Osmotically assisted reverse osmosis (OARO) for low-carbon treatment of shale gas fracturing wastewater at full scale

During hydraulic fracturing in shale gas extraction, substantial volumes of flowback and produced water (FPW) containing inorganic salts, heavy metals, and chemical additives are generated. Current FPW treatment technologies are limited by high operating costs, high carbon footprint, as well as difficulties in mixed salt disposal. This study established a green and low-carbon FPW treatment system at full scale, integrating high-density sedimentation, dissolved air flotation, chemical precipitation, sand filtration, nanofiltration, reverse osmosis, all membrane brine concentration (AMBC), mechanical vapor recompression, and chemically modified zeolite adsorption. To the first time in FPW treatment, the innovative, energy-saving AMBC unit based on the osmotic assisted reverse osmosis (OARO) was employed, which reduced the volume of brine entering the mechanical vapor recompression (MVR) unit by 40%, electricity consumption by 48.53% and carbon emission by 55.36%. Effective cleaning strategies were developed for killing the dominant fouling bacteria Myroides on nanofiltration membrane. Efficient recovery of industrial-grade sodium chloride further reduced the net cost to as low as 8.07 USD·m −3 , with effluent quality consistently meeting the stringent discharge standards and overall toxicity reduced by 98%.