The present investigation shows that the agricultural by-products like bengal gram husk, tur dal husk, and tamarind husk can be used as an effective adsorbent in the adsorption of dyes. Adsorption dynamics, isotherms, pH effect and adsorbent dosage on the removal of dyes for all the adsorbates were examined. In addition desorption of the dyes from the loaded adsorbents were also carried out.

The uptake of dyes increased with increase in the agitation time till the equilibrium was reached. At any contact time, increase in initial adsorbate concentration decreased the percent adsorption and increased the amount of adsorbate uptake (q) per unit weight of the adsorbent.

The effect of adsorbent dosage on the adsorption of dyes showed that the percentage of dye removed increased with increase in adsorbent dosage due to increased adsorption surface area. For all the adsorbents studied adsorbent dosage of 1g – 2g/L was sufficient for adsorption of 90% of the initial dye concentration.

Irrespective of the type of the adsorbent, the optimum pH for the removal of methylene was 6-11; rhodamine B - 7-11. Amaranth and fast green, both anionic dyes were absorbed at pH 2.0. The amount of the dye removed at optimum pH increased with increase in initial dye concentration but the percentage absorbed decreased with increase in initial dye concentration.

Adsorption data for wide ranges of adsorbate concentrations and adsorbent doses were treated by Langmuir and Freundlich isotherms. All the adsorbents and adsorbates followed the Langmuir and Freundlich isotherms. Comparison of the adsorption capacity of the four adsorbents with that cited in literature reveals that bengal gram husk, tur dal husk and tamarind husk had a higher biosorption capcity than the adsorbents reported in literature.

Values of the equilibrium parameter (R_L) from Langmuir isotherm and n values from the Freundlich isotherm indicate that the adsorption process is favorable for all the dyes. The equilibrium data also fit well with the Freundlich adsorption isotherm for all the adsorbents and adsorbates (dyes) studied.

The Lagergren rate constant of absorption for different concentrations for the dyes by the adsorbents used in the study are generally in the range of 9.00 X 10^-3 to 1.03 x 10^-1 L/min.

Desorption and regeneration studies of the adsorbates showed that regeneration and recovery of the adsorbates is possible. Chemisorption/ion exchange was the main mechanism by which the adsorbates (dyes) were attached to the adsorbents. Physical adsorption played a minimal role in the process. Since about 85% of dyes and 70 % of the dyes still remained on sorbents, it indicates that most of dyes are able to form strong bonds with the adsorbents.

The infrared spectral analysis of the adsorbents showed that Carbon bonded with hydrogen and oxygen atoms played a major role in the adsorption of dyes. The absorption spectra revealed that –C-O, C-N and C=O bonds were predominant in the surface of the adsorbents and played a major role in the adsorption process.

The analysis of the carbon, hydrogen and nitrogen content of the husk, showed relatively low percentage of nitrogen, revealing the low content of protein in the adsorbents. This is advantageous over the protein rich algal and fungal biomass projected as dye biosorbents, since proteinious materials are likely to putrefy under moist conditions. Further, most dye sorption reported in literature is based on algal and fungal biomass, which must be cultured, collected from their natural habitats and pre-processed, if available as discards and transported under special conditions, thus introducing the factor of additional costs. In contrast, BGH, TDH, TH and CH as agro-industrial wastes have negligible cost and have also proved to be an efficient biosorbent for the removal of dyes. Furthermore, these adsorbed dyes can be easily desorbed and the biomass be incinerated for final disposal. These biosorbents are of low cost; its utility will be economical and can be viewed as a part of a feasible waste management strategy.