Effect of hydraulic loading on bioremediation of municipal wastewater using constructed wetland planted with vetiver grass, Addis Ababa, Ethiopia

Gravel-based pilot horizontal subsurface flow constructed wetland planted with vetiver grass (Vitiveria zinaniodes) and unplanted operated at two hydraulic loading rates: 0.025 m/d and 0.05 m/d was carried out over a 3-year period. The aim of the study was to evaluate the effect of plant and hydraulic loading rate on the organic and nutrient removal performance of the constructed wetland system planted with vetiver grass (Vitiveria zinaniodes) in the removal of chemical oxygen demand (COD), total nitrogen (TN), total phosphorus (TP) from municipal wastewater. The removal efficiencies of COD, TN, and TP in the planted cell decreased from 95 to 90.8%, 95.2 to 86.8% and 95.2 to 88.5%, respectively, with an increase in HLR from 0.025 to 0.05 m/d. The estimated above-ground biomass of dry weights of vetiver harvested ranged from 10.1 to 10.3 kg DW/m2, the nutrients uptake increased with plant age from 2.4 to 14.6 g N/kg DW and 0.8 to 8.5 g P/kg DW and above-ground biomass nutrient standing stock ranged from 147.5 to 150.4 g N/m2 and 85.5 to 87.5 g P/m2 in 16 months. The higher removal efficiency of COD, TN, and TP was achieved in HSSFCW planted with vetiver grass as compared to unplanted at both hydraulic loading rate operations. The results concluded that both applications of HLR are capable of removing organic matter and nutrients efficiently and vetiver grass can be used for remediation of pollutants in municipal wastewater in Addis Ababa. © 2019, Springer Nature Switzerland AG.