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Improvement of mixing can lead to an enhancement of photobioreactors productivity, provided that the adverse effect of shear forces is kept below the fragility- threshold of cells. Implementation of a swirling decaying flow induced by a tangential inlet in an annular photobioreactor was investigated. The study focused on a compromise solution between the mixing and the resulting shear stress, and various hydrodynamical characteristics were measured for five types of tangential inlets and three Reynolds number values. Comparison with a pseudo-axial flow induced by a radial inlet indicates that swirling flows are suitable in the particular application of microalgal cultures. L'amelioration du melange peut permettre une meilleure productivite des photobioreacteurs, dans la mesure ou l'effet indesirable des contraintes de cisaillement est garde en-dessous du seuil de fragilite des cellules. On a etudie l'effet d'un ecoulement declinant tourbillonnaire induit par une entree tangentielle dans un photobioreacteur annulaire. L'accent a ete mis sur un compromis entre le melange et la contrainte de cisaillement qui en resulte, et diverses caracteristiques hydrodynamiques ont ete mesurees pour cinq types d'entrees tangentielles et trois valeurs du nombre de Reynolds. La comparaison avec un ecoulement pseudo-axial induit par une entree radiale indique que les ecoulements tourbillonnaires conviennent a l'application particuliere des cultures de microalgues.

The antiproliferative activities of several extracts from cultivated microalgae in France have been studied against bronchopulmonary and epithelial cell lines, respectively (A549, NSCLC-N6 and SRA 01/04). The algal extracts, of Diatomae (Odontella aurita, Chaetoseros sp.), as well as of Haptophyceae: Isochrisys aff. galbana, appeared as the most active among all the assayed species, expressing a broad spectrum of in vitro antiproliferative activity of well-differentiated pathologic cells such as NSCLC-N6 by terminal differentiation. Bio-guided fractionation of the above referred extracts, led us to the isolation, of the carotenoid fucoxanthin. Fucoxanthin has been structurally determined, through modern spectral means and has been studied separately for its activities.

Experimental observations of cell size variations in the proliferating rhodophyte Porphyridium cruentum cul- tured under fully controlled conditions showed significant decreases from inoculation to a steady state in the che- mostat with 0.23 d � 1 dilution rate and to a minimum in batch, dropping in size by ratios of over 10. To numerically simulate these variations, we assumed that the cell is made up of two categories of components that behave differ- ently during the interphase and mitosis. These have been called essential (EC) and accessory (AC) components. It is assumed that the cell divides once the EC have doubled in size, regardless of the AC's state. The experimental cell weight time courses were correctly simulated by a model of synchronous cell kinetics based on these assumptions. The EC's specific growth rate was 1.5 times that of the whole cell, when no limitation occurred. The increase in cell weight observed during batch cultures after nutrient ex- haustion was suitably simulated by assuming that EC growth stops when a limiting nutrient is exhausted. Several parameters characterizing the cell kinetics were defined, particularly the minimum minimorum EC or cell weight (26 and 15 pg for chemostat and batch, respectively), which was influenced by the cultivation method, and the maximum whole cell weight (224 to 244 pg), which de- pended on the inoculum's age. The influence of culture conditions on the amount of essential and accessory com- ponents contained in a cell was examined. A new approach was developed with respect to these compartments to de- termine the most suitable strategy and conduct a predictive approach for valuable molecule production. B 2004 Wiley Periodicals, Inc.

Light is the main limiting factor in photoautotrophic-intensive production of microorganisms, and improvement of its use is an important concern for photobioreactor design and operation. Swirling flows, which are known to improve mass and photon transfers, were applied to annular light chambers of a photobioreactor and studied by simulation and microalgal culture. Two hydrodynamic conditions were compared: axial flow generating poor radial mixing, and tangential flow generating three-dimensional swirling motion. Batch and continuous cultures of the Rhodophyte Porphyridium cruentum were performed in a 100-L, 1.5-m 2 , fully controlled photobioreactor with eight light chambers. The inlet design of these chambers was modified to create the hydrodynamic conditions for comparison. Various intensities of swirling motion were used, characterized by the velocity factor (VF), defined as the ratio between annular chamber flow and inlet aperture sections. Experiments were performed within the range of photon flux densities (PFD) optimizing the yield of light energy transformation into living substance for the species and the temperature used. Culture kinetics with swirling flows generated by apertures of VF = 2, 4, and 9 were compared with pseudoaxial VF = 2 chosen as reference. Batch cultures with VF = 4 swirling flow showed no significant difference, whereas continuous cultures proved more discriminating. Although no significant difference was obtained for VF = 2, a 7% increase of steady-state productivity and a 26% decrease in time required to reach this steady state were obtained with VF = 4 swirling flow. This beneficial effect of swirling flow could have accounted for increased mixing. Conversely, VF = 9 swirling flow resulted in a 9% decrease of steady-state productivity and a 9% increase in the time required to reach this steady state, a negative effect that could have accounted for increased shear stress. CO 2 bioconversion yield at steady state showed a 34% increase for VF = 4. These results suggest that swirling motion makes microalgal cultures more efficient, provided that the resulting adverse effects remain acceptable. Experimental investigation was completed by a theoretical approach in which simulation of continuous cultures of P. cruentum was based on the hydrodynamic conditions achieved in the photobioreactor. Although the results obtained with pseudoaxial flow were correctly predicted, simulations with swirling flow showed a marked enhancement of productivity not observed experimentally. The influence of side effects induced by increased mixing (particularly hydrodynamic shear stress) was considered with respect to modeling assumptions. Comparison of experimental results with theoretical simulation provided a better understanding of the mixing effect, a key factor in improving the efficiency of such bioprocesses.

