Remediation of Spent Caustic in the Wastewater of Oil Refinery by Photo-Fenton Process

Background & Aims of the Study: Currently, the advanced oxidation processes have received increasing attention for the treatment of industrial wastewater. In the present study, the photo-Fenton process was used for the remediation of the spent caustic in the wastewater of Kermanshah Oil Refining Company in Iran. The effluent comprising spent caustic is toxic dark brawn with a high level of alkalinity. Materials and Methods: Diluted wastewater covering the spent caustic from Kermanshah Oil refinery was used in this study in September 2018. In addition, the effects of operative factors, such as the initial concentrations of hydrogen peroxide (H2O2), ferrous ion, and initial chemical oxygen demand (COD), have been investigated. The response surface method and Box-Behnken design of experiments were employed to examine the effects of three independent variables on the response function to obtain the optimum conditions. Results: Analysis of variance was performed to determine the significance of the effects of independent variables on the response function. Various amounts of variables were optimized for the removal of COD. At optimum conditions (i.e., an H2O2 concentration of 600 mg/l, ferrous concentration of 145 mg/l, and initial COD of 300 mg/l), the removal efficiency for COD was 91.5% after 60 min of reaction. Conclusion: According to the obtained results, the suggested quadratic model demonstrated good correctness. The statistical analysis showed that the model was satisfactory to predict the performance of the process. The wastewater containing spent caustic cannot proficiently be degraded by ultraviolet radiation and hydrogen peroxide (H2O2) oxidation separately; however, the photo-Fenton method is verified to be operative and can considerably degrade this pollutant. One of the main disadvantages of this process in the treatment of spent caustic is that the optimum pH is near 3, and a considerable amount of acid is needed to neutralize and acidify the alkalinity of spent caustic.