Rheological properties of concentrated slurries of harvested, incubated and ruptured Nannochloropsis sp. cells

Abstract

Biorefining of microalgae biomass requires processing of high-solids (> 10%) slurries. To date there is little knowledge of how processes for weakening and rupturing microalgae cells affect the rheological properties of these materials. To fill this gap in the literature, the rheological properties of concentrated slurries of marine microalgae Nannochloropsis sp. were investigated as a function of processing and solids concentration (12, 20 and 24% w/w). Freshly harvested, incubated (autolysed), and high-pressure homogenised (HPH) slurries were found to be shear thinning up to a shear rate of approximately 200 s − 1. Viscosity increases were far more prominent for partially processed versus unprocessed algal pastes at the higher concentrations. Slurry viscosity as a function of cell volume fraction could not be fitted to the Krieger-Dougherty model due to a network structure resulting from extracellular polymeric substances (EPS) and the intracellular cell components released during incubation and cell rupture. The 24% slurry, which was near the close packing limit, was much more viscous than the less concentrated slurries when comprising whole cells (i.e. harvested and incubated slurries). Cell rupture by HPH completely altered the characteristics of the slurry, increasing the viscosity of even the less concentrated slurries, and producing irreversible shear thinning behaviour. The magnitude of the increases in viscosities and the irreversible shear thinning behaviour observed in this study, have significant implications for processing and optimising the solids concentration of algal slurries.

Recovery of soluble proteins from Chlorella vulgaris by bead-milling and microfiltration: Impact of the concentration and the physicochemical conditions during the cell disruption on the whole process

“…The biomass paste was thawed and diluted with softened water at different concentrations (30-60-90 g/LDW). The 3 biomass concentrations tested were chosen for their different rheological behaviour [20][21][22]: 30 g/LDW (watery solution), with Newtonian behaviour, where the viscosity is independent of applied stresses (viscosity: 0.002 Pa s); 60 g/LDW, the transition between Newtonian and non-Newtonian, where a strong shear thinning behaviour can be observed when the applied stress exceeds a critical value (viscosity: 0.006 Pa s); 90 g/LDW (sticky liquid) with non-Newtonian behaviour, where yield stress behaviour can be observed (viscosity: 0.03 Pa s [11,22]) For the cell disruption experiments, Dyno-mill multi lab (WAB, Switzerland) was operated in pendulum mode as described by Montalescot et al 2015 [11]. The rotational speed was kept to 10 m/s, while the feed flow rate was 200 mL/min.…”

Transport of Compressed Woody Biomass: Correlating Rheology and Microcompounder Measurements

“…The flow index reported is slightly higher than 1, which might be related to the biomass heterogeneous properties and has been observed before for pretreated corn stover modeled as a power-law fluid . The zero-shear viscosity for compressed −3/8″ FR at 30% moisture content is 74,000 Pa·s, which is higher than concentrated homogenized algae slurries of 24 wt %, untreated corn stover slurries of 32 wt %, and pretreated corn stover slurries of 20 wt % having zero-shear viscosities of 10,000, 10,000, and 20,000 Pa·s, respectively. , …”

“…At a constant screw speed of 10 rpm (26 s –1 ), viscosity linearly decreases with increasing moisture content (Figure b). Reducing the moisture content in the biomass compression context is somewhat similar to increasing the solids concentration in biomass slurries. , Since biomass slurries were previously investigated using traditional rheometers and geometries, the range of concentrations is smaller than solids contents in this study. For instance, the viscosity of pretreated corn stover at equivalent shear rates increased by roughly an order of magnitude for an increase in solids content by 5 wt % (in a range of 5–17%) .…”

Process Design of Microalgae Slurry Pump

“…For the above-mentioned fluid that requires high-lift delivery, a ZGB type pump can be used, which is a single-stage singlesuction centrifugal slag/slurry pump. The typical processing shear rates of centrifugal pumps are within a range of 5 to 300 s − 1 [16], which will help reduce the viscosity [17]. Because the diameter of the pipeline is 100 mm, the 100ZGB type slurry pump can be selected.…”