General Introduction
Chapter − 1
General Introduction
1.1. Introduction
Water is an elixir of life. It covers about three quarters of the earth’s surface
area. About 95% of earth’s water is in the oceans, which is unfit for human
consumption and other uses because of its high salt content. Of the remaining 5%,
about 4% is locked in the polar ice caps. The remaining 1% constitutes all the fresh
water in the hydrological cycle including ground water reserves. Only 0.1% is
available as fresh water in rivers, lakes and streams, which is suitable for human
consumption [1, 2].
The merits of water are decreasing day by day due to pollution. Water is said
to be polluted, if its physical and chemical properties are altered due to the addition of
unwanted matter, which makes it unfit for its intended use, although natural
phenomena such as volcanoes, algae blooms, storms and earthquakes also cause
major changes in water quality and the ecological status of water [3, 4]. Water
pollution has many causes and characteristics. Increase in nutrient loading may lead to
eutrophication. Organic wastes such as sewage impose high oxygen demands on the
receiving water leading to oxygen depletion with potentially severe impacts on the
whole ecosystem.
Industries discharge a variety of pollutants in their effluents
including heavy metals, resin pellets, organic toxins, oils, nutrients and solids [5-14].
Discharges can also have thermal effects, especially those from power stations and
these too reduce the available oxygen. Silt-bearing runoff from many activities
including construction sites, deforestation and agriculture can inhibit the penetration
of sunlight through the water column, restricting photosynthesis and causing
blanketing of the lake or river bed, in turn damaging ecological systems. [15]
Effects of Water Pollution
•
Waterborne diseases like typhoid, amoebiasis, diardiasis, ascariasis,
hookworm, respiratory infections, hepatitis, encephalitis, gastroenteritis,
diarrhea, vomiting, and stomach aches
•
Parkinson’s disease, multiple sclerosis, Alzheimer’s disease, heart disease and
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General Introduction
even death
•
Cancer, including prostate cancer and non-Hodgkin’s lymphoma
•
Hormonal problems that can disrupt reproductive and developmental
processes
•
Damage to the nervous system
•
Liver and kidney damage
•
Damage to the DNA
•
Damage of sea foods chain
•
Damage to people may be caused by vegetable crops grown/washed with
polluted water
1.2. Water Quality Parameters
A number of parameters are considered to check the quality of water. Table
1.1 shows certain parameters with permissible limits as prescribed by Bureau of
Indian Standard for domestic water supplies.
Table 1.1. Indian standard specification for drinking water IS: 10500.
S. No.
Parameter
Desirable limit Permissible limit
1
Colour (Hazen Units)
5
50
2
Turbidity (NTU)
10
25
3
pH
6.5-8.5
9.2
4
Total hardness
300
600
5
Ca
75
200
6
Mg
30
100
7
Cu
0.05
1.5
8
Fe
0.3
1
9
Mn
0.1
0.5
10
Chlorides
250
1000
11
Sulphates
150
400
12
Nitrates
45
No relaxation
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General Introduction
13
Fluoride
0.6 to 1.2
Not less than 0.6 and
max limit 1.5
14
Phenols
0.001
0.002
15
Hg
0.001
No relaxation
16
Cd
0.01
No relaxation
17
Se
0.01
No relaxation
18
As
0.05
No relaxation
19
Cyanide
0.05
No relaxation
20
Pb
0.1
No relaxation
21
Anionic detergents
0.2
1
22
Cr(VI)
0.05
No relaxation
23
Polynuclear aromatic
--
-0.03
hydrocarbon
24
Mineral oil
0.01
25
Residual free chlorine
0.2
26
Pesticide
Absent
--
27
Radioactive
--
--
28
Alkalinity
200
600
29
Al
0.03
0.2
30
B
1
5
Unit; mg/l, otherwise mentioned
1.3. Classification of Water Pollutants
Water pollution can be classified as point source and non point source. Point
source of pollution occurs when harmful substances are emitted directly into water
body. A non point source delivers pollutants indirectly through environmental
changes. An example of this type of water pollution is when fertilizer from a field is
carried into a stream by rain, in the form of run off which in turn effects aquatic life.
Pollution arising from non point sources accounts for a majority of the contaminants
in streams and lakes. Water pollutants can be broadly classified into the following
four major categories:
•
Organic pollutant
•
Inorganic pollutant
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General Introduction
•
Suspended solids and sediments
•
Radioactive material
1.3.1. Organic Pollutant
Organic substances comprise a potentially large group of pollutants,
particularly in urban environments. Even at low levels, some of these organic
pollutants can be hazardous to human health, particularly if the exposure is long term.
Some organic pollutants also play an important role in the formation of photochemical
smog. Motor vehicle emissions are a major source of these pollutants together with
the petroleum and chemical industries, emissions from waste incinerators, service
stations, domestic solid fuel and gas combustion, cigarette smoke, spray painting, dry
cleaning and other solvent usage etc. The pathogenic microorganisms present in
polluted water causes water born diseases such as cholera, typhoid, dysentery, polio
and hepatitis in humans [16] . The pesticides, detergents, insecticides, dyes and other
industrial chemicals are toxic to plants, animals and humans, as these chemicals may
enter the hydrosphere either by spillage during transport and use or by intentional or
accidental release of wastes from their manufacturing establishments. Oil pollution
results in the reduction of light transmission through surface waters, thereby reducing
photosynthesis by marine plants. Further, it reduces the dissolved oxygen in water and
endangers water birds, coastal plants and animals. Thus, oil pollution leads to
unsightly and hazardous conditions, which are deleterious to marine life and sea food
[17].
1.3.2. Inorganic Pollutants
Inorganic pollutants comprise of mineral acids, inorganic salts, finely divided
metals or metal compounds, trace elements, cyanides, sulphates, nitrates,
organometallic compounds and complexes of metals with organics present in natural
waters. The metal-organic interactions involve natural organic species [18]. These
interactions are influenced by redox equilibria, acid-base reactions, colloid formation
and reaction involving microorganisms in water. Metal toxicity in aquatic ecosystems
is also influenced by these interactions. Various metals and metallic compounds
released from anthropogenic activities add up to their natural background levels in
water. Some of these trace metals play essential roles in biological processes, but at
higher concentrations, they may be toxic to biota [19].
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General Introduction
1.3.3. Suspended Solids and Sediments
Sediments are mostly contributed by soil erosion by natural processes,
agricultural development, strip mining and construction activities. Suspended solids in
water mainly comprise of silt, sand and minerals eroded from the land. Soil erosion by
water, wind and other natural forces are very significant for tropical countries like
India leading to qualitative and quantitative degradation of the soil in land area. Thus,
soil may get removed from agricultural land to the areas where it is not at all required,
such as water reservoirs [20-22]. Soil particles eroded by running water ultimately
find their way into water reservoirs and such a process is called ‘siltation’. Reservoirs
and dams are filled with soil particles and other solid materials, because of siltation.
This reduces the water storage capacity of the dams and reservoirs and thus shortens
their life. Apart from the filling up of the reservoirs and harbours, the suspended
solids present in water bodies may block the sunlight required for the photosynthesis
by the bottom vegetation. This may also smother shellfish, corals and other bottom
life forms. Deposition of solid in quiescent stretches of streams impairs the normal
aquatic life in the streams. Further, sludge blankets containing organic solids
decompose, leading to anaerobic conditions and formation of obnoxious gases. The
tremendous problem of soil erosion can be controlled by proper cultivation practices
and efficient soil and forest management techniques. The organic matter content in
the sediments is generally higher than that in soils. Sediments and suspended particles
exchange cations with the surrounding aquatic medium and act as repositories for
trace metals such as Cu, Co, Ni, Mn, Cr and Mo [23]. Suspended solids such as silt
and coal may injure the gills of the fish and cause asphyxiation.
1.3.4. Radioactive Materials
Radioactive pollution can be defined as the release of radioactive substances
or high energy particles into the water or earth as a result of human activity, either by
accident or by design. The sources of such waste are nuclear weapon testing or
detonation, the nuclear fuel cycle including mining, separation and production of
nuclear materials for use in nuclear power plants or nuclear bombs and accidental
release of radioactive material from nuclear power plants. The radioactive isotopes
found in water include Sr90, I131, Cs137, Cs141, Co60, Mn54, Fe55, Pu239, Ba140, K40 and
Ra226. These radioactive isotopes are toxic to life forms [24-27].
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General Introduction
1.4. Dyes
Since this thesis deals with the removal of dyes which falls under the category
of organic pollutant, the following section is devoted to the brief description of dyes.
A coloured substance can act as a dye only when it fulfills the following conditions:
•
It must have suitable colour.
•
It must be able to attach itself permanently to the fabric.
•
The fixed dye must have fastness properties. Its colour should not fade in
light. It should be rasistant to the action of water, dilute acid, alkalies,
detergents and organic solvents used in dry cleaning.
Mauveine, was the first synthetic organic dye containing N-phenyl
phenosafranine, produced by William Henry Perkin in 1856. Thousands of synthetic
dyes have since been prepared. At present, almost all the dyes are synthetic and are
prepared from very few starting materials, such as benzene, phenol, aniline, etc. These
starting materials are obtained from coal tar and hence synthetic dyes are also known
as coal tar dyes [28].
According to Otto N. Witt (1876), the colour of the organic compounds is
associated with the presence of certain groups in the molecules called
“chromophores” and the colour is augmented by the presence of certain groups called
“auxochromes”.
