Environmental Engineering Reference
In-Depth Information
8.6.
A model for designing constructed wetlands pro-
posed by the USEPA is given by
the summer and winter months yielded the follow-
ing data for BOD removal:
c
c
Lwdn
Q
c
/
c
0
e
=
A
exp
−
0 7
.
K A
1 75
.
Distance from
(8.28)
T
v
Entrance (m)
Summer
Winter
0
0
0.52
0.52
where
c
e
is the effluent concentration,
c
0
is the influ-
ent concentration,
A
is the fraction of BOD
5
removed as settleable solids near the headworks of
the wetland,
A
v
is the specific surface area for
microbial activity (m
2
/m
3
),
L
,
w
, and
d
are the
length, width, and depth of the wetland,
n
is the
porosity, and
Q
is the flow rate. The temperature-
dependent rate constant,
K
T
, can be estimated by
the relation
67
0.36
0.40
134
0.41
0.20
200
0.30
0.19
267
0.27
0.17
334
0.17
0.17
Measurements also indicated average summer and
winter temperatures of 17.8 and 3°C, respectively,
summer and winter average flows of 35 and
18.0 m
3
/d, respectively,
A
= 0.52,
n
= 0.75,
w
= 4 m,
d
= 0.14 m (summer) and 0.24 m (winter), and
K
20
= 0.0057 d
−1
. Estimate the value of
A
v
that best
characterizes the wetland, and quantify the error
bars that should be associated with the proposed
wetland model.
T
−
20
K
=
K
( . )
1 1
T
20
where
T
is the temperature and
K
20
is the rate con-
stant at 20°C. Measurements at a 334-m-long
wetland channel located in Ontario, Canada, during
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