Impact of nozzle operation on mass transfer in jet aerated loop reactors. Characterization and comparison to an aerated stirred tank reactor

The impact of mass transfer on productivity can become a crucial aspect in the fermentative production of bulk chemicals. For highly aerobic bioprocesses the oxygen transfer rate (OTR) and productivity are coupled. The achievable space time yields can often be correlated to the mass transfer performance of the respective bioreactor. The oxygen mass transfer capability of a jet aerated loop reactor is discussed in terms of the volumetric oxygen mass transfer coefficient k_La [h^?1] and the energetic oxygen transfer efficiency E [kgO₂ kW^?1 h^?1]. The jet aerated loop reactor (JLR) is compared to the frequently deployed aerated stirred tank reactor. In jet aerated reactors high local power densities in the mixing zone allow higher mass transfer rates, compared to aerated stirred tank reactors. When both reactors are operated at identical volumetric power input and aeration rates, local k_La values up to 1.5 times higher are possible with the JLR. High dispersion efficiencies in the JLR can be maintained even if the nozzle is supplied with pressurized gas. For increased oxygen demands (above 120 mmol L^?1 h^?1) improved energetic oxygen transfer efficiencies of up to 100 % were found for a JLR compared to an aerated stirred tank reactor operating with Rushton turbines.     

Scale-up and application of a cyclone reactor for fermentation processes

A cyclone reactor for microbial fermentation processes was developed with high oxygen transfer capabilities. Three geometrically similar cyclone reactors with 0.5?l, 2.5?l and 15?l liquid volume, respectively, were characterized with respect to oxygen mass transfer, mixing time and residence time distribution. Semi-empirically correlations for prediction of oxygen mass transfer and mixing times were identified for scale-up of cyclone reactors. A volumetric oxygen mass transfer coefficient k _L a of 1.0?s^?1 (available oxygen transfer rate with air: 29?kg?m^?3?h^?1) was achieved with the cyclone reactor at a volumetric power input of 40?kW?m^?3 and an aeration gas flow rate of 0.2?s^?1. Continuous methanol controlled production of formate dehydrogenase (FDH) with Candida boidinii in a 15?l cyclone reactor resulted in more than 100% improvement in dry cell mass concentration (64.5?g?l^?1) and in about 100% improvement in FDH space-time yield (300?U?l^?1?h^?1) compared to steady state results of a continuous stirred tank reactor.     

Xanthan batch fermentations: compared performances of a bubble column and a stirred tank fermentor

Fermentations of Xanthomonas campestris, NRRL B-1459, were carried out in a bubble column fermentor (BCF) and in a stirred tank fermentor (STF) to allow comparison of representative variables measured during the microbial growth and the gum production. The microbial growth phase was described by a logistic rate equation where maximum cell concentration was provided by nitrogenous compounds balance. The average value of the maximum specific growth rate was higher in the bubble column (μ _M =0.5 h^?1) than in the stirred reactor (μ _M =0.4 h^?1). The upper values of xanthan yield (Y _g-x =0.65 kg xanthan/kg glucose; Y _{O 2?x} xanthan/kg oxygen) and specific production rate (q _x =0.26 kg xanthan/kg biomass · h) were measured when the oxygen transfer coefficient was kept up above 80 h^?1 in the STF fermentor. In the bubble column the fermentation achieved in the same culture medium lasts two times longer than in the stirred aerated tank; this was attributed to the low value of the oxygen transfer coefficient (K _L a =20 h^?1) at the beginning of the gum synthesis phase. The results obtained in the stirred tank were the basis to estimate the optimal biomass concentration which enables to achieve a culture in non-limiting oxygen transfer conditions. Nevertheless, the transfer characteristics were more homogeneous in the bubble column than in the stirred tank where dead stagnant zones were observed. This is of primary importance when establishing fermentation kinetics models.     

