Maximizing Secondary Wet Weather Treatment Capacity at ... - pncwa

Maximizing Secondary Wet Weather
Capacity at the Columbia Boulevard
Wastewater Treatment Plant
Adrienne Menniti 1 , Bruce Johnson 1 , Glen Daigger 1 ,
Samuel Jeyanayagam 1 , Lynne Chicoine 1 , Paul Suto 2 , Vu
Han 2 , Chris Selker 2 , Mike Stebbins 2 , Mike Ciolli 2
1. CH2M HILL
2. City of Portland Bureau of Environmental Services

Portland Rain Fall Patterns
70
60
We don’t get more total rain than other ciBes….
Yearly Total Rainfall (in)
50
40
30
20
10
0
New York, NY Miami, FL Boise, ID Seattle, WA Portland, OR
Average from 1971-­‐2000 data from NOAA
2

Portland Rainfall Patterns
180
We get lower intensity rain more oLen
150
Annual Days of Rain
120
90
60
30
0
New York, NY Miami, FL Boise, ID Seattle, WA Portland, OR
Average from 1981-­‐2010, data from NOAA
3

Portland Rainfall Patterns
Plant Influent Flow (mgd)
300
250
200
150
100
50
Seasonal weather paRerns translate to highly
variable influent flows all winter long
0
12/25/2008 4/28/2009 8/30/2009 1/1/2010 5/5/2010 9/6/2010
Date
4

Columbia Boulevard WWTP
Largest wastewater treatment plant in Oregon
– Average Winter Flow = 90 mgd
Serves 614,000 people
Discharges to the Columbia River
Recent CSO storage improvements covey more
wet weather flows to treatment plant, increasing
peak flow from 300 mgd to 450 mgd
5

Columbia Boulevard WWTP
Dry Weather Treatment Train
8 Parallel
Aera8on Basins
8 Square
Secondary Clarifiers
Permit
Limits Monthly (mg/L) Weekly (mg/L)
BOD 30 45
TSS 30 45
Includes sodium hypochlorite disinfec8on
Headworks
Dry Weather
Primary Clarifiers
6

Columbia Boulevard WWTP
Wet Weather Treatment Train
The wet weather primary clarifiers also provide storage for excess wet weather flow
during small rain events
Wet Weather
Chemically Enhanced
Primary Clarifiers
Permit
Limits Monthly (mg/L) Weekly (mg/L)
BOD 45 65
TSS 45 65
Wet Weather
Screening Facility
Headworks
Includes sodium hypochlorite disinfec8on
7
7

CBWTP Aims to Maximizes Flow Receiving Secondary
Treatment
300
Influent Flow
Secondary Flow
250
Plant is regularly pushing
secondary treatment capacity
to achieve this goal
Flow (mgd)
200
150
100
50
0
12/25/2008 4/28/2009 8/30/2009 1/1/2010 5/5/2010 9/6/2010
Date
8

Challenges to Maximizing Secondary Treatment
1. High historical SVI values
600
500
Design SVI = 200 mL/g
SVI (mL/g)
400
300
200
100
0
12/25/2008 4/28/2009 8/30/2009 1/1/2010 5/5/2010 9/6/2010
Date
9

Challenges to Maximizing Secondary Treatment
2. Lack of Automation in Secondary Process (wasting, DO control)
600
SVI (mL/g)
500
400
300
200
Extreme SVI excursion caused
by manual wasting approach.
Plant over wasted during a
strong rain event, washing out
selector.
100
0
12/25/2008 4/28/2009 8/30/2009 1/1/2010 5/5/2010 9/6/2010
Date
10

Challenges to Maximizing Secondary Treatment
3. Lack of Wet Weather Operating Modes
All the gates along the old complete mix
distribution channel must be opened manually
to step feed flow on current basins
11

Challenges to Maximizing Secondary Treatment
4. Poor clarifier design and performance
Shallow (12.5 ft deep), square, peripheral-feed, peripheral-withdraw
Effluent
Feed
12

Project Goals
1. Maximize peak flow treated through secondary
process
Provide wet weather operating modes
2. Maintain stable operation during all flow conditions
Maintain well settling sludge across all operating modes, provide
tools to address settleability issues
3. Simple operation and intuitive control
Decision to shift operating mode is intuitive, solutions are simple
and robust to operate
4. Improve secondary clarifier performance
Use CFD to evaluate potential clarifier improvements
13