Dye = Chromogen + Auxochrome
The important chromophores are nitroso, nitro, azo, azoxy, azomethine,
ethynyl, azo amine, carbonyl, o-quinonoid, p-quinonoid etc. Auxochromes are unable
to produce colour itself, but can deepen the colour produced by chromophore.
Auxochromes are certain acidic or basic groups eg. −COOH, −SO3H, −OH, −NH2,
−NHR, −NH2 etc.
1.4.1. Nomenclature and Classification of Dyes
The commercial names of dyes are frequently followed by letters, some of
which have special designation. For example, B stand for blue, BB or 2B stand for
more bluish and the numbers (2, 3, 4 etc.) indicate the intensity of shade. G stands for
yellow and occasionally for greenish. R stands for reddish. [29].
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General Introduction
Most of the commercial dyes are classified in terms of colour, structure or
method of application in the Colour Index (C.I.), which is edited every three months
since 1924 by the "Society of Dyers and Colourists" and the “American Association
of Textile Chemists and Colourists". The last edition of the Colour Index lists about
13000 different dyes. Each dye is assigned to a C.I. generic name determined by its
application and colour. Dyes may be classified in two ways
•
According to the methods of application
•
According to their chemical constitution
1.4.1.1. Classification According to Methods of Application
1.4.1.1.1. Direct or Substantive Dyes
These can be directly applied to the fiber. These dyes are two types.
(i) Acid Dyes
These are the sodium salts of the colour acids containing sulfonic and
phenolic groups. These are always used in an acidic solution. They dye silk and
wool (animal fiber) directly. For example- Maritus yellow, orange II, naphthol
yellow etc.
(ii) Basic Dyes
These are either hydrochloride or zinc chloride complexes of colour bases
which are directly used for silk or wool in basic medium. Azo dyes and triphenyl
methane dyes are the typical example of this class.
1.4.1.1.2. Mordent Dyes
These are unable to attach themselves to the fiber. Therefore, they require a
pretreatment of fiber with the certain substance called “mordent” like tannin or
tannic acid. The mordent gets itself attached to the fiber and then combines with the
dye to form an insoluble coloured complex. Alizarin, anthraquinone and azo dyes
belong to this class.
1.4.1.1.3. Vat Dyes
These dyes are insoluble in water, but their reduced form is soluble in an
alkali solution whereby leuco vat is obtained. The leuco compound is adsorbed on
fiber and upon exposure to the air, is oxidized to the dye which remains fixed to the
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General Introduction
cloth. Indigo and anthraquinone vat dyes are the good example of this class.
1.4.1.1.4. Ingrain Dyes
These are synthesized within the fiber and may be applied to both animal and
vegetable fibers by diazotization and coupling process. The colour obtained in this
type of dyeing are also called ice colour because diazotization and coupling process
are carried out at low temperature. Para red is an example of ingrain dyes.
1.4.1.1.5. Sulphur Dyes
These are similar to vat dyes and are sulphur containing complex, which are
insoluble in water, but soluble in cold alkaline solution of sodium sulphide. These
also form leuco complex. These dyes are dark in colour, inexpensive and have good
fastness propertis. Sulphur black is an example of this class and are used for dyeing
cotton.
1.4.1.1.6. Disperse Dyes
These dyes are used to dye acetate rayons, dacron, nylon and other synthetic
fiber. The fiber to be dyed is dipped in a dispersion of finely divided dye in a soap
solution in the presence of some solubilising agent such as phenol, cresol or benzoic
acid. The adsorption onto the fiber is carried out at high temperature and pressure.
Important example of this class is fast pink B and celliton fast blue.
1.4.1.1.7. Pigment Dyes
These dyes form insoluble compounds or lakes with salts of Ca, Cr, Ba, Al
or phosphomolybdic acid. These dye molecules contains −OH and −SO3H groups.
Due to their fastness to light, heat, acids and bases, they are valuable for paints,
printing ink, synthetic plastic, fibers, rubbers etc. Lithol red, pigment red and acid
red are the member of pigment dyes.
1.4.1.1.8. Solvent or Sprit Soluble Dyes
These are simple azo or triarylmethane bases or anthraquinone which are
used to colour oils, waxes, varnishes, lipsticks, dressings and gasoline.
1.4.1.1.9. Food Dyes
These are harmless and used in colouring food, candles, confectionaries and
cosmetics.
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General Introduction
1.4.1.2. Classification According to Their Chemical Constitution
This classification is useful for the chemists who are interested in the synthesis
and chemical constitution of dyes. Table 1.2 represents the classification of dyes
based on their chemical constitution.
Table 1.2. Classification of dyes based on their chemical constitution.
S. No. Class of Dyes
Remark
Example
1
Nitro group as chromophores ,
Fast green,
phenolic as auxochrome in o-
Napthol green Y
Nitroso
postion
2
Nitro
Nitro group as chromophore
Martius yellow,
Napthol yellow S
3
Anthraquinone
Presence
of
chromophore Alizarin red S,
=C=O and =C=C arranged in Alizarin blue
anthraquinone complex
4
Triphenylmethane
Quinonoid group as chromophore
Malachite green,
and acidic –OH and basic −NH2,
Methyl violet
−NHR, etc group as auxochrome
5
Diphenylmethane
NH=C= group as chromophore,
Auraine−O
also contains a diphenylmethane
nucleus
6
Phthaleins
Regarded as derivative of
Phenolphthalein
triphenylmethane
7
Xanthene
=C=O or =C=N- as chromophore
Eosin
8
Thiazole
>C=O, S−C, etc as chromophore
Premuline
9
Azo dye
−N=N− as chromophore
(i) Acid azo
(ii) Basic azo
Acidic group as –COOH, −SO3H, Methyl orange
−OH as auxochrome
Amino or substituted amino
Aniline yellow
group as auxochrome
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General Introduction
1.4.2. Source of Dye Pollution and Hazardous Effects
Dyes are extensively used in textiles, paper, rubber, plastics, leather,
cosmetics, pharmaceuticals and food industries, resulting in a steadily growing
demand and production. Today there are more than 10,000 synthetic dyes available
commercially and more than 7×105 tonnes are produced annually [30, 31] . Synthetic
dyes usually have a complex aromatic molecular structure which possibly comes from
coal tar based hydrocarbons such as benzene, naphthalene, anthracene, toluene,
xylene, etc. [32]. From an environmental point of view, the disposal of synthetic dyes
is of great concern [33]. Dyes are known pollutants that not only affect aesthetic merit
but also reduce the sun light penetration and photosynthesis thereby increasing the
biological oxygen demand and causing lack of dissolved oxygen that sustains aquatic
life and some are considered toxic, even carcinogenic for human [34, 35]. The
harmful effects of the few important dyes are presented in Table 1.3.
Table 1.3 . Some important dyes and their hazardous effects.
Dye
Hazardous Effects
Methylene blue
Toxic to blood, reproductive system, liver, upper respiratory
tract, skin and eye contact (irritant), central nervous system
Rhodamine B
Causes respiratory tract irritation, eye and skin irritation,
digestive tract irritation, adverse reproductive and fetal effects in
animals, vomiting and diarrhea
Fast green
Tumors of the liver, testes, or thyroid.
Fast ponceau
Mutagen and a potential carcinogen; highly toxic, skin and eye
disazo dye
irritant, must never be handled during pregnancy
Fast red salt B
Potential carcinogen, irritant to eyes and the respiratory tract,
very toxic
Malachite green
Accumulates in the tissues, liver, thyroid gland and bladder
Crystal violet
Mutagen and mitotic poison
Eosin
Carcinogenic, estrogenic and clastogenic properties
Congo red
Mutagenic, hazardous in case of skin contact, eye irritant
Diamond black
Thyroid cancers, mutagenic effects, DNA-damaging
Dye production and textile industries are the major source of colour pollution.
Easton, [36] estimated the degree of fixation for different dye/fibre combinations
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General Introduction
which is indicated in Table 1.4.
Table 1.4. Estimated degree of fixation for different dye/fiber combinations.
Dye class
Fiber
Degree of fixation (%)
Lost to effluent (%)
Acid
Polyamide
80-95
5-20
Basic
Acrylic
95-100
0-5
Direct
Cellulose
70-95
5-30
Disperse
Polyester
90-100
0-10
Metal-complex
Wool
90-98
2-10
Reactive
Cellulose
50-90
10-50
Sulphur
Cellulose
60-90
10-40
Vat
Cellulose
80-95
5-20
Choy et al., [37] reported that 10–20% of dyes in the textile sector is lost in
residual liquors through incomplete exhaustion and washing operations.
These
coloured effluents pollute surface water and ground water system. Due to the large
degree of organics present in these molecules, the effluents of textile and related
industry have to be treated carefully before discharge. This has resulted in a demand
for environment friendly technologies to remove the dyes from effluents.
1.5. Wastewater Treatment
Various treatment methods used in sewage and industrial wastewater
treatment are as follows
1.5.1. Preliminary Treatment
The aim of preliminary treatment is the removal of gross solids such as large
floating and suspended solid matter, grit, oil and grease if present in considerable
quantities. Large quantities of floating rubbish such as cans, cloth, wood and other
objects present in wastewater are usually removed under preliminary treatment.
1.5.2. Primary Treatment
Primary treatment involves the removal of gross solids, gritty materials and
excessive quantities of oil and grease, followed by the removal of the remaining
suspended solids as much as possible. This is aimed at reducing the strength of the
wastewater and also to facilitate secondary treatment.
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General Introduction
1.5.3. Secondary Treatment
Biological processes involve bacteria and other microorganisms to remove the
dissolved and colloidal organic matter present in wastewaters. These processes may
be aerobic or anaerobic. Secondary treatment reduces BOD, it also removes
appreciable amounts of oil and phenol. However, commissioning and maintenance of
secondary treatment systems is expensive.
