Bubble Column Research Articles

The Degradation of Furfural from Petroleum Refinery Wastewater Employing a Packed Bubble Column Reactor Using O3 and a CuO Nanocatalyst

Furfural is one of the main pollutant materials in petroleum refinery wastewater. This work used an ozonized bubble column reactor to remove furfural from wastewater. The reactor applied two shapes of packing materials and two dosages of CuO nanocatalyst (0.05 and 0.1 ppm) to enhance the degradation process. The results indicated that adding 0.1 ppm of nanocatalyst provided an efficient rate of furfural degradation compared to that of 0.05 ppm. Also, the packing materials enhanced the furfural degradation significantly. As a result, the contact area between the gas and liquid phases increased, and a high furfural removal efficiency was achieved. It was found that the CuO nanocatalyst generated more (OH•) radicals. At a treatment time of 120 min and an ozone flow of 40 L/h, the furfural degradation recorded values of 80.66 and 78.6% at 10 and 20 ppm of initial concentration, respectively. At 60 ppm, the degradation efficiency did not exceed 74.16%. Furthermore, the kinetic study indicated that the first-order mechanism is more favorable than the second-order mechanism, representing the furfural degradation with a correlation factor of 0.9837. Finally, the furfural reaction can be achieved successfully in a shorter time and at low cost.

Effects of internals on macroscopic fluid dynamics in a bubble column

The effects of internals on liquid mixing and gas–liquid mass transfer have rarely been investigated in bubble columns, and the commonly used measurement method overestimates significantly overall gas holdup. Firstly, gas holdup measurement method is improved by conducting multi-point liquid level measurement and using net fluid volume instead of bed volume to calculate gas holdup. Then, a stable conductivity method for liquid macromixing has been established by shielding large bubbles using #16 nylon mesh. Subsequently, the influences of internal coverage (=12.6%, 18.9% and 25.1%) on macroscopic fluid dynamics in a bubble column with a free wall area are systematically investigated. It is found that the presence of internals has a notable effect on macroscopic fluid dynamics. The overall gas holdup and gas–liquid volumetric mass transfer coefficient decrease, and the macromixing time decreases with the increase of internal cross-sectional area coverage. These are mainly caused by the uneven distribution of airflow due to the low resistance in the free wall area. This design makes maintenance easier, but in reality, the reactor performance has decreased. Further improvements will be made to the reactor performance based on such a configuration through flow guidance using baffles.

Bubble boundary R-CNN: A multitask model for segmenting and reconstructing overlapping bubbles

When measuring the dynamic characteristics of bubbles using image-based methods, the images including complex overlapping of bubbles with irregular shape pose a huge challenge to current bubble reconstruction algorithms. Based on the Mask R-CNN architecture, a multitask model “Bubble Boundary R-CNN” is proposed for detection, segmentation and shape reconstruction of overlapping bubbles with high deformation at high gas velocities. By leveraging shared deep features from detection and segmentation, model achieves flexible bubble reconstruction and accurate size distribution extraction from high gas velocity bubble flows. To overcome the limitations of Mask R-CNN and address the challenges posed by high-deformation and overlapping bubbles, a semantic segmentation auxiliary head and the Boundary-preserving Mask Head (BMask Head) are introduced to enhance edge information and extract bubble boundary features. Additionally, an Overlapping Boundary Prediction Network (OBPN) is proposed to reconstruct boundary features that are lost due to bubble occlusion and predict the complete bubble shapes. The optimized model shows its ability to flexibly and accurately reconstruct overlapped and deformed bubbles by varying occlusion rates and circularity. The new model has also proven its reliability when applied to bubble images from a bubble column at gas velocities of up to 0.067 m3/s. In future work, more efforts are needed to further enhance the detection capability of the model and reduce missed and multiple detections at high gas velocity.