Project Goals
1. Maximize peak flow treated through secondary
process
Provide wet weather operating modes
14

Two Types of Wet Weather Events
1. Several small to moderate rain events with dry weather in between
400
Influent Flow
Plant Influent Flow (mgd)
350
300
250
200
150
100
50
0
5/12 5/17 5/22 5/27 6/1 6/6 6/11 6/16
Time (days)
15

Two Types of Wet Weather Events
2. Long rain events that fills the CSO storage tunnels
300
Influent Flow
Plant Influent Flow (mgd)
250
200
150
100
50
Completion of CSO storage tunnel project
in Nov. 2011 increased peak and duration
0
3/28 3/29 3/30 3/31 4/1 4/2
Time (days)
16

Two Wet Weather Operating Modes
Step feed is the normal operating mode
RAS
1 2 3 4 5 6 7
65% 35%
To Secondary
Clarifiers
RAS
1 2 3 4
5
6
7
To Secondary
Clarifiers
Aerobic RAS Storage
Primary Effluent
Pipe Bridge
Anaerobic
Anaerobic/aerobic swing
Aerobic
Wet weather maximum month treatment capacity = 98 mgd
with 40% clarifier derating factor
17

Two Wet Weather Operating Modes
Wet Weather Step feed is provided for use during small to medium rain events
• Constant flow maintained to zone 1
• Remaining flow pushed to zone 6
• Avoids an operating mode shift for typical rain events
RAS
Adjustable set point
1 2 3 4 5 6 7
Remaining Flow
To Secondary
Clarifiers
RAS
1 2 3 4
5
6
7
To Secondary
Clarifiers
Aerobic RAS Storage
Primary Effluent
Pipe Bridge
Anaerobic
Anaerobic/aerobic swing
Aerobic
Wet weather maximum month treatment capacity = 110 mgd
with 40% clarifier derating factor
18

Two Wet Weather Operating Modes
Step feed with RAS Storage is provided for use during large rain events
• Upstream feed point shifted to zone 2
• Provides storage of RAS to protect inventory from washout
• Further reduces clarifier solids loading rate
RAS
1 2 3 4 5 6 7
65% 35%
To Secondary
Clarifiers
RAS
1 2 3 4
5
6
7
To Secondary
Clarifiers
Aerobic RAS Storage
Primary Effluent
Pipe Bridge
Anaerobic
Anaerobic/aerobic swing
Aerobic
Wet weather maximum month treatment capacity = 116 mgd
with 40% clarifier derating factor
19

Project Goals
1. Maximize peak flow treated through secondary
process
Provide wet weather operating modes
2. Maintain stable operation during all flow conditions
Maintain well settling sludge across all operating modes, provide
tools to address settleability issues
20

Maintain Well Settling Sludge
Two types of selectors provided:
Anaerobic selector at Zones 1 and 2
Aerobic selector at Zone 6
RAS
1 2 3 4 5 6 7
65% 35%
To Secondary
Clarifiers
RAS
1 2 3 4
5
6
7
To Secondary
Clarifiers
Aerobic RAS Storage
Primary Effluent
Encourages PAO growth to
remove soluble BOD
anaerobically.
Pipe Bridge
Small, baffled zone creates
high F:M, encouraging rapid
uptake and storage of soluble
BOD by heterotrophs
Anaerobic
Anaerobic/aerobic swing
Aerobic
21

Maintain Well Settling Sludge
Automated SRT control incorporated into design to avoid
washing out anaerobic selector
RAS
TSS Probe
RAS BOX
WAS
TSS Probe
TSS Probe
RAS
1 2 3 4 5 6 7
65% 35%
To Secondary
Clarifiers
RAS
1 2 3 4
5
6
7
To Secondary
Clarifiers
TSS Probe
TSS Probe
Aerobic RAS Storage
Primary Effluent
Pipe Bridge
Anaerobic
Anaerobic/aerobic swing
Aerobic
22

Provide Tools for Sludge Settleability Control
Highly oxygenated wet weather flows can disrupt the anaerobic zone
RAS
1 2 3 4 5 6 7
65% 35%
To Secondary
Clarifiers
RAS
1 2 3 4
5
6
7
To Secondary
Clarifiers
Aerobic RAS Storage
Primary Effluent
Anaerobic/aerobic swing zone
maintains sufficient anaerobic
SRT under these conditions
Pipe Bridge
Anaerobic
Anaerobic/aerobic swing
Aerobic
23

