Transcript Nanofilters for Clean Water

STEM ED/CHM Nanotechnology 2009
Nanofilters for Clean Water
Today’s Agenda
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The problem: adequate clean water
Kinds of filters
Desalination of salt water
Cleaning polluted water
Hands on nanofiltration experiment
The Problem: Adequate Clean
Water
Despite the apparent abundance of clean
water in most of the US and the developed
world, more than 20% of the Earth’s
population lacks clean, safe drinking
water.
Sources: http://www.battelle.org/environment/images/water-drop.jpg
http://www.tribuneindia.com/2004/20040718/pb3.jpg
How is the World’s Water
Distributed?
• Less than 3% of Earth’s water is fresh
water
• Most of it (97%) is undrinkable salt water
in the oceans
• Of the fresh water, most is in ice caps and
glaciers, and some is in ground water
• Less than 1% is in more easily accessible
surface water (lakes, swamps, rivers, etc.)
Source: http://ga.water.usgs.gov/edu/watercyclesummary.html#global
No Single Cause for the Water
Crisis
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Climate and geography
Lack of water systems and infrastructure
Depleting aquifers
Inadequate sanitation and pollution
• 2.6 billion people (40% of the world’s population) lack
access to sanitation systems that separate sewage from
drinking water
• Inadequate sanitation and no access to clean water have
been highly correlated with disease
• Will worsen with increasing population,
affluence
How Can We Address the Water
Crisis?
• Use less water
– More efficient irrigation, like drip irrigation; cover irrigation
ditches
– Low-flow shower and toilets; recycle gray water
– Use native plants for crops and landscaping; no lawns in AZ
– Eat less meat (especially beef)
– Fix leaky distribution systems (Quabbin reservoir)
• Find new sources of clean water
– Icebergs? Pump aquifers more and more? Use tankers?
• Treat the undrinkable water that we have
– Use reverse osmosis to desalinize salt (ocean) water
– Clean polluted water using filters, chemicals, and UV light
Repairs to the leaky
distribution system from
the Quabbin Reservoir
located in Western
Massachusetts have
reduced the demand for
new supplies for the
Boston area.
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Pollution in Fresh Water
Sewage is the most common
Pesticides and fertilizers
Industrial waste dumping
High levels of minerals from
natural sources
– Wells in Bangladesh have
dangerous arsenic levels
Sources: http://www.marenrecycling.com/polluted_water.JPG
http://mainegov-images.informe.org/agriculture/pesticides/drift/mstblow1.gif
Water Filtration
• Systems for cleaning polluted water
typically use a series of filters to remove
smaller and smaller particles
• Seawater desalination facilities also use
filters
Filters Are Everywhere
Window and door screens
are filters – they let air in
and keep out insects
Filters in the Home
Dryer filters
remove lint
Air conditioning and
furnace filters remove dust
Faucet screens trap small
pebbles and other debris
Coffee filters block the
grinds
Coffee Filter Scanning Electron
Microscope Image
http://www.princeton.edu/~pccm/outreach/scsp/mixturesandsolutions/
diatoms/coffee_filter.html
Filters in
the Car
Air, oil, fuel, and other filters remove
harmful materials
Filter Principles
• Some filters block
particles too big to
pass through holes,
like window screens
or cell membranes
http://en.wikipedia.org/wiki/File:Schematic_size.jpg
Filter Principles
• Some filters use
electrical forces to
trap or block particles.
– Electrostatic air
cleaners place a
charge on airborne
particles, then collect
the charged particles.
