Abstract
BackgroundFlat-panel photo-bioreactors (PBRs) are customarily applied for investigating growth of microalgae. Optimal design and operation of such reactors is still a challenge due to complex non-linear combinations of various impact factors, particularly hydrodynamics, light irradiation, and cell metabolism. A detailed analysis of single-cell light reception can lead to novel insights into the complex interactions of light exposure and algae movement in the reactor.ResultsThe combined impacts of hydrodynamics and light irradiation on algae cultivation in a flat-panel PBR were studied by tracing the light exposure of individual cells over time. Hydrodynamics and turbulent mixing in this air-sparged bioreactor were simulated using the Eulerian approach for the liquid phase and a slip model for the gas phase velocity profiles. The liquid velocity was then used for tracing single cells and their light exposure, using light intensity profiles obtained from solving the radiative transfer equation at different wavelengths. The residence times of algae cells in defined dark and light zones of the PBR were statistically analyzed for different algal concentrations and sparging rates. The results indicate poor mixing caused by the reactor design which can be only partially improved by increased sparging rates.ConclusionsThe results provide important information for optimizing algal biomass productivity by improving bioreactor design and operation and can further be utilized for an in-depth analysis of algal growth by using advanced models of cell metabolism.
Highlights
Flat-panel photo-bioreactors (PBRs) are customarily applied for investigating growth of microalgae
The present study aims at investigating the relationship of hydrodynamics and light reception by single algal cells in more detail, on a single-cell level beyond averages of light intensity, with a focus on the statistical distribution of light exposure of algal cells as they move inside the PBR
The hydrodynamic and particle tracing simulations are independent from the light intensity simulations, as is evident from Eqs. 1–5
Summary
Flat-panel photo-bioreactors (PBRs) are customarily applied for investigating growth of microalgae. PBRs can be of different shapes and sizes, e.g., tubular, bubble columns, flat-panel, and airlift reactors [6,7,8,9]. Most of these are sparged with air bubbles with elevated CO2 concentrations, which serves for two purposes: firstly to improve the mixing of algal cells in the reactor, and secondly to increase the mass transfer of CO2 from gas to liquid phase by increasing the interfacial area between gas and liquid in the PBR and improving the rate of photosynthesis [10, 11]
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