenolic hydroxyl groups, which together contributed to the stability of PB's electron exchange capacity (EEC). In comparison, PB showed a more pronounced enhancing effect on AD performance than straw biochar (SB). Recycling experiments indicated a substantial enhancement in cumulative methane production, as recycled PB yielded 94 mL CH₄/g VS at a dosage of 0.5 g biochar/g TS_fed, outperforming fresh biochar. These findings underscore the stable structural and functional properties of PB during AD, supporting its potential for long-term recycling and sustainable use in waste management and bioenergy production.