Low-load domestic sewage treatment system and process adopting variable biofilm process

Abstract

The invention relates to a low-load domestic sewage treatment system and process based on a variable biofilm process, and relates to the technical field of sewage treatment. The system comprises a pump station forebay, solid-liquid separation equipment for removing slag sand, hair and fibers in sewage, an intermediate water tank, a coagulation reaction tank, a composite polymer filler filtering system for removing SS and TP in raw water, a sewage inlet biochemical unit for removing COD, BOD, NH3-N and TN in sewage, and a cloth filter for further removing SS, which are arranged and communicated in sequence. The sewage treatment device has the advantages of meeting the water quality standard, adapting to working condition changes and flexibly and adjustably treating sewage on the premise that the occupied area is small.

Description

Technical Field

[0001] The present application relates to a low-load domestic sewage treatment system and process using a variable biofilm method, and particularly to the technical field of sewage treatment. Background Art

[0002] In the mainstream process of current urban sewage treatment plants for capacity expansion, there are certain limitations in both the pretreatment and biochemical process sections. Especially in the south where the influent water quality concentration is relatively low, higher requirements are put forward for capacity expansion and transformation.

[0003] First of all, the operation effect of traditional pretreatment processes is poor. For example, a fine grille can generally only remove pollutants of 1 mm and above, and it cannot effectively intercept suspended pollutants such as hair and fine residues in sewage; the design and operation of a grit chamber are only based on the standard of removing sand particles of about 0.2 mm, and the actual operation effect strongly depends on the influent flow pattern; the primary sedimentation tank has a large floor area and consumes biodegradable carbon sources.

[0004] In the case of insufficient influent carbon sources, most sewage treatment plants have cancelled the primary sedimentation tank, resulting in a large amount of inorganic particles entering the biochemical tank, further increasing the load pressure on the subsequent system. Poor pretreatment will lead to serious siltation of the reaction tank, reduction of the effective volume, poor sludge activity and reduced treatment capacity of the biochemical unit, and serious entanglement, blockage and wear of equipment; too many inorganic particles entering the biochemical tank will increase the sludge concentration and the amount of excess sludge for the activated sludge process, and for the biofilm method, problems such as filter media blockage are likely to occur.

[0005] Regarding the biochemical process again, at present, the activated sludge process is the mainstream process in urban sewage treatment plants, and AAO accounts for more than 90%. However, various activated sludge processes do not have obvious advantages in dealing with the working conditions of relatively low sewage water quality concentration in the southern region. Especially during expansion, due to its high volumetric load, the floor area of the facilities is too large to meet the expansion requirements; at the same time, the activated sludge process cannot withstand water volume shocks and is helpless in the case of combined sewage during the rainy season in the southern region, resulting in frequent overflow pollution, which is one of the main reasons for the black and odorous urban water bodies.

[0006] The biofilm method is a sewage treatment method in which microorganisms grow attached in the form of a biofilm on a carrier and biochemical reactions are carried out to remove pollutants. Compared with the activated sludge method, its greatest characteristics are 1. High pollutant load, short residence time of the facility, and small floor area; 2. Strong ability to resist hydraulic shock load; 3. Functional bacteria such as nitrifying bacteria prefer attached growth, which is convenient for enrichment, and the biochemical environment is single and stable, avoiding the adverse effects caused by the alternation of aerobic and anoxic conditions.

[0007] Traditional biological membrane processes also have certain drawbacks. Taking the aerated biological filter (BAF) process, a typical fixed-bed form, as an example, it generally uses the secondary biochemical effluent as the influent and cannot directly treat raw sewage. As a result, the goal of overall process land saving cannot be achieved, and problems such as filter clogging may occur when the influent concentration is high. Taking the MBBR process, a typical fluidized-bed form, as an example, its denitrification rate is restricted by the reflux ratio and cannot meet the requirements of high denitrification rates. At the same time, the volumes of the anaerobic, anoxic, and aerobic units are fixed, and there is no possibility of adjustment according to water quality changes, lacking flexibility.

