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 Smithpaul.smith@optimatics.com

Joel Wilson – Wastewater Team Leaderjoel.wilson@optimatics.com