AC25 Modifying a BNR Facility for Low DO Operation and Operating it to Get There

CWEA Members: $35.00
Non-Members $45.00

Presentation Description: The Los Angeles County Sanitation Districts and Carollo Engineers, Inc. have participated in a Department of Energy project called “Transforming Aeration Energy in Resource Recovery Facilities through Suboxic Nitrogen Removal.” The project seeks to operate the activated sludge process at dissolved oxygen (DO) levels that are significantly below 1.0 mg/L while maintaining nitrification. The aeration process in a water recovery facility (WRF) typically consumes approximately 50% of the total energy of the plant. This project aims to reduce that energy consumption from 1500 to below 650 Kwh/MGD . This project involved pilot work as well as conducting full-scale modifications at the Pomona WRF to accommodate low DO operation.

The Pomona WRRF was built about 50 years ago and has not had any significant controls modifications since then. This may be typical of many WRF's in California. This presentation will cover in detail the significant modifications that were made to the facility and the costs. The old single speed centrifugal process air compressors were replaced with turboblowers. The old aeration control had one valve which controlled numerous aeration zones. New valves and flowmeters were installed to allow individual aeration zone control. A third-party control system was installed to allow precise DO control as well as ammonia-based aeration control. A solids retention time control system was also provided. To facilitate these control systems additional instrumentation, including sensors for ammonia, nitrate, DO, TSS, and sludge blankets, were installed. Details on the installation and maintenance of these sensors will be discussed.

The project team will also discuss the approach to reducing the DO while maintaining compliance. Results of low DO activated sludge transition will be presented. This project is due to be completed at the end of September 2024. Pomona WRF is currently operating an average daily DO of 0.85 mg/L. There is some disagreement about how low DO activated sludge works. It may be different organisms doing the nitrification or the existing population adapting to the low DO. The presentation will provide batch kinetic and nitrification test results as well as microbial analysis to try to provide an answer to that question.

Learning Objectives:
Upon completion, the participant will be able to understand the equipment and controls required to perform low DO operation.
Upon completion, the participant will be able to formulate a plan to transition a facility to low DO operation.
Upon completion, the participant will be able to understand the costs and benefits associated with low DO operation."