J.L. García Sánchez

Comparison between extraction of lipids and fatty acids from microalgal biomass

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 continuous culture of Porphyridium cruentum in a tubular photobioreactor: quantitative analysis of the daily cyclic variation of culture parameters

The present work reports on the daily cyclic variation of oxygen generation rates, carbon consumption rates, photosynthetic activities, growth rates and biochemical composition of the biomass in a pilot plant continuous outdoor culture of the microalgae Porphyridium cruentum. A linear relationship between the external irradiance and the average irradiance inside the culture was found. In addition, the oxygen generation and carbon consumption rates were found to be a function of the average irradiance inside the culture. A reduction in photosynthetic activity of the cells at noon and recovery in the afternoon was also observed. Therefore, the cells showed a short-term response of parameters such as oxygen generation rate as well as carbon consumption rate with external and average irradiance; a model of photosynthesis rate considering photoinhibition is proposed. This model is a useful tool for the operation and scaleup of tubular photobioreactors, and can be used for determining CO2 requirements of the system. The higher the photosynthesis rates, the lower the carbon losses, ranging from 25% at noon to 100% during the night. The growth rate showed a linear relationship with the daily mean average irradiance inside the culture with a long-term response. Likewise, a linear relationship among the oxygen generation rate and the growth rate was obtained. With respect to the biochemical composition of the biomass, the cells showed a long-term response of metabolic routes to mean daily culture conditions. During the illuminated period, energy was stored as carbohydrates and synthesis of proteins was low. During the night, the stored carbohydrates were consumed. The fatty acid dry weight (DW) content decreased during the daylight period, whereas the fatty acid profile, as total fatty acids, was a function of growth rate. A short-term variation of exopolysaccharides synthesis with solar irradiance was also observed, i.e. the higher the external irradiance the higher the excretion of exopolysaccharides as a protection against adverse culture conditions.

n-3 PUFA productivity in chemostat cultures of microalgae

Eicosapentaenoic (EPA) and docosahexaenoic (DHA) acid productivities from chemostat cultures of an isolate of Isochrysis galbana have been studied. The productivities reached in the interval of dilution rates between 0.0295 h−1 and 0.0355 h−1 were 1.5mg·1−1·h−1 for lipids, 300 μg·1−1·h−1 for EPA and 130μg1·1−1·h−1 for DHA. Furthermore, light attenuation by mutual shading, and agitation speed influences on growth and fatty acid composition were analysed. A model relating steady-state dilution rates to internal average light intensity has been proposed, the parameter values of which obtained by non-linear regression were: maximum specific growth rate (μmax)=0.0426 h−1; the affinity of cells to light (Ik) = 10.92 W·m−2; the exponent (n) = 5.13; regression coefficient (r 2)=0.9999.Eicosapentaenoic (EPA) and docosahexaenoic (DHA) acid productivities from chemostat cultures of an isolate of Isochrysis galbana have been studied. The productivities reached in the interval of dilution rates between 0.0295 h−1 and 0.0355 h−1 were 1.5mg·1−1·h−1 for lipids, 300 μg·1−1·h−1 for EPA and 130μg1·1−1·h−1 for DHA. Furthermore, light attenuation by mutual shading, and agitation speed influences on growth and fatty acid composition were analysed. A model relating steady-state dilution rates to internal average light intensity has been proposed, the parameter values of which obtained by non-linear regression were: maximum specific growth rate (μmax)=0.0426 h−1; the affinity of cells to light (Ik) = 10.92 W·m−2; the exponent (n) = 5.13; regression coefficient (r2)=0.9999.

Influence of power supply in the feasibility of Phaeodactylum tricornutum cultures

The influence of fluid‐dynamic conditions on the yield of Phaeodactylum tricornutum microalgal cultures was analyzed in two stages: first, the influence of air flow rate; second, the influence of using fluid‐moving pumps for recirculating the culture. With respect to the air flow rate, the yield of the cultures increased with the aeration rate up to values of 2.0 v/v/min, then stress was observed and the yield of the cultures decreased. With respect to the influence of mechanical power supply for liquid impulsion, three different types of pumps—centrifugal, pulse, and peristaltic—were essayed at different power supplies. The cultures were stressed for the three types of pumps essayed. For each pump, the higher the power supply the lower was the Fv/Fm value and the higher was the stress at which cells were exposed. The highest measured stress was when the culture was moved with the centrifugal pump. Despite measured stress, for all the experiments stable steady states were reached, thus indicating that cells reduced their yield but did not die, as was verified by cell viability measurements. It was observed that the increase of the power supply improved the frequency of light exposition thus enhancing the yield of the cultures. However, the higher the power supply, the lower the microeddy length scale; therefore, stress could appear. Data demonstrated that the microeddy length scale was always much higher than cell size and therefore the turbulence was not responsible for stress. Also, the mass transfer was discarded as responsible for yield reduction. It was concluded that the shear rate was the factor determining the existence of stress phenomena. The evaluation of these shear rates demonstrated that values above 30–80 s−1 damaged the cells strongly. These data were verified in an outdoor pilot‐scale tubular photobioreactor that was implemented with the same type of pumps, thus demonstrating the necessity to take into account this factor in the design and scale‐up of microalgal photobioreactors.

