Solar photochemical technology for potable water treatment : disinfection and detoxifications

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Title:
Solar photochemical technology for potable water treatment : disinfection and detoxifications
Physical Description:
xx, 269 leaves : ill. ; 29 cm.
Language:
English
Creator:
Cooper, Adrienne Teresa, 1962-
Publication Date:

Subjects

Subjects / Keywords:
Environmental Engineering Sciences thesis, Ph.D   ( lcsh )
Dissertations, Academic -- Environmental Engineering Sciences -- UF   ( lcsh )
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bibliography   ( marcgt )
non-fiction   ( marcgt )

Notes

Thesis:
Thesis (Ph.D.)--University of Florida, 1998.
Bibliography:
Includes bibliographical references (leaves 163-175).
General Note:
Typescript.
General Note:
Vita.
Statement of Responsibility:
by Adrienne Teresa Cooper.

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University of Florida
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All applicable rights reserved by the source institution and holding location.
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aleph - 029537927
oclc - 40470966
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AA00022876:00001

Table of Contents
    Title Page
        Page i
        Page ii
    Dedication
        Page iii
    Acknowledgement
        Page iv
        Page v
    Table of Contents
        Page vi
        Page vii
        Page viii
    List of Tables
        Page ix
        Page x
        Page xi
    List of Figures
        Page xii
        Page xiii
        Page xiv
        Page xv
        Page xvi
        Page xvii
    Key to symbols
        Page xviii
    Abstract
        Page xix
        Page xx
    Chapter 1. Introduction
        Page 1
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    Chapter 2. Review of solar based water treatment
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    Chapter 3. Experimental design and methods
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    Chapter 4. Results and discussion
        Page 54
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    Chapter 5. Summary and conclusions
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    References
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    Appendix A. Experimental data
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    Appendix B. Light measurement
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    Biographical sketch
        Page 269
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Full Text









SOLAR PHOTOCHEMICAL TECHNOLOGY
FOR POTABLE WATER TREATMENT:
DISINFECTION AND DETOXIFICATION










By

ADRIENNE TERESA COOPER


















A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 1998























Copyright 1998

by

Adrienne Teresa Cooper

























This dissertation is dedicated to my grandmothers, Gewenith
Manning and the late Ethel Cummings, who were women for their time and to my nephew Fatin D. Cooper who is the future.












ACKNOWLEDGMENTS

The research conducted for this dissertation was supported by the National Science Foundation through the University of Florida College of Engineering Minority Engineering Doctoral Initiative.

Appreciation is expressed to my committee chairman Dr. Thomas Crisman and cochairman Dr. D. Y. Goswami for their sage advice and unwavering support over the last few years. Acknowledgment and gratitude are extended to committee member Dr. Michael Annable for his support and generous provision of access to analytical equipment and laboratory facilities; to committee member Dr. Seymour S. Block whose knowledge of disinfection has served as a valuable resource and who graciously allowed me the use of his laboratory; committee member Dr. Paul Chadik, who helped to steer me in the right direction from the very beginning; to Sanjay Puranik for sharing his knowledge of analytical chemistry; to Chuck Garretson for making available his wealth of mechanical capabilities, keen insight and ever present smile; to Michael McCaskill and Michael Oliver for their diligent assistance in the laboratory; and to Barbara Walker and Berdenia Monroe for their administrative support and friendship. My gratitude and thanks are due to committee member Dr. Jonathan Earle for his guidance, encouragement, confidence and that extra push when I needed it.




iv







The insight, support and friendship of my colleagues in the Solar Energy Group, the Center for Wetlands and Environmental Engineering Sciences have truly enriched my learning experience here at the University of Florida, and they, in their own ways, have contributed to the achievement of this goal.

A special thank you is extended to the entire Earle family, Celia, Jeremy, Kevin and Mrs. Yvonne Earle, for being my "Gainesville Family." My parents Dr. and Mrs. Trenton Cooper, my sister Mrs. Edris Anifowoshe, and my nephew, Fatin Cooper, have provided invaluable support in every way imaginable. I want to convey a loving thank you to my special friend, Abdoulaye Kaba, for his support during the writing of this dissertation. Others have provided valuable support, insight, friendship and shoulders over the last years including Sonja Jonas, Clayton Clark, the Makaveli Gainesville Tennis Crew, and the Black Graduate Student Organization.

Finally and most importantly, I would like to give praise to the Creator for making it all possible.


















V













TABLE OF CONTENTS

page


ACKNOWLEDGMENTS ...................................................................... iv

LIST OF TABLES ............................................................................... ix

LIST OF FIGURES ............................................................................ xii

KEY TO SYMBOLS ......................................................................... xviii

ABSTRACT ...................................................................................... xix

CHAPTERS

1 INTRODUCTION ............................................................................ 1

Research Significance ...................................................................... 1
Theory of Photochemical Water Treatment ......................................... 4
Photocatalysis ............................................................................. 5
Photosensitization ....................................................................... 8
The Solar Resource ........................................................................ 10
Research Objectives ....................................................................... 12

2 REVIEW OF SOLAR BASED WATER TREATMENT ......................... 14

Physical Processes ......................................................................... 15
Distillation Processes ................................................................ 15
Passive distillation ................................................................ 15
Active distillation ................................................................. 21
Pasteurization Processes ........................................................... 24
Photo Processes ............................................................................. Z7
Solar Disinfection ...................................................................... 28
S O D IS ...................................................................................... 28
H alosol .................................................................................... 29
Photocatalysis ........................................................................... 29
Photosensitization ..................................................................... 30
Summary ..................................................................................... 32





vi







3 EXPERIMENTAL DESIGN AND METHODS .................................... 34

Choice of Experimental Parameters ................................................ 34
Contaminants .......................................................................... 35
Catalyst Choice ......................................................................... 35
Choice of Photosensitizer ........................................................... 37
Reactor Design ......................................................................... 39
p H ........................................................................................... 43
Catalyst/Sensitizer Concentration ............................................... 44
Laboratory Experimental Design ..................................................... 45
Materials and Methods .................................................................. 46
Reaction Vessels ....................................................................... 46
Bacterial Inoculation ................................................................. 47
Reactor Chamber ...................................................................... 49
Photocatalysis Reactor Setup ...................................................... 49
Photocatalysis Sampling and Analysis ........................................ 50
Photosensitization Reactor Setup ................................................ 51
Photosensitization Sampling and Analysis .................................. 52
Combination Experimental Setup, Sampling and Analysis ............ 52
Experiments for Confirmation of Previous Work with Bromacil ..... 53
4 RESULTS AND DISCUSSION ......................................................... 54

Dye Photosensitization ................................................................... 54
General Comments About Experimental Data .............................. 56
Statistical Treatment of the Data ................................................. 58
Presentation of Results and Identification of General Trends ......... 62 Data Analysis by ANOM ............................................................ 81
Effect of Sunlight ....................................................................... 82
Effect of pH ............................................................................... 86
Effect of Dye Concentration ......................................................... 89
Effect of Initial Coliform Density ................................................. 97
Reactor Efficacy ........................................................................ 99
Summary ................................................................................ 101
Photocatalysis with Titanium Dioxide ............................................. 102
General Comments About Experimental Data ............................. 104
Statistical Treatment of the Data ................................................ 105
Presentation of Results and Identification of General Trends ........ 105 Data Analysis by ANOM ........................................................... 112
Effect of Light .......................................................................... 113
Effect of pH .............................................................................. 117
Effect of Ti02Concentration ....................................................... M
Multiple Parameter Effects ....................................................... M
Effect of Initial Colony Density on Disinfection ............................. 129
Other Effects ............................................................................ 131
Photocatalysis vs. Air Stripping ................................................. JM
Summary ................................................................................ 134
Ti02Photocatalysis Combined With Methylene Blue ......................... 135
General Comments About Experimental Data ............................. 136


vii







Statistical Treatment of the Data ................................................ 137
Disinfection ............................................................................. 1x
Detoxification .......................................................................... 142
Summary ................................................................................ 152
Kinetic Considerations .................................................................. 152
Detoxification .......................................................................... 152
Disinfection ............................................................................. 154
General Summary of Results ......................................................... 157

5 SUMMARY AND CONCLUSIONS ................................................. 159

Summary .................................................................................... 159
Process Efficacy Comparison for Simultaneous Treatment ........... 159
Drinking Water Quality ............................................................ 160
Conclusions ................................................................................. 160
Recommendations for Future Work ................................................ 161

REFERENCES .................................................................................. 163

APPENDICES

A EXPERIMENTAL DATA ............................................................... 176

B LIGHT MEASUREMENT .............................................................. 260

BIOGRAPHICAL SKETCH ................................................................ 269
























viii













LIST OF TABLES

Tablepag

1-1. Spectral Distribution of Solar Radiation.............................. 11

2-1. Examples of Photocatalytic Treatment of Water and Wastewater .... 30 2-2. Examples of Photocatalytic Treatment of Water and Wastewater .... 31 2-3. Summary of Photosensitized Treatment of Water and Wastewater..3 3-1. Photostability of Semiconductor Oxides Tested by Carey and Oliver
(1980) ...............................................................3

3-2. Order of Effectiveness of Dyes at 104M Concentration on E. Coli
After 24 Hours Exposure to Light at Room Temperature........ 40 3-3. Design for TiO2 Photocatalytic Lab Experiments .................... 46

3-4. Design for Photosensitization Lab Experiments ..................... 46

3-5. Design for Combination Lab Experiments ........................... 46

4-1. Insolation Measurements from Dye Sensitization Experiments ...55 4-2. Descriptive Statistics of Measured Data for all Experiments........ 56 4-3. Average Standard Deviations for all Dye Photosensitization
Experiments ........................................................57

4-4. Mean Fractional Survival ( 31%) of E. coli @ t= 30 minutes in MB
Experiments ........................................................59

4-5. Mean Fractional Survival (25%) of E. coli in MB Experiments ...65 4-6. Mean Fractional Survival (13%) of E. coli in RB Experiments...68 4-7. Benzene (5 1) and Toluene (29) Concentrations (ppb) in MB
Experiments ........................................................70

4-8. Benzene ( 46) and Toluene ( 36) Concentrations (ppb) in RB
Experiments ........................................................70



ix








4-9. Normalized Benzene (0.09) and Toluene ( 0.11) Concentration in
MB Experiments ................................................... 76

4-10. Normalized Benzene (0.06) and Toluene (0.07) Concentration in RB
Experiments ........................................................77

4-11. Calculated ANOM Values for Dye Photosensitized Disinfection ...82 4-12. Sunlight Subgroup Averages for Dye Photosensitized Disinfection;
Values are Fractional Survival of E. coli.......................... 83

4-13. pH Subgroup Averages for Dye Photosensitized Disinfection. Values
are Fractional Survival of E. coli.................................. 86

4-14. Dye Concentration Subgroup Averages in Disinfection Experiments.
Values are Fractional Survival of E. Coli......................... 90

4-15. Mean Fractional Survival of Bacteria in TiO2 Experiments........ 107 4-16. Mean Concentration of BTEX (ppb) in TiO2 Experiments........... 108

4-17. Calculated ANOM Values for TiO2 Photocatalysis.................. 113

4-18. LTV Light Subgroup Averages for TiO2 Photocatalysis. Values are
Fractional Survival of Bacteria and Normalized Chemical
Concentration...................................................... 114

4-19. pH Subgroup Averages for TiO2 Photocatalysis. Values are
Fractional Survival of Bacteria and Normalized Chemical
Concentration...................................................... 117

4-20. TiO2 Concentration Subgroup Averages for Disinfection. Values are
Fractional Survival of Bacteria and Normalized Chemical
Concentration...................................................... 121

4-21. Mean Values for Fractional Survival as a Function of Light, pH and
TiO2 Concentration at t=240 Minutes ...........................12
4-22. Mean Normalized Benzene Concentration After 30 Minutes in TiO2
Experiments ....................................................... 129

4-23. Descriptive Statistics for Initial Colony Density in TiO2 Experimentsl30 4-24. Vapor Pressure Values for BTEX components...................... 133

4-25. Measured Sunlight Intensity in Combination Experiments ....... 136 4-26. Average Standard Deviations for all Combination Experiments..137 4-27. Mean Fractional Survival (14.1%) of E. Coli in Combination
Experiments ....................................................... 139

x







4-28. Calculated ANOM Values for Combination Experiments ............. 139

4-29. Sunlight Subgroup Averages for Combined Experiments. Values are
Fractional Survival of Bacteria and Normalized Chemical
C oncentration ..................................................................... 139
4-30. Photochemical Subgroup Averages for Combination Experiments;
Values are Fractional Survival of E. coli and Normalized
Chem ical Concentration ...................................................... 140

4-31. Mean Concentration (ppb) of Benzene (120) and Toluene (199) in
Combination Experiments; IT.,, Ag= 433-833 W/m IUV, Ag =25-40
W /m ................................................................................... 147

4-32. Experimental First Order Rate Constants (min') for Ti02
Photocatalytic Experiments .................................................. 153

4-33. Correlation Statistics for Least Squares Linear Regression of Kinetic
Data; Confidence Level is 95% .............................................. 154

4-34. First Order Rate Constants for All Photochemical Disinfection
E xperim ents ....................................................................... 157
4-35. Time to Complete Destruction by Photochemical Treatment .......... 158


























xi













LIST OF FIGURES

Fi~yure ag

1-1. Graphical Representation of the Generation of e-/h+ Pairs and
Recombination by Photocatalytic Reaction on the Surface of
aSemiconductor Particle .................................................... 7

2-1. Conventional Passive Solar Basin Still ...................................... 17

2-2. Schematic of Flash Distillation Using Solar Collector .................... 22

3-1. TiO2 Reaction Vessel .............................................................. 47

3-2. Photosensitization Reaction Vessel ......................................... 48

3-3. Graphical Representation of Bacterial Inoculation ................... 48

3-4. Ultraviolet Light and Dark Reactor Chamber ............................ 50

4-1. MB Destruction of E. coli in Sunlight; (a) pH =10, Iavg= 542-696 W/m2
(b) pH =7, Iavg = 665-891 W /m2 .................................................. 63
4-2. Destruction of E. coli in sunlight with 1 mg/L MB; (a) pH =10) Iavg=
542-696 W/m2 and (b) pH 7, I = 665-891 W/m2 ..................... 64
4-3. RB Destruction of E. coli in Sunlight; (a) pH = 7, Iag = 746-856 W/m2
(b) pH = 10, Iavg= 715-775 W/m ............................................ 67

4-4. RB Destruction of E. coli at pH =7, Iavg = 715-775 W/m2; (a) 5 mg/L RB
and (b) 10 m g/L RB ................................................................ 68
4-5. Benzene Concentration as a Function of Time and MB Concentration
in Sunlight; (a) pH=10, Iavg = 542-696 W/m2 (b) pH=7, Iavg = 665-891 W /m 2 ................................................................................... M
4-6. Toluene Concentration as a Function of Time and MB Concentration
in Sunlight; (a) pH =10, Iavg = 542-696 W/m2 (b) pH=7, Iag = 665-891 W /m 2 ................................................................................... M
4-7. Benzene Concentration as a Function of Time and RB Concentration
in Sunlight; (a) pH =10, Iavg = 715-775 W/m2 (b) pH=7, Iavg = 746-856 W /m 2 ............................................................................... 74



xii







4-8. Toluene Concentration as a Function of Time and RB Concentration
in Sunlight; (a) pH =10, Iavg = 715-775 W/m2 (b) pH=7, lavg = 746-856 W /m 2 ............................................................................... 75

4-9. Normalized Benzene Concentration in Sunlight with 0.1 mg/L MB,
(a) pH =10, Iavg = 542-696 W/m2 (b) pH=7, Iavg = 665-891 W/m2 ....... 78
4-10. Normalized Toluene Concentration in Sunlight with 0.1 mg/L MB;
(a) pH =10, Iavg = 542-696 W/m2 (b) pH=7, 'avg = 665-891 W/m2 ....... 79
4-11. Normalized Benzene Concentration in Sunlight with 0.1 mg/L RB, (a)
pH =10, Iavg = 715-775 W/m2 (b) pH=7, Iavg = 746-856 W/m2 ...... 80
4-12. Normalized Toluene Concentration in Sunlight with 0.1 mg/L RB, (a)
pH =10, Iavg = 715-775 W/m2 (b) pH=7, Iavg = 746-856 W/m2 ........... 81
4-13. Significance of Sunlight, Based on ANOM, in MB Experiments (a) 5
Minutes (b) 15 Minutes (c) 30 Minutes .................................. 84
4-14. Significance of Sunlight, Based on ANOM, in RB Experiments; (a) 5
Minutes (b) 15 Mintues (c) 30 Minutes ..................................... 85
4-15. Significance of pH, Based on ANOM, in MB Experiments; (a) 5
Minutes (b) 15 Minutes (c) 30 Minutes .................................. 87

