Transcript Activated Slduge Process Control

Simultaneous Nitrification and
Denitrification at Fresno
Presented by
Ronald G. Schuyler, PE, DEE, and Joe R. Tamburini
Rothberg, Tamburini, and Winsor, Inc.
and
Steven Hogg and Kim Toepfer
City of Fresno
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Thanks to all of the FresnoClovis operations staff for
making this approach work!
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Operational Problems
•
•
•
•
High organic load (>40 lb BOD/103 ft3)
High temperature (80ºF+)
Easy nitrification
Easy secondary clarifier denitrification
 Blanket on top!
• Poor sludge settleability
• High effluent TSS
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The Fresno Treatment System
Plant 2
B Side
To
Percolation
Ponds
Headworks
Primary
Clarifiers
A Side
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A Side Activated Sludge
Plant 2
Primary
Effluent
Side-A
Effluent
to
Percolation
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Wastewater Characteristics
Parameter
A-Side Flow
Influent BOD
Pri. Eff. BOD
Effluent BOD
Effluent TSS
Effluent NH3
1/019/01
Ave.
18.3
315
228
35
38
12
1/01-9/01 10/01- 10/01Peak Mo. 10/02 10/02
Ave. Peak Mo.
29.3
23.4 30.4
366
307
332
290
195
238
45
32
81
158
33
105
25
9
20
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Fraction of total plant inflow, %
Industrial Contribution
100%
90%
80%
Industrial contribution - BOD
70%
Industrial contribution - flow
60%
50%
40%
35.7% ± 3.2%
30%
20%
11.6% ± 0.8%
10%
0%
1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002
Date
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Design Parameters
• Original A-Side Design
 Q = 50 MGD
 Influent BOD/TSS – 240 mg/L
• Based on CPE performed in May 2003
 Aeration basin limited
 Primary effluent BOD of 238 mg/L
+ Two-year average value
 33.3 MGD @ 238 BOD
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Effluent Limitations
Parameter
Mo. Average
Daily Max
Flow
80 (an. Ave.) 88 (max mo)
BOD5, mg/L
40
80
TSS, mg/L
40
80
Set. solids, mL/L
0.2
0.5
EC, umhos/cm
Source+500
0r <900
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Historical Control Approaches
• Nitrification/denitrification issues exist even
though nitrification was not required
 Normal AS plants nitrify at normal MCRT at high T
• Minimize denitrification in secondary clarifiers
 Minimize nitrification in aeration tank
+ Very low MCRT
+ 1.5-2.0 Days
 RSF high to minimize solids detention time in the
clarifier
 Lower DO – approximately 1.0 mg/L
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Historical Results
• Worked well with lower organic loading
 High-rate activated sludge
 Effluent BOD/TSS usually < 40/40
+ Clarifier denitrification during low organic loading
+ High SVI, but controllable
 Tanks off-line saved money
• Increased organic loading mid 2001
 Food processing industries come on line
 Zoogloeal slime production from sugars, acids
and alcohols
 Higher SVI
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Project Objectives
• Treat higher organic load
• Increase the stability of mixed liquor
 Reduce zoogloeal slime
 Reduce SVI (historically very high)
• Control nitrification/denitrification
 Nitrify some for EC control
 Minimize clarifier denitrification
• Reduce effluent TSS
• Minimize oxygen requirements
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Possible Approaches
• Anoxic section - MLE
 High $ for barriers and recycle piping/pumps
 Excess design and construction time
 May not mesh with next plant upgrade
• On/Off aeration
 Old, unstable fine-bubble aeration grid that could fall
apart
 Square tanks with only air mixing and one influent
point
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Modified Approach
• Increase MCRT to provide more stable MLSS
 Reduce zoogloeal slime production
 Reduce F/M to reasonable value
• Use low DO environment




Minimize nitrification
Maximize denitrification in aeration tank
Minimize denitrification in clarifiers
Control low-DO filaments
+ 0.3-0.4 mg/L possibly too low for low DO filaments
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Results
• Load
 Flow
 Organic
• Air
 DO
 Flow rate
• MCRT
• SVI
• Effluent quality




