Oxidation-biotreatment-membrane combined process for external reuse of shale gas wastewater

The external reuse of shale gas wastewater (SGW) is inevitable and challenging from the long-term perspective of the shale gas industry. Among the numerous reuse methods of SGW, pretreatment-membrane combined processes are regarded as a suitable and effective method. In this work, an integrated oxidation-biologically active filtration (BAF)-ultrafiltration (UF)-reverse osmosis (RO) process is firstly proposed for the external reuse of SGW. The results indicated that pre-oxidation, especially O3 pre-oxidation, can effectively improve the efficiency of removing organic matter in the subsequent BAF process, despite the variable feed chemistry and salinity (1.2%-2.3%). Herein, after ozonation, the removal rate of dissolved organic carbon in the BAF system was increased by 1.1–1.3 times. Meanwhile, oxidation-BAF, especially O3-BAF, can also significantly reduce UF membrane fouling (7%-60%) in the subsequent UF system compared with that of the alone BAF system. The principal mechanism of UF membrane fouling mitigation was that oxidation-BAF increased the cohesion energy between foulants and foulants and the adhesion energy between foulants and the UF membrane, making it more difficult for foulants to adsorb on or deposit on the membrane pores and membrane surface. In addition, the effluent of the integrated process can meet the water quality standards for SGW external reuse. Therefore, the O3-BAF-UF-RO process proposed here has broad engineering application potential for desalination, removal of organic pollutants, and realization of safe reuse of SGW.