Quantitative relationships between left ventricular ejection and wall thickening and geometry.

The quantitative relationships that exist between left ventricular (LV) wall shortening, wall thickening, and geometry during LV ejection are not well defined. We used a mathematical model to measure these parameters in 40 patients with various LV geometries studied by echocardiography. As opposed to wall shortening, the percent contribution of wall thickening to LV ejection (% delta Vh) was 25 +/- 2% in normal subjects; in all the patients, it varied from 18 to 45% and was inversely correlated (r = 0.94) to the midwall radius-to-wall thickness ratio (R/h) of the ventricle at end diastole. On the other hand, the ratio of the quantity of blood ejected per unit of LV wall volume magnitude of delta V/V omega magnitude of varied from 0.20 to 1.20 (normal subjects 0.83 +/- 0.11) and was directly correlated (r = 0.94) to R/h; using independent data in the literature, we also found a similar relationship (r = 0.80) between the ratio of quantity of blood ejected per unit of LV mass (magnitude of delta V/M omega magnitude of) and R/h. Patients with presumably abnormal myocardial function did not satisfy the relationship between magnitude of delta V/V omega magnitude of or magnitude of delta V/M omega magnitude of and R/h.(ABSTRACT TRUNCATED AT 250 WORDS)     

Potential application of monolith packed columns as bioreactors, control of biofilm formation

Monolith reactors combine good mass transfer characteristics with low-pressure drop, the principle factors affecting the cost effectiveness of industrial processes. Recently, these specific features of the monolith reactors have drawn the attention toward the application of the monolith reactor in multiphase reaction systems. In this study, we explore the potential application of monolith reactors as bioreactor requiring gas-liquid mass transfer for substrate supply. It is demonstrated on theoretical grounds that the monolith reactor is a competitive alternative to conventional gas-liquid bioreactors such as stirred tanks, packed beds, and airlift bioreactors because it allows for a significant reduction of the energy dissipation that is normally required for gas-liquid contacting. A potential problem of monolith reactors for biological processes is clogging due to biofilm formation. This paper presents experimental results of a study into the formation and possible removal of biofilms during operation of a monolith reactor as suspended cells bioreactor. The results indicate that biofilm formation may be minimized and postponed by a proper choice of operating conditions. Periodic biofilm removal could straightforwardly be achieved by rinsing with water at moderate pressures and allows for stable operation for prolonged periods of time.     

Energy-spilling reactions of Streptococcus bovis and resistance of its membrane to proton conductance.

Glucose-excess cultures of Streptococcus bovis consumed glucose faster than the amount that could be explained by growth or maintenance, and nongrowing chloramphenicol-treated cells had a rate of glucose consumption that was 10-fold greater than the maintenance rate. Because N,N-dicyclohexylcarbodiimide, an inhibitor of the membrane-bound F1F0 ATPase, eliminated the nongrowth energy dissipation (energy spilling) without a decrease in ATP and the rate of energy spilling could be increased by the protonophore 3,3',4',5-tetrachlorosalicylanilide, it appeared that a futile cycle of protons through the cell membrane was responsible for most of the energy spilling. When the rate of energy spilling was decreased gradually with iodoacetate, there was only a small decrease in the phosphorylation potential (delta G'p) and the theoretical estimate of H+ per ATP decreased from 4.2 to 3.6. On the bases of this ratio of H+ to ATP and the rate of ATP production, the flux of protons (amperage) across the cell membrane was directly proportional to the rate of energy spilling. Amperage values estimated from delta G'p were, however, nearly twice as great as values which were estimated from the heat production (delta H) of the cells [amperage = (0.38 x wattage)/delta p]. The last comparison indicated that only a fraction of the delta G of ATP hydrolysis was harvested by the F1F0 ATPase to pump protons. Both estimates of amperage indicated that the resistance of the cell membrane to proton conductance was inversely proportional to the log of the energy-spilling rate.     

