Cianobactérias isoladas de lagos naturais do Parque Estadual do Rio Doce- MG potencialmente produtoras de biocombustível

Abstract

The interest in biofuels has increased due to search for energy resources with less environmental impact that would ensure energy security in the future. Recently, microalgae and cyanobacteria have been considered as a promising source for biofuels and chemical feedstocks. This interest in the cyanobacteria it is due mostly to their main advantages that include simplicity of culture, higher photosynthetic efficiency and growth rates, higher biomass production and oil productivities compared to typical terrestrial oil-seed, and higher rates of CO2 fixation and O2 release. However, the current challenge is still arrested in the need of reducing the production costs so that this energy source becomes economically viable compared to the traditional fuels. This main objective this work was to investigate the potential of the cyanobacteria as raw material in the biofuel production in controlled laboratorial conditions and to evaluate the productive potential of those oils. First, we performed studies to choose the cyanobacteria species and the best cultivation conditions. Then, we selected four species of Microcystis. Initially, we evaluated the effects of the culturing media and the levels of nitrogen and phosphorus on the growth, biomass productivity and lipid production. These results indicate that a culture media poorer in nutrients can favour the cellular growth and to stimulate the accumulation of lipids. This result affects directly the costs in the production of the cultivation reducing the consumption of nutrients in the cultivation systems. All of the species demonstrated potential as biomass source for biodiesel production, among the species M. protocystis presented the largest lipid production. We also investigate the use of the strategy of co-culture among five cyanobacteria and two microalgae species. The results indicate that the co-culture strategy resulted in significant increase in the productivity and lipid content. Additionally, the oil obtained from most cyanobacteria and microalgae in mono- and co-culture was excellent for biodiesel production according to estimated empirical equations to qualify the biodiesel. We also evaluated the use of the strategy of two-stage cultivation in four Microcystis. This cultivation approach showed to be an effective strategy to increase the lipid content for biodiesel production from all Microcystis species tested. Moreover, it also revealed not affected the fatty acid composition in these species thus suggesting this strategy of cultivation can be applied for biodiesel production since the basic properties of biodiesel will not be modified. Finally, all the results obtained in this study by several approaches demonstrate that the cyanobacteria can be a potential resource for biodiesel production. It is highlighted that the plasticity of the species allows them to be grown in more limited conditions of nutrients without affecting lipid production. This characteristic may be an alternative to reduce costs and a possible solution for a growing environmental problem. Besides, the approaches studied here should be improved for the production of biodiesel.