Emilio Molina Grima

Comparative evaluation of compact photobioreactors for large-scale monoculture of microalgae

Engineering analyses combined with experimental observations in horizontal tubular photobioreactors and vertical bubble columns are used to demonstrate the potential of pneumatically mixed vertical devices for large-scale outdoor culture of photosynthetic microorganisms. Whereas the horizontal tubular systems have been extensively investigated, their scalability is limited. Horizontal tubular photobioreactors and vertical bubble column type units differ substantially in many ways, particularly with respect to the surface‐to‐volume ratio, the amount of gas in dispersion, the gas‐liquid mass transfer characteristics, the nature of the fluid movement and the internal irradiance levels. As illustrated for eicosapentaenoic acid production from the microalga Phaeodactylum tricornutum, a realistic commercial process cannot rely on horizontal tubular photobioreactor technology. In bubble columns, presence of gas bubbles generally enhances internal irradiance when the Sun is low on the horizon. Near solar noon, the bubbles diminish the internal column irradiance relative to the ungassed state. The optimal dimensions of vertical column photobioreactors are about 0.2 m diameter and 4 m column height. Parallel east‐west oriented rows of such columns located at 36.8°N latitude need an optimal inter-row spacing of about 3.5 m. In vertical columns the biomass productivity varies substantially during the year: the peak productivity during summer may be several times greater than in the winter. This seasonal variation occurs also in horizontal tubular units, but is much less pronounced. Under identical conditions, the volumetric biomass productivity in a bubble column is 60% of that in a 0.06 m diameter horizontal tubular loop, but there is substantial scope for raising this value.

Shear stress tolerance and biochemical characterization of Phaeodactylum tricornutum in quasi steady-state continuous culture in outdoor photobioreactors.

A bubble column and two airlift photobioreactors (a draft-tube sparged vessel and a split-cylinder device) of the same general design (0.19 m column diameter, 2 m tall, 0.06 m 3 working volume) were evaluated for outdoor continuous culture of the microalga Phaeodactylum tricornutumat a dilution rate of 0.03 h −1 . At a daily averaged irradiance (photosynthetically active) value of 900 Em −2 s −1 , all bioreactors attained a quasi steady-state biomass concentration of ∼ 1k g m −3 and a biomass productivity of ∼0.3 kg m −3 per day when the aeration velocity was 0.01 m s −1 . The microalgal cells were susceptible to aeration-associated hydrodynamic stress if the superficial aeration velocity exceeded 0.01 m s −1 . Supplementing the culture medium with 0.02% or more carboxymethyl cellulose (CMC), allowed stable culture under conditions that had previously damaged the cells. The average elemental composition of the biomass was: 49.2% C, 6.3% H, 0.8% N, and 1.3% S. The chlorophylls, carotenoids, and pigments content of the biomass changed with irradiance within a given day. Low irradiance favored accumulation of the light capture pigments. Increasing daily irradiance led to accumulation of carbohydrates. Some of the carbohydrate accumulated during the day was consumed at night and partly converted to proteins. Eicosapentaenoic acid (EPA, 20:5n3) constituted between 27 and 30% of the total fatty acids present, or 2.6–3.1% of the dry biomass. The other main fatty acids present were palmetic acid (16:0), palmoleic acid (16:1n7), and myristic acid (14:0). On average, these three fatty acids constituted 16.9% (16:0), 14.0% (16:1n7) and 9.4% (14:0) of the total fatty acids present.

Acyl lipid composition variation related to culture age and nitrogen concentration in continuous culture of the microalga Phaeodactylum tricornutum

