Centra l Env i ronmen ta l Author i ty Parisara M a w a t h a

Maligawatta New Town C o l o m b o 10 SRI 1ANKA.

T e l e p h o n e No: 449455/6, 437487/8/9 Fax No: 01-446749

GOVERNMENT OF THE DEMOCRATIC SOCIALIST REPUBLIC OF SRI LANKA

I N D U S T R I A L P O L L U T I O N C O N T R O L G U I D E L I N E S

No. 6 — Textile Processing Industry

ISBN 955-9012-05-3 Rs 100.00

INDUSTRIAL POLLUTION CONTROL GUIDELINES-

Mo e Textile Processing Industry

CEA Library

06222 Prepared by the Central Environmental Authority With Technical Assistance from The Government of the Netherlands

1992/93

First edition 1992

>/\o>. U 2 No

6 x §

Published by the Central Environmental Authority Parisara Mawatha Maligawatta New Town Colombo 10 SRI LANKA

Telephone No:449455/6, 437487/8/9, 439073/4/5/6 Fax No: 01-446749

This document may be reproduced in full or in part with due acknowledgement to the Central Environmental Authority

ISBN 955-9012-05-3

Front Cover Design & concept by W A D D Wijesooriya Artwork by Somasiri Herath

024/waddw/guidee

PREFACE

The Government of Sri Lanka is promoting rapid industrialization in order to create better employment opportunities for the growing work force of the country, and to increase the income level of the people. At the same time the Government is conscious of the fact that some of the existing industries significantly contribute to the deterioration of the quality of the environment in the country, especially in the urbanised and industrialized areas. Ill-planned industrialization will no doubt accelerate the process of environmental degradation.

The Government has, therefore, introduced environmental legislation to enhance environmental protection and pollution control*. .The Central Environmental Authority (CEA) is the lead agency in the implementation and enforcement of the environmental legislation. It has initiated various programmes for the protection of the environment, with special attention on industrial pollution control.

The CEA has requested technical and financial assistance from the Government of The Netherlands for a number of projects in this field.

As a result technical assistance for a programme which consist of the following projects was provided by the Government of The Netherlands:-

1 D e v e l o p m e n t of environmental quality standards on the basis of designated uses .

2 . Development and updating of emission/discharge standards and pollution control guidelines for selected priority industries

3 . Feasibility studies on pollution control for priority industries or industrial sectors

4 . Study tour to The Netherlands for Sri Lankan officers involved in compliance procedures in the Environmental Protection Licensing Scheme (enforcement)

Under project No 2 above, industrial pollution control guidelines, were prepared for the following eight(8) industrial sectors, considered as major polluters in Sri Lanka:-

1. Natural Rubber Industry 2 . Concentrated Latex Industry 3 . Desiccated Coconut Industry 4 . Leather Industry 5. Dairy Industry 6. Textile Processing Industry 7. Pesticide Formulating Industry 8. Metal Finishing Industry

The main objective of the preparation of these guidelines was to assist the Central Environmental Authority in industrial pollution control with special reference to the introduction of the Environmental Protection Licensing Scheme.

In the preparation of these guidelines attention w a s focused on the generation of liquid, gaseous and solid wastes and their impacts on the environment. In the process aspects of industrial counselling, including in-plant measures to prevent and reduce waste generation and measures to improve occupational safety and health were also considered. Alternative methods were discussed for end-of-pipe treatment of liquid . gaseous and solid wastes .

Existing wastewater discharge quality standards were considered and intermediate standards ( with respect to the phased installation of treatment systems) were proposed in these guidelines.

The guidelines were mainly prepared on the basis of data available on industrial pollution and its abatement in sri Lanka, from studies and reviews carried out in the past and from missions to Sri Lanka specifically carried out for preparation of these guidelines.

The project was directed by Mr K G D Bandaratilake. Director of the Environmental Protection Division of the CEA, and coordinated by Mr W A D D Wijesooriya, Senior Environmental Scientist of the CEA. The CEA project team consisted of Mr C K Amaratunga and Mr S Seneviratne, Environmental Officers.

Technical assistance was given by a team of BKH Consulting Engineers, Comprises Dr I van der Putte (team leader), Mr J G Bruins and Mr H J F Creemers.

This document contains pollution control guidelines for Textile Processing Industry.

G K Amaratunga Chairman Central Environmental Authority

Contents

1. INTRODUCTION

Page

1

2. PRODUCTION OF FINISHED TEXTILE 2 2.1 Production data 2 2.2 Production processes 2

3. WASTE PRODUCTION AND ENVIRONMENTAL IMPACTS 7

3.1 Introduction 7 3.2 Liquid wastes 8 3.3. Gaseous wastes 9 3.4. Solid wastes 9 3.5. Environmental impacts 10

4. INDUSTRIAL COUNSELLING

4.1 Introduction 12 4.2 In-plant waste reduction 12 4.3 Improvement of occupational safety and health 14 4.4 Energy conservation 14

5. WASTEWATER TREATMENT 15

5.1 Introduction 15 5.2 Pretreatment methods 16 5.3 Separate treatment of process wastewaters 17 5.4 Physical/chemical treatment methods 17 5.5 Biological treatment methods 18 5.6. Wastewater treatment alternatives 20 5.7. Outline design of wastewater treatment plant for a cluster textile mills 24

6. AIR POLLUTION CONTROL AND SOLID WASTE DISPOSAL 28

6.1 Air pollution control 28 6.2 Solid waste disposal 28

7. DISCHARGE AND EMISSION STANDARDS 30

7.1 Wastewater discharge quality standards 30 7.2 Emission standards 30

8. REFERENCES 31

List of Annexes

Annex I Preliminary design of a central wastewater treatment plant for a cluster 32 of textile mills

Annex II Standards for industrial emissions in Thailand 36

1. INTRODUCTION

The textile and garments industry is the most important industrial sector in Sri Lanka. In 1990 the combined garments, textile and leather goods industry accounted for around 32% of the total value of the industrial production, and for around 32% of the value of the industrial exports. Direct and indirect employment in the textile and garments industry are estimated to be around 500,000.

The textile industry manufactures finished cloth from imported raw materials. Most of the locally produced cloth is used by the local garments industry.

Manufacture of finished cloth from raw fibre (cotton and synthetic) involves 3 major operations:

1. spinning; 2. weaving/knitting; 3. finishing.

Spinning and weaving are essentially dry processes and cause therefore relatively minor pollution problems. Significant pollution problems are, however, caused by the various finishing operations, including desizing, washing, scouring, mercerizing, bleaching, dyeing/printing and various types of final treatment processes.

The finishing processes consume large quantities of water producing substantial volumes of liquid waste which is a significant source of water pollution in Sri Lanka. The textile industry is also associated with significant occupational health hazards, such as exposure to noise, dust and obnoxious vapours.

This document describes guidelines for prevention and reduction of waste generation, improvement of occupational safety and health, wastewater treatment methods, air pollution control measures and solid waste disposal.

The wastewater discharge quality standards, as introduced by the Sri Lanka. Government are also discussed and some modifications for these standards and intermediate standards are proposed.

1

2. PRODUCTION OF FINISHED TEXTILE

2.1 Production data

In Sri Lanka 3 integrated textile mills and approximately 15 other textile mills are carrying out textile processing operations. In the integrated textile mills raw fibres are processed into finished cloth. In the other mills imported or locally manufactured raw cloth is processed into finished cloth.

General data on the "textile processing industry in Sri Lanka are summarized in table 2.1 (source: Environmental Protection Licence application forms, CEA).

2.2 Production processes

a) Manufacture of cotton fabrics

The textile industries in Sri Lanka produce fabrics from cotton fibres, synthetic fibres or mixtures of these fibres. The production processes for manufacture of finished cloth from the different types of fibre are described hereafter. The various stages in the textile production process using cotton as raw material are described below and shown schematically in figures 2.1 and 2.2.

