Bubble Column Research Articles

Tertiary treatment of dairy wastewater applying a microalga-fungus consortium

ABSTRACT This paper aimed to apply filamentous fungi (Penicillium oxalicum and Cunninghamella echinulata), the microalga Tetradesmus obliquus and their co-culture in advanced treatment (tertiary treatment) of cheese whey. The bioremediation process was carried out in agitated flasks and bubble column bioreactors with different concentrations of chemical oxygen demand (COD) (223–1663 mg L − 1), total nitrogen (TN) (13–61 mg L − 1), and total phosphorus (TP) (3–26 mg L − 1). The results obtained in shaken flasks showed a superiority of the consortium compared to the systems with separated species. In this sense, the treatment was carried out in a bubble column reactor, and the consortium formed by the microalga and the fungus C. echinulata showed a greater efficiency (at a light intensity of 100 µmol m − 2 s − 1), promoting by the symbiosis to reach removal efficiencies of up to 93.7, 78.8 and 93.4% for COD, TN and TP, respectively; meeting Brazilian and European standards for discharge into water bodies. In addition, no pH adjustment was required during the co-culture treatment, demonstrating the buffering effect of using these two types of microorganisms. Therefore, the use of the consortium formed by T. obliquus and C. echinulata as a remediator was highly promising to promote the advanced treatment of cheese whey.

Microstructured gas-liquid-(solid) interfaces: A platform for sustainable synthesis of commodity chemicals.

Gas-liquid-solid catalytic reactions are widespread in nature and man-made technologies. Recently, the exceptional reactivity observed on (electro)sprayed microdroplets, in comparison to bulk gas-liquid systems, has attracted the attention of researchers. In this perspective, we compile possible strategies to engineer catalytically active gas-liquid-(solid) interfaces based on membrane contactors, microdroplets, micromarbles, microbubbles, and microfoams to produce commodity chemicals such as hydrogen peroxide, ammonia, and formic acid. In particular, particle-stabilized microfoams, with superior upscaling capacity, emerge as a promising and versatile platform to conceive high-performing (catalytic) gas-liquid-(solid) nanoreactors. Gas-liquid-(solid) nanoreactors could circumvent current limitations of state-of-the-art multiphase reactors (e.g., stirred tanks, trickle beds, and bubble columns) suffering from poor gas solubility and mass transfer resistances and access gas-liquid-(solid) reactors with lower cost and carbon footprint.

Maximization of uricase production in a column bioreactor through response surface methodology-based optimization

Uricase (EC 1.7.3.3) is an oxidoreductase enzyme that is widely exploited for diagnostic and treatment purposes in medicine. This study focuses on producing recombinant uricase from E. coli BL21 in a bubble column bioreactor (BCB) and finding the optimal conditions for maximum uricase activity. The three most effective variables on uricase activity were selected through the Plackett–Burman design from eight different variables and were further optimized by the central composite design of the response surface methodology (RSM). The selected variables included the inoculum size (%v/v), isopropyl β-d-1-thiogalactopyranoside (IPTG) concentration (mM) and the initial pH of the culture medium. The activity of uricase, the final optical density at 600 nm wavelength (OD600) and the final pH were considered as the responses of this optimization and were modeled. As a result, activity of 5.84 U·ml−1 and a final OD600 of 3.42 were obtained at optimum conditions of 3% v/v inoculum size, an IPTG concentration of 0.54 mM and a pH of 6.0. By purifying the obtained enzyme using a Ni-NTA agarose affinity chromatography column, 165 ± 1.5 mg uricase was obtained from a 600 ml cell culture. The results of this study show that BCBs can be a highly effective option for large-scale uricase production.

