Caractérisation du comportement des aérosols microbiens dans les réseaux de ventilation d'espaces occupés

La qualité microbienne de l air intérieur représente un enjeu sanitaire important, notamment dans le secteur professionnel. Ces travaux de thèse ont permis d étudier les conditions favorisant le développement des espèces microbiennes collectées sur des médias fibreux utilisés dans des CTA, ainsi que leur réentrainement an aval de la filtration, susceptible de dégrader la qualité de l air. La première partie de l étude s est déroulée en laboratoire à partir de la filtration d un consortium bactérien fongique composé de Staphylococcus epidermidis et Penicillium oxalicum. L influence de trois paramètres a été étudiée sur la croissance microbienne : le taux d humidité relative (HR) de l air, la nature du média fibreux, la présence/absence de flux d air. Les résultats ont révélé notamment que quelles que soient les conditions,S. epidermidis n arrive pas à croître. En revanche, lorsque l HR de l air approche 100%, P. oxalicum se développe sur les filtres et des spores sont relarguées en aval des filtres après une reprise de la filtration. Une seconde partie de l étude a consisté à travailler avec un aérosol atmosphérique semi urbain. Deux unités de filtration d air ont fonctionné pendant 5 mois en parallèle. La ventilation d une des deux unités a été stoppée chaque week-end et redémarrée en début de semaine. Un suivi de la température, de l humidité de l air, de la perte de charge des filtres et de la concentration des particules totales dans l air en amont de la filtration a été assuré tout au long de l étude. Les concentrations en microorganismes cultivables ont été mesurées chaque semaine en amont et en aval de chaque filtre, notamment au redémarrage de la ventilation. En fonction des variations saisonnières de la concentration des microorganismes, les résultats ont montré en particulier des efficacités de filtration vis-à-vis des particules bactériennes faibles, voire négatives, dans l unité de filtration fonctionnant en continu.Microbial indoor air quality is an important issue in particular in the professional sector. This thesis aims to investigate the conditions leading to microbial development on to fibrous filters and to microbial release down stream of filters that could decrease air quality. The first part of the thesis was realized on laboratory and consisted in the filtration of a microbial consortium composed with Staphylococcus epidermidis (bacterium specie) and Penicillium oxalicum (fungi specie). The effects of three parameters on the microbial behavior were studied : the relative humidity (RH) of the air, the filter material, the airflow presence/absence. Whatever conditions, S. epidermidis did not grow up. However, P. oxalicum has demonstrated its ability to develop itself when RH was close to 100% and some P. oxalicumspores were released downstream of filter after growth, when ventilation was restarted. The second part of the thesis consisted in working with a semi-urban outdoor air. Two air handling unit (AHU) have operated during 5 months. The ventilation of one AHU was stopped each week-end and restarted each beginning of week. Temperature and RH of the air, filters pressure drop and total concentration of PM in air before filtration were monitored. Concentration of total cultivable microorganisms upstream and downstream of both filters was also measured each week, in particular at the restart of ventilation for one AHU. According to seasonal variations of microbial concentrations, results have revealed for instance that the filtration efficiency of cultivable bacteria was particularly weak, and sometimes negative, for the AHU operating continuously.NANTES-ENS Mines (441092314) / SudocSudocFranceF

Application of sludge-based carbonaceous materials in a hybrid water treatment process based on adsorption and catalytic wet air oxidation

This paper describes a preliminary evaluation of the performance of carbonaceous materials prepared from sewage sludges (SBCMs) in a hybrid water treatment process based on adsorption and catalytic wet air oxidation; phenol was used as the model pollutant. Three different sewage sludges were treated by either carbonisation or steam activation, and the physico-chemical properties of the resultant carbonaceous materials (e.g. hardness, BET surface area, ash and elemental content, surface chemistry) were evaluated and compared with a commercial reference activated carbon (PICA F22). The adsorption capacity for phenol of the SBCMs was greater than suggested by their BET surface area, but less than F22; a steam activated, dewatered raw sludge (SA_DRAW) had the greatest adsorption capacity of the SBCMs in the investigated range of concentrations (<0.05 mol L−1). In batch oxidation tests, the SBCMs demonstrated catalytic behaviour arising from their substrate adsorptivity and metal content. Recycling of SA_DRAW in successive oxidations led to significant structural attrition and a hardened SA_DRAW was evaluated, but found to be unsatisfactory during the oxidation step. In a combined adsorption–oxidation sequence, both the PICA carbon and a selected SBCM showed deterioration in phenol adsorption after oxidative regeneration, but a steady state performance was reached after 2 or 3 cycles