[0008] In summary, the influent concentrations of most urban sewage treatment plants in the south are generally low, the operating load rates are high, and at the same time, they are facing the pressure of upgrading or in-situ expansion. Therefore, it is extremely important to develop a treatment process that can meet water quality standards and be flexibly adjustable to working conditions under extremely limited land occupation. Summary of the Invention

[0009] For [purpose not specified in the original], the present application provides a low-load domestic sewage treatment system and process using a variable biological membrane method.

[0010] In the first aspect The present application provides the following technical solutions: A low-load domestic sewage treatment system using a variable biological membrane method, comprising a pumping station forebay, a solid-liquid separation device for removing slag, sand, hair, and fibers from sewage, an intermediate water tank, a coagulation reaction tank, a composite polymer filler filtration system for removing SS and TP from raw water, a sewage influent biochemical unit for removing COD, BOD, NH3-N, and TN from sewage, and a fabric filter for further removing SS, which are arranged and connected in sequence.

[0011] By adopting the above technical solutions, the low-load domestic sewage treatment system can effectively achieve the hierarchical treatment of sewage. First, through the coordinated action of the pumping station forebay and the solid-liquid separation device, solid impurities such as slag, sand, hair, and fibers in the sewage are efficiently removed, thereby reducing the burden on subsequent treatment units and protecting the normal operation of equipment. Secondly, after adjusting the water quality and quantity in the intermediate water tank, the combination of the coagulation reaction tank and the composite polymer filler filtration system is used to further remove the suspended solids (SS) and phosphorus (TP) that are difficult to precipitate in the raw water, improving the pretreatment effect. Furthermore, the sewage influent biochemical unit deeply purifies organic pollutants such as chemical oxygen demand (COD), biochemical oxygen demand (BOD), ammonia nitrogen (NH3-N), and total nitrogen (TN) to ensure that the main pollution indicators of the effluent meet the discharge or reuse standards. Finally, with the help of the fabric filter, tiny particulate matter is accurately intercepted, making the finally discharged wastewater meet higher clarity requirements. The entire process is designed reasonably and compactly, and the connection between each link is smooth, significantly improving the overall treatment efficiency of low-load domestic sewage.

[0012] Optionally, the sewage inlet biochemical unit includes multiple groups of variable biofilm reactors arranged in sequence, and two adjacent reactors are interconnected.

[0013] By adopting the above technical solution, the sequential arrangement of multiple groups of variable biofilm reactors and the interconnection between adjacent reactors enable the sewage to flow continuously between multiple reactors, increasing the stability and flexibility of the treatment process. This design helps to optimize the removal effects of COD, BOD, NH3-N, and TN in the sewage, while improving the shock resistance and treatment efficiency of the system.

[0014] Optionally, a single variable biofilm reactor can switch between aerobic nitrification and anoxic denitrification modes.

[0015] By adopting the above technical solution, the variable biofilm reactor in the low-load domestic sewage treatment system has the ability to switch between aerobic nitrification and anoxic denitrification modes. This design enables the treatment system to flexibly adjust the working mode according to the types and concentration changes of pollutants in the sewage, thereby effectively meeting the treatment requirements under different water quality conditions. Specifically, this technical means significantly improves the adaptability and treatment efficiency of the system, ensuring the stable compliance of the effluent quality.

[0016] Optionally, the variable biofilm reactor includes a pool body, an upper diversion channel, a sawtooth inlet and outlet weir, a packing interception screen, a mobile diversion channel, an aeration device, and a blower for delivering gas to the aeration device.

[0017] By adopting the above technical solution, the variable biofilm reactor consists of a pool body, an upper diversion channel, a sawtooth inlet and outlet weir, a packing interception screen, a mobile diversion channel, an aeration device, and a blower, realizing the efficient treatment of sewage. The pool body serves as the main structure, providing spatial support for the entire reaction process; the design of the upper diversion channel and the sawtooth inlet and outlet weir optimizes the water flow distribution, improves the inlet and outlet efficiency, and reduces the short-circuit phenomenon; the packing interception screen effectively prevents the loss of packing, ensuring the stable operation of the system; the mobile diversion channel enhances the operation flexibility and can adjust the water flow direction as needed; the aeration device, combined with the blower, ensures sufficient oxygen supply, meeting the growth requirements of aerobic microorganisms, thereby enhancing the organic matter degradation efficiency and ammonia nitrogen removal capacity.