Statistical Analysis of Bubble Parameters from a Model Bubble Column with and without Counter-Current Flow

Bubble columns are widely used in numerous industrial processes because of their advantages in operation, design, and maintenance compared to other multiphase reactor types. In contrast to their simple design, the generated flow conditions inside a bubble column reactor are quite complex, especially in continuous mode with counter-current liquid flow. For the design and optimization of such reactors, precise numerical simulations and modelling are needed. These simulations and models have to be validated with experimental data. For this reason, experiments were carried out in a laboratory-scale bubble column using shadow imaging and particle image velocimetry (PIV) techniques with and without counter-current liquid flow. In the experiments, two types of gases—relatively poorly soluble air and well-soluble CO2—were used and the bubbles were generated with three different capillary diameters. With changing gas and liquid flow rates, overall, 108 different flow conditions were investigated. In addition to the liquid flow fields captured by PIV, shadow imaging data were also statistically evaluated in the measurement volume and bubble parameters such as bubble diameter, velocity, aspect ratio, bubble motion direction, and inclination. The bubble slip velocity was calculated from the measured liquid and bubble velocities. The analysis of these parameters shows that the counter-current liquid flow has a noticeable influence on the bubble parameters, especially on the bubble velocity and motion direction. In the case of CO2 bubbles, remarkable bubble shrinkage was observed with counter-current liquid flow due to the enhanced mass transfer. The results obtained for bubble aspect ratio are compared to known correlations from the literature. The comprehensive and extensive bubble data obtained in this study will now be used as a source for the development of correlations needed in the validation of numerical simulations and models. The data are available from the authors on request.

Screening for alkaliphilic microalgae for carbon capture from ambient air and food production

SummaryThe production of alkaliphilic microalgae can contribute to address the challenging cost of using pure carbon dioxide in large reactors. At high pH values, carbon dioxide is rapidly scavenged and the supply rates of dissolved inorganic carbon from the atmosphere to alkaline media are high. The present study aimed to identify microalgal strains that can cope with high alkalinity and aeration rates. Eight strains were studied and the microalgae Chlorella vulgaris, Scenedesmus almeriensis and Nannochloropsis gaditana were the only ones that were able to grow under these conditions. Their biomass productivities using laboratory‐scale bubble columns with no pH control and high aeration flow were 0.20 ± 0.03, 0.24 ± 0.03 and 0.08 ± 0.01 g·L−1·day−1, respectively. The production of the two former was scaled up to pilot‐scale bubble columns. Overall, the amount of atmospheric carbon dioxide that was transformed into biomass was in the range of 10%–30%, depending on the strain used and the photobioreactor setup. The biomass was rich in proteins and β‐carotene, both valuable products, highlighting the potential production of food ingredients while capturing carbon dioxide from the atmosphere.

Absorption of CO2 by Tetra-n-Butylammonium Bromide Semiclathrate Hydrate Slurries in a Bubble Column with Temperature Swing

Absorption of CO₂ by Tetra-<i>n</i>-Butylammonium Bromide Semiclathrate Hydrate Slurries in a Bubble Column with Temperature Swing

Towards a mechanistic model of oxidase deactivation in a bubble column

Despite the many advantages of biocatalysis, enzyme stability remains an issue. This work investigates the long-term kinetic stability of a water-forming NAD(P)H-oxidase (NOX2), an enzyme of potential industrial interest for NAD(P)H regeneration, in a bubble column sparged with air, which enables reasonable oxygen transfer but without drastic enzyme deactivation. Experiments have been performed with the particular goal of explaining the observed two-stage deactivation trend. We show evidence supporting the hypothesis that the first stage is related to the adsorption of enzymes to the interface, followed by a subsequent deactivation stage at the interface.The characterization of NOX deactivation in the bubble column setup, complemented by additional’quiescent’ experiments, has enabled the development of a first principles model as the first step towards a complete mechanistic model of oxidase deactivation at gas–liquid interfaces.

Hydrodynamic characterization of bubble column using Dynamical High Order Decomposition approach

Bubble columns play a crucial role in a wide range of industries, including chemical and biochemical processes, petrochemicals, and environmental engineering. Understanding the dynamics of bubble columns is essential for optimizing their performance in various applications. This study proposes a data-driven approach for analyzing the dynamics of a two-dimensional bubble column system. We conducted simulations with varying superficial velocities and generated a comprehensive training dataset encompassing the entire velocity and pressure fields to achieve this. We then compared the performance of two approaches, the Fast Fourier Transformation (FFT) and the High-Order Dynamic Mode Decomposition (HODMD), in representing the system’s dynamics. Our findings demonstrate that the conventional FFT approach fails to adequately capture the complex dynamics of the dispersed multiphase flow system. This limitation arises due to the distribution of frequencies along the domain. Conversely, our work highlights the success of the HODMD method in accurately representing the system’s dynamics using only a few arbitrary sampling points within the domain. The implications of this study are significant, as it sheds light on the potential benefits of employing HODMD for analyzing bubble column dynamics. By utilizing this approach, industrial processes can be optimized more effectively across various applications.

