Process Flow of Effluent Treatment in a Textile Industry-1

Process Flow of Effluent Treatment in a Textile Industry

Typically the following process flow of effluent treatment is followed in a typical textile industry;

Screening

The purpose of screening is to filter out the loose impurities. Thus wood, paper plastic bags etc. can be removed by this method. A method of progressive filtering is followed where first the matter is passed through coarse screens and then through fine screens.

Oil and Grease Removal

Many units discharge water mixed with oil. The purpose of this equipment is to remove the oil. Since surface density of oil and grease is less than water, the oily substance come on the surface of the water and can be skimmed.

Cooling and Equilization

The effluent from the primary treatment is cooled ( cooling towers are employed for this purpose) and then uniformly mixed using equlisation tank. It takes in any sudden gush of effluents as well as slow rate of effluent and feeds to the subsequent processes in a uniform way.

pH Adjustment ( Acid or Alkaline Dosing)

The waste from the Textile Industry is rarely pH neutral. To increase the efficiency of biological treatment and coagulation/flocuculation a pH of 6-8 is needed. Generally Sodium hydroxide is used to neutralise acidic waste and hydrochloric acide is used to neutralize alkaline waste. Generally the effluents from the dyeing industry have high pH and hence an acid addition is required.

Aeration 

It is reuqired to control BOD. Two main methods are used: one in which water is mechanically agitated so that air from atomoshphere may enter into the water, second method is introducing the air in the water through blowers and using diffusers to diffuse the air uniformly.

Prechlorination

Generally organic matter present in the effluent takes oxygen from the water, which increases its oxygen demand, to avoid that chlorine is added to oxidise the matter.

Clarification

The purpose of clarification is to remove any suspended solids by coagulation and flocculation. It is done using flash mixer. In flash mixer, alum solution is dosed as coagulant.

The flocculated water flows upwards towards tube settler. The suspended solids settle down.

This settling can also be done using lamella filter

Lamella Filter

It achieves solid liquid separation by directing the liquid between a seris of inclined plates called lamellae. It settles suspnded solids by gravity.



To be continued

An Excellent Document on Denim Effluent Treatment Process is here

Sources:

http://www.scribd.com/doc/4678823/Etp-Manual-Std-Denim

http://www.sharpengineering.co.in/Iffluent_Equipments.aspx

http://www.jfc-cetp.com/envinfo.html

http://www.iichemrc.org/Lamella.pdf

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Effluent Generated at various Processes of Textile Manufacturing

Effluent Generated at various Processes of Textile Manufacturing

Textile manufacturing involves conversion of Fibers into garments. At each process some amount of liquid is used. However, it is not that each process leads to generation of efflents. Typically coversion to yarn involves no generation of effluents. It is the sizing and processing where most of the efflent is generated which needs to be treated. Given below is a list of the processes along with the information about effluent generated.

1. Fiber Preparation and Yarn Spinning: 

There is very little effluent generated in these processes.

2. Slashing/Sizing

The Effluent contains BOD, COd, metals, cleaning waste and size.

3. Weaving, Knitting and Tufting

There is very little effluent generated in these processes.

4. Desizing

The effluent contains BOD from water-soluble sizes, synthetic size, lubricants, biocides and anti-static compounds.

5. Scouring

The effluent contains disinfectants and insecticide resudes, NaOH, detergents, fats, oils, pectin, wax, knitting lubricants, spin finishes and spent solvents.

6. Bleaching

The effluent contains hydrogen peroxide, sodium silicate or organic stabilizer. The effluent also contains high pH.

7. Singeing and Heat Setting

There is very little effluent generated in these processes.

8. Mercerising

The effluent contains high pH and Sodium Hydroxide.

9. Dyeing

The effluent contains metals, salts, surfacftants, toxics, organic processing assistants, cationic material, color, BOD, sulfide, acidity or alkalinity and spent solvents.

10. Printing

The effluent contains suspended Solids, urea, solvents, color, metal, heat , BOD and foam.

11. Finishing

The effluent contains BOD, COD, suspended solids, toxics and spent solvents.

Read Also

Textile Effluent Treatment-1
Textile Effluent Treatment-2

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Effluent Treatment in Textile Industry-2

Bleaching and Dyeing

It is estimated that to dye 1 kg of cotton with reactive dyes, 0.6-0.8 kg of NaCl, 30-60 grams of dyestuff and 70-150 liter of water is required. Once the dyeing operation is over, the wastewater must be treated before reuse. Coagulation and Membrane Technique ( nanofilteration  or reverse osmosis) are among the processes suggested for the treatment of water. 

Coagulation and Flocculation

Natural and wastewater contain small particles. They are suspended in water in a form called as a colloid. These particles carry the same charges, and repulsion prevents them from combining into larger particles to settle. Thus, some chemical and physical techniques are applied to help them settle. The phenomenon is known as coagulation. A well known method is the addition of electrolyte. Charged particulates combine with ions neutralizing the charges. The neutral particulates combine to form larger particles, and finally settle down. Historically Alum is used for this purpose but it makes the pH of the solution slightly basic. 

