Internal Loop Airlift Bioreactor Research Articles

Experimental study and mathematical modeling of the pectinases production by Aspergillus flavipes FP-500 in an airlift bioreactor

Mathematical models are indispensable for designing, optimizing, and controlling large-scale bioprocesses. In the present work, the production of pectinases was studied experimentally using an internal loop airlift bioreactor, pectin as a substrate, and Aspergillus flavipes FP-500 as a biocatalyst. The N-tanks-in-series (NTIS) model was implemented to predict the behavior of fungal growth, pectin and dissolved oxygen consumption, pectinases production, and the oxygen mass transfer rate from gas phase to liquid culture medium. A double Monod-Logistic kinetic model was used to describe the biomass growth rate as a function of biomass, pectin, and dissolved oxygen concentrations. In contrast, a Luedeking-Piret kinetic model was used to describe the production rate of endo and exo pectinases. A hydrodynamic model was utilized to estimate gas hold-ups, volumetric mass transfer coefficients, and air inflow velocities. Good agreement was observed between the experimental data and the theoretical results, demonstrating the predictive capacity of the NTIS model to describe pectinase production, the oxygen consumption rate, and the oxygen evolution in the gas phase. The model highlighted its robust capability to capture the critical parameters of aerobic fermentation processes. Therefore, it could be used as a tool for the scalability of the airlift bioreactors.

Effect of geometrical modifications on the mixing and enzymatic conversion of structured lipids in internal-loop airlift bioreactors

Airlift bioreactors present a compelling alternative for reactions utilizing immobilized enzymes, offering advantages over stirred tank and packed-bed reactors. This study proposed a new configuration for an internal-loop airlift bioreactor (1 L working volume) to produce structured triglycerides using immobilized lipases in a viscous fluid. Different internal tube configurations were studied, which varied in diameter (17.5–78.6 mm), angle (-2,0,5,10 and 12°), and the addition of a rounded bottom to the bioreactor, which improved the three-phase mixture flow. The hydrodynamic effect caused by these modifications was evaluated by studying the mixing time. The best internal tube configuration, featuring a truncated cone-shaped, exhibited a 5° angle and a 64.5-mm diameter, resulting in a mixing time of 54 s. This value was about three times less than the mixing time obtained by the standard tube (171 s) at 2 vvm. Sequentially, grape seed oil acidolysis reactions with capric acid (C10) catalyzed by the Lipozyme RM IM were performed, obtaining structured MLM triglycerides with an incorporation degree of 32.32% ± 1.01%. These results indicated good biocatalyst operational stability, with a half-life of 14.13 days. Thus, this work unveils a new configuration for an airlift bioreactor collectively driving promising advancements in structured lipid production.

Use of an internal loop airlift bioreactor to produce polyhydroxyalkanoates by Stenotrophomonas rhizophila

Use of an internal loop airlift bioreactor to produce polyhydroxyalkanoates by Stenotrophomonas rhizophila

Optimal Design of Double Stage Internal Loop Air-Lift Bioreactor

Biorefinery systems play a critical role in the transition towards a sustainable bioeconomy, and bioreactors are a key component in these systems. While mechanically stirred reactors have been extensively studied, there is a lack of research on pneumatically driven systems like air-lift reactors (ALRs). This study aims to address this gap by examining the hydrodynamic behavior of a double draft tube airlift bioreactor using Computational fluid dynamics simulations. Ten different geometric configurations were investigated, with variations in draft tube placement, liquid height, distance between draft tubes and draft tube diameters. Results showed that the placement of the draft tubes heavily influenced hydrodynamic behavior, with smaller distances between draft tubes and a funnel configuration leading to higher velocities. Stable downcomer velocities were achieved by maintaining a consistent distance between the bottom clearance and the sum of the distance between draft tubes and the bottom clearance on the top clearance. The model was validated against literature experimental data. This study provides insight into the optimal design of ALRs, which can contribute to the development of more efficient and effective bioreactor systems. The findings can be used to forecast the most optimal configurations of airlift bioreactors and have significant value for the development of more efficient biorefining concepts in light of the increasing importance of studying biorefineries and their components in the shift towards a biomass-based economy.

