Assessment of synergistic effect of UV h2o2 integrated disinfection process

ASSESSMENT OF SYNERGISTIC EFFECT OF UV/HYDROGEN
PEROXIDE INTEGRATED DISINFECTION PROCESS

SOWPATI JAYAKER

NATIONAL UNIVERSITY OF SINGAPORE
2010


ASSESSMENT OF SYNERGISTIC EFFECT OF UV/ HYDROGEN
PEROXIDE INTEGRATED DISINFECTION PROCESS

SOWPATI JAYAKER
B. Sc (Chemical Technology),
Loyola Academy (affiliated to Osmania University), India.

A THESIS SUBMITTED
FOR THE DEGREE OF MASTER OF ENGINEERING
DIVISION OF ENVIRONMENTAL ENGINEERING AND SCIENCE
NATIONAL UNIVERSITY OF SINGAPORE
2010


ACKNOWLEDGEMENTS
First of all, I would like to thank the Lord, God and Almighty, whom I personally believe
is supreme and sovereign. It is He that I believe has strengthened me and helped me to
persevere through all the thick and thin and has placed me in the midst of all the people
that I have mentioned in this acknowledgement.

I would like to record my earnest gratitude to A/P Hu Jiangyong for her guidance,
supervision and direction from the very early stage of this research. Her wide-ranging

expertise made her a constant source of ideas and her passion in drinking water treatment
has exceptionally inspired and enriched my growth as a student and as a researcher. Most
importantly, she provided me unwavering encouragement and support in various ways
especially when I was in difficult times. One could not wish for a more considerate and
more thoughtful supervisor. I am indebted to her in many ways.

I could never thank the staff of Water Science and Technology Laboratory enough,
including S.G. Chandrasegaran, Michael Tan, Tan Xiaolan, Lee Leng Leng, and Tan
Hwee Bee for their kind assistance and technical support in ensuring the successful
completion of this study. I would also like to thank all my fellow post-graduate students,
especially Guo Huiling, Elaine Quek, Mark Goh Voon Wei and research staff Chu
Xiaona, Dr. Park Se Keun for their advice and company that alleviated my work stress in
the laboratory. I would not have made it this far without all of them.

i


I would like to thank the church that has been so loving and caring, especially all the
friends in the church and the care group members for their continual prayers,
encouragement and not only moral but also practical support when I and my family was in
need of help. The support from the church during my daughter’s birth was extraordinary
and unforgettable.

I would like to thank my wife, Sheeba, who has sacrificed a lot for the sake of my studies.
This thesis would not have come to completion without her constant encouragement and
support. Thank you my love. I would like to thank my sweet little daughter, Jayneeta
whom God has blessed us with. She has been our stress relief in the times of distress.

Finally, I would like to thank everybody who was important to the successful realization
of my thesis, as well as expressing my apology that I could not mention personally one by

one.

ii


ACKNOWLEDGMENTS
SUMMARY

i
vii

LIST OF FIGURES

x

LIST OF TABLES

xii

NOMENCLATURE

xiii

CHAPTER 1: INTRODUCTION

1

1.1

Drinking Water Disinfection

1

1.2

Selection of Disinfection Strategy

3

1.3

Disinfectants as Oxidants: A Better Strategy

6

1.4

Research Objectives

8

1.5

Thesis Organization

8

CHAPTER 2: LITERATURE REVIEW

9

2.1

Alternative Disinfectants

2.2

UV Disinfection

10

2.2.1

Use of UV light in drinking water treatment

12

2.2.2

UV sources and lamp technologies

15

2.2.2.1 Mercury emission lamps

16

2.2.2.2 Low pressure lamps

18

2.2.2.3 Medium pressure lamps

19

Advanced Oxidation Processes (AOPs)

