Airlift column photobioreactors for Porphyridium sp. culturing: Part I. effects of hydrodynamics and reactor geometry

A Detailed Hydrodynamic Study of the Split-Plate Airlift Reactor by Using Non-Invasive Gamma-Ray Techniques

This study focused on detailed investigations of selected local hydrodynamics in split airlift reactor by using an unconventional measurements facility: computed tomography (CT) and radioactive particle tracking (RPT). The local distribution in a cross-sectional manner with its radial’s profiles for gas holdup, liquid velocity flow field, shear stresses, and turbulent kinetic energy were studied under various gas velocity 1, 2 and 3 cm/s with various six axial level z = 12, 20, 40, 60, 90 and 112 cm. The distribution in gas–liquid phases in the whole split reactor column, the riser and downcomer sides, including their behavior at the top and bottom sections of the split plate was also described. The outcomes of this study displayed an exemplary gas–liquid phases dispersion approximately in all reactor’s zones and had large magnitude over the ring of the sparger as well as upper the split plate. Furthermore, the outcomes pointed out that the distribution of this flow may significantly impacts the performance of the split reactor, which may have essential influence on its performance particularly for microorganisms culturing applications. These outcomes are dependable as benchmark information to validate computational fluid dynamics (CFD) simulations and other models.

Computational Fluid Dynamics Simulation of Hydrodynamics in a Two-Stage Internal Loop Airlift Reactor with Contraction-Expansion Guide Vane

Global circulation and liquid back mixing adversely affect the continuous production of a multistage internal airlift loop reactor. A contraction-expansion guide vane (CEGV) is proposed and combined with a two-stage internal loop airlift reactor (TSILALR) to suppress the liquid back mixing between stages. A computational fluid dynamics (CFD) simulation is conducted to evaluate the performance of the CEGV in the TSILALR. The bubble size distribution and turbulent flow properties in the TSILALR are considered in the CFD simulation by using the population balance model and RNG k-ε turbulence model. The CFD model is validated against the experimental results. The deviations in the gas holdup and mean bubble diameter between the simulation and experimental results are less than 8% and 6%, respectively. The streamlines, flow pattern, bubble size distribution, and axial liquid velocity in the TSILALRs with and without the CEGV at superficial velocities of 0.04 and 0.08 m/s are obtained by CFD simulation. It has been shown that the CEGV generated local circulation flows at each stage instead of a global circulation flow in the TSILALR. The average global gas holdup in the TSILALR with a CEGV increased up to 1.98 times. The global gas holdup increased from 0.045 to 0.101 and the average axial velocity in the riser decreased from 0.314 to 0.241 m/s when the width of the CEGV increased from 50 to 75 mm at the superficial gas velocity of 0.08 m/s.

Multiscale numerical workflow describing microalgae motion and light pattern incidence towards population growth in a photobioreactor

In this article, a numerical workflow describing the microalgal growth inside of a photobioreactor is proposed. CFD is used to compute reactor internal hydrodynamics taking into account marine impeller rotation and sparged bubbles motion. Lagrangian approach is used to track microalgae motion inside of the culture vessel. The illumination across the reactor is obtained using the classical Beer-Lambert's law. The combination of light field and cell motion allows to reconstruct the light history of each microalgae. These histories are then supplied to Han's model which predicts individual growth rate and experienced photodamages. Once computed, several thousands of trajectories are agglomerated at the population level yielding the photobioreactor performances. After having ensured properties convergence, this procedure is applied to a large range of optical density (0 to 4.0), i.e. cell concentration, and incident light intensities (0 to 2000 μmolPhoton/m2/s). From this exploration, it is possible to determine the photobioreactor response surfaces in terms of growth rate and photodamages. These are latter used to propose an optimal lighting strategy for biomass production - reducing photobioreactor operation time by 16% compared to classical two-step procedure - and assist light induced stress with the aim of triggering secondary metabolites production.

Advances in the production of bioactive substances from marine unicellular microalgae Porphyridium spp

Porphyridium spp. are a group of unicellular marine microalgae belonging to the Rhodophyta, which evolved over one billion years and are a source of a variety of natural active components. They can naturally and efficiently accumulate phycobilin, sulfated polysaccharides, polyunsaturated fatty acids and other bioactive substances. At present, numerous attempts have been made to explore the species Porphyridium spp., whereas mainly focused on cultivation methods, metabolism regulation and the function and application of bioactive products. There is a lack of systematic summary of the existing research conclusions. In this paper, we summarized the representative results related to culture and metabolism, analyzed and discussed the existing bottleneck restrictions for their large scale application, and proposed the potential industrial development and research direction in the future. This paper is expected to provide reference and thread for research and application of Porphyridium spp..

New horizons in culture and valorization of red microalgae

Research on marine microalgae has been abundantly published and patented these last years leading to the production and/or the characterization of some biomolecules such as pigments, proteins, enzymes, biofuels, polyunsaturated fatty acids, enzymes and hydrocolloids. This literature focusing on metabolic pathways, structural characterization of biomolecules, taxonomy, optimization of culture conditions, biorefinery and downstream process is often optimistic considering the valorization of these biocompounds. However, the accumulation of knowledge associated with the development of processes and technologies for biomass production and its treatment has sometimes led to success in the commercial arena. In the history of the microalgae market, red marine microalgae are well positioned particularly for applications in the field of high value pigment and hydrocolloid productions. This review aims to establish the state of the art of the diversity of red marine microalgae, the advances in characterization of their metabolites and the developments of bioprocesses to produce this biomass.

