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.     

Effect of biomass concentration and mycelial morphology on fermentation broth rheology

The effect of biomass concentration and mycelial morphology on fungal fermentation broth rheological properties has been investigated. In previous work it had been shown that commonly used rheological parameters, such as the power law consistency and flow behavior indices, could be correlated successfully with the broth biomass concentration and clump morphological parameters of roughness and compactness. More recent work on a broader range of data showed a correlation between roughness and compactness; consequently, it was not correct to use both of these morphological variables simultaneously in rheological parameter correlations. Furthermore, earlier correlations were only made using clump morphological parameters, as clumps were found to be around 90% of the biomass in batch fermentations. In the present work it was found that the percentage of clumps fell to around 30% to 40% of a sample during the later stages of fed-batch fermentations. No clear relationship between the flow behavior index and biomass concentration was found, at least for those phases of the fermentation in which the viscosities were high enough for the rheology to be characterized by a disk turbine rheometer. The mean value of the flow behavior index was found to be 0.35 +/- 0.1 (standard deviation) throughout both batch and fed-batch fermentations, although some significant deviations from this value were observed early and very late in the fermentations. Correlations for the consistency index, measured using a disk turbine rheometer, were based on the biomass concentration and the mycelial size (represented by the mean projected area or the mean maximum dimension of all the mycelia). These correlations were reasonably successful for both fed-batch and batch fermentations. The correlation using the mean maximum dimension was preferred to that using the mean projected area, as the former is independent of magnification. The proposed correlation is: where K is the consistency index (Pa. s(n>)), C(m) is the biomass concentration as dry cell weight (g L(-1)), and D is the mean maximum dimension (microm). It should be noted that small changes in the exponent on the biomass concentration (alpha) may dramatically affect any predictions. Consequently, caution in the use of this correlation (and that based on mean projected area) is advocated, although its accuracy may be suitable for operational or design purposes.     

Construction and application a vane system in a rotational rheometer for determination of the rheological properties of <Emphasis Type="Italic">Monascus ruber</Emphasis> CCT 3802

The objectives of this work were the construction and adaptation of a vane system in a rotational rheometer; calibration of vane system using a mineral oil, and determination of rheological properties of the broth fermentation of Monascus ruber CCT 3802 at high cell density. Batch fermentation was carried out with glucose as the sole carbon source in a Bioflo III bioreactor. The consistency index (K) and flow behavior index (n) of the broth fermentation of M. ruber were characterized at different biomass concentrations and were adequately described by a power law model. The K and n values were significantly affected by biomass concentrations. K values ranged from 0.375 to 11.002 Pa s ⁿ when evaluated at biomass concentrations from 25.67 to 63.20 g L⁻¹. The pseudoplastic behavior was confirmed by values of n that ranged between 0.157 and 0.254. Simple empirical correlations have been proposed to quantify the dependence of the power law terms on fungal biomass concentration.     

Multivariate models for prediction of rheological characteristics of filamentous fermentation broth from the size distribution

The main purpose of this article is to demonstrate that principal component analysis (PCA) and partial least squares regression (PLSR) can be used to extract information from particle size distribution data and predict rheological properties. Samples from commercially relevant Aspergillus oryzae fermentations conducted in 550 L pilot scale tanks were characterized with respect to particle size distribution, biomass concentration, and rheological properties. The rheological properties were described using the Herschel-Bulkley model. Estimation of all three parameters in the Herschel-Bulkley model (yield stress (tau(y)), consistency index (K), and flow behavior index (n)) resulted in a large standard deviation of the parameter estimates. The flow behavior index was not found to be correlated with any of the other measured variables and previous studies have suggested a constant value of the flow behavior index in filamentous fermentations. It was therefore chosen to fix this parameter to the average value thereby decreasing the standard deviation of the estimates of the remaining rheological parameters significantly. Using a PLSR model, a reasonable prediction of apparent viscosity (micro(app)), yield stress (tau(y)), and consistency index (K), could be made from the size distributions, biomass concentration, and process information. This provides a predictive method with a high predictive power for the rheology of fermentation broth, and with the advantages over previous models that tau(y) and K can be predicted as well as micro(app). Validation on an independent test set yielded a root mean square error of 1.21 Pa for tau(y), 0.209 Pa s(n) for K, and 0.0288 Pa s for micro(app), corresponding to R(2) = 0.95, R(2) = 0.94, and R(2) = 0.95 respectively.     

