Use of Cationized Cotton for Textile Effluent Color Reduction

ABSTRACT

KARNIK, POONAM. Use of Cationized Cotton for Textile Effluent Color Reduction.

(Under the direction of Dr. Brent Smith and Dr. Peter Hauser)

The liquid effluents from the textile industry mainly consist waters colored by the

dyes used in the coloring of textile yarns and fabrics. These dyes can be removed by

adsorption onto adsorbing materials like cotton. Waste cotton fibers can be cationized using a

quaternary ammonium compound like 3-chloro-2-hydroxypropyltrimethylammonium

chloride to their cationic form. This cationic form can be used as the adsorption medium for

USE OF CATIONIZED COTTON FOR TEXTILE EFFLUENT COLOR

REDUCTION

by

POONAM PRAFULL KARNIK

A thesis submitted to the Graduate Faculty Of

North Carolina State University

in partial fulfillment of the

requirements for the Degree of

Master of Science

TEXTILE CHEMISTRY

Raleigh

2002

APPROVED BY:

--- ---

Dr. Brent Smith Dr. Peter Hauser

Chair of Advisory Committee Co-chair of Advisory Committee

---

Dr. Tom Johnson

Use Of Cationized Cotton For Textile Effluent Color Reduction

Copyright



2002

by

Biography

iii

Acknowledgements

The author wishes to express her sincere appreciation and thanks to her committee

chairmen Dr. Brent Smith and Dr. Peter Hauser for their guidance, advice and patience over

the past two years. The author would also like to thank committee member Dr. Thomas

Johnson.

Hearty thanks to Dei Castelleija of the Dow Chemical Company for supplying Quat

188 and for the nitrogen analyses. I would also like to thank Adham Tabba, Jeff Krauss,

Lynell Williamson and Dr. Keith Beck for their invaluable help and for helping me with my

research and getting me out of rough spots.

Most of all I would like to thank my family especially my fiancé Abhijit and friends

for their love and support and for standing by me when I needed them most.

