Crossflow filtration of yeast broth cultivated in molasses

A broth of yeast cells cultivated in molasses was crossfiltered with a thin-channel module. The permeation flux gradually decreased at a constant cell concentration. The flux was much lower than that obtained for yeast broth cultivated in yeast extract, polypeptone, and dextrose (YPD) medium during the filtration. The flux did not depend on the membrane pore size (0.45 to 5 mum). The steady-state flux was one-twentieth that calculated for a cake filtration mode from the amount of cake per unit filtration area and the specific resistance of the cake measured in a dead-end filtration apparatus. The lower flux was due to small particles (most of which were less than 1 mum in diameter) in the molasses. The mehanism of crossflow filtration of broths of yeast cells cultivated in molasses was clarified by analysis of the change in flux with time and observations with scanning electron microscopy. At the initial stage of crossflow filtration the yeast cells and particles from the molasses were deposited on the membrane to form the molasses were deposited on the membrane to form a cake in a similar way to dead-end filtration. After the deposition of cells onto the membrane ceased, the fine particles from molasses formed a thin layer, which had higher resistance than the cake formed next to the membrane. The backwashing method was effective to increase the flux. The flux increased low when the pore size was 0.45 to 0.08 mum, but using larger pores of 3 to 5 mum it returned almost to the bases line. (c) 1994 John Wiley & Sons, Inc.     

Factors affecting the performance of crossflow filtration of yeast cell suspension

Factors affecting the performance of crossflow filtration were investigated with a thin-channel module and yeast cells. In crossflow filtration of Saccharomyces cerevisiae cells cultivated with YPD medium (Yeast extract, polypeptone, and dextrose) and suspended in saline, a steady state was attained within several minutes when the cell concentration was low and the circulation flow rate was high. The steady-state flux and the change in flux during the initial unsteady state were explained well by conventional filtration theory, with the amount of cake deposited and the mean specific resistance to the cake measured in a dead-end filtration apparatus used in calculation. When the circulation flow rate was lower than a critical value, a part of the channel of the crossflow filtration module was plugged with cell cake, and thus the steady-state flux was low. In crossflow filtration of suspensions of commercially available baker's yeast, the flux gradually decreased, and the flux after 8 h of filtration was lower than the value calculated by filtration theory. Fine particles contaminating the baker's yeast was responsible for the decrease. A similar phenomenon was responsible for the decrease. A similar phenomenon was observed in crossflow filtration of a broth of S. cerevisiae cells cultivated in molasses medium, which also contains such particles, had no effect of the permeation flux during crossflow filtration. (c) 1993 John Wiley & Sons, Inc.     

Broth conditions determining specific cake resistance during microfiltration of Bacillus subtilis

The effects of broth pH, pressure, temperature, and fermentation medium on specific cake resistance were studied for dead-end microfiltration of Bacillus subtilis. Decreases in pH and transmembrane pressure decreased the specific cake resistance for cells grown in both complex and defined media. With the complex medium, the reduction in resistance with temperature decrease did not offset the flux decrease caused by the increase in viscosity. The greatest decrease in specific cake resistance occurred with adjustment of pH to 7.5 for cells grown in defined medium. For those cells the change in pH resulted in aggregation leading to a large increase in flux.     

Membrane fouling in crossflow filtration: Implications for measurement of the steady state specific cake resistance

Summary When the crossflow specific cake resistance is determined from measurements of the steady state cake mass and filtrate flux, an apparent value is obtained which is equal to the true value only if membrane fouling is negligible. The apparent specific resistance can increase with increasing crossflow velocity and pure-water membrane resistance, and exhibit a minimum with respect to transmembrane pressure.     

