促溶剂对雷斯青霉发酵液流变特性的影响

目的:促溶剂通常用于甾体生物催化过程以提高底物溶解度,但在发酵液中添加促溶剂对菌体形态及发酵液特性的影响还少有报道。方法:利用旋转流变仪和顺磁分析仪分别对发酵液的流变特性及体积氧传递系数KLa进行监测。结果:无论是否添加促溶剂,发酵液都表现出非牛顿流体力学特性,但添加3%1,2丙二醇后同一时期发酵液稠度系数减小大约17%,而流动指数平均增加8%。结论:添加促溶剂使得发酵液表观黏度减小,体积氧传递系数增大,从而有利于甾体化合物的生物转化。     

翼形轴流桨在红霉素发酵中的应用研究

在20t工业发酵罐中,研究了翼形轴流桨搅拌对红霉素发酵过程的影响。重点考察了粘度,溶氧,效价等过程参数变化,以及搅拌功耗与发酵产量之间的关系。研究结果表明：（1）与传统的涡轮搅拌桨相比,翼形轴流桨搅拌其发酵过程参数（粘度,溶氧,效价等）随时间的变化曲线有明显的差异;（2）在相同的生产条件下,用翼形轴流桨代表涡轮桨可有效提高生产效率。     

搅拌对红霉素发酵的影响

在20t工业发酵罐中,研究了涡轮桨和翼形轴流桨搅拌对红霉素发酵过程的影响,重点考察了粘度、溶氧、效价、搅拌电流和糖代谢等过程参数的变化,以及搅拌功耗与发酵产量之间的关系。研究结果表明：(1)不同的搅拌桨搅拌其发酵过程参数(粘度,溶氧,效价等)随时间的变化曲线有明显的差异;(2)搅拌功耗同发酵产量之间的关系,翼形桨明显不同于涡轮桨;(3)在相同的生产条件下,用翼形桨代替涡轮桨可节省搅拌功耗。     

Rheological,Mass Transfer,and Mixing Characterization of Cellulase-Producing Trichoderma reesei Suspensions

Steady and dynamic shear measurements are utilized to characterize the rheological behavior of Trichoderma reesei RUT-C30 fungal suspensions during batch growth on xylose (soluble substrate) or cellulose (particulate solid substrate) at three different fermentor impeller speeds (250, 400, and 550 rpm). Biomass concentrations versus time were unimodal on xylose and bimodal on cellulose. This behavior is consistent with relatively rapid, early growth on easily metabolized growth medium components (yeast extract), followed by a second, slower growth phase due to hydrolysis of recalcitrant cellulose by increasing cellulase concentrations. Critical dissolved oxygen (DO) concentration for T. reesei growth on cellulose was found to be 0.073 mmol/L. The DO was kept above this level by supplementing the air feed with pure oxygen, implying that mass transfer limitations were not the cause of bimodal cell growth. Steady shear rheological data showed shear thinning behavior and a yield stress for all broth samples regardless of substrate. Casson and Herschel−Bulkley constitutive equations fit steady shear data well. Dynamic shear measurements on broth suspensions indicated “gel-like” behavior at low strains, with microstructural breakdown at larger displacements. Time variations of the Casson model parameters (yield stress and Casson viscosity) and dynamic moduli (elastic and viscous modulus) followed both cell mass and morphology: a single maximum in all rheological variables resulted when cells were grown on xylose or on cellulose at impeller speeds of 400 or 550 rpm, and dual maxima were observed for cellulose-grown cells at 250 rpm.     

On-line rheological measurements and control in fungal fermentations

A system for on-line rheological measurements and control in filamentous fermentations is presented. The output signals from the control unit can be used in terms of process control. Diluting the broth in a growth controlled feed pattern was found to influence the viscosity of the broth and lead to process improvements. Just diluting the fermentation broth to keep the viscosity below a preset value was seen to give only temporary process improvements. The higher the viscosity, the less effective the viscosity controlled dilutions. The failure to get full control over the viscosity by the dilution techniques used is caused by the large number of factors influencing the rheological properties of an Aspergillus niger culture. The factors shown in this work to influence the rheological properties of the fermentation broth were the biomass concentration, the specific growth rate, mixing qualities (impeller speed and working volume), and the dissolved oxygen concentration. (c) 1992 John Wiley & Sons, Inc.     

