Cultivating microalgae in desert conditions: Evaluation of the effect of light‐temperature summer conditions on the growth and metabolism of nannochloropsis qu130

Temperature and light are two of the most crucial factors for microalgae production. Variations in these factors alter their growth kinetics, macromolecular composition and physiological properties, including cell membrane permeability and fluidity. The variations define the adaptation mechanisms adopted by the microalgae to withstand changes in these environmental factors. In the Qatar desert the temperature varies widely, typically between 10° and 45 °C There are also wide variations in light intensity, with values of over 1500 μmolhν.m−2s−1 in summer. A study of the effects of these thermal and light fluctuations is therefore essential for large‐scale outdoor production systems, especially during the summer when temperature and light fluctuations are at their highest. The aim of this work is to study the impact of temperature and light intensity variations as encountered in summer period on the Nannochloropsis QU130 strain, which was selected for its suitability for outdoor cultivation in the harsh conditions of the Qatar desert. It was carried out using lab‐scale photobioreactors enabling simulation of both constant and dynamic temperature and light regimes. Biomass productivity, cell morphology and biochemical compositions were examined first in constant conditions, then in typical outdoor cultivation conditions to elucidate the adjustments in cell function in respect of fluctuations. The dynamic light and temperature were shown to have interactive effects. The application of temperature cycles under constant light led to a 13.6% increase in biomass productivity, while a 45% decrease was observed under light and temperature regimes due to the combined stress. In all cases, the results proved that N. sp. QU130 has a high level of adaptation to the wide fluctuations in light and temperature stress. This was shown through its ability to easily change its physiology (cell size) and metabolic process in response to different cultivation conditions.This research was funded by University of Qatar and University of Nantes

HVP-photobioreactor for intensified microalgal culture

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INFLUENCE D'UN ECOULEMENT TOURBILLONNAIRE SUR L'ACCES A LA LUMIERE DES MICROALGUES (CONCEPTION D'UN PHOTOBIOREACTEUR ET MODELISATION DE LA CROISSANCE D'UNE CULTURE DE PORPHYRIDIUM PURPUREUM)

NANTES-BU Sciences (441092104) / SudocSudocFranceF

Knowledge models for the engineering and optimization of photobioreactors

International audienceThe modeling of microalgal photosynthetic biomass production draws some support from the abundant literature on bioprocess modeling, in particular when mineral or CO 2 mass-transfer limitations on growth rates are considered in the same way as substrate and O 2-transfer limitations in engineered bacterial cultivation. However, photosynthetic biomass growth exhibits highly specific features owing to its need for light energy: unlike dissolved nutrients, assumed to be homogeneous in well-mixed conditions, light energy is heterogeneously distributed in the culture due to absorption and scattering by cells, independently of the mixing conditions. As light is the principal energy source for photosynthesis, this heteroge-neity alone sets microalgal cultivation systems apart from other classical biopro-cesses, as they are generally limited by light transfer inside the culture media. Hence the design, optimization and control of photobioreactors (PBRs) require specific approaches. This chapter deals with developing useful knowledge models for engineering microalgal cultivation systems. Prerequisites and main concepts will be presented. Concrete illustrations will be given that use modeling to gain a deeper understanding of the complex influence of light transfer on the process, and to predict bio-mass productivities as a function of cultivation system engineering variables (espe-cially depth of culture) and operating settings (residence time and incident light flux) in both artificial constant light and natural sunlight conditions. 10.2 Theoretical background for radiation measurement and handling 10.2.1 Main physical variables Given the crucial importance of radiative transfer description in photobioreactor modeling, it is essential to have a broad overview of the main physical quantities and definitions involved in radiation measurement and theory, together with a thorough knowledge of the conversion factors linking the two main practical systems of units (joules and micromoles of photons). There is often much confusion on these points in the microalgal growth modeling literature, conducive to misinterpretation of related physical and physiological processes. This section gives

Production d’hydrogène par les microorganismes photosynthétiques

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Three-Dimensional Swirl Flow Velocity-Field Reconstruction Using a Neural Network With Radial Basis Functions

International audienceFor many studies, knowledge of continuous evolution of hydrodynamic characteristics is useful but generally measurement techniques provide only discrete information. In the case of complex flows, usual numerical interpolating methods appear to be not adapted, as for the free decaying swirling flow presented in this study. The three-dimensional motion involved induces a spatial dependent velocity-field. Thus, the interpolating method has to be three-dimensional and to take into account possible flow nonlinearity, making common methods unsuitable. A different interpolation method is thus proposed, based on a neural network algorithm with Radial Basis Functions

Numerical investigation of hydrodynamic and mixing conditions in a torus photobioreactor

International audienceIt is well-known that the response of photosynthetic microorganisms in photobioreactor (PBR) is greatly influenced by the geometry of the process, and its cultivation parameters. The design of an adapted PBR requires understanding of the coupling between the biological response and the environmental conditions applied. Cells culture under well-defined conditions are thus of primary interest. A particular lab-scale PBR has been developed for this purpose. It is based on atorus shape, that enables light to be highly controlled while providing a very efficient mixing, especially along the light gradient in the culture, that it is known to be a key-parameter in PBR running. A complete characterization of hydrodynamicconditions is presented, using computational fluids dynamics (CFD). After validation by comparison with experimental measurements, a parametric study is conducted to characterize important hydrodynamics features with respect to PBR application (light access, circulation velocity, global shear-stress), and then to investigate a possible optimization of the process via modification of the impeller used for culture mixing. The final part of the study is devoted to a detailed investigation of mixing performance of the torus PBR, by numerically predicting dispersion of a passive tracer in various configurations. The high degree of mixing observed shows the great potential of such innovative geometry in the field of photosynthetic microorganisms cultivation, especially for the design of a lab-scale process to conduct experiments under well-controlled conditions (light and flow) for modeling purpose

Hydrodynamics influence on light conversion in photobioreactors: An energetically consistent analysis

International audienceHydrodynamics conditions are supposed to affect light conversion in photobioreactors (PBRs), by modifying light availability of suspended photosynthetic cells. The present study aims at rigorously analyzing mixing conditions influence on PBR efficiency. Investigation is based on a Lagrangian formulation, which is well adapted to characterize individual cell history. Its association with a radiative-transfer model to characterize light availability is emphasized. Such approach has already been applied in PBR modeling, but with an oversimplified formulation where both cell trajectories and radiative transfer were solved independently. As energetic balances on the material and photonic phases will show, it is however necessary to introduce influence of the heterogeneous light access implied by non-ideal mixing conditions in the non-linear radiation field resolution. The proposed energetically consistent Lagrangian method will be finally associated to a standard photo-synthetic growth model to simulate batch cultivation in a torus PBR, retained here as a practical example. Although hydrodynamics will be introduced in the calculation, simulations will show that, without a dynamic interaction between photosynthetic conversion and fluctuating light regimes implied by cell movement along light gradient (the so-called light/dark cycles effects), PBR efficiency for a given species is only dependent on the light input and reactor geometry, according to the first principle of thermodynamics

Production industrielle de microalgues et cyanobactéries

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