A Pilot Scale Study of Low Dissolved Oxygen Nutrient Removal Supplemented with Ammonia-Based Aeration Controls

Abstract

In order to refine a previously acclimated pilot to low dissolved oxygen (DO) conditions for nutrient removal, ammonia-based aeration control was introduced in an effort to successfully remove ammonia throughout an entire year. Historical operations of the low DO pilot, operated at a fixed DO setpoint of 0.5 mg/L, allowed for efficient nutrient removal until water temperatures decreased with drastic seasonal changes present in at the Nine Springs Wastewater Treatment Plant in Madison, WI. By implementing ammonia-based aeration controls in the secondary treatment process, triggered by operator adjustable ammonia setpoints, the pilot was allowed to operate between high and low DO modes to call for additional oxygen when ammonia loads increased, and call for less oxygen, as an energy saver, when an ammonia setpoint is achieved. In addition, data from the ammonia probe was compiled and summarized which provides an enhanced understanding of the process that was previously not possible to obtain. This shows the daily, and even hourly, variability that the pilot experiences in response to influent loadings and seasonal transitions. In comparing the first iteration of ammonia-based controls with the previous years of fixed DO operation, recommendations and enhancements are provided to optimize the process for future work. The study provided insight into the various physical configurations to be considered with the control strategy and also evaluates the side effects, both positive and negative, that come with implementing ammonia-based controls on a low DO pilot reactor.