Principles of process selection for urban sewage treatment plants
The process selection of urban sewage treatment plants should generally follow four principles:
1) technology is reasonable.
We should correctly handle the dialectical relationship between the advanced nature and maturity of technology. On the one hand, we should pay attention to the advanced technical indicators of the process, and at the same time, we should fully consider the national conditions and the nature of the project suitable for China. Urban sewage treatment project is different from general point source treatment project. As an urban infrastructure project, it has the characteristics of large scale and high investment, and it is a century-long plan, and it must be guaranteed to be 100% successful. The choice of technology pays more attention to maturity and reliability, so we emphasize the rationality of technology rather than simply advocating advanced technology. Technical risks must be minimized.
2) Economy and energy saving.
Saving engineering investment is an important prerequisite for building urban sewage treatment plants. Reasonable determination of treatment standards, selection of simple and compact treatment technology, as far as possible to reduce land occupation, and strive to reduce the cost of foundation treatment and civil engineering. At the same time, we must give full consideration to saving electricity and drug consumption and minimize operating costs. This is particularly important for China's existing economic affordability.
3) Easy to manage.
Urban sewage treatment is a new industry in China, and professionals are relatively scarce. In the process of process selection, the existing domestic operation and management level must be fully considered, the equipment should be as simple as possible, the maintenance should be convenient, and reliable and practical automation technology should be adopted appropriately. Special attention should be paid to the adaptability of the process itself to water quality changes and the stability of treated water.
In fact, any process always has advantages and disadvantages, and the key lies in its applicability. In engineering practice, we should analyze the specific situation, adjust measures to local conditions, make comprehensive comparison, learn from each other's strengths and make a better choice.
2. Overview of the leading technologies of urban sewage treatment plants.
1)AB process
AB technology was first put forward by German professor Bohuke. In this process, the aeration tank is divided into two parts: high load and low load, and each part has an independent sedimentation and sludge reflux system. The residence time of high-load stage (stage A) is about 20-40 minutes, mainly due to biological flocculation and adsorption, and incomplete oxidation reaction occurs at the same time. The organism is dominated by short-generation flora, and BOD is removed by more than 50%. Section B is similar to conventional activated sludge process, with lower load and longer sludge age.
AB method A has high efficiency and strong buffering capacity. Section B plays the role of effluent control and has good treatment stability. For high concentration sewage treatment, AB method has good applicability and high energy saving benefit. Especially when sludge digestion and biogas utilization processes are adopted, the advantages are the most obvious.
However, the output of AB sludge is relatively high, and the organic content of sludge in one stage is extremely high, so it is necessary to carry out subsequent stabilization treatment of sludge, which will increase certain investment and expenses. In addition, because more BOD is removed in stage A, the carbon source may be insufficient and it is difficult to realize the denitrification process. For the occasion of low sewage concentration, it is difficult to operate in section B, and it is also difficult to give full play to its advantages.
At present, only A-level process is adopted, and the effect is better than the first-level treatment. As a transitional process, it has a good advantage in cost performance. Generally suitable for discharging rivers and seas.
2)SBR process
SBR technology was applied as early as the early 20th century, but it has not been popularized because of the difficulty and complexity of manual management. The method integrates water inlet, aeration and sedimentation in a pool. Generally, it is composed of multiple ponds, and the working state of each pond changes in turn, and a single pond intermittently discharges water from the skimmer, so it is also called sequencing batch activated sludge process.
This process changes the traditional distribution of aeration tank and sedimentation tank from spatial distribution to time distribution, forming an integrated intensive structure, which is conducive to the realization of compact module layout and the greatest advantage is to save land. In addition, it can also reduce sludge backflow and save energy. In the typical SBR process, the water is stopped during precipitation, and static precipitation can obtain higher precipitation efficiency and better water quality.
CASS and CAST processes developed from SBR have new features in phosphorus and nitrogen removal and automatic control.
However, SBR process requires high automation control, which requires a large number of electrically controlled valves and mechanical skimmers. It will not run if there is a slight fault, and it is generally necessary to introduce a full set of imported equipment. Because of the multi-function of one pool, the related equipment has to be idle, and the number of aeration heads and the capacity of blowers must be slightly larger. The total volume of that pool is not reduce. In addition, because the skimming depth is usually 1.2-2m, the outlet water level must be designed according to the lowest skimming water level, so the total hydraulic elevation is about 1m higher than that of the general process, and the energy consumption will also be improved.
