California Using Subsurface Brackish Water for Irrigation

June 7, 2015

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June 7, 2015 – Renewable desalination is allowing California to recover irrigation water, clean it and reuse it for crops. In charge of the project, an independent water producer named WaterFX.

What is renewable desalination?

An evaporation technology that draws power from a concentrated solar still to clean brackish drainage or water pumped from salt saturated aquifers. For every 100 liters of water, 93 are fully recovered leaving 7 liters of salt brine. Even the salt brine is harvested for commercial use.

The system is close-looped allowing the water and precipitated salts to be recycled. Because power is derived from a solar thermal array its carbon footprint is virtually zero. The water it uses is local and a resource that in the past has been allowed to drain away.

In an article posted in The Fresno Bee yesterday, entitled “Who needs an ocean? San Joaquin Valley projects give new life to salty water,” the writer, Mark Grossi, describes the WaterFX facility, “a mirrored solar array longer than a football field, collecting heat to boil salt and other impurities out of irrigation drainage.”

Instead of expensive coastal desalination technology and a complex infrastructure for pumping the water these plants produce to where it is needed inland for farms in the San Joaquin Valley, this technology derives all of its water locally. Considering the value of farm produce produced here annually, worth $37 billion US, desalination using this technique could prove an industry lifesaver.

And there is no shortage of brackish water to draw from. According to the U.S. Geological Survey, significant volumes of salty aquifer are trapped in the clay layers that underlie the valley floor. This water isn’t as salty as ocean water but without renewable desalination is unfit for irrigation.

WaterFX calls its system, Aqua4. The current pilot project features a 115 meter (377 foot) mirrored solar array, called a Sky Trough, that focuses heat on a tube filled with mineral oil. The oil is heated to 350 Celsius (660 Fahrenheit) and that energy is then transferred through a heat exchanger to the salt water where it produces steam which then gets distilled into pure freshwater. The pilot which is a zero-carbon technology will produce 2.7 billion liters (717 million gallons) of freshwater annually. The water because it is distilled will need to have minerals added to it but that is a small inconvenience considering the economic advantages and benefits it will bring to the river valley’s hard pressed agricultural sector which you know, if you have been reading this blog, is seriously stressed after four years of continuous drought.

WaterFX hopes to implement 35 Aqua4 installations. Expected project lifespan for each is thirty years.