Environmental Engineering Reference
In-Depth Information
Thus, the bioconcentration factor is
]
org,
i
[
A
k
s
i
(k
d
i
+ μ
i
)
K
BW
=
=
(6.279)
[
A
]
w
10
−
3
W
−γ
i
0.01
W
−γ
i
Since
k
s
i
=
(E
i
/p
i
)
,
k
d
i
=
k
s
i
/K
ow
(Thomann, 1989) and
μ
i
=
,
we can write
K
OW
.
1
K
BW
=
(6.280)
10
−
6
(K
OW
/E)
1
+
10
6
.As
K
ow
increases, the value of
K
BW
decreases due to decreasing
E
and increasing
The above equation indicates that
K
BW
goes through a maximum at a
K
ow
=
μ
i
.
The ideas presented in this section are solely to make the reader aware of the
applications of chemical kinetics principles to obtain the steady-state concentration of
pollutants in a given food chain. Numerous parameters are needed and only average
values are justifiable. These limitations are indicative of the state of knowledge in
this area.
6.6 APPLICATIONS IN GREEN ENGINEERING
Manufacturing industries have traditionally relied on what is called “end-of-the-pipe”
waste treatment philosophy to take care of the inevitable pollutant releases to the
environment. This philosophy involves treating the waste stream (air, water, or solid
waste), that is, pollution control, at the end of the manufacturing process so as to
decrease the amount discharged to the environment. In many cases, this also led
to a significant portion of valuable materials at trace concentrations being returned
to the environment. As processes became “greener,” more emphasis was placed in
recovering and recycling valuable species from the waste, thus reducing the amount
releasedandalsoreducingthepollutioncontrolcosts.Aspollutionregulationsbecame
more stringent, emphasis was placed on reducing the amount of pollutant produced at
the source itself. Thus was born the concept of “environmentally conscious design”
or otherwise called “green engineering” (Allen and Shonnard, 2002). Figure 6.73
describes the difference between a “traditional” and “green” process.
To make a process design more environmentally conscious, one has to have meth-
ods and tools to properly evaluate the environmental consequences of the various
chemical processes involved and products therein. This means that we have to be able
to quantify environmental impacts and guide product design changes. Figure 6.74
shows the various items we need to carry out an environmentally conscious design of
a chemical process.
Green engineering follows a set of core principles laid down in 2003 in what
is known as the “Sandestin Declaration,” which are given in Table 6.19. A def-
inition of “Green Engineering” is “the design, commercialization, and use of
processes and products that are feasible and economical while minimizing (i) risk
to human health and the environment, and (ii) generation of pollutants at the source”
(http://www.epa.gov/oppt/greenengineering). Closely aligned with the principles of
greenengineeringaretwootherrelatedconcepts:(i)sustainabilitydefinedas“meeting
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