A systematic study of chromium solubility in the presence of organic matter: consequences for the treatment of chromium‐containing wastewater

The treatment objective for wastewater containing Cr(VI) and/or Cr(III) is the reduction of Cr(VI) to the less toxic Cr(III) and the sequestering of Cr(III) from the water streams. The presence of organic matter in the wastewater and in a bioreactor environment may alter the solubility behavior of Cr(III), resulting in poor sequestering and Cr(III) removal from the soluble phase. Systematic experimental solubility results for Cr(III) were obtained in the presence of organic molecules often encountered in industrial effluents containing chromium as well as in biological treatment systems. Chromium solubility curves were determined experimentally from synthetic solutions of Cr(III) in contact with organic acids (acetic, oxalic, citric and ascorbic), amino acids (alanine and aspartic), proteins (albumin and casein) and synthetic nutrient media (yeast extract, nutrient broth and peptones). Experimental data sets were generated for each one of the above organics at three different initial organics concentrations in order to quantify the role of the relative abundance of organic matter in the solubility behavior of Cr(III). A progressive increase of trivalent chromium solubility was systematically observed when the relative abundance of organic ligands to Cr(III) exceeds 10, indicating the existence of a threshold above which the solubility of Cr(III) increases significantly. The hexacoordinate and octahedral character of Cr(III) complexes may explain the need for ligand excess also pointing to a treatment strategy suggesting the relative abundance of organic moieties should be kept below the above threshold. Copyright © 2007 Society of Chemical Industry     

Bridge condition modelling and prediction using dynamic Bayesian belief networks

The development of a condition-based deterioration modelling methodology at bridge group level using Bayesian belief network (BBN) is presented in this paper. BBN is an efficient tool to handle complex interdependencies within elements of engineering systems, by means of conditional probabilities specified on a fixed model structure. The advantages and limitations of the BBN for such applications are reviewed by analysing a sample group of masonry bridges on the UK railway infrastructure network. The proposed methodology is then extended to develop a time dependent deterioration model using a dynamic Bayesian network. The condition of elements within the selected sample of bridges and a set of conditional probabilities for static and time dependent variables, based on inspection experience, are used as input to the models to yield, in probabilistic terms, overall condition-based deterioration profiles for bridge groups. Sensitivity towards various input parameters, as well as underlying assumptions, on the point-in-time performance and the deterioration profile of the group are investigated. Together with results from ‘what if’ scenarios, the potential of the developed methodology is demonstrated in relation to the specification of structural health monitoring requirements and the prioritisation of maintenance intervention activities.     

Computing Nash Equilibria for Scheduling on Restricted Parallel Links

We consider the problem of routing n users on m parallel links under the restriction that each user may only be routed on a link from a certain set of allowed links for the user. So, this problem is equivalent to the correspondingly restricted scheduling problem of assigning n jobs to m parallel machines. In a Nash equilibrium, no user may improve its own Individual Cost (latency) by unilaterally switching to another link from its set of allowed links.     

A new approach for the characterization of the pore structure of dual porosity rocks

For the realistic representation of the pore space of dual porosity rocks, a new method of pore structure characterization is developed by combining experimental Hg intrusion/retraction curves with back-scattered scanning electron microscope (BSEM) images and inverse modeling algorithms. The pore space autocorrelation function measured by processing the digitized BSEM images is combined with the surface fractal dimension estimated from the high pressure Hg intrusion (MIP) data to derive a synthetic small-angle neutron scattering (SANS) intensity function, the inversion of which provides a volume-based pore body radius distribution (PBRD). The volume-based PBRD is fitted with a multimodal number-based PBRD consisting of two component distributions: one representing the macroporosity and another one representing the microporosity. Based on arguments of percolation theory, analytical mathematical models are developed to describe the Hg intrusion in and retraction from dual pore networks in terms of the complete PBRD, pore throat radius distribution (PTRD) of macroporosity, drainage accessibility functions (DAFs) of both porosities, and imbibition accessibility functions (IAFs) of both porosities. Inverse modeling of the Hg intrusion data set enables us to estimate the PTRD and DAFs. Inverse modeling of the Hg retraction datasets enables us to estimate a set of primary and secondary IAFs. The method is demonstrated by the pore structure characterization of four outcrop samples of carbonate and sandstone rocks. Analytic approximate equations developed from the critical path analysis (CPA) of percolation theory enable us to calculate explicitly the absolute permeability and the formation factor of the porous rocks using the estimated parameters (PBRD, PTRD, DAF) of the macroporosity. The measured permeability of cores is predicted satisfactorily and observed discrepancies may be attributed to large length-scale macro-heterogeneities which are not evident in BSEM images and Hg porosimetry data.     

Design and Evaluation of Adiabatic Arithmetic Units

Adiabatic design is an attractive approach to reducingenergy consumption in VLSI circuits after exhausting the potentialof conventional energy-saving techniques. Despite the plethoraof adiabatic logic architectures that have been proposed in recentyears, several practical considerations in the design of nontrivialadiabatic circuits remain largely unexplored. Moreover, it isstill unclear whether adiabatic circuits of significant sizeand complexity can achieve substantial savings in energy dissipationover corresponding conventional designs. We recently designedseveral low-power arithmetic units using a dual-rail adiabaticlogic design style. We also designed static CMOS versions ofthese units and compared their energy dissipation with theircorresponding adiabatic designs. In this paper we describe ourimplementations, discuss architecture and logic-level issuesrelated to our adiabatic designs, and present the findings ofour empirical comparison. Our results suggest that adiabaticlogic can be used for the implementation of relatively complexVLSI circuits that dissipate significantly less energy than theircorresponding CMOS designs.     

Metal precipitation in an ethanol-fed, fixed-bed sulphate-reducing bioreactor

A batch upflow fixed-bed sulphate-reducing bioreactor has been set up and monitored for the treatment of synthetic solutions containing divalent iron (100mg/L and 200mg/L), zinc (100mg/L and 200mg/L), copper (100mg/L and 200mg/L), nickel (100mg/L and 200mg/L) and sulphate (1700 mg/L and 2130 mg/L) at initial pH 3-3.5, using ethanol as the sole electron donor. The reactor has been operated at the theoretical stoichiometric ethanol/sulphate ratio. Complete oxidation of ethanol has been achieved through complete oxidation of the intermediately, microbially produced acetate. This is mainly attributed to the presence of Desulfobacter postgatei species which dominated the sulphate-reducing community in the reactor. The reduction of sulphate was limited to about 85%. Quantitative precipitation of the soluble metal ions has been achieved. XRD and SEM-EDS analyses performed on samples of the produced sludge showed poorly crystalline phases of marcasite, covellite and wurtzite as well as several mixed metal sulphides.     

Comparison of tree and straight-line clocking for long systolic arrays

A critical problem in building long systolic arrays lies in efficient and reliable synchronization. We address this problem in the context of synchronous systems by introducing probabilistic models for two alternative clock distribution schemes: tree and straight-line clocking. We present analytic bounds for the Probability of Failure and the Mean Time to Failure, and examine the trade-offs between reliability and throughput in both schemes. Our basic conclusion is that as the one-dimensional systolic array gets very long, tree clocking becomes more reliable than straight-line clocking.