1.5.4. Tertiary Treatment
It is the final treatment, meant for “polishing” the effluent from the secondary
treatment processes and to improve the quality further. The main objectives of tertiary
treatment are the removal of fine suspended solids, bacteria, dissolved inorganic
solids and final traces of organics. Schematic representation of wastewater treatment
is shown in Fig. 1.1 [38] .
Fig 1.1. Schematic representation of wastewater treatment [38].
Depending upon the required quality of the final effluent and the cost of
treatment that can be afforded in a given situation, the major methods for coloured
wastewater treatment can be divided into three classes:
•
Biological treatment
•
Chemical treatment
•
Physical treatment
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General Introduction
1.6. Biological Treatments
Biological treatment processes are very useful and remove all types of
dissolved degradable substances. Biodegradation is the process by which organic
substances are broken down by other living organisms. Organic material can be
degraded aerobically with oxygen, or anaerobically, without oxygen. A term related to
biodegradation is biomineralisation, in which organic matter is converted into
minerals. White-rot fungi are able to degrade dyes using enzymes, such as lignin
peroxidases (LiP), manganese dependent peroxidases (MnP). Other enzymes used for
this purpose include H2O2-producing enzymes, such as, glucose-1-oxidase and
glucose-2-oxidase, along with lactase, and a phenoloxidase enzyme [39-41].
The ability of bacteria to decolorize the wastewater has been investigated by a
number of research groups under the anaerobic and aerobic condition. [42-45]. These
microbial systems have the drawback of requiring a fermentation process and are
therefore unable to cope with larger volumes of textile effluents. This process is time
taking, may require nutrients, very large aeration tanks, lagoons, land areas and many
toxic compounds are not removed.
Dead bacteria, yeast and fungi have also been used for the purpose of
decolorizing dye-containing effluents. Textile dyes vary greatly in their chemistry and
therefore their interactions with micro-organisms depend on the chemistry of a
particular dye and the specific chemistry of the microbial biomass [46]. The use of
biomass has its advantages, especially if the dye-containing effluent is very toxic.
Biomass adsorption is effective when conditions are not always favorable for the
growth and maintenance of the microbial population. Adsorption by biomass occurs
by ion exchange [47].
1.7. Chemical Treatment
1.7.1. Ozone Treatment
Ozone wastewater treatment is a thorough and effective oxidation process and
is a suitable disinfectant for the organic matter found in wastewater. Ozone is a very
good oxidizing agent due to its high instability (oxidation potential - 2.07) compared
to chlorine, another oxidizing agent (1.36) and H2O2 (1.78). The dosage applied to the
dye-containing effluent is dependent on the total colour and residual COD to be
removed with no residue or sludge formation [48]. After ozone treatment,
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General Introduction
chromophore groups in the dyes are generally organic compounds with conjugated
double bonds that can be broken down forming smaller molecules, resulting in
reduced colouration [49]. These smaller molecules may have increased carcinogenic
or toxic properties, and so ozonation may be used alongside a physical method to
prevent this. Decolouration occurs in a relatively short time.
Ozone for the treat wastewater has many benefits
•
Kills bacteria effectively.
•
Oxidizes substances such as iron and sulphur so that they can be filtered out of the
solution.
•
There are no nasty odours or residues produced from the treatment.
•
Ozone converts into oxygen quickly and leaves no trace once it has been used.
The disadvantages of using ozone as a treatment for wastewater are
•
The treatment requires energy in the form of electricity, which is costly and
cannot work when the power is lost.
•
The treatment cannot remove dissolved minerals and salts.
•
Ozone treatment can sometimes produce by-products such as bromate that can
harm human health if not controlled.
•
A major disadvantage of ozonation is its short half-life (20 min).
1.7.2. Photochemical Treatment
Photochemical treatment is degradation of a photodegradable molecule caused
by the absorption of photons, particularly those wavelengths found in sunlight, such
as infrared radiation, visible light and ultraviolet light. Various processes like
UV/H2O2, UV/Fenton’s reagent, UV/O3 etc are photochemical methods based on the
formation of free radicals due to UV irradiation. The UV-based methods in the
presence of a catalyst, e.g. a semiconductive material such as TiO2 and ZnO have also
shown to distinctly enhance colour removal [50, 51]. Thus, different combinations
such as ozone/TiO2, ozone/TiO2/H2O2 and TiO2/ H2O2 have been investigated, but
they are enormously influenced by the type of dye, dye concentration and pH [52].
Degradation is caused by the production of high concentrations of hydroxyl radicals.
The rate of dye removal is influenced by the intensity of the UV radiation, pH, dye
14
General Introduction
structure and the dye bath composition [53]. There are some advantages of
photochemical treatment of dye-containing effluent i.e. no sludge is produced and
foul odours are greatly reduced. The main disadvantage of this method is production
of secondary pollutant.
1.7.3. Electrochemical Destruction
This is a relatively new technique, which was developed in the mid 1990s. It
has some significant advantages for use as an effective method for dye removal by
oxidation reactions using electricity [54]. There is little or no consumption of
chemicals and no sludge build up. The breakdown metabolites are generally not
hazardous leaving it safe for treated wastewaters to be released back into water ways.
It shows efficient and economical removal of dyes and a high efficiency for colour
removal and degradation of recalcitrant pollutants [55, 56]. Relatively high flow rates
cause a direct decrease in dye removal and the high cost of electricity is the main
disadvantage of this technology.
1.8. Physical Treatment
1.8.1. Coagulation/Flocculation
Coagulation/flocculation is a commonly used process in water and wastewater
treatment in which compounds such as ferric chloride or polymer are added to
wastewater in order to destabilize the colloidal materials which cause the small
particles to agglomerate into larger settleable flocs [57, 58]. The first step, coagulation
is the addition of a coagulant to the wastewater and mixing. This coagulant
destabilizes the colloidal particles that exist in the suspension, allowing particle
agglomeration. Flocculation is the physical process of bringing the destabilized
particles in contact to form larger flocs that can be more easily removed from the
solution. The main advantage of the conventional processes like coagulation and
flocculation is decolourization 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 [59, 60].
1.8.2. Filtration Method
Filtration methods such as ultrafiltration, nanofiltration and reverse osmosis
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General Introduction
have been used for water reuse and chemical recovery. These methods has the ability
to clarify, concentrate and most importantly, to separate dye continuously from
effluent [61, 62]. Membrane filtration has some special features unrivalled by other
methods i.e. they are resistance to, temperature, an adverse chemical environment and
microbial attack. The specific temperature and chemical composition of the
wastewater determine the type and porosity of the filter to be applied [63]. The main
drawbacks of membrane technology are the high investment costs, the potential
membrane fouling and the production of a concentrated dye bath which needs to be
treated [47]. The recovery of concentrates from membranes, e.g. recovery of the
sodium hydroxide used in the mercerizing step or sizing agents such as polyvinyl
alcohol (PVA), can attenuate the treatment costs [63]. Water reuse from dye bath
effluents has been successfully achieved by using reverse osmosis. However, a
coagulation and micro-filtration pre-treatment was necessary to avoid membrane
fouling [64]. A very good option would be to consider an anaerobic pre-treatment
followed by aerobic and membrane post-treatments, in order to recycle the water
1.8.3. Ion-Exchange
The use of ion exchangers for demineralization of water is well known. Ion
exchange has not been widely used for the treatment of dye-containing effluents,
mainly due to the opinion that ion exchangers cannot accommodate a wide range of
dyes [53, 65]. Wastewater is passed over the ion exchange resin until the available
exchange sites are saturated. Both cation and anion dyes can be removed from dyecontaining effluent this way. Advantages of this method include no loss of adsorbent
on regeneration, reclamation of solvent after use and the removal of soluble dyes.
Despite the simplicity of its operation, a major disadvantage is the high cost of ionexchanger, its regeneration process and its ineffectiveness for all kind of dyes
treatments [66].
1.8.4. Adsorption
Adsorption is one of the most efficient methods for the removal of colour,
odour, organic and inorganic pollutants from industrial effluents. Adsorption process
is considered better in water treatment because of the convenience, ease operation and
simplicity of design. Adsorption operations exploit the ability of certain solids
preferentially to concentrate specific substances from solution onto their surfaces.
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General Introduction
Conventional and Non-conventional adsorbents are used in this approach.
Activated carbon is the most widely used conventional adsorbent for this purpose
because of its extensive surface area, microporous structure, high adsorption capacity
and high degree of surface reactivity. However, its widespread use in wastewater
treatment is sometimes restricted due to its high cost and poor regeneration capacity
[67-69]. During the last decades, a lot of studies on dye adsorption by various nonconventional adsorbents such as algae [70-74], fungi [75-78], industrial wastes [7983], clays [84-87], polymers [88-91], metal oxides [92-95], composites [96-99],
agricultural wastes [100-103] etc. have been undertaken in order to find out an
alternate to the costly conventional adsorbent. It has been found that various
adsorbents developed from different origins show little or poor sorption potential for
the removal of dyes as compared to commercial activated carbon. Therefore, the
search to develop efficient adsorbents is still going on.
