Bioprospecção de microalgas de corpos de água da região sudoeste do Paraná

Abstract

Microalgae are sustainable sources of bioproducts for the food, pharmaceutical, and bioenergy industries. In terms of bioremediation, microalgae are important in wastewater and greenhouse gas treatment. However, high production costs make large-scale application unfeasible. One solution is to integrate microalgae cultivation with wastewater treatment to reduce costs. Bioprospecting explores microorganisms to obtain bioproducts, and microalgae stand out due to their presence in diverse environments. Consortium cultivation of microalgae is advantageous in open cultivation systems compared to monocultures, as it is more resistant to environmental variations. This study aimed to bioprospect a microalgal community from the Southwest region of Paraná, using swine farming digestate as the cultivation medium, to establish a culture with biotechnological potential. Samples were collected from freshwater bodies and cultivated for seven months in fed-batch mode. The cultures were conducted in synthetic medium (modified BBM) and supplemented with a low concentration of swine digestate, until a consortium with consistent characteristics was obtained using the aging technique. In the end, it was possible to obtain microalgae resistant to temperature and pH variations and tolerant to swine digestate. Subsequently, the microalgae were morphologically identified, and the presence of Chlorella sp., Scenedesmus sp., Desmodesmus sp., Monoraphidium sp., Tetradesmus sp., Monoraphidium contortum, Tetradesmus obliquus, and Desmodesmus opoliensis was verified. Afterward, cultures were conducted in 0.5 L bioreactors under non-sterile conditions, without temperature or pH control, testing different concentrations of digestate (0 to 60%) and initial pH (4 to 8), using a Central Composite Rotational Design 22 (CCRD 22). In this phase, microbial growth kinetic parameters were determined, with a maximum specific growth rate (µmax) of 0.109 d-1 and generation time (tg) of 6.38 days. Additionally, CCRD 22 response surface graphs and contour curves showed that maximum cellular concentration (1.00 - 1.16 g/L) was obtained in a medium containing up to 23 % digestate at a neutral to slightly alkaline pH (7.2 to 8.0). Based on the optimized conditions in CCRD 22, cultivation was performed in a 5 L reactor for 15 days, and by the end of cultivation, 1.21 g/L of cells were obtained, containing 24.5% lipids, with a cell productivity (Px) of 0.081g/L.d. It is concluded that the bioprospected microalgal consortium has the potential for application in open, non-sterile, large-scale cultivation systems, either for treating swine farming wastewater or other biotechnological applications.