1. Nanofilters for Clean Water
STEM ED/CHM Nanotechnology 2009
Nanofilters for Clean Water

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

3. 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:

4. 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.)
If you consider the earth’s water, the green bar, out of all the earths water, 97% of it is salt water. Only 3% of it is fresh water.
Source:

5. 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

6. 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

7. 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.

8. 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:

9. 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

10. Filters Are Everywhere
Window and door screens are filters – they let air in and keep out insects

11. Filters in the Home Dryer filters remove lint
Air conditioning and furnace filters remove dust

12. Faucet screens trap small pebbles and other debris
Coffee filters block the grinds

13. Coffee Filter Scanning Electron Microscope Image

14. Filters in the Car
Air, oil, fuel, and other filters remove harmful materials

15. Filter Principles
Some filters block particles too big to pass through holes, like window screens or cell membranes

16. 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.

17. 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

18. 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

19. 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

20. Water Filtration Categories
Microfiltration
Ultrafiltration
Nanofiltration
Reverse Osmosis

21. 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

22. Membrane Filter Technology

23. 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:

24. An ultrafiltration plant in Jachenhausen, Germany
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:

25. 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:

26. 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.

27. 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!

28. 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

29. Desalination by Distillation

30. Seawater Distillation Plants
Saudi Arabia
Abu Dhabi Emirate
desalination.com

31. 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.

32. 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

33. 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

34. 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.

35. How Osmosis Works Solution
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

36. 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)

37. Reverse osmosis plant for Bahrain (under construction)

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

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

40. 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

41. 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:

42. Chemicals toxic to bacteria could be implanted in nanomembranes
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

43. Electricity moving through a membrane
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

44. 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!

45. 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.

46. 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

47. 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.

48. 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

49. 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

50. 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

51. 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

52. References
Maker of Millipore filters
nanosense.org/activities/finefilters/index.html
Maker of argonide nanofilters
National Academy of Sciences Kirkland Museum