Jc. Ogbonna et al., SEQUENTIAL HETEROTROPHIC AUTOTROPHIC CULTIVATION - AN EFFICIENT METHOD OF PRODUCING CHLORELLA BIOMASS FOR HEALTH FOOD AND ANIMAL FEED/, Journal of applied phycology, 9(4), 1997, pp. 359-366
Sequential heterotrophic/autotrophic cultivation method was investigat
ed for production of high concentration of Chlorella biomass with high
cellular protein and chlorophyll contents. By using autotrophic growt
h medium, which contains glucose as organic carbon source, for heterot
rophic culture, the protein and chlorophyll contents of the cells coul
d be increased by simply illuminating the culture broth and aerating w
ith CO2-enriched air at the end of the heterotrophic culture. A system
was then constructed for continuous sequential heterotrophic/autotrop
hic production of algal biomass. The system was composed of the conven
tional mini-jar fermenter for the heterotrophic phase and a tubular ph
otobioreactor for the autotrophic phase. The exhaust gas from the hete
rotrophic phase was used for aeration of the autotrophic phase in orde
r to reduce the CO2 emission into the atmosphere, With this system, it
was possible to produce high Chlorella biomass concentration (14 g L-
1) containing 60.1% protein and 3.6% chlorophyll continuously for more
than 640 h. During the steady state, about 27% of the CO2 produced in
the heterotrophic phase was re-utilized in the autotrophic phase. Whe
n the tubular photobioreactor was replaced with a 3.5-L internally ill
uminated photobioreactor, the productivity increased from 2 g L-1 d(-1
) to 4 g L-1 d(-1). However, the chlorophyll content of the cells was
lower due to the lower light supply coefficient of the photobioreactor
.