A solar-powered desalination plant should begin producing water from an aquifer in Arizona that’s clean enough for livestock to drink by early 2014. It’s the latest step in efforts to develop an off-grid water treatment system that can produce clean drinking water for rural communities in the Navajo Nation, a semi-autonomous Native American region covering parts of Arizona, New Mexico and Utah. Currently, drinking water must be hauled in from miles away.
Following a proof-of-concept study by the University of Arizona, the pilot will scale up the technology to increase the volume of water processed. The aim is to provide enough drinking water for Navajo ranchers’ livestock – about 100 gallons a day. Ultimately, the process will be further developed so that it produces water clean enough for human consumption. The local Native American communities will maintain and run the system once it is completed.
The plant will process water from an aquifer tens of metres underground. The water is brackish (briny), with a total dissolved solid content between 1000 and 3000 parts per million. To make it drinkable for livestock, the water quality needs to be improved by around a third, which means mixing distilled water processed by the plant with poorer quality water drawn from a well.
The process uses electricity from solar PV panels to pump the brackish water up from the aquifer, and heat from solar thermal panels to bring the water to almost boiling point. The heated water passes through a series of membranes that filter out the contaminants. Distilled water is captured for blending with the well water. Any excess brine is sent to an on-site evaporation pond.
The solar-powered pumping system supplies around ten gallons a minute. “It’s a good curve, with the productivity of the solar plant matching the peak demand, as the livestock need more water in the summer”, explains Mitch Haws, from the Phoenix area office of the Bureau of [water] Reclamation.
Cogenra, a company headquartered in California, is supplying the combined solar technology. “Water desalination powered by solar energy is developing into a huge market opportunity, whether it’s reverse osmosis-based desalination powered by photovoltaic-derived electricity, or solar thermal desalination”, says Mani Thothadri, Vice President of Product Management, Cogenra.
“Solar powered desalination has been studied for some time, but the cost of implementing this technology has been prohibitive”, adds Professor Stephen Gray, Director of the Institute for Sustainability and Innovation, Victoria University. “However, the decreasing cost of PV cells and the more ready availability of thermal systems, such as membrane distillation, is making it more attractive – particularly for small-scale systems where grid electricity is not readily available.” – Sara Ver Bruggen
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