Mechanism of enhanced oxygen transfer in fermentation using emulsified oxygen-vectors

Limitations of oxygen transfer in fermentation can be solved using auxiliary liquids immiscible in the aqueous phase. The liquids (called oxygen-vectors) used in this study were hydrocarbon (n-dodecane) and perfluorocarbon (forane F66E) in which oxygen is highly soluble (54.9 mg/L in n-dodecane and 118 mg/L in forane F66E at 35 degrees C in contact with air at atmospheric pressure). It has been demonstrated that the use of n-dodecane emulsion in a culture of Aerobacter aerogenes enabled a 3. 5-fold increase of the volumetric oxygen transfer coefficient(k(L)a) calculated on a per-liter aqueous phase basis. The droplet size of the vector played a crucial role in the phenomena. When a static contact between gas bubble and vector droplet was established in water, the vector covered the bubble, in agreement with positive values of the spreading coefficient for these fluids. The determination of the oxygen transfer coefficients (k(L)) in a reactor with a definite interfacial area enabled the main resistance to be located in the boundary layer of the waterside either for a gas-water or a vector-water interface. Because oxygen consumption by weakly hydrophobic cells can only occur in the aqueous phase, the oxygen transfer is achieved according to the following pathway: gas-vector-water-cell. Finally, a mechanism for oxygen transfer within this four-phased system is proposed.     

添加氧载体及表面活性剂对番茄红素发酵的影响

通过添加氧载体（正十二烷、正己烷、过氧化氰）,有效改善发酵体系中的氧传递速率,从而促进了三孢布拉氏霉菌合成番茄红素的能力。实验结果表明,在第0d加入1．0％的正已烷、正十二烷时番茄红素的生成量分别提高了25．32％、72．84％,在第1d,添加50μL/100mL过氧化氢时番茄红素的生成量提高了40．35％,在加入正十二烷的同时,再加入表面活性剂Trilorl—x100,Tween20,Tween80,Span-20等,可使番茄红素的产量最多提高114．83％．     

Studies on Oxygen Transfer in Submerged Fermentations

The unsteady-state gas analysis method for the determination of oxygen transfer rate in shaken cultures was applied to the glutamic acid fermentation. This method was essentially based on the measurement of oxygen tension of gas phase in flasks. Major intentions of this application were to clarify the problems of oxygen transfer, to establish the measure of aeration effectiveness and to design the best aeration condition in the glutamic acid fermentation. Correlations of the fermentation to the level of dissolved oxygen, the rate of oxygen transfer, overall oxygen transfer coefficient and oxygen demand of cells were examined. As a measure of aeration effectiveness, the rate of oxygen transfer actually occurring in the fermentation seemed to be preferable, and was found to be above 7 × 10^?7 mol/ml-min for attaining the maximum productivity. Extremely high or low oxygen supply resulted in less productivity.     

Effects of controlled gas environments in solid-substrate fermentations of rice

The gas environment is solid-substrate fermentations of rice significantly affected levels of biomass and enzyme formation by a fungal species screened for high amylase production. Constant oxygen and carbon dioxide partial pressures were maintained at various levels in fermentations by Aspergillus oryzae. Control of the gas phase was maintained by a “static” aeration system admitting oxygen on demand and stripping excess carbon dioxide during fermentation. Constant water vapor pressures were also maintained by means of saturated salt solutions. High Oxygen pressures stimulated amylase productivity significantly. On the other hand, amylase production was severely inhibited at high carbon dioxide pressures. While relatively insensitive to oxygen pressure, maximum biomass productivities were obtained at an intermediate carbon dioxide pressure. High oxygen transfer rates were obtained at elevated oxygen pressures, suggesting, in view of the stimulatory effect of oxygen on amylase production, a stringent oxygen requirement for enzyme synthesis. Solid-substrate fermentations were highly advantageous as compared with submerged cultures in similar gas environments. Not only were amylase productivities significantly higher, but the enzyme was highly concentration in the aqueous phase of the semisolid substrate particles and could be extracted in a small volume of liquid. Results of this work suggest that biomass and product formation in microbial processes may be amenable to control by the gas environment. This is believed to offer an interesting potential for optimizing selected industrial fermentation processes with respect to productivity and energy consumption.     

