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1.
The reliability of the process of Ramanathan and Gaudy (Biotechnol Bioeng., 13 , 125 (1971)) for the completely mixed activated-sludge process holding the recycle cell concentration, XR, as a system constant with respect to step changes in hydraulic retention time was investigated. The experiments were run at initial dilution rates of ?, ?, ¼, and ½ hr?1 treating a soft drink bottling wastewater. The influent substrate concentration was maintained at 1000 mg/liter chemical oxygen demand and the hydraulic recycle ratio at 0.3. The recycle sludge concentration was maintained at about 7000 mg/liter. It was found that the system could accommodate hydraulic shock loads up to 200% positive changes and down to 50%negative changes without disruption of the effluent quality. Shorter retention time of the range studied, from 2 to 8 hr, has the advantage of shorter response time with respect to the response of the concentration of biological solids in the reactor. 相似文献
2.
In a previous report it was concluded that steady-state operation of completely mixed reactors for growth of heterogeneous microbial populations, i.e., activated sludge processes, was extremely difficult to attain if maintenance of a constant sludge recycle ratio, c, was required, and equations were devised in which the concentration of cells in the recycle, xR, rather than the recycle ratio, was constant. In this report the equations are developed and computational analysis shows the effect on substrate and cell concentrations in the reactor of operational variables such as inflowing feed concentration, hydraulic recycle ratio, recycle sludge concentration, dilution rate, and the biological “constants” μm, ks, and Y. The stabilizing effect of operating with constant xR on the dilute-out pattern is shown. 相似文献
3.
For better operational control of the completely mixed oxygen activated sludge process (CMOAS), a study concerning the kinetics, performance, and operational stability of the Ramanathan-Gaudy model was conducted. Short-term experiments were conducted at various dilution rates (1/9, 1/6, 1/3, 1/1.5, and 1/1.0 hr?1) by using two recycle solids concentration values (5000 and 10,000 mg/liter). The influent substrate was an actual industrial organic wastewater (soft drink waste) and its concentration was maintained at 1000 mg/liter COD. The hydraulic recycle ratio, α, was maintained at 0.30. It was found that for CMOAS system with constant recycle cell concentration, a “steady state” with respect to reactor biological solids and effluent COD at different dilution rates could be attained. No appreciable dilute-out of reactor biological solids and substrate was observed up to the dilution rate of 1 hr?1 for both systems of different XR (5000 and 10,000 mg/liter). For the system of XR = 5000 mg/liter, except the dilution rate of hr?1, the effluent filtrate COD was lower than 100 mg/liter, the aerator biological solids concentration was about 1550 mg/liter, and the COD removal efficiency was higher than 90% for all dilution rates. For the system of XR = 10,000 mg/liter, the effluent filtrate COD was lower than 71 mg/liter, the aerator biological solids concentration was about 2750 mg/liter, and the COD removal efficiency was higher than 90% throughout all the dilution rates selection in the present study. The value of the Sludge Volume Index (SVI) was the range of 37.0 to 58.5 and provided good settleability of sludge. The sludge yield was 0.53 for the system of XR = 5000 mg/liter and 0.57 for the system of XR = 10,000 mg/liter. The carbohydrate and the protein content of the cells were 10.1–21.6% and 35.6–50.6%, respectively. For predicting the reactor biological solid and effluent COD of the CMOAS system by using the Ramanathan-Gaudy model, two sets of values for the biological kinetic constants should be considered since it provided the best fit of predicted values of the observed values. In the present study, μm = 0.4 hr?1, ks = 92 mg/liter for 1/3 ? D ? 1, and μm = 0.05 hr?1, ks = 11.1 mg/liter for 1/9 ? D < 1/3 were used to calculate the predicted values of reactor biological solid and effluent filtrate COD. 相似文献
4.
