This work presents the application of expert control strategies for a successful and stable operation of partial nitrification. A high-strength ammonium wastewater was treated in a continuous pilot plant with a configuration of three reactors in series plus a settler. The system was operated at mild temperature (around 25°C) and at high sludge retention time to obtain a significant nitrifying biomass concentration. The implemented control system with expert supervisory rules provided a stable and robust operation of the partial nitrification system even when the pilot plant was subjected to several disturbances as change in influent concentration, failure of aeration in one reactor and operation with variable biomass concentration. The control system was based on local feedback control loops for dissolved oxygen and pH with proper setpoints for nitrite oxidizing bacteria (NOB) inhibition and an inflow control loop based on Oxygen Uptake Rate (OUR) measurements, which allowed working at the current maximum ammonium oxidation capacity. Two additional expert rules were implemented for automatically determine the required OUR setpoint in accordance with the biomass activity and to produce a fast load decrease when a system overload was detected.

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