Energy conversion in an internally illuminated annular-plate airlift photobioreactor

Algal-derived therapeutics, bioactive molecules, and fuels produced in photobiore-actors (PBRs) are of great scientific and economic interest, but the high cost of production still prevents their widespread use. Specifically, the cost of the energy inputs and the control of the photonic inputs that enable production optimization continue to be problematic. To this end, a novel 55-L annular-plate airlift PBR (APAPBR) with internal illumination was designed and characterized for the batch production of algal biomass. The APAPBR was able to convert mixing and photonic energy inputs into Chlorella pituita SG1 biomass at an efficiency of 0.064 (J biomass [J input](-1)), or 0.27 g dry cell weight (DW) W-1 d(-1). Thanks to a high degree of photon capture and the airlift effect that provided energy-efficient mixing and mass transfer, this energy conversion is 54% of the theoretical maximum as determined in previous studies. Under these efficiency conditions, C. pituita SG1 was able to grow photoautotrophically to 3.9 +/- 0.2 gDW L-1. Additionally, a mathematical approach was used to predict the mean light intensity with the highest biomass yield per unit of photonic input and the maximum biomass concentration achievable under the given process conditions. These predictions were validated in our system by the experimental cultivation data. This APAPBR represents a simple, innovative, and energy-efficient PBR configuration that could decrease the cost of phototrophic bioprocesses and enable novel bioprocesses that require a high degree of control over the photonic input.