Dye and chemical oxygen demand removal from textile wastewater using a scoria-based horizontal subsurface flow constructed wetland planted with Chrysopogon zizanioides

• Textile effluents pose major environmental risks due to high COD and dye levels. • A scoria-based wetland planted with vetiver was developed for wastewater treatment. • The system ran at 0.021 m³/day flow rate with a 5-day hydraulic retention time. • Planted wetland removed 95.1% COD and 95.4% dye from textile wastewater. • Results suggest strong potential for large-scale textile wastewater treatment use The textile industry drives economic growth but faces environmental challenges due to high wastewater generation. Therefore, this study was conducted with the objective of removing chemical oxygen demand (COD) and dye from textile industrial wastewater using a horizontal subsurface flow constructed wetland. The constructed wetland was developed using scoria as a filter medium and was planted with vetiver grass to enhance pollutant removal. The wetland operated with a hydraulic retention time of 5 days and an average flow rate of 0.021m³/day. The wastewater was characterized for various physicochemical parameters, including pH, temperature, COD, dissolved oxygen (DO), biochemical oxygen demand (BOD), Total nitrogen (TN), Total phosphorus(TP), dye concentration, and electrical conductivity, revealing a significant pollutant load. Before treatment, the COD and dye concentrations of wastewater from the Ketema Kebede (KK) textile industry were determined to be 995.1 mg/L ± 14.85 and 377.63 mg/L ± 34.71, respectively. After treatment, the planted constructed wetland achieved COD and dye removal efficiencies of 94.32 ± 0.96 and 95.42 ±1.37, respectively. Meanwhile, the unplanted constructed wetland achieved COD and dye removal efficiencies of 88.11 ± 1.02 and 90.95 ±1.20, respectively. Overall, this study demonstrated that a scoria-based horizontal subsurface flow constructed wetland planted with vetiver grass exhibits promising COD and dye removal efficiency, highlighting its potential application for large-scale industrial textile wastewater treatment.