Manufacturing Practices, Waste Generation and Effluent Treatment in Textile Industries

2014 Centre for Environmental Technology Development, Demonstration and Dissemination (CETeDDD), IIT-M. Manufacturing Practices, Waste Generation an...
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2014

Centre for Environmental Technology Development, Demonstration and Dissemination (CETeDDD), IIT-M.

Manufacturing Practices, Waste Generation and Effluent Treatment in Textile Industries

-A Report on Textile Dyeing Units

CETeDDD, IIT-M 2014 CONTENTS Chapter I

Introduction 1. 2. 3. 4. 5. 6. 7. 8.

Chapter 2

The Indian Scenario Textile manufacturing process Textile dyeing Raw materials and chemicals used in textile wet processing Environmental impacts of textile dyeing Pollutants in textile waste water Wastewater characteristics Treatment of textile dyeing effluent

Case studies from Tamilnadu 1. Karur 2. Kancheepuram

Chapter 3

Best management practices for pollution prevention 1. Introduction 2. General methods for waste minimization in textile dyeing industries 2.1 Identifying the process 2.2 Reducing the water use 2.3 Reducing the chemical use 2.4 Reducing solid wastes 2.5 Reducing air emissions 3. Waste minimization in specific textile processes 3.1 Sizing 3.2 Desizing 3.3 Scouring 3.4 Bleaching 3.5 Singeing 2

CETeDDD, IIT-M 2014 3.6 Mercerizing 3.7 Batch processes 3.8 Dyeing 3.9 Printing 3.10 Finishing

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CETeDDD, IIT-M 2014

CHAPTER I

INTRODUCTION

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CETeDDD, IIT-M 2014 1. The Indian Scenario Textile industry contributes nearly 14 % of the total industrial production in India. There are about 10,000 garment manufacturers and 2100 bleaching and dyeing industries in India. The textile industry of India operates largely in the form of clusters with roughly 70 textile clusters producing 80% of the country’s total textiles. Majority are concentrated at Tirupur and Karur in Tamil Nadu, Ludiyana in Punjab and Surat in Gujarat.

State-wise distribution of textile industries Pondicherry West Benga Uttar Pradesh Tamil Nadu Rajasthan Punjab Orissa Maharashtra Madhya Pradesh Kerala Karnataka Jammu & Kashmir Himachal Pradesh Haryana Gujara Delhi Bihar Assam Andhra Pradesh 0

100

200

300

Fig.1 State-wise distribution of textile industries in India.

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400

500

600

700

800

CETeDDD, IIT-M 2014 2. Textile Manufacturing Process

Sizing

Desizing

Scouring

Bleaching

Finishing

Rinsing

Mercerizing

Dyeing

Fig. 2 The textile manufacturing process.

The processes followed in textile industries are spinning of fiber to yarn, sizing to improve stiffness, scouring, kiering and desizing to remove excess sizing materials, bleaching to remove pectin and wax from the yarn and fabric and coloring and printing to provide desired color and design to the cloth. Sizing Sizing is a process that adds strength and smoothing coating to the thread before it is woven into fabric There are two types of sizing agents: Natural sizing agents: starch and its derivatives, cellulose and its derivatives and protien based sizing agents Synthetic sizing agents: Polyacrylates, modified polyesters, polyvinyl alcohol based styrol/maleic acid coplymers Desizing

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CETeDDD, IIT-M 2014 Desizing is done to remove the sizes that have been attached to the yarns during the weaving process. Different methods for desizing are enzymatic desizing, oxidative desizing, acid steeping, rot steeping desizing with hot caustic soda treatment and hot washing with detergent. Scouring Fibres contain different impurities that can interfere with dyeing and finishing. Scouring is the process of removing these impurities. It can be done either with water or with solvents. Scouring agents include detergents, soaps, and various assisting agents, such as alkalis, wetting agents, defoamers, and lubricants. After scouring, the goods are thoroughly rinsed to remove excess agents. Bleaching Bleaching is commonly used to remove natural colouring from cotton, blend fabrics or yarn, and is sometimes required on wool and some synthetic fibres.. It has three technologies: sodium hypochlorite bleaching; hydrogen peroxide bleaching and sodium chlorite bleaching. Sodium hypochlorite bleaching and sodium chlorite bleaching are the most commonly used processes. Mercerising Mercerising improves strength, lustre and dye affinity of cotton fabrics. A cold sodium hydroxide solution is applied which causes the fibers to swell and adopt a circular cross section. The solution is washed away in an acid wash Dyeing Dyeing mainly aims at dissolving the dye in water, which will be transferred to the fabric to produce colored fabric under certain conditions. Finishing In the final stage, the fabric is subjected to various finishing processes in order to improve its specific characteristics like water proofing, fire resistance etc. 7

CETeDDD, IIT-M 2014 3. Textile Dyeing

Dyeing is the aqueous application of color to the textile substrates, mainly using synthetic organic dyes and frequently at elevated temperatures and pressures in some of the steps. There is no dye which dyes all existing fibers and no fiber which can be dyed by all known dyes. This process includes diffusion of the dye into the liquid phase followed by adsorption onto the outer surface of the fibers, and finally diffusion and adsorption on the inner surface of the fibers. Depending on the expected end use of the fabrics, different fastness properties may be required.

Dyeing can be carried out as a continuous or batch process. The most appropriate process to use depends on several factors, such as type of material, generic type of fiber, size of dye batch and quality requirements for the dyed fabric, but batch processes are more commonly used to dye textile materials. The dye can be fixed to the fiber by several mechanisms, generally in aqueous solution, and may involve primarily four types of interaction: ionic, Van der Waals and hydrogen interactions, and covalent bonds.

