Rheological properties of microalgae slurry under subcritical conditions for hydrothermal hydrolysis systems

Hydrothermal hydrolysis is an effective pretreatment for biogas production from microalgae via fermentation. The rheological properties of microalgae slurry under subcritical conditions significantly affect the heat transfer performance and hence the energy requirement of hydrothermal reactors. In this study, we investigated the rheological properties of microalgae slurry under subcritical conditions (2 MPa, 100-200 °C). For the first time, we found that the apparent viscosity of microalgae slurry under subcritical conditions first drastically increased, and then gradually decreased with the increasing temperature, which is quite different with the variation trend at low temperatures (<70 °C). In addition, the temperatures corresponding to the maximum apparent viscosities were different at different shear rates, which was probably due to the combined effects of starch gelatinization and protein denaturation at high temperatures. Finally, the relationship of the apparent viscosity of microalgae slurry with the temperature and shear rate was obtained.