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7/16/2019 Membrane Separation Technology
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Membrane Separation Processes
Neha Kathayat
Rugved PathareDaksh Pratap Singh
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Overview
Introduction
Ultrafiltration
Reverse Osmosis
Electrodialysis
Summary
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Overview
Introduction
Ultrafiltration
Reverse Osmosis
Electrodialysis
Summary
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Overview
Introduction
Ultrafiltration
Reverse Osmosis
Electrodialysis
Summary
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Overview
Introduction
Ultrafiltration
Reverse Osmosis
Electrodialysis
Summary
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Overview
Introduction
Ultrafiltration
Reverse Osmosis
Electrodialysis
Summary
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Overview
Introduction
Ultrafiltration
Reverse Osmosis
Electrodialysis
Summary
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Introduction
Strathmann defines a membrane as “aninterphase separating two phases and
selectively controlling the transport of materials between those phases”
Since the 1960s a new technology using
synthetic membranes for processseparations has been rapidly developed
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Introduction
Strathmann defines a membrane as “aninterphase separating two phases and
selectively controlling the transport of materials between those phases”
Since the 1960s a new technology using
synthetic membranes for processseparations has been rapidly developed
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Advantages offered
Ambient temperature operation
Relatively low capital and running costs
Modular construction
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Advantages offered
Ambient temperature operation
Relatively low capital and running costs
Modular construction
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Advantages offered
Ambient temperature operation
Relatively low capital and running costs
Modular construction
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General Classification
Most of the membrane processes arepressure driven barring a few like
electro dialysis (ED). Pressure driven process includes micro
filtration (MF), ultra-filtration (UF),reverse osmosis (OS)
Micro filtration, Ultra filtration, Reverse-Osmosis are different with respect topore-size of membrane
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General Classification
Most of the membrane processes arepressure driven barring a few like
electro dialysis (ED). Pressure driven process includes micro
filtration (MF), ultra-filtration (UF),reverse osmosis (OS)
Micro filtration, Ultra filtration, Reverse-Osmosis are different with respect topore-size of membrane
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General Classification
Most of the membrane processes arepressure driven barring a few like
electro dialysis (ED). Pressure driven process includes micro
filtration (MF), ultra-filtration (UF),reverse osmosis (OS)
Micro filtration, Ultra filtration, Reverse-Osmosis are different with respect topore-size of membrane
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Historical Perspective
Following the end of World War II , the USGovt. became concerned about the shortageof water before the end of century.
The US Dept. set up the Office of Saline
Waters (OSW), and committed substantialfinancial resources to the development of various separation processes for waterdesalination, a significant portion of whichwas dedicated to the development of membranes for desalination, continuing thework up to 2 decades.
Result was development of RO and UF and itsno co-incidence that US is the world leaderon this front.
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Ultra filtration
A Pressure Driven
Membrane SeparationProcess
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Membrane Structure and Fabrication
The thin skin on thesurface: usually 0.1 to 1 in thickness.
Permits high hydraulicpermeability
The more open poroussubstructure (typically
120 in thickness)provides goodmechanical support.
Virtually eliminates
internal pore-fouling.
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Today UF membranes are made from
thermally and chemically stable syntheticpolymers like PVC, PAN, polyimides(PI),polysulphone(PS) ,PVDF.
In addition there are inorganic UF
membranes made from zirconium andaluminium oxides.
Plasticizers are necessary for some
membranes, if they are to be dried, toprevent collapse of the pores duringdrying.
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Today UF membranes are made from
thermally and chemically stable syntheticpolymers like PVC, PAN, polyimides(PI),polysulphone(PS) ,PVDF.
In addition there are inorganic UF
membranes made from zirconium andaluminium oxides.
Plasticizers are necessary for some
membranes, if they are to be dried, toprevent collapse of the pores duringdrying.
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Today UF membranes are made from
thermally and chemically stable syntheticpolymers like PVC, PAN, polyimides(PI),polysulphone(PS) ,PVDF.
In addition there are inorganic UF
membranes made from zirconium andaluminium oxides.
Plasticizers are necessary for some
membranes, if they are to be dried, toprevent collapse of the pores duringdrying.
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Modification
Additionalstrength is
provided bycasting themembrane on aspun-bonded
poly-ethylene orpolypropylenebacking.
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Pore Size Determination
UF membranes have “diffuse cut-off” characteristics.
