this dissertation is submitted to -...
TRANSCRIPT
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COLOR REMOVAL FROM SYNTHETIC DYE AND TEXTILE WASTEWATERS USING
ADSORBENT PREPARED FROM PSYLLIUM HUSK.
By
SOMAIA M. O. TAYEH
School of Civil Engineering
Universiti Sains Malaysia
Engineering Campus
June 2012
This dissertation is submitted to
UNIVERSITI SAINS MALAYSIA
As partial fulfillment of requirements for the degree of
MASTER OF SCIENCE (ENVIRONMENTAL
ENGINEERING)
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ACKNOWLEDGEMENTS
First of all, I would like to express my grateful to Allah SWT for all his gifts, that this
thesis was completely finished. Then my grateful also dedicated to my parents for all
their pray and supporting me to go forward in my study.
I would like to express my grateful thanks to my supervisor Dr. Irvan Dahlan for his
guidance, motivation and endless supports during this project.
I cannot forget to thank my small family, my husband Bassam and my children Wala`,
Bara` and Shahd, for their continued patience and encouragement throughout all my
study.
Finally, I present a lot of thanks for all people who contributed with their helps directly or
indirectly in finishing my thesis.
Thank you all very much.
Somaia
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TABLE OF CONTENTS
ACKNOWLEDGEMENTS ………………………………..…….................
TABLE OF CONTENTS………………………….…..……………………..
LIST OF TABLES………………………………………………..…............
LIST OF FIGURES………………………………………..….……………..
LIST OF PLATES…………………………………………….....…………..
ABSTRAK………………………………………………….……………….
ABSTRACT…………………………………………………......................
CHAPTER ONE: INTRODUCTION
1.1 Background…………………………………………..……………….
1.2 Problem statement……………………………...…………………….
1.3 Objectives of the study……………………………….…..................
1.4 Scope of study………………………………………..………………
1.5 Organization of the thesis ……………………..……………………..
CHAPTER TWO: LITERATURE REVIEW
2.1 Introduction……………………………………………..……………
2.2 Textile wastewater……………………………………………………
2.2.1 Textile wastewater characteristics………………..…………..
2.2.2 Dyes…………………………………………………………..
2.2.3 Types of dyes…………………………….…………………..
2.2.4 Impact of dyes ……………………..………………………..
2.2.5 Direct blue71 (DB71)………………………………………..
2.2.6 Color Scales (ADMI and APHA)…………………………….
2.2.6a APHA/PtCo standard………………………………….
2.2.6b ADMI Scale…………………………………………...
2.2.7 Textile wastewater treatment…………………………………
2.2.6a Physical Treatment……………………………………
2.2.6b Physico-chemical Treatment………….………………
2.2.6cBiological Treatment………………………..…………
2.3 Adsorption……………………………………………………………
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2.3.1 Adsorption process………………………..….………………
2.3.2 Adsorption Isotherms……………………...…………………
2.3.2a Langmuir Isotherm……….………..………………….
2.3.2b Freundlich Isotherm……..…………………………….
2.4 Activated carbon and low-cost Adsorbents……………..……………
2.5 Psyllium husk………………………………………………………...
2.6 Magnetic adsorbents…………………….……………………………
2.7 Summary ………………………………………………...…………...
CHAPTER THREE: MATERIALS AND METHODOLOGY
3.1 Experimental flow chart……………………………………………...
3.2 Materials and Chemicals………………………….………………….
3.3 Preparation of reference solutions……………………………………
3.3.1 Preparation of 1% w/v Na2CO3………………………………
3.3.2 Preparation of 5 M NaOH…………………….……………...
3.3.3 Preparation of 2 N H2SO4…………………………………….
3.3.4 Preparation of dye solution…………………….……………..
3.4 Equipments and glassware………………………….………………...
3.5 Adsorbent Preparation……………………………….……………….
3.5.1 Preparation of raw psyllium husk…………..………………...
3.5.2 Preparation of Quaternized adsorbent………………………..
3.5.3 Preparation of psyllium husk/CoFe2O4 adsorbent (PH/CFO)……
3.6 Batch Experimental Studies…………………………………………..
3.6.1 Preliminary batch study…………………….………………...
3.6.2 Adsorption of DB71 from synthetic wastewater…………......
3.6.2a Effect of contact time………………………………….
3.6.2b Effect of adsorbent amount……………………………
3.6.2c Effect of shaking rate………………………………….
