Aeration is a costly and energetically expensive process used for biological nutrient removal (BNR) at many wastewater facilities. Significant progress has been made in the last 5 years transitioning wastewater treatment plants from conventional BNR at high aeration rates (>1.5 mg DO/L) to low dissolved oxygen (DO) operation (< 1.0 mg DO/L). Operating with low DO or suboxic biological nutrient removal (SBNR) (DO <0.7 mg/L) have emerged as effective strategies to reduce energy while providing consistent BNR by exerting selective pressure on microbial communities involved in nitrification, nitrogen (N) removal, and biological phosphorus (P) removal to adapt and perform effectively at very low DO concentrations. This type of operation is relevant to Kentucky and Tennessee wastewater facilities facing conflicting priorities of budget constraints, sustainability goals, and more stringent nutrient limits. This presentation focuses on the Los Angeles County Sanitation District’s Pomona Water Reclamation Plant (PWRP), where the 15 MGD full-scale Modified Ludzack-Ettinger (MLE) facility performing nitrification was transitioned from conventional BNR to low DO/SBNR operations as part of a Department of Energy-funded project (DOE DE-EE0009509). The presentation includes: •An overview of important system modifications for low DO/SBNR operations. •The importance of advanced controls for process performance. •The stepwise approach implemented to achieve low DO operations. •Energy and performance comparisons between baseline and low DO operations. PWRP was retrofitted with high-speed dual-core turbo centrifugal blowers, new aeration control valves and actuators, flow meters, nutrient sensors, and a third-party software package using solids retention time and ammonia-based aeration control (ABAC) within its machine learning based aeration control algorithms. The demonstration at PWRP aimed to operate the activated sludge process at the DO levels below 1.0 while maintaining nitrification and reducing aeration energy consumption by 50%. Over the course of this project, PWRP successfully transitioned from average DOs from 2.0 – 3.0 mg/L to 0.8 mg/L and reduced aeration energy consumption from 1400 kWh/MG to 650 kWh/MG. Preliminary data also suggests a significant decrease in nitrous oxide emissions, likely due to lower agitation and gas stripping from less turbulent aeration. A combination of ABAC controls on ammonia and limiting the DO operating range allowed Pomona to maintain effluent ammonia concentrations comparable levels prior to the low DO conversion regardless of DO operational range and at the same aerobic solid’s retention time. The ABAC system allowed the process to respond quickly to changing DO demands and sudden daily influx of TKN and ammonia. In addition, phosphorus removal improved in the later phases of the project (at lower DOs), achieving averages below 0.2 mg P/L through biological phosphorus removal, despite that PWRP is not designed for phosphorus removal. In addition, a 3-week test demonstrated that effluent ammonia can be controlled at 1, 1.5, and 2.5 mg/L each, meaning ammonia supplementation for chloramination at PWRP was eliminated (an additional cost savings).