Flow uniformity and hydraulic efficiency improvement of deep-water constructed wetlands

• Meandering flow can create greater flow uniformity and avoid short-circuiting flow, thus improving hydraulic efficiency.
• Installing both emergent obstructions and submerged obstructions on the same side of the inlet and outlet is recommended in shallow-water wetlands.
• In deep-water constructed wetlands, installing emergent obstructions markedly improves flow uniformity and hydraulic efficiency, whereas submerged obstructions have only a slight effect.
• The meandering channel formed by the emergent obstructions not only delays the peak arrival time and reduces the short-circuiting areas but also increases the aspect ratio and creates a longer flow path.
• The findings of this study encourage wetland scientists and wetland engineers to initiate plans for the restoration/creation of deep-water wetlands and combination wetlands with both shallow-water and deep-water areas.

Free-water surface constructed wetlands (FWSs) are designed to treat wastewater. Previous studies have indicated that hydraulic efficiency influences treatment performance and that shallow-water FWSs always yield greater hydraulic efficiency than do deep-water FWSs. This study presents effective ways to improve the flow uniformity and hydraulic efficiency of deep-water FWSs by utilizing different allocations and varying numbers of obstructions. A reliable computational model is employed to simulate the flow conditions and tracer concentrations from numerous hypothetical cases. The differences between emergent obstructions (EOs) and submerged obstructions (SOs) were examined. Improving the efficiency of shallow-water and deep-water FWSs is discussed. Installing obstructions on the same side of the inlet and outlet is recommended for avoiding flow circulation. Meandering flow formed by EOs can avoid short-circuiting flow and reduce dead zones, thus resulting in more uniform flow and greater hydraulic efficiency. SOs were found to have minor and inconsistent effects in improving hydraulic efficiency. We conclude that an alternative method for increasing the aspect ratio of a fixed-dimension wetland is to use EOs to create a meandering flow pattern and longer flow path. The findings of this study encourage wetland scientists and wetland engineers to plan the restoration/creation of deep-water wetlands and combination wetlands with both shallow-water and deep-water areas.