3.6.2d Effect of initial dye concentration…………………….
3.6.2e Effect of pH…………………………………………...
3.6.2f Effect of temperature…………………………………..
3.6.3 Adsorption of color from textile wastewater………………
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3.6.3a Effect of adsorbent amount……………………………
3.6.3b Effect of shaking rate………………….………………
3.6.3c Effect of temperature………………………………….
3.7 Isotherm and kinetic studies………………………………………….
3.8 Characterization………………………………………………………
3.8.1 DR 2800 spectrophotometer analysis………………………...
3.8.2 Particle size distribution analysis…………………………….
3.8.3 Scanning electron microscope (SEM) analysis………………
CHAPTER FOUR: RESULTS AND DISCUSSION
4.1 Introduction…………………………………………………………..
4.2 Preliminary Batch Study ……………………………………………..
4.3 Batch experiments for synthetic wastewater…………………………
4.3.1 Effect of contact time……………………………..…………
4.3.2 Effect of adsorbent amount……………………..…………….
4.3.3 Effect of shaking rate………………………..………………..
4.3.4 Effect of initial dye concentration……………..…………….
4.3.5 Effect of pH………………………………………………….
4.3.6 Effect of temperature…………………………………………
4.4 Batch Experiments for Real Textile Wastewater…………………….
4.4.1 Effect of adsorbent amount……………….…………………..
4.4.2 Effect of shaking rate…………………………………………
4.4.3 Effect of temperature………………………….……………...
4.5 Adsorption kinetics…………………………………….…………….
4.6 Adsorption isotherm………………………………………………….
4.6.1 Langmuir isotherm…………………………………………...
4.6.2 Freundlich isotherm…………………………….…………….
4.7 Characterization of magnetic PH/CFO-Ac adsorbent………………..
4.7.1 Particle Size Distribution analysis……………………………
4.7.2 Surface morphology analysis (SEM)…………………………
CHAPTER FIVE: CONCLUSIONS AND RECOMMENDATIONS
5.1 Conclusions…………………………………………………………..
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5.2 Recommendations……………………………………………………..
REFERENCES………………………………………………………………..
APPENDICES
APPENDIX A………………………………………………………...............
APPENDIX B………………………………………………………...............
APPENDIX C………………………………………………………...............
APPENDIX D………………………………………………………...............
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LIST OF TABLES
Table 2.1: Acceptable concentrations for discharge of industrial effluent…………….
Table 2.2: Textile Industry Wastewater Characteristics…………………………….....
Table 2.3: Properties of physisorption and chemisorptions…………………………...
Table 2.4: Chemical composition of psyllium husk……………………………...........
Table 2.5: Mineral analysis of psyllium husk………………………………………….
Table 3.1: Summary of Batch Studies …………...……………………………………
Table 4.1: Kinetic parameters for adsorption of DB71 onto PH/CFO-Ac…………….
Table 4.2: Adsorption Types based on RL value………………………………………
Table 4.3: Langmuir and Freundlich isotherm model constants ……………………...
Table A.1: Effect of dye concentration on sorbent selection…………………………..
Table A.2: Effect of sorbent amount on sorbent selection ……………………………
Table B.1: Effect of contact time on the adsorption of DB71…………………………
Table B.2: Effect of adsorbent amount on the adsorption of DB71…………………..
Table B.3: Effect of shaking rate on the adsorption of DB71…………………………
Table B.4: Effect of initial dye concentration on the adsorption of DB71…………….
Table B.5: Effect of PH on the adsorption of DB71…………………………………..
Table B.6: Effect of temperature on the adsorption of DB71…………………………
Table C.1: Effect of sorbent amount on adsorption of color from textile wastewater...
Table C.2: Effect of shaking rate on adsorption of color from textile wastewater……
Table C.3: Effect of temperature on adsorption of color from textile wastewater…….
Table D.1 Data and calculations for the kinetic study…………………………………
Table D.2 Experimental data and Calculations for isotherm study……………………
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LIST OF FIGURES
Figure 2.1: Structure of direct blue71……………………………………………..........
Figure 2.2: schematic illustrations of adsorption steps……………………….………...
Figure 3.1: Flow Chart of the study………………………………………….…………
Figure 4.1: Sorbent selection based on (a) dye concentration (b) sorbent amount……..
Figure 4.2: Effect of contact time on adsorption of DB71 from synthetic wastewater...
