Avaliação da produção de oxigênio do fitoplâncton Nannochloropsis oculata, utilizando os regimes batelada e semi contínuo

Abstract

It is increasingly possible to observe the effects caused by the advances in environmental problems together with pollution, which directly affect the lives of the population, causing an increase in the greenhouse effect and, consequently, a decrease in the oxygen present in large urban centers. Microalgae, also known as phytoplankton, are autotrophic organisms, present on the ocean surface, which use the oxygen gas dissolved in the water for their respiration and release, through the photosynthetic process, approximately 70 to 90% of the oxygen contained in the atmosphere. Photosynthesis, carried out mostly by these phytoplankton, is extremely important for maintaining a pleasant climate, life in aquatic environments and producing the oxygen used by all living beings. The phytoplankton Nannochloropsis oculata is widely studied due to its high growth rate and efficient reproduction, making it essential for the health of aquatic ecosystems, contributing significantly to the production of oxygen. Its nutritional composition, rich in polyunsaturated fatty acids, is of great benefit due to its biotechnological potential and is also used in the production of feed for fish and other aquatic organisms, due to its essential nutrients. The high resistance of this phytoplankton to variations in environmental conditions allows its efficient cultivation in different systems, standing out for its adaptability. This species also has a great capacity to produce extra and intracellular polysaccharides. Within this context, this study aimed to perform the reproduction of the phytoplankton Nannochloropsis oculata in batch reactor, which allow precise control over the cultivation conditions of this type of phytoplankton, and the semi-continuous reactor, which promotes continuous and stable growth, aiming to identify the optimal cultivation conditions for this species of algae. As an example of these optimal conditions, it is possible to highlight the reproduction rate of this organism, where, once this rate is maintained constant, the cultivation environment can be optimized to maximize photosynthesis and, consequently, oxygen production. During the experiment, it was observed that the pH of the medium varied throughout the process, impacting the photosynthetic rate. In the semi-continuous regime, after partial renewal of the culture, the pH decreased, but then rose again, influencing the stability of the system. In addition, a progressive darkening of the culture was recorded, suggesting an increase in cell density and possible limitation of the light available to the innermost cells. The experimental part of this study was developed by varying the reactor regimes, which were initially carried out in batch mode, followed by a semicontinuous system for advanced and optimized treatment of the process. The bioreactors were built in a manner similar to an aquatic environment, preserving all the characteristics of their source water, such as: pH (8.0-10.0), temperature (25-30ºC) and lighting (16h with light - 8h without light). After the phytoplankton reproduction time, approximately 6- 7 days, the photosynthesis rate was determined in order to determine the oxygen production of each reactor. At the end, it was possible to compare the efficiency of the systems used, identifying the batch regime as the one that provided the highest oxygen production, with a value of 6 mg/L O2, compared to the semi-continuous regime, which presented 4 mg/L O2. The results indicate that the batch system was more efficient in oxygen production, due to the lower interference in the photosynthetic process.