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Subdivision wastewater treatment system
Abstract: Description Hospitals, harbors, parks, commercial centers, newly built suburban residential areas, high-level residential areas, sanatoriums, schools, farms, fisheries, hunting grounds, etc. can be referred to as the district, we most often What we encounter is mainly a relatively independent area consisting of one or more functions such as residential area, sanatorium, commercial center, institution and school, etc. Its drainage system is usually not covered by the urban municipal pipe network. According to the local environmental standards, independent sewage treatment facilities must be set up, which is what we refer to as community sewage treatment.
Keywords: sewage treatment
One, Overview
Hospitals, ports, parks, commercial centers, new suburban residential areas, high-level residential areas, sanatoriums, schools, farms, fishing, hunting grounds, etc. can be referred to as a small area, we most often encountered mainly by the residential areas, sanatoriums, commercial centers, institutions, schools, and other functions or a variety of functions of a relatively independent area, its drainage system is usually not covered by the municipal network. Independent area, its drainage system is usually not in the city municipal pipe network coverage. According to local environmental standards, must set up independent sewage treatment facilities, which is what we refer to as the neighborhood sewage treatment.
The capacity of the sewage system in small districts, countries do not have a unified limit. The former Soviet Union has suggested that the treatment capacity of a single structure should not exceed 1400 m3 / d, the United States will be limited to the treatment capacity of small plants in the range of 3785 m3 / d. According to the situation in China, it is recommended that the treatment plant equal to or less than 4000 m3 / d is defined as a small area sewage treatment plant.
District sewage is different from municipal wastewater (often including some industrial wastewater), belonging to the category of domestic sewage. Its water quality and quantity characteristics can be summarized as follows: water quality and quantity changes, low pollutant concentrations, that is, lower than the city sewage, sewage biochemistry is good, less difficult to deal with.
District sewage treatment process based on district sewage discharged into the water body of different functions, commonly used treatment methods are: septic tanks, primary treatment (initial sedimentation tank), biological secondary treatment and secondary treatment and then disinfection after reuse. Due to the small amount of sewage treatment water in the district, the management level is not high, so, in the process design, as far as possible, the choice of no sludge or less sludge treatment process, in order to prevent secondary pollution caused by poor sludge treatment. At present, the more commonly used treatment processes are: ① sewage → regulator → initial sedimentation tank → biological contact oxidation tank → two sedimentation tank → water, biological contact oxidation is the most widely used method, the main advantage is a short residence time, easy to hang the film, especially suitable for the equipment, the construction of the buried doubled by the environmental protection company and the user's favor, but due to the maintenance and management and anti-corrosion of the equipment and other aspects of the problem in recent years the application of the limitations. But if built underground reinforced concrete form, set up personnel access for maintenance, this underground construction in the community water treatment has a larger market, but this way of dealing with the general scale is small, the daily discharge of less than a few hundred tons of sewage in the community is ideal. Thousands of tons of sewage treatment in the community, the recommended way to use the ground construction, biological treatment can be used in contact oxidation, can also be used in SBR or its improved CASS process, aeration is recommended to use low-noise fans or underwater aerators. ② Sewage → regulating tank → coagulation and sedimentation → filtration → water, the degree of treatment is not required, and the amount of water is small, this process can be used, with a small footprint, small odor, simple management and other advantages. In addition, in the aerobic biological treatment before the addition of acidification and hydrolysis, is conducive to reducing energy consumption and improve the total removal rate of the system. Living quarters usually have a large area of green space, if the sewage treatment is used back to water the green space, roads, washing cars, should be added after the treatment of water disinfection or other complementary measures.
Second, the community sewage treatment plant design principles
1. Treatment of water requirements and the degree of treatment
Generally speaking, different neighborhoods on the water requirements vary greatly. Should be based on China's "ground environmental quality standards" (GB3838-88) and "comprehensive sewage discharge standards" (GB8978-96) of the relevant provisions of the local environmental protection department to determine the degree of treatment to ensure that the effluent water quality. If the effluent water is treated by land treatment method, it will be calculated according to the requirements of land treatment method;
2. The design and construction of sewage treatment facilities must be combined with the overall planning and architectural features of the district, i.e., the appearance should be designed to harmonize with the district's architectural environment for the sake of aesthetics;
3. Strive for simplicity and practicability in the sewage treatment process to facilitate the management;
4. The elevation in the Layout should try to use three-dimensional layout, make full use of underground space. The layout should be compact to save land;
5. The location of the sewage treatment plant should be located as far as possible in the downwind direction of the community, and a certain distance from other buildings, in order to reduce the impact on the environment;
6. Equipped with equipment, stereotypes, modularity, easy construction and installation, easy to operate, stable equipment performance,
suitable for phased construction;
7. High degree of treatment, sludge production is small, and as far as possible, the use of energy-saving treatment technology;
8. Treatment structures on the hydraulic load and organic load of the adaptive range of large, so that the system has a better ability to withstand the impact of the load.
