Treated Wastewater for Thirsty Power Plants

Last month I wrote about the energy-water resource crunch — the fact that many power plants require huge amounts of water, an increasingly scarce resource.

A reader in Washington, D.C., wrote in to say that some power plants in that area are resolving this dilemma by using treated wastewater in their cooling towers.

Intrigued, I ran the concept by Michael Webber, an assistant professor of mechanical engineering at the University of Texas and the author of a recent Scientific American article on energy and water.

“It’s a good idea, easy to do, works just fine, has been demonstrated to work reliably, but isn’t widely implemented, yet,” responded Mr. Webber, in an e-mail message.

Around 50 power plants are using treated wastewater for cooling, according to a study (PDF) of the subject last year by Argonne National Laboratory, with the quantity of water going into power plants being roughly the same as that being used to irrigate crops.

While some of the water is returned to the source after it is used in cooling, withdrawing such large quantities can still be a problem — in times of drought, for example, according to John Veil, the report’s author.

“Part of the reason that more plants are not currently using reclaimed water is that when those plants were built, most of them could find ground or surface water allocations for their water needs. Today, that is much less likely,” said Mr. Veil in an e-mail message.

Besides the D.C.-area plants, which The Washington Post reported last year would also reduce the volume of treated sewage going into the Potomac River, other examples include a natural gas plant near Austin, Tex., and the Palo Verde nuclear plant in Arizona.

“This is a desert here. We don’t have any choice,” said Jim McDonald, a spokesman for Arizona Public Service, which operates the Palo Verde plant and owns the largest share of it. He believes it is the only nuclear plant in the country to reuse treated wastewater — which it has done since opening in 1986.

He emphasizes that the wastewater, which comes from Arizona’s biggest cities and is brought in by pipe, is treated again at the plant. All of it evaporates from a pond after being used at the plant, and the pond “becomes very similar to the Great Salt Lake — a heavy concentration of salt,” he said.

The question of cost (yes, it can be expensive to use treated wastewater) is “completely site-specific,” Mr. Veil wrote. “The cost of using reclaimed water — the wastewater industry’s term of choice for treated municipal wastewater — depends on how much treatment the wastewater treatment plant already provides, how much additional treatment would be required to meet the power plant’s operational requirements, and how far the reclaimed water must be piped.”

Treated wastewater does have another, more controversial use, as The New York Times wrote about last year: some cities are turning it back into tap water, after heavy scrubbing.

Source: greeninc.blogs.nytimes.com