Ionic interactions result from interactions between oppositely charged ions present in the dyes and fibers, such as those between the positive center of the amino groups and carboxyl groups in the fiber and ionic charges on the dye molecule, and the ionic attraction between dye cations and anionic groups (-SO3- and –CO2-) present in the acrylic fiber polymer molecules. Typical examples of this type of interaction can be found in the dyeing of wool, silk and polyamide. Van der Waals interactions come from a close approach between the π orbitals of the dye molecule and the fiber, so that the dye molecules are firmly "anchored" to the fiber by an affinity process without

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CETeDDD, IIT-M 2014 forming an actual bond. Typical examples of this type of interaction are found in the dyeing of wool and polyester with dyes with a high affinity for cellulose.

Hydrogen interactions are formed between hydrogen atoms covalently bonded in the dye and free electron pairs of donor atoms in the center of the fiber. This interaction can be found in the dyeing of wool, silk and synthetic fibers such as ethyl cellulose.

Covalent bonds are formed between dye molecules containing reactive groups (electrophilic groups) and nucleophilic groups on the fiber, for example, the bond between a carbon atom of the reactive dye molecule and an oxygen, nitrogen or sulfur atom of a hydroxy, amino or thiol group present in the textile fiber. This type of bond can be found in the dyeing of cotton fiber.

The dyeing process involves three steps: preparation, dyeing and finishing, as follows:

1. Preparation 2. Dyeing 3. Finishing Preparation is the step where unwanted impurities are removed from the fabrics before dyeing. This can be carried out by cleaning with aqueous alkaline substances and detergents or by applying enzymes. Many fabrics are bleached with hydrogen peroxide or chlorine-containing compounds in order to remove their natural color. Finishing involves treatments with chemical compounds aimed at improving the quality of the fabric. Permanent press treatments, water proofing, softening, antistatic protection, soil resistance, stain release and microbial/fungal protection are all examples of fabric treatments applied in the finishing process

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CETeDDD, IIT-M 2014 4. Raw materials and chemicals used in Textile wet processing The raw materials for textile units include natural and synthetic fibers. Natural fibers are cotton, jute, flax, wool and silk. Synthetic fibers include rayon, polyester, polyvinyl derivatives etc. Natural Fibers Cotton

The white downy fibres clothing the seeds of the cotton plant.

Jute

Fibre obtained from the bark of plants from India and Pakistan. Traditionally used in the production of sacking, mats and carpet backing

Flax

Blue flowering plant, the stems of which provide the fibres used to make linen.

Wool

A fine, soft, wavy fibre with a scaly surface forming the fleece of sheep and goats.

Silk

A strong lustrous fibre produced by the silk worm.

Synthetic fibres Derivatives of oil

nylon, polyester, polyacrylonitrile, polypropylene and polyvinyl derivatives.

Semi-synthetic Rayon

semi-synthetic polymer made from cellulose.

Chemicals used in textile manufacture range from soaps and detergents to sizing agents and chemicals used to impart different properties such as water repellency, flame retardancy, crease resistance and easy care finishes. The following figure shows the use of chemicals in different stages of textile manufacture.

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CETeDDD, IIT-M 2014 Soaps, Detergent, alkali, wetting agents, lubricants etc

Hot water, Detergent

Size agents

Sizing

Desizing

Bleaching agent, water

Scouring

alkali

Bleaching

Mercerizing

Dye, Water, auxiliary chemicals

Specific property enhancing agents

Finishing

Rinsing

Dyeing

Fig. 3 Chemicals used in different stages of textile manufacture. The auxiliary chemicals used in textile wet processing is shown in the table below: Table 1. Auxiliary chemicals used in textile wet processing Description

Composition

Function

Processing step

Salts

Sodium chloride, Sodium sulphate Acetic cid, Sulphuric acid Sodium hydroxide, sodium carbonate Phosphates EDTA

Neutralize zeta potential of the fiber, retarder pH control

Dyeing

Acids Bases Buffers Sequestering agents, Chelates Surface active agents

Oxidising agents Reducing agents Carriers

Anionic, cationic and non ionic

Hydrogen peroxide, sodium nitrite Sodium hydrosulphite Sodium sulphide Phenyl Phenols, chlorinated benzenes

pH control pH control Complex hardness retarder Softeners, disperse dyes, regular dye application, wetting agents, emulsifiers Insolubilize dyes Solubilize dyes, remove unreacted dyes Enhance absorption

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Preparation, dyeing, finishing Preparation, dyeing, finishing Dyeing Preparation, dyeing Preparation, dyeing, finishing

Dyeing Dyeing dyeing

CETeDDD, IIT-M 2014 5. Waste water characteristics Textile manufacturing is among the major industrial water users. To produce one kg of textile fabrication about 200 liters of water is used. Pre-treatment wastewater accounts for about 45% of the total, and dyeing/printing process wastewater accounts for about 50%~55%, while finishing process produces little. Table 2. Waste water characteristics of textile industry

Property

Standard

Cotton

Synthetic

Wool

pH

5.5-9

8-12

7-9

3-10

BOD5 mg/L

30-350

150-750

150-200

5000-8000

COD mg/L

250

200-2400

400-650

10,000-20,000

TDS mg/L

2100

2100-7700

1060-1080

10,000-13,000

6. Environmental Impacts of Textile Dyeing Units

A large proportion of the environmental issues are related to the use and discharge of water in textile dyeing units. The textile dyeing industry is a water-intensive process that uses large quantities of chemicals and energy—and one that causes an enormous amount of unnecessary pollution. This is because it consumes large quantities of water and produces large volumes of wastewater from different steps in the dyeing and finishing processes. A lot of chemicals are added to the process for cleaning and dyeing purposes. Improving dyehouse performance provides a significant opportunity to reduce the environmental impact of textile production. 12

