Removal of cadmium(II) ions using Saccharomyces cerevisiae and Leuconostoc mesenteroides immobilized in silica materials by two processing methods

Abstract

Two processing methods for preparation of microbial biomass-silica biosorbent to remove cadmium ions from aqueous solution were developed. The first method involved a slow addition of sulphuric acid into previously prepared dispersion of viable Saccharomyces cerevisiae or Leuconostoc mesenteroides biomass in sodium silicate solution. The obtained material was mesoporous with irregular shape and size between 1 and 10 μm. The second method for the immobilization of microbial biomass by silica gel entrapment was developed in order to restrict desorption of microbial cells and to obtain larger particles with uniform size. The obtained particles were spherical with average particle size of 1.5 mm. Both materials with viable L. mesenteroides cells displayed higher removal efficiency compared the efficiency of materials that containing viable S. cerevisiae cells. Infrared spectra revealed an intensive secretion of dextran by Leuconostoc mesenteoides cells in the presence of cadmium ions. EDS maps clearly showed the dispersion of cadmium in the cross-section of microbial biomass-silica biosorbent. The maximum theoretical binding adsorption capacity for the silica-alginate-S. cerevisiae composite was 54 mg/g. The adsorption capacity for the silica-alginate-L. mesenteroides composite obtained after 24 cycles was about 93 mg/g. The extracellular secretion of dextran by L. mesenteroides cells immobilized in silica-alginate composite enabled efficient removal of cadmium ions. The efficiency of Cd(II) removal by microbial composite was not affected by the presence of co-existing ions at initial cadmium concentration of 1 and 4 mmol/L.