Effect of antifoam addition on gas-liquid mass transfer in stirred fermenters

The influence of three well-known antifoaming agents (polypropylene glycol, silicone and soybean oil) on gas-liquid mass transfer in stirred tanks is studied, both in model and in fermentation media. The effect of antifoam concentration, ionic strength, viscosity, agitation speed and gas flow rate are investigated. It is found that antifoam addition at low concentrations markedly decreases the gas-liquid volumetric mass transfer coefficient, k_La, for the three antifoam agents tested. Although the major effect is on the film coefficient k_L, some effect is also detected on the specific area, a. It is found that the influence of viscosity and antifoam addition are not cumulative: each tends to attenuate the other's effect on mass transfer. Both for silicone and for soybean oil, but not for PPG in the concentration range studied, there is an antifoam concentration above which further antifoam addition starts to improve k_La.     

Effect of Corn steep liquor supplementation and scale up on Lactococcus starter production

Summary Three Lactococcus strains (Lactococcus ssp. lactis var. diacetylactis, Lactococcus ssp. lactis cremoris and Lactococcus ssp. lactis var. lactis) isolated from the Tunisian lben were grown at constant pH on CSL medium in stirred fermentors for lactic starters production. The agitation required to homogenate alkali used to pH control should be low because it affects the Lactococcus growth. Scale up from 20-liter fermentor to 400-liter fermentor was carried out at constant impeller tip speed below 150 cm s^у. The CSL supplementation and fed-batch with glucose increased the yield in the upper 10¹⁰ cfu/ml. The consumed glucose during fermentation was converted into lactic acid and cell. Before fed-batch, the maximum specific growth rate of Lactococcus ssp. lactis var. diacetylactis was around 1 h^у and the number of cells increased 20 to 40 times according to inoculum size. After fed-batch, the glucose consumption rate remains constant but specific growth rate decreased and number of cell trebled only.     

Dynamics of mycelial aggregation in cultures of Aspergillus oryzae

Previous work has shown that in many mycelial fermentations the predominant morphological form is clumps (aggregates) which cannot be further reduced by dilution. During fermentation, the clump size and shape is affected by fragmentation, which in turn depends on agitation conditions. This paper addresses the question of whether mycelial aggregation can also occur during a fermentation. The dynamics of changes in mycelial morphology due to aggregation were investigated in 5.3-L chemostat cultures of Aspergillus oryzae by imposing a step decrease in agitation speed from 1,000 to 550 rpm under conditions of controlled non-limiting dissolved oxygen tension, with a steady-state biomass concentration of 2 g/L. The mean projected area (size) of the mycelia, measured using image analysis, increased from 5,300녘 µm² (at 1,000 rpm) to 9,400덌 µm² (at 550 rpm). This change occurred too rapidly for it to be solely caused by mycelial growth. Instead, it is proposed that the increase in size was indeed due to aggregation, probably due to physico-chemical affects such as hydrophobicity or charge interactions. Aggregation was also shown to occur in 4-L aerated batch cultures at higher biomass concentrations (5.3 and 11.2 g/L) in which the agitation speed was decreased from 1,100 to 550 rpm. Experiments were also conducted off-line in a mixing vessel in the absence of oxygen. In this case, aggregation was not observed. Thus, though the cause of aggregation at this stage is not clear, aerobic metabolism appears to be required.     

Periodic operation of bioreactors for autocatalytic reactions with Michaelis-Menten kinetics

The performance of an isothermal tubular bioreactor carrying out autocatalytic reactions obeying Michaelis-Menten Kinetics is analyzed for improvement in the average yield of product B. Under steady-state condition, the reactor is shown to exhibit input multiplicities in the yield of B with the mean residence time. Simulation results show that a significant improvement in the average yield of B is obtained under feed substrate concentration cycling. The two values of mean residence time giving identical yield under conventional steady-state operation is shown to give distinctly different behaviour under periodic operation. The lower value of the residence time gives improved average yield of B. The performances of the reactor with power law kinetics and that with the Michaelis-Menten kinetics show distinct average yield under periodic operation even though steady-state operation gives identical yield.     

