Reuse of Water in Cotton Pretreatment

8/12/2019 Reuse of Water in Cotton Pretreatment

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Reuse of Water in Cotton Pretreatments 2011

NIFT, GANDHINAGAR Page 1

REUSE OF WATER IN

COTTON PRETREATMENT

A

Report

SUBMITTED IN THE PARTIAL FULFILLMENT OF THE

REQUIREMENT FOR THE PROJECT OF

MASTERS

IN

FASHION TECHNOLOGY

NATIONAL INSTITUTE OF FASHION TECHNOLOGY

BY

SOUVIK MANDAL

NATIONAL INSTITUTE OF FASHION TECHNOLOGY

GANDHINAGAR, GUJARAT


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ABSTRACT

Water savings, reclamation and reuse in industry are topics of increasing

economic interest due to increasing water scarcity and costs. For this reason, research

and development activities within this topic is increasing, methods and tools for

analyzing water savings and reuse possibilities are being developed, and solutions are

being implemented. Textile processing is one of the largest and oldest industries

worldwide and responsible for substantial resource consumption and pollution. The

wet processing part of the industry, i.e. pre-treatment, dyeing, printing and finishing,

is especially polluting and resource consuming in terms of water, energy and

chemicals. It entails a vast variety of water consuming processes, and like in most

industries, freshwater is used in all processes with almost no exceptions. It was knownfor many years that fresh water is not needed by all processes taking place in textile

wet treatment. However conservatism and consideration for product quality in the

industry have until recently prevented substantial water reuse from breaking through

in practice.

One of the aspects for water conservation is reusing the same bath for several

times. This technique can be used only in pre-treatments i.e. scouring and bleaching.

It can save water as well as chemicals on large extent in scouring as whole bath is

reused. In bleaching except H2O2all auxiliaries in bath can be reused. Minimization

in the effluent load can be observed by tests carried out on effluent from each process

of scouring and bleaching. To observe the efficiency of the processes carried out

samples from each process are tested.


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INTRODUCTION

Auxiliary chemicals used in textile mills are developed to be resistant to

environmental influences. Disposal of water can result in wastage and also results in

groundwater contamination, gas formation and problems with odors. As regulations

become more stringent, companies are forced towards more technologically

sophisticated treatment methods. This results in an increased cost for water

management. More and more companies realize that water consumption at the source

is necessary to reduce the cost of treatment.

In 1990, Congress passed the Pollution Prevention Act. This act reaffirms the

federal objective of the Emergency Planning and Community Right-To-Know Act

(Title III of SARA of 1986). (Ref 10)

Pollution prevention is defined as those measures that eliminate or reduce

pollution prior to off-site recycling or treatment. In the Pollution Prevention Act, the

Congress defines a multimedia waste management hierarchy. Source reduction stands

at the top of the waste management hierarchy and is followed by reuse.

Reducing the volume of water released through this act can be accomplished

by conservation and more efficient use of resources. Source reduction can be achieved

by the following techniques: optimization/conservation of chemicals, chemical

substitution process modification, equipment modification and improved maintenance

and housekeeping. The objective of this research is to reduce water and chemical

drainages in the textile wet processing industry. This was achieved through an

extensive literature review. In the literature review, the different textile wet

processing operations are briefly discussed, and a description of various source

reduction techniques is provided. [10]


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LITERATURE REVIEW

The preparation, dyeing and finishing of textile products consume large

amounts of energy, chemicals and water. These wet-processing operations require the

use of several chemical baths that, often at elevated temperature, give the desired

characteristics to the yam or fabric. This section describes the different wet-

processing techniques used in the production of cotton fabric. The same techniques

are used when other types of fiber are processed, but differences will occur in the

amount of raw materials required. Cotton has been chosen for this literature review

because 70% by weight of the fibers processed are cotton fibers. Furthermore,

processing natural fibers requires more processing than manufactured fibers. (Ref 10)

The sequence for cotton wet processing is schematically represented in Figure.

These processes are usually done in batch, continuous or semi-continuous systems. In

batch systems, the machine is loaded with a fixed amount of fabric, chemical

solutions are added, and the process is conducted. After processing, the chemical bath

is discharged, and the fabric is washed. Subsequent processing is usually done in the

same machine. In continuous systems, the chemical mix is placed in pans, and the

fabric runs through the machine continuously. (Ref 6)

Cotton wet processing can be divided into three steps. Preparation removes all

the natural impurities from the cotton and chemical residuals from previous

processing. Natural impurities include waxes, oils, proteins, mineral matter and

residuals seeds. The cotton contains a significant amount of contaminants resulting

from the widespread use of fertilizers, insecticides and fungicides. Previous knitting

or weaving processes leave residuals of knitting oils and sizing chemicals on the

surface of the cotton fibers. All these impurities must be removed before dyeing,

because they can interfere with the dyeing process. Insufficient preparation can result

in an uneven dyeing, can cause spotting or can even damage the fabric permanently.


