What is the principle of rural sewage treatment?

"Eleventh Five-Year Plan" puts forward the construction of a new socialist countryside, a major historical task, and clearly defined "production development, affluent life, civilized countryside, village cleanliness, democratic management" construction goals. Strengthening the treatment of sewage in rural areas is an integral part of the improvement of village appearance and an important part of the construction of the new socialist countryside. Environmental pollution caused by rural sewage is not only a potential safety hazard for rural water sources, but also exacerbates the crisis of freshwater resources, makes irrigation of arable land ineffective, and jeopardizes the survival and development of farmers. Therefore, to strengthen the construction of rural sewage collection, treatment and resource utilization facilities, to avoid the pollution of rural water, soil and agricultural products caused by the direct discharge of sewage, and to ensure the safety of rural water sources and the physical and mental health of farmers, it is an important part of the new rural construction to strengthen the infrastructure construction and to promote the improvement of villages, and it is also an urgent problem that needs to be solved for the improvement of the rural living environment.　First, the environmental problems arising from the rural sewage generated by the country's rural areas produce more than 8 billion tons of sewage each year, while 96% of the villages do not have drainage channels and sewage treatment systems, sewage discharged at will. Some people describe the current situation of the human environment in China's rural areas in this way: if the country's villages are combined into 10 villages, 4 villages do not have piped water; 3 villages in the pigsties or toilets next to a well for people to drink; 10 villages are dirty water to the outside world; 9 villages are still using the traditional dry latrines; 9 villages are still randomly find a place to fill up landfill garbage; 4 villages are not able to get out of the rains; 5 villages can not get in the night.　　China's rural sewage has the following characteristics: (1) wide and scattered. The geographic distribution of villages is characterized by dispersed geographical distribution resulting in scattered sewage, which is difficult to collect. (2) Multiple sources. In addition to sewage from human feces and kitchen, there is also sewage generated from household cleaning and leaching of domestic garbage piles. For example, laundry wastewater from Taihu Lake accounts for 21.6% of domestic sewage, and about 17.9% from Chaohu Lake and Dianchi. (3) Rapid growth. With the improvement of farmers' living standards and the change of rural lifestyles, the amount of domestic sewage generated has also grown. (4) Low treatment rate. Lishui City, Zhejiang Province, as an example of rural pollution [3], each year the city's rural human feces and urine produced a total of about 1.8 million tons, the amount of septic tank treatment is about 230,300 tons, the treatment rate of only 12.9%.　　Untreated sewage is discharged indiscriminately, seriously polluting the rural ecological environment, directly threatening the health of the masses of farmers and the economic development of rural areas. On the one hand, untreated sewage flows into low-lying rivers, lakes and ponds and other surface water bodies, seriously polluting all kinds of water sources; on the other hand, sewage is also a source of spread of disease contagion and spread of diseases, easy to cause part of the region of infectious diseases, endemic diseases and human and animal **** disease occurs and prevalence. At present, the national rural water penetration rate is only about 34%, there are more than 300 million farmers have drinking water safety problems. In Lishui City, Zhejiang Province, farmers in the water quality of household water sampling test results, 63 water samples of E. coli, turbidity and other major indicators exceeded 72%. The low water quality of the water source and rural sewage untreated direct discharge has a direct causal relationship.　　Second, foreign rural sewage treatment technology route The highest goal of sewage treatment is to achieve resource consumption reduction (Reduce), product value reuse (Reuse) and waste material recycling (Recycle), the use of water resources to be realized from the "water supply - water - drainage" unidirectional line. The utilization of water resources should realize the transition from the unidirectional linear water resources metabolism system of "water supply - water use - drainage - sewage reuse" to the closed-loop water resources recycling system. For the decentralized domestic sewage in rural areas, the decentralized sewage treatment system (Decentralized Sanitation and Reuse, DESAR), which has a simple process, guaranteed treatment effect, and easy operation and maintenance, is a choice with the best comprehensive benefits, which contains the double significance of wastewater treatment and resource utilization, and emphasizes the quality of on-site treatment and recovery of nutrients as much as possible. Nutrients are recovered as much as possible.　　