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EmTech: A Hybrid Solution for Cheap Desalination

Tapping huge reservoirs of brackish water could make desalination far more practical.
September 23, 2014

Desalination takes a surprising amount of energy, but in California many communities are actually using just as much energy to pump fresh water to where it’s needed. 

John Lienhard, a professor of water and food at MIT, offered a potentially better solution at our EmTech conference this morning. Like so much in energy efficiency, it’s a hybrid approach. He suggests building a system that involves both pumping and desalination.

Desalinating enough seawater to fill 1,000 one-liter bottles consumes the same amount of energy as running a microwave continuously for three hours. Even in theory, the minimum amount of energy you need would still require the equivalent of running a microwave for an hour (see “A Cheaper Way to Clean Water” and “How Carbon Wonder-Materials Are Promising to Revolutionize Desalination”).

The only way to use less energy than that, Lienhard says, is to find less salty water, also known as brackish water. And it so happens that many places have vast underground reservoirs of it. Texas, for example, which consumes a few million acre feet of water per year, has 2.7 billion acre-feet of brackish water. Why wait for breakthroughs in materials to make desalination widely affordable? Instead, pump that brackish water a relatively short distance to the surface and then desalinate it. In many places this might slash energy use and make desalination more affordable.

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