Studies on mechanisms and efficiencies of wastewater treatment with constructed wetland,mainly from developed countries,conducted mainly in the past 2 decades are reviewed.The mechanisms of wastewater treatment by wetlands are extremely complicated,including a series of physical,chemical,and bio chemical processes,such as special and non special adsorption,exchange,sedimentation,assimilation,decomposition,volatilization,and so on.There are lots of components,e.g.plants,soils,and microorganisms,in wetlands making contributions to water quality improvement.Of all plants in constructed wetlands, Phragmites communis is used most widely and frequently.But wetlands covered by this single species are inferior to those covered by many species including it and other plants with reference to removal efficiency of nutrients and pollutants.In order to consummate theories about constructed wetlands for wastewater treatment,and to further improve removal efficiencies of pollutants and wetland ecosystem health,the following research fields are suggested to consolidate or further conduct in the future:① deeper and more systemic research on mechanisms of wastewater purification by wetlands;② studies on sustainable development of constructed wetland;③ experimentation on the suitability of local and indigenous wetland macrophytes for removal of nutrients and heavy metals from different types of wastewater;④ exploration for better constructing,maintaining,and using measures to maximize the wastewater treatment efficiency;⑤ controlling disease vectors and animal pests,and preventing them from jeopardizing human health and lives;and ⑥ ascertaining reasons producing noxious and odorous gases and then trying to control them effectively.