The influence of culture age and nitrogen concentration on the distribution of fatty acids among the different acyl lipid classes has been studied in continuous cultures of the microalga Phaeodactylum tricornutum. The culture age was tested in the range of 1.15-7 days, controlled by adjusting the dilution rate of fresh medium supplied. The effect of nitrogen concentration was tested from saturating conditions to starvation by modifying nitrate concentration in the fresh medium. Culture age had almost no influence on the fatty acid content; 16:0, 16:3 and 20:5 increased moderately wherein the level of 16:1 decreased when the culture age decreased. Culture age had no effect on the total fatty acid content that remained around 11% of dry weight. Conversely, culture age had a greater impact on lipid classes, producing changes in amounts of triacylglycerols (TAG) which ranged between 43% and 69%, and galactolipids (GLs) that oscillated between 20% and 40%. In general, the content of polar lipids of the biomass decreased with culture age. The other factor assayed, nitrogen content, affected the fatty acid profile. Saturated and monounsaturated fatty acids accumulated when the nitrogen concentration was decreased. The experiments regarding the effect of nitrogen concentration on lipid species were carried out with cells of an average age of 3.5 days. A decrease of the nitrogen concentration caused the GL fraction to decrease from 21 to 12%. Conversely, both neutral lipids (NLs) and phospolipids (PLs) increased from about 73 to 79% and from 6 to 8%, respectively. In these experiments, TAG was the lipid class with the highest increase, from 69 to 75%.

Producing drugs from marine sponges.

Marine sponges are potential sources of many unique metabolites, including cytotoxic and anticancer compounds. Natural sponge populations are insufficient or inaccessible for producing commercial quantities of metabolites of interest. This review focuses on methods of producing sponge biomass to overcome supply limitations. Production techniques discussed include aquaculture in the sea, the controlled environments of aquariums, and culture of sponge cells and primmorphs. Cultivation in the sea and aquariums are currently the only practicable and relatively inexpensive methods of producing significant quantities of sponge biomass. In the future, metabolite production from cultured sponge cells and primmorphs may become feasible. Obtaining a consistent biomass yield in aquariums requires attention to many factors that are discussed in this work.

Microalgae, Mass Culture Methods

Introduction Bioreactors for Microalgae Mass Culture Open Raceways Enclosed Photobioreactors Physical Factors That Influence Biomass Productivity Light Availability inside a Photobioreactor The Light Saturation Constant and the Photoinhibition Phenomenon Biomass Productivity Fluid Dynamics and Mixing Gas–Liquid Mass Transfer Temperature Photosynthetic Efficiency Absorbed Photon Flux Operational Considerations Concluding Remarks Nomenclature Acknowledgments Bibliography Keywords: fluid dynamics; gas–liquid mass transfer; light distribution; microalgae mass culture; outdoor production; photosynthetic efficiency; tubular reactor

Progress towards a controlled culture of the marine sponge Pseudosuberites andrewsi in a bioreactor

Explants of the tropical sponge Pseudosuberites andrewsi were fed with the marine diatom Phaeodactylum tricornotum. The food was supplied either as intact algae or as a filtered crude extract. Growth (measured as an increase in underwater weight) was found in both experiments. The explants fed with intact algae increased to an average underwater weight of 255% of the initial weight in 45-60 days. The explants fed with crude extract increased to an average of 200% of the initial weight in 30 days. These results show that it is possible to grow a sponge using a single microorganism species as a food source. In addition, it was demonstrated that sponges are also capable of growing on non-particulate food. Therefore, this study is an important step forward towards the development of controlled, in vivo sponge cultures.

Characterization of shear rates in airlift bioreactors for animal cell culture

Abstract A well established analysis of energy dissipation in the riser, downcomer and the bottom sections of split-cylinder airlift bioreactors (aspect ratio=7.6 and 14.5; equal riser-to-downcomer cross-sectional area ratios of 1.0) was used to characterize shear rates in those systems for application to animal cell culture. Shear rates were evaluated for suspensions of typical microcarriers (loading =0–30 kg m −3 ; particle diameter=(150–300)×10 −6 m; density 1030–1050 kg m −3 ) encountered in anchorage-dependent cell culture and for microcarrier-free liquids. For the reactors tested, the highest shear rates were encountered in the bottom zone; the riser had lower shear rate values, while the downcomer was the most quiescent. The shear rates in various zones ranged over 0–12 000 s −1 for a riser superficial gas velocity range of 0–6.7×10 −3 m s −1 which is typical for cell culture. In all zones, the shear rates increased with increasing aeration rate. Shear rates declined with increasing loading of microcarriers, but were not substantially affected by the carrier diameter or density. Relative to the microcarrier free system, even small amounts of carriers (6 kg m −3 ) lowered the maximum prevailing shear rate to about 4000 s −1 . The shear rates were extremely sensitive to the length scale of the fluid eddies when the eddy length-to-carrier diameter ratio was less than or equal to unity. The results showed quantitatively how the shear rate in various zones of airlift reactors may be manipulated by modifications to operational and geometric parameters. The methodology presented allowed for characterization of shear rates in the bulk flow, unlike existing studies that provide information only on wall shear rates which are not particularly relevant to shear sensitive bioprocesses.

