Characterization of the cylinderical split internal-loop photobioreactor with scenedesmus microalgae: Advanced culturing, modeling, and hydrodynamics

Microalgae are fast growing photoynthetic microorganisms and it have very wide range of industrial applications such as biofuels and wastewater treatment. These cells can be grown in a wide variety of systems ranging from open culture systems (e.g., ponds) to closed culture systems of photobioreactor (e.g., airlift). The open culture systems exist in the external environment, and hence, are not intrinsically controllable. However, the microalgae production in enclosed photobioreactors faces prohibitively high production costs with special difficulty in reactor design and scale-up. The light availability and utilization efficiency in the photobioreactor in terms of design and scale-up consider as the major problem in this system. It has been found that hydrodynamics and mixing can significantly improve the biomass yield by enhanced the light use efficiency. However, the hydrodynamics analysis, and their interacts with photosynthesis in real culturing system is remain unclear. The overall objective of this study is to advance the understanding of hydrodynamics’ role in the photosynthesis and thus the photobioreactor performance. The local flow dynamics in a split internal-loop photobioreactor were study by applied a sophisticated Radioactive Particle Tracking (RPT) and advanced Computer Tomography (CT) techniques. Based on the findings, fundamentally based dynamic modeling approach is developed for photobioreactor performance evaluation, which integrates the knowledge of photosynthesis, hydrodynamics, and irradiance. Finally, Scenedesmus sp. was grown in split column. The biomass concentrations, flow dynamics, physical properties, and irradiance distribution of the culturing systems were monitored. Good agreements between the predictions by the developed dynamic model and the experimental data were achieved, indicating the applicability of the dynamic model in industrial interested condition --Abstract, page iv

Advanced CFD model of multiphase photobioreactors for microalgal derived biomass production

Development of more efficient algal photobioreactors (PBRs) is driven by increasing interest in algaculture for the production of fuels, chemicals, food, animal feed, and medicine, as well as carbon capture. While at present, the cost and microalgae production capacity are one of its restrictions when competition with other biodiesel feedstock. The objective of the present work is to develop and validate better computational models to investigate the interplay between fluid hydrodynamics, radiation transport and algae growth, which is crucial to determine the performance and scalability of algae photobioreactors. First, a detailed review of the pertinent information required for developing a comprehensive computation model for photobioreactors was conducted. The current status of the submodels, including hydrodynamics and mass transfer multiphase CFD models, radiation transport models, microalgae growth rate models, and coupling method for developing a comprehensive model for PBRs was outlined. Second, an Eulerian two-fluid model for gas-liquid Taylor-Couette flow was proposed and validated. The CFD was based on the RANS approach with constitutive closures for interphase forces and liquid turbulence. The model was validated by comparison with previously published experimental data. The mechanism of bubble radial non-uniformity distribution was discussed and the relative importance of various interphase forces was demonstrated. Third, the validated two fluid CFD model was employed to simulate the local values of the mass transfer coefficient based on the Higbie theory. A novel approach was proposed to estimate the mass transfer exposure time. This approach automatically selects the appropriate expression (either the penetration model or eddy cell model) based on local flow conditions. The simulation predictions agree well with experimental foundlings, which demonstrates that the adaptive mass transfer model has the ability to correctly description of both local and global mass transfer of oxygen in a semi-batch gas–liquid Taylor–Couette reactor. Forth, microalgae culture experiment was conducted to identify the limiting factor in the Taylor-Couette photobioreactor. The characteristic time scales for mixing, mass transfer and biomass growth was compared. It is found that algal growth rate in Taylor vortex reactors is not limited by fluid mixing or interphase mass transfer, and therefore the observed biomass productivity improvements are likely attributable to improved light utilization efficiency (high-frequency light/dark cycles). Fifth, a commonly used Lagrangian strategy for coupling the various factors influencing algal growth was employed whereby results from computational fluid dynamics and radiation transport simulations were used to compute numerous microorganism light exposure histories, and this information, in turn, was used to estimate the global biomass specific growth rate. The simulation predictions were compared with experimental measurements and the origin of weaknesses of the commonly used Lagrangian approach model was traced. Sixth, an alternative Eulerian computational approach for predicting photobioreactor performance was proposed, wherein a transport equation for algal growth kinetics is solved, thereby obviating the need to carry out thousands of particle tracking simulations. The simulation predictions were compared with experimental measurements and commonly used Lagrangian approach model

