This paper analyzes China's built Shanghai Bailonggang, Guangzhou Xinhua, Baoji City High-tech Zone, Tongliao City sewage treatment plant, the Taihu Lake area, the Three Gorges reservoir area sewage treatment plant operation, and found that the operation of its operation generally exists in the operation of a low loading rate, the quality of water intake fluctuations in the quantity of water, the quality of the water difficult to stabilize and meet the standards, etc., through the depth of the analysis of the reasons for the scientific put forward a targeted countermeasures to solve the problem, so as to provide China's urban sewage treatment plant, as a key link in the sewage treatment infrastructure. In order to provide reference for the stable operation of China's urban wastewater treatment plant for the comprehensive management of the water environment to contribute to the comprehensive implementation of the "Water Pollution Prevention and Control Plan", the country's cities have carried out the black stinky water body remediation work.
Urban sewage treatment plants play an important role in ensuring the safety of the water environment, the construction of sewage treatment plants is an important means of solving urban water pollution.
The "13th Five-Year Plan" for the construction of national urban wastewater treatment and recycling facilities proposes that by the end of 2020, full coverage of urban wastewater treatment facilities should be realized, with the rate of urban wastewater treatment reaching 95%, and that of counties no less than 85%. During the "Ninth Five-Year Plan" period, China's key river basin water pollution prevention and control plan began to be implemented, the construction and operation of urban sewage treatment facilities began to become the main way to implement the responsibility of water pollutant reduction targets.
In the central financial funds and related policies, after the "Eleventh Five-Year Plan", "Twelfth Five-Year Plan" development, China's wastewater treatment plant construction has made progress by leaps and bounds, the number of urban sewage treatment plants and the scale of the rapid increase in urban sewage treatment plant, the capacity of urban sewage treatment continues to improve. Urban sewage treatment capacity is constantly improving.
Statistics show that by the end of 2016, the urban sewage treatment rate reached 93.44%, of which the centralized sewage treatment rate was 89.8%. As of 2010, there were 2,496 urban sewage treatment plants nationwide***, an increase of 140% compared to 2006. By the end of 2016, the number of urban sewage treatment plants reached 3,552, an increase of 29% compared with 2010.
However, the continuous improvement of the sewage treatment rate and treatment capacity is still in contradiction with the pollution of the water environment. The 2016 China Environmental Status Bulletin published by the Ministry of Environmental Protection (MEP) shows that 32% of the 1,940 monitoring sections of surface water across the country are still class IV or below. By the end of 2017, the number of black-smelling water bodies in cities nationwide identified by the Ministry of Housing and Urban Construction and the MEP was 2,100.
Meanwhile, the emission standards of sewage treatment plants have been improving, and the Action Plan for the Prevention and Control of Water Pollution, released in 2015, explicitly proposed that the existing urban sewage treatment facilities should be renovated according to local conditions and meet the corresponding emission standards or recycling requirements by the end of 2020; urban sewage treatment facilities in sensitive areas (key lakes, key reservoirs, and catchment areas of nearshore waters) should reach Class I-A emission standards by the By the end of 2017 to fully meet the Class A emission standards, the built-up area of the water quality of the body of water does not reach the surface water Ⅳ standards of the city, the new urban wastewater treatment facilities to implement the Class A emission standards; by 2030, strive to improve the quality of the national water environment in general, and the water ecosystem function initial restoration.
Because of China's urban wastewater generally exists in the water quality and quantity of water changes in the magnitude of low carbon and nitrogen ratio, high inorganic suspended solids content, low water temperature in winter, the impact of industrial toxic and harmful pollutants and other prominent issues, significantly affecting the normal operation of wastewater treatment facilities, the water is difficult to stabilize and meet the standards. Even in the case of discharge to meet the standards, the water quality in line with the primary A/B standards is still close to V water (Table 1), is an important source of pollution of the water environment.
Table 1 China's urban sewage treatment plant discharge standards for the main pollutants index comparison Unit:mg/L
Some of the suburban combination of residents due to indiscriminate throwing, indiscriminate discharge of domestic sewage, the water environment has also brought serious harm. To this end, the authors of this paper in-depth analysis of China's representative sewage plants in the north and south of the problems and reasons, and put forward countermeasures, in order to provide reference for the stable operation of China's urban sewage treatment plants, and contribute to the comprehensive management of the water environment.
1 Problems and causes analysis
1.1 Operation load rate is generally low, and some of them are overloaded
According to the Operation, Maintenance, and Safety of Urban Wastewater Treatment Plants Technical Regulations (CJJ60-2011) issued by the Ministry of Housing and Urban Construction in 2012, the annual treated water volume of urban wastewater treatment plants should be more than 95% of the planned targets. The operation load rate of sewage treatment plants in most areas of China is low, making it difficult to meet the requirements of the Ministry of Housing and Urban Construction.
