Dyestuff Industry Treatment
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Transcript of Dyestuff Industry Treatment
Dyestuff Industry Treatment
Dyestuff Industry
Three sub-segments, namely dyes, pigment and intermediates.
The dye intermediates are petroleum downstream products
These are essential inputs in major industries like textiles, plastics, paints, paper and printing inks.
Types of Dyes
Direct dyes: Small dyeing houses Easy to apply No auxillary chemicals
Basic dyes: Bright colours. Weak organic acids (such as tannic
acid)
Sulfur dyes: Dark colours These are sulfur compounds applied usually
with sodium sulfide. Effluent from this dyeing consists of
considerable amount of sulfide.
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.
More volume of effluents
Naphthol dyes : Beta-naphthol is first applied to the
fabric, dried and treated with a developer for coupling and diazotization after which the colour is formed.
This is followed be soaping and alkali treatment.
Developing dyes : Sodium nitrite , acid and beta-naphthol. Effluents from this dyeing contains no.
of chemicals
Effluent
Sources of effluent Dyeing and printing industries
Textile industries Paper and ink manufacturing industries
Cosmetics Pharmaceuticals Food
Properties of effluent before processing Impart colour to water bodies even if present
in small quantity Not harmful but undesirable for aesthetic
reason 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.
Salts of chromium and aluminium & iron as mordants in dyes
Toxic to fish & microbial organisms The discharge of heavy metals into
aquatic ecosystems Increase in alkalinity of water The turbidity and colour along with
oil and scum create an unsighty appearance.
The mineral materials, mostly sodium salts increase salinity of the water.
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.
High permanganate value ( 4hrs) 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.
Characteristics of Dyeing wastesDyes pH BOD Gallon wastes
per 1000 lb goods
Aniline Black
- 40 - 55 15,000 -23,000
Basic 6 -7.5 100 - 200 18,000 – 36,000
Developed colours
5 -10 75 -200 8,900 -25,000
Direct 6.5 - 7.6 220 - 600 1,700 – 6,400
Indigo 5 -10 90 - 1700 600 – 6,000
Naphthol 5 -10 15 - 675 2,300 – 16,800
Sulfur 8 - 10 125 -1,500 2,900 – 25,600
Vats 5 -10 125 – 1,500
1,000 – 20,000
Sr.No.
Characteristics Results
1. Temperature 50º C
2. pH value 10.5
3. Phenolphthalein alkalinity (as CaCO3), mg/l
13600
4. Total alkalinity (as CaCO3), mg/l
16100
5. Total solids, mg/l 40000
6. Total Suspended solids, mg/l 25200
Characteristics of Dyeing Effluent
Sr.No. Characteristics Results
7. Total Dissolved Solids, mg/l 29800
8. Dissolved Fixed Solids, mg/l 24060
9. Permangnate value (4hrs), mg/l
376
10. Chemical Oxygen Demand, mg/l
1490
11. Chlorides (as Cl), mg/l 1800
12. Oils & Grease, mg/l 1800
Technologies/ Current Practices
Requirements
Effluent treatment comprising primary (physico-chemical) and secondary (biological) system is in practice. Some of the units have also provided tertiary treatment and incinerators for non-biodegradable waste.
Possibilities for adaptation of cleaner process options for reducing the water consumption and effluent generation; better management practices for segregation and reuse/recycle of the treated effluent; effective utilization of raw materials; improvement in efficiency of process; and recovery of by-products. The effluent generated from manufacturing of some of the dyes and intermediates such as H-acid is not biodegradable, which requires process sludge.
Where H-acid : 1-amino,8-hydroxynaphthalene-3,6-disulphonic acid
Gaseous emissions such as SO2, NO2, HCl, and NH3 are generally scrubbed.
Properly designed scrubber with recovery reuse of scrubbed liquid is required.
Gypsum, iron sludge and sludge from ETP are generated as solid waste. The gypsum and iron sludge can be used in the cement and pigment industries, The sludge is either disposed off on land/secured landfill or sent to other user industries.
Cleaner process technologies e.g. catalytic hydrogenation, use of spent acid after nitration for acidification of fusion mass, which can eliminate generation of iron and gypsum sludge.
Primary treatment
ScreeningEqualizationNeutralizationChemical coagulation
Screening
Screen is a device with opening generally of uniform size, that is used to retain the coarse solids found in wastewater.
Removal of debris and solid wastes.
Equalization Regulation of flow
rate, also maintains pH levels of the system.
Neutralization
Chemical coagulation
Secondary treatment
Trickling filter Activated sludge process Aerated lagoon Oxidation pond Oxidation ditch Aerobic Degradation of Dyes
Anaerobic digestion Biosorption
Trickling filter
Activated sludge process
Aerated lagoon
Oxidation pond
Pond aeration or lake aeration Increase in the oxygen saturation
of the water. Dissolved oxygen (DO) Fish and other aquatic animals Aerobic bacteria Pond bottoms of organic soils
demand larger amounts of oxygen.
Oxidation ditch
Oxidation ditch
Aerobic Degradation of Dyes Inefficient treatment
Resistance to biological oxidation Poor adsorption of dyes
Example : Three anionic dyes i.e CL reactive violet 15, reactive blue 19 and reactive red 5 were neither removed nor biodegraded by activated sewage sludge even after 20 days of incubation.