[0018] Second aspect This application also discloses a low-load domestic sewage treatment process using the variable biofilm method, which utilizes the above-mentioned low-load domestic sewage treatment system using the variable biofilm method, and includes the following steps: S1. Remove pollutants such as garbage, scum, and plant residues in the sewage through a solid-liquid rapid separation device, and reduce the contents of COD and SS. The composite polymer filler filtration system can further remove organic nitrogen and TP. S2. According to the impact of the change in TN concentration in the influent in different seasons on the system, switch the aerobic nitrification and anoxic denitrification functions of the variable biofilm reactor as needed. In the aerobic nitrification mode, flexibly switch between the fluidized bed and fixed bed dual modes to achieve the operation mode under different influent flow rates and achieve the effect of resisting hydraulic shock. S3. Further remove SS through a cloth filter tank to improve the SS index of the effluent.

[0019] By adopting the above technical solutions, pollutants such as garbage, scum, and plant residues in the sewage can be removed, and the contents of COD and SS can be reduced. Combined with fiber bundle filtration, organic nitrogen and TP can be further removed, effectively improving the purification ability in the pretreatment stage and reducing the burden on the subsequent treatment units. Moreover, in response to the change in the TN concentration of the influent in different seasons, the variable biofilm reactor can switch between the aerobic nitrification and anoxic denitrification modes as needed, enhancing the adaptability and flexibility of the system. In the aerobic nitrification mode, it can also flexibly switch between the fluidized bed and fixed bed dual modes, thereby optimizing the operation mode under different influent flow rates and significantly improving the ability to resist hydraulic shock. Finally, SS is further removed through a cloth filter tank to ensure that the effluent quality meets the standards stably and improve the effect and reliability of the overall treatment process.

[0020] Optionally, the filler density in the variable biofilm reactor is 1.05 - 1.08 g / cm3, the shape is a porous plastic sphere with a diameter of 20 mm, which can be in a fluidized state when the gas volume is large, and the filling ratio is 60 - 70%.

[0021] By adopting the above technical solutions, the filler density is set to 1.05 - 1.08 g / cm³ to ensure good suspension performance of the filler in water and avoid excessive weight leading to increased energy consumption. The filler shape is designed as a porous plastic sphere with a diameter of 20 mm, which increases the specific surface area, is conducive to the attachment and growth of microorganisms, and improves the biological treatment efficiency. When the gas volume is large, the filler can be in a fluidized state, enhancing the mass transfer effect and mixing uniformity, and further improving the reaction rate. The filling ratio is controlled at 60 - 70%, which not only ensures sufficient space for the biofilm carrier but also leaves appropriate gaps to reduce the risk of blockage and optimize the water flow distribution.

[0022] Optionally, in the aerobic nitrification mode, the variable biofilm reactor selects the operation mode of the packing in the reaction tank according to the pollutant load rate of the influent. When the pollutant load of the influent is low, the variable biofilm reactor is adjusted to the fixed-bed mode. At this time, the biofilm is fixed, and the water flow passes through the packing layer for biochemical reaction to reduce the aeration volume and save the energy consumption of the aeration in the stirring part. The air-water ratio can be reduced to 3:1 - 5:1. When the pollutant load of the influent increases, the variable biofilm reactor is adjusted to the fluidized-bed mode. At this time, the packing is in a fluidized state, the biochemical reaction efficiency is accelerated, and at the same time, the air volume increases, and the air-water ratio is 4:1 - 10:1.

[0023] By adopting the above technical solution, the treatment process can flexibly adjust the operation mode of the variable biofilm reactor according to the change of the pollutant load of the influent. Thus, the aeration demand can be significantly reduced, and the energy consumption can be reduced. This design of mode switching effectively achieves the balance between energy conservation and consumption reduction and high-efficiency treatment, and at the same time enhances the ability of the system to resist water quality fluctuations.

[0024] Optionally, in the anoxic denitrification mode, the variable biofilm reactor operates in the fixed-bed mode; the residence time is 0.4 - 0.6 hours, the nitrate nitrogen volume load: 0.80 - 1.30 kg nitrate nitrogen / (m3 filter material · d), and air washing is used for backwashing. The air washing intensity is 20 L / m2·s, the duration is 6 - 8 min, and the backwashing period is 24 hours.