Characterization of packed-bed in the downcomer of a concentric internal-loop airlift bioreactor

A packed-bed basket containing corn cob powder was used for the adaptation of a concentric-tube airlift reactor for enzymatic reactions. The bed was inserted in the downcomer region of the bioreactor generating a decrease in liquid downflow. To characterize the liquid velocity through the packed-bed and calculate the residence time, the intrinsic permeability was determined using Darcy’s law, resulting in 1.275 × 10−9 m2 (40-mesh particle size), and the pressure difference was calculated using the riser gas holdup, reaching values up to 56.6% for water at 3.5 vvm. Thus, a superficial liquid velocity model was obtained to describe the liquid velocity at different airflow rates and bed lengths, covering a wide range of support masses commonly used in enzymatic reactions. The model also allows the variation of viscosity, caused by different reaction temperatures and the use of larger bed sizes for scaling. Using the dye tracer method, it was possible to visualize the flow through the bed and corroborate the residence times obtained by the model for a wide range of airflows. Therefore, it describes the use of a basket filled with potential enzyme support, contributing to the applicability of pneumatic systems as enzymatic bioreactors, particularly internal-loop airlift reactors.

Production of extracellular α-amylase by single-stage steady-state continuous cultures of Candida wangnamkhiaoensis in an airlift bioreactor.

The kinetics of growth and α-amylase production of a novel Candida wangnamkhiaoensis yeast strain were studied in single-stage steady-state continuous cultures. This was performed in a split-cylinder internal-loop airlift bioreactor, using a variety of carbon sources as fermentation substrates. Results showed that the steady-state yields of cell mass from carbohydrates were practically constant for the range of dilution rates assayed, equaling 0.535 ± 0.030, 0.456 ± 0.033, and 0.491 ± 0.035 g biomass/g carbohydrate, when glucose, maltose, and starch, respectively were used as carbon sources. No α-amylase activity was detected when glucose was used as the carbon source in the influent medium, indicating that α-amylase synthesis of C. wangnamkhiaoensis is catabolically repressed by glucose. Contrastingly, maltose and starch induce synthesis of α-amylase in C. wangnamkhiaoensis, with starch being the best α-amylase inducer. The highest α-amylase volumetric and specific activities (58400 ± 800 U/L and 16900 ± 200 U/g biomass, respectively), and productivities (14000 ± 200 U/L·h and 4050 ± 60 U/g biomass·h, respectively) were achieved at a dilution rate of 0.24 h-1 using starch as the carbon source. In conclusion, single-stage steady-state continuous culture in an airlift bioreactor represents a powerful tool, both for studying the regulatory mechanisms of α-amylase synthesis by C. wangnamkhiaoensis and for α-amylase production. Furthermore, results showed that C. wangnamkhiaoensis represents a potential yeast species for the biotechnological production of α-amylase, which can be used for the saccharification of starch. This offers an attractive renewable resource for the production of biofuels (particularly bioethanol), representing an alternative to fossil fuels with reduced cost of substrates.

Effectiveness of various bioreactors for thraustochytrid culture and production (Aurantiochytruim limacinum BUCHAXM 122).

This study aimed to develop bioreactors for cultivation of thraustochytrid, Aurantiochytrium limacinum BUCHAXM 122, that are low in cost and simple to operate. Obtaining maximum biomass and fatty acid production was a prerequisite. Three bioreactor designs were used: stirred tank bioreactor (STB), bubble bioreactor (BB) and internal loop airlift bioreactor (ILAB). The bioreactors were evaluated for their influence on oxygen mass transfer coefficient (kLa), using various spargers, mixing speed, and aeration rates. Biomass and DHA production from STB, BB, ILAB were then compared with an incubator shaker, using batch culture experiments. Results showed that a bundle of eight super-fine pore air stones was the best type of aeration sparger for all three bioreactors. Optimal culture conditions in STB were 600 rpm agitation speed and 2 vvm aeration rate, while 2 vvm and 1.5 vvm aeration provided highest biomass productivity in BB and ILAB, respectively. Antifoam agent was needed for all reactor types in order to reduce excessive foaming. Results indicated that with optimized conditions, these bioreactors are capable of thraustochytrid cultivation with a similar efficiency as cultivation using a rotary shaker. STB had the highest kLa and provided the highest biomass of 43.05 ± 0.35 g/L at 48 h. BB was simple in design, had low operating costs and was easy to build, but yielded the lowest biomass (27.50 ± 1.56 g/L). ILAB, on the other hand, had lower kLa than STB, but provided highest fatty acid productivity, of 35.36 ± 2.51% TFA.

