Flux limitation in ultrafiltration: Osmotic pressure model and gel layer model

The characteristic permeate flux behaviour in ultrafiltration, i.e., the existence of a limiting flux which is independent of applied pressure and membrane resistance and a linear plot of the limiting flux versus the logarithm of the feed concentration, is explained by the osmotic pressure model. In the mathematical description presented here, a quantity ΔΠn/(Rmk) is introduced which is the ratio of the resistance caused by the osmotic pressure and the resistance of the membrane itself. For high values of this quantity (19) the flux is practically limited by the osmotic pressure. p]Factors leading to high values of the quantityΔΠnn/(Rmk) are discussed and it is concluded that in the ultrafiltration of medium molecular weight solutes (10,000 to 100,000 daltons) osmotic pressure limitation is more likely than gel layer limitatio

Dairy farms: constraints and recommendations for enhancing health, welfare and food saftey (Workshop results)

Results - It is necessary to improve the information to the public (who are the taxpayer and pay the subsidies) about organic farming as a system, that improves animal health and welfare. - Consumers must get accurate information about the organic products they buy. - Producers should be informed about organic farming before they convert (so they know what to expect): they should be told about the regluations and pointed to the available information about organic farming. - Veterinarians should be informed (part of the teaching curriculum in vet schools) about the holistic system, the importance of preventive health management on organic farms and about alternative treatments. - In communication to the policy makers (the government), organic farming should be presented as a different farming system and not as a conventional system with some alteration

Investigation of liquid-liquid demixing and aggregate formation in a membrane-forming system by means of pulse-induced critical scattering (PICS)

Phase separation phenomena in the quasi-ternary system cellulose acetate (CA)/dioxane/water, used as a typical system in the preparation of polymeric membranes for ultrafiltration and reverse osmosis applications, were investigated by means of pulse-induced critical scattering (PICS). Both the cloud point curve and spinodal curve were determined for CA concentrations up to 20% (w/w). The influence of maleic acid (used as an additive in order to improve the membrane performance) on the position of the binodal and spinodal curves and the demixing kinetics were investigated

Hydrodynamic resistance of concentration polarization boundary layers in ultrafiltration

The influence of concentration polarization on the permeate flux in the ultrafiltration of aqueous Dextran T70 solutions can be described by (i) the osmotic pressure model and (ii) the boundary layer resistance model. In the latter model the hydrodynamic resistance of the non-gelled boundary layer is computed using permeability data of the Dextran molecules obtained by sedimentation experiments. It is shown both in theory and experiment that the two models are equivalent

Resistance to the permeate flux in unstirred ultrafiltration of dissolved macromolecular solutions

The flux decline during the unstirred ultrafiltration of dissolved macromolecular solutions such as polyethylene glycol and dextran solutions was measured at different pressures from I to 4 x 105 Pa and different bulk concentrations from 0.1 to 0.55 kg/m3 with three types of polysulfone membranes. On the basis of the concept that a concentrated solution layer (not a gel layer) is formed on the membrane surface, the hydraulic resistance of the boundary layer was defined with the help of solvent permeability of dissolved macromolecules. The cake filtration theory was employed to analyze the flux decline behaviour. This simple theory worked well and the effective boundary layer concentrations calculated with the boundary layer resistance model developed here were physically quite reasonable. The calculated boundary layer concentrations depend on the applied pressure. The origin of this dependency might be the step concentration profile assumed in the cake filtration theory

The unstructured Scaldis model: a new 3D high resolution model for hydrodynamics and sediment transport in the tidal Scheldt

In the framework of the projects "Integral Plan for the Upper Sea Scheldt" and "Agenda for the Future", the SCALDIS model, a new unstructured high resolution model of the tidal Scheldt is developed in TELEMAC 3D (Telemac-Mascaret software platform). Starting from the stated model purpose, a weighted dimensionless cost function is set up that attributes equal weight to the vertical and the horizontal tide. By adapting the bottom roughness, the cost function is minimized during model calibration. Quantification of the model skill and cost function calculation is done using the VIMM toolbox which is developed and maintained at Flanders Hydraulics Research. The quantified model skill of the SCALDIS model shows that the model is well suited to assess the effects of changing the bathymetry and geometry of the Scheldt river on water levels, velocities, tracer dispersion and residence times, and that the hydrodynamics can be used as the basis for sediment transport calculations (both cohesive and non-cohesive)