Mixotrophic growth of Chlorella 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 the Chlorella 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.