Environmental Engineering Reference
In-Depth Information
tool in screening sites for toxic pollutants and identifying and quantifying
hotspots where there are likely to be serious toxicity constraints to intrinsic
bioremediation of normally degradable, organic pollutants
(Killham &
Paton 2003 ).
Figure 12.6 therefore represents a time course of bioremediation at the site as
various constraints were alleviated and the bioremediation proceeded
progressively further. At the start of the time course, the tox-map highlights that
there were three particularly toxic areas of the site (designated by increasingly
bright red) which are delineated by a yellow boundary representing site material
that is too toxic for degradation by micro-organisms (predominantly BTEX
degrading bacteria) and hence for any intrinsic bioremediation to occur.
Removal of the co-contaminants on this site was particularly challenging.
The chlorinated solvents generally require anaerobic conditions for the reduc-
tive dechlorination of these hydrocarbons (Bouwer 1994 ). It was therefore
necessary to only air-sparge sufficiently (often in controlled pulses) to encour-
age aerobic BTEX degradation but not to damage or kill the anaerobic micro-
bial community able to degrade the chlorinated solvents. The metals represent
an even greater challenge as they cannot be removed by microbial bioremedia-
tion, but they can be converted into a non-available form, and it was this latter
strategy that was adopted (through urea hydrolysis which raised the pH
and precipitated out the metals). This at least temporarily removed the toxic
constraint imposed on mineralisation of the target organic contaminants by
the metals, and enabled the hydrocarbon contamination to be successfully
bioremediated.
Case study 2
The second case study involves a large hydrocarbon contaminated site in
Aberdeen. It was originally a railway siding and train fuelling depot and so
most of the contamination was diesel from trains. The contamination was
quite extensive, and had migrated to considerable depth in the alluvial, sandy
Caption for Figure 12.6. (cont.)
the manipulations coupled to microbial biosensor testing detailed in Fig. 12.1 to
progressively identify constraints to bioremediation and alleviate them through site
engineering. Figure 12.6 therefore represents a time course of bioremediation at the site
as various constraints were alleviated and the bioremediation proceeded progressively
further. At the start of the time course, the tox-map highlights that there were three
particularly toxic areas of the site (designated by increasingly bright red) which are
delineated by a yellow boundary representing site material that is too toxic for
degradation by micro-organisms (predominantly BTEX degrading bacteria) and hence
for any intrinsic bioremediation to occur. See colour plate section .
Search WWH ::




Custom Search