The treatment of phenolic contaminants from shale gas drilling wastewater: a comparison with UV-Fenton and modified UV-Fenton processes at neutral pH

Abstract

In a shale gas field, wastewater from drilling processes contains many recalcitrant and toxic pollutants. These pollutants are difficult to dispose in a classical wastewater treatment system. In this study, a comparative experiment was conducted to check the treatment efficiency of a UV-Fenton process at pH = 3 and a modified UV-Fenton process at neutral pH with real drilling wastewater, which was collected by a coagulative effluent in a sewage treatment plant in a shale gas field, Chongqing. The consumption of Fenton reagents and the rate of removal of COD and BOD₅ during three processes were evaluated in order to obtain an optimal process. In addition, phenolic contaminants in the effluent were measured by GC-MS and 7 of them were singled out to serve as an evaluation standard for effective treatment, which has not been reported in previous experiments. The results showed that three UV-Fenton processes had the ability to treat drilling wastewater and a modified UV-Fenton process with carboxymethyl-β-cyclodextrin (CMCD) had positive effects on the treatment of phenolic contaminants at neutral pH with minimal reagent consumption (Fe²⁺ = 14 mg L⁻¹ and H₂O₂ = 768 mg L⁻¹). It was demonstrated that modified UV-Fenton with CMCD could extend the pH range in the treatment process and avoid negative effects in UV-Fenton process at acidic pH.