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WASTE WATER TREATMENT OF TEXTILE INDUSTRIES OF BANGLADESH

SUBMITTED BY - EXAMINATION ROLL NO : 2347 SESSION : 2007-2008 DEPARTMENT OF APPLIED CHEMISTRY & CHEMICAL ENGINEERING UNIVERSITY OF DHAKA DHAKA-1000 BANGLADESH

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ACKNOWLEDGEMENTS

First of all I express my unfathomable admiration to almighty Allah, who is so kind and keep me

healthy and give me capability to complete my project work in due time.

I am profoundly beholden to my cherished teacher, Dr. ANM Hamidul Kabir, Assistant Professor,

Department of Applied Chemistry & Chemical Engineering, and Dr. Ajoy Kumar Das, Professor,

Department of Applied Chemistry & Chemical Engineering, University of Dhaka, for their kind

instruction to keep forward my project work, and for providing all the amenities throughout the

research work and also about writing this paper. Their continuous assistance, positive criticism,

back-up and motivation have made this thesis successful.

I am also thankful to Professor Dr. Dilruba Huq, Course Coordinator,4 th year honours

Examination- 2008, Department of Applied Chemistry & Chemical Engineering, University of

Dhaka, for her pedagogic guidance and dynamic collaboration.

I also like to articulate my gratitude to my respected teacher Dr. Md.Nurul Amin,my project

guide,for his kind assistance & guidance without which the entire project will be totally impossible.

I would like to convey my heartfelt thanks to my entire respectable teachers of the Department of

Applied Chemistry & Chemical Engineering, University of Dhaka, for their assistance and co-

operation.

I would also like to thank S.M.Estiar Haque, M.S. Session : 2003-2004, Department of Applied

Chemistry & Chemical Engineering from whom I have got valuable help to complete the project.

And finally my earnest thanks to all my friends, family members and well-wishers for their

encouragement and repercussion.

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S.I. No Contents Page No

1. Introduction 4 2. Abstract 7

3. Definition of industrial wastewater treatment process

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4. Source of wastewater 8 5. Characteristics of wastewater 12

6. Methods and equipments used in wastewater treatment

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7. Environmental effects of wastewater on receiving streams

8. Guideline and discharge standards of the industry permit systems

9. Current industrial environmental status

10. Hazards and their control

11. Treatment options of wastewater

12. Overall comments about wastewater treatment process

13. Conclusion

INTRODUCTION

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Textile industry is providing one of the most basic needs of people, “Cloth”. It has a unique

position in the world of industry as self reliant industry from the production of raw material to the

delivery of finished products with substantial value addition at each stage of processing. It makes a

major contribution to the country in economy.

Bangladesh is one of the developing countries in the world,which is trying to become a middle-

income country. The developing countries with the poverty problem, have also many other

problems. One of the most important topics currently being discussed throughout the world, in

terms of human health risks as well as socio-economic paradigms, is environmental

pollution,especially water pollution.

Industrial pollution is an area of growing environmental concern in Bangladesh. The country still

has a relatively small industrial base (including manufacturing, construction, mining and utilities)

contributing about 18% of GDP (2008-09). The manufacturing sub-sector accounts for about half

of this contribution and it grew at a rate of 5.1% between 1972 and 2010. With the growth of the

ready-made garments sector, the textile sector is also growing at a high rate in recent years.

There are increasing efforts to develop the industrial sector of the country by both stimulating the

local industries and attracting foreign investors. As a result, the growth rate of the industrial sector is

expected to rise. The growth rate of the manufacturing sector has been projected to be 5.6 % for the

year 2010 (ADB, March 2010). As Bangladesh attempts to attain economy development by replacing

its agricultural base with industries and rural enterprises with urban centers, pollution and other

environmental impacts of industries are becoming critical in development planning. (Bhattacharya et

al., 1995).

Bangladesh has been late in the process of industrialization. The industrial sector plays a pivot

role for accelerated economic growth as well as rapid employment generation. Before

liberation(1971), some simple process industries like jute, textiles, sugar mills, pulp and paper

mills, a small fertilizer plant, a cement factory, a mini steel mill, a few pharmaceutical units,

bottling and packaging and several minor dockyards comprised the industrial base of the

country. Thus,the industrialization in Bangladesh (the then East Pakistan) began in the 1950s at a

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very slow pace with the primary focus on agro-based industries such as jute, cotton and sugar. After

independence in 1971, there was renewed interest in industrial development within the limited and

fragile post-war infrastructure.

At that time, within the overall objective of attaining a self-reliant economy, the First Five Year

Plan (1973-1978) of the country adopted an import substitution strategy for industrialization with

emphasis on domestic production of basic needs and investment goods. During the last thirty eight

years, the nation’s industrialization efforts were channeled mainly through the public sector. A

major portion of public investments was devoted to new capacity creation in chemical fertilizers

and in the establishment of several basic engineering industries, while both the public and private

sectors invested in textiles and clothing. Some investments were also made in balancing,

modernization and expansion of some of the existing jute and textile mills.On the whole, the most

significant industrial growth has been recorded after 1982 particularly the development of the

garments, textile and dyeing sectors. (Bhattacharya et al., 1995).

Based primarily on the agricultural raw materials, with very limited land and huge unemployed

labour force, Bangladesh now seeks a solution in industrialization because there are no other

alternatives to her into a middle income country. The country’s aspiration for industrialization also

matches that of other developing countries seeking the same goal, which are made to believe that

industry is central to the economies of modern societies. But in many other developed countries, the

indiscriminate discharge of industrial wastes into ecosystems has been restricted through strict

regulations. Unfortunately, we are lagging behind. With the growth of industry at about 10% of

GDP, enhanced industrial pollution is likely to create an alarming situation.

Bangladesh has now about 30,000 industrial units of which about 24,000 are small and cottage and

remaining 6,000 large and medium. Production for all industrial groups has increased by 46% since

1981, with some groups such as textile products, industrial chemicals and pharmaceuticals

increasing by 20 to 4000 percent over last ten years (DoE, 1992).Among all of them, the ready-

made garment sector has become one of the largest manufacturing sectors in Bangladesh with

approximately 4490 apparel manufacturing units registered under the Bangladesh Garment

Manufactures and Exporters Association (BGMEA) in 2008.

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Gazipur has seen a phenomenal rise in the industrial sector during the last decade. In Gazipur,

textile mills particularly, represent an important economic sector. The bulk of the textile products of

these industries are exported. Several Textile Mills and Apparals are situated in Gazipur district. It

is located about 30 km North of Dhaka. They produce all types of textile products which are

exported to the foreign country.

The technological problems resulting from the discharge of effluents from Textile Mills and

Apparals into drainage have been among the most important water and soil pollution problem in this

area. High concentrations of arsenic and heavy metals such as Cu, Cd, Zn, Pb, Cr. Mn and Fe have

been reported in this area. Soils are the most important sink of trace elements. This problem is

aggravated because the affected soil and water from the drainage is used directly for agriculture

purposes. In this situation, it is necessary to evaluate different parameters [ pH, BOD(Biochemical

oxygen demand),COD(Chemical oxygen demand),TSS(Total suspended solids),TDS(Total

dissolved solids),Oil & grease,Colour,Temperature etc.] and the presence of mineral

elements( which are toxic to soil and plant as well as to human health )and compare with their

threshhold limits in such soils which are toxic to soil and plant as well as to human health.

Consequently, textile industry effluents are posing a growing problem. This project will allow us to

determine the level of pollution in textile industries which,in fact, will be helpful to create awareness

among the public as well as the policy makers about the importance of installing ‘Effluent Treatment

Plant’ in various polluting industries.

In this way the characteristics of effluent very greatly. So the random discharge of industrial wastes

and effluents pollute the ecosystem in Bangladesh and ultimately, the water-soil-plant-food system

including fisheries of the riverine delta of Bangladesh. (Faisal et al., 2000; Gain, P. (Ed.). 1998; De,

A. K. 1993; Haq, S.A. 1989; Chowdhury N., 1989; Nakos,G. 1983; Saxena, M.M.1990; Stemberg

et al., 1981; Tan kim, H.,1994).

With this view in mind, the present project was done to:

Define industrial wastewater treatment process

Identify the sources of wastewater

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Give an idea about characteristics of wastewater

Describe methods and equipment used in wastewater treatment

Inform about environmental effects of wastewater on receiving streams

Give information about guideline and discharge standards of the industry permit systems

Give conception about current industrial environmental status

Identify hazardous substances produced in textile industry and give information about their

controlling process

Give direction to new treatment options of wastewater

Make overall comments about wastewater treatment process

ABSTRACT

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The present project is aimed to highlight the importance of industrial wastewater treatment

process,particularly for textile industries . The textile effluent contains highly toxic dyes, bleaching

agents, salts, acids,alkalis,fats,oils,greases. Heavy metals like As, Pb, Cd, Cu, Zn, Fe and Mn are

also found in the textile effluents, which are usually not properly treated before its discharge. So

they may have harmful effects on the surrounding soil properties, because the element of those soils

may be transferred from soil to plants. By examining the chemical properties of the soil and also

toxicity present in it due to industrial waste using AAS (Atomic Absorption Spectroscopy) indicate

that the sludge and surrounded soils are not suitable for agricultural or other purposes.So waste

water treatment or effluent treatment is must to prevent pollution of receiving streams of water and

soil.

1.What is industrial wastewater treatment

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Industrial activities generate a large number and variety of waste products which are generally

discharged into water streams.The ultimate disposal of wastewater can only be onto the land or into

the water. But whenever the water courses are used for the ultimate disposal,the waste water is

given a treatment to prevent any injury to the aquatic life in the receiving water.This treatment can

be done by various mechanisms and processes. So, industrial wastewater treatment can be defined

as “ The mechanisms and processes used to treat waters that have been contaminated in some way

by anthropogenic industrial or commercial activities prior to its release into the environment or its

re-use.”

Most industries produce some wet waste although recent trends in the developed world have been to

minimise such production or recycle such waste within the production process. However, many

industries remain dependent on processes that produce wastewaters.So waste water treatment plant

is designed to remove inorganic substances,organic substances,acids or alkalies,toxic

substances,colour producing substances,oil and other floating substances produced during the

industrial activities and processes.

But before proceeding with the design of the treatment plant itself,it is essential to determine :

1) Sources of the wastewater,

2) The characteristics of the raw wastewater,

3) The required characteristics of the treatment plant effluent,which will not pollute the

receiving water course beyond certain acceptable limits.

2.Sources of the wastewater

In Textile processing, the characteristics of the waste produced in some major operation involved

are as follows:

Sizing: The wastewater is generally colored and contains starch, polyvinyl alcohol and

softeners. It has high BOD and high content of dissolved suspended solids.

Desizing, scouring and mercerizing: The waste contains starch, acids, alkali silicates and

enzymes.

Bleaching: The effluent contains chlorine, hypochlorite and peroxide.

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Dyeing and finishing: The waste contains heavy metals and arsenic as their salts is used in

these sections.

To design a wastewater treatment plant,determination of the source units of the wastewater is

necessary. Industry of a specific category has its own source of wastewater.These sources of

wastewater are different units of the industry. In case of a textile mill, wastewater generating units

are :

(i) Knit dyeing units, (ii) Woven dyeing units, (iii) Denim plants, (iv) Printing units, and

(v) Garments washing units.

i) Knit dyeing unit :Knit dyeing is the dyeing process where organized knits(cloth manufactured from thread/yarn )are

dyed by using weave.

This dyeing process is classified by following 4 steps according to the usage of knit :

Yarn→Weaving→Forming→Turning→Refining,

Bleaching→Dyeing→Later treatment→Softening→Dehydration,

Drying→Pre-shrinking→Inspection packaging.

Yarn→Weaving→Forming→Turning→Refining,

Bleaching→Dyeing→Later treatment→Dehydration & Drying→Softening→Tendering→

Inspection packaging.

Knit→Weaving→Forming→Turning→Mercerizing→Refining,

Bleaching→Dyeing→Later treatment→Softening →Dehydration & Drying→Pre-

shrinking→Inspection packaging.

Yarn→Weaving→Forming→Turning→ Mercerizing→Refining ,

Bleaching→Dyeing→Later treatment→Softening →Tendering→Inspection & Packaging.

Some machineries used for Knit dyeing units are stated below :

a) Knit Fabric Atmospheric Dyeing machine,

b) ASMA631 High Temperature High Pressure Dyeing Machine,

c) Fabric Rolling Machine,

d) ASME-C High Temperature Fabric Dyeing Machine,

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e) SME-500D high temperature and high pressure dyeing machine ,

f) High Temperature and High Speed Dyeing Machine,

g) High-Temperature and High-Pressure Fabric Dyeing Machine ,

h) H. T. H. P "O" Type Soft Flow fabric dyeing machine,

i) Krsna Fabric Dyeing Machine Textile Processing Machines.,

j) WBD High Temperature Double Overflow Dyeing Machine,

k) ASME-B HT HP Jet Overflow Dyeing Machine,

l) Dual Flow High Temperature Rapid Dyeing Machine,

m) Soft Overflow Dyeing Machines,

n) High temperature high speed Fabric Dyeing machine long tube .

ii) Woven dyeing unit

A woven is a cloth formed by weaving. It only stretches in the bias directions (between the warp

and weft directions), unless the threads are elastic. Woven cloth usually frays at the edges, unless

measures are taken to counter this, such as the use of pinking shears or hemming.

Structure of the woven fabric is formed by vertical and horizontal interlaced yarn.In Woven dyeing

units ,dyes used to dye woven cloth are the source of wastewater.

Some machineries used for Woven dyeing units are given below :

a) ASME-C High Temperature Fabric Dyeing Machine,

b) High Temperature and High Speed Dyeing Machine,

c) WBD High Temperature Double Overflow Dyeing Machine,

d) ASME-B HT HP Jet Overflow Dyeing Machine,

e) Soft Overflow Dyeing Machines,

f) High temperature high speed Fabric Dyeing machine long tube .

iii) Denim plants

Denim is a rugged cotton twill textile, in which the weft passes under two (twi-"double") or more

warp fibers, producing the familiar diagonal ribbing identifiable on the reverse of the fabric. It is a

coarse, twilled, sturdy cotton cloth used as for jeans, overalls, and uniforms.

Some machineries used to manufacture denim are given below :

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a) Industrial Sewing Machine BL-6000,

b) Selling 3-Needle Feed-Off-The-Arm 2-Chainstitch Machine,

c) 3D Effects Whisker (wrinkle Effect) Machines ,

d) Ultrasonic Fixing Machine,

e) 4-Head Computerized Sequin Hot Fix Machine,

f) Jean Washing Dying Machines,

g) Sell Weaving Loom,

h) Laser Cutting Machine,

i) Multimedia Multifunction Embossing Debossing Machine,

j) Machine Embroidery etc.

In the denim manufacturing plants,the source of wastewater is different types of

dyes,salts,alkalies,acids used to manufacture denim.

iv) Printing units

Printing is similar to dyeing, except that print colour is applied to specific areas of the cloth. Dyes

and auxiliaries are similar to those used in fabric dyeing; however, the color application techniques

are quite different. Textiles are usually wet-printed by roller, rotary screen or flatbed screen printing

methods.

v) Garments washing units

Modern Washing units are equipped with Heavy duty washing plant, Hydro extractor, Stain

removing machines to ensure quality. If garment dyeing is done to the product and "white" is in

line, garment washing is an economical way to "shrink" the white product so that the sizing is

consistent with the product that is garment dyed. If artwork is applied to white garments, using

garment washing is used to preshrink the product that makes benefit in two ways:

First, the washing process removes most contaminants, making the application of artwork (screen

print, batik, garment paints, etc.) easier. Second, there is less risk that artwork will be negatively

affected by shrinkage that would take place during home laundering. Many customers want product

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that is "pre-shrunk." Garment washing enables to provide pre-shrunk product.Many processes are

used for washing.The most important processes are : Whitening, Weathering, Stone washing, Acid

washing ,Distressing, Softening etc.

In these five units,different types of dyestuffs and other auxiliaries are used which are the sources of

wastewater.

A) Dyestuffs

In the textile mill units, dyestuffs are generally used in dyeing and finishing sections. They are of

many structural varieties, such as, acidic, basic, azo, diazo, anthroquinone based and metal complex

dyes.

Textile dyestuffs can be grouped into 14 categories or classes:

(1) acid dyes, (2) direct (substantive) dyes, (3)azoic dyes, (4)disperse dyes,

(5)sulfur dyes, (6) fiber reactive dyes, (7)basic dyes, (8) oxidation dyes,

(9) mordant(chrome) dyes, (10) developed dyes, (11) vat dyes, (12) pigments,

(13) optical/fluorescent brighteners, (14) solvent dye.

Application and characteristics of some important types of dyestuffs is described below :

Vat: the dye is put on the goods in their reduced state and is then oxidized. These dyes have

excellent light and wash fastness;

Developed: the dye is applied to the cloth and diazotized, and the colour is developed with a

secondary chemical called the developer. The dyes have good wash fastness;

Sulfur: the dye is put on the cloth in a reduced state and is then oxidized, producing good fastness

to light and washing;

Direct: applied directly to the cloth. These are usually low-cost dyes, easy to apply but not very

fast;

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Fiber reactive dyes : a reactive dye is a dye which reacts chemically with the cellulose molecules

(i.e. the cotton itself). These are quite widely used.

Dyes of different chemical constitution are also used in textile industry. Application and

characteristics of some important dyestuffs are described below :

Naphthol: the naphthol is applied to the fabric and passed through the developer for coupling.

This produces bright colors and good fastness to light, wash, and bleach;

Aniline Black: the aniline is oxidized on the goods by air or steam aging, producing excellent

fastness to light;

Different dyes and chemicals are required to treat different types of fibres. While different stage of

operation generates different types of effluents, different types of dyes generate different level of

toxicity.

B) Auxiliaries

Auxiliary substances used with dyes in the textile mill units are :

1) Na2S, 2) Na2SO4, 3) NaOH, 4) NaHOCl(Sodium hypochlorite), 5) Na2SO3, 6) ) NH4SO4,

7) Surfactant (LAS,BIAS,CIAS) , 8) H202 , 9) CH3COOH, 10)Paraffin, 11) Cellulose, 12) Starch, 13)

P.V.A, 14) C.M.C, 15) Oil, 16) Fats, 17) Soap etc.

3.Characteristics of wastewater

Characterization of the raw wastewater is essential in the planning for effective and economical

methods of water pollution control.Due to the varying nature of the industrial wastes,many of the

recent installations have designed their treatment units with due consideration to the raw waste

characteristics,and the effluent characteristics,as established by the DOE(Department of

Environment),Bangladesh .

Almost all industries discharge water containing wastes from some stages of their manufacturing

process,but industrial wastes are not same in every case.They are very difficult to generalize.The

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wastes include the raw materials,process chemicals,final products,process intermediates,process by-

products,and impurities in raw materials and process chemicals.

In general, according to some common characteristics of the effluents from industries, wastes can be

classified as follows :

a) Wastes containing organic substances that deplete the oxygen content of the receiving streams

and impose a great load on the biological units of the sewage treatment plant.

b) Wastes containing inorganic substances like carbonates,chlorides,nitrogen etc. that render the

water body unfit for further use and sometimes encourage the growth of some undesirable micro-

plants in the body of the water

c) Wastes containing acids or alkalis which make the receiving stream unsuitable for the growth of

fish and other aquatic life there,and cause serious difficulties in the operation of sewage treatment

plants.

d) Wastes containing toxic substances like cyanides,sulphides,acetylyne,alcohol,petrol etc. which

cause damage to the flora and fauna of the receiving streams,affect the municipal treatment

processes and sometimes endanger the safety of the workmen.

e) Wastes containing colour producing substances like dyes,which though not toxic,are aesthetically

objectionable when present in the water supplies.

f) Wastes containing oil and other floating substances,which not only render the streams

unsightly,but interfere with the self-purification of the same,and the operations of the sewage

treatment plants.

Wastes can also contain suspended matters,oxygen demanding organic matter, heavy metals

(As,Hg,Pb etc),pathogenic organisms and non bio-degradable organics.

On the basis of processes & operations ,the industrial waste can broadly be classified as :

(a) Wastewater for process and wash,

(b) Waste for cooling,

(c) Sanitary waste.

The amount of pollution created by wastes is characterized in terms of parameters such as :

i) pH,

ii) BOD(Biochemical oxygen demand),

iii) COD(Chemical oxygen demand),

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iv) TSS(Total suspended solids),

v) TDS(Total dissolved solids),

vi) Oil & grease,

vii) Colour,

viii) Temperature etc.

i) pH :

pH is a measurement of the acidity or basicity of a solution. It approximates but is not equal to

p[H], the negative logarithm (base 10) of the molar concentration of dissolved hydrogen ions (H+);

a low pH indicates a high concentration of hydrogen ions , while a high pH indicates a low

concentration. Pure water is said to be neutral, with a pH close to 7.0 at 25 °C (77 °F). Solutions

with a pH less than 7 (at 25 °C (77 °F)) are said to be acidic and solutions with a pH greater than 7

(at 25 °C (77 °F)) are said to be basic or alkaline.

pH can be measured by pH meter.

ii) BOD(Biochemical oxygen demand) :

Biochemical oxygen demand or BOD is a measurement of the uptake rate of dissolved oxygen by

the biological organisms in a body of water. It is not a precise quantitative test, although it is widely

used as an indication of the quality of water.

The BOD5 test

There are two recognized methods for the measurement of BOD :

i) Dilution method

To ensure that all other conditions are equal, a very small amount of micro-organism seed is added

to each sample being tested. This seed is typically generated by diluting activated sludge with de-

ionized water. The BOD test is carried out by diluting the sample with oxygen saturated de-ionized

water, inoculating it with a fixed aliquot of seed, measuring the dissolved oxygen (DO) and then

sealing the sample to prevent further oxygen dissolving in. The sample is kept at 20 °C in the dark

to prevent photosynthesis (and thereby the addition of oxygen) for five days, and the dissolved

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oxygen is measured again. The difference between the final DO and initial DO is the BOD. The

apparent BOD for the control is subtracted from the control result to provide the corrected value.

The loss of dissolved oxygen in the sample, once corrections have been made for the degree of

dilution, is called the BOD5. For measurement of carbonaceous BOD (cBOD), a nitrification

inhibitor is added after the dilution water has been added to the sample. The inhibitor hinders the

oxidation of nitrogen.

BOD can be calculated by:

Undiluted : Initial DO - Final DO = BOD Diluted : ((Initial DO - Final DO)- BOD of Seed) * Dilution Factor

ii)Manometric method

This method is limited to the measurement of the oxygen consumption due only to carbonaceous

oxidation. Ammonia oxidation is inhibited.

The sample is kept in a sealed container fitted with a pressure sensor. A substance that absorbs

carbon dioxide (typically lithium hydroxide) is added in the container above the sample level. The

sample is stored in conditions identical to the dilution method. Oxygen is consumed and, as

ammonia oxidation is inhibited, carbon dioxide is released. The total amount of gas, and thus the

pressure, decreases because carbon dioxide is absorbed. From the drop of pressure, the sensor

electronics computes and displays the consumed quantity of oxygen.

The main advantages of this method compared to the dilution method are:

simplicity: no dilution of sample required, no seeding, no blank sample

direct reading of BOD value

continuous display of BOD value at the current incubation time.

Furthermore, as the BOD measurement can be monitored continuously, a graph of its evolution can

be plotted. Interpolation of several graphs on a similar water may build an experience of its usual

evolution, and allow an estimation of the five days BOD after as early as the first two days of

incubation.

iii) COD(Chemical Oxygen Demand)

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The chemical Oxygen Demand (COD) test is commonly used to indirectly measure the amount of

organic compounds in water. Most applications of COD determine the amount of organic pollutants

found in surface water (e.g. lakes and rivers), making COD a useful measurement of water quality.

It is expressed in milligrams per liter (mg/L), which indicates the mass of oxygen consumed per

liter of solution. Older references may express the units as parts per million (ppm).

Overview

The basis for the COD test is that nearly all organic compounds can be fully oxidized to carbon

dioxide with a strong oxidizing agent under acidic conditions. The amount of oxygen required to

oxidize an organic compound to carbon dioxide, ammonia, and water is given by:

This expression does not include the oxygen demand caused by the oxidation of ammonia into

nitrate. The process of ammonia being converted into nitrate is referred to as nitrification. The

following is the correct equation for the oxidation of ammonia into nitrate.

The second equation should be applied after the first one to include oxidation due to nitrification if

the oxygen demand from nitrification must be known. Dichromate does not oxidize ammonia into

nitrate, so this nitrification can be safely ignored in the standard chemical oxygen demand test.

The International Organization for Standardization describes a standard method for measuring

chemical oxygen demand in ISO 6060 .

History

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For many years, the strong oxidizing agent potassium permanganate (K Mn O 4) was used for

measuring chemical oxygen demand. Measurements were called oxygen consumed from

permanganate, rather than the oxygen demand of organic substances. Potassium permanaganate's

effectiveness at oxidizing organic compounds varied widely, and in many cases biochemical

oxygen demand (BOD) measurements were often much greater than results from COD

measurements. This indicated that potassium permanganate was not able to effectively oxidize all

organic compounds in water, rendering it a relatively poor oxidizing agent for determining COD.

Since then, other oxidizing agents such as ceric sulfate, potassium iodate, and potassium dichromate

have been used to determine COD. Of these, potassium dichromate (K2Cr2O7) has been shown to be

the most effective: it is relatively cheap, easy to purify, and is able to nearly completely oxidize

almost all organic compounds.

In these methods, a fixed volume with a known excess amount of the oxidant is added to a sample

of the solution being analyzed. After a refluxing digestion step, the initial concentration of organic

substances in the sample is calculated from a titrimetric or spectrophotometric determination of the

oxidant still remaining in the sample.

Using potassium dichromate

Potassium dichromate is a strong oxidizing agent under acidic conditions. (Acidity is usually

achieved by the addition of sulfuric acid.) The reaction of potassium dichromate with organic

compounds is given by:

where d = 2n/3 + a/6 - b/3 - c/2. Most commonly, a 0.25 N solution of potassium dichromate is

used for COD determination, although for samples with COD below 50 mg/L, a lower

concentration of potassium dichromate is preferred.

In the process of oxidizing the organic substances found in the water sample, potassium dichromate

is reduced (since in all redox reactions, one reagent is oxidized and the other is reduced), forming

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Cr3+. The amount of Cr3+ is determined after oxidization is complete, and is used as an indirect

measure of the organic contents of the water sample.

Blanks

Because COD measures the oxygen demand of organic compounds in a sample of water, it is

important that no outside organic material be accidentally added to the sample to be measured. To

control for this, a so-called blank sample is required in the determination of COD (and BOD -

biochemical oxygen demand - for that matter). A blank sample is created by adding all reagents

(e.g. acid and oxidizing agent) to a volume of distilled water. COD is measured for both the water

and blank samples, and the two are compared. The oxygen demand in the blank sample is

subtracted from the COD for the original sample to ensure a true measurement of organic matter.

Measurement of excess

For all organic matter to be completely oxidized, an excess amount of potassium dichromate (or any

oxidizing agent) must be present. Once oxidation is complete, the amount of excess potassium

dichromate must be measured to ensure that the amount of Cr3+ can be determined with accuracy.

To do so, the excess potassium dichromate is titrated with ferrous ammonium sulfate (FAS) until all

of the excess oxidizing agent has been reduced to Cr3+. Typically, the oxidation-reduction indicator

Ferroin is added during this titration step as well. Once all the excess dichromate has been reduced,

the Ferroin indicator changes from blue-green to reddish-brown. The amount of ferrous ammonium

sulfate added is equivalent to the amount of excess potassium dichromate added to the original

sample. and also we can determine COD by boiling the water sample and we can determine CO2

ratio by the infra-red analyzer

Preparation of Ferroin Indicator reagent

A solution of 1.485 g 1,10-phenanthroline monohydrate is added to a solution of 695 mg

FeSO4·7H2O in water, and the resulting red solution is diluted to 100 mL.

Calculations

The following formula is used to calculate COD:

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where b is the volume of FAS used in the blank sample, s is the volume of FAS in the original

sample, and n is the normality of FAS. If milliliters are used consistently for volume measurements,

the result of the COD calculation is given in mg/L.

The COD can also be estimated from the concentration of oxidizable compound in the sample,

based on its stoichiometric reaction with oxygen to yield CO2 (assume all C goes to CO2), H2O

(assume all H goes to H2O), and NH3 (assume all N goes to NH3), using the following formula:

COD = (C/FW)(RMO)(32)

Where, C = Concentration of oxidizable compound in the sample,

FW = Formula weight of the oxidizable compound in the sample,

RMO = Ratio of the no of moles of oxygen to no of moles of oxidizable compound in their

reaction to CO2, water, and ammonia

For example, if a sample has 500 wppm of phenol:

C6H5OH + 7O2 → 6CO2 + 3H2O

COD = (500/94)(7)(32) = 1191 wppm

iv) TSS(Total Suspended Solids)

Total suspended solids is a water quality measurement usually abbreviated TSS.

Measurement

TSS of a water sample is determined by pouring a carefully measured volume of water (typically

one litre; but less if the particulate density is high, or as much as two or three litres for very clean

22

water) through a pre-weighed filter of a specified pore size, then weighing the filter again after

drying to remove all water. The gain in weight is a dry weight measure of the particulates present in

the water sample expressed in units derived or calculated from the volume of water filtered

(typically milligrams per litre or mg/L).

It is recognized that if the water contains an appreciable amount of dissolved substances (as

certainly would be the case when measuring TSS in seawater), these will add to the weight of the

filter as it is dried. Therefore it is necessary to "wash" the filter and sample with deionized water

after filtering the sample and before drying the filter. Failure to add this step is a fairly common

mistake made by inexperienced laboratory technicians working with sea water samples, and will

completely invalidate the results as the weight of salts left on the filter during drying can easily

exceed that of the suspended particulate matter.

Although turbidity purports to measure approximately the same water quality property as TSS, the

latter is more useful because it provides an actual weight of the particulate material present in the

sample. In water quality monitoring situations, a series of more labor intensive TSS measurements

will be paired with relatively quick and easy turbidity measurements to develop a site-specific

correlation. Once satisfactorily established, the correlation can be used to estimate TSS from more

frequently made turbidity measurements, saving time and effort. Because turbidity readings are

somewhat dependent on particle size, shape, and color, this approach requires calculating a

correlation equation for each location. Further, situations or conditions that tend to suspend larger

particles through water motion (e.g., increase in a stream current or wave action) can produce

higher values of TSS not necessarily accompanied by a corresponding increase in turbidity for the

reason that particles above a certain size (essentially anything larger than silt) are not measured by a

bench turbidity meter (they settle out before the reading is taken) but contribute substantially to the

TSS value.

Definition problems

Although TSS appears to be a straightforward measure of particulate weight obtained by separating

particles from a water sample using a filter, it suffers as a defined quantity from the fact that

particles occur in nature in essentially a continuum of sizes. At the lower end, TSS relies on a cut-

off established by properties of the filter being used. At the upper end, the cut-off should be the

23

exclusion of all particulates too large to be "suspended" in water. However, this is not a fixed

particle size but is dependent upon the energetics of the situatuion at the time of sampling: moving

water suspends larger particles than does still water. Usually it is the case that the additional

suspended material caused by the movement of the water is of interest.

These problems in no way invalidate the use of TSS; consistency in method and technique can

overcome short-comings in most cases. But comparisons between studies may require a careful

review of the methodologies used to establish that the studies are in fact measuring the same thing.

TSS( in mg/L)=(dirty pad weight in grams-clean pad weight in grams)/mL of sample*1,000,000

v) TDS(Total Dissolved Solids)

Total Dissolved Solids (often abbreviated TDS) is a measure of the combined content of all

inorganic and organic substances contained in a liquid in molecular, ionized or micro-granular

(colloidal sol) suspended form. Generally the operational definition is that the solids must be small

enough to survive filtration through a sieve the size of two micrometer. Total dissolved solids are

normally discussed only for freshwater systems, as salinity comprises some of the ions constituting

the definition of TDS. The principal application of TDS is in the study of water quality for streams,

rivers and lakes, although TDS is not generally considered a primary pollutant (e.g. it is not deemed

to be associated with health effects) it is used as an indication of aesthetic characteristics of drinking

water and as an aggregate indicator of the presence of a broad array of chemical contaminants.