Some foreign countries have accumulated a lot of experience in the research and application of rural decentralized domestic sewage treatment technology, which is worth studying and learning from.　　(a) Australia's "FILTER" sewage treatment and reuse system The system uses sewage irrigation to achieve the purpose of sewage treatment, which can effectively achieve the dual objectives of pollutant removal and sewage reduction, both to meet the crop's demand for water and nutrients, but also to reduce the nitrogen, phosphorus and potassium content of sewage, to avoid direct discharge of sewage into the water body, resulting in water enrichment. water body, resulting in eutrophication of the water body. The removal rates of total phosphorus (TP), total nitrogen (TN), biological oxygen demand (BOD5) and chemical oxygen demand (CODcr) by this system can reach 97%~99%, 82%~86%, 93% and 75%~86%, respectively [6] (P79-81).　　(ii) Soil capillary infiltration system This system will cast the sewage allocation to the soil surface with a certain structure of the infiltration trench, pollutants through physical, chemical, microbial degradation and plant absorption and utilization of treatment and purification. The United States, Japan, Australia, Israel, Russia and Western Europe and other countries have been attaching great importance to the research and application of the system, in the process, purification methods and construction facilities to achieve stereotypes and serialization, and the preparation of the corresponding technical specifications. The technology of suspended solids, organic matter, ammonia, total phosphorus and Escherichia coli removal rate are high, generally up to 70% ~ 90% [7] (P953-964), and less capital investment, low operating costs, easy maintenance, the entire system is buried in the ground, does not emit odor, can ensure a more stable operation in winter, to facilitate the local treatment of sewage and reuse. Therefore, for the increasingly tense contradiction between supply and demand of water resources, sewage pollution is becoming more and more serious in the vast rural areas, the technology has a strong technical and economic advantages. Wastewater treatment units, you can also consult the sewage treasure project service platform with similar sewage treatment experience.　　(C) Artificial wetland treatment system The system is generally composed of artificial substrate (mostly gravel) and marsh plants (reeds, cattail, cordyceps and hemp, etc.), which is a unique ecosystem of "soil-plants-microorganisms", utilizing a variety of plants, animals, microorganisms and soil. It is a unique "soil-plant-microorganism" ecosystem, which utilizes various plants, animals, microorganisms and soil's ****same action to filter and absorb pollutants in sewage step by step to achieve the purpose of purifying sewage. This technology has been widely used in Europe, North America, Australia and New Zealand, etc. Its disadvantage is that it requires a large amount of land and has to solve the problem of adequate oxygen supply in the soil and water, as well as being affected by the temperature and plant growing season.　　(iv) Biofilm technology The biofilm method is an artificial treatment technology mainly applied to decentralized domestic wastewater treatment, including two kinds of anaerobic and aerobic biofilms. Anaerobic or aerobic microorganisms attach to the surface of the carrier to form a biofilm to adsorb and degrade the pollutants in the sewage to achieve the purification purpose. This method has simple equipment, low operating costs and high treatment efficiency. The reactor is generally composed of three parts: filler (carrier), water distribution device and drainage system, using inorganic filler (ceramic, slag, activated carbon, etc.) and organic (PVC, PP, plastic, fiber, etc.). At present, the new biofilm reactor and immobilized microbial technology has also been widely studied (e) Stabilization pond The technology is mainly the use of bacteria and algae *** with the role of removing pollutants in the sewage, with little capital investment, low operating costs, simple maintenance, easy to operate, can effectively remove organic matter and pathogens in the sewage and no need to deal with the advantages of sludge. Germany and France, respectively, there are all kinds of stabilization ponds 3,000 and 2,000, and the United States has all kinds of stabilization ponds tens of thousands. Oswald of the United States proposed and developed a high-efficiency algae ponds, maximizing the use of oxygen produced by algae, making full use of bacteria and algae **** biological relationship, efficient treatment of pollutants.　　(F) integrated integrated device treatment technology The development of small and medium-sized sewage treatment integrated device integrating pre-treatment, secondary treatment and depth treatment is a trend in the development of decentralized sewage treatment at home and abroad. Japan's research integrated device is mainly used anaerobic - aerobic - two-sink combination process, both degradation of organic matter and denitrification function, its effluent BOD?5?