When salt is removed from seawater in desalination plants, the byproduct is – not surprisingly – a lot of highly-concentrated salty brine. Ordinarily, this is just dumped back into the sea, which can harm the environment. Thanks to a new treatment process, however, that brine could actually be used to desalinate more water.
Developed by a research team at MIT, the proprietary system incorporates what are described as "well-known and standard chemical processes." These include a nanofiltration process to initially remove unwanted compounds from the brine, followed by one or more stages of electrodialysis. As a result, the brine is converted into useful chemicals such as sodium hydroxide.
More commonly known as caustic soda, sodium hydroxide is often utilized to change the acidity of seawater entering desalination plants, which in turn helps to prevent fouling of the filtration membranes that are used to remove the salt. Ordinarily, plant operators have to buy the chemical. With the MIT system, though, they would be able to produce even more than they need, on-site. The excess could then be sold for use in other applications.
Other chemicals that could be produced from the brine include hydrochloric acid, sales of which would likewise be a source of revenue. And as an added bonus, the scientists suggest that plants could save money by no longer needing to pump their brine out into the ocean.
Plans now call for the technology to be trialled and refined in a prototype desalination plant, with an eye toward ultimately reducing the system's equipment costs and power requirements.
A paper on the research was recently published in the journal Nature Catalysis.
Source: MIT