SBR process is generally suitable for small and medium-sized occasions where land is scarce and equipment is imported. Add comments
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. tx mix | 2009- 12-04 20:46: 10
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Ecological engineering and sewage treatment system
Ecological engineering generally refers to an artificially designed engineering system with biological population as the main structural component and certain functions, with macro and human participation in regulation.
Basic functions: to form a dynamic balance through a certain coordination structure; The transformation, decomposition, enrichment and regeneration of substances are carried out on the basis of multi-layer nutritional structure.
Ecological engineering type
Ecological engineering of multi-layer utilization of matter and energy
Material transformation and regeneration ecological engineering
Pollution-free ecological engineering
Multifunctional pollution self-purification ecological engineering
Industrial-agricultural joint ecological engineering
Application method of ecological engineering
Oxidation pond method: biological oxidation pond is an ecosystem that uses the synergistic effect of algae and bacteria to treat waterless water. Bacteria mainly use oxygen produced by algae to decompose organic matter flowing into the pond; Inorganic substances in the decomposition products, as well as a part of small molecular organic substances, become the nutritional sources of algae.
Oxidation pond process
Biological composition: algae, bacteria and micro-animals.
Features: simple structure, low energy consumption and convenient operation and management.
Type: facultative pond, anaerobic pond, aerobic high-efficiency pond, purification pond and aerated pond.
Aquatic plant pond
Constructed wetland treatment system
Wetland is an ecosystem, which keeps shallow surface water for a long time every year to maintain the growth of large aquatic plants.
Constructed wetland is an artificial ecosystem that simulates natural wetland and is used to treat wastewater.
Sewage land treatment system
An engineering facility that uses the purification ability of land and its microorganisms and plant roots to treat pretreated sewage or wastewater, and at the same time uses the water and fertilizer in it to promote the growth of crops, pastures or trees.
Using the self-purification ability of terrestrial ecosystem to purify sewage.
Difference between sewage land treatment system and sewage irrigation
The land treatment system carries out necessary pretreatment of sewage;
The land treatment system is a sewage treatment facility that runs continuously all year round;
The land treatment system has a complete engineering system and can be controlled, and the bottom seepage control system can effectively control the possible pollution of sewage to groundwater;
The land treatment system plants cash crops that are beneficial to sewage treatment, and generally does not plant crops that can be eaten directly.
This is what we learned in class, I hope I can help you! I just finished the exam this Thursday, and I also took this question! Add comments
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. sun7680 1 1 1
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CCAS process, namely continuous circulating aeration system, is a continuous influent SBR aeration system. This process is improved on the basis of SBR (sequencing batch reactor). SBR process has been successfully developed as early as 19 14, but it is difficult to be popularized and applied in large sewage treatment plants due to complicated manual operation and management, backward monitoring methods and easy blockage of aerators. SBR process is generally considered to be suitable for small sewage treatment plants. Since the 1960s, automatic control technology and monitoring technology have developed rapidly, and a new type of non-clogging microporous aerator has also been successfully developed, which has created conditions for the wide use of intermittent treatment. 65438-0968 The University of New South Wales in Australia cooperated with ABJ Company in the United States to develop the aerobic activated sludge process with continuous water inflow, periodic drainage and prolonged aeration. 1986, the US National Environmental Protection Agency officially recognized CCAS as an innovative alternative technology (I/A) and became the most advanced computer-controlled biological phosphorus and nitrogen removal process.
CCAS process has low requirements for sewage pretreatment, and only mechanical grid and grit chamber are set with the spacing of15 mm.. The core of biological treatment is CCAS reaction tank, and the functions of phosphorus removal, nitrogen removal and degradation of organic matter and suspended matter are all completed, and the effluent can meet the standard.
The pretreated sewage continuously enters the pre-reaction tank at the front of the reaction tank, and most of the soluble BOD in the sewage is adsorbed by activated sludge microorganisms, and enters the reaction zone at a low flow rate (0.03-0.05 m/min) from the holes at the lower part of the partition walls of the main reaction zone and the pre-reaction zone. In the main reaction zone, the process of "aeration, idleness, sedimentation and decanting" is operated periodically, so that the wastewater can be decarbonized and denitrified in the repetition of "aerobic-anoxic" and dephosphorized in the repetition of "aerobic-anaerobic". The duration of each process and the operation of the corresponding equipment are controlled by the computer according to pre-programmed and adjustable programs.