TABLE OF CONTENTS

page

LIST OF FIGURES………..……….……….… viii

LIST OF TABLES….………..………….………. x

LIST OF SYMBOLS AND ABBREVIATIONS.………. xi

1. INTRODUCTION……….. 1

1.1 Background……….…………. 1

1.2 Research Objectives………. 2

1.3 Cotton Dyeing……….. 2

1.4 Sources of Pollution………. 3

1.5 Pollution Control Practices……….. 3

1.6 Introductory Remarks About Color Removal….………. 5

2. OVERVIEW OF EXISTING COLOR REMOVAL METHODS. 9

2.1 Adsorptive Methods………. 14

2.1.1 Granular Activated Carbon Adsorption……… 14

2.1.2 Natural Wastes……….. 15

2.1.3 Chitosan……… 16

2.1.4 Synthetic Resin Adsorption……….. 16

2.2 Precipitative Techniques………. 16

2.2.1 Electrochemical Precipitation……….. 17

2.2.2 Polymer Flocculants………. 17

2.3 Reactive Decolorization Methods………..……….……. 18

v

Table of Contents continued

2.3.1a. Chemical Reduction……… 19

2.3.1b. Chemical Oxidation……… 19

2.3.1c. Biological Oxidation………... 21

2.3.2 Light and Irradiation Treatments………... 21

2.4 Preliminary Treatment Processes………. 22

2.4.1 Equalization……… 22

2.4.2 Neutralization………. 22

2.4.3 Disinfection……… 22

2.5 Primary Treatment Processes……… 23

2.5.1 Screening……… 23

2.5.2 Sedimentation……… 23

2.5.3 Flotation………. 24

2.5.4 Flocculation……… 24

2.6 Secondary Treatments………... 24

2.6.1 Chemical Separation……….. 25

2.6.2 Coagulation……… 25

2.6.3 Biological Oxidation……….. 26

2.7 Tertiary Processes………. 26

2.7.1 Chemical Oxidation……… 26

3. COTTON AND ADSORPTION………. 27

Table of Contents continued

3.1.1 Sources of Cellulose………... 27

3.1.2 Chemical Structure of Cellulose…..………... 27

3.1.3 Cationization of Cotton………... 29

3.2 Adsorption Onto Cotton…….……… 33

3.2.1 Process Variables..………..………… 34

3.2.2 Isotherm Models……..……….……….. 37

4. EXPERIMENTAL………..………… 40

4.1 Equipment………. 40

4.2 Substrate……… 43

4.3 Chemicals and dyes……….. 43

4.4 Test equipment and conditions for treatment……… 45

4.5 Procedure……….. 46

4.5.1 Causticization……… 46

4.5.2 Cationization………. 46

4.5.3 Ultimate Sorption Capacity Studies………. 47

4.5.4 Absorbance measurements……… 48

4.5.5 Testing……… 48

5. RESULTS………...……… 50

5.1 Preliminary Experiments…..……… 50

5.1.1 Results of cationization……….……… 50

vii

Table of Contents continued

5.2.1 Results of absorbance measurements………..………. 51

6. DISCUSSION OF RESULTS…………..……… 58

6.1 Preliminary Studies……… 58

6.2 Ultimate Sorption Capacity Studies……….….……….… 61

6.3 Results and Discussion……….. 71

7. SUMMARY AND CONCLUSIONS……….. 72

8. SUGGESTIONS FOR FUTURE RESEARCH……….………….. 74

BIBLIOGRAPHY……….………... 76

APPENDICES……….. 78

Appendix 1: Listing of Dyestuffs………. 79

Appendix 2: Calibration Curves for Standard Solutions of dyes

used……….. 84

Appendix 3: Results of Ultimate Sorption Capacity Studies…….. 89

List of Figures

page

CHAPTER 2

2.1 Classification of the different dye removal methods….……..…… 10

2.2 Methods of color removal……… 11

CHAPTER 3

3.1

Structure of Cellulose……….……….… 28

3.2

Formation of epoxy radical under alkaline conditions……… 31

3.3

Cationization of cotton using 2,3-epoxypropyltrimethylammonium

chloride under alkaline conditions……….………. 32

3.4

Reaction of 2,3-epoxy propyltrimethylammonium chloride under

aqueous alkaline conditions……… 33

3.5

Nernst isotherm model……….…... 37

3.6

Langmuir isotherm model………... 38

3.7

Rearranged Langmuir isotherms………. 39

CHAPTER 4

4.1 Boekel Grant ORS-200 shaker bath and its setup……….. 41

4.2 Setup of Werner-Mathis Laboratory Jumbo Jet (JFO)………….……….. 42

4.3

Setup of Varian-Cary UV-Visible spectrophotometer for

absorbance measurements……….. 43

CHAPTER 5

5.1

Untreated and cationized cotton fibers dyed with Direct Red 81……….. 51

ix

List of Figures continued

5.3

Langmuir isotherm plot of Cf vs Cs of untreated cotton for Acid Red 1… 55

5.4

Langmuir isotherm plot of Cf vs Cs of 10% cationized cotton for

Direct Brown 115……… 56

5.5

Langmuir isotherm plot of 1/Cf vs 1/Cs of untreated cotton for Acid

Red 1……… 56

5.6

Langmuir isotherm plot of 1/Cf vs 1/Cs of 10% cationized cotton for

Direct Brown 115……… 57

CHAPTER 6

6.1

Plot of treatment method vs %N add-on………. 58

6.2

Plot of KL vs %N add-on for acid dyes………... 63

6.3

Plot of KL vs %N add-on for direct dyes….………... 63

6.4

Plot of KL vs %N add-on for reactive dyes..………... 64

6.5

Plot of Sf vs %N add-on for acid dyes…..………... 65

6.6

Plot of Sf vs %N add-on for direct dyes……….…. 65

6.7

Plot of Sf vs %N add-on for reactive dyes....………... 66

List of Tables

page

CHAPTER 1

1.1

Typical Color Source Reduction Activities…..………. 7

CHAPTER 5

5.1 Analysis of nitrogen content………. 50

5.2 Diluted dyebaths for absorbance measurements..………. 52

5.3 Total Sorption Capacity results for Acid Red 1 on untreated

cotton fibers……….………. 54

5.4 Total Sorption Capacity results for Direct Brown 115 on 10%

cationized cotton fibers……… 55

CHAPTER 6

6.1 Data for KL and Sf of Acid Red 1………. 61

6.2

Precision in measuring absorbance for Acid Red 1 on untreated

cotton fibers………. 67

6.3

Precision in measuring absorbance for Direct Brown 115 on 10%

xi

List of Symbols and Abbreviations

ADMI American Dye Manufacturers Institute color determination method

APHA American Public Health Association color determination method

BOD biological oxygen demand

COD chemical oxygen demand

Cf concentration of dye in sorbent (mg/g)

Cs concentration of dye in solution (g/L)

a*l coefficient of absorption

a absorptivity

l path length

Chapter 1

Introduction

1.1 Background

Although water is abundant on Earth, since almost 97% of the water contains salt, it

is not suitable for drinking or for the various industrial purposes. Of the remaining 3%, two

thirds is in the form of ice and snow leaving only about 1% of the total water as fresh water.

Of this fresh water ground water accounts for about 98% and the surface water is only about

2%. Thus of the total amount of water present on Earth, only about 0.02% is available in the

lakes and streams. Therefore such a limited resource is very precious and needs conservation

_.

The textile industry is a water intensive industry with water being used in every

stage of wet processing from sizing, desizing, scouring and bleaching of fibers to the dyeing,

finishing and printing of fabrics. Every textile plant requires large volumes of water and

produces high volumes of effluent wastewater

_{. The typical textile dye wastewater}

composition is quite complex. These waste streams contain dyeing process auxiliaries that

may include xylenes, phenols, buffers, bleaches and scouring agents, water softeners,

surfactants, enzymes, caustic compounds and acids.

Due to the federal, state and local regulations, textile manufacturers must limit the

discharge of color from their plants. The ability to economically eliminate or lower the

by-end-of-the-pipe treatment of the wastewater. However conventional aerobic biological

treatment of wastewater is not sufficiently effective in removing most of the dyes from

wastewater. Tertiary treatment is required to remove the color before discharging the water to

the environment.

Previous treatablility efforts have revealed that when a high proportion of

acid red dyes are present in the wastewater, removal of color has been extremely difficult.

Modern technologies focus on either source reduction techniques or treatment of the

wastewater streams. This thesis will focus on the problem of removing and/or reducing color

from textile wastewater streams.

1.2 Research Objectives

The decolorization method being investigated in this thesis makes use of cationized

cotton fibers as an adsorbent to remove dyes from the effluent water. Cotton in itself has high

affinity for certain classes of dyes. It is the most widely used fiber. Each year there are

millions of pounds of waste cotton fibers produced during carding and other such processes

that convert the fiber to the final yarn or fabric form. These fibers can be used to reduce color

in wastewaters from dyeing plants and find a suitable use for the waste cotton fibers that are

being disposed off in landfills. This project is thus two – fold, first finding a viable and

economical method for cleaning up the effluent wastewater and secondly finding a suitable

use for the waste fibers produced.

1.3 Cotton Dyeing

fabrics are generally preferred for their natural feel and drape. For dyeing these cotton

fabrics, direct and fiber reactive dyes among others, are used since they provide a complete

color range and ease of application. However the dyeing methods employed for these dyes

are energy and water intensive pollution generating processes.

1.4 Sources of Pollution

The sources of pollution are the natural impurities extracted from the fibers and the

chemicals used in the processing of fibers. The main factors affecting the quality and

quantity of the effluents generated include unit operations comprising the overall textile

process and the extent of in-house conservation measures in practice.

Direct, reactive, acid, disperse, premetallized, vat and basic dyes account for about

85% of the total dyes used in the textile industry.

The total dye consumption of the textile

industry alone is in excess of 10

kg/yr worldwide. Even if it is estimated that a maximum of

90% of dye goes onto the fabrics, approximately 10

kg/yr of dyes would be discharged into

the waste streams by the textile industry.

