Desalination Has a Waste Problem

Photo above: The Ras Abu Fontas desalination plant supplies freshwater for Doha, Qatar. It draws seawater from the Persian Gulf. Photo © J. Carl Ganter / Circle of Blue

Brine production is 50 percent higher than was assumed, UN study finds.

By Brett Walton, Circle of Blue

  • Brine is generally defined as water with a salt concentration higher than 50 parts per thousand, though some brines can be several times saltier
  • Average salinity of the world’s oceans is roughly 35 parts per thousand
  • The amount of brine generated by the world’s nearly 16,000 desalination plants is 50 percent larger than earlier assumptions
  • Just four countries on the Arabian Peninsula account for 32 percent of global desalinated water but 55 percent of global brine production

The waste product from desalination is growing too large to ignore, argues a paper from a United Nations think tankthat provides the first estimate of global brine production from desalination.

Producing fresh water in the driest parts of the world by removing the salt from sea water is resulting in a deluge of brine, especially in the Middle East and North Africa.

The amount of brine generated by the world’s nearly 16,000 desalination plants is 50 percent larger than earlier assumptions, according to researchers at the United Nations University Institute for Water, Environment, and Health.

Just four countries on the Arabian Peninsula — Saudi Arabia, United Arab Emirates, Kuwait, and Qatar — account for 32 percent of global desalinated water but 55 percent of global brine production. And brine is a problem that is growing alongside the rising demand for reliable freshwater. The world’s desalination capacity is expected to nearly double in the decade ending in 2020.

Earlier assumptions about brine production were largely guesses that did not take into account the latest facility-level data, says Manzoor Qadir, a study co-author.

Desalination brine, which can be laden with residual chemicals from the treatment process as well as excess heat, is damaging to the marine environment. Most coastal desalination facilities discharge their waste back into the ocean.

“We should highlight this so that governments can take steps to minimize the impacts,” Qadir told Circle of Blue. The study was published online in the journal Science of the Total Environment.

Desalination is seen as a steady, though energy-hungry and costly, means of satisfying freshwater demands in dry countries. It produces drinkable water by stripping out salts, mostly from sea water but also from brackish groundwater. The salts, however, do not disappear. They are instead concentrated in a hyper-saline brine.

Brine is generally defined as water with a salt concentration higher than 50 parts per thousand, though some brines can be several times saltier. Average salinity of the world’s oceans is roughly 35 parts per thousand.

The amount of brine produced during desalination hinges on the interaction between the desalination technology and the source water. Membrane treatment is more efficient, while saltier water generates more brine. A common pairing, Qadir said, is a reverse osmosis desalination facility that uses sea water. For every 10 gallons that enters, these types of facilities produce roughly 4 gallons of drinkable freshwater. The rest is brine.

To estimate global brine production, the research team used an industry database maintained by Global Water Intelligence, which lists each facility’s desalination technology, source water, and capacity. They then combined these factors with outside studies of how effectively different desalination technologies produce fresh water.

Middle Eastern countries produce a higher share of brine for two reasons. First, they often boil sea water to remove the salts, a less efficient method than membrane technologies. Thermal desalination became prominent in the region because of easy access to fossil fuels.

Second, the source water is saltier. The Persian Gulf, because of high evaporation rates and little freshwater inflow, has salt concentrations between 40 and 45 parts per thousand. The UAE’s Environment Agency says that waters near desalination plant outfalls, where brine is discharged, can be another 5 to 10 parts per thousand higher.

Brines are typically send back to the sea because it is cheaper, Qadir said. The next evolution for the desalination industry should be brine management, he hopes.

Companies are already developing technologies to convert the salts and metals in brines into usable products. But more research is needed to find technologies that are “low energy consumption, low chemical consumption, and low cost,” according to a 2017 survey of the field.

To Qadir’s mind, resources are available, if countries want to expend them. Two-thirds of desalination plant are located in high-income countries, according to the study.

“If they can afford desalination, they can afford environmentally friendly disposal of the brine,” Qadir Said..

Brett Walton writes about agriculture, energy, infrastructure, and the politics and economics of water in the United States. He also writes the Federal Water Tap, Circle of Blue’s weekly digest of U.S. government water news. He is the winner of two Society of Environmental Journalists reporting awards, one of the top honors in American environmental journalism: first place for explanatory reporting for a series on septic system pollution in the United States(2016) and third place for beat reporting in a small market (2014). Brett lives in Seattle, where he hikes the mountains and bakes pies. Contact Brett Walton