In-pond strain selection of euryhaline Tetraselmis sp. strains for reliable long-term outdoor culture as potential sources of biofuel and other products

Abstract

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.