CETeDDD, IIT-M 2014 Wastewater from dyeing units is often rich in color, containing residues of reactive dyes and chemicals, such as complex components, many aerosols, high chroma, high COD and BOD as well as much more recalcitrant materials. The wastewater contains considerable amounts of hazardous pollutants, and heavy metals are very common. The presence of dyes in waste water has been pointed out by the CPCB as a critical pollution problem posed by the textile industries. This is because presence of even very low concentrations of dyes in effluent is highly visible and undesirable. During the dyeing process it has been estimated that the loss of colorants to the environment can reach 10–50%. Some dyes are highly toxic and mutagenic, and also decrease light penetration and photosynthetic activity, causing oxygen deficiency and limiting downstream beneficial uses such as recreation, drinking water and irrigation. Some of the hazards caused by the chemicals used in dyeing sector are listed below: Dyeing also contributes to air emissions. Many chemicals used in dyeing are volatile.

Detergents

Non-ionic detergent based on nonyl-phenolethoxylates

Non bio-degradable, generates toxic metabolites highly poisonous to fish

Stain remover:

Carry solvents like CC14

ozone depletion, ten times more than CFC

Oxalic acid

used for rust stain removal

toxic to aquatic organisms boosts COD

Sequestering agents

Polyphosphates like Trisodium, Polyphosphate, Sodium hexameta phosphate

banned in Europe still used in India and house hold detergents

Bleaching

Chlorine bleaching

itching, harmful

Dyeing

Amino acid liberating groups

carcinogenic, internationally banned

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CETeDDD, IIT-M 2014 7. Pollutants in Dye Wastewater

Quite a large amount of dyes leaves the process in an unfixed state, the exact amounts and kind of pollution depends on the used dyes and the used process. Dyeing contributes to most of the metals and almost all of the salts and colour present in the overall textile effluent. For some dyeing processes, about 75% of the salts end up in the wastewater. The main pollutants are organic matters which come from the pre-treatment process of pulp, cotton gum, cellulose, hemicellulose and alkali, as well as additives and dyes using in dyeing and printing processes. For dyeing wastewater, the first consideration is the organic pollutants, color and heavy metal ions. Heavy metals are typically used in textiles dyes to achieve brilliance in colours. Other minor sources of metals include impurities in materials other than dyes, including fibres, salts, caustic, and soda ash. Chromium concentrations in dyes with chrome as a formulation component vary from 3 to 83 parts per million (ppm). Chrome can be found in several dye classes or types, including acid dyes, pre-metallized dyes, and mordant dyes. Chromium may be present as an intentional component of dye formulation or it may be present as an impurity in dyestuff. Metals used in dye formulation may be “bound” or “unbound”. Bound metals are those in which the metal forms an integral structural element. An unbound metal is one that is not structurally bound to the dye molecule, but that simply exists in some quantity in the dye formulation. Not all dye wastes come from the dye bath; dye wastes also result from handling, weighing, small-scale routine working losses, implement and drum cleaning, and spills.

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CETeDDD, IIT-M 2014 8. Treatment of wastewater from dyeing units Each type of waste / waste stream represents an individual problem which can be solved only by taking into consideration the following factors: •

Local conditions



Dyestuff and chemical used



Amount and composition of the waste water



Local drainage conditions



Region



Main sewage channel



Sewage characteristics etc.

Effluents treatment plants are the most widely accepted approaches towards achieving environmental safety. However, no single treatment methodology is suitable for any kind of effluent treatment. Therefore, the treatment of waste stream is done by various methods, which include physical, chemical and biological treatment depending on pollution load. The treatment processes may be categorized into preliminary, primary, secondary and tertiary treatment process. Typical unit operations for effluent treatment includes: Preliminary and Primary Treatment Physical - equalisation, screening, settling Chemical - neutralisation, lime addition, alum addition, iron salt addition Secondary treatment Biological - activated sludge, extended aeration, lagoons Physical/chemical - powdered actvated carbon addition to biological process Tertiary treatment Physical - secondary clarification, mixed media filtration, ultrafiltration, granular activated carbon, powdered activated carbon Chemical - ozonation, chlorination 15

CETeDDD, IIT-M 2014 Typical Effluent Treatment Plant for Textile Dyeing Effluent:

Screening

Equalization/ neutralisation tank

Flash mixer

Clariflo cculator

Clarifier Sludge bed

Aerator

Aerator

Outlet

Fig. 4 Typical effluent treatment scheme for textile effluent. Any coarse and large particles are removed from the effluent by passing it through a bar screen. Then it enters an equalization/neutralization tank in which air is blown from the bottom to prevent settling of the suspended solids. The retention time of the effluent in this tank is normally 4 to 8 hours and during this time, hydrochloric/sulphuric acid can be dosed into the tank to adjust the pH. Then it is pumped to the flash mixer, where alum or any other coagulant solution is mixed and vigorously stirred by means of mechanical stirrers. The effluent is then sent to the clariflocculator, which is similar to an equalization tank, but circular in construction. here the effluent is retained for 8 hours, during which period most of the suspended solids (mostly inorganic settle down at the bottom of the tank. The sludge from the bottom of the tank is swept by a mechanical rake arm and is sent to sludge beds. The scum layer containing oil, grease, etc, floating on the surface is removed by a slow moving mechanical skimmer arm and is dumped into a scum chamber. The chemically treated effluent is then sent to the aerator for biological treatment. In two successive circular, open tanks fitted with surface aerator units, the effluent is vigorously churned and thereby the BOD is reduced due to intimate contact with 16

