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Studies on microalgae species and strain selection have demonstrated the potential of a broad range of algal species suitable for large-scale mass production, but provided little data on the reliability and productivity of the cultures under outdoor conditions over a long period. Long-term studies as part of the development of large-scale microalgae mass production are essential at small scale to minimise expenditure in scaling-up and large-scale operations. The current study describes the long-term semi-continuous culture of 4 wild-type isolates of euryhaline Tetraselmis sp. grown in 1 m2 raceway ponds outdoors in 7% (w/w NaCl) saline water enriched with N and P without any additional carbon source under the environmental conditions in Perth, Western Australia. The long-term investigation indicated that Tetraselmis MUR-231 was not able to grow outdoors, while Tetraselmis strains MUR-167, MUR-230 and MUR-233 grew outdoors over long periods. Tetraselmis MUR-167 was cultured for over 16 months outdoors before terminated due to cell clump formation and heavy biofilm development on the pond walls, whereas Tetraselmis strains MUR-230 and MUR-233 were cultured in semi-continuous culture over 20 months. The latter two strains grew at high solar irradiance with daily maximum values of 58890 W m−2 and temperatures ranging from about 40 to 0 °C. Both strains had a similar average specific growth rate of 0.19 day−1 over the experimental period. Maximum biomass productivities were 9.11 g m−2 day−1 and 9.99 g m−2 day−1 for Tetraselmis MUR-230 and MUR-233, respectively. The maximum total lipid productivity of 4.30 g m−2 day−1 of Tetraselmis MUR-230 was slightly higher than Tetraselmis MUR-233 (4.05 g m−2 day−1). These results clearly indicate the potential of these two Tetraselmis strains for commercial application, such as a high lipid yielding feedstock under minimal culture management conditions in arid and semi-arid coastal regions such as northern Western Australia. [ABSTRACT FROM AUTHOR]

This research assessed the efficacy of three harvesting methods on a strain of Dunaliella viridis. While there is strong potential to use lipids from microalgae as a feedstock for biofuels to replace petroleum-based fuel, at present microalgal harvesting for biofuel production is not yet economically feasible or energy efficient. pH-induced flocculation (by adjusting the pH of exponentially growing cells), indirect electrocoagulation (applying aluminum hydroxide coagulant to culture), and hollow fiber filtration (separating biomass from medium using tangential flow) were compared as potential harvesting mechanisms for small-scale (3-10 L) and large-scale (30-150 L) volumes of D. viridis. Both pH-induced flocculation and electrocoagulation yielded significant biomass recovery (>95 %), but both methods required removal of added chemicals and/or coagulant before the medium could be reused. In contrast, hollow fiber filtration did not require added chemicals or coagulant, and as another advantage, the filtrate was successfully reused as culture medium without apparent detrimental effects on cell size, cell shape, or cell production. When high salinity stress was imposed on the concentrate produced from the filtration method, total fatty acids (FAs) did not increase. However, total FAs did significantly increase after hollow fiber filtration (49 %) in comparison to FA content before filtration (36 %). This research indicates that hollow fiber filtration as a commercial harvesting mechanism offers attractive advantages as a harvesting mechanism for microalgae such as Dunaliella, relative to pH-induced flocculation and indirect electrocoagulation. [ABSTRACT FROM AUTHOR]

The phenotypic and phylogenetic diversity of micro-algae capable of accumulating triacylglycerols provides a challenge for the accurate determination of biotechnological potential. High-yielding strains are needed to improve economic viability and their compositional information is required for optimizing biodiesel properties. To facilitate a high-throughput screening programme, a very rapid direct-derivatization procedure capable of extracting lyophilized material for GC analysis was compared with a scaled-down Folch-based method. This was carried out on ten micro-algal strains from 6 phyla where the more rapid direct-derivatization approach was found to provide a more reliable measure of yield. The modified Folch-based procedure was found to substantially underestimate oil yield in one Chlorella species ( P < 0.01). In terms of fatty acid composition however, the Folch procedure proved to be slightly better in recovering polyunsaturated fatty acids, in six out of the ten strains. Therefore, direct-derivatization is recommended for rapid determination of yields in screening approaches but can provide slightly less compositional accuracy than solvent-based extraction methods. [ABSTRACT FROM AUTHOR]

The use of microalgae for biofuel production has the potential to reduce fossil fuel consumption. Ideal candidate species of microalgae for bio-oil production need both relatively high growth rates and lipid content. Here, we report on the effects of temperature, nutrients (N, Si), and salinity on growth rates and lipid content of the common freshwater diatom, Fragilaria capucina (Desm), isolated from western Lake Erie. At low NaCl salinity, growth rate increased rapidly from 10 to 20°C, and then further increased slowly from 20 to 30°C, with a maximum specific growth rate of 0.61 day. Growth rate declined with increasing salinity (e.g., reduced by ca. 50 and 100% at 137 and 274 mmol L NaCl, respectively), and increased with increased N and Si concentration until ca. 100 μmol L for each (with >85% of maximum growth rate at 10 μmol L). Lipid content (% total lipid per dry mass) in nutrient-replete cultures was 14% and (1) increased to >30% at low N and, especially, low Si; (2) was lower at 30°C vs. 20 or 10°C; and (3) decreased with salinity. Thus, F. capucina accumulates lipid to high levels even under N, Si, and temperature levels that permit a high growth rate for this species, and hence, this species is a candidate for use in biofuel production. [ABSTRACT FROM AUTHOR]

Current research investigating the importance of diversity for biofuel lipid production remains limited. In contrast, the relationship between diversity and productivity within terrestrial and algal primary producers has been well documented in ecology. Hence, we set out to investigate, experimentally, whether diversity may also affect lipid production in micro-algae. We investigated the growth and lipid production of micro-algae using species from all major algal groups. Algae were grown in a large number of treatments differing in their diversity level. Additionally, we compared the growth and lipid production of laboratory communities to natural lake and pond phytoplankton communities of different diversity. Our results show that lipid production increased with increasing diversity in both natural and laboratory micro-algal communities. The underlying reason for the observed 'diversity-productivity' relationship seems to be resource use complementarity. We observed higher lipid production of highly diverse algal communities under the same growth and resource supply conditions compared to monocultures. Hence, the incorporation of the ecological advantages of diversity-related resource-use dynamics into algal biomass production may provide a powerful and cost effective way to improve biofuel production. [ABSTRACT FROM AUTHOR]