DOCTORAL DISSERTATION

CHARACTERISTICS OF DYEING WASTEWATER
TREATMENT BY OZONATION AND
ELECTROCOAGULATION COMBINED SYSTEM

Student: Huynh Thi Ngoc Han
Advisor: Prof. Yong Soo Yoon

2015

ENVIRONMENTAL ENGINEERING
CHEMICAL ENGINEERING
THE GRADUATE SCHOOL – DANKOOK UNIVERSITY
박사학위논문


오존과 전기분해를 이용한 염색폐수처리 특성
CHARACTERISTICS OF DYEING WASTEWATER
TREATMENT BY OZONATION AND
ELECTROCOAGULATION COMBINED SYSTEM

제출자: 권옥란
지도교수: 윤용수

2015

화학공학과
환경공학전공
단국대학교 대학원

CHARACTERISTICS OF DYEING WASTEWATER
TREATMENT BY OZONATION AND
ELECTROCOAGULATION COMBINED SYSTEM

by
HUYNH THI NGOC HAN

A thesis is submitted in partial fulfillment of the
requirements for the degree of Doctor of philosophy

Environmental Engineering
Chemical Engineering
The graduate School of Dankook University

December 2015


HUYNH THI NGOC HAN의 박사학위 논문을

합격으로판정함
심사일: 2015.12.08
심사위원장

(인)

심사위원

(인)


심사위원

(인)

심사위원

(인)

심사위원

(인)
단국대학교 대학원


ABSTRACT
Characteristics of dyeing wastewater treatment by ozonation and
electro-coagulation combined system
Environmental Engineering
Department of Chemical Engineering
Graduate school
Dankook University

Student: Huynh Thi Ngoc Han
Advisor: Prof. Yoon Yong Soo

In this study, treatment of dyeing wastewater, containing CI AR 114 dye, was
performed by ozonation, the electrocoagulation and the ozonation-electrocoagulation
combined system. Ozonation was carried out in a bubble column reactor. A part of this
study evaluated the effects of operating parameters such as the gas flow rate, initial
dye concentration, pH, temperature on the removal efficiency of ozonation treatment.

The volumetric mass transfer coefficient and the enhancement factor were determined
through the experimental method. The performance by ozonation was assessed
through the removal efficiency of dye concentration, color and COD in batch reactor
and continuous reactor with counter current, cocurrent flows.
In the electrocoagulation, aluminum was used as cylindrical electrodes which were
directly connected to DC power supply. This study determined the effects of the
current density, pH, initial dye concentration, conductivity on the removal efficiency
by EC treatment in batch reactor. The optimal conditions determined in the batch
reactor were applied into the continuous reactor. The treatment performances by

i


electrocoagulation were evaluated in all the batch and continuous reactor. Energy
consumption, volume and mass of generated sludge were determined.
In addition, this dyeing wastewater was treated by the ozonation-electrocoagulation
combined system. HRT of each reactor was determined. Evaluation for the energy
consumption, volume and mass of generated sludge were performed as well. This
combined system was compared with the separate ozonation and EC base on the
removal efficiency, reaction time, energy consumption and generated sludge.
The results indicated that the ozonation, electrocoagulation and the combined system
were feasible for this wastewater treatment with high removal efficiency. In the
ozonation, with 40 min HRT, the remaining of dye, color and COD in treated water
were less than 2.5 mg/L, 32 Pt-Co and 16.5 mg/L. The dye, color and COD removal
efficiencies were 97.5%, 95.9% and 79%, respectively. The reaction of AR 114 dye
and ozone followed the first – order rate law. The treatment performance by
ozonation was significantly affected by following variables, ozone gas flowrate,
initial pH value, initial dye concentration and temperature. The volumetric mass
transfer coefficient was 0.021 min-1 and the enhancement factor was in a range of
10.22~10.93 with 30 min reaction time.