Anti-GA3-Me Antiserum with High Specificity toward the 13-Hydroxyl Group of C19-Gibberellins

Membrane clarification of green tea extract was studied as a treatment to reduce sediments in packaged drinks and as a pretreatment for concentration processes. The flux and variation of components were examined in dead-end and crossflow filtration with several types of membranes. In dead-end ultrafiltration, the flux reduction rate was small, although the initial flux was similar to the final flux in microfiltration. Prefiltration was effective in decreasing the reduction rate of flux. As the pore size of microfiltration membranes became smaller, the dry weight decreased gradually and the optical transmission at 660 nm increased. By ultrafiltration, 30–50% pectin, 3–11% catechins and, 7–20% caffeine were rejected. Crossflow filtration was effective in keeping the flux high. The ultrafiltration spiral membrane (pore size: 0.008 μm) was selected for repeated batch clarification of prefiltered green tea crude extract and showed reproducible performance.     

New insights into membrane fouling in a submerged anaerobic membrane bioreactor based on characterization of cake sludge and bulk sludge

A laboratory-scale submerged anaerobic membrane bioreactor (SAnMBR) treating thermomechanical pulping whitewater was operated for over 7 months to investigate and compare the characteristics of cake sludge and bulk sludge during stable state operation period. Serial analysis showed that cake sludge had a smaller particle size distribution (PSD), much higher specific filtration resistance (1.34 × 10¹⁴ m/kg), 1.5 times higher bound EPS and significantly different microbial community as compared with bulk sludge. Further analysis indicated that small flocs, bound EPS and inorganic materials play important role in cake formation process. The formed cake layer was found to have a heterogeneous structure. The results obtained in this study indicated that cake formation process started from attachment of small flocs and/or specific bacterial clusters which colonize the surface of the membrane and provide enhanced conditions that allow for cake formation to progress.     

Improvement of performance for cross-flow membrane filtration of pullulan broth

To improve the performance of cross-flow membrane filtration of pullulan broth from Aureobasidium pullulans, the effect of the cultivation conditions was examined. In particular, the sucrose concentration in the medium was changed over a wide range. By decreasing the sucrose concentration the distribution of morphology of the microbial cells in the broth changed; the yeast-like form became predominant and, as a result, the specific resistance of the microbial cake was lowered. When the broth was fermented with a sucrose concentration of 2.5% or lower, the filtration characteristics were greatly improved by periodic closure of permeation during cross-flow filtration.On leave from Hayashibara Co., Ltd., Amase-minamimachi, Okayama 700, Japan Correspondence to: K. Nakanishi     

Modeling the influence of slurry concentration on Saccharomyces cerevisiae cake porosity and resistance during microfiltration

Filtration of an isotonic suspension of baker's yeast through a 0.45‐μm membrane was studied at two different pressures, 40 and 80 kPa, for yeast concentrations ranging from 0.14 to 51 kg/m³ (dry weight). For a yeast volume fraction above 0.06 (～21.8 kg/m³), the porosity of the yeast cake is less dependent on the suspension concentration. For highly diluted suspensions, the specific cake resistance approaches a minimum that depends on the filtration pressure. Correlation functions of cake porosity and specific cake resistance were obtained for the concentration range investigated showing that the Kozeny–Carman coefficient increases when the applied pressure increases. Both filtration pressure and slurry concentration can be process controlled. In the range of moderate yeast concentration, the filtrate flux may be increased by manipulating the filtration pressure and the slurry concentration, thereby improving the overall process efficiency. The complex behavior of yeast cakes at high slurry concentration can be described by a conventional model as long as part of yeast cells are assumed to form aggregates, which behave as single bigger particles. The aggregation effect may be accounted for using a binary mixture model. © 2012 American Institute of Chemical Engineers Biotechnol. Prog., 2012     

A new sensor,the “filtration probe,” for quantitative characterization of the penicillin fermentation. II. The monitor of mycelial growth

Biomass concentration during penicillin production can be estimated rapidly and with reasonable accuracy using the “filtration probe.” The basis for the measurement is the volume of the filter cake which, in contrast to the conventional “packed-cell volume” measured by centrifugation, is only moderately affected by the morphology of the mycelia. The influence of the mycelial morphology on the specific filter cake volume [ υ (cm³ cake/g dry cells)] can additionally, to a large extent, be predicted from the (specific) filtration resistance of the broth. During the rapid (exponential) growth period, the specific cake volume is, however, more variable and typically exhibits a transient maximum value. The presence of such a maximum can be explained by a simple model for exponential growth of single mycelial particles. this model is based upon conventional kinetics for hyphae elongation and branching and applies well to experimental data (filtration behavior as well as microscopic studies) provided hyphae fragmentation is negligible (i.e., at high growth rates, μ ? μ_max).     

