Nowadays, advanced oxidation processes (AOPs) are receiving increasing attention to be used for industrial wastewater treatment. In this study, the wastewater of Shazand Oil Refinery Company in Iran was treated using photo-Fenton method as a branch of AOPs. Box–Behnken design was used to reduce the number of tests and to conduct the statistical analysis of the results. The aim of this study was to reduce the chemical oxygen demand (COD) of industrial wastewater and obtain the optimum condition in the removal of COD. For this purpose, the effects of operating factors such as hydrogen peroxide concentration (10–30 mM), iron ion concentration (0.7–2.1 mM), and pH (2–6) were investigated. The results of the analysis of variance showed that the operating parameters were effective. The initial COD of industrial wastewater was about 3400 mg l−1, and in the achieved optimum conditions, approximately 75% of initial COD was removed and the amounts of other parameters such as biological oxygen demand (BOD), total organic carbon (TOC), and total dissolved solid were reduced significantly. The BOD5 to COD ratio of the treated wastewater was increased considerably. Moreover, the kinetic study revealed pseudo-first-order reactions for the removal of COD. Accordingly, as a figure of merit, the “electrical energy per order” was determined at 25.04 kWh m−3 order−1, showing low electrical energy consumption and high economical profit in comparison with high COD removal.