20

2.3.1

Principles of AOPs

22

2.3.1.1 Peracetic acid/UV radiation (PAA/UV)

22

2.3.1.2 Hydrogen Peroxide/UV radiation (H2O2/UV)

23

2.3.1.3 Ozone/UV radiation (O3/UV)

23

2.3.1.4 Ozone/H2O2 (O3/H2O2)

24

Applications of AOPs

27

2.3

2.3.2
2.4

Hydroxyl (*OH) Radicals
2.4.1

2.4.2

9

28

*

29

2.4.1.1 *OH radical scavenging reactions

31

*

33

OH radical chemistry

OH radicals and disinfection

iii


2.4.3
2.5

2.6

*

OH radicals detection and quantification

34

Integrated UV Disinfection Systems

38

2.5.1

UV/PAA

39

2.5.2

UV/O3

40

2.5.3

UV/H2O2

42

2.5.3.1 UV/H2O2 synergy

44

Effect of Water Matrix on UV/H2O2 Integrated Disinfection

45

2.6.1

Effect of organic matters

45

2.6.2

Effect of turbidity

47

2.6.3

Effect of anions

49

CHAPTER 3: MATERIALS AND METHODS

52

3.1

Real Water Characteristics

52

3.2

Chemical Reagents and UV Sources

53

3.2.1

3.3

3.4

Emission spectra of LP, MP and FMP and absorbance spectrum

for H2O2

56

3.2.2

Operational parameters and sample water characteristics

56

3.2.3

Sample preparation

57

Disinfection Experiments

58

3.3.1

Preparation and enumeration of microorganisms

59

3.3.2

Hydrogen peroxide (H2O2) disinfection

60

3.3.2.1 H2O2 estimation

62

3.3.3

UV irradiation

62

3.3.4

UV disinfection

66

3.3.5

UV/H2O2 disinfection

66

OH Radical Estimation Experiments

67

*

3.4.1

Fenton’s reaction

68

3.4.1.1 Estimation of residual H2O2 concentration

69

3.4.1.2 Determination of phenol degradation rate constant

70

3.4.1.3 Determination of *OH radical concentration

72

iv


CHAPTER 4: RESULTS AND DISCUSSION
4.1

Determination of *OH Radical Rate Constant for Phenol Degradation

4.2

Disinfection Performance of MS2 Coliphage by UV/H2O2 Integrated
System

4.2.1

4.2.2

4.2.3

4.2.4

4.2.5
4.3

73
73

75
Effect of UV dose on MS2 log inactivation

75

4.2.1.1 LPUV/H2O2

75

4.2.1.2 MPUV/H2O2

76

4.2.1.3 FMPUV/H2O2

77

Effect of H2O2 concentration on MS2 log inactivation

79

4.2.2.1 LPUV/H2O2

79

4.2.2.2 MPUV/H2O2

80

4.2.2.3 FMPUV/H2O2

80

Synergistic effect of UV/H2O2 integrated disinfection

82

4.2.3.1 LPUV/H2O2

82

4.2.3.2 MPUV/H2O2

83

4.2.3.3 FMPUV/H2O2

84

*

84

4.2.4.1 LPUV/H2O2

84

4.2.4.2 MPUV/H2O2

89

4.2.4.3 FMPUV/H2O2

91

OH radical concentration of UV/H2O2 integrated disinfection

*

Synergy and OH radical correlation for different lamp sources 92

Effect of Synthetic Water Matrix on MPUV/H2O2 Integrated System

94

4.3.1

Effect of organic matter

94

4.3.1.1 MS2 log inactivation

95

4.3.1.2 Synergy

96

4.3.1.3 *OH radical concentration

98

Effect of turbidity

99

4.3.2.1 MS2 log inactivation

99

4.3.2

4.3.3

4.3.2.2 Synergy

101

4.3.2.3 *OH radical concentration

102

Effect of bicarbonate ion ( HCO3− )

103
v


4.3.4

4.3.3.1 MS2 log inactivation

103

4.3.3.2 Synergy

105

4.3.3.3 *OH radical concentration

106

Effect of chloride ion ( Cl − )

