Ultraviolet Photocatalytic Treatment of Petroleum Refinery Wastewater: A Case Study of Azzawiya Refinery, Libya

Abstract

Abstract

           Petroleum refinery wastewater contains complex mixtures of refractory organic and inorganic contaminants that are difficult to remove using conventional treatment technologies. This study investigated the feasibility of ultraviolet (UV)-assisted photocatalytic oxidation using zinc oxide (ZnO) as a photocatalyst for the treatment of wastewater collected from the Azzawiya Oil Refinery, Libya. Wastewater samples obtained after the API oil separator were characterized based on pH, chemical oxygen demand (COD), and turbidity. The photocatalytic performance was evaluated by examining the effects of ZnO dosage, solution pH, ferrous ion (Fe²⁺) concentration, and ferric ion (Fe³⁺) concentration on COD removal under UV irradiation. Experimental results demonstrated that photocatalytic efficiency was strongly influenced by the operating conditions. The optimum treatment performance was achieved using a ZnO dosage of 0.6 g L⁻¹ at pH 5. The addition of iron ions further enhanced the degradation process by suppressing electron–hole recombination and promoting hydroxyl radical generation. The highest COD removal efficiency of 78.41% was obtained at a ferrous ion concentration of 10 mg L⁻¹, while ferric ions achieved a maximum COD removal of approximately 73% at an optimum concentration of 15 mg L⁻¹. The proposed degradation pathway indicated that aromatic hydrocarbons and phenolic compounds were progressively oxidized into intermediate products before complete mineralization into carbon dioxide and water. Overall, the findings demonstrate that UV/ZnO photocatalysis, particularly when enhanced with ferrous ions, represents an effective advanced oxidation process for improving the quality of petroleum refinery wastewater and offers considerable potential as a polishing treatment for refinery effluents.