Optimization of Simultaneous Nitrification Denitrification Performance in Different ENR Process Configurations

This paper reports details of nitrogen balance and simultaneous nitrification and denitrification (SND) occurrence, including specific nitrification rate and half DO saturation coefficient under low DO conditions, in five different wastewater process configurations where total nitrogen (TN) consistently achieves 3-5 mg/l discharge limits without external carbon addition. It also examines the full scale, real time nitrogen load and nitrogen removal profile along the aeration basin via the online instruments at the Washington Sanitary Suburban Commission's Seneca WWTP, MD, and Jefferson Peaks, NJ. Six months of full scale experiments at Seneca provide experience with a control strategy based on DO and air flow set point, ammonia and NOx measurements, and aerated swing zone volume for maximizing nitrogen removal. At Jefferson Peaks process control was limited by plant mixing condition and blower minimum VFD speed. The SND optimization, however, has been improved by minimizing DO spikes during low flow and no flow periods. The Seneca experience and successful application of the control strategy in European WWTPs could provide an opportunity for future process control automation based on continuous online DO and nutrient parameters. This paper provides insight on developing control strategies to optimize SND performance with different process configurations based on DO and air flow information, ammonia and NOx concentrations, as well as the variation of required aerobic volume that swings between aerobic and anoxic zones.