Tuesday, May 7, 2019

Science & Technology: Low Enthalpy Geothermal Could Power New Desalination Method

New desalination method could get industry – and the environment – out of a very salty pickle (New Atlas)

"Hypersaline brine" is industrial waste-water with salt levels that exceed even that of seawater. It's a big, expensive, destructive problem which a team of engineers at Columbia University in New York City hope to solve with their solvent-based method of desalination.

The "temperature swing solvent extraction" or TSSE method – developed by a Columbia Engineering team led by assistant professor Ngai Yin Yip – is beautifully simple. It uses a solvent with temperature-dependent water solubility. Vary the temperature, and you vary the solubility. This solvent is added to the brine, where it floats above the denser salt-laden liquid. At room-temperature, water from the brine is drawn into the solvent. After this stage, the solvent is drawn off and warmed via low-grade heat under 70° C (158°F). The "temperature swing" nature of the solvent subsequently demixes it from the water (remember, this is a temperature-dependent solvent, where at higher temperatures, it holds less water). The resulting desalinated water then settles to the bottom, and is collected.

And speaking of sustainability, the low-heat requirements for the process is one of its most appealing elements. Depending on the location of the technology, this low, sub 70° C heat can be supplied conventionally at low cost, or sustainably from sources such as low-concentration solar, on-site waste heat from industrial processes or shallow-well geothermal.

Membrane-less and Non-Evaporative Desalination of Hypersaline Brines by Temperature Swing Solvent Extraction.  By Chanhee Boo, et al. Environmental Science & Technology, DOI: 10.1021/acs.estlett.9b00182