9. The population in the small area is gradually increasing. Therefore, the community sewage treatment plant should be based on predictable development planning as the basis for flow design. According to our situation, a 20-year design cycle can be considered.
Three, the community wastewater treatment process
According to the principle of wastewater treatment in the community, the treatment effect should be selected to stabilize, produce less mud, energy-saving treatment methods. Various types of buildings in the district system are generally built with septic tanks, so septic tanks should be combined with sewage treatment methods.
Several commonly used treatment processes:
(1) Sewage→grid→regulating tank→lifting pump→contact oxidation tank→sedimentation tank→water
(2) Sewage→grid→regulating tank→lifting pump→aeration tank→sedimentation tank→water
sludge reflux
(3) Sewage→grid→regulating tank→lifting pump→SBR tank or CASS → effluent
dosing
↓
(4) sewage → grating → regulating tank → lifting pump → coagulation and sedimentation → filtration → effluent (physical and chemical methods)
Reuse process: Biological treatment of effluent and then coagulation, filtration and disinfection
In the beginning of the process is generally to be considered to set up homogenizing tanks, this is because of the community in the quality and quantity of water are more varied than urban sewage treatment This is because the district in the quality and quantity of water are more varied than the municipal wastewater treatment plant. The equalization tanks are generally located after the grates. Physical and biochemical treatment is the core part of pollutant removal.
Four, combined sewage treatment plant or equipment
Combined treatment plant sold in assembled or easy to assemble standardized equipment components. Buried equipment in the country was all the rage, the main advantage is that construction is fast, does not occupy the ground green space, many design units and users are very welcome, the designers choose equipment is very simple, and to design sewage treatment plant workload is large, so, very much like to use equipment-based products. Environmental protection company manufacturing equipment lucrative, and civil engineering lower profits, therefore, companies do advertising and public relations. But the actual application shows that there are really a lot of problems, the maintenance of equipment management difficulties, the operation of the assessment of the inconvenience of a single machine to deal with the limited amount of water, service life and so on are to be time to verify, therefore, the buried equipment has been very controversial, and now, buried equipment heat has cooled down. Built in the underground maintenance, easy to operate (with personnel operating space) sewage treatment design should be recommended. Thousands of tons of wastewater treatment plant is recommended above ground. In the amount of water is not large, the site is very tight can still consider using buried equipment. Buried equipment does process flow are generally used in two contact oxidation and sedimentation process, hydraulic retention time is generally 2 hours, sewage into the equipment before the first water regulation and upgrading.
Fifth, the principle of SBR and CASS treatment process and parameter selection
(a) Sequencing batch activated sludge method (SBR)
The core of the SBR is the SBR reaction tank, the pool set of homogenization, primary sedimentation, biodegradation, secondary sedimentation and other functions in one. A complete operating cycle of a typical SBR process consists of five stages, namely, the influent stage, the reaction stage, the sedimentation stage, the drainage stage and the idle stage. From the first water intake to the second water intake is called a work cycle.
From the current research, application and development trend of aerobic biological treatment of wastewater, SBR is called a simple, fast and low-consumption wastewater treatment process. Compared with the continuous activated sludge method, SBR method has the following characteristics: ① SBR device structure is simple, flexible operation, convenient operation and management. ② investment, low operating costs, Ketchum et al. The statistical results show that: the SBR method for small town sewage treatment, than with ordinary activated sludge method to save 30% of the capital investment. ③ It can inhibit the growth and reproduction of filamentous bacteria, not easy to happen sludge expansion, sludge index SVI is lower, which is conducive to the sedimentation and thickening of activated sludge. ④ SBR is in the process of aerobic/anaerobic alternating operation, which can realize nitrogen and phosphorus removal while removing carbon substances. ⑤ The SBR treatment process system is compactly arranged and saves land occupation. (6) The operation stability is good, and can withstand the impact of large water quality and water quantity. (7) The operation control parameters can be controlled by computer, easy to realize the system optimization operation.
