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Fig. 17.24 SEM
micrographs of
a montmorillonite clay
showing a poorly layered
particle of 40 9 20 lm with
irregular surface, and b the
same sample after
impregnation with crude oil,
showing a well-layered
particle of about
10 lm 9 10 lm and
surrounded by small particles
of about 1 lm of diameter,
not observed in the original
clay sample. This image
shows the dissolution of the
clay crystal edges (Cosultchi
et al. 2004 ). Reprinted from
Cosultchi et al. ( 2004 ).
Copyright (2004) with
permission from Elsevier
Adsorption of petroleum compounds also occurs in sandy aquifer materials,
which are characterized by a much lower surface area. An example is the irre-
versible sorption of benzene in a sandy aquifer, from an unconfined alluvial plain
near the Han River in South Korea (Baek et al. 2003 ). In a laboratory column
experiment, it was observed that peak arrivals following pulse and step injection of
KCl and benzene coincide well, although the relative peak concentration of ben-
zene was much lower than that of KCl (Fig. 17.25 ).
Aerobic and anaerobic biodegradation of hydrocarbons comprising various
terminal electron acceptors is considered an important pathway for natural atten-
uation of petroleum hydrocarbons in groundwater. Most dissolved petroleum
hydrocarbons are biodegradable under aerobic conditions (Kao et al. 2010 ).
However, the prevalence of electron acceptors such as nitrate and sulfate, as well
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