Impact of different structures of biochar on decreasing methane emissions from sewage sludge composting

Methane (CH₄) emissions from sewage sludge composting can be reduced by using biochar more effectively. This study investigates the impact of different structure of biochar on CH₄ emissions during sewage sludge composting. Corncob biochar (CB, pore size = 35.3990 nm), rice husk biochar (RB, pore size = 3.4242 nm) and wood biochar (WB, pore size = 1.6691 nm) were applied to the composting. The results showed that biochar decreased CH₄ emissions, mainly through the indirect effect of improving the pile environment. Compared with the control group (CK), the biochars with smaller pore structures, WB and RB, reduced CH₄ emissions by 41.83% and 33.59%, respectively, compared to only 8.20% for CB, which has a larger pore structure. In addition, RB and WB increased the free air space (FAS) by more than 10% and CB improved the microbial diversity. Methanothermobacter was reported in WB and RB, with an abundance of 45.45% in WB. Redundancy analysis (RDA) showed that pore size was positively correlated with the CH₄ emission rate. The results of this study can provide a theoretical reference for CH₄ reduction from biochar co-composting of sewage sludge.