Liaoning province's sewage treatment plants with an average monthly load of 80% or more account for only 32% of the total number of sewage plants. Tongliao economic and technological development zone sewage treatment plant status quo water has not reached the design value, nearly half of the treatment facilities idle. Guangxi urban sewage treatment plants with a load rate of 60% or more in 2010 accounted for 65% of the total number of sewage plants. The average operating load of 176 sewage treatment plants in the Three Gorges Reservoir Area was only 56.5% in 2014.
The average operating load rate of the nation's built sewage treatment plants is only 65% to 70%, much lower than Germany's average operating load rate of 95% for sewage treatment plants in 2008. And some cities due to rapid economic development, population growth is too fast, sewage treatment plants have been overloaded, treatment pressure.
The main reason for the low loading rate of sewage treatment facilities is that the plant network construction is not complementary, sewage network coverage and collection rate is low. Sewage treatment plants can only play a role in pollution control if they are used in conjunction with the sewage network.
Because of the sewage plant construction is relatively simple, centralized, short construction period, the pipeline network construction is relatively complex, involved in a wide range of long construction period, China's city managers generally rebuild the plant, light pipeline network, light management.
Data shows that as of 2016 the country*** has 3,552 urban sewage treatment plants, an increase of 29% compared to 2010, and the length of drainage pipes increased by only 17%. The supporting pipeline network is not synchronized with the construction of sewage treatment plants, resulting in some sewage treatment plants being built and facing the embarrassing situation of having no sewage to treat.
Some cities have only constructed trunk sewers in advance, due to the lack of funds in place to promote the slow construction of branch pipe networks. Part of the city's new pipeline network there are many problems can not be connected with the existing trunk, such as the design elevation and the existing trunk is not consistent, the existing trunk water clogging and so on.
Constructed pipe network did not lead to "weaving network into a piece", sewage collection rate is low. Another reason is that the sewage plant design scale does not match the actual situation. As part of the city of sewage treatment plant construction of the preliminary work is not enough attention to the source of sewage and collection of sewage lack of detailed planning and full justification, pipeline network, pumping stations and other auxiliary facilities are relatively lagging behind the construction of the design scale is often based on theoretical design calculations. In the relatively economically backward areas, the actual per capita water consumption and pollutant emissions are relatively low, resulting in the design scale is large, the actual amount of sewage is not enough.
And in some of the more rapidly developing cities, with the rapid economic development and the continuous improvement of the living standards of the residents, the amount of sewage production continues to increase. Sewage plant design scale lags behind the population and economic growth rate, sewage plant treatment capacity is insufficient, overload operation phenomenon.
1.2 Inlet water quality and quantity fluctuations, and the design value does not match
The raw water quality and quantity of sewage plant is an important factor affecting the stability of sewage treatment process operation. China's urban sewage plant influent water quality and quantity fluctuations, part of the sewage plant influent load fluctuations can reach -47% to 4%.
Shanghai Bailonggang sewage plant influent BOD5 average daily concentration fluctuation range of 14 ~ 382mg / L, CODCr fluctuation range of 96 ~ 824mg / L. Kunming City, combined flow system drainage area sewage treatment plant influent by the rainy season, suspended solids fluctuations. In addition to water quality fluctuations, some sewage plant influent water quality organic matter concentration is different from the design value, which seriously affects the effect of sewage treatment.
Baoji High-tech Zone Wastewater Treatment Plant, the actual quality of influent water in addition to NH3-N and TN, all other indicators are higher than the design value. Baoji Shilipu Wastewater Treatment Plant influent TP higher than the design value, the other indicators are lower than the design value.
Analysis of the reasons, mainly drainage network rain and sewage diversion is not complete, pipe network leakage, along the river interception of sewage impact on the sewage treatment system. China's old city drainage system is generally rain and sewage combined system, and later some cities changed to intercepted combined system.
Combined flow drainage system, sewage treatment plant water quality is affected by a variety of factors. During the rainy season, the drainage network collects both domestic sewage and a large amount of rainwater, causing fluctuations in the amount of water in the sewage plant.
In which the initial rainwater pollutant concentration is high, pollution is serious, some pollutant indicators are higher than the concentration of sewage in the dry season, resulting in fluctuations in water quality. In our country, due to the untimely maintenance of pipe network, the old pipe network leakage is serious, groundwater, river water and rainwater mixing also directly affects the amount of water into the sewage treatment plant, water quality.
