Nitrogen removal processes in constructed wetlands

Constructed wetlands can effectively remove nitrogen from wastewaters and diffuse run-off from land. In mature wetlands the dominant N removal process is generally microbial denitrification. N removal from ammonium-rich wastewaters is frequently limited by insufficient oxygen for initial nitrification. Alternative microbial N removal processes, including anaerobic ammonium oxidation, may be important in these situations. Emergent plants enhance N removal mainly via indirect effects on physico-chemical and microbial processes. In particular, they promote settling and retention of suspended solids, transport oxygen into the root-zone, provide surfaces for biofilm growth, and produce organic substrates for denitrifying bacteria.