POLLUTION CONTROL IN DYE INDUSTRY

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POLLUTION CONTROL IN DYE INDUSTRY

• K.Suthagar
• National Centre for Catalysis Research

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• Introduction
• A dye can generally be described as a
  colored substance that has an affinity to
  the substrate to which it is being applied. The
  dye is generally applied in an aqueous solution,
  and may require a mordant to improve the fastness
  of the dye on the fiber
• Both dyes and pigments appear to be colored
  because they absorb some wavelengths of light
  preferentially. In contrast with a dye, a
  pigment generally is insoluble, and has no
  affinity for the substrate.

Electronic excitation energies
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• s ? s
• p ? p
• n ? s
• n ? p
• aromatic p ? aromatic p
• Chromophore it is a functional groups which
  are unsaturated and they cause a compound
  to become coloured.
• Examples of chromophores are NN-,
  -CC-, -CN- and -CO.
• 1. Transitions involving s, p, and n electrons
• 2. Transitions involving charge-transfer
  electrons
• 3. Transitions involving d and f electrons

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• Auxochrome
• Auxochromes are groups that does not impart
  color to the compound but increase the
  color of the compound. Functional groups such as
  hydroxyl (OH), amino ( -NH2), nitro (-NO2),
  alkyl (-R), OH, OR, NH2, NHR, NR2, SH are
  common examples for auxochrome. The effect
  of the auxochrome is due to its ability
  to extend the conjugation of a chromophore
  by the sharing of non-bonding electrons.
• Bathochromic Effect
• Hypsochromic shift
• Hyperchromic Effect
• Hypochromic Effect

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Pictorial representation of bathochromic shift
and hypsochromic shift in the absoption
spectra
Typical data on some chromophre
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CLASSIFICATION OF DYES

• Acid Dyes

These are generally applied to textile fibers
from dye baths containing acid. Most have one or
two sodium sulfonate (SO3Na) groups which are
water soluble and capable of bonding with fibers
having cationic sites. They give a wide range
of bright colors on textiles, especially
when monoazo and anthraquinone structures are
used.
Basic dyes
Basic dyes were developed to dye negatively
charged acrylic fibers, forming ionic bonds.
They owe their name to the presence of aromatic
amino (basic) groups, and in this case a
cationic amino group is present. Generally,
they have excellent brightness and color
strength, their lightfastness is often Low.
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• Direct dyes

• Direct Dyes or substantive dyeing is normally
  carried out in a neutral or slightly alkaline
  dyebath, at or near boiling point, with the
  addition of either sodium chloride (NaCl) or
• sodium sulfate (Na2SO4).
• Direct dyes are used on cotton, paper, leather,
  wool, silk and nylon. They are also used as pH
  indicators and as biological stains.
• Direct dyes are anionic colorants that have
  affinity for cellulosic fibers. They were the
  first dyes with the ability to dye cotton in the
  absence of a mordanting agent, giving rise
• to the term direct-cotton dyes.

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• Sulfur Dyes

Sulfur dyes are water-insoluble dyes that
are applied to cotton. These are mainly give
dull shades. While yellow, red, brown,
olive, and blue colors can be produced,
sulfur dyes are most important for their
ability to deliver washfast black shades on
cotton
Examples of (a) sulfur yellow and (b) red dye
structures
Azo Dyes It is a technique in which an
insoluble azoic dye is produced directly onto
or within the fibre. This is achieved by
treating a fibre with both diazoic and
coupling components. With suitable adjustment of
dyebath conditions the two components react to
produce the required insoluble azo dyes. This
technique of dyeing is unique, in that the
final color is controlled by the choice of the
diazoic and coupling components
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• Vat Dyes
• Water insoluble and fast dyes applied along
  with strong reducing agents (sodium hydro
  sulfite) and alkali to make the dye soluble.
• The cloth is then exposed to air for oxidation.
• The excess alkali remaining on the cloth is
  neutralized by scouring.
• Vat dyes have mainly anthraquinone (82) or
  indigoid/thioindigoid (9) structures, with the
  former having better fastness properties
• Vat dyes are easier to reoxidize than sulfur dyes
  and the oxygen in air is often the agent
  used. As would be anticipated, most vat dyes
  display high wash fastness

Representative Anthraquinone vat dye
structures (a) Vat Red 13, (b) Vat Black 27,
(c) Vat Orange 2, (d) Vat Blue 4, and (e) Vat
Green 1.
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DYESTUFF INDUSTRY TREATMENT

• The presence of residual color, high levels of
  electrolytes, toxic substances (e.g., metals and
  unreacted raw materials) in dye application
  processes produce wastewaters that poses
  unacceptable environmental risks.
• In the case of textile dyeing operations, the
  concerns raised can arise from incomplete
  dye bath exhaustion and the presence of
  dyeing auxiliaries and metal ions that are
  toxic to aquatic life.

