Fenton process enhanced by metal sulfide for treating the actual evaporated mother liquid of gas field wastewater

Abstract Evaporated mother liquor of gas field wastewater (EML-GFW) is a form of wastewater generated by the triple-effect evaporation treatment of gas field wastewater containing complex pollutants. In this study, four metal sulfides, CuS, ZnS, MoS2, and WS2, were used to strengthen the Fenton process in EML-GFW treatment. The optimum Fenton/ZnS process for the highest removal of TOC from EML-GFW was achieved at the initial pH of 3.0 and in a mixture of FeSO4·7H2O:ZnS:H2O2 in the ratio of 30 g/L:10 g/L:1.2 mol/L, with a TOC removal efficiency of 74.5%. The organic components analysis of EML-GFW over four distinct periods demonstrated that the presence of N,N-dimethylethanolamine (DMEA) persisted and accounted for the greatest proportion of pollutants, identifying it as the characteristic pollutant. The TOC removal mechanism by Fenton/ZnS was revealed via analysis of organic materials obtained from the Fenton/ZnS process, tert-butanol quenching experiment, and illumination experiment. ZnS-generated hole–electron pairs under illumination, which promoted the reduction of Fe3+ to Fe2+, followed by an acceleration of •OH generation, thus improving TOC removal efficiency. The Fenton/ZnS process improved the treatment of EML-GFW in the laboratory, providing strong data support and theoretical guidance for expanding this technology at the gas field project site.