Efficient removal of organic contaminants in real shale gas flowback water using Fenton oxidation assisted by UV irradiation: Feasibility study and process optimization

•High TOC removal and synergistic effects were achieved using UV-Fenton process.•Operating conditions of the UV-Fenton process were optimized using response surface methodology.•TOC removal by the UV-Fenton process can be explained by second-order kinetics.•A possible degradation mechanism of dibutyl phthalate was proposed.