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Nanofiltration May Help In Reaching Target UN Water Goals

by Adrianna Kuzma

Quantity is every bit as much an issue as quality when it comes to water for developing nations. In my last column, I talked about the benefits of using a nano-teabag technology as a short term solution to global water problems in third world countries where infrastructure is unavailable. Many developing countries lack roads, plumbing, and electricity. Where there is infrastructure, however, nanofiltration can be very effective at catching micro bacteria and other contaminants that could be harmful to human beings.  Looking at the benefits and the drawbacks of nano-membranes is necessary to decision making about this new technology.

Just as a reminder to my readers, nanotechnology is so small that 6000 of the nano-particles could fit on the head of a pin. Nanotechnology is the science of using these nano-sized molecules to catch micro-organisms and contaminants such as those found in river water. To help visualize this, picture a fine mesh kitchen sieve. The sieve is like the filter or membrane  used to clean water. In using nanotechnology, the water cleaning filter acts as a semipermeable membrane, with holes or pores to allow some items through—in this case, letting water molecules through but catching bacteria and viruses.   The large food items in the kitchen sieve stay, but water passes through the sieve.

This image illustrates how small nanotechnology is compared to DNA, bacterium, and a large water droplet.  The Future of Nanotechnology.  Web. 22 June 2012. http://futureforall.org/nanotechnology/nanotechnology.htm

 

 

 

There are primarily four types of membranes, each representing a smaller pore size and increased ability to capture contaminants. Moving from largest to smallest (in terms of pore-size): microfiltration (0.1 microns ) and ultrafiltration (0.01 microns) are good, but nanofiltration offers even smaller pores (0.001 microns) to filter out pollutants and bacteria, and reverse osmosis (at 0.0001 microns) provides the smallest pores. Although it sounds small, microfiltration does not remove bacteria, and viruses can move right through the pores. Whereas microfiltration cannot remove viruses from the water, ultrafiltration can. And whereas ultrafiltration does not stop bivalent ions (two or more charges of ions), such as lead and mercury, nanofiltration is able to remove toxic metals and unwanted bivalent ions.

 

This image shows a sponge-like nano filter and a close up of the pores. Nanomembranes can be tailored to catch specific contaminants or bacteria by incorporating into the membrane nanoparticles toxic to the specific bacteria targeted. Nanosense. Stanford Research Institute. Web. 22 June 2012. http://www.scribd.com/doc/33490659/FF-NanofiltrationSlides

 

 

Nano-particles jointly form a large surface area or net to catch pollutants in water. One type of nano membrane can be explained by a further analogy. Imagine a volleyball net stretched across the pipe where the water enters. With a nano membrane that builds in ion-repelling materials, the net of nano particles catches the contaminants (the volleyballs) by electrifying the ions in the contaminants, such as toxic metals. This produces a net of electricity that basically organizes the ions into channels based on their negative charge. This allows the neutral water to pass through the channel with the negative toxic ions lined up at the end of the channel (Gen). So, in terms of the volleyball comparison, the volleyball toxins line up along the surface of the net. Each hole in the volleyball net represents a channel where the water molecules (the golf balls) line up and pass through.

As with reverse osmosis membranes, nano-membranes can filter out ions and small contaminates. At this time, reverse osmosis is perhaps the most common type of membrane on the market for such water treatments as desalinization. Reverse osmosis, or RO, is a process whereby water is put under great pressure to flow through a polymer membrane which strains out contaminants or pollutants in the water such as salts, bacteria, and lime. In reverse osmosis, water flows to the solute or brine side of the tank.   Pressure is required to push the water back through the membrane. The diagram below shows this reverse flow of water back through the membrane. If no applied pressure is introduced, the two tanks will reach equal height.

This illustration shows reverse osmosis in the three stages: 1) water that is not safe to drink because it contains a dissolved solid such as salt flows through the membrane from right to left, 2) the concentration of dissolved solids mixes to become uniform across the membrane but the solute, such as salt, stays on the left until 3)  pressure must be applied on the left tank to move the water in the reverse direction, to the right side.  “Nano filtration and Reverse Osmosis.” Water Treatment Solutions: Lenntech.  Web 24 June 2012.  http://www.lenntech.com/nanofiltration-and-rosmosis.htm

While the technology for such reverse osmosis membranes have become conventional in desalinization, nanofiltration is less common. The big difference–and the reason for the interest in nano membranes–is that nanofiltration is much less expensive–about half the cost of reverse osmosis, because nano membranes do not require the high pressure that reverse osmosis membranes do. As seen in the diagram above, showing a reverse osmosis membrane, the water must be forced back through the membrane in the reverse direction, requiring more extensive energy inputs than nanofiltration.