Dynamic bioreactor operation: effects of packing material and mite predation on toluene removal from off-gas

Recent studies have focused on using vapor-phase bioreactors for the treatment of volatile organic compounds from contaminated air streams. Although high removal capacities have been achieved in many studies, long-term operation is often unstable at high pollutant loadings due to biomass accumulation and drying of the packing medium. In this study, three bench-scale bioreactors were operated to determine the effect of packing material and fungal predation on toluene removal efficiency and pressure drop. Toluene elimination capacities (mass toluene removed per unit packing per unit time) above 100 g m(-3) h(-1) were obtained in the fungal bioreactors packed with light-weight, artificial medium, and submersion of the packing in mineral medium once per week was found to provide sufficient moisture and nutrients to the biofilm. The use of mites as fungal predators improved performance by increasing the overall mineralization of toluene to CO(2), and by dislodging biomass along the bioreactor.     

Energy dissipation as a key factor for electroporation of protoplasts

Energy dissipation (ε) during electroporation was theoretically determined to be ε=0.5CV ₀ ² for the various combinations of capacitance (C) and initial voltage (V ₀). Experiments on asparagus protoplasts established that electroporation efficiency (EE) and survival rate were directly proportional to energy dissipation during electroporation. A positive linear relationship exists between energy dissipation per unit volume and EE, whereas energy dissipation per unit volume and survival rate of protoplasts are related in a negative linear manner. At the same energy level, longer time constants were more effective at increasing EE. This suggest that energy dissipation approximating rectangular waveforms is more important than that dissipated as sharply decaying exponential waveforms. With energy as the key parameter, the optimization of electrical parameters for efficient electroporation is greatly simplified, is not machine-dependent, and generally applies to all species.     

Computational fluid dynamics analysis of mixing and gas–liquid mass transfer in wave bag bioreactor

Single use bioreactors provide an attractive alternative to traditional deep-tank stainless steel bioreactors in process development and more recently manufacturing process. Wave bag bioreactors, in particular, have shown potential applications for cultivation of shear sensitive human and animal cells. However, the lack of knowledge about the complex fluid flow environment prevailing in wave bag bioreactors has so far hampered the development of a scientific rationale for their scale up. In this study, we use computational fluid dynamics (CFD) to investigate the details of the flow field in a 20-L wave bag bioreactor as a function of rocking angle and rocking speed. The results are presented in terms of local and mean velocities, mixing, and energy dissipation rates, which are used to create a process engineering framework for the scale-up of wave bag bioreactors. Proof-of-concept analysis of mixing and fluid flow in the 20-L wave bag bioreactor demonstrates the applicability of the CFD methodology and the temporal and spatial energy dissipation rates integrated and averaged over the liquid volume in the bag provide the means to correlate experimental volumetric oxygen transfer rates (k_La) data with power per unit volume. This correlation could be used as a rule of thumb for scaling up and down the wave bag bioreactors.     

Bioreactor with a semi-fixed packing: anaerobic lactose to lactic acid fermentation

The bioreactor with a semi-fixed packing consists of frames with stretched “Raschell”-type sacks on them. This construction enables the attainment of a larger interfacial area of the biofilm carrier per unit reactor volume as well as the easy removal of the exausted biomass at certain biofilm thickness. In the present paper the batch anaerobic conversion of lactose to lactic acid in this reactor with immobilized bacteria Lactobacillus casei is studied. The dilution rate of the feeding substrate solution was 1?mm/s. Comparison of our experimental results with data, obtained for free cells and other construction of bioreactors with immobilized cells is made. It is shown that the used immobilised biocatalyst is superior to free bacterial cells, or attached to the inner pores of polyurethane foam.     

Effects of stratification in a fluidized bed bioreactor during treatment of metalworking wastewater

