بررسي ميزان حذف كادميوم از آب به وسيله توده باكتريايي در فيلتر سيليسي بيولوژيكي

Background and purpose: Studies show that surface or subsurface water in some areas near to the pollutant sources, to an extent higher than the permisible potable limit are contaminated with cadmium. There are different reports about biological absorption of cadmium in high concentrations (present in industrial effluents) by bacterial biomass, but there is less report about removing of low concentrations cadmium (present in the contaminated water resources) with the above mentioned method. Aim of this study was to determine cadmium adsorption isotopes (0.2 to 5 mg/liter) by bacterial biomass, pH effects, biomass concentration on absorption isoterms, and also to determine efficiency rate of silicious containig column having adhered biomass to remove cadminum from water. Materials and methods: Cadmium absorption isoterms determined by biomass at different pH, corresponded ASTM method. Effect of biomass concentration on the rate of cadmium absorption on the unit of biomass weight (q), rate of cadmium absorption by fresh and nonfresh biomass, and also rate of cadmium deabsorption from biomass due to contact with distilled water were determined_ Breakthrough curves related to the water containing cadmium for concentration of 0.5 mg/liter at em ply bed contact time (EBCT) for 15 and 30 minutes was plotted. Results : With increase in initial concentration of cadmium, rate of its absorption on the weight unit of biomass (q) was high, but removing efficiency declined. Absorption of cadmium on bacterial biomass corresponded the first grade synthetic equilibrium. With increase in concentration of biomass, absorption rate of cadmium on the weight unit of biomass (q) declined. Increase in pH caused acceleration of cadmium absorption. Rates of cadmium absorption by fresh biomass and non fresh biomass were nearly the same. Rate of cadmium absorption from biomass due to contact with distilled water was obtained. For 0.5 mg/liter concentration of cadmium, at the remaining times of 15 and 30 minuts. of breakthrough after passing of water were 40 and 85 folds volum of empty bed respectively. Conclusion: Cadmium absorption by biomass is generaly physical and corresponds the first grade synthetic.