Discussion on the application of rural sewage treatment technology in different regions of China

With the gradual acceleration of China's urbanization process, the construction of sewage treatment facilities in the majority of rural areas has also received greater attention. Due to the great differences in topography, climate, economy and living habits in different regions, the selection of rural sewage treatment technology needs to be adjusted according to the actual situation in each region to maximize its effectiveness. Based on the basic geographical characteristics of the six regions in China, this paper will make a comparative analysis of the generation characteristics of rural domestic sewage in the region, and briefly discuss the application conditions of the current major mainstream rural sewage treatment technologies in different areas of China, in order to provide references for exploring rural domestic sewage treatment technologies according to local conditions.

Regional characteristics of rural sewage treatment in China

According to the "Regional Rural sewage Treatment Technical Guide" issued by the Ministry of Housing and Urban-Rural Development, China's rural domestic sewage treatment work is divided into six regions: northeast, North China, Northwest, central and South, southeast and southwest. The reference index of domestic sewage quality applicable to localization in six regions is the basic reference for the construction of rural sewage treatment facilities. The characteristics and main problems of rural sewage production in each region are analyzed as follows.

Northeast region

China's northeast generally refers to the narrow sense of the northeast three provinces (Heilongjiang, Jilin, Liaoning) and the broad sense of Inner Mongolia East five league region. The whole region is located in the middle temperate zone and the cold temperate zone, which is a temperate monsoon climate, with mild and rainy summer and cold and dry winter. The terrain conditions are mainly in the vast northeast plain, but also distributed in the large and small Xingan Mountains, Changbai Mountains, Liaodong hills and other mountainous and hilly areas. Rural areas in Northeast China are mostly in economically underdeveloped areas, where villages are dispersed and sewage treatment levels are low. For example, in 2018, only 4.9% of rural areas in Jilin Province built centralized or partially centralized treatment facilities. Affected by the cold climate in winter, the average daily discharge of rural sewage in Northeast China is low, and the content of nitrogen and phosphorus in water is high. The extremely cold climate will greatly restrict the efficiency of the biochemical process of sewage treatment. Therefore, the selection of sewage treatment technology in northeast China should take low temperature adaptability, low cost, easy maintenance and high nitrogen and phosphorus removal efficiency as the main objectives.

North China

North China mainly refers to the North China Plain area of Beijing, Tianjin, Inner Mongolia, Hebei, Shanxi, Shandong, Henan and other provinces and cities most of the area. The whole is a temperate monsoon climate, hot and rainy in summer, cold and dry in winter. The terrain is mainly plain, and water resources are scarce. North China is the main agricultural producing area of China, with dense rural population, numerous villages and huge sewage production, but the per capita sewage production is less than that of the south. The level of economic development in the region is relatively unbalanced, the infrastructure of some arid areas is relatively backward, the phenomenon of disorderly discharge is common, the sewage treatment level in some rural areas is low, and the indicators of organic matter, nitrogen, phosphorus and suspended matter in the effluent are high. In North China, the whole year is relatively dry, and the precipitation is usually concentrated in summer. The selection of sewage treatment technology should focus on the circulation of water resources.

Northwest China

The northwest region mainly includes most of Xinjiang, Qinghai, Gansu, Ningxia, Shaanxi and other provinces. The region is mainly in the temperate and warm temperate continental climate, the local temperate monsoon climate, the overall drought, the average annual temperature is low. The terrain is mainly plateau, mountain and desert, and the population mainly gathers in Hetao plain and oasis. Rural areas in the northwest have traditionally used little water for living, with most villages still using dry latrines and lacking artificial drainage systems. And due to the large degree of rural population loss, many sewage treatment facilities are difficult to operate normally. For the arid areas in the northwest, the sewage treatment facilities should adopt the economical and simple technical route as far as possible.

