On the Effect of Hydraulic Retention Time and Loading Rates on Pollutant Removal in a Pilot Scale Wetland

Abstract: This study examines the potential of Coix lacryma jobi commonly known as Job tears as a wetland plant, and the effect of short Hydraulic Retention Time (HRT) and loading rates on the treatment efficiency of a vertical flow constructed wetland.  Effluents from an anaerobic lagoon system were collected and used as influents for the constructed wetlands. The influents were subjected to 3, 5 and 7 days HRT and 43.73 and 19.91 m³/m²/day loading rate, over a period of 6 weeks. Results from the study shows that the control cell in the system was effective in the removal of phosphorus, (PO₄), Ammonia, Ammonium, COD, TDS, DO, and TSS at the higher HRT of 7 days. Similarly, the level of treatment increased as a result of higher HRT, except for the pH which showed no significant difference. Loading rates of 19.91 m³/m²/day at 7 days HRT was effective in the treatment of phosphorus, PO_4, COD and TSS with removal efficiency of 89.1, 84.4, 92.0 and 61.3 % respectively. Parameters such as NH₄⁺-N, NH₄, NH₃, TDS showed significant removal by the wetland system at a loading rate of 19.91 m³/m²/day and HRT of 7 days.  Coix lacryma jobi as a wetland plant, at HRT of about 7days and much lower loading rates is capable of removing pollutants in wastewater.