Microalgae Biofixation of CO2 and Fertilizer Production for Greenhouse Gas Abatement

75974B Microalgae biofixation is a candidate technology for abating the emissions of greenhouse gases, particularly CO2, while simultaneously producing fuels and chemicals. One approach is to use nitrogen-fixing microalgae (cyanobacteria) cultivated in large open ponds and harvested to produce both renewable fuels (e.g., methane, and possibly, in the future, ethanol or hydrogen) and organic nitrogen fertilizers (as substitutes for chemical fertilizers). However, a major issue is productivity, measured in tons of fertilizers and biofuels that can be produced per acre (hectare) of ponds per year. In this project, cultures of nitrogen-fixing cyanobacteria will be cultivated in open ponds, with the harvested algal biomass digested to generate methane gas and a liquid organic fertilizer suitable for crop production. Productivity will be maximized by selecting for high productivity strains and by developing mutants with reduced light harvesting pigments. During Phase I, wild-type strains of nitrogen-fixing cyanobacteria were isolated and cultivated indoors, and work on outdoor mass cultures was initiated. The anaerobic digestion of cyanobacterial biomass was determined, and selection low pigment- high productivity strains were selected for further study. Phase II will emphasize the outdoor mass culture of both wild-type and low-pigment mutant strains to determine maximum productivity, in terms of both of both carbon dioxide sequestration into biomass and nitrogen fixation. Genetic selection techniques will be used to develop algal strains with low phycobiliprotein content and higher productivities, due to reduced self-shading and photoinhibition. Commercial Applications and Other Benefits as described by the awardee: The technology should contribute to the production of organic fertilizer in U.S. agriculture, of particular importance after the establishment of the USDA National Organic Plan. One immediate commercial application would be in the production of Spirulina, a commercial microalga used as a food and food supplement.