Thesis on Ion Exchange - Ken McClure
Transcript of Thesis on Ion Exchange - Ken McClure
THE EFFECTS OF ALKALINITY ON THE ABILITY OF ION-EXCHANGE
RESINS TO REMOVE NATURAL ORGANIC MATTER AND ORGANIC
CONTAMINANTS
by
Ken McClure
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF
BACHELOR OF APPLIED SCIENCE
in
THE FACULTY OF APPLIED SCIENCES
(Chemical and Biological Engineering)
THE UNIVERSITY OF BRITISH COLUMBIA
(Vancouver)
April 2011
ii
Abstract
Many drinking water treatment options exist for small communities, but are too costly
at a small scale. The advanced oxidation process (AOP) is one method to treat drinking water
and oxidize harmful organic contaminants; however, natural organic matter (NOM) needs to be
removed prior to AOP to increase the feasibility. Ion-exchange resins are effective and
relatively economic at removing NOM from drinking water; however, alkalinity is common in
groundwater supplies to be treated and its effects on resins are unclear.
Batch kinetic and Freundlich isotherm experiments were performed on synthetic
Suwannee River water at 7.5 mg/L and bicarbonate concentrations from 0 to 100 mg/L to
quantify the effects of alkalinity on the ability of SIR-22P-HP and MIEX® resins to remove NOM,
and to determine the removal of atrazine herbicide. Batch kinetics revealed that bicarbonate
was removed four times faster than NOM; moreover, despite the competition for removal, 6%
more NOM was removed with SIR-22P-HP after 6 hours at 50 mg/L bicarbonate compared to
without bicarbonate. A salting-out effect due to the high concentration of bicarbonate likely
destabilizes the hydrophobic NOM fractions, thus decreasing their size and allowing for
diffusion through the interstitial spaces in the resin. Freundlich isotherm experiments indicated
that the benefits of alkalinity for NOM removal were most significant for low concentrations of
NOM in the liquid phase. Additional experiments that adsorb NOM and bicarbonate separately
onto SIR-22P-HP support this theory.
Preliminary experiments with MIEX® indicated that MIEX® is superior at removing NOM
than SIR-22P-HP is per gram, especially for chromophoric compounds, and a lower ratio of resin
to NOM needs to be used to quantify the effects of alkalinity on MIEX®. Lastly, atrazine was not
removed by either SIR-22P-HP or MIEX® during batch kinetics—likely because atrazine is a
neutral species and takes no part in ion-exchange.
iii
Table of Contents
Abstract ............................................................................................................................................ii
List of Figures .................................................................................................................................. vi
List of Tables ................................................................................................................................. viii
Nomenclature ................................................................................................................................. ix
Acknowledgements ......................................................................................................................... xi
1. Introduction ................................................................................................................................ 1
2. Thesis Statement......................................................................................................................... 4
2.1 Specific Objectives ................................................................................................................. 4
3. Literature Review ........................................................................................................................ 5
3.1 Natural Organic Matter ......................................................................................................... 5
3.2 Alkalinity ................................................................................................................................ 5
3.3 Atrazine ................................................................................................................................. 6
3.4 Conventional Methods to Remove NOM .............................................................................. 7
3.4.1 Coagulation/flocculation ................................................................................................ 7
3.4.2 Ultra-filtration ................................................................................................................. 7
3.4.3 Granular Activated Carbon ............................................................................................. 8
3.5 Ion Exchange Resins .............................................................................................................. 8
3.6 Characteristics of Anion Exchange Resins ............................................................................. 8
3.6.1 Acrylic and Styrene Polymeric Backbones ...................................................................... 8
3.6.2 Strong Base and Weak Base Anion Exchangers.............................................................. 9
3.6.3 Type I and Type II Functional Groups ............................................................................. 9
3.6.4 Water Content ................................................................................................................ 9
3.6.5 Total Exchange Capacity ............................................................................................... 10
3.6.6 Resin Particle Size ......................................................................................................... 10
3.6.7 Sorption Mechanisms ................................................................................................... 10
3.7 Resins Studied ..................................................................................................................... 11
3.7.1 SIR-22P-HP .................................................................................................................... 12
iv
3.7.2 Magnetic Ion-Exchange Resin ....................................................................................... 12
4. Materials and Methodology ..................................................................................................... 13
4.1 Synthetic NOM Preparation ................................................................................................ 13
4.2 Resin Preparation ................................................................................................................ 14
4.2.1 Regeneration ................................................................................................................ 14
4.2.2 Determination of Resin Dry to wet Mass Ratio ............................................................ 16
4.3 Batch Kinetic Experiments................................................................................................... 17
4.3.1 Experimental Parameters ............................................................................................. 17
4.3.2 Experimental Procedure ............................................................................................... 18
4.4 Batch Freundlich Isotherms ................................................................................................ 18
4.4.1 Experimental Parameters ............................................................................................. 19
4.4.2 Experimental Procedure ............................................................................................... 19
4.5 Alkalinity Experiments ......................................................................................................... 20
4.5.1 Experimental Parameters ............................................................................................. 20
4.5.2 Experimental Procedure ............................................................................................... 20
5. Analytical Methods ................................................................................................................... 22
5.1 Dissolved Organic Carbon ................................................................................................... 22
5.2 Ultra-violet Absorbance at 254 nm ..................................................................................... 22
5.3 Alkalinity .............................................................................................................................. 23
5.4 Atrazine ............................................................................................................................... 24
5.5 Molecular Weight Distribution ............................................................................................ 25
6. Results and Discussion .............................................................................................................. 26
6.1 Batch Kinetics ...................................................................................................................... 26
6.1.1 Dissolved Organic Carbon ............................................................................................. 26
6.1.2 Absorbance of Ultra-violet Light................................................................................... 28
6.1.3 Alkalinity ....................................................................................................................... 31
6.1.4 Atrazine ......................................................................................................................... 32
6.1.5 Apparent Molecular Weight Distribution ..................................................................... 33
6.2 Freundlich Adsorption Isotherms ........................................................................................ 36
v
6.2.1 Dissolved Organic Carbon ............................................................................................. 37
6.2.2 Absorbance of Ultra-violet Light................................................................................... 41
6.2.3 Alkalinity ....................................................................................................................... 44
6.3 Alkalinity Experiments ......................................................................................................... 49
6.3.1 Dissolved Organic Carbon ............................................................................................. 49
6.3.2 Absorbance of Ultra-violet Light................................................................................... 51
6.3.3 Alkalinity ....................................................................................................................... 52
7. Future Work .............................................................................................................................. 54
7.1 Solution Ionic Strength and Alkalinity ................................................................................. 54
7.2 Regeneration ....................................................................................................................... 54
7.3 Atrazine ............................................................................................................................... 54
7.4 Magnetic Ion-Exchange ....................................................................................................... 55
8. References ................................................................................................................................ 56
Appendix A – Calibration Data ...................................................................................................... 59
Appendix B – Raw and Worked Data ............................................................................................ 61
B.1 Batch Kinetics ...................................................................................................................... 61
B.1.1 Kinetic Fitting Curves .................................................................................................... 63
B.2 Freundlich Isotherms .......................................................................................................... 65
B.3 Alkalinity Experiments ......................................................................................................... 69
Appendix C – Sample Calculations ................................................................................................ 70
C.1 Kinetic Fitting Functions ...................................................................................................... 70
C.2 Initial Removal Rate for Batch Kinetics ............................................................................... 71
C.3 Freundlich Isotherms Parameters ....................................................................................... 72
C.4 Alkalinity .............................................................................................................................. 73
vi
List of Figures
FIGURE 1: MOLECULAR STRUCTURE OF ATRAZINE HERBICIDE ....................................................................................................... 6
FIGURE 2: SORPTION MECHANISMS OF NOM REMOVAL BY IEX RESINS (TAN & KILDUFF, 2007) ..................................................... 11
FIGURE 3: COMPARISON OF THE REMOVAL OF DOC BY SIR-22P-HP RESIN AT 0 AND 50 MG/L INITIAL BICARBONATE CONCENTRATIONS.
