Around 16,000 desalination plants worldwide transform undrinkable salt water into drinking water. However, there are significantly more problematic residues than expected, reports an international research team in the journal “Science of the Total Environment”. The amount of environmentally harmful brine contaminated with chemicals is about 50 percent higher than previously assumed. There is an urgent need to develop better treatment methods for the residues in order to avoid polluting the environment and reduce disposal costs. Only then can the drinking water supply of present and future generations be guaranteed, write the scientists working with Seong-mu Kang from the Canadian branch of the United Nations University (Ontario).

Especially in regions with water scarcity, people depend on drinking water from desalination plants. “Around 1.5 to 2 billion people live in water-stressed areas where, at least for parts of the year, the available resources are insufficient to meet the demand,” says Vladmir Smakhtin, one of the scientists involved. In the study supported by the United Nations, the team first determined the number of desalination plants currently in operation in existing databases. The researchers also checked how much drinking water these systems produce and what quantities of residues occur.

A total of 15,906 desalination plants are in operation in 177 countries around the world. They produce 95 million cubic meters of fresh water every day. The scientists report that a good half of the desalination capacity is located in the Middle East and North Africa. In Western Europe, most of the plants are in Spain. According to the researchers, 142 million cubic meters of brine accumulate every day worldwide – around 50 percent more than previously assumed. In one year, that would be enough to cover the US state of Florida by a good 30 centimeters, according to a statement in the study.

The salt solution has a significantly higher salt content than normal seawater. It also contains chemicals and dissolved metals. They are added to the salt water to prevent clogging or damage to the desalination plants through the accumulation of insoluble salts or algae, sand, and microorganisms. Copper and chlorine were among the most problematic admixtures.

What happens to this salt solution depends, among other things, on the location of the desalination plant. The mixture is often fed back into the sea, and sometimes it is pumped into other bodies of water, into deep wells or drainage channels or into brine ponds for evaporation. This can cause significant damage to the ecosystems in question, the researchers write. The brine inflow lowers the oxygen and reduces the proportion of dissolved oxygen in the water, explains the scientist involved, Edward Jones. “High salinity and reduced dissolved oxygen levels can have a significant impact on aquatic life; the resulting ecological effects can be seen throughout the food chain.”

The waste product also offers economic opportunities, the researchers emphasize. The salts and metals it contains – including magnesium, sodium, calcium, potassium, bromine, and lithium – could be recovered and used by industry. However, the technology is not mature and recovery is currently not competitive.

“There is a need to implement this research and turn an environmental problem into an economic opportunity,” says co-author Manzoor Qadir. “This is especially important in countries that produce large amounts of brine with relatively little efficiency, such as Saudi Arabia, the United Arab Emirates, Kuwait, and Qatar.”

Another disadvantage of the currently operated desalination plants is: They are considered to be very energy-intensive.


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