Nanomembranes in Water Treatment

By Will Soutter

Topics Covered

Introduction to Water Treatment
Nanotechnology for Water Treatment
Waterless Toilet Initiative
Nanopore Sterilization
Conclusion
Sources

Introduction to Water Treatment

Water treatment encompasses several industrial-scale processes that are used to make water acceptable for specific applications such as for drinking water, industrial use, medical use, and many others. The key objective of all water treatment processes is the removal of contaminants, or at least reduction of the concentration of these contaminants so that water becomes suitable for a specific end-use.

There are several ways of treating water, some of which are listed below:

  • Water conditioners – used to treat hard water to improve heating and cleaning efficiency, and increase lifespan of water-using appliances.
  • Activated carbon (AC) water filters – remove chlorine and organic contaminants from water.
  • Ultraviolet (UV) water filters – destroy almost all bacteria and viruses in the water. High processing capacity, but do not remove dead cells or other contaminants.
  • Water distillers – This is very similar to the natural water cycle process. The distilled water is free from almost all kinds of contaminants. Running costs are high, however, and the processing capacity is very low.
  • Sand filters – removes most bacteria and turbidity and has a high filtration capacity. Effective for ponds and swimming pools.
  • Reverse osmosis – effectively removes foul smell, taste or color, anything that will make the water unappealing or unhealthy. This method recovers only 5% of the water passing through it.

Nanomaterials could help to make water treatment plants more efficient and cheaper to run, as well as potentially making them easier to build in developing countries where the clean water supply is limited. Image credit: InterLinc

Nanotechnology for Water Treatment

Nanotechnology is a key feature of a lot of modern water treatment research and novel treatment methods. It has been shown that nanostructured materials can improve present polymeric and ceramic water treatment membranes.

The most promising nanomaterials for this field include catalytic and zeolitic nanoparticle-coated ceramic membranes, isoporous block copolymer membranes, aligned nanotube membranes, bio-inspired membranes like hybrid protein-polymer biomimetic membranes and hybrid inorganic–organic nanocomposite membranes.

It must be noted that bio-inspired membranes are very far from commercial reality, but have shown highly promising performance enhancements in initial studies. Some nanocomposite membranes, such as thin film zeolite composites, should be simpler to implement commercially, however, and do offer a considerable increase in performance over conventional membrane technology.

Waterless Toilet Initiative

Cranfield University is taking part in a scheme to develop hygienic waterless toilets that promise to transform lives of nearly 2.5 billion people globally who do not have access to basic sanitation. This project has received funding of nearly $800,000 from the ‘Reinvent the Toilet Challenge’ of the Bill & Melinda Gates Foundation Water, Sanitation and Hygiene initiative.

There are several areas that do not have access to affordable sanitation, and these areas also typically have unreliable or non-existent water, electricity and sewage supplies. The Cranfield team have proposed a nanomembrane toilet as a sustainable sanitation solution, which will be capable of treating human waste without water or external energy, enabling it to be transported away safely, and even reused as fertilizer or fuel. The waste sludge is passed through membranes to remove contaminants, and re-collected as a vapour for re-use - the whole system is powered by the user, so no external power is required.

Nanomembranes can filter microbes and contaminants from water more efficiently than conventional materials - however, they are still some way from commercialization. Image credit: Nanomembrane Research Group, University of Rochester.

Nanopore Sterilization

The University of Buffalo has conducted research into new nanomaterials for the separation of bacteria from drinking water.

The UB research team developed a block copolymer which forms a nanomembrane containing pores of 55 nm in diameter - easily large enough for water to flow through, but too small for bacteria.

Lead researcher Javid Rzayev stated that whilst the team were able to make the pores as small as 50 nm, increasing the pore size ever so slightly resulted in increased water flow, which translates to savings in processing time and therefore cost, without significantly changing the effectiveness of the sterilization process.

Rzayev and colleagues removed one of the polymers in order to create evenly spaced polymers in the material. The relatively large size of the pores was because of the innovative architecture of the original block copolymers that were made from bottle-brush molecules resembling round hair brushes, with molecular "bristles" that protrude all the way around a molecular backbone.

Conclusion

Ongoing research proves that nanotechnology can contribute significantly to the advancement of water treatment technology. The available performance benefits are currently outweighed by the cost of implementing the new technology for the most part, but as research progresses, and the nanofabrication industry grows and improves, this will begin to change.

One major concern regarding the use of nanotechnology in water treatment, as with in many other areas, is the impact of nanomaterials on health and the environment, an area that is being extensively studied and analyzed. It is believed that with a common framework for risk assessment, risk research and risk management, novel nanomaterials, especially in wastewater and water treatment, will play an important role in ensuring sufficient and potable water to meet the growing global demand.

Sources

 

Date Added: Jan 8, 2013 | Updated: Jun 11, 2013
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