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

volatilization of some compounds, so safety issues must be considered,
especially when using a concentrated peroxide solution.
The success of a Fenton’s reagent treatment is strongly dependent on solid
matrix characteristics and the contaminant availability (Flotron et al., 2005; Nam
et al., 2001). Hydrophobic contaminants in aged soils are less susceptible to
chemical oxidation because of their adsorption to organic material and diffusion
into micropores. This renders them unavailable for the hydroxyl radicals
produced during Fenton’s reactions, which are generated in the aqueous phase
(Sedlak and Andren, 1994; Bogan et al., 2003). The presence of black carbon,
for example, will limit the availability of PAHs to chemical oxidation (Lundstedt et
al., 2006).
The amount of organic matter present also affects oxidation success. Bogan and
Trbovic (2003) showed that Fenton’s reagents can be more successful at higher
organic matter contents. Since most PAH compounds partition to organic matter,
oxidation of organic matter by the reagent will release PAH compounds and
render them more available to chemical oxidation. They found that if less than
5% organic matter was present, the pollutants were adsorbed in the micropores
and were less available for chemical oxidation. However, large amounts of
organic matter will also result in scavenging of the OH - radicals, so higher
reagent concentrations must be added to achieve PAH oxidation (Flotron et al.,
2005; Lundstedt et al., 2006).
The addition of a cosolvent may improve the oxidation process by enhancing
compound desorption. Ethanol addition has been shown to increase the removal
of Benzo[a]pyrene (Lee and Hosomi, 2001). Others have reported beneficial
effects from using vegetable oil (Bogan et al., 2003), surfactants (Nadarajah et
al., 2002) and cyclodextrins (Lindsey et al., 2003) as cosolvents to improve the
extraction of recalcitrant HMW PAHs and make them more available to oxidation.
Bogan et al. (2003) and Lee et al. (2002) used vegetable oil or ethanol
extractions before oxidation to enhance desorption of PAHs and improve the
overall degradation process. Lundstedt et al., (2006) found that ethanol pretreatment
enhanced the PAH transformation thereby making them more available
for the hydroxyl radicals. However, they also found that Fenton’s reagent caused
an increase in oxidation products, mostly quinones. Compounds like 1-indanone,
anthracene-9,10-dione, 1-methylanthracenedione, 2-methylanthracenedione,
1,8-naphthalic anhydride, benz[a]anthracene-7,12-dione and two compounds
tentatively identified as hydroxy-9-fluorenones were found at higher
concentrations after treatment. These compounds are generally less toxic and
more susceptible to microbial degradation (Moody et al., 2005).
Fenton’s oxidation can also be used in combination with bioremediation
techniques (Nam et al., 2001). However pH adjustment is not practical under field
conditions and is prohibitive to microbial growth. A modified Fenton’s treatment
with no pH adjustment or no addition of Fe has shown to be effective.
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