In the EC treatment, with 5.12 min HRT, the remaining of color, dye and COD were
57 Pt-Co, 7.3 mg/L and 4.6 mg/L. The color, dye and COD removal efficiencies were
92.6%, 92.7% and 94.1%, respectively. The treatment process followed the saturation
rate law. The treatment performance by EC was significantly affected by the current
density and the initial dye concentration. In the other hand, pH and conductivity did
not remarkably affect the removal efficiency by EC treatment. However, conductivity
had directly effect on the operating cost. Volume and mass of generated sludge were
110 mL/L and 450.7 mg/L with 5.12 min HRT.
Results of the combined system were obtained very good on this wastewater treatment.
With 2 min reaction time in the ozonation reactor and 0.85 min in the EC reactor, the
remaining of dye, color and COD were 4.9 mg/L, 57 Pt-Co and 22.7 mg/L,
respectively. The removal efficiencies reached 94.25%, 93% and 80.6% with respect
to dye, color and COD treatments. Volume and mass of generated sludge were 30
mL/L and 77 mg/L.

ii


Depending on energy requirement of the ozone generator, the DC supply power,
calculated energy consumptions were 2.13 kWh/m3, 1.8 kWh/m3 and 0.39 kWh/m3
with respect to the ozonation, the EC treatment and the combined system.
These results demonstrated that all of the ozonation, the electrocoagulation and the
combined system can effectively treat the dyeing wastewater containing AR 114 dye.
Among them, the combined system has shown impressive advantages when compare
to the others. It is not only because of the high removal efficiency but also it consumed
less energy, produced less generated sludge and took shorter reaction time than the
separate ozonation and electrocoagulation treatments. With these advantages, the
combined system will become a reasonable selection in the dyeing wastewater
treatment.
Keywords: CI Acid Red 114 dye, electrocoagulation; textile wastewater; dyeing wastewater,

Aluminum electrode, ozonation, bubble column, counter current, cocurrent, combined
ozonation with electrocoagulation.

iii


ACKNOWLEDGEMENTS
Foremost, I would like to express my special appreciation and gratitude to my advisor,
Professor Yong Soo Yoon, for his support for my Ph.D study and research in Korea. I
would like to thank you for your teaching, helps and encouraging not only in my
research, but also in my personal life. They have been priceless on both research as
well as on my career.
I would like to thank Professor Il Hyun Jung and all Professors in Department of
Chemical Engineering, Dankook University, for their useful teaching, advices and
helps during this course.
My sincere gratitude to Professor Dinh Tuan Nguyen, Mr. Tuan Long Tran, Ho Chi
Minh University of Natural Resources and Environment, who provided me an
opportunity and good conditions to attend this Ph.D course. Beside that, they usually
give me their helpful advices in my career as well as in my life.
I wish to thank to Mr. Sa Dong Kim, President of Design and Construction Tech, for
his helps and supports during my studying time in Korea.
My sincere thanks also goes to my labmates, including Pham Hung Duong, Dr. Dinh
Duc Nguyen, Cong Minh Pham, Hong Tuan Pham, Jin Ah Kim, Yong Seok Jung and
Sohyun Lee who helped me too much in my studying and research process.
I also thank to all my friends and my colleagues, who encouraged and shared the
difficulties in work.
I want to express a special thanks to my family. I am deepest grateful to my parents in
law, my parents, my sister and brothers, for all sweet love, unconditional helps and
supports that are strong motivation helped me overcome the difficult situations in this
studying period and my life. At the end, I would like express appreciation to my

beloved husband, Pham Hung Duong, who contributes an important part in this
research and my life.

iv


LIST OF CONTENTS
ABSTRACT..................................................................................................................... i 
ACKNOWLEDGEMENTS ........................................................................................... iv 
LIST OF CONTENTS .................................................................................................... v 
LIST OF FIGURES ....................................................................................................... ix 
LIST OF TABLES ........................................................................................................ xii 
NOTATION & ABBREVIATION ............................................................................... xv 
CHAPTER 1: INTRODUCTION ................................................................................... 1 
1.1 

