EFFECTS OF SHEAR-FLOW ON PHOTOSYNTHESIS IN A DILUTE SUSPENSION OF MICROALGAE

This study investigates the effects of shear stress on photosynthesis in dilute suspensions of Spirulina platensis and Chlorella by measurin g the oxygen production rate using a coaxial, double-rotating-cylinder apparatus that generates Couette shear flow. Our device enables up to 0.6 Pa shear stress to be applied, which has the hydrodynamic effect of generating the algal motion and acutely augmenting the oxygen produ ction rate of Spirulina, primarily because the surface area of algae e xposed to illumination is increased. However, there is shear-flow limi tation on any increase in oxygen production, and the shear stress at m aximum oxygen production rate tends to decrease with increasing temper ature. The comparative study with Chlorella showed the reverse relatio nship between oxygen production and shear stress, and the cause of thi s difference is discussed in terms of several factors such as size, sh ape, hydrodynamic stress capacity and others.