Uptake short time response

Fig.1 Theoretical uptake curves for isothermal diffusion-controlled system showing a long time asymptote according to Eq. 2 or 3b and b form of short time response plotted in accordance with Eq. 3a. Note that the initial slope is quite insensitive to the particle shape (the equivalent radius r is defined as the radius of a sphere with the same surface-to-volume ratio as the actual particles)...

Temporal variations over short time scales have also been accounted for in this model. They are a result of the diurnal pattern of water uptake which peaks at midday and is zero at night. At night, however, the direction of water fluxes can revert, this hydraulic lift being responsible for water efflux from roots at the top of the root system, especially from those roots growing in the topsoil when it dries out (Caldwell et al., 1998). 

Newcombs et al. [115] examined tlie competition between 2-methyllsobomeol (MTB) and DOM during a 4-hr contact time and under equilibrium conditions (3-5 days) using a series of PACs with different pore size distributions, and a reservoir DOM sample and its different size fractions. At short contact times (< 1 hr), tire order of MTB removal in the presence of the smallest size DOM fraction by different carbons did not follow the same order of MIB removal measured at equilibrium conditions. Despite their higli equilibrium uptakes, mlcroporous coconut shell carbons with narrow pore size distributions showed slower MIB uptake rates compared to steam- and wood-based carbons. Therefore, the most effective PAG depends on contact time, and different PACs should be evaluated at the contact time of practical application. It was also shown that under simultaneous adsorption conditions, the low molecular weight components of DOM were primarily responsible for the competition effect [9,115]. 

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