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Green means clean: biomass and metal accumulation
Abstract
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Metal removal by seven strains of Bacillus and Micrococcus was investigated. The culture age of the cells had little or no effect on their sorption capacity. Using the Langmuir isotherm, it was possible to determine that Bacillus subtilis ATCC 6633 had the highest maximum sorption capacity for uranium while a Micrococcus sp. strain presented the highest affinity. pH of the solution affected the sorption of uranium, copper, cadmium and zinc by B. subtilis. Hydrochloric acid was effective for desorption of uranium from pre‐loaded biomass. The presence of other ion inhibited uranium sorption in the following order: Cu2+>Zn2+>Mg2+Cd2+>Ca2+>K+.
Abstract The viscous nature of fermentation broths has a marked effect on many parameters and process conditions within the bioreactor, often resulting in changes in microbial behavior and product formation. Although fermentation processes that involve significant changes in broth rheology have attracted much research interest, significant problems still remain. Particular difficulties remain in relation to processes where the broth develops pronounced non-Newtonian characteristics. This article reviews some of the models developed to describe these fermentation fluids and their limitations; the bioreactor types employed and their mode of operation; the problems encountered because of the nature of the fluids, for example, monitoring and control; and the gradients found in such systems. To illustrate the above, four specific processes are described in detail — the production of filamentous biomass (SCP) and three extracellular microbial polysaccharides, xanthan, pullulan, and scleroglucan.
A novel biosorbent from Azolla filiculoides was used in fixed-bed sorption columns and allowed quantitative determination of the characteristic process parameters which could then be used for performance comparison and process design. An zinc sorption capacity of 31.3mg/g predicted at a flow rate 480ml/h and pH 6.2, closely corresponded to the value observed. Lowering the influent pH to 4, the influent Zn2+ concentration to 50mg/l and increasing the flow rate to 800ml/h (residence time: 2.6 min), resulted in decreased sorption capacities by 15.3, 7.7 and 9.6%, respectively.
Biomass from several fungal species removed thorium from solution in 1M HNO(3), pH 0-1. Thorium uptake was saturable with increasing thorium concentration, although the equilibria did not correspond to a simple ad sorption isotherm. Thorium uptake was altered by the biomass concentration, the uptake per unit biomass being reduced at high biomass concentrations. The presence of Al(3+) and Fe(3+) only slightly inhibited uptake of thorium while Ca(2+), Mg(2+), and Na(+) had no effect. Thus fungal biomass appears capable of removing thorium from solution under chemical conditions existing in acid waste liquors. Thorium uptake was increased by pretreatment using detergent and also, in the case of filamentous fungi, varied with the culture conditions, which implies that the thorium uptake characteristics of fungal biomass are able to be manipulated by these or similar means for optimum performance.