External-loop Airlift Bioreactor Research Articles

Pilot scale production of high-content mycoprotein using Rhizopus microsporus var. oligosporus by submerged fermentation and agro-industrial by-products

While mycoprotein has gained traction as a human food source, its potential as a nutrient for animals remains largely unexplored. The mycoprotein-producing Rhizopus microsporus var. oligosporus, a fungus traditionally used for human food in Indonesia, is promising. It could revolutionise animal nutrition once it is Generally Recognized as Safe (GRAS) and is a biosafety level 1 (BSL1) organism. To enhance sustainably, we propose using sugar cane molasses (SM) and corn steep liquor (CSL) as nutrient sources. Also, we investigated the growth of R. microsporus var. oligosporus in five 14 L external-loop airlift bioreactors using CSL as the sole nutrient source. After 96 h of fermentation, at 25 °C and 0.5 vvm, the mycelium produced had an average biomass yield of 38.34 g L−1, with 70.18 % (m v−1) crude protein (mycoprotein). This bioprocess, which is scalable and economically viable, produces high amounts of mycoprotein for animal feed using CSL, a cost-effective agro-industrial by-product, providing a practical solution to the growing demand for animal protein.

Preparation of Komagataeibacter xylinus Inoculum for Bacterial Cellulose Biosynthesis Using Magnetically Assisted External-Loop Airlift Bioreactor.

The aim of this study was to demonstrate the applicability of a novel magnetically assisted external-loop airlift bioreactor (EL-ALB), equipped with rotating magnetic field (RMF) generators for the preparation of Komagataeibacter xylinus inoculum during three-cycle repeated fed-batch cultures, further used for bacterial cellulose (BC) production. The fermentation carried out in the RMF-assisted EL-ALB allowed to obtain an inoculum of more than 200× higher cellular density compared to classical methods of inoculum preparation. The inoculum obtained in the RMF-assisted EL-ALB was characterized by a high and stable metabolic activity during repeated batch fermentation process. The application of the RMF-assisted EL-ALB for K. xylinus inoculum production did not induce the formation of cellulose-deficient mutants. It was also confirmed that the ability of K. xylinus to produce BC was at the same level (7.26 g/L of dry mass), regardless of inoculum age. Additionally, the BC obtained from the inoculum produced in the RMF-assisted EL-ALB was characterized by reproducible water-related properties, mechanical strength, nano-fibrillar structure and total crystallinity index. The lack of any negative impact of inoculum preparation method using RMF-assisted EL-ALB on BC properties is of paramount value for its future applications, including use as a biomaterial in tissue engineering, wound healing, and drug delivery, where especially BC liquid capacity, nanostructure, crystallinity, and mechanical properties play essential roles.

An innovative bioprocess for methane conversion to methanol using an efficient methane transfer chamber coupled with an airlift bioreactor

Biosynthesis of methanol from methane as a direct method takes place at ambient temperature and pressure which causes a considerable reduction in process costs. In this study an efficient methane transfer chamber along with an external-loop airlift bioreactor were developed to dissolve methane and oxygen in the culture separately. Mass transfer coefficients for oxygen in the bioreactor and methane in the transfer chamber were obtained 97.2h−1 and 70.8h−1 respectively. Two strains of methanotroph bacteria (AS1 and AS2) were also isolated from activated sludge. Factorial design of experiments for operational parameters showed a maximum productivity for AS1 strain at 28°C when using nitrate as nitrogen source. Batch runs in airlift bioreactor using the AS1 strain and optimized operating parameters represented a peak of 1600mg/L in methanol synthesis during the first 3:30h without using inhibitor for methanol dehydrogenase (MDH) enzyme. Sequencing batch process, at the next step, was used to create intermediate lag phase and to increase the stability of microorganisms by forming flocs. The results of this study cleared that the designed system is safe and efficient to scale-up, and it can be considered as a potential alternative method in the production of methanol.

