Evaluation of the biosequestering potential of in the removal of hexavalent chromium from aqueous solution: batch and continuous flow fixed-bed column bioreactor studies

In this study, the adsorption capacity of free and loofa sponge-entrapped microalga Kirchneriella contorta to remove Cr/sup 6+/ from aqueous solution was investigated. This is the first reported study of biosorption by K. contorta. The effects of the experimental conditions, such as pH, initial Cr/sup 6+/ concentration, sorbent-sorbate contact time, and quantity of sorbent mass, on Cr/sup 6+/ removal efficiency were studied. The Cr/sup 6+/ sorption on K. contorta was found to be highly pH dependent and the maximum uptake capacity was achieved at pH 1.0. The adsorption isotherms study showed the maximum sorption capacity of the loofa sponge-immobilized biomass of K. contorta (LIBKC) of 100.84 mg g/sup -1/, which was much higher than 80.61 mg g/sup -1/ of the free biomass of K. contorta (FBKC). The adsorption equilibrium data showed a better fit on the monolayer Langmuir adsorption isotherms model with the regression coefficient (r/sup 2/) greater than 0.99 for both FBKC and LIBKC. The rate of Cr/sup 6+/removal followed the pseudo second-order kinetics equation. The LIBKC on treatment with NaOH resulted in 97% Cr/sup 6+/ recovery and its complete regeneration. The regenerated LIBKC was reused in five repeated cycles without appreciable loss of its metal sorption ability. The potential of LIBKC in a fixed-bed continuous flow column bioreactor for the sorption of Cr/sup 6+/ from the metal contaminated water was also investigated. (author)