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Desizing:

After the weaving process, the sizes have to be removed from the fabric

because they interfere with subsequent processing steps. Sizes have, in general, a high

biological oxygen demand (BOD) and will contribute significantly to the waste load

of the mills effluent. Three methods frequently used in textile processing are acid

desizing, enzyme desizing, and oxidative desizing. The goal of these different

methods is to hydrolyze thestarch. Unlike starch, synthetic starches stay intact during

desizing, can be recovered and reused.

Scouring:Scouring is typically performed in an alkaline solution and high temperature

environment. The removal of natural impurities is based upon saponification and

hydrolysis at high pH and temperature. Soaps and detergents added during scouring

may precipitate with calcium, magnesium and iron (3+) if present. These metals are

therefore removed by the addition of reducing and sequestering agents. The

sequesterants will form strong complexes with calcium, magnesium and iron (2+) at

high pH. The reducing agents are added to reduce Fe3+ to Fe2+. The removal ofnatural impurities can be done in a single process or can be combined with desizing

and/or bleaching. The use of sequestering and reducing agents can be avoided when

softened water is used. Scouring is usually the first step in the processing of knitted

goods and will remove the knitting oils which were applied to the yarn prior to

knitting.

Bleaching:Almost all fabric containing cellulosics are being bleached to remove the

natural colored matter. Three chemicals are commonly used are hydrogen peroxide,

sodium hypochlorite and sodium chlorite. In sodium hypochlorite bleaching, the

washed, and scoured fabric is passed through a dilute sodium hypochlorite bath for

impregnation (saturator) and stored in a J-box or a large pit. After bleaching, the

goods are washed and treated with antichlor (NaHSO3) to remove any traces of

bleach. Bleaching with sodium chlorite is most efficient at pH 4.02. However,

chlorine dioxide, a gas with a low threshold limit value for inhalation, is formed at


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this pH. Sufficient care must be taken to protect operators from chlorine dioxide

fumes. Hydrogen peroxide bleaching is carried out under alkaline conditions. (Ref 25)

As a result, scouring and peroxide bleaching can often be conducted in one step.

During peroxide bleaching, stabilizers are added for two reasons. Stabilizers

inactivate metal impurities that may cause catalytic decomposition of hydrogen

peroxide. They also act as buffers. A stabilizer frequently used is colloidal sodium

silicate.

Water usage:

Experience has shown that the amount of water required in textile processing

varies widely, even between similar wet processing at different sites. The data shown

in Table give typical quantities water used for various types of processes. This

indicates the site-specific nature and details of water use in various processing

situations. Many mills have very high water costs, especially when the water is being

purchased from a municipal system. These operations usually are much more

conservative with water than others with less costly sources.

Water Uses in Textile Wet Processing:

Various textile wet processes are influenced in different ways by the presence

of impurities in the water supply. There are several major water use categories to be

considered, including water for processing, potable purposes, utility, and laboratory

use. Each requires different water-quality parameters. Process uses (preparation,

dyeing, and finishing) Include making concentrated bulk chemical stock solutions,

substrate treatment solutions (bleach, dye bath, or finish mix), and washing. Utility

use includes noncontact uses such as cooling water, boiler use, humidifier systems,

equipment cleaning, etc. If provided to employees in drinking fountains, etc. These

potable water supplies must be free of toxic and bacterial contaminants, many of

which are of little or no consequence in processing situations. On the other hand, the

presence of chlorine, iron, and treatment chemicals commonly found in potable water

can have a major impact on textile processes.

It is common practice in some mills 'to use potable water for the laboratory

supply while using non potable water for production processing. Since potable water

is usually chlorinated, it can alter the shade of dyeing or cause other effects on

processing. This sometimes contributes to poor lab-to dye house correlations for dye


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on mechanical factors, such asbath and fabric turnover rate or "contacts", liquor ratio,

turbulence and other mechanical considerations and physical flow characteristics.

Thus, lower liquor ratio and reduced total water use do not always correlate closely as

one might expect. One water conservation strategy which is widely practiced by dyers

of cotton fabrics is reverse dyeing using and fiber reactive dyes.

Other routine strategies involve combining, bleaching, scouring, and or

desizing, dyeing of two fibers in one bath for blends whenever possible; and

combining the scouring and dyeing of synthetics or cotton when strict shade

requirements do not have to be met. These are widely practiced and vary greatly with

end user requirements, shade, fastness, specific blend, and equipment.

(Ref 1)

Sources and characteristics of water

There are many sources of water, the most common being "Surface sources, such

as

Rivers Deep wells Municipal or public water Reclaimed waste streams

These water sources vary widely in types and concentrations ofcontaminants.

Many impurities which commonly occur in textile water sources affect textile

processes in various ways, both positively and detrimentally. The most common

impurities, which are present in almost all water supplies to some extent, are:


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Heavy metals: iron, copper, and manganese Water hardness: Calcium and magnesium Miscellaneous anions Sediment, clay, suspended solids Acidity, alkalinity, and oil and grease Dissolved solids

Testing for commonly occurring contaminants in water

There are many quick qualitative spot tests for detection of trace quantities

of ions and elements in water. In some cases other ions may interfere with the test for

a specific ion, so care must be taken in conducting these tests. There are also

quantitative tests for determining the exact concentration of cations such as calcium,

magnesium, iron, copper, and manganese in water. These ions are usually analyzed by

EDTA (ethylene diamine tetracetic acid) titration and the techniques and procedures

are summarized the following is a description of quick spot tests for commonly

occurring contaminants. Because of long term (seasonal) and short term variations in

water quality, testing should be done on a fairly frequent basis toreally get a goodidea of the actual overall water quality available to the mill. Before attempting these

or any other chemical tests, be familiar with all necessary safe handling precautions

for allchemicals involved. If in doubt, consult the manufacturer of the chemical.

(ref. 16)

Suspended matter:The presence of sediment, clay, and suspended matter canbedetermined by filtration. A 50to 100 ml sample of water is filtered with suctionthrough a glass fiber filter which has been pre - weighed to the nearest milligram. The

collected solids are washed several times with distilled water, and the filter containing

the solids then dried at 103% for 1 hour, cooled in a glass desiccators, and weighed.

The suspended matter is then calculated as follows:

Mg of residue *1000

ppm total suspended solids = -----------------------------------------

ml ofwater sample


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Dissolved solids are obtained by determining total solids and subtracting total

suspended solids. Total solids are determined by evaporating a sample of the water or

dryness and determining the weight of residue. To do this, weigh a clean dry weighing

dish to the nearest milligram, then add 100 ml of the water to the dish and evaporate

at 103%. Cool In a desiccators and weigh the dish containing the residue. Dissolved

solids can be calculated as follows:

total solids weight * 1000

ppmtotal solids = -------------------------------------------------

ml ofwater sample

Dissolved solids = total solids minus total suspended solids

The alkalinity of water is a measure of the water's capacity to neutralize an

acid. It is, therefore, related to the water's buffering capacity, orits capacity to resist a

change in pH asacid is added. Alkalinity determination is usually made by titrating to

an end point with an indicator or pH meter, and is reported as ppm carbonate.

Alkalinity due to carbonates, bicarbonates, and hydroxides is determined by this

procedure. A 50ml sample ofwater is pipetted into a 250ml Erlenmeyer flask. Twodrops of methyl orange indicator are added and the water is titrated with 0.02 N

sulphuric acid to the end point. Total alkalinity is calculated as follows:

ml sulphuric acid * 1000

Total alkalinity (ppm as CaCo3,) = -------------------------------------

ml ofwater sample

Dissolved or emulsified oil and grease in water can be determined

gravimetrically by extraction with trichlorotrifluoroethane followed byevaporation of

the solvent. The procedure is quite detailed, other organic materials interfere, and

there is usually some loss of short chain hydrocarbons in the evaporation of the

solvent. The procedure for the analysis is described in a joint publication by the

Public Health Association, American Water Works Association, and Water Pollution


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Control Federation: This reference Is also an excellent source for standard methods of

analysis of contaminants in water.(ref 16)

(Ref 1)


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On-Site Water Purification

Perhaps the most common type of water purification practiced on site is the

use of filters. These fall in to three broad categories, including sand and gravel filters

for particulates and sediment, carbon filters for chlorine and organics, and ion-

exchange systems for metals and anions. These are effective if properly used.

However in many cases the expected degree of protection is not obtained. One

practice which defeats the effectiveness of filters is bypassing. This is done in some

cases when the water demand is high, such as during start up shifts. Also, poor

maintenance of filter' media can render a filter system ineffective. It is not unusual to

see a wet-processing operation with filters which have not had the media changed in

several years. These must be replaced or regenerated in accordance with the

manufacturer's recommendations in order to maintain good performance. Finally, the

water must be pre-treated if necessary to insure that the filter can do its job. Iron from

deep wells, for example, can pass through filters in soluble form, then become

oxidized in a clear well to produce a brown stain and sediment on substrate. In order

toaccomplish complete removal, iron should be oxidized prior to filtration. (Ref 13)

SPECIFIC WATER CONSUMPTION

The specific water consumption is calculated using the following formulae.

Amount of water consumed

Specific water consumption = -------------------------------------------

Amount of product produced

Water is consumed both in process operation like washing and also in

boilers for getting steam. The specific water consumption of the various processing

units audited is given in Figure. There is a wide variation of specific water

consumption in these units in view of the variation of the product being produced, the

variation in the machinery used and also due to the variation in the process applied in

different stages of processing. However, after accounting for these variations based on

the benchmarks, it is observed that all these audited units still consume excessive

water. Hence, there is a considerable potential for water conservation. These excess

usages occur due to the following factors:-


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Over-usage of water in the winches. Due to high temperature, flash steam escapes from the dye liquor. Leakage of water in pipelines and equipments, etc. Dead storage in the sump and feed water tank and also leakage in these

systems.

Excessive usage of water for cleaning, gardening and labour usage. Improper process sequencing. Reprocessing operations.

Normally the excessive water usage considering the wastage alone in most of

the units works out to be 10% 20% on the average. Since the water is bought from

outside, it is necessary to reduce the wastage to the lowest minimum, which willdecrease the overall production cost.


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(Ref 4)


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(Ref.no.4)

WATER BALANCE IN UNITS

Figure 3 provides the average water use balance of the audited units. From the

total water balance, it is observed that about 12% to 15% of water is lost due to

washing and

other leakages.

WATER CONSERVATION MEASURES

A number of measures can be adopted for saving the water consumption,

which are listed below:

Reduction in wastewater volume. Washing and rinsing improvements. Improvement in the quality of water by proper water treatment. Recovering the condensate from the indirect use of steam and using it

as process water.

Use of steam in indirect manner helps to recover the pure condensate and this

can be used as boiler feed water. This will reduce the make-up of water required for

the plant. The amount of effluent from the process also gets reduced.

(Ref 4)


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(Ref.no.4)

Washing and Rinsing

These are the most common operations in textile processing. Many processes

involve washing and rinsing stages and therefore optimization of these processes can

conserve significant amounts of water. The washing and rinsing requires about 70% -

75% more water than the other stages like bleaching and dyeing. Several typical

washing and rinsing processes include

drop and fill batch washing overflow batch washing continuous washing

Based on the system and equipment it is possible to adopt an appropriate

process so that water use can be controlled. Moreover, in many type of operations,

wash water can be reused for cleaning purposes. In printing, clean up activities can be

performed with used wash water including screen and squeeze cleaning, collar strip,

clean up equipment and facilitates cleaning.


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A typical preparation department may also reuse wash water as follows:

Reuse scour rinses for desizing Reuse mercerise wash water for scouring Reuse bleach wash water for desizing Reuse water-jet loom wash water for desizing

Water Consumption in Textiles

Water is used extensively throughout textile processing operations. Almost all

dyes, specialty chemicals, and finishing chemicals are applied to textile substrates

from water baths. In addition, most fabric preparation steps, including desizing,

scouring, bleaching, and mercerizing, use aqueous systems. The amount of water used

varies widely in the industry, depending on specific processes operated at the mill,

equipment used, and prevailing management philosophy concerning water use.

Reducing water consumption in textile processing is important for furthering pollution

prevention efforts, due in part because excess water use dilutes pollutants and adds to

the effluent load. Mills that currently use excessive quantities of water can achieve

large gains from pollution prevention. A reduction in water use of 10 to 30 percent

can be accomplished by taking fairly simple measures. A walkthrough

Audit can uncover water waste in the form of:

Hoses left running. Broken or missing valves. Excessive water use in washing operations. Leaks from pipes, joints, valves, and pumps. Cooling water or wash boxes left running when machinery is shut down. Defective toilets and water coolers.

In addition, many less obvious causes of water waste exist. These causes are

presented below by subcategory, unit process, and machine type.(ref 14)

Subcategory

Textile operations vary greatly in water consumption. Figure 1 summarizes the

water consumption of various types of operations. Wool and felted fabrics processes

are more water intensive than other processing subcategories such as wovens, knits,

stock, and carpet. Water use can vary widely between similar operations as well. For

example, knit mills average 10 gallons of water per pound of production, yet water


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use ranges from a low of 2.5 gallons to a high of 45.2 gallons. These data serve as a

good benchmark for determining whether water use in a particular mill is excessive.

(Ref. No. 2)


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Water consumption varies greatly among unit processes, as indicated in Figure

2. Certain dyeing processes and print after-washing are among the more intensive unit

processes. Within the dye category, certain unit processes are particularly low in

water consumption (e.g., pad-batch).

Machine Type

Different types of processing machinery use different amounts of water,

particularly in relation to the bath ratio in dyeing processes (the ratio of the mass of

water in an exhaust dye bath to the mass of fabric). Washing fabric consumes greater

quantities of water than dyeing. Water consumption of a batch processing machine

depends on its bath ratio and also on mechanical factors such as agitation, mixing,

bath and fabric turnover rate (called contact), turbulence and other mechanical

consideration as well as physical flow characteristics involved in washing operations.

These factors all affect washing efficiency. In general, heating, wash, and dye baths

constitute the major portion of energy consumed in dyeing. Therefore, low bath-ratio

dyeing equipment not only conserves water but also saves energy, in addition to

reducing steam use and air pollution from boilers. Low-bath-ratio dyeing machines

conserve chemicals as well as water and also achieve higher fixation efficiency. But

the washing efficiency of some types of low-bath-ratio dyeing machines, such as jigs,

is inherently poor; therefore, a correlation between bath ratio and total water use is not

always exact.

Process Water Conservation

Washing

Washing and rinsing operations are two of the most common operations in

textile manufacturing that have significant potential for pollution prevention. Manyprocesses involve washing and rinsing stages, and optimizing wash processes can

conserve significant amounts of water. In some cases, careful auditing and

implementation of controls can achieve

Waste water reductions of up to 70 percent. The washing and rinsing stages of

preparation typically require more water than the other stages (e.g., bleaching,

dyeing). (Ref 2)


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Several typical washing and rinsing processes include:

Drop and fill batch washing. Overflow batch washing. Continuous washing (countercurrent, horizontal, or inclined washers)

A report on water consumption for a typical continuous bleach range found

that consumption was more than 11,000 gallons per hour, or 270,000 million gallons

per day. (See Figure 3.) Washing stages accounted for 9,900 gallons per hour, or 90

percent of the total. The application of the following simple, low-technology methods

of water conservation reduced water use:

Properly regulating flows: 300 gallons per hour savings. Counter flowing bleach to scour: 3,000 gallons per hour savings. Counter flowing scour to desize: 3,000 gallons per hour savings.

The total water savings without process modification was 150,000 million

gallons per day, or 55 percent of water use. A process modification such as a

combined one-stage bleach and scour also would save 6,200 gallons of water per

hour, or an additional 150,000 million gallons per day, along with energy savings.

(Ref no. 2)


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Drop-Fill versus Overflow Washing

In the drop/fill method of batch washing, spent wash water is drained and the

machine is refilled with a fresh wash bath. The fabric or other substrate in the

machine retains much of the previous bath, perhaps as much as 350 percent owg. This

percentage can be reduced by mechanical means (e.g., extraction, blow down).

Comparison of several methods of washing after bleaching shows the benefits of

countercurrent wash methods, see Figure 4. Methods five and six, which implement

countercurrent washing, produce savings of 26 and 53 percent compared with the

standard drop/fill method. These results are based on comparisons of washing

processes that would produce the same degree of reduction of fabric impurities using

computer models. Countercurrent washing processes require the addition of holding

tanks and pumps. The capital cost of setting up such a reuse system typically is less

than Rs.2221000 and generates estimated savings of Rs.4219900 annually. In many

cases, reducing wastewater also reduces the need for expensive waste treatment

systems. (ref 16)

(Ref no. 2)


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Reusing Wash Water

Many strategies can be applied for reusing wash water. Three of the most

common strategies are countercurrent washing, reducing carryover, and reusing wash

water for cleaning purposes.

Countercurrent Washing

The countercurrent washing method is relatively straightforward and

inexpensive to use in multi-stage washing processes. Basically, the least contaminated

water from the final wash is reused for the next-to-last wash and so on until the water

reaches the first wash stage, after which it is discharged. This technique is useful for

washing after continuous dyeing, printing, desizing, scouring, or bleaching. An

important variant of the countercurrent principle is horizontal or inclined

washers. Horizontal or inclined washing is more efficient because of the inherent

countercurrent nature of water flow within the process. The mechanical construction

of an inclined or horizontal countercurrent washer has to be much better than a

traditional vertical washer, however. Sloppy roll settings, weak or undersized rolls,

unevenness, bends, bows, biases, bearing play, or other misalignments within the

machine are much more important in a horizontal or inclined washer because the

weight of water pressing down on the fabric can cause it to sag, balloon, or stretch. If

properly constructed and maintained, horizontal or inclined washers can produce

high-quality fabrics while saving money and water.

Reducing Carryover

Because the purpose of washing is to reduce the amount of impurities in the

substrate, as much water as possible must be removed between sequential washing

steps in multistage washing operations. Water containing contaminants that is not

removed is .carried over into the next step, contributing to washing inefficiency.

Proper draining in batch drop/fill washing and proper extraction between steps in the

continuous washing process are important. Often, 350 percent owg is carried over in

typical drop/fill procedures. This amount can be reduced in some batch machines

(e.g., yarn package dyeing, stock dyeing) by using compressed air or vacuum blow

down between washing steps. In continuous washing operations, squeeze rolls or

vacuum extractors typically extract water between steps. (ref. 13)


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Equipment employing vacuum technology to reduce drag out and carryover of

chemical solutions with cloth, stock, or yarn is used to increase washing efficiency in

multistage washing operations.

In one case history, a processor installed vacuum slots after each wash box in

an existing multistage continuous washing line and was able to reduce the number of

boxes from eight to three. Wash boxes with built-in vacuum extractors are available

for purchase, as well as washers for prints that combine successive spray and vacuum

slots without any bath for the fabric to pass through. Because the fabric is never

submerged, bleeding, marking off and staining of grounds is minimized, and water

use decreases. Another washer configuration with internal recycling capabilities is the

vertical counter flow washer, which sprays re circulated water onto the fabric and uses

rollers to squeeze waste through the fabric into a sump, here it is filtered and re

circulated. The filter is unique, consisting of continuous loops of polyester fabric that

rotate continuously and are cleaned of filtrate at one end with a spray of clean water.

This construction allows for maximum removal of suspended solids from water

before discharge or reuse in another process. High-efficiency washing with low water

use results. Energy use decreases greatly because less water must be heated.(ref 25)

A typical preparation department may also reuse wash water as follows:

Reuse scour rinses for desizing Reuse mercerize wash water for scouring Reuse bleach wash water for scouring Reuse water-jet loom wash water for desizing Recycle kier drains to saturator

Work Practices

Workers can greatly influence water use. Sloppy chemical handling and poor

housekeeping can result in excessive cleanup. Poor scheduling and mix planning also

can require excessive cleanup and lead to unnecessary cleaning of equipment like

machines and mix tanks. Leaks and spills should be reported and repaired promptly.

Equipment maintenance, especially maintenance of washing equipment, is essential.

Inappropriate work practices waste significant amounts of water, and good procedures

and training are important. When operations are controlled manually, an operations

audit checklist is helpful for operator reference, training, and retraining. In one case


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history, a knitting mill experienced excessive water use on beck dyeing machines. A

study of operating practices revealed that each operator was filling the machines to a

different level. Some operators filled the becks to a depth of 16 inches, others as much

as 24 inches. Also, the amount of water used for washing varied. Some operators used

an overflow procedure, and others used drop/fill or half baths(repeatedly draining

half of the bath, then refilling it). Inspection of the written procedures showed that the

fill step simply said fill. The wash step simply saidwash. Without training and

without a specific operating procedure, operators were left to determine water use on

their own. This case may seem extreme, but even the best mills, which have well-

documented production procedures, often do not have documented cleaning

procedures. Cleaning operations that contribute large amounts of pollution to the total

waste stream include machine cleaning, screen and squeegee cleaning, and drum

washing.

Engineering Controls

Every mill should have moveable water meters that can be installed on

individual machines to document water use and evaluate improvements. In practice,

mills rarely measure water use but rely on manufacturers claims concerning

equipment and water use. The manufacturers estimates are useful starting points for

evaluating water consumption, but the actual performance of equipment depends on

the chemical system used and the substrate. Therefore, water use is situation-specific

and should be measured on-site for accurate results. The water meters should be

regularly maintained and calibrated. Other important engineering controls, some of

which have been discussed in other sections of this chapter, include:

Flow control on washers Flow control on cooling water (use minimum necessary) Countercurrent washing High extraction to reduce drag out Recycle and reuse Detection and repair of leaks Detection and repair of defective toilets and water coolers (ref 2)

Machinery should be inspected and improved where possible to facilitate

cleaning and to reduce susceptibility to fouling. Bath ratios sometimes can be reduced


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by using displacers that result in lower chemical requirements for pH control as well

as lower water use.

Process Changes

Processing Bath Reuse

Water from many processes can be renovated for reuse by a variety of

methods. Several research efforts are underway. In a few operations, up to 50 percent

of the treated wastewater is recycled directly back from the effluent to the raw-water

intake system with no adverse effects on production. In some cases, specific types of

wastewater can be recycled within a process or department. Examples are dye bath

reuse, bleach bath reuse, final rinse reuse as a loading bath for the next lot, wash

water reuse, countercurrent washing, and reuse for other purposes.

Bleach Bath Reuse

Cotton and cotton blend preparation (e.g., de-sizing, scouring, bleaching) are

performed using continuous or batch processes and usually are the largest water

consumers in a mill. Continuous processes are much easier to adapt to wastewater

recycling/reuse because the waste stream is continuous, shows fairly constant

characteristics, and usually is easy to segregate from other waste streams.

Waste-stream reuse in a typical bleach unit for polyester/cotton and 100-

percent cotton fabrics would include:

Recycling J-box and kier drain wastewater to saturators Using countercurrent washing Recycling continuous scour wash water to batch scouring Recycling washer water to back gray blanket washing Recycling washer water to screen and squeegee cleaning Recycling washer water to color shop cleanup Recycling washer water to equipment and facility cleaning Reusing scour rinses for de-sizing Reusing mercerize wash water for scouring (ref 16)


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Preparation chemicals (including optical brighteners and tints), however, must

be selected in such a way that reuse does not create quality problems such as spotting.

Batch scouring and bleaching are less easy to adapt to recycling of waste streams

because streams occur intermittently, drains generally go into pits and are not easily

segregated, and batch preparation steps frequently are combined. With appropriate

holding tanks, however, bleach bath reuse can be practiced in A similar manner to dye

bath reuse, and several pieces of equipment are now available that have the necessary

holding tanks. The spent bleach bath contains all of the alkali and heat necessary for

the next bleaching operation. Peroxide and chelates must be added to reconstitute the

bath. Like dye bath reuse, the number of reuse cycles in bleach bath reuse is limited

by impurity buildup. The main impurities are metals, such as iron, that can interfere

with the bleaching reaction. New types of rope bleaching units for knits featuring six

to 12-stage jet transport systems have made continuous bleaching of most knit styles

possible. These units were introduced in the late 1970s and typically produce 40

pounds per minute of knit fabric or more than one million pounds per month based on

a three-shift, six-day operation. These machines have become very popular with large

knit processors because of their flexibility and ability to conserve energy, water, and

chemicals. They also have complete built-in countercurrent capabilities. These units

are being promoted for use in after washing fiber reactive and other types of dyes

(e.g., after pad batch dyeing) in addition to use as continuous knit preparation ranges.

Final Rinse Reuse as Loading Bath for Next Lot

One simple technique that saves water and, in some cases, BOD loading is to

reuse the final bath from one dyeing cycle to load the next lot. This technique works

well in situations where the same shade is being repeated or where the dyeing

machine is fairly clean. A good example of this technique is acid dyeing of nylon

hosiery. The final bath usually contains an emulsified softener that exhausts onto the

substrate, leaving the emulsifier in the bath. This technique can serve as the wetting

agent for loading the next batch, thus saving the water, heat, and wetting agent and

associated BOD.


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EXPERIMENTAL PLAN

1 SELECTION OF MATERIAL

2 SELECTION OF CHEMICALS

3 SELECTION OF PROCEDURE

4 SCOURING

5 BLEACHING

6 TESTING

7 RESULTS AND DISCUSSION


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Selection of material

The material for the project is to be selected which is available in the industry

100% cotton fabric:-- Plain derivative (2/2)- PPI : 74- EPI : 76- Count : warp

Weft:

- GSM :Selection of auxiliaries

GRADES

Wetting agent LR Caustic soda LR Hydrogen peroxide(50%) LR Stabilizer LR Soda ash LR Sequestering Agent LR Scourex IR

Testing Equipment:-

Tensile strength tester CCM (Minolta Treepont system) pH meter TDS meter


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BLEACHING:

1. Fabric taken : 100gms2. Recipe used:

i. H2O2 : 2% owfii. Soda ash : 2 gpliii. Stabilizer : 1/3rdof H2O2

iv. Time : 90 minutesv. Temperature : 95oC

vi. MLR : 1:203. The same bath is used 6 times. Every time the water reduced is replenished

by the hot water of the same process done.

4. Tests carried out for liquor and fabric after each process

TESTING PROCEDURES

1. Determination of Alkalinity

1. Take 25 ml of sample in conical flask and add 3 to 4 drops of phenolphthaleinindicator. If the sample becomes pink, the titrate the solution against 0.02 N

HCl from burette until the pink colour disappear. Record the amount of acid

used and proceed further as given below (if pink colour does not appear note it

as P=0)

2. Add 3 drops of Methyl Orange indicator in the flask, titrate against 0.02NHCl. Note the first change in colour from yellow to orange. Note amount of

titrant used. (One more flask with 100 ml sample and 3 drops of Methyl

Orange indicator should kept ready aside for comparison.

3. Let P be the quantity of standard 0.02 N HCl used for titration withPhenolphthalein indicator and M be the total volume of 0.02N HCl used for

titration. For 100 ml of water we have following formulae to determine

alkalinity.

a. When P=M, hydroxyl in ppm = P*10b. If P>M/2, then hydroxide alkalinity in ppm = (2P-M)*10 and Normal

carbonate alkalinity is equal to 2(M-P)*10


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c. If P=M/2, then normal carbonate alkalinity is equal to M*10d. If P


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viii. Record the volume of FAS as V2ml. COD of the sample corresponds to(V2-V1).

Calculation:

Volume of sample taken= 20 ml

Volume of 0.1 N FAS used in sample titration = V1

Volume of 0.1 N FAS used in blank titration = V2

Volume of 0.1 N FAS equivalent to K2Cr2O7 Used for COD = (V2-V1)

N1V1= N2V2

N1* 20 = 0.1*(____-____)

Therefore COD = (____-____) * 0.1 *8 g/lit

(____-____)* 40 mg/lit

4. DETERMINATION OS TS, TSS AND TDS:-A. DETERMINATION OF TS:-

i. Take a china clay dish and weigh it accurately.ii. Pipette out 50 ml of well mixed sample into a china clay

dish.

iii. Evaporate the sample to dryness by heating on a steambath.

iv. Wipe outer side of a dish and lay the residue for 1 hour at100 to 1050C.

v. Transfer the dish to the desiccators and wait till it attainsthe room temperature.

vi. Repeat the drying and weighing till the weight is constantwithin the limit of 0.5 mg.

B. DETERMINATION OF TSS:-i. Filter the known of the sample through an asbestos filter in

a previously weighted good crucible.

ii. Keep the crucible at 100 to 1050C for 1 hour.


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iii. Cool and reweigh the crucible.

C. DETERMINATION OF TDS:-Carry out the same procedure as that of total solid of the filtrate

collected from procedure for suspended matters.

CALCULATION:-

106* wt. of residue from filtrate after evaporation

Total dissolved solids = ----------------------------------------------------------------------

Volume of water sample taken


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RESULTS AND DISCUSSION

Characteristics of Scouring Liquor & Scoured fabric samples

ParametersProcesss

1

Processs

2

Processs

3

Processs

4

Processs

5

Processs

6

pH 10.7 10,7 10.5 10.5 10.4 9.8

Alkalinity 31.2 31.1 30 29.8 29.5 29

TDS (ppm) 5600 6100 6900 7820 8541 9432

TS (ppm) 6110 6712 7657 8625 9384 10308

TSS (ppm) 510 612 757 805 843 876

COD(ppm) 855 902 947 1002 1041 1096

BOD(ppm) 360 452 546 665 742 852

CAC 0.8 0.9 0.6 0.8 0.9 0.8

Absorbency


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Graphical presentation of comparison of characteristic parameters of Scouring

baths:

0

2000

4000

6000

8000

10000

12000

1 2 3 4 5 6

ppm

Processes

Solid Content present in liquor bath

TDS

TS

TSS

0

200

400

600

800

1000

1200

1 2 3 4 5 6

ppm

Processes

BOD & COD present in liquor bath

BOD

COD


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BLEACHING

Characteristics of bleaching Liquor & bleached fabric samples

Parameters Process1 Process2 Process3 Process4 Process5 Process6

pH 9.5 9.7 9.7 9.5 9.6 9.7

TDS 2720 2760 2825 2878 2907 2956

TS 2892 2962 3041 3102 3137 3193

TSS 190 202 215 224 230 237

COD 445 534 639 728 842 947

BOD 155 197 242 295 343 392

Whiteness

Index66.51 65.12 64.05 60.04 57.55 52.31


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Graphical presentation of comparison of characteristic parameters of Bleaching

baths:

0

500

1000

1500

2000

2500

3000

3500

1 2 3 4 5 6

ppm

Proccesses

TDS

TS

TSS

0

100

200

300

400

500

600

700

800

900

1000

1 2 3 4 5 6

ppm

Processes

BOD & COD present in liquor bath

BOD

COD


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In same bath 6 different samples are scoured by maintaining same treatment

conditions. Different tests are carried out after each process for liquor and fabric as

stated above. It is observed that all 6 samples showed good absorbency as well as very

less strength loss compare to original sample. Scouring bath tests showed increase in

TS, TSS, TDS as well as BOD and COD, these increase takes place because of

continuous increase of impurities. After 6th scouring total solid content increased

(10308ppm) so that implementation of 7thscouring process was impossible.

Similarly, bleaching of 6 samples is carried out. Bleaching bath tests showed

very less increase in TS, TSS, TDS, COD, and BOD than that of scouring bath.

Bleached samples showed good whiteness index values up to 4 th bleached sample.

After 4thbleach Whiteness index value came less than 50.

0

10

20

30

40

50

60

70

1 2 3 4 5 6

WhitenessInde

x

Processes

Whiteness Index

Series1


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CONCLUSION:

Therefore it is possible to reduce the water consumption in cotton

pretreatments by reusing the same bath. Same scouring and bleaching bath

can be used up to 6 times and 4 times respectively. Scoured fabrics treated with

process1 showed strength loss of 9% and Process6 showed strength loss of 7%.

There is no significant difference between whiteness index values of

conventionally bleached and fabric bleached with process 1 to 4. It helps to

reduce the effluent load so that the effluent treatment cost is also reduced

substantially with saving of water and chemical costs.


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References:

1. Dr. Brent Smith, James Rucker, Dept. of Textile Chemistry, Water and TextileWet Processing, American Dyestuff Reporter, July 1999, pp 15 to 23

2. Water Efficiency in Textile Processes, New Cloth Market.3. Dr. A. I. Wasif, Dr. S. K. Chinta & H. T. Deo, Effluent Treatment in Textile Wet

Processing Bleaching of Polyester-cotton fabric, Indian Journal of Fibre and

Textile Research, Vol. 33, March 2008, pp 73-79

4. Prof. S. Balchandran, Dr. R. Rudramoorthy, Efficient Water Utilization in TextileWet Processing, IE (I) Journal-TX vol. 89, August 2008 pp 26-29.

5. H. Wenzel and H.H. Knudsen, Water savings and reuse in the Textile Industry6. Jay Ritchlin and Paul Johnston, Zero Discharge, Published by Reach for Unbleached

Foundation

7. James L. Clark, Water Conservation through scouring bath reuse, Georgia WaterResources Conference, held March 20-22, 1997.

8. S. Eswaramoorthi, K. Dhanapal and J. Karpagam, Zero Discharge - TreatmentOptions for Textile Dye Effluent

9. A. H. Little, Measures taken aginst water pollution in the textile industries, ShirleyInstitute, Didsbury, Manchester M20 8RX, UK

10.Ms. Ilse Hendrickx, Gregory D. Boardman, Pollution prevention studies inthe textile wet processing industry.

11.B. Ramesh Babu, A.K. Parande, S. Raghu, and T. Prem Kumar, Cotton TextileProcessing: Waste Generation and Effluent Treatment, Journal of cotton science,

Volume 11, Issue 3, 2007

12.Waste minimization guide for the textile industry, by Susan Barclay and ChrisBuckley

13.Reuse of wastewater of the textile industry after its treatment with a combinationof physico-chemical treatment and membrane technologies by, Department of

Chemical and Nuclear Engineering, Universidad Politcnica of Valencia, Camino

de Vera s/n, 46071 Valencia, Spain Received 1 February 2002; accepted 15

February 2002

14.ACHWAL, W. B., Environmental aspects of textile chemical processing(part I). Colourage, vol 37, no 9. September 1990, p 40-42.


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