1. STOP CHASING THE SOLIDS
REDUCED DESIGN FLOWS FOR THE
NEW WAS THICKENING FACILITY AT
ASHBRIDGES BAY TREATMENT
PLANT
1
S. Liver*, S. Atlin**, P. Coleman*, and R. McKinley**
* Black & Veatch
**City of Toronto
3. PROJECTOVERVIEW
• Driver:
Stop co-thickening in PCs as part of City‘s overall Wet
Weather Flow Strategy and abandon aged DAF
thickening
• Objective:
Construct WAS Thickening Facility with sufficient
capacity so that all future WAS flows can be thickened
through a single process.
PROJECT OVERVIEW
1
4. WAS Pumps and WAS Piping
•Automate WAS pumps
•Replace 12 PLCs with GE RX31 PLCs
Incineration Facility Conversion to TWAS
•Demolish Incineration and Waste Heat Recovery Facility
•Construct new facility on existing pile foundations
•Integrate TWAS facility with adjacent buildings
•Design basis: 26 MLD
•Preselect centrifuges, relocate 2 centrifuges from HTP
•New workshop, administration space, storage areas
2
3
1
1
2
DAF Building
•Convert to Storage Building
•Remove equipment, piping, pumps
•New main floor to cover DAF tanks
•Perform work after TWAS Facility
is commissioned
3
ASHBRIDGES BAY TREATMENT PLANT
6. WHYCONSIDERREDUCEDDESIGNFLOWS
• Quantities measured didn’t match CAS theory
• Contribution of solids from Humber and North
Toronto confounded data
• Historical dataset affected by biosolids “outlets”
• Requirement to Nitrify
• “Phantom RAS”
DRIVERS FOR CONSIDERING REDUCED
DESIGN FLOWS
6
7. WHYCONSIDERREDUCEDDESIGNFLOWS
MASS BALANCE - SIMPLIFIED
7
Influent: 818 MLD
Secondary ClarifierBOD RemovalPrimary Clarifier
Thickening
Co-Thickening
WAS Flow Rate
North Toronto
Humber
Sewer Shed
Splitter Box
“Phantom RAS”
10. ANALYTICALAPPROACH
1. Statistical Data Review of 2012 and “New
Operating Regime” August-December 2013
2. Factors affecting WAS volume
3. Development of Mass Balance
4. Reconciling 2011 Engineering Study Report
proposed design point
STATISTICAL ANALYSIS
10
11. ANALYTICALAPPROACH
• findings
DATA REVIEW - THE BOX AND WHISKER
PLOT
11
Maximum
Half of the values are
within this box
Minimum
Median
Half of the values are above
and below this value
12. ANALYTICALAPPROACH
12
DATA REVIEW - TOTAL WAS FLOW RATE
0
10
20
30
40
50
60
70
2007-2009 Feb2012 toDec 2012 Aug 2013 toDec 2013
WASFlowRate(MLD)
2011 Engineering
Study Report Data
2012 Data
New Operating
Regime Data
13. ANALYTICALAPPROACH
DATA REVIEW – CO-SETTLING FLOW
130
5
10
15
20
25
30
35
40
45
50
2007-2009 Feb2012 toDec 2012 Aug 2013 toDec 2013
Co-SettlingFlow(MLD)
2011 Engineering
Study Report Data
2012 Data
New Operating
Regime Data
14. ANALYTICALAPPROACH
DATA REVIEW – DAF FLOW
14
0
5
10
15
20
25
30
2007-2009 Feb2012 toDec 2012 Aug 2013 toDec 2013
WASFlowtoDAF(MLD)
2011 Engineering
Study Report Data
2012 Data
New Operating
Regime Data
15. ANALYTICALAPPROACH
DATA REVIEW – WAS THICKNESS
150.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
Feb2012 toDec 2012 Aug 2013 toDec 2013
WASConcentration(%w/w)
2012 Data
New Operating
Regime Data
16. ANALYTICALAPPROACH
DATA REVIEW – FLOW VS. CONCENTRATION
16
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500 9000 9500 10000
WASFlowRate(MLD)
WAS Concentration (mg/L)
Y axis: Flow in MLD
X Axis: Concentration in mg/L
18. ANALYTICALAPPROACH
• Thickening
‐ Co-Thickening
‐ DAF or Centrifuge
• Solids Load from Humber & NTP
• Impact of Nitrification
• Evaluation at current flows
• Evaluation at plant-rated flow (818 MLD)
MASS BALANCE USED TO EVALUATE:
18
20. ANALYTICALAPPROACH
20
MASS BALANCE: 2012 – 2013 PRODUCTION
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500 9000 9500 10000
WASFlowRate(MLD)
WAS Concentration (mg/L)
Yr 2012
25th-75th %ile
Yr 2013 - Aug-Dec
25th-75th %ile
Average 2012 -2013 Sludge Production
~ 88,070 kg/d
52% of WAS to Co-Settling
21. ANALYTICALAPPROACH
21
FACTORS AFFECTING VOLUME – CO-SETTLING
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500 9000 9500 10000
WASFlowRate(MLD)
WAS Concentration (mg/L)
Yr 2012
25th-75th %ile
Yr 2013 - Aug-Dec
25th-75th %ile
Impact of No Co-Settling
88,070 kg/d -> 68,156 kg/d
23% less WAS as mass
The New Normal
No need to co-settle when new facility is built
52% Co-Settling
0% Co-Settling
22. ANALYTICALAPPROACH
22
FACTORS AFFECTING WAS VOLUME - SRT
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500 9000 9500 10000
WASFlowRate(MLD)
WAS Concentration (mg/L)
Yr 2012
25th-75th %ile
Yr 2013 - Aug-Dec
25th-75th %ile
SRT 6 days -> 3 days = 10% more WAS mass
SRT 6 days -> 9 days = 5% less WAS mass
3 day SRT
9 day SRT
23. ANALYTICALAPPROACH
23
FACTORS AFFECTING WAS VOLUME - HUMBER
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500 9000 9500 10000
WASFlowRate(MLD)
WAS Concentration (mg/L)
Yr 2012
25th-75th %ile
Yr 2013 - Aug-Dec
25th-75th %ile
Why can't you use textbook numbers?
28% of the WAS Mass is due to the Humber TP
With HTP
Without HTP
25. FINDINGS
•26 MLD WAS
‐ 818 MLD (ABTP rated capacity)
‐ Humber at rated capacity
‐ No co-thickening
‐ 6 day SRT (SRT impact is less than 10%)
‐ Peaking Factor 30% on mass basis
‐ 5,000 mg/L WAS concentration (minimum at peak
flow)
DESIGN POINT - RECOMMENDATION
25
26. FINDINGS
• Recommend Reducing Design Flow from
37 MLD to 26 MLD
- Peaking Factor 30% on mass basis
- 5,000 mg/L WAS Concentration
• 5 Duty – 2 Standby “40-inch bowl” centrifuges
• Key Reasons:
- Installing centrifuges eliminated co-settling and
“recycle of solids”
- Improved solids control vs. 2007-2009 operation
IMPLICATIONS
26
