Sun, 18 May 2014 09:07:35 PDT
One of the drawbacks of desalination is the enormous amount of energy it takes to turn salt water into fresh water. A potential solution has launched in the dry heat of California’s Central Valley, where a pilot project is using solar energy to operate a new kind of desal system.
In San Joaquin Valley’s Panoche water and drainage district, where the experimental solar desalination project is based, the water is brackish—less salty than the ocean, but still too salty to be easily used for agriculture. Plants that can handle brackish water, such as pistachios and wheatgrass, dot the landscape, watered by reclaimed runoff. Salts from the soils accumulate every time the water is reused, and eventually the water becomes too salty to be usable.
That’s where the new technology comes in. The salty stuff can now be turned into fresh water by a row of curved mirrors that bend the sun’s rays, focusing it on long tubes containing mineral oil. The heat from the oil generates steam, which separates water from the minerals and salts. Because heat can be held in a thermal storage unit, the system can also run at night or when the sun isn’t shining.
Sound simple? At its core, it is. “Basically, all we’re doing is boiling water,” explains Matt Stuber, cofounder of WaterFX, the company that created the technology. “We’re distilling the water, capturing the heat in the steam so we can reuse it in a very efficient manner.”
With fresh water becoming more and more scarce from Israel to Australia, desalination technologies are popping up everywhere. Most use reverse osmosis, which pushes water through a series of membranes to squeeze progressively more stuff out of the liquid. That takes a lot of energy, and only about half the water going in comes out clean. The remaining sludge is a super-salty mixture that often gets discharged back into the ocean, which can have deleterious effects. WaterFX’s technique, on the other hand, makes 93 gallons of clean water for every 100 gallons of brackish water coming in. The remaining material comes out as a solid cake of selenium and salts that can be used as filler in building projects or fertilizers, or purified and sold as sea salt.
Another problem with reverse osmosis is that it only works well near the ocean. “The water chemistry in groundwater is very different from seawater, and the chemistry happens to be predominantly the things that are contribute to technology failures—the worst things you ever want to deal with,” says Stuber. WaterFX’s system only uses about a third of the energy of a similarly sized reverse osmosis operation, which makes the price competitive, Stuber adds.
In California’s Central Valley, where roughly a third of American produce is grown each year, the prospects aren’t good. The region likely won’t receive any water deliveries this year through the federal irrigation program, and the historical record indicates the potential for droughts that last a century.
Even if the current drought were to end, the salinization of the soil from decades of intensive irrigation is making more and more of the Valley into marginal cropland—making Stuber’s technology a potential fix regardless of what the weather does.
WaterFX plans to expand. The current pilot project can put out about 11,000 gallons of fresh water per day. If all goes well, the company will build a larger plant capable of producing 2 million gallons of treated water per day, which Stuber claims is at the lower end of the scale. The plant design is modular, so it only takes about six months to build a new one.
Stuber says he’s seen a lot of interest throughout the Southwest to produce clean and sustainable water for agriculture in dry regions. Agriculture consumes about 80 percent of California’s water to produce just 3 percent of its economic output—a ratio residents aren’t likely to tolerate as growth and a changing climate diminish supply.
“Using oil and gas just isn’t an option to produce water,” Stuber says.
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Original article from TakePart
- Nature & Environment
- California’s Central Valley
- brackish water