A new approach for predicting the fate of micropollutants in activated sludge wastewater treatment.

The current understanding of activated sludge conditions and configurations that favour the removal of micropollutants (MPs) is equivocal. This study conducted a series of activated sludge process trials using pilot-scale reactors and a synthetic feedstock, to achieve controlled and representative conditions. The fate of ten perfluoroalkyl substances (PFAS), four brominated flame retardants, two triazoles, three pharmaceuticals, three bio-/pesticides, one phthalate, one nonylphenol and four metals was studied with three levels of mixed liquor suspended solids (1-3 g/L), three redox configurations and three levels of dissolved organic carbon in the feed (starch vs. acetate). The tested range of operational conditions had a limited effect on MP removals (standard deviation < 20%, n = 6), demonstrating the resilience of the activated sludge process. At the same time, this indicated that such process interventions may not achieve improved removal efficiency. A new approach based on three confidence levels was proposed to support the prediction of the likely fate of MPs in biological wastewater treatment (sludge, sludge/effluent, effluent, effluent/degraded, degraded). High confidence was assigned to substances with consistent behaviour in both the control and the test reactor, while low confidence was linked to concentrations near or below the reporting limit and inconsistent or partial removal. Finally, the MPs were analysed in the particulate, the colloidal and the truly dissolved fraction of the activated sludge effluent to inform the selection of suitable post-treatment processes, which are deemed necessary for a high-quality final effluent.