PRODUCTIVITY OF SPIRULINA IN A STRONGLY CURVED OUTDOOR TUBULAR PHOTOBIOREACTOR

The effect of different flow rates (from 0.18 m/s to 0.97 m/s) on the productivity of Spirulina grown outdoors in a strongly curved tubular photobioreactor (CTP) was studied. The results were compared to those obtained with a conventional photobioreactor made with straight tubes to form a loop (STP). The cultures were operated at a biomass concentr ation of 10 g/l dry weight. The productivity of the culture increased by about 39% and 29% in the CTP and STP respectively when the flow rat e of the culture was increased from 0.18 mis to 0.75 m/s. A further in crease of the flow rate did not result in any increase of the producti vity in either of the photobioreactors. The better performance of the culture observed in the CTP was attributed to an intermittent illumina tion pattern resulting from a secondary flow motion generated in the b ends. The power required for the induction of the same flow rate insid e the two types of photobioreactor changed significantly. At a Reynold s number of 4000, the power absorbed by the CTP was 25% higher than th at required for water recycling in the STP and rose by more than 40% a t a Reynolds number of 20000.