MEMBRANE TECHNOLOGIESByPeter S. Cartwright, PECWQA PROFESIONAL DEVELOPMENT SEMINARMay 4, 2007

United States OfficeEuropean office8324 16th Avenue SouthPresident Kennedylaan 94Minneapolis, MN 55425-17422343 GT OegstgeestPhone: (952) 854-4911The NetherlandsFax: (952) 854-6964Phone: 31-71-5154417pscartwright@msn.comFax: 31-71-5156636www.cartwright-consulting.com

Cartwright Consulting Co.

Water Contaminants

ClassTypical ExampleSuspended solidsDirt, clay, colloidal materialsDissolved organicsTrihalomethanes, synthetic organic chemicals, humic acids, fulvic acidsDissolved ionics (salts)Heavy metals, silica, arsenic, nitrateMicroorganismsBacteria, viruses, protozoan cysts, fungi, algaeGasesHydrogen sulfide, methane, radon

Filtration Range

Particle SizeHuman Hair ~ 75 micronsYeast Cell = 3.00 micronsBacteria = 0.45 micronsFerric Iron Molecule = 0.001 microns

Relative Sizes of Particlesxxx

SubstanceMicronsInchesGrain of table salt1000.0039Human hair800.0032Lower limit of visibility400.0016Milled flour250.0010Red blood cells80.0003Bacteria20.0001

Conventional dead-end Filtration

Crossflow Filtration

Sweeping by Tangential FlowFeedConcentratePermeateMembrane

Continuous process resulting in automatic and uninterrupted operationLow energy utilization involving neither phase nor temperature changesModular design no significant size limitationsMinimal moving parts with low maintenance requirementsNo effect on form or chemistry of the contaminantDiscrete membrane barrier to ensure physical separationNo chemical addition requirements

Membrane Separation Technologies Features

Microfiltration

Microfiltrationxxx

Ultrafiltration

Ultrafiltration

Nanofiltration

Osmosis

Osmosis

Reverse Osmosis

Reverse Osmosis Applied

Reverse Osmosisxxx

Reverse Osmosis

Reverse Osmosis

Pure Water Layer Theory

RO FundamentalsSemi-permeable membrane uses two mechanisms for removal of impurities:

Rejection (repels mineral salts involving dielectric and molecular forces)

Sieving (does not allow particulate matter to pass on a small scale ~0.0005 microns. Tiny organics and gas molecules can pass.)

Osmotic PressureEquationp = 1.19(T + 273) SMip = Osmotic Pressure (psi)T = Water Temperature (oC)Mi = Molar Concentration of individual ions (gmol/L)

Typical Osmotic Pressures (25oC)

CompoundConc. (mg/L)Conc. (mol/L)Osmotic Pressure (psi)NaCl35,0000.6398NaCl1,0000.017111.4NaHCO31,0000.011912.8Na2SO41,0000.007056MgSO41,0000.008313.6MgCl21,0000.01059.7CaCl21,0000.0098.3Sucrose1,0000.002921.05Dextrose1,0000.005552.0

Solute Concentration as a Function of Osmotic Pressure

RO Performance EquationsOsmotic Pressure: The pressure, due to the effect of TDS in the feed water, that must be overcome in order to generate product water flow.For monovalent salts, assume 1 psi of osmotic pressure per 100 mg/L of TDS.For multivalent salts, assume psi of osmotic pressure per 100 mg/L of TDS.

R.O. Contaminant RejectionCTA-Cellulosic MembraneTFC-Thin Film Composite

All rejections nominal for 60 psi net pressureand at 77oF

InorganicsCTA RejectionTFC RejectioninorganicsCTA RejectionTFC RejectionSodium85-90%90-95%Fluoride85-90%90-95Calcium90-95%93-98%Phosphate90-95%93-98%Magnesium90-95%93-98%Chromate85-90%90-95%Potassium85-90%90-95%Cyanide85-90%90-95%Iron90-95%93-98%Sulfate90-9593-98%Manganese90-95%93-98%Boron30-40%55-60%Aluminum90-95%93-98%Arsenic+360-70%70-80%Copper90-95%93-98%Arsenic+585-90%93-98%Nickel90-95%93-98%Selenium90-95%93-98%Zinc90-95%93-98%Radioactivity90-95%93-98%Strontium90-95%93-98%Biological&ParticlesCadmium90-95%93-98%Bacteria>99%>99%Silver90-95%93-98%Protozoa>99%>99%Mercury90-95%93-98%Amoebic Cysts>99%>99%Barium90-95%93-98%Giardia>99%>99%Chromium90-95%93-98%Asbestos>99%>99%Lead90-95%93-98%Sediment/Turbidity>99%>99%Chloride85-95%90-95%OrganicsBicarbonate85-90%90-95%Organics MW>300>90%>99%Nitrate40-50%85-90%Organics MW

Membrane Comparisons

CellulosicThin Film CompositeEffect of BacteriaSome bacteria will attackVery bacteria resistantpH Range4.0 8.52.0 11.0Chlorine ToleranceExcellent ResistancePoor Resistance 200 - 1000 ppm hrs.% RejectionNominal TDS dependence92%Decreases as TDS Increases95%ConstantNitrate Rejection0% - 65%40% - 90%Temperature Limit87oF (31oC)112oF (45oC)

Membrane Technology Comparison Chart

FeatureMicrofiltrationUltrafiltrationNanofiltrationReverse OsmosisPolymersCeramics, sintered metals, polypropylene, polysulfone, polyethersulfone, polyvinylidene fluoride, polytetrafluoroethy-lieneCeramics, sintered metals, cellulosics, polysulfone, polyethersulfone, polyvinylidene fluorideThin film composites, cellulosicsThin film composites, cellulosicsPore Size Range (micrometers)0.01 - 1.00.001 - 0.010.0001 - 0.001100,0002,000 - 100,000300 - 1,000100 - 200Operating Pressure Range

Membrane Devices

Plate & Frame

Capillary (Hollow) Fiber

Hollow Fiber UF

Tubular

Tubular Membrane Elements

Spiral Wound

Membrane Element Configuration Comparison * Membrane area per unit volume of element ** Tolerance to suspended solids

Element Configura-tionPacking Density *Fouling Resistance **Capillary FiberMediumHighPlate and FrameLowHighSpiral WoundMediumModerateTubularLowhigh

Membrane Schematic

Concentration Effectsx

Concentration Factor vs. Percent Recovery

POU RO Performance EquationsProduction Rate: The rate at which product water is made directly from the RO membrane. It is customarily expressed at Standard Operating Conditions (50-60 psi for POU at 77oF) by applying the appropriate conversion factors.Conversion Factor: ml/min x 0.38 = gal/day

Reverse Osmosis RecoveryRecovery: the percentage of feed water that passes through the membrane as product water. (i.e. how efficiently water is being used to make product water)

Reverse Osmosis RecoveryExample: A membrane is making 10 gallons per day as product, while 40 gallons go to drain. What is the recovery?

Feed Water = product + reject = 10 + 40 = 50

Recovery = product/feed = 10/50 = 20%

Note: at 50% recovery, reject water TDS is double that of the feed water

Generic POU RO System Flow Diagram

Generic Undersink RO Installation

RO System ControlsProduct Water Check Valve: Protects membrane from back pressure.Automatic Shut-off Valve: Maintains storage tank pressure between to 2/3 feed line pressure.Brine Flow Restrictor: Maintain reject rinse flow at 3x to 5x product flow; Membrane life and water quality; Prevent water wasting.

Typical Pure Water System

Aerobic MBR Applications

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