In legend and in practice, turning saltwater into sweet water is old news. Aristotle mused about desalination in the fourth century B.C. In the second century, sailors boiled seawater and collected the fresh condensate in sponges — the first documented desalination system. Even the Old Testament mentions desalination, albeit divinely accomplished. Today, thousands of desalination plants in 150 countries produce almost 30 billion gallons of fresh water every day — a testament to their effectiveness. The United States’ largest desalination plant, located in Carslbad, California, produces 50 million gallons daily.
But desalination is, arguably, the most expensive of all water supply alternatives. The expense of just building a large plant can exceed $100 million. Once the fresh water flows, it must be pumped at great cost to distribution points. At an overall cost of $3 to $4 per 1,000 gallons, desalination is considerably pricier than options such as storm-water recovery and water recycling and reuse. And both of the dominant desalination technologies — thermal and membrane — require enormous energy input.
“Climate change has made many wet places a lot wetter and many dry places much, much drier,” said Bahman Abbasi, assistant professor in at the campus in Bend. “If we had the ability to desalinate water exactly where people are struggling to get enough clean water, we could ease a lot of needless suffering.”
A novel desalination system devised by Abbasi offers a better solution. Supported by $2 million from the Department of Energy — the largest award in OSU-Cascades history — Abbasi is leading a team of researchers to develop a modular, portable, self-contained desalination plant. The group includes investigators from Michigan State University, the University of Maryland, and the University of Nevada, Reno.
In Abbasi’s system, high-speed air jets atomize and evaporate incoming saltwater. “It’s like if you blow too hard into a bowl of soup and it splashes all over the place,” he said. “Later in the process, we dehumidify the air so the fresh water condenses out, and we collect the salt separately.”
By comparison, traditional evaporative desalination requires powerful blowers and high-pressure pumps that hog energy. Abbasi emphasizes that the new system, though it is a type of thermal desalination, does not distill water. Rather, it humidifies and dehumidifies air. That little distinction means far less energy consumption. In addition, most of the heat that powers the process is recovered, so very little energy is wasted.
Each desalination module will measure about the size of an office desk. Multiple units mounted onto vehicles could be transported to the point of consumption, as long as there’s access to saltwater. The water intake pumps will draw their power from onboard solar panels, while the desalination phase will run on heat from solar collectors.
“Once desalination starts, the process becomes entirely thermally driven,” Abbasi said. Output can be regulated by adding or removing modules.
The system will be capable of handling water with extremely high salinity — perhaps 30 percent or more. (For reference, seawater contains about 3.5 percent salt.) Because the modules are able to process high concentrations of salt, the system could be used as the final stage at some existing desalination plants to wring out the last drops of water. Generally, desalination plants return some residual, highly concentrated brine to the ocean, which can devastate marine life. But Abbasi’s design will result in “zero liquid discharge,” meaning the only byproducts are fresh water and salt solids — most importantly magnesium chloride, the principal precursor to magnesium metal and a saleable commodity.
Abbasi predicts that a working prototype will be up and running in about three years.
In addition to the obvious impact that water shortages have on individuals and communities, they carry geopolitical ramifications as well. In 2012, the U.S. intelligence community issued a report on global water security that warned of political instability — even open conflict — arising from water scarcity in developing nations.
"Thousands of people die every month because they don’t have potable water. It’s a huge problem around the world,” Abbasi said. “I have this idea of gutting an old school bus and retrofitting it with desalination modules. Without any need to connect to the electrical grid, we could take it almost anywhere and make fresh water accessible to poor, drought-stricken areas of Northeastern Africa, for instance, where there’s lots of coastline and lots of sunlight for power. That’s my vision. That’s my goal."
MOMENTUM, College of Engineering, Winter 2019
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