Date of Award
Masters of Science in Chemical Engineering
Chemical and Biomedical Engineering
Of the many alternative resources capable of generating biofuel, microalgal oil serves as a promising feedstock. Unfortunately, biodiesel production from microalgae is currently hindered by high operational costs. One primary causes for these high costs is the large quantity of freshwater required for cultivation. This experiment was designed to assess the feasibility of growing the green, freshwater microalgae Scenedesmus dimorphus in an increasingly saline environment. Both average yield coefficients and growth rates were monitored with increasing salt concentration. Determination of average yield coefficients allows for process scale-up and the optimization of production costs by minimizing raw material waste. Salinity was measured in terms of total specific gravity (TSG). The typical TSG levels for freshwater and open seawater are 1.000 and 1.025-1.030, respectively.
Microalgae were grown in a 5L photobioreactor in batch mode with freshwater, 1.006, and 1.009 TSG media. The growth rate, average yield coefficients and lipid content were analyzed under these conditions. Low salinity levels had little impact on growth rate, while increasing salinity to 1.009 TSG resulted in a reduction in the growth rate by 40%. Substrate consumption over time was monitored using Inductively Coupled Plasma – Optical Emission Spectroscopy to calculate the average yield coefficients for magnesium, iron and phosphorus. Magnesium and iron average yield coefficients increased from freshwater values at 1.006 TSG, while the average yield coefficient for both of these elements showed a reduction from freshwater values at 1.009 TSG. The average yield coefficient for phosphorus did not change at 1.006 TSG but increased at 1.009 TSG.
Lipid content and biodiesel fuel properties were also calculated to estimate the quality of fuel derived from S.dimorphus oil. Lipid content seemed to increase from freshwater (1.96% up to 3.28%) to 1.011 TSG but decline at a TSG of 1.015. The cetane number, along with the oxidative stability index, did not appear to be significantly influenced by salt concentration. The cold filter plugging point appeared to increase with salinity, indicating that growing microalgae in a saline environment will reduce the performance of biodiesel in colder climates.
Cohara, Morgan L., "Determination of Growth Kinetics, Yield Coefficients and Biodiesel Properties for the Green Microalgae Scenedesmus Dimorphus in Freshwater and Saline Medias" (2018). ETD Archive. 1084.