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Effluent Treatment Process in Garment Manufacturing

Importance, merits, de-merits, techniques, technologies used in Textile Effluent Treatment Plants (ETP)

1 4,432

The textile industry is one of the leading sectors in the economy as it contributes to total industrial production. The untreated textile wastewater can cause rapid depletion of dissolved oxygen if it is directly discharged into the surface water sources due to its high BOD value. The effluents with high levels of BOD and COD values are highly toxic to biological life.

The high alkalinity and traces of chromium which is employed in dyes adversely affect the aquatic life and also interfere with the biological treatment processes. The quality of such effluent can be analyzed by their physicochemical and biological analysis. Monitoring of the environmental parameters of the effluent would allow having, at any time, a precise idea on performance evaluation of ETP and if necessary, appropriate measures may be undertaken to prevent adverse impact on the environment. The obtained results will be very much useful in the identification and rectification of operational and maintenance problems and they can be also utilized to establish methods for improvement.

Textile Effluent

Textile effluent and its management

Every country is aiming at Common Effluent Treatment Plants for the development of zero discharge solutions for the bleaching and dyeing units. The total effluent treatment capacity is designed based on the Mill size, based on the effluents generated in these mills.

Selection of technology and design for the engineering for the CETP is Pipeline for effluent conveyance, Pre‐treatment works, Reverse Osmosis plant, Evaporator plant, Recovered water distribution system and many more advanced technologies.

Textile Effluents and its management 

  • As textile industry is one of the largest industries in the world and different fibers such as cotton, silk, wool as well as synthetic fibers are all pre‐treated, processed, colored and after being treated using large amounts of water and a variety of chemicals, there is a need to understand the chemistry of the textile effluents very
  • The textile waste characteristic needs to be understood clearly
  • Different methods and aspects of Textile Effluents and their management to save the environment from polluting the same needs to be understood
  • Major pollutants in textile wastewaters are high suspended solids, chemical oxygen demand, heat, color, acidity, and other soluble substances whose chemistry will be emphasized

ETP Process Design for a Textile factory

Introduction

The textile industry is one of the largest and most complicated industrial chains in the manufacturing industry. The production of a textile requires several stages of mechanical processing such as spinning, knitting, weaving, and garment production, which seem to be insulated from the wet treatment processes like sizing, de-sizing, scouring, bleaching, mercerizing, dyeing, printing, and finishing operations, but there is a strong interrelation between dry processes and consecutive wet treatments. The textile industry emits a wide variety of pollutants from all stages in the processing of fibers, fabrics, and garment production

Stages of Textile Processing

 

Textile industry Share

Country Value in ($ billion) Share (%)
China 94.4 32.1
EU27 76.6 26.1
India 15.0 5.1
United States of America 13.8 4.7
Korea Republic 12.4 4.2
Turkey 10.8 3.7
Pakistan 9.1 3.1
Indonesia 4.8 1.6
Vietnam 3.8 1.3
Bangladesh 1.6 0.5
Rest of the World 51.7 17.5
Total 294 99.9

Textile production flow diagram

 

List of harmful Chemicals used in Textile Industry

  • Detergents mainly nonyl‐phenol ethylates‐ generates toxic metabolites which is poisonous to fish
  • Stain remover: Carry solvents like CCl4 can cause ozone depletion
  • Oxalic acid used for rust stain removal: are toxic to aquatic organisms and also boots COD
  • Sequestering agents: Polyphosphates like Trisodium polyphosphate and sodium hexametaphosphate: are banned chemicals
  • Printing gums: preservatives like pentachlorophenol can cause dermatitis, liver and kidney damage are all banned chemicals
  • Fixing agent: Formaldehyde and Benzidine are banned internationally
  • Bleaching: Chlorine bleaching caused itching and is harmful
  • Dyeing: Azo dyes which release amines are banned because they are known carcinogens

Textile Waste Characteristics

The pollutant features of textile wastes differ widely among various Organic substances such as dyes, starches, and detergents in effluent undergo chemical and biological changes which consume dissolved oxygen from the receiving stream and destroy aquatic life

Such organics should be removed to prevent septic conditions and avoid rendering the stream water unsuitable for municipal, industrial, agricultural and residential uses.

 

Process Wastewater Solid Wastes Emission
Fiber preparation Little or none Fiber waste and packaging waste Little or none
Yarn spinning Little or none Packaging wastes, sized yarn, fiber waste, cleaning, and processing waste Little or none
Sizing BOD, COD, metals, cleaning waste, size Fiber lint, yarn waste, packaging waste, unused
starch-based sizes
VOCs
Weaving Little or none Packaging waste, yarn, and fabric scraps used oil Little or none
Knitting Little or none Packaging waste, yarn, and fabric scraps Little or none
Tufting Little or none Packaging waste, yarn, and fabric scraps, off-spec fabric Little or none
Desizing BOD from sizes lubricants, biocides, anti-static
compounds
Packaging waste, fabric lint, yarn waste, cleaning and maintenance materials VOCs from glycol esters
Scouring Disinfectants, insecticide residues, NaOH, detergents oils, knitting lubricants, spin finishes, spent solvents Little or none VOCs from glycol esters and scouring solvents
Bleaching H2O2, stabilizers, high pH Little or none Little or none
Singeing Little or none Little or none Small amounts of exhaust gasses from the burners exhausted with components
Mercerizing High pH, NaOH Little or none Little or none
Heat setting Little or none Little or none Volatilization of spin finish agents- synthetic fiber manufacture