The stability of the model of a completely mixed activated-sludge process holding the recycle sludge concentration, XR, as a system constant subjected to pH, temperature, potassium cyanide, and phenol shock loading was investigated. Soft-drink bottling wastewater was used and maintained at 1000 mg/liter chemical oxygen demand (COD). The hydraulic ratio and recycle sludge concentration were maintained at 0.3 and 7000 mg/liter, respectively. An initial dilution rate of ¼ hr?1 was maintained for pH and temperature shock loading, with ¼ and ? hr?1 for KCN shock loading and ¼, ?, and \documentclass{article}\pagestyle{empty}\begin{document}$\frac{1}{16}$\end{document} hr?1 for phenol shock loading. It was found that the present system could handle pH shock loading as low as 4.0 and as high as 10.4 without any serious disruption of biological solid concentration and filtrate COD. At pH 4.0 shock loading, filamentous organisms were predominant. Temperature shock loading could be handled from 23 to 36°C without any leakage of effluent filtrate COD. At 46°C temperature shock, a 14 hr period was required to recuperate to the new steady state and provided only 85% of COD removal efficiency. For KCN (50 mg/liger) and phenol (85 mg/liter) shock loading, the dilution rates should be lower than \documentclass{article}\pagestyle{empty}\begin{document}$\frac{1}{16}$\end{document} hr?1 in order to shorten the transient period and improve the effluent quality. Biological kinetic constants included cell yield value, maximum growth rate, and the saturation constant, which was varied with the qualitative shock applied. 相似文献
5.
Torsten Ingestad Olof Hellgren Hans Hesseldahl Ann-Britt Lund Ingestad 《Physiologia plantarum》1996,98(3):667-676
Methods to control carbon and nutrient uptake at different availability of carbon were tested on plants of birch (Betula pendula Roth.) and tomato (Lycopersicon esculentum Mill. cv. Solentos). The present paper accounts for the methods and the possibility to maintain steady-state, i.e., a long-term and stable physiological state of acclimated plants. Steady-state comprises, by definition, equality between constant relative growth rates, and relative uptake rates of carbon and nutrients. Two methods were tested. The first, not previously applied, method (a), was based on a constant relative addition rate of carbon, RAC. In the second method (b), a constant concentration of CO2 in the air, ca, was used to attain non-limiting conditions. The methods are analogous to those used by us to control plant nutrition, and the generality of fluxes to quantify supply as well as uptake and growth was verified. Thus, different RAC resulted in clear-cut responses, from strong reduction to non-limitation of uptake and growth, whereas different ca levels in the range 100 to 700 ppm had comparatively small effects, with an unclear causality. Non-limiting conditions were achieved at ca≥ 200 ppm. Effects reported in the literature have been based upon the control of ca, similarly to method (b), whereas results comparable to those obtained with method (a) are lacking. Transpiration rate increased rapidly at ca < 200 ppm CO2, and at low RAC levels, ≤ 0.1 day?1, wilting tendencies were observed. Elevated ca, 500 or 700 ppm, did not increase the relative growth rate (RG) but reduced transpiration and increased both nitrogen productivity (growth rate per unit of nitrogen in the plant) and transpiration productivity (growth rate per unit of water transpired by the plant). Obviously, effects of ca may be due to changed transpiration rate rather than to changed quantitative availability of CO2. Relative uptake (RUC) and growth (RG) rates were closely equal to the RAC applied (RAC? RUC? RG); i.e., the purely mathematical conditions defining steady-state were fulfilled. This unambiguous and straightforward test of reliability confirms that experimental artefacts did not produce uncontrolled or unintended effects, so that the new technique allows an accurate control of CO2 uptake and plant growth. The results add to previous databases and reference systems, where limiting conditions grade and classify plant performance as deviations from maximum growth. Evidently, methodology in experimentation and in evaluation of plant responses, can be based upon unifying concepts and general theories. 相似文献
6.
Rhodospirillum rubrum was grown continuously and photoheterotrophically under light limitation using a cylindrical photobioreactor in which the steady state biomass concentration was varied between 0.4 to 4 kg m–3 at a constant radiant incident flux of 100 W m–2. Kinetic and stoichiometric models for the growth are proposed. The biomass productivities, acetate consumption rate and the CO2 production rate can be quantitatively predicted to a high level of accuracy by the proposed model calculations.