A Cold Flow Model of Interconnected Slurry Bubble Columns for Sorption-Enhanced Fischer–Tropsch Synthesis

For technical application with continuous operation of sorption-enhanced (SE) reactions, e.g., Fischer–Tropsch, a special reactor concept is required. SE processes are promising due to the negative effects of water on conversion and catalyst. The reactor concept of two interconnected slurry bubble columns combines the reaction with in situ water removal in the first, and sorbent regeneration in the second column with continuous exchange of slurry between the two. The liquid circulation rate (LCR) between the columns is studied in a cold flow model, measured by an ultrasonic sensor. The effects of different operating and geometric parameters, e.g., superficial gas velocity, liquid level and tube diameter on gas holdup and LCR are discussed and modelled via artificial intelligence methods, i.e., extremely randomized trees and neural networks. It was found that the LCR strongly depends on the gas holdup. The maximum of 4.28 L min−1 was reached with the highest exit, widest tube and highest superficial gas velocity of 0.15 m s−1. The influence of liquid level above the exit was marginal but water quality has to be considered. Both models offer predictions of the LCR with errors &lt; 6%. With an extension of the models, particle circulation can be studied in the future.

Advances in design of internals: Applications in conventional and process intensification units

Internals within reactors play an important role in the chemical industry, and numerous studies focus on their investigation and development. This review discusses the application of internals in both conventional and Process Intensification (PI) units, including stirred tanks, fluidized beds, bubble columns, tubular vessels, trickle beds, spinning disks, rotating packed beds, rotating fluidized beds, and microreactors. It emphasizes enhancing mass and heat transfer through internals such as baffles, packing, heat exchange elements, and wall modifications. Recurring themes include phase distribution, interfacial area, slip velocities, heat transfer, and pressure drop. While internals offer benefits, challenges such as fouling and catalyst attrition are acknowledged, yet often under-quantified. Practical aspects, including manufacturing and safety, are often overlooked. The review highlights the urgent need for comprehensive evaluations, incorporating detailed Computational Fluid Dynamics (CFD) simulations and experimental studies. Based on previous research, this work aims to provide insights into innovative reactor designs that ultimately lead to optimal efficiency and energy balance in chemical processes.

Effect of gas flow rate and nozzle diameter on bubble size and shape distributions in bubble column

The influence of gas flow rates and nozzle diameters on bubble size and aspect ratio distributions was studied using high-speed photography with an image processing algorithm. Results reveal bimodal probability density distributions (PDD) of bubble diameter under all nozzle diameters, with one peak near 1.5–2 mm and the another in the larger bubble range. Increasing gas flow rates from 0.1 to 0.2 L/min leads to a higher probability density of large bubbles, indicating prevalent bubble coalescence. As the gas flow rate rises to 1.2 L/min, the peak shifts to smaller bubble diameters, and the bubble breakage becomes dominant. For 1–2 mm bubbles, shape is less influenced by gas flow rates, while 3–9 mm bubbles exhibit aspect ratio PDD peaks at an aspect ratio (E) of 0.5 across all gas flow rates. The Iguchi and Chihara model can better predict the variation of bubble departure diameter with increasing gas flow rates.

Computational fluid dynamics modelling of large-scale bubble columns: from the mono-dispersed to the pure heterogeneous flow regime

This study proposes a CFD model to simulate large-scale bubble columns operating in different flow regimes. Transient 3-D simulations were performed employing a commercial code (ANSYS Fluent), and the numerical results were compared with available experimental data. The superficial gas velocity ranges between 0.0037 m/s and 0.2 m/s, covering both the mono-dispersed and pure-heterogenous flow regimes, where bubbles coalescence and breakup were modelled. The results have been critically analysed, and the discrepancies between the numerical and experimental results have been deeply commented on, setting the stage for future improvements.