Similar findings for sulphonated water soluble dyes.
Role of fungi and bacteria Aerobic oxidation Majority of White rot group Degrade variety of dyes Production of ligninolytic enzymes Example: laccase, lignin
peroxidase, manganese peroxidase and manganese independent peroxidase.
Broad substrate specificity
One of the most studied fungus Phanerochaete chrysosporium has been shown to degrade large spectrum of azo, anthraquinone and triphenylmethane dyes, with decolorization efficiency of more than 90%.
Other examples of white rot fungi degrading industrially relevant azo dyes are Geotrichum candidum, Trametes versicolor, T.modesia, T. pocas, Pleurotus ostreatus, Bjerkandera adustand.
Examples of fungus
Examples of Bacteria Streptomyces species and
Flavobacterium ATCC 39723 Extracellular peroxidases Ability to degrade xenobiotic
compounds including dyestuffs. Several other bacteria such as
Citrobacter sp., Kurthia sp., Corynebaterium and Mycobacterium sp., and mixed culture of Pseudomonas mendocina and P. alcaligenes degrade triphenylmethane dyes.
Controversy about aerobic degradation In many reports on the aerobic
metabolism of azo dyes, the bacterial strains were grown on complex media aerobically and incubated under static conditions in the presence of azo dyes.
These static cultures presumably become rapidly oxygen depleted and the reactions observed should be viewed as an anaerobic decolorization of dyes.
Anaerobic degradation of dyes Anaerobic conditions
Decolorisation of azo dyes.
Baughman and Weber (1994)
Biologically mediated reductionof azo dyes to the corresponding amines.
An upflow anaerobic fixed film bioreactor
Bone char as a support matrix A cattle dung slurry as a
source of anaerobic bacteria Decolorization of reactive
dyestuff industrial effluent Average colour removal and
COD removal efficiency was found to be 70% and 50% respectively at organic loading rate of 7.88 kg COD/m3/day.
Main advantage of fixed film bioreactor
Retention of active biomass in form of a biofilm attached to a support
Without recirculation of biomass or addition of fresh biomass
Efficient mass transfer and waste stabilization.
Fed batch processes using Pseudomonas luteola was shown to effectively decolorize reactive 22 dye.
BIOSORPTION A property of certain types of
inactive, dead, microbial biomass to bind and concentrate heavy metals from even very dilute aqueous solutions
Biomass acts as a chemical substance, as an ion exchanger of biological origin
Cell wall structure of certain algae, fungi and bacteria
These biomass types can accumulate in excess of 25% of their dry weight in deposited heavy metals: Pb, Cd, U, Cu, Zn, even Cr and others
A complex phenomenon where the metallic species could be deposited in the solid biosorbent through different sorption processes of ion exchange, complexation, chelation, microprecipitation, etc.
Reverse osmosis Electrodialysis Ultrafiltration Adsorption on powered
activated carbon Membrane filtration Nanofiltration
Tertiary treatment
Reverse Osmosis
Removal of bacteria, salts, sugars, proteins, particles, dyes, and other constituents
The separation of ions with reverse osmosis is aided by charged particles.
Dissolved ions that carry a charge, such as salts, are more likely to be removed by the membrane than those that are not charged, such as organics.
Electrodialysis The ionic components (heavy metals) are
separated through the use of semi-permeable ion selective 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.
The disadvantage is the formation of metal hydroxides, which clog the membrane.
Ultrafiltration
They are pressure driven membrane operations that use porous membranes for the removal of heavy metals. The main disadvantage of this process is the generation of sludge.
Adsorption on powered activated carbon
The most commonly used method of dye removal by adsorption.
Effective for adsorbing cationic, mordant and acid dyes, and to a slightly lesser extent, dispersed, direct, vat, pigment and reactive dyes
Performance depends on the type of carbon used and the characteristics of the wastewater.
Disadvantage: activated carbon is expensive; it has to be reactivated, which can result in 10-15% loss of sorbent.
Membrane filtration
Clarify, concentrate and separate dye continuously from effluent
Resistance to temperature, to an adverse chemical environment, and to microbial attack.
Disadvantages – disposal of the residue, high capital cost and the need for membrane replacement.
Nanofiltration Nanofiltration membranes are similar to
reverse osmosis membranes in several respects except the degree of removal of monovalent ions such as chlorides etc.
Reverse osmosis membranes provide 90 to 99% removal of ions while nanofiltration membrane are used for the selective removal of ions from 50 % to 90 %.
It depends upon the material and manufacturing of the membrane.
Treatment of water from many surface supplies like wells, rivers or lakes.
Specific Tolerances for Dyestuff effluentsSr.N
o. Characteristics
Tolerance limits
1. pH value 5.5 to 9.0
2. Suspended solids,mg/l max. 100
3. Dissolved solids (inorganics), mg/l
2100
4. Zinc (as Zn) mg/l, max. 5
5. Colour Absent
6. Biochemical Oxygen Demand, mg/l, max.(5 days at 20 º C)
30
7. Chemical oxygen demand, mg/l, max
250