........................................................................................................................................................................... 26
FIGURE 4: ABSORBANCE OF UV254 OF THE LIQUID PHASE FOR TREATMENT WITH SIR-22P-HP SHOWING AN ENHANCED REMOVAL OF
CHROMOPHORIC SPECIES AT 50 MG/L OF BICARBONATE INITIALLY .................................................................................... 29
FIGURE 5: SPECIFIC UV ABSORBANCE OF THE LIQUID PHASE SHOWING A LOWER INITIAL SUVA THAN AFTER A LONG CONTACT TIME ....... 30
FIGURE 6: REMOVAL OF BICARBONATE BY SIR-22P-HP RESIN SHOWING RAPID INITIAL REMOVAL OF BICARBONATE............................. 31
FIGURE 7: REMOVAL OF ATRAZINE BY SIR-22P-HP RESIN SHOWING THAT ATRAZINE WAS NOT REMOVED .......................................... 33
FIGURE 8: APPARENT MOLECULAR WEIGHT DISTRIBUTION OF NOM SOLUTION AT 0 MG/L BICARBONATE TREATED WITH SIR-22P-HP
SHOWING THE DECREASE IN ABSORBANCE OF LOW TO MEDIUM MW SPECIES WITH TIME ....................................................... 34
FIGURE 9: APPARENT MOLECULAR WEIGHT DISTRIBUTION OF NOM SOLUTION AT 50 MG/L BICARBONATE TREATED WITH SIR-22P-HP
SHOWING THE DECREASE IS ABSORBANCE OF LOW TO MEDIUM MW SPECIES WITH TIME ....................................................... 35
FIGURE 10: APPARENT MOLECULAR WEIGHT DISTRIBUTION OF NOM SOLUTION SHOWING THE REDUCTION OF MEDIUM MW SPECIES WAS
IMPROVED AFTER SIX HOURS OF CONTACT WITH SIR-22P-HP AT 50 MG/L BICARBONATE THAN WITHOUT BICARBONATE ............ 36
FIGURE 11: FREUNDLICH ISOTHERM FOR THE EQUILIBRIUM DISTRIBUTION OF DOC FOR SIR-22P-HP .............................................. 38
FIGURE 12: FREUNDLICH ISOTHERM FOR THE EQUILIBRIUM DISTRIBUTION OF DOC FOR MIEX ........................................................ 39
FIGURE 13: THE AMOUNT OF DOC REMOVED AS A FUNCTION OF THE AMOUNT OF MIEX ADDED TO SOLUTION SHOWS THAT NEARLY ALL
DOC CAPABLE OF BEING REMOVED OCCURRED WITH 20 MG OF MIEX IN THE 100 ML SOLUTION ........................................... 40
FIGURE 14: FREUNDLICH ISOTHERM FOR THE EQUILIBRIUM DISTRIBUTION OF CHROMOPHORIC UV ABSORBING COMPOUNDS FOR SIR-22P-
HP ....................................................................................................................................................................... 41
FIGURE 15: FREUNDLICH ISOTHERM FOR THE EQUILIBRIUM DISTRIBUTION OF CHROMOPHORIC SPECIES, REPRESENTED AS ABSORBANCE, FOR
MIEX ................................................................................................................................................................... 43
FIGURE 16: ABSORBANCE AS A FUNCTION OF THE AMOUNT OF MIEX ADDED TO SOLUTION SHOWS THAT MIEX REMOVES ALL OF THE
CHROMOPHORIC IT CAN AFTER 20 MG ADDED AND SIR-22P-HP WAS NOT AS EFFECTIVE ...................................................... 44
vii
FIGURE 17: FREUNDLICH ISOTHERM FOR THE EQUILIBRIUM DISTRIBUTION OF BICARBONATE SHOWING THAT RATIO BETWEEN BICARBONATE
AND DOC IN THE LIQUID PHASE DOES NOT AFFECT THE AMOUNT OF BICARBONATE REMOVED BY SIR-22P-HP .......................... 45
FIGURE 18: FREUNDLICH ISOTHERM FOR EQUILIBRIUM DISTRIBUTION OF BICARBONATE IN AN NOM SOLUTION TREATED WITH MIEX ..... 46
FIGURE 19: FREUNDLICH ISOTHERM FOR THE EQUILIBRIUM DISTRIBUTION OF BICARBONATE FOR BOTH SIR-22P-HP AND MIEX SHOWING
MIEX GENERALLY HAS A WEAKER AFFINITY FOR BICARBONATE ......................................................................................... 48
FIGURE 20: THE AMOUNT OF BICARBONATE REMOVED AS A FUNCTION OF THE AMOUNT OF RESIN ADDED TO SOLUTION SHOWS THAT SIR-
22P-HP HAS A MUCH GREATER EQUILIBRIUM REMOVAL OF BICARBONATE THAN MIEX ........................................................ 49
FIGURE 21: BOX PLOT OF THE DOC IN SOLUTION AFTER TREATMENT WITH SIR-22P-HP WHERE: RESIN A HAD BOTH NOM AND
BICARBONATE IN SOLUTION; RESIN B HAD ONLY NOM IN SOLUTION; RESIN C HAD FIRST BICARBONATE IN SOLUTION AND THEN
SUBSEQUENTLY TREATED AN NOM ONLY SOLUTION ....................................................................................................... 50
FIGURE 22: BOX PLOT OF THE ABSORBANCE OF CHROMOPHORIC COMPOUNDS IN SOLUTION AFTER TREATMENT WITH SIR-22P-HP WHERE:
RESIN A HAD BOTH NOM AND BICARBONATE IN SOLUTION; RESIN B HAD ONLY NOM IN SOLUTION; RESIN C HAD FIRST
BICARBONATE IN SOLUTION AND SUBSEQUENTLY TREATED AN NOM ONLY SOLUTION ........................................................... 51
FIGURE 23: BOX PLOT OF THE BICARBONATE IN SOLUTION AFTER TREATMENT WITH SIR-22P-HP WHERE: RESIN A HAD BOTH NOM AND
BICARBONATE IN SOLUTION; RESIN B HAD ONLY BICARBONATE IN SOLUTION; RESIN C TREATED FIRST AN NOM SOLUTION AND THEN
SUBSEQUENTLY TREATED A BICARBONATE ONLY SOLUTION ............................................................................................... 53
FIGURE 24: ATRAZINE CALIBRATION CURVE FOR HPLC ANALYSIS TO CONVERT AREA UNDER THE ATRAZINE PEAK TO A CONCENTRATION
BETWEEN 0 TO 750 ΜG/L ........................................................................................................................................ 59
FIGURE 25: ATRAZINE CALIBRATION CURVE FOR HPLC ANALYSIS TO CONVERT AREA UNDER THE ATRAZINE PEAK TO A CONCENTRATION
BETWEEN 1000 TO 10000 ΜG/L .............................................................................................................................. 59
FIGURE 26: MOLECULAR WEIGHT DISTRIBUTION CALIBRATION CURVE FOR HPSEC ANALYSIS TO CONVERT RETENTION TIME TO MOLECULAR
WEIGHT ................................................................................................................................................................. 60
viii
List of Tables
TABLE 1: BENCH SCALE REGENERATION PROCEDURE FOR ION-EXCHANGE RESINS ........................................................................... 15
TABLE 2: UPDATED BENCH SCALE REGENERATION PROCEDURE FOR ION-EXCHANGE RESINS .............................................................. 16
TABLE 3: REMOVAL KINETIC CONSTANT AND INITIAL REMOVAL RATE OF DOC FOR SIR-22P-HP ...................................................... 28
TABLE 4: REMOVAL KINETIC CONSTANT FOR ABSORBANCE OF UV254 FOR SIR-22P-HP .................................................................. 29
TABLE 5: REMOVAL KINETIC CONSTANT AND INITIAL REMOVAL RATE OF BICARBONATE BY SIR-22P-HP ............................................. 32
TABLE 6: FREUNDLICH ISOTHERM K AND N CONSTANT PARAMETERS AND R2 FOR DOC ISOTHERMS WITH SIR-22P-HP ........................ 39
TABLE 7: FREUNDLICH ISOTHERM K AND N CONSTANT PARAMETERS AND R2 FOR ABSORBANCE ISOTHERMS WITH SIR-22P-HP ............. 42
TABLE 8: FREUNDLICH ISOTHERM K AND N CONSTANT AND R2 FOR ALKALINITY ISOTHERMS WITH SIR-22P-HP ................................... 45
TABLE 9: FREUNDLICH ISOTHERM K AND N CONSTANT PARAMETERS AND R2 FOR ALKALINITY ISOTHERMS WITH MIEX .......................... 48
TABLE 10: DETERMINATION OF THE DRY TO WET MASS RATIO OF SIR-22P-HP AND MIEX ............................................................. 60
TABLE 11: RAW AND WORKED DATA FOR BATCH KINETIC TRIAL WITH SIR-22P-HP FOR 0 MG/L OF BICARBONATE INITIALLY .................. 61
TABLE 12: RAW AND WORKED DATA FOR BATCH KINETIC TRIAL WITH SIR-22P-HP FOR 50 MG/L OF BICARBONATE INITIALLY ................ 62
TABLE 13: DOC FITTING FUNCTION FOR SIR-22P-HP AT 0 MG/L BICARBONATE ......................................................................... 63
TABLE 14: DOC FITTING FUNCTION FOR SIR-22P-HP AT 50 MG/L BICARBONATE ....................................................................... 63
TABLE 15: ABSORBANCE FITTING FUNCTION FOR SIR-22P-HP AT 0 MG/L BICARBONATE .............................................................. 64
TABLE 16: ABSORBANCE FITTING FUNCTION FOR SIR-22P-HP AT 50 MG/L BICARBONATE ............................................................ 64
TABLE 17: ALKALINITY FITTING FUNCTION FOR SIR-22P-HP AT 50 MG/L BICARBONATE ............................................................... 65
TABLE 18: INITIAL VALUES FOR ABSORBANCE, DOC, AND BICARBONATE FOR TESTS WITH SIR-22P-HP AND MIEX ............................. 65
TABLE 19: RAW AND WORKED DATA FOR SIR-22P-HP ISOTHERM TRIAL AT 0 MG/L INITIAL BICARBONATE CONCENTRATION ................. 66
TABLE 20: RAW AND WORKED DATA FOR SIR-22P-HP ISOTHERM TRIAL AT 50 MG/L INITIAL BICARBONATE CONCENTRATION ............... 66
TABLE 21: RAW AND WORKED DATA FOR SIR-22P-HP ISOTHERM TRIAL AT 100 MG/L INITIAL BICARBONATE CONCENTRATION ............. 67
TABLE 22: RAW AND WORKED DATA FOR MIEX ISOTHERM TRIAL AT 0 MG/L INITIAL BICARBONATE CONCENTRATION........................... 67
TABLE 23: RAW AND WORKED DATA FOR MIEX ISOTHERM TRIAL AT 50 MG/L INITIAL BICARBONATE CONCENTRATION ........................ 68
TABLE 24: RAW AND WORKED DATA FOR MIEX ISOTHERM TRIAL AT 100 MG/L INITIAL BICARBONATE CONCENTRATION ...................... 68
TABLE 25: RAW AND WORKED DATA FOR ALKALINITY EXPERIMENTS WITH SIR-22P-HP ................................................................. 69
TABLE 26: STATISTICAL PARAMETERS AS DETERMINED USING BUILT IN EXCEL FORMULAS TO CONSTRUCT BOX PLOTS ............................ 69
ix
Nomenclature
Symbol Definition
ABS Absorbance
AER Anion-Exchange Resin
AEX Anion-Exchange
AMW Apparent Molecular Weight
AOP Advanced Oxidation Process
BV Bed Volume (mL)
°C Degrees Celsius
C Concentration of NOM in Solution (mg/L)
CaCO3 Calcium Carbonate
Cf Final Concentration
Cl- Chlorine Ion
cm¯¹ Inverse Centimeters Representing Path Length
CO2 Carbon Dioxide
Da Daltons
DBP Disinfection By-Product
DOC Dissolved Organic Carbon (mg/L)
DOCfit Fitted Value for Dissolved Organic Carbon (mg/L)
DOCo Initial Dissolved Organic Carbon Concentration (mg/L)
DOCr Residual Value of Dissolved Organic Carbon from Fitting (mg/L)
GAC Granular Activated Carbon
H2O Water
HCl Hydrochloric Acid
HPLC High-Performance Liquid Chromatography
HPSEC High-Performance Size Exclusion Chromatography
IEX Ion-Exchange
K Freundlich Isotherm Constant
k Removal Kinetic Constant (min-1)
L Litre
x
M Mass of Adsorbate
MIEX® Magnetic Ion Exchange Resin
min Minutes
mL Millilitre
MW Molecular Weight
n Freundlich Isotherm Constant
N Normality
NaCl Sodium Chloride
NOM Natural Organic Matter
No. Number
·OH Hydroxyl Radical
q Mass Adsorbate/Mass Adsorbent
R2 Linear Regression Goodness of Fit
rpm Revolutions per Minute
SBA Strong Base Anion
SIR-22P-HP An Ion-exchange Resin
STDEV Standard Deviation
SUVA Specific Ultra-violet Absorbance
TOC Total Organic Carbon
UBC University of British Columbia
μg Micrograms
UV Ultra-violet
UV254 Ultra-violet at 254 Nanometers Wavelength
V Volume of Solution
Vs Volume of Sample
Vt Volume of Titrant
WBA Weak Base Anion
wt% Weight Percentage
Xo Initial Value of a Parameter of Choice
Xf Final Value of a Parameter of Choice
xi
Acknowledgements
I would like to thank Dr. Madjid Mohseni and Dr. Gustavo Imoberdorf for being so
inclusive and accommodating with their research group. I appreciate their interest in the
results of my experiments as they were realized and our discussions of possible causes for the
unexpected and intriguing results. I appreciate Dr. Imoberdorf’s extraordinary patience that he
displayed throughout the semester, especially as I sat in the hall in the early morning for nearly
a week to catch him on his way to his office to discuss my results.
I would also like to thank RES’EAU WaterNet and the entire advanced oxidation research
team for their help along the way. Clara’s sense of humour made collecting data on the HPLC
much more interesting as we were outsmarted by it for weeks, and I appreciate all the help she
offered from her own time without hesitation.
1
1. Introduction
The treatment of drinking water is a growing world issue in society as water supplies are
stressed due to rising global population. In particular, smaller communities such as First
Nations communities in Canada are under a constant water boil advisory due to water quality
issues (Eggertson, 2008). Moreover, organic contaminants such as pesticides and herbicides
are an issue in some of these water supplies. Various treatment solutions exist to treat
contaminated water; however, many are not suitable for a small scale. One potential solution
is to use advanced oxidation process (AOP) based on the hydroxyl radical. Hydroxyl radicals
oxidize pollutants into non-toxic forms in a complex reaction mechanism simplified as shown in
equation (1):
(1)
The challenge with AOP is that harmless natural organic matter (NOM) is also oxidized in
the simplified undesired side reaction as shown in equation (2):
(2)
As a result, the feasibility and efficiency of AOP is reduced due to the competitive effect
of hydroxyl radicals being scavenged to oxidize the harmless NOM present in the water being
treated. Thus, it is desirable to remove NOM prior to AOP. The removal of NOM increases the
feasibility of AOP by reducing the energy and/or material consumption of AOP as well as
reducing the amount of disinfection by-products (DBP) that form as a result from treatment and
free chlorine in solution.
NOM is a complex mixture of organic components such as humic and fulvic acids, amino
acids, low molecular weight (MW) acids, carbohydrates, and proteins typically present in
2
drinking water sources at 2 to 10mg/L and may form carcinogenic DBPs if treated with chlorine
(Bolto, Dixon, Eldridge, & King, 2004). Additionally, NOM fouls membranes, allows for bacterial
re-growth, affects taste, increases turbidity, and affects the colour of the water. Therefore, it is
vital that research be conducted into methods for economic and effective water treatment
solutions to remove NOM prior to AOP.
