New Water Filters Kill E.Coli Bacteria
Published on by Water Network Research, Official research team of The Water Network in Technology
Indian Institute of Science DevelopedLow-cost Water Purification Membrane Capable of Filtering out Objects Greater Than One Micron Size and Also KillingE. ColiBacteria
The novel membrane with pores as small as 0.57-0.68 microns was developed by mixing two polymers — polyethylene (PE) and polyethylene oxide (PEO) — at 180 degree C. Unlike PE, PEO is water-soluble and the two polymers are immiscible.
"We want them to be immiscible as we want to remove one of them, in this case the PEO which is water soluble," said Dr. Suryasarathi Bose, Assistant Professor, Department of Materials Engineering, IISc. He is the corresponding author of the paper. Tiny holes came into being once the water-soluble polymer was removed.
In order to create pores that are sub-micron in size, the amount of PEO polymer distributed in the PE matrix should also be sub-micron in size. To achieve this, only a tiny amount of PEO was taken compared with PE. Also, the polymers mixed at 180 degree C were sheared at high speed to produce tiny droplets of PEO. "The higher the shear rate, the smaller the droplets," Prof. Bose said.
The PEO droplets on the matrix were then removed to create tiny holes. "We take the mixture and dip it in water. As soon as we dip the mixture, the PEO gets dissolved in water leaving behind tiny holes in the PE matrix," he explained.
Going further, the researchers rendered the membrane antibacterial against E.coli. For this, grapheme oxide (GO) was mixed with PE and PEO and the graphene oxide was made functional with amine groups. The tablet-shaped samples with tiny holes are hydrophobic (water repellent) in nature.
Since the holes were sub-micron in size, pressure was required to force water through the holes. "The pressure used varied from one to seven psi. Flux [rate of water flow] increased as the pressure applied increased," said Prof. Bose.
"Since pressure was used to force water through the tiny holes, the hydrophobic nature of the tablet would not have mattered," said Prof. Bose.
The membrane filtered all solid substances that were more than one micron in size. "By itself, the membrane cannot remove salinity. For that, one has to use reverse osmosis," Prof. Bose said.
When put into a colony ofE. colibacteria, the tablets reduced theE. colicolony at 37 degree C; measurements were made 24 hours after the tablets were left in the bacterial colony.
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