Solar Desalination and Brine Management using Non-Contact Heating

Abstract:

Dwindling freshwater reserves and rapidly increasing global water demand has brought the treatment of non-traditional water sources, e.g. wastewater from thermoelectric power plants and oil and gas extraction produced water, to the forefront. The complex composition of these brines results in high energy consumption, thereby necessitating the integration of desalination technologies with renewable sources such as solar energy. Evaporation ponds are one such embodiment that harness solar energy to passively evaporate water from brines to achieve zero-liquid discharge (ZLD). However, direct utilization of solar energy for evaporation is limited by the transparency of water at visible and near-infrared wavelengths, resulting in low evaporation efficiencies. To address this, we demonstrate a simple photo-thermal device that leverages the inherent absorption properties of water by converting sunlight into mid-infrared thermal emission. This causes radiative heat localization at the water’s surface, resulting in over a two-fold enhancement in the water vapor flux at a solar-thermal efficiency of 43%. Furthermore, the non-contact nature of radiative heating eliminates corrosion risks, thus making the device uniquely suited for passive management and disposal of high salinity brines. These photo-thermal converters can also be applied to hybrid membrane-thermal desalination systems based on forward osmosis (FO) for water recovery for beneficial reuse. In FO, a draw solution drives water flux across the membrane, but separation of the draw from water, i.e., draw regeneration, presents an energy bottleneck. To address this, we use a novel class of thermally responsive draw solutes that can be regenerated using radiative heating for clean water production. The photo-thermal device delivers infrared wavelengths that overlap with the absorption spectrum of water-draw mixtures to thermally induce phase separation. Lab-scale tests with produced water feeds from southern California demonstrate the potential of this modular technology for energy-efficient and low-cost desalination.