Effect of Cr+3 on the efficiency and performance of the sequencing batch reactor (SBR) system for treatment of tannery industrial wastewater

Abstract

The study focused on the treatment of tannery industrial wastewater (TIW); TIW containing 10 mg/L Cr3+ (TIW + 10 Cr3+) and synthetic tannery industrial wastewater (STIW) containing Cr+3 concentrations of 0, 5, 10, 20, 30 and 40 mg/L using a sequencing batch reactor (SBR) system at hydraulic retention times (HRT) of 1.5, 3 and 5.0 d and concentrations of mixed liquor suspended solids (MLSS) of 1,000, 2,000, 3,000, 4,000 and 5,000 mg/L removal efficiency were determined. The highest Cr+3, COD, BOD5, TKN and TN removal efficiencies of 87.5 ± 0.2, 96 ± 0, 96 ± 1, 88.5±0.1 and 61.0 ± 0.5%, respectively, were detected with STIW + 5 Cr+3 at MLSS of 5,000 mg/L and HRT of 3 d. Cr+3 gave a strong repression effect to the growth and activity of young bio-sludge, and the effect increased with increase in Cr+3concentration or loading. However, older bio-sludge showed strong resistance to Cr+3 toxicity and had higher Cr+3 adsorption yield than younger bio-sludge. The SBR system with raw TIW showed the highest Cr3+, COD, BOD5, TKN and TN removal efficiencies of 96.9 ± 0.2, 98 ± 1, 99 ± 0, 69.2±0.0 and 60.3 ± 0.1%, respectively, at HRT of 5 d and MLSS of 5,000 mg/L. Efficiency with TIW was reduced by addition of Cr+3. However, the efficiency was recovered with increase in HRT. The system containing TIW + 10 Cr3+ showed the highest Cr+3, COD, BOD5, TKN and TN removal efficiencies of 95.6 ± 0.3, 98 ± 1, 99 ± 0, 68.6±0.0 and 60.0 ± 0.1%, respectively, with SVI less than 100 mL/g at HRT of 5 d and MLSS of 5,000 m/L.