Electro-activated persulfate oxidation (EC/PS) for the treatment of real oilfield produced water: Optimization, developed numerical kinetic model, and comparison with thermal/EC/PS and EC systems

Abstract

In this study, the performance and efficiency of electrocoagulation (EC), electro-activation of persulfate (EC/PS), and thermal activated-EC/PS for the treatment of two real produced water (PW) samples using iron electrodes were studied. To optimize and find out the effect of operating conditions on the different responses for EC and EC/PS, response surface methodology (RSM) was implemented. The results showed that EC process had considerable performance in the removal of H2S (96 %), oil and grease (O&G) (98–99 %), turbidity (91–97 %), phosphate phosphors (94 %), and heavy metals (92 %). EC/PS was introduced as an effective and a compact method for the removal of soluble hydrocarbons and nitrogen-ammonium (N-NH4+). The results indicated that at the current density of 35 A/m2, PS of 30 mM, reaction time of 30 min, N-NH4+ and chemical oxygen demand (COD) removal efficiency increased to 37 % and 71–94 %, respectively. To further increase the ammonia removal, EC/PS was integrated into thermal-PS activation at 65 °C, and the results showed that the ammonia removal by thermal/EC/PS reached about 69 %. According to gas chromatography/mass spectrometry (GC/MS), EC/PS was able to effectively eliminate most of the hydrocarbons. Moreover, a new kinetic model based on a novel algorithm and the main reactions occurring during EC/PS was developed to predict the COD removal efficiency, and the results indicated that it could predict COD removal efficiency with the acceptable accuracy. The estimated operating costs and energy consumption for EC/PS demonstrated that this process was more economical and efficient than other advanced oxidation processes (AOPs).