Design of a 1000 L pilot-scale airlift bioreactor for nitrification with application of a three-phase hydrodynamic mathematical model and prediction of a low liquid circulation velocity

In this study, a 1000L pilot scale internal loop airlift bioreactor was operated and compared to a mathematical model to determine the best design for optimal supply of oxygen for nitrification and sufficient air for biomass fluidization. The design model is based on parameters such as geometry, carrier density, and airflow of the 1000L pilot scale bioreactor. The model predicts a range of superficial air velocities (0.009–0.013m/s) under which the airlift bioreactor was fluidized. Three superficial air velocities (0.009m/s, 0.011m/s and 0.013m/s) were experimentally tested in the pilot plant and the obtained circulation velocities were compared with the predicted design scenarios. The predicted velocity was in agreement with the measured velocity. The aim of the mathematical model and the calculations of different geometry scenarios was to define the optimal geometry design for the physical model. The results show that the ratio of the cross-sectional area between the riser and the downcomer of 1.33 resulted in the lowest superficial liquid velocity of 0.076m/s in the riser at a relative low superficial air velocity of 0.011m/s and a carrier density of 1030kg/m3. This bioreactor design enabled longest retention time of particles in the oxygenated riser.

Biodegradation of diethyl phthalate from synthetic wastewater in a batch operated internal loop airlift bioreactor

In the present study, biodegradation of diethyl phthalate (DEP) was carried out with a mixed culture of aerobic bacterial strains isolated from soil contaminated with municipal wastewater. They were identified as Bacillus sp. and Micrococcus sp. based on morphological, biochemical and molecular characteristics. For the treatment of synthetic wastewater containing DEP, an internal loop airlift bioreactor was designed and fabricated. Experiments were carried out for various initial concentrations (100-1500 mg/l) in a batch mode using a mixed culture of isolates. Mass balance and stoichiometric investigation suggested efficient degradation of DEP with a yield of 0.81 g/g if two-thirds of carbon from substrate converted to biomass. Gas chromatography-Mass spectroscopy analysis detected monoethyl phthalate (MEP) and phthalic acid (PA) sequentially to confirm hydrolysis of DEP. Enzymatic assay of the esterase production (929.5 U/l for 1000 mg/l of DEP) was responsible for hydrolysis of DEP to MEP. Growth kinetic study delivered the best fit of experimental data with the Haldane model with the correlation coefficient (r2) 0.95. Biokinetic constants indicated that the high concentrations of DEP inhibited the growth rate of bacteria while dissolved oxygen estimation suggested that the DEP biodegradation was oxygen limited.

Phenol Biodegradation by Pseudomonas putida in an Airlift Reactor: Assessment of Kinetic, Hydrodynamic, and Mass Transfer Parameters

An airlift biofilm reactor was employed to study phenol biodegradation by Pseudomonas putida. Hydrodynamic tests were also conducted in a conventional column to facilitate the comparison of the dynamic behavior in different types of columns. The three-phase airlift column offered better aeration than the conventional column as liquid and solid circulation in the downcomer favored bubble breakup, increasing oxygen dissolved in the liquid phase and favoring the phenol biodegradation process. Kinetic parameters of phenol biodegradation by P. putida were obtained in an agitated batch reactor, with the initial phenol concentration varying from 10 to 750 mg/L. Experimental data were fitted using different microbial growth models found in literature. The Yano and Koga model, which considers the formation of multiple inactive enzyme–substrate complexes, fitted well with our experimental data, with a correlation coefficient, R 2 = 0.952. An internal loop airlift bioreactor was used for aerobic phenol biodegradation in which polystyrene particles were utilized to support biomass immobilization. Several tests were performed by varying the influent phenol concentration, hydraulic retention time, upstream flow, and superficial air velocity. It was concluded that until an influent phenol concentration of approximately 300 mg/L, phenol acted as the limiting substrate. For higher phenol concentrations, oxygen became the limiting substrate. An increase in the oxygen concentration resulted in the complete consumption of phenol under high phenol concentration of 500 mg/L.

