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

Ana Barros,Raúl Barros,Jaime Páramo,João Varela,Peter Schulze,Dinis Maurício,Luísa Gouveia,Luísa Barreira,Ana Marques,Tamára Santos,Joana Silva,Hugo Pereira

doi:10.1038/s41598-018-23340-3

Ana Barros, Raúl Barros + Show 10 more

Open Access

https://doi.org/10.1038/s41598-018-23340-3

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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.

Highlights

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
The culture velocity was tested in 2.5 m3 pilot-scale tubular PBR using three different culture velocities: 0.65, 1.01 and 1.35 m s−1
The same pattern was observed for the volumetric and areal biomass productivities (0.14–0.15 g L−1 d−1 and 12.9–13.6 g m−2 d−1, respectively), where no significant differences were observed (p > 0.05) under all velocities tested (Table 1)

Summary

Introduction

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. CTP4 is a robust candidate for industrial-scale production with promising biomass productivities and photosynthetic efficiencies up to 3.5% of total solar irradiance. Mass culture of microalgae can be achieved in open (e.g., open ponds or raceways) or closed (e.g., photobioreactors; PBR) production systems (Fig. 1). This allows the cultivation of most microalgal strains[5,10,11] with higher areal and volumetric biomass productivities[5,7]. In order to meet the full potential of microalgal biomass, the selection of robust and fast-growing strains is crucial to develop feedstocks that can effectively grow in large-scale industrial facilities[12,13]. CTP4 presents promising features as compared to common microalgal feedstocks The biomass of this microalga can be recovered through natural cell sedimentation, decreasing the total culture volume down to 20% within 6 hours[14]. This property is essential to significantly decrease harvesting costs, one of the most costly steps of culturing and retrieving microalgae from an aqueous growth medium[16]

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