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Residential sewage treatment system
Hospitals, ports, parks, commercial centers, newly-built suburban residential areas, advanced residential areas, nursing homes, schools, farms, fishing grounds, hunting grounds, etc. Can be called residential areas. We often encounter relatively independent areas with one or more functions, such as residential areas, nursing homes, commercial centers, government agencies and schools, and their drainage systems are usually not covered by urban municipal pipe networks. According to local environmental protection standards, independent sewage treatment facilities must be set up, which is what we call residential sewage treatment.
Keywords: sewage treatment
I. Overview
Hospitals, ports, parks, commercial centers, newly-built suburban residential areas, advanced residential areas, nursing homes, schools, farms, fishing grounds, hunting grounds, etc. Can be called residential areas. We often encounter relatively independent areas composed of residential areas, nursing homes, commercial centers, government schools and other functions, and their drainage systems are usually not covered by urban municipal pipe networks. According to local environmental protection standards, independent sewage treatment facilities must be set up, which is what we call residential sewage treatment.
There are no uniform restrictions on the treatment capacity of residential sewage systems in various countries. The former Soviet Union suggested that the treatment capacity of a single structure should not exceed 1400 m3/d, while the United States limited the treatment capacity of small factories to 3,785 m3/d ... According to China's national conditions, it is suggested that the treatment plant with a capacity equal to or less than 4,000 m3/d should be defined as a domestic sewage treatment plant.
Residential sewage is different from urban sewage (often including some industrial wastewater) and belongs to the category of domestic sewage. The characteristics of water quality and quantity can be summarized as follows: the water quality and quantity change greatly, the pollutant concentration is low, that is, lower than that of urban sewage, the sewage has good biodegradability and is difficult to treat.
The treatment process of domestic sewage is different according to the function of domestic sewage discharged into water body. Common treatment methods include septic tank, primary treatment (primary sedimentation tank), biological secondary treatment and disinfection and reuse after secondary treatment. Due to the small sewage treatment capacity and low management level in the residential area, the treatment process with no sludge or less sludge should be selected as far as possible in process design to prevent secondary pollution caused by poor sludge treatment. At present, the commonly used treatment processes are: ① sewage → regulating tank → primary sedimentation tank → biological contact oxidation tank → secondary sedimentation tank → effluent. Biological contact oxidation is the most widely used method, and its main advantages are short residence time and easy film formation, which is especially suitable for equipment. Buried construction is favored by environmental protection companies and users, but its application has been limited in recent years due to problems such as maintenance management and equipment anticorrosion. However, if underground reinforced concrete construction is adopted and personnel passages are set up for maintenance, this underground construction method has a large market in residential water treatment, but this method is generally small in treatment scale and ideal for residential areas with daily sewage discharge below several hundred tons. It is recommended to use ground construction, contact oxidation, SBR or its improved CASS process for biological treatment, and use low-noise fan or underwater aerator for aeration. (2) Sewage → regulating tank → coagulation and sedimentation → filtration → effluent, which requires low degree of treatment and small amount of water. The process can be used, and has the advantages of small floor space, small smell and simple management. In addition, adding acidification and hydrolysis before aerobic biological treatment is beneficial to reduce energy consumption and improve the total removal rate of the system. Living quarters usually have a large area of green space. If the treated sewage is reused for watering green spaces, roads and washing cars, disinfection or other auxiliary measures should be added to the treated water.
Second, the design principles of sewage treatment plants in residential areas
1. Requirements and treatment degree of treated sewage
Generally speaking, the requirements of different communities for effluent are very different. The treatment degree should be determined according to the relevant provisions of China's Ground Environmental Quality Standard (GB 3838-88) and Integrated Wastewater Discharge Standard (GB 8978-96) and the requirements of local environmental protection departments to ensure the effluent quality. If the land treatment method is adopted, it shall be calculated according to the requirements of the land treatment method;
2. The design and construction of sewage treatment facilities must be combined with the overall planning and architectural characteristics of the community, that is, the appearance design should be coordinated with the architectural environment of the community in order to be beautiful;
3. The sewage treatment process is as simple and practical as possible and easy to manage;
4. The vertical layout shall be three-dimensional as far as possible to make full use of underground space. The layout should be compact to save land;
5. The sewage treatment plant should be located in the downwind of the community as far as possible, keeping a certain distance from other buildings to reduce the impact on the environment;
6. The equipment is stereotyped and modularized, with convenient construction and installation, simple operation and stable equipment performance.