4-16. Significance of pH, Based on ANOM, in RB Experiments; (a) 5
Mintues (b) 15 Minutes (c) 30 Minutes ..................................... 88
4-17. Statistical Significance of MB Concentration, Based on ANOM, on
Disinfection in Sunlight; (a) 5 Minutes (b) 15 Minutes (c) 30
M inutes ........................................................................... 91
4-18. Statistical Significance of RB Concentration, Based on ANOM, on
Disinfection in Sunlight; (a) 5 Minutes (b) 15 Minutes (c) 30
M in utes ............................................................................... 92
4-19. Comparison of Disinfection Efficacy of Control and 0.1 mg/ L MB in
Sunlight at 5 minutes, Based on ANOM .................................. 93
4-20. Comparison of Disinfection Efficacy of Control and 1 mg/L MB in
Sunlight at 5 minutes, Based on ANOM .................................. 94
4-21. Comparison of Disinfection Efficacy of Control and 5 mg/L MB in
Sunlight at 5 minutes, Based on ANOM .................................. 94
4-22. Comparison of Disinfection Efficacy of Control and 10 mg/L MB in
Sunlight at 5 minutes, Based on ANOM .................................. 95
4-23. Comparison of Disinfection Efficacy of 0.1 mg/ L and 10 mg/L MB in
Sunlight at 5 minutes, Based on ANOM .................................. 95


xiii







4-24. Comparison of Disinfection Efficacy of 1 mg/ L and 10 mg/L MB in
Sunlight at 5 minutes, Based on ANOM ............................... 96
4-25. Comparison of Disinfection Efficacy of 5 mg/ L and 10 mg/L MB in
Sunlight at 5 minutes, Based on ANOM .................................. 96
4-26. Fractional Survival of E. coli in sunlight at t=30 minutes as a
Function of MB Concentration; Bars are One Standard Deviation
...........................l.,,.......................97
4-27. Least Squares Regression of Natural Logarithm of Fractional
Survival of E. coli as a Function of MB Concentration at t=5
M inutes ........................................................................... 98
4-28. Initial Colony Count vs. Fractional Survival of E. coli at t=60 Minutes
for M B Experim ents .............................................................. 98
4-29. Initial Colony Count vs. Fractional Survival of E. coli at t=30 Minutes
in RB Experim ents ............................................................ 99
4-30. TiO2 Photocatalytic Disinfection in UV Light (29 W/m2); Error Bars
are One Standard Deviation; (a) pH = 4 (b) pH = 7 ..................... 106
4-31. Destruction of Benzene in Reactors 3 and 4 as a Function of Time;
Reactors Contained 0.01% TiO2 and were Irradiated for 60
minutes under UV Lamps (29 W/m2) ..................................... 110
4-32. Benzene Concentration in UV Light (29 W/m2) as a Function of Time
and TiO2 Concentration; Error Bars are One Standard Deviation.
(a) pH =4, (b) pH = 7 .............................................................. 110
4-33. Toluene Concentration in UV Light (29 W/m2) as a Function of Time
and TiO2 Concentration; Error Bars are One Standard Deviation.
(a) pH =4, (b) pH = 7 .............................................................. 111
4-34. m&p Xylene Concentration in UV Light (29 W/m2-) as a Function of
Time and TiO2 Concentration; Error Bars are One Standard
Deviation. (a) pH =4, (b) pH = 7 ............................................... 112
4-35. Significance of UV Light (29 W/m2), Based on ANOM, on Bacteria in
TiO2 Experiments at 120 Minutes ........................................... 115
4-36. Significance of UV Light (29 W/m2), Based on ANOM, on Benzene in
Ti02 Experiments (a) 30 Minutes (b) 60 Minutes ...................... 115
4-37. Significance of UV Light (29 W/m2), Based on ANOM, on Toluene in
TiO2 Experiments (a) 30 Minutes (b) 60 Minutes ...................... 116
4-38. Effect of UV Light (29 W/m2) on Fractional Survival of Bacteria in All
Reactors in TiO2 Experiments; Bars are One Standard Deviationll6


xiv







4-39. Significance of pH, Based on ANOM, to Bacteria Destruction in TiO2
Experiments at 120 M inutes .................................................. 118
4-40. Significance of pH, Based on ANOM, to Benzene Destruction in TiO2
Experiments (a) 30 Minutes (b) 60 Minutes ............................. 119
4-41. Significance of pH, Based on ANOM, to Toluene Destruction in TiO2
Experiments (a) 30 Minutes (b) 60 Minutes ............................. 120
4-42. Significance of TiO2 Concentration, Based on ANOM, on Bacteria in
Photocatalysis Experiments at 120 Minutes ............................ 121
4-43. Significance of TiO2 Concentration, Based on ANOM, on Benzene in
Photocatalysis Experiments; (a) 30 Minutes (b) 60 Minutes ....... 122 4-44. Significance of TiO2 Concentration, Based on ANOM, on Toluene in
Photocatalysis Experiments; (a) 30 Minutes (b) 60 Minutes ....... 123

4-45. Comparison of Control vs. 0.01% TiO2 on Photocatalytic Disinfection
at 120 Minutes, Based on ANOM ........................................... 124
4-46. Comparison of Control vs. 0.05% TiO2 on Photocatalytic Disinfection
at 120 Minutes, Based on ANOM ........................................... 124
4-47. Comparison of Control vs. 0.10% TiO2 on Photocatalytic Disinfection
at 120 Minutes, Based on ANOM ........................................... 125
4-48. Comparison of 0.01% vs. 0.05% TiO2 on Photocatalytic Disinfection at
120 Minutes, Based on ANOM ............................................... 125

4-49. Comparison of Control vs. 0.01% TiO2 on Photocatalytic Destruction of
Benzene at 60 Minutes, Based on ANOM ............................. 126
4-50. Comparison of Control vs. 0.05% TiO2 on Photocatalytic Destruction of
Benzene at 60 Minutes, Based on ANOM ................................ 126
4-51. Comparison of Control vs. 0.10% TiO2 on Photocatalytic Destruction of
Benzene at 60 Minutes, Based on ANOM ................................ 127
4-52. Comparison of 0.01% vs. 0.05% TiO2 on Photocatalytic Destruction of
Benzene at 60 Minutes, Based on ANOM ............................. 127
4-53. Fractional Survival of Bacteria as a Function of UV Light (29 W/m2)
and pH in TiO2 Experiments; Bars are One Standard Deviation
............................................130
4-54. Effect of UV Light (29 W/m') and pH on the Destruction of Benzene in
TiO2 Experiments; Bars are One Standard Deviation ............... 130
4-55. Initial Colony Count vs. Fractional Survival of Bacteria at t=120
Minutes for TiO2 Photocatalysis ............................................. 131

xv







4-56. Normalized Concentrations of BTEX Components in pH 7 Dark
Experiments with 0.01% TiO2 ..................................133.

4-57. Normalized Concentrations of BTEX Components in pH 4 Dark
Experiments with 0.01% TiO2 .................................... 134

4-58. Destruction of E. coli in Sunlight (ITot, Avg = 433-853 W/m IUV, Avg = 25-40
W/m2) in Combination Experiments............................. 138

4-59. Significance of Sunlight ('Tot Avg = 433-853 W/m2, 'UVAvg = 25-40 W/m2)
on E. coli Destruction, Based on ANOM, in Combination
Experiments; (a) 5 Minutes (b) 15 Minutes (c) 30 Minutes ...... 141

4-60. Significance of Photochemical on E. coli Destruction, Based on
ANOM, in Combination Experiments; (a) 5 Minutes (b) 15
Minutes (c) 30 Minutes ............................................ 143

4-61. Significance of TiO2 vs MB on E. coli Destruction, Based on ANOM, in
Combination Experiments; (a) 5 Minutes (b) 15 Miiues (c) 30
Minutes ............................................................ 144

4-62. Significance of TiO2 vs Both on E. coli Destruction, Based on ANOM,
in Combination Experiment; (a) 5 Minutes (b) 15 Minutes (c) 30
Minutes ............................................................ 145

4-63. Significance of MB vs Both on E. coli Destruction, Based on ANOM,
in Combination Experiments; (a) 5 Minutes (b) 15 Minutes (c) 30
Minutes ............................................................ 146

4-64. Normalized Concentration as a Function of Time in Combination
Experiments. 'rot Avg = 433-833 WWm, 'UVAvg = 25-40 W/m2; (a)
Benzene (b) Toluene................................................147

4-65. Significance of Photochemical on Benzene Destruction, Based on
ANOM, in Combination Experiments; (a) 30 Minutes (b) 120
Minutes ............................................................ 148

4-66. Significance of Photochemical on Toluene Destruction, Based on
ANOM, in Combination Experiments; (a) 30 Minutes (b) 120
Minutes ............................................................ 149

4-67. Significance of TiO2 vs Both on Benzene Destruction, Based on
ANOM, in Combination Experiments; (a) 30 Minutes (b) 120
Minutes ............................................................ 150

4-68. Significance of TiO 2vs Both on Toluene Destruction, Based on
ANOM, in Combination Experiments; (a) 30 Minutes (b) 120
Minutes.............................................................151




xvi







4-69. Least Squares Linear Regression of First Order Rate Equation for
Disinfection in UV Light (29 W/M2) with 0.05% TiO2 and PH = 4; r 2 = 0.90, p-value = 0.0025............................................. 155

4-70. Least Squares Linear Regression of First Order Rate Equation for
Disinfection in UV Light (29 W/m') with 0. 10% TiO2 and pH = 7; r' = 0.55, p-value = 0.0 19.............................................. 155

4-71. Least Squares Linear Regression of First Order Rate Equation for
Disinfection in Sunlight (7 15-775 W/m2) with no photochemical
and pH = 10; r' = 0.99, p-value = 0.0001 ........................... 156

4-72. Least Squares Linear Regression of First Order Rate Equation for
Disinfection in Sunlight (746-856 W/m') with 1 mg/L RB and pH=
7; r' = 0.95, p-value = 0.0003........................................ 156



































xvii












KEY TO SYMBOLS

X. Wavelength, nm
h Planck's constant, 6.625 x 10-'Js
C Speed of light, 3.0 x 1010 cm/s
E Band gap energy, ev
hv Light energy
h+ Positive hole in the valence band
e Electron
eExcited singlet state of component X 3X* Excited triplet state of component X
X* Excited state of component X
X* Singlet state of component X
x Triplet state of component X
R Hydrocarbon group
Isc Solar constant
Ct Concentration at time, t
Nt Colony density at time, t
I Insolation, W/m2
s Standard Deviation
Grand Average of all Data in ANOM XSubgroup Average for ANOM s Average standard deviation
RAverage Range H ANOM Critical Value
v degrees of freedom
d2 2 bias correction factor for ANOM
significance factor












xviii












Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

SOLAR PHOTOCHEMICAL TECHNOLOGY
FOR POTABLE WATER TREATMENT:
DISINFECTION AND DETOXIFICATION By

Adrienne Teresa Cooper

August 1998

Chairperson: Thomas Crisman Cochairperson: D. Yogi Goswami Major Department: Environmental Engineering Sciences

Clean water is scarce in many countries, and the goal of universal access to water and sanitation has not yet been achieved. Standard water treatment techniques are often expensive both in capital investment and operation and maintenance, particularly in lesser developed communities where resources are scarce.

Solar photochemistry has shown promise as an appropriate alternative technology for treatment of water, and provides potential for simultaneous disinfection and destruction of organic chemicals. The need for simultaneous treatment arises when conditions of contamination of source water, such as ground water, occurs. Potential sources of

contamination are industrial and agricultural runoff or leakage of underground storage tanks (gasoline) and sewerage lines.




xix







In a series of bench scale experiments, three photochemical technologies, TiO2 photocatalysis, dye photosensitization and a combination of dye photosensitization and TiO2 photocatalysis, were evaluated for their efficacy for simultaneous removal of coliform bacteria and aromatic hydrocarbons in drinking water under a variety of pH and photochemical concentration conditions.

Series of 100 ml and 500 ml reactors, containing various

concentrations of TiO2, and two pH levels (4 and 7), were inoculated with mixed bacteria species, benzene, toluene, and xylene, and illuminated under ultraviolet light for several hours. Under most conditions both the chemical and bacteriological contaminants were destroyed within an hour.

In photosensitization experiments, the 500 ml reactors were charged with several concentrations of rose bengal or methylene blue and neutral, pH 7, or basic, pH 10, water. After inoculation with Escherichia coli, benzene and toluene, the reactors were illuminated for four hours in sunlight. In all cases, the water was disinfected within one hour; however, destruction of the chemical contaminants did not occur.

The 500 ml hybrid reactors, loaded with 0.01% TiO2 and/or 5 mg/L methylene blue, were also illuminated in sunlight. The inoculations of Escherichia coli, benzene, and toluene were completely destroyed after two hours in all of the reactors which contained TiO2; however, the presence of methylene blue inhibited the reaction.







xx












CHAPTER 1
INTRODUCTION

Research Sienificance

Clean and safe water is a requirement for healthy living and development. While concerns with most water related diseases have been virtually eliminated in most developed regions, such as Western Europe and North America, diseases related to either the quantity or quality of water supply are still a major problem in other parts of the world

In 1977 Stein reported that 25,000 deaths occurred daily from water borne diseases. In an effort to reduce these deaths, the United Nations declared the ten year period from 1981 to 1990 the International Drinking Water Supply and Sanitation Decade. The goal of the decade was to provide universal access to safe water and sanitation. While many advances were made during this period to increase the supply of safe drinking water for the global human population, universal access has yet to be achieved. According to World Health Organization (WHO) estimates, as of 1990, 18% of urban populations and 36% of rural populations (approximately 1.23 billion people) are still without access to safe drinking water supplies (Christmas 1990). An inexpensive supply of clean water is one of the most pressing public health issues facing developing communities.

Over 10 million deaths result from more than 250 million new cases of water borne diseases yearly (Hazen and Toranzos 1990). During 1993


1





2

there were 272,500 reported cases of cholera in Sub-Saharan Africa and Latin America, with death rates of 3% and 1%, respectively. In 1994 WHO reported a decrease in the availability of clean water in several countries of Sub-Saharan Africa. Their estimates, based on the continuation of current trends, suggest that by the year 2025, the supply of renewable fresh water per person in the worst drought-affected countries of the continent will represent 15% of the 1955 values (WHO 1994). In many developing communities, water related infections caused by poor biological drinking water quality or lack of water supply are the most urgent public health issues. The water related infections are acute, tending to act quickly, causing illness and sometimes death. However, the chemical quality of water is also of growing concern.

In the 1970s it was discovered that disinfection by chlorination of water containing humic substances generates chloroform and other trihalomethanes (THMs). THMs are known animal carcinogens (Clark 1992; Glaze et al. 1993a; Moser 1992; Packham 1990; Stevens et al. 1989), raising concerns about chemical disinfection by-products and their toxicological effects on the population.

Rachel Carson (1962) brought the issue of pesticide contamination of water and soil to the forefront. The growth of industry and the prevalence of agricultural pesticides and fertilizers s cause concern for the effect of these discharges on the chemical quality of water. An increase in motorized transportation leads to contaminated runoff and the potential for leakage of benzene, toluene and other aromatic hydrocarbons. These

activities can have a severe impact on drinking water sources. The effect of





3

chemical contaminants on public health is more often chronic, building over time and causing long term illness (Droste and McJunkin 1982).

Standard water treatment techniques are very well defined in the United States and other developed countries. However, due to differences in economics and infrastructure, these treatments are not necessarily readily transferable from the developed to the developing world, including some lesser developed areas of developed nations. The operational and capital costs for this technology are often too expensive for developing communities.

The development of community appropriate technology for treatment of drinking water is critical if universal access to a safe water supply is to be achieved. Utilization of available natural resources, where feasible, provides a greater opportunity for a sustainable drinking water supply. This requires innovative and creative technology.

While no one technology can meet all of the needs of a community, solar photochemical oxidation holds promise as a viable alternative to standard, more expensive methods. The efficacy of the photocatalytic reaction has been demonstrated for biological contaminants (Block et al. 1997; Ireland et al. 1993) and chemical contaminants (Blake 1994; Legrini et al. 1993). Therefore, it is reasonable to expect that the simultaneous destruction of both chemical and biological contaminants can be accomplished, although it has not been reported. While some investigations of simultaneous disinfection and detoxification with dye photosensitization have been undertaken (Acher 1984; Acher and Rosenthal 1977; Eisenberg et al. 1987a; Eisenberg et al. 1986), these





4

processes have not been optimized, nor have they been compared directly with photocatalysis. The success of previous studies indicates that solar photochemical technology, when properly integrated with conventional treatment, has the potential to address the technical issues of water treatment facing a community.