Apple pomace as a substrate for fungal chitosan production in an airlift bioreactor

Abstract The aim of this work was to evaluate apple pomace as carbon source for fungal chitosan production in an external-loop airlift bioreactor by Gongronella butleri. Apple pomace has high moisture content, insoluble carbohydrates such as cellulose, hemicellulose and lignin, reducing sugars like glucose and fructose and other sugars such as sucrose. Due to its high content of sugars, apple pomace can be a potential substrate for fungal chitosan production. To improve chitosan production from apple pomace, the effect of the nitrogen sources NaNO3 and (NH4)2SO4 and specific aeration rate of 0.1, 0.3 and 0.6 vvm was investigated. The ammonium sulfate and specific aeration rate of 0.6 vvm had significant effect (p

Optimization of growth conditions and continuous production of inulinase using immobilized Aspergillus niger cells

Aim The aim of the study was the optimization of growth conditions for the production of inulinase as well as the continuous production of the enzyme in an airlift bioreactor using Aspergillus niger cells. Methods First, inulinase production by A. niger cells, using different carbon and nitrogen sources, was studied on a shake flask level. Second, the cells were adsorbed onto different carriers, and their production over several successive batches was tested. Finally, the economically-favorable continuous production of inulinase by A. niger cells immobilized onto linen fibers was carried out in an airlift bioreactor using crude inulin juice as the fermentation medium. Results Although all tested substances resulted in the biosynthesis of certain amounts of inulinase enzyme, the highest titer of 163.5 U/ml was obtained when the producing cells were incubated for 96 h at 27πC and 180 rpm in a fermentation medium containing both inulin and peptone as sole carbon and nitrogen sources, respectively. Moreover, when the cells of the tested microorganism were adsorbed onto different carriers, especially linen fibers, their productivity was also successfully maintained, to different extents, for five successive batches. However, as commercially pure inulin is very expensive and available in only small quantities, the fermentation medium was later substituted by a crude inulin extract obtained by mechanical crushing and filtration of Jerusalem artichoke tubers. The crude inulin juice was able to sustain inulinase production during the second batch cultivation of A. niger cells that were immobilized by their adsorption onto linen fibers to a satisfactory level of about 122 U/ml. Furthermore, the use of the previously mentioned crude inulin preparation was also compared with the use of either complete or minimal media, composed solely of 1% pure inulin, for the continuous production of inulinase enzyme by A. niger cells that were immobilized in their maximum production phase and packed inside an external loop airlift bioreactor. The results of this experiment were very encouraging as, using this technique, an inulinase production of about 838 U/ml over an incubation period of 48 h was obtained compared with a production of about 996 and 1013 U/ml, which resulted from the use of either minimized or complete media, respectively, for the same incubation period. Conclusion The method adopted in this study for inulinase production is simple, economic, time saving, and nontoxic to the microorganism. Moreover, the loaded linen fiber pads are reusable.

Investigation of mixing characteristics in a packed-bed external loop airlift bioreactor using tomography images

The present research work introduces a recirculated airlift bioreactor (biocontactor), which combines advantages of packed bed and external loop airlift bioreactors. This bioreactor is characterized by an internal gas redistributor placed between two beds of packing in the riser while working fluid recirculates through an external downcomer. The main objective of this research work was to characterize the mixing hydrodynamics of this reactor through the non-intrusive flow visualization technique of electrical resistance tomography (ERT). The tomography images were employed to examine the effects of packing, gas redistributor, sparger configuration, gas flow rate, and liquid height on the mixing time and superficial liquid velocity. Results showed that the mixing time in the bioreactor was decreased with an increase in the superficial gas velocity in the riser. It was found that at a constant riser superficial gas velocity, the mixing time was increased and the superficial liquid velocity decreased when a cross shaped sparger was replaced by a circular sparger, which had the same diameter, and the same number and size of holes. Results also showed that mixing time increased and the superficial liquid velocity decreased by reducing the liquid height in the bioreactor, in addition to installing the internal gas redistributor and packing in the riser. The presence of the internal gas redistributor and packing reduced the cross-sectional area available for flow and increased resistance in the liquid flow path. Results, which were obtained from this study, can be utilized to improve mixing in external loop airlift bioreactors for wider range of applications.

