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The Characterization of TiO2-coated Quartz Membranes and Their Application in NOM Degradation
by
Huda Oda
A thesis submitted in conformity with the requirements for the degree of MASc Civil Engineering
« Graduate Department of Civil Engineering University of Toronto
© Copyright by Huda Oda 2016
ii
The Characterization of TiO2-coated Quartz Membranes and
Their Application in NOM Degradation
Huda Oda
Masters of Applied Science
Department of Civil Engineering
University of Toronto
2016
Abstract
This research characterized novel TiO2-coated porous quartz disks (membranes) physically and
chemically. Uncoated and TiO2-coated membranes were examined and compared using SEM
images among other methods, which confirmed the presence of TiO2 deposits. The general
adsorption characteristics and photoreactivity of these membranes was evaluated with methylene
blue, MB, degradation experiments conducted in both batch configuration and in an enclosed
reactor operated in down-flow and up-flow modes. Up-flow mode was found to be the most
reliable reactor configuration, and 40 – 70% MB removal was achieved in this mode using 0.2 –
0.5 mg/L MB. The degradation of natural organic matter, NOM, has been evaluated using both
lab-prepared and river waters under photolytic, dark and photocatalytic conditions. Unexpectedly,
no significant decrease in DOC or UV-254 was observed in photocatalytic experiments compared
to results from the adsorption or photolytic experiments, suggesting that adsorption was the
prominent process of NOM removal under the conditions tested.
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Acknowledgments
As in any research, there are always good and bad times. There were many frustrating times during
my research and without the support of my supervisor and certain individuals, this research would
not have been completed. So, I would like to give my heartfelt thanks to my supervisor, Susan
Andrews, for her enduring patience and continuous support. She lent me encouragement, expertise,
and advice when I needed them. It has been great having her as a supervisor and mentor. I would
like to also give thanks for the second reviewer of my thesis, Ron Hofmann, and to Robert
Andrews.
This research was funded in part by the NSWERC Strategic Project Grant. Project partners were
Trojan UV, Peterborough Utilities Commission (PUC), Regional Municipalities of York and Peel,
University of Waterloo Centre for Advanced Materials Joining (CAMJ) and Department of
Biology, and the University of Toronto DWRG. Thanks to the designer and manufacturers of the
membrane reactor and TiO2-coated quartz membranes: Mélisa Hatat-Fraile, Robert Liang, and
Maricor J. Arlos. Additional thanks to the Southern Ontario Water Consortium (Solar Simulator)
and PUC (raw water supply).
Special thanks to Jim Wang for his constant support in the lab and to Stephanie Gora for her
patience and thoroughness in answering my questions and providing input. I thank Aki Kogo for
her assistant and support. The assistance and knowledge of the brilliant DWRG team us much
appreciated; this includes Jacque-Ann Grant, Divyam Beniwal, Dikshant Sharma, Yijing Cui and
Sarah Larlee.
Most importantly, I give my most sincere thanks to my family and friends, whose support was
paramount to finishing this research. I name my parents Iman Sadik and Abd Al-Majeed Oda for
their inspirations. Special thanks to my sister and best friend Zahraa Oda for advice and unending
encouragement. I dedicate this thesis to these three individuals who are my life’s anchors.
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Table of Contents
Acknowledgments (if any) ............................................................................................................. iii
Table of Contents ........................................................................................................................... iv
List of Tables ............................................................................................................................... viii
List of Figures ..................................................................................................................................x
Nomenclature ............................................................................................................................... xvi
Chapter 1 Introduction .....................................................................................................................1
1.1 Background ..........................................................................................................................1
1.2 Research Objectives .............................................................................................................2
1.3 Outline of Thesis Chapters...................................................................................................3
Chapter 2 Literature Review ............................................................................................................5
2.1 Available NOM Removal Technologies ..............................................................................5
2.2 TiO2 Photocatalysis ..............................................................................................................6
2.2.1 Process Mechanisms ................................................................................................6
2.3 TiO2 Materials ....................................................................................................................10
2.3.1 Suspended Nanomaterial .......................................................................................10
2.3.2 Immobilized Nanomaterial ....................................................................................11
2.3.3 Factors Affecting TiO2 Material Performance .......................................................12
2.4 Reactor Design and Operation ...........................................................................................14
2.5 DBP Formation ..................................................................................................................17
2.6 Research Gaps ....................................................................................................................18
Chapter 3 Materials and Methods ..................................................................................................19
3.1 Materials ............................................................................................................................20
3.1.1 List of Reagents and Equipment ............................................................................20
3.1.2 TiO2-coated Membrane Preparation ......................................................................22
3.1.3 Reactor Design and Assembly ...............................................................................23
v
3.1.4 Model River Water Preparation .............................................................................27
3.2 Analytical Methods ............................................................................................................27
3.2.1 Natural Organic Matter Analyses (UV-254 and DOC) .........................................27
3.2.2 UV Fluence Rate ....................................................................................................28
3.3 Experimental Protocols ......................................................................................................29
3.3.1 Physical Membrane Characterization ....................................................................29
3.3.2 Batch TiO2 Photocatalysis .....................................................................................31
3.3.3 Down-flow TiO2 Photocatalysis ............................................................................31
3.3.4 Up-flow TiO2 Photocatalysis .................................................................................33
3.3.5 NOM Degradation Experiments – Model and Natural River Water .....................36
3.4 Quality Assurance & Quality Control Measures ...............................................................37
3.5 Chapter 3 Summary ...........................................................................................................38
Chapter 4 Physical Membrane Characterization............................................................................39
4.1 SEM Analysis ....................................................................................................................39
4.1.1 SEM Characterization of Fresh Uncoated Quartz Membrane ...............................40
4.1.2 SEM Characterization of a Fresh TiO2-coated Membrane ....................................42
4.1.3 SEM Characterization of Membrane Profiles ........................................................45
4.2 Additional Characterization ...............................................................................................49
4.3 Chapter 4 Summary ...........................................................................................................51
Chapter 5 Operational Evaluation and Membrane Reactivity Characterization ............................52
5.1 MB Degradation in Batch Mode ........................................................................................52
5.2 MB Degradation in Down-flow Mode ...............................................................................53
5.3 MB Degradation in Up-flow Mode....................................................................................55
5.4 Reusability Tests ................................................................................................................58
5.4.1 Batch Mode ............................................................................................................58
5.4.2 Up-flow Mode ........................................................................................................61
vi
5.5 Chapter 5 Summary ...........................................................................................................63
Chapter 6 NOM Degradation Test Results and Discussion ...........................................................65
6.1 Model River Water ............................................................................................................67
6.1.1 MRW UV-254 Absorbance ...................................................................................67
6.1.2 MRW DOC Concentrations ...................................................................................70
6.1.3 MRW SUVA Results .............................................................................................72
6.2 Otonabee River Water........................................................................................................74
6.2.1 ORW UV-254 Absorbance ....................................................................................74
6.2.2 ORW DOC Concentrations....................................................................................76
6.2.3 ORW SUVA Results..............................................................................................77
6.3 MRW vs ORW ...................................................................................................................79
6.3.1 UV-254 and DOC Results .....................................................................................79
6.3.2 Qualitative Considerations .....................................................................................81
6.4 Chapter 6 Summary ...........................................................................................................84
Chapter 7 Conclusions ...................................................................................................................85
Chapter 8 Recommendations .........................................................................................................87
Chapter 9 References .....................................................................................................................88
Chapter 10 Appendices ..................................................................................................................93
10.1 Supplementary SEM Characterization ...................................................................................93
10.1.1 Additional Characterization of a Used TiO2-coated membrane in NOM
Degradation Experiments.......................................................................................93
10.1.2 Characterization of a Used TiO2-coated membrane in MB Degradation
Experiments ...........................................................................................................96
10.2 Experimental Data for NOM Degradation Experiments ...................................................98
10.2.1 Calibration Data .....................................................................................................98
10.2.2 Measured Experimental Flow Rates ......................................................................99
10.2.3 Data Tables for MRW Experiments ....................................................................100
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10.2.4 Data Tables for ORW Experiments .....................................................................102
10.2.5 Usage Sequence of a TiO2-coated Membrane, 0611-07 ......................................104
10.2.6 QA/QC .................................................................................................................108
10.3 Experimental Data for System Optimization Experiments ..............................................109
10.3.1 Down-flow Mode .................................................................................................109
10.3.2 Up-flow Mode ......................................................................................................110
10.3.3 Reusability Supplemental Data ............................................................................112
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List of Tables
Table 1: List of reagents used in this study................................................................................... 20
Table 2: List of equipment and supplier information ................................................................... 21
Table 3: Summary of NOM degradation experiments .................................................................. 37
Table 4: MRW Photolysis test Exp A results ............................................................................. 100
Table 5: MRW Photolysis Exp B results .................................................................................... 100
Table 6: MRW Adsorption Exp Aresults .................................................................................... 100
Table 7: MRW Adsorption Exp B results ................................................................................... 101
Table 8: MRW Photocatalysis Exp A results ............................................................................. 101
Table 9: MRW Photocatalysis Exp B results .............................................................................. 101
Table 10: ORW Adsorption Exp A results ................................................................................. 102
Table 11: ORW Adsorption Exp B results ................................................................................. 102
Table 12: ORW Photocatalysis Exp A results ............................................................................ 102
Table 13: ORW Photocatalysis Exp B results ............................................................................ 103
Table 14: The sequence of use of Membrane 0611-07. The membrane remained in the reactor
after the end of an experiment, unless otherwise indicated. ....................................................... 104
Table 15: Flow rate and retention time measurements for one-pump system in down-flow
configuration. The bold flow rates were the ones employed during experimentation. ............... 109
Table 16: Flowrate and retention time used for sampling – down-flow configuration with two
pumps .......................................................................................................................................... 109
Table 17: Flow rate and correspong flux values obtained for 4-8 µm frit glass membrane support
..................................................................................................................................................... 110
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Table 18: Flow rate and retention time used for sampling – first two 0.5-mg/L initial
concentration experiments .......................................................................................................... 111
Table 19: Percent difference values of expected and actual retention times for the four MB
degradation tests. Positive values indicate shorter retention times than expected and negative
values indicate longer retention times than expected. – rest of 0.5-mg/L initial concentration
experiments ................................................................................................................................. 111
Table 20: Summary of percent removals of each test and basic statistics for experiments utilizing
initial concentration of MB of 0.5 mg/L. The average reflects the mean of all removal values in
one row........................................................................................................................................ 111
Table 21: Percent difference in actual retention times – MB degradation experiments with initial
concentration of 0.2 and 0.1 mg/L .............................................................................................. 112
x
List of Figures
Figure 1: A realistic model of the process of TiO2 photocatalysis. Adapted from Herrmann, 2010.
......................................................................................................................................................... 7
Figure 2: Effect of (A) catalyst loading, (B) light wavelength, (C) initial reactant concentration,
(D) room temperature, and (E) radiant flux on the reaction rate of photocatalysis. Source:
Herrmann, 2010. ........................................................................................................................... 10
Figure 3: Schematic diagram of a reactor incorporating a submerged membrane with TiO2
slurries. Source: Fu et al., 2006..................................................................................................... 15
Figure 4: A schematic of pilot-scale Photo-CatTM photocatalytic membrane reactor. Source:
Benotti et al., 2009 ........................................................................................................................ 16
Figure 5: Schematic of pilot-scale Photo-Cat Lab® photocatalytic membrane reactor. Source:
Gerrity et al., 2009. ....................................................................................................................... 16
Figure 6: Diagram outlining the types and general sequence of experiments conducted in this
research ......................................................................................................................................... 19
Figure 7: Batch reactor setup; (a): a new membrane secured into holder, (b:) membrane and
holder positioned into solution in a 250 mL beaker, the batch reactor is being irradiated by the
solar simulator ............................................................................................................................... 24
Figure 8: (a) A blow-out of membrane reactor assembly. Note that ports and valves were
excluded in this diagram; (b) a top view of assembled reactor, and (c) the membrane reactor in
up-flow mode ................................................................................................................................ 25
Figure 9: (a) UVA lamp as positioned for TiO2/UVA experiments, and (b) corresponding
emission chart ............................................................................................................................... 26
Figure 10: Epoxy mount containing a sample of a fresh uncoated quartz and a fresh TiO2-coated
membrane ...................................................................................................................................... 30
Figure 11: Schematic of down-flow experimental setup with one pump. Note: the diagram is not
scale............................................................................................................................................... 32
xi
Figure 12: Schematic of down-flow experimental setup with two pumps. Note: the diagram is not
to scale. ......................................................................................................................................... 33
Figure 13: Schematic of up-flow experimental setup utilizing a UVA lamp. Note: the diagram is
not to scale .................................................................................................................................... 34
Figure 14: SEM images in SEI mode of plain quartz at 5, 000x magnification ........................... 41
Figure 15: SEM images in BES mode of a plain quartz membrane sample at (a) 2000x
magnification and (b) 10,000x magnification; (c) shows the qualitative inorganic composition of
the membrane at the location labelled “Spectrum 1”. ................................................................... 41
Figure 16: SEM images in SEI mode of a gold-coated plain quartz membrane sample at (a)
2000x magnification and (b) 5000x magnification ....................................................................... 42
Figure 17: SEM images in BES mode of a TiO2-coated membrane sample at (a) 2000x
magnification and (b) 10,000x magnification; and (c & d) the relative inorganic composition of
the membrane at the locations labelled “Spectrum 1” and “Spectrum 2”. ................................... 43
Figure 18: SEM images in SEI mode of a gold-coated TiO2-coated membrane sample at (a)
2000x magnification and (b) 5000x magnification ....................................................................... 44
Figure 19: SEM images in BEC mode for the profile of an uncoated quartz membrane at (a)
1000x magnification and (b) 5000x magnification, and of a TiO2-coated membrane at (c)1000x
magnification and (d) 5000x magnification. ................................................................................. 46
Figure 20: Line scan analysis of TiO2-coated sample, Location 1; (a) Profile of Ti concentration,
(b) Profile of Ti and Si concentrations, and (c) concentration plots of silicon, sodium, aluminum,
potassium, calcium and titanium................................................................................................... 47
Figure 21: Image of TiO2-coated sample at a different location with larger sample size at (1)
1000x magnification and (b) 5000x magnification. An element map of (c) silicon and (d)
titanium ......................................................................................................................................... 48
Figure 22: Tauc plot derived from UV-vis DRS spectra of P25 and TiO2-coated membrane.
Adapted from Arlos et al. (2016). ................................................................................................. 50
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Figure 23: Raman Spectra of fresh uncoated and fresh TiO2-coated quartz membranes. Adapted
from Arlos et al. (2016). ............................................................................................................... 50
Figure 24: MB removal by P25, uncoated quartz membranes, and TiO2-coated quartz membrane
....................................................................................................................................................... 53
Figure 25: Percent removal of MB with a TiO2-coated membrane .............................................. 54
Figure 26: Percent removal of MB with a TiO2-coated membrane .............................................. 55
Figure 27:Results of MB degradation tests using solution of 0.5 mg/L initial concentration in up-
flow mode. Error bars reflect experimental variability. ................................................................ 56
Figure 28: Results of MB degradation tests using solution of 0.2 mg/L initial concentration in up-
flow mode. Error bars reflect experimental variability ................................................................. 57
Figure 29: Results of MB degradation tests using solution of 0.1 mg/L initial concentration in up-
flow mode. Error bars reflect experimental variability ................................................................. 58
Figure 30: Average percent removal of MB using TiO2-coated and quartz membranes .............. 60
Figure 31: Effect of air-drying on membranes after being used six times and left to dry overnight;
(a) unused TiO2-coated quartz membrane, (b) used and dried TiO2-coated membrane, and (c)
used and dried uncoated quartz membrane ................................................................................... 61
Figure 32: Percent removal results of reusability test; (a) results obtained from membrane 0328-
01 and (b) results obtained from memrane 0330-01 ..................................................................... 62
Figure 33: Percent removal results of reusability test employing a TiO2-coated quartz membrane
consecutively without air-drying first, and then with air-drying between uses. ........................... 63
Figure 34: MRW NOM degradation UV-254 results (a) photolysis test, (b) adsorption test, and
(c) photocatalysis test. The y-intercepts represent the UV-254 absorbance of raw feed water. ... 69
Figure 35: MRW NOM degradation DOC results (a) photolysis test, (b) adsorption test and (c)
photocatalysis test. The y-intercepts represent the DOC concentration of raw feed water. Error
bars represent the standard deviation associated with analytical variability ................................ 71
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Figure 36: SUVA plots for MRW NOM degradation tests; (a) photolysis test, (b) adsorption test,
and (c) photocatalysis test. The y-intercepts represent the SUVA values of raw feed water. ...... 73
Figure 37: ORW NOM degradation UV-254 results (a) adsorption test and (b) photocatalysis
test. The y-intercepts represent the UV-254 absorbance of raw feed water. Error bars represent
the standard deviation associated with experimental variability. ................................................. 75
Figure 38: ORW NOM degradation DOC results: (a) adsorption test results and (b)
photocatalysis test results. The y-intercepts represent the DOC concentrations of raw feed water.
