The effluent treatment in developing countries is expensive and major cost is associated with the dependence on imported technologies and chemicals. The indigenous production of treatment techniques and chemicals locally, or use locally available non-conventional materials to treat pollutants seems to be the solution to the increasing problem of treatment of effluents. In this regard, there has been a focus on the use of appropriate low cost technology for the treatment of wastewater in developing countries in recent years. Technically feasible and economically viable pretreatment procedures with suitable biomaterials based on better understanding of the metal biosorbent mechanism(s) are gaining importance. Activated carbons of agricultural waste products as low cost adsorbents have been reported till now. However, there is an additional cost involved in the processing of the agricultural wastes to convet the same to activated carbon, which is posing economic difficulties necessitating research on alternate adsorbents with equivalent potential of activated carbon.

The objective of the present study was to find out the adsorption capacity of the four husks namely Tur dal (Cajanus cajan) husk (TDH); bengal gram husk (BGH), seed coat of Cicer arientinum; coffee (Coffee arabica) husk (CH) and tamarind (Tamarindus indica) pod shells (TH) for the removal of dyes from aqueous solutions so as to facilitate comparison with other adsorbents and provide a sound basis for further modification of the adsorbent to improve its efficiency.

The four adsorbents chosen for the present study is available in plenty in tropical regions. Adsorption properties of these adsorbents have not yet been reported in literature. The four dyes chosen are methylene blue, rhodamine B, fast green and amaranth.

The dyes like Trisodium 2-hydroxy-1-(4-sulphonato-1-naphthylazo) naphthalene-3,6-disulphonate (Amaranth) are widely used for colouring textiles, paper, phenol-formaldehye resins, wood and leather. These dyes were also employed as food additives in jams, jellies, ketchup and cake decoration before its legal prohibition to use as colouring agent for food and beverages. It has now been well proved that higher concentration of these dyes can adversely affect human/animal health and can cause tumour, allergic and respiratory problems. There are also some evidences, which suggest that it may also cause birth defects. They are all water-soluble dyes with high solubility and thus difficult to remove by common chemical treatments.

Keeping these environmental, ecological and societal health issues in view, it is considered necessary to attempt and provide an easy, feasible, economical and reliable method for the removal of dyes. Hence, adsorption by locally available, environmentally-friendly and cost effective adsorbents have been explored and exploited.

The objective is achieved through:

1. Characterisation of the adsorbents for their carbon, nitrogen and sulphur content
2. Characterisation of functional groups on the surface of the adsorbent that contributes to the biosorption of dyes used in the present study through infrared spectroscopy.
3. Determination of the agitation/equilibrium time, pH and effect of adsorbent at different initial dye concentrations.
4. Calculation of the adsorption capacity and intensity using Langmuir and Freundlich isotherm models,
5. Desorption of dyes from dye loaded adsorbents to determine the mechanism of adsorption.
6. Comparison between the adsorbents for their adsorption capacity with those found in literature.