Bioaccumulation of 137Cs by Immobilized Bacterial Species Isolated from Radioactive Wastewater

摘要

The increases of environmental concern over the accumulation of the long term impact radioactive nuclides e.g. 137Cs encourage the isolation of bacterial species resistant to radioactive nuclides and could accumulate such nuclides. Bacterial species isolated from hazardous liquid wastes at Hot Laboratories Centre were investigated for their removal of 137Cs from waste solutions. The biosorption capacities of the free and immobilized biomass were studied using batch experiments at optimum conditions. Different immobilization matrices namely; calcium alginate (CA), chitosan (CTS), chitosan-alginate (CTS/CA) and polyvinyl alcohol-alginate (PVA/CA) were examined for use in the biosorption system. The effects of the immobilized weight, beads numbers and initial 137Cs activity on the removal efficiency were studied. Although, the results indicated that control CA and PVA/CA gel beads had nearly the same and the higher removal efficiency, the CA-immobilized beads showed higher removal percent than that of PVA/CA-immobilized beads. The immobilized system achieved maximum biosorption capacities at 137Cs solution activity of 15000 Bq/ml, where 62.2, 66.5 and 46.9 KBq/g dry weight were removed by CA and CA-immobilized Bacillus pumilus and Bacillus licheniformis beads, respectively. Reused experiments for the control CA and CA- immobilized bacteria beads were studied for three cycles. The elution percent increased after the second cycle followed by increase in the removal percent. The studied CA-immobilized system could be used for more than one cycle with removal efficiency of about 50 % of the first cycle.