In the previous issue of "Create near natural water plant, enjoy water purification Park∣ BEWG constructed wetland practice" (click the title on the left to view the content of the previous issue), we introduced the characteristics of BEWG wetland products and typical cases of tail water wetlands of sewage plants. In this issue, we will focus on another important application scenario of constructed wetlands: River and lake water purification.

The causes and treatment of water environment pollution in river basins have a certain complexity. In recent years, with the promotion and implementation of various water treatment work, water environmental pollution has been basically curbed and effectively improved, but the impact factors such as rainy season overflow, agricultural non-point sources, lack of high-quality natural runoff supply still exist, and the water environmental quality often fluctuates and repeats periodically. As an ecological and low-carbon water purification technology, constructed wetland can further purify river and lake water by bypass or in-situ treatment mode, and become an important guarantee for long-term water quality compliance.

At the beginning of this year, the opinions on promoting the utilization of sewage resources jointly issued by ten ministries and commissions pointed out that when implementing the regional recycled water recycling project, it is necessary to build engineering facilities such as constructed wetland water purification according to local conditions at the key nodes, and further purify and improve the discharged water and slightly polluted river water after reaching the standard, and then incorporate them into the regional water resource dispatching and management system".

As early as in the comprehensive management of Xinfeng River Basin in Daxing District of Beijing, which was launched by BEWG in 2017, this idea of recycling reclaimed water was adopted and achieved good results. Now let's take a look at the contribution of constructed wetlands to the ecological revitalization of Xinfeng River, a northern urban river?

The last kilometer is the wetland

Xinfeng River is located in the north of Daxing District in Beijing, with a total length of 30.1km. As an important flood control and drainage channel in Daxing District, Beijing, the Xinfeng River was once heavily polluted and its ecosystem was seriously damaged. Some river sections were judged as black and smelly water bodies.

Since March 2017, BEWG and its subsidiary BHZQ have been entrusted by the Daxing District Water Bureau to comprehensively promote the treatment of the Xinfeng River Basin. In order to solve the problems of large and scattered pollution sources, wide area of polluted water bodies, scarcity of regional water resources and so on, a technical route based on a multi-source water replenishment system mainly based on reclaimed water and an important means of improving the quality of constructed wetlands is proposed.

The project introduces about 46.355 million m³every year to ensure ecological base flow and realize "both river and water". On this basis, two constructed wetlands with a processing capacity of 46000 m³/d will be built to bypass the water quality of the main stream and important tributaries, completing the "last kilometer" of the Xinfeng River to meet water quality standards. Combined with the ecological restoration of wetlands and rivers, the project finally achieved "both fish and grass" and "human-water harmony" in the Xinfeng River system, effectively meeting the hydrophilic needs of the surrounding citizens and improving their happiness.

Bypass purification of Key Tributaries to preserve water quality

Take Annan wetland as an example. The wetland is located at the estuary of the Annan tributary into the Xinfeng River. It is mainly used for the bypass purification treatment of the Annan tributary water body, and the effluent is discharged into the main stream of the Xinfeng River. The wetland adopts the combined process of "forebay + composite subsurface flow wetland + surface flow wetland", and the designed treatment scale is 22300 M³/d. The design goal is that the wetland effluent in non rainy season is better than class IV surface water, and the wetland effluent in rainy season reaches class V surface water.

Since the operation of water supply, the monitoring data shows that the average concentration of the main indicators (COD, ammonia nitrogen, total phosphorus) of Annan wetland can be steadily increased from surface water class IV~V to surface water class II~IV. among them, the ammonia nitrogen concentration can be purified from average surface water class V to surface water class II, with an average removal rate of 74%, and the volatility of effluent is significantly reduced. The wetland has achieved the goals of reducing the pollution load of tributaries and ensuring the stability of water quality in the main stream of Xinfeng River.

Winter insulation test research to ensure stable operation

The winter in Beijing is cold and dry, and the monthly average temperature is below 0℃. In the coldest January in Beijing, the average temperature is only minus 3℃ and the lowest is minus 8℃. The water temperature entering the subsurface flow wetland unit also drops below 2℃. Therefore, Annan wetland faces the challenge of operating at extreme low temperature in winter.

In order to ensure the operation effect of Annan wetland in winter, BEWG has carried out experimental research on various insulation methods and operation parameters of constructed wetland collection and distribution pipelines and subsurface flow wetland units, and finally ensured that the main water quality assessment indicators are stable and up to standard in winter. According to the analysis of the test data, the average removal rate of ammonia nitrogen in January can reach 80%, which is basically the same as that in April when the average water temperature is higher than 15 ℃.

