(322d) Photoautotrophic Growth and Lipid Production Kinetics of the Microalgae Scenedesmus Dimorphus

The design and optimization of culture systems for microalgae for biofuel production are complicated by the conflicting requirements for high biomass productivity and high oil content.  Reactor models that are needed for this optimization rely on models of the algae growth and lipid productivity kinetics.  Unlike heterotrophic growth of most microorganisms, photoautotrophic growth of algae can have multiple limiting nutrients, further complicated by potential light limitation.  Factorial experimental designs were conducted to identify the nutrients, and their concentration ranges, that are potentially limiting for growth and oil production of the microalgae Scendesmus dimorphus.  The individual and interactive effects of six groupings of the components of  3N-BB medium on growth rate, lipid content, and total biomass yield of  S. dimorphus  were determined.   Trace metal and vitamin concentrations were reduced to 1/6 the level of 3N-BB medium without adversely affecting growth rates and biomass concentration, while concentrations of  CaCl₂ and  K₂HPO₄/KH₂PO₄ were reduced to 1/10 that of 3N-BB without adversely affecting biomass and lipid concentrations.   Lipid productivity was maximized at the lowest  NaNO₃ concentration  (1/10 that in 3N-BB) and independent of  MgSO₄ concentration, while the interaction of these two chemicals enhanced biomass concentration.   Initial substrate experiments were then conducted to determine in greater detail the effects of magnesium sulfate, sodium nitrate, and potassium phosphate on biomass growth.  Kinetic models for growth rate and substrate consumption were developed from the data and validated.  These fundamental kinetic models can then be used in a variety of reactor styles and configurations in order to identify the system and operating parameters