Review of hydraulic conditions optimization for constructed wetlands

Hydraulic conditions exert a comprehensive and vital influence on constructed wetlands (CWs). However, research on this subject is relatively limited. Hydraulic parameters can be categorized into design and operational parameters based on their properties. The design parameters are represented by the hydraulic gradient, substrate porosity, and aspect ratio, while operational parameters are represented by the hydraulic retention time, hydraulic loading rate, and water depth. These parameters directly or indirectly affect the operational lifespan and pollutant removal performance of CWs. Currently, the primary measures for optimizing the hydraulic conditions of CWs involve hydraulic structure and numerical simulation optimization methods. In this review, we aimed to elucidate the impact of hydraulic conditions on CW performance and summarize current optimization strategies. By highlighting the significance of hydraulic parameters in enhancing pollutant removal and extending operational lifespan, this review provides valuable insights for improving CW design and management. The findings will be useful for researchers and practitioners seeking to optimize CW systems and advance the application of nature-based solutions for wastewater treatment. [Display omitted] •Hydraulic conditions significantly impact CW lifespan and purification performance.•The importance of hydraulic gradients in CWs has been overlooked.•Hydraulic structures and numerical simulations optimize hydraulic conditions of CWs.