Measurement of TDS

The two principal methods of measuring total dissolved solids are gravimetry and conductivity.

Gravimetric methods are the most accurate and involve evaporating the liquid solvent to leave a

residue that can subsequently be weighed with a precision analytical balance (normally capable

of .0001 gram accuracy). This method is generally the best, although it is time-consuming and leads

to inaccuracies if a high proportion of the TDS consists of low boiling point organic chemicals,

which will evaporate along with the water. If inorganic salts comprise the great majority of TDS,

gravimetric methods are appropriate.

24

Electrical conductivity of water is directly related to the concentration of dissolved ionized solids in

the water. Ions from the dissolved solids in water create the ability for that water to conduct an

electrical current, which can be measured using a conventional conductivity meter or TDS meter.

When correlated with laboratory TDS measurements, conductivity provides an approximate value

for the TDS concentration, usually to within ten-percent accuracy.

vi) Oil and Grease

The term oil and grease,as commonly used,includes the fat,oils,waxes and other related constituents

found in waste water.Oils and fats are mainly due to the sizing process and also as oils and grease

come in contact with the fabric during the processing.Apart from this small amount oils are found in

the cellulose fibers.These oils and fats are removed during scouring process and finally pass with the

wastewater.If the wastewater contains oils and fats,they form a layer at the top surface of the

wastewater.As a result,oxygen can’t come in contact with the water and it becomes difficult to

increase DO level.

Oil and grease discharged into the environment typically has deleterious effects.Oily wastes

discharge may have objectionable odours,cause undesirable appearance,burn on the surface of

receiving water creating potential safety hazards and consume dissolved oxygen necessary to forms

of life in water.Bioassay data indicate that oil is toxic to fish,.In greater quantities,it limits oxygen

transfer,hindering biological activity.

Oil and grease affect respiration of fish by adhering to the gills,it adhere to and destroy algae and

plankton.Feeding and reproduction of water life(plant,insect,and fish) is affected by oils and

fats.Aesthetics is affected by sheens of oils.

vii) Colour

Colour of wastewater is imparted by dyes.The loss of dyes to effluent can be estimated to be 10% for

deep shades,2% for medium shades and minimal for light shades however the loss of dyes is mainly

depending on the class of dyes.Dyes are present in the effluent at the concentrations of 10 mg/L to

50 mg/L with 1 mg/L visible to the naked eye.Dyes are complex organic compounds which are

refractory in aerobic treatment systems.Some contains metals such as Cr,Cu and Zn.

25

In the aquatic environment,dyes can undergo bio-concentration,ionization,abiotic oxidation, abiotic

and microbial reduction and precipitation.The ionic dyes such as acid,direct,basic and metal complex

dyes will not volatilize,whereas,in principle;solvent,disperse,vat and sulphur dyes have the potential

to be volatile.Sorption should also play a major role as dyeing is a sorption process.Hydrolic

reactions are not important because if the dyes survive the biological treatment process,it is unlikely

to degrade rapidly in the environment.Photochemical reactions may be important,as dyes are good

absorber of solar energy.Aquatic plants will not be able to produce food by the process of

photosynthesis,as a result their life will be endangered.It is expected that anionic dyes would react

with ions like calcium and magnesium to form insoluble salts and thereby reduce the concentration

available for other biological reactions.Redox reactions would also be considered,as in early vat

dyeing processes,the dyes were reduced microbially before chemical replacements were

introduced.Reduction in the environment would most likely occur under anaerobic conditions.Two

methods are widely used for discolouration.One is – physical sedimentation of dyes by coagulating

and flocculating;here dyes are removed completely.On the other hand,Ozonization is applicable for

discolouration where it breaks the pie bond of chromophoric group of dyes but dyes may remain in

discharge water.

viii) Temperature

Temperature of water is a very important factor for aquatic life.It controls the rate of metabolic and

reproductive activities,and determines which aquatic species can survive.Different aquatic species

require different quantities of DO to survive in the water.Temperature inversely affects the rate of

transfer of gaseous oxygen into dissolved oxygen.On the other hand, at higher temperature,the

metabolic rate of aquatic plants and animals increases producing an increase in oxygen demand.

International regulations related to water temperature and aquatic life classifies water according to

temperature :

*"Class 1 Cold Water Aquatic Life ",that should never have temperatures exceeding 20 ⁰ C,

*"Class 1 Warm Water Aquatic Life ",that should never have temperatures exceeding 30 ⁰ C.

These regulations also state that temperature for these classes shall maintain a normal pattern of day

to day and seasonal fluctuations with no abrupt changes and shall have no increases in temperature

of a magnitude,rate,and duration deemed harmful to the resident aquatic life.Generally,a maximum 3

⁰ C increase over a minimum of a 4-hr period,lasting 12 hours maximum,is deemed acceptable.

26

Temperature preferences among aquatic species vary widely,but all species tolerate slow,seasonal

changes better than rapid changes.Respiration of organisms is temperature related ; respiration rates

can increase by 10% or more per 1⁰ C temperature rise.Therfore,increased temperature not only

reduces oxygen availability,but also increases oxygen demand,which can add to physiological stress

of organisms.Increased temperature influence the activity of bacteria and toxic chemicals secreted by

the bacteria in water.

In case of Textile production, a number of wet processes are involved that may use solvents.

Emissions of volatile organic compounds (VOCs) mainly arise from textile finishing, drying

processes, and solvent use. VOC concentrations vary from 10 milligrams of carbon per cubic meter

(mg/m3) for the thermosol process to 350 mg carbon/m3 for the drying and condensation process.

Process wastewater is a major source of pollutants (see Table 1). It is typically alkaline and has high

BOD—from 700 to 2,000 milligrams per liter(mg/L)—and high chemical oxygen demand(COD), at

approximately 2 to 5 times the BOD level. Wastewater also contains solids, oil, and possibly toxic

organics, including phenols from dyeing and finishing and halogenated organics from processes such

as bleaching. Dye wastewaters are frequently highly colored and may contain heavy metals such as

copper and chromium.Wool processing may release bacteria and other pathogens. Pesticides are

sometimes used for the preservation of natural fibers, and these are transferred to wastewaters during

washing and scouring operations. Pesticides are used for mothproofing, brominated flame retardants

are used for synthetic fabrics, and isocyanates are used for lamination .Wastewaters should be

checked for pesticides such as DDT and PCP and for metals such as mercury,arsenic, and copper.

Air emissions include dust, oil mists, acid vapors, odors, and boiler exhausts. Cleaning and

production changes result in sludges from tanks and spent process chemicals, which may contain

toxic organics and metals.

A sample of wastewater characteristics of a textile industry is given on the following page :

27

Table 1. Wastewater Characteristics in the Textile Industry

Waste volume BOD TSS Other pollutants Process and unit (U) (m3/U) ( kg/U) (kg/U) (kg/U)

Wool processing (metric ton of wool)a

Average unscoured stockb 544 314 196 Oil 191Average scoured stock 537 87 43 Cr 1.33Process-specific Phenol 0.17Scouring 17 227 153 Cr 1.33Dyeing 25 27 Phenol 0.17Washing 362 63Carbonizing 138 2 44 Oil 191Bleaching 12.5 1.4 Cr 1.33 Phenol 0.17Cotton processing (metric ton of cotton)Average compoundedc 265 115 70 Process-specific Yarn sizing 4.2 2.8 Desizing 22 58 30 Kiering 100 53 22 Bleaching 100 8 5 Mercerizing 35 8 2.5 Dyeing 50 60 25 Printing 14 54 12

Other fibers (metric ton of product)Rayon processing 42 30 55Acetate processing 75 45 40Nylon processing 125 45 30Acrylic processing 210 125 87Polyester processing 100 185 95

a. The pH varies widely, from 1.9 to 10.4.b. The average compounded load factors listed are based on the assumption that only 20% of the product is mercerized (only nonwoolen components are mercerized) and 10% is bleached.c. The average compounded load factors listed are based on the assumption that only 35% of the product is mercerized, 50% of the product is dyed, and 14% of the product is printed.Source: Economopoulos 1993.

In case of Bangladesh,the characteristics are a little bit different. Effluent(wastewater) characteristics

of Partex Denims Ltd( Chandora,Kaliakoir,Gazipur) surveyed by Aquatech Engineering Services

Ltd is given on the following page :

28

S.I No Water quality parameters

Unit Values

01 pH - - - - - - 8 - 14 02 BOD mg/L,5days 600 - 2500 03 COD mg/L,day 2500 - 4200 04 TSS mg/L 300 - 500 05 TDS mg/L 4000 - 8500 06 Oil & grease mg/L 30 - 60 07 Colour Co-pt unit 10900 Co-pt 08 Temperature ˚C 60˚C

4.Methods and equipments used in wastewater treatment

29

The method of treatment of an industrial waste depends on various factors such as :

(a) Nature of industrial waste,

(b) BOD and COD of the effluent,

(c) pH value of the effluent,

(d) Suspended solids present,

(e) Total solids present,

(f) Pollutants present,

(g) Toxic chemical substances present etc.

The treatment of industrial wastewater may be accompanied in part or as a whole either by the

biological processes,or by processes very special for the industrial wastewater only.The important

factors,which affect the planning for a industrial wastewater treatment plants are :

1) The discontinuity and season of discharged wastes,

2) High concentration of the waste,

3) Non biodegrability and toxicity of some wastes.

Goals of industrial wastewater treatment should be :

i) Reduction of suspended matters,

ii) Reduction of oxygen demanding organic and inorganic matter,

iii) Reduction of toxic(heavy) metals,

iv) Removal of colour producing substances,

v) Removal of oil and other floating substances.

These operations can be carried out by several methods of treatment.According to the effectiveness

of removing the pollutants,the treatments are classified as follows:

a) Pretreatment,

b) Primary treatment,

c) Secondary treatment,

d) Advanced /Tertiary treatment.

a) Pretreatment

30

Many industrial-wastewater streams should be pretreated prior to discharge to municipal sewerage

systems or even to a central industrial sewerage system. Pretreatment of individual streams should

be considered whenever these streams might have an adverse effect on the total treatment system.

Following methods are used for pretreatment process :

i) Equalization,

ii) Neutralization,

iii) Grease and oil removal,

iv) Removal of Toxic Substances.

Short description about these processes are given below :

i) Equalization

When strong wastes from the factories are dumped in batches,it often causes a sudden increase in

the characteristics of the waste such as pH, BOD,temperature etc.This will produce detrimental

loads.Hence it is necessary to equalise the discharge by holding up water in retaining basins and

releasing it slowly in batches.The effluent from an equalization process has been found to be much

consistent in characteristics.The pH, BOD,COD etc are stabilized and suspended heavy solids are

settled.Such stable effluents are also easy to be treated effectively as well as efficiently.

Equalization is also capable of producing even such effluents which don’t require any further

treatment.

So,when the characteristics of the waste vary in a day and also the discharge rate is not uniform or

continuous,the waste may require Equalization before it is subjected to the treatment.Equalization

consists of holding the waste for some pre-determined time in a continuously mixed basin,which

produces an effluent of fairly uniform characteristics.

To reduce the strength of waste,a no of methods beside equalization can be used such as –

* Process and raw material changes,

* Equipment modification,

* By-product recovery,

* Segragation of wastes etc.

* Process and raw material changes

31

The volume of industrial waste can be reduced by changing the process of material.For example,the

highly polluted waste because of use of starch as a sizing agent in textile industry is the main source

of pollution.If it is replaced by cellulosic sizing agent,the pollution load can be reduced to a great

extent.

* Equipment modification

The strength of pollutants entering the water bodies can also be reduced by changing the equipment

or by making modifications in the equipment.Large quantities of pollutants have actually been

reduced even affecting a very slight change in the equipment.For example,in poultry farms,if traps

are provided on the discharge lines to prevent feather and pieces of fat entering,water pollution is

reduced.

* By-product recovery

The recovery of useful products from industrial wastes not only reduces pollution but also to saving

in expenditure.For example in pulp and paper mill,the wood chips are cooked in NaOH and

Na2SO4. A black liquid,known as black liqour is produced as a result of release of lignins.

The black liqour is highly alkaline and has high BOD. Its treatment is expensive as well as very

difficult.Hence it is profitable to recover the chemicals from black liqour for reuse,which not only

reduces the pollution load but also the strength of waste liquid which is responsible for pollution of

water bodies.

* Segregation of wastes

The relatively less volume and highly toxic wastes can be segregated from the main stream and can

then be treated separately by solar evaporation,incineration etc.As a result pollution load on

biological treatment units is much reduced.The waste containing highly toxic substances can be

segregated as well as incinerated.

ii) Neutralization

Acidic or basic wastewaters must be neutralized prior to discharge. If an industry produces both

acidic and basic wastes, these wastes may be mixed together at the proper rates to obtain neutral pH

levels. Equalization basins can be used as neutralization basins. When separate chemical

neutralization is required, sodium hydroxide is the easiest base material to handle in a liquid form

and can be used at various concentrations for in-line neutralization with a minimum of equipment.

Yet, lime remains the most widely used base for acid neutralization. Limestone is used when

32

reaction rates are slow and considerable time is available for reaction. Sulfuric acid is the primary

acid used to neutralize high-pH wastewaters unless calcium sulfate might be precipitated as a result

of the neutralization reaction. Hydrochloric acid can be used for neutralization of basic wastes if

sulfuric acid is not acceptable. For very weak basic wastewaters carbon dioxide can be adequate for

neutralization.

iii) Grease and Oil Removal

Grease and oils tend to form insoluble layers with water as a result of their hydrophobic

characteristics.These hydrophobic materials can be easily separated from the water phase by gravity

and simple skimming, provided they are not too well mixed with the water prior to separation. If the

oils and greases form emulsions with water as a result of turbulent mixing, the emulsions are

difficult to break. Separation of oil and grease should be carried out near the point of their mixing

with water. In a few instances, air bubbles can be added to the oil and grease mixtures to separate

the hydrophobic materials from the water phase by flotation. Chemicals have also been added to

help break the emulsions. American Petroleum Institute (API) separators have been used

extensively by the petroleum industry to remove oils from wastewaters. The food industries use

grease traps to collect the grease prior to its discharge. Unfortunately,grease traps are designed for

regular cleaning of the trapped grease. Too often they are allowed to fill up and discharge the

excess grease into the sewer or are flushed with hot water and steam to fluidize the grease for easy

discharge to the sewer. A grease trap should be designed for a specific volume of grease to be

collected over specific time periods. Care should be taken to design the trap so that the grease can

easily be removed and properly handled. Neglected or poorly designed grease traps are worse than

no grease traps at all.

iv)Removal of Toxic Substances

Recent federal legislation of U.S.A has made it illegal for industries to discharge toxic materials in

wastewaters. Each industry is responsible for determining if any of its wastewater components are

toxic to the environment and to remove them prior to the wastewater discharge. The EPA has

identified a number of priority pollutants which must be removed and kept under proper control

from their origin to their point of ultimate disposal. Major emphasis has recently been placed on

heavy metals and on complex organics that have been implicated in possible cancer production.

33

Pretreatment is essential to reduce heavy metals below toxic levels and to prevent discharge of any

toxic organics. Fortunately, toxic organics can ultimately be destroyed by various chemical

oxidation systems. Incineration appears to be the most economical method for destroying toxic

organics.

To make incineration economical, the organics must be kept separated from the dilute wastewaters

and treated in their concentrated form. If the heavy metals cannot be reused, they must be

concentrated and placed into insoluble materials which will not leach the heavy metals. Toxic

substances currently pose the greatest challenge to industries since very little attention has been

paid to these materials in the past.

b) Primary treatment

Wastewater treatment is directed toward removal of pollutants with the least effort. Suspended solids are

removed by either physical or chemical separation techniques and handled as concentrated solids.BOD is

lowered moderately.

Following methods are used for pretreatment process :

i) Screening,

ii) Degritting,

iii) Sedimentation,

iv) Chemical precipitation.

i) Screening

Fine screens such as hydroscreens are used to remove moderate size particles that are not easily

compressed under fluid flow. Fine screens are normally used when the quantities of screened

particles are large enough to justify the additional units. Mechanically cleaned fine screens have

been used for separating large particles. A few industries have used large bar screens to catch large

solids that could clog or damage pumps or equipment following the screens.

ii) Degritting

34

Industries with sand or hard, inert particles in their wastewaters have found aerated grit chambers

useful for the rapid separation of these inert particles. Aerated grit chambers are relatively small,

with total volume based on 3-min retention at maximum flow. Diffused air is normally used to

create the mixing pattern shown in Fig. 25-44, with the heavy, inert particles removed by

centrifugal action and friction against the tank walls. The air flow rate is adjusted for the specific

particles to be removed. Floatable solids are removed in the aerated grit chamber. It is important to

provide for regular removal of floatable solids from the surface of the grit chamber;otherwise,

nuisance conditions will be created. The settled grit is normally removed with a continuous screw

and buried in a landfill.

FIG. 25-44 Schematic diagram of an aerated grit chamber.

iii) Sedimentation

Before an industrial waste is subjected to a Chemical or Biological treatment,or both,it may be

required to separate the suspended matter by physical operations like Sedimentation and Floatation.

Sedimentation tanks are to be provided only when the waste contains high percentage of settlable

solids.(Fig 1)

35

On the other hand, Floatation is employed to separate fine particles with very low settling

characteristics.This process consists of creation of fine air bubbles in the waste body by the

introduction of air to the system.The rising air bubbles attach themselves to the suspended particles

and thereby increase the buoyancy of the particles.The particles thus lifted to the liquid surface are

removed by skimming.

_ _ _ _ _ _ _ _ _ _ _

_ _ _ _ _ _ _ _ _ _ _

_ _ _ _ _ _ _ _ _ _ _

∞

Fig : Sedimentation Tank

Fig.Schematic diagram of a circular sedimentation tank Fig.Schematic diagram of a rectangular sedimentation tank.

iv) Chemical precipitation

Lightweight suspended solids and colloidal solids can be removed by chemical precipitation and

gravity sedimentation. In effect, the chemical precipitate is used to agglomerate the tiny particles

into large particles that settle rapidly in normal sedimentation tanks. Aluminum sulfate, ferric

chloride, ferrous sulfate,lime, and polyelectrolytes have been used as coagulants. The choice of

36

coagulant depends upon the chemical characteristics of the particles being removed, the pH of the

wastewaters, and the cost and availability of the precipitants. While the precipitation reaction results

in removal of the suspended solids, it increases the amount of sludge to be handled. The chemical

sludge must be considered along with the characteristics of the original suspended solids in

evaluating sludge-processing systems.

Normally, chemical precipitation requires a rapid mixing system and a flocculation system ahead of

the sedimentation tank. With a rectangular sedimentation tank, the rapid-mixer and flocculation

units are added ahead of the tank. With a circular sedimentation tank the rapid-mixer and

flocculation units are built into the tank. Schematic diagrams of chemical treatment systems are

shown in Figs. 25-47 and 25-48. Rapid mixers are designed to provide 30-s retention at average

flow with sufficient turbulence to mix the chemicals with the incoming wastewaters. The

flocculation units are designed for slow mixing at 20-min retention. These units are designed to

cause the particles to collide and increase in size without excessive shearing. Care must be taken to

move the flocculated mixture from the flocculation unit to the sedimentation unit without disrupting

the large floc particles.

The parameter used to design rapid mix and flocculation systems is the root mean square velocity

gradient G, which is defined by equation

G = ( P _ ) 1/2 ( 1 )

VU sec

where: P = Power input to the water (ft-lb/sec)

V = Mixer or flocculator volume (ft)3

U = Absolute viscosity of water (lb-sec/ft2)

37

Fig. Schematic diagram of a chemical precipitation system for rectangular sedimentation tanks.

Fig. Schematic diagram of a chemical precipitation system for circular sedimentation tanks.

Optimum mixing usually requires a G value of greater than 1000 inverse seconds. Optimum

flocculation occurs when G is in the range 10–100 inverse seconds.

Chemical precipitation can remove 95 percent of the suspended solids, up to 50 percent of the

soluble organics and the bulk of the heavy metals in a wastewater. Removal of soluble organics is a

function of the coagulant chemical, with iron salts yielding best results and lime the poorest. Metal

removal is primarily a function of pH and the ionic state of the metal. Guidance is available from

solubility product data.

38

c) Secondary treatment

Secondary treatment utilizes processes in which microorganisms, primarily bacteria, stabilize waste

components. The mixture of microorganisms is usually referred to as biomass. A portion of the

waste is oxidized, releasing energy, the remainder is utilized as building blocks of protoplasm. The

energy released by biomass metabolism is utilized to produce the new units of protoplasm. Thus,

the incentive for the biomass to stabilize waste is that it provides the energy and basic chemical

components required for reproduction. The process of biological waste conversion by biological

treatment process is illustrated by Eq. (25-15).

Waste + Biomass + Electron More + End products:

(electron donor) acceptor Proper biomass Oxidized electron

environmental conditions donor

Reduced electron

acceptor

As this equation indicates, the waste generally serves as an electron donor, necessitating that an

electron acceptor be supplied. A variety of substances can be utilized as electron acceptors,

including molecular oxygen, carbon dioxide, oxidized forms of nitrogen, sulfur, and organic

substances. The characteristics of the end products of the reaction are determined by the electron

acceptor. Table 25-39 is a list of typical end products as a function of the electron acceptor. In

general, the end products of this reaction are at a much lower energy level than the waste

components, thus resulting in the release of energy referred to above. Although this process is

usually utilized for the stabilization of organic substances, it can also be utilized for oxidation of

inorganics.

For example, biomass-mediated oxidation of iron, nitrogen, and sulfur is known to occur in nature

and in anthropogenic processes.

Equation (25-15) describes the biomass-mediated reaction and indicates that proper environmental

conditions are required for the reaction to take place. These conditions are required by the biomass,

not the electron donor or acceptor. The environmental conditions include pH, temperature,

nutrients, ionic balance, and so on. In general,biomass can function over a wide pH range generally

from 5 to 9.

39

However, some microbes require a much narrower pH range; i.e.effective methane fermentation

requires a pH in the range of 6.5–7.5.It is just as important to maintain a relatively constant pH in

the process as it is to stay within the range given above. Microorganisms can function effectively at

the extremes of their pH range provided they are given the opportunity to acclimate to these

conditions. Continual changes in pH are detrimental, even if the organisms are on the average near

the middle of their effective pH range. A similar situation prevails for temperature. Most organisms

Table 25-39 Electron Acceptors and End Products for Biological Reactions Electron acceptors End productMolecular oxygenOxidized nitrogenOxidized sulfurCO2, acetic acid, formic acidComplex organics

Water, CO2, oxidized nitrogenN2, N2O, NO, CO2, H2OH2S, S, CO2, H2O CH4, CO2, H2

H2, simple organics, CO2, H2O

can function well over a broad range of temperature but do not adjust well to frequent fluctuations

of even a few degrees. There are three major temperature ranges in which microorganisms function.

The psychrophilic range (5° C to 20° C), the mesophilic range (20° C to 45° C), and the

thermophilic range (45° C to 70° C). In general the microbes that function in one of these

temperature ranges cannot function efficiently in the other ranges. As it is generally uneconomical

to adjust the temperature of a waste, most processes are operated in the mesophilic range.

If the normal temperature of the waste is above or below the mesophilic range, the process will be

operated in the psychrophilic or thermophilic range as appropriate. However, occasionally the

temperature of the waste is altered to improve performance. For example,some anaerobic treatment

processes are operated under thermophilic conditions, even though the waste must be heated to

achieve this temperature range. This is carried out in order to speed up the degradation of complex

organics and/or to achieve kill of mesophilic pathogens. It should be noted that any time the

biological operation of a process moves away from its optimum or most effective range, be it pH,

temperature, nutrients, or what have you, the rate of biological processing is reduced.

All microorganisms require varying amounts of a large number of nutrients. These are required

because they are necessary components of bacterial protoplasm. The nutrients can be divided into

three groups: macro, minor, and micro. The macronutrients are those that comprise most of the

biomass. These are given by the commonly accepted formula for biomass (C60H87O23N12P). The

40

carbon, hydrogen,and oxygen are normally supplied by the waste and water, but the nitrogen and

phosphorous must often be added to industrial wastes to ensure that a sufficient amount is present.

A good rule is that the mass of nitrogen should be at least 5 percent of the BOD, and the mass of

phosphorous should be at least 20 percent of the mass of nitrogen. One of the major operational

expenses is the purchase of nitrogen and phosphorous for addition to biologically based treatment

processes.

The quantities of nitrogen and phosphorous referred to above as required are actually in excess of

the minimum amounts needed. The actual amount required depends upon the quantity of excess

biomass wasted from the system and the amount of N and P available in the waste. This will be

expanded upon later in this section. The minor nutrients include the typical inorganic components

of water. These are given in Table 25-40. The range of concentrations required in the wastewater

for the minor nutrients is 1–100 mg/L. The micronutrients include the substances that we normally

refer to as trace metals and vitamins. It is interesting to note that the trace metals include virtually

all of the toxic heavy metals. This reinforces the statement made above that toxicity is a function of

concentration and not an absolute parameter. Whether or not the substances referred to as vitamins

will be required depends upon the type of microorganisms required to stabilize the waste materials.

Many microorganisms have the ability to make their own vitamins from the waste components;

thus, a supplement is not needed. However, occasionally the addition of an external source of

vitamins is essential to the success of a biologically based waste-treatment system. In general, the

trace nutrients must be present in a waste at a level of a few micrograms per liter.

One aspect of the basic equation describing biological treatment of waste that has not been referred

to previously is that biomass appears on both sides of the equation. As was indicated above, the

only reason that microorganisms function in waste-treatment systems is because it enables them to

reproduce. Thus, the quantity of biomass in a wastetreatment system is higher after the treatment

process than before it.

Table : Minor and Micro Nutrients Required for Biologically Mediated ReactorsMinor 1–100 mg/LSodium, potassium, calcium, magnesium, iron, chloride, sulfateMicro 1–100 μg/LCopper, cobalt, nickel, manganese, boron, vanadium, zinc, lead, molybdenum,various organic vitamins, various amino acids

41

This is favorable in that there is a continual production of the organisms required to stabilize the

waste. Thus, one of the major reactants is, in effect, available free of charge. However, there is an

unfavorable side in that unless some organisms are wasted from the system, an excess level will

build up, and the process could choke on organisms.The wasted organisms are referred to as sludge.

A major cost component of all biologically based processes is the need to provide for the ultimate

disposal of this sludge.

Biologically based treatment processes probably account for the majority of the treatment systems

used for industrial waste management because of their low cost and because most substances are

amenable to biological breakdown. However, some substances are difficult to degrade biologically.

Unfortunately, it is not possible at present to predict a priori the biodegradability of a specific

organic compound; rather, we must depend upon experience and testing. The collective experience

of the field has been put into compendia by EPA in a variety of documents. However, these data are

primarily qualitative.

There have been some attempts to develop a system of prediction of biodegradability based on a

number of compound parameters such as solubility, presence or absence of certain functional

groups, compound polarity, and so on. Unfortunately, none of these systems has advanced to the

point where reliable quantitative predictions are possible.

Another complication is that some organics that are easily biodegradable at low concentration exert

a toxic effect at high concentration.Thus, literature data can be confusing. Phenol is a typical

compound that shows ease of biodegradation when the concentration is below 500 mg/L but poor

biodegradation at higher concentrations.

Another factor affecting both biodegradation and toxicity is whether or not a substance is in

solution. In general, if a substance is not in solution, it is not available to affect the biomass. Thus,

the presence of a waste in substances that can precipitate, complex, or absorb other waste

components can have a significant effect on reports of biodegradability and/or toxicity. A

quantitative estimate of toxicity can be obtained in terms of the change in kinetic parameters (time,

waste concentration ,biomass concentration , influent waste concentration ,treated waste

concentration , reactor hydraulic retention time)of a system.

42

Fig: Diagram of a suspended growth system. Fig : Diagram of a fixed-film system.

Table : Favorable (F) and Unfavorable (U)Combinations of Electron Acceptor, Waste Strength,and Reactor Type Suspended growth reactorElectron acceptor Waste strength ConditionAerobic Low–modest FAerobic High UAnoxic Low–modest FAnoxic High UAnaerobic Low–modest UAnaerobic High F Fixed film reactorElectron acceptor Waste strength ConditionAerobic Low FAerobic Modest–high UAnoxic Low–modest FAnoxic High UAnaerobic Low–modest FAnaerobic High F

Activated Sludge Process

This treatment process is the most widely used aerobic suspended growth reactor system. It will

consistently produce a high-quality effluent (BOD5 and SS of 20–30 mg/L). Operational costs are

higher than for other secondary treatment processes primarily because of the need to supply

molecular oxygen using energy-intensive mechanical aerator- or sparger-type equipment.

Removal of soluble organics, colloidal, particulates, and inorganics are achieved in this system

through a combination of biological metabolism,adsorption, and entrapment in the biological floc.

43

Indeed, many pollutants that are not biologically degradable are removed during activated sludge

treatment by adsorption or entrapment by the floc.

For example, most heavy metals form hydroxide or carbonate precipitates under the pH conditions

maintained in activated sludge, and most organics are easily adsorbed to the surface of the

biological floc.A qualitative guide to the latter is provided by the octanol-water partition coefficient

of a compound.

All activated sludge systems include a suspended growth reactor in which the wastewater, recycled

sludge, and molecular oxygen are mixed. The latter must be dissolved in the water; thus the need

for an energy-intensive pure oxygen or air supply system. Usually, air is the source of the molecular

oxygen rather than pure oxygen. Energy for mixing of the reactor contents is supplied by the

aeration equipment.

All systems include a separator and pump station for sludge recycle and sludge wasting. The

separator is usually a sedimentation tank that is designed to function as both a clarifier and a

thickener. Many modifications of the activated sludge process have been developed over

the years and are described below. Most of these involve differences in the way the reactor is

compartmentalized with respect to introduction of waste, recycle, and/or oxygen supply.

Modifications The modifications of activated sludge systems offer considerable choice in

processes. Some of the most popular modifications of the activated sludge process are illustrated in

Fig. 25-54. Conventional activated sludge uses a long narrow reactor with air supplied along the

length of the reactor. The recycle sludge and waste are introduced at the head end of the reactor

producing a zone of high waste to biomass concentration and high oxygen demand. This

modification is used for relatively dilute wastes such as municipal wastewater. Step aeration

systems distribute the waste along the length of the aerator, thus reducing the oxygen demand at the

head end of the reactor and spreading the oxygen demand more uniformly over the whole reactor.

In the complete mix system, the waste and sludge recycle are uniformly distributed over the whole

reactor,resulting in the waste load and oxygen demand being uniform in the entire reactor.

Complete-mixing activated sludge is the most popular system for industrial wastes because of its

ability to absorb shock loads better than other modifications. Contact stabilization is a modification

of activated sludge that is best suited to wastewaters having high suspended solids and low soluble

organics. Contact stabilization employs a short-term mixing tank to adsorb the suspended solids and

44

metabolize the soluble organics, a sedimentation tank for solids separation, and a reaeration tank for

stabilization of the suspended organics.

Extended-aeration systems are actually long-term-aeration, completely mixed activated-sludge

systems. They employ 24- to 48-hr aeration periods and high mixed-liquor suspended solids to

provide complete stabilization of the organics and aerobic digestion of the activated sludge in the

same aeration tank. The oxidation ditch is a popular form of the extended-aeration system

employing mechanical aeration. Pure-oxygen systems are designed to treat strong industrial wastes

in a series of completely mixed units having relatively short contact periods. One of the latest

modifications of activated sludge employs powdered activated carbon to adsorb complex organics

and assist in solids separation. Another modification employs a redwood medium trickling filter

ahead of a short-term aeration tank with mixed liquor recycled over the redwood-medium tower to

provide heavy microbial growth on the redwood as well as in the aeration tank.

