Estudo da cinética de crescimento da microalga Scenedesmus sp. em meios de cultivo salobros.

Abstract

Microalgae are unicellular microorganisms that can grow in both freshwater and saltwater. They are chlorophyll and are practically in all kinds of water on the planet. Its cultivation is increasingly attracting interest since the applicability has been observed in several segments, such as in the treatment of water, nutrition and energy generation. The microalgae Scenedesmus sp. is chlorophyllated, unicellular and uninucleate and belongs to Scenedesmaceae family, genus Scenedesmus. This microalgae is more common in fresh water and can be found less frequently in brackish water with salinity between 0.05 and 3% salts (500-30000 ppm). It has ellipsoidal shape, linear colonies and grouped in numbers 4, 8, 16 or 32. This study aimed growth kinetics study of microalgae Scenedesmus sp. in brackish means, by producing two synthetic culture media with the addition of NaCl and MgCl2 salts, with a view to possible subsequent utilizations of brackish water for the production of microalgae. It has been found that the presence of salts influences the growth of such microorganisms. Analyzing the microbial growth curves of the microalgae Scenedesmus sp., it was noted that, in the means containing magnesium chloride, the Lag phase or latency hardly occurred, with the exception of media with concentration of 8000 mg.L-1, indicating that the microalgae took less time to adapt to the medium with addition of MgCl2, compared with media containing NaCl. It was also found that the influence of chloride ion in the growth of microalgae was decreased due to the presence of sodium and magnesium ions, nutrients that are important in cellular metabolism. By analyzing the calculated kinetic parameters (maximum growth rate, productivity of biomass and generation time), it was observed that the best results were obtained in media containing magnesium chloride, indicating a better growth kinetics in these media compared to those containing NaCl. This was due to the fact that Mg is classified as a macronutrient or essential nutrient, important for cell metabolism of microalgae, and sodium is classified as a micronutrient (required in smaller amounts). The influence of that ion (Mg) in microalgae growing has been more observed than sodium ions influence. Based on the kinetic results, the possibility of the microalga Scenedesmus sp growth. in brackish means has been verified.