## 1 Introduction  
Recent advances in technology have improved the efficiency of the wastewater treatment process and paved the way for recycled water use. Nonetheless, the challenge of optimizing the treatment process while reducing operational and capital costs continues. The process of nitrification is often utilized by wastewater treatment facilities to meet ammonia effluent permit levels. To achieve full nitrification, that is, the conversion of ammonia to nitrate, the nitrifying biomass requires enough dissolved oxygen (DO), several nutrients, and an appropriate retention time [1]. One area of potential operational savings in the nitrification process is energy consumption, specifically from the mechanical blowers needed to support the aerobic portion of the treatment process [2]. The optimization of aeration through ammonia-based aeration control (ABAC) systems encourages operation at low DO concentrations. An ABAC system is composed of an open-loop and closed-loop controller that sets DO setpoints in the treatment aeration basin to maintain a predetermined ammonia setpoint at the effluent [3, 4]. This decreases the overall energy consumption of the facility while maintaining high-quality effluent. Since aeration typically contributes a large percentage of a wastewater treatment plant's energy costs due to the operational cost associated with large blowers, the development of control efforts to optimize the aeration process is essential. Moreover, utilization of novel aeration control strategies to optimize the biological processes such as nitrification or phosphorus removal, has shown to decrease plant chemical usage without sacrificing effluent quality [2]. Wastewater treatment facilities with nitrification systems typically operate at elevated levels of aeration with a concentration above 2 mg DO/L to avoid nitrification failures and satisfy biological oxygen demand (BOD) removal as well. Studies have shown, however, that complete nitrification can occur at low levels of DO concentrations [2]. Operating at 0.5 mg DO/L rather than 2 mg DO/L, the overall oxygen transfer efficiency increases by 16%, which translates to a 10% energy saving for the overall treatment plant [1,2]. Low DO operation can, however, create a treatment environment susceptible to sludge bulking due to the growth of filamentous bacteria. Studies have shown that lower DO concentrations (0.5-2.0 mg DO/L) produced sludge with poorer settling properties and higher turbidities in the effluent than higher DO concentrations (2.0-5.0 mg DO/L). The cause was found to be the growth of filamentous bacteria; filamentous microorganisms can compete with floc-forming organisms at low DO levels (<1.5 mg/L) [2]. Strategies to control aeration use specific parameter-measuring devices in combination with control programs to provide cost-saving alternatives. Sensors are used to measure nutrients such as ammonia, nitrate, nitrite, phosphorus and DO are used to operate the aeration control strategy. As a result, the application of these measuring instruments must be appropriate to avoid measuring errors and minimize the risk of violating permit limits. Most conventional wastewater treatment plants are not originally designed for use with real-time control (RTC) systems and thus require equipment upgrades. Nonetheless, the evolution of Supervisory Control and Data Acquisition (SCADA) systems in treatment facilities has allowed facilities to remotely monitor and control the process. RTC can therefore be integrated into SCADA through the capacity of distributed control systems (DCS), which control plant operation through remote terminal units (RTUs) and proportional-integral-derivative (PID) control algorithms [5]. With the increasing global demand for water accessibility and improved sanitary standards, the advancement of wastewater treatment processes and technologies is critical for societies to thrive.