AN INTEGRATED CONTROL STRATEGY FOR THE ACTIVATED SLUDGE PROCESS
VITASOVIC, ZDENKO ZDENKO
Doctor of Philosophy
The objective of this study was to develop an integrated control strategy for the activated sludge process. For the purpose of this study, the system included the influent pump station, the biological reactor, the air supply and distribution system, and the solids-liquid separator. A comprehensive dynamic model was developed for the system and control was superimposed on the model. The overall model of the system consisted of deterministic and stochastic components. The models for individual process units were taken from the literature and modified where necessary to include features necessary for control strategy development. Computer simulations were used to investigate the control strategies, interactions between the control loops, interactions between process units, and between design and operation. A limited amount of data was available from a full scale experiment conducted at a wastewater treatment plant in Houston, Texas. The objective function was to minimize operating costs and permit limits were treated as constraints. The control strategy for the biological reactor was based on a definition of process state consisting of a combination of D.O. concentration and specific oxygen uptake rate. A rule based controller was designed to maintain the optimal process state. Computer simulations suggested that control of flow between the biological reactor and the separator was capable of eliminating high frequency variations in flow rate. This strategy was proposed for minimizing adverse effects on clarification. For low-friction-head, high-static-head pump stations, on/off pumping was found to require less energy than variable speed pumping or automatic throttling of the discharge. Due to the small size of the wet well, variable speed pumping was found to be incapable of significantly dampening variations in influent flow rate.
Sanitary and municipal engineering