Nomenclature:
C
X, biomass concentration (kg m–3) D, dilution rate (h–1) Ea, mean mass absorption coefficient (m2 kg–1) I
, total available radiant light energy (W m–2) K, half saturation constant for light (W m–2) R
W, boundary radius defining the working illuminated volume (m) r
X, local biomass volumetric rate (kg m–3 h–1) <r
X>, mean volumetric growth rate (kg m–3 h–1) V
W, illuminated working volume in the PBR (m–3).
Greek letters:
, working illuminated fraction (–) M, maximum quantum yield (–) bar, mean energetic yield (kg J–1). 相似文献
7.
The balance equations to a continuous plug flow recycle reactor performing a protease-mediated autocatalytic reaction were analytically developed under the assumption of a Michaelis-Menten type of mechanism. The necessary condition for the recycle ratio that leads to the minimum reactor volume was set up and the resulting expression was numerically solved for the optimum ratio of recycle, R opt, as a function of the desired conversion of reactant (or pro-enzyme) into product (or enzyme), X PE, for selected values of the relevant dimensionless parameters, i.e. the ratio of total concentrations of enzyme and product moieties, γ, and the ratio of the Michaelis-Menten parameter to the total concentration of product moiety, K m *. It was numerically proven that variation of K m * by five orders of magnitude centered around unity did not affect R opt to a significant extent, whereas an empirical expression for R opt versus γ and X PE could be found and successfully fitted to the results of several numerical runs. 相似文献
8.
Dominick Damiano Chul-Soo Shin Nai-hu Ju Shaw S. Wang 《Applied microbiology and biotechnology》1985,21(1-2):69-77
Summary A continuous single stage yeast fermentation with cell recycle by ultrafiltration membranes was operated at various recycle ratios. Cell concentration was increased 10.6 times, and ethanol concentration and fermentor productivity both 5.3 times with 97% recycle as compared to no recycle. Both specific growth rate and specific ethanol productivity followed the exponential ethanol inhibition form (specific productivity was constant up to 37.5 g/l of ethanol before decreasing), similar to that obtained without recycle, but with greater inhibition constants most likely due to toxins retained in the system at hight recycle ratios.By analyzing steady state data, the fractions of substrate used for cell growth, ethanol formation, and what which were wasted were accounted for. Yeast metabolism varied from mostly aerobic at low recycle ratios to mostly anaerobic at high recycle ratios at a constant dissolved oxygen concentration of 0.8 mg/kg. By increasing the cell recycle ratio, wasted substrate was reduced. When applied to ethanol fermentation, the familiar terminology of substrate used for Maintenance must be used with caution: it is not the same as the wasted substrate reported here.A general method for determining the best recycle ratio is presented; a balance among fermentor productivity, specific productivity, and wasted substrate needs to be made in recycle systems to approach an optimal design.Nomenclature
B
Bleed flow rate, l/h
-
C
T
Concentration of toxins, arbitrary units
-
D
Dilution rate, h-1
-
F
Filtrate or permeate flow rate, removed from system, l/h
-
F
o
Total feed flow rate to system, l/h
-
K
s
Monod form constant, g/l
-
P
Product (ethanol) concentration, g/l
-
P
o
Ethanol concentration in feed, g/l
-
PP}
Adjusted product concentration, g/l
-
PD
Fermentor productivity, g/l-h
-
R
Recycle ratio, F/F
o
-
S
Substrate concentration in fermentor, g/l
-
S
o
Substrate concentration in feed, g/l
-
V
Working volume of fermentor, l
-
V
MB
Viability based on methylene blue test
-
X
Cell concentration, g dry cell/l
-
X
o
Cell concentration in feed, g/l
-
Y
ATP
Cellular yield from ATP, g cells/mol ATP
-
Y
ATPS
Yield of ATP from substrate, mole ATP/mole glucose
-
Y
G
True growth yield or maximum yield of cells from substrate, g cell/g glucose
-
Y
P
Maximum theoretical yield of ethanol from glucose, 0.511 g ethanol/g glucose
-
Y
P/S
Experimental yield of product from substrate, g ethanol/g glucose
-
Y
x/s
Experimental yield of cells from substrate, g cell/g glucose
-
S
NP/X
Non-product associated substrate utilization, g glucose/g cell
-
k
1, k2, k3, k4
Constants
-
k
1
APP
, k
2
APP
Apparent k
1, k3
-
k
1
TRUE
True k
1
-
m
Maintenance coefficient, g glucose/g cell-h
-
m
*
Coefficient of substrate not used for growth nor for ethanol formation, g glucose/g cell-h
-
Specific growth rate, g cells/g cells-h, reported as h-1
- m
Maximum specific growth rate, h-1
-
v
Specific productivity, g ethanol/g cell-h, reported as h-1
-
v
m
Maximum specific productivity, h-1 相似文献
9.
