Cultivation of diatom skeletonema costatum in airlift photobioreactor

Abstract

This work aimed to examine the performance of 3 L airlift photobioreactor system on the cultivation of Skeletonema costatum compared to that in bubble column. Firstly, the experiment was set out to determine appropriate medium for Skeletonema costatum where it became apparent that the standard F/2 medium (Guillard's medium) could only yield the best growth character when the silicon concentration increased 4 times than the normal value. The cultivation of cell in airlift photobioreactor was found to provide a slightly better performance than the bubble column where the maximum cell concentration, specific growth rate, and productivity in the airlift were 4.6 x 106 cell mL-1, 0.07 h-1, and 6.6 x 104 cell s-1 compared with 3.81 x 106 cell mL-1, 0.06 h-1, and 4.1 x 104 cell s-1 in the bubble column of the same size (3L) and operated at the same aeration rate (usg = 1.5 cm s-1) and light intensity (34 mol photons m2 s1). This was because the airlift photobioreactor allowed circulatory flow in the system, minimizing cell precipitation and enhancing light utilization efficiency, and this positively affected the cell growth. In batch culture, the optimal operation was found to occur when the ratio between downcomer and riser cross sectional area (Ad:Ar) was 3.27, the superficial gas velocity (usg) was 1.5 cm s1 and the light intensity was 34 mol photons m2 s1