Effect of temperature on the oxygen production capacity and growth of scenedesmus almeriensis

The optimal temperature and irradiance to maximise oxygen production were 39.3 °C and 512.5 μmol photons·m−2·s−1, respectively. These values were obtained by photorespirometry, which is a quick method to measure the photosynthetic and respiration rates of microalgae at a laboratory scale. With these conditions, the global oxygen production rate of S. almeriensis was 246.23 mgoxygen·gbiomass−1·h−1. When the culture temperature was controlled at 39.3 °C for 1 h per day, the daily oxygen production capacity of S. almeriensis increased from 3129.5 mgoxygen·gbiomass−1 to 3778.5 mgoxygen·gbiomass−1. However, keeping the temperature at 39.3 °C for a longer time caused a damage to the photosynthetic apparatus. This was validated using laboratory-scale bubble columns. The damage was reversible when heating the cells for <2 h, but keeping the temperature of the culture at 39.3 °C for 3 h led to an irreversible damage and a 6 % decrease in the photosynthetic performance. Controlling the overheating of microalgal cultures is crucial to maximise growth. In addition, the duration of the exposure to high temperatures should also be included into growth and taken in consideration.

Effect of solid loading and particle size on bubble behavior and flow field structure in slurry bubble column

The complexity of fluid dynamics in a slurry bubble column reactor introduces significant uncertainty in reactor design and scale-up. This paper investigates the hydrodynamic performance of the gas–liquid–solid system within the reactor by employing computational fluid dynamics-population balance modeling numerical simulations alongside particle image velocimetry (PIV) experiments. The effect of superficial gas velocity and particle conditions on the overall gas holdup were analyzed, focusing on the effects of particle size and solid concentration on bubble size, bubble behavior, flow field structure, and local gas holdup distribution at high superficial gas velocities. Bubble size was evaluated using calibrated image measurements, and the impact of varying solid conditions was thoroughly explored. The results revealed that an increase in solid size correlated with higher gas holdup and smaller bubble sizes, whereas a greater solid concentration resulted in decreased gas holdup and larger bubble sizes. PIV experiments indicated that bubbles exhibited a tendency to migrate toward the central region of the reactor, leading to the formation of larger bubbles that accelerated the rise of surrounding bubbles, while smaller bubbles near the wall moved downward. As the slurry bed height increased, the range of local gas holdup distribution expanded, resulting in a symmetrical distribution of radial local gas holdup in the fully developed stage at a height of 0.16 m.

Single and multi-objective optimization of sweeping gas membrane distillation with double-stage bubble column dehumidifier

Single and multi-objective optimization of sweeping gas membrane distillation with double-stage bubble column dehumidifier

Pros and cons of airlift and bubble column bioreactors: How internals improve performance

Gas fermentation is a promising technology of high commercial interest, particularly for capturing CO2 and CO from industrial off-gases to reduce greenhouse gas emissions and replace fossil fuels for bulk chemical production. Therefore, evaluating promising bioreactor settings ab initio is a crucial step. Whereas alternate configurations may be tested in laborious scale up studies, the procedure may be accelerated by in silico studies that accompany or even partially replace wet-lab work once the models are validated. In this context, the current study compares various pneumatically agitated reactor types – bubble column reactor (BCR), annulus- and center-rising internal-loop airlift reactor (AR-IL-ALR and CR-IL-ALR), and external-loop airlift reactor (EL-ALR) – to identify advantages and disadvantages for the given application based on computational fluid dynamics (CFD) models. Process performance is optimized by introducing internal structures to guide the flow. Despite a significant increase in the mass transfer coefficient (kLa) through internal modifications, the CR-IL-ALR still exhibited the poorest performance. The optimized AR-IL-ALR demonstrated good mixing and, after introducing an open-cone shaped internal in the head part and a conical bottom, superior mass transfer, achieving an enhancement over 10 % in the mass transfer coefficient to 315 1/h. This study thereby outlines the potential of internal structures for process improvement, as well as the value of a priori in silico design of reactor configurations.

Real Case Study of 600 m3 Bubble Column Fermentations: Spatially Resolved Simulations Unveil Optimization Potentials for l-Phenylalanine Production With Escherichia coli.