Figure 4.3: Effect of adsorbent amount on adsorption of DB71 From…………………
Synthetic wastewater
Figure 4.4: Effect of shaking rate on adsorption of DB71 from synthetic wastewater…
Figure 4.5: Effect of initial dye concentration on adsorption of DB71 from…………
synthetic wastewater
Figure 4.6: Effect of pH on the adsorption of DB71 from synthetic wastewater……....
Figure 4.7: Effect of temperature on the adsorption of DB71 from synthetic..
wastewater
Figure 4.8: Effect of sorbent amount on adsorption of color from textile wastewater...
Figure 4.9: Effect of shaking rate on adsorption of color from textile wastewater……
Figure 4.10: Effect of temperature on adsorption of color from textile wastewater……
Figure 4.11: The variation of adsorption capacity of DB71 onto PH/CFO-Ac with…...
adsorption time
Figure 4.12: Pseudo-first-order kinetic plot for adsorption of DB71 onto PH/CFO-Ac
Figure 4.13: Pseudo-second-order kinetic plot for adsorption of DB71 onto PH/CFO-Ac
Figure 4.14: Linearized Langmuir isotherm………………………….……………….
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Figure 4.15: Linearized Freundlich isotherm…………………………………...……..
Figure 4.16: Particle size distribution of prepared PH/CFO-Ac adsorbent……………
Figure 4.17: Particle size distribution of spent adsorbent with high removal efficiency.
Figure 4.18: Particle size distribution of spent adsorbent with low removal efficiency
Figure 4.19: Comparison of size distributions for prepared and spent adsorbent………
Figure 4.20: Raw psyllium husk in SEM investigations……………………………….
Figure 4.21: Comparison of prepared and spent adsorbent in SEM investigations……
Figure 4.22: Prepared and spent adsorbent in SEM investigations…………………….
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LIST OF PLATES
Plate 3.1: Raw psyllium husk (PH)…………………………….………………………
Plate 3.2: Digital balance………………………………..…………………….……….
Plate 3.3: pH meter……………………………....………………………….………..
Plate 3.4 SK-600 shaker…………………………….………………………..………..
Plate 3.5: Shaker Incubator…………………………………………………..………..
Plate 3.6: Filtration Pump…………………………………...…………..…………….
Plate 3.7: DR 2800 Spectrometer…………………………………………….………..
Plate 3.8: Facile refluxing route ……………………………..………………..……….
Plate 3.9: Preparation of quaternized adsorbent……………………………………….
Plate 3.10: Preparation of psyllium husk/CoFe2O4 adsorbent (PH/CFO)……………..
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Penyingkiran Warna dari Pencelup Sintetik dan Air Sisa Tekstil Menggunakan
Bahan Penjerap Disediakan dari Sekam Psyllium
ABSTRAK
Penyingkiran warna dari efluen tekstil telah diberikan banyak perhatian
dalam beberapa tahun lepas oleh proses penjerapan menggunakan adsorbents kos
rendah. Dalam kajian ini, bahan penjerap sekam psilium/CoFe2O4 (PH/CFO),
disintesiskan melalui satu langkah mudah laluan refluks dan telah digunakan
sebagai bahan penjerap untuk penyingkiran warna dari pelarut pencelup sintetik
dan air buangan tekstil. Kajian kelompok menunjukkan bahawa kecekapan
penyingkiran terbaik bahan penjerap berada di pH 9.0, suhu 30oC (untuk pelarut
sintetik) dan 40oC (untuk air buangan tekstil), kadar goncangan sebanyak 150 rpm
(untuk pelarut sintetik) dan 280rpm (untuk air buangan tekstil), dan masa sentuh 2
jam. Bahan penjerap PH/CFO menunjukkan kecekapan penyingkiran lebih tinggi
pada kecekapan awal pencelup yang tinggi. Pada masa yang sama, kecekapan
bahan penjerap bertambah dengan berkurangnya jumlah bahan penjerap yang
digunakan. Data eksperimen berpadanan baik dengan model Langmuir dengan
keupayaan jerapan satu lapisan 188.7mg/g. Penjerapan ilmu kinetik didapati
mengikuti model kinetik pseudo- aturan kedua. Analisis saiz partikel dan
pemerhatian SEM disediakan dan dibelanjakan penjerap telah dijalankan, analisis
saiz zarah menunjukkan taburan saiz zarah yang homogenus untuk kedua-dua
sampel. Pemerhatian SEM menunjukkan bahawa zarah pewarna yang
didepositkan seragam ke permukaan PH/CFO penjerap.