Algae are utilized diversely in aquaculture, but theirmain applications are related to nutrition. They areused in toto, as a sole component or as a foodadditive to supply basic nutrients, color the flesh ofsalmonids or for other biological activities. The needfor nutritional sources safer than traditional animalproducts has renewed interest in plants in general andalgae in particular. This report deals principallywith the nutritional role of microalgae inaquaculture.The larvae of molluscs, echinoderms andcrustaceans as well as the live prey of some fishlarvae feed on microalgae. Though attempts have beenmade to substitute inert particles for thesemicro-organisms which are difficult to produce,concentrate and store, only shrimp and live prey forfish will accept inert food, and only shrimp accept itfully. Several studies have confirmed that a live,multi-specific, low-bacteria microalgal biomassremains essential for shellfish hatcheries. Majoradvances are expected from new production systemdesigns and operations, from batch-run open tanks tomore sophisticated continuously run and closed loopreactors. Studies are underway to simplify hatcheryoperations by replacing biomass produced on-site withrun-times by that produced and preserved elsewhere.Although still promising, they have not given rise, sofar, to any application for molluscs. Otherapplications of microalgae in aquaculture, from greenwater to making salmon flesh pinker, are examined.Whether produced on or off-site, there remains thequestion of cost effectiveness of microalgalproduction systems. This can only be achieved bysubstantial upscaling and improved quality control.

Since food transformation obeys the same rules in both plant and animal kingdoms, data describing that of fish and microalgae, selected for their aquatic habitat and simple physiology, have been analyzed. It appears that three conditions must be observed in both cases: (i) fasting provokes weight loss, (ii) maximum growth is achieved with a feed ration known as saturation, and decreases beyond that; (iii) between rations of maintenance and of saturation, there is an optimal ration providing maximum transformation yield. Transformation models available in the literature were analyzed with respect to the mathematical constraints resulting from these rules. A three-parameter function to verify them was proposed, then applied to a few experimental series available for fish ( Oncorhynchus nerka ) and microalgae ( Porphyridium cruentum ). The satisfactory nature of the adjustments obtained suggests that the model is applicable to other cases, which are discussed.

A new type of preparative photobioreactor for high quality production of microalgae is developed for hatchery-nursery of marine animals, as well as for fine chemicals extraction. Of modular conception, two artificial light photobioreactors in plastic and stainless steel are designed so as to provide strictly controlled conditions in an attempt to increase quality and diminish cost prices. They are assessed for production of Porphyridum cruentum and compared to conventional transparent tanks and solar photobioreactors. The concentration and productivity obtained are ten-fold higher than with hatchery tanks, which leads to a significant drop in cost price of biomass. Comparison is also made with a 10 m2 solar photobioreactor operated in the south of France, for which biomass cost price is half that of 1.5 m2 artificial light photobioreactor. Extrapolations erasing size discrepancy show that the cost price of the two technologies are not very different.

Low-energy and low-cost separation of microalgae from water is important to the economics of microalgae harvesting and processing. Flotation under vacuum using a vacuum gas lift for microalgae harvesting was investigated for different airflow rates, bubble sizes, salinities and harvest volumes. Harvesting efficiency (HE) and concentration factor (CF) of the vacuum gas lift increased by around 50% when the airflow rate was reduced from 20 to 10 L min(-1). Reduced bubble size multiplied HE and CF 10 times when specific microbubble diffusers were used or when the salinity of the water was increased from 0 parts per thousand to 40 parts per thousand. The reduction in harvest volume from 100 to 1 L increased the CF from 10 to 130. An optimized vacuum gas lift could allow partial microalgae harvesting using less than 0.2 kWh kg(-1) DW, thus reducing energy costs 10-100 times compared to complete harvesting processes, albeit at the expense of a less concentrated biomass harvest. (C) 2012 Elsevier Ltd. All rights reserved.

Experimental observations of cell size variations in the proliferating rhodophyte Porphyridium cruentum cultured under fully controlled conditions showed significant decreases from inoculation to a steady state in the chemostat with 0.23 d(-1) dilution rate and to a minimum in batch, dropping in size by ratios of over 10. To numerically simulate these variations, we assumed that the cell is made up of two categories of components that behave differently during the interphase and mitosis. These have been called essential (EC) and accessory (AC) components. It is assumed that the cell divides once the EC have doubled in size, regardless of the AC's state. The experimental cell weight time courses were correctly simulated by a model of synchronous cell kinetics based on these assumptions. The EC's specific growth rate was 1.5 times that of the whole cell, when no limitation occurred. The increase in cell weight observed during batch cultures after nutrient exhaustion was suitably simulated by assuming that EC growth stops when a limiting nutrient is exhausted. Several parameters characterizing the cell kinetics were defined, particularly the minimum minimorum EC or cell weight (26 and 15 pg for chemostat and batch, respectively), which was influenced by the cultivation method, and the maximum whole cell weight (224 to 244 pg), which depended on the inoculum's age. The influence of culture conditions on the amount of essential and accessory components contained in a cell was examined. A new approach was developed with respect to these compartments to determine the most suitable strategy and conduct a predictive approach for valuable molecule production.

