Quantifying Charge Effects on Fouling Layer Strength and (Ir)Removability during Cross-Flow Microfiltration

Fouling of membranes is still an important limiting factor in the application of membrane technology. Therefore, there is still a need for an in-depth understanding of which parameters affect the (ir)removability of fouling layers, as well as the mechanisms behind fouling. In this study, fluid dynamic gauging (FDG) was used to investigate the influence of charge effects between negatively charged foulant particles and cations on cake cohesive strength. Fouling cakes’ thicknesses and cohesive strengths were estimated during membrane operations, where microfiltration (MF) membranes were fouled in a feed-and-bleed cross-flow filtration system with low and highly negatively charged polystyrene-polyacrylic acid core-shell particles. In addition, an added procedure to determine the irremovability of cakes using FDG was also proposed. Comparing layers formed in the presence and absence of calcium ions revealed that layers formed without calcium ions had significantly lower cohesive strength than layers formed in the presence of calcium ions, which is explained by the bridging effect between negatively charged particles and calcium ions. Results also confirmed more cohesive cakes formed by high negative charge particles in the presence of calcium compared to lower negative charge particles. Hence, it was demonstrated that FDG can be used to assess the cohesive strength ((ir)removability) of cake layers, and to study how cake cohesive strength depends on foulant surface charge and ionic composition of the solution

Gav studiefremdriftsreformen øget fremdrift? : En analyse af studieadministrative data

Med studiefremdriftsreformen (SFR) blev der i 2014 (SFR#1) indført skærpede krav til fremdriften for studerende på landets videregående uddannelser. På Københavns Universitet (KU) blev reglerne lempet i 2016 (SFR#2). I denne artikel undersøger jeg, hvordan skiftende regler om studieaktivitet har påvirket fremdriften ved BA- og KA-uddannelserne i folkesundhedsvidenskab ved KU. Udfaldsmålet i undersøgelsen er de studerendes gennemsnitlige antal beståede ECTS-point per år, analyseret i en generaliseret lineær mixed model. Analysen af studieadministrative data for 974 studerende indskrevet på årgangene 2009-2020 viser, at den gennemsnitlige fremdrift var på 45,64 (95 % KI 44,99; 46,29) ECTS-point per år. Sammenlignet med perioden før SFR steg fremdriften med 3,36 (95 % KI 1,70; 5,01) ECTS-point per år i SFR#1-perioden, men faldt i den efterfølgende SFR#2-periode (difference=0,38 [95 % KI -1,03; 1,79]) tilbage på samme niveau som udgangspunktet før SFR (referenceperiode). Fremdriftsfaldet fra SFR#1- til SFR#2-perioden skyldes sandsynligvis, at særlig KA-studerende i folkesundhedsvidenskab i stigende grad er blevet opmærksomme på KUs minimumskrav til studieaktivitet