Advanced Aeration Control in Action: Diagnosing and Resolving Infrastructure Limitations

[b]APPLICABILITY[/b] Advanced aeration controls play a vital role in modern wastewater treatment by enabling low dissolved oxygen (DO) operation, improving energy efficiency, and reducing greenhouse gas emissions. However, the effectiveness of these control strategies is often constrained by infrastructure limitations, including legacy blower and piping configurations, blower turndown and staging, and sensor placement and reliability. As a result, many facilities struggle to realize the benefits of advanced aeration control without first addressing system-level constraints. This presentation offers a first-of-its-kind approach to diagnosing and overcoming these challenge through a combination of innovative, state-of-the-industry modeling and monitoring approaches. Drawing on a real-world case study, this work provides a step-by-step methodology for evaluating each aspect of a complex full-scale aeration system, including physical limitations, controls, and operational process decisions. This presentation provides actionable insights for professionals looking to understand and troubleshoot aeration system performance. Attendees will gain knowledge for evaluating existing systems, improving operational reliability, and achieving tighter process control. [b]RESULTS AND OUTCOMES[/b] [i]Methodology[/i] Metro Water Recovery's Northern Treatment Plant (NTP) (Denver, CO) has a rated capacity of 28.8 MGD and features four bioreactors configured as a seven-stage Bardenpho process with step-feed (Figure 1). Aeration is supplied by six high-speed turbo blowers, serving eight individually controlled aerobic zones in each bioreactor. NTP is implementing an advanced aeration controller (AAC) and is unable to maintain setpoints under certain conditions, indicating infrastructure limitations (Figure 2). Efforts to bring additional blowers online under these conditions have resulted in surge, further complicating system performance and troubleshooting. The primary objective of this work was to conduct a comprehensive, state-of-the-industry analysis of the aeration system to identify restrictions or deficiencies preventing the system from achieving required airflow demands when employing AAC. The methodology included: 1. A review of record drawings and onsite verification of existing conditions to validate system layout, physical constraints, and component conditions. 2. Process modeling conducted in BioWin to define treatment conditions and verify the operational capacity of the aeration system (Shown exemplary in Table 1). 3. AFT Arrow modelling to simulate airflow dynamics and identify bottlenecks in the system (Figure 3). 4. Onsite, real-time off-gas testing using Carollo's I-FLOAT to confirm key aeration design assumptions like alpha factor and oxygen transfer efficiency, which are critical for validating model outputs, ensuring accurate calibration, and help identify broken pipes previously not known (Shown exemplary in Figure 4). 5. The capacity and programming of the blowers were reviewed in collaboration with the manufacturer, including assessing control logic and implementing operational constraints to identify performance limitations. This approach provided an understanding of the system's limitations, enabling the identification of actionable improvements to enhance DO control, alleviate peak flow challenges, and facilitate AAC operation. [b]Result[/b] The analysis revealed significantly elevated blower discharge pressures in nearly all scenarios during peak diurnal loadings and high air velocities within Zones 1B and 1C under specific treatment conditions (Table 2). The discharge pressures in each scenario placed the existing blower system near or beyond surge conditions (Figure 5).

To address these issues, three solutions were evaluated by the project team:
• Option A: Upsize the piping and control valves in Zones 1B and 1C, reducing the air velocities and resulting pressure drops.
• Option B: Increase the piping in Zones 1B and 1C, extending modifications back to the main aeration lateral. This approach offers more significant pressure reductions but requires greater construction effort.
• Option C: Combine Option A's piping changes with an additional drop leg and diffuser manifold in Zone 1C. While this option does not substantially reduce blower pressures, it may improve process performance under low DO conditions. NTP is currently evaluating next steps for the aeration system from a holistic perspective, balancing operational and capital approaches to address the identified challenges. In addition, a blowoff valve was installed to assist with blower staging, and multiple control strategies have been implemented, including most-open-valve and pressure-based control tied to influent flow. The project team is coordinating with the blower manufacturer to achieve greater blower turndown and operate at greater pressures, which is currently limited by the blower's 'dynamic mean speed' control logic.

[b]Conclusions/Outcomes[/b] This work provides a novel, systematic approach to troubleshooting aeration systems, with findings that can be extrapolated to improve efficiency and performance in similar facilities, allowing for the implementation of AACs. The methodology and case study outcomes offer practical solutions to identify and address airflow limitations, optimize advanced aeration control, and enhance energy efficiency across diverse wastewater treatment projects.