The operations to convert cotton fibres into finished doth can be divided into the dry. processing operations and the wet processing operations. The subsequent process steps in the dry section are carried out without the use of water. During this process the cotton fibres are converted into gray cloth. In the wet processing operations the gray cloth is further processed into finished cloth by treatment in water baths with different solutions of chemicals. The subsequent operations, carried out for the manufacture of cotton fabrics, are:

Dry processes

Blowing: Cotton in bales comes to the blow room, where the fibres are loosened and excess dust is removed and the cotton is wound in rolls known as laps.

Carding: The raw cotton fibres are further cleaned and aligned parallel into a web, which is gathered together to form a sliver. Short fibres and dust are eliminated.

Combing: Optional process for high quality yarn. Slivers are combed to eliminate short fibres upto 1 /4 inches.

Drawing: Several slivers are combined to form a single sliver to improve strength and uniformity of yam. Blending of different fibres takes place at this stage.

Roving: The drawn yarn is dou^'^d and given a twist resulting in a single thread.

2

Spinning:

Winding:

Warping:

Wetting:

Sizing:

Weaving/knitting

Wet processes

Singeing:

Desizing:

Scouring:

Bleaching:

The yarn is further drawn and twisted and spun into bobbins.

The thread is wound onto cardboard cones. Defects in the thread are controlled and eliminated.

Mechanical stretching of fibres and setting onto beams in the pattern required for weaving.

The act of inserting the cross threads in the weaving process. The weft is wound previously onto pins.

The warp thread is treated with sizing agents such as starch in order to impart strength and stiffness which are necessary for the subsequent weaving operation. Antiseptics, penetrants, softeners, and other additives may also be added.

Yarn is woven or knitted into grey cloth.

When better quality smooth cloth is desired the producing fibres on the surface of the cloth are singed by flame treatment.

The size added in the weaving process is removed to prepare the cloth for dyeing and further processing, by hydrolysing the starch to glucose with acid (sulphuric acid) or enzyme treatment in the presence of penetrants (salt) for a period of 3 to 12 hours. The spent reagents, hydrolysed products and penetrants are removed by means of a water rinse.

Treatment with caustic soda and sodium carbonate at 100°C for a few hours removes natural and acquired impurities such as natural waxes, pectins, grease, oil, dirt etc. Penetrants may also be added to aid pectin in scouring operations. Resulting effluent after treatment is pale brown in colour. The cloth is washed and rinsed until no brown colour is retained in the rinse water. The continuous scouring method with steam drying is most commonly used.

Coloured impurities natural or acquired are removed in bleaching, which is achieved by treatment with sodium or calcium hypochlorite or hydrogen peroxide at 100 °C for 30 minutes. Hydrogen Peroxide is added when white cloth or yarn is desired. Penetrants are added to impart better contact. Subsequent rinsing removes all the waste.

3

Mercerising: Cloth to be dyed is treated with a cold caustic soda solution for a few minutes, while the cloth is kept under tension. Mercerizing swells the fibres and imparts fabric lustre and dye affinity of the cloth.

Dyeing: This process can be carried out in various ways, depending on the type of dye used and the method of application; e.g:

Dye is applied in the reduced state and oxidized. Used for cotton and polyviscose blends. Not used very commonly* in Sri Lanka.

Dye is applied in the reduced state and oxidized to develop the colour.

Aniline applied on cloth is oxidized by air or steam to develop the colour.

Coloured dye is applied directly on the cloth. These dyes are water soluble and mostly used for cottons and polyviscose blends.

The dye is synthesized on the fibre. The naphthol is applied to the~fabric and passed through a developer.

This method is used for nylon and polyester fibres.

This is a new development in the dyeing techniques. Tht colour results through chemical reaction with the fabric. Used mostly for cotton.

The methods in use are roller printing, screen printing (manual method is also in use) and the modern rotary screen printing which imparts a better quality print to the fabric. The dye is applied in the form of a paste. Printing paste may contain dye thickeners, hydroscopic substances, penetrates, binders, catalysts, water and other chemicals. Some of the chemicals used are starch, gums, synthetic resins, urea, emulsifying oils, (kerosene oil), di-ammonium phosphate etc.

Ageing: The dyed or printed cotton is aged in order to fix the dye by steam treatment or by other means.

Washing: Excess dye, penetrants, and binder on cloth are removed by washing with detergents and soap. This increases the colour fastness in the fabric.

Stentoring: Tension is applied to cloth by stretching to give dimensional stability to cloth.

Finishing: Depending on the finish tequired (e.g. crease, soft, water repellent etc) various agents are add<=d. Sizing with starch, polyvinyl acetate, addition of softeners, fungicides etc. are made at this stage.

Calendering: This is carried out when a shiny satin finish is required.

(1) Vat dyeing:

(2) Sulphur dyeing.

(3) Aniline dyeing:

(4) Direct dyeing:

(5) Naphthol dyeing:

(6) Disperse dyeing:

(7) Reactive dyeing:

Printing:

4

2.1 Data on production processes, products, capacity and workforce of industrial textile processing industries in Sri Lanka

N a m e of i n d u s t r y l o c a t i o n p r o d u c t i o n p r o c e s s P r o d u c t s a n d c a p a c i t y T o t a l w o r k f o r c e

N a g i n d a s Industry , Dehiwela

Ve lona G r o u p , K a t u b e d d a

K a b o o l L a n k a ( integrated) . Thulhir iya

B a k s o n Texti les, Ra tma lana*

H y b r o Industr ies, Ratmaiana

Swastik Text i les, Dehiwela

V e y a n g o d a Texti les ( integrated) , V e y a n g o d a

Dye ing t o f in ish ing Texti le p r o c e s s i n g

S c o u r i n g t o w e a v i n g / kni t t ing to f in ishing

S p i n n i n g to w e a v i n g / kni t t ing to f in ishing

B l e a c h i n g / d y e i n g t o f in ishing

Dye ing t o f in ishing

Weav ing t o f in ishing

S p i n n i n g t o w e a v i n g / kni t t ing to f in ishing

Fabr ics a n d curta in 150 mater ia ls

Fabr ics - 24 ,000 m / m o n t h 1320 G a r m e n t s - 360.000 p i e c e s / m o n t h

Y a r n - 90 .000 k g / m o n t h 3016 Grey c l o t h - 1.487,000 m / m o n t h F in ished fabr ics - 400 ,000 m / m o n t h

Fabr ics 10,000 m / d 240

Fabr ics 1,200,000 m / m o n t h 250

Fabr ics - 3000 m / d 681

Y a r n - 6 0 0 0 k g / d 2500 Fabr ics - 40,000 m / d

E s k i m o F a s h i o n Knit & Wear, N e g o m b o

K u n d a m a l , Ra tmalana

J .B . Text i les Industr ies, Wellamprirya

P u g p d a Texti les ( integrated) , P u g o d a

Dye ing Garments

W a r p i n g t o f in ish ing

S c o u r i n g t o f in ishing

S p i n n i n g t o w e a v i n g / kn i t t ing t o f in ish ing

G l o v e s - 2 m i l . p a i r s / a n n u m 1160 T igh ts - 5 m i l . p a i r s / a n n u m Pantyhose -2 5 0 , 0 0 0 / a n n u m

Fabr ics - 5,000 m / d 350

Synthet ic texti les - 8500 752 m / d N y l o n f ish ing nets a n d tw ine - 6 0 0 k g / d

Fabr ics - 60 ,000 m / d 3000

Cey lon Synthet ic Texti les, C o l o m b o

Sigir: W e a v i n g Mil ls, K a t u b e d d a

Fairl ine Text i les Industr ies, M o u n t Lavinia

As ian C o t t o n Mil ls L td , M o u n t Lavinia

Texti le P r o c e s s i n g Industr ies, Ja-Ela

Y a r n preparat ion W e a v i n g t o f in ish ing

Weav ing t o dry ing

Dye ing t o f in ish ing

D u r o Synthet ic Text i les, Kelaniya W e a v i n g t o f in ish ing

M K C Industr ies, Ja-Ela Dye ing to finishing

Sarees - 15,000 m / m o n t h Sui t ings - 125,000 m / m o n t h Shirr ing - 75,000 m / m o n t h Dress fabr ics - 1 5 0 , 0 0 0 m / m o n t h

