With the rapid development of economy and urbanization in our country, hundreds of WWTPs built around 2000 in the economically developed domestic economy are faced with the fact that they are surrounded by urban development zones and become "factories in cities". Due to noise, malodour etc. Environmental pollution and uncoordinated landscape and other reasons, urgent reconstruction. In the context of building a sponge city, planning the layout of a sewage treatment plant from the perspective of water resources co-ordination and overall consideration of the underground sewage treatment plant built in the city facilitates the purification of sewage and surface water pollution. These are new strategic thinking on water recycling. At the same time, the following aspects also reflect the advantages of underground sewage treatment plants: the construction of underground sewage treatment plants in the upper and middle reaches of urban waterways facilitates the recycling of reclaimed water for reuse; the construction of underground sewage treatment plants in cold areas Can solve the insulation of sewage treatment facilities to achieve the normal operation of the sewage treatment plant; sewage treatment plant site surrounding environmental requirements are high or limited land area may also choose to build underground sewage treatment plants. Underground sewage treatment plant development process Foreign large-scale urban underground drainage and sewage treatment system has made good progress. The world's first underground sewage treatment plant was built in Finland in 1932 with an underground rainwater treatment capacity of 600,000 m3 / d for its underground Helsinki facility. In 1942, Stockholm, the capital of Sweden, built the world's first modern rock underground sewage treatment plant with excellent geological conditions and advanced excavation technology and has been successfully operating for more than 70 years. At present, many countries are developing underground sewage treatment plants, such as the United States, Britain and Japan. In these countries, underground sewage treatment plants have achieved good economic and social benefits. With the rapid economic development in China, at present, the level of industrialization in China has reached world advanced level. The equipment and key technical problems that have hindered the development and utilization of underground space are now breaking through one after another, including the disaster prevention technology for underground space , Ventilation technology, lighting technology, waterproof technology, environmental control technology, excavation and support construction technology, the cost of underground space development and utilization is gradually reduced, and the feasibility of underground sewage treatment plant design is gradually enhanced. Domestic underground sewage treatment plant construction since around 2010 began, has been completed dozens of seats, daily processing scale from tens of thousands of cubic meters to 600,000 cubic meters, the construction of underground sewage treatment plant suitable for our people and less land, climate differences The larger national conditions, in line with the development trend of modern metropolitan public facilities to the underground, therefore, with the intensification of water environment control efforts in our country, underground sewage treatment plants in our country will certainly have very good prospects for development. At present, China has no norms on underground sewage treatment plants, design experience is relatively inadequate. Underground sewage treatment plant layout is divided into: all underground type layout (single stamped), all underground type layout (double stamped) and semi-underground layout (double stamped). Underground sewage treatment plant technology Underground sewage treatment plants mostly use the main structure of the building layout of the total wall structure of the box-type structures, the use of high-technology unit more technology portfolio, the core of biological treatment to use more improved A2 / o, MBBR, MBR, BAF; depth treatment According to the different objects to be removed more use deep bed filtration, active sand filtration, high precipitation, magnetic coagulation sedimentation, fiber filtration, filter cloth, ultrafiltration and other small footprint, high efficiency process. According to the characteristics of the underground sewage treatment plant equipped with high standard deodorant process, ventilation and fire safety, underground lighting, emergency safety facilities and other advanced technology so that the overall process to adapt to the sewage treatment plant underground mode, while achieving high water standards and green energy . In the core section of biological treatment, there are many improved A2 / o processes. At present, the process is very mature and reliable in China. The A2 / o program has a longer process flow but lower operating costs. By controlling the proportion of mobile packing in the biological reaction tank, MBBR process can form a symbiosis system of activated sludge and biofilm process, and can also form a biofilm system with biofilm as the main treatment function, which is more suitable for underground sewage Treatment plant upgrade, improve the water quality of the situation. In view of the current need to improve water environment and wastewater resource utilization, many cities such as Beijing, Hefei, Tianjin and Hohhot have proposed more stringent effluent standards, and the good elasticity of the process can lay the foundation for further water quality improvement. MBR process bioreactor sludge concentration is high, the required biological pool of small size, most of the depth treatment only need to be disinfected, the most savings in the above processes, but more MBR ancillary equipment, operating requirements and high membrane Cleaning will cost more manpower and resources, film replacement costs higher. Depth treatment part of the need for effluent ammonia, total nitrogen further checks, you can choose both nitrogen and SS function of the deep-bed filter, activated sand filter; phosphorus, SS for the purpose of choice can be efficient precipitation, magnetic mixing Coagulation sedimentation, fiber filtration, filter cloth filter, ultrafiltration and other processing unit or unit combination. Floor layout and vertical considerations; underground sewage treatment plant concentrated in a limited underground tank, to coordinate the good process, a variety of pipelines, ventilation deodorant, fire, traffic, operation and maintenance of all aspects of the relationship to ensure organic convergence, To achieve intensive integration, so as to effectively save space to reduce the volume of underground boxes, to achieve the purpose of saving investment. Process options, should choose the efficient combination of units to meet the functional division of the plane, easy to arrange deodorant, pipelines, power supply, fan, dosing, disinfection, sludge dewatering and the organic link between the process. In particular, pay attention to the structure of the electrical, deodorant, underground space ventilation, fire safety, accident drainage safety design. Landscape design is the highlight of underground sewage treatment plants, with the top of the underground box load capacity of reasonable allocation of landscape, shrubs, trees and so on. Debate: Is the underground sewage treatment plant an opportunity or trap? In the past two years, the construction of underground sewage treatment plants in China is rapid, which is rare in other countries. Optimizing the layout of WWTPs from the perspective of sustainable development of the city makes it more convenient for underground sewage treatment plants to be built in the urban built-up areas for the convenience of building sewage and liquefying plants nearby and using them for landscape and municipal services and optimizing the allocation of water resources. Underground sewage treatment plants can effectively use underground space, save land, to meet the needs of different levels of planning, there will be some room for development in the country. Underground sewage treatment plant brings together many aspects of technology, equipment, materials, civil construction, intensive design, compared with the above-ground sewage treatment plant there is little experience, but also need to continue to sum up.
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