Introduction

In developing countries like India, industries cannot afford to use conventional wastewater treatment chemicals like alum, ferric chloride, polymer flocculants and coal based activated carbon as they are not cost-effective. An inexpensive and more easily available adsorbent would make the removal of pollutants an economically viable alternative. Agricultural wastes like tamarind pod shells are discarded in the agricultural sector in India. Disposal of agricultural by-products is currently a major economic and ecological issue, and the conversion of by-products to adsorbents, represents a possible alternative. Dyes are used extensively in industries including textiles, paper and leather. The effluents emanating from these industries are often highly coloured, and the disposal of their wastes into the environment can be extremely undesirable. Once in the environment, they may show toxic and genotoxic effects toward organisms (Yesilada et al. 2003). Dyes are usually of synthetic origin, with complex aromatic molecular structures, making them very stable and difficult to biodegrade (Aksu 2005). In particular, printing and dyeing unit wastewaters contain several types of coloring Several research works has been performed to search for efficient and low-cost materials to remove methylene blue and other basic dyes from aqueous solution, including rice husk (Vadivelan and Kumar 2005) beech sawdust (Batzias and Sidiras 2004), agroindustry wastes (Garg et al. 2004) and activated carbon from date pits (Abdulkarim et al. 2002). However, as the adsorption capacities of the above adsorbents are not large, new absorbents are still under development. The main focus of this study was to evaluate the biosorption capacity of a novel, low cost, and renewable biomass, tamarind pod shells for the removal of Methylene blue and Amaranth as model compounds for anionic and cationic dyes. In a tropical country like India, tamarind pod shell is found in plenty and is discarded as waste, as they have very less calorific value. The effects of pH, contact time, initial dye concentration and biomass dosage on the biosorption capacity were investigated. Moreover, kinetic and equilibrium models were used to fit the experimental data.