Solar-driven desalination and resource recovery of shale gas wastewater by on-site interfacial evaporation

The safe and economical management of shale gas flowback and produced water (FPW) with the goal of zero-liquid discharge (ZLD) is of paramount significance to the sustainable development of the energy industry. This challenge is still widely impending, due to severe limitations related to the complexity of FPW streams and high costs associated with their treatment. A long-term feasible solution is represented by solar-driven interfacial evaporation (SIE), a low-cost and environmentally friendly desalination technology. Technical and economic analyses show that even in the Sichuan Basin, where solar intensity is low and the volume of FPW is large, 4000 m2 of solar still would be sufficient to accomplish ZLD with a capital cost lower than $ 1 m−3, significantly cheaper than traditional membrane-based and thermal-based technologies (with costs above $ 15 m−3). Beneficial products, including condensate water and crystalline salts, may also be effectively recovered in this process, although design improvements are needed in this area. This study also discusses possible solutions to address the passage of volatile organic compounds into the effluent and to achieve the smart recovery of strategic resources, such as lithium and rare earth elements. The major current challenges of solar-driven evaporation for the beneficial management of FPW are scaling and fouling, cost-effective latent heat recovery, the scalability of the systems, and efficient water production and salts harvesting. These issues require ad hoc research efforts, analyses, and pilot testing.