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  The major cause of the release of dyestuffs into the environment is by the
  discharge of aqueous effluents from industrial dyehouses rather than during
  the domestic dyeing process. Indeed, the amount of dye found in receiving
  waters (rivers, sewers etc) attributable to domestic dyes is probably
  insignificant compared to that from other domestic sources e.g. toilet flush
  blocks and fabric softeners. However, the small amount of dye attributable to
  domestic dyeing still has an environmental effect.

  Below are some relevant points :-

  1. The high level of colourfastness of modern dyestuffs to fabrics is such that
     losses to the environment after the actual dyeing process are negligible.

  2. Dyestuffs have generally low toxicity to fish and other aquatic lifeforms and
     do not tend to bioaccumulate over a period of time.

  3. The majority of dyestuffs have low toxicity to micro-organisms and do not
     generally interfere with the bacterial processes necessary, for instance,
     at water treatment plants.

  4. A recent paper has shown that any contamination of agricultural land with
     dyes has a negligible effect on crops.

  5. Biodegradability - To be of use, dyes must have a high degree of stability
     to chemical processes and light. Therefore, it is not surprising that they
     give poor results in short term tests for aerobic biodegradability. As a
     general guideline, no more than 20% of the dye is biodegradable in a
     standard OECD Aerobic test.

  Dyes are, however, prone to anaerobic degradation. The substantive nature
  of dyes is such that when they are discharged into receiving waters they
  are likely to be adsorbed onto suspended solids, which find their way into
  aquatic sediment. The anaerobic nature of the sediment is such that the
  dye is likely to be destroyed by reductive processes.

  The chemicals produced as a result of these reduction processes will
  themselves degrade easily to harmless substances.

  In summary, the likely fate of dyes released into the environment is
  adsorption onto solid sediment and destruction by anaerobic processes
  either in a land fill site or on the river bed. The products of this process
  are harmless to the environment.



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