Dynamics of nitrogen transformation depending on different operational strategies in laboratory-scale tidal flow constructed wetlands

The influence of different flooded/drained (F/D) time ratios and different effluent flow rates on the dynamics of nitrogen transformations in three laboratory-scale tidal flow constructed wetland systems (TFCWs-A, B. and C) under varying NI4+-N and COD influent loadings was investigated in this study. Good organic matter removal performance up to 90% was achieved for all experimental TFCWs under inflow concentrations of 300 and 150 mg/L regardless of F/D and effluent flow rate. The ammonium removal efficiency of wetland with F/D = 3 h:3 h (55%) was higher than that of the wetland with F/D = 5 h:1 h (47%) under an ammonium inflow concentration of 60 mg/L, indicating the positive effect of longer drained and shorter flooded time on tidal-operated wetlands under nitrification. In addition, more uniform oxygen distribution and better nitrification capacity within the wetland might be achieved with a relatively slow effluent flow rate of 0.025 L/s. TFCWs were shown to be a robust and reliable option to achieve high TN removal of 70% due to its repeated cycle of "wet" and "dry" periods, particularly for the treatment of wastewater with high organic content. Moreover, F/D and effluent flow rates of tidal flow constructed wetlands exhibited no significant effect on phosphorus removal in this study. Other techniques, such as pretreatment or post treatment, require further investigation. (C) 2014 Elsevier B.V. All rights reserved.