Polysaccharide production: Experimental comparison of the performance of four mixing devices

This investigation was undertaken with the objective to compare experimentally the performance of four different mixing devices for the production of the polysaccharide pullulan with Aureobasidium pullulans (2552). Fermentations were performed using identical bioreactors with respectively an assembly of three Rushton turbines (RTB), a helical ribbon impeller (HR) and two different reciprocating plates (RPB1, RPB2). Each mixing vessel had identical geometry and working volume (18 L). These four fermentations were performed with an equal level of power input per unit volume (1000?W/m³) and gas flow rate (0.5 vvm, 9 L/min). For each system, the evolution of biomass, polysaccharide concentration, dissolved oxygen and agitation speed or frequency were recorded as a function of time along with the rheological properties of the culture broths. The type of mixing device used had a significant impact on the rate of biomass production and on polysaccharide physical properties. However, the rate of polysaccharide production appears to be less sensitive to the bioreactor design. The overall productivity, which represents the ability of micro-organisms to convert rapidly substrate into biomass and polysaccharide, was maximised using the RPB2 system. The quality of the synthesised polysaccharide, in terms of viscosity producing power, was highest using the HR system but the overall productivity was very low. Thus, the best compromise between productivity and product quality was achieved with the RPB2.     

Modeling enzyme production with Aspergillus oryzae in pilot scale vessels with different agitation, aeration, and agitator types

The purpose of this article is to demonstrate how a model can be constructed such that the progress of a submerged fed-batch fermentation of a filamentous fungus can be predicted with acceptable accuracy. The studied process was enzyme production with Aspergillus oryzae in 550 L pilot plant stirred tank reactors. Different conditions of agitation and aeration were employed as well as two different impeller geometries. The limiting factor for the productivity was oxygen supply to the fermentation broth, and the carbon substrate feed flow rate was controlled by the dissolved oxygen tension. In order to predict the available oxygen transfer in the system, the stoichiometry of the reaction equation including maintenance substrate consumption was first determined. Mainly based on the biomass concentration a viscosity prediction model was constructed, because rising viscosity of the fermentation broth due to hyphal growth of the fungus leads to significant lower mass transfer towards the end of the fermentation process. Each compartment of the model was shown to predict the experimental results well. The overall model can be used to predict key process parameters at varying fermentation conditions.     

CFD simulation of mixing for high-solids anaerobic digestion

A computational fluid dynamics (CFD) model that simulates mechanical mixing for high-solids anaerobic digestion was developed. Numerical simulations of mixing manure slurry which exhibits non-Newtonian pseudo-plastic fluid behavior were performed for six designs: (i) one helical ribbon impeller; (ii) one anchor impeller; (iii) one curtain-type impeller; (iv) three counterflow (CF-2) impellers; (v) two modified high solidity (MHS 3/39°) impellers; and (vi) two pitched blade turbine impellers. The CFD model was validated against measurements for mixing a Herschel-Bulkley fluid by ribbon and anchor impellers. Based on mixing time with respect to mixing energy level, three impeller types (ribbon, CF-2, and MHS 3/39°) stand out when agitating highly viscous fluids, of these mixing with two MHS 3/39° impellers requires the lowest power input to homogenize the manure slurry. A comparison of digestion material demonstrates that the mixing energy varies with manure type and total solids concentration to obtain a given mixing time. Moreover, an in-depth discussion about the CFD strategy, the influences of flow regime and impeller type on mixing characteristics, and the intrinsic relation between mixing and flow field is included.     

Carbon monoxide mass transfer for syngas fermentation in a stirred tank reactor with dual impeller configurations

This study compares the power demand and gas-liquid volumetric mass transfer coefficient, kLa, in a stirred tank reactor (STR) (T = 0.211 m) using different impeller designs and schemes in a carbon monoxide-water system, which is applicable to synthesis gas (syngas) fermentation. Eleven different impeller schemes were tested over a range of operating conditions typically associated with the "after large cavity" region (ALC) of a Rushton-type turbine (D/T = 0.35). It is found that the dual Rushton-type impeller scheme exhibits the highest volumetric mass transfer rates for all operating conditions; however, it also displays the lowest mass transfer performance (defined as the volumetric mass transfer coefficient per unit power input) for all conditions due to its high power consumption. Dual impeller schemes with an axial flow impeller as the top impeller show improved mass transfer rates without dramatic increases in power draw. At high gas flow rates, dual impeller schemes with a lower concave impeller have kLa values similar to those of the Rushton-type dual impeller schemes but show improved mass transfer performance. It is believed that the mass transfer performance can be further enhanced for the bottom concave impeller schemes by operating at conditions beyond the ALC region defined for Rushton-type impellers because the concave impeller can handle higher gas flow rates prior to flooding.     

