Effect of biochar structure on H2S emissions during sludge aerobic composting: insights into microscale characterization and microbial mechanism

In order to evaluate the effect of biochar structure on hydrogen sulfide (H 2 S) emissions during sludge aerobic composting, corncob biochar, beech biochar, and rice husk biochar were used as exogenous additives, which have different microscopic characteristics. The results showed that biochar reduced H 2 S emissions mainly by the indirect effect of the pile. Specifically, the cumulative emission of H 2 S in the corncob biochar group, beech biochar group, and rice husk biochar group decreased by 12.91%, 50.47%, and 36.21% compared with the control group without biochar addition, respectively. Then, it was observed by X-ray diffraction that sulfur and sulfate were formed on corncob biochar and rice husk biochar as well as sulfur was formed on beech biochar. Besides, according to microbial community analysis, the addition of beech biochar reduced the abundance of Hydrogenispora in mature stages and inhibited sulfur-related respiration compared with the other groups. In addition, the redundancy analysis showed that main factors that affected H 2 S emissions during aerobic composting were pile temperature and pH, followed by organic matter. What’ more, the influence of biochar structure on H 2 S emissions depended on the total pore volume, followed by the specific surface area and the average pore diameter. This study provided evidence for biochar structure and microbial mechanism to affect H 2 S emissions from the sludge aerobic composting pile.