In the context of climate change and the circular economy, most municipal wastewater treatment plants are not efficient because they generate huge amount of organic sludge, which in turn requires costly post-treatment by biological processes such as anaerobic digestion. An emerging solution is to add biochar to improve anaerobic digestion efficiency by enhancing microbial activity, aiding in the breakdown of complex organic compounds, producing more biogas, and promoting overall reactor stability. Here, we review the effects of adding biochar in anaerobic digestion, with emphasis on digester performance, process stability, biochar properties, and mechanisms. We discuss methane production, lag phase, electrical conductivity, volatile fatty acids, ammonia nitrogen, pH, and oxidation–reduction potential. We also review the process inhibition by biochar addition, with focus on phenols, heavy metals and microbial composition. Biochar properties are controlled by feedstock type, pyrolysis temperature, specific surface area, electrical conductivity, carbon and mineral content, electron exchange capacity, aromaticity, and particle size. We found that 6–16 g/L biochar supplementation consistently yielded higher cumulative specific methane compared to control without biochar, across diverse conditions and substrate types. Biochar’s role is explained by four mechanisms: enhancing functional microbes, facilitating direct interspecies electron transfer, improving the degradation of refractory compounds, and increasing reactor stability.

在气候变化和循环经济的背景下，大多数城市污水处理厂效率不高，因为它们会产生大量有机污泥，而这又需要通过厌氧消化等生物过程进行昂贵的后处理。一种新兴的解决方案是添加生物炭，通过增强微生物活性来提高厌氧消化效率，帮助分解复杂的有机化合物，产生更多的沼气，并促进整体反应器的稳定性。在这里，我们回顾了在厌氧消化中添加生物炭的影响，重点是消化器性能、工艺稳定性、生物炭特性和机制。我们讨论甲烷产量、滞后期、电导率、挥发性脂肪酸、氨氮、pH 值和氧化还原电位。我们还回顾了添加生物炭对过程的抑制作用，重点关注酚类、重金属和微生物成分。生物炭特性受原料类型、热解温度、比表面积、电导率、碳和矿物质含量、电子交换能力、芳香度和粒径控制。我们发现，在不同的条件和基质类型中，与不含生物炭的对照相比，添加 6-16 g/L 生物炭始终能产生更高的累积比甲烷。生物炭的作用可以通过四种机制来解释：增强微生物功能、促进种间电子直接转移、改善难熔化合物的降解以及提高反应器稳定性。