May 25, 2019 | Updated: 10:06 PM EDT

Waste brine from desalination: A useful source of chemicals

Feb 14, 2019 08:33 AM EST

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Desalination Plant
(Photo : By Unknown - http://www.water.gov.il/Hebrew/Planning-and-Development/Desalination/Pages/desalination-%20stractures.aspx, CC BY-SA 4.0,)

The world's arid coastal regions utilize desalination in producing water they need for drinking and for agriculture. In 2017, the desalination market in Middle East and Africa reached $7.9 billion. However, this industry produces a great amount of waste product in the form of highly concentrated brine by disposing it back into the seas. This method is economically disadvantageous because of its high cost and must be carefully managed in order to protect the marine ecosystems. MIT engineers have discovered a better method of disposing brine. 

A new study was published in the journal Nature Catalysis  and in two other papers by MIT research scientist Amit Kumar. Other members include John H. Lienhard V is a professor of mechanical engineering and professor of water and food as well as the director of the Abdul Latif Jameel Water and Food Systems Lab. Their method shows how brined can be converted into useful chemicals. '

Products from brine

Sodium hydroxide and other products can be produced from the said method. Sodium hydroxide, also known as caustic soda, can be utilized in pretreating seawater that goes into the desalination plant. Water acidity is changed that prevents polluting membranes that filter out salty water. Pollution of these membranes result to failture and interruptions in reverse osmosis desalination plants. 

"The desalination industry itself uses quite a lot of it," Kumar says of sodium hydroxide. "They're buying it, spending money on it. So if you can make it in situ at the plant, that could be a big advantage." The potential for sodium hydroxide produced from the brine is great and could be marketable. 

In addition to sodium hydroxide, hydrochoric acid can also be manufactured on site through established methods in chemical processing. Hydrocholoric acid (HCl) is a source of hydrogen, used in chemical production,and in cleaning components of the desalination plant. 

Benefits of converting brine

The desalination industry produces more than 100 billion liters of water on a daily basis. Concentrated brine from this process also has a similar volume. Current policies mandate adequate salt dilution but needs costly pumping systems. The economical and ecological benefits of converting brine are clearly seen. "Environmentally safe discharge of brine is manageable with current technology, but it's much better to recover resources from the brine and reduce the amount of brine released," Lienhard says.

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