A Special Kind of Plastic Pipe Could Be the Solution for California’s Water Woes
When drought grabs hold of a region—as it has in epic proportions in California—desalination seems like an obvious way to get the freshwater we need for drinking, cooking, and irrigating crops. But the process of removing salt from saline water is pricey, typically costing twice as much as building a reservoir or recycling wastewater.
What if you could flip the process, extracting pure water vapor from saltwater?
That’s the approach U.K.-based Design Technology & Innovation took to develop a new irrigation system that pumps saltwater into underground pipes but only releases freshwater vapor into the soil—the salt remains trapped inside.
What’s the secret? A special kind of plastic dubbed Dutyion.
“We basically stumbled across a plastic with a particular ability to allow water vapor to pass through it, but virtually nothing else,” said DTI’s Mark Tonkin, who developed the application over a five-year period.
In the irrigation system, the pipes are installed underground and filled by gravity from saltwater tanks above. Plants receive freshwater from the water vapor that permeates through the pipe walls and then condenses. The pipes need to be flushed periodically to get the salt out, but pumping or pressurizing is not necessary.
Tonkin first tested the Dutyion Root Hydration System in 2007, growing vegetables inside a U.K. greenhouse. Soon after, the system was pilot tested in extreme conditions—providing water to 200 tree saplings in the desert in the United Arab Emigrates.
After one false start, all but two of the trees were growing and sprouting in a six-week period.
“It’s designed to be really simple and easy to operate,” said Tonkin. “It doesn’t require high tech or a lot of training to use.”
The company is also developing applications that use the Dutyion material to isolate wastewater contaminants inside the pipe, which can be used by industry and municipal utilities to extract freshwater from contaminated water.
Over the next several months, the company plans to release the first commercial units using Dutyion technology for “dewatering”—removing water in waste treatment systems.
“With this technology you can literally dry out industrial wastewater or sewage slurry,” Tonkin said. “You can take all the water out, and what you’re left with you can turn into valuable products such as fertilizer. In a lot of places around the world at the moment, it’s pumped straight into the sea almost untreated, and in other places it’s literally pumped into watercourses.”
“We’re in the process of the final design—the first commercial-scale design—of the first units to go out for use in the U.K. and in Kuwait,” Tonkin added. These will be tested as a way to refine the design before it goes on the global market.
Most of the first commercial units—which have been bought by private companies—will be used for dewatering, but at least one unit will be used to recover the water, he said.
Because the systems (housed in shipping containers) can only process about 10,000 liters of water a day, they’re more for supplemental or emergency use rather than a primary solution.
Tonkin said he can’t estimate the cost to install a Dutyion Root Hydration System because it depends how the technology is used, but he conceded that the plastic material is not cheap. He added that he expects the costs to come down after a larger volume of the material is produced.
Still, with freshwater becoming more expensive day by day, the cost element will become less of an issue, he said.