Use of solar photochemical technology for water treatment has the potential to provide a solution which is technically, economically and socially acceptable, manifested by the following potential benefits:
The use of the sun as a primary driver results in a renewable and

essentially free source of energy for the reaction
Photochemical oxidation results in complete destruction of

pollutants, which is preferable to dissipation, concentration or

change of form
9 Since very small quantities of sensitizer or catalyst are required,

and little if any external energy besides the sun, the technology

has the potential for low capital and maintenance costs
0 The process is easily adaptable to a small scale, and therefore,

suitable for rural and suburban communities

Theory of Photochemical Water Treatment

Photochemical water treatment is an oxidation process which involves the use of a chemical as a catalyst or sensitizer for indirect photolysis of a contaminant within the water. When exposed to light of the appropriate wavelength, which is governed by the photochemical used, the photosensitizer or photocatalyst generates a reactive species, an hydroxyl or





5

peroxy radical, which subsequently reacts with the contaminant species (Ollis et al. 1989; Schiavello 1988; Teichner and Formenti 1985). This indirect process opens a much wider range of contaminants to destruction by photochemical means than would be available using only direct photolysis. The photochemical water treatment processes evaluated herein are photocatalysis, photosensitization and a combination of the two. The distinction between photocatalysis and photosensitization is based on the nature of the photochemical used.

Photocatalvsis

Photocatalysis, or photocatalytic oxidation, for water treatment applications refers to a heterogeneous oxidation reaction involving solid semiconductor surfaces. The reaction occurs via the irradiation of a semiconductor catalyst, such as titanium dioxide (TiO2), zinc oxide (ZnO), or cadmium sulfide (CdS), with visible or ultraviolet (UV) light. The reaction is possible because of the structure of the semiconductor. The optical bandgap of a semiconductor is an area devoid of energy levels, between the highest occupied energy band, the valence band, and the lowest unoccupied energy band, the conduction band. When a semiconductor absorbs light with energy greater than the energy of the semiconductor's optical band gap, photoexcitation results (Bahnemann et al. 1991; Mills et al. 1993). For example, since TiO2 has an optical band gap energy of 3.2 eV, absorption occurs with light of wavelengths less than 388 nm, ultraviolet light, as indicated by equation 1-1 (Zhang et al. 1994b).





6


he = (6.625x1T34jS)(3.oxl0lO cm )x( 1eV
..e 1.6xl- -9j )= 388nm ( 1-1)


The resulting excitation leads to the promotion of excess free electrons, e-, to the conduction band, leaving positive "holes," h', in the valence band, referred to as electron/hole (e-/h+) pairs. Equation 1-2 describes this process (Carey and Oliver 1980; Oliver and Carey 1986). The electrons and holes are highly energetic and very mobile (Turchi et al. 1989).


TiO2+ hv =* h+ + e- (1-2)

There are two paths that the e-/h+ pairs can take. They can either recombine and deactivate, or migrate to the surface of the semiconductor and react with surface species as shown in equations 1-3 to 1-5. Figure 1-1 is a graphical representation of this process for a single semiconductor particle.


OH + h' OH* (1-3)

H20(ads) + h+ OH* + H+ (1-4)

e- + O2-> HO*- (1-5)

If reactions 1-3 to 1-5 take place, reactive species are formed, which in turn are able to oxidize organic contaminants in the water. The less recombination which takes place, the more efficient the semiconductor is as a photocatalyst.





7

The peroxy radical, HO', disproportionates further to form more hydroxyl radicals, OH, which combine with organic substrate to form oxidation products as shown in reaction 1-6 (Blake et al. 1991; Ireland et al. 1993; Oliver and Carey 1986). If enough catalyst and light are present, a OH" + substrate oxidation products (1-6)

pseudo chain reaction occurs resulting in complete mineralization of organics. It is thought that the process for the destruction of biological substrate is very similar, with the oxidation of proteins, lipids or nucleic acids resulting in inhibition of respiration or growth of the microorganism (von Sonntag 1987).




Reduction


T hv > cond nd---- -- Adso 0tin of2
excitation

combination recomi t An

Adsorption
/ ofnH20
alenc oH2


Electron Energy Oxidation


Figure 1-1. Graphical Representation of the Generation of e-/h+ Pairs and
Recombination by Photocatalytic Reaction on the Surface of a Semiconductor Particle; After Bahnemann et al. (1991) and
Tseng and Huang (1990)





8

Photosensitization

Sensitized photolysis, also referred to as photosensitization or photodynamic action, is another method of indirect photolysis very similar to photocatalytic oxidation. In photosensitization, energy is transferred from a photochemically excited molecule to an acceptor. The sensitizer (S), often a dye, absorbs light and is photochemically excited to a higher energy state. This process may offer an advantage over the photocatalytic process because the sensitizers can absorb light in the visible spectrum, allowing for use of a greater percentage of available sunlight. The reaction proceeds via the triplet excited state, owing to its longer lifetime relative to the singlet excited state (Foote 1968; Larson et al. 1989) as shown in equation 1-7.


S + hv 'S* (excited singlet) -- 3S* (excited triplet) (1-7)


The excited sensitizer (S*) then transfers some of its excess energy to an acceptor, forming a reactive, transient form of oxygen, singlet oxygen, 102 (Larson and Weber 1994). Acceptors can be either organic material

(OM) or dissolved inorganic species such as molecular oxygen, 02. The intermediate reactive species produced from the reaction of the triplet sensitizer with organic material subsequently reacts with atmospheric oxygen under aerobic conditions (equation 1-8).


'S* + OM -+ transient specia + 02 -. oxidation products + S (1-8)

When the S' transfers its excess energy to molecular oxygen instead of OM, the oxygen molecule changes from its ground electronic state, the triplet state ('1g02), to the excited singlet state, '02. The organic matter is





9

then oxidized by the '02 to form oxidation products. Acher and Rosenthal (1977) described the mechanism by reactions 1-9 and 1-10: 3S* + 31g02-4 S + '02 (1-9)

102+ OM -4 oxidation products (1-10)


When '02 combines with unsaturated organic compounds (UC), it yields free radicals which readily combine with nucleic acids, lipids and proteins for destruction of microorganisms as demonstrated by reactions 111 to 1-13 (Acher and Rosenthal 1977).

102+ UC -4 ROOR --R (1-11)

RO" + RH --4 ROH + R" (1-12)

R"+02 -4 ROO', etc. (1-13)

The wavelength of light absorption is specific for each sensitizer. Methylene blue and rose bengal are widely used dye sensitizers which absorb in the visible region at Xmax 668 nm and Xmax 549 nm, respectively (Acher and Juven 1977).

Ideal sensitizers are defined as those compounds which exhibit the following criteria (Acher and Rosenthal 1977):

induce reactions with visible light,

are chemically stable during radiation or degrade to a sensitizing

species,
are free of reactive functional groups,





10

have good light absorption capacity, and are soluble in water but easy to remove.

Compounds which exhibit these qualities most efficiently are dyes, such as fluorescein and phenothiazine derivatives, flavins, certain porphyrins and polycyclic aromatic hydrocarbons (Foote 1968). For the purposes of water treatment, the latter two are too toxic; however, the others are acceptable. The sensitizers which have shown the most promise for both disinfection and detoxification, and which were evaluated for this research, are methylene blue and rose bengal. These dyes have been found to be relatively easily removed by precipitation with bentonite clay (Acher and Rosenthal 1977).

The Solar Resource


The sun can be modeled as a blackbody with a steady-state temperature of 5800K radiating approximately 6.416 x 107 W/m2 from its surface (Wieder 1992). The intensity of the sun's radiation on an object is inversely related to the square of its distance from the sun (Hsieh 1986). Since the distance of the earth from the sun varies throughout the year, the amount of sunlight reaching the atmosphere of the earth is not constant. However, a value termed the Solar constant, I, is the amount of solar radiation reaching a surface normal to the rays of sun outside the earth's atmosphere at a mean earth-sun distance of 1.5 x 1011 m (Hsieh 1986). Based on measurements, the established value of the Solar constant is 1377 W/m' (Randall and Bird 1989). Solar radiation reaching the atmosphere of the earth emits energies of wavelengths from gamma to radio, with most of





11

it concentrated in the visible region. The spectral distribution of the solar radiation outside the earth's atmosphere is given in Table 1-1.


Table 1-1. Spectral Distribution of Solar Radiation % of Total
0.00 0.395 (gamma to ultraviolet) 8.24
0.40 0.70 (visible) 38.15
0.71 2.00 (near infrared) 45.61
2.00 - (infrared to radio) 6.51
urce: Thekaekara (1976)



The amount of solar radiation, also referred to as insulation, available at the earth's surface at a given time is dependent on the prevailing climatic conditions, the level of atmospheric pollution and the angle at which the sun strikes the surface (Hsieh 1986). Scattering and absorption of radiation, due to the presence of ozone, gas molecules, particulate matter and water vapor (including clouds), account for a significant reduction in the solar radiation incident on the earth's surface (Barry and Chorley 1992). The path length of the solar radiation in the atmosphere, which changes with the time of day and latitude, determines the amount of extinction of radiation by these parameters (Hsieh 1986). Approximately 4-6% of the solar radiation reaching the earth's surface is in the ultraviolet wavelength range (Goswami 1995). The remainder of incident radiation is in the visible and near infrared range. Using historical weather data the direct beam incident radiation for a given location in space and time can be calculated with reasonable accuracy (Randall and Bird 1989).





12

The photochemical oxidation process is governed by the absorption of light within the wavelength of effectiveness of the catalyst or sensitizer used. For the TiO, photocatalytic process, the ultraviolet part of the spectrum, wavelengths below about 390 nm, is the most critical (Goswami 1995). This process, therefore, is well suited for areas where cloudiness prevails, as the ultraviolet light is often present both as scattered and direct beam radiation.

Photosensitization works with visible light, which is the greater part of direct beam incident radiation. The sensitizers evaluated in this work, methylene blue and rose bengal, are most effective in the blue (- 670 nm) and red (- 550 rn) ranges, respectively (Acher and Juven 1977).


Research Objectives


There exists a need for research, at all levels, tailored to address the needs of smaller, and possibly lesser developed, communities. The direct transfer of technology from one community to another is one of the solutions. However, it cannot serve as a replacement for the development of regional and community specific technology to solve regional and community specific problems.

In order for this more localized technology development to occur, however, the information base must be expanded. One primary method for the appropriate expansion of the information base is the conduction of research which is more focused on the needs specific to these communities. The investigation of basic techniques, technologies and processes which





13

may differ from the mainstream is key to the provision of tools necessary for the advancement and development of all communities.

The research reported herein is an effort to add some knowledge to that information base, and addresses two key areas of photochemical technology:

simultaneous treatment of chemical and microbiological

pollutants,

comparative efficacies of photosensitization, photocatalysis and

combined photosensitization and photocatalysis,

While the research reported herein is not a solution to the problem of water supply, it is anticipated that the knowledge derived from this research could be applied to accept or reject one option, photochemical treatment, as a partial solution. In the process of creating a better reality, the best that one can wish for is options and the information to adequately evaluate those options.












CHAPTER 2
REVIEW OF SOLAR BASED WATER TREATMENT

The use of sunlight for water treatment is not a recent phenomenon. Documented evidence for solar distillation systems exists as far back as 1551 when Arab alchemists used glass vessels and concave mirrors to distill water (Malik et al. 1982). However, technologies for solar based water treatment have changed dramatically in recent years. The development of photochemical technologies have significantly expanded the application potential for solar based water treatment processes. What follows is an exploration of the various methods of water treatment which use solar energy as the primary driver, and a review of the current state of related research.

Solar based water treatment processes can be roughly categorized as either physical or chemical. Physical processes are those processes which use the sun as a source of heat energy. Distillation and heat pasteurization fall into the physical process category. The chemical processes are those which involve a chemical reaction either directly or indirectly induced by light. These photolytic processes include ultraviolet disinfection and a number of photochemical processes.









14





15

Physical Processes

Distillation Processes

The most studied solar based water treatment process is desalination by distillation. Solar distillation involves the use of sunlight to evaporate saline or brackish water for the purpose of collecting the desalinated condensate. Two approaches have been taken in the development of solar distillation units. The first, and more conventional, involves the direct absorption of solar energy by saline water, called passive solar distillation. The second, active solar distillation, is similar to a standard chemical distillation process using sunlight as the heat energy source for indirect heating of the water. In this type of unit, evaporation is in a centralized facility (Malik et al. 1982; Rajvanshi 1979). Passive distillation

Passive solar distillation is easily understood when compared to the natural process of the hydrologic cycle. In the hydrologic cycle, the sun provides energy which warms the water of the oceans and other large water bodies, causing evaporation. Convective wind energy transports this vapor into the atmosphere where it condenses and produces precipitation. The precipitation either directly, as rain, or indirectly, as melted snow, recharges fresh water sources: lakes, rivers, streams, underground springs and groundwater aquifers.

The solar distillation process is a simulation of this process in manufactured facilities. The sun warms the collected body of saline or brackish water and causes evaporation. The water vapor is carried by





16

convective winds, induced by the appropriate construction, and, upon cooling, the vapor condenses as pure distilled water.

The conventional design for passive distillation systems is the basintype solar still (Figure 2-1). The bottom surface of the basin is black to enhance the absorption of radiation by the saline or brackish water, supplied either continuously or batchwise (Malik et al. 1982; Rajvanshi 1979). The basin is covered with a transparent, air tight cover which slopes downward to facilitate transport of the condensate as a thin film into a collection trough (Malik et al. 1982; Rajvanshi 1979). Solar radiation penetrates the cover, generally glass or plastic, and is absorbed by the water, warming it to induce evaporation. The temperature differential between the cover, which does not absorb much radiation, and the water surface leads to air convection currents which move the water vapor to the underside of the cover. The cool temperatures of the basin cover, relative to the water temperature, cause condensation, and the water forms a thin film which is collected via troughs. Basin stills can be either shallow or deep, depending upon the design and operational requirements. Shallow basins stills have water depths ranging from 1.25 cm (0.5 in) to 5 cm. ( 2 in) and deep basin still water depths range anywhere from over 5 cm (2 in) up to 91 cm. (3 ft) (Rajvanshi 1979).

The first modem commercial solar still was installed in 1872 in the northern part of Chile, designed by Swedish engineer Carlos Wilson. The glass covered basin type solar still was 4700 m' and operated for many years treating feedwater with a salinity of 140,000 ppm (Howe and Themat 1977; Malik et al. 1982). Work conducted at the University of California's





17

Engineering Field Station in Richmond, California, concentrated on reducing capital costs and improving efficiency of the basin still by changing the geometric configuration. Designs tested included a circular still, several trough type stills with rounded or v-shape bottoms and stairstepped stills. The general conclusion of this work was that the basin type solar stills were not economically competitive in any of the tested configurations (Howe and Tliemat 1977).




SOLAR
RADIATION


GLAss COVER CONDENSATE
CNFILM
COLLECTION
TROUG
CONVECTIVE
WINDS

DISTILLATE

SALINE WATER IN BASIN WATER


BLACKENED BASIN BOTTOM
BRINE OUT

Figure 2-1. Conventional Passive Solar Basin Still; After Malik et al. 1982 and Rajvanshi (1979)


At the University of Florida's Solar Energy and Energy Conversion Laboratory, Rajvanshi (1979) evaluated the efficacy of dyes as a means of increasing the efficiency of solar distillation. Using deep basin stills he added dye to saline water to increase radiation absorption and alter the heat





18

transfer rate. Three dyes, black napthylamine, red carmoisine, and a dark green mixture were used. The water treated with up to 500 ppm dye had an increased output of as much as 29% on clear days, however, no increase in output was observed with the dyes on completely cloudy days. Both the red and green dyes degraded when exposed to sunlight, however, the black dye, which also exhibited the largest increase in evaporation rate, did not visibly degrade with exposure to sunlight.

Other research has focused on developing and improving the conventional basin type passive still. What emerged was the tilted tray solar still, wick solar stills, and double basin stills (Al-Karaghouli and Minasian 1995; Higazy 1995; Howe and Tliemat 1977; Malik et al. 1982).

The tilted tray solar still is a variation of the basin type solar still in which the basin is broken into a series of narrow strips arranged like steps. Each strip is on a different elevation, bringing the water surface much closer to the transparent cover, and increasing the operating efficiency. Generally these types of stills have very shallow basins. While the efficiency is increased, so is the capital cost, making this type of still infeasible for commercialization (Howe and Tliemat 1977).

