application of horizontal sub-surface flow constructed wetland for treatment of wastewater in foreign countries and iran

background: selection of different wastewater treatment methods depends on the kind of wastewater, geographical position of the community, quantity and quality of wastewater and effluent, technology and finance. natural wastewater treatment methods are simple, cheap and acceptable for developing countries specially small and remote countries and wetland is one of these methods. wetlands include two categories: natural and constructed. moreover, constructed wetlands are of two types of sub-surface flow and free water surface. the aim of this paper is to investigate wetland usage backgrounds and history of application in iran and other countries. methods: this is a review of the practical work and comparison of constructed subsurface flow wetland system's efficiency in wastewater treatment in iran and foreign countries. findings: in many countries average of removal efficiency by wetland for bod, tss, tp and tn was about 91.6%, 81.6%, 78.8% and 70.8% respectively, and for iran they were 77%, 83%, 78%, and 83%, respectively. conclusion: the results of the current research showed that in foreign countries wetland systems are used for all kinds of wastewater and have good removal efficiency, unfortunately in iran wetland is not widly used and it has only been used in a few domestic cases.