Light is the main limiting factor in photoautotrophic-intensive production of microorganisms, and improvement of its use is an important concern for photobioreactor design and operation. Swirling flows, which are known to improve mass and photon transfers, were applied to annular light chambers of a photobioreactor and studied by simulation and microalgal culture. Two hydrodynamic conditions were compared: axial flow generating poor radial mixing, and tangential flow generating three-dimensional swirling motion. Batch and continuous cultures of the Rhodophyte Porphyridium cruentum were performed in a 100-L, 1.5-m(2), fully controlled photobioreactor with eight light chambers. The inlet design of these chambers was modified to create the hydrodynamic conditions for comparison. Various intensities of swirling motion were used, characterized by the velocity factor (VF), defined as the ratio between annular chamber flow and inlet aperture sections. Experiments were performed within the range of photon flux densities (PFD) optimizing the yield of light energy transformation into living substance for the species and the temperature used. Culture kinetics with swirling flows generated by apertures of VF = 2, 4, and 9 were compared with pseudoaxial VF = 2 chosen as reference. Batch cultures with VF = 4 swirling flow showed no significant difference, whereas continuous cultures proved more discriminating. Although no significant difference was obtained for VF = 2, a 7% increase of steady-state productivity and a 26% decrease in time required to reach this steady state were obtained with VF = 4 swirling flow. This beneficial effect of swirling flow could have accounted for increased mixing. Conversely, VF = 9 swirling flow resulted in a 9% decrease of steady-state productivity and a 9% increase in the time required to reach this steady state, a negative effect that could have accounted for increased shear stress. CO(2) bioconversion yield at steady state showed a 34% increase for VF = 4. These results suggest that swirling motion makes microalgal cultures more efficient, provided that the resulting adverse effects remain acceptable. Experimental investigation was completed by a theoretical approach in which simulation of continuous cultures of P. cruentum was based on the hydrodynamic conditions achieved in the photobioreactor. Although the results obtained with pseudoaxial flow were correctly predicted, simulations with swirling flow showed a marked enhancement of productivity not observed experimentally. The influence of side effects induced by increased mixing (particularly hydrodynamic shear stress) was considered with respect to modeling assumptions. Comparison of experimental results with theoretical simulation provided a better understanding of the mixing effect, a key factor in improving the efficiency of such bioprocesses.

A deterministic Markov process was developed to estimate the efficiency of a fully controlled photobioreactor by calculating the growth of the Rhodophyte Porphyridium cruentum. It was assumed that microalgal growth, in strictly controlled and non-nutrient-limited conditions, is a function of the amount of light energy received. The light sources delivered a continuous 206 microE m(-2) s(-1) average photon flux density to cultures reaching concentrations of 3 g l(-1) in batch and 0.7 g l(-1) in chemostat. The concentration time-courses calculated compared satisfactorily with measured results for both batch and continuous cultures. The quality of simulation in these two cases validated the hypotheses made, especially for the linearity of light bioconversion, and allowed the model to be used for further exploration of the photobioreactor-operating domain. Distribution of the specific growth rate as a function of time and radial position was compared for the two simulated cases. The use of an initial batch of several days prior to the dilution of a continuous culture proved theoretically beneficial for overall production. The influence of the dilution rate and of light-path length on surface productivity and concentration at steady state were demonstrated.

International audience; Knowledge of the flow field can be very useful for reactor design and optimization. Data concerning the displacement and trajectories of reactive elements are of primary interest for a better understanding of process running. Results can be deduced from computational fluid dynamics or experimental measurements. However, numerical simulation is difficult to achieve for complex flow such as swirling decaying flow, and trajectories need to be calculated on the basis of velocity field measurements. This problem can be simplified by using a Lagrangian formulation, in which case the only major difficulty is to express the influence of turbulence on calculated trajectories. Velocity fluctuations can be considered as pure random functions or related to turbulence correlations. These two methods were used to calculate trajectories of elementary fluid particles in a swirling decaying flow on the basis of hydrodynamic characteristics obtained by particle image velocimetry (PIV) studies. Trajectory dispersion was then compared with experimental results obtained by PIV measurements of the instantaneous flow field. This comparison shows the great dependence of velocity fluctuation (and thus of trajectories) on spatial correlations. Finally, the correct mathematical formulation of velocity fluctuation was checked by using the trajectory calculation algorithm to determine residence time distribution (RTD). A comparison with experimental RTD confirmed the efficiency of the method for determining trajectories in swirling decaying flow.