Wick still designs utilize an absorbent material (wicking), usually black to absorb radiation, as a facing on a glass covered inclined plane. Saline water is introduced along the upper edge of the inclined plane and trickles down saturating the wicking. The primary difficulty with this design is an inability to maintain a uniformly wet surface (Howe and Tliemat 1977).





19

Double basin stills utilize the latent heat of the condensing water vapor, thereby increasing the daily yield over the conventional basin design. The double basin still has two transparent covers. The inner glass cover acts as a second, very shallow basin, with water running over it like a thin film from a pipe in the center. The heat from the water condensing on the underside of the lower basin cover is used to aid vaporization of the water on the topside, which then condenses on the upper cover. The distilled water is drained and collected from the underside of both transparent covers (Malik et al. 1982).

During World War II Dr. Maria Telkes designed an inflated plastic still for use with the life rafts of the United States armed forces (Howe and Themat 1977). The design was similar to the basin still, however, it utilized a saturated sponge as the absorption media, and the entire assembly was designed to float on top of the water. Distillate was collected in a bottle at the bottom of the unit. These types of stills were referred to as floating sponge solar stills and reportedly over 200, 000 of them were produced during the war (Howe and Thernat 1977).

Higazy (1995) reported on the design and performance of a floating sponge solar still for desalination of sea water. The still design was based on the original design by Telkes. In Higazy's design water was pumped into the bottom of the still and constituted the bottom layer. Above that layer was a plastic sponge covered with a black cloth, which was where the radiation was absorbed and then transferred by conduction to the sea water. He examined two still designs, a single sloped cover which used mirrors to increase the radiation absorption area and double sloped cover, evaluating





20

the parameters of insulation intensity, temperature and the sponge properties (thickness and density). The primary improvement of this system over Telke's was that the use of plastic parts eliminated the problem of corrosion.

Higazy's experiments were conducted using tap water and it was not indicated whether salts were added to simulate the saline environment produced by sea water, although the physical and behavioral properties were very similar. The design had no provisions for drainage of sea water or periodic removal of the salts from the still and or the sponge, and eventually problems might result from salt accumulation.

Al-Karaghouli and Minasian (1995) developed a new type of passive solar still using a floating-wick and compared the still to conventional basin solar still and the tilted wick solar still. They also introduced azimuth and altitude tracking to increase the incident solar radiation on the still. The floating wick still was a conventional basin type solar still which contained a blackened jute wick floated on a polystyrene sheet. The unit floated no more than 0.5 cm above the still water level. The benefit of the floating wick still was due to the capillary action of the jute cloth, which was prepared in a corrugated shape to restrict salt accumulation to the upper parts. The stills used for comparison were made with the same materials and similar style to the floating wick for direct comparison. The floating wick solar still had a higher output than the other stills with which it was compared.

The use of a corrugated shape solved the problem of scale formation and, due to the capillary action of jute cloth, the wick stayed uniformly wet. Consequently, in the summer months the floating wick still had a





21

higher output, versus comparable performance with the wick still during the cooler months. Tracking increased the output on all of the stills but was particularly impressive with the floating wick still, almost doubling the performance without tracking and having at least 30% higher output than the conventional basin still with tracking (Al-Karaghouli and Minasian 1995).

Solar distillation technology is fairly well established and has proven useful for small scale desalination of water. However, research has not advanced to the point where large scale processes are economically competitive with more conventional methods of distillation. Active distillation

Active solar stills are those systems in which the sun's energy is captured external to the distillation system, either as thermal energy or photovoltaic electrical energy used to generate heat. In both cases the generated heat is then applied to the distillation unit. They can operate in conjunction with the conventional basin still, or they can be designed like a conventional flash distillation unit. Figure 2-2 shows a standard schematic for an active solar still which uses a solar collector and multistage flash distillation.

Prasad and Tiwari (1996) conducted a thermal analysis of a concentrator-assisted solar distillation unit to optimize the inclination of the glass cover. They determined that the angle of inclination had an effect on the yield of this active solar distillation system, with an increase in yield which corresponded to an increase in the angle of inclination. For the climatic conditions studied (Delhi, India, latitude 28' N, longitude 77' E) an





22

angle of 75' was found to be optimal. The increased angle also led to a decrease in operating temperatures and evaporative heat losses.
SOLAR RADIATION



LU W
0
< VAPOR
HEAT
ExcmmeE
BRINE FLASH CHAMBERS FEED
COULD BE ULINE
ONE U141T WA-MR


Figure 2-2. Schematic of Flash Distillation Using Solar Collector; After
Malik et al. (1982)


Farwati (1997) conducted a comparison of a multi-stage flash distillation system using solar energy input with flat plate versus compound parabolic collector (CPQ systems. The conditions used for evaluation were monthly average climatic conditions for Benghazi, Libya. Both collectors had an aperture area of one square meter. The compound parabolic collector was able to achieve a higher water temperature for entry into the flash distillation system (122'C vs 80'C) and a larger monthly average daily output with maxima of 64.9 liters for the CPC and 43.7 liters for the flat plate collector system in the month of August. Both systems operated with auxiliary heaters. Using the solar collectors alone, the CPC had a maximum monthly average daily distillate output of around 40 liters and the flat plate collector one of about 25 liters.

Kumar and Tiwari (1996) compared performance of flat plate collector solar distillation systems in several operating modes. They





23

examined the systems with and without flow over the glass cover, operating in active versus passive mode and in double effect passive mode (i.e. second glass cover with water flow over the cover closest to the basin). They found that water flow over the glass cover gave the highest yield, as this decreased the condensation surface temperature and utilized the latent heat of condensation providing additional distillation. The system was a single basin solar still made of fiber-reinforced plastic, coupled with a flat plate collector and was really a hybrid of the passive and active system. The double effect mode did not enhance performance because of the difficulty of maintaining low and uniform flow rates over the glass cover. Tests were run with 1 m' area of cover and collector. On average the active mode with water flow yielded 7.5 liters per day, the passive mode yielded 2.2 liters per day, and the active without water flow yielded 3.9 liters per day.

Sing and Tiwari (1993) evaluated and compared the yields and thermal efficiencies of those types of solar stills recommended for rural or urban applications The types of stills evaluated were: 1) passive single basin, 2) passive double basin, 3) multiwick single basin, 4) multiwick double basin, 5) active single basin and 6) active double basin. As anticipated, the double basin stills outperformed the single basin counterparts in both daily yield and thermal efficiency. Of the systems studied, the active double basin had the highest yield while the multiwick double basin had the best thermal efficiency. However, the use of the double basin was not recommended with high salinity feedwater (> 20,000 ppm). The multiwick single basin was suggested for moderate salinity (<1500







ppm) and the double basin designs were only recommended if technical personnel were not readily available.

Pasteurization Processes


Pasteurization, or thermal disinfection, is the application of heat for a specified time in order to destroy harmful microorganisms (Parker 1984). The pasteurization process is best known for it's use in the food and beverage industry, particularly for the pasteurization of milk. Recently, this technology has been examined for it's use for drinking water. In order to sterilize water by pasteurization, the water must be heated to a temperature of 72'C (16 1'F) for a minimum of 15 seconds (Cheremisinoff et al. 1981). Pasteurization can be obtained at lower temperatures, as low as 55 65'C (134 1490F); however, the required residence time increases significantly as the temperature is reduced (Ciochetti and Metcalf 1984; Joyce et al. 1996). The lower temperatures are attainable by solar heating. One primary benefit of thermal disinfection over the photooxidation process is that light penetration is not required, thereby making it effective in high turbidity water.

Andreatta et al. (1994) reviewed the use of pasteurization devices in the developing world with reference to several different styles of systems. The solar box cooker, solar puddles and flow through systems similar to solar hot water heaters have all been used as pasteurizers.

The solar box cooker used as a pasteurizer is the least expensive, but also the most unreliable. A method for ensuring that the appropriate temperature has been reached is required and sometimes difficult to verify.





25

Another drawback is that it is strictly a batch method, so the water is not available throughout the day (Andreatta et al. 1994).

A flow through device can be manufactured using readily available materials such as an automobile radiator thermostat valve and black painted tubing. The design is a simple heat exchanger, and several design variations have been tested. Flat configurations have been demonstrated to be more effective than tubular varieties, although the tube exchanger may be simpler to construct. The temperature control is very important, and the design is critical in order to have the appropriate residence time. The primary benefits of the flow through pasteurizer are the availability of water throughout the day, easier control and ability to process larger quantities of water (Andreatta et al. 1994).

The solar puddle is a low cost large area device. It resembles a solar basin still in that there is a trough and a cover of clear plastic, however, since the water is not saline, there is no need to separate the condensate from the water in the puddle. For the puddle, determining that the appropriate water temperature and residence time is reached is difficult (Andreatta et al. 1994).

Ciochetti & Metcalf (1984) evaluated the use of a solar box cooker (SBC) for pasteurization of water. They found that temperatures for milk pasteurization (651C) for several hours were sufficient to kill most waterborne pathogens including viruses. Vertical temperature

differentials were found within containers, and the position of both the jug in the SBC and the SBC itself had a significant effect on temperature and consequently sterilization. Tests were conducted in northern California





26

and required temperatures for pasteurization were reached for approximately six months of the year, from mid-March through midSeptember.

Joyce et al. (1996) investigated the thermal contribution of sunlight to the inactivation of fecal coliforms with both onside testing and laboratory simulations. Their research was focused on the use of pasteurization for household systems. Using transparent 2-liter plastic bottles, of the type used for carbonated beverages, the water was heated to a temperature of about 55 'C, the same temperature recorded for 2-liter bottles of water in full sunshine in Kenya (latitude, 1'29'S; longitude, 36'38T). Complete disinfection was obtained after 7 hours at 550C.

Burch and Thomas (1997) evaluated the feasibility of solar pasteurization for water treatment in developing communities, comparing it with other technologies traditionally employed in that arena. They concluded that solar pasteurization, preceded by roughing filtration for high turbidity water, was not economically competitive when compared with slow sand filtration, chlorination, and UV disinfection. However, it was the most effective of the four for a broad spectrum of microbiological contaminants and had the lowest maintenance requirements. Flow

through solar pasteurization was slightly less costly than existing batch processes, and the cost could be reduced more with the use of a thin-film polymer system currently under study (Burch and Thomas 1997).

Solar pasteurization is not a feasible method for large water purification systems, however, it shows clear promise for small remote communities, household needs or emergency situations in areas with







several hours of sunshine throughout the day. Pasteurization has the benefit of providing disinfection regardless of the turbidity of the water. One major hurdle is the ineffectiveness on cloudy days, which may be circumvented by having storage available and purifying larger quantities of water on clear days for cloudy day use.

Photo Processes


Experiments on the effect of sunlight on microorganisms were conducted as early as the late 19th century. Downes and Blount (1877) observed the disappearance of turbidity, as an indication of the presence or absence of microorganisms, from acidic urine placed in sunlight for several hours. Since that time, much has been learned about the effect of light, specifically ultraviolet radiation, on the inactivation of microorganisms.

In the early 1900s direct photolysis by ultraviolet (UV) radiation was used for disinfection of potable water (Wolfe 1990). While this method was abandoned in favor of chlorination, problems with chlorine disinfection byproducts have encouraged researchers to take another look at UV. Recent studies on the use of UIV for drinking water have proven more successful (Slade et al. 1986; Wolfe 1990). Direct photolysis, however, only affects those species which can directly absorb light, primarily microorganisms.

Indirect photolysis, photosensitization or photocatalysis, provides another alternative. When exposed to light of the appropriate wavelength, the photosensitizer or photocatalyst generates a reactive species, such as a hydroxyl radical or peroxy radical, which subsequently reacts with the







contaminant species. This opens a much wider range of contaminants to destruction by photochemical means and creates the possibility of simultaneous destruction of microbiological and chemical contaminants. Solar Disinfection

Solar disinfection is direct photolysis by radiation from the ultraviolet spectrum (wavelengths shorter than 390 inn) sometimes referred to as photodynamic inactivation. Acra et al. 1990 have used sunlight for small scale disinfection of drinking water by direct photolysis of microbiological contaminants. Acra et al. (1990) postulated that a minimum solar UV-A intensity of 17.8 W/m' was required for 99.9% inactivation of fecal coliform based on field testing of solar disinfection reactors. The residence time required to reach these levels of inactivation ranged from 90 minutes to 2.5 hours depending on the microorganism (Acra et al. 1990). The data indicated that a longer residence time, achieved by recirculation, lower flow rates, or increased reactor volume, could also lead to inactivation (Acra et al. 1990). They found that bacterial destruction wsa exponential as a function of solar UV-A intensity and time. The major problem encountered was the growth of phytoplankton in the reactor (Acra et al. 1990).

In studies for the inactivation of Escherichia coli in sunlight, Shah et al. (1996) found that the rate of inactivation was related to the initial colony density. At very high initial densities of E. coli, inactivation was not sufficient for provision of safe drinking water. SODIS

A hybrid technology which combined the benefits of UV disinfection and heat pasteurization was proposed by Sommer et al. (1997). With the







SODIS reactors water was heated to a temperature of 501C and subjected to solar UV-A providing both thermal and UV disinfection. Complete

inactivation of fecal coliform in 2.5 hours was reported, even on completely cloudy days. The hybrid technology was more effective on the partly cloudy to completely overcast days when compared to pasteurization alone at 70'C. Halosol

The halosol process is a combination of the use of halogens and sunlight developed at the American University in Beirut, Lebanon in the late 1970s to early 1980s. The process involves treatment with large doses of sodium hypochlorite or iodine solutions followed by exposure to radiation. The intended benefit is disinfection of small volumes of heavily polluted water followed by the removal of excess halogens for taste and odor control (Acra et al. 1990).
Photocatalysis

The most commonly studied indirect photolysis reaction for water and wastewater treatment is photocatalysis using titanium dioxide, TiO2, as a catalyst. Laboratory, pilot and field studies have demonstrated TiO2 catalyzed photodegradation of a wide range of organic chemicals (Table 2-1) including alcohols, aldehydes, alkanes, alkenes, amines, aromatics, carboxylic acids, dioxins, dyes, fuel constituents, halogenated hydrocarbons, herbicides, ketones, mercaptans, pesticides, polychlorinated biphenyls, solvents, surfactants and thioethers (Aithal et al. 1993; Das et al. 1994; Ellis 1991; Goswami and Jotshi 1992; Legrini et al. 1993; Mills et al. 1993; Ollis 1986; Zhang et al. 1994b). Several researchers have





30

demonstrated the inactivation of microorganisms in water by TiO2

photocatalysis (Table 2-2).


Table 2-1. Examples of Photocatalytic Treatment of Water and Wastewater INVESTIGATOR(S) CONTAMINANT(S) .CATALYST
'Low et al. (1991) Amines TiO2
... ....................... ....................................................... .................. : ............... .......... . .. . .. . .. ............................... ......... ............... . . . . .
Abdullah et al. (1990) Aniline TiO
Goswami et al. (1993) and Oberg (1993) enzene, Toluene, Ethylbenzene, TiO, Xylene
;Barbeni et al. (1987) Chlorinated Aromatics TiO,
Matthews (1986) :Chlorinated Benzenes -iO
Ahmed andli (1984 Hsiaoet al.' ,Halogenated Hydrocarbons, TiO (1983), Matthews (1986), Nguyen and Solvents (THMs, TCE, etc.) Ollis (1984), Ollis (1985), Pruden and
Ollis (1983a), and Pruden and Ollis
(1983b)
Harada et al. (1990) Organophosphorous Insecticides TiO/Pt
Al-Ekabi et al. (1989), Goswami" et al. Phenols & Chlorophenols TiO, 1992 and Li et al. (1992)
Pelizzetti et al. (1988) Polychlorinated Dioxins and 'iO ZnO, CdS
Polychlorinated Biphenyls IiOPt & Fe O
Maillard-Dupuy et al. (1994) Pyridine TiO,
Pelizzetti et al. (1990) S-Triazine Herbicides -TiO ,
Pelizzetti et al. (1989) Surfactants TiO2



Photosensitization


The body of literature on the use of photosensitization for water

and/or wastewater is much less extensive than that for photocatalysis with

TiO2. Most of the work with regard to microorganisms has been done in the

medical field (Tratnyek et al. 1994). However, some work on virus

inactivation and wastewater treatment was conducted in the early 1970s

(Gerba et al. 1977a; Gerba et al. 1977b; Hobbs et al. 1977; Sargent and

Sanks 1976). Recently, researchers have investigated the use of

immobilized sensitizers for coliform destruction (Savino and Angeli 1985).