Southeast region

The southeast region is mainly the provinces along the southeast coast of our country, the southeastern hills run through the whole region, the internal rivers are densely covered, and the countryside is usually distributed in the mountain valley zone. The whole is basically a subtropical monsoon climate, hot and rainy in summer, mild and humid in winter. The level of rural economic development in the southeast coastal areas is uneven, the economy of the Yangtze River Delta and the Pearl River Delta is developed, the rural population density is large, and the problems of water pollution and water shortage are obvious. Fujian, Guangdong, Hainan and other provinces have a large area of underdeveloped mountainous areas, a large number of rural population, and the cost of construction of sewage pipe network in hilly areas is high, and sewage is generally discharged directly into rivers in the early stage. Considering the rural water environment problem and the difference of economic development level in southeast China, targeted sewage treatment technology should be selected in practice.

Central and southern region

The central south region refers to most areas on both sides of the Qinling-Huaihe River line. The terrain and geomorphology in the region are highly complex, with mountains, hills and plains ubiquitous, dense river networks, and most of them are located in important water systems. The whole is located in the warm temperate zone to the middle temperate monsoon climate zone, with high temperature and rain in summer and little rain in winter. The level of rural economic development in the region is not balanced, and because it is located in the customary border between the north and the south, the difference of rural living habits is obvious. The villages on the northern side of the Qinling-Huaihe River line often have dry latrines and composting habits, and the amount of sewage produced is small, and simpler treatment technologies such as septic tanks can be used. The villages on the south side of the Qinling-Huaihe River line are mostly built near water, and the sewage is often directly discharged into ponds and other water bodies, which is suitable for using constructed wetlands or multi-pond technology of existing ponds.

Southwest China

The southwest region includes Sichuan, Guizhou, Yunnan, Chongqing, Tibet, Guangxi and other provinces and cities, with a large regional span, and the terrain is dominated by plateaus, mountains and hills. There are various climatic conditions in the region, such as monsoon climate, plateau climate and alpine cold zone climate. Except for the gentle terrain of Sichuan Basin, which has been an important agricultural area since ancient times, other regions are mainly mountainous rural areas with relatively backward economic development level, and residents' traditional awareness of sewage treatment is relatively weak. With the development of rural tourism in recent years, the sewage production in rural areas in southwest China has increased rapidly, and the demand for supporting construction of sewage treatment infrastructure in rural areas is also increasing. It is suitable to adopt corresponding decentralized or centralized treatment facilities according to the scale of personnel gathering and topography.

At present, the sewage treatment modes in villages and towns in China include scattered treatment, centralized treatment in villages and treatment in urban drainage network. Generally, small settlements of single or several households are suitable for decentralized small sewage treatment equipment or natural treatment mode, larger villages can build village-level sewage treatment stations for centralized treatment, and rural villages can discharge sewage into the urban sewage network and transport it to the urban sewage treatment plant.

China's rural distribution area is wide, but with the gradual rise of urbanization rate, the future rural population will be significantly reduced, rural sewage treatment technology is bound to develop in the direction of decentralization, small, low cost and high efficiency. Using the existing natural conditions as much as possible and integrating the ecological sewage treatment technology with the environment will be the main trend of the future construction of rural sewage treatment facilities in China. According to the characteristics of decentralized and centralized sewage treatment technology, this paper discusses the differences of technical routes in six regions in China.

Distributed processing technology

The distributed sewage treatment technology includes small constructed wetland, land treatment, stabilization pond, purification biogas digester, and small integrated treatment equipment. According to the "Rural domestic sewage treatment Project construction and investment Technical Guide" issued by the Ministry of Ecology and Environment, the capital construction cost of commonly used distributed treatment technology is mainly 1500 yuan/T-3000 yuan /t, but the construction cost of small integrated treatment equipment can reach 10,000 yuan /t or more. The treatment scale of most distributed treatment facilities is less than 10t/d, and the stabilization pond technology is more suitable for large-scale distributed sewage.

In the engineering practice in different areas of our country, the choice of distributed sewage treatment technology should consider the local terrain and climate conditions. In northern China, the climate is generally dry, water resources are scarce, and sewage discharge is small, which is suitable for ecological treatment technology such as land percolation, constructed wetland and stabilization pond. However, considering the cold winter in the northern region, especially in the northeast, the effect of conventional ecological treatment technology will be affected to a certain extent, and it is necessary to improve the technical facilities such as constructed wetlands and stabilization ponds according to the regional climate characteristics. In northwest China, perennial drought, poor water resources, fragile ecological conditions, less water consumption for residents, suitable for septic tank or biogas pond treatment, larger villages can use upflow anaerobic biological filter, ditch land treatment, low temperature oxidation pond and other processes, but also make full use of abandoned ponds or swallowlands in arid areas for transformation.

