CHAPTER 1 INTRODUCTION - Information and Library...
Transcript of CHAPTER 1 INTRODUCTION - Information and Library...
CHAPTER 1
INTRODUCTION
Dyes and coloring materials are being used by almost every industry
producing household goods, textile, food, paints, pulp and paper, printing etc. The
release of toxic and hazardous dyes from these industries has created a global concern
due to their immense toxicity toward mankind. Many dyes and pigments are toxic and
have carcinogenic and mutagenic effects that affect aquatic biota and also humans
[Geo et al., 2010]. Color impedes light penetration, retards photosynthetic activity
and also has a tendency to chelate metal ions which result in micro-toxicity to fish and
other organisms. The toxic and hazardous intermediates/substances created by these
dyes after undergoing oxidation and reduction in water further increase the need for
their removal from wastewater. Thus, industrial dye effluents are an increasingly
major concern and need to be effectively treated before being discharged into the
environment in order to prevent these potential hazards.
Dyes and dye intermediates industry is an important sector of the Indian
chemical industry. This sector has grown at a very fast pace after independence and
nearly half of its production is being exported today. India is now the second largest
producer of dyes and intermediaries in Asia. A remarkable feature of the Indian
dyestuff industry is the co-existence of units in the small, medium and large sectors,
actively involved in the manufacture of dyestuffs and their intermediates. The
industry is characterized by the co-existence of a small number of players in the
organized sector (around 50 units) and a large number of small manufacturers (around
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1,000 units) in the unorganized sector. The distribution of these units is skewed
towards with western region (Maharashtra and Gujarat) accounting about 90%. In
fact, nearly 80% of the total capacity is in Gujarat, where there are nearly 750 units.
[http://myiris.com/shares/sectors/sectorReport.php?secode+dyestuff&peercode=AII&
fname=./data/dyestuff/dyestuff.htm].
Over seven hundred types of dyes and organic pigments are now being
manufactured in the country (both by the organized and the unorganized sector). In
India, only one third of the dyestuff producing industries are in organized sector. The
rest come from the unregulated small-scale sector, which produces more than half of
India's aggregate volume. The domestic textile industry, which consumes up to 80 per
cent of the dyestuffs produced, looks for manageable costs rather than consistent
quality. So the bulk of its demand for dyes is met by the small- scale sector.
The small-scale sector's substantially lower investment in pollution control
measures also makes it more economical. With its need for dyeing and printing, the
textile sector is probably the worst offender when it comes to release colored effluent
discharge. Ludhiana, Panipat, Pali, Bichchri, Patancheru, Jetpur, Ahmadabad, Surat
and Tirupur are some of the country's most polluted zones. Dyes are soluble and
essentially used in paints, inks, textiles and polymers etc. India is a major exporter of
dyes, mostly due to ban on production of some of the dyes and intermediates in the
developed countries due to pollution. The Indian companies together accounts for
around 6.6 % of the world‘s production. India produces 64,000 tonnes of dyes, 2 per
cent of which (7,040 tonnes) are directly discharged into the environment.
[http://www.centralchronicle.com/20050228/2802303.htm].
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Within India, the major players in the pigments industry are Color Chem and
Sudarshan Chemicals while in the dyestuff industry companies such as Atul, Clariant
India, Dystar, Ciba Specialities and IDI are important players in terms of market
share.
Colored paper is obtained by dyeing the paper stock or the paper surface.
Additionally, fixing agents and other additives are used to improve dye fixation and to
obtain better dyeing results. In the process, it also discharges colored pulping effluent
in water. Color in the wastewater is mainly due to dyes. A wide variety of colored
paper is made using various types of dyes. In the years 1998 and 2001, the sector
discharged more than 100 tonnes of unused dyes. Dyeing operations are water-
intensive. Cellulose dyeing uses massive amounts of salt, whose presence in effluent
leads to very high amount of total dissolved solids in the effluent water. Dyes and
color pigments also contain metals such as copper, nickel, chromium, mercury and
cobalt which are difficult to remove from wastewater. Moreover, the unused dyes and
color released in effluent from dyeing vats interfere with the transmission of light in
the water body that receives the effluent.
Textile dyes, printing inks, pigments, acids, paints and colors are used in
plastics like food colors. The color is introduced into objects to improve aesthetic
value. The desired effect is achieved by incorporating into a substance - say a cloth, a
lipstick or an ink. The manner, in which colorants impart color to an object, makes
their effluent an environmental or health problem.
