1. The current situation of rural domestic sewage treatment

1.1 There are problems in urban sewage engineering

(1) The pollution of water bodies by the existing sewage pipe network still exists. Since some urban areas are still confluence, it is impossible to avoid the situation of sewage entering the river during the rainy season and polluting the water body.

(2) The current drainage system is not perfect. Some neighborhoods and urban villages have not built drainage stations or the collected sewage has not been discharged into the sewage treatment plant, and some existing stations are no longer available.

(3) The treatment effect of sewage treatment is unstable. Current situation of sewage plants Due to the partial use of rain-sewage combined system system, the amount of sewage is large in the rainy season, which has a short-term load impact on the sewage plant and adversely affects the treatment effect of the sewage plant.

1.2 Current situation of rural domestic sewage treatment

(1) Source characteristics of rural domestic sewage. The main sources of rural domestic sewage in Zoucheng City are the following three aspects: domestic washing sewage, such as laundry, showering, washing the ground, etc.; second, kitchen sewage; The third is the drainage of feces and their flushing.

(2) Water quality characteristics of rural domestic sewage. Rural domestic sewage mainly contains organic matter, ammonia, nitrogen, phosphorus, bacteria, viruses, parasite eggs, etc., generally BOD5≤150mg/L, CODcr≤350mg/L, NH3-N≤35mg/L; pH value 6-8, SS≤ 400mg/L, color (dilution factor) ≤100, from the data analysis, rural domestic sewage contains a very small amount of metals and other toxic and harmful substances, nitrogen and phosphorus account for a certain proportion, water quality fluctuations are relatively large, and biodegradability is good.

(3) The spatio-temporal distribution characteristics of rural domestic sewage.

The discharge of rural domestic sewage is directly related to the degree of rural economic development and population density, the discharge of domestic sewage in townships is more than that of villages, the discharge of domestic sewage in economically developed townships is more than that of underdeveloped townships, and the domestic drainage of rural residents in Taiping, Beisu and other townships is relatively high, and the concentration of ammonia and phosphorus in sewage is relatively high. The organic matter content is lower than that of underdeveloped townships, and the discharge of rural domestic sewage in economically underdeveloped Tianhuang Town and Zhangzhuang Town is smaller, but the concentration of pollutants is high.

2. Planning of rural sewage treatment system

The sewage treatment mode in this region is divided into four levels according to the sewage treatment model of the United States: in-situ treatment, cluster treatment, community centralized treatment, and regional centralized treatment, which correspond to retail, rural, small-town, and urban-scale sewage. At the same time, according to the risk of environmental sensitivity, public health, sewage characteristics and treatment complexity, the US EPA proposes five management models of sewage decentralized treatment system: owner consciousness, maintenance contract system, operation permit system, management entity operation and maintenance system, and management entity ownership system.

2.1 Centralized treatment plan

(1) Centralized treatment in urban areas and surrounding rural settlements.

After all sewage in each village is collected through sewage pipes, it is uniformly connected to the sewage pipe network of neighboring municipalities, and then used the urban sewage treatment plant for unified treatment. This collection and treatment mode has the advantages of low investment, short construction period, fast effect, and convenient unified management, which not only saves the investment of sewage treatment stations in rural areas, but also has good sewage treatment effect and operation management guarantee.

(2) Centralized treatment plan for townships and surrounding rural settlements.

Towns that cannot be included in the urban sewage pipe network need to build township sewage treatment plants, and villages located within 1km of the main pipe of the township and sewage can flow into the main pipe should be given priority to be included in the centralized treatment of the township sewage pipe network, and the discharge standards of the planned township sewage treatment plants should reach the first-class A standard.

2.2 Decentralized processing

(1) Joint treatment of multiple settlements (villages).

