Bacterial pathogen incidences in sludge from Swedish sewage treatment plants

This study surveyed the presence of bacterial pathogens in eight Swedish sewage treatment plants (STPs), with four different treatment methods, focusing on detection of zoonotic bacteria in raw and treated sludge. Salmonella spp., Listeria monocytogenes, Campylobacter coli and jejuni, Escherichia coli O157 and indicator bacteria were investigated. Samplings were performed from July 2000 to June 2002, resulting in 64 raw sludge samples and 69 treated sludge samples. The samples from raw sludge (67%) and treated sludge (55%) were positive for Salmonella; 49 different serotypes were detected. Restriction enzyme analysis and pulsed field gel electrophoresis of Salmonella serotypes indicated that Salmonella persists in STPs and that there is a continuous supply of new strains. There are differences in treatment methods concerning the reduction of pathogens and indicator bacteria. If spread on arable land, sludge increases the environmental load of pathogens; this increases the risk for spreading diseases to people and animals.     

Estimation of total equivalent temperature difference values for multilayer walls and flat roofs by using periodic solution

A theoretical methodology was developed to find total equivalent temperature difference (TETD) values for multilayer flat roofs and walls of buildings. The TETD values based on time lag and decrement factor are estimated using measured hourly solar radiation on a horizontal surface and outside air temperatures. The time lag and decrement factor are obtained numerically using periodic solution of one-dimensional transient heat transfer problem for the building structures. The problem is initially formulated using a differential equation and the appropriate initial and boundary conditions. It is then converted into dimensionless form and solved by application of complex finite Fourier transform (CFFT). The solution is used to find hourly variation of temperature inside the structure, the heat gain to the building through the structure, the highest and lowest temperatures at the inner and outer surfaces of the roofs and walls, and the time periods involved in reaching these temperatures. Sol-air temperatures for different directions as well as time lag and decrement factor are obtained, and these are used to determine the TETD values of the structures.     

The definition of partnering as a Wittgenstein family‐resemblance concept

This article on partnering and family‐resemblance makes two contributions to the debate about the definition of partnering in construction. The first is a distinction between general prerequisites, components and goals when discussing the concept. In order to understand what is specific about partnering the focus should be on the components, which are identified through a literature review. The second contribution is to apply Ludwig Wittgenstein's idea of family‐resemblance to the partnering concept. His idea is that a complex concept can be understood as a network of overlapping similarities. From the literature review it is concluded that there are two necessary components in partnering – trust and mutual understanding – and that a number of different components can be added to form a specific variant of partnering. This provides a new method to define the vague and multifaceted concept of partnering in a flexible and structured way.     

Assessing,exploring, and monitoring quality of offset colour prints

Variations in offset print quality relate to numerous parameters of printing press and paper. To maintain a constant high print quality press operators need to assess, explore and monitor quality of prints. Today assessment is mainly done manually. This paper presents a novel system for assessing and predicting values of print quality attributes, where the adopted, random forests (RFs)-based, modeling approach also allows quantifying the influence of different paper and press parameters on print quality. In contrast to other print quality assessment systems the proposed system utilises common, simple print marks known as double grey-bars. Novel virtual sensors assessing print quality attributes using images of double grey-bars are presented. The inferred influence of paper and printing press parameters on quality of colour prints shows clear relation with known print quality conditions. Thorough analysis and categorisation of related work is also given in the paper.     

A Microprocessor Controlled System For Photoelectrochemical Measurements

ABSTRACT

An automatic system for measuring photocurrent of electrodes as a function of excitation wavelength and electrode potential is described. Applications to a chemically modified transparent Sn0₂ electrode and an oxide-covered tantalum electrode are shown.     

Synthesis and properties of chitosan-modified poly(vinyl butyrate)

Modification of chitosan by grafting of vinyl butyrate was carried out in homogeneous phase using potassium persulfate as redox initator and 1.5% acetic acid as solvent. The percent grafting and grafting efficiency were analysed and the high grafting efficiency up to 94% was observed. The effects of reaction variables such as monomer concentration, initiator concentration, temperature and reaction time were investigated. It was observed that the solubility of chitosan was markedly reduced after grafting with vinyl butyrate. The grafted product is insoluble in common organic solvents as well in dilute organic and inorganic acids. Characterization of the graft copolymers were carried out by using Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC) and Scanning Electron Microscopy (SEM) technics. Characteristic signal of carbonyl group was observed at 1,731 cm^−1 which belongs to the poly vinyl butyrate segments in the graft copolymer. The melting transition of the chitosan main chain in the copolymer shifted to 124°C from its original value 101°C. In addition to these, we have also studied topology of the graft copolymer and the SEM micrograph showed continuous homogenous matrix which means there is no phase separation.     