Types of textile waste produced

Process Possible Pollutants Nature of Effluent
Desizing Starch, glucose, PVA, resins, fats, and waxes do not exert a high
BOD.
Very small volume, high BOD (30-50% of total), PVA.
Kiering Caustic soda, waxes, soda ash, sodium silicate, and fragments of
cloth.
Very small, strongly alkaline, dark color, high BOD values (30% of total)
Bleaching Hypochlorite, chlorine, caustic soda, hydrogen peroxide, acids. Small volume, strongly alkaline, low BOD (5% of total)
Mercerizing Caustic soda Small volume, strongly alkaline, low BOD (Less than 1% of total)
Dyeing Dyestuff, mordant, and reducing agents like sulfides, acetic acids
and soap
Large volume, strongly colored, fairly high BOD (6% of total)
Printing Dye, starch, gum oil, china clay, mordants, acids, and metallic salts Very small volume, oily
appearances, fairly high BOD.
Finishing Traces of starch, tallow, salts, special finishes, etc. Very small volume, less alkaline, low BOD.

Sources of water pollution at various stages of processing.

Textiles and Garments are one of the oldest and largest industries in the world. The textile industries have great economic significance by virtue of their contribution to overall industrial output and employment generation in so many countries. The textile industry utilizes various dyes, chemicals, and large amounts of water during the production process. The wastewater produced during this process contains a large number of dyes and chemicals containing trace metals such as Cr, As, Cu, and Zn which are capable of harming the environment and human health. The textile wastewater causes hemorrhage, ulceration of skin, nausea, skin irritation, and dermatitis. The chemicals present in the water block the sunlight and increase the biological oxygen demand thereby inhibiting the photosynthesis and reoxygenation process

Country Value ($ Billion) Share (%)
China 94.4 32.1
European Union 27 76.6 26.1
India 15.0 5.1
United States of America 13.8 4.7
Korea Republic 12.4 4.2
Turkey 10.8 3.7
Pakistan 9.1 3.1
Indonesia 4.8 1.6
Vietnam 3.8 1.3
Bangladesh 1.5 0.5
Rest of the World 51.7 17.5
Total 294 99.9

Major Exporters of Textiles

Country Value ($ Billion) Share (%)
China 153.8 35.6
European Union 27 116.4 27.1
Bangladesh 19.9 4.6
India 14.4 3.3
Turkey 13.9 3.2
Vietnam 13.2 3.1
Indonesia 8.0 1.8
United States of America 5.2 1.2
Pakistan 4.6 1.1
Korea Republic 1.8 0.4
Rest of the World 79.8 18.5
Total 431 99.9

Water consumption in textile industries, by type of fabrics

Fabric Water consumption (kg/kg)
Cotton 250-350
Wool 200-300
Nylon 125-150
Rayon 125-150
Polyester 100-200
Acrylic 100-200

Water consumption in textile industries, by type of process

Process Water consumption (%)
Bleaching, finishing 38
Dyeing 16
Printing 8
Boilerhouse 14
Humidification (Spinning) 6
Humidification (weaving) 9
Sanitary, Domestic 9

Textile Wastewater Problem

  • Treatment of wastewater – will definitely reduce the waste, prevent and make positive effects on its further uses
  • Strong rinse waters from dye operations may be used to make up new dyebaths, while weak rinses may be recycled through in‐plant water treatment units
  • The savings in the material in the first case may be enough to pay for the cost of treatment of the latter case

Chemicals used in Textile Industry

  • Synthetic organic dyes, bleaches, and detergents Some chemicals are biodegradable‐ starch, however, others such as dyes are non-biodegradable Thus the effluents could have lower dissolved oxygen concentrations which means higher BOD and COD
  • Solids in textile wastewater come from the fibrous substrate and process chemicals, this disturbs the aquatic life by showing oxygen transfer and reducing light penetration

Inorganic chemicals

  • High concentrations of soluble inorganic salts may make the discharge water stream unsuitable for industrial and municipal use
  • Metals such as chromium and zinc are toxic to aquatic life and should be removed before discharge
  • Certain carrier chemicals used in dyeing, such as phenol may add bad taste and odor as well.

