Influence of nitrifying conditions on the biodegradation and sorption of emerging micropollutants

High biodegradation efficiencies of different emerging micropollutants were obtained with nitrifying activated sludge (NAS) working at high nitrogen loading rates (NLR), that boosted the development of biomass with high nitrifying activities (>1 g N-NH4+/g VSS d). Come-tabolic biodegradation seemed to be responsible for the removal of most compounds due to the action of the ammonium monooxygenase enzyme. NAS showed a different affinity for each compound, probably due to steric hindrance, activation energy limitations or the presence of specific functional groups. Increasing loading rates of micropollutants were removed at shorter hydraulic retention times, although the biodegradation efficiencies of compounds with slow/intermediate kinetics, such as fluoxetine, erythromycin, roxithromycin and trimethoprim, diminished due to kinetic and/or stoichiometric limitations. Solids retention time, always above the minimum to avoid the washout of nitrifiers, did not enhance the biodegradation of any of the selected compounds, with the exception of diclofenac. Regarding sorption, the solid–liquid distribution coefficients (Kd) obtained in NAS were very similar to those found in conventional activated sludge by other authors. No correlation between Kd values and any of the operational parameters was found for the selected substances.

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► The fate of 11 emerging contaminants was determined in a pure nitrifying reactor.
► Influence of nitrifying activity, hydraulic and solids retention time was evaluated.
► Sorption coefficients in pure nitrifying sludge were determined.
► Cometabolic biodegradation of some compounds was observed.
► Kinetic and/or stoichiometric limitations compromised biodegradation of some compounds.