Light-dependent growth kinetics enable scale-up of well-mixed phototrophic bioprocesses in different types of photobioreactors.

Scaling of phototrophic bioprocesses can be extremely challenging especially when reactor types in the considered scales differ. In this study, the mean integral photon flux density was used to transfer light-dependent growth kinetics of Nannochloropsis salina 40.85 and Nannochloropsis gaditana 2.99 grown with constant LED irradiation from flat-plate gas-lift photobioreactors (0.09 m2) to thin-layer cascade photobioreactors (8 m2). Even though completely different reactors were used, comparable growth rates were achieved on both scales with both strains by application of comparable mean light availabilities in the microalgae suspensions. In contrast, the light-dependent growth kinetics change significantly when irradiation varies dynamically (day-night cycles). The maximum intra-day growth rate of N. salina with dynamic climate simulation was doubled to 0.07 h-1 compared to constant irradiation, but tolerance of the microalgae against excessive irradiation was drastically reduced compared to constant irradiation. Because of that, predicting growth of N. salina in a physically simulated day-night climate would require the determination of the light-dependence of growth with dynamically varying conditions.