Cr(VI) Bioremediation Using Rhodotorula mucilaginosa Residual Biomass: An Innovative and Sustainable Approach

The residual biomass of Rhodotorula mucilaginosa RCL11, obtained post-carotenoid extraction, was evaluated as a biosorbent for Cr(VI). Three biomass preparations were assessed: chemically treated biomass (post-extraction), heat-inactivated biomass, and untreated biomass. Using 4 g/l of biomass, complete removal of 26 μg/ml Cr(VI) was achieved within 48 h, and 52 μg/ml was removed in 168 h. Chemically treated biomass exhibited the highest efficiency, achieving up to 60% Cr(VI) removal in 48 h. Analytical methods confirmed that chromium adsorption primarily occurred on the cell surface, initiating immediately upon contact, with adsorption efficiency influenced by increased biomass concentration, acidic pH, and prolonged contact time. The findings indicated that the Cr(VI) biosorption fitted the pseudo-second-order as high coefficient of determination values were achieved compared to the pseudo-first-order kinetic model. Vibrational spectroscopy analysis revealed interactions between metals and microbial cells, confirming the binding of hexavalent chromium and highlighting a strong biosorption mechanism. This study demonstrates that R. mucilaginosa RCL11 biomass, particularly following chemical treatment, acts as an effective, sustainable biosorbent for Cr(VI) remediation. These findings support the use of industrial residual yeast biomass as a cost-effective bioremediation strategy, integrating waste management with biorefinery applications.