Researchers Seek Cheaper, Energy-efficient Ways of Producing Clean Water

Having enough clean drinking water has been a challenge in many parts of the world, whether it’s a place where water is scarce or abundant. The World Health Organization finds 3 in 10 people globally still lack safe drinking water at home.

The U.S. Department of Energy has just announced it is providing up to $15 million in funding for projects to develop solar desalination technology to create freshwater at a lower cost. Even before the announcement, researchers had been working on better ways to desalinate water.

“We can take any quality of water that we’re starting with and we can turn it into any quality of water that we desire at the end, and the only real challenge or limitation has to be overcome is how much does it cost and how much energy does it take to go from here to here,” said Eric Hoek, co-founder and Chief Executive Officer of Water Planet Inc.

Cheaper energy

Water treatment plants are largely driven by electricity. A cheaper source of energy is the sun.

“What’s changed in the last five to 10 years, solar has gotten cheap,” Hoek said.

“The only reason that that has not taken over the world at this point is that it’s still intermittent. The sun goes up and it comes down. You have power when it’s up and don’t when it’s down. What you need to make that a continuous base load is you need batteries, which you can charge up during the day, discharge at night, and the cost of batteries is still currently pretty high.”

Household system

Qilin Li at Rice University is building a desalination system that uses solar energy with broad drinking water applications for “individual households or small communities that live in remote locations, especially those who don’t have access to municipal water supply, don’t have a stable supply of electricity. This technology can be an ideal technology,” Li said.

Her solar-powered desalination system can “also benefit megacities in developing countries that don’t have the extensive water and power infrastructure we enjoy here in developed countries, and that kind of relief perhaps in not providing all the water for the whole city, but can relieve some of their need or dependency on the power grid,” Li said.

The goal of Li’s system is to make it modular and cost efficient so it could either meet the needs of a small household or a large community.

Li and her team created a reactor to distill water using heat from the sun. Water turns into vapor, goes through a porous membrane and becomes pure water. Li says a low cost coating on the membrane developed at Rice University makes this unique.

“So it (membrane) harvests the sunlight, converts the photon energy in the sunlight to heat highly efficiently to generate water vapor, and it also serves a separation function to keep the contaminants on the dirty side of the membrane and only allow pure water vapor to go through,” Li said.

Waste heat

The sun is not the only low cost source of energy. Amy Childress’ lab at the University of Southern California (USC) looks at how waste heat that comes from manufacturing can be used as a resource.

“With waste heat you’re going to have cycles and spikes. We’ve gone out to the field, measured waste heat at an industrial site. We come back. We plug that into our system, so that we can repeat that waste heat curve over and over and watch the response of membranes to the waste heat,” said Childress, who directs USC’s Civil and Environmental Engineering Department’s environmental engineering program.

Her lab looks at how waste heat would impact the longevity and properties of a membrane.

Childress says the work in her lab will be helpful in the development of better membranes.

Filters in demand

There is high demand for membranes that help produce clean water. Water Planet’s PolyCera® membrane used to treat wastewater, is finding broader applications.

“We have a lot of interest now around the world, not just in industrial wastewater, but we’re actually making point-of-use under-the-sink water filters for applications in India, in China and here in the U.S. We’re making membranes that are being tested now for deployment offshore in sea water desalination to produce drinking water in barges and in platforms,” Hoek said.

With nearly 30 percent of the world’s population lacking safe drinking water at home, researchers will continue to work on harnessing free energy to clean water.
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