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Nanofilters for Clean Water. STEM ED/CHM Nanotechnology 2009. Today’s Agenda. The problem: adequate clean water Kinds of filters Desalination of salt water Cleaning polluted water Hands on nanofiltration experiment. The Problem: Adequate Clean Water.

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nanofilters for clean water

Nanofilters for Clean Water

STEM ED/CHM Nanotechnology 2009

today s agenda
Today’s Agenda
  • The problem: adequate clean water
  • Kinds of filters
  • Desalination of salt water
  • Cleaning polluted water
  • Hands on nanofiltration experiment
the problem adequate clean water
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.


how is the world s water distributed
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.)


no single cause for the water crisis
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 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
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.

pollution in fresh water
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


water filtration
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
Filters Are Everywhere

Window and door screens are filters – they let air in and keep out insects

filters in the home
Filters in the Home

Dryer filters remove lint

Air conditioning and furnace filters remove dust

coffee filter scanning electron microscope image
Coffee Filter Scanning Electron Microscope Image


Filters in the Car

Air, oil, fuel, and other filters remove harmful materials

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

filter principles16
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 principles17
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

filter geometries
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

membrane water filters
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

water filtration categories
Water Filtration Categories
  • Microfiltration
  • Ultrafiltration
  • Nanofiltration
  • Reverse Osmosis
water filtration systems
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

membrane filter technology
Membrane Filter Technology

  • 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


  • 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


  • 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


the problem with salt water
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 water27
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
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
desalination by distillation
Desalination by Distillation

seawater distillation plants
Seawater Distillation Plants

Saudi Arabia

Abu Dhabi Emirate

on the international space station
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.

desalination 2 methods32
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
about osmosis
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.

how osmosis works
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)


Kane and Sternheim General Physics

reverse osmosis
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)


Tuos reverse osmosis plant provides 10% of Singapore’s water


Racks of elements containing reverse osmosis membranes (Israel). This plant produces 13% of the country’s domestic water supply.

  • 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
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


new nanomembranes i
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

new nanomembranes ii
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 electricityand repel oppositely charged particles, but let water through

Water-loving tubes

Electricity moving through a membrane

1 nm sized nanopores repel electronegative objects
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
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.

making the filter
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
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
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
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
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
nanosense hands on experiment ii
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
  • Maker of Millipore filters
  • Maker of argonide nanofilters
  • National Academy of Sciences Kirkland Museum