A reassessment of mixing cost in fermentation processes

The gas–liquid oxygen transfer rate is a key step in the production of antibiotics in submerged fermentation. If the gas–liquid oxygen mass transfer rate is not equal to the required liquid–solid oxygen mass transfer rate at a particular cell concentration, then productivity of the particular fermentation operation will not be the maximum possible value. One way to increase the productivity of a given fermentation tank installation is to increase the cell concentration and to increase the oxygen transfer by changing the mixer and air supply to match the new requirements. In order to evaluate the cost of making this change to the larger mixing equipment, a typical cost example is given which can easily be modified for other combinations of production cost and mixer cost. As an example, it is seen that a considerable savings can result from a given installation by primarily changing the oxygen transfer ability of the equipment to utilize a given fermentor more efficiently. Production cost savings of 8 to 25% are shown in the example cited.     

Oxygen transfer enhancement in aqueous/perfluorocarbon fermentation systems: II. Theoretical analysis

Two theoretical approaches were examined to quantify observed experimental oxygen transfer enhancements in aqueous/perfluorocarbon (pfc) fermentation systems. Steady-state macroscopic balance results indicated that enhancements in the presence of reaction were a function of the gas bubble-to-droplet diameter ratio for pfc-in-water dispersions, but primarily a function of only the droplet diameter for water-in-pfc dispersions. The problem of unsteady-state diffusion into a semi-infinite composite medium was employed to predict enhancements in the absence of reaction based on the relative permeabilities of the perfluorocarbon and water phases. Since potential enhancements exceeded actual enhancements in the presence of an oxygen consuming reaction for water-in-pfc dispersions, the use of less expensive, lower oxygenpermeable oil phases is recommended in practice.     

油脂在抗生素发酵工业中的应用

发酵工业中使用油已有较长的历史,由于(1)油的绝对价格比淀粉质原料的高;(2)油脂代谢需要消耗大量的氧,使供氧能耗上升;(3)不同的油或同一种油,生产批次不同可能对发酵造成影响等原因。油在发酵过程中主要作为消泡剂和碳源。事实上,在发酵工业中油具有多种用途 。     

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。     

Studies on Oxygen Transfer in Submerged Fermentations

This paper refers to the application of gas analyzers for the determination of oxygen transfer rate, showing examples in the studies and the performances of submerged fermentations. Oxygen and carbon dioxide analyzers were set to monitor the gas streams to and from the fermentor. Continuous data on the concentrations of oxygen and carbon dioxide in the air streams were thus provided throughout the fermentation. Distinctive characters of this method were applicability to fermentors in practice and ability of obtaining data directly relating to the fermentations.

The modification of sulfite oxidation method for the determination of oxygen transfer rate from air into liquid or of a measure of aeration effectiveness was made. The proposed method was the application of gas analyzers in the studies on submerged fermentation. Some comparative discussions were made between this and the conventional titrimetric method. This modified method could be applied to biological systems with no alteration, therefore, it was made possible to compare the sulfite solution with the biological systems in relation to the problems on oxygen transfer.     

Measuring oxygen diffusion coefficients with polarographic oxygen electrodes. II. Fermentation Media

Fermentation media consist of a large number of chemicals which composition undergoes alteration during the course of fermentations. In consequence, the conventional methods and correlations for gas diffusion coefficient measurement and prediction cannot be easily applied to such systems. Oxygen diffusion coefficients have been measured in simulated chemical systems as well as in complex solutions of nutrient broth, using the polarographic technique introduced in a previous article. It is identified that sugars and salts are the major factors influencing oxygen diffusion coefficients in these aqueous fermentation media. The effect of salts on oxygen diffusion coefficients in electrolyte solutions has been found to be well correlated with the square root of total ionic strength of electrolyte solutions. The individual effect of glucose and its combined effect with salts are explored in order to reach rational correlations capable of predicting oxygen diffusion coefficients in synthetic fermentation media. For aqueous solutions of glucose plus salts, it is observed that the log-additive relationship can be used to account for the combined effect. Finally, a linear correlation has been established in measuring oxygen diffusion coefficients in aqueous solutions having different concentrations of nutrient broth.     

