The model was subsequently validated with the data from April 06, 2022 to April 25, 2022 using the eight calibrated parameters (Figure ). The accuracy of the orthophosphate prediction (RMSESP: 0.02 g-P•m -3 ) for the validation period, when the system upset was alleviated, was improved compared to the calibration period. On the other hand, the accuracy of microalgae biomass (RMSEVSS: 187 g VSS•m -3 ) and biomass yield (RMSEYIELD: 309 g-biomass produced•g-P removed -1 ) predictions deteriorated as the model-predicted biomass concentration began to deviate from the observed performance starting on April 16, 2022. The MAPEs for the 5-day (SRT) moving average of biomass yield were 18.5% and 31.3% for the calibration and validation periods, respectively. We attribute this to the changes in the influent orthophosphate concentration: as the influent orthophosphate (the limiting nutrient) gradually decreased starting April 17, 2022 (Figure ), the PM 2 predicted functional microalgae biomass (XALG) would decrease (Figure )