Efficient wastewater treatment in petroleum refineries: Hybrid electro-fenton and photocatalysis (UV/ZnO) process

Abstract

In this study, a new hybrid system composed of a photo-catalysis (UV/ZnO) process combined with an electro-Fenton (EF) process equipped with a micro porous graphite air diffusion cathode (MPGADC) was used to treat petroleum refinery wastewater (PRW). The hybrid system was operated in a batch recycle mode and its performance was investigated and optimized using a response surface methodology (RSM). Three operating parameters affecting on the removal efficiency (RE%) of chemical oxygen demand (COD) were investigated including current density (2–10 mA/cm2), ZnO dosage (0.05–0.35 g/L), and Fe2+concentration (0.05–0.15 mM). Results showed that the optimum operating conditions can be achieved using a current density of 6.44 mA/cm2, with ZnO dosage of 0.35 g/L, and concentration of Fe2+ ions at 0.05 mM in which RE% of 90.15% was obtained with requiring a total electrical energy consumption (EECT) of 19.102KWh/m3. Furthermore, analysis of variance (ANOVA) exhibited a high value of determination coefficient (R2) close to 98.24% indicating a satisfactory fit between the obtained regression model and the experimental results. Moreover, ANOVA results revealed that current density has the most significant effect on RE% with a contribution of 52.41% followed by ZnO dosage and Fe2+ concentration both of them with a contribution of 11.64%. The comparison between the individual photo-catalysis process and hybrid process showed that RE% increases from 77.83% to 90.15% making an enhancement by 15.83% in RE% while EECT decreased from 27.171to 19.102KWh/m3 making a reduction by 29.7% in EECT. Hence, combining EF with photo-catalysis process improves the efficiency and reduced the required energy in comparison with the individual photo-catalysis process. Therefore, the combined process could be considered as an alternative, sustainable, green and cost-effective method for treatment of refinery wastewaters.