The Effect of a Pacific Northwest Light Cycle on Growth and Lipid Accumulation in the Green Microalgae, Botryococcus braunii for the Production of Biodiesel

There is high demand for clean, inexpensive, alternative fuel sources to supplement or replace fossil fuels. Algae have strong potential as an alternative energy source due to its high oil content. The alga, Botryococcus braunii, has been studied extensively due to its unique ability to store hydrocarbons along the exterior of the cell.   These hydrocarbons, which have been shown to make up 15-76% of their dry weight, can be extracted and converted to a variety of fuels (Li et.al, 2005). Investigating extraction methods including the use of glass beads, a variety of solvents, variable temperatures, and microwaves allows researchers to analyze the impact on the efficiency of extraction.  The efficiency of variable extraction techniques can help us estimate the scale and capability of profitable production.  Investigation of variable growing conditions can help researchers determine optimum conditions for maximizing hydrocarbon yields while lowering production costs.  While oil from B. braunii is still too expensive to produce commercially, utilization of natural light outdoors can lower the overall cost of production.  Outdoor growth in rooftop photobioreactors give the algae a controlled growth environment that is not subject to the contamination of open ponds and allows for the regulation of an optimum carbon dioxide concentration. Our work models the normal outdoor light levels found in the Pacific Northwest and applies our prior research findings that B.braunii achieves optimal growth while exposed to near ambient levels of carbon dioxide. Hydrocarbon yields and chlorophyll counts of algae exposed to light intensities averaging 780 lux for a daily cycle of 8 hours of light were compared with that of algae grown under standard conditions at a light intensity of 10 klux for a daily cycle of 12 hours of light (Zhang et.al, 1998).  Studying these conditions allows us to estimate the amount of supplemental light needed for optimal growth during the fall and winter for an outdoor photobioreactor.  This type of data is critical to evaluating the role algal-derived biodiesel might play in a suite of alternative energy sources for the Pacific Northwest.