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