Monitoring gradient formation in a jet aerated bioreactor

Jet aerated loop reactors (JLRs) provide high mass transfer coefficients (k_La) and can be used for the intensification of mass transfer limited reactions. The jet loop reactor achieves higher k_La values than a stirred tank reactor (STR). The improvement relies on significantly higher local power inputs (～10⁴) than those obtainable with the STR. Operation at high local turnover rates requires efficient macromixing, otherwise reactor inhomogeneities might occur. If sufficient homogenization is not achieved, the selectivity of the reaction and the respective yields are decreased. Therefore, the balance between mixing and mass transfer in jet loop reactors is a critical design aspect. Monitoring the dissolved oxygen levels during the turnover of a steady sodium sulfite feed implied the abundance of gradients in the JLR. Prolonged mixing times at identical power input and aeration rates (～100%) were identified for the JLR in comparison to the STR. The insertion of a draft tube to the JLR led to a more homogenous dissolved oxygen distribution, but unfortunately a reduction of mixing time was not achieved. In case of increased medium viscosities as they may arise in high cell density cultivations, no gradient formation was detected. However, differences in medium viscosity significantly altered the mass transfer and mixing performance of the JLR.     

Genetically engineered Escherichia coli FBR5: Part I. Comparison of high cell density bioreactors for enhanced ethanol production from xylose

Five reactor systems (free cell batch, free cell continuous, entrapped cell immobilized, adsorbed cell packed bed, and cell recycle membrane reactors) were compared for ethanol production from xylose using Escherichia coli FBR5. In the free cell batch and free cell continuous reactors (continuous stirred tank reactor‐CSTR) productivities of 0.84 gL^?1 h^?1 and 1.77 gL^?1 h^?1 were achieved, respectively. A cell recycle membrane reactor resulted in the highest productivity of 55.56 gL^?1 h^?1, which is an increase of 66‐fold (e.g., 6614%) over the batch reactor. Calcium alginate gel CSTR resulted in a productivity of 2.04 gL^?1 h^?1 whereas adsorbed cell packed bed reactor resulted in a productivity of 4.39 gL^?1 h^?1. In the five reactor systems, ethanol concentrations ranged from 18.9 to 40.30 gL^?1 with metabolic yields from 0.44 to 0.51. Published 2012 American Institute of Chemical Engineers Biotechnol. Prog., 2012     

Investigations of cephalosporin C production in an airlift tower loop reactor

Summary Cephalosporin C was produced by Cephalosporium acremonium in a 60 l airlift loop reactor on complex medium (with 30 kg/m³ peanut flour) in fed-batch operation. A final product concentration of 5 kg/m³ and a maximum productivity of 45 g/m³ h were attained. On-line analysis was used to determine ammonia, methionine, phosphate, reducing sugar and cephalosporin C by an autoanalyser, glucose by a flow injection analyser and cephalosporin C, penicillin N, deacetoxycephalosporin C, deacetylce-phalosporin C and methionine by HPLC. The volumetric productivity of the stirred tank reactor was higher than that of the airlift reactor because of differences in cell concentration. Specific productivities in relative to cell mass were similar in the two reactors. The substrate yield coefficient in the airlift reactor was twice that in the stirred tank reactor.Nomenclature E _o2 efficiency of oxygen transfer with regard to the specific power input - K _La volumetric mass transfer coefficient - OTR oxygen transfer rate - P power input - PR volumetric productivity of CPC - q _a volumetric aeration rate/broth volume (vvm) - SPR specific productivity with regard to RNA - V _L broth volume in reactor - z relative height of the aerated reactor     

Application of an airlift bioreactor to the nystatin biosynthesis

Pilot plant studies were performed using a concentric-tube airlift bioreactor of 2.5 m³ fermentation volume. The results have proven the relative merits of such a system in the biosynthesis of nystatin, produced by Streptomyces noursei, in submerged aerobic cultivation and batch operation mode. The results were compared to those obtained in a pilot-scale stirred tank bioreactor of 3.5 m³ fermentation volume. The fermentation processes in the two fermentation devices were similar with respect to substrate utilization, biomass production and nystatin biosynthesis. In the riser section, the dissolved oxygen concentration was higher than that in the downcomer. The volumetric oxygen mass transfer coefficient was dependent on the rheological behaviour of the biosynthesis liquids, which was not constant during the fermentation process. The total energy consumption for nystatin production in the airlift bioreactor was 56% of that in the stirred tank, while the operating costs represented 78% of those in the stirred tank bioreactor.     

