Wastewater Collection System Optimization
An Innovative Approach to Capital Improvement Planning
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Collection System Improvement Options / Objectives
Combinations of Alternatives
Conveyance / Treatment
I/I Reduction
Flow Equalization
Capital Cost
O&M Cost
Enviro / Social
Impact
Level of Risk
Options Analysis Process
New Zealand
North Shore City, New Zealand
Auckland North Shore CityNorth Shore City
Service Area – 130 km2
Coastline – 141 km
Existing Population – 227,000
Population in 2056 – 374,000
Population increase of 65%
Total Length of Sewer – 1346 km
Total Length of Trunk – 112 km
Pump Stations – 18
Calibrated Hydraulic Model
17-Year Long Time Series
NSCC Optimisation – Existing Network
Existing Trunk Network
Planning Objectives
Overflow frequency < 6-months (based on 2056 17-year LTS)
Pressure main velocity < 2.5 m/s
Perform options analysis for:I/I reduction, conveyance,
storage, and WWTP upgrade
Identify least-cost solution
NSCC Optimisation
Overflows in Existing Network
for 2056 6-month Event
Improvement Options
Parallel sewer main – 105 kmDiversion sewer main – 55 km
Pump station upgrades – 18New pump stations – 7
I/I reduction – 51 sub-cat’s
WWTP Upgrades - 1
Storage locations > 200
Over 109 option configurations
NSCC Optimisation – Improvement Options
Improvement OptionsImprovement Options
Parallel sewer main – 105 km (dark blue)Diversion sewer main – 55 km (blue)
Improvement Options
Parallel sewer main – 105 kmDiversion sewer main – 55 km
Pump station upgrades – 18 (purple)New pump stations – 7 (yellow)
Improvement Options
Parallel sewer main – 105 kmDiversion sewer main – 55 km
Pump station upgrades – 18New pump stations – 7
I/I reduction – 51 sub-cat’s (shaded)
Note: Substantial rehabilitation completed by NSCC over past 10 years
Improvement Options
Parallel sewer main – 105 kmDiversion sewer main – 55 km
Pump station upgrades – 18New pump stations – 7
I/I reduction – 51 sub-cat’s
WWTP Upgrades – 1
Improvement Options
Parallel sewer main – 105 kmDiversion sewer main – 55 km
Pump station upgrades – 18New pump stations – 7
I/I reduction – 51 sub-cat’s
WWTP Upgrades - 1
Storage locations > 200
Over 1060 Possible Configurations
Improvement Options – Relief Sewers Improvement Options – Pump Stations Improvement Options – I/I ReductionImprovement Options – WWTP Upgrade Improvement Options – StorageImprovement Options – Too many for trial-and-error
NSCC Optimisation – Improvement OptionsImprovement Options – Relief Sewers Improvement Options – Pump Stations Improvement Options – I/I ReductionImprovement Options – WWTP Upgrade Improvement Options – StorageGenetic Algorithm Optimisation
• Find the best solution to a problem that has many possible solutions
• Evolutionary, directed search technique• GA optimisation linked with hydraulic model
Options Analysis Process
- Import Hydraulic Model - Import Sewer Costs / OptionsFormulate Optimisation Model
Cost Table ID Gravity Sewer - Open Cut
Diameter (mm)
Total Pipe Cost by Depth ($/m)
0m - 2m 2m - 3m 3m - 4m 4m - 5m
141 1,072 1,396 1,773 2,145
198 1,141 1,479 1,876 2,274
311 1,275 1,651 2,078 2,507
396 1,447 1,832 2,287 2,743
493 1,648 2,061 2,546 3,031
554 1,908 2,339 2,880 3,394
625 2,092 2,541 3,105 3,640
704 2,323 2,795 3,375 3,934
762 2,276 2,708 3,246 3,766
838 2,521 2,970 3,557 4,100
914 2,937 3,410 3,992 4,559
995 3,215 3,706 4,309 4,895
1213 4,539 4,539 5,183 5,828
1372 4,930 4,930 5,616 6,298
1590 5,775 5,775 6,531 7,276
1830 7,041 7,041 7,853 8,650
Cost Table ID Pressure Main - Open Cut
Diameter (mm)
Total Pipe Cost by Depth ($/m)
0m - 2m 2m - 3m 3m - 4m 4m - 5m
0 0 0 0 0
141 958 1,227 1,514 1,795
198 1,022 1,306 1,612 1,920
277 1,104 1,408 1,734 2,062
311 1,152 1,466 1,801 2,139
396 1,354 1,681 2,038 2,400
440 1,432 1,770 2,139 2,514
493 1,546 1,900 2,283 2,673
554 1,767 2,138 2,580 3,000
