377 research outputs found

    Radionuclide Leaching from Residual Soils: Screening Study

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    Four soil samples, collected from a National Priorities Listed site contaminated with uranium, thorium, and radium, were leached for two, seven, and 30 days. The nonleached soils, leached soils, and leachates were analyzed using gamma spectroscopy, alpha spectroscopy, and delayed neutron activation. Unleached and leached soils had low radionuclide activities, and four different leaching solutions had no significant observable effect upon the resulting leachate activity. Three of the soils produced leachates with uranium activities below the expected primary drinking water standard of 30 Āµg/L for uranium, but the leachate from the fourth soil had an unacceptably high concentration of uranium (653 Āµg/L) despite the low activity of the original, unleached soil. Distribution coefficients calculated for uranium ranged from 100 to 12,000 mL/g, while distribution coefficients for 226Ra, 228Ra, 228Th, 137Cs, and 40K ranged from 1 to 20 mL/g. The uranium distribution coefficient was strongly correlated to the leachate alkalinity, suggesting that conditions resulting in high alkalinity yield a high potential to leach uranium

    Mass Transfer and Benzene Removal from Air using Latex Rubber Tubing and a Hollow-Fiber Membrane Module

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    A Dense-Phase Latex Rubber Tube and a Polyporous Propylene Hollow-Fiber Membrane Module (HFMM) Were Investigated for Control of Benzene-Contaminated Gas Streams. the Abiotic Mass Flux Observed through the Latex Tube Was 3.9-13 Mg/(MinĀ·m2) for 150 Ppm of Benzene at Various Gas and Liquid Flow Rates, While a 100-Fold Lower Mass Flux Was Observed in the HFMM. after Seeding with an Aromatic-Degrading Culture Enriched from Activated Sludge, the Observed Removal Was 80% of 150 Ppm, Corresponding to a Mass Flux of 45 Mg/(MinĀ·m2). the Observed Mass Flux through the HFMM during Biofiltration Also Rose, to 0.4 Mg/(MinĀ·m2). Because the HFMM Had a 50-Fold Higher Surface Area Than the Latex Tube, the Observed Benzene Removal Was 99.8%. Compared to Conventional Biofilters, the Two Reactors Had Modest Elimination Capacities, 2.5-18 G/(M3Ā·h) in the Latex Tube Membrane Bioreactor and 4.8-58 G/(M3Ā·h) in the HFMM. Although the HFMM Had a Higher Elimination Capacity, the Gas-Phase Pressure Drop Was Much Greater

    Thermal decomposition of vinyl- and allylsilane platinum(II) complexes and platinum(II)catalysed synthesis of (E),(E)-1,4-diphenyl-1,3-butadiene

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    Thermal stabilities of Pt(II) complexes: K[PtCl3(CH2=CHSiMe3)], K[PtCl3(CH2=CHCH2SiMe3)], K[(acac)PtCl(CH2=CHSiMe3)] and [PtCl(CH2=CHCH2SiMe3)]2, were examined. All complexes were found to be stable at room temperature but they decomposed without melting above about 90 oC. The allylsilane complex decomposed above about 125 oC. All complexes liberated chlorotrimethylsilane on decomposition, showing the facile cleavage of the C-Si bond by nucleophilic attack on the silicon by the chloride ion. (E),(E)-1,4-diphenyl-1,3-butadiene was stereoselectively synthesised in good yield from (E)-Ī²-styrylsilane in the presence of Zeiseā€™s salt.Ā KEY WORDS: Thermal analysis, Vinyl- and allylsilane platinum(II) Ļ€-complexes, Platinum(II) catalysed synthesis, (E),(E)-1,4-diphenyl-1,3-butadieneĀ Ā Bull. Chem. Soc. Ethiop. 2008, 22(3), 445-448

    Biological Fixed-Film Systems

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    The Microbiological Degradation of Wastewater and its Application using a Fixed-Film Reactor is Reviewed. the Technical and Technological Characteristics, as Well as the Efficiency of Nitrification and Denitrification Processes Were Taken into Consideration. the Review Elucidated the Experimental Measurements of Effective Diffusive Permeabilities and Effective Diffusion Coefficients of Biofilms

    Membrane Process for Biological Treatment of Contaminated Gas Streams

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    A Hollow Fiber Membrane Bioreactor Was Investigated for Control of Air Emissions of Biodegradable Volatile Organic Compounds (VOCs). in the Membrane Bioreactor, Gases Containing VOCs Pass through the Lumen of Microporous Hydrophobic Hollow Fiber Membranes. Soluble Compounds Diffuse through the Membrane Pores and Partition into a VOC Degrading Biofilm. the Hollow Fiber Membranes Serve as a Support for the Microbial Population and Provide a Large Surface Area for VOC and Oxygen Mass Transfer. Experiments Were Performed to Investigate the Effects of Toluene Loading Rate, Gas Residence Time, and Liquid Phase Turbulence on Toluene Removal in a Laboratory-Scale Membrane Bioreactor. Initial Acclimation of the Microbial Culture to Toluene Occurred over a Period of Nine Days, after Which a 70% Removal Efficiency Was Achieved at an Inlet Toluene Concentration of 200 Ppm and a Gas Residence Time of 1.8 S (Elimination Capacity of 20 G M-3 Min-1). at Higher Toluene Loading Rates, a Maximum Elimination Capacity of 42 G M-3 Min-1 Was Observed. in the Absence of a Biofilm (Abiotic Operation), Mass Transfer Rates Were Found to Increase with Increasing Liquid Recirculation Rates. Abiotic Mass Transfer Coefficients Could Be Estimated using a Correlation of Dimensionless Parameters Developed for Heat Transfer. Liquid Phase Recirculation Rate Had No Effect on Toluene Removal When the Biofilm Was Present, However. Three Models of the Reactor Were Created: A Numeric Model, a First-Order Flat Sheet Model, and a Zero-Order Flat Sheet Model. Only the Numeric Model Fit the Data Well, Although Removal Predicted as a Function of Gas Residence Time Disagreed Slightly with that Observed. a Modification in the Model to Account for Membrane Phase Resistance Resulted in an Underprediction of Removal. Sensitivity Analysis of the Numeric Model Indicated that Removal Was a Strong Function of the Liquid Phase Biomass Density and Biofilm Diffusion Coefficient, with Diffusion Rates Below 10-9 M2 S-1 Resulting in Decreased Removal Rates

    Permeation of Several Gases through Elastomers, with Emphasis on the Deuterium/hydrogen Pair

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    The Diffusion and Permeation Coefficients for He, H2, D2, O2, and N2 in a Variety of Elastomers Were Measured by Simple Manometric Methods. the Elastomers Studied Were Butyl Rubber; HypalonĀ® 40 and 45; VitonĀ® E60 and GF; HydrinĀ® 100 and Filled HydrinĀ® 100; KratonĀ® G, FG, and KG VTEOS; EPDM; Epoxidized Natural Rubber; and Neoprene. Consistent with Earlier Studies, Elastomers with Higher Glass Transition Temperatures Exhibited Lower Diffusion Coefficients. the Ratio of Diffusion Coefficients of the Hydrogen Isotope Pair Differed from the Purely Molecularā€weightā€based Prediction. Deuterium\u27s Slightly Smaller Size Relative to Hydrogen is Consistent with Observed Deviations from the Molecularā€weightā€based Diffusion Coefficient Ratio. Ā© 1993 John Wiley & Sons, Inc. Copyright Ā© 1993 John Wiley & Sons, Inc
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