Urs Peter Fringeli 《The Journal of membrane biology》1980,54(3):203-212
Summary Attenuated total reflection infrared spectroscopy has been used to determine the equilibrium distribution of the peptide antibiotic alamethicinR
F30 between dipalmitoyl phosphatidylcholine bilayers and the aqueous environment. The distribution coefficientK=c
eq
W
/c
eq
M
turned out to be concentration dependent, pointing to alamethicin association in the membrane with increasing concentration in the aqueous phase (c
eq
W
). This concentration was varied within 28 and 310nm, i.e., in a range typical for black film experiments. Furthermore, diffusion coefficients of alamethicin in the hydrophobic phase of the membrane (D
M) and across the membrane/water interface (D
I) have been estimated from the time course of the equilibration process. It was found that the diffusion rate of the uncharged analogueR
F50 is about 10 times higher than that of theR
F30 component, exhibiting one negative charge at theC-terminus. The time constants for transmembrane diffusion of alamethicinR
F30 varied between 2.2 hr at low concentration and 3.2 hr at higher concentration. The corresponding low concentration value of theR
F50 component was found to be 0.25 hr. 相似文献
10.
Growth kinetics of heterogeneous populations of sewage origin were studied in completely mixed reactors of the once-through type at a high concentration of incoming substrate, 3000 mg/l glucose, and in systems employing cell feedback or sludge recycle at an incoming substrate concentration of 1000 mg/1 glucose. The recycle flow rate employed was 25% of the incoming feed flow, and the concentration of cells in the recycle was maintained as closely as possible at 150% of the cell concentration in the reactor. Studies were made at various dilution rates. Throughout these studies, batch experiments using cells grown at the various dilution rates were made to determine ks and μm values. As in previous studios using heterogeneous populations, the relationship between specific growth rates μ and substrate concentration S was represented better by the Monod equation than by any other which was tested. The growth “constants” μm, ks, and Y were found to fall in the same general range as those determined in previous studies in once-through systems operated at 1000 mg/l glucose. It was observed that cell recycle, even at the relatively low concentration factor employed in these studies, greatly enhanced the flocculating and settling characteristics of the cells. 相似文献
11.
Degradation of 4-chlorophenol by enriched mixed cultures utilizing phenol and glucose as added growth substrate 总被引:2,自引:0,他引:2
Two mixed cultures, phenol-oxidizing (PO) and glucose-oxidizing (GO), were cultivated in two parallel chemostat reactors.
