Wastewater Collection System Optimization An Innovative Approach to Capital Improvement Planning COPYRIGHT – OPTIMATICS PTY LTD

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 City Service Area – 130 km 2 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 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 month Event

Improvement Options Parallel sewer main – 105 km Diversion sewer main – 55 km Pump station upgrades – 18 New pump stations – 7 I/I reduction – 51 sub-cat’s WWTP Upgrades - 1 Storage locations > 200  Over 10 9 option configurations NSCC Optimisation – Improvement Options Improvement Options Parallel sewer main – 105 km (dark blue) Diversion sewer main – 55 km (blue) Improvement Options Parallel sewer main – 105 km Diversion sewer main – 55 km Pump station upgrades – 18 (purple) New pump stations – 7 (yellow) Improvement Options Parallel sewer main – 105 km Diversion sewer main – 55 km Pump station upgrades – 18 New 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 km Diversion sewer main – 55 km Pump station upgrades – 18 New pump stations – 7 I/I reduction – 51 sub-cat’s WWTP Upgrades – 1 Improvement Options Parallel sewer main – 105 km Diversion sewer main – 55 km Pump station upgrades – 18 New pump stations – 7 I/I reduction – 51 sub-cat’s WWTP Upgrades - 1 Storage locations > 200  Over Possible Configurations Improvement Options – Relief SewersImprovement Options – Pump StationsImprovement Options – I/I ReductionImprovement Options – WWTP UpgradeImprovement Options – StorageImprovement Options – Too many for trial-and-error

NSCC Optimisation – Improvement Options Improvement Options – Relief SewersImprovement Options – Pump StationsImprovement Options – I/I ReductionImprovement Options – WWTP UpgradeImprovement 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 / Options Formulate Optimisation Model - Import Pump Station Costs - Import WWTP Upgrade Costs - Import Storage Costs - Import RDII Reduction Costs - Define Planning Criteria Overflow Frequency No overflows in selected design storm event/s Velocity 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 Criteria Min Cover Criteria - Optimizer WCS

Current Solution – Being Processed Processing 1 st generation Performing 200 fully dynamic model simulations of various trial solutions Cost Item Capital 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 1 st generation Performing 200 fully dynamic model simulations of various trial solutions Cost Item Capital 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 - $1079 M Best solution in 1 st generation Total of 200 trial solutions evaluated Actual processing time: 8 minutes (120 cores) Cost Item Capital Cost ($M) O&M ($M) Total Cost ($M) Sewer Main Pump Station Storage I/I Reduction1670 WWTP Upgrade000 TOTAL ($M)

Current Solution - $831 M Best solution in 32 nd generation Total of 6,400 trial solutions evaluated Actual processing time: 4 hours (120 cores) Cost Item Capital Cost ($M) O&M ($M) Total Cost ($M) Sewer Main Pump Station Storage I/I Reduction 1000 WWTP Upgrade 909 TOTAL ($M)

Current Solution - $674 M Best solution in 100 th generation Total of 20,000 trial solutions evaluated Actual processing time: 12.5 hours (120 cores) Cost Item Capital Cost ($M) O&M ($M) Total Cost ($M) Sewer Main Pump Station Storage I/I Reduction 530 WWTP Upgrade 909 TOTAL ($M)

Current Solution - $558 M Best solution in 350 th generation Total of 70,000 trial solutions evaluated Actual processing time: 44 hours (120 cores) Cost Item Capital Cost ($M) O&M ($M) Total Cost ($M) Sewer Main Pump Station Storage I/I Reduction 420 WWTP Upgrade 909 TOTAL ($M)

Optimised Solution - $540 M Best solution in 450 th generation Total of 90,000 trial solutions evaluated Actual processing time: 56 hours (120 cores) Cost Item Capital Cost ($M) O&M ($M) Total Cost ($M) Sewer Main Pump Station Storage I/I Reduction 420 WWTP Upgrade 909 TOTAL ($M)

Options Analysis Process

Objective: Run Optimizer WCS without storage 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 Item Capital 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 Item Capital 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 - $809 M Best solution in 450 th generation Total of 90,000 trial solutions evaluated Actual processing time: 56 hours (120 cores) Cost Item528 Capital Cost ($M) O&M ($M) Total Cost ($M) Sewer Main Pump Station Storage --- I/I Reduction --- WWTP Upgrade 1070 TOTAL ($M)

Solution Comparison – $809 M / $540 M Best solution in 450 th generation Total of 90,000 trial solutions evaluated Actual processing time: 56 hours (120 cores) Cost Item Conveyance Only ($M) Least Cost ($M) Saving Sewer Main Pump Station Storage -111 I/I Reduction -42 WWTP Upgrade 1079 TOTAL ($M) % 33% Saving $540 M$809 M

Solution Comparison – $809 M / $540 M Best solution in 450 th generation Total of 90,000 trial solutions evaluated Actual processing time: 56 hours (120 cores) Cost Item Conveyance Only ($M) Least Cost ($M) Saving Sewer Main Pump Station Storage -111 I/I Reduction -42 WWTP Upgrade 1079 TOTAL ($M) % 33% Saving $540 M$809 M

Options Analysis Process

Objective: Run Optimizer WCS with WWTP peak inflow limited 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 Item Capital 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 Item Capital 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 450 th generation Total of 90,000 trial solutions evaluated Actual processing time: 56 hours (120 cores) Cost Item Conveyance Only ($M) Least Cost ($M) Min WWTP Inflow ($M) Sewer Main Pump Station Storage I/I Reduction WWTP Upgrade TOTAL ($M) Conveyance-Only No WWTP Upgrade Optimised 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 Smith Joel Wilson – Wastewater Team Leader