Use of modeling for controller tuning

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In the mid-1990's Dr. Ekster pioneered the use of a computerized model of activated sludge process for tuning of SRT controller. Computer modeling consists of several steps. First, the filed data is collected and an activated sludge computer model (Fig.1) is calibrated using this data.

Fig.1 Picture of modeling software layout used for system modeling.

Then using methodology developed by Dr. Ekster, time basis for SRT calculations is selected. Time basis is plant specific and depends on wastewater flow and characteristics, plant design, etc. A criterion for time basis selection is closeness of calculated SRT and dynamic SRT. The computer model is used to simulate an effect of waste flow change on both dynamic SRT and calculated SRT.
An example of simulation results is shown on Figure 2.

SRT

Fig.2 Results of computer simulation.

After selection of time basis for SRT calculations, PID tuning coefficients are found for SRT controller with help of computer modeling. Finally, the behavior of controller is modeled for "what if" situations. Based on the modeling results SRTmaster^TM final tuning coefficients are selected.

The benefits of applying Dr. Ekster's approach to solving the "real world" problems are well documented. Software based on Dr. Ekster's approach is now successfully controlling activated sludge processes worldwide.