The unique structure and operation mode of CCAS process make it have unique advantages in technology:
(1) During aeration, sewage and sludge are completely mixed, which ensures the removal rate of BOD and COD, and the removal rate is as high as 95%.
(2) The repeated operation modes of "aerobic-anoxic" and "aerobic-anaerobic" strengthen phosphorus absorption and nitrification-denitrification, so that the removal rate of nitrogen and phosphorus reaches over 80% and the effluent index is qualified.
(3) During precipitation, the whole CCAS reaction tank is in a completely ideal precipitation state, and the effluent suspended solids (SS) is extremely low, and the low SS value also ensures the phosphorus removal effect.
The disadvantage of CCAS process is that each pool runs intermittently at the same time, and manual control is almost impossible. Relying on computer control requires high quality of management personnel in the treatment plant and strict requirements on design, training, installation and debugging.
B. Overview of the development of urban sewage treatment plants at home and abroad
Water is an important factor of economic development and social sustainable development. With the continuous expansion of city scale and the increase of population, water pollution has become a major problem. Urban sewage is an important cause of water pollution in rivers and lakes at present, and it is one of the main reasons that restrict the sustainable development of many cities. "Environmental protection" is the basic national policy of China. China's sustainable development strategy and countermeasures in 2000 require that the centralized treatment rate of urban sewage should reach 20%. At present, China is in a period of great development of urban sewage treatment, especially with the implementation of the national strategy of developing the western region, the environmental and ecological protection in the central and western regions has been put on the agenda.
Since the industrial revolution 200 years ago, people have paid more and more attention to the treatment of urban domestic sewage. Urban sewage treatment rate has become an important symbol of a region's civilization or not. In the past 200 years, urban sewage treatment has developed from the initial natural treatment and simple primary treatment to the advanced treatment and reuse of sewage by various advanced technologies. The treatment process has also developed from the traditional activated sludge process and oxidation ditch process to A/O, A2/O, AB and SBR (including CCAS process) to meet different effluent requirements. Compared with foreign developed countries, China's urban sewage treatment started late, and the current urban sewage treatment rate is only 6.7%. While vigorously attracting foreign advanced technology, equipment and experience, we must combine the development of China, especially the local actual situation, and explore an urban sewage treatment system suitable for the actual situation in China.
Combined with the actual situation in China and drawing lessons from foreign advanced technology and experience, the construction of urban sewage treatment plants should meet the following development directions:
(1) province of total investment. As a developing country, China needs huge funds for its economic development, so strictly controlling the total investment is of great benefit to the national economy.
(2) Low operating cost. Operating cost is an important factor for the normal operation of sewage treatment plants, and it is also one of the main indicators to judge the quality of a set of processes.
(3) It occupied a province. China has a large population, and per capita land resources are extremely scarce. Land resources are an important factor in the development and planning of many cities in China.
(4) Effect of nitrogen and phosphorus removal. With the eutrophication of large-scale water environment in China, nitrogen and phosphorus removal from sewage has become an urgent problem. China's latest national integrated wastewater discharge standard (GB8978- 1996) also clearly stipulates that it is applicable to all pollutant discharge units, and very strictly stipulates the phosphate discharge standard and ammonia nitrogen discharge standard. This means that most urban sewage treatment plants should consider the problem of nitrogen and phosphorus removal in the future.
(5) Organic combination of modern advanced technology and environmental protection engineering. The appearance and perfection of modern advanced technology, especially computer technology and automatic control system equipment, has provided strong support for the development of environmental protection engineering. At present, most sewage treatment plants in developed countries abroad adopt advanced computer management and automatic control systems to ensure the normal operation of sewage treatment plants and stable and qualified effluent, but China is still relatively backward in this respect. Computer control and management will also be the development direction of urban sewage treatment plants in China.
Process comparison of several treatment systems
In order to choose the most reliable urban sewage treatment system in technology, the most economical in investment and the most convenient in management, combined with the local actual situation, we investigated and compared the mature experience and development trend of sewage treatment plants at home and abroad.
