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matter, they are isolated from the degrading organisms and

are protected from intracellular degradation. On the other

hand, bacteria may also be sorbed. If bacteria and

contaminants are sorbed on adjacent sites on the soil

surface, the uptake of the contaminants by the sorbed

bacteria is facilitated (Ogram et al. 1985).

 Isotherm models can be used to predict the sorption and

desorption behavior of the contaminants, and thus help to

design groundwater/soil reclamation programs. Although

equilibrium may not be reached in reality, the prediction

may serve as a guide to the direction of mass transfer.


 3.3 Degradation of Phenolic Compounds

 Many processes can contribute to the degradation of

phenolic compounds in the environment. Among these are

photolysis, chemical oxidation, hydrolysis, volatiliza-tion

and biodegradation. Each process needs special conditions

in order to proceed and has its own role in the degradation

of these compounds from the subsurface environment.


3.3.1 Photolysis


 Phenol has long been known to form reddish high

molecular weight material when exposed to sunlight and air.

It can undergo photolysis either in the phenolate anion form

(maximum absorbance at 270 nm) or in the undissociated

molecule (maximum absorbance at 310 nm). Experimental

irradiation of phenol at 254 nm in the presence of oxygen

yields a phenoxy radical intermediate that subsequently give