625 1,932 2,322 2,783 3,221
704 2,199 2,611 3,082 3,542
Gravity Sewer - Trenchless
Diameter (mm) Total Pipe Cost ($/m)
0 0
141 740
198 1,084
311 1,445
440 2,435
554 3,499
610 4,056
762 5,809
914 10,030
1067 11,683
1213 12,988
1440 15,159
1590 16,441
1830 18,364
2020 20,768
Pressure Main - Trenchless
Diameter (mm) Total Pipe Cost ($/m)
0 0
141 886
220 1,219
277 1,385
352 1,717
440 2,946
493 3,124
554 3,435
610 4,434
686 6,531
762 7,792
838 8,438
- Import Pump Station Costs - Import WWTP Upgrade Costs - Import Storage Costs - Import RDII Reduction Costs
Cost of Rehab ($/m pipe length)
Current RDII (% Rainfall Entering Subcatchment)
4% 5% 6% 7% 8% 9% 10% 11% 12% 13% 14% 15%
Target RDII
(% Rainfa
ll Enteri
ng Subcatchme
nt)
0% - - - - - - - - - - - -1% - - - - - - - - - - - -2% - - - - - - - - - - - -3% 400 400 - - - - - - - - - -4% 0 304 400 400 - - - - - - - -5% - 0 200 359 400 400 - - - - - -6% - - 0 155 268 350 400 400 400 400 - -7% - - - 0 126 218 287 336 372 398 400 4008% - - - - 0 107 185 245 290 325 351 3719% - - - - - 0 92 161 214 256 288 314
10% - - - - - - 0 81 142 190 229 26011% - - - - - - - 0 72 127 171 20712% - - - - - - - - 0 64 114 15513% - - - - - - - - - 0 58 10414% - - - - - - - - - - 0 5315% - - - - - - - - - - - 0
- Define Planning Criteria
Overflow Frequency
No overflows in selecteddesign storm event/sVelocity Constraint
Pressure main velocity < 2.5 m/s
Minimum Cover
Top of pipe to ground surface> 900mm
- Link Option Data to Model
Pipe Cost Tables
Diameter Options
Velocity CriteriaMin Cover Criteria
- Optimizer WCS
Current Solution – Being Processed
• Processing 1st generation• Performing 200 fully dynamic model
simulations of various trial solutions
Cost ItemCapital
Cost ($M)O&M
($M)Total Cost
($M)
Sewer Main
Pump Station
Storage
I/I Reduction
WWTP Upgrade
TOTAL ($M)
Run Optimisation Model
Current Solution – Being Processed
• Processing 1st generation• Performing 200 fully dynamic model
simulations of various trial solutions
Cost ItemCapital
Cost ($M)O&M
($M)Total Cost
($M)
Sewer Main
Pump Station
Storage
I/I Reduction
WWTP Upgrade
TOTAL ($M)
Run Optimisation Model
Current Solution - $1079 M
• Best solution in 1st generation• Total of 200 trial solutions evaluated• Actual processing time: 8 minutes (120 cores)
Cost ItemCapital
Cost ($M)O&M
($M)Total Cost
($M)
Sewer Main 391 97 489
Pump Station 92 39 131
Storage 165 127 292
I/I Reduction 167 0 167
WWTP Upgrade 0 0 0
TOTAL ($M) 815 263 1079
Current Solution - $831 M
• Best solution in 32nd generation• Total of 6,400 trial solutions evaluated• Actual processing time: 4 hours (120 cores)
Cost ItemCapital
Cost ($M)O&M
($M)Total Cost
($M)
Sewer Main 331 78 409
Pump Station 89 40 128
Storage 107 77 185
I/I Reduction 100 0 100
WWTP Upgrade 9 0 9
TOTAL ($M) 637 195 831
Current Solution - $674 M
• Best solution in 100th generation• Total of 20,000 trial solutions evaluated• Actual processing time: 12.5 hours (120 cores)
Cost ItemCapital
Cost ($M)O&M
($M)Total Cost
($M)
Sewer Main 269 61 330
Pump Station 82 34 116
Storage 94 72 166
I/I Reduction 53 0 53
WWTP Upgrade 9 0 9
TOTAL ($M) 507 167 674
Current Solution - $558 M
• Best solution in 350th generation• Total of 70,000 trial solutions evaluated• Actual processing time: 44 hours (120 cores)
Cost ItemCapital
Cost ($M)O&M
($M)Total Cost
($M)
Sewer Main 230 49 280
Pump Station 77 33 110
Storage 67 51 117
I/I Reduction 42 0 42
WWTP Upgrade 9 0 9
TOTAL ($M) 425 133 558
Optimised Solution - $540 M
• Best solution in 450th generation• Total of 90,000 trial solutions evaluated• Actual processing time: 56 hours (120 cores)
Cost ItemCapital
Cost ($M)O&M
($M)Total Cost
($M)
Sewer Main 217 48 265
Pump Station 79 33 112
Storage 64 47 111
I/I Reduction 42 0 42
WWTP Upgrade 9 0 9
TOTAL ($M) 412 128 540
Options Analysis Process
Objective:
Run Optimizer WCS withoutstorage or I/I reduction options
Develop solution for conveyance-only
