The problem of water pollution has always been the most important environmental problem in China. It mainly comes from industrial wastewater discharged from excessive standards and domestic sewage that has not been treated directly into water bodies [1]. With the acceleration of urbanization in China, the proportion of domestic sewage discharge has increased year by year. In 2006, the total discharge of wastewater in the country was 53.7 billion m3, of which domestic sewage discharge was 29.75 billion m3, accounting for 55.4% of total sewage discharge [2]. At present, the domestic sewage treatment plants used in large and medium-sized sewage treatment plants in China have traditional activated sludge method, biological contact oxidation method, A/O process, A/A/O process, oxidation ditch process, etc., and the treatment effect is good. Skillful. However, they all rely on perfect drainage network and strong financial support for urban drainage network can not cover the living quarters, the economy is relatively backward rural and small urban areas and the need for a separate organization to deal with particular waste water The unit's sewage treatment is not very suitable. The emergence of underground sewage treatment technology has made up for this shortcoming and opened up a new way for the treatment of small-scale domestic sewage. The underground sewage treatment technology refers to a sewage treatment technology that buryes the main structure in the sewage treatment facility underground or semi-underground. It mainly has the characteristics of small footprint, low noise, no odor, little influence by climate, convenient management and high processing efficiency. 1 Types and application status of buried sewage treatment technology 1.1 Buried unpowered domestic sewage treatment technology 1.1.1 Early buried non-powered domestic sewage treatment technology China has developed a series of buried unpowered domestic sewage treatment technologies from the late 1980s to the mid-1990s, such as domestic sewage treatment biogas digesters and CL landfills. The type does not consume electricity domestic sewage treatment equipment, A-A2/O energy-free sewage purification system, HW series non-power efficient domestic sewage purification equipment, GW self-cleaning domestic sewage treatment technology and A2/O2 non-powered domestic sewage treatment technology. The main processes of these treatment technologies mostly use the traditional theory of anaerobic digestion-aerobic degradation, two-stage biofilm method to purify sewage and feces, and the sewage runs on the principle of hydraulic potential without self-power. It is widely used in some provinces and cities in China due to its investment, no running cost, easy maintenance and management. The basic process is: domestic sewage → anaerobic digestion → anaerobic biological filtration → contact oxidation → discharge. 1.1.2UUAR In 2005, Shen Dongsheng and others from the Department of Environmental Engineering of Zhejiang University studied the buried unpowered anaerobic compliance treatment technology (UUAR) for rural domestic sewage. The technology adopts the method of self-flow of domestic sewage, applies anaerobic biofilm technology and the principle of pushing flow, and adopts underground anaerobic pipeline type or baffled reactor device with fixed hollow spherical filler to be the sole processing equipment, and is attached to hollow spherical shape. Specially domesticated and specialized anaerobic or anaerobic microorganisms on the inner and outer surfaces of the packing remove organic pollutants, pathogenic bacteria and some nitrogen and phosphorus in domestic sewage to achieve the purpose of purifying domestic sewage [3]. The effluent water quality has reached the national secondary discharge standard and has no daily operating expenses, which is suitable for the dispersion treatment of rural domestic sewage. 1.2 Buried power domestic sewage treatment technology 1.2.1 Early buried-type powered domestic sewage treatment technology China's research on buried-type powered domestic sewage treatment technology also began in the late 1980s. The new WSZ buried domestic sewage treatment plant developed in 1994 is: sewage → regulating tank → primary sedimentation tank → contact oxidation tank → secondary sedimentation tank → disinfection tank. The residence time of the adjustment tank is 4-8h. In order to save the floor space, the vertical sedimentation tank is adopted in the primary sedimentation tank and the secondary sedimentation tank, and the semi-soft filler is set in the contact oxidation tank, and the residence time is 2.5-3.2h; The high-efficiency domestic sewage purification tank technology researched by Yang et al. is based on a traditional septic tank, adding an aeration device in the aerobic zone, adding a sedimentation zone and increasing the sludge return system. In addition, at the bottom of the second anaerobic zone Part of the floating packing is accumulated to prevent sludge loss and increase the load of the purification tank. 1.2.2 A/O method + chemical dephosphorization method The first stage sewage treatment plant of Zhouzhuang Town, Kunshan City, Jiangsu Province, uses the buried A/O method + chemical dephosphorization process to treat local domestic sewage. After adjusting the uniform water quality and quantity of water, the domestic sewage continuously flows through the anoxic tank, the aerobic tank and the second settling tank for biochemical treatment. Denitrification and denitrification treatment is carried out in an anoxic tank, and decarbonization and nitrification are carried out in an aerobic tank. Chemicals are added before the second settling tank, and phosphorus is removed by chemical methods. The excess sludge is sent to the sludge concentration tank for sludge digestion, stabilization, concentration, dehydration treatment, and regular transportation to avoid secondary pollution. The effluent meets the first-class discharge standard of the urban secondary sewage treatment plant in the Integrated Wastewater Discharge Standard GB8978-96 [4]. 