COD removal and toxicity decrease from tannery wastewater by zinc oxide-assisted photocatalysis: a case study

Abstract

This work reports the optimization of degradation conditions and toxicity decrease in the tannery wastewater, collected in the retanning and dyeing steps. This effluent was filtered, diluted in a 1:200 proportion, and investigated as a case study on a bench scale by heterogeneous photocatalysis. These conditions were attained when the suspension, containing 1 g L⁻¹ of ZnO and effluent, was irradiated for 4 h at pH 8.0 and 30°C. Physico-chemical parameters such as chemical oxygen demand (COD) decreased from 15,023 to 350 mg O₂ L⁻¹; fifth-day biochemical oxygen demand (BOD₅) from 4374 to 10 mg O₂ L⁻¹; total solids from 28,500 to 188 mg L⁻¹; total organic carbon (TOC) from 4685 to 4.93 mg L⁻¹, and turbidity from 331 to 1.15 NTU after 4 h of irradiation. The LC₅₀ increase from 14.90% to 56.82% in the lethality assay of Artemia salina L. microcrustacean as well as the dissolved oxygen of 6.45 mg L⁻¹ indicated efficiency in this treatment.

Keywords:

• tannery wastewater
• COD
• ZnO
• heterogeneous photocatalysis
• toxicity

Acknowledgements

The authors acknowledge CNPq by the financial support, and M.C.H. is also grateful to CAPES for the scholarship.