Mechanistic Modeling of Rotating Algal Biofilms

Biofilm-based microalgal cultivation systems have emerged as a promising alternative to conventional suspended growth methods, offering improved light utilization and biomass productivity. Among these, Rotating Algal Biofilm (RAB) systems are particularly advantageous by subjecting cells to short periodic light/dark (L/D) cycles to mitigate photoinhibition. Through experimental validation and modeling, this study demonstrates that optimized L/D cycles enhance photosynthetic efficiency by temporally diluting high-intensity light. To investigate the impact of light regimes, a model was developed based on Han's photosynthesis framework, incorporating respiration dynamics for broad ranges of cycle times and L/D ratios. Calibrated with experimental data, it accurately predicts biofilm behavior under varying light conditions. A key innovation is the integration of respiration variations during intermittent illumination, providing insights into growth dynamics across frequencies and duty cycles. Key findings show that high light frequencies reduce photoinhibition and enhance growth at given intensities. Increasing the light fraction improves growth rates by reducing peak intensity and shortening dark periods. The model elucidates biofilm responses to fluctuating light and offers strategies for reactor optimization. This study advances algal biofilm photophysiology understanding and provides a predictive tool for optimization and scaling up biofilm-based cultivation systems.