Rheology of microalgae concentrates and its influence on the power
consumption of enzymatic hydrolysis processing
Abstract
The optimization of downstream processing is a critical step in any
microalgae-related process. The microalgal biomass is separated from the
initial diluted cultures to form a concentrated slurry, the properties
of which greatly influence the design and performance of further
processing steps, such as enzymatic hydrolysis. In this work, the
rheological behaviour of two microalgae concentrates produced both in
freshwater (Scenedesmus almeriensis) and seawater (Nannochloropsis
gaditana) were studied. Measurements were performed on the entire range
of biomass concentrations, from 0.5 g/L to 264 g/L. Non-Newtonian
behaviour was observed whatever the water type and biomass concentration
used, especially at high biomass concentrations above 10 g/L. The
rheological data were adjusted to the Power Law model, and the
consistency and flow behaviour indexes were correlated with the biomass
concentration. The results show that the freshwater and seawater biomass
exhibited different behaviour, with freshwater slurries being more
viscous than seawater ones. The high viscosity of freshwater slurries
requires increased energy consumption for mixing, with an estimated cost
increase of 60% when using them under the non-Newtonian conditions
considered. These findings highlight the considerable effect of algae
biomass rheology on the mixing power required during microalgae biomass
processing.