i INVESTIGATION OF FOULING MECHANISMS ON ION EXCHANGE MEMBRANES DURING ELECTROLYTIC SEPARATIONS By Matthew James Edwards A thesis submitted to the faculty of The University of Mississippi in partial fulfillment of the requirements of the Sally McDonnell Barksdale Honors College. Oxford, MS 2019 Approved by: __________________________________ Advisor: Dr. Alexander M. Lopez _________________________________ Reader: Dr. Adam Smith __________________________________ Reader: Dr. John H. O’Haver
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INVESTIGATION OF FOULING MECHANISMS ON ION EXCHANGE MEMBRANES DURING ELECTROLYTIC SEPARATIONS
By Matthew James Edwards
A thesis submitted to the faculty of The University of Mississippi in partial fulfillment of the requirements of the Sally McDonnell Barksdale Honors College.
Oxford, MS 2019
Approved by:
__________________________________ Advisor: Dr. Alexander M. Lopez
_________________________________
Reader: Dr. Adam Smith
__________________________________ Reader: Dr. John H. O’Haver
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Ó2019 Matthew James Edwards
ALL RIGHTS RESERVED
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DEDICATION
I would like to dedicate this Capstone Project to my parents, Michael and Nidia Edwards.
Their support and commitment to my education has been unfailing for as long as I can
remember. I am thankful for everything they have done. It is with their help that I am
privileged to attend The University of Mississippi, and I will forever be grateful.
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ACKNOWLEDGEMENTS
I would first like thank Dr. Alexander M. Lopez and The University of Mississippi
Chemical Engineering Department for the opportunity to work on this research project.
The guidance, patience, and willingness to work with and teach an undergraduate student
has been beneficial and inspiring to me during my time here at Ole Miss.
Second, I would like to thank Dr. Paul Scovazzo for providing guidance on how to write
this thesis and for allowing me to use his lab and equipment as well.
I would also like to thank all the graduate students of the Chemical Engineering
Department, primarily Saloumeh Kolahchyan. The willingness to take the time to answer
my questions, to guide me in how use all the equipment in the lab, and to show me how
to follow lab protocols required for the completion of my thesis research.
Finally, I would like to thank the Honors College for the numerous opportunities
throughout college to expand my academic career, and my thesis committee for taking
time to read, edit, and further improve this manuscript.
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ABSTRACT MATTHEW JAMES EDWARDS: Investigation of Fouling Mechanisms on Ion
Exchange Membranes During Electrolytic Separations (Under the direction of Dr. Alexander M. Lopez)
The global water crisis is a major problem in our developing world due to the
increasing growth of our global population, the depletion of natural water resources, and
the continuing contamination of existing water resources as a result of industrialization.
Membrane separation is a potential solution for these issues. Electrodialysis (ED) is a
separation process which employs membranes to separate inorganic and organic
substances. This study investigated how different fouling agents influenced membrane
surface characteristic and separation efficiency within an electrodialysis system. While
applicable for waste water, this study focuses on model salt water solutions with various
fouling agents added to study various fouling mechanisms. Results indicated that sodium
alginate creates a clear gel on the membrane surface, sodium hydroxide minimally
decreases the separation efficiency, and bovine serum albumin has a faster separation time.
The major implications of this study are that sodium alginate in an ED system impedes ion
diffusion and decreases the separation efficiency, the increased amount of hydroxide ions
in the solution from sodium hydroxide increases the pH, and its minimal effect means that
the membrane separation is not in part effected by change in pH levels. The final
implication is that bovine serum while having a faster separation time, increases the power
used, and more investigation is needed to understand how this complex protein affects the
surface of the unmodified membranes.
