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MEMBRANE TECHNOLOGY FOR WATER TREATMENT
D. JAGAN MOHAN
New Technology Research Centre
University of West Bohemia
Plzen, Czech Republic
Fresh Water Need..Fresh Water Need..
0.0001 0.001 0.01 0.1 1 10 100m
hairCrypto-sporidium
smallest
micro-organi
sm
polio virus
Suspended solidsSuspended solids
ParasitesParasites
BacteriaBacteria
Org. macro. moleculesOrg. macro. molecules
VirusesViruses
ColloidsColloidsDissolved saltsDissolved salts
Sand filtrationSand filtration
MicrofiltrationMicrofiltration
UltrafiltrationUltrafiltration
NanofiltrationNanofiltration
Reverse OsmosisReverse Osmosis
Membranes for Water TreatmentMembranes for Water Treatment
Asymmetric. In a cross section, one can see two different structures, a thin
dense layer and below a porous support layer.
Symmetric. A cross section shows a uniform porous structure.
• Integral: the layers are continuous.
• Composites: the active layer (thickness 0.1-1 μm) is supported over a
highly porous layer (50-150 μm), sometimes both layers are of different
materials.
Membrane Separations
The cross section shows a uniform and regular structure
SurfaceCross section
Symmetric ceramic membrane (Al2O3)
Symmetric Membranes
Polysulfone supportPA membrane surface
Polyester Fabric
Thin Film Polyamide Membrane
top layer thickness
(0.1-1m)
sub layer thickness
(50-150 m)
The flux is inversely proportional to the thickness.
commercial interest
Pore GeometryPore Geometry
PS Support
PA Layer
PS Support
PA Layer
Cross-FlowFeed Water
SemipermeableMembrane
(~0.2 micrometers)
Asymmetric CAMembrane
Porous Interior
(~0.5 mm thick)
Flux
Permeate
Aqueous Phase
Organic Phase (Heptane, etc.)
N
NH2
COCl
C
COCl
H
O
+ HClReaction
+ Acid Chloride
COCl
COCl
COCl
Random Structure
Cross-Link or Extension Cross-Link or Extension
Cross-Link or Extension
Diffusion
NH2
NH2
Di-Functional Amine+
Polyamide (~100 nm)
NHCONH2 CONH NHCO
CONH COOH
Pressurized feed
Amine group
Carboxylic groupAmide link
Functional groups in the active layer
Reverse osmosis (RO)
Support Layer(Polysulfone)
Selective barrier(polyamide)~150 nm
Catalytic Membrane Materials...
PA Layer
Polyester Support
Porous PS
Pure water
N-N CH 3
CH 3
=O
Catalyst(s)(Pd, PEIs, etc.)
Charged membranes
Positively charged membrane
+ + + + +
++++++
Na+
Ca++
SO4--Cl-
-- - - - -- - - - - -
Cl-Na+
Ca++
SO4--
Negatively charged membrane
Quaternary ammonium groups like -N+ (CH3)4 Cl-
contribute to the fixed positive charge of the membrane
Negatively charged groups like SO3H+, COOH groups contribute to the negative charge of the membranes
Feed Retinate(Concentrate)
Permeate(Filtrate)
Membrane
Membrane Separations
Simple scheme of a membrane module
f
p
f
pf
C
C
C
CCR 1100 100 (%)
Cp
Cf
Rejection :
Crossflow Mode
Feed
Recirculation
Filtrate
Membrane
Concentrate
Pump
Feed
PumpMembrane
Filtrate
Dead End Mode
Materials Used
Synthetic polymeric membranes
Hydrophobic
Hydrophilic
PTFE, teflonPVDFPPPE
Cellulose estersPSF/PESPI/PEIPAPEEK
Ceramic membranes
Alumina, Al2O3
Zirconia, ZrO2
Titania, TiO2
Silicium Carbide, SiC
1. Bio-organic Fouling
The Issues...
Molecular Adsorption
2. Physico-Chemical Integrity
De-lamination
PA
PS
Flux loss Solute
passage
Membrane fouling is referred to as the deposition or adsorption of
the particles
contained in the feed stream on the membrane surface or in the
membrane pores
This gel layer forms a secondary barrier to flow through the
membrane
Membrane fouling has a negative impact on filtration performance as it decreases the permeate flux
↓ flux
↓ membrane
life
↑ energy use
Membrane Fouling
Schematics of membrane fouling mechanisms: (A) pore blockage, (B) poreconstriction, (C) intermediate blockage and (D) cake filtration.
• Physical/chemical/biological plugging of
membranes by inorganic salts, dissolved organic
matters, colloids, bacteria, etc.
• Affects permeate water quality
• Increases operational burden and cost
• Reduces permeate water flux
• Reduces feed water recovery
• Damages membranes
Membrane FoulingMembrane Fouling
Membrane
Cleaning chemicals (if needed)
Filtrate Tank
Cleaning in Backwash mode
Cleaning in Forward Flush mode
Pump
Feed
Membrane
Concentrate
Structure-related parameters (pore size, pore size distribution, top layer thickness,
surface porosity) Permeation-related parameters
(actual separation parameters using solutes that are more or
less retained by the membranes - ‘cut-off’ measurements*)
Instruments : SEM, TEM, GPC, DMA, bubble point method, porosimetry,
AFM, IR (structural determination) etc.
* ‘cut-off’ is defined as the molecular weight which is 90% rejected by the membrane
Characterization of membrane
Membrane Configurations
Membrane Configurations
1. Waste-water treatment
2. Clarification of fruit juice, wine and beer
3. Ultrapure water in the semiconductor industry
4. Metal recovery as colloidal oxides or hydroxides
5. Cold sterilization of beverages and pharmaceuticals
6. Medical applications: transfusion filter set, purification of
surgical water
7. Continuous fermentation
8. Purification of condensed water at nuclear plants
9. Separation of oil-water emulsions
Some Industrial Applications
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