System-Level Optimisation of Vetiver-Based Constructed Wetlands for Aquaculture Greywater Treatment Using Structural Equation Modelling

Urban and peri-urban aquaculture is expanding, bringing with it an increasing challenge: greywater laden with organic matter, suspended solids, and microorganisms that pose risks to surrounding aquatic environments. Ecological engineering provides a promising solution. Constructed wetlands, purpose-built for natural purification, can sustainably treat this wastewater. In this study, we evaluate a vetiver-based constructed wetland and examine how operational parameters influence treatment effectiveness. The series of phytoremediation experiments was conducted, varying discharge rate, vetiver stem density, and hydraulic retention time. Treatment performance was assessed by monitoring biological oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), and fecal coliform levels. To better understand the influence of operational variables on treatment outcomes, we used partial least squares structural equation modelling (PLS-SEM). The findings are definitive: the constructed wetland reduced organic contaminants and microbial loads under all tested conditions. Higher vetiver density and extended water retention significantly enhanced pollutant removal, owing to improved sedimentation, filtration around plant roots, and increased microbial activity. The structural model emphasises the importance of these operational factors in achieving better water quality, highlighting the benefits of integrating hydraulic and biological processes in wetland design. This research advances ecological engineering by linking experimental phytoremediation studies with system-level modelling. Our results contribute to optimising nature-based wastewater treatment in aquaculture and support more effective water management in peri-urban areas.