What are the principles of rural sewage treatment?

The "Eleventh Five-Year Plan" puts forward the major historical tasks of building a new socialist countryside, and clarifies the construction goals of "production development, affluent life, civilized rural style, neat village appearance, and democratic management". Strengthening the treatment of rural domestic sewage is an integral part of village appearance improvement and an important part of the construction of a new socialist countryside. Environmental pollution caused by rural domestic sewage is not only a potential safety hazard for rural water sources, but also aggravates the crisis of fresh water resources, making farmland irrigation unable to be effectively guaranteed, and endangering the survival and development of farmers. Therefore, strengthening the construction of rural domestic sewage collection, treatment and resource utilization facilities, avoiding rural water, soil and agricultural product pollution caused by direct discharge of domestic sewage, ensuring the safety of rural water sources and the physical and mental health of farmers is an important step in strengthening infrastructure in the construction of new rural areas. Construction and promotion of village improvement work is an important part of the work, and it is also an urgent issue that needs to be solved to improve the rural living environment. 1. Environmental problems caused by domestic sewage in rural areas Rural areas across the country produce more than 8 billion tons of domestic sewage every year. However, 96% of villages have no drainage channels and sewage treatment systems, and domestic sewage is discharged at will. Someone described the current situation of the living environment in rural China like this: If the villages across the country were merged into 10 villages, 4 villages would have no running water; 3 villages would have a well next to the pig pen or toilet for people to drink; 10 villages would have no running water; They all poured dirty water out; 9 villages still used traditional dry toilets; 9 villages still found random places to bury garbage; 4 villages couldn't get out when it rained; 5 villages couldn't enter at night. my country's rural domestic sewage has the following characteristics: (1) Wide and scattered. The scattered geographical distribution characteristics of villages cause sewage to be dispersed and difficult to collect. (2) There are many sources. In addition to sewage from human feces and kitchens, there is also sewage from household cleaning and domestic waste accumulation and infiltration. For example, laundry wastewater in Taihu Lake accounts for 21.6% of domestic sewage, and Chaohu and Dianchi Lake account for about 17.9%. (3) Growth is fast. With the improvement of farmers' living standards and changes in rural lifestyles, the production of domestic sewage has also increased. (4) The processing rate is low. Taking the rural pollution situation in Lishui City, Zhejiang Province as an example [3], the total amount of human feces and urine produced in the city's rural areas every year is about 1.8 million tons, and the amount treated by septic tanks is about 230,300 tons, with a treatment rate of only 12.9%. The wanton discharge of untreated domestic sewage seriously pollutes the rural ecological environment and directly threatens the health of farmers and the economic development of rural areas. On the one hand, untreated domestic sewage flows naturally into low-lying rivers, lakes, ponds and other surface water bodies, seriously polluting various water sources; on the other hand, domestic sewage is also the source of the spread of disease infections, easily causing infectious diseases and The occurrence and prevalence of endemic diseases and diseases affecting humans and animals. At present, the penetration rate of tap water in rural areas across the country is only about 34%, and more than 300 million farmers still have drinking water safety issues. Among the sampling test results of farmers' household water quality in Lishui City, Zhejiang Province, 72% of the 63 water samples had major indicators such as E. coli and turbidity exceeding the standard. The low water quality in water source areas has a direct causal relationship with the direct discharge of rural domestic sewage without treatment. 