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Coming to terms with the menace of pollution has been a major worry for the Dyers in face of increasing pressure from the strict environmental laws. This section gives a comprehensive view of the Pollutants in the dyeing units and importantly how to control it effectively.
What is Dye » Pollution Control Dyeing Units

Difference Between Pigments and Dyes Pollution Control Dyeing Units Dyeing Concepts

Perhaps one of the industry that is under the strong radar of the environmental agencies is the Dyeing units and the Dyestuff industries as a whole. The nature of pollution that accompanies this industry is primarily due to the non-biodegradable nature of the dyes along with the strong presence of toxic trace metals/acid/alkali/ carcinogenic aromatic amines traceable in the effluents. The following table illustrates the pollutants associated with some of the very popular dyes.

Types of Pollution that is associated with various dyes:

Class Fiber Nature of Pollution
Direct Cotton Salt, unfixed Dyes, copper salts, cationic fixing agents
Reactive Cotton Salt, unfixed Dyes, Alkali
Vat Cotton Alkali, oxidizing agent, reducing agent
Sulphur Cotton Alkali, oxidizing agent, reducing agent, unfixed dyes
Acid Wool Unfixed dyes, organic dyes
Disperse Polyester Carriers, reducing agent, organic acids
1:2 Metal complex dyes Wool Metals, organic acids
(Types of Pollutants associated with various Dyes)

Types of Pollutants

  • Air pollutants: The major air pollutants from dye manufacturing units include:
    • Volatile organic compounds (VOCs)
    • Nitrogen oxides (NOx)
    • Hydrogen chloride (Hcl)
    • Sulphur oxides (Sox)

  • Liquid Pollutants: They are the effluents results from batch operation as the equipment is cleaned and they usually contain toxic organic residues. The following table illustrates the parameters of liquid effluents.

    Effluents from Dye Manufacturing mg/ltr(except for pH)
    Max Value
    PH 6-9
    BOD 30
    COD 150
    TSS 50
    Oil and Grease 10
    Phenol 0.5
    Copper 0.5
    Zinc 2
    Aox 1

  • Solid wastes: They include iron sludge, gypsum and sludge from treatment facilities.
Controlling Pollution

It is a good omen that Dye manufacturers and dyeing units have finally recognised the profoundity of the environmental impact of using dyes. Brainstorming in this direction has led to the development of new dyes that has:
  • Lower toxicity.
  • Much improved levelling and exhaust characteristics.
  • Narrower quality tolerances.
Improvements in Dyes: Following developments shows the keenness of Dye manufacturers towards environment. Although these dyes may be a bit expensive, but considering the potential long term savings made from efficient dye use and a lower effluent cost. It is worth every penny.
  • Development of fiber-reactive dyes for fibers like cellulosics, that has stable fixation rates without regard to variations in dyeing conditions, like liquor ratio, quantities of salt or alkali temperature, time etc.
  • Metal-free reactive dyes that has high fixation rates along with minimum salt consumption.
  • Low-sulphide or even sulphide-free dyes.
  • Formulating granular dyestuff that are easy to handle and dissolve and that reduces dust generation.
  • The gradual withdrawal and newer replacement for azo-dyestuffs that are threat as a potential carcinogenic.
  • Researches made into dyestuffs with biodegradable formulating agents.
Improvement in Dyeing units: The dyeing units are also not left behind when it comes to addressing the problem of controlling pollution. Some of this effective steps are highlighted below.
  • Effective recycle of cone-dye cooling water.
  • Air conditioning system water is recycled.
  • Disseminating knowledge to workers for proper utilization of water and power consumption.
  • Installation of screens in drain lines that reduces the solid particles in effluents.
  • Proper implementation of a maintenance plan for steam traps.
  • Digital monitoring systems for use in boilers.

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