31

Table 2-2. Examples of Photocatalytic Treatment of Water and Wastewater
SPECIAL
'INVESTIGATOR (S) CONTAMINANT(S) CATALYST CONDITIONS
. . ........... ........ ....................... ............... . . ................................................................. ..................................... . . ............... ................. :
iBlock et al. (1997) Escherichia coli, Serratia TiO2
marcescens,
JIreland et al. (1993), Wei Escherichia coli :et al. (1994) and Zhang et
:al. (1994a)
.Matsunaga et al. (1988) -Escherichia coli _Ti02 Immobilized
......m Membrane
Matsunaga et al. (1985) tshrci :oi atbclu TiO2/Pt PtLoaded
icidophilus, Saccharomycces catalyst
cerevisiae
i' a tl................................... ............... 19 3 a i ls.......... ........................................ ......... ................................................... st a o h r o h l si i 2'i................................
:Patel (1993) B8acillus stearothermophilus MiO2
i spores, Escherichia coli,
.Micrococcus luteus,
Pseudomonas aeruginosa,
:Serratia marcescens,
Staphylococcus aureus
.............. -t i 9 2 ................................. z t e t c s o r n s ......................... ........................... ........ ...................... .i ...........................................
Stoet al. (1992) Streptococcus sobrinus
Sjogren and Sierka (1994) batriopaeM2T0 Adto of Iron
t p a e M 2 ............................ i % ....... ............



The remainder of the work on wastewater treatment has been

conducted by only a few researchers working in concert. Their

investigations on the treatment of wastewater and sewage effluents using

methylene blue and rose bengal have shown that the technology was viable

in laboratory, pilot and field scale demonstrations (Acher 1984; Acher et al.

1994; Acher et al. 1990; Acher and Juven 1977; Acher and Rosenthal 1977;

Eisenberg et al. 1987a; Eisenberg et al. 1986; Eisenberg et al. 1988). In

addition to the microbiological contaminants, this work addressed

wastewater and the specific industrial contaminant bromacil, indicating

some viability for simultaneous treatment. The use of flavins was

demonstrated for the destruction of herbicides and other organics such as

phenol and aniline (Larson et al. 1989; Larson et al. 1991; Schlauch 1987).

A brief summary of work in this area is shown in Table 2-3.








Table 2-3. Summary of Photosensitized Treatment of Water and Wastewater
INVESTIGATORS) -CONTAMINANTS ;SENSITZR(S) CONDMONS
.Acher and Juven 1977 Escherichia coli :MB, RB oxidation pond
s ewage water
Acher et al. 1990 ifecai coliform, OMB ilot plant sewage
-enterococci, coliforms,: Wffluents
polio viruses .. ........... I
iGerba et al. (1977a) and coliform & polio virus 'MB -ensitized for 24 h
'Gerba et al. (1977b)
. ............... .. .. ....... -... ................... ....... ........... ........................ ...................................... .. .. .. .. ....... ..........................................
Hobbs et al. 1977 coliform & polio virus ::MB
!Savino and Angeli 1985 E. coli MB RB, eosin Immobilized dyes
..... ................... .................................... ............................................ .......... ............ ....... .. ...................... ..........................................
:Burkhard and Guth (1976) Triazine Herbicides :Acetone 'Crosby and Wong (1973) 2,4,5-T 'Riboflavin & Acetone
Hadden et al. (1994), and ip -cresol, phenol *MB, rhodamine 6G, high pH (9-10) :Sargent and Sanks (1976) :neutral red, RB
:malachite green,
:hematoporphyrin-D,
L-hydrochloride,
acridine orange &
:others
l~so~ d ~i~i 89 .......... .... ........... I.a ] e i" ..........1- ...- o-- -............. --.......................................Larson et al. 1989 -Aniline & phenols :Riboflavin (RF)
:Schlauch 1987 Triazine Herbicides MB, RF
Aer an osenthal 1977 fcloiorC ,MBRBAerated sewage
-MBAS effluents
!: ch'e :" 9S~~~~~i ..................... a h : : o i ...... .......... .~ B a :.................a ......................................
Acher 1984 'Organics, E. coli, MB & RB(Algae, Vastewater
bacteriophages, polio bacteria & viruses) vrus & algae
'Acher et al. (1994) secondary effluent :MB wastewater
'Eisenberg et a]. 1987 coliform & bromacil :MB secondary sewage
............i ............. ....... ........... ............. - ............ ...... ....... .. .......- -.... ...-.............................. e o ; g e
i i i effluent !



Summary


In terms of effectiveness, the photochemical processes are preferable

for overall water treatment to both the physical processes and straight solar

disinfection, with the exception of desalination, with which it is not

comparable. These processes are effective on both microbiological

contaminants as well as on a wide range of chemical contaminants.

However, in order for these methods to be commercially viable on a large

scale, additional research must be conducted. There are three primary





33

areas where efforts should be concentrated: separation of the photochemical from the water, including immobilization, elucidation of harmful intermediates in lieu of complete mineralization and development of cost efficient or optimal operating parameters. For disinfection the photochemical processes compare favorably to solar disinfection, pasteurization, SODIS and halosol. Any of these process can be viewed as appropriate, particularly for household or small community applications. In locations where sunshine is in large supply and technically trained personnel and fossil fuels are in shorter supply, the use of solar based processes for treatment of water may prove to be a satisfactory alternative.












CHAPTER 3
EXPERIMENTAL DESIGN AND METHODS Choice of Experimental Parameters

The performance of a photochemical reactor system is affected by a myriad of variables, only a few of which can be controlled. While the choice of photoreactant and the availability of light of the appropriate wavelength range are the two most critical variables, there are other, more subtle changes in reaction conditions that enhance or degrade the reaction efficiency. Both the concentration and the physical form of the catalyst or sensitizer have a marked influence on the efficacy of a given reactor (Matthews 1991; Wyness et al. 1994). Beyond those factors already mentioned, pH, the presence or absence of dissolved oxygen, reactor design, and the nature of the contaminants exhibit the most significant effect on process reaction rates (Acher et al. 1994; Befford et al. 1993; Hidden et al. 1994; Kawaguchi and Furuya 1990).

Development of the experimental design was predicated on analysis of reported work and preliminary experiments in consideration of the aforementioned variables. The choices made for the research reported herein regarding each parameter were noted at the end of the applicable section.






34





35

Contaminants

Some unique problems identified with groundwater throughout the United States Virgin Islands (USVI) served as a basis for the selection of contaminants for this study. Used as source for drinking water, much of the USVI groundwater is chemically contaminated with light hydrocarbons from leaking fuel tanks.' In addition, due to leakage from underground sewerage, the microbiological contamination is rather extensive.2 A 1986 study of USVI waters found microbiological

contamination in the form of Streptococcus, Klebsiella, Acinetobacter spp., Enterobacter, Pseudomonas, Salmonella and Escherichia coli (Canoy and Knudsen 1986).
To simulate contamination from leaking fuel tanks, benzene, toluene and xylene were used as chemical contaminants. E. coli, Serratia

marcescens and Pseudomonas aeruginosa were used as microbiological contaminants, indicative of the contamination identified by Canoy and Knudsen (1986), and what might be present from leaking sewerage. Catalyst Choice

A number of semiconducting materials have been tested for use as photocatalysts in water and wastewater treatment. In order for a material to be effective for solar photocatalytic water treatment, it must be photoactive, able to use visible and/or near UV light, biologically and chemically inert, stable under irradiation, inexpensive, and non-toxic to humans and aquatic organisms (Carey and Oliver 1980; Mills et al. 1993).


1 From private conversation with Bruce Green of Carribean Infratech.
2 Ibid.





36

Several researchers have tested semiconductors for photoactivity, including barium titanate, BaTiO3, cadmium sulfide, CdS, tungsten oxide, WO,3, titanium dioxide, TiO2, zinc oxide, ZnO, and zinc sulfide, ZnS (Blake 1994). On the whole, TiO2 is more active than the others (Blake 1994). Barbeni et al. (1985) evaluated four other semiconductor oxides relative to TiO2 for the photocatalytic degradation of pentachlorophenol and found photocatalysis to be the most efficient. In studies of the destruction of dichlorobenzene using ZnO, WO3, platinized TiO2 and untreated TiO2, the TiO, photocatalyzed samples reacted faster (Pelizzetti et al. 1988).

Carey and Oliver (1980) evaluated several semiconductor oxides for stability under irradiation in neutral aqueous solution (Table 3-1). Of the semiconductors tested, only those containing titanium were found to be photostable. With an optical band gap of 2.4 eV, CdS is highly photoactive and excited by visible light, appearing to be attractive as a photocatalyst. However, as is typical for semiconductors which absorb visible light, it is not photostable and tends toward photoanodic corrosion (Davis and Huang 1991; Mills et al. 1993). In the case of cadmium sulfide this leads to the precipitation of undesirable and ultimately toxic compounds, as shown in equation 3-1.


CdS + 2h' -+ Cd2+ + S (3-1)


Considering all of the evidence TiO2 seems to be the most desirable for photocatalytic processes to date. TiO2 in anatase form is the most





37

commonly used, due to its chemical stability, ready availability and photoactivity (Blake 1994; Zhang et al. 1994b).


Table 3-1. Photostability of Semiconductor Oxides Tested by Carey and Oliver (1980)
Semiconductor Photostable
BaTiO3 yes
CaTiO3 yes
MgTiO3 yes
SrTi03 yes
TiO2 (anatase) yes
TiO2 (rutile) yes
V205 no
ZnO no
ZnTiO3 yes


There have been a number of efforts to increase the efficiency of TiO2 by surface modification of the catalyst or substitution doping. Loading of the Ti02 surface with noble metals has been used to enhance electron transfer (production of hydroxyl radicals) and to prolong the life of the oxidation site at the exterior surface (Blake 1994; Zhang et al. 1994b). Silver-loading of anatase TiO2 increases the efficiency for the destruction of chloroform and urea by 10% and 67%, respectively (Kondo and Jardim 1991). Other metals used for surface modification are Pt, Rh, Cu, Ni and Pd. While these metals have been shown to increase efficiency, the cost and complexity of the surface deposition process are prohibitive for use in most communities. Substitution doping of TiO2 presents the same difficulty. For these reasons anatase TiO2, Degussa P25, was used for this research. Choice of Photosensitizer

In addition to the chemical criteria outlined previously for photosensitizers, they must also be inexpensive and non-toxic. Methylene





38

blue is the photosensitizer commonly used in water treatment research. It is preferred because it is inexpensive, absorbs preferentially at 670 nm, a wavelength which easily penetrates wastewater effluent, and has a very low toxicity. Methylene blue is administered orally in humans for medicinal purposes (Gerba et al. 1977b; Hobbs et al. 1977).

Martin and Perez-Cruet (1987) evaluated a number of dyes for suitability as sensitizers. Using sterile sea water with a salinity of 28 ppt, twelve dyes were studied for absorption tendency by clams (Mercenaria mercenaria) and photodynamic action against Escherichia coli. Of the dozen dyes tested, five were considered suitable for further testing by Martin and Perez-Cruet, and rose bengal showed the most promise. Table 3-2 shows the order of effectiveness of selected dyes against E. coli as determined by Martin and Perez-Cruet (1987).

Other researchers have found methylene blue to be the preferred dye sensitizer, although rose bengal seems to work almost as well under most circumstances (Acher and Rosenthal 1977; Gerba et al. 1977b; Sargent and Sanks 1976; Savino and Angeli 1985). Several researchers (Larson et al. 1989; Mopper and Zika 1987; Schlauch 1987) have investigated the use of flavin sensitizers. Their research suggests that riboflavin and lumichrome are both good photosensitizers.

Acetone is the one other photosensitizer which seems to have given good results for water treatment. In tests for the photodecomposition of the herbicide 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), both acetone and riboflavin showed promise (Crosby and Wong 1973). Burkhard and Guth





39

(1976) also found acetone effective for the photodegradation of triazine herbicides. However, acetone is known to cause systemic effects when ingested by humans (Sax and Lewis 1989).

Based on this information it appears that the research of photosensitizers is less conclusive than that for photocatalysts, warranting further testing. Therefore, both methylene blue and rose bengal were selected for further evaluation.

Reactor Desien

The overwhelming majority of the research on reactor design for photochemical water treatment has been conducted for semiconductor photocatalysis, primarily with TiO2 (Blake 1994). However, since the reactions follow similar mechanisms, the same principles should apply to both photocatalysis and photosensitization.

The two major reactor options are reactors using catalyst suspended in slurry or those in which a fixed supported catalyst is employed (Blake 1994). While the bulk of the research for water and wastewater treatment has been conducted using slurries of titanium dioxide, there has also been a great deal of research in the area of immobilizing the catalyst using a number of different media, with varying results (Blake 1994). Benefits for the use of supported catalyst are the elimination of the need for separation and recovery of the catalyst and a possible increase in the reaction rate (Zhang et al. 1994b).

Researchers at the University of Florida tested both flat plate photoreactors (Wyness et al. 1994) and shallow pond reactors (Bedford et al.





40


1993) for the destruction of 4-chlorophenol (4-CP) using TiO2 adhered to

fiberglass mesh. They found that the same reactor systems performed

better with the slurry catalyst than with the fiberglass mesh. For the flat

plate configuration, reaction rates were two to five times faster (Wyness et

al. 1994).



Table 3-2. Order of Effectiveness of Dyes at 10-4 M Concentration on E. Coli After 24 Hours Exposure to Light at Room Temperature

Light Intensit5 E. coli colony coverage in quadrant areasa, mean + SD Dye gEm-2 sec- 1 1 2 3 4
Control 75 8.70.5 8.0 1.1 4.5 2.0 0.8 0.4
Control 300c 9.0 0.5 9.0 0.5 6.6 0.9 1.2 0.4
Rose Bengal 75 0 0 0 0
300 0 0 0 0
Erythrosine 75 7.0 1.4 0 0 0
300 0 0 0 0
Eosin Yellowish 75 6.0 2.8 0.5 0.7 0 0
300 1.0 0.5 0 0 0
Zinc Phthalocyanine- 75 7.0 1.4 4.0 4.2 0 0
tetrasulfonate 300
Acridine Orange 75 8.0 0.5 1.5 0.7 0.5 0.7 0
300 5.5 3.5 0.5 0.7 0 0
Methylene Blue 75 9.0 0.5 4.5 0.7 1.0 0.5 0
300
Fluorescein Sodium 75 9.0 0.5 7.5 0.7 3.5 0.7 0.3 0.1
Salt 300 8.5 0.7 2.0 2.8 0 0
Alphazurine A 75 9.0 0.5 7.5 2.1 1.5 0.7 0
300 9.0 0.5 8.5 0.7 4.5 2.1 0.5 0.7
Rosolic Acid 75 9.0 0.5 6.0 2.8 2.0 1.4 0
300
Alcian Blue 75 9.0 0.5 7.5 0.7 2.0 1.4 0.5 0.7
300
Hematoporphyrin 75 9.0 0.5 8.5 0.7 4.5 3.5 1.6 2.1
300 9.0 0.5 8.5 0.7 4.5 0.7 0.8 0.4
Alizarine S 75 9.0 0.5 9.0 0.5 4.5 2.1 0.8 0.4
Monohydrate 300 9.0 0.5 9.0 0.5 5.0 1.4 1.0 0.5
aStreaked areas: 1, first streak; 2, streaks from first streaks; 3, streaks from second streak; 4, streaks from third streaks. bTemperature, 250C. CTemperature, 280C. Source: Martin and Perez-Cruet (1987).





41


Zhang et al. (1994) compared the performance of a number of different optimized catalyst support options with TiO2 slurry using a flat plate reactor configuration. Of those supports tested, all except glass beads performed as well as, or slightly better than, the slurry, with silica gel performing best.

Hofstadler (1994) evaluated titanium dioxide-coated fused-silica glass fibers for the degradation of 4-CP and reported degradation rates 1.6 times higher than with TiO2 slurry. Some other silica based supports which have been evaluated were coated sand (Matthews 1991) and glass (Lu et al. 1993). Matthews found that suspensions of TiO2 coated sands were much easier to deal with in terms of separation, but were mass transfer limited. The work by Lu et al., using TiO2 supported on the inner surface of a glass tube reactor, indicated the possibility of catalyst reuse.

Fox et al. (1994) examined the effect of zeolite supported TiO2 and TiO2 pillared clays on the degradation of alcohols and found a slight decrease in photoactivity relative to TiO2 slurry. Matsunaga et al. (1988) found TiO2 supported on an acetylcellulose membrane to be effective for the destruction of Escherichia coli. Other supports tested for TiO2 were activated carbon (Uchida et al. 1993), ceramic membranes (Aguado et al. 1994), wood chips (Berry and Mueller 1994), metal, polymer, and thin films (Blake 1994).