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Colour Removal from Synthetic Dye and Textile Wastewater Using
Adsorbent Prepared from Psyllium Husk
ABSTRACT
Color removal from textile effluents has been given much attention in the last
few years by the adsorption process using low cost adsorbents. In this study, psyllium
husk/CoFe2O
4 adsorbent, (PH/CFO), was synthesized by a simple one-step refluxing
route and was used as adsorbent for the removal of color from synthetic dye solution and
textile wastewater. The batch experiments showed that the best removal efficiency of the
adsorbent was at pH 9.0, temperature 30oC (for synthetic wastewater) and at 40oC (for
textile wastewater), shaking rate 150 rpm (for synthetic wastewater) and 280rpm (for
textile wastewater), and at contact time 2 hours. The PH/CFO adsorbent showed higher
removal efficiency at higher initial dye concentrations. At the same time, the adsorbent
efficiency was increasing by decreasing the amount of adsorbent used. The experimental
data fitted well with the Langmuir model with a monolayer adsorption capacity of
188.7mg/g. The adsorption kinetics was found to follow pseudo-second-order kinetic
model. The particle size analysis and SEM observations of prepared and spent adsorbent
where carried out, particle size analysis showed a homogenous particle size distribution
for both samples. SEM observations showed that the dye particles deposited uniformly
onto the surface of PH/CFO adsorbent.
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CHAPTER ONE
INTRODUCTION
1.1 Background
Due to the increase in the world population and development of industrial
applications, environmental pollution problem became very important, especially
wastewater pollution problem. Communities produce both liquid and solid wastes. The
liquid waste -wastewater- is essentially the water supply of the community after it has
been used in a variety of applications. Wastewater handling, disposal & treatment are
serious worldwide problem. Many industrial and agricultural activities use water in an
excessive way. However, it is now well known that the fresh water resources are limited
and fragile, so they must be protected.
Discharge of sanitary wastewater, industrial effluent and agricultural field’s
runoff can be the main source of freshwater pollution. This causes many diseases for
human, and it is known that 70-80% of illness in developing countries is related to water
contamination, particularly for children and women (WHO/UNICEF, 2000).
Textile industries consume large volumes of water and chemicals for wet
processing of textiles. The chemical reagents used are very diverse in chemical
composition, ranging from inorganic compound to polymers and organic compound
(Correia et al., 1994). The color is an evident indicator of water pollution by the dyes.
Industrial dye effluents are visible even at concentrations lower than 1 mg/l. Moreover,
some dyes and their degradation products are carcinogenic (Ahn et al., 1999). Also, some
dyes are harmful to aquatic life in rivers where they are discharged. Since, dye can reduce
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light penetration into the water thereby decreasing the efficiency of photosynthesis in
aquatic plants and hence having adverse impact on their growth (Che Ani, 2004)
1.2 Problem statement
Textile wastewater is generally high in both color and organic content. Effluents
discharged from dyeing industries are highly colored and they can be toxic to aquatic life
in receiving waters (Lee et al., 1999, Kadirvelu et al., 2003). Color removal from textile
effluents has been given much attention in the last few years, not only because of its
potential toxicity, but mainly due to its visibility problems (Morais et al., 1999). The total
dye consumption of the textile industry worldwide is in excess of 107 kg/year, and an
estimated 90% of this ends up on fabrics. Consequently, 1000 tonnes/year or more of
dyes are discharged into waste streams by the textile industry worldwide (Ahmad et al.,
2007).
Development of the appropriate techniques for treatment of dye wastewater is
important for the protection of natural water. To eliminate dyes from aqueous colored
effluents and reduce their ecological consequences, several biological and chemical
techniques have been proposed: anaerobic/aerobic degradation (Ahmed et al., 2007),
coagulation/flocculation (Papić et al., 2000) and also oxidative/reductive chemical and
photochemical processes (Lucas and Peres, 2006). Due to relatively high operating costs
and low removal efficiencies using the above-mentioned processes, textile, pulp and
paper industries seldom apply these to treat their effluents.
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Among several chemical and physical methods, the adsorption has been found to
be superior to other techniques in water reuse methodology because of its capability for
adsorbing a broad range of different types of adsorbates efficiently, and simplicity of
design. Many researchers researched for cheaper substitutes, which are relatively
inexpensive, and are at the same time endowed with reasonable adsorptive capacity.
