It is entirely conceivable that the engineered nanoparticles that seem like today's water treatment panacea, could be tomorrow's ecological dynamite. The potential for the use of nanoparticles in water treatment such as water filtration is too compelling to ignore, despite the potential risks.
Here, Rachael Benstead, senior aquatic ecotoxicologist at Translational science and research organisation, Fera Science Ltd, helps plot a roadmap to a future in which we can take advantage of the benefits of nanotechnology in water and mitigate against the drawbacks.
Nanoparticles are particles between one and 100 nanometers (nm) in size surrounded by an interfacial layer consisting of ions, inorganic and organic molecules. Though usually associated with modern science, nanoparticles have been used as far back as fourth century Rome and were first described in scientific terms by Michael Faraday in his 1847 paper.
A nanoparticle behaves as a whole unit with respect to its transport and properties and is commonly used in many areas of innovation including manufacturing, agriculture, business, medicine and public health.
Within water and wastewater treatment in particular, nanoparticles and other nanotechnology such as nanofilters are now entering the commercial market, which is expected to grow at a compound annual growth rate of 9.7 per cent during the next five years. This is largely due to reducing costs and pressure to supply clean drinking water to the world’s growing population.
The most remarkable example is perhaps the use of nanofilters for reverse osmosis. Reverse osmosis is widely accepted as the best way to desalinate water and involves feeding water through a semipermeable membrane. Traditionally, this was much too energy intensive to be viable for most uses. However, much less pressure is required to pass water across nanofilters than traditional filters, making the process up to fifty per cent more efficient by using nanotechnology.
Other advantages of nanotechnology are more directly related to the small size. The huge surface area to volume ratio that can only be achieved by such small particles means the material is likely to be much more reactive. This increased reactivity can mean substances that are well understood in their bulk state might respond differently to expectations in its nanoparticle state. They also have an extremely high mobility, allowing them to react with a large number of molecules in a very fast timescale.
This means, in addition to desalination, nanoparticles can be used to remove sediments, chemical effluents, charged particles and even kill bacteria by releasing silver ions.
However, some of these benefits may also pose risks to the environment if nanoparticles are inadvertently released, either through use or accidentally through spills or steam released during the manufacturing process.
Some synthetic nanoparticles could be directly toxic to microbes, plants and animals, where others may provide a secondary risk. For example, silver ions released to kill bacteria during water treatment will devastate biological populations, with knock-on effects to the entire ecosystem. Silver ions effectively kill bacteria, removing a food source for other organisms further up the food chain.
The toxic effects of many nanoparticles are not yet fully understood, especially as they are much more reactive than their large-scale bulk equivalents. This could lead to untested and unrecognised, interactions with biological materials. In addition, the fate and behaviour of these particles in the environment is very difficult to properly track and study, with insufficient analytical techniques currently available for the detection and measurement of nanoparticles.
This being said, there have not yet been any reports of adverse reactions to human health and nanotechnologies promise great benefits, especially in environments where clean water is scarce. However, future research into interactions, conducted to closely mimic the natural environment, such as in a large-scale flow-through mesocosm like Fera’s E-Flows mesocosm, is crucial to determine whether nanotechnology really is the panacea of water treatment.
Nanoparticles and nanofilters offer great potential for water treatment, particularly when facing the challenge of how to produce clean water for those in developing countries. However, the risks of using small, reactive particles, which could inadvertently end up in the water system and affect biological ecosystems cannot be overlooked. Further testing must be carried out before nanoparticles can be deemed safe to enter the water supply, in order to mitigate the risk of devastating biological communities.
The ground-breaking E-Flows mesocosm project, developed, designed, managed and operated by Fera Science Ltd in partnership with the Centre for Crop Health and Protection (CHAP), supported by Innovate UK, will provide scientific research opportunities across a wide range of industries.