[0025] By adopting the above technical solution, the effective removal and load management of nitrate nitrogen are realized, the cleaning and regeneration effect of the packing are ensured, the service life of the system is extended, and the long-term stable treatment performance is maintained.

[0026] In summary, the present application includes at least one of the following beneficial technical effects: 1. It can cope with low-concentration influent, get rid of the bondage of the hydraulic flow regime, and the sewage influent biochemical unit operates in the form of a flexible and variable biofilm. The combination of the two can withstand the water volume impact load; at the same time, the residence time of each unit of the present invention is short, and the floor area is small, which can save land for the transformation or expansion of existing facilities; 2. It can carry out denitrification through endogenous denitrification. If the influent concentration is high, a composite carbon source is added for efficient denitrification; it can efficiently remove COD, BOD, NH3-N, and TN; 3. It can greatly reduce the occurrence of phenomena such as hair, fiber entanglement, and blockage, and can greatly remove slag, sand, hair, and fiber materials with a particle size of more than 0.2 mm. Description of the Drawings

[0027] Figure 1 It is a schematic diagram of the overall structure of the embodiment of the present application; Figure 2It is a schematic diagram of the switching between aerobic mode and anoxic mode of the sewage inlet biochemical unit in the embodiment of the present application; Figure 3 It is a schematic diagram of the switching between fluidized bed and fixed bed in the aerobic mode of the sewage inlet biochemical unit in the embodiment of the present application. In the figure, 1 is the forebay of the pumping station; 2 is the solid-liquid separation equipment; 3 is the intermediate water tank; 4 is the coagulation reaction tank; 5 is the composite polymer filler filtration system; 6 is the sewage inlet biochemical unit; 61 is the variable biofilm reactor; 611 is the tank body; 612 is the upper diversion trough; 613 is the sawtooth water inlet weir; 614 is the filler interception screen; 615 is the mobile diversion trough; 616 is the aeration device; 617 is the fan; 618 is the intermediate fixed diversion trough; 7 is the intermediate lift pump; 8 is the chemical dosing device; 9 is the raw water lift pump; 10 is the fabric filter. Detailed implementation manners

[0028] The following further elaborates on the present application in conjunction with the attached Figure 1 - attached Figure 3 drawings for a more detailed description.

[0029] First aspect An embodiment of the present application is: a low-load domestic sewage treatment system using a variable biofilm method. Referring to Figure 1 the figure, it includes a forebay of the pumping station 1, a solid-liquid separation equipment 2 for removing slag, sand, hair and fiber in sewage, an intermediate water tank 3, a coagulation reaction tank 4, a composite polymer filler filtration system 5 for removing SS and TP in raw water, a sewage inlet biochemical unit 6 for removing COD, BOD, NH3-N and TN in sewage, and a fabric filter 10 for further removing SS, which are arranged in sequence and connected.

[0030] Among them, the forebay of the pumping station 1 is the water inlet end of the whole process. The solid-liquid separation equipment 2 is the solid-liquid separation equipment 2 for removing slag, sand, hair and fiber in sewage in the prior art. The filter cloth used can be specially woven from a new type of polymer material, and its surface structure is dense, reducing the phenomenon of hair and fiber entanglement and blockage. Its filtration effect can remove more than 95% of slag, sand, hair and fiber substances above 0.2mm, the SS interception rate is above 30%, and the particulate COD interception rate is 15-25%. At the same time, in order to ensure its filtration effect, the filter cloth can be continuously washed through a high-pressure backwashing device, and the high-pressure backwashing device for continuous washing and continuous slag discharge can be used to continuously wash and discharge slag for the filter cloth, and the backwashing water volume per ton of water is less than 0.7L / h.

[0031] The composite polymer filler filtration system 5 is a composite polymer filler filter used in the prior art to remove SS and TP in raw water. The selected composite polymer filler filtration system 5 is usually mainly composed of a water distribution system, a water inlet area, a guide baffle, a pre-sedimentation area, a filtration area, a backwashing tank, a filter material backwashing fan, a mud pump and a control system; the pre-sedimentation area includes a filter area, a buffer sedimentation area, and a mud storage hopper; the filtration area includes granular suspended fiber filter material, an outlet overflow weir and a filter material baffle, etc.

