The influence of aeration rate on the sorption of emerging pharmaceuticals in activated sludge.

The sorption of pharmaceuticals on activated sludge during the wastewater treatment process has been widely studied and considered one of the main mechanisms for the removal of these micropollutants from domestic sewage. Understanding the removal mechanism is important to reduce the environmental risk associated with these compounds. To the best of our knowledge, no data are reporting the influence of the aeration rate and, consequently, of the physicochemical properties of the sludge flocs, on the sorption of pharmaceutical compounds. In this context, the influence of the aeration rate (2, 5, and 8 L min) on the physical properties of the sludge and the sorption of two emerging pharmaceuticals, 17-alpha-ethynylestradiol (EE2) and diclofenac (DCF), was evaluated. The pharmaceuticals were analyzed by Solid Phase Extraction and Liquid Chromatography, and the sludge by Laser Particle Size Analyzer and Settling Curves. As a result, higher sorption for 17-alpha-ethinylestradiol (78-96%) in comparison to diclofenac (23-43%) was observed, corroborating the greater hydrophobicity of EE2. Higher pharmaceuticals removal rates were observed for the highest aeration (10.02 µgEE2 gSST and 3.99 µgDCF gSST) in comparison to the lowest one (7.81 µgEE2 gSST and 2.58 µgDCF gSST), what can be attributed to structural and surface changes in flocs. Smaller and more dispersed flocs were observed when aeration was increased (104.4 µm for 8 L min and 63.8 µm for 2 L min). The results suggest that the increase in aeration seems to be promising for the removal of pharmaceuticals by sorption in sewage sludge, especially for the hydrophobic ones.