Large-scale fermentations (»100 m³) often encounter concentration gradients which may significantly affect microbial activities and production performance. Reliably investigating such scenarios in silico would allow to optimize bioproduction. But related simulations are very rare in particular for large bubble columns. Here, we pioneer the spatially resolved investigation of a 600 m³ bubble column operating for Escherichia coli based l-phenylalanine fed-batch production. Microbial kinetics are derived from experimental data. Advanced Euler-Lagrange (EL) computational fluid dynamics (CFD) simulations are applied to track individual bubble dynamics that result from a recently developed bubble breakage model. Thereon, the complex nonlinear characteristics of hydrodynamics, mass transfer, and microbial activities are simulated for large scale and compared with real data. As a key characteristic, zones for upriser, downcomer, and circulation cells were identified that dominate mixing and mass transfer. This results in complex gradients of glucose, dissolved oxygen, and microbial rates dividing the bioreactor into sections. Consequently, alternate feed designs are evaluated splitting real feed rates in two feeds at different locations. The opposite reversed installation of feed spots and spargers improved the product synthesis by 6.24% while alternate scenarios increased the growth rate by 11.05%. The results demonstrate how sophisticated, spatially resolved simulations of hydrodynamics, mass transfer, and microbial kinetics help to optimize bioreactors in silico.

Hydrophobicity of Benzene-Based Surfactants and Its Effect on Bubble Coalescence Inhibition.

Bubble coalescence plays a critical role in optimizing biological and industrial processes, impacting efficiency in areas such as fermentation, wastewater treatment, and foaming control. While the relationship between chemical structure and bubble coalescence has been thoroughly explored for inorganic ions, limited data exist on organic ions and surfactants, despite their widespread use in these industries. This study addresses this gap by investigating the effects of surfactant hydrophobicity and bubble size on coalescence behavior at a flat air-liquid interface and within a bubble column. Surface tension measurements were employed to assess surfactant hydrophobicity, while bubble size and coalescence time were analyzed to determine their respective influences. The results reveal a novel quantitative relationship between surfactant hydrophobicity and the half-coalescence inhibition concentration (HCIC), a new variable introduced in this study. This relationship demonstrates that as hydrophobicity increases, the HCIC also rises, providing a new relationship between surfactant hydrophobicity and bubble coalescence. While it is well-known that more hydrophobic molecules delay coalescence, this is the first time a direct, proportional relationship has been established with HCIC, offering a new parameter for predicting and controlling coalescence phenomena.

Microbial Protein and Metabolite Profiles of Klebsiella oxytoca M5A1 in a Bubble Column Bioreactor.

The production of microbial proteins (MPs) has emerged as a critical focus in biotechnology, driven by the need for sustainable and scalable alternatives to traditional protein sources. This study investigates the efficacy of two experimental setups in producing MPs using the nitrogen-fixing bacterium Klebsiella oxytoca M5A1. K. oxytoca M5A1, known for its facultative anaerobic growth and capability to fix atmospheric nitrogen, offers a promising avenue for environmentally friendly protein production. This research compares the performance of a simple bubble column (BC) bioreactor, which promotes efficient mixing and cross-membrane gas transfer, with static fermentation, a traditional method lacking agitation and aeration. The study involved the parallel cultivation of K. oxytoca M5A1 in both systems, with key parameters such as microbial growth, glucose utilization, protein concentration, and metabolite profiles monitored over a 48 h period. The results indicate that the BC bioreactor consistently outperformed static fermentation regarding the growth rate, protein yield, and glucose utilization efficiency. The BC exhibited a significant increase in protein production, reaching 299.90 µg/mL at 48 h, compared to 219.44 µg/mL in static fermentation. The organic acid profile reveals both synthesis and utilization regimes of varying patterns. These findings highlight the advantages of the BC bioreactor for MP production, particularly its ability to maintain aerobic conditions that support higher growth and yield.

A Carbon Capture and Utilization Process for the Production of Solid Carbon Materials from Atmospheric CO2 - Part 1: Process Performance.