Comparative study of the fermentation of D-glucose/D-xylose mixtures with Pachysolen tannophilus and Candida shehatae

We have performed a comparative analysis of the fermentation of the solutions of the mixtures of D-glucose and D-xylose with the yeasts Pachysolen tannophilus (ATCC 32691) and Candida shehatae (ATCC 34887), with the aim of producing bioethanol. All the experiments were performed in a batch bioreactor, with a constant aeration level, temperature of 30v°C, and a culture medium with an initial pH of 4.5. For both yeasts, the comparison was established on the basis of the following parameters: maximum specific growth rate, biomass productivity, specific rate of substrate consumption (q_s) and of ethanol production (q_E), and overall ethanol and xylitol yields. For the calculation of the specific rates of substrate consumption and ethanol production, differential and integral methods were applied to the kinetic data. From the experimental results, it is deduced that both Candida and Pachysolen sequentially consume the two substrates, first D-glucose and then D-xylose. In both yeasts, the specific substrate-consumption rate diminished over each culture. The values q_s and q_E proved higher in Candida, although the higher ethanol yield was of the same order for both yeasts, close to 0.4 kg kg^у.     

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.     

Process development of continuous hydrogen production by Enterobacter aerogenes in a packed column reactor

Hydrogen bioproduction from agro-industrial residues by Enterobacter aerogenes in a continuous packed column has been investigated and a complete reactor characterization is presented. Experimental runs carried out at different residence time, liable of interest for industrial application, showed hydrogen yields ranging from 1.36 to 3.02 mmol_H2mmol^у_glucose or, in other words, from 37.5% to 75% of the theoretical hydrogen yield. A simple kinetic model of cell growth, validated by experimental results and allowing the prediction of biomass concentration profile along the reactor and the optimization of superficial velocity, is suggested. By applying the developed approach to the selected operative conditions, the identification of the optimum superficial velocity v_0,opt of about 2.2 cm h^у corresponding to the maximum hydrogen evolution rate H£_2g,max, was performed.     

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。     

Mixing time in airlift reactors during citric acid fermentation

Citric acid fermentations using strain Aspergillus niger were carried out in three airlift reactors of volumes of 10, 35 and 200 liters. Mixing times were measured at the beginning and the end of fermentation. It has been shown that the mixing time at the end of fermentation is approximately equal to the duration of one circulation period. This was due to the flow regime transition caused by the change of rheological properties of the mould broth during fermentation.     

In situ oxygen microelectrode measurements of bottom-ice algal production in McMurdo Sound, Antarctica

In-situ estimates of fast-ice algal productivity at Cape Evans, McMurdo Sound, in 1999 were lower than at the same site in previous years. Under-ice irradiance was between 0 and 8 µmol photons m^-2 s^-1; the ice was between 1.9 and 2.0 m thick and the algal biomass averaged 150 mg chl a m^-2, although values as high as 378 mg chl a m^-2 were recorded. Production on 11 and 12 November was between 0.053 and 1.474 mg C m^-2 h^-1. When the data from 11 November were fitted to a hyperbolic tangent function, a multilinear regression gave estimates for P_max of 0.571 nmol O₂ cm^-2 s^-1, an ! of 0.167 nmol O₂ cm^-2 s^-1 µmol^-1 photons m^-2 s^-1 and an E_k of 3.419 µmol photons m^-2 s^-1. A P_max of 2.674 nmol O₂ cm^-2 s^-1, an ! of 0.275 nmol O₂ cm^-2 s^-1 µmol^-1 photons m^-2 s^-1, r of 0.305 nmol O₂ cm^-2 s^-1 and an E_k of 9.724 µmol^-1 photons m^-2 s^-1 were estimated from the 12 November data. The sea-ice algal community was principally comprised of Nitzschia stellata, Entomoneis kjellmanii and Berkeleya adeliensis. Other taxa present included N. lecointei, Fragilariopsis spp., Navicula glaciei, Pleurosigma spp. and Amphora spp. Variations in the method for estimating the thickness of the diffusive boundary layer were not found to significantly affect the measurements of oxygen flux. However, the inability to accurately measure fine-scale variations in biomass is thought to contribute to the scatter of the P versus E data.     

