Hydrothermal acid pretreatment of Chlamydomonas reinhardtii biomass for ethanol production

Certain microalgae have been known to use light and various carbon sources to produce carbohydrates, mainly in the form of starch. This is one of the pertinent feedstocks replacing agricultural products for the production of bioethanol by yeast. This study focuses upon dilute acid hydrothermal pretreatments at low cost and high efficiency to compete with current methods, and employs Chlamydomonas reinhardtii UTEX 90 as the feedstock. With dry cells of 5% (w/v), the algal biomass was pretreated with sulfuric acid (1-5%) under temperatures from 100 to 120°C, from 15 to 120 min. As a result, the glucose release from the biomass was maximum at 58% (w/w) after pretreatment with 3% sulfuric acid at 110°C for 30 min. This method enabled not only starch, but also the hydrolysis of other oligosaccharides in the algal cell in high efficiency. Arrhenius-type of model equation enabled extrapolation of some yields of glucose beyond this range. The pretreated slurry was fermented by yeast, Saccharomyces cerevisiae S288C, resulting in an ethanol yield of 29.2% from algal biomass. This study suggests that the pretreated algal biomass is a suitable feedstock for ethanol production and can have a positive impact on large-scale applied systems.