The retention R (in percent) may be definedas ,R = 100 ( 1- ( Cuf / CR ) )
The convention states that the molecular
weight cut-off of the membrane is equal to the molecular weight of the globular proteins which are 90% retained by the membrane .
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Retention Characteristics
1. Size and shape considerations
2. Adsorption losses
3. Charged membranes
4. Pressure effects
5. Temperature effects
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1. Size and Shape considerations
Retention differswith linear or
sphericalstructure of molecules.
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2. Adsorption losses
The polymer which makes the UFaffects the retention if it adsorbs the
species on the membrane surface. Retention of membranes are often
measured in stirred cells.
A mass balance on cell, integrated overtime t .
R = 100 * (ln( Cf / Co ) )/ln( Vo / Vf ))
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3. Charged membrane
Charged UF membrane reject low conc.Of salts, because the fixed chargedgroup on membrane skin reject ionicsolutes via repulsion of co ions.
Obviously, divalent, trivalent ions arerejected better than monovalent ions.
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4. Effect of pressure
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5. Effect of temperature
It has been found experimentally for alarge no.of membranes systems and
feed streams that the permeation rateis inversely proportional to fluidviscosity.
Viscosity of water decreases by 2.5%
for every C rise, researchers refer to3% rule that flux increases 3% per 1 C as rule of thumb.
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Evaluation of Mass Transfer
Co-efficient To evaluate m.t.c, laminar parabolic velocity profileis assumed to be established at the channelentrance
Leveque’s solution gives, Sh = 1.62 ( Re Sc dh / L)0.33
(For 100< (Re Sc dh /L) <5000) Generally, K = .816 (γ D2 /L )0.33
γ = the fluid shear rate at the membrane surface.= 6U/b for rectangular slits.= 8U/d for circular tubes.
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Evaluation of Mass Transfer
Co-efficient To evaluate m.t.c, laminar parabolic velocity profileis assumed to be established at the channelentrance
Leveque’s solution gives, Sh = 1.62 ( Re Sc dh / L)0.33
(For 100< (Re Sc dh /L) <5000) Generally, K = .816 (γ D2 /L )0.33
γ = the fluid shear rate at the membrane surface.= 6U/b for rectangular slits.= 8U/d for circular tubes.
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Evaluation of Mass Transfer
Co-efficient To evaluate m.t.c, laminar parabolic velocity profileis assumed to be established at the channelentrance
Leveque’s solution gives, Sh = 1.62 ( Re Sc dh / L)0.33
(For 100< (Re Sc dh /L) <5000) Generally, K = .816 (γ D2 /L )0.33
γ = the fluid shear rate at the membrane surface.= 6U/b for rectangular slits.= 8U/d for circular tubes.
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UF Plant Design
Mode of operation
The arrangement of membrane moduleand their mode of operation can affectthe economics as much as the moduledesign.
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Applications
Semi conductor industry
Reclamation of waste lubricating oil
Decontamination of crude oil
Waste treatment
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Applications
Semi conductor industry
Reclamation of waste lubricating oil
Decontamination of crude oil
Waste treatment
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Applications
Semi conductor industry
Reclamation of waste lubricating oil
Decontamination of crude oil
Waste treatment
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Applications
Semi conductor industry
Reclamation of waste lubricating oil
Decontamination of crude oil
Waste treatment
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Summarizing U.F
Twenty-five years of invention.
Reliable and economic.
Eliminated severe pollution problems. Recovery of by-products adds to the profit.
Grafting eliminates fouling problems.
Stringent environmental controls may
necessitate UF. Bio-reactors using UF, have tremendous
potential for continuous enzyme reactors.
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Reverse Osmosis
A Pressure Driven
Membrane SeparationProcess
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Osmosis
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Reverse Osmosis
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R.O membranes
High resolution electron microscopycannot resolve the extensive pore in the
separating layer of the R.O. membranes Therefore it is generally considered that
they do not contain pores and that they
operate mainly by “solution diffusion” mechanism
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Solution diffusion mechanism
Introduced by SOLTANEIH and GILL.