Introduction ..................................................................................................... 1 

1.2 

Objectives of this study ................................................................................... 2 

1.3 

Scope of this study ........................................................................................... 3 

1.4 

Research Methods............................................................................................ 4 


1.4.1 Published document references.............................................................................. 4 
1.4.2 Experimental method ............................................................................................. 4 
1.4.3 Data analysis .......................................................................................................... 4 
1.5 

Scientific and practical significance of this study ........................................... 4 

1.5.1 

Scientific significance of this study ................................................................. 4 

1.5.2 New features of this study...................................................................................... 5 
1.5.3 Practical significance of this study. ....................................................................... 5 
CHAPTER 2: BACKGROUND ..................................................................................... 6 
2.1 Characteristics of the dyeing wastewater and CI Acid Red 114 dye. ....................... 6 
2.2.1 Physical treatments ................................................................................................ 9 
2.2.2 Chemical treatments............................................................................................. 11 

v


2.2.3 Biological treatment ............................................................................................. 12 
2.3 Electrocoagulation treatment .................................................................................. 12 
2.3.1 Theory of electrocoagulation ............................................................................... 14 
2.3.2 Reaction mechanism ............................................................................................ 16 
2.3.3 Previous studies of the electrocoagulation in the generally dyeing wastewater and
the namely CI AR 114 dye containing wastewater treatment ........................................ 16 
2.4 Ozonation process ................................................................................................... 18 
2.4.1 Ozonation mechanism .......................................................................................... 19 
2.4.2 Kinetics model of ozonation. ............................................................................... 22 

2.4.3 Bubble column reactor background ..................................................................... 25 
2.5 Previous studies on CI AR 114 dye treatment overview ........................................ 27 
CHAPTER 3: EXPERIMENTS .................................................................................... 30 
3.1 Characteristics of the synthetic wastewater ............................................................ 30 
3.2 Equipments and instruments ................................................................................... 30 
3.2.1 The ozonation treatment ...................................................................................... 30 
3.2.2 The electrocoagulation treatment ......................................................................... 31 
3.2.3 The combined system .......................................................................................... 35 
3.3 Experimental procedure .......................................................................................... 36 
3.3.1 The ozonation treatment ...................................................................................... 36 
3.3.2 The electrocoagulation treatment ......................................................................... 37 
3.3.3 The combined system .......................................................................................... 39 
3.4 Measurements and analysis methods ...................................................................... 39 
3.5 Calculation of experimental parameters method .................................................... 40 
3.5.1 General calculation method ................................................................................. 40 

vi


3.5.2 The ozonation process.......................................................................................... 41 
3.5.3 The electrocoagulation process ............................................................................ 42 
3.5.4 Data analysis ........................................................................................................ 43 
CHAPTER 4: RESULTS AND DISCUSSION ............................................................ 44 
4.1 Characteristics of the dyeing wastewater containing AR 114 dye treatment by the
ozonation. ...................................................................................................................... 44 
4.1.1 The gas holdup ..................................................................................................... 44 
4.1.2 The effect of gas velocity ..................................................................................... 45 
4.1.3 The volumetric mass transfer coefficient ............................................................. 47 
4.1.4 The enhancement factor ....................................................................................... 47 
4.1.5 The effect of pH ................................................................................................... 48 

4.1.6 The effect of initial dye concentration ................................................................. 51 
4.1.7 The effect of temperature ..................................................................................... 52 
4.1. 8 The removal efficiency by ozonation treatment in the BOM ............................. 54 
4.1. 9 The removal efficiency by ozonation in the COM ............................................. 55 
4.2 Characteristics of the dyeing wastewater containing AR 114 dye treatment by the
electrocoagulation. ........................................................................................................ 60 
4.2.1 The effect of pH value ......................................................................................... 60 
4.2.2 The effect of current density ................................................................................ 63 
4.2.3 The effect of initial dye concentration ................................................................. 65 
4.2.4 The effect of conductivity .................................................................................... 67 
4.2.5 The removal efficiency by EC treatment in the BOM ......................................... 69 
4.2.6 The removal efficiency by EC treatment in the COM. ........................................ 72 
4.3 Characteristics of the dyeing wastewater containing AR 114 dye treatment by the
ozonation-electrocoagulation combined system. .......................................................... 75 
vii


