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Prepared By : Mazadul Hasan sheshir ID: 2010000400008 13th Batch Wet Processing Technology Email: mazadulhasan@yahoo.com Southeast University Southeast University Department Of Textile Engineering I/A 251,252 Tejgaon Dhaka Bangladesh
INTRODUCTION: INTRODUCTION: Waste water is very similar in textile processing, which do harms for environment and regular activities of mankind. Water is used various textile processes, they are mentioned below- cleaning the raw material, many different industrial processes (sizing, desizing, scouring, bleaching, mercerizing, dyeing, printing and finishing), and rinsing steps during the whole production.
What is closer process control: What is closer process control: Closer process control is a process, which control the pollution load in textile effluent. By this process, the pollution load can be reduced by 30-40percent.
The closer process controlled by The closer process controlled by following implements: following implements: Reduction in chemical usage. Recovery and re-use of chemicals. Process modification. Flow or volume reduction.
Reduction in chemical usage: Reduction in chemical usage: In the finishing operation, the starch is used in large quantities. The unutilized eventually joins the effluent stream. Its amount should be optimized though it is estimated that it will always remain somewhat in excess of what is required. Obviously, this excess should be diverted for different ratio. In summer it should be sun-dried and in winters it should be evaporated thus obtained should be disposed of as solid waste.
In bleaching operations, chlorine and per oxides are used. They should be mixed with dyeing effluent in order to decolorize it. In kiering mercerizing processes caustic soda is used in large quantities. It should be recycled by readjusting its concentration.
Process modification: Process modification: Certain change in processes can reduce the amounts and concentrations of waste materials. E.g.change in dyeing method(use of Exhaust dyeing , Standing bath dyeing , Pad-batch dyeing ). Exhaust dyeing: Exhaust dyeing in which a batch of fibre is dyed from a liquor that is used only once and then discarded. This technique enables dyers to produce matching colours on different batches of fibre with relative case (provided that the composition of the dye liquor and the dyeing conditions are carefully controlled) but obviously leads to the wastage of chemicals that are not consumed in the dye bath. However, provided that dyes which exhaust well are used, the loss of dyestuff is negligible and other chemicals used in the dye bath are relatively cheap.
Standing bath dyeing: Standing bath dyeing is basically similar to exhaust dyeing. However, after the first dyeing the dye bath is replenished with dyestuff and chemicals and a further dyeing is carried out. This replenishment may be repeated several times. Experience is required to calculate the exact amount of dyestuff and chemicals needed for replenishment. Pad-batch dyeing: Pad-batch dyeing is a recently-developed method based on the use of reactive dyes. It is often carried out in the cold and uses low liquor to fibre ratios (1: 1 compared with 20: 1 for exhaust dyeing).
Recovery and re-use of chemicals: Recovery and re-use of chemicals: Size selection Replace starch-based sizes with synthetic sizes. The advantages of this is a reduced pollution load as synthetic sizes have lower BOD levels, and they can be recycled for reuse. Desizing The effluent from desizing will contain the sizes that were added onto the yarn before weaving/knitting. Using and recycling synthetic sizes in place of starch sizes will reduce the pollution load from desizing.
Scouring Detergents should be easily biodegradable. Avoid the following detergents: linear alkyl benzene sulphonate; dialkyl-dimthyl ammonium chloride with poor biodegradability (e.g. EDTA; phosphonic acid). Reuse scour wash water for desizing. Recycle continuous scour wash water to batch scouring. Bleaching Replace the use of chlorites and hypochlorite's with hydrogen peroxide. Ensure that bleaching is carried out efficiently. Recycle bleach wash water for scouring. Use vacuum slots to remove excess solution which can then be reused.
Mercerizing: Recycling of sodium hydroxide through evaporation for reuse in mercerizing or scouring will decrease the pollution load and chemical consumption. General Use modern equipment. Replace batch processes with continuous processes. Install counter-current washing. Combine processes such as desizing, bleaching and scouring. Replace harmful chemicals with those of lower environmental impact. Reuse wash water for cleaning equipment and screens.
Flow or volume reduction: Flow or volume reduction: The waste flow may be reduced by the reuse of process water, counter flow waste, segregation of weak waste for disposer without treatment, changes in process and other similar means.
Conclusions: Conclusions: The textile industry emits a wide variety of pollutants from all stages in the processing of fibers and fabrics. These include liquid effluent, solid waste, hazardous waste, emissions to air and noise pollution. It is important to investigate all aspects of reducing wastes from the textile industry, as not only will it result in improved environmental performance, but also substantial savings for the individual companies.