Reuse of medical face masks in domestic and community settings without sacrificing safety: Ecological and economical lessons from the Covid-19 pandemic

The need for personal protective equipment increased exponentially in response to the Covid-19 pandemic. To cope with the mask shortage during springtime 2020, a French consortium was created to find ways to reuse medical and respiratory masks in healthcare departments. The consortium addressed the complex context of the balance between cleaning medical masks in a way that maintains their safety and functionality for reuse, with the environmental advantage to manage medical disposable waste despite the current mask designation as single-use by the regulatory frameworks. We report a Workflow that provides a quantitative basis to determine the safety and efficacy of a medical mask that is decontaminated for reuse. The type IIR polypropylene medical masks can be washed up to 10 times, washed 5 times and autoclaved 5 times, or washed then sterilized with radiations or ethylene oxide, without any degradation of their filtration or breathability properties. There is loss of the antiprojection properties. The Workflow rendered the medical masks to comply to the AFNOR S76-001 standard as “type 1 non-sanitory usage masks”. This qualification gives a legal status to the Workflow-treated masks and allows recommendation for the reuse of washed medical masks by the general population, with the significant public health advantage of providing better protection than cloth-tissue masks. Additionally, such a legal status provides a basis to perform a clinical trial to test the masks in real conditions, with full compliance with EN 14683 norm, for collective reuse. The rational reuse of medical mask and their end-of-life management is critical, particularly in pandemic periods when decisive turns can be taken. The reuse of masks in the general population, in industries, or in hospitals (but not for surgery) has significant advantages for the management of waste without degrading the safety of individuals wearing reused masks

Influence on permeability of the structural parameters of heterogeneous porous media

WOS:000255724600003International audiencePredicting the macroscopic properties of porous media used in treatment processes is a complex task regarding 3-D structures at micro-, meso- and macro-levels. Currently, information is scarce concerning the influence, at a microscopic level, of the 3-D structure of fibrous media on the physical laws governing their macroscopic behaviour. Nevertheless, the relationship between macroscopic properties (pressure drop, treatment efficiency) and microstructure can be assessed thanks to suitable structure modelling theories. In this context, the present study proposes and compares different methods (mercury porosimetry and image analysis) for the structure characterization at a microscopic level Of filtering fibrous media, such as nonwoven and woven fabrics. The results obtained show a porous structure gradient in the thickness of the nonwoven media studied in terms of porosity, pore size and tortuosity factor. Moreover, the influence on structural parameters of media compression, when submitted to friction forces exerted by flow during filtration tests, is established. A model for the determination of multi-level pore size distributions from mercury porosimetry data is proposed. The "equivalent pore" model is used to estimate the tortuosity factor. The influence of measured structural parameters on fibrous media permeability is studied in a classical model for flow through fibrous media

Characteristics of fixed beds packed with anisotropic particles - Use of image analysis

WOS:000172287100004International audienceFixed beds of anisotropic particles are commonly involved in chemical engineering processes: beds of cylindrical catalyst pellets or beds of wood shavings in paper industry. The characterization of the spatial variations of their structural properties is of great importance for flow modelling purposes. In this work, we intend to produce new data concerning a bed of long cylinder (h/ d = 5.29) and a bed of flat plates (e/a = 0.209). This study focuses on the characterization of top and bottom effects, as well as wall effects. The experimental procedure is based on the study of sections of packed beds consolidated with a resin. The captured images of successive transverse and longitudinal sections of the beds are treated and analysed, thanks to an image analysis software. The local variation of the voidage is determined in both the transverse and the longitudinal directions of the beds. Furthermore, mean intercept lengths and mean numbers of particles are measured and discussed. Concerning flat plates, an anisotropic ratio calculated from intercept measurements is compared to that previously obtained from pressure drop measurements. The main results of this work concern the enlightening of wall effects and end effects importance for the two studied beds compared to beds of spheres studied in the literature. (C) 2001 Elsevier Science B.V. All rights reserved

