Numerical investigation of hydrodynamic and mixing conditions in a torus photobioreactor

Abstract

It is well-known that the response of photosynthetic microorganisms in photobioreactor (PBR) is greatly influenced by the geometry of the process, and its cultivation parameters. The design of an adapted PBR requires understanding of the coupling between the biological response and the environmental conditions applied. Cells culture under well-defined conditions are thus of primary interest. A particular labscale PBR has been developed for this purpose. It is based on a torus shape, that enables light to be highly controlled while providing a very efficient mixing, especially along the light gradient in the culture, that it is known to be a key-parameter in PBR running. A complete characterization of hydrodynamic conditions is presented, using computational fluids dynamics (CFD). After validation by comparison with experimental measurements, a parametric study is conducted to characterize important hydrodynamics features with respect to PBR application (light access, circulation velocity, global shear-stress), and then to investigate a possible optimization of the process via modification of the impeller used for culture mixing. The final part of the study is devoted to a detailed investigation of mixing performance of the torus PBR, by numerically predicting dispersion of a passive tracer in various configurations. The high degree of mixing observed shows the great potential of such innovative geometry in the field of photosynthetic microorganisms cultivation, especially for the design of a lab-scale process to conduct experiments under well-controlled conditions (light and flow) for modeling purpose.

Design principles of photo‐bioreactors for cultivation of microalgae

“…Aspect 5: Mixing and auxiliary energy Although volumetric mass transfer is more than 2 orders of magnitude lower in photo-bioprocesses than heterotrophic stirred tank reactors (lower biomass concentration, lower specific turnover rates) mixing is an important issue. Along the light gradient in the culture, it is known to be a key-parameter in PBR operation [28] as indicated in aspect 3. Of equal importance is enhancing mass transfer along the main axis of the reactor, which is the axial direction in tubes or the upward direction in plates and columns (aspect 4).…”

Modelado de la Producción de Biomasa Microalgal en un Fotobiorreactor de Burbujeo Anular y Configuración Variable

“…Se han presentado modelados de la evolución de la biomasa sobre consideraciones geométricas y fluidodinámicas diversas para beneficio del diseño y el escalamiento de las unidades de producción (Sánchez Mirón et al, 2002, Luo et al, 2004, Wu y Merchuk, 2004, Pruvost et al, 2006, Pawar, 2016 y considerando el análisis del aporte de diversos parámetros que afectan el proceso de reproducción celular. Entre éstos se tienen, por su mayor influencia, los inherentes a la magnitud de la energía lumínica captada por la biomasa (Barbosa et al, 2003, García-Malea López et al, 2006, Merchuk et al, 2011, la relación área iluminada a volumen de cultivo (Mirón et al, 1999, Joshi et al, 2001, Xu et al, 2009, la transferencia y el secuestro de CO2 (Kumar y Das, 2012, Ying et al, 2013, Kong y Vigil, 2014, Hosseini et al, 2015 e incluso el estrés celular de origen hidromecánico (Michels et al, 2010, López Rosales et al, 2015, los dos últimos afectados por detalles como el tamaño de burbujas y la velocidad superficial del gas (Vial et al, 2002, Barbosa et al, 2004.…”

Comparative Analysis of Hydrodynamics Behavior of Microalgae Suspension Flow in Circular, Square and Hexagonal Shape Photo Bioreactors

“…In this context, U-loop horizontal tubular photo bioreactor is more efficient than other considering their large illumination area and easily scaling up capacity [15] [16] [17] [18]. From this point of view, investigations were limited only to analyse the growth model in case of horizontal u-loop tubular photo bioreactor.…”