Coordination of elemental sulfur and organic carbon source stimulates simultaneous nitrification and denitrification toward low C/N ratio wastewater

The feasibility of inducing simultaneous nitrification and denitrification (SND) by S⁰ for low carbon to nitrogen (C/N) ratio wastewater remediation was investigated. Compared with S⁰ and/or organics absent systems (−3.4 %∼5.0 %), the higher nitrogen removal performance (18.2 %∼59.8 %) was achieved with C/N ratios and S⁰ dosages increasing when S⁰ and organics added simultaneously. The synergistic effect of S⁰ and organics stimulated extracellular polymeric substances secretion and weakened intermolecular binding force of S⁰, facilitating S⁰ bio-utilization and reducing the external organics requirement. It also promoted microbial metabolism (0.16 ∼ 0.24 μg O₂/(g VSS·h)) and ammonia assimilation (5.9 %∼20.5 %), thereby enhancing the capture of organics and providing more electron donors for SND. Furthermore, aerobic denitrifiers (15.91 %∼27.45 %) and aerobic denitrifying (napA and nirS) and ammonia assimilating genes were accumulated by this synergistic effect. This study revealed the mechanism of SND induced by coordination of S⁰ and organics and provided an innovative strategy for triggering efficient and stable SND.