When coupled with nano-filtration or NF membranes, reverse osmosis membranes are called dense membranes. These two membranes can remove a whole range of “dissolved species such as ions” in water (Müller). In other words, while combined RO and NF membranes are more effective at removing contaminants (than traditional desalinization processes) when they have smaller pores, they require more energy to push the water through the membranes. So, the energy costs of electricity presumably go up once membranes are combined. In some cases, the addition of membranes to the system may serve as a pretreatment to prevent membrane fouling.

This diagram (big pores on the left and smaller pores on the right) describes how each of membrane filters out specific contaminants that would harm the human body and how they can be combined to have the maximum effect. Nanosense.  Stanford Research Institute Web. 22 June 2012.  http://www.scribd.com/doc/33490659/FF-NanofiltrationSlides

A membrane that catches nano-particles before they go out into the environment is NSM, which means nano-sized membranes. In simple terms, Muller states that this means “NSM do not contain any nano-particles and must be clearly distinguished from membranes with integrated nano-particles (nano-enhanced membranes)” (Müller).  Apparently, the NSM membranes have nanosized pores to allow the water through but catch the nano-particles out of the water. As a result, this membrane does not have environmental impacts or adverse effects on human health and ecosystems because it does not allow nano-particles to move through the membrane (Müller). While this would be the best choice for cleaning water to standards safe for drinking (and to avoid adverse environmental impacts) this membrane may require greater energy and electricity inputs.

Requiring less time than conventional water treatment, nanofiltration typically occurs in a single treatment and produces cleaner water. Nanofiltration seems particularly well suited to treating ground water because of its ability to soften water and remove pesticides. Those developing nations where salt removal is not the top priority and where farmers use nitrates seem especially good candidates for low pressure nanofiltration systems. As water from wells and underground sources is less available, rivers and lakes become a source of water. Agricultural run-off  from food crops and livestock make surface water more difficult to purify because of such occurrences as bacteria from livestock (Nicoll). Nanofiltration utilizes several polymer layers or sheets of filter materials. Most often, these sheets are rolled vertically to fit into a cylinder, as seen in the following diagram.

Illustration of a nano-membrane that shows the layers of filters as they are rolled around a collection pipe. “Membrane Technology and Research.” 2011. http://www.mtrinc.com/faq.html

In the past, poor people have been forced to purchase water tokens as a result of the World Bank’s making loans to developing countries conditional on the privatization of their water. Although intended to get water into poor regions quickly, privatization did not work because the people did not have the means to pay even modest water fees and instead went to other sources (i.e. polluted surface water). Nanotechnology involves high tech costs and demands. Upfront costs include the following: research, upgrading equipment and training personnel as well as building infrastructure such as roads (Berger). Taken collectively, these expenses can become a barrier to introducing nanotechnology.

There are other problems when introducing high-tech methods into impoverished areas. According to the authors of “Nanotechnology and The Challenge of Clean Water,” when a company goes into on area without clean water to build a plant, the employees often expect to build and go home. The success of such a facility, however, requires that the people living there understand how nanotechnology works. In a pilot program in which the scientists set up workshops and involved the native people in discussions, each member of the community took a role to keep the water clean (Hillie, Hlophe). Although the UN does have volunteers who can be sent in to help set up nano-membranes for water treatment, long-term commitment by the community receiving the assistance is essential.

There are environmental and health concerns about nanotechnology as well. These include contamination resulting from the technology itself, the difficulty of containing the nano-particles, and the absence of studies about the effects on humans. Within the water cleaning membranes are nano-filters made of polymers that hold the nano-particles inside. This cleans the water with the nano-particles going into the main stream of fresh water. In 2008, there was a concern that the nano-particles are staying in the water, and scientists have not yet studied the effects on humans (Dickson). Some membranes use nano-particles such as metal, dendrimers, and clays to clean the water. These are usually not considered toxic materials; however, the concern is that their accumulation in the body could be toxic.

There are several health concerns about cleaning water with nanotechnology. One of these concerns is its size. Since nanotechnology is so small, it can be hard to contain the nano-particles.  Researchers would need to make sure nano-particles do not contaminate the environment and harm aquatic life. Because of its size, moreover, scientists do not know what nano-particles can do to a human body once they are consumed in water or concentrated in the body of fish. By comparison, pregnant women are warned not to eat clams, for instance, because of the accumulated mercury contained in them. This means that there may be traces of nano-particles in the water left behind after it is cleaned. People are concerned that nano-particles may be toxic because there has not been a study showing that they are not.

A related concern is public acceptance, and as Maclurcan points out, nanotechnology is not universally embraced. People might view nanotechnology as science fiction or not even real. It might look like a high-tech solution or a quick fix that is highly impractical for Third World countries where it would cost a lot of money to implement (Maclurcan). However, despite the need to overcome misconceptions, the use of nanotechnology for water treatment is not as radical an application as it might be in other fields. In fact, the concept itself is basic even to conventional water cleaning which works by filtering out or in other ways contaminants.