Provide Tools for Sludge Settleability Control
Influent VFAs can decrease during wet weather making
selector difficult to maintain
RAS
1 2 3 4 5 6 7
65% 35%
To Secondary
Clarifiers
RAS
1 2 3 4
5
6
7
To Secondary
Clarifiers
Aerobic RAS Storage
Primary Effluent
Pipe Bridge
Anaerobic
Anaerobic/aerobic swing
Aerobic RAS storage zone can be
intermittently aerated to increase VFA
production during long rain events
Thanks to Dr. David Stensel for this idea!
Aerobic
24

Project Goals
1. Maximize peak flow treated through secondary
process
Provide wet weather operating modes
2. Maintain stable operation during all flow conditions
Maintain well settling sludge across all operating modes, provide
tools to address settleability issues
3. Simple operation and intuitive control
Decision to shift operating mode is intuitive, solutions are simple
and robust to operate
25

Decision to Shift Operating Mode is Intuitive
During wet weather events, plant staff set flow rate to secondary process
Plant Influent
Secondary Influent
400
350
300
Flow (mgd)
250
200
150
100
50
0
0 5 10 15 20 25 30 35 40
MLSS Inventory
Time (days)
Secondary Process BOD Loading
26

Decision to Shift Operating Mode is Intuitive
The maximum flow rate to Zone 1 is also an operator set point. Excess flow is
automatically directed to Zone 6 of each basin.
So, operators don’t need to initiate the change to wet weather step feed.
Shift to Step Feed with RAS Storage is manually initiated but
automatically executed
RAS
Adjustable set point
1 2 3 4 5 6 7
Remaining Flow
To Secondary
Clarifiers
RAS
1 2 3 4
5
6
7
To Secondary
Clarifiers
Aerobic RAS Storage
Primary Effluent
Pipe Bridge
Anaerobic
Anaerobic/aerobic swing
Aerobic
27

Additional Tools to Maximize Secondary Treatment
Instrumentation provided for SRT and stepfeed control allows tracking of
clarifier solids loading rate
Channel Flow
Meter
RAS
TSS Probe
1 2 3 4 5 6 7
65% 35%
To Secondary
Clarifiers
RAS
1 2 3 4
5
6
7
To Secondary
Clarifiers
Channel Flow
Meter
Primary Effluent
Channel Flow
Meter
Pipe Bridge
TSS Probe
Aerobic RAS Storage
Anaerobic
Anaerobic/aerobic swing
Aerobic
Long term experience may allow an automated control strategy to adjust the
secondary process flow based on clarifier solids loading rate
28

Project Goals
1. Maximize peak flow treated through secondary
process
Provide wet weather operating modes
2. Maintain stable operation during all flow conditions
Maintain well settling sludge across all operating modes, provide
tools to address settleability issues
3. Simple operation and intuitive control
Decision to shift operating mode is intuitive, solutions are simple
and robust to operate
4. Improve secondary clarifier performance
Use CFD to evaluate potential clarifier improvements
29

Clarifier Assessment Approach
1. Use historical data to understand clarifier
performance
2. Perform clarifier stress testing to calibrate CFD
model
3. Use CFD to determine clarifier failure mechanism
4. Evaluate potential improvements using CFD
30

Clarifier Capacity Analysis Based on Historical Data
March 2010 Rain Event Allowed Historical Stress Testing
Secondary Flow Rate
Blanket Depth
Secondary Flow Rate (MGD)
160
140
120
100
80
60
40
20
0
Peak flow event provided consistent
secondary flow for 3 days
3/26/2010 3/27/2010 3/28/2010 3/29/2010 3/30/2010 3/31/2010 4/1/2010 4/2/2010 4/3/2010
Blanket Depth (ft)
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Clarifier blanket meters show a strong
increase in blanket depth during storm
3/26/2010 3/27/2010 3/28/2010 3/29/2010 3/30/2010 3/31/2010 4/1/2010 4/2/2010 4/3/2010
31

Clarifier Capacity Analysis Based on Historical Data
March 2010 Rain Event Allowed Historical Stress Testing
7.0
15 3/27/2010 3/28/2010 3/29/2010 3/30/2010 3/31/2010 4/1/2010
3/27/2010 SVI = 205 mL/g
6.0
Blanket Depth (ft)
5.0
4.0
3.0
2.0
1.0
0.0
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0
Clarifier SLR (ppd/sf)
32

