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Filtration has broad applications in academic and industrial research as well as in product development. In general, filter-nutsch or filter-pressure approaches are applied. Recently, an analytical photo-centrifugal set up was introduced as a new laboratory technique to characterize membranes and filterability of samples (suspensions, protein solutions, extracts, etc.).Analytical centrifugal filtration (ACF) is based on continuous in-situ measurement of spatial resolved light transmission through a centrifugal filtration cell monitoring the volume decrease of the sample (top) or the filtrate increase (bottom) by STEP-Technology®). Centrifugal acceleration for dispersion separation can be simply set by programming rotor revolutions from 200 – 5000 rpm. Up to 12 samples (0,2 ml -1 ml) can be analyzed simultaneously. Different procedures can be applied to characterize membrane resistance and filterability of various sample types (diluted or concentrated macromolecule solutions or suspensions).In this paper the basic measuring technique of ACF, the newly designed centrifugal filtration cells are described and corresponding quantitative analysis discussed...

International audience; Es wird eine neue Applikation der analytischen Zentrifugation zur Bestimmung von Filtermedium- bzw. Membranwiderständen vorgestellt. Zum Einsatz kommt eine analytische Mehrproben-Zentrifuge, welche in situ Änderungen der Partikelkonzentration der gesamten Probe während der Zentrifugation mittels STEP-Technologie® zeitlich verfolgt und darüber hinaus auch zur Volumenbestimmung genutzt werden kann. Speziell entwickelte Filtrationsmesszellen nehmen die zu filtrierende Probe, als auch das anfallende Filtrat auf und ermöglichen den Einsatz unterschiedlicher Filtermedien. Bis zu 12 Messzellen können auf dem Rotor platziert werden. Der Filtrationsdruck wird durch die auf die Probe wirkende Zentrifugalkraft erzeugt, welche einfach über die Rotorumdrehungsgeschwindigkeit programmiert werden kann. Es werden Maximaldrücke von bis zu 5·105 Pa realisiert. Typische Probenvolumina liegen bei 1 ml. Es kommen Filtermedien mit einer Dicke von einigen Mikrometern bis zu 6 mm und einem Durchmesser von 7 mm zum Einsatz. Beispielhaft werden Resultate von ausgewählten Filtermedien (keramische Flachmembranen (IKTS), mikroporöse PP-Filme (TreoPore), gerakelte Polymermembranen (IPF) und hydrophile PVDF Membranen von Durapore) vorgestellt. Das entwickelte analytische Verfahren stellt eine neue Labortechnik zur Charakterisierung von flächigen Filtermedien sowie der Filtrierbarkeit von Dispersionen und Lösungen (z.B. Suspensionen, Protein-Lösungen, Extrakte, etc.) dar. Es erfordert keine externe Druckerzeugung und minimalen Reinigungsaufwand. Aufgrund der geringen Probenvolumina und Filtermediengröße ist es für Entwicklungsprojekte und sehr werthaltige Proben von Vorteil. Das Verfahren ist prinzipiell mit der klassischen Filternutsche im Sinne einer Mikro-Nutsche vergleichbar.

Il existe une grande diversité des techniques pour la mesure de la filtrabilité de suspensions. Cependant, les techniques existantes ne sont pas adaptées à la caractérisation rapide d’un grand nombre de petits échantillons (surtout, des échantillons liquides). Depuis quelques années l’Université Technologique de Compiègne et la société LUM GmbH travaillent sur le développement de la centrifugation analytique pour la caractérisation accélérée de la filtrabilité des suspensions et dispersions. La méthode consiste à réaliser des essais de filtration à l’aide de la centrifugation analytique puis à analyser les courbes de la filtration centrifuge obtenues pour en extraire des propriétés des solutions. La comparaison simple des courbes de filtration obtenues permet de classifier les échantillons selon leur filtrabilité. De plus, l’analyse des courbes de filtration permet la caractérisation quantitative de la filtrabilité : détermination de la résistance de la membrane colmatée, de la résistance spécifique du gâteau et des propriétés de réversibilité de la compression du gâteau. La méthode d’analyse des données dépend de la nature des échantillons : deux méthodes adaptées pour des suspensions concentrées et des solutions des colloïdes sont validées actuellement . Le congrès MemPro6 sera l’occasion de présenter les résultats les plus récents sur l’ultra- et la microfiltration centrifuge pour la caractérisation de la filtrabilité des solutions

