Developing a 3D Hydrodynamic and Water Quality Model for Floating Treatment Wetlands to Study the Flow Structure and Nutrient Removal Performance of Different Configurations

Abstract

Floating treatment wetlands (FTWs) are widely used in surface water. The nutrient removal performance depends on both physical processes and chemical/biological transformations in FTWs. However, research describing the coupling processes of hydrodynamic and water quality in the system remains limited. Therefore, a coupled three-dimensional model of hydrodynamic and water quality for FTWs was developed based on the Environmental Fluid Dynamics Code (EFDC). Additional plant drag terms were added to the momentum equations to simulate the suspended canopy effect, and the chemical/biological processes occurring in FTWs were integrated into the original water quality equations simultaneously. The fully calibrated model was used to compare the hydrodynamic characteristics and nutrient removal performance of seven FTW configurations. The modeling results showed that the main stream would turn to the bottom and side of the plant root zone because of the block in FTWs. The differences in the hydrodynamic characteristics among the seven configurations led to a difference in water quality improvement effects. Segmenting a single FTW into a pair of parallel FTWs could achieve the maximum nitrogen and phosphorus mass removal. The results of the study are useful for designing an optimal FTW configuration in surface water.