Biotechnological Aspects of Soil Decontamination - Biotechnologies and Biomimetics for Civil Engineering - page 374

alternatives to remove metal contaminants from the soils. This technology is
particularly cost-effective and well established in mineral industry.
17.3 Chemical Techniques
A range of chemical processes have been applied to soil to destroy or convert
pollutants into less toxic forms, to extract them, or to immobilize them. Wood
( 2001 ) suggested that chemical treatments can be highly specific for some pol-
lutants, e.g., PCBs and halogenated alkanes.
17.3.1 Oxidation-Reduction Reaction
Chemical treatment by reductive as well as oxidative mechanisms may be used to
detoxify or decrease the mobility of metal contaminants (Evanko and Dzombak
1997 ). This is commonly used for waste water treatment. Oxidation reactions
detoxify, precipitate, or solubilize metals and involve addition of potassium per-
manganate, hydrogen peroxide, and hypochlorite, or chlorine gas. Neutralization
reactions are performed to adjust the pH of acidic or basic soils (lime). Reduction
reactions are induced through the addition of alkali metals, such as sodium, sulfur
dioxide, sulfite salts, and ferrous sulfate. Sometimes chemical treatment is used to
pretreat the soil for solidification or other treatments. These reactions are, how-
ever, not specific and, therefore, there is a risk of converting other metals into more
toxic or mobile forms. Arsenic is most applicable for chemical oxidation since As
(V) is less toxic than As (III). Hg, Pb, Se, and Ag are also applicable for reduction.
These chemical treatments can be performed in situ by injection into ground water,
but have the potential to introduce further contamination.
Over the last two decades, Fenton treatment has emerged as a viable remedi-
ation technology for PAH-contaminated soils. Several reviews on various Fenton-
based treatments for contaminated soils have been published (Cravotto et al.
2005 ). In these works, PAHs have been grouped as hydrophobic or semi-volatile
contaminants. PAHs are known to be toxic, mutagenic, carcinogenic, and tera-
trogenic, most commonly found at sites contaminated with coal tar and creosote,
especially as the heritage from the manufactured gas plants (MGP) and wood
treatment facilities of the last few centuries. Effective decontamination of the soil
can be achieved by using advanced oxidation process (AOPs), which is based on
Fenton's reaction (hydrogen peroxide catalysed by iron), involving solely one or a
combination of physical, chemical, biological, and thermal processes .Faster and
more efficient degradation of recalcitrant compounds such as PAHs can be
achieved using AOPs (Cravotto et al. 2007 ).