2. Foreign rural domestic sewage treatment technical routes The highest goal of sewage treatment is to achieve resource consumption reduction (Reduce), product value reuse (Reuse) and waste material recycling (Recycle). The utilization of water resources must be achieved from "water supply" The one-way linear water resources metabolism system of "water supply-drainage" has transitioned to the closed-loop water resources circulation system of "water supply-water supply-drainage-sewage reuse". For the decentralized domestic sewage in rural areas, the decentralized sewage treatment system (Decentralized Sanitation and Reuse, DESAR) with simple technology, guaranteed treatment effect, and easy operation and maintenance is a choice with the best comprehensive benefits. It includes sewage treatment and resource utilization. Taking advantage of the dual meaning, it emphasizes on-site processing and recycling of nutrients 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 worthy of learning and reference. (1) Australia's "FILTER" sewage treatment and reuse system. This system uses sewage irrigation to achieve the purpose of sewage treatment. It can effectively achieve the dual goals of pollutant removal and sewage reduction. It can not only meet the needs of crops for water and nutrients, but also It can reduce the nitrogen, phosphorus and potassium content in sewage and prevent sewage from being directly discharged into water bodies, causing eutrophication of water bodies. The removal rates of total phosphorus (TP), total nitrogen (TN), biological oxygen demand (BOD5) and chemical oxygen demand (CODcr) of this system can reach 97%~99%, 82%~86%, and 93% respectively. and 75%~86%[6](P79-81). (2) Soil capillary percolation system This system distributes sewage into a percolation ditch with a certain structure on the soil surface. Pollutants are treated and purified through physical, chemical, and microbial degradation and plant absorption and utilization. The United States, Japan, Australia, Israel, Russia and Western Europe and other countries have always attached great importance to the research and application of this system, and have standardized and serialized the process flow, purification methods and construction facilities, and compiled corresponding technical specifications.

This technology has high removal rates of suspended solids, organic matter, ammonia nitrogen, total phosphorus and E. coli, generally reaching 70%~90%[7](P953-964). It also has low infrastructure investment, low operating costs and easy maintenance. , the entire system is buried underground and will not emit odor, ensuring stable operation in winter and facilitating on-site treatment and reuse of sewage. Therefore, this technology has strong technical and economic advantages for the vast number of rural areas where the contradiction between water supply and demand is becoming increasingly tense and domestic sewage pollution is becoming increasingly serious. Units with wastewater that need to be treated can also go to the Wastewater Bao project service platform to consult companies with similar wastewater treatment experience. (3) Constructed wetland treatment system This system is generally composed of artificial substrate (mostly gravel) and marsh plants (reeds, cattails, rushes, hemp, etc.) growing on it. It is a unique "soil-plant- The "microbial" ecosystem uses the synergistic effects of various plants, animals, microorganisms and soil to gradually filter and absorb pollutants in sewage to achieve the purpose of purifying sewage. This technology has been widely used in countries such as Europe, North America, Australia, and New Zealand. Its disadvantages are that it requires a large amount of land, and must solve the problem of sufficient oxygen supply in the soil and water, and is affected by temperature and plant growth seasons. (4) Biofilm technology Biofilm method is an artificial treatment technology mainly used in dispersed domestic sewage treatment, including anaerobic and aerobic biofilms. Anaerobic or aerobic microorganisms adhere to the surface of the carrier and form a biofilm to adsorb and degrade pollutants in sewage to achieve purification purposes. This method has simple equipment, low operating costs and high processing efficiency. The reactor generally consists of three parts: filler (carrier), water distribution device and drainage system. The fillers used include inorganic (ceramsite, slag, activated carbon, etc.) and organic (PVC, PP, plastic, fiber, etc.). At present, new biofilm reactors and immobilized