Water Scarcity

Pratiksha Dongare has developed a system that effectively removes salt and other minerals from brackish water using solar energy and nanophotonics. (Credit: Courtesy of Pratiksha Dongare) Editor's Note: Pratiksha Dongare is a winner of The Story Exchange's first annual Women In Science Incentive Prize. Pratiksha Dongare ran her first real-world science experiment in ninth grade. In Karanja, her hometown in central India, she engineered “soak pits” to treat wastewater sustainably, testing materials like sand, charcoal, grass, coconut husks and earthen pots. That ambitious project launched her career as a scientist looking for creative solutions to intractable issues adversely impacting humanity. “I always wanted to do research in something that will help the world but I had no idea how I do it. I just had this willingness that I want to do something on that path,” she says. Since then, Dongare has fueled that drive to do good with advanced degrees in applied physics, leading to major innovations in water purification and, more specifically, solar-driven desalination. That need has grown steadily over the past decade or so due mainly to population growth and drought in places already water-stressed. Roughly 300 million people in 183 countries now rely on about 20,000 “de-sal” plants worldwide from drought-stricken California to water-starved Saudi Arabia, according to the nonprofit International Desalination Association. Regardless of where they are, de-sal operations present similar challenges — they are costly, inefficient and/or energy-intensive. Of the two main types of commonly used de-sal techniques, the most widely used is reverse-osmosis, when saline water percolates through a membrane to become fresh water, which is expensive and wasteful. The other is a thermal process through which heated water passes, condensing into clean water on the other side. The technique works fairly well but it uses a lot of energy, and often fossil fuels, meaning major carbon emissions. That’s where Dongare’s cutting-edge work in solar desalination comes in. Over the past several years, she and her team at Rice University have developed a system that effectively removes salt and other minerals from brackish water using solar energy and nanophotonics (harnessing light on the scale of nanometers) to supply thirsty places with potable water. It works by using membranes coated with inexpensive, sunlight-absorbing nanoparticles that transform the filter into a super-efficient heat source. The process increases the output of purified water by 50 percent without using fossil fuels. Unlike traditional de-sal plants that rely on conventional electricity and the infrastructure that supplies it, Dongare’s device is also potentially useful in remote areas, on a domestic and community scale. Not satisfied with those advancements, Dongare figured out how to capture and use the abundant energy generated during that phase change, when the water cools from vapor, to keep the system running off the grid, reliably, and long after nightfall. That technology, called Solar Thermal Resonant Energy Exchange Desalination, or STREED, is membrane-free and can — at least in theory — pump out over 26,000 gallons of freshwater per day. Dongare and her colleagues at Rice are now partnering with the Austin-based startup, Localized Water Solutions, to scale up the technology and bring it to the marketplace. Addressing global water shortages has been a driving force in Dongare’s research for several years, in part because it was important to her ninth-grade self, who used to do science experiments with her father. In her hometown, she says, “there was water scarcity growing up, so one place that we lived, we would get water once a week. And we would fill up every container that we could find in our home.” Despite the lack of opportunities for, and expectations of, girls in her hometown, Dongare’s parents believed she could be a change agent and a force for good. “There are lots of restrictions that I still see now. When I look back, I feel that was very unfair,” she says. “I was very fortunate to have parents who, though they lived in such a small place, they saw the potential in me that I didn't realize at that time. Now I feel very fortunate that they let me do whatever I wanted to do and that was a big thing.”

Water Scarcity

Using Solar Energy to Purify Water

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