Fibrous media plugging modelling for liquid filtration

WOS:000081787300007International audienceThe aim of this work is to model the plugging curve of fibrous media for depth and surface filtration. The model links the evolution of pressure drop versus the injected mass of pollutants to structural properties of the media. Furthermore, thanks to the model, it is possible to predict the fibrous composition of a medium, which conforms to given filtration properties. First, a review of the typical fibrous media for engine oil filtration formed in our Laboratory is proposed, and, the measured filtration properties as well as the methods used for the characterization of structural properties of the media during plugging are presented. Then, an explanation of the evolution of structural properties is proposed. In the second part, the results of the structural property characterization during plugging are used to develop a model of the pressure drop evolution as a function of the injected mass of pollutants. Then, correlation laws linking the model parameters to the structural properties of the medium are given and the model is used to predict the plugging curve of two typical filtering media

Oxydation photocatalytique de composés organiques volatils et suivi de leurs intermédiaires réactionnels (étude en réacteurs statique et dynamique à des concentrations typiques de l'air intérieur)

La photocatalyse hétérogène est une technique d oxydation utilisée pour l élimination des Composés Organiques Volatils (COV). L objectif est d étudier la dégradation des COV initiaux et la production d intermédiaires réactionnels lors de la mise en oeuvre de ce procédé dans des conditions proches de l air intérieur (concentration des COV en mélange). TroisCOV modèles (toluène, décane, trichloréthylène) sont étudiés séparément puis en mélange dans un réacteurstatique puis dans un réacteur dynamique multi-pass. Les résultats obtenus montrent que (i) l efficacité dedégradation dépend de la nature et du nombre de COV à traiter, des caractéristiques du média photocatalytiqueet des conditions opératoires, (ii) les intermédiaires majoritaires et les plus persistants sont les aldéhydeslégers, (iii) l élimination des aldéhydes est inhibée lorsque les COV initiaux sont en mélange, (iv) l augmentation du temps de résidence sur le matériau photocatalytique permet une élimination plus rapide des COV initiaux et des sous-produits.Heterogeneous photocatalysis is a technique of oxidation used for the removal of Volatile Organic Compounds (VOCs). Aim is to study the degradation of initial VOCs and the production of reaction intermediates during this process in conditions close to the indoor air (VOC concentration in mixture). Three model VOCs (toluene, decane, trichloroethylene) are studied separately and then in mixture in a static reactor and in a dynamic multi-pass reactor. The obtained results show that (i) the degradation efficiency depends on the nature and the number of VOCs, on the photocatalyst characteristics and on process conditions, (ii) the major and the most persistent intermediates are light aldehydes, (iii) the elimination of aldehydes is inhibited when the initial VOCs are in mixture, (iv) increasing the residence time on the photocatalyst provides a higher removal rate of initial VOCs and of byproducts.NANTES-ENS Mines (441092314) / SudocSudocFranceF

Image analysis: a useful tool for porous media characterization

WOS:000187466500013International audienceno abstrac

Fibrous media plugging modelling for liquid filtration

WOS:000081787300007International audienceThe aim of this work is to model the plugging curve of fibrous media for depth and surface filtration. The model links the evolution of pressure drop versus the injected mass of pollutants to structural properties of the media. Furthermore, thanks to the model, it is possible to predict the fibrous composition of a medium, which conforms to given filtration properties. First, a review of the typical fibrous media for engine oil filtration formed in our Laboratory is proposed, and, the measured filtration properties as well as the methods used for the characterization of structural properties of the media during plugging are presented. Then, an explanation of the evolution of structural properties is proposed. In the second part, the results of the structural property characterization during plugging are used to develop a model of the pressure drop evolution as a function of the injected mass of pollutants. Then, correlation laws linking the model parameters to the structural properties of the medium are given and the model is used to predict the plugging curve of two typical filtering media