Filter Principles
• Chemical filters are
based on
molecular forces
– Activated carbon is
very porous so it
has a large surface
area and can
adsorb or react
with large amount
of material in water
filtration systems
http://en.wikipedia.org/wiki/Activated_carbon
Filter Geometries
• Some use a single layer
such as a screen or a
membrane with pores to
block particles
– Window screen
• Others have an extended
medium that gradually
traps particles
– Sand or gravel beds for
water filtration
http://www.worldhungeryear.org/why_speaks
/19_files/image014.gif
Membrane Water Filters
• A membrane is a thin material that has pores
(holes) of a specific size
• Membranes trap larger particles that won’t fit
through the pores of the membrane, letting
water and other smaller substances through to
the other side
http://www.alting.fr/index.aspx
Water Filtration Categories
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Microfiltration
Ultrafiltration
Nanofiltration
Reverse Osmosis
Water Filtration Systems
• Pebbles, sand, & charcoal filter out large particles
• Membranes filter out smaller particles
• It is cost efficient to use a series of membranes to filter
increasingly smaller particles and microorganisms
http://www.alting.fr/images/cross_flow_details.gif
Membrane Filter Technology
http://www.netl.doe.gov/technologies/pwmis/techdesc/membrane/
Microfiltration
• Typical pore size: 0.1
microns (100 nm)
• Very low pressure
• Removes clay,
suspended materials,
bacteria, large viruses
• Does not filter
Microfiltration water plant, Petrolia, PA
– small viruses, protein
molecules, sugar, and
salts
A microfilter membrane
Sources: http://www.waterworksmw.com/rack%201%20&%202b.jpg http://www.imc.cas.cz/sympo/41micros/Image126.gif
Ultrafiltration
• Typical pore size: 0.01
microns (10 nm)
• Moderately low pressure
• Removes viruses, protein,
and other organic
molecules
• Does not filter ionic
particles like
– lead, iron, chloride ions;
nitrates, nitrites; other
charged particles
An ultrafiltration plant in
Jachenhausen, Germany
Source: http://www.inge.ag/bilder/presse/bildmaterial/referenzen/jachenhausen.jpg
Nanofiltration
• Typical pore size: 0.001 micron
(1 nm)
• Low to moderate pressure
• Removes toxic or unwanted
bivalent ions (ions with 2 or
more charges), such as
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Lead
Iron
Nickel
Mercury (II)
Nanofiltration water cleaning
serving Mery-sur-Oise, a suburb
of Paris, France
Source: http://www.wateronline.com/crlive/files/Images/10899070-E891-11D3-8C1F-009027DE0829/newwater1.gif
The Problem With Salt Water
• People and most land plants and animals
cannot use salt water
• Seawater is much saltier than your body
fluids or cells. When it enters the stomach,
water from cells in that area comes
rushing out to try to equalize the
concentrations. Many cells may die due to
sudden dehydration.
The Problem With Salt Water
• Also, when your stomach fills rapidly with water
from the cells, it causes you to throw up, so you
lose almost twice as much water as the amount
you originally drank.
• Finally, human kidneys can only make urine
about 1/4 as salty as sea water. Therefore, to
get rid of all the excess salt taken in by drinking
salt water, you have to urinate more water than
you drank, so you die of dehydration!
Desalination – 2 Methods
1. Distillation: use heat to evaporate salt water
and condense water vapor
– Expensive: requires a lot of thermal energy
– Sometimes uses the waste heat from a nuclear or
other electric power plant to reduce costs
(cogeneration)
– Some pesticides and fertilizers have lower boiling
points than water and are not removed
– Some salts may migrate into distillate along walls
– Water is tasteless and lacks minerals unless further
treated
– Used in Saudi Arabia, elsewhere
Desalination by Distillation
http://www.millipore.com/labwater/lw3/purificationtechniques
Seawater Distillation Plants
Saudi Arabia
Abu Dhabi Emirate
desalination.com
www.watertechnology.net/projects/shuaiba/s
huaiba5.html
On the International Space Station
Water is recovered
from urine by
distillation in a system
installed in 2008 to
reduce the amount of
water that needs to be
launched.
http://www.watertechnology.net/projects/iss_water_recovery/
Desalination – 2 Methods
2. Reverse osmosis: Membrane with 0.1
nm holes, high pressure
– A practical large scale desalination method,
less expensive than distillation without
cogeneration
– Semipermeable membrane allows water to
pass but not ions or other larger molecules
About Osmosis
• Osmosis is a process that requires a
semipermeable membrane
– It is permeable to water, allowing water
molecules to pass freely through its pores
– It is impermeable to certain other molecules,
which cannot pass through it
• Youtube video
More water molecules strike
the membrane on the pure
water side (left), causing a
net diffusion of water across
the membrane. The water
level rises until equal
numbers of water molecules
travel in each direction.
http://hyperphysics.phyastr.gsu.edu/hbase/kinetic/ospcal.html
How Osmosis Works
• More molecules strike the membrane on the pure
water side (a), causing a net diffusion of water across
the membrane, raising the water level until there is
equilibrium (b).
– This explains the rise of sap in sugar maples
– Could theoretically be a power source (river meets sea)
Solution
Kane and Sternheim
General Physics
Reverse Osmosis
• Equilibrium occurs when the pressure due to the
water molecules is equal on both sides of the
membrane (not equal concentrations)
– The rate at which water molecules hit the membrane
is determined by their partial pressure
– Osmotic pressure is the pressure that must be
applied to stop the flow of water across the
membrane
• Reverse Osmosis occurs when enough pressure
is applied on the solution side to reverse the
flow.
