Micropollutant removal by attached and suspended growth in a hybrid biofilm-activated sludge process

• Micropollutant removal in a biofilm-activated sludge process was investigated.
• The micropollutant removal capacity differed between the sludge and the biofilm.
• Several micropollutants showed higher removal with the biofilm than with the sludge.
• Oxic and anoxic conditions affected the removal of some micropollutants.
• Diverse pathways seem to be involved in degradation of micropollutants.

Removal of organic micropollutants in a hybrid biofilm-activated sludge process was investigated through batch experiments, modeling, and full-scale measurements. Batch experiments with carriers and activated sludge from the same full-scale reactor were performed to assess the micropollutant removal rates of the carrier biofilm under oxic conditions and the sludge under oxic and anoxic conditions. Clear differences in the micropollutant removal kinetics of the attached and suspended growth were demonstrated, often with considerably higher removal rates for the biofilm compared to the sludge. For several micropollutants, the removal rates were also affected by the redox conditions, i.e. oxic and anoxic. Removal rates obtained from the batch experiments were used to model the micropollutant removal in the full-scale process. The results from the model and plant measurements showed that the removal efficiency of the process can be predicted with acceptable accuracy (±25%) for most of the modeled micropollutants. Furthermore, the model estimations indicate that the attached growth in hybrid biofilm-activated sludge processes can contribute significantly to the removal of individual compounds, such as diclofenac.