| dc.description.abstract | The forefront of the 21st century presents ongoing challenges in economics, energy, and environmental remediation, directly correlating with priorities for U.S. national security. Displacing petroleum-derived fuels with clean, affordable renewable fuels represents a solution to increase energy independence while stimulating economic growth and reducing carbon-based emissions. The U.S. government embodied this goal by passing the Energy Independence and Security Act (EISA) in 2007, mandating 36 billion gallons of annual biofuel production by 2022. Algae possess potential to support EISA goals and have been studied for the past 30-50 years as an energy source due to its fast growth rates, noncompetitive nature to food markets, and ability to grow using nutrient waste streams. Algae biofuels have been identified by the National Research Council to have significant sustainability concerns involving water, nutrient, and land use. Utilizing municipal wastewater to cultivate algae provides both water and nutrients needed for growth, partially alleviating these concerns. This dissertation demonstrates a pathway for algae biofuels which increases both sustainability and production of high-value products. Algae are cultivated in pilot-scale open ponds located at the Lawrence Wastewater Treatment Plant (Lawrence, KS) using solely effluent from the secondary clarifier, prior to disinfection and discharge, as both water and nutrient sources. Open ponds were self-inoculated by wastewater effluent and produced a mixed-species culture of various microalgae and macroalgae. Algae cultivation provided further wastewater treatment, removing both nitrogen and phosphorus, which have devastating pollution effects when discharged to natural watersheds, especially in large draining watersheds like the Gulf Coast. Algae demonstrated significant removal of other trace metals such as iron, manganese, barium, aluminum, and zinc. Calcium did not achieve high removal rate but did present a significant portion of algae biomass total weight; wastewater treatment using nitrification requires significant daily additions of buffers, most commonly lime or calcium hydroxide. Accumulation of these ions and metals in wastewater-cultivated algae results in a biomass with substantial amount of inorganic ash content. The cultivated biomass was converted to a carbon-rich biocrude, similar to petroleum crude oil, through a process called hydrothermal liquefaction (abbreviated as HTL), which uses subcritical water (water just below its supercritical point) as the chemical driving force for conversion. Biomass HTL produces four product fractions; liquid biocrude, solids (referred to as biochar), an aqueous product (referred to as aqueous co-product; abbreviated as ACP), and gasses. Many factors contribute to the overall viability of using algae HTL biocrude as a petroleum displacement, particularly yield and quality are important for overall economics and ability to utilize existing refining infrastructure, respectively. The HTL product distribution and quality of wastewater-cultivated algae has been found to be extremely unique with significant advantageous over controlled fertilized growth strategies. Biocrude yields of were typically lower but substantially higher quality with lower oxygen content and higher amounts of direct fuel distillate fractions. This phenomenon is contributed to the fact that large amounts of pure-phase substituted hydroxyapatite (a calcium orthophosphate material) are synthesized in-situ, providing catalytically active sites. Hydroxyapatite (abbreviated HA) is a widely studied material for bone (and dental) tissue regeneration purposes and its acid-base catalytic properties. The specific HA produced during HTL of wastewater-cultivated algae presents unique characteristics for performance and tunability in each respective application, providing novel economic value streams for the production of algal biofuels. The overall work of this dissertation concludes Lawrence Wastewater Treatment Plant could produce 10-18 barrels of crude oil and over 2 metric tons of refined hydroxyapatite per day for the creation of revenue sales. The work within this dissertation encompasses novelty of characterization methods, HTL feedstocks, and identification of high-value products. Overall, efforts to demonstrate the feasibility of a sustainable biofuel strategy resulted in formulating hypotheses which led to novel discoveries in creating high-value heterogeneous catalysts and biomedical materials. The works presented have the potential to produce an overall process capable of selling significant quantities of biofuels as a by-product and not as the main economic generator, laying the foundation of breakthrough technology which can meet and potentially exceed the $3 per gal biofuel target. | |
