Ammonia Removal Processes for Urine in an Upflow Macrophyte System

Abstract

Constructed wetlands represent an alternative technology for the removal of nitrogen from wastewater, although removal mechanisms are poorly understood. Detailed studies of ammonia removal from diluted urine in a vertical upflow macrophyte system were made in a column fitted with sampling ports, filled with sand, and planted with common reed (Phragmites australis). Variations in profiles for ammonia, nitrate, and dissolved oxygen were interpreted for a range of initial ammonia concentrations and loadings. The profiles demonstrate that the previously proposed mech anism of root oxygenation promoting bacterial nitrification/denitrification may have been overemphasized. In systems with sufficient root density and an upflow regime, luxury plant uptake with rhizome storage dominates N removal. Plant uptake of ammonia regulates oxygen demand and provides suitable conditions, both in terms of oxygen and ammonia concentrations, for additional bacterial nitrification. Consequently, higher concentrations and loading rates of ammonia can be treated by an upflow macrophyte system as compared to a bacterial system alone.