Effects of simultaneous denitrification and desulfurization and changes of microbial community structure with corncob solid slow-release carbon source under different S/N ratios

Industrial wastewaters contain high concentrations of sulfate and nitrate. Methanol, ethanol, and acetic acid are often used as the external carbon sources to remove pollutants in wastewater. However, they carry a hefty price. In this study, using low-cost corncob as solid slow-release carbon source, we investigated the effects of different S/N ratios (5:8, 5:5, and 5:2) on simultaneous denitrification and desulfurization, and microbial community structure under continuous flow conditions. Results showed that nitrate concentration in effluent was maintained below 5 mg/L throughout the experiment. Concurrently, 34.89%, 73.59%, and 88.22% of sulfate was removed, respectively, at the beginning of each stage, without the release of hydrogen sulfide. Microbial community analysis showed that heterotrophic denitrifying bacteria, sulfate-reducing bacteria, autotrophic denitrifying bacteria, and hydrolyzing bacteria co-existed in the reactor at different S/N ratios. In particular, the relative abundance of autotrophic denitrifying bacteria increased with the increase of S/N ratio. Furthermore, the copies of key functional genes of nirK , nirS , dsrA , and dsrB also reached the highest when S/N ratio was 5:2. Therefore, simultaneous denitrification and desulfurization by using solid slow-release carbon sources provided theoretical references for practical applications. • Solid slow-release carbon source is an alternative strategy for water treatment. • Solid slow-release carbon source realizes ISDD process without secondary pollution. • Moderate S/N ratio stimulates N and S transformation under mixotrophic condition.