Modeling of the Sorption Dynamics in Multicomponent Ion-Exchange Systems with Consideration of Complexation Reactions on the Basis of the Surface Complexation Theory

The sorption dynamics in multicomponent ion-exchange systems with consideration of complexation reactions in solution is theoretically described by solving (on a computer) nonlinear material balance equations and kinetic equations of internal diffusion. Equilibria in multicomponent ion-exchange systems are characterized using the surface complexation theory. According to this theory, fixed groups of an ion exchanger and counterions form complexes located in different layers (Stern layers) at different distances from the surface. These layers constitute a circuit of series-connected capacitors. The fundamental advantage of such an approach is the fact that equilibria in multicomponent systems can be described in terms of a set of parameters obtained for binary systems. Additional account is taken of complexation reactions in the solution in the space between sorbent grains in an ion-exchange column. The H⁺–A–B three-component metal-ion exchange in various systems (A, B = Zn²⁺, Co²⁺, Ni²⁺, Cd²⁺, Ca²⁺, and Na⁺) is studied. Comparison is made between the results of numerical calculations of the characteristics of the H⁺–A ^{n +}–B ^{n +} ion exchange in multicomponent systems containing metal ions with and without consideration of chemical reactions.     

Screw Machines with Longitudinal Circulating Liquid. Communication 1. Pressure-Flow Rate Characteristics

The possibility of organizing longitudinal circulation of polymeric fluids along the channels of screw machines is demonstrated; it levels out the concentrations of additives, required because of the imprecise operation of metering systems in time, and averaging of the temperature of the fluid along the length of the screw. The pressure-flow rate characteristics of screw machines with longitudinal fluid circulation are investigated and the operating conditions in the presence and absence of longitudinal circulation are determined. The region of geometric screw dimensions where longitudinal circulation of polymeric fluid cannot be organized is determined.     

Results from the monitoring of pesticide residues in fruit and vegetables on the Danish market, 2000-01

To check compliance with the maximum residue levels in foods and to monitor the residue levels to enable an evaluation of the exposure of the Danish population to pesticides, a monitoring programme for pesticides residues in fruit and vegetables was performed. Sampling plans were designed based on previous findings and on consumption data. Samples (n = 4404) of mainly fresh conventionally and organically grown fruit and vegetables were collected at wholesalers and importers and at food processing companies. Of the samples, 3% were frozen products and 5% organically grown. Of the samples, 34% were of Danish origin, with 66% from other countries. Two accredited laboratories performed analyses of the samples using capillary gas chromatography, liquid chromatography and a spectrophotometric method. Reporting levels were set at the lowest calibration level or at the limit of determination. Residues were found in 60% of the samples of fruit but in only 18% of the vegetable samples. Residues above the maximum residue levels were found in 6% of all samples of fruit and in 2% of the vegetable samples.     

Aluminium content of Spanish infant formula

Levels of aluminium in 82 different infant formulae from nine different manufacturers in Spain were determined by acid-microwave digestion and graphite furnace atomic absorption spectrophotometry. The influence of aluminium content in tap water in reconstituted powder formulae was examined and an estimate was made of the theoretical toxic aluminium intake in comparison with the provisional tolerable weekly intake (PTWI). Possible interactions between aluminium and certain essential trace elements added to infant formulations have been studied according to the type or main protein-based infant formula. In general, the infant formulae contained a higher aluminium content than that found in human milk, especially in the case of soya, preterm or hydrolysed casein-based formulae. Standard formulae gave lower aluminium intakes amounting to about 4% PTWI. Specialized and preterm formulae resulted in a moderate intake (11-12 and 8-10% PTWI, respectively) and soya formulae contributed the highest intake (15% PTWI). Aluminium exposure from drinking water used for powder formula reconstitution was not considered a potential risk. In accordance with the present state of knowledge about aluminium toxicity, it seems prudent to call for continued efforts to standardize routine quality control and reduce aluminium levels in infant formula as well as to keep the aluminium concentration under 300 μg l^-1 for all infant formulae, most specifically those formulae for premature and low birth neonates.     

Time‐dependent heat transfer coefficient of a wall

A time‐dependent coefficient of heat transfer is proposed for the computation of thermal power required, so that a room temperature reaches a desired value within a given time. A mathematical formulation of the room heating transient phenomenon is constructed in a dimensionless form. Using an integral approximate solution an analytical expression for this coefficient is provided and it is verified by diagrams adopted by DIN 4701. Copyright © 2003 John Wiley & Sons, Ltd.     

Measurement of three-phase transformer derating and reactive power demand under nonlinear loading conditions

The measurement of real and apparent power derating of three-phase transformers is important for transformers feeding nonlinear loads. This paper presents a new digital data-acquisition method for measuring derating and reactive power demand of three-phase transformers under full or partial load conditions. The accuracy requirements of the instruments employed (potential, current transformers, shunts, voltage dividers, optocouplers volt- and current meters) are addressed. Application examples demonstrate the usefulness of this new digital data-acquisition method.     

Biofilm adaptation to sulfate reduction in anaerobic immobilized biomass reactors sujected to different COD/sulfate ratios.

Various aspects of biofilm adaptation to sulfate reduction in horizontal-flow anaerobic immobilized biomass (HAIB) reactors subjected to increasing sulfate concentrations and different COD/sulfate ratios are presented and discussed. Four bench-scale HAIB reactors filled with vegetal carbon (R1 and R2) and polyurethane foam matrices (R3 and R4) were utilized. Influent sulfate concentrations ranging from 500 to 3000 mg/L were applied at COD/sulfate ratios ranging from 5.0 to 1.7. Reactors R1 and R4 were operated with higher sulfate loads than those applied to R2 and R3. For the same COD/sulfate ratio, the highest sulfate reduction efficiency (approximately 80%) was displayed by the vegetal carbon reactor (R2) subjected to low sulfate loads. According to the results of our molecular biology analyses, the different support materials provided different biomass colonization conditions. The lowest diversity of sulfate-reducing bacteria was found in the HAIB filled with polyurethane foam matrices operating with high sulfate loads.