Characteristics of cross-flow filtration of pullulan broth

Cross-flow filtration of culture broth from Aureobasidium pullulans, which elaborates pullulan, was done with a thin channel-type module and microfiltration membranes made of different materials and with different pore sizes. Various factors affecting the results of the filtration were studied. The specific resistance of the microbial cake was found to be higher than that of bakers yeast, the cells of which are about the same size as an A. pullulans cell, and resistance increased with cultivation time. The flux and transmission of pullulan through the membrane decreased with cultivation time as the specific resistance increased. The flux and transmission ] of pullulan depended on the structure and pore size of the membrane and also on the pH of the broth. With a polysulphone membrane with a nominal pore size of 2.0 m, transmission was nearly 100% with negligible leakage of cells and the flux was high when the pH of the broth was adjusted to 2.0.On leave from Hayashibara Co., Ltd., Amase-minamimachi, Okayama 700 Japan Correspondence to: K. Nakanishi     

Prediction of membrane fouling in MBR systems using empirically estimated specific cake resistance

The focus of this study was to empirically estimate the specific cake resistance (SCR) by the variation in shear intensity (G) in four laboratory-scale MBRs. The control reactor (MBR₀) was operated with aeration only while other MBRs (MBR₁₅₀, MBR₃₀₀ and MBR₄₅₀) were operated with aeration and mechanical mixing intensities of 150, 300 and 450 rpm, respectively. It was found that the SCR was strongly correlated (R² = 0.99) with the fouling rates in the MBRs. Moreover, the contribution of cake resistance (R_c) to the total hydraulic resistance (R_t) was predominant compared to the irreversible fouling resistance (R_f). On this basis, the cake filtration model was selected as a predictive tool for membrane fouling. This model was modified by replacing the SCR with its empirical shear intensity relationship. The modified model can predict the fouling rate for a given shear intensity (G) within 80 and 250 s⁻¹ in a MBR system.     

Transient and stationary operating conditions on performance of lactic acid bacteria crossflow microfiltration

A filtration rig equipped with a tubular alumina membrane was used to study the performance of crossflow microfiltration of Lactobacillus helveticus. Experiments were performed at constant permeation flux. High cell concentrations and fast transient conditions to the stationary J adversely affected permeability. Membrane fouling was due to a fast irreversible layer formation and to a reversible cell cake. This microbial deposit characteristics were dependent on the ratio permeation flux/wall shear stress, J/tau(w). Fouling was faster and more severe when J/tau(w) was greater than a critical value of 1.15 L(-1) . h(-1) . m(-2) . Pa(-1). The disordered structure of this cell cake seemed to lead to a macromolecule deposit between the cells which adversely affected the membrane permeability. (c) 1996 John Wiley & Sons, Inc.     

In situ filtration of Anchusa officinalis culture in a cell-retention stirred tank bioreactor

Summary The effect of agitation and aeration on filtration of Anchusa officinalis culture in a stirred tank bioreactor integrated with an internal filter unit was investigated. Increases in suction head of the pump that drove the filtration process were measured at impeller speeds of 100 and 200 rpm. Surprisingly, suction head attained at 200 rpm was about 40% higher than at 100 rpm. Direct observation of the cake deposition process in the reactor using a dilute cell suspension revealed that the filter cake formed at 100 rpm was thicker, but less compact. Aeration at 0.4 vvm was shown to have little effect on the filtration rate, since the bulk fluid flow was dominated by the impeller hydrodynamics. The initial flux can be recovered by filter backwashing with compressed air at a flow rate of 0.6 vvm for a duration of 5 minutes.     

