The toxic issue of brine

17 January 2019

splashing water

splashing water

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Desalination plants are pumping out 50% more toxic brine waste than previously thought, and the environmental impacts have so far been overlooked, a new study shows...

Desalination plants convert salty water, like seawater, into freshwater for drinking and irrigation. They are exceptionally energy-hungry, so they tend to be used mainly in areas with very limited access to conventional water sources such as rainfall, river flow or meltwater. But left over after the "de-sal" process is a highly concentrated, toxic brine waste, which is currently just being thrown back into the ocean where it can have devastating effects on the local ecology. And experts are expecting the global de-sal footprint to enlarge considerably over the coming decades. 

"The problem of water scarcity is increasing in the world due to population growth and economic growth, and also due to climate change and contamination, reducing the amount of available conventional resources of water,” explains Wageningen University researcher and author of a new study into the scale and impacts of desalination, Edward Jones. 

Published in Science of the Total Environment, Jones' analysis shows that the volume of brine effluent being produced by desalination is at least 50% larger than originally believed: although the precise outputs will depend upon the salinity of the water source, desalination technology used, and local conditions, on average, for every litre of freshwater produced through desalination, 1.5 litres of toxic brine are left behind. And with 16,000 desalination plants operating around the world, that means 142 million cubic metres of hypersaline brine are being discharged daily - enough to cover the entire UK under a foot of toxic brine in a year.

The brine is a problem because it contains high concentrations of salts as well as chemicals used in the desalination process itself. Usually, plants dispose of it directly into the ocean, without further treatment. As a result, water quality suffers and  dissolved oxygen levels plummet, potentially harming marine life.

As the pressure on freshwater grows into the future, forecasters predict that use of desalination technology will grow significantly, so steps need to be taken to protect the environment too, not just the water supply.

“Brine management techniques and management options need to improve to reduce the potential problems of brine being discharged into the environment into the future,” says Jones.

It’s not all doom and gloom, though, as Jones and his colleagues point out in their study: this environmental challenge could be transformed into an economic opportunity because there is potential for the brine itself to be "mined" for valuable salts and metals. These are normally present in seawater only in tiny quantities, which makes them costly to extract directly. But the highly-concentrated salt-rich brines contain these elements in much greater abundances, making recovery far more economically viable.

But will the world listen? We'll have to take that with a pinch of salt...

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