Effect of plate distance on light conversion efficiency of a Synechocystis culture grown outdoors in a multiplate photobioreactor

Abstract

In this work, the performance of a vertical multiplate photobioreactor is analyzed and presented. The photobioreactor consisted of 20 vertical plates (1 m² each) connected by manifolds and a working volume of 1300 L. The total area occupied (footprint) was 10 m², while the illuminated area was 40 m², therefore the ratio of illuminated area to volume ratio was about 30 m^-1. The performance of the photobioreactor was evaluated using a culture of Synechocystis PCC 6803, circulated by a centrifuge pump. The results showed that the amount of light captured by the photobioreactor at a plate spacing of 0.5 m was 90.2 % of the light incident on the horizontal surface, while at a plate spacing of 1.0 m, 50.3 % was captured. The corresponding biomass yield, calculated based on the ground area occupied by the reactor, was 26.0 g m^-2 day^-1 and 7.2 g m^-2 day^-1, when the plates were spaced at 0.5 m and 1.0 m respectively. Therefore, the light conversion efficiency calculated based on the ground area was significantly higher in the configuration with a plate spacing of 0.5 m, reaching 5.43 % based on PAR (photosynthetically active radiation), and 2.44 % based on solar radiation, giving a value 3.7 higher than when the plates were spaced 1.0 m apart. It was concluded that the light conversion efficiency might be further improved by reducing the plate spacing while also reducing the culture light path.

Keywords: Light conversion efficiency; Light dilution; Microalgae mass culture; Synechocystis; Vertical photobioreactor.