Presentation on theme: "Nanofilters for Clean Water"— Presentation transcript:
1Nanofilters for Clean Water STEM ED/CHM Nanotechnology 2009Nanofilters for Clean Water
2Today’s Agenda The problem: adequate clean water Kinds of filters Desalination of salt waterCleaning polluted waterHands on nanofiltration experiment
3The 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:
4How is the World’s Water Distributed? Less than 3% of Earth’s water is fresh waterMost of it (97%) is undrinkable salt water in the oceansOf the fresh water, most is in ice caps and glaciers, and some is in ground waterLess 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:
5No Single Cause for the Water Crisis Climate and geographyLack of water systems and infrastructureDepleting aquifersInadequate sanitation and pollution2.6 billion people (40% of the world’s population) lack access to sanitation systems that separate sewage from drinking waterInadequate sanitation and no access to clean water have been highly correlated with diseaseWill worsen with increasing population, affluence
6How Can We Address the Water Crisis? Use less waterMore efficient irrigation, like drip irrigation; cover irrigation ditchesLow-flow shower and toilets; recycle gray waterUse native plants for crops and landscaping; no lawns in AZEat less meat (especially beef)Fix leaky distribution systems (Quabbin reservoir)Find new sources of clean waterIcebergs? Pump aquifers more and more? Use tankers?Treat the undrinkable water that we haveUse reverse osmosis to desalinize salt (ocean) waterClean polluted water using filters, chemicals, and UV light
7Repairs to the leaky distribution system from the Quabbin Reservoir located in Western Massachusetts have reduced the demand for new supplies for the Boston area.
8Pollution in Fresh Water Sewage is the most commonPesticides and fertilizersIndustrial waste dumpingHigh levels of minerals from natural sourcesWells in Bangladesh have dangerous arsenic levelsSources:
9Water FiltrationSystems for cleaning polluted water typically use a series of filters to remove smaller and smaller particlesSeawater desalination facilities also use filters
10Filters Are Everywhere Window and door screens are filters – they let air in and keep out insects
11Filters in the Home Dryer filters remove lint Air conditioning and furnace filters remove dust
12Faucet screens trap small pebbles and other debris Coffee filters block the grinds
13Coffee Filter Scanning Electron Microscope Image
14Filters in the CarAir, oil, fuel, and other filters remove harmful materials
15Filter PrinciplesSome filters block particles too big to pass through holes, like window screens or cell membranes
16Filter PrinciplesSome filters use electrical forces to trap or block particles.Electrostatic air cleaners place a charge on airborne particles, then collect the charged particles.
17Filter 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
18Filter GeometriesSome use a single layer such as a screen or a membrane with pores to block particlesWindow screenOthers have an extended medium that gradually traps particlesSand or gravel beds for water filtration
19Membrane Water Filters A membrane is a thin material that has pores (holes) of a specific sizeMembranes trap larger particles that won’t fit through the pores of the membrane, letting water and other smaller substances through to the other side
21Water Filtration Systems Pebbles, sand, & charcoal filter out large particlesMembranes filter out smaller particlesIt is cost efficient to use a series of membranes to filter increasingly smaller particles and microorganisms
23Microfiltration Typical pore size: 0.1 microns (100 nm) Very low pressureRemoves clay, suspended materials, bacteria, large virusesDoes not filtersmall viruses, protein molecules, sugar, and saltsMicrofiltration water plant, Petrolia, PAA microfilter membraneSources:
24An ultrafiltration plant in Jachenhausen, Germany Typical pore size: 0.01 microns (10 nm)Moderately low pressureRemoves viruses, protein, and other organic moleculesDoes not filter ionic particles likelead, iron, chloride ions; nitrates, nitrites; other charged particlesAn ultrafiltration plant in Jachenhausen, GermanySource:
25Nanofiltration Typical pore size: 0.001 micron (1 nm) Low to moderate pressureRemoves toxic or unwanted bivalent ions (ions with 2 or more charges), such asLeadIronNickelMercury (II)Nanofiltration water cleaning serving Mery-sur-Oise, a suburb of Paris, FranceSource:
26The Problem With Salt Water People and most land plants and animals cannot use salt waterSeawater 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.