Some research has also been conducted on the immobilization of photosensitizers. Savino and Angeli (1985) examined the effectiveness of methylene blue, rose bengal, and eosin on polystyrene beads, and





42

methylene blue on granular activated carbon, silica gel, and XAD-2 (polystyrene resin). They found that all of the immobilized dyes were effective for the destruction of Escherichia coli, but methylene blue on activated carbon was the most effective.

Keeping the initial criteria in mind, ease of use and low operational and capital cost, a number of reactor designs were quickly ruled out. The methods for immobilizing catalyst all require fairly extensive preparation, including precipitation and calcination, in almost all cases. Therefore, the current research was conducted using suspended TiO2 and dissolved sensitizers. The question of the feasibility of immobilized catalyst and/or sensitizer was left for another study.

There are a number of options available for the specific design of a reactor using slurry catalyst. In computer simulations of the destruction of TOE in batch flat plate and parabolic reactors, flat plate reactors yielded a larger treatment volume than did the concentrating and one-axis tracking parabolic reactors (Saltiel et al. 1992). Wyness et al. (1994) found that flat plate reactors were effective for chemical photodegradation with suspensions of titanium dioxide. Bedford et al. (1993) found that the shallow pond configuration was effective for the destruction of 4-OP. This minimalist configuration is attractive because of its potential for low capital and maintenance costs.

For photosensitization the reactors have more closely resembled chemical reactors. Plug-flow reactors were successfully tested for the treatment of secondary effluent (Eisenberg et al. 1988), and continuous flow reactors showed promise in the sensitized photodegradation of





43

chlorophenols (Li et al. 1992). Acher et al. (1990; 1994) successfully used a series of tank reactors which were similar to the shallow pond configuration evaluated by Bedford et al. (1993). The laboratory reactors for this study were designed to mimic the shallow pond configuration.



TiO2 is significantly affected by the pH of the aqueous solution in which it is suspended. Particle size and charge and the position of the valence and conduction bands are all a function of the pH of the solution (Mills et al. 1993). Block et al. (1997) found a neutral to acidic pH range best for the TiO2 photocatalyzed inactivation of bacteria.

A number of researchers have investigated the effects of pH on the photocatalytic degradation rate of organics in aqueous suspensions (Bahnemann et al. 1991; Glaze et al. 1993b; Kawaguchi and Furuya 1990; Matthews 1986; Tseng and Huang 1990; Tseng and Huang 1991; Vidal et al. 1994). Kawaguchi and Furuya (1990) reported an increase in photocatalytic effect in acidic solution. The general consensus is that pH has little (no more than one order of magnitude) effect on the reaction rate, but that neutral pH provides the most efficient degradation. Other apparent pH effects are attributed to anionic effects from chemicals used for pH control. While pH was not a major factor in the photocatalytic reactions, it was necessary to seek an optimum pH for the simultaneous treatment of chemical and microbiological contaminants. In the research reported herein, photocatalytic experiments were conducted at neutral and acidic pH.





44

Photosensitization is much more pH dependent. In studies of methylene blue photodisinfection processes, pH values ranging from 8.6 to 10 were found to be optimum (Acher et al. 1994; Acher et al. 1990; Gerba et al. 1977b; Melnick et al. 1976). The same pH dependence was seen with methylene blue and rose bengal for the photodegradation of organic chemicals (Hadden et al. 1994; Li et al. 1992). In photosensitization of bromacil using methylene blue and rose bengal, reaction rates increased as pH values increased, with the highest rates at pH 9-10 (Eisenberg et al. 1986; Eisenberg et al. 1988). Based on this information, the sensitizer experiments for this research were conducted in neutral and basic environments.

Catalyst/Sensitizer Concentration

The concentration of the photocatalyst and photosensitizer needed to be optimized in order to obtain meaningful comparison data. An optimum of 0.1% TiO2 concentration was found to be effective for BTEX by Goswami et al. (1993) and Oberg (1993). Patel (1993) and Block et al. (1997) found that 0.01% TiO2 concentration worked best for the photocatalytic destruction of bacteria. Therefore a range of TiO2 concentrations, from 0.01% to 0.1% were tested in the laboratory in order to optimize the concentration for simultaneous photocatalysis.

In pilot plant studies Eisenberg et al. (1988) found that concentration of methylene blue ranging from 1 to 10 mg/1 were sufficient for the photooxidation of bromacil. Acher and Juven (1977) conducted

photosensitization experiments with sewage effluent and reported an increase in the destruction of coliforms with a corresponding increase in





45

methylene blue concentration, up to 5.0 mg/l. However, in pilot plant studies, smaller concentrations (less than 1.0 mg/1) were effective (Acher et al. 1994) and concentrations higher than 0.9 mg/I methylene blue hindered light penetration (Acher and Rosenthal, 1977). The photosensitization screening experiments for this research were conducted at several levels of concentration, ranging from 0.01 mg/l to 10 mg/.

Laboratory Experimental Design

In this research full factorial designs were used for both the photocatalytic and photosensitization experiments. While the designs differed slightly the parameters tested were the same, catalyst/sensitizer concentration, pH, and light. A two dimensional control was imbedded in the experimental design by way of the dark experiments and the level with no photochemical. For the photocatalytic experiment four levels of catalyst concentration, two levels of pH, two levels of light, and redundant reactors were used, as shown in Table 3-3. For each of the two dye sensitizers tested, methylene blue and rose bengal, five levels of sensitizer concentration, two levels of pH, and two levels of light were used, as shown in Table 3-4. The photocatalytic experiments were repeated twice and the photosensitization experiments were repeated three times.

In the combination experiments no pH adjustments were made. The experiments were conducted with 5 mg/L methylene blue and 0.01% TiO2. Controls for this experiments were no photochemicals, TiO2 only and methylene blue only. The full design, repeated three times, is shown in Table 3-5.





46


Table 3-3. Design for TiO2 Photocatalytic Lab Experiments
Treatment One Treatment Two
Contaminants BTEX and Bacteria BTEX and Bacteria
L i'g 'h t .... ........... ................. ............................. N.... o... n.... e............. .........................................No n e." o* ... n...e'.............................................N n
Light... N one........ ............... N one.....
pH Neutral, 7 (0.5) Acid,.4 (0.5)
TiO2 Concentration None 0.01% 0.05% 0.10% None 0.01% 0.05%:0.10%
Contaminants BTEX and Bacteria BTEX and Bacteria
Light UV Lamps @ 29 W/m UV Lamps @ 29 W/m
n .... ... .. ... ........ .. ... ... ........ i4... ..................... ............... ... .... ................. ...... ............... ..... ... ......... .......
pHNutral, 7 (0.5) Acid, 4 (0.5)
.......... ... .. .. .... ... ... e.......... . ......... ......... .. . .. . ............. ... .. ...: ? : : :
Tb oncentration INone 0.01% 0.05% 0.10% None 0.01% 0.05% f0.10%0/





Table 3-4. Design for Photosensitization Lab Experiments

Treatment One Treatment Two
Contaminants BTEX and Bacteria BTEX and Bacteria
Lgt .None None
.L g t ......................................... ........ ...... .- ... ............... ... ....... ............... ............... ...................... N .. ............................
pH Basic, 10 (0.5) Basic, 10 (0.5)
ye Conc., mg/L None 0.10 1 5 10 None 0.10 1 5 10
Contaminants BTEX and Bacteria BTEX and Bacteria
. ..... ig. ....................... ............................... .... .. ............ ..... .. .. ........ ..... .. h t....................
........ Sunlight Sunlight
pH Basic, 10 (0.5) Basic, 10 (0.5)
9eo .................... ... .. -- ... ..... .... .. .. .......... ... .. ...N..' 9N .. ........o





Table 3-5. Design for Combination Lab Experiments
Treatment One Treatment Two
Contaminants BTEX and Bacteria BTEX and Bacteria
... g .............................. ...... ...... ......................... o.e. ..................... .... .... .... ....................... S o: .............. .......- ........... .
Light None .None
Photochemical None 0.01% TiO2 5 mg/L MB' Both iNoneO01% TiO25 mg/b MB. Both



Materials and Methods


Reaction Vessels

The photocatalysis reaction vessels were covered Pyrex dishes

(Figure 3-1), which allowed light transmission above wavelengths of X > 300





47

rum, the shortest wavelength that reaches the earth's surface from the sun (Hsieh 1986). This filtered out the germicidal effects of the ultraviolet light which would not be present in naturally occurring sunlight.



Water line
Lid removed to take
samples


60 m ----------100 mm


Figure 3-1. TiO2 Reaction Vessel


In order to eliminate problems of air stripping and ensure that the reactor was airtight, a slightly modified version of the photocatalytic reaction vessel was used for both photosensitization and the combination experiments. The reactor was equipped with a glass blown sampling port plugged with a butyl rubber septum and sealed with parafilm (Figure 3-2). The reactors were filled to the rim of the vessel in order to minimize head space.



Bacterial Inoculation

Cultures were prepared using trypticase soy broth nutrient, and incubated for 24 hours at 35*C. Three serial dilutions of 1:100 were





48


prepared using distilled deionized water. Photocatalytic reactors were inoculated with 400 0l of E. coli, 400 gl of Serratia marcescens and 200 gl of Pseudomonas aeruginosa, using the 2nd dilution of each culture.

Water line


Sample port
Parafilm to with septum
seal 60 mm



100 mm


Figure 3-2. Photosensitization Reaction Vessel


Only E. coli was used for photosensitization experiments, and the reactors were inoculated with 45 gl of the first dilution of the culture. In all cases the third dilution was used to confirm that the cultures were viable. This procedure is shown graphically in Figure 3-3.

E. coi culture DilutionsInitial Count E. odi in Trypticase :10 1 Agar Plate
Slant Soy Broth (Incubated)
Dncubated)


> >

", hot mxatalysis
photosensitization'"
"1

Experimental
Glass Reactor



Figure 3-3. Graphical Representation of Bacterial Inoculation





49

Initial bacterial densities in the reactors ranged from 103 to 104 colonies per ml, with most values falling around 3.5 x 103 colonies per ml. Bacteria were obtained from American Type Culture Collection (ATCC). Reactor Chamber

The reactor chamber was used for all of the photocatalytic experiments and the dark experiments for photosensitization. The

chamber was a metal box equipped with 32 ultraviolet low-pressure mercury lamps and painted in flat black (Figure 34). The lamps were purchased from Southern New England Ultraviolet, model RPR-3500. The design output of the lamps was 3500A. Reactors were placed approximately 35 cm from the light source, at which point the ultraviolet irradiation measured was 29 W/m2. External light was blocked via a hinged metal door which fit snugly over the chamber. The lamps were turned off for the dark experiments.

Photocatalysis Reactor Setup

The reactors were loaded with deionized distilled and pH adjusted water and a combination of bacteriological and volatile organic chemical (VOC) contaminants, for a total volume of 100 ml. The chemical

contaminants were approximately 1 ppm each of benzene, toluene and mixed xylenes, referred to as BTEX, and the bacterial species were Escherichia coli, Pseudomonas aeruginosa and Serratia marcescens. Redundant reactors were placed for two to four hours in a reactor chamber either with or without light.





50
.. ..... .... .......................
............ ....... .........
.............. ..........
.............. ..........















Figure 3-4. Ultraviolet Light and Dark Reactor Chamber


As shown in Table 3-3, four Ti02 concentrations were used for the experiments: 0.1%, 0.05%, 0.01% and none. The catalyst used was Degussa P-25. The water was adjusted to an acid pH (4.0 0.5) and a neutral pH (7.0 0.5) with hydrochloric acid and sodium hydroxide. After pH adjustment the water was autoclaved to remove any microbiological contamination. The 100 ml reactors were illuminated for 2 to 4 hours in the reactor chamber.

Photocatalysis Sampling and Analysis

Samples for chemical analysis were taken prior to irradiation, after 5 minutes, 15 minutes, 30 minutes and one hour of irradiation and at the same time intervals in the dark chamber. Samples were taken with a sterile syringe and placed directly into amber borosilicate screw cap vials with Teflon TM septa, and refrigerated until analysis. The samples were analyzed by a modification of the EPA purge and trap method using an SR





51

8610 gas chromatograph with PID detector (Abeel et al. 1994; Bellar and Lichtenber 1974; Oberg 1993). The method used was sensitive to a low concentration of about 1 ppb for the components in question.

For evaluation of disinfection efficacy, duplicate petri dishes containing plate count agar nutrient were inoculated with 100 41 from each reactor. Two replicates were taken at 0, 30, 60, 120 and 240 minutes, yielding four counts for each set of conditions per experiment. The inoculated plates were spread and incubated for 24 hours at 35C. After 24 hours the number of bacterial colonies on each plate were counted. Photosensitization Reactor Setup

The reactors were loaded with deionized, distilled, pH adjusted water and a combination of bacteriological and volatile organic chemical (VOC) contaminants to the top of the container, a total volume of approximately 450 ml. The chemical contaminants were approximately 1 ppm benzene and 1 ppm toluene, referred to as BTEX, and the bacterial species was Escherichia coli, as noted above. The reactors were placed either in sunlight or in a closed, dark reactor chamber (Figure 3-4) for four hours and constantly agitated with a magnetic stirrer.

As outlined in Table 3-4, five sensitizer concentrations of either methylene blue or rose bengal, were used for the experiments: 0.1 mg/I, 1.0 mg/1, 5 mg/I, 10 mg/I and none. Both the methylene blue and the rose bengal were purchased from Fisher Scientific. The water was adjusted to a neutral pH (7.0 0.5) and a basic pH (10.0 0.5) using sodium hydroxide. After pH adjustment the water was autoclaved to remove any microbiological contamination.





52

Photosensitization Sampling and Analysis

A sterilized 10 ml syringe was used for taking samples via the sample port. Samples were taken at 0, 5, 15, 30, 60, 120 and 240 minutes by sterilized syringe and transferred into amber borosilicate screw cap vials with TeflonTM septa, and refrigerated in a standard commercial refrigeration unit until they were analyzed.

For evaluation of disinfection efficacy, petri dishes containing plate count agar nutrient were inoculated, in triplicate, with 100 Rl from each sample. Three replicates were taken per sample. The inoculated plates were spread and incubated for 24 hours at 350C. After 24 hours the number of bacterial colonies on each plate were counted. Chemical analysis was the same as that used for TiO2 photocatalysis. Combination Experimental Setup. Sampling and Analysis

The setup, sampling, and analyses for the combination experiments were very similar to that of the photosensitization experiments. The reactors were loaded with deionized, distilled water and a combination of bacteriological and volatile organic chemical (VOC) contaminants to the top of the container, a total volume of approximately 450 ml. The chemical contaminants were approximately 1 ppm benzene and 1 ppm toluene, referred to as BTEX, and the bacterial species was Escherichia coli, as noted above. The reactors were placed either in sunlight or in a closed, dark reactor chamber (Figure 3-4) for one hour and constantly agitated with a magnetic stirrer.

As outlined in Table 3-5, four photochemical concentrations of methylene blue and/or TiO2 were used for the experiments: no





53

photochemical, 0.01% TiO2, 5 mg/I methylene blue, and 0.01% TiO2 and 5 mg/I methylene blue.
A sterilized 10 ml syringe was used for taking samples via the sample port. Samples were taken at 0, 5, 15, 30, 60, 120 into amber glass screw cap vials with TeflonTM septa. The samples were refrigerated in a standard commercial refrigeration unit until they were analyzed.

For evaluation of disinfection efficacy, petri dishes containing plate count agar nutrient were inoculated with 100 pl from each sample. Three replicates were taken per sample. The inoculated plates were spread and incubated for 24 hours at 35C. After 24 hours the number of bacterial colonies on each plate were counted. Chemical analysis was the same as that used for TiO2 photocatalysis.

Experiments for Confirmation of Previous Work with Bromacil

One set of experiments was conducted to confirm the previous work with photosensitizers in which methylene blue was used for the destruction of bromacil in wastewater. Duplicate photosensitization reaction vessels (Figure 3-2) were loaded with approximately 1300 ppb bromacil, 5 mg/L methylene blue and deionized water. After irradiation in sunlight for four hours, the reactor contents were analyzed by GCMS. The bromacil used for the experiments was tech grade obtained from E. I. DuPont de Nemours and Company, Inc.












CHAPTER 4
RESULTS AND DISCUSSION

The results of laboratory experiments are presented and discussed in 'this chapter. The results are divided by experiment type: dye photosensitization, TiO2 photocatalysis and combination experiments. A general discussion is presented at the end of the chapter. Raw data for all experiments are contained in Appendix A.

Dye Photosensitization

Laboratory experiments were conducted to determine the effects of dye concentration and pH on the destruction rate of Escherichia coli and aromatic hydrocarbons (benzene and toluene) in sunlight. As described in Chapter 3, the experiments were conducted with the following treatments:

methylene blue (MB) and rose bengal (RB),

0 sunlight and dark,

0 pH 10 and pH 7,

0 0, 0.1, 1, 5 and 10 mg/L of dye.

