Brauer Hall, room 12
Dr. Muthanna Al-Dahhan, Professor
Department of Chemical & Biochemical Engineering
Missouri University of Science & Technology, Rolla
Multi-Scale Experimentation and Modeling Applied on Advancing the Culturing of Microalgae for Bio-Energy, Sustainable Environment and High Value Products
Fast growing microalgae and cyanobacteria in both open ponds and in enclosed photobioreactors (PBRs) represent interested source for bio-energy (oil, biomass gasification and anaerobic digestion), CO2 fixation, industrial flue gas treatment, wastewater treatment, high value products (pharmaceutical, chemicals, pigments), feed, single cell protein, and others. They need light (sun or artificial lights), non-agriculture lands, CO2 and inorganic compounds (nitrates, phosphates, etc.) to grow through the process of photosynthesis. The availability of light is a major factor in controlling the biomass productivity. In fact, due to severe self-shading effects, the light intensity decreases sharply with distance from the illuminated surface, especially for dense cultures and strong external irradiance. This greatly reduces the light usage efficiency, because too high irradiance may cause photoinhibition while too low light intensity cannot support the cell’s growth (i.e., photolimitation). Mixing of the culture, i.e., moving the cells efficiently in and out of the illuminated zones at suitable time scales for the photosynthesis, is able to significantly enhance the biomass productivity as reported by many researchers. However, the patterns of the cells’ movement inside the PBRs or the ponds and how they affect photosynthesis remain unclear. Hence, not only the photosynthetic kinetics and the irradiance characteristics, but also the hydrodynamics (i.e., liquid flow field, cell movement, shear stress, holdup distribution, etc.) play a significant role in the biomass productivity and the reactor or culturing performance. Although substantial work exists on culturing of phototrophs; however, most of the work is empirical and has been applied to specific processes, largely due to the lack of the essential hydrodynamic information. Generally, these studies have assumed that the microorganisms use the light with the same efficiency no matter how the light is delivered. They take into account only volume averaged irradiance, but disregard the dynamic feature, i.e., the light fluctuations due to the chaotic cells’ movement, shear stress distribution within the reactors or the culturing media, and the photoinhibition effects, etc. As a result, reliable modeling, design and scale-up of culturing microalgae whether in open or enclosed PBRs for the growth of phototrophic culture in general require extensive, costly and labor-intensive empirical developmental efforts.
Accordingly, to overcome these shortcomings, we have demonstrated a new approach by integrating multiscale experimentation and modeling to properly, and reliably predict the microalgae growth and to evaluate the operating, design and scale up parameters of PBRs on the culturing performance, and on key transport and hydrodynamic parameters by implementing advanced measurement and computing techniques. The methodology is based on the integration of the reactor hydrodynamics and irradiance field with dynamic growth photosynthesis. For the first time we have quantified the detailed mixing and hydrodynamics of a split photobioreactor during algal growth via advanced measurement techniques (such as radioactive particle tracking (RPT) for 3D cells’ movement, velocity field and turbulent parameters measurements, gamma ray computed tomography (CT) for cross sectional phases distribution measurements along the reactor height, 4-point optical fiber probe for bubble properties (velocity, size, interfacial area, local holdup) measurements, and optical probe for mass transfer measurements). These measurements are being used as benchmarking data for evaluation and validation of the computational fluid dynamics (CFD) models and interfacial forces closures to be integrated into the developed methodology instead of using the advanced measurement techniques that are not always available. To integrate the hydrodynamics and irradiance model with the dynamic growth of microalgae, dynamic growth kinetics for microalgae strains need to be developed. Therefore, we investigated in a separate effect experiment, the dynamic growth kinetics of a selected bioenergy producing microalgae strain.
In this presentation, the methodology, results and finding will be discussed. In addition, an overall view of my research laboratories and outline of some of on going projects will be presented.
Organizer / Host: Dr. Ramani