4.3.1 Determine HRT for each reactor in the combined system ................................... 75 
4.3.2 The treatment efficiency by the combined system............................................... 78 
4.3.3 Comparisons of the combined system, the separate ozonation and the
electrocoagulation treatment ......................................................................................... 79 
CHAPTER 5: CONCLUSIONS ................................................................................... 82 
REFERENCES ............................................................................................................. 84 
APPENDICES .............................................................................................................. 91 
Appendices A. Data of experiments ............................................................................. 91 
Appendices B. Pictures of equipments using in this study ......................................... 103 
Appendices C. Results of Anova analysis with alpha 0.05 ......................................... 106 

viii



LIST OF FIGURES
Fig 2.1 General electrocoagulation process .................................................................. 14 
Fig. 3.1 Schematic diagram of the ozonation system ................................................... 33 
Fig. 3.2 Schematic diagram of the electrocoagulation treatment in the batch reactor .. 34 
Fig. 3.3 Schematic diagram of the electrocoagulation in the continuous reactor ......... 34 
Fig. 3.4 Schematic diagram of the combined system. .................................................. 35 
Fig. 3.5 Calibration curve of dissolved CI AR 114 dye concentration. ........................ 40 
Fig. 4.1 Gas holdup as a function of gas flow rate ....................................................... 44 
Fig. 4.2 Effect of gas flow rates on the generated gas bubbles ..................................... 45 
Fig. 4.3 The removal efficiency by ozonation with various gas flow rates .................. 46 
Fig. 4.4 Plot of experimental graphical analysis for the volumetric mass transfer
coefficient ..................................................................................................................... 47 
Fig. 4.5 The effect of pH value on the ozonation treatment efficiency. ....................... 50 
Fig. 4.6 The removal efficiencies by ozonation treatment with various initial dye
concentrations ............................................................................................................... 51 
Fig. 4.7 The treatment efficiency by ozonation in the BOM ........................................ 55 
Fig. 4.8 The treatment efficiency by ozonation in the COM - the counter current flow56 
Fig. 4.9 The removal efficiencies by ozonation in the COM with the cocurrent flow . 57 
Fig. 4.10 Variation of pH value and conductivity during the ozonation treatment: (a) in
the BOM, (b) in the COM with the counter current, (c) in COM with the cocurrent. .. 58 
Fig. 4.11 Comparisons of the removal efficiency by ozonation treatment between the
BOM and COM- counter current. ................................................................................. 59 
Fig. 4.12 The color, dye, COD removal efficiencies with various initial pH values .... 61 
Fig. 4.13 Variation of pH during the electrocoagulation process in the BOM ............. 62 

ix


Fig. 4.14 Variation of conductivity with various initial pH values in the BOM .......... 62 

