Development of a mathematical model for a secondary settling tank in wastewater treatment plants with control purposes

Sedimentation is one the most important processes in the understanding of wastewater treatment plants, and secondary settling tanks have been frequently investigated with mathematical models for design and operation. Modeling of secondary settling tanks has been a difficult problem due to highly coupled dynamics and non-linearity in the settling of sludge particles. A process control engineering approach is required to formulate the settling process and provide feedback control solutions for compensation of disturbances like rainfall and overflow. The main purpose of this research is to develop a mathematical model that covers all significant dynamics involved in the secondary settling tank of a typical wastewater treatment plant. The developed model is simple enough for computer simulations and convenient for feedback control applications, and it allows for freedom to maneuver with hindered settling, compression and dispersion properties of the suspended solids in a settling tank. Computer simulations are performed for testing the developed model in realistic conditions, and results are analyzed. A discussion of the simulation results is presented to reveal the efficacy of the developed model and possible implementation for feedback control solutions.