Optimization of effective parameters in arsenite oxidation process with Cl₂, H₂O₂, and O₃ using response surface methodology

This study explores a comprehensive study on the effective parameters in As(III) oxidation process with the high initial concentration of 5 mg/L by using of H₂O₂, O₃, and Cl₂ oxidants. For this purpose, As(III) oxidation process was successfully optimized using a Box–Behnken design with response surface methodology (RSM). A three-level-four-variable design was applied with three numerical factors including oxidant dosing (1, 2 and 3 times the stoichiometric molar ratio), pH (6, 7 and 8), time (1, 5 and 10 min), and oxidant type (H₂O₂, O₃, and Cl₂). Oxidation results showed the highest percentage of As(III) oxidation at zero levels of oxidant dosing, pH, and time variables were achieved by Cl₂ oxidant compared to O₃ and H₂O₂ oxidants. According to factors F-values, time, oxidant type, and oxidant dosing factors are the most effective factors on As(III) oxidation efficiency, respectively and pH factor and its interactions indicated the slight effects. The optimal oxidation conditions were oxidant dosing of 1.89 ratio, pH= 7.75, t=4.06 min by Cl₂ oxidant causing complete As(III) oxidation. Finally, validation of the proposed optimal conditions for As(III) oxidation was investigated by conducting the oxidation process under the optimal conditions with real well water sample with a specific As(III) concentration of 5 mg/L, yielding an oxidation efficiency of 99.8% and 99.5%, respectively. The findings provide new insight into superior efficiency of Cl₂ compared to H₂O₂ and O₃ oxidants in oxidation of As(III) as an effective approach to solve the low removal efficiency problem of As(III).