Fate of wastewater trace organic chemicals in vegetated biofiltration systems

Vegetated biofiltration system (VBS) is an effective green technology for urban stormwater and greywater treatment. However, VBS is yet to be optimised for effective treatment of wastewater, particularly if it contains trace organic chemicals (TrOCs). The effect of plant species has not been addressed under TrOC wastewater loading. This study tested and evaluated the effectiveness of VBS over a one-year period in removing six TrOCs commonly found in wastewater, namely Caffeine (CAF), Paracetamol (PCM), Sulfamethoxazole (SMX), N diethyl‑meta-toluamide (DEET), Bisphenol A (BPA) and Ibuprofen (IBU). Eleven VBS configurations were tested in a year-long laboratory column study to explore the role of seven different plant species (with differing characteristic), varied soil media depths, and soil characteristics, on the fate of TrOCs in the systems. The effect of different operational conditions (e.g., dosing volume and regime) on removal efficiency was investigated. The results indicated VBS was able to maintain a high removal rate (>95 %) of CAF, BPA, and IBU throughout the experiment, followed by PCM (>79 %), SMX (50 %-80 %), and DEET (<12 %). Plant species significantly impacted the removal of SMX and DEET (p<0.05), with C. indica as the best performer. Reducing hydraulic loading rate and decreasing daily dosing volume and frequency contributed positively to the PCM, SMX, and DEET removal rates. Noticeable accumulations of SMX, DEET, and BPA (8.2, 43.1, and 54.5 ng·g-1, respectively) were detected in the filter media, particularly within the saturated zone. Higher chemical concentrations (i.e., CAF and DEET) were found in plant root tissue than in plant shoot tissue. This study offers valuable insights into VBS's design and operational aspects for removing TrOCs.