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Sources of effluent

• Dyeing and printing
• industries
• Textile industries
• Paper and ink manufacturing industries
• Cosmetics
• Pharmaceuticals
• Food

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Properties of effluent

• Impart colour to water bodies even if
  present in small quantity
• Reduces light penetration and photosynthesis
• Carcinogenic or mutagenic
• Azo dyes are more toxic as they affect
  microbes thereby affecting biological
  degradation treatment.
• Dyes increases BOD of effluent thereby
  affecting aquatic life
• Toxic to fish microbial organisms
• The discharge of heavy metals into aquatic
  ecosystemsIncrease in alkalinity of water
• The turbidity and colour along with oil and
  scum create an unsighty appearance.
• The mineral materials, mostlysodium salts
  increase salinity of the water.

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Volume of effluent

• The volume of effluent generated in dyeing
  is comparatively more.
• It contains dyes, mordants, acids (acetic acid),
  alkalis, nitrites, chromium salts, sodium
  chloride and soaps.
• These effluents are usually hot, highly
  coloured with a high pH and sulfide content
• Care must be taken while neutralising these
  liquors as acid may liberate hydrogen sulfide
  gas.
• Removal of Sulfides by treatment with
  chlorine or hypochlorites
• Spent vat dyes are strongly alkaline and
  have fairly high permanganate value

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Effluent Treatment Methods

• Physical Methods
• Adsorption
• Activated carbon adsorption has been widely
  studied as a waste treatment method for the
  removal of different classes of dyes from
  wastewater.
• Factors such as the choice of
  activated carbon, temperature, pH, contact time,
  and dosage must be taken into consideration for
  optimum removal of dyes from wastewater
• The most commonly used method of dye
  removal by adsorption. It can be Effective for
  adsorbing cationic, mordant and acid dyes and
  reactive dyes
• Performance depends on the type of
  carbon used and the characteristics of the
  wastewater.

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Equalization
Regulation of flow rate, also maintains pH
levels of the system.
Neutralization
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Adsorptive Bubble Separation

• Surface-active material, which may be ionic,
  molecular, colloidal, or macroparticulate in
  nature, is selectively adsorbed at the
  surface of bubbles rising through the
  liquid.
• 9899.8 of Direct Blue1 was removed from
  wastewater

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Chemical methods

• Fentons reagent (Fe2/H2O2) has been used
  commercially to oxidize and decolorize
  effluents containing a number of azo,
  anthraquinone, and reactive dyes.
• Dyes removed in these studies include reactive
  azo and anthraquinone dyes.
• Titanium Dioxide (TiO2)
• The cationic dye Rhodamine B, Basic Violet
  10 and the anthraquinone mordant dye
  Alizarine Red (Mordant Red 3) can be
  decomposed by Ti02 in the presence of visible
  light. Degradation occurs via the interaction of
  dye with hydroxyl radicals (OH.). Two of the
  final degradation products are phthalic acid and
  carbon dioxide.

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Borohydride Reduction

• Sodium borohydride is one of the strongest
  water soluble reducing agent commercially
  available
• SO2 is produced when borohydride is used in
  combination with bisulfite catalysis in the
  pH rang e of 5 8 which readily reduces azo
  dyes
• The utility of this process involving a
  variety of azo dyes, giving percent colour
  reduction of 83-99 for acid, direct, and
  reactive dyes and 74-99.9 for metalized
  direct and phthalocyanine dyes
• This method was extended to industrial
  wastewater containing either a mixture of azo
  disperse dyes or azo reactive black dyes.
• These solutions were treated with a mixture of
  400500 mg/L Na2S2O5, 1225 mg/L NaBH4, and 0200
  mg cationic flocculant, reducing color by 93 99

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Structures of dyes removed using biological
treatments Acid Blue 113 (13), Acid Yellow 17
(14), Direct Red 16 (15), Disperse Blue 73 (16),
and Vat Golden Yellow
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Bioaugmentation and Bioremediation

• These methods are currently used by the
  textile and dyestuff industries to
  decolorize waste water using enzymes.
• In this regard, enzymes such as laccases,
  lignin peroxidases, and manganese peroxidases
  have proved effective in cleaving aromatic
  rings

Structures of dyes used in borohydride reduction
studies (1) direct Red 254, (2) direct yellow
4, (3) acid red 1, (4) acid red 361, (5) reactive
red 24, (6) reactive red 120
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Metal Complexed Dyes

