Design points for river bypass constructed wetland: take a river bypass constructed wetland in North China as an example

River bypass constructed wetland is one of the common engineering measures for river water environment control. The implementation of boundary conditions is complex and, although it has been widely used in China, few systematic studies have been carried out on its engineering application. Through the collection and data analysis of engineering cases, the functional positioning and design objectives, design technical route and boundary conditions of constructed wetland in river bypass were systematically sorted out, and the key points of process selection, general layout, process unit design, vertical elevation design and key single project design were analyzed. Taking a bypass constructed wetland project with a river treatment scale of 200 000 m³/d in North China as a case, and the application of design key points in the case project was expounded in detail. The case wetland adopted the combination treatment technology of facultative pond + horizontal subsurface current wetland + surface flow wetland + aerobic pond, and there were 7 treatment zones. Each partition was arranged in series with internal treatment units. The river inlet could be discharged by gravity after lifted by the facultative pond. When the influent water quality in winter reached Grade Ⅳ of Environmental Quality Standards for Surface Water (GB 3838-2002), the wetland effluent could meet the design goals and objectives, and the operation cost was low (0.1 yuan/m³).