Dynamic and local gas holdup studies in external loop recirculating airlift reactor with two rolls of fiberglass packing using electrical resistance tomography

AbstractBACKGROUND: Airlift bioreactors have been used extensively in biotechnology industries in recent years in a variety of arrangements and applications. The insertion of packing inside the bioreactors has the potential to provide high productivity within a compact size through utilizing immobilized species.RESULTS: A novel recirculating external loop airlift bioreactor that has two rolls of fiberglass packing and a gas distributor in between was designed and built. Electrical resistance tomography (ERT) images showed that the gas holdup increased after installing the packing and the gas distributor. Gas holdup in the riser increased with decreasing static liquid height in the bioreactor. This decreased the liquid superficial velocity, which contributed to a higher gas holdup in the bioreactor. Results also showed that riser gas holdup varied slightly with different sparger configurations. Higher gas holdup increases the oxygen mass transfer rate by increasing the residence time and interfacial mass transfer area.CONCLUSION: ERT results showed that fiberglass packing with an installed gas distributor in bioreactors can achieve higher gas holdup at higher superficial gas velocity. This can contribute to improved conversion in bioreactors with packing through utilizing higher biomass concentrations and higher oxygen concentration. © 2012 Society of Chemical Industry

Catalytic resolution of racemic ethyl lactate to produce D‐lactic acid by immobilized cells of Rhizopus sp. WS0128

AbstractD‐Lactic acid can be produced by either chemical or biochemical methods and is an important raw material or intermediate used in many fields including pesticides and herbicides production, and as polymers with promising applications in medical areas. Esterase produced by Rhizopus sp. WS0128 was effective in the catalytic resolution of racemic ethyl lactate to produce optically pure D‐lactic acid. The cells of Rhizopus sp. WS0128 were immobilized by entrapping them into calcium alginate gels, and the fermentation of the immobilized cells was carried out in an external‐loop airlift bioreactor (ELAB) (11.5 l). Optimal growth conditions for the microorganism were determined such that the maximum esterase activity of the immobilized cells reached 57.9 U/g cells after 48 h of fermentation. The immobilized cells of Rhizopus sp. WS0128 containing abundant esterase could be used directly as a biocatalyst in the enantioselective hydrolysis of ethyl lactate. The optimal hydrolysis reaction conditions were initial substrate concentration 160 g/l, temperature 40 °C, pH value 7.5 and reaction time 3.5 h. Under these conditions, the hydrolysis yield of ethyl lactate was 43.4% and the optical purity of D‐lactic acid was 96.3%. The immobilized cells were quite stable and could be utilized repeatedly in the biocatalytic process for at least six batches, where the average hydrolysis yield of ethyl lactate and the average optical purity of D‐lactic acid were 43.1% and 95.9%, respectively. This research work showed a promising process of D‐lactic acid preparation by biotransformation. Copyright © 2010 Curtin University of Technology and John Wiley & Sons, Ltd.

Effects of superficial gas velocity and fluid property on the hydrodynamic performance of an airlift column with alcohol solution

In the present study, the influence of superficial gas velocity and fluid properties on gas holdup and liquid circulation velocity in a three-phase external loop airlift column using polystyrene (0.0036 m diameter and 1025.55 kg/m3 density) and nylon-6 (0.0035 m diameter and 1084.24 kg/m3 density) particles with aqueous solutions of alcohols (isoamyl alcohol and propanol) as liquids were investigated. The column was constructed using acrylic tube of inner diameter 0.084m and 2.6m in height. The gas holdup in the riser increased with increase in superficial gas velocity for air-alcohol-solid system. The presence of alcohol surfactants increased the gas holdup in the riser. It was also found that an increase in the superficial gas velocity increased the liquid circulation velocity for air-alcohol-solid system. Correlations were proposed for the prediction of gas holdup and liquid circulation velocity. Keywords: External loop airlift bioreactor, three-phase, effect of additives, hydrodynamics