CETeDDD, IIT-M 2014 atmospheric oxygen. Optimum value of suspended solids is maintained by recycling some organic sludge from the succeeding clarifier using sludge pumps. Clarifier, the final unit in the effluent treatment plant, is also a circular , open tank. the effluent is held in the unit for about 8 hours. A portion of the settled sludge is sent back to the aeration tank and the excess sludge is sent to the sludge bed. The clear treated effluent flows by gravity into the drain. Sludge bed consists of graded metal layers with a thick layer of sand at the top. The excess water passes through the layers into the drain. The soil sludge is allowed to dry and is removed time to time. Before final disposal of sludge containi9ng hazardous materials like pesticides, chlorinated hydrocarbons, etc, it may have to be incinerated at a temperature of about 990-1480oC. Studies have shown that the most widely used aerobic digestion process using activated sludge does not fully degrade textile effluent, neither does it substantially reduce its toxicity. The effluents will require further treatments to eradicate the harmful components. The additional treatments include oxidation, adsorption or fine filtration.

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CETeDDD, IIT-M 2014

CHAPTER 2 CASE STUDIES FROM TAMILNADU

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CETeDDD, IIT-M 2014 Karur, TN.

Karur ,Tamil Nadu, India is an industrial town located on the bank of river Amaravathi. Cotton yarn bleaching and dyeing is one of the major industrial activities in Karur Town. The waste water let out from this industry is a major environmental concern. Out of 487 units, 391 units are members in common effluent treatment plant (CETP). 8 CETPs are in operation. The remaining 96 units have provided individual effluent treatment plant (IETP). After treatment the effluent is let into Amaravathi river a tributary of river Cauvery. Several studies have been carried out to assess the quality of effluent discharge from CETPs. The performance report reveals that the total dissolved solids, chlorides, bio chemical oxygen demand, and chemical oxygen demand are exceeding the permissible inland surface water discharge standards. The discharge of partially treated effluent has adversely affected the river water quality as well as the groundwater quality. In order to protect the river and the groundwater, Tamil Nadu Pollution Control Board (TNPCB) have directed all the dyeing units to provide Reverse Osmosis (RO) plant with Reject Management System (RMS) and recycle the entire treated effluent so as to achieve Zero Liquid Discharge (ZLD).

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CETeDDD, IIT-M 2014 Table 1 : Raw effluent quality of bleaching and dyeing units

pH TSS ppm TDS ppm BOD ppm COD ppm

6.91 - 7.86 120 - 268 5764 - 7120 53 - 172 248 - 352

CETP flow diagram, Karur, TN.

The current CETP outlet characteristics do not comply with the CPCB standards and requires proper management before it is discharged onto the land.

(Data and figures adapted from R. Rajamanickam and S. Nagan, 2010 and Marimuthu et al, 2013.)

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CETeDDD, IIT-M 2014 Kancheepuram, TN. Kancheepuram city in Tamil Nadu is another textile dyeing hub where there are both silk and cotton dyeing units. 60 tiny and small-scale dyeing units are located in the midst of residential areas, particularly along river Vegavathy in the Southern part of the town.

The effluent from silk dyeing units is directly sent to the sewer line where it gets mixed up with domestic waste water. Waste stabilization pond which was designed for the domestic waste water receives this mixed waste water. The cotton dyeing units are located in the North part of the city and the effluent from these units is sent to a CETP.

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CETeDDD, IIT-M 2014 Waste water characteristics of a cotton dyeing and silk dyeing unit in Kancheepuram, Table 2:

pH

Cotton Silk 6.9 7.18

EC µS/cm TDS ppm BOD ppm COD ppm Cr ppm

3115

1390

2025

904

573

1950

14365

6980

9.9

11.8

Quality of the treated effluent is shown in Table 3:

pH EC µS/cm TDS ppm BOD ppm COD ppm Cr ppm

6.78 2700 1755 300 600 13.1579

The current discharge parameters do not comply with the PCB standards and proper management of the waste water is required.

(Data and figures adapted from Indumathi et al, 2013.)

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CETeDDD, IIT-M 2014

CHAPTER 3

BEST MANAGEMENT PRACTICES FOR POLLUTION PREVENTION

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CETeDDD, IIT-M 2014 1. Introduction

Waste management involves two major components, pollution control and pollution prevention. Pollution control is commonly called the end of the pipe solution. This method is usually applied in an independent unit from the main production plant called “Effluent Treatment Plant”. In this method we treat the waste effluent after being generated by several chemical, physical and biological techniques in order to dispose it after that. This method is the most expensive .The other method is called the Preventive method, where we prevent the waste effluent from being generated in the first place either by source and strength reduction or by volume reduction. In the same time we manage its reuse and recycle. The preventive method is based on proper waste minimization techniques. Waste minimization is the application of a systematic approach to reducing the generation of waste at source. Waste minimization prevents the waste from occurring in the first place, rather than treating it once it has been produced by end-of-pipe treatment methods. Waste minimization is important because it reduces  operating costs  risk of liability and end-of-pipe treatment  improves process efficiency  enhances public image  protects health and environment and  improves employee morale. Waste is not only materials that are excess to requirements, but represents a loss of company profits. Waste minimization is achieved through source reduction by making process and product changes. Product changes include increasing product life, and designing for less environmental impact. Process changes include improved operating practices, improved housekeeping, change in raw materials, change in technology, in-house reuse or recycling. End-of-pipe treatment is only considered after source reduction.