Error bars represent the standard deviation associated with experimental variability .................. 77
Figure 39: SUVA plots for ORW NOM degradation tests; (a) adsorption test, and (b)
photocatalysis test. The y-intercepts represent the SUVA values of raw feed water. Error bars
represent the standard deviation associated with experimental variability ................................... 78
Figure 40: Combined SUVA results of (a) adsorption tests and (b) photocatalysis tests. Error bars
indicate the standard deviation associated with experimental variability ..................................... 80
Figure 41: (a) Filtered suspended particles from a raw water sample and (b) the TiO2-coated
membrane (0611-07) after multiple uses showing particulate residue ......................................... 81
Figure 42: SEM images in BES mode of a used TiO2-coated membrane – 0611-07 – sample at
(a) Location 1 at 2000x magnification and (b) its relative inorganic composition at the location
labelled as Spectrum 1; and at (c) Location 2 at 2000x magnification and (b) its relative
inorganic composition at the location labelled as Spectrum 2. ..................................................... 82
Figure 43: SEM images in SEI mode of a gold-coated a used TiO2-coated membrane – 0611-07 –
sample at (a) 1000x, (b) 2000x, (c) 5000x, and (d) 10,000x magnification ................................. 83
Figure 44: (left) Membrane 0611-07, and (right) SEM image of first piece of a TiO2-coated
membrane used in NOM degradation experiments at 600x magnification – BES mode ............. 93
Figure 45: SEM image of first piece of a TiO2-coated membrane used in NOM degradation
experiments at 5 000x magnification – BES mode ....................................................................... 94
xiv
Figure 46: SEM image of second piece of a TiO2-coated membrane used in NOM degradation
experiments at 2 000x magnification – BES mode ....................................................................... 94
Figure 47: SEM image of second piece of a TiO2-coated membrane used in NOM degradation
experiments at 5 000x magnification – BES mode ....................................................................... 95
Figure 48: SEM image of second piece of a TiO2-coated membrane used in NOM degradation
experiments at 20 000x magnification – BES mode ..................................................................... 95
Figure 49: SEM image of a TiO2-coated membrane used in an MB degradation experiments at 5
000x magnification – BES mode ................................................................................................. 96
Figure 50: SEM image of a TiO2-coated membrane used in an MB degradation experiments at 5
000x magnification – BES mode .................................................................................................. 96
Figure 51: SEM image of a gold coated TiO2-coated membrane used in an MB degradation
experiments at 2 000x magnification – SEI mode ........................................................................ 97
Figure 52: SEM image of a gold coated TiO2-coated membrane used in an MB degradation
experiments at 2 000x magnification – SEI mode ........................................................................ 97
Figure 53: Calibration curve for UV-254 made from KHP absorbance ....................................... 98
Figure 54: A typical DOC calibration curve produced by the TOC Analyzer ............................. 98
Figure 55: Measured and expected flow measurements for MRW NOM degradation experiments
....................................................................................................................................................... 99
Figure 56: Measured and expected flow measurements for MRW NOM degradation experiments
....................................................................................................................................................... 99
Figure 57: QC chart for UV-254; check standards were of a theoretical concentration of 5 mg/L
KHP............................................................................................................................................. 108
Figure 58: QC chart for DOC check standards were of a theoretical concentration of 5 mg/L
KHP............................................................................................................................................. 108
xv
Figure 59: Pictures of first TiO2-coated membrane utilized in reusability testing in batch mode
(a) after first use, (b) after second use, (c) after third use, and (d) after air-drying overnight .... 113
Figure 60: Percent removal of MB from solution after each of five uses of first TiO2-coated
membrane subjected to reusability testing .................................................................................. 114
Figure 61: Colour of TiO2-coated membrane after each use in the first test; a) after first use, b)
after second use, c) after third use, d) after fourth use, e) after fifth use, and f) after sixth use. 115
Figure 62: Colour of plain quartz membrane after (a) third use and (b) after sixth use. ............ 115
Figure 63: Photos of membrane 0328-01 throughout reusability tests in up-flow mode ........... 116
Figure 64: MB removal results of reusability tests performed on a second TiO2-coated
membrane, 0330-xx .................................................................................................................... 116
Figure 65: Photos of membrane 0330-xx throughout reusability testing in up-flow mode. ....... 117
xvi
Nomenclature
Ag Silver
C Carbon
CB Conduction band
Cl Chlorine
Cl2 Chlorine gas
cm Centimeter
cm2 Centimeter squared
CSTR Continuously stirred tank reactor
DBP Disinfection by-product
DI Deionized
DOC Dissolved organic carbon
DWRG Drinking Water Research Group
E Band gap energy, Einstein (energy of one mole of photons)
e- Electron
e. g. For example
Eq. Equation
Eqs. Equations
eV Electron volt
fp Formation potential
g Gram
H Hydrogen
h+ Hole (valence band hole formed by loss of an electron)
H+ Hydrogen ion
h Planck’s constant
hv Photon energy
H2O Water molecule
H2O2 Hydrogen peroxide
HA Humic acid
HAA Haloacetic acid
HO* Hydroxyl radical
HO- Hydroxyl ion
hr Hour
I Iodine
i.e. In essence
k Reaction rate constant
Kads Adsorption constant
L Liter
L-H Langmuir-Hinshelwood
LC-OCD Liquid chromatography – organic carbon detection
M Mole per liter
xvii
m3 Cubic meter
MB Methylene blue
MDL Method detection limit
mg Milligram
Milli-Q® Ultrapure laboratory grade water
min Minute(s)
mL Milliliter
MP Medium pressure
N Nitrogen
N2 Nitrogen gas
NB Nanobelts
ng Nanogram
NH3 Ammonia
nm Nanometer
NOM Natural organic matter
NSERC Natural Science and Engineering Research Council
O Oxygen
O2 Oxygen gas
O2*- Super oxide molecule
O3 Ozone
P25 Aeroxide® P25 industry standard nanostructured TiO2 particles
PEC Photoelectrocatalysis
PES Polyethersulfone
pH Reciprocal of hydrogen ion
PPCP Pharmaceuticals and personal care products
PUC Peterborough Utilities Commission
QA/QC Quality assurance/quality control
r Reaction rate
R Organic molecule
R- Negatively charged organic molecule
R* Organic radical
R2 Coefficient of determination
RF Reflection factor
ROS Reactive oxygen species
rpm Rotation per minute
s Second(s)
SEM Scanning electron microscope
SiO2 Silicon dioxide (silica)
sp Specific (normalized to DOC)
SUVA Specific ultraviolet absorbance
t Time
xviii
THM Trihalomethane
THNM Trihalonitromethane
Ti Titanium
TiO2 Titanium dioxide
TiO2/UV Titanium dioxide photocatalysis
US EPA United States Environmental Protection Agency
UV Ultraviolet
UV-254 Ultraviolet absorbance at 254 nm wavelength
UV-Vis Ultraviolet and visible light
UVA Ultraviolet light, 315 – 400 nm
UVB Ultraviolet light, 280 – 315 nm
UVC Ultraviolet light, 200 – 280
V Volt(s)
VB Valence band
WF Water factor
WTP Water treatment plant
ºC Degrees Celsius
R∞ Reflectance at infinitely thick sample
λ Wavelength
α Absorption capacity
µ Micro
µg Microgram
µm Micrometer
µL Microliter
® Registered trademark
[ ] Concentration (mol/L)
< Greater than
˃ Less than
/ Divided by
% Percent
= Equal sign, or carbon to carbon double bond in organic molecules
↔ Reversible chemical reaction (in equilibrium)
→ Chemical reaction direction
+ Plus
- Minus
@ at
1
Chapter 1 Introduction
1.1 Background
As water is essential to all living organisms including humans, water quality and treatment is
always of utmost importance. It was only last century when chlorine was first widely accepted as
an effective disinfection method, but about sixty years later, it was discovered that disinfection
with chlorine comes at the price of disinfection by-product, DBP, formation. Extensive studied
have been published regarding the formation and health effects of DBPs since then, and most
conclude that DBPs are harmful to human health with potential carcinogenic effects. It has been
determined that that higher concentrations of natural organic matter, NOM, in the raw water
increase the production of DBPs. NOM is present in all natural water sources, ground and surface.
Besides enhancing the production of DBPs, NOM produces undesirable colour and taste in treated
water if not sufficiently removed as well as providing nutrients for bacterial growth and carriers
for heavy metals and trace pesticides (Zhang et al., 2009). Therefore, it is vital to remove NOM
from raw water, preferably before chlorination to reduce DBP formation.
Of the current popular methods for NOM removal is the process of coagulation and flocculation,
but this process does not provide complete removal. Filtration and adsorption processes can also
be applied for NOM removal, but it is the advanced oxidation processes, AOPs, that have stirred
much interest among researchers of this field recently. These include processes that employ
hydrogen peroxide, H2O2, ozone, O3, and TiO2 coupled with ultraviolet, UV, light. TiO2 is an
attractive option because it is stable under UV light, abundant in nature, and poses minimal health
risk to human (Rincon and Pulgarin, 2006) and the environment. Subsequently, the heterogeneous
process of TiO2 photocatalysis and its application to water treatment was of interest to many
researchers including the authors. TiO2 photocatalysis uses TiO2 as a catalyst when irradiated with
UV light to generate reactive oxygen species, ROS, including the highly reactive hydroxyl radical,
OH*, that can degrade all organic compounds in theory (Zhang et al., 2008). The use of TiO2 in
suspension has many advantages including high surface area that facilitates adsorption and
photocatalysis; however, post-treatment separation of the nanoparticles is difficult and requires
large capital and high energy input. Consequently, immobilizing TiO2 nanoparticles onto a fixed
substrate seems an intuitive alternative. The disadvantages of immobilized TiO2 include reduced
2
surface area and the potential of membrane fouling. However, if the operational conditions were
optimized to minimize the negative effects while maximizing NOM degradation efficiency,
immobilized TiO2 can then become both a novel and a practical technique that can be applied in
full-scale water treatment plants.
In this research, TiO2-coated membranes that were created by immobilizing TiO2 particles onto
fibrous silicate-based quartz membranes using the sol-gel method. These membranes were
characterized physically by a scanning electron microscope, SEM, as well as a Tauc plot and
Raman spectra. The reactivity of the membranes was investigated using methylene blue, MB,
degradation experiment in multiple reactor configuration including batch, down-flow and up-flow.
The ability of these membranes was then evaluated by performing NOM degradation experiments
that were analyzed by measuring the UV absorbance at 254 nm wavelength, UV-254, and
dissolved organic carbon, DOC, concentrations.
1.2 Research Objectives
The objective of the current research was to evaluate the potential of applying TiO2-coated
quartz membranes to drinking water treatment, namely their effectiveness in degrading NOM.
The hypothesis was that TiO2-coated quartz membranes can degrade NOM in natural water
sources to – at least – a comparable degree to P25 TiO2 nanoparticles. This research also
considered the performance of said membranes in batch and flow-through configurations to
determine optimum operational conditions. The specific objectives of this research can be
considered the following:
1. Characterize TiO2-coated membranes with a chemical probe (methylene blue)
2. Evaluate and optimize membrane reactor operating conditions
3. Determine the reusability of the TiO2-coated membranes
4. Evaluate the membranes’ capability for NOM degradation
3
1.3 Outline of Thesis Chapters
Chapter 2 provides a brief overview of common technologies to remove NOM in water
treatment systems. It reviews the literature pertinent to TiO2 photocatalysis and briefly
discusses the types of TiO2 nanomaterials and reactor configurations researched. The
possible formation of disinfection byproducts, DBPs, as a result of TiO2 photocatalysis is
also reviewed.
Chapter 3 provides an overview of the materials and methods used for the experiments
conducted in this research. Analytical procedures for DOC and UV-254 measurements
are summarized. The protocols followed in methylene blue, MB, degradation
experiments in batch, down-flow, and up-flow modes and in NOM degradation
experiments in up-flow mode are reviewed.
Chapter 4 discusses the results of the physical characterization of uncoated and TiO2-
coated quartz membranes. Their analysis and comparison using a scanning electron
microscope, SEM, is discussed in detail. Additional characterization results – those of
Tauc plots and Raman spectra – are also summarized.
Chapter 5 provides an overview of MB experiments results performed to optimize the
membrane reactor configuration and characterize the photoreactivity of TiO2-coated
quartz membranes. The removal of MB by P25 TiO2 nanoparticles, uncoated quartz
membranes, and TiO2-coated quartz membranes in batch configuration are discussed. The
results of MB degradation experiments in down-flow configurations with one and two
pumps and in up-flow configuration are summarized. In addition, the results of
reusability tests performed in batch and up-flow modes are explained.
Chapter 6 provides an overview of the NOM degradation results performed in up-flow
mode using model river water, MRW, and Otonabee River water, ORW. The NOM
degradation patterns presented as UV-254, DOC, and SUVA are summarized and
discussed.
Chapter 7 contains concluding remarks for this research and recommendations for future
research is provided in Chapter 8.
4
Chapter 9 lists the references utilized throughout the period of this research.
Chapter 10 houses the supplemental data to this research such as raw data and
calculations, calibration curves, QA/QC data, additional SEM images, and further
reusability tests data.
5
Chapter 2 Literature Review
2.1 Available NOM Removal Technologies
High levels of natural organic matter, NOM, is a concern in drinking water treatment because it is
considered a major precursor of disinfection by-products, DBPs, a significant factor in membrane
fouling a source of undesirable colour and odour in water. For that reason, much attention has been
focused on optimizing current NOM removal strategies and researching innovative NOM
degradation techniques. Popular technologies that are employed in water treatment plants include
coagulation and flocculation, adsorption, and advanced oxidation processes, AOPs.
Conventional coagulation and flocculation is very limited in removing NOM, but enhanced
coagulation using iron chloride, FeCl3, has been shown to improve NOM removal up to 50%
measured as dissolved organic carbon, DOC (Philippe et al., 2010). However, even with the
improved performance of enhanced coagulation, a large portion of the initial NOM remains in
solution. Adsorption techniques such that of activated carbon have been shown to be highly
effective in removal of organics by the process of adsorption. Activated carbon in granulated
(GAC) and powdered (PAC) forms has high adsorbance capacity due to the high surface area and
affinity to organic molecules of variable sizes (Shon et al., 2005). However, activated carbon is
expensive and tends to lose its efficiency as it ages; factors affecting the aging rate include the
amount and quality of NOM-containing water passing through. Therefore, activated carbon can
easily become a huge expense in water treatment plant operation.
Advanced oxidation processes, AOPs, are energy intensive, highly effective process that can
convert recalcitrant organic pollutants such as dyes and pharmaceuticals and personal care
products (PPCPs) into relatively harmless, low-weight organic or inorganic molecules. These
processes may employ various semiconductors for catalysis including TiO2, ZnO, Fe2O3, SnO2,
WO3, and CdS (Alrousan et al., 2009 and Hu et al., 2013). During the process, highly reactive,
transitory species are generated one of which is the hydroxyl radical. Hydroxyl radicals are
extremely reactive and non-selective oxidation agents with oxidation potential is 2.80 eV, second
only to fluorine, which is highly toxic (Alrousan et al., 2009 and Sokolowski et al., 2014).
Furthermore, they react 106-1012 times faster than alternative oxidants such as ozone (Liang et al.,
6
2014). These characteristics allow for the effective degradation and even mineralization of
recalcitrant organic matter including bacteria and inorganic compounds into smaller molecules or
their elemental constituents (Hu et al., 2013). Some of the popularly studied AOPs are organic
oxidation by hydrogen peroxide, ozone, and Photo-Fenton which can be coupled with UV
irradiation.
An attractive alternative the current NOM removing strategies is TiO2 photocatalysis. TiO2
photocatalysis is a heterogeneous process whereby TiO2 acts a catalyst to drive oxidation reactions
of organics. It can synergize between adsorption as well as photodegrdation of organics to achieve
optimal removal that requires no chemical addition, low cost, and minimal negative environmental
impacts. Although not a common method of NOM removal, photolysis is often mentioned when
TiO2 photocatalysis is discussed. Photolysis uses light irradiation, usually UV light, in theory can
degrade organic molecules by breaking them down to smaller ones as in Eq. 1. Although this
process has been applied to pathogen inactivation with considerable success (McGuigan et al,
2012), its ability to degrade organic molecules have been shown to be very limited (Rincon and
Pulgarin, 2006 and Wiszniowski et al., 2002).
𝑅 − 𝑋 + ℎ𝑣 → 𝑜𝑥𝑖𝑑𝑎𝑡𝑖𝑜𝑛 𝑝𝑟𝑜𝑑𝑢𝑐𝑡 (Eq. 1)
2.2 TiO2 Photocatalysis
2.2.1 Process Mechanisms
TiO2 photocatalysis has garnered much attention from researchers recently due to its potential as
a non-toxic, economical and effective technology. The process involves the simultaneous
occurrence of oxidation and reduction reactions caused by the photogeneration of electron-hole
pairs. Electrons at the outer shell of a TiO2 particle absorb UV light of energy equal or higher than
its energy gap (reported to be between 3.0 to 3.2 eV) causing its photo-excitation to a higher energy
level, the conduction band, CB (Wiszniowski et al., 2002, Shon et al., 2005, Herrmann, 2010, and
Rincon and Pulgarin, 2006). When electrons are promoted in that way, they leave behind positively
charged electron holes in the valence band, VB. The result is the formation of electron-hole pairs,
e-/h+, Eq. 2. Figure 1 summarizes the mechanisms in action for the process of TiO2 photocatalysis.
7
Figure 1: A realistic model of the process of TiO2 photocatalysis. Adapted from Herrmann,
2010.
Since the excited electrons are unstable and the holes are very transient, and many times, e-/h+
pairs recombine to return to their original state (Ma et al, 2009 and Sokolowski et al., 2014).
However, some electron holes move to the surface and participate in various important oxidation
reactions to produce ROS in the presence of dissolved oxygen and water molecules (Hoffmann et
al., 1995) that help decompose organic molecules. At the surface, molecules of high
electropotential such as dissolved oxygen capture the CB electrons and produce ROS species
through successive reduction reactions as outlined in Eqs. 3 - 7. The positive holes in the VB can
also oxidize water molecules forming ROS (O2*, H2O2, and OH*), Eqs. 8 - 10, which in turn
oxidize organic matter. The excited electrons and positive holes that make their way to the particle
surface can also degrade organic molecules directly as in Eqs. 10 and 11. In fact, the positive holes
are considered the dominant oxidant in the mineralization of organic compounds by some
researchers (Shon et al., 2005). These ROS produced at the surface, OH* in particular, have high
oxidation potential enabling them to degrade recalcitrant organic matter and inactivate numerous
pathogenic microorganisms.
𝑇𝑖𝑂2 + ℎ𝑣 → 𝑇𝑖𝑂2(𝑒− + ℎ+) (Eq. 2)
𝑒− + 𝑂2 ↔ 𝑂2∗− (Eq. 3)
8
𝑂2∗− + 𝐻+ → 𝐻𝑂2
∗ (Eq. 4)
2𝐻𝑂2∗− → 𝑂2 + 𝐻2𝑂2 (Eq. 5)
𝑒− + 𝑂2∗− + 2𝐻+ ↔ 𝐻2𝑂2 (Eq. 6)
𝑒− + 𝐻2𝑂2 + 𝐻+ ↔ 𝑂𝐻∗ + 𝐻2𝑂 (Eq. 7)
ℎ+ + 𝐻2𝑂 ↔ 𝐻+ + 𝑂𝐻∗ (Eq. 8)
2ℎ+ + 𝐻2𝑂 ↔ 𝐻2𝑂2 (Eq. 9)
ℎ+ + 𝑂𝐻− ↔ 𝑂𝐻∗ (Eq. 10)
ℎ+ + 𝑅𝑋𝑎𝑑 → 𝑅𝑋𝑎𝑑∗+ (Eq. 11)
𝑒− + 𝑅𝑋𝑎𝑑 → 𝑅𝑋𝑎𝑑∗− (Eq. 12)
Degradation of organic matter by TiO2 photocatalysis does not only occur as a results of reactions
with the photo-induced generation of ROS. Adsorption of pollutants onto TiO2 particles plays a
major role in removal process. The adsorption processe has been reported to be influenced, at least
in part, by irradiation, photoadsorption (Liang et al., 2014a). This is the process by which a
reactant, A, is photoadsorbed on a catalyst by absorbing a photon, Eq. 13.
𝐴ℎ𝑣,𝑐𝑎𝑡𝑎𝑙𝑦𝑠𝑡 → 𝐴𝑎𝑑𝑠 (Eq. 13)
In general, the adsorption of molecules on a TiO2 surface has been mostly described by the
Langmuir-Hinshelwood (LH) mechanism (Herrmann, 2010). The L-H mechanism describes the
reaction kinetics between two adsorbed molecules. It suggests that both participants of a reaction
adsorb to the TiO2 surface before they undergo a bimolecular reaction. This has been applied in
describing the degradation of organic substrates on TiO2 surfaces in the presence of oxygen. Eqs.
14 - 16 describe this process, where A denotes one reactant, B denotes another participating
reactant, and S denotes a semiconductor (TiO2) (Liang et al., 2014a).
𝐴 + 𝑆 ↔ 𝐴𝑆𝑎𝑑𝑠 (Eq. 14)
𝐵 + 𝑆 ↔ 𝐵𝑆𝑎𝑑𝑠 (Eq. 15)
9
𝐴𝑆𝑎𝑑𝑠 + 𝐵𝑆𝑎𝑑𝑠 ↔ 𝑃𝑟𝑜𝑑𝑢𝑐𝑡 (Eq. 16)
“In applying the L-H model, two important assumptions are made:
1. Equilibrium is established and the reaction rate is less than the adsorption/desorption rate
2. The concentration of adsorbed species covering the TiO2 surface is in equilibrium with the
concentration of species in bulk solution” (Liang et al., 2014)
Herrmann (2010) effectively summarizes the L-H reaction kinetics as applied to heterogeneous
photocatalysis: For a general bimolecular reaction as in Eq. 17, the rate varies according to Eq. 18,
where θi is the surface coverage of a reactant. The surface coverage is proportional to the
adsorption capacity, Ki, and the concentration of reactant, Xi, Eq. 19.
𝐴 + 𝐵 → 𝐶 + 𝐷 (Eq. 17)
𝑟 = 𝑘𝜃𝐴𝜃𝐵 (Eq. 18)
𝜃𝑖 =𝐾𝑖𝑋𝑖
1+𝐾𝑖𝑋𝑖 (Eq. 18)
Generally, one of the two reactants is either in excess or maintained at a constant concentration.
The reaction rate then become as in Eq. 19, where k’ is the pseudo-true rate constant.
𝑟 = 𝑘′𝜃𝐴 = 𝑘′𝐾𝐴𝐶𝐴
1 + 𝐾𝐴𝐶𝐴 (Eq. 19)
The kinetics of photocatalysis is governed by five parameters: catalyst loading, light wavelength,
initial pollutant concentration, radiant flux, and room temperature. Figure 2 illustrates the effects
of these parameters on the reaction rate.
10
Figure 2: Effect of (A) catalyst loading, (B) light wavelength, (C) initial reactant
concentration, (D) room temperature, and (E) radiant flux on the reaction rate of
photocatalysis. Source: Herrmann, 2010.
2.3 TiO2 Materials
2.3.1 Suspended Nanomaterial
The form in which the TiO2 catalyst is applied further varies results. TiO2 can be made into a
myriad of nanomaterials such as nanoparticles, nanofibres, nanowires, and nanomembranes. Most
commonly, TiO2 is prepared in nano-sized particles, commonly Degussa P25, which is available
as the commercial standard (Sokolowski et al., 2014). These nanoparticles, or slurries, need to be
in continuous suspension in solution while reacting. They have a high specific area per mass ratio
(~51 m2/g) (Chong et al., 2010 and Hu et al., 2013) and thus high adsorption capacity (Qu et al.,
2013). This allows them to be applied in removal of recalcitrant organic constituents of water and
pathogen inactivation (Chong et al., 2010 and Qu et al., 2013). One of the main challenges with
using TiO2 nanoparticles in suspension is the need to separate them from the water after use, which
requires substantial energy input as well as sludge management. Microfiltration and ultrafiltration
11
has been used to accommodate the separation requirement of TiO2 slurries, but membrane fouling
becomes a major hurdle to the feasibility of this process in large-scale applications (Hu et al., 2013,
Choo et al., 2001, and Zhang et al., 2009). Conventional sedimentation and cross-flow processes
have been applied as a post-treatment steps as well (Fernandez-Ibanez et al., 2003, and Doll and
Frimmel, 2005). Another challenge with TiO2 nanoparticle suspensions is the potential of
formation aggregates of bigger particle sizes than the original (Zhang et al., 2009), which can
reduce adsorption efficiency and hinder light passage through solution if not optimized.
