Study On Hydraulic Efficiency Of Horizontal Subsurface Flow Constructed Wetlands

Horizontal flow constructed wetlands have been successfully employed to remove classical contaminants fromwastewaters, such as the organic load,nutrients and pathogens. However, poor hydrodynamic behavior is commonly found resulting in preferential pathways, water entrapment, enlarging the area of dead zone, and variations in both the hydraulic residence time (HRTD) and, consequently, the wetland's hydraulic efficiency. Meanwhile, some of the factors that influence the constructed wetland's hydrodynamic behaviour are wind, vegetation, flow parameters, temperature, medium, inlet-outlet location, diaphragm and width-to-length ratio.This paper describes a numerical model study that has been undertaken to investigate the effects of vegetaion, inlet-outlet location, the wave flow made by diaphragms and the grain size of medium on the wetland's hydraulic efficiency. And effects of these factors on flow patterns of saturated fluids in a horizontal subsurface-flow constructed wetland were investigated experimentally using a quasi two-dimensional flow cell representing a vertical cross-section in the longitudinal direction of the wetland. The filter medium consisted of heterogeneous glass beads. Flow through the filter bed was visualized by injecting dyed fluid into the water-saturated model. Next, the hydraulic parameters which included hydraulic retention time, effective volume fraction and hydraulic efficiency were obtained using chloride tracer. The conclusion were obtained by the analysis of hydraulic parameters and flow patterns. Next, effects of the inlet and outlet position on the spatial patterns of nitrogen in a lab scale horizontal subsurface flow constructed wetland(HSSFCW) system were investigated experimentally.The results indicated that in the simulated constructed wetland filled with porous media with grain sizes ranging from 4 to 9mm, the pore velocity was smaller, the mean retention time was longer, the dead area was smaller,and the effective volume and hydraulic effciency were higher. The flow patterns were similar in the first few minutes when the dye was injected into the same inlet. The inlet and outlet location can change the flow patterns and flow paths, Using inlet-outlet configurations that forced the flow through larger portions of the filter bed and opposing the gravity-driven flow increased the treatment efficiency. Meanwhile, the inlet-outlet configurations effected on the flow paths, the position of enrichment area of ammonia nitrogen carbon source, the of DO. The desolved oxgen in the sewage provide favorable factors for the degradation of ammonia nitrogen. The roots of vegetation that forced the flow through larger porsitions of the filter bed improved the hydraulic performance. The wave flow that forced the flow through larger positions and increased the effective volume fraction and the mean hydraulic time increased the hydraulic efficiency.