During wastewater treatment, biofilm-coated sand particles stratified in a fluidized bed bioreactor (FBB); particles coated by thicker biofilm segregated toward the top of the bed. Stratification was so well developed that at least two co-existing regions of significantly different mean biofilm thickness were visually distinct within the operating FBB. The observed stratification is attributed to differences in forces of drag, buoyancy, shear, and collisional impact, as well as differences of collision rate within the different regions. Particles with thick biofilm (thickness >100 μm) near the top of the bed consumed substrate at significantly lower rates per unit biomass than particles with thin biofilm (10-20 μm) near the bottom of the bed, thereby suggesting that substrate mass-transfer resistance through biofilm may limit biodegradation rates in the upper portion of the FBB. Large agglomerates of biomass floc and sand, which formed at the top of the fluidized bed, and sand particles with thick biofilm were susceptible to washout from the FBB, causing operational and treatment instability. Radial injection of supplemental liquid feed near the top of the bed increased shear and mixing, thereby preventing formation and washout of agglomerates and thickly coated sand particles. Supplemental liquid injection caused the mean specific biomass loading on the sand to increase and also increased the total biomass inventory in the FBB. Rates of biodegradation in the FBB appeared to be limited by penetration of substrates into the biofilm and absorption of oxygen from air into the wastewater. Copyright 1999 John Wiley & Sons, Inc.     

Extractive biofilm membrane bioreactor with energy recovery from excess aeration and new membrane fouling control

Hybrid biofilm membrane bioreactor (BF-MBR) system featuring new mechanisms for recovering the excess energy from air bubbling flow in the biofilm reactor and for controlling membrane biofouling was preliminarily investigated in this study. Alternative design of the biofilm reactor was developed to utilize the bubbling flow from the lower aerobic chamber to generate a mechanical mixing in the upper anoxic chamber in the vertical biofilm reactor. Suspended solid (SS) concentration in the system was hydrodynamically controlled to be lower than 70 mg/L. The ultraviolet (UV) inactivation unit was integrated with the membrane filtration tank to limit biological activities for biofoulant productions and to decelerate the unwanted biofilm formation in the permeate tube. Membrane relaxations at various operating conditions were studied for optimum membrane fouling reductions under low SS environment. Combinations of membrane relaxation and the UV inactivation significantly prolonged sustainable operation periods of the membrane filtration in the BF-MBR process.     

Prediction of optimal biofilm thickness for membrane-attached biofilms growing in an extractive membrane bioreactor

This article presents a mathematical model of membrane-attached biofilm (MAB) behavior in a single-tube extractive membrane bioreactor (STEMB). MABs can be used for treatment of wastewaters containing VOCs, treatment of saline wastewaters, and nitrification processes. Extractive membrane bioreactors (EMBs) are employed to prevent the direct contact between a toxic volatile pollutant and the aerated gas by allowing counterdiffusion of substrates; i.e., pollutant diffuses from the tube side into the biofilm, whereas oxygen diffuses from the shell side into the biofilm. This reduces the air stripping problems usually found in conventional bioreactors. In this study, the biodegradation of a toxic VOC (1,2-dichloroethane, DCE) present in a synthetic wastewater has been investigated. An unstructured model is used to describe cell growth and cell decay in the MAB. The model has been verified by comparing model predicted trends with experimental data collected over 5 to 20-day periods, and has subsequently been used to model steady states in biofilm behavior over longer time scales. The model is capable of predicting the correct trends in system variables such as biofilm thickness, DCE flux across the membrane, carbon dioxide evolution, and suspended biomass. Steady states (constant biofilm thickness and DCE flux) are predicted, and factors that affect these steady states, i.e., cell endogeneous decay rate, and biofilm attrition, are investigated. Biofilm attrition does not have a great influence on biofilm behavior at low values of detachment coefficient close to those typically reported in the literature. Steady-state biofilm thickness is found to be an important variable; a thin biofilm results in a high DCE flux across the membrane, but with the penalty of a high loss of DCE via air stripping. The optimal biofilm thickness at steady state can be determined by trading off the decrease in air stripping (desirable) and the decrease in DCE flux (undesirable) which occur simultaneously as the thickness increases. (c) 1996 John Wiley & Sons, Inc.     