In some southern areas, due to the front-end pipe network construction is not perfect, the sewage plant dry season water volume is small, the need to extract the river water; but in the rainy season, the amount of rain sewage network and far more than the sewage plant's treatment scale, resulting in a large fluctuation of water quality in the dry and rainy seasons.
The impact of the interception system along the river on the sewage treatment system is another reason for the fluctuation of water quality and quantity. As a transitional product in the process of combined flow system transformation, the river interceptor system is more common in some southern cities.
The system can greatly improve the river's long-standing black odor, but there are some problems. The combined water collected by the system during the rainy season contains a large amount of rainwater, leading to an increase in the amount of wastewater treated by the sewage plant in the dry and rainy seasons year after year, and the load of the sewage treatment plant during the rainy season is generally large.
And most of the interceptor box culvert system has not yet been equipped with the appropriate end of the treatment facilities, carrying a large number of pollutants in the first small rain directly into the sewage plant, resulting in fluctuations in the quality of the water, the treatment effect is difficult to guarantee.
In addition, China is in the stage of rapid economic development, regional economic differences are obvious. Relatively economically developed, densely populated areas of the city continues to expand, but the actual rate of expansion and planning is often inconsistent, resulting in the growth of sewage and sewage plant design scale is inconsistent.
When the amount of sewage over the design scale, the sewage treatment plant is in the "not enough to eat" state, when the design scale exceeds the actual demand for treatment, but also cause the "big horse and cart" phenomenon.
Northwest China's sewage treatment facilities are due to insufficient number of services, pipeline network supporting poor and other issues in the "not enough" state, which affects the quality of water intake of sewage treatment plants.
1.3 The quality of effluent water is difficult to meet the standard stably, and NH3-N and TN exceed the standard
Most of China's existing wastewater treatment plants implement the "Pollutant Emission Standards for Urban Wastewater Treatment Plants" (GB18918-2002) level 1 standard, in which the implementation of level 1A standards accounted for 29.3% of the total number of standards, and the implementation of level 1B standards is close to 60%. By the end of 2016, only 30% of China's wastewater plants' tail water had reached the Class I-A standard, and as many as 70% of the wastewater treatment plants' discharge standards were at or below the Class I-B discharge standard.
Most of the sewage plants mainly exceed the standard pollutants for NH3-N, TN, Shanghai Bailonggang Wastewater Treatment Plant using the A2/O process, the effluent NH3-N Class B compliance rate of only 46%, TN Class B compliance rate of 68%.
Three Gorges reservoir area 176 sewage plant primary B compliance rate of 60.7%, Tongliao sewage plant primary A compliance guarantee rate of less than 50%, Baoji Shilipu sewage plant NH3-N, TN primary A compliance guarantee rate of 42.4%, 42.5%.
Guangzhou Xinhua Wastewater Treatment Plant effluent TN and NH3-N in January-March occasionally exceeded the standard, can not be stabilized to meet the standards of Class A. Sewage treatment plant effluent water quality does not meet the standards, can not give full play to the effectiveness of not only reduces the investment benefits of sewage plant, but also to the sewage plant operation and management difficulties, should be fully caused by the operation of the manager's attention.
The process is a sewage plant treatment effect of the key factors to ensure that China's urban sewage plant using the process is mainly ordinary activated sludge process, oxidation ditch and its improved process, A2/O and its improved process, SBR and its improved process, A/O and its improved process and aeration of the biological filtration tank (BAF) process, which six types of processes covering more than 90% of the country's urban wastewater treatment plant of the main These six types of processes cover the main body of more than 90% of urban wastewater treatment plants in China.
The above processes have the function of nitrogen removal, but in actual operation, due to fluctuations in the quality and quantity of influent water or not in line with the design value, overloading of the biological treatment facilities, insufficient carbon source, carbon and nitrogen ratio is insufficient, the effluent is difficult to meet the discharge standards.
When the concentration of BOD5, TN and TP in the influent water of the sewage treatment plant is lower than the designed influent concentration, it seriously affects the effect of sewage treatment from various aspects. On the one hand, the low concentration of BOD5 in the wastewater leads to insufficient organic matter required by the microorganisms in the biological treatment unit, which affects the nitrogen removal effect of denitrification stage.
On the other hand, when the concentration of pollutants in the influent water is low, the amount of aeration in the biological reactor is higher than the microbial demand. If you can't adjust the aeration amount of the aeration tank in time, it is easy to over-aeration, resulting in poor activated sludge precipitation and separation effect.
