Category Archives: Wet Processing Technology

Dyeing & Printing || Differences Between Dyeing And Printing

Dyeing and printing are the two major wet processing techniques for coloration of fabric. In the dyeing process; only one color is produced but in the printing process; various types of colored design are produced on the fabric surface. Dyeing is done on grey fabric but printing could be done on both pre-treated fabric and colored fabric.

Difference Between Dyeing And Printing: There is a lot of difference between dyeing and printing process. Here, I have mentioned some major difference between dyeing and printing.

Dyeing Printing
1. By the dyeing process, dyes are applied on the whole fabric equally. 1. By the printing process, dyes are applied on the fabric localizedly to produce desired design.
2. Fabric, yarn and fibers are dyed by dyeing. 2. Generally printing is done on fabric.
3. In a dyeing process, dyes are applied on the both sides of the fabric. 3. Dyes are applied on olnly one side of the fabric.
4. No precise design is required for dyeing. 4. Design is must for printing.
5. In a dyeing process, only one dye is used. 5. In a printing process, one or more dye is used.
6. Precise temperature is required for dyeing. 6. In printing, it is not necessary to maintain precise temperature.
7. Thickener is not required for dyeing. 7. Thickener is must for printing paste preparation.
8. The density of dye solution is less than the density of printing paste. 8. In printing, the density of printing paste is higher than dye solution density.
9. Huge amount of water is required for dyeing. 9. Small amount of water is required for printing.
10. Steaming or curing is not necessary for dyeing. 10. Steaming or curing is must for printing to fix the dyes or pigments on the surface of the fabric.
11. Dyeing is comparatively cheaper than printing. 11. Printing is costly than dyeing.
12. Dyed fabrics are soft. 12. Printed fabrics are hard and harsh.

Characteristics Of Process Waste Streams Of Textile Industry | Industrial Effluent Impacts

Textile industry is the huge sector where a large amount of waste streams or effluents are produced. The effluent which is produced in different sector of textile industry is dangerous for the environment. Mainly effluent is produced from desizing, scouring, bleaching, mercerizing, dyeing, printing, finishing, washing and others process. This type of waste water contains harmful chemicals for the environment, for this reason it needs to purify before discharge to the environment. Effluent treatment plant is used for treated the effluent which is come from the textile or other chemical industry.

Characteristics of Process Waste Streams of Textile Industry: Now, I will show you the process unit of textile industry from where effluent is produced, possible pollutant contain in water and nature of waste water. It must help us to get the general concept about the effluent of the textile industry and we can set up ETP for treated the effluent.

Desizing: We know that, size materials are apply on the yarn surface in weaving sector. The removing process of size materials from the fabric is called desizing. Possible pollutant in water is Starch, Glucose, CMC, PVC, Resins, Fats, and Oils etc. The nature of the waste water is high BOD (35-50%) of total.

Scouring: Scouring is the process by which impurities of the textile materials are removed. Possible pollutant in water is NaOH, Na2CO3, Waxes, Grease, Fragments of cotton etc. Nature of waste water is strongly alkaline, dark color, high BOD (30%) of total.

Bleaching: Natural color of the textile materials are removed by the bleaching process. Possible pollutant in water is Na(0Ocl)Cl, NaOH, Cl2, H2O2, Na2O2, acids etc. Nature of waste water is alkaline, BOD (5%) of the total.

Mercerizing: It is an additional process to improve the physical properties of the fiber. Possible pollutant in water is NaOH, H2SO4, Na2CO3 etc. Nature of waste water is strongly alkaline, BOD (less than 1%).

Dyeing: Dyeing unit is the main production house of waste water. Waste water which is produced in yarn dyeing, woven dyeing or knit dyeing unit is highly polluted. Possible pollutant in water is various Dyes, Salts, Acids, Alkalis, Soap, and Detergent etc. Nature of waste water is strongly colored, fair BOD (6%) of the total.

Printing: Various type of decorous design is formed by the printing process. Possible pollutant in water is Colors, Pigments, Gums, Oils, Acids, different salt and other auxiliaries. Nature of waste water is highly colored, oily appearance, BOD (6 to 10%) of the total.

Finishing: Different types of finishing are applied in the finishing section. Possible pollutant in water is Traces of Starch, Resins, Softeners, and Stiffeners etc. Nature of waste water is low BOD (2 to 4%) of the total.

To protect the environment from the harmful effect of the effluent of the textile industry, the owner of the industry should set up an Effluent Treatment Plant (ETP).

Working Procedure Of Effluent Treatment Plant (ETP) | Treatment Of Waste Water

Effluent Treatment Plant (ETP) is essential to purify the waste water which is come from different types of manufacturing industry like textile, ternary, dyes and chemical manufacturing industry, pharmaceuticals etc. Different environment saving organizations are trying to protect the environment from the harmful effect of the effluent. Different waste water has different characteristics which pollute the water.

Process flow chart of effluent treatment with effluent treatment plant: Following is the basic structure of effluent treatment plant.

Effluent from different manufacturing industry

Primary Filtration

Cooling and Mixing

Neutralization (by acid or alkali)

Chemical Co-agulation

Settling and Separation of Sludge

Pressure Filtration


Now, I like to give a short description about the sequence of operation in effluent treatment plant.

Primary Filtration: It is the first stage of effluent treatment plant, where effluent is come from weaving, dyeing, printing or finishing unit. Here primary filtration is performed to remove solid waste particles.

Cooling and Mixing: In this stage, different types of effluent are mixed and cool down by the help of motor which run a fan.

Neutralization Tank: After cooling and mixing; effluent is transferred to neutralization tank by the help of pump. Here, acid or alkali is mixed to neutralize the effluent. A pH meter is placed in the neutralization tank.

Co-agulant Bath: After neutralization of effluent; effluent is transferred to a co-agulant bath. Here, co-agulant is added with the effluent.

Settling Tank: In here; effluent separates from the water and it found in the lower level of the tank. Effluent is like as sludge.

Pressure Filter: Here, filtration is done under pressure. A certain amount of pressure is created here.

Carbon Filtration: It is an optional filter process.

Discharge to Drain: After completion of all the process, the effluent becomes purify and it becomes safe to drain to the environment.

When treated water is drain to the environment it is checked by the different testing lab. Different standard is maintained during discharge of the treated effluent.