Effect of anoxic:oxic ratio on the efficiency and performance of sequencing batch reactor (SBR) system for treatment of industrial estate wastewater containing Cr³⁺ and Ni²⁺

Abstract

Application of sequencing batch reactor (SBR) system for treatment of synthetic industrial estate wastewater (SIWW) containing high Cr³⁺ and Ni²⁺ concentrations of 3.0 mg/L (SIWW + Cr³⁺ and SIWW + Ni²⁺) at hydraulic retention time (HRT) of 1.5 d at various oxic:anoxic ratios of 19:0, 13:6, 11:8, and 9:10 in the reaction step of operation was examined. The highest Ni²⁺ and Cr³⁺ removal efficiencies of 93.1 ± 0.9% and 95.4 ± 0.2%, respectively, were detected with SIWW + Cr³⁺ and SIWW + Ni²⁺ at the oxic:anoxic ratio of 9:10. Moreover, the maximum Cr³⁺ and Ni²⁺ adsorption abilities of bio-sludge in the system were 36.00 ± 9.80 and 31.59 ± 9.67 mg/g of bio-sludge at the 19:0 oxic:anoxic ratio. Heavy metals (HM) adsorption abilities could be increased by adding anoxic period in the reaction step. The average Cr³⁺ and Ni²⁺ adsorption abilities of bio-sludge at oxic:anoxic ratio of 9:10 were 20.8 ± 4.1 mg Ni²⁺/g bio-sludge and 23.12 ± 6.0 mg Cr³⁺/g bio-sludge. Cr³⁺ and Ni²⁺ concentrations of 3.0 mg/L had a strong repression effect on the growth and activity of the carbonaceous BOD₅ removal microbes (heterotrophic bacteria). However, they slightly affected nitrifying and denitrifying bacteria. Nitrifying and denitrifying bacteria were the main microbes for HM adsorption mechanism in the SBR system. The advantage of SBR system was that after adding anoxic period in the reaction step, removal efficiencies of organic matter and HM increased.

Keywords:

• Adsorption
• Chromium
• Heavy metals
• Industrial estate wastewater
• Nickel
• Sequencing batch reactor (SBR)

Acknowledgments

The authors wish to express deep gratitude to King Mongkut’s University of Technology Thonburi for providing research materials and equipment for this project.