(C) cyclic aeration activated sludge method (CASS process)
CASS (Cyclic Activated Sludge System) process is internationally recognized in recent years to deal with domestic sewage and industrial wastewater treatment of advanced technology. The process is based on the sequential batch activated sludge method (SBR), the reaction tank along the length of the design of two parts, the front part of the biological selection area, also known as the pre-reaction area, the rear part of the main reaction area, in the rear of the main reaction area installed in the lifting of the automatic skimming device, aeration, sedimentation, drainage and other processes in the same pool cycle cycle operation, eliminating the conventional activated sludge method of the second sedimentation tank and the sludge reflux system.
(D) CASS and SBR aeration mode selection
As most of the district is a residential area, the environmental requirements are relatively high, therefore, the construction of sewage plant should be given full consideration to noise nuisance and sewage plant operators working environment, the use of underwater aerators instead of the traditional blower aeration can be an effective solution to noise pollution. In addition, due to the unique operation of the CASS process, the use of underwater aerators can save complex piping and valves, easy to install and maintain, the use of flexible, according to the inlet and outlet of the water to open a different number of units, in order to ensure that the effect of the conditions, to achieve the purpose of economic operation.
(E) CASS and SBR skimmer selection
Skimmer is a key component of the CASS process, whether its performance is stable and reliable directly affects the normal operation of the CASS process. At present, the domestic and foreign skimmer is still in the research and development, according to the principle of skimmer currently used can be divided into three types, namely, float, rotary and siphon type. The key to the development of skimmer is to solve the decanting process, the weir mouth, water guide hose and lift control device and the dynamic balance between the water flow, so that it can be adjusted with the different amount of water discharged into the floating weir submerged depth, and with the water level uniformly rise and fall, the drainage of the sludge on the bottom of the interference to the minimum, to ensure that the effluent quality of water is stable.
The skimmer developed by our institute is of screw rotating type, and the main components of automatic skimming device are: decanter, hose that can be disturbed, water level controller, retractable push rod and drive motor. Among them, the decanter is also called automatic floating weir, the upper part of the weir and prevent scum from entering the water float, the lower part of the outlet pipe and play a supporting role, partially submerged in the water, through the retractable push rod so that the square weir to achieve a continuous and uniform discharge of supernatant in the reaction pool. Practical application shows that the developed skimming device has reached the advanced level of similar products at home and abroad. With the advantages of smooth lifting and lowering, even drainage, automatic control, low price, etc., the study not only meets the needs of the project, but also innovative, is one of the special confidential technology.
Fifth, the main design parameters of sewage treatment district
SBR design parameters: sludge load 0.1-0.15kgBOD5/kgMLSS.d, sludge age 20-30 days
Working cycle of 12 hours, of which, the water intake of 2.5 hours (aeration or non-aeration), the reaction of 6 hours, precipitation 0.75-1 hours, 2 hours of drainage, idle 0.5 hours (aeration or no aeration), the water is discharged. Drainage 2 hours, idle 0.5~0.75 hours. Effluent index: COD <50mg/L, BOD5 <20mg/L, SS <10mg/L
CASS design parameters: sludge load 0.1-0.2kgBOD5/kgMLSS.d, sludge age 15-30 days
Hydraulic retention time of 12 hours, the work cycle of 4 hours, of which the aeration is 2.5 hours, sedimentation 0.75 hours, drainage 0.75 hours. 0.75 hours, drainage 0.5~0.75 hours, effluent indicators are similar to SBR.
Sixth, sludge treatment
Water treatment volume of thousands of tons, generally used after the concentration of dewatering treatment, small-scale general concentration of dung trucks regularly transported to landfill or for agricultural fertilizer.
Seven, small area sewage treatment plant site selection and layout
Small area system site selection and plant layout in the basic principles of large plants are the same. But taking into account the uniqueness of the community system in the selection of service objects and processes, in the plant site selection and layout should also take into account the characteristics of the community system.
1. Plant site planning
(l) and service areas should be a certain distance from the health protection zone
(2) wind direction (does not affect the service area and the surrounding area)
(3) transportation and water and electricity supply.
(4) It is easy to take into account the unified management of other life support facilities in the district.
2. Spacing between the plant roads and structures
Smaller equipment and structures due to the selection of the cell system, the plant traffic, maintenance and sanitation requirements of the space required is correspondingly small. The plant should be designed with sufficient vehicular access, road width design can be based on the radius of gyration of light vehicles. The spacing between the main structures can be considered between 3-5m. Abstract: For the existing sewage treatment plant in the city in the process of construction and operation and management of the problems exposed, from the construction scale and process to determine the perspective of comparative analysis, and should pay attention to the link put forward the views.
Because industrial wastewater treatment facilities are generally small-scale, highly technical, flexible process combinations, the structure is usually steel, even if the internal pipeline interspersed more, operation and maintenance is not too difficult. Industrial wastewater treatment is technically similar to municipal wastewater treatment, but if the design of industrial wastewater treatment facilities simply apply in the municipal wastewater treatment works will bring a lot of unforeseen problems.