Polysialic acid production using Escherichia coli K1 in a disposable bag reactor

Polysialic acid (polySia), consisting of α‐(2,8)‐linked N‐acetylneuraminic acid monomers plays a crucial role in many biological processes. This study presents a novel process for the production of endogenous polySia using Escherichia coli K1 in a disposable bag reactor with wave‐induced mixing. Disposable bag reactors provide easy and fast production in terms of regulatory requirements as GMP, flexibility, and can easily be adjusted to larger production capacities not only by scale up but also by parallelization. Due to the poor oxygen transfer rate compared to a stirred tank reactor, pure oxygen was added during the cultivation to avoid oxygen limitation. During the exponential growth phase the growth rate was 0.61 h^?1. Investigation of stress‐related product release from the cell surface showed no significant differences between the disposable bag reactor with wave‐induced mixing and the stirred tank reactor. After batch cultivation a cell dry weight of 6.8 g L^?1 and a polySia concentration of 245 mg L^?1 were reached. The total protein concentration in the supernatant was 132 mg L^?1. After efficient and time‐saving downstream processing characterization of the final product showed a protein content of below 0.04 mg_protein/g_polySia and a maximal chain length of ～90 degree of polymerization.     

Ethanol production by immobilized whole cells ofZymomonas mobilis in a continuous flow expanded bed bioreactor and a continuous flow stirred tank bioreactor

Continuous ethanol fermentation by immobilized whole cells ofZymomonas mobilis was investigated in an expanded bed bioreactor and in a continuous stirred tank reactor at glucose concentrations of 100, 150 and 200 g L^–1. The effect of different dilution rates on ethanol production by immobilized whole cells ofZymomonas mobilis was studied in both reactors. The maximum ethanol productivity attained was 21 g L^–1 h^–1 at a dilution rate of 0.36 h^–1 with 150 g glucose L^–1 in the continuous expanded bed bioreactor. The conversion of glucose to ethanol was independent of the glucose concentration in both reactors.     

Biodegradability of diesel oil

In batch culture diesel oil was degraded rapidly, with a maximum growth rate (for a consortium of microorganisms) of 0.55 h^-1. The corresponding yield Y _SX was 0.1 Cmol/Cmol. In a continuous stirred tank reactor the maximum dilution rate was about 0.25 h^-1, with a yield of 0.3 Cmol/Cmol. With a residence time of 1 day 82% of the influent oil was degraded. In the batch reactor, of the mixture of linear and branched alkanes the linear alkanes were degraded fastest and with the highest yield. Only after most of the linear alkanes had disappeared were the branched alkanes consumed. In a CSTR a large part of the branched alkanes was not degraded.     

The ejector loop reactor: Application for microbial fermentation and comparison with a stirred‐tank bioreactor