Effluent characteristics from the typical textile industry

Process Composition Nature
Sizing Starch, waxes, carboxymethyl cellulose, polyvinyl alcohol. High in BOD & COD
Desizing Starch, waxes, carboxymethyl cellulose, polyvinyl alcohol. High in BOD, COD, suspended
solids, dissolved solids.
Scouring Caustic soda, waxes, grease, soda ash, sodium silicate, fibers, surfactants, sodium phosphate. Dark-colored, High pH, COD, dissolved solids.
Bleaching Hypochlorite, Caustic soda, sodium silicate,
hydrogen peroxide, surfactants, sodium phosphate.
Alkaline suspended solids.
Mercerizing Caustic soda. High pH, low COD, high
dissolved solids.
Dyeing Various dyes, mordants, reducing agents, acetic acid soap Strongly colored, High COD,
dissolved solids, low SS
Printing Pastes, starch, gums, oil, mordants, acids, soaps. Highly-colored, High COD, oily
appearance, SS
Finishing Inorganic salts. Slightly Alkaline, low BOD.

Wastewater characteristics: Process-wise

Important Characteristics of Wastewater from Textile Industry

Parameter Range
pH 6-10
Temperature (°C) 35-45
Total d solids (mg/L) 8,000-12,000
BOD (mg/L) 80-6,000
COD (mg/L 150-12,000
Total suspended solids (mg/L 15-8,000
Total dissolved solids (mg/L) 2,900-3,100
Chlorine (mg/L) 1,000-6,000
Free chlorine (mg/L) <10
Sodium (mg/L) 70%
Trace metals (mg/L
Fe <10
Zn <10
Cu <10
AS <10
Ni <10
B <10
F <10
Mn <10
V <10
Hg <10
PO4 <10
Co <10
Oil and Grease (mg/L) 10-30
TNK (mg/L 10-30
NO3-N (mg/L <15
Free Ammonia (mg/L <10
Sulphate (mg/L 600-1000
Silica (mg/L <15
Total Kjeldahl Nitrogen (mg/L 70-80
Color (Pt-Co) 50-2,500

Some Textile wastewater pollution regulations are imposed by several countries.

Parameter CC ME China BIS Hong Kong FEPA ME X THA PHI IN DO BD SL
pH 6.5-
8.5
6-9 5.5-
9
6-10 6-9 6-
8.5
5-9 6-9 6-9 6.5-9 6-
8.5
Temperature
(°C)
30 50 43 40 40 40-45 40
Color (Pt-Co) 100 80 Non e 1
(Lovibon d)
1
(Lovibon d)
100-
200
30
TDS (mg/L) 200
0
2100 2000 2000-
5000
1200 2100 21
00
TSS (mg/L) 40 150 100 800 30 30-150 90 60 100 50
0
Sulphide
(mg/L)
200 100
0
2000 1000 200 1000 20
00
Free Chlorine
(mg/L)
100
0
1000 1000 1000
COD (mg/L) 80 200 250 2000 80 <12 5 120-
400
200-
300
250 200 60
0
BOD (mg/L 50 60 30 800 50 <30 20-60 30-200 85 150 20
0
Oil and Grease
(mg/L)
10 20 10 300 5-15 5 10 30
Dissolved
Oxygen (mg/L)
600
0
³4000 1000-
2000
4500-
8000
Nitrate (mg/L) 130
00
1000
0
20000 100
00
10000 45
00
0
Ammonia
(mg/L)
0.1 500 0.2 5000 60
Phosphate
(mg/L)
<40 00 100
0
500
0
5000 5000 200
0
20
00
Calcium (mg/L) 20000 20000 24
00
0
Magnesium (mg/L) 200
00
20000 15
00
0
Chromium
(mg/L)
1 100 100 <100 50 500 50-500 500 2000 50
Aluminium
(mg/L)
5 <1000 500
0
Copper (mg/L) <10 00 200
0
300
0
1000 <1000 100
0
1000 1000 200
0
500 30
00
Manganese
(mg/L)
5 200
0
2000 1000 5.0 200 5000 1000-
5000
5000 50
0
Iron (mg/L) 300 300
0
500 20000 100
0
1000-
20000
500
0
2000 10
00
Zinc (mg/L) 30 500
0
500
0
1500 <10000 100
00
5000-
10000
500
0
5000 10
00
0
Mercury (mg/L) 0.0
26
0.01 1 0.05 5 5 10 1

Note: CCME-Canadian Council of Ministers of the Environment, BIS-Bureau of Indian Standards, FEPA-Federal Environmental Protection Agency (USA), Mex-Mexico, Tha- Thailand, Phi-Philipines, Indo-Indonesia, Bd- Bangladesh SL-Srilanka
The removal of the processing units.

Items Raw Water (regulating Biochemical treatment system Physiochemical treatment system
tank) Effluen t Removal rate Effluent Removal rate
pH 8-12 7-8 6-9
CODcr (mg/L) 1000-2000 100-
200
90 £100 50
BOD5 (mg/L 300-600 15-30 95 £30
Color (times) 100-600 60 80 £40 35

PERMISSIBLE STANDARDS IN INDIA

S.No. Parameter Permissible limits
(disposal to inland surface water)
1 pH 5.5 to 9.0
2 TSS <100 mg/l
3 Oil & Grease <10 mg/l
4 BOD <30 mg/l
5 COD <250 mg/l
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