SEQUENTIAL HETEROTROPHIC AUTOTROPHIC CULTIVATION - AN EFFICIENT METHOD OF PRODUCING CHLORELLA BIOMASS FOR HEALTH FOOD AND ANIMAL FEED/

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 .