This thesis concerns the caracterisation and the modeling of the photosynthetic growth of the mic... more This thesis concerns the caracterisation and the modeling of the photosynthetic growth of the microalga Chlamydomonas reinhardtii in photobioreactor. The hydrodynamic effect on the photosynthetic conversion in PBR was also emphasized. This work has been performed in two steps: in the first one, the photosynthetic response at continuous light was characterized. In a second one, a light emitting diodes panel (LED) was used in the investigation on the effect of intermittent light on the volumetric biomass productivity, so as to simulate hydrodynamics influence on photosynthetic conversion (light/dark cycles effect). Experiments in physical limitation by light and light-limited culture allowed to define parameters governing the maximum volumetric biomass productivity in PBR: the incident photon flux density (PFD), the specific illuminated area (alight) and the working illuminated volume fraction (γ). A kinetic model for the photosynthetic growth of C. Reinhardtii in continuous light was...
Le mélange amidon/protéines sériques est souvent mis en oeuvre dans des conditions industrielles ... more Le mélange amidon/protéines sériques est souvent mis en oeuvre dans des conditions industrielles pour ses propriétés épaississantes, sans en maîtriser complètement les paramètres de traitement. La texture finale résulte d’un changement de structure intervenant pour les deux constituants dans une plage de température restreinte (65-75°C) et soumis aux conditions de l’ensemble du traitement. Le comportement rhéologique d’un mélange amidon/protéine sériques (3% amidon de maïs cireux réticulé/1,5% de protéines sériques) a été étudié après traitement thermomécanique sur une plage de 90 à 110°C à deux échelles : au laboratoire dans un réacteur de 1,2L et à l’échelle pilote dans un échangeur tubulaire (Actini) à 50L/h. Le cisaillement a été imposé dans ce dernier cas par le passage à travers la vanne de contre-pression située après la section de chambrage/refroidissement. Nous avons mesuré les propriétés rhéologiques en écoulement et en régime harmonique sur le mélange et sur l’amidon seul...
In microalgae cultivation, the combination of light attenuation and culture mixing exposes the mi... more In microalgae cultivation, the combination of light attenuation and culture mixing exposes the microalgae to fluctuating light regimes, which is a factor that can interact with cell metabolism and affect photosynthetic conversion. Here we investigate the effect of light/dark cycles (L/D cycles) on the growth of microalga Chlamydomonas reinhardtii using a photobioreactor equipped with a light-emitting diode (LED) panel to simulate L/D cycles. The L/D cycles applied were engineered to mimic L/D cycles obtained in photobioreactor operating conditions, i.e. L/D cycle frequencies and light attenuation conditions applied during the light period. Long-term experiments were run in continuous mode to investigate whether cells adapt to applied L/D cycles. For cycles of duration higher than 40 s, microalgal response was close to the response assuming no L/D cycle effect (no light integration). Biomass growth rate showed responses at durations below 12 s, which points to partial light integration resulting in an increase of measured biomass growth rate. This increase is known as the "L/D cycle effect", where L/D cycle frequencies are found to generate positive effects for photosynthetic conversion. To investigate whether the growth increase was explained by L/D cycle effects, results were compared against the predictions of a kinetic model assuming no light integration but time-solved for light regimes corresponding to L/D cycles applied experimentally. The model was found to very accurately represent any of the light regimes applied, including those leading to an increase in biomass growth rate. It was then concluded that expected primary coupling between L/D cycles and photosynthetic conversion was negligible. The main influence was on pigment adaptation, which when integrated into the kinetic model assuming no L/D cycle effects was found to very accurately predict culture growth under all light regimes.