Ion-exchange (IEX) has been researched extensively since the late 1970’s as a potential
method for removing NOM from water. Anion-exchange (AEX) is the reversible exchange of
anions from an insoluble solid resin to a surrounding source of water to be treated (Cornelissen,
et al., 2007). Particularly, AEX is more effective at removing low to medium molecular weight
humic and fulvic substances than coagulation and is a cheaper alternative to using granular
activated carbon (GAC) (Heijman, Van Paassen, Van der Meer, & Hopman, 1999). Anion-
exchange resins (AER) have demonstrated to be an effective pretreatment step to water
treatment and show promise to increasing the efficiency of AOP (Humbert, Gallard, Suty, &
Croue, 2005). AERs function primarily by exchanging Cl- in the resin with anionic NOM in a
solution—thus charge neutrality is maintained. AERs also adsorb neutral species onto their
structure to a lesser extent. AERs can be regenerated on site with brine and can last for years
in a treatment facility (Heijman, Van Paassen, Van der Meer, & Hopman, 1999).
Students with the advanced oxidation laboratory at the University Of British Columbia
(UBC) have previously studied three AERs. However, the effect alkalinity has on AERs is unclear.
It is believed that alkalinity has a competitive effect with NOM uptake by resins since alkaline
species are negatively charged. Since alkalinity is significant in many water sources, it is
important to understand the effects of alkalinity on the performance of resins to remove NOM
3
prior to AOP. Moreover, since AOP is primarily used to treat drinking water supplies
contaminated with organic pollutants, it is important to understand how resins interact with
pollutants. Studies with 2,4-D herbicide at UBC have indicated that 2,4-D is removed by AERs.
However, it is unclear how resins interact with pollutants of a different nature. 2,4-D is acidic
and participates in ion-exchange; however, atrazine is neutrally charged and cannot participate
in ion-exchange. On the other hand, atrazine may physically adsorb onto the resin structure to
an extent.
4
2. Thesis Statement
To determine the effects of alkalinity on the ability of ion-exchange resins to remove
natural organic matter and organic contaminants as a pre-treatment step to improve the
feasibility of the advanced oxidation process.
2.1 Specific Objectives
1. Examine the effects of alkalinity on the ability of anion-exchange resins to remove
natural organic matter.
2. Examine the removal of Atrazine using anion-exchange resins.
5
3. Literature Review
3.1 Natural Organic Matter
Drinking water sources typically contain around 2 to 10 mg/L of NOM, of which only 10
to 30% has been classified, resulting from the decay of living matter (Boggs, Livermore, & Seitz,
1985). NOM can cause colour, taste, and odour problems in water (Christman & Ghassemi,
1966). Its presence can also lead to downstream biological re-growth (Van der Kooij, 2003).
Furthermore, disinfection by-products can form from NOM fractions after chemical disinfection
(Rook, 1974). NOM also causes membrane fouling when using filtration methods (Amy & Cho,
1999). NOM is harmless; however, it competes with organic pollutants which are the target of
hydroxyl radicals in AOP (Sarathy & Mohseni, 2007).
3.2 Alkalinity
Alkalinity is a measure of the ability of a solution to neutralize acids to the equivalence
point. Alkalinity of water may be due to the presence of one or more ions such as hydroxides,
carbonates, or bicarbonates. The effects of bicarbonate have been studied previously in
literature and with the advanced oxidation research group at UBC. The research group at UBC
conducted a preliminary study with bicarbonate and found that NOM removal in the presence
of bicarbonate was decreased possibly due to competition for ion-exchange sites between the
anionic NOM and anionic bicarbonate. Moreover, studies have shown that bicarbonate is
removed from solution by IEX resins (Boyer & Singer, 2007).
On the other hand, some basic studies with alkalinity have shown that bicarbonate
present at 120 mg/L did not detrimentally affect hydrophobic acid NOM uptake by one resin,
6
but instead that NOM uptake was slightly increased by the presence of bicarbonate (Croue,
Violleau, & Legube, 1999). However, this effect has not been measured for hydrophilic acid
NOM fractions. The observation was explained by a phenomenon called the salting-out effect.
The salting-out effect occurs because the presence of bicarbonate at a high concentration
increases the ionic strength of the NOM solution to be treated substantially. The increased ionic
strength destabilizes the hydrophobic NOM species resulting in a compression of the
hydrophobic compounds’ structure. Size exclusion for large compounds exists within the
interstitial space of a resin; however, the smaller size of the compressed hydrophobic NOM
species allows for more NOM to diffuse into the interstitial space of a resin structure to
participate in ion-exchange.
3.3 Atrazine
AOP is typically performed to treat water contaminated with a pollutant. Atrazine is a
commonly used herbicide with known mutagenic effects to amphibians and other species.
Moreover, atrazine is a known endocrine disrupting compound to humans (Benotti, Trenholm,
Holady, Stanford, & Snyder, 2009). Figure 1 depicts the molecular structure of atrazine showing
that it is non-ionic in nature.
Figure 1: Molecular structure of Atrazine herbicide
7
It is important to understand how using resins as a pretreatment step to AOP affects the
concentration of atrazine. Studies have shown that atrazine is poorly removed by most resins
including MIEX® because it is non-ionic (Humbert, Gallard, Suty, & Croue, 2005). Atrazine
concentrations between 1 μg/L to 200 μg/L resulted in adsorption efficiencies of only 7% onto
MIEX® (Humbert, Gallard, Suty, & Croue, 2005).
3.4 Conventional Methods to Remove NOM
3.4.1 Coagulation/flocculation
Coagulation/flocculation is one potential treatment method to remove NOM prior to
AOP. Flocculating agents such as iron or aluminum compounds cause colloids and other
suspended particles in the water to form flocs and settle. This process removes approximately
40 to 70% of the NOM from the water (Croue, Violleau, & Legube, 1999).
Coagulation/flocculation more effectively removes large MW species than IEX; as a result,
coagulation/flocculation has been shown to complement IEX since resins selectively remove
low to medium MW NOM species preferentially (Bolto, Dixon, Eldridge, King, & Linge, 2002).
3.4.2 Ultra-filtration
Ultra-Filtration is another method to remove NOM prior to AOP. Ultra-filtration is
mostly effective at removing high MW species and high charge density hydrophobic species
(Humbert, Gallard, Jacquemet, & Croue, 2007). Ultra-filtration is only effective at removing 10
to 50% of NOM present in water and membrane fouling becomes an issue as the MW cut-off is
decreased (Humbert, Gallard, Jacquemet, & Croue, 2007).
8
3.4.3 Granular Activated Carbon
Activated carbon is an effective method to remove NOM; however, the production and
regeneration costs of GAC make it uneconomical as a pretreatment process to remove NOM in
many cases (Montgomery, 1985).
3.5 Ion Exchange Resins
Ion Exchange resins are an effective and relatively inexpensive method for removing
humic substances from drinking water (Bolto, Dixon, Eldridge, King, & Linge, 2002; Heijman,
Van Paassen, Van der Meer, & Hopman, 1999). NOM is largely uncharacterized; however, it is
known that NOM contains mostly aromatic and aliphatic groups (Tan, Kilduff, Kitis, & Karanfil,
2005). NOM behaves like large negatively charged colloids or as small anionic poly-electrolytes
(Bolto, Dixon, Eldridge, & King, 2004). As a result, AERs are effective at removing NOM from
water due to an exchange of anionic species between the resin and the NOM in solution
(Fearing, et al., 2004). Removal efficiencies by IEX can be as high as 80% for a <1000 Da feed
solution of 6.5 mg/L dissolved organic carbon (DOC) and up to 95% for a 5000-10000 Da
solution with an initial total organic carbon (TOC) of 9 mg/L (Fu & Symons, 1990). Thus, resins
have been shown to be a promising solution to remove NOM prior to downstream treatment.
3.6 Characteristics of Anion Exchange Resins
3.6.1 Acrylic and Styrene Polymeric Backbones
The polymeric backbone of resins influences NOM removal. Resins with a polystyrene
structure are more selective at removing aromatic compounds than resins with a polyacrylic
structure (Humbert, Gallard, Suty, & Croue, 2005). This selectivity is attributed to a
9
combination of electrostatic interactions and hydrophobic bonding (Bolto, Dixon, Eldridge, &
King, 2004). When the water content of the resin is high (>70%), however, there is no
difference in performance of resins with an acrylic or a styrene structure (Tan & Kilduff, 2007).
3.6.2 Strong Base and Weak Base Anion Exchangers
Strong base anion (SBA) resins are found to more effectively remove NOM than weak
base anion (WBA) resins by demonstrating higher loading capacities for NOM (Brattebo,
Odegaard, & Halle, 1987). WBA resins, however, are less expensive than SBA resins and require
lower chemical requirements to regenerate: SBA resins require salt and alkali well in excess of
stoichiometric amounts; whereas, WBA resins require lime and mineral acid only slightly above
equivalent levels (Bolto, Dixon, Eldridge, & King, 2004).
3.6.3 Type I and Type II Functional Groups
There are two types of SBA resins based on quaternary ammonium functional groups.
Type I (trimethyl-ammonium) functional groups remove NOM more effectively than Type II
resins. Resins with Type II (dimethylethanol-ammonium) functional groups are less selective at
removing aromatic NOM; however, they are easier to regenerate (Cornelissen, et al., 2007). On
the other hand, Type II resins have a higher affinity for hydrophilic NOM than Type I because
Type II resins have an OH- group closer to the quaternary nitrogen giving Type II more polarity
than Type I resins (Bolto, Dixon, Eldridge, King, & Linge, 2002; Boyer & Singer, 2007)
3.6.4 Water Content
Resins with high water content have a low degree of cross linking and a more open
structure. As a result, NOM, particularly larger species, have easier access to diffuse through
10
the resin pores to the exchange sites (Cornelissen, et al., 2007). The performance of resins is
best indicated by water content rather than polymeric structure or if the resin is gel or
macroporous (Bolto, Dixon, Eldridge, King, & Linge, 2002).
3.6.5 Total Exchange Capacity
Total exchange capacity indicates the amount of counter-ions available for IEX and also
gives insight to the service cycle length of the resin before needing to be regenerated
(Montgomery, 1985). Manufacturers provide a wet-volume capacity of their resins; however,
the effective capacity of the resin, which is a fraction of the total exchange capacity, must be
determined in the lab (Montgomery, 1985). Furthermore, water content is a better indicator of
how a resin will perform than total exchange capacity (Bolto, Dixon, Eldridge, King, & Linge,
2002).
3.6.6 Resin Particle Size
Small resin particle sizes have a larger overall external surface area which allows for
higher removal kinetics since more exchange sites are available (Montgomery, 1985). However,
there is a trade-off between the increasing pressure drop of fluid in a column with decreasing
resin particle size (Montgomery, 1985). The hydraulic pressure drop is one of the main deciding
factors as to whether IEX is feasible or not because pressure drop increases the operational
costs of treatment substantially (Montgomery, 1985).
3.6.7 Sorption Mechanisms
Two mechanisms are responsible for NOM removal by resins. The dominant mechanism
is ion-exchange where Cl- counter ions displace from the resins and exchange with anionic NOM
11
species in the water (Tan & Kilduff, 2007). To a lesser extent, physical adsorption also occurs
between neutral NOM species and the resin polymer backbone on the order of 7% uptake of
the initial NOM in the sample or less (Tan & Kilduff, 2007). It has been observed that Cl-
exchange with anionic NOM by IEX occurs with a 1:1 stoichiometry at pH 7.5 (Fu & Symons,
1990). Figure 1 shown below depicts the two sorption mechanisms that occur between resins
and NOM. Ion-exchange in (a) depicts counter-ion displacement from the resin and an
electrostatic interaction between the ionic functional groups. Physical adsorption in (b) shows
van der Waals interactions between the hydrophobic moieties on the NOM and the polymeric
backbone of the resin.
Figure 2: Sorption mechanisms of NOM removal by IEX resins (Tan & Kilduff, 2007)
3.7 Resins Studied
Two resins were studied to firstly compare how efficient MIEX® is compared to SIR-22P-
HP. SIR-22P-HP has been previously studied by students and found to be very effective at
removing NOM. Additionally, the effects alkalinity has on NOM removal by resins was tested
with resins of two different types in terms of mean resin bead diameter, macroporous vs. gel
structure, and polymer backbone composition.