Fabr ics - 5000 m / d

Fabr ics - 12,000 m / d

Fabr ics - 10,000 m / d

Fabr ics - 30 ,000 m / d

250

180

4 5 0

130

S o u r c e : Licence application forms (Ref. 1) n.a. = n o data avai lable 5

Raw Material

B l o w i n g

I C a r d i n g

C o m b i n g

Drawing

i R o v i n g

i S p i n n i n g

i W i n d i n g

Weft ing Warping i

Sizing

W e a v i n g / k n i t t i n g

I Cray Cloth

Figure 2.1 Dry process stage in textile manufacture

Gray cloth

I S i n g e i n g

I Oesiz ing

i S c o u r i n g

I B l e a c h i n g

i Mercer i z ing

i F r a m i n g Dye ing

i A g e i n g

Pr int ing

i A g e i n g

S ten tor ing

I Final T rea tment

I Ca lender ing

i Finished cloth

Figure 2.2 Wet process stages in textile manufacture

b) Processing of synthetic fabrics

The manufacturing process of textile from synthetic fibres, is basically the same as that of cotton textile manufacture. There are, however, some differences, which do have an important bearing on the nature of the pollution problem associated with the processing of synthetic fibres. Because of the poor moisture retention capacity in synthetic fibres, static electricity can be generated during spinning and weaving. Therefore fibres are treated with antistatics and lubricants. Since the dye affinity of synthetic fibres is very poor, either special carrier chemicals or dyeing at high temperature and pressure have to be applied.

A number of antistatics, lubricants and chemical carriers has been listed below:

Sizing agents/antistatics/lubricants Carriers

Polyvinyl alcohol Styrene based resins Polyalkaline glycol Gelatins

Phenol Meta creosol Paraphenyl-phenbl Aniline

6

3. WASTE PRODUCTION AND ENVIRONMENTAL IMPACTS

3.1 Introduction

In Sri Lanka three integrated textile mills carry out all three processes ot spinning, weaving and finishing, whereas approximately 15 plants carry out only the finishing of woven cloth.

Spinning and weaving are dry processes without any generation of wastewater. Finishing, however, is a wet process which generates significant quantities of waste­water. The volume and composition of the wastewater from the finishing processes depend on the type of fibre and on the type of process. Finishing of natural fibres (cotton and wool) generates much larger waste loads than finishing of synthetic fibres. Textile finishing consists of 3 main process steps:

- pretreatment - dyeing or printing - final treatment

Wastewater generation from these steps is briefly described below:

1. Pretreatment

Pretreatment of the woven cloth consists of desizing, scouring, bleaching and mercerizing (see Chapter 3). These processes generate relatively large quantities of wastewater with a high concentration of organics (BOD and COD), a high pH, and a high concentration of chlorine, in case hypochlorite has been used as a bleaching agent. The caustic soda, used for mercerizing, is recovered in many textile mills. These processes generate a wastewater volume of approximately 70 m 3 / t cloth. The organic waste load amounts to approximately 115 kg COD per tonne cloth (if 1 tonne cloth is equivalent to 10,000 m). These data are valid for typical textile mills in Sri Lanka, processing as well cotton as synthetic fibres.

2. Dyeing and printing

Wastewaters from these processes may contain considerable concentrations of dyes, heavy metals and other substances used tc optimize the process efficiency, such as salts and carriers (aromatic compounds).

3. Final treatment

The wastewater from final treatment operations contains residues of the chemicals used in these processes. Some of these chemicals, e.g. pentachlorophenol and permethrin (agents for protection against rot, moth and mould) are potentially toxic.

The wastewater volume from dyeing or printing and final treatment amounts to approximately 30 m 3 / t cloth. The organic waste load is about 25 kg COD per tonne cloth.

The composition of the wastewaters arising from the individual textile processing operations has been summarized in table 3.1.

7

Table 3.1 Composition ot wastewaters from the individual textile processing operations

Operation Effluent constituents

Desizing Enzymes, Acids, Sodium chloride (NaCI), Starch and Glucose.

Scouring Spent caustic soda (NaOH), Surfactant, Sodium phosphate (Na 3POJ, Natural organic substances (waxes, grease and oil).

Bleaching Sodium silicate, Sodium hydroxide, Sodium phosphate, Surfactant and Chelating agent. (Peroxide)

Bleaching (Hypochlorite)

Spent Hypochlorite, Sodium hydroxide, Sodium carbonate, Sodium sulphite, Oxalic acid.

Mercerizing Spent Sodium hydroxide, Suspended solids, (foreign material and wax) (This wastewater is generally concentrated and reused).

Dyeing and Printing

Organic acids, Acetic acid. Kerosene, Solvents, Pigments and Sodium carbonate.

Final Treatment Detergents, Starch, Resins, Chlorinated aromatic organic com­pounds

Liquid wastes

According to data extracted from the Environmental Protection License Application Forms, the wastewater volume from 14 textile processing industries (approximately 70% of the total number of major textile processing industries) amounts to approximately 8000 m 3 /d with a waste load of about 13,300 kg COD/d. The textile processing industries in Sri Lanka are probably the second polluters after the natural, rubber industry, which jointly generates a liquid waste load of about 45,000 kg COD/d.

Presently five textile industries are operating a wastewater treatment system or are constructing one. Two of these textile mills are constructing a biological treatment system which consists of a equalization/neutralization tank, an aeration tank, a secondary sedimentation tank and sludge drying beds. In one integrated textile mill such a system is in operation. This system has been extended with three polishing lagoons for post-treatment of the effluent.

Another integrated textile mill operates a wastewater treatment plant which consists of a series of ponds. Some of the ponds contain water hyacinths.

Very sophisticated wastewater treatment is applied in a garment factory in one of the export processing zones. The system, known as electro-chemical treatment, consists of an equalization tank, neutralization, a holding tank, 5 reactors with plate

consists of an equalization tank, neutralization, a holding tank, 5 reactors with plate tlectrodes and settling tanks. In the reactors the pollutants are oxidised and the beakdown products subsequently coagulate into settleable floes, which are then separated from the water in the settling tanks. The sludge is dewatered in filter prtsses.

3.3 Ga-.eous Wastes

Air pollution from the textile processing industries can be classified into two categories being stack emissions and vapours containing organic solvents from the dyeing and printing processes.

3.3.1 Stack Emissions

Sttam is used for various textile manufacturing processes. Oil fired boilers are used to generate steam. The emissions from the oil fired boilers contain Nitrogen Oxides(NOJ, Sulfur Oxides(SOJ and soot. Several methods are available in the industrialized countries, but these methods are not practised in Sri Lanka as yet. Sorre examples of available methods are: flue gas desulphurization (wet and dry prorasses) for SO, removal: low NO, combustion techniques; conversion of fuels (i.e. jse of lighter fuels); denitrification of flue gas for NO„ removal; and systems for collection of soot and dust from fluegas such as gravitational dust collectors, inertial separators, centrifugal collectors, filtrating collectors, wet collection devices and electric precipitation.

The methods which are practised most frequently in Sri Lanka are the efficient operation of oil fired boilers by ensuring a proper air/fuel ratio, thereby minimizing emissions of soot, and by the increase of stack height to mitigate nuisance from smoke particularly to residents around the factory.

3.3.2 Vapours from the dyeing and printing processes

These vapours, containing organic solvents, emanate obnoxious odours causing nuisance to the direct vicinity of the factories. Local exhaust ventilation systems are normally installed in the dyeing and printing sections, in such a way that the obnoxious vapours are sucked and subsequently boosted into the upper atnosphere.

3.4 Solid Wastes

Tertile mills produce relatively little quantities of solid wastes. The solid wastes originate mainly from the spinning and weaving processes as carried out in the integrated textile mills. These wastes are called "cotton waste", which consist of pieces of yarn and cloth. Generally the cotton waste is graded in Hie mill. The cotton waste with little dust is sold for domestic purposes. Considerable quantities of packing materials such as cardboard, polythene etc. may originate from the textile mills as solid waste.