The PO culture was enriched on phenol, and the GO culture was enriched on glucose. Batch biodegradation experiments were conducted
to examine the degradation of 4-chlorophenol (4-CP) under various substrate conditions. The results indicate that in the absence
of added growth substrate, 4-CP transformation by PO culture was complete at S
c
o
/X
o (initial 4-CP concentration/initial biomass concentration) 0.27 and that by GO culture was complete at S
c
o
/X
o = 0.09. In the presence of 5–500 mg phenol/l, the phenol dosage required to achieve the complete transformation of 4-CP was
60 mg/l at S
c
o
/X
o = 1, increasing to 120 mg/l at S
c
o
/X
o = 2, and to 180 mg/l at S
c
o
/X
o = 5. As glucose was added to the GO culture at a concentration of over 5–500 mg chemical oxygen demand (COD)/l, 4-CP was
not completely transformed at S
c
o
/X
o = 5 [S
c
o
= 50 mg/l, X
o
= 10 mg/l volatile suspended solids (VSS)]. These two cultures in utilizing added growth substrate were easily switched between
glucose and phenol. Overall, the capacity of PO culture to degrade 4-CP, expressed as T
c (4-CP mass consumed /biomass inactivated, having unit of mg 4-CP/mg VSS), was 0.15–0.80, which compares with T
c values of 0.05–0.26 for GO culture. This work shows that adding phenol as a growth substrate is preferable over adding glucose,
as it enhances 4-CP transformation, but a final choice should take into account both degradation efficiency and the risk of
phenol toxicity. 相似文献
12.
The kinetics of reextraction of penicillin from the LA-2-penicillin complex-n-butylacetate solution by phosphate buffer was investigated experimentally and theoretically. The concentration time functions can be described by a mathematical model in a wide range of pH-values and complex concentrations.List of Symbols
a
P
[m2/m3]
specific interfacial area
-
c
A
, c
Ai
[mMol]
concentration of amine in the bulk of the organic phase and at the interface
-
c
AHP
, c
AHPi
[mMol]
concentration of the complex in bulk of the organic phase and at the interface
-
c
H
, c
Hi
[mMol]
concentration of the proton in the bulk of the aqueous phase and at the interface
-
c
P
, c
Pi
[mMol]
concentration of the penicillin acid anion in the bulk of the aqueous phase and at the interface
-
J
A
, J
AHP
, J
P
[mMol · cm · s–1]
fluxes of amine, complex and penicillin acid anion
-
k
A
, k
AHP
, k
P
[cm · s–1]
mass transfer coefficients of amine, complex and penicillin acid anion
-
K
G
[mMol2]
equilibrium constant
-
t [k]
extraction time 相似文献
13.
The availability and demand of biosynthetic energy (ATP) is an important factor in the regulation of solvent production in steady state continuous cultures of Clostridium acetobutylicum. The effect of biomass recycle at a variety of dilution rates and recycle ratios under both glucose and non-glucose limited conditions on product yields and selectivities has been investigated. Under conditions of non-glucose limitation, when the ATP supply is not growth-limiting, a lower growth rate imposed by biomass recycle leads to a reduced demand for ATP and substantially higher acetone and butanol yields. When the culture is glucose limited, however, biomass recycle results in lower solvent yields and higher acid yields.List of Symbols
A
600
absorbance at 600 nm
- ATP
adenosine triphosphate
-
C
imol/dm3
concentration of componenti in the fermentor
-
C
i
0
mol/dm3
concentration of componenti in the feed
-
D h–1
dilution rate
-
F dm3/h
feed flow rate
- FdH2
ferredoxin, reduced form
- NAD
nicotinamide adenine dinucleotide, oxidized form
- NADH
nicotinamide adenine dinucleotide, reduced form
- NfF mmol/g/h
NADH produced from oxidation of FdH2 per unit biomass per unit time
-
P dm3/h
filtrate flow during biomass recycle operation
-
PCRP C-mole carbon per C-mole glucose utilized
percent of (substrate) carbon recovered in products
-
R
recycle ratio,P/F
-
SPR mmol/g/h
specific production rate
-
X
imol product/100 mol glucose utilized
product yield
-
Y
ATP g biomass/mol ATP
biomass yield on ATP
-
Y
GLU g biomass/mol glucose
biomass yield on glucose
-
Y
ig biomass/mol
biomass yield on nutrienti
-
h–1
specific growth rate 相似文献
14.