1.5 Pollution Control Practices

State-of-the-art pollution prevention practices are well documented. The current

commercial textile pollution prevention practices include material substitution, process

modification, inventory control, better management techniques, recovery and reuse. The

textile industry has developed a relatively comprehensive approach to pollution prevention

important environmental issues such as color residues in textile dyeing and printing

wastewater.

.

The first synthetic dye was produced in the 1860s when Perkin oxidized aniline to

produce Mauvine.

By the early 1880s diazotization was a known reaction and many

chemists like Greiss, Walter and Boettiger attempted to synthesize commercially useful dyes

using this reaction. During this time the dye manufacturers’ goals were to produce low cost

dyes with high tinctorial value, brilliance and good application and fastness properties. Until

now the emphasis has been on the production of dyes with improved stability and hence

more resistance to treatment. This can been seen from the increase in fading units of the dyes

over the years. For example in the 1880s the dyes would fade in 5 standard fading units

(SFU) of light exposure. But by 1980, 50 to 100 SFU light was considered to be standard. It

is predicted that the next generation of dyes for automotive uses that are under current

development will be able to withstand up to 1000 SFU

.

Chemists in their endeavor to develop highly stable dyes have produced color wastes

from dyeing and printing operations that are difficult to treat.

From the environmental

standpoint, the more stable the dyes are, the more difficult they are to degrade after use.

The challenge thus, is to resolve the conflicting objectives of product quality and dye waste

treatability by developing dyes that are more treatable, less persistent and thus less

offensive

.

The textile industry therefore needs a new generation of dyes that have better

treatability and higher exhaustion thus leaving less color residue in the effluents and

1.6 Introductory Remarks About Color Removal

Large amounts of dyestuffs are used for textile dyeing processes including a wide

range of structurally diverse dyes. Direct dyes have only a limited wet fastness that can be

improved to a certain degree with the various fixing treatments. However when dyeing

medium or deep shades, the resulting fastness is sometimes not enough

. Due to this a

substantial amount of the direct dyestuffs are found in the effluent wastewater. When fiber

reactive dyes were introduced in 1956, it was thought that these dyes would overcome the

limitations of the direct dyes. Fiber reactive dyes have better overall fastness properties than

the direct dyes. However their main limitation is their poor fastness to chlorine. Another

problem with the fiber reactive dyes is their lack of affinity due to which complete color

fixation is not achieved. Much of the dye reacts with water and is wasted.

. About 90% of

the fiber reactive dyes are seen to pass through the activated sludge sewage treatment plants

without any change and are discharged into the water bodies like rivers and oceans

. This

can cause environmental problems.

. There is concern over the possible toxicity and

carcinogenity of the dyes being used. This has led to increasing interest in the pollution

potential of the dyes. Not all dyes that are currently being used can be degraded or removed

by physical or chemical processes, and sometimes the degradation products are found to be

more toxic than the dyes themselves.

The three main sources of color in textile wastewater streams are poor exhaustion of

dyes onto the fabric, inefficient handling of the dyes during their use, and the subsequent

washing off of the dyes. Although the percent of colored species in the effluents are very

man. The main reasons for the discharged dyes being an environmental problem in the

effluents include:

•

the dyes are highly detectable pollutants due to their colors,

•

the dyes can also impede light penetration thus upsetting biological processes and

productivity within the receiving body of water,

•

causing direct destruction of the aquatic communities,

•

some classes of the dyes are difficult to treat and degrade for removal from the effluent

streams,

•

the dyes can interfere with the ultraviolet disinfection processes of waste treatment

tertiary treatment systems

.

The main difficulties involved in the removal of dyes from the wastewater occur

because the dye structures are highly stable molecules that can resist degradation by light,

chemical, biological and other means. The composition of waste streams is varied containing

not only the different dyes and their mixtures, but also other chemicals like the salts and

surfactants that are used during the dyeing, printing, and finishing operations. The pH of the

effluents varies widely and there can be other particulate and undissolved suspended

matter

.

The most widely used means of reducing color in the effluent is a good source

reduction program. The different activities for source reduction can be classified into the

following four classes: administrative controls, engineering controls, process and product

design, and work practices. Table 1.1 shows the different classes of source reduction

activities. These activities reduce emissions, lower costs and result in improved productivity

Table 1

:

Typical Color Source Reduction Activities

Administrative

Controls

Engineering

Controls

Process/ Product

Design

Work Practices

Employee

training/attitude

Implements,

containers (design,

adequacy, clean-up)

Shade/fiber

selection

Dry capture

(vacuum, broom and

dustpan)

Color waste

monitoring

Dispensing method

(auto dosing

systems)

Exhaustion (dye

process –

temperature, time,

salt, pH, liquor

ratio)

Avoid batch dumps

of dye mixes

Reward system for

source reduction

efforts

Segregation of color

waste

Dye class selection

Screen and

squeegee cleaning

Purchasing policy

(returnable

containers)

Primary control

measures (drag-out)

Equipment selection Orderly

housekeeping and

work practices.

Incoming quality

control procedures

on dyes and

chemicals

Floor drain, drum

washer controls

Redye reduction

Dyebath

renovation/reuse

Optimized fixation

Minimize

specialty

chemicals in dye

bath

Source: Anthony Koonce, Color Reduction in Textile Wastewater Via Chitin Adsorbent, Masters Thesis in Textile Chemistry, North Carolina State University, 1993.

One way to reduce the color in the effluents is to improve the efficiency of

exhaustion of the dyes on the fabric. If 100% exhaustion could be achieved then there would

be no color in the effluents and the color effluent problems would be limited to controlling

spills. This would also ensure maximum shade reproducibility. However according to

kinetics and thermodynamics, 100% color transfer is not possible with most dye – fiber

To remove color from the effluent after it leaves the mill, the offending colored

species can be chemically destroyed or physically removed from the wastewater. To destroy

the colored species, biological or chemical decolorization methods can be used, but these

leave organic residues in the effluents. Physical removal of the colored species can be done

by precipitation and ion exchange. However there are problems associated with each of these

methods too. There is another physical method for the removal of the dye species from the

effluents that involves the use of cationized cotton fibers as the adsorbent. This method is

discussed further in this work. Other methods include recycling of the process waters directly

or after some treatment to reclaim or remove the salts and processing agents

.