Current development of analytical centrifugation methods facilitates the experimental characterization of dispersion stability and optimization of separation processes (such as centrifugation and filtration). Nevertheless, theoretical analysis of the centrifugal data remains rather complex. In addition, different side effects can influence the centrifugal process and complicate data interpretation. The present paper proposes a simple method for characterization of filterability of concentrated aggregated suspensions by centrifugal consolidation. Different experimental protocols were tested in order to reduce the influence of side effects. Selection of the optimal protocol was based on X-ray analysis of local (spatially resolved) consolidated sample structure. The multistep centrifugal consolidation with constant centrifugal acceleration ratio is suggested. Data analysis based on a single numerical solution of a basic consolidation equation yields the pressure dependency of specific cake resistance. A satisfactory correspondence (15% difference) was observed between the pressure dependency of specific cake resistance determined from the proposed multistep centrifugal consolidation, and conventional constant pressure dead-end filtration experiments for the studied concentrated aggregated kaolin suspension in the pressure range of 7.5…170 kPa.

International audience; The article introduces a novel method for accelerated analysis of membrane fouling during ultrafiltration of colloids: centrifugal ultrafiltration with a stepwise change of centrifugal rotation speed. The method allows simultaneous analysis of membrane fouling for different colloidal samples in a single analytical centrifugation experiment. The analysis for determination of fouled membrane resistance, specific cake resistance and reversibility of the filter cake compression is provided. The method applicability was tested with bovine serum albumin solutions at different protein concentrations. Fouled membrane resistance as well as pressure dependency of specific cake resistance was determined in a wide pressure range of 10…450 kPa. Results obtained with the help of the proposed method were in a good agreement with those obtained using the conventional method of constant pressure dead-end ultrafiltration.

The article is devoted to the application of analytical centrifugation for the measurement and analysis of centrifugal ultrafiltration kinetics. The model of centrifugal ultrafiltration of colloids accounting for the cake formation, compression and possible decompression is proposed. The method for the determination of filter cake properties (pressure dependency of specific cake resistance) from the results of batch centrifugal ultrafiltration experiment is presented. The method was tested for the determination of filterability of model samples: aqueous solutions of protein (bovine serum albumin) and nanoparticle suspension (Laponite RD). The pressure dependency of specific cake resistance was determined in the range of 10−500 kPa from the results of centrifugal ultrafiltration experiments at different centrifugal rotation speeds. The obtained values of specific resistance were in good correspondence with those measured in a series of reference constant pressure dead-end filtration tests.

The knowledge of pressure dependency of filterability (particle volume fraction φ and specific cake resistance α) is essential for optimization of sludge dewatering operations (settling, centrifugation, dead-end filtration-consolidation). The analytical centrifugation is a promising alternative to the classical laboratory methods of the filterability measurement (constant pressure dead-end filtration, compression permeability experiments) due to the possibility of automated many samples characterization. A number of methods are available for the analysis of centrifugal consolidation data (i.e.,dependency of centrifugal consolidation kinetics and sediment height on centrifugal acceleration) and characterization of sludge filterability, which are based on the idealized representation of a sample (usually, concentrated and aggregated suspension) behaviour in the centrifugal field [1-4]. However, recent works suggest that centrifugal consolidation can be influenced by side different effects (as wall friction [5] and particles segregation [6]) that must be taken into account (or eliminated by appropriate choice of the experimental protocol) for the correct characterization of filterability. Objective: Our current work is devoted to the development of a new method and protocols for the determination of pressure dependency of filterability of concentrated aggregated suspensions (pressure dependency of particle volume fraction φ and specific cake resistance α) from the centrifugal consolidation data (two-stage and multistage centrifugal consolidation kinetics).Methods: The method is based on the comparison of experimental characteristic consolidation time with the values tabulated for samples with different filterability. The tabulated values of characteristic consolidation time are obtained by the numerical solution of basic consolidation equation [7] for moderately compressible samples. The method was tested on the aqueous kaolin suspensions. Different experimental protocols were studied (Lumisizer): a) single stage centrifugation different constant centrifugal accelerations; b) two-stage centrifugation (centrifugal pre-consolidation at low centrifugal acceleration followed by centrifugation at different higher accelerations); c) multistage centrifugal consolidation (pre-consolidation followed by centrifugal acceleration ramping); Results: The x-ray transmission analysis (Lumireader x-ray) revealed that the single stage centrifugation can result in formation of nonhomogeneous sediment (probably, due to the particles segregation at high centrifugal acceleration), while two-stage and multistage experiments yields sediments with homogeneous solid pressure distribution. Conclusions: Sample pre-consolidation at low centrifugal acceleration is necessary for the correct analysis of the filterability be the method of centrifugal consolidation. The kinetics of two- and multistage centrifugal consolidation can be analyzed with the help of the developed method in order to determine the pressure dependency of the specific cake resistance in the wide solid pressure range.