This paper reports the rheological properties of algae slurries as a function of cell concentration. From both energy and economic perspectives, the algae slurry for producing biofuels should have rheological attributes that minimizes the pumping power requirements while delivering the maximum amount of biomass from the cultivation fields to the biorefinery. To achieve this, an accurate knowledge of the rheological properties of algae slurries as a function of cell concentration is necessary. This study measures the rheological properties of eight different concentrations of Nannochloris sp. in ASP-m nutrient media ranging from 0.5 to 80 kg dry biomass/m3. Strain controlled dynamic frequency sweep tests, transient step rate tests, and steady rate sweep tests were performed with an ARES-TA Rheometer using a double wall couette cup and bob attachment. Shear rates ranged from 5–270 s−1. The results show that the concentrations of 10 kg/m3 and below behaved as Newtonian fluids with a dynamic viscosity of 1.1×10−3 Pa-s while the concentrations of 20 kg/m3 and above behaved as shear thinning non-Newtonian fluids. Finally, an energy analysis was performed where a non-dimensional bioenergy transport efficiency was defined as the ratio of the energy content of transported algae biomass to the required pumping power. The results show that an optimal biomass concentration minimizing pumping requirements occurs at the highest dry biomass concentration.

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