Water Consumption in Textile Industry

Water Consumption in Textile Processing Industry

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.

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.

Figure-1

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 use ranges from a low of 2.5 gallons to a high of 45.2 gallons.

Textile industry is a leading consumer of water and it ranks among ten top water consuming industries. Table-1 shows the approximate consumption of water for the processing of various textile fibres.

Table-1 

Water Consumption by Textile Industry in Various Processes

      Substrate …………………Water consumption (kg/kg of fabric)

• Cotton …………………250-350 
• Wool …………………..200-300 
• Nylon ………………….125-150 
• Rayon …………………125-150 
• Polyester ………………100-200 
• Acrylic …………………100-200 

Cotton fibres require the largest amount of water for its preparation. In general, the water consumption in a process house is about three times the consumption of all other units put together (Table-2). The water consumption in the bleaching section is highest.

Table-2 

Water Consumption Pattern in Textile Mills

       Process ……………………………Water consumption (% of total)

• Bleaching, Finishing ……………38 
• Dyeing ………………………16 
• Printing ……………………….8 
• Boiler House …………………14 
• Humidification (spinning) ………6 
• Humidification (weaving)……… 9 
• Sanitary, Domestic etc……….. 9 

The conventional preparatory processes of textiles namely, desizing, scouring, bleaching, and washing are highly water consuming operations and consequently energy-intensive (Table-3).

Table-3 

Consumption of Water and Energy in Kiers and J-Box Processes

Process ……Consumption of water 1/kg……Consumption of steam kg/kg

                                       (J-Box Processes)

• Desizing …………………………3 …………………..….0.25 
• Washing ……………………….20 …………………..…0.35 
• Scouring ………………………2 ………………………..1.75 
• Washing ………………………..20 …………………..…0.30 
• Bleaching ………………………2 ……………………….1.00 
• Washing ……………………….40 ……………………….0.60 

          Total ……………………………87 ……………………..4.20 

        
         Conventional kier-boiling …100 ……………………….5.10 

 

Water Purification Process for Textile Wet Processing Industry

Water Purification :

Conventional softening treatment plant may not remove the impurities in water to the recommended permissible level. Demineralized or reverse osmosis technique is needed for removal of TDS from water but is costly. Water purification in the process house normally consists of flocculation, sedimentation, filtration and ion exchange. Hard water is normally softened using one or combination of methods.

Soda-alum process
Hard water is first pumped into the reaction tank and then aluminium sulphate is added to it as floculant. About 20-30 min is allowed to react and then the impurities are allowed to settle for about 30 min before filtration. 

Many floculants need alkali as an assistant floculant. If additional alkali is not added, the total alkalinity is reduced and part of aluminium sulphate, being water soluble may pass through the filter. As aluminium hydroxide and metals precipitate downwards, clear water arrives at the top and is decanted.

Lime-soda process
In this process lime and sodium carbonate are added to precipitate the calcium and magnesium salts as temporary hardness.

For permanent hardness the reactions are

The softened water is usually slightly alkaline with 1-4 degree residual hardness.

Base exchange process
When hard water is passed through a bed consisting of zeolites, which are synthetic material systems composed of complex sodium, aluminium and silicate salts (Na2Z), the calcium and magnesium ions are exchanged. The displacing reactions for temporary hardness are :

For permanent hardness the reactions are :

The process is reversible and the bed (Na2Z) can be regenerated by passing concentrated salt solution. This method of water softening yields a very soft water (0.5-1 o hardness).

Water softening by demineralisation systems can be accomplished using either mixed bed (both cation and anion resin in one bed) or two bed system (resins remain seperated according to their charges). The active sites of the resins are limited and the sites are filled when water passes through these columns and must be regenerated again. Their ion-exchange capacity is greater than that of zeolite.