Developing Sustainable Water Purification Technologies - The NEWT Center
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Developing Sustainable
Water Purification
Technologies
The NEWT Center
DEVELOPING SUSTAINABLE
WATER PURIFICATION
TECHNOLOGIES
A significant proportion of the world’s population has little to
no access to clean water, and the water consumed by industrial
activities continues to grow. Researchers from the Nanotechnology
Enabled Water Treatment (NEWT) Center, which is headquartered
at Rice University, are developing cutting-edge purification
technologies that can provide communities with access to clean
and safe drinking water. They are also creating new wastewater
treatment methods that allow the reuse of industrial effluent,
to minimise freshwater withdrawals by industries. Instead of
conventional methods that use large amounts of chemicals and
energy, NEWT technologies are chemical free, and often utilise solar
energy.
Responding to Water Shortages is to enable access to water of suitable The migration of water vapour from
quality almost anywhere in the world the saltwater side to the freshwater
Many people across the globe do by developing next-generation, easy- side occurs to a greater extent when
not have access to clean water, and to-deploy modular treatment systems the difference in temperature across
there remains a vital need to provide enabled by nanotechnology. the membrane is higher. When the
communities with potable water temperature of the saltwater is high,
supplies. Seawater and other saline or Membrane Distillation the extent to which vaporisation occurs
compromised water sources are often is similarly high. Likewise, when the
readily available, but these supplies are One purification method that NEWT freshwater temperature is low, the
typically unsuitable for consumption, researchers are working to improve is extent to which condensation occurs is
given their high concentrations of called ‘membrane distillation’. In the also high.
salts, microbes, toxic metals, and other process of membrane distillation, hot
contaminants. Such water sources need saltwater is passed over a membrane These factors do, however, reveal an
to be purified before they can be used. on one side, while cold, freshwater flows inherent limitation with membrane
on the other side of the membrane. distillation. The act of vaporisation
Multiple research teams from the The membrane is porous, but keeps lowers the temperature of the hot,
‘Nanotechnology Enabled Water the saltwater and freshwater streams saltwater side and the process
Treatment’ (NEWT) Center are working apart. The temperature difference of condensation increases the
to tackle these urgent problems. Funded across the membrane and between temperature of the cold, freshwater
by the US National Science Foundation, the two streams causes hot water from side. The membrane also transfers
the Center is made up of researchers the saltwater side to vaporise through some of the heat energy from the
from Rice University, Arizona State the membrane and join with the colder saltwater side to the freshwater side.
University, Yale University, and the freshwater stream. The process does These and other temperature-related
University of Texas at El Paso, with not require the use of chemicals and, factors subsequently reduce the
expertise spanning diverse disciplines, overall, separates water from saltwater difference in temperature across the
including environmental engineering, solutions. membrane, therefore lowering the
chemical engineering, materials science, volume of water that can migrate across
chemistry and physics. NEWT’s vision it. To maximise the migration of water
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vapour, one would need to maintain a NESMD is relatively cheap to operate, For applications that require large
large temperature difference across the since any potential purification volumes of water 24 hours a day,
membrane. plant would not need to heat the such as industrial applications, NEWT
entire volume of saltwater. The researchers have also developed
Harnessing the Sun’s Energy NEWT researchers hope that their ‘dual-power membranes’. These
environmentally friendly purification membranes harness energy directly
Maintaining the temperature difference process can be applied at different from sunlight when it is available,
can be achieved by heating the scales – from whole communities and can then operate on electricity at
membrane itself. Researchers from the down to individual households, many night. One team of NEWT researchers
NEWT Center found that by adding a of whom will not be connected to the developed a dual-power membrane
layer that can absorb solar energy to national grid. comprising a nanolayer of boron nitride
the membrane surface on the saltwater on a stainless-steel wire cloth, which
side, and then directing sunlight to this The team also investigated other demonstrates superior performance,
layer, they were able to increase the energy-absorbing materials for NESMD. making it suitable for industrial
quantity of water vapour transferred. In one study, they applied ‘silica’, the applications.
