Modeling, Simulation, and Control of Dissolved Oxygen in Activated Sludge Wastewater Treatment via PID Controller: Reducing Energy Costs

Abstract

This research explores the control of Dissolved Oxygen (DO) in Activated Sludge-based Residual Treatment Plants (ASRTP) using a classic Proportional-Integral-Derivative (PID) controller. In addition to DO control, the system monitors Redox Potential (RP) and Turbidity, ensuring a well-regulated treatment process. The DO levels in the reaction tank are regulated by adjusting the aerators based on the existing Chemical Oxygen Demand (COD) of nutrients and a pre-conducted respirometry analysis. The data indicates that energy consumption can be reduced by up to 66.83%, leading to equivalent financial savings of 73,151.38 dollars, equivalent to 1,406,757.21 kWh per year. The system was tuned to achieve a target DO concentration of 8.0 mg/l within one hour. During this period, the aerators were off for 40.1 minutes and operational for 19.9 minutes. Notably, the aeration system initially operated at 90% of its maximum intensity but subsequently maintained a reduced intensity of 60%, further contributing to energy savings by minimizing both operation time and intensity. Additionally, the DO response was simulated in LabView using the differential equation for DO dynamics in the WWTP, incorporating respirometry parameters like initial oxygen levels, sludge oxygen consumption, and aeration rates. Practical and theoretical responses were compared for validation. PID tuning was done in MATLAB and implemented in LabView, integrating sensors and actuators.