Improving aeration efficiency through suboxic BNR strategies

Biological nutrient removal (BNR) has long been a central component to wastewater treatment, enabling water resource recovery facilities to meet stringent nitrogen and phosphorus limits. However, traditional BNR processes rely heavily on high levels of aeration, making it one of the most energy-intensive aspects of treatment. In fact, aeration can account for up to 60% of a facility’s total energy use.

A recent article in Water Environment & Technology by Carollo’s Natalie Beach and Michelle Young, along with other collaborators, explores how lowering aeration to suboxic levels can dramatically improve energy efficiency while maintaining strong nutrient removal performance. The article highlights real-world demonstrations of this approach and how advanced controls and operator engagement are transforming the next generation of WRRFs.

Exploring the Benefits of a Suboxic BNR Operation

Instead of maintaining high DO concentrations, suboxic biological nutrient removal (SBNR) operates between 0.2 and 1.0 mg/L of dissolved oxygen. While counterintuitive to many operators, this approach can save substantial energy, reduce chemical use, support simultaneous nitrification and denitrification, and even stabilize biological phosphorus removal.

“Reducing DO influences the microbial ecology of the system,” the authors explain. “Under oxygen-limited conditions, certain bacteria adapt while others increase in numbers to continue performing critical treatment functions.” Studies show that key microbial groups remain active under suboxic conditions when the system is properly managed.

From Research to Practice: The Pomona WRP Demonstration

To put SBNR into practice, Carollo led a U.S. Department of Energy–funded demonstration project, “Transforming Aeration Energy in Water Resource Recovery Facilities Through Suboxic Nitrogen Removal,” at the Pomona Water Reclamation Plant (WRP) in California. Working with partners at the Los Angeles County Sanitation Districts, the team implemented a full-scale low-DO retrofit that combined machine learning-based aeration control with high-efficiency turbo blowers and responsive valve systems.

This integrated approach allowed the facility to precisely manage airflow and DO concentrations in real time. The results were striking: Pomona WRP reduced average DO from 2.0 to 0.48 mg/L and cut aeration energy by 60%, all while maintaining ammonia removal below permit limits and improving phosphorus stability.

Operator engagement was key to this success. The team adopted a phased approach to lower DO gradually, defining safe operational boundaries and providing data-driven support to build confidence. “Operator buy-in is critical,” the authors note. “Engaging operators early in the process and clearly defining safety parameters increased confidence and ensured smoother implementation.”

As utilities strive to meet increasingly stringent nutrient limits while reducing energy consumption and carbon emissions, suboxic BNR presents a promising path forward. With modern control systems, advanced aeration equipment, and committed operators, facilities can move beyond the high-DO paradigm toward a future defined by smarter, cleaner, and more sustainable wastewater treatment.

Read the full article in Water Environment and Technology to learn more.