Rheology of microalgae concentrates and its influence on the power consumption of enzymatic hydrolysis processing

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 microalgal 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 biomasses exhibited different behaviours, with freshwater slurries being more viscous than seawater ones. The high vis-cosity 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 consider-able effect of algal biomass rheology on the mixing power required during microalgal biomass processing.

Automated summary

The optimization of downstream processing in microalgae-related processes is crucial, as the rheological behavior of the concentrated slurry greatly impacts further processing steps. Research on microalgal concentrates in freshwater and seawater revealed different rheological properties, with freshwater slurries being more viscous and requiring increased energy consumption for mixing, resulting in a potential 60% cost increase.