Develop Control Strategy to Maximize Nitrogen Removal and Minimize Operation Cost in Wastewater Treatment by Online Analyzer

Conventional biological nitrogen removal is achieved by a sequence of nitrification and denitrification. Typical control strategies involve cost effective processes including aeration intensity (power consumption), adequate denitrification volume (reactor size) and supplemental carbon requirements. Dynamic adaptation of the aerated volume in response to the changing of the nitrogen load is the key to maximize nitrogen removal in activated sludge systems. This process can meet minimum aerobic volume requirements for complete nitrification and therefore maximize denitrification volume by installing online analyzers to provide real time control. In accordance with the Chesapeake Bay enhanced nutrient removal (ENR) mission, many WWTP will face more stringent nutrient discharge limits in the future. Thus the effort to optimize process performance to minimize future O&M costs associated with ENR requirements will become intensified. Online analyzers provide process stability to achieve future ENR discharge limits. This paper examines a full scale, real time nitrogen load and nitrogen removal profile along the aeration basin via an online analyzer at Washington Sanitary Suburban Commissions Seneca WWTP, Md. The 6 months of full scale experiments provide firsthand experience on a control strategy based on DO and air flow set point, ammonia and NOx measurements and aerated swing volume for maximizing nitrogen removal. During the test period, ammonia, nitrite, nitrate and total phosphorous concentrations have been reported instantaneously. The laboratory data agrees well with online analyzer measurements. Ammonia and NOx concentrations near the head of the aerobic zone and at end of the aeration basin are critical to achieving TN below 3 mg/l. The manually controlled swing zone on/ off and air flow adjustment at Seneca plant response well to nitrogen load variation resulting overall improvement of nitrogen removal. The Seneca experience and the success of control strategy in European wastewater treatment works could provide a dimension of future process control automation based on continuous online DO and nutrient parameters in The Unites States. This paper also evaluates operational data at Seneca wwtp and summarizes the experiences of operation strategies and the BNR processs optimization gained during the last few years. Simultaneous nitrification and denitrification (SND) was also observed based on nitrogen mass balance data which accounted for about a 60% nitrogen loss in the WSSC Seneca system.