As indicated previously, success with the activated sludge process requires that the biomass have

good self-flocculating properties. Significant research effort has been expended to determine the

conditions that favor the development of good settling biomass cultures.

These have indicated that nutritional deficiency, levels of dissolved oxygen between 0 to 0.5 mg/L,

and pH values below 6.0 will favor the predomination of filamentous biomass. Filamentous

organisms settle and compact poorly and thus are difficult to separate from liquid. By avoiding the

above conditions, and with the application of selector technology, the predomination of filaments in

the biomass can be eliminated. A selector is often a short contact (15–30 min) reactor set ahead of

the main activated sludge reactor. All of the recycle sludge and all of the waste are routed to the

selector. In the selector, either a high rate of aeration (aerobic selector) is used to keep the dissolved

oxygen above 2 mg/L, or no aeration occurs (anaerobic selector) so that the dissolved oxygen is

zero. Because filamentous organisms are microaerophilic, they cannot predominate when the

dissolved oxygen level is zero or high. The anaerobic selector not only selects in favor of

nonfilamentous biomass but also fosters luxury uptake of phosphorous and is used in systems where

phosphorous removal is desired.

45

Fig. 25-54 Schematic diagrams of various modifications of the activated-sludge process. (a) Conventional activated sludge.(b) Step aeration. (c) Contact stabilization. (d) Complete mixing. (e) Pure oxygen. ( f ) Activated biofiltration (ABF). (g) Oxidation ditch.

Aeration Systems These systems control the design of aeration tanks. Aeration equipment has two

major functions: mixing and oxygen transfer. Diffused-aeration equipment employs either a

fixedspeed positive-displacement blower or a high-speed turbine blower for readily adjustable air

volumes. Air diffusers can be located along one side of the aeration tank or spread over the entire

bottom of the tank. They can be either fine-bubble or coarse-bubble diffusers. Fine bubble diffusers

are more efficient in oxygen transfer but require more extensive air-cleaning equipment to prevent

them from clogging as a result of dirty air. Mechanical-surface-aeration equipment is more efficient

46

than diffused-aeration equipment but is not as flexible. Economics has dictated the use of large-

power aerators, but tank configuration has tended to favor the use of greater numbers of lower-

power aerators. Oxidation ditches use horizontal rotor-type aerators. Mixing is a critical problem

with mechanical-surface aerators since they are a point-source pump of limited capacity.

Experience has indicated that bearings are a serious problem with mechanical-aeration equipment.

Wave action generated within the aeration tank tends to produce lateral stresses on the bearings and

has resulted in failures and increased maintenance costs. Slow-speed mechanical-surface-aeration

units present fewer problems than the high-speed mechanical-surface aeration units. Deep tanks,

greater than 3.0 m (10 ft), require draft tubes to ensure proper hydraulic flow through the aeration

tank.

Short-circuiting is one of the major problems associated with mechanical aeration equipment.

Combined mechanical- and diffusedaeration systems have enjoyed some popularity for industrial-

waste systems that treat variable organic loads. The mechanical mixers provide the fluid mixing

with the diffused aeration varied for different oxygen-transfer rates.

Diffused-aeration systems transfer from 20 to 40 mg/(L O2.h).Combined mechanical- and diffused-

aeration systems can transfer up to 65 mg/(L O2.h), while mechanical-surface aerators can provide

up to 90 mg/(L O2.h). Pure-oxygen systems can provide the highest oxygen-transfer rate, up to 150

mg/(L O2.h). Aeration equipment must provide sufficient oxygen to meet the peak oxygen demand;

otherwise,the system will fail to provide proper treatment. For this reason, the peak oxygen demand

and the rate of transfer for the desired equipment determine the size of the aeration tank in terms of

retention time. Economics dictates a balance between the size of the aeration tank and the size of

the aeration equipment. As the cost of power increases, economics will favor constructing a larger

aeration tank and smaller aerators. It is equally important to examine the hydraulic flow pattern

around each aerator to ensure maximum efficiency of oxygen transfer. Improper spacing of aeration

equipment can waste energy.

There is no standard aeration-tank shape or size. Aeration tanks can be round, square,or rectangular.

Shallow aeration tanks are more difficult to mix than deeper tanks. Yet aeration-tank depths have

ranged from 0.6 m (2 ft) to 18 m (60 ft). The oxidation-ditch systems tend to be shallow, while

some high-rate diffused-aeration systems have used very deep tanks to provide more efficient

oxygen transfer.

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Regardless of the aeration equipment employed, oxygen-transfer rates must provide from 0.6 to 1.4

kg of oxygen/kg BOD5 (0.6 to 1.4 lb oxygen/lb BOD5) stabilized in the aeration tank for

carbonaceous oxygen demand. Nitrogen oxidation can increase oxygen demand at the rate of 4.3 kg

(4.3 lb) of oxygen/kg (lb) of ammonia nitrogen oxidized.

At low oxygen-transfer rates more excess activated sludge must be removed from the system than at

high oxygen-transfer rates. Here again the economics of sludge handling must be balanced against

the cost of oxygen transfer. The quantity of waste activated sludge will depend upon wastewater

characteristics. The inert suspended solids entering the treatment system must be removed with the

excess activated sludge. The soluble organics are stabilized by converting a portion of the organics

into suspended solids, producing from 0.3 to 0.8 kg (0.3 to 0.8 lb) of volatile suspended solids/kg

(lb) of BOD5 stabilized.

Biodegradable suspended solids in the wastewaters will result in destruction of the original

suspended solids and their conversion to a new form. Depending upon the chemical characteristics

of the biodegradable suspended solids, the conversion factor will range from 0.7 to 1.2 kg (0.7 to

1.2 lb) of microbial solids produced/kg (lb) of suspended solids destroyed. If the suspended solids

produced by metabolism are not wasted from the system, they will eventually be discharged in the

effluent. While considerable efforts have been directed toward developing activated-sludge systems

which totally consume the excess solids, no such system has proved to be practical.The concept of

total oxidation of excess sludge is fundamentally unsound and should be recognized as such.

Sedimentation Tanks These tanks are an integral part of any activated-sludge system. It is essential

to separate the suspended solids from the treated liquid if a high-quality effluent is to be produced.

Circular sedimentation tanks with various types of hydraulic sludge collectors have become the

standard secondary sedimentation system. Square tanks have been used with common-wall

construction for compact design with multiple tanks. Most secondary sedimentation tanks use

center-feed inlets and peripheral-weir outlets. Recently, efforts have been made to employ

peripheral inlets with submerged orifice flow controllers and either center-weir outlets or peripheral

weir outlets adjacent to the peripheral-inlet channel.

Scum baffles around the periphery of the sedimentation tank and radial scum collectors are standard

equipment to ensure that rising solids or other scum materials are removed as quickly as they form.

48

Hydraulic sludge-collection tubes have replaced the center sludge well, but they have caused a new

set of operational problems. These tubes were designed to remove the settled sludge at a faster rate

than conventional sludge scrapers. To obtain good hydraulic distribution in the sludge-collection

tubes, it was necessary to increase the rate of return sludge flow and decrease the concentration of

return sludge.

The higher total inflow to the sedimentation tank created increased forces that lifted the settled-

solids blanket at the wall, causing loss of excessive suspended solids and lower effluent quality.

Operating data tend to favor conventional secondary sedimentation tanks over hydraulic sludge-

collection systems. Return-sludge rates normally range from 25 to 50 percent for MLSS

concentrations up to 3300 mg/L. Most return-sludge pumps are centrifugal pumps with capacities

up to 100 percent raw-waste flow.

Gravity settling can concentrate activated sludge to 10,000 mg/L, but hydraulic sludge-collecting

tubes tend to operate best below 8,000 mg/L. The excess activated sludge can be wasted either from

the return sludge or from a separate waste-sludge hopper near the center of thetank. The low solids

concentrations result in large volumes of waste activated sludge in comparison with primary sludge.

Unfortunately, the physical characteristics of waste activated sludge prevent significant

concentration without the expenditure of considerable energy. Gravity thickening can produce 2

percent solids, while air flotation can produce 4 percent solids concentration. Centrifuges are able to

concentrate activated sludge from 10 to 15 percent solids, but the capture is limited.

Vacuum filters can equal the performance of centrifuges if the sludge is chemically conditioned.

Filter presses and belt-press filters can produce cakes with 15 to 25 percent solids. It is very

important that the excess activated sludge formed in the aeration tanks be wasted on a regular basis;

otherwise, effluent quality will deteriorate. Care should be taken to ensure that sludge-thickening

systems do not control activated sludge operations. Alternative sludge-handling provisions should

be available during maintenance on sludge-thickening equipment. At no time should final

sedimentation tanks be used for the storage of sludge beyond that required by daily operational

variations.

Anaerobic/Anoxic Activated Sludge The activated sludge concept (i.e., suspended growth reactor)

can be used for anaerobic or anoxic systems in which no oxygen or air is added to the reactor. An

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anoxic activated sludge is used for systems in which removal of nitrate is a goal or where nitrate is

used as the electron acceptor. These systems(denitrification) will be successful if the nitrate is

reduced to low levels in the reactor so that nitrate reduction to nitrogen gas does not take place in

the clarifier-thickener. Nitrogen gas production in the clarifier will result in escape of biological

solids with the effluent as nitrogen bubbles floating sludge to the clarifier surface. For nitrogen

reduction, a source of organics (electron donor) is required. Any inexpensive carbohydrate can be

effectively used for nitrate removal.

Many systems utilize methanol as the donor because it is rapidly metabolized; others use the

organics in sewage in order to reduce chemical costs. Nitrate reduction is invariably used as part of

a system in which organics and nitrogen removal are goals. In such systems, the nitrogen in the

waste is first oxidized to nitrate and then reduced to nitrogen gas. Anaerobic activated sludge has

been used for strong industrial wastes high in degradable organic solids. In these systems, a high

rate of gasification takes place in the sludge separator so that a highly clarified effluent is usually

not obtained. A vacuum degasifier is incorporated in such systems to reduce solids loss. Such

systems have been used primarily with meat packing wastes that are warm, high in BOD and yield a

high level of bicarbonate buffer as a result of ammonia release from protein breakdown.

All of these conditions favor anaerobic processing. The use of this process scheme provides a high

BSRT (15–30 days), usually required for anaerobic treatment, at a low HRT (1–2 days).

Lagoons Lagoons are low-cost, easy-to-operate wastewater treatment systems capable of producing

satisfactory effluents. Nominally,a lagoon is a suspended-growth no-recycle reactor with a variable

degree of mixing. In lagoons in which mechanical or diffused aeration is used, mixing may be

sufficient to approach complete mixing (i.e., solids maintained in suspension). In other types of

lagoons, most solids settle and remain on the lagoon bottom, but some mixing is achieved as a

result of gas production from bacterial metabolism and wind action. Lagoons are categorized as

aerobic, facultative, or anaerobic on the basis of degree of aeration. Aerobic lagoons primarily

depend on mechanical or diffused air supply. Significant oxygen supply is also realized through

natural surface aeration. A facultative lagoon is dependent primarily on natural surface aeration and

oxygen generated by algal cells. These two lagoon types are relatively shallow to encourage surface

aeration and provide for maximum algal activity.

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The third type of lagoon is maintained under anaerobic conditions to foster methane fermentation.

This system is often covered with floating polystyrene panels to block surface aeration and help

prevent a drop in temperature. Anaerobic lagoons are several meters deeper than the other two

types. Lagoon flow schemes can be complex, employing lagoons in series and recycle from

downstream to upstream lagoons. The major effect of recycle is to maintain control of the solids. If

solids escape the lagoon system, a poor effluent is produced.Periodically controlled solids removal

must take place or solids will escape.

Lagoons are, in effect, inexpensive reactors. They are shallow basins either cut below grade or

formed by dikes built above grade or a combination of a cut and dike. The bottom must be lined

with an impermeable barrier and the sides protected from wind erosion.These systems are best used

where large areas of inexpensive land are available.

Facultative Lagoons These lagoons have been designed to use both aerobic and anaerobic

reactions. Normally, facultative lagoons consist of two or more cells in series. The settleable solids

tend to settle out in the first cell and undergo anaerobic metabolism with the production of organic

acids and methane gas, which bubbles out to the atmosphere. Algae at the surface of the lagoon

utilize sunlight for their energy in converting carbon dioxide, water, and ammonium ions into algal

protoplasm with the release of oxygen as a waste product.

Aerobic bacteria utilize the oxygen released by the algae to stabilize the soluble and colloidal

organics. Thus, the bacteria and algae form a symbiotic relationship as shown in Fig. 25-56. The

interesting aspect of facultative lagoons is that the organic matter in the incoming wastewaters is

not stabilized but rather is converted to microbial protoplasm,which has a slower rate of oxygen

demand. In fact, in some facultative lagoons inorganic compounds in the wastewaters are converted

to organic compounds with a total increase in organics within the lagoon system.

Facultative lagoons are designed on the basis of organic load in relationship to the potential sunlight

availability. In the northern part of the United States facultative lagoons are designed on the basis of

2.2 g/(m2.day) [20 lb BOD5/(acre.day)]. In the middle part of the United States the organic load can

be increased to 3.4 to 4.5 g/(m2.day) [30 to 40 lb BOD5/(acre.day)], while in the southern part the

organic load can be increased to 6.7 g/(m2.day) [60 lb BOD5/(acre.day)]. The depth of lagoons is

normally maintained between 1.0 and 1.7 m (3 and 5 ft). A depth less than 1.0 m (3 ft) encourages

the growth of aquatic weeds and permits mosquito breeding. In dry areas the maximum depth may

51

be increased above 1.7 m (5 ft) depending upon evaporation. Most facultative lagoons depend upon

natural wind action for mixing and should not be placed in screened areas where wind action is

blocked.

Effluent quality from facultative lagoons is related primarily to the suspended solids created by

living and dead microbes. The long retention period in the lagoons allows the microbes to die off,

leaving a small particle that settles slowly. The release of nutrients from the dead microbes permits

the algae to survive by recycling the nutrients.

Thus, the algae determine the ultimate effluent quality. Use of series ponds with well-designed

transfer structures between ponds permits maximum retention of algae within the ponds and the

best-quality effluent. Normally the soluble BOD5 is under 5 or 10 mg/L with a total effluent BOD5

under 30 mg/L. The effluent suspended solids will vary widely during the different seasons of the

year, being a maximum of 70 to 100 mg/L in the summer months and a minimum of 10 to 20 mg/L

in the winter months. If suspended-solids removal is essential, chemical precipitation is the best

method available at the present time. Slow sand filters and rock filters have been studied for

suspended-solids removal; they work well as long as the effluent suspended solids are relatively

low, 40 to 70 mg/L.

Aerated Lagoons These lagoons originated from efforts to control overloaded facultative lagoons.

Since the lagoons were deficient in oxygen, additional oxygen was supplied by either mechanical

surface aerators or diffused aerators. Mechanical surface aerators were quickly accepted as the

primary aerators because they could be quickly added to existing ponds and moved to strategic

locations.

Unfortunately, the high-speed, floating surface aeration units were not efficient, and large numbers

were required for existing lagoons.

The problem was simply one of poor mixing in a very shallow lagoon.Eventually, diffused aeration

equipment was added to relatively deep lagoons [3.0 to 6.0 m (10 to 20 ft)]. Mixing became the

most significant parameter for good oxygen transfer in aerated lagoons. From an economical point

of view, it was found that a completely mixed aerated lagoon with 24-h retention provided the best

balance between mixing and oxygen transfer. As the organic load increased, the fluid retention time

also increased. Short-term aeration permitted metabolism of the soluble organics by the bacteria,

but time did not permit metabolism of the suspended solids. The suspended solids were combined

52

with the microbial solids produced from metabolism and discharged from the aerated lagoon to a

solids-separation pond. Data from the short-term aerated lagoon indicated that 50 percent BOD5

stabilization occurred, with conversion of the soluble organics to microbial cells. The problem was

separation and stabilization of the microbial cells. Short-term sedimentation ponds permitted

separation of the solids without significant algae growths but required cleaning at frequent intervals

to keep them from filling with solids and flowing into the effluent. Long-term lagoons permitted

solids separation and stabilization but also permitted algae to grow and affect effluent quality.

Aerated lagoons were simply dispersed microbial reactors which permitted conversion of the

organic components in the wastewaters to microbial solids without stabilization. The residual

organics in solution were very low, less than 5 mg/L BOD5. By adding oxygen and improving

mixing, the microbial metabolism reaction was speeded up, but the stabilization of the microbial

solids has remained a problem to be solved.

Anaerobic Lagoons These lagoons were developed when a major fraction of the organic

contaminants consisted of suspended solids that could be removed easily by gravity sedimentation.

The anaerobic lagoons are relatively deep [8.0 to 6.0 m (10 to 20 ft)], with a short fluid-retention

time (3 to 5 days) and a high BOD5 loading rate, up to 3.2 kg/(m3.day) [200 lb/(1000 ft3.day)].

Microbial metabolism in the settled-solids layer produces methane and carbon dioxide, which

quickly rise to the surface, carrying some of the suspended solids. A scum layer that retards oxygen

transfer and release of obnoxious gases is quickly produced in anaerobic lagoons. Mixing with a

grinder pump can provide a better environment for metabolism of the suspended solids. The key for

anaerobic lagoons is adequate buffer to keep the pH between 6.5 and 8.0. Protein wastes have

proved to be the best pollutants to be treated by anaerobic lagoons, with the ammonium ions

reacting with carbon dioxide and water to form ammonium bicarbonate as the primary buffer. High-

carbohydrate wastes are poor in anaerobic lagoons since they produce organic acids without

adequate buffer, making it difficult to maintain a suitable pH for good microbial growth.

Anaerobic lagoons do not produce a high-quality effluent but are able to reduce the BOD load by

80 to 90 percent with a minimum of effort. Since anaerobic lagoons work best on strong organic

wastes, their effluent must be treated by either aerated lagoons or facultative lagoons. An anaerobic

lagoon is simply the first stage in the treatment of strong organic wastewaters.

53

Fig. 25-56 Schematic diagram of oxidation-pond operations.

Fixed Film Reactor Systems A major advantage of fixed film systems is that a flocculent-type

biomass is not necessary as the biomass remains in the reactor attached to inert packing. Biomass

does periodically slough off or break away from the packing, usually in large chunks that can be

easily removed in a clarifier. On the other hand, the time of contact between the biomass and the

waste is much shorter than in suspended growth systems, making it difficult to achieve the same

degree of treatment especially in aerobic systems.

Aerobic, anoxic, and anaerobic fixed film systems are utilized for waste treatment.

Aerobic systems including trickling filters and rotating biological contactors (RBC) are operated in

a nonflooded mode to ensure adequate oxygen supply. Other aerobic, anoxic, and anaerobic

systems employ flooded reactors. The most common systems are packed beds (anaerobic trickling

filter) and fluidized or expanded bed systems.

Trickling Filters For years trickling filters were the mainstay of biological wastewater treatment

systems because of their simplicity of design and operation. Trickling filters were displaced as the

primary biological treatment system by activated sludge because of better effluent quality. Trickling

filters are simply fixed-medium biological reactors with the wastewaters being spread over the

surface of a solid medium where the microbes are growing. The microbes remove the organics from

the wastewaters flowing over the fixed medium. Oxygen from the air permits aerobic reactions to

occur at the surface of the microbial layer, but anaerobic metabolism occurs at the bottom of the

microbial layer where oxygen does not penetrate.

Originally, the medium in trickling filters was rock, but rock has largely been replaced by plastic,

which provides greater void space per unit of surface area and occupies less volume within the

filter. A plastic medium permitted trickling filters to be increased from a medium depth of 1.8 m (6

54

ft) to one of 4.2 m (14 ft) and even 6.0 m (20 ft). The wastewaters are normally applied by a rotary

distributor or a fixed spray nozzle. The spraying or discharging of wastewaters above the trickling-

filter medium permits better distribution over the medium and oxygen transfer before reaching the

medium. The effluent from the trickling-filter medium is captured in a clay-tile underdrain system

or in a tank below the plastic medium. It is important that the bottom of the trickling filter be open

for air to move quickly through the filter and bring adequate oxygen for the microbial reactions.

If a high-quality effluent is required, trickling filters must be operated at a low hydraulic-loading

rate and a low organic-loading rate.

Low-rate trickling filters are operated at hydraulic loadings of 2.2 × 10−5 to 4.3 × 10−5 m3/(m2.s) [2

million to 4 million gal/(acre.day)].High-rate trickling filters are designed for 10.8 × 10−5 to 40.3 ×

10−5 m3/(m2.s) [10 million to 40 million gal/(acre.day)] hydraulic loadings and organic loadings up

to 1.4 kg/(m3.day) [90 lb BOD5/(1000 ft3.day)]. Plastic-medium trickling filters have been designed

to operate up to 108 × 10−5 m3/(m2.s) [100 million gal/(acre.day)] or even higher, with organic

loadings up to 4.8 kg/(m3.day) [300 lb BOD5/ (1000 ft3.day)]. Low-rate trickling filters will produce

better than 90 percent BOD5 and suspended-solids reductions, while high-rate trickling filters will

produce from 65 to 75 percent BOD5 reduction. Plastic- medium trickling filters will produce from

59 to 85 percent BOD5 reduction depending upon the organic-loading rate. It is important to

recognize that concentrated industrial wastes will require considerable hydraulic recirculation

around the trickling filter to obtain the proper hydraulic-loading rate without excessive organic

loads. With high recirculation rates the organic load is distributed over the entire volume of the

trickling filter for maximum organic removal. The short fluid-retention time within the trickling

filter is the primary reason for the low treatment efficiency.

Rotating Biological Contactors (RBC) The newest form of trickling filter is the rotating

biological contactor with a series of circular plastic disks, 3.0 to 3.6 m (10 to 12 ft) in diameter,

immersed to approximately 40 percent diameter in a shaped contact tank. The RBC disks rotate at 2

to 5 r/min. As the disks travel through the wastewaters, a small layer adheres to them. As the disks

travel into the air, the microbes on the disk surface oxidize the organics. Thus, only a small amount

of energy is required to supply the required oxygen for wastewater treatment. As the microbes build

up on the plastic disks,the shearing velocity that is created by the movement of the disks through

55

the water causes the excess microbes to be removed from the disks and discharged to the final

sedimentation tank.

Rotating biological contactors have been very popular in treating industrial wastes because of their

relatively small size and their low energy requirements. Unfortunately, there have occurred a

number of problems which should be recognized prior to using RBCs. Strong industrial wastes tend

to create excessive microbial growths which are not easily sheared off and which create high

oxygen-demand rates with the production of hydrogen sulfide and other obnoxious odors.

The heavy microbial growths have damaged some of the disks and caused some shaft failures. The

disks are currently being covered with plastic shells to prevent nuisance odors from occurring. Air

must be forced through the covered RBC systems and be chemically treated before being

discharged back into the environment. Recirculation of wastewater flow around the RBC units can

distribute the load over all the units and reduce the heavy initial microbial growths. RBC units also

work best under uniform organic loads, requiring surge tanks for many industrial wastes. The net

result has been for the cost of RBC units to approach that of other treatment units in terms of

organic matter stabilized.

RBCs should be designed on both a hydraulic-loading rate and an organic-loading rate. Normally,

hydraulic-loading rates of up to 0.16 m3/(m2.day) [4 gal/(ft2.day)] of surface area are used with

organic loading rates up to 44 kg/(m2.day) [9 lb BOD5/(ft2.day)]. Treatment efficiency is primarily a

function of the fluid-retention time and the organic-loading rate. At low organic-loading rates the

RBC units will produce nitrification in the same way as low-rate trickling filters.

Packed-Bed Fixed-Film Systems These systems were originally termed anaerobic trickling filters

because the first systems were submerged columns filled with stones run under anaerobic

conditions (Fig. 25-57). A wide variety of packed media is now used ranging in size from granules

40 mesh to 7.5-cm (3−in) stones. Many systems use open structure plastic packing similar to that

used in aerobic trickling filters.

The systems using granular media packing are used for anoxic denitrification. They are usually

downflow, thus serving the dual function of filtration and denitrification. Contact times are short

(EBCT < 15 min), but excellent removal is achieved due to the high level of biomass retained in the

reactor. Pacing the methanol dose to the varying feed nitrate concentration is crucial. Frequent,

short-duration backwash (usually several times per day) is required or the nitrogen bubbles formed

56

will bind the system, causing poor results. Extended backwash every two to three days is required

or the system will clog on the biomass growth. Thus, several units in parallel or a large holding tank

are needed to compensate for the down time during backwash. Backwash does not remove all the

biomass; a thin film remains coating the packing. Thus, denitrification begins immediately when

theflow is restored.

The systems using the larger packing are used in the treatment of relatively strong, low-suspended-

solids industrial waste. These systems are closed columns usually run in an upflow mode with a gas

space at the top. These are operated under anaerobic conditions with waste conversion to methane

and carbon dioxide as the goal. Effluent recycle is often used to help maintain the pH in the inlet

zone in the correct range 6.5–7.5 for the methane bacteria. Some wastes require the addition of

alkaline material to prevent a pH drop. Sodium bicarbonate is often recommended for pH control

because it is easier to handle than lime or sodium hydroxide, and because an overdose of

bicarbonate will only raise the pH modestly. An overdose of lime or sodium hydroxide can easily

raise the pH above 8.0. Table 25-44 gives some performance data with systems treating industrial

wastes. HRTs of 1 to 2 days are used, as the buildup of growth on the packing ensures a BSRT of

20–50 days. It should be possible to lower the HRT further, but in practice this has not been

successful because biomass starts to escape from the system or plugging occurs. Some escape is due

to high gasification rates, and some is due to the fact that anaerobic sludge attaches less tenaciously

to packing than aerobic or anoxic sludge. These systems can handle wastes with moderate solids

levels.

Periodically, solids must be removed from the reactor to prevent plugging of the packing or loss of

solids in the effluent.

Fig : Anaerobic process

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Biological Fluidized Beds This high-rate process has been used successfully for aerobic, anoxic,

and anaerobic treatment of municipal and industrial wastewaters. Numerous small- and largescale

applications for hazardous waste, contaminated groundwater, nontoxic industrial waste and

municipal wastewater have been reported . The basic element of the process is a bed of solid carrier

particles, such as sand or granular activated carbon, placed in a reactor through which wastewater is

passed upflow with sufficient velocity to impart motion or fluidize the carrier. An active growth of

biological organisms grow as firmly attached mass surrounding each of the carrier particles. As the

wastewater contaminants pass by the biologically covered carrier, they are removed from the

wastewater through biological and adsorptive mechanisms. Figure 25-58 is a schematic of the

process.

The influent wastewater enters the reactor through a pipe manifold and is introduced downflow

through nozzles that distribute the flow uniformly at the base of the reactor. Reversing direction at

the bottom, the flow fluidizes the carrier when the fluid drag overcomes the buoyant weight of the

carrier and its attached biomass layer. During startup (before much biomass has accumulated), the

flow velocity required to achieve fluidization is higher than after the biomass attaches. Recycle of

treated effluent is adjusted to achieve the desired degree of fluidization. As biomass accumulates,

the particles of coated biomass will separate to a greater extent at constant flow velocity.

Thus, as the system ages and more biomass accumulates, the extent of bed expansion increases (the

volume of voids increases). This phenomenon is advantageous because it prevents clogging of the

bed with biomass. Consequently, higher levels of biomass attachment are possible than in other

types of fixed film systems. However, eventually, the degree of bed expansion may become

excessive. Reduction of recycle will reduce expansion but may not be feasible because recycle has

several purposes (i.e., supply of nutrients, alkalinity, and dilution of waste strength). Control of the

expanded bed surface level is automatically accomplished using a sensor that activates a biomass

growth control system at a prescribed level and maintains the bed at the proper depth. A pump

removes a portion of the attached biomass, separates the biomass and inert carrier by abrasion, and

pumps the mixture into a separator. Here the heavy carrier settles back into the fluidized bed and

the abraded biomass, which is less dense, is removed from the system by gravity or a second pump.

Other growth control designs are also used. Effluent is withdrawn from the supernatant layer above

the fluidized bed. The reactor is usually not covered unless it is operating under anaerobic

conditions and methane, odorous gases, or other safety precautions are mandated.

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When aerobic treatment is to be provided to high concentrations of organics, pure oxygen or

hydrogen peroxide may be injected into the wastewater prior to entering the reactor. Liquid oxygen

(LOX) or pressure swing absorption (PSA) systems have been used to supply oxygen. Air may be

used at low D.O. demands.

In full-scale applications, this process has been found to operate at significantly higher volumetric

loading rates for wastewater treatment than other processes. The primary reasons for the very high

rates of contaminant removal is the high biologically active surface area available(approximately

1000 ft2/ft3 of reactor) and the high concentration of reactor biological solids (8,000–40,000 mg/L)

that can be maintained. Because of these atypical high values, designs usually indicate a 200–500

percent reduction in reactor volume when compared to other fixed film and suspended growth

treatment processes.

Of special note is the enhancement to the process when granular activated carbon (GAC) is used as

the carrier. Because GAC has adsorptive properties, organic compounds present in potable waters

and wastewater at low concentrations, often less than ten mg/L, are removed by adsorption and

subsequently consumed by the biological organisms that grow in the fluidized bed. The BTEX

compounds, methylene chloride, chlorobenzene, plastics industry toxic effluent, and many others

are removed in this manner. BTEX contamination of groundwater from leaking gasoline storage

tanks is a major problem, and sixteen full-scale fluidized bed process applications have been made.

Contaminated groundwater is pumped to the ground surface for treatment using the fluidized bed in

the aerobic mode. Often the level of BTEX is 1–10 mg/L and about 99 percent is removed in less

than ten minutes detention time. Installations in operation range in size from 30 to 3000 gpm. The

smaller installations are often skidmounted and may be moved from location to location at a given

site.

A major advantage of this process over stripping towers and vacuum systems for treating volatile

organics (VOCs) is the elimination of effluent gas treatment.

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Fig. 25-58 Schematic of fluidized bed process.

A third type of reactor system with some similarity is the upflow anaerobic sludge blanket (UASB)

system. Here, a flocculent biomass is retained in the reactor with no recycle of sludge necessary.

The sludge is maintained in the system by the use of a relatively low flow rate. The sludge formed

seems to be granular in nature and has a relatively high specific gravity.

It is thought that the presence of small particles of CaCO3 and/or clay in the waste may contribute to

the formation of the dense sludge.

A diagram of this system is shown in Fig. 25-56. The supplier of this system provides a startup seed

of this granular-type biomass. The anaerobic filter, UASB, and fluidized bed reactors have all been

used for anaerobic treatment of industrial wastes, as each is specially suited for use in anaerobic

treatment.

Suitability of Biological Treatment Process

When the waste substances are biodegradable,with or without acclimatization,the biological process

is by far the most desirable treatment process.The treatability of an industrial waste may be assessed

by conducting laboratory tests on BOD/COD ratio.If the ratio is greater than 0.6,the wastes are

biologically treatable without acclimatization;if the ratio ranges from 0.3 to 0.6,the waste needs

acclimatization for biological treatment; if the ratio is less than 0.3,other methods are suggested for

the treatment.The acclimatization involves the gradual exposure of the waste in increasing

concentration to the seed or initial microbiological population,under a controlled condition.

This design criteria for the conventional biological treatment processes may be different for different

types of industrial wastes.The system parameters for particular type of industrial wastes may be

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determined by laboratory experiments.In the absence of any actual test result,the performance data

of similar type of waste may be used for design.

In some cases,while the commonly available microbiological population fails to achieve the

biological oxidation,some special type of micro-organisms do well. So,for the effective metabolism

of some complex organic substances,development of suitable microbial culture containing specific

group of organisms is necessary. As for example,some micro organisms which are phenolytic in

action,and often found in well manured soil,have been identified,and are employed in the activated

sludge treatment of coke oven effluents.

Most of the industrial wastes don’t contain sufficient amount of nutrients for good microbial

growth.For effective biological treatment of this type of wastes nutrients are added to the reactors in

the form of Urea,Superphosphate or any other compound containing Nitrogen and Phosphorus. For a

balanced growth of micro-organisms in a rector,the BOD : N : P ratios of 100 : 5: 1 in aerobic

systems and 100 : 2.5 : 0.5 in anaerobic systems are to be maintained.

