Biomedical Engineering Reference
In-Depth Information
250
16
Total number RODs
Percentage RODs MNA
14
200
12
10
150
8
100
6
4
50
2
0
0
Year
Figure 1.7. RODs for MNA at National Priorities List (NPL) sites (adapted from USEPA,
2007
). The
bars represent the number of RODs per year, and the line shows the percentage of those RODs that
were for MNA for that year.
However, when natural attenuation processes are either nonexistent or not sufficiently
protective or rapid, other more aggressive bioremediation techniques may be useful or neces-
sary. In general, the simplest alternative is biostimulation through addition of nutrients and/or
other reagents to promote the growth and activity of the desired organisms. However, if the
necessary organisms are not present or are at low population levels, then bioaugmentation
could provide an advantage. Often, due to cost and time issues, bioaugmentation is performed
regardless of the actual degradation conditions at a site, to provide greater certainty and faster
treatment. Chapter 5 of this topic provides a more detailed discussion of bioaugmentation
implementation in the context of chlorinated solvent degradation.
1.4.1 Technical Analysis/Site Evaluation
Proper site evaluation provides valuable information for any remediation strategy. The first
step is a thorough analysis of the site to be remediated, with an eye for whether bioaugmenta-
tion is necessary and for any factors that would hinder degradation. Table
1.2
describes some of
the factors that should be monitored, and the review by van Veen et al. (
1997
) details factors
that inhibit inoculum survival. A good site evaluation can determine whether or not bioaug-
mentation will be successful, and thus save the responsible party both time and money.
Physical and chemical factors, such as pH, temperature, soil type, humidity, pollutant
location and nutrient availability, play crucial roles in the success of bioaugmentation. While
these factors can hinder any remediation strategy if out of the acceptable range, bioaugmenta-
tion is particularly susceptible to environmental conditions since living organisms are being
injected
in situ
. The failure of bioaugmentation often has been tied to field scenarios that were
not accurately mimicked by preliminary soil microcosms. Pollutant location also can limit the
success of bioaugmentation. For example, if the pollutant is located deep in bedrock - like some
dense nonaqueous phase liquids (DNAPLs) - then bioaugmentation is difficult because injec-
tions of organisms and amendments can be problematic. Some soil types might make it
difficult for the bacteria to adhere (McGechan and Lewis,
2002
). If there is more than one
target pollutant, the use of different remediation strategies as well as multiple or sequential
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