Incineration of solid waste (i.e. cotton waste with dust and packing materials) is normally practised in the textile mills. In some textile mills these solid wastes together with firewood or saw dust are used in fire wood boilers.

9

In many textile and garment factories the solid wastes are collected by private contractors in order to be disposed of at official disposal sites, operaed and controlled by the Authorities. In many such cases however little is known o'the final destiny of the waste, due to the absence of proper disposal sites and tre lack of control by the Authorities.

The Colombo Municipal Council (CMC) is responsible for collection and disposal of solid wastes in the Colombo Municipal area. The solid wastes are collected by the municipal services or brought by the house holds to temporary collection sites. Low-lying lands are used as disposal sites. However much of the waste finds its way into drains and watercourses, where it causes deterioration of the water quality and exacerbates flooding.

3.5 Environmental impacts

Wastes arising from the textile processing industries may cause pollution of land, air and surface water. The environmental impacts of the textile processing industries are briefly described in the following.

3.5.1 Wastewater discharge

Wastewater from textile processing contains various components which are harmful for, the aquatic environment and are toxic for man and animal in the case of ingestion or physical contact (see table 3.1). Textile processing wastewaters contain oil and biodegradable organic compounds, which may cause anaerobic conditions in receiving surface waters, resulting in die off of fish and other water organsms and emission of foul odours.

Presently most textile processing industries discharge their wastewaters into the nearest surface water. A few factories have wastewater treatment facilities, but the treatment efficiency of the existing wastewater treatment systems is generaly low.

In many cases the textile processing wastewater is, after discharge, diluted to such a degree, that little or no damage to the receiving water is observed.

However in a number of cases the discharges of textile processing wastewater contribute significantly to serious pollution of surface water.

The most salient examples of surface water pollution, caused by discharges of industrial wastewaters of which textile processing wastewaters are the most important, are the Bolgoda Lake and the Lunawa Lake in the Ratmalana/Moratuwa area. Both lakes receive wastewater from the 5 textile processing industries in Ratmalana.

The Lunawa Lake, which is a tidal lagoon with brackish water, is already seriously polluted. The lake is unsuitable for fisheries or any other purpose. The environmental nuisance, caused by this lake, is however somewhat reduced by the periodic inflow of clean water from the Ocean.

10

The Bolgoda Lake is an inland lake, which has an important tupction for fishery and ^ recreation. Some parts of the lake are seriously polluted. ,due to discharges of 7 industrial and domestic wastewaters and also by illegal'-dumping of solid wastes along the embankments and in adjoining low-lying lands, if fffiffel degradation] of the lake continues, it will become completely unsuitable for tWpurposes , it is used for presently. \

3.5.2 Gaseous emissions

Gaseous emissions from textile processing industries generally cause little air pollution or nuisance (or the environment. However, complaints regarding nuisance caused by emissions of obnoxious vapours from textile processing industries have been made however by Ratmalana civilians living in the vicinity of these industries.

3.5.3 Solid waste disposal

Solid wastes arising from textile processing industries include pieces of yarn, pieces of cloth and packing materials such as polythene. In some of the textile processing industries these wastes are burnt in the open air within the premises of the industry causing nuisance to the surroundings.

In some other cases the solid wastes are dumped along the road sides or in drains or water courses, causing deterioration of the water quality and clogging ol drains and water courses.

11

4. INDUSTRIAL COUNSELLING

4.1 Introduction

The industrial counselling procedures are directed towards the introduction of environmentally sound technology ("clean technology"). Clean technologies contribute to more efficient production methods by saving energy and raw materials and reducing emissions to air, water and soil. They include good housekeeping measures, modification of production processes and raw materials use, as well as recycling of waste and process waters.

Industrial counselling aims at environmentally sustainable industrial development by promoting a combination of in-plant pollution control and end-of-pipe treatment in order to protect the environment and to optimize the conservation of energy and raw materials.

Additional advantages of the application of cleaner production processes are the reduction of safety hazards and the improvement of occupational health. Therefore, initial investments aimed at pollution control become more cost effective.

In this chapter in-plant pollution control measures and methods to improve occupational safety and health are proposed.

4.2 In-plant waste reduction

The production of waste from the textile processing operations can be prevented or reduced by numerous different measures. Such measures include replacement of toxic process chemicals by less harmful chemicals, process modifications and good housekeeping practices. A number of possible inplant measures to prevent or reduce pollution is discussed hereafter.

- Replacement of hypochlorite by hydrogen peroxide

Hypochlorite (NaOCI) used for bleaching, can be replaced by hydrogen peroxide (H202) for most bleaching operations. Hypochlorite has to be used only when a very high degree of whiteness is required and for bleaching of some types of artificial fibres.

- Recovery of caustic soda from mercerizing

The discharge of caustic soda (NaOH) from the mercerizing process can be reduced by concentrating the waste stream (by means of evaporation) to its original strength. The recovered caustic soda can be used in the production process.

- Recovery ot sizing agents

Recovery of Carboxy Methyl Cellulose (CMC), a synthetic sizing agent from spent sizing solutions is carried out successfully in textile processing plants.

Recovery of glucose from wastewater from starch desizing may also be a possibility to reduce the organic waste load from textile processing.

12

Reduction of waste from dyeing

By optimizing the dyeing process, the waste load can be reduced significantly. An example of a less polluting dyeing technique is direct dyeing in a jig. The applicability of this technique is however limited.

- Use of synthetic detergents instead of soaps

The organic waste load from textile processing can be reduced significantly by using synthetic detergents instead of natural oil based soaps. The use of synthetic detergents is now applied widely in the textile industry.

- Reduction of the water use

The water use for washing, as carried out after various process steps, can be reduced by applying counter current washing. In this process less polluted washing waters are re-used for washing. The use of water for dyeing and printing can be reduced by modifying the processes to some extent.

- Reduced use of chemicals for dyeing and printing

The use of dyeing and printing chemicals can be reduced by various methods for process optimization, e.g. reduction of the dye bath volume and application of computerized systems for mixing and addition. Dye stuffs and printing pastes can be reused in some cases (only for dark colours).

- Substitution of toxic carriers

In a number of dyeing techniques carriers have to be used in order to establish an adequate dye uptake by the cloth. Most carriers are complex organic compounds, including black list substances, such as di- and trichlorobenzene. Usefully mixtures of different carriers are applied. Most carriers are hard to biodegrade and toxic to some extent.

For these reasons it is preferable to apply dyeing techniques without the use of carriers and toxic carriers should be substituted by less toxic ones.

Good housekeeping practices

Waste loads from textile processing can be reduced by various good housekeeping practices. Such practices include the use of minimal quantities of process water and chemicals and washing water; avoidance of spillages; and separate disposal of spent dye and print baths.

Extensive studies have to be carried out before most of the above mentioned techniques for waste reduction can be applied at full scale in existing factories. It is therefore emphasized that these techniques can only be introduced in a long term programme in which all possible measures for waste reduction are studied step by step.

13

4.3. Improvement of occupational safety and health

Occupational safety and health aspects concern physical, chemical, biological and mental hazards and stresses present in the working environment. The improvement of occupational safety and health aims at the protection of workers at the workplace and its immediate environment against hazards such as heat, dust, noise, vibration, toxic chemicals, airborne pollutants, mechanical hazards, explosions and radiation. It also includes the adaptation of installations and processes to the physical and mental capacity of the workers.

Measures which could be adopted to improve occupational safety and health in the textile industry are discussed in the following.

Occupational health and working conditions in textile mills can be affected by dust, excessive noise and solvent vapours of organic solvents from printing and dyeing processes.

Exposure of workers to dust and fibres is mainly caused by bale opening, blowing, carding, spinning and weaving. Exposure to dust can be reduced by installing adequate ventilation systems and appropriate maintenance of these systems, and by providing protective equipment to the workers.

Excessive noise occurs mainly in the spinning and weaving sections. Noise problems could be solved by modernizing the machinery. The workers should be provided with protective equipment.

Exposure to vapours from organic solvents used in dyeing and printing can be reduced by installing suction hoods above the equipment in combination with adequate ventilation.

