Treatment of Oil-Based Produced Water and Spent Caustic Wastewater Using Advanced Electrochemical Technology

Oil-based produced water (PW) and spent caustic (SC) are challenging industrial waste streams generated from petroleum and petrochemical industries. Their complex physiochemical nature, and the recent strict Saudi discharge regulations necessitate advanced treatment methods. This study aims to evaluate the treatment of both waste streams using a batch-mode pilot-scale advanced electrochemical system (AOT). The objective includes optimizing COD removal by investigating the effects of key operating parameters including current density, pH, and air flow rate. In this study, synthetic PW and pretreated authentic ethylene plant SC were treated in a two-separate set of experiments. The PW used in this study had a total dissolved solids (TDS) concentrations of 16,000 mg/L and organic carbon (COD) concentration of 250 mg/L, while SC has TDS of 23000 mg/L and COD of 670 mg/L. The AOT unit consists of anodic oxidation (AO) and in-situ generation of strong oxidants (i.e. hydrogen peroxide) in the electrolytic cell. The electro-cell is outfitted with a boron-doped diamond (BDD) anode and gas diffusion (GDE) cathode. The investigation verified the influential role of diverse operational factors in the treatment process. The results showed that for the PW, a TOC removal of 84% was achieved at pH 12, 200 mA/cm² electric current density and a circulation rate 0.2 L/min within 4 hours. The results of the SC treatment part showed a maximum COD removal of 90% at pH 4,150 mA/cm² electric current density and circulation rate 0.2 L/min within 3 hours. It was found that adding iron and air did not lead to any considerable improvement of the COD reduction of both PW and SC. This work clearly demonstrated that electrochemical post treatment is an efficient, cost-effective and environmentally friendly technique for the treatment of both pretreated spent caustic and oil-based produced water.