Self-desalinating sea water takes the pressure off industry

Scientists at Murdoch University have invented a ‘self-desalination’ system that requires no electricity at all and is carbon neutral.

Current methods of desalination employed across the globe consume extremely large quantities of electricity in order to apply the high amount of pressure required as part of the process. As noted by Murdoch’s Dr Ralf Cord-Ruwisch, “The high cost associated with desalination is primarily due to the high pressure that must be applied to sea water in order to separate the water and salt from one another in the process of reverse osmosis.”

Now, together with Professor Liang Cheng, Dr Cord-Ruwisch has devised a ‘self-desalination’ concept that uses pressure generated by highly concentrated salt brine as the energy source to desalinate the less salty sea water. The merits of the concept have been evaluated by a research team led by Professor Wendell Ela.

“Normally, we use electricity to pressurise the water and drive reverse osmosis,” Professor Ela said. “Ralf and Liang’s device skips the electricity step, so it’s not only simpler, but the environmental impact is immediately smaller.”

PhD student Ivonne Tshuma has been working with the team to gather data and mathematically model the process to enhance the design of the original prototype. She said concentrated salt brine is the ‘secret ingredient’ to the system’s success, which replaces the need for a pump to apply the necessary pressure to the sea water.

“The pressure generated between the concentrated brine and the brackish water pushes brackish water through the membrane, producing drinking quality water,” Tshuma said. “The result is that the salt is left behind in one chamber, while desalinated water is produced in the other.”

Once her research is complete, Tshuma is hoping to work with a company to fabricate the desalination system in commercial quantities, so it can benefit remote communities throughout the world which have limited access to water and power.

“As the result of my research, I am so confident that it is possible to produce potable water from brackish water and possibly even sea water without the need for electricity,” she said. “My next steps are to rebuild the device on a larger scale so it can be taken out of the lab and then trialled in a remote location to see if it can meet the water requirements of a small household.”

The research team believes the process could have impact in areas where salt lakes are located near brackish water sources or the coast, such as in regional Australia or as an extreme example, Lake Garabogazkoel in Turkmenistan.

“These areas have access to large amounts of salt brine to provide the fuel needed to complete the process of seawater desalination — with the resulting products being potable water and a somewhat diluted brine, which goes back out into the salt lake for continued concentration,” Dr Cord-Ruwisch said.

“In principle, this could allow for the use of renewable energy from solar evaporation, without the intermittency problems associated with other renewable energy sources.”

The team is currently seeking an industry partner to help them develop a customised membrane for use in their desalination device.

Image caption: Third-year PhD student Ivonne Tshuma, Dr Ralf Cord-Ruwisch and Professor Liang Cheng have researched and developed a revolutionary way of desalinating saltwater without the need for electricity.