Numerical Simulation of Mass Transfer Characteristics of Gas–Liquid Bubble Columns and an Improved Mass Transfer Model

Numerical Simulation of Mass Transfer Characteristics of Gas–Liquid Bubble Columns and an Improved Mass Transfer Model

H2S-laden biogas triggers sulfur amino acids production in microbial protein synthesized during mixed culture fermentation by methane and sulfur oxidizing bacteria

Biogas can be converted into high-value bioproducts through fermentation processes. This study proposes a conversion platform where sulfide-rich biogas is utilized as the substrate for the growth of a mixed culture of methane- and sulfur-oxidizing bacteria for the production of high-value and protein-rich microbial biomass. The role of several process variables such as biomethane vs biogas, synthetic vs real biogas, biogas composition and H2S concentration during the fermentation process performed in bubble column reactors was evaluated in terms of biomass growth, yield and volumetric productivity, protein content and amino acids profile as well as microbial community composition and evolution. Despite the presence of 1500 ppm of equivalent H2S in the synthetic biomethane or biogas (CH4:CO2 ratio of 70:30), good performances in terms of biomass growth (559.9 ± 13.3–677.8 ± 46.8 mg of volatile suspended solids (VSS) per liter), biomass yield (0.042 ± 0.004–0.050 ± 0.08 mg VSS per mg of CH4-equivalent chemical oxygen demand (CH4-COD)) as well as protein content (51.9 ± 3.6% − 59.2 ± 3.6% g protein/g VSS) were achieved. The presence of increasing sulfide concentrations until 4000 ppm of equivalent H2S was well tolerated by the mixed culture and increased the production of valuable S-amino acids, i.e., cysteine and methionine (61.3 mg/g biomass and 58.3 mg/g biomass, respectively), which was up to 2.50 and 2.57 times higher than in the absence of sulfide, respectively.

Plasma Bubble Column Reactor: A High Throughput Reactor Design for Water Treatment

Plasma Bubble Column Reactor: A High Throughput Reactor Design for Water Treatment

CFD simulations of a bubble column containing enhanced oil recovery chemicals

AbstractChemical enhanced oil recovery (EOR) methods return produced water containing polymers and surfactants which poses a water treatment challenge at offshore facilities. The present work shows that numerical simulations of gas‐water systems containing these chemicals remain challenging. Computational fluid dynamics (CFD) was used to predict gas holdup in a laboratory bubble column containing brine and EOR chemicals. The synthetic produced water was treated as non‐Newtonian in the simulations to match the experimentally‐determined physical properties. Two‐ and three‐dimensional numerical simulations were performed, and the latter were shown to be more appropriate through statistical analysis. Three classical drag models were assessed, and the results indicated that none of them could account for the high liquid viscosities and low surface tensions encountered in the system. A modification to the drag model of Tomiyama et al. (1988) was proposed to account for drag increases at low bubble Reynolds numbers when liquid apparent viscosity is high and surface tension is low. The importance of considering the interaction between apparent viscosity and surface tension was also shown through statistical analysis. CFD predictions of gas holdup showed that the proposed drag modification reduced errors from approximately 30% to less than 10% when compared to the experimental data. Radial profiles of the axial liquid velocity were also assessed and are apparently related to gas holdup prediction.

Bubble dynamics under the influence of the Marangoni force induced by a stratified field of contamination

The Marangoni effect assumes significance in bubbly flows when temperature or concentration gradients exist in the domain. This study investigated the hydrodynamics of single bubbles under the influence of the Marangoni force induced by stratified fields of dissolved sugar, providing a numerical framework for examining these phenomena. A laboratory-scale bubble column and high-speed imaging were utilized to analyze the bubble behavior. The OpenFOAM-based geometric volume of the fluid solver was extended by incorporating the solutocapillary Marangoni effect, and a passive scalar transport equation for the sugar concentration was solved. The results revealed that small bubbles entering regions with elevated sugar concentrations experienced deceleration, transitioning into linear paths, while those departing from regions with high sugar concentrations exhibited fluctuations and meandering. Furthermore, the concentration gradient leads larger bubbles to meander throughout the entire column, without a notable increase in their velocity. The intensity of these behaviors is governed by the magnitude of the Marangoni force. The findings provide a better understanding of single bubble hydrodynamics in complex environments.

