1. CAKE ENHANCED CONCENTRATION
POLARIZATION IN NANOFILTRATION: A
TRANSIENT ELECTROKINETIC MODEL AND
EXPERIMENTAL OBSERVATION
Md Abdullaha Al Mamun
AIChE Annual Meeting
October 31, 2012

2. Outline
• Nanofiltration and colloidal fouling
• Objectives
• Transient electrokinetic model
• Experimental setup, materials, and method
• Model predictions and experimental observations
• Concluding remarks
November 28, 2016 AIChE Annual Meeting 2012 2

3. Membrane Processes
November 28, 2016 AIChE Annual Meeting 2012 3
UF Pore size: 5-100 nm RO Pore size: < 1 nm
MF Pore size: 100-1000 nm NF Pore size: 1-5 nm

4. Fouling in NF Processes
November 28, 2016 AIChE Annual Meeting 2012 4
Membrane
Hence, combined fouling of these constituents manifest in
a very complex manner
However, colloidal fouling in presence of ions
•Simpler, yet capturing the fundamentals of combined
fouling mechanisms

5. Colloidal Fouling Mechanism
Cake Enhanced Concentration Polarization (CECP)
November 28, 2016 AIChE Annual Meeting 2012 5
Permeation drag
Electrostatic repulsion
Cross flow
Electroosmotic back flow
and reduced hindered diffusion
Cake layer growth, CECP and Cake
Enhanced Osmotic Pressure (CEOP)
Pressure gradient

6. Objectives
Limitation of previous CECP models
• Neglected the influence of cake volume fraction on
electroosmotic back flow and coupling between transient
growth of cake layer and CECP
November 28, 2016 AIChE Annual Meeting 2012 6
 Develop a mechanistic model of performance decline due
to combined fouling of colloids and ions in NF processes
 Cell model of electroosmosis
 Transient growth of cake layer and CECP
 Conduct cross flow nanofiltration experiments to
investigate the influential parameters and validate the
developed model

7. Transient Electrokinetic Model
Electroosmotic back flow
Levine-Neale cell model of
electrophoresis
Electroosmotic back flow
Levine-Neale cell model of
electrophoresis
Hydrodynamic resistance
Kuwabara cell model
Hydrodynamic resistance
Kuwabara cell model
Transient growth of cake layer
Unsteady mass balance of colloids within cake layer
Transient growth of cake layer
Unsteady mass balance of colloids within cake layer
Electrolyte transport and hindered diffusivity
Mass balance equation of ion and diffusive tortuosity of porous bed
Electrolyte transport and hindered diffusivity
Mass balance equation of ion and diffusive tortuosity of porous bed
Transmembrane osmotic pressure (TMOP) and film theory
van’t Hoff relation and Darcy’s law
Transmembrane osmotic pressure (TMOP) and film theory
van’t Hoff relation and Darcy’s law
November 28, 2016 AIChE Annual Meeting 2012 7

8. Schematic of Setup
November 28, 2016 AIChE Annual Meeting 2012 8
Feed stream
Bypass stream
Permeate stream
Retentate stream
Data acquisition
Cooling water

9. Experimental Protocol
November 28, 2016 AIChE Annual Meeting 2012 9
Experimental results
Primary
•Permeate flux
•Observed rejection
•Deposited mass
Secondary
•TMOP
•Pressure drop across the
cake layer
•Cake volume fraction

10. Materials and Instruments
Membrane
• Aromatic polyamide
composite membrane: NF90
• Resistance: 4×1013
m-1
• Observed NaCl Rejection: 90%
• RMS roughness: 65 μm
• Zeta Potential: -18 mV at pH 7
to 9 in 10 mM NaCl
Silica and Salt
• Snowtex-ZL (Nissan
Chemicals)
• Hydrodynamic Diameter:
100 nm
• Zeta Potential: -35 mV at
pH 7 and 10 mM NaCl
solution
• 99% NaCl (Sigma Aldrich)
November 28, 2016 AIChE Annual Meeting 2012 10
Instruments
Dynamic light scattering, Acoustic and electroacoustic spectrometer,
UV-VIS spectrometer, and Field emission scanning electron microscopy

11. Electroosmotic Back Flow
November 28, 2016 AIChE Annual Meeting 2012 11
Zeta potential
Pressure drop ratio: the ratio of total pressure drop including
the electroosmotic back flow to the pressure drop due to
hydrodynamic resistance only
Pressure drop ratio
•Exhibits a maximum value
with respect to κa for fixed
volume fraction
•Increases with the zeta
potential

12. Effect of Volume Fraction
Electroosmotic back flow is important when Debye layer
thickness, κ-1
, is comparable with cell radius, b
Electroosmotic back flow is important when Debye layer
thickness, κ-1
, is comparable with cell radius, b
November 28, 2016 AIChE Annual Meeting 2012 12
Volume fraction

13. Comparison of Transient Fouling
300 ppm Silica, 10 mM NaCl, pressure 965
kPa, cross flow velocity 0.1 m/s and porosity
0.5
Cake volume fraction
•Only adjustable
fitting parameter
•Obtained from
experimental porosity
•Constant over the
filtration time
November 28, 2016 AIChE Annual Meeting 2012 13

14. Goodness of Fit
November 28, 2016 AIChE Annual Meeting 2012 14
Criterion
Response
Flux decline Salt rejection Deposited Mass Normalized CEOP
RMSE 0.033 0.043 0.096 0.029
R 0.959 0.952 0.901 0.965
R2
0.92 0.906 0.813 0.931
Root Mean Squared Error (RMSE), Correlation Coefficient (R) and Coefficient of Determination (R2
)

15. For lower pressure
•Less flux decline
•Less mass deposition
•Less increase in %TMOP
Important result
•Silica deposition and flux
decline reach to steady state at
critical flux
Operating Pressure, 965 and 689 kPa
November 28, 2016 AIChE Annual Meeting 2012 15

16. For higher cross flow velocity
• Higher percent flux decline
Due to
• Less initial TMOP
• Higher initial permeate flux (vi)
• More mass deposition
• Higher increase in %TMOP
Cross Flow Velocity, 0.1 and 0.2 m/s
November 28, 2016 AIChE Annual Meeting 2012 16

17. Concluding Remarks
• Mechanistic model has been developed
• Track experimental results with one adjustable constant
parameter
• Electroosmotic back flow is important for higher zeta
potential and volume fraction within2<κa<25
• Operation of filtration process at or below the critical flux is
beneficial for the membrane performance
November 28, 2016 AIChE Annual Meeting 2012 17

18. Acknowledgement
• NSERC Industrial Research Chair Program in
Water Quality Management for Oil Sands
Extraction
• University of Alberta
• Dr. Mohtada Sadrzadeh and Dr. Subir
Bhattacharjee
• Group members at CCFLab
November 28, 2016 AIChE Annual Meeting 2012 18
Thank You

19. November 28, 2016 AIChE Annual Meeting 2012 19