[0032] The filter material of the selected composite polymer filler filtration system 5 is a granular fiber filter material made of microporous composite fiber material, in the shape of a cube with a side length of 8-12 mm, and a porous space inside; the filter material has a slightly smaller specific gravity than water, and during use, the filter material floats on the upper part of the water layer; the porosity distribution of the filter material layer is uniform, ensuring the consistency of the size of the water flow channel during filtration, and no water flow short circuit phenomenon occurs. The filter material layer is regularly aerated and backwashed, with a backwash interval of 3-6 hours and an aeration cleaning intensity of 0.4-0.6Nm3 / m2 / min.

[0033] The composite polymer filler filtration system 5 selected in this embodiment has a COD and SS removal rate of 40-60%; when PAC is added, the TP removal rate is 80-90%.

[0034] A raw water lift pump 9 is provided between the pump station fore pool 1 and the solid-liquid separation device 2 for connecting the two. An intermediate lift pump 7 is installed between the intermediate water tank 3 and the coagulation reaction tank 4. A dosing device 8 for adding additional drugs between the intermediate water tank 3 and the coagulation reaction tank 4 is provided on one side of the intermediate lift pump 7. The dosing device 8 is a drug feeding device in the prior art.

[0035] Reference Figure 2 and Figure 3 The sewage inlet biochemical unit 6 includes a plurality of groups of variable biofilm reactors 61 arranged in sequence, and two adjacent groups of reactors are connected to each other. The sewage inlet biochemical unit 6 is referred to as MFR for short, and the variable biofilm reactor 61 includes a tank body 611, an upper guide groove 612, a sawtooth inlet and outlet weir, a filler interception screen 614, a movable guide groove 615, an intermediate fixed guide groove 618, an aeration device 616 and a fan 617 for conveying gas into the aeration device 616.

[0036] A single variable biofilm reactor 61 can switch between two modes: aerobic nitrification (MFR-O) and anoxic denitrification (MFR-A). It is combined in the form of a series connection of multiple sets of equipment, and the combination ratio is adjusted according to the actual influent. Generally, the combination ratio of aerobic to anoxic is 3:1 to 7:1, the total residence time is 1.2 to 1.6 hours, the BOD5 volume load is 0.60 to 0.88 kg BOD5 / (m3 filter material·d); the ammonia nitrogen volume load is 0.15 to 0.32 kg ammonia nitrogen / (m3 filter material·d). The filler selected in the sewage influent biochemical unit 6 has a density slightly greater than that of water, which is 1.05 to 1.08 g / cm3, and its shape is a porous plastic sphere with a diameter of 20 mm. It can be in a fluidized state when the gas volume is large. The filling ratio is 60 to 70%.

[0037] In the aerobic nitrification mode, the variable biofilm reactor 61 selects the operation mode of the filler in the reaction tank according to the pollutant load rate of the influent. When the pollutant load of the influent is low, the variable biofilm reactor 61 is adjusted to the fixed bed mode. At this time, the biofilm is fixed, and the water flow passes through the filler layer for biochemical reaction to reduce the aeration gas volume and save the energy consumption of the aeration in the stirring part. The air-water ratio can be reduced to 3:1 to 5:1; when the pollutant load of the influent increases, the variable biofilm reactor 61 is adjusted to the fluidized bed mode. At this time, the filler is in a fluidized state, the biochemical reaction efficiency is improved, and at the same time the gas volume increases, and the air-water ratio is 4:1 to 10:1.

[0038] In the anoxic denitrification mode, the variable biofilm reactor 61 operates in the fixed bed mode. The residence time is 0.4 to 0.6 hours, and the nitrate nitrogen volume load is 0.80 to 1.30 kg nitrate nitrogen / (m3 filter material·d). Backwashing is carried out by air washing, the air washing intensity is 20 L / m2·s, the duration is 6 - 8 min, and the backwashing cycle is 24 hours.