107

4.3.4.1 MS2 log inactivation

107

4.3.4.2 Synergy

109

*

110

4.3.4.3 OH radical concentration
4.4

Effect of Real Water Matrix on MPUV/H2O2 Integrated System

111

4.4.1

MS2 log inactivation

111

4.4.2

Synergy

114

4.4.3

*

116

OH radical concentration

CHAPTER 5: CONCLUSIONS AND RECOMMENDATIONS

117

5.1

Conclusions

117

5.2

Recommendations

121

REFERENCES

123

PUBLICATIONS

138

vi


SUMMARY
Advanced oxidation processes (AOPs) were one among the suggested options to tackle
the problems encountered with chlorine disinfection. Their ability to deal with
disinfection and decontamination at one go was the key for such a consideration.
Especially, the Ultra violet light/hydrogen peroxide (UV/H2O2) process has received
particular attention for potential application in treatment of drinking water. The combined
action of UV/H2O2, which is inactivating microorganisms as well as oxidizing organic
matter, was successfully demonstrated by a few researches. This ability to minimize the
DBP precursors and to oxidize certain micro pollutants and at the same time to be able to
provide disinfection are attributed to the hydroxyl (*OH) radicals produced. *OH radicals
are generated by photolysis of the peroxidic bond when H2O2 absorbs UV light directly.
Use of short wave UV wavelengths (200–280 nm) was reported to achieve the most
efficient *OH radical yields. Synergistic effect reported for UV/H2O2 was one of the key
benefits especially for disinfection. UV/H2O2 disinfection comprises of two modes of
inactivation, the first being UV and the second being *OH radical mediated. It is generally
agreed that *OH radicals generated play a key role in synergy. However, there have been
reports where decreased *OH radical concentration did not show a corresponding decrease
in the log inactivation, but rather an increase in log inactivation. This phenomenon was
observed in UV/H2O2 treatment of surface water and it was attributed to the production of
other reactive oxygen species (ROS) and also to the *OH radical generating action of the
natural organic matter (NOM), which are generally considered as scavengers. It was also
reported that the *OH radical production was dependent on the UV lamp source that was
used. So the log inactivation, synergy and the *OH radical concentration are dependent on

vii


the UV light source and the water matrix. Thus, in this study three different light sources
were used, which are low pressure UV (LP), medium pressure UV (MP) and filtered
(>295 nm) medium pressure UV (FMP). MP was selected for further study as this showed
the highest potential to produce *OH radicals.

Log inactivation of MS2 coliphage, for UV alone was as expected, the highest for MP and
the lowest for FMP. H2O2 addition enhanced the log inactivation differently for the three
lamp sources. There was no significant reduction beyond 10 mg/L H2O2 for LP, but there
was generally an increasing log inactivation trend for MP and FMP with increase in H2O2.
With an increase in the UV dose, synergistic effect decreased for LP, increased for FMP
and there was no clear trend for MP. The highest concentration of *OH radicals were
produced for MP and the lowest for FMP. A correlation between synergy and *OH radical
concentration showed that the linear correlation for MP was the highest, around 74.8%,
for LP was around 23.6% and for FMP was the lowest, around 16.4%.

The impact of the synthetic water matrix and the real water matrix was assessed by
comparing to the results obtained for deionised (DI) water using MPUV/H2O2 system.
With the increase in the TOC, there was a gradual and significant impact on the log
inactivation for UV alone. However, H2O2 addition helped in countering this negative
effect of TOC. In general TOC positively influenced the synergy and negatively
influenced *OH radical production. The increase in the turbidity reduced the log
inactivation slightly. H2O2 addition did not help much in countering the slightly negative
effect of turbidity. In general turbidity affected both synergy and *OH radical production

viii

negatively. There was an enhancement in the log reduction for UV alone in the presence
of bicarbonate ions ( HCO3− ) and H2O2 addition narrowed down the enhancement
achieved. HCO3− ions negatively influenced both synergy and *OH radical production.
There was an enhancement in the log reduction for UV alone in the presence of chloride
ions ( Cl − ) and H2O2 addition narrowed down the enhancement achieved only slightly in
comparison to HCO3− . Cl − ions in general negatively influenced synergy with occasional
positive effects and negatively influenced *OH radical production. There was only a slight
impact of the real water matrix on log inactivation for UV alone. Log inactivation
sustained and increased with H2O2 addition. Real water matrix positively influenced
synergy only at 30 mg/L H2O2 and negatively influenced *OH radical production.

ix


LIST OF FIGURES
Figure 2.1 Electromagnetic spectrum

11

Figure 2.2 Energy emission when electrons return from activated state to original state 16
Figure 2.3 Typical Emission spectrum of low pressure mercury lamps

19

Figure 2.4 Typical emission spectrum of medium pressure mercury lamps

20

Figure 2.5 Reaction of *OH radical with organic substrate, M in the
presence of HCO3- ion

32

Figure 2.6 Composition of the CO2/(H2CO3)/ HCO3-/CO32-/H2O
system as a function of pH

33

Figure 3.1 Calibration curve for HA (TOC)