《Journal of Fermentation Technology》1987,65(3):319-323
By culture of Saccharomyces cerevisiae with cell recycle using tangential microfiltration, high cell concentrations are obtained (in the range of 0 to 345 gl−1 dry-weight). The rheological properties of the cell suspension during the cell growth were studied. Over a wide range of biomass concentration (X<275 gl−1D.W.) the power-law model was found adequate to describe the rheological behaviour of the broth. Pronounced non-Newtonian (pseudoplastic) behaviour occurred for X > 75 gl−1. Experimental correlations for apparent viscosity (na, mPa.s) and power-law index vs. biomass concentration (X, gl−1) were established: na = (1+0.012X)2 suitable over the whole range of concentration up to 275 gl−1 D.W. na = 1+0.04X in the low concentration range; X<100 gl−1D.W. Beyond the cell concentration of 275 gl−1 D.W. the viscosity increases suddenly. 相似文献
15.
Enzyme production in a cell recycle fermentation system was studied by computer simulations, using a mathematical model of -amylase production by Bacillus amyloliquefaciens. The model was modified so as to enable simulation of enzyme production by hypothetical organisms having different production kinetics at different fermentation conditions important for growth and production. The simulations were designed as a two-level factorial assay, the factor studied being fermentation with or without cell recycling, repression of product synthesis by glucose, kinetic production constants, product degradation by a protease, mode of fermentation, and starch versus glucose as the substrate carbon source.The main factor of importance for ensuring high enzyme production was cell recycling. Product formation kinetics related to the stationary growth phase combined with continuous fermentation with cell recycling also had a positive impact. The effect was greatest when two or more of these three factors were present in combinations, none of them alone guaranteeing a good result. Product degradation by a protease decreased the amount of product obtained; however, when combined with cell recycling, the protease effect was overshadowed by the increased production. Simulation of this type should prove a useful tool for analyzing troublesome fermentations and for identifying production organisms for further study in integrated fermentation systems.List of Symbols
a
proportionality constant relating the specific growth rate to the logarithm of G (h)
-
a
1
reaction order with respect to starch concentration
-
a
2
reaction order with respect to glucose concentration
-
c
starch concentration (g/l)
-
c
0
starch concentration in the feed (g/l)
-
D
dilution rate (h–1)
-
e
intrinsic intracellular amylase concentration (g product/g cell mass)
-
E
extracellular amylase concentration (g/l)
-
F
volumetric flow rate (l/h)
-
G
average number of genome equivalents of DNA/cell
-
K
1
intracellular repression constant
-
K
2
intracellular repression constant
-
K
s
Monod saturation constant (g/l)
-
k
3
product excretion rate constant (h–1)
-
k
I
translation constant (g product/g mRNA/h)
-
k
d
first order decay constant (h–1)
-
k
dw
first order decay constant (h–1)
-
k
gl
rate constant for glucose production (g/l/h)
-
k
m, dgr
saturation constant for product degradation (g/l)
-
k
st
rate constant for starch hydrolysis (g/l/h)
-
k
t1
proportionality constant for amylase production (g mRNA/g substrate)
-
k
t2
proportionality constant for amylase production (g mRNA *h/g substrate)
-
k
w
protease excretion rate constant (h–1)
-
k
wt1
proportionality constant for protease production (g mRNA/g substrate)
-
k
wt2
proportionality constant for protease production (g mRNA *h/g substrate)
-
k
wI
translation constant (g protease/g mRNA/h)
-
m
maintenance coefficient (g substrate/g cell mass/h)
-
n
number of binding sites for the co-repressor on the cytoplasmic repressor
-
Q
repression function, K1/K2 less than or equal to 1.0
-
Q
w
repression function, K1/K2 less than or equal to 1.0
-
r
intrinsic amylase mRNA concentration (g mRNA/g cell mass)
-
r
m
intrinsic protease mRNA concentration (g mRNA/g cell mass)
-
R
ex
retention by the filter of the compounds x=: C starch, E amylase, or S glucose
-
R
t
amylase transport rate (g product/g cell mass/h)
-
R
wt
protease transport rate (g protease/g cell mass/h)
-
R
s
rate of glucose production (g/l/h)
-
R
c
rate of starch hydrolysis (g/l/h)
-
S
0
feed concentration of free reducing sugar (g/l)
-
s
extracellular concentration of reducing sugar (g/l)
-
t
time (h)
-
V
volume (1)
-
w
intracellular protease concentration (g/l)
-
W
extracellular protease concentration (g/l)
-
X
cell mass concentration (dry weight) (g/l)
-
Y
yield coefficient (g cell mass/g substrate)
-
substrate uptake (g substrate/g cell mass/h)
-
specific growth rate of cell mass (h–1)
-
d
specific death rate of cells (h–1)
-
m
maximum specific growth rate of cell mass (h–1)
-
m,dgr
maximum specific rate of amylase degradation (h–1)
This study was supported by the Nordic Industrial Foundation Bioprocess Engineering Programme and the Center for Process Biotechnology, The Technical University of Denmark. 相似文献
16.