Nitrous Oxide Abatement Coupled with Biopolymer Production As a Model GHG Biorefinery for Cost-Effective Climate Change Mitigation.

N2O represents ∼6% of the global greenhouse gas emission inventory and the most important O3-depleting substance emitted in this 21st century. Despite its environmental relevance, little attention has been given to cost-effective and environmentally friendly N2O abatement methods. Here we examined, the potential of a bubble column (BCR) and an internal loop airlift (ALR) bioreactors of 2.3 L for the abatement of N2O from a nitric acid plant emission. The process was based on the biological reduction of N2O by Paracoccus denitrificans using methanol as a carbon/electron source. Two nitrogen limiting strategies were also tested for the coproduction of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) coupled with N2O reduction. High N2O removal efficiencies (REs) (≈87%) together with a low PHBV cell accumulation were observed in both bioreactors in excess of nitrogen. However, PHBV contents of 38-64% were recorded under N limiting conditions along with N2O-REs of ≈57% and ≈84% in the ALR and BCR, respectively. Fluorescence in situ hybridization analyses showed that P. denitrificans was dominant (>50%) after 6 months of experimentation. The successful abatement of N2O concomitant with PHBV accumulation confirmed the potential of integrating biorefinery concepts into biological gas treatment for a cost-effective GHG mitigation.

Biological Nitrous Oxide Abatement by Paracoccus denitrificans in Bubble Column and Airlift Reactors

Nitrous oxide (N2O), with a global warming potential 300 times higher than that of CO2, represents 6.2 % of the total greenhouse gas emission inventory worldwide. Furthermore, N2O is considered the most critical O3- depleting substance emitted in this XXI century. In spite of the environmental relevance of this pollutant, very little research on biotechnologies for the treatment of N2O emissions has been conducted. In this study, the potential of a bubble column (BCR) and an internal loop airlift (ALR) bioreactors of 2.3 L was evaluated for the abatement of N2O from industrial emissions from nitric acid plants along 62 days of operation. The systems were inoculated with a methylotrophic Paracoccus denitrificans strain (DSM 413) and continuously supplied with methanol as a carbon and electron donor source for the anoxic reduction of N2O. The simulated waste gas consisted of a N2 gas stream containing 1 ± 0.1 % of O2 and 3377 ± 312 ppmv of N2O at the inlet of theBCR and 1 ± 0.1 % of O2 with N2O concentration of 3617 ± 342 ppmv at the inlet of the ALR. This N2-laden stream was supplied at a constant flow rate of 110 ml min-1 in each reactor. The performance of the BCR was characterized by a steady state N2O removal efficiency (RE) of 87 ± 3 % with CO2 productions of 308 ± 36 gm-3 d-1 and total suspended solid (TSS) concentrations of 867 ± 109 mg L-1. On the other hand, the ALR showed a N2O RE of 88 ± 2 % with productions of CO2 of 346 ± 28 g m-3 d-1 and TSS concentrations of 874 ±88 mg L-1. This work constitutes, to the best of our knowledge, the first systematic study of a biotechnology for the continuous abatement of N2O from nitric acid plants.

Degradation of Phenolic Compounds in Palm Oil Mill Effluent by Silica‐Immobilized Bacteria in Internal Loop Airlift Bioreactors

Palm oil mill effluent (POME) is usually treated using biological systems. However, phenolic compounds remain in the treated POME. This study aimed to remove phenolic compounds from POME using silica‐immobilized Methylobacterium sp. NP3 and Acinetobacter sp. PK1. Treated POME samples were collected from the final stabilization ponds of two palm oil mills in Thailand. In batch experiments, the silica‐immobilized bacteria effectively degraded 100–500 mg/L phenolic compounds (e.g., caffeic acid, ferulic acid, 4‐hydroxybenzoic acid, catechol, and 3‐methylcatechol) in synthetic wastewater and completely removed up to 1000 mg/L amended phenol from both treated POME samples. When 25 g/L silica‐immobilized bacteria were used in an internal loop airlift bioreactor with a hydraulic retention time of 5 h, 83 and 60% of the initial 26.7 and 112 mg/L phenolic compounds in the treated POME samples were removed. The bioreactor was operated continuously for 1200 h, and scanning electron microscopy revealed that the bacteria remained trapped inside the silica matrix. This bioreactor could be used for post‐treatment of POME.

