Most of my country’s population lives in small towns and rural areas, and the pollution of rural sewage to the water environment has attracted increasing attention. Except for the low sewage treatment rate in the western region, the sewage treatment rate in rural areas of my country has generally increased. However, my country has a vast territory, and the environmental conditions, living habits and economic conditions of towns and villages in different regions vary greatly. How to do a good job in decentralized sewage treatment according to local conditions, the experience of developed countries is worth learning.
my country’s main decentralized sewage treatment technology
There are mainly the following types of rural sewage treatment technologies in my country (see Figure 1): biofilm technology, activated sludge treatment technology, ecological treatment technology, land treatment technology, and combined biological and ecological treatment technology. Application degree, and have successful cases of operation management. From the perspective of sewage treatment scale, the water treatment capacity is generally below 500 tons.
1. Advantages and disadvantages of rural sewage treatment technology
In the practice of rural sewage treatment, each process technology shows the following advantages and disadvantages:
Activated sludge method: flexible control and automatic control, but the average cost per household is high, and special personnel are required for operation and maintenance.
Constructed wetland technology: low construction cost, but low removal rate and inconvenient operation and management.
Land treatment: construction, operation and maintenance are simple, and the cost is low, but it may pollute groundwater and require long-term operation and maintenance management.
Biological turntable + plant bed: suitable for the southern region, but difficult to operate and maintain.
Small sewage treatment station: close to the treatment method of urban domestic sewage. The advantage is that the effluent water quality is good, and the disadvantage is that it cannot meet the needs of rural agricultural sewage.
Although some places are promoting “non-powered” rural sewage treatment technology, “powered” sewage treatment technology still accounts for a large proportion. At present, in many rural areas, land is allocated to households, and there are few public lands, and the land utilization rate in economically developed areas is very low. High, less land resources available for sewage treatment. Therefore, “dynamic” sewage treatment technology has a good application prospect in areas with less land use, developed economy and high water quality requirements. Sewage treatment technology that saves energy and reduces consumption has become the development trend of decentralized domestic sewage treatment technology in villages and towns.
2. Combination mode of rural sewage treatment technology
my country’s rural sewage treatment technology combination mainly has the following three modes:
The first mode is MBR or contact oxidation or activated sludge process. The sewage first enters the septic tank, then enters the biological treatment unit, and finally discharges into the surrounding water body for reuse. Rural sewage reuse is more common.
The second mode is anaerobic + artificial wetland or anaerobic + pond or anaerobic + land, that is, the anaerobic unit is used after the septic tank, and after ecological treatment, it is discharged into the environment or enters agricultural use.
The third mode is activated sludge + artificial wetland, activated sludge + pond, contact oxidation + artificial wetland, or contact oxidation + land treatment, that is, aerobic and aeration devices are used after the septic tank, and an ecological treatment unit is added Strengthen nitrogen and phosphorus removal.
In practical applications, the first mode accounts for the largest proportion, reaching 61%).
Among the above three modes, MBR has a better treatment effect and is suitable for some areas with high water quality requirements, but the operating cost is relatively high. The operating cost and construction cost of constructed wetland and anaerobic technology are very low, but if considered comprehensively, it is necessary to increase the aeration process to achieve a more ideal water effluent effect.
Decentralized sewage treatment technology applied abroad
1. United States
In terms of management system and technical requirements, the decentralized sewage treatment in the United States operates under a relatively complete framework. At present, the decentralized sewage treatment system in the United States mainly has the following technologies:
septic tank. Septic tanks and land treatment are commonly used technologies abroad. According to German survey data, about 32% of sewage is suitable for land treatment, of which 10-20% are unqualified. The cause of the failure may be that the system pollutes the groundwater, such as: excessive use time; excess hydraulic load; design and installation problems; operation management problems, etc.
sand filter. Sand filtration is a very commonly used sewage treatment technology in the United States, which can achieve a good removal effect.