A large variety of toxic or dangerous chemicals is used in textile processing. Special measures have to be taken in handling and storage of dangerous chemicals. Contact with these chemicals should be avoided by providing proper storage facilities by careful handling and by using protective cloths.

4.4 Energy conservation

Large amounts of energy, including electricity and fuel oil for steam production, are used in textile mills. There are numerous possibilities to reduce energy consumption, including intensive control of electricity consumption (good housekeeping) and heat recovery from the boilers for steam production.

14

5. WASTEWATER TREATMENT

5.1 Introduction

Wastewater treatment systems ol textile processing industries generally consist of biological and physical/chemical treatment processes, or of combinations of these processes.

Wastewater from textile processing can also be discharged, after some pretreatment, into a municipal sewer system and subsequently be treated in a municipal wastewater treatment plant. Separate pretreatment of the different process wastewaters at the mill is also applied. In this case the pretreated wastewaters are combined into one flow and further treated in a central treatment plant, or discharged into a municipal sewer system.

Pretreatment methods, which are usually applied, are screening, neutralization and equalization. The most frequently used physical/chemical method, is coagulation/flocculation.

Other physical/chemical methods, which may be applied in case of very strict wastewater discharge quality standards, are activated carbon adsorption, membrane filtration and ozone oxidation.

Biological methods, used for treatment of textile processing wastewaters are activated sludge, aerated ponds, rotating biological contactors and trickling filters.

The choice of a wastewater treatment system depends on the local conditions and on a number of selection criteria, such as investment costs, operation and maintenance costs, system efficiency and reliability, availability of land, skilled personnel and local effluent discharge quality standards. Based on the local conditions the textile processing industries can be divided into 3 categories:

1. Industries characterized by an isolated location

Examples of such industries are the large integrated textile mills and a number of other isolated plants. These industries have or should have their own treatment facilities.

2. Industrial areas with only one textile processing industry amongst industries of other types

In such industrial areas it should be considered, whether the textile industry should install a pretreatment system, whereas the effluent of the pretreatment system is treated in a combined system with the (pre-treated) wastewaters from other industries in the area.

3. Industrial areas with a concentration of textile processing industries

Examples of such areas can be found in Ratmalana and in Ja-Ela. In the industrial area of Ratmalana 5 textile processing industries are in operation. These industries generate most of the industrial wastewater in this area (probably more than 90 %).

15

In such an area it should be considered to install a combined, plant for treatment of the textile processing wastewaters, and the wastewaters from other industries in the area.

A number of unit processes for pretreatment and separate treatment and a number of alternatives for combined wastewater treatment systems are described below.

5.2 Pretreatment methods

Textile processing wastewaters have to be pretreated before they can be treated by biological or physical/chemical methods. The type of pretreatment system, to be applied, depends on the type of treatment system that is selected for further treatment. Most commonly applied pretreatment methods are:

- screening - equalization

- neutralization.

These pretreatment methods are briefly described in the following.

Screening Screens are applied for the removal of coarse materials, such as pieces of cloth and yarn, from the wastewaters. The screens should be installed in the wastewater outlets from the separate production processes. Series of screens with gradually narrower mesh widths should be installed.

Equalization

Wastewaters from textile processing are often characterized by an irregular flow pattern. By storing the wastewater in an equalization tank it is possible to create an uniform flow rate to the following treatment step. Shock loads are prevented by equalization.

Equalization is not required if the following treatment step has a long retention time (more than 24 hours).

Neutralization

Some textile processing wastewaters (e.g. from scouring and bleaching) have a high pH (>10), and the combined wastewater generally also has a high pH (>9.5). Before the wastewater can be treated by a biological or a physical/chemical method, the pH of the wastewater should be reduced to a specific level. Reduction of the pH can be carried out by mixing the wastewater with flue-gases-from the boilers or by adding an acid solution.

The application of pretreatment for combined or separated wastewater flows is discussed further in chapter 5.6.

16

Separate treatment ot process wastewaters

Process wastewaters from the various textile production processes can be treated separately. This might be more effective and economical than combined treatment of all wastewaters, since the different unit processes of the separate treatment system are applied for specific concentrated waste streams, whereas diluted waste streams, requiring little or no treatment, are discharged directly or are treated in a central treatment plant.

A disadvantage of separate treatment is that such a system has much more system components than a combined wastewater treatment plant. Consequently the operation and maintenance of a separate system may be more complicated and the investment costs may be higher.

The application of separate treatment is further discussed in Chapter 5.6.

Physical/chemical treatment methods

Wastewaters from dyeing, printing and finishing processes (textile finishing wastewaters) contain pigments, (chlorinated) organic compounds, heavy metals and a great variety of other compounds, added in the production processes. Physical/chemical treatment processes are usually applied, when these wastewaters are treated in a separate system.

A number of physical/chemical treatment methods is briefly discussed below.

1. Coagulation/flocculation

In the coagulation process destabilization of the colloid particles in the wastewater takes place by means of addition of specific chemicals. As a result these particles grow into floes (flocculation). By adsorption of more colloidal and suspended substances the mass of the floes increases. The floes can be separated from the wastewater by sedimentation, flotation or filtration. Sedimentation is the most applied separation method. Coagulation/flocculation is an effective method for removal of phosphorus, micro-organisms, heavy metals and various other impurities. Coagulating agents, most frequently used in wastewater treatment are iron(Fe3*)- and aluminium(AI3') salts and lime. The flocculation process efficiency is improved by addition ol poly-electrolytes. A coagulation/flocculation system generally consists of a coagulation tank (with vigorous mixing of wastewater and coagulating chemicals, retention time of about 3 minutes); a flocculation tank (with slow mixing, retention time of about 20 minutes); and a sedimentation tank.

For treatment of textile finishing wastes by coagulation/flocculation approximately 300 mg/l Al-salt and 5 mg/l poly-electrolyte have to be added to the wastewater. According to literature data the COD removal efficiency of this process is approximately 40 %, and the colour removal efficiency 50-70 %. (lit. USEPA)

2. Activated carbon adsorption

In the activated carbon adsorption treatment process the wastewater is led through a filter of activated carbon granules.which are characterized by a very high specific surface. Impurities, especially organic molecules are removed from the wastewater

17

by adsorption to the surface of the activated carbon. This is an effective system for treatment of textile finishing wastewaters with a colour removal efficiency of approximately 90 %. (USEPA)

Prior to activated carbon adsorption the wastewater has to be pretreated to remove suspended solids and oil. Disadvantages of activated carbon adsorption are the complicated operation and the high costs. For these reasons this system is presently not considered as a feasible system for treatment of textile processing wastewaters.

3. Membrane filtration

Various membrane filtration systems are available for treatment of industrial wastewaters.

Best known membrane filtration systems are:

microfiltration, to remove particles with a diameter between 0.1 and 30 ultrafiltration, to remove particles with a diameter between 0.002 and 1 j i m hyperfiltration (or reverse osmosis) to remove dissolved particles

In membrane filtration the wastewater is pressed through the membrane, resulting in a diluted stream and a concentrated stream, which contains the impurities. Membrane filtration is an effective method for removal of heavy metals and organic pollutants. Prior to membrane filtration the wastewater often has to be pretreated for removal of suspended solids, pH adjustment or precipitation of dissolved particles. Due to the high costs of this system it is presently not considered feasible for treatment of textile finishing wastewaters.

4. Ozone oxidation

Ozone is a strong oxidizing agent. It degrades organics, which are non­biodegradable. As a result ozone oxidation is an effective method for removal of the colour from textile finishing wastewaters.

However due to the high costs of this process it is presently not considered feasible for treatment of textile finishing wastewaters.

5.5 Biological treatment methods

The following biological treatment methods are applied for treatment ot textile processing wastewaters:

- activated sludge - aerated ponds

- rotating biological contactors (RBC)

a) Activated sludge In the activated sludge process wastewater is led into a tank, where it is mixed with floes of aerobic micro-organisms (activated sludge). The mixture of wastewater and activated sludge is kept in suspension and aerated by mechanical aerators or by

18

supply of diffused air. Organic matter and suspended solids in the wastewater are absorbed by the active micro-organisms, which biodegrade the organic matter aerobically, utilizing it as a substrate for the growth of new cells and as a source of energy. As a result the quantity of sludge in the aeration tank increases. Part of the micro-organisms in the aeration tank is oxidized (endogenous respiration) into inert solids (mineralization).

