Geoscience Reference
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EXAMPLE 24.54
Problem:
Using the data below, design a conventional aeration tank:
MGD = 1 million gal/day
BOD from primary clarifier = 110 mg/L
MLSS = 2000 mg/L
Design F/M = 0.5 per day
Design aeration period, t = 6 hr
Solution:
(
133 690 110 1
2000
,
)(
)( )
050
.
=
(
)
V
14,706 ft
3
V
=
1
7.48 ft /gal
1day
24 hr
=
10
6
22 ft
3
Aeration tank volume( )
V
==×
(1
gpd)(6 h
r)
33,4
3
Assume a depth of 10 ft and a length of twice the width:
33 422
10
,
2
A
=
=
3342 ft
( ()
2
ww
=
3342
w
=
41 ft
l
=
82
ft
24.7.1.12 Lawrence and McCarty Design Model
Over the years, numerous design criteria utilizing empirical and rational parameters based on bio-
logical kinetic equations have been developed for suspended-growth systems. Based on practice, the
basic Lawrence and McCarty (1970) model is widely used in the industry. The basic Lawrence and
McCarty design equations used for sizing suspended-growth systems are provided below.
24.7.1.12.1 Complete Mix with Recycle
For a complete mix system, the mean hydraulic retention time (HRT) θ for the aeration basin is
θ =
V
/
Q
(24.52)
where
θ = Hydraulic retention time (day).
V
= Volume of aeration tank (m
3
).
Q
= Influent wastewater flow (m
3
/day).
The mean cell residence time (θ
c
) is expressed as
X
Xt
θ
c
=
(24.53)
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