microbial technologies have also been extensively studied. (5) Stable pond This technology mainly uses the synergistic effect of bacteria and algae to remove pollutants in sewage. It has the advantages of low infrastructure investment, It has the advantages of low operating cost, simple maintenance, easy operation, effective removal of organic matter and pathogens in sewage, and no need for sludge treatment. Germany and France have 3,000 and 2,000 stabilizing ponds of various types respectively, while the United States has tens of thousands of stabilizing ponds of various types. Oswald of the United States proposed and developed high-efficiency algae ponds, which maximize the use of oxygen produced by algae, make full use of the biological relationship between bacteria and algae, and efficiently treat pollutants. (6) Integrated integrated device treatment technology The development of small and medium-sized sewage treatment integrated devices that integrate pretreatment, secondary treatment and advanced treatment is a trend in the development of decentralized sewage treatment at home and abroad. The integrated device studied in Japan mainly uses anaerobic-aerobic-secondary sedimentation tank combination technology, which has the functions of degrading organic matter and denitrification. Its effluent BOD?5?<20 mg/L, TN<20 mg/L, in recent years The membrane treatment technology developed in China can carry out in-depth treatment of BOD and TN. Many European countries have developed small sewage treatment integrated devices based on SBR, moving bed biofilm reactor, biological turntable and trickling filter technologies, combined with chemical phosphorus removal. 3. my country’s exploration of rural domestic sewage treatment. my country has been developing decentralized domestic sewage treatment technology since the 1980s. There are many non-power or micro-power low-energy integrated sewage treatment devices in various forms. has been applied, but the current usage rate of this decentralized technology is low and there are still many problems. On the one hand, the biological treatment efficiency is low, especially the nitrogen and phosphorus removal rate is very low. Nitrogen and phosphorus pollution is the main cause of eutrophication of water bodies. If a breakthrough cannot be made in this technology, the application prospects of this type of technology will inevitably be limited. On the other hand, the currently implemented decentralized sewage treatment only initially realizes the collection, treatment and discharge of decentralized sewage, and is far from realizing the real purpose of decentralized treatment - reuse, that is, on-site treatment and on-site reuse of sewage. Realize wastewater resource utilization. In view of the increasingly serious problem of domestic sewage in rural areas, proactive measures are urgently needed. In recent years, with the enhancement of local economic strength, especially developed provinces, after their economic development reaches a certain stage, they have gradually realized the importance of rural domestic sewage treatment problems, and began to adopt some practical, reasonable, low energy consumption and low operating cost methods. technology to treat sewage; some underdeveloped areas with dense populations also realize that if rural domestic sewage is not effectively treated, it will trigger a series of problems in rural medical and economic construction, and even cause the emergence and spread of infectious diseases. Therefore, the improvement of The level of attention paid to rural domestic sewage treatment issues. (1) Anaerobic biogas digester treatment technology In the practice of domestic sewage treatment in rural my country, the most versatile, frugal, and able to combine environmental and social benefits is the anaerobic biogas digester. It organically combines sewage treatment with its rational utilization and realizes the resource utilization of sewage. Most of the organic matter in the sewage produces biogas after anaerobic fermentation. The fermented sewage has most of the organic matter removed to achieve purification purposes; the biogas generated can be used as energy for bathrooms and household cooking; the sewage after anaerobic fermentation can be used For irrigation water and ornamental water. In rural areas, there are a large number of raw materials that can be used as biogas: crop straws and human and animal excrement.