Serial lantern-shaped draft tube enhanced flashing light effect for improving CO2 fixation with microalgae in a gas-lift circumflux column photobioreactor

A novel serial lantern-shaped draft tube (LDT) that generates vortices is proposed to increase radial velocity between dark and light regions for improving CO₂ fixation with microalgae in a gas-lift circumflux column (GCC) photobioreactor. Clockwise vortices are generated in the downflow outerloop of the GCC photobioreactor with LDT. Radial velocity was improved from 1.50 to 4.35 × 10^-2 m/s, thereby decreased liquid cycle period between dark and light regions by 1.9 times. Mixing time decreased by 21%, and mass transfer coefficient increased by 26% with LDT. Liquid radial velocity in the downflow outerloop and mass transfer coefficient in the GCC photobioreactor both first increased and then decreased when single-lantern height was increased. Peak CO₂ fixation rate increased from 0.62 to 0.87 g/L/d, microalgal biomass yield increased by 50%. Removal efficiencies of pollutants (chemical oxygen demand, ammonium, tilmicosin, and ethinylestradiol) in wastewater were 62-90% with microalgae growth in GCC photobioreactor with LDT.

Effects of shear stress on microalgae - A review

Cultivation of microalgae requires consideration of shear stress, which is generated by operations such as mixing, circulation, aeration and pumping that are designed to facilitate mass and heat transfer as well as light distribution in cultures. Excessive shear stress can cause increased cell mortality, decreased growth rate and cell viability, or even cell lysis. This review examines the sources of shear stress in different cultivation systems, shear stress tolerance of different microalgal species and the physiological factors and environmental conditions that may affect shear sensitivity, and potential approaches to mitigate the detrimental effects of shear stress. In general, green algae have the greatest tolerance to shear stress, followed by cyanobacteria, haptophytes, red algae, and diatoms, with dinoflagellates comprising the most shear-sensitive species. The shear-sensitivity of microalgae is determined primarily by cell wall strength, cell morphology and the presence of flagella. Turbulence, eddy size, and viscosity are the most prominent parameters affecting shear stress to microalgal cells during cultivation.

Integrating planar waveguides doped with light scattering nanoparticles into a flat-plate photobioreactor to improve light distribution and microalgae growth

Industrially manufactured planar waveguides doped with light scattering nanoparticles, which can dilute and redistribute the intense incident light within microalgae suspension more uniformly, were introduced into a flat-plate photobioreactor (PBR) with a width of 25cm to alleviate the adverse effect of poor light penetrability on microalgae growth. Compared with the flat-plate PBR without waveguides, the illumination surface area per unit volume in the proposed PBR was increased by 10.3 times. During the whole cultivation period, the illuminated volume fractions in the proposed PBR were 21.4-410% higher than those in the flat-plate PBR without waveguides. Consequently, attributed to the optimized light distribution in the proposed PBR, a 220% improvement in biomass production was obtained relative to that in the flat-plate PBR without waveguides. Furthermore, higher light output intensities emitted from the planar waveguide surfaces and increased microalgae growth rates were achieved by decreasing the length of planar waveguides.

Microalgae cultivation in a novel top-lit gas-lift open bioreactor

This work investigated a top-lit open microalgae bioreactor that uses a gas-lift system to enable deeper production depths, thereby significantly reducing the footprint. Growth of Scenedesmus sp. in a one-meter deep system by sparged with 6% CO2-enhanced air was evaluated. The results gave comparable volumetric biomass productivity (0.06 g(dw) L(-1) day(-1)), but around three-times higher areal productivity (60.0 g(dw)m(-)(2) day(-)(1)) than reported for traditional raceways. The lipid content of the Scenedesmus sp. was increased by 27% with an enhanced level of CO2 in the sparging gas.

Photobioreactors for microalgal cultures: A Lagrangian model coupling hydrodynamics and kinetics

Closed photobioreactors have to be optimized in terms of light utilization and overall photosynthesis rate. A simple model coupling the hydrodynamics and the photosynthesis kinetics has been proposed to analyze the photosynthesis dynamics due to the continuous shuttle of microalgae between dark and lighted zones of the photobioreactor. Microalgal motion has been described according to a stochastic Lagrangian approach adopting the turbulence model suitable for the photobioreactor configuration (single vs. two-phase flows). Effects of light path, biomass concentration, turbulence level and irradiance have been reported in terms of overall photosynthesis rate. Different irradiation strategies (internal, lateral and rounding) and several photobioreactor configurations (flat, tubular, bubble column, airlift) have been investigated. Photobioreactor configurations and the operating conditions to maximize the photosynthesis rate have been pointed out. Results confirmed and explained the common experimental observation that high concentrated cultures are not photoinhibited at high irradiance level.