Effect of bio-sludge concentration on the efficiency of sequencing batch reactor (SBR) system to treat wastewater containing Pband Ni

The removal efficiency of sequencing batch reactor (SBR) system with synthetic industrial estate wastewater (SIEWW) containing Ni²⁺ or Pb²⁺ was increased with the increase of mixed liquor suspended solids (MLSS). But, the sludge volume index (SVI) of the system was increased up to higher than 100 mL/g under MLSS of up to 4000 mg/L. Also, the effluent NO₃⁻ was decreased with the increase of MLSS. The heavy metals (Ni²⁺ or Pb²⁺), BOD₅, COD and TKN removal efficiencies of SBR system with SIEWW containing 5 mg/L heavy metal (Ni²⁺ or Pb²⁺) under MLSS of 3000 mg/L were 83–85%, 96–97%, 95–96% and 83–94%, respectively. The increase of heavy metal (Ni²⁺ or Pb²⁺) concentrations of SIEWW from 5 to 50 mg/L were not significantly effected to both COD and BOD₅ removal efficiencies (they were reduced by only 4–5%), but they were strongly effected to both TKN and heavy metals removal efficiencies (they were reduced by 15 and 20–30%, respectively). Both Ni²⁺ and Pb²⁺ could repress the growth of both nitrification and denitrification bacteria. And Ni²⁺ was more effective than Pb²⁺ to reduce the heavy metals removal efficiency. The SBR system could be applied to treat the industrial estate wastewater (IEWW) containing both Pb²⁺ and Ni²⁺ even the heavy metals concentrations was up to 5 mg/L, but the removal efficiency was quite low and excess bio-sludge did not produce. However, the system efficiency could be increased with the increase of BOD₅ concentration of the wastewater. The Pb²⁺, Ni²⁺, COD, BOD₅ and TKN removal efficiencies of the system with IEWW containing 500 mg/L BOD₅, 5 mg/L Ni²⁺ and 5 mg/L Pb²⁺ under HRT of 3 days were 85.68 ± 0.31%, 87.03 ± 0.21%, 86.0 ± 0.5%, 94.04 ± 0.4% and 90.5 ± 0.9%, respectively. And the effluent SRT, SS and SVI of the system were 44.7 ± 0.6 days, 150 ± 6 mg/L and 100 mL/g, respectively.