Special care should be taken in regard to the toxic wastes.Toxicity may be of acute or chronic

type,and may be to humans,plants,animals or to micro-organisms responsible for aerobic or

anaerobic biological treatment.Some of the toxic wastes like phenols,cyanides,formaldehydes etc.

yield to acclimatized growths of normal or special type of bacteria.Some other toxic metal ions like

Copper,Zinc,Chromium etc. interfere with the biological oxidation by tying up the enzymes

essentially required for microbial growth.As such these must be pretreated chemically before the

waste is subjected to biological treatment.

d) Advanced /Tertiary Treatment(Physical-Chemical treatment)

Some of the industrial wastes,amenable to biological treatment,may require prior physical

treatment; some requires only chemical treatment without any biological treatment.Some of the

chemical and physico-chemical processes employed in the Industrial wastes treatment for the

removal of dissolved inorganic materials are :

(i) Reverse osmosis,

(ii) Electrodialysis,

(iii) Chemical oxidation,

(iv) Chemical precipitation,

(v) Adsorption,

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(vi) Ion Exchange,

(vii)Thermal Reduction,

(viii)Air stripping.

By these processes,refractory organic compounds,colours,tastes,ionic and molecular contaminants,

plant nutrients etc can be removed.

i) Reverse osmosis

When a permeable membrane separates a dilute and concentrated solution,the osmotic pressure

drives the water molecules from the dilute solution,through the membrane to establish an

equilibrium.This natural response is reversed in the reverse osmosis process,where the waste water

containing dissolved salts are filtered through a semipermeable membrane such as cellulose acetate

at a pressure higher than the osmotic pressure.In this type of treatment,pre- treatment of the waste

such as Activated carbon adsorption or chemical precipitation followed by some kind of filtration is

necessary.

ii) Electrodialysis

In electrodialysis,the flow of ionic substances is initiated by providing an electrical potential

between two electrodes and the substances are filtered by using an ion-selective membrane ahead of

the electrodes.The separation of substances in this process requires sets of alternate cation and anion

permeable membranes in between the electrodes as shown in the following schematic diagram :

E- C A C A C A E+ Legend :

C = Cation Permeable Membrane, A = Anion Permeable Membrane, E+ = Cathode, + + + + - E- = Anode, → ← - ← - ← - ← CW = Concentrated waste, → → → DW = Diluted waste.

CW DW CW DW CW DW CW

Fig 1 : Schematic diagram of Electrodylasis Process When the wastewater is passed through such cells,alternate cells of concentrated and dilute wastes

are formed.Electrodialysis also requires some pre-treatment as in reverse osmosis.

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iii) Chemical oxidation

The chemical oxidation consists of addition of chemicals like chlorine & ozone to reduce the BOD

loading on the subsequent biological process,or to reduce substances like ammonia,cyanide etc.

iv) Chemical precipitation

Chemical precipitation consists of coagulation either by alum or ferric salts as well as treatment of

lime.

v) Adsorption

Adsorption involves the passage of pre-treated waste water through fixed bed Activated Carbon

column,and and is used only as a tertiary treatment unit,to remove non-biodegradable organics like

synthetic detergents,colour and odour.The regeneration of the exhausted bed is accomplished by

oxidizing and thus removing the adsorbed organics in a furnace at a temperature of about

925˚C.Other commercially available materials like clay,fly ash etc.are also recommended as

potential adsorbents.

vi) Ion Exchange

Ion exchange involves similar passage of wastewater through a fixed bed synthetic ion exchange

resin bed,where some of the undesirable cations or anions of the waste are exchanged for Sodium or

Hydrogen ions of the resin. Ion exchange bed requires regeneration,and special care should be taken

for the treatment of the waste produced due to regeneration.

vii) Thermal reduction

Thermal reduction involves the burning and thereby oxidation of some refractory and toxic

substances( like organic cyanide).

viii) Air stripping

Air stripping involves the passage( down flow) of a liquid waste through a packed tower,which is

equipped with an air blower at the bottom.This process is a modification of aeration process used for

the removal of gases from the waste water.

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Figure : Air Stripping Process.

The chemical and physico-chemical treatments involve a significant recurring cost,and chemical

oxidation and precipitation required additional facilities for the treatment of large quantity of sludge

produced. So,the chemical treatment should be provided only when it becomes unavoidable.

SLUDGE PROCESSING

Objectives Sludges consist primarily of the solids removed from liquid wastes during their

processing. Thus, sludges could contain a wide variety of pollutants and residuals from the

application of treatment chemicals; i.e., large organic solids, colloidal organic solids, metal sulfides,

heavy-metal hydroxides and carbonates, heavy-metal organic complexes, calcium and magnesium

hydroxides, calcium carbonate, precipitated soaps and detergents, and biomass and precipitated

phosphates. As sludge even after extensive concentration and dewatering is still greater than 50

percent by weight water, it can also contain soluble pollutants such as ammonia, priority pollutants,

and nonbiologically degradable COD.

The general treatment or management of sludge involves stabilization of biodegradable organics,

concentration and dewatering, and ultimate disposal of the stabilized and dewatered residue. A large

number of individual unit processes and unit operations are used in a sludge-management scheme.

Those most frequently used are discussed below. Occasionally, only one of these is needed, but

usually several are used in a series arrangement.

Because of the wide variability in sludge characteristics and the variation in acceptability of treated

sludges for ultimate disposal (this is a function of the location and characteristics of the ultimate

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disposal site), it is impossible to prescribe any particular sludge-management plan. In the lines

below, name of individual sludge treatment processes and operations is presented :

1) Increasing Concentration of sludges: i)Thickening and ii)Flotation.

2) Stabilization of sludges : i) Anaerobic Digestion, ii) Aerobic Digestion,

iii) High Lime Treatment.

3) Dewatering of sludges : i) Centrifugation , ii)Vacuum Filtration , iii)Pressure Filtration,

iv) Belt-Press Filter , v)Sand Beds.

SLUDGE DISPOSAL

Incineration Incineration has been used to reduce the volume of sludge after dewatering. The

organic fractions in sludges lend themselves to incineration if the sludge does not have an excessive

water content. Multiple-hearth and fluid-bed incinerators have been extensively used for sludge

combustion.

A multiple-hearth incinerator consists of several hearths in a vertical cylindrical furnace. The

dewatered sludge is added to the top hearth and is slowly pushed through the incinerator, dropping

by gravity to the next lower layer until it finally reaches the bottom layer. The top layer is used for

drying the sludge with the hot gases from the lower layers. As the temperature of the furnace

increases, the organics begin to degrade and undergo combustion. Air is used to add the necessary

oxygen and to control the temperature during combustion.

It is very important to keep temperatures above 600° C to ensure complete oxidation of the volatile

organics. One of the problems with the multiple-hearth incinerator is volatilization of odorous

organics during the drying phase before the temperature reaches combustion levels. Even

afterburners on the exhaust-gas line may not be adequate for complete oxidation. Air-pollution-

control devices are required on all incinerators to remove fly ash and corrosive gases. The ash from

the incinerator must be cooled, collected, and conveyed back to the environment, normally to a

sanitary landfill for burial. The residual ash will weigh from 10 to 30 percent of the original dry

weight of the sludge. Supplemental fuels are needed to start the incinerator and to ensure adequate

temperatures with sludges containing excessive moisture, such as activated sludge. Heat recovery

from wastes is being given more consideration. It is possible to combine the sludges with other

wastes to provide a better fuel for the incinerator.

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A fluid-bed incinerator uses hot sand as a heat reservoir for dewatering the sludge and combusting

the organics. The turbulence created by the incoming air and the sand suspension requires the

effluent gases to be treated in a wet scrubber prior to final discharge. The ash is removed from the

scrubber water by a cyclone separator. The scrubber water is normally returned to the treatment

process and diluted with the total plant effluent. The ash is normally buried.

Sanitary Landfills Dewatered sludge, either raw or digested, is often buried in a sanitary landfill to

minimize the environmental impact. Increased concern over sanitary landfills has made it more

difficult simply to bury dewatered sludge. Sanitary landfills must be made secure from leachate and

be monitored regularly to ensure that no environmental damage occurs. The moisture content of

most sludges makes them a problem at sanitary landfills designed for solid wastes, requiring

separate burial even at the same landfill.

Land Spreading The nutrient content of most sludges makes them useful as fertilizers or as soil

conditioners if properly mixed with the surface soil. Land spreading has gained in popularity in

agricultural areas. Normally, the rate of application of sludge to land is controlled by the nitrogen

content of the sludge. Since nitrogen uptake varies with different crops, nitrogen application is

limited to approximately twice the annual uptake of nitrogen by the proposed crop.

Approximately one-half of the nitrogen is readily available in sludge. Nutrient release with sludge

is slower than with chemical fertilizers, allowing the nutrients to become available as the crop needs

it. Activated sludge appears to be an excellent soil conditioner because the humus material in the

sludge provides a good matrix for root growth, while the nutrient elements are released in

approximately the right combination for optimal plant growth. There is a growing concern over

heavy metals in some sludge, and care should be taken to minimize heavy-metal concentrations in

sludges placed on the land. Since heavy metals cannot be easily removed from sludges, it is

important to prevent them from entering the wastewater-treatment system.

Greater concern will be placed on other potentially toxic or hazardous materials, including some

organic compounds such as pesticides and PCBs. Land spreading of sludge requires careful

application of the sludge at the surface and its mixing with the soil. Soil microbes will assist in

further stabilization of any biodegradable organics remaining.

Land spreading of sludge will become more popular as energy and nutrients become scarcer.

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So,selection of a particular method to be used in the wastewater treatment in a particular

industry depends on the effluent requirements and the characteristics of the wastewater.It must

be borne in mind that before a treatment policy is fixed up for a particular industry, the scope of

recycling and reclamation(recovery) of the wastes must be considered for a better management of

industrial waste water.Seggregation of strong wastes from the weak wastes sometimes reduces the

problem.

As textile industry wastewater is highly alkaline,it has high amount of BOD, high amount of

suspended solids,chemical and biological treatment methods are chosen to treat wastewater.

In case of Bangladesh,there is no single, ideal ETP for a textile dyeing industry but the best options

consist of several units. The combination of these units will vary depending on the exact type and

function of the processing plant, which is determined to a large degree by the nature of the effluent.

Typically an ETP for a textile industry would consist of primary, secondary and tertiary treatment

to ensure the best performance; however, in countries where resources are limited and factories

must minimize their outgoings, they are less likely to adopt advanced treatment methods. In

Bangladesh for example, ion exchange, electro-dialysis and reverse osmosis have only recently

been introduced for wastewater treatment and the uptake is still limited.

Consequently the combination of units in an ETP in Bangladesh can vary considerably depending

on: the size of the factory; the exact nature of the industrial process and thus the waste being

generated; the funds available to construct and operate the ETP; the compliance criteria specified by

buyers (if any); and the engineering consultants contracted to design and construct the ETP. This

makes is more difficult to create a generic model for monitoring but guidance can be given based on

the type of units and the performance standards typically expected for those units.

A combination of physico-chemical and biological units are most commonly used in textile dyeing

industries in Bangladesh , although pure physicochemical plants have also been observed by the

project team. Depending on the combination of physicochemical and biological units selected the

removal efficiency of key constituents differs: the ranges of percentage removal rates are given in

Table 2. As can be seen they can vary considerably depending on the type of units (for example a

low rate non-submerged trickling filter can achieve a BOD removal efficiency of 80-90 per cent

while the range for a high rate system is 65-90 per cent); the retention time is also an important

factor for certain units, such as sedimentation tanks .

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Table 2: Typical removal rates for ETP componentsComponent Constituent % Removal rateFine screens BOD

TSS 5-55 5-55

Primary sedimentation tanks BOD TSS

25-40 50-70Depending on type and detention time

Biological:Trickling filtersActivated sludge

BODBOD and TSS

50-90Final effluent quality10 mg/L

Anaerobic COD 65-95 Note: removal rate depends on type of system within each category of which there are many.

A typical ETP consists of an entrance-screening unit followed by an equalization tank and the

physicochemical unit, which is usually a combination of neutralization,coagulation, flocculation

and clarifier (primary clarifier) unit. One or more biological treatment units along with a clarifier

are used after the physicochemical treatment units. The number depends on: the quality of the

influent; the performance of previous units; the type of biological unit; and the efficiency of a single

biological unit. Finally, wastewater from the biological unit is treated with filters (generally sand or

activated carbon filters) depending on the wastewater quality. Overall an ETP comprised of an

appropriate combination of physico-chemical and biological treatment units can remove upwards of

90 per cent of BOD and COD .

In addition to BOD, COD and TSS, parameters of importance are colour, odour, total dissolved

solids (TDS), turbidity, conductivity, dissolved oxygen (DO), pH, alkalinity, hardness, metals and

ions.

For biological treatment, microorganisms may be monitored along with sludge volume index (SVI)

and stirred sludge volume index (SSVI).

In order to address the issues of increasing water pollution from textile industries and inadequate

treatment, the project “Managing Pollution from Small and Medium-Scale Industries in

Bangladesh” was initiated. It was funded by the EU Asia Pro Eco Programme and the DFID

Knowledge and Research Programme, between 2003 and 2006. The aim of the project was to

reduce pollution while maintaining the profitability of the industries and thereby ensure the incomes

of the employees as well as the livelihoods of those who depended on the natural resources that

68

were being impacted. The activities therefore involved cleaner production and improved wastewater

treatment.

The project was implemented by the Stockholm Environment Institute (SEI), the Bangladesh

Centre for Advanced Studies (BCAS) and the University of Leeds, UK.

In this component of the project, the team comprised of :

1.Mohidus Samad Khan of Australian Pulp and Paper Institute, Dept of Chemical Engineering,

Monash University, Clayton, VIC 3800, Australia;

2.Shoeb Ahmed of Department of Chemical and Biomolecular Engineering, North Carolina State

University, Raleigh. NC 27695, USA;

3.Alexandra E. V. Evans of International Water Management Institute, 127 Sunil Mawatha,

Pelawatte, Battaramulla, Sri Lanka;

4.Matthew Chadwick of Stockholm Environment Institute, University of York, UK ;worked with a

composite textile industry that had recently introduced an ETP but did not have much experience in

operating it. The purpose of the work was three-fold:

1. To assist in diagnosing any problem with the ETP and to advise the factory team in optimal

management;

2. To initiate a simple but effective system to regularly check the function of the major components

of the ETP in that particular factory and to calculate the overall performance of the system; and

3. To use this to create a generic set of guidelines for other textile factories to develop their own

monitoring procedures.

The data collected by the factories could be used to make the process more efficient and cost

effective; whilst also providing proof to the Department of Environment that they are complying

with the law and to international buyers that they are complying with their corporate environmental

responsibility criteria .

The factory has a conventional ETP with physicochemical and biological units as shown in Figure

1.

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Figure 1: Block diagram of a model ETPEFFLUENT TREATMENT PLANT FOR TEXTILE INDUSTRY(SAMPLE 2)

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5. Environmental effects of wastewater on receiving streams

Water and soil are undoubtedly the most precious natural resource that exists on earth. They are

essential for everything on planet to grow and prosper. Industrial wastes and effluent are

undesirable byproducts of economic development and technological advancement. When

improperly handled and disposed, industrial wastes imperil both human health and environment.

Human exposures to industrial wastes have led to health effects ranging from headaches, nausea,

lung, and skin irritation, to serious ailments like congenital malformation.

“The industrial revolution and our modern civilization turn the soil,water and air we live into waste

basket in which dust, noxious fumes, toxic gases, mist, metals, odor and smoke are thrown.”

(Manivaskam., 1989).

The ecological state of hydrosphere is becoming ever imbalanced due to technical and industrial

advancements as well as population explosion. Vast changes are taking place in the environment

itself. Man is exploiting the natural resources for his own interest and many such instances has

disturbed the environment to such an extent that it is becoming unfit for inhabitation by living

being.

Environmental pollution has been defined as an unfavorable alteration of our surroundings, wholly

or largely as byproducts of man’s action through direct or indirect effects of changes in energy

patterns, radiation levels, chemical and physical constitutions and abundance of organisms that will

be or may be harmful to human and other lives, living conditions and cultural assets or cause

wastage of our raw material resources (Asthana and Asthana, 2001 ).

Environment and industrial activity are intimately related and utilization of resources without due

consideration of the environment may lead to degradation of it with disastrous consequences.

Environmental pollution through industrialization is now assuming a serious problem throughout

the world. Industrial pollutant refers to the presence of any elemental, ionic or molecular species in

or around an industry or industrial area at a concentration which has been accidentally raised as a

consequence of human activity and causes an adverse effect on life and environment. “The

recognition of the associated environmental hazards either connected with trace element deficiency

or living organisms or enrichment of toxic metals in the food chain and ground water is justification

for many studies of the reaction of metals such as Mn, Cu, Zn, Cr, Cd, Fe, B and As with soil or

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different soil components and model substances to behave like soil materials” (Kabata and Pendias,

1984).

In textile mill dyestuffs are used in dyeing and finishing sections. They are of many structural

varieties, such as, acidic, basic, azo, diazo, anthroquinone based and metal complex dyes. They are

harmful for all living being. Textile industry waste waters and the sludge contain a variety of heavy

metals which can contaminant soils as well as surface and ground water sources when discharged

on land or water body.

The dye related industries in particular, are known to produce consistently toxic effluents that have

been shown by many scientists to be potent relative to other industrial discharges. As industrial

technology improves, the characteristics of industrial discharge sources become complicated and

the toxicity of industrial effluents can also become more complicated and heavier.

5.1 Effects of heavy metals in wastewater on receiving streams(soil & water)

Pollution is a fascinating topic of which soil & water pollution are an integral part. Of all the gifts

of nature, none is more indispensable to man than soil. Soil is one of the four requisites for life.

Along with sunlight, air and water, soil nourishes all plant life, most animal life, and supports

human life. Without it, this planet of ours would have been as barren as the moon. Soil is the

primary recipient of many of the waste products and toxic chemicals or pollutants used in modern

industry and contaminated by a number of organic, inorganic compound and heavy metals. The

heavy metals not only affect plants but also affect soil biota especially the bacterial populations

which are associated with almost all of the soil and plant process (Ibekwe et al.,1995 ) In this way,

such pollutants are likely to affect directly or indirectly the important natural processes. Among

heavy metals, chromium, cadmium and mercury are extremely poisonous; lead, nickel,

molybdenum and fluorine are moderate; and boron, copper, manganese and zinc are relatively low

in toxicity (Dara, 1997 ).

The uptake of heavy metals by plants from contaminated soils is of great interest because an excess

of dietary intake of some of these heavy metals might be deleterious to the health of the consumers.

The application of waste water to the crop is not new and it has been practiced from ancient days.

This is one of the ways how heavy metals and other pollutants accumulate in plants.

Contaminant or hazards may be defined as something that causes a deviation from the normal

composition of an environment. Contaminants are not classified as pollutants unless they have some

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detrimental effects (De, 2000). On the other hand, pollutant is a term which may be defined as a

substance present in nature, in quantities greater than natural abundance due to natural or human

activities and that has a detrimental effect on the different entities of environment (Dara, 2002).

These elements are widely used in industry, particularly in metal-working or metal-plating and in

the agriculture. An oversupply of these contaminants produces toxic effect and might be lethal

eventually to the organisms. These are very toxic because, as ions or compound forms, they are

soluble in water and may be readily absorbed into living organisms (Kannan, 1997).

Until now,about 42 trace elements(which are part of hazards) are detected in textile industry

effluents :

1.Titanium, 2.Tin, 3.Iodine, 4.Manganese, 5.Magnesium, 6.Copper, 7.Vanadium, 8.Chlorine,

9.Aluminium, 10.Mercury, 11.Samarium, 12.Tungsten, 13.Molybdenum, 14.Uranium,

15.Lanthanum, 16.Cadmium, 17.Arsenic, 18. Antimony, 19. Zirconium, 20.Bromine,

21.Sodium, 22.Potassium, 23.Cerium, 24. Calcium, 25. Lutetium, 26.Europium,

27.Selenium, 28.Terbium, 29. Thorium, 30.Chromium, 31.Ytterbium, 32. Hafnium,

33. Barium, 34. Neodymium, 35. Cesium, 36. Silver, 37. Nickel, 38. Scandium,

39.Rubidium, 40.Iron, 41.Zinc, 42.Cobalt.

Detrimental effects of some of them on human and aquatic life is given below :

Titanium

When titanium compounds react with water,they form hydrochloric acid,and other titanium

compounds, such as titanium hydroxide and titanium oxychlorides. The hydrochloric acid may

break down or be carried in the air. Some of the titanium compounds may settle out to soil or water.

In water, they sink into the bottom sediments.They may remain for a long time in the soil or

sediments.Titanium compounds can be very irritating to the skin, eyes, mucous membranes, and

the lungs. They are corrosive because they react strongly with water to produce hydrochloric

acid. The reaction products, especially hydrochloric acid, cause the harmful health effects and burns

that can occur after exposure to titanium compounds.

Tin

Various types of tin compounds may be present in textile industry wastewater.Bis(tributyltin) oxide

is one of them.If released to the atmosphere, an estimated vapor pressure of 7.8X10-6 mm Hg at 25

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deg C indicates bis(tributyltin) oxide will exist in both the vapor and particulate phases. Vapor-

phase bis(tributyltin) oxide will be degraded in the atmosphere by reaction with photochemically-

produced hydroxyl radicals; the half-life for this reaction in air is estimated to be 1.5 hours.

Particulate-phase bis(tributyltin) oxide will be removed from the atmosphere by wet and dry

deposition. If released to soil, bis(tributyltin) oxide will be expected to strongly bind to soil and will

have low mobility. Volatilization from near-surface soil is not expected to be an important fate

process. Biodegradation half-lives for bis(tributyltin) oxide range from 15 to 20 weeks in soil. If

released to water, bis(tributyltin) oxide will exist mainly as tributyltin cation which will strongly

bind to sediment. Bis(tributyltin) oxide may react with sulfides present in sediment which would

lead to the formation of bis(tributyltin) sulfide. The photodegradation half-life of bis(tributyltin)

oxide in water will be at least a few to several months. Biodegradation half-lives for bis(tributyltin)

oxide range between 6 days and 35 weeks in water and water-sediment mixtures. Bis(tributyltin)

oxide expected to exist in the dissociated form in the environment and therefore volatilization from

water surfaces is not expected to be an important fate process. Monitoring studies indicate that

tributyltin cations are very persistent in sediment from the marine environment, especially in anoxic

sediment where half-lives range from 2 to 3 years. Tributyltin cations bioconcentrate in aquatic

organisms. Occupational exposure to bis(tributyltin) oxide may occur through inhalation of dust

and dermal contact with this compound at workplaces where bis(tributyltin) oxide is produced or

used. Monitoring data indicate that the general population may be exposed to bis(tributyltin) oxide

via the ingestion of contaminated fish and other seafood and through dermal exposure to paints and

other products containing the bis(tributyltin) oxide.

Iodine Iodine is an essential constituent in the diet and is required for normal function of the

thyroid gland. Dietary iodine reaches the circulation in the form of iodide (I−) (Hardman et al.,

1996). Long-term repeated ingestion of iodine in amounts that exceed dietary requirements results

in a toxic syndrome called iodism. Initial symptoms of iodism are an unpleasant brassy taste,

burning of the mouth and throat, and soreness of the teeth and gums. Increased salivation,

inflammation of mucous membranes of the nose (rhinitis), eye and mouth, sneezing, laryngitis,

bronchitis, and skin rashes are frequently observed (Hardman et al., 1996). Prolonged intake of very

large amounts of iodine (approximately ten times the recommended daily dietary allowance) can

lead to enlargement of the thyroid, a condition called goiter (NAS, 1980). Studies of the effects of

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long-term inhalation of iodine vapors by humans are not available. Studies in laboratory animals

indicate that long-term inhalation of iodine vapor disrupts thyroid function and reduces the ability

of the lungs to take up oxygen. Adverse changes in the lungs of exposed animals include edema,

scaling of bronchial epithelium, and bleeding (HSDB, 2001).. The direct acute toxicity of iodine is

due to its irritant properties (NAS, 1980). In excessive amounts, elemental iodine (I2) is corrosive

and irritates tissue via allroutes of exposure (inhalation, ingestion, and skin contact).

Ingested iodine reportedly has a metallic taste and stains oral mucous membranes brown (HSDB,

2001). The toxic effects of ingested iodine are primarily due to its corrosive action on the

gastrointestinal tract (Hardman et al., 1996). Ingested iodine may cause vomitting, a drop in blood

pressure, headache, and delirium.

Manganese Manganese, an essential trace element for aquatic and terrestrial biota, is only

slightly to moderately toxic to aquatic organisms in excessive amounts. It is present in almost all

organisms, and often ameliorates the hazard posed by other metals. It gives water an unpleasant

appearance and taste.

Magnesium Magnesium is present in all natural waters. It is an essential element required in

small amounts by all living organisms. It is a major contributor to drinking water hardness.

Copper Copper is an essential substance to human life, but in high doses it can cause anemia,

liver and kidney damage, and stomach and intestinal irritation. People with Wilson's disease are at

greater risk for health effects from overexposure to copper.

Copper poisoning has been observed in kidney dialysis patients due to use of contaminated water or

leaching from dialysis membranes. Acute ingestion of excessive copper can cause the following

symptoms

Diarrhoea

Epigastric pain and discomfort

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Blood in the urine

Liver damage

Low blood pressure

Nausea

Vomiting

Kidney failure due to severe intravascular haemolysis.

Vanadium Vanadium may cause respiratory problems and inhibition of Na and K in ATP

production in human and plant life.

Chlorine Chlorine is found naturally as chloride in groundwater. It can cause water to have a

salty taste. Chloride may also be an indicator of saltwater intrusion or sewage contamination.

Chloride is often the first sign of deteriorating groundwater quality.

Flourine Fluorine is a poisonous pale yellow gaseous element found in Group VIIb (i.e. the

Halogen Group of elements) of the periodic table. Fluorine is the most reactive element known. It

reacts violently with water liberating oxygen and forming hydrofluoric acid (HF). Fluorine even

reacts with some of the normally inert noble gases such as Krypton and Xenon.

Elemental fluorine and the fluoride ion are highly toxic. The free element has a characteristic

pungent odor, detectable in concentrations as low as 20 ppb, which is below the safe working level.

Small amounts of sodium fluoride help reduce tooth cavities, but high levels can harm human

health. In children whose teeth are forming, high fluoride exposure can cause dental fluorosis with

visible changes in the teeth. In adults, high flouride exposure over a long time can lead to skeletal

fluorosis with denser bones, joint pain, and a limited joint movement. This is extremely rare in the

U.S.

Fluorine, hydrogen fluoride, and fluorides have not been classified for carcinogenic effects. Studies

in people have not shown fluorides to be carcinogenic, and the studies in animals are mixed. More

research is in progress.

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Acute toxicity has occurred by ingestion of household products containing high levels of fluoride

such as certain insecticides. The mechanism of fluoride toxicity is conversion in the stomach to

hydrofluoric acid. Gastrointestinal symptoms predominate and include nausea, vomiting, diarrhea,

and abdominal pain.

The U.S. Environmental Protection Agency (EPA) sets a maximum amount of 4 milligrams

fluoride per liter of drinking water (4 mg/L). EPA recommends that states limit fluoride in drinking

water to 2 mg/L.

The Occupational Safety and Health Administration (OSHA) limits an 8-hour work day, 40-hour

work week to 0.2 milligrams of fluorides per cubic meter air (0.2 mg/m3). The level for hydrogen

fluoride is 2.5 mg/m3). The highest level of fluoride allowed by OSHA for an 8-hour work day, 40-

hour work week is 2.5 mg/m3.

Aluminium Soluble aluminum salts are irritants when inhaled as aerosols [Hathaway et al. 1991].

Although inhalation of aluminum powder of particle size 1.2 um, given over 10- or 20-minute

periods several times weekly resulted in no adverse health effects among humans over several

years, several other studies report X-ray evidence of pulmonary fibrosis [Hathaway et al. 1991].

Some patients on long-term hemodialysis develop speech disorders, dementia, or convulsions. This

syndrome is associated with increased concentration of aluminum in serum, brain, muscle, and bone

[Amdur et al. 1991; Hathaway et al. 1991]. There is some evidence that Alzheimer's disease may be

linked to aluminum content in the body [Amdur et al. 1991]. Analysis of the aluminum content in

the brains of persons dying from Alzheimer's have shown increased levels, although brain

aluminum levels vary greatly. A second correlating factor is that neurofibrillary tangles (NFTs)

have been identified in both aluminum encephalopathy and in Alzheimer's disease [Amdur et al.

1991]. However, it has been shown that the NFTs produced by the two conditions are structurally

and chemically different and that NFTs are present in several other neurological disorders. It

appears that the aluminum content of the brain is less an issue relating to exposure to aluminum

than an issue of a blood-brain barrier defect or compromise of some kind [Amdur et al. 1991].

Mercury Mercury is a toxic substance which has no known function in human biochemistry or

physiology and does not occur naturally in living organisms. The toxicity of mercury is primarily

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associated with ionic Hg(II). However, absorption, tissue distribution and biotransformation are

influenced significantly by the valence state of the metal. Inorganic mercury poisoning is associated

with tremors, gingivitis and/or minor psychological changes, together with spontaneous abortion

and congenital malformation.

Ingestion of oxidized mercury can result in abdominal cramping, ulceration and renal toxicity.

Mercury has a strong affinity for sulfur, and mercury's primary mode of toxic action in living

organisms is thought to be the interference of enzyme function and protein synthesis by binding to

sulfhydryl or thiol groups. Because it is a fundamental element, mercury is not metabolized by

Phase I or II reactions, however excretion is associated with oxidation of mercury and mercury

compounds to the water soluble divalent form. Renal excretion is the primary route of elimination

of oxidized mercury, and because of its strong affinity for protein (including that in the epithelium

of the nephrons) renal toxicity is commonly associated with mercury exposure. Proteinuria, a

condition in which urine contains an abnormal amount of protein, is one of the primary symptoms

associated with mercury exposure to Hg(II).

By comparison, organic mercury is highly lipophilic (high affinity affinity for fat tissues). Both

MeHg and Hg° cross the placental and blood-brain barrier where they can be oxidized (via the

peroxidase-catalase pathway, which is present in most tissues), trapped and accumulated in these

tissues.

The nervous system is the critical organ for toxic exposure to both methyl and elemental mercury.

Methyl mercury can react directly with important receptors in the nervous system, such as the

acetycholine receptors in the peripheral nerves. The effects of mercury on the nervous system range

from irritability, excitability and parasthesia (numbing of the extremities) at low levels of exposure,

to tremors, violent muscle spasms and death in the extreme. While carcinogenicity and

mutagenicity (the power to cause mutation) are not commonly associated with mercury exposure,

mercury can cross the placental barrier where exposure can lead to spontaneous abortion, congenital

malformations and severe neurological defects such as cerebral palsy. Mercury affects the

developing fetus by interfering with normal neuronal development; it may also affect cell division

during critical stages of formation of the central nervous system.

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The model emerging to explain the toxic effect of mercury is a continuous dose-effect relationship

where low level exposure results in subtle changes in brain function as indicated by psychological

tests. Recent research also suggests that low level exposure to mercury may potentiate or amplify

the genetic damage associated with environmental mutagens, such as radionuclides.

Because of the extreme and pronounced toxicity of mercury, environmental contamination due to

increased industrial use of the metal has resulted in many episodes of human poisonings. One of the

earliest and best known examples of environmental mercury poisoning occurred in Japan in 1953

with the first reported cases of 'Minamata disease'. An international investigation revealed that

inorganic mercury released to Minamata Bay from a nearby acetaldehyde plant had been converted

to methyl mercury by microorganisms in the bay sediments. The MeHg formed was

bioaccumulated by fish and shellfish, a staple of the nearby population. Symptoms of the 'disease'

were typical of MeHg poisoning, ranging from paresthesia to severe birth defects and death.

