Clean drinking water is one of the most basic needs for humans, yet almost 783 billion people worldwide do not have access to it. Each year an estimated 6 to 8 million people die globally as a consequence of water-related diseases. These statistics reinforce the absolute necessity that is clean drinking water and the devastating results of inaccessibility to this necessity.

The suitability of water for human consumption requires that the water not only not be turbid but be free from toxins as well. Turbidity refers to the loss of transparency in the water due to visible impurities while toxins, which must be removed, are chemical secretions of organisms — particularly bacteria and fungi — that cause disease.

To make water sanitary for drinking needs, both of these impurities require proper expulsion from the water source. Many of the traditional techniques of purifying water focus exclusively on one kind of impurity. For example, the chlorination method can only kill microorganisms, whereas filtration can only remove sizable impurities. However, nanotechnology might be able to do both.

Today, the use of nanoparticles has revolutionized industry, from nanoparticle-coated bandages to food containers. Nanotechnology is essentially the application of nanoparticles, particles ranging from 1 to 100 nanometers in size. These particles can be of various species: pure metals like silver, metal compounds like zinc oxide or even nonmetals like carbon and silicon.

As in other fields, nanoparticles have a part in purifying contaminated water. Nanoparticles of varying sizes and chemical properties are being used to rectify both turbidity as well as microbial toxins. The usefulness of the nanoparticles depends on their size-to-area ratio, which magnifies the chemical as well as physical properties of the substance the nanoparticle is made of.

The use of nanoparticles such as carbon nanotubes and graphene rely on this increased surface area of the nanoparticle to maximize the adsorption of heavy metal ions as well as other pollutants. Many metal nanoparticles such as iron — which is currently being used on commercial levels for water treatment purposes as well – can function in the same way as carbon adsorption by forming bimetallic couples with inorganic, heavy metals in the water.

Additionally, the chemical reactivity of the nanoparticles is enhanced by the increase in the metal’s surface area. Nanoparticles, such as titanium, employ this quality to remove pollutants. Chemically reactive nanoparticles are being used to remove micro pollutants by changing the pollutant into an innocuous form through redox reactions.

Another major use of nanoparticles is in the removal of microbes. The presence of microorganisms such as bacteria and fungi can lead to buildup of microbial toxins. These toxins can lead to serious diseases, such as diarrhea and cholera.

Nanoparticles can combat these problems, by first killing harmful microbes and then by neutralizing the effects of the toxins. Silver nanoparticles are known for their antimicrobial properties. The presence of silver causes fatal DNA mutations in the microbes. The use of desalinating nanoparticles of carbon can also cause microbial cell death by disrupting the cellular osmotic balance. Both these approaches eliminate harmful microorganisms from water. Moreover, nanoparticles such as titanium oxide can react with toxins from microbes, which results in degradation of the toxin to a harmless chemical.

These attributes and a wide range of possible applications make the usage of nanoparticles for the purposes of water purification very promising. However, researchers need to carefully weigh the safety of nanoparticle-treated water intake as well as potential environmental consequences against the prospective benefits of nanotechnology.

– Atifah Safi

Sources: UMExpert, Elsevier, NCBI, USGS, Nanoiron
Photo: O Exotextiles