Nutrient removal efficiency and resource economics of vertical flow and horizontal flow constructed wetlands

In order to reduce the very high costs of sewage disposal in the new federal states of Germany, more decentralized purification systems need to be established. To attain higher surface water quality, and thereby the acceptance of such systems by governmental authorities, good removal rates for organic substances and also for nutrients (N, P) are necessary. Constructed wetlands for wastewater treatment (reed-bed systems) in Germany and in the USA have been used successfully. This study compares the purification performances of constructed horizontal flow wetlands (HFW) and vertical flow wetlands (VFW), including: (1) a small horizontal flow wetland (HFW); (2) a sloped HFW; (3) a larger HFW; (4) a stratified vertical flow wetland (VFW); and (5) an unstratified VFW. It is shown that both the horizontal flow and vertical flow systems can remove more than 90% of organic load and of total N and P, if there is an effective precleaning step, and if the specific treatment area is great enough ( > 50 m(2)/m(3) per d). HFWs have an advantage in long-term removal of P because it is bound to organic substances to a high degree. Decentral and semicentral natural treatment systems also save material (76%) and energy (83%) for their function compared with central technical systems. (C) 2001 Elsevier Science B.V. All rights reserved.