Abstract
Constructed wetlands (CWs) have emerged as multifunctional, nature-based infrastructures for the bioremediation of polluted water bodies. This review critically synthesises recent advances in CW design typologies, treatment mechanisms, and technological innovations, with particular emphasis on their strategic deployment as eco-buffer zones at watershed interfaces. Unlike existing reviews that treat CWs primarily as engineering infrastructure, this review advances the argument that design decisions are ecologically inseparable from treatment outcomes. A critical synthesis of global performance data reveals mean removal efficiencies of 78% for biochemical oxygen demand (BOD), 62% for total nitrogen (TN), 45% for total phosphorus (TP), and > 90% for faecal coliforms, with hybrid systems outperforming single-flow configurations by 15–25%. Crucially, this review demonstrates that these treatment metrics are inextricably linked to ecological outcomes: the same design parameters driving pollutant attenuation simultaneously create habitat mosaics that support diverse taxa ranging from 50 to over 300 species, depending on system scale and typology. For example, while Free Water Surface (FWS) systems offer high macro-habitat value for avifauna and amphibians, subsurface and hybrid configurations generate specialized redox gradients that foster unique microbial and benthic diversity, validating their dual function as functional eco-buffers. However, broader deployment is constrained by critical challenges. Bioelectrochemical systems (BES-CWs) achieve up to 85% antibiotic removal in laboratories, yet field validation reveals only a 10–17% improvement, exposing a significant lab-to-field translation gap. Furthermore, long-term phosphorus substrate saturation (10–15 years), unresolved greenhouse gas accounting, and regulatory frameworks that fail to recognise CWs as legitimate wetland ecosystems limit their scalability. We advocate for a transdisciplinary research agenda bridging ecological engineering, biotechnology, data science, and governance to realise the full potential of CWs as economically viable nature-based solutions aligned with SDGs 6 and 15.