Sanganer town, district Jaipur (Rajasthan, India), is famous worldwide for its
dyeing and printing industries. There are about 400 industries involved in textile
printing processes, which discharge effluents into nearby ponds and drains, 3
withoutany treatment. These effluents contain highly toxic dyes, bleaching agents,
salts, acids, and alkalis. Heavy metals like cadmium, copper, zinc, chromium and iron
are also found in the dye effluents. Textile workers are exposed to such waters with
no control over the length and frequency of exposure. Further, as the untreated
effluents are discharged into the environment they can cause severe contamination of
surface and underground water. Environmental pollution caused by such textile
effluents results in adverse effects on flora, fauna and the general health of not only
the textile workers, but also the residents of Sanganer town [Nupur et al., 2005].
Cotton textile industry wastewater generated by the different production steps
(i.e. sizing of fibers, scouring, desizing, bleaching, washing, mercerization, dyeing
and finishing) has high pH and temperature. It also contains high concentrations of
organic matter, non-biodegradable matter, toxic substances, detergents, soaps, oil,
grease, sulfide, alkalinity, and suspended and dissolved solids. Because of the low
biodegradability of many textile chemicals and dyes, biological treatment is not
always effective for textile industry wastewater.
1.1 CONSUMPTION PATTERN OF DYES
Dyestuff is a broad term which includes dyes and pigments. A dye is a colored
substance or an organic compound, which when applied in a solution to a fabric,
imparts a color resistant to washing. They are largely used by the textiles, paper and
leather industry, with textiles accounting for over 80% in India. This links the
dyestuff industry's fortunes to that of the textile industry. Dyes are classified
according to various systems. The detailed description of dyes is given in section 1.2.
There are different types of dyes and their applications mentioned in Table1.1. The
different types of dyes used in paper industry are given in Table 1.2. 4
Table 1.1 Classification of dyes and their applications
Group Application
Acid Wool, silk, paper, synthetic fibers, leather
Azoic Printing Inks and Pigments
Basic Silk, wool, cotton
Direct Cotton, cellulosic and blended fibers
Disperse dyes Synthetic fibers
Reactive Cellulosic fiber and fabric
Mineral and pigments dyes Cotton, cellulosic, blended fabric, paper
Sulphur Cotton, cellulosic fiber
Vat dyes Cotton, cellulosic and blended fiber
Table 1.2 Dyes used in paper industry
Sr.
No. Dyes Quality of Paper
Consumption in
colored paper board,
kg per tonne of paper
1 Methylene
Blue
File board, maplitho 2.5 - 3.5
2 Brilliant Green Cover paper 0.8 - 1.0
3 Methyl Violet Violet poster, maplitho paper,
cream wove, colored wove
8.0 - 9.0
4 Scarlet Red File board 0.6 - 1.0
5 Acid Orange Buff board, buff manila board 5.0 - 6.0
6 Malachite
Green
File board, colored 1.0 - 2.0
7 Metanil Yellow File board, colored poster 2.5 - 4.5
8 Sunfast Yellow File board, colored poster, buff
manila board
4.0 - 5.0
9 Auramine File board 0.5 - 1.0
10 Rhodamine File board, pink colored poster,
maplitho, duplex board, cover
paper
1.5 - 2.0
Source: [Freeman, 1995]
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1.2 DIFFERENT TYPES OF DYES
(a) Acid dyes
Acid dyes are all water-soluble salts (usually sodium or potassium salts) of
colored aromatic organic acids, which dissociate in water to form colored anions.
Acid dyes are highly water soluble. These dyes are neutral or slightly alkaline water
solution, fair to good light fastness and low affinity for wood fibers.
[http://www.dyespigments.net/types-of-dyes.html].
The family of acid dyes is very vast and diverse, varying widely in their
methods of dyeing, application and end use of the dyed fabric. A choice of dyes
should be made considering sometimes-incompatible factors such as level dyeing,
fastness, brightness and ease of application. Care must be taken to use the appropriate
method as prescribed for a given dye. A number of acid dyes are also used to dye
nylon.
(b) Azoic dyes
The word 'Azoic' is the distinguishing name given to insoluble azo dyes that
are not applied directly as dyes, but are actually produced within the fiber itself. This
is done with impregnating the fiber with one component of the dye, followed by
treatment in another component, thus forming the dye within the fiber. The formation
of this insoluble dye within the fabric makes it very easy to washing.