Improved bacterial nanocellulose production from glucose without the loss of quality by evaluating thirteen agitator configurations at low speed

Thirteen agitator configurations were investigated at low speed in stirred-tank reactors (STRs) to determine if improved crude bacterial nanocellulose (BNC) productivity can be achieved from glucose-based media while maintaining high BNC quality using Komagataeibacter xylinus ATCC 23770 as a model organism. A comparison of five single impellers showed the pitched blade (large) was the optimal impeller at 300 rpm. The BNC production was further increased by maintaining the pH at 5.0. Among the single helical ribbon and frame impellers and the combined impellers, the twin pitched blade provided the best results. The combined impellers at 150 rpm performed better than the single impellers, and after optimizing the agitation conditions, the twin pitched blade (large) and helical ribbon impellers performed the best at 100 rpm. The performances of different agitators at low speed during BNC production were related to how efficiently the agitators improved the oxygen mass transfer coefficient. The twin pitched blade (large) was verified as providing the optimum performance by an observed crude BNC production of 1.97 g (L×d)⁻¹ and a BNC crude yield of consumed glucose of 0.41 g g⁻¹, which were 2.25 and 2.37 times higher than the initial values observed using the single impeller respectively. Further characterization indicated that the BNC obtained at 100 rpm from the STR equipped with the optimal agitator maintained high degree of polymerization and crystallinity.     

Influence of impeller type on mass transfer in fermentation vessels

Radial flow Rushton impellers were compared qualitatively with axial flow hydrofoil impellers (Maxflo T and A315) at the pilot scale. Six types of impellers were compared for qualitative differences in mass transfer. Measurements were conducted using three model systems: water, glycerol and Melojel (soluble starch). Power measurements were obtained using watt transducers, which although limited in accuracy and prone to interferences, were able to provide useful qualitative monitoring results. While there was little effect of impeller type on mass transfer as measured by the rapid pressure increase technique, significant qualitative differences were observed using the rapid temperature increase technique specifically for the Melojel and glycerol model systems. The Miller correlation, relating gassed-to-ungassed power, was used effectively to qualitatively evaluate the power drop upon gassing for both the model systems and a Streptomyces fermentation for the various impeller types. A high oxygen demand Streptomcyes fermentation then was conducted in fermenters possessing each type of impeller. Performance was not adequate with the A315 impellers pumping upwards and the small diameter Maxflo T impellers. Peak titers and profiles of the estimated apparent broth viscosity varied depending upon the impeller type. Mass transfer rates generally declined with higher viscosities when other fermentation operating conditions where held constant. Overall, values for OUR, k _L a, P _g /V _L and other calculated mass transfer and power input quantities for the A315 pumping upwards and undersized Maxflo T (D _T /D _I ?=?2.3) impellers were at the lower end of the range obtained for the larger Maxflo T (D _T /D _I ?=?1.8–2.0) and A315 impellers pumping downwards. Rushton impellers generally behaved qualitatively similar to hydrofoil impellers based on these calculated quantities.     

Shear conditions in clavulanic acid production by Streptomyces clavuligerus in stirred tank and airlift bioreactors

In biochemical processes involving filamentous microorganisms, the high shear rate may damage suspended cells leading to viability loss and cell disruption. In this work, the influence of the shear conditions in clavulanic acid (CA) production by Streptomyces clavuligerus was evaluated in a 4-dm(3) conventional stirred tank (STB) and in 6-dm(3) concentric-tube airlift (ALB) bioreactors. Batch cultivations were performed in a STB at 600 and 800 rpm and 0.5 vvm (cultivations B1 and B2) and in ALB at 3.0 and 4.1 vvm (cultivations A1 and A2) to define two initial oxygen transfer conditions in both bioreactors. The average shear rate ([Formula: see text]) of the cultivations was estimated using correlations of recent literature based on experimental data of rheological properties of the broth (consistency index, K, and flow index, n) and operating conditions, impeller speed (N) for STB and superficial gas velocity in the riser (UGR) for ALB. In the same oxygen transfer condition, the [Formula: see text] values for ALB were higher than those obtained in STB. The maximum [Formula: see text] presented a strong correlation with a maximum consistency index (K (max)) of the broth. Close values of maximum CA production were obtained in cultivations A1 and A2 (454 and 442 mg L(-1)) with similar maximum [Formula: see text] values of 4,247 and 4,225 s(-1). In cultivations B1 and B2, the maximum CA production of 269 and 402 mg L(-1) were reached with a maximum [Formula: see text] of 904 and 1,786 s(-1). The results show that high values of average shear rate increase the CA production regardless of the oxygen transfer condition and bioreactor model.     

