The Role of Temperature

This is an important parameter particularly for naturally occurring mixed cultures of organisms in the natural environment temperature may result in important changes in the composition of the microbial flora as well as on the rates for different processes. An illustrative example of its importance includes the following. An anaerobic sediment sample was incubated with 

6-tetrachlorobiphenyl at various temperatures between 4 and 66°C (Wu et al. 1997a,b). The main products were 2,4,6- and 2,3,6-trichlorobiphenyl and 2,6-dichlorobiphenyl the first was produced maximally and discontinuously at 12 and 34°C, the second maximally at 18°C, and the third was dominant from 25 to 30°C. Dechlorination was not observed above 37°C. 

Collectively, there is therefore extensive evidence for the anaerobic dechlorination of PCBs but the extent and specificity of this depends on both the organism and the degree and pattern of substituents in the congener. 

Mixed cultures of organisms that were isolated from sediments contaminated with PCBs and polybrominated biphenyls (PBBs) were shown to debrominate PBBs under anaerobic conditions (Morris et al. 1992), and the dominant congener—2,2, 4,4, 5,5 (245-245)-hexabromobiphenyl—could be successively debrominated to 2,2 -dibromobiphenyl. However, in sediments from the most heavily contaminated site containing contaminants in addition to PBBs, very little debromination occurred and the recalcitrance was attributed to the toxicity of the other contaminants (Morris et al. 1993). 

Ingenious experiments to which reference has already been made have used addition of specific PCB congeners that are more readily dechlorinated to prime dechlorination at specific positions (Bedard and Quensen 1995). They have been extended to the use of dibrominated biphenyls in the presence of malate to stimulate dechlorination of the hexachloro- to nanochlorobiphenyls (Bedard and Quensen 1995). Results from these experiments provide valuable evidence of important differences between anaerobic dechlorination and anaerobic debromination, and the greater facility of the latter. 

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From the Arrhenius form of Eq. (70) it is intuitively expected that the rate constant for chain scission kc should increase exponentially with the temperature as with any thermal activation process. It is practically impossible to change the experimental temperature without affecting at the same time the medium viscosity. The measured scission rate is necessarily the result of these two combined effects to single out the role of temperature, kc must be corrected for the variation in solvent viscosity according to some known relationship, established either empirically or theoretically. 

Mergence of the binodial with the nonsolvent-solvent axis shows that the polymer concentration in the more dilute phase becomes vanishingly small when the proportion of nonsolvent exceeds appreciably that at the critical point. These features clearly parallel those observed in two-component systems, with the nonsolvent-solvent ratio assuming the role of temperature in the latter. It may be shown that they are not critically dependent on the particular values assigned to the... 

The role of temperature may be of particular significance for mixed cultures of organisms in the natural environment, or when they are used in laboratory studies. Temperature may effect important changes both in the composition of the microbial flora and on the rates of reaction. Greatest attention has hitherto been directed to hydrocarbons and PCBs. Some illustrative examples of important issues that are especially relevant to bioremediation include the following ... 

Many contaminated sites are located in areas with temperatures considerably less than 15°C, and investigations into the role of temperature have therefore been carried out. Some of the cardinal results have been discussed in Chapter 4, and it may be concluded that although the rates at 4-5°C may be low, selection of organisms for adaptation to the ambient temperature will generally ensure that degradative activity is retained. There may, however, be selective degradation of specific groups of components in mixtures such as PCBs. 

So far, what has been examined is the effect of the concentrations of the reactants and the products on the reaction rate at a given temperature. That temperature also has a strong influence on reaction rates can be very effectively conveyed by considering the experimentally found data on the formation of water from a mixture of hydrogen and oxygen. At room temperature the reaction will not take place hence the reaction rate is zero. At 400 °C it is completed in 1920 h, at 500 °C in 2 h, and at 600 °C the reaction takes place with explosive rapidity. In order to obtain the complete rate equation, it is also necessary to know the role of temperature on the reaction rate. It will be recalled that a typical rate equation has the following form ... 

The study of polymerization kinetics allows us to understand how quickly a reaction progresses and the role of temperature on the rate of a reaction. It also provides tools for elucidating the mechanisms by which polymerization occurs. In addition, we are able to study the effect of catalysts on the rates of polymerization reactions, allowing us to develop new and better catalysts based on the measured performance. 