27The 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!
28Desalination – 2 Methods Distillation: use heat to evaporate salt water and condense water vaporExpensive: requires a lot of thermal energySometimes 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 removedSome salts may migrate into distillate along wallsWater is tasteless and lacks minerals unless further treatedUsed in Saudi Arabia, elsewhere
30Seawater Distillation Plants Saudi ArabiaAbu Dhabi Emiratedesalination.com
31On 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.
32Desalination – 2 Methods Reverse osmosis: Membrane with 0.1 nm holes, high pressureA practical large scale desalination method, less expensive than distillation without cogenerationSemipermeable membrane allows water to pass but not ions or other larger molecules
33About OsmosisOsmosis is a process that requires a semipermeable membraneIt is permeable to water, allowing water molecules to pass freely through its poresIt is impermeable to certain other molecules, which cannot pass through itYoutube video
34More 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.
35How 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 maplesCould theoretically be a power source (river meets sea)SolutionKane and Sternheim General Physics
36Reverse OsmosisEquilibrium 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 pressureOsmotic pressure is the pressure that must be applied to stop the flow of water across the membraneReverse Osmosis occurs when enough pressure is applied on the solution side to reverse the flow.Youtube demo (reverse osmosis desalination)
37Reverse osmosis plant for Bahrain (under construction)
38Tuos reverse osmosis plant provides 10% of Singapore’s water
39Racks 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.
40Nanofilters Used to purify polluted water Used as pre-filter for reverse osmosis in desalination systemsLower pressure requiredLower operating costsAnd special properties of nanosized particles can be exploited!We can design new nanofilters that catch particles smaller than they would catch based on size aloneScientists are exploring a variety of methods to build new nanomembranes with unique properties to filter in new and different ways
41New Nanofilters are Unique! Nanomembranes can be uniquely designed in layers with a particular chemistry and specific purposeInsert particles toxic to bacteriaEmbed tubes that “pull” water through and keep everything else outSignal to self-cleanImage of a nanomembraneSource:
42Chemicals toxic to bacteria could be implanted in nanomembranes New Nanomembranes IImagine having layers of membranes into which specialized substances are placed to do specific jobsYou can put a chemical in the filter that will kill bacteria upon contact!Chemicals toxic to bacteria could be implanted in nanomembranesSource: Unknown
43Electricity moving through a membrane New Nanomembranes IIEmbed “tubes” composed of a type of chemical that strongly attracts (“loves”) waterWeave into the membrane a type of molecule that can conduct electricity and repel oppositely charged particles, but let water throughWater-loving tubesElectricity moving through a membrane
441 nm Sized Nanopores Repel Electronegative Objects 1-2 nm sized pores create an electric field over the openingRepels negatively charged particles dissolved in waterMost pollutants from agriculture, industry, and rivers are negatively chargedBut water can get through!
45NanoCeram® FiltersThe 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.
46Making the FilterThe 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
47Manufactured 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.
48Nanofilter Biotech Applications Removal of contaminants from incoming waterPrefiltering for reverse osmosis filters instead of ultrafiltersFiltering endotoxins, bacteria and virus endotoxinsFiltering hazardous pharmaceutical waste before disposalSeparation of proteins
49Nanofiltration Summary At the nanoscale, filters can be constructed to have properties designed to serve a particular purposeScientists 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
50NanoSense Hands on Experiment I Cleaning “river water”Made from distilled water, salt, crushed leaves, dirt, sand, copper sulfate pentahydrate, ironFilter with gravel, sand, activated charcoal, nanofilterUse test strips for ions – iron, copper, chlorine, nitrates, nitrites – after each step
51NanoSense Hands on Experiment II Comparing ultrafiltration (25 nm pores) with nanofiltration (2000 nm pores, 2 nm fibers)Use diluted ink with 2 nm particlesCompare clarity of filtered water, color of filter afterwardsCompare pressure required
52ReferencesMaker of Millipore filtersnanosense.org/activities/finefilters/index.htmlMaker of argonide nanofiltersNational Academy of Sciences Kirkland Museum