Highly efficient treatment of petrochemical spent caustic effluent via electro-Fenton process for COD and TOC removal: optimization and experimental

Abstract

Caustic is commonly used in oil and gas refineries to remove CO2, H2S, organic sulfur, and acidic compounds; however, spent caustic must be treated considering the type of wastewater in refinery and petrochemical units due to their hazardous characteristics. This research aims to reduce the chemical oxygen demand (COD) and the total organic carbon (TOC) from the used caustic effluent of the olefin unit of Ilam Petrochemical Company employing the electro-Fenton method. The affecting parameters, such as H2O2 concentration, reaction time, pH, and current density on the COD and TOC removal rate, were investigated. An experimental design by response surface methodology (RSM) based on the Box–Behnken method with the considered factors was considered to study the setup’s effectiveness and optimize the conditions. The outcomes revealed that by increasing the H2O2 concentration from 11 to 18 mgL, the COD removal efficiency was enhanced from 68 to 93%. On the other hand, by increasing the reaction time after 15 min, the COD and TOC removal efficiency decreased. The same trend was observed by increasing the current density after the optimal value. The optimal conditions were acquired at pH = 4, current density = 20 mAcm2, H2O2 concentration = 18 mgL, and reaction time = 15 min. The promising results confirmed that the electro-Fenton could be an excellent treatment technique in Ilam Petrochemical Unit as a spent caustic treatment. © 2023, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.