Microalgae have remarkable potential for producing biofuels and bioproducts, and for sequestering carbon dioxide from industrial flue gases. Economical production of algal biofuels will require using nutrients from wastewater and a free source of carbon. The proposed research will involve managing wastewater treatment by mixotrophic microalgae to achieve efficient biofuel production. Mixotrophic algae can grow on either organic carbon sources or atmospheric carbon dioxide. The research has the practical goal of providing an alternative system for biofuel production leading to new industries with high global impact in the areas of energy and agriculture sustainability. Specifically, the use of biofuels produced from microalgal lipids and polysaccharides has been proposed as a potential solution to worldwide challenges related to fossil fuel scarcity and global warming. Furthermore, culturing microalgae in wastewater can improve water quality, and prevent problems associated with "food vs. fuel" competition on limited agriculture lands. This project will also train research and educational leaders who will gain knowledge of fundamental principles and applications of biological engineering and biotechnology. Students will develop an ability to work in multidisciplinary teams to achieve research goals, and gain understanding of the broader issues (global environmental and economic impacts, public/societal views) in the field, preparing them to contribute to science and policy related to energy sustainability. This research will benefit K-12 education through integration of algal research into elementary school science curriculums. It will also benefit undergraduate education through enhanced integration of algal research into an engineering design class at University of California, Davis.
Microalgae have been considered as a viable biofuel feedstock due to their productivity and associated higher-value by-products. Recent reports indicate that sustainable economic production of algae for bioenergy will require mixotrophic production on wastewater and waste carbon dioxide. The growth rate of microalgae, uptake of organic carbon, and accumulation of intracellular lipid and polysaccharide products resulting from mixotrophic production will likely be different from heterotrophic and autotrophic production that have been primarily studied to date. Mixotrophic conditions can improve lipid productivity by an order of magnitude. However, these cultures can exhibit low efficiency in converting the carbon source into biofuel precursors. For example, when cultured on glucose, glycerol, and acetate, a model strain of microalgae converted only 10-40% of the substrate energy into lipids and starch. In contrast, yeast cultures can convert glucose to ethanol with 70% efficiency on an energy basis. Elucidating what contributes to lower efficiency in algae is critical for designing algal-based systems for wastewater treatment and biofuel production. The goal of the proposed research is to develop algae cultivation and wastewater management systems that lead to higher substrate utilization efficiencies for biofuel production and organic matter removal from wastewater. Management options include strain selection and algae acclimation, rate and timing of substrate addition and management of wastewater composition. An additional goal is to determine bottlenecks in substrate utilization by microalgae. These goals will be achieved through three objectives. The first objective is to determine if acclimation of microalgae to organic carbon reduces substrate utilization efficiency and develop strategies to overcome this challenge. The second objective is to vary organic carbon and co-factor addition to algae using fed-batch reactors to determine if substrate supply rate impacts conversion efficiency, and the third objective is to use results from objectives 1 and 2 to tailor microalgae production variables for cultivation on food processing wastewaters. This may include application of substrate supply strategies developed in earlier objectives and supplementation of co-factors deficient in wastewaters. Metabolomic profiling techniques will be used to elucidate metabolic responses to different management strategies. This research is expected to inform the decision making process on how to manage microalgae and wastewater for achieving sustainable biofuel production.