Suitable for phased construction;
7. The treatment degree is high, the sludge output is low, and energy-saving treatment technology is adopted as far as possible;
8. The treatment structure has wide adaptability to hydraulic load and organic load, which makes the system have good impact load resistance.
The population of this community is increasing gradually. Therefore, sewage treatment plants in residential areas should take predictable development planning as the basis for process design. According to the situation in China, a design cycle of 20 years can be considered.
Third, the residential sewage treatment process
According to the principle of sewage treatment in residential area, the treatment method with stable treatment effect, less sludge production and energy saving is selected. Septic tanks are generally built in various buildings in the community system, so septic tanks should be combined with sewage treatment methods.
Several common treatment processes:
(1) Sewage → Grille → Regulating Pool → Lift Pump → Contact Oxidation Pool → Sedimentation Pool → Effluent.
(2) Sewage → grille → regulating tank → lifting pump → aeration tank → sedimentation tank → effluent.
Sludge reflux
(3) Sewage → grille → regulating pool → lifting pump →SBR pool or CASS→ effluent.
Quantitative feeding
↓
(4) Sewage → grille → regulating tank → lifting pump → coagulation and sedimentation → filtration → effluent (physical and chemical method).
Reuse process: the effluent from biological treatment is coagulated, filtered and disinfected.
In the early stage of the process, it is generally necessary to consider setting up a homogenization tank, because the change of water quality and quantity in the residential area is greater than that in the urban sewage treatment plant. The homogenization pool is generally located behind the grid. Physicochemical and biochemical treatment are the core parts of pollutant removal.
Four, combined sewage treatment plant or equipment
Modular processing equipment is sold with standard equipment components that are assembled or easy to assemble. In China, underground equipment was all the rage. Its main advantages are fast construction speed and no occupation of ground green space. Many designers and users are very welcome. It is simple for designers to choose equipment, but the workload of designing sewage treatment plants is very large. So they like to use equipment products. Environmental protection companies are profitable in manufacturing equipment and low in civil engineering. Therefore, enterprises have made great efforts in advertising and public relations. However, the practical application shows that there are many problems such as difficult equipment maintenance and management, inconvenient operation assessment, limited water treatment capacity of single machine, long service life and so on. Therefore, there has been a great controversy over buried equipment, and now the heat of buried equipment has cooled down. The design method of sewage treatment which is built underground and easy to maintain and operate (there is room for personnel to operate) should be recommended. Above-ground sewage treatment plant is recommended. Buried equipment can still be considered when the water quantity is not large and the site is very tight. The process flow of buried equipment generally adopts two-stage contact oxidation precipitation process, and the hydraulic retention time is generally 2 hours. Before the sewage enters the equipment, adjust and upgrade the water quantity.
5. Principle and parameter selection of 5.SBR and CASS treatment processes.
sequencing batch reactor activated sludge process
The core of SBR is SBR reaction tank, which integrates the functions of homogenization, primary precipitation, biodegradation and secondary precipitation. A complete operation cycle of typical SBR process consists of five stages, namely, water inflow stage, reaction stage, precipitation stage, drainage stage and idle stage. From the first water inflow to the second water inflow, it is called a working cycle.
From the current research, application and development trend of aerobic biological treatment of sewage, SBR is a simple, rapid and low-consumption sewage treatment process. Compared with continuous activated sludge process, SBR process has the following characteristics: ①SBR device has simple structure, flexible operation and convenient operation and management. (2) Low investment and operation cost. The statistical results of Ketchum et al. show that SBR process can save 30% capital investment compared with ordinary activated sludge process. ③ It can inhibit the growth and reproduction of filamentous bacteria, and it is not easy to cause sludge bulking, and the sludge index SVI is low, which is beneficial to the precipitation and concentration of activated sludge. (4) (4) SBR is in the process of aerobic/anaerobic alternate operation, and nitrogen and phosphorus are removed at the same time of carbon removal. ⑤SBR process system is compact and saves land. ⑥ Good operation stability, and can bear large impact of water quality and quantity. ⑦ All operation control parameters can be controlled by computer, which is easy to realize the optimal operation of the system.
