Method for preventing viscous sludge from bulking and blocking denitrification system

Abstract

The invention relates to a method for preventing viscous sludge from bulking and blocking a denitrification system, which is characterized in that a plate frame tank is arranged between a secondary sedimentation tank and a filter tank and is used for intercepting the sludge in a viscous bulking state; the method comprises the following steps: collecting a plate frame filler adhered with viscous bulking sludge, carrying out air blast and chemical micro-stimulation, refluxing generated growth factors for promoting the bulking of the viscous sludge to a biochemical pool, shortening the hydraulic retention time of the biochemical pool, promoting the bulking and outbreak of the viscous sludge, and carrying out physical separation on the viscous sludge, so that the treatment period of the bulking of the viscous sludge can be shortened; the invention provides a simple, energy-saving, economical and easy-to-control water treatment process for relieving viscous sludge bulking.

Description

Technical Field

[0001] The invention relates to the technical field of sewage treatment, and in particular to a method for preventing sticky sludge from swelling and clogging a denitrification system. Background Art

[0002] The activated sludge process is the most widely used biological treatment method for domestic sewage and industrial wastewater. In the process of the activated sludge process, sewage and activated sludge enter the aeration tank together to form a mixed liquid. Aeration provides dissolved oxygen in the sewage and provides power for the mixed liquid, making it in a strong stirring state, improving the mixing of sludge and sewage, and strengthening mass transfer, thereby promoting the metabolism of aerobic microorganisms in the activated sludge and purifying the sewage.

[0003] The denitrification filter is a treatment unit that combines biological denitrification and filtration functions. Usually, the denitrification deep bed filter uses 3-4 mm quartz sand medium filter material. The filter can ensure that the suspended solids in the effluent are less than 5 mg / L and the total nitrogen (TN) in the effluent is 5-7 mg / L.

[0004] Sludge bulking is one of the common problems of the activated sludge process. It refers to the phenomenon that the sludge structure is loose, the volume is increased, the sludge settling ratio (SV) value is increased, and it is difficult to settle and separate, affecting the effluent water quality. Among them, the expansion of non-filamentous bacteria mainly occurs when the wastewater temperature is low and the sludge load is too high. At this time, the bacteria adsorb a large amount of organic matter, which has a low metabolic rate. A large amount of high-viscosity extracellular secretions accumulate outside the cells, which belong to high-concentration organic matter, which greatly increases the surface adhesion and makes it difficult to float and precipitate. At the same time, it is difficult to remove this substance from the water by flocculants alone. The old sticky substance will become a catalyst for the new sticky substance, resulting in more and more serious sticky expansion. When the expanded sludge enters the denitrification filter, it will cause the surface of the filter to be easily blocked or compacted, which will deteriorate the denitrification effect.

[0005] At present, most methods to solve the problem of sticky sludge bulking are to increase the sludge return ratio; increase aeration to prevent the formation of anaerobic conditions; add nutrients to adjust the material balance in the mixed liquid, but the above methods will increase the operating costs of the sewage treatment plant. Summary of the invention

[0006] 1. The purpose of the present invention is to provide a process operation method for quickly solving the problem of viscous swelling of sludge. A movable plate-frame filler is placed at the rear end of the second sedimentation tank. The viscous swelling sludge is separated by the adhesion interception and hydraulic shearing action of the plate-frame filler. At the same time, the adhered saturated filler is sent to the gas flushing tank for regeneration, and a low concentration of fungicide is used for chemical stimulation to make the swelling sludge further secrete a protective liquid and serve as a growth factor for the viscous sludge, promote the agglomeration of viscous sludge in the aeration tank, induce the swelling of viscous sludge, and quickly enter the outbreak period of sludge swelling (obvious white foam is generated on the surface of the biochemical tank). After the viscous sludge swelling breaks out, the viscous sludge is thoroughly physically separated by artificial auxiliary sludge discharge and plate-frame interception.

