Recent Advances in Biochar-Mediated Enhancement of Anaerobic Digestion: Performance, Mechanisms, and Sustainability Prospects

With global economic growth, energy demand has significantly increased. Anaerobic digestion (AD) is crucial for converting organic waste into renewable bioenergy, but its efficiency is often constrained by challenges like ammonia inhibition, volatile fatty acids (VFAs) accumulation, and microbial instability. This review consolidates recent progress in using biochar as an additive to augment AD performance, unraveling its dual-edged impacts and underlying mechanisms. Biochar, derived from diverse feedstocks via pyrolysis or hydrothermal carbonization, enhances AD through multiple pathways: reducing ammonia toxicity via physical adsorption and microbial community modulation; alleviating VFAs stress by buffering pH and accelerating VFAs degradation; enriching functional methanogens through its porous habitat; and facilitating direct interspecies electron transfer to optimize energy metabolism. Mechanistic analyses reveal that biochar’s high specific surface area, surface functional groups, and conductivity are critical for these effects. In addition, this paper discusses the economic feasibility and long-term sustainability of using biochar in AD systems, while identifying existing research gaps and suggesting directions for future studies. This review aims to provide up-to-date knowledge to improve AD efficiency, identify current research limitations, and propose recommendations for advancing more environmentally friendly and efficient energy recovery strategies.