Alternative Methods of Microalgae Cultivation and Dewatering to Increase the Sustainability of Biodiesel Production

Diminishing fossil fuel reserves and elevated atmospheric carbon dioxide (CO2) concentrations have increased the demand for fossil fuel alternatives. The primary goal of this research was to explore alternatives to various phases of algae biodiesel production. Algae biodiesel is a promising alternative fuel because it does not compete with a human feedstock and produces higher yields per unit area than other feedstocks. Microalgae cultivation requires freshwater and nutrients, while other phases require significant amounts of electrical energy and solvents. Three alternatives are presented that aim at reducing the demands of cultivation, dewatering, and lipid extraction. The first alternative used crustacean zooplankters that inhabit facultative aerobic wastewater lagoons, as a biofuel feedstock. Zooplankton biomass was measured in local wastewater lagoons, in order to estimate how much biodiesel could be produced. It was found that 1120 +/- 560 L of biodiesel could be produced annually from two lagoons. In a separate study, nutrient and metal rich municipal landfill leachate was used to cultivate microalgae in a variety of environmental conditions (light intensity, leachate concentration). It was found that the chlorophyte Chlorella protothecoides growing on 10% landfill leachate at 220 micromol photons m-2 s-1achieved growth rates of 0.7 d-1. The third alternative focused on using the crustacean zooplankton Daphnia pulex as a biological harvester of algal lipid. Using Daphnia as a biodiesel feedstock is advantageous because they are larger organisms, and therefore easier to remove from suspension. Experiments were conducted to determine how much lipid could be recovered when extracting from zooplankton that had grazed dense cultures of the chlorophyte Chlamydomonas reinhardtii. It was found that 97% of lipid was lost when extracting from zooplankton, as compared to extracting directly from the algae. It was also found that extracted lipid yield was not significantly different when decreasing homogenization time of wet or dry C. reinhardtii. When using dry Daphnia as a feedstock, lipid yields were significantly less with decreasing homogenization time, but the same was not true when using wet Daphnia as a feedstock. From these results we would suggest if using Daphnia as a feedstock for biofuel that it is less energy intensive to extract from wet biomass. Each of these studies proved to be feasible ventures, but varied in degrees of sustainability potential.