(c) Basic and modified basic dyes
MAUVENE, the first to be discovered by Perkin, was a basic dye and most of
the dyes which followed, including magenta, malachite green and crystal violet, were
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of the same type. Basic dyes are cationic, which means that the colored part has
a positive charge, when they are dissolved in water. They will bond to either carboxyl
or sulfonic acid groups on a fiber, via the formation of salt links with these anionic
groups in the fiber [www.scribd.com/doc/29028809/different-types-of-dyes]. Basic
dyes include the most brilliant of all the synthetic dyes known, but unfortunately they
have dull color and are difficult to wash. Basic dyes will dye wool and silk from an
acid bath and are used where brightness is of prime consideration. Basic dyes are used
extensively for dyeing cut flowers, dried flowers, also dyeing jute sisal, raffia, coir
and wood (toys). With the introduction of acrylic fiber a new range of 'modified' basic
dyes were perfected for dyeing of this material.
(d) Direct dyes
These are soluble in water and have direct affinity for all cellulose fibers.
Some will also dye silk and wool. By continuous research this group of dyes has been
supplemented with dyes of good fastness to light and washing. As these dyes, when
dyed without additives, do not exhaust well, an addition of salt is required to improve
the yield of the dye and obtain deeper shades. Generally, the wash fastness of these
dyes is inferior but there are a number of after treatments available to improve the
wash fastness of the dyeing. Most direct dyes can be stripped of the use of stripping
salts (Sodium Hydrosulphite) without harmful effects on the fibers.
(e) Disperse dyes
The introduction of a new regenerated cellulose acetate fiber in 1920 led to the
development of an entirely new range of dyes. It was found that cellulose acetate (or
Celanese) fiber had hardly any affinity for water-soluble dyes. These are substantially
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water-insoluble non ionic dyes for application to hydrophobic fibers from aqueous
dispersion. They are used predominantly on polyster and to a lesser extent on nylon,
cellulose, cellulose acetate and acrylic fibers.
[www.scribd.com/doc/29028809/different-types-of-dyes].
(f) Reactive dyes
This is an entirely a different class of dye introduced to the market in 1956.
They react chemically with the fiber being dyed and if correctly applied, cannot be
removed by washing or boiling. The main feature of the dyestuff is its low affinity to
cellulose; therefore large amount of salt is required to force its deposition on the
fabric [www.textileschool.com/School/TextileFinishing/TypesofDyes.aspx].
(g) Mineral and pigment dyes
Although it is preferred to use water soluble dyes in textile dyeing for two
reasons; ease of application and greater softness of the fabric. Mineral khaki is used in
cotton army equipment because of its cheapness and because it also renders fabric
resistant to rotting and attack by insects in damp conditions. The introduction of heat
setting synthetic resin has opened new fields in textile printing. Mineral and organic
pigments, as used in paint manufacture, can now be applied to any fabric and rendered
wash fast after heat treatment.
(h) Sulphur dyes
The first Sulphur dye was discovered in France in 1873, and further work done
by Raymond Videl enabled the manufacture of 'Videl black". Its outstanding fastness
to light, washing and boiling far surpassed any cotton black known at that time. The
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general disadvantage of the sulphur dyes that they produce dull shades and lack a red.
The main advantage lays in their cheapness, ease of application and good wash-
fastness. In their normal state sulphur dyes are insoluble in water but are readily
soluble in the solution of sodium sulphide. Sulphur dyes are organic compounds
containing sulfur or sodium sulfide. In this form they have high affinity to the all
cellulose fibers [www.textileschool.com/School/TextileFinishing/TypesofDyes.aspx].
(g) Vat dyes
INDIGO, probably the oldest dye known to man is one of the most important
members of this group. Natural indigo extracted from the plant 'Indigofera tinctorie'
was used by the Egyptians in 200 BC. The first synthetic indigo was introduced to the
textile trade in 1897 and had the effect of completely replacing the natural product.
Although the vat dyes may be divided into three chemical groups, they are similar if
that they are insoluble in water and become water soluble when reduced in the
presence of an alkali. After dyeing, the fabric is oxidized and the dye again becomes
water insoluble. Because of the time consuming and costly procedure in reducing vat
dye into a water-soluble complex, dye manufacturers have produced a stabilized
water-soluble vat dye. This dye can be applied to cotton and viscose rayon by the
methods used by applying direct cotton dyes. After the dyeing, a simple treatment
restores the vat dye to its normal insoluble state. Solubilized vat dyes have an affinity
for cellulose and animal fibres.