Other suspended TiO2 nanomaterial have been produced in the forms of nanotubes, nanowires,
nanofibers, and nanorods. These one-dimensional nanomaterials have the advantage of an easier
separation and recovery due to their longer size while retaining high surface area (Zhang et al,
2009). Zhang et al. (2008) used a direct grafting method to fabricate free standing TiO2 nanotubes
that achieved humic acid, HA, degradation comparable to P25 nanoparticles. Macak et al. (2007)
compared the efficiency of TiO2 nanotubes’ efficiency in removing organic pollutants to that of
P25 particles and found that the nanotubes performed better than the nanoparticle suspensions.
The properties of the nanotubes allowed for faster transfer of reactants to the nanotube surface (Qu
et al., 2013). Zhang et al. (2009) synthesized titanium nanowires of 20-100 nm in diameter using
the hydrothermal method and they observed a reaction rate of the decomposition of HA closely
comparable to that of P25 nanoparticles. Therefore, one-dimensional TiO2 nanomaterials show a
promise in surpassing nanoparticles in organic degradation efficiency.
2.3.2 Immobilized Nanomaterial
Membranes provide physical barrier to contaminant passage by size-sieving. Many types of
membranes are available including polymeric membranes, commonly used in microfiltration and
ultrafiltration, ceramic membranes, and inorganic membranes, such as silica- and alumina- based
membranes. The ideal membrane is stable under various operational conditions, is highly selective
to easily achieve water quality requirements, provides molecular flux, and requires as small of
driving force or pressure as possible (Zhang et al., 2008). TiO2 nanoparticles can be immobilized
onto membranes in a variety of ways. They can be electrospinned to form nanofiber mats that
further yield nanofiber membranes with high multifunctionality that can remove micron-sized
pollutants (Qu et al, 2013). Nanocomposite membranes incorporate hydrophilic nanomaterials like
TiO2 into polymeric membranes to reduce membrane fouling and enhance their thermal stability
12
(Qu et al, 2013). In addition to the physical separation by sieving effect of the membranes,
reactants can be removed by adsorbing onto TiO2 particles and degraded by photocatalysis.
Thin film nanocomposites, TFN, incorporate nanomaterials such as nano-Ag and nano-TiO2 on
their surface to form an active layer that can degrade organics and inactivate waterborne pathogens
(Qu et al, 2013). Nanoparticles can be coated on a fixed surface to create immobilized TiO2 films
using various methods including the sol-gel method, which is employed in this research. Compared
to nanoparticles, films that incorporate TiO2 exhibit reduced photocatalysis rate and capacity due
to the much smaller surface area available for adsorption and fewer sites available for
photocatalysis to occur (Marugan et al., 2008). Nonetheless, TiO2 immobilized films have many
advantages that make it more attractive for applications in practical water treatment processes. For
example, films eliminate the very energy- and cost-intensive step of separation and recovery of
tiny nanoparticles.
One-dimensional TiO2 materials such as nanowires and nanotubes can be further matted into TiO2
membranes, a promising albeit not well researched alternative. Furthermore, in addition to the
synergistic effect of surface adsorption and photocatalytic degradation of TiO2 photocatalysis,
membranes can perform ultrafiltration to further remove water contaminants (Hu et al., 2007).
Figure 4 shows how contaminants such as bacteria can be removed from solution by size sieving,
chemical adsorption and cake formation.
2.3.3 Factors Affecting TiO2 Material Performance
2.3.3.1 Surface Area
Photocatalysis occurs at the surface of the TiO2 catalyst where two major interactions occur. One
is the interaction between organic molecules in solution with CB electrons and/or VB holes, which
leads to oxidation and then degradation. The other interaction is that between ROS and organic
molecules in solution. Hence, surface area plays a vital role in the extent of photocatalysis and
higher surface areas are desirable.
13
2.3.3.2 Energy Level Position and Interface Nature
Many factors other than surface area affect the photocatalytic properties of TiO2 such as position
of energetic levels, mobility and mean lifetime of electron-hole pairs, and the nature of the
interface. The method of preparation of TiO2 catalyst interface influences its Photoactivity. For
example, a smooth lattice results in more electron-hole pair recombination than a defective lattice
(Liang et al., 2014). Different positions of energy levels form direct and indirect bands gaps. A
direct band gap describes the situation where the top VB (energy level) lies directly below the
bottom of the CB (higher energy level) without a change in lateral momentum. On the other hand,
an indirect band gap describes a situation where the energy in the CB is shifted by a change in
momentum (Liang et al., 2014).
TiO2 has attributes of both gap types: the direct band in the range of 3.58-3.79, and the indirect
band in the range of 3.05-3.4 eV (Habibi et al., 2007). Habibi et al. (2007) tested various physical
characteristics of TiO2 films they prepared and investigated their effects on photodegradation
capacity. They found that the fundamental optical transition in the films is direct, and that the direct
band gap increased with increasing annealing temperature and film thickness.
2.3.3.3 Crystal Phase
TiO2 can have two crystal phases, anatase and rutile. The ratio of anatase to rutile crystal phases
depends on the preparation methods and materials. Habibi et al. (2007) found that anatase
increasingly dominates the crystal lattice as annealing temperature increases. Moreover, studies
have shown that the anatase phase of TiO2 is more photoreactive than rutile and absorbs UVA light
better (Habibi et al., 2007, Luttrell et al, 2014, and Sokoloswki et al., 2014).
14
2.4 Reactor Design and Operation
There are two main types of photocatalytic reactors that can be utilized for TiO2 photocatalysis:
reactors that used suspended TiO2 particles, slurry reactor, and reactors that employ immobilized
onto an inert surface, membrane reactors. The total irradiated surface area of catalyst per unit
volume and the distribution of irradiated light within a reactor are two factors that need to be
considered when choosing and configuring a reactor (Chong et al., 2010).
The slurry reactor has been the most popular type of reactor used for TiO2 photocatalysis due to
the exceptional distribution of suspended TiO2 particles in solution. The well-distributed particles
allow for high total surface area per unit volume, thereby increasing the efficiency of the
photocatalytic degradation of contaminants (Chong et al., 2010). The separation of TiO2
nanoparticles from solution after treatment can be performed by settling tanks or conventional
sedimentation, cross flow filtration, and membrane filtration (microfiltration, MF, and
ultrafiltration, UF) (Chong et al., 2010 and Fernandez-Ibanez et al., 2003).
Photocatalytic membrane reactors have been designed in various ways in search of optimizing the
efficiency of organic removal by membranes that incorporate TiO2. Some researchers designed
hybrid reactor system whereby more than one process was incorporated in the same reactor. Such
reactor designs allow for the use of the continuous operation of a slurry reactor without much loss
of TiO2 particles. Fu et al. (2006), for example, designed a laboratory-scale reactor consisting of a
submerged MF membrane module coupled with TiO2 slurries, forming two reaction zones
separated by a rotating baffle, Figure 3. The first zone is where photocatalytic oxidation of
contaminants occurs and the second zone provides membrane separation. The researches applied
this reactor to the degradation of fulvic acid, FA, and found that the presence of TiO2 nanoparticles
increased the flux through the MF membrane and reduced the potential for membrane fouling.
15
Figure 3: Schematic diagram of a reactor incorporating a submerged membrane with TiO2
slurries. Source: Fu et al., 2006.
Purifics Inc (London, ON) manufactured two pilot-scale configurations of photocatalytic reactors
that use TiO2 slurries with UV light as a method of treatment and a cross-flow ceramic membrane
unit for TiO2 particle recovery. The recovered TiO2 is recycled to enter the reactor stream again.
One of the designs, Photo-CatTM employs 32 UV lamps in series that can be controlled
individually (Benotti et al., 2009 and Chong et al., 2010); see Figure 4. It has a capacity of up to 2
Mgal/day and a footprint of 678 cm2, and it has showed effectiveness in removing organic
compounds (Qu et al., 2013). Benotti et al. (2009) described the reactor in more detail and
evaluated it in terms of the degradation of 32 pharmaceutical and endocrine-disturbing substances.
They found that the majority of the tested compounds were degraded by more than 70%. The
second reactor design, Photo-Cat Lab®, employs eight low-pressure UV lights in series for
irradiation and an air compressor that provides oxygen to the system and air pulses to clean the
surface of the ceramic membrane filter (Gerrity et al., 2009), Figure 5. These two designs show
that industrial applications of photocatalytic membrane reactors are likely possible.
16
Figure 4: A schematic of pilot-scale Photo-CatTM photocatalytic membrane reactor. Source:
Benotti et al., 2009
Figure 5: Schematic of pilot-scale Photo-Cat Lab® photocatalytic membrane reactor.
Source: Gerrity et al., 2009.
17
2.5 DBP Formation
The major concern with NOM removal is their ability to react with disinfectants, mainly chlorine,
to form disinfection by-products (DBPs). Chlorination releases regulated DBPs including
trihalomethans (THMs), haloacetic acids (HAAs), haloketones, aldehydes, chloral hydrate, and
HANs; chloramination also yields THMs, HAAs, nitrosamines, and HANs; and ozone produces
ketones, aldoketoacids, and carboxylic acids. Unfortunately, the effects of UV/TiO2 on toxicity or
DBP formation in drinking water applications are not well established due to the small number of
studies in this area. However, the potential of TiO2 photocatalysis forming harmful DBPs is still
present. Some studies have detected genotoxic degradation products in UV/TiO2 systems when
treating pesticides under unsuitable conditions (Sokolowski et al., 2014). The effect of UV/TiO2
on toxicity may depend on the initial raw water characteristics and operating conditions.
Potentially, hydroxyl radicals produced during this processes may oxidize bromide or iodide ions
in water forming HOBr and HOI. These compounds can react with NOM to produce brominated
or iodinated organics that have harmful effects (Sokolowski et al., 2014).
TiO2 photocatalysis may have indirect effects on DBP formation. Usually, UV/TiO2 is used a pre-
treatment to chlorination in order to remove NOM before contact with chlorine and decrease DBP
formation potential (DBPfp). Hence, UV/TiO2 may cause DBPs indirectly in two ways:
I. Incomplete degradation of organic matter
If the UV/TiO2 disinfection conditions were not optimized, degradation of organic matter
may not realize mineralization, hence leaving low molecular weight and low aromatic
molecules such as aldehydes and alcohols. Furthermore, the fragmentation of aromatic
structures within NOM may expose convenient sites for chlorine to attack and for DBPs.
II. Fragmentation of NOM
The process of TiO2 photocatalysis preferentially degrades larger molecules and attacks
aromatic and conjugated structures. This is attributed to the high electron densities of these
compounds that are more vulnerable to OH* attack, and the presence of more functional
groups that can interact with TiO2. The degradation of these compounds into low molecular
organic or inorganic compounds may introduce new intermediate chemicals in the water
18
than can later react with chlorine to produce DBPs (Shon et al., 2005 and Sokolowski et
al., 2014).
2.6 Research Gaps
TiO2 photocatalysis is an emerging attractive technology with great promise for applications in
water treatment processes. The key accomplishment that needs to be achieved is the design of
reliable and effective TiO2 nanomaterials that can be easily incorporated in an easy-to-use reactor
with minimal cost. Though a few efficient bench-scale and pilot-scale slurry reactors have been
achieved, less significant progress has been made to produce successful reactors that incorporate
immobilized TiO2 photocatalysts. This work characterizes and investigates the reliability of
innovative TiO2-coated quartz membranes as pertains to NOM degradation.
This research considers both short- (up to a few minutes) and long-term (up to 120 minutes)
irradiation durations in batch mode that can be representative of batch reactor systems. More
importantly, it also considers short- (as low as 2 minutes) and long-term (up to 20 minutes)
irradiations in a unique flow-through photocatalytic membrane reactor that may be considered
representative of flow-through treatment systems used in water treatment plants. This is contrary
to most research where the irradiation times were long (a few hours), with some research having
the irradiation time stretch up to 24 hours. From an engineering perspective, it is vital to be able
to reuse TiO2 materials used for NOM degradation. Hence, this research evaluates the reusability
of TiO2-coated quartz membranes in both batch and flow-through modes while incorporating no-
cost material recovery methods. In the majority of related research, TiO2 nanomaterials were
recovered at some, if not considerable, cost and energy input. This research contributes to the body
of knowledge of the capacity of TiO2 photocatalysis to degrade NOM and the feasibility of
immobilized TiO2 in water treatment application.
19
Chapter 3 Materials and Methods
The purpose of this research is to evaluate the performance of immobilized titanium dioxide, TiO2,
onto quartz membranes. Experiments were conducted to characterize membrane structure and
reactivity, to optimize the reactor setup, and to assess the degradation of organic matter by the
process of TiO2 photocatalysis. Figure 6 shows the general sequence of experiments conducted.
The materials used in these experiments are summarized in Section 3.1, while the analytical
methods and experimental procedures are explained in Sections 3.2 and 3.3.
In summary, preliminary experiments were conducted in batch mode and under simulated solar
irradiation to ascertain the durability of the membranes and to evaluate the extent of degradation
of methylene blue, MB, under photocatalytic conditions. Further experimentation was then
conducted with a flow-through reactor and, predominately, under UVA light. The reactor system
was optimized by testing a few flow configurations until it was determined that an up-flow
configuration allowed for the most reliability and reproducibility. Henceforth, the up-flow mode
was utilized for conducting MB and natural organic matter, NOM, degradation experiments.
Figure 6: Diagram outlining the types and general sequence of experiments conducted in this
research
Ass
esse
me
nt
of
TiO
2-c
oat
ed
Mem
bra
nes
Physical Membrane Characterization
Optimization and Reactivity
Characterization
Preliminary MB Degradation Experiments
Batch Mode
Down-flow Mode
Up-flow Mode
Reusability Tests
Batch Mode
Up-flow Mode
NOM Degradation
MRW Source
ORW Source
20
3.1 Materials
This section provides an overview of all materials and equipment used for this research. The
reagents and equipment are summarized in Subsection 3.1.1. More detailed description of the
types of reactors – batch and flow-through – are presented in Subsection 3.1.2. Finally, the
procedure for preparing model river water is summarized in Subsection 3.1.3.
3.1.1 List of Reagents and Equipment
The reagents and equipment used in this research are summarized in Tables 1 and 2. Any
deviations are noted in the text as appropriate.
Table 1: List of reagents used in this study
Use and Reagent, Purity Manufacturer/Supplier, Product/Model Number
All procedures
Milli-Q® Water (18.2 MΩcm,) Ultrapure water prepared by Milli-Q® system
NOM degradation
Model river water Prepared in laboratory
Otonabee River water Peterborough Utilities Services Inc.
Preliminary MB degradation
TiO2 P25 powder, 99.5% Sigma Aldrich (Oakville, ON), 71846-100G
Methylene blue hydrate, 97% Fluka Analytical
Model water preparation
Alginic Acid Sigma-Aldrich (Oakville, ON) A7003-100G
Suwannee River NOM RO isolation, (International Humic Substances Society,
St. Paul, MN, USA), 2R101N
Calcium chloride dehydrate
Sigma-Aldrich (99% purity, St. Louis, MO, USA)
Sodium nitrate
Calcium sulphate dihydrate
Sodium hydroxide
Sodium bicarbonate
Sodium hydroxide, 97% BDH, VWR Analytical, 1310-73-2
Magnesium chloride hexahydrate, 99% EMD Millipore Ltd (Etobicoke, ON), 172571
TOC Analyzer
Compressed nitrogen gas, N2, Ultra high
purity Praxair (Mississauga, ON)
21
Table 2: List of equipment and supplier information
Use and Equipment Manufacturer/Supplier, Product/Model Number
All procedures
Milli-Q® System EMD Millipore (Mississauga, ON)
Preliminary MB degradation
Solar simulator Photo Emissions Tech. Inc. (Camarillo, CA, USA),
SS150AAA
MB and NOM degradation
Blak-Ray® long wave ultraviolet lamp UVP (Uplands, CA, USA), Model B 100AP
Sylvania 100W mercury medium skirted spot
lamp bulb
Canadian NDE Technology (Toronto, ON), UVP P/N
34-0054-01
MB degradation and model water prep
Thermix® stirrer Fisher (USA), 14-493-120MR
Analytical balance (+/-1 mg) Ohaus (Florham Park, NJ), AP210
Photolysis/adsorption tests
Uncoated quartz membranes VWR (Mississauga, ON), 89187-092
TiO2 Photocatalysis, Adsorption tests
TiO2-coated quartz membranes University of Waterloo (Waterloo, ON)
MB degradation, batch mode
TiO2 membrane support and holder for batch
tests University of Waterloo (Waterloo, ON)
MB and NOM degradation, flow-through setup
Membrane reactor University of Waterloo (Waterloo, ON)
Masterflex® L/S®, easy-load® II Peristaltic
pump
Cole-Parmer (Vernon Hills, IL, USA), Model 77202-
60
Masterflex® L/S®, Norprene® tubing Cole-Parmer (Vernon Hills, IL, USA), 06404-13
MB and NOM degradation, up-flow mode
50 mm fritted glass membrane support for
reactor (Porosity E, 4-8 µm) Ace Glass Inc. (Vineland, NJ), 7176-46
MB degradation, down-flow mode
50 mm fritted glass membrane support for
reactor (ultrafine porosity, 0.9 – 1.4 µm) Ace Glass Inc. (Vineland, NJ), 7176-320
MB and NOM degradation
0.45 µm x 47 mm Supor®-450 PES membrane
filters PALL, Life Sciences (Mississauga, ON), 60173
DOC analysis
TOC analyzer OI analytical (College Station, TX, USA), Aurora
model 1030, auto-sampler model 1088
MB degradation and UV-254 analysis
22
Hewlett Packard 8452A Diode Array UV-Vis
spectrophotometer Agilent Technologies (Mississauga, ON)
1 cm quartz cuvette Agilent Technologies (Mississauga, ON), 5061-3387
5 cm quartz cuvette Agilent Technologies (Mississauga, ON), 5063-6554
UV Fluence Rate
USB4000 radiometer Ocean Optics Inc. (Dunedin, FL, USA), QP600-1-uv-
vis
SEM Analysis
Scanning Electron Microscope JOEL USA, Model JSM-6610LV
3.1.2 TiO2-coated Membrane Preparation
The experiments performed in this research were centered around assessing the performance of
immobilized TiO2 onto quartz membranes. To that end, membranes were prepared and supplied
by M. Hatat-Fraile from the University of Waterloo. Silicate-based microfiber quartz membranes
(Type A/E, 50 mm diameter, pore size of 1 µm) were purchased from Pall corporation (VWR
International) and coated with at the Centre for Advanced Material Joining (CAMJ) laboratories
at University of Waterloo using the sol-gel method. Hatat-Fraile et al. (2013) explain the coating
process of non-porous alumina supports in detail, which was similar to the process of coating
porous quartz membranes. the difference in the two coating processes is reported by Arlos et al.
(2016).
To summarize, titanium dioxide was synthesized in the lab by mixing equal volumes of 2-propanol
solution with tetra-isopropoxide solution (TTIP) through a static T-mixer at equal flow rates. The
resultant solution contained active TiO2 sol-gels with which the uncoated quartz membranes were
coated. A dipping reactor was utilized to dip-coat the prepared membranes with TiO2. This dipping
process was repeated six times before the newly-coated membranes were dried overnight at 70 ºC
and then calcined at 400 ºC for one hour (Arlos et al., 2016). Finally, the membranes were washed
with Milli-Q® again to remove any remnant loose particles.
For the experiments of this research, uncoated and TiO2-coated membranes were stored in petri-
dishes in a dry environment until use. After use, a membrane would be extracted from its holder
and placed on a metallic mesh to dry by exposure to air. Then, the membrane would either be
reused shortly afterwards or stored in a petri-dish for future use.
23
3.1.3 Reactor Design and Assembly
Two reactor types were utilized in conducting this research, a batch reactor and a flow-through
reactor. The batch reactor was used in conjunction with irradiation from the solar simulator for
preliminary methylene blue, MB, degradation experiments, while the flow-through reactor was
used for system optimization experiment, as well as MB and natural organic matter, NOM,
degradation experiments. The batch reactor setup is detailed in Subsection 3.1.3.1, and the flow-
through reactor setup is explained in Subsection 3.1.3.2.
3.1.3.1 Batch Reactor
The batch experiments were conducted in a batch reactor consisting of a 250 mL beaker and a
membrane holder that allowed for the suspension of a filter membrane, uncoated or TiO2-coated.
A membrane holder made of two plastic rings (50 mm diameter) and a circular metallic mesh was
held the membrane in use in place. The membrane was placed above the mesh and in-between the
plastic rings to allow for exposure to irradiation from above the reactor. The membrane was
secured in position by bolts and nuts as shown in Figure 7(a). The membrane holder assembly was
then positioned into a 250 mL beaker containing with 200 mL of MB working solution, Figure
7(b). The membranes in each experiments were retained at the same height to ensure that the
distance from the light source – the solar simulator – to the membrane surface remains constant;
that distance was approximately 35 cm. Therefore, the membranes were fixed at a constant height
in the membrane holder such that the membrane was submerged at 2 cm from the solution surface.