12
3.7.1 SIR-22P-HP
SIR-22P-HP resin is provided from Resintech in a moist chloride form as spherical beads
mostly between 297 μm to 853 μm in diameter (mean diameter of 500 μm). SIR-22P-HP has
unique porous polystyrene with divinylbenzene backbone with a gel structure and water
content of 75%. SIR-22P-HP had the highest performance for NOM removal in a test against 19
different resins because of its high water content and gel structure (Bolto, Dixon, Eldridge, King,
& Linge, 2002). SIR-22P-HP is suitable to operate between pH 0 to 14 and up to a maximum
temperature of 76 °C. SIR-22P-HP is a SBA exchanger with Type I (tri-methyl ammonium)
functional group. (Resintech SIR-22P-HP, 2010)
3.7.2 Magnetic Ion-Exchange Resin
Magnetic ion-exchange (MIEX®) is provided from Orica Watercare in a moist, pre-used,
but regenerated form. MIEX® is unique because the mean particle diameter is 180 μm (2 to 5
times smaller than conventional resins) which provides more external surface area to allow
rapid sorption kinetics (Humbert, Gallard, Suty, & Croue, 2005). The smaller bead size also
limits the interstitial space within each resin bead that NOM must diffuse through. The
magnetic iron-oxide component of MIEX® allows the small resin beads to agglomerate and
settle faster. MIEX® has an acrylic backbone, a macroporous structure, and is a SBA exchanger.
Depending on the characteristics of water to be treated, MIEX® can remove 30% to over 70% of
all DOC (Mergen, Jefferson, Parsons, & Jarvis, 2007). Studies have shown that MIEX® does not
remove high MW compounds > 5000 Da (Fearing, et al., 2004). Additionally, removal of NOM
using MIEX® is water specific as high MW species can quickly saturate or block the interstitial
space in the resin (Mergen, Jefferson, Parsons, & Jarvis, 2007).
13
4. Materials and Methodology
To determine the effects of alkalinity on the efficiency of resins to remove NOM, two
major experiments were performed. The first experiment was to conduct batch kinetics
experiments involving the measurement of DOC, absorbance of UV254, bicarbonate
concentration, and atrazine concentration. The second experiment was to construct Freundlich
isotherms to determine K and n constants from DOC concentration, absorbance of UV254,
bicarbonate concentration, and atrazine concentration isotherms. Data obtained from these
two experiments provided two means of quantifying the effects of alkalinity on the
performance of resins to remove NOM and how the resins interact with atrazine pollutant at
low concentrations.
4.1 Synthetic NOM Preparation
Suwannee River water has been used extensively in literature for experiments with ion-
exchange resins (Boyer & Singer, 2007; Croue, Violleau, & Legube, 1999) Therefore, for the
purpose of comparing experimental findings with those in literature the Suwannee River
Aquatic NOM (International Humic Standards Society catalogue # IR101N) water was used.
Suwannee River water comes from the Suwannee River near the north-eastern edge of the
Okefenokee Swamp near Fargo, Georgia, USA. The NOM is isolated using XAD-8 resin
adsorption and reverse osmosis concentration techniques and shipped in 500 mg glass sample
vials requiring cold storage.
A total of 24 L of synthetic Suwannee River water solution was produced by weighing
out 480 mg of dry Suwannee River NOM and adding it to 2 L of de-ionized ultrapure water
(processed with the ELGA Purelab Option-Q® system). The 2 L solution was filtered twice using
14
Whatman No. 1 paper to remove suspended particles larger than 11 μm. Afterwards the
solution was filtered once using Whatman No. 42 paper to filter suspended particles larger than
2.5 μm which is similar to a sand filtration unit upstream of an ion-exchange column (Bolto,
Dixon, Eldridge, King, & Linge, 2002). 254 mL of a 9.45 mg/L atrazine stock solution, as
determined from High-Performance Liquid Chromatography (HPLC), was filtered using
Whatman No. 42 paper and added to the 2 L of filtered NOM solution. The NOM solution was
then pH balanced to 6.0 using 0.1 N NaOH then diluted with de-ionized ultrapure water to 24 L
and then further pH balanced to 7.0 using 0.1 N NaOH. This method minimized the amount of
dilution resulting from pH balancing past the target of 24 L. The final NOM solution had a DOC
concentration of 7.5 mg/L after filtering with 100 μg/L of atrazine—a low enough concentration
to be detectable by HPLC without affecting the results of NOM removal by AERs. The NOM
solution was stored in a cold room at 5°C until needed.
4.2 Resin Preparation
Resins need to be eluted of any organic material and regenerated with chlorine before
any analytical work can be performed. Additionally, the dry to wet mass ratio of a resin can be
used to weigh out a consistent dry mass of resin for experimentation based on the wet mass
weighed.
4.2.1 Regeneration
The resins came from the supplier in air tight polyethylene containers in a wetted form.
The resins were rinsed twice with de-ionized water each for 30 minutes to remove any residual
organics. The resins were then regenerated according to Table 1 adapted from Bolto et al.
15
(2002) and Humbert et al. (2005). Approximately 100 mL of resin was regenerated in each cycle
in a 2 L Erlenmeyer flask stirred at 90 rpm with a magnetic stirrer.
Table 1: Bench scale regeneration procedure for ion-exchange resins
Stage Replicates Solution Concentration Volume Contact time
N L min
1 1 De-ionized water 2 10 2 2 NaOH 0.1 2 120
3 1 De-ionized water 2 30 4 2 HCl 0.1 2 120 5 1 De-ionized water 2 30 6 2 NaCl 1 2 120 7 4 De-ionized water 2 120
Between each stage the resins were separated from solution using a vacuum driven
filter and Whatman No. 1 filter paper. An updated resin regeneration procedure from Orica
Watercare for bench scale regeneration is in Table 2. This method reduces the number of
stages required to perform one regeneration cycle. Additionally, the amount of regenerant
required is only 3 bed volumes (BV) rather than 2 L (19 BVs). In other words, 100 mL of
regenerated resin requires only 300 mL of regenerant per stage. Finally, the resins could be
separated from solution between each stage much faster by decanting the solution for disposal,
rinsing the resins with de-ionized water, and then decanting the rinse water.
16
Table 2: Updated bench scale regeneration procedure for ion-exchange resins
Stage Replicates Solution Concentration Volume Contact time BV min
1 1 De-ionized water 3 10 2 2 NaOH and NaCl 0.1 N and 10 wt% 3 30 3 1 NaCl 10 wt% 3 30 4 2 HCl and NaCl 0.1 N and 10 wt% 3 30 5 2 NaCl 10 wt% 3 30 7 4 De-ionized water 3 30
The method in Table 2 regenerated resins as effectively as the method in Table 1;
however, the updated procedure reduces regeneration time to 6 hours instead of 22 hours.
Additionally, the total regenerant usage is minimized substantially in the updated procedure
since only 3 BVs of regenerant are needed rather than 19 BVs. The regenerant strength of 10
wt% NaCl in the updated procedure instead of 1.0 N NaCl solution (approximately 6 wt%)
increased the regenerant strength of solution which offset the decreased contact time and
decreased solution volume required for the procedure.
SIR-22P-HP was regenerated using the procedure in Table 1 and MIEX was regenerated
using the procedure in Table 2. Regeneration for either method had to be repeated several
times and the resin had to be allowed to sit in a de-ionized water solution for 24 hours until the
water could be tested using a TOC analyzer to ensure the DOC content of the water was low to
ensure most of the organics were removed from the resin.
4.2.2 Determination of Resin Dry to wet Mass Ratio
The dry to wet ratio for both the SIR-22P-HP and MIEX® resins were determined in order
to convert a wet mass of resin to its equivalent dry mass without having to heat the resin to
remove the water content prior to weighing out for every experiment. Heating a resin to
17
remove its water content takes a long time and could damage the resin if too high a
temperature is used. Additionally, rehydrating a resin places too much osmotic pressure on the
resin. Therefore, three different quantities of each resin were separated from solution using a
vacuum driven filter and Whatman No. 1 filter paper, were weighed, and then placed in an
oven at 60°C for 24 hours before being reweighed. The dry to wet ratio is calculated using
equation 3 below and averaged out between the three trials.
100.(%)wet
dry
m
mRatio
(3)
The dry to wet mass ratio of SIR-22P-HP was determined to be 19.0% and the dry to wet
mass ratio of MIEX was calculated to be 27.0% and raw data can be found in Appendix A.
4.3 Batch Kinetic Experiments
Batch kinetic experiments were performed because the diffusion of NOM through the
interstitial space of resins takes time. Batch kinetic experiments can determine the effects of
alkalinity on removal kinetics of DOC from the liquid phase to the resin. Analytical results
quantify the DOC, absorbance of ultra-violet (UV) light at 254 nm, bicarbonate, and atrazine
removal kinetics as a function of contact time with a resin in suspended solution. Additionally,
high-performance size exclusion chromatography (HPSEC) illustrates the molecular weight
distribution of chromophoric NOM compounds after treatment with AERs.
4.3.1 Experimental Parameters
The variables for the kinetic experiment were to use two initial levels of alkalinity and
ten different time intervals from 0 to 6 hours. One kinetic trial was conducted at 0 mg/L
bicarbonate initially and the other was conducted at 50 mg/L bicarbonate initially. The resins
18
were in contact with solution for 1, 3, 5, 10, 15, 30, 60, 120, 240, and 360 minutes. The
constant experimental parameters were to use 100 mL of NOM solution with an initial DOC
concentration of 7.5 mg/L and an atrazine pollutant concentration of 100 μg/L. Only SIR-22P-
HP resin was tested using batch kinetic trials due to time limitations.
4.3.2 Experimental Procedure
A single sample was prepared by measuring out 100 mg of the equivalent dry mass of
resin and quickly rinsing it with NOM solution into a 250 mL Erlenmeyer flask to the 100 mL line
and then placing the flask in an orbital shaker/incubator unit at 25°C and 200 rpm. A stopwatch
was used to ensure each sample was agitated for its specific contact time. Once completed, the
sample was quickly removed from the shaker and the resins settled to the center of the beaker
due to sedimentation and the centrifugal force from the shaking. The solution was quickly
removed from the flask using a 60 mL syringe to remove 60 mL of solution and then placed into
two separate clean amber glass DOC sampling vials. Between samples the syringe was cleaned
with de-ionized water and dried as much as possible.
4.4 Batch Freundlich Isotherms
The Freundlich adsorption isotherm was used for adsorption isotherm experiments
because the isotherm has a high goodness of fit (R2) for the adsorption of NOM onto AERs
(Heijman, Van Paassen, Van der Meer, & Hopman, 1999). Freundlich K and n constants were
obtained through this experiment as a means to quantitatively assess the effectiveness of
resins to remove DOC in the presence of alkalinity and to determine the extent the resin
interacts with atrazine. Analytical results quantify the equilibrium DOC, chromophoric UV254
19
absorbing species, and bicarbonate distribution between the liquid and solid phase for various
equilibrium conditions.
4.4.1 Experimental Parameters
The variables for the isotherm experiment were to use three initial levels of alkalinity,
four different concentrations of resin, and two different resins. One isotherm trial was
conducted at an initial concentration of 0 mg/L bicarbonate, another at 50 mg/L bicarbonate
initially, and a third at 100 mg/L bicarbonate. The amount of resin in solution was varied rather
than the initial concentration of DOC because this allowed for only one NOM solution to be
prepared for more comparable results. The dry mass equivalent of resins used was 2, 20, 50,
and 100 mg as determined from the dry to wet mass ratio. Both SIR-22P-HP and MIEX were
tested separately. The constant experimental parameters were to use 100 mL of NOM solution
with an initial DOC concentration of 7.5 mg/L and an atrazine pollutant concentration of 100
μg/L. Resins in contact with NOM solution were held constant at 25°C.
4.4.2 Experimental Procedure
A single sample was prepared by measuring out the specific equivalent dry mass
required. The resin was then rinsed with the NOM solution quickly into a 250 mL Erlenmeyer
flask to the 100 mL line and placed in an orbital shaker at 25°C and 200 rpm. The initial time
was recorded and 48 hours later the samples were removed from the shaker and the resins
were allowed to settle to the center of the beaker. The solution was quickly removed from the
flask using a 60 mL syringe and placed into two separate clean amber glass DOC sampling vials.