Companies have developed products to pretreat cotton to give it a cationic charge

to enable it to take up dye more efficiently and without the use of electrolytes by increasing

the dye – fiber interactions. Since acid, direct, and fiber reactive dyes are anionic dyes,

cationically charged cotton is expected to have high affinity for these dyes. Maximum color

Chapter 2

Overview of Existing Color Removal Methods

Achieving adequate or complete color removal is quite difficult. No one specific

type of treatment will suffice for all dyeing effluents and the most effective form of

treatment will depend on the type of dyeing performed and the chemical composition of

the dyebath. Consequently, to achieve decolorizations complying with the environmental

regulations in a cost-effective manner, thorough characterizations of the wastewater and

comprehensive bench-scale treatabililty studies are essential in the selection of a viable

treatment system.

There are many methods for removal of color from the effluent

wastewater that have been described in the literature.

These methods can be

classified according to the type of the method, as reactive, precipitative, and adsorptive

etc. There can also be other methods for classifying these methods based on the class of

the dyes, structures of the dyes or the characteristics of the effluent streams. However

such a classification can be limited in its use because some methods may be partially

useful for a wide range of dyes and dyeing systems. Figure 2.1 gives an outline of the

classification of the different dye removal methods.

There is another method of classification for the color removal processes as

Figure 2.1

: Classification of the different dye removal methods

Source: Anthony Scott Koonce, Color Reduction in Textile Wastewater Via Chitin Adsorbent, Masters Thesis in Textile Chemistry, North Carolina State University, 1993.

Carbon

Peat Moss Wood Pulp Cotton fibers

Natural Wastes Chitosan Polymeric Adsorption Techniques

Iron Hydroxide Electrochemical

Precipitation

Polymeric Precipitation Techniques

Reductive

Ozonalysis Chlorine

Oxidative Biological Chemical

Non ionizing (UV) Ionizing (e beam) Light

Figure 2.2

: Methods of color removal

Source: Gordon McKay, Waste Color Removal from Textile Effluents, American Dyestuff Reporter, April, 1979, pages 29 – 34.

Equalization

Neutralization

Disinfection Preliminary

Screening

Sedimentation

Flotation

Flocculation Primary

Chemical Separation

Coagulation

Biological Oxidation Secondary

Chemical Oxidation

Gamma Radiation

Foam Fractionation

Although biological techniques remain the most widely used treatment methods,

increasingly stringent environmental regulations, particularly for the removal of toxic

organics and colors, have induced a few mills to install advanced physical/chemical

methods such as granular activated carbon adsorption, ozonation and reverse osmosis.

The effectiveness of the decolorization techniques can be measured by different

methods as given in Standard Methods for the Examination of Water and Wastewater.

These methods can be used to measure the true and apparent colors of the sample. The

apparent color of a sample is the perceived color that includes the combined effect of

colored material, turbidity and suspended solids. The true color is only due to the

dissolved colorant in the sample with the turbidity and suspended matter removed by

filtration or centrifuge. Turbidity is seen due to the scattering of light by small particles,

suspended matter or air bubbles.

The simplest method for evaluation of relatively small amounts of color in

natural water samples is by comparison of the sample with known colored samples. This

method is known as the APHA (American Public Health Association) method. This

method involves the use of known concentrations of solutions containing potassium

chloroplatinate and cobaltous chloride, also called cobalt platinum, CoPt, standard. Color

units or the so-called APHA units can be calculated based on the concentrations of the

standard solutions. While this technique is also used for measuring the color level of

textile mill effluents, it can lead to misleading results because the APHA procedure

places substantial emphasis on the reddish-yellow hues associated with natural

waters.

spectrophotometers are used to measure color. This method involves filtering the sample

to remove suspended solids, determination of the tristimulus values

spectrophotometrically, determination of the Munsell value by reference to tables and a

simple arithmetic calculation to arrive at the ADMI value.

The main drawback of the

APHA as well as the ADMI method is the requirement of filtration to reduce turbidity.

Since the appearance of wastewater is the real aesthetic pollutant, the filtration step can

change the character of the wastewater such that the measured color no longer correlates

with appearance. On the other hand if the sample is not filtered, the color measurement is

not reproducible.

Another method that also uses spectrophotometers for color measurement, uses

tristimulus filters instead of set wavelengths of light, but gives similar results to

ADMI.

The Beer – Lambert law is most commonly used to determine the concentration

of a dye solution. The Beer – Lambert equation is used to calculate the concentration of a

dye solution based on the absorption of monochromatic light by the dye molecules in the

solution. The Beer – Lambert law depends on the path length of light through the sample,

the concentration of the solution and the amount of incident light transmitted and/or

absorbed by the dye molecules.

Most dye and water solutions follow the Beer –

Lambert law for small concentrations of the dye. To get the calibration of a sample,

solutions of known concentrations of the dye are measured for their absorbance values

and from the resulting calibration equation, the unknown concentration of the sample can

be calculated by measuring the percent transmission of light through the sample, using a

2.1 Adsorptive Methods

Adsorption is a physiochemical wastewater treatment process that is gaining

prominence as a means of producing quality effluents that are low in concentrations of

dissolved organics.

The adsorptive methods of decolorization use a sorbent medium

that physically removes the dye ions and other contaminants from the effluent through

physicochemical process of adsorption.

In adsorption, the dissolved molecules are

attracted to the surface of the adsorbent by physical/chemical forces.

However there are

many factors that need to be considered while using these adsorbents. Most important

among them are the cost and availability of the sorbents. Disposal of the spent sorbent is

also of primary concern.

In recognition of the need for a more complete treatment of wastewater, an

Advanced Waste Treatment Research (AWTR) program was initiated in the United

States during 1960. The objectives of this program were to evaluate and develop

additional and alternative treatment methods for producing a satisfactory effluent for

discharge into the receiving waters or for direct subsequent reuse as a water supply.

Different methods of treatment were examined in the AWTR program and it was found

that adsorption was one of the most promising techniques for removal of perdurable

dissolved organic contaminants.