Integration of Dynamic Growth Modeling and Hydrodynamics in an Internal-Loop Split Photobioreactor

In this study, new high-quality experimental data for culturing green microalgae Scenedesmus in tubular and cylindrical split airlift photobioreactors were obtained under different operating conditions. The obtained experimental data of culturing microalgae Scenedesmus in a tubular photobioreactor were used for determining the kinetic parameters of the photosynthetic reaction. On the other hand, the culturing of green microalgae in a split airlift photobioreactor was used to measure the microalgae cell trajectory using an advanced radioactive particle tracking (RPT) technique. The obtained results in terms of kinetic parameters of the photosynthetic reaction and microalgae cell trajectory were integrated for the first time to obtain the three-state dynamic growth model. This integration between dynamic growth and cell trajectories will provide a direct and comprehensive tool for photobioreactor analysis, which is essential for proper and efficient reactor design and scale-up for large-scale biomass production. © 2021 Society of Chemical Industry (SCI)

Sustainability tradeoffs within photoautotrophic cultivation systems: integrating physical and lifecycle modeling for design and optimization

2018 Summer.Includes bibliographical references.Photoautotroph-based biofuels are considered one of the most promising renewable resources to meet the global energy requirements for transportation systems. Long-term research and development has resulted in demonstrations of microalgae areal oil productivities that are higher than crop-based biofuels, about 10 times that of palm oil and about 130 times that of soybean. Cyanobacteria is reported to have ~4 times the areal productivity of microalgae on an equivalent energy basis. Downstream of this cultivation process, the cyanobacteria biomass and bioproducts can be supplied to biorefineries producing feed, biomaterials, biosynthetic chemicals, and biofuels. As such, cyanobacteria, and microalgae-based systems can be a significant contributor to more sustainable energy and production systems. This research presents novel means to be able to analyze, integrate, assess, and design sustainable photoautotrophic biofuel and bioproduct systems, as defined using lifecycle assessment methods (LCA). As part of a broad collaboration between industry, academia, and the national laboratories, I have developed models and experiments to quantify tradeoffs among the scalability, sustainability, and technical feasibility of cyanobacteria biorefineries and microalgae cultivation systems. A central hypothesis to this research is that the lifecycle energy costs and benefits, the cultivation productivity, and the scalability of any given organism or technology is governed by the fluid mechanics of the photobioreactor systems. The fluid characteristics of both open raceway ponds and flat photobioreactors, are characterized through industrial-scale experiment and modeling. Turbulent mixing is studied by applying Acoustic Doppler Velocimetry (ADV), Particle Image Velocimetry (PIV), and computational fluid dynamics (CFD) characterization tools. The implications of these fluid conditions on photoautotrophic organisms are studied through cultivation and modeling of the cyanobacteria, Synechocystis sp. PCC6803. Growth-stage models of this cyanobacteria include functions dependent on incident radiation, temperature, nutrient availability, dark and photo-respiration. By developing an integrated approach to laboratory experimentation and industrial-scale growth experiments, we have validated models to quantify the scalability and sustainability of these novel biosystems. These capabilities are utilized to perform long-term and industrially-relevant assessments of the costs and benefits of these promising technologies, and will serve to inform the biological engineering research and development of new organisms