These studies include the use of coal, fly ash, activated clay, palm-fruit bunch, Bagasse
pith, cellulose-based waste, peat, bentonite, slag and fly ash, rice husk, activated sludge,
etc (Ahmad et al., 2007).
Psyllium husk has not been investigated as adsorbent for color removal from dye
solutions and textile wastewater. This research studied the adsorption for color removal
from synthetic and real textile wastewater, using an adsorbent prepared from psyllium
husk.
1.3 Objectives of the study
The main aim of this study is to apply the adsorption technique as a treatment
method to remove dyes and color from synthetic dye and real textile wastewaters, by
using an adsorbent prepared from an inexpensive and readily available material which is
psyllium husk. Also, the study aims to achieve the following measureable objectives:
1- To prepare and characterize adsorbent from psyllium husk using quaternized and
magnetic methods.
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2- To investigate the ability of the best psyllium husk adsorbent for removal of color
from synthetic dye and textile wastewater under various operating conditions (initial
dye concentration, amount of sorbent, shaking rate, contact time, pH, temperature ).
3- To determine the kinetic behavior and isotherms for the adsorption process of color
onto psyllium husk adsorbent.
1.4 Scope of study
The scope of this study is the removal of color from textile waste water and from
synthetic solution contained direct blue 71 dye. The best adsorbent was selected from
many types of adsorbents prepared from psyllium husk. Characterization of psyllium
husk adsorbent was carried out with Particle Size Distribution analyzer (Mastersizer
2000) and Scanning Electron Microscopy (SEM).
Batch experiments were carried out for the adsorption of dye onto the psyllium
husk adsorbent. The effect of the following parameters was investigated: adsorbent
amount, initial dye concentration, contact time, shaking rate, pH, and temperature.
Moreover the best fitting adsorption isotherm models were examined using the most
widely applied isotherm models. Adsorption isotherms are helpful in demonstrating the
extent of homogeneity of the adsorption sites and the affinity of these sites towards the
adsorbed molecules.
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1.5 Organization of the thesis
There are five chapters in the thesis Chapter one provides an introduction and
background of the study. Chapter two presents a review of the literature. It reviews the
textile wastewater: its characteristics and treatment, Dyes: their types and impacts,
Adsorption: process, kinetics and isotherm models, Types of adsorbents: activated carbon
and psyllium husk. Chapter three covers the experimental part. This chapter is divided
into 4 sections. The 1st section presents the materials, chemicals, equipments and
adsorbent preparation methods used in the experiments. The 2nd
section explains the
preliminary study to select the best adsorbent. The 3rd
section explains the main batch
studies (applied on synthetic and real textile wastewater). And the 4th
section is for the
characterization of the adsorbents. Chapter four presents the experimental results
together with the discussion. It is grouped into 4 sections. The 1st section presents the
results for preliminary study. The 2nd
section gives results of the main batch studies for
synthetic dye solution and real textile wastewater. The 3rd
section presents the results of
kinetic and equilibrium studies. And the 4th
section gives the results for the
characterization of the adsorbents. Finally, Chapter five gives the conclusions and
recommendations of the thesis.
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CHAPTER TWO
LITERATURE REVIEW
2.1 Introduction
Wastewater pollution creates many problems of turbidity, odor, color, and many
other problems. The quality of waste water can be characterized by physical, chemical
and biological parameters (Metcalf and Eddy, 2003). Physical parameters include color,
odor, temperature, solids, turbidity, density and conductivity. Chemical parameters
include biochemical oxygen demand (BOD), chemical oxygen demand (COD), pH,
acidity, alkalinity, chlorides, sulphates, nitrogen (organic, ammonia, nitrite, and nitrate),
metals such as mercury (Hg), lead (Pb), chromium (Cr), nickel (Ni), copper (Cu), and
zinc (Zn). Biological parameters include the presence of bacteria and other
microorganisms. Fifth Schedule of Environmental Quality Act 1974, under
Environmental Quality (Industrial Effluent) Regulation 2009, listed the maximum
acceptable conditions for discharge of industrial effluent or mixed effluent of standard A
and B as shown in Table 2.1.
