Clogging in constructed wetlands: Mechanisms, quantitative diagnosis, and optimized mitigation strategies

Clogging remains a critical bottleneck limiting the long-term hydraulic performance, treatment stability, and pollutant removal efficiency of constructed wetlands (CWs). This review systematically synthesizes the current understanding of clogging development in CWs, demonstrating that system deterioration is governed by the coupled interactions of physical solids accumulation, biological biofilm/extracellular polymeric substances growth, and chemical precipitation processes rather than by any single mechanism. A comprehensive diagnostic framework is proposed to explicitly link microscopic pore-blocking processes with macroscopic hydraulic responses, thereby improving early detection and severity assessment. Building on this framework, a multi-level identification system integrating hydraulic, material, and operational metrics is developed for progressive clogging diagnosis and management. To move beyond conventional descriptive reviews, an analytic hierarchy process-based decision framework was established to quantitatively compare mainstream clogging prevention and remediation technologies using two core dimensions: integrated control effectiveness and techno-economic feasibility. The results identify pre-interception and bidirectional flow alternation as the highest-ranked prevention and restoration strategies, with composite scores of 3.52/5 and 4.341/5, respectively. Their combined application provides a clear performance advantage over alternative options. In addition, emerging next-generation strategies-including quorum sensing-mediated bioregulation, intelligent sensor networks, and data-driven predictive control-are critically evaluated as promising tools for adaptive clogging management. Future research should prioritize standardized diagnostic thresholds, long-term field validation, parameter optimization, and integration of smart monitoring with operational control. Furthermore, a graded implementation strategy is proposed to improve applicability under different economic and technical conditions, thereby enhancing the scalability, resilience, and sustainability of CW systems for global water management.