Landlocked No More: Desalination Goes Inland

Brian Clark Howard | Tue Jan 3 2012 |

“In my neighborhood in Amman, Jordan, we only have eight hours of water service a week during the summer,” Amer Sweity says.

Sweity, 30, is working on his PhD in desalination technology at the Zuckerberg Institute for Water Research at Ben-Gurion University of the Negev in southern Israel, where he is the first Jordanian doctoral student at the university.

“Sometimes we have to wait weeks for it to come. But when you have kids, they need to drink, so then you have to buy it from trucks—and it’s expensive.”

Jordan is one of the world’s most water-stressed countries. With more than 10 million Israelis and Palestinians relying on two main aquifers and the heavily tapped Sea of Galilee-Jordan River system, the king of Jordan has warned that there may one day be a war over this vital resource.

Sweity wants to help solve this problem by using the knowledge he’s gaining in Israel to build the first desalination plant in Jordan.

Desalination 2.0

For years, desalination has been seen as an answer to the world’s growing water woes, but the process has historically been expensive, highly energy intensive, and has resulted in salty waste that has sometimes caused problems. What’s more, desalination plants are traditionally located on the coasts, making it difficult to move water inland—especially for landlocked countries like Jordan.

In response, Jack Gilron—an expert on inland desalination and one of Sweity’s advisors at the Zuckerberg Institute—and his team have built pilot plants on a semi-industrial scale to test the feasibility of a new inland desalination system.

The department demonstrated 97 – 98 percent recovery of freshwater from saltwater, compared to the current industry average of around 80 percent.

As with many other desalination plants and water filters, the core technology is reverse osmosis. In this process, water is pushed through a selectively permeable membrane, which blocks salts and many undesirable chemicals but allows water molecules to flow through.

In the past, dealing with the resulting wastewater has been a challenge. “Inland desalination has a terrific problem with salt concentrate,” Gilron says. “Plants on the coast can dilute the concentrate easily back into the sea, but if you put it on the ground you will destroy the soil.”

The Zuckerberg Institute Desalination and Water Treatment Department combines use of reverse osmosis and electrodialysis technologies. The department demonstrated 97 – 98 percent recovery of freshwater from saltwater, compared to the current industry average of around 80 percent. Another technology being developed by Gilron uses reverse osmosis alone to increase recoveries up to approximately 92 percent. This slashes the amount of salty brine left over, meaning there is less pollutant to store or process.

Switching the flow

The secret to the improved reverse osmosis technology is a system of valves and ultrasound sensors that reverses the flow of water being treated in the desalination plant before the salt has time to start precipitating out onto the exchange membrane. “It’s like zeroing out the clock, or juggling,” Gilron says.

Most plant operators use anti-scaling compounds to prevent that precipitation, but that only works for so long: up to about 80 – 85 percent water recovery, depending on the composition. But after that, the membrane starts to get clogged. By keeping ahead of precipitation, the new system can achieve higher recovery rates, while still generating a steady stream of freshwater.

Gilron explains that the valve switching normally occurs on the time frame of “a few hours to a few days.” He says the innovation saves about nine cents per cubic meter of recovered freshwater, or roughly $32,000 a year for a small inland desalination operation.

At Rotec Ltd.—the company Gilron’s group spun off to commercialize the technology—they’re retrofitting flow reversal onto an existing desalination plant to increase recovery from 80 percent to 92 percent and decrease brine volume from 20 percent to eight percent of the original feedwater.

Gilron’s team has also developed machines that take advantage of the desert breezes to dry out the salt, creating a solid salt to store in landfills or put to use.

The flow-reversal technology, together with ultrasonic triggering, was co-developed with researchers at the University of Colorado and received funding from NATO’s Science for Peace and Security program. Gilron’s group has secured a patent with three more patents pending. Rotec Ltd. is currently developing and marketing the technology to manufacturers for use in small inland desalination plants around the world.

Salty solutions

So what happens to the small amount of waste brine that is produced by the flow reversal process? Gilron’s team has also developed machines that take advantage of the desert breezes to dry out the salt. Vaguely resembling desert coolers, they increase the evaporative surface 40 times, according to Gilron, so it dries out faster.

The end result is solid salt, which then can be stored in a landfill or put to use somewhere else.

The flow-reversal process doesn’t eliminate all of the concerns with desalination; it still takes a hefty amount of energy to run the pumps. The group is working with other researchers at Ben-Gurion to pair the plants with efficient concentrated solar power, to provide a renewable option.

It’s also true that reverse osmosis isn’t able to remove all potential contaminants from water, particularly when it comes to complex and low-concentration chemicals like pharmaceuticals, pesticides, and industrial solvents. But those issues also threaten conventional water supplies.

Water for peace

Sweity is continuing to work with the Zuckerberg Institute and remains focused on tapping the vast aquifers of brackish groundwater that geologists say underlie his home country of Jordan. Ultimately, he hopes desalination can lead to more peace throughout the region.

A practicing Muslim, Sweity admitted, “It’s complicated for an Arab to come to Israel to study. Some friends cut you off. But by helping serve the environment, we can try to bridge the gap. Water is crucial for all of us.”