Between sampling the syringe was cleaned with de-ionized water and dried as much as
possible.
20
4.5 Alkalinity Experiments
Further experimentation was required to confirm the possibility of the salting-out effect
due to the increased ionic strength of solution due to the presence of alkalinity. The alkalinity
experiments tested three different scenarios with SIR-22P-HP. These three experiments give
some information as to whether the presence of alkalinity in solution interacts with NOM and
whether alkalinity competes for the same ion-exchange sites that NOM uses.
4.5.1 Experimental Parameters
All initial DOC concentrations were 7.5 mg/L and initial bicarbonate concentrations were
100 mg/L for tests requiring either. Contact time of the solution with SIR-22P-HP was only for 2
hours. However, the variable of the experiment was to either first adsorb DOC onto the resin
then bicarbonate, or first adsorb bicarbonate onto the resin then DOC. The control experiment
was the situation with both DOC and bicarbonate present at the same time in solution to be
treated to simulate the conditions seen in batch kinetics. The only difference was that the
initial bicarbonate concentration was increased from 50 mg/L to 100 mg/L to enhance the
effects of alkalinity on the treatment process.
4.5.2 Experimental Procedure
The first case was where SIR-22P-HP treated a solution with NOM and bicarbonate
(labeled resin A). The second case was where SIR-22P-HP treated either an NOM only solution,
or a bicarbonate only solution depending on the analysis (labeled resin B). The third case was
where SIR-22P-HP treated either an NOM solution first then a bicarbonate solution, or a
bicarbonate solution first then a NOM solution depending on the analysis being performed
(labeled resin C). A sample was prepared using the same method as in section 4.3.2, but only a
21
contact time interval of 2 hours was used, and the resin was rinsed into the Erlenmeyer flask
with either the NOM solution, bicarbonate solution, or a composite solution of both depending
on the experiment as discussed in section 4.5.1.
22
5. Analytical Methods
5.1 Dissolved Organic Carbon
The DOC in a sample was measured using a Shimadzu TOC-VCPH series analyser with an
ASI-5000 auto-sampler. The TOC analyzer measures all dissolved and suspended organic
carbon in a sample of approximately 15 mL by oxidizing the sample with pure oxygen and
measuring the amount of CO2 evolved. The error of measurement of the machine is
approximately 0.1 mg/L. AERs only exchange chlorine anions with anionic aqueous species;
therefore, only the dissolved fraction of NOM in a sample was of interest. All samples were
filtered to remove suspended compounds greater than 2.5 μm to facilitate this.
5.2 Ultra-violet Absorbance at 254 nm
Absorbance of UV at 254 nm is an important parameter to measure because it indicates
the amount of aromatic (hydrophobic) organic species in the treated NOM solution. Aromatic
compounds are known to be the largest contributor of harmful DBPs formed from downstream
treatment (Norwood & Christman, 1987). The determination of absorbance of UV254 was
conducted using a Shimadzu mini-UV 1240® spectrophotometer. The spectrophotometer was
allowed to warm-up for 45 minutes prior to testing any sample and the wavelength was set to
UV at 254 nm. A fused silica-quartz cell with a path length of 10 mm was used because a plastic
cell absorbs UV at 254 nm. The spectrophotometer was calibrated to zero absorbance with a
reference blank of 3.3 mL de-ionized water in a clean quartz cell prior to sample analysis. Prior
to a sample being measured, approximately 1 mL of the sample was pipetted into the cell to
rinse it, and then discarded. Next, 3.3 mL of the sample was pipetted into the quartz cell and
polished with a Kim-wipe® tissue to remove any light scattering/absorbing residue on the cell
23
before analysis. The sample was then placed into the unit, the lid was closed, and the
absorbance measurement was recorded. All samples were discarded down the sink after
measurement. The spectrophotometer was re-zeroed with de-ionized water every 15 minutes
to maintain accuracy.
5.3 Alkalinity
Bicarbonate anions are also likely to participate in ion-exchange in conjunction with
DOC. Alkalinity was measured by first pipetting 20 mL of a sample along with 150 μL of
Bromocresol Green indicator into a 40 mL glass beaker with a magnetic stir bar. The beaker
was then placed on a magnetic stirrer beneath a 10 mL micro-burette filled with 0.005 N HCl.
Each sample was titrated from a blue colour to its end-point observed as a yellowish-green
colour. The exact colour was compared to a 50 mL Erlenmeyer flask filled with 100 mg/L
bicarbonate that had been previously titrated until 100 mg/L CaCO3 was calculated to use as a
reference. The flask was filled to the top and filled with plastic film to prevent CO2 from
changing the pH of the solution and affecting the colour. The calculation to convert volume of
titrant consumed to mg/L of bicarbonate, reported as mg/L CaCO3, is shown in equation (4)
where Vt is the volume of titrant consumed, N is the normality of the titrant, and Vs is the
volume of sample being titrated.
(4)
24
5.4 Atrazine
The concentration of atrazine pollutant present in all samples initially at 100 μg/L was
tested with HPLC. The apparatus used was the Dionex UltiMate 3000 using Chromeleon version
7.0 software. The column in the HPLC has a different affinity for different organics; an organic
molecule with a high affinity for the column will have a high retention time. Essentially organics
‘stick and release’ based on their affinity for the column. At the end of the column a UV
detector set to UV light at 280 nm detects the absorbance of atrazine in the sample. The
calibration curves to convert the area under the atrazine peak to concentration in μg/L are in
Appendix A. The elluent for the HPLC is 58% methanol, 2% acetic acid, and 40% de-ionized
water by volume at 22°C. The synthetic Suwannee River water was filtered through Whatman
No. 42 paper to remove suspended compounds greater than 2.5 μm that could obstruct the
column.
Prior to analysis, the HPLC oven temperature was set to 35°C; the UV lamp set to 280
nm; the elluent was allowed to purge one full cycle; the syringe was primed a total of 10 cycles;
the buffer loop was washed with 300 μL of 10% methanol and 90% de-ionized water cleaning
solution; and the needle was externally washed with the same cleaning solution. 1.7 mL of
each sample requiring analysis was pipetted into clear glass vials and sealed with a twist-on lid
with an injection membrane on top. The maximum retention time for each sample was set to 5
minutes and the atrazine peak appeared after approximately 3 minutes.
25
5.5 Molecular Weight Distribution
The molecular weight distribution of samples was determined through high-
performance size exclusion chromatography. The apparatus used was the Waters Alliance 2695
separation system and 2998 photodiode array detector at 260 nm using Empower 2 version 6.1
software. The column in the HPSEC has a high porosity; as a result, smaller molecules travel
slower though the column due to diffusion. The calibration curve to convert retention time to
apparent molecular weight (AMW) in Daltons can be found in Appendix A. The elluent for the
HPSEC was 0.05 M of Sodium Acetate that had been filtered through Whatman No. 42 filter
paper to remove impurities greater than 2.5 μm that could clog the porous column.
Prior to analysis the elluent and wash fluid levels were topped up. The degasser was
turned on and a wet prime was carried out for 0.2 min at 7.5 mL/min. Then the solvent was
equilibrated in the degasser chamber by setting a flow rate of 0.000 mL/min for 5 minutes.
Lastly, the column was equilibrated a minimum of 10 column volumes and the injector was
purged for six loop volumes. 1.7 mL of each sample was pipetted into clear glass vials with an
injection membrane on the lid. Each sample has a total analysis time of 15 minutes in the
HPSEC.
26
6. Results and Discussion
6.1 Batch Kinetics
All raw and worked data for batch kinetic trials and the fitting curve data are located in
Appendix B. Sample calculations are provided in Appendix C. All figures in section 6.1 with the
exception of apparent molecular weight distributions have error bars for one standard
deviation which are generally too small in most cases to stand out from the data points. The
initial concentration of DOC in solution was 7.5 mg/L for all kinetic experiments. Furthermore,
pH measurements using a pH meter revealed that pH was constant around pH 7 in kinetic trials.
6.1.1 Dissolved Organic Carbon
Figure 3 compares the removal of DOC from solution as a function of contact time with
SIR-22P-HP. Two independent trials were tested with 0 mg/L bicarbonate initially in one trial
and 50 mg/L bicarbonate initially in the other.
Figure 3: Comparison of the removal of DOC by SIR-22P-HP resin at 0 and 50 mg/L initial bicarbonate
concentrations.
0
1
2
3
4
5
6
7
8
0 100 200 300 400
DO
C (m
g/L)
Contact Time (min)
0 mg/L Bicarbonate Fit
50 mg/L Bicarbonate Fit
27
The kinetic data has been fitted with a fitting curve according to a first-order rate
equation (5). The equation utilizes a residual fitting error that is minimized to approximate the
best fit curve. Solver in excel was used to simultaneously minimize residual DOC (DOCr) and the
kinetic rate constant (k).
(5)
The initial amount of DOC removed in the presence of bicarbonate was similar during
the first 30 minutes of contact with SIR-22P-HP. The effects of alkalinity on the removal of DOC
became very apparent after a contact time greater than 30 minutes. The removal of DOC in the
presence of alkalinity at 50 mg/L bicarbonate was increased by approximately 6% after 6 hours.
The increased removal of DOC in the presence of alkalinity was not expected initially because
NOM and bicarbonate should compete for exchange sites on the resin. Consequently, the
increase in DOC removed was possibly due to the salting-out effect resulting from the increased
ionic strength of solution in the presence of alkalinity as discussed in section 3.2.
Table 3 shows the removal kinetic constant used to develop the fitting curve from
equation (5) and the initial removal rate of DOC as alkalinity is varied as determined from
equation (6). Equation (6) calculates the amount of DOC removed between 0 and 5 minutes of
contact time with the resin to estimate the initial removal rate of DOC.
(6)
28
Table 3: Removal kinetic constant and initial removal rate of DOC for SIR-22P-HP
The initial removal rate of DOC in the presence of an initial concentration of 50 mg/L
bicarbonate was slightly higher by 0.031 mg · L-1 · min-1 (or 11%) than without bicarbonate
present. This result helps confirm the salting-out theory because a faster initial removal rate of
NOM in the presence of bicarbonate means that a higher concentration of DOC was able to
participate in ion-exchange initially.
6.1.2 Absorbance of Ultra-violet Light
Figure 4 shows the same trend for UV254 absorbance as was observed for DOC removal.
The difference in absorbance of the solution becomes significant after 30 minutes of contact
time with SIR-22P-HP. The absorbance of the NOM solution decreased by an additional 7% after
6 hours in the presence of bicarbonate initially at 50 mg/L. Absorbance of UV254 reflects the
concentration of chromophoric compounds, typically aromatic (hydrophobic) compounds.
Therefore, a decrease of absorbance in the presence of alkalinity confirms that the removal of
hydrophobic NOM species is enhanced.
29
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0 100 200 300 400
Ab
sorb
ance
(1/c
m)
Contact Time (min)
0 mg/L Bicarbonate Fit
50 mg/L Bicarbonate Fit
Figure 4: Absorbance of UV254 of the liquid phase for treatment with SIR-22P-HP showing an enhanced
removal of chromophoric species at 50 mg/L of bicarbonate initially
The kinetic data has been fitted with a fitting curve according to the first-order rate
equation (7). The equation was used to determine the removal kinetic constant in the same
manner as described for equation (5) on page 27. Table 4 lists the removal kinetic constant of
absorbance of UV254 used to construct the fitting curve for the cases of bicarbonate initially at 0
and 50 mg/L
(7)
Table 4: Removal kinetic constant for absorbance of UV254 for SIR-22P-HP
30
The specific UV absorbance (SUVA) is another method of interpreting UV absorbance.
