Modelling the dynamic long-term performance of a full-scale digester treating sludge from an urban WRRF using an extended version of ADM1

The optimization of full-scale digesters requires the development of models able to describe the main process performances, due to the strategic role of anaerobic digestion in the sustainability of Water Resource Recovery Facilities (WRRFs). In this study, an extended version of the Anaerobic Digestion Model No. 1 (ADM1) was developed to simulate the long-term performance of a full-scale anaerobic digester treating primary and activated sludge of a large WWRF (300,000 p.e.). Monitored data were collected over 973 days and analyzed in order to provide reconciled datasets for modeling purposes. A comprehensive influent characterization in terms of biodegradability extent, COD and N content was carried out by combining measurements of several parameters and Biochemical Methane Potential (BMP) tests to provide a compatible ADM1 substrate fractionation. The model was calibrated by comparing simulation results against both routine plant measurements and data from a dedicated measuring campaign. Disintegration constants and particulate inert fractions were the sole estimated model parameters. Disintegration constants determined in the calibration step resulted in values 5-times greater than those initially estimated from BMP tests. The model was able to accurately predict digestate composition in terms of TSS, VSS, COD, N and P as well as biogas production and methane content. It was demonstrated that a precise description of the anaerobic co-digestion of sewage sludges relies on the estimation of solubilization kinetic parameters together with the use of two different composite variables representing each substrate. The developed model proved to be a useful tool that can be integrated in a plant-wide model to assess plant process interactions under different operating conditions