Scale-up and large-scale production of Tetraselmis sp. CTP4 (Chlorophyta) for CO2 mitigation: from an agar plate to 100-m3 industrial photobioreactors.

Industrial production of novel microalgal isolates is key to improving the current portfolio of available strains that are able to grow in large-scale production systems for different biotechnological applications, including carbon mitigation. In this context, Tetraselmis sp. CTP4 was successfully scaled up from an agar plate to 35- and 100-m3 industrial scale tubular photobioreactors (PBR). Growth was performed semi-continuously for 60 days in the autumn-winter season (17th October - 14th December). Optimisation of tubular PBR operations showed that improved productivities were obtained at a culture velocity of 0.65-1.35 m s-1 and a pH set-point for CO2 injection of 8.0. Highest volumetric (0.08 ± 0.01 g L-1 d-1) and areal (20.3 ± 3.2 g m-2 d-1) biomass productivities were attained in the 100-m3 PBR compared to those of the 35-m3 PBR (0.05 ± 0.02 g L-1 d-1 and 13.5 ± 4.3 g m-2 d-1, respectively). Lipid contents were similar in both PBRs (9-10% of ash free dry weight). CO2 sequestration was followed in the 100-m3 PBR, revealing a mean CO2 mitigation efficiency of 65% and a biomass to carbon ratio of 1.80. Tetraselmis sp. CTP4 is thus a robust candidate for industrial-scale production with promising biomass productivities and photosynthetic efficiencies up to 3.5% of total solar irradiance.