Lntensification of mixing and homogenisation of culture medium in photobioreactors for microalgae production
- Autores: Vojtech Belohlav
- Directores de la Tesis: Enrica Uggetti (dir. tes.), Lukas Kratky (codir. tes.), Tomas Jirout (codir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2021
- Idioma: español
- Materias:
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- Resumen
Due to the large volume of the processed medium in pilot or industrial cultivation systems, it is difficult to illuminate the entire layer of the culture medium, which results in the formation of dark zones. Due to insufficient mixing, also an unbalanced utilization of nutrients contained in the culture medium or formation of temperature gradients can occur. Microalgal biofilm formation attached to the transparent walls of closed photobioreactors (PBRs) is also a significan! limitation associated with scaling-up, since it can significantly reduce the intensity of incident light. According to those factors, the hydrodynamic conditions of the culture medium are an importan! parameter in the scaling-up of cultivation systems, since it affects the mixing and the homogeneity of the culture medium. Efficient mixing can: 1) allow all microalgal cells to reach the irradiated area (light zone) of the culture medium; 2) prevent the formation of temperature gradients or sedimentation of microalgal cells; 3) intensify mass transfer resulting in more efficient utilization of nutrients. Moreover, the intensification of flow in the a rea clase to the transparent walls of the cultivation system can also result in an in crease of wall shear stress and a reduction of biofilm formation. The aim of this thesis was to study the influence of hydrodynamic conditions on parameters affecting the production of microalgae in two cultivation systems: a hybrid horizontal tubular photobioreactor (HHT PBR) and a closed flat panel photobioreactor (FP PBR). To this end, a multi-physical model was created to study the effect of hydrodynamic conditions on microalgae cultivation. Based on the experimental measurements, a numerical model simulating the hydrodynamic conditions in transparent HHT PBR tubes was validated. Through the model, the influence of different operating conditions on the mixing of the culture medium were investigated.
The developed multi-physical model allowed to investigate the influence of operating conditions on the distribution of light in the culture medium and the production of microalgae, The model showed that, in systems working with a large !ayer of culture medium or a high concentration of microalgae, the intensification of mixing increases the production of microalgae. To do this, the hydrodynamic conditions in the cultivation system should be brought as clase as possible to the state where the entire volume of the culture medium is ideally mixed. This state can be achieved by increasing the flow rate in the tubes or by using static mixers installed in the tubes of the PBR.
Hydrodynamics in FP PBR were more complex than in HHT PBR. By comparing the created ydrodynamic model with experimental measurements, the influence of hydrodynamics on the prevention of biofilm formation was specified as well. The created hydrodynamic model allowed to optimize the operating and design parameters of the FP PBR. In arder to intensify the mixing and homogenize the flow of the culture medium in the FP PBR, a static mixer was designed. Compared to the empty FP PBR chamber, the homogenization time was reduced and the homogenous flow in the chamber was ensured by the installed static mixer The multi-physical model developed in this thesis has preved to be an efficient tool to understand the influence of hydrodynamic conditions on microalgae production. Based on experimental measurements and numerical models, the operating conditions of HHT PBR and FP PBR were optimized. To further intensify the mixing and homogenize the flow of the culture medium, a static mixer was designed, which demonstrated a positive effect on the hydrodynamic conditions of the culture system. Overall, the created numerical model is a useful tool to improve existing cultivation systems, to acquire knowledge during the scale-up of cultivation systems or for designing novel PBRs.
