Thiol-modified cellulose nanofibrous composite membranes for chromium (VI) and lead (II) adsorption

Oxidized cellulose nanofibers (CNF), embedded in an electrospun polyacrylonitrile (PAN) nanofibrous scaffold, were grafted with cysteine to increase the adsorption capability for chromium (VI) and lead (II). Thiol-modified cellulose nanofibers (m-CNF) were characterized by titration, FT-IR, energy dispersive spectroscopy (EDS) and SEM techniques. Static and dynamic Cr(VI) and Pb(II) adsorption studies of m-CNF nanofibrous composite membranes were carried out as a function of pH and of contact time. The results indicated these membranes exhibited high adsorption capacities for both Cr(VI) (87.5 mg/g) and Pb(II) (137.7 mg/g) due to the large surface area and high concentration of thiol groups (0.9 mmol of –SH/gram m-CNF). The morphology and property of m-CNF nanofibrous composite membranes was found to be stable, and they could be used and regenerated multiple times with high recovery efficiency.     

The Single-Fiber Collision Rate and Filtration Efficiency for Nanoparticles I: The First-Passage Time Calculation Approach

We describe an approach to filtration-efficiency calculations as an alternative to the traditional depth filtration theory. The new approach involves linking the single-fiber efficiency to the collision rate coefficient/kernel between nanoparticles and fibers, and correspondingly inferring the collision kernel via dimensionless mean first-passage time (MFPT) calculations. This method has the advantage of easily incorporating the influences of particle diffusion, inertia, and particle size; therefore, all filtration mechanisms can be considered simultaneously. Through non-dimensionalization of the equation of motion for a particle in MFPT calculations (the Langevin equation), it is shown that both the single-fiber efficiency E_f and dimensionless particle-fiber collision kernel, H, are functions of the ratio of particle radius to filter-fiber radius, R, the solid volume fraction in the filter, V_f, the ratio of particle persistence distance to the particle-filter collision distance, Kn_D (the diffusive Knudsen number), and the ratio of the particle translational kinetic energy to the thermal energy χ_f. Using a Kuwabara flow-cell model to define the geometry and flow field, MFPT calculations are used to determine H and E_f for nanoparticles in atmospheric pressure systems, i.e., when particle inertia is negligible but when diffusion and interception act in tandem to collect particles. From MFPT results, regression equations for both H and E_f are developed. A comparison is made between MFPT results and commonly invoked depth-filtration single-fiber efficiency relationships, experimentally measured values, and H equations derived from Sherwood number correlations based upon measurements of heat transfer from a fluid flowing perpendicular to an array of cylinders. Good agreement is found with both measurements and previously developed equations over a wide range of parameter space.

Copyright 2014 American Association for Aerosol Research     

On the tuning of predictive controllers: Impact of disturbances,constraints, and feedback structure

The impact of problem formulation modifications on predictive controller tuning is investigated. First, the proposed tuning method is shown to adapt to disturbance characteristic changes and thus, takes full economic advantage of the scenario. The second topic concerns point‐wise‐in‐time constraints and the impact of constraint infeasibility. Specifically, we shift the tuning question from selection of nonintuitive weighting matrix parameters to that of a few key parameters and results in a rather intuitive trade‐off between expected profit and expected constraint violations. Finally, we show that simple modifications will allow for the consideration of various feedback structures, including computational delay and partial state information. The overall conclusions of the work are that the results of the automated algorithm will help build an intuitive understating of the dynamics of the process and ultimately result in a higher level trade‐off between profit and constraint observance. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3473–3489, 2014     

Gradientenbetontechnologie

The technology of graded concrete – From the development of concrete mixtures and the conceptual design to the automatized manufacturing In accordance with the principle form follows force, the DFG Priority Programme (SPP) 1542 – Leicht Bauen mit Beton – focuses on energy efficient building elements which are designed specifically for desired operational demands. This concept is a specific adaption of the component's inner structure and works in parallel to the optimization of its outer shape which is often limited due to the outer geometry of slabs, walls and supporting pillars. The technology of graded concrete provides an innovative possibility to adapt the inner structure of a concrete component in order to meet defined static and structural‐physical requirements. The challenging demands imposed by the technology of graded concrete require a holistic approach including the development of the concrete mixtures, the design of the building components and finally the automatized manufacturing. In collaboration between the departments ILEK, IWB and ISYS of the University of Stuttgart a complete process chain for the manufacturing of functionally graded concrete components was realized. This approach for concrete results in fully recyclable building elements with significant savings in mass and energy.     

Exploring the Substrate Specificity and Enantioselectivity of a Baeyer–Villiger Monooxygenase from Dietzia sp. D5: Oxidation of Sulfides and Aldehydes

Baeyer–Villiger monooxygenases (BVMOs) are valuable enzymes for specific oxyfunctionalization chemistry. They catalyze the oxidation of ketones to esters, but are also capable of oxidizing other chemical functions, namely aldehydes and heteroatoms such as sulfur, nitrogen, selenium and boron. The oxidation specificity and enantioselectivity of a newly characterized BVMO (BVMO4) from a strain of Dietzia towards sulfide- and aldehyde substrates have been studied. BVMO4 could react with sulfides containing an aromatic group. The presence of a substituent on the aromatic group was tolerated when they were in the meta- and para position and the oxidations yielded predominantly the (R)-sulfoxides. Similarly, BVMO4 displayed a higher activity for aldehydes containing a phenyl group, but long aliphatic aldehydes, namely octanal and decanal, were also accepted as substrate by this enzyme. The major oxidation products of the aldehyde substrates were the respective carboxylic acids in contrast to formate ester that was obtained in most of the previous reports. The Baeyer–Villiger oxidation of the substrate 2-phenylpropionaldehyde was studied in further detail and the corresponding acid product was obtained with good regio- and enantioselectivity. This is a unique feature for BVMO4 and is of great interest for further exploration of an alternative biocatalytic process.     