Another method is to use high-molecular-weight material to attract or trap the particulates and settle down together. Such a process is called flocculation. Starch and multiply charged ions are often used.

Here the basic advantage is that the dye molecules themselves are removed which is better than other methods where dye molecules are decomposed and produce harmful and toxic aromatic compounds. 

The disadvantage is that in coagulation process, large amount of sludge is created which may become  a pollutant itself and increase the treatment cost.

This method is useful for removing the insoluble dyes, but the cost of treating the sludge increases.

Ultrafilteration and Nanofilteration


Ultrafilteration filters substances with sizes less than  than 10^-7 to 10^-8 m . It can effectively remove suspended organic solids. It can not remove multivalent ions. It needs low water pressure to operate.

Nano filteration filters substances with size less than 10^-8 to 10^-10 m. It can remove multivalent ions. 

Reverse Osmosis

It can remove substances with size less than 10^-9 to 10^-11m. It can remove multivalent as well as monovalent ions.

When a compartment containing a dilute solution is connected to another compartment containing a concentrated solution by a semipermeable membrane, water molecules move from the dilute solution to concentrated solution. This phenomenon is called osmosis.

By applying pressure in the higher concentration solution, water molecules migrate from a high concentration solution to a low concentration solution. This method is called reverse osmosis water filter system. ( Source )

An excellent FAQ on Reverse Osmosis can be found here .

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A Note on Medical Textiles

Textiles act as an interface between man and treament. Depending upon the area of application, the medical textiles are categorises as Non-implantable, implantable and healthcare and hygiene products.

Non implantable material are external to the body, with or without skin contact. It includes absorbant pad, bandages and plasters among others. These material should have good padding characteristics and should be non sticking to the wound. Air and vapor permeability is requrired so that the material is comfortable to the patient. They should have high absorbancy and should be soft and pliable.

Implantable materials are used in place of defective body parts. It includes sutures and soft tissue implants. These materials should have compatibility with the natural body systems. They should be durable and resistant to alkali and acidic media. Of course, they should have functionality for the purpose for which they are applied.

Healthcare and hygine products are not directly used in medical treatment, rather they are used for good hygiene application and healthcare. It includes surgical clothing and surgical covers. They should have high bacterial and viral resistance. They should be hygienic and should have softness and breathablitity. They should have required strength.

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Textile and Comfort

People have always been interested in the connection between clothing and physical well-being.Comfort has its physiological, physical-chemical and psychological components. Major components in case of textiles are Warmth, Absorbing capacity and humidity, General comfort , Cloth convenience , Skin perception , Weight and Softness. Out of these major part of comfort is directly related to the body temperature. Thus any clothing can be measured on comfort by the fact that how well it can regulate the temperature of the body. Sweating is the most effective way the human body has of cooling down. How well can a clothing provide comfort depends upon (among other factors) how well it can handle sweating.

The most effective cooling is achieved by sweat evaporating directly on the skin. Thus any clothing that behaves closest to the skin is comfortablee. The ability of a textile to transport perspiration in the form of vapour through itself and out to the exterior is generally referred to as its breathability. It is incorrect to use the terms breathability (or resistance to water vapour) and air permeability interchangeably, because low air permeability does not in itself result in lower breathability. The best example of this is modern wind- and waterproof membranes, which allow very little air to permeate in from outside (windproof), but still allow evaporated perspiration to pass through from the inside.

Fiber characteristics influence breathability the most. However contrary to popular belief,synthetic fibers are not always bad in terms of comfort. If textiles made from synthetic fibres were properly designed, they could not only offer the same heat and moisture management qualities as natural fibres but even exceed them.For example in in double faced clothings, layers of natural and synthetic fibres were combined, yet kept separate. The synthetic fibres of the "double face material" were next to the skin and conducted perspiration quickly and efficiently away from the body and into the outer cotton layer. In combination, the two materials were far more comfortable than cotton, because of the drier feeling on the skin."

There are some interesting developments in getting comfort characteristcs of fabrics they include a gradual variation in the fineness of the fibres and yarns from the inner surface of the textile to the outer surface. It improves moisture management; because the resulting narrowing of the capillaries (denier gradient) means that the moisture can be transported away from the skin really effectively. Other measeures include integrating electrical and electronic components such as heating or cooling elements. The latest battery technology and innovative methods of processing and wiring.


Sources:

http://www.innovationintextiles.com/articles/732.php

http://www.technica.net/NT/NT3/comfort_clothing.htm
 

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Various Chemicals Used in Textile Industry

Various Chemicals used in Textile Industry


Pre-treatment Chemicals

De-sizing Agent

This is used to remove the different types of sizes (Starch, waxes etc.) from the fabric/yarn

Wetting and Penetrating Agent

This is needed to reduce the surface tension of water and thus increase the absorbency of the water to the fabric

Sequestering Agent & Protective Colloid

This is needed to reduce the hardness of water and thus make ideal conditions for washing

Scouring Agent

This is needed to remove the oil , fats etc from the fabric.

