Fractional order controllers for urban wastewater treatment systems

One of the important issues affecting the quality of the results obtained in the control of wastewater treatment plants is the influence of influent variations on the effluent quality. Thus, treating the influent as a periodical disturbance has enabled us already to obtain a significant result in the control of these systems. But the results are more modest if there are irregularities on the influent diurnal variation. In the present paper a new solution has been proposed to the problem of reducing the effect of quasi-periodic disturbances in wastewater treatment urban plants, solution that uses a fractional-order subsystem. Since the process parameters change with the operating regime and the controller contain a fractional-order subsystem, the Quantitative Feedback Theory (QFT) frequency method has been used in order to design a robust controller for the considered control loop. The proposed control structure has been validated on a Activated Sludge Model No. 1 (ASM1) based WWTP implemented in SIMBA®.