For this reason, the concern about regulation is critical. The nanotechnology may not be monitored effectively. According to Dickson, for instance, a nano filter could fail to disinfect the water and if not monitored this would be a serious problem. In effect, there is a need to oversee the nanotechnology in progress (Dickson). Therefore, it is crucial that the UN scientists do not set up a nano-system in a development region and then leave without teaching people how to monitor and maintain the technology. There is a potential for membrane fouling, which means that the particles are strained out and eventually accumulate on the membrane itself, clogging up the pores in the process of cleaning water. To stop this fouling from happening, the manufacturers can install a backwash and micro bubbles to clean the membrane completely for reuse.

As with the introduction of any new technology, there are issues related to market failure, intellectual property rights, and non-cooperative groups. If nanotechnology is accepted, these concerns need to be addressed. From a strictly business perspective, the introduction of nanotechnology may result in market failure. For example, as with the teabag technology discussed in my last column, if the nano-membrane were only marketed to those who already have access to good water, it will not provide safe drinking water to the most impoverished people. In addition, intellectual property rights are a concern. If the company making the nano membranes finds their technology being duplicated by others, there may be little incentive to sell this technology in the future. Finally there is a concern that groups may not cooperate. Getting various groups of stakeholders, such as government officials, private companies, and end-users (consumers), to cooperate is largely a matter of educating everyone involved concerning the benefits of safe drinking water. Companies selling nanotechnology materials and services, such as nano-membranes, to developing countries need to provide the long- term commitment to assisting both with implementing and maintaining these systems.


This photograph shows the relative size of the membranes, seen in a shelving unit. The man pictured is holding one of the membranes. “The State Government Kicked Off the Commissioning of RO facility between Gogha in Saurashtra and Dahej in South Gujarat.” The Times of India 25 Jan. 2012. Web. http://article.wn.com/view/2012/01/25/Essar_Projects_to_commission_Ro_Ro_facility_to_connect_Saura/

Although these concerns need to be addressed, there are distinct benefits that make nano- membranes particularly attractive for developing countries. Where there is minimal support infrastructure, nano-membrane filtration systems compare favorably to conventional water treatment due to their compact design and automation. One clear advantage of nanotechnology is its ability to target specific contaminants or pollutants in water. Nano-membranes can be designed to eliminate particular contaminants in the water, and this may result in a pinpoint system that is more cost effective than selecting a membrane containing separate filters for every potential contaminant. The relatively small size of nano-particles allows the membranes to strain out specific contaminants that would harm the public at large. For instance, some of the contaminants are bacteria, salts, mercury, and arsenic. Conventional water purification uses membranes but not to the degree of these nano-scaled membranes that can target and strain out micro-contaminants but also disease-causing organisms (Müller). The flexibility in cleaning specific contaminants in water makes nano- membrane especially desirable, allowing it to be tailored for the needs of developing countries.

The long-term savings make the initial costs worth the investment. By putting in water-cleaning technology, people can stay healthy; therefore, they can avoid losing wages due to sick days and thus maintain support for their families. In addition, the government is not overloaded with costs of healthcare for the poor. Over the long haul, these savings could mount up, and all these hidden but nonetheless real benefits could cover some of the costs of setting up nanotechnology facilities and equipment that saves lives. Because of such long -term savings, governments should be encouraged to take a lead in implementing nanotechnology. India, for instance, is working to build private and public cooperation (Fostering 7). Government officials should be involved in the development of nano-membrane water treatment to make it affordable for the public. This is because a government only needs to pay for the supplies and the workers while a private company would additionally have to pay their shareholders.

“Technology adaptation” means that the people must be taught about nanotechnology– how it works, and how it can benefit the community at large (Hillie, Hlophe). When teaching people, it’s important to keep the steps simple (Hubley 234). Although people must also be taught that not all water is safe to drink. It’s not enough to stop there. Hubley states: “water-related diseases such as cholera, typhoid, and diarrhea cannot be eliminated by providing clean drinking water alone, but by increasing the quantity of water available, promoting the use of latrines and a comprehensive range of hygiene measures” (234). Teaching people about the consequences allows them to become wiser about the direct health benefits.

Nanotechnology is going to be important in the future because the natural supply of fresh water is dwindling. The 2015 goal of water safety will probably not be met, but the UN should keep progressing with this goal by facilitating nanofiltration systems for recommended locations in developing countries where sufficient infrastructure exists. The UN can provide guidelines to insure that nanotechnology is judiciously introduced. Whereas the nano teabag technology discussed in last month’s column meets the goal of providing an immediate point source of clean water, it does not address the long-term and large scale need for safe water. Nanofiltration systems can answer that bigger problem by providing high quality water in a way that can be more readily upgraded than conventional water treatment facilities. In addition, because membranes are enclosed in tanks, water security is less of a concern than it might he with conventional systems that are open to the elements. Some view nanotechnology as not just a secure and safe water cleaning method but as a way to help developing nations advance their leadership (Maclurcan). Developing expertise can improve the economic life of these development communities. So there are many benefits beyond just delivering clean water.

