Synchronization of fluid-dynamics related and physiological time scales and algal biomass production in thin flat-plate bioreactors

Abstract

Experiments on ultrahigh density unicellular algae cultures in thin flat-plate bioreactors (thickness ≤2 cm) indicate that: i) Optimal areal biomass production rates are significantly higher than in traditional ponds or raceways, ii) productivity grows for radiation levels substantially higher than one sun; saturation emerging, possibly, at intensities of about four suns, and iii) optimal volumetric and areal production rates as well as culture densities increase as reactor thickness is reduced. The observations are reproduced within the framework of a simple model, which takes into account the random motion of cells across the reactor thickness, and the competing effects of two physiologically significant time scales. These are TR, the time that elapses from the moment a reaction center has collected the number of photons required for one photosynthetic cycle until it is available again for exploiting impinging photons (1–10 ms), and TW, an average of the decay time characteristic of photon loss processes (several ms to several tens of ms).