Study of different membrane spargers used in waste water treatment : characterisation and performance

In urban waste water treatment, a novel gas sparger based on flexible rubber membrane has been used for the last ten years. The objective of this present work is to compare two flexible membranes (the new membrane and the old membrane provided by ONDEO-DEGREMONT group) used in waste water treatment. For this purpose, the different membrane properties (hole diameter, pressure drop, critical pressure, deflection at the centerline and elasticity) have been characterized. The bubble generation at the membranes with a single orifice and with four orifices have been studied and their performances have been compared in terms of interfacial area and power consumption. From the experimental and theoretical approach, the new membrane is less elastic (or more rigid) than the old membrane. The bubble diameters generated from the new membrane remain constant with the gas velocity through the orifice, whereas they increase logarithmically for the old membrane. The inverse behaviours are observed in terms of the bubble formation frequency. Moreover, the bubbles generated from the new membrane have significantly larger sizes and lower formation frequencies than those obtained with the old one. From these results, it can be noted that the new membrane has a behaviour comparable to a rigid orifice. No coalescence phenomenon at the bubble formation is observed from the new and the old membranes with four orifices. The interfacial area and the power consumption are evaluated and show slight differences between the interfacial area provided by the old and the new membranes for one value of power consumption

Investigations in an external-loop airlift photobioreactor with annular light chambers and swirling flow

Photosynthetic microorganisms could serve as valuable compounds, but also for environmental applications. Their production under controlled conditions implies to design specific reactors, named photobioreactors, in which light supply is the main constraint. This paper was devoted to an original external-loop airlift photobioreactor (PBR) with annular light chambers in which a swirling motion was induced. The aim was to characterize this novel geometrical configuration in terms of gas–liquid hydrodynamics, and to test its potentiality for algal cultures. This PBR consisted of two identical columns connected by flanges defining tangential inlets, each column being made of two transparent concentric tubes (6 L in liquid volume, 50 m−1 in specific illuminated area). Firstly, the global flow characteristics (circulation and mixing times) were determined by a tracer method and modelled by an axial dispersed plug flow with complete recirculation (Péclet number). By means of a double optical probe, both local and global time-averaged parameters of the gas phase were measured, namely void fraction, bubble velocity, frequency and size. The gas–liquid mass transfer were also characterized, in tap water and in culture medium, by measuring overall volumetric mass transfer coefficients. In a second time, cultures of the microalga Chlamydomonas reinhardtii were run in batch mode. The variations of biomass concentration and pigment content with time from inoculation were successfully obtained. All these findings highlighted: (i) some significant differences in terms of gas–liquid hydrodynamics between the present PBR and the usual airlift systems, (ii) the interest of this configuration for algal cultures, even if complementary studies and technological improvements are still required for definitively validating its scale-up

The CNRS-Summer School PHOTOCHEM on Preparative and Applied Photochemistry from 16th to 21st September 2018 in Anglet, France

Over the last decade, photochemistry has seen a remarkable comeback with significant contributions to green chemistry, organic synthesis, waste treatment, chemical engineering, continuous-flow technologies and new light sources. At the same time, the neglect of this research area by academia as well as industry has caused an urgent need for training in photochemical principles, reactor engineering and applications. Historically, France has been a key location in photochemical research and manufacturing. The first comprehensive Summer School on Photochemistry, chaired by Dr Karine Loubière, was thus organized as an École Thématique of the Centre National de la Recherche Scientifique (CNRS). The event took place between September 16th and 21st 2018 at the Atlantic seaside location of Anglet in the Southwest of France

Modélisation en génie des procédés par analyse dimensionnelle. Méthode et exemples résolus

Les principes de l’analyse dimensionnelle, associée à la théorie de similitude et à des essais sur maquette, ont été établis au cours des quatre derniers siècles par de grands noms de la science, depuis les travaux de Galilée et de Newton jusqu’aux études emblématiques de Froude (carènes de bateaux) et de Reynolds (écoulements de liquides). Paradoxalement, force est de constater qu’ils ne sont aujourd’hui que rarement présentés dans nos formations en génie des procédés comme un outil générique et d’avenir, et de fait très peu mis en pratique.L’objectif de cet ouvrage est de démontrer que l’analyse dimensionnelle demeure une voie fiable, robuste et pertinente pour comprendre, dimensionner, modéliser et conduire les procédés complexes de transformation de la matière en réacteur en dégageant une vision synthétique et physique des interactions produit/procédé. En mobilisant les acquis des recherches récentes dans le domaine, ce livre revient en détail sur le cadre théorique qui permet de respecter les principes de la théorie de similitude dans le cas de procédés mettant en œuvre un matériau dont une propriété physique est constante, puis, et c’est l’une de ses principales originalités, non constante ; il indique enfin les règles à suivre pour construire rigoureusement une relation de procédé (corrélation semi empirique) entre nombres sans dimension et mobiliser cette connaissance pour raisonner l’extrapolation. Des cas résolus et des exemples originaux issus essentiellement des travaux de recherche des auteurs en génie des procédés permettent d’illustrer les approches conceptuelles et de renforcer la pédagogie de l’ensemble.Pratique et synthétique, cet ouvrage s’adresse aux élèves ingénieurs en génie des procédés, de niveau bac + 2 au master, et bien sûr, aux ingénieurs, doctorants et scientifiques confirmés, soucieux de tirer le meilleur profit de leurs expérimentations sur des équipements de laboratoire et pilotes

Dimensional Analysis of Food Processes

This book deals with the modeling of food processing using dimensional analysis. When coupled to experiments and to the theory of similarity, dimensional analysis is indeed a generic, powerful and rigorous tool making it possible to understand and model complex processes for design, scale-up and /or optimization purposes.This book presents the theoretical basis of dimensional analysis with a step by step detail of the framework for applying dimensional analysis, with chapters respectively dedicated to the extension of dimensional analysis to changing physical properties and to the use of dimensional analysis as a tool for scaling-up processes. It includes several original examples issued from the research works of the authors in the food engineering field, illustrating the conceptual approaches presented and strengthen the teaching of all. Discusses popular dimensional analysis for knowledge and scaling-up tools with detailed case studies Emphasises the processes dealing with complex materials of a multiphase nature Introduces the concept of chemical or material similarity and a framework for analysis of the functional forms of the propoert

Accurate Measurement of the Photon Flux Received Inside Two Continuous Flow Microphotoreactors by Actinometry

International audienceIn this study, the photon flux received in two continuous flow microphotoreactors was measured by actinometry (potassium ferrioxalate). The microphotoreactorshad two different geometries and were irradiated by either a polychromatic or a monochromatic light source. A model considering the partial absorption of photons through the reactor depth and, if required, the polychromatic character of the light source and the dependence of the actinometer properties on the wavelength were formulated to describe the variation of the actinometer conversion with the irradiation time. The photon flux received in the microphotoreactors could be thus accurately calculated as a function of the emitted wavelength. The same methodology was then applied to measure the photon flux received in a batch immersion well photoreactor. The radiant power received in each photoreactor was compared to that emitted by thelamp and major differences were found, thus confirming the need for this kind of in situ measurement. Finally, some guidelines based on a knowledge of the photon fluxwere proposed to compare various photoreactors. They revealed in particular that the choice of the most efficient photoreactor depended on the criteria chosen to evaluatethe performances (i.e. productivity, Space Time Yield)