The mixture is led from the aeration tank into a sedimentation tank, where the floes settle into a sludge. Part of the settled sludge is returned to the aeration tank in order to maintain a constant activated sludge concentration in the aeration tank. The remainder of the sludge (surplus sludge) is removed and disposed of.

Some different types of activated sludge wastewater treatment systems exist. The differentiation between the systems has been based on the organic loading rate of the system (kg BOD/kg dry sludge per day). High load, low load and ultra-low load systems are in use. Low and ulta-low load systems are generally preferred for treatment of textile processing wastewater, because of the better effluent quality and the higher reliability of these systems.

b) Aerated ponds

Various types of pond systems for treatment of wastewater exist: anaerobic ponds, facultative ponds, aerated ponds and maturation ponds.

In anaerobic ponds organic matter is biodegraded by anaerobic bacteria.

In facultative ponds aerobic biodegradation takes place in the upper layers of the pond and anaerobic biodegradation at the bottom. Oxygen is mainly-supplied by algae.

In aerated ponds the organic matter is biodegraded aerobically. Oxygen is supplied artificially, usually by means of mechanical surface aerators.

Maturation ponds are used to improve the quality of the effluents from other types of ponds.

Aerated ponds are the only type of ponds, which can be used for treatment of textile processing wastewaters, due to the high concentration of colour and of organics which are hard to biodegrade.

Two different types of aerated pond systems are applied in wastewater treatment:

Completely mixed aerated ponds

In this type of pond the whole contents are kept in suspension and in aerobic condition by mechanical action. The effluent of these ponds has a high concentration of suspended solids (including active biomass), and should be further treated in a settling tank or pond. Settled sludge may be recirculated to the aerated pond. Excess sludge has to be disposed of.

19

Facultative aerated ponds

In this type of pond only the top layers are kept in aerobic condition by mechanical action. As a result aerobic biodegradation of organic matter takes place in the top layers. The lower layers of these ponds are not affected by the mechanical aerators. As a result settling of suspended solids takes place in the lower layers. Anaerobic conditions prevail in the lower layers causing anaerobic biodegradation of settled organic matter.

c) Rotating biological contactors

A rotating biological contactor unit (RBC) consists of a porous filter medium mounted to an horizontal shaft. The filter medium provides a surface for the growth of a film of active micro-organisms. The RBC slowly rotates through a tank to which the wastewater is fed. During its rotation the RBC lifts up a quantity of wastewater, resulting in an intensive contact between the wastewater, the biomass on the filter surface and oxygen from the air. The film of micro-organisms absorbs organic matter from the wastewater, which is biodegraded aerobically in the process of substrate utilization by the micro-organisms for growth and formation of new cells. The effluent of the RBC tank is led into a sedimentation tank in which excess sludge, washed off from the contact surface, settles.

Discussion

All biological methods, described above, can be used for treatment of textile processing wastewaters.

The selection of a particular method depends greatly on the local conditions. The availability of land for installation of a wastewater treatment plant near the factory is one of the most important selection criteria. If ample land is available, the facultative aerated pond system may be chosen since this system is characterized by relatively low costs for investment and operation, and by simple operation and maintenance. If little land area is available, the RBC system may be chosen since this system requires the least land area of the three systems described above.

5.6 Wastewater treatment alternatives

After pretreatment or separate treatment of textile processing wastewaters the treated effluents can be combined into one flow and subsequently be discharged into a sewerage system and be further treated in a central wastewater treatment plant, that also treats wastewaters from other industries or municipal wastewater.

The textile mill may also install its own wastewater treatment plant for further treatment of the pretreated wastewaters. This will generally be the case if the mill cannot be connected to a central system, e.g. because of its isolated location.

For both possibilities a number of alternatives has been described in the following sections.

20

5.6.1 Discharge to a central wastewater treatment system

When it is possible to treat the textile processing wastewaters in a central wastewater treatment plant the following two alternative methods for pretreatment at the factory may be applied:

Alt. 1. Separate pretreatment

The separate treatment system consists of:

a) screening of desizing, scouring and bleaching wastewaters

b) physical/chemical treatment of dyeing, printing and final treatment wastewaters

This system consists of the following components: - screens - equalization - chemicals addition - coagulation - flocculation - sedimentation - sludge dewatering and drying

The effluents of a) and b) are combined into one flow and subsequently discharged to the central wastewater treatment plant. Alternatives for the central treatment system are not discussed in this report, since this subject does not belong to the scope of this study.

Alt. 2. Combined pretreatment of all textile processing wastewaters

This system is similar to Alternative 1.b).

Discussion

The selection of one of the alternatives depends on the type of the factory and on the proportion between the quantities of wastewater from desizing/scouring/ bleaching and from dyeing/printing/finishing. For integrated textile mills, with approximately equal quantities of both types of wastewater, Alternative 1 should be selected, since in this case the costs of Alternative 1 will be much lower than of Alternative 2, because of the smaller size of the system components and lower chemical requirements.

For other types of textile processing industries, with relatively little wastewater from desizing/scouring/bleaching, Alternative 2 should be chosen.

5.6.2 Complete treatment of textile processing wastewaters at the factory

If the textile mill has no possibility to discharge its wastewater to a central wastewater treatment, it has to install its own treatment facilities in order to be able to fulfil the effluent discharge quality standards (see Chapter 7).

A complete wastewater treatment plant generally consists of pretreatment, followed by physical/chemical and/or biological treatment.

21

Below a number of alternative systems for complete treatment of textile processing wastewaters at the factory has been described.

Alt. 1. Simple pretreatment and low-load activated sludge

All factory wastewaters are combined into one flow and are led, after screening and neutralization, into the aeration tank. Equalization is not required because of the long retention time in the aeration tank. Wastewater from personal use is led separately into the aeration tank. Addition of nutrients (Nitrogen and Phosphorus) to the wastewater may be required, to create the optimum proportion between organics and nutrients. This system tias the following components:

- screening - chemicals addition (pH correction and nutrients) - aeration tank - sedimentation tank with sludge recirculation - surplus sludge dewatering and drying

The effluent quality of this system fulfils the discharge quality standards for BOD and COD, but the colour removal of this system is little.

Alt. 2. Simple pretreatment and lacultative aerated pond

All processing wastewaters are combined into one flow, which, after screening, neutralization and nutrients addition is led into the facultative aerated pond. Wastewater from personal use is led directly into the facultative aerated pond. The effluent of the facultative aerated pond is led into a maturation pond, in which further biodegradation and settling of solids take place. This system has the following components: - screening - chemicals addition - facultative aerated pond - maturation pond

The effluent quality of this system fulfils the discharge quality standards for BOD and COD. As a result of the long retention time in this system colour removal is somewhat better than of alternative 1.

Alt. 3. Physical/chemical pretreatment and rotating biological contactors

All processing wastewaters are combined into one flow. After screening and equalization the wastewater is led into a coagulation/flocculation unit, and subsequently into a RBC unit. The wastewater from personal use is led directly into the RBC unit, preferably after pretreatment in a septic tank. This system has the following components:

- screening - equalization - coagulation, flocculation, sedimentation • septic tanks for pretreatment of wastewater from personal use - nutrients addition

- RBC's - sedimentation - sludge dewatering and drying

The effluent quality of this system fulfils the discharge quality standards for BOD and COD. Colour removal is better than of Alternatives 1 and 2.

Alt. 4. Separate pretreatment and rotating biological contactors

In this system the wastewaters from desizing/scouring/bleaching (stream A) and from dyeing/printing/finishing (stream B) are pretreated in separate systems. After pretreatment streams A and B are combined with the wastewater from personal use (stream C) into one flow (stream D), which is led into the RBC unit. This system has the following components:

Stream A : - screening equalization neutralization

Stream B : - screening chemicals equalization addition coagulation/flocculation/sedimentation sludge dewatering and drying

Stream C : - screening - septic tanks

Stream D : - nutrients addition - RBC's

sedimentation sludge dewatering and drying

This system results in the same effluent quality as Alternative 3. The advantage of Alternative 4 in comparison with Alternative 3 is the smaller chemicals use, but the disadvantage of Alternative 4 is the larger number of system components, resulting in more complicated operation and maintenance.

