Outdoor culture of a cyanobacterium with a vertical flat-plate photobioreactor: effects on productivity of the reactor orientation, distance setting between the plates, and culture temperature

The ability of a photobioreactor to fix CO2 was evaluated with the thermophilic cyanobacterium, Synechocystis aquatilis SI-2. The reactor consisted of three to five flat plates of transparent acrylic plastic standing upright and in parallel and giving a 0.015-m light path. The reactor was 0.8 m high and 1 m long with 9 1 working volume. The effects of the orientation of the vertical bioreactor, distance between the plates, and culture temperature on the productivity of biomass were investigated during the summer of 1998 in Kamaishi (39 degrees N, 142 degrees E), Japan. When the illuminated surface reactor was placed in an east-west-facing orientation, the biomass productivity was roughly 1.4-fold higher than that obtained in a north-south-facing orientation, because the former received more solar energy than the latter. The productivity based on the overall land area was the same for plates set either 0.25 m or 0.5 m apart. However, the volumetric productivity of the reactor in which the plates were set 0.25 m apart was lower than that when the plates were set 0.5 m apart, since the former plates received relatively lower solar irradiation because of severe mutual shading. When the culture temperature was maintained in its optimal range (37-43 degrees C), the productivity was 50% greater than that obtained in a culture at ambient temperature (20-44 degrees C). The biomass productivity and CO2 fixation rate were investigated under various experimental conditions. The maximum rate of 53 g CO2 m(-2) day(-1) was achieved in the temperature-regulated culture with the reactor set in an east-west-facing orientation, the distance between plates being 0.25 m.