(3) Circulating aeration activated sludge process (CASS process)
CASS (Circulating Activated Sludge System) process is an internationally recognized advanced process for treating domestic sewage and industrial wastewater in recent years. The process is based on sequencing batch reactor (SBR). The reaction tank is designed into two parts along the length direction. The front part is the biological selection area, also called the pre-reaction area, and the back part is the main reaction area. An automatic skimming device is installed at the back of the main reaction zone, and the processes of aeration, sedimentation and drainage run periodically in the same tank, thus eliminating the secondary sedimentation tank and sludge reflux system of the traditional activated sludge process.
(Selection of aeration modes of CASS and SBR.
Because most of the residential areas are residential areas, the requirements for the environment are relatively high. Therefore, the construction of sewage plant should fully consider the noise disturbing people and the working environment of sewage plant operators. Using underwater aerator instead of traditional blower for aeration can effectively solve the problem of noise pollution. In addition, due to the unique operation mode of CASS process, the use of underwater aerator can save complex pipes and valves, which is convenient to install and maintain, flexible to use, and can start different units according to the inlet and outlet conditions, so as to achieve the purpose of economic operation under the condition of ensuring the effect.
(the choice of CASS and SBR skimmers
Slag skimmer is the key component of CASS process, and its stability and reliability directly affect the normal operation of CASS process. At present, the research and development of oil skimmer at home and abroad is still going on. According to the principle currently used, oil skimmers can be divided into three types, namely, floating ball type, rotary type and siphon type. The key to the development of skimmer is to solve the dynamic balance between weir, guide hose, lifting control device and water flow in the process of decanting, so that it can adjust the immersion depth of floating weir with different displacement, rise and fall evenly with the water level, minimize the interference of drainage on sediment, and ensure the stability of effluent quality.
The water skimmer independently developed by our hospital belongs to lead screw rotary type. The main components of the automatic skimmer are: decanter, disturbance hose, water level controller, telescopic push rod and driving motor. Among them, the decanter is also called automatic floating weir, and the upper part is weir and buoy to prevent scum from entering the water outlet. The lower outlet pipe also plays a supporting role, partially submerged in water, so that the square weir can continuously and uniformly discharge the supernatant in the reaction tank through the telescopic push rod. The practical application shows that the skimming device has reached the advanced level of similar products at home and abroad. It has the advantages of smooth lifting, uniform drainage, automatic control and low price. This study not only meets the needs of the project, but also is innovative and belongs to one of the special safety technologies.
Five, the main design parameters of residential sewage treatment
Design parameters of SBR: sludge load 0.1~ 0.15 kgbod5/kgmlss.d, sludge age 20~30 days.
The working cycle is 12 hour, in which water inflow is 2.5 hours (with or without aeration), reaction is 6 hours, precipitation is 0.75~ 1 hour, drainage is 2 hours, and idling is 0.5~0.75 hours. Effluent indicators: COD < 50mg mg/L, BOD5 < 20mg mg/L, SS <10mg/L.
CASS design parameters: sludge load 0. 1~0.2kgBOD5/kgMLSS.d, sludge age 15~30 days.
The hydraulic retention time is 12 hour, and the working period is 4 hours, including 2.5 hours of aeration, 0.75 hours of sedimentation and 0.5-0.75 hours of drainage. The effluent index is similar to SBR.
Six, sludge treatment
When the sewage treatment capacity is 1000 tons, it is generally concentrated and then dehydrated. When it is small-scale, it is generally transported to landfill or used as agricultural fertilizer by dung trucks regularly.
Seven, residential sewage treatment site selection and layout
The site selection and factory layout of the community system are basically the same as those of large factories. However, considering the uniqueness of community system in the choice of service objects and processes, the characteristics of community system should also be considered in the site selection and layout.
1. Site planning
(l) The service area should be at a certain distance from the health protection.
(2) Wind direction (does not affect the service area and surrounding areas)
(3) Transportation and water and electricity supply.
(4) It is convenient to consider the unified management of other living security facilities in the community.
2. The distance between the road and the building in the factory.
Because the residential system uses smaller equipment and structures, the space required for transportation, maintenance and sanitation in the factory area is correspondingly smaller. Adequate vehicle passages should be designed in the factory area, and the road width can be designed according to the turning radius of light trucks. The spacing between main structures can be considered as 3-5m.
reference data
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Discussion on Optimization and Comparison of Sewage Treatment Processes
Paper Keywords: urban sewage treatment operation management process selection
In view of the problems exposed in the construction and operation management of existing urban sewage treatment plants, this paper makes a comparative analysis from the perspectives of construction scale and process determination, and puts forward some opinions on the links that should be paid attention to.