The team’s new technology, referred main constituent of sand and glass,
to as ‘nanophotonics enabled solar covered with gold to the surface of the Another group of researchers fabricated
membrane distillation’ (NESMD), can membrane. The researchers found that a dense, non-porous ‘pervaporation’
thus be powered locally, using free, the carbon black materials absorb more membrane from a polymer called
clean and widely available energy from of the high-energy radiation in sunlight, Nexar™. The team found that their
the Sun. comprising blue and violet light, membrane exhibited a salt separation
whereas the silica-gold materials absorb performance superior to commercial
In the team’s NESMD technology, the more of the low energy radiation, pervaporation membranes, and
layer on the membrane that absorbs corresponding to red and yellow light. equivalent to that of commercial
sunlight is called ‘carbon black’ – a Both NESMD membrane compositions membrane distillation membranes.
substance similar to activated charcoal. performed more effectively than
Sunlight is directed through an array of conventional membranes, maintaining In another study, NEWT scientists
lenses to the carbon black layer, which the temperature difference needed to used egg-shell waste to develop a
absorbs nearly all frequencies of visible prolong vaporisation. highly efficient dual-power membrane.
light, transferring the energy as heat to Specifically, they used the egg
the membrane. membrane, found just inside the
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shell, whose porous structure efficiently allows the selective
movement of water into and out of the egg during incubation
and hatching. In the manufacture of egg-containing products,
these membranes are often discarded along with the shells.
Therefore, combined with the use of renewable energy from
the sun, the team’s technology represents an even more
environmentally-friendly and sustainable solution to water
purification.
Selective Removal of Ions
In addition to their efforts to remove common salts from
water, NEWT researchers have also been working on methods
that remove contaminant ions that are far less abundant
than common salts. For example, nitrate and chromate are
negatively charged ions that cause a range of human health
problems. Sulphate and calcium ions, although non-toxic
at typical concentrations, can form solid deposits that cover grew nanocrystals of a cobalt-containing compound. Applying
surfaces and cause a range of problems in homes and industrial a positive voltage to the conductive graphene material allowed
processes. Removal of these ions is challenging because highly it to attract the negatively-charged chromate ions, while the
abundant common salt ions interfere with the treatment nanocrystals could then efficiently trap the ions in place.
processes. By then applying a negative voltage to the electrode, the
researchers were able to release the chromate into a saltwater
Most techniques for removing calcium involve chemical stream for disposal.
treatments. Thus, NEWT researchers wanted to develop an
alternative method that can selectively remove calcium ions Deactivation of Microbes
from water using a process known as ‘electrosorption’. During
electrosorption, ions that have an opposite charge to that of The chemical-free deactivation of microbes in water is another
an electrode are attracted to the electrode, removing these important part of NEWT’s research portfolio. Boiling large
ions from water. Then, the charge on the electrode is reversed, volumes of water to kill bacteria is considered inefficient.
releasing the ions into a saltwater stream that will be disposed Instead, the team developed a method of successfully
of. The research team developed nanocoatings, which, when disinfecting water that uses gold nanorods or carbon black to
applied to the electrode surface, allow calcium to approach the channel solar energy into the water. This results in localised
electrode faster than the interfering common ions. This makes heating of the water, which subsequently kills nearby microbes.
the electrode surface highly selective to calcium ions and
provides a very effective method of calcium ion removal. Following a different approach, another team of NEWT
researchers designed UV-light side-emitting optical fibres that
In several other studies, NEWT research teams developed can disinfect flowing water and prevent the growth of biofilms
electrodes that can remove negatively-charged ions, including on surfaces, which would otherwise harbour pathogens such
sulphate. Some salts of sulphate ions are very insoluble in as Legionella. By depositing a layer of silica nanoparticles onto
water, and over time they can contribute to water scaling. At the surface of each optical fibre, the researchers could cause
higher concentrations, sulphate ions can even be converted the germicidal UV light to become scattered from the side of
into hydrogen sulphide by bacteria. Hydrogen sulphide is a the fibre like a glowstick. Upon testing their technology on E.
toxic gas and its production is particularly problematic in the oil Coli and other bacteria, the team was able to effectively kill
and gas industries, where sulphate and bacteria are abundant over 99% of the bacteria in water samples and in slimy biofilms
in the water used during crude oil extraction and processing. growing on surfaces.
