Constructed Wetland Cell 2 is designed to flood and drain in the same way as a tidal marsh. This influences oxygen concentrations by alternating aerobic and anaerobic environments within the same space. This design approach manipulates time to vary the processing environment, in contrast to cell 1 which makes use of different spaces to create aerobic and anaerobic environments. Both cell 1 and cell 2 enhance nitrogen transformations and phosphorus storage by the same processes, however.
The filter materials used in this cell were chosen to permit fairly rapid water movement within the surface layer and slow movement within the cell depths. This simulates the relatively quick flow of water at the surface of a natural tidal marsh and the slower flow within the soil of the marsh.
A solar powered valve controls the flooding and draining of cell 2. Alternating aerobic and anaerobic environments created by fill and draw (flood and drain) work together to remove nitrogen from wastewater through a nitrification-denitrification process. Nitrogen transformation requires a brief aerobic step (nitrification), followed by an anaerobic process (denitrification) that may take up to 7 days.