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CETeDDD, IIT-M 2014 Waste Minimization

Input material changes

Source Reduction

Technological changes

Increasing Product life Designing for less environmental impact

Product changes

Process changes

Improved operating practices Improved housekeeping Process recycling

Raw material Changes: Input material changes for waste minimization can be achieved by material purification and substituting the materials with less toxic materials. Technological Changes: Major technological changes that can be adopted for waste minimization include  Layout changes  Increased automation  Improved process efficiency  Improved equipment performance and  Use of new technology

Improved operating practices:

The following are the methods that can contribute to improved operating performance:  Operating maintenance procedures 25

CETeDDD, IIT-M 2014  Management practices  Stream segregation  Material handling improvements  Product scheduling  Inventory control  Training  Waste segregation

Major challenges in implementing pollution prevention practices There are several challenges that a company face that prevent them from implementing pollution prevention practices. This could be due to one or more of the following barriers: 1. Financial barrier 2. Institutional barrier 3. Technical barrier 4. Regulatory barrier 5. Time barrier

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CETeDDD, IIT-M 2014 2. General Methods for Waste Minimization in Textile dyeing industries This can be broadly put into three main catogories as 1. Identifying the process 2. Reducing the chemical use and 3. Reducing the water use 4. Reducing Solid waste 5. Reducing air emissions

2.1 Identifying the process

Yarn

Alkali

Water

Soap

Bleaching agent

Water

Scouring/Deg umming

Bleaching

Acid

Auxiliary chemicals

Water with chemicals

Water with chemicals

Water

Dyeing

Dye

Water with chemicals

To Effluent treatment

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CETeDDD, IIT-M 2014 Scouring Scouring is done to remove hydrophobic components from the primary wall (e.g. pectin, protein and organic acids) and the cuticle (waxes and fats). The process also improves the water absorbency for uniform dyeing. The choice of scouring agents depends on nature of fibre and nature of impurities to be removed. The chemicals used in the process are alkalies (NaOH, Na2CO3 etc) and surfactants (anionic, cationic, nonionic). Conventional processes involves boiling the yarn in aqueous solution of NaOH and soap. Sometimes a combination of NaOH and Na2CO3 is also used. Even though alkaline scouring is effective and the costs of NaOH are low, the scouring process is rather inefficient because it consumes large quantities of water and energy. It is clear that this process needs to be improved considerably to meet today's energy and environmental demands. Degumming &Washing The process of removing gum (sericin) from silk is called degummimg. The gum content of silk varies according to quality and origin. The extent of degumming gives rise to different varieties of silk. During the degumming process, soil, stain, oil and fats sticking to the material will also be removed. Thus, degummimg is synonymous with the scouring process used for cotton. Degumming is effectd by careful treatment of silk with high pressure water, acids, alkalies, soaps and synthetic detergents. After degumming, the silk is thoroughly washed with lots of water at 50 to 60oC containing 1ml/L ammonia for 15 - 20 min. This is followed by rinsing baths.

Bleaching

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CETeDDD, IIT-M 2014 Bleaching is used to remove natural colouring from yarn. Used chemicals include sodium hypochlorite and hydrogen peroxide, as well as optical brighteners. Also some auxiliary compounds are used and released to the wastewater. Conventional bleaching involves the use of calcium or sodium hypochlorite. The use of chlorine containing bleach agents leads to the formation of highly toxic chlorinated organic by products (AOX) during the bleaching process as well as effluents discharged there from.

Dyeing During the step, the dyes and chemical aids such as surfactants, acids, alkali/bases, electrolytes, carriers, leveling agents, promoting agents, chelating agents, emulsifying oils, softening agents etc are applied to the textile to get a uniform depth of color with the color fastness properties suitable for the end use of the fabric. The water use in dyeing is high. Water is used not only in the dyeing process, but also for rinsing of the dyed products. Apart from dyes, different auxiliary chemicals that are used also end up in the wastewater.

2.2 Reducing the water use Establish the water balance This is the key step in identifying any opportunities in reducing the water usage. There should be a balance between the total water consumption and the total water discharge, taking into account all the evaporation losses, rainwater additions etc. This should be extended to individual processes also. Allocate water use to individual processes. For example: process water and ancillary water users. Identify options for reducing water usage

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CETeDDD, IIT-M 2014 This includes simple housekeeping techniques such as repair leaks and faulty valves, turning off running taps and hoses, turn off water when machines are not in use etc. Advanced water reducing options are also to be explored, like reducing the number of process steps, reducing the water use in each step and reusing the process water. The following steps can be taken as a guideline for reducing water consumption: 1. Repair leaks, faulty valves etc A simple method of determining if leaks exist is to take incoming water meter readings before and after a shut-down period when no water is being used. A difference in the readings could indicate a leak. 2. Turn off Running Taps and Hoses Encourage workers to turn off taps and hoses when water is not required. The fixing of hand triggers to hoses also reduces water consumption. 3. Turn off Water when Machines are not Running Encourage workers to turn off machines and water during breaks and at the end of the day. Avoid circulating cooling water when machines are not in use. 4. Reduce the Number of Process Steps This involves a study of all the processes and determining where changes can be made. For example, fewer rinsing steps may be required if a dye with high exhaustion is used. 5. Optimize Process Water Use Examples include using batch or stepwise rinsing rather than overflow rinsing, introducing counter-current washing in continuous ranges, and installing automatic shut-off valves. 6. Recycle Cooling Water Cooling water is relatively uncontaminated and can be reused as make-up or rinse water. This will also save energy as this water will not require as much heating. 7. Re-use Process Water This requires a study of the various processes and determining where water of lower quality can be used. For example, final rinse water from one process can be used for the first rinse of another process 8. Using Water Efficient Processes and Equipment 30

CETeDDD, IIT-M 2014 Although replacing outdated equipment with modern machines which operate at lower liquor ratios and are more water efficient requires capital investment, the savings that can be made ensure a relatively short pay-back period. 9. Sweeping Floors Instead of washing the floors of the dye house and kitchens, rather sweep up any spillages and wash down only when essential. Not only will this reduce water use, but also the concentration of contaminants to drain as the waste is disposed of as solids. 10. Reusing Water from Auxiliary Processes The water used in the rinsing of ion-exchange columns and sand filters can be reused elsewhere in the factory.

