Environmental Engineering Reference
In-Depth Information
called Customblen [
38
]. The bioremediation was very successful, as shown in a joint
monitoring program conducted by Exxon, the USEPA and the Alaska Department of
Environmental Conservation [
36
]. Furthermore, this was achieved with no detectable
adverse environmental impact [
4
,
36
,
37
]. Since then, bioremediation has been used
on a limited site as part up of the cleanup of the Sea Empress spill [
46
], and has
been demonstrated on experimental spills in marine or brackish environments on
the Delaware Bay [
48
], a Texas wetland [
26
], a fine-sand beach in England [
45
],
mangroves in Australia [
40
], and an Arctic shoreline in Spitsbergen [
35
].
Due to these successes, it is desirable to include bioremediation in responses to
future spills where oil strands on rocky or inaccessible shorelines. In this situation
currents can be used to carry the nutrients to the polluted zones instead of release
it directly on the site. For such case, an important factor in achieving successful
biostimulation, is obtaining an ideal (critical) concentration of nutrients needed for
maximum growth of the organisms, and keeping this concentration as long as pos-
sible. This can become a difficult task taking into account that appropriate point for
releasing the nutrients is unknown, and also because of physical influences, such
as differences in densities, wave movements, and tidal influences. Tracer studies are
often used to examine how the motion of the water and nutrients are influenced under
different situations [
2
,
3
].
In this chapter, a strategy is proposed for the remediation of oil-polluted marine
environments which uses the fluid dynamic in a limited water region
D
to distribute a
nutrient (nitrogen or phosphorus) and stimulate biodegradation in a few oil-polluted
zones
ʩ
i
of
D
,1
≤
≤
N
. For example, some recreation or aquaculture areas can be
chosen as such zones. By the strategy, the nutrient released at points
r
1
,
i
r
2
,...,
r
N
of domain
D
with discharge rates
Q
1
(
spreads by currents
and turbulent diffusion and reaches all the contaminated zones. Moreover, a critical
mean concentration of nutrient
c
i
(higher than the natural concentration) should
be achieved and maintained in each oil-polluted zone
t
),
Q
2
(
t
), . . . ,
Q
N
(
t
)
ʩ
i
within a certain time to
properly stimulate the growth of the oil degrading microorganisms [
2
]. This time
interval is denoted below as
[
T
−
˄,
T
]
. It should be noted that an adequate set of
N
i
release rates
1
does not always exist, that is at times, this strategy fails. In
particular, this can happen when the release points
{
Q
i
(
t
)
}
=
N
i
{
r
i
}
1
are improperly chosen
=
with respect to the flow and the location of zones
ʩ
i
, or when the time
T
is not large
enough to let the nutrient to reach all the zones. In order to prevent such situations
the problem is solved in two stages. In the first stage, each zone
ʩ
i
is considered
separately from other and contains just one source. A variational problem is posed
and solved in order to find both the optimal location of release point
r
i
in the zone
and the optimal release rate
Q
i
(
N
.
We prove that this problem has unique solution. In the second stage, we consider the
process of dispersion of nutrient in all zones together. Due to advection by currents,
the nutrient released in one zone can reach other polluted zones. Therefore we need to
specify (modulate) the strength of all release rates
Q
i
(
t
)
to reach the concentration
c
i
in
ʩ
i
,1
≤
i
≤
in order to fulfil the critical
mean concentrations
c
i
in all the polluted zones during the time interval
t
)
[
T
−
˄,
T
]
.
To this end, we introduce a positive coefficient
ʳ
i
to modulate each release rate
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