[www.textileschool.com/School/TextileFinishing/TypesofDyes.aspx].
1.3 DISCHARGE STANDARDS FOR INDUSTRIAL WASTEWATERS
Standards for the discharge of wastewaters from various industries are directly
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linked to the wastewater regulations and the water pollution control policies in force
in the country/state concerned. After reviewing the technological capability and the
limitations of the wastewater treatment systems as existing in the industries; the
Pollution Control Board/Ministry of Environment and Forests, Govt. of India, have
fixed maximum allowable limits of the pollutants for different industries as given in
Tables 1.3 - 1.7.
Table 1.3 MINAS for cotton textile industries (composite and processing)
Parameter Concentration not to exceed,
milligram per liter (except
for pH and bioassay)
Common : pH 5.5. to 9.0
Suspended solids 100
Bio-chemical oxygen demand, 5
days 20oC
150
Oil and grease 10
Bio-assay test 90% survival of fish of after
96 hours
Special :
Total chromium (as Cr) 2
Sulphide (as S) 2
Phenolic compounds (as C6H5OH) 5
Source: http://www.cpcb.nic.in/standard41.htm
Table 1.4 MINAS for dye and dye intermediate industry
Parameter Concentration not to exceed milligrams per
liter (except for pH, temperature and bio-
assay)
Suspended Solids 100
pH 6 to 8.5
Temperature
Shall not exceed 5oC above the ambient
temperature of the receiving body.
Mercury (as Hg) 0.01
Hexavalent Chromium (as Cr) 0.1
Total Chromium (as Cr) 2.0
Copper (as Cu) 3.0
Zinc (as Zn) 5.0
Nickel (as Ni) 3.0
Cadmium (as Cd) 2.0
Chloride (as Cl) 1000
Sulphate (as SO4) 1000
10
Phenolic Compounds
(as C6H5OH)
1.0
Oil ad Grease 10
Bio-assay Test (with 1:8
dilution of effluents)
90% survival of Test animals after 96 hours.
Source: http://www.cpcb.nic.in/standard41.htm
Table 1.5 Composite woolen mill: wastewater discharge standards
Parameter Concentration not to exceed,
milligram per liter (except for
pH and bioassay)
Common : pH 5.5. to 9.0
Suspended solids 100
Bio-chemical oxygen demand,
5 days 20oC
150
Oil and grease 10
Bio-assay test 90% survival of fish after 96
hours
Special :
Total chromium (as Cr) 2
Sulphide (as S) 2
Phenolic compounds (as
C6H5OH)
5
Source: http://www.cpcb.nic.in/standard41.htm
Table 1.6 Dye and dye intermediate industry (Wastewater discharge standards)
Parameter Concentration not to exceed milligrams per liter
(except for pH, temperature and bio-assay)
pH 6.0 – 8.5
Color Hazen Unit 400.0
Suspended Solids 100.0
BOD (3 days at 27oC) 100.0
Oil and Grease 10.0
Phenolics as C6H5OH 1.0
Cadmium as Cd 0.2
Copper as Cu 2.0
Manganese as Mn 2.0
Lead as Pb 0.1
Mercury as Hg 0.01
Nickel as Ni 2.0
Zinc as Zn 5.0
Chromium as Cr6+
0.1
Total Chromium 2.0
Bio-assay test 90% survival in 96 hours.
Source: http://www.cpcb.nic.in/standard41.htm
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Table 1.7 MINAS for pulp and paper mills
Table 1.7a MINAS for small pulp and paper mill
Parameter Discharged on to surface water Disposal on
land
PH 5.5 - 9.0 5.5 - 9.0
Suspended solids (mg/l) 100 100
BOD (mg/l) 30 100
Table 1.7b MINAS for large pulp and paper mills, capacity > 24,000
Tonnes/annum
Parameter Concentration
PH 7.5 - 8.5
Suspended Solids (mg/l) 50
BOD (mg/l) 30
COD (mg/l) 350
TOCl (kg/tonne of paper) 2
Table 1.7c MINAS for caustic chlorine plant
Parameter Concentration
PH 5.5-9.0
Mercury in the final effluent (mg/l) 0.01
Mercury bearing wastewater
generation
10 kilo-liter/tonne of caustic produced
Source: Central Pollution Control Board, New Delhi website
1.4 TOXICITY OF COLOR AND DYES
The worldwide high level of production and extensive use of dyes generate
colored wastewater which causes environmental pollution. Dyes and pigments are
widely used in textile, leather, paper, plastic and other industries. The effluents of
these industries are characterized by fluctuating pH with large load of suspended
solids and COD [Sivraj et al., 2001]. Discharging large amount of dyes into water
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resources, accompanied by organics, bleaches and salts, can affect the physical and
chemical properties of fresh water. The color of the effluent discharged into receiving
waters affects the aquatic flora and fauna, and causes many water borne diseases.
