Enhanced removal of refractory organic pollutants from high-salinity mining wastewater by E-peroxone process

High-salinity mining wastewater is produced in the process of zero discharge. Due to its complex composition and high organic concentration, its treatment has become a worldwide problem. Hence, it is urgent to develop efficient technologies to remove refractory organics from high-salinity wastewater. E-peroxone process is a novel advanced oxidation process, and its advantages of high efficiency, good flexibility, and environmental friendliness make it a promising technical option for deep removal of organics from high-salinity wastewater. In term of this, this study firstly analyzed organic compounds in a high-salinity mining wastewater from western China with gas chromatography-mass spectrometry (GC-MS). A total of 15 organic compounds were detected, and they can be divided into three species, that is, macrocyclic siloxanes, esters, and nitriles and amides. Among them, dimethyl phthalate (DMP), an ester compound, showed a high peak signal, with its peak area accounting for 20.38%. Hence, DMP was selected as the characteristic compound of the high-salinity mining wastewater to investigate its removal kinetics and reaction mechanism in the E-peroxone process, based on which the technical and economic feasibility of E-peroxone process for the treatment of practical high-salinity wastewater was further explored. Results show that DMP was difficult to be efficiently removed by conventional ozonation due to its relatively low ozone reactivity. In contrast, by electrochemically in-situ generating hydrogen peroxide in conventional ozonation, the E-peroxone process obviously increased the hydroxyl radical (•OH) concentration in the reaction system by 1 order of magnitude, and thus significantly accelerated and enhanced the removal of DMP in the solution. Further theoretical calculations show that the C4 and C8 sites on the benzene ring of DMP are the dominant reaction sites for •OH attack, and transformation products of this reaction pathway were also detected. For the treatment of practical high-salinity mining wastewater, the E-peroxone process also exhibited the highest organic mineralization efficiency and the lowest energy consumption compared with conventional electrolysis and ozonation. Therefore, the results of this study demonstrated the technical and economic feasibility of the E-peroxone process for deep removal of organics from high-salinity wastewater, showing a promising application potential.