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Thrust 2 - Desalination
"Advanced Membrane Materials
for Water Treatment"
Harry Ridgway, Res. Director
Orange County Water District
Fountain Valley, California
&
Robert L. Riley, President
Separation Systems Technology
San Diego, California
Advanced Materials for
Water Purification
Background...
Modern water treatment is rapidly
becoming dependent on membranes.
Bio-organic fouling is the major problem
with the current generation of membrane
separations (Example = biofouling).
Opportunities exist for innovation in the
design of improved membrane materials
for water purification.
Popular Membrane Materials...
Asymmetric
Cellulose Acetate
General Properties...
•random, helical, non-X-linked
•dense, smooth, neutral surface
•low flux/high salt rejection
•poor organics rejection
•chlorine tolerant
•low fouling tendency
•can be biodegraded
Popular Membrane Materials...
Polyamide Thin-Film
Composites (TFCs)
General Properties...
•random, X-linked
•rough, charged surface
•high flux/salt rejection
•good organics rejection
•chlorine sensitive
•high fouling tendency
•not biodegradable
Feed Water
Flux
Cross-Flow
Semipermeable
Membrane
(~0.2 micrometers)
Porous
Interior
Asymmetric CA
Membrane
(~0.5 mm thick)
Permeate
Thin-Film Composite (TFC) Membranes...
(Polyamide Layer)
How are modern TFC
membrane materials made?
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
Ultrastructure of TFC Membranes...
PA Layer
PS Support
PA Layer
PS Support
AFM Image of
PA Surface
AFM Image of
PA Surface
The Issues...
-Flux loss
-Solute passage
1. Bio-organic
Fouling
Molecular Adsorption
Flux & Organics Rejection
De-lamination
2. PhysicoChemical 1
Integrity
PA
2
3
PS
Chlorine Attack
Swelling
The Challenge...
...is to design a new generation of
advanced membrane materials having...
1. Low-fouling surfaces
2. Greater physico-chemical integrity
3. Improved flux and solute rejections
The Approach...
Bacteria and organics respond to a host
of membrane surface properties.
A multi-variate approach is needed to
identify which properties of membranes
contribute to bio-organics adsorption.
Correlation of Membrane Surface Properties
with Bacterial Attachment
Multivariate Models
Membrane
Properties
(independent variables)
MLR Analysis
PC Analysis
Cluster Analysis
ANN Analysis
Bacterial
Adhesion
(dependent variable)
Material Matrices...
Hydrophobicity & Pore Aspect Ratio
Flux
Thickness
Charge
A
B
C
D
E
F
G
H
I
Flux & Pore Diameter
Hydrophobic
Roughness
SPEES-PES...
Polymer B
Polymer A
SO3H
=
CH3
O
O
n
O
O
polysulfone (PS)
O
S
=
+
O
S
=
S
O
=
O
=
C
O
O
=
CH3
1
O
sulfonated polyether-ethersulfone/polyethersulfone (SPEES/PES)
(sulfonation number = SPEES/PES = 1/5)
Charged
Neutral
Membranes
Knoell et al., 1999, Journal of Membrane Science
5
Bacteria Respond to Multiple Signals...
Membrane
Hydrophobicity
Membrane
Topology
Membrane
Charge
Bacterium A
(Mycobacterium)
Bacterium B
(Flavobacterium)
Knoell et al., 1999
Research Directions...
•Anti-fouling surfaces
-neutral, hydrophilic, smooth
•Oxidation-resistant surfaces
-new materials (e.g., CPTC)
•Enhanced flux & solute rejection
-increased cross-linking; catalytic membranes
-More X-linking
-Tri-amines, etc.
-Stereochemistry
-Other polymers?
Directions...
Surface Modifications...
-smooth, hydrophilic, neutral,
mobile, renewable
Anti-fouling
Surfaces
Chemical Directions...
Resistance
Catalytic
Structural Surfaces
Directions...
Integrity
-Charged PS layer
-Fully aromatic
-Glut. X-link MPD
Directions...
Incorporation
of catalyts in
membranes
To Increase the Hydrophilicity of TFC Surfaces...
-OH
3-amino-1- CH2
propanol CH2
CH2
H N H
..
Un-Reacted
Acid Chloride O
Cl
C
Covalent
Amide-OH
-OH
CH2
CH2
CH2
N
O
H
C
PA Membrane
HCl
To Improve Chlorine Resistance...
X X X
X
X
Catalytic Membrane Materials...
Catalyst(s)
(Pd, PEIs, etc.)
PA Layer
Porous PS
Polyester
Support
Pure water
Mobile Membrane Surfaces...
+
Magnetic Particles
PA Layer
Porous PS
Polyester
Support
Kishore Rajagopalan [[email protected]]
Self-Assembling Renewable Surfaces...
Isolation &
Purification
Re-Assembly
Flexibacter polymorphus
a marine gliding bacterium
(Ridgway et al. 1977. J. Bacteriol.)
Pore-Like Structure
•Transport?
•Stability?
Self-assembled crystalline protein-lipid arrays
Hierarchical self-assembly: 2 states of organization
•
•
Self-organization of long actin protein rods into 2D crystalline sheets
Spontaneous folding of sheets into nested tubules
Potential applications
•
•
Molecular ‘fly-paper’ for bacteria
Spontaneous entrapment of bacteria in tubules
Gerard C. L. Wong et al., Science 288, 2035-2039 (2000)
UIUC
Stanford
Catalysis
Catalytic Membranes
TFCs
ACFs, Macrocycle Gates,
Hyperbranched PEIs, etc.
Biofilms &
Oxidation Studies
Clark-Atlanta
Surface-Active Materials
for Disinfection
SST
Synergies
& Collaborations...
Surface-Modified
TFC Membranes
Novel Materials & Processes
for Water Purification
Surfaces, Biofilms,
Mol. Modeling & Evals.
Pilot-Scale Studies &
Demonstrations
Applications R&D &
Evaluations
Biofilms
OCWD
Industry Affiliates
Waste Management
Expected Benefits of Research...
New knowledge of
materials/interactions
Less pretreatment,
cleaning, downtime
Lower Costs of
Desalination
More robust LF
membranes
Improved flux, rejection,
efficiency, lifetime
End of Thrust #2...
"Desalination"
Next Presentation...
Thrust #3..."Membrane Fouling
and Mitigation"