Nanometer-thick films of titanium oxide acting as electrolyte in the polymer electrolyte fuel cell

0-18 nm-thick titanium, zirconium and tantalum oxide films are thermally evaporated on Nafion 117 membranes, and used as thin spacer electrolyte layers between the Nafion and a 3 nm Pt catalyst film. Electrochemical characterisation of the films in terms of oxygen reduction activity, high frequency impedance and cyclic voltammetry in nitrogen is performed in a fuel cell at 80 °C and full humidification. Titanium oxide films with thicknesses up to 18 nm are shown to conduct protons, whereas zirconium oxide and tantalum oxide block proton transport already at a thickness of 1.5 nm. The performance for oxygen reduction is higher for a bi-layered film of 3 nm platinum on 1.5 or 18 nm titanium oxide, than for a pure 3 nm platinum film with no spacer layer. The improvement in oxygen reduction performance is ascribed to a higher active surface area of platinum, i.e. no beneficial effect of combining platinum with zirconium, tantalum or titanium oxides on the intrinsic oxygen reduction activity is seen. The results suggest that TiO₂ may be used as electrolyte in fuel cell electrodes, and that low-temperature proton exchange fuel cells could be possible using TiO₂ as electrolyte.     

On the influence of Pt particle size on the PEMFC cathode performance

Colloidal suspensions of almost spherical and crystalline Pt nanoparticles between 1.6 and 2.6 nm in diameter and with narrow size distribution were synthesized using the phase transfer method (PTM) with alkylamines, C_m>nm>NH₂, as stabilizing agents. Batches of such homogenous Pt-C_m>nm>NH₂ (m>nm> = 8, 12) nanocrystals were deposited onto Vulcan XC-72 carbon powder, and the activity for the oxygen reduction reaction (ORR) of this series of Pt/C materials was evaluated under PEMFC conditions. The aim was to elucidate whether this type of stabilized Pt nanoparticles were as active for the ORR as a corresponding commercial Pt/C material, and if any difference in mass activity could be observed between catalysts with different Pt particle size. In the PEMFC experiments, i.e. voltammetry in oxygen and nitrogen, it was found that, after an initial electrode activation, the ORR activity of the catalysts prepared from the alkylamine-stabilized Pt nanoparticles deposited on carbon was as high as that of the employed commercial reference catalyst. In fact, all samples in the Pt/C series showed high and very similar ORR activity normalized to Pt-loading, without significant dependence on the initial Pt particle size. However, pre- and post-electrochemical characterization of the Pt/C material series with TEM showed that structural changes of the Pt nanoparticles occurred during electrochemical evaluation. In all samples studied the mean Pt particle size increased during the electrochemical evaluation resulting in decreased differences between the samples explaining the observed similar ORR performance of the different materials. These results emphasize the necessity of post-operation characterization of fuel cell catalysts when discussing electrocatalytic activity. In addition, employing complex preparation efforts for lowering the Pt particle size below 3 nm may have limited practical value unless the particles are stabilized from electrochemical sintering.     

The fate of fuel-nitrogen during gasification of biomass in a pressurised fluidised bed gasifier

The distribution of fuel-nitrogen in gases, tar and char from gasification of biomass in a pressurised fluidised bed gasifier was investigated. Four species of biomass: birch, Salix, Miscanthus and Reed canary grass were gasified at 0.4 MPa and 900 °C. Oxygen-enriched nitrogen was used as fluidising agent. As a reference, gasification of Daw Mill coal was also carried out under the same experimental conditions. The experimental results illustrate that both the nature of the original fuels and the chemical structure of the nitrogen in the fuel have influence on the distribution of fuel-nitrogen in gases (NH₃, HCN, NO), tar and char under the employed experimental conditions. The present work also shows that the types of nitrogen heterocyclic compounds (NHCs) in the tar from different kinds of biomass are the same and the major compound is pyridine. However, the distribution of the various NHCs in the tar from the four species of biomass varies: the higher the content of fuel-nitrogen, the higher the concentration of two-ring NHCs in the tar. An effective method for extracting NHCs from the acidic absorption of the product gas was introduced in the present work. The method makes use of solid phase extraction (SPE) by a silica-based C₁₈ tube to extract the NHCs which subsequently were analysed by gas chromatography (GC) with flame ionisation detection (FID). The recovery and reproducibility of the SPE technique for NHCs is discussed.