The classic criticism of desal is that it takes a tremendous amount of energy to process seawater, and we really shouldn’t be burning any more fossil fuels than we need to be.
But a less chattered-about problem is the effect on the local environment: The primary byproduct of desal is brine, which facilities pump back out to sea.
Unfortunately, scientists haven’t had a good idea of just how much brine the 16,000 operating desal facilities worldwide have been producing.
Researchers report today that global desal brine production is 50 percent higher than previous estimates, totaling 141.5 million cubic meters a day, compared to 95 million cubic meters of actual freshwater output from the facilities.
Bad news for the environment, to be sure, but things aren’t altogether dire: Desal tech is rapidly evolving, so plants are getting far more efficient, both in the brine they produce and the energy they use.
RO facilities now produce 69 percent of desalinated water worldwide.
Advances in membrane technology mean facilities require less and less pressure, and therefore energy, to filter seawater.
With thermal, 75 percent of the water you bring in might leave as brine.
“It also depends on the feedwater,” or input water, says Edward Jones, coauthor on the new study and an environmental scientist at Wageningen University in the Netherlands.
“Reverse osmosis is least efficient when you’re desalinating highly saline water, such as seawater.
Jones et al./Science of the Total EnvironmentThis is an important consideration because not all desal facilities are processing seawater.
That’s part of the reason why coastal plants in the Middle East and Northern Africa produce an astounding proportion of the world’s desal brine.
A total of 173 countries and territories run desal plants, but only four nations—Saudi Arabia, the United Arab Emirates, Kuwait, and Qatar—produce 55 percent of global desal brine, according to the new study.
“So there’s still going to be these plants operating which produce vast quantities of brine, particularly in the Middle East, where they’ve got a very established network of thermal desalination plants.”
Jones et al./Science of the Total Environment”Increasing water scarcity is the major driver,” says Manzoor Qadir, coauthor on the new study and assistant director of the United Nations University Institute for Water, Environment, and Health.
Inland, a plant might evaporate the water in pools and cart away the remaining salt.
But brine is more than just hypersaline water—it can be loaded with heavy metals and chemicals that keep the feedwater from gunking up the complicated and expensive facility.
“The antifoulants used in the process, particularly in the pretreatment process of the source water, accumulate and discharge to the environment in concentrations that can potentially have damaging effects on the ecosystems,” says Jones.
A plant run by Poseidon Water, for instance, produces 10 percent of San Diego County’s water supply.
Done Katch’ng up but want to read more? Read more here.