Complementary Production of Biofuels by the Green Alga Chlorella vulgaris

Abstract

There is increasing growing concerns about global warming and rising of oil prices. The aim of the current work was to evaluate the potential of the green alga Chlorella vulgaris as a renewable energy source in term of biofuels. Alga was hetero-trophically grown under both vegetative and induction-conditions. Induction was proceed to enhance cell metabolites mainly oils (for biodiesel) and carbohydrates (for bioethanol-production). BG-II growth medium was used for vegetative growth, while such medium was enriched by ferrous sulfate, sodium acetate and sodium chloride under high light irradiation for induction purposes. De-fatted dried algal cells were subjected to bioethanol production through three different treatments prior yeast fermentation to increase the fermentable sugars content after oils were extracted from algae. This includes direct treatment by Tricoderma sp., acid hydrolysis and molasses addition. Saccharomyces cerevisiae was used in fermentation action. Results indicated that the oil content of stressed algal cultures was raised to be 14.8% with 26.7% of total carbohydrates versus to 32.14% of crude protein. Fatty acids profile resulted in an increase of saturated fatty acids by about 10.65 %, while unsaturated fatty acids were decreased by 18.57%. Third day of incubation seems to be the optimum for direct fermented or pre acid hydrolyzed-alga in terms of yeast biomass, consumed sugar and alcohol percent By such time 15% of molasses represented the same manner. Also, the maximum alcohol content (38.7%) by acid hydrolyzed; while direct fermentation resulted in 28.7% versus to 36.3% of molasses addition.

Keywords

• Chlorella vulgaris; acid hydrolysis; molasses; yeast; fatty acid; bioalcohol.