Effect of shear on morphology and erythromycin production in Saccharopolyspora erythraea fermentations

A complex medium was used to investigate the effects of shear on the S. erythraea fermentation at 7-l scale. Maximum biomass was 11.1 - 0.5 g l^у at 1250 rpm (tip speed = 4.45 ms^у), whereas it was 12.7 - 0.2 g l^у at 350 rpm (tip speed = 1.07 ms^у). Specific erythromycin production was not stirrer speed dependent in the range of 350 to 1000 rpm and decreased by 10% at stirrer speed of 1250 rpm. Morphological measurements using image analysis showed that the major axis of the mycelia (both freely dispersed and clumps) decreased after the end of the rapid growth phase to a relatively constant value (equilibrium size) dependent on the stirrer speed. The mechanical properties of the cell wall were examined by disruption of fermentation broth in homogeniser and it was shown that mechanical strength of the cell wall increased in a large extent during deceleration phase.     

Influence of climate-driven shifts in biomass allocation on water transport and storage in ponderosa pine

Conifers decrease the amount of biomass apportioned to leaves relative to sapwood in response to increasing atmospheric evaporative demand. We determined how these climate-driven shifts in allocation affect the aboveground water relations of ponderosa pine growing in contrasting arid (desert) and humid (montane) climates. To support higher transpiration rates, a low leaf:sapwood area ratio (A_L/A_S) in desert versus montane trees could increase leaf-specific hydraulic conductance (K_L). Alternatively, a high sapwood volume:leaf area ratio in the desert environment may increase the contribution of stored water to transpiration. Transpiration and hydraulic conductance were determined by measuring sap flow (J_S) and shoot water potential during the summer (June-July) and fall (August-September). The daily contribution of stored water to transpiration was determined using the lag between the beginning of transpiration from the crown at sunrise and J_S. In the summer, mean maximum J_S was 31.80LJ.74 and 24.34Dž.05 g m^-2 s^-1 for desert and montane trees (a 30.6% difference), respectively. In the fall, J_S was 25.33NJ.52 and 16.36dž.64 g m^-2 s^-1 in desert and montane trees (a 54.8% difference), respectively. J_S was significantly higher in desert relative to montane trees during summer and fall (P<0.05). Predawn and midday shoot water potential and sapwood relative water content did not differ between environments. Desert trees had a 129% higher K_L than montane trees in the summer (2.41᎒^-5 versus 1.05᎒^-5 kg m^-2 s^-1 MPa^-1, P<0.001) and a 162% higher K_L in the fall (1.97᎒^-5 versus 0.75᎒^-5 kg m^-2 s^-1 MPa^-1, P<0.001). Canopy conductance decreased with D in all trees at all measurement periods (P<0.05). Maximum g_C was 3.91 times higher in desert relative to montane trees averaged over the summer and fall. Water storage capacity accounted for 11 kg (11%) and 10.6 kg (17%) of daily transpiration in the summer and fall, respectively, and did not differ between desert and montane trees. By preventing xylem tensions from reaching levels that cause xylem cavitation, high K_L in desert ponderosa pine may facilitate its avoidance. Thus, the primary benefit of low leaf:sapwood allocation in progressively arid environments is to increase K_L and not to increase the contribution of stored water to transpiration.     

