Scale-up of tubular photobioreactors

The effect of the light/dark cycle frequency on the productivity of algal c ulture at different day-averaged irradiance conditions was evaluated for Ph aeodactylum tricornutum grown in outdoor tubular photobioreactors. The phot obioreactor scale-up problem was analyzed by establishing the frequency of light-dark cycling of cells and ensuring that the cycle frequency remained unchanged on scale-up. The hydrodynamics and geometry related factors were identified for assuring an unchanged light/dark cycle. The light/dark cycle time in two different tubular photobioreactors was shown to be identical w hen the linear culture velocity in the large scale device (U-LL) and that i n the small scale unit (U-LS) were related as follows: U-LL = f(9/7)/alpha U-8/7(LS). Here f is the scale factor (i.e., the ratio of large-to-small tube diameter s), alpha is a function of the illuminated volumes in the two reactors, and 'dark' refers to any zone of the reactor where the light intensity is less than the saturation value. The above equation was tested in continuous cul tures of P. tricornutum in reactors with 0.03 m and 0.06 m diameter tubes, and over the workable culture velocity range of 0.23 to 0.50 m s(-1). The p redicted maximum realistic photobioreactor tube diameter was about 0.10 m f or assuring a culture performance identical to that in reactors with smalle r tubes.