Eukaryotic microalgae also represent a promising alternative renewable source of feedstock for biofuel production. With over 40,000 identified species, microalgae are one of the more diverse groups of organisms on Earth. They naturally produce large quantities of many biomaterials, including lipids/oil. Nature has had ca. 4 billion years to engineer strains with unique abilities to grow robustly in diverse environmental conditions and evolve unique metabolic characteristics such as intracellular lipid storage, with a growth potential an order of magnitude greater than terrestrial crop plants due to their extraordinarily efficient light and nutrient utilization. The exploitation of naturally occurring photosynthetic microalgae, collected and isolated over the past 25 years for production of renewable liquid fuels, initially in collaboration with the Aquatic Species Program of the DOE, and subsequently at Arizona State University, provides a green and renewable resource of feedstock biomass to meet increasing energy needs and especially the demand for liquid fuels. Over the past two decades, our algal-based biofuel research has progressed from screening and evaluation of naturally occurring algal strains that exhibit high growth rate and high oil content to genetic improvement of selected strains for robustness in performance under diverse environmental and culture conditions, to large-scale photobioreactor design and optimization, to outdoor mass culture and downstream processing (i.e., harvesting, dewatering, and drying), to algal oil extraction, pretreatment, and oil conversion to biodiesel and jet fuel, to systems/process scale-up analysis, and life cycle assessment. One of the field demonstration photobioreactors developed for algae feedstock production is shown below.
Challenges to be addressed include refinement of the cultivation process, downstream processing of biomass, and development of an economic feasibility model for commercialization of algae-based biofuels and biomaterials.
The microalgal research and development effort couples the use of microalgae for biofuels production with environmental bioremediation. Microalgae naturally remove and recycle nutrients (such as nitrogen and phosphorous) from water and wastewater and carbon dioxide from flue-gases emitted from fossil fuel-fired power plants, providing an added environmental benefit. The integration of wastewater bioremediation and carbon sequestration with biofuel production in a novel field-scale bioreactor has been demonstrated. Although algal biomass residues derived from the oil extraction process can be used for animal feed or fertilizer, we are currently exploring, in collaboration with our industrial partners, the opportunity for using biomass residues to produce ethanol, and methane, and high-value biomaterials, such as biopolymers, carotenoids, and very long-chain polyunsaturated fatty acids. Collaboration with industrial partners to provide flue gas (APS), animal wastewater (United Dairymen of Arizona), commercial algal feedstock production capabilities (PetroAlgae), technical assistance with conversion of algae oil to biofuels (UOP and Honeywell Aerospace Division), and assistance with marketing of algal feedstock (Cargill) has either been initiated or is on-going.