Transcript Nanotechnology for Water Purification

Dr. Shamsa Kanwal
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The scarcity of clean water is expected to worsen in the future
due to over usage, lack of conservation methods and dwindling
natural supply of clean water, even in countries with significant
water resources.
Many hazardous pollutants enter the water supply through
many channels, including waste disposal, industry effluent
release or rain water drainage. Such pollutants need to be
removed before the water can be consumed. However, most
water purification technologies are not accessible to
economically disadvantaged people around the world.
The challenge for scientists is to develop robust water
purification methods that could carry out water treatment at
low cost, with minimal energy consumption and using less
chemicals in the process so as to reduce negative impact on the
environment.
" exhibit key physicochemical properties that make them
particularly attractive as high capacity and selective
adsorbents for water treatment,"
"They can increase their affinity toward compounds
including dissolved solutes such as toxic metal ions and
organic pollutants. This is how nanostructuring allows you
to achieve better performance.“
By knowing how the nanoscale works, we can make much
more efficient absorbents that target certain types of
pollutants that we couldn't do before, and it allows us to
treat water better, treat water more cheaply and treat
water faster than we have in the past, and those kinds of
products are starting to show up out there."
As a whole, the development of nanotechnology in
membranes, adsorbents and other filtration
techniques is starting to grow and be increasingly
utilized across the water sector.
 Along with membranes and adsorbents, substances
like nanocatalysts and nanoporous materials can also
aid the water and wastewater treatment process.
 In all, researchers are finding that nanotechnology
can be used in nearly any type of purification process
and offers a number of advantages to water
professionals and consumers alike looking to utilize its
applications.
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There are several nanotechnology approaches
to water purification currently being
investigated and some already in use. "Water
treatment devices that incorporate nanoscale
materials are already available, and human
development needs for clean water are
pressing,"
Researchers at the D.J. Sanghvi College of Engineering, india
Continued…
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The impurities that nanotechnology can
tackle depend on the stage of purification of
water to which the technique is applied.
It can be used for removal of sediments,
chemical effluents, charged particles,
bacteria and other pathogens.
Toxic trace elements such as arsenic, and
viscous liquid impurities such as oil can also
be removed using nanotechnology.
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"The main advantages of using nanofilters, as
opposed to conventional systems, are that
less pressure is required to pass water across
the filter, they are more efficient, and they
have incredibly large surface areas and can be
more easily cleaned by back-flushing
compared to conventional methods,"
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Carbon nanotube membranes can remove almost all
kinds of water contaminants including turbidity, oil,
bacteria, viruses and organic contaminants. Although
their pores are significantly smaller carbon nanotubes
have shown to have an equal or a faster flow rate as
compared to larger pores, possibly because of the
smooth interior of the nanotubes.
Nanofibrous alumina filters and other nanofiber
materials also remove negatively charged
contaminants such as viruses, bacteria, and organic
and inorganic colloids at a faster rate than
conventional filters.
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Water purification membranes enhanced by
plasma-treated carbon nanotubes are ideal for
removing contaminants and brine from water.
The study paves the way for the next
generation of portable water purification
devices, which could provide relief to the 780
million people around the world who face
every day without access to a clean water
supply.
* HuiYing Yang, Zhao Jun Han, Siu Fung Yu, Kin Leong Pey, Kostya Ostrikov, Rohit Karnik. Carbon nanotube
membranes with ultrahigh specific adsorption capacity for water desalination and purification. Nature
Communications, 2013; 4
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These membranes could be integrated into
portable water purification devices the size of a
tea pot that would be rechargeable, inexpensive
and more effective than many existing filtration
methods. Contaminated water would go in one
end, and clean drinkable water would come out
the other.
"Small portable purification devices are
increasingly recognised as the best way to meet
the needs of clean water and sanitation in
developing countries and in remote locations,
minimising the risk of many serious diseases,"
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"The large industrialized purification plants
we see in other parts of the world are just not
practical -- they consume a large amount of
energy and have high labor costs, making
them very expensive to run."
