PHYSICAL AND RHEOLOGICAL PROPERTIES OF ACTIVE FLUIDS UNDER SHEAR STRESS: SUSPENSIONS OF SYNECHOCYSTIS

Design of photobioreactors (PBRs) for microalgae and cyanobacteria cultivation involves the interplay between fluid flow, microbe biokinetics, and radiative transport phenomena, in which the physical and rheological properties of the active fluid play a crucial role. In this study, we focus on the variation of physical and rheological properties of dilute suspensions of Synechocystis sp. CPCC534 with the shear stress applied to the fluid. Experiments were carried out at three different stirring rates in well-controlled conditions and the results were compared with stationary conditions where only molecular diffusion and cell motility govern the transport phenomena, and cell growth. Our results show that the growth and biomass production of Synechocystis sp. under various shear conditions were improved significantly, and the yield was nearly doubled by adding agitation to the system. The viscosity of Synechocystis suspensions, subjected to different shear stress levels, was measured with two different methods. The viscosity data showed shear stress independent Newtonian behavior. However, the viscosity of Synechocystis suspensions increased moderately with cell volume fraction up to 10%, beyond which it increased more rapidly. The shear stress history of the cell suspensions did not show any effect on the fluid viscosity.