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Drought Tech: How Solar Desalination Could Help Parched Farms

| May 9, 2014 | 4 Comments
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By Alice Daniel

Farmers on the western side of the San Joaquin Valley can count on two things: sunshine and water that’s polluted and salty where minerals have built up in the soil. Now a Northern California entrepreneur is using one to clean up the other in the Panoche Water and Drainage District near the little town of Firebaugh, about 50 miles northwest of Fresno.

This solar desalination plant uses curved mirrors to capture the sun's energy and separate the salt from the water. (Alice Daniel/KQED)

This solar desalination plant uses curved mirrors to capture the sun’s energy and separate the salt from the water. (Alice Daniel/KQED)

It’s called a “drainage district” because farms around here have to get rid of excess salty irrigation water, explains ranch manager Wayne Western (yes, that’s his name). An elaborate system of underground drains and pumps collects the runoff. The district then recycles that water on 6,000 acres of more salt-tolerant crops.

“These are pistachios right here, they’re 13 years old,” he says, walking through an orchard that’s getting some of the reclaimed water.

“The district is doing this for its growers because if they didn’t, at some point you’d have to retain your own runoff water,” says Western. “If you’ve got nowhere to go with it, after awhile, you’re not going to be growing anything in that ground.”

‘Not in our wildest dreams did we ever think we could have revenue generated from this wastewater.’

The residual water is laden with salts and other contaminants such as selenium, which is toxic in high concentrations. The district reuses this water not only on pistachios, he says, but also on another salt-tolerant crop, Jose tall wheatgrass.

“Our whole goal here was to get rid of the wastewater,” says Dennis Falaschi, who runs the district. “Not in our wildest dreams did we ever think we could have revenue generated from this wastewater.”

The revenue comes from selling the wheatgrass, which is used for cattle feed, and the pistachios. As it turns out, cattle need a certain amount of selenium. But there’s still the problem of the brackish runoff from these salt-tolerant crops. By 2016, environmental regulations will put a stop to dumping it into the San Joaquin River. Falaschi says finding another solution is paramount, if tricky.

“Over the course of the last 15 years, we must have tried out 20-to-25 different treatment processes and you know, you end up spending a lot of time and a lot of hours on something that just doesn’t work,” he says.

But now there’s one idea that’s starting to look a little brighter. Falaschi points to a row of curved mirrors that stretch out near a field of wheatgrass.

“The equipment that we’re looking at here — with the exception of the solar panels — is pretty much shelf-item stuff,” he says. “I mean, you know, you’re looking at a boiler, and then you have a plumbing system that actually runs through.”

‘If we can treat this water, we’ve managed our drainage problem, but we’ve also created supplemental water.’

It’s an experimental solar desalination plant, funded by the district with a million-dollar state grant. The project looks a bit like a spaceship on this vast expanse of land.

“If we can treat this water, we’ve managed our drainage problem, but we’ve also created supplemental water,” says Falaschi. “That’s why we’re excited.”

“It’s actually a lot like back when you were a kid and you would play with a magnifying glass on the sidewalk to burn things,” explains Aaron Mandell, the founder of WaterFX, which designed the solar plant. “We don’t actually burn things but it’s the same concept; you concentrate solar energy and you can generate very high temperatures.”

An absorption pump that Mandell and his team designed reduces by half the energy it takes to evaporate water. The project also uses a reflective mirror-like film to focus the sun on long tubes containing mineral oil. The heat from the oil is piped into evaporators to generate steam.

“So the heat that we generate from the sun basically separates water and salt,” he says. The process produces potable water which the company can then sell, along with some of the minerals distilled out, like selenium and even boron. The project is timely with California three years into a drought, but Mandell says, that wasn’t his motivation.

‘Even if the drought were to end right now, we would still need desalination as a more reliable source of water going forward.’

“Even if the drought were to end right now, we would still need desalination as a more reliable source of water going forward,” he says. “Because the real problem is that the water supply in California and many of the Western states is actually no longer reliable.”

WaterFX will soon build a much larger plant, this one funded by investors. It’s slated to treat about 2 million gallons a day. Mandell says it will cost about $450 to produce an acre-foot of water. That’s more than farmers here pay for surface water but about half the total operating costs of a conventional desalination plant that uses reverse osmosis.

Dennis Falaschi says his water district will provide the 75-acre site and probably be the main customer. Farmers this year received no water from the federal Central Valley Project, so the onus, he says, is on Water FX.

“You showed us the baby steps you can perform. Now go out and do the big steps,” says Falaschi. “And if you perform? That’s why the world goes around. I get water, you get money.”

Alice Daniel reports out of The California Report’s Central Valley bureau.

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Category: Chemistry, Engineering, News, Water

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KQED Science brings you award-winning science and environment coverage from the Bay Area and beyond by the flagship Northern California PBS and NPR affiliate.
  • Mace2009

    Not described is a key part of the proposal: What happens to the left over brine? Part of the reason these salts are building up in groundwater is that they have no where to go. The salty waste water from this desalination still needs disposal, and if it is not taken out of the watershed, then the salts go right back into the ground and the groundwater.

  • cetude

    Desalination is not an old concept – in fact, it’s easily done with distilling. The problem is what to do with the leftover salt..It makes matters much, much worse.

  • DiscusBS

    I hope to see more of these in the southern San Joaquin. It is good to see agriculture take some responsible actions towards correcting long term problems. Brine can be further dried or trucked directly when a significant volume is accumulated.

  • eladz

    hmm all that salt what to do with it ? someone built a hotel I believe