Effectiveness of Pilot-scale Multi-Pond Constructed Wetland System (MPCWS) for Tropical Island Domestic Sewage Treatment

Domestic sewage pollution poses a threat to both human and ecosystem health. Constructed wetland systems (CWS), a nature-based solution (NBS), offer a robust and cost-effective approach for treating domestic sewage. This study evaluates the performance of a pilot-scale free water surface flow wetland, the Multi-Pond Constructed Wetlands System (MPCWS), comprising five sequential ponds: sedimentation pond (SP), oil screening pond (OSP), nutrient removal pond (NRP), treatment pond (TrP), and open water pond (OWP). Four of these ponds (OSP, NRP, TrP, and OWP) were planted with 21 native tropical wetland plant species. The performance of each pond was assessed to determine overall treatment efficiency. The system's performance was compared with a control pond without macrophytes and individual septic tanks (ISTs) to assess the effects of plant uptake and benchmark its effectiveness against conventional systems. Results showed that SP and OSP were particularly effective in removing Total Suspended Solids (TSS) and Oil and Grease (O&G), respectively. The NRP achieved significant reductions in Biochemical Oxygen Demand (BOD₅) and Chemical Oxygen Demand (COD). Overall, the MPCWS demonstrated comparable or superior performance to traditional treatment systems, especially in Ammoniacal Nitrogen (AN) removal. Notably, the presence of tropical wetland plants had a significant effect only on Total Phosphorus (TP) removal. These findings suggest that MPCWS is a viable alternative for domestic sewage treatment, particularly in remote or low-population areas such as tourism islands.