Treatment performance of integrated vertical-flow constructed wetland plots for domestic wastewater

Two pilot-scale integrated vertical-flow constructed wetlands (IVCWs) in parallel were employed to evaluate domestic wastewater treatment performance at a loading rate of 250 mm/d, and each was planted with two different plant species: Typha orientalis and Arundo donax var. versicolor (Plot 1), and Canna indica and Pontederia cordata (Plot 2). The results showed that different plant combinations offered no significant improvement in pollutant removal efficiencies (p > 0.05). The mean removal efficiencies associated with Plot 1 and Plot 2 were 59.9% vs. 62.8% for COD, 15.0% vs. 12.8% for TN, and 52.0% vs. 51.1% for TP, respectively. The mean mass removal rates (g m−2 d−1) were 44.3 vs. 46.4 for COD, 1.27 vs. 1.08 for TN, and 0.393 vs. 0.386 for TP, respectively. It was noted that nitrification was the limited step for TN removal. Dissolved oxygen (DO) in the wetland beds was a dependence factor for the removals of organic matter and nitrogen, and it could be used to predict removal rates of chemical oxygen demand (COD) and total nitrogen (TN). Low temperatures had a negative impact on nutrient removals, especially for TN.