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A new desalination method for California water woes?

February 26, 2010 | 10:13 am

Chart_processThe Los Angeles Department of Water and Power’s rationing program has reduced the city’s water use to an 18-year low.  But Los Angeles’ long-term water challenges are well-documented. Why can’t the city take advantage of the sea to solve its water shortage?  Because conventional approaches to desalination, the removal of salt from water, are too energy-intensive, and therefore too expensive, for widespread use. As a result, the total capacity of all of California’s desalination plants is little more than a 10th of Los Angeles’ annual water consumption.

A desalination plant that would provide water for 100,000 homes is moving forward in San Diego.

Traditional desalination occurs through one of two processes.  The first is distillation, during which water is heated and evaporated before the resulting vapor is condensed to form fresh water.  The second and more common method is reverse osmosis, during which water is forced through a membrane through which salt cannot pass. 

A Canadian startup, Saltworks Technologies, is promoting a new, innovative process that it claims will reduce desalination electricity costs by up to 80%.  The key to understanding Saltworks’ thermo-ionic desalination process is appreciating the chemical nature of salt, which is composed of positively charged sodium and negatively charged chlorine ions. 

To produce fresh water, Saltworks uses four seawater solutions.  Saltworks’ process begins when it uses solar or waste heat to partially evaporate the first seawater solution, increasing the solution’s salinity.  The extra-salty seawater is then connected through separate membranes to the second and third natural (less salty) seawater solutions, each of which are connected through distinct membranes to the fourth seawater solution. Through osmosis, salty water then moves from the first extra-salty solution to the (less salty) second and third solutions.

Importantly, the extra-salty solution is connected to the second solution through a membrane that permits only positively charged sodium ions to pass and to the third solution through a membrane that allows only negatively charged chlorine ions to pass.  To maintain their electrical balance, the second and third solutions pull negatively charged chlorine and positively charged sodium ions, respectively, from the fourth seawater solution.  As a result, the fourth solution is stripped of its positive and negative ions and desalinated.

“I am an engineer and my first reaction is, this is elegant,” said David Gold, head of clean technology investments at Access Venture Partners.

Incorporated in 2008, Saltworks has already won several Canadian government grants worth a total of about $2 million. The firm is operating a 1,000-liter-a-day pilot project in a Vancouver harbor facility.  

“We’re looking for up to $10 million of Series A financing for continued operations, intellectual property protection, deploying pilot plants at four key customer sites around the world, and starting economy of scale manufacturing,” said Malcolm Man, Saltworks’ vice president of business development.

If investors’ reaction is any guide, it won’t be too long before Saltworks closes its first round of funding.  Commercial success, however, may prove more elusive.  “It is an early-stage [company] and there are a lot of questions about the cost of the membranes and scaling up,” said Gold.

Water rationing it is – for now.

-- Yoni Cohen

Graphic: How the nontraditional desalination process works; credit: Saltworks Technologies.