One of the critical implementation challenges with real-time control (RTC) of a wastewater collection system is moving from the planning stage involving hydraulic modeling into operations. Often, the modeling produces control rules that do not translate cleanly into directions of operations, or trying to capture operational methods into the model is nearly impossible due to the dynamic decision process undertaken uniquely with each wet weather event. This bi-directional disconnect between the model control rule actions and operations leads to confusion and degradation of the results as they are implemented from the model to the system or captured from the system into the model. Add the capabilities of a modern control system into the mix, and the situation is even more complex.
The City of Columbus, Ohio formed an RTC team that crossed typical boundaries and involved operations, modeling and instrumentation and controls engineers. One of the key items was to construct the modeling rules to be directly relatable to the operations methods and the control system programming. Often modeling rules used fixed positions or flow rates that do not represent how the control system or operations adapt to differing wet weather conditions. PID (Proportional, Integral & Derivative) actions are commonly used on the control system to allow plant operations to maintain a fixed set point. The control action of a gate may vary over a wide range to maintain a fixed set point. This is a substantially different action than fixed positions based on conditional rules. For several of the larger historical rainfall events in the last 17 years, the Columbus RTC effort used the City’s system-wide hydraulic computer model and made use of the PID controls to emulate existing RTC actions by the plant control system and operational methods that were focused at three key areas; the Whittier Street Storm Tanks Regulator Gates, the Scioto Main Relief (SMR) weir gate, and the Jackson Pike Waste Water Treatment Plant (WWTP) pumping rules. This paper will illustrate the advantages of incorporating PID controls for the City of Columbus RTC planning study by highlighting the enhanced capability of PID control modeling which creates a tool that translates easily between operations and modeling