Adsorption generally depends on the nature of adsorbate, adsorbent and
solution conditions. Structural properties of the adsorbate molecule or ion have an
influence on its adsorption. The solution conditions like pH, temperature, co-ions etc.
may alter the adsorption of adsorbate. The adsorption also depends on the adsorbent
characteristics such as size, shape, surface area, porosity, functional groups on the
surface, surface charge etc. Therefore characterization of the adsorbent is very
important to understand the mechanism of adsorption process. There are many
techniques which are generally used to characterize the adsorbent. Some of them are:
•
The Brunauer-Emmett-Teller (BET) analysis – to determine the surface
area and pore structure of the adsorbent.
•
Zeta potential and Zero point charge analysis – to determine the surface
charge on the adsorbent.
•
Elemental analysis – to study the elemental composition such as C, N, H, O
etc of the adsorbent.
•
Boehm titration analysis – to determine the concentration of oxygenated
surface groups on the adsorbent.
•
Scanning electron microscopy (SEM) – to examine the surface morphology
of the adsorbent.
17
General Introduction
•
Transmission electron microscopy (TEM) – to determine the shape and size
of the adsorbent.
•
Fourier transform infrared spectroscopy (FTIR) analysis – to determine
the presence of functional groups on the adsorbent.
•
X-ray diffraction (XRD) analysis – to determine the amorphous or
crystalline nature of the adsorbent.
•
Thermal analysis – to determine the thermal stability of the adsorbent.
•
Inductively coupled plasma-mass spectrometer (ICP-MS) - The analysis of
the impurities composition, namely, Al, Ca, Cu, Fe, Li, Mg, Mn, P, Ti, V, and
Zn in the adsorbent.
1.9. Theoretical Aspects of Adsorption
1.9.1. Adsorption
The term adsorption was first used by “Kayser” in 1881 and it refers strictly
to the existence of higher concentration of any particular component at the surface of
the liquid or solid phase than in the bulk. The adsorption may be of two types namely
physical and chemical. The physical adsorption occurs mainly due to weak forces like
ion-dipole, dipole-dipole, polarization or induced dipole, Van der Waals force etc.
The physical adsorption is reversible, temporary in character. It usually involves
lesser heat exchange. While chemical adsorption is due to formation of chemical
linkages between adsorbate and adsorbent. The chemical adsorption is non reversible
and is carried out at high temperature. It is characterized by a large heat change during
adsorption.
1.9.2. Mechanism of Adsorption
A solid surface in contact with a solution has the tendency to accumulate a
layer of solute molecules at the interface due to imbalance of surface forces. This
accumulation of molecules is a vectorial sum of the forces of the attraction and
repulsion between the solution and the adsorbent. Majorities of the solute ions or
molecules, accumulated at the interface are adsorbed onto the large surface area
within the pores of adsorbent and relatively a few are adsorbed on the out side surface
of the adsorbent. Adsorption from an aqueous solution is influenced largely by the
competition between the solute and solvent molecules for adsorption sites. The
18
General Introduction
tendency of a particular solute to get adsorbed is determined by the difference in the
adsorption potential between the solute and the solvent when the solute-solvent
affinity is large. The low adsorption capacity of polar adsorbents like zeolite for solute
in a polar solvent like water is an example of this phenomenon. In general, the lower
the affinity of adsorbent for the solvent, the higher will be adsorption capacity for
solutes. A polar (or non polar) adsorbent will preferentially adsorb the more polar (or
non polar) component of a non- polar (or polar) solute.
Many factors influence the rate of adsorption and extent to which a particular
solute can be adsorbed. The general effects of some more important factors like nature
of adsorbent and adsorbate, concentration, extent of agitation, pH, temperature,
contact time, etc., are summarized in Table 1.5.
Table 1.5. Effects of various operational parameters on adsorption.
Parametrs
Agitation/relative velocity
Effects
At low agitation film diffusion is rate controlling. At
high agitation pore diffusion is rate limiting.
Contact time
Adsorption increases with increase in contact time
until equilibrium achieved.
Adsorbent characteristics
Adsorption is a surface phenomenon. Adsorption rate
increases with decreasing particle size of adsorbent
and presence of surface charges.
Size and shape of adsorbate
Adsorption usually decreases, as the size of the
molecules becomes large due to steric effect.
Concentration
Rate of adsorption increases with increase in
concentration. Rate constant is directly proportional to
concentration.
pH
Strong influence on adsorption due to change in ionic
concentrations of water and solutes.
Temperature
Affects rate and capacity of adsorption.
1.9.3 Adsorption Isotherm
The relation of dye concentration in the bulk and the adsorbed amount at the
interface is a measure of the position of equilibrium in the adsorption process and can
generally be expressed by one or more of a series of isotherm models. The accuracy
19
General Introduction
of these isotherms to simulate experimental data varies and is greatly influenced by
the specific interactions between the adsorbate and adsorbent. The interpretation of
adsorption data through theoretical or empirical equations is essential for the
quantitative estimation of the adsorption capacity or amount of the adsorbent required
to remove the unit mass of pollutant from wastewater. Different isotherms that are
commonly used for the dyes adsorption process and the linear equations of the applied
models are
Langmuir model:
(Ce/qe) = (Ce/qm) + (1/ qmb)
(1)
Freundlich model:
ln qe = ln KF + (1/n) ln Ce
(2)
Temkin model:
qe = B ln A + B ln Ce
(3)
Dubinin-Radushkevich model:
ln qe = ln qm – B1∑ 2
(4)
∑ = RT ln (1 + 1/Ce)
(5)
E = 1 2.B
1
(6)
where Ce is the equilibrium dye concentration in the solution (mg/l), b is the
Langmuir adsorption constant (l/mg) and qm is the theoretical maximum monolayer
adsorption capacity (mg/g). KF (mg/g) and n are Freundlich isotherm constants
indicating the capacity and intensity of the adsorption, respectively. A is equilibrium
binding constant (l/mg) and B is related to the heat of adsorption. B1 is the D–R
model constant (mol2 kJ−2) related to the mean free energy of adsorption per mole of
the adsorbate and ∑ is the polanyi potential. E is mean free energy of adsorption
(kJ/mol).
The Langmuir isotherm is generally more appropriate to a monolayer
adsorption where all binding sites are energetically equivalent and there is neither
interaction between adsorbed molecules nor the transmigration of adsorbate in the
plane of the surface [104,105]. Meanwhile, the Freundlich isotherm can be used for
non-ideal sorption that involves heterogeneous sorption [106,107].
Temkin isotherm [108] contains a factor explicitly taking into account of the
adsorbent–adsorbate interactions. By ignoring the extremely low and large value of
concentrations, the model assumes that heat of adsorption (as a function of
temperature) of all molecules in the layer would decrease linearly rather than
logarithmic with coverage [109]. As implied in the equation, its derivation is
20
General Introduction
characterized by a uniform distribution of binding energies (upto some maximum
binding energy [110].
Dubinin–Radushkevich isotherm [111] is generally applied to express the
adsorption mechanism with a Gaussian energy distribution onto a heterogeneous
surface [112]. The model has often successfully fitted well to high solute activities
and the intermediate range of concentrations data, but has unsatisfactory asymptotic
properties and does not predict the Henry’s law at low pressure [113]. The approach
was usually applied to distinguish the physical and chemical adsorption.
1.9.4. Adsorption Kinetics
The study of adsorption kinetics is important in wastewater treatment because
it provides valuable information on the reaction pathways and the mechanism of
sorption. In addition, predicting the solute uptake rate is of utmost importance in
designing an appropriate wastewater treatment plant because it can control the
residence time of solute at the solid-solution interface. Various kinetic models have
been proposed by different research groups where the adsorption has been treated as a
pseudo-first order [114], a pseudo-second order [115], Elovich [116] and intraparticle
diffusion [117]. The linear equations of kinetic model are
Pseudo-first order model:
log (qe−qt) = log qe− (k1t/2.303)
(7)
Pseudo-second order model:
t/ qt = (1/ k2qe2) + (t/ qe)
(8)
Elovich model:
qt = (1/β) ln (αβ) + (1/β) ln t
(9)
where qe and qt are the amount of adsorption at equilibrium and at time t in (mg/g). k1
(1/min) and k2 (min g/mg) are the rate constant for the pseudo-first and pseudosecond order adsorption kinetics. α is the initial adsorption rate in (mg/g min) and β is
related to the extent of surface coverage and the activation energy for chemisorptions
in (g/mg).
Intra-particle diffusion model
The adsorption can be described by three consecutive steps:
•
The transport of adsorbate from bulk solution to the outer surface of the
adsorbent by molecular diffusion, known as external or film diffusion.
•
Internal diffusion, i.e. the transport of adsorbate from the particle surface into
21
General Introduction
interior sites.
•
The adsorption of solute molecules from the active sites into the interior
surfaces of pores.
To determine rate limiting step (either film diffusion or intraparticle diffusion)
as well as the corresponding rate constants, Weber and Morris intra-particle diffusion
model is widely used.
qt = Kid t1/2 + C
(10)
where, Kid is the intra-particle diffusion rate constant. The adsorption rates for intraparticle diffusion (Kid) under different conditions were calculated from the slope of
the linear portion of the respective plot with units of mg/g min0.5.
1.9.5. Adsorption Thermodynamics
Thermodynamic parameters are evaluated to confirm the nature of the
adsorption process. The thermodynamic constants, free energy change, enthalpy
change and entropy change are calculated to evaluate the thermodynamic feasibility
and the spontaneous nature of the process. Thermodynamic parameters such as
standard free energy change (∆Gº), enthalpy change (∆Hº) and entropy change (∆Sº)
are calculated using the following equations:
Kc = Cac/ Ce
(11)
where, Kc is the equilibrium constant. Cac and Ce are the equilibrium constants (mg/l)
of the dye on the adsorbent and in the solution respectively. ∆G0 was calculated from
the Gibb’s equation:
∆Gº = − RT ln Kc
(12)
where, T is the temperature in Kelvin and R is gas constant (8.314 J/mol K). ΔHo and
ΔSo were obtained from the slope and intercept of Van’t Hoff plot of ln Kc versus 1/T.
ln Kc = (∆Sº/ R) − (∆Hº/ RT)
(13)
On the basis of thermodynamic parameters following conclusion can be made
for the adsorption process. If:
22
General Introduction
ΔHo
+ve
Endothermic process
ΔHo.