Ejector loop reactors (ELR) are successfully used in industrial chemical processes for gas/liquid reactions. They achieve higher mass transfer rates compared to the stirred‐tank reactor (STR) at comparable specific power input. Insufficient oxygen transport and shear stress induced growth inhibition are limiting parameters during microbial fermentation. Due to its better mass transfer characteristics, the ELR was expected to have beneficial effects on biomass and recombinant protein production. One concern, however, was whether the ELR's shear stress characteristics would have a negative effect. This study evaluated the suitability of using the Buss‐Loop® Reactor (BLR), one of the most advanced ELR technologies, as a bioreactor. The well‐studied STR was used as a reference. A lab scale BLR was adapted for microbial fermentation. Mass transfer rates and specific power inputs were within the same order of magnitude in the ELR and the reference STR. Maximum values of 207 and 205 h^?1 at power inputs of 6.9 and 9.7 W/L were measured in the ELR and STR, respectively. During batch fermentation of Escherichia coli K12 MG1655, maximum cell densities were higher in the ELR (OD600 of 22) than in the STR (OD600 of 18). Green fluorescence protein (GFP) production with pGS1 was comparable; however, more GFP was released into the media in the ELR. This indicates higher cell disruption compared to the STR. Despite this drawback of the first prototype, our work clearly demonstrates the potential of the ELR as a system for microbial fermentations.     

Cultivation of the oleaginous yeast Cryptococcus curvatus in a new reactor with improved mixing and mass transfer characteristics (Surer®)

Summary Cultivation and lipid production using the yeast Cryptococcus curvatus has proven to be efficient in a fed-batch fermentation using a stirred tank reactor. Scale up of this reactor however results in changing mixing and mass-transfer characteristics. In this paper we report cultivation of the yeast in a new type of reactor (Surer^®), which can easily be scaled up. A high cell density (91 gl^–1) and a lipid production rate of 0.42 g lipid l^–1h^–1 were obtained.     

Performance and characterization of a newly developed self-agitated anaerobic reactor with biological desulfurization

The continuous operation of a newly developed methane fermentation reactor, which requires no electricity for the agitation of the fermentation liquid was investigated, and the extent of the biological desulfurization was monitored. Inside the reactor, the continual change in the liquid level and the self-agitation, occurring between 5 and 16 times every day, distributed the organic load near the inlet port of the reactor, as well as providing a nutrient supply to the hydrogen sulfide oxidizing bacteria. At different COD_Cr loading rates (5, 7, 10 kg m³ d⁻¹), the reactor achieved a biogas production yield of 0.72-0.82 m³ g⁻¹-TS, a COD_Cr reduction of 79.4-85.5% and an average of 99% hydrogen sulfide removal. This investigation demonstrated that the self-agitated reactor is comparable in digestion performance to the completely stirred tank reactor (CSTR) investigated in a previous study, and that the desulfurization performance was significantly enhanced compared to the CSTR.     

Bioprocess engineering characteristics of the horizontal stirred tank

Bioreactor performance studies of the recently developed horizontal stirred tank with a volume of 421 have been carried out for fermentation with Trichosporon cutaneum. Quantification on the basis of measured oxygen transfer capacity and power consumption is presented and compared with data for a conventional vertical tank bioreactor.During the experiments it has been observed that two different forms of morphology of Trichosporon, i.e. the normal yeast-form (Y) with single cells and a mycelium-form (M) with filamentous cells, are present in the horizontal stirred tank when working with the original strain (DSM 70698). After separation both forms were characterized and later on used for bioreactor performance studies in the horizontal and vertical stirred tank. Results of oxygen efficiency show the drastic effect of the morphology change on bioreactor performance. Finally different bioreactors are quantitatively compared on the basis of oxygen transfer, power consumption and productivity using the reference fermentation system Trichosporon cutaneum.List of Symbols F m³/h flow rate (volumetric) - k _La1/h volumetric transfer coefficient of OTR - M Nm torque - n 1/s rotational speed - P Nm/s power - V m³ volume - V _G1/min gas flow rate - x kg/m³ biomass concentration - ^* morphology index - ^* engineering (specific) viscosity - _app Ns/m² apparent viscosity - ₀ N/m² yield stress (Casson law) - t _1/e h measured time acc. to momentum method [17] - tEh characteristic time of electrode response - t _Gh mean residence time of gas phase Abbreviations CFR completely filled reactor - CRR cyclic ring reactor (torus) - JLR jet loop reactor - HSTR horizontal stirred tank reactor - M mycelium-form of Trichosporon cutaneum - O₂-eff O₂-efficiency - OUR O₂-uptake rate - OTR O₂-transfer rate - STR stirred tank reactor - ThLR thin layer reactor - VSTR vertical stirred tank reactor - Y yeast-form of Trichosporon cutaneum The work presented in this paper was supported by an Austrian Research Grant (FFWF, Project no. 4496)     