2.1.1 Granular Activated Carbon Adsorption

Activated carbon is the most widely used adsorbent for wastewater treatment.

Activated carbon can be produced by heating a raw material like wood, lignite or coal in

waste water treatments like filtration, dechlorination and color removal.

Although

activated carbon can remove a multitude of pollutants, it is mainly used for the removal

of dissolved organics.

It readily adsorbs most dissolved organic compounds because

crushed carbon has a large surface area due to a large number of pores and this large

surface area is effective in adsorbing the organic compounds.

Only the smaller

organics and large complex molecules are adsorbed poorly or not at all.

It is ineffective

in removing disperse, vat and pigment dyes from their pure solutions but is quite

effective in decolorizing reactive, basic, azoic and 1:2 metal complex dyeing wastewater

and also for removing color from mixed effluents.

2.1.2 Natural Wastes

Besides activated carbon and synthetic polymeric resins, multitudes of

adsorbents have been tried with varying degrees of success for decolorizing dye house

discharges. These include peat, wood, clays, silica gel, bauxite, fly ash, brown coal,

lignite slag and sludge from aluminium production factories. The work presented here

looks at waste cotton fibers as potential adsorbents for color removal.

Cellulose and viscose have been used together with other adsorbents like

activated carbon and nylons for dye adsorption from textile mill wastewater. Cellulose

fibers after being treated with acidic chitin containing solutions are said to have enhanced

dye adsorption capacities that can exceed those of common activated carbons. McKay et

al. have reported the use of teak wood bark, rice husk, cotton waste, coal, hair and

bentonite clay for the adsorption and desorption of eight dyes that include two each of

materials for sorption of selected dyes. It was suggested that rice husk, bark, cotton waste

and hair could adsorb only the basic dyes. However such a limitation can be overcome by

selecting appropriate operating conditions since cellulose fibers can adsorb both direct

and acid dyes and protein fibers can adsorb acid dyes.

A proposed flow sheet as shown below can be used in the waste treatment plant

to get the required dye removal in accordance with the EPA regulations.

2.1.3 Chitosan

Chitosan has been used successfully as an adsorbent for removing color from

textile wastewater. From the studies carried out it was found that chitosan had high

affinity for acid dyes.

2.1.4 Synthetic Resin Adsorption

Synthetic polymeric adsorbents are hard, insoluble beads of porous polymer

characterized by a spectrum of surface polarities and a wide variety of surface areas,

porosities and pore size distributions. Resins can be used similar to activated carbon i.e.

packed in columns.

2.2 Precipitative Techniques

The precipitative methods remove color by changing the solubility of the dye

Adsorption

pH

adjustment

Physico-chemical

treatment /

biological

oxidation

Wastewater

Treated

such that the dye molecules settle out of the solution or by co-precipitation by sorbing

onto an auxiliary precipitative material. Like the adsorptive methods, these methods also

involve physical removal of the colored species from wastewater. Most of the

precipitative methods include reacting the material with iron hydroxide or using a

polymer flocculating material.

2.2.1 Electrochemical Precipitation

In this method an electrical cell with two or more plates is used and an electrical

current is passed through it. This releases the iron and the hydroxide ions into the

solution. The reactions taking place are as follows,

Anode reaction: Fe Æ Fe

+ 2e

-Cathode reaction: 2H

O + 2e

Æ H

+ 2OH

-Solution reaction: Fe

+ 2OH

Æ Fe(OH)

Most of the dyes can be removed by electrochemical precipitation and

decolorization is quick to the order of seconds to minutes. Hence this method is useful for

treating large volumes of waste. However, large amounts of electricity and expensive

equipment are required to set up and maintain this process. Also there is a problem of

sludge disposal.

2.2.2 Polymer Flocculants

The impurities present in wastewater can vary in size from a few angstrom units

Dyes are usually smaller in size and hence they are soluble in water, except for some

pigment, vat, sulfur, and disperse dyes.

Polymers can be used to flocculate suspended materials in water including dyes.

Polymers are high molecular weight long chain compounds and hence can bond with

other molecules with cohesive Van der Waals forces and hydrogen bonds. As more and

more molecules aggregate into a larger unit, the aggregate loses its solubility and

precipitates.

The polymer flocculant is added as a suspension to the wastewater and the used

polymer and dye are removed by clarification during settling. The most commonly used

polymer flocculents are polyethylene oxide, hydrolyzed polyacrylamide, polyacrylic acid,

polystyrene sulphonate and polydiallyldimethyl ammonium.

A common problem faced by the above-mentioned sorption and precipitation

methods is the disposal of the solid waste generated. This problem is acute in the case of

industrial sludges from precipitative methods where disposal can be a problem.

2.3 Reactive Decolorization Methods

In the reactive methods of color removal, a part of the chromophore is destroyed

that results in a colorless product. Molecules that have conjugated

π

bonds in their

structure can absorb visible light that is re-emitted at the same or different wavelengths.

If the reflected or transmitted light is in the visible region, it is detected as color.

However when the conjugation is broken into smaller molecules, the dye no longer

methods of color reduction. But most of the new synthetic dyes are produced to withstand

such degradation, making this process difficult.

2.3.1 Chemical Treatments

The chemical treatments involve reductive, oxidative and biological methods of

decolorization. Oxidation using chlorine and ozone are the most widely used chemical

treatments. Many azo dyes are susceptible to these treatments because of the ability of the

nitrogen-nitrogen bond to be oxidized. Very often the reaction products are not

significantly colored, however many of the reduction products can have acute and

chronic effects on human and aquatic life.

2.3.1a Chemical Reduction

For certain classes of dyes like azo dyes reductive decolorization with reagents

like sodium hydrosulphite and stannous chloride have been shown to be feasible.

2.3.1b Chemical Oxidation

Reactive dyes create problems due to high solubilities and stable chemical

structures after hydrolysis. They have lower affinities as compared to the other classes of

dyes, hence they tend to exhaust less. Since many of the reactive dyes are resistant to

degradation, aggressive methods of chemical oxidation have been developed to handle

reactive dye discharges in textile wastewater.

