Water for Textile Wet Processing

 

Water  (Textile Wet Processing)

Textile industry is the third largest consumer of water in the world. Wet processing engineering is one of the major streams in textile engineering. In every stages of wet processing huge amount of water is used. Soft water is the life line of textile wet processing as well as textile industry for better production quality. In below table I have given total water consumed in different stages during wet processing.

• Water is a chemical substance with the chemical formula H2O.
• Its molecule contains one oxygen and two hydrogen atoms connected by hydrogen bond.
• Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice and gaseous state, water vapour or steam.
• In wet processing water consumption is greater than the amount of fibres processed.
• Water is a universal cleaning agent as rinsing and washing operations alone consume enormous amount of water.           
• In industries, the daily requirement of water is about 200000-300000 gallons.

Water Consumed During Wet Processing

• Bleaching -- 38% 

• Dyeing -- 16%

• Printing -- 8%

• Boiler -- 14%

• Other Uses -- 24%

Some Important Parameters of Water:

Color : 

Color normally indicates the presence of soluble and suspended matter , which affects the textile wet processing . The color of water is measured in terms of Hazen units, by comparing it with a color of a standard solution. A Hazen unit is the color produced by dissolving 1 ppm platinum in the form of chloroplatinic acid , in the presence of 2 ppm cobalt chloride.

Turbidity: 

Turbidity is caused by the scattering of light by suspended matter which may be organic or inorganic in nature. The turbidity of water is measured against a standard solution having a standard turbidity value 1000 units.

pH: 

pH is the measure of H+ ions concentration , its value indicates the nature of water ,such as neutral , acidic or alkaline. .pH of less than 7 indicates acidic , neutral at 7 and alkaline when above 7. The pH scale is having value from 0 to 14.

Total Dissolved solids(TDS):

TDS comprise of inorganic salts and small amounts of organic matter that is dissolve in water. The TDS is measured in ppm (mg/ltr).

Total Suspended Solids(TSS):

The suspended solids are discrete particles which are insoluble in water .These can be removed by filtration and are also measured in ppm.

Alkalinity:

The alkalinity is due to the presence of bicarbonates , carbonates or hydroxides. Alkalinity is divided into caustic alkalinity ( above pH 8.2) and total alkalinity above pH 4.5.( Bicarbonate and caustic alkalinity).

Acidity:

Most natural waters are buffered by a CO2 / HCO3 system. Corbonic acid is not fully neutralized until a pH of 8.2 and will not depress pH below 4.5. CO2 acidity is in the pH range of 8.2 to 4.5 , mineral acidity due to industrial waste is below pH 4.5. 

Disadvantages of Hard or Unsuitable water usage in textile processing

1. Formation of hard soaps with calcium and magnesium ions , which results into shade change.
2. Carbonates of calcium and magnesium precipitate iron and aluminum mordant and substantive cotton dyestuffs.
3. Some dyes got duller and even scum formation happens in the hard water.
4. The metal ion impurities such as iron and copper , is a problem in the peroxide bleaching baths, iron is responsible for reducing the brightness of many dyes and is also objectionable in the washing off operations.
5. Hard water is responsible for scale formation in the boilers.
6. If temporary hardness is high , the soft scales are formed which causes corrosion.

Desirable Water Quality Parameters for Textile Wet Processing 

1. pH→6.5-7.5
2. TDS→ 300 ppm
3. Color→ 5 Hazen No.
4. Residue on ignition→ 250 ppm
5. Total Hardness→ 30 ppm
6. COD →nil
7. Turbidity→ nil
8. Suspended Solids→ nil
9. Copper →0.01 ppm
10. Iron →0.01 ppm
11. Chromium→ 0.01 ppm
12. Manganese→ 0.05 ppm
13. Aluminium→ 0.2 ppm
14. Chloride →150 ppm
15. Sulphate →150 ppm
16. Nitrite→ nil