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Healdsburg’s Aaron Mandell wants to build a $30 million desalination plant in the San Joaquin Valley that would use the warmth of the sun to distill former irrigation water and reuse it on thirsty farms.

Mandell, an engineer and former Boston resident who has helped start a half-dozen companies, is the second Sonoma County entrepreneur with a business that takes an unorthodox approach to desalination — and who sees opportunity in a historic drought for boosting fresh water supplies.

“I don’t think the problem is going away anytime soon,” said Mandell, chairman and co-founder of WaterFX, a startup that now operates a trial plant in remote farmland along Highway 5 about 60 miles west of Fresno.

The solar distillation plant’s most striking feature may be its SkyTrough, a curved, reflective channel longer than a football field that can heat a pipe filled with mineral oil to roughly 660 degrees Fahrenheit. That is far hotter than needed to distill water that has been tainted not only with salt but also with such chemicals as boron and selenium.

With water shortages seemingly a way of life, California should imitate Israel in using desalination so successfully that it could become a water exporter, Mandell said. But the state’s businesses and municipalities need to do so in a way that doesn’t increase greenhouse gases and exacerbate climate change.

“The way to do that is to use a clean energy source that’s truly sustainable,” he said. For Mandell, sunshine fits the bill.

Four years of drought are prompting Central Valley farmers to look for new ways to meet their water needs.

“I think everybody is trying to stretch the supplies every way they can,” said Jennifer Bowles, executive director of the nonprofit Water Education Foundation in Sacramento. She recently spoke to a farmer who not only installed drip irrigation but also put up photovoltaic solar panels in order to provide the electricity needed to operate the new water system.

The challenge of finding adequate supplies of water is hardly confined to the Golden State.

Global water consumption is expected to increase 55 percent between 2000 and 2050, according to Securing Water For Food, an international coalition that includes the U.S. Agency for International Development and U.S. Bureau of Reclamation. As well, the United Nations estimates that by 2025, 1.8 billion people will live in areas with water scarcity, and two-thirds of the world’s population will face “water stressed conditions.”

To boost supplies, about 16,000 desalination plants have been built around the world. The prevailing technology involves reverse osmosis, which uses intense pressure and filtration to separate salt from water. But other methods are under trial, and their boosters insist that they can provide clean water while greatly reducing energy costs.

Desalination is often pictured as a process of drawing drinking water from the world’s oceans, the purpose of a $1 billion plant under construction on the coast at Carlsbad in San Diego County. But some entrepreneurs and experts see a greater opportunity in purifying brackish groundwater.

“It’s going to be much, much bigger than seawater desalination,” predicted John Webley, CEO of the Petaluma-based desalination company, Trevi Systems.

Webley, a former telecom company founder and the owner of Santa Rosa’s landmark McDonald Mansion, said brackish water requires far less energy to make potable than seawater.

His 5-year-old company has about 30 employees and is testing its “forward osmosis” desalination technology in the United Arab Emirates, Kuwait, Southern California and near San Francisco Bay.

Mandell, who moved with his family to Healdsburg two years ago, also spends his days as CEO of Seattle-based AltaRock Energy. That company in 2009 briefly conducted experimental drilling at The Geysers geothermal fields in northern Sonoma County.

Mandell formerly helped found Oasys, a company that has worked in forward osmosis desalination. And this spring Quidnet Energy, an energy storage startup in which Mandell is a co-founder and investor, announced it has received seed funding from various philanthropists, including the foundation of actor Will Smith and actress Jada Pinkett Smith.

A common thread among these companies is the nexus between water and energy and how it typically takes one to process or produce the other, Mandell said.

Founded three years ago, WaterFX has four employees and plans to open a main office in San Francisco, he said.

The company’s trial distillation plant, built with a $1 million state grant, lies near the Fresno County town of Firebaugh on land of the Panoche Water and Drainage District. The WaterFX plant is able to take former irrigation water and remove salts and other chemicals at the rate of 10 gallons per minute, or 14,000 gallons a day.

The trial plant functions by using the sun’s rays to heat mineral oil, which in turns heats and evaporates the water. The distillation system is able to clean and capture more than 90 percent of the processed water, Mandell said.