The landscape of natural integration of plant water system is perfect

Annan wetland uses plants and water systems to form a landscape environment that organically integrates ecological function wetlands, cultural landscape elements, rural landscape, and wetland water system landscape to form a spatial pattern surrounded by mountains and forests from north to South and flowing water systems on a large scale. The composite subsurface flow wetland unit is divided into 9 kinds of native aquatic plants, including reed, yellow flag, scirpus, Sagittaria Sagittifolia, willow herb, etc. The surface flow wetland unit forms a natural meandering wetland landscape through the topographic design of ecological islands and rich aquatic plants such as lotus, water lily and banana-plant.

Construction waste recycling to achieve sustainable development

Annan wetland covers a total area of 551 mu and was originally located in the industrial compound of Nangong village, Yinghai town. The project always adheres to the concept of environmental protection and ecology in the demolition, vacation and brownfield reconstruction and construction. The permeable footpath base, bedding and surface layer in the wetland are all made of crushed and screened construction waste, and the reclaimed kerb of construction waste is 4400m, with a total of 3690m³of construction waste；The square in the wetland is mainly paved with the old red bricks produced by demolition and retreat, and a total of 396000 old red bricks are reused.

Wetland science is educational and fun, which achieves man-water in harmony

For a long time, BEWG has regarded environmental science education as an important part of corporate social responsibility. Relying on Annan wetland, Xinfeng River project has set up various forms of environmental science popularization bulletin boards and interactive facilities along the tour route, and planned specific places for visitors to visit nurseries, experience nature, hold activities, cultivate plants and exchange used things. Covering an area of 5000m², the wetland fun experience area and the "black technology" exhibition area of Xinfeng River intelligent water management platform can help tourists intuitively understand the past and present lives of Xinfeng River management and wetland water quality purification knowledge.

In response to the children's interests and needs, the Xinfeng River project has carefully planned a variety of environmental education courses, such as "Beautiful story of Xinfeng River", "Magical central control room", "Environmental Protection Tips", "Fun water purification experiment" and "Exploration tour", so that the children can have an in-depth understanding of reclaimed water treatment, wetland ecological restoration, biodiversity protection and other knowledge, Enhance the awareness of environmental protection and water conservation

Since its opening, Annan wetland has attracted people from all walks of life and citizens to visit and learn from it, which not only provides an example for wetland scientific research, but also becomes a popular destination for environmental education in southern Beijing.

The effectiveness of treatment is not limited to the improvement of water quality

After more than three years of treatment, the black and odorous water bodies in the whole basin of Xinfeng River have been eliminated, and the water environment quality has been greatly improved. In 2019, the annual average values of the main water quality indicators cod, NH3-N and TP of Shaobingzhuang sluice at leave-boundary section of Xinfeng River decreased by 48.75%, 92.61% and 85.68% respectively compared with 2016. The water environment quality in the basin has been improved from inferior class V before treatment to class IV of surface water.

The effect of water ecological restoration is remarkable, and the level of water ecological health has been greatly improved. There are 28 species of aquatic plants in Xinfeng River Basin, with a total coverage of 40%; There are about 20 kinds of fish, including crucian carp, bitterling, abbottina rivularis, hypseleotris swinhonis, etc; Macrobenthos recovered well, the species and number of birds gradually increased, and the biodiversity of aquatic ecosystem significantly improved. At present, the comprehensive index of ecological health of Xinfeng River is 86.99, which has reached the "health" level, an increase of 200% compared with the pre-project treatment (2016).

The recycling of regional reclaimed water with constructed wetlands as an important means has injected new vitality into the Xinfeng River. The former Xinfeng River has changed from a "mosquito River" into an ecological corridor, and the value of the waterfront space has increased significantly. Residents are full of praise for the "great change" of the river at their home, and their enthusiasm for getting close to nature is growing day by day. In 2020, Xinfeng River was rated as "Beautiful river and lake in Beijing"; In 2021, the Beijing Daxing Xinfeng River Basin integrated management PPP Project was selected into the list of typical cases of green government and social capital cooperation (PPP) projects, and was reported as a case by the official Wechat of the Ministry of Ecological Environment.

With the change of water ecological environment management from pollution treatment performance to ecological performance, the composite value of ecological purification technology is becoming more and more important. It is believed that in the future, the constructed wetland products of BEWG will play an indispensable role in the "great change" of more rivers and lakes.

Constructed wetland is a comprehensive ecosystem

Deliver of "oxygen" and vitality for water body improvement

It also provides people with hydrophilic leisure space

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