Aerobic treatment. Aerobic treatment is applied in many places in the United States, and the treatment scale is generally 1.5-5.7t/d, using the biological turntable method or activated sludge method. In recent years, the United States has also attached great importance to the effective handling of nitrogen and phosphorus utilization. Most of the nitrogen in the United States is found in wastewater. It is important to reduce subsequent processing costs through early separation.
In addition, there are disinfection, nutrient removal, source separation, and N and P removal and recovery.
2. Japan
Japan’s decentralized sewage treatment technology is relatively well-known for its septic tank treatment system. The sources of domestic sewage in Japan are somewhat different from those in my country. It is mainly collected according to the classification of laundry wastewater and kitchen wastewater.
Septic tanks in Japan are installed in areas that are not suitable for pipe network collection and where the population density is relatively low. Septic tanks are designed for different populations and parameters. Although the current septic tanks are being replaced from generation to generation, they are still dominated by sinks. After the AO reactor, anaerobic, deoxidizing, aerobic, sedimentation, disinfection and other processes, it should be said that the A septic tank is in normal operation. The relatively successful application of septic tanks in Japan is not just a technical issue, but a relatively complete management system under a complete legal framework, forming a relatively successful case. At present, there are application cases of septic tanks in our country, and it should be said that there are also markets in Southeast Asia. Countries such as Southeast Asia, Indonesia, and the Philippines are also affected by Japan’s decentralized sewage treatment policy. Malaysia and Indonesia have formulated their own domestic technical specifications and guidelines for septic tanks, but in practice these specifications and guidelines may not be suitable for their current economic development status.
3. European Union
In fact, there are some economically and technologically developed countries within the EU, as well as some economically and technologically backward regions. In terms of economic development, they are similar to China’s national conditions. After achieving an economic breakthrough, the EU is also working hard to improve sewage treatment, and in 2005 passed the EU standard EN12566-3 for small-scale decentralized sewage treatment. This standard should be said to be a way to adapt measures to local conditions, geographical conditions, etc., to choose different treatment technologies, mainly including septic tanks and land treatment. Among other series of standards, comprehensive facilities, small sewage treatment plants and pretreatment systems are also included.
4. India
After briefly introducing the cases of several developed countries, let me introduce the situation of developing countries in Southeast Asia that are relatively close to my country’s economically underdeveloped regions. Domestic sewage in India mainly comes from kitchen wastewater. In terms of sewage treatment, septic tank technology is currently the most widely used in Southeast Asia. But the general problem is similar to that of our country, that is, all kinds of water pollution are very obvious. With the support of the Government of India, actions and programs to effectively scale up septic tanks are underway, with specifications for septic tank treatment and contact oxidation technology in place.
5. Indonesia
Indonesia is located in the tropics. Although the rural economic development is relatively backward, the domestic sewage of local residents is mainly discharged into rivers. Therefore, the rural health conditions in Malaysia, Thailand, Vietnam and other countries are not optimistic. The application of septic tanks in Indonesia accounts for 50%, and they have also formulated relevant policies to promote the use norms and standards of septic tanks in Indonesia.
Advanced foreign experience
To briefly summarize, developed countries do have a lot of advanced experience that my country can learn from: the standardization system in developed countries is very complete and standardized, and there is an efficient operation management system, including professional training and civic education. , while the principles of sewage treatment in developed countries are very clear.
Specifically include: (1) Clarify the responsibility for sewage treatment, and at the same time, the state supports the decentralized treatment of sewage through funds and policies; formulate corresponding standards to regulate and guide decentralized sewage treatment; (2) establish fair, standardized, and efficient administrative management and industry management system to ensure the effective development and long-term operation of decentralized sewage treatment; (3) Improve the scale, socialization, and specialization of the construction and operation of decentralized sewage facilities to ensure benefits, reduce costs, and facilitate supervision; (4) Specialization (5) publicity and education and citizen participation projects, etc.
In the process of practical application, the successful experience and the lessons of failure are summed up to realize the sustainable development of my country’s decentralized sewage treatment technology.
Cr.antop
Post time: Apr-13-2023