The experiments conducted in batch mode were irradiated with light from the solar simulator
(Photo Emission Tech., In., SS150AAA). The solar simulator emitted light with a spectrum that
matches that of natural solar radiation with an intensity of roughly 108 mW/cm2 (300 -1100 nm),
of which only 13.4 mW/cm2 was available from the UV range required for TiO2 photocatalysis
(Sokolowski, 2014).
24
Figure 7: Batch reactor setup; (a): a new membrane secured into holder, (b:) membrane and
holder positioned into solution in a 250 mL beaker, the batch reactor is being irradiated by
the solar simulator
3.1.3.2 Flow-Through Membrane Reactor
The membrane reactor was designed and manufactured at the University of Waterloo as part of a
collaborative project (NSERC Grant: Removal of Drinking Water Contaminants with Innovative TiO2
Nanowire Membranes). The reactor was designed to allow for flow-through, crossflow and recycled
flow configurations. In this research, only the flow-through feature was utilized. The aim was to
reproduce a system similar to a typical conventional dead end membrane unit reactor used in water
treatment plants.
The reactor is made of stainless steel and is composed of two main parts, top and bottom (Figure
8). Both parts feature two ports through which flow is controlled with open-close valves. The
inside of the reactor is a chamber that houses the test membrane, through which water can pass
from inlet to outlet. The top and bottom parts of the reactor feature 3-mm circular quartz glass
windows that allow for irradiation to pass through and into the reactor chamber. The location of
the windows allows for irradiation source to be located above or below the reactor or from both
directions. The reactor chamber’s inner depth measures 4.1 cm in total, including the height added
25
by the membrane holders, making the chamber volume approximately 39 cm3. Two plastic place
rings fit inside two metal holders, in-between which the membrane support (a porous fritted glass
disk) and the membrane are placed. Two membrane supports of different porosities were employed
for different types of experiments in this research. The first is an ultrafine membrane support (0.9
– 1.4 µm porosity) and the second is of Porosity Class E (4 – 8 µm). The plastic place rings help
cushion the membrane support and the membrane when pressure is exerted inside the reactor,
thereby allowing some flexibility. To further avoid breakage, the membrane support was soaked
for two days before first use (Hatat-Frailer, 2015), and kept submerged in Milli-Q® water between
uses.
Figure 8: (a) A blow-out of membrane reactor assembly. Note that ports and valves were
excluded in this diagram; (b) a top view of assembled reactor, and (c) the membrane reactor
in up-flow mode
26
The assembled reactor is shown in Figure 8(b) and (c). Once all parts are in place, the top part is
secured to the bottom part by six bolts and nuts. Water is conveyed in and out of the reactor via
two types of tubing. The in-use port on the top part of the reactor is connected to a 60.5 cm
Masterflex Norprene® tubing (Cole-Parmer, 06404-13). The in-use port on the bottom part of
the reactor is connected first to 17 cm clear polyethylene plastic tubing, then to 152 cm
Masterflex Norprene tubing. Depending on the reactor configuration (down-flow or up-flow),
the conveyed water is either irradiated before being filtered through the membrane (uncoated or
TiO2-coated quartz) or the water is irradiated after passing through the membrane. Once the water
is treated, it leaves the reactor through another port, where a sample can be collected. The
irradiation source for all experiments, except the preliminary MB degradation experiments, was a
B-AP100 UVA mercury spot lamp (UVP, Uplands, CA, USA). The emission spectrum for this
lamp features a sharp peak at 365 nm, Figure 9 (Cambruzzi, 2016). The lamp irradiance is
investigated in more depth in Subsection 3.2.3.
Figure 9: (a) UVA lamp as positioned for TiO2/UVA experiments, and (b) corresponding
emission chart
27
3.1.4 Model River Water Preparation
Model river water was prepared according to the method used in a similar study by Sokolowski
(2014). It requires the combination of three stock solutions: a salt mixture, a calcium sulphate
solution, and a humic and alginic acid mixture. The salt mixture was prepared by dissolving 0.22
g of calcium chloride dihydrate, 0.84 g of magnesium chloride hexahydrate, and 0.04 g of sodium
nitrate in Milli-Q® water to make a 1 L solution. The calcium sulphate solution was prepared by
dissolving 0.29 g of calcium sulphate dihydrate into one liter of Milli-Q® water. The humic and
alginic acid solution was prepared by mixing 0.25 mL of freshly made 1.0 M sodium hydroxide
with 0.026 g of Suwannee River NOM, 0.05 g of alginic acid, and Milli-Q® water to make a 100
mL solution. The stock solutions were stored at 4 °C for a maximum of two weeks. Model river
water was produced by mixing 100 mL of the salt mixture, 333 mL of the calcium sulphate
mixture, 10 mL of the humic and alginic acide mixture, and 0.126 g of sodium bicarbonate. This
working solution was stored at 4 °C for a maximum of one week.
3.2 Analytical Methods
3.2.1 Natural Organic Matter Analyses (UV-254 and DOC)
Water containing natural organic matter, NOM, was evaluated by measuring the UV absorbance
at 254 nm, a reflection of aromatic compounds concentration, and the concentration of dissolved
organic carbon (DOC). Samples of 40 mL were collected in duplicates and filtered through 0.45
μm membrane filters (PALL Life Sciences, Supor©-450, 47 mm). The filtered samples were
collected in 40 mL amber vials. The absorbance at 254 nm was measured with a UV-Vis
spectrophotometer (Agilent Technologies) within the same day and according to Standard Method
5910 B (APHA, AWWA, and WEF, 2012).
The samples were then acidified with sulphuric acid to pH <2 and stored in the refrigerator at 4 °C
until further analysis. The samples were analyzed in the TOC analyzer (O-I-Analytical, Aurora
Model 1030) according to the wet-oxidation method outlined in Standard method 5310 D. The
calibration curves for the DOC analysis were prepared using a 1000 mg/L KHP (potassium
hydrogen phthalate) stock solution. See Appendix 10.2.1. Five standard solutions were prepared
with concentrations ranging from 0.625 – 10 mg/L, and check standards were prepared at 5 mg/L
28
to be analyzed once for every ten samples. Where they were not prepared on the same day of
analysis, the calibration and check standards were also acidified to pH <2 with sulphuric acid.
3.2.2 UV Fluence Rate
The UV irradiance associated with the UVA lamp used in NOM degradation experiments was
determined with the a USB4000 radiometer (Ocean Optics Inc.). The fluence rate was calculated
for wavelengths 330 – 400 nm, a range in which the lamps spectral peak occurs (see Figure 9 (b)).
The calculations were carried out according to the procedure outline by Bolton and Linden (2003)
and with the assistance of Bolton® Excel Spreadsheet for fluence calculations of a medium-
pressure lamp with a shallow suspension depth, less than 2 cm (Bolton 2002). The fluence rate at
a height equal to that of the membrane surface when the membrane reactor is setup was corrected
for a divergence factor and a petri factor, but not a sensor factor. The divergence factor corrects
for the divergence of light beam, and the petri factor corrects for the irradiation variance over the
liquid sample surface area. These factors were calculated to be 0.95 and 0.74, respectively. The
sensor factor corrects for the variation of the detector sensitivity over a wavelength band of 200 –
300 nm, which falls out of the above-mentioned wavelength range of the UVA lamp used here,
and so it was not included in the fluence rate calculations. The distance from the lamp source to
the water surface was 18.5 cm and the solution volume above the membrane surface was
approximately 10 mL. The absorbance coefficients of raw water (i.e. Otonabee River water) for
wavelengths of 330 – 400 nm were determined with the UV-Vis spectrophotometer, and then
averaged over 5 nm wavelength increments.
29
3.3 Experimental Protocols
This section gives an overview of the protocols followed in carrying out the experiments in this
research. The bulk of the physical characterization of uncoated and TiO2-coated membranes was
completed with a scanning electron microscope, SEM; the method followed is summarized in
Subsection 3.3.1. Preliminary experiments were conducted to characterize the reactivity of TiO2-
coated quartz membranes and to evaluate the operational conditions of the flow-through membrane
reactor. To that end, methylene blue, MB, degradation experiments were first carried out in batch
mode (Subsection 3.3.2) to determine whether the membranes could degrade MB and the
approximate extent of that degradation. Further experiments were conducted in the flow-through
membrane reactor. In order to optimize the reactor’s operation, a number of down-flow setup
conditions, the methods of which are outlined in Subsection 3.3.3, were tested before settling on
the up-flow configuration as the most reliable setup, Subsection 3.3.4.
3.3.1 Physical Membrane Characterization
The microscopic structure of three membranes was characterized under a scanning electron
microscope (SEM, JEOL JSM-6610LV). These membranes were a fresh (unused) uncoated quartz,
a fresh TiO2-coated membrane, and a used membrane. The used membrane was employed in seven
experiments evaluating NOM degradation (Membrane ID: 0611-07; refer to Table xx in Section
3.3.5). All samples – pieces of about 1 cm2 – were analyzed under low-vacuum using Backscatter
Electron Scan (BES) mode, at first. Different sample pieces of these three membranes were then
gold-coated and analyzed again under the SEM; this time, under high-vacuum and Secondary
Electron Image (SEI) mode.
The profile of samples of the fresh uncoated quartz and the TiO2-coated membrane were also
characterized under the SEM. This was done by embedding the samples in an epoxy mount.
Characterizing the profile of a used membrane (i.e. Membrane 0611-07) was not possible with this
method due to the presence of organic molecules. The mounting process was performed by a
specialist technician at room temperature and inside a desiccator chamber under primary vacuum.
The sample pieces were inserted into a metallic coil spring, and the assembly was then inserted
into a plastic mould. A mix of clear epoxy resin and hardener named Epothin (Beuhler) was poured
into the mould and cured for 24 hours (Kretschmann, 2016). After the curing period, the resin had
polymerized with the samples and spring embedded within it, see Figure 10. The resultant mount
30
was then ground on an abrasive cloth material, with a focus on the intended plane of examination,
to smooth out its surfaces. After grinding, the mount was polished on a hard cloth with a small
amount of, first, a 9 µm diamond suspension and, second, a 1 µm diamond suspension
(Kretschmann, 2016). A final polishing step was performed on another hard cloth and with a small
amount of aluminum oxide dissolved in water. The polishing process further smooths out the
intended plane of examination. The mount was then cleaned with hexane, gently wiped, and dried
with air. Finally, the mount was gold-coated and inserted into the SEM machine for analysis. More
detailed description of the mounting process can be found on the Australian Microscopy and
Microanalysis Research Facility website (AMMRF, 2014).
Additional characterization of the membranes including Raman Spectroscopy and diffracted ray
spectroscopy was conducted by project collaborators at the University of Waterloo (Liang et al.,
2014 and Arlos et al., 2016). The results were supplied to this research for further understand of
the materials used.
Figure 10: Epoxy mount containing a sample of a fresh uncoated quartz and a fresh TiO2-
coated membrane
31
3.3.2 Batch TiO2 Photocatalysis
As preliminary testing of the TiO2-coated membranes, MB degradation experiments were first
carried out in batch mode and with simulated solar irradiation. An MB solution of 5 mg/L
concentration made from methylene blue hydrate (97% purity from Fluka Analytical) was
prepared for these experiments as per Sokolowski’s (2014) preliminary experiments. A TiO2-
coated membrane was secured in a membrane holder and then placed into a 250 mL beaker
containing 200 mL of the MB solution. Before the placement of the membrane with its holder, a
small magnetic stirrer was dropped into the beaker to allow for continuous stirring while the
sample was being irradiated. The beaker with its contents was then placed on top of a Thermix®
stirrer and inside the solar simulator chamber. The sample solution was irradiated for time periods
of 5, 10, 15, 30, 60, 90, and 120 minutes. After each irradiation session, an aliquot of the sample
was analyzed in the UV-Vis spectrophotometer at a wavelength of 665 nm.
The above experiments were repeated using uncoated quartz membranes instead of TiO2-coated
ones for comparison purposes, and again repeated with TiO2 particle (P25, Sigma-Aldrich)
suspension at a concentration of 0.1 g/L for comparison purposes. Furthermore, some of the used
uncoated and TiO2 were employed repeatedly in MB degradation experiments in order to evaluate
the reusability of the membranes and the reproducibility of the removal data. The results of these
repeated experiments are reported in Section 5.4: Reusability Tests.
3.3.3 Down-flow TiO2 Photocatalysis
Down-flow experiments utilized the flow-through membrane reactor to produce a system with
continuous flow through which water is treated with TiO2 photocatalysis. The system was first set
up with one peristaltic pump (Masterflex®) pushing the working MB solution of 0.5 mg/L
concentration into the reactor as in Figure 11. The pump was connected to the reactor’s inlet by
152 cm tubing (Masterflex® Norprene®, size 13) and a 17 cm length of clear plastic tubing (inner
diameter: 0.5 cm) and to the reactor’s outlet by a 60 cm tubing (Masterflex® Norprene®, size 13).
A CoorsTek membrane support of ultrafine porosity (0.9 – 1.4 μm, Ace Glass Inc.), onto which a
new TiO2-coated quartz membrane was placed, was used for these experiments. The reactor was
then placed into the solar simulator chamber. The speed at which the water was transferred through
the reactor was controlled by the pump rotation speed, and the speeds employed corresponded to
retention times of about 3-30 minutes. Once a pump speed was set, water was allowed to flow
32
through the reactor sufficiently to ascertain the absence of any air bubbles and the observation of
a consistent speed. Then, 20 mL samples were collected following a range of target retention times
(Table 15 in Appendix 10.3.1). Aliquots from the samples were analyzed for MB concentration in
the UV-Vis spectrophotometer (Agilent Technologies) at 665 nm.
Figure 11: Schematic of down-flow experimental setup with one pump. Note: the diagram is
not scale.
The above configuration was later adjusted by adding another pump in order to obtain a constant
water level above the membrane while retaining a wide range of retention times (up to 30 minutes).
See Figure 12. To that end, one peristaltic pump (Masterflex®) was connected to the reactor’s inlet
to transfer the test solution from a 500 mL Erlenmeyer flask into the reactor, and another such
pump was connected to the reactor’s outlet to pull the solution out. Both connections were made
with the same tubing described in the previous setup. A CoorsTek ultrafine (0.9 – 1.4 um porosity,
Ace Glass Inc.) fritted glass disc supported a TiO2–coated quartz or an uncoated quartz membrane.
The feed container was a 500 mL Erlenmeyer flask holding 0.5 mg/L MB working solution.
Samples were collected in a 25 mL volumetric flask until the 25 mL mark was reached, and the
33
duration of sampling was timed and recorded. After each change in the pump’s rotational speed
setting, MB solution was allowed to run through for, at least, the duration of the retention time
associated with the new speed before sampling. The samples were then analyzed using a UV-Vis
spectrophotometer and their concentrations were calculated. For this configuration, the inlet and
outlet pump speeds were initially set to equal each other, but this setting soon proved to fail at
keeping a constant water level above the membrane. Therefore, due to the inability to reproduce
the operating conditions, the configuration was further altered from down-flow mode to up-flow
mode, as described in the next subsection.
Figure 12: Schematic of down-flow experimental setup with two pumps. Note: the diagram
is not to scale.
3.3.4 Up-flow TiO2 Photocatalysis
The up-flow configuration was tested for its ability to control the outflow more reliably and
consistently than down-flow configuration. Two possible concerns that were associated with this
setup: 1) the fragile membranes may not withstand the pressure applied from the bottom and may
tear quickly, and 2) the upward water movement may loosen the TiO2 particles adhered to the
membrane, thereby deeming the membranes ineffective. Experiments were conducted to test
34
whether the membranes remained intact and, if they did, to assess their ability to remove MB from
solution.
To achieve an up-flow configuration, a peristaltic pump was used to pump solution from the feed
container (a 500 mL beaker) through a 152 cm long tubing (Masterflex® Norprene®, size 13) and
a 15 cm clear plastic polyethylene tubing (inner diameter: 0.5 cm) to the reactor’s inlet located in
the reactor’s bottom part (Figure 13). The solution accumulated up through the chamber while
being irradiated with UVA light from above using a medium pressure Blak-Ray® spot lamp (UVP,
Model B 100AP) until it reached the outlet orifice located on the upper part of the reactor. The
volume of the water accumulated inside the reactor before reaching the outlet tubing was calculated
to be 30.5 mL. The outlet is connected to another shorter piece of tubing (60.5 cm) through which
the treated water exited the system to either a waste container or a graduated cylinder when samples
were collected. This system allowed for a constant liquid level inside the reactor and for higher
experimental reproducibility.
Figure 13: Schematic of up-flow experimental setup utilizing a UVA lamp. Note: the
diagram is not to scale
35
To better characterize the operating conditions of this setup, the flow rates associated with the
pump’s speeds of 10 – 300 rpm were verified, and the retention times were then calculated using
the flow rate and reactor volume measurements. To evaluate the performance of TiO2-coated
quartz membranes in this mode, MB degradation experiments were conducted using various MB
solution concentrations. An MB solution concentration of 0.5 mg/L was first tested for MB
removal in five replicate experiments. In comparison with MB concentrations utilized in previous
experiments, this lower concentration allowed more light to pass the solution and reach the TiO2-
coated membrane, thereby activating more sites on the membrane that drive the photocatalytic
reactions. MB solution concentrations of 0.2 mg/L and 0.1 mg/L were also investigated to better
evaluate the degradation pattern of MB. For the first two 0.5 mg/L MB degradation experiments,
an ultrafine CoorsTek membrane support (0.9 – 1.4 µm porosity, Ace Glass Inc.) was used. This
support was replaced with a more porous CoorsTek membrane support (4 – 8 µm porosity, Ace
Glass Inc.) for the remaining experiments. The change was prompted by the expected
heterogeneity of water sources to be used in later experiments. The more porous support can filter
out the large water components while allowing smaller particles to pass through and be adsorbed
onto the membrane and/or degraded photocatalytically.
The MB degradation tests employed a new TiO2-coated quartz membrane for every experiment.
After placing the membrane on the support and assembling the reactor, the peristaltic pump was
set to push the MB solution into the reactor at pump rotational speeds ranging from 15 – 300 rpm,
which corresponded to retention times ranging from approximately 50 – 2 minutes, respectively.
Refer to Table 17 in Appendix 10.3.2. The Blak-Ray® UVA lamp was turned on at the beginning
of an experiment and warmed up for at least 10 minutes. After the solutions were allowed to run
through the system for at least twice the retention time corresponding to the set pump speed, 25
mL samples were collected in a graduated cylinder. Sample aliquots of 12 – 15 mL were
transferred to a 5 cm quartz glass cuvette for analysis in the UV-Vis spectrophotometer (Agilent
Technologies). Once an experiment was concluded, the reactor was dissembled and the used
membranes were air-dried by placing them on an elevated metallic mesh that allowed air to reach
both sides of the membrane. Air-drying overnight was accidently found to be effective in cleaning
the used membranes to a significant extent. This method is discussed in more detail in Section 5.4.
36
3.3.5 NOM Degradation Experiments – Model and Natural River Water
The ability of the TiO2-coated membranes to adsorb or degrade organic matter was further
evaluated by conducting NOM degradation experiments. Natural river water, namely Otonabee
River water, and model river water were utilized as the water sources for these experiments.
Otonabee River water, ORW, (Peterborough Water Treatment Plant – unchlorinated influent) is
characterized by its high organic content in addition to inorganic and particulate constituents.
Model river water, MRW, was prepared with Suwannee River NOM (IHSS); it consists
predominately of NOM, thereby minimizing the effects of other constituents’ effects on NOM
degradation. Consequently, experiments utilizing MRW were expected to lend knowledge
regarding the degradation of NOM almost exclusively
The experimental setup was in up-flow mode as described in the previous section (Subsection 3.3.4
and Figure 13). A peristaltic pump conveyed water from a feed tank into the membrane reactor in
up-flow mode, where it was irradiated with a UVA spot lamp (Blak-Ray®, UVP B 100AP) for
approximately 2 – 20 minutes. Samples of 40 mL were collected at the outlet in a 50 mL graduated
cylinder and then vacuum-filtered through 0.45 µm membrane filters (Supor®-450, PALL Life
Sciences). The samples were analyzed for UV-254 on the same day, acidified, and then analyzed
in the TOC Analyzer (O-I Analytical) for DOC measurements. Where it was not feasible to
perform the DOC analysis on the same day, the samples were stored at 4 °C for a maximum of
two weeks before analysis.
The NOM degradation experiments were performed under photocatalytic and dark conditions. For
photocatalysis tests, TiO2-coated quartz membranes were employed and the water was exposed to
UVA irradiation. For adsorption tests, TiO2-coated quartz membranes were utilized without any
exposure to light. A third type of testing – a photolysis test – was performed for experiments using
MRW to understand the degradation of NOM more comprehensively. The photolysis test
employed an uncoated quartz membrane with exposure to UVA irradiation. Note the TiO2-coated
quartz membranes used respective tests were not always replaced with a new one in every
experimental run. Table 3 gives a tabular summary of the NOM degradation experiments
performed with information about the membranes used in individual experiments. Labels for
identifying individual membranes were created with the date of their first use and the number of
any subsequent uses. The first four digits of the Membrane ID indicates the date on which the
37
membrane was first used, and the last two digits after the hyphen indicate the number of uses of
the membrane. For example, Membrane ID 0616-02 was first used on June 16th, and it was its
second when Photolysis Experiment B was conducted.