56

Figure 3.2 Emission spectra of LP, MP and FMP and absorbance spectrum for H2O2

57

Figure 3.3 UV collimated beam apparatus

66

Figure 4.1 Plot of Eq 3.15 at constant Phenol to H2O2 ratio

74

Figure 4.2 Effect of LP dose on MS2 disinfection at constant H2O2 concentration

76

Figure 4.3 Effect of MP dose on MS2 disinfection at constant H2O2 concentration

77

Figure 4.4 Effect of FMP dose on MS2 disinfection at constant H2O2 concentration

78

Figure 4.5 Effect of H2O2 concentration on MS2 disinfection at constant LP dose

79

Figure 4.6 Effect of H2O2 concentration on MS2 disinfection at constant MP dose

80

Figure 4.7 Effect of H2O2 concentration on MS2 disinfection at constant FMP dose

81

Figure 4.8 Synergistic and antagonistic effects for LPUV/H2O2

82

Figure 4.9 Synergistic effects for MPUV/H2O2

83

Figure 4.10 Synergistic effects for FMPUV/H2O2

84

Figure 4.11 Concentration of *OH radical with the increase in LP dose

85
x


Figure 4.12 Concentration of *OH radical with the increase in MP dose

90

Figure 4.13 Concentration of *OH radical with the increase in FMP dose

91

Figure 4.14 Correlation of synergy and *OH radical for the three lamp sources

93

Figure 4.15 Effect of TOC on MS2 log inactivation

95

Figure 4.16 Effect of TOC on synergy

97

Figure 4.17 Effect of TOC on *OH radical concentration

98

Figure 4.18 Effect of turbidity on MS2 log inactivation

100

Figure 4.19 Effect of turbidity on synergy

101

Figure 4.20 Effect of turbidity on *OH radical concentration

103

Figure 4.21 Effect of bicarbonate ion on MS2 log inactivation

104

Figure 4.22 Effect of bicarbonate ion on synergy

106

Figure 4.23 Effect of bicarbonate ions on *OH radical concentration

107

Figure 4.24 Effect of chloride ion on MS2 log inactivation

109

Figure 4.25 Effect of chloride ( Cl − ) ion on synergy

110

Figure 4.26 Effect of chloride ( Cl − ) ions on *OH radical concentration

111

Figure 4.27 Effect of real water matrix on MS2 log inactivation

112

Figure 4.28 Effect of real water matrix on synergy

115

Figure 4.29 Effect of real water matrix on *OH radical concentration

116

xi


LIST OF TABLES
Table 2.1 Oxidation potentials of a few of the strong oxidants

28

Table 3.1 Measured water quality parameters of filtered lake water

52

Table 3.2 Operational and water quality parameters

57

Table 4.1 *OH radical rate constant for phenol degradation for different R
values in Fenton’s reaction

74

xii


NOMENCLATURE
*

Hydroxyl radical

ATCC

American Type Culture Collection

CFU

Colony forming units

DBPs

Disinfection by-products

DNA

Deoxyribonucleic acid

FMP

Filtered medium pressure

HAA

Haloacetic acids

HO2*

Hydroperoxyl radical

LP

Low pressure

MCL

Maximum Contaminant Level

MP

Medium pressure

NOM

Natural organic matter

NTU

Nephelometric turbidity units

PFU

Plaque forming units

RNA

Ribonucleic acid

ROS

Reactive oxygen species

THMs

Trihalomethanes

TOC

Total organic carbon

TSB

Tryptic soya broth

USEPA

United States Environmental Protection Agency

UV

Ultraviolet

OH

xiii


Chapter 1: Introduction

Introduction

1.1

Drinking Water Disinfection

Water is one of the most indispensable necessities for human survival. Ensuring
microbiological safety of drinking water is of supreme importance. Disinfection is an
important step in ensuring that water is safe to drink. This step in water treatment is
crucial in safeguarding public health. Epidemics like typhoid and cholera were common
100 years ago. These epidemics were traced back to the consumption of unsafe water in
the late 1800s. Identification of the root cause for the epidemics very soon led to the
discovery of disinfectants in order to reduce the occurrence of epidemics. Disinfection is a
major factor in the reduction of epidemics since then. The key aspect of disinfection step
in the water treatment train is to ensure that water is free from pathogens. Disinfection is
generally placed towards the end of the treatment train to protect human beings from

pathogens and there by safeguarding human health. Disinfection of drinking water is one
of the major public health advances in the 20th century. A wide range of disinfectants and
disinfection technologies have emerged over the period of time ever since disinfection has
been discovered to control typhoid outbreak in 1908 in Chicago.

