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

Abstract

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.

Experimental and Model-Based Analysis to Optimize Microalgal Biomass Productivity in a Pilot-Scale Tubular Photobioreactor

“…. , 0.71 g X l −1 d −1 (de Vree et al, 2015;Pereira et al, 2018), confirming the feasibility of the Pr opt values obtained here.…”

“…, 1.03 g X l −1 ) are within a typical range for both, lab-scale and outdoor production of Nannochloropsis sp. in tubular photobioreactors (Olofsson et al, 2012;Pfaffinger et al, 2016;Pereira et al, 2018). The experimental variability regarding c X,0 is rather high within the investigated small pilotscale experiments.…”

Growth performance, biochemical composition and sedimentation velocity of Tetraselmis sp. CTP4 under different salinities using low-cost lab- and pilot-scale systems

“…raceways), environmental factors, such as evaporation and local precipitation, can significantly increase and decrease, respectively, the salt concentration in the medium (Fon-Sing and Borowitzka, 2016). On the other hand, in closed systems (photobioreactors), salinity up- and downshifts can be crucial to manage natural occurring contaminants with lower halotolerance (Pereira et al., 2018). In addition, growing microalgal cultures in low-salt media might decrease production downstream costs related to the management of saltwater discharges.

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“…In addition, Tetraselmis sp. CTP4 has previously been reported as a euryhaline, fast growing and robust microalgal strain, which holds high potential for scale-up in industrial production facilities (Pereira et al., 2018) as well as high sedimentation rates (Pereira et al., 2016).…”

Microalgae: Cultivation Aspects and Bioactive Compounds

“…Isolation by serial dilution consists in diluting successively a non-pure algae sample to decrease cellular density per volume to such level that a simple seeding from this diluted solution will likely originate a single-type colony, as described by Thomas et al [29]. Isolation using agar plates follows the same procedure for bacteria and other microorganisms: a solid agar-nutrient medium is prepared using a suitable composition based on the natural environment of microalgae or desirable features [30]. The medium will not only provide the conditions for organisms to grow but will also prevent contamination from external sources by manipulating its pH, temperature, and composition.…”