Production of high-density Chlorella culture grown in fermenters

Abstract

The freshwater microalga Chlorella vulgaris was grown heterotrophically in fed-batch 50–600-L fermenters at 36°C, on aerated and mixed nutrient solution with urea as a nitrogen and glucose as a carbon and energy source. Cell density increased from the initial value 6.25 to 117.18 g DW L−1 in 32 h in the fermenter 50 L at a mean growth rate 3.52 g DW L−1 h−1. The DW increase in the fermenter 200 L was from 7.25 to 94.82 g DW L−1 in 26.5 h at a mean growth rate 3.37 g DW L−1 h−1. Mean specific growth rate I¼ was about 0.1 h−1 in the both fermenters, if nutrients and oxygen were adequately supplied. The DW increase in the fermenter 600 L was from 0.8 to 81.6 g DW L−1 in 66.5 h at a mean growth rate 1.22 g DW L−1 h−1 and I¼â€‰= 0.07 h−1. A limitation of the cell growth rate in 600 L fermenter caused by a low dissolved oxygen concentration above cell densities higher than 10 g DW L−1) occurred. Specific growth rate decreased approximately linearly with increasing glucose concentration (25–80 g glucose L−1) at the beginning of cultivation and decreased with the time of cultivation. The cell yield was 0.55–0.69 g DW (g glucose)−1. The content of proteins, I²-carotene, and chlorophylls in the cells steadily increased and starch content decreased, by keeping aerated and mixed culture another 12 h in fermenter after the cell growth was stopped due to glucose deficiency.