According to the World Health Organization (WHO), roughly 785 million people worldwide lack a clean source of drinkable water.
Desalination could be the key to meet the world’s drinking water needs.
This year, we have seen a few different ways to desalinate water, including a desalination device that also harvests lithium & H2 from seawater affordably and a portable lamp that converts half a liter of saltwater into 45 days of light.
Korean engineers have developed a nanofiber membrane that turns seawater into drinkable water by a membrane distillation process.
In addition, the membrane can operate efficiently for long periods.
In this process, the saltwater on one side of the membrane is heated, while the fresh water on the other side stays cold.
To repel the liquid water, the membrane is hydrophobic. However, water vapor from the hot side can still pass through the pores. A vapor pressure difference then causes it to drift to the cold side, re-condensing as freshwater.
This is a problem because the buildup of salts and other pollutants on the membrane can affect its hydrophobicity. Eventually, the brine seeps through and turns the freshwater less fresh, leading to the membrane having to be replaced.
With this in mind, scientists at the Korea Institute of Civil Engineering & Building Technology (KICT) produced more advanced membranes. These were made through a process called co-axial electrospinning, where two different materials – a polymer called PVDF-HFP and silica aerogel – are mixed during the printing process.
The rough polymer surface repels the water, while the silica aerogel acts like a thermal insulator, keeping the cold side from getting warmed up by the hot side. That keeps the difference in vapor pressure high, making the membrane more efficient.
In lab tests, the KICT team ran the novel membrane for 30 days and discovered that it still filtered out 99.99% of the salt even after all that time. That’s a considerably farther runtime than other electrospun nanofiber membranes, which the team claims struggle to last over 50 hours of continual use before they start to leak.
Dr. Yunchul Woo, the study’s lead researcher, concluded:
The co-axial electrospun nanofiber membrane has strong potential for the treatment of seawater solutions without suffering from wetting issues and could be the appropriate membrane for pilot-scale and real-scale membrane distillation applications.
The research was published on January 4, 2021, in the Journal of Membrane Science.