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The bioreduction of soluble hexavalent uranium (U(VI)) to insoluble tetravalent uranium (U(IV)) is an attractive bioremediation strategy for the clean-up of contaminated groundwater. High levels of the common occurring co-contaminant, nitrate (NO3(-)), can potentially interfere with uranium bioremediation. In this study, treatment of a synthetic groundwater containing a mixture of NO3(-) and U(VI) was investigated in a sulfur-limestone autotrophic denitrifying (SLAD) bioreactor that was coupled in series with a bioreactor packed with zero-valent iron (Fe(0), ZVI) and sand. An additional aim of the study was to explore the possible role of biological activity in enhancing the reduction of U(VI) by Fe(0). The SLAD reactor removed NO3(-) efficiently (99.8%) at loadings of up to 20 mmol NO3(-) L(r)(-1) d(-1), with near stoichiometric conversion to benign dinitrogen gas (N(2)). The ZVI bioreactor subsequently removed uranium (99.8%) at high (0.22 mM) and low (0.02 mM) influent concentrations of the radionuclide. Aqueous uranium was reliably eliminated to below the maximum contaminant level of 30 µg L(-1) (0.13 µM) when the ZVI reactor was operated at average empty bed hydraulic retention times as low as 2.3 h, demonstrating the feasibility of the sequential treatment strategy in packed bed bioreactors. Sequential extraction of the ZVI reactor packing confirmed that uranium was immobilized as U(IV). Uranium removal was enhanced by microbial activity as confirmed by the increased rate of uranium removal in batch assays inoculated with effluent from the ZVI bioreactor and spiked with Fe(0) compared to abiotic controls.

-Liquid-liquid extraction using aqueous two-phase systems is a highly efficient technique for separation and purification of biomolecules due to the mild properties of both liquid phases. Reliable data on the phase behavior of these systems are essential for the design and operation of new separation processes; several authors reported phase diagrams for polymer-polymer systems, but data on polymer-salt systems are still relatively scarce. In this work, experimental liquid-liquid equilibrium data on water + polyethylene glycol 8000 + magnesium sulfate and water + polyethylene glycol 8000 + sodium sulfate aqueous two-phase systems were obtained at 35°C. Both equilibrium phases were analyzed by lyophilization and ashing. Experimental results were correlated with a mass-fraction-based NRTL activity coefficient model. New interaction parameters were estimated with the Simplex method. The mean deviations between the experimental and calculated compositions in both equilibrium phases is about 2%.

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