Silicone & Non Silicone Defoamers

These are needed to reduce the foam created during the process of treatment of fabric

Non-Silicate Peroxide stabilizer

This is used to stabilize the peroxide of hydrogen peroxide in the pretreatment process.

Peroxide Killer

This is used to clear the residual peroxide from the fabric

Polyester Weight Reducing Catalyst

This is used to reduce the weight of the polyester fabric during the caustic addition process

Anti-back Staining Agent

This is used to prevent the staining of the pockets during the denim fabric treatment

Dyeing Chemicals

Sequestering Agent

It is used to reduce the hardness of water and thus make ideal condition for processing

Silicone & Non Silicone Defoamers

These are used to reduce the foam created during the process

Buffering Agent

These are used to maintain the pH of dye bath throughout the dyeing process

Polyester Dyeing Carriers

These are used to facilitate easy absorption and penetration of dyes by the polyester fabric

Dispersing Agent & Oligomer Removing Agent

This is used to maintain the dispersion of dyes in the dyeing process and help to remove oligomers

Levelling Agent

This is used to get even dyeing and even colour depth effect

Lubricants

To reduce the friction between fabric to fabric and fabric to machine and to reduce the creation of creases in the fabric

Washing off Agent

To remove the unfixed dyes from the fabric

Dye-fixing Agent

To fix the dyes on to the fabric

Soda Ash Substitute

To substitute soda ash in the dyeing process of cotton.

Cationising Agent for Pigment Dyeing

To provide required cationic charge to the fabric in the pigment dyeing process

Printing Chemicals:

Dispersing, Penetrating, Swelling, Levelling & Defoaming Agent

This is used to provide depth and even level printing effect, being added in the printing paste

Fixation Accelerators

These are used to provide depth and fixation of dyes to the polyester printing fabric in loopager machine during the disperse printing process

Binders Acrylic, Self Thickening for Gold & Flock

These are used to bind the pigment or dyes onto the fabric

Fixers in Pigment Printing

These are used to provide fastness to the print

Thickeners

These are used to provide viscosity to the printing paste to facilitate required printing effect

White Inks

These are used to provide printing effect onto the fabric

Washing Off Agent

This is needed to remove the unfixed dye from the printed fabric

Finishing Chemicals:

Stiffeners

This is used to provide stiff finish effect to the fabric

Softeners

These are used to provide soft finish effect to the fabric

Silicone Emulsion

This is used to provide silky and soft finish effect to the fabric

Wax Finishing Agent

This is used to provide waxy finish to the fabric

Anti Static Agent

This is used to reduce the static power of the fabric

Water Repellant & Soil Resisting Agent

This is used to provide water repellency and dust repellency to the fabric

Polyurethane Finishing Agent

This is used to provide bouncy feel to the fabric

Crease Recovery Agent

This is used to reduce the crease and provide wrinkle free effect to the fabric

Delustering Agent

This is used to remove the luster from the viscose fabric

Anti-pilling & Anti-Slip Agents

These are used to remove the hairing and pilling problems from the fabric and also provide anti-slip effect

Enzymatic Bio-polishing Agent

This is used to remove the surface protruding fibers from the knit substrates and denim and thus improvise the surface feel

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Influence of Fiber Fineness and Maturity in spinning Process

Influence of Fiber Fineness and Maturity on spinning Process

Fiber Fineness

Fiber fineness determine how many fibers are present in the cross section of a yarn of given thickness. Additional fibers in the cross section not only provide additional strength but also a better distribution in the yarn. Minimum 30 fibers are needed, usually over 100 fibers are required. Fiber fineness influences spinning limit, drape of the fabric, yarn strength, luster, yarn evenness, handle, yarn fullness and productivity. Productivity is influenced by reduced end breakage rate.

In a conventional spinning process, fine fibers accumulate to the core and coarse fibers in the periphery.

Fiber fineness is measured in dtex which is equal to ratio of mass in dgrams and length in km. Decitex is equal to the product of Micronaire value of the cotton and 0.394.

Cotton fibers are generally classified as very fine if they have a micronaire value upto 3.1; fine if they have value between 3.1 to 3.9; medium if they have it between 4.0 to 4.9; slightly coarse between values of 5 to 5.9 and coarse if they have a micronaire value above 6.

Fiber Maturity

Cotton fiber consists of cell wall and lumen. The maturity index depends upon the thickness of the cell wall. The fibers are considered ripe if they have maturity index between 50-80 percent, unripe if they have MI between 30 to 45% and dead when they have it less than 25%.

Unripe fibers have neither adequate strength nor adequate longitudinal thickness. They lead to loss of yarn strength, neppiness, high proportion of short fibers, varying dyeability, processing difficulties mainly at the card.

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World Textile Industry Report

Please click this link for world textile industry report

Introduction to textile Processes

Please refer to the link here.