Biosorption characteristics of unicellular green alga Chlorella sorokiniana immobilized in loofa sponge for removal of Cr(III).

Loofa sponge (LS) immobilized biomass of Chlorella sorokiniana (LSIBCS), isolated from industrial wastewater, was investigated as a new biosorbent for the removal of Cr(III) from aqueous solution. A comparison of the biosorption of Cr(III) by LSIBCS and free biomass of C. sorokiniana (FBCS) from 10-300 mg Cr(III)/L aqueous solutions showed an increase in uptake of 17.79% when the microalgal biomass was immobilized onto loofa sponge. Maximum biosorption capacity for LSIBCS and FBCS was found to be 69.26 and 58.80 mg Cr(III)/g biosorbent, respectively, whereas the amount of Cr(III) ions adsorbed onto naked LS was 4.97 mg/g. The kinetics of Cr(III) biosorption was extremely rapid and equilibrium was established in about 15 and 20 min by LSIBCS and FBCS, respectively. The biosorption equilibrium was well defined by Langmuir adsorption isotherm model. The biosorption kinetics followed the pseudo-second order kinetic model. The biosorption was found to be pH dependent and the maximum sorption occurred at the solution pH 4.0. Desorption studies showed that 98% of the adsorbed Cr(III) could be desorbed with 0.1 mol/L HNO3, while other desorbing agents were less effective in the order: EDTA > H2SO4 > CH3COOH > HCl. The regenerated LSIBCS retained 92.68% of the initial Cr(lII) binding capacity up to five cycles of reuse in continuous flow-fixed bed columns. The study revealed that LSIBCS could be used as an effective biosorbent for the removal of Cr(III) from wastewater.