Table 3: Summary of NOM degradation experiments
Water
Source Test Type
Experiment
ID
Membrane
Type
Light
Type
Membrane
ID
NOM
Degradation
Tests
MRW
Photolysis Experiment A Quartz UVA 0616-01
Experiment B Quartz UVA 0616-02
Adsorption Experiment A TiO2-coated None 0611-02
Experiment B TiO2-coated None 0611-03
Photocatalysis Experiment A TiO2-coated UVA 0609-02
Experiment B TiO2-coated UVA 0609-04
ORW
Adsorption Experiment A TiO2-coated None 0611-04
Experiment B TiO2-coated None 0611-05
Photocatalysis Experiment A TiO2-coated UVA 0611-06
Experiment B TiO2-coated UVA 0611-07
3.4 Quality Assurance & Quality Control Measures
Batch experiments evaluating MB degradation by TiO2-coated quartz membranes were performed
using uncoated quartz membranes, which can be considered as a blank. Batch MB degradation
experiments were also performed using P25 TiO2 nanoparticles as it is considered a standard for
TiO2 nanomaterials.
MB degradation experiments in down-flow were conducted in duplications whenever feasible. Up-
flow MB degradation experiments were performed in duplicates for experiments using 0.1 – 0.2
mg/L MB solution and in multiple replicates for experiment employing 0.5 mg/L MB solution.
38
NOM degradation experiments involved performing blank tests using uncoated quartz membranes
and control tests using TiO2-coated quartz membranes under dark conditions. All NOM
degradation experiments were performed in duplicates. All DOC analysis and the UV-254
measurements for experiments using ORW involved duplicate analytical results. Check standards
of 3 mg/L were analyzed for UV-254 and DOC at a ratio no less of one check standard to every
ten samples.
Quality control practices were also performed in operating the experiment setups. This included
running raw MB solution or water through the flow-through reactor system for a time no less than
twice the retention time corresponding to the set pump speed before commencing sampling. For
both MB degradation and NOM degradation experiments, the actual retention time for each sample
was measured and compared with the corresponding expected retention time. In addition, light
source were warmed up before starting experimentation: the solar simulator was warmed up for at
least 30 minutes and the UVA lamp was warmed up for at least 10 minutes.
3.5 Chapter 3 Summary
In this chapter, the methods and materials utilized in this research were outlined. Methylene blue,
MB, degradation experiments were first conducted in batch mode where the employed membranes,
uncoated and TiO2-coated quartz, were stationary at a fixed height in solution while irradiated by
simulated solar light. MB degradation experiments were also conducted in flow-through mode in
the membrane reactor to optimize operational parameters. Down-flow configurations with one and
two pumps were tested but found unreliable. Up-flow configuration with one inlet pump was
evaluated with MB degradation experiments, and this mode was found to yield reproducible
results. Accordingly, the degradation of natural organic matter, NOM, was evaluated in up-flow
mode.
39
Chapter 4 Physical Membrane Characterization
In this section, the results of analyzing two types of membranes under a scanning electron
microscope, SEM, is discussed. The analysis was done on a fresh quartz (Subsection 4.1.1) and
fresh TiO2-coated (Subsection 4.1.2). In Subsection 4.1.3 the SEM analysis of the profiles of a
fresh quartz and a fresh TiO2-coated membrane are reported. Note that a third membrane was
analyzed under the SEM, and the results of this analysis are discussed in Section 6.3.2: Qualitative
Considerations. Section 4.2 discusses the properties of the uncoated and TiO2-coated quartz
membranes using other characterization tools including Tauc plots and Raman Spectroscopy.
Some characteristics of the quartz membranes, such as the compositional material (quartz
microfibers) and general porosity (1 µm) were available from the manufacturer (VWR). One goal
of performing some in-house characterization was to confirm these characteristics in uncoated
quartz membranes and examine how they differ in fresh and used TiO2-coated membranes; refer
to Section 6.3.2. The results of these characterizations also revealed new information regarding
the composition and porosity of membranes, confirmed the deposition of TiO2 on the microfibers
of the coated membranes, and provided better understanding of possible ways the morphology of
these membranes affects experimental results.
4.1 SEM Analysis
Two unused membranes were analyzed using a scanning electron microscope, SEM, (JEOL JSM-
6610LV): a fresh plain quartz membrane and fresh TiO2-coated membrane. Samples of these
membranes were analyzed under low-vacuum using Backscatter Electron Scan (BES) mode first.
This mode allows for the analysis of samples with organic content, and it produces images that
may be used for identifying contrast between areas of different composition when the sample
surface is level. That is, contrast between areas may reflect difference in atomic mass: brighter
areas represent metals of higher atomic mass than metals represented by darker areas. Different
sub-samples pieces of these membranes were then gold-coated and analyzed again under the SEM.
This time, images were taken under high vacuum in Secondary Electron Image (SEI) mode. This
mode produces images of higher quality and resolution than BES, especially at high
40
magnifications. However, this mode is not suitable for analyzing organic samples or samples with
traces of organic matter, unless they are gold-coated.
The next two subsections discuss the characterization of a fresh quartz membrane and a fresh TiO2-
coated membrane. The images included are considered representative of the membrane; more
images can be found in Appendix 10.1.1.
4.1.1 SEM Characterization of Fresh Uncoated Quartz Membrane
The structure of a fresh uncoated quartz membrane is complex, as determined by the SEM under
multiple modes. The microfibers making up the membrane are of differing diameters. Figures 14-
16 show images of different areas of one fresh uncoated quartz membrane. Figure 14 shows that
the membrane microfiber diameter can ranging from 0.13 – 2.3 µm. These fibers are enmeshed
and entangled in a very random way: some are straightly laid in varying directions, while others
are looped or curved. Further, it can be observed from Figure 15(b) that this complexity continues
with the membrane’s depth, deeming the membrane surface a rough one. The changeable structure
and varying microfiber size make it very difficult to estimate the porosity of these membranes
from SEM images for two reasons. First, it cannot be conclusively said that all dark areas suggest
the total absence of material or the presence of a pore. Second, the dark areas are mostly irregular
in shape. Therefore, the path that the water takes through the membrane is a tortuous, indirect one
and not necessarily straight through (i.e. perpendicular to the image plane).
The chemical composition of the membrane was qualitatively determined while the SEM machine
was in BES mode. The microfibers are not only composed of silicon, but also of considerable
levels of sodium, magnesium, aluminum, and calcium as per Figure 15(c). It is worth noting that
this composition analysis is limited to providing qualitative, or at best semi-quantitative,
indications of prominent inorganic constituent.
A sample of the uncoated quartz membrane was gold coated and examined in SEI mode, Figure
16. Comparing these images to those taken in BES mode, the only observable difference is the
improved clarity of the images at higher resolution.
41
Figure 14: SEM images in SEI mode of plain quartz at 5, 000x magnification
Figure 15: SEM images in BES mode of a plain quartz membrane sample at (a) 2000x
magnification and (b) 10,000x magnification; (c) shows the qualitative inorganic
composition of the membrane at the location labelled “Spectrum 1”.
42
Figure 16: SEM images in SEI mode of a gold-coated plain quartz membrane sample at (a)
2000x magnification and (b) 5000x magnification
4.1.2 SEM Characterization of a Fresh TiO2-coated Membrane
SEM images of a fresh TiO2-coated membrane were taken in BES mode and in SEI mode after
gold coating. The BES images (Figure 17(a) and (b)) reveal particulate deposits of TiO2 onto the
microfiber mesh. They are mainly identified by irregularities on individual microfiber surfaces.,
but the bright areas are also suggestive of TiO2 particles and agglomerates: titanium is heavier than
silicon and so appears brighter in BES mode (Murty et al., 2013 and JOEL, 2015). However, some
of the bright areas also may simply be due to the unevenness of the membrane surface.
Nonetheless, the qualitative composition results in Figures 17(c) and (d) clearly indicate three
titanium-containing peaks, which further confirmed the presence of titanium dioxide. The titanium
peaks associated with Spectrum 2 are all higher than the respective titanium peaks associated with
Spectrum 1. This difference in titanium concentrations is consistent with the location of Spectrum
2 being at brighter area than that of Spectrum 1.
43
Figure 17: SEM images in BES mode of a TiO2-coated membrane sample at (a) 2000x
magnification and (b) 10,000x magnification; and (c & d) the relative inorganic
composition of the membrane at the locations labelled “Spectrum 1” and “Spectrum 2”.
A gold coated sample of the same fresh TiO2-coated membrane was analyzed under high vacuum
in SEI mode, Figure 18. These images are much more well-defined than those taken in BES mode
and individual features can be more readily identified. Arlos et al. (2016) found the TiO2 coating
on their membranes to be in the form of TiO2 agglomerates. From the images in Figure 18, it can
be observed that the deposits of TiO2 onto the silicate microfibers are non-uniform and come in
different forms. Numerals (i) to (iv) in Figure 18 identify the following features of the sample:
(i) TiO2 particles may interact with each other to form irregularly shaped films in between
individual microfibers.
(ii) TiO2 deposits form plaques and/or agglomerates onto some microfiber in some areas.
(iii) TiO2 appears as individual particles attached to microfibers in some areas.
44
(iv) The dominant form of TiO2 deposit is in the form of a coating to individual microfibers,
thereby increasing their size.
The irregularity of the TiO2 coating adds to the complexity of the membrane morphology, thereby
making it very difficult to make conclusions that apply to all TiO2-coated membranes. Although
the images in Figures 17 and 18 belong to the same membrane, the difference in the amount and
form of TiO2 deposition is clearly considerable. Hence, it can be concluded that some sites on a
TiO2-coated membrane may be more active during photocatalysis than other sites on the same
membrane. Consequently, the variability in coating in different areas of a TiO2-coated membrane,
and from membrane to membrane, may cause variability in its reactivity, for example in the
degradation natural organic matter
Figure 18: SEM images in SEI mode of a gold-coated TiO2-coated membrane sample at (a)
2000x magnification and (b) 5000x magnification
45
4.1.3 SEM Characterization of Membrane Profiles
SEM images the profiles of a fresh quartz and a TiO2-coated membranes were obtained under high
vacuum and backscatter electron composition mode (BEC). This mode allows for qualitative
analysis of the membranes’ compositions, including line scans and element mapping.
Figure 19 shows two shots of each membrane at 1000 and 5000 magnifications. For ease of
analysis, the locations for these images were carefully chosen to include a cross-sectional area of
a microfiber that is perpendicular to the plane of view that has a large diameter. Note that not all
fibers are perpendicular to the plane of view; this is evident by the presence of elliptical and
irregularly shapes. This is also true for when a similar area on a TiO2-coated membrane sample
was examined, Figures 19(c) and (d). Theoretically, it was expected to observe a distinct ring
representing the TiO2 coating at the outer circumference of a microfiber. However, when
comparing the SEM images of the uncoated quartz and TiO2-coated membranes, no obvious
difference in the microfibers’ layering can be observed. However, a difference in the diameter can
be seen (as estimated from Figures 19(b) and (d)) to 13.8 µm and 14 µm for the uncoated and
coated membranes, respectively. Though this may indicate an increase in diameter due to added
layer of the TiO2 coating, it may also be due to the non-uniformity of microfiber size.
Since no direct observations can be made from the images in Figure 19 to differentiate the TiO2-
coated sample from the quartz, compositional analysis was conducted in the form of a “line scan”
and an “element map”. A line scan is a tool that produces a qualitative measure of the
concentrations of elements present across a sample area; in this case, the cross-section of a
microfiber. Figures 20(a) and (b) show the concentrations of titanium and silicon across a sample
microfiber, respectively. As can be observed, there are distinct peaks of titanium concentration at
the edges of the microfibers, while the concentration of silicon remains constant and much higher
than the concentration of titanium across the membrane. This suggests that most of the fiber is
made of silicon while titanium is only considerably present at the outer surface of the microfiber,
which is expected as titanium was only applied as a coating. Figure 20(c) compares the
concentrations of the main elements that make up the silicate-based microfiber quartz membrane;
these include sodium, calcium, potassium, and aluminum besides silicon. Note that titanium
concentration is almost always below the other elements’ concentrations; however, it’s the only
one with two distinct peaks.
46
Figure 19: SEM images in BEC mode for the profile of an uncoated quartz membrane at (a)
1000x magnification and (b) 5000x magnification, and of a TiO2-coated membrane at
(c)1000x magnification and (d) 5000x magnification.
47
Figure 20: Line scan analysis of TiO2-coated sample, Location 1; (a) Profile of Ti
concentration, (b) Profile of Ti and Si concentrations, and (c) concentration plots of silicon,
sodium, aluminum, potassium, calcium and titanium.
48
An element map produces a two-dimensional image of the sample showing the relative
concentration of a pre-set group of compositional elements. The concentrations shown are a
function of colour intensity on the map; the brighter pixels suggest higher concentrations. An
element map was produced for a location on the TiO2-coated membrane that displays a larger
sample size (more than one microfiber’s cross-section) than the location at which the line scan was
acquired. See Figure 21(a) and (b). Figure 21(c) and (d) show the map for the silicon and titanium
concentrations, respectively, which are of most interest to the current study. The titanium map
confirms that titanium is indeed present on all exposed microfiber surfaces; these include the
microfiber cross-sections in focus and those that are deeper into the plane and/or out of focus. The
silicon map reflects the location of only the cross-sections or interiors of the exposed microfibers,
confirming the microfibers’ silicon base.
Figure 21: Image of TiO2-coated sample at a different location with larger sample size at
(1) 1000x magnification and (b) 5000x magnification. An element map of (c) silicon and (d)
titanium
49
4.2 Additional Characterization
The band gap of the TiO2 immobilized on the quartz membrane has been determined by generating
a Tauc plot. A y-axis of a Tauc plot displays the measurements of (αhvn), while the x-axis measures
photon energy (hv). The symbol α represents the absorption coefficient, h represents Planck’s
constant, v is the light frequency, and n is equal to 2 for materials of direct transition and 0.5 for
material with indirect transition, such as TiO2. The absorption capacity, α, can be calculated by the
following formula:
𝛼 =(1 − 𝑅∞)
2
2𝑅∞
where 𝑅∞ is the reflectance of an infinitely thick sample with respect to a reference for each
wavelength (Liang et al, 2013). The Tauc plot can be used to find the band gap of a material by
determining the point of intercept of a tangent when drawn at the point of inflection (Liang et al,
2014). The band gaps for P25 and immobilized TiO2 on the coated membranes were determined
to be 3.1 eV and 3.2 eV, respectively, using Figure 22. These band gaps correspond with light
wavelengths of 400 – 410 nm (Arlos et al., 2016), which is mainly UV light (Luttrell et al., 2014).
The Raman spectra associated with uncoated quartz membranes and TiO2-coated membranes was
obtained. Raman spectroscopy measures the Raman shift of scattered photons, which can give
information about the crystalline structure of a material under examination (Kumar and Kumbhat,
2016). TiO2 is mainly found in phases of anatase, rutile, or a combination of these two. These
phases can be identified by characteristic Raman shift values. Those associated with anatase
include 144 cm-1, 399 cm-1, and 639 cm-1 (Ohsaka et al, 1978) The Raman plot in Figure 23
suggests that the uncoated quartz membranes have no crystalline structure, while the TiO2-coated
ones are mostly made of crystals in the anatase phase. Anatase has the advantage of a smaller
indirect band gap than its direct gap, unlike rutile, whose direct and indirect band gaps are the same
(Luttrell et al., 2014). The smaller indirect gap allows for a longer lifetime of charge carriers, e-
and h+, which in turn allows for a higher photocatalytic activity (Luttrell et al., 2014 and Arlos wet
al., 2016).
50
Figure 22: Tauc plot derived from UV-vis DRS spectra of P25 and TiO2-coated membrane.
Adapted from Arlos et al. (2016).
Figure 23: Raman Spectra of fresh uncoated and fresh TiO2-coated quartz membranes.
Adapted from Arlos et al. (2016).
51
4.3 Chapter 4 Summary
The physical characterization of uncoated and TiO2-coated quartz membranes was examined using
a scanning electron microscope, SEM, and investigated with DRS and Raman spectra. From the
SEM images, it was determined that uncoated quartz membranes are made of a complex mesh of
silicate-based microfibers with variable diameters. In addition, the uncoated quartz membrane
composition included traces of metals such as sodium, calcium and magnesium. The SEM images
of a TiO2-coated quartz membrane showed that TiO2 deposits of various forms, including distinct
TiO2 particles and TiO2 agglomerates, produce variable degrees of coating on the surface of one
membrane. Hence, some sites on a TiO2–coated membrane may be more active than others on the
same membrane. SEM images of the profiles of an uncoated and TiO2-coated quartz membranes
further confirmed the presence of TiO2 on the membrane microfibers’ surfaces. A Tauc plot of
P25 TiO2 particles and TiO2-coated quartz membranes demonstrations the band gaps of these
materials to be 3.1 and 3.2, respectively. Raman spectra for an uncoated and TiO2-coated quartz
membranes show that no crystalline phase is present in the uncoated membrane and anatase is the
dominant crystalline phase of the TiO2-coated membranes.
52
Chapter 5 Operational Evaluation and Membrane Reactivity
Characterization
The reactivity of TiO2-coated quartz membranes for degrading organic materials was evaluated
by conducting methylene blue, MB, degradation experiments. These experiments were first done
in batch mode, the simplest system configuration, whose results are discussed in Section 5.1. As
the flow-through reactor was incorporated in the system’s setup, MB degradation experiments
were conducted in down-flow mode (using one and then two pumps) and in up-flow mode. The
results of these experiment are discussed in Sections 5.2 and 5.3, respectively.
5.1 MB Degradation in Batch Mode
The degradation of MB using P25 TiO2 (Sigma-Aldrich) particle suspension, uncoated quartz
membranes and TiO2-coated quartz membranes was evaluated in batch mode. The results are
summarized in Figure 24. The degradation of MB increased with increasing time durations when
P25 TiO2 suspension was used. In contrast, the MB removal was generally constant when the
uncoated quartz and TiO2 quartz membranes were utilized with percent removals ranging from 60
– 74% and 80 – 90%, respectively. However, TiO2-coated quartz membranes were more effective
than the uncoated quartz membranes in removing MB. Furthermore, while the MB removal
efficiency of P25 was initially lower than the efficiencies of the uncoated and TiO2-coated quartz
membranes, it became the highest efficiency after 60 minutes of irradiation.
The results suggest a hierarchy in the capacity of the different materials employed in these
experiments for organic degradation: P25 was the top performer (after 60 minutes), then TiO2-
coated membranes, then uncoated quartz membranes. When comparing a TiO2 particle suspension
and a TiO2-coated membrane, the particle suspension provided larger TiO2 surface area and,
thereby, higher number of active sites for photocatalysis. Therefore, it was expected that a P25
suspension would be more effective at removing MB than a TiO2-coated membrane under the
same conditions. On the other hand, when comparing materials that incorporated TiO2 with those
that did not – for example, an uncoated quartz membrane – under simulated solar light, MB
removal could still occur due to adsorption and photolysis processes. Similar distinctions among
the performance of different TiO2–based materials have been reported in literature (Tayade et al.,
2015, Hu et al., 2013, Liang et al., 2014, and Arlos et al., 2016).
53
Figure 24: MB removal by P25, uncoated quartz membranes, and TiO2-coated quartz
membrane
Besides lending information about the performance of different materials utilized, the results of
these experiments show that all three treatment materials seem to roughly reach their maximum
capacity of MB removal after approximately 60 minutes. For this reason, an irradiation time of 60
minutes was selected to conduct reusability tests in batch mode, which will be discussed later in
Section 5.4. The most important conclusion that was drawn from these experiments, however, is
that the novel TiO2-coated membranes showed promise in removing organic matter from water.
5.2 MB Degradation in Down-flow Mode
MB degradation experiments were also conducted in down-flow mode with one and two peristaltic
pumps (Section 3.3.3) in order to evaluate the reliability of the systems. In these experiments, MB
solution of initial concentration of 5 mg/L was run through the system, and the solar simulator was
the source of irradiation. In addition, only TiO2-coated membranes were utilized for these
experiments. Aliquots of samples collected after 3 – 30 minutes of irradiation time were analyzed
with the UV-Vis spectrophotometer (Agilent Technologies) at a wavelength of 665 nm.
Figure 25 shows the MB removal results obtained in down-flow configuration with one pump.
