Mixotrophic growth ofChlorella sorokiniana in outdoor enclosed photobioreactor

Abstract

Chlorella sorokiniana was cultured in heterotrophic or mixotrophic mode in outdoor enclosed tubular photobioreactor. The culture temperature was maintained at 32–35 °C. At night, theChlorella culture grew heterotrophically, and 0.1 M glucose was completely consumed. The biomass growth yield of glucose was 0.35 ± 0.001 g-biomass g-glucose⁻¹. During the day, the algal culture grew mixotrophically and the biomass growth yield was 0.49 g-biomass g-glucose⁻¹ in low density culture (initial biomass concentration, X_o = 2 g l⁻¹), 0.56 g-biomass g-glucose⁻¹ in medium density culture (X_o = 4 g l⁻¹) and 0.46 g-biomass g-glucose⁻¹ in high density culture (X_o = 7 g l⁻¹). The daily area productivity of the culture, with X_o = 4 g l⁻¹ corresponded to 127 g-biomass m⁻² d⁻¹ during the day and 79 g-biomass m⁻² d⁻¹ during the night. In all the cultures, the dissolved O₂ concentration increased in the morning, reached the maximum value at noon, and then decreased in the afternoon. The dissolved CO₂ concentration remained at 3 mBar in the morning and increased in the afternoon. Glycolate was not found to accumulate in culture medium.