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:

(Types of Pollutants associated with various Dyes)

• 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) Parameter	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.

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.