In addition, the lack of warming measures in the southern region in winter, resulting in low temperature of the influent water, not conducive to the growth of nitrification denitrification bacteria, the effluent NH3-N, TN concentration can not be guaranteed. In addition to the process reasons, sewage plant operation and management level also has an important impact on the quality of water.
The operation of the sewage plant is a complex process, the operator should be in the water quality, environmental conditions change conditions, make full use of the flexibility of the various processes to make appropriate adjustments, and timely detection and resolution of problems.
Operators should have a certain amount of physical, chemical and microbiological knowledge, but also need to understand the basic knowledge of sewage treatment, the role of plant structures and the meaning of laboratory indicators and their application.
In foreign countries, the operation of wastewater treatment plants are usually implemented by a doctor. In the country, due to the salary level and other reasons for the limitations of most of the sewage plant employees generally low level of education, technical literacy is insufficient, often based on experience to operate the sewage plant of the various processes and facilities, a serious constraint on and impact on the overall level of operation of the sewage treatment plant.
1.4 Other problems
With the industrialization and urbanization process, the ecological environment of the suburban combination of problems is increasingly prominent. This "combination" is the combination of city and countryside, agriculture and industry, farmers and citizens, full of an uncertain and dynamic transition and transformation.
Construction waste and domestic garbage are piling up in suburban villages, and residents are discharging sewage indiscriminately. The small rivers running through the area are blackened, with garbage floating in them, making them seriously polluted.
If it cannot be effectively controlled, it threatens the health of local residents at times. Due to the imperfections of institutional measures and inadequate management, it makes the suburban areas to appear such a difficult problem. The development of industrial parks is increasingly significant in promoting economic development, but the ensuing environmental pollution is also intensifying.
Large centralized industrial parks generally have sewage treatment plants, for a large number of, small and medium-sized industrial enterprises of wastewater, the use of pre-treated with the park's domestic sewage combined treatment, the actual operation of the process there are a number of problems arise.
One is the actual amount of water does not match the design. In the park sewage treatment plant design stage, due to the development of the scale of insufficient prediction, the actual amount of sewage beyond the sewage treatment plant capacity. Some enterprises due to unstable production conditions, so that the sewage treatment plant treatment capacity is insufficient.
The second is that the actual quality of water intake does not match the design. The actual type of enterprises in the park is inconsistent with the planning, resulting in large changes in the characteristics of sewage, making it difficult for the sewage plant to meet the discharge standards.
2 Countermeasures and Suggestions
2.1 The government coordinates the planning, and the construction of sewage treatment plants and pipeline networks is synchronized
Government departments should combine their respective functions, coordinate and organize scientifically to achieve long-term management of sewage treatment plants [11]. Housing and construction departments, in conjunction with environmental protection, development and reform commission and other departments, follow the footsteps of urban development, take the lead in the preparation of sewage treatment plants, sewage pipe network of the integrated planning, planning and design of sewage treatment plants with forward-thinking.
Local governments should formulate policies to promote the standardization of the operation of sewage treatment plants, and price, housing, finance and other departments jointly, according to local conditions to study and formulate the local economic and social development level of sewage treatment fee system.
The financial sector should increase the capital investment in sewage treatment plants, innovate the investment, construction and operation mode, and raise the salary level of sewage plant operators, thus attracting high-level and high-quality talents for operation and management. Environmental protection departments should strengthen the sewage treatment plant water quality inspection and supervision, the remediation of ineffective to be seriously investigated.
2.2 Improve the sewage collection system, realize the water concentration "double enhancement"
In order to give full play to the efficacy of the sewage plant, we must adhere to the plant network, the drainage network and sewage plant as a whole construction. First of all, to speed up the construction of new sewage pipe network, built from the "user - branch pipe - trunk - sewage treatment plant" path is complete, smooth connection, efficient operation of the sewage collection system, to improve the built sewage plant operating load.
Secondly, we should strengthen the transformation of the old pipe network, the leakage of the pipe network, drainage outlets, check wells for repair, reduce the siltation of the pipeline, to ensure that the collection of sewage water quality, water quality and stability. Furthermore, it is necessary to thoroughly carry out the renovation of the combined flow system pipe network, difficult to renovate the area to speed up the construction of interception, storage and other facilities to reduce the rainy season rain on the impact of sewage plant water quantity and quality.
2.3 source decentralized disposal of early rainfall, reduce the magnitude of changes in the amount of sewage into the plant
In response to the problem of early rainfall impact on the quality of water intake, it is appropriate to source decentralized disposal. From the characteristics of early rainwater and early rainwater disposal experience at home and abroad, early rainwater should be used to source decentralized collection, decentralized disposal, etc.; early rainwater centralized collection is very difficult, the main reason is that if you set up a centralized collection system, the upstream early rainwater arrives downstream has long been clean rainwater, it is difficult to ensure that the collection of early rainwater can be collected to the early rainfall of 20 ~ 30 minutes ago.
