Tannery wastewater with high biological oxygen demand (BOD5) was treated with ZnO-ZnFe2O4composite photocatalyst supported on activated carbon under visible light irradiation. Only 9% of BOD5 in the raw effluent were removed via adsorption on the surface of the photocatalyst in the dark for two hours. Photocatalysis with ZnO-ZnFe2O4 composite photocatalyst on activated carbon support removed 90% of BOD5 in two hours. For all the photocatalysis, complete BOD5removal of the wastewater sample could not be achieved. The photocatalytic effiency was found to increase with increase in the power of the light sources employed. The kinetics of decrease of the value of BOD5 fitted to the pseudo first order kinetic model (R2 = 0.9601). The derived value of the apparent rate constant for the photocatalytic decrease of the value of BOD5 was 0.049 min-1.
Key words: Photocatalyst, BOD5, ZnO-ZnFe2O4, tannery, wastewater.
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