A novel sulfur autotrophic denitrification in-situ coupled sequencing batch reactor system to treat low carbon to nitrogen ratio municipal wastewater: Performance, niche equilibrium and pollutant removal mechanisms.

A novel integrated sulfur fixed-film activated sludge in SBR system (ISFAS-SBR) was proposed to treat the low C/N ratio municipal wastewater. The effluent total inorganic nitrogen (TIN) and PO-P decreased from 17 mg/L and 3.5 mg/L to 8.5 mg/L and 0.5 mg/L, and higher nitrogen removal efficiency was contributed by the autotrophic denitrification. Microbial response characteristics showed that catalase (CAT), reduced nicotinamide adenine dinucleotide (NADH) and extracellular polymeric substance (EPS) alleviated the oxidative stress of sulfur carrier to maintain cell activity, while metabolic activity analysis indicated that the electron transfer rate was enhanced to improve mixotrophic denitrification efficiency. Meanwhile, the increased key enzyme activities further facilitated nitrogen removal and sulfur oxidation process. Additionally, the microbial community, functional proteins and genes revealed a niche equilibrium of C, N, S metabolic bacteria. Sulfur autotrophic in-situ coupled SBR system enlarged a promising strategy for treatment of low C/N ratio municipal wastewater.