Improved Design Of Horizontal Subsurface Flow Constructed Wetland In Cold Regions

As a new ecological way to treat sewage, constructed wetland technology, born in the1960’s. was good in treatment effect, less investment, easy to operate and maintain, less secondary pollution, etc. After half a century of development, its theoretical research has become mature and has been employed to treat various sewages all over the world. However, due to the different methods in engineering design and the influence of low temperature, its development and application were restricted in the northern cold region. In this paper, based on numerous relative literatures and engineering projects in constructed wetland design, a constructed wetland system was built to befit the low temperature there. The system was planned to treat the effluent from a sewage treatment plant, which guaranteed the water supply safety of downstream water source.Main achievements and conclusions are as follows:(1) A horizontal subsurface flow constructed wetland was built. With deliberately investigation and survey, and based on comparison of different sites and schemes, a treatment process consisting of an inflow control room, a subsurface flow constructed wetland (SFCW) and a landscape pond was designed to treat the effluent from a wastewater treatment plant; learning from relative literature and previous engineering projects, design parameters and macrophytes were discussed in detail and hydraulic conditions in the system were improved, then osmosis and flood control and monitoring of pollutants were also stated in the dissertation.(2) A multipurpose water control room was constructed. As a part of the constructed wetland system, the pretreatment facility functions in four aspects:①regulating the water level of inflow so as to meet the hydraulic condition in the system;②ensuring the designed inflow rate and overflowing the extra part;③monitoring the suspended substance of the runoff from sewage treatment plant, pretreating or making a drainage to the waterway in order to alleviate clogging;④Acting as a management room to facilitate daily operation and maintenance, etc.(3) Inflow and outflow configurations were improved. Considering the low temperature and condition of project site in northern cold region, all of the pipelines were buried deep and sand cushion was employed to warm them:we designed double-deck perforating inflow configuration to improve water distribution. which also guaranteed the operation, even though when top of the substrate was frozen in winter:in the middle of the constructed wetland unit, a shielded wall and regulating wells were designed to enhance water distribution and regulate the water level in the unit, thus ensure the performance of pollution disposal.