Effect of ammonium sulphate concentration and agitation speed on the kinetics of alginate production by Azotobacter vinelandii DSM576 in batch fermentation

Growth and alginate production by Azotobacter vinelandii DSM576 as a function of initial ammonium sulphate concentration (0.45–1.05 g l⁻¹) and agitation speed (300–700 rpm) were studied in batch fermentations at controlled pH. The time course of growth, alginate production and substrate consumption and the effect of nitrogen concentration and agitation speed on kinetic parameters and on maximum alginate molecular weight (MW) was modelled using empirical equations. The kinetics of growth, alginate production and polymerization were deeply affected by agitation speed and, to a lesser extent, by inorganic nitrogen concentration. Average and maximum specific growth rate and maximum alginate MW all increased with agitation speed, and were higher at intermediate ammonium sulphate concentration. Maximum alginate MW (>250,000) was obtained at high agitation speed (600–700 rpm) and alginate depolymerization was limited or did not occur at all when the agitation speed was higher than 500 rpm, while at 400 rpm depolymerization significantly reduced the alginate. However, alginate yield was negatively affected by increasing agitation speed. A good compromise between alginate yield (>2 g l⁻¹) and quality (MW>250,000) was obtained with agitation speed of 500–600 rpm and 0.75–0.90 g l⁻¹ of ammonium sulphate. Journal of Industrial Microbiology & Biotechnology (2000) 25, 242–248. Received 23 February 2000/ Accepted in revised form 04 August 2000     

Determination of power consumption and volumetric oxygen transfer coefficient in bioreactors

A torque meter has been developed for determining the power consumption in a bench stirred tank. The device has been bonded in the stirrer shaft inside a commercial bench fermentor, in order to avoid frictional losses in the mechanical seal. Power consumption measurements in ungassed and gassed systems were obtained at different agitation and aeration conditions, for Newtonian and non-Newtonian fluids. Also, a "simple modified sulfite method" for volumetric oxygen transfer coefficient (k_La) determination was developed and the experimental data were correlated with the gassed power (P_g) by using well-known correlations presented in the literature.     

Oxygen transfer characteristics of a centrifugal, packed-bed reactor during viscous xanthan fermentation

The oxygen transfer properties of a novel, centrifugal, packed-bed reactor (CPBR) during viscous xanthan fermentation were determined with respect to the effects of the arrangement of the centrifugal, packed bed (CPB) and the recirculation loop (RL). Characterized by the maximum volumetric transfer coefficient (k_La) in xanthan broth, the aeration efficiency of CPBR was compared to those in stirred-tank reactors (STR) equipped with disc turbines (DT) or marine propellers (MP), and to that in a water-in-oil emulsion (WIO). As expected, STR-WIO showed the highest k_La (0.038 s^-1 at 2%) among all systems studied due to reduced broth viscosity; however, practical difficulties exist in product recovery. It was found that, at 3.5% xanthan the k_La in CPBR (0.018 s^-1) was higher than that of STR (0.005 s^-1) and close to that of STR-WIO (0.020 s^-1), indicating improved oxygen transfer at such a xanthan concentration. The exterior baffles along the rotating fibrous matrix offer additional agitation in the viscous broth. A gas-continuous arrangement, in which the CPB was kept above the broth, was able to elevate k_La to 0.023 s^-1, higher than that of STR-WIO. The external RL operated by a peristaltic pump was found to play an important role in CPBR aeration by providing better gas-liquid contact. With the improved oxygen transfer efficiency in CPBR at high xanthan concentrations, the CPBR system is practically the preferred system for xanthan fermentation. The characteristic roles of CPB arrangement and the RL should be considered primarily during scale-up operation.     

