Investigating pharmaceutical compound removal in a vertical-flow constructed wetland using sludge-based biochar microcosms.

In this study, we investigated the efficiency of biochar-based vertical-flow constructed wetlands (VF-CWs) for the refining of secondary-treated effluents from a facility treating mixed domestic-industrial textile wastewaters The lab-scale design setup consisted of 12 microcosms divided into: (i) planted microcosms with biochar substrate (BC-P, n=3), (ii) unplanted microcosms with biochar substrate (BC-U, n=3), (iii) planted microcosms with gravel substrate (G-P, n=3), and (iv) unplanted microcosms with gravel substrate (G-U, n=3). The biochar was produced by co-pyrolysis of a 70/30 (w/w) mixture of sawdust and biological sludge. Tanks were filled according to the European VF-CWs design and the obtained microcosms were fed 4 times a day in "tidal" mode with a 6-hour cycle (1.2 L/h). Thirty-nine pharmaceutical compounds introduced by 2015-2022 European “watch lists” were used as target model group (-0.4<5.8) to evaluate VF-CW removal efficiency (RE%), analyzing inlet and outlet wastewaters by reversed-phase liquid chromatography-tandem mass spectrometry, using an injection volume of 100 µL (sub-ng/L to low ng/L method sensitivity) and acquiring in both negative and positive ESI polarities. VF-CWs integrated with biochar showed an initial quantitative RE% (i.e., 85-100%). Some of the targeted pharmaceuticals exhibited a constant removal rate (e.g., REdiclofenac>80%) throughout the experimental period, whilst for most compounds the RE% was satisfactory (i.e., ≥70%) for about three months before rapidly decreasing (e.g., REcarbamazepine=98%→27%). However, after 8 months of operation, the RE% of BC-P and BC-U (~37%) was higher than in G-P (~12%) and did not show negative removals. These outcomes confirm the effectiveness of the sludge-based biochar as a standalone adsorbent for wastewater depuration from emerging contaminants, also supporting its application in phytoremediation systems, promoting contaminant biological degradation processes and assimilation by plants. The proposed application is promising for sustainable wastewater management by limiting wastes and contributing to agricultural reuse.