Paracetamol removal in subsurface flow constructed wetlands

In this study two pilot scale Horizontal Subsurface Flow Constructed Wetlands (HSFCWs) near Lecce, Italy, planted with different macrophytes (Phragmites australis and Typha latifolia) and an unplanted control were assessed for their effectiveness in removing paracetamol. Residence time distributions (RTDs) for the two beds indicated that the Typha bed was characterized by a void volume fraction (porosity) of 0.16 and exhibited more ideal plug flow behavior (Pe = 29.7) than the Phragmites bed (Pe = 26.7), which had similar porosity. The measured hydraulic residence times in the planted beds were 35.8 and 36.7 h when the flow was equal to 1 m3/d. The Phragmites bed exhibited a range of paracetamol removals from 51.7% for a Hydraulic Loading Rate (HLR) of 240 mm/d to 87% with 120 mm/d HLR and 99.9% with 30 mm/d. The Typha bed showed a similar behavior with percentages of removal slightly lower, ranging from 46.7% (HLR of 240 mm/d) to >99.9% (hydraulic loading rate of 30 mm/d). At the same HLR values the unplanted bed removed between 51.3% and 97.6% of the paracetamol. In all three treatments the paracetamol removal was higher with flow of 1 m3/d and an area of approx. 7.5 m2 (half bed) than in the case of flow equal to 0.5 m3/d with a surface treatment of approx. 3.75 m2. A first order model for paracetamol removal was evaluated and half lives of 5.16 to 10.2 h were obtained.