Modeling method for combining fluid dynamics and algal growth in a bubble column photobioreactor

Abstract

A comprehensive modeling method for algal growth in a photobioreactor is introduced. The model integrates fluid dynamics, mass transfer and the growth kinetics of algae. Availability of light, nutrients and carbon source as well as oxygen inhibition on growth is considered. The modeling approach has three-stages: (1) Detailed prediction of the flow field by Computational Fluid Dynamics (CFD), (2) Division of the computational domain into larger compartments (blocks or zones), and (3) Compartmental modeling. Compartmentalization is performed because calculations with CFD would be very time consuming. Use of the compartmental model allows fast calculation of several concurrent phenomena while accuracy of the important flow parameters is retained. The approach uses a dynamic model called photosynthetic factory to model algal biomass growth. The combination of fluid dynamics and light distribution in the reactor model is important because the fluid dynamics defines the time–irradiance profile the algal cell experiences. Adequate mixing is therefore not only important for mass transfer but for light distribution as well. The movement of biomass in the column between light and dark areas allows for the continuation of growth even at high biomass concentrations, where light is only available on the sides of the reactor. The model is inherently capable of predicting this behavior from the fluid dynamics without the need to define time–irradiance profiles i.e. light–dark cycles. A comprehensive model such as this is needed for photobioreactor design and scale up, because the phenomena in the reactor are all interdependent.