Rethinking aeration: Enhancing efficiency and biological nutrient removal with low dissolved oxygen operations

Aeration is one of the most energy-intensive processes at water resource recovery facilities, often accounting for 45 to 60 percent of a plant’s total energy demand. As utilities look for ways to reduce operating costs while maintaining reliable treatment performance, low dissolved oxygen (DO) operations are gaining attention as an effective strategy.

In a recent article published in The Splash by the Oklahoma Water Environment Association, Carollo’s Natalie Beach and Michelle Yong explore how low DO aeration strategies can enhance biological nutrient removal (BNR) while significantly reducing energy consumption. Their article highlights lessons learned from implementing low DO operations at the Pomona Water Reclamation Plant operated by the Sanitation Districts of Los Angeles County.

Improving Biological Nutrient Removal with Low Dissolved Oxygen

Traditional activated sludge processes typically operate at dissolved oxygen concentrations above 2 mg/L to support nitrification. Low DO treatment strategies, by contrast, operate below 1 mg/L. At these lower oxygen concentrations, microbial communities adapt to maintain nitrification, nitrogen removal, and biological phosphorus removal while requiring less aeration energy.

Low DO operations apply selective pressure on microorganisms, allowing treatment systems to maintain strong nutrient removal performance while reducing the energy needed to deliver oxygen to the process.

Implementing Low DO Operations at Full Scale

To better understand how low DO BNR can be implemented in full-scale systems, Carollo led a research effort funded by the U.S. Department of Energy focused on transforming aeration energy in water resource recovery facilities.

The Pomona Water Reclamation Plant provided a valuable case study. The facility was preparing for a major aeration system upgrade, as its aging blowers offered limited airflow flexibility and contributed to energy use exceeding 1,300 kWh per million gallons treated.

To support low DO operations, the plant implemented several improvements, including high-efficiency turbo blowers, upgraded airflow control valves, additional online monitoring instruments, and an ammonia-based aeration control system that uses machine learning to adjust aeration in real time.

Achieving Energy Savings While Maintaining Effluent Quality

Using a phased implementation strategy, Pomona operators gradually lowered DO setpoints while maintaining stable treatment performance. The facility ultimately reduced aeration energy consumption from approximately 1,300 kWh per million gallons treated to about 550 kWh per million gallons, well below typical industry ranges.

At the same time, the plant maintained ammonia discharge performance comparable to historical operations. Temporary DO increases during periods of high influent loading helped maintain compliance while preserving the overall low DO operating strategy.

Pomona’s experience demonstrates how advanced aeration controls, targeted equipment upgrades, and careful process optimization can enable more energy-efficient wastewater treatment.

To learn more about low dissolved oxygen operations and the lessons from Pomona’s implementation, read the full article in The Splash.