Comparison of Treatment Performance between Constructed Wetlands with Different Plants

Constructed wetlands have gained much importance for treating domestic, industrial and agricultural wastes and are considered as an effective secondary or tertiary treatment method. The main characteristics affect the removal efficiency of constructed wetland are the vegetation type, hydraulic residence time and substrate. The aim of the present study is to examine effect of vegetation type on organic and nutrient removal under varying hydraulic residence time in constructed wetlands. With this in mind, we have designed, constructed and operated two pilot-scale horizontal subsurface flow constructed wetlands having two different wetland vegetation plants in our open-air laboratory receiving pre-treated domestic wastewater by varying hydraulic residence time as 2, 4, 6 and 8 days. The influent wastewater is rich in orgnic matter with high variability presence of nutrients. In the first unit, the removal efficiency of COD, BOD, TN, and TP was increased from 39 to 69%, 29 to 56%, 23 to 45% and 25 to 75% when there was an increase in HRT from 2 days to 8 days respectively. In the second unit, the removal efficiency of COD, BOD, TN, and TP was increased from 31 to 68%, 25 to 52%, 26 to 36% and 40 to 77% when there was an increase in HRT from 2 days to 8 days respectively. It was found that vegetation type influenced concentration reduction. A 6-day hydraulic residence time is suggested for an acceptable level of treatment in these systems.