Some dyes are carcinogenic and others after transformation or degradation yield
compounds such as aromatic amines, which may be carcinogenic or otherwise toxic
[Maguire, 1995]. Ludhiana, Panipat, Pali, Bichchri, Patancheru, Jetpur, Ahmedabad,
Surat and Tirupur are some of the country's most polluted zones.
In addition, dyes accumulate in sediments at many sites, especially at
locations of wastewater discharge, which has an impact on the ecological balance in
the aquatic system. Ground water systems are also affected by these pollutants
because of leaching from soil [Sharma et al., 1999]. Thus, dyes in wastewater have to
be removed before it is discharged into a water body or on land.
There are a group of textile dyes that can cause bladder cancer in people who
worked with or around the dyes. These textile dyes are known as benzidine dyes. The
colored dye effluents are generally considered to be highly toxic to the aquatic biota
and affect the symbiotic process by disturbing the natural equilibrium through
reduced photosynthetic activity due to the coloration of the water in streams. The
nonbiodegradable, toxic and inhibitory nature of spent dye baths has a considerable
deleterious effect on the environmental matrix (water and soil). Some dyes are
reported to cause allergy, dermatitis, skin irritation, cancer and mutations in humans
[Gao et al., 2010].
1.5 COLOR
Color measurement and representation
There are three methods of color measurement:
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1. Visual comparison method
2. Spectrophotometric method
3. Tristimulus filter method
It should be noted that color is pH dependent and when representing color, pH
should be indicated.
Out of the above methods spectrophotometric method is very useful and
efficient in wide range of color solution. We can use it in two ways. First we can give
the color in the Hazen unit. 1 Hazen unit is corresponding to the color of 1 mg/l
solution of Pt-Co. We can make some different unit standard solutions by varying
concentration of the Pt-Co solution. We take the transmittance of the solution by
spectrophotometer and make a calibration chart. The sample is taken, the turbidity is
removed and then transmittance is checked. This will give the color unit of the
sample.
Secondly, if one does not require color unit and only change is to be measured
then there is no need to prepare calibration chart with Pt-Co solution. The calibration
chart can be prepared by the sample only and at any stage we can check the
concentration of the sample. The color can also be represented as the load in kg per
tonne of the effluent or kg per tonne of product produced.
1.6 TREATMENT METHODS OF DYE BEARING WASTEWATER
Currently, various chemical, physical and biological treatment methods are
used to remove dyes from wastewater. Various chemical methods are oxidative
processes, H2O2-Fe (II) salts (Fentons reagent), ozonation, photochemical, sodium
hypochloride (NaOCl), cucurbituril and electrochemical destruction.
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In electrochemical method, electricity is used which provide powerful tool
for driving chemical reaction. The chlorides of calcium, magnesium, potassium and
sodium are most commonly used electrolytes. Electrochemical methods have been
successfully applied in the purification of several industrial wastewaters as well as
landfill leachate [Vlyssides et al., 1999]. Many dyes may be effectively decolorized
using chemical oxidizing agents such as chlorine in the form of liquid or gas. Ozone is
a more powerful oxidant than chlorine and it is used for oxidizing dye wastewater.
Environmentally, H2O2 is a friendly oxidant [Hosny et al., 2005].
The degradation of organic matter in colored solutions of different classes of
dyes by ozonation in the presence of activated carbon was investigated. The
combination of activated carbon with ozone enhanced the decolorization of the
solutions and especially the mineralization of the organic matter. Activated carbon
acts both as an adsorbent and as a catalyst in the reaction of ozonation [Patrı´cia et al.,
2005].
