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Waste waters generated at various stages of textile dyeing, differ in composition , strength and volume. There pollution load is high and they arise mostly from spent dye bath that are principally composed of
dyes (mainly unexhausted, hydrolyzed and surface deposited dyes), dispersing agents, surfactants, electrolytes, acids, alkalis, etc., which are unexhausted and have been washed away from the dyed material.
These effluents are characterized by their intense color, high chemical oxygen demand (COD), salinity and fluctuating pH.
Of all the waste, color is the first contaminant to be recognized because of its visibility to human eye. The discharge of highly colored water is not only aesthetically displeasing, but also interferes with
the transmission of light. This upsets the biological processes and the productivity in the receiving streams. In addition, many colorants are harmful to certain organisms and may cause direct destruction of aquatic communities. Color
hinders the penetration of sunlight which is very much essential for the photosynthesis by marine plants. Even the discharge of highly colored waste water from city sewer has its damaging effect.
From environmental protection point of view, color removal becomes an integral part of textile effluent treatment prior to its discharge to the environment for reuse. Normally de-colorization methods are divided
into four sub groups:
- Chemical methods
- Physico-Chemical methods
- Physical Methods
- Biological Methods
Among the four methods, chemical method is one of the popular method and directly or indirectly be means of some chemical reactions, it is responsible for removing dye from waste water. Chemical methods
consists of the following processes:
- Oxidation
- Reduction
- Photolytic Treatment
- Electro Chemical Treatment
- Flocculation/Coagulation
- Fenton Reagent process.
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