Physiological basis of spacing effects on tree growth and form in Eucalyptus globulus

We examine the effects of spacing and layout on the growth and form of 3- to 4-year-old Eucalyptus globulus in a farm forestry context. Four planting layouts were chosen. These represented the range commonly in use in farm forestry: block plantings (2Ǹ m), triple rows (2Ǹ m) at 10-m intervals, single rows (2᎒ m) and isolated trees (10᎒ m). The physiological significance of key results is interpreted in terms of changes in the parameters of a simple plantation growth model. Under conditions where levels of direct light are high, for example during summer, block-planted trees intercepted only 38% of the light intercepted by isolated trees. On a stand basis, however, the combination of incident radiation and ground coverage declined with lower stand densities. While stand leaf area index declined from around 6 to 1 with increased spacing, individual tree leaf areas rose from around 50 m² in block plantings to 150 m² in isolated trees. The proportion of above-ground biomass found in stems declined with increasing spacing as the mass in foliage and branches increased. Stems accounted for 65% of above-ground biomass in block-planted trees but only 35% in isolated trees. The contributions of leaves and branches correspondingly rose from 19% to 35% and from 16% to 29%, respectively. Changes in biomass distribution were accompanied by increasing branch number, branch thickness, flatter branch angles and the longer retention of lower branches with greater spacing. These changes have implications for the merchantability of the timber. The efficiency of above-ground radiation conversion was constant at 0.67 g MJ^-1 irrespective of spacing. We estimated that foliar maintenance respiration (R_m) accounted for about 90% of above-ground R_m. On a stand basis R_m costs block plantings 23.90 t DM ha^-1 year^-1 (50% annual above-ground photosynthetic production) compared with 6.22 t DM ha^-1 year^-1 (40% annual above-ground photosynthetic production) in stands of isolated trees.     

Effect of deletion of chitin synthase genes on mycelial morphology and culture viscosity in Aspergillus oryzae

The objective of this study was to quantify the effect of disrupting two chitin synthases, chsB and csmA, on the morphology and rheology during batch cultivation of Aspergillus oryzae. The rheological properties were characterized in batch cultivations at different biomass concentrations (from 3.4-22.5 g kg(-1) biomass) and the power-law model adequately described the rheological properties. In the cultivations there were pellets, clumps, and freely dispersed hyphal elements. The different morphological fractions were quantified using image analysis. The apparent viscosity of the fermentation broth was significantly affected by the biomass concentration, the morphology, and also by pH. The chsB disruption strain had lower consistency index K values for all biomass concentrations investigated, which is a desirable trait for industrial Aspergillus fermentations.     

自絮凝酵母SPSC01悬浮液的流变行为

用旋转黏度计测定了自絮凝颗粒酵母悬浮液的流变特性,并考察了其流变特性的影响因素,如菌体生物量、葡萄糖质量浓度、温度等。结果表明：自絮凝颗粒酵母悬浮液呈假塑性非牛顿流体,其流变特性服从幂律指数模型,随着菌体浓度的增大,稠度系数增大,流动行为指数减小;絮凝悬浮液的表观黏度随着糖浓度的增加有所增加,同一生物量下稠度系数k随着糖浓度的增加而增加,流动行为指数n随着糖浓度的增加变化很小,悬浮液的表观黏度随着温度的升高而降低;相同生物量下的流变指数随温度的升高而升高,而稠度系数随温度升高有所下降。     

Rheological properties of chromosomal and plasmid DNA during alkaline lysis reaction

The experimental apparatus for the simultaneous L-lactic acid fermentation by Rhizopus oryzae immobilized in calcium alginate beads and product separation process was set up in which a three-phase fluidized-bed bioreactor was used as a fermentor and an external electrodialyzer as a separator, and a pump was applied to recycle the fermentation broth between the bioreactor and the separator. The L-lactic acid produced in the fermentor was separated in the separator, product inhibition was alleviated without any addition of alkali or alkali salts and the product purification process could be simplified. The specific productivity and the yield in electrodialysis fermentation (ED-F) process operated in continuous feeding mode were almost the same as that in CaCO₃-buffered fermentation process. A mathematical model of L-lactic acid production in ED-F process was also suggested, in which the model equations for the bioreactor and the electrodialyzer were combined to describe the simultaneous fermentation and product separation. The model predictions were in good agreement with the experimental data.     

