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 federa l states of Germany, more decentralized purification systems need to be est ablished. To attain higher surface water quality, and thereby the acceptanc e of such systems by governmental authorities, good removal rates for organ ic substances and also for nutrients (N, P) are necessary. Constructed wetl ands for wastewater treatment (reed-bed systems) in Germany and in the USA have been used successfully. This study compares the purification performan ces of constructed horizontal flow wetlands (HFW) and vertical flow wetland s (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 verti cal flow systems can remove more than 90% of organic load and of total N an d P, if there is an effective precleaning step, and if the specific treatme nt 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 mater ial (76%) and energy (83%) for their function compared with central technic al systems. (C) 2001 Elsevier Science B.V. All rights reserved.