Prior to the widespread use of disinfectants, many people became ill or died because of
contaminated water. Disinfection reduces or eliminates illnesses acquired through
1


Chapter 1: Introduction

drinking water. Primary disinfection kills or inactivates bacteria, viruses, and other
potentially harmful organisms in drinking water. Effective disinfection of adequately
filtered influent water or raw water of suitable quality can be accomplished by either
chemical or physical means such as the use of chlorine, chlorine dioxide, ozone or
ultraviolet light (UV). However, the disinfection processes will not be as effective on
influent waters of inferior quality. Some disinfectants are more effective than others at
inactivating certain potentially harmful organisms. The selection of an appropriate
disinfection process depends upon site-specific conditions and raw water characterization
that is unique to each drinking-water system. Process selection decisions must consider
and balance the need to inactivate human pathogens while minimizing the production of
disinfection by-products. Commonly accepted chemical disinfectants are free chlorine,
monochloramine, chlorine dioxide and ozone. UV disinfection is often used as a physical
disinfection method. The application of UV light is an acceptable primary disinfection
process. Disinfection processes may be different for different utilities based on their
disinfection needs and also to meet regulatory requirements.

Secondary disinfection provides long-lasting water treatment as the water passes through
pipes to consumers. Secondary disinfection is made possible by maintaining residual

disinfectant while the water is supplied through the distribution systems. Residual
disinfectant maintains water quality by killing potentially harmful organisms that may get
into the water as it moves through pipes. Drinking water is typically treated before it
passes through the pipes, however, water is not sterile and can contain low levels of
microorganisms that survive through treatment and distribution and also there is a

2


Chapter 1: Introduction

possibility of regrowth of microorganisms due to the presence of nutrients in the water.
More so if UV or advanced oxidation processes (AOPs) involving UV are employed as
primary disinfection barrier, there is also a possibility of repair, by which the
microorganisms that were rendered inactive could be active again. So some residual
disinfectants are necessary to account for repair and also for regrowth. Microbes can grow
on pipe surfaces forming a thin biofilm layer. In some cases, biofilms have been known to
harbor pathogens that cause diseases, especially in severely immunocompromised
persons. The presence of residual disinfectant (secondary disinfection) is also thought to
help inactivate pathogens that might enter into a water distribution system through
contamination, as well as prevent microbial interactions with pipe wall biofilms (Propato
and Uber, 2004).

1.2

Selection of Disinfection Strategy

A decision making process has to be used in order to determine whether the current
primary disinfectant can meet disinfection and disinfection by products (DBPs)
requirement. The first aspect of the decision making process is the microbial limits.

Giardia lamblia, Legionella, HPC, total coliform turbidity, and viruses are the regulated

pathogens (EPA guidance manual, 1999). Process modification has to be considered, if
the existing primary disinfectant is not able to meet the inactivation requirements. To
move the application point of disinfectant, increase dose, increase contact time, or adjust
pH are some of the strategies for process modification. The cases in which meeting the
disinfection requirements is not viable by process modification of the existing primary
3


Chapter 1: Introduction

disinfectant, a new disinfectant has to be considered. The second aspect of the process is
the DBPs limits. Under varying water quality conditions, 80% of the MCL is set as an
action level to determine the change of treatment practices, to meet the established limits
on a consistent basis. Pretreatment optimization (i.e., coagulation, filtration, etc) or
process modifications such as moving the disinfection point can possibly reduce the
DBPs. In cases where the optimized processes do not meet the microbial and DBPs
requirements, a new disinfectant is needed.

If the decision making process reveals that a new primary disinfectant is required or
desired because of better public health protection, this decision requires the knowledge of
the keys components such as TOC concentration, bromide concentration and whether the
treatment comprises of filtered or non-filtered system. A high TOC concentration
indicates a high potential for DBP formation. In such scenarios, the decision will favor
those disinfectants that will not produce DBPs or will produce the least amount of DBPs.
Precursor removal and enhanced coagulation are used to reduce TOC during treatment
optimization. “High TOC” quantifies the potential to produce DBPs and is defined as one
of the conditions, TOC exceeds 2 mg/L or TTHM exceeds MCL (0.08 mg/L under Stage
1 disinfection byproduct rule, DBPR) or HAA5 exceeds MCL (0.06 mg/L under Stage 1

DBPR). Formation of hypobromous acid and bromate ion discourages the use of strong
oxidants such as ozone and ozone/peroxide (peroxone) as a primary disinfectant for
waters with high bromide concentration (0.1 mg/L). In the unfiltered systems wherein
there is no benefit of biofiltration to reduce ozonation byproducts or biodegradable
organic matter (BOM)Zred, the use of ozone or peroxone is strongly discouraged.