<20 mg / liter, TN <20 mg / liter, in recent years the development of membrane treatment technology, can be on the BOD and TN for deep treatment. Many European countries have developed SBR, moving bed biofilm reactor, biological rotary table and drip filtration tank technology, combined with chemical phosphorus removal of small sewage treatment integrated device.　　Third, China's exploration of rural sewage treatment in China from the 80s of the last century to carry out the development of decentralized treatment of domestic sewage technology development and development work, many forms of non-powered or micro-powered low-energy type of integrated sewage treatment devices have been applied, but at present the decentralized technology of the use of a relatively low rate, there are still many problems. On the one hand, the biological treatment efficiency is low, especially manifested in the very low removal rate of nitrogen and phosphorus. Nitrogen and phosphorus pollution is the main cause of eutrophication of water bodies, if we can not make a breakthrough in this technology, the prospects for the application of this type of technology will inevitably be limited. On the other hand, the current implementation of decentralized sewage treatment is only a preliminary realization of decentralized sewage collection, treatment and discharge, far from realizing the real purpose of decentralized treatment - reuse (Reuse), that is, in situ treatment of wastewater and local reuse, to achieve sewage resources. In view of the increasingly serious problem of rural sewage, there is an urgent need to take positive measures. In recent years, with the enhancement of local economic strength, especially in developed provinces after a certain stage of economic development, gradually recognized the importance of rural sewage treatment problems, and began to use some practical, reasonable, low energy consumption and low operating costs of the technology to deal with sewage; some densely populated underdeveloped areas also recognize that, if you don't take effective treatment of rural sewage, it will trigger the rural medical and Economic construction and other aspects of the series of problems, and even cause the generation and spread of infectious diseases, thus, raising the importance of the issue of rural domestic sewage treatment.　　(I) Anaerobic biogas digester treatment technology In China's rural sewage treatment practice, the most versatile, thrifty, and able to reflect the combination of environmental benefits and social benefits of sewage treatment is anaerobic biogas digester. It organically combines sewage treatment with its rational use and realizes the resourcefulness of sewage. Most of the organic matter in the sewage is fermented anaerobically to produce biogas, and the fermented sewage is purified by removing most of the organic matter; the biogas produced can be used as energy for cooking in bathrooms and homes; and the anaerobically fermented sewage can be used as water for watering and ornamental water. In the countryside, there are a lot of raw materials that can be utilized as biogas: crop residues and human and animal manure. Research shows that crop residues can increase its energy utilization efficiency by 4-5 times compared with direct combustion through biogas fermentation; the utilization rate of nutrients and energy can be increased by 20% by using biogas liquid and biogas residues as fodder; through the anaerobic fermentation of manure (biogas liquid and biogas residues), there is no loss of nutrients of carbon, phosphorus and potassium, and it is transformed into active nutrients that can be directly utilized. -Biogas fertilizer applied to farmland can replace some chemical fertilizers. The biogas digester process is simple, low-cost (about one thousand yuan for a household), and the operating cost is basically zero, which is suitable for farmers' families to adopt. Moreover, in combination with rural kitchen, latrine and circle conversion, pigsty sewage and domestic sewage can be used as farmland fertilizer after anaerobic fermentation in biogas digesters, and the methane liquid is collected through pipeline network and then centrally purified, and the effluent water quality meets the national standard and then discharged.　　Biogas digester treatment technology has been effectively promoted and used in some places in China. In Zhejiang province, 352 villages have implemented biogas projects for life purification, with a cumulative total of 833,000 cubic meters of biogas digesters, treating 81.7 million tons of domestic wastewater annually and producing 42.95 million cubic meters of biogas, which can replace nearly 30,000 tons of standard coal annually. Sichuan Province, in conjunction with the construction of new rural areas, to carry out "rural cleaning project", to households or joint households as a unit, the construction of biogas digesters and domestic sewage anaerobic purification tanks, effective solution to human and animal feces, domestic sewage, garbage pollution and other rural environmental problems, the emergence of a clean home and the village of a clean and tidy new outlook.　　