Global Dialogue on Nanotechnology and the Poor ... - Nanowerk

nanotechnology,
water, & development
[3.2.2] Attapulgite Clays, Nanoporous Zeolites,
and Nanoporous Polymers
Other source materials for nanofilters include zeolites, attapulgite clays,
and nanoporous polymers. Zeolites, attapulgite clays, and polymers
have been used for many years to purify water. Recent improvements
in scientists’ ability to see and manipulate on the nanoscale allow for
greater precision in designing these materials, for instance, allowing
much greater control over pore size of membranes. 58
Attapulgite clays are naturally occurring materials, which are locally
available in many places around the world. A study looking at the use
of attapulgite clay membranes to filter waste water from a milk
factory in Algeria showed that using the locally available clay in the
filtration process offered an economical and effective method for
reducing the amount of whey and other organic matter to make the
wastewater safe to drink. 59
Zeolites are microporous crystalline solids with well-defined
structures. Generally they contain silicon, aluminium, and oxygen in
their framework and cations, water, and/or other molecules within
their pores. Many occur naturally as minerals and are extensively
mined in many parts of the world. Others are synthetic and are
made commercially for specific uses or produced by research
scientists trying to understand more about their chemistry.
Zeolites can be used to separate harmful organics from water
and to remove heavy metal ions from water. 60
Researchers at Los Alamos National Laboratory have developed a
new class of nanoporous polymeric materials that can be used to
reduce the concentration of common organic contaminants in water
to parts-per-trillion levels. 61 These organic nanoporous polymers with
narrow pore-size distribution (0.7 – 1.2 nm) have been synthesized
using cyclodextrins as basic building blocks.The researchers say that
the binding between organic contaminants and the nanoporous
polymer is 100,000 times greater than the binding between organic
contaminants and activated carbon, which is commonly used in
wastewater treatment.These materials can be used for the
purification of municipal water supplies or for recycling and
reuse of industrial wastewater.
Organization
Table 4: Specific Examples of Nanoporous Polymers
Los Alamos National
Laboratory
Country
United States
Type of Technology
Developed a new class of
nanoporous polymeric
materials that can be used
to reduce the concentration
of common organic
contaminants in water to
parts-per-trillion levels.
Link
[3.2.3] Desalination
Desalination is the removal of dissolved salts from raw or untreated
water by either thermal or membrane processes. A thermal process
uses heat to evaporate water, which is then collected by condensation.
In a membrane process, pressure is applied to force the raw water
through a membrane that retains the dissolved salts. 62 Reverse
osmosis (RO) membranes can retain all the salt, whereas other
membrane processes, such as nanofiltration (NF), selectively retain
some salts. Desalination is carried out for various reasons, including
limited freshwater, increasing demand, global warming, regulation,
cost effectiveness, and politics.
A reverse osmosis (RO) desalination plant consists of the following
sequence of stages: feed water intake system, pre-treatment facility,
high-pressure feed pumps, RO membrane, desalinated water
conditioning system. A pressure of 40 – 80 bars is required for the
permeation of water through the RO membrane for the desalination
of seawater.Two membrane sheets are glued together and spirally
wound around a perforated central tube.The product water exits
through this tube. 63
Nanotechnology is used in Israel for the desalination of saline
waters.The Grand Water Research Institute of the Israel Institute of
Technology 64 is working with corporate and other partners to treat
salt water and create fresh sources for drinking water and irrigation.
They are using reverse osmosis whereby pressure is applied to salt
water, forcing the fluid through a very fine membrane resulting in
(virtually) pure water.
‘‘
The major setback of desalination
is that production costs are very
high. … It is expected that
nanotechnology… will drive down
’’
the costs of desalination.
A major impediment to wider
adoption of desalination
technology is high production
costs. A third of the costs are
http://www.lanl.gov/
required for supplying the
energy that forces the water
through the membrane.
Although significant
advancements in technology
have extended membrane life
58
Cientifica,“Nanoporous Materials,” 2003, .
59
K. Khider et al.,“Purification of Water Effluent from a Milk Factory by Ultrafiltration Using Algerian Clay Support,” Desalination, 167, 2004, pp. 147 – 151,
.
60
British Zeolite Association, .
61
M. C. Roco, et al. (eds.),“Visions for Nanotechnology Research and Development in the Next Decade,” Interagency Working Group on Nanoscience, Engineering, and Technology,
Loyola College, Maryland, September 1999, Section 10,“Nanoscale Processes in the Environment,” pp. 143 – 153 and Los Alamos National Laboratory,“Nanoporous Polymers for
Water Purification,” .
62
Filtration Industry Analyst, op. cit.
63
Filtration Industry Analyst, op. cit.
64
The Stephen and Nancy Grand Water Research Institute, .
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