We present experimental results demonstrating that, relative to continuous illumination, an increase of a factor of 3-10 in the photon efficiency of algal photosynthesis is attainable via the judicious application of pulsed light for light intensities of practical interest (e.g., average-to-peak solar irradiance). We also propose a simple model that can account for all the measurements. The model (1) reflects the essential rate-limiting elements in bioproductivity, (2) incorporates the impact of photon arrival-time statistics, and (3) accounts for how the enhancement in photon efficiency depends on the timescales of light pulsing and photon flux density. The key is avoiding ''clogging'' of the photosynthetic pathway by properly timing the light-dark cycles experienced by algal cells. We show how this can be realized with pulsed light sources, or by producing pulsed-light effects from continuous illumination via turbulent mixing in dense algal cultures in thin photobioreactors.

Photobioreactors (PBRs) demonstrating very high bio-productivity involve a complex interaction between biomass density, light path, light intensity, and timescales of random cell movement. This work presents a new reactor model capable of simulating the effects of the above-mentioned parameters on the biomass productivity of a PBR. The work presented in this paper includes (i) development of photosynthesis model based on occupancy of charge carriers associated with the linear electron transport chain of photosystem-II, (ii) tuning and validation of the kinetics model using flashing light data reported in the literature, and (iii) reactor model development by integrating kinetics with a simple flow depiction including the effect of boundary layer thickness.For the first time, the role of the boundary layer in determining the productivity of PBRs is elucidated.

In this work, a photosynthetic kinetic model was employed for identifying the opportunities for improving the light utilization efficiency of an algae in a flashing light regime. The model was used to understand the impact of light/dark cycle times, light intensity, PI curve characteristics, and strain properties on the light utilization efficiency. The model recommended that for any light intensity the light flash time should be optimized only to reduce fast charge carriers in a single flash and reoxidize 50% or a slightly higher fraction of fast charge carriers in a subsequent dark period. The photon rate of 2 charges per light flash resulted in maximum efficiency. The model was then used to predict the impact of a few other opportunities such as a higher specific growth rate with a low saturation light intensity, lower respiration loss rate, and higher fraction of fast charge carriers on the light utilization efficiency. Model simulations suggest that more than 20% improvement in the light utilization efficiency is achievable.

Photobioreactors (PBRs) demonstrating very high bio-productivity involve a complex interaction between biomass density, light path, light intensity, and timescales of random cell movement. This work presents a new reactor model capable of simulating the effects of the above-mentioned parameters on the biomass productivity of a PBR. The work presented in this paper includes (i) development of photosynthesis model based on occupancy of charge carriers associated with the linear electron transport chain of photosystem-II, (ii) tuning and validation of the kinetics model using flashing light data reported in the literature, and (iii) reactor model development by integrating kinetics with a simple flow depiction including the effect of boundary layer thickness. For the first time, the role of the boundary layer in determining the productivity of PBRs is elucidated.