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131.
Accurate pseudoanalytical solution for steady-state biofilms 总被引:3,自引:0,他引:3
An extremely accurate pseudoanalytical solution for the flux of substrate into a steady-state biofilm is developed. The standard deviations between the substrate fluxes computed from the pseudoanalytical solution and the numerical solution were less than 2.6%. Additional advantages of the pseudoanalytical solution are that it has no inaccuracies around S(min) (*) = 1 and it is composed of single continuous functions applicable to the whole S(min) (*) region. 相似文献
132.
Biofilm detachment mechanisms in a liquid-fluidized bed 总被引:10,自引:0,他引:10
Chang HT Rittmann BE Amar D Heim R Ehlinger O Lesty Y 《Biotechnology and bioengineering》1991,38(5):499-506
Bed fluidization offers the possibility of gaining the advantages of fixed-film biological processes without the disadvantage of pore clogging. However, the biofilm detachment rate, due to hydrodynamics and particle-to-particle attrition, is very poorly understood for fluidized-bed biofilm processes. In this work, a two-phase fluidized-bed biofilm was operated under a constant surface loading (0.09 mg total organic carbon/cm(2) day) and with a range of bed height (H), fluid velocities (U), and support-particle concentrations (C(p)). Direct measurements were made for the specific biofilm loss rate coefficient (b(s))and the total biofilm accumulation (X(f)L(f)). A hydrodynamic model allowed independent determination of the biofilm density (X(f)), biofilm thickness (L(f)), liquid shear stress (tau), and Reynolds number (Re). Multiple regression analysis of the results showed that increased particle-to-particle attrition, proportional to C(p) and increased turbulence, described by Re, caused the biofilms to be denser and thinner. The specific detachment rate coefficient (b(s)) increased as C(p) and Re increased. Almost all of the 6, values were larger than predicted by a previous model derived for smooth biofilms on a nonfluidized surface. Therefore, the turbulence and attrition of bed fluidization appear to be dominant detachment mechanisms. 相似文献
133.
Model of steady-state-biofilm kinetics 总被引:1,自引:0,他引:1
134.
Bernd Schröder Ina Rittmann Ernst Pfeffer Gerhard Breves 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(1):43-51
Unidirectional flux rates of Ca2+ across gastrointestinal tissues from sheep and goats were measured in vitro by applying the Ussing-chamber technique. Except for the sheep duodenum, mucosal to serosal Ca2+ flux rates (J
ms) exceeded respective flux rates in the opposite direction (J
sm) in both species and in all segments of the intestinal tract. This resulted in net Ca2+ flux rates␣(J
net = J
ms − J
sm) ranging between −2 and 9 nmol · cm−2 · h−1 in sheep and between 10 and 15 nmol cm−2 · h−1 in goats. In sheep, only J
net in jejunum, and in goats, J
netin duodenum and jejunum were significantly different from zero. Using sheep rumen wall epithelia, significant J
net of Ca2+ of around 5 nmol · cm−2 · h−1 could be detected. Since the experiments were carried out in the absence of an electrochemical gradient, significant net
Ca2+ absorption clearly indicates the presence of active mechanisms for Ca2+ transport. Dietary Ca depletion caused increased calcitriol plasma concentrations and induced significant stimulations of
net Ca2+ absorption in goat rumen. J
net of Ca2+ across goat rumen epithelia was significantly reduced by 1 mmol · l −1 verapamil in the mucosal buffer solution. In conclusion, there is clear evidence for the rumen as a main site for active
Ca2+ absorption in small ruminants. Stimulation of active Ca2+ absorption by increased plasma calcitriol levels and inhibition by mucosal verapamil suggest mechanistic and regulatory similarities
to active Ca2+ transport as described for the upper small intestines of monogastric species.
Accepted: 31 July 1996 相似文献
135.
Dog GM1 gangliosidosis: characterization of the residual liver acid beta-galactosidase. 总被引:1,自引:0,他引:1 下载免费PDF全文
The residual liver acid beta-galactosidase activity from the first documented case of GM1 gangliosidosis in dogs was partially purified and characterized with respect to kinetic properties, thermostability, isoelectric point, molecular weight, and antigenicity. The GM1 dog liver beta-galactosidase appears to be identical with the normal dog liver enzyme in all properties examined. The canine disease is strikingly different from the human disease in the amount of enzyme that is present in the tissue. Unlike the human disease, in which normal amounts of catalytically defective beta-galactosidase are present, in dog GM1 gangliosidosis, only 1% of normal beta-galactosidase protein is detectable. 相似文献
136.
137.