In order to ensure reproducibility of the results, each set of experiments was conducted three times. A complete set of experiments was represented by one reactor for each of the sets of conditions highlighted above, for a total of 40 reactors per set. Five reactors were run at a time, each reactor containing a different concentration of a single dye (either methylene blue or rose bengal) with all other parameters the same.


54





55

Samples were taken from each reactor at 0, 5, 15, 30, 60, 120 and 24.0 minutes and refrigerated immediately. Three replicates were plated from each sample for microbiological analysis. The remainder of the 0, 60 and 240 minute samples was refrigerated and saved for chemical analysis.

For the experiments conducted in sunlight, the light was measured and recorded over the duration of the experiment, and ranged from 542 W/m2 to 892 W/m2 The average total insolation (incident z-jar radiaion) measured in each experiment is given in Table 4-1 and graphs of the total insolation are shown in Appendix B.


Table 4-1. Insolation Measurements from Dye Sensitization Experiments
set Conditions Insolation, W/m2
........ 1- M ethy.ene B lue................. pH...... 7........................ 685...............................
#1Methylene Blue, pH 10 671
Rosyee Benga, pH 0 76
Rose Bengal, pH 10 715
# 2 Methylene Blue, pH 7 665
Methylene Blue, pH 10 542
Rose Bengal, pH 7 856
Rose Bengal, pH 10 775
#3 Methylene Blue, pH 7 892
Methylene Blue, pH 10 696
Rose Bengal, pH 7 841
Rose. Bengal, pH. 10 749



Experimental sets were conducted on different days, and though efforts were made to minimize the differences between sets, both solar insolation and initial contaminant concentrations did vary from one set to another. The mean, standard deviation, and range of these parameters for all experiments are shown in Table 4-2.





56

Table 4-2. Descriptive Statistics of Measured Data for all Experiments MB Parameter Mean StdDev Mini Max
Sunlight, W/m2 692 112 542 891
Sunlight, pH 7, W/m' 743 129 665 891
Sunlight, pH 10, W/m' 641 50 542 696
Initial Coliform Density, cfulL x 10' 784 365 27 1453
Initial Benzene concentration, ppb 676 210 377 1218
Initial Toluene concentration, ppb 314 139 136 770
IRB Parameter Mean SbdDev Mini Max
Sunlight, WfM2 781 56 715 856
Sunlight, pH 7, W/m' 815 60 746 856
Sunlight, pH 10, W/M2 746 30 715 775
Initial Coliform Density, efufb x 10' 816 375 187 1680
Initial Benzene concentration, ppb 560 262 296 1407
Initial Toluene concentration, ppb 426 226 155 1026



The data, as well as the impact of each of the measured and

controlled parameters, are explored in more detail below, and results are compared with the work of Eisenberg et al. 1987b, Acher et al. (1994), and Acher et al. (1990), for the photosensitized disinfection and bromacil destruction in secondary treated wastewater effluent. General Comments About Exjerimental Data

The average standard deviation of the disinfection data was 25% for methylene blue experiments and 13% for rose bengal experiments (Table 43). Plates on which the colonies were not individually identifiable and those with severe contamination were not counted, which resulted in the loss of approximately 20% of the 840 plates in a given experimental set. Due to contamination of the incubator, all 105 of the plates from the sunlight, pH 10, methylene blue experiment in set number two had to be discarded. In a few instances the samples were dropped and broken before they could be plated.





57

The initial (t=0) disinfection samples for the dark, pH 10, rose bengal experiment in set number one were abnormally, though consistently, low. The low values were attributed to not allowing time for adequate mixing in the reactors prior to drawing the first sample. Since the values were consistent from one reactor to the next, the data could not be treated as outliers, but accommodations were required for accurate interpretation. For this set of data, the fractional survival values were calculated using the

5 minute instead of the zero minute samples.

The average standard deviations of the detoxification data were 10%, or less, of the average values as shown in Table 4-3. Sample loss for detoxification occurred when the sample was dropped and broken prior to analysis, which occurred twice in experimental set number three. The samples on either side of the dropped sample, 8., were analyzed, and the sample value for the desired time was interpolated. When the dropped sample was an initial sample, 330, the 5 minute sample was substituted. Chemical samples were generally analyzed within two weeks of the experiment.


Table 4-3. Average Standard Deviations for all Dye Photosensitization Experiments
Benzene (ppb) Toluene (ppb) E. Coli
dDev Avg SWDev Avg % oftotal
M ethylene Blue 51 578 29 ..................... 5" ............. ..2.5-3......5.....25....
Rose Bengal 46 487 36 363 13





58

Statistical Treatment of the Data

Microsoft Excel version 5.0 for the Macintosh was used for statistical analysis of the data. For the more common calculations, including least squares linear regression, the functions available in the software package were used. All other values were calculated using the equations as noted throughout this section.

Since the sample sizes were generally small (less than 30), the entire populations were used to calculate standard deviation from Equation 4-1.

S.D. = jnjx'-(YX) 2 (4-1)

n 2

For disinfection data analysis, the fractional survival and percent destruction of colony forming units (cfu) were used for reporting and analyzing the data. The values used for disinfection data analysis were obtained by taking the average of the plates for each sample collected within an experimental set, calculating fractional survival (or % destruction) and averaging those values across experiments for use. The data, obtained in this way for methylene blue at 30 minutes, are shown in Table 4-4.

In situations where calculations resulted in a negative percent destruction, the percent destruction was set to zero. In some instances the fractional survival exceeded 2.0, specifically, the data from the dark, pH 10, rose bengal experiment in set one. For that data set, the fractional survival was calculated relative to the 5 minute samples, i.e. fractional survival Nt/N5.





59


Table 4-4. Mean Fractional Survival ( 31%) of E. coli @ t-- 30 minutes in MB Experiments

Set# Sunrlight-pHl0 1SunfightpH7 :DarkpH1lO DarkpH7
Cotd1 0.000 0.172 1.113 1.500
2 0.534 1.013 0.169
3 0.084 0.082 0.364 0.503
Average .020620.830 0.724
0.1 mgfL 1 0000.013 0.592 1.547'
2 0.155 0.84 1 0.068
3 0.009 0.000 0.583 0.540
Average 0.005 0560.672 0.718
1 gL 0.000 0.007 0.494 0.779
2 0.013 0.538 0.101
3 0.000 0.000 0.000 0.502
Average 0.000 0.007 0.344 0.46 1
5 mgL1 0.000 0.002 0030 0.000
2 0.016 0.007 0.000
3 0.000 0.000 0.08 1 0.473
Aege0.000 006039 0.158
1mgL1 0.000 0. ....01..... 6 0.011 0.034*..
2 0.000 0.000 0.018
3 0.000 0.000 0.004 0.195
Aeae0.000 0.005 0.005 0.082




Detoxification data were treated in a similar manner. The

concentration data, as parts per billion (ppb), for each experimental set

were normalized to the initial concentration (Ct/C0). The normalized values

were averaged across experimental sets. Since only one data value existed

per sample for each experimental set, standard deviations were calculated

across sets only. Outliers were identified using the ASTM recommended

criterion for single samples (ASTM 1988) which uses the following test:



T,= I(x xA/s (4-2)

The critical value of Tn is a function of the number of observations and is

obtained from a table (ASTM 1988). Using this criterion, one value was

found to be an outlier at a significance level of 10% (5% for toluene) and





60

subsequently discarded. The outlying sample, the 240 minute, 1 mg/L sample from RB, dark, pH 10 in experimental set number two, was thought to have been poorly capped, resulting in volatilization of the sample prior to analysis.

The data were viewed in several ways. An initial observation was conducted for the detection of trends and to determine if the desired effect was achieved. These trends were displayed as a function of time for all of the average values as x-y scatter plots. If trends of the desired effect, destruction of contaminants with time, were detected, the data were analyzed further for the impact of specific parameters on the final results as described below.

Analysis of Means (ANOM) was applied to obtain a statistical snapshot of the effect of specific parameters on the outcome. In this method, mean values and statistical deviations were used to clarify the significance of each parameter. The ANOM is a variation on a process control chart and allows for the exploratory analysis of several parameters simultaneously (Mason et al. 1989). A relatively conservative a-level of 0.05 was chosen to minimize the probability of false alarms. A smaller a-level was not desirable as it might have resulted in missed signals and would be inappropriate for this type of exploratory analysis (Wheeler 1990).

The Pooled Variance Estimator was used for determination of Estimated SD M as shown below. Decision limits for the ANOM charts were calculated using the following equations (Wheeler 1990):





61


Estimated SD M = qS' (4-3)


(Estimated SD ON = Estimated SD W (4-4)


UDL,, = X + H (Estimated SD 06) (4-5)


LDLx = X H (Estimated SD (9)) (4-6)

where:

s standard deviation of X,

average of observations in a subgroup,

S2 average variance of X,

n number of observations per subgroup,

X grand average of all observations,

H ANOM critical value at a selected a, from table (Wheeler 1990),

UDLX upper decision limit, and

LDLX lower decision limit.

Averages which were outside of the decision limits were considered to be statistically significant, and those parameters were determined to be influential

In some instances the data were graphically represented. For this analysis, data were simply categorized according to the parameters of interest, and standard deviation and mean values were calculated using the Microsoft Excel functions. These values were then charted, either as scatter plots or bar charts. Where appropriate, least squares linear





62

regression, also using Microsoft Excel, was performed to identify specific trends and relationships.

Where clear destruction of contaminants was seen, kinetics were considered. Results were fitted to first order kinetic equations, and experimental reaction rate constants were obtained for comparison to published data. This information is presented in the section on kinetic considerations, which includes kinetic data for all relevant experimental sets.

Presentation of Results and Identification of General Trends

While disinfection in the presence of aromatic hydrocarbons was achieved with both rose bengal and methylene blue, simultaneous detoxification was not observed with either dye. Under the conditions tested, the presence of MB increased the disinfection rate of water contaminated with E. coli over sunlight alone.

MB photosensitized disinfection at pH 10 (Figure 4-1a) appears to be slightly more effective than MB photosensitized disinfection at pH 7. At pH 10, all AM concentrations resulted in at least a 99.5% coliform reduction after thirty minutes of irradiation, compared to 9601b reduction with sunlight alone. With 10 mg/L MB, complete coliform. destruction was achieved after only five minutes of irradiation. No coliforms appeared in any of the samples taken after irradiation began. The intensity of sunlight in these experiments ranged from 542 to 696 W/m'.

Destruction at pH 7 was not quite as dramatic (Figure 4-1b). The coliform reduction after 30 minutes ranged from 99.5% with 10 mg/L MB to 96% with 0.1 mg/L MB. Comparatively, only a 74% reduction was attained






63


with sunlight alone. The intensity of sunlight ranged from 665 W/m2 to

891 W/m2. Differences between pH 10 and pH 7 cannot be attributed to

differences in light intensity since, as shown in Tables 4-1 and 4-2, the

intensity was greater in the pH 7 experiments even though less reduction

was achieved. The difference in values for control reactors would lead one

to conclude that any pH effect was a function of the general disinfection

mechanism rather than of the photosensitization process specifically.



100%
90%
80%
S70% --- Control
60%- --0.1 mg/L
250% 1 mglL
0% ---- 10 mg/L
0 -K-5 mg/L
40%
30%- -IC 10 mg/L
20%
10% Avg S.D. 14.5%
0%
0 15 30 45 60

(a) Time (minutes)



100%

80%
-4- Control
0
60% -3- 0.1 mg/L
2
-A- I mg/L
S40%
S-X- 5 mg/L 20% Avg S. D. 25.4% -- 10 mgL

0%
0 15 30 45 60
Time (minutes)
(b)
Figure 4-1. MB Destruction of E. coli in Sunlight; (a) pH =10, Iavg= 542-696
W/m2 (b) pH =7, Iavg = 665-891 W/m2






64


In the presence of at least 1 mg/L MB and sunlight (542 696 W/m2),

complete disinfection occurred within 5 to 30 minutes. However, in the

absence of MB with the same intensity sunlight, complete disinfection

required at least 60 minutes (Figure 4-2). Complete disinfection did not


occur at all in the dark, although a 99% coliform reduction was observed

with 10 mg/L MB in the dark. Mean fractional values for the methylene


blue experiments are presented in Table 4-5.


100% .
90%
80%
c 70% 60% S50%
40% .
30%
20%
10% AVG S.D. =16.6%
0%
0 15 30 45 60
Time (minutes)
-4-No MB, Sunlight --A-I mg/L MB, Sunlight
---No MB, Dark -1I-lmg/L, MB Dark
(a)




100%

80%

60%

o 40%

20% Avg S.D. =28%

0%
0 15 30 45 60
Time (minutes)

-4-o MB, Sunlight ---1 mg/L, Sunlight Nb L--- No MB, Dark X- mg/L, Dark


Figure 4-2. Destruction of E. coli in sunlight with 1 mg/L MB; (a) pH =10,
Iavg= 542-696 W/m2 and (b) pH 7, Iavg = 665-891 W/m2





65


Table 4-5. Mean Fractional Survival (25%) of E. coli in MB Experiments

Control Sunlight pH 10 Sunlight pH 7 Dark pH 10 Dark pH 7
N51No 1.133 0.811 0.954 0.671
N151No 0.707 0.428 0.626 0.493
N30/No 0.042 0.262 0.830 0.724
N60/No 0.000 0.013 0.681 0.858
N120/No 0.000 0.000 0.449 0.063
0.000 0.000 0.365 0.008
0.1 mg/L
N/No 0.030 0.65 1 0.867 0.609
N151No 0.002 0.234 0.766 0.613
N30/No 0.005 0.056 0.672 0.718
N60/No 0.000 0.016 0.600 0.363
N120/No 0.000 0.005 0.299 0.141
........... ....... .................. -: ..I............................... oI o ................................. 2 5...................... .. 7 !.............
I mg/L
N5/No 0.000 0.194 0.700 0.622
N151No 0.000 0.011 0.581 0.657
N30/No 0.000 0.007 0.344 0.461
N601No 0.000 0.006 0.223 0.312
N120/No 0.000 0.002 0.040 0.329
N240/NO 0.000 0.000 0.006 0.08 1
5 mgfL
N.. No 0.006 0.000 0.109 0.299
N151No 0.003 0.014 0.118 0.209
N3o/No 0.000 0.006 0.039 0.158
N601oN 0.001 0.002 0.039 0.139
N120/No 0.000 0.002 0.000 0.160
N240/No 0.000 0.000 0.005 0.012
10 mg/L
N5/No 0.000 0.000 0.000 0.176
N11No 0.000 0.010 0.002 0.160
N301No 0.000 0.005 0.005 0.082
N6o/No 0.000 0.002 0.002 0.076
N120/No 0.000 0.000 0.000 0.023
N240/No 0.000 0.000 0.005 0.052



Rose bengal was less effective for photochemical disinfection than

was MB. The presence of RB had little, if any, positive effect on the

disinfection rate over sunlight alone, although the experiments at pH 7

appeared to exhibit some photochemical disinfection (Figure 4-3a).

In the experiments conducted at pH 10 (Figure 4-3b), RB had no

positive effect on disinfection over sunlight alone. Coliform reduction of





66

greater than 99.9% was observed by 60 minutes in sunlight alone; however, in the presence of RB the same coliform reduction was not evident until the 240 minute samples with 0.1 mg/L RB and the 12 minute samples for all other RB concentrations. Coliform reduction was about the same by 30 minutes regardless of the RB concentration, with a low of 81% for 10 mg/b RB and a high of 90% with 1 mg/b RB. The control, sunlight alone, had a coliform reduction of 88%. The differences are not significant, as all values fall within the average standard deviation of 21%. The average intensity of sunlight in these experiments ranged from 715 to 775 W/m'.

As was evidenced in the experiments with MB, disinfection appeared to be less effective at the neutral pH value of 7 (Figure 4-3a). The exception was with the higher concentrations of RB, 5 and 10 mg/b (Figure 4-4), where coliform reductions by 30 minutes were 961% and 97%, respectively. In comparison, coliform reduction in sunlight alone (746-856 W/m') by 30 minutes was 77%, 78% with 0.1 mg/b RB and 89%/ with 1 mg/b RB. Mean values for the fractional survival of E. coli in the rose bengal experiments are shown in Table 4-6.

While some reduction in both benzene and toluene concentration was observed with both dyes under every set of conditions, there was a substantial amount of contaminant (130 550 ppb) remaining in the water (Tables 4-7 and 4-8) after four hours. Initial concentrations ranged from 139 1400 ppb as shown in Table 4-2. Figures 4-5 to 4-8 show the concentration of benzene and toluene as a function of time at various dye concentrations.






