REMOVAL OF CHROMIUM (VI) IONS BY USING BIOFILM-BIOMASS OF YARROWIA LIPOLYTICA

摘要

Biofilm formation by two marine strains of Yarrowia lipolytica (NCIM 3590 and NCIM 3589) in the presence or absence of Cr (VI) ions was compared. The morphology of the yeast biofilms under stress of metal ions was studied by scanning electron microscope (SEM) and light microscope observations. Biofilm-mediated removal of Cr (VI) ions from aqueous solutions with respect to pH, temperature, biomass, contact time and initial concentration of metal ions was studied. Maximum Cr (VI) biosorption was observed at pH 2.0 and at a temperature of 35°C. Increase in biomass resulted in a decreased metal uptake. With an agitation speed of 130 rpm, equilibrium was observed within 2 h. Under optimum conditions, biosorption was enhanced with increasing concentrations of Cr (VI) ions. Biofilm-biomass of NCIM 3590 and NCIM 3589 displayed specific uptake values of 500 ± 5.53 mg/g and 424 ± 5.3 mg/g at 500 ppm, respectively. The adsorption data fitted well to the Langmuir, Freundlich isotherms and followed the pseudo-second-order kinetics. The surface sequestration of Cr (VI) by Y. lipolytica was confirmed by SEM-energy dispersive spectrometer (SEM-EDS) observations. Presence of metal ions was also demonstrated by a transmission electron microscope (TEM). Fourier transform infrared (FTIR) spectroscopy revealed the involvement of different functional groups such as hydroxyl, carboxyl, and amide groups on the yeast cell surfaces in Cr (VI) binding.