Whites' neighbourhood racial preferences and neighbourhood racial composition in the United States: evidence from the multi‐city study of urban inequality

Within the housing segregation literature major disagreements have developed over two fundamental issues: (1) the role that whites' aversion to racially mixed neighbourhoods plays in causing modern segregation in the US; and (2) the factors that underlie this aversion, including the effects of inter‐racial contact on whites' neighbourhood racial preferences and whether these preferences reflect neighbourhood stereotyping as opposed to pure racial prejudice. Extant evidence on these issues is either old or indirect. This paper provides direct evidence on these issues using new data from the Multi‐City Study of Urban Inequality. The results suggest that (1) whites' neighbourhood racial preferences play an important role in explaining the racial composition of their neighbourhoods; (2) inter‐racial contact in neighbourhoods and workplaces leads to a greater willingness among whites to live with blacks; and (3) although younger and more educated whites express a stronger taste for integration than other whites, the magnitude of these differences leads to only a small increase in the black percentage of the neighbourhood. In addition, the results provide no evidence in support of the hypothesis that whites stereotype black neighbourhoods rather than blacks per se.     

Comparison of 2-chlorobenzoic acid biodegradation in a membrane bioreactor by B. cepacia and B. cepacia bearing the bacterial hemoglobin gene

Degradation of 2-chlorobenzoic acid (2-CBA), a model recalcitrant chlorinated organic compound, by pure cultures of Burkholderia cepacia strain DNT with (transformed B. cepacia) and without (untransformed B. cepacia) the bacterial hemoglobin (Vitreoscilla hemoglobin, VHb) gene, vgb, was investigated in parallel membrane bioreactors (MBRs). This was done aseptically to prevent contamination during the operation of the MBRs. The objective was to determine whether the degradation of 2-CBA by cometabolism, using acetate as a primary carbon source, under hypoxic conditions might be enhanced for vgb-bearing cells in MBRs. The 2-CBA removal efficiency of transformed B. cepacia (97-99%) was slightly higher than that of untransformed B. cepacia (95-99%) at all stages. The average amount of chloride released from 2-CBA by transformed cells was also higher than for untransformed cells, 92-96% compared to 64-84% of the maximum theoretical amount, the exact value depending on the operating conditions. These results indicate that 2-CBA degradation/transformation is not accompanied by the stoichiometric release of chloride for the untransformed strain. The difference between percentages of 2-CBA removal and chloride release by untransformed cells was attributed to persistence, under hypoxic conditions, of the 2-CBA chlorine atom in 2-CBA metabolites. Growth of transformed cells was also significantly enhanced under hypoxic conditions compared to untransformed cells. For varying media compositions, the transformed cells reached higher cell densities (3.2-5.4 g/L) relative to untransformed cells (2.8-4.7 g/L) at food to microorganism ratios ranging from 0.44-0.59 to 0.38-0.49 g COD/g biomass-d The observed yields thus ranged from 0.16-0.20 and 0.15-0.18 g TSS/g COD for untransformed and transformed cells, respectively. The value of the yield depended on medium composition. The MBR system using vgb-containing B. cepacia maintained a high biomass concentration without oxygen limitations and provided cell-free effluent. Hence, it may be useful for treating high volumes of water contaminated with low levels of recalcitrant organics.     

Correlations between differential absorbance and the formation of individual DBPs

This study examined correlations between the differential absorbance at 272nm (deltaA272) and the formation of disinfection by-products (DBPs) in chlorinated water from the Tolt River, a water source for Seattle, WA. The DBPs investigated included chloroform (CHCl3), dichlorobromomethane (CHCl2Br), mono-, di- and trichloroacetic acids (MCAA, DCAA, and TCAA, respectively), chloral hydrate (CH), dichloroacetonitrile (DCAN) and 1,1,1-trichloropropanone (TCP). Whereas the kinetics of DBP formation are complex and are non-linear, the same DBP data represented as a function of deltaA272 are quite simple. Absorbance decreases when the water is chlorinated, i.e., deltaA272 is always negative. The DBP vs. -deltaA272 correlations can almost always be quantified by linear equations, at least above some threshold value of -deltaA272, with R2 values > 0.95. The only DBP that did not follow this trend was CH, for which an exponential relationship better described the data. TCP and DCAN were unstable at pH 7 and 8, but at pH 6 linear correlations between their concentrations and -deltaA272 were as strong as those for the more stable DBPs. The threshold -deltaA272 value is approximately the same for many of the DBPs studied, supporting the hypothesis that individual DBPs are released following the formation of a common intermediate, or at least a small group of similar intermediates. The DBP vs. -deltaA272 correlations may have practical value since they provide an alternative approach for monitoring the formation of individual DBP species on-line, but the generality of the relationships needs to be further examined.     

Effects of thermal treatment on halogenated disinfection by-products in drinking water

The influence of heating or boiling on the formation and behavior of disinfection by-products (DBPs) was investigated in DBP-spiked reagent water, municipal tap water, and synthetic water containing chlorinated aquatic humic substances. Thermal cleavage of larger halogenated species leads to both formation of smaller chlorinated molecules (including THMs and HAAs) and dechlorination of organics. In parallel with their formation from larger molecules, THMs can be volatilized, and this latter process dominates the change in their concentration when water is boiled. HAAs are not volatile, but they can be destroyed by chemical reactions at elevated temperatures, with the net effect being loss of trihalogenated HAAs and either formation or loss of less chlorinated HAAs. Although other identifiable DBPs can be generated at slightly elevated temperatures, in most cases their concentrations decline dramatically when the solution is heated.