Constructed wetlands as nature-based solutions for wastewater treatment: A scoping review of iucn global standard reporting and complementary advanced oxidation polishing

Wastewater treatment remains a critical challenge for water security, ecological integrity, and public health. Constructed wetlands (CWs) are widely advanced as nature-based solutions (NbS) because they use ecosystem processes for water purification and can deliver ecological co-benefits. This scoping review mapped 36 peer-reviewed studies (2010–2025; 63 extracted records) evaluating CWs used alone or within CW-based treatment trains incorporating advanced oxidation processes (AOPs) as pre-treatment or post-polishing. Outcomes covered conventional pollutants, selected micropollutants, and microbial indicators; PFAS and antibiotic-resistance indicators were assessed where reported. Vertical subsurface-flow and hybrid CWs generally reported high removal of COD, TN, and TP and meaningful reductions of indicator bacteria, supporting secondary treatment objectives. Micropollutant evidence was heterogeneous and compound-specific; carbamazepine showed limited attenuation. PFAS reporting in the mapped corpus was sparse and, where present, indicated variable, compound-dependent attenuation rather than demonstrable absence. No included studies provided extractable antibiotic-resistance gene outcomes. AOP units (e.g., ozonation, UV/H₂O₂, photo-Fenton) were associated with positive within-study deltas in some cases but were matrix-dependent and carry energy/chemical demands and potential transformation products requiring monitoring. IUCN Global Standard assessment was applied to the CW intervention only, revealing stronger reporting for problem framing and design intent and persistent gaps in equity, inclusiveness, and policy coherence.