Top Banner
Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009
52

Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

Mar 27, 2015

Download

Documents

Daniel Sanders
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Page 1: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

Nanofilters for Clean Water

STEM ED/CHM Nanotechnology 2009

Page 2: 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

Page 3: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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

Page 4: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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

Page 5: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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

Page 6: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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

Page 7: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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.

Page 8: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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

Page 9: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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

Page 10: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

Filters Are Everywhere

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

Page 11: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

Filters in the Home

Dryer filters remove lint

Air conditioning and furnace filters remove dust

Page 12: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

Faucet screens trap small pebbles and other debris

Coffee filters block the grinds

Page 13: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

http://www.princeton.edu/~pccm/outreach/scsp/mixturesandsolutions/diatoms/coffee_filter.html

Coffee Filter Scanning Electron Microscope Image

Page 14: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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

Filters in the Car

Page 15: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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

Page 16: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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.

Page 17: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

http://en.wikipedia.org/wiki/Activated_carbon

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

Page 18: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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

Page 19: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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

Page 20: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

Water Filtration Categories

• Microfiltration • Ultrafiltration• Nanofiltration• Reverse Osmosis

Page 21: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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

Page 22: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

Membrane Filter Technology

http://www.netl.doe.gov/technologies/pwmis/techdesc/membrane/

Page 23: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

Sources: http://www.waterworksmw.com/rack%201%20&%202b.jpg http://www.imc.cas.cz/sympo/41micros/Image126.gif

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

A microfilter membrane

Microfiltration water plant, Petrolia, PA

Page 24: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

Source: http://www.inge.ag/bilder/presse/bildmaterial/referenzen/jachenhausen.jpg

An ultrafiltration plant in Jachenhausen, Germany

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

Page 25: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

Source: http://www.wateronline.com/crlive/files/Images/10899070-E891-11D3-8C1F-009027DE0829/newwater1.gif

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

Page 26: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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.

Page 27: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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!

Page 28: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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

Page 29: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

Desalination by Distillation

http://www.millipore.com/labwater/lw3/purificationtechniques

Page 30: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

Seawater Distillation Plants

desalination.com

Saudi Arabia

www.water-technology.net/projects/shuaiba/shuaiba5.htmlAbu Dhabi Emirate

Page 31: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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/

Page 32: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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

Page 33: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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

Page 34: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/ospcal.html

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.

Page 35: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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

Page 36: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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)

Page 37: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

Reverse osmosis plant for Bahrain (under construction)

http://www.water-technology.net/projects/durrat-desalination/

Page 38: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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

http://www.water-technology.net/projects/tuas/

Page 39: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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/

Page 40: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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

Page 41: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

Source: http://sciencematters.berkeley.edu/archives/volume2/issue10/images/story2-2.jpg

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

Page 42: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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

Page 43: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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

Page 44: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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!

Page 45: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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

Page 46: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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

Page 47: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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.

Page 48: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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

Page 49: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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

Page 50: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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

Page 51: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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

Page 52: Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009.

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/