The successful operation of a process that converts atmospheric CO2 into solid carbon products is presented as an alternative to fossil based solid carbon production. In a first step, CO2 is removed from the atmosphere by a direct air capture (DAC) unit. The gas is then mixed with hydrogen and enters a methanation unit. Depending on the operation conditions, gas mixtures consisting of mainly methane with either H2 or CO2 as side-component are obtained. After precipitating the water formed during the methanation step, the remaining gas mixture is fed into a bubble column reactor filled with liquid tin. During the rise of the gas bubbles, methane is thermally split up into hydrogen and solid carbon. The latter is continuously removed from the liquid metal surface as a fine powder by pneumatic conveying. This article is the first of two articles, focusing on the performance of the methanation and methane pyrolysis steps. The experimental results are complemented by thermodynamic analyses and reaction modelling. A detailed analysis of the solid carbon product of the process is presented in the second part.

Development and validation of a 1D gas–liquid model for dissolved Mn(II) removal by oxidation process in a square bubble column

Modeling multiphase reactors requires an in-depth multidisciplinary analysis of various phenomena including the chemical kinetics, oxygen mass transfer, as well as the simulation of flows within these contactors. In this study, a 1D model of two-phase flow for Mn(II) removal from drinking water by aeration process is developed and validated. This model is based on the Eulerian description of two-phase gas–liquid flow with the comparison between a one-medium bubble size and a two-bubble class description to represent the bubble population in the heterogeneous flow regime. All the relevant chemical species are simulated by coupling hydrodynamics, gas–liquid mass transfer, and reaction kinetic. A pseudo-first-order model accounting for homogeneous and heterogeneous kinetics is considered for Mn(II) oxidation. The performance of the developed 1D model is compared and validated with experimental data. The 1D model was able to predict quantitatively Mn oxidation as a function of pH, initial Mn(II) and initial Mn(IV) concentrations.

Microbial Consortia in the Remediation of Single-Use Waste: The Case of Face Masks

This study presents the results of evaluating hydrocarbonoclastic consortia in the biodegradation of microplastics derived from single-use, triple-layered polypropylene face masks. The choice of this carbon source was driven by the need to address the increase in single-use waste generated during the recent SARS-CoV-2 pandemic, as the use of face masks was a mandatory protective measure. Two bubble column bioreactors were used, each containing hydrocarbonoclastic consortia sourced from the Port of Veracruz and the Gulf of Mexico. The biodegradation activity of these consortia was assessed by observing the physical appearance of microplastic samples under a stereoscope and a microscope, as well as by calculating the weight loss of polypropylene after 15 days. The results revealed that the consortium from the Gulf of Mexico, with a maturity of 1 year, showed a higher capacity for polypropylene biodegradation, achieving a 19.98% degradation rate. This consortium also demonstrated more stable kinetics during the experimentation period. In contrast, the younger consortium from the Port of Veracruz exhibited a lower biodegradation rate of 3.77% and variable growth kinetics. Hydrocarbonoclastic bacteria identified within the consortia included Pseudomonas aeruginosa, Enterococcus faecalis, and Vibrio parahaemolyticus, among others. The hydrocarbonoclastic consortia have the potential to biodegrade from various forms of plastic waste, including single-use face masks.

Design of Flat Loop Reactor with Bubble Column Circulation, Algae Growing Equipment

Abstract Based on the flow modeling and operational experience of the previous cylindrical loop reactor, we designed a sheet reactor combined with a loop reactor. The design with a cylindrical cross-section was applied to an equivalent cross-section (sheet) of several squares arranged next to each other. In accordance with the sedimentation processes experienced in the outlet branch, we created an algae trap, thereby reducing the flow to the level necessary for sedimentation. With this, I would like to achieve the already experienced, nearly 10-fold increase in algae concentration compared to the one in the mainstream.

