Slow colloidal aggregation and membrane fouling

We observed that the concept of critical flux, although established on physical bases, does not describe all typical fouling situations found in membrane filtration. We especially focus on the slow flux decline that is observed in many industrial membrane applications, and that has found several types of explanations that we briefly discuss. In order to get a better understanding of this situation, we have considered the orders of magnitude of the slow aggregation kinetics that are expected to happen within a boundary layer, on an ultrafiltration or microfiltration membrane in operation. The results help to understand that whereas the critical flux is limiting cross-flow filtration of stable colloids, it should be combined to kinetics aspects of slow aggregation in cases of colloids of intermediate stability (metastable). We discuss some consequences on the design and operation of processes using membrane filtration

Calibration of ultrafiltration membranes against size exclusion chromatography columns

Using the extension of the concept of universal calibration parameter, yielding a relation between the hydrodynamic volume of molecules and the elution volume in sizeexclusionchromatography (SEC), to retention coefficients in ultrafiltration (UF), we propose a direct calibration of UF membranes against chromatography columns. Plotting the retention coefficient by one given UF membrane of a series of probe molecules versus their elution volume in SEC chromatography provides a calibration curve for this membrane. For a wide range of retentions, such calibration can be directly used to predict the retention of any molecule: one only needs to measure its exclusion volume by the SEC column, and read the retention by the calibrated membrane on the calibration curves. The method has been tested with dextran and PEG for the calibration, and milk proteins as test molecules, for three different membranes. The predicted values of the retention are in rather good agreement with those experimentally measured in a UF cell

Distributions of critical flux: modelling, experimental analysis and consequences for cross-flow membrane filtration

This paper discusses the distribution of critical flux (DCF) in cross flow filtration. These distributions are described here by a normal function with a mean critical flux and its standard deviation. The DCF model allows the description, through an analytical relationship, of the variation in steady state permeate flux with trans-membrane pressure. Both strong and weak forms of critical flux, which can be observed on a membrane operating in cross-flow mode, are depicted. A simple graphical method to determine the mean critical flux and its standard deviation from experimental results is derived from the theoretical model. The theoretical trends are compared to experimental data and show good agreement for cross flow filtration of latex and BSA suspensions. The distribution function parameters obtained by fitting the DCF model to experiments are compared to critical flux measured via a pressure step method. We thus propose a tool to analyse filtration results and to determine new global parameters for critical conditions (mean value and its standard deviation), which appears to be a good way to account for fouling complexity

Experimental study of the effects of hypochlorite on polysulfone membrane properties

Although chemical solutions are widely employed to clean membranes, they can also be responsible for changes in membrane properties. The two major drawbacks are then either the functional properties of the membrane gradually change, so the production can no longer meet requirements in terms of volume or quality, or the membrane simply breaks up (hollow fibers), and the system has to be shut down during maintenance. The aim of this experimental study was to gain a better understanding of the effect of hypochlorite cleaning solutions in different conditions (various pHs and temperatures) on the changes observed on an ultrafiltration hollow fiber membrane made from polysulfone (PSf) and polyvinylpyrrolidone (PVP). A wide range of methods characterizing the material have been used, from the atomic scale (ESCA) up to the module scale by force measurements on fibers. Exposure to sodium hypochlorite at rather high concentration seems to lead to chain breaking in the PSf molecules (gel permeation chromatography results). The consequences are changes in the membrane texture (scanning electron microscopy images), which are closely related to changes in the mechanical properties of the membrane. Membrane permeability appears to be poorly sensitive to such changes, which can be related to the fact that the permeability relies on the skin properties mainly

Social relation recognition in egocentric photostreams

© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.This paper proposes an approach to automatically categorize the social interactions of a user wearing a photo-camera (2fpm), by relying solely on what the camera is seeing. The problem is challenging due to the overwhelming complexity of social life and the extreme intra-class variability of social interactions captured under unconstrained conditions. We adopt the formalization proposed in Bugental’s social theory, that groups human relations into five social domains with related categories. Our method is a new deep learning architecture that exploits the hierarchical structure of the label space and relies on a set of social attributes estimated at frame level to provide a semantic representation of social interactions. Experimental results on the new EgoSocialRelation dataset demonstrate the effectiveness of our proposal.Peer ReviewedPostprint (author's final draft