• One of the most serious environmental problems in
  the dye, textile, and leather industries is
  associated with the manufacture and use of
  metallized azo dyes that are complexed with
  chromium or cobalt to obtain desirable fastness
  properties
• various chemical, physical, and biological
  methods, such treatments can be expensive
  and may result in sludges that must be disposed
  by incineration or land filling
• In view of an emphasis on pollution prevention
  instead of waste treatment, the merits of
  substituting iron (Fe) for chromium (Cr) and
  cobalt (Co) in a group of commercially important
  acid dyes.
• Fe-complexed dyes as environmentally friendly
  alternatives to widely used Cr and Co complexed
  acid dyes

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Electrodialysis

• The ionic components (heavy metals) are
  separated through the use of semi-permeable
  ionselective membranes.
• Application of an electrical potential
  between the two electrodes causes a
  migration of cations and anions towards
  respective electrodes
• Because of the alternate spacing of cation
  and anion permeable membranes, cells of
  concentrated and dilute salts are formed

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Membrane Bioreactor in Textile Waste Water
Treatment

• Utilization of membrane filtration results in the
  retention of active micro-organisms, extra
  cellular enzymes generated by these
  micro-organisms for degradation of the
  organics present in the effluent
• Some micro-organisms, especially nitrifiers,
  are slowly growing one, their loss shall reduce
  the efficiency of the treatment system and
  nutrient removal
• In the MBR, these organisms are retained and
  a better treatment is achieved
• In addition retention of active enzymes secreted
  by mico organisms taking part in the
  metabolization of organics present in the
  textile waste water is an important aspect of MBR
  technology
• Maintenance of higher concentration of these
  enzymes shall result in rapid and better
  degradation of complex organic molecules present
  in the textile waste water.
• The overall efficiency of BOD (Biological
  Oxygen Demand) and COD (Chemical Oxygen Demand)
  removal is improved

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• MBR is normally designed to incorporate two
  zones viz., i) anoxic ii) aerobic
• Some bacteria can use oxygen as an electron
  acceptor when it is available, and in the
  absence of oxygen the same bacteria can
  switch the respiration mode to utilize
  nitrate/nitrite as electron acceptors
  (facultative bacteria) and these can be used in
  both in anoxic as well as in aerobic conditions
  
• As MBR configuration involves anoxic, aerobic,
  and membrane compartments with re-circulation
  from the membrane zone to the anoxic zone, the
  anoxic zone shall have very low levels of
  dissolved oxygen brought back by the
  recirculating effluent.
• The bacteria growing under anoxic condition
  has the capability to break down
  recalcitrant macromolecules, which is then
  digested by the aerobic bacterial population
  persisting in the aerobic zone.
• In this way, a significant portion of the dye
  stuff and other organics could be broken down
  and oxidized. Thus, anoxic biological degradation
  is an important step if we consider MBR
  treatment for textile waste water

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• If X is the inflow, and therefore outflow,
  anaerobic to aerobic and, aerobic to
  membrane flow is 4X, with a recirculation
  from membrane compartment to anaerobic being 3X
• When ever the feed quality changes, its
  characteristics are dampened by this
  re-circulation as the feed waste water gets
  diluted by the re-circulating fluid, and any
  oscillations in effluent parameters are dampened
• The dampening effect shall be linear for all
  parameters having linear relationship with
  concentration viz., BOD, COD, TDS (Total
  Dissolved Solids

Recirculation pattern inside MBR compartments
This stabilized output water quality is due
to the prevalence of a steady-state
condition inside the MBR compartments due
to the maintenance of high microbial activity
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Advantages of MBR

• Membrane Bioreactors have proven to be quite
  effective in removing both organic and
  inorganic contaminants as well as biological
  entities from waste water.
• The removal of organic, inorganic, and
  microbiological organisms along with suspended
  material present an excellent output from these
  systems whereby the biofouling and chemical
  scaling of the reverse osmosis system could
  be drastically minimized.
• It also minimizes use of cleaning
  chemicals in the secondary treatment.
• High molecular weight organic compounds, which
  are not readily biodegradable in conventional
  systems, are retained in MBR. Thus, their
  residence time is prolonged and the
  possibility of biodegradation is improved.

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REFERENCES

• 1. www.wikipedia.org
• 2. Y. R. Sharma, Elements of organic
  spectroscopy, S. Chand Company LTD, New Delhi,
  India.
• 3. Kirk Othmer, Encyclopedia of chemical
  technology, 5th
• Edition, 9th Volume, Wiley Interscience, John
  Wiley Sons, Inc., Publication
• 4. S.Eshwaramoorthi, K. Dhanapal and D.S.Chauhan,
  Environment With People's Involvement
  Co-ordination in India, Coimbatore, India,
  www.ecpconsulting.in
• 5. http//www.scribd.com/doc/12949482/Dyestuff-Ind
  ustry-Treatment, 2003

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Thank you