Nanofilters%20for%20Clean%20Water

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Nanofilters for Clean Water
STEM ED/CHM Nanotechnology 2009
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Todays Agenda

• The problem adequate clean water
• Kinds of filters
• Desalination of salt water
• Cleaning polluted water
• Hands on nanofiltration experiment

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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 Earths population lacks clean,
  safe drinking water.

Sources http//www.battelle.org/environment/image
s/water-drop.jpg
http//www.tribuneindia.com/2004/20040718/pb3.jpg
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How is the Worlds Water Distributed?

• Less than 3 of Earths 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/watercyclesum
mary.htmlglobal
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No Single Cause for the Water Crisis

• Climate and geography
• Lack of water systems and infrastructure
• Depleting aquifers
• Inadequate sanitation and pollution
• 2.6 billion people (40 of the worlds
  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

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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

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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_wa
ter.JPG http//mainegov-images.info
rme.org/agriculture/pesticides/drift/mstblow1.gif
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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

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Filters Are Everywhere
Window and door screens are filters they let
air in and keep out insects
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Filters in the Home
Dryer filters remove lint
Air conditioning and furnace filters remove dust
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Faucet screens trap small pebbles and other debris
Coffee filters block the grinds
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Coffee Filter Scanning Electron Microscope Image
http//www.princeton.edu/pccm/outreach/scsp/mixtu
resandsolutions/diatoms/coffee_filter.html
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Filters in the Car
Air, oil, fuel, and other filters remove harmful
materials
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Filter Principles

• Some filters block particles too big to pass
  through holes, like window screens or cell
  membranes

http//en.wikipedia.org/wiki/FileSchematic_size.j
pg
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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.

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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
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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
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Membrane Water Filters

• A membrane is a thin material that has pores
  (holes) of a specific size
• Membranes trap larger particles that wont fit
  through the pores of the membrane, letting water
  and other smaller substances through to the other
  side

http//www.alting.fr/index.aspx
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Water Filtration Categories

• Microfiltration
• Ultrafiltration
• Nanofiltration
• Reverse Osmosis

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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
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Membrane Filter Technology
http//www.netl.doe.gov/technologies/pwmis/techdes
c/membrane/
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Microfiltration

• Typical pore size 0.1 microns (100 nm)
• Very low pressure
• Removes clay, suspended materials, bacteria,
  large viruses
• Does not filter
• small viruses, protein molecules, sugar, and salts

Microfiltration water plant, Petrolia, PA
A microfilter membrane
Sources http//www.waterworksmw.com/rack20120
202b.jpg http//www.imc.cas.cz/sympo/41micros/Ima
ge126.gif
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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/bildmater
ial/referenzen/jachenhausen.jpg
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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
• Lead
• Iron
• Nickel
• Mercury (II)

Nanofiltration water cleaning serving
Mery-sur-Oise, a suburb of Paris, France
Source http//www.wateronline.com/crlive/files/Im
ages/10899070-E891-11D3-8C1F-009027DE0829/newwater
1.gif
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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.

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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!

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Desalination 2 Methods

• 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

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Desalination by Distillation
http//www.millipore.com/labwater/lw3/purification
techniques
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Seawater Distillation Plants
Saudi Arabia www.water-technology.net/projects/shu
aiba/shuaiba5.html
Abu Dhabi Emirate
desalination.com
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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.water-technology.net/projects/iss_water
_recovery/
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Desalination 2 Methods

• 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

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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

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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.phy-astr.gsu.edu/hbase/kinetic
/ospcal.html
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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
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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)

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Reverse osmosis plant for Bahrain (under
construction)
http//www.water-technology.net/projects/durrat-de
salination/
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Tuos reverse osmosis plant provides 10 of
Singapores water
http//www.water-technology.net/projects/tuas/
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Racks of elements containing reverse osmosis
membranes (Israel). This plant produces 13 of
the countrys domestic water supply. http//www.wa
ter-technology.net/projects/israel/
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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

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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/archive
s/volume2/issue10/images/story2-2.jpg
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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!

Chemicals toxic to bacteria could be implanted in
nanomembranes
Source Unknown
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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
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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!

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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_overv
iew.pdf
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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

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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.

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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

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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

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NanoSense Hands on Experiment I

• Cleaning river water
• 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

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NanoSense Hands on Experiment II

• Comparing ultrafiltration (25 nm pores) with
  nanofiltration (2000 nm pores, 2 nm fibers)
• Use diluted ink with 2 nm particles
• Compare clarity of filtered water, color of
  filter afterwards
• Compare pressure required

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References

• www.millipore.com/labwater/lw3/purificationtechniq
  ues 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/