添加表面活性剂改善丁醇萃取发酵性能

研究了各种表面活性剂对丁醇萃取发酵的影响。丁醇发酵中有大量H2、CO2气体生成,生成的气泡携带发酵溶剂产物（丁醇、丙酮）进入萃取液相,促进了水相中发酵毒性产物向萃取液相的移动。研究发现,表面活性剂可以降低气-液膜的表面张力,促使大气泡破碎,从而使发酵产气以较小气泡的形式穿过萃取液相。添加表面活性剂可以强化发酵溶剂产物从水相到萃取相的移除速度,缩短发酵产物在油水两相中达到平衡的时间。有利于提高发酵生产强度。以地沟生物柴油为萃取剂,吐温-80的添加量为质量分数0．140％时,与对照相比（无表面活性剂的萃取发酵）,相同发酵时间内萃取相中丁醇体积分数提高了21．2％．总溶剂生产强唐也提高了16．5％．     

Oxygen transfer to mycelial fermentation broths in an airlift fermentor

Oxygen transfer rates and gas holdups were measured in mycelial fermentation broths of Chaetomium cellulolyticum and Neurospora sitophila, each cultured in a 1300-L pilot-plant-scale airlift fermentor. These cultures exhibited highly non-Newtonian flow behavior coupled with a substantial decrease in oxygen transfer rates. The volumetric mass transfer coefficients in these cultures were found to be 65-70% lower than those in water. The data were compared with the available correlations obtained for simulated fermentation broths. In general, the data for C. cellulolyticum are in satisfactory agreement with the correlations for the model media but the data for N. sitophila are higher than that predicted by the correlations. Model media based correlations are found to be applicable to the fermentation processes if the culture medium does not possess a high yield stress.     

Hydroxyethylation of Comenic Acid

A small jar fermentor was developed in order to investigate the effect of oxygen supply on hydrocarbon fermentation. Several indices to oxygen transfer were examined with this small jar fermentor. Conditions for suitable oxygen supply were examined in l-glutamic acid fermentation from hydrocarbon by use of shaking flasks and these small jar fermentors. The data indicated that the rate of oxygen transfer ought to be more than 14.3 × 10^?7 mole/ml·min in order to obtain satisfactory results. The coefficient of oxygen transfer rate (K_La/H) decreased as the fermentation went on, so the supply of oxygen enriched gas mixture was effective to increase the production of l-glutamic acid.     

Simple system for controlling dissolved oxygen concentration in laboratory fermentors

A simple system for the control of oxygen transfer in laboratory fermentation units has been devised. This system employs pure oxygen to elevate the driving force for oxygen transfer. In addition, the aeration is controlled in a closed loop manner in order to minimize total exit flow of the gas from the fermentor. Fermentation study using Bacillus stearothermophilus grown on n-dodecane at 55°C illustrates excellent carbon recovery as well as the ease of controlling oxygen transfer.     

Russian Article pp. 335-340

Industrial processes of cultivation of aerobic microorganisms are characterized by too small transportation rates of oxygen from a gas into a cell. The search for new ways of productivity increase by means of intensification of oxygen mass transfer in the fermentation process is of great importance. The possibilities for use of chelate transition metal complexes (CTMC) capable of binding oxygen in biosynthetic processes have been studied. The formation of labial complex of the studied substances with oxygen is shown by spectrophotometry. The increase of the oxygen delution rate in water in the presence of CTMC is shown by physical absorbtion method. The rate increase of oxygen mass transfer from gas into liquid is calculated on the base of the sulphite method. The use of CTMC in the role of oxygen carriers in the yeast cultivation leads to the biomass increase up to 20%.     

