Growth-based dynamic light transmission modeling and optimization in microalgal photobioreactors for high efficiency CO2 fixation

Light availability greatly affects microalgal photosynthetic carbon sequestration and biomass production. However, the continuously changing light transmission during microalgal growth poses a significant challenge for enhancing their performance from the light optimization perspective. In this study, the growth-dependent light transmission characteristics in microalgal suspensions were investigated. As microalgae grew, the light saturation regions within the microalgal suspension expanded initially and then contracted, while the light inhibition expanded and the light limitation regions continuously shrank. Although biomass accumulation was relatively slow during the early growth stage (time <50 h) with biomass concentrations below 0.5 g/L, rapid changes in light attenuation occurred. Furthermore, the light-dependent local growth kinetic was developed to predict microalgal growth and CO2 fixation potential during growth. A contraction of the local microalgal CO2 fixation and specific growth rate distribution curve towards the incident light source occurred with its growth. Finally, the performance-enhancing effects of light optimization strategies on flat plate photobioreactors were analyzed based on the above model. Microalgal growth potential and CO2 fixation performance in the flat plate reactor with 2 cm light path could be increased by up to 188% when the growth-based light intensity enhancement strategy was adopted. It could be further increased by approximately 31% when the light was changed from single-sided to double-sided illumination (same light energy input), and the maximum net profit from microalgal cultivation could be enhanced by 60%. In conclusion, this study provides a unique insight into promoting microalgal carbon sequestration and biomass production from the light optimization perspective.