Bioremoval of cadmium from aqueous solution by black gram husk (Cicer arientinum)

Husk of black gram (Cicer arientinum), a waste of no commercial value, was investigated as a new biosorbent of cadmium from low concentration aqueous solutions. With 99.99% sorption efficiency from 10 mg l^-1 cadmium solution, the biomass required at saturation was 0.8 g mg^-1 cadmium. Biosorption was rapid and equilibrium was achieved in 30 min. Among the various desorbing agents tested, 99.89% cadmium recovery was achieved with 0.1 M HCl. Sorption efficiency of cadmium during six biosorption–desorption cycles in batch operations declined, which was traceable to 39.0% black gram husk (bgh) weight loss. This decline was only 9.71% when compensated for biomass loss, which is comparable to 10.45% decline during six cycles in fixed bed column bioreactor in which biomass loss was only 5.98%. On plotting breakthrough curves it was noted that bgh in the fixed bed column was capable of bringing down cadmium concentration from 10 to 0.1 mg l^-1 in 35.5 l volume. Biosorption of cadmium was not effected in the presence of other cations. Comprehensive characterization of parameters indicate bgh to be an excellent material for biosorption of cadmium to treat wastewaters containing low concentration of the metal. As an agrowaste, the advantage of application of this material as a metal biosorbent in a fixed bed column bioreactor system, in comparison with those based on immobilized algae or biomass of algal, fungal and bacterial origin, is considered.