Modelling mixing parameters in concentric-tube airlift bioreactors

The mixing behaviour of the liquid phase in concentric-tube airlift bioreactors of different scale (RIMP: V_L=0.070 m³; RIS-1: V_L=2.50 m³; RIS-2: V_L=5.20 m³) in terms of mixing time was investigated. This mixing parameter was determined from the output curves to an initial Dirac pulse, using the classical tracer response technique, and analyzed in relation to process and geometrical parameters, such as: gas superficial velocity, x_SGR; top clearance, h_S; bottom clearance, h_B, and ratio of the resistances at downcomer entrance, A_d/A_R. A correlation between the mixing time and the specified operating and geometrical parameters was developed, which was particularized for two flow regimes: bubbly and transition (x_SGRА.08 m/s) and churn turbulent flow (x_SGR> 0.08 m/s) respectively. The correlation was applied in bioreactors of different scale with a maximum error of ᆲ%.     

Viable bacterial biomass and functional diversity in fresh and marine waters in the Canadian Arctic

Bacterial biomass and functional diversity in four marine and four freshwater samples, collected from Resolute Bay, Nunavut, Canada, were studied using fluorescent nucleic-acid staining and sole-carbon-source utilization. Viable microbial counts using the LIVE/DEAD BacLight Viability Kit estimated viable marine bacterial numbers from 0.7 to 1.8᎒⁶ cells/l, which were lower than viable bacterial numbers in freshwater samples (2.1-9.9᎒⁶ cells/l) (RCBD-ANOVA). Calculations of the Shannon-Wiener diversity index and average well colour development were based on substrate utilization in ECO-Biolog plates incubated at 4°C and 20°C for 38 and 24 days, respectively. The Shannon-Wiener diversity of the marine water samples was significantly greater ( x _H'=2.40ǂ.08, P <0.005; RCBD-ANOVA) than that of freshwater samples ( x _H'=1.20ǂ.00, P <0.005; RCBD-ANOVA). Differences in microbial diversity between fresh and marine water samples at 4°C ( x _4°C =2.01) and 20°C (x_20°C =2.31) were also detected by RCBD-ANOVA analysis. Interactions between water type and incubation temperature were not significant ( F =1.926, F _c=5.12). Principal component analysis revealed differences in metabolic substrate utilization patterns and, consequently, the microbial diversity between water types and samples.     

Joint aerobic biodegradation of wastewater from table olive manufacturing industries and urban wastewater

Wastewater generated in the elaboration of table olives has been treated using activated sludge from a municipal wastewater plant after adequate acclimation. To avoid bactericide properties of some chemical structures present in this type of effluents, synthetic urban wastewater has been used to dilute the original wastewater. The main parameters affecting efficiency of biological processes have been studied. Thus, initial biomass concentration, temperature up to 303 K (upper working temperature limit = 313 K) and initial substrate concentration exerted a positive influence on COD degradation rate. The optimum pH was found to be around 7, experiencing a slight inhibition on cell activity at pH 4. Under the experimental conditions investigated other parameters like polyphenol content, absorbance at 254 nm and total organic carbon were also reduced to some extent. Only nitrates amount was increased after the biological process took place. A kinetic model based on Monod equation was proposed and applied to experimental results. The maximum specific growth rate was calculated by means of the aforementioned kinetic model. The value of this parameter as a function of temperature was fitted to an Arrhenius expression, w_max = 9.43 2 10¹⁰ exp(72021/RT) h^у (R in J mol^у K^у283 K < T < 303 K, pH , 7-10).