Dennis Falaschi, the water district’s manager, said the trial plant has shown excellent results, and he regularly fields calls from farmers elsewhere in the Central Valley wondering if it might help solve their problems. But to qualify as amazing technology, the system must be able to work on a much larger scale, he said, “and that’s what we hope to do in our next step.”

That next step, the proposed $30 million plant, would produce an estimated 2,200 acre-feet of water a year, or nearly 2 million gallons per day. Mandell said he would like to eventually expand annual production to 5,000 acre-feet, which he said could supply enough water for 10,000 homes or 2,000 acres of cropland.

To raise the needed funds, Mandell hopes within the next six weeks to begin seeking $10 million from investors who would purchase stock in the business via a state-sanctioned public offering. WaterFX plans to borrow the remaining $20 million.

The proposed plant is currently undergoing a required environmental review. Mandell said he hopes to begin construction by the end of the year and to have the plant in operation next summer.

Using desalination for irrigation is virtually unheard of in the United States, said Tom Davis, director of the Center for Inland Desalination Systems at the University of Texas at El Paso. For various reasons, agricultural irrigation is typically the cheapest of any water sold, making it hard to for desalination operators to compete.

As well, Davis said, he has yet to see large-scale success with alternative technologies to reverse osmosis systems. For example, purifying water through solar distillation has been known for over 2,000 years “and people are still struggling to make it worthwhile doing it,” he said.

However, Davis suggested that times may be changing. His university is working in partnership with a Louisiana engineer who is seeking to market a solar distillation technology to industrial customers.

Both that engineer’s work and the university’s own team over the past two years have been semifinalists in the Desal Prize, which is sponsored by Securing Water for Food. The international group seeks to encourage cost-effective, sustainable methods for providing clean water for people and farms in developing companies.

After placing second in the competition this year, Davis and the university team members plan to take their system to Latin America to purify groundwater for small farmers.

The Firebaugh area seems a natural place to try out the WaterFX plant. The farmers there don’t just want to clean up the water. They need to clean it.

Left undisturbed, the salty, spent irrigation water gets trapped underground and rises into the root zone, killing most plants. As a result, many farmers in the west San Joaquin Valley have placed perforated pipes about 8 feet beneath their cropland, Falaschi said. The pipes serve like a French drain to capture the water and remove it from beneath the farms.

But something still has to be done with the water. It once drained into the Kesterson National Wildlife Refuge west of Merced, but that stopped three decades ago after an outcry because waterfowl and other wildlife there were poisoned by the selenium-laden drainage.

After that, the San Joaquin River became a depository for the spent irrigation water, but efforts are underway to end such discharges. They include a new, $30 million reverse osmosis plant that the U.S. Bureau of Reclamation has built at the Panoche water district, Falaschi said. In early operation, it was able to clean water at a rate of about 250 gallons per minute.

Danny Merkley, director of water resources for the California Farm Bureau Federation in Sacramento, said new technology like the WaterFX plant one day may provide two benefits to California: Cleaning water more efficiently for reuse while preventing a build-up of salts on prime farmland, thus allowing it to continue to help feed a growing global population.

“I would think processes like this one would be a great way to keep valuable land in production,” Merkley said.

Mandell estimated the Central Valley may annually produce 1 million acre-feet of spent irrigation water that could be cleaned and recycled, perhaps allowing its reuse multiple times.

For its proposed Firebaugh plant, WaterFX estimates it can sell the processed water back to farms for about $450 an acre-foot. That would be higher than the cost of federal-supplied Central Valley Project water, when available, but still a price that Falaschi said could be attractive for farmers of such high-end crops as almonds, pistachios, wine grapes, melons and fresh-market tomatoes.

In order for WaterFX to make a major impact, Mandell said, “we think you have to get to small scale first.” By that he means he wants to build desalination systems small enough to be able purify water for individual farms.

He likened the approach to the installation of solar systems that have become common on California roofs. The individual systems combine to produce a significant amount of electricity.

“We think the same thing can happen with water,” he said.

You can reach Staff Writer Robert Digitale at 521-5285 or robert.digitale@pressdemocrat.com. On Twitter @rdigit