2.3 Reducing the chemical use The majority of chemicals applied to the fabric are washed off and sent to drain. Therefore, reducing chemical consumption can lead to a reduction in effluent strength and therefore lower treatment costs, as well as overall savings in chemical costs. Following steps can be adopted as simple options for reducing the chemicals use: 1. Recipe optimization Recipes are generally fail-safe designed which results in the over-use of chemicals. Optimizing the quantity of chemicals required will lead to more efficient chemical use and lower costs. Continual updating of recipes should be carried out when new dyestuffs enter the market as, in general, less of these chemicals are required.

2. Dosing control Overdosing and spillages can be reduced by mixing chemicals centrally and pumping them to the machines. Check that manual measuring and mixing is carried out efficiently and automatic dispensers are properly calibrated.

3. Pre-screen chemicals and raw materials Avoid dyestuffs containing heavy metals, solvent-based products and carriers containing chlorinated aromatics. Safety data sheets should be obtained from the chemical manufactures to 31

CETeDDD, IIT-M 2014 obtain information such as toxicity, BOD and COD. Check that raw materials do not contain toxic substances. Check that companies will accept expired raw materials for disposal.

Advanced options for reducing chemical use include: 1. Chemical substitution Review chemicals used in the factory and replace those hazardous to the environment with those that have less of an impact. Use dyes that have high exhaustion rates and require less salt. Specifically :  replace metal-containing dyes  use bi-reactive dyes in place of mono-reactive  avoid the use of APEO detergents and replace with more biodegradable alternatives  replace stilbene optical brighteners with alternatives, or eliminate altogether  dye wool with dyes that do not require after-chroming

2. Chemical recovery and reuse Chemical use may be reduced through recovery and reuse. For example, sodium hydroxide from mercerizing can be recovered through evaporation. Dye baths may be reused and size can be recovered for reuse.

3. Adopting improved technology Investigate the feasibility of changing to cleaner technologies. This results in less chemicals being used (and in particular, salt) and reduces water consumption significantly.

2.4 Reducing Solid Waste In terms of volume, solid waste is the second largest waste stream in the textile industry next to liquid effluent. There are a number of waste minimization options available to reduce solid waste, and these include :  Reducing the amount of packaging material by improved purchasing practices such as ordering raw materials in bulk or returnable intermediate bulk containers (IBCs). This reduces spillages, handling costs, exposure of workers to chemicals and the amount of storage space required. 32

CETeDDD, IIT-M 2014  Purchasing chemicals in returnable drums. Enquire if vendors will accept unwashed drums as this will reduce the waste water generated in the factory. If possible, ordering chemicals in IBCs rather than bags as these are easily broken, causing spillages.  Purchasing yarn on reusable plastic cones rather than cardboard cones.  Reducing seam waste through effective training programmes.  Selling waste fibers, sweeps, rags, yarn and cloth scraps.

2.4 Reducing Air Emissions Some steps to reduce the emissions to air include:  Decreasing emissions of organic solvents by changing to water-based products.  Using scrubbers to collect particulate matter.  Optimizing boiler operations to reduce the emissions of nitrous and sulphur oxides.  Pre-screening chemicals using the Material Safety Data Sheets to ensure that chemicals are not toxic.  Identifying sources of air pollution and quantifying emissions.  Designing and manufacturing products that do not produce toxic or hazardous air pollutants.  Avoiding fugitive air emissions from chemical spills through improved work practices.

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CETeDDD, IIT-M 2014 3. Waste Minimization in Specific Textile Processes 3.1 Sizing Size selection in sizing: Replace starch-based sizes with synthetic sizes. The advantages of this are a reduced pollution load as synthetic sizes have lower BOD levels and they can be recycled for reuse. Sizing raw materials: Test incoming raw materials for toxic compounds. Purchase size in bulk in drums rather than bags etc. as this produces less solid waste and reduces the chances of spills due to breakages. Sizing recipe optimization: Ensure that only the minimum required size is added onto the yarn. This reduces chemical consumption as well as the pollution load to drain during desizing.

3.2 Desizing The effluent from desizing will contain the sizes that were added onto the yarn before weaving/knitting. The presence of sizing ingredients in the fabric hinders processes, such as dyeing,

printing, and finishing. For example, the presence of starch can hinder the penetration of the dye into the fiber, which necessitates removal of starch prior to dyeing or printing. Starch is removed or converted into simple water soluble products either by hydrolysis (by enzymatic preparations or dilute mineral acids) or by oxidation (by sodium bromide, sodium chlorite, etc.) In general, about 50% of the water pollution is due to waste water from desizing, which has a high BOD that renders it unusable. The problem can be mitigated by using enzymes that degrade starch into ethanol rather to anhydroglucose. The ethanol can be recovered by distillation for use as a solvent or fuel, thereby reducing the BOD load. Alternatively, an oxidative system like H2O2 can be used to fully degrade starch to CO2 and H2O. Using and recycling synthetic sizes in place of starch sizes will reduce the pollution load from desizing.