SUVA is the UV254 absorbance divided by the DOC concentration and is an indicator of the
relative concentration of hydrophobic species (Singer, 1999). SUVA is significant because it
indicates whether hydrophobic or hydrophilic species are being preferentially removed;
consequently, a preferential removal of hydrophobic species may indicate that the salting-out
effect is occurring. Figure 5 shows the SUVA of the liquid phase as a function of contact time
with SIR-22P-HP. The figure indicates that hydrophilic compounds are initially removed the
fastest (SUVA from 4.6 to 5.6 L · mg¯¹ · m¯¹) until an equilibrium removal between hydrophobic
and hydrophilic compounds occurs after 2 hours (constant SUVA). There is no significant
difference beyond error in the SUVA between the trials with and without bicarbonate which
neither supports nor contradicts the salting-out theory because more information is needed.
Figure 5: Specific UV Absorbance of the liquid phase showing a lower initial SUVA than after a long
contact time
0
1
2
3
4
5
6
7
0 100 200 300 400
SUV
A (L
/mg·
m)
Contact Time (min)
0 mg/L Bicarbonate
50 mg/L Bicarbonate
31
6.1.3 Alkalinity
Figure 6 shows the removal of bicarbonate from solution onto SIR-22P-HP as a function
of contact time for 50 mg/L of bicarbonate initially. The actual initial bicarbonate concentration
measured by titration was 47.5 mg/L, so the observed end-point colour of titration or the 0.005
N HCl titrant may have been slightly inaccurate. The figure shows a rapid initial removal of
bicarbonate from solution almost four times faster initially than DOC was removed in Figure 3
until approximately 7 mg/L bicarbonate remains in solution where removal discontinues. It was
expected that AERs would remove bicarbonate because bicarbonate is negatively charged, thus
it should participate in ion-exchange.
Figure 6: Removal of bicarbonate by SIR-22P-HP resin showing rapid initial removal of bicarbonate
The 100 mg of equivalent dry mass of SIR-22P-HP did not remove all bicarbonate
because the adsorption/ion-exchange of bicarbonate is a reversible process; furthermore, the
resin may not have enough exchange sites to remove all of the bicarbonate. The slight increase
32
of bicarbonate by 2 mg/L at 4 and 6 hours contact time may be outliers because the titration
method is not easily repeatable; furthermore, the samples had less time to absorb CO2 from the
head space of the vials they were stored in which would acidify and react with bicarbonate.
The kinetic data has been fitted with a fitting curve according to the first-order equation
(8). The equation was used to determine the removal kinetic constant in the same manner as
described for equation (5) on page 27. Table 5 lists the removal kinetic constant of absorbance
of UV254 used to construct the fitting curve for the cases of 0 and 50 mg/L initial concentration
of bicarbonate.
Table 5: Removal kinetic constant and initial removal rate of bicarbonate by SIR-22P-HP
6.1.4 Atrazine
The removal of atrazine by SIR-22P-HP is shown in Figure 7. The initial concentration of
atrazine measured by HPLC was 95 μg/L. The concentration of atrazine did not decrease as a
function of contact time with SIR-22P-HP. Because atrazine is non-ionic it does not participate
in ion-exchange and only had the opportunity to physically adsorb onto the resin. However, the
results indicate that atrazine did not physically adsorb onto the resin to any significant extent
observable beyond the error of the HPLC. Furthermore, the isotherm experiments for SIR-22P-
HP and MIEX also indicated that atrazine was not removed by either resin. Tests at higher
(8)
33
concentrations of atrazine where the error of the HPLC is less significant would need to be
conducted to observe a possible physical adsorption of atrazine.
Figure 7: Removal of atrazine by SIR-22P-HP resin showing that atrazine was not removed
6.1.5 Apparent Molecular Weight Distribution
The AMW distribution based on absorbance of chromophoric compounds in solution is
shown in Figure 8 for the initial condition at 0 minutes up to a contact time of 6 hours with SIR-
22P-HP at 0 mg/L bicarbonate. The figure shows a rapid decrease of absorbance within 30
minutes of contact. The absorbance continued to decrease with a slowing rate for the contact
time tested as expected as exchange sites become occupied. Moreover, the figure indicates
that low MW compounds are removed the fastest, followed by medium MW compounds. High
MW compounds are removed to a minimal extent only.
0
20
40
60
80
100
0 100 200 300 400
Atr
azin
e (μ
g/L)
Contact Time (min)
0 mg/L Bicarbonate
50 mg/L Bicarbonate
34
Figure 8: Apparent molecular weight distribution of NOM solution at 0 mg/L bicarbonate treated with
SIR-22P-HP showing the decrease in absorbance of low to medium MW species with time
The AMW distribution shown in Figure 9 for an initial concentration of 50 mg/L
bicarbonate for SIR-22P-HP shows the same trends as seen in Figure 8. However, the
absorbance after 6 hours was noticeably lower for medium MW compounds centered near
approximately 4000 Da.
35
Figure 9: Apparent molecular weight distribution of NOM solution at 50 mg/L bicarbonate treated
with SIR-22P-HP showing the decrease is absorbance of low to medium MW species with time
Figure 10 compares the initial AMW distribution to the final AMW distribution after 6
hours of contact time with SIR-22P-HP for both initial conditions of 0 mg/L bicarbonate and 50
mg/L bicarbonate. The figure shows a clear reduction of medium MW species between 1000
and 6000 Da for the case of 50 mg/L of bicarbonate in solution initially. This result agrees with
the salting-out theory because medium MW compounds had the opportunity to diffuse through
the interstitial resin space when they were previously excluded due to their larger size at 0
mg/L bicarbonate. The enhanced removal of UV absorbing, medium MW, DBP forming NOM
offers a practical advantage to the industry where the removal of these compounds is
enhanced in the presence of alkalinity which is common in groundwater supplies.
36
Figure 10: Apparent molecular weight distribution of NOM solution showing the reduction of medium
MW species was improved after six hours of contact with SIR-22P-HP at 50 mg/L bicarbonate than
without bicarbonate
6.2 Freundlich Adsorption Isotherms
The Freundlich adsorption isotherm model given in equation (9) is a model that relates
the equilibrium amount of adsorbate adsorbed by the solid resin phase, q, to the equilibrium
concentration of the adsorbate in the liquid phase, C. K and n are the Freundlich isotherm
constants.
(9)
37
For any given value of the exponent n, a high value for K indicates that the resin has a
greater capacity of adsorption sites. Moreover, for any given value of the constant K, an
exponent n that is high indicates that the resin has a high degree of affinity for the adsorbate.
(Cornelissen, et al., 2007)
The value of q can be determined from experimental results according to equation (10).
Xo is some initial parameter such as the initial DOC, absorbance, or bicarbonate in solution. Xf is
some final parameter such as the final DOC, absorbance, or bicarbonate in solution after
treatment at equilibrium with the IEX resin. V is the volume of solution and M is the dry mass
of resin in the solution.
Equation (9) can be linearized according to equation (11) in order to obtain the K value
from the intercept and the n value from the slope of a linear regression fit.
Raw and worked data for Freundlich isotherms can be found in Appendix B. Sample
calculations are available in Appendix C. The initial concentration of DOC in all trials was 7.5
mg/L
6.2.1 Dissolved Organic Carbon
Figure 11 shows the isotherm for DOC for treatment with SIR-22P-HP. The figure
indicates that bicarbonate does not affect the removal of DOC significantly at a high equilibrium
concentration of DOC in the liquid phase. Consequently, more than enough low to medium
(10)
(11) )log(1
)log()log( fCn
Kq
38
MW species were present to occupy most of the ion-exchange sites, so the salting-out effect
did not add an extra benefit and a situation could exist at high concentrations of DOC where
alkalinity is detrimental due to competition. However, at a low concentration of DOC in the
liquid phase the presence of bicarbonate allowed more DOC to adsorb in the resin at
equilibrium. This agrees with the results seen in section 6.1.1. This conclusion only applies to
the DOC range tested which was between 0.5 and 7.5 mg/L.
Figure 11: Freundlich Isotherm for the equilibrium distribution of DOC for SIR-22P-HP
The Freundlich isotherm K and n constant parameters are presented in Table 6. The
table also shows that the isotherms have a very high goodness of fit (R2) indicating that the
Freundlich isotherm is an exceptionally good fit for the data. As initial bicarbonate
concentration in solution increases, both the K and n constant parameters increase as well.
This indicates that more sites have become available for NOM to adsorb on the resin as well the
affinity between the resin and the DOC may be higher as alkalinity increases.
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
-0.5 0.0 0.5 1.0
log
(q, [
mg/
g])
log (DOC, [mg/L])
0 mg/L Bicarbonate
50 mg/L Bicarbonate
100 mg/L Bicarbonate
39
Table 6: Freundlich isotherm K and n constant parameters and R2 for DOC isotherms with SIR-22P-HP
Figure 12 shows the isotherm for the equilibrium distribution of DOC for MIEX. At a high
concentration of DOC in the liquid phase there appears to be no significant difference between
DOC adsorbed onto the resin in the presence of bicarbonate. However, the results for DOC at a
low concentration of DOC in the liquid are more ambiguous. The concentration of DOC initially
in solution was too low for the concentrations of MIEX used in the experiment.
0.0
0.5
1.0
1.5
2.0
2.5
-0.2 0.0 0.2 0.4 0.6 0.8 1.0
log
(q, [
mg/
g])
log (DOC, [mg/L])
0 mg/L Bicarbonate
50 mg/L Bicarbonate
100 mg/L Bicarbonate
Figure 12: Freundlich isotherm for the equilibrium distribution of DOC for MIEX
40
Figure 13 shows the DOC in the liquid phase as a function of the amount of MIEX added
to solution. The four different concentrations of resin used were 2, 20, 50, and 100 mg dry
mass of MIEX in 100 mL of NOM solution with 7.5 mg/L DOC initially. However, at 20 mg of
MIEX the resin appeared to fully remove as much DOC from solution as possible for MIEX
because the DOC concentration did not decrease as MIEX concentration increased. The
concentration of DOC was constant around approximately 1 mg/L for MIEX present above 20
mg. DOC was not removed to zero because some NOM is non-ionic and will not participate in
ion-exchange. Additionally, neutral NOM species did not appear to physically adsorb to MIEX to
a significant extent. Size exclusion for large MW species and a high obstruction of interstitial
pores by large compounds may also limit the amount of DOC capable of diffusing into the resin
structure and exchanging onto MIEX; however, more experiments are needed for MIEX to make
conclusions.
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
0 20 40 60 80 100
DO
C (m
g/L)
Dry Mass of MIEX (mg)
0 mg/L Bicarbonate
50 mg/L Bicarbonate
100 mg/L Bicarbonate
Figure 13: The amount of DOC removed as a function of the amount of MIEX added to solution shows
that nearly all DOC capable of being removed occurred with 20 mg of MIEX in the 100 mL solution
41
Bicarbonate did not appear to enhance DOC removal for MIEX which may confirm the
possibility that interstitial pores become clogged with large MW compounds easily for MIEX
(possibly because of its polymer backbone or macroporous structure rather than gel structure)
and competition for exchange sites by bicarbonate out-weighs the benefits of size reduction
from the salting-out effect.
6.2.2 Absorbance of Ultra-violet Light
Figure 14 shows the isotherm for absorbance for treatment with SIR-22P-HP. The
absorbance isotherm follows the same trends as in Figure 11 as expected. At a high
concentration of chromophoric compounds in solution the effects of increased alkalinity in
solution appear to be minimal for the range of DOC tested. Again, at lower concentrations of
chromophoric compounds in solution the effects of increased alkalinity in solution enhance the
adsorption of chromophoric species onto SIR-22P-HP.
Figure 14: Freundlich Isotherm for the equilibrium distribution of chromophoric UV absorbing
compounds for SIR-22P-HP
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
-2.0 -1.5 -1.0 -0.5 0.0
log(
q,
[1/g
·cm
])
log(Absorbance, [1/cm])
0 mg/L Bicarbonate
50 mg/L Bicarbonate
100 mg/L Bicarbonate
42
The Freundlich K and n constant parameters for the adsorption isotherm are
summarized in Table 7. The goodness of fit (R2) values are very high for the 50 and 100 mg/L
initial bicarbonate trials and acceptable for the 0 mg/L trial. Since K and n parameters are
coupled and not completely independent of each other, the opposite trends for K and n in
Table 7 as initial bicarbonate concentration is increased do not offer any insight as to the
affinity or capacity of the resin for chromophoric species.
