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

1. Fenton’s reagent – formation of hydroxyl radical (to be discussed in more
detail in Chemical Techniques for Enhancing PAH Degradation)
H2O2 + Fe 2+ → • OH + OH − + Fe 3+
2. Ozone – formation of hydroxyl radical or direct oxidation by ozone radical
(to be discussed in more detail in Chemical Techniques for Enhancing
PAH Degradation)
O3 → HO2 - → • OH
O3 +O2 •- → O •3-
3. Sodium persulfate – formation of persulfate anions (standard oxidation
potential of 2.0V); additions of metals can subsequently create sulfate
radicals (standard oxidation potential of 2.6V)
Na2S2O8 → S2O8 − + 2Na +
S2O8 − + Fe 2+ → 2SO4 •- + Fe 3+
The mechanism by which free radicals attack PAHs is similar for all free radicals
and works by the following examples of hydroxyl radical oxidation with reaction 1
usually initiating ring cleavage (Ferrarese et al., 2008; Flotron et al., 2005):
1) R + • OH → • ROH (hydroxyl addition)
2) ROH + • OH → • R + H2O (hydrogen abstraction)
In recent investigations the use of potassium permanganate (KMnO4) has also
shown some success. The reaction proceeds without the formation of a radical
species. The reaction occurs due to the high oxidation state (+7) of the
manganese atom in the permanganate salt.
MnO4 − +4H + +3e − → MnO2(s) +2H2O
Although permanganate is a strong oxidant, with a standard oxidation potential of
1.7V, it lacks the ability to attack the benzene ring. The inability to attack the
benzene ring has limited the use of potassium permanganate in PAH
degradation (Ferrarese et al., 2008).
In complex soil mixtures, the use of advanced oxidation processes can become
complicated by soil organic matter, which has the ability to scavenge nonselective
oxidants as well as sequester PAHs into hydrophobic pores. To
overcome PAH solubility issues, previous investigations have increased oxidant
concentrations. Care must be taken when using this approach; however, as over
application of the oxidant can cause self consumption of the radical species
(Ferrarese et al., 2008). Other investigations have sought to overcome low PAH
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