Minamata was the first identified example of the in situ methylation and bioaccumulation of

mercury in fish. Inorganic mercury released by the plant would have had little impact on human

health because of its poor adsorption. Mercury methylation by naturally occurring benthic

organisms, however, resulted in greatly increased exposure because MeHg is more readily absorbed

by living organisms. Fish can bioamplify MeHg by a factor of one million and are a significant

source of mercury in the diets of humans and other fish loving animals. Minimata demonstrated that

fish and shellfish which accumulated concentrations of MeHg toxic to humans and wildlife showed

no abnormality in many cases.

Cadmium Cadmium and solutions of its compounds are toxic, particularly in soluble and

respirable forms, being more easily absorbed through inhaled dusts and fumes. Chronic dust or

fume exposure can irreversibly damage the lungs, producing shortness of breath and emphysema.

The risks of absorption via dermal contact is negligible. The International Agency for Research on

Cancer lists cadmium metal and several of its compounds as carcinogens. Because of its toxicity,

the use of cadmium is regulated by the U.S. Environmental Protection Agency (EPA) and other

regulatory control agencies.

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Eating food or drinking water with very high levels of chromium severely irritates the stomach,

causing vomiting and diarrhea. Cadmium mainly accumulates in the kidneys and liver and can lead

to serious kidney failure, nephrotoxicity, renal stone formation, bone disease and persistent

proteinuria at high exposures. Cadmium stays in the body a very long time and can build up from

many years of exposure to low levels. Recent studies have shown that the effects are reversible at

low exposures, once exposure to cadmium is reduced. Other effects from acute cadmium exposures

include:

muscle cramps

salivation

sensory disturbances

liver injury

convulsions

shock

renal failure.

Other potential effects of long-term cadmium exposure include:

high blood pressure

iron-poor blood

liver disease

nerve or brain damage

lung damage

fragile bones

intestinal damage

A balanced diet can reduce the amount of cadmium taken into the body from food and drink.

Animal studies suggest that more cadmium is absorbed into the body if the diet is low in calcium,

protein, or iron, or is high in fat. Some epidemiological studies have suggested a link between

drinking hard water and some degree of protection from hypertension. In some studies, younger

animals absorbed more cadmium and were more likely to lose bone and bone strength than adult

animals.

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Animals exposed en-utero to high cadmium levels suffered behavior abnormalities, learning

deficits, low birth weight, and skeletal abnormalities, but birth defect potential in humans is not

well known. Small portions of cadmium can cross the placenta, and cadmium can be present in

breast milk if the mother carries elevated levels.

The major route for cadmium intake for non smokers is ingestion of trace cadmium in foodstuffs of

natural origin or from the use of phosphate fertilizers and sludge on agricultural soils. Smokers have

elevated blood and tissue concentrations of cadmium from cigarette smoke. Whole blood and urine

levels are useful indicators of cadmium exposure. Cadmium toxicity can be assessed by urinary

excretion of low mass proteins such as alpha-1-macroglobulin or retinol binding protein. Long term

exposure causes abnormalities in Ca, P and vitamin D metabolism.

For the general world population, average daily cadmium intake, from all sources, is in the range of

10-25 µg/day and has decreased steadily over the past 20 years. Smoking doubles the average daily

intake. The tolerable daily cadmium intake established by the World Health Organization (WHO) is

60 µg/day for adult women and 70 µg/day for adult men.

Potential sources of cadmium exposure include refinery or smelter dust, plating baths, and silver

soldering. Tobacco leaves naturally accumulate and concentrate relatively high levels of cadmium,

which is volatilized during burning, and contributes significantly to a smoker's exposure to

cadmium. Each cigarette contains from 0.5 to 2.0 µg of cadmium, 10% of which is inhaled.

Smokers exhibit significantly elevated cadmium body burdens when compared to non-smokers.

The Department of Health and Human Services (DHHS) has determined that cadmium and

cadmium compounds may reasonably be anticipated to be carcinogens.

The EPA has set a limit of 5 parts of cadmium per billion parts of drinking water (5 ppb or 0.005

mg/L). Drinking water levels which are considered "safe" for short-term exposures: For a 10-kg (22

lb.) child consuming 1 liter of water per day, a one- to ten-day exposure to 0.04 mg/L; a longer-

term (up to 7 years) exposure to 0.005 .

Although zinc and cadmium commonly are found together in nature, the two behave different

biologically. While zinc is an essential element in almost all biological systems, playing an

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important role in metalloenzyme catalysis, metabolism, and genetic material replication, cadmium

can damage the kidneys and lungs, and is not easily removed from affected tissues.

Chromium Chromium often accumulates in aquatic life, adding to the danger of eating fish that

may have been exposed to high levels of chromium.

Selenium Selenium is needed by humans and other animals in small amounts, but in larger

amounts can cause damage to the nervous system, fatigue, and irritability. Selenium accumulates in

living tissue, causing high selenium content in fish and other organisms, and causing greater health

problems in human over a lifetime of overexposure. These health problems include hair and

fingernail loss, damage to kidney and liver tissue, damage to circulatory tissue, and more severe

damage to the nervous system.

Silver Unlike other "essential" elements such as calcium, human bodies don't need silver to

function. Though silver was once used in medical applications, modern substitutes have largely

superceded these uses, and there would be no ill health effects from going through life without ever

contacting silver.

This does not happen, however. Trace amounts of silver are in the bodies of all humans and

animals. We normally take in between 70 and 88 micrograms of silver a day, half of that amount

from our diet. Humans have efficient methods of dealing with that intake, however. Over 99 percent

is readily excreted from the body.

Unlike other metals such as lead and mercury, silver is not toxic to humans and is not known to

cause cancer, reproductive or neurological damage, or other chronic adverse effects.

Occasionally, sensitive individuals suffer allergic reactions — contact dermatitis or eye irritation —

after exposure to powdered silver, silver solutions or dental fillings. Ingesting silver compounds,

such as in medicines, can sometimes irritate the stomach.

In its pure metal form or in ores, silver does not dissolve and is not considered an environmental

risk. But high doses of certain compounds of silver have been found to highly toxic to aquatic life

forms, such as fish.

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Scientists once believed that metals that existed as free ions were most likely to pose a risk to living

things, since these forms tend to react more readily with biological molecules. Studies of fish and

zooplankton exposed to high doses of silver nitrate (a form of the metal containing large quantities

of free ions) confirmed that silver in this form is indeed highly toxic to aquatic creatures. This ionic

form of silver interferes with an enzyme (sodium/potassium ATPase) that regulates the levels of

potassium and sodium in fish. Disturbing the sodium/potassium equilibrium has fatal effects: Fish

quickly lose ions from their blood, water seeps into their body tissues, and they die from

cardiovascular collapse. Similar effects were found in tiny aquatic animals called zooplankton.

Though these effects are dramatic, this ionic form of silver is rarely found outside a laboratory.

Scientists now suspect that lower doses of silver compounds over longer periods of time may have

more subtle but equally worrisome effects on fish and other aquatic organisms — affecting the

reproductive system in sensitive species. Researchers are investigating the effects of chronic silver

exposure on aquatic life.

The Environmental Protection Agency (EPA) recommends that the concentration of silver in public

drinking water supplies not exceed one milligram per liter of water — one part per million —

because of the skin discoloration that may occur from chronic silver exposure. The agency also

requires that spills or accidental releases of 1,000 pounds or more of silver be reported.

Nickel Nickel released in industrial waste-water ends up in soil or sediment where it strongly

attaches to particles containing iron or manganese. By drinking water that contains small amounts

of nickel,people can be exposed to nickel. People who drank water containing high amounts of

nickel had stomach ache and suffered adverse effects to their blood and kidneys.

Damage to the lung and nasal cavity has been observed in rats and mice breathing nickel

compounds. Eating or drinking large amounts of nickel has caused lung disease in dogs and rats and

has affected the stomach, blood, liver, kidneys, and immune system in rats and mice, as well as

their reproduction and development.

Nickel does not appear to accumulate in fish or in other animals used as food.

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Iron Iron is the fourth most abundant, by weight, of the elements that make up the earth’s crust.

Common in many rocks, it is an important component of many soils, especially clay soils where it

is usually a major constituent. The dissolved iron concentration in Iowa’s groundwater can range

from less than 1 mg/l up to 20 mg/l (USGS Groundwater Monitoring Data).

The ferrous, or bivalent (Fe++), and the ferric, or trivalent (Fe+++) ions, are the primary forms of

concern in the aquatic environment, although other forms may be in organic and inorganic

wastewater streams. The ferrous (Fe++) form can persist in waters void of dissolved oxygen and

originates usually from groundwater or mines when these are pumped or drained. For practical

purposes, the ferric (Fe+++) form is insoluble.

Iron is an objectionable constituent in water supplies for either domestic or industrial use. Iron can

affect the taste of beverages and can stain laundered clothes and plumbing fixtures. The EPA red

book (1976) recommended a criterion of 0.3 mg/l for domestic water supply uses for iron.

At certain concentrations, iron can also be toxic to aquatic life. The EPA red book (1976)

recommended a criterion of 1.0 mg/l for freshwater aquatic life protection.

Large amounts of ingested iron can cause excessive levels of iron in the blood. High blood levels of

free ferrous iron react with peroxides to produce free radicals, which are highly reactive and can

damage DNA, proteins, lipids, and other cellular components. Thus, iron toxicity occurs when there

is free iron in the cell, which generally occurs when iron levels exceed the capacity of transferring

to bind the iron. Damage to the cells of the gastrointestinal tract can also prevent them from

regulating iron absorption leading to further increases in blood levels. Iron typically damages cells

in the heart, liver and elsewhere, which can cause significant adverse effects, including coma,

metabolic acidosis, shock, liver failure, coagulopathy, adult respiratory distress syndrome, long-

term organ damage, and even death. Humans experience iron toxicity above 20 milligrams of iron

for every kilogram of mass, and 60 milligrams per kilogram is considered a lethal dose.

Overconsumption of iron, often the result of children eating large quantities of ferrous sulfate

tablets intended for adult consumption, is one of the most common toxicological causes of death in

children under six. The Dietary Reference Intake (DRI) lists the Tolerable Upper Intake Level (UL)

for adults as 45 mg/day. For children under fourteen years old the UL is 40 mg/day.

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Zinc

Toxicity

Although zinc is an essential requirement for good health, excess zinc can be harmful. Excessive

absorption of zinc suppresses copper and iron absorption. The free zinc ion in solution is highly

toxic to plants, invertebrates, and even vertebrate fish. The Free Ion Activity Model is well-

established in the literature, and shows that just micromolar amounts of the free ion kills some

organisms. A recent example showed 6 micromolar killing 93% of all Daphnia in water.

The free zinc ion is a powerful Lewis acid up to the point of being corrosive. Stomach acid contains

hydrochloric acid, in which metallic zinc dissolves readily to give corrosive zinc chloride.

Swallowing a post-1982 American one cent piece (97.5% zinc) can cause damage to the stomach

lining due to the high solubility of the zinc ion in the acidic stomach.

There is evidence of induced copper deficiency at low intakes of 100–300 mg Zn/day; a recent trial

had higher hospitalizations for urinary complications compared to placebo among elderly men

taking 80 mg/day. The USDA RDA is 15 mg Zn/day. Even lower levels, closer to the RDA, may

interfere with the utilization of copper and iron or adversely affect cholesterol. Levels of zinc in

excess of 500 ppm in soil interfere with the ability of plants to absorb other essential metals, such as

iron and manganese. There is also a condition called the zinc shakes or "zinc chills" that can be

induced by the inhalation of freshly formed zinc oxide formed during the welding of galvanized

materials.

The U.S. Food and Drug Administration (FDA) has stated that zinc damages nerve receptors in the

nose, which can cause anosmia. Reports of anosmia were also observed in the 1930s when zinc

preparations were used in a failed attempt to prevent polio infections. On June 16, 2009, the FDA

said that consumers should stop using zinc-based intranasal cold products and ordered their removal

from store shelves. The FDA said the loss of smell can be life-threatening because people with

impaired smell cannot detect leaking gas or smoke and cannot tell if food has spoiled before they

eat it. Recent research suggests that the topical antimicrobial zinc pyrithione is a potent heat shock

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response inducer that may impair genomic integrity with induction of PARP-dependent energy

crisis in cultured human keratinocytes and melanocytes.

Poisoning

Zinc is highly toxic in parrots and poisoning can often be fatal. The consumption of fruit juices

stored in galvanized cans has resulted in mass parrot poisonings with zinc.

Cobalt

Exposure to cobalt can occur through oral or dermal(skin) routes.Mammals,including humans,are

exposed to natural sources of cobalt like water.Taking excessive amounts of cobalt may result to –

i) Heart diseases,

ii) Weak Reproductive systems,

iii) Decrease in red blood cells.

Lead

Lead poisoning has been a significant public health problem for centuries since lead is a cumulative

poison. Exposure to lead and lead compounds can be toxic to humans and wildlife. Potential effects

in humans are abdominal cramps, learning disabilities, attention deficit disorder, constipation,

anemia, tiredness, nerve damage, vomiting, convulsions, anorexia, and brain damage. Wildlife and

waterfowl are also frequently poisoned through the ingestion of lead and lead shot. Toxic effects

occur to the central nervous system and resulting long-term neurobehavioral and cognitive deficits

occur even with mildly elevated blood lead levels.

5.2 Effects of textile wastewater on river water

The quality of water is of vital concern for mankind since it is directly linked with human welfare.

Due to the recent industrial revolution and developments in the fields of science and technology, a

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large number of chemicals compound has been introduced into the environment. f these textile

industries play a vital role because they use and discharge huge amount of water.

By definition, water pollution is a state of deviation from the pure condition, whereby its normal

function and properties are affected. Water pollution disturb the normal uses of water for public

water supply such as-

Recreation and aesthetics.

Fish, other aquatic life and wild life.

Agriculture.

Industry etc.

5.3 Effects of textile waste water on dissolved oxygen

Dissolve oxygen is an essential requirement of aquatic life, i.e. plant and animal population in any

water body. The optimum dissolve oxygen in natural water is 4-6 ppm. Industrial wastes from

textile industries undergo bacterial activity in the presence of dissolve oxygen, the net result being

the de-oxygenating process and quick depletion of dissolve oxygen.

Reaction is as follows:

C+O2 = CO2

When the water dissolve oxygen is depleted, the water is said to become anaerobic. Often, however,

the dissolve oxygen does not drop to zero and the water recovers without anaerobiosis.

5.4 Effects of textile waste water on the quality of water

Due to the water pollution quality of water is decreased. When the rate of oxygen overwhelms the

rate of water supply, the water may become anaerobic. An aerobic stream has bubbling gas. The gas

is formed because oxygen is no longer available to act as hydrogen acceptor and ammonia,

hydrogen sulfide and other gases are formed. In addition, the odor of hydrogen sulfide will

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advertise the anaerobic condition for some distance, the water is usually black or dark and fungus

grows.

The quality of water depends on the following parameters :

i) pH,

ii) BOD,

iii) COD,

iv) TDS,

v) TSS,

vi) Temperature etc.

i) Effects on pH

pH is a measure of the amount of free hydrogen ions in water. Specifically, pH is the approximate

value of the negative logarithm of the molar concentration of hydrogen ions.

pH = -log[H+]

Because pH is measured on a logarithmic scale, an increase of one unit indicates an increase of ten

times the amount of hydrogen ions. A pH of 7 is considered to be neutral.

Acidity increases as pH values decrease, and alkalinity increases as pH values increase.Most natural

waters are buffered by a carbon-dioxide-bicarbonate system, since the carbon dioxide in the

atmosphere serves as a source of carbonic acid.

H2CO2 --> HCO3 + H+ pK ~ 7.5

This reaction tends to keep pH of most waters around 7 - 7.5, unless large amounts of acid or base

are added to the water. Most streams draining coniferous woodlands tend to be slightly acidic (6.8

to 6.5) due to organic acids produced by the decaying of organic matter. Natural waters in the

Piedmont of Georgia also receive acidity from the soils. In waters with high algal concentrations,

pH varies diurnally, reaching values as high as 10 during the day when algae are using carbon

dioxide in photosynthesis. pH drops during the night when the algae respire and produce carbon

dioxide.

The pH of water affects the solubility of many toxic and nutritive chemicals; therefore,the

availability of these substances to aquatic organisms is affected. As acidity increases due to

industrial wastewater , most metals become more water soluble and more toxic. Toxicity of

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cyanides and sulfides also increases with a decrease in pH (increase in acidity). Ammonia, however,

becomes more toxic with only a slight increase in pH.

Alkalinity is the capacity to neutralize acids, and the alkalinity of natural water is derived

principally from the salts of weak acids. Hydroxide, carbonates, and bicarbonates are the dominant

source of natural alkalinity. Reactions of carbon dioxide with calcium /magnesium carbonate in the

soil creates considerable amounts of bicarbonates in the soil.

Organic acids such as humic acid also form salts that increase alkalinity. Alkalinity itself has little

public health significance, although highly alkaline waters are unpalatable and can cause

gastrointestinal discomfort.

ii) Effects on BOD

Natural organic detritus and organic waste from waste water treatment plants, failing septic

systems, and agricultural and urban runoff, acts as a food source for water-borne bacteria. Bacteria

decompose these organic materials using dissolved oxygen, thus reducing the DO present for fish.

Biochemical oxygen demand (BOD) is a measure of the amount of oxygen that bacteria will

consume while decomposing organic matter under aerobic conditions. Biochemical oxygen

demand is determined by incubating a sealed sample of water for five days and measuring the loss

of oxygen from the beginning to the end of the test. Samples often must be diluted prior to

incubation or the bacteria will deplete all of the oxygen in the bottle before the test is complete.

If effluent with high BOD levels is discharged into a stream or river, it will accelerate bacterial

growth in the river and consume the oxygen levels in the river. The oxygen may diminish to levels

that are lethal for most fish and many aquatic insects. As the river re-aerates due to atmospheric

mixing and as algal photosynthesis adds oxygen to the water, the oxygen levels will slowly

increase downstream. The drop and rise in DO levels downstream from a source of BOD is called

the DO sag curve.

The main focus of wastewater treatment plants is to reduce the BOD in the effluent discharged to

natural waters as more value of BOD means more amount of bacteria will decompose high amount

of dissolved oxygen,thus reducing high amount of DO present for fish without which fishes can’t

exist . Wastewater treatment plants are designed to function as bacteria farms, where bacteria are

fed oxygen and organic waste. The excess bacteria grown in the system are removed as sludge, and

this “solid” waste is then disposed of on land.

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iii) Effects on COD

Chemical oxygen demand (COD) is the same as BOD,the only difference is COD does not

differentiate between biologically available and inert organic matter, and it is a measure of the total

quantity of oxygen required to oxidize all organic material into carbon dioxide and water.Industrial

wastewater increases COD which means more amount of bacteria will decompose high amount of

dissolved oxygen,thus reducing high amount of DO present for fish without which fishes can’t exist

.

iv) Effects on TDS

All natural waters contain some dissolved solids due to the dissolution and weathering of rock and

soil. Dissolved solids are determined by evaporating a known volume of water and weighing the

residue. Some but not the entire dissolved solids act as conductors and contribute to conductance.

Industrial Wastewaters with high total dissolved solids (TDS) are unpalatable and potentially

unhealthy. Water treatment plants use flocculants to aggregate suspended and dissolved solids into

particles large enough to settle out of the water column in settling tanks. A flocculent is a chemical

that uses double-layer kinetics to attract charged particles.

v) Effects on TSS and Turbidity

Sediment enters streams via upland soil erosion, bank erosion, and land sliding.Sediment is a

natural component of streams, but excessive sediment can be carried into streams and rivers from

erosion of unstable streambanks, construction sites, agricultural activities, and urban runoff.

Sediment moves downstream in a river in two forms: suspended load and bed load. Suspended load

includes the particles in suspension in the water column. The red-brown color of Georgia Piedmont

streams is due to clay and colloid particles in suspension. Bed load refers to the sediment pushed

along the bottom of the channel. Coarser substrate such as sand and gravel tends to move as bed

load, not suspended load.

Sediment is usually measured as a concentration of total suspended solids (TSS), which is the dry

weight after filtering a water sample, expressed in mg per liter. To determine a suspended sediment

load (mass/time), the TSS concentration must be multiplied by the flow rate (volume/time).

Turbidity is another indicator of the amount of matter suspended in water; it measures the amount

of light that is scattered or absorbed.

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Suspended silt and clay, organic matter, and plankton can contribute to turbidity. Photoelectric

turbidimeters measure turbidity in nephelometric turbidity units (NTUs). Turbidity units are

supposed to correspond to TSS concentrations, but this correlation is only approximate.

Turbidity in a stream fluctuate before, during and after stormflow.

The new general NPDES stormwater permit for constructions sites requires that the difference in

turbidity not exceed 25 NTU downstream from a construction site compared to upstream. If this

criterion is exceeded and if Best Management Practices (BMPs) are not properly designed, installed

or maintained, then the permittee is subject to fines and third party lawsuits .

Turbidities of 10 NTU or less represent very clear waters; 50 NTU is cloudy; and 100-500 or

greater is very cloudy to muddy. Some fish species may become stressed at prolonged exposures of

25 NTUs or greater. Furthermore, Barnes (1998) recommended that to maintain native fish

populations in Georgia Piedmont Rivers and streams, that random monthly values should never

exceed 100 NTU; that no more than 5 percent of the samples should exceed 50 NTU; and no more

than 20% should exceed 25 NTU.

Similarly, average TSS concentrations in the range of 25-80 mg/L represent moderate water quality.

An average concentration of 25 mg/L has been suggested as an indicator of unimpaired stream

water quality (Holbeck-Pelham and Rasmussen, 1997). Some states use 50 mg/L as a screening

level for potential impairment to waterbodies.

Fine sediment deposited on the streambed can fill gravel spaces, eliminating spawning habitat for

some fish species and also eliminating habitat for many invertebrate species.

Turbidity and or TSS can reduce light penetration, decreasing algal growth, and low algal

productivity can reduce the productivity of aquatic invertebrates, a food source of many fish. High

turbidity levels affect fish feeding and growth; the ability of salmonids to find and capture food is

impaired at turbidities from 25 to 70 NTU. Gill function in some fish may also be impaired after 5

to 10 days of exposure to a turbidity level of 25 NTU.

Turbidities of less than 10 describe very clear waters. Waters with turbidity in excess of 50 are quite

cloudy, and waters with turbidities exceeding 500 are downright muddy.

Large bed loads can also reduce or eliminate pool habitat essential to low-flow and summer survival

of fish. Essentially, channels with high bed loads tend to feature shallower water and a larger wetted

perimeter. Channel bed topography as well as the size distribution of sediments on the bottom of

the channel (referred to as substrate) are vital factors for the productivity of many fish species.

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Pools provide resting areas for fish, protection from terrestrial and avian predators, and sometimes

provide cooler water, which lowers metabolic needs. Areas of cool water in streams and lakes are

called thermal refugia.

vi) Effect on Temperature

Metabolic rate and the reproductive activities of aquatic life are controlled by water temperature.

Metabolic activity increases with a rise in temperature, thus increasing a fish’s demand for oxygen;

however; an increase in stream temperature also causes a decrease in DO, limiting the amount of

oxygen available to these aquatic organisms.

With a limited amount of DO available, the fish in this system will become stressed. A rise in

temperature can also provide conditions for the growth of disease-causing organisms.

Water temperature varies with season, elevation, geographic location, and climatic conditions and is

influenced by stream flow, streamside vegetation, groundwater inputs, and water effluent from

industrial activities. Water temperatures rise when streamside vegetation is removed. When entire

forest canopies were removed, temperatures in Pacific Northwest streams increased up to 8 o C

above the previous highest temperature.

Water temperature also increases when warm water is discharged into streams from industries.

5.5 Effect on the fish species of water

The outward evidence of an anaerobic stream is accompanied by adverse effects on aquatic life.

Types and number of species change drastically downstream from the pollution discharge point.

Increased turbidity, settled solid matter, and low dissolved oxygen all contribute to a decrease in

fish life.

5.6 Effect on photosynthesis rate of aquatic plants

The effluents released from textile industry have a mixture of chemicals used in the digestion of

raw materials, cellulose fibers, and dissolve lignin. These chemicals like pentachlorophenol and

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sodium pentachlorophenate as well as methyl macaptan are brownish in color and lower the

photosynthetic rate of aquatic communities by hindering sunlight penetration into the water column.

5.7 Effects on crops

The untreated textile industries wastes have adverse effects on crop. Soluble salts, needed by the

industries, are responsible for cost damage. They cause crop loss, soil loss, metallic corrosion and

lead to costly cleansing activities.

Chen et al (1991) showed that the rice seed germination rate and the amount Chlorophyll decrease

remarkably with increasing Pb concentration.

5.8 Effects of Untreated Textile Wastes on Soil

Soil is a natural resource and major part of the environment. People depend on soil for their basic

needs but soiled environment are under tremendous pressure due to industrial expansion. Soil gets

enormous quantities of wastes products each year which mainly include unlimited varieties of

liquid industrial wastes. The wastes are the potential source of soil pollution through their direct or

indirect disposal on the land. The residual release from the plant infiltrate into the soil and later

back to the surface as a result of irrigation. The chemical and metallic pollutant pore their hazardous

effects in soil creating disastrous effects on living organism. Industrial wastes contain heavy metals

which have potential toxicity and may be able to process of soil formation. It reduces the capacity

of the forest to maintain fertility of the soil. These act phytotoxic even a small quantity

Of all the industries of Bangladesh, the Textile industry appears to be the one of the major source of

pollution for agriculture soil, with Naraynjanj being most affected.

Studies on the properties of soil,collected from the textile area revealed that soluble salts from

textile effluents enhanced the soil EC that adversely affect the seedling establishment. Textile

industry has been found to discharge significant amounts of Cr,Cu, Cd, Zn, Mn, Fe and Pb . High

levels of Cr, Zn, Mn, Cu and Pb was observed in the main waste disposal point, which exceeded

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toxic level range in the soils. Grass accumulated higher amount of Chromium that of paddy and

water hyacinth in these areas and exceed the allowable limit.

5.8.1 Effects on soil physical properties

Soil physical properties such as soil structure, texture, porosity, particle density, water holding

capacity, soil temperature are seriously affected by Textile industries wastes. The destruction of soil

structure results

Decrease in water holding capacity.

Decrease in the infiltration capacity.

Decrease in aeration.

Decrease in the temperature of the soil.

Suspended solid can blanket the soil, thereby interfering with the soil moisture. As a result of these

agriculture sector of our country gives a big tool due to textile industry.

5.8.2 Effects on soil chemical properties

Soil chemical properties such as pH, decomposition of organic matter, and availability of plant

nutrients are adversely affected by textile industries wastes. Textile industries activity emits

arsenic and So2.These makes the soil very acidic. The low pH affects the decomposition of organic

matter, availability of plant nutrient, microbial activity etc.

Organic matter cans influence the solubility of heavy metals in soil in different ways. It can

increase the solubility of heavy metals by forming soluble organic complexes, but on the other

hand the ability of organic matter immobilize heavy metals has also been reported. Colloidal

organic matter has a strong affinity to the heavy metals cations thereby replacing major plant

nutrients and then be precipitated or be leached from the soil solution. Textile industrial wastes

containing several heavy metals such as Pb, Cd, Cr, Cu, Fe, Zn, and As etc can accumulate the

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soil. Their continuous use for irrigation of agricultural land may result in metal accumulation on

the surface soil (Gupta et al., 1988).

5.8.3 Effect on soil biological properties

Micro-organisms are the component of the soil, which decompose the organic matter of the soil.

Textile industries wastes containing metallic contaminants (e.g., Pb, Cd, Cr, Cu, Fe, Zn, and As

etc.) destroy bacteria and beneficial micro-organisms of the soil. Heavy metals tend to precipitate

phosphate compounds and catalyze their decomposition. These metals are considered to be

indestructible poisons and their accumulation in the soil for a long period may be highly fatal to

living organisms. High concentration of heavy metals with a low pH in the contaminated soil

makes it unfavorable for microbial activities. Many beneficial micro-organisms become inactive in

acidic condition. As a result nitrifying, nitrogen fixing and other bacteria are decreased which are

beneficial for soil fertility. Again certain diseases causing organism prevail in acid conditions,

which adversely affect the fertility of the soil.

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6.Guideline and discharge standards of the industry permit systems

Increasing industrialisation and lack of waste treatment is leading to a major water pollution problem

in many parts of Bangladesh, impacting on aquatic ecosystems and the population who depend on

them for their livelihood activities. However, Bangladesh has a well developed set of environmental

policies, Acts and Rules that deal with industrial pollution of water, soil and air.

Responsibility for control and abatement of water pollution falls to the Department of

Environment(DOE) within the Ministry of Environment and Forest (MoEF). Broadly, DOE are

mandated to set and enforce environmental regulations for all forms of pollution and media (air,

water and soil).Specifically in relation to water pollution, DOE are responsible for: pollution

control; setting water quality standards (WQS) for water use and discharge; defining environmental

impact assessment(EIA) procedures; issuing environmental clearance permits; and declaring and

protecting degraded ecosystems (UNEP, 2001).

The Ministry of Water Resources through several of its agencies, particularly the Water Resources

Planning Organization (WARPO) and the Bangladesh Water Development Board (BWDB), are

responsible for all other forms of water management in Bangladesh. The BWDB is principally

responsible for implementation, operation and maintenance of water related projects, whilst

WARPO is mandated to advise on policy, planning and regulation of water resources.

The policies and laws through which the BWDB, WARPO and DOE operate include: the National

Water Policy; the National Environment Policy and Rules; and the Environmental Conservation

Act. There are more than 200 laws aimed at addressing environmental issues in the country.

In the history of environmental policy and legislation of Bangladesh,different legislations have been

passed at different times.Name of some important legislations are stated below:

1. Environmental Pollution Control Ordinance, 1977 ,

2. National Environmental Policy, 1992,

3. National Environmental Management Plan, 1995,

4. Environment Conservation Rules, 1997,

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5. The Environmental Court Act 2000,

6. The Environmental Court Act(Amended) 2002,

7. The EIA Guidelines for Industry

Although having dispute over the title, the EIA Guidelines for Industries cover significant water

sector interventions,including flood control embankments, polder and dykes and roads and bridges.

All these water sector interventions for under the ‘Red’ category of industrial units. These require,

in theory, for proposed project construction, re-construction and extension.

In general the policies and legislation in place to protect water from industrial and other effluent is

well constructed and comprehensive. The Environmental Conservation Act and Environmental

Conservation Rules, and National Water Policy have adequate clauses relating to industrial

pollution. This includes water quality protection, effluent discharge monitoring, zoning regulations

for new industries and strengthening of the regulatory system for agrochemical pollution

control(UNEP, 2001). The two exceptions to this are concerns over the failure to establish the

Wetland Policy, which after several years has still not been put before parliament, and the apparent

overlap in mandates of the MoEF and WARPO and NWRC in developing and implementing

policies regarding water resources development and management. However, such concerns are

insignificant in comparison to those in relation to the institutional capacity and capability to enforce

them. There are few action programmes and a lack of skills and expertise to take appropriate actions

to ensure that both government and private sector developments properly address environmental

concerns. With few exceptions there is still a lack of institutional awareness let alone capabilities to

address policy goals and objectives. Through the Bangladesh Environment Management Program

(BEMP) and the Sustainable Environmental Management Program(SEMP), the DOE is currently

working towards improved water quality monitoring, and estimation of pollution loads in rivers and

watercourses, as well as trying to strengthen the institutional arrangements through which these will

occur. There have also been initiatives such as the development of Guidelines for EIA applicable to

several sectors, including flood control and drainage. However, there are few initiatives that aim to

tackle the serious problem of water resource degradation that already exists in Bangladesh. The

DOE have no guidelines on clean-up and no time bound targets. The absolute numbers of polluting

industries that need to be dealt with are conservatively estimated to be 1000 in Dhaka and 600 in

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Chittagong (UNEP, 2001). There are no estimates outside these two large cities. Moreover, it is

generally accepted that no realistic strengthening or expansion of the DoE in the future will be able

to cope with all the problems. It is viewed that there is no real expectation that DOE could cope

with even a fraction of the problems.

