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Removal of naproxen and bezafibrate by activated sludge under aerobic conditions: Kinetics and effect of substrates

Naproxen and bezafibrate fall into the category of pharmaceuticals that have been widely detected in the aquatic environment, and one of the major sources is the effluent discharge from wastewater treatment plants. This study investigated the sorption and degradation kinetics of naproxen and bezafibrate in the presence of activated sludge under aerobic conditions. Experimental results indicated that the adsorption of pharmaceuticals by activated sludge was rapid, and the relative adsorbabilities of the two‐target compounds were based on their log Kow and pKa values. The adsorption data could be well interpreted by the pseudo–second‐order kinetic model. The degradation process could be described by the pseudo–first‐order kinetic model, whereas the pseudo–second‐order kinetics were also well suited to describe the degradation process of the selected compounds at low concentrations. Bezafibrate was more easily degraded by activated sludge compared with naproxen. The spiked concentration of the two‐target compounds was negatively correlated with k1 and k2s, indicating that the substrate inhibition effect occurred at the range of studied concentrations. Chemical oxygen demand (COD) did not associate with naproxen degradation; thus, COD is not an alternative method that could be applied to investigate natural organic matter's impact on degradation of pharmaceuticals by activated sludge.