Effects of air-lift reactor dimensions on its hydrodinamic characteristics

In this study the hydrodynamic characteristics of the external loop airlift bioreactors were investigated. The influence of reactor height and solid particles concentration on the mean liquid circulation velocity was examined. Also, the possibility of theoretical prediction of this liquid circulation velocity was assessed. The correlation originally proposed by Glennon et al. (Chem. Eng. Commun. 121 (1993) 183-192) for two phase system liquid velocity prediction was extended and corrected for application to three phase systems. The accuracy of this new correlation was tested on our experimental data. The corrected correlation shows higher accuracy than the originally proposed one. In addition, the influence of reactor geometry and solid loading on reactor working performances was established.

Toluene vapor remediation in a continuous packed bed loop bioreactor

AbstractAn external loop airlift bioreactor with a small amount (99% porosity) of stainless steel mesh packing inserted in the riser section was used for bioremediation of a toluene polluted air stream. The packing enhanced VOC and oxygen mass transfer rates and provided a large surface area for cell immobilization. Using a mixed culture, fed‐batch and continuous runs at five different dilution rates were completed with toluene in the polluted air as the only carbon source. Above 99% and 93.6% toluene removals were achieved at toluene loading rates up to 88.1 and 149.1 g/(m3 h), respectively. The bioreactor responded quickly to a toluene load shock of 33 g/(m3 h) at high inlet toluene loadings. After 185.8 days operation, no plugging problems were observed in the column. A mathematical model is shown to accurately predict transient and steady state data. © 2008 American Institute of Chemical Engineers Environ Prog, 2008

Dependence of slip velocity on operating parameters of air-lift bioreactors

In this study we analyzed the quality of local mixing in external loop air-lift bioreactors for two hydrodynamic regimes in terms of slip velocity. In particular, the effects of design and operating parameters (e.g., reactor geometry, superficial gas velocity and flow regime) on the slip velocity were determined. Several correlations found in the literature based on theoretical models of fluid flow and several semi-empirical and empirical correlations were examined and the applicability of all the proposed correlations was tested on available experimental data. The most accurate correlations for the prediction of the slip velocity in each bioreactor operating regime were identified. New correlations for homogeneous and heterogeneous flow regimes were developed. These correlations are among the most accurate and have increasing accuracy with increase of superficial gas velocity. They also give insight into how the change in geometry properties or gas flow will alter the slip velocity. This is very important in the design and optimization of air-lift bioreactors.

생물반응기 유형에 따른 잔나비불로초(Ganoderma applanatum)의 균사체 및 수용성 다당체 생산 특성

In order to select a suitable bioreactor type for the submerged cultivation of Ganoderma applanatum, both growth characteristics and polysaccharides production were compared among four different types of bioreactor. These include an external-loop type air-lift bioreactor (ETAB), a balloon type air bubble bioreactor (BTBB), a column type air bubble bioreactor (CTBB) and a stirrer type bioreactor (STB). The mycelial biomass produced from the reactors were in decreasing order: ETAB () > BTBB () > STB () > CTBB (). Maximal soluble exopolysaccharides () and endopolysaccharides (2.7%) were also obtained from ETAB. Thus, the ETAB was most suitable for submerged culture of G applanatum mycelium. Based on the results, ETAB was chosen for further detailed study. The most effective aeration rate for the mycelial growth in ETAB ranged from 0.05 to 0.1 vvm. For the maximal production, the mycelium at the initial growth stage needed low aeration rate to reduce cell damages by fluid flow. However, as the mycelia grew, the culture became viscous and thus needed higher aeration. The molecular weight of exopolysaccharides obtained from the culture grown in ETAB was higher than that from the culture grown in other bioreactors.

