CEE
CEE 3640
3640
Spring
2011
Spring2015
2011
Step-Wise
Step-Wise Procedures
Procedures for
for Determining
Determining Oxygen
Oxygen Sag
Sag in
in River
River from
from WWTP
WWTP Discharge
Discharge
1.
1. Compile
Compile data
data for
for the
the WWTP
WWTP discharge
discharge and
and the
the stream
stream into
into which
which itit isis discharging.
discharging.
The
The data
data should
should include:
include: Flow
Flow for
for each
each (MAKE
(MAKE SURE
SURE YOU
YOU USE
USE THE
THE SAME
SAME
UNITS
UNITS FOR
FOR BOTH
BOTH FLOWS,
FLOWS, WWTP
WWTP DISCHARGE
DISCHARGE IS
IS NORMALLY
NORMALLY GIVEN
GIVEN AS
AS
MGD,
WHIL
A
RIVER
FLOW
IS
NORMALLY
PRESENTED
AS
CFS.
USE
MGD, WHIL A RIVER FLOW IS NORMALLY PRESENTED AS CFS. USE ONE
ONE
OR
OR THE
THE OTHER
OTHER UNIT,
UNIT, BUT
BUT DO
DO NOT
NOT MIX
MIX UNITS
UNITS IN
IN YOUR
YOUR
CALCULATIONS);
CALCULATIONS); BOD5
BOD5 for
for each;
each; Temperature
Temperature for
for each;
each; DO
DO for
for each.
each.
2.
2. Determine
Determine the
the BODultimate
BODultimate for
for each
each flow.
flow. The
The BOD
BOD in
in the
the WWTP
WWTP and
and often
often in
in the
the
Stream
will
have
units
of
BOD5.
Since
the
BOD
test
is
run
at
STANDARD
Stream will have units of BOD5. Since the BOD test is run at STANDARD
TEMPERATURE
TEMPERATURE of
of 20°C,
20°C, you
you should
should use
use the
the k1
k1 value
value @
@ 20°C
20°C == 0.23/d
0.23/d for
for
NORMAL
NORMAL DOMESTIC
DOMESTIC WW
WW and
and for
for the
the STREAM
STREAM seeded
seeded with
with WW
WW bacteria.
bacteria. Use
Use
the
the BOD
BOD equation
equation to
to convert
convert from
from BOD5
BOD5 to
to BODultimate:
BODultimate:
-k1t
Y
Y == Lo
Lo (1
(1 –– ee-k1t))
knowing
knowing Y
Y == measured
measured BOD5,
BOD5, k1
k1 == 0.23/d,
0.23/d, tt == 55 d.
d. This
This will
will yield
yield an
an Lo
Lo for
for the
the
WW
WW effluent
effluent and
and an
an Lo
Lo for
for the
the Stream
Stream
3.
3. Determine
Determine the
the Ultimate
Ultimate BOD
BOD of
of the
the mixture,
mixture, but
but taking
taking aa FLOW
FLOW WEIGHTED
WEIGHTED
AVERAGE
AVERAGE Lo
Lo for
for the
the mixture
mixture of
of the
the WW
WW and
and the
the Stream.
Stream. This
This isis the
the Lo
Lo value
value in
in
the
Oxygen
Sag
equation.
the Oxygen Sag equation.
4.
4. Determine
Determine the
the Temperature
Temperature of
of the
the Mixture
Mixture of
of WW
WW ++ Stream
Stream == Tmix,
Tmix, by
by calculating
calculating
the
FLOW
WEIGHTED
AVERAGE
Temperature.
This
is
the
temperature
the FLOW WEIGHTED AVERAGE Temperature. This is the temperature that
that isis
assumed
assumed to
to apply
apply in
in the
the Stream
Stream after
after WW
WW input,
input, and
and isis used
used to
to adjust
adjust the
the oxygen
oxygen
uptake
uptake rate,
rate, k1,
k1, and
and the
the reaeration
reaeration rate
rate constant,
constant, k2,
k2, to
to actual
actual Stream
Stream temperature
temperature
conditions.
conditions.