In the south of China, there are many mountains and hills and dense river networks. The technology of land infiltration and constructed wetland may be restricted by the existing rural terrain and slope. Therefore, in the selection of distributed sewage treatment technology, rural areas in southern China are suitable to consider the existing terrain factors and develop integrated composite processes of constructed wetlands, stabilization ponds, septic tanks, biogas digesters, anaerobic biological treatment and other technical units. For example, constructed wetlands in mountainous areas of Hubei province combine the composite treatment processes of anaerobic and drop water contact oxidation. Anaerobic biological treatment + constructed wetland + oxidized pond complex engineering facilities in Yunnan Dianchi Basin countryside.

Centralized processing technology

The commonly used centralized treatment technologies of rural sewage include activated sludge method, oxidation ditch method, biological contact oxidation method, sequencing batch activated sludge method (SBR), membrane bioreactor method (MBR), and large-scale constructed wetland method. According to the survey of the preparation team of the "Technical Guide for the construction and investment of Rural domestic sewage treatment Projects", the treatment scale of China's rural centralized sewage treatment facilities is generally below 500m3/d, and most of the facilities serve a village population of less than 5,000 people. The treatment scale of centralized sewage treatment facilities varies greatly, and centralized treatment technology can be selected when the general daily treatment capacity exceeds 20t, and the treatment capacity can reach up to 2500t/d. SBR, MBR and other new technologies occupy a small area, easy operation and management, high removal efficiency and do not require the construction of supporting sedimentation tank, is a more promising rural sewage treatment technology, but the current investment and construction cost is still high.

Comparison of centralized treatment techniques for rural domestic sewage

The construction of centralized sewage treatment facilities has been explored for a long time in the rural areas with high economic development level such as Northeast, North and southeast of China. The winter temperature in Northeast China is low, so it is suitable to adopt improved biological treatment, ecological treatment and multiple composite processes for the high cold climate. For example, a rural area in Heilongjiang Province adopted the composite technology of biological contact oxidation and double-layer subsurface flow constructed wetland to successfully cope with the extreme temperature up to -35℃. In North China and Northwest China, it is suitable to use the centralized treatment technology with constructed wetlands as the core, and appropriately add the unpowered anaerobic filter which is relatively simple to maintain for pretreatment. The water resources in South China are abundant, and the amount of domestic sewage produced by rural residents is large. For areas with better economic conditions, SBR, MBR and other technologies with less land area and higher treatment efficiency can be appropriately used. In general, the southern rural areas are suitable for the use of biological + ecological treatment processes, such as the combination of biological contact oxidation and constructed wetlands. For villages built near mountains and rivers, if there is a pond near the village, it can also be transformed into a constructed wetland system on the spot.

Neutral inorganic mineral coagulant water purification agent for small integrated water treatment equipment:

Luteng ecological mineral water purification agent is based on montmorillonite and other mineral clay as the main raw material, pure natural mineral components, non-toxic to the human environment and fish in water, the dosage of only about 1/3 of the general flocculant. Cost saving, capital investment is small, there is no need to build a large sewage treatment plant, the water quality after treatment can reach an amazing level 1 transparency, the treatment speed is fast, and the addition of agents only takes tens of seconds to make the sludge water separation reach the discharge standard. Because of the short sewage treatment time, it can greatly improve the efficiency of waste water recycling.

The treated water can be used for:

1. Farmland irrigation, afforestation and seedling cultivation;

2, urban miscellaneous water, including greening, toilet flushing, road flushing, building construction, vehicle flushing, fire fighting, etc.;

3, industrial water, including cooling, washing, boiler, process, product water;

4, environmental water, including recreational landscape water, ornamental landscape water, wetland environmental water;

5. Supplement source water, including surface water and groundwater

Scope of application

Lakes, ponds, rivers and other static or slow flow rate of turbid green algae water bodies, urban and rural domestic and industrial sewage, oily wastewater.