4


Chapter 1: Introduction

The selection of secondary disinfection is primarily driven by primary disinfection.
However, assimilable organic carbon (AOC) concentration, DBP formation potential
(DBPFP) and distribution system retention time are the three important aspects that has to
be considered in selecting a secondary disinfection strategy. AOC generation is possible if
a strong oxidant like ozone is used as a primary disinfectant in waters rich in TOC and
AOC concentration of higher than 0.1 mg/L after filtration is considered high. To prevent
the regrowth in the distribution systems, the water containing high AOC has to be
additionally treated with biological or GAC treatment to stabilize the finished water.
Disinfection by-product formation potential (DBPFP) serves as an indication of the
amount of organic byproducts that could be expected to form in the distribution system if
chlorine is used. Because DBP formation continues in the distribution system, the DBP
content at the plant effluent should be limited. A high DBPFP is defined as a water
meeting one of the two criteria which are total trihalomethanes (TTHM) seven-day
formation exceeds the MCL (0.08 mg/L under Stage 1 DBPR); or HAA5 seven-day
formation exceeds the MCL (0.06 mg/L under the Stage 1 DBPR). In a large distribution
system, booster stations may be required to maintain the disinfection residual. Since
chlorine dioxide has an upper limit for application, its usage may not be feasible if
relatively high doses are required to maintain a residual in the distribution system. A
distribution system retention time is considered high if it exceeds 48 hours. (EPA

guidance manual, 1999).

5


Chapter 1: Introduction

1.3

Disinfectants as Oxidants: A Better Strategy

Most disinfectants are strong oxidants and/or generate oxidants as byproducts (such as
hydroxyl free radicals, *OH) that react with organic and inorganic compounds in water.
While disinfection is the primary focus of the disinfectants, many of the disinfectants like
ozone are also used for other purposes in drinking water treatment, such as taste and odor
control, improved flocculation, and nuisance control. Because DBPs are produced
irrespective of the intended purpose of the oxidant, it is important to also address uses of
disinfectants as oxidants in water treatment. Two approaches are commonly used to
reduce the formation of DBPs during drinking water treatment. The first approach
consists of using a non-chlorine-based disinfection process as a ‘primary’ disinfectant
prior to addition of chlorine based ‘secondary’ disinfectant. The overall disinfection
efficiency remains the same, however the amount of chlorine needed is significantly
reduced. Therefore, the quantity of DBPs formed is comparatively lower. UV treatment
unlike other chlorine based disinfectants and ozone, produces no known DBPs, because it
does not involve the use of any chemicals. The second approach consists of reducing the
amount of NOM in the raw water prior to chlorination using a combination of chemical
and physical processes (e.g. coagulation/flocculation and filtration). An alternative group
of technologies that can potentially be used to minimize the formation of DBPs are
advanced oxidation processes (AOPs) (Zhou and Smith, 2001; Oppenlander, 2003). In
AOPs, *OH are formed. These radicals are extremely reactive and are capable of

oxidizing some of the NOM present in raw water sources (Langlais et al., 1991;
Gottschalk et al.,2000). As a result, AOPs have been documented to reduce the total
6


Chapter 1: Introduction

organic carbon (TOC) concentration and the trihalomethane formation potential (THMFP)
of raw source water (Amirsardari et al., 2001; Kusakabe et al., 1990; Sierka and Amy,
1985; Glaze et al., 1982; Peyton et al., 1982). The most common processes used to
generate *OH is through the use of combined catalytic oxidants such as ozone-ultraviolet
(O3/UV), hydrogen peroxide-ultraviolet (H2O2/UV) and hydrogen peroxide-ozone
(H2O2/O3) (Gottschalk et al., 2000). Although all three processes can produce *OH, the O3
based oxidants produce ozonation DBPs. Therefore the UV/H2O2 process is preferred
over the other two processes. UV/H2O2 treatment for organic contaminant control offers
an enormous disinfection potential. Based on the results reported, UV/H2O2 can generally
be applied as a disinfection barrier against all microorganisms (Kruithof et al., 2002).
Lubello et al (2002) reported only slight synergistic benefits for UV/H2O2 treatment of
wastewater, while Koivunen and Tanski (2005) observed no synergies but some
antagonism in peptone water for MS2 coliphage. The potential of UV/H2O2 process for
virucidal (MS2) inactivation was evaluated and *OH exposure (CT) was calculated to
present a relationship between the *OH dose and microbial inactivation (Mamane et al,
2007). However, the relationship between synergy and *OH concentration was not made
clear. This relationship is very crucial to acquire a better understanding concerning the
synergy and the contribution of *OH to the synergy. Thus, in UV/H2O2 integrated
disinfection system, synergism could be understood better, and the contribution of *OH
and UV to the synergy can be clearly demonstrated by establishing the relationship
between the synergy and the *OH concentration.

