Removal of Nitrate and Phosphate from Domestic Wastewater using Constructed Wetlands Planted with Water Hyacinth in Anambra State

Eutrophication of water bodies in Anambra State, South East Nigeria, driven by poorly treated domestic wastewater discharge, has degraded aquatic ecosystems in communities along the River Niger flood plain. This study evaluates the nutrient removal efficiency of pilot-scale surface flow constructed wetlands planted with Eichhornia crassipes for treating domestic sewage from a peri-urban community in Onitsha. Three parallel pilot wetland cells, each with a surface area of 12 m2, were operated at hydraulic retention times of 3, 5, and 7 days with an unplanted control cell for comparison. Influent and effluent samples were collected twice weekly over 12 weeks and analysed for nitrate, phosphate, ammonium, biological oxygen demand, total suspended solids, and pH. Results demonstrated that the 7-day retention cell achieved nitrate removal of 88.3% and phosphate removal of 79.6%, both substantially exceeding the unplanted control. Biological oxygen demand removal across all planted cells exceeded 85%. Plant biomass production averaged 14.2 kg/m2/month and was assessed for potential use as animal feed and biogas feedstock. The study establishes hydraulic retention time as the most critical design variable for nutrient removal in the wetland system and recommends full-scale installation for communities along the Anambra River basin. Keywords: constructed wetlands, water hyacinth, nitrate removal, phosphate removal, Anambra State