A study of the growth and hydrogen production of Cyanothece sp. ATCC 51142

Hydrogen (H2) has long been promoted as an ideal fuel, as it permits a completely clean combustion and has great potential to provide clean power needed for transport and electricity generation. The unicellular, nitrogen-fixing cyanobacterium Cyanothece sp. ATCC 51142 is a promising strain with a remarkable capability of producing large quantities of H2. Under anaerobic condition, the cyanobacterium carries out the biological fixation of atmospheric nitrogen (N2) into ammonia (NH3), concurrently producing H2 as by-product. The aim of this thesis was to improve our understanding of the growth and H2 production of Cyanothece sp. ATCC 51142 in order to develop a continuous and practical cyanobacterial H2 production process. In order to achieve effective H2 production, it is prerequisite to grow dense and healthy Cyanothece 51142 cultures. Favourable cyanobacterial growth conditions included a continuous illumination at 207 - 320 μmol m-2 s-1, temperature of 35 °C and nitrogen-replete (addition of nitrate salts) condition. The critical temperature, which induces photoinhibition upon the cyanobacterium, was found at 40 °C. In the case of H2 production, favourable conditions included a continuous illumination at low light intensities of 46 – 92 μmol m-2 s-1, temperature of 30 °C, nitrogen-fixing (sole presence of atmospheric N2) and photoheterotrophic (sole presence of organic glycerol substrate) growth condition. In order to effectively handle incompatible requirements between the cyanobacterial growth and its sequential H2 production, a novel two-stage chemostat photobioreactor (PBR) system was designed and developed, with an aim to improve H2 production yield as well as extend its production duration. The system has been operated non-stop for consecutive 31 days without any losses in its performance and subsequently demonstrated a remarkable improvement in H2 production, with more than 6.4 times higher yield than that of a single-stage batch system. With the continuous mode of operation, a continuous collection of produced biomass from the PBR is also permitted (more than 7.3 times improvement in biomass yield than that of a single-stage batch system). At an industrial scale, this biomass could undergo further downstream processing to generate a multistreamline of high valued by-products such as e.g. vitamins, pharmaceuticals and human nutrition, which can subsequently contribute to a significant improvement in an economic viability of biohydrogen process.Open Acces

Computational analysis of dynamic light exposure of unicellular algal cells in a flat-panel photobioreactor to support light-induced CO2 bioprocess development

Cyanobacterial cell factories trace a vibrant pathway to climate change neutrality and sustainable development owing to their ability to turn carbon dioxide-rich waste into a broad portfolio of renewable compounds, which are deemed valuable in green chemistry cross-sectorial applications. Cell factory design requires to define the optimal operational and cultivation conditions. The paramount parameter in biomass cultivation in photobioreactors is the light intensity since it impacts cellular physiology and productivity. Our modeling framework provides a basis for the predictive control of light-limited, light-saturated, and light-inhibited growth of the Synechocystis sp. PCC 6803 model organism in a flat-panel photobioreactor. The model here presented couples computational fluid dynamics, light transmission, kinetic modeling, and the reconstruction of single cell trajectories in differently irradiated areas of the photobioreactor to relate key physiological parameters to the multi-faceted processes occurring in the cultivation environment. Furthermore, our analysis highlights the need for properly constraining the model with decisive qualitative and quantitative data related to light calibration and light measurements both at the inlet and outlet of the photobioreactor in order to boost the accuracy and extrapolation capabilities of the model

Analyzing and Modeling of Photobioreactors by Combining First Principles of Physiology and Hydrodynamics

Mixing in Photobioreactors is Known to Enhance Biomass Productivity Considerably, and Flow Dynamics Play a Significant Role in the Reactor\u27s Performance, as They Determine the Mixing and the Cells\u27 Movement. in This Work We Focus on Analyzing the Effects of Mixing and Flow Dynamics on the Photobioreactor Performance. based on Hydrodynamic Findings from the CARPT(Computer Automated Radioactive Particle Tracking) Technique, a Possible Mechanism for the Interaction between the Mixing and the Physiology of Photosynthesis is Presented, and the Effects of Flow Dynamics on Light Availability and Light Intensity Fluctuation Are Discussed and Quantitatively Characterized. Furthermore, a Dynamic Modeling Approach is Developed for Photobioreactor Performance Evaluation, Which Integrates First Principles of Photosynthesis, Hydrodynamics, and Irradiance Distribution within the Reactor. the Results Demonstrate the Reliability and the Possible Applicability of This Approach to Commercially Interesting Microalgae/cyanobacteria Culture Systems. © 2004 Wiley Periodicals, Inc