Vitis vinifera culture in a non-conventional bioreactor: the reciprocating plate bioreactor

This paper is concerned with the potential use of a reciprocating plate bioreactor (RPB) for suspended plant cell cultures. The agitation mechanism of the RPB system, a plate stack, was first evaluated in pure water and in pseudocells medium of 20, 40 and 60% of PCV. As the pseudocell concentration increases, the oxygen mass transfer coefficient, K_La, significantly decreases. Correlations were established for each plate stack and concentration with good prediction of K_La. Three fermentations were performed with Vitis vinifera cells, two in the RPB system and one in shake flasks. Shake flask cultures showed better performance whereas the first fermentation performed with the RPB showed the lowest performance. The lower growth observed was attributed to the operating conditions for aeration and the dissolved oxygen control strategy. CO₂ stripping in the initial portion of the fermentation led to lower biomass growth. The second fermentation, with more appropriate operating conditions, appears to follow the trend of shake flask cultures but was terminated after 5 days due to contamination. The RPB has the potential to be used for suspended plant cell cultures but significant research needs to be performed to find optimal operating conditions but, more importantly, to make appropriate modifications to ensure the sterility of the bioreactor over long time periods.     

Robust multiple-input-multiple-output control of non-linear continuous fermentation processes

In this study, the removal of nitrate (NO₃^m) ions from aqueous streams with liquid membrane technique has been investigated. Among the other parameters (temperature, pH, acceptor phase type and medium concentration), the stirring speed was chosen as process parameter. From the experimental results, it has been determined that the reaction was diffusion controlled. The transport efficiency of nitrate ions increased with increasing stirring speed. The membrane entrance and exit rate constants (k_1d, k_2m and k_2a respectively) were linearly dependent on the stirring speed ratios of 100 to 250 rpm. Coupled transport of nitrate ions through a liquid membrane in 85% n-hexane-15% tricloromethane as diluent, containing tetraoctyl ammonium chloride (TOACl) as a carrier was examined at various stirring speeds. Membrane entrance (k_1d) and exit rates (k_2m and k_2a) increase with increasing the stirring speeds. The diffusion of the nitrate ion-carrier complex through the narrow stagnant layers was found to be rate determining step. The membrane was stable during the transport experiments. There is no leakage of carrier or nitrate ion-carrier complex to both aqueous phases and also, no supplementary water penetration into the membrane. This favours interfacial reaction of nitrate ion and carrier.     

Rotating simplex method of optimization of physical parameters for higher production of extracellular pectinases in bioreactor

Rotating simplex method of optimization has been successfully used to determine the optimal conditions for extracellular pectinase production by Aspergillus niger in batch bioreactor. Maximum production of 1.132 U of polymethylgalacturonase, 1.313 U of polygalacturonase and 0.0091 U of pectinlyase was obtained at pH (controlled). 3.38; agitation rate, 483 rpm and aeration rate, 2.12 vvm. These conditions were found to be more suitable for pectinase production.     

Combined dissolved oxygen and pH control strategy to improve the fermentative production of l-isoleucine by Brevibacterium lactofermentum

The effect of both dissolved oxygen (DO) and pH on l-isoleucine production by batch culture of Brevibacterium lactofermentum was investigated. A two-stage agitation speed control strategy was developed, and the isoleucine production reached 23.3 g L⁻¹ in a relative short time (52 h), increased by 11.6% compared to the results obtained in the single agitation speed control process. In order to make sure whether the combination of DO and pH control can boost the production by a mutual effect, different control modes were conducted, based on the data obtained from the two-stage agitation speed control strategy and the analysis of kinetics parameters at different pH values. The results showed that the mode of combining two-stage DO with two-stage pH control strategy was the optimal for isoleucine production. The isoleucine production can reach 26.6 g L⁻¹ at 56 h, increased by 14.3% comparing to that obtained by the single two-stage DO control strategy.     

Studies of a pelleted growth form of Rhizopus nigricans as a biocatalyst for progesterone 11α-hydroxylation

The noncoagulative type of pellet formation can be induced in submerged cultivation of the filamentous fungus Rhizopus nigricans. The size and constitution of the hyphal agglomerates obtained varied with changes in inoculum size and agitation speed for given media composition and cultivation conditions. The physiological state of mycelium, used for a further process of biotransformation, was estimated by following the growth kinetics, pH value and substrate utilization during submerged cultivation. Namely, differences in pellet morphology and physiology affect the ability of R. nigricans to hydroxylate progesterone at the 11α position. A repeated batch procedure revealed the best maintenance of biotransformation capacity for pellets, obtained from the growth phase of cultivation at high agitation speed and with low inoculum size.     

