.Microalgae, as photosynthetic organisms, are cultivated in photobioreactors for various industrial applications. Light intensity, a critical factor influencing their growth rate, is inherently nonuniform within photobioreactors. In regions distant from the illuminated surface, microalgae experience photolimitation due to insufficient photon availability, hindering optimal activation of the photosynthetic machinery. Conversely, near the illuminated surface, excessive light intensity can damage key photosynthetic proteins, leading to photoinhibition. While mixing in photobioreactors does not alter the light gradient, it influences the light exposure history of cells through hydrodynamic advection. In this study, we employ Han's mechanistic model to describe the dynamics of photon harvesting and its consequences, including photoinhibition and photolimitation. First, we calculate the time-averaged growth rate for arbitrary continuous light signals, revealing how mixing impacts growth under the assumption of periodic light signals generated by hydrodynamics. Next, we address the computational challenge of estimating growth rates in photobioreactors using computational fluid dynamics (CFD), modeling a single-phase incompressible fluid. Finally, we analyze the case of a raceway pond, evaluating errors arising when growth rate is estimated without accounting for hydrodynamics. We analytically demonstrate that the gain in growth is related to the cell movement along the light gradient. Our results show that in predominantly laminar hydrodynamic regimes, hydrodynamics has only a marginal effect on microalgal growth. Moreover, we show that the average productivity can be estimated based on a static approximation of the average growth rate taking into account the light distribution, with an error lower than 10%.Keywordsmicroalgaeaverage growth ratecomputational fluid dynamicsHan modelraceway pondmixingMSC codes92B9934A0534C2534A3476B07
U et al. (Thu,) studied this question.