The aim of this study was to establish and validate a model for the photosynthetic growth of Chla... more The aim of this study was to establish and validate a model for the photosynthetic growth of Chlamydomonas reinhardtii in photobioreactors (PBRs). The proposed model is based on an energetic analysis of the excitation energy transfer in the photosynthesis apparatus (the Z-scheme for photosynthesis). This approach has already been validated in cyanobacteria (Arthorspira platensis) and is extended here to predict the volumetric biomass productivity for the microalga C. reinhardtii in autotrophic conditions, taking into consideration the two metabolic processes taking place in this eukaryotic microorganism, namely photosynthesis and respiration. The kinetic growth model obtained was then coupled to a radiative transfer model (the two-flux model) to determine the local kinetics, and thereby the volumetric biomass productivity, in a torus PBR. The model was found to predict PBR performances accurately for a broad set of operating conditions, including both light-limited and kinetic growth regimes, with a variance of less than 10% between experimental results and simulations.
Photosynthetic hydrogen production under light by the green microalga Chlamydomonas reinhardtii w... more Photosynthetic hydrogen production under light by the green microalga Chlamydomonas reinhardtii was investigated in a torus-shaped PBR in sulfur-deprived conditions. Culture conditions, represented by the dry biomass concentration of the inoculum, sulfate concentration, and incident photon flux density (PFD), were optimized based on a previously published model (Fouchard et al., 2009. Biotechnol Bioeng 102:232-245). This allowed a strictly autotrophic production, whereas the sulfur-deprived protocol is usually applied in photoheterotrophic conditions. Experimental results combined with additional information from kinetic simulations emphasize effects of sulfur deprivation and light attenuation in the PBR in inducing anoxia and hydrogen production. A broad range of PFD was tested (up to 500 µmol photons m(-2) s(-1) ). Maximum hydrogen productivities were 1.0 ± 0.2 mL H₂ /h/L (or 25 ± 5 mL H₂ /m(2) h) and 3.1 mL ± 0.4 H₂ /h L (or 77.5 ± 10 mL H₂ /m(2) h), at 110 and 500 µmol photons m(-2) s(-1) , respectively. These values approached a maximum specific productivity of approximately 1.9 mL ± 0.4 H₂ /h/g of biomass dry weight, clearly indicative of a limitation in cell capacity to produce hydrogen. The efficiency of the process and further optimizations are discussed.
This thesis concerns the caracterisation and the modeling of the photosynthetic growth of the mic... more This thesis concerns the caracterisation and the modeling of the photosynthetic growth of the microalga Chlamydomonas reinhardtii in photobioreactor. The hydrodynamic effect on the photosynthetic conversion in PBR was also emphasized. This work has been performed in two steps: in the first one, the photosynthetic response at continuous light was characterized. In a second one, a light emitting diodes panel (LED) was used in the investigation on the effect of intermittent light on the volumetric biomass productivity, so as to simulate hydrodynamics influence on photosynthetic conversion (light/dark cycles effect). Experiments in physical limitation by light and light-limited culture allowed to define parameters governing the maximum volumetric biomass productivity in PBR: the incident photon flux density (PFD), the specific illuminated area (alight) and the working illuminated volume fraction (γ). A kinetic model for the photosynthetic growth of C. Reinhardtii in continuous light was...
Le mélange amidon/protéines sériques est souvent mis en oeuvre dans des conditions industrielles ... more Le mélange amidon/protéines sériques est souvent mis en oeuvre dans des conditions industrielles pour ses propriétés épaississantes, sans en maîtriser complètement les paramètres de traitement. La texture finale résulte d’un changement de structure intervenant pour les deux constituants dans une plage de température restreinte (65-75°C) et soumis aux conditions de l’ensemble du traitement. Le comportement rhéologique d’un mélange amidon/protéine sériques (3% amidon de maïs cireux réticulé/1,5% de protéines sériques) a été étudié après traitement thermomécanique sur une plage de 90 à 110°C à deux échelles : au laboratoire dans un réacteur de 1,2L et à l’échelle pilote dans un échangeur tubulaire (Actini) à 50L/h. Le cisaillement a été imposé dans ce dernier cas par le passage à travers la vanne de contre-pression située après la section de chambrage/refroidissement. Nous avons mesuré les propriétés rhéologiques en écoulement et en régime harmonique sur le mélange et sur l’amidon seul...