Chlorine, ozone and hydrogen peroxide are the chemical oxidants that are widely

inexpensive in capital and operating costs and because it creates no sludge requiring

incineration or landfilling. But although it has these advantages, some dyes may be

bleached by the addition of chlorine and the color returns in a reducing environment.

Chlorination can also lead to the formation of chlorinated hydrocarbons. As a

decolorization technique for textile mill effluents, chlorination is used most often as a

post-treatment step after biological treatment.

Although the oxidizing power of ozone is nearly twice that of chlorine, ozone

cannot be shipped because it is unstable and has a half-life of only several minutes.

Therefore it needs to be generated on-site from air or oxygen. Ozonation is a very

versatile water and wastewater treatment process. In addition to removing color, ozone

can inactivate pathogenic microorganisms, remove taste and odor, eliminate soluble iron

and manganese and oxidize refractory and toxic organic compounds. Ozonation can often

make refractory wastes more amenable to biological treatment and in some cases

ozonation prior to activated carbon adsorption can lead to enhanced adsorption of

dissolved organics. Direct, acid and basic dyes are rapidly decolorized but insoluble and

disperse dyes respond poorly to ozonation.

The only problems associated with ozonation are the expensive materials

required to build and operate a ozonalysis plant and the electricity required to produce

ozone in addition to the safety hazards involved.

Fenton’s reagent, which is a combination of ferrous iron and hydrogen peroxide,

can also be used as an oxidizing agent. The ferrous radical acts as the oxidizing species

pure dye solutions but its effectiveness decreases when treating wastes containing high

volumes of organic auxiliaries.

2.3.1c Biological Oxidation

This treatment is widely used for the purification of domestic and industrial

wastewater because it is relatively inexpensive, versatile and highly effective. The

conventional activated sludge process and its modifications are the most popular methods

used. The activated sludge process relies on microorganisms in suspension to oxidize

soluble and colloidal organics with molecular oxygen.

While the activated sludge process or bioaeration is capable of providing high

BOD, COD, TOC and SS removals, it is less effective for color removal.

Although

biological treatments are widely used for purification of the textile mill wastewater, they

are not efficient in removing the more resistant dyes.

Since the synthetic dyes used by

the textile industry are formulated to resist breakdown under oxidizing conditions, most

dyes are extremely resistant to biological degradation. Color removal by activated sludge

is quite erratic ranging from 10 to 80% usually less than 50%.

Furthermore, the sludge resulting from the biological processes has to be

disposed by using drying beds and sand filters etc. It is this problem of sludge disposal

and higher legal standards for the quality of effluent discharges that makes other

treatment processes more attractive.

2.3.2 Light and Irradiation Treatments

high frequency radiation can break organic chemical bonds by increasing the vibrational

energies of the atoms in molecules. As these energies increase, the atoms can no longer

maintain the covalent bonds with neighboring atoms and the bonds break.

Titanium

dioxide can be used as a photo catalyst in the aqueous medium with UV or solar light.

2.4 Preliminary Treatment Processes

Preliminary treatment processes include equalization, neutralization and

disinfection. Disinfection can also be carried out at the end of the treatment process.

2.4.1 Equalization

Equalization is carried out by mixing different wastes to ensure that variations

and shock loadings are not introduced to the secondary treatment process. Variations in

loading can be eliminated by mixing highly concentrated waste with very dilute waste. If

the waste streams are not controlled lagoons used for equalization can become

odoriferous and objectionable to the surrounding community.

2.4.2 Neutralization

Many of the dye operations are carried out under acidic or basic conditions,

hence the effluent pH is liable to vary. Neutralization is carried out to adjust the pH of the

wastewater according to the type of treatment process.

2.4.3 Disinfection

fold; it can destroy some of the wastes that can be toxic to the microbes in the secondary

process and secondly it can prevent septic floc, pathogenic organisms and undesirable

algae from reaching the receiving stream. When the disinfectant is added in the final

treatment step it is usually for the latter reason. The chemicals that are most commonly

used as disinfectants are chlorine and its derivatives.

2.5 Primary

Treatment

Processes

The primary treatments include screening, sedimentation, floatation and

flocculation involving the removal of grit and solid material that can be made to settle or

float out of solution.

2.5.1 Screening

Screening is used to remove solids like undissolved chemicals, fibers, dirt and

grit.

2.5.2 Sedimentation

In sedimentation the force of gravity is used to remove settlable solids from the

wastewater. Depending on nature of the solids present in the suspension, sedimentation

can be classified as discrete, flocculent and zone settling. The settlable solids are

deposited on the bottom of a tank to form a watery sludge that is mechanically removed

2.5.3 Flotation

This process is used to remove suspended solids from wastes or for the

separation and concentration of sludges. In flotation the waste flow or a portion of the

clarified effluent is pressurized between 3 to 5 bar in the presence of sufficient air to

approach saturation. This pressurized air-liquid mixture is then released to atmospheric

pressure in the flotation unit when minute air bubbles are released from the solution. The

sludge flocs and suspended solids are floated by the minute air bubbles that attach

themselves to and become enmeshed in the floc particles. This air-solid mixture then rises

to the surface from where it can be skimmed off.

2.5.4 Flocculation

Flocculation differs from the above-mentioned techniques in that it uses

chemical precipitation to cause separation. Flocculation can either be used to increase the

rate of sedimentation and flotation or as a separate settlable solids reduction technique.

Coagulants are used to hold the solids together by molecular forces thus increasing the

size of the particles. The resulting bulky gelatinous particles known as flocs can be

removed by sedimentation, flotation or filtration.

2.6 Secondary Treatments

The secondary treatments that are used in textiles to reduce the organic textile

2.6.1 Chemical Separation

This technique uses chemical absorption or bonding to separate the dissolved

contaminants from the textile effluents. The contaminants are in a colloidal form with a

molecular or particle size from 10

to 10

m. The stability of a non-gelatinous colloid is

due to electrostatic forces and neutralization of this charge can result in flocculation and

precipitation.

