Controle policromático de luz aplicado à produção de microalgas

Abstract

Microalgae have drawn the attention of the biotechnology industry for being natural synthesizers of high added value products such as β-carotene, astaxanthin, lutein, docosahexaenoic acid, proteins, and pigments. However, its biotechnological exploration is far behind when compared to the use of yeasts and bacteria. The main technological challenge that needs to be overcome is light attenuation, which provides these microorganisms with an inhomogeneous light environment, implying non-optimized growth. Considering these premises, the main objective of this Thesis was to develop an automatic control of photosynthetically active radiation (PAR), using Fuzzy logic, in order to optimize productivity and reduce costs in the production process. And for the full development of the polychromatic light controller, the study was divided into five stages: i) the first one was responsible for providing all the necessary experimental apparatus for the controlled and uncontrolled cultures used for the validation of the proposed system, which includes two light panels, the power controller circuit, and a special capacitor. Each luminous panel was made up of white, red, green and blue LEDs. The power circuit, made up of transistors and resistors, allows the individual manipulation of the intensity of each wavelength. The special condenser was developed with a Peltier chip, eliminating the need to use another thermal bath in the process, reducing costs and simplifying the apparatus used; ii) the second stage included the development of a PAR sensor, which is the indispensable system for monitoring the PAR during cultivation and also for guiding the controller. The developed system was patented and was ten times cheaper than commercial sensors available on the market; iii) the third stage included the development of the software responsible for monitoring and controlling the variables of the photobioreactor, which was registered as SUPERSYS_Photo®, being therefore the most important interface during the execution of crops, saving the data, configuring the controller set points such as the ideal PAR, the emission wavelength, the photoperiods, as well as the gas feed rate; iv) the fourth step was essential to characterize the effects of light quality on the biochemical fraction of Scenedesmus obliquus (not yet discussed in the literature), which allowed us to understand the biochemical behavior of the species when subjected to different wavelengths (white, blue, red and mixture of blue and red). These results were essential for defining the wavelength used as a setpoint in the light controller, optimizing the production of proteins in the final composition of the cultures, which, according to the results presented, Scenedemus obliquus synthesizes a greater fraction of proteins when cultivated under blue light compared to conventional white light; v) the fifth and final stage actually included the development of the polychromatic light controller based on Fuzzy logic, which was able to increase cell productivity by more than 200% in Scendemus obliquus cultures and reduce power costs by 30% electrical. Therefore, in general, this research has greatly contributed to the development of processes, control and automation in microalgal cultures, paving the way for an expansion of the scale of cultivation with a favorable cost/benefit ratio.