Photobioreactor Technologies for High-throughput Microalgae Cultivation

The evaluation and optimisation of microalgae cultivation process for biomass, lipid and high value chemicals production requires experimental investigation of several interacting variables. This thesis addresses the development of a range of small-scale photobioreactor technologies and shows how they can be applied for rapid, early stage evaluation and scale-up of microalgae cultivation processes. In particular, the work focuses on the engineering evaluation of a novel shaken miniature photobioreactor (mPBr) and a single-use photobioreactor (SUPBr) that can be adapted for both phototrophic and heterotrophic cultivation. A prototype twin-well mPBr was initially designed and fabricated with light provided from cool white light emitting diodes (LED). This was scaled-out to a 24-well mPBr system (4 mL working volume) on a novel shaken platform. High power warm white LEDs provided a maximum light intensity of 2000 µmolm‾²s‾¹. In both systems, surface aeration (via a semipermeable membrane) and mixing were provided by orbital shaking. Real-time control of temperature, relative humidity and CO2 levels was achieved via incubator level control. Amongst the tested geometries of the mPBr, round base and pyramid base gave the best performance. The mass transfer coefficient (kLa) values in the 24-well were measured between 20 – 88 h‾¹ and visual observation of fluid hydrodynamics showed an increase in total surface area with increased shaking frequency. Negligible evaporation was observed at 90% relative humidity for light intensity of < 400 µmolm‾²s‾¹ and at 32 °C, while light intensity variation across the platform is in the range ± 20 µmolm‾²s‾¹. Evaluation of phototrophic culture kinetics of Chlorella sorokiniana in both mPBr designs showed good reproducibility between wells. The best culture performance occurred at 380 µmolm‾²s‾¹, 300 rpm and 5% CO2, where final biomass concentration and total lipid concentration achieved were 9 ± 0.2 gL‾¹ and 55% w/w respectively. The SUPBr comprised a transparent polymeric CultiBagTM operated on the illuminated rotary shaken platform described above. Mixing time values were determined over the range 40 - 220 rpm and were generally less than 40 s. Hydrodynamic studies showed three distinct flow regimes at various shaking frequencies: in-phase, transitional and out-of-phase. Under optimal flow regime, the highest cell concentrations achieved was 6.7 gL‾¹ ± 0.3. Doubling the total working volume resulted in 35 - 40% reduction in biomass concentration due to an increase in the light path length. Phototrophic scale-up criteria from mPBr to SUPBr was successfully achieved based on light–path length and kLa values. Comparison of final biomass concentrations showed similar performance of 6 ± 0.2 gL‾¹ and comparable total lipid production of 25 – 30% by weight at a light intensity of 180 ± 20 µmolm‾²s‾¹. Furthermore, application of the shaken 24-well system for heterotrophic cultivation of microalgae and scale-up to a 7.5 L stirred tank bioreactor was also shown. Cells were cultured in 24 parallel wells, shake flasks and a 7.5 L bioreactor with working volumes of 4 mL, 100 mL and 4000 mL respectively using glucose (10 gL‾¹) as the main carbon source. Constant k(L)a was chosen as scale-up criteria and the values range between 30 – 60 h‾¹. Final biomass concentrations showed good agreement in the range of 4.5 ± 0.5 gL‾¹ and total lipid production of 43 – 50% by weight for the three systems. Overall, the results show the utility of the mPBr and SUPBr technologies for the rapid evaluation and scale-up of both phototrophic and heterotrophic microalgae cultivation conditions