Ning Yan Rongjie Li Hua Xu Ling Li Lihui Yang Yongming Zhang Rui Liu Bruce E. Rittmann 《Biodegradation》2016,27(2-3):145-154
2,4,6-Trichlorophenol (TCP) is a biologically recalcitrant compound, but its biodegradation via reductive dechlorination can be accelerated by adding an exogenous electron donor. In this work, acetate and formate were evaluated for their ability to accelerate TCP reductive dechlorination, as well to accelerate mono-oxygenation of TCP’s reduction product, phenol. Acetate and formate accelerated TCP reductive dechlorination, and the impact was proportional to the number of electron equivalents released by oxidation of the donor: 8 e? equivalents per mol for acetate, compared to 2 e? eq per mol for formate. The acceleration phenomenon was similar for phenol mono-oxygenation, and this increased the rate of TCP mineralization. Compared to endogenous electron equivalents generated by phenol mineralization, the impact of exogenous electron donor was stronger on a per-equivalent basis. 相似文献
138.
Chlorinated aromatic compounds challenge our environment and wastewater treatment processes due to their biorecalcitrance
and inhibition. In particular, 2,4,5-trichlorophenol (TCP) seems to demonstrate greater resistance to biodegradation than
other trichlorophenols and is a known uncoupler of the electron transport chain, although little work addresses this compound
specifically. Here, we investigate the biorecalcitrance, inhibition, and adaptation to 2,4,5-trichlorophenol by aerobic mixed
microbial communities. We show that 2,4,5-trichlorophenol is strongly resistant to biodegradation at concentrations greater
than 40 μM, demonstrates inhibition to respiration in direct proportion to 2,4,5-trichlorophenol concentration (with 50% inhibition
projected near 85 μM 2,4,5-trichlorophenol), and does not sustain biomass in continuous reactors, even when all input 2,4,5-trichlorophenol
is degraded. Communities showed consistent adaptation patterns to 2,4,5-trichlorophenol at concentrations of 10 μM and 20 μM,
but these patterns diverged at concentrations greater than 40 μM. Finally, thermodynamic approximations were used to estimate
the yield of 2,4,5-trichlorophenol as 0.165 gVSS/gCOD, a low value that partially explains why biodegradation of 2,4,5-trichlorophenol
did not sustain the biomass. In particular, we estimated that the minimum concentration to support steady-state biomass (S
min) is approximately 180 μM, a value much larger than the 40-μM concentration that is strongly resistant to biodegradation.
Thus, readily biodegradable concentrations of 2,4,5-trichlorophenol are too low to sustain the biomass that biodegrades it. 相似文献
139.
We expand the biogeochemical program CCBATCH to describe transport processes in 1-D ground-water systems. We use the expanded
CCBATCH with our biogeochemical framework for metal detoxification in sulfidic systems to study complex bio-protection scenarios.
In particular, in our numerical experiments we expose a consortium of sulfate-reducing bacteria and fermenting bacteria to
a toxic concentration of Zn2+ in a 1-D system with precipitation of zinc-sulfide solids turned off or on. Our results confirm the key role of sulfide precipitation
in detoxification when coupled effects of transport and biological processes are considered. The potential of sulfide as a
detoxifying agent in bio-protection is explained by its high mobility, its high affinity for metals, and its high rate of
production in sulfidic systems. Thus, our numerical results offer important evidence for the gradient-resistance mechanism
and validate that a metal-resistance criterion developed from an analytical solution is accurate for defining when bio-protection
should succeed. 相似文献
140.
H2 thresholds, concentrations below which H2 consumption by a microbial group stops, have been associated with microbial respiratory processes such as dechlorination,
denitrification, sulfate reduction, and methanogenesis. Researchers have proposed that observed H2 thresholds occur when the available Gibbs free energy is minimal (ΔG ≈ 0) for a specific respiratory reaction. Others suggest that microbial kinetics also may play a role in controlling the
thresholds. Here, we comprehensively evaluate H2 thresholds in light of microbial thermodynamic and kinetic principles. We show that a thermodynamic H2 threshold for Methanobacterium bryantii M.o.H. is not controlled by ΔG for methane production from H2 + HCO3−. We repeatedly attain a H2 threshold near 0.4 nM, with a range of 0.2–1 nM, and ΔG for methanogenesis from H2 + HCO3− is positive, +5 to +7 kJ/mol-H2, at the threshold in most cases. We postulate that the H2 threshold is controlled by a separate reaction other than methane production. The electrons from H2 oxidation are transferred to an electron sink that is a solid-phase component of the cells. We also show that a kinetic threshold
(S
min) occurs at a theoretically computed H2 concentration of about 2400 nM at which biomass growth shifts from positive to negative. 相似文献