(ii) stabilization pond treatment technology in our country, especially in water-scarce arid areas, stabilization pond is the implementation of sewage resource utilization of effective methods, in recent years has become China's efforts to promote a technology. Compared with the traditional secondary biological treatment technology, high-efficiency algae ponds have many unique properties, for the relatively abundant land resources, but the technical level is relatively backward in rural areas, it is a more popularized sewage treatment technology. Li Xudong et al. used high-efficiency algae pond system to treat rural domestic wastewater in Taihu Lake area, the average removal rate of COD?cr? is more than 70%, the average removal rate of ammonia nitrogen (NH?3-N) is as high as 93%, and the average removal rate of phosphorus is 55%; Chen Peng used the high-efficiency algae ponds to treat urban domestic wastewater, and achieved stable treatment results: the average removal rate of CODcr, BOD5, NH3-N and TP reaches 75%, 75%, 75%, 75%, 75%, 75%, 75%, 75%, 75%, 75% and 50% respectively, and the average removal rate of ammonia nitrogen and phosphorus is 55%, respectively. The average removal rates of CODcr, BOD5, NH3-N and TP reached 75%, 60%, 91.6% and 50% respectively.　　(iii) Artificial wetland treatment technology At present, Beijing, Shenzhen and other cities have adopted this technology to treat domestic sewage. The wetland project of Maguhe River by Fuxian Lake in Chengjiang County, Yunnan Province was completed and operated in October 2003, which can purify more than 40,000 cubic meters of sewage per day, and the purified water quality is better than the standard of three types of surface water. Relevant studies show that under the condition of low concentration of pollutants in the influent water, the removal rate of artificial wetland on BOD5 can reach 85%~95%, the removal rate of CODcr can reach more than 80%, and the removal rate of phosphorus and nitrogen can reach 90% and 60% respectively.　　(D) soil percolation technology Underground soil percolation method is increasingly being emphasized in China. Shenyang Institute of Applied Ecology, Chinese Academy of Sciences, "Eighth Five-Year Plan", "Ninth Five-Year Plan" period of research shows that in the cold northern regions of China, the use of underground soil infiltration treatment of domestic sewage is feasible, and the effluent can be reused as water; in 1992, the Beijing Municipal Research Institute of Environmental Protection Science In 1992, Beijing Research Institute of Environmental Protection Science conducted a research on the purification effect and green space utilization of underground soil percolation method for domestic sewage treatment; Tsinghua University, in the major project of the Ministry of Science and Technology of China in 2000, firstly popularized the application of underground soil percolation system in rural areas, and achieved good results: the organic matter and nitrogen, phosphorus and so on in domestic sewage have a high removal rate and stability, and the removal rate of CODcr, BOD5, NH3-N and TP is more than 80% respectively. TP removal rate of more than 80%, 90%, 90% and 98% respectively. In addition, zhejiang, guangdong, tianjin and jiangsu and other places were in no power, buried anaerobic treatment system, rain and sewage separation network transportation centralized treatment and biological treatment of sewage bacteria and other technology way to explore and try, also have made some progress.　　Fourth, accelerate the rural domestic sewage treatment policy approach to protect the rural water environment is to ensure the development of agricultural production, the creation of a beautiful countryside basis. To carry out rural sewage treatment is to change the status quo of disorderly discharge of rural sewage, improve the living conditions of farmers and the need to build a new socialist countryside. China has more than 600,000 administrative villages, more than 2.5 million natural villages, living in more than 200 million households, due to the situation of each place is very different, rural sewage treatment can not implement a one-size-fits-all policy, we must be adapted to local conditions, categorization guidance, put forward in line with the reality of each place of sewage treatment methods and measures.　　(A) the treatment of rural sewage as an important part of the construction of new rural areas to take full advantage of the national new rural construction of a good policy environment, to strengthen the treatment of rural sewage around. Based on the multiple causes of rural sewage pollution, the construction of sewage treatment facilities should be supported in conjunction with the new rural construction of latrines, kitchens and circles. Comprehensive measures should be taken in the formulation of relevant policies and regulations, supervision and management and the establishment of a technical support system for the comprehensive management of rural water pollution, to strengthen the control of pollution sources, promote the construction and effective operation of sewage treatment facilities, and realize the improvement of the rural water environment.　　