Works Cited

Berger, Michael. “Some Nanotechnology Risks Worry Scientists More Than The Public. Nanowerk. 26 Nov. 2007. Web. 8 May 2012. http://www.nanowerk.com/spotlight/spotid=3419.php 

Crossette, Barbara. “Scrutinizing Millennium Goal Claims as 2015 Looms.”  Pass Blue: Covering the UN. 16 April 2012. Web. 15 May 2012.  http://passblue.com/2012/04/16/scrutinizing-millennium-goal-claims-as-2015-looms

Dickson, David. “When Small is Not Always Beautiful.” Science and Development Network. 2 August 2004. Web. 3 May 2012.  http://www.scidev.net/en/editorials/when-small-is-not-always-beautiful.html

Fostering “Nanotechnoloy to Address Global Challenges: Water Organisation for Economic Co-operation and Development.” Organization for Economic Co-Operation and Development. 2011. Web. 1 May 2012. http://www.oecd.org/dataoecd/22/58/47601818.pdf

Gen, Boomer.  “Cleaning Water Thru The Nanotechnology.” Manilla Bulletin.com  12 April 2012.  Web.  22 June 2012.  http://www.mb.com.ph/articles/356843/cleaning-water-thru-the-nanotechnology

Grimshaw, David.  “Nanotechnology For Clean Water: Facts and Figures.” Science and Development Network. 6 May 2009.  Web. 2 May 2012. http://www.scidev.net/en/features/nanotechnology-for-clean-water-facts-and-figures.html

Hillie, Thembela , and Mbhuti Hlophe. “Nanotechnology and The Challenge of Clean Water.” Nature Nanotechnology 21 October 2007. Web. 10 May 2012. http://www.nature.com/nnano/journal/v2/n11/full/nnano.2007.350.html

Hubley, J.H. “Barriers to Health Education in Developing Countries.” Health Education Research. 1.4 1986, 233-45.

Maclurcan, Donald C. “Nanotechnology and Developing Countries – Part 1: What Possibilities.” Azonano  30 Sept, 2005. Web. 2 May 2012. http://www.azonano.com/article.aspx?ArticleID=1428

Membrane Image. MTR “Membrane Technology and Research.” 2011. Web. 6 May 2012. http://www.mtrinc.com/faq.html

“Mozambique: Guitar Hero.” Frontline World. 27 May 2008. Web. 7 May 2012. http://www.pbs.org/frontlineworld/watch/player.html?pkg=704_moz&seg=1&mod=0

Müller, Nicole. “Nanostructured Membranes for Water Treatment Environment Nano Observatory Briefing.” OdservatoryNano 13 March 2011.  Web. 3 May 2012. http://bwcv.es/assets/2011/7/26/ObservatoryNANO_Briefing_No.13_Nanostructured_Membranes_for_Water_Treatment.pdf

Nicoll, Harold. “Nanofiltration Membranes.”  Water and Wastes Digest.” Web. 26 June 2012.  http://www.wwdmag.com/membranes-nanofiltration/nanofiltration-membranes

Thate, Karine. “Cleaning Our Water with Nanotechnology.”  Museum of Science, Boston.  NSF Center for High-rate Nanomanufacturing . 1 Oct. 2011.  Web. 19 June 2012.  http://www.youtube.com/watch?v=X3_E24WcMI8

About the Author: Adrianna is a homeschooler from Indiana. She loves to sew and has made Regency ball gowns as well as fleece pet beds. She plays the cello, loves cats, and is passionate about caring for the planet. She recently produced a video on bottled water that won a national award.

3 Comments

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  1. Adrianna,
    Your article is superb. Not only did I learn all about Nanotechnology, I felt your desire to better our world and to help the less fortunate. Your writing technique is very professional, and I am very impressed. It’s exciting to learn from the next generation who will lead our country and world to hopefully a better place. Keep up your hard work, your dedication, and passion for the planet. I know I will see your name in LIGHTS in the future! Congratulations on a job well done!

  2. Well written and informative. Nano-enabled membranes are a key component for nanofiltration. The production process of such a nanofilter should be ecological and facile. Scientist could develop it sooner rather than later.

  3. Dear Ms Kuzma,

    Well written. Nano-enabled membranes are a key component in nanofiltration. Such as nanopores, porosity,morphology, surface characteristics, orientation, etc. Nevertheless, the production method should be ecological, facile, and cost-effective for more uses worldwide. I am sure that nanomaterial scientits can develop and commercialise them sooner rather than later. The shortage of clean water will become a chronic problem within a decade.

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