The new strategy of using humic acid loaded biochar to enhance the anaerobic digestion of cow manure for methane production

Anaerobic digestion is a beneficial way to convert organic waste resources, such as cow manure, into clean energy through microbial actions. However, when biochar was used as an additive to promote the efficiency of anaerobic digestion, there was a problem that the number of oxygen-containing functional groups was small, resulting in a limited effect on improving the electronic transport efficiency of the anaerobic digestion system. In this study, a high oxygen functional group containing humic acid biochar was prepared using ball milling technology to enhance reactivity and improve the anaerobic digestion performance of cow manure. The results showed that humic acid biochar had a more excellent performance in improving the gas production efficiency of cow manure AD. The addition of humic acid biochar did not significantly affect methane content. The humic acid biochar with a milling time of 8 h showed the best promotion effect in the anaerobic digestion system, and the methane yield reached 110.49 mL/gVS, which was 43.16% higher than that of the control group. The addition of humic acid biochar stimulated the secretion of extracellular polymers and enhanced interspecific electron transfer, leading to increased activity of key enzymes, including coenzyme F420. As a result, hydrogen-producing methanogens were enriched, methanogenic pathways were enhanced, and methane production was ultimately increased. Therefore, it improves intermediate product yield and utilization efficiency, thereby increasing methane production, and has great potential in the treatment of refractory organic waste.