Study on flow pattern of vertical flow constructed wetlands by reaction theory

To obtain an optimal designing of vertical flow constructed wetlands(VFCWS) and a better understanding the processes in the systems, the reaction theory is employed to determine residence time distribution (RTD) and the flow pattern of VFCWS with different feeding strategies. Results indicate that the actual flow pattern of the system under different operating are all deviated from the ideal plug flow (PF) and complete stirred flow(CST). The complete stir tanks in series(TIS) with delay model can provied a better fit to the data of tracer response curves through assesse the accuracy of flow models with TIS and TIS with delay. The number of TIS with delay ranged from 2.6to 3.3. Furthermore, analysis results of RTD theory indicate that identical volume of batches and batch frequency but higher flow rate can increase volume utilizing rate and decrease the disperison number which represent a better hydraulic behaviour. Identical hydraulic loading and flow rate but less feeding intervals between batches can improve hydraulic efficiency of the system as well. Study results provide some referrences for optimal design and operation of VFCWS with intermittent feeding.