Contribution of sulfur-containing precursors to release of hydrogen sulfide in sludge composting

Hydrogen sulfide (H₂S) production during composting can impact the environment and human health. Especially during the thermophilic phase, H₂S is discharged in large quantities. However, in sludge composting, the contributions of different sulfur-containing precursors to H₂S fluxes, key functional microorganisms, and key environmental parameters for reducing H₂S flux remain unclear. Analysis of cysteine (Cys), methionine (Met), and sulfate (SO₄^2-) concentrations, multiple stepwise regression analysis, and Kyoto Encyclopedia of Genes and Genomes (KEGG) annotation analysis of metagenomes showed that Cys was the main contributor to the production of H₂S and that Met was among the main sources during the first three days of composting, while the SO₄^2- contribution to H₂S was negligible. Fifteen functional genera involved in the conversion of precursors to H₂S were identified by co-occurrence network analysis. Only Bacillus showed high temperature resistance (>50 °C) and the ability to reduce H₂S. Redundancy analysis showed that total carbon (64.0 %) and pH (23.3 %) had significant effects on functional bacteria. H₂S had a quadratic relationship with sulfur-containing precursors. All microbial network sulfur-containing precursors metabolism modules showed a highly significant relationship with Cys.