Phenotypic and genomic characterization of Methanothermobacter wolfeii strain BSEL, a CO2-capturing archaeon with minimal nutrient requirements.

A new variant of Methanothermobacter wolfeii was isolated from an anaerobic digester using enrichment cultivation in anaerobic conditions. The new isolate was taxonomically identified via 16S rRNA gene sequencing and tagged as M. wolfeii BSEL. The whole genome of the new variant was sequenced and de novo assembled. Genomic variations between the BSEL strain and the type strain were discovered, suggesting evolutionary adaptations of the BSEL strain that conferred advantages while growing under a low concentration of nutrients. M. wolfeii BSEL displayed the highest specific growth rate ever reported for the wolfeii species (0.27 ± 0.03 h-1) using carbon dioxide (CO2) as unique carbon source and hydrogen (H2) as electron donor. M. wolfeii BSEL grew at this rate in an environment with ammonium (NH4+) as sole nitrogen source. The minerals content required to cultivate the BSEL strain was relatively low and resembled the ionic background of tap water without mineral supplements. Optimum growth rate for the new isolate was observed at 64°C and pH 8.3. In this work, it was shown that wastewater from a wastewater treatment facility can be used as a low-cost alternative medium to cultivate M. wolfeii BSEL. Continuous gas fermentation fed with a synthetic biogas mimic along with H2 in a bubble column bioreactor using M. wolfeii BSEL as biocatalyst resulted in a CO2 conversion efficiency of 97% and a final methane (CH4) titer of 98.5%v, demonstrating the ability of the new strain for upgrading biogas to renewable natural gas.IMPORTANCEAs a methanogenic archaeon, Methanothermobacter wolfeii uses CO2 as electron acceptor, producing CH4 as final product. The metabolism of M. wolfeii can be harnessed to capture CO2 from industrial emissions, besides producing a drop-in renewable biofuel to substitute fossil natural gas. If used as biocatalyst in new-generation CO2 sequestration processes, M. wolfeii has the potential to accelerate the decarbonization of the energy generation sector, which is the biggest contributor of CO2 emissions worldwide. Nonetheless, the development of CO2 sequestration archaeal-based biotechnology is still limited by an uncertainty in the requirements to cultivate methanogenic archaea and the unknown longevity of archaeal cultures. In this study, we report the adaptation, isolation, and phenotypic characterization of a novel variant of M. wolfeii, which is capable of maximum growth with minimal nutrients input. Our findings demonstrate the potential of this variant for the production of renewable natural gas, paving the way for the development of more efficient and sustainable CO2 sequestration processes.

Application and parameterization of a one‐dimensional multifluid population balance model to bubble columns

AbstractA one‐dimensional (1D) multifluid population balance model approach is presented as a compromise between computational effort and accuracy. The approach is used to test process scenarios, perform sensitivity analysis, and provide a reliable reactor scale‐up and optimization tool. The article focuses on a mini‐plant batch bubble column, where the scale‐up behavior in terms of bubble column height, gas flux, and composition of the liquid phase is investigated. Although simplifications were made, the model requires calibration to experimental data using different calibration methods. An optimal calibration procedure is found that minimizes experimental effort while maximizing scalability. The model was tested on various liquid‐phase compositions, and it was found to reproduce experimental data accurately. However, the model cannot reproduce flow regime changes and does not perform well across substance systems. The study shows that the applied 1D multifluid population balance approach is a valuable and reliable tool in multiphase reactor scale‐up and optimization.

Bubble Size “Bimodal” Distribution Enhances Mixing and Mass Transfer in Slurry Bubbling Column Reactor

Bubble Size “Bimodal” Distribution Enhances Mixing and Mass Transfer in Slurry Bubbling Column Reactor