Aside from normal experimental variability, the results show a general constant patters of removals
in the two runs conducted. Interestingly, the removal results of the first run are mostly negative,
0
20
40
60
80
100
0 5 30 60 90 120
Per
cen
t M
B R
emo
val (
%)
Irradiation Time (min)
P25 Uncoated Quartz TiO2-coated Quartz
54
which is counter-intuitive. At a glance, this implies that colour or some other light-absorbing
material was being added to the solution as time passes. However, it can be postulated that the
increase in colour or turbidity in the analyzed samples may be due to the dislodging of some TiO2
particles from the membrane surface into solution. The same TiO2 membrane was employed for
Run 2, the removal results of which were all positive. Hence, it can be suggested that after the first
use, most of the of the loose particles that were prone to dislodging from the membrane surface
had already been displaced such that the results of the second run were not affected.
Figure 25: Percent removal of MB with a TiO2-coated membrane
The removal of MB from solution in this configuration was not impressive, and the results were
not reliably reproduced. This was mainly due to the inability of said system to maintain a depth of
water or solution above the membrane in the reactor chamber. Thus, further experimentation was
deemed unnecessary and the configuration was altered to include a second pump.
Figure 26 shows the percent removal of MB using the second down-flow configuration that
incorporated two pumps; the flow rates and retention time measurements are appended in
Appendix 10.3.2. The removal is positive for all samples and ranges from 6% to 25%. Neglecting
the singularly high removal value of 25%, the remaining samples show comparable removal values
of around 5 – 10%. Hence, the removal pattern could be said to be constant, and the results
confirmed the ability of TiO2-coated membranes to remove MB from solution even if the removal
capacity was not major. Nonetheless, the most notable concern with this system configuration was
-30
-20
-10
0
10
20
30
40
50
0 5 10 15 20 25 30 35
% M
B R
emo
val
Retention Time in NMR (min)
Run 1 Run 2
55
the uncertainty of a constant water level in the reactor chamber, thereby making reproducing
similar MB removal results difficult. Accordingly, further testing with different system
configuration was warranted.
Figure 26: Percent removal of MB with a TiO2-coated membrane
5.3 MB Degradation in Up-flow Mode
Since it was established that the membrane reactor system in down-flow mode was not reliable,
other system configurations were considered, of which up-flow mode was the most notable. In up-
flow mode, a peristaltic pump (Cole-Parmer) pushed water through the reactor filling first the
bottom reactor part then the top until water reached the outlet port. See Section 3.3.4 for details on
the experimental setup. MB degradation experiments were conducted using this mode with a fresh
TiO2-coated membrane for each experiment and initial MB solution concentrations of 0.5 mg/L,
0.2 mg/L and 0.1 mg/L. To compensate for the low concentrations used in these experiments, a 5
cm cuvette was utilized for analyzing sample aliquots in the UV-Vis spectrophotometer. The
testing of different initial concentration was required in order to search for an optimal
concentration that would allow maximum light penetration while producing a reliable MB removal
pattern.
Figure 27 shows the MB percent removal results of five replicate experiments of initial MB
concentration of 0.5 mg/L. The retention times utilized in these experiments ranged from 2 – 50
0
5
10
15
20
25
30
0 5 10 15 20 25 30
% M
B R
emo
val
Retention Time (min)
56
minutes. Since the retention time range for individual experiments were not always the same,
smaller time spans were used to plot the average percent removal against the average retention
time in a particular time span. See Tables 18 – 20 in Appendix 10.3.2 for further details. The results
in Figure 27 show increasing MB removal values with increasing irradiation time with an average
removal of approximately 40 – 70 percent, which is substantially higher than the removal results
obtained in previous down-flow experiments. This may be largely due to the fact that the
concentration was reduced by ten times in these experiment while the light source was changed
from simulated solar light to UVA light of higher energy. Hence, the light penetration through
solution and to the membrane surface, where the reaction occurs, was compounded by these two
changes in operational conditions. Furthermore, the up-flow configuration resulted lower flow
rates for the same pump speed setting in down-flow configuration, which means the reaction time
was longer in up-flow mode than in down-flow mode configurations.
Figure 27:Results of MB degradation tests using solution of 0.5 mg/L initial concentration in
up-flow mode. Error bars reflect experimental variability.
0
10
20
30
40
50
60
70
80
90
100
0 5 10 15 20 25 30 35 40 45
% M
B R
emo
val
Retention Time
0306-01 0309-01 0328-01
0402-01 0404-01 Average
57
Figure 28 shows the percent removal of MB from solution when the initial concentration was
approximately 0.2 mg/L. The results show an slightly increasing patter of percent removal with
increasing irradiation time with the average removal ranges between 56 – 73%. These results are
very similar to the patterns observed in previous up-flow experiment with initial MB concentration
of 0.5 mg/L, but with smaller range of percent removal. In fact, since the experiment utilizing a
0.2 mg/L MB concentration was only duplicated, more replicates may prove the MB removal
pattern to be generally constant. In other words, although the pattern shown in Figure xx15 suggest
some increase over time, this may not be statistically accurate without more replicates.
Figure 28: Results of MB degradation tests using solution of 0.2 mg/L initial concentration
in up-flow mode. Error bars reflect experimental variability
Figure 29 shows the results of duplicate experiments conducted with initial MB concentration of
approximately 0.1 mg/L. The results present an overall constant pattern and very high removal
percentage (80 – 100%). Although promising, the near 100% removal values are unlikely to be
entirely due to the complete degradation of MB in solution. Instead, it is more probable the MB
concentrations were below the spectrophotometer’s detection limit. Further investigation of MB
degradation with initial concentration of 0.1 mg/L may provide a more solid conclusion; however,
for the purpose of this research, such initial concentration did not show promise of reproducing
reliable results.
0
20
40
60
80
100
0 5 10 15 20 25 30 35 40
% M
B R
emo
val
Retention Time (min)
58
Figure 29: Results of MB degradation tests using solution of 0.1 mg/L initial concentration
in up-flow mode. Error bars reflect experimental variability
5.4 Reusability Tests
One important characterization of the TiO2 membranes was establishing the extent of their
reusability. To that end, reusability tests, in the form of methylene blue, MB, degradation
experiment, on uncoated and TiO2-coated quartz membranes were conducted in batch and up-flow
modes. Preliminary batch reusability experiments revealed that the performance of TiO2
membranes was consistent after multiple uses; refer to Appendix 10.3.3.1. Accordingly, repeat
experiments were conducted in batch mode to prove this theory, and the results are discussed in
Subsection 5.4.1. TiO2-coated quartz membranes were also consecutively used in multiple
experiments to evaluate their reusability in up-flow mode; the results are discussed in Subsection
5.4.2.
5.4.1 Batch Mode
In order for the membranes to be reused, it was hypothesized that they needed to be cleaned. Hence,
preliminary reusability tests involving cleaning membranes by photobleaching were conducted. In
those experiments, a membrane – uncoated or TiO2-coated quartz – that had been used once in
batch mode was again inserted into a 250 mL beaker containing 200 mL of Milli-Q® water. The
batch reactor was then placed under simulated solar light to induce the bleaching of colour from
the membrane matrix. The results of these preliminary experiments showed that no significant
bleaching of colour occurs after eight hours of irradiation. Therefore, another option for cleaning
the membranes was sought – namely, air-drying. It was observed that exposing used membranes
0
20
40
60
80
100
0 5 10 15 20 25 30 35 40
% M
B R
emo
val
Retention Time (min)
59
to air contributed substantially to the reduction of the colour (MB) adsorbed onto the membrane.
Henceforth, the reusability experiments conducted in batch mode employed air-drying overnight
as a method of cleaning the membranes before their next use.
The procedure for the MB degradation experiments carried out for reusability tests in batch mode
is described in detail in Subsection 3.3.2 under Experimental Protocols. A used and air-dried
uncoated quartz or TiO2-coated quartz membrane was secured in membrane holders and placed
inside a beaker containing 200 mL of 5.0 mg/L MB solution. The “reactor” was then placed on a
stirring plate and into the solar simulator (Photo Emissions Tech. Inc.) to be irradiated for 60
minutes after one minute in the dark. The treated samples were then filtered through PES
membrane filters of 0.45 µm porosity, and an aliquot from each sample was transferred to a 1 cm
quartz glass cuvette for analysis in the UV-Vis spectrophotometer (Agilent Technologies).
Figure 30 shows the percent removal of MB after each use for an uncoated quartz membrane and
a TiO2-coated quartz membrane. Both membranes were evaluated for MB degradation in batch
mode six times. The removal results of the uncoated quartz membrane range from about 17 – 35%,
and those of the TiO2-coated quartz membrane range from about 35 – 55%. One obvious
observation is that percent removal results of the TiO2-coated membrane is always higher than that
of the uncoated quartz membrane. The difference between the two sets of results are consistent:
about 20% for the first three uses and about 10% for last three uses. In addition, both removal
patterns show more steadiness after the fourth use, which may indicate that the membranes reach
an equilibrium after four uses. Change in uncoated and TiO2-coated quartz membrane
performances occurring at the same time was previously observed in non-reusability MB
degradation experiments in batch mode as well; refer to Section 5.1. Therefore, it may be
postulated that, although the TiO2-coated membranes are superior to uncoated quartz membranes
in removing organic matter from solution, both types of membrane yield similar removal patterns.
This may be largely due to comparable adsorption and/or filtration capacities.
60
Figure 30: Average percent removal of MB using TiO2-coated and quartz membranes
Qualitatively, the colour adsorbed onto the uncoated and TiO2-coated quartz membranes darkened
after each use, refer to Appendix 10.3.3.1 for related images. Nonetheless, the shade of blue
observed on the uncoated quartz membrane was different than that observed on the TiO2-coated
quartz membrane. This was likely due to the difference in membrane composition caused by the
added layer of TiO2 coating. The two membranes also appeared differently after air-drying
overnight. Figure 31 shows the colour a new TiO2-coated quartz membrane and a used and air-
dried TiO2-coated quartz membrane and an uncoated quartz membrane. It can also be observed
from the figure that although air-drying overnight reduces the colour observed on the membranes
significantly, the membranes’ do not revert back to their original white colour. This means that
there were still some remnants of MB molecules attached to the membranes’ microfibers that could
not be removed by mere air-drying. Other researchers have applied annealing at 250 ºC (Hu et al.,
2013) and recalcination at 400 ºC (Arlos et al., 2016) as cleaning methods for similar membranes.
They have reported that the membranes maintained their ability to degrade organic compounds
when reused.
61
Figure 31: Effect of air-drying on membranes after being used six times and left to dry
overnight; (a) unused TiO2-coated quartz membrane, (b) used and dried TiO2-coated
membrane, and (c) used and dried uncoated quartz membrane
5.4.2 Up-flow Mode
Reusability MB degradation experiments were also conducted in up-flow mode, since it was the
most reliable configuration achieved in this research. Two TiO2-coated quartz membranes were
utilized consecutively at pump speeds corresponding to 5.3- and 3.1-minute retention times with
MB initial concentration of approximately 0.5 mg/L. The solution was illuminated with a UVA
spot lamp (UVP Blak-Ray®) and sample aliquots were analyzed in the UV-Vis spectrophotometer
(Agilent Technologies) at 665 nm using a 5 cm quartz cuvette. After each use, the membrane was
taken out of the reactor and placed on an elevated metallic mesh to air-dry overnight before the
next use.
Figure 32 shows the percent MB removal results after each use of one of the membranes utilized
in the up-flow reusability tests (Membrane ID: 0328-01). For both retention times, the removal
results fluctuate as the number of use increases, but their fluctuations are consistent with each
other. This suggests that the inconsistent pattern may be largely due to experimental variability
rather than true increase or decrease in removal values. The removal percentage results range from
nearly 45 – 65% for a retention time of 5.3 minutes and from nearly 30 – 70% for a retention time
of 3.1 minutes. These ranges are comparable with the range of MB removal results obtained from
the batch reusability tests, which suggests a promising potential for the reuse of TiO2-coated quartz
membrane.
62
Figure 32: Percent removal results of reusability test; (a) results obtained from membrane
0328-01 and (b) results obtained from memrane 0330-01
The qualitative consideration associated with the employed membranes are discussed in Appendix
10.3.3.2. In summary, and as related to the above-mentioned membrane, air-drying the membrane
bleached it from the adsorbed blue colour to a significant extent, but never fully. This was also
observed when air-drying membranes used in reusability tests in batch mode. However, the degree
of bleaching achieved for up-flow reusability test membranes was considerably less than the that
achieved when membranes used in down-flow experiments were air-dried. Therefore, it can be
concluded that membranes used in up-flow mode were more prone to staining than those used in
down-flow mode, suggesting at a increased adsorption or absorption capacity of these membranes.
In addition, the staining pattern on reusability membranes differ, which indicates that the hydraulic
dynamics related to solution flowing through a membrane is different from one membrane to
another.
To further characterize the reusability of the TiO2-coated quartz membrane, another reusability
test employing such membrane was conducted by consecutively utilizing the membrane in MB
degradation experiments without air-drying between uses, and then with air-drying between uses.
The results of this test are summarized in Figure 33. The removal pattern clearly decreased as the
number of uses increased, indicating that the membrane’s capacity to remove MB decreases with
added use. This reduction in performance was likely due to a decrease in adsorption capacity and
a reduction in the number of sites available for photocatalysis. On the other hand, as seen in the
63
results of the last two uses, when the membranes were air-dried overnight between uses, their
performance improved. In fact, the removal results of the last uses were comparable to the initial
removal values. This is true for results associated with both retention times.
Figure 33: Percent removal results of reusability test employing a TiO2-coated quartz
membrane consecutively without air-drying first, and then with air-drying between uses.
5.5 Chapter 5 Summary
The reactivity of the TiO2-coated quartz membranes was characterized by conducing MB
degradation experiments in multiple reactor configurations. The objective of these experiment was
to assess the capacity of uncoated quartz and TiO2-coated quartz to degrade MB from solution. In
all configurations, the TiO2-coated quartz membranes performed better than the uncoated quartz
membranes, which can be attributed to their photocatalytic capacity. The flow-through reactor
system was also evaluated in search of a reliable configurations that can yield reproducible results.
Down-flow mode with one and two pumps as well as up-flow mode were explored, and it was
found that up-flow mode was the most reliable. Furthermore, MB solutions with initial
concentration of 0.2 – 0.5 mg/L resulted in reproducible patterns of increasing MB percent removal
with increasing irradiation time. The average MB removal results ranged from 40 – 70%.
Reusability MB degradation tests were also carried out in batch and up-flow modes to assess the
extent of reusability of TiO2-coated membranes. It was found that the ability of these membranes
64
to degrade MB was relatively consistent when they were air-dried between uses. However, the
membranes’ performance was reduced with increasing number of use when they were not air-dried
between uses.
65
Chapter 6 NOM Degradation Test Results and Discussion
This section reviews the experimental results of photocatalytic degradation of natural organic
matter, NOM, using uncoated and TiO2-coated quartz membranes. The results of NOM
degradation in Otonabee River water, ORW, are presented and discussed in Subsection 6.1, while
those in model river water, MRW, which was prepared using Suwanee River NOM, are presented
and discussed in Subsection 6.2. The two sets of results are compared in Subsection 6.3 to examine
possible similarities in degradation patterns, and to determine whether TiO2 photocatalysis is more
efficient at degrading certain fractions of NOM.
The degradation of NOM in both model river water and Otonabee River water was evaluated using
the membrane reactor in up-flow mode. Model river water, MRW, was prepared using Suwannee
River NOM (International Humic Substances Society, St. Paul, MN, USA) according to the
procedure described in Section 3.1.4. Otonabee River water, ORW, was obtained from the
Peterborough Water Treatment Plant’s unchlorinated intake line. A suite of three test types was
performed for both water sources. NOM degradation control experiments were performed using
uncoated quartz membranes and UVA irradiation (referred to as “photolysis experiments”).
Experiments employing TiO2-coated membranes with no irradiation were also conducted to assess
the extent of NOM adsorption (referred to as “adsorption experiments”). TiO2 photocatalysis
experiments employed TiO2-coated membranes and UVA irradiation (referred to as
“photocatalysis experiments”). Each of these tests was duplicated. In each of these experiments,
samples were collected at flow rates corresponding to retention times of approximately 1.7, 3.1,
4.4, 6.9, 9.4, and 20 minutes. Shorter retention times were not feasible due to system’s pump
speeds and pressure (?) limitations, and longer retention times were not feasible due to time
constraints. The flow rate corresponding to 20 minutes in this configuration produced a flux
through the membrane similar to that the typical flux through conventional microfiltration
membranes (approximately 2275 L m-2 d-1). Refer to Section 3.3.5 for a more detailed experimental
procedure and Tables xx13? in Appendix 10.3.3 for detailed system hydraulic measurements.
Measured flow rates and possible effects on results are discussed in Appendix xx10.2.2.
The full suite of three tests (photolysis, adsorption, and photocatalysis) was completed for NOM
degradation in model river water. NOM degradation in Otonabee River water, the photolysis
66
experiments were excluded because no significant NOM degradation in MRW was observed under
photolytic conditions only. For all experiments, the UV absorbance at a wavelength of 254 nm,
UV-254, and the dissolved organic carbon, DOC, concentrations were measured. UV-254 is
indicative of the aromaticity of organic matter present in a sample, and it is often associated with
the level of humic substances. DOC is a measure of the total dissolved organic carbon
concentration of a sample, but it does not reflect the degradation of NOM into intermediate
products. Using these two measures, the data was normalized by calculating the specific UV
absorbance, SUVA, which is the ratio of UV-254 absorbance to DOC concentration. SUVA helps
identify patterns that suggest factors influencing photocatalytic membrane reactivity with NOM.
67
6.1 Model River Water
Three types of NOM degradation tests were performed using model river water, MRW: a
photolysis test, an adsorption test, and a photocatalysis test. The results of these tests are discussed
in this section. The experiments were conducted using the membrane reactor in up-flow mode with
the Blak-Ray® UVA lamp as the irradiation source. Furthermore, new membranes were utilized
for each of the three different tests as detailed in Section 3.3.5. The UV absorbance at a wavelength
of 254 nm, UV-254, results and the dissolved organic carbon, DOC, concentrations are
summarized in Subsections 6.1.1 and 6.1.2. In addition, the specific UV absorbance, SUVA, data
is summarized in Subsection 6.1.3. Individual experiment results are displayed rather than average
results to better acknowledge the variability between individual experiments. New membranes
were utilized for each of the three different tests.
6.1.1 MRW UV-254 Absorbance
Figure 34 summarizes the UV-254 absorbance results for all three types of experiments performed
with MRW. The majority of experimental results shows a generally constant pattern with little, if
any, decrease in absorbance after 20 minutes of irradiation. Photolysis Experiment A’s results
deviate substantially from the other experiments’ results in both intensity and fluctuation of
absorbance values over irradiation time, which suggests that the variability was not true but due to
special conditions including the fact that this experiment employed a fresh membrane. That is, the
loose particulates that may have been released to solution could have caused an increase in sample
turbidity when it was analyzed by the UV-Vis spectrophotometer. Accordingly, the increase in
absorbance values was likely due to the release of loose particulates from the membrane surface.
On the other hand, all other experiments’ results show constant absorbance patterns, the
reproducibility of which suggests reliability of the results.
Theoretically, TiO2 photocatalysis degrades NOM more effectively than solely photolysis or
adsorption because the effect of adsorption is compounded with the effect of the photocatalytic
production of hydroxyl radicals. However, the similarity in UV-254 patterns in all three test types
(photolysis, adsorption, and photocatalysis) suggests that the operational conditions of the system
did not have a significant effect on NOM degradation. One likely explanation is that the majority
of the NOM particles in the MRW was simply filtered and/or adsorbed onto the membranes and
not much passed through to the top surface of the membrane to be exposed to UV irradiation. in
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other words, not much of the NOM content underwent the process of photolysis or TiO2
photocatalysis. This can be further supported by the UV-254 results of the adsorption test
(approximately 0.041 – 0.043) being closely comparable to those of the photolysis (approximately
0.039 – 0.04 for Photolysis Experiment B) and photocatalysis tests (0.040 – 0.042).
Comparing the UV-254 results of experiments within one type of test, they were not always
consistent with each other. The experiments’ results of the photolysis test varied greatly from one
experiment to another. Where Experiment A’s absorbance values fluctuated with irradiation time
and ranged from approximately 0.04 to 0.047, those of Experiment B were steady and ranged from
approximately 0.039 to 0.04. The absorbance results of the adsorption test experiments were the
most consistent with each other with many points coinciding, indicating minimal experimental
variability. On the other hand, the absorbance results of the photocatalysis test experiments, though
stable within an individual experiment, do not match in values. That is mainly due to the difference
in initial absorbance, which corresponds to that of raw MRW. Nonetheless, from the data acquired,
it can be concluded that the degradation of aromatic NOM (i.e. humic acids) in MRW follows a
steady pattern of minimal deviation from the original content level when uncoated quartz or TiO2-
coated quartz membranes are employed with or without UV irradiation.
69
Figure 34: MRW NOM degradation UV-254 results (a) photolysis test, (b) adsorption test,
and (c) photocatalysis test. The y-intercepts represent the UV-254 absorbance of raw feed
water.
