Kinetic and thermodynamic evaluation of cod removal from pharmaceutical industry wastewater by Fenton oxidation

Chemical oxygen demand (cod) removal from pharmaceutical industry wastewater by fenton oxidation and absorbance change of the wastewater in ultraviolet (uv) and visible range were investigated in this study. kinetic and thermodynamic data were obtained from oxidation reaction. photo-fenton and sono-fenton oxidations were additionally studied to compare the results with fenton oxidation. the cod values of raw wastewater were between 2360 mg/l and 3930 mg/l. ferrous iron and h2o2 dosage, reaction time and temperature were studied to find optimum conditions. according to results, optimum fe(ii)/h2o2 ratio was found as 1/5. fenton reaction was observed to be fast in the first 10 minute and then reached to the equilibrium in 60 min. conductivity, oxidation/reduction potential (orp) and ph values were also measured. maximum removal efficiencies were obtained as 79% for fenton, 90% for photo-fenton and 86% for sono- fenton oxidation. it was concluded that the oxidation reactions followed pseudo-second-order reaction kinetic. the changes in gibbs free energy were calculated as -4.6, -3.2, -0.9 and -0.2 kj/mol for the temperatures of 283 k, 293 k, 313 k and 333 k, respectively. fenton process was evaluated to be spontaneous and exothermic under natural conditions.