−ve
Exothermic process
ΔGo
+ve
Non-spontaneous process
o
ΔG
−ve
Spontaneous process
ΔSo
+ve
Increase in randomness at solid/solution interface
ΔSo
−ve
Decrease in randomness at solid/solution interface
1.9.6. Design of Large-Scale Batch Adsorption System
The experimental data and the models obtained for any adsorption study can
be used in designing a large scale batch system for dyes containing liquid. In order to
achieve a desirable removal of dyes on large scale for a given initial dye concentration
and a finite liquid volume, the amount of adsorbent to be used and the residence time
of the liquid in the batch need to be determined. For a given equilibrium
concentration, Ce, the amount of dye adsorbed onto the adsorbent at equilibrium, qe,
can be estimated from the Langmuir isotherm model. The required amount of
adsorbent, mD, to treat a volume of liquid, VD, can then be calculated as given below:
mD = (Ci-Ce) VD/ qe
(14)
where Ci is the initial dye concentration in liquid. In practical, there would be a tradeoff between the maximized utilization of the adsorbent and the adsorption time since
the adsorption rate is very low when the equilibrium approaches. The adsorption
system would thus usually be designed at less than 100% saturation of the adsorbent,
such as 90–95% saturation [118,119].
The residence time (cycle time) of the liquid in the batch could then be
estimated using the pseudo-second order kinetics. The design amount of dye removal
qt, can be estimated as below
qt = (Ci−Ct)VD/mD
(15)
where Ct is the specified (or design) dye concentration remaining in the liquid at the
end of the adsorption cycle.
23
General Introduction
1.10. Objectives
The overall objective of the thesis is preparation and characterization of
adsorbents for the removal of dyes from aqueous medium under wide range of
conditions. The specific objectives of the study are:
• To preparation and characterization of adsorbent.
•
To determine the equilibrium time of dye adsorption.
•
To determine the optimum concentration of the dye and solution pH at which
maximum adsorption occur.
•
To study the effect of temperature and determine the values of the
thermodynamic parameters.
•
To study the kinetics and diffusion rate of dye adsorption.
•
To study the adsorption isotherm of dye adsorption.
1.11. Significance and Future Prospect of the Study
Adsorption is a fundamental process in the physicochemical treatment of
wastewaters, a treatment which can economically meet today's higher effluent
standards and water reuse requirements. This study is of general interest to
applications relating to solid/liquid interface and wastewater remediation. This study
shall give an idea about the mechanism of adsorption of different dyes on the
adsorbent surface, which also has the scope of enhancing the basic understanding of
the adsorption process under different conditions.
The effective design and application of the adsorption operation in
physicochemical treatment requires performance prediction, which in turn requires
thorough knowledge of the process itself and of the interplay of control and response
variables. Once the process is defined thermodynamically and kinetically and
conditions of specific operation are delineated, mathematical modeling techniques can
be employed for forward prediction of performance and adsorber design.
The findings from this research have many potential applications such as it can
be used to evaluate sorption performance and design the reactors for wastewater
purification at large scale. Furthermore, variations in the interaction force between
surfaces, due to sorption of charged species, can be used to develop sensors. Synthetic
24
General Introduction
organic/inorganic composites are potential materials for the wastewater purification.
Such kind of materials helps to generate nanosheet as well as nanofilter for the
purification of wastewater.
1.12. Organization of Thesis
The thesis has been organized in six chapters.
Chapter-1 is an introductory chapter which deals with water and dye pollution,
wastewater treatment technologies, various aspects of adsorption process and survey
of literature.
Chapter-2 explores the adsorption efficiency of bael shell carbon for the
removal of congo red dye. In this chapter efforts have been made to explain the
adsorption mechanism on the basis of different functional groups present on the
adsorbate and adsorbent surface.
Chapter-3 presents the adsorption of malachite green from aqueous solution
using treated ginger waste in batch and column process.
Chapter-4 deals with the kinetics and thermodynamics of brilliant green
adsorption onto carbon/ iron oxide nanocomposite.
In chapter-5, polyaniline/ iron oxide composite and amido black 10 have been
used as model adsorbent and adsorbate, respectively.
Chapter-6 describes the preparation and characterization of alumina reinforced
polystyrene for the removal of amaranth dye from aqueous solution.
1.13. Survey of Literature
Various kind of conventional and non-conventional adsorbents have been used
for the removal of dye. Recent literature survey on the adsorbent used for the removal
of dyes form aqueous solution and wastewater are summarized in Table 1.6.
25
General Introduction
Table. 1.6. Survey of literature
Adsorbent
Dyes
Unburned
Basic
carbon
Acid black 1
Remark
violet
Reference
3 The adsorption of dye increased with
[119]
increasing temperature but decreased
with
increasing
particle
size
and
followed pseudo-second order kinetic
model.
Activated
Methylene blue
The effect of acidic treatments of
carbons
Crystal violet
activated carbons on dye adsorption was
Rhodamine B
investigated. For methylene blue, the
[120]
adsorption shows an order of AC > ACHCl > AC-HNO3 while for crystal
violet and rhodamine B, the adsorption
order is AC-HCl > AC > AC-HNO3.
Sawdust
Methylene
blue Sulphuric acid treatment increases the
Red basic 22
[121]
sorption capacity of sawdust because of
opening of the lignocellulosic matrix’s
structure and the increasing of the BET
surface area and number of dye binding
sites.
Bentonite
Reactive blue 19
The maximum monolayer adsorption
[122]
capacity of dodecyltrimethylammonium
modified bentonite was found to be
206.58 mg/ g.
Activated
Acid green 25
palm ash
The maximum adsorption capacities of
[123]
the activated palm ash for removal of
AG25 dye was determined with the
Langmuir equation and found to be
123.4, 156.3 and 181.8 mg/g at 30, 40,
and 50 °C, respectively.
Hectorite
Reactive orange
Batch experiments were carried out for
122
the adsorption process in terms of effect
[124]
of pH, adsorbent dosage, contact time,
26
General Introduction
effect
of
salts
concentrations.
and
different
Experimental
dye
results
show that acidic pH favours maximum
dye removal.
Aspergillus
Reactive brilliant
Four materials sodium carboxymethyl-
fumigatus
red
beads
Reactive brilliant alcohol and chitosan were prepared as
[125]
K-2BP cellulose, sodium alginate, polyvinyl
blue KN-R by
supports
for
entrapping
fungus
Aspergillus fumigatus. The adsorption
efficiencies of reactive brilliant red K2BP and reactive brilliant blue KN-R by
CTS immobilized beads were 89.1%
and 93.5% in 12 h respectively.
Sepiolite
Reactive blue 221
The adsorption kinetics of CI reactive
[126]
blue 221, onto sepiolite was investigated
in aqueous solution in a batch system
with respect to stirring speed, contact
time, initial dye concentration, pH, and
temperature. The experimental data
fitted very well the pseudo-second order
kinetic model and also followed the
intra-particle diffusion model.
Jalshakti
Methylene
blue, The
adsorption
of
dyes
reaches
Safranine
T, equilibrium in 60–90 min and follows
Rhodamine
B, the Langmuir and Freundlich isotherm
Crystal
[127]
violet, models. The particle diffusion study
Malachite green, showed that the initial boundary layer
Brilliant
green, diffusion was followed by intraparticle
Basic fuchsine
diffusion model.
Carbon
Procion red MX- Langmuir isotherm and pseudo-second
nanotubes
5B
order
kinetic
model
fitted
[128]
the
experimental results well.
Diatomace-
Methylene blue
The acid treated diatomite was used to
[129]
27
General Introduction
ous silica
adsorb methylene blue from aqueous
solutions. The equilibrium data were
fitted to different adsorption isotherms
and the best fit was obtained using
Langmuir
isotherm.
The
maximum
loading capacity was found 126.6 mg/g
at 30 0C and increases slightly as the
temperature increases.
Zeolite
Reactive black 5 The adsorption capacity of Reactive Red
Reactive red 239
[130]
239 was found to be two times higher
than reactive blue 5 due to the
hydrophilicity of the dye molecules. The
calculated
maximum
adsorption
capacity increased with increasing initial
dye concentration, but there is no linear
relationship with pH and temperature.
Clay
Methylene blue
The removal of a basic dye, methylene
[131]
blue from aqueous solution on a natural
Moroccan
clay
mineral
has
been
investigated and maximum adsorption
capacity was found to be 135 mg/g.
Bituminous
Methylene blue
The adsorption mechanism was found to
coal
Basic red
follow
pseudo-second
intraparticle-diffusion
order
and
models,
with
[132]
external mass transfer predominating in
the first 5 min of the experiment.
Activated
Methylene blue
Activated carbon derived from waste
Carbon
Acid blue 25
wood pallets treated with phosphoric
Acid red 151
acid was used for adsorption of dye. The
Reactive red 23
effect pH on the adsorption of different
[133]
classes of dyes signified the importance
of both electrostatic interaction and
chemical adsorption.