Table 7: Freundlich isotherm K and n constant parameters and R2 for absorbance isotherms with SIR-
22P-HP
Figure 15 shows the absorbance isotherm for MIEX. The absorbance isotherm follows
the same trend as Figure 12. The figure confirms that the adsorption of chromophoric species
is not significantly different at different bicarbonate concentrations for high concentrations of
chromophoric species in solution because there is enough low to medium MW compounds to
occupy the ion-exchange sites. Furthermore, the effect of alkalinity on the adsorption of
chromophoric species at low concentrations of chromophoric species in solution is ambiguous
because only 20 mg of MIEX was needed to adsorb most of the chromophoric compounds in
solution (absorbance decreased from 0.346 cm-1 to less than 0.02 cm-1, or a 94% reduction).
43
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
-2.0 -1.5 -1.0 -0.5
log(
q,
[1/g
·cm
])
log(Absorbance, [1/cm])
0 mg/L Bicarbonate
50 mg/L Bicarbonate
100 mg/L Bicarbonate
Figure 15: Freundlich isotherm for the equilibrium distribution of chromophoric species, represented
as absorbance, for MIEX
Figure 16 compares the change in absorbance after treatment for both MIEX and SIR-
22P-HP. MIEX removed nearly all chromophoric compounds from solution with a low
concentration of MIEX; however, SIR-22P-HP required the advantage of the salting out effect
and a significantly higher concentration of resin to remove chromophoric compounds to the
same extent as MIEX. MIEX removed nearly all the chromophoric species from solution and to
a greater extent than DOC in general which may indicate that MIEX has a higher affinity for
chromophoric species than non-chromophoric species and further experiments are needed to
determine what characteristics between MIEX and chromophoric species make the affinity so
high. Consequently, the absorbance of the solution was so low after treatment with MIEX that
HPSEC analysis could not be performed to determine the AMW distribution.
44
0.00
0.10
0.20
0.30
0.40
0 20 40 60 80 100
Ab
sorb
ance
(cm
¯¹)
Dry Mass of MIEX (mg)
0 mg/L Bicarbonate - MIEX
50 mg/L Bicarbonate - MIEX
100 mg/L Bicarbonate - MIEX
0 mg/L Bicarbonate - SIR-22P-HP
50 mg/L Bicarbonate - SIR-22P-HP
100 mg/L Bicarbonate - SIR-22P-HP
Figure 16: Absorbance as a function of the amount of MIEX added to solution shows that MIEX
removes all of the chromophoric it can after 20 mg added and SIR-22P-HP was not as effective
6.2.3 Alkalinity
Figure 17 shows the alkalinity adsorption isotherm for treatment with SIR-22P-HP. The
slopes of the isotherms for both cases of initial bicarbonate concentration to DOC ratio are very
similar and indicate that different ratios of initial bicarbonate to DOC in solution do not affect
the adsorption of bicarbonate per gram of SIR-22P-HP significantly. This observation may be
because bicarbonate is small and is not subject to size exclusion in the resin; consequently,
there is a limit to the total number of ion-exchange sites available and bicarbonate does not
outcompete NOM for exchange sites. This conclusion is only valid for the range of DOC tested
which was between 0.5 and 7.5 mg/L.
45
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
0.5 1.0 1.5 2.0 2.5
log
(q, [
mg/
g])
Log (Bicarbonate, [mg/L])
50 mg/L Bicarbonate
100 mg/L Bicarbonate
Figure 17: Freundlich isotherm for the equilibrium distribution of bicarbonate showing that ratio
between bicarbonate and DOC in the liquid phase does not affect the amount of bicarbonate removed
by SIR-22P-HP
The Freundlich K and n parameters for the alkalinity isotherm for treatment with SIR-
22P-HP are presented in Table 8. The R2 values for the isotherms are very low which
demonstrates how much variability there is for titrating bicarbonate with only 20 mL of sample.
Error could be minimized in the method if samples much greater than 20 mL were titrated;
however, there was a limit to how much solution was leftover for titration.
Table 8: Freundlich isotherm K and n constant and R2 for alkalinity isotherms with SIR-22P-HP
Figure 18 shows the alkalinity isotherm for treatment with MIEX at 50 mg/L and 100
mg/L initial bicarbonate concentrations. A high initial ratio of bicarbonate to DOC in solution
46
resulted in lower amounts of bicarbonate adsorbed onto MIEX. The expected result would be
that a higher ratio initially would either enhance or not affect the adsorption of bicarbonate.
However, the result shown in Figure 18 indicates otherwise, so further experiments with less
error would be needed to determine why a higher initial ratio of bicarbonate to DOC resulted in
less bicarbonate being adsorbed than with a lower ratio.
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
1.0 1.2 1.4 1.6 1.8 2.0 2.2
log(
q,
[mg/
g])
log(Bicarbonate, [mg/L])
50 mg/L Bicarbonate
100 mg/L Bicarbonate
Figure 18: Freundlich isotherm for equilibrium distribution of bicarbonate in an NOM solution treated
with MIEX
The Freundlich K and n constants for the alkalinity isotherm for treatment with MIEX are
presented in Table 9. The R2 values are still unacceptably low for the isotherm profile indicating
that there is substantial error in the titration method used to determine alkalinity.
47
Table 9: Freundlich isotherm K and n constant parameters and R2 for alkalinity isotherms with MIEX
Figure 19 compares the alkalinity isotherms for treatment with both MIEX and SIR-22P-
HP. The results for which resin adsorbs more alkalinity for given equilibrium concentrations of
bicarbonate in the liquid phase are mixed and inconclusive.
1.4
1.6
1.8
2.0
2.2
2.4
2.6
0.5 1.0 1.5 2.0 2.5
log
(q, [
mg/
g])
Log (Bicarbonate, [mg/L])
50 mg/L Bicarbonate - MIEX
100 mg/L Bicarbonate - MIEX
50 mg/L Bicarbonate - SIR-22P-HP
100 mg/L Bicarbonate - SIR-22P-HP
Figure 19: Freundlich isotherm for the equilibrium distribution of bicarbonate for both SIR-22P-HP and
MIEX showing MIEX generally has a weaker affinity for bicarbonate
Figure 20 clearly shows that SIR-22P-HP removes bicarbonate from solution to a greater
extent than MIEX does. It is apparent that as the concentration of MIEX is increased in solution
the removal of bicarbonate is increased. Therefore, there are not an abundance of exchange
48
sites available within MIEX since it takes more MIEX to remove the same amount of
bicarbonate that SIR-22P-HP could with less resin.
0
20
40
60
80
100
0 50 100
Bic
arb
on
ate
(mg/
L)
Dry Mass of Resin (mg)
50 mg/L Bicarbonate - MIEX
100 mg/L Bicarbonate - MIEX
50 mg/L Bicarbonate - SIR-22P-HP
100 mg/L Bicarbonate - SIR-22P-HP
Figure 20: The amount of bicarbonate removed as a function of the amount of resin added to solution
shows that SIR-22P-HP has a much greater equilibrium removal of bicarbonate than MIEX
6.3 Alkalinity Experiments
6.3.1 Dissolved Organic Carbon
Three separate experiments shown in Figure 21 were performed, in triplicate trials to
obtain error ranges, in order to help confirm the salting-out theory. Alkalinity experiments
were only performed on SIR-22P-HP. Resin A was freshly regenerated that initially had 7.5
mg/L DOC and 100 mg/L of bicarbonate in solution. Resin B was freshly regenerated that
initially had only 7.5 mg/L of DOC. Resin C first treated a solution with an initial concentration
of only bicarbonate at 100 mg/L. Afterwards, resin C was then treated with a solution
containing 7.5 mg/L of DOC initially.
49
2.2
2.3
2.4
2.5
2.6
2.7
2.8
A (Fresh) B (Fresh) C (Treated Bicarbonate First)
DO
C (
mg
/L)
Resin
Figure 21: Box plot of the DOC in solution after treatment with SIR-22P-HP where: Resin A had both
NOM and bicarbonate in solution; Resin B had only NOM in solution; Resin C had first bicarbonate in
solution and then subsequently treated an NOM only solution
After treatment with SIR-22P-HP for 2 hours, Resin A had the greatest removal of DOC.
This result was expected and supports the salting-out theory because it was expected that the
high ionic strength due to bicarbonate in solution may have caused the hydrophobic NOM in
solution to compress in size and be more easily removed by IEX. The error bars for the trials
performed on resin B and C indicate that there is no statistical difference between the two
experiments. However, the difference in medians between the two trials may be explained by
the fact that since bicarbonate first adsorbed onto Resin C, some of the exchange sites that
NOM could have occupied were unavailable. This would mean that chlorine would dissociate
easier from the resin than bicarbonate would, possibly due to size or charge differences.
50
6.3.2 Absorbance of Ultra-violet Light
Figure 22 shows the absorbance of UV254 for the same experiment shown in Figure 21
and it follows the same trends. UV254 absorbance decreased the most when both NOM and
bicarbonate were together in solution with SIR-22P-HP as seen with Resin A than when NOM or
bicarbonate was adsorbed separately. Directly comparing resin A to resin B, resin A had the
advantage of the salting-out effect whereas resin B did not. Additionally, when resin C first
treated a solution containing 100 mg/L bicarbonate and then treated a solution containing 7.5
mg/L DOC, the amount of DOC removed was not as high as in case B where DOC was removed
by a fresh resin. This supports the idea that bicarbonate does not reversibly dissociate from the
resin as easily as chlorine ions in order to free up exchange sites for DOC. These results support
the conclusions made in section 6.3.1.
0.13
0.14
0.15
0.16
0.17
A (Fresh) B (Fresh) C (Treated Bicarbonate First)
Ab
sorb
ance
(cm
¯¹)
Resin
Figure 22: Box plot of the absorbance of chromophoric compounds in solution after treatment with
SIR-22P-HP where: Resin A had both NOM and bicarbonate in solution; Resin B had only NOM in
solution; Resin C had first bicarbonate in solution and subsequently treated an NOM only solution
51
6.3.3 Alkalinity
Figure 23 shows the opposite trend for bicarbonate than for DOC and absorbance as
seen in Figure 21 and Figure 22. When resin A treated the solution with DOC at 7.5 mg/L and
bicarbonate initially at 100 mg/L, the amount of bicarbonate removed from solution onto the
resin was 7% less than for the case with resin B where only bicarbonate was in solution.
Therefore, the presence of NOM in solution reduced the amount of bicarbonate that could be
removed because NOM and bicarbonate compete for the same sites. Alkalinity does not
outcompete NOM for exchange sites either since Resin A simultaneously removed 68% of the
DOC and 81% of the bicarbonate. For the case with Resin C where DOC was first removed from
a solution onto the resin then a solution with 100 mg/L bicarbonate was treated, the amount of
bicarbonate removed from solution was more than in resin A and less than for resin B. This
result was also expected because some of the DOC reversibly dissociated from the resin and
exchanged with bicarbonate. The DOC of the bicarbonate solution (with 0 mg/L DOC initially)
after removing bicarbonate was 0.4 mg/L.
52
11
13
15
17
19
A (Fresh) B (Fresh) C (Treated NOM First)
Bic
arb
on
ate
(m
g/L
)
Resin
Figure 23: Box plot of the bicarbonate in solution after treatment with SIR-22P-HP where: Resin A had
both NOM and bicarbonate in solution; Resin B had only bicarbonate in solution; Resin C treated first
an NOM solution and then subsequently treated a bicarbonate only solution
53
7. Future Work
7.1 Solution Ionic Strength and Alkalinity
The results from the experiments in this research have raised a lot of new questions
regarding alkalinity and the salting-out effect and its effects on resins of different types. In this
research, SIR-22P-HP, a Type I, SBA, polystyrene, with a large diameter (between 0.297 mm to
0.853 mm in) was most extensively studied with bicarbonate; however, the effect of alkalinity
on resins with different polymer structures and characteristics is essential. Additionally, more
conclusive experiments to confirm the salting-out effect need to be conducted by varying the
ionic strength of solutions to be treated with compounds other than bicarbonate.
