Remediation and Management of Contaminated Soil - Sustainable Practices in Geoenvironmental Engineering - page 411

The disposal of the treated ine particles varies depending on the type and levels of the
contaminants.
Mixtures of metals and organic contaminants may require sequential washing with
different additives to target the various contaminants. Soil washing processes generally
use hot water to reduce the viscosity of hydrocarbons. The increased temperature also
increases the solubilities of metal salts. The treated soil can then be washed to remove any
residual wash solution prior to disposal. Ideally, the wash solution should be recycled.
Costs of soil washing are usually in the order of $70 to $190/m 3 depending on site size and
complexity (Racer Software, Remedial Action Plan, 2006). Although extensively used in
Europe, fullscale processes are less common in the United States. Laboratory feasibility
tests should be conducted to determine optimal conditions (chemical type and dosage,
contact time, agitation, temperature, and extraction steps to meet regulatory require-
ments). As spent washwater can be a mixture of soluble contaminants and ine particles,
treatment is thus required to meet reuse or disposal requirements. Full-scale demonstra-
tions may be required to demonstrate the feasibility of newly developed treatment pro-
cesses. Presently, wastewater management systems act as a foundation for modern public
health and environment protection. The idea of most suitable wastewater management
systems is to use less energy, allow for elimination or beneicial reuse of biosolids, restore
natural nutrient cycles, have much smaller footprints, be more energy eficient, and design
to eliminate exposed wastewater surfaces, odors, and hazardous by-products (Daigger
and Crawford, 2005). In addition to the technical aspects of a wastewater treatment tech-
nology, selection of a particular technology should be based on all aspects that determine
its sustainability.
11.4 Chemical/Thermal Remediation
Chemical remediation includes the use of amendments, oxidation as well known by
Fenton's reactions, and electrochemical remediation.
11.4.1 Oxidation
Oxidation (USEPA, 2006) has been used in situ or ex situ for complete chemical destruc-
tion of many toxic organic chemicals and partial oxidation prior to bioremediation. The
compounds become less hazardous or toxic. The oxidants can include ozone, permanga-
nate, hydrogen peroxide, sodium persulfate, and Fenton's reagent. High treatment efi-
ciencies of greater than 90% can be achieved for unsaturated aliphatics such as TCE and
aromatic compounds such as benzene. Eficient degradation depend on the concentration
of oxidant, the contaminant properties and concentration and site characteristics such as
pH, temperature, and the concentration of other oxidant-consuming substances including
natural organic matter, minerals, carbonate, and other scavengers of free radicals.
The oxidant, known as Fenton's reagent, destroys a variety of wastes and generates no
harmful by-products. Fenton's reagent was invented by Fenton in 1894. Today there are
several methods known as “modiied” Fenton's reaction where different additives increase
the oxidizing eficiency by increasing the pH tolerance, increasing the reaction time, and
producing more and more stable radicals.