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TABLE OF CONTENTS
TABLE OF FIGURES vii
LIST OF ABBREVIATIONS viii CHAPTER 1: INTRODUCTION 1 Electrodialysis Overview 1 Current state-of-the-Art 2
CHAPTER 2: EXPERIMENTAL 6
Materials and Instrumentation Used 6 Description of Analytical Procedures 8 CHAPTER 3: RESULTS AND DISCUSSION 11
CHAPTER 4: CONCLUSIONS AND RECOMMENDATIONS 25 LIST OF REFERENCES 27 APPENDIX 29
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TABLE OF FIGURES
Figure 1: Custom Pendant Drop Apparatus 7
Figure 2: Dilution rate of control sodium chloride solution 11 Figure 3: Dilution rate of a low and high concentrations of sodium alginate 13
Figure 4: Image demonstrating visual fouling 14
Figure 5: Dilution rate of a sodium hydroxide at low and high concentrations 15
Figure 6: Average dilution rate of a low concentration of Bovine Serum 16
Figure 7: 50 nm scan of membrane soaked in deionized water 18
Figure 8: 50 nm scan of membrane soaked in NaCl solution 19
Figure 9: 50 nm scan of membrane soaked in sodium alginate solution 19
Figure 10: 50 nm scan of membrane soaked in sodium hydroxide solution 20
Chart 1: Average contact angle of deionized water with membranes soaked in different solutions The more hydrophobic the membrane the greater the angle created by the tangent
line at the point the water droplet touches the membrane. Less scaling and fouling are
equated with a hydrophobic membrane. Based on contact angles sodium alginate should
have the greatest amount of fouling when compared to the other solutions tested. This
parallels what was documented in the electrodialysis fouling trials. Another comparison
that parallels what is seen in the electrodialysis is the similarity in between the contact
angle of the sodium chloride-soaked and sodium hydroxide-soaked membranes. Having
similar contact angles means that these membranes have a similar tendency for fouling,
and the trends establish in the electrodialysis trials provide a graph with a similar trend to
dilution [Graph 3]. Bovine serum has the greatest angle and therefore the greatest
hydrophobicity and this would correlate to the least amount of fouling, which also
correlates with the dilution trends established in the electrodialysis trials.
Using this method there are possible limitations. In order to not have the strong
force of water-water attraction affect the surface tension of the water droplet the
membranes are dried before they are tested. This could essentially cause the water droplet
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to be absorbed to the dried membrane surface. This could affect the membrane surface by
altering the surface nature by exposing the more hydrophilic components. Also, a reduction
in contact angle with time can be the result of the absorbing of water warping the
membrane. Based on a study at Seoul National University, captive bubble method is a more
reliable method for testing contact angle and is recommended for further investigation in
this study [11].
The final analysis conducted with soaked membranes is microscope imaging. This
was done to establish a visual correlation between the atomic force microscope scans to
attempt to prove or disprove the reliability of images that are considered to have be
successful. Using a standard lab microscope 100x images were taken.
Based on visual representation from the microscopy imaging, there is a problem
with the atomic force microscope image given for sodium hydroxide. Visually the other
membranes appear comparable to the AFM scans. This confirms that the error in AFM
scans was related specifically with the sodium hydroxide solution-soaked membrane.
Based off observations, the main difference is the darker pigmentation which is an effect
of soaking the membranes in a sodium hydroxide solution. Since this is the notable
difference between the membranes, and standard microscopy allows us to establish sodium
hydroxide solution-soaked membrane as the only inconsistent scan, it can be concluded
that the limitation of the AFM scans is that dark pigmentation causes error in the
needle/cantilever approach using the refraction of a red laser.
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CHAPTER 4: CONCLUSIONS AND RECOMMENDATIONS
This study focuses primarily on the issue of external fouling. The “clogging of a pore”
because of small particle size being able to enter the porous layers of the membrane know
as internal fouling are not studied [16]. Conclusions made are based of the principal that
the cause and effect relationships viewed are the cause of a layer of precipitate or absorbed
organic molecule on the membrane surface and this causes transport resistance on the
membrane [1]. Fouling caused by sodium alginate is largely detrimental to the efficiency
of the membranes in an electrodialysis system and should be avoided in operation if
possible. A further study into the potential for low levels of sodium alginate creating a
stable path for electrical current to flow. This is a similar concept used in
electrodeionization which is a modified form of electrodialysis which uses resin beads to
allows for sufficient ionic conductivity even when the water is depleted of ions. Sodium
hydroxide has minimal effect on the increase of fouling in a standard salt water solution
and this also equates that small changes in the pH of a solution also has a minimal effect
on the efficiency of an electrodialysis system. Furthermore, initial findings show that
biological component, specifically protein, increases the power thus the electrical current
operating in the system. However, another aspect to consider is the possibility of
irreversible fouling. Irreversible fouling is defined as not being able to be counteracted by
physical cleaning or certain pretreatment, and a gradual change in the membranes
resistance could affect the results of the trials [15]. It is recommended another set of trials
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be ran using the membranes with the original NaCl control solution to determine if such a
change has occurred.
