Efficient Saccharification of the Microalga Chlorella vulgaris and its Conversion into Ethanol by Fermentation

Abstract

The third-generation bioethanol production depends on the utilization of algae as raw material and an excellent source of polysaccharides, which can be fermented to bioethanol. The microalga Chlorella vulgaris is suitable for bioethanol production due to its carbohydrate content. In this study, the chemical pretreatments of acidic and alkaline pretreatments of Chlorella vulgaris biomass showed that the maximum reducing sugars and total carbohydrate concentrations produced from acidic pretreatment of the algal biomass by using 2% sulfuric acid (H2SO4) at 120 °C for 30 min were (24.77 g/100 g dried biomass) and (16.08 g/100 g dried biomass), respectively. The bioethanol released from the biomass was increased gradually until the 5th day (14.32 g/100 g dried biomass). The maximum bioethanol produced after 2% (w/v) of sodium hydroxide (NaOH) at 120 °C for 30 min. alkaline pretreatment was (21.54 g/100 g dried biomass) reducing sugar, (15.72 g/100 g dried biomass) total carbohydrate and the produced bioethanol concentration on the 4th day (7.74 g/100 g dried biomass). At the same time, the physical pretreatments were done by microwaves and ultrasonication. The highest reducing sugars after ultrasonication, (18.97 g/100 g dried biomass) which fermented to (16.19 g/100 g dried biomass) bioethanol at the 4th fermentation day. While microwaves pretreatment reached (11.22 g/ 100 g dried biomass) reducing sugars, that synthesis (2.91 g/100 g dried biomass) at the 5th fermentation day. This work concluded that 2% H2SO4 was the best treatment method, which resulted in the highest concentrations of reducing sugars, total carbohydrate, and bioethanol.