Donohue’s Nathan Cassity is one of the presenters featured at the upcoming Wastewater Administrators Conference held by the Michigan Water Environment Association on January 22-23. Nathan’s presentation titled “Low Level DO Operations: Impact on Energy, Nutrients, and Ecology” examines two full scale facilities that operate consistently under low DO (dissolved oxygen) conditions (DO setpoints less than 1 mg/L): the Trinity River Authority (TRA) Central Regional Wastewater System (CRWS) Treatment Plant in Texas and the Stevens Point, Wisconsin, Wastewater Treatment Plant.
Low DO operation has been shown to decrease energy usage while increasing simultaneous nitrification and denitrification (SND). This has benefits for energy consumption, nitrogen removal, biological phosphorus accumulation, and has the effect of concentrating nutrients into sidestreams for increased recovery potential.
TRA has been evaluating low DO operation at full scale for energy savings and nutrient removal. The full scale testing began in September 2012. When the full facility is operated under low DO conditions, airflows were consistently reduced by 25%. The Stevens Point Facility operates at a DO of approximately 0.8 mg/L during warm weather and 1.5 mg/L during cold weather. The Stevens Point facility operates at a low sludge retention time (SRT) to limit nitrification, but still observes ammonium removal during periods of operation. The facility has also selected for large, dense flocs in the mixed liquor, which significantly improve treatment performance and effluent quality.
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