Fouling of dairy components on hydrophobic polytetrafluoroethylene (PTFE) membranes for membrane distillation

This study investigates fouling of membranes during membrane distillation (MD) of two model dairy feeds — skim milk and whey, as well as their major single components. Every MD experiment was conducted for 20 hat 54 C feed inlet temperature and 5 C permeate inlet temperature using PTFE membranes. Performance was assessed in terms of throughput (flux) and retention efficiency.Skim milk flux was found to be lower but stable overtime compared to whey.The study using single components as well as combinations the reofrevealed that fouling was primarily driven by proteins and calcium, but only in combination.Lactose also played a role to a lesser extent in the protein/membrane interactions, possibly due to preferential hydration,but did not interact with the membrane polymer directly. However lactose was found to deposit once an anchorpoint to the membrane was established by other components. Skim milk showed strong adhesion from its principle proteins, caseins;however salts were needed to form a thick and dense cake layer.Caseins seem to form a layer on the membrane surface that prevents other components from interacting with the membrane polymer.Wheyproteins, on the other hand, deposited to alesse rextent. In general membrane distillation was found to be a process that generates high quality water with retention of all tested components >99% while simultaneously concentrating whey or skim milk

Performance assessment of membrane distillation for skim milk and whey processing

AbstractMembrane distillation is an emerging membrane process based on evaporation of a volatile solvent. One of its often stated advantages is the low flux sensitivity toward concentration of the processed fluid, in contrast to reverse osmosis. In the present paper, we looked at 2 high-solids applications of the dairy industry: skim milk and whey. Performance was assessed under various hydrodynamic conditions to investigate the feasibility of fouling mitigation by changing the operating parameters and to compare performance to widespread membrane filtration processes. Whereas filtration processes are hydraulic pressure driven, membrane distillation uses vapor pressure from heat to drive separation and, therefore, operating parameters have a different bearing on the process. Experimental and calculated results identified factors influencing heat and mass transfer under various operating conditions using polytetrafluoroethylene flat-sheet membranes. Linear velocity was found to influence performance during skim milk processing but not during whey processing. Lower feed and higher permeate temperature was found to reduce fouling in the processing of both dairy solutions. Concentration of skim milk and whey by membrane distillation has potential, as it showed high rejection (>99%) of all dairy components and can operate using low electrical energy and pressures (<10kPa). At higher cross-flow velocities (around 0.141m/s), fluxes were comparable to those found with reverse osmosis, achieving a sustainable flux of approximately 12kg/h·m2 for skim milk of 20% dry matter concentration and approximately 20kg/h·m2 after 18h of operation with whey at 20% dry matter concentration

Focus on the research utility of intravascular ultrasound - comparison with other invasive modalities

Intravascular ultrasound (IVUS) is an invasive modality which provides cross-sectional images of a coronary artery. In these images both the lumen and outer vessel wall can be identified and accurate estimations of their dimensions and of the plaque burden can be obtained. In addition, further processing of the IVUS backscatter signal helps in the characterization of the type of the plaque and thus it has been used to study the natural history of the atherosclerotic evolution. On the other hand its indigenous limitations do not allow IVUS to assess accurately stent struts coverage, existence of thrombus or exact site of plaque rupture and to identify some of the features associated with increased plaque vulnerability. In order this information to be obtained, other modalities such as optical coherence tomography, angioscopy, near infrared spectroscopy and intravascular magnetic resonance imaging have either been utilized or are under evaluation. The aim of this review article is to present the current utilities of IVUS in research and to discuss its advantages and disadvantages over the other imaging techniques

Fouling mechanisms of dairy streams during membrane distillation

This study reports on fouling mechanisms of skim milk and whey during membrane distillation (MD) using polytetrafluoroethylene (PTFE) membranes. Structural and elemental changes along the fouling layer from the anchorpoint at the membrane to the topsurface of the fouling layer have been investigated using synchrotron IR micro-spectroscopy and electron microscopy with associated energy dispersive X-ray spectroscopy(EDS)Initial adhesion of single components on a membrane representing a PTFEsurface was observed in-situ utilizing reflectometry.Whey components were found to penetrate into the membrane matrix while skim milk fouling remained on top of the membrane. Whey proteins had weaker attractive interaction with the membrane and adhesion depended more on the presence of phosphorus near the membrane surface and throughout to establish the fouling layer. This work has given detailed insight into the fouling mechanisms of MD membranes in major dairy streams, essential for maintaining membrane distillation as operational for acceptable times, therewith allowing further development of this emerging technology

Warum es im Rußland der Frühen Neuzeit keinen Bauernkrieg gab: Komparatistische Vorüberlegungen zu einer kommunikationsgeschichtlichen Revision eines alten Paradigmas“

Griesse M. Warum es im Rußland der Frühen Neuzeit keinen Bauernkrieg gab: Komparatistische Vorüberlegungen zu einer kommunikationsgeschichtlichen Revision eines alten Paradigmas“. In: Hausmann G, Rustemeyer A, eds. Imperienvergleich. Beispiele und Ansätze aus osteuropäischer Perspektive. Festschrift für Andreas Kappeler. Forschungen zur Osteuropäischen Geschichte, 75. 2009: 465-487

Direct Contact Membrane Distillation of Dairy Process Streams

Membrane distillation (MD) was applied for the concentration of a range of dairy streams, such as whole milk, skim milk and whey. MD of a pure lactose solution was also investigated. Direct contact MD (DCMD) mode experiments were carried out in continuous concentration mode, keeping the warm feed/retentate and cold permeate stream temperatures at 54 °C and 5 °C respectively. Performance in terms of flux and retention was assessed. The flux was found to decrease with an increase of dry-matter concentration in the feed. Retention of dissolved solids was found to be close to 100% and independent of the dry-matter concentration in the feed. Fourier Transform Infrared Spectroscopy (FTIR) of the fouled membranes confirms organics being present in the fouling layer