1. Reasonably determine the scale of construction
The construction of urban sewage plants to determine the planning, according to the city's overall planning and drainage planning, the construction of sewage pipe network and sewage treatment plants in stages, according to the goal of water environmental protection, phased implementation, gradually in place. Urban drainage construction is a systematic project involving urban pipe and canal renovation, sewage collection, transportation (including pumping stations), sewage treatment and discharge utilization, as well as sludge disposal and other issues in.
2. Urban sewage treatment plant process selection
The selection of specific engineering requirements include:
① Reasonable technology. Advanced and mature technology, adaptability to changes in water quality, water standards and high stability, sludge is easy to deal with.
② economic and energy saving. Small power consumption, low cost, occupies less space.
③ Easy to manage. Convenient operation and management, reliable equipment.
④ Attention to the environment. Plant layout and coordination with the surrounding environment, pay attention to plant noise control and odor management, greening, roads and phased construction combined.
(1) aerobic biological treatment technology is the world's urban sewage treatment plants commonly used sewage treatment process, divided into activated sludge and biofilm method. Activated sludge method is the artificial strengthening of water self-purification, is to make microbial groups "live together" in the activated sludge, activated sludge in the reactor - aeration tank is suspended, and sewage extensive contact, so that the sewage purification technology; biofilm method is the artificial strengthening of soil self-purification, is to make microbial groups in the form of a film, and the biological membrane method is to make microbial groups in the form of a film, and the biological membrane method is to make microbial groups in the form of a film. Biofilm method is an artificial enhancement of soil self-purification, is to make the microbial population in the form of a membrane attached to the surface of the object, in contact with the sewage, so that sewage purification technology. Activated sludge method, biofilm method and its variant variant process, each with its own characteristics and application conditions, in the selection of the time, should be based on the water quality of each region, the amount of water, the receiving body of water, climate, the environment, the economic situation and other conditions to determine.
(2) activated sludge process in the purification mechanism, there is no breakthrough, after decades of development and innovation, now has a traditional activated sludge method based on a variety of operating modes, such as A/O phosphorus removal process, A/O denitrification process, A2/O simultaneous denitrification and phosphorus removal process, oxidation ditch process, A/B method, a variety of SBR method, carrier activated sludge, integrated activated sludge method and so on. In recent years, the activated sludge method has been widely used. In recent decades, the biggest progress of the activated sludge method is the introduction of anaerobic mechanism into the biochemical reaction pool, so that the anaerobic and aerobic conditions in the biochemical pool at the same time or repeated cycles to achieve, but the basic principles of the process and the standard method is the same.
(3) anaerobic - aerobic activated sludge process (A/O method), is a variation of the standard activated sludge method with biological selection function and both nitrogen and phosphorus removal function. The so-called anaerobic is the biochemical reaction section of dissolved oxygen tends to zero state. In this environment, the metabolic function of specialized aerobic microorganisms - filamentous bacteria is sharply reduced, their reproduction is inhibited, and anaerobic bioselection is performed, thus preventing sludge expansion.A/O activated sludge process adds an anaerobic section to the front section of the universal activated sludge method, and realizes the function of phosphorus removal or nitrogen removal through the change of the sludge loading. On the basis of A/O method, A2/O method has been developed, i.e., anoxic section is added between anaerobic and aerobic sections to realize simultaneous phosphorus removal and denitrogenation, due to the small adaptive range of sludge load, so it is often carried out according to one of the functions of removing phosphorus or denitrogenation in the actual operation.Because of the features of stable effluent quality, low energy consumption and convenient operation and management, A/O and A2/O processes are most frequently used in domestic and foreign large and medium-sized wastewater treatment plants. Plant adopted the most.
(4) carrier activated sludge method, is the activated sludge method in the reaction tank with solid particles or soft, semi-flexible filler, in order to increase the amount of microorganisms per unit of reaction space, to improve the reactor volume load. It is a good combination of activated sludge method and biofilm method, which is generally suitable for sewage plant dredging and renovation to improve the treatment capacity, and its core technology is the patented filler, and in recent years, the Lin Bubble process has been applied to Dalian Chunliu Sewage Plant and Tieling Sewage Plant as its representative.