2.2 Textile wastewater
The textile industry, apart from being an important contributor to the economy of
many countries, is also a major source of various liquid, solid and gaseous wastes. This
kind of industrial activity can have a negative impact on the environment, both in terms
of pollutant discharge as well as of water and energy consumption. Although the amount
of water used and wastewater generated is largely dependent upon the specific type of
operations followed, in general, dyeing, washing, and finishing operations spend the
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greatest demand (Gurnham, 1965). For instance, and as reported by that the volume of
wastewater generated by dyeing and finishing operations ranged from 73 to 167m3 per
ton of product (Fongsatitkul et al., 2004).
Table 2.1: Acceptable concentrations for discharge of industrial effluent or mixed
effluent of standards A and B (DOE, 2012).
Parameter Unit Standard
A B
Temperature oC 40 40
pH Value – 6.0-9.0 5.5-9.0
BOD5 at 20oC
COD (Textile industry)
mg/L
mg/L
20
80
50
250
Suspended Solids mg/L 50 100
Mercury mg/L 0.005 0.05
Cadmium mg/L 0.01 0.02
Chromium,Hexavalent mg/L 0.05 0.05
Chromium, Trivalent mg/L 0.20 1.0
Arsenic mg/L 0.05 0.10
Cyanide mg/L 0.05 0.10
Lead mg/L 0.10 0.5
Copper mg/L 0.20 1.0
Manganese mg/L 0.20 1.0
Nickel mg/L 0.20 1.0
Tin mg/L 0.20 1.0
Zinc mg/L 2.0 2.0
Boron mg/L 1.0 4.0
Iron (Fe) mg/L 1.0 5.0
Silver mg/L 0.1 1.0
Aluminium mg/L 10 15
Selenium mg/L 0.02 0.5
Barium mg/L 1.0 2.0
Fluoride mg/L 2.0 5.0
Formaldehyde mg/L 1.0 2.0
Phenol mg/L 0.001 1.0
Free Chlorine mg/L 1.0 2.0
Sulphide mg/L 0.50 0.50
Oil and Grease mg/L 1.0 10
Ammoniacal Nitrogen mg/L 10 20
Colour ADMI* 100 200
*ADMI–American Dye Manufacturers Institute
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2.2.1 Textile wastewater characteristics
Textile wastewater is characterized mainly by measurements of biochemical
oxygen demand (BOD), chemical oxygen demand (COD), suspended solids (SS) and
dissolved solids (DS). Typical characteristics of textile industry wastewater are presented
in Table 2.2, which show a large extent of variation from plant-to-plant and sample-to
sample. As presented in Table 2.2, COD values of textile wastewater are extremely high
as compared to other parameter. In most cases BOD/COD ratio of the textile wastewater
is around 0.25 that implies that the wastewater contains large amount of non-
biodegradable organic matter (Al-Kdasi et al., 2004).
Table 2.2: Textile Industry Wastewater Characteristics (Al-Kdasi et al., 2004)
Parameters Values
pH 7.0 - 9.0
Biological Oxygen Demand (mg/L) 80 - 6000
Chemical Oxygen Demand (mg/L) 150 -12000
Total Suspended Solids (mg/L) 15 - 8000
Total dissolved solids (mg/L) 2900 - 3100
Chloride (mg/L) 1000 - 1600
Total Kjeldahl Nitrogen (mg/L) 70 - 80
Color (Pt-Co) 50 - 2500
2.2.2 Dyes
Dyes are synthetic organic compounds that are increasingly being produced and
used as colorants in many industries worldwide, including textile, plastic, paper, etc
(Crini, 2006, Wu and Tseng, 2008). The wastewater generated by the processes of these
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industries usually contains up to around 10% of used dye (Forgacs et al., 2004). The total
dye consumption of the textile industry worldwide is more than 107 kg/year, 90% ends on
fabrics. So, 1000 tones/year of dyes are discharged into waste streams. (Ahmad et al.,
2007).
2.2.3 Types of dyes
There are many structural varieties of dyes, such as, acidic, basic, disperse, azo,
diazo, anthroquinone based and metal complex dyes. The azo dyes, characterized by
having an azo group consisting of two nitrogen atoms (─N≡N─), are the largest class of
dyes used in textile industry (Sun et al., 2007). Inside the azo dyes there are wide types of
dyes, namely acid, reactive, disperse, vat, metal complex, mordant, direct, basic and
sulphur dyes. Also, there are many structural varieties of dyes that fall into either the
cationic, nonionic or anionic type. Anionic dyes are the direct, acid and reactive dyes
(Mishra and Tripathy, 1993). Nonionic dyes refer to disperse dyes because they do not
ionize in an aqueous medium (Baughman and Perenich, 1988).
