Non-Membrane, Low Temperature and Low Emission Water Desalination Using Directional Solvent Extraction

Developing cost effective and energy efficient water treatment technologies is critical for expanding water resources to meet municipal, agricultural, power plant cooling, and other needs. While technologies to remove normal contaminants, such as particulates and biological organisms, are mature and efficient, removing ions (desalination) requires more sophisticated processes, such as reverse osmosis (RO) and thermal distillation. RO uses fine membranes and high-pressure pumps, and thermal distillation relies on intensive high temperature thermal energy, making both technologies very energy intensive. Rather than using costly electricity or high-quality heat for water treatment, the directional solvent extraction (DSE) process can utilize abundant low-quality waste heat from sources like power plant condensers and solar thermal energy to treat a wide variety of water sources, including seawater, brackish water, and condenser blow-down water.

This study provides the analysis of the feasibility and cost implications of using DSE methods as an alternative desalination technology. The performance data of a continuous DSE prototype with a footprint of 50(L)×25(W)×50(H) cm³, which can produce water with salinity lower than 700 ppm consistently at a rate of 25 ml per hour, are also presented. An electrocoalescer for speeding up the separation process of the water-in-DA emulsion is introduced. An economic feasibility studies based on the laboratory testing data is also developed to compare the DSE costs to the other state-of-the-art desalination technologies for a large-scale desalination plant. Recommendations and a pathway for building full-scale plants are proposed based on the economic analysis.

The study shows that DSE can be a viable process that utilizes low-grade waste heat to desalinate seawater. The thermodynamic calculation and economic analysis suggest that DSE presents a great opportunity to tackle the two most predominant challenges in the current state-of-the-art desalination processes by eliminating reliance on membrane-based separation, and the use of expensive, nonrenewable, fossil fuel derived, intensive high temperature thermal sources. Once it is mature and widely deployed, DSE technology promises to considerably lower desalination costs and help ameliorate the global water scarcity problem.