Sterling Water, NMSU Create Low-cost Desalination

Sterling Water LLC and Arrowhead Center, Inc. concluded license agreement negotiations to accelerate the break-through low-cost water desalination system developed by New Mexico State University (NMSU) engineers.

The zero-emission technology can convert saltwater to pure drinking water on a round-the-clock basis – and its energy needs are so low existing solar technology or even the waste heat of an air conditioning system could power it, according to a company press release.

A successful proof-of-concept model was developed last year confirming suspicion that the innovation represented a major step in the sustainable desalination industry. The NMSU-led project transferred the science and prototype model from lab bench to a market capable product. The research team, led by Nirmala Khandan, Ph.D., in the College of Engineering, discovered an entire paradigm shift. The inaugural unit produced more than 200 gallons per day or enough pure water to meet the need for about 15 people.

Kevin Boberg, Arrowhead Center chief executive officer, traces the origins of the technology to a process, first developed by researchers in Florida, that makes distillation of saline water possible at relatively low temperatures – 45 to 50 degrees Celsius (113 to 122 degrees Fahrenheit) rather than the 60 to 100 C (140 to 212 F) required by most distillation processes.

The system uses the natural effects of gravity and atmospheric pressure to create a vacuum in which water can evaporate and condense at near-ambient temperatures. The vacuum is created between two 30-foot vertical tubes – one rising from a tank of saline water and the other from a tank of pure water – connected by a horizontal tube.

“Nature will always seek equilibrium,” George Forbes, managing director of Sterling Water, explained. “The contrasting fresh and salty water pools will seek to be the same at normal temperatures. The trick is to drive the reaction to our desired outcome.”

A nominal increase in the headspace water temperature induces the flow to go in the fresh water direction, so that pure, distilled water collects on one side and the brine concentrate is left behind in a separate container. A temperature increase of only 10 to 15 degrees is needed.

The result is that you can use low-grade heat like solar energy or waste heat from a diesel engine, refrigerator, or air conditioner. The configuration adapts to various existing heat sources and liberates the product from the conventional infrastructure like electricity. Sterling Water’s version is powered by a solar panel. Forbes noted, “We favor solar power since the spare energy also drives pumps that manage the source water and we can store energy overnight to maintain continuous production.”

As with any desalination process, the system leaves behind a brine concentrate that must be disposed of, and some potential users may be put off by the unit’s height. Sterling Water intends to address these two issues with their next generation commercial version they are readying for the market. “When you aggregate the entire process from end-to-end, the overall cost of desalination by this process becomes almost insignificant which opens the possibilities in uses never before thought possible. We believe this changes the game for our planet...” Forbes said.

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