5.
5. Determine
Determine the
the Dissolved
Dissolved Oxygen
Oxygen (DO)
(DO) of
of the
the Mixture.
Mixture. Again,
Again, use
use aa taking
taking aa FLOW
FLOW
WEIGHTED
AVERAGE
to
determine
the
DOmix.
WEIGHTED AVERAGE to determine the DOmix.
6.
6. Determine
Determine the
the Initial
Initial Deficit
Deficit of
of the
the Mixture.
Mixture. This
This Do
Do isis determined
determined by
by calculating
calculating the
the
difference
between
the
Saturation
DO
concentration,
Cs,
of
the
Mixture
of
WW
+
difference between the Saturation DO concentration, Cs, of the Mixture of WW +
Stream
Stream at
at the
the Mixture
Mixture Temperature,
Temperature, Tmix,
Tmix, and
and the
the actual
actual DO
DO of
of the
the mixture,
mixture, DOmix,
DOmix,
calculated
calculated in
in Step
Step 5.
5. The
The Cs
Cs at
at Tmix
Tmix isis determined
determined from
from Table
Table A.10
A.10 in
in the
the appendix
appendix
of
of you
you textbook.
textbook.
Do
Do == Cs
Cs @
@ Tmix
Tmix -- DOmix
DOmix
7.
7. Adjust
Adjust the
the oxygen
oxygen uptake
uptake rate,
rate, k1,
k1, and
and the
the reaeration
reaeration rate,
rate, k2,
k2, to
to the
the WW
WW ++ Stream
Stream
Mixture
Mixture Temperature,
Temperature, Tmix,
Tmix, using
using the
the theta
theta equation:
equation:
T2
T2 - - T1
T1
kkT2T2
== "
"
kkT1T1
where
where T1
T1 == 20°C,
20°C, T2
T2 == Tmix,
Tmix, and
and theta
theta == 1.072
1.072 for
for biological
biological reactions
reactions (k1
(k1
correction),
correction), and
and 1.016
1.016 for
for physical
physical reactions
reactions (k2
(k2 correction).
correction).
8.
8. With
With these
these values
values of
of Lo,
Lo, Do,
Do,
and Tmix
Tmix adjusted
adjusted k1
k1 and
and k2,
k2, the
the time
time to
to the
the critical
critical
!
! and
deficit
deficit can
can be
be determined
determined using
using the
the following
following equation:
equation:
PLEASE
PLEASE NOTE
NOTE the
the placement
placement of
of brackets
brackets and
and parentheses.
parentheses. This
This isis the
the corrected
corrected
equation
from
the
lecture
notes
where
the
brackets
were
inadvertently
left
equation from the lecture notes where the brackets were inadvertently left off!
off!
9. From tc, calculate the Critical Deficit, Dc, that represents the lowest DO that the
stream will experience. The Critical Deficit equation is as follows:
11
CEE 3640
Spring 2011
CEE 3640
Spring 2015
2011
9. From tc, calculate the Critical Deficit, Dc, that represents the lowest DO that the
stream will experience. The Critical Deficit equation is as follows:
10.
10.The
TheMinimum
MinimumDO
DOthat
thatwill
willoccur
occurin
inthe
theStream
Streamatatthis
thisDc
Dcpoint
pointisisdetermined
determinedby:
by:
Minimum
MinimumDO
DO==Cs
Cs@
@Tmix
Tmix--Dc
Dc
11.
11.ItItisisthis
thisMinimim
MinimimDO
DOthat
thatmust
mustbe
bechecked
checkedwith
withthe
theStream
StreamStandard
Standardfor
forthe
the
Designated
DesignatedBeneficial
BeneficialUse
Useto
todetermine
determineififthe
theuse
usewill
willbe
bemaintained
maintainedwithout
without
additional
additionaltreatment
treatmentof
ofthe
theWWTP
WWTPdischarge.
discharge.
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