Water security is becoming an urgent global challenge. Hundreds of millions of people already live in water-scarce regions, and the UN projects that by 2030 about half the world’s population will be living in highly water-stressed areas. This will be a crisis even for developed countries like the U.S., where water managers in 40 states expect freshwater shortages within the next 10 years. As the global population and GDP grow, so will the demand for freshwater. And, with the continuing rise of global temperatures, water shortages will only get worse.

Desalination processes are increasingly being relied upon to augment water supplies. In fact, global desalination capacity is projected to double between 2016 and 2030. But these processes are expensive and can be harmful to the environment. The ultrahigh salinity brines that are the byproduct of desalination can be several times that of seawater salinity and its management options are especially challenging for inland desalination facilities such as those in Arizona, California, Florida, and Texas.

Over the past year, Columbia Engineering researchers have been refining their unconventional desalination approach for hypersaline brines—temperature swing solvent extraction (TSSE)—that shows great promise for widespread use. TSSE is radically different from conventional methods because it is a solvent-extraction-based technique that does not use membranes and is not based on evaporative phase-change: it is effective, efficient, scalable, and sustainably powered. In a new paper, published online June 23 in Environmental Science & Technology, the team reports that their method has enabled them to attain energy-efficient zero-liquid discharge (ZLD) of ultrahigh salinity brines—the first demonstration of TSSE for ZLD desalination of hypersaline brines.

“Zero-liquid discharge is the last frontier of desalination,” says Ngai Yin Yip, an assistant professor of earth and environmental engineering who led the study. “Evaporating and condensing the water is the current practice for ZLD but it’s very energy intensive and prohibitively costly. We were able to achieve ZLD without boiling the water off—this is a major advance for desalinating the ultrahigh salinity brines that demonstrates how our TSSE technique can be a transformative technology for the global water industry.”

Yip’s TSSE process begins with mixing a low-polarity solvent with the high salinity brine. At low temperatures (the team used 5 °C), the TSSE solvent extracts water from the brine but not salts (which are present in the brine as ions). By controlling the ratio of solvent to brine, the team can extract all the water from the brine into the solvent to induce the precipitation of salts—after all the water is “sucked” into the solvent, the salts form solid crystals and fall to the bottom, which can then be easily sieved out.