Regulation of influent sulfide concentration on anaerobic denitrifying sulfide removal

The objective of this study is to find a comprehensive regulation for sulfide removal and elemental sulfur transformation based on the denitrifying sulfide removal process. The experiment was performed based on several influent sulfide concentrations (150-600 mg/L) and nitrate-to-sulfur (N/S) molar ratios (0.5-2.0) at reaction times of 24 and 48 h. Sulfide and nitrate removals were mainly dependent on the influent sulfide concentration at sulfide concentrations of 150-200 and 400-600 mg/L, but on the N/S ratio at sulfide concentrations of 250-350 mg/L. Up to 99.7% and 93.8% of sulfide and nitrate were removed, respectively, with 26.5% of elemental sulfur formed at sulfide concentrations of 250-350 mg/L (N/S of 1.0). Only 4-9.4% of elemental sulfur was formed, with sulfide and nitrate removals of 99.9% and 98.7%, respectively, at sulfide concentrations of 150-200 mg/L. Meanwhile, 46.9-94.7% of sulfate was formed with a nitrogen gas conversion rate of 18.2-57.1%. Fewer microorganisms were detected by fluorescence in situ hybridization (FISH) at high sulfide concentrations of 400-600 mg/L, suggesting that the processes of anaerobic denitrification and desulfurization were inhibited.