Climate change and energy demand are calling for more sustainable fuels such as biomethane produced by anaerobic digestion of organic waste. Biochar addition to waste is presumed to enhance the efficiency of methane production, yet individual reports disclose contradictory results. Therefore, we performed a meta-analysis of 27 selected publications containing 156 paired measurements of control and biochar-amended treatments to assess the impact of biochar on the methanogenic performance. Results show that biochar promotes biomethane production substantially with a high Hedge's d value of 5.7 ± 1.04, yet sporadic publications report a methane decline. Methanogenic performance is statistically controlled by feedstock type, pyrolysis temperature and biochar concentration, but not controlled by pH, size, surface area and methanogen species. These findings should help to tune the parameters of anaerobic digestion with biochar to optimize biomethane productions. Moreover, our results cast some doubt on the efficiency of adding biochar to soil to sequester carbon in soils because biochar promotes methane generation and, in turn, emissions of methane, a greenhouse gas, to the atmosphere.

气候变化和能源需求正在呼吁使用更具可持续性的燃料，例如通过有机废物的厌氧消化而产生的生物甲烷。据推测，将生物炭添加到废物中可以提高甲烷生产效率，但个别报告披露了相互矛盾的结果。因此，我们对27个选定的出版物进行了荟萃分析，其中包含156个配对对照和生物炭处理的测量值，以评估生物炭对产甲烷性能的影响。结果表明，生物炭促进生物甲烷生产基本上具有高对冲的d值5.7±1.04，但零星的出版物报道甲烷下降。产甲烷性能在统计学上受原料类型，热解温度和生物炭浓度的控制，但不受pH值，尺寸，表面积和产甲烷菌种类的控制。这些发现应有助于调整生物炭厌氧消化的参数，以优化生物甲烷的生产。此外，我们的结果对在土壤中添加生物炭以隔离土壤中的碳的效率提出了一些疑问，因为生物炭促进了甲烷的产生，进而促进了向大气中排放甲烷（一种温室气体）的排放。