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

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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



4.5 Alkalinity Experiments ......................................................................................................... 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



6.2.3 Alkalinity ....................................................................................................................... 44

6.3 Alkalinity Experiments ......................................................................................................... 49



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.


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.


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.


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.


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


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)



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


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


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


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.


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


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


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



0 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


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


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])





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)





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


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


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

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Fu, P. -K., & Symons, J. M. (1990). Removing Aquatic Organic Substances by Anion Exchange

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Natural Organic Matter as a Pre-treatment Step to Improve the Efficacy of the UV/H2O2

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Heijman, S. V., Van Paassen, A. M., Van der Meer, W. J., & Hopman, R. (1999). Adsorptive

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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

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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

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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

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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

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Table 12: Raw and worked data for batch kinetic trial with SIR-22P-HP for 50 mg/L of bicarbonate initially

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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

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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

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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

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Table 19: Raw and worked data for SIR-22P-HP isotherm trial at 0 mg/L initial bicarbonate concentration


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Table 22: Raw and worked data for MIEX isotherm trial at 0 mg/L initial bicarbonate concentration

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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

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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

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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)

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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

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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)

Thesis on Ion Exchange - Ken McClure

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