Alt. 5. Separate pretreatment and facultative aerated pond

This system is basically the same as Alternative 4 , but a facultative aerated pond is included instead of RBC's. This system is less complicated than Alternative 4 , since no equalization of stream A, and no septic tanks for stream C are required.

Alt. 6. Separate pretreatment and low load activated sludge

This system is also basically the same as Alternative 4 , but the RBC's have been replaced by a low load activated sludge process. Alternative 6 does not require equalization of stream A nor septic tanks for pretreatment of stream C.

23

Discussion

For textile processing plants with relatively little wastewater from desizing, scouring and bleaching one ot the alternatives 1, 2 or 3 may be chosen. The (inal system selection depends mainly on the availability of land, and on the local effluent discharge quality standards.

For integrated textile mills one of the alternatives 1, 2, 4, 5 or 6 may be chosen, also depending on availability of land and local effluent discharge quality standards.

The advanced physical/chemical treatment methods, described in section 5.4, have not been included in the alternative treatment systems, because of the very high costs of these processes. Application of these methods is presently not considered feasible.

5.7. Outline design of a wastewater treatment plant for a cluster of textile mills

In section 5.1 is described that the selection of a wastewater treatment system mainly depends on the type and location of the mill. An example design of a wastewater treatment system for a cluster of textile processing mills, to be installed in 2 stages, has been described in the following sections. The system is equivalent to alternative 3 (see chapter 5.6), but low load activated sludge is applied instead of RBC's.

This system was selected for this example design, because it has already proven to be an efficient system for treatment of textile processing wastewaters in other countries.

The wastewater treatment plant to be installed in 2 stages has the following components:

Stage 1

- collection sump and screens

All wastewaters are pumped (or flow by gravity) into the collection sump, in which the wastewater passes through screens to remove coarse materials. (The wastewaters from the individual factories should also be screened before entering the sewerage system to prevent clogging of it.)

equalization/neutralization tank

From the sump the wastewater is led into the equalization/neutralization tank, in which the wastewater is mixed and an acid solution is added in order to reduce the pH of the usually alkaline textile industry wastewater. The pH is corrected to a optimum value for the following process step (to be determined by experiments).

- oil trap

The wastewater is pumped with a continuous equal flow into the oil trap in order to remove oil arid, crease. * •

24

coagulation tank

The wastewater flows into the coagulation tank where the wastewater is mixed with coagulating chemicals.

- flocculation tank

The wastewater flows into the flocculation tank, where floes are formed. The contents of the flocculation are stirred slowly. The flocculation process can be improved by adding poly-electrolytes.

sedimentation tank

The wastewater flows into the sedimentation tank where the floes settle into a sludge. The sludge is drawn off at the bottom of the tank and subsequently led into a sludge holding tank for storage and thickening of the sludge. From this tank the sludge is pumped into the sludge drying beds for dewatering and drying. The supernatant from the sludge holding tank is recycled to the collection sump. The effluent is discharged to the selected receiving water or led into the aeration tank of the secondary treatment plant (Stage 2).

The dewatered and dried sludge is removed at regular intervals and disposed of to a solid waste disposal site, approved by the Authorities.

Stage 2

aeration tank

The effluent of the sedimentation tank flows into the aeration tank where it is mixed with activated sludge and aerated by mechanical action.

Nutrients (N and P) may have to be added to the wastewater for optimum performance of the activated sludge micro-organisms.

secondary sedimentation tank

The mixture of wastewater and activated sljdge flows into the secondary sedimentation tank where the sludge is separated from the water. Part of the sludge is recycled to the aeration tank. The excess sludge is led into drying beds. The dried sludge is transported to an approved solid waste disposal site. The effluent is discharged.

A lay-out of the wastewater treatment plant has been shown in Figure 5.1 (Stage 1) and in Figure 5.2 (Stage 2).

* The preliminary design is described in more detail in Annex I.

25

P r o c e s s w a s t e w a t e r s

C o l l e c t i o n s u m p

E q u a l i z a t i o n

N e u t r a l i z a t i o n

ft

-©

O i l t r a p

C o a g u l a t i o n

F l o c c u l a t l o n

L e a c h a t e t r o m s l u d g e d r y i n g b e d s

S u p e r n a t a n t

t o S l u d g e d r y i n g b e d s

S l u d g e h o l d i n g t a n k

S l u d g e

E f f l u e n t d i s c h a r g e o r t o S t a g e 2

S e d i m e n t a t i o n t a n k

0 200 400 600 800 Cm

Figure 5.1 Lay-out of wastewater treatment plant (Stage 1)

26

E f f l u e n t f r o m S t a g e 1

r e c y c l e

A e r a t i o n t a n k

t o S l u d g e h o l d i n g t a n k

( S t o g e 1)

S l u d g e

S e d i m e n t a t i o n t a n k

E f f l u e n t d i s c h a r g e

0 200 400 600 800 Cm ' ' I I I

Figure 5.2 Lay-out of wastewater treatment plant (Stage 2)

6. AIR POLLUTION CONTROL AND SOLID WASTE DISPOSAL

6.1 Air pollution control

The problems, related to gaseous emissions, consist mainly of adverse effects on the health of the factory workers due to inadequate ventilation, which results in exposure to dust and obnoxious vapours from printing and dyeing operations (see Chapter 4). Complaints on exposure to these vapours have also been made by civilians living in the vicinity of textile processing plants (as in Ratmalana). This is mainly caused by the direct emission of these vapours into the air without application of a stack of sufficient height.

Textile mills often burn their solid wastes in the open air, which in some cases causes nuisance for the neighbourhood and for the mill itself. Other textile mills employ contractors to collect and dispose of their solid wastes. This is often practised in an irregular and uncontrolled manner, characterised by dumping of wastes at illegal sites such as embankments of water courses, where it damages the quality of the environment.

The problems related to gaseous emissions and solid wastes can be mitigated by relatively simple measures and by better control by the authorities.

The exposure to dust and vapours in the factory can be reduced by installation of better ventilation and suction equipment in the dyeing and printing sections. The ventilated air should be treated by dust collectors before emission into the air. The gases, collected by the suction equipment should be treated by gas scrubbers, and subsequently be emitted into the air by a stack of sufficient height, in order to enhance adequate dilution of the vapours, still present in the emitted gases.

It is adopted as a general rule for boilers that the stack height should be 216 times the neighbouring building height. With a minimum of 9 meters. The minimum stack height can also be calculated from the emission load.

The following relation exists between stacklight (H) and the amount ot gaseous emissions (Qg):

H = (H in meters, Q g in kg/hr)

For emissions of particulate matter (Q.J the following formula can be used to calculate the minimum stack height:

H = 74 (Qp)0'27 (H in meters, Q p in tonnes/hr)

6.2 Solid waste disposal

Burning of solid wastes in the open air should be stopped. A regular system for solid waste collection and transport to authorized disposal sites should be developed on responsibility and under supervision of the local authorities.

The waste sludges from the wastewater treatment plant, particularly when physical/chemical treatment is carried out, should be treated as toxic waste. Hazardous waste disposal sites should be allocated, controlled and maintained by the authorities.

29

DISCHARGE AND EMISSION STANDARDS

Wastewater discharge quality standards

The Government ot Sri Lanka has set specific quality standards for the discharge of textile industry wastewater into inland surface waters. These standards are given in Table 7.1

Table 7.1 Quality standards for discharge of textile industry wastewater into inland surface waters (maximum allowable levels)

PH 6.5 to 8.5 Temperature 40° C BOD 50 mg/l COD 250 mg/l Oil, grease 10 mg/l Phenolic compounds 1 mg/l Sulphides 2 mg/l Chromium, total 2 mg/l Chromium, hexavelant 0.5 mg/l Copper 3 mg/l Zinc 5 mg/l Ammonium Nitrogen (N) 60 mg/l Chloride 70 mg/l

The maximum allowable BOD concentration can only be achieved by complete biological treatment. Since complete biological treatment presently is not feasible for most textile processing industries, it is considered that the present standards are not realistic.

