Forecasting the Removal of Chemical Contaminants of Emerging Concern in Activated Sludge Treatment—A Practical, Site-Calibrated Model Supporting Implementation of the EU Urban Wastewater Treatment Directive Recast

A practical model to forecast the removal of contaminants of emerging concern (CECs) in activated sludge (AS) wastewater treatment plants (WWTPs) was developed. Eight full-scale campaigns were conducted in three AS-WWTPs (seven reactor datasets); 57 CECs were analyzed, 22 quantified in influent, and 13 CECs used for model calibration. The previously observed sigmoidal correlation between CEC removal and biodegradation rate (kbio) was validated and a pseudo-first-order kinetic model was adapted to include a lumped correction factor ‘a’ in addition to Mixed Liquor Suspended Solids (MLSS), Hydraulic Retention Time, and a CEC biodegradation constant (kbio). Model transferability was assessed using two WWTPs from a previous study. A global ‘a’ value provided a first approximation, while site-specific calibration improved R2 from 0.71–0.83 to 0.90–0.95. ‘a’ ranged from 0.19 (oxidation ditch; nitrification rate 5.8 g N-NH4/(kgVSS·d)) to 0.61 (anaerobic/anoxic/oxic AS system; 27 g N-NH4/(kg VSS·d)). The model supports AS operational scenario analysis and integration with advanced treatments to meet the 80% CEC (micropollutant) removal target of the revised Urban Wastewater Treatment Directive. In an illustrative ForecastTool scenario, increasing MLSS from 3 to 5 g/L increased AS removal of six CECs (from the twelve listed in the directive) from 32% to 45%, reducing the modeled ozone dose from 16 to 12 g/m3. The model requires site-specific calibration of ‘a’.