Effect of bio-sludge concentration on the efficiency of sequencing batch reactor (SBR) system to treat wastewater containing Pb2+ and Ni2+.

The removal efficiency of sequencing batch reactor (SBR) system with synthetic industrial estate wastewater (SIEWW) containing Ni(2+) or Pb(2+) 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 100mL/g under MLSS of up to 4000 mg/L. Also, the effluent NO(3)(-) was decreased with the increase of MLSS. The heavy metals (Ni(2+) or Pb(2+)), BOD(5), COD and TKN removal efficiencies of SBR system with SIEWW containing 5mg/L heavy metal (Ni(2+) or Pb(2+)) under MLSS of 3000 mg/L were 83-85%, 96-97%, 95-96% and 83-94%, respectively. The increase of heavy metal (Ni(2+) or Pb(2+)) concentrations of SIEWW from 5 to 50mg/L were not significantly effected to both COD and BOD(5) 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 Ni(2+) and Pb(2+) could repress the growth of both nitrification and denitrification bacteria. And Ni(2+) was more effective than Pb(2+) to reduce the heavy metals removal efficiency. The SBR system could be applied to treat the industrial estate wastewater (IEWW) containing both Pb(2+) and Ni(2+) even the heavy metals concentrations was up to 5mg/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 BOD(5) concentration of the wastewater. The Pb(2+), Ni(2+), COD, BOD(5) and TKN removal efficiencies of the system with IEWW containing 500 mg/L BOD(5), 5mg/L Ni(2+) and 5mg/L Pb(2+) 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 100mL/g, respectively.