Environmental Engineering Reference
In-Depth Information
HO
+
OH
=>
HO
+
HO
22
2
2
+
−
2
HO
=>
HO
+
2
−
−
HO
+ >
O
OO
+
2
2
2
2
The coexisting oxidation-reduction reactions associated with a modiied Fenton's pro-
cess promote enhanced desorption and degradation of recalcitrant compounds (Fenton,
1893, 1895; Fenton and Jackson, 1899). These include compounds such as carbon tetrachlo-
ride and chloroform, which were previously considered untreatable by Fenton's chemistry.
There is a complete mineralization of organic matter. The breakdown is fast, within days,
typically minutes to hours, depending on the concentration of H
2
O
2
. The process has some
effects on the residual free phase.
Modiied Fenton's reagent, hydrogen peroxide, and potassium permanganate were
applied to aromatic hydrocarbons (PAHs) contaminated sediments (Ferrarese et al., 2008).
They concluded that the optimal oxidant dosages determined were quite high, as sorbed
PAH mineralization requires very vigorous oxidation conditions, especially for soils and
sediments with high organic matter content. Their results indicated that the optimal oxi-
dant dose must be carefully determined under site-speciic conditions. Kellar et al. (2009)
have used a sodium-based Fenton reagent in the United States in in situ and ex situ appli-
cations. The method has been proposed for the remediation of sediments near a chlo-
rinated solvent site in Pennsylvania. Wet air oxidation requires high temperatures and
pressures but is capable of destroying PCBs and PAHs. Large quantities of water are not
detrimental to the process. Costs are high at large scale, however.
Oxidation/reduction of heavy metals is another method for remediating in situ and
ex situ soils, sediments sludges, and ash. A detoxiication technology called TR-DETOX
involves the percolation of inorganic and organic reagents to reduce heavy metals to their
lowest valence state. The stabilized solids achieve the TCLP requirements and are consid-
ered as no longer leachable. The TR-DETOX technology can also be applied along with
biological treatment (bioremediation) to ensure degradation of organic contaminants. One
of the main chemicals is sodium polythiocarbonate that forms a precipitate that becomes
less soluble over time. Lime, silicates, and Portland cement are not added, and costs are
usually about one quarter of stabilization/solidiication processes. A unique characteristic
is electronic addition of reagent. Pilot tests are required to determine the most appropriate
formulation (Mulligan et al., 2001).
11.4.2 Nanoremediation
Nanoremediation involves the application of nanomaterials to transform or reduce the
toxicity of the contaminants. The advantage of the addition of the nanoparticles to soil
is that they can be transported further due to their small size. Zero-valent iron (nZVI) is
the most common with particles ranging from 10 to 100 nm in size. Information from 45
sites was reviewed as a representative of the total projects under way using nanomateri-
als for site remediation (Karn et al., 2009). They concluded that nanoremediation could
reduce costs and the time of cleaning up large-scale contaminated sites but eliminating
the need disposal of contaminated soil, and reducing some contaminant concentrations to
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