Extremely high-salinity water streams present difficulties for many types of processing equipment, such as membranes and filters, and most commercial treatment methods involve thermal evaporators or crystallization, which are energy-intensive and require special anti-corrosion materials. A new membrane-less, non-evaporative process called Temperature Swing Solvent Extraction (TSSE; diagram) enables the extraction of freshwater from hypersaline brine without the production of any harmful byproducts. “TSSE operates by using a thermally switchable solvent that has the unique ability to change its affinity for water depending on temperature. At cool temperatures, the solvent binds to freshwater, selectively extracting it from brine. Applying a minimal temperature swing causes the solvent to release the water, enabling the recovery of pure freshwater with near 100% solvent recyclability,” explains Shannon Knee, CEO and founder of Cetos Water (New York, N.Y.; www.cetoswater.com), the developer of the TSSE process. The process can be customized to achieve complete water extraction, leaving solid minerals behind as waste, and enabling a true zero-liquid-discharge process. Knee likens the process to a “sponge” that soaks up water at cooler temperatures and squeezes out freshwater at higher temperatures.
Although TSSE is a thermal process, it operates at much lower temperatures than evaporation or crystallization processes since the water does not need to be boiled. “Our thermal footprint is low enough that it can leverage free industrial waste heat. Also, TSSE extracts water rather than removing specific contaminants, enabling us to treat a wide range of brine compositions without materially re-engineering the process,” adds Knee. Whereas certain impurities and high salinity can clog membranes and crust up distillation equipment, TSSE is not hampered by the presence of complex contaminants, making it able to handle wastewater from a broad variety of sources, including produced water from oil-and-gas extraction, mine tailings, desalination effluent and industrial waste.
Cetos Water has extensively laboratory-tested TSSE and is working to build a system that can produce 1,000L/day of purified water in the coming months.