Immobilization of Saccharomyces cerevisiae on a natural zeolite for the biosorption of radioisotopes

In recent years, intensive attempts have been made to remove toxic heavy metals and radionuclides from wastewater. Uranium is one of the most threatening elements due to its radioactivity and high toxicity. Significant amounts of uranium are released into the environment throughout the nuclear fuel cycle. Biosorption technology offers advantages such as low operating cost and high efficiency for metal removal from aqueous solutions. In this work, the sorption of uranyl ions from aqueous solutions by Saccharomyces Cerevisiae (SC) as free cells and in immobilized form on zeolite clinoptilolite was investigated. First, a characterization of the natural zeolite was carried out by classical chemical analysis, XRD, FTIR and TG/DTG, and then the influence of solution pH, temperature, contact time and initial concentration on uranyl sorption was investigated. The concentration range of uranyl in the solution was between 0.02 and 1 mmol L-1, which was determined by the inductively coupled plasma optical emission spectrometry (ICP-OES) method. Genetic algorithm and mathematical steps were applied to the membrane bioreactor (MBR) and the results showed that the experimental data matched well with the logistic model. In addition, the immobilization yeast cells of 17.1 × 108 cells ml-1 concentration on clinoptilolite was optimized and observed using a scanning electron microscope (SEM). More results demonstrated that metal binding was carried out extracellularly at the cell wall surface and the rate of uranyl ion sorption by free yeast cells of SC is rapid. The equilibrium adsorption ratio for all samples was calculated, and it was showed that the points corresponding to initial concentrations lower than about 0.1 mmol L-1 have a higher and closer absorption fraction. Moreover, at concentrations higher than 0.2 mmol L-1, the adsorption rate decreases compared to lower concentrations.