Construction of artificial wetland needs to occupy a large amount of land, which is a major factor restricting the promotion of artificial wetland for Chinese cities where land is becoming increasingly scarce. The Wuhe wetland, for example, occupies an area of ****800 hectares, which is 40 times the land area required to build a sewage treatment plant with the same treatment capacity. However, the construction of artificial wetlands by using the long unused river's old course is not only not occupying urban land but also improving the utilization rate of land for many waterfront cities, and the Wuhe Wetland is a case in point. The case study of Linyi Wuhe Wetland shows that scientific design and construction of artificial wetland is of great theoretical and practical significance for purifying urban tail water, improving the health of residents along the river, developing wetland eco-tourism, upgrading the quality of natural ecological environment of the city, and realizing the coordinated sustainable development of the socio-economical and ecological environments. At the same time, it also plays an important role in promoting the popularization of artificial wetlands in more cities in China.
Vegetation: Wetland plants should be mainly local species, which can fully ensure the adaptability and survival rate of wetland plants on the one hand, and reduce the cost of purchasing seedlings on the other hand, and thirdly, it is able to update and replace the vegetation in time when it dies. Wetland plants are required to be as rich as possible, which is important for the following aspects
l Stabilizing the wetland substrate, avoiding or reducing the formation of stagnant area or short circuit of water flow, so that the water flow can be evenly distributed to the various treatment units of the wetland;
l Absorbing carbon, nitrogen, phosphorus, sulfur, heavy metals and so on in the water in the wetland;
l Providing habitat and food for the microbial organisms, fishes and birds; and habitat and food;
l The diversity of wetland vegetation in shape, size, color, etc. also creates an aesthetic value for the wetland;
l The growth of wetland plants also increases the productive capacity of biomass.
Treatment unit: Based on the field research, the current topography and geomorphology of the Wuhe wetland is used as the texture, and engineering measures are used to level the ground of the wetland treatment unit, so that the wetland treatment unit embodies the diversity in shape, and provides a platform for the growth of wetland plants and the purification of wetland water quality.
4 Analysis of water purification effect of Wuhe Wetland
Wuhe Wetland is designed with an average daily capacity of 300,000 tons of sewage, and the residence time of water in the wetland is 7 days. A monitoring station (M1, M2 and M3) was set up at the two inlets and outlets of Wuhe Wetland to monitor the water quality of the influent from Trap River and South Blossom River and the effluent from the wetland (Figure 1). CODcr, NH3-N, BOD, SS and TP were selected as water quality analysis factors. Table 2 shows that the Wuhu River wetland has high removal rates of CODcr, NH3-N, BOD, SS and TP, which are 84.8%, 98.7%, 81.6%, 88.9% and 95.1%, respectively, and are all higher than the designed removal rates. Practice shows that the Wuhe wetland not only meets the design requirements, but also has outstanding performance in the absorption of nitrogen, phosphorus, potassium and so on.