BOD
TSS
Ammonia
Nitrate – no data but
less than 8-10 if limited
clarifier DN
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Operating Realities
• System prone to nitrify even in less than ideal
conditions
• Operators shifted flows around the system as
needed depending on the system conditions
• DO controlled at the end of the aeration tanks only
• DO probe calibration infrequent
• Problems with instrument calibration accuracy
• Problems convincing operators of requirement to
maintain low DO
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2
c-0
2
De
Se
p-0
2
Ma
y-0
60.00
Fe
b-0
2
v-0
1
No
Ju
l-0
1
Ap
r-0
1
Ja
n-0
1
Oc
t- 0
0
MGD
Flow,
Flow (MGD)
A Side Flow Rate
Project Initiated
50.00
40.00
30.00
20.00
10.00
0.00
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No
v-0
0
Ja
n -0
1
Ma
r-0
Ma 1
y-0
1
Ju
l- 0
1
Se
p-0
1
No
v-0
1
Ja
n -0
2
Ma
r-0
Ma 2
y-0
2
Ju
l- 0
2
Se
p-0
2
Oc
t-0
2
De
c-0
2
Space Load, lbs BOD/1000 cu. ft./day
80.0
70.0
10.0
Space Load
Inf BOD
60.0
50.0
80000
40.0
60000
30.0
40000
20.0
Project Initiated
0.0
BOD Loading, lbs/day
Organic Load
120000
100000
20000
0
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Aeration Tank Dissolved Oxygen
1.00
Project Initiated
0.90
Higher
MCRT
0.70
Lower
MCRT
0.60
0.50
Lower
MCRT
0.40
0.30
0.20
Very Low MCRT
0.10
De
c-0
2
Se
p-0
2
Ma
y-0
2
2
Fe
b-0
No
v-0
1
Ju
l- 0
1
01
Ap
r-
Ja
n -0
1
00
0.00
Oc
t-
Average DO (mg/L)
0.80
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Air Flow Rate and Space Loading
70.0
70.0
70.0
Project Initiated
Air Flow
1.60
1.60
Space
Air
FlowLoading
AirAir/Q
Flow
1.40
1.40
Air/Q
1.20
1.20
50.0
50.0
50.0
1.00
1.00
40.0
40.0
40.0
0.80
0.80
30.0
30.0
30.0
0.60
0.60
20.0
20.0
20.0
0.40
0.40
10.0
10.0
10.0
0.20
0.20
0.0
0.0
0.00
0.00
NN
Noo
vv--0-0
00
JJaan
n--00
11
MM
Maa
rr--00
11
MM
Maa
yy--00
11
JJuull-001
1
S
S
Seep
p---00
11
No
NN
ovv--0
-011
JJaann-002
2
M
M
Maar
r--002
2
M
M
Maay
y--002
2
J
Juul-0
l-0 2
2
S
S
e
Se p-p-002
2
O
Occt-0
t-0 2
DDee 2
De cc--0
c-002
2
Flow
Flow (mscf)
(mscf)
60.0
60.0
60.0
1.80
1.80
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Air Flow/Q (Mscf / MGD)
Air
80.0
80.0
80.0
Oxygen Transfer Efficiency
AOTE = SOTE(α)
[(βC
sw
]
– CL)/Cs θ(T-20)
As CL get smaller, the transfer rate increases.
(βCsw – CL)/Cs For instance in a situation such as Fresno’s
with little initial nitrification, a transfer efficiency increase
of about 10% would be expected with a drop in DO from the
0.9 mg/L to 0.2 mg/L with β = 0.95, Csw = 8.0 mg/L and Cs
= 9.17 mg/L. Nitrification would improve that further by
increasing α.
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00
01
2
De
c-0
2
Se
p-0
2
Ma
y-0
2
Fe
b-0
8.0
No
v-0
1
Ju
l- 0
1
Ap
r-
Ja
n -0
1
Oc
t-
MCRT (days)
MCRT
9.0
Project Initiated
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
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2
c-0
2
De
Se
p-0
2
Ma
y-0
600
Fe
b-0
2
v-0
1
No
Ju
l-0
1
Ap
r-0
1
Ja
n-0
1
Oc
t-0
0
SVI (mL/g)
SVI
700
Project Initiated
500
400
300
200
100
0
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Organic Acids
Volatile Organic Acids, mg/L
140
Consistently high SVI from
Thiothrix and type 021N
120
100
80
60
40
25 mg/L (typical)
20
0
Aug-03 Sep-03 Oct-03 Nov-03 Dec-03 Jan-04 Feb-04 Mar-04 Apr-04
Date
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Effluent Quality
80
Project Initiated
BOD
TSS
NH3
High
MCRT
60
50
High
Organic
Load
40
30
20
10
De
c-0
2
Se
p-0
2
Ma
y-0
2
2
Fe
b-0
No
v-0
1
Ju
l- 0
1
01
Ap
r-
Ja
n -0
1
00
0
Oc
t-
Concentration (mg/L)
70
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Results
• Allowed significantly higher flow rate – 22%
• Allowed 12% increase in BOD mass loading
• Reduced effluent parameter concentrations
 BOD - 7.5%
 TSS - 14%
 NH3 - 28%
• Air requirements per MGD reduced 22%
• Reduced zoogloeal slime
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Results
• Provided acceptable effluent quality under
significantly overloaded conditions
• Clarifier denitrification controlled
 DO < 0.35 mg/L
• Low numbers of low-DO filaments
 DO < 0.4 mg/L
• There are always process instabilities that make it
difficult to identify a specific causative agent
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Lessons Learned
• Quality DO meter capable of controlling at
ultra-low level
• Accurate and frequent DO meter calibration
required
• Low-DO filament population would “tell
us” proper DO level
• Relying on “hard and fast” DO target a
mistake
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More Lessons Learned
• Nose and eyes tell when DO was too low
• Biology of the system “told us” the correct MCRT
– now 5-6 days typically
• Low DO, simultaneous N/DN proven successful
 Stable process
 Operational reliability
• Trial and error testing required
• Approach saves energy (and chemicals)
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Questions
• ?
• ?
• ?
Ron Schuyler
[email protected]
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