28
General Introduction
Bentonite
Methylene blue
Batch adsorption tests for removal of
[134]
methylene blue dye from aqueous
solutions
onto
bentonite
were
investigated using sulphuric acid and
microwave treated bentonite. The uptake
of
dye
by
the
microwave-treated
bentonite was the highest, followed by
the acid-treated and finally the untreated
bentonite.
Poly [N-vinyl Orange-II
Adsorption of dyes increases with
pyrrolidone/
Reactive orange- increase in solution concentration. The
2-methacryl-
13
oyloxye-thyl)
Reactive orange- increases in the following order: OR-
trimethyl-
14
[135]
binding ratio of the hydrogel/dye system
II>RO-14>RO-13
ammonium
chloride]
Calix[4]arene Direct violet 51
Physical adsorption, hydrogen bonding
β-
Methyl orange
and formation of an inclusion complex
cyclodextrin
Titanium yellow
were the main forces involved in the
Oraing II
sorption of dye onto adsorption surface.
Disperse blue 56
The pH had a considerable influence on
Disperse red
adsorption
Sawdust
and
optimum
pH
[136]
[137]
for
adsorption of disperse dyes was found to
be in the range of 2–3. The data were
fitted well to pseudo-first order equation.
Chitosan/
Congo red
A series of novel chitosan/organomont-
organomont-
morillonite
morillonite
synthesized and used for the removal of
dye.
The
nanocomposites
adsorption
kinetics
[138]
were
and
isotherms were in good agreement with
a pseudo-second order equation and the
Langmuir equation.
Wood fungus
Congo red
The biosorption equilibrium data obeyed
[139]
29
General Introduction
the Langmuir and Temkin isotherms
well. Acidic pH was favorable for the
biosorption of the dye. Studies on the pH
effect
and
desorption
show
that
chemisorption seems to play a major
role in the biosorption process.
Peat
Yellow CIBA
The maximum adsorption capacities
Dark blue CIBA
were between 15 and 20 mg/ g. The
Navy CIBA WB
Langmuir extended model indicated that
Red CIBA WB
there was competition for adsorption
[140]
sites and without interaction between
dyes.
Montmorillo-
Eriochrome black The adsorption property of montmorillo-
nite
T
nite modified with a cetylpyridinium
Orange II
chloride was investigated. In single-
Methyl orange
solute sorption, the sorption affinity, as
Thioflavin
T represented
Methylene
blue coefficient
Crystal violet
by
Freundlich
sorption
and
Langmuir
sorption
[141]
capacity, was in the order of EBT > OR
>MO for anionic dyes and in the order
of TT > MB > CV for cationic dyes.
Chitin
Black DN
The adsorption and desorption studies
Scarlet R
were carried out at pH 3 and 11,
Brilliant
[142]
orange respectively. the highest efficiency of
3R
desorption, nearly 100%, was obtained
for brilliant orange 3R and lower ones
for rcarlet R and black DN, at 89% and
90%, respectively.
Chitosan
Acid green 25
The equilibrium data have been studied
Acid orange 10
using
Acid orange 12
Redlich-Peterson equations. The best
Acid red 18
correlations were obtained using the
Acid red 73
Langmuir
Langmuir,
isotherm
Freundlich
suggesting
[143]
and
the
30
General Introduction
mechanism involves one process step of
dyes complexing with the free amino
group.
Bentonite
Quinalizarin
The
results
showed
the
largest
[144]
adsorption capacity of the homoionic
bentonite; the saturation level was
reached, the high adsorption capacity
(79 meq/100 g), close to the cation
exchange capacity of the synthesized
bentonite (89 meq/100 g), indicates a
strong interaction between the dye
molecule and the adsorbent.
Sand
Coomassie blue
Malachite
65-70% adsorption was reported under
[145]
green the optimum sorption condition. The
Safranin orange
adsorption kinetics followed the pseudosecond order equation for all dyes.
Caulerpa
Astrazon
lentillifera
FGRL
blue The adsorption reached equilibrium
within the first hour and the kinetic data
Astrazon
red fitted well with the pseudo-second order
GTLN
Astrazon
Luffa
[146]
kinetic model. Increasing salinity of the
golden system caused a decrease in adsorption
yellow
capacity possibly.
Methylene blue
The adsorption isotherms could be well
cylindrica
defined with Langmuir model instead of
fibers
Freundlich model. The thermodynamic
[147]
parameters of MB adsorption indicated
that the adsorption was exothermic and
spontaneous.
The
average
MB
adsorption capacity was found out as 49
mg/g
Poly(N,N
Apollofix red
The
dimethyl-
Apollofix yellow
P(DMAEMA) hydrogel was found to
aminoethyl-
adsorption
capacity
of
[148]
increase from 85 to 131 mg/g for AR
31
General Introduction
methacrylate)
dry gel and from 58 to 111 mg/g for AY
dry gel with decreasing pH of the dye
solutions.
Titanate
Basic green 5
Effects of the pore structure variation on
nanotubes
Basic violet 10
[149]
the basic dyes adsorption of TNT were
discussed. Moreover, the adsorption
mechanisms of basic dyes from aqueous
solution onto TNT were examined with
the aid of model analyses of the
adsorption equilibrium and kinetic data
of BG5 and BV10.
Alginate/
Methylene blue,
The ionic interaction between the dye
polyaspartate
Malachite green
molecule and gel matrix appears to be
hydrogels
Methyl orange
responsible for the efficient adsorption
[150]
of cationic dyes in this system. Type-S
adsorption isotherms were obtained,
which is characteristic of a weak solute–
solid interaction.
Polyaniline
Orange G
Methylene
Polyaniline emeraldine salt was
blue
Rhodamine B
Alizarine cyanine
green
Coomassie
[151]
synthesized by chemical oxidation and
used for the adsorption of sulfonated
dyes from water. A mechanism was
proposed based on the chemical
interaction of PANI with the sulfonate
brilliant blue R-
group of the dyes.
250
Remazol brilliant
blue
Activated
carbons
Acid blue 15
Activated
carbons
prepared
from
[152]
sunflower seed hull have been used as
adsorbents for the removal of acid blue
15. The optimum conditions for AB-15
removal were found to be pH
3,
32
General Introduction
adsorbent dosage 3 g/l and equilibrium
time 4 h at 30 0C.
Sludge
Reactive red 2
The maximum monolayer adsorption
Reactive red 141
was found to be 53.48 mg/g and 78.74
[153]
mg/g, for RR2 and RR141, respectively.
The equilibrium adsorption capacity for
the dye RR2 increased with increase in
the packed column height from 15 to 30
cm in the proportion 1 : 1.7 with a fixed
flow rate of 12 ml/min, and for an
increase in the flow from 8 to 16 ml/
min.
Hydrogel-
Safranine-T
clay nano-
Brilliant
composite
blue
The equilibrium was established within
[154]
cresyl 10 min and maximum adsorption was
found to be 484.2 and 494.2 mg/g for
the ST and BCB dyes, respectively.
Pleurotus
Methylene blue
ostreatus
The adsorption isotherm of methylene
[155]
blue followed the Langmuir model and
the maximum adsorption capacity was
70 mg of dye per g of dry fungus at pH
11, 70 mg/l dye, and 0.1 g/l fungus
concentration,
respectively.
The
percentage of desorbed methylene blue
was 80% by 1M H2SO4.
Activated
Methylene blue
carbon
Adsorption process was attained to the
[156]
equilibrium within 5 min. The adsorbed
amount MB dye on activated carbon
slightly changed with increasing pH,
and
temperature,
indicating
an
endothermic process.
Carbon
Direct yellow 86
The adsorption percentage of direct dyes
nanotubes
Direct red 224
increased
as
CNTs
dosage,
[157]
NaCl
addition and temperature increased. The
33
General Introduction
capacity of CNTs to adsorb DY86 and
DR224 was 56.2 and 61.3 mg/g.
Bottom
ash Metanil yellow
For both adsorbents, the adsorption
De-oiled
process has been found governing by
soya
film diffusion, and saturation factors for
[158]
columns have been calculated as 99.15
and 99.38%, respectively.
Polyacrylam-
Basic blue 12
The adsorption studies indicated that the
ide/nanoclay
Basic blue 9
rates
Basic violet 1
nanocomposite hydrogels increased in
of
dye
uptake
by
[159]
the
the following order: BB 9 > BB 12 >
BV 1. In the dye absorption studies, Stype
adsorption
in
the
Giles
classification system was found for the
BB 12 and BV 1 dyes, whereas L-type
was observed for the BB 9 dye.
Perlite
Congo red
The dye adsorption equilibrium was
[160]
rapidly attained after 40 min of contact
time and followed pseduo-first order
kinetic.
Rice
ash
husk Methylene blue
Congo red
The maximum percentage removal of
[161]
MB was 99.939%, while 98.835%
removal was observed for CR. Batch
desorption studies revealed that 50%
acetone solution was optimum for CR,
while desorption of MB varied directly
with acetone concentration
Fly ash
Acid blue 113
Adsorption of dyes has been studied
Tartrazine
from their single and binary solutions.
[162]
Modeled isotherm curves using isotherm
parameters
of
the
Freundlich
Dubinin-
Radushkevich
and
equations
adequately fit to equilibrium data.
34
General Introduction
Equilibrium adsorption of AB in binary
solutions has been quite well predicted
by the extended Freundlich and the
Sheindorf-Rebuhn-Sheintuch models
Activated
Basic blue 9
The pseudo-second order model for the
carbon cloth
Basic red 2,
kinetics and the Freundlich isotherm
Acid blue 74
model for the equilibrium of the
[163]
adsorption were found to fit the
experimental data reasonably well.