With the suggestion that the last common genetic ancestor is a hyperthermophile, the role of temperature on the origins of life is important. The lower temperature limit in water is limited by the phase transition from liquid to ice. This is a problem because the density of ice is lower than that of water and the increase in volume on freezing will cause the cell structure to become disrupted in the same way that pipes burst in the winter. The lower limit for bacterial growth reported so far is -20°C, which is the temperature at which intracellular ice is formed. Adaptation to the cold requires a considerable salt content to depress the melting point of water the Don Juan Pond in Antarctica, which has a saturated CaCE solution, preserves the liquid phase at temperatures as low as —53°C. 

Arp. H.P.H.and Schmidt. T.C. Air-water transferor MTBE, its degradation products, and alternative fuel oxygenates the role of temperature. Environ. Sci. Technol, 38(20) 5405-5412, 2004. 

So far we have examined the effect of concentration of reactants and products on the rate of reaction, all at a given temperature level. To obtain the complete rate equation, we also need to know the role of temperature on reaction rate. Now in a typical rate equation we have... 

Liger-Belair, G., Villaume, S., Cilindre, C., and Jeandet, P. (2009b). Kinetics of CO2 fluxes outgassing from champagne glasses in tasting conditions The role of temperature. /. Agric. Food Chem. 57,1997-2003. 

Moisture. As anticipated, moisture contents of the powder samples decreased with decreasing temperature differentials between inlet and exit air temperatures when either inlet or exit air temperature was held constant (Figure 2). The sample with the highest temperature differential ( T=120 C) and lowest exit air temperature (T=80 C) had the highest moisture content (7.8%) of all the powder samples. The role of temperature differential on product moisture content is apparent from either data series in Figure 2. While the sample dried at 280 C inlet and 105 C exit air temperatures had the greatest temperature differential, the... 

M. Brebu, M. Azhar Uddin, A. Muto, Y. Sakata, and C. Vasile, The role of temperature program and catalytic system on the quality of acryl-onitrile-butadiene-styrene degradation oil, /. Anal. Appl. Pyrolysis, 63 (l) 43-57, March 2002. 

Reynolds, W.W. and Casterlin, M.E. (1980). The role of temperature in the environmental physiology of fishes. In Environmental Physiology of Fishes (M.A. Ali, ed.), pp. 497-518. NATO Advanced Study Institute Series, No. 35. Plenum Press, New York. 

An Earth example not previously discussed deals with the roles of temperature and pressure on the density of ice cores (Marion and Jakubowski 2004). Gow (1971) has shown that the density of deep ice cores under pressure relaxes elastically as soon as the cores are extracted. In Fig. 5.9, we used our model parameters to calculate how the density of an ice core from Antarctica (Gow et al. 1968 Gow 1971) would vary with core temperature at 1 atm, which is what is measured at the surface with corrections for temperature, to the same core under both temperature and pressure constraints. At 1 atm pressure, the core density changes linearly with temperature (Fig. 5.9), in agreement with our model (Fig. 3.2) and the Gow (1971) results (see his table 1). In contrast, the density of the ice core subjected to both temperature... 

The transition probabilities can be strictly determinated or stochastic. In the latter case the cellular automata noise plays the role of temperature in... 

The role of temperature on the foam stability has been studied in gravitational field [63,72], It was proved that temperature influences strongly the foam lifetime, especially for foams from nonionic surfactants, such as oxyethylene derivatives of alkylphenols, alcohols and acids. 

A physical interpretation of Equation (35) is possible if one notes that it is mathematically analogous to Fourier law of heat conduction. The constant factor in the right-hand side plays the role of thermal conductivity, and the local incident radiation GA(r) plays the role of temperature. In that sense, differences in the latter variable among neighboring regions in the medium drive the diffusion of radiation toward the less radiated zone. Note that the more positive the asymmetry parameter, the higher the conductivity that is, forward scattering accelerates radiation diffusion while backscatter-ing retards it. 

Colin, H. et al. The role of temperature in reversed-phase high performance Uquid chromatography using pyrocarbon-containing adsorbents. J. Chromatogr. 1978,166,41-65. 

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