Residual cod reduction in biologically treated leather tanning effluents by advanced treatment processes

Biological treatment of effluents from industrial wastewaters often requires further treatment to comply with discharge standards. In this paper, an advanced oxidation processes and activated carbon adsorption were applied. Direct ozone reaction provided 70 % COD reduction. A readily oxidizable part of the substrate was defined. Catalytic ozone oxidation using ferric chloride proved to be very effective. Oxidation by ozone at pH 13 was fast and resulted in complete mineralization. The efficiency of O ₃/H ₂O ₂ system was dependent on O ₃/H ₂O ₂ ratio and at 1 mol/l mol ratio a better COD reduction than that of ozone alone was obtained. A kinetic equation was derived for the slower part of O ₃/H ₂O ₂ (1 mol/ 1 mol) oxidation. Adsorption experiments were conducted using powdered and granular carbon. The time to attain the equilibrium was found to be long and COD removal efficiencies were below 25%. Use of powdered activated carbon in combination with an activated sludge process was recommended.