Amberlite
Allura red
Adsorption decreased with increase in
IRA-900
Sunset yellow
solution pH and increased with increase
Amberlite
[164]
in temperature.
IRA-910
Euphorbia
Acid yellow17
Thermally
macroclada
Acid orange 7
macroclada carbon was used for the
carbon
removal
continuous
systems.
activated
of
dyes
packed
The
by
Euphorbia
batch
[165]
and
bed
adsorption
maximum
adsorption
capacity of AY17 and AO7 onto
activated carbon was found to be 161.29
and 455 mg/g, respectively by Langmuir
isotherm at 55 ºC. Maximum desorption
was observed at pH 11 by NaOH.
Lemon peel
Methyl orange
The adsorption capacities of lemon peel
Congo red
adsorbent for dyes were found 50.3 and
[166]
34.5 mg/g for MO and CR, respectively.
The adsorption data was well described
by the Langmuir model and pseudo-first
order kinetic model
MCM-41
Crystal violet
The calcined and sulfated MCM-41 was
[167]
used for the removal of CV. Freundlich
and pseudo-second order rate models
ware appropriate model to explain the
35
General Introduction
adsorption isotherm and kinetics. The
thermodynamic studies suggested that
the adsorption is exothermic in nature.
Hydrilla
Malachite green
verticillata
Response surface methodology was
used
for
designing.
The
[168]
optimum
conditions for maximum removal of
malachite
green
from
an
aqueous
solution of 75.52 mg/l were as follows:
adsorbent dose (11.14 g/L), pH (8.4),
temperature (48.4°C) and contact time
(194.5 min).
Organo-
Congo red
attapulgite
The amount adsorbed of CR on the
organo-attapulgite
increasing
increase
dye
[169]
with
concentration,
temperature and by decreasing pH.
Kinetic and desorption studies both
suggest that chemisorption should be the
major mode of CR removal.
β-cyclo-
Methylene blue
dextrin
β-cyclodextrin
exhibited
adsorption
[170]
capability toward methylene blue 105
mg/ g. carboxyl and ester groups were
mainly involved in the adsorption of
dye.
Activated
Methylene blue
Carbon
The removal increased from 74.20 to
[171]
93.58% with decrease in concentration
of dye from 100 to 60 mg/l at 30 °C,
150 rpm, and pH 5.3. The removal
exhibited an increasing trend with
increasing temperature, exhibiting the
endothermic nature of adsorption.
Polyaniline
Orange G
P-toluenesulfonic
acid
(PTSA)
and
Methylene blue
camphorsulfonic acid (CSA) dopped
Rhodamine B
polyaniline was used for the removal of
[172]
36
General Introduction
Malachite green
dyes.
The
maximum
dye
Alizarine cyanine
adsorption/removal by PANI clearly
green
depends on the nature of the dopant (the
Brilliant blue R
order being CSA > PTSA > HCl.
250
Remazol brilliant
blue R
Silica
Acid orange 10
Monoamine modified silica particles
Acid orange 12
have been used for the removal of
[173]
dyes.The adsorption of AO 10 followed
pseudo-first order kinetics whereas AO
12
followed
pseudo-second
order.
Desorption of the loaded dyes was
carried out at pH 10 and found to be
10.4 and 91.6% for AO-12 and AO 10,
respectively.
Clinoptilolite
Amido black 10B
Clinoptilolite has a limited adsorption
Safranine T
capacity for amido black 10B (0.0112
[174]
mg/g) and has a good adsorption
capacity for safranine T (0.05513 mg/g).
Magnetic/
Methyl
orange The adsorbent was prepared by blending
cellulose/
Methylene blue
[175]
Fe2O3 nanoparticles with cellulose and
activated
activated
carbon
via
an
optimal
carbon
dropping technology The sorbent could
composite
efficiently adsorb the organic dyes from
wastewater, and the used sorbents could
be recovered completely.
Activated
Remazol red B
sepiolite
The optimum contact time and pH were
[176]
found to be 120 min., pH 2–3 and it was
found that the adsorption capacity of
acid activated sepiolite was higher than
that of thermal one.
Activated oil Reactive red 120
The Freundlich model and pseudo-
[177]
37
General Introduction
palm ash
second order kinetics agreed very well
with
the
experimental
data.
The
maximum monolayer adsorption was
found to be 376.41 mg/g at 50°C.
Trichoderma
Rhodamine 6G
The maximum adsorption was found to
harzianum
Erioglaucine
be at pH of 8 and 4 for the removal of
rhodamine
6G
and
[178]
erioglaucine
respectively. Adsorption of dyes onto
fungal biomass satisfied the Langmuir
and Freundlich adsorption isotherms.
Polyacrylami
Malachite green
de-bentonite
Methylene
composite
Crystal violet
Amine functionalized Polyacrylamide-
[179]
blue bentonite composite adsorbent behaved
like a cation exchanger and more than
99.0% removal of dyes was observed at
the pH range 5.0 to 8.0. Four adsorption
desorption cycles (using 0.1 M HNO3)
were
performed
without
significant
decrease in adsorption capacity.
Stipa
Acid blue 25
The sorption capacities were obtained as
tenacessima
Acid yellow 99
follows: 541, 513, 395, and 223 mg/g,
L alfa fiber
Reactive
[180]
yellow respectively, for acid blue 25, acid
23
yellow 99, reactive yellow 23, and acid
Acid blue 74
blue 74. The percentage of desorbed dye
varied between 52% for acid blue 74,
70% for reactive yellow 23, 76% for
acid yellow 99 and 78% for acid blue
25.
zeolite
Methylene blue
The maximum adsorption capacities of
[181]
MB by the three zeolites calculated
using the Langmuir equation, ranged
from
23.70
to
50.51
mg/g.
The
adsorption of MB by zeolite was
essentially due to electrostatic forces.
38
General Introduction
Regeneration
of
used
zeolite
was
achieved by thermal treatment.
Poly(MAA)-
Safranine
T, A series of poly(MAA)-cross linked
starch
Methylene blue,
pregelled starch graft copolymer were
Crystal violet
used for the removal of basic dyes.
[182]
Adsorption of dyes increased with
increase in starch grafting, contact time,
solution
pH,
agitation
speed
and
adsorbent dose.
Activated
Malachite green
carbon
The kinetic sorption data fitted well to
[183]
the second-order kinetic model. It was
found that the Langmuir isotherm have
the
high
correlation
coefficients
compared to the Freundlich
Fly ash
Acid orange
The adsorption equilibrium of ARBG
Acid red BG
could reach in 1.5 h, faster than that of
[184]
AOII. The saturated adsorptive amount
of ARBG and AOII on the fly ash was
3.15 and 1.10 mg/g at 20 ºC.
Multiwalled
Methylene
carbon
Orange II
blue The removals of OII and MB by
[185]
adsorption on MWCNT were maximum
nanotubes
at pH 3.0 and pH 7.0, respectively.
Carbon
While for CNF, the optimum values of
nanofibers
pH were 9.0 and 5.0 for OII and MB,
respectively. Equilibrium data were well
described by the Langmuir isotherm.
Calcite
Methylene
blue Competitive Adsorption of basic dyes
Safranine T
[186]
onto calcite in single and binary
component
systems.
Extended
Freundlich and Langmuir models fit to
MB–ST adsorption in binary solutions.
γ-Fe2O3
Acid red dye 27
The equilibrium was achieved in less than
[187]
4 minutes. The removal of AR27
39
General Introduction
decreased with the increase in solution
pH and temperature. The addition of
chloride and nitrate anions has no
remarkable influence on AR27 removal
efficiency. The adsorption process was
found to be spontaneous, exothermic and
physical in nature
Polymer/
Disperse
bentonite
SBL
Vat
blue The
sorption
polyepicholorohyscarlet
property
of
[188]
drin-dimethylamine
R and bentonite composite was investigated
Reactive violet K- for non-ionic dyes and anionic dyes. The
3R
Langmuir model was the most suitable to
Acid dark blue describe non-ionic dye adsorption, but for
2G
anionic dyes the Freundlich model was
best.
Chitosan/zinc Direct blue 78
The equilibrium data of AB26 and DB78
oxide
adsorption followed with Langmuir and
Acid black 26
Tempkin
isotherms,
respectively.
[189]
In
addition, adsorption kinetics of both dyes
was found to conform to pseudo-second
order kinetics.
chitosan/
Methyl orange
About 71.0 % of MO was adsorbed
kaolin/
within 180 min from 20 mg/l MO
γ-Fe2O3
solution at pH = 6.0 by 1.0 g/L adsorbent
[190]
dosage.
Bottom ash
Crystal violet
Pseudo-second order kinetics was found
De-oiled
to describe the adsorption of the dye.
soya
Recovery of the dye was made by eluting
[191]
HCl solution through the exhausted
columns and almost 95% and 78% of the
dye was recovered from BA and DOS
columns, respectively.
Polyaniline
Methylene blue
The binding sites of the interactions
[192]
40
General Introduction
nanotubes
available in the NTs (amine and imine
nitrogens) and according to Langmuir
adsorption isotherm the majority of the
adsorption was due to one site (imine
nitrogens) which has a lone pair of
electrons that can increase interaction
with the cationic MB dye.
Activated
Crystal violet
Both the rate and extent of adsorption and
carbon cloth
Basic blue 7
electro sorption of dyes were found to
Basic blue 11
increase in the order of BB-7 < BB-11 <
[193]
CV. The main type of attractive at natural
pH was expected to be dispersion forces
between
π-electrons
of
polycyclic
aromatic rings and of the ACC surface.
