Desalination plants produce more waste brine than than previously thought

There’s enough wastewater from the world’s facilities to cover Florida a foot deep—here’s why that’s a potential problem.

By Tik Root Read full National Geographic article here

As clean freshwater has become scarcer around the world—especially in arid regions such as the Middle East and North Africa—those countries that can afford it have increasingly turned to desalination. That energy-intensive process extracts salt from sea (or other saline) water, transforming it into water that’s fit for human consumption. There are now nearly 16,000 desalination plants either active or under construction across the globe.

“[But] they don’t just produce desalinated water,” explains Manzoor Qadir, a researcher at the United Nations University in Canada. “They also produce brine.” Brine is the concentrated salt water that’s left after desalination. But Qadir says, “there is no comprehensive assessment” of how much is being produced. …Qadir’s team analyzed available literature as well as a database of roughly 20,000 desalination plants (including some that are no longer active)….

The literature had long assumed a one-to-one ratio. But Qadir’s study found that the average desalination plant actually produced 1.5 times more brine than desalinated water—fifty percent more than previously thought. That translates to 51.8 billion cubic meters of brine each year, which Qadir says is enough to cover all of Florida, a foot deep.

….Arguably best known [deleterious impact of desalination] is the copious amount of fossil fuels that are often used to power the plants, resulting in a significant amount of emissions. Most desalination plants work by reverse osmosis, meaning energy is needed to push water past a membrane at high pressure in order to separate the salt (learn more how it works). A typical plant takes an average of 10 to 13 kilowatt hours of energy per every thousand gallons processed. That energy use adds to the cost of the process. A recent desalination plant in California cost a billion dollars, and now provides about ten percent of the drinking water of the county of San Diego. The cost, and environmental impacts, of this overall industry have spurred researchers to look for alternatives, including developing more efficient separation membranes and desalination units that can be powered by solar energy. (Learn more about these emerging efforts.)

On the intake side, Burt says that small organisms such as fish larvae and coral can get sucked into a plant. But the greater risk comes at the other end of the process, when the brine is put back into the ocean (where the majority of desalination is done)…..

“Brine will be substantially higher in salinity than normal oceanic water,” he said. “The brine discharge is also warm.” Those conditions, he says, can make it more difficult for marine life in the immediate vicinity of the discharge to survive or thrive.

What Burt is more concerned about, however, are the chemicals that are often in the brine. Qadir’s study points to copper and chlorine as particularly troublesome compounds. …

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