Horizontal Subsurface Flow CW's: Operation
A HSSF is filled with a filter material through which the wastewater must flow. The wastewater is distributed at the inlet and flows horizontally through the filter material below the surface of the wetland. The filter material can be anything from coarse sand to light expanded clay aggregate. The inlet zone exists of a larger medium which ensures a uniform distribution of the influent across  the system. The outlet is connected to a level control that provides a constant water level. The system is planted with emergent macrophytes. Removal mechanisms are based on both aerobic and anaerobic conditions. See animated GIF below.
Constructed Wetlands