[0039] When the variable biofilm reactor 61 switches to anoxic nitrification reaction, the upper part of the middle fixed diversion trough 618 is adjusted to a closed mode to prevent the influent from short-circuiting directly through the inlet and outlet weir trough at the upper part; the movable diversion trough 615 on the side is moved to a vertical state close to the side wall of the equipment to remove the diversion function. After the blower 617 stops aeration, the filler stops fluidizing, and the sediment accumulates into a fixed bed shape. The influent enters from the right inlet weir trough and passes through the entire fixed bed filler area through the "U"-shaped overflow channel, and reacts with the denitrifying bacteria on the filler to complete the denitrification process. Moreover, according to the phased change of the influent water quality, the ratio of the aerobic and anoxic sections can be adjusted to achieve a higher denitrification rate. When the influent TN concentration is high, to ensure the denitrification rate, a high-efficiency composite carbon source can be added to the anoxic variable biofilm reactor 61 section to strengthen the denitrification effect.

[0040] In the aerobic nitrification mode, the operation mode of the packing in the reaction tank is selected according to the pollutant load rate of the influent. When the pollutant load of the influent is low, the variable biofilm reactor 61 is adjusted to the fixed-bed mode. At this time, the biofilm is fixed, and the water flows through the packing layer for biochemical reactions to reduce the aeration volume and save the energy consumption of the aeration in the stirring part.

[0041] Refer to Figure 3 , the initial state is the fluidized-bed mode. At this time, single (left) side aeration is carried out to achieve the "O"-shaped annular flow state. The packing is fully fluidized, and the biochemical reaction efficiency is improved. The gas-water ratio is 4:1 to 10:1; when the pollutant load of the influent decreases, the movable diversion trough 615 is placed in the vertical wall-attached state to cancel the diversion effect, and the "O"-shaped packing annular flow state is destroyed. The gas-water ratio drops to 3:1 to 5:1. At this time, the packing begins to settle and accumulate to form the fixed-bed mode.

[0042] The second aspect The embodiment of the present application also discloses a low-load domestic sewage treatment process by the variable biofilm method, which uses the above-mentioned low-load domestic sewage treatment system by the variable biofilm method, and includes the following steps: S1. Remove pollutants such as garbage, scum, and plant residues in the sewage through the solid-liquid rapid separation equipment, and reduce the contents of COD and SS; cooperate with the composite polymer packing filtration system 5 to further remove organic nitrogen and TP; S2. According to the impact of the change of the influent TN concentration in different seasons on the system, switch the aerobic nitrification and anoxic denitrification functions of the variable biofilm reactor 61 as needed. In the aerobic nitrification mode, the dual-mode flexible conversion between the fluidized bed and the fixed bed is realized to achieve the operation mode under different influent flow rates and achieve the effect of resisting hydraulic shock; S3. Further remove SS through the fabric filter 10 to improve the effluent SS index.

[0043] The packing density in the variable biofilm reactor 61 is 1.05 to 1.08 g / cm3, and the shape is a porous plastic sphere with a diameter of 20 mm. It can be in a fluidized state when the gas volume is large, and the filling ratio is 60 to 70%.

[0044] When the variable biofilm reactor 61 is in the aerobic nitrification mode, the operation mode of the packing in the reaction tank is selected according to the pollutant load rate of the influent water. When the pollutant load of the influent water is low, the variable biofilm reactor 61 is adjusted to the fixed-bed mode. At this time, the biofilm is fixed, and the water flow passes through the packing layer for biochemical reaction to reduce the aeration volume and save the energy consumption of the aeration in the stirring part. The air-water ratio can be reduced to 3:1 - 5:1. When the pollutant load of the influent water increases, the variable biofilm reactor 61 is adjusted to the fluidized-bed mode. At this time, the packing is in a fluidized state, the biochemical reaction efficiency is accelerated, and at the same time, the air volume increases, and the air-water ratio is 4:1 - 10:1.

[0045] When the variable biofilm reactor 61 is in the anoxic denitrification mode, it operates in the fixed-bed mode; the residence time is 0.4 - 0.6 hours, the nitrate nitrogen volume load: 0.80 - 1.30 kg nitrate nitrogen / (m3 filter material · d), the backwashing is carried out by air washing, the air washing intensity is 20 L / m2·s, the duration is 6 - 8 min, and the backwashing cycle is 24 hours.