Heterogeneous photocatalysis has been considered as a cost effective
alternative for the purification of dye containing wastewater. Indeed, recent studies
have demonstrated that photocatalysis can be used to mineralize organic compounds
or degrade dyes using TiO2 under UV irradiation. Moreover, photocatalysis does not
require expensive oxidants and can be carried out at mild temperature and pressure
[Abdelkahhar et al., 2005].
Physical treatment methods for the removal of dyes are adsorption, membrane
filtration, ion exchange, irradiation and electrokinetic coagulation. Surfactants and
dyes with high molecular weights are successfully removed by the
coagulation/flocculation processes followed by sedimentation, flotation and filtration
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respectively. The main advantage of the conventional processes like coagulation and
flocculation is decolorization of the waste stream due to the removal of dye molecules
from the dye bath effluents, and not due to a partial decomposition of dyes, which can
lead to an even more potentially harmful and toxic aromatic compound. The major
disadvantage of coagulation/flocculation processes is the production of sludge. The
production of large amounts of sludge occurs, and this results in high disposal costs
[Gahr et al., 1994]. However, the sludge amount could be minimized if only a low
volume of the highly colored dye bath could be eliminated by this chemical treatment
directly after the dyeing process [Vera et al. 2005]. In electrocoagulation, pollutants
were destroyed such as organic to carbon dioxide and water at anode.
Electrocoagulated sludge contains less bound water besides being more shear resistant
and readily filterable.
Ion-exchange has not been widely used for the treatment of dye-containing
effluents [Slokar and Le Marechal, 1997]. Advantages of this method include no loss
of adsorbent on regeneration, reclamation of solvent after use and the removal of
soluble dyes. A major disadvantage is cost. Organic solvents are expensive and the
ion exchange method is not very effective for disperse dyes [Mishra and Tripathy,
1993].
Membrane filtration is suitable for water recycling within a textile dye plant if
the effluent contains low concentration of dyes, but it is unable to reduce the
dissolved solid content, which makes water re-use a difficult task.
Ionizing radiation may be promising for the treatment of textile dye waste
effluents, because the effect of radiation can be intensified in aqueous solution in
which the dye molecules are degraded effectively by the primary products formed
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from the radiolysis of water [Getoff and Lutz, 1985]. Dye containing effluent may be
treated in a dual-tube bubbling reactor. This method showed that some dyes and
phenolic molecules can be oxidized effectively at a laboratory scale only [Hosono et
al., 1993].
The removal of color by using biological treatment is widely used. The use of
wood rotting fungus, white Rot fungi has been used for effective color removal. Other
fungi such as, Hirschioporus larincinus, Inonotus hispidus, Phlebia tremellosa and
Coriolus versicolor have also been shown to decolorize dye-containing effluent
[Banat et al., 1996; Kirby, 1999]. The microorganism used are Pseudomonas
pseudomallei 13NA, Rhodotorulae rubra and Rhodotorulae sp., P. chrysosporium
BKM-F-1767 Bacillus subtilis IFO 13719, Nocardia globerula, Nocardia coralline,
P. chrysosporium ME446, Coriolus versicolor, Funalia trogii, Laetiporus sulphureus,
Cyathus bulleri, Cyathus stercoreus Cyathus striatus, P. chrysosporium NCIM 1197
and P. chrysosporium MTCC no. 787 [Pearce et al., 2003].
