Effect of photobioreactor inclination on the biomass productivity of an outdoor algal culture

Abstract

The profile of photon flux density incidented on a tubular-loop photobioreactor in the day could be altered by inclining the bioreactor at an angle with the horizontal. The photon flux density at noon decreased with increasing angle of inclination, whereas the photon flux density in the early morning and late afternoon increased with increasing angle of inclination. The overall photosynthetic radiance received by the bioreactor inclined at 0, 25, 45, and 30° was 1:0.89:0.77:0.62. Regardless of the angle of bioreactor inclination, the overall biomass output rate of a fed-batch culture over an 8-h/day period was comparable (25-30 g-biomass m-2 bioreactor surface area day-1). As a bioreactor inclined at an angle occupied smaller land area, the daily biomass output rate per land area of a bioreactor inclined at 80° (130 g-biomass m-2 land) was about six times of that obtainable at horizontal position (21-g biomass m-2 land). The bioenergetic growth yield from the absorbed photosynthetic radiance was not a constant but an inverse function of the photon flux density. The quasi-steady state chlorophyll content of the Chlorella cells varied between 36 and 53 mg g-1 cells. Photoinhibition of the maximum photosynthetic capacity was not observed in this study.