– Youtube demo (reverse osmosis desalination)
Reverse osmosis plant for Bahrain (under
construction)
http://www.water-technology.net/projects/durrat-desalination/
Tuos reverse osmosis
plant provides 10% of
Singapore’s water
http://www.water-technology.net/projects/tuas/
Racks of elements containing reverse osmosis membranes (Israel).
This plant produces 13% of the country’s domestic water supply.
http://www.water-technology.net/projects/israel/
Nanofilters
• Used to purify polluted water
• Used as pre-filter for reverse osmosis in
desalination systems
– Lower pressure required
– Lower operating costs
• And special properties of nanosized particles
can be exploited!
– We can design new nanofilters that catch particles
smaller than they would catch based on size alone
• Scientists are exploring a variety of methods to
build new nanomembranes with unique
properties to filter in new and different ways
New Nanofilters are Unique!
• Nanomembranes can be
uniquely designed in layers
with a particular chemistry
and specific purpose
– Insert particles toxic to
bacteria
• Embed tubes that “pull”
water through and keep
everything else out
– Signal to self-clean
Image of a
nanomembrane
Source: http://sciencematters.berkeley.edu/archives/volume2/issue10/images/story2-2.jpg
New Nanomembranes I
• Imagine having layers
of membranes into
which specialized
substances are
placed to do specific
jobs
– You can put a
chemical in the filter
that will kill bacteria
upon contact!
Source: Unknown
Chemicals toxic to bacteria
could be implanted in
nanomembranes
New Nanomembranes II
• Embed “tubes”
composed of a type of
chemical that strongly
attracts (“loves”)
water
• Weave into the
membrane a type of
molecule that can
conduct electricity
and repel oppositely
charged particles, but
let water through
Water-loving tubes
Electricity moving
through a membrane
1 nm Sized Nanopores Repel
Electronegative Objects
• 1-2 nm sized pores create an electric field
over the opening
– Repels negatively charged particles dissolved
in water
– Most pollutants from agriculture, industry, and
rivers are negatively charged
• But water can get through!
NanoCeram® Filters
• The active ingredient of the
filter media is a nano alumina
fiber, only 2 nm in diameter.
The nano fibers are highly
electropositive.
• Separate particles by charge,
not size; pores are large (2
microns)
• The filter retains all types of
particles by electroadsorption,
including silica, natural organic
matter, metals, bacteria, DNA
and virus.
http://www.argonide.com/publications/product_overview.pdf
Making the Filter
• The nano fibers are first
dispersed and adhered to
glass fibers. The nano
alumina is seen as a fuzz
on the two glass fibers.
• Other fibers are added
and the mixture is
processed at a paper mill
to produce a non-woven
filter.
• Because the nano
alumina is dispersed,
particles have easy
access to the charged
surface
Manufactured Like Paper (Low Cost)
• Much like a standard filter,
the NanoCeram®
electropositive fibrous filter
media mechanically sieves
particles larger than its
average pore size.
• However, the NanoCeram®
also adsorbs smaller
particles throughout its entire
fibrous structure,
• Used as prefilter in reverse
osmosis instead of
ultrafilters.
Nanofilter Biotech Applications
• Removal of contaminants from incoming
water
• Prefiltering for reverse osmosis filters
instead of ultrafilters
• Filtering endotoxins, bacteria and virus
endotoxins
• Filtering hazardous pharmaceutical waste
before disposal
• Separation of proteins
Nanofiltration Summary
• At the nanoscale, filters can be constructed to
have properties designed to serve a particular
purpose
• Scientists and engineers are now experimenting
to create membranes that are low-cost yet very
effective for filtering water to make it drinkable!
• These inventions may help to solve the global
water shortage
NanoSense Hands on Experiment I
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Cleaning “river water”
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Made from distilled
water, salt, crushed
leaves, dirt, sand, copper
sulfate pentahydrate, iron
Filter with gravel, sand,
activated charcoal,
nanofilter
Use test strips for ions –
iron, copper, chlorine,
nitrates, nitrites – after
each step
NanoSense Hands on Experiment II
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Comparing ultrafiltration
(25 nm pores) with
nanofiltration (2000 nm
pores, 2 nm fibers)
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Use diluted ink with 2 nm
particles
Compare clarity of
filtered water, color of
filter afterwards
Compare pressure
required
References
• www.millipore.com/labwater/lw3/purificationtechniques
Maker of Millipore filters
• nanosense.org/activities/finefilters/index.html
• www.argonide.com/publications/product_overview.pdf
Maker of argonide nanofilters
• http://www.drinking-water.org/flash/splash.html National
Academy of Sciences Kirkland Museum
• http://www.understandingnano.com/water.html
• http://www.brianlaks.com/nanofilters.htm
• http://www.water-technology.net/