Production of phytase (myo-inositolhexakisphosphate phosphohydrolase) by Aspergillus niger van Teighem in laboratory-scale fermenter

The growth and production pattern of phytase by a filamentous fungus, Aspergillus niger van Teighem, were studied in submerged culture at varying agitation rates and controlled and uncontrolled pH conditions. Allowing the initial culture to grow under neutral condition with subsequent decline in pH resulted in increased phytase productivity. A maximum of 141 nkat/mL phytase was obtained when the broth pH was maintained at pH 2.5 as compared to 17 nkat/mL units at controlled pH 5.5. The culture morphology and rheological properties of the fermentation broth significantly varied with the agitation rate. The volumetric oxygen transfer coefficient was determined at different phases of fungal growth during batch fermentation using static gassing out and dynamic gassing out methods. The oxygen transfer coefficient (k(L)a) of the fermenter was found to be 125 h(-)(1) at 500 rpm as compared to 38 h(-)(1) at 200 rpm. The oxygen transfer rates at different phases of growth were significantly affected by cell mass concentration and fungal morphology. During the course of fermentation there was a gradual decline of k(L)a from 97 h(-)(1) on day 2 to 63 h(-)(1) on day 6 of fermentation, after which no significant change was observed. The degree of agitation considerably influenced the culture morphology where shear thinning of filamentous fungus was observed with the increase in agitation.     

The effect of agitation and aeration on the synthesis and molecular weight of gellan in batch cultures of Sphingomonas paucimobilis

The effects of agitation and aeration upon synthesis and molecular weight of the biopolymer gellan were systematically investigated in batch fermenter cultures of the bacterium, Sphingomonas paucimobilis. High aeration rates and vigorous agitation enhanced growth of S. paucimobilis. Although gellan formation occurred mainly in parallel with cell growth, the increase in cells able to synthesise gellan did not always lead to high gellan production. For example, at very high agitation rates (1000 rpm) growth was stimulated at the expense of biopolymer synthesis.Maximal gellan concentration was obtained at 500 rpm agitation and either 1 or 2 vvm aeration (12.3 and 12.4 g/l gellan, respectively). An increase in aeration (from 1 to 2 vvm) enhanced gellan synthesis only at low agitation rates (250 rpm). However, high aeration or dissolved oxygen was not necessary for high gellan synthesis, in fact oxygen limitation always preceded the phase of maximum gellan production and probably enhanced polysaccharide biosynthesis.Some gellan was formed even after glucose exhaustion. This was attributed to the intracellular accumulation of polyhydroxyalkanoates, (such as polyxydroxybutyrate) which were found in S. paucimobilis cells indicating the existence of a carbon storage system, which may contribute to gellan biosynthesis under glucose-limiting conditions.The autolysis of the culture, which occurred at the late stages of the process, seemed to be triggered mainly by limitations in mass (nutrient) transfer, due to the highly viscous process fluid that gradually develops. Rheological measurements generally gave a very good near real time estimate of maximum biopolymer concentration offering the possibility of improved process control relative to time consuming gravimetric assay methods.While mechanical depolymerisation of gellan did not occur, high aeration rates (2 vvm) led to production of gellan of low molecular weight (at either 250 or 500 rpm). This effect of aeration rate upon gellan molecular weight is reported here for the first time, and is important for the properties and applications of gellan. Mechanisms which may have led to this are discussed, but control of molecular weight of the biopolymers is clearly an area needing further research.     

On-line rheometer for the monitoring of polymer fermentations: Operating conditions

A turbine rheometer was developed and tested for on-line measurements of rheological properties of fermentation broths. The organism used in the test broth wasAureobasidium pullulans. Although the rheometer constants were found to be dependent on the nature of calibration fluids used, the variations in these constants had little effect on the measured rheological parameters of the power law equation. The rheological parameters did not vary with liquid flow rate through the on-line rheometer, and the repeatability of the measured rheological parameters were high. The broth showed some tendency to thixotropic (time-dependent) behaviour, but this was found to be negligible after 15 seconds of shear.     

