Kinetics of hydrolysis of microalgae biomass during hydrothermal pretreatment

Hydrothermal pretreatment is an efficient method for increasing the biogas yield and the amount of energy generated via the anaerobic digestion of microalgae biomass. Few studies have investigated the effects of pretreatment conditions on the rate of the hydrolysis of microalgae biomass into carbohydrates and proteins and the changes in hydrolysis residues, which significantly limit further performance enhancement. In this study, we analyzed the effects of pretreatment conditions on the hydrolysis characteristics and rate of microalgae biomass hydrolysis into carbohydrates and proteins. The results revealed that the yields of soluble carbohydrates and proteins increased with increasing pretreatment temperature and retention time. Conversely, the yields remained unchanged as the mass fraction of microalgae biomass in the microalgae slurry increased from 1% to 10%. The activation energies for the hydrolysis of microalgae biomass into carbohydrates and proteins were 35.07 and 39.66 kJ/mol, respectively. During hydrothermal pretreatment, organic matter within microalgae biomass was converted into relatively small molecules with poor stability, and hydrolysis exposed the major functional groups of microalgae biomass. This study provides guidance for controlling the hydrolysis reaction, designing hydrolysis reactors, and predicting the yields of carbohydrates and proteins.