Sustainable Recovery of Potable Water from Saline Waters

A new low-temperature phase change desalination process capable of being driven by low-grade or waste heat sources was developed and demonstrated at prototype scale. The proposed process is based on simple but sound scientific principles, and has the potential to produce potablequality water in a sustainable manner, without any reliance on grid power. In this project, theoretical experimental studies were conducted to characterize and demonstrate the feasibility of the process. Based on theoretical simulations, a typical absorption refrigeration system driven by a 25 m2 solar collector and rated at a cooling rate of 3.25 kW (0.975 tons of refrigeration for typical domestic application) can produce 4.5 kg/h (108 L/d) of desalinated water. The net grid energy required for this case was 208 kJ/kg of desalinated water. The feasibility of an alternate configuration that could be driven solely by solar energy incorporating solar photovoltaic panel and a battery bank was demonstrated at prototype scale. Results of this study showed that a freshwater production rate of 0.25 kg/h (6 L/d) can be sustained at evaporation temperatures as low as 40ºC using a solar PV panel of area 6 m2. The study also demonstrated that the system was able to produce EPA-recommended potable-quality water from the effluent of a municipal wastewater treatment plant, with the following removal efficiencies of key contaminants: > 93% total dissolved solids; >95% nitrates; > 97% ammonia; and > 99.9% coliform bacteria. Since this process can be driven entirely by renewable or waste energy, unlike the traditional desalination processes, it does not contribute to any greenhouse gas emissions.