Nanoscale water treatment needs innovative engineering
Engineering a useable product is the key to making nanotechnology work for water treatment, says Ashok Raichur.
The fast-evolving world of nanotechnology captivates researchers in fields ranging from health and nutrition to agriculture and environment. In particular, many developing countries are investigating how nanotechnology might improve access to clean water, with a lot of lab work done over the past decade on nanoparticles in water treatment. Brazil, China, India, Saudi Arabia and South Africa all have centres dedicated to nanotechnology research that study water treatment.
Scientists have overcome the initial challenge of producing nanoparticles themselves. But using them effectively for large-scale water treatment is more difficult, andnanotechnology's full potential has yet to be realised. While there are promising applications for household use, for example, researchers at the Atomic Centre in Mumbai, India are making progress on water filters using carbon nanotubes, commercial products in the developing world are still few and far between, especially products that are affordable to the global poor.
Yet the unique properties of nanoscale particles makes them particularly well suited for treating water. They can potentially improve processes such as adsorption, catalysis and disinfection. Nanoparticles often have enhanced catalytic properties. For example, nano titanium dioxide is much better than conventional micron-sized particles at degrading organic molecules harmful to the environment. Similarly, nano titanium dioxide and nanosilver are more potent disinfectors of drinking water. More importantly, nanoparticles can be easily designed to produce tailor-made particles for specific applications.
With demand rising in developing countries, using nanotechnology to produce clean and safe drinking water seems a viable option.
But making the leap to commercial applications is complicated and is still a distant goal for most developing countries. Just producing nanomaterials in quantities large enough for industrial applications is challenging and can be expensive.
Nanomaterials can also pose problems when they are handled and used. Put simply, their very small size makes them easily airborne and hard to contain. And their unknown environmental and health risks means that they must be completely removed before the water is discharged — to avoid contaminating the environment or food chains.
But filtering nanoparticles is nearly impossible. Their tiny size lets them easily block filter media. Given the large scales water treatment plants operate at, filtering nanoparticles can also be an expensive operation, adding to the cost of water treatment.
There are widespread concerns about the potentially toxic effects of nanoparticles entering the food chain. We don't yet know how nanoparticles affect the human body. Due to their size, nanoparticles can pass through various barriers and reach sensitive organs such as the brain and heart, and are also difficult to remove from the body. Nanotoxicology is a new area of research. Researchers the world over are investigating the effects of nanoparticles on various life forms. And while the ill effects remain far from understood, we must be careful when using nanoparticles — especially for water treatment.
Innovative engineering needed
Overcoming the difficulties of nanotechnology water treatments means developing innovative solutions to engineer a usable product. One answer could be to develop methods where the nanoparticles need not be suspended in the water. For example, one can stick — or 'immobilise' — the nanoparticles onto suitable materials such as steel or polymer sheets,which in turn can be easily dipped in and out ofwater tanks to work as catalysts or adsorbents.
This needs care to retain nanoparticles' size and integrity so as to keep the benefits of operating at the nanoscale. But if it can be done, immobilisation is a good technique since it would keep water free of nanoparticles during and after water treatment. We, here at the Indian Institute of Science, Bangalore, are developing such a technique for degrading organic molecules using nano titanium dioxide. The results have been very promising and we are working closely with the University of Johannesburg to scale up the process in the near future.
Along with engineering solutions, nanotech researchers also need to work with doctors and other scientists to fully understand the toxic effects of nanoparticles and their fate in the environment.
The need of the hour, especially in developing countries, is to develop new materials to efficiently produce clean drinking water. But the bigger challenge is to develop innovative ways to harness the novel properties of nanomaterials to the maximum benefit of mankind, without harming the environment.
Ashok Raichur is associate professor in the Department of Materials Engineering at the Indian Institute of Science in Bangalore, India.