Pilot-scale constructed wetlands for urban runoff discharging to Sebkha Sijoumi (Tunis, Tunisia): Performance, environmental impact, and cost under field conditions.

This study evaluated a pilot-scale hybrid constructed wetland designed to treat urban runoff, residual wastewater, and combined sewer overflows discharging into Sebkha Sijoumi (Tunis, Tunisia), during both summer and winter seasons. In summer, the system achieved > 80% chemical oxygen demand (COD) removal, maintaining a stable effluent of ∼40 mg/L at an 18-h hydraulic retention time (HRT), whereas winter operation required an HRT of 48 h. Ammonium removal ranged from 50 to 100%, consistent with active nitrification-denitrification processes. In winter effluents, aluminum, selected long-chain per- and polyfluoroalkyl substances (PFAS), and ofloxacin were below detection limits, whereas diclofenac, bisphenol A, and short-chain perfluorobutanoic acid (PFBA) showed limited removal. Life cycle assessment indicated that the construction phase dominated environmental impacts, while operational emissions and water consumption were 97% lower than those of conventional treatment processes. Despite higher capital costs (1.76 €/m3; ≈US$1.90/m3), negligible operating costs (0.0023 €/m3; ≈US$0.0025/m3) suggest long-term economic benefits. These results highlight the potential of nature-based solutions for sustainable urban runoff management.