BACKGROUND Mycobacterium sp. biomass was used for removal of Cr(III) and Cr(VI) species from aqueous systems. Experimental results were processed with different kinetic, isotherm and thermodynamic models. Studies of the effect of co-ions, biomass characterization and desorption were also undertaken. RESULTS Cr(III) and Cr(VI) sorption on Mycobacterium sp. biomass followed Ho pseudo-second-order kinetics. The Langmuir isotherm model described the biosorption of both chromium species, whereas the Temkin isotherm model for Cr(III) and Hill-der Boer isotherm model for Cr(VI), respectively. Selectivity for Cr(III) and Cr(VI) biosorption was observed in binary mixtures with As(V), Mg+2, Ca+2, Cl-, SO4-2, CO3-2 and PO4-3 ions from 5 to 200 mg L-1 and with Cu+2, Ni+2, Co+2, Cd+2, Mn+2 and Zn+2 ions up to 20 and 50 mg L-1 for Cr(III) and Cr(VI) respectively. In multi-ions systems, selectivity of both chromium species was achieved at a concentration of co-ions up to 10 mg L-1. The thermodynamic parameters indicated the spontaneous and feasible nature of biosorption processes. Amine and carboxylic groups are mainly responsible in both chromium species binding, and the phosphate group is also involved in Cr(VI) sorption. Mycobacterium biomass exhibited almost the same removal efficiency up to five subsequent biosorption-desorption cycles for the two chromium species. CONCLUSION Mycobacterium sp. biomass can be used as efficient and economic biomass for removal of both chromium species from contaminated water. (c) 2013 Society of Chemical Industry