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CETeDDD, IIT-M 2014 3.3 Scouring Incoming raw material should be screened for toxic chemicals as these will be removed during the scouring process. Detergents should be easily biodegradable. Avoid the following detergents: linear alkylbenzenesulphonate; nonylphenoletoxylate; dialkyldimthyl ammonium chloride; distearyl dimethyl ammonium chloride; dimethyl ammonium chloride; sulphosuccinates; alkylphenolethoxylates; complexing agents with poor biodegradability (eg, EDTA; phosphonic acid; NTA; phosphonates). Reuse scour washwater for desizing. Recycle continuous scour washwater to batch scouring.

3.4 Bleaching Natural color matter in the yarn imparts a creamy appearance to the fabric. In order to obtain white yarn that facilitates producing pale and bright shades, it is necessary to decolorize the yarn by bleaching. Hypochlorite is one of the oldest industrial bleaching agents. The formation of highly toxic chlorinated organic by-products during the bleaching process is reduced by adsorbable organically bound halogen (AO x). Over the last few years, hypochlorite is being replaced by other bleaching agents . An environmentally safe alternative to hypochlorite is peracetic acid. It decomposes to oxygen and acetic acid, which is completely biodegradable. One of the advantages of peracetic acid is higher brightness values with less fiber damage. The use of chlorites and hypochlorites can also be replaced with hydrogen peroxide. Ensure that bleaching is carried out efficiently. Recycle bleach wash water for scouring. Use vacuum slots to remove excess solution which can then be reused.

3.5 Singeing: Little or no pollution arises from singeing. Ensure that air scrubbers are installed to trap particles that are burnt off the fabric. Cooling water can be reused elsewhere in the factory. Remove lint from the pad solution to reduce the frequency of dumping.

3.6 Mercerizing: In order to impart luster, increase strength, and improve dye uptake, cotton fiber and fabric are mercerized in the gray state after bleaching. Essentially, mercerization is carried out by treating cotton material with a strong solution of sodium hydroxide (about 18–24%) and washing-off the caustic after 35

CETeDDD, IIT-M 2014 1 to 3 min, while holding the material under tension. Cotton is known to undergo a longitudinal shrinkage upon impregnation with this solution. This can be prevented by stretching it or holding it under tension. The material acquires the desired properties of luster, increased strength, dye uptake, and increased absorbency. The large concentrations of NaOH in the wash water can be recovered by membrane techniques. Use of ZnCl2 as an alternative method leads to an increase in the weight of fabric and in dye uptake, and allows easy recovery of NaOH. Moreover, the process is ecologically friendly and does not require neutralization by acetic or formicacid.

3.7 Batch processing: There are a number of waste minimization options for batch processing. These include cascading multiple rinsing operations. Reusing softening baths with reconstitution. Reusing preparation baths (scouring and bleaching) with reconstitution after filtration to remove impurities. Segregating coloured effluent streams from clean streams (preparation and rinsing) to ensure that only concentrated effluent is treated. This clean effluent may be used elsewhere in the factory. Installing automatic shut-down of water in overflow cooling when the required temperature has been reached. Replacing outdated machines with high liquor ratios with more modern equipment. Carrying out softening on a pad mangle. Replacing batch-wise rinsing with continuous rinsing with counter current flow.

3.8 Dyeing In the dyeing process, water is used to transfer dyes and in the form of steam to heat the treatment baths. Cotton, which is the world’s most widely used fiber, is a substrate that requires a large amount of water for processing. For example, to dye 1 kg of cotton with reactive dyes, 0.6–0.8 kg of NaCl, 30–60 g of dyestuff, and 70–150 l of water are required. Once the dyeing operation is over, the various treatment baths are drained, including the highly colored dye bath, which has high concentrations of salt and organic substances.

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CETeDDD, IIT-M 2014 According to USEPA, best management practices for pollution prevention in dyeing processes begin with careful selection of dye. Desirable features of a batch dye include:  high fixation  low toxicity  absence of metals  appropriateness for the intended end-use  correct and combatible application procedures and  high probability of right first time production

Careful selection of dyes is important. Dyes should have high fixation/exhaustion, low toxicity, absence of metals, and be appropriate for the end use. Correct and efficient application procedures must be used and right-first-time production should be achieved. The main areas for waste minimization include : Using low liquor ratios; Using automated dye and chemical dosing systems; Reusing dyebaths, rinse water and softening baths; Ensuring a good cloth preparation; Optimizing pH and salt for each recipe; Avoiding the use of auxiliaries that reduce or retard exhaustion; Using bireactive dyes; Using the newer low-salt reactive dyes; Optimizing dyeing temperatures; Avoiding the addition of more chemicals to offset the effects of other chemicals -- use other non-chemical methods such as procedural or mechanical alterations or change the dye selection; Replacing the use of acetic acid in neutralizing after dyeing with formic acid or dilute hydrochloric acid (acetic acid adds to the COD of effluent). In continuous dyeing, the key pollution prevention goals should be to :  maximize dye fixation  minimize wash off  avoid discards and machine cleaning waste during startup, stopoff and changes of colour and style. General pollution control measures include: •

operating at the lowest possible bath ratio 37

CETeDDD, IIT-M 2014 •

Minimizing redye procedures



Avoiding shading additions



minimizing the use of auxillaries



minimizing the use of water

The greatest costs in reprocessing are associated with the cost of dyes and chemicals -- typically, the costs can increase by as much as 30%. In dyeing polyester, avoid the use of carriers by upgrading dye machinery or replace with less harmful alternatives. Good fabric preparation increases the chance of right-first-time dyeing as fixation is improved. Dye fixation onto cotton can be improved by mercerising the yarn or fabric prior to dyeing.

