Mathematical modeling of wastewater treatment plants foroperational costs minimization

In this work, state of the art mathematical models (ASM,1 ASM3, and ADM from the International Water Association) are applied to simulate the behavior of the biological units (activated sludge with predenitrification and anaerobic digestion) of the wastewater treatment plant of S. Colombano (FI), the main aim of the modeling exercise being the simulation of various operational strategies for cost minimization. Two commercially available simulation platforms were used: AQUASIM (Eawag, CH) and WEST (DHI, Denmark). Two years operational data were used for model validation. Required modifications are discussed and an integrated model including both water and sludge lines is presented. Satisfactory predictions were obtained for effluent concentrations, mixed liquor suspended solids in the activated sludge basin and COD removal efficiency of the anaerobic digester. Finally, the integrated model was used for scenarios analyses, including the prediction of the impact on operational costs of two a alternative operational strategies (1) the regulation of the aeration rate in the nitrification tank based on a set-point value for the effluent ammonium concentration; (2) a decrease in the sludge age from 40 to 10d. Reduction in the operational costs from 11 to 23% were predicted by the implemented models.