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