SUBSURFACE MACROPHYTE SYSTEMS IN WASTEWATER TREATMENT
There is a growing need and demand for the removal of nutrients from the wastewater of isolated households and small rural communities; ecological engineering through natural and constructed wetland systems shows promise in meeting stringent wastewater treatment criteria. Wetlands constructed with different hydraulic designs have shown a range of nutrient removal efficiencies. Vertical stratification has been observed in subsur-
face, horizontal flow systems where passage of water through the bottom of the systems limits both microbial transformation and root uptake of nitrogen. Vertical flow wetland systems have a greater potential for nitrogen removal. The vertical upflow system provides a more even root distribution, increases the water-root contact and induces luxury plant uptake, while the vertical downflow system provides the oxygen required for nitrification. An important feature of vertical wetland systems with root uptake/storage is that nitrogen and associated nutrients can potentially be recycled for agricultural applications.