Experimental behavior of a whole cell immobilized dextransucrase biocatalyst in batch and packed bed reactors

Dextransucrases from Leuconostoc mesenteroides have been used to produce a diversity of controlled structure oligosaccharides with potential industrial applications. This is the case of !(1̄) branched glucooligosaccharides produced by L. mesenteroides NRRL B-1299 dextransucrase. In order to establish an industrial scale process with the immobilized enzyme, a biocatalyst was produced by whole cell entrapment in alginate beads. The main physical and physicochemical properties of the biocatalyst were determined and the hydrodynamic behavior in a packed bed reactor studied. It was possible to produce spherical beads of 0.2 cm diameter containing the insoluble part of L. mesenteroides culture (cells and insoluble polymer) with an activity of 4 IU/g. Immobilization yield reached 93% with an effectiveness factor of 0.995 for particles of d_p < 0.2 cm. Due to the complexity of dextransucrase mechanism and kinetics, data obtained from initial rate measurements failed to describe the results obtained from the batch and continuous reactors. Therefore, apparent K_M and V_max data were used for the reactor modeling. It was found that under the conditions studied, the reaction rate was controlled by external mass transfer limitations.     

Enhanced riboflavin production by recombinant Bacillus subtilis RF1 through the optimization of agitation speed

Dissolved oxygen is one of the most important bioprocess parameters that could affect cell growth and product formation, and it is easy to control by changing agitation speed. In this work, the effects of agitation speed on the performance of riboflavin production by recombinant Bacillus subtilis RF1 was investigated in fed-batch fermentation. The lower agitation speed (600 rpm) was beneficial for cell growth and riboflavin biosynthesis in the initial phase of fermentation process. While, during the later phase, higher agitation speed (900 rpm) was favor for cell growth and riboflavin biosynthesis. Thus, a two-stage agitation speed control strategy was proposed based on kinetic analysis, in which the agitation speed was controlled at 600 rpm in the first 26 h and then switched to 900 rpm to maintain high μ for cell growth and high q _p for riboflavin production during the entire fermentation process. However, it was observed that a sharp increase of agitation speed resulted in an adverse effect on cell growth and riboflavin synthesis within a short time. To avoid this phenomenon, a multi-stage agitation speed control strategy was set up based on the two-stage control strategy, the maximum concentration of riboflavin reached 9.4 g l^?1 in 48 h with the yield of 0.051 g g^?1 by applying this strategy, which were 20.5 and 21.4 % over the best results controlled by constant agitation speeds.     

Reactor kinetics for submerged aerobic biofilms

Sclerotium rolfsii ATCC 15205 was cultivated in continuous culture (48 l reactor volume) for scleroglucan production. The maximum volumetric productivity (Q_Pvmax) amounted to 7.2 g/ld and was more than twice as high as in comparable batchwise cultivations. In addition, the relation between (a) volumetric productivity (Q_P [g/ld]) and product yield (Y_{Glucan/Glucose} [1]), (b) volumetric productivity and product quality (M_W [g/mol]), and (c) product quality and impeller tip speed (Nd [m/s]) was studied in continuous culture. It was found, that an increase in volumetric productivity led to a decline in product yield and product quality. Furthermore, an impeller tip speed of >0.7 m/s decreased the attainable product quality considerably. Based on these results, the impact of the operational setpoint of the process in terms of oxygen supply and reactor scale on the economics of scleroglucan production was discussed. In contrast to batchwise cultivation, scleroglucan production in continuous culture proved to be not feasible under non-aseptic conditions.     

Manganese peroxidase production by Bjerkandera sp. BOS55

The white-rot fungus Bjerkandera sp. BOS55 has been suggested as a good alternative for the production of ligninolytic enzymes, specially Manganese peroxidase (MnP), by its potential ability to degrade complex compounds. However, the application of this fungus requires the complete knowledge of the fermentation pattern in submerged cultures, conditions similar to those existing in industrial size reactors. For this purpose, the nutritional and environmental factors enabling high ligninolytic activity were studied. According to the results, under limitation and sufficiency of nitrogen, there is a threshold concentration for nitrogen from which MnP is produced. However, under nitrogen excess, the ligninolytic stage of the fungus was coincident with growth, with no apparent substrate limitation according to existing levels of carbon and nitrogen. Concerning carbon concentration, MnP synthesis took place independently of glucose concentration, this indicating that carbon limitation does not seem to be the triggering factor for MnP secretion. Other two environmental factors were studied: oxygenation and agitation, but no significant effect on MnP production was observed, a quite different aspect from the behaviour of other known fungi like Phanerochaete chrysosporium.     