The effects of non-Newtonian fermentation broth viscosity and small bubble segregation on oxygen mass transfer in gas-lift bioreactors: a critical review

This review paper deals with the effects of non-Newtonian fermentation broth viscosities on gas–liquid mixing and oxygen mass transfer characteristics to provide knowledge for the design and development of gas-lift bioreactors, which can operate satisfactorily with high viscosity fermentation broths. The effect of small bubble segregation is also examined.     

Bioreactor scale-up and oxygen transfer rate in microbial processes: An overview

In aerobic bioprocesses, oxygen is a key substrate; due to its low solubility in broths (aqueous solutions), a continuous supply is needed. The oxygen transfer rate (OTR) must be known, and if possible predicted to achieve an optimum design operation and scale-up of bioreactors. Many studies have been conducted to enhance the efficiency of oxygen transfer. The dissolved oxygen concentration in a suspension of aerobic microorganisms depends on the rate of oxygen transfer from the gas phase to the liquid, on the rate at which oxygen is transported into the cells (where it is consumed), and on the oxygen uptake rate (OUR) by the microorganism for growth, maintenance and production.     

Gas-liquid mass transfer in bioreactor with three-phase inverse fluidized bed

In the present study the oxygen mass transfer from the gas to the aqueous phase in a Three-Phase Inverse Fluidized Bed (TPIFB) has been studied. A pilot scale TPIFB has been designed and constructed. For determination of the volumetric oxygen mass transfer coefficient the elegant dynamic method, described by Dang et al. (1977) was used. The influence of hydrodynamic parameters, e.g., superficial velocities of the gas and liquid phases on the mass transfer rate was studied. In the range of variables covered, it was found that the superficial liquid velocity had a weak effect on the mass transfer whereas the gas flowrate affects the mass transfer positively. The results for the volumetric oxygen transfer coefficient in the TPIFB were compared to reported values of that coefficient, measured in a classic three-phase fluidised bed under similar hydrodynamic conditions and solid phase properties. The comparison demonstrated a two-fold increase of the oxygen transfer rate in the inverse bed over that in the classic one.     

Optimal design of airlift fermenters

In this article a modeling of a draft-tube airlift fermentor (ALF) based on perfect backmixing of liquid and plugflow for gas bubbles has been carried out to optimize the design and operation of fermentation units at different working capacities. With reference to a whey fermentation by yeasts the economic optimization has led to a slim ALF with an aspect ration of about 15. As far as power expended per unit of oxygen transfer is concerned, the responses of the model are highly influenced by k_La However, a safer use of the model has been suggested in order to assess the feasibility of the fermentation process under study.     

Prediction of gas-liquid mass transfer coefficient in sparged stirred tank bioreactors

Oxygen mass transfer in sparged stirred tank bioreactors has been studied. The rate of oxygen mass transfer into a culture in a bioreactor is affected by operational conditions and geometrical parameters as well as the physicochemical properties of the medium (nutrients, substances excreted by the micro-organism, and surface active agents that are often added to the medium) and the presence of the micro-organism. Thus, oxygen mass transfer coefficient values in fermentation broths often differ substantially from values estimated for simple aqueous solutions. The influence of liquid phase physicochemical properties on kLa must be divided into the influence on k(L) and a, because they are affected in different ways. The presence of micro-organisms (cells, bacteria, or yeasts) can affect the mass transfer rate, and thus kLa values, due to the consumption of oxygen for both cell growth and metabolite production. In this work, theoretical equations for kLa prediction, developed for sparged and stirred tanks, taking into account the possible oxygen mass transfer enhancement due to the consumption by biochemical reactions, are proposed. The estimation of kLa is carried out taking into account a strong increase of viscosity broth, changes in surface tension and different oxygen uptake rates (OURs), and the biological enhancement factor, E, is also estimated. These different operational conditions and changes in several variables are performed using different systems and cultures (xanthan aqueous solutions, xanthan production cultures by Xanthomonas campestris, sophorolipids production by Candida bombicola, etc.). Experimental and theoretical results are presented and compared, with very good results.