Recombinant protein production by engineered Escherichia coli in a pressurized airlift bioreactor: A techno-economic analysis

ABSTRACT Standard cultivation protocols for high cell-density cultures of recombinant E. coli rely on air enrichment with oxygen to prevent oxygen limitation. This way of increasing oxygen supply impacts on process economics due to the high cost of pure oxygen. Reactor pressurization is an alternative approach to improve oxygen mass transfer. In the present study, the performance of pressurized airlift bioreactor in growing r E. coli cells was evaluated. Experiments were performed in a pressurized internal-loop airlift bioreactor (ALB) and in a non-pressurized stirred tank reactor (STR), both with 5 L working volume, equipped with a system for automatic control and monitoring of pressure, temperature, pH, and dissolved oxygen. Pressurization showed to be crucial to improve ALB performance in biomass formation (29 g DCW L −1 ) and protein production (201 mg protein g DCW −1 ), resulting in protein productivity (240 mg protein −1 h −1 ) and energy efficiency (11 g protein kWh −1 ) similar to the achieved in STR (200 mg protein L −1 h −1 and 13 g protein kWh −1 , respectively). Due to the high cost of pure oxygen, air enrichment revealed to be economically unfeasible for ALB. By pressurizing the bioreactor up to 0.41 MPa, without pure oxygen supply, an 8.7-fold increase in economic efficiency is estimated, what shows the potential of this innovative strategy for aerobic cultures.

The growth of oleaginous Rhodotorula glutinis in an internal-loop airlift bioreactor by using mixture substrates of rice straw hydrolysate and crude glycerol

The conversion of lignocellulosic biomass (LCB) to microbial oils is attracting a growing amount of attention. However, the growth of the oleaginous yeast Rhodotorula glutinis on LCB hydrolysate (mainly rice straw) only will lead to a low lipid mass fraction, in the range of 10–20%. This study shows that the addition of crude glycerol to the LCB hydrolysate medium can efficiently raise the lipid mass fraction to the range of 30–40%. Crude glycerol is a by-product in the biodiesel production process. The use of renewable LCB hydrolysate and crude glycerol would greatly reduce the substrate cost for microbial oil production using R. glutinis. In addition, the results of experiments show that a low-cost airlift bioreactor is a more suitable fermentation process for the growth of R. glutinis than the use of a conventional agitation tank. When using mixed carbon sources of LCB hydrolysate with 30 kg m−3 of reducing sugars and 30 kg m−3 of crude glycerol, a maximal cell mass of 21.4 kg m−3 and lipid mass fraction of 58.5 ± 6.2 were achieved in an internal loop airlift bioreactor, and this process may have the potential to be applied in scale-up production.

Growth of oleaginous Rhodotorula glutinis in an internal-loop airlift bioreactor by using lignocellulosic biomass hydrolysate as the carbon source

The conversion of abundant lignocellulosic biomass (LCB) to valuable compounds has become a very attractive idea recently. This study successfully used LCB (rice straw) hydrolysate as a carbon source for the cultivation of oleaginous yeast-Rhodotorula glutinis in an airlift bioreactor. The lipid content of 34.3 ± 0.6% was obtained in an airlift batch with 60 g reducing sugars/L of LCB hydrolysate at a 2 vvm aeration rate. While using LCB hydrolysate as the carbon source, oleic acid (C18:1) and linoleic acid (C18:2) were the predominant fatty acids of the microbial lipids. Using LCB hydrolysate in the airlift bioreactor at 2 vvm achieved the highest cell mass growth as compared to the agitation tank. Despite the low lipid content of the batch using LCB hydrolysate, this low cost feedstock has the potential of being adopted for the production of β-carotene instead of lipid accumulation in the airlift bioreactor for the cultivation of R. glutinis.