Compare conveyance-only solution cost with least-cost solution
NSCC Optimisation – Conveyance-Only Scenario
Formulate Optimisation Model - Conveyance-Only Scenario
Switch-Off: I/I Reduction OptionsSwitch-Off: Storage Options
Conveyance-Only Optimisation Scenario
• Processing optimisation scenario• Performing 90,000 fully dynamic model
simulations of various trial solutions
Cost ItemCapital
Cost ($M)O&M
($M)Total Cost
($M)
Sewer Main
Pump Station
Storage
I/I Reduction
WWTP Upgrade
TOTAL ($M)
Run Optimisation Model
Conveyance-Only Optimisation Scenario
• Processing optimisation scenario• Performing 90,000 fully dynamic model
simulations of various trial solutions
Cost ItemCapital
Cost ($M)O&M
($M)Total Cost
($M)
Sewer Main
Pump Station
Storage
I/I Reduction
WWTP Upgrade
TOTAL ($M)
Run Optimisation Model
Conveyance-Only Solution - $809 M
• Best solution in 450th generation• Total of 90,000 trial solutions evaluated• Actual processing time: 56 hours (120 cores)
Cost Item528Capital
Cost ($M)O&M
($M)Total Cost
($M)
Sewer Main 430 98 528
Pump Station 133 41 174
Storage - - -
I/I Reduction - - -
WWTP Upgrade 107 0 107
TOTAL ($M) 670 139 809
Solution Comparison – $809 M / $540 M
• Best solution in 450th generation• Total of 90,000 trial solutions evaluated• Actual processing time: 56 hours (120 cores)
Cost ItemConveyance
Only ($M)Least
Cost ($M)Saving
Sewer Main 528 265
Pump Station 174 112
Storage - 111
I/I Reduction - 42
WWTP Upgrade 107 9
TOTAL ($M) 809 540 33%
33% Saving
$540 M$809 M
Solution Comparison – $809 M / $540 M
• Best solution in 450th generation• Total of 90,000 trial solutions evaluated• Actual processing time: 56 hours (120 cores)
Cost ItemConveyance
Only ($M)Least
Cost ($M)Saving
Sewer Main 528 265
Pump Station 174 112
Storage - 111
I/I Reduction - 42
WWTP Upgrade 107 9
TOTAL ($M) 809 540 33%
33% Saving
$540 M$809 M
Options Analysis Process
Objective:
Run Optimizer WCS with WWTP peak inflowlimited to 3000 L/s
Develop CEA Curve for NSCC
NSCC Optimisation – WWTP Min. Inflow Scenario
Formulate Optimisation Model - WWTP Min. Inflow Scenario
Set max WWTP capacity to 3000 L/s
WWTP Min. Inflow Optimisation Scenario
• Processing optimisation scenario• Performing 90,000 fully dynamic model
simulations of various trial solutions
Cost ItemCapital
Cost ($M)O&M
($M)Total Cost
($M)
Sewer Main
Pump Station
Storage
I/I Reduction
WWTP Upgrade
TOTAL ($M)
Run Optimisation Model
WWTP Min. Inflow Optimisation Scenario
• Processing optimisation scenario• Performing 90,000 fully dynamic model
simulations of various trial solutions
Cost ItemCapital
Cost ($M)O&M
($M)Total Cost
($M)
Sewer Main
Pump Station
Storage
I/I Reduction
WWTP Upgrade
TOTAL ($M)
Run Optimisation Model
Preliminary Solution Comparison
• Best solution in 450th generation• Total of 90,000 trial solutions evaluated• Actual processing time: 56 hours (120 cores)
Cost ItemConveyance
Only ($M)Least
Cost ($M)Min WWTP Inflow ($M)
Sewer Main 528 265 227
Pump Station 174 112 98
Storage - 111 211
I/I Reduction - 42 59
WWTP Upgrade 107 9 0
TOTAL ($M) 809 540 602Conveyance-Only
No WWTP UpgradeOptimised
Solution
Conclusion – Value of Optimisation
Capital cost savings
Reduce energy costs
Leverage investment already made in hydraulic modelling
Achieve multi-criteria objectives
Perform sensitivity analyses
The real value of optimisation
is not in finding a single,
absolute optimal solution…
… but rather in having an
efficient planning tool which,
when integrated with sound
engineering judgment,
can be used to help develop
robust, cost-effective and
highly defensible solutions…
planning engineers greater
confidence in the output
from models and modelers
more time to participate
in engineering.
Wastewater Collection System Optimization
An Innovative Approach to Capital Improvement Planning
Paul [email protected]
Joel Wilson – Wastewater Team [email protected]