Fig. 4.15 Potential is a function of current density with conductivity of 1500 µS/cm . 63 
Fig. 4.16 Comparisons of the color, dye, COD removal efficiencies (a) and the energy
consumption (b) vs reaction time between various current densities in the BOM. ...... 64 
Fig. 4.17 Variation of the removal efficiency with various initial dye concentrations. 66 
Fig. 4.18 Potential as a function of conductivity in the electrocoagulation treatment .. 67 
Fig. 4.19 Comparisons of the removal efficiency between various conductivities ...... 68 
Fig. 4.20 The removal efficiency by the electrocoagulation process versus reaction
time in the BOM. .......................................................................................................... 70 
Fig. 4.21 The energy consumption for the COD, color, dye removals vs reaction time71 
Fig. 4.22 Dissolved aluminum as a function of reaction time in the case of 2.2 mA/cm2
current density............................................................................................................... 71 
Fig. 4.23 The volume and mass of generated sludge in the BOM as functions of rection
time. .............................................................................................................................. 72 
Fig. 4.25 The COD, color, dye removals versus reaction time in the COM ................. 73 
Fig. 4.26 Generated sludge in 1 liter treated water by EC in the COM ........................ 74 
Fig. 4.27 Energy consumption vs various HRT in the COM ........................................ 74 
Fig. 4.28 The removal efficiency by the combination system with various HRT of the
ozonation and electrocoagulation reactors. ................................................................... 76 
Fig. 4.29 Energy consumption of the combined system with various HRT in ozonation
and EC reactors. ............................................................................................................ 77 
Fig. 4.30 Comparisions of the generated sludge mass between various HRT in
ozonation reactor........................................................................................................... 78 
Fig. B.1 Ozone generator ............................................................................................ 103 
Fig. B.2 Dual DC power supply.................................................................................. 103 
Fig. B.3 Hacth-DR 2800 ............................................................................................. 103 
x


Fig. B.4 Digital reactor block DRB 200 ..................................................................... 103 
Fig. B.5 Centrifugal machine MF550 ......................................................................... 103 

Fig. B.6 HS – 3300, water analyzer & spectrophotometer ......................................... 103 
Fig. B.7 Ozonation system .......................................................................................... 104 
Fig. B.8 Continuous electrocoagulation reactor ......................................................... 105 

xi


LIST OF TABLES
Table 2.1 Unfixed dyes ................................................................................................... 6 
Table 2.2 Characteristics of typical untreated textile wastewater. .................................. 7 
Table 2.3 Characteristic of textile wastewater from each processing ............................. 8 
Table 3.1 Characteristics of the synthetic wastewater .................................................. 30 
Table 3.2 Dimensions of the cylindrical aluminum electrodes ..................................... 32 
Table 4.1 Data in the enhancement factor determination ............................................. 48 
Table 4.2 Comparisons of the combined system, the separate ozonation and the
electrocoagulation treatment ......................................................................................... 79 
Table A.1. Conditions of the gas holdup experiments. ................................................. 91 
Table A.2. The results of the gas holdup experiments. ................................................. 91 
Table A.3. The data of determination of the volume mass transfer coefficient. ........... 91 
Table A.4. Variation of dissolved ozone concentration with bubbling time ................ 92 
Table A.5. The variation of COD, dye concentration, color with ozonation time and
different gas flowrates .................................................................................................. 92 
Table A.6. The variation of COD, dye concentration, color with ozonation time and
different initial dye concentration ................................................................................. 93 
Table A.7. The variation of COD, dye concentration, color with ozonation time and
different initial pH value. .............................................................................................. 94 
Table A.8. The variation of COD, dye concentration, color with ozonation time and
different temperature..................................................................................................... 94 
Table A.9. The variation of COD, dye concentration, color with ozonation time in
BOM process (gas flowrate of 0,7 L/min, temperature 20oC) ...................................... 95 

Table A.10. The variation of COD, dye concentration, color with ozonation time in
COM process – counter current (gas flowrate of 0,7 L/min, temperature 20oC) .......... 95 
xii