70
6.1.2 MRW DOC Concentrations
Figure 35 presents the DOC concentration results acquired from the photolysis, adsorption, and
photocatalysis tests performed with MRW. The DOC results show more fluctuations within
individual experiments’ data than their UV-254 counterparts. However, considering normal
variability within individual experiments, it can be said that the DOC results showed general
constancy over time. In addition, the DOC concentrations after 20 minutes of irradiation/retention
time were similar to those of raw MRW. Therefore, it can be concluded that NOM had not
undergone complete degradation to any significant degree under the three experimental conditions.
Interestingly, if the fourth data point (at about 4 minutes) were to be deemed an outlier, the
Photolysis Experiment A DOC results mostly conformed to the patterns created by the results of
the rest of the experiments, unlike its UV-254 results. Then, it can be said that both photolysis
experiments indicated almost no change in DOC concentrations even after 20 minutes of UV
treatment: the initial and final DOC concentrations was approximately 2.3 and 2.2 mg/L for
Experiment A and Experiment B, respectively. The adsorption experiments showed the most
consistency in the two experiments’ results suggesting better reproducibility than the two other
tests. The results of Photocatalysis Experiment A were very stable at approximately 2.2 mg/L over
irradiation time, if the second data point (approximately 2 minutes) was considered an anomaly.
In contrast, the results of Photocatalysis Experiment B fluctuate between about 2.15 – 2.25 mg/L,
but this can be attributed to normal variability of experimentation and the complex phenomena of
adsorption and desorption as the particles interact with the membrane. Arlos et al. (2016) also
observed similar fluctuation in the degradation pattern of norfluxoetine, a micro-contaminant,
when treated under similar conditions. Further testing may be required to be performed to elucidate
the NOM degradation patterns.
71
Figure 35: MRW NOM degradation DOC results (a) photolysis test, (b) adsorption test and
(c) photocatalysis test. The y-intercepts represent the DOC concentration of raw feed
water. Error bars represent the standard deviation associated with analytical variability
72
6.1.3 MRW SUVA Results
Figure 36 shows the SUVA data for the experiments performed with MRW. SUVA helps
elucidating NOM degradation trends based on the UV-254 and DOC data. In general, the SUVA
patterns of the three tests were consistent with the corresponding the UV-254 and DOC data in
that they were mainly constant in value with not much fluctuation. Most notably, the pattern of
SUVA results of Photolysis Experiment A is similar to its UV-254 pattern, which suggests that the
UV-254 values for this experiment were the main driver for the production of such SUVA pattern.
Accordingly, in here too, the dominant SUVA trends for the three tests can be said to be constant,
of value of about 0.018, if the SUVA results of Photolysis Experiment A were disregarded as
outliers, which was possibly due to the introduction of loose membrane particulates into solution.
Accordingly, the relative constancy of the level of degradation of NOM under the three types of
tests suggest that the effect of the different operational conditions was insignificant. However,
studies have shown significant different in organic degradation under photolysis, dark and
photocatalytic conditions. Therefore, it is more likely that the constancy of the experimental results
was due to effect of adsorption of NOM molecules onto the membranes followed by their
desorption into solution. This causes an overall constant level of NOM in solution since the
adsorption and desorption phenomena balance. This also means that the equilibrium is reached
quickly with these membranes. In the case of photocatalysis experiments, the photocatalytic
degradation of NOM appears to be insignificant. Further experimentation is needed to determine
the driving cause behind this; however, a possible explanation may that any photocatalytic
degradation of NOM was mostly incomplete.
In conclusion, no significant degradation of NOM was observed under any of the three operational
conditions evaluated. If any degradation occurred, it was likely incomplete without increasing the
level of aromatic fractions.
73
Figure 36: SUVA plots for MRW NOM degradation tests; (a) photolysis test, (b) adsorption
test, and (c) photocatalysis test. The y-intercepts represent the SUVA values of raw feed
water.
74
6.2 Otonabee River Water
Section 6.2.1 and 6.2.2 summarize the water’s UV-254 absorbance the DOC concentration results
for the adsorption and photocatalysis tests, respectively. Section 6.2.3 summarizes the
corresponding specific UV absorbance, SUVA, data of these tests. Individual experiment results
are presented rather than average results to better acknowledge the experimental variation
associated with experiments of the same type.
Two types of experiments were performed using Otonabee River water, ORW, as the natural water
source and a Blak-Ray® UVA spot lamp (UVP) for UVA irradiation. The experimental procedure
was the same as the experiments conducted with MRW and as detailed in Section 3.3.5. Only two
types of tests were conducted, an adsorption and a photocatalysis test, unlike the experiments
performed with MRW. The photolysis test was excluded due to the insignificant degradation of
NOM under only UV irradiation when compared with the photocatalysis and adsorption tests. The
minimal effect of only UV irradiation on the degradation of NOM has been established by many
studies including Goslan et al., (2005), Zhang et al. (2008), Valencia et al. (2013).
6.2.1 ORW UV-254 Absorbance
Figure 37 shows the UV-254 results for the two tests (adsorption and photocatalysis) performed
using ORW. The absorbance results are stable and consistent in all experimental results except
those of Adsorption Experiment A, where the UV-254 absorbance values fluctuate and are much
higher (approximately 0.125 – 0145) than Adsorption Experiment B (approximately 0.122). The
significant increase in absorbance can be attributed to the dislodging of loose membrane
particulates (likely TiO2 particles) and their migration into the bulk solution. Therefore, the
absorbance values of Adsorption Experiment A were likely influenced by the turbidity of the
sample due to suspended particulates, and, accordingly, they cannot be relied upon to reflect the
level of aromatic NOM in the samples.
The photocatalytic UV-254 results were consistently constant as the irradiation time increased. In
addition, the results of Photocatalysis Experiment A were always higher than those Photocatalysis
Experiment B. This difference in the results of the first and second experiment of the photocatalysis
test was also observed with MRW. The reason garnered from the fact that in both tests, the initial
75
UV-254 absorbance values were lower in the second experiments than in the first, a reduction that
was likely caused by a slight settlement of particulates in the feed solution as experiments were
run.
Figure 37: ORW NOM degradation UV-254 results (a) adsorption test and (b) photocatalysis
test. The y-intercepts represent the UV-254 absorbance of raw feed water. Error bars
represent the standard deviation associated with experimental variability.
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6.2.2 ORW DOC Concentrations
The DOC results of the adsorption and photocatalysis tests are summarized in Figure 38. The
relatively constant patter of adsorption and degradation of NOM remained constant throughout
irradiation. However, while the adsorption experiments’ results were closely comparable to each
other, some fluctuation was observed in the results of the photocatalytic experiments. Aside from
the normal variability in experimentation, the fluctuations can be attributed to the desorption of
adsorbed molecules from the membrane’s surface once equilibrium was reached. The DOC
concentrations in both the adsorption and photocatalysis tests were closely similar in magnitude
and trend, which suggests no obvious advantage of the photocatalytic conditions over the dark.
This implies that the main contributing factor to any change in NOM concentrations in the treated
waters was the adsorption of the molecules on the TiO2-coated membrane.
77
Figure 38: ORW NOM degradation DOC results: (a) adsorption test results and (b)
photocatalysis test results. The y-intercepts represent the DOC concentrations of raw feed
water. Error bars represent the standard deviation associated with experimental
variability
6.2.3 ORW SUVA Results
The SUVA data for the adsorption and photocatalysis results of experiment performed with ORW
further confirm the UV-254 and DOC pattern previously discussed, Figure 39. The degradation
pattern of NOM seemed generally constant with the results of Adsorption Experiment A being the
highest in value and most fluctuating. The large error further suggest that the pattern formed by
78
the results of this first experiment, which was mainly influenced by the higher UV-254 results,
were unreliable. On the other hand, the SUVA results of the photocatalytic experiments, although
generally steady, were lower in value in Experiment B than Experiment A. This hints at a possibly
higher degradation of NOM in Experiment B than that in Experiment A; however, further testing
is required to elucidate this theory.
Figure 39: SUVA plots for ORW NOM degradation tests; (a) adsorption test, and (b)
photocatalysis test. The y-intercepts represent the SUVA values of raw feed water. Error
bars represent the standard deviation associated with experimental variability
79
6.3 MRW vs ORW
In this section, the NOM degradation results of experiments performed with model river water,
MRW, and Otonabee River water, ORW, are compared quantitatively and qualitatively. The UV
absorbance at 254 nm, UV-254, and dissolved organic carbo, DOC, results of both sets of
experiment are discusses in Subsection 6.3.1. The qualitative features observed in those
experiments are discussed in Subsection 6.3.2.
6.3.1 UV-254 and DOC Results
The specific UV absorbance, SUVA, associated with the results of NOM degradation experiments
performed with MRW and ORW are summarized in Figure 40. In both sets of tests, the range of
the SUVA values are comparable between each category of experiments (i.e. adsorption and
photocatalysis). However, these values are about twice as high in experiments conducted using
ORW than experiments conducted using MRW. That is because the organic matter content of
ORW is higher than that of MRW. In addition, the dominant pattern observed was constant with
little fluctuation over time. The fluctuations observed can be attributed to normal experimental
variability and the complex process of adsorption and desorption of molecules onto and from a
membrane surface. The results of ORW Adsorption Experiment A clearly differed from the rest
of the results due the high SUVA values and more prominent fluctuations. These were mainly due
to unexpectedly high UV-254 absorbance results, see Figure 37, which may have been influenced
by the dislodgment of loose membrane particulates into solution.
The graphs also show that the SUVA values of the first experiment of each of the tests were often
higher than those of the second experiment. This can be attributed to a partial settlement of
particles in the feed container over the duration of an experiment. This means that the NOM
concentration in the water source of the second experiment of a test may have been lower than that
of the first experiment.
It was expected that degradation of NOM under photocatalytic conditions to be higher than under
dark conditions since both adsorption and photocatalysis processes occur under photocatalytic
conditions. However, this was not the case when the photocatalysis and adsorption test results are
compared. The SUVA values show that the photocatalysis results are either very close to or lower
80
than the adsorption results. This may suggest that the photocatalysis contribution to NOM
degradation was minimal while adsorption was the main treatment process.
Figure 40: Combined SUVA results of (a) adsorption tests and (b) photocatalysis tests.
Error bars indicate the standard deviation associated with experimental variability
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6.3.2 Qualitative Considerations
In addition to the quantitative results, it is worthy to note the qualitative conditions of the
membranes that have been used in these experiments. The experimental procedure for NOM
degradation tests using MRW and ORW was the same; however, no particulate residue was
observed after filtering raw MRW through a 0.45 µm filter membrane while it was observed when
filtering raw ORW, Figure 41(a). The visible particulate residue was not surprising as the natural
water source had a higher level of organic matter in its matrix than in MRW. On the other hand,
the residue was not visible when treated ORW samples were filtered, which was due to the fact
that most of the particulates were filtered first by the membrane support in the reactor and then by
the membrane itself. In fact, when the reactor was dissembled, the membrane support needed to
be rinsed more than once to remove the particulates adhered to its surfaces. Furthermore,
particulate residue is observed on the membrane itself, Figure 41(b). Note also that the membrane
had become more delicate and prone to tearing after multiple uses.
Figure 41: (a) Filtered suspended particles from a raw water sample and (b) the TiO2-
coated membrane (0611-07) after multiple uses showing particulate residue
It was interesting to see the particulate residue on the morphology of the membrane, so it was
examined under a scanning electron microscope, SEM. Figures 42 show BES images of two
locations on Membrane 0611-07, and summarizes the relative compositions at one point in each
location. While Figure 42(a) shows apparently clean microfibers with few indications of TiO2
deposits, Figure 42(b) clearly illustrates the considerable presence of foreign deposits on the
microfibers. The point at which Spectrum 2 was taken was likely a part of a living organism or a
82
microorganism. The BES process removes carbon-based materials that would be prevalent in
living organisms and so carbon was not detected in the compositional spectra at either location.
Nonetheless, the increased concentration of sodium and the appearance of magnesium, calcium
and aluminum peaks in Figure 42(d) may indicate biological presence.
Figure 42: SEM images in BES mode of a used TiO2-coated membrane – 0611-07 – sample
at (a) Location 1 at 2000x magnification and (b) its relative inorganic composition at the
location labelled as Spectrum 1; and at (c) Location 2 at 2000x magnification and (b) its
relative inorganic composition at the location labelled as Spectrum 2.
A sample of the same membrane was gold coated and examined in SEI mode, Figure 43. The
images of this location show the extent of particulate deposits onto the membrane more clearly.
However, the particulate residue was non-uniform: in some areas, it was thickly deposited such
that individual microfibers cannot be distinguished, while in other areas, the microfibers were
clearly visible and to a considerable depth, as evident in Figures 43(b) and (c). This change in the
morphology of the membrane likely posed added resistance to the flow of water through the
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membrane. Furthermore, the particulate residue did not only form a layer of foreign – likely,
organic – matter on the surface of the membrane, but it also interwove to some extent into the
microfiber mesh, as evident in Figure 43(d). The process of TiO2 photocatalysis could have been
affected in two contrasting ways by the formation of such layer. On one hand, the formed layer
could reduce the amount of UVA irradiation that reached the membrane surface, thereby deeming
some of the membrane’s sites photocatalytically inactive. On the other hand, the added layer could
enhance the adsorption and filtration capacity of the membrane, which may have caused higher
removal of NOM particulate from the samples. These two phenomena were likely to have
happened simultaneously such that the effect of one was more or less neutralized by the other;
however, additional testing is needed to reveal the extent of each effect.
Figure 43: SEM images in SEI mode of a gold-coated a used TiO2-coated membrane – 0611-
07 – sample at (a) 1000x, (b) 2000x, (c) 5000x, and (d) 10,000x magnification
84
6.4 Chapter 6 Summary
The degradation of natural organic matter, NOM, in model river water, MRW, was evaluated under
three operational conditions: 1) uncoated membrane under UVA irradiation – “photolysis test”, 2)
TiO2-coated membrane in the dark – “adsorption test”, and 3) TiO2-coated membrane under UVA
irradiation – “photocatalysis test”. The adsorption and photocatalysis tests were also conducted to
evaluate NOM degradation in natural river water obtained from the Otonabee River, ORW, in
Peterborough, ON. For all tests, the collected samples were analyzed for absorbance at 254 nm,
UV-254, and dissolved organic carbon, DOC, concentrations, and the specific UV absorbance,
SUVA, was calculated.
The results showed comparable degree of degradation under all three conditions with minimal
deviation from the raw analytical parameter, and this was true both MRW and ORW tests.
Nonetheless, the UV-254 and DOC results of experiments using ORW were about two times
higher than those using MRW, which was caused by the elevated NOM content in ORW relative
to MRW. The relative constancy of NOM degradation over time under different conditions suggest
that adsorption was the main process by which any removal occurred. Therefore, due to the
complexity of adsorption and desorption after reaching a steady-state equilibrium, fluctuations in
the results were generally neutralized over time. It was also observed that new membranes may
release loose particulates from their surfaces into solution, thereby overestimating the UV-254
absorbance results. As such, filtering raw water through 0.45 µm filter membrane may allow better
understanding of the photocatalytic degradation of NOM.
Examining a TiO2-coated membrane that was used multiple times with ORW under a scanning
electron microscope, SEM, revealed the presence of considerable amounts of particulate residue
on some areas of the membrane. This residue layer could have reduced the amount of light that
reached the membrane surface and/or increased the adsorption capacity of the membrane. Further
testing, including investigating the degradation of individual NOM fractions, are needed to
elucidate the results of this research and to investigate the performance of TiO2-coated quartz
membranes more deeply.
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Chapter 7 Conclusions
Although TiO2 photocatalysis is an advanced oxidation process that has shown great promise in
the field of drinking water treatment, its adsorption has been party limited by the need to separate
the TiO2 nanoparticles from the treated water. Immobilizing TiO2 particles onto a solid surface
would have the advantage of eliminating this post-treatment separation requirement and increasing
the ease of reuse. In this research, with the help of project collaborator from the University of
Waterloo, TiO2 particles were immobilized onto silicate-based quartz membranes following the
sol-gel method. The main objective was to characterize these membranes’ structure and reactivity.
The following points summarize the main findings of this study:
Preliminary tests evaluating the degradation of methylene blue, MB, were conducted in
batch mode and under simulated solar irradiation. The TiO2-coated membranes were able
to remove MB from solution with comparable efficiency (80-90%) to P25 TiO2 particle
suspension (90-100%) after 60 minutes of irradiation.
A bench-scale membrane reactor that was designed to house 50 mm membranes and allow
flow-through conditions was subsequently used to evaluate the TiO2-membranes. MB
degradation experiments were conducted using different configurations of the reactor to
arrive a reliable setup that can yield reproducible results, and this was determined to be the
up-flow mode.
The effect of initial MB solution concentration was explored. MB solutions with initial
concentrations of 0.2 – 0.5 mg/L yielded reproducible patterns of increasing MB percent
removal with increasing irradiation time. The average MB removal results of these
experiments ranged from 40 – 70%.
MB degradation tests were also carried out in batch and up-flow modes to assess the extent
of reusability of TiO2-coated membranes. The ability of these membranes to degrade MB
was relatively constant when they were air-dried between uses. However, the membranes’
performance was diminished with increasing number of uses when they were not air-dried,
or cleaned in any way, between uses.
After ascertaining the reliability of the membrane reactor system setup and the capability of TiO2-
coated membranes to degrade MB, which is an organic dye, experiments were conducted to
86
evaluate the degradation of natural organic matter, NOM, in this optimized system using both
model river water, MRW, prepared with Suwannee River NOM and natural river water from the
Otonabee River, ORW.
The results showed comparable degradation under all tested conditions with minimal
deviation from the initial DOC or UV-254 values. The relative consistency of the degree
of NOM degradation over time under different conditions suggests that adsorption was the
main process by which any removal occurred. Therefore, once an approximate steady-state
equilibrium was achieved, fluctuations in the results were generally neutralized over time.
The raw UV-254 and DOC measurements for experiments using ORW were about twice
as high as those using MRW, which was caused by the higher NOM content in ORW
relative to MRW.
The difference in organic/particulate content in the two water sources was also evident
qualitatively. The membranes used for NOM degradation experiments using ORW
displayed particulate residue on its surface after use, and when it was examined under the
SEM, areas of considerable amounts of particulate residue could be identified. This residue
layer could have affected the photocatalytic process by reducing the amount of light that
reached the membrane surface and increasing the adsorption capacity of the membrane due
to the cake layer effect. These simultaneous contrasting effects of the residue layer likely
contributed to minimizing the photocatalytic tests’ effects over time.
Additionally, it is worth noting that new membranes may release loose particulates from
their surfaces into solution causing an overestimation of the UV-254 absorbance results.
Hence, this needs to be considered carefully in future experiments to minimize or account
for the effect of dislodged particles.
87
Chapter 8 Recommendations
This research endeavoured to better understand the behaviour of these unique membranes as they
might be applied to drinking water treatment in a flow-through reactor, and while they showed
great promise in degrading methylene blue, MB, less significant degradation of natural organic
matter, NOM, was observed. However, the current experimental method might be improved as
follows to better understand the phenomena and the extent of NOM degradation by TiO2-coated
quartz membranes:
New uncoated or TiO2-coated quartz membranes could be washed with raw water in up-
flow mode a couple of times before collecting samples for analysis in order to minimize
the effect of the dislodgement of membrane surface particles into solution
Raw water could be filtered before undergoing treatment through the membrane reactor
in order to remove the bulk of large suspended particulates. This may maximize the time
before steady-state equilibrium is reached, thereby providing better insight regarding the
photocatalytic degradation of NOM
Analyzing the NOM fractions in raw and treated water samples can lend knowledge
regarding which fraction is most and least degraded by TiO2-coated quartz membranes
Further research recommendation to elucidate the potential of applying TiO2-coated quartz
membranes in water treatment and their effectiveness in degrading NOM from natural water
include investigations into:
Effect of influent water quality parameters (pH, alkalinity, turbidity)
Disinfection by-products formation potential
Use of doped TiO2-coated quartz membranes (Ag, I/N) to increase sensitivity to specific
wavelength of light
Effect and categorization of membrane fouling (reversible, non-reversible)
Once the potential and behaviour of these TiO2-membranes are more well-known, testing can be
moved from bench-scale to pilot-scale in order to successfully optimize the operating conditions
for full-scale applications.
88
Chapter 9 References
A Guide to Scanning Microscopy (2015). Joel Solutions for Innovation, Accessed August 9,
2016: http://www.jeolusa.com/RESOURCES/Electron-Optics/Documents-
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Alrousan, D.M.A., Dunlop, P.S.M., McMurray, T.A., and Byrne, J.A. (2009) Photocatalytic
inactivation of E. coli in surface water using immobilized nanoparticle TiO2 films, Water
Research, 43, pp. 47-54
American Public Health Association (APHA), American Water Works Association (AWWA),
Water Environment Federation (WEF), 2012. Standard Methods for the Examination of Water
and Wastewater, 22nd ed. Baltimore, Maryland, USA.
