The petrochemical industry is a part of chemical industry that produces chemical products using raw materials from oil or natural gas. Ethylene oxide (EO) and ethylene glycol (EG) are petrochemicals used in many other industries. Combining these materials into the process of producing these chemicals with water leads towater pollution. Among the common methods of chemical purification, advanced oxidation processes (AOPs) are one of the methods used to purify industrial wastewater. AOPs include the production of a very strong and non-selective oxidizing agent (hydroxylradical) to destroy organic pollutants in industrial wastewater. AOPs, particularly the Fenton and photo-Fenton processes, are used to remove or convert toxic pollutants that are recalcitrant. The current study was conducted with the aim of using Fenton process as well as UV and microwave (MW) irradiation to reduce the organic load of EO/EG plant effluent of Marun Petrochemical Complex. In order to optimize Fenton process for effluent CODreduction, the effect of reaction time (intervals of 15, 30, 60 and 120 min), pH (2, 3, 4, 5, 6 and 7), concentrations of ferrous sulfate (50, 100, 200, 300, 400 and 600 mg/L) and hydrogen peroxide concentrations (250, 500, 750, 1000 and 1250 mg/L) were investigated. Then, the effect of COD concentrations (770, 1000, 1800, 2700 mg/L) on reaction efficiency was investigated under previous optimal conditions. The effect of MW irradiation power (100, 180, 300, 450, 600 and 800 W)and UV (UV-A, UV-B and UV-C) on COD removal was investigatedconsidering the optimum results of previous sections. The results showed that optimum reaction conditions for FP included time of 30 min, pH 3, ferrous sulphate concentration of 200 mg/L and 1000 mg/L hydrogen concentration, which resulted ina reduction of 73.7% of effluent COD. Furthermore,the highest COD removal by MW irradiation (600 W) and UV-C radiation was 65 and 75%, respectively after 10 and 5 minutes. Investigating the effect of different concentrations of COD on reaction efficiency in optimal conditions revealed that the highest removal efficiency was for COD concentration of 770 mg/L which resulted in 87 and 92% reduction in Fenton and photo-Fenton process, respectively. Finally, it can be concluded that Fenton and photo-Fenton processes had a high potential in COD reduction of EO/EGplant effluent ofMarun Petrochemical Complexin laboratory experiments and could be used in combination with other wastewater treatment methods. Keywords : Advanced Oxidation Processes (AOPs), Microwave, Chemical Oxygen Demand (COD), Industrial Wastewater, EO/EG Plant of Petrochemical Industry