LAUSR

The saccharification of Chlorella sp. biomass by single and combined commercial carbohydrase enzymes, Termamyl SC, Dextrozyme GA, and Cellic CTec2, was investigated. A substrate concentration of 100-g volatile solids (VS)/L was optimal for all the enzymes used. The optimal enzyme dosages for Termamyl SC, Dextrozyme GA, and Cellic CTec2 were 160-units/g VS, 320-units/g VS, and 40–filter paper units/g VS, respectively. The maximum reducing sugar yield, 130-mg/g VS, was obtained with a Dextrozyme GA treatment, which is equivalent to 38.37% hydrolysis efficiency based on carbohydrate content. A combined-enzyme treatment with Cellic CTec2, Termamyl SC, and Dextrozyme GA raised the reducing sugar yield and hydrolysis efficiency to 186.69-mg/g VS and 54.85%, respectively. Scanning and transmission electron microscopic images indicated morphological alterations in Chlorella sp. cells as an effect of enzyme treatment. Enzyme treatment improved the hydrogen production, hydrogen production rate, and hydrogen yield from Chlorella sp. biomass. The maximum hydrogen yield, 42.24-mL/g VS added , was obtained from a Dextrozyme GA–hydrolyzed microalgae biomass. This was 82.46% higher than that obtained from untreated biomass (23.15-mL H 2 /g VS added ). Fourier-transform infrared analysis revealed that the functional groups of Chlorella sp. biomass, especially carbohydrates, were modified by both enzymatic treatment and the hydrogen fermentation process. This work demonstrated the efficient saccharification of Chlorella sp. biomass using combined cell wall– and starch-degrading enzymes. The results also elucidate that the pretreatment of Chlorella sp. biomass by commercial glucoamylase is a promising approach to solubilize internal starch granules and promote biohydrogen production without the addition of any cell wall–degrading enzyme.