Separation process of a binary protein solution by ultracentrifuge with an angle rotor was discussed by considering the calculated distribution of concentration in an ultracentrifugal tube. The weight fraction of the desired protein and the recovery index after the ultracentrifugation were calculated from the distribution of the concentration. When the weight fraction after the ultracentrifugation is given, the optimal ultracentrifugal time was determined so as to maximize the recovery index.List of Symbols
c
B
kg/cm3
concentration of Bovine serum albumin
-
c
L
kg/cm3
concentration of Lysozyme
-
D cm2/s
diffusion coefficient
-
d cm
diameter of ultracentrifugal tube
-
R
dimensionless collecting range
-
r
*
dimensionless radial coordinate
-
r
1 cm
minimum radius of ultracentrifugal tube
-
r
2 cm
maximum radius of ultracentrifugal tube
-
s s
sedimentation constant
-
t s
ultracentrifugal time
-
X
L
weight fraction of Lysozyme
-
X
LO
initial weight fraction of Lysozyme
-
Y
L
recovery index of Lysozyme
-
inclination of ultracentrifugal tube
-
s–1
angular velocity of rotation 相似文献
17.
The influence on the excess scattering function P(μ) of flutuations in the electron density ρ within a macromolecule is treated, to the approximation that the solvent is a structureless medium of constant electron density ρ0. The results for P(μ) and the apparent value of the mean square radius Rapp2, can be expressed as functions of the excess electron density Δρ: P(μ) = X(μ) + (Δρ)?1Y(μ) + (Δρ)?2Z(μ) and Rapp2 = Rx2 + (Δρ)?1Ry2 + (Δρ)?2Rz2, where X(μ) and Rx2 depend only on the shape of the macromolecule, while Y(μ) and Ry2 as well as Z(μ) and Rz2 depend on the shape and the fluctuations in ρ. By varying the electron density of the solvent, the contributions of the shape and the internal structure of the macromolecule can be resolved. The quantities Rx2, Ry2, and Rz2 are evaluated for seven models to illustrate the relative importance of these contributions for representative structures. 相似文献
18.
Composition and distribution of internal resistance in three types of microbial fuel cells 总被引:3,自引:0,他引:3
High internal resistance is a key problem limiting the power output of the microbial fuel cell (MFC). Therefore, more knowledge
about the internal resistance is essential to enhance the performance of the MFC. However, different methods are used to determine
the internal resistance, which makes the comparison difficult. In this study, three different types of MFCs were constructed
to study the composition and distribution of internal resistance. The internal resistance (R
i) is partitioned into anodic resistance (R
a), cathodic resistance (R
c), and ohmic resistance () according to their origin and the design of the MFCs. These three resistances were then evaluated by the “current interrupt”
method and the “steady discharging” method based on the proposed equivalent circuits for MFCs. In MFC-A, MFC-B, and MFC-C,
the R
i values were 3.17, 0.35, and 0.076 Ω m2, the values were 2.65, 0.085, and 0.008 Ω m2, the R
a values were 0.055, 0.115, and 0.034 Ω m2, and the R
c values were 0.466, 0.15, and 0.033 Ω m2, respectively. For MFC-B and MFC-C, the remarkable decrease in R
i compared with the two-chamber MFC was mainly ascribed to the decline in and R
c. In MFC-C, the membrane electrodes’ assembly lowered the ohmic resistance and facilitated the mass transport through the
anode and cathode electrodes, resulting in the lowest R
i among the three types. 相似文献
19.
