(429c) High Density Cultivation of a Heat-Resistant Microalga Chlorella Sorokiniana for Biodiesel Production

High density cultivation of a
heat-resistant microalga Chlorella sorokiniana

for
biodiesel production

Tingting Li, Yubin
Zheng, Shulin Chen

Department of
Biological Systems Engineering,

Washington State
University, Pullman, WA 99164

Abstract

Microalgae are
considered to be outstanding potential sources for biofuel
production and thus have attracted growing interest. Heterotrophic algae cultures have
the advantages of fast growth without subjection to light limitation, high
biomass concentration for easily harvesting and high lipid content for
biodiesel production. The green alga Chlorella
sorokiniana has the capability to
accumulate a high content of lipid heterotrophically, however, the high cell density cultivation in fermentor has not been well examined yet.  In this study, we firstly made a
comparison between phototrophic and heterotrophic culture of C. sorokiniana,
and the data showed the heterotrophic cultured algae had twice higher lipid
production. Then, effects of temperature, carbon source, nitrogen source and
C/N ratio on the biomass and lipid production of C. sorokiniana were evaluated. The
results stated that the biomass and lipid reached 20.3 g/L and 5.4 g/L after 72
hours cultivation with 40 g/L glucose and 4 g/L potassium nitrate at 37^oC,
which were approximately 4 and 6 folds respectively higher compared with the
culture without optimization. Interestingly, the best culture temperature for C. sorokiniana
was 37^oC since most Chlorella
species preferred the environmental temperature in the range of 25 to 30^oC.
Moreover, the temperature had significant effects on the fatty acid profile and
a higher content of oleic acid (C18:1) but a lower content of linolenic acid (C18:3) was observed at higher temperature.
The low temperature led the algae to accumulate unsaturated fatty acid,
especially polyunsaturated fatty acid, because the low melting point was very
important for the fluidity of the cell membrane at low temperature. Finally,
fed-batch cultivation in fermentor was conducted with
the optimal conditions and the dry biomass and lipid production for C. sorokiniana
was significantly increased. These results demonstrated
that heterotrophic culture of the microalga C. sorokiniana
had the great capability for biodiesel production. The finding is very
significant because a special microalga was presented
in this study with the characteristics of high lipid content and
heat-resistant.