Response of Tisochrysis lutea [Prymnesiophycidae] to aeration conditions in a bench-scale photobioreactor

Abstract

The effects of superficial gas velocity (Ugr), gas entrance velocity (ν), and bubble size on the growth of Tisochrysis lutea was investigated in 600-mL photobioreactors operated with airlift pumps. Superficial gas velocities, calculated from measured air flow rates, ranging from 7 to 93 mm s−1 were created using a 1.6-mm diameter syringe. We tested the effects of sparger velocity over a range of 2.48 to 73.4 m s−1 and the effects of bubble size by using two styles of air stones and an open glass pipette, which created a bubble sizes in the range of 0.5 to 5 mm. We calculated oxygen mass transfer coefficient, kLa, values for all experimental conditions. Cell growth increased linearly with increased superficial gas velocity and decreased with increased sparger velocity. Results indicated that smaller bubble size leads to some initial cell damage, but after time, the increased gas transfer as reflected by the kLa value produced higher growth than larger bubbles. Two mechanisms were observed to correlate with cell damage in T. lutea: increasing velocity at the sparger tip and bubble bursting at the surface. These results demonstrate a method to test sensitivity of T. lutea to aeration, which is important for the design of airlift systems.