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

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 1gL(-1) of ZnO and effluent, was irradiated for 4h at pH 8.0 and 30 degrees C. Physico-chemical parameters such as chemical oxygen demand (COD) decreased from 15,023 to 350mg O-2 L-1; fifth-day biochemical oxygen demand (BOD5) from 4374 to 10mg O2L-1; total solids from 28,500 to 188mgL(-1); total organic carbon (TOC) from 4685 to 4.93mgL(-1), and turbidity from 331 to 1.15NTU after 4h 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 6.45mgL(-1) indicated efficiency in this treatment.