Contaminated Land and Bio-Remediation - Environmental Biotechnology: Theory and Application - page 98

events or acute pollution incidents. With limited resources typically available for
remediation work, treatment trains offer the possibility of maximising their util-
isation by enabling responsible management decisions to be made on the basis
of meaningful cost/benefit analysis.
This has proven to be an ever more important area over the last 10 years,
particularly since increased experience of land remediation successes has
removed many of the negative perceptions which were previously commonplace
over efficiency, speed of treatment and general acceptability. For many years
remediation techniques, and bioremediation especially, were seen in a number of
countries as just too costly compared with landfill. As changes in waste legislation
in several of these regions have driven up the cost of tipping and wrought consid-
erable restrictions on the amount of biodegradable material entering landfills, the
balance has swung the other way, making remediation the cheaper option. There
is a certain irony that the very alternative which for so long held back the devel-
opment of remediation should now provide such a strong reason for its use. In the
future, the increasing usage of extensive technologies seem set to continue the
trend, since they offer the optimum cost/benefit balance, with intensive processes
becoming specialised for fast response or heavy contamination applications.
In addition, the 'treatment train' approach, by combining technologies to their
maximum efficiency, offers major potential advantages, possibly even permitting
applications once thought unfeasible, like diffuse pollution over a large area.
The Suitability of Bioremediation
Bioremediation as a biotechnological intervention for cleaning up the residual
effects of previous human activities on a site typically relies on the inherent
abilities and characteristics of indigenous bacteria, fungi or plant species. In the
present discussion, the emphasis will concentrate on the contribution made by
the first two types of organisms. The use of plants, including bioaccumulation,
phytoextraction, phytostabilisation and rhizofiltration, all of which are some-
times collectively known as phytoremediation, is examined as part of a separate
chapter. Thus, the biological mechanisms underlying the relevant processes are
biosorption, demethylation, methylation, metal-organic complexation or chela-
tion, ligand degradation or oxidation. Microbes capable of utilising a variety of
carbon sources and degrading a number of typical contaminants, to a greater or
lesser extent, are commonly found in soils. By enhancing and optimising condi-
tions for them, they can be encouraged to do what they do naturally, but more
swiftly and/or efficiently. This is the basis of the majority of bioremediation and
proceeds by means of one of the three following general routes.
Mineralisation , in which the contaminant is taken up by microbe species,
used as a food source and metabolised, thereby being removed and destroyed.
Incomplete, or staged, decomposition is also possible, resulting in the generation
and possible accumulation of intermediate by-products, which may themselves
be further treated by other microorganisms.