Influence of the substrate type and position of plant species on clogging and the hydrodynamics of constructed wetland systems

Abstract

The present work evaluated the influence of the filling substrate material, the presence of plants and position of plant species on the saturation and hydrodynamic behavior in horizontal subsurface flow constructed wetlands (HSSF-CWs). For this, six HSSF-CWs were used which differed with regards to the type of substrate (gneiss gravel or crushed PET bottles), presence of plant species and their position (consortium between Tifton 85 grass and elephant grass). For the treatment of wastewater from a milk cooling tank (WWMT), it was observed that there was a higher solids concentration and a greater extent of runoff in HSSF-CWs cultivated and filled with gravel after one year and eight months of operation, which was due the contribution of solids, resulting from substrate wear and the presence of the root entanglement. Crushed PET bottles may be a viable alternative substrate in HSSF-CWs because they are inert, present low wear and contribute fewer to pore clogging solids. It was observed that the sequence of plant species also influenced the runoff length, having greater extent of surface flow in units with elephant grass followed by Tifton 85 grass. Despite the higher solids concentration and greater surface flow, the beds filled with gravel and cultivated with the plants showed better hydrodynamic conditions than the other treatments, which indicates the importance of analyzing the characteristics of the solids and the effect of pore space expansion by the roots.