Research shows that biogas fermentation of crop straw can increase its energy utilization efficiency by 4 to 5 times compared with direct combustion; biogas slurry and biogas residue as feed can increase the utilization of nutrients and energy by 20%; through anaerobic fermentation There is no loss of nutrients in manure (biogas slurry, biogas residue), carbon, phosphorus and potassium, and they are converted into active nutrients that can be directly used - the application of biogas fertilizer on farmland can replace some chemical fertilizers. Biogas digesters are simple in process, low in cost (approximately one thousand yuan per household), and have basically zero operating costs, making them suitable for farmers to use. Moreover, combined with the renovation of kitchens, toilets and pens in rural areas, pig house sewage and domestic sewage can be anaerobically fermented in biogas digesters and used as farmland fertilizer. After the biogas slurry is collected through the pipe network, it is centralized and purified until the effluent quality reaches national standards. emission. Biogas digester treatment technology has been effectively promoted and used in some places in my country. There are 352 villages in Zhejiang Province that have implemented domestic purification biogas projects. A total of 833,000 cubic meters of biogas digesters have been built, with an annual domestic sewage treatment of 81.7 million tons, an annual biogas output of 42.95 million cubic meters, and an annual replacement of nearly 30,000 standard coals. In conjunction with the construction of new rural areas, Sichuan Province has carried out the "Rural Cleaning Project" to build biogas digesters and domestic sewage anaerobic purification tanks on a household or joint-household basis to effectively solve rural environmental problems such as human and animal feces, domestic sewage, and garbage pollution, and the emergence of homes Clean and tidy new look of the village. (2) Stabilizing pond treatment technology In my country, especially in water-scarce and arid areas, stabilizing ponds are an effective method for implementing sewage resource utilization. In recent years, it has become a technology that our country has been promoting. Compared with traditional secondary biological treatment technology, high-efficiency algae ponds have many unique properties. For rural areas with relatively abundant land resources but relatively backward technical levels, it is a sewage treatment technology with more promotion value. Li Xudong and others used a high-efficiency algae pond system to treat rural domestic sewage in the Taihu area. The average removal rate of COD?cr? was more than 70%, the average removal rate of ammonia nitrogen (NH?3-N) was as high as 93%, and the average removal rate of phosphorus was 55% %; Chen Peng used high-efficiency algae ponds to treat urban domestic sewage and achieved stable treatment results: the average removal rates of CODcr, BOD5, NH3-N and TP reached 75%, 60%, 91.6% and 50% respectively. (3) Constructed wetland treatment technology At present, cities such as Beijing and Shenzhen have adopted this technology to treat domestic sewage. The Maliao River Wetland Project by Fuxian Lake in Chengjiang County, Yunnan Province was completed and put into operation in October 2003. It can purify more than 40,000 cubic meters of sewage every day. The purified water quality is better than the third category of surface water standards. Relevant studies have shown that when the concentration of influent pollutants is low, the removal rate of BOD5 in constructed wetlands can reach 85% to 95%, the removal rate of CODcr can reach more than 80%, and the removal rates of phosphorus and nitrogen are respectively Can reach 90% and 60%. (4) Soil infiltration technology Underground soil infiltration method has received increasing attention in our country. Research conducted by the Shenyang Institute of Applied Ecology, Chinese Academy of Sciences during the “Eighth Five-Year Plan” and “Ninth Five-Year Plan” periods showed that it is feasible to use underground soil infiltration method to treat domestic sewage in cold regions in northern my country, and the effluent can be reused as reclaimed water; in 1992, Beijing The Academy of Environmental Protection Sciences has conducted research on the purification effect of underground soil capillary percolation in treating domestic sewage and the utilization of green space; Tsinghua University was the first to promote the application of underground soil percolation systems in rural areas in 2000, a major project of the Ministry of Science and Technology, and achieved Good results: It has high removal rate and stability for organic matter, nitrogen, phosphorus, etc. in domestic sewage. The removal rates of CODcr, BOD5, NH3-N and TP are greater than 80%, 90%, 90% and 98 respectively. %. In addition, Zhejiang, Guangdong, Tianjin and Jiangsu have also explored and applied technical methods such as powerless, underground anaerobic treatment systems, rainwater and sewage separation pipe network transportation and centralized treatment, and biological sterilization to treat sewage. Tried and made some progress. 4. Policy approaches to speed up rural domestic sewage treatment Protecting the rural water environment is the basis for ensuring the development of agricultural production and creating a beautiful countryside. Carrying out rural domestic sewage treatment work is necessary to change the current situation of disorderly discharge of rural domestic sewage, improve farmers' living conditions and build a new socialist countryside. There are more than 600,000 administrative villages and more than 2.5 million natural villages in our country, which are home to more than 200 million rural households. Due to the vast differences in local conditions, rural domestic sewage treatment cannot implement a one-size-fits-all policy. We must adapt to local conditions, provide classified guidance, and propose policies that are consistent with the actual conditions of each region. Domestic sewage treatment methods and measures. (1) Treat rural domestic sewage as an important part of new rural construction. It is necessary to make full use of the good policy environment of the country's new rural construction to strengthen the treatment of rural domestic sewage in various places. Based on the various causes of domestic sewage pollution in rural areas, it is necessary to build supporting sewage treatment facilities in conjunction with the work of improving toilets, kitchens and housing estates in the construction of new rural areas. Comprehensive measures should be taken in the formulation of relevant policies and regulations, the cooperation of supervision and management, and the establishment of a technical support system for comprehensive rural water pollution control to strengthen the control of pollution sources, promote the construction and effective operation of sewage treatment facilities, and achieve the improvement of the rural water environment.

