Many arid, coastal regions of the world rely on desalination to get potable water from the salty seas. This reliance is going to increase as climate change triggers droughts and water scarcity. But desalination is costly, uses a lot of energy, and produces waste brine—a concentrated soup of salt and chemical—that can harm marine ecosystems.
A new desalination device that converts brine into useful chemicals could help. Its developers at Stanford University say it could make desalination affordable and environmentally benign. “By reimagining brine as a resource, we aim to incentivize its collection and treatment before discharge,” said chemical engineering professor Will Tarpeh in a press release.
Desalination plants around the world today produce about 27 billion gallons of drinking water each day, resulting in a similar amount of brine. The waste brine is usually pumped back into the ocean, where it causes salinity and acidity spikes that can disrupt ecosystem health and harm sea life.
The Stanford team built and tested a desalination device based on a technology called electrochemical water splitting. The device, reported in ACS Sustainable Chemistry & Engineering, uses electrical energy to trigger chemical reactions that split brine into positively charged sodium and negatively charged chlorine ions. These ions then combine with other elements to form sodium hydroxide and hydrochloric acid.
Sodium hydroxide is an important chemical used to produce soap, paper, and detergent. Importantly, it is also used in the desalination process itself to pretreat seawater before removing salts. Hydrochloric acid is also used in many industrial processes and for cleaning at desalination plants. Making these useful chemicals as a byproduct of desalination would bring down the cost of desalination. Plus, using the brine this way would cut the costs of disposing it, which can account for up to a third of total desalination expenses.
The concentration of the chemicals that the device produces is 100 times lower than that needed for commercial use. But the work still provides a proof-of-concept and the researchers plan to further improve the process so it can be tested at a desalination plant.
Source: Linchao Mu, Yichong Wang, and William A. Tarpeh. Validation and Mechanism of a Low-Cost Graphite Carbon Electrode for Electrochemical Brine Valorization. ACS Sustainable Chem. Eng.