Danger desorption

Denaturation of one or both partners of the affinity pair is done either by changing pH, by salts, or by chaotropic substances. This kind of desorption is easy to do, but there is danger of irreversible... 

An important realization that has been attained in recent years is that the processes of adsorption, desorption and rearrangement on the catalyst surface may themselves produce multiple reaction rates or oscillations. Wicke (35) and his colleagues found this some years ago and the reviews of Sheintuch and Schmitz (58) and Scheintuch (59) show how wide-spread the phenomenon is. It is dangerous to mention names when I am sure to omit many important ones but those of Yablonskii, Slin ko and their colleagues in Russia, Eigenberger and Hugo in Germany,... 

The association between xenobiotics and sediments has been discussed in Section 3.2, and it is now clearly established that many xenobiotics can be recovered from contaminated sediments which may act as a "sink" for these compounds. Whereas it is certainly true that during aging in both soil and in sediments, these compounds become less accessible to biota, it seems rather dangerous to postulate that their hazard also diminishes with time (Alexander 1995). Desorption may occur slowly over long periods of time (ten Hulscher et al. 1999), and levels after bioconcentration may reach unacceptable levels and, in extreme situations, pose a toxic hazard to humans through consumption of fish. In a wider context, the toxicity of xenobiotics to terrestrial organisms is addressed in Section 7.3.6. 

Overall, it appears that PAH desorption in an electrokinetic cell could be enhanced by use of n-butylamine or ethanol as a cosolvent, but actual removal efficiencies are very low. Therefore, further study is required to achieve high removal efficiencies in cosolvent-enhanced systems. Moreover, the application of cosolvent requires care because cosolvents are flammable and explosive, which could pose particular dangers in electrokinetic applications (Saichek and Reddy, 2005a). 

In Fig. 9.2-1 an adsorption unit with two fixed beds is depicted. The fluid to be treated passes downward through the bed. At the same time the second bed is regenerated by a fluid which is flowing from the bottom to the top. This can be advantageous with respect to the efficiency of the desorption step however, the danger of fluidization exists at high velocities, compare Sect. 3. 

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