In the dense village area with a large distribution of plain areas in the Zou City area, the residential population is concentrated and contiguous, and sewage treatment stations can be jointly built for unified collection and centralized treatment, that is, the residential agglomeration area chooses low-lying areas with drainage conditions to jointly build sewage treatment stations, and multi-villages build a unified sewage pipe network, and the sewage collected by farmers is collected into the pipe network and transported to the sewage treatment station for treatment. It is planned that new rural communities need to build sewage treatment stations, and residential areas around new rural communities can consider extending the pipe network for sewage collection and centralized treatment, and the sewage treatment and discharge standards will reach the first-class B standard.

(2) Centralized treatment of a single settlement (village).

It is suitable for village settlements with concentrated rural households, large village population and far away from towns, mainly through the construction of sewage pipe network to collect sewage, concentrate on small and medium-sized sewage treatment equipment and adopt ecological treatment mode to treat rural sewage, which can achieve the advantages of cost saving, simple construction, convenient management, and guaranteed effluent water quality.

(3) Single-household or decentralized processing mode.

It refers to the collection of farmers' sewage by joint households or single households and then treated separately, which has the characteristics of flexible layout, saving pipe network laying costs, simple construction, etc., and is suitable for villages with small population size, too small sewage volume to form runoff and cannot be collected.

2.3 Rural domestic sewage treatment process

(1) "Microdynamic anaerobic aerobic + landscape green space" treatment technology.

The treatment process uses the method of ecosystem management to purify sewage, only micro power or less power, low operating cost, relatively simple management, and has the effect of beautifying the environment, which is suitable for large-scale decentralized sewage treatment, the sewage volume can be 50~200m3/d, and the serving population is about 250~1000 people and 60~250 households. The process flow is: sewage → grid→ microdynamic anaerobic aerobic tank→ sedimentation tank→landscape green space→ discharge This technology combines microdynamic anaerobic aerobic sewage treatment technology with landscape construction, and compared with the pure ecological treatment process, it has strong adaptability to the climate and stable and reliable treatment effect; The operating cost is low, the amount of sludge generated is small, the maintenance is simple, and the landscape green space can beautify the surrounding environment and reduce secondary pollution.

(2) "Domestic sewage purification digester" treatment technology.

The treatment process is a combination of anaerobic fermentation technology and facultative biological filtration technology, under the condition of anaerobic and facultative anaerobic to decompose and convert the organic matter in the domestic sewage into CH4, CO2 and water, to achieve the purpose of purification and treatment of domestic sewage, this mode is suitable for small-scale decentralized sewage treatment, the sewage volume should be 20~50t/d, serving a population of about 100~250 people, 25~60 households. The process flow is:

The sewage → discharged → → the front treatment area (anaerobic fermentation) → the post-treatment area (biological filter) of the grid.

This technology combines anaerobic aerobic sewage treatment technology with rural biogas energy and ecological agriculture, and the treatment effect is stable and reliable. Low operating cost, easy maintenance, and less secondary pollution.

(3) "buried anatomic anaerobic treatment" treatment technology.

The treatment process is also the use of anaerobic microorganisms to ferment and decompose organic matter to achieve sewage purification, this mode is suitable for small-scale decentralized sewage treatment, the sewage volume should be 50~150t/d, serving a population of about 200~500 people, 50~100 households. The process flow is: sewage → grid→ multi-stage anaerobic → contact biochemical → discharge.

This technology combines anaerobic aerobic sewage treatment technology with rural biogas energy and ecological agriculture, and the treatment effect is stable and reliable. Low operating cost, easy maintenance, and less secondary pollution.

3. Conclusion

Only by continuously strengthening the construction of sewage collection, treatment and resource utilization facilities can we effectively avoid serious pollution of water, soil and agricultural products caused by domestic sewage, and ensure the safety of centralized drinking water sources and people's physical and mental health. Therefore, domestic sewage treatment is of great practical significance, has far-reaching social impact on improving people's livelihood and building a harmonious society, and has considerable economic, social and environmental benefits.