Tc(VII) reduction and accumulation by immobilized cells of Escherichia coli

Resting cells of Escherichia coli, immobilized in a flow-through bioreactor, coupled the oxidation of formate or hydrogen to Tc(VII) reduction and removal from solution. Cells, pregrown anaerobically in a hollow-fiber membrane bioreactor, were challenged with 50 muM Tc(VII) in a carrier solution of phosphate-buffered saline. The radionuclide accumulated within the membrane component of the reactor, corresponding to the localization of the cells. Negligible Tc removal was noted in a reactor containing a mutant deficient in active Tc(VII) reductase, when supplied with formate as an electron donor. Formate or hydrogen was supplied as the electron donor for Tc(VII) reduction to cells immobilized in reactors operated in transverse (crossflow) and direct (dead-end filtration) modes, respectively. Flow-rate activity relationships were used to compare the performance of the reactors. A flow rate of 2.4 mL h(-1) supported the removal of 50% of the Tc from solution in a reactor operated in transverse mode with formate as an electron donor. In contrast, a flow rate of 0.7 mL h(-1), supported comparable Tc removal when hydrogen was introduced to a reactor operated in direct mode. The reduced reactor efficiency, when hydrogen was used as an electron donor, could be attributed, in part, to poor delivery of the gas to the cells. The biocatalyst was highly stable in the reactor; no loss in activity was noted over 200 h of continuous use. (c) 1997 John Wiley & Sons Inc. Biotechnol Bioeng 55: 505-510, 1997.     

Baleen Hydrodynamics and Morphology of Cross-Flow Filtration in Balaenid Whale Suspension Feeding

The traditional view of mysticete feeding involves static baleen directly sieving particles from seawater using a simple, dead-end flow-through filtration mechanism. Flow tank experiments on bowhead (Balaena mysticetus) baleen indicate the long-standing model of dead-end filtration, at least in balaenid (bowhead and right) whales, is not merely simplistic but wrong. To recreate continuous intraoral flow, sections of baleen were tested in a flume through which water and buoyant particles circulated with variable flow velocity. Kinematic sequences were analyzed to investigate movement and capture of particles by baleen plates and fringes. Results indicate that very few particles flow directly through the baleen rack; instead much water flows anteroposteriorly along the interior (lingual) side of the rack, allowing items to be carried posteriorly and accumulate at the posterior of the mouth where they might readily be swallowed. Since water flows mainly parallel to rather than directly through the filter, the cross-flow mechanism significantly reduces entrapment and tangling of minute items in baleen fringes, obviating the need to clean the filter. The absence of copepods or other prey found trapped in the baleen of necropsied right and bowhead whales supports this hypothesis. Reduced through-baleen flow was observed with and without boundaries modeling the tongue and lips, indicating that baleen itself is the main if not sole agent of crossflow. Preliminary investigation of baleen from balaenopterid whales that use intermittent filter feeding suggests that although the biomechanics and hydrodynamics of oral flow differ, cross-flow filtration may occur to some degree in all mysticetes.     

Comparison of different options for harvest of a therapeutic protein product from high cell density yeast fermentation broth

Recovery of therapeutic protein from high cell density yeast fermentations at commercial scale is a challenging task. In this study, we investigate and compare three different harvest approaches, namely centrifugation followed by depth filtration, centrifugation followed by filter-aid enhanced depth filtration, and microfiltration. This is achieved by presenting a case study involving recovery of a therapeutic protein from Pichia pastoris fermentation broth. The focus of this study is on performance of the depth filtration and the microfiltration steps. The experimental data has been fitted to the conventional models for cake filtration to evaluate specific cake resistance and cake compressibility. In the case of microfiltration, the experimental data agrees well with flux predicted by shear induced diffusion model. It is shown that, under optimal conditions, all three options can deliver the desired product recovery ( >80%), harvest time ( <15 h including sequential concentration/diafiltration step), and clarification ( <6 NTU). However, the three options differ in terms of process development time required, capital cost, consumable cost, ease of scale-ability and process robustness. It is recommended that these be kept under consideration when making a final decision on a harvesting approach.     

