Development of a novel sterilized thin-film photobioreactor for efficient microalgae cultivation by mixotrophic mode

Abstract

Microalgae-assisted aquaculture has recently garnered significant attention due to the potential of microalgae as feed additives, immunostimulants, and for water quality management in aquaculture systems. To achieve high productivity of algal biomass, there is an urgent need for efficient and cost-effective photobioreactors (PBRs) for microalgae cultivation. In the present study, a novel sterilized thin-film photo-bioreactor (STFPBR) was developed that allows for various trophic modes of microalgal culture. The gas distributor and operational conditions of the STFPBR were optimized accordingly. The results demonstrated that the biomass of C. pyrenoidosa achieved with a coarse sand gas distributor was 42.21 % higher than that obtained using a nano-ceramic gas distributor. The optimal light intensity provided to the STFPBR for microalgae growth was 120 μmol m⁻² s⁻¹, while increasing the light intensity to 160 μmol m⁻² s⁻¹ did not result in any significant difference in biomass concentration. The oxygen content of the air (∼21 %) was sufficient for C. pyrenoidosa growth under mixotrophic conditions. The increased oxygen content in the aeration gas negatively affected microalgae growth. In comparison to photoautotrophic cultivation, utilizing mixotrophic and heterotrophic modes resulted in an over two-fold increase in algal biomass yields. Nevertheless, heterotrophically grown microalgae exhibited the lowest protein content (39.72 %) and chlorophyll concentration (10.24 mg g⁻¹). Conversely, exposure to light during mixotrophic cultivation significantly enhanced both algal protein content (47.87 %) and chlorophyll concentration (16.10 mg g⁻¹). Overall, our findings highlight the pioneering development of STFPBR system designed for efficient and convenient cultivation of microalgae.