7

Chapter 1: Introduction

1.4

Research Objectives

The primary objective of this study was to assess the synergistic effect of the AOP,
UV/H2O2 integrated disinfection system, using MS2 coliphage as the target
microorganism. The significance of the *OH radicals in the UV/H2O2 synergism was also
investigated. The effect of the water matrix such as TOC, turbidity and the presence of
certain ions on *OH radical concentration as well as UV/H2O2 synergism were studied.

1.5

Thesis Organization

Detailed literature review about background of UV disinfection and AOPs and some
details about the integrated UV disinfection systems are provided in Chapter 2. Materials
and methods used in this study are described in Chapter 3. The experimental results are
discussed in Chapter 4. Final conclusions that are drawn based on the experimental results
are presented in Chapter 5.

8


Chapter 2: Literature Review

Literature Review

2.1

Alternative Disinfectants

Chlorine has been the most commonly used disinfectant since its first use in 1908.
However in 1970s it was first reported that chlorine can form by-products which may be
carcinogenic in nature. Ever since then there has been an extensive research conducted
and many studies indicated that chlorine can react with naturally-occurring materials in
the water to form unintended DBPs which may pose health risks (Fallon and Fliermans,
1980; Cheh et al., 1980; Maruoka and Yamanaka, 1980; Ringhand et al., 1987). Some
pilot-plant studies also confirmed the same (de Greef et al., 1980; Zoetemanet al., 1982;
Kruithof et al., 1985; Miller et al., 1986). Stricter health regulations with regards to the
levels of DBPs have been implemented which impacted the use of chlorine as a
disinfectant. Apart from this, there are specific microbial pathogens, such as
Cryptosporidium, that are resistant to traditional disinfection practices. In 1993,
Cryptosporidium caused 400,000 people in Milwaukee to experience intestinal illness.

More than 4,000 were hospitalized, and at least 50 deaths have been attributed to the
outbreak. There have also been Cryptosporidiosis outbreaks in Nevada, Oregon, and
Georgia over the past several years (USEPA, 1998). Formation of mutagenic and
carcinogenic agents in the water treated with chlorine and its inability to deal with certain
pathogens had prompted research to seek alternative disinfection methods that would

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Chapter 2: Literature Review

minimize environmental and public health impacts. Wide arrays of disinfectants and

disinfection technologies have emerged over the period of time ever since the discovery
of DBPs. Use of chloramine, Ozone, UV light and combination of these disinfectants with
a weaker disinfectant H2O2 are some of the strategies adopted to overcome the problems
that surfaced with chlorine disinfection.

2.2

UV Disinfection

UV disinfection involves the use of UV radiation for disinfection. UV radiation is part of
the electromagnetic spectrum that lies between the x-rays and the visible light regions,
and spans the wavelengths from 100 to 400 nm (Figure 2.1). Within the short wavelength
range for UV radiation, the spectrum is further divided into four sub-regions (USEPA,
1999) as described. The first is UV-A region comprising of wavelengths from 314 to 400
nm. The wavelengths between 300 and 400 nm are sometimes called near UV. UV-B is
the second in line ranging from wavelengths 280 to 315 nm, also called medium UV. The
wavelengths 200 to 280 nm categorized as third region called UV-C region. This region is
of great importance as far as UV disinfection is concerned. The fourth region is called
vacuum UV which comprises of wavelengths 100 to 200 nm. This part of UV has
wavelengths that are strongly absorbed by water and air. This part of the UV is capable of
directly causing a cleavage of the water molecule leading to the production of *OH
radicals.

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