Table A.11. The variation of COD, dye concentration, color with ozonation time in
COM process – cocurrent (gas flowrate of 0,7 L/min, temperature 20oC) ................... 96 
Table A.12. The variation of COD, dye concentration, color with electrocoagulation
time and different current density ................................................................................. 96 
Table A.13. The variation of COD, dye concentration, color with electrocoagulation
time and different initial dye concentrations. ............................................................... 97 
Table A.14. The variation of COD, dye concentration, color with electrocoagulation
time and different pH values. ........................................................................................ 98 
Table A.15. The variation of COD, dye concentration, color with electrocoagulation
time and different conductivity. .................................................................................... 99 
Table A.16. The variation of COD, dye concentration, color with electrocoagulation
time in BOM process (current density 2.2 mA/cm2, pH ~7, conductivity of 1500
µs/cm) ........................................................................................................................... 99 
Table A.17. The variation of COD, dye concentration, color with different HRT in
COM processes (current density 2.2 mA/cm2, pH ~7, conductivity of 1500 µs/cm) . 100 
Table A.18. Volume and mass of generated sludge with different HRT in COM
processes (current density 2.2 mA/cm2, pH ~7, conductivity of 1500 µs/cm) ........... 100 
Table A.19. The variation of COD, dye concentration, color in combination system
with HRT of ozonation process 3.33 min (3 L/min) and different HRT of
electrocoagulation process in COM (current density 2.2 mA/cm2, pH ~7, conductivity
of 1500 µs/cm) ............................................................................................................ 101 
Table A.20. The variation of COD, dye concentration, color in combination system
with HRT of ozonation process 2.5 min (4 L/min) and different HRT of
electrocoagulation process in COM (current density 2.2 mA/cm2, pH ~7, conductivity
of 1500 µs/cm) ............................................................................................................ 101 

Table A.21. The variation of COD, dye concentration, color in combination system
with HRT of ozonation process 2.0 min (5 L/min) and different HRT of

xiii


electrocoagulation process in COM (current density 2.2 mA/cm2, pH ~7, conductivity
of 1500 µs/cm) ............................................................................................................ 102 
Table A.22. Volume and mass of generated sludge from combination system with 2
min, 2.5 min, 3.33 min ozonation and 1.024 min electrocoagulation (current density
2.2 mA/cm2, pH ~7, conductivity of 1500 µs/cm) ...................................................... 102 
Table C.1 Anova analysis result of the effect of gas flow rate on gas holdup in
ozonation process ........................................................................................................ 106 
Table C.2 Anova analysis result for the effect of gas flow rate on removal efficiencies
in ozonation process.................................................................................................... 106 
Table C.3 Anova analysis result of the effect of pH on removal efficiencies in
ozonation process ........................................................................................................ 109 
Table C.4 Anova analysis result of the effect of initial dye concentration on removal
efficiencies in ozonation process ................................................................................ 112 
Table C.5 Anova analysis result of the effect of temperature on removal efficiencies in
ozonation process ........................................................................................................ 115 
Table C.6 Anova analysis result of the effect of pH on removal efficiencies in
electrocoagulation process .......................................................................................... 117 
Table C.7 Anova analysis result of the effect of current density on removal efficiencies
in electrocoagulation process ...................................................................................... 120 
Table C.8 Anova analysis result of the effect of initial dye concentration on removal
efficiencies in electrocoagulation process .................................................................. 123 
Table C.9 Anova analysis result of the effect of conductivity on removal efficiencies in
electrocoagulation process .......................................................................................... 126 


xiv


NOTATION & ABBREVIATION
a

Specific gas–liquid interfacial area [m–1]

Abs

Absorption spectrum

ADMI

American Dye Manufacturer’s Institute

AR

Acid Red

BOD

Biological oxygen demand

CI

Colour index

COD


Chemical oxygen demand

CO3

Concentration of dissolved ozone in water [molL-1]

C O* 3

Equilibrium concentration of dissolved ozone in water [molL-1]

db

Bubble diameter [m]

DC

Direct current

DO3

Diffusivity of ozone [m2 s–1]

DNA

Deoxyribonucleic Acid

E

Enhancement factor


EC

Electrocoagulation

LD50

Lethal Dose, 50%

GAC

Granular activated carbon

Ha

Hatta number

He

Henry’s law constant [atm mole fraction–1]

HRT

Hydraulic retention time [s]

kd

Kinetic constant of ozone decomposition [units depending on the order
of reaction]

xv



kL

Liquid phase individual mass transfer coefficient [m s–1]

kLa

Volumetric mass transfer coefficient [s–1]

NO3

Absorption rate or flux of ozone [molm–2 s–1]

PAC

Powder activated carbon

PO3

Partial pressure of ozone in gas [Pa]

rd

Rate of ozone decomposition [molm–3 s–1]