Influence of the gas phase on a large-scale bubble column fluid dynamics: Gas holdup, flow regime transitions, and bubble size distributions

We present the results of an experimental study of a large-diameter bubble column operating in batch mode with air or CO2 as the gas phase and water as the liquid phase. The bubble column has an inner diameter of 0.24 m and is 5.3 m in height. The superficial gas velocity varied between 0.0037 m/s and 0.0233 m/s. The experimental investigation consists of gas holdup measurements and image analysis. Flow regime transitions were detected by gas holdup measurements, and image analysis was used to investigate the bubble size distributions. The results suggest that the homogeneous flow regime is stabilized when CO2 is used as the gas phase. The gas holdup is higher for the CO2-water system at fixed superficial gas velocity, especially in the heterogeneous flow regime. In the homogeneous flow regime, the mean bubble diameter and the fraction of large bubbles are lower for the CO2-water system, explaining the higher gas holdup.

Semi-continuous cultivation of microalgae to treat coal mine effluent in pilot scale: Nutrient removal, biodesalination and fatty acid composition analysis

Coal excavation is associated with discharge of an enormous amount of mine water rich in salt and trace metal ions, which require efficient treatment before use. Considering the potentiality of microalgae for high salt tolerance, salt removal and metallic pollutant removal from aqueous system, present study focuses semi-continuous cultivation of candidate microalgae Chlorella pyrenoidosa (NCIM 2738) in bubble column reactor (BCR) and open raceway pond (ORP) for nutrient supplemented coal mine effluent (NSCME) treatment. In between different hydraulic retention times (HRTs), HRT 6 d provide maximum average biomass productivity of 950 mg L−1 d−1 in BCR and 728.4 mg L−1 d−1 in ORP. HRT 9 d facilitates a maximum lipid content of 1.8 g L ̶ 1 in BCR and 1.4 g L ̶ 1 in ORP. Further, HRT 9 d had the maximum COD removal efficiency (96.5 % in BCR and 94.2 % in ORP) and maximum salinity removal efficiency (93 % in BCR and 92 % in ORP). Fatty acid methyl esters (FAME) characterization highlighted potential biodiesel applicability with cetane number (CN) of 53.94. Energy dispersive X-ray spectroscopy (EDS) revealed an excess amount of salt and metal ions deposition on the surface of harvested microalgae samples. Outdoor large-scale C. pyrenoidosa cultivation can be integrated with coal mine closure plans to meet sustainable development goals (SDGs) 6, 7 and 13.

Estimation of gas hold-up in bubble columns using wall pressure fluctuations and machine learning

We present a novel approach to estimate gas hold-up in bubble columns using wall pressure fluctuations – without requiring knowledge of operating flow regime, column configuration or physical properties. The approach uses machine learning and pressure fluctuations acquired from a wall mounted pressure sensor. The approach is validated by carrying out experiments with different physical properties of liquid (deionised water, deionised water – alcohol [ethanol, propanol and butanol] mixture up to 2 % alcohol, deionised water – glycerine (30 %), tap water). The majority of the data was obtained with 0.1 m diameter bubble column. Data with tap water in this column was obtained for four different spargers. Data with tap water was also obtained for 0.15 m and 0.33 m diameter bubble columns. Gas velocity was varied up to 0.1 m/s. The covered physical properties, sparger configurations, column diameter and gas velocities span different flow regimes. An artificial neural network (ANN) based model was developed to relate characteristics of wall pressure fluctuations and superficial gas velocity to the gas hold-up. The approach was validated by comparing predicted results with the experimental data unseen by the ANN model. The approach demonstrates the feasibility of using wall pressure fluctuations with machine learning to estimate key characteristics without prior knowledge of column configuration, flow regimes or physical properties.