Continuous bioremediation of phenol‐polluted air in an external loop airlift bioreactor with a packed bed

AbstractAn external loop airlift bioreactor with a small amount (99% porosity) of stainless steel mesh packing inserted in the riser section was used for bioremediation of a phenol‐polluted air stream. The packing enhanced volatile organic chemical and oxygen mass transfer rates and provided a large surface area for cell immobilization. Using a pure strain of Pseudomonas putida, fed‐batch and continuous runs at three different dilution rates were completed with phenol in the polluted air as the only source of growth substrate. 100% phenol removal was achieved at phenol loading rates up to 33 120 mg h−1 m−3 using only one‐third of the column, superior to any previously reported biodegradation rates of phenol‐polluted air with 100% efficiency. A mathematical model has been developed and is shown to accurately predict the transient and steady‐state data. Copyright © 2006 Society of Chemical Industry

Optimal Preparation of Immobilized Liposome-Bound Cellulase for Hydrolysis of Insoluble Cellulose in an External Loop Airlift Bioreactor

Immobilized liposome-bound cellulase (ILC) was optimally prepared for the ILC-catalyzed hydrolysis of insoluble cellulose in an external loop airlift bioreactor. The liposomes with mean diameters of 200, 100, and 50 nm were used to prepare three kinds of ILCs, i.e., ILC(200), ILC(100) and ILC(50), respectively. The activity and stability of ILC(100) were examined with soluble cellulose (CMC) in addition to the insoluble substrate of cellulose powder (CC31) in a shaking flask as well as the airlift bioreactors. The experiments were carried out with 45 degrees C and pH 4.8 being found to be optimal for the activity. The activity of ILC(100) was stable in either airlift or shaking flask bioreactor during the five times repeated hydrolyses of CC31 corresponding to a total reaction time of 240 h. This confirmed that the cellulase molecules were covalently bonded to the liposomes covalently bound to the chitosan gel beads. Nevertheless, the activity of ILC(100) with CMC steadily decreased throughout the repeated reactions, suggesting an adverse effect of CMC on the ILC(100) activity. Among the three ILCs, ILC(50) was found to be the most stable and productive biocatalyst during the repeated hydrolyses of insoluble CC31 in the airlift bioreactor. More than 70% of the initial activity of ILC(50) was retained even after the six times repeated reactions for 288 h. Conversely, the ILC(200) was found to be the most unstable catalyst. Such a difference in stability among these ILCs was suggested to be caused by the difference in physical stability of their liposome membranes to the liquid shear stress due to the rising bubbles and circulating liquid as well as that in the amount of the cellulase molecules unstably incorporated in the membranes. ILC(50) was thus shown to have the most potential for an efficient hydrolysis of insoluble cellulose in a practical airlift bioreactor.

Volatile Organic Chemical Mass Transfer in an External Loop Airlift Bioreactor with a Packed Bed

A stainless steel mesh packing with 99.0% porosity was installed in the riser section of an external loop airlift bioreactor (ELAB) to develop a new bioreactor that is a combination of a traditional ELAB and a packed-bed bioreactor. The gas holdup and mass-transfer rates of three volatile organic chemicals (VOCs) were studied in this ELAB, both with and without the packing. When the packing was used, the overall volumetric mass-transfer coefficient increased to values of 0.005 and 0.004 s-1, an average increase of 65.1% and 33.4% for toluene and benzene, respectively. The packing increased gas holdup and decreased bubble size in the bioreactor, both contributing to the improvements in the mass-transfer rates. A difference was observed between absorption and desorption rates of VOCs, which was explained by the change in gas bubble sizes in the presence of VOCs. A dynamic spatial model was used to predict the transient concentration distribution in the ELAB with and without a packed bed. The mass-transfer c...

Hydrodynamic and oxygen mass transfer in an external loop airlift bioreactor with a packed bed

A stainless steel mesh packing with 99.0% porosity has been inserted in the riser section of an external loop airlift bioreactor (ELAB). The hydrodynamic characteristics and oxygen mass transfer rates of the ELAB, both with and without packing, were compared. The packing increased the overall volumetric oxygen mass transfer coefficient by an average factor of 2.45 compared to the unpacked column. The packing increased gas holdup, decreased bubble size, and decreased liquid circulation rates in the bioreactor, all of which contributed to the dramatic improvement in the oxygen mass transfer rates. A dynamic, spatial model was used to predict the transient, oxygen concentration distribution in the ELAB with and without a packed bed. This model was compared to simulating the ELAB as a completely stirred reactor and demonstrated improved prediction of the cyclical changes in liquid oxygen concentrations. The oxygen mass transfer coefficient was determined as a best fitting parameter of the model and at higher gas superficial velocities was found to increase to values approaching 0.021 s −1 using the small amount of packing. Finally, simplified correlations were developed to predict the oxygen mass transfer coefficient in the ELAB with and without the packed bed.