Ca2+/H+-exchange mechanisms in myometrial plasmalemma cells

Transport of 45Ca2+ into vesicules of hog myometrium plasmolemma under dissipation conditions of opposite-directed transmembrane gradient of protons (delta pH) was investigated. When studying some time regularities of the process, H+ dissipation was determined to have little effect on the initial velocity Vo (18 and 25 nmol Ca2+/1 mg of protein per 1 min at delta pH = 0 and delta pH = 1.5, respectively) and the time of semiaccumulation of cation (1.1 and 2.1 min). Estimation of Ca2+ accumulation concentrational dependence in the vesicules in Vo (30 s) revealed that Ca2+ input into vesicules was limited by binding the cation with carboxyl residues of Ca2+ channel external part. This effect is a consequence of the absence of Ca(2+)-transport systems in the vesicules on the background of quick filling of the intervesicular space by the cation as well as discrimination of Ca2+ sorption process by the vesicules inner surface under operating in the Vo regime. The value K0.5 = 0.5 microM for Ca2+ obtained conforms to physiological meaning of the imagined Kd, Ca2+ binding with four glutamate residues of Ca2+ channel external part. Dissipation of the artificial delta pH = 1.5 on the vesicular membrane leads to increasing the affinity for Ca2+ (to 0.1 microM at constant value of Vmax (40 nmol Ca2+/1 mg of protein per 1 min). We have also demonstrated irreversibility of the process tested and substrate specificity. The results obtained permit to suppose that delta pH dissipation provides for some conformational changes of the channel structure resulting in increasing Ca2+ affinity for the transporting system as well as increases the membrane permeability for the cation. The latter means the interrelation of two most important signal molecules such as Ca2+ and H+ in the cell is capable to occur on the level on Ca2+ separate channels.     

Metabolic response of biofilm to shear stress in fixed-film culture

AIMS: In a biofilm reactor, detachment force resulting from hydraulic shear is a major factor that determines the formation and structure of steady state biofilm. The metabolic response of biofilm to change in shear stress was therefore investigated. METHODS AND RESULTS: A conventional annular reactor made of PVC was used, in which shearing over the rotating disc surface was strictly defined. Results from the steady state aerobic biofilm reactor showed that the biofilm structure (density and thickness) and metabolic behaviour (growth yield and dehydrogenase activity) were closely related to the shear stress exerted on the biofilm. Smooth, dense and stable biofilm formed at relatively high shear stress. Higher dehydrogenase activity and lower growth yield were obtained when the shear stress was raised. Growth yield was inversely correlated with the catabolic activity of biofilm. The reduced growth yield, together with the enhanced catabolic activity, suggests that a dissociation of catabolism from anabolism would occur at high shear stress. CONCLUSION: Biofilms may respond to shear stress by regulating metabolic pathways associated with the substrate flux flowing between catabolism and anabolism. A biological phenomenon, besides a simple physical effect, is underlying the observed relation between the shear stress and resulting biofilm structure. SIGNIFICANCE AND IMPACT OF THE STUDY: A hypothesis is proposed that the shear-induced energy spilling would be associated with a stimulated proton translocation across the cell membrane, which favours formation of a stronger biofilm. This research may provide a basis for experimental data on biofilm obtained at different shear stresses to be interpreted in relation to energy.     

Effect of agitation intensities on fungal morphology of submerged fermentation

Both parallel fermentations with Aspergillus awamori (CBS 115.52) and a literature study on several fungi have been carried out to determine a relation between fungal morphology and agitation intensity. The studied parameters include hyphal length, pellet size, surface structure or so-called hairy length of pellets, and dry mass per-wet-pellet volume at different specific energy dissipation rates. The literature data from different strains, different fermenters, and different cultivation conditions can be summarized to say that the main mean hyphal length is proportional to the specific energy dissipation rate according to a power function with an exponent of -0.25 +/- 0.08. Fermentations with identical inocula showed that pellet size was also a function of the specific energy dissipation rate and proportional to the specific energy dissipation rate to an exponent of -0.16 +/- 0.03. Based on the experimental observations, we propose the following mechanism of pellet damage during submerged cultivation in stirred fermenters. Interaction between mechanical forces and pellets results in the hyphal chip-off from the pellet outer zone instead of the breakup of pellets. By this mechanism, the extension of the hyphae or hair from pellets is restricted so that the size of pellets is related to the specific energy dissipation rate. Hyphae chipped off from pellets contribute free filamentous mycelia and reseed their growth. So the fraction of filamentous mycelial mass in the total biomass is related to the specific energy dissipation rate as well.To describe the surface morphology of pellets, the hyphal length in the outer zone of pellets or the so-called hairy length was measured in this study. A theoretical relation of the hairy length with the specific energy dissipation rate was derived. This relation matched the measured data well. It was found that the porosity of pellets showed an inverse relationship with the specific energy dissipation rate and that the dry biomass per-wet-pellet volume increased with the specific energy dissipation rates. This means that the tensile strength of pellets increased with the increase of specific energy dissipation rate. The assumption of a constant tensile strength, which is often used in literature, is then not valid for the derivation of the relation between pellet size and specific energy dissipation rate. The fraction of free filamentous mycelia in the total biomass appeared to be a function of the specific energy dissipation in stirred bioreactors. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 715-726, 1997.     

