Environmental Engineering Reference
In-Depth Information
Likewise, dewatering of saturated solids is necessary because all of the
moisture has to be driven off before contaminants can be efficiently desorbed.
3.4.6 Pump and treat
Pump-and-treat methods pump any contaminated water from the ground
and treat it either at an on-site plant or off-site. The advantage of this system
is that the contaminant is actually removed entirely from this system. This
is one of the most traditional methods of remediation, but it is not the most
effective method for all contaminants. For contaminants that bind very
closely to the soil, such as polycyclic aromatic hydrocarbon (PAHs), desorp-
tion of the contaminant from the soil to the groundwater is very slow. When
the groundwater is pumped out of the system, the contaminant present in
the aqueous phase is also removed, but a significant portion of the contam-
inant still remains present in the ground and will leach out in the future. In
order for pump and treat to be effective, it must be done over a long period,
in order to give the contaminant sufficient time to desorb from the soil.
However, this option becomes much more cost efficient and timely with the
addition of surfactants, such as amphiphilic polyurethane nanoparticles,
extracellular polymers, and cyclodetrins, that will loosen the bond of the
contaminant to the soil particles and increase the apparent solubility of the
contaminant (Tungittiplakorn et al., 2004). The addition of surfactants will
greatly increase the mass recovery rate for this method.
3.4.7 Stabilization
In stabilization, the contaminant is trapped within the soil matrix and is
effectively removed from being a future threat. It is a nondestructive method
and relies on the strength of the bond between the contaminant and the soil
particles or additive for its immobilization. The contaminated soil is then
often removed and placed in a landfill. Unfortunately, this method can cause
the volume of the soil to increase by as much as 20%, which increases
disposal costs. Stabilization can occur in two ways — through either covalent
bonding or pore trapping. Binding occurs when the contaminant actually
becomes part of the binder (such as cement or fly ash). Entrapment occurs
when the contaminant becomes trapped in the pores of an additive, but that
contaminant may be released if that additive is ever crushed (Magar, 2003).
Stabilization requires leaching monitoring in order to confirm that the con-
taminant stays locked in the matrix. Because the contaminant is not
destroyed, there is a possibility that it could be removed in the future.
One form of stabilization that has been examined recently is the use of
plants to trap the contaminant and also increase microbial growth so that
the contaminant can be destroyed. Phytoremediation, as this is called, con-
tains two components: phytodecontamination, which removes the contam-
inant from the soil by taking it up into the plant, and phytostabilization, in
which the plant helps to lock the contaminant in place. The latter is often
