USE OF IMMOBILIZED BIOFILM OF CITROBACTER SP FOR THE REMOVAL OF URANIUM AND LEAD FROM AQUEOUS FLOWS

Under appropriate growth conditions with suitable support a Citrobacter sp. formed a cohesive biofilm. When subsequently challenged with soluble lead or uranium much of the metal was accumulated, comparable to that of polyacrylamide immobilized cells, with metal deposition visually apparent. Metal uptake occurs via phosphatase mediated cleavage of organic phosphate to precipitate liberated HPO//4**2** minus as insoluble metal phosphate. Both types of immobilized cell liberated comparable amounts of HPO//4**2** minus from metal-free flows, but uranium accumulation was less than that observed for lead. Full potential to accumulate U was attained only after storage of the cells prior to U exposure, while maximum Pb accumulation and HPO//4**2** minus liberation occurred with freshly harvested and stored cells. These findings are discussed.