Real-Time Dynamic Control of Nitrification and Denitrification in an Intermittently Aerated Activated Sludge System for Enhanced Nitrogen Removal and Energy Efficiency: Toward Sustainable Operation

Advanced control systems have been recently implemented in wastewater treatment plants (WWTPs) to optimize activated sludge processes, reduce operational costs, and decrease energy consumption, with the aim of moving toward sustainable operation. Real-time dynamic control of NH4+-N and NO3−-N concentrations is important for the optimization of biological nitrogen removal (BNR) processes. This study presents an advanced control strategy based on continuous monitoring of NH4+-N and NO3−-N concentrations at 22.8–25.1 °C to enhance nitrogen removal performance. Specifically, the control performance of an intermittently aerated and fed activated sludge (IAF-AS) system treated with domestic wastewater was evaluated using a controller under two different scenarios: (i) normal conditions at constant ammonium nitrogen loading rate (ALR) and (ii) varied conditions with a sudden increase in ALR. The effect of temperature changes on BNR efficiency was not analyzed. In both scenarios, the optimal duration ratio of the nitrification and denitrification phases was determined, which depended on the ALR. In the first scenario, at a constant ALR of 0.2 g L−1 d−1, the controller kept the duration of nitrification and denitrification at a low level, succeeding in complete nitrogen removal in less than 60 min. In the second scenario, when the ALR exceeded 0.3 g L−1 d−1, the controller dynamically extended these phases to achieve the effluent endpoints of 2 mg L−1 NH4+-N and 1 mg L−1 NO3−-N. The results show that the use of real-time dynamic control is of great importance, as the nitrogen removal efficiency is maximized by minimizing the anoxic/aerobic duration ratio, thus significantly reducing the aeration energy requirement and operating cost.