An analytic approach for nonlinear collisional fragmentation model arising in bubble column

The phenomenon of coagulation and breakage of particles plays a pivotal role in diverse fields. It aids in tracking the development of aerosols and granules in the pharmaceutical sector, coagulation or breakage of droplets in chemical engineering, understanding blood clotting mechanisms in biology, and facilitating cheese production through the action of enzymes within the dairy industry. A significant portion of research in this direction concentrates on coagulation or linear breakage processes. In the case of linear case, bubble particles break down due to inherent stresses or specific conditions of the breakage event. However, in many practical situations, particle division is primarily due to forces exerted during collisions between particles, necessitating an approach that accounts for nonlinear collisional breakage. Despite its critical role in a wide array of engineering and physical operations, the study of this nonlinear fragmentation phenomenon has not been extensively pursued. This article introduces an innovative semi-analytical method that leverages the beyond linear use of equation superposition function to address the nonlinear integro-partial differential model of collisional breakage population balance. This approach is versatile, allowing for the resolution of both linear/nonlinear equations while sidestepping the complexities associated with discretization of domain. To assess the precision of this method, we conduct a thorough convergence analysis. This process utilizes the principle of contractive mapping in the Banach space, a globally recognized strategy for verifying convergence. We explore a variety of kernel parameters associated with collisional kernels, alongside breakage and initial distribution functions, to derive novel iterative solutions. Comparing our findings with those obtained through the finite volume method regarding number density functions and their integral moments, we demonstrate the reliability and accuracy of our approach. The consistency and correctness of our method are further validated by depicting the errors between the exact and approximated solutions in graphical and tabular formats.

Enhancing nutrient bioavailability in distillery wastewater through electrochemical oxidation for microalgal growth: Insights on biomass yield, nutrient utilisation, and VFA-assisted carbon capture

Two-stage treatment of distillery wastewater (DWW) via electrochemical oxidation (EO) using Ti-RuO2 anodes (35 cm2 area) followed by mixotrophic microalgal treatment was investigated. In the first-stage, EO of DWW has improved the bioavailability of nitrogen and phosphorus at 3.95–5.14 mg/Ah and 0.43–1.02 mg/Ah, respectively, which had strong correlation with current density. EO also reduced ∼30 % TOC, 53 % COD and ∼44 % TN. In the second-stage, the ability of a novel microalgae, Asterarsys quadricellulare to mitigate the toxicity of electrochemically oxidised DWW (EO-DWW) while utilising the nutrients effectively was investigated. The mixotrophic algal growth effectively utilised 85 % phosphate and 91 % nitrate present in EO-DWW at a corresponding growth rate of 0.73 d−1. The algal biomass was found to have ∼15 % carbohydrates, ∼12 % lipids and ∼33 % proteins. Subsequently, a bench-scale bubble column photobioreactor investigation was carried out to understand the carbon dynamics during the growth of Asterarsys quadricellulare. The metabolic uptake of monocarboxylic volatile fatty acids (VFA) and nitrate were found to release OH− ions, which eventually helped in dissolving CO2 in the reactor through a diffusion-limited process. The total energy spent in bench-scale EO system was 840 kWh (3024 kJ) per L of DWW, and the energy recovery potential of second-stage algal reactor was ∼8.7 %. The microtoxicity experiments with Alivibrio fischeri revealed that two-stage treated DWW was found to be safe for reuse as the microalgal growth has abated the toxicity of EO-DWW.

Hydrodynamics of molten media bubble columns for hydrogen production through methane pyrolysis

Methane pyrolysis using a molten media bubble column reactor is a promising technique for hydrogen production with low carbon dioxide emissions at a feasible price. Understanding the bubble dynamics in molten media is essential to elucidate the reaction mechanisms and establish design requirements for efficient reactors. Computational fluid dynamics provides an effective means to understand the hydrodynamics in opaque molten media. This research used the volume of fluid method to study the effects of gas injection rate as well as variations in gas and molten media (iron, aluminum, and a salt mixture of sodium bromide and potassium bromide in a 48.7:51.3 molar ratio) properties on bubble dynamics. The computational model was first validated using existing experimental and empirical observations. This study makes fundamental contributions to the understanding of bubble dynamics in molten media. First, it was confirmed that gas properties had a small effect on bubble dynamics. The difference in bubble diameters between argon at ambient temperature and 1600 °C was less than 10%. Second, it was found that the volumetric gas injection rate and molten media properties significantly impacted the bubble dynamics, including the bubble diameter and flow regime. Future work will build on these findings to recommend appropriate operating conditions and molten media for specific pyrolysis reactor designs.