Forecasting the Removal of Micropollutants and Chemical Contaminants of Emerging Concern in Activated Sludge Treatment—A Practical Model Supporting the Implementation of the New EU Directive on Urban Wastewater Treatment

A practical model to forecast the removal of micropollutants and other chemical Contaminants of Emerging Concern (CECs) in Activated Sludge (AS) systems was developed. Full-scale campaigns were carried out in three AS-WWTPs to evaluate the influence of the Mixed Liquor Suspended Solids (MLSS), Hydraulic Retention Time (HRT), and nitrification conditions. 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, in addition to MLSS, HRT, kbio, a lumped-correction factor ‘a’. The transferability of the approach was further assessed using data from two WWTPs analysed in a previous study. The “a” value ranged from 0.19 (oxidation ditch at a nitrification rate of 5.8 g N-NH4/(kg VSS·d)) to 0.61 (A2O with 27 g N-NH4/(kg VSS·d)), suggesting a potential influence of reactor configuration and nitrification activity. This model allows WWTP managers optimizing AS performance and assessing its combination with advanced treatments needed to comply with the 80% removal efficiency for micropollutant indicators set by the revised Urban Wastewater Treatment Directive. Increasing MLSS from 2 to 5 g/L, increases AS removal from 23% to 45% and thus decreases ozone dose from 20 to 12 g/m3.