Contaminated Land and Bio-Remediation - Environmental Biotechnology: Theory and Application - page 93

Biological
Biological methods involve the transformation or mineralisation of contaminants
to less toxic, more mobile, or less toxic and more mobile, forms. This can include
fixation or accumulation in harvestable biomass crops, though this approach is
discussed more fully later in Chapter 7.
The main advantages of these methods are their ability to destroy a wide range
of organic compounds, their potential benefit to soil structure and fertility and
their generally non-toxic, 'green' image. On the other hand, the process end-point
can be uncertain and difficult to gauge, the treatment itself may be slow and not
all contaminants are conducive to treatment by biological means.
Chemical
Toxic compounds are destroyed, fixed or neutralised by chemical reaction. The
principal advantages are that under this approach, the destruction of biologically
recalcitrant chemicals is possible and toxic substances can be chemically con-
verted to either more or less biologically available ones, whichever is required.
On the downside, it is possible for contaminants to be incompletely treated, the
reagents necessary may themselves cause damage to the soil and often there is a
need for some form of additional secondary treatment.
Physical
This involves the physical removal of contaminated materials, often by concen-
tration and excavation, for further treatment or disposal. As such, it is not truly
remediation, though the net result is still effectively a clean up of the affected
site. Landfill tax and escalating costs of special waste disposal have made remedi-
ation an increasingly cost-effective option, reversing earlier trends which tended
to favour this method. The fact that it is purely physical with no reagent addition
may be viewed as an advantage for some applications and the concentration of
contaminants significantly reduces the risk of secondary contamination. However,
the contaminants are not destroyed, the concentration achieved inevitably requires
containment measures and further treatment of some kind is typically required.
Solidification/vitrification
Solidification is the encapsulation of contaminants within a monolithic solid of
high structural integrity, with or without associated chemical fixation, when it is
then termed 'stabilisation'. Vitrification uses high temperatures to fuse contami-
nated materials.
One major advantage is that toxic elements and/or compounds which cannot be
destroyed, are rendered unavailable to the environment. As a secondary benefit,
solidified soils can stabilise sites for future construction work. Never-the-less,