Remediation of PAH-Contaminated Soils and Sediments: A ...

encountered with biodegradation, and may result in a faster and more efficient
degradation of HMW compounds (Kawahara et al., 1995; Nam et al., 2001; Watts
et al., 2002). Combining chemical oxidation processes with biodegradation may
enhance PAH removal since chemical oxidation byproducts of PAHs are more
water-soluble and available to biodegradation (Nam et al., 2001; Matscheko et
al., 2002). Some researchers have suggested that biodegradation procedures be
used as a polishing step after the bulk of contaminants is removed by other
means (Lundstedt et al., 2006).
Chemical oxidation procedures have some other advantages over
biodegradation in that the processes can be better controlled since the conditions
can be modified. They are also relatively insensitive to external environmental
disturbances (Rivas, 2006). Conversely, there is always a possibility of wastage
of chemical reagent added, especially when the sediments/soils have high
organic matter content, which will also be oxidized. High organic matter content
may increase the cost of treatment but can also increase PAH availability since
sorbed PAHs will be released from organic matter during oxidation (Rivas, 2006).
Remediation by chemical oxidation suffers from some of the same problems as
other remediation technologies. Any treatment method designed to eliminate
PAHs must consider the strong sorption of PAH compounds into micropores
which may render them inaccessible to oxidation processes. Transfer to solution
can be very slow and diffusion controlled; therefore, slowing degradation. More
aged soils/sediments usually have a lower overall PAH availability and therefore
the contaminant will be less susceptible to the chemical oxidation resulting in
lower efficiency of removal (Bogan and Trbovic, 2003). When a complex mixture
of PAH compounds has been present in soils for many years, remediation with
chemical oxidation is far more difficult (Nam et al., 2001; Guha et al., 1999).
Soil chemical processes can be enhanced through several oxidation techniques
to increase PAH degradation. The two most popular of these processes are (Yin
and Allen, 1999):
� Ozone treatment
� Fenton’s reagents
Both methods utilize the formation of non-specific hydroxyl radicals oxidizing
agents which are capable of oxidizing persistent organic contaminants. Hydroxyl
radicals are strong, relatively unspecific oxidants that react with most organic
contaminants, including PAHs (Haag and Yao, 1992). They degrade organic
compounds either by hydrogen abstraction or by hydroxyl addition.
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