The main purpose of constructing constructed wetland

As a "kidney of the earth", wetlands are responsible for the purification and treatment of natural water bodies on the earth. With the gradual reduction and extinction of natural wetlands in cities, constructed wetlands have attracted more and more attention and development for their unique advantages.

1. Constructed wetland has high treatment efficiency.

According to the different flow patterns, constructed wetland sewage treatment system can be divided into surface flow constructed wetland and subsurface flow constructed wetland. Surface flow constructed wetland is similar to natural wetland, and sewage overflows from the surface of wetland. This kind of constructed wetland has simple structure and low project cost, but it occupies a large area and has limited sewage removal capacity. Moreover, because the sewage overflows on the surface of the filler, mosquitoes and flies are easy to breed, and it is easy to cause adverse effects on the surrounding environment. In the subsurface constructed wetland, sewage enters the packed bed from one end of the wetland and flows between the gaps of the packing in the form of horizontal or vertical subsurface flow, which can make full use of the adsorption and interception of biofilm on the surface of the packing, rich plant roots and plant roots to achieve the effect of removing high nitrogen and phosphorus; On the other hand, because water flows below the wetland surface, the treatment effect is less affected by climate fluctuation, and the drier habitat can be used for the growth of mesophytes, with better sanitary conditions. In recent years, according to different sewage treatment purposes, compound constructed wetlands have been developed, that is, one or more surface flow constructed wetlands and one or more subsurface flow constructed wetlands are connected in series or in parallel, which is beneficial to nitrification and denitrification and achieves better nitrogen removal effect.

Second, constructed wetlands have multiple ecological service functions.

The main design purpose of constructed wetland is to purify sewage. In addition, constructed wetlands can provide a variety of ecological services. Constructed wetlands can absorb carbon dioxide, release oxygen to regulate regional microclimate, generate carbon fixation through plant biomass, block dust and reduce noise. Constructed wetland system can promote the growth of plants, increase the green area, provide habitats for animals and plants, and help protect biodiversity in sewage purification projects. Constructed wetland can not only treat the surface water quality of urban parks, green landscape water, rivers and lakeshore, but also provide people with more comfortable living environment and educational and entertainment purposes, which has remarkable social, environmental and economic benefits.

Although natural wetlands also have the functions of carbon sequestration, education and entertainment, their sewage treatment capacity is obviously lower than that of sewage treatment plants and constructed wetlands. Although the sewage treatment plant has a certain sewage treatment capacity, it does not have the above other ecological service functions. Constructed wetland system can not only be used as a sustainable landscape ecosystem, but also achieve the purpose of sewage treatment and give full play to the multiple ecological functions of wetland plants. In China, where the contradiction between man and land is tense, it is undoubtedly a development model of sewage treatment worth popularizing.

Thirdly, the plants in constructed wetlands are recycled.

Plants in constructed wetland are the core of sewage treatment, which play an important role in the process of sewage treatment, including directly absorbing pollutants such as nitrogen and phosphorus, promoting redox reaction and aerobic microbial activity in root zone through oxygen transfer in root system, and enhancing and maintaining hydraulic transfer of medium. There are four main types of plants planted in constructed wetlands: floating plants (such as water lilies), floating plants (such as Eichhornia crassipes), emergent plants (such as reeds) and submerged plants (such as Ceratophyllum). At present, emergent plants are widely used in constructed wetland sewage treatment system. The research on plants in constructed wetlands at home and abroad mostly focuses on the nitrogen absorption efficiency of plants, the interaction mechanism between plants and microorganisms, and the selection and configuration of plants. In fact, constructed wetland plants can not only remove pollutants from wastewater, but also directly absorb and utilize effective nitrogen, phosphorus and other nutrients in wastewater for their normal growth, thus achieving the purpose of promoting the recycling of nutrients in wastewater, but the research in this area has been ignored. At present, in the constructed wetlands actually operated in China, plants are generally not properly treated after harvest, resulting in resource waste and secondary pollution. If these plants are collected as biomass energy raw materials, the reuse of constructed wetland system can be realized, and the contradiction between the supply of raw materials for traditional biomass power generation and the competition for land by crops may be solved.