Making Nutrient Removal Work Smarter: Full-scale Demonstration of Transitioning into Low-DO BNR

Presentation Description: Many Bay Area wastewater treatment plants will need significant upgrades to meet anticipated TIN limits by 2034, and with these regulations, utilities are increasingly testing process changes at full scale before committing to major capital projects. This presentation shares results from a two-year low dissolved oxygen (DO) demonstration at NEW Water in Green Bay, Wisconsin showing how to design, operate, and evaluate such trials.
Instead of immediately implementing a 2019 plan recommending aeration basin upgrades, NEW Water piloted low-DO control in one test basin while operating a parallel control basin at conventional setpoints (~2 mg/L). DO in the test basin was progressively reduced to < 0.5 mg/L in later phases.
Key outcomes:
• Aeration Energy Savings: Sustained 22–32% reduction in daily airflow to the test basin, even under varying influent loads.
• Chemical Savings: Ferric chloride dose reduced by ~60% (1,200 gallons vs. 3,000 gallons in the control) while maintaining more stable effluent phosphorus.
• Nutrient Performance: Effluent nitrate decreased with lower DO; TP removal improved despite lower chemical addition. NH₄-N and TSS remained below permit limits.
• Process Understanding: Bench-scale and in-situ testing quantified nitrification/denitrification rates, defining an optimal DO range for simultaneous nitrification-denitrification (SND).
• N₂O Emissions: Initially spiked when DO dropped to 0.5 mg/L, then stabilized to high-DO levels as the microbial community acclimated.
The demonstration also revealed limitations in traditional aeration system design for low-DO operation. Early valve and sensor issues caused unstable airflow, emphasizing the need for precise valve control, accurate airflow measurement, and strategic sensor placement. Adjustments improved performance and control stability.
Execution relied on close collaboration between operations, engineering, and research staff, supported by a live Power BI dashboard integrating lab, SCADA, and bench-scale data. Weekly review meetings enabled rapid setpoint optimization — including further DO reduction to 0.3 mg/L when performance allowed.
The results give NEW Water the confidence to proceed with a full-scale aeration upgrade using low-DO control and advanced mixing, informed by real-world performance data. This case study provides a roadmap for utilities aiming to reduce aeration energy, chemical costs, and nutrient loads while managing N₂O risk.