Most water purifiers work by trapping bacteria
in tiny pores of filter material. Pushing water
through those filters requires electric pumps
and consumes a lot of energy. In addition, the
filters can get clogged and must be changed
periodically. The new material, in contrast,
has relatively huge pores, which allow water
to flow through easily. And it kills bacteria
outright, rather than just trapping them.
David T. Schoen, Alia P. Schoen, Liangbing Hu, Han Sun Kim, Sarah C. Heilshorn, Yi Cui. High Speed
Water Sterilization Using One-Dimensional Nanostructures. Nano Letters, 2010; 10 (9): 3628
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Contact with silver and electricity can destroy
bacteria!
Therefore spreading sub-microscopic silver
nanowires onto cotton, and then by adding a
coating of carbon nanotubes, which gives the
filter extra electrical conductivity.
Tests of the material on E. coli-tainted water
showed that the silver/electrified cotton killed
up to 98 percent of the bacteria. The filter
material never clogged, and the water flowed
through it very quickly without any need for a
pump.
Scientists have developed a way to transform
ordinary sand -- a mainstay filter material used
to purify drinking water throughout the world -into a "super sand" with five times the filtering
capacity of regular sand.
The new material could be a low-cost boon for
developing countries, where more than a billion
people lack clean drinking water, according to
the report in the ACS journal Applied Materials &
Interfaces.
Wei Gao, Mainak Majumder, Lawrence B. Alemany, Tharangattu N. Narayanan, Miguel A. Ibarra, Bhabendra K. Pradhan,
Pulickel M. Ajayan. Engineered Graphite Oxide Materials for Application in Water Purification. ACS Applied Materials &
Interfaces, 2011, DOI: 10.1021/am200300u
Sand has been used to purify water for more than 6,000
years, and sand or gravel water filtration is endorsed by
the World Health Organization.
 Studies of a nanomaterial called graphite oxide (GO)
suggest that it could be used to improve sand filtration in
a cost-effective way.
 A simple method has been developed to coat sand grains
with graphite oxide, creating a super sand that
successfully removed mercury and a dye molecule from
water. In the mercury test, ordinary sand was saturated
within 10 minutes of filtration, while the super sand
absorbed the heavy metal for more than 50 minutes.
 Its filtration "performance is comparable to some
commercially available activated carbon,"
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Tomato peels can effectively remove different contaminants
in water, including dissolved organic and inorganic chemicals,
dyes and pesticides, and they can also be used in large scale
applications.
 Similar to tomato peels, apple peels can also remove a range
of dissolved water pollutants through the adsorption process.
In order to enhance the ability of apple peels towards
extraction of negatively charged pollutants, researchers
immobilised naturally occurring zirconium oxides onto the
surface of apple peels.
 Zirconium loaded apple peels were found to be able to extract
anions such as phosphate, arsenate, arsenite, and chromate
ions from aqueous solutions. This method of water
purification can also be used for large scale applications.
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Scientists are struggling that the findings on the use
of apple and tomato peels for water purification
can be applied to benefit economically and
technologically disadvantaged farmers living in
remote villages, who depend on contaminated
ground water or local rivers for their daily water
needs. They intend to work with nongovernmental organisations to transfer their
research findings and knowledge to benefit the
people.
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Have put the conservatism of the water industry aside, and are
thinking smaller to make sure people don't go thirsty.
In South Africa, the humble teabag has inspired a way to clean
water 1-litre at a time. In the mouth of an ordinary drinking
bottle sits a teabag-like net that is a nanotech marvel.
Developed by Eugene Cloete at Stellenbosch University in South
Africa, the inside of the biodegradable teabag is coated with thin
water-soluble polymer nanofibres that have been impregnated
with anti-microbial agents and spun into a fine mesh.
The material filters out most contaminants – up to 99.99% of
bacteria. The "tea leaves" inside the bag are activated carbon,
which can suck out heavy metals and other contaminants.
As yet the tea bag remains a prototype, the final version,
intended for consumers, is still being developed by the company
AquaQure. But there is already much hope that this filter could
make a big difference to the lives of people who do not have
easy access to clean water.
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