The only clean-up strategy that is likely to have any impact on the current dire situation is one

based on mobilization of other organizations and the general public including public-private

partnerships. What the initial findings of this research suggest is that such an approach could draw

heavily on the economic argument for change – businesses are losing money due to inefficient

practices, practices that can be improved at little or no cost. It is therefore in the interests of all that

the current situation improves.

On the next page,following informations are listed on tables :

* Classification of Industrial Units and Projects Based on Impact and Location( Table 1)

* Waste Quality Standards for Discharge Point of Industrial Units and Projects( Table 2)

* Discharge quality standards for Integrated Textile Mill and Large Processing Unit(Table 3)

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Table 1: Classification of Industrial Units and Projects Based on Impact and Location

Category Impact Examples of industries Application requirementsGreen Least

Most

TV, radio & watch manufacture,book binding, rope and mat production, tea packing,candle, motorcycle and toy assembly, cork product, laundry(except washing)

• General information on the industrial unit or project;• Description of the manufactured product andraw materials; and• A “No Objection Certificate” from the local authority.

Amber A Livestock (below specified numbers), grinding mills, saw mill, cinema, dry cleaning,printing press, industrial machinery, brass/bronzesouvenir manufacture, plastic and rubber goods (not PVC)

In addition to the above:• A process flow diagram;• Layout plan showing an effluent treatmentplant (ETP);• Waste discharge arrangements;• Outline of relocation or rehabilitation plant(where applicable); and• Other necessary information (whereapplicable).

Amber B PVC products, synthetic fibre,edible oil, brick, hotel, foundry,jute mill, plastic product, potablewater and soft drinks,galvanising, animal feed, ink,stone crushing, fish and meat processing, pathology, water treatment plant, soap, tea processing, leather goodsmanufacture, furniture, livestock(over specified numbers)

In addition to the above :• Planned industrial unit or project must submit a Feasibility Report and an InitialEnvironmental Examination (IEE) Report,including Process Flow Diagram, Layout Plan,showing ETP and diagram of ETP;• Existing industrial unit or project must submit an Environmental Management Plan (EMP) Report including Process Flow Diagram,Layout Plan, showing ETP and diagram of ETP and information on its function.• Pollution Effect Abatement Plan along with Emergency Plan for adverse environmental impact.

Red Leather producing (tannery),formaldehyde, urea and TSPfertilizer, mineral projects, oilrefinery, chemicals, paper andpulp, sugar, distillery, fabricdyeing and chemical treatment,iron and steel, acids, plastic rawmaterials,electroplating,industrial estate, sewage treatment

In addition to the above:• The IEE Report must include an Environmental Impact Assessment (EIA)based on program outline previously approved by the DOE including Layout Plan and Process Flow Time Frame Diagram.

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Table 2: Waste Quality Standards for Discharge Point of Industrial Units and Projects

Parameter (Unit) Inland surface water Irrigated LandAmmoniacal Nitrogen (mg/L) 50 75Free Ammonia (mg/L) 5 15Arsenic (mg/L) 0.2 0.2BOD5 (mg/L) 50 100Boron (mg/L) 2 2Cadmium(mg/L) 0.05 0.5Chloride (mg/L) 600 600Total Chromium (mg/L) 0.5 1.0COD (mg/L) 200 400Hexavalent Chromium (mg/L) 0.1 1.0Copper (mg/L) 0.5 3.0Dissolved Oxygen (mg/L) 4.5-8 4.5-8Electrical Conductivity (micro mho/cm) 1200 1200Fluoride (mg/L) 7 10Sulphide (mg/L) 1 2 Iron (mg/L) 2 2Total Kjeldahl Nitrogen (mg/L) 100 100

Lead (mg/L) 0.1 0.1 Manganese (mg/L) 5 5 Mercury(mg/L) 0.01 0.01 Nickel (mg/L) 1.0 1.0 Nitrate Molecule (mg/L) 10.0 10.0 Oil and Grease (mg/L) 10 10 Phenol Compounds (C6H5OH) (mg/L) 1 1Dissolved Phosphorus (mg/L) 8 10pH 6-9Selenium (mg/L) 0.05 0.05Zinc (mg/L) 5.0 10.0Total Dissolved Solids (mg/L) 2100 2100Temperature (˚C) - Summer - Winter

40 45

40 45

Total Suspended Solids (mg/L) 150 200Cyanide (mg/L) 0.1 0.2

Table 3: Discharge quality standards for Integrated Textile Mill and Large Processing Unit

Parameter LimitTotal Suspended Solids 100 mg/LBOD5 ,20oC 150 mg/LOil and Grease 10 mg/LTotal soluble solids 2100 mg/LWastewater Flow 100 L/kg of fabric processedpH 6.5 – 9

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Classified for dyes used• Total chromium as Cr molecule• Sulphide as S molecule• Phenolic compounds as C6H5OH

2 mg/L 2 mg/L 5 mg/L

In case of Bangladesh,the ready-made garment sector has become one of the largest manufacturing

sectors in Bangladesh with approximately 4490 apparel manufacturing units registered under the

Bangladesh Garment Manufactures and Exporters Association (BGMEA) in 2008 [1]. The growth

in this sector, and other small and medium scale enterprises, undoubtedly has a positive effect on

national economic development but there are also negative implications. In particular, the large

volumes of water consumed and the water pollution generated through the dyeing process can have

a severe impact on the local environment. Khan et al. [2] reported that a semi-automated composite

textile industry of 10 tons of capacity produces 1250 m3 of effluent each day, which contains an

assortment of chemicals including salts, dyes and bleaches.The rapid but unplanned growth of

industrial clusters,with several factories discharging large amounts of untreated or poorly treated

wastewater, has led to serious localized water pollution. As a result, water bodies and agricultural

land are displaying reduced productivity and the biological diversity of these ecosystems is

threatened. The result is not only environmental degradation but also a reduction in the nutrition

and incomes of families that traditionally depended on these resources; and they are not always the

same people who get benefit from the jobs created by the factories.

One solution is to ensure that all the effluent is properly treated before it is discharged. The

Bangladesh Environment Conservation Act (1995) and Rules(1997) make provision for this,

categorizing factories according to their ability to pollute and stating the measures that must be

taken to address this, including treatment. Under the 1997 Rules fabric dyeing and chemical

processing industries are categorized as“Red industries”, which is the highest category in the Rules

and for which an effluent treatment plant (ETP) is mandatory. Under these Rules factories must

treat as well as monitor the quality of their wastewater and stay within national discharge quality

standards (Table 1) :

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Table 1: Discharge quality standards for classified industries composite textile plants

Parameter Limit (mg/L)

pHTotal Suspended Solid (TSS), (mg/L) BOD5 20˚C, (mg/L) COD (mg/L) Oil and Grease, (mg/L) Total Dissolved Solid (TDS), (mg/L) Waste Water Flow

6.5-910050/150*200**102100100 L/Kg of fabric processing

Special parameters based on classification ofof dyes usedTotal Chromium (as Cr molecule), (mg/L) Sulfide (as S molecule), (mg/L) Phenolic compounds as C6H5OH, (mg/L)

2

25

* BOD limit of 150 mg/L implies only with physico-chemical processing** No official standard for COD of textile effluent but the general standard for discharge to inland surface water is 200 mg/L

In Bangladesh,there can also be two types of discharge standard values of the industry permit systems.One type is for inland river and another is for irrigation land. Discharge standards (into inland river & into irrigation land) of the industry permit systems for a textile industry according to the EIA guidelines compiled by DOE(Department of Environment) is given below :

S.I No Water quality parameters

Unit Standard value for discharging into*

Inland river On land for irrigation 01 pH 6 - 9 6 - 9

02 BOD mg/L,5days < 50.0 <100 03 COD mg/L,day < 200.0 < 400 04 TSS mg/L < 150.0 < 200.0 05 TDS mg/L < 2100 < 2100 06 Oil & grease mg/L < 10 < 10 07 Colour Co-pt unit < 150 < 150 08 Temperature ˚C < 30˚C < 30˚C

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7. Current Industrial Environmental Pollution Status

Pollution control issues are relatively recent in Bangladesh. With few exceptions, the industries are

not equipped with pollution control systems. With the advent of industrialization, untreated wastes

and highly toxic effluents, especially of heavy metals and organic pollutants are discharged directly

into the natural systems at random that impairs the quality of water, soil and sediments (DoE,

1992).

Treatment of industrial waste effluent has so far been considered a low priority, because policy

planners had a feeling of complacency that industrial pollution is still at a very low level. Due to

lack of awareness as well as the absence of strong punitive actions, the practice of circulating waste

and effluent into water bodies including ponds, canals, creeks and rivers still remains widespread.

These waste and effluents contain heavy metals, toxic substance and in the some case, high amount

of nitrate and ammonia nitrogen. They pollute natural water system as well as groundwater. They,

thereby create serious environmental hazards, endanger human health and cause problems to

aquatic lives. Some of heavy metals and phytotoxic and some are toxic to both plants and animals

through their entry into the water-soil-plant-food system. The serious public health hazards they

create are to some extent minimized as the waste and effluents are mostly fleshed out into the sea

during the rainy season. But excessive localized pollution is already threatening the sustainability of

the resource base and having effects on the health if people, most of who are affected or unaware or

hardly have any other choices. (Naruzzaman M 1995; Ullah et al., 1995; Bashar MA 1999; Islam et

al., july,2002; Nuruzzaman et al., 1998; Roads et al., 1989; Page et al., 1981; Rahman, M.A. 1997).

Within the Earth Summit in Rio and the Kyoto Protocol in Japan, the 1990s have been a significant

decade in reshaping conventional development thinking into sustainable development. This new

trend guides us to clean up existing industries and develop new one with minimum environmental

impacts. In this process, development of recycling systems, waste exchange and industrial ecology

will replace the linear industrial processes with a more circulatory structure. (EDA. 1990).

By having a small industrial base Bangladesh is in an advantageous position for getting a head start

in developing clean and sustainable industries. The wise approach is to learn from the mistakes of

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the already industrialized countries and take proactive measures in planning and managing the

industrial sector. (Faisal et al., 2000; Gain, P. (Ed.). 1998; De, A. K. 1993; Haq, S.A. 1989;

Chowdhury N., 1989; Nakos,G. 1983; Saxena, M.M.1990; Stemberg et al., 1994).

According to the The Ministry of Environment and Forest (1997), Government of Bangladesh,

dumping of soil and liquid wastes from various Industries is causing serious environmental

degradation in Bangladesh. These effluents contain 10 to 100 times the allowable levels of

pollutants permissible for human health. They pollute our soils as well as groundwater. Once the

ground water is polluted, it is virtually impossible to purity it even in highly technically advanced

industrial countries and thereby endangering human health, aquatic lives and crop production. The

effluents may contain heavy metal like Ni, Pb, Cr, Cu, Hg, Mn, Zn or Fe. Some of these are toxic to

plants and some are toxic to both plants and animals (Page et al., 1981; Baath, 1989; Roads et al.,

1989; Gerzabek and Ullah, 1990; Ullah et al., 1995).

Fig : Industrial effluent from a textile dyeing industry.

According to officials of the Department of Environment (DoE), dumping of solid and liquid waste

of various industries is not only poisoning the water but also causing hindrance to movement of

river vessels by making the rivers too shallow. The people living surrounding these rivers are

leading a subhuman life in the stench of the chemical waste and poisons in river water. Many

people are suffering from various water-borne and skin diseases after using the septic water of these

rivers. Fishes are dying off and adjoining croplands are losing fertility alarmingly as water

pollution causes both land and air pollution.

The sequences of industrial pollution cover three inter linked events :

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emission and entry of pollutants into physical environment → entry and fate of pollutants in

biological environment and contamination of biological chain → toxic effects and impact upon

human (Dara, 1997).

Textile industry waste waters and the sludge contain a variety of heavy metals, which can

contaminant soils as well as surface and ground water sources when discharged on land or water

body. Pollution of natural waters, soils and vegetation with waste effluents arising from textile

industries has become a serious problem in Bangladesh, as textile industries growth and

development have been on a very large scale and they consume large volumes of water and

chemicals for wet processing of textiles.

7.1 Impact on river water

Water is the most vital element among the natural resources, and is crucial for the survival of all

living organisms including human, food production, and economic development. Today, nearly 40

percent of the world’s food supply is grown under irrigation, and a wide variety of industrial

processes depend on water (BCAS, 2000). Moreover, in Bangladesh, the environment, economic

growth, and developments are all highly influenced by the quality and quantity of surface and

groundwater. Seasonal availability of surface and groundwater is highly responsive to the monsoon

climate and physiography of the country. In terms of quality, the surface water of the country is

vulnerable to pollution from untreated industrial effluents and municipal wastewater, runoff from

chemical fertilizers and pesticides, and oil and lube spillage in the coastal area from the operation of

sea and river ports. Water quality also depends on effluent types and discharge quantity from

different type of industries, types of agrochemicals used in agriculture, and seasonal water flow and

dilution capability by the river system (DHV, 1998).

Originating as the Yarlung Zangbo Jiang in China's Xizang Autonomous Region (Tibet) and

flowing through India's state of Arunachal Pradesh, where it becomes known as the Brahmaputra, it

receives waters from five major tributaries that total some 740 kilometers in length. At the point

where the Brahmaputra meets the river Tista in Bangladesh, it becomes known as the Jamuna. This

mighty network of four river systems flowing through the Bangladesh Plain drains an area of some

1.5 million square kilometers. The numerous channels of the Padma-Meghna, its distributaries, and

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smaller parallel rivers that flow into the Bay of Bengal are referred to as the mouths of the Ganges.

The rivers of Bangladesh mark both the physiography of the nation and the life of the people. About

700 in number, these rivers generally flow to the south. The rivers also drain excess monsoon

rainfall into the Bay of Bengal. Thus, the great river system is at the same time the country's

principal resource and its greatest hazard (U.S. Library of Congress, 2002).

7.1.1 River Water Quality in Bangladesh

The river water quality is an important concern to a nation, because surface water used for

agricultural, industrial and drinking purposes and as well as aquatic ecosystems. The aquatic

environment for fish and aquatic biodiversity can be affected from harmful substances in the water

and ultimately a threat to food chain contamination. A variation of inland surface water quality is

noticed due to seasonal rainfall variation and river water flow, operation of industrial units,

municipal wastewater and use of agrochemicals. “Water quality” is a term used here to express the

suitability of water to sustain various uses or processes. Any particular use will have certain

requirements for the physical, chemical, or biological characteristics of water. Consequently, a

range of variables, which limit water use, can define water quality. Quantity and quality demands of

different users will not always be compatible, and the activities of one user may restrict the

activities of another, either by demanding water of a quality outside the range required by the other

user or by lowering quality during use of the water (Meybeck etal, 1996).

Overall, inland surface water quality in the monsoon season is within tolerable limit with respect to

the standard set by the Department of Environment (DoE) given in table 1. However, quality

deteriorates in the dry season. The salinity intrusions in the Southwest region and pollution

problems in industrial areas are significant. River water quality around Dhaka is so poor that water

from the surrounding rivers can no longer be considered as a source of water supply for human

consumption (DoE, 2001). Mainly the surface water of the country is vulnerable to pollution from

untreated industrial effluents and municipal wastewater, runoff from agro-chemical fertilizers and

pesticides, and oil and lube spillage from the operation of sea and river ports.

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Table-1: standard limits for drinking waterSl. No. Parameter Unit Standards

1. Aluminum mg/L 0.22. Ammonia (NH3) ,, 0.53. Arsenic ,, 0.056. BOD520°C ,, 0.27. Boron ,, 1.08. Cadmium ,, 0.0059. Calcium ,, 7510. Chloride ,, 150 – 600*16. Chromium (total) ,, 0.0517. COD ,, 420. Color Hazen 1521. Copper mg/L 124. DO ,, 626. Hardness (as CaCO3) ,, 200 – 50027. Iron ,, 0.3 – 1.028. Kjeldhl Nitrogen (total) ,, 129. Lead ,, 0.0530. Magnesium ,, 30 – 35 31. Manganese ,, 0.1 34. Nitrate ,, 10 36. Odour ,, Odourless38. pH ,, 6.5 – 8.540. Phosphate ,, 641. Phosphorus ,, 042. Potassium ,, 1247. Sodium ,, 20048. Suspended particulate matters ,, 1050. Sulfate ,, 40051. Total dissolved solids ,, 100052. Temperature °C 20-3055. Zinc mg/L 5

Source: (DoE, 1997).

In Bangladesh, industrial units are mostly located along the banks of the rivers. There are obvious

reasons for this such as provision of transportation for incoming raw materials and outgoing

finished products. Unfortunately, as a consequence, industrial units drain effluents directly into the

rivers without any consideration of the environmental degradation. The most problematic industries

for the water sector are textiles, tanneries, pulp and paper mills, fertilizer, industrial chemical

production and refineries. A complex mixture of hazardous chemicals, both organic and inorganic,

DoE, 1997

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is discharged into the water bodies from all these industries usually without treatment (WARPO,

2000a).

The highest numbers of industrial establishments in the country are located in the North Central

(NC) region, which comprises about 49 per cent of the total sector. About 33 per cent of the

industries in the NC region are textiles, apparels, and tanneries, of which Dhaka district accounts

for almost half and Narayanganj about 32 per cent. About 65 per cent of the total chemicals,

plastics, and petroleum industries are also located in the NC region, and concentrated in and around

Dhaka, Narayanganj and Gazipur districts (WARPO, 2000a).

7.1.2 Impacts of Water Pollution

The increasing urbanization and industrialization of Bangladesh have negative implications for river

water quality. The pollution from industrial and urban effluents in some water bodies and rivers has

reached alarming levels. The long-term effects of this contamination by organic and inorganic

substances, many of them toxic, are severe. The aquatic environment for fish and aquatic

biodiversity can be affected from harmful substances of industrial pollution. The aquatic

ecosystems pollution will also reflect negative impact on irrigation water; animal health and toxic

chemicals entering through food chain will be incalculable.

The overall surface water quality in the monsoon season is within tolerable limits, with a few

exceptions, including the rivers Buriganga, Balu, Shitalakhya, Karnaphuli, and Rupsha. Water of

the river Balu is badly contaminated by urban and industrial wastes from Tongi and the effluent

flowing out through the Begubari Khal, most of which emanates from the Tejgaon industrial area in

Dhaka. In the rivers Balu and Turag, water quality in the dry season becomes worse, with DO

concentrations becoming almost zero (Saad, 2000).

The extreme examples of this type of effect are near Dhaka at Konabari and Savar, where industrial

effluents are discharged into nearby land and water bodies without any treatment. Surface water

pollution will gradually stimulate due to the dispersed locations of industrial implementation.

Among the polluted areas, the worst problems are in the River Buriganga, where the most

significant source of pollution appears to be from tanneries in the Hazaribagh area. In the dry

season, the Dissolved Oxygen (DO) level in the river becomes very low or zero. The seasonal

variation of water quality in the Buriganga is linked with seasonal variation of water flow and the

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operation of tanneries. The second most polluted river is the Sitalakhya, flowing on the east of

Dhaka.Industrial units at Narayanganj and Demra are one of the main sources of pollution.

Monitoring data of DoE demonstrated that the concentration of DO in the river Sitalakhya varies

between 2.1 to 2.9 mg/L during low tide. Water of the river Balu is badly contaminated by urban

and industrial wastes from Tongi and the effluent flowing out through the Begunbari Khal, most of

which emanates from the Tejgaon industrial area in Dhaka. In the rivers Balu and Turag, water

quality in the dry season becomes worse, with DO concentrations becoming almost zero (DoE,

1993).

The second most polluted river is the Sitalakhya, flowing from the east of Dhaka. Industrial units at

Narayanganj and Demra are one of the sources of the pollution. Monitoring data of the DoE

demonstrated that the concentration of dissolved oxygen in the river Sitalakhya beside the fertilizer

factory varies between 2.1 to 2.9 mg/L during low tide (DoE, 1993) and pH varies between 7.1 to

6.5 at 1981 to 1990 (DoE, 1997). The Bangladesh Center for Advanced Studies (BCAS), analyzed

that EC of Sitalakhya River cross the limit and it was 110 mgL -1 during 1980 but aggressive

industrialization and improper agricultural activities, it is rise up to 1440 mgL -1 during 1998 and

TDS rises 216 to 446 mgL-1. A number of textile and leather industries discharge their industrial

effluents into a nearby small water body, the results showed that levels of COD, TSS and DO in the

water exceeded standard limits. It also showed that the total chromium concentration in sediments

and wastewaters near the discharge points of the local tannery and textile industries is very high.

The concentrations of zinc, lead, and cadmium were also found to be higher than the national

standards (BCAS, 2000).

There are increasing efforts to develop the industrial sector of the country by both stimulating the

local industries and attracting foreign investors. As a result, the growth rate of the industrial sector

is expected to rise. The growth rate of the manufacturing sector has been projected to be 11% for

the year 2000 (World Bank, 1997). As Bangladesh, attempts to attain economic development by

replacing its agricultural base with industries and rural enterprises with urban centers, pollution, and

other environmental impacts of industries are becoming critical in development planning.

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7.1.3 How to control the pollution

No civilization can survive and thrive without clean water. We as a nation are fortunate to have

plenty of this vital resource. However, the quality of this valuable resource is deteriorating very fast

without any action plan. It is only through a better understanding of the sources of pollution and

processes that affect the quality of water that we can save this precious resource for us and for our

future generations. Moreover, surface water and groundwater are inter-related. The quality of

groundwater can only be ensured through a better protection of surface water and recharge areas on

the ground.

If strict environmental monitoring is enforced as per the Environmental Conservation Rules of 1997

and other relevant environmental laws, many of the industries of Bangladesh will be come forward

to protect water pollution. So, with proper policies, laws, acts, and enforcement of laws, the point

sources of pollution in a watershed can be controlled by constructing effluent treatment plant. Non-

point sources of pollution included: agricultural run-off, urban run-off, fertilizers, pesticides, acid

rain, animal waste, raw sewage, septic tank leakage, household waste, etc. Understanding of a

problem, however, is only half of the solution. Other half of the solution lies in communal actions;

all of us can play a role in preserving the quality of water. We all need to join hands to protect this

invaluable resource, as well as our existence as a nation. Since the sources of pollution is not known

or identified, it becomes problematic to control their discharge into rivers and streams in a

watershed. This information needs to disseminate to the general public through public meetings,

newspapers, education, website, and other mass media for public awareness and to incorporate law

and policy makers.

7.2 Current Status of Effluent Treatment Plants

A study was conducted by the Stockholm Environment Institute (SEI), the Bangladesh Centre for

Advanced Studies (BCAS) and the University of Leeds, UK to address the issues of increasing

water pollution from textile industries and inadequate treatment & the project “Managing Pollution

from Small and Medium-Scale Industries in Bangladesh” was initiated. It was funded by the EU

Asia Pro Eco Programme and the DFID Knowledge and Research Programme, between 2003 and

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2006. The aim of the project was to reduce pollution while maintaining the profitability of the

industries and thereby ensure the incomes of the employees as well as the livelihoods of those who

depended on the natural resources that were being impacted. The activities therefore involved

cleaner production and improved wastewater treatment.

As a component of the project, the team was comprised of :

1. Mohidus Samad Khan of Australian Pulp and Paper Institute, Dept of Chemical Engineering,

Monash University, Clayton, VIC 3800, Australia;

2. Shoeb Ahmed of Department of Chemical and Biomolecular Engineering, North Carolina State

University, Raleigh. NC 27695, USA;

3. Alexandra E. V. Evans of International Water Management Institute, 127 Sunil Mawatha,

Pelawatte, Battaramulla, Sri Lanka;

4. Matthew Chadwick of Stockholm Environment Institute, University of York, UK ;worked with a

composite textile industry that had recently introduced an ETP but did not have much experience in

operating it.

In this study ,only the parameters considered to be of most importance or which give an indication

of overall pollution load (e.g. BOD and COD) were measured.This reflected the type of waste, the

national standards, and the facilities and funds that a factory would have available to them for

monitoring. Since this method was intended to be repeated regularly it could not be overly complex

or expensive.

The units that would be sampled in a standard monitoring programme of a typical ETP are

summarized in Table 3 along with the parameters that would be analysed for. Monitoring just a few

simple parameters may facilitate the assessment of the performance of the whole plant, if done in an

effective and systematic way.

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Table 3: List of parameters checked at different sampling points

Unit Parameters Sampling point

Equalization tank pH, TDS, TSS, BOD, COD, Temperature

Outflow

NeutralizationTank

pH Outlet, to ensure that the acid or alkali has beenproperly mixed

Coagulation andFlocculation

pH Outlet

Primary Clarifier TSS, TDS, COD, pH, BOD OutflowBiological Reactor

DO, pH, samples of activatedsludge for microscopic examination,Temperature

In aeration basin

Secondary Clarifier

BOD, COD, TSS Outflow

Treated Water pH, TDS, TSS, BOD, COD Outlet

The factory in which the research was conducted undertakes knitting, dyeing and sewing of cotton

(usually referred to as a composite factory); it has a daily production capacity of 10 tonnes which is

split between dark colours (35 per cent), medium shades (15 per cent), light shades (30 per cent)

and bleached whites (20 per cent).

The factory has a conventional ETP with physicochemical and biological units as shown in Figure

1. The major units of the ETP were selected for sampling as indicated in Figure 1 and described in

Table 4.

Two sets of samples were collected from each of these points: one set was collected in the morning

and the other set in the evening. The samples were preserved below 4 ⁰C and transported to the

analytical laboratory as quickly as possible to minimize the effect of spontaneous chemical

reactions and microbial activity in the samples. Samples testing started within 24hrs of collection.

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Table 4: List of sampling location and objective of the sampling

Sample ID Location of Sampling Objective 1 Outflow of Equalization Tank To find out the effluent (untreated) water

characteristics(after equalization and before P-C)

2 Outflow of Tube Settler-1 To analyze the performance of Coagulation and Flocculation units

3 Outlet of Biological Reactor-1 To analyze the performance of Biological Reactor-1

4 Outlet of Biological Reactor-2 To analyze the performance of Biological Reactor-2

5 Outlet of ETP(treated water) To analyze the performance of Tube Settler-2, Activated Carbon Filter and Sand Filter.Also to check whether the discharge water is Compliant with Bangladesh legislation or not.

It should be noted that due to the nature of the dyeing process, which can take between six and

twelve hours, the effluent reaching the treatment plant can vary throughout the day. The samples

collected were therefore a composite of several dying batches which had been combined in the

equalization tank. The assumption is that the equalization tank is of sufficient capacity and well

mixed enough to ensure the effluent passing through the system is of consistent quality. It is also

assumed that the dyeing operations taking place do not vary significantly enough for this to effect

quality over the period being studied. These are large assumptions but it is normal for such

assumptions to be made in routine monitoring of an ETP and is also a pragmatic approach when

effluent treatment is an additional activity to the core business of the industry,and one that rarely

results in increased profit.

Five key parameters were selected for analysis: pH; TDS; TSS; BOD5 and COD, because they are

included in the discharge quality standards for textile industries in Bangladesh and they are the

parameters most commonly used to monitor ETP performance.

Results

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In this study two sampling events were undertaken and the analysis of the results is preliminary.

However, the result analysis provides the ETP managers an initial indication of how the results can

effectively be used to monitor the performance of the treatment plant.

There was an improvement in all parameters except TDS from the inflow of the treatment plant to

the outflow.Some were however still outside the discharge quality standards for textile industries in

Bangladesh, including TDS, BOD5, and COD (Table 5 and Table 6).

Table 5: Results for morning analysis

Parameters Units Bangladesh Sample No Pollution load Standards 1 2 3 4 5 removed (%) pH —– 6.5-9 9.44 9.76 9.82 7.68 7.71 –TDS mg/L 2100 4395 4301 4819 5196 5550 -26.3TSS mg/L 100 92 58 31 54 65 29.3BOD5 mg/L 50 (/150*) 1000 450 350 240 195 80.5COD mg/L 200 1287 648 510 364 291 77.4

*BOD limit 150mg/L implies only with Physico-Chemical processing

Table 6: Results for evening analysis

Parameters Units Bangladesh Sample No Pollution load Standards 1 2 3 4 5 removed (%) pH —– 6.5-9 9.83 9.97 9.87 7.1 7.35 –TDS mg/L 2100 6852 4137 6598 4891 5168 24.6TSS mg/L 100 133 64 80 92 79 40.6BOD5 mg/L 50 (/150*) 1050 500 375 300 215 79.5COD mg/L 200 1419 713 559 433 311 78.1

*BOD limit 150mg/L implies only with Physico-Chemical processing

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pHAt the inflow to the first biological reactor (point 2) the pH was outside the limits required for

bacterial growth which are between pH 4.0 and 9.5 with an optimal range of pH 6.5 - 7.5 . The

desired pH was reached only after the second biological reactor which means that the pH is likely to

have impacted negatively on biological activity in the treatment units (Figure 2).

Figure 2: The pH at different stages of the ETP

TDS

The TDS values were high and remained so throughout the process (Figure 3). They varied greatly

throughout the course of the evening monitoring period and in the morning sampling they actually

increased rather than decreased through the system. As a result the TDS value in the treated water

was at leastdouble the Bangladesh standards for TDS of 2100 mg/L.

Overall there was a 24 per cent reduction in TDS in the evening and a 26 per cent increase in the

morning.The main increase was observed in the first biological unit - the difference between the

outflow from physicochemical units, and the outflow of the first biological unit i.e. between

sampling points 2 and 3 (Figure 4).

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Figure 3: TDS at different stages of the ETP

Figure 4: Percentage TDS removal in different stages of the ETP

BOD and COD

The trends observed for BOD5 and COD had similar characteristics to each other, both in the

morning and evening. A significant reduction was observed in both parameters from the inflow to

the outflow (Figure 5). However, the effluent quality still did not meet the Bangladesh standards of

50 mg/L for BOD5 and 200 mg/L for COD (Table 1).

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Figure 5: The BOD5 and COD at different stages of the ETPThe most dramatic reduction in BOD5 was observed after the flocculation and coagulation stage in

which 52-55 per cent was removed (Figure 6). This represents a satisfactory performance of the

physicochemical units although it can be generally expected that a well run physico-chemical unit

can remove 50-80 per cent of total BOD5 . The biological reactors performed poorly reducing the

BOD5 value by only 7-12 per cent.

Figure 6: The BOD5 removal in different stages of the ETPThe situation was very similar for the COD with the biological reactors apparently underperforming

(Figure 7).

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Figure 7: The COD removal in different stages of the ETP.

A typical ETP consisting of physico-chemical and biological units can remove 90 per cent or more

of the BOD or COD present in the initial influent, when the ETP is operated efficiently . After a

series of treatment this ETP removed approximately 80 per cent of the BOD5 load (Figure 6) and 78

per cent of the COD load (Figure 7), which was not good enough to meet the national (BD) or

international (e.g. US EPA) standards

Discussion

Sample factory

The overall performance of the ETP is inadequate to meet the national discharge quality standards

and therefore requires immediate interventions to address the problems. Many of these may be

management rather than structural and should therefore not require any significant financial outlay

by the factory, in fact better management of the plant could actually reduce costs.

A major issue that needs to be addressed in the equalization tank is the pH. The dosing of an acid

(usually hydrochloric acid) would lower the pH and thus bring it to within the limits required for

biological activity which would help to ensure a healthy population of bacteria in the two biological

treatment units. This would result in an overall improvement in the treatment,

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particularly in the reduction of organic matter, measured as BOD which needs to be reduced further

in order to meet the national standards.

The TSS values of the influent were below the national standard and remained low during the

treatment process. This is unsurprising as the effluent from textile dyeing processes generally has

low TSS.

Total dissolved solids are a particular problem for textile dyeing industries because a large quantity

of salt is required in the process, all of which is disposed of with the final effluent. The TDS values

in the sample factory showed considerable variation throughout the treatment process. This may be

a result of different influxes of chemicals discharged over the course of the

dyeing process and the factory should check this more regularly so that they better understand their

waste and can manage the treatment better.

It would however be expected that the equalization tank would lessen the variation, which suggests

that the equalisation tank may not be of sufficient capacity or have a long enough retention time.

