vii
TABLE OF CONTENTS
CHAPTER NO.
1
TITLE
PAGE NO.
ABSTRACT
iii
LIST OF TABLES
xii
LIST OF FIGURES
xv
LIST OF SYMBOLS AND ABBREVIATIONS
xx
INTRODUCTION
1
1.1
GLOBAL WATER SCENARIO
1
1.2
TANNERY INDUSTRY
2
1.2.1 Preliminary Processing
5
1.2.2 Tanning
5
1.2.3 Post Tanning
6
1.2.4 Finishing
6
1.2.5 Mechanical Finishing Processes
and Applying a Surface Coat
1.3
7
1.2.6 Global Perspective
8
1.2.7 Indian Perspective
9
1.2.8 Tannery Pollutants
11
TREATMENT METHODS FOR TANNERY
EFFLUENT
12
1.3.1 Conventional
12
1.3.2 Advanced Oxidation Process (AOP)
13
viii
CHAPTER NO.
1.4
1.5
1.6
2
PAGE NO.
1.3.3 Electrochemical Treatment Techniques
14
ELECTRO OXIDATION
16
1.4.1 Direct Oxidation
17
1.4.2 Indirect Oxidation
17
ELECTROCHEMICAL REACTORS
18
1.5.1 Selection of Electrochemical Reactors
20
1.5.2 Rotating Disc Electrochemical Reactor
20
SCOPE OF THE PRESENT RESEARCH
22
LITERATURE REVIEW
23
2.1
TANNERY INDUSTRY
23
2.2
TREATMENT METHODS
24
2.2.1 Conventional Methods
24
2.2.2 Advanced Oxidation Process (AOP)
26
ELECTROCHEMICAL TREATMENT
27
2.3.1 Electro Oxidation
28
2.4
RESIDENCE TIME DISTRIBUTION
38
2.5
ELECTROCHEMICAL REACTORS
48
2.5.1 Rotating Disc Electrode
49
RESPONSE SURFACE METHODOLOGY
50
2.3
2.6
3
TITLE
MATERIALS AND METHODS
53
3.1
EXPERIMENTATION
53
3.1.1 Sample
53
3.1.2 Rotating Disc Electrochemical Reactor
55
PERFORMANCE OF RDE REACTOR
59
3.2
ix
CHAPTER NO.
TITLE
PAGE NO.
3.2.1 Experimental Apparatus and Procedures
for Residence Time Distribution
3.3
4
59
3.2.2 Non Ideal Reactor Model
61
COMPUTATIONAL FLUID DYNAMICS
62
RESULTS AND DISCUSSION
66
4.1
66
RESIDENCE TIME DISTRIBUTION MODEL
4.1.1 Effect of Flow Rate on Exit Age Distribution 78
4.1.2 Effect of Rotation Speed on Exit Age
Distribution
4.2
4.3
79
COMPARISON OF RTD WITH MODEL
81
4.2.1 Unequal volume
81
4.2.2 Equal volume
82
4.2.3 Active Center Compartment Volume
82
4.2.4 Color Removal Efficiency
86
COMPUTATIONAL FLUID DYNAMICS
87
4.3.1 Flow Pattern without Cathode Rotation
87
4.3.2 Flow Pattern Generated by the RDE
Reactor with Cathode Rotation
4.3.3 Model Validation
91
98
4.3.4 Effect of Flow Rate and Rotational
Speed on Turbulent Parameters
(TKE, TI) and Colour Removal
100
4.3.5 Effect of Flow Rate and Rotational
Speed on Vorticity Magnitude
4.4
103
ELECTRO – OXIDATION
106
4.4.1 Electro Oxidation Mechanism
106
x
CHAPTER NO.
TITLE
PAGE NO.