2.6.2 Coagulation

Coagulation is due to two mechanisms, perikinetics or electrokinetic coagulation

and orthokinetic coagulation. Electrokinetic coagulation is one in which the zeta potential

is reduced by ions or colloids of opposite charge to a level below the Van der Waals

attractive forces. Orthokinetic coagulation is one in which the micelles aggregate and

form clumps that agglomerate the colloidal particles.

It is one of the most effective and economical techniques for decolorizing textile

mill wastewaters. It is most suited for the removal of disperse, vat and sulfur dyes. The

most widely used coagulant is lime although alum and iron salts are also used. Alum

sludge is generally the most voluminous while treatment with ferric sulfate generates less

sludge than alum but more than lime. Also lime sludge settles fast and dewaters easily on

2.6.3 Biological Oxidation

Biological treatment depends on the oxygen requirements. Aerobic oxidation

uses the free oxygen dissolved in the mixed liquor to convert wastes in the presence of

microorganisms to more microorganisms, and carbon dioxide.

2.7 Tertiary Processes

Tertiary treatment processes have been developed as the legal standards for the

quality of effluent discharges have been raised to values exceeding the limits of

conventional treatment processes. The tertiary processes like chemical oxidation,

adsorption and ion exchange have been well developed.

2.7.1 Chemical Oxidation

Chemical oxidation can be carried out using chlorine or ozone although ozone

has not yet achieved the popularity of chlorine mainly due to the cost and efficiency of

Chapter 3

Cotton And Adsorption

3.1 Chemistry of Cellulose

3.1.1 Sources of Cellulose

There are different sources of cellulose like loose cotton, slivers, yarns, fabrics,

mercerized cotton, viscose and cuprammonium rayons, cellophane sheets, filter paper etc.

3.1.2 Chemical Structure of Cellulose

There are many methods that can be used to characterize the structure of cellulose.

However most of these methods are based on solubilization or chemical decomposition of the

cotton fibers prior to characterization. Non-destructive and non-intrusive methods like x-ray

diffractometry and infrared spectroscopy are applied to a limited degree. X-ray

diffractometry is applicable to a limited degree because cellulose is available in fibrous form

and analyses of diffraction patterns from fibrous polymeric materials require a significant

number of assumptions about the structure of monomeric entities. The application of infrared

spectroscopy is limited because of two reasons. The first reason is that the optical

heterogeneities in cellulose are such that Rayleigh scattering of electromagnetic radiation is

quite high in the infrared region. So it is difficult to record the infrared spectra in which the

effect of scattering is separated from the effect of absorption. The second reason is that

infrared spectroscopy is sensitive to highly polar bonds, hence the absorptions due to

With the development of lasers Raman spectroscopy can now be used to study the

structure of cellulose. Raman spectroscopy has two advantages. The first advantage is that

with a good spectrometer it is possible to completely eliminate the problems associated with

scattering. The second advantage of Raman spectroscopy is that since the Raman spectrum

results from the polarizability of molecular bonds, it is highly sensitive to the skeletal

motions of highly covalent bonds and least sensitive to the highly polar hydroxyl and water

bonds.

The three polymorphic forms of cellulose that are commonly encountered are

cellulose I, cellulose II, and cellulose III. Cellulose I is considered to be the native form and

cellulose II can be manufactured from the native form by treatment in strongly swelling

caustic solutions. Cellulose III is produced by the action of ammonia on cellulose.

Non-equivalent glycosidic linkages are present in cellulose.

The pattern of hydrogen bonding in cellulose is as seen in Figure 3.1.

Figure 3.1

: Structure of cellulose

Native cellulose when exposed to intense radiation from an argon ion laser

fluoresces at a level to mask the Raman spectrum. This has been traced back to the residues

of transition metal ions retained in the cellulose. Cellulose can be treated to reduce this

fluorescence and get fairly good Raman spectra. When cellulose is studied under Raman

spectroscopy, a number of very sharp intense bands are seen in the skeletal stretching region

between 1000 and 1160 cm

and one intense band is seen the angle bending region at about

O O

CH₂OH O O H

O OH

O O H

O CH₂OH HO

OH _CH

378cm

. The appearance of these bands indicates the presence of extensive ordering in the

cellulosic structure.

When cellulose is mercerized i.e. treated with caustic solutions, it converts to an

alternative polymorphic form. So we can expect a response in the spectrum indicating this

change. In the Raman spectra of mercerized cellulose, the sharp intense bands previously

observed in the spectra of native cellulose, appear to be broadened suggesting greater

irregularity in the structure of the mercerized material. In addition to this broadening of some

of the intense bands that are unshifted in frequency, there is a change in the low frequency

region. In the spectrum of native cellulose the most intense band in the low frequency region

is at 378cm

and for the mercerized cellulose, this band is much reduced in intensity and is

seen as only a slight shoulder on a new fairly strong peak appearing at 350cm

.

3.1.3 Cationization of Cotton

Cellulose fibers when immersed in water produce a negative zeta potential and most

of the dye classes suitable for cotton are anionic in nature. The negative charge on the fiber

repels the anionic dye ions and consequently the exhaustion of the dye bath is limited.

However this zeta potential can be easily offset by salt concentrations of a few ppm, about 10

– 100ppm. Direct, acid, and reactive dyes are the most widely used anionic dyes for cotton.

To enhance their exhaustion on cotton, a high concentration of salt like sodium chloride or

sodium sulphate is added to the dye bath.

Water is highly structured with hydrogen bonds at low temperatures. When ions

(dye anions, ionic sites or hydrogen bonding sites on a fiber) are placed in water, water forms

water structure and decreases solubility of the dye and frees the sites so that they are more

accessible to the dye. These high salt concentrations that are of the order of 10,000 –

100,000ppm can cause environmental problems. But in the absence of these electrolytes a

large part of the dye remains unexhausted and gets discharged in the effluent streams.

To

overcome these problems cationization of cotton has been studied.

Cationic cotton is cotton that is modified to contain a quaternary group. Such

cationic cotton has an enhanced affinity for anionic dyes. This is because when cotton is

cationized with a reactive type of quaternary ammonium compound it forms an integral part

of the cellulose chain.

Schlack

was the first to report the ability of aminated epoxy derivatives to modify

cellulose and to notice the increased affinity of the modified cellulose towards acid dyes.

