US team develops desalination process for hypersaline brines

Engineers at Columbia University in New York City have developed a desalination method that they claim is more effective and efficient than existing processes

hypersaline brines
Illustration showing fresh water production from hypersaline brines by temperature swing solvent extraction. Image: Chanhee Boo/Columbia Engineering

The process has been developed specifically to treat the so-called hypersaline brines, produced through a range of industrial process such as oil and gas production.

These brines, which contain far higher concentrations of dissolved salts than ocean water, are challenging to treat, and present a growing environmental concern around the world.

Currently, hypersaline brines are desalinated either by membrane (reverse osmosis) or water evaporation (distillation). However, reverse osmosis methods are ineffective for high-saline brines because the pressures applied in reverse osmosis scale with the amount of salt: hypersaline brines require prohibitively high pressurisations.

Distillation techniques, which evaporate the brine, are very energy-intensive.

The process developed by the Columbia team, an approach described as temperature swing solvent extraction (TSSE) is claimed to be able to desalinate brines with up to seven times the concentration of seawater far more efficiency than existing methods.

Based on a separation method widely employed for chemical engineering processes, TSSE utilises a low-polarity solvent with temperature-dependent water solubility for the selective extraction of water over salt from saline feeds. Because it is membrane-less and not based on evaporation of water, it can sidestep the technical constraints that limit the more traditional methods. Importantly, TSSE is powered by low-grade heat (< 70 deg C) that is inexpensive and sometimes even free.

A study published in Environmental Science & Technology Letters describes how TSSE removed up to 98.4 per cent of the salt, which is comparable to reverse osmosis.

The findings also demonstrated high water recovery >50 per cent for the hypersaline brines, also comparable to current seawater desalination operations. But, unlike TSSE, reverse osmosis cannot handle hypersaline brines.

“Our results show that TSSE could be a disruptive technology – it’s effective, efficient, scalable, and can be sustainably powered,” said project leader Ngai Yin Yip, assistant professor of earth and environmental engineering at Columbia.

“We think TSSE will be transformational for the water industry,” he added. “It can displace the prevailing practice of costly distillation for desalination of high-salinity brines and tackle higher salinities that RO cannot handle. This will radically improve the sustainability in the treatment of produced water, inland desalination concentrate, landfill leachate, and other hypersaline streams of emerging importance. We can eliminate the pollution problems from these brines and create cleaner, more useable water for our planet.”

Yip is now working on further refining how TSSE works as a desalination method so that he can engineer further improvements in performance and test it with real-world samples in the field.