Optimal Shale Water Pre-Treatment. Depending on its final destination, the water must undergo a different set of treatments that are designed depending on the wastewater physicochemical characteristics and on the requirements of the final desalination treatment selected. In general, water must undergo a set of initial pre-treatments to remove some components (TSS, divalent and trivalent ions, organics, microorganisms, etc.) and/or to prepare the water for the following desalination treatment. In this context «pre-treatment» can be defined as the set of treatments that flowback water must undergo before desalination. This definition include also all the treatments is desalination could be eventually not necessary for instance, in the case of direct re-use of the wastewater. We developed a superstructure optimization based approach [1] that allows determining the optimal structural configuration and operating conditions for the pre-treatment of the shale gas waste water, taking into account different alternatives of water uses and desalination process (such as membrane or thermal technologies). The superstructure is staged based. In the first stage, the best alternative for removing large particles (filtration). The second stage removes small particles (if necessary) or simply send the water to the next stage where it is decided how to remove colloidal particles and scale forming ions (coagulation/precipitation, electrocoagulation, flocculation). In the fourth stage, particles formed in previous one are removed by sedimentation, dissolved air flotation or granular filtration. Then the water is disinfected and if needed some extra treatment could be necessary (e.g. ultrafiltration) especially if desalination is carried out with membrane based technologies.