Because industrial wastewater treatment facilities are generally small in scale, highly technical, flexible in process combination, and usually made of steel, it is not too difficult to operate and maintain even if there are many internal pipelines. Industrial wastewater treatment is similar to urban sewage treatment in technology, but if the design idea of industrial wastewater treatment facilities is simply applied to urban sewage treatment projects, it will bring many unexpected problems.
1. Reasonably determine the construction scale
The determination of urban sewage plant construction planning is to build sewage pipe network and sewage treatment plant by stages according to the overall urban planning and drainage planning, and to implement them by stages according to the water environment protection objectives. Urban drainage engineering construction is a systematic project, involving the reconstruction of urban pipelines and ditches, sewage collection and transportation (including pumping stations), sewage treatment and discharge utilization, sludge disposal, etc.
2. Process selection of urban sewage treatment plant
The selection requirements for specific projects include:
① The process is reasonable. Advanced and mature technology, strong adaptability to water quality changes, high effluent quality and stability, and easy sludge treatment.
② Economical and energy-saving. Low power consumption, low cost and less land occupation.
③ Easy to manage. Convenient operation and management, reliable equipment.
④ Pay attention to the environment. The layout of the factory should be coordinated with the surrounding environment, pay attention to the noise control and odor control in the factory, and do a good job in the combination of greening, road construction and phased construction.
⑴ Aerobic biological treatment technology is widely used in urban sewage treatment plants all over the world, which can be divided into activated sludge method and biofilm method. Activated sludge process is an artificial enhancement of water self-purification, and it is a technology that makes microbial groups "inhabit" on activated sludge. Activated sludge is suspended in reactor-aeration tank and widely contacts with sewage to purify sewage. Biofilm method is a method of artificially strengthening soil self-purification, and it is a technology that makes microbial communities attach to the surface of objects in the form of membranes and contact with sewage to purify sewage. Activated sludge process, biofilm process and their variants have their own characteristics and applicable conditions. When selecting them, they should be determined according to the water quality, quantity, receiving water body, climate, environment and economic conditions of each region.
⑵ There is no breakthrough in the purification mechanism of activated sludge process. After decades of development and innovation, there are many operation modes based on the traditional activated sludge process, such as A/O phosphorus removal process, A/O nitrogen removal process, A2/O simultaneous nitrogen and phosphorus removal process, oxidation ditch process, A/B process, various SBR processes, carrier activated sludge process and integrated activated sludge process. In recent ten years, the biggest progress of activated sludge process is to introduce anaerobic mechanism into biochemical reaction tank, so that anaerobic and aerobic conditions can coexist or be realized repeatedly and periodically in biochemical tank, but its basic process principle is consistent with the standard method.
⑶ Anaerobic-aerobic activated sludge process (A/O process) is a standard activated sludge process with biological selection function and nitrogen and phosphorus removal function. Anaerobic means that the dissolved oxygen in the biochemical reaction section tends to zero. In this environment, the metabolic function of obligate aerobic microorganism-filamentous bacteria is forced to drop sharply, which inhibits its reproduction and plays an anaerobic biological selection role, thus preventing sludge bulking. A/O activated sludge process is to add an anaerobic stage to the previous stage of general activated sludge process, and realize the function of phosphorus removal or nitrogen removal through the change of sludge load. A2/O method is developed on the basis of A/O method, that is, adding anoxic section between anaerobic section and aerobic section to realize simultaneous phosphorus and nitrogen removal. Because of its small adaptability to sludge load, it is often carried out as a function of phosphorus removal or nitrogen removal in actual operation. A/O process and A2/O process are widely used in large and medium-sized sewage plants at home and abroad because of their stable effluent quality, low energy consumption and convenient operation and management.
(4) Carrier activated sludge process is to add solid particles or soft and semi-soft fillers into the activated sludge process reaction tank to increase the microbial biomass per unit reaction space and increase the reactor volume load. It is a good combination of activated sludge process and biofilm process, and is generally suitable for tapping potential and improving the treatment capacity of sewage treatment plants. Its core technology is patented filler, and in recent years, it is represented by forest bubble process in Dalian Liu Chun Sewage Treatment Plant and Tieling Sewage Treatment Plant.