Extraction of saponifiable lipids from wet microalgal biomass for biodiesel production.

Saponifiable lipids (SLs) were extracted with hexane from wet biomass (86 wt% water) of the microalga Nannochloropsis gaditana in order to transform them into fatty acid methyl esters (FAMEs, biodiesel). The influence of homogenization pressure on SL extraction yield at low temperature (20-22 °C) was studied. Homogenization at 1700 bar tripled the SL extraction yield. Two biomass batches with similar total lipid content but different lipidic compositions were used. Batch 1 contained fewer SLs (12.0 wt%) and neutral saponifiable lipids (NSLs, 7.9 wt%) than batch 2 (21.6 and 17.2 wt%, respectively). For this reason, and due to the selectivity of hexane toward NSLs, high SL yield (69.1 wt%) and purity (71.0 wt%) were obtained from batch 2. Moreover, this extract contains a small percentage of polyunsaturated fatty acids (16.9 wt%), thereby improving the biodiesel quality. Finally, up to 97.0% of extracted SLs were transformed to FAMEs by acid catalyzed transesterification.

Solvent Extraction for Microalgae Lipids

This chapter analyzes the solvent extraction and fractionation of algal oil for biodiesel production. Initially the basic thermodynamic principles for the dissolution of materials into solvents are outlines. For a rational design of solvent or solvent system to be used, a crucial step in the downstream processing, a quantitative approach is explained, based on the calculation of the solubility parameters (polarity index, solubility parameters and dipole moments) for the solvent and the lipid class to be extracted. This allows a great reduction in the experimental design in lipid extraction. The possible pre-treatments of biomass are then studied. The core of the chapter is devoted to analyzing the extraction of lipids from both dry and paste biomass, and how to solve some problems that occur due to the nature of lipids present and the possibility of their prior fractionation. The following section discusses an alternative to the extraction of lipids for biofuel, namely the direct extraction of fatty acids from biomass by means of a direct saponification of both dry and paste biomass and their eventual fractionation. Then we analyze the direct production of FAMEs (biodiesel) through a direct transesterification of wet paste biomass. The pros and cons of the three methods are also analyzed. Finally, the chapter also provides an assessment of a case study for processing the wet biomass produced in a 1 ha plant of tubular photobioreactors.

New Culture Approaches for Yessotoxin Production from the Dinoflagellate Protoceratium reticulatum

Fed‐batch and perfusion cultures were carried out in a traditional glass 2‐L bioreactor with the toxic dinoflagellate Protoceratium reticulatum. The maximum cell concentration obtained was 2.3 × 105 cell·mL−1, which is almost 1 order of magnitude higher than the maximum previously referenced for this species. L1 medium was shown to be clearly deficient in nitrate and phosphate for this strain, and addition of highly concentrated aliquots of these nutrients allowed higher cell concentrations to be obtained. This species consumed high amounts of nitrate and phosphate, 2.1 × 10‐3 and 2.3 × 10‐4 μmol·h−1·cell−1, respectively. However, this consumption produced a very low number of cells compared to other classes of microalgae, indicating that this species is, like other dinoflagellates, a poor competitor in terms of utilization of inorganic nutrients. Higher production of toxins and pigments was strongly associated with cell number in the culture, with maximum values of 700 ng·mL−1 and 1321 μg·mL−1, respectively. Most yessotoxins remained within the cells and not in the cell‐free culture medium, and their production was not related to either the age of the culture or the cell growth phase.