Biosorption and bioreduction of Cr(VI) by a microalgal isolate, Chlorella miniata

The ability and mechanism of a microalgal isolate, Chlorella miniata to remove Cr(VI) were investigated. Kinetic studies indicated that both biosorption and bioreduction were involved in the Cr(VI) removal. The adsorbed Cr(VI) was reduced to Cr(III), and desorption studies indicated that Cr(III) occupied most of the adsorption sites on the biomass. The equilibrium time for Cr(VI) removal was dependent on various factors including initial pH, biomass and Cr(VI) concentrations. Equilibrium study showed that the Cr(VI) removal capacity was negatively related to the initial pH, and the biosorption capacity of total Cr [Cr(III) and Cr(VI)] reached the maximum at initial pH of 3.0. The spectrum of Fourier Transform Infrared Spectrometer analysis (FTIR) further confirmed that amino group on the algal biomass was the main adsorption site for Cr(VI) biosorption in acidic pH while the reduced Cr(III) was mainly sequestered by carboxylate group. The comparison between biosorption-bioreduction and direct bioreduction kinetic models proved that biosorption of Cr(VI) was the first step, followed by Cr(VI) bioreduction and Cr(III) biosorption on the algal biomass.