Sc

Schmidt number


SS

Suspended solid

TS

Total solid

TDS

Total dissolved solid

TSS

Total suspended solid

ug

Superficial gas velocity [ms-1]

z

Stoichiometric coefficient

Greek letters
εg

Gas holdup

μL


Liquid viscosity [kgm–1 s–1]

ρL

Liquid density [kgm–3]

σL

Surface tension [Nm–1]

xvi


CHAPTER 1: INTRODUCTION
1.1 Introduction
The dyeing wastewater, especially, containing CI AR 114 dye causes serious
problems to the environment. Because it not only influences the receiving
environment by large amounts of wastewater containing high pollutants
concentration but also strongly affects the heath of humans and animals that use
water from these sources due to the toxicity, carcinogens of many released dyes and
their breakdown products [24, 64, 3, 17].

CI AR 114 dye is evaluated as

carcinogenicity. It has carcinogenic activity to humans and animals. Although there
are inadequate evidences for carcinogenicity in humans, there are sufficient
evidences in experimental animals. For examples, from US National Toxicology
Program (1991), CI AR 114 dye was tested in the drinking water to rats and it
confirmed as a carcinogen [55]. Many treatment methods may be used in order to

remove pollutants in the dyeing wastewater such as adsorption with highly porous
solid, irradiation by gamma rays or electron beams, membrane processes (micro–
filtration, ultra-filtration, nano–filtration, RO), oxidation processes, coagulation–
flocculation, electrocoagulation and biological treatment [64]. However, the
brightly colored types of dye, water soluble reactive and acidic dyes can not be
effectively removed through conventional treatment system [64]. CI AR 114 dye is
one of these dye types due to it has red color, belongs acidic dye and has solubility.
Treatment of CI AR 114 dye have been studied by some of the treatment methods
such as adsorption treatment, biological treatment and photochemical oxidation [18,
35, 39, 27, 7, 8, 38, 15, 19]. Although these methods presented effectiveness on CI
AR 114 dye removal, they released large amount of second waste solid, had high
operation cost, long reaction time and they do not suit the large volume and high
pollutants concentration wastewater. Therefore, it is necessary to carry out more
studies on the CI AR 114 dye treatment by other methods to find out suitable
methods that can result high removal efficiency as well as overcome the
remaining limitations of previous studies.

1


The electrocoagulation method is well known for more than a century as it is one of
the promising methods based on the electrochemical technology in the 21st century.
There are many studies on electrocoagulation using aluminum and/or iron electrodes
to remove various types of dye carried out in recent years. Most studies showed that
the dye removal efficiencies were high, from 83% to 100% [56, 62, 30-32, 4, 6, 11, 13,
29,43, 61]. More noticeable advantages were less generated sludge and good
adaptation capacity to different volume and pollution loads. Therefore, the
electrocoagulation treatment may be a reasonable choice for the treatment of
wastewater containing CI AR 114 dye.
Beside the electrocoagulation, ozone can decompose the aromatic rings of some textile

dyes, azo dyes and other organic pollutants in wastewater. The advantages of this
process are the absence of increasing volume of wastewater and no secondary waste
solid production (sludge) [42, 12]. Therefore, the ozonation may be a satisfied method
for the treatment of this wastewater as well.
In some of the previous studied showed that the treatment efficiency by ozonation was
able to be enhanced by combined with other substances such as H2O2, UV, TiO2 [47,
48, 51]... Ozone enhanced the electrocoagulation process with iron electrodes were
researched and received good results [34, 51, 52]. Therefore, the system combined the
ozonation and the electrocoagulation (aluminum electrodes) may be an alternative way
for wastewater treatment that has not been researched yet. This combined system may
accumulate all the advantages of ozonation and EC.
For these reasons, the ozonation, electrocoagulation and the combined system were
carried out for the treatment of the dyeing wastewater containing AR 114 dye.