2.2.4 Impact of dyes
Dyes are the most problematic pollutants of textile wastewaters. This fact occurs
because after the basic dyeing process is finished, 10% - 15% of the textile dyes is lost in
wastewater stream during dyeing operation (Muruganandham and Swaminathan, 2004).
Most of the dyes are toxic and carcinogenic compounds; they are also recalcitrant and
thus stable in the receiving environment, posing a serious threat to human and
environmental health (Crini, 2008). Accordingly, to protect humans and the receiving
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ecosystem from contamination, the dyes must be eliminated from the dye-contained
wastewaters before being released into the environment.
2.2.5 Direct blue71 (DB71)
Direct dyes are commonly used in the printing process of the textile industry.
Most of the printing process-textile factories belong to the small factory group (home-
made textile products) (Gupta et al., 1992, Hu, 1996, Wong and Yuen, 1996, Slokar and
Majcen Le Marechal, 1998, Soares et al., 2001). One of the direct dyes is direct blue71,
with the molecular formula C40H27N7Na4O13S4 (molecular weight 1029.88), Figure 2.1
shows the structure of direct blue71.
Figure 2.1: Structure of direct blue71 (DB71) (Habibi and Mikhak, 2012).
The most widely used methods of dye removal from dye-containing industrial effluents,
have been classified under three categories: chemical, physical and biological. Currently
the main methods of textile dye treatment are physical and chemical means concentrating
on cheaper and effective alternatives.
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2.2.6 Color Scales (APHA and ADMI)
2.2.6a APHA/PtCo standard:
The American Public Health Association (APHA) Index was developed in the 1890s as a
visual indicator of the purity of wastewater, where color is due to the presence of
naturally-occurring organic materials such as leaves, bark, roots, humus, and peat.
Today, APHA is used as a metric for purity in the chemical, oil, plastics, and
pharmaceutical industries. This scale serves to quantify the appearance of yellowness, a
visual indicator of product degradation due to light and/or heat, the presence of
impurities, and the effects of processing. APHA – recommended standard of 1 color unit
being equal 1mg/L platinum as chloroplatinate ion, The test of measuring color for this
scale is Platinum-Cobalt Standard Method, and it shows the results in mg/L Pt-Co. (Lab)
2.2.6b ADMI Scale:
The American Dye Manufacturer’s Institute (ADMI) scale was developed for the
measurement of wastewater containing dyestuffs and textile effluents. This scale may be
used on clear liquids of any color. The ADMI adopted the Platinum-Cobalt Standard of
the American Public Health Association (APHA) as the standard for color value.
Although this standard is yellow, the ADMI method works for all hues.
ADMI units are based on the total color difference of APHA solutions from
distilled water. Distilled water has a value of zero in ADMI units, as it does in APHA
units. An ADMI value of 500 is assigned to a solution having a total color difference
from distilled water equal to the total color difference from distilled water of the APHA
stock solution, which has an APHA value of 500 (Lab).
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2.2.7 Textile wastewater treatment
The treatment of textile wastewater is very complex, because the raw materials
processed and the intermediate products manufactured vary greatly in their nature and
composition. The composition of waste varies even in same industry as a result of
transition from one raw material to another and continual changing of process lines and
also due to type of fabric manufactured. Before treatment, a separation of different types
of wastewater into following group takes place (Yadav and Dhir, 2008):
i. Concentrated liquids (e.g., dyeing, finishing, printing)
ii. Medium polluted wastes (e.g., washing, rinsing)
iii. Low to zero polluted wastes (e.g., cooling water).
The various methods of treatment of textile wastewater have been used as physical
treatment, physico-chemical treatment, biological treatment and advanced oxidation
processes.
2.2.6a Physical Treatment
Physical processes such as sedimentation, equalization, segregation, filtration
(e.g., sand filter) are capable of removing the suspended solids, however the removal of
organic load is found to be negligible. Physical processes followed by physico-chemical
or biological process show good results (Fiola and Luce, 1998).
2.2.6b Physico-chemical Treatment
There are many physico-chemical processes have been used for textile wastewater
treatment such as chemical coagulation/ flocculation (Fe2+/3+, Al3+, polyelectrolyte) (Papić