Microbial biomass production from rice straw hydrolysate in airlift bioreactors

Rice straw is a by-product of rice production, and a great bioresource as raw biomass material for manufacturing value-adding protein for animal feedstock, which has been paid more and more attention. In the present work, utilizing rice straw hydrolysate as a substrate for microbial biomass production in 11.5 L external-loop airlift bioreactors was investigated. Rice straw hydrolysate obtained through acid-hydrolyzing rice straw was used for the culture of yeast Candida arborea AS1.257. The influences of gas flow rate, initial liquid volume, hole diameter of gas sparger and numbers of sieve plates on microbial biomass production were examined. The best results in the external-loop airlift bioreactor were obtained under 9.0 L initial liquid volume, 1.1 (v/v)/min gas flow rate during culture time of 0–24 h and 1.4 (v/v)/min gas flow rate of 24–48 h at 29 ± 1 °C. The addition of the sieve plates in the riser of the external-loop airlift bioreactor increased productivity. After 48 h, under optimized operation conditions, crude protein productivity with one sieve and two sieves were 13.6 mg/mL and 13.7 mg/mL, respectively, comparing 12.7 mg/mL without sieves in the airlift bioreactor and 11.7 mg/mL in the in the 10-L mechanically stirred tank bioreactor. It is feasible to operate the external-loop airlift bioreactors and possible to reduce the production cost for microbial biomass production from the rice straw hydrolysate.

Nitrogen compounds removal in a packed bed external loop airlift bioreactor

A packed bed external loop airlift bioreactor (PBELAB) was proposed as an alternative treatment system for wastewater containing ammonia and nitrate compounds. The 60L PBELAB consisted of aeration and non-aeration zones, both of which were packed with plastic bioballs to enhance the surface area for the attachment of bacteria. The system was able to achieve complete removal of all nitrogen compounds with simultaneous nitrification and denitrification, i.e., ammonia was decomposed in the aeration zone and nitrate was biodegraded in the non-aeration zone. At normal operation, the nitrification rate obtained from the system was in the range of 0.14-0.87 gNH3-N/m2d and the denitrification rate was 0.04 gNO3-N/m2d. The factors found to have great influence on the system included dissolved oxygen concentration and biofilm thickness. In addition, PBELAB was proven to perform well under nitrate shock load condition.

Enhanced Oxygen Mass Transfer in an External Loop Airlift Bioreactor Using a Packed Bed

A small quantity of nylon mesh packing inserted in the riser section of an external loop airlift bioreactor (ELAB) was found to increase the overall volumetric oxygen mass transfer coefficient by a factor of 3.73 compared to an unpacked riser. The packing increased gas holdup, decreased bubble size, and decreased liquid circulation rates in the bioreactor, all of which contributed to the dramatic improvement in oxygen mass transfer. A dynamic, spatial model was developed to predict the mass transfer behavior between air bubbles and the continuous liquid phase in the ELAB with and without a packed bed. The model demonstrated superior accuracy compared to simulating the ELAB as a well-mixed vessel and also correctly predicted the cyclical behavior in liquid oxygen concentrations. The oxygen mass transfer coefficient was determined as a best fitting parameter of the model and was found to increase to 4.2 × 10-3 s-1 using a small amount of packing (96.3% porosity) compared to the unpacked ELAB. This is similar to values measured in well-mixed bioreactors operating at the same aeration rates. The ELAB containing a packed bed is a novel bioreactor with much higher mass transfer and increased surface area for cell immobilization, and therefore it has potential to greatly enhance gas−liquid fermentations and other gas−liquid biochemical operations.