1、 Project background
The second tributary of Songhua River, the second tributary of Yitong River, is the mother river of Changchun. The natural length of the reach in the urban area of Changchun City (from Baxia section of Xinlicheng Reservoir to wanbaolan River Gate) is about 47.137km, the length of the middle channel (from Sihua gate to South Ring Road, figure 1) is about 15.88km, the average width of the channel is 140m, the narrowest part is 110m, the average gradient of the middle channel is about 0.5 ‰, the average water depth is about 2.5m, and the total water capacity is about 0.5 ‰ About 6.3 million m3. Since 1986, the Yitong River has been renovated many times in Changchun City, and the greening and flood control construction of the urban section of the river have been basically completed. After the completion of Xinlicheng Reservoir in the upper reaches, the Yitong River has lost its stable source water supply and has become the main channel for carrying natural rainfall and urban drainage. The water pollution, river sedimentation and water ecological function have been lost. The middle section of Yitong River has become a black and smelly water body.
2、 Governance objectives
Changchun city put forward the plan of water quality cross-section treatment for the seriously polluted Yitong River, made clear the goal of treatment, strengthened comprehensive treatment, and comprehensively promoted the battle of water treatment and quality improvement. According to the requirements of Jilin Province water pollution prevention and control target responsibility letter, the Yitong River reaches the class V standard in 2020 (ammonia nitrogen < 2.0mg/l, TP ≤ 0.4mg/l, cod ≤ 40mg / L, dissolved oxygen > 3.0 ~ 5.0mg / L).
3、 Current situation of water pollution
The water pollution in the middle part of Yitong River Basin is serious. The index of COD, ammonia nitrogen and TP is far beyond the limit value standard of class V of surface water, so it belongs to the black and smelly water body. The ecological basic flow is seriously insufficient, only the upstream southeast sewage plant is the only stable water supply source, the current water supply is about 61000 tons / day, the river water power is poor, and the water quality can not meet the target requirements; the water ecosystem is seriously degraded, and the water body basically loses the self purification capacity.
4、 General idea and technical route
The selection of the technical route for the comprehensive treatment of the river basin should follow the principles of "applicability, comprehensiveness, economy, long-term effectiveness and safety", combined with the actual situation of the middle section of the Yitong River Basin, the project takes "source control and pollution interception, internal treatment, live water supply and ecological restoration" as the comprehensive treatment technical route, in which source control and pollution interception and internal treatment are the premise and basis for other work.
Pollution control of combined system overflow
According to the treatment progress of combined system pipeline overflow at home and abroad, at present, there are two measures for pollution control: source control and end control. For the middle section of Yitong River, the water flow is poor. Considering that the middle section of Yitong River in Changchun City is basically the old city and the confluence system is difficult to be reconstructed, it is determined that the project mainly adopts regulation and storage for confluence overflow pollution, and 11 regulation and storage pools are constructed to control non-point source pollution.
Regional non-point source control of diversion system
In order to solve the problem of non-point source pollution in the area of diversion system, lid measures and a combination of infiltration, stagnation, storage, purification, use and discharge measures are adopted. The diversion non-point source pollution control project is a part of the water ecological project in the middle section of the Yitong River, which needs to meet the requirements of water quality and quantity entering the Yitong River.
The sediment in the middle section of Yitong River is seriously polluted, and some areas appear mud spots floating up, black and smelly. According to the current situation of sediment pollution in the middle reaches of Yitong River, the treatment measures are: sludge removal + covering + microbial in-situ remediation. Dredging can effectively reduce the sediment pollution in the polluted area, and can effectively prevent the sediment pollution after clay covering
Live water supply
Considering that the current source of water of Yitong River is mainly from the return water of urban sewage treatment plant and the sewage and rainwater entering the river, and the climate of the drainage basin is relatively dry, the water replenishment plan of this project is to build 3 new sewage plants along the coast and upgrade 1 sewage plant for ecological water replenishment. The advantage of the scheme is that the water quality and quantity are stable, which can not only meet the demand of make-up water and the planning layout of renewable water utilization, but also improve the pollutant reduction capacity by combining with the sewage collection and treatment system.
For the light pollution area, the in-situ sediment improvement project can reduce the release of sediment pollution. The investment is moderate and the comprehensive effect is good.
In this project, 13 side circulating contact oxidation projects, oxidation pond projects and constructed wetland projects are designed to reduce the pollutants continuously entering the river and improve the water environment.
(1) The side circulation contact oxidation project mainly uses the current pond in the beach land to connect the Yitong River and the pond, and arranges floating wetland, artificial water grass, submerged plants, aeration and oxygenation (the aeration device is relatively fixed with the floating wetland) and other measures in the pond. The river water is in full contact with the measures in the pond to remove the organic matter, nitrogen, phosphorus and other pollutants in the water body, so as to make the effluent for a long time Keep the surface water to achieve the purpose of water purification and ecological restoration.
(2) Oxidation pond, also known as stabilization pond or biological pond, is a kind of sewage biological treatment technology, which has been artificially and properly trimmed land and set up a dike and anti-seepage layer. It mainly relies on the natural biological purification function to purify the sewage. The slow flow and long-term retention of sewage in the pond can degrade the organic pollution and purify the sewage through the metabolic activities of microorganisms living in the sewage and the comprehensive effects of various organisms including aquatic plants.
(3) The constructed wetland system includes pond system unit, subsurface flow wetland unit and surface flow wetland unit. The river water of Yitong River is lifted to the pond by pump for buffering and settling to remove particles, and then enters the subsurface flow wetland unit. The water body is purified by the function of substrate filler in the subsurface flow wetland and the absorption of reed and other plants. The sewage after the subsurface flow wetland treatment enters the surface flow constructed wetland In the wetland, the pollutants are removed through the absorption of wetland plant roots, and at the same time, the water surface landscape of the wetland can be built.