Energetic evaluation of an internally illuminated photobioreactor for algal cultivation

An annular internally illuminated photobioreatcor (IIPBR) configuration based on the airlift/bubble column principles was developed and validated at an 18 l prototype scale using Scenedemus sp. and Nannochloropsis salina in batch and semi-continuous modes, at constant light supply and constant gas-to-culture volume ratio, but at varying CO(2)-to-air ratios. Highest biomass production was recorded at CO(2)-to-air ratio of 4% with Scenedesmus sp. and at 1% with Nannochloropsis salina. The energetic performance of this IIPBR was quantified in terms of biomass productivity per unit energy input, P/E (g W(-1) day(-1)), considering energy input for illumination and for pneumatic mixing and circulation. Under optimal conditions, the IIPBR evaluated in this study achieved P/E of 1.42 g W(-1) day(-1) for Scenedesmus sp. and P/E of 0.34 g W(-1) day(-1) for Nannochloropsis salina. These P/E values are better than those estimated for airlift and bubble column photobioreactor configurations reported in the literature.