Nutrient Removal Efficiency of Constructed Wetlands Planted with Tropical Macrophytes: Implications for Decentralized Wastewater Treatment at Aturukuku Sewerage Works

Constructed wetlands are increasingly promoted as sustainable, low-energy wastewater treatment technologies, particularly in regions with limited financial and technical capacity. However, nutrient removal performance in constructed wetlands varies widely with vegetation type and system design. This study evaluated the nitrogen and phosphorus removal efficiency of laboratory-scale constructed wetlands planted with selected macrophyte species under controlled hydraulic conditions. Influent and effluent samples were analysed for ammonia nitrogen and soluble phosphorus using spectrophotometric methods compliant with ISO/IEC 17025 standards. Statistical evaluation was conducted using one-way analysis of variance (ANOVA) and linear regression to assess species effects and relationships between plant growth and nutrient uptake. Results showed substantial reductions in nutrient concentrations, with ammonia decreasing from 6.99 mg/L to 2.22 mg/L and soluble phosphorus from 17.47 mg/L to 3.05 mg/L. Wetlands planted with Cyperus papyrus achieved the highest removal efficiencies, averaging 82% for ammonia and 76% for soluble phosphorus. ANOVA confirmed that macrophyte species had a statistically significant effect on nutrient removal (p < 0.05). Regression analysis revealed a strong positive correlation between plant biomass and nutrient uptake (R² > 0.60), highlighting the importance of vegetation productivity in treatment performance. The findings demonstrate that appropriate macrophyte selection can significantly enhance nutrient removal in constructed wetlands. The study supports the use of locally adapted species such as Cyperus papyrus for decentralised wastewater treatment and safe water reuse in tropical regions, particularly in East Africa.