Miniaturized Culture for Heterotrophic Microalgae Using Low Cost Carbon Sources as a Tool to Isolate Fast and Economical Strains

Microalgae are well known for their ability to grow photoautotrophically, however higher biomass yields have been reported when microalgae was grown heterotrophically. The feasibility of large scale cultures of microalgae in heterotrophic conditions is still limited by, among other things, the high cost of nutrients and organic substrates used in this type of cultivation. This work aims to explore the utilization of different low cost carbon sources for the cultivation of two different strains of microalgae. Cassava wastewater, sugarcane molasses, glycerol, xylose, sucrose and sodium acetate were tested as carbon sources for Chlorella vulgaris and Scenedesmus bijugus cultures. Glucose and fructose were also tested as reference carbon sources. The methodology of miniaturized growth allowed the screening of different substrates and conditions of the medium much faster than other methodologies (shaking flasks, bioreactor). The results demonstrate the feasibility of the miniaturized culture methodology in the development and evaluation of heterotrophic cultivation of microalgae. The main observed problems were settling of cells, evaporation of the medium during the experiment and interference in spectrophotometric reading (caused by water condensation on the lid), which had to be solved to adapt the methodology of miniature culture to heterotrophic microalgae cultivation. The evaluated microalgae strains presented different growth behaviours in the different carbon sources tested. Cassava wastewater and sugarcane molasses hydrolyzed allowed higher biomass production and proved to be a suitable low cost substrate for increasing algae-based processes feasibility.