7.2 Regeneration
It was observed that the bench-scale regeneration procedure was inefficient in terms of
chemical requirements and its ability to reversibly remove NOM from resins to be regenerated
as determined from TOC analysis and the colour of the resin. Research needs to be conducted
on the efficacy of the bench-scale resin regeneration procedure by quantifying the reduction in
performance of a resin after several NOM solution treatments and regeneration cycles.
7.3 Atrazine
Atrazine was not removed by either SIR-22P-HP or MIEX to a significant extent beyond
the error of the HPLC. A more extensive study with atrazine at a higher concentration than 100
μg/L should be conducted in order to support or reject evidence from literature that a small
fraction of atrazine could be removed from solution by physical adsorption onto resins.
54
7.4 Magnetic Ion-Exchange
Preliminary experiments performed on MIEX® in this research along with literature
research indicate that MIEX® is extremely effective at removing DOC from solution, especially
chromophoric compounds. The isotherm tests indicated that experiments to quantify the
effectiveness of MIEX® should be done with lower concentrations of resin in a NOM solution to
be treated since 20 mg of dry MIEX® was enough resin to remove nearly all of the 7.5 mg/L
NOM in a 100 mL solution. MIEX® has a small average diameter, so the salting-out effect due
the presence of alkalinity on MIEX should be studied further. Additionally, the possibility that
the interstitial space within MIEX is easily obstructed by high MW species needs to be studied
by testing source waters with a lower fraction of high MW species than Suwannee River water.
It is recommended with MIEX that jar tests be performed rather than using a shaker/incubator
because MIEX slowly accumulated along the sides of the beaker during shaking. This effectively
removed some MIEX from solution continuously during shaking. However, this was not
observed for SIR-22P-HP. Moreover, Orica Watercare recommends jar test experiments and
provides a well-tested procedure. The jar test was not performed because experiments were
already performed on SIR-22P-HP using the shaking method at 200 rpm; thus, the difference
between the two methods would have affected the comparability of results from treatment
with the two resins.
55
8. References
Amy, G., & Cho, J. (1999). Interactions Between Natural Organic Matter (NOM) and
Membranes: Rejection and Fouling. Water Science Technology 40 , 131-139.
Benotti, M. J., Trenholm, R. A., Holady, J. C., Stanford, B. D., & Snyder, S. A. (2009).
Pharmaceuticals and Endocrine Disrupting Compounds in U.S. Drinking Water. Envronmental
Science Technology 43 , 597-603.
Boggs, S., Livermore, G., & Seitz, M. G. (1985). Humic Macromolecules in Natural Water. Rev.
Macromol. Chem. Phys. C25 , 599-657.
Bolto, B., Dixon, D., Eldridge, R., & King, S. (2004). Ion Exchange for the Removal of Natural
Organic Matter. Reactive & Functional Polymers 60 , 171-182.
Bolto, B., Dixon, D., Eldridge, R., King, S., & Linge, K. (2002). Removal of Natural Organic Matter
by Ion Exchange. Water Research 36 , 5057-5065.
Boyer, T. H., & Singer, P. C. (2007). Stoichiometry of Removal of Natural Organic Matter by Ion
Exchange. Environmental Science and Technology 42 , 608-613.
Brattebo, H., Odegaard, H., & Halle, O. (1987). Ion Exchange for the Removal of Humic Acids in
Water Treatment. Water Resources 21 , 1045-1052.
Christman, R. F., & Ghassemi, M. (1966). Chemical Nature of Organic Color in Water. Water
Works Association 58 , 723.
Cornelissen, E., Moreau, N., Siegers, W. G., Abrahamse, A. J., Rietveld, L. C., Grefte, A., et al.
(2007). Selection of Anionic Exchange Resins for Removal of Natural Organic Matter (NOM)
Fractions. Water Research 42 , 413-423.
Croue, J. P., Violleau, D., & Legube, B. (1999). Removal of Hydrophobic and Hydrophilic
Constituents by Anion Exchange Resin. Water Science Technology 40, No 9 , 207-214.
Eggertson, L. (2008). Investigative Report: 1766 Boil-Water Advisories Now in Place Across
Canada. Canadian Medical Association Journal 178 , 10.
Fearing, D. A., Banks, J., Guyetand, S., Monfort-Eroles, C., Jefferson, B., Wilson, D., et al. (2004).
Combination of Ferric and MIEX for the Treatment of a Humic Rich Water. Water Research 38 ,
2551-2558.
56
Fu, P. -K., & Symons, J. M. (1990). Removing Aquatic Organic Substances by Anion Exchange
Resins. J. AWWA 82 , 70-77.
Graham, T. L. (2010). Delineation of the Most Effective Ion Exchange Resin for the Removal of
Natural Organic Matter as a Pre-treatment Step to Improve the Efficacy of the UV/H2O2
Advanced Oxidation Process. Vancouver: UBC.
Heijman, S. V., Van Paassen, A. M., Van der Meer, W. J., & Hopman, R. (1999). Adsorptive
Removal of Natural Organic Matter During Drinking Water Treatment. Water Science
Technology , 183-190.
Humbert, H., Gallard, H., Jacquemet, V., & Croue, J. P. (2007). Combination of Coagulation and
Ion Exchange for the Reduction of UF Fouling Properties of a High DOC Content Surface Water.
Water Research 41 , 3803-3811.
Humbert, H., Gallard, H., Suty, H., & Croue, J. P. (2005). Performance of Selected Anion
Exchange Resins for the Treatment of a High DOC Content Surface Water. Water Research 39 ,
1699-1708.
Mergen, M. R., Jefferson, B., Parsons, S. A., & Jarvis, P. (2007). Magnetic ion-exchange resin
treatment: Impact of water type and resin use. Water Research 42 , 1977-1988.
Montgomery, J. M. (1985). Water Treatment Principles and Design. JMM Consulting Engineers
Inc. Toronto: John Wiley and Sons.
Norwood, D. L., & Christman, R. F. (1987). Structural Characterization of Aquatic Humic Material
2. Phenolic Content and its Relationship to Chlorination Mechanism in an Isolated Squatic Fulvic
Acid. Environmental Science Technology 21 , 791-798.
Orica Watercare: MIEX Resins. (2010). Retrieved December 6, 2010, from Orica Watercare Ltd.:
http://www.miexresin.com/index.asp?page=9
Resintech SIR-22P-HP. (2010). Retrieved March 31, 2011, from Excel Water:
http://www.excelwater.com/downloads/tannin.pdf
Rook, J. J. (1974). Formation of Haloforms During Chlorination of Natural Waters. Water
Treatment Examination 23 , 234-243.
57
Sarathy, S., & Mohseni, M. (2007). The Impact of UV/H2O2 Advanced Oxidation on Molecular
Size Distribution of Chromophoric Natural Organic Matter. Environmental Science and
Technology 41 , 8315-8320.
Singer, P. C. (1999). Humic Substances as Precursors for Potentially Harmful Disinfection By-
products. Water Science and Technology 40 , 25-30.
Tan, Y., & Kilduff, J. E. (2007). Factors Affecting Selectivity During Dissolved Organic Matter
Removal by Anion-Exchange Resins. Water Research 41 , 4211-4221.
Tan, Y., Kilduff, J. E., Kitis, M., & Karanfil, T. (2005). Dissolved Organic Matter Removal and
Disinfection Byproduct Formation Control Using Ion Exchange. Desalination 176 , 189-200.
Van der Kooij, D. (2003). Biodegradable Compounds and Biofilm Formation in Water Treatment
and Dsitribution. Sapporo: Hokkaido University Press.
58
Appendix A – Calibration Data
Figure 24: Atrazine calibration curve for HPLC analysis to convert area under the atrazine peak to a
concentration between 0 to 750 μg/L
Figure 25: Atrazine calibration curve for HPLC analysis to convert area under the atrazine peak to a
concentration between 1000 to 10000 μg/L
59
Figure 26: Molecular weight distribution calibration curve for HPSEC analysis to convert retention time
to molecular weight
Table 10: Determination of the dry to wet mass ratio of SIR-22P-HP and MIEX
60
Appendix B – Raw and Worked Data
B.1 Batch Kinetics
Table 11: Raw and worked data for batch kinetic trial with SIR-22P-HP for 0 mg/L of bicarbonate initially
61
Table 12: Raw and worked data for batch kinetic trial with SIR-22P-HP for 50 mg/L of bicarbonate initially
62
B.1.1 Kinetic Fitting Curves
Table 13: DOC Fitting Function for SIR-22P-HP at 0 mg/L Bicarbonate
Table 14: DOC Fitting Function for SIR-22P-HP at 50 mg/L Bicarbonate
63
Table 15: Absorbance Fitting Function for SIR-22P-HP at 0 mg/L Bicarbonate
Table 16: Absorbance Fitting Function for SIR-22P-HP at 50 mg/L Bicarbonate
64
Table 17: Alkalinity Fitting Function for SIR-22P-HP at 50 mg/L Bicarbonate
B.2 Freundlich Isotherms
Table 18: Initial values for absorbance, DOC, and bicarbonate for tests with SIR-22P-HP and MIEX
65
Table 19: Raw and worked data for SIR-22P-HP isotherm trial at 0 mg/L initial bicarbonate concentration
Table 20: Raw and worked data for SIR-22P-HP isotherm trial at 50 mg/L initial bicarbonate concentration
66
Table 21: Raw and worked data for SIR-22P-HP isotherm trial at 100 mg/L initial bicarbonate concentration
Table 22: Raw and worked data for MIEX isotherm trial at 0 mg/L initial bicarbonate concentration
67
Table 23: Raw and worked data for MIEX isotherm trial at 50 mg/L initial bicarbonate concentration
Table 24: Raw and worked data for MIEX isotherm trial at 100 mg/L initial bicarbonate concentration
68
B.3 Alkalinity Experiments
Table 25: Raw and worked data for alkalinity experiments with SIR-22P-HP
Table 26: Statistical parameters as determined using built in Excel formulas to construct box plots
69
Appendix C – Sample Calculations
C.1 Kinetic Fitting Functions
Calculation is for SIR-22P-HP DOC kinetic trial after 1 minute at 50 mg/L bicarbonate
The equation is:
Where:
DOCfit = Fitted DOC concentration (mg/L)
DOCr = Residual DOC concentration (mg/L)
DOCo = Initial DOC concentration (mg/L)
k = removal kinetic constant (min-1)
t = time (min)
;
;
The error was calculated as:
;
;
;
Procedure for determining k:
1. Take the sum of the error column
2. Arbitrarily enter a value for k and DOCr that is greater than 0
3. Run Excel solver to numerically minimize the total error by manipulating k and DOCr
a. Set a constraint where k and DOCr must be greater than 0, if required
The calculations for absorbance fit and alkalinity fit follow the same procedure as the DOC fit
calculation
70
C.2 Initial Removal Rate for Batch Kinetics
Calculation is for SIR-22P-HP DOC kinetic trial between 0 to 5 minutes at 50 mg/L bicarbonate
The equation is:
Where:
DOCt=0 = DOC concentration at 1 minute (mg/L)
DOCt=5 = DOC concentration at 3 minutes (mg/L)
t0 = 0 minutes
t5 = 5 minutes
t = time (min)
71
C.3 Freundlich Isotherms Parameters
Calculation is for SIR-22P-HP DOC isotherm trial at 20 mg dry mass resin at 50 mg/L bicarbonate
The equation is:
Where:
q = amount of adsorbate adsorbed into 1 g of resin
Xo = Initial value of adsorbate
Xf = Final value of adsorbate
V = Volume of liquid phase (L)
M = mass of resin (g)
Thus:
Log10(q) values can be plotted versus log (Xf) values to obtain an isotherm. Then, a linear
regression yields values in the form of:
Taking 10^(intercept) and 1/(slope) results in the K and n values, respectively
)log(1
)log()log( fCn
Kq
72
C.4 Alkalinity
Calculation is for SIR-22P-HP alkalinity kinetic trial after 1 minute at 50 mg/L bicarbonate
The equation is:
Where:
Vt = Volume of titrant consumed (mL)
N = Normality of titrant
Vs = Volume of sample being titrated (mL)