Improvements in ATAD using quantitative feedback control and nonlinear generator of optimal operating points

This paper presents a new control approach that maximizes pasteurization and stabilization levels of the sludge treated in Autothermal Thermophilic Aerobic Digesters (ATAD). Working points are given to a feedback control structure as feedforward actions on the batch average temperature set point and on the air flow bias. These references change non-linearly between batches in response to unknown biodegradable content of the influent. A fuzzy system makes those decisions based on the temperature profile of the current batch. The linear feedback controller is designed according to Quantitative Feedback Theory (QFT), to achieve certain performance in response to changing operating points. The determined air flow-rate remains constant during the batch. The strategy brings the ATAD to maximum temperature (limited by the substrate) through optimum aeration. Results have been proven on an ATAD benchmark model, showing a significant aeration energy saving versus manual control in same effluent quality conditions.