EPA from Isochrysis galbana. Growth conditions and productivity

The marine microalga Isochrysis galbana Parke is presented as an alternative source of eicosapentaenoic acid (EPA). The effects of growth conditions on polyunsaturated fatty acid productivity with special attention to EPA and docosahexaenoic (DHA) acids were studied. The variables tested were: aeration flow rate, nitrate concentration, temperature, light intensity, micronutrient and vitamin concentration, and pH. Growth conditions producing the greatest EPA yields of over 200 μg/litre/h, are indicated as a starting point for a large scale mass culture system which would develop I. galbanas potential.

Analysis of photobioreactors for culturing high-value microalgae and cyanobacteria via an advanced diagnostic technique: CARPT

Abstract Photosynthetic algal cultures are a potential source of many high-value products. In photobioreactors (PBR), the availability and the intensity of the light, which are affected by the cells’ movement, are the major factors controlling the biomass productivity. Hydrodynamics, hence, play a significant role in the reactors performance, as they determine not only the flow field, i.e. liquid flow and mixing, shear stresses, etc., but also the movements of the cells. In this work, computer-automated radioactive particle tracking (CARPT) technique was employed to evaluate its feasibility for characterizing PBRs. Liquid velocity profiles, cells’ movement, and the temporal irradiance patterns obtained by coupling the cells’ trajectories and the irradiance distribution model have been determined. The effects of the biomass concentration, reactor geometry, and the aeration rate on the irradiance patterns are discussed. The results demonstrate that the CARPT technique is promising for PBR analysis. It provides fundamental information needed to advance the cells’ growth prediction and modeling, and the design, scale-up and operation of PBRs.

Effect of pesticide concentration on the degradation process by combined solar photo-Fenton and biological treatment

The influence of pesticide concentration, expressed as dissolved organic carbon (DOC), on combined solar photo-Fenton and biological oxidation treatment was studied using wastewater containing a mixture of five commercial pesticides, Vydate, Metomur, Couraze, Ditumur and Scala. Two initial DOC concentrations, 200 mg L(-1) and 500 mg L(-1) were assayed. Variation in biodegradability with photocatalytic treatment intensity was tested using Pseudomonas putida. Thus the mineralisation required for combining with biodegradation of intermediates by activated sludge was 33% and 55% at 200 mg L(-1) and 500 mg L(-1), respectively. Biotreatment was carried out in a stirred tank in sequencing batch reactor (SBR) mode. As revealed by the biodegradation kinetics, intermediates generated at the higher pesticide concentration caused lower carbon removal rates in spite of the longer photo-Fenton treatment time applied. One strategy for treating water with high concentrations of pesticides and overcoming the low biodegradability of photo-Fenton intermediates is to mix it with a biodegradable carbon source before biological oxidation. This combination of photo-Fenton and acclimatized activated sludge in several SBR cycles led to complete biodegradation of a concentrated pesticide solution of 500 mg L(-1) DOC in approximately 5h with a carbon removal efficiency of 90%.

Outdoor culture of Isochrysis galbana ALII-4 in a closed tubular photobioreactor

Abstract Growth and fatty acid composition of Isochrysis galbana ALII-4 in batch and semicontinuous outdoor culture in a closed tubular photobioreactor are reported. Specific growth rate at the exponential phase was 0.38 d −1 , higher than that obtained in previous indoor experiments. At biomass concentration above 2 g l −1 net biomass productivity obtained in three successive semicontinuous cultures was 0.32 g l −1 d −1 . A daily cyclic variation in the fatty acid profile was observed. From morning to afternoon, 14:0, 16:0 and 16:1 n 7 content increased, although it decreased during darkness renewing the cycle again with daylight. On the other hand, no daily variation was observed in polyunsaturated fatty acid content. The EPA generation rate during linear growth, with an average content of 2.56%, was 8.2 mg l −1 d −1 . The present study was conducted uninterruptedly in February and March, 1994, in Almeria, Spain (latitude 36° 50′ N, longitude 2° 27′ W).

Fatty acid variation among different isolates of a single strain of Isochrysis galbana

Abstract Fatty acids of 42 isolates of a single strain of Isochrysis galbana were analysed. The data showed an evident between-isolates variability in fatty acid content. Underlying genetic variation is suggested as the explanation and biological and practical implications are discussed.

Biochemical productivity and fatty acid profiles of Isochrysis galbana Parke and Tetraselmis sp. as a function of incident light intensity

The effects of incident light intensity (15-218 W m−2) on growth and biochemical composition (protein, lipid, chlorophyll and fatty acid profiles) of the marine microalgae Isochrysis galbana Parke and Tetraselmis sp. were examined under controlled laboratory conditions in batch cultures. The maximum specific growth rates reached for I. galbana Parke and Tetraselmis sp. were 0·32 h−1 and 0·059 h−1, respectively. Growth became light saturated between 80 and 100 W m−2 for both species. The different biochemical compound productivity values were fited to the same empirical equation. Tetraselmis sp. yielded the highest protein and chlorophyll productivities, while lipid productivity was highest in Isochrysis galbana. The greater eicosapentaenoic acid (EPA) concentrations and productivity were found in Isochrysis galbana Parke.