4.4.2 Characteristics of the Effluent
4.5
109
OPTIMIZATION OF ELECTROCHEMICAL
REACTOR CONFIGURATIONS
110
4.5.1 Batch Reactor
110
4.5.1.1 Effect of Current Density
112
4.5.1.2 Effect of Cathode Rotation Speed
113
4.5.1.3 Effect of Initial pH
115
4.5.2 Batch Recirculation Reactor
117
4.5.2.1 Effect of Electrolyte Flow Rate
4.5.3 Once Through Reactor
118
122
4.5.4 Performance Comparison of the
4.6
4.7
Reactors
125
4.5.5
Specific Energy Consumption
125
4.5.6
Kinetic Study
126
SOPHISTICATED ANALYTICAL
INSTRUMENTS
127
4.6.1 GC-MS Analysis
127
4.6.2
FT – IR Analysis
129
PILOT SCALE STUDY
131
4.7.1 Response Surface Methodology (RSM)
131
4.7.2 The Combined Effect of Operating
Parameters on Dye Effluent Degradation
135
4.7.3 Electrolysis Performance Under
Optimum Condition
140
4.7.4 Analytical Instruments
140
4.7.4.1 FT-IR
140
4.7.4.2 UV-Visible
142
4.7.4.3 HPLC
143
xi
CHAPTER NO.
5
TITLE
PAGE NO.
SUMMARY AND CONCLUSIONS
144
5.1
SUMMARY AND CONCLUSIONS
144
5.2
SCOPE FOR FUTURE WORK
146
REFERENCES
147
LIST OF PUBLICATIONS
165
CURRICULUM VITAE
166
xii
LIST OF TABLES
TABLE NO.
1.1
TITLE
Water consumption in various leather
processing stages
2.1
8
Literature collection on organic effluent, EO,
Reactor configurations
3.1
PAGE NO.
36
Initial characteristics and the discharge norms
according to Tamilnadu pollution control
board (TNPCB)
3.2
55
Specifications of Rotating disc electrochemical
reactor
60
3.3
Non-ideal reactor model equations for RTD
61
3.4
Boundary conditions for stationary domain
65
4.1
Experimental observation of RTD for pulse
input. Q=30 lph, N= 0 rpm
4.2
Experimental observation of RTD for pulse
input. Q=30 lph, N= 150 rpm
4.3
74
Experimental observation of RTD for pulse
input. Q=60 lph, N= 250 rpm
4.6
72
Experimental observation of RTD for pulse
input. Q=30 lph, N= 500 rpm
4.5
70
Experimental observation of RTD for pulse
input. Q=30 lph, N= 250 rpm
4.4
68
76
Experimental observation of RTD for pulse
input. Q=90 lph, N= 250 rpm
77
xiii
TABLE NO.
4.7
TITLE
PAGE NO.
Experimental parameters calculated at
different operating conditions
79
4.8
Variation of Reactor Active Volumes (V1, V2)
82
4.9
Characteristics of the secondary effluent
collected at Pallavaram CETP
4.10
Effect of current density on the performance of
the batch electrochemical reactor
4.11
109
116
Effect of cathode rotation speed on the
performance of the batch electrochemical
reactor
4.12
Effect of initial pH on the performance of the
batch electrochemical reactor
4.13
117
117
Effect of electrolyte flow rate on the
performance of the batch recirculation
electrochemical reactor
4.14
121
Effect of cathode rotation speed on the
performance of the batch recirculation
electrochemical reactor
4.15
Effect of current density on the performance of
the batch recirculation electrochemical reactor
4.16
122
Effect of initial pH on the performance of the
batch recirculation electrochemical reactor
4.17
121
122
Effect of electrolyte flow rate on the
performance of the once through
electrochemical reactor
4.18
123
Effect of current density on the performance of
the once through electrochemical reactor
123
xiv
TABLE NO.
4.19
TITLE
PAGE NO.
Effect of cathode rotation speed on the
performance of the once through
electrochemical reactor
4.20
Effect of initial pH on the performance of the
once through electrochemical reactor
4.21
131
Design of experiments and response for dye
effluent degradation
4.24
127
Range of independent variables used in dye
effluent degradation
4.23
124
Major organic compounds observed in raw
effluent
4.22
124
133
Estimated regression coefficient and
corresponding t- and P-values for percentage
of chemical oxygen demand removal
4.25
134
ANOVA for percentage of chemical oxygen
demand removal
135
xv
LIST OF FIGURES
FIGURE NO.
