Analysis Of Pharmaceutical Compounds In Influent And Effluent Wastewater Of Vertical-Flow Constructed Wetlands Integrated With Biochar

A proper treatment of wastewater is essential before its discharge into natural water reservoirs or before its reuse. Constructed wetlands (CWs) are a depuration technology used worldwide for wastewater treatment because of its low external energy requirements, easy operation and good integration with the environment and landscape. Biochar may be attractive as a robust multifunctional medium in CWs for adsorbing micropollutants, supporting plant growth, and providing environments for microbe communities because of its unique physicochemical properties. This study aims at evaluating the removal efficiency towards selected pharmaceutical compounds (PhCs) and their transformation products (TPs) by a vertical-flow CW implemented by using granular biochar (average diameter 10 mm), together with sand and gravel with different diameters as filling media, and planted with Phragmites australis (CW-BC-P). The removal efficiency of this system was compared to the ones obtained by a CW filled as CW-BC-P, but unplanted (CW-BC-U) and a planted CW in which the biochar was replaced with gravel of the same diameter (CW-G-P). All CWs were fed with urban wastewater from the Sidi Thabet municipality (Tunisia). Quantitative determination of PhCs in wastewater was performed by liquid chromatography coupled with electrospray ionization tandem mass spectrometry (LC-MS/MS). Influent and effluent of an Imhoff tank, the latter feeding the three CWs were analysed to obtain information on the concentration of PhCs before and after each treatment. Nineteen out of the thirty-nine investigated PhCs and TPs were detected in at least one sample. These compounds belong to the following categories. (i) Non-steroidal anti-inflammatory drugs, (ii) Beta-blockers, (iii) Antibiotics, (iv) Psychiatric drugs, (v) Antihypertensives, (vi) Antifungals, (vii) Statins. Overall, these results indicate that vertical CWs play an important role in the reduction of the concentrations of most of the studied PhCs, with the exceptions of CBZ and FLC, due to their peculiar behaviour in these systems. However, the removal efficiency shown by the CW-BC-U was surprisingly lower than the corresponding unplanted CW, thus suggesting that the sorption ability of biochar could be decreased by the presence of the root system due to a number of reasons. One hypothesis is that the release of plant exudates may contribute to saturate the sorption ability of biochar, while another refers to the occurrence of hydraulic short-circuiting inside the planted system that decrease the contact between wastewater and biochar. A lower efficiency of plants to support the degradation of PhCs can also be hypothesized in the presence of biochars since CW-BC-P shows in some cases a removal lower than CW-G-P. This study demonstrated that CWs can be a cost-effective and sustainable alternative for removing selected PhCs. The three investigated CW systems led to a considerable reduction of a broad range of pharmaceuticals typically present in treated wastewater. On the other hand, the use of sorbent media inside the bed does not seem to offer clear advantages in terms of PhCs removal, probably due to complex chemical and physical interactions between plant and biochar.