Cities that have built the first small rain collection system, should be added to the corresponding end of the treatment facilities to reduce the first small rain on the water quality of sewage treatment plants. Conditional access to the sewage treatment plant for treatment, should be demonstrated that the sewage treatment plant has the conditions for reception before access.
2.4 Strengthen the pipeline network refinement management, prevention
Emphasis on the daily management and maintenance of the built sewage network, strengthen the pipeline network refinement management [12]. The first is to strengthen the daily inspection, the stock of pipe network "repair measurement", "regular physical examination" and repair.
The use of CCTV and QV means of internal pipeline testing, to grasp the distribution of its disease and the extent of the pipeline repair to provide the basis. Secondly, we should implement a regular dredging system to ensure that the sewage pipe is normally open to water.
At present, most of the urban pipelines still use manual desilting, not only the working environment is poor, and inefficient, unable to meet the demand. The introduction of high-tech desilting means, such as desilting robots, to achieve automatic and efficient desilting.
Again, the drainage network data for information processing, the establishment of sewage network water quality online monitoring system, real-time mastery of water quality. When the water quality is abnormal can be found in a timely manner when the pipe section has problems, and remind the sewage treatment plant to take effective countermeasures [34].
2.5 Optimize the service scope of the sewage treatment plant, upgrading and expanding capacity
The sewage treatment plant is generally located in the urban construction area, with the urban construction and urban renewal, the urban sewage volume grows faster while the sewage treatment plant or the sewage system expansion difficulties in the contradiction is increasingly prominent.
To the sewage plant overload operation of the area, through the adjustment of the scope of service to solve the sewage treatment plant sewage incremental problem has an important significance. At the same time, consider upgrading the treatment capacity of sewage treatment plants, sewage plant expansion.
In accordance with the requirements of GB18918-2015 "Pollutant Emission Standards for Urban Sewage Treatment Plants (Exposure Draft)", the new sewage treatment plants since July 1, 2016 and the existing urban sewage treatment plants in the sensitive areas since 2018 have implemented the Class I-A standard.
The renovation of sewage treatment plants with lower discharge standards, rationally selecting renovation measures according to local conditions, and improving the quality of effluent water. Upgrade transformation path generally includes hydraulic transformation, equipment transformation and process upgrading and transformation, etc., of which the sewage treatment process transformation is the key to improve the quality of the effluent water.
TN and NH3-N are mainly removed through the biochemical system, these two indicators are the main target pollutants of the biochemical system renovation.TN removal effect is subject to the influent carbon and nitrogen ratio, due to most of China's wastewater treatment plant influent carbon and nitrogen ratio is low, can be improved by improving the mode of operation, the rational use of internal carbon source, or the way to add the carbon source, to improve the denitrification capacity.
When the NH3-N does not meet the standard, aeration biofilter can be added after the secondary biological treatment. When it comes to specific projects, in accordance with the principle of "one plant, one policy, separate categories" to develop appropriate technology programs.
2.6 collection and dispersal, integrated water management
The main urban areas of the city's domestic sewage should be centralized, through the construction of a perfect sewage network will be collected to the sewage treatment plant centralized treatment. In the suburban areas, there are conditions for the construction of pipe network of the city should gradually improve the pipe network system, centralized treatment of sewage. Short-term can not build pipe network system, should take measures to decentralized treatment.
Decentralized integrated sewage treatment device, with mobile and flexible, high degree of automation and control, treatment effect is good, there have been a large number of decentralized sewage treatment in urban villages and other applications, is the solution to the combination of peri-urban water pollution effective measures.
The problem of industrial park sewage plant is not a business problem, the need for reform and development to solve the problem, and increase the control of emissions from sources of pollution, industrial enterprises should strictly enforce the relevant regulations to ensure that wastewater meets the standards for discharge.
3 Conclusion
The urban sewage treatment and recycling facilities is an indispensable infrastructure for urban development, is an important means of reducing exogenous pollution of water bodies, to ensure its safe, stable and efficient operation of the water environment is of great significance.
Currently China's sewage treatment plant operation there are still some problems, targeted summary of existing problems, can lay the foundation for the future scientific management of sewage plants. Only the government departments to coordinate planning, strengthen the top-level design, and constantly improve the sewage collection system, strengthen the pipeline network of fine management, upgrading and expansion of construction, in order to give full play to the environmental benefits of sewage treatment plants, improve the quality of the urban water environment, and promote the effectiveness of the water environment management for a long time to maintain.
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