1.7 COMPARISION OF VARIOUS ADSORBENTS
Dyes and pigments are widely used as the coloring agents. Dyes are used in
textiles, food and beverage industries and printing processes. The total dye
consumption of the textile industry worldwide is in excess of 107 kg per year [Ahmad
et al., 2010]. However, approximately 1 million kg/yr of dyes are discharged into
water streams by the textile industry [Cestari et al., 2010]. The cost of adsorption
process is mainly dependent on the cost of adsorbent used for the removal of
dye from wastewater. Activated carbon (AC) is the most popular adsorbent, which
has been used with great success. It becomes more problematic for developing
countries to afford the cost and demand of activated carbon. However, due to high
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cost of GAC and about 10-15 % loss during its regeneration, alternate adsorbents are
being explored. Many researchers have studied the feasibility of using low cost
materials, such as saw dust (SD) [Kalavathy and Miranda, 2010; Sharma et al., 2009;
Ahmad et al., 2009], bagasse fly ash[Mane et al., 2007a], rice husk ash [Mane et al.,
2007b], waste orange peel [Namasivayam et al., 1996], banana pith [Namasivayam et
al., 1998], bottom ash [Gupta et al., 2004; Gupta et al., 2009; Mittal et al., 2005], and
deoiled soya [Mittal et al., 2008]. The other low cost adsorbents such as rice husk
[McKay et al., 1986], kaolin [Nandi et al., 2009], bentonite clay [Ramkrishna and
Viaraghavan, 1997], neem leaf powder [Bhattacharya and Sharma, 2003], powdered
activated sludge [Kargi and Ozmıhc, 2004], perlite [Dogan and Alkan, 2004] and
powdered peanut hull [Gong et al., 2005] were used. Natural and modified clays like
sepiolite [Mahir et al., 2005], zeolite [Armagan et al., 2004], bamboo dust [Kannan
and Sundaram, 2001], coconut shell [Manju et al., 1998], groundnut shell [Kannan
and Sundaram, 2001], rice straw [Hameed and EI-Khaiary 2008], duck weed
[Waranusantigul et al., 2003], sewage sludge [Otero et al., 2003], sawdust carbon
[Jadhav and Vanjara, 2004], agricultural waste and timber industry waste carbons
[Bansal et al., 2009] and gram husk [Jain and Sikarwar, 2006] as low cost adsorbents
used by earlier researchers for removal of various dyes from wastewaters. Critical
review of low cost adsorbents for wastewater treatment has been presented by earlier
researchers [Gupta and Suhas, 2009; Mall et al., 1996; Bailey et al., 1999; Demirbas,
2009]. Hence, low cost materials are sorely needed which are comparable to activated
carbon in terms of adsorption capacity, economic feasibility and should be locally
available. The total cost for the preparation of 1 kg of adsorbent is Rs. 36/-, Rs. 81/-,
Rs. 29/- and Rs. 35/- for activated tamarind seeds, activated neem leaves, activated
sawdust, and activated flyash respectively. The commercially available adsorbent
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(activated carbon) is for Rs. 500 per kg. This indicates that the cost associated with
these adsorbents is quite lesser when compared to that of commercial activated carbon
In general; technical applicability and cost-effectiveness are the key factors that play
major roles in the selection of the most suitable adsorbent. Various low-cost
adsorbents derived from agricultural waste, industrial by-product or natural material
are evaluated and compared to those of activated carbon [Kurniawan et al., 2006].
Saw dust shows suitable alternative to activated carbon for the removal of dyes from
wastewaters [Khattri and Singh, 2009; Ozacar and Sengil, 2005].
1.8 SAW DUST AS BEST AVAILABLE ADSORBENT
The by-products from the forestry and agricultural industries could be
assumed to be low-cost adsorbents since they are abundant in nature, inexpensive,
require little processing and are effective materials [Demirbas, 2009]. Saw dust is an
abundant by-product of the wood industry that is either used as cooking fuel or as
packing material [Garg et al., 2004]. Saw dust is easily available at negligible price
[Hameed and Khaiary, 2008]. The role of saw dust materials in the removal of
pollutants from aqueous solutions has been reviewed [Shukla et al., 2002]. Sawdust
has proven to be a promising effective material for the removal of various dyes.
Various researchers have utilized Beech sawdust [Batzias and Sidiras, 2007], Oak
wood saw dust [Ferrero, 2007], Neem sawdust (Azadirachta indica) [Khattri and
Singh, 2009] and Pine wood saw dust [Khattri and Singh, 2009; Ozacar and Sengil,
2005] for removal of dyes. Teakwood saw dust [Naiya et al., 2005], saguan (Tectona
grandis) wood saw dust [Sharma et al., 2009], Raw saw dust (RSD) [Kalavathy and
Miranda, 2010], Meranti tree sawdust [Ahmad, et al., 2009], Indian Rosewood saw
dust (Dalbergia sissoo) [Garg et al., 2004] and Hard-wood sawdust [Dutta et al.,
2001] was also utilized for removal of harmful substances from wastewater. Timber
19
of Indian Eucalyptus wood tree is widely used for furniture making and the waste
sawdust so produced is generally used as cooking fuel due to its zero or negligible
cost.
1.9 BRILLIANT GREEN: PROPERTIES AND HEALTH EFFECTS
Color Index (C.I.) = 42040, chemical formula = C27H34N2 O4 S, Molecular weight =
482.62; Nature = basic green 4. The Molecular structure of BG is shown in Fig. 1.1.
The properties and health effects of BG are mentioned in Table 1.8.
