MEMBRANE TECHNOLOGY
FOR WATER TREATMENT
D. JAGAN MOHAN
New Technology Research Centre
University of West Bohemia
Plzen, Czech Republic
Fresh Water Need..
Membranes for Water Treatment
Dissolved salts
Suspended solids
Colloids
Viruses
Bacteria
Parasites
Org. macro. molecules
0.0001
0.001
0.01
0.1
polio
virus
Reverse Osmosis
Nanofiltration
smallest
microorganism
1
100mm
10
Cryptosporidium
Ultrafiltration
hair
Sand filtration
Microfiltration
Membrane Separations
Symmetric. A cross section shows a uniform porous structure.
Asymmetric. In a cross section, one can see two different structures, a thin dense
layer and below a porous support layer.
• 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.
Symmetric Membranes
The cross section shows a uniform and regular structure
Cross section
Surface
Symmetric ceramic membrane (Al2O3)
Thin Film Polyamide Membrane
Polyester Fabric
Polysulfone support
PA membrane surface
Pore Geometry
top layer thickness
(0.1-1mm)
sub layer thickness
(50-150 mm)
The flux is inversely proportional
to the thickness.
commercial
interest
PA Layer
PS Support
PA Layer
PS Support
Feed Water
Flux
Cross-Flow
Semipermeable
Membrane
(~0.2 micrometers)
Porous
Interior
Asymmetric CA
Membrane
(~0.5 mm thick)
Permeate
Organic Phase (Heptane, etc.)
+ Acid Chloride
Cross-Link or Extension
Cross-Link or Extension
O
Diffusion
Reaction
+ HCl
H
Cross-Link or Extension
Aqueous Phase
+
Random
Structure
Di-Functional Amine
Functional groups in the active layer
Pressurized feed
Polyamide
(~100 nm)
NH2
NHCO
CONH
NHCO
Amine group
CONH
COOH
Amide link
Carboxylic group
~150 nm
Selective barrier
(polyamide)
Support Layer
(Polysulfone)
Reverse osmosis (RO)
Catalytic Membrane Materials...
Catalyst(s)
(Pd, PEIs, etc.)
PA Layer
Porous PS
Polyester
Support
Pure water
Charged membranes
Cl-
Na+
Ca++
SO4--
Cl+
+
+
+
+
+
+
+
+
+
+
Positively charged membrane
Quaternary ammonium groups like
-N+ (CH3)4 Cl- contribute to the
fixed positive charge of the
membrane
SO4--
Na+
Ca++
- - - - - - - - - - Negatively charged membrane
Negatively charged groups like SO3H+,
COOH groups contribute to the negative
charge of the membranes
Membrane Separations
Cf
Feed
Retinate
Membrane
Permeate
(Filtrate)
(Concentrate)
Cp
Simple scheme of a membrane module
 C f  Cp 

Cp 




Rejection : R(%)  100
 100 1 
 C



C
f
f




Crossflow Mode
Recirculation
Concentrate
Feed
Membrane
Pump
Filtrate
Dead End Mode
Feed
Membrane
Pump
Filtrate
Materials Used
Synthetic polymeric membranes
Hydrophobic
Hydrophilic
PTFE, teflon
PVDF
PP
PE
Cellulose esters
PSF/PES
PI/PEI
PA
PEEK
Ceramic membranes
Alumina, Al2O3
Zirconia, ZrO2
Titania, TiO2
Silicium Carbide, SiC
The Issues...
 Flux loss
 Solute passage
1. Bio-organic
Fouling
Molecular Adsorption
De-lamination
2. Physico-Chemical
Integrity
PA
PS
Membrane Fouling
 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
↓ flux
↓ membrane life
↑ energy use
Schematics of membrane fouling mechanisms: (A) pore blockage, (B) pore
constriction, (C) intermediate blockage and (D) cake filtration.
 Membrane fouling has a negative impact on filtration performance as it decreases the
permeate flux
Membrane Fouling
• 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
Cleaning in Backwash mode
Membrane
Cleaning chemicals (if needed)
Filtrate Tank
Cleaning in Forward Flush mode
Concentrate
Feed
Pump
Membrane
Characterization of membrane



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
Membrane Configurations
Membrane Configurations
Some Industrial Applications
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