Effective fractionation of microalgae biomass as an initial step for its utilization as a bioenergy feedstock

Abstract

• S. obliquus was effectively fractionated by mild (un)catalyzed hydrothermal processes. • Soluble sugars were mainly present as soluble oligosaccharides. • Protein was mainly retained in the solid fraction. • Dilute acid hydrolysis allowed higher oligosaccharides yield at mild conditions. • Co-production of added-value oligosaccharides in marine biorefineries. Scenedesmus obliquus , a biotechnologically recognized microalga, was grown in 70 L vertical photobioreactors using non-supplemented secondary brewery wastewater as a culture medium. Upon collection, by mechanical means, the cells were subjected to hydrothermal (autohydrolysis) and dilute acid hydrolysis (0.5% sulfuric acid) pre-treatments were carried out using pressure micro-reactors under isothermal conditions up to 300 min. Both processes enabled a high recovery of soluble sugars (∼50%) that were, in a great majority, present in the added-value oligomeric form (92% and 90.5% for autohydrolysis and dilute acid hydrolysis, respectively). Protein solubilization also presented relevant yields (35% removal), with dilute acid hydrolysis allowing both higher oligosaccharides and protein productivities at a milder temperature. As compared to the current whole microalgae biomass-based upgrade strategies, the use of these mild processes is extremely promising, as they will enable the future co-production of added-value oligosaccharides, and protein, which can be relevant co-products of a biofuels-based biorefinery.