67





100%90%
80%
c: 70% -- Control
2 -0-0.1 mg/IL
V 60%
-A-- 1 mg/L
Vi 50% o 40%
30% X 10 mg/L
20% Avg S. D. 20.6%

10%
0%
0 15 30 45 60
Time (minutes)
(a)




100% E
90%
80%
C 70% Control
60%- 0.1 mg/L
-; 50% -f-1 mgIL
a 40% ~ 5 mg/L
30% -2 --10 mg/L
20% AVG S.D. = 16.1%
10%
0%
0 15 30 45 60
Time (minutes)
(b)

Figure 4-3. RB Destruction of E. coli in Sunlight; (a) pH = 7, Iavg = 746-856
W/m2 (b) pH = 10, Iavg = 715-775 W/m2



The experimental values for both benzene and toluene in MB showed

fairly consistent reductions, with normalized concentrations ranging from

0.59 to 0.87 after four hours. Both the greatest and smallest reductions

corresponded to control reactors, sunlight at pH 10 and dark at pH 7,

respectively.






68




100%
90% Avg S.D. = 23.6 c 8 0 % "

.2 70%
1 60%
2 50%- 40%
D30%
20%
1 0 % -,s
0%
0 15 30 45 60
Time (minutes)
-- No RB, Sunlight -X- 5 mgL RB, Sunlight
(a) ---No RB, Dark 5 mg/L, Dark



100% 90%
80%

2 70%
U 60%
W50%
40% .
30% ...
2 0 %" .
10%- Avg S.D.= 18.8%

0 15 30 45 60
Time (minutes)
-- No RB, Sunlight X-10 mg/L RB, Sunlight ( 0 No RB, Dark l- 10 mg/L RB, Dark
(b)

Figure 4-4. RB Destruction of E. coli at pH =7, avg = 715-775 W/m2;
(a) 5 mg/L RB and (b) 10 mg/L RB



Examination of the normalized data (Tables 4-9 and 4-10) did not yield

a different conclusion. Neither chemical contaminant exhibited a


substantial difference in behavior between control and non-control reactors

in either MB or RB experiments, as seen from Figures 4-9 to 4-12.


In RB experiments reductions ranging from 15% to 36% for benzene

and 24% to 47% for toluene in sunlight were observed. One reactor, the

dark control reactor at pH 10, exhibited no reduction at all. However, since

the other controls, both in sunlight and in dark, had destruction rates








which were in the middle of the range for the non-control reactors, this

cannot be considered an indication that photochemical action took place.



Table 4-6. Mean Fractional Survival (13%) of E. coli in RB Experiments

Control Sunlight pH 10 Sunlight pH 7 Dark pH 10 Dark pH 7
N5/No 0.668 0.714 0.961 0.925
N151No 0.315 0.458 1.074 0.729
N301No 0.122 0.226 0.952 0.762
N60/No 0.000 0.001 0.795 0.527
N20/No 0.000 0.000 0.660 0.512
N240/N0 0.000 0.003 0.381 0.331
.............. ....................... .................................... ........... ........... -................................................ ........ o 3 l..................................................... o3 ............
0.1 mg/L
N5/N, 0.541 0.599 0.846 0.717
N15/No 0.381 0.216 1.058 0.545
N301No 0.131 0.221 0.930 0.649
N60/No 0.002 0.006 0.797 0.696
N120/No 0.005 0.000 0.617 0.552
N4/O 0.000 0.000 0.269 0.451
1lmg/L
N 5/ 0 .498 ................ 0..-62.4 ........1.02 8 .... ----- 0 .436.....
N151No 0.241 0.462 1.007 0.678
N30/No 0.102 0.110 1.033 0.530
NGO/No 0.009 0.001 1.107 0.625
N120/NO 0.000 0.000 0.838 0.499
N24o/No 0.000 0.003 0.461 0.292

0.707 0.562 0.966 0.681
N15No 0.447 0.371 1.006 0.970
N30/No 0.150 0.044 1.015 0.693
N601No 0.006 0.007 0.920 0.650
N120/No 0.000 0.000 0.597 0.820
N240/No 0.000 0.000 0.334 0.640
10 mg/L
N5/N0 0.5 55 0.5 16 0.9 89 0.74 6
N151No 0.451 0.365 0.884 0.551
N30/No 0.188 0.029 0.918 0.537
N601No 0.002 0.000 0.888 0.666
N120/No 0.000 0.004 0.659 0.490
N0/No 0.000 0.000 0.388 0.478





70


Table 4-7. Benzene (5 1) and Toluene (29) Concentrations (ppb) in MB Experiments

BENZENE Time (min) Sunlight pH 10 Sunlight pH 7 Dark pH 10 Dark pH 7
Cnrl095 3 609 632 630.
60 686 593 565 643
240 522 545 476 545
0.1 mg/L 0 767 622 59r7 646
60 578 533 583 533
240 513 482 399 495
1lmg/L 0 733 642 729 705
60 643 555 521 554
240 544 527 419 500
5 mgfL 0 707 658 604 662
60 626 502 562 597
240 564 418 385 491
10 mgfL 0 762 583 596 679
60 567 535 565 548
240 478 456 4.31 483
TOLUENE Time (min) Sunlight pH 10 Sunlight pH 7 Dark pH 10.Dark pH 7
499ro 07 310
60 298 250 224 312
240 214 221 176 234
0.1 mgfL 0 358 282 264 324
60 248 217 245 243
240 210 158 141 211
1 mg/L, 0 326 297 319 357
60 275 235 207 256
240 226 208 157 209
5 mg/L 0 330 300 261 327
60 261 215 248 281
240 230 160 131 203
10 mgIL 0 347 266 255 331
60 233 225 227 261
240 183 171 155 211



The greatest apparent reductions seemed to correspond to higher

initial concentrations and exposure to sunlight. This type of behavior

would be consistent with benzene and toluene being trapped in the vapor

space above the water line. Although head space was kept to a minimum,

as the samples were drawn from the reactor, head space increased.

Though temperature was not a consistently measured parameter, an

increase in temperature was observed, probably due to sunlight and friction





71


from the magnetic stirrers. The combination of temperature and head

space increase would necessarily lead to volatilization of the chemical

contaminants in the vapor space. Spot temperature checks with

temperature strips on the outside reactor glass yielded values in excess of

96'F in sunlight.



Table 4-8. Benzene ( 46) and Toluene ( 36) Concentrations (ppb) in RB Experiments

BENZENE Time (min) Sunligh -t ..p H 10 Sunlight pH 7 Dark pH 10 Dark pH 7
Cnri0 7 16 746 432 4 97
60 692 557 446 466
240 499 539 447 425
0.1lmg/L 0 542 657 478 504
60 508 541 474 440
240 463 508 371 417
1 mg/b 0 593 618 463 516
60 533 513 399 438
240 389 504 332 379
5 mg/L 0 611 646 437 515
60 516 524 434 413
240 386 476 350 365
10 mg/b 0 583 635 483 461
60 420 513 438 419
240 375 483 371 341
TOLUENE Time (min) Sunlight pH 10 Sunlight pH 7 Dark pH -10 Dark pH 7
C.......... 0, 543", 541. 27 ......21 ...
60 486 415 283 385
240 338 370 289 349
0.1 mg/b 0 401 493 318 442
60 367 394 311 387
240 310 367 250 346
1 mg/b 0 427 481 30Y7 464
60 367 374 246 368
240 259 355 195 303
5 mg/b 0 458 491 294 443
60 364 373 282 338
240 246 317 206 284
10 mg/b 0 416 483 323 410
60 298 375 281 349
240 255 329 223 275





72




1000


800
-0- Control
CL 600
600 --X- 0.1 mg/L
-- 1 mg/L
N 400
-E3 5 mg/L

200 Avg S.D. = 71.16 ppb 6 10 mg/L

0 I
0 60 120 180 240
*Referenced to intemat
Time (minutes) sanded, Corob
(a)












700 600
500 ---Control
0 --E-6-0.1 mg/L
-400
---1 mg/L
S300 ---X5 mg/L
20 10 mg/L
m 200
100 Avg S.D. = 48.25 ppb

0
0 60 120 180 240
Time (minutes) Reer'nceto rna
standard, chlorobenzene.
(b)
Figure 4-5. Benzene Concentration as a Function of Time and MB
Concentration in Sunlight; (a) pH=10, Iavg = 542-696 W/m2
(b) pH=7, Iavg = 665-891 W/m2





73




500

400
-*- Control
C.
a 300 -X--0.1 mg/L
C-------- 1 mg/L
S200
0- -5 mg/L
100 --10 mg/L
Avg S.D. = 42.82 ppb

0
0 60 120 180 240
Time (minutes)
*Referenced to internal
(a) standard, chlorobenaene.











350

300

250 -0- -Control
.- -30.1 mg/L 200
-&1 mg/L
2 150 --X-5 mg/L

100 10 mg/L

50 Avg S.D = 23.45 ppb
0 i i
0 60 120 180 240
Time (minutes) "eferen I wtea
standard. chlorobenzene.
(b)
NC






Figure 4-6. Toluene Concentration as a Function of Time and MB
Concentration in Sunlight; (a) pH =10, Img = 542-696 W/m2
(b) pH=7, I. = 665-891 W/m2





74



800 700
600 Control
500 -0.1 mg/L
400 -&-1 mg/L
0 -X5 mg/L
300
20 ---10 mg/L
m 200 Avg S. D. = 74.41 ppb 10 mg/L
100
0
0 60 120 180 240
*Referenced to internal
Time (minutes) standard. chorobetzene
(a)









800 700
-600 ---Control
CL500 --0.1 mg/L
( 400 --A-1 mg/L
r 300 -X-5 mg/L
a)
S200 -3110 mg/L
~200 -Avg S. D. = 36.02 ppb 10 mg/L
100
0 1 i ii
0 60 120 180 240
*Referenced to internal
Time (minutes) stard, boob&ene
(b)
Figure 4-7. Benzene Concentration as a Function of Time and RB
Concentration in Sunlight; (a) pH =10, Iavg = 715-775 W/m2
(b) pH=7, I.avg = 746-856 W/m2





75




600
500
-- -Control
S400 -E-0.1 mg/L
-A-1 mg/L
e300
0 X-5 mg/L
200 --10 mg/L
100 Avg S. D. = 57.09 ppb
100

0 1i
0 60 120 180 240
Time (minutes) "Rndce dto ndem
(a)










600

500
400 --Control
S--E-0.1 mg/L a 300 1 mg/L
S--X-5 mg/L 200
200--10 mg/L 100 Avg S.D. = 27.07 ppb

0
0 60 120 180 240
*Referencd to inimal
Time (minutes) -ndWd, chorobeene
(b)
Figure 4-8. Toluene Concentration as a Function of Time and RB
Concentration in Sunlight; (a) pH =10, Iavg = 715-775 W/m2
(b) pH=7, IaV = 746-856 W/m2





76


Table 4-9. Normalized Benzene (0.09) and Toluene ( 0.11) Concentration in MB Experiments
BENZENE Sunlight pH 10 Sunlight pH 7 Dark pH 10 Dark pH 7
Control

N6o/No 0.78 0.96 0.90 1.01
N120/No 0.59 0.86 0.75 0.87
0.1 mg/L
N60/No 0.77 0.88 1.02 0.83
N24o/No 0.67 0.80 0.68 0.77
1 mg/L
N6o1No 0.86 0.85 0.72 0.79
N24o/No 0.71 0.80 0.59 0.71
5mg/L
N60/No 0.87 0.76 0.95 0.90
N240/No 0.77 0.65 0.65 0.75
10 mg/L
N60iN0 0.75 0.92 0.98 0.81
0.63 0.77 0.74 0.72
TOLUENE Sunlight pH 10 Sunlight pH 7 Dark pH 10 Dark pH 7
Control
N6o1No 0.70 0.88 0.85 0.99
N120/NO 0.49 0.77 0.68 0.76
0.1 mg/L
N6oiNo 0.72 0.80 0.98 0.76
N240/No 0.57 0.57 0.58 0.63
1 mg/L
N60/No 0.82 0.77 0.66 0.71
N240/No 0.64 0.67 0.51 0.58
5 mg/L
N60/No 0.77 0.72 1.01 0.84
N240/NO 0.64 0.54 0.55 0.63
10 mg/L
N601No 0.70 0.85 0.92 0.78
N24oiNo 0.53 0.62 0.65 0.63





77


Table 4-10. Normalized Benzene (0.06) and Toluene (0.07) Concentration in RB Experiments
BENZENE Sunlight pH 10 Sunlight pH 7 Dark pH 10 Dark pH 7
Contr ..

N601No 0.94 0.81 1.04 0.95
N120/No 0.68 0.74 1.02 0.86
0.1 mg/L
N6/No 0.93 0.87 1.00 0.87
N240/N0 0.85 0.77 0.71 0.81
1 mg/L
N60No 0.90 0.83 0.84 0.91
N240/NO 0.65 0.81 0.71 0.78
5 mg/L
N6/No 0.84 0.82 1.00 0.81
N240/NO 0.64 0.73 0.81 0.69
10 mg/L
N6/No 0.72 0.85 0.90 0.95
N24No 0.66 0.74 0.77 0.75
TOLUENE Sunlight pH 10 Sunlight pH 7 Dark pH 10 Dark pH 7
Contml
N601No 0.86 0.82 1.01 0.94
N120No 0.58 0.69 1.03 0.81
0.1 mg/L
NwINo 0.89 0.83 0.99 0.89
N24/NO 0.76 0.71 0.65 0.75
1 mg/L
N6o1No 0.87 0.79 0.78 0.89
N240/NO 0.59 0.73 0.65 0.71
5mg/L
Nr/N0 0.78 0.78 0.96 0.78
N240/NO 0.53 0.64 0.69 0.61
10 mg/L
NwINO 0.71 0.82 0.87 0.91
N24o/NO 0.62 0.65 0.69 0.65





78



1.20

1.00

0.80

Q 0.60
0
0.40

0.20 Avg S.D. = 0.07

0.00 1
0 60 120 180 240
Time (minReferened to internal Time (minutes) standard, chbrobenzee
--No MB, Sunlight ---0.10 mg/L, Sunlight
-e-No MB, Dark --- 0.10 mg/L, Dark
(a)









1.20
1.00

0.80 -,

S0.60

0.40

0.20 Avg S. D. = 0.04

0.00
0 60 120 180 240
Referenced to internal Time (minutes) s rd.bv ior enzene o- No MB, Sunlight --30.1 mg/L, Sunlight
-No MB, Sunlight -+-0.1 mgIL, Dark
(b)

Figure 4-9. Normalized Benzene Concentration in Sunlight with 0.1 mg/L
MB, (a) pH =10, Iag = 542-696 W/m2 (b) pH=7, Iag = 665-891 W/m2





79




1.00 0.90 0.80 0.70 0.60 0.50
0.40
0.30
0.20 Avg S.D. = 0.07
0.10
0.00 1 i i i
0 50 100 150 200
SReferenced to intemal Time (minutes) "stardd o "ob
-O-No MB, Sunlight --30.1 mg/L, Sunlight
-X-No MB, Dark ----0.1 mg/L, Dark
(a)











1.00 I
0.90 0.80 0.70 0.60 S0.50
0.40
0.30 Avg S.D. = 0.05
0.20 0.10
0.00 ---0 60 120 180 240
Referenced to internal Time (minutes) standard, chlobenzene F -No MB, Sunlight -0- 0.1 mg/L, Sunlight
-1--No MB, Dark -+-0.1 mg/L, Dark
(b)
Figure 4-10. Normalized Toluene Concentration in Sunlight with 0.1 mg/L
MB; (a) pH =10, Ia, = 542-696 W/m (b) pH=7, I.avg = 665-891 W/m2





80



1.20
1.00

0.80
0
S0.60
0.40

0.20 Avg S.D. = 0.28
0.00 I
0 60 120 180 240
*Referenced to internal Time (minutes) ndard,co benzene

--No MB, Sunlight -E--0.1 mg/L, Sunlight
---No MB, Dark --+-0.1 mg/L, Dark
(a)










1.00 0.90 0.80 0.70 o 0.60 2 0.50 0.40 0.30
0.20 Avg S. D. = 0.05
0.10
0.00
0 60 120 180 240
*Referenced b, eternal Time (minutes) standard, ch. benzene
---No MB, Dark --0.1 mg/L, Sunlight
No MB, Dark ---- 0.1 mg/L, Dark
(b)
Figure 4-11. Normalized Benzene Concentration in Sunlight with 0.1 mg/L
RB, (a) pH =10, Iavg = 715-775 W/m2 (b) pH=7, I.avg = 746-856 W/m2