Due to limited access and limited time, surface characterization using atomic force
microscope and microscopy was not done with bovine serum but based off the fact that the
average contact angle of sodium hydroxide has the largest standard deviation it appears
that there is more going on with a complex biological molecule than can be analyzed in
this study. Further investigation into biological fouling and proteins in an electrodialysis
system is recommended.
Another point of further investigation is the effect of spacers on membrane fouling.
Spacers block part of the membrane surface and do have a tendency to foul as well [11]. In
between electrodialysis trials the spacers had to be cleaned in order to remove trapped
particles. This spacing, while necessary to provide a path for water to flow, would affect
the accumulation of unwanted fouling and therefore directly influences how fouling occurs
on the surface of the membranes.
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LIST OF REFERENCES [1] V. Lindstrand, G. Sundstrom and A.-S. Jonsson, "Fouling of electrodialysis
membranes by organic substances," Elsevier, pp. 91-102, 1999.
[2] R. W. Baker, "Ion Exchange Membrane Processes - Electrodialysis," in Membrane Technology and Applications, Second Edition, John Wiley & Sons, Ltd., 2004, pp. 393-423.
[4] F. Valero, A. Barceló and R. Arbós, "Electrodialysis Technology. Theory and Applications.," Aigues Ter Llobregat, pp. 1-20.
[5] M. Vaselbehagh, H. Karkhanechi, R. Takagi and H. Matsuyama, "Effect of polydopamin coating and direct electric current application on anti-fouling properties of anion exchange membranes in electrodialysis," Journal of Membrane Science, vol. 515, pp. 98-108, 2016.
[6] X. Zhao, R. Zhang, Y. Liu, M. He, Y. Su and C. Gao, "Anitfouling membrane surfac construction: Chemistry plays a critical role," Journal of Membrane Science, no. 551, pp. 145-171, 2018.
[7] M. Vaselbehagh, H. Karkhanechi, R. Takagi and H. Matsuyama, "Effect of Polydopamine coating and direct electric current application of anti-biofouling properties of anion exchange membranes in electrodialysis," Journal of Membrane Science, 2016.
[8] W. Guo, H.-H. Ngo and J. Li, "A mini-review of membrane fouling," Bioresource Technology, vol. 122, pp. 27-34, 2012.
[11] Y. Liu, S. Yang, Y. Chen, J. Liao, J. Pan, A. Sotto and J. Shen, "Preperation of water-based anion-exchange membrane from PVA for anti-fouling in the electrodialysis process," Journal of Membrane Science , vol. 570, pp. 130-138, 2019.
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[12] H.-. J. Lee, J.-S. Park and S.-H. Moon, "A Study on Fouling Mitigation Using Pulsing Electric Fields in Electrodialysis of Lactate Containing BSA," Korean J. Chem. Eng., vol. 19, no. 5, pp. 880-887, 2002.
[13] T. Rijnaarts, J. Moreno, M. Saakes, W. de Vos and K. Nijmeijer, "Role of anion exchange membrane fouling in reverse electrodialysis using natural feed waters," Colloids and Surfaces, vol. 560, pp. 198-204, 2019.
[14] L. Wang, X. Wang and K.-i. Fukushi, "Effects of operational conditions on ultrafiltration membrane fouling," Desalination, vol. 229, pp. 181-191, 2008.
[15] Y. Baek, J. Kang, P. Theato and J. Yoon, "Measuring hydrophilicity of RO membranes by contact angles via sessile drop and captive bubble method: A comparative study," Elsevier, pp. 23-28, 2012.
[16] Q. She, R. Wang, A. G. Fane and C. Y. Tang, "Membrane fouling in osmotically driven membrane processes," Journal of Membrane Science, vol. 499, pp. 201-233, 2016.
[17] W. Gao, H. Liang, J. Ma, M. Han, Z.-L. Chen, Z.-s. Han and G.-b. Li, "Membrane fouling control in ultrafiltration technology for drinking water production," Desalination, vol. 272, pp. 1-8, 2011.
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APPENDIX
NaCl Trials:
Figure 15: Trial 1 NaCl dilution
Figure 16: Trial 2 NaCl dilution
0.000
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0 50 100 150 200
Cond
uctiv
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dilute
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0 20 40 60 80 100 120 140 160 180
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Figure 17: Trial 3 NaCl dilution 250 mg SA trials: