Unit IV Garment Washing and Finishing

7/28/2019 Unit IV Garment Washing and Finishing

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GARMENT FINISH

Finishing

Finishing is the heart of textile processing.

It makes garments attractive, comfortable & finishing can incorporate desirable properties.

Value addition = {(Technology) + (Innovation)} x Quality Object:

To increase attractiveness and/or serviceability of the fabric

METHOD OF APPLICATION:

There are two methods of garment finishing.

Dip process.

Tumbling process

Dip process: - • Dip the garment inside out in finishing chemical keeping MLR 1:5. Washing machine may be

used.

• Rotate the garment for 20 min.

• Hydro extract the garment to 70 to 80% pick up.

• Tumble dry at 70°C to moisture content 10 — 12 %.

• Turn the garment right side out.

• Iron/steam press the garment to set the creases at desired places.

• Cure at 150 — 160°C

Tumble method: -

• In this process the garment are placed (inside out) into a machine with sealed (not perforated)

cylinder and application of recipe by either pumping or spraying.

• The drum is turned for 20 min there should not be excessive dripping of chemicals from the

garment. If so more tumbling time is allowed.

• This method is being used more and more due to the fact that there is no wastage of chemicals.

• After saturation the garments are hydro extracted tumble dry at 70°C to 10 — 20 % pick up

moisture content.

• The iron and steam press the garments to remove/set creases. Cure at 150 — 160°C for 8 -10 min.

Important features: -

• MLR should not be less than 1: 0.85 for the garment weighing 600 gm and 1:1 for those weighing

more than 600 gm.

• Minimum time of tumbling should be 20 min.



• Tumble rotation speed 20-30 rpm.

• Tumble drying temp. Should not be more than 70°C.

• Moisture retention after drying should be 10 -12%.

Wash Down Effects

It can be achieved by a variety of garment processing techniques which are mainly dependent on physical

and on chemical abrasion of the surface dye there by producing different wash down or break-in looks.

In garment washing the seams, waistband, pockets, cuffs, etc develop a contour, which can be obtained by

washing in garment from only.

Washing down of garments is the latest development in fashion technology. Washing brings out special

effects changing the feel and look of garments

Five good reasons can be attributed for washing the garments.

To influence physical properties such as softness, handle, drape or fall, absorbency, creasing etc.

To influence appearance by altering the nature of yarn of fabric or lusture.

To create shrinkage & effects of shrinkage like puckering of garments.

To create abrasion & related effects.

To create a trend in fashion with consistent quality & brand image with range of finishes.

Denim washing

It is the aesthetic finish given to the denim fabric to enhance the appeal and to provide strength

.Indigo jeans were once the only item processed by the garment wash method

• Emphasis is on

Comfort , Softness, Fashion Trends Favor, The Broken-in Look and Worn/Faded

seams that can only be achieved through garment processing

DENIM WASHES ARE OF TWO TYPES:

1. Mechanical washes

Stone wash

Micro sanding

2. Chemical washes

Denim bleaching

Enzyme wash

Acid wash

Any of these procedures can be modified

– To fit a particular situation,

– Depending upon garment type (i.e., heavyweight denim versus lightweight chambray),



– Available equipment, and

– Process flow.

Also, some of these procedures yield garments suitable for over dyeing, which may create a whole new

look.

PROCEDURE

1. Garments can be inverted to minimize unwanted abrasion streaks (especially useful when preset creases

are present).

2. Load machine with garments.

3. Desize with alpha amylase enzyme and detergent.

4. Drain.

5. Rinse.

6. Fill machine with water and heat to 60◦C. The liquor ratio can range from 10:1 to 20:1. A number of

synthetic detergents can be used. Also, alkaline products such as soda ash or caustic soda can be added inamounts ranging from 0.5 to 2.0 grams/liter.

7. Wash/tumble action for 20-60 minutes, depending upon desired effect.

8. Drain and rinse.

9. Apply softener.

10. Tumble dry.

11. Invert garments, if previously turned.

12. Press, if required.

STONEWASH

• In the process of stone washing, freshly dyed jeans are loaded into large washing machines and

tumbled with pumice stones



• It means Pre washed, abraded, faded either regular or irregular looks are produced by subjecting

the dyed garments to severe washing treatments

In order to accelerate the garment wash effect and to give garments an even more unique appearance,

desirable look and softer hand, abrasive stones were introduced to the wash bath.

• Variations in composition, hardness, size shape and porosity make these stones multifunctional.

The process is quite expensive and requires high

capital investment.

• Pumice stones give the additional effect of a faded

or worn look as it abrades the surface of the jeans

like sandpaper, removing some dye particles

from the surfaces of the yarn.

• A variety of natural and synthetic stones are

available for stonewashing with perhaps the most

widely used being pumice or volcanic rock.

As the stones are used, they slowly disintegrate, reducing the severity of the stonewash effect over a

period of time.

The stones not only abrade the fabric but also gradually abrade the inside of the rotary drum.

A machine used for stonewashing should not be used to dye delicate articles or when abrasion would

be detrimental to the fabric.

It’s gives used look because of varying degrees of abrasion in areas such as the waistband, pocket

and seems

DEGREE OF COLOUR FADING

It‘s mainly depends on

Garments to stone ratio

Washing time

Size of stone

MLR

Load of garments

Stone weight 0.5-3

Selection of stone

• Stone should be selected of the proper hardness, shape, and size for the particular end product.

• It should be noted that large, hard stones last longer and may be suited for heavy weight fabrics

only.

• Smaller, softer stones would be used for light weight fabrics and more delicate items.



• STONE WT. /FABRIC WT. = 0.5 TO 3 /1

• It depends on the degree of abrasion needed to achieve the desired result.

Stones can be reused until they completely disintegrate or washed down the drain

PROCEDURE

1. Load stones into machine.

2. Load garments into machine (ratio usually 0.5 - 3.0 part weight stones:1 part weight garments).

3. Desize with alpha amylase enzyme and detergent. Liquor ratio approximately 5-8:1.

4. Rinse.

5. Refill and tumble with stones 30 to 90 minutes, depending upon desired effect. Liquor ratio 5-8:1 at 50-

70◦C. Scouring additives can also be used.

6. Drain. Separate garments from stones (garments can be transferred to another machine).

7. Rinse.

8. Apply softener (garments can be transferred to another machine for softening).

9. Extract and unload.

10. De-stone and tumble dry.

11. Press, if required

BACK STAINING OR RE-DEPOSITION:

• The dye removed from denim material after the treatment with cellulose or by a conventional

washing process may cause "back staining‖ or "redeposition‖.

• Re-coloration of blue threads and blue coloration of white threads, resulting in less contrast

between blue and white threads.

PROBLEMS CAUSED BY STONES:

• Damage to wash machineries and garment due to stone to machine and machine to stone abrasion



• Increase in labor to remove dust from finished garments.

• Water pollution during disposal of used liquor.

• Back staining and re deposition.

REMEDY OF BACK STAINING

• Adding dispersion/suspension agent to wash cycle.

• Intermediate replacement of wash liquor.

Using alkaline detergent like sodium per borate with optical brightener as after wash

LIMITATIONS OF STONE WASHING:

• Quality of the abrasion process is difficult to control outcome of a load of jeans is never uniform,

little percentage always getting ruined by too much abrasion.

• The process is non-selective.

• Metal buttons and rivets on the jeans in the washing machines get abraded.

• This reduces quality of the products and life of equipment, and increases production costs.• Stones may turn into powder during the process of making the garment grayish in color and rough

too

• Provides rougher feel than enzyme wash

• Stone may lead the harm to the machine parts

STONEWASH EFFECT:

• In traditional washing process, volcanic rocks or pumice stones are added to the garments during

washing as abradant. Due to ring dyeing and heavy abrasion fading is more apparent but less

uniform.

• The degree of colour fading depends on the garment to stone ratio, washing time, size of stones,

material to liquor ratio and load of garments.

• Normally after desizing, stone wash process starts with pumice stone addition in rotary drum type

garment washer.

• Process time varies from 60-120 mins.

• Stone wash effect is one of the oldest but highly demanded washing effects.

• Stone wash process gives ―used‖ look or ―vintage‖ on the garments, because of varying degree of

abrasion in the area such as waistband, pocket, seam and body.

• There are many limitations and drawbacks associated with stone washing process, which can be

overcome by using new enzyme based washing technology.

• This technology also helps to conserve water, time, energy and environment



ENZYME WASH

Cellulase enzymes are natural proteins which are used in denim garment processing to get stone wash look

on to the denim garments without using stones or by reducing the use of pumice stone.

Cellulase attacks primarily on the surface of the cellulose fibre, leaving the interior of the fibre as it is, by

removing the indigo present in the surface layer of fibre.

Cellulase enzyme is classified into two classes:

Acid Cellulase:

It works best in the pH range of 4.5-5.5 and exhibit optimum activity at 50°C.

Neutral cellulase:

It works best at pH 6 however its activity is not adversely affected in the range of pH 6-8 and show

maximum activity at 55°C

Acid cellulose

Recipe and Condition

• Cellulose 450 AP (OWG) 0.5 – 1 gm/l

• Lube pro VX ( crease inhibitor) 0.5 – 1 gm/l

• White MRC (anti-redepositing agent) 1 – 2 gm/l

• Treat at 50°C and pH – 5 for 30-45 mins

Neutral cellulose

Recipe and Condition

• Americos cellucom 110 OM (OWG) 0.5 – 1 gm/l

• Lube pro VX ( crease inhibitor) 0.5 – 1 gm/l

• Americos White MRC (anti-redepositing agent) 1 – 2gm/l

• Treat at 50°C and pH – 5 for 30-45 mins

PROCEDURE

1. Load stones in machine (normally 0.5 - 2.0 part weight stones: 1 part weight garments) if applicable.

2. Load garments.

3. Desize with alpha amylase enzyme and detergent.

4. Rinse.

5. Add cellulase enzyme (amount, pH, temperature, and cycle time dependent upon type of fabric and

desired effects; manufacturer's recommendations should be followed).

6. Adjust pH as recommended.

7. Tumble 30-90 minutes.

8. Drain.



9. Rinse well (70◦C).

10. Drain.

11. Rinse well (70◦C).

12. Drain. Separate garments from stones if used (garments can be transferred to another machine).

13. Apply softener.

14. Extract and unload.

15. De-stone and tumble dry.

16. Press, if require

Advantage of enzyme washing

• Soft handle and attractive clean appearance is obtained without severe damage to the surface of

yarn.

• Simple process handling and minimum effluent problem.

•

Better feel to touch and increased gloss or luster.• Prevents tendency of pilling after relatively short period of wear.

• Can be applied on cellulose and its blend.

• Due to mild condition of treatment process is less corrosive.

• Fancy colour - flenced surface can be obtained without or a partial use of stone.

• More reproducible effect can be obtained.

• It allows more loading of the garment into machines

• Environmental friendly treatment.

• Less damage to seam edges and badges.

• Wear and tear of equipment is minimum due to absence of stone.

• Use of softener can be avoided or minimised.

• Easy handling of floor and severs as messy sludge of stones does not interfere.

• Due to absence of stone, labour intensive operation of stone removal is not required.

• Homogenous abrasion of the garments.

• Puckering effect can also be obtained

ACID WASH

• It is done by tumbling the garments with pumice stones presoaked in a solution of sodium

hypochlorite (5 to 10%) or potassium permanganate (3 to 6%) for localized bleaching resulting in a

non uniform sharp blue/white contrast.

• To remove the colour only on the surface of the garment and produces a frosted appearance

• In this wash the color contrast of the denim fabric can be enhanced by optical brightening.

• The advantage of this process is that it saves water as addition of water is not required.



Procedure:

Soak the stones in solution of sodium hypochlorite (5 to 10%) or potassium permanganate (3 to

6%) for 1-2 hrs

Stones should be drained of excess liquor with help of mesh

Placed stones and garments in machine

Tumble for 30 mins or until desire effects are achieved. Results are dependent up on the dyestuff,

fabric, and concentration of chemical, stones, additives, and equipment

In some cases, stones can be used ( resoaking, porosity )

Rinse

Apply softener

Tumble dry

Press, if req.

Limitations of acid wash:

• Acid washed, indigo dyed denim has a tendency to yellow after wet processing.

• The major cause is residual manganese due to incomplete neutralization, washing or rinsing.

Remedy:

• Manganese is effectively removed during laundering with addition of ethelene- diamine -tetra

acetic acid as chelating agent.

• Acid washing jeans avoided some of problems of stone wash, but came with added dangers,

expenses, and pollution

MICROSANDING

There are 3 ways for this technique:

• Sandblasting

• Machine sanding

• Hand sanding or hand brushing



Used in various ways: -

• Flat surfaces (tables, ironing boards)

• On the dummy (inflatable dummies, sometimes standing, sometimes flat, sometimes 'seated')

• Various templates can be used to create a 3D effect.

SAND BLASTING

Sand blasting technique is based on blasting an abrasive material in granular, powdered or other

form through a nozzle at very high speed and pressure onto specific areas of the garment surface to be

treated to give the desired distressed/ abraded/used look.

• It is purely mechanical process, not using any chemicals.

• It is a water free process therefore no drying required.

• Variety of distressed or abraded looks possible.

• Any number of designs could be created by special techniques

Advantages : Pure chemical process

Water free process therefore no need drying

Variety of distresses or abraded looks possible

Any number of designs could be created by special finishes

Wrinkle Free Finish (or) Anticrease Finish (Or) Wash- N- Wear Finish

• Cotton fabrics are mainly selected for apparels because of their durability, ability to with stand the

rough laundering, good absorption, comfort to wear and ability to take up awide range of dyestuffs.

• The main headache with the cotton fabric is CREASE formation during washing, laundering and

in use. It is an undesirable property and hence the crease resistant finish is to be given. It is called

as Anti-crease finish or Crease resistant or Crease recovery finish or 'Wash-n- Wear‗ finishes.

Object of Anti-crease finish

• Cotton, viscose fabrics form creases during washing, laundering and in use.

• To prevent it, the anti-crease finish is given. It is called as Anti-crease finish or Crease resistant or

Crease recovery finish or 'Wash-n- Wear' finishes.

• As the resins are used, it is also called as 'Resin finishing'.

• It is a permanent chemical finish.

• To keep the fabric flat smooth and free from undesirable creases

Usually cotton, linen, viscose and cuprammonium rayon are finished with resin

Depends on



1. Amount and type of resin

2. Amount and type of catalyst

3. Curing conditions

4. Quality of cotton

5. Process preceding finishing and possible damage

MECHANISM OF CREASE FORMATION

• Cotton cellulose molecular chain contains OH groups in both amorphous and crystalline region.

• When a load is applied on to cotton fabric, the cellulose chain bends and this bending remains

permanent since the chains are In-elastic.

• The hydrogen bonds form, between the adjacent chains in the crystalline region are broken and

new hydrogen bond are formed at the folding points and in amorphous region, which do not allow

the chain to return. Hence the creases are formed.

Method to prevent creases• The method of minimizing the formation of creases involves cross-linking the OH groups of

adjacent cellulosic chains by means of cross-linking agents.

• The introduction of cross-links imparts dimensional stability and elasticity to the fibrous material

an makes it crease resistant and crease recoverable.

• The most commonly used cross-linking agents are nothing but resins. The resins react with OH

groups of cellulose forming cross links which is durable

Advantages of resin finishing

• It improves the Crease Resistance and Crease Recovery property

• It reduces the shrinkage of fabric during laundering

• It improves the resilience, drape and handle

• It imparts a smooth and quick drying property

• It improves the Dimensional stability and weight

• It increase the strength of rayons in both wet and dry states

• It gives resistance to degradation by light and laundering

• It improves the fastness to light and wash

• It prevents the inter-molecular slippage in the fibre

• It becomes partially water proof and rot proof

Disadvantages

• It decreases the tensile strength and tearing strength

• It decreases the abrasion resistance

• It gives harsh and stiff feel



• It gives an unpleasant odour

• It turns yellow after chlorine bleaching

Resins

The following the resin the are used for resin finishing

• DMU Di Methylol Urea

• DMEU Di Methylol Ethylene Urea

• DMDHEU Di Methylol Di Hydroxy Ethylene Urea

• TMM Tri Methylol Melamine

Recipe

For Shirting cloth (Cotton, PIC, PN)

• DMU/DMDHEU 80 -100 gpl cross-linking resin

• MgCl2 - 8 - 10 gpl catalyst for cross linking reaction

• PE emulsion 20 gpl Lubricant• Reactive softener 30 gpl softener

Process

• Padding in two bowl padding mangle with 80% expression at room temperature

• Drying in stenter with minimum tension at 70 - 80°C

• Cure at 120°C -150°C for 2-5 min Cross-linking and polymerization takes place

• Washing and soaping - I-2gpl soap or TRO and 2-4 gpl soda ash at 50 -60°C for 10 min acidity is

neutralised

• Softening and drying - rinsed in water with softener

• Stentering

Peach wash:

• Velvet feel is provided to the basic over dyed fabrics / garments with soft handle.

Salt finish:

Washed with a high sodium content finish for increasing abrasion levels

PEACH SKIN EFFECT DENIM

• This effect is created by treating the fabric in order to form a fine protruding, hair-like covering

resembling the surface of a peach.

• The effect can be achieved by a careful selection of the fabric and a tightly controlled wash with a

combination of neutral cellulose enzyme and stone.

• This treatment is often carried out on ecru jeans that are to be garment dyed.

• The extent of the surface effect depends on the fabric used as well as on the cellulose dose and

treatment time.



• If an equally high amount of acid cellulose is used, the surface will turn out very smooth with

absolutely no fuzz on the face.

LASER TECHNOLOGY

• It is a computer controlled process for denim fading.

• This technique enables patterns to be created such as lines and/or dots, images, text or even

pictures.

• It is water free fading of denim.

• Being an automatic system, chances of human error are slim.

• Also called spray painting in denims.

This technique has relatively high cost

Important question

TWO MARKS

1. Resin finish is meant for __________ the crease recovery of cotton fabrics

2. Differentiate between chemical and mechanical finishes?

3. Give the advantages and disadvantages for resin finishing

4. Give the advantages and disadvantages for acid wash finish

5. Give the advantages for garment wash

6. Write the merits and demerits of sand blasting wash

7. State the mechanism of wrinkle free finish

8. Write the merits and demerits of enzyme wash

9. What is wash-n-wear finish?

10. Mention the process details required for enzymes wash

11. What are the uses of stenter?

12. State the importance of anti crease finish?

13. Give the concept of compressive shrinkage?

14. How do you classified for finishing process

15. mention the type of cellulose used in enzyme wash

12 MARKS

16. Briefly explain about enzyme wash, sand blasting, stone wash, peach finish

17. Explain the wrinkle- free finishing of cotton fabric

18. Explain the different method of application in garment finishing



Pollution is the introduction of contaminants into an environment that causes instability, disorder,

harm or discomfort to the physical systems or living organisms

THE RAW WATER QUALITY CRITERIA FOR INLAND SURFACE WATER USED AS

DRINKING WATER SOURCE AND FOR BATHING AS RECOMMENDED BY WHO & ISO:

EFFLUENT DISCHARGE STANDARDS

Parameter WHO ISO

pH 6-9 6-9Total Dissolved solids 1500 mg/lit (upper limit) Not given

Iron 50 mg/lit (upper limit) Not given

Nitrogen as N03 45 mg/lit Not given

Fluoride 1.5 mg / lit 1.5 mgl lit

BOD 6 mg/lit 3 mgl lit

COD 10 mg/lit Not given

Phenolic substances 0.002mg/lit 0.001 mg/lit

Cyanide 0.2mg/lit 0.1 mg/lit

Chromium 0.05mgllit 0.05mg/lit

Lead 0.05mg/lit 0.10mg/lit

Arsenic 0.05mg/lit 0.02mg/lit

Chlorides Not Given 600 mg/lit

S.No. Parameter

Standards

Inlandsurface

water

Public

sewers

Onlandfor

irrigation

Marinecoastal

areas

1. pH 5.5- 9.0 5.5 - 9.0 5.5 - 9.0 5.5 - 9.0

2. Suspended Solids mg/lit 100.0 600.0 200.0 100.0

3.Total dissolved solids

mg/lit2100 -- 2100 --

4.Biological Oxygen demand

mg/lit30.0 350.0 100.0 100.0

5.Chemical Oxygen demand

mg/lit250.0 -- --- 250.0

6. Sulphates mg/lit 1000.0 1000.0 1000.0 ---

7. Chlorides mg/lit 1000.0 1000.0 600.0 ---

8. Oils & grease mg/lit 10.0 20.0 10.0 20.0

9. Lead (as pb) mg/lit 0.1 1.0 -- 2.0

10. Total Chromium 2.0 --- 2.0 2.0



Standards of Water for Drinking (IS: 15000 - 1983)

Effects Of Textile Processing Industry

Si.No. Characteristics Desirable Limit Maximum

permissible

limit

1. pH value 6.5- 8.5 No relaxation

2. Odour Un objectionable --

3. Colour (Hazen unit), maximum 10 --4. Taste Agreeable --

5. Turbidity (NTU) Maximum 5 10

6. Total dissolved solids (ppm), maximum 500 --

7. Total hardness (as CaC03), (ppm) maximum 300 600

8. Chloride (as CI) (ppm) maximum 250 1000

9. Residual free chlorine (ppm) minimum 0.2 0.5

10.Total Coli form organisms, MPNI 100 ml,

maximum10 10

11. Pesticides Nil Nil

12.Radio active materialsa) - emitters, lC/ml, maximum 10-

8--

b)P - emitters, lC/ml, maximum 10- ---

Origin Characteristics

SizingStarch, generally coloured, high BOD, suspended solids, PVA, bad odour, softener,

oils fats

Desizing Starch, hydrolysd starch, bad odour , enzymes, salt, acidic pH

Scouring

Alkalies, surfactants, saponified oils, hydrolysed pectin's, proteins, suspended

solids, oil, High pH, silicates with high BOD, natural colours and TDSMercerising High alkali, suspended solids, TDS

BleachingChlorines, hypochlorites, alkali, peroxides, silicates, suspended solids, fattyalcohols.

DyeingDyes, salt, alkalies, acids, detergents, chromium, copper, high BOD & COD and

TDS Dyeing

PrintingDyes, alkali, acids, chromium, copper, thickeners polymers, detergents high BOD &

COD, waxes, oils fatty alcohol.

FinishingSilicones, suspended & dissolved solids, cationic compounds organic & inorganic

compounds

Carbonising Carbonized cellulose, High acidity, TDS.

SyntheticsHot colour, high BOD & COD, alkali, organic solvents, acidity, TDS, peroxides,

hydrolysed PVA, Acrylics etc.

Polyester weight

reductionHigh alkalinity, Turbidity, High BOD / COD

Wool scouringHot, highly coloured, high BOD & COD, suspended & dissolved solids, grease,

soaps, and alkalies

Silk degumming

and preparationDissolved solids, high BOD, high Turbidity, Bad odour, TDS



CONSTITUENTS OF WATER

The constituents of water are,

– Colour

– Turbidity

– Suspended solids

– Dissolved solids

– pH value

– Acidity

– Alkalinity

– Metals such as Fe, Mg, As, Cu

– Salts such as Chlorides, Sulphates, Sulphides and Nitrates.

– Gases such as Cl2, Oxygen, CO2

– Oils and Greasy contaminates.

The Effect of water on Textile Processing:

The various constituents of water has tremendous effect on various textile processing operations.

Colour:

The colour of water affects the whiteness of bleached fabric, the tone of the dyed and printed

fabrics.

Turbidity:

Suspended solids which cause turbidity results in stain formation, dye precipitation, coagulation,

uneven dyeing, specky dyeing and patchy dyeing results.

These cause severe problems, particularly on package dyeing machines.

These solids close the pores and affect the uniform circulation of dye liquor

Suspended solids:

These cause similar effects on the fabrics, as in the case of turbidity because most of the turbidity is

due to suspended solids.

Dissolved solids:

Dissolved solids cause much severe problems for the dyer. The nature of salts present in the water

contributes to dissolved solid content which cause disastrous effects.

These solids affect exhaustion, rate of dyeing, even dyeing, level dyeing and fastness properties of the

dyes.



pH Value:

The pH of water has tremendous effects on textile processing. Too acidic or alkaline pH may inhibit

enzyme activity.

Acidity may bring about acid hydrolysis in reactive dyeing.

Hence appropriate pH has to be maintained for the various processes.

Similarly alkaline pH in acid dyeing of silk / wool will affect acidic pH required for dyeing.

Metals:

• Metals like Manganese, Aluminum, Iron, Copper, and other heavy metals cause staining.

• They also cause low dye exhaustion, colour stains, precipitation, corrosion of tanks, pipes, tone

variations and high effluent load.

• Severe problems are reported in vat dyeing also.

• Iron and manganese are highly objectionable and these hydroxides combine with fatty acids giving

metal soaps.

• The natural colour of silk is affected by the presence of heavy metals.

• For e.g. Ferrous ions give greenish tone, chrome ions give orangish tone.

Salts:

• Sulphates, sulphites, sulfides, chlorides, nitrates, discharged in the water cause staining and corrosion.

• Nitrites prevent corrosion along with H2S04 when used in solublised vat dyeing. Nitrates used in

excess, cause stains by forming compounds of amino groups.

Hardness:

• In general, calcium and magnesium ions as salts of chlorides, sulphates, carbonates, bi-carbonates

contribute to hardness of water.

• Hardness of water results in patchy dyeing, specky dyeing, poor exhaustion of dyes, results in

precipitation of dyes, which causes colour stains, tone variations, etc.

• The most important factor is that of soaps, getting precipitated in hard water, causing improper

soaping, emulsification and saponification.



Waste Water Treatment Process

Classification of waste water treatment process

Primary Treatment

Secondary Treatment

Tertiary Treatment



PRIMARY TREATMENT

Screening

Sedimentation

Equalization

Neutralisation

Mechanical flocculation &

Chemical coagulation

SECONDARY TREATMENT

Aerated lagoon

Trickling filtration

Activated sludge process

Oxidation ditch & pond

Anaerobic digestion

Thermal evaporation

TERTIARY TREATMENT

Oxidation technique

Electrolytic precipitation & Foam fractionation

Membrane technologies

Electrochemical processes

Ion exchange method

Photo catalytic degradation

Adsorption (Activated Carbon etc.)



Primary Treatment

After the removal of gross solids, gritty materials and excessive quantities of oil and grease, the

next step is to remove the remaining suspended solids as much as possible.

Aim

• Reducing the strength of the waste water

• To facilitate secondary treatment.

Screening:

Screen is the synonyms of filtration.

Here action is nothing but the filtration or separation of suspended solid from the liquor or raw

effluent

Coarse suspended matters such as rags, pieces of fabric, fibres, yarns and lint are removed.

Bar screens and mechanically cleaned fine screens remove most of the fibres.

The suspended fibres have to be removed prior to secondary biological treatment; otherwise they

may affect the secondary treatment system.

They are reported to clog trickling filters, seals or carbon beads

Drain from two different units

A net of iron having 1 sq. inches of each hole.

It separates the different foreign materials like bulk of trees, leaves, polyethylene bag etc..

To treat 100 cubic meter per hour, here three screening chamber are used

Suspended solid which can pass through the first filter are finally filtered here.

The screen has around 250-300 slits per sq inches.

This screening system has automatic wiping action with four wipers or brush.



Cotton fibers, yarns with the liquor are deposited on the screen and raw effluent passes through the

slits.

This is a simple filtering method

The screen is curved around 90 degree angle

Sedimentation:

The suspended matter in textile effluent can be removed efficiently and economically by

sedimentation.

This process is particularly useful for treatment of wastes containing high percentage of settable solids

or when the waste is subjected to combined treatment with sewage.

The sedimentation tanks are designed to enable smaller and lighter particles to settle under

gravity.

The most common equipment used includes horizontal flow sedimentation tanks and centre-feed

circular clarifiers.

The settled sludge is removed from the sedimentation tanks by mechanical scrapping into

hoppers and pumping it out subsequently.

Equalization:

Effluent streams are collected into ‗sump pit‘. Sometimes mixed effluents are stirred by rotating

agitators or by blowing compressed air from below.

The pit has a conical bottom for enhancing the settling of solid particles.

Neutralisation :

Normally, pH values of cotton finishing effluents are on the alkaline side.

Hence, pH value of equalized effluent should be adjusted. Use of dilute sulphuric acid and boiler flue

gas rich in carbon dioxide are not uncommon.

Since most of the secondary biological treatments are effective in the pH 5 to 9, neutralisation step is

an important process to facilitate



Chemical coagulation and Mechanical flocculation:

Finely divided suspended solids and colloidal particles cannot be efficiently removed by simple

sedimentation by gravity.

In such cases, mechanical flocculation or chemical coagulation is employed.

In mechanical flocculation,

The textile waste water is passed through a tank under gentle stirring ;

The finely divided suspended solids coalesce into larger particles and settle out.

Specialized equipment such as clariflocculator is also available, wherein flocculation chamber is a part

of a sedimentation tank.

Chemical coagulation

In order to alter the physical state of colloidal and suspended particles and to facilitate their removal

by sedimentation, chemical coagulants are used. It is a controlled process, which forms a floc

(flocculent precipitate) and results in obtaining a clear effluent free from matter in suspension or in the

colloidal state.• The degree of clarification obtained also depends on the quantity of chemicals used.

• In this method, 80-90% of the total suspended matter, 40-70% of BOD, 30-60% of the COD and

80-90% of the bacteria can be removed.

• However, in plain sedimentation, only 50-70% of the total suspended matter and 30-40% of the

organic matter settles out.



• Most commonly used chemicals for chemical coagulation are alum, ferric chloride, ferric

sulphate, ferrous sulphate and lime

Secondary Treatment

• The main purpose of secondary treatment is to provide BOD removal beyond what is achievable

by simple sedimentation.

• It also removes appreciable amounts of oil and phenol.

In secondary treatment,

The dissolved and colloidal organic compounds and colour present in waste water is removed or

reduced and to stabilize the organic matter. This is achieved biologically using bacteria and other

microorganisms. Textile processing effluents are amenable for biological treatments. These processes

may be aerobic or anaerobic

In this treatment, Biodegradable organic impurities are removed by aerobic bacteria. Removes upto

90% of the oxygen demanding wastes, This is done by trickling filter or

activated sludge process.

In aerobic processes,

Bacteria and other microorganisms consume organic matter as food.

They bring about the following sequential changes:

(i) Coagulation and flocculation of colloidal matter

(ii) Oxidation of dissolved organic matter to carbon dioxide

(iii) Degradation of nitrogenous organic matter to ammonia, which is then converted into nitriteand eventually to nitrate.

Anaerobic treatment

It is mainly employed for the digestion of sludge. The efficiency of this process depends upon pH,

temperature, waste loading, absence of oxygen and toxic materials.

Some of the commonly used biological treatment processes are described below:

Aerated lagoons

Trickling filters


Oxidation ditch

Oxidation pond

Anaerobic digestion



Trickling filter process

It is a circular tank and is filled with either coarse or crushed rock. Sewage is sprayed over this bed by

means of slowly rotating arms. When sewage starts percolating downwards, micro organisms present

in the sewage grow on the surface of filtering media using organic material of the sewage as food.

After completion of aerobic oxidation the treated sewage is taken to the settling tank and the sludge is

removed. This process removes about 80-85% of BOD.

• Spherical stones of 2-10 cm size

• 1-3 mts of stone bed depth normally employed


Activated sludge is biologically active sewage and it has a large number of aerobic bacteria's, which

can easily oxidize the organic impurities.

The sewage effluent from primary treatment is mixed with the required amount of activated sludge.

Then the mixture is aerated in the aeration tank (Fig.). Under these condition, Air supply organic

impurities of the sewage get oxidized rapidly by the microorganisms.

After aeration, the sewage is taken to the sedimentation tank. Sludge settle down in this tank, called

activated sludge, a portion of which is used for seeding fresh batch of the sewage. This process

removes about 90-95% of BOD



Oxidation Ponds

Oxidation Ponds are also known as stabilization ponds or lagoons.

They are used for simple secondary treatment of sewage effluents. Within an oxidation pond

heterotrophic bacteria degrade organic matter in the sewage which results in production of cellular

material and minerals.

The production of these supports the growth of algae in the oxidation pond.Growth of algal

populations allows furthur decomposition of the organic matter by producing oxygen.

Typically oxidation ponds need to be less than 10 feet deep in order to support the algal growth

Oxidation ponds : A pond that contains partially treated wastewater which is then left to allow the

growth of algae and bacteria which decompose the rest of the waste.

Oxidation Pond: A man-made (anthropogenic) body of water in which waste is consumed by bacteria,

used most frequently with other waste-treatment processes; a sewage lagoon

http://www.rpi.edu/dept/chem-eng/Biotech-Environ/FUNDAMNT/streem/glossary.htm


http://cancerweb.ncl.ac.uk/cgi-bin/omd?oxidation+pond


http://www.babylon.com/definition/Oxidation_Pond/English







Anaerobic Digestors

Anaerobic digestors are large fermentation tanks which are continuously operated under anaerobic

conditions, as seen below.

Anaerobic decomposition could be used for direct treatment of sewage, but it is economically

favorable to treat the waste aerobically. Large-scale anaerobic digestors are usually used for

processing of the sludge produced by primary and secondary treatments. It is also used for the

treatment of industrial effluents which have very high BOD levels.

The mechanisms for mechanical mixing, heating, gas collection, sludge addition and removal of

stabilized sludge are incorporated into the design of large-scale anaerobic digestors. Anaerobic

digestion uses a large variety of nonmethanogenic, obligately, or facultatively anaerobic bacteria

In the first part of the process, complex organic materials are broken down and in the next step,

methane is generated. The final products of anaerobic digestion are approximately 70% methane and

30% carbon dioxide, microbial biomass and a non biodegradable residue.

Disposal of sludge

This is the last stage in the sewage treatment. Sludge formed from different steps can be disposed

by

(I) DUMPING INTO LOW-LYING AREAS.

(II) BURNING OF SLUDGE (INCINERATION),

(III) DUMPING INTO THE SEA,

(IV) USING IT AS LOW GRADE FERTILIZERS












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Unit IV Garment Washing and Finishing