The TDS values also increased at some stages of the treatment process (Figure 4). These increases

appear to be associated with chemical dosing to the treatment plant (in this case possibly nutrients

in the biological treatment unit) which implies that the ETP operator is adding

excessive quantities of chemicals. It may also relate to the dosing of incompatible chemicals and the

underperformance of the biological reactor, which in turn is in part due to the poor control of pH.

Implications for other factories

The monitoring programme used in this factory was simple and quick, yet it clearly highlighted

some significant problems with the management of the system that were having a detrimental

impact on its efficiency.

As expected it aided the identification and diagnosis of problems within certain units. This is of far

greater benefit to the ETP manager than the knowledge that the ETP is not meeting national

standards.

It is essential that the pH in the biological units is maintained between pH 4 and 9.5 and ideally

between 6.5 and 7.5 if the bacteria are to remain alive and active and thus treat the waste. This is

reasonably simple to achieve if an automatic monitoring and dosing system is installed. Monitoring

and dosing can be done manually but it is far more efficient and practical to install

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such a system because the pH can fluctuate significantly throughout the day, depending on the

processes in the factory.

The dosing of other chemicals must also be correct otherwise the TSS and TDS may not be

reduced, and may even increase. Managers of ETPs should regularly monitor the units in the plant

where chemical dosing takes place so that they know their waste and can be more accurate in their

dosing of chemicals. It is also good practice to perform laboratory jar tests on different types of

waste from the factory for the same reason.

Although the BOD5 and COD reduced through the system the concentrations were still above the

national standards in the final effluent. This means that there is scope for improvement through

better operation of the plant. It may be necessary to ensure that the biological reactors are

adequately aerated and that the correct nutrient composition is being added to “feed” the bacteria,

as textile effluent contains very little of the nutrients, including nitrogen and phosphorus, required

for a healthy and active bacterial population. Maintaining the purity of the chemical nutrients used

is also very important in order to avoid an increase in TDS.

Factory treatment plants could potentially be modified to receive urine from the toilets (or the liquid

portion of septic tanks), which would provide the nutrients without the needs for chemical dosing

(although further steps may be required for pathogen removal if the urine is not separated from the

faeces at source).

Conclusion

In Bangladesh and other countries in the region effluent treatment from textile dyeing factories and

other industrial processes is usually required by law and often expected by international buyers.

Despite this, treatment is regularly below standards and is rarely checked either by the factory,

environment departments or buyers. There are a several reasons for this but the bottom line is

usually a lack of funds and technical expertise. These reasons are also why factories have been

found to run their ETPs sub-optimally. This study shows that through the process of simple

monitoring of key parameters at strategic places in the treatment plant, the ETP manager would be

able to optimize the treatment process and potentially save money by reducing the chemicals and

energy needed to run the system.

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The main problems experienced by factories with ETPs are inadequate treatment due to incorrect

dosing of chemicals required in the treatment process or inactivity and even death of necessary

micro-organisms, due to the pH, insufficient oxygen or lack of nutrients.

All of these can be addressed through better management; usually chemical dosing. By regularly

monitoring and understanding their wastewater properly ETP managers can make effective

decisions to achieve optimal ETP functioning.

Furthermore, factories supplying international buyers can use this data to demonstrate their ‘green’

credentials and thus generate more business or at the very least maintain their share in an

increasingly competitive market.

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8. Hazards and their control

8.1 Hazards

Hazards or hazardous wastes can be defined as “anything which,because of its

quantity,concentration,or physical,chemical,or infectious characteristics may cause,or significantly

contribute to,an increase in mortality;or cause an increase in serious irreversible,or incapacitating

reversible,illness;or pose a substantial present or potential risk to human health and environment

when improperly treated,stored,transported,or disposed of,or otherwise managed.”

More specifically,RCRA(Resource Conservation & Recovery Act) defines a substance as hazardous

if it posseses any one of the following four characteristic attributes :

reactivity,ignitability,corrosivity,or toxicity.Briefly,

Ignitable substances are easily ignited and burn vigorously and persistently.Examples include

volatile liquids,such as solvents,whose vapours ignite at relatively low temperatures(defined as 60⁰

C or less).

Corrosive substances include liquids with pH less than 2 or greater than 12.5,and those that are

capable of corroding metal containers.

Reactive substances are unstable under normal conditions.They can cause explosions and/or

liberate toxic fumes,gases,and vapours when mixed with water.

Toxic substances are harmful or fatal when ingested or absorbed.Toxicity is determined using a

standardized laboratory test,called the extraction procedure.A substance is designated as being EP

toxic if an extract contains any of the eight toxic elements or six pesticides listed in table 5.1 in

concentrations greater than the values given.

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Table : List of Hazardous substancesEPA hazardous waste number

Contaminant Maximum concentration(mg/L)

D004 Arsenic 5.0 D005 Barium 100 D006 Cadmium 1.0 D007 Chromium 5.0 D008 Lead 5.0 D009 Mercury 0.2 D010 Selenium 1.0 D011 Silver 5.0 D012 Endrin 0.02 D013 Lindane 0.4 D014 Methoxychlor 10.0 D015 Toxaphene 0.5 D016 2,4-D (2,4- dichlorophenoxyaceticacid) 10.0 D017 2,4,5-TSilvex(2,4,5-trichlorophenoxypropionicacid) 1.0

A wide variety of materials were identified by analysis of textile waste waters from 3 different sites

by Brent Smith,Professor of Polymer and Textile Chemistry,College of Textiles,North Carolina

State University,Raleigh, North Carolina .They are listed below :

Site #l

This sample contained a substantial amount of inorganic and organic components. About 34

different volatile organic compounds (VOC’s) were evolved from waste water sample # l, which

was the effluent from the pretreatment system of a typical pigment printing operation in central

North Carolina. The VOC’s were trapped in the off gases from the waste water sample and

separated into 34 distinct peaks by gas chromatography. Each of the 34 peaks was then analyzed by

mass spectrometry.

The identified compounds are shown below (grouped by the type of compound, not necessarily by

the order of elution from the gas chromatograph).

1. Perchloroethylene

2. Aliphatic Hydrocarbons, including a wide variety of materials of C8 to C15. Many

of these were are cyclic and/or branched. There were a total of 18 different materials,

including:

trimethyl cyclohexane isomers (3)

propyl cyclohexane

hexyl cyclohexane

ethyl cyclohexane

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methylethyl cyclohexane

methyl n-propyl cyclohexane

butyl cyclohexane

deca hydro naphthalene

butyl ethyl cyclopentane

methyl decane isomers (3)

four other C9 - C12 hydrocarbons which were not identified.

3. Aromatic hydrocarbons - a variety of materials, including:

xylene isomers (3)

ethyl benzene

trimethyl benzene isomers

methyl ethyl benzene

4. Several other poorly identified hydrocarbons - (C6 - C15).

Based on the above, it appears that a petroleum distillate product such as varsol or Stoddard solvent

is in the waste water.The other non-volatile components of this sample included both organic and

inorganic materials. The total non-volatile solids were 526 ppm, of which 23% or 121 ppm were

organic and 77% or 405 ppm were inorganic.

A total of 8 non-volatile organic components were identified:

Mw Chemical Detected

310 Docosane

312 1,2-Benzenedicarboxylic acid, butylphenylmetyhl ester

324 Tricosane

352 Pentacosane

366 Docosane, ll-butyl

380 Heptacosane

446 1,2-benzenedicarboxylic acid diisodecyl ester

610 Lucenin 2

The inorganic portion showed components as listed in Table X. The high antimony content likely

results from residual polymerization catalyst in the polyester used as a raw material at this site. The

high titanium levels result from delusterants in the polyester and other fibers. Also titanium is used

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as a pigment “white” color. The bromine is from a flame retardant foam back coating used on

draperies. Sodium chlorine is from the salt used in dyeing ground shades. The silver source could

not be located.

Table X – List of trace elements :

1.Titanium, 2.Tin, 3.Iodine, 4.Manganese, 5.Magnesium, 6.Copper, 7.Vanadium, 8.Chlorine,

9.Aluminium, 10.Mercury, 11.Samarium, 12.Tungsten, 13.Molybdenum, 14.Uranium,

15.Lanthanum, 16.Cadmium, 17.Arsenic, 18. Antimony, 19. Zirconium, 20.Bromine,

21.Sodium, 22.Potassium, 23.Cerium, 24. Calcium, 25. Lutetium, 26.Europium,

27.Selenium, 28.Terbium, 29. Thorium, 30.Chromium, 31.Ytterbium, 32. Hafnium,

33. Barium, 34. Neodymium, 35. Cesium, 36. Silver, 37. Nickel, 38. Scandium,

39.Rubidium, 40.Iron, 41.Zinc, 42.Cobalt.

Site #2

Twelve volatile organic materials were identified in this sample, including:

1. 2-Propanone, 2. Dichloro methane, 3.Alpha-Pinene, 4. Camphene, 5.beta-Myrcene,

6. Isicineole, 7. Benzene lmethyl-4(l-methylethyl), 8. D-Limonene, 9. Gamma-terpinene,

10. Alpha-terpinene, 11. 1,2,3- trichloro Benzene.

The non-volatile materials comprised 1084 ppm in the sample. Of these, 10% or 108 ppm were

organic and 90% or 976 ppm were inorganic. The organic materials are shown in Table XI, and the

inorganic materials in Table XII. The non-volatile organic materials appear to result from low

molecular weight cyclic oligomer (“trimer”) from high temperature dyeing of polyester. The high

potassium levels are due to the use of potassium silicate and potassium hydroxide in preparation

processes. These are preferred by some production mills because they repurtdle rinse off more

easily than the more commonly used sodium analogs.

Table XI - Nonvolatile Organic Materials

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Identified in Sample #2

1,2 Benzenedicarboxyllic Acid, bis (l-methyl ethyl) ester

Hexanedioic Acid, mono (2-ethyl hexyl) ester

41 trace elements were also found in sample 2 which includes gold and excludes chlorine & sodium

fom Table X.

Sample #3

This sample has no volatile organic compound.Non volatile organic compounds found are listed

below :

1.Cyclohexanone, 2.Cyclohexanol, 3. 2-chloro Cyclohexanone, 4. 1-chloro,4-isocyanato Benzene,

5. Hexadecane, 6.Hexadecanoic Acid , 7. Dibutyl 1,2-Benzenedicarboxylic acid , 8. Docosane,

9. butyl phenylmethyl ester of 1,2-Benzenedicarboxylic acid, 10.Tricosane,

11. dioctyl ester of Hexanedioic acid.

21 trace elements were also found in sample 3.

Sample #4

This sample contained 4 volatile organic compounds :

1. thiobis Methane,

2. dichloro Methane,

3. Chloroform ,

4. Toluene.

A total of 4 non-volatile organic components were identified:

1. Hexadecanoic Acid ,

2. dioctyl ester of Hexanedioic acid,

3. 1,2-Benzenedicarboxylic acid bis (2-methoxyethyl) ester ,

4. 1,2-Benzenedicarboxylic acid bis butyl(2-ethylhexyl) ester.

40 trace elements were also found in sample 4.

Sample #5

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This sample contained 4 volatile organic compounds :

1. dichloro Methane,

2. 2-ethyl,1-hexanol,

3. Limonene,

4. Trichlorobenzene.

A total of 5 non-volatile organic components were identified:

1. 1,2-Benzenedicarboxylic acid bis (2-methoxyethyl) ester ,

2. Dodecanamide ,N,N- bis(2-hydroxyethyl),

3. Docosane,

4. Tetratetraconsane,

5. 9-octyl Heptadecane.

40 trace elements were also found in sample 5.

In case of Bangladesh, huge amount of chlorinated solvents are found in wastewater streams that is

used in the textile industry in the scouring operation as degreasing agents and as dye carriers.

Chlorinated solvents become hazardous waste after use in these operations.

The solvents used as dye carriers contain various dyestuffs which are complex organic compounds

that are refractory (nonbiodegradable) and hazardous. Dyestuffs contain heavy metals, such as

chromium, copper and zinc, and organics(seen from the samples). Only about 50 weight percent of

commercial dye is dyestuff. The remainder is usually nonhazardous filler (such as sugar) and

surfactant. The dyestuff ends up in the waste solvent which may be recovered on-site or sent for

off-site recycling. Some spent dyes may be released to the water treatment systems.

8.2 Controlling of Hazards

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The scouring hazardous waste includes contaminated liquid solvent, bottoms recycling should be

practiced, the scouring equipment. from solvent stills when on-site and bottom sludge that arises in

cleaning The land disposal ban on chlorinated solvents, which should be implemented, requires the

generators of chlorinated solvents to dispose of these waste by either using the services of an off-

site recycler or a destructive incinerator. Recycling companies should pick up the waste solvent or

the contaminated still bottoms and return virgin, or a mixture of virgin and reclaimed solvent to the

company.

Pollution or hazard prevention programs should focus on reduction of water use and on more

efficient use of process chemicals to minimize hazards and to control them. Process changes might

include the following:

• Match process variables to type and weight of fabric (reduces wastes by 10–20%).

• Manage batches to minimize waste at the end of cycles.

• Avoid nondegradable or less degradable surfactants(for washing and scouring) and spinning oils.

• Avoid the use, or at least the discharge, of alkylphenol ethoxylates. Ozone-depleting substances

should not be used, and the use of organic solvents should be minimized.

• Use transfer printing for synthetics (reduces water consumption from 250 L/kg to 2 L/kg

of material and also reduces dye consumption).Use water-based printing pastes, when feasible.

• Use pad batch dyeing (saves up to 80% of energy requirements and 90% of water consumption

and reduces dye and salt usage).For knitted goods, exhaust dyeing is preferred.

• Use jet dyers, with a liquid-to-fabric ratio of 4:1 to 8:1, instead of winch dyers, with a ratio of

15:1, where feasible.

• Avoid benzidine-based azo dyes and dyes containing cadmium and other heavy metals. Do not use

chlorine-based dyes.

• Use less toxic dye carriers and finishing agents.Avoid carriers containing chlorine, such as

chlorinated aromatics.

• Replace dichromate oxidation of vat dyes and sulfur dyes with peroxide oxidation.

• Reuse dye solution from dye baths.

• Use peroxide-based bleaches instead of sulfur and chlorine-based bleaches, where feasible.

• Control makeup chemicals.

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• Reuse and recover process chemicals such as caustic (reduces chemical costs by 30%) and size

(up to 50% recovery is feasible).

• Replace nondegradable spin finish and size with degradable alternatives.

• Use biodegradable textile preservation chemicals. Do not use polybrominated diphenylethers,

dieldrin, arsenic, mercury, or pentachlorophenol in mothproofing, carpet backing, and other

finishing processes. Where feasible, use permethrin for mothproofing instead.

• Control the quantity and temperature of water used.

• Use countercurrent rinsing.

• Improve cleaning and housekeeping measures (which may reduce water usage to less than 150

m3/t of textiles produced).

• Recover heat from wash water (reduces steam consumption).

Replacement of existing processes with more eco-friendly processes can also reduce

hazards.Description of some of the processes are given on the following page :

Biotechnological Process

Textile industries of Bangladesh can be considerably benefitted by adopting following eco-friendly

biotechnological processes listed below on the table for reducing textile effluents :

Process Earlier method Biotechnological optionDesizingStarch size is used to strengthen the fabric so that it withstands further weaving process.But this size needs to be removed afterwards since sized cloth shows less uptake of dyes.

Oxidizing agents or sodium hydroxide are used but it damages the fabric.

Superior thermostable and resistant (to chemicals) bacterial analyses should be used to degrade starch size.

Scouring and BleachingTo remove pectins,waxes,colour,residual seed coatings,honeydew sugars and insect secretions which cause stickiness and severe processing problems.

Xylanase enzymes should be used.

BleachingChlorine or hydrogen peroxide is used as bleaching agents.Series of washes are required(between primary bleaching and dyeing) to

Enzyme catalyse with wide pHoptima should be used to degrade excess hydrogen peroxide.Water consumption can

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remove remaining H2O2. be reduced.BiostoningTo achieve dye fading,contrast and broken fibers as per fashion.

Pumice stone is used.Extreme fading,abrasion,more machine wear,more cost of maintenance are the problems.

Cellulase enzyme should be used for uniform and quality finishing of fabric.

BiopolishingTo remove fine surface fuzz(protruding fine fibres) and fibrils (which give rough look and stiff touch) from cotton and viscose fabrics.

Cellulase enzyme should be used to remove fuzz from fabric and to give it a permanent softening effect.

Carbonising“Lungies” are made by weaving polyester and cotton threads.Cotton fibres are then destroyed.This gives light net effect to the fabric.

65 % sulphuric acid is used. New cellulase enzyme ‘softzyme’ can be used as a replacement to acid treatment.

Silk DegummingTo remove impurities like,wax gums and sericin,a protein substance that covers the silk fibre or fibroin.These impuritiesmake silk coarse and lustreless

Conventionally done by using alkaline soaps.

Enzymatic(Degummase) degumming removes sericin by proteolytic action without doing any harm to fibroin.Better quality silk with luster,treatment at lower temperature,no use of soaps are the advantages.

Jute retting Conventional retting with microbial attack on jute was uncontrolled process taking days or even weeks.

Rettizyme does controlled and reproducible retting in less than 24 hours.Enzyme solution can be recycled.

Wool finishingTo get increased comfort(reduced prickle,greater softness) and improved surface appearance and pilling performance.

Protease enzymes should be used.

Using of ‘Air Dye’ Technology in Dyeing

The textile industry has a big pollution problem. The World Bank estimates that 17 to 20 percent of

industrial water pollution comes from textile dyeing and treatment. They’ve also identified 72 toxic

chemicals in water solely from textile dyeing, 30 of which are cannot be removed. This represents

an appalling environmental problem for the clothing designers and other textile manufacturers.

With consumers eager to purchase eco-friendly products, water pollution from dye houses and

coloration treatments could be a major hurdle for apparel manufacturers. How can a company claim

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to sell a “green” shirt if the dyeing process used to color the garment wastes and pollutes water?

Some companies have taken action and removed dyes from certain garments, but it seems unlikely

that everyone would be happy with off-white or beige as the only choices at the store. Consumers

want color and variety in their clothing.

Fortunately, for companies producing goods with synthetic fabric there is a solution: AirDye®.

AirDye is a dyeing process that uses air instead of water to dye garments, allowing companies to

create garments with vivid designs and colors, without polluting water and environment.

Here are the facts about AirDye technology:

Uses 95 percent less water

Emits 84 percent less Green House Gases (GHG)

Requires 87 percent less energy

Reduces damaging of goods (Up to one percent of goods are damaged using AirDye

compared to 10 percent of traditionally dyed garments)

No Rules Wash®.  Wash at any temperature, with whites or colors, with or without bleach

Allows for new designs. Dye different sides of a single piece of fabric different colors or

designs

When creating eco-friendly clothing, drapes, or even carpet, it is important not to forget the role dye

plays as an environmental ill. Consumers are becoming quite conscious of how bad traditional

textile dyeing is for the environment but have put up with it until now because there has not been a

viable alternative. AirDye is that alternative.

Here’s an example of how Air Dye compares to the traditional wet dye process for 25,000 medium

mens t-shirts:

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This unique dyeing process is already used to create vibrant, double-sided swimsuits for Miss

Peaches Swimwear, used with 100% recycled PET for eco-chic t-shirts by A Lot To Say, ground-

breaking hospitality industry window coverings from Hunter Douglas Hospitality, designer

handbags by JulieApple, and mostly recently, the runway fashions of New York design house

Costello Tagliapietra.

In the race to “go green,” companies need an advantage. They will get that by using this ‘Air Dye’

technology.

Using of Natural Dye(Indigo) for dyeing

Science Daily (Jan. 7, 2009) —Research Scientist Anne Vuorema of MTT Agrifood Research

Finland proves in her doctoral dissertation that glucose can serve as a reducing agent of indigo. This

finding is significant for devising more ecological dyeing practices for the textile industry.

Indigo is a vat dye and it needs to be reduced to its water-soluble leuco-form before dyeing. This

allows the actual dye to pass on to textile fibres. Glucose is known to be a good reducing agent, and

Vuorema’s work demonstrates that it also works with indigo.

Glucose dyeing seems to suit plant-derived fibres, such as cotton and flax, which withstand a high

pH (11–12). However, at this stage it cannot be recommended for animal fibres, such as wool and

silk (which can only withstand a pH of up to 9).

Anne Vuorema’s field of study is not widely known, and there are perhaps only 20 researchers

worldwide whose work focuses on plant-derived indigo. Vuorema and MTT launched the indigo

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research as part of the EU Spindigo project in 2001–2004. The project prompted questions which

Vuorema attempted to answer in her dissertation.

Vuorema works as an external researcher for MTT Plant Production Research. The Finnish Cultural

Foundation granted a scholarship for her doctoral dissertation in three years. In 2007, the Academy

of Finland funded her research at the University of Bath in England. This is where she has

conducted most of her electrochemical research.

Vuorema conducted her research at the University of Bath and the University of Reading in 2004–

2006. Professor Philip John at the University of Reading was the leader of the Spindigo project and

he also supervised Vuorema’s research in Reading.

Anne Vuorema’s research provides answers that enable researchers to improve the extraction of

indigo from the leaves of dyer’s woad (Isatis tinctoria L.). Her work enhances the energy efficiency

of dyeing and can potentially promote the profitable use of plant-derived indigo.

Dyer’s woad is the best known of all indigo-producing plants in Europe. Plant-derived indigo was

commonly produced until the early 20th century when synthetic indigo replaced it. The blue dye

used in jeans, for instance, is nowadays synthetically produced from oil, in a process which wastes

non-renewable natural resources and burdens the environment with synthetic chemicals.

Electrochemical reduction enables a clean process

In her dissertation research, Anne Vuorema developed a new electrochemical method for

determining the purity of indigo. She reduced plant-derived indigo using glucose and measured the

indigo concentration in the mixture using a new method. This is a great improvement in

determining the purity of plant-derived indigo.

The method can also be applied to assess the purity of other similar chemicals.

“The degree of purity of plant-derived indigo is fairly low. Crude indigo has a dye content of less

than 50%, while synthetic indigo has a dye content of over 95%. The impurities and means to

reduce them are not yet well known,” Vuorema explains.

Businesses look for guaranteed standard quality of dye. At the same time, ecologically geared

companies are looking for increasingly natural methods for dyeing fabrics, among other things.

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“Plant-derived indigo is a marginal, alternative product, and it does not currently compete with

synthetic indigo,” Vuorema says.

Vuorema also investigated indirect electrochemical reduction. She discovered that 1.8-

dihydroxyanthraquinone was an efficient catalyst for glucose-induced reduction. Electrochemical

reduction can only be introduced by major companies as it requires investment in special

equipment.

“We still need to achieve a lower pH in glucose reduction and solve the matter of impurities,”

Vuorema muses.

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9. Treatment options of wastewater

Chemical & Biological treatment( To remove colour)

The adsorption of colored compounds from the textile dyeing effluents of Bangladesh on granulated

activated carbons produced from indigenous vegetable sources by chemical activation with zinc

chloride was studied by Ajoy Kumar Das & Mohammad Mainul Karim of Department of Applied

Chemistry and Chemical Engineering, University of Dhaka, Bangladesh; and Sang Hak Lee of

Department of Chemisty, Kyungpook National University, Taegu , Republic of Korea.

The most important parameters in chemical activation were found be the chemical ratio of ZnCl 2 to

feed (3:1), carbonization temperature (450–465 °C) and activation time (80 min). The adsorbances

at 511 nm (red effluent) and 615 nm (blue effluent) were used for color estimation. It is established

that at optimum temperature (50 °C), time of contact (30–40 min) and adsorbent loading (2 g l−1),

activated carbons developed from Segun saw-dust and water hyacinth showed substantial capability

to remove coloring materials from the effluents. It is observed that adsorption of reactive dyes by

all sorts of activated carbons is higher than disperse dyes. It is explained that activated carbon,

because of its acidic nature, can better adsorb reactive dye particles containing large number of

nitrogen sites and –SO3Na group in their structure. The use of carbons would be economical, as

saw-dust and water hyacinth are waste products and abundant in Bangladesh.

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10. Overall Comments

On the following pages,pollution prevention for the textile industry is reviewed, including a brief

summary of present practices and an analysis of future needs and opportunities. Barriers and

facilitating factors are also identified.

10.1 Introduction

The textile industries of Bangladesh has a major impact not only on the nation’s economy but also

the economic and environmental quality of life in many communities. Textiles is the leading

provider of manufacturing jobs, with Gazipur as the nation’s number one place in primary textile

employment and production.

Textile processing requires the use of vast amounts of water, chemicals and energy, and therefore it

has important effects on environmental quality in textile manufacturing regions. In Gazipur alone,

there are about 200 permitted textile wastewater point discharge sources, as well as hundreds of

municipal systems in which textile operations are significant industrial users.This indicates the

immense potential of pollution source reduction.

Air quality issues are also important in textiles, with facilities in Gazipur alone reporting air toxics

emissions . In addition to air toxics concerns, most textile mills operate steam generation plants

which produce boiler emissions.

Although small in comparison to public utility electric power generating plants, textile sources are

significant. In addition, the emerging issue of textiles and indoor air quality which is now under

intense scrutiny.

Solid waste is also produced in large quantities, and hazardous waste in small quantities in some

operations.

In many cases, destruction of these wastes is not feasible for economic, technical or political

reasons. For example, Savar ranks 1st nationally in the production of hazardous waste,but has no

permitted hazardous waste disposal facility.

In light of all of the above, it is easy to see the regional and national importance of pollution control

in textile operations.

10.2 State of the Art: Commercial Textile Pollution Prevention Practices

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Textile waste amounts and characteristics are well documented, as are state of the art pollution

prevention practices. To summarize those documents, current commercial textile pollution

prevention practices include

Chemical alternatives, substitutions

Consumer, installer, end user information

Design stage planning of processes, products, facilities

Developing markets for wastes

Enhanced chemical expertise and general industry competence

Equipment maintenance and operations audit

Global, integrated view of manufacturing

High extraction, low carryover process step separations

Incoming raw material quality control

Inventory control

Maintenance, cleaning, nonprocess chemical control

Material utilization in cutting and sewing

New and improved equipment

Optimized chemical handling practices

Process alternatives

Process modification,

Raw material prescreening (prior to use)

Raw material substitution

Reducing disinformation, politics

Risk assessment methods, data, and procedures

Scheduling to minimize machine cleaning

Segregation, direct reuse

Standard tests, methods and definitions

Technology transfer of pollution prevention successes

Training programs, worker attitudes

Waste audit

Several types of wastes have already been successfully targeted by the industry, with emphasis on

four specific problem areas.

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The first problem area is hard-to-treat wastes, ie wastes which are persistent or resistant to normal

treatment. For textiles, these wastes include color, metal, phosphate, phenol and certain organic

materials, especially surfactants which resist biodegradation. Because of the extremely expensive

and difficult procedures involved in removing these via wastewater treatment, source reduction is

an economical and attractive alternative to treatment.

A second major accomplishment of the textile industry is source reduction of waste which becomes

widely dispersed when discharged. Wastes from textile processes often are reduced or captured for

recycle/reuse by process modifications at the source because, once discharged, they tend to become

widely dispersed and hard to treat. Machinery design, chemical substitution, procedure changes or

primary control measures can often accomplish better results at lower cost than treatment. In

addition, reclaimed waste in concentrated form (ie not dispersed) usually has its highest potential

commercial reuse value.

The third type of waste is offensive or hazardous wastes, especially materials of high aquatic

toxicity. For textiles, these include metals, various types of organic solvents and surfactants. In

many instances, chemical substitutions can effectively reduce production of undesirable process by-

products. Frequently, treatment of these hazardous or toxic process wastes leads to undesirable

waste treatment solids, for example, metal bearing sludges.

The final problem area is large volume wastes. These cam be successfully reduced by process

modification, chemical substitution, and on-site or off-site reuse. Each of the above types of waste

may originate from a variety of textile operations.

The textile industry has an outstanding documented record of pollution prevention activities. Many

case histories of reduction/conservation strategies are available. Case histories, in-plant techniques,

and actual production experiences have generally resulted in economic gains for the processor as a

separate benefit from the waste reduction, as well as providing improved compliance with permits

and/or pretreatment specifications.

One should go beyond this view of success, however, to define specific identifiable needs and

opportunities for the textile industry to advance its already extensive efforts in the area of

pollution prevention.

10.3 Technical Needs and Opportunities for Pollution Prevention

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Several specific technical needs, if met, will increase the ability of the textile industry to reduce

pollution at its sources. The two main opportunities for advancing pollution prevention in textiles

are:

Technology transfer of successful strategies

Addressing global needs, not assignable to any specific process

10.3.1 General Needs

Overall technical needs and opportunities which conceptually should not be limited to any one

specific process include :

Developing overall global views of pollution prevention,

Applying known pollution prevention technologies,

Information systems for optimal decision, and

Improving process understanding.

10.3.2.1 Global View

Unlike most industries, textiles is highly fragmented, which makes developing an overall global

outlook is particularly difficult. Most textile manufacturers have initiated pollution reduction on a

process by process basis, but few have achieved the kind of global thinking which transcends

individual process boundaries, and can produce maximum results. At each processing step,

decisions are made which impact downstream processes, beginning with product design, continuing

through each process and ultimately involving even the consumer as well. In many cases,

processing assistants are added only to be later removed by energy and chemically intensive

scouring procedures. Additives include lubricants, spin finishes, agricultural chemicals, size

materials, knitting oils, winding lubricants and tints. The challenge is to develop an overall global

pollution prevention scheme which transcends individual operations. Such an outlook would

consider the downstream impact of processing residues in terms of interferences and

incompatibilities. To implement this global perspective requires better information exchange

systems, which in most cases do not exist in the textile manufacturing complex. This information

issue is discussed in more detail below. Another requirement is incentives, which can be difficult to

establish in a fragmented manufacturing complex such as textiles.

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Global needs include not only the issues of design, additives’ effects on downstream processing and

the need for later removal by scouring, but also developing an overall view of manufacturing in

terms of containers, machine parts, print screens, drums, mix tanks, etc to reduce solvent loss, drag

out, and impurity build up. This affects not only the process’ pollution, but also the product quality.

Such thinking should extend even to consumer use of product in terms of aftermarket treatments,

cleaning solvents, use conditions, installation and maintenance; keeping in mind that the product

itself will eventually become a waste.

10.3.2.2 Accurate Information

Application of known technologies based on documented studies often produces great benefits,

however, accurate information about the pollution potential of various processes and products is

needed, to ensure optimal results. A surprising amount of confusing information is distributed,

however, for two fundamental reasons. One is the lack of standardized environmental terminology

and testing methods, and the other is the propagation of obsolete data from old literature. The latter

is a greater problem in textiles than other industries because, despite the fact that textiles is a mature

industry, its chemistry has been developed relatively recently. The entire industry changed with the

commercialization of synthetic fibers in the late1980’s . Unfortunately, pollution information

developed prior to 2000 is nill and is not quoted in textile reviews in spite of excellent and easily

accessible information sources. Most of this lack of information was developed during a time when

commercial processing was not comparable to modern practices. An improved comprehensive and

critically accurate literature review is now in press for the textile mills. The opportunity is to

accomplish great pollution reduction while at the same time increasing profits by using proven

methods. The challenge is to critically review literature in terms of modem textile commercial

practice as well as the best pollution prevention practices.

10.3.2.3 Information Distribution

Another major global need is to develop information distribution systems which will facilitate

maximum pollution reduction practices. In essence there are two types of information structures

which must be united. In textiles there is quite a large gap between the management information

systems and technical information systems. The challenge is to provide management, sales and

design personnel with information which enables proper decision making, eg product design,

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process selection, scheduling, and marketing. Although management and technical information

must differ in format to accommodate differing backgrounds, ie less technical experience of

management/sales/design vis a vis less business experience of chemists/engineers, it must have

significant correlation and unification of technical and business concepts. There have been several

attempts to develop such information systems with significant degrees of success.

