Effects of High Salinity on Nitrogen Removal Efficiency and Microbial Community Structure in a Three-Stage AO System
Shengyu Shi, Pengfei Cui, Shasha Wang, Jun Long +1
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70% confidenceA three-stage AO reactor's nitrogen removal performance was affected by high salinity, with removal rates decreasing and microbial community structure changing.
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Abstract
This study investigated the nitrogen removal performance of a three-stage AO reactor for refractory TN and the changes in microbial community structure within the activated sludge system under varying sodium chloride concentration conditions. Under an influent sodium chloride concentration of 0 g/L with sufficient carbon source, the removal rates of Total Nitrogen (TN), Chemical Oxygen Demand (CODcr), and Ammonium (NH4+-N) remained stable at 98%, 99.7%, and 99.9%, respectively. When the sodium chloride concentration increased to 20 g/L, the activity of AOB was significantly inhibited, with removal efficiency rates dropping to 83%, 89%, and 70%, respectively, and the NAR increasing to 91.97%. Analytical results demonstrated that both ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) exhibited inhibited metabolic activities, with NOB experiencing earlier functional impairment. Under NaCl concentrations ≤ 10 g/L, conventional nitrogen removal via nitrification–denitrification (ND) remained dominant. When NaCl concentrations exceeded 10 g/L, due to the accumulation of NO2−-N, the phyla Planctomycetota and Proteobacteria maintained dominance in the microbial community, while partial nitrification (PN) and denitrification pathways gradually replaced ND. Extracellular polymeric substance (EPS) secretion emerged as the primary microbial defense mechanism against salinity stress. Experimental findings informed proposed strategies including phased acclimatization for salt-tolerance enhancement, EPS production regulation, and targeted enrichment of functional consortia, which collectively improved the denitrification efficiency by 18.7–22.3% under salinity levels ≤ 20 g/L. This study provides theoretical foundations and technical references for process optimization in hypersaline industrial wastewater treatment systems.
Key findings
- High salinity (20 g/L NaCl) significantly inhibited AOB activity, reducing TN, CODcr, and NH4+-N removal rates.
- NOB exhibited earlier functional impairment than AOB under high salinity conditions.
- Conventional nitrogen removal via nitrification-denitrification remained dominant under NaCl concentrations ≤ 10 g/L.
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- Water
- Year
- 2025