[0046] The embodiments of this specific implementation manner are all preferred embodiments of this application, and do not limit the protection scope of this application accordingly. The same components are denoted by the same reference numerals. Therefore, all equivalent changes made according to the structure, shape, and principle of this application should be covered within the protection scope of this application.

Claims

1. A low-load domestic sewage treatment system using a variable biofilm method, characterized in that: The invention comprises a pump station forebay (1), a solid-liquid separation device (2) for removing slag, hair and fiber in sewage, an intermediate water tank (3), a coagulation reaction tank (4), a composite polymer filler filtration system (5) for removing SS and TP in raw water, a sewage inlet biochemical unit (6) for removing COD, BOD, NH3-N and TN in sewage, and a filter cloth filter tank (10) for further removing SS, which are arranged and connected in sequence.

2. A low-load domestic sewage treatment system using a variable biofilm method according to claim 1, characterized in that: The sewage inlet biochemical unit (6) comprises a plurality of groups of variable biofilm reactors (61) arranged in sequence, and two adjacent groups of variable biofilm reactors (61) are interconnected.

3. A low-load domestic sewage treatment system using a variable biofilm method according to claim 2, characterized in that: A single variable biofilm reactor (61) can switch between aerobic nitrification and anoxic denitrification modes.

4. A low-load domestic sewage treatment system using a variable biofilm method according to claim 3, characterized in that: The variable biofilm reactor (61) comprises a tank body (611), an upper flow guide trough (612), a sawtooth water inlet weir (613), a filler intercepting screen (614), a movable flow guide trough (615), an aeration device (616), and a fan (617) for conveying gas into the aeration device (616).

5. A low-load domestic sewage treatment process using a variable biofilm method, characterized in that: A low-load domestic sewage treatment system using a variable biofilm method as claimed in claim 3 comprises the following steps: S1. Remove pollutants such as garbage, scum, and plant residues from sewage through solid-liquid rapid separation equipment, and reduce the content of COD and SS; cooperate with the composite polymer filler filtration system (5) to further remove organic nitrogen and TP; S2. According to the impact of the change of TN concentration in different seasons on the system, the variable biofilm reactor (61) is switched between aerobic nitrification and anoxic denitrification as needed. In the aerobic nitrification mode, the fluidized bed and fixed bed dual modes are flexibly switched to achieve the operation mode under different influent flow rates and achieve the effect of resisting hydraulic shock. S3. SS is further removed through the filter cloth filter (10) to improve the SS index of the effluent.

6. A low-load domestic sewage treatment process using a variable biofilm method according to claim 5, characterized in that: The packing density in the variable biofilm reactor (61) is 1.05-1.08 g / cm3, and the shape is a porous plastic sphere with a diameter of 20 mm. When the gas volume is large, it can be in a fluidized state, and the filling ratio is 60-70%.

7. A low-load domestic sewage treatment process using a variable biofilm method according to claim 6, characterized in that: The variable biofilm reactor (61) is in aerobic nitrification mode and selects the packing operation mode of the reaction tank according to the pollutant load rate of the influent. When the pollutant load of the influent is low, the variable biofilm reactor (61) is adjusted to a fixed bed mode. At this time, the biofilm is fixed and the water flows through the packing layer to carry out biochemical reaction, so as to reduce the aeration gas volume and save the energy consumption of the aeration in the stirring part. The gas-water ratio can be reduced to 3:1-5:

1. When the pollutant load of the influent increases, the variable biofilm reactor (61) is adjusted to a fluidized bed mode. At this time, the packing is in a fluidized state, the biochemical reaction efficiency is accelerated, and the gas volume is increased. The gas-water ratio is 4:1-10:

1.

8. A low-load domestic sewage treatment process using a variable biofilm method according to claim 7, characterized in that: The variable biofilm reactor (61) is operated in fixed bed mode under anoxic denitrification mode; the residence time is 0.4-0.6 hours, the nitrate nitrogen volume load is 0.80-1.30 kg nitrate nitrogen / (m3 filter material·d), backwashing is performed by air washing, the air washing intensity is 20 L / m2·s, the duration is 6-8 min, and the backwashing cycle is 24 hours.

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