Fig. 1.1 Molecular structure of BG
Table 1.8 Properties and health effects of BG
Sr.
No.
Name of property and
health effects
Properties and health effects
1 Appearance Yellow-green to green powder
2 Odor Odorless
3 Melting Point 210 oC (410
oF) Decomposes
4 Vapor Density (Air=1) 16.6
5 % Volatiles by volume
@ 21oC (70
oF)
0
6 Boiling Point No information found
7 Stability Stable under ordinary conditions of use and
storage
8 Hazardous
Decomposition Products
May form carbon oxides, nitrogen oxides, and
sulfur oxides when heated to decomposition.
(Prepared by: Environmental Health & Safety,
(U.S.A.)
9 Inhalation May cause irritation to the respiratory tract.
Symptoms may include coughing and shortness
of breath
10 Ingestion Causes irritation to the gastrointestinal tract.
Symptoms may include nausea, vomiting and
diarrhea
11 Skin Contact May cause irritation with redness and pain
12 Eye Contact BG contains a cationic dye. Similar dyes have
caused permanent injury to the eyes of humans
and laboratory animals
13 LDLo 5 mg/kg (skin and eye irritant)
14 LD50 Not available
15 Fire Extinguishing Media Dry chemical, foam, water or carbon dioxide
16 Environmental Terrestrial: High mobility in soil and is likely to
leach. Aquatic: Will not adsorb to suspended
solids or organic matter. Atmospheric: Remain as
particulates and is removed by wet deposition.
Will not biodegrade and has a low
bioconcentration potential.
[http://www.merckmedicus.com/pp/us/hcp/thcp_dorlands_content.jsp?pg=/ppdocs/us/
common/dorlands/dorland/dmd-g-023.htm].
[http://www.jtbaker.com/msds/englishhtml/b3840.htm,
http://www.sussex.ac.uk/Units/safety/sgn/sgn27.pdf].
BG is effective against gram-positive bacteria. The main advantage of BG
over the more common antiseptics such as iodine is that it does not irritate mucous
membranes. Gram-positive bacteria are those that are stained dark blue or violet by
Gram staining. This is in contrast to Gram-negative bacteria, which cannot retain the
crystal violet stain, instead taking up the counter stain (safranin or fuchsine) and
appearing red or pink. Gram-positive organisms are able to retain the crystal violet
stain because of the high amount of peptidoglycan in the cell wall. Gram-positive cell
walls typically lack the outer membrane found in Gram-negative bacteria.
BG dye is used for various purposes, e.g. biological stain, dermatological
agent, veterinary medicine, an additive to poultry feed to inhibit propagation of mold,
intestinal parasites and fungus [Nandi et al., 2009].
21
It is also extensively used in textile dying and paper printing [Mittal et al.,
2008]. About 0.8–1.0 kg of BG is utilized per tonne of paper produced [Mane et al.,
2007a, b]. However, in humans, BG causes irritation to the gastrointestinal tract;
symptoms include nausea, vomiting and diarrhea [Mittal et al., 2008]. It also causes
irritation to the respiratory tract, leading to cough and shortness of breath. Skin
contact causes irritation with redness and pain [Mittal et al., 2008]. BG may form
hazardous products like carbon oxide, nitrogen oxide, and sulfur oxides when heated
to decomposition.
1.10 CONGO RED: PROPERTIES AND HEALTH EFFECTS
The CR dye [C.I. = 22120, chemical formula = C32H22N6Na2O6S2, FW = 696.7,
max = 500 nm]. The structure of CR is illustrated in Fig. 1.2.
CR (1-naphthalenesulfonic acid, 3, 3-(4, 4-biphenylenebis (azo)) bis (4-amino-)
disodium salt) is a benzidine-based anionic disazo dye [Mall et al., 2005]. CR
containing effluents are generated from textiles, printing and dyeing, paper, rubber,
plastics industries, etc [Cheng et al., 2011]. Due to its structural stability, CR is
difficult to biodegrade [Ahmad and Kumar 2010]. This dye is known to metabolize to
benzidine, a known human carcinogen [Mall et al., 2005]. It is investigated as a
mutagen and reproductive effector. It is a skin, eye, and gastrointestinal irritant. It
may affect blood factors such as clotting, and induce somnolence and respiratory
problems [Mittal et al., 2009].
Fig. 1.2 Molecular structure of CR
22
NH2
SO3Na
N N N N
NH2
SO3Na