16 / 2023-04-26 20:58:09

Emission of volatile sulphur compounds during swine manure composting Source identification, odour mitigation and assessment

Swine manure composting,Volatile sulphur compounds,Source identification,Odour mitigation and assessment,Ferric oxide

Compared to GHGs and ammonia, VSCs exhibit less emission but much lower odour thresholds during composting. Despite aeration to support aerobic microbes for organic biodegradation, anoxic and anaerobic regions occur in composting piles to induce the growth and activity of sulphur-reducing bacteria (SRB) for VSC production. Nevertheless, little is known about sources of these VSCs in composting as sulphur is embedded in both organic and inorganic substances in livestock manure, such as methionine, cysteine, sulphate (SO₄^2-) and sulphite (SO₃^2-). Thus, this study aimed to identify the sources of volatile sulphur compounds (VSCs) and evaluate their mitigation by ferric oxide (Fe₂O₃) during swine manure composting. Four chemicals, including L-cysteine, L-methionine, sodium sulphite, and sodium sulphate, were further added to simulate organic and inorganic sulphur-containing substances in swine manure to track VSC sources during composting. Results show that sulphur simulants induced the emission of six common VSCs, including methyl sulphide (Me₂S), dimethyl sulphide (Me₂SS), carbonyl sulphide (COS), carbon disulphide (CS₂), methyl mercaptan (MeSH), and ethyl mercaptan (EtSH), during swine manure composting. Of them, COS, CS₂, MeSH and Me₂SS were predominantly contributed by the biodegradation of methionine and cysteine, while Me₂S and EtSH were dominated by the reduction of sulphite and sulphate. Further Fe2O3 addition at 1.5% of total wet weight of composting materials immobilized elemental sulphur and inhibited sulphate reduction to reduce the emission of VSCs by 46.7% – 80.9%. Furthermore, odour assessment indicated that adding Fe₂O₃ into composting piles significantly reduced the odour intensity level to below 4, the odour value of VSCs by 47.1% – 81.3%, and thus the non-carcinogenic risk by 68.4%.