Abstract:
Dyes and Dye Intermediates industry is an important sector of the Indian Chemical Industry. The Indian companies together account for around 6.6 % of the world production. Dyes and pigments are widely used in textile, leather, paper, plastic, food and other industries. India produces 64,000 tonnes of dyes, 2 percent of which - 7,040 tonnes are directly discharged into the environment.
Discharging large amount of dyes into water resources, accompanied by organics, bleaches, and salts, can affect the physical and chemical properties of fresh water. The colour of the effluent discharged into receiving waters affects the aquatic flora and fauna, and causes many water borne diseases. Many dyes and pigments have toxic as well as carcinogenic, mutagenic and teratogenic effects on aquatic life and also on humans. The dyes are, generally, stable to light, oxidizing agents and heat, and their presence in wastewaters offers considerable resistance to their biodegradation, and thus upsetting aquatic life. Ludhiana, Panipat, Pali, Bichchri, Patancheru, Jetpur, Ahmedabad, Surat and Tirupur are some of the country's most polluted zones.
Various treatment processes used for the removal of dyes from the waste water include adsorption, coagulation and sedimentation, chemical oxidation, photochemical, electrochemical technique, chlorination, ozonation, irradiation, ion exchange, reverse osmosis, membrane separation, biological treatment, etc. Adsorption is the best available techniques for the removal of dyes from the waste water which is economically feasible. Variety of adsorbents are available which can be utilized for treatment of dye bearing wastewater. Usually activated carbon is used for adsorption. But due to its high cost there is need of low cost adsorbent. During recent years large numbers of low cost adsorbents have been investigated.
