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According to According to the World Health Organization (WHO), around 785 million people around the world do not have a source of clean drinking water. Desalination could be the key to meeting the world’s drinking water needs. This year we have seen different ways to desalinate water, including a desalination device that also collects lithium and H2 from seawater at an affordable price and a portable lamp that converts half a liter of salt water in 45 days of light.
Korean engineers have developed a nanofiber membrane that transforms seawater into drinking water through a membrane distillation process. In addition, the membrane can function effectively for long periods of time.
In this process, the salt water on one side of the membrane is heated, while the fresh water on the other side remains cold. To repel liquid water, the membrane is hydrophobic. However, water vapor from the hot side can still pass through the pores. A difference in vapor pressure then causes it to drift to the cold side, re-condensing as fresh water.
This is a problem because the accumulation of salts and other pollutants on the membrane can affect its hydrophobicity. Eventually, the brine seeps in and makes the soft water less cool, requiring the membrane to be replaced.
With this in mind, scientists from Korea Institute of Civil Engineering and Building Technology (KICT) has produced more advanced membranes. These were made through a process called coaxial electrospinning, where two different materials – a polymer called PVDF-HFP and a silica airgel – are mixed during the printing process.
The rough polymer surface repels water, while the silica airgel acts as a thermal insulator, preventing the cold side from getting warm from the hot side. This keeps the vapor pressure difference high, making the membrane more efficient.
In lab tests, the KICT team ran the new membrane for 30 days and found that it still filtered 99.99% of the salt, even after all this time. That’s a considerably longer runtime than other electrospun nanofiber membranes, which the team says struggle to last for more than 50 hours of continuous use before they start to leak.
Principal investigator of the study, Dr Yunchul Woo, concluded:
The electrospun nanofiber coaxial membrane has great potential for processing seawater solutions without suffering from wetting problems and could be the appropriate membrane for pilot scale and full scale membrane distillation applications.
The research was published on January 4, 2021 in the Journal of Membrane Science.
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