Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Supervisor

Dr. Amarjeet Bassi

Abstract

Sustainable and clean fuels are in demand due to the perceived negative effects on health and environment with current use of fossil fuels. Lipids from microalgae offer a potential approach to obtain sustainable biofuels. In this study a two step process was adopted: investigation of culture conditions to find optimal points for lipid productivity and cellulose content, followed by an investigation of microalgae disruption for lipid recovery.

In the first phase of the research the effect of culture conditions on Chlorella vulgaris biomass concentration and the ratio of lipid productivity/cellulose content were studied. Response surface methodology was applied to optimize the culture conditions. The response model for biomass concentration led to a predicted maximum of 1.12 g dw L-1 when carbon dioxide and sodium nitrate concentrations were 2.33% vv-1 and 5.77 mM, respectively. For lipid productivity/cellulose content ratio the maximum predicted value was 0.46 (mg lipid L-1d-1)(mg cellulose mg biomass-1)-1 when carbon dioxide concentration was 4.02% vv-1 and sodium nitrate concentration was 3.21 mM. Also a common optimum point for both models was also found.

For the second phase of the study, the optimized Chlorella vulgaris microalgae obtained in the first phase was subjected to high pressure steaming as a hydrothermal treatment for recovery of bio-crude, and analysis by empirical modeling allowed finding operating points in terms of target temperature and microalgae concentration for high bio-crude and glucose yields. Within the range covered by these experiments the best conditions for high bio-crude yield were temperatures higher than 174˚C and low biomass concentrations (<5 g/L). For high glucose yield there were two suitable operating ranges, either low temperatures (<105˚C) and low biomass concentrations (<4 g/L); or low temperatures (<105˚C) and high biomass concentrations (<110 g/L).

To finalize this study, microalgae with different lipid and cellulose content was used to calculate the bio-crude recovery efficiency applying high pressure steaming. This thermal treatment allowed extracting 97.94±8.26% of the total lipids. The biomass with the highest cellulose content was later subjected to high pressure steaming as a pre-treatment for glucose production via enzymatic hydrolysis, and the glucose yield for this process was 0.28 g.gbiomass-1.

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