Effect of protein, polysaccharide, and oxygen concentration profiles on biofilm cohesiveness

It is important to control biofilm cohesiveness to optimize process performance. In this study, a membrane-aerated biofilm reactor inoculated with activated sludge was used to grow mixed-culture biofilms of different ages and thicknesses. The cohesions, or cohesive energy levels per unit volume of biofilm, based on a reproducible method using atomic force microscopy (F. Ahimou, M. J. Semmens, P. J. Novak, and G. Haugstad, Appl. Environ. Microbiol. 73:2897-2904, 2007), were determined at different locations within the depths of the biofilms. In addition, the protein and polysaccharide concentrations within the biofilm depths, as well as the dissolved oxygen (DO) concentration profiles within the biofilms, were measured. It was found that biofilm cohesion increased with depth but not with age. Level of biofilm cohesive energy per unit volume was strongly correlated with biofilm polysaccharide concentration, which increased with depth in the membrane-aerated biofilm. In a 12-day-old biofilm, DO also increased with depth and may therefore be linked to polysaccharide production. In contrast, protein concentration was relatively constant within the biofilm and did not appear to influence cohesion.     

Effect of Protein, Polysaccharide, and Oxygen Concentration Profiles on Biofilm Cohesiveness

It is important to control biofilm cohesiveness to optimize process performance. In this study, a membrane-aerated biofilm reactor inoculated with activated sludge was used to grow mixed-culture biofilms of different ages and thicknesses. The cohesions, or cohesive energy levels per unit volume of biofilm, based on a reproducible method using atomic force microscopy (F. Ahimou, M. J. Semmens, P. J. Novak, and G. Haugstad, Appl. Environ. Microbiol. 73:2897-2904, 2007), were determined at different locations within the depths of the biofilms. In addition, the protein and polysaccharide concentrations within the biofilm depths, as well as the dissolved oxygen (DO) concentration profiles within the biofilms, were measured. It was found that biofilm cohesion increased with depth but not with age. Level of biofilm cohesive energy per unit volume was strongly correlated with biofilm polysaccharide concentration, which increased with depth in the membrane-aerated biofilm. In a 12-day-old biofilm, DO also increased with depth and may therefore be linked to polysaccharide production. In contrast, protein concentration was relatively constant within the biofilm and did not appear to influence cohesion.     

Biomass growth monitoring using pressure drop in a cocurrent biofilter

The possibility of following the biomass growth by pressure drop measurement was investigated in an aerated cocurrent upflow fixed-bed bioreactor continuously fed with wastewater containing industrial organic pollutants. The experiments were carried out in a biological filtration oxygenated reactor (Biofor) pilot plant packed with expanded clay balls (Biolite) of 2.7-mm diameter, which served as biomass carriers. The column was equipped for on-line pressure drop measurements. Correlation between pressure drop measurements and Reynolds numbers of air and water were determined in experiments carried out without biomass. Under operating conditions with biomass, it was demonstrated that column clogging and the operating time between washing cycles can be predicted depending on the volumetric organic load for a given total organic carbon inlet concentration. The biological activity of the fixed biomass was estimated from the oxygen consumption rate per unit time and carrier area. The oxygen consumption rate measurements demonstrated that the biological activity depends on the inlet substrate concentration, and that the Biofor column was most efficient between 75 and 100 g m-3 of total organic carbon inlet concentration. In the course of the wastewater treatment, using pressure drop measurements, the equivalent diameter of the Biolite particles, the reduced column macroporosity, and the biofilm thickness were calculated. An expression correlating biofilm density and biofilm thickness, as determined from the pressure drop measurements, was proposed. Good agreement was found between the fixed biomass in the reactor, determined as volatile suspended solids, and the biologically active biomass, estimated by respirometry. Copyright 1998 John Wiley & Sons, Inc.     