1.2 Objectives of this study
The specific objectives of this study were:
Ozonation treatment:
+ Investigate and assess treatment efficiency of wastewater containing AR 114 dye
by ozonation using a bubble column reactor with batch operation mode and
continuous operation mode including co-current and counter current flows.
2


+ Evaluate the effects of the pH, gas flow rate, reaction time, temperature, initial dye
concentration on the removal efficiency by ozonation through color, dye
concentration and COD parameters and determine reasonable operating condition
for this process.
+ Evaluate the volumetric mass transfer coefficient, enhancement factor, gas holdup,
and reaction rate coefficient that will be useful for ozonation reactor design.
Electrocoagulation treatment:

+ Assess the dyeing wastewater treatment ability of the electrocoagulation method
using aluminum electrodes in the batch and continuous reactors.
+ Evaluate the effects of current density, pH value, reaction time, conductivity and
initial dye concentration on the treatment efficiency by electrocoagulation and
suggest the suitable operating condition.
+ Determine the reaction order, reaction rate coefficient of this process.
+ Evaluate the energy consumption, volume and mass of generated sludge.
The combined system:
+ Assess the treatment efficiency by the ozonation and electrocoagulation combined
system through the dye, color, COD removal efficiency.
+ Determination of the suitable HRT in each reactor, volume and mass of generated
sludge, energy consumption.
+ Compare the combined system with the separate ozonation, electrocoagulation
treatment based on the treatment performance, treatment time, energy consumption,
volume and mass of generated sludge.

1.3 Scope of this study
+ This study was carried out with bench scale in experimental room.

+ Wastewater used in this study was synthesized from CI AR 114 dye powder and
tap water. Dye concentration was controlled in range of 40 - 100 mg/L.
3


1.4 Research Methods
1.4.1 Published document references.
To get background and research orientation for this study, some related documents
(books, articles…) were collected, selected and studied, including:
+ Characteristics of dyeing wastewater and CI AR 114 dye.
+ The methods can be used to treat the dyeing wastewater.

+ Mechanism, reaction kinetics of ozonation and electrocoagulation.
+ Published articles which studied on CI AR 114 dye treatment and the dyeing
wastewater treatment by the ozonation, the electrocoagulation.
1.4.2 Experimental method
+ Each experiment was repeatedly carried out 3 times to ensure the reliability of
collected data.
+ Experiments were performed in both the batch and continuous reactors
+ Dedicated equipments were applied to analyze COD, color, dye concentration in
wastewater before and after treatment. pH, conductivity, temperature were also
observed during experimental processes.
1.4.3 Data analysis
COD, color, dye concentration, pH, conductivity were observed, analyzed and
collected during experimental processes. Collected data was statistically analyzed by
statistical function - ANOVA with α = 0.05 in Microsoft Excel

1.5 Scientific and practical significance of this study
1.5.1 Scientific significance of this study
In this study, all of results is collected and analyzed from experimental data that have
clear scientific evidences. The calculation and data analysis are performed by
mathematical statistics to ensure scientific property of this study.
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1.5.2 New features of this study.
Treatment of dyeing wastewater containing AR 114 dye by the electrocoagulation, the
ozonatio and the ozonation-electrocoagulation combined system have not been studied
yet. Especially, the combination of ozonation and electrocoagulation with aluminum
electrodes is a completely new treatment method in wastewater treatment. So this
study will issue three new ways for treating AR 114 dye in wastewater and a new
method for the dyeing wastewater treatment. And since these results, these methods

can be applied in the dyeing wastewater treatment containing not only AR 114 but also
other dyes or become background for development of the other studies.
1.5.3 Practical significance of this study.
The results of this study can be applied to design the treatment plant of real
wastewater containing AR 114 dye or other dyes that have same properties with AR
114 dye. They can be good selection in development countries as they are satisfied
requirements of wastewater treatment. For some developing countries where these
methods may not be applied now due to high technology, they will become good
selection in future because of their advantages as small required area, less or no
second waste solid production and high efficiency that suit the development trend of
wastewater treatment technology and society.

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