Champetier and Merle

have studied the modification of hydroxylated polymers including

cellulose by epoxy diethylamine – 3 – propane followed by an ethyl iodide quaternization to

yield ion exchangers and have reported the properties of the modified polymers to acid dyes.

Japanese research workers at Hokkaido University

have studied the improvement of

fastness of acid dyes on cellulosic and vinylic fibers preliminarily treated with glycidyl

trimethylammonium chloride. In all these studies the preliminary cellulose modification was

carried out by use of quaternary ammonium epoxy compounds.

Trialkylammonium salts can be prepared by the action of a secondary or tertiary

amine on epichlorohydrin followed by quaternization with an alkyl halide or sulfate.

Epoxypropyltrimethylammonium chloride also called glycidyltrimethylammonium chloride

aqueous solution of glycidyltrimethylammonium chloride. The general formula of these

compounds is

where R

is methyl, R

may be methyl ethyl, tert-butyl or benzyl, R

may be methyl or ethyl

and X

is chloride or bromide. While studying the stability of Glytac in water, it was

observed that the hydrolysis rate remained low in a neutral medium up to 10

°

C and was low

up to 60

°

C in a neutral medium and at 20

°

C in an alkaline medium. But the hydrolysis is

marked at 100

°

C in a neutral medium and as low as 40

°

C in an alkaline medium.

3-chloro-2-hydroxypropyltrimethylammonium chloride is a compound containing a

chloro-hydroxy group. It forms 2,3-epoxypropyltrimethylammonium chloride in-situ under

alkaline conditions as shown in Figure 3.2.

Figure 3.2

: Formation of epoxy radical under alkaline conditions.

Source: Adham Tabba, Cationization of Cotton with 2,3-epoxypropyltrimethylammonium chloride, Masters

Thesis in Textile Chemistry, North Carolina State University, 2000.

Epoxy radical of 3-chloro-2-hydroxypropyltrimethylammonium chloride (Quat 188) can

react with cellulose under alkaline conditions according to the path as shown in Figure 3.3.

CH

H

C

O

CH

N

R

R

R

X

CH₃ CH₃ CH₃ CH₂ CH CH₂ N Cl OH

CH₂ CH CH₂ N O

This reaction can proceed under conditions that can be easily achieved in any dyehouse.

Therefore it was of interest to investigate the possibility of using quaternary chloro-hydroxy

ammonium compounds for fixing an epoxy radical on cellulose in alkaline medium so as to

add a cationic radical to it and therefore modify its affinity towards dyes. The use of

positively charged quaternary ammonium compounds leads to the formation of ionic bonds

with negatively charged anionic groups of dyes.

Figure 3.3

: Cationization of cotton using 2,3-epoxypropyltrimethylammonium chloride

under alkaline conditions.

Source: Adham Tabba, Cationization of Cotton with 2,3-epoxypropyltrimethylammonium chloride, Masters

Thesis in Textile Chemistry, North Carolina State University, 2000.

One side reaction of 2,3-epoxypropyltrimethylammonium chloride in aqueous alkaline

medium is the formation of 2,3-dihydroxypropyltrimethylammonium chloride as shown in

Figure 3.4. This product cannot react with cotton. However this reaction is unavoidable.

OH

-H

N

CH₃ CH3

CH₃

C CH

O

CH2

O CH

CH CH

OH

N

CH

CH

Figure 3.4

: Reaction of 2,3-epoxypropyltrimethylammonium chloride under aqueous

alkaline conditions.

Source: Adham Tabba, Cationization of Cotton with 2,3-epoxypropyltrimethylammonium chloride, Masters

Thesis in Textile Chemistry, North Carolina State University, 2000.

3.2 Adsorption onto Cotton

When a textile fiber is immersed in a dye solution under suitable conditions, the

fiber becomes colored; the color of the solution decreases and dyeing is said to have

occurred. Dyeing is different from imbibition in which the fiber merely becomes saturated

with the dye solution and hence looks stained while the concentration of the dye in the

solution remains unchanged. In the case of dyeing, the affinity of the dye is the driving force

for the transfer of dye from the solution to the fiber. Affinity is defined as the force of

attraction between a substrate and the dye or another substance under the given conditions

when the latter is selectively extracted from the application medium by the substrate.

Sorption is a complex process in which a component moves from one medium/phase

to another and this occurs at the interface of the two media. The difference between

adsorption and absorption is absorption is a bulk phenomenon while adsorption is a surface

phenomenon. Desorption on the other hand is the release of the substance from the

sorbent.

Excluding the diffusion of the sorbate, in this case the dye molecules, in the

solution, there are three steps involved in the adsorption process.

The first step is the

CH

CH CH

N

CH

O

CH

CH

OH

H

O

CH

CH CH

N

CH

transport of the adsorbate through the boundary layer to the exterior of the sorbent, in this

case the cationized cotton fibers. This is followed by the diffusion of the adsorbate or dye

molecules into the porous structure of the sorbent. The final step is the diffusion and binding

of the dye molecule with the interior structure of the cotton fibers.

Depending on different factors like flow rate, temperature, agitation/bath circulation,

crystallinity of the sorbent, porosity of the cotton fibers etc., any of the above mentioned

steps can become the rate determining steps. If the flow rate is high enough, the boundary

layer surrounding the sorbent particle will be small enough to let the following two steps to

be the rate determining steps. If however the flow velocity is low enough for a large

boundary layer to be developed, the first step becomes the rate-determining step.

The important process variables affecting the sorption process include sorbent

characteristics, sorbent surface area, dye particle size, dye class and characteristics, dye

concentration, temperature of dye bath, pH, flow rate etc.

3.2.1. Process Variables

The sorbent characteristics can have significant effects on the sorption process.

Many of the commonly used sorbents have a highly porous structure or exhibit

electrochemical activity. Sorbents like carbon have highly porous structures that can give

large surface areas. Large surface areas are ideal for creating Van der Waals forces of

attraction between the sorbent and the incoming dye molecules. At the same time the pore

diameter governs the size of the dye molecule that can enter the sorbent structure. Ionic