Abstract Net nitrate uptake rates were measured and the kinetics calculated in non-nodulated Pisum sativum L. cv. Marma and Lemna gibba L. adapted to constant relative rates of nitrate-N additions (RA), ranging from 0.03 to 0.27 d?1 for Pisum and from 0.05 to 0.40 d?1 for Lemna, Vmax of net nitrate uptake (measured in the range 10 to 100 mmol m?3 nitrate, i.e. ‘system I’) increased with RA in the growth limiting range but decreased when RA exceeded the relative growth rate (RGR), Km was not significantly related to changes in RA. On the basis of previous 13N-flux experiments, it is concluded that the differences in Vmax at growth limiting RA are attributable to differences in influx rates. Linear relationships between Vmax and tissue nitrogen concentrations were obtained in the growth limiting range for both species, and extrapolated intercepts relate well with the previously defined minimal nitrogen concentrations for plant growth (Oscarson, Ingemarsson & Larsson, 1989). Analysis of Vmax for net nitrate uptake on intact plant basis in relation to nitrogen demand during stable, nitrogen limited, growth shows an increased overcapacity at lower RA values in both species, which is largely explained by the increased relative root size at low RA. A balancing nitrate concentration, defined as the steady state concentration needed to sustain the relative rate of increase in plant nitrogen (RN), predicted by RA, was calculated for both species. In the growth limiting range, this value ranges from 3.5 mmol m?3 (RA 0.03 d?1) to 44 mmol m?3 (RA 0.21 d?1) for Pisum and from 0.2 mmol m?3 (RA 0.05 d?1) to 5.4 mmol m?3 (RA 0.03 d?1) for Lemna. It is suggested that this value can be used as a unifying measure of the affinity for nitrate, integrating the performance of the nitrate uptake system with nitrate flux and long term growth and demand for nitrogen. 相似文献
20.
S. Shipovskov 《Biocatalysis and Biotransformation》2013,31(6):455-465
Microbial theophylline oxidase (ThOx) is a redox enzyme catalysing 8-hydroxylation of theophylline to form 1,3-dimethyluric acid. In this work, ThOx has been characterized as a fragile haem-containing protein complex composed of several non-covalently bound dynamic domains with molecular weights of around 60 and 210 kDa, and capable of formation of 1.5 MDa assemblies as well. The rate of theophylline oxidation by ThOx with the non-physiological electron acceptor ferricyanide was 0.17 s?1, approaching that with cytochrome c, 0.33 s?1. The apparent catalytic constant depended on the electron acceptor concentration. At concentrations lower than 0.2 mM the reaction did not fit the Michaelis–Menten scheme, and some non-catalytic processes dominated in the overall reaction. The kinetics of ThOx catalysis were also studied at electrodes modified with self-assembled monolayers (SAM) of hydroxyl- and amine-terminated alkanethiols. Different compositions of the SAM provide different orientations of ThOx on these layers. Depending on the orientation of ThOx onto the SAM-modified electrodes, the heterogeneous electron transfer (ET) constant, ks, which characterizes the ET reaction between the electrodes and the haem of ThOx (Eo/ of 87 mV (NHE)) was 0.4 s?1 and 3.2 s?1. Only the low-ET-rate orientation appeared to be productive for the electrocatalytic function of ThOx, giving a reaction similar to that with ferricyanide and cytochrome c. The apparent efficiency of ThOx bioelectrocatalysis in the absence of mediators was substantially lower than that mediated by ferricyanide or cytochrome c. This lower efficiency is consistent with a correspondingly lower amount of ThOx being in direct ET contact with the electrodes and thus involved in electrocatalysis. 相似文献