Nutrient Recovery Models for Wastewater Treatment Using PHREEQC and ADM1

Nutrient recovery models (NRMs) for wastewater treatment systems integrate physicochemical and biochemical processes using PHREEQC and Visual MINTEQ for equilibrium speciation. The methodology includes a four-step procedure for selecting key species and reactions, accounting for redox states, complexation, and mass balances. A reduced model is developed per unit process to enhance simulation speed, with driving forces derived from PHREEQC scripts. The NRM-AD model extends ADM1 to include acid-base, ion-pairing, and redox reactions, predicting digestate quality and performance. Validation at a full-scale digester in Madrid shows good agreement for COD, biogas, pH, and P, though SO4 removal and H2S are underpredicted. Model improvements include database reduction, use of empirical transfer equations, and development of a custom 'Nutricover.dat' database. The NRM library is verified and validated under steady and dynamic conditions, with a 3–5× speedup achieved.