Influence of volumetric oxygen transfer coefficient (kLa) on xylanases batch production by Aspergillus niger van Tieghem in stirred tank and internal-loop airlift bioreactors

Oxygenation is an important parameter involved in the design and operation of mixing-sparging bioreactors and it can be analyzed by means of the oxygen mass transfer coefficient (kLa). In this study, batch fermentations in stirred tank bioreactor (STB) and airlift bioreactor (ALB) were operated under a range of kLa values, in attempts to optimize and compare the activities of extracellular xylanase and β-xylosidase synthesized by the fungus Aspergillus niger van Tieghem, using corncob as inducer source. The higher xylanase levels were observed on STB (9000Ul−1; kLa=30h−1), while the β-xylosidase production was similar in both bioreactors. However, when the enzymatic activity was compared for the same kLa value (12h−1) in STB and ALB, the xylanase and β-xylosidase productions were higher in ALB (7000Ul−1 xylanase; 2100Ul−1 β-xylosidase) than STB (4500Ul−1 xylanase; 1800Ul−1 β-xylosidase).

Airlift bioreactor containing chitosan-immobilized Sphingobium sp. P2 for treatment of lubricants in wastewater

An internal loop airlift bioreactor containing chitosan-immobilized Sphingobium sp. P2 was applied for the removal of automotive lubricants from emulsified wastewater. The chitosan-immobilized bacteria had higher lubricant removal efficiency than free and killed-immobilized cells because they were able to sorp and degrade the lubricants simultaneously. In a semi-continuous batch experiment, the immobilized bacteria were able to remove 80–90% of the 200mgL−1 total petroleum hydrocarbons (TPH) from both synthetic and carwash wastewater. The internal loop airlift bioreactor, containing 4gL−1 immobilized bacteria, was later designed and operated at 2.0h HRT (hydraulic retention time) for over 70 days. At a steady state, the reactor continuously removed 85±5% TPH and 73±11% chemical oxygen demand (COD) from the carwash wastewater with 25–200mgL−1 amended lubricant. The internal loop airlift reactor's simple operation and high stability demonstrate its high potential for use in treating lubricants in emulsified wastewater from carwashes and other industries.

Study of pressure fluctuations in an internal loop airlift bioreactor

AbstractThe origin and coupling of pressure fluctuations in an internal loop airlift bioreactor are investigated. The pressure fluctuations in the reactor are divided into two categories: global pressure fluctuations and local pressure fluctuations. It is found that the coupling between global pressure fluctuations and local pressure fluctuations mainly focuses in the frequency region between 10 and 30 Hz. Local pressure fluctuations in the reactor are strongly affected by pressure waves originating from the air‐supply system, while pressure fluctuations caused by the bubble eruption at the liquid surface have less influence on local pressure fluctuations. Based on the coherence analysis, the pressure signal at a certain position in the reactor is decomposed into three different parts: coherent part, joint incoherent part and exclusive incoherent part. The energy ratios of these different parts are helpful to study the interaction among pressure fluctuations from different sources. Three flow regimes were identified from the evolution of the energy ratio of the joint incoherent part. © 2011 Canadian Society for Chemical Engineering

Studies on growth kinetics of predominantly Pseudomonas sp. in internal loop airlift bioreactor using phenol and m-cresol

Growth profile of predominantly Pseudomonas species was studied using wastewater containing phenol and m-cresol, as single and multi component systems in an internal loop airlift bioreactor (ILALR). The species utilized for the study was isolated from a wastewater treatment plant. The reactor was operated at both lower and higher hydraulic retention time (HRTs), 4.1 h and 8.3 h, respectively. The inlet phenol and concentration was varied between 100 and 800 mg/L with 800 mg/L as shock loading concentration for an HRT of 8.3 h. For 4.1 h HRT, the concentration was varied 100 and 500 mg/L using 500 mg/L as a shock loading concentration. The study showed complete degradation of both phenol and m-cresol, when present individually at an HRT of 8.3 h with an enriched biomass output. The specific growth rate of the culture at various phenol and m-cresol concentrations was fitted to a Monod model. The biokinetics value showed good potential of Pseudomonas species employing the internal loop air lift bioreactor in utilizing high strength phenolics containing wastewater. Culture growth profile with both phenol and m-cresol as mixtures also showed decreased lag times with complete utilization of the phenolics.