Enhancing the lipid content of Scenedesmus obtusiusculus AT-UAM by controlled acidification under indoor and outdoor conditions

This work explores the influence of controlled acidification on lipid accumulation in S. obtusiusculus AT-UAM under N-deplete conditions. The protocol included determination of the acidification procedure (CO2 or HCl) and the application chronology in flat panel photobioreactors, operated under controlled conditions. The highest lipid content and productivity of 60% glipids gDCW−1 and 85 mg L−1 d−1, respectively, were obtained when controlled acidification to pH of 5.5 was applied after 80 h of operation under N-depletion. The strategy was also applied successfully in a larger scale using different configurations such as bubble-column photobioreactors and raceway ponds, operated outdoors, yielding a maximum lipid content of 45% glipids gDCW−1 in both systems. Globally, the lipid content increased almost twice the value obtained without acidification in indoor and outdoor conditions. The analysis revealed that no major changes in fatty acid profile occurred, suggesting a high specificity of the microalga toward lipid production; however, significant changes in the ultrastructure of the subcellular components and the cell wall were observed. [Display omitted] •Controlled acidification under N-depletion increased lipid content in S. obtusiusculus.•Acidification was applied when the pH dampening capacity of microalgae diminished.•The strategy was effectively applied to photobioreactors operated outdoors.•No changes in FAME profile resulted after controlled acidification.•The highest lipid content ever reported, 60%, was obtained with the acid pH strategy.