Clarifier Capacity Analysis Based on Historical Data
March 2010 Rain Event Allowed Historical Stress Testing
7.0
6.0
3/27/2010 SVI = 205 mL/g
3/28/2010 SVI = 202 mL/g
15 3/27/2010 3/28/2010 3/29/2010 3/30/2010 3/31/2010 4/1/2010
Blanket Depth (ft)
5.0
4.0
3.0
2.0
1.0
0.0
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0
Clarifier SLR (ppd/sf)
33

Clarifier Capacity Analysis Based on Historical Data
March 2010 Rain Event Allowed Historical Stress Testing
7.0
6.0
15 3/27/2010 3/28/2010 3/29/2010 3/30/2010 3/31/2010 4/1/2010
3/27/2010 SVI = 205 mL/g
3/28/2010 SVI = 202 mL/g
Blanket Depth (ft)
5.0
4.0
3.0
2.0
1.0
0.0
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0
Clarifier SLR (ppd/sf)
34

Clarifier Capacity Analysis Based on Historical Data
March 2010 Rain Event Allowed Historical Stress Testing
7.0
6.0
15 3/27/2010 3/28/2010 3/29/2010 3/30/2010 3/31/2010 4/1/2010
3/27/2010 SVI = 205 mL/g
3/28/2010 SVI = 202 mL/g
3/29/2010 SVI = 213 mL/g
Blanket Depth (ft)
5.0
4.0
3.0
2.0
Solids flux analysis - the clarifiers failed at a
point 40% less than the theoretical capacity
1.0
0.0
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0
Clarifier SLR (ppd/sf)
35

Clarifier Failure Mechanism
Failure exacerbated at high SVI because the sludge blanket is less dense
At failure, dispersed layer extends
throughout clarifier and outlet
arrangement carries TSS over weir
`
The turbulence
creates a dispersed
sludge layer above
the thick blanket at
high flows
Influent flow jets into
the sludge blanket
36

Clarifier Failure Mechanism
Also used CFD to define clarifier capacity
Effluent TSS (mg/L)
400
350
300
250
200
150
100
50
Solids flux analysis with CFD results - the
clarifiers failed at a point 20% less than the
theoretical capacity
The design is flexible enough to
accommodate higher clarifier capacity
0
10 12 14 16 18 20 22
Clarifier Solids Loading Rate (ppd/sf)
37

Clarifier Improvements
Examined Modified Baffle Design
Original baffle arrangement
Modified baffle arrangement
Effluent
Effluent
Avoids upflow
created by inlet
Feed
Feed
Protects sludge
blanket from influent
energy
38

Clarifier Improvements
Failure mechanism the same with modified baffle
Effluent TSS (mg/L)
180
150
120
90
60
Original Baffle
Modified Baffle
Modified baffle doesn’t increase capacity, it reduces the
severity of clarifier failure
No modifications to secondary clarifiers in
this project
30
0
Pre-failure
At failure
39

Conclusion
1. Project is currently under construction and will come
online by June of 2014
2. CFD helped us understand clarifier failure mechanism
but no cost effective improvements found
3. Wet weather flows receiving secondary treatment will
be maximized by:
– Incorporating step feed for normal operation and two wet weather
operating modes
– Addressing sludge settleability issues and providing tools to
maintain well settling sludge
– Implementing a high degree of automation to accommodate the
highly dynamic winter time flows and simplify treatment plant
operation
40

Thank You!
Questions
Contact InformaBon
adrienne.menniti@ch2m.com

State Point Analysis to Define Clarifier Capacity
Solids Loading Rate
30
25
= 25.9 ppd/L 2 20
Slope = -­‐ RAS rate = 40 MGD
15
10
Depends on SVI
Mass Flux Rate, lbs/day/ft2
5
Slope = overflow rate = 1,000 gpd/
L 2
SVI = 205 mL/g
Ideal Clarifier
Q inf = 125 MGD
MLSS = 2,350 mg/L
SVI = 205 mL/g
RAS = 40 MGD
SLR = 25.9 ppd/L 2
0
0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000
Concentration, mg/L
30
25
Solids flux analysis - the clarifiers failed at a
point 40% less than the theoretical capacity
20
15
= 15.2 ppd/L 2
Solids Loading Rate
Mass Flux Rate, lbs/day/ft2
10
5
40% deraBng
Q inf = 125 MGD
MLSS = 1,380 mg/L
SVI = 205 mL/g
RAS = 40 MGD
SLR = 15.2 ppd/L 2
0
0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000
Concentration, mg/L