UC Davis

This dissertation focuses on microalgae cultivation on nutrient-dense food waste permeate (FWP) for biofuel feedstock production and wastewater remediation. My work identifies methods for microalgae cultivation on nutrient-dense waste streams and the effect of this concentrated waste stream on microalgae growth and productivity and their resultant remediation capacity. Chapter 1 discusses the commercial value of microalgae-derived natural products, the current economic challenges of producing these algae products, specifically biofuels. This chapter describes the use of wastewater, specifically anaerobic digester effluent and its byproducts, as a potential method to reduce the cost of microalgae cultivation. Further, the inherent benefits and challenges of anaerobic digestion technology and the use of its nutrient-dense waste streams as an alternative nutrient source for microalgae cultivation are discussed. Chapter 2 discusses the microplate screening methodology that was implemented to evaluate ten different microalgae strains and their ability to be cultivated on various permeate conditions. Strains and conditions identified in the microplate studies (10-mL) were scaled up to larger batch cultures (250-mL), and a baseline culturing method was established. Out of the 10 strains evaluated at microplate scale (10-mL), only four demonstrated robust growth on the FWP used throughout this research. Resultant nutrient concentration changes were monitored alongside microalgae growth, and the final analyses demonstrate the feasibility of using the waste biogas from anaerobic digestion in a microalgae cultivation system. Chapter 3 describes methods to optimize biomass productivity of microalgae on a stripped and unstripped FWP by focusing on two possible inhibitory characteristics of FWP: (1) the high ammonia concentrations and (2) the low phosphorus concentrations. This chapter discusses the use of nitrifying bacteria to reduce the high ammonia concentrations while maintaining the high nitrogen concentrations. This chapter also discusses altering N/P ratios in FWP using phosphorus supplementations to address the relatively low initial phosphorus concentrations. Chapter 4 discusses methods to optimize lipid production in C. sorokiniana and C. vulgaris by implementing a nitrogen deplete phase. An additional application of an H2O2 stressor to further enhance lipid production is discussed. Analysis of these experiments suggests a nitrogen deplete phase should enhance lipid productivity in both C. sorokiniana and C. vulgaris, but the additional H2O2 stressor is only effective in enhancing lipid accumulation in C. sorokiniana. This chapter also details my work in identifying, evaluating, and optimizing both extraction and quantification methodologies for neutral lipid quantification in harvested microalgae biomass. Further discussion regarding necessary future investigations is presented.