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Nanotechnology for water filtration
By Priyam Kumar


As the whole world is becoming a small village, it seems the small sized nano technology has the answer to the world's fast growing problem of drinking water availability. Nanotechnology is study of matter on an atomic or molecular scale, rather nano-scale.

While nano technology can have many applications, its utility in purification of water is now being realized. It has been found that it is much easier to deal with water purification and desalination at a very small, i.e. nano scale.

The traditional method of water filtration has been Reverse Osmosis. It involves using pressure to force a solution to pass through a semi permeable membrane, leaving solute on one side and pure solvent to pass through, thus helping in removing impurities.

Another novel process is that of ultra filtration, where hydrostatic pressure forces water through a semi permeable membrane, allowing pure water to pass through and leaves the larger sized bacteria and viruses behind. The nano filtration process lies in between these two processes, being closer to the ultra filtration process. It involves Cross Flow filtration. In this process, the water feed is passed tangentially to the filter membrane, letting only pure water to pass through. The nano filtration follows closely to the ultra filtration process, except the pore sizes of the membranes in nano filters are below 100 nanometers and thus even small salts or viruses find it hard to pass through.

The basic principle of nano filtration lies in the fact that the chemical properties of basic elements involved tend to be different and easier to manipulate at a molecular or atomic level. Hence nano filtration tends to be a better process. Besides, the operating costs of nano filtration are lower.

Also a study in South Africa found that Reverse Osmosis though produced potable water from brackish groundwater, it removed many major nutrients like Calcium and Magnesium ions placing nutrient levels below WHO standards.

Another study found that sand filtration inter chlorination system was not as effective in removing arsenic from drinking water as nano filtration process.

Realising the opportunity, many companies have made investments in developing nanofiltration related technologies and membranes. In 2004, the Nano Water Congress held in Amsterdam showcased how nanotechnology can be used to create clean drinking water from contaminated and salt water.

In India, Tata Group launched a new water purifier, known as Tata Swach, for poor rural households in India that have no electricity or running water. It uses cheap materials like rice husk ash with silver nano particles to kill bacteria and viruses in the water. It is said to be the world's cheapest water filter with approximate cost at Rs. 1000 (USD 20-25). The cost of purifier is Rs. 749 and the cartridge is Rs. 299, and thus the overall cost is far below any water purifier available. Like Tata, many companies are trying to create cheap filters for poor people to use across the world.

The British company NanoMagnetics has produced magnetic nanoparticles to desalinate water. It has helped the US Army to gain pure water in Afghanistan and Iraq. The nano particles created by the company are small scale particles such as carbon nanotubes and fullerenes, which operate at a very low level with various bacteria, viruses and pathogens, or any particles at that level.

There have been concerns regarding toxicity of nano particles in water purification. As yet, there has been no certainty as to the extent of the damage by nano particles. It has been discovered that there are two forms of nano particles-active and passive. Passive particles present no or lesser risks, whereas active particles move in the environment and can cause higher risks.

What future implications nanotechnology holds are yet to be conceived and are very uncertain, even if promising. The governments need to keep a check on the research and should not allow private companies to create monopoly control over it. Toxicity and the complete nature of nanofiltration also need to be checked.

Besides companies, governments of Sri Lanka, Brazil, Cuba, South Africa, USA, European Union, India and others are investing heavily on research for using nanotechnology to clean water. Participation of government shows that the technology will not be monopolized by private players and can also help to aid the poor.

However, if the technology can provide bacteria and virus free clean drinking water to all, especially the poor and deprived people across the world, then the technology deserves to be encouraged and applied.

Priyam Kumar  |  priyamwriter@gmail.com

Priyam Kumar is an Engineering student.

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