Evaluation of effectiveness factor of immobilized enzymes using Runge-Kutta-Gill method: how to solve mathematical undetermination at particle center point?

The internal effectiveness factor of immobilized enzymes was analysed assuming the Michaelis-Menten kinetics to be valid. This factor can be analytically evaluated for cases where C_sdK_M or C_s€K_M. When this kinetic equation is used in its original form, the effectiveness factor can be evaluated only using a numerical technique, such as the Runge-Kutta-Gill method. This method presents a 0/0 type undetermination when applied to the center of a cylindrical or spherical catalyst particle. The undetermination was eliminated here by using L'Hôpital's rule and an expression valid only for the center of the particle was developed.     

Behaviour of pelagic larvae of four coral-reef fish species in the ocean and an atoll lagoon

In-situ behaviour of settlement-stage larvae (10-30 mm) of four coral-reef fishes - Acanthurus triostegus, Chromis viridis, Neoniphon argenteus and Ptereleotris sp. - differed between lagoon and ocean at Rangiroa Atoll, Tuamotu Islands, French Polynesia. Divers released 130 larvae individually in midwater, and recorded larval swimming speed, depth and direction. All species swam faster than average currents, and C. viridis swam faster in the lagoon than in the ocean. Vertical distribution behaviour of all species differed between ocean and lagoon, generally by larvae swimming deeper in the ocean. Nearly all individual larvae swam directionally. Within a species, distribution of average bearings of individual larvae was not directional, nor did it differ between ocean and lagoon. Larvae detected predators 3-6 m away, and stopped or changed depth or direction to avoid them. We therefore reject the 'simplifying assumptions' that reef-fish larvae are passive or that their behaviour is independent of location. Behavioural flexibility of settlement-stage reef-fish larvae has implications for dispersal, retention and population connectivity. This constitutes the first report of larval reef-fish behaviour in the open ocean. However, in the ocean, many larvae descended rapidly below safe diving depth, and adult remoras interfered, making in-situ study of larval behaviour difficult.     

An Optimisation of Asymmetry Evaluation of Molecules within the Folding-Unfolding Method

This article concerns the study of the folding-unfolding (Continuous Symmetry Measure, CSM) method of Avnir et al. (Zabrodsky, H.; Peleg, S.; Avnir, D. J. Am. Chem. Soc. 1992, 114, 7843) for quantitative evaluation of the asymmetry of molecular objects. It is shown that a series of modifications to the folding-unfolding method are expedient. An efficient solution for optimisation problems in the folding-unfolding method has been proposed. It allows a significant speed up of the calculations and provides better results. Differences in the behaviours of the original and optimised folding-unfolding methods for various molecular structures are investigated.     

A method for reconstructing three-dimensional dive profiles of marine mammals using geomagnetic intensity data: results from two lactating Weddell seals

The under-ice behavior of two free-ranging female Weddell seals (Leptonychotes weddellii) was studied using geomagnetic, acceleration and velocity sensors at Big Razorback Island in McMurdo Sound, Antarctica. The seals' body angle and posture were calculated from the acceleration data and the heading from the geomagnetic intensity data. Together with swim speed, the seals' three-dimensional underwater dive path, heading and even posture were reconstructed for each dive. Each instrument was deployed for 2 days, during which time these females made multiple, deep (₞ m) dives, with average maximum depths of 236ᆯ m (n=4) and 244끁 m (n=40). Each seal appeared to choose a particular heading on which to descend. These headings were significantly different between seals and bouts (Watson's U² test, P<0.05). These new instruments and methodologies are shown to provide valuable information on the fine-scale and complex movements of diving animals.