Optimizing the Operation of the Mill Creek Basin through Innovative Real-Time Control Strategy

Purpose Wastewater utilities face increasing challenges to operate and maintain their collection systems more effectively to ensure capacity, performance, and resiliency. In recent years, there has been a transformation in the approach to the operation and management of collection systems through real-time control and optimization. With that vision in mind, the Metropolitan Sewer District of Greater Cincinnati (MSDGC) developed a watershed Supervisory Control and Data Acquisition (SCADA) system that links remote facilities and collection system sensors in a shared communication and control network. The purpose of this presentation is to demonstrate how MSDGC achieved success in optimizing the operation of its collection system through the implementation of an innovative market-based control strategy to globally control remote assets in real-time through a watershed SCADA system, maximizing the utilization of existing infrastructure and minimizing releases to the environment. Benefits of Presentation MSDGC has implemented an intelligent sewer system that has progressed through the three distinct levels of a real-time control system: local, regional, and global. Initially, local control was implemented at each of its remote real-time control facilities. While this remains the fundamental control strategy for these assets, once the watershed SCADA system linked the remote facilities and collection system sensors in a shared communication and control network, MSDGC achieved regional control of these assets. At this stage, the facilities were able to optimize their operations based on relevant sensor data from across the basin. For example, a remote chemically enhanced high-rate treatment (CEHRT) facility in MSDGC's collection system was tied into the watershed SCADA system and then operated autonomously based on data from level sensors strategically located at hydraulic choke points downstream and along feeder pipes upstream that anticipate what flows will reach the facility. The final component was the implementation of the market-based control strategy, this enabled the real-time control and the remote high-rate treatment facilities to work together to fully utilize the available capacity in their shared downstream interceptor sewer during wet weather. This has achieved a level of global control that coordinates all the controllable assets in the basin to maximize conveyance to the wastewater treatment plant and minimize overflows across the entire basin. Figure 1 shows a general overview of the Mill Creek interceptors and remote facilities. This presentation demonstrates the implementation of innovative market-based control for MSDGC's Ross Run and Mitchell Avenue Real-Time Control (RTC) facilities. Market-based control is a novel technology that can achieve the following outcomes: - Rapid implementation of collection system controls - Overflow reduction benefits just by changing control programming - Minimal capital investment in infrastructure The market-based control strategies were developed in storm water management model (SWMM) technology, such as PySWMM. Market-based control technology cannot typically be implemented in traditional SWMM engines. The modeling completed for the project overlaid the market-based control methodologies on the SWMM simulation engine to estimate key-performance indicators (KPIs) for MSDGC. KPIs developed for this project were Combined Sewer Overflow (CSO) volume and occurrences, Wastewater Treatment Plant (WWTP) volume, and flooding. Two approaches to continuous modeling were completed. A typical year storm event and a 19-year spatial rainfall storm event were run. The 19-year spatial rainfall storm event was derived from approximately 40 rain gauges in the MSDGC service area. The rain gauge data was processed to develop timeseries data for each CSO sewershed. These timeseries were input into the collection systems model to simulate estimated spatial dynamics of the rainfall/runoff process. Programmable Logic Controller (PLC) logic for SCADA implementation was derived from the market-based control modeled logic. The PLC programming utilized a prorated gate adjustment with a maximum gate change per time step to approximate a proportional-integral-derivative control at the RTC sites without requiring extensive tuning of control parameters. The project also developed a software component to efficiently monitor and characterize CSO control performance. Xylem aggregated flow monitoring data from several sources. For collection system level sensors and flow meters, an extract transform load (ETL) program was developed to transfer data from a telemetry vendor application programming interface (API). For facility sensors, an ETL was developed to transfer data from SCADA servers to Xylem's cloud database. Xylem developed visualizations of the Mill Creek Interceptors response to real-time control at the Ross Run and Mitchell Ave RTC facilities. Visualization of the RTC performance on a storm event basis facilitated monitoring and characterization of efficacy of the CSO controls. The software platform allows MSDGC staff to continuously assess CSO control performance at the RTC sites without the need to spend capital or operational budget on consulting costs. Figure 2 shows an example of the Mill Creek Interceptor visualization. Status of Completion Implementation of market-based control programming was completed at the Ross Run and Mitchell Avenue Real-Time Control facilities in October 2020. The market-based control strategy for a third application at MSDGC's Wooden Shoe Real-Time Control facility is currently in the implementation phase, with completion anticipated in early 2023. Conclusion MSDGC evaluated the impact of the globally coordinated control strategy through a hydraulic modeling analysis using both the 1970 typical year and 19-years of historical spatial rainfall data collected by MSDGC. This analysis showed that MSDGC achieve approximately 48 MG of CSO reduction in the Typical Year scenario and an average 30 million gallons per year of CSO reduction in the spatial rainfall scenario. With the cost of CSO reduction in both scenarios calculated to be less than $0.01 per gallon. MSDGC has demonstrated success in optimizing the operation of the collection system and remote facilities by implementing a global control strategy using an innovative market-based control logic. This global control strategy incorporates data from multiple sensors located across the basin and coordinates the operation of the facilities to fully utilize the available capacity in their shared downstream interceptor sewers during wet weather. This allows MSDGC to leverage existing assets beyond their original design intent to maximize the conveyance to the Wastewater Treatment Plant and minimize overflows across the basin.