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Earth Sense: Making salt water drinkable is doable but difficult
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It’s an ironic fact that more than two-thirds of the Earth’s surface is covered by water, yet there always seems to be a shortage in many places.

The problem with most of the world’s water is it is in the oceans, which means it’s salty. For drinking purposes, salt water can be considered poisonous. We can’t use it for irrigation, either, because it harms terrestrial plants.

When I was living on the Atlantic Coast, salty rain from Hurricane Fran burned the front lawn and killed several young trees. But couldn’t we take the salt out make the water consumable? Yes, but not “simply.”

Desalination is a complex and energy-hungry process. Two methods are currently in use: multistage flash distillation and reverse osmosis.

The first method boils the water rapidly, then makes it condense again, leaving the salt behind. Obviously, a great deal of heat energy is required to make this happen.

The second method consists of forcing seawater through a fine membrane that lets water molecules pass but traps the mineral content. It’s similar to the water exchange process in body cells, only in reverse. Because we’re dealing with quantities in the thousands of gallons, massive pumps are needed to force the water through the filter membranes. That, too, uses lots of energy. The brine left behind, a salty sludge, poses a massive waste disposal problem.

Even if desalination were an easy task, it still wouldn’t help North Georgia much. Water is heavy. One gallon weighs more than 8 pounds.

Gainesville’s Riverside Water Treatment Plant is at an elevation of 1,200 feet. The city provides about 17 million gallons of water per day. To transport this amount from the ocean would require lifting 136 million pounds 1,200 feet high, and moving the same weight a distance of 230 miles from the ocean. Clearly, other solutions are much cheaper for our region.

This doesn’t mean desalination is a moot issue. Recent improvements in technology, published this month at the Massachusetts Institute of Technology and in the United Kingdom, promise more efficient treatment of the salty brine that’s left behind at waste. The new methods are also said to be more energy-efficient. Coastal locations around the world may have reasons to hope for a richer and less expensive water supply.

Rudi Kiefer, Ph.D. is a professor of physical science and director of sustainability at Brenau University. His column appears Sundays and at gainesvilletimes.com.

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