Freshwater reserves are being depleted at a rapid rate due to population growth, economic development, and water use across different sectors. Desalination can be used to address the growing demand for fresh water, but the high salinity byproduct of this process, referred to as brine, must be managed. This has led to a push towards zero liquid discharge (ZLD) to maximize water recovery by treating the brine close to saturation. To this end, we present air gap diffusion distillation (AGDD) as a thermally driven and membrane-less process that can achieve ZLD with minimal scaling/fouling on polymeric heat transfer surfaces. In this work, we evaluate the performance of AGDD in terms of the water flux (permeate collected) and energy consumption (gain output ratio). A coupled heat and mass transfer model is developed to simulate brine concentration from a salinity of 70,000 mg/L up to near ZLD conditions in a counterflow operation for latent heat recovery. In addition, a parametric study is performed to understand the impact of flowrate, inlet temperature, salinity, and surface area on the overall performance. The development of such a modular brine concentration process has the potential to enable widespread deployment of desalination in inland regions.

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