Intermediate standards with a BOD of 150 mg/l and a COD of 600 mg/l are proposed for the operation of the first stage treatment system consisting of physical/chemical treatment. The present standards do not specify any value for the colour intensity of the wastewater to be discharged. Since the colour of textile processing wastewater is an important problem, it is considered to develop also a standard for the colour of the wastewater to be discharged.

Emission standards

In Sri Lanka no standards have been set for gaseous emissions into the atmosphere. Boilers, used in the textile industry for the production of steam, generate emissions containing nitrogen oxides, sulphur oxides and soot.

In addition organic solvents from the dyeing and orinting processes cause emissions of obnoxious vapours. Therefore it is useful to refer to existing "Industrial Emission Standards" for specified sources, as proposed for Thailand by the Thailand Ministry of Industry. These standards are provided in Annex II (Ref. 6).

REFERENCES

1. Feasibility studies on pollution control for priority industries in Sri Lanka: The textile industry. Central Environmental Authority, Sri Lanka, 1991

2. Environmental aspects of textile industry in Sri Lanka, NBRO-Environmental Series-ll, Sri Lanka, 1987

3. Annual survey of industries. Dept. of Census and Statistics, Sri Lanka, 1990

4. Review of industrial pollution regulation in Sri Lanka, BKH Consulting Engineers, The Netherlands, 1991

5. Environmental Guidelines, Environment Department, World Bank, Washington, 1988

6. Laws and Standards on pollution control in Thailand, 2nd ed., Environmental Quality Standards division, office of the National Environment Board, Thailand, 1989.

7. Industrial Water Pollution, N.L Nemerow, Addision & Wesley, 1978

8. Emission regulations part IV, Central Board for the Prevention and Control of Water Pollution, New Delhi, 1987.

31

ANNEX I

PRELIMINARY DESIGN OF A CONTROL WASTEWATER TREATMENT

PLANT FOR A CLUSTER OF TEXTILE MILLS

DESIGN PARAMETERS

For preparation of the preliminary design data on wastewater volumes and composition, data provided by the industries in their Environmental Protection Licence application forms have been used. On the basis of the above mentioned data the following wastewater characteristics have been used tor the preliminary

Wastewater flow PH COD

DESIGN CRITERIA

1065 8.5

1270

m 3 /d (45 m 3/h)

mg/l

The following design criteria for calculating the dimensions of the various plant components have been used.

- equalization tank volume

- oil trap retention time

- coagulation tank retention time mixing power

• aluminium salt addition

• polyelectrolyte addition

• flocculation tank retention time mixing power

sedimentation tank surface loading rate retention time

aeration tank sludge loading rate

concentration

oxygen requirement 1. substrate oxidation 2. endogenous respiration Aerator performance Sludge production

Required ratio COD/ nutrients

60% of daily flow

2 h

3 200

minutes W/m 3

300 mg Al per litre wastewater (optimum addition to be determined by tests)

5 mg per litre wastewater (optimum to be determined by tests)

20 50

minutes W/m 3

0.5 m 3 /m7h 2 h

0.35

0.25 0.15

1.3 0.5

COD

kg COD/kg dry solids/d sludge dry solids kg/rri3

kg 0 2 / k g COD k 9 ° 2 / k g dn/ solids in aeration tank kg 0 2 /kW.h kg dry solids per kg COD removed minus 0.04 kg dry solids per kg dry solids in aeration tank N : P = 250 : 5 : 1

33

secondary sedimentation tank surface loading rate retention time

0.5 m 3 /m»/h 2 h

sludge drying beds drying time 20 d sludge depth in bed 0.2 m

PRELIMINARY DESIGN OF THE CENTRAL WASTEWATER TREATMENT PLANT

The dimensions of the various components of the wastewater treatment plant are the following:

Stage 1

1. Collection sump Volume 30 m 3

Depth 3.5 m Pump capacity Screens

2. Equalization/neutralization tank Volume 640 m 3

Depth 4 m Pump capacity 45 m 3 /h Chemical addition equipment

3. Oil trap Volume 90 m 3

Depth 1.5 m Length 12 m Width 5 m

4. Coagulation tank Volume 2.5 m 3

Mixer 0.5 kW Chemical addition equipment

5. Flocculation tank Volume 15 m 3

Depth 1 m Length 6 m Width 2.5 m Mixer 0.75 kW

6. Sedimentation tank Surface area 90 m 2

Volume 200 m 3

Depth 6 m Sludge production 1.5 t/d (30 m 3 /d) Effluent COD 550 mg/l

34

7. Sludge holding tank Volume Depth Reduction of sludge volume to Sludge pump capacity

100 m 3

3 m 20 m 3

10 m 3 /h

8. Sludge drying beds Surface area 2000 Recirculation of leachate to collection sump

Stage 2

9. Aeration tank Nutrient addition equipment Waste load Sludge quantity Tank volume Depth Length Width COD removal (70 %) Sludge growth Oxygen requirement

Aeration capacity

10. Secondary sedimentation tank Dimensions as item no. 6 Sludge recirculation pump capacity Sludge wastage

580 1680 420

3 17.5

8 400 130 390

15

2*50 130

Sludge is wasted to drying beds of Stage 1 Effluent COD 150

kg COD/d kg dry solids m 3

m m m kg/d kg/d kg Oj/d (17 kg/h) kW

m 3 /h kg/d (20 m 3 /d)

mg/l

ANNEX II

STANDARDS FOR INDUSTRIAL EMISSIONS IN THAILAND

A n n e x " s , a n d a r d s for industrial emissions in Thailand (Ref. 6)

Substances Sources

Particulate

Smoke opacity

Aluminium

Alcohol Aldehyde Ammonia Antimony Aromatics Asbestos Arsenic Beryllium Carbonyls Chlorine Ethylene Ester Fluorine Hydrogen Chloride Hydrogen Fluoride Hydrogen Sulphide Cadmium Copper

Lead

Mercury CO SO,

NO,

Nitric acid Organic material Phosphoric acid Sulfur trioxide

Sulfuric acid

- Boiler & furnace Heavy oil as fuel Coal as fuel

- Steel manufacturing - Cement plant and calcium

carbide plant - Rock and gravel aggregate

plants (production capacity more than 50,000 tons/year)

• Other source Boiler and furnace

Furnace or smelter

any source any source gas plant any source any source any source any source any source Burning refuse any source from production or by usage any source any source any source any source any source any source any source

any source

any source any source H2SO« production Other activities: • Bangkok and its vicinities - other area Combustion source HN0 3 production and others any source any source any source any source also in combination with H2SO< any source

Proposed Standard Values

0.3 g/Nm 3

0.5 g/Nm 3

400 mg/Nm 3

400 mg/Nm 3

400 mg/Nm 3

500 mg/Nm 3

not exceed 40% Ringlemann scale (dust) 300 mg/Nm 3

(Al) 50 mg/Nm 3

0.05 Ib/min 0.05 Ib/min 25 ppm 25 mg/Nm 3

0.05 Ib/min 27 yg/Nm 3

20 mg/Nm 3

10 (ig/Nm 3

25 ppm 20 mg/Nm 3

0.03 Ib/min 0.05 Ib/min 0.3 lb/ton P ,O s

200 mg/Nm* 10 mg/Nm 3

100 ppm 1.0 mg/Nm 3

dust 300 mg/Nm 3

(Cu) 20 mg/Nm 3

dust 100 mg/Nm 3

(Pb) 30 mg/Nm 3

0.1 mg/Nm 3

1,000 mg/Nm 3

500 ppm

400 ppm 700 ppm 1,000 mg/Nm 3

2,000 mg/Nm 3

70 mg/Nm 3

0.01 Id/min 3 mg/Nm 3

35 mg/Nm 3

as H 2 S 0 4

35 mg/Nm 3

37