Prof. Kaustubha Mohanty and Dr. Senthilmurugan Subbiah, Department of Chemical Engineering, IIT Guwahati, have recently published the results of this research in the journal Environmental Technology & Innovation, in a paper co-authored by their research scholar, Naveenkumar Ashok Yaranal.
IIT stated Plastic pollution is rampant all over the world and while there is some level of awareness, the seriousness is not yet understood. Micro-plastics – plastic pieces smaller than one-fifth of an inch – are now found in almost all oceans and marine animals. What’s worse, sea salt has been found to have considerable amounts of micro-plastic.
Research performed in East Asia has shown that 90 percent of the table salt brands sampled worldwide has micro-plastics. Another study by IIT Bombay showed that eight brands of Indian sea salt were contaminated with micrometre sized particles of polyesters, polyethylene terephthalate (PET), polyamide, polyethylene, and polystyrene. Micro-plastics ingested by human beings can disrupt hormones, leading to infertility, and cause nervous system problems, and even cancer.
While there have been many studies to identify and quantify micro-plastics in various food products, including salt, there have been fewer attempts at finding ways to remove them.
“In our hollow fibre membrane filter, hundreds of tiny straw-like tubes are bundled together to create a filter matrix,” explained Dr. Mohanty. The walls of these tubes are filled with microscopic pores, and when water is passed through the tubes, the micro-plastics are trapped inside, thus freeing water of this pollutant.
Hollow fibre membranes are already used extensively in daily life applications such as RO pre-treatment, industrial water/wastewater, juice processing, and other biotech applications, including in dialysis membranes used for kidney ailments. The hollow fibres are made of many kinds of materials and the ones used by the IITG team was made of polypropylene and a silk protein called sericin.
“We were able to remove 99.3 % of the micro-plastics present in seawater, without any reduction in the salt content”, said the key researcher. If this filtered water is used to extract salt, it would be free from micro-plastics. The researcher clarifies that this can only remove micro-plastics from seawater before salt extraction, and obviously cannot remove micro-plastics that get added during salt production, such as through the use of descaling agents in the desalination process itself.
Some advantages of hollow fibre membrane technology that make it promising for pre-treatment of seawater include simplicity of installation and use, cost effectiveness, no need for power supply, no generation of waste, and operability under low water pressure.