1.3 Buried integrated small domestic sewage treatment technology Buried integrated small domestic sewage treatment technology refers to the small scale of treatment, integrating the functions of various parts of the sewage treatment process, including pretreatment, biological treatment, sedimentation and disinfection. The domestic sewage treatment plant is buried in the underground to treat domestic sewage. At present, the integrated underground processing technology is divided into biological contact oxidation method, SBR method, A/O and A2/O process according to the process. The treatment device can be made into a steel-formed equipment for overall laying or steel-concrete structure on-site casting [5]. 1.3.1 ZW integrated buried sewage treatment device The device consists of a FRP shell and a liner to form a central aeration zone and a surrounding sludge sedimentation digestion zone, together with a leaf exposure and an electric control cabinet to form a complete sewage treatment system. [6]. After the sewage is pretreated into the ZW integrated equipment, the sewage is first completely mixed with the original mixed liquid by aeration, so that the organic matter is efficiently degraded. The effluent enters the sedimentation zone through the lower diversion slit, and the sedimentation zone has a double-conical section, which is favorable for sludge sedimentation. The whole set adopts the process of continuous water inflow and intermittent aeration. The hydraulic retention time is up to 20h, and the effluent water quality can reach the first-class B standard of pollutant discharge of national urban sewage treatment plant (GB18918-2002). The process flow is: sewage → fine grid → submersible sewage pump → adjustment tank → ZW integrated equipment → qualified discharge. 1.3.2 Buried SBR Process The buried SBR process is commonly used to treat residential sewage. The sewage is removed from the larger suspended solids through the grid and flows into the collecting well. After the uniform water quality, it is transported to the SBR reaction tank by the lift pump. The organic matter is degraded into inorganic salts, water and carbon dioxide by adsorption and decomposition of aerobic microorganisms. The excess sludge produced is digested by the sludge digestion tank and then taken out by the suction truck for processing. The difference between this process and the traditional SBR process is that the decanter adopts the power lifting type instead of the traditional gravity flow; the excess sludge is transported to the sludge digesting tank by the submersible sewage pump; the aerator uses a submersible aerator, and the intake pipe is set. There are electronically controlled valves. The whole process has simple structure, compact layout, saves land occupation, low investment operation cost, no need to adjust the pool and the second settling tank, and is not easy to cause sludge expansion. The effluent can meet the first-level emission standard in the Integrated Wastewater Discharge Standard (GB8978-1996). 1.3.3 Buried integrated biofilter process In 2008, Cao Dawei of Southeast University and others developed a ground-based integrated biofilter process. The main body is an integrated structure, which consists of an anoxic tank, a biological filter and a sedimentation tank. After the sewage enters the anoxic tank, a push flow is formed along the baffle, and the effluent flows into the biological filter through the semi-tubular overflow water distributor. The biofilter is naturally ventilated by a draft tube, and the two-stage splash tray is used to enhance the oxygenation effect. The effluent flows into the sedimentation tank for solid-liquid separation, and the supernatant is partially returned to the anoxic tank, and the rest is discharged. The effluent quality reached the first-class standard of “Emission Standards for Pollutants in Urban Sewage Treatment Plants†(GB18918-2002). 1.4 Scope of application analysis By consulting the literature and data, three kinds of buried domestic sewage treatment technologies are compared from the aspects of common processes, treatment effects, investment operation costs and scope of application, as shown in Table 1. Name buried type unpowered treatment technology buried power treatment technology buried integrated treatment technology common process anaerobic digestion + anaerobic biological filtration + contact oxidation biological contact oxidation method, SBR method, A / O and A2 / O The process biological contact oxidation method, SBR method, A/O and A2/O process treatment effect is close to the secondary treatment. The basic treatment can reach the standard. The secondary treatment can reach the standard treatment level up to 1000m3/d below 10000m3/d below 3000m3/d. The construction cost is lower and the capital construction cost is higher. The equipment cost is the main operating cost. The operating cost is basically lower than the operating cost. The maintenance management of 0.3 yuan/m3 is convenient. It can be operated by the PLC automatic control system. Urban living quarters in rural areas with complex economic and technical bases and inadequate drainage network; small town sewage treatment plants (station) areas with good economic and technological foundations; residential areas that cannot be covered by urban drainage networks; schools , hotels, restaurants, nursing homes, etc. 2 Conclusions Buried domestic sewage treatment technology is mature, occupying land, good treatment effect, wide application range, is the urban sewage treatment system Supplementary supplements provide a new way for the treatment of small dispersed pollution sources of domestic sewage. However, from the practical application situation, the technology still has some shortcomings, such as high investment operation cost, lack of emergency discharge measures, and short equipment life. If we can make breakthroughs in these problems through corresponding technical measures, the buried domestic sewage treatment technology will have a better prospect of promotion and application. Double head embroidery machine Double Head Computer Embroidery Machine,Computer Embroidery Machine Double Head,Industrial Sewing And Embroidery Machine,Industrial Digital Embroidery Machine Ningbo World Wide Electric techonology CO.,Ltd , https://www.nbmy-sewmachine.com