Heterocatalytic Fenton oxidation process for the treatment of tannery effluent: kinetic and thermodynamic studies

Background, aim, scope: Treatment of wastewater has become significant with the declining water resources. The presence of recalcitrant organics is the major issue in meeting the pollution control board norms in India. The theme of the present investigation was on partial or complete removal of pollutants or their transformation into less toxic and more biodegradable products by heterogeneous Fenton oxidation process using mesoporous activated carbon (MAC) as the catalyst. Materials and methods: Ferrous sulfate (FeSO<SUB>4</SUB>.7H<SUB>2</SUB>O), sulfuric acid (36 N, specific gravity 1.81, 98% purity), hydrogen peroxide (50% v/v) and all other chemicals used in this study were of analytical grade (Merck). Two reactors, each of height 50 cm and diameter 6 cm, were fabricated with PVC while one reactor was packed with MAC of mass 150 g and other without MAC served as control. Results and discussion: The oxidation process was presented with kinetic and thermodynamic constants for the removal of COD, BOD, and TOC from the wastewater. The activation energy (Ea) for homogeneous and heterogeneous Fenton oxidation processes were 44.79 and 25.89 kJ/mol, respectively. The thermodynamic parameters Δ G, Δ H, and Δ S were calculated for the oxidation processes using Van't Hoff equation. Furthermore, the degradation of organics was confirmed through FTIR and UV-visible spectroscopy, and cyclic voltammetry. Conclusions: The heterocatalytic Fenton oxidation process efficiently increased the biodegradability index (BOD/COD) of the tannery effluent. The optimized conditions for the heterocatalytic Fenton oxidation of organics in tannery effluent were pH 3.5, reaction time-4 h, and H<SUB>2</SUB>O<SUB>2</SUB>/FeSO<SUB>4</SUB>.7H<SUB>2</SUB>O in the molar ratio of 2:1