In microalgae cultivation, the combination of light attenuation and culture mixing exposes the mi... more In microalgae cultivation, the combination of light attenuation and culture mixing exposes the microalgae to fluctuating light regimes, which is a factor that can interact with cell metabolism and affect photosynthetic conversion. Here we investigate the effect of light/dark cycles (L/D cycles) on the growth of microalga Chlamydomonas reinhardtii using a photobioreactor equipped with a light-emitting diode (LED) panel to simulate L/D cycles. The L/D cycles applied were engineered to mimic L/D cycles obtained in photobioreactor operating conditions, i.e. L/D cycle frequencies and light attenuation conditions applied during the light period. Long-term experiments were run in continuous mode to investigate whether cells adapt to applied L/D cycles. For cycles of duration higher than 40 s, microalgal response was close to the response assuming no L/D cycle effect (no light integration). Biomass growth rate showed responses at durations below 12 s, which points to partial light integration resulting in an increase of measured biomass growth rate. This increase is known as the "L/D cycle effect", where L/D cycle frequencies are found to generate positive effects for photosynthetic conversion. To investigate whether the growth increase was explained by L/D cycle effects, results were compared against the predictions of a kinetic model assuming no light integration but time-solved for light regimes corresponding to L/D cycles applied experimentally. The model was found to very accurately represent any of the light regimes applied, including those leading to an increase in biomass growth rate. It was then concluded that expected primary coupling between L/D cycles and photosynthetic conversion was negligible. The main influence was on pigment adaptation, which when integrated into the kinetic model assuming no L/D cycle effects was found to very accurately predict culture growth under all light regimes.
The aim of this study was to establish and validate a model for the photosynthetic growth of Chla... more The aim of this study was to establish and validate a model for the photosynthetic growth of Chlamydomonas reinhardtii in photobioreactors (PBRs). The proposed model is based on an energetic analysis of the excitation energy transfer in the photosynthesis apparatus (the Z-scheme for photosynthesis). This approach has already been validated in cyanobacteria (Arthorspira platensis) and is extended here to predict the volumetric biomass productivity for the microalga C. reinhardtii in autotrophic conditions, taking into consideration the two metabolic processes taking place in this eukaryotic microorganism, namely photosynthesis and respiration. The kinetic growth model obtained was then coupled to a radiative transfer model (the two-flux model) to determine the local kinetics, and thereby the volumetric biomass productivity, in a torus PBR. The model was found to predict PBR performances accurately for a broad set of operating conditions, including both light-limited and kinetic growth regimes, with a variance of less than 10% between experimental results and simulations.
Photosynthetic hydrogen production under light by the green microalga Chlamydomonas reinhardtii w... more Photosynthetic hydrogen production under light by the green microalga Chlamydomonas reinhardtii was investigated in a torus-shaped PBR in sulfur-deprived conditions. Culture conditions, represented by the dry biomass concentration of the inoculum, sulfate concentration, and incident photon flux density (PFD), were optimized based on a previously published model (Fouchard et al., 2009. Biotechnol Bioeng 102:232-245). This allowed a strictly autotrophic production, whereas the sulfur-deprived protocol is usually applied in photoheterotrophic conditions. Experimental results combined with additional information from kinetic simulations emphasize effects of sulfur deprivation and light attenuation in the PBR in inducing anoxia and hydrogen production. A broad range of PFD was tested (up to 500 µmol photons m(-2) s(-1) ). Maximum hydrogen productivities were 1.0 ± 0.2 mL H₂ /h/L (or 25 ± 5 mL H₂ /m(2) h) and 3.1 mL ± 0.4 H₂ /h L (or 77.5 ± 10 mL H₂ /m(2) h), at 110 and 500 µmol photons m(-2) s(-1) , respectively. These values approached a maximum specific productivity of approximately 1.9 mL ± 0.4 H₂ /h/g of biomass dry weight, clearly indicative of a limitation in cell capacity to produce hydrogen. The efficiency of the process and further optimizations are discussed.
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Papers by Hosni Takache