The researchers demonstrated effective and selective removal
of sulphate ions from water using novel nano-electrode Multidisciplinary Nanotechnology Research
materials in the electrosorption process.
Evidently, the work performed by the NEWT researchers is
Using a similar approach, NEWT scientists also conducted very comprehensive. Their collaborative and multidisciplinary
research on the selective removal of a negatively charged ion efforts will prove vital to the health and wellbeing of
called chromate. This highly toxic chemical can cause cancer, communities and individuals across the world who do not have
and is a widely occurring contaminant in groundwater. In their access to clean water, particularly as climate change and a
study, the researchers created an electrode made from a type growing human population continue to place greater stress on
of graphene called ‘reduced graphene oxide’, upon which they our global water supplies.
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The NEWT Center
Nanotechnology-Enabled Water Treatment (NEWT) Center
Rice University
Houston, TX
USA
Organic Framework−Reduced Graphene Oxide Nanomaterial
for Selective Removal of Chromate from Water in an
Electrochemical Process, Environmental Science & Technology,
2020, 54, 20, 13322.
M Lanzarini-Lopes, B Cruz, S Garcia-Segura, A Alum, M
Abbaszadegan, P Westerhoff, Nanoparticle and Transparent
Polymer Coatings Enable UV-C Side-Emission Optical Fibers for
Inactivation of Escherichia coli in Water, Environmental Science
& Technology, 2019, 53, 10880.
PD Dongare, A Alabastri, O Neumann, P Nordlander, NJ Halas,
Solar thermal desalination as a nonlinear optical process,
PNAS, 2019, 116, 27.
This research was carried out by academic members of the J Kim, A Jai, K Zuo, R Verduzco, S Walker, M Elimelech, Z Zhang,
Nanotechnology Enabled Water Treatment Center, NEWT, X Zhang, Q Li, Removal of calcium ions from water by selective
a collaboration of research teams from across the US, with electrosorption using target-ion specific nanocomposite
headquarters at Rice University. The principal investigators electrode, Water Research, 2019, 160, 445.
of the team are Professor Pedro Alvarez, Professor Qilin Li PJJ Alvarez, C Chan, M Elimelech, N Halas, and D Villagran,
and Professor Naomi Halas from Rice University, Professor Emerging opportunities for nanotechnology to enhance water
Menachem Elimelech from Yale University and Professor Paul security, Nature Nano, 2018, 13, 634.
Westerhoff from Arizona State University. In addition to their
research partnerships with universities and industries across K Zuo, J Kim, A Jain, T Wang, R Verduzco, M Long, Q Li, Novel
the world, the NEWT Center is also committed to providing high Composite Electrodes for Selective Removal of Sulfate by the
school students and teachers, as well as undergraduates and Capacitive Deionization Process, Environmental Science &
postgraduates, with hands-on research experiences. Technology, 2018, 52, 9486.
S Loeb, C Li, J-H Kim, Solar Photothermal Disinfection using
CONTACT Broadband-Light Absorbing Gold Nanoparticles and Carbon
Black, Environmental Science & Technology, 2018, 52, 205.
E: info@newtcenter.org
PD Dongare, A Alabastri, S Pedersen, KR Zodrow, NJ Hogan,
W: https://newtcenter.org/
O Neumann, J Wu, T Wang, A Deshmukh, M Elimelech, Q
Li, P Nordlander, NJ Halas, Nanophotonics-enabled solar
FUNDING
membrane distillation for off-grid water purification, PNAS,
2017, 114, 27.
US National Science Foundation
J Wu, KR Zodrow, PB Szemraj, Q Li, Photothermal
FURTHER READING nanocomposite membranes for direct solar membrane
distillation, Journal of Materials Chemistry A, 2017, 5, 23712.
ER Thomas, A Jain, SC Man, Y Yang, MD Green, WS Walker, F
Perreault, ML Lind, R Verduzco, Freestanding self-assembled
sulfonated pentablock terpolymer membranes for high flux
pervaporation desalination, Journal of Membrane Science,
2020, 613, 118460.
K Zuo, X Huang, X Liu, EM Gil Garcia, J Kim, A Jain, L Chen, P
Liang, A Zepeda, R Verduzco, J Lou, and Q Li, A Hybrid Metal−
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