1.1
TITLE
General flow diagram of leather tanning
process
1.2
14
Mechanism on (a) direct oxidation, (b) indirect
oxidation
1.4
4
Advanced Oxidation Processes for wastewater
treatment
1.3
PAGE NO.
16
Classification of electrochemical reactors
according to electrode geometry and configuration
19
1.5
Idealized flow pattern of RDE.
21
3.1
Flow diagram for treatment Process carried out in
Common Effluent treatment Plant at Pallavaram,
India
3.2
54
Experimental setup of Rotating Disc
Electrochemical reactor (RDE)
57
3.3
Photograph of the Rotating Disc Electrode
58
3.4
Experimental setup of RDE for RTD
60
3.5
Assumptions for RDE
62
3.6
Domains split up using a moving reference frame
63
4.1
Effect of liquid flow rate on RTD
78
4.2
Effect of rotational speed on RTD curves in
an RDE
4.3
80
Comparison of model simulation of
saravanathamizhan et al (2009) with experimental
observation for the pulse input for the
cases I and II
81
xvi
FIGURE NO.
4.4
TITLE
PAGE NO.
Comparison of model simulation of exit age
distribution with experimental observation of
increasing centre volume
4.5
83
Comparison of simulated E(t) distribution with
experimental observation in an RDE for pulse
input
4.6
84
Comparison of simulated E(t) distribution with
experimental observation in an RDE for pulse
input
4.7
85
Comparison of simulated E(t) distribution with
experimental observation in an RDE for pulse
input
4.8
Confirmation of RTD conditions through color
removal efficiency
4.9
85
87
Velocity contours plot without rotation of
cathode (a) 30 lph, (b) 60 lph, (c) 90 lph along
z-x axis.
4.10
Velocity magnitude as a function of position
at (a) Q= 30 lph, (b) Q= 60 lph,(c) Q= 90 lph
4.11
94
Velocity contour plot of Q=60 lph for
(a)N= 150 rpm, (b) 250 rpm, (c) 500 rpm
4.14
93
Velocity contour plot of Q=30 lph for (a) N= 150
rpm, (b) 250 rpm, (c) 500 rpm
4.13
90
Flow Pattern in RDE Reactor at
Q=30 lph, N= 250 rpm
4.12
88
95
Velocity contour plot of Q=90 lph for (a) N= 150
rpm, (b) 250 rpm, (c) 500 rpm
96
xvii
FIGURE NO.
TITLE
4.15
Velocity Vectors at Q= 60 lph, N= 500 rpm
4.16
CFD Model Validation through comparison
PAGE NO.
97
between experimental exit age distribution with
CFD at 30 lph and 500 rpm
4.17
Transient Contours of Tracer Mass Fraction along
YZ axis at Q=30 lph, N=500 rpm
4.18
104
Volume Averaged Vorticity Magnitude as a
function of rotational speed.
4.23
103
Contours of Vorticity Magnitude at Q= 30
lph (a) 150 rpm, (b) 250 rpm, (c) 500 rpm
4.22
102
Variation of averaged turbulent intensity with
rotational speed
4.21
101
Effect of flow rate and rotational speed on
percentage colour removal.
4.20
99
Contours of Turbulent Intensity at Q= 30 lph
(a) 150 rpm, (b) 250 rpm, (c) 500 rpm
4.19
98
105
Effect of current density on percentage TOC
removal in batch mode at cathode rotation
speed: 250 rpm, pH: 7.5
4.24
113
Effect of cathode rotation speed on
percentage TOC removal in (a) batch mode at
current density: 15mA/cm2, pH: 7.5
4.25
114
Effect of initial pH on percentage TOC
removal in (a) batch mode at current density:
15mA/cm2, cathode rotation speed: 500 rpm
115
xviii
FIGURE NO.
