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Category: Applied and Industrial Microbiology
Microalgal Culture as a Feedstock for Bioenergy, Chemicals, and Nutrition, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555816827/9781555815127_Chap40-1.gif /docserver/preview/fulltext/10.1128/9781555816827/9781555815127_Chap40-2.gifAbstract:
The current product range of algal biomass has been expanded to include fine chemicals and secondary metabolites as products of higher value as well as bioenergy products, the latter typically coupled to wastewater treatment or using carbon credits to offset costs. While commodity products such as protein, algal oil, and bioenergy products remain of great interest, these require improvements in productivities to be economically feasible as independent products. While optimal microalgal culturing systems vary greatly with application, the following characteristics should be considered for culture system design and operation: provision of CO2 and removal of O2, provision of nutrients, temperature, pH control, salinity, light provision, mixing, mass and heat transfer, and hydrodynamics. Natural media use seawater, while artificial seawater recipes attempt to mimic the composition of natural seawater using laboratory chemicals. Many types of photobioreactors are suitable for laboratory culturing of algae. Algae can be grown in bubble columns; however, external or internal loop airlift reactors are more effective as photobioreactors for algal growth owing to the development of defined flow patterns with a concomitant increase in mass and heat transfer. Currently the exploitation of algal biotechnology is in its infancy, with a great range of biodiversity remaining to be explored. Further to this, the significant downstream processing costs incurred require emphasis on both improving product concentration and identifying low-energy unit operations suited to the efficient processing of large volumes of algal suspensions.
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Parameters that can be manipulated in algal culture. (Adapted from reference 25 .)
Dependence of photosynthetic rate on light intensity, illustrating limitation and inhibition.
Average absorbance across the range of visible light wavelengths for five microalgal species (Chlorella, Scenedesmus, Nannochloropsis, Isochrysis, and Phaeodactylum).
Correlation between algal oil productivity, biomass productivity, and oil content under nutrient-replete conditions ( 23 ).
Simplified metabolic pathway illustrating CO2 fixation and metabolism to biomass and triacylglycerides. TCA, tricarboxylic acid.
Examples of currently commercially available algal products a
Characteristics of some algal groups relevant to microalgal biotechnology
Frequently used general-purpose media for microalgaea
Comparison of open and closed reactor systems for algal growth a
Variation in biomass productivity with photobioreactor systems reported for algal culture a
Typical algal growth rates and example product contents and productivities a
Typical algal cell size a