Mixing power, external convection, and effectiveness in bioreactors

The phenomena of mixing and mass transfer of substrates to microorganisms greatly affect the biochemical reactions which take place in fermentation processes. The effect that agitation power has on the observable reaction kinetics involved in beer fermentation has been studied in different types of bioreactors, from laboratory to industrial scale. With this aim in mind, an effectiveness factor, eta, is introduced which is defined as the relation between the existing rate of reaction, whichever bioreactor is considered, and the reaction rate in the well-mixed, and therefore presumably homogeneous, bioreactor with no diffusional limits. The limitation to homogeneously supplying nutrient material to the cells produces a decrease in this effectiveness factor, which has been correlated to the energy dissipation rate with a similar slope to that which appears in an existing correlation in the literature between this energy and the mass transfer coefficient. Additionally, a dimensionless reaction-convection number, N(RC), which is a function of the power input per unit volume, is proposed, which has been appropriately employed in correlating the effectiveness factor for the types of processes in which convection may be the key resistance factor. (c) 1996 John Wiley & Sons, Inc.     

Energy dissipation and pulse wave attenuation in the canine carotid artery

This paper presents methods for calculating, for a segment of artery in vivo, (1) viscous and viscoelastic energy dissipation as a function of time, and (2) the viscous and viscoelastic components of the frequency-dependent attenuation coefficient. The calculations require measurement of arterial diameter and of intra-arterial pressure and flow-rate at two sites along the vessel. Viscous energy dissipation is calculated from the radius-dependent velocity shear in the lumen given by linear theory from the pressure measurements. The attenuation coefficient for a given harmonic of heart rate is calculated as half the sum of the viscous and viscoelastic components at that frequency of the energy dissipated per unit length by forwardtravelling waves, divided by the forward-wave flow work input to the segment at that frequency. Measurements in canine carotid arteries indicate that wall viscoelasticity contributes relatively little to energy dissipation per cardiac cycle and pulse wave attenuation.     

Dependence of photosynthetic rates on leaf density thickness in deciduous woody plants grown in sun and shade

Comparisons of photosynthetic rates were made on leaves of ten species of woody dicotyledons grown in the field under full sun or under a canopy which transmitted approximately 18% of full light. Photosynthesis and dark respiration were measured and compared on various bases: area, chlorophyll, fresh weight of lamina, density thickness (fresh weight per unit area), and protein.

Light-saturated photosynthesis per unit area or unit chlorophyll was about 1.5 times greater in the sun leaves than in the shade leaves and essentially equal per unit fresh weight or unit protein. Sun leaves were thicker but the enzymes per unit fresh weight remained constant as thickness varied. Chlorophyll per unit area remained about constant; chlorophyll per unit fresh weight varied inversely with changes in leaf thickness. Thus, density thickness variation is important in photosynthetic adaptation to sun and shade. This is also shown by the relationship between light-saturated photosynthesis per unit area and density thickness.

     

Effect of flow regime on the architecture of a Pseudomonas fluorescens biofilm

A comparison of the effects of laminar versus turbulent flow regime on the characteristics of a single-species biofilm is presented. The study was carried out by growing Pseudomonas fluorescens biofilms in a flow cell and studying the different layers of the biological matrix with a confocal laser-scanning microscope. The following conclusions were obtained: i) a higher concentration of cells was found in the upper layers of the microbial films than in their inner layers, regardless of the flow regime; ii) the fraction of cells in the overall biofilm mass decreased with time as the film grew; and iii) under laminar flow the total number of cells was higher than in biofilms formed under turbulent flow, but the latter had a higher number of cells per unit volume. Such conclusions, together with the fact that the biofilms were more dense and stable when formed in contact with turbulent flows, favor the design of more compact and efficient biofilm reactors operating in turbulent conditions.