Effect of NaCl and Na₂SO₄ Salinity on Denitrification Efficiency and Sludge Settleability of SBR at Low Dissolved Oxygen

A continuous experiment was carried out using SBR process to treat wastewater containing saline and effects of NaCl and Na₂SO₄salinity(ρ(Na₂SO₄) and ρ(NaCl)) on the denitrification and activated sludge settleability were investigated at 0.3 mg/L of low dissolved oxygen when sodium acetate was used as carbon source.The results showed that the salinity increased gradually and η(NH₄⁺-N) and η(TN-N) were higher than 80% and 70% when ρ(Na₂SO₄) and ρ(NaCl) were lower than 14 g/L and 18 g/L,respectively.14 g/L of ρ(Na₂SO₄) and ρ(NaCl) wastewater was added one-time to investigate the effect of salinity shock on the denitrification effciency.η(NH₄⁺-N) and η(TN-N) were lower than 55% at initial operation,and η(NH₄⁺-N) and η(TN-N) were increased to 80% and 70%,respectively,with the operation time increasing.Furthermore,the sludge settleability was influenced bythe salinity.The total ρ(EPS) and SVI were 680 mg/L and 100 mL/g,respectively,when the salinity was 0 g/L.ρ(EPS) and SVI were 950 mg/L and 75 mL/g,respectively,when ρ(Na₂SO₄) was 14 g/L.ρ(EPS) and SVI were 1 200 mg /L and 65 mL /g,respectively,when ρ(NaCl) was 14 g /L.NaCl and Na₂SO₄could increase the settleability of sludge.