Scale-up of tubular photobioreactors

The effect of the light/dark cycle frequency on theproductivity of algal culture at differentday-averaged irradiance conditions was evaluated forPhaeodactylum tricornutum grown in outdoortubular photobioreactors. The photobioreactor scale-upproblem was analyzed by establishing the frequency oflight–dark cycling of cells and ensuring that thecycle frequency remained unchanged on scale-up. Thehydrodynamics and geometry related factors wereidentified for assuring an unchanged light/dark cycle.The light/dark cycle time in two different tubularphotobioreactors was shown to be identical when thelinear culture velocity in the large scale device(ULL) and that in the small scale unit (>ULS)were related as follows:ULL = \frac f 9/7 \alpha8/7 ULS.Here f is the scale factor (i.e., the ratio oflarge-to-small tube diameters), α is afunction of the illuminated volumes in the tworeactors, and `dark' refers to any zone of the reactorwhere the light intensity is less than the saturationvalue. The above equation was tested in continuouscultures of P. tricornutum in reactors with 0.03 mand 0.06 m diameter tubes, and over the workableculture velocity range of 0.23 to 0.50 m s-1. Thepredicted maximum realistic photobioreactor tubediameter was about 0.10 m for assuring a cultureperformance identical to that in reactors with smaller tubes.