10.3.5 Technical Understanding

At a fundamental level, even some of the most common and straightforward textile chemicals and

processes are not well understood by experts, much less production supervisors, workers and

managers. For example, conditions leading to unreacted monomer and catalyst in fiber, the process

of bleaching, the role of spin finishes, surface phenomena (eg fouling), preparation processes, and

dye aggregation are, in many cases, poorly understood. This is true for machines, fiber, chemical

and process issues. Other examples include the role of chlorinated solvents in cleaning; optimal

methods for use of non-production chemical cleaners for dye machines, pad rolls, printing screens

and rollers; the role of knitting oils and warp sizes; and how silicate stabilizes peroxide bleaching.

The opportunity is to reduce pollution through better fundamental understanding of processes and

systems.

10.3.6 Textile Wastes of Concern and Emerging Issues

As indicated above, the textile industry has already developed a relatively comprehensive approach

to pollution prevention by source reduction for several types of wastes. However there is still much

to be done. Currently, the textile industry is being called on to address even more difficult

challenges in pollution control. Further efforts and resources will be required to solve the new

important emerging environmental issues, i.e

Indoor air quality,

Color residues in textile dyeing/printing wastewater,

Massive discharges of electrolytes,

Toxic air emissions,

Improving treatability of wastes,

Elimination of low levels of metals from wastewater,

Aquatic toxicity, and

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Technology transfer of existing pollution reduction knowledge.

In addition to these new regulatory challenges, there are some very high volume waste streams

which deserve attention. These are salt, knitting oils and warp sizes.

One major technical challenge is to provide management, design, scheduling and planning

departments with credible and convincing forecasting of future constraints and requirements based

on technically accurate assessments of future regulatory issues, as listed above. A critical study

defining best pollution reduction management practices for specific future regulatory problems

would provide a basis for developing better industrial pollution prevention programs.

It is not feasible to solve the above problems by treatment systems alone. In fact, improving waste

treatment processes themselves often depends on producing more treatable, less dispersable, or less

persistent wastes. Also, treatment is in many cases more efficient on concentrated waste,therefore

mixing together offensive or otherwise incompatible wastes is undesirable. Thus, future

improvements in waste treatment are in a sense related to pollution prevention.

10.3.7 Product Design and Production Scheduling

One particularly important need is to introduce engineering considerations into fabric design and

production scheduling. Presently, textile fabric design is primarily coloristic, artistic and aesthetic.

Production scheduling is usually market driven with secondary consideration of problems

created,for example, by excessive color changes and associated machine cleaning. Better design

systems based on engineering and chemical principles will improve environmental and other

process considerations. Designers and scheduling departments are rarely aware of product attributes

(eg colors) which produce high pollution loads, cause scheduling difficulties or require excessive

machine cleaning. The opportunity is to provide artificial intelligence or expert systems which will

assist designers and process schedulers. Examples include not only color selection, but also fiber

blend selection, knit or woven constructions, etc. The same reasoning applies to sales/customer

relationships which should, but often do not, consider the environmental impact of product

specifications.

Emissions Factors

Advancements in engineering methodology are also needed in risk assessment and waste audits.

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Most mills use either direct measurement of waste for existing processes, or mass balance estimates

at the design stage to determine potential wastes from processes. Direct measurement of waste is

often difficult, and of course can not be done at the design stage before process start up.

Mass balance estimates have severe limitations, in that the difference between large volume of raw

materials and large volume of product leaves a small difference for the waste number, which (being

the difference of two large numbers) is highly uncertain. Thus one can see the need for standard

emissions factors for textile operations.

Using emission factors to predict the ultimate fate of pollutants can greatly improve waste audit

accuracy. Also, the simplicity of using standard emissions factors provides an opportunity to

examine processes more efficiently, thereby reducing more pollution with a given amount of

resources (eg time, personnel). This also offers an opportunity to better evaluate processes in terms

of problem wastes and to target high volume wastes from inefficient processes (eg garment dyeing)

as well as difficult waste from efficient processes (e..g flame retardant backcoating).

Finally, emissions factors are one of the few accurate ways to predict trace and fugitive emissions

such as hydrocarbons and metals.

Textiles, unlike most industries, has no standard emissions factors for many specific raw materials

and processes. There are two notable studies which estimate amounts of certain pollutants based on

production volume, but the pollutants included in that data are very limited. Since the completion of

these studies, there have been further regulations of priority pollutants, locally regulated organic

compounds and toxic air pollutants. The need is to understand the environmental fate of all process

chemicals, to identify the precursors of chemical wastes, and to develop emissions factors for

various production situations. Then, process engineers and schedulers will have the opportunity to

control these pollutants at the planning stage. Emissions factors are a key to planning because many

of the most offensive toxic air and water pollutants from textiles either are fugitive emissions or

result from trace impurities in high volume raw materials. In this case, mass balance is essentially

useless in any practical sense. It is very important that these studies include maintenance and

machine cleaning chemicals as well as process chemicals.

Standard Tests and Nomenclature

Another need is for engineering definitions and standard test protocol of waste and environmental

parameters. At present, even the term “biodegradable” is not defined. Well defined, quantitative

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understandable ratings for environmental and waste attributes (eg aquatic toxicity, treatability) will

enable engineers to make better assessments of risk, process trade offs and the like.

Specific Opportunities for Unit Processes

The previous information defines global needs and opportunities which can be applied to specific

processing situations as indicated in the following sections.

Fibers: Synthetic and Natural

There are several needs and opportunities from the fiber perspective. These include, for synthetics,

the development of improved spin finishes and fibers with lower amounts of residual monomer and

catalyst and for natural fibers, elimination of minerals, metals and agricultural residues including

biocides. Also, better fiber selection could afford the opportunity to reduce the amount of chemical

finishing required.

Spin Finishes

Proprietary spin finishes are added to synthetic fibers to provide fiber lubrication and other

desirable properties, such as static electricity control. The chemical composition of spin finishes is a

closely guarded trade secret but, in almost all cases, they must be removed prior to dyeing and

finishing to ensure uniform penetration of fabric by dyes and finishes, and to avoid reaction or

precipitation with incompatible downstream process chemicals. Also, volatile components of these

spin finishes produce air pollution when vaporized by high temperature processes such as

heatsetting, dye thermofixation, drying and curing of finishes. To prevent these problems, spin

finishes must be scoured from the goods prior to dyeing and finishing, thereby producing polluted

wastewater. Thus there is a need for better ways to control the surface and electrical properties of

fibers without the use of additives which interfere with downstream processing, quality, and

associated pollution potential. The challenge is first to better understand the role of fiber lubricity in

textile processes and textile structures, and then to use that knowledge to develop better spin

finishes, which do not interfere or pollute. Desirable lubricity and electrical properties could

potentially be provided by polymer surface modifications, such as introducing permanent additives,

or by physico-mechanical treatment (eg plasma).

High Purity Fibers

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Another challenge is to produce synthetic fibers with minimum amounts of unreacted monomer,and

to use less harmful catalysts and additives (eg delusterants) in polymerization reactions.

Many toxic pollutants from textile wet processing operations have been identified . They are in

many cases the same materials which can be extracted from raw fibers. Making polymerization

reactions more efficient and more robust to process variations potentially would reduce or eliminate

these undesirable pollutants from wastewater streams of wet processors.

Natural fibers present a similar challenge, but different pollution issues are involved. Agricultural

residues such as pesticides, herbicides and defoliants can lead to aquatic toxicity and other problems

from preparation wastewater. Processing solutions tend to leach metals out of textile substrates.

The challenge is to develop cleaner agricultural production practices, to inherently increase insect

and disease resistance, requiring less chemical additives, or perhaps safer or less

offensive additives.

Dyes

The first synthetic textile colorant was produced in the 1860’s when Perkin oxidized aniline to

produce Mauvine. By the early 1880’s, diazotization was a known reaction, and chemists like

Greiss, Walter and Boettiger attempted to synthesize commercially useful dyes with that method.

During the ensuing century of dye development, thousands of synthetic colorants have been

produced and used commercially. Traditionally, dye manufacturers’ goals have been produce low

cost dyes with high tinctorial value, brilliance, and good application and fastness properties; in

particular, high resistance to washing, cracking, light, oxidation (ozone), reduction (gas fading),

chlorine attack, acids and alkalis, etc. Although safety has, over time, become a consideration in the

synthesis of dye from intermediates, treatability has not been a significant consideration in dye

design. Dye research, until now, has focused on dyes with improved stability, thus more resistant to

treatment. For example: in the 1880’s, dyes would fade in 5 standard fading units (SFU) of light

exposure. By 1980, 50 to 100 SFU light was the norm. The next generation of dyes under current

development for automotive uses will withstand over 1000 SFU. Chemists, by their success at

developing highly stable dyes, have produced very difficult to treat color wastes from dyeing and

printing operations. The challenge is to resolve the competing objectives of product quality and dye

waste treatability by developing dyes which are more treatable, less dispersable, less persistent and

less offensive.

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New Generation Dyestuffs

As indicated above, the textile industry needs a new generation of dyestuffs based on better

treatability, higher exhaustion thus-less color residue in wastewater, and safer intermediates, while

maintaining desirable tinctorial, cost and fastness properties. The application properties of these

dyes of the future should be adequate in terms of repeatability, compatibility with existing

equipment, controllability, etc. This new generation of dyes should require fewer chemical dyeing

assistants, especially salt, retarders and accelerants. Fiber reactive dyes for cotton, which are the

fastest growing class of dyes over the last 20 years, are promising for this major opportunity to

reduce or eliminate some of the most intractable emerging problems enumerated above, ie

Color residues in dyeing and printing wastewater,

Massive electrolyte discharges,

Aquatic toxicity,

Toxic air emissions,

Improving treatability of wastes, and

Elimination of low levels of metals from wastewater.

One approach which has been proposed is to make dyes more reactive, however without higher

affinity properties the above goals can not be accomplished.

Another important opportunity is the development of azo dyes baaed on iron instead of other more

harmful metal ions such as cobalt, nickel, chromium, nickel, lead, and zinc. This line of research

has already shown promise in substituting iron for cobalt in Acid Bed 182 and Acid Blue 171, and

also iron for chromium in Acid Black 172.(19) These new dyes are non mutagenic and of course do

not introduce undesirable metals in dyeing wastewater.Use of eco-friendly natural dyes should also

be considered.

New Application Methods

There is also the need to develop new application methods especially for existing fiber reactive

dyes on cotton. One successful approach is pad batch dyeing, which is well known. Other methods

are also needed, especially for tubular knits and other substrates not adaptable to pad batch dyeing.

Using alternative electrolytes or other methods to control dye affinity and exhaustion via solubility

control and fiber zeta potential is another opportunity which begs investigation.

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Proprietary Issues

The need for better disclosure of chemical constitution of chemical specialties is important. The

same challenge exists for dyes. In the past, dyes have been classified by chemical structure and

applications factors in the CoZour Index. For nontechnical business reasons, this indexing system

seems to be coming to an end, due to the withdrawal of support by many of the major dyestuff

companies. In the future, dyes will become more proprietary, like specialty products, with

associated loss of information for the user. Lack of information in the future will make evaluation

of pollution problems, substitutions, etc even more difficult for textile mills because they will know

less about the chemical constitution and structure of the dyes which they are using.

Chemical Specialties

Specialty textile processing assistants are a unique group of products, which are not understood

very well by outsiders to the textile industry. They are used in large quantities with relatively little

information about their pollution potential. Listings contained over 5000 products in 100 categories

which were marketed by 175 companies under 1800 trade names. Each product is a proprietary

blend of chemical commodities. The composition is not revealed to the user, nor are the pollution

characteristics (eg aquatic toxicity).

There is a clear need for disclosure of user information, which is in a sense a business issue,

including potential incompatibilities with upstream process residues. But there are also technical

needs of better data on these mixtures, as well as more accurate aquatic toxicity data. Toxicity

reduction programs are often frustrated because comparative evaluation of substitute chemicals is

almost impossible. Test results for aquatic toxicity often correlate poorly between labs due to

nonstandardized test conditions, species variations, etc.

The incentive to establish a good pollution prevention program is often economic. These programs

are often justified through a “pollution prevention pays profits” type of thinking. The need for better

risk/benefit assessment and more realistic waste goals, as well as realistic forecasting of benefits

and liabilities therefore is critical. The challenge is to eliminate the barrier of poor technical

information described above. This also contributes to the better technical understanding of

processes discussed earlier.

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Chemical Commodities

In addition to specialties, textiles uses massive amounts of commodity chemicals, eg acid, alkali,

salt, warp size, fiber, water. A typical cotton production facility might use commodities that is

greater that the weight of product produced. It is not unusual to find cotton dyehouses which

discharge 3000 ppm of salt in the wastewater. There are two needs in this area. The first challenge

is to reduce the amounts of commodities, especially salt, required for dyeing. The second is to

determine the trace impurities in commodities and to seek better sources of commodities, or better

methods of manufacturing commodities, which reduce or eliminate offensive trace materials.

The second major need, to identify and eliminate trace impurities from commodity raw materials, is

crucial. Tests of textile wastewater have clearly shown the presence of toxic materials which also

have been detected as impuritiesin fibers and chemical commodities. Further work shows

that these toxic wastewater pollutants are present in significant amounts in high volume raw

materials (eg fibers) as well as salt and alkalis. Major needs exist in this area, especially related to

zinc in salt, low level impurities in fibers (ie monomer, catalyst, delusterants), metals in caustic, and

impurities (eg metals, organics) in raw water supplies.

The current practice of reusing waste commodities internally or from other industries can cut

consumption and associated pollution discharge of commodities. This is generally a good practice,

but impurities must be considered also. Caution and more information with respect to the above is

needed in the reuse of commodities.

Yarn Formation: Spinning

In yarn spinning, routine waste production is minimal and more or less unavoidable. Also, most

waste is recycled into further uses. Therefore the main opportunities are related to additives and

how they affect downstream processing, much like spin finishes discussed previously. Targets for

consideration include tint oversprays, winding emulsions, coning oils, lubricants, and in some cases

biocides used for mildew suppression. This is an area where global attitudes can contribute greatly.

In some cases the yam mill also applies sizes or lubricants, which will be reviewed under fabric

formation in the next section. The need is to assure compatibility of additives with downstream

processes, and to eliminate potential interferences to later processes. The challenge is to develop

specific products for spinning mill use which have minimal downstream impact. This has been done

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to a certain extent with low BOD winding emulsions and waxes which do not pollute when

removed, but not with other spinning additives noted above.

Fabric Formation

Sizes and knitting oils added to yarns before and during fabric processing are one of the greatest

routing intentionally created pollution stream in textiles. Typically 6% or more of the weight of the

goods is added as size or knitting oil, only to be removed and discarded in the next step of the

process (preparation/desizing). Although size recovery is possible, knitting oils are never

recovered. Although there are a few spectacularly successful size recovery systems in operation,

the textile industry, for several valid reasons, makes no use of size recovery. This is equivalent to

thousands upon thousands of tons of intentionally created waste, making it along with water, salt

and cutting room waste the highest volume waste materials in textile manufacturing, and perhaps all

US manufacturing. The need is to dramatically reduce this. The challenges are to:

Remove logistical and technical barriers to size reclamation and reuse

Provide more incentives for recovery

Develop fabric forming methods which require minimal sizes and knitting lubricants

Design yarns and fabric structures which require less sizes and lubricants to create Recovery can

only be done with certain types of sizes, notably polyvinyl alcohol (PVA), which is roughly one

third of the total size used. The remainder comprises non recoverable sizes, such as starch. Less

than one third of all PVA is recovered. There are several technical and business barriers, including

the practice of applying PVA in mixtures with sizes which inhibit recovery, high expense of

shipping recovered PVA concentrate solutions, mixing goods containing different sizes at the

desizing plant, and lack of understanding of recovery potential.

Regardless of the approach taken, there is a clear need for significant efforts to reduce what is

undoubtedly two of the largest industrial waste streams in all of US industrial manufacturing: warp

sizes and knitting oils.

Fabric Structures

Certain indoor air quality factors are also a function of fabric design, structure and formation.

Preliminary modeling of pollutant exchange zones shows that fabric structure, air permeability and

velocity slip factors are all important parameters in the emission, sorption and release of indoor air

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pollutants by textiles and multilayer textile containing products. The opportunity is to design textile

containing products which inherently produce improved indoor air quality and minimize pollutant

exchange by understanding fabric/air interactions at the microscopic level. Of course, another

opportunity in indoor air quality is to design and produce fabrics which inherently require less

chemical stabilization, thus eliminating the need for chemical finishing, with associated reductions

in manufacturing pollution as well as lower risk of air emissions from applied chemicals.

Wet Processing: Preparation, Dyeing, and Finishing

Typically over 50% of pollution from textile preparation, dyeing and finishing processes results

from removal of upstream processing residues which, if not removed, would interfere with dyeing

and finishing. A significant portion of pollution also results from application of chemical fabric

stabilizers, stiffeners, softeners, etc to adjust the characteristics of the fabric to suit the intended end

use. Thus, pollution prevention in wet processing is intimately related to the global views advocated

throughout this document. If it were not for the need to remove contaminants via preparation and

overcome technical design deficiencies via finishing, dyeing and printing would be the main tasks

in textile wet processing.

Pollution reduction has been utilized very successfully in wet processing. Even so, there are still

significant opportunities for advancement. Many of these are related to chemical specialties and

commodities discussed previously, as well as technology transfer of successful methods already

used by more sophisticated operations.

Dyeing Controls

One important need is to improve process control, especially in dyeing operations. The resulting

color consistency, coupled with appropriate numerical color specifications, could provide the

opportunity to cut adjacent garment (product) panels or parts from widely separated areas of fabric,

thus diminishing waste potential in cutting and sewing by improving marker efficiency. In order to

do that, more uniform fabrics are needed. There are many factors which are beyond the dyer’s

control. The use of controllable factors to offset uncontrollable variations and thus produce more

consistent color repeats has been proven in the laboratory, using non parametric methods such as

neural network and fuzzy logic based real-time multi-channel adaptive control algorithms. The

economic and pollution control benefits of achieving this in commercial dyeing operations will be

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immense. This will not only apply to improved material utilization for piece dyed goods, but also

yam waste will be reduced in weaving and knitting through better yarn utilization in yarn dyed

fabrics.

Another need is better parametric models of complex dye systems (eg fiber reactives) for control

purposes. Quite sophisticated parametric thermodynamic and kinetic dyeing models are available

for many dye classes, however there are still major opportunities for improving these models and

also for utilizing them in parametric control algorithms or for the purpose of “training” non

parametric control models. The challenge is to develop methods of parameter estimation which are

simple and economical enough to apply in commerce. Another challenge is to develop parametric

models which are simple enough to be useful in commerce, but at the same time robust and

sophisticated enough to achieve highly accurate predictions of dyeing behavior. This may seem to

be impossible to achieve, but recent work indicates the possibility is real. A barrier to progress in

this area is the perception that this research is too fundamental for industry to support, and

simultaneously too applied to attract traditional basic research support.

Salt

One need which stands out in the near future for cotton dyeing is salt reduction. At this time, the

salt requirements for fiber reactive dyes, which are the most important dye class for cotton, are 50%

to 100% on weight of goods. It is not unusual to find textile mill effluents with 3000 ppm salt from

cotton dyeing operations. The total quantity of salt discharged from textile dyeing operations may

be on the order of magnitude of 400 million pounds annually. It all becomes waste. The role of salt

in dyeing is to promote dye exhaustion from the dye bath on to the fiber by decreasing the solubility

of dyes in water, and by electrical effects including fiber zeta potential. Reduction of salt in cotton

dyeing processes usually results in lower dyebath exhaustion, and therefore more color in dye

wastewater. Reduction of salt from the current levels of up to 3000 ppm to desired limits of only

250 or less ppm will require significant developments in several areas including machinery,

dyestuffs and dye application processes.

Machine Cleaning

At present, the textile industry schedules dyeing production based primarily on delivery times and

cost factors. Two major pollution sources from continuous as well as batch operations are dumping

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unused portions of mixes and machine cleaning which may be necessary between shades. Machine

cleaners are generally among the most toxic and offensive chemicals used in textile wet processing.

Dye machine cleaning requirements are highly dependent on the sequencing of colors; ideally

grouping colors within chroma families (eg red, yellow, blue), and sequencing from light to dark

and from brighter/brilliant to duller/greyish. At present, “smart” scheduling systems which can

minimize machine cleaning are not used for dyehouse scheduling. The need is to schedule dyeing

production in such a way as to reduce pollution by minimizing machine cleaning as well as mix

dumps. The opportunity is fairly straightforward, and the technical barriers to this are minimal.

The barriers are discussed under “Accurate Information”.

Scheduling improvements are not the only way to reduce machine cleaning requirements. There

re opportunities also to understand fouling and cleaning processes better, and to develop :

Dyeing systems which do not foul machines,

Machine configurations and easy to clean surfaces (eg Teflon(R))

Less toxic and more biodegradable machine cleaners.

Robust Dyeing Systems

Poor dye work and associated off quality, rework and pollution is often caused by the presence of

upstream processing residues in fabric. The purpose of preparation is to remove these. However,

preparation processes s ometimes are not completely successful in removing all contaminants.

There is a need for dyeing systems which are more robust toward previously added materials (e.g.

spin finishes, agricultural chemicals, sizes, oils, tints, winding emulsions). Such systems could

reduce or eliminate the need for preparation.Using of natural dye with glucose as reducing agent

or using the Air Dyeing technology may be an option. The challenge is somehow to overcome

the proprietary nature of specialties and globally select compatible processing assistants. The

barriers to this are great, but the potential rewards of such an approach would be immense.

There should be some works in this area by a consortium of textile companies and Universities .

Automation

Equipment automation is a major focus of textile process improvement over the last 10 years. At a

recent, International Textile Machinery Association exhibition there were less than 100 companies

showing dyeing machinery, but over 150 showing microprocessor controllers, chemical dispensing

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systems, etc. Automation can produce good results in quality, productivity and pollution

reduction,because routine waste levels are decreased, cleanup is easier, mixes are made more

accurately, and human errors are reduced. On the other hand, the relative importance of

malfunctions and spills,increases. Also there is a tendency for technical supervision to lose contact

with automatedprocesses. When a process is automated, routine maintenance becomes relatively

more important.

Maintenance and supervisory practices which have been used in the past with less automated

systems may not be optimum when automation is installed. The challenge is to determine the

optimum technology of pollution control for automated processes, and to determine how that differs

from current practices.

Finishing and Fabric Design

Finishes are applied to provide desirable end use characteristics, as well as to facilitate product

formation (eg cutting and sewing). Proper engineering-oriented fabric designs can eliminate some

or all of the need for finishing, particularly in terms of shrinkage, curling, and sewing lubricants.

Also, it is possible to stabilize properly designed fabrics without chemicals by the use of

mechanical finishes. Much finishing research in recent times has focused on chemical finishing, not

mechanical. The opportunity is to substitute mechanical treatments (e.g.compacting,Sanforizing(R))

for chemical treatments. For these to be successful, it is necessary to correlate three items: fabrics

designs which require less chemical stabilization, finishing machinery whichcan accomplish better

end use performance, and compatible fabric specifications which accommodate the use of

mechanical finishing through proper design of textile assemblies (e.g garment constructions).

Indoor Air Quality

Finishing has direct impact on indoor air quality because many finish chemicals contain low

molecular weight, reactive materials (e.g. formaldehyde) which may later be emitted in the

consumer’s use area. Also, certain finishes (eg soil release, water repellent) change the fiber’s

critical surface energy and thus alter the sorption/reemission characteristics of fabrics. There is a

potential opportunity to improve indoor air quality by understanding these factors.

Most textiles are combined with other items in the final consumer product, and the combinations

are essentially innumerable. Textile manufacturers do not generally know which components will

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be combined nor in what manner. For example, an upholstery fabric could be combined with other

fabrics, batting, fiberfill, open or closed cell foams, stiffening innerliners, etc. On the other hand,the

product fabricator generally does not have good information about incompatible combinations in

terms of emissions and sorption/reemissions. This makes product design difficult. Better

information on combinations and synergisms will enhance indoor air quality.

Consumer Issues

The final link in the production chain is the consumer. Opportunities for source reduction include

the development of post consumer recycling of textile products as mentioned above for denim,

installation and maintenance improvements to improve life expectancy of textile products,

installation and use information for improved indoor air quality, products which do not soil or do

not show soil thus require less cleaning solvents and aftermarket care requirements.Discarded

carpets are another potential source for post consumer recycled fiber.

Better information for consumers about environmental impact would require standardization of

tests/terms such as “biodegradable”.

Business Opportunities and Needs for Pollution Prevention

In addition to technical needs and opportunities above, there are some business issues which also

deserve comment. Quite a lot of pollution prevention success has been achieved within individual

production units in textile operations. Even greater opportunities exist in pollution reduction

programs which transcend production facility boundaries.A In many cases, the barriers and

challenges are non technical. These will be reviewed here.

Priorities and Commitments

The need for global views and better information exchanges are controlled to a large extent by

business priorities and commitments. The technical staff at a particular manufacturing site can

develop and implement procedures for pollution reduction. But the need to develop global views of

manufacturing can only be achieved by a higher level technical understanding across production

unit boundaries. A prime requirement for this is better technical cognizance by those who operate

across boundaries, ie management. Information exchange in this sense is not an end in itself, but

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only an enabling mechanism for actually understanding the predicament of other manufacturing

stages. The opportunity is to develop special global business relationships among suppliers, various

manufacturing sites and customers to reduce pollution.

Marketing of Waste

In some cases, wastes are unavoidable so it is important to view waste as a by product or secondary

resource with value. Opportunities to market waste by products should be sought. The business

barrier is that the waste almost always sells for less profit than the primary products, therefore the

sales incentive is low. However, when costs of collection and disposal, as well as potential liability,

are considered the situation may be more profitable than it first seems. There is also a technical

barrier in the sense that many operations are reluctant to buy waste materials as raw material inputs

for quality and safety reasons. With so many disincentives, valuable opportunities may be

overlooked, based on generalized business views about marketing wastes.

Consumer Information

There is a need for to get more information on product use, installation and combination synergisms

from manufacturing to the customers. Marketing is a critical link in this chain. Some industries do

an excellent job of this. There is a need in textiles to emulate these other successful techniques (eg

technical product bulletins, product specifications). As an example, a chair with upholstery will

include particle board, foam, fiber fill, stiffeners, upholstery, paint, etc all in combination. The

fabricator of the chair does not know how combinations will interact because technical information

bulletins are normally not available on textile fabrics. The manufacturers of each component

usually have no information concerning component combinations.

Conflicting Goals

One conflicting goal is dye stability vs. dye waste treatability. There are even more difficult and

hard to define conflicting goals in nontechnical areas. Some of the more prevalent will be reviewed

below.

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Water Conservation Penalty

An often encountered example of nontechnical conflicting goals which inhibit pollution prevention

is the relationship of textiles and municipal sewer systems. One particular dilemma, called

the“water conservation penalty,” is often encountered. Most cities charge a fee for excess BOD

over a preset concentration limit. This causes textile mills typically to adopt specialty processing

assistants with lower BOD. Textile operations are often encouraged by such BOD surcharge

regulations to make undesirable substitutions of non-degradable (low BOD) surfactants. These tend

to pass through treatment systems and increase aquatic toxicity in the treated effluent.

Toxicity reduction in many cases is frustrated for several reasons :

Difficult substitute chemical evaluation because of poor correlation between labs

Many chemical specialties are proprietary

Technically correct substitutions are punished by regulatory measures (eg. surcharges)

Another example is waste segregation and capture. If there is no way to dispose of captured

hazardous concentrated wastes (which is often the case), then the processor has little incentive to

capture the waste for disposal in its concentrated form. Keeping hazardous waste out of sewers is

often desirable but not rewarded.

Situations such as the above are difficult to resolve with positive results, and attempts to do so

usually develop into little more than long drawn out posturing. The need in this case is a greater

understanding of the impact of regulations by those who write and adopt municipal sewer

ordinances. The opportunity to accomplish genuine pollution prevention could be greatly advanced

by genuine cooperation.

Quality Conflicts

Usually, the goals of economic gain and pollution prevention are very compatible, since high

processing efficiency and low waste are essentially two sides of the same coin. Also, high quality

attitude of workers and pollution control through orderly work practices, etc go hand in hand. But

occasionally these goals conflict, and when that happens, the result can be one of the most difficult

situations in which to implement a pollution prevention program.

Typically this happens in very high priced, high quality, low volume specialty manufacturing

situations such as paper-making felts, coated fabrics, offset printing blankets, and high quality

printing. In these cases, the cost of waste is insignificant in terms of product value. Without

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economic incentives, progress is slow in pollution prevention. Also, the cost of product loss (off

quality, seconds) is so great that conversion efficiency is totally dominant and waste raw materials

have essentially no value compared to product. The opportunity is to study these situations, and

develop incentives and more applicable pollution prevention measures and techniques.

Risk/Benefit Assessments

Better risk assessment and more realistic waste goals are needed. In many cases, one part of the

risk/benefit balance is clear, but the other part is vague, nebulous or poorly understood. Sometimes

the barrier is poor technical understanding of processes. Another barrier is a cost system which

views waste costs and liabilities as an overhead items, not direct cost items.

Human Resources

There is a clear need for more technical understanding among textile managers. Cost and liabilities

(civil and criminal) are the responsibility of management in most cases, so it behooves the industry

to develop informed management teams. Strangely, the largest textile universities of the world have

somehow misinterpreted this as a need to include more management in textile curricula by

diminishing technical content of programs. The numbers of graduating textile management majors,

who have minimal quantitative skills and minimal understanding of science, technology and

engineering, far surpasses the numbers of technical graduates. The need is to bring educational

criteria for various textile groups (management, design, engineering, chemistry, technology) closer

together in terms of educational experiences.

In the same vein, there is a need to embody pollution prevention concepts in higher education.

University education provides for interaction of engineers and chemists with managers and

designers in general curricula to foster communications and a common perspective between these

groups. The opportunity is to develop human resources to tackle tough future pollution reduction

problems. The challenge is to create technical environmental competence in graduates. Few if any,

educational institutions have achieved this, but efforts should be underway to implement such

programs.

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11. ConclusionHuman beings have been living in this world for thousands of years after creation. They set their first

footprint towards civilization when they discovered the method of lighting fire.Then they invented

wheel,pottery ;discovered iron, make copper,bronze and various tools.These advancements were

furher enhanced by the Greek and Roman civilization . After that ,the civilization advances toward

the middle age.

The middle age was dominated by the Arabs,who,inspired by the Quran,the message of the

Creator,and his messenger Muhammad(SM),started to spread the light of knowledge throughout the

whole world and taking the responsibility of advancement of human civilization.During this

time,textile industry flourishes by the progress of cottage industry by them.Hand made cloths made

by the Arabs spread out the whole world for its fineness.Maslin of Bengal was created and becomes

famous due to the influence of the ideology of Islam.

After the renessaince of Europe by the French revolution,industrial revolution changes the whole

world.It replaces the Islamic civilization and gives power to the European civilization.The industrial

Revolution was started when James Watt invented the Steam engine.Arkwright invented the thread

cutting machine, which was the first step towards the modern textile industry. Now-a-days,the

modern era of civilization has ameliorated to its highest peak where various types of industries has

flourished.

When industries started functioning from its beginning,disposal of wastes was not taken into serious

account,Solid wastes were dumped into river or lake while liquid wastes or effluents were

discharged into the river indiscriminately.Environmental effects or pollution was not taken into

account as there was no idea about them at that time.

During the time of sixties and seventies,environmental effects of industrial effluents were considered

as a matter of concern .Different types of serious environmental accidents made the governments of

different countries to set up various guidelines and standards to control the pollution.

Now-a-days,environment is not considered as a dump site for effluents,rather protection of it is

taken into serious account. But as Bangladesh can’t become a full-scale industrially developed country

due to the fuel and energy crisis,environment is not considered as a matter of concern. For example,

many textile industries don’t have any ETP(Effluent Treatment Plant),which is mandatory.It is hoped

that this scenario would change as early as possible.If the government make steps to create industrial

task force which will help to maintain rules and regulatations strictly,this hope will become true.

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May the Almighty help the people of Bangladesh to make it as a full-scale industrially developed

country.

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