Effect of the degree of dilution of the antibiotic fermentation broths on the filtration indices]

Dilution of the fermentation broths with water before the mycelium separation lowered the specific cake resistance. The effect of the dilution on the filtration duration was different and depended on the fermentation broth type. As for the erythromycin fermentation broth, the time of its filtration decreased after the dilution, while the filtration time of the fermentation broths of the other 2 antibiotic-producing organisms increased after the dilution.     

Yeast suspension filtration: flux enhancement using an upward gas/liquid slug flow-application to continuous alcoholic fermentation with cell recycle

This study deals with the use of an upward gas/liquid slug flow to reduce tubular mineral membrane fouling. The injection of air into the feedstream is designed to create hydrodynamic conditions that destabilize the cake layer over the membrane surface inside the filtration module complex. Experimental study was carried out by filtering a biological suspension (yeast) through different tubular mineral membranes. The effects of operating parameters, including the nature of the membrane, liquid and gas flowrates, and transmembrane pressure, were examined. When external fouling was the main limiting phenomenon, flux enhancements of a factor of three could be achieved with gas sparging compared with single liquid phase crossflow filtration. The economic benefits of this unsteady technique have also been examined. To investigate the possibility of long-term operation of the two-phase flow principle, dense cell perfusion cultures of Saccharomyces cerevisiae were carried out in a fermentor coupled with an ultrafiltration module. The air injection allowed a high and stable flux to be maintained over 100 h of fermentation, with a final cell concentration of 150 g dry weight/L. At equal biomass level, a twofold gain in flux could be attained compared with classical steady crossflow filtration at half the cost.     

Filtration of a bacterial fermentation broth: harvest conditions effects on cake hydraulic resistance

The hydraulic resistance of cakes formed during the ultrafiltration of Streptomyces pristinaespiralis broths has been investigated for different harvesting conditions. S. pristinaespiralis broth was harvested after the point of microorganism activity declines (0-h aged broth) and afterwards held for different durations of up to 16 h (16 aged broths). Aging behavior occurring between the end of microorganism activity and harvest was compared for different acidification procedures (pH) and the mechanisms for which the hydraulic resistance of the cake is affected by aging have been investigated. For broths harvested under conditions where the acidification is fixed at pH 2 or 3, hydraulic resistance associated with cake build-up is directly determined by the interactions between the cells. Holding broths beyond 5 h contributes to a release of a soluble component from the cell surface. Enhanced cell surface interactions then turn the cake structure into a more open one and reduce the specific hydraulic resistance. For broths harvested under conditions where the acidification is fixed at pH 4, hydraulic resistance associated with cake build-up is both determined by cell interactions and cell morphology. The cause of the increase in specific hydraulic resistance with aging is due to the binding of a soluble component released by the microorganisms, which decreases the cell surface interactions.     

Growth behaviors of bacteria in biofouling cake layer in a dead-end microfiltration system

The growth behaviors of three bacterial species, i.e. Escherichia coli, Pseudomonas putida and Aquabaculum hongkongensis, in biofouling cake layer (attached form) were investigated using an unstirred dead-end continuous microfiltration system, and were compared with those in suspended form. Results showed that all the three bacteria had larger average growth rates in suspended form than in attached form under high substrates levels. Under oligotrophic conditions, the average growth rates in the attached form were faster than those in the suspended form, especially for A. hongkongensis. The growth behaviors analysis presented the same results due to all the tested bacteria had higher maximum growth rate and saturation constant in suspended form than attached form, indicating the dominant growth mode would be shifted from attached form to suspended form with substrate concentration increase. Finally, total filtration resistance determined in the experiments increased significantly with the bacterial growth in filtration system.