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Evaluación de las condiciones de cultivo autotrófico de microalgas Chlorella para la producción de Biodiesel.

Renewable energies are energies of great interest around the world. They allow expanding the world's energy matrix and permit to reduce the use of fossil fuels, reducing the impact of them on the environment and the economy. There are different types of renewable energies such as wind, geothermal, hydro, biofuels, among others. Biofuels are renewable energies that use biomass to generate energy; one of them is the biodiesel, which is a biodegradable, renewable and non-toxic fuel, made from monoalkyl esters of long chain fatty acids that can come from the lipids found in the microalgae cells. Lipids are extracted from microalgae using organic solvents and then with transesterification biodiesel is produced. The lipid content in microalgae can be incremented by optimizing the growing conditions. The advantages of biodiesel generated from microalgae over other biofuels are that they do not require large areas of land for their cultivation and biodiesel generated has an energy density similar to petroleum diesel. In this research project autotrophic culture conditions are evaluated, under batch and semibatch bioassays, in order to find the best conditions and maximize the lipid content in microalgae Chlorella. In the first phase of this research project, microalgae were harvested with fertilizer medium and cultured in proteose medium. The result was that the microalgae were in good conditions for using them in experiments. The effects of different sodium bicarbonate concentrations, higher concentrations and lower concentrations, cultivation periods, and the effectiveness of stirring on biomass production and lipid content were tested in batch and semibatch bioassays. The results revealed that the adequate sodium bicarbonate concentration was 0.10 g L-1 with a cultivation period of four days at magnetic stirrer, producing a lipid content of 11.03%. However, it couldn’t be established which stirring technique was the best; therefore the other experiments in this research were conducted by stirring with an orbital shaker. Bioassays were performed under semibatch conditions with different sodium bicarbonate concentrations and lipid extraction frequencies: periodic extractions, whenever microalgae finished their exponential growth phase, and a single extraction at the end of the bioassay. The highest lipid content, 6.89%, was found in the semibatch bioassay with a sodium bicarbonate concentration of 0.1 g L-1. However, the percentage of lipids by periodic extractions, 6.89%, and by a unique extraction, 6.38%were very similar so it is recommended doing only a single extraction at the end of the bioassay in order to save resources. Finally, the installation and operation of the tubular photobioreactor was designed for autotrophic cultivation of microalgae Chlorella. The design of the installation and operation of the photobioreactor included criteria such as the supply of the carbon source, lighting, mixing, monitoring and removal of oxygen in gas form in the photobioreactor.