At present, most urban sewage treatment plants at home and abroad adopt primary treatment and secondary treatment. The primary treatment adopts physical methods, mainly through grid interception, precipitation and other means to remove large suspended solids and sand particles in wastewater. This treatment process is relatively mature at home and abroad, with little difference. The secondary treatment adopts biochemical method, which mainly removes suspended solids, dissolved organic matter, nitrogen, phosphorus and other nutrients from wastewater by means of microbial life movement. At present, there are many ways to deal with this process. To sum up, the representative processes mainly include traditional activated sludge process, oxidation ditch, A/O or A2/O process, SBR and CCAS process. At present, these representative processes have practical applications at home and abroad.
Second, SPR high turbidity sewage treatment technology
Nowadays, natural fresh water resources have been fully developed, and natural disasters are becoming more and more frequent. The shortage of water resources has posed a very serious threat to the economy and citizens' life in many cities around the world. The water shortage crisis has become a reality we are facing. The important way to solve the problem of urban water shortage should be to convert urban sewage into urban water supply source. Urban sewage is available nearby, stable in source and easy to collect, and it is a reliable and stable water supply source. After purification, urban sewage can be mainly used as municipal greening, landscape water and industrial water for reuse.
Urban sewage recycling project includes sewage collection system, sewage purification treatment technology and its system, sewage transmission and distribution system, reuse water application technology and monitoring system. Among them, the sewage purification and regeneration technology and its system are the key, the sewage purification and treatment process should be simple and reliable, the investment and operation costs should be affordable for the city's economic strength, and the treated effluent quality should meet the reuse requirements.
The traditional "primary treatment" and "secondary treatment" water treatment technologies and equipment used for many years have been difficult to meet the purification requirements of high turbidity and high concentration sewage, and the treated effluent can not meet the water quality requirements of urban reclaimed water reuse. Along the traditional process route, we can only further increase the traditional "three-stage treatment" equipment system, which can neither avoid the huge and complex traditional two-stage biochemical treatment system nor avoid the traditional three-stage filtration and adsorption treatment system with very expensive investment and operation costs. These are precisely the taboos to realize sewage reuse. Therefore, the environmental protection market urgently needs new sewage treatment technology and equipment with higher purification efficiency. The treated effluent can meet the existing environmental protection standards and can be reused in cities, and the investment and operating costs should be acceptable to the economic strength of existing cities.
The newly invented "SPR high turbidity sewage purification system" (American invention patent) combines the "primary treatment" and "tertiary treatment" procedures of sewage into one, and puts them into a water tank of the SPR sewage purifier, which can be quickly completed in 30 minutes. It is allowed to directly inhale high-turbidity sewage with suspended matter (turbidity) as high as 500 mg/L to 5000 mg/L, and the suspended matter (turbidity) of treated effluent is lower than 3 mg/L (degree); It is allowed to directly inhale high-concentration organic sewage with CODcr of 200mg/L ~ 800mg/L, and the CODcr of the treated effluent can be reduced to less than 40 mg/L. Only with the engineering investment equivalent to that of conventional primary and secondary sewage treatment plants and the operating cost lower than that of conventional secondary treatment, the effect of tertiary treatment level can be achieved, and the regeneration and reuse of urban sewage can be realized.
The SPR sewage treatment system firstly separates the dissolved pollutants from the real solution by chemical methods to form colloidal particles or tiny suspended particles with solid interfaces; Select efficient and economical adsorbents to separate organic pollutants and chromaticity in sewage; Then all kinds of colloidal particles and suspended particles in sewage are condensed into large and dense flocs by microscopic physical adsorption; Then, relying on the principles of fluid mechanics such as cyclone and filtration hydraulics, the floc and water can be quickly separated in the self-designed SPR high turbidity sewage purifier. After the clean water is filtered by the self-formed dense suspended mud layer in the tank, it reaches the tertiary treatment level, and the effluent is reused; Sludge is highly concentrated in the concentration chamber and discharged under pressure at regular intervals. Because of its low moisture content and good dewatering performance, sludge can be directly sent to a mechanical dewatering device, and the dewatered mud cake can also be used to make sidewalk tiles, thus avoiding secondary pollution.
The newly invented SPR sewage purification technology has the advantages of simple and reliable process, low investment and operation cost, less land occupation and good purification effect, which will open up a new way for the reuse of urban sewage in the world today. After the reuse of urban sewage, it provides a second fresh water source for the city and an indispensable condition for the sustainable development of the city, and its economic and social benefits are immeasurable.