31 No. 4
Nanotechnology: An Answer to the World’s Water Crisis?
by Alan Smith
As the world’s population rises from 6.5 billion today to 9 billion by 2050, access to fresh water will become even more important in the near future. Unfortunately, 97 percent of the world’s water is salt water; of the remaining 3 percent, two- thirds are frozen.1 As well as being scarce, the remaining 1 percent of the world’s water supply is not evenly distributed, and this shortage is clearly a serious problem for developing countries.
The World Health Organization (WHO) has estimated2 that 80 percent of illnesses in the developing world are water related, resulting from poor water quality and lack of sanitation. There are 3.3 million deaths each year from diarrheal diseases caused by
E. coli, salmonella and cholera bacterial infections, and parasites and viral pathogens. In the 1990s, the number of children who died of diarrhea was greater than the sum of people killed in conflicts since World War II.
- 215 tonnes of H20 to produce 1 tonne of steel
- 300 tonnes of H20 to produce 1 tonne of paper
- 1000 tonnes of H20 to produce 1 tonne of grain
- 15 000 tonnes of H20 to produce 1 tonne of beef
In 2004, IUPAC held a conference in Paris on Chemistry in Water intended to address some of the WHO statistics relating to water supplies. At that conference, the use of nanotechnology was only mentioned briefly, but, in recent years, interest has escalated.
In a report,3 the Organization for Economic Co-operation and Development and Allianz highlighted how nanotechnologies for water treatment are expected to impact the developing world. PLoS Medicine, a policy forum for improving healthcare in society, has also identified4 the importance of improved water treatment as one of the top 10 ways nanotechnology will change lives. A third, more recent, paper also considered the top 10 ways nanotechnologies will affect us, and clean water is listed among them.5 Clearly, nanotechnologies are set to make a considerable impact on the water sector, most likely through three main areas: purification and wastewater treatment, monitoring, and desalination.
Purification and Wastewater Treatment
Water for People: Water for Life, a UNESCO study,6 reports that disinfection of water at the point of use has consistently proven to be the most cost-effective treatment method, putting the onus on the poor to ensure their drinking water is clean. In the developed world, what is being described as nanofiltration is receiving a lot of attention from water-treatment companies. Nanofiltration purifies water not by forcing it through tiny holes but by using a positive charge to attract negatively charged viruses and bacteria. TriSep Corporation, based in the USA, offers two nanofiltration membranes developed by DuPont; one removes color, iron, and hardness, and the other removes divalent ions and low molecular weight compounds, such as sugars. Argonide Corporation, also in the USA, has developed a highly electropositive filter, NanoCeram, that rapidly absorbs particles, no matter how small. The company is also promoting a new virus- and protein-separation process with a nanoalumina fiber that they claim removes 99.9999 percent of bacteria, viruses, and protozoan cysts. FilmTec Corporation, a subsidiary of Dow Chemical Company, makes high-quality reverse osmosis and nanofiltration elements for a wide variety of industrial, municipal, commercial, and home drinking-water applications. A number of other U.S. companies, such as EMembrane, Inc., KX Industries, Taasi, and so forth, have also developed nanofiltration systems.
The suitability of the above examples for remote locations is not clear, but nanofiltration membranes have been used in a rural village in South Africa7 for providing drinking water where the community water was contaminated with nitrates, chlorides, phosphates, and sulfate pollutants. The process uses four flat-sheet nanofiltration membranes and a reverse osmosis membrane.
Other techniques use the high surface area of nanoparticles or nanoclays to absorb pollutants, while an additional method uses nanoparticulate catalysts to break down contaminants. A promising development from the University of South Australia8 is the use of pure silica coated with an active material to remove toxic chemicals, bacteria, viruses, and other hazardous materials from water. The claims are that these particles, coated with a nanometer thin film of active material, are more effective and cost less than conventional water-purification methods and could be used for small and large quantities of water.
A further development is the use of carbon nanotubes, hollow carbon fibers only one nanometer in diameter. Seldon Laboratories of Vermont has developed a nanomesh fabric made of fused carbon nanotubes that it says can filter out all bacteria, viruses, and other waterborne pathogens to U.S. Environmental Protection Agency potable water standards. The company claims that the mesh also removes lead, arsenic, and uranium. Researchers at Rensselaer Polytechnic Institute in the USA and Banaras Hindu University in India claim to have devised a simple method of producing carbon nanotube filters that remove microscale to nanoscale contaminants, such as nanometer-size polio viruses from water, as well as larger pathogens, such as E. coli and Staphylococcus aureus bacteria.
The University of Aberdeen is working with partners to develop a new technology that uses sunlight to treat dirty water and generate electricity at the same time.9 Proof of concept has been demonstrated, and now they are scaling up to verify earlier indications that the process is more cost effective and environmentally friendly than existing technology and can treat chemical and biological contaminants. A photoelectrocatalyst is mounted into an electrochemical cell; when it reacts with light, the catalyst interacts with any organic matter in the water, oxidizing them across the catalyst’s surface.
