- Wastewater is pumped intermittently into distribution lines within the crushed brick which helps spread the water for vertical movement into the sand below.
- Water then moves down through the sand layer which contains fine brick material. Iron, which gives brick its red color, attracts and stores phosphorus.
- The soil filters rest on a coarse brick layer which prevents water from the wetland from wicking up into the soil filters and maintains the desirable wet/dry environments.
- Water flows vertically past the coarse brick layer and into the marsh which has a variable water level (WL in diagram). The constructed wetland under the soil filter mimics either a high or low marsh depending on the water level, which is externally controlled.
- Since wastewater is rich in microbes, organic materials, and therefore odor, a charcoal layer near the surface of the soil filter is designed to prevent the movement of objectionable odors into the surrounding courtyard.
The combination of soil filters and marshes with both dry and wet environments is excellent for changing nitrogen to a desirable form, for storing phosphorus, and for filtering out organic materials and pathogens(House, Waterwise, Winter, 1995). A tipper bucket at the exit drain of cell 1 provides useful information about the flow rate through the cell.
The marsh supports wetland plants whose roots are crowded with microbes . The plants pump oxygen from the air into the flooded sand around their roots. The microbes living on and near root surfaces then remove potential pollutants as they feed on the oxygen. The plants themselves also take up contaminants while their roots secrete a substance that kills some pathogenic bacteria.