It states that the membrane is non
porous, and that solvent and solutescan only be transported across themembranes by first dissolving in, and
subsequently diffusing through, themembrane
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HAASE and BELFORT model
The solvent flux through the membraneis proportional to pressure gradient:
For the solute it is found that:
)(11 P K J
222 C K J
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Thus, solvent (water) flow occurs onlywhen | ΔP| > |ΔΠ|, solute flow isindependent of | ΔP|
Hence, increasing the operatingpressure increases the effectiveseparation
Typically for brackish water (1.5-2kg/m3 salts), |ΔΠ| = 0.1- 0.7MPa and| ΔP| = 3-8 MPa
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Thus, solvent (water) flow occurs onlywhen | ΔP| > |ΔΠ|, solute flow isindependent of | ΔP|
Hence, increasing the operatingpressure increases the effectiveseparation
Typically for brackish water (1.5-2kg/m3 salts), |ΔΠ| = 0.1- 0.7MPa and| ΔP| = 3-8 MPa
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Thus, solvent (water) flow occurs onlywhen | ΔP| > |ΔΠ|, solute flow isindependent of | ΔP|
Hence, increasing the operatingpressure increases the effectiveseparation
Typically for brackish water (1.5-2kg/m3 salts), |ΔΠ| = 0.1- 0.7MPa and| ΔP| = 3-8 MPa
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Salt rejection
Rejection of ions at R.O membranesdepends on valence
The rejection of organic moleculesdepends on molecular weights
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Membrane modules
There are currently four genericconfigurations for membranes inindustrial use :
1. Tubular modules2. Hollow fiber modules3. Flat plate modules
4. Spiral wound modules.
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Tubular module
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Hollow fiber modules
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Flat- sheet module
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Spiral wound modules
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Plant configuration
Batch Recirculation
Feed and Bleed configuration
Continuous Single-pass
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Plant configuration
Batch Recirculation
Feed and Bleed configuration
Continuous Single-pass
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Plant configuration
Batch Recirculation
Feed and Bleed configuration
Continuous Single-pass
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Batch Recirculation
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Feed and Bleed Configuration
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Single pass configuration
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Applications
In some applications the product is theretentate, and the objective is toconcentrate or purify the retained
species and in others the product ispermeate.
Whereas, in some both retentate and
filtrate are important. For example, if avaluable product or by-product is apollutant in a waste stream, recoveryand use of the product will often pay
for pollution abatement.
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R.O. in water treatment
R.O. is a well-established large scaleindustrial process for the desalination of
brackish water More than 1000 units in operation, each
capable of producing 105 m3 /day of
drinking water
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Membranes employed
The two basic membranes employedin in the commercial R.O. systems are
1. The Thin Film Composite (TFC)membranes
2. Cellulose acetate blend (CAB)
membranes
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Membranes employed
The two basic membranes employedin in the commercial R.O. systems are
1. The Thin Film Composite (TFC)membranes
2. Cellulose acetate blend (CAB)
membranes
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Membranes employed
The two basic membranes employedin in the commercial R.O. systems are
1. The Thin Film Composite (TFC)membranes
2. Cellulose acetate blend (CAB)
membranes
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Case Study: R.O at MRL
Objective is to reuse sewage water asprocess water for MRL
Spiral wound module employed.
MRL uses advanced composite membrane(ACM) which is in TFC form.
It is made by first casting the porous
polysulfone film on fabric support. The thin(0.05- 0.2 μ) polyamide membrane is thenformed on the film surface by polymerizationof an aromatic diamine and cycloaliphatictricarbonyl chloride
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Advantages of ACM
Excellent biological stability
Excellent chemical stability except
toward Cl. Resistant to membrane compaction
Longer life as compared to CAB
membranes.
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Advantages of ACM
Excellent biological stability
Excellent chemical stability except
toward Cl. Resistant to membrane compaction
Longer life as compared to CAB
membranes.
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Advantages of ACM
Excellent biological stability
Excellent chemical stability except
toward Cl. Resistant to membrane compaction
Longer life as compared to CAB
membranes.
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Advantages of ACM
Excellent biological stability
Excellent chemical stability except
toward Cl. Resistant to membrane compaction
Longer life as compared to CAB
membranes.
