Comparison of Fenton and Ozone Oxidation for Pretreatment of Petrochemical Wastewater: COD Removal and Biodegradability Improvement Mechanism  
[PERSON]  
1 Tianjin Key Laboratory of Clean Energy and Pollution Control, School of Energy and Environment Engineering, Hebei University of Technology, Tianjin 300401, China; [EMAIL_ADDRESS] (S.C.); [EMAIL_ADDRESS] (M.K. ); [EMAIL_ADDRESS] (T.R. ); [EMAIL_ADDRESS] (R.L. ); [EMAIL_ADDRESS] (T.R. ); [EMAIL_ADDRESS] (R.L. ); 20212130315@stu. Advanced oxidation technologies (AOPs) [4] with the potential to degrade various organic pollutants mainly include the Fenton/photo-Fenton method, the photocatalytic oxidation method, the ozone oxidation method, the ultrasonic oxidation treatment method, etc. [5; 6], and have been proved to be an effective wastewater treatment technology which can generate hydroxyl radicals (\({}^{\bullet}\)OH) (E\({}_{0}\) = 2.80 V) and other radicals with strong oxidizing properties, which can effectively improve the biodegradability of effluent by high treatment efficiency and strong operability in the pretreatment of petrochemical wastewater [7; 8]. Under certain pH conditions, the reaction of Fe\({}^{2+}\) and H\({}_{2}\)O\({}_{2}\) occurs to generate \({}^{\bullet}\)OH in a very simple and cost-effective way via Fenton oxidation [9], an advanced oxidation technology for effectively treating refractory organic wastewater, in which molecular organic pollutants are degraded to small molecular organic pollutants or mineralized to CO\({}_{2}\) and H\({}_{2}\)O [10]. [PERSON] et al. [11] used electro-Fenton technology to pretreat petrochemical wastewater, and then carried out advanced treatment using the activated sludge method, showing that under the conditions of pH = 3, current of 160 mA, and a H\({}_{2}\)O\({}_{2}\) concentration of 65 mM, the COD removal rate was improved to 79%, while the B/C value increased from 0.44 to 0.776 after 30 min, which proved that the biodegradability of wastewater was greatly improved. Similarly, solar Fenton technology was used by [PERSON] et al. [12] to pretreat refinery wastewater, and showed that after 180 min of reaction at 694.7 mg/L H\({}_{2}\)O\({}_{2}\), 67.3 mg/L Fe\({}^{2+}\), and pH = 12, COD and TOC decreased to 79.6 % and 73.2 %, respectively, while the B/C values reached 0.36 to 0.62, also proving that the biochemical properties of the pretreated petrochemical wastewater were improved. Ozone is regarded as a strong oxidant with a strong oxidizing ability [13], rapid reaction, as well as being green and high efficiency, which can not only directly oxidize pollutants, but also produce \({}^{\bullet}\)OH to effectively mineralize organic pollutants, successfully realizing water purification without secondary pollution [14]. [PERSON] et al. [15] and [PERSON] et al. [16] treated petrochemical wastewater by combining ozone oxidation pretreatment with advanced biological activated carbon treatment, and coagulation-ozonation (ICO) integration, respectively, and effectively improved biodegradability. Fenton oxidation and ozone oxidation degrade organic pollutants by different mechanisms. Ozone oxidation mainly reacts directly with the unsaturated bonds of organic pollutants through its own oxidizing properties, and has certain limitations that only a part of organic pollutants' oxidation was promoted because of its selective oxidizing properties [17]. In contrast, the strong oxidizing \({}^{\bullet}\)OH, which can degrade organic pollutants non-selectively, was generated in Fenton oxidation [18]. Although the pretreatment of petrochemical wastewater by Fenton and ozone oxidation have been studied, the comparison of Fenton and ozone oxidation on the COD removal of petrochemical wastewater and biodegradability improvement mechanism is still lacking. In this work, the petrochemical wastewater was pretreated by Fenton and ozone oxidation, and the variations in COD, BOD\({}_{5}\), and B/C in the two systems were systematically compared.