Performance and stoichiometry of Sharon-DSR integrated system for synchronous nitrogen and sulfur removal from low C/N wastewater.

Traditional denitrification technologies for N-S co-contaminated wastewater exhibit high organic carbon consumption and an imbalance in the microbial community. This study developed a serial Sharon-DSR integrated reactor for synchronous elimination of nitrogen and sulfur. The upstream Sharon unit performs partial nitrification and sulfate reduction to produce nitrite and sulfide, while the downstream DSR reactor is inoculated with Pseudomonas sp. C27 realizes coupled autotrophic and heterotrophic denitrification. Single-factor continuous-flow tests were conducted to clarify the effects of influent pH, HRT, and the molar C/N ratio on system performance. Combined with electron conservation, the ternary kinetic diagram and full-process electron balance were used to analyze stoichiometric mechanisms. Results showed the optimal operational conditions were pH 7.8, HRT 16 h, and C/N = 1.0. At this regime, the Sharon unit achieved 73.7% ammonium removal, and the DSR reactor obtained 83.7% nitrite removal and 80.9% sulfide removal. The ternary diagram visualized how C/N modulates two denitrification branches. Stoichiometric calculations revealed that autotrophic denitrification supplied 36.2% of total electrons via in situ-generated sulfide, significantly reducing the exogenous organic carbon dosage and mitigating the high-carbon consumption defect of conventional low-C/N wastewater treatment processes, with whole-system electron closure exceeding 93%. This work illuminates the stoichiometric regulation of key parameters underlying low-carbon operation. It provides quantifiable parameter data and a theoretical basis for energy-saving engineering applications of simultaneous N-S removal from low-C/N industrial wastewater.