5] Oxidation ditch method, developed by the Dutch Basville in 1950s, mainly includes several technical forms, such as Carroussel, Sangou, Integration and Obert. Oxidation ditch method is a closed biochemical reaction ditch, which is powered by turntable or brush for oxygenation and water flow. Simple process and low requirements for operation and management. It is mostly used to prolong aeration, resulting in less sludge and easy dehydration. Oxidation ditch method has been widely used in southern and central and western regions of China.
[6] A/B method (absorption-biodegradation) is a two-stage biochemical reaction system. The first stage is biosorption, with high sludge load and short reaction time (30 minutes); The second stage is a common biochemical reaction tank, and the sludge load is the same as that of the common activated sludge process. The first and second stages of A/B process have secondary sedimentation tanks and sludge reflux systems, which are mostly used for high-concentration domestic sewage. Its typical domestic applications are Urumqi Hedong Sewage Treatment Plant and Qingdao He Haibo Sewage Treatment Plant.
(7)SBR- sequencing batch reactor is a water treatment process invented by British scholars Ardern and Locket in 19 14. In the early 1970s, Professor R.Irvine of Natre Dame University in the United States made a systematic and in-depth study on SBR process in the laboratory scale, and in 1980, with the support of the US Environmental Protection Agency (EPA), the world's first SBR sewage treatment plant was rebuilt and operated in Culwer City, Indiana.
⑻ The intermittent circulation extended aeration activated sludge system was developed in 1968 by the University of New South Wales in Australia and ABJ Company in the United States. 1976, the world's first ICEAS process sewage treatment plant was put into operation. Compared with the traditional SBR, the biggest feature of ICEAS is that the pre-reaction zone is set at the water inlet of the reactor, and the whole treatment process is continuously filled with water and intermittently drained, with no obvious reaction stage and idling stage, and the treatment cost is lower than that of the traditional SBR. The typical application of this process in China is Kunming No.3 Sewage Treatment Plant, which has great influence in China.
(9) Biofilm method is another widely used biochemical treatment method for sewage. This treatment method is to make bacteria, fungi and other microorganisms and protozoa, metazoa and other microorganisms attach to the carrier or filter material for growth and reproduction, and form membrane biological sludge-biofilm on it. When sewage comes into contact with biofilm, organic pollutants in sewage are absorbed by microorganisms on biofilm as nutrients, so that sewage is purified and microorganisms themselves can reproduce.
3. According to the comparative analysis of the above processes and technologies, combined with the sewage quality in Kuitun City, it is considered that the more suitable treatment processes are as follows:
The first scheme: A/O process.
The biggest progress of activated sludge process in recent twenty years is to introduce anaerobic mechanism into biochemical reaction tank. The intermittent operation of anaerobic and aerobic has brought new technical and economic effects to the activated sludge process, such as biological nitrogen removal, biological phosphorus removal and biological selection.
Anaerobic-aerobic activated sludge process (A/O process) is a standard activated sludge process with biological selection function and denitrification function.
The second scheme: Dart -IAT process.
Dat-IAT- aeration tank on demand-intermittent tank is a new SBR process. It is between the traditional activated sludge process and the typical SBR, and adopts the operation mode of continuous water inflow and continuous-intermittent aeration, which is suitable for the situation that the water quality and quantity of inlet water change greatly. The main structure consists of aerobic pool DAT pool and intermittent aeration pool IAT pool. DAT tank is continuously aerated, and its effluent enters IAT tank from the middle wall, and IAT tank continuously feeds water and intermittently drains water. At the same time, IAT pool sludge DAT pool. Belonging to the extended aeration process, it is actually a combination of A/O denitrification process and traditional SBR. The sludge load in this industry is low, so it has the characteristics of strong impact resistance and strong denitrification function. The sewage treatment plant in Tianjin Technological Development Zone and the sewage treatment plant in Sanbaotun, Fushun should use this industrial country, which is a SBR process suitable for large amount of water.
4. Comparison of scientific process schemes:
It is necessary to compare the process schemes (mainly biological treatment schemes) according to local conditions. The comparison of process schemes should be objective and comprehensive. Under the same influent and effluent conditions, its design parameters should include comprehensive analysis of various pollutants removal rate, aeration time, sludge load and volume load, aeration amount and oxygen utilization rate (and power efficiency), sludge output (and sludge index), etc. With abundant data, we can brainstorm, foster strengths and avoid weaknesses, which is reasonable in technology, economical, convenient in management and reliable in operation, and beneficial to the near future.
reference data
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