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An antibacterial water purification membrane resistant to slime

Scientists at IISc have designed a membrane which can remove bacterial contamination from water, while at the same time preventing biofouling, or the accumulation of micro-organisms on the membrane.

Bacterial contamination of water is a major health concern. Biofouling accounts for almost half the cases of membrane fouling, and is a serious problem: it can block the filtration process, cause damage to the membrane and increase the cost of purification process.

 The newly designed membrane has a matrix made of polyethylene – the same material that is used to manufacture plastic bags. It is a preferred choice to make such membranes due to its low cost, strength, durability and stability.

To make a porous membrane for ease of purification, polyethylene oxide (PEO) was mixed with polyethylene during the manufacturing process and later on washed out to create tiny pores. The porous membrane obtained was then coated with another polymer called 'chitosan'. Chitosan is a hydrophilic (water loving), non-toxic compound with inherent antimicrobial properties. The role of chitosan is to make the membrane 'antibacterial' and prevent biofouling. Chitosan coating also converts the original hydrophobic polyethylene membrane to a hydrophilic one, which makes the filtration process more efficient. Normally, coating of a membrane might lead to reduction in flow rate of water through the membrane; however chitosan improved the membrane efficiency, without any compromise in the flow rate.

The study represents the first demonstration of chitosan being used as a ‘polymer brush’ on polythene membranes for water purification. The membranes were effective in the removal of turbidity, flocculants and suspended particles from contaminated water. The advantages of this technology in comparison to the previously reported technologies for water purification is that it involves less cost and can be scaled-up without the need for extensive infrastructure. This membrane might be very useful as a pre-filter to extend the life time of commonly used RO (reverse-osmosis) membranes.

The study was also able to demonstrate that the chitosan coated membranes could efficiently filter bacterial species Escherichia coliand Staphylococcusaureuswhen water contaminated with these bacteria was passed through the membrane. Different chemical groups – like the nitrogen-containing amine group present in chitosan – might act on the bacterial cell membrane, which eventually leads to death of bacteria by rupturing.

When asked about its potential industrial applications, one of the authors Dr. Suryasarathi Bosesaid “this technology would be very useful for commercial use in future because the methodology adopted here and the technology employed in preparation is industrially viable and does not require intensive infrastructure. More importantly, they are eco friendly. The added advantage is that polyolefins are chemically inert and hence these membranes can be used in various industries, especially in the food/dairy industries”.

About the authors

Dr. Suryasarathi Bose is an Assistant Professor at Department of Materials Engineering, Indian Institute of Science, Bangalore-560012, Karnataka, India. Prof. Giridhar Madras is a Professor at Department of Chemical Engineering, Indian Institute of Science.Prasanna Kumar S Muralis a research scholar at Center for Nano Science and Engineering, Indian Institute of Scienceand Banothu Kumar is student at Department of Chemical Engineering, Indian Institute of Science.

About the study

The paper appeared online in the journal ACS Sustainable Chemistry & Engineering