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Thin Film Composites
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Process block diagram
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Pretreatment
R.O almost always requirespretreatment to control fouling
Pretreatment scheme1. Addition of HCl to control pH
2. Addition of SHMP to avoid calciumsulfate scale
3. Micron cartridge filter to removeparticles greater than 10 μ size
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Pretreatment
R.O almost always requirespretreatment to control fouling
Pretreatment scheme1. Addition of HCl to control pH
2. Addition of SHMP to avoid calciumsulfate scale
3. Micron cartridge filter to removeparticles greater than 10 μ size
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Pretreatment
R.O almost always requirespretreatment to control fouling
Pretreatment scheme1. Addition of HCl to control pH
2. Addition of SHMP to avoid calciumsulfate scale
3. Micron cartridge filter to removeparticles greater than 10 μ size
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Pretreatment
R.O almost always requirespretreatment to control fouling
Pretreatment scheme1. Addition of HCl to control pH
2. Addition of SHMP to avoid calciumsulfate scale
3. Micron cartridge filter to removeparticles greater than 10 μ size
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Permeate water characteristics
pH = 7.5
TDS = 400 ppm
Total Hardness as CaCO3= 100ppm
Free ammonia = 0.1 ppm
Nitrates = 1ppm
Silica = 10 ppm
BOD =2ppm COD= 5ppm
total Phosphates = 0.1 ppm
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ACM characteristics
Membrane configuration = spiral wound
Material = polyamide
Supplier = dupont
Dimension= 8” dia x 40” long
Rated operating pressure = 200-350 psig
Temperature range = 0-45oC
pH range = 4-11 Membrane SA = 37.2 m2
Cl tolerance = 0.25 ppm (pH>8) ; 0.1ppm(pH<8)
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Permeate can be used as
Process water
Landscaping, gardening
Ground water discharge for controllingintrusion of sea water into the groundwater table
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Summarizing R.O
Can be widely used as captive wastewater recycle plants in industries
Used for the production of drinkingwater in European countries. Largestsuch plant produces 140000 m3 / daywater for north Paris
In temperate climates nanofiltration ismore economical on this regard.
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Electrodialysis
An electrically driven
membrane separationprocess.
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Flow-diagram for ED
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The membranes
Thin films of polymeric chains containingelectrically charged functional sites.
Anion-exchange membrane (e.g. withquartenary ammonium groups)
Cation-exchange membranes (i.e. withsulfonate groups)
Various methods of producing
Close to 98% efficiency
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ED Stack
1: Polypropylene end plate 2: Electrode 3: Electrode chamber 4: spacer-sealing PVC 5: Spacer fabric 6: Screws 7: Steel frame 8: Inlet anode cell 9: Inlet concentrate cell 10: cation exchange membrane
11: AAM 12: Inlet diluate cell 13: Inlet cathode chamber
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Process configurations
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Typical process configuration
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Typical Applications
Demineralization
Concentration of electrolytes
Ion-replacement reactions
Metathesis reactions
Separation of electrolysis products
Fractionation of electrolytes
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Electrodialysis reversal (EDR)
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Cation-neutral ED
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Limiting current density
Transference number is the fraction of current carried by an ion
t+
for cations and t-
for anions ts
- for anion through solution (say .5)
tm- for anion through anion exchange
membrane (say 1.0)
So at membrane there is a depletionlayer set up
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Contd…
At a certain current theconc. becomes 0
This is called limiting
current density Beyond this H+ and OH-
is transported acrossthe membrane
Loss of efficiency andppt of salts due to pHchanges
Ilim= limiting currentdensity
D= diffusion coefficient
F= Faraday’s const.
l=Equivalent filmthickness
)(
lim
smi t t l
DF
zC
i
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Typical process configuration
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Typical Applications
Demineralization
Concentration of electrolytes
Ion-replacement reactions Metathesis reactions
Separation of electrolysis products
Fractionation of electrolytes
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Electrodialysis reversal (EDR)
Deals with fouling of the membrane andscale formation
Reversal of polarityseveral times anhour along withalternation of conc.
and demin stream Useful with Ni, Zn,
Fe salts etc
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Variations of ED
Cation exchangeand neutralmembrane
Elimination of anionmembrane
Greater flexibility inselecting flow rates
and feed and o/pconc
Electrosorption
Neutral inner layerbetween a cation ex
membrane andanion ex membrane
During normaloperation the
neutral gets loadedand in reverse getsunloaded
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Compact water purification electrodialysis units are connected directly to themain water supply system through a flexible hose.
The pressure of 1 –3 atm is quite sufficient,because their operating pressure is within 0.3 –0.4atm. Thus, in comparison with RO there is no need of additional pump of high pressure;
as a result there is another main advantage:consumers have the opportunity to regulate themselves the taste of water by means of a simpleturn of the tap;
residual chlorine in water does not influence thedesalination process, therefore there is no need of cartridges before treatment;
simplicity and slight adjustment of the process,low power consumption and low cost of units promises a great advantage in the future;
when using these units there is no need of
bottle water purchase.
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Seawater desalination with ED