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

OPTIMISATION DE L'HYDRODYNAMIQUE DANS DES PHOTOBIOREACTEURS A HAUTE PRODUCTIVITE VOLUMIQUE POUR EVITER LE DEVELOPPEMENT DE BIOFILM

International audienc

Filterability of exopolysaccharides solutions from the red microalga Porphyridium cruentum by tangential filtration on a polymeric membrane

International audienceThe red microalga Porphyridium cruentum is exploited industrially for its exopolysaccharides (EPS) and pigments production. EPS produced by P. cruentum are partially released and dissolved into the surrounding environment, they can be recovered from the culture medium after removing the cells. This paper presents a parametric study of the ultrafiltration of EPS solutions on organic membrane. The EPS solutions were produced in conditions representative of an industrial production. They were filtered at lab-scale on a flat, PES 50 kDa MWCO membrane in a complete recirculation mode of permeate and retentate. Permeate flux-transmembrane pressure (TMP) curves were established up to the limiting flux for the filtration of solutions with various values of concentration in EPS (0.10 to 1.06 kg GlcEq.m), fluid tangential velocity (0.3 to 1.2 m.s) and temperature (20 and 40 °C). The reversible and irreversible parts of fouling were evaluated for each experiment and the critical flux was determined for an intermediate EPS concentration (0.16 kg GlcEq.m). The results showed that EPS solutions had a strong fouling capacity. When filtering the lowest concentrated solution (0.10 kg GlcEq.m) with moderate fouling conditions, the overall fouling resistance was approximately half of the membrane and the share of irreversible/reversible fouling was 88 and 12%. However, the part of reversible fouling becomes predominant when approaching the limiting flux. Permeate fluxes which were obtained allow to estimate that a VRR of approximately 10 could be obtained when concentrating EPS solutions using PES membranes in flat or tubular modules but not in spiral-wound

Caractérisation, modélisation de la croissance photosynthétique de Chlamydomonas reinhardtii en photobioréacteur et mise en évidence du couplage à l'hydrodynamique

Cette thèse porte sur l étude de la croissance photosynthétique de la microalgue Chlamydomonas reinhardtii en photobioréacteur. Les travaux ont porté en première étape sur la caractérisation de la réponse en lumière continue. Ensuite, l étude s est poursuivie en caractérisant les effets des cycles de lumière/obscurité générés par un panneau de diodes électroluminescentes (DEL) sur la productivité volumique en biomasse afin d étudier l effet de l hydrodynamique sur la conversion photosynthétique (light/dark cycles effect). Les expérimentations en limitation physique stricte et en photolimitation ont permis d une part de définir les paramètres gouvernant la productivité volumique maximale en PBR, à savoir: la densité de flux incidente (PFD), la surface spécifique éclairée (alight) et la fraction volumique éclairée (g). Il a été également possible d établir un modèle cinétique de la croissance de C. reinhardtii en lumière continue. Ce modèle est basé sur une approche prédictive reposant sur la Thermodynamique des Processus Irréversibles (TPI), et prenant en compte les contributions respectives de la croissance photosynthétique et de la respiration à la lumière sur la cinétique globale. La dernière partie de ce mémoire concerne les expérimentations réalisées en lumière intermittente où différents régimes d éclairement ont été testés. Des cycles longs (>40s) se sont révélés avoir un effet négatif sur la croissance. Pour des cycles plus courts ( 40s), a negative effect on the mean volumetric growth rate hase been observed. Shorter cycles (<12s) showed a non-linear coupling between cycles frequencies and the photosynthetic growth, emphasizing on interaction with dynamic response of the microorganism metabolismNANTES-BU Sciences (441092104) / SudocSudocFranceF

Développement d'un photobioréacteur solaire intensifié en vue de la production à grande échelle de biomasse microalgale

NANTES-BU Sciences (441092104) / SudocSudocFranceF

Étude des voies métaboliques de production d'hydrogène chez la microalgue Chlamydomonas reinhardtii et transposition en photobioréacteur

A partir du constat que la consommation énergétique et les risques environnementaux associés se sont considérablement accrus ces dernières années, des pistes nouvelles sont aujourd'hui étudiées pour développer l'utilisation d'énergies alternatives propres et renouvelables, et l'hydrogène semble dans ce contexte être une solution sérieuse. Sa production par voie photobiologique a fait l'objet de ce travail, dont l'objectif est d'exploiter les capacités photosynthétiques des microalgues afin d'élaborer à terme un procédé de production d'hydrogène à partir d'énergie solaire et d'eau sans dégagement parallèle de gaz à effet de serre. Des expérimentations pour la compréhension des phénomènes métaboliques intervenant dans la production d'hydrogène chez l'espèce Chlamydomonas reinhardtii - ont donc été menées et les résultats obtenus ont été transposés au niveau d'un photobioréacteur torique développé spécifiquement pour cette applicationConsidering the recent increase in energy consumption and associated environmental risks, new trails are followed today to develop the use of clean and renewable alternative energies, and in this context hydrogen seems to be a serious solution. The aim of this work is then to exploit microalgae photosynthetic capacities in order to devise a process for hydrogen production from only water and solar energy without greenhouse gas release. Experiments for the comprehension of the metabolic pathways implied in hydrogen production in Chlamydomonas reinhardtii species were thus carried out and the results obtained were scaled up to the level of a torus photobioreactor specifically developed for this application.NANTES-BU Sciences (441092104) / SudocNANTES-Ecole Centrale (441092306) / SudocSudocFranceF

Kinetic modeling of the photosynthetic growth of Chlamydomonas reinhardtii in a photobioreactor

International audienc

Investigation of the coupling between growth and TAG extraction stages in solar conditions for biodiesel production by microalgae

International audienc