Adaptation of acidogenic sludge to increasing glycerol concentrations for biohydrogen production

Hydrogen is a promising alternative as an energetic carrier and its production by dark fermentation from wastewater has been recently proposed, with special attention to crude glycerol as potential substrate. In this study, two different feeding strategies were evaluated for replacing the glucose substrate by glycerol substrate: a one-step strategy (glucose was replaced abruptly by glycerol) and a step-by-step strategy (progressive decrease of glucose concentration and increase of glycerol concentration from 0 to 5 g L^?1), in a continuous stirred tank reactor (12 h of hydraulic retention time (HRT), pH 5.5, 35 °C). While the one-step strategy led to biomass washout and unsuccessful H₂ production, the step-by-step strategy was efficient for biomass adaptation, reaching acceptable hydrogen yields (0.4?±?0.1 mol_H2?mol^?1 _{glycerol consumed}) around 33 % of the theoretical yield independently of the glycerol concentration. Microbial community structure was investigated by single-strand conformation polymorphism (SSCP) and denaturing gradient gel electrophoresis (DGGE) fingerprinting techniques, targeting either the total community (16S ribosomal RNA (rRNA) gene) or the functional Clostridium population involved in H₂ production (hydA gene), as well as by 454 pyrosequencing of the total community. Multivariate analysis of fingerprinting and pyrosequencing results revealed the influence of the feeding strategy on the bacterial community structure and suggested the progressive structural adaptation of the community to increasing glycerol concentrations, through the emergence and selection of specific species, highly correlated to environmental parameters. Particularly, this work highlighted an interesting shift of dominant community members (putatively responsible of hydrogen production in the continuous stirred tank reactor (CSTR)) according to the gradient of glycerol proportion in the feed, from the family Veillonellaceae to the genera Prevotella and Clostridium sp., putatively responsible of hydrogen production in the CSTR.     

Amaranth decoloration by Trametes versicolor in a rotating biological contacting reactor

Sequential batch and continuous operation of a rotating biological contacting (RBC) reactor and the effects of dissolved oxygen on the decoloration of amaranth by Trametes versicolor were evaluated. Amaranth belongs to the group of azo dyes which are potential carcinogens and/or mutagens that can be transformed into toxic aryl amines under anaerobic conditions. Cultivation of T. versicolor in a stirred tank reactor was found to be unsuitable for amaranth decoloration due to significant biomass fouling and increase in medium viscosity. Assuming that decoloration follows first-order kinetics, amaranth was decolorized more rapidly when T. versicolor was immobilized on jute twine in a RBC reactor operated either in a sequential batch (k=0.25 h^–1) or in a continuous (0.051 h⁻¹) mode compared to a stirred tank reactor (0.015 h⁻¹). Oxygen was found to be essential for decoloration with the highest decoloration rates occurring at oxygen saturation. Although longer retention times resulted in more decoloration when the RBC was operated in the continuous mode (about 33% amaranth decoloration), sequential batch operation gave better results (>95%) under similar nutrient conditions. Our data indicate that the fastest decoloration should occur in the RBC using nitrogen-free Kirk’s medium with 1 g/l glucose in sequential batch operation at rotational speeds and/or aeration rates which maintain oxygen saturation in the liquid phase.     

