(351e) Bifurcation Analysis of Wastewater Treatment Operation Conference: AIChE Annual MeetingYear: 2013Proceeding: 2013 AIChE Annual MeetingGroup: Computing and Systems Technology DivisionSession: Complex and Networked Chemical and Biochemical Systems II Time: Tuesday, November 5, 2013 - 4:35pm-4:55pm Authors: Ozturk, M. C., Illinois Institute of Technology Teymour, F., Illinois Institute of Technology Raju Ganesan, A. K., Illinois Institute of Technology Anderson, P. R. Bifurcation Analysis of Stickney Water Reclamation Plant Wastewater treatment plants (WWTPs) are an integral part of modern day communities, ensuring a clean environment and providing clean water. For almost a century, several technical enhancements to WWTPs have been made to improve the treatment process. However, as with many industrial processes, the necessity of sustainable operation has emerged in the last decade, as a result of the embraced sustainability policies throughout the world. A major portion of the energy consumption in WWTPs is attributed to the need for forced aeration in the activated sludge process. Aeration is critical for maintaining biomass activity, increasing the dissolved oxygen concentration in the wastewater, and ensuring proper mixing in the tank. Most WWTPs operate at unnecessarily high aeration conditions to ensure adherence to specification limits. It should be obvious that a better understanding of the complex behavior of the process would naturally lead to optimized and more cost-effective operation. Mathematical modeling offers deep insight into the workings of a process, especially when coupled with a bifurcation analysis approach, as we present in this study. A thorough bifurcation analysis leads to the classification and quantification of the entire operating space, thus allowing for a global view of operational constraints and risks. It can also serve as a decision tool for designing novel control strategies, such as an "agent-based control framework". In this study, we focus on Stickney Water Reclamation Plant (WRP) in West Chicago, which is the world's largest WWTP. We use a recently developed model of the Stickney WRP, which was validated with historical data from the plant from 2001 to 2009. The process is modeled as a 1-D continuous reactor (discretized as a train of 48 CSTR tanks) followed by a settler/clarifier with return activated solids recycling. The kinetic model is based on the widely used Activated Sludge Model no. 1 (ASM1). A custom continuation algorithm was used to carry out the bifurcation analysis on the resulting 480 algebraic (originally ordinary differential) equations. Attention was given to effluent concentrations of ammonia, dissolved oxygen and the biomass in evaluating the analysis results. This is the first instance of a bifurcation analysis of such a comprehensive model for the activated sludge process. Previous studies were limited to simplified models that were not validated against existing installations. When the total wastewater flow rate into the plant was used as a bifurcation parameter, multiple steady states can be broadly located, even in the vicinity of the nominal flow rate used by the process. The steady state set consists of a steady state where the coexistence of two biomass species (autotrophic and heterotrophic) is possible, states where only heterotrophs or autotrophs can exist, and a washout steady state at which no biomass exists. This finding has important implications on the operation of the WWTP. Similar observations are made when ammonia loading and water temperature are considered as bifurcation parameters. We also used the bifurcation approach to analyze the behavior of the plant during major storm events that result in sustained increased inflow owing to the nature of the combined flow situation into the sewer network of Chicago and most major cities. The results show that permit violation may occur during the long transients of storm events. Possible remedial actions are proposed. One chief aim of this study was the assessment of air usage at different conditions; hence a bifurcation analysis on airflow was performed indirectly by varying the mass transfer coefficient of dissolved oxygen. Results show that it is possible to reduce the airflow by about 40-60% of the nominal value, without causing an increase in ammonia or a decrease in dissolved oxygen. This represents significant energy savings for this process. Therefore, it is possible to achieve the sustainability goals of WWTPs, should proper control strategies are implemented. We are currently working on encapsulating the knowledge gained from the bifurcation study into an Agent-Based system (ABS) for monitoring and control of the cyber-physical system resulting from the combination of the treatment process, a sensor network, and the ABS.