3.9 Printing Printing is mainly done by a flat or rotary screen, and after every lot of printing some residual paste is left in the wastewater. This can be reused for printing of similar shades by adding new stock. Screenfree printing methods, such as ink-jet printing and electrostatic printing, have been developed that make use of an electronic control of color distribution on fabric. Screen-free printing methods are attractive for pollution mitigation. Pollutants associated with printing include suspended solids, solvents, foam, colour and metals, and in general, large volumes of water are consumed during the washing-off stages. The main areas of waste minimization in printing include raw material conservation, product substitution, process and equipment modifications, material handling, scheduling and waste recovery. Other options include: •

Waste minimization in the design stages can eliminate the need for dyes containing metals.



Careful selection of surfactants.



Reducing air emissions by replacing solvents with water-based alternatives.



Routine and careful maintenance of printing equipment.



Training employees in the practices of good housekeeping. 38

CETeDDD, IIT-M 2014 •

Reusing water from washing the print blanket.



Turning off wash water when machine is not running.



Installing automated colour kitchens.



Reusing left over print paste.



Removing excess paste from drums, screens and pipes by dry techniques (wiping with a squeegee, etc) before washing with water. This reduces the colour load discharged to drain.



Careful scheduling to prevent expiration of print pastes before use.



Investigating alternatives to urea as this increases the nitrogen in the effluent.

3.10 Finishing There are a number of finishing processes that are carried out on the fabric after dyeing and/or printing. These can be achieved by chemical or mechanical methods. Some waste minimization options are listed below : •

Design fabrics such that the need for chemical finishes are minimised.



Use mechanical alternatives to chemical finishes.



Use low add-on methods.



Minimize volatile chemical use.



Avoid mix discards through careful preparation.



Install automated chemical dispensing systems.



Train employees in good housekeeping practices.



Use formaldehyde-free cross-linking agents.



Reduce solid waste by reducing the need for selvedge trimming through



better width control, training workers and collecting selvedge trim for resale.



Investigate the use of spray application of finishes as these have a low add-on and require no residual dumping at the end of a run.

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CETeDDD, IIT-M 2014 References 1. 2. 3. 4. 5. 6.

7. 8.

9. 10. 11. 12.

13. 14. 15. 16. 17.

18. 19. 20. 21.

Water and chemical use in the textile dyeing and finishing industry, Environmental Technology Best Practice Programme, GG62 Guide. Dyehouse selection, NRDC, April 2012. Best practices for textile mills to save money and reduce pollution in bangladesh, NRDC, December 2012. Manual, Best management practices for pollution prevention in the textile industry, EPA/625/R-96/004. BAT guide for textile industry, T.C., Cevre Ve Sehircilik, Bakanligi, September 2012. T. Marimuthu, S. Rajendran, M. Manivanan, An analysis of efficiency and water quality parameters of dye effluent treatment plant, Karur, Tamilnadu, India, Journal of environmental science, computer science and engineering and technology, 2013, 2 (3), 567-571. R. Rajamanickam and S. Nagan, Performance study of common effluent treatment plants of textile dyeing units in karur, Tamilnadu (India), Journal of environmental research and development, 5 (3) 2010, 623-630. Dr Indumathi M Nambi, Dr K. P. Sudheer, Dr G. Suresh kumar, A comprehensive study for investigating wastewater reuse for agriculture in kancheepuram municipality, report submitted to IRAC, IAHR, Poondi, September 2013. Maruf Mahfuz, Effluent treatment plant process sequence in textile industry. Venceslau M. Correia, Tom Stephenson and Simon J. Judd, Characterisation of textile wastewaters- a review, Environmental technology, 15:10, 917-929. Bisschops and H. Spanjers, Literature review on textile wastewater characterisation, Environmental technology, 24:11, 1399-1411. Anju Singh, Richa Gautam and swagat kishore Mishra, Performance evaluation of a common effluent treatment plant treating textile wastewaters in india, Journal of environmental research and development, 5 (3A) 2011, 696706. Guide for assessment of effluent treatment plants, Department of environment, Ministry of environment and forest, Bangladesh, June 2008. Farrukh Rafiq, Environmental issues and challenges in indian SMEs with reference to leather tannery industry, National conference on emerging challenges for sustainable business, 2012. Chapter 6, Textile Dyes: Dyeing Process and Environmental Impact, Eco-Friendly Textile Dyeing and Finishing, Edited by Melih Günay, ISBN 978-953-51-0892-4, 260 pages, Publisher: InTech Chemical Technology in the Pre-Treatment Processes of Textiles, By S.R. Karmakar Environmental issues and its impacts associated with the textile processing units in Tiruppur, Tamilnadu. Jayanth sarathi N, Karthik R, Logesh S, Srinivas Rao K, Vijayanand K, 2011 2nd International Conference on Environmental Science and Development IPCBEE vol.4 (2011) © (2011) IACSIT Press, Singapore. Meenaz Hassanali, Pollution prevention practices in small and medium sized metal finishers, September 2005. Susan Barclay and Chris Buckley, Waste Minimisation Guide for the Textile Industry A Step Towards Cleaner Production, 2000, The Pollution Research Group, University of Natal, Durban, South Africa. http://www.indiantextilejournal.com/articles/FAdetails.asp?id=1431 https://www.cotton.org/journal/2007-11/3/upload/jcs11-141.pdf

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