Production of alginate by Azotobacter vinelandii grown at two bioreactor scales under oxygen-limited conditions

The oxygen transfer rate (OTR) was evaluated as a scale-up criterion for alginate production in 3- and 14-L stirred fermentors. Batch cultures were performed at different agitation rates (200, 300, and 600 rpm) and airflow rates (0.25, 0.5, and 1 vvm), resulting in different maximum OTR levels (OTR_max). Although the two reactors had a similar OTR_max (19 mmol L^?1 h^?1) and produced the same alginate concentration (3.8 g L^?1), during the cell growth period the maximum molecular weight of the alginate was 1,250 kDa in the 3-L stirred fermentor and 590 kDa in 14-L stirred fermentor. The results showed for the first time the evolution of the molecular weight of alginate and OTR profiles for two different scales of stirred fermentors. There was a different maximum specific oxygen uptake rate between the two fermenters, reaching 8.3 mmol g^?1 h^?1 in 3-L bioreactor and 10.6 mmol g^?1 h^?1 in 14-L bioreactor, which could explain the different molecular weights observed. These findings open the possibility of using $ q_{{{\text{O}}_{ 2} }} $ instead of OTR_max as a scaling criterion to produce polymers with similar molecular weights during fermentation.     

Improving the production yield and productivity of 1,3-dihydroxyacetone from glycerol fermentation using <Emphasis Type="Italic">Gluconobacter oxydans</Emphasis> NL71 in a compressed oxygen supply-sealed and stirred tank reactor (COS-SSTR)

In this study, a compressed oxygen gas supply was connected to a sealed aerated stirred tank reactor (COS-SSTR) bio-system, leading to a high-oxygen pressure bioreactor used to improve the bio-transformative performance in the production of 1,3-dihydroxyacetone (DHA) from glycerol using Gluconobacter oxydans NL71. A concentration of 301.2 ± 8.2 g L^?1 DHA was obtained from glycerol after 32 h of fed-batch fermentation in the COS-SSTR system. The volumetric productivity for this process was 9.41 ± 0.23 g L^?1 h^?1, which is presently the highest obtained level of glycerol bioconversion into DHA. These results show that the application of this bioreactor would enable microbial production of DHA from glycerol at the industrial scale.     

Continuous fermentation of sweet whey permeate for propionic acid production in a CSTR with UF recycle

Summary Propionic acid was produced byPropionibacterium acidi-propionici from sweet-whey permeate in a stirred tank reactor (CSTR) with cell recycle by ultrafiltration. The highest volumetric productivity achieved was 14.3 g.l^–1. h^–1, with a biomass of 100 g.l^–1 (dry weight). More concentrated product can be obtained by electrodialysis of the cell free fermentation medium.     

Screening of two terrestrial cyanobacteria for biotechnological production processes in shaking flasks,bubble columns,and stirred tank reactors

Terrestrial cyanobacteria are rarely used for biotechnological processes, although they show great potential in terms of value-added substances. Cyanobacteria from arid habitats are of particular interest because they tolerate higher temperatures and feature a different product spectrum compared with their aquatic counterparts. In addition, terrestrial cyanobacteria may represent an interesting source of pharmaceutical products. To investigate the future use of these organisms in biotechnological processes, the growth rates of Trichocoleus sociatus (formerly Microcoleus sociatus) and Nostoc muscorum were examined using three different cultivation systems: shaking flasks, bubble columns, and stirred tank reactors. Parameters including pH, temperature, CO₂ level, and power dissipation were investigated quantitatively in the three systems for their impact on growth rate. The highest growth rate of the terrestrial cyanobacteria could be achieved in a stirred tank reactor under enriched CO₂ concentration. In this system, the growth rate was 1.15 day^-1?±?0.08 (2 % vol.) for T. sociatus and 0.72 day^-1?±?0.22 (5 % vol.) for N. muscorum, based on dry weight. Furthermore, a basic mathematical model was created as an add-on to predict growth rates of terrestrial cyanobacteria based on their dependency on temperature, pH, and substrate concentration, in general. This model was used to estimate growth of N. muscorum in stirred tank reactor experiments with an accuracy of 98.8 % and with 75 % accuracy for T. sociatus.