(ii) to determine the technical route of domestic sewage treatment in various places according to local conditions Based on the status quo of general underdevelopment of China's rural areas, the level of economic and social development of rural areas, regional characteristics, natural geographic conditions and environmental objectives are not the same, the vast majority of the rural areas should be used cost-effective, simple and easy to implement, resource-saving, reliable and able to highly integrated with the local natural environment of the sewage treatment technology, according to local conditions to make the The discharge and treatment of domestic sewage is harmless and resourceful. In some villages distributed densely, the level of economic development is good in rural areas, efficient and strengthened micro-power ecological treatment integrated technology and equipment has great technical and economic superiority; other centralized water supply of the vast rural areas, according to its socio-economic development and water environmental protection objectives, through the transformation of rural rivers, ponds and wetlands, build a moderately strengthened composite ecological treatment of non-power integrated system. Integrated system. These integrated technologies and equipment have the potential advantage of treating rural domestic wastewater under centralized water supply conditions because of their low cost, high efficiency, no power or micro-power and other significant features.　　(C) continue to strengthen the rural sewage treatment technology research Due to China's rural areas are vast and numerous, sewage treatment technology has a long-term benefits and the vast market, we must mobilize colleges and universities and scientific research institutions to strengthen the relevant technology research. For the main problems existing in the current treatment technology, research and development of new three low and one high (low energy consumption, low investment, low cost and high efficiency) decentralized sewage resource treatment technology, and improve the depth of sewage treatment, increase the function of nitrogen and phosphorus removal in order to control the eutrophication of the water body.　　(D) raise funds for the construction and operation of sewage treatment facilities Rural sewage treatment has a strong public welfare, and requires a certain scale of capital investment, relying solely on the farmers themselves to invest in a certain degree of difficulty. To combine the practice of new rural construction, take the state support, local subsidies, farmer support and enterprise participation, etc., widely raise funds, the formation of diversified inputs, multi-channel mobilization of the participation mechanism, so that the sewage treatment project can be successfully put into practice and operation.　　(E) to strengthen the construction of rural sewage treatment planning To absorb and learn from foreign advanced technology on the basis of an effective combination of anaerobic, aerobic biological artificial treatment technology and natural purification system, planning and rural economic level, regional characteristics, natural conditions, environmental objectives compatible with the domestic sewage treatment process and effective operation and management mode. Domestic sewage treatment should be combined with local economic restructuring, the development of green, pollution-free industries and products, the effective development and utilization of animal and plant resources in the process of ecological sewage treatment, the realization of the virtuous cycle of water, sustainable use of water resources and the promotion of animal and plant breeding and growth.　　(F) standardize the market access standards, limit the entry of poor quality equipment into the market At present, China's small sewage treatment device market competition is very fierce, there is vicious competition, and the design is not standardized, the lack of uniform technical requirements and design standards, the lack of consideration for the operation and management, for the future operation and management of the operation and management of a great deal of risk and hidden trouble. Should be combined with China's national conditions, with reference to foreign experience, put forward for decentralized wastewater treatment of technical standards, design rules and operational specifications, so that the standardization of engineering design and operation and management standardization, to promote the development of new results of marketization and industrialization. Strengthen the supervision and management of the project, improve the quality of construction and operation of the treatment facilities, to ensure that the treated sewage can meet the discharge standards