Sepiolite
Methylene blue
Pansil
The Sips model agrees well with the
[194]
experimental data, and the pseudo-second
order kinetic model reproduces properly
the kinetic experimental data of the
system MB-sepiolite. The highest MB
adsorption was obtained at acid pH for
sepiolite and at basic pH for pansil.
Chitosan
Remazol brilliant
The adsorption behavior of two dyes of
blue RN
different nature/class on several chitosan
Basic blue
derivatives was studied. The adsorbents
used
were
functional
grafted
groups
with
(carboxyl,
[195]
different
amido,
sulfonate, N-vinylimidazole) to increase
their adsorption capacity and cross-linked
to improve their mechanical resistance.
The experimental equilibrium data were
successfully fitted to the LangmuirFreundlich isotherms.
MCM-41
Methylene blue
The decrease in temperature or the
[196]
41
General Introduction
increase in pH enhanced the adsorption of
dye onto MCM-41. The Freundlich and
Redlich-Peterson models expressed the
adsorption isotherm better than the
Langmuir model.
Turbinaria
Acid blue 9
The optimum conditions for maximum
conoides
[197]
removal of acid blue 9 from an aqueous
solution of 100 mg/l were found as
follows: temperature (33 ºC), adsorbent
dose (3 g/l), contact time (225 min),
adsorbent size (85 mesh) and agitation
speed (226 rpm).
Industry
Malachite green
Pyrolysed industry waste materials: one
waste
de-inking paper sludge (HP) and one
materials
organic sludge from virgin pulp mill (RT)
[198]
were used as adsorbent for the removal of
MG. Maximum adsorption obtained by
Langmuir equation was higher for the
adsorbent from HP (982 mg/g) than RT
(435 mg/g).
Glycidyl
Congo red
The maximum adsorption capacity of the
methacrylate-
reactive fiber for CR is 16.6 mg/g fiber.
g-poly
The rates of adsorption were found to
(ethylene
conform to the pseudo-second order
terephthalate)
kinetics with good correlation. It was
fiber
found that the adsorption isotherm of CR
[199]
fitted Freundlich model.
Mustard cake Rhodamine-B
The optimum contact time, pH and dose
Activated
was found to be 6 h, 2.3 and 5 g/L,
carbon
respectively. The on going adsorption
[200]
validates both the Langmuir and the
Freundlich adsorption isotherms.
Boron
Acid
red
183 The adsorption capacities of AR183 and
[201]
42
General Introduction
industry
Reactive blue 4
RB4 on waste in single dye solutions
were found to be 9.11 x 10−5 mol3/g and
waste
7.33 x 10−5 mol3/g respectively. Because
of competitive adsorption, the adsorption
capacities
in
binary solutions were
reduced to 7.43 x 10−5 mol3/g and 6.37 3
x 10−5 mol3/g, respectively. In column
experiments, the adsorption of dyes from
single and binary solutions was fit well
by the Thomas model.
Graphite
Methylene
blue The amount of the dyes, methylene blue
oxide
Malachite green
[202]
and malachite green, adsorbed on the
graphite oxide was much higher than that
on graphite, and the adsorption capacity
based on the Langmuir isotherm is (351
and 248) mg/g, respectively, much higher
than activated carbon. The adsorption
mechanism was proposed as electrostatic
attraction.
Multiwalled
Methylene blue
In the absence of electrochemistry, the
carbon
Methyl orange
MWNT filter completely removed all dye
nanotube
[203]
from the influent solution until a near
monolayer of dye molecules adsorbed to
the MWNT filter surface.
Palm
shell Reactive red 141
pH 4 was suitable for the adsorption of
Reactive blue 21
both reactive dyes onto chitosan and was
powder
Chitosan
[204]
independent of pH in the ramge pH 2-9
using palm shell as the adsorbent. The
process of dye removal followed pseudosecond order kinetics.
p-tert-butyl-
Reactive red 45
The sorption of selected azo dyes is
calix[8]arene
Reactive black 5
highly
pH
dependent
and
[205]
newly
immobilized material has potentially
43
General Introduction
more effective sorbent as compared to
pure silica as well as p-tert-butylcalix[8]arene. The optimized pH for the
effective removal of RB5 and RR45 dyes
was 9 and 3, respectively.
Magnetic/
Methyl orange
A novel type of magnetic porous
triazine-
carbonaceous
polymeric
based
(covalent triazine-based framework), has
framework
been synthesized by a facile microwave-
[206]
material,
enhanced high-temperature ionothermal
method.
The
maximum
adsorption
capacity of composites was found to be
291
mg/g
at
0.889
mmol/g
dye
concentration.
Chitosan
Direct
red
23 The isotherm data of direct red 23 and
Acid green 25
[207]
acid green 25 in single and binary
systems followed Tempkin isotherm. In
addition adsorption kinetics of dyes was
studied in single and binary systems and
rate sorption was found to conform to
pseudo-second order kinetics
Magnetic
Methylene blue
The superparamagnetic mesoporous silica
silica
Acridine orange
microspheres
was
synthesized
[208]
and
modified with anhydride functionalized
silane to graft carboxylic groups and
developed for removing basic dye. The
results showed that the as-prepared
adsorbent
exhibits
high
adsorption
capacity, extremely rapid adsorption rate
and separation convenience for basic dye.
Carbon
Acid blue 113
Two type of high surface area carbons
Reactive red 241
namely, a carbon xerogel and a templated
[209]
carbon was used a adsorbent for the
44
General Introduction
removal of dyes. Dispersive forces were
involved in the adsorption mechanism,
resulting from the interaction of the
delocalized π electrons in the carbon
basal planes, and the free electrons of the
aromatic rings and multiple bonds of the
dye molecules.
Bagasse
Methylene blue
The sorption performance of raw bagasse
[210]
(RB) and tartaric acid-modified bagasse
(TAMB) was investigated. Maximum
decolorization (78.16%) for RB was
achieved at 0.82 g of adsorbent dosage,
pH 9.4, 122 rpm of shaking speed, 44
min of contact time and 55°C. For
TAMB,
maximum
decolorization
(99.05%) was achieved at 0.78 g
adsorbent dosage, pH 9.4, shaking speed
of 120 rpm, 34 min contact time and
49°C.
Styrene–
Anthranilic acid
Styrene–divinylbenzene
copolymer
divinyl-
p-aminobenzoic
functionalized with a-hydroxyphosphonic
benzene
acid
acid was used for the removal of three
copolymer
Bromaminic acid
dyes. The adsorption capacity and the
[211]
percentage of removal, increase with the
increasing
of
the
initial
dye
concentration.
Yeast sludge
Reactive blue 49
The biosorption capacity was maximum
[212]
at initial pH 3 that the effect of
temperature on biosorption of reactive
blue 49 was only slight in relation to the
large biosorption capacity (25 º C, 361
mg/g) according as the biosorption
capacity decreased only 43 mg/g as the
45
General Introduction
temperature increased from 25 to 50 º C.
Activated
Methyl red
The dye adsorption process followed
carbon
pseudo-second
multiwalled
involvement of an intra-particle diffusion
carbon
mechanism. The adsorption process was
nanotubes
endothermic in nature.
Activated
Acid violet 17
carbon
order
model
[213]
under
Maximum colour removal was observed at
[214]
pH 2. The adsorption increased with the
increase in adsorbent dosage. As the
adsorption capacity increased with the
increase in temperature, the process was
concluded to be endothermic.
Hollow
Methyl orange
The experiment shows that the adsorption
chitosan
Xylenol orange
capacities of the two dye-hollow chitosan
[215]
microsphere systems are higher than those
stated in other literature using chitosan
particles. The difference in the degree of
adsorption may also be attributed to the size
and chemical structure of the dye molecule.
Na-alginate/
Basic violet 7
acrylamide
The maximum amount of dye adsorbed was
[216]
found to be 78.1.0 mg/g at pH 9.0. By
increasing ionic strength the adsorption of
the dye was decreased.
Activated
Malachite green The maximum removal of MG was
carbon
[217]
obtained at pH 6 as 99.86% for adsorbent
dose of 1 g/50 ml and 25 mg/l initial dye
concentration at room temperature.
Volcanic
ashes
Methylene blue
Volcanic ashes (VAs) and Ti-modified
[218]
volcanic ashes (TVA) were investigated
adsorbents to remove methylene blue
(MB). TVA displayed higher and faster MB
adsorption than VA. MB adsorption data
described satisfactorily by the Langmuir
46
General Introduction
equation, whereas adsorption kinetic data
fit a pseudo-second order kinetics model.
Polyamido-
Methyl violet
xime resins
Poly(acrylic
acid–amidoxime)
[P(AA–
[219]
AO)] and poly(maleic acid–amidoxime)
[P(MA–AO)] resins were used for the
removal of methyl violet. The equilibrium
data was described well by the Langmuir
isotherm model with maximum adsorption
capacities of 398.4 and 396.8 mg/g for
P(AA–AO) and P(MA–AO), respectively.
Waste
yeast
beer Methyl orange
The adsorption capacities of Fe3+, Mg2+,
[220]
Ca2+ and Na+ modified biomass for methyl
orange were 90.8, 51.3, 23.0, and 20.6
mg/g, which were 30, 17, 8, and 7 times
that
of
the
unmodified
biomass,
respectively. Results showed that 96.9 and
80.0% of the methyl orange could be
desorbed from the Fe3+, and Mg2+, modified
biomass at pH 12.
47
General Introduction
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