(5) oxidation ditch method, developed in the fifties by the Dutch Bassville, mainly Carrousel (Carrousel) type, three ditch type, integrated, Orbel (Orbal) type and other forms of technology. Oxidation ditch method is a closed biochemical reaction ditch, to turn the disk or brush for oxygenation and water flow power, simple process, low requirements for operation and management, mostly used for delayed aeration, producing less sludge, sludge is easy to dewater. Oxidation ditch method is widely used in the southern region of China and the central and western regions.
(6) A/B method (Absoption-Biodegradation), is a two-stage biochemical reaction system. A level of biological adsorption, high sludge load, short reaction time (30 minutes); the second level for the general biochemical reaction tank, sludge load with the ordinary activated sludge method.A/B method of the first and second levels have their own secondary sedimentation tanks and sludge reflux system, mostly used for high concentration of domestic wastewater, and its typical domestic application for the Urumqi Hedong Wastewater Treatment Plant and Qingdao HaiBoHei Wastewater Treatment Plant.
(7) Sequencing Batch Activated Sludge (SBR-Sequencing Batch Reactor) is a water treatment process invented by British scholars Ardern and Locket in 1914, and in the early 70s, Prof. R. Irvine of the Natre Dame University of the U.S. carried out systematic and in-depth research on the SBR process at the laboratory scale.
And in 1980, under the funding of the U.S. Environmental Protection Agency (EPA), the city of Culver City, Indiana, remodeled and put into production the world's first SBR method of sewage treatment plant.
(8) Intermittent Cyclic Extended Aeration Activated Sludge (ICEAS-Intermittent Cyclic Extended System) was developed in 1968 by the University of New Wales, Australia, in cooperation with ABJ Corporation, U.S.A. The first ICEAS process wastewater treatment plant was put into operation in 1976. ICEAS compared with the traditional SBR, the most important feature is: a pre-reaction area at the inlet end of the reactor, the entire treatment process of continuous water intake, intermittent drainage, no obvious reaction phase and idle phase, so the treatment cost is lower than the traditional SBR. The process is typically used in China for the third Kunming sewage treatment plant, which has a greater impact in the country.
(9) biofilm method, is another widely used sewage biochemical treatment method. This treatment method is to make bacteria and fungi of a class of microorganisms and protozoa, post-biotic animals of a class of micro-organisms attached to the carrier or filter media growth and reproduction, and the formation of membranous biological sludge on it - biofilm. Sewage and biofilm contact, sewage organic pollutants as nutrients for the microorganisms on the biofilm ingestion, sewage purification, microbial reproduction and proliferation.
3, according to the above process technology comparison and analysis, combined with the water quality of sewage in Kuitun City, it is considered that the more suitable treatment process is preferred as follows:
The first program: A/O process
The biggest progress of the activated sludge method in the past two decades is the introduction of the anaerobic mechanism into the biochemical reaction tank, anaerobic, aerobic intermittent cycle operation to the activated sludge method to bring a new technology economic effects, i.e. biological nitrogen removal, biological phosphorus removal, biological selection, etc.
The anaerobic- aerobic activated sludge denitrification process (A/O method) is a variation of the standard activated sludge method with the function of biological selection and nitrogen removal.
The second program: DAT-IAT process
Aerobic intermittent aeration system (DAT-IAT-Demand AerationTank-Intermittent Tank) is a new SBR process. It is between the traditional activated sludge method and the typical SBR, using continuous water intake continuous - intermittent aeration mode of operation, suitable for water quality and quantity of water intake changes in the case of large. The main structure is composed of aerobic pool DAT pool and intermittent aeration pool IAT pool, DAT pool continuous intake continuous aeration, its effluent from the middle wall into the IAT pool, IAT pool continuous intake intermittent drainage. At the same time, IAT pool sludge DAT pool. It is a delayed aeration process, in fact, for the combination of A/O denitrification process and traditional SBR, the industry has a low sludge load, so it is characterized by high shock resistance and denitrification. The industry is used domestically in Tianjin Technology Development Area Wastewater Treatment Plant and Fushun Sanbotun Wastewater Treatment Plant, which is a SBR process suitable for larger water volumes.
4, the scientific comparison of process programs:
The local conditions for the process program (mainly biological treatment program) comparison is necessary. Comparison of process programs strive to be objective and comprehensive, in the same water intake, water conditions, the design parameters should include the removal of various pollutants, aeration time, sludge load and volumetric loading, aeration and oxygen utilization (and power efficiency), sludge production (and sludge index), etc. for a comprehensive analysis of the data can be a wealth of collective wisdom, avoiding the shortcomings, according to the technically reasonable, economically cost-effective, manageable, reliable and conducive to near and near, the biological treatment of water. Convenient, reliable and conducive to the combination of near- and long-term principles, the optimization of the choice of technology programs.
References
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