Effects of agitator configuration and rotational speed on the production of extracellular polysaccharide by Xanthomonas cucurbitae PCSIR B-52

A strain of Xanthomonas cucurbitae PCSIR B-52, efficiently produced extracellular polysaccharide using partially deproteinized low-acid cheese whey without hydrolysis. The effects of the agitator configuration and rotational speed on the viscosity of the fermented broth and the productivity of extracellular polysaccharide based on bacterial growth were evaluated in a batch process. Agitation was performed by a six-bladed disc turbine impeller and by a similar agitator, equipped with six vertically attached stabilizing fins. Comparatively, the magnitude of the decrease in the DO tension resulting from increased viscosity of the broth was less with the stabilizing-fin agitator due to increased system damping. A drastic increase in the mechanical agitation speed after 30-h fermentation, however, increased the broth viscosity and the accumulation of polysaccharide. Moreover, the volume of the macromixing region decreased with increasing rotational speed of agitator.     

Production and rheological characteristics of the microbial polysaccharide gellan

B. MANNA, A. GAMBHIR AND P. GHOSH. 1996. Sphingomonas paucimobilis was used for the synthesis of the microbial polysaccharide gellan. In a 60 h fermentation, polysaccharide yield and productivity obtained were 0.45 g gellan per g glucose consumed and 0.21 g I⁻¹ h⁻¹ respectively. The broth showed pseudoplastic behaviour with yield stress. The requirement of the solvent propanol to precipitate gellan from the broth depended on the volume of the broth rather than on gellan concentration. The addition of salt to the broth reduced the propanol requirement. Attempts to separate cells from the highly viscous broth by microfiltration were not successful. Ultrafiltration reduced the propanol requirement but appreciable membrane fouling and loss of gellan was observed.     

Oxygen transfer kinetics of riboflavin fermentation by Ashbya gossypii in agitated fermentors

Effects of agitation and aeration rates on volumetric oxygen transfer coefficient and oxygen uptake rate of a riboflavin broth containing Ashbya gossypii were investigated in three batch, sparged, and agitated fermentors having the working volumes of 0.42, 0.85, and 2.5 l. The change of oxygen uptake rate with time at 250 rev min⁻¹ stirring and vvm aeration rates was shown. The volumetric oxygen transfer coefficients and maximum oxygen uptake rates obtained have been correlated to mechanical power inputs per unit volume of the fermentation broth and the superficial air velocities.     

Power consumption of three impeller combinations in mixing Xanthan fermentation broths

Xanthan gum fermentation represents a good model for the study of the mixing of rheologically complex culture broths. Most of the previous work on power consumption dealt with ‘standard’, single impellers and used model fluids to simulate xanthan broths. This work describes the characterization of three dual-impeller combinations (D/T = 0·53) for the mixing of dehydrated—reconstituted fermentation broths of Xanthomonas campestris that had matched rheology to the actual broths. The bottom impeller was a Rushton turbine (RT) and the top impeller was another RT, a 45° pitched blade turbine (PT) or an A-310 Lightnin mixer (A310). The experiments were carried out in a tank of 0·0094 m³ working volume equipped with an air bearing dynamometer. The power was measured in a wide range of xanthan concentrations (5–40 kg m⁻³) in aerated (0·25, 0·5 and 1·0 vvm) and unaerated conditions. Unaerated power number (Po) vs. Reynolds number (Re) curves showed similar trends for the three combinations. Exponents close to −1 were obtained in the laminar region. A minimum in Po (Po_min) occurred at Re = 30–40, then increasing to a plateau value which was evident at Re> 200. In the transition region Po_min values were 4·3 (RT and RT), 3·6 (RT and PT) and 2·4 (RT and A310). The aerated power data for (RT and PT) and (RT and A-310) showed higher torque instabilities than the dual RT combinations at higher xanthan concentrations. The higher the xanthan concentrations, the higher the drop in power and the less important the effect of the aeration rate. Among the combinations tested, when using Rushton turbines, the well-mixed ‘cavern’ reached the tank wall (i.e., fluid motion was observed) at the lowest volumetric power input. High