(2) Determine the technical route for domestic sewage treatment in various regions according to local conditions. Based on the current situation that my country's rural areas are generally underdeveloped, the economic and social development levels, regional characteristics, natural geographical conditions and environmental objectives of rural areas in various regions are different. The vast majority of rural areas should adopt economic Sewage treatment technology that is effective, simple, resource-saving, reliable in process and highly integrated with the local natural environment can make domestic sewage discharge and treatment harmless and resourceful according to local conditions. In some rural areas with densely distributed villages and good economic development levels, highly efficient and enhanced micro-power ecological treatment integrated technology and equipment have great technical and economic advantages; in other vast rural areas with centralized water supply, it can be based on their socio-economic development According to the conditions and water environment protection objectives, a moderately strengthened non-power composite ecological treatment integrated system will be constructed by transforming rural rivers, ponds and wetlands. These integrated technologies and equipment have potential advantages in treating rural domestic sewage under centralized water supply conditions due to their significant features such as low cost, high efficiency, and no power or micro power. (3) Continue to strengthen research on rural domestic sewage treatment technology. Due to the large number of people in rural areas in my country, domestic sewage treatment technology has long-term benefits and a broad market. Colleges and universities and scientific research institutions must be mobilized to strengthen research on related technologies. In view of the main problems existing in current treatment technology, research and develop 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 and increase nitrogen removal. The function of phosphorus is to control eutrophication of water bodies. (4) Raise funds for the construction and operation of domestic sewage treatment facilities from multiple sources Rural domestic sewage treatment has a strong public welfare nature and requires a certain scale of capital investment. It is difficult to rely solely on farmers' own investment. It is necessary to combine the practice of new rural construction and adopt methods such as national support, local subsidies, farmer support and enterprise participation to widely raise funds and form a participation mechanism with diversified investment and multi-channel mobilization, so that domestic sewage treatment projects can be successfully implemented and operation. (5) To strengthen the planning of rural domestic sewage treatment construction, we should effectively combine anaerobic and aerobic biological artificial treatment technology with natural purification systems on the basis of absorbing and learning from foreign advanced technologies. The planning should be based on the rural economic level, regional characteristics, and Domestic sewage treatment processes and effective operation and management models that are suitable for natural conditions and environmental objectives. Domestic sewage treatment should be combined with the adjustment of local economic structure, develop green, pollution-free industries and products, effectively develop and utilize animal and plant resources in the process of ecological pollution control, and achieve a virtuous cycle of water, sustainable use of water resources and Promote the breeding and growth of animals and plants. (6) Standardize market access standards and restrict inferior equipment from entering the market. At present, the market competition for small sewage treatment equipment in my country is very fierce, and there is vicious competition. Moreover, the design is not standardized, there is a lack of unified technical requirements and design standards, and there is a lack of consideration for operation and management. , bringing great risks and hidden dangers to future operation and management. Technical standards, design rules and operating specifications for decentralized sewage treatment should be proposed based on my country's national conditions and foreign experience, so as to standardize engineering design and operation management, and promote the marketization and industrialization of new results.

Strengthen project supervision and management, improve the construction quality and operation quality of treatment facilities, and ensure that treated sewage can be discharged up to standard