Showing papers by "E. Molina Grima published in 1994"

A mathematical model of microalgal growth in light-limited chemostat culture

Abstract: A mathematical model for light-limited growth of a continuous microalgal culture is proposed. Average light intensity inside the photobioreactor was calculated, taking light attenuation by algae into account. The biomass absorption coefficient was determined by means of two new parameters, the pigment-free biomass, Y B , and the total pigment absorption, Y p (absorption coefficient normalized to total pigment content). The model reproduced the steady states reached and the dynamic behavior of the system when the dilution rate was changed

Comparison between extraction of lipids and fatty acids from microalgal biomass

Abstract: Seven solvent mixtures have been used to extract the lipid fraction of lyophilized biomass ofIsochrysis galbana. Six of them were composed of biocompatible solvents. Each method was carried out under relaxed operating conditions (i.e., one hour at room temperature) with extraction in a nitrogen atmosphere to prevent autooxidation and degradation of polyunsaturated fatty acids (PUFAs). Apart from the well-established Bligh and Dyer method [Can. J. Biochem. Physiol. 37:911 (1959)] (Cl3CH/MeOH/H2O, 1∶2∶0.8, vol/vol/vol), which rendered the highest yield of lipids (93.8%), ethanol (96%) and hexane/ethanol (96%), 1∶2.5 vol/vol produced the best results (84.4 and 79.6%, respectively). To obtain free fatty acids, KOH was added to the solvent mixtures used to extract the total lipids, except for Cl3CH/MeOH/H2O, and direct saponification was carried out at 60°C for 1 h or at room temperature for 8 h. The highest yields obtained by direct saponicification were 81% with hexane/ethanol (96%), 1∶2.5, vol/vol and 79.8% with ethanol (96%). Partial yields of the mainn-3 PUFAs found inI. galbana, stearidonic acid (SA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), were calculated for both extraction methods. For lipid extraction with ethanol (96%), yields of 91, 82 and 83% were obtained for SA, EPA and DHA, respectively. When direct saponification was used, hexane/ethanol (96%; 1∶2.5, vol/vol) produced the best yields of (91, 79 and 69% for SA, EPA and DHA, respectively).

Outdoor chemostat culture of Phaeodactylum tricornutum UTEX 640 in a tubular photobioreactor for the production of eicosapentaenoic acid.

Abstract: A tubular photobioreactor, based on an external loop airlift, has been used for outdoor continuous culture of the microalga Phaeodactylum tricornutum UTEX 640, rich in eicosapentaenoic acid (EPA). The effect of dilution rate on the biomass productivity and EPA production were examined. A maximum biomass productivity of 2.57 g⋅day−1⋅litre−1 was reached at an optimum cellular density of 7.12 g⋅litre−1. At around 2times1017 quanta⋅s−1⋅cm-2 photosynthetic activity seemed to become light-saturated. As the dilution rate increased, the fatty acid profile in biomass dry weight changed and EPA became the major fatty acid. We believe that this outdoor production of EPA from this species is the highest ever obtained (47.8 mg⋅day−1⋅litre-1). On the basis of these data it would seem advisable to use tubular photobioreactor technology for the production of very valuable microalgal products

Effect of dilution rate on eicosapentaenoic acid productivity of Phaeodactylum tricornutum UTEX 640 in outdoor chemostat culture

Abstract: Eicosapentaenoic acid (EPA) volumetric productivity from an outdoor chemostat culture ofPhaeodactylum tricornutum UTEX 640 in a 50-l tubular photobioreactor varies with dilution rate, reaching a maximum of 47.8 mg l−1 d−1 at D=0.36 d−1. Continuous culture at high dilution rates' is proposed as the most adequate operating mode to maximize polyunsaturated fatty acid production.

Outdoor turbidostat culture of the marine microalga Tetraselmis sp.

Abstract: . Biomass productivity, photosynthetic efficiency and fatty acid profiles of the marine microalga Tetraselmis sp. in a turbidostat culture system using an outdoor photobioreactor are described. The maximum productivity depended on the units in which it was expressed; it reached 5·41 × 10−3 g/l/h in volumetric units, and 7·26g/m2/day in surface units, the former at the smallest culture depth (0·12m) and the latter at the greatest culture depth (0·25 m). Data from the experiments were adjusted to an equation for light limitation. The comparison of fatty acid composition at both depths showed that biosynthesis of polyunsaturated fatty acids (PUFAs), including eicosapentaenoic acid (EPA), was favoured when available light was low (0·17 m). Moreover, fatty acid 16:0 seemed to be an indicator of the type of limitation in the culture, i.e. nutrient or light limitation.

Estudio de macronutrientes para la producción de PUFAs a partir de la microalga marina Isochrysis galbana

Abstract: Marine microalgae are presented as alternative sources for polyunsaturated fatty acids production. A macronutrient optimization method for culture media commonly used for Isochrysis galbana growth is discussed. This microalga has been reported as a good RUFA producer. The optimization was conducted applying the response surface technique, parameters tested being nitrate, phosphate, ferric citrate and manganese chloride concentrations and the suplementary CO 2 in the bubbling air. The results show the evidence of growth limitation with the initial culture media and it is proposed a second optimization step considering as design variables the different ratios between media components.