The developed world is looking at the analysis of a wide variety of contaminants in water.10 Nanotechnology offers the potential for faster and more sensitive measurements; for example, in the health-care sector, the goal is to detect diseases before they have taken hold on the body. Promising nanotechnology applications for monitoring water already exist, but they tend to be specific to industrial applications where ultrapure water is being used.
An exciting development on the detection front comes from NanoSight in the UK,11 which has a system that can detect waterborne nanoparticles and viruses in real time.
- Metals: Cd, Cu, Pb, Hg, Ni, Zn, As, Cr, Al, Be, Ag
- Nutrients: PO43-, NH3, NO3-, total P, total N
- Algae: cyanobacterial toxins
- Biological: biological agents for terrorism, E. coli, viruses, bacteria, parasites
- Other: cyanide, organics, antiobiotics, chlroacetic acid, PBDEs
As noted before, most of the world’s water is salt water, and, despite technologies having been around for many years now, desalination is a very energy-intensive procedure with costly infrastructure and it tends to be expensive. The conventional process uses reverse osmosis, where extremely high pressure forces saline or polluted waters through the pores of a semipermeable membrane. Water molecules under pressure pass through these pores, but salt ions and other impurities cannot, resulting in highly purified water. However, nanotechnology solutions can greatly reduce the costs of desalination and are actually being used in such places as Israel and U.S. municipalities (e.g., Long Beach, California). Researchers at University of California at Los Angeles have developed a new reverse osmosis membrane that promises to reduce the cost of seawater desalination and wastewater reclamation. The new membrane uses a uniquely cross-linked matrix of polymers and engineered nanoparticles designed to draw in water ions but repel nearly all contaminants. These new membranes are structured at the nanoscale to create molecular tunnels through which water flows more easily than contaminants.
The nanocoated silica system from Australia, mentioned above, has been suggested as a very attractive alternative for desalination.
The Meridian Institute in the USA has focused on how nanotechnologies can help the poor and has produced a report7 with case studies entitled Nanotechnology, Water Development. The main issues that need to be resolved include the following:
- accessibility to technologies
- ease of operation
- fair distribution
A number of conferences have addressed the need for improved water-treatment methods, but it is unclear what action or progress has been taken, and they are more focused on improving the situation in developed countries. With thousands of children dying each day, the issues for developing countries need to be addressed very rapidly by some of the leading organizations that should be helping solve the problems. At the earliest opportunity, an assessment comparing the costs of currently accessible technologies that generate clean water with those in development is needed. This would provide a better view of what target technologies governments should be chasing. Developments in nanotechnology for water treatment are merely drops in the ocean; a great deal of progress has been made in the last five years, but more is needed—quickly.
|A current IUPAC project entitled Analysis of the Usage of Nanoscience and Technology in Chemistry will map and critically study the use of the prefix “nano” in various fields of chemistry. The last few years have shown a wide proliferation of the terminology related to nanotechnology and nanoscience in chemistry. Today, all high-impact chemistry journals contain a large number of papers devoted to this growing area, as many conferences include specific sessions on nanotechnology. This project is the first step toward recommendations on the use of chemistry terminology related to nanoscience and nanotechnology, in order to avoid confusion; for more information, see <www.iupac.org/web/ins/2007-040-2-200>.
1. For water-related information, see the Freshwater website from the Government of Canada’s Environment Department: <www.ec.gc.ca/WATER/e_main.html>.
2. See WHO website for data information: <www.who.int/household_water/en/>.
3. Opportunities and Risks of Nanotechnologies, Organization for Economic Co-operation and Development and Allianz report, June 2005.
4. F. Salamanca-Buentello, et al. (2005) Nanotechnology and the Developing World. PLoS Med 2(5): e97. doi:10.1371/journal.pmed.0020097
5. “Top Ten Ways Nanotechnoloogy Will Impact Life in the Next Ten Years,” Nanotechnology Law and Business Journal 4(3), 2007.
6. UNESCO has published three reports on water; see <www.unesco.org/water/wwap/wwdr/index.shtml>.
7. Meridian Institute report, Nanotechnology, Water and Development, 2006.
8. P. Majewski, “Purifying Powder,” Nano Magazine no. 7, June 2008.
9. Nanotechnology for Sustainable Water Purification, DTI Report, Case Study, <www.berr.gov.uk/files/file28138.pdf>.
10. S. Morgan, Commercialising Nanotechnology in Water, Nanotechnology Victoria, Melbourne, June 2006.
11. NanoSight’s website can be accessed at <www.nanosightuk.co.uk>.
Alan Smith <[email protected]> is the founder of AZ-TECH Consulting Services <www.az-technology.org>. Smith has significant experience in nanotechnology and is the author of numerous articles on different aspects of nanotechnology, and has lectured worldwide on the topic. Until recently, he was an associate director of the UK’s Micro Nano Technology Network and a member of the Nanotechnology Industry Association. He is a member of the IUPAC Bureau and a member of the Committee on Chemistry and Industry.
last modified 1 July 2009.
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