Optimization of Real-Time Control With Green and Gray Infrastructure Design for a Cost-Effective Mitigation of Combined Sewer Overflows

Abstract

An innovative optimization-simulation framework is applied to a case study of the Province of Quebec, Canada, to optimize the spatial distribution of green infrastructure (GI), the capacity and location of gray infrastructure, and the parameters specific to real-time control (RTC) operating rules of a sewer system for reducing combined sewer overflows (CSOs) frequency and volume. GI, gray infrastructure, and RTC are applied either individually or in integration through eight optimization scenarios which are simulated over a nine-year period of historical rainfall data. Among all scenarios, spatial optimization of GI with RTC leads to maximal CSO volume reduction (98%) and is the most cost-effective option analyzed (70$/m3 of seasonal average CSO reduction compared to 140$/m3 for the scenario involving gray infrastructure alone). However, it requires a high GI implementation level and the CSO frequency under this scenario is sensitive to varying GI design parameters. The findings suggest that the best alternative for CSO control is the integration of the optimization of green and gray infrastructures with RTC as it still provides high CSO volume reduction (95%) and remains a cost-effective solution (90$/m3 of CSO reduction), while providing robustness under cost and design uncertainties.