4.26
TITLE
PAGE NO.
Effect of wastewater flow rate on percentage
TOC removal in batch recirculation mode at
current density: 15mA/cm2, cathode rotation
speed: 500 rpm, pH: 7.5
4.27
119
Effect of current density on percentage TOC
removal in batch recirculation mode at
cathode rotation speed: 250 rpm, pH: 7.5,
flow rate: 60 lph
4.28
119
Effect of cathode rotation speed on percentage
TOC removal in batch recirculation mode at
current density: 15mA/cm2, pH: 7.5, flow rate: 60
120
lph
4.29
Effect of initial pH on percentage TOC removal in
batch recirculation mode at current density:
15mA/cm2, cathode rotation speed: 500 rpm, flow
rate: 60 lph
4.30
120
GC-MS Spectra of the organic pollutants in (a)
raw effluent; (b) treated effluent
128
4.31
FT – IR spectra of (a) Raw (b) Treated effluent
130
4.32
Photograph of treated samples collected at (a)
0, (b) 30, (c) 60, (d) 90, (e) 120, (f) 150
minutes of treatment respectively at the
optimum condition
4.33
Combined
effects
131
of
supporting electrolyte
concentration and cathode rotation speed on
percentage of chemical oxygen demand removal:
(a) contour plot and (b) response surface
136
xix
FIGURE NO.
4.34
TITLE
Combined
effects
of
PAGE NO.
supporting electrolyte
concentration and electrolyte flow rate on
percentage of chemical oxygen demand removal:
(a) contour plot and (b) response surface
4.35
138
Combined effects of current density and
electrolyte flow rate on percentage of
chemical oxygen demand removal: (a)
contour plot and (b) response surface
4.36
139
Colour and chemical oxygen demand removal and
pH of methyl orange with electrolysis time at
optimum conditions
140
4.37
FT - IR spectra of (a) raw and (b) treated effluent
141
4.38
UV–Vis spectra of dye house effluent during the
process of electro-oxidation for different time
4.39
intervals
142
HPLC plot of (a) raw (b) treated effluent
143
xx
LIST OF SYMBOLS AND ABBREVIATIONS
ANNOVA
- Analysis of variance
D/uL
- Axial dispersion number
N
- Cathode rotation speed (rpm)
COD
- Chemical oxygen demand (mg/l)
Q
- Circulation volumetric flow rate (lph)
CETP
- Common effluent treatment plant
CFD
- Computational fluid dynamics
C
- Concentration at time ‘t’
C(t)
- Concentration of tracer at exit (g/l)
tc
- Contact time (min)
A
- Cross sectional area perpendicular to the direction of flow
(cm2)
I
- Current (A)
CD
- Current density (mA/cm2)
DF
- Degree of freedom
C
E( )
- Difference in TOC (mg/l)
- Dimensionless exit age distribution
- Dimensionless Time
Ve
- Effluent volume (l)
EO
- Electro oxidation
EC
- Energy consumption (kWh/kg of TOC)
E(t)
- Exit age distribution (min-1)
FT-IR
GC-MS
HPLC
Fourier transform – infrared
- Gas chromatography – mass spectra
High pressure liquid chromatography
xxi
tm
- Hydraulic residence time (Sec)
Ci
- Initial concentration (mg/l)
MS
- Mean square
n
- Number of tanks
k
- Rate constant (min-1)
R2
- Regression coefficient
RTD
- Residence time distribution
RSM
- Response surface methodology
RDE
- Rotating disc electrochemical reactor
SS
- Sum of square
t
- Time (Sec)
TDS
- Total dissolved solids (mg/l)
TOC
- Total Organic Carbon (mg/l)
TSS
- Total suspended solids (mg/l)
TI
- Turbulent intensity
TKE
- Turbulent kinetic energy
UV-Visible
- Ultraviolet – visible spectroscopy
2
- Variance
V
- Voltage (V)
VR
- Volume of the reactor (l)

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