AMMRF: Australian Microspcoty and Microanalysis Research Facility. (2014) Scanning
Electron Microscope Training Module: Sample Preparation, Accessed Aug. 16, 2016:
http://www.ammrf.org.au/myscope/sem/practice/sample/#prettyPhoto
Arlos, M. J., Hatat-Fraile, M., Liang, R., Bragg, L. M., Zhou, N. Y., Andrews, S. A., and Servos,
M. R. (2016) Photocatalytic decomposition of organic micropollutants using immobilized TiO2
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93
Chapter 10 Appendices
10.1 Supplementary SEM Characterization
10.1.1 Additional Characterization of a Used TiO2-coated membrane in NOM Degradation Experiments
Figure 44: (left) Membrane 0611-07, and (right) SEM image of first piece of a TiO2-coated
membrane used in NOM degradation experiments at 600x magnification – BES mode
94
Figure 45: SEM image of first piece of a TiO2-coated membrane used in NOM degradation
experiments at 5 000x magnification – BES mode
Figure 46: SEM image of second piece of a TiO2-coated membrane used in NOM
degradation experiments at 2 000x magnification – BES mode
95
Figure 47: SEM image of second piece of a TiO2-coated membrane used in NOM
degradation experiments at 5 000x magnification – BES mode
Figure 48: SEM image of second piece of a TiO2-coated membrane used in NOM
degradation experiments at 20 000x magnification – BES mode
96
10.1.2 Characterization of a Used TiO2-coated membrane in MB Degradation Experiments
Figure 49: SEM image of a TiO2-coated membrane used in an MB degradation
experiments at 5 000x magnification – BES mode
Figure 50: SEM image of a TiO2-coated membrane used in an MB degradation
experiments at 5 000x magnification – BES mode
97
Figure 51: SEM image of a gold coated TiO2-coated membrane used in an MB degradation
experiments at 2 000x magnification – SEI mode
Figure 52: SEM image of a gold coated TiO2-coated membrane used in an MB degradation
experiments at 2 000x magnification – SEI mode
98
10.2 Experimental Data for NOM Degradation Experiments
10.2.1 Calibration Data
Figure 53: Calibration curve for UV-254 made from KHP absorbance
Figure 54: A typical DOC calibration curve produced by the TOC Analyzer
y = 0.022x + 0.006R² = 0.992
0.00
0.05
0.10
0.15
0.20
0.25
0 2 4 6 8 10
UV
Ab
sorb
ance
(@
25
4 n
m)
KHP Concentration (mg/L)
y = 4753x + 380R² = 0.9997
0
10000
20000
30000
40000
50000
60000
0 2 4 6 8 10 12
Are
a co
un
t
DOC Concentration (mg/L)
99
10.2.2 Measured Experimental Flow Rates
Figure 55: Measured and expected flow measurements for MRW NOM degradation
experiments
Figure 56: Measured and expected flow measurements for MRW NOM degradation
experiments
0
2
4
6
8
10
12
14
16
18
20
0 2 4 6 8 10 12 14 16 18 20
Act
ual
Flo
w R
ate
(m
L/m
in)
Expected Flow Rate (mL/min)
Photolysis A
Photolysis B
Dark B
Dark A
Photocatalysis A
Photocatalysis B
Photocatalysis C
Diagonal
0
2
4
6
8
10
12
14
16
18
20
0 5 10 15 20
Act
ual
Flo
w R
ate
(m
L/m
in)
Expected Flow Rate (mL/min)
Dark A
Dark B
Photocatalysis A
Photocatalysis B
Photocatalysis C
Diagonal
100
10.2.3 Data Tables for MRW Experiments
10.2.3.1 Photolysis Test Results
Table 4: MRW Photolysis test Exp A results
Sample Actual RT
(min)
Modified
DOC (mg/L)
DOC STDEV
(mg/L)
UV-254 SUVA
Average Raw 2.32 0.046 0.042 0.018
30 rpm 17.2 2.29 0.021 0.042 0.018
60 rpm 8.32 2.30 0.010 0.040 0.017
80 rpm 6.16 2.35 0.023 0.042 0.018
130 rpm 3.88 2.51 0.009 0.046 0.018
200 rpm 2.44 2.26 0.028 0.045 0.020
300 rpm 1.73 2.32 0.005 0.044 0.019
Table 5: MRW Photolysis Exp B results
Sample Actual RT
(min)
Modified
DOC (mg/L)
DOC STDEV
(mg/L)
UV-254 SUVA
Average Raw 2.211 0.077 0.039 0.018
30 rpm 19.48 2.23 0.048 0.039 0.017
60 rpm 9.15 2.22 0.026 0.039 0.017
80 rpm 6.91 2.26 0.039 0.039 0.017
130 rpm 4.24 2.27 0.012 0.039 0.017
200 rpm 2.69 2.34 0.049 0.040 0.017
300 rpm 1.84 2.31 0.059 0.040 0.017
10.2.3.2 Adsorption Test Results
Table 6: MRW Adsorption Exp Aresults
Sample Actual RT
(min)
Modified
DOC (mg/L)
DOC STDEV
(mg/L)
UV-254 SUVA
Average Raw 2.28 0.05541 0.0429 0.019
30 rpm 19.2 2.26 0.019 0.040 0.018
60 rpm 9.61 2.26 0.029 0.042 0.018
80 rpm 7.09 2.32 0.027 0.041 0.018
130 rpm 4.31 2.31 0.019 0.041 0.018
200 rpm 2.83 2.36 0.001 0.042 0.017
300 rpm 1.98 2.31 0.015 0.042 0.018
101
Table 7: MRW Adsorption Exp B results
Sample Actual RT
(min)
Modified
DOC (mg/L)
DOC STDEV
(mg/L)
UV-254 SUVA
Average Raw 2.38 0.053 0.042 0.018
30 rpm 19.43 2.21 0.006 0.041 0.018
60 rpm 9.50 0.042
80 rpm 7.03 2.34 0.047 0.041 0.018
130 rpm 4.23 2.33 0.018 0.041 0.018
200 rpm 2.86 2.37 0.052 0.041 0.017
300 rpm 1.92 2.29 0.060 0.041 0.018
10.2.3.3 Photocatalysis Test Results
Table 8: MRW Photocatalysis Exp A results
Sample Actual RT
(min)
Modified
DOC (mg/L)
DOC STDEV
(mg/L)
UV-254 SUVA
Average Raw 2.21 0.030 0.040 0.018
30 rpm 21.4 2.14 0.002 0.038 0.018
60 rpm 10.2 2.18 0.009 0.040 0.018
80 rpm 7.73 2.18 0.031 0.040 0.018
130 rpm 4.51 2.18 0.033 0.044 0.020
200 rpm 3.05 2.26 0.010 0.040 0.018
300 rpm 2.11 2.36 0.007 0.040 0.017
Table 9: MRW Photocatalysis Exp B results
Sample Actual RT
(min)
Modified
DOC (mg/L)
DOC STDEV
(mg/L)
UV-254 SUVA
Average Raw 2.27 1.21 0.042 0.018
30 rpm 20.1 2.20 1.27 0.041 0.019
60 rpm 9.38 2.13 1.23 0.041 0.019
80 rpm 6.93 2.26 1.31 0.041 0.018
130 rpm 4.36 2.19 1.26 0.041 0.019
200 rpm 3.11 2.26 1.30 0.041 0.018
300 rpm 1.69 2.18 1.26 0.042 0.019
102
10.2.4 Data Tables for ORW Experiments
10.2.4.1 Adsorption Test Results
Table 10: ORW Adsorption Exp A results
Sample Actual RT
(min)
Modified
DOC (mg/L)
DOC STDEV UV-254 UV-254 STDEV SUVA SUVA
STDEV
Average Raw 3.86 0.095 0.124 0.002 0.032 0.001
30 rpm 18.4 3.94 0.006 0.125 0.003 0.032 0.001
60 rpm 8.78 3.99 0.074 0.133 0.003 0.033 0.001
80 rpm 7.08 4.05 0.038 0.144 0.011 0.035 0.003
130 rpm 5.14 4.03 0.231 0.138 0.001 0.034 0.002
200 rpm 2.67 3.89 0.071 0.143 0.002 0.037 0.001
300 rpm 1.83 3.94 0.065 0.132 0.008 0.034 0.002
Table 11: ORW Adsorption Exp B results
Sample Actual RT
(min)
Modified
DOC (mg/L)
DOC STDEV UV-254 UV-254 STDEV SUVA SUVA
STDEV
Average Raw 4.2 0.013 0.124 0.001 0.001 0.000
60 rpm 10.2 4.12 0.113 0.122 0.001 0.030 0.001
80 rpm 7.45 4.01 0.169 0.123 0.001 0.031 0.001
130 rpm 4.48 3.92 0.051 0.122 0.003 0.031 0.001
200 rpm 3.74 4.05 0.006 0.123 0.001 0.030 0.000
300 rpm 2.05 4.07 0.055 0.121 0.001 0.030 0.000
10.2.4.2 Photocatalysis Test Results
Table 12: ORW Photocatalysis Exp A results
Sample Actual RT (min)
Modified DOC (mg/L)
DOC STDEV UV-254 UV-254 STDEV SUVA SUVA STDEV
Average Raw
4.05 0.119 0.128 0.002 0.032 0.001
30 rpm 19.2 4.01 0.054 0.135 0.003 0.033 0.001
60 rpm 9.2 3.92 0.086 0.127 0.009 0.032 0.001
80 rpm 6.8 3.91 0.016 0.125 0.001 0.032 0.000
130 rpm 4.2 3.93 0.092 0.130 0.001 0.033 0.001
200 rpm 2.8 4.02 0.027 0.127 0.002 0.032 0.000
300 rpm 1.9 4.09 0.063 0.128 0.002 0.031 0.001
103
Table 13: ORW Photocatalysis Exp B results
Sample Actual RT
(min)
Modified
DOC (mg/L)
DOC STDEV
(mg/L)
UV-254 UV-254 STDEV SUVA SUVA
STDEV
Average Raw 3.89 0.067 0.126 0.001 0.032 0.001
30 rpm 18.4 3.72 0.075 0.112 0.002 0.032 0.001
60 rpm 8.91 3.93 0.043 0.122 0.001 0.031 0.000
80 rpm 6.61 4.09 0.174 0.123 0.002 0.030 0.001
130 rpm 4.09 3.84 0.093 0.120 0.001 0.031 0.001
200 rpm 2.69 3.71 0.108 0.122 0.001 0.033 0.001
300 rpm 1.84 3.89 0.059 0.122 0.001 0.031 0.001
104
10.2.5 Usage Sequence of a TiO2-coated Membrane, 0611-07
Table 14: The sequence of use of Membrane 0611-07. The membrane remained in the reactor after the end of an experiment, unless
otherwise indicated.
# of
Use
Type of
Experiment
Water
Source
UV-254 Results DOC RESULTS
1st Prelim
Photocatalysis
Exp C
Model
River
Water
Samples taken from lowest to highest speed – not
in random order
Membrane was kept on a mesh to air-dry for three days then separately in a dry petri dish until next use (11 days)
0.036
0.037
0.038
0.039
0.040
0.041
0.042
0.043
0.044
0 5 10 15 20 25
Ab
sorb
ance
(@
25
4 n
m)
Irradiation Time (min)
1.80
1.90
2.00
2.10
2.20
2.30
0 5 10 15 20 25
DO
C (
mg/
L)
Irradiation Time (min)
105
2nd Adsorption
Exp A
Model
River
Water
From this experiment and on, samples were taken
randomly
3rd Adsorption
Exp B
Model
River
Water
Membrane was kept on a mesh to air-dry until next use (5 days)
The 4th use was for an aborted experiment.
0.038
0.040
0.042
0.044
0.046
0 10 20 30
UV
25
4 A
bso
rban
ce
Time (min)
2.10
2.20
2.30
2.40
2.50
2.60
0 5 10 15 20 25
DO
C (
mg/
L)
Time (min)
0.038
0.040
0.042
0.044
0.046
0 10 20 30
UV
25
4 A
bso
rban
ce
Time (min)
2.10
2.20
2.30
2.40
2.50
2.60
0 5 10 15 20 25
DO
C (
mg/
L)
Time (min)
106
5th Photocatalysis
Exp A
Otanabee
River
Water
Membrane was kept on a mesh to air-dry until next use (8 days)
6th Photocatalysis
Exp B
Otanabee
River
Water
0.11
0.12
0.13
0.14
0.15
0.16
0 5 10 15 20 25
UV
-25
4 A
bso
rban
ce
Irradiation Time (min)
3.5
3.7
3.9
4.1
4.3
4.5
0 5 10 15 20 25
DO
C C
on
c (m
g/L)
Irradiation Time (min)
0.11
0.12
0.13
0.14
0.15
0.16
0 5 10 15 20
UV
-25
4 A
bso
rban
ce
Irradiation Time (min)
3.5
3.7
3.9
4.1
4.3
4.5
0 5 10 15 20
DO
C C
on
c (m
g/L)
Irradiation Time (min)
107
7th Adsorption
Exp A
Otanabee
River
Water
8th Adsorption
Exp B
Otanabee
River
Water
0.11
0.12
0.13
0.14
0.15
0.16
0 5 10 15 20
UV
-25
4 A
bso
rban
ce
Time (min)
3.5
3.7
3.9
4.1
4.3
4.5
0 5 10 15 20
DO
C C
on
c (m
g/L)
Time (min)
0.11
0.12
0.13
0.14
0.15
0.16
0 10 20 30
UV
-25
4 A
bso
rban
ce
Time (min)
3.5
3.7
3.9
4.1
4.3
4.5
0 5 10 15
DO
C C
on
c (m
g/L)
Time (min)
108
10.2.6 QA/QC
Figure 57: QC chart for UV-254; check standards were of a theoretical concentration of 5
mg/L KHP
Figure 58: QC chart for DOC check standards were of a theoretical concentration of 5
mg/L KHP
-0.1
0
0.1
0.2
0.3
0.4
UV
-25
4 A
bso
rban
ce +1/-1 STDEV
-1/+1 stdev
Average
-2/+2 stdev
+2/-2 stdev
Data
3
4
5
6
7
8
9
10
DO
C C
on
cen
trat
ion
(mg/
L)
+1/-1 STDEV
-1/+1 stdev
Average
-2/+2 stdev
+2/-2 stdev
Data
109
10.3 Experimental Data for System Optimization Experiments
10.3.1 Down-flow Mode
Table 15: Flow rate and retention time measurements for one-pump system in down-flow
configuration. The bold flow rates were the ones employed during experimentation.
Pump Speed (rpm) Approximate Flow Rate
(mL/min)
Approximate Retention Time
(min)
100 7 3
90 6 3.5
80 5.1 4.1
70 4.5 4.7
60 3.9 5.4
50 3.4 6.2
40 2.7 7.8
30 1.95 11
20 1.35 16
10 0.68 31
Volume accumulated until water reaches outlet 21 mL
Table 16: Flowrate and retention time used for sampling – down-flow configuration with two
pumps
Outlet Pump
Speed (rpm)
Inlet Pump
Speed (rpm)
Flow rate
(mL/min)
Expected
Retention Time
(min)*
Actual Retention
Time (min)*
100 150 7 3.5 3.5
80 130 5.1 4.3 4.3
60 110 3.9 5.6 5.5
40 80 2.7 9.6 9
20 70 1.35 17.8 17
10 60 0.68 35.7 30.5
* Based on 25mL volume collected
110
10.3.2 Up-flow Mode
Table 17: Flow rate and correspong flux values obtained for 4-8 µm frit glass membrane
support
Pump speed (rpm) Flow rate (mL/min) Flux Theo RT (min) based on 30.5 ml
10 0.49 733 62.2
10
15 0.75 1123 40.7
20 1.00 1497 30.5
30 1.52 2275 20.1
40 2.2 3293 13.9
50 2.75 4116 11.1
55 3 4490 10.2
60 3.25 4864 9.38
70 3.75 5613 8.13
80 4.4 6586 6.93
90 4.8 7184 6.35
110 6 8980 5.08
130 7 10477 4.36
150 8 11974 3.81
180 9.1 13620 3.35
200 9.8 14668 3.11
220 13.9 20804 2.19
250 15.5 23199 1.97
260 16.9 25294 1.80
280 17.4 26043 1.75
300 18.1 27090 1.69
320 20 29934 1.53
350 22 32928 1.39
111
Table 18: Flow rate and retention time used for sampling – first two 0.5-mg/L initial
concentration experiments
Pump Speed
(rpm)
Flow rate
(mL/min)
Expected
Retention Time
(min)*
Actual Retention
Time (min)*
Actual Retention
Time (min)*
Duplicate 1 Duplicate 2
10 0.5 50 50.25 47.5
15 0.76 33 33.75 31
20 1.07 23 24.5 23
30 1.66 15 16.75 15
40 2.25 11 12 11
55 3.1 8 8.75 8.25
90 4.87 5 5.67 5
* Based on 25mL volume collected
Table 19: Percent difference values of expected and actual retention times for the four MB
degradation tests. Positive values indicate shorter retention times than expected and negative
values indicate longer retention times than expected.
Expected RT (min) 0328-01 0330-01 0402-01 0404-01
71 19 8
47 13 10
35 23 12 -16 4
23 19 8 -15 3
12 14 4 -12 2
6 15 0 -14 -11
4 23 16 -10 7
2 0 -13 -24 -14
Table 20: Summary of percent removals of each test and basic statistics for experiments
utilizing initial concentration of MB of 0.5 mg/L. The average reflects the mean of all removal
values in one row
RT
Span
(min)
Average
RT
(min)
MB % Removal
0306-01 0309-01 0328-01 0402-01 0404-01 Average STDEV
30-50 40.0 53.0 57.7 80.5 72.6 70.1 66.8 10.1
23 23.0 50.9 55.3 51.0 56.1 66.3 55.9 5.6
10-15 12.5 33.3 60.8 51.0 47.2 61.1 50.7 10.3
6-8 7.0 36.3 40.9 48.0 52.0 58.3 47.1 7.8
2-5 3.5 32.5 48.2 30.0 50.7 48.9 42.1 8.9
112
Table 21: Percent difference in actual retention times – MB degradation experiments with
initial concentration of 0.2 and 0.1 mg/L
Theoretical RT (min) % Difference in RT (%)
0418-01 0419-01 0420-01 0421-01
35 24.3 -24.1 -2.4 -5.0
23 23.6 -24.4 9.1 -9.3
11 21.1 -24.0 3.5 -8.7
8 17.4 -20.9 1.9 -7.6
5 18.2 -9.5 4.8 -2.3
2.5 0.7 -38.7 -18.2 -25.6
10.3.3 Reusability Supplemental Data
10.3.3.1 Batch mode
The idea behind the second theory is that the membrane would lose some of its capacity to help
degrade MB after first use, but its capacity would remain the same after each subsequent use. To
that effect, the membrane from the previous experiment was deemed essentially new after 7.5
hours of photobleaching and a night of drying.
The first reusability tests involved a TiO2-coated membrane used in batch mode and irradiated
using the solar simulator. An irradiation time of 60 minutes was used again. The membrane was
used five times over a duration of two days, see Figure XX. After each use, the membrane was
inserted into a fresh sample of MB and the treated sample was filtered and analyzed with a
spectrophotometer.
113
Figure 59: Pictures of first TiO2-coated membrane utilized in reusability testing in batch
mode (a) after first use, (b) after second use, (c) after third use, and (d) after air-drying
overnight
The percent removal of MB using the same membrane five consequent times is depicted in Figure
XX. The removal varies from 23.29% to 36.65%. The removals after multiple uses of the TiO2-
coated membrane are comparable. The data should be verified with replicates. If verified, this may
show potential of effective reusability with no necessary treatment between uses.
114
Figure 60: Percent removal of MB from solution after each of five uses of first TiO2-coated
membrane subjected to reusability testing
Further testing of reusability with uncoated and TiO2-coated quartz membranes was conducted as
discussed in Section 5.4. the figures below show the appearance of these membranes as they
were used multiple times.
27
23
30
37
30
0
5
10
15
20
25
30
35
40
1 2 3 4 5
% R
EMO
VA
L O
F M
B
NUMBER OF USE
115
Figure 61: Colour of TiO2-coated membrane after each use in the first test; a) after first use,
b) after second use, c) after third use, d) after fourth use, e) after fifth use, and f) after sixth
use.
Figure 62: Colour of plain quartz membrane after (a) third use and (b) after sixth use.
116
10.3.3.2 Up-flow mode
Figure 63: Photos of membrane 0328-01 throughout reusability tests in up-flow mode
Figure 64: MB removal results of reusability tests performed on a second TiO2-coated
membrane, 0330-xx
0
20
40
60
80
100
0 1 2 3 4 5 6 7 8
MB
% R
emo
val
Number of Use
RT = 5.3 min RT = 3.1 min
117
Figure 65: Photos of membrane 0330-xx throughout reusability testing in up-flow mode.