Conference Agenda

New and expanded facilities must respond to a full range of future conditions and operating scenarios to ensure system performance and regulatory compliance over their design life. Operators’ perspectives are an essential part of the design process, especially to provide guidance on system controls. Jacobs engaged with the Bureau of Environmental Services’ (BES) operations staff during early design of two new secondary clarifiers which resulted in more certainty with complex control schemes and the potential to reduce cost and risk during startup and commissioning. Presentation includes viewpoints from Jacobs, BES engineering, and BES operations staff.

The Secondary Treatment Expansion Program (STEP) includes the addition of two new circular 145-ft diameter secondary clarifiers at the Columbia Boulevard Wastewater Treatment Plant (CBWTP) that will be the largest clarifiers in the state of Oregon. CBWTP treats up to 450 million gallons per day with the combination of a wet weather treatment system and a secondary treatment system. STEP is increasing capacity through the secondary treatment system and changing the flow split between the two systems.

Early design workshops highlighted the complexity of the flow split scenarios (multiple flow streams and multiple control points) and effectively communicating how control decisions impacted hydraulic performance was challenging. Jacobs developed a design-level digital twin of the CBWTP secondary treatment system, so operations staff could engage with the flow parameters using the same visual interface and control logic as the constructed facility. The digital twin combined a detailed, dynamic hydraulic and simplified solids model, database structure, and instrumentation and controls narrative to simulate plant performance under a range of flow scenarios. Once the scenarios and control logic were developed, the design was stress-tested, using the tool, in an efficient and low risk environment. The operators’ input during design refined control logic and narratives which will allow for more intuitive operation and smoother startup and commissioning to meet regulatory compliance goals.

The Puget Sound Nutrient General Permit (PSNGP) became effective on January 1, 2022 and requires larger dischargers implement optimization to maintain nitrogen discharge below action levels established by the permit. The Wastewater Treatment Division (WTD) of King County operates three large treatment facilities, South Plant, Brightwater, and West Point. As allowed by the PSNGP, WTD elected a bubbled action level for compliance flexibility, instead of individual action levels for each facility. This presentation discusses actions taken by WTD under its bubbled action level in 2022 to comply with the PSNGP.
This presentation will describe the optimization planning work that HDR Engineering, Inc. (HDR) conducted with WTD staff and discuss lessons learned from optimization strategy implementation. HDR used WRF 4973, Guidelines for Optimizing Nutrient Removal Plant Performance, as a guide for screening optimization strategies. HDR led a collaborative process with WTD staff to assess current influent and effluent nitrogen loadings, identify, model and screen potential optimization strategies, and engage staff in reviewing and selecting strategies.
Previous testing at South Plant indicated that the facility could be operated in Ludzack-Ettinger mode during dry weather conditions to accomplish partial nitrogen removal, and this was selected as the initial optimization strategy as it could be implemented immediately with limited to no capital improvement. At Brightwater, a construction project is underway which will allow the plant to operate at low dissolved oxygen levels and increase nitrogen removal while improving process stability.
The PSNGP requires continual planning and adaptive management to respond to optimization challenges and maintain discharges below action levels. Both South Plant and Brightwater leveraged flexibility in implementation. They used trials and troubleshooting to maximize their success, and identified several potential strategies to improve outcomes, including an interim alkalinity feed system at South Plant.
As a result, WTD complied with the PSNGP in 2022 by staying more than 10 percent under the action level. Lessons learned from the first year optimization planning will be shared, along with a discussion of how WTD is planning to build and operate under an adaptive management framework for optimization planning and implementation.