[0007] 2. This method can greatly shorten the conditioning period of non-filamentous viscous sludge bulking, and also reduce the operating cost of traditional conditioning methods.

[0008] Aiming at the problem of sludge loss and clogging of denitrification filter bed caused by sticky sludge expansion in conventional activated sludge process. In combination with the above background technology, the present invention provides a method of using physical interception to directly remove sticky flocs, and at the same time uses chemical stimulation to promote the cell self-protection mechanism and increase the production of cell secretions. The secretion protection liquid can serve as a growth factor for sticky sludge, promote the outbreak of sticky sludge expansion, and improve the physical removal rate. The main content is: a method to prevent sticky sludge expansion from clogging the denitrification system.

[0009] The technical solution of the present invention is as follows: A plate-and-frame tank and a tertiary sedimentation tank are added between the secondary sedimentation tank and the denitrification filter tank to intercept the viscous mud-water mixture that is severely expanded and difficult to be broken, and to prevent the viscous mud-water mixture from entering the denitrification filter tank and causing the filter tank to be blocked. After the plate-and-frame filler intercepts the sludge, the plate-and-frame filler that has completed the biofilm can be sent to the air flushing tank for demoulding and regeneration. At the same time, a low-concentration sterilizing liquid is added to chemically stimulate the viscous sludge to promote the production of cell secretions. The secretion liquid is re-invested in the biochemical tank as a growth factor that promotes sludge expansion, accelerating the growth of viscous sludge until the plate-and-frame filler can intercept all the viscous sludge, which is conducive to complete removal using physical methods. The specific methods are as follows: A method for preventing sticky sludge from swelling and clogging a denitrification system, the denitrification system comprising a biochemical tank, a secondary sedimentation tank, a plate-frame tank, a tertiary sedimentation tank, a denitrification filter tank and an air flushing tank which are connected in sequence; the air flushing tank is connected to the biochemical tank.

[0010] The mud-water mixture in the biochemical pool enters the secondary sedimentation tank for mud-water separation. The precipitated sludge is passed through the sludge return system and the sludge discharge system to ensure that the sludge concentration in the biochemical pool is 2000-5000 mg / L, thereby maintaining the normal reaction in the biochemical pool.

[0011] The sludge that cannot be precipitated, i.e., the viscous mud-water mixture, passes through the plate and frame tank with the effluent water. The sludge-water mixture with low sludge specific gravity passes through the plate and frame tank with the water flow, and its coagulation structure is destroyed in the process. It can enter the tertiary sedimentation tank and the denitrification filter tank through the interception effect of the plate and frame filler, and flocculants (such as polyiron-based flocculants and / or polyaluminum-based flocculants) are added to increase the sedimentation of the sludge to ensure that the suspended solids entering the filter tank do not exceed 20 mg / L. Because the sludge loss caused by sludge expansion is large, this part of the sludge can be returned to the secondary sedimentation tank to participate in the biochemical reaction.

[0012] The viscous sludge with high swelling degree will not destroy its own structure with the hydraulic action of the water flow, and will be trapped on the plate and frame filler due to its high adhesion characteristics. When the plate and frame filler forms a film and affects the liquid flux, the plate and frame filler can be unloaded and transported to the air flushing tank.

[0013] After the plate and frame filler is sent to the air flushing tank, air flushing is used to desorb the adhered expanded sludge to complete the filler regeneration. The detached expanded sludge is left in the air flushing tank. By adding low-concentration fungicides, the expanded sludge is promoted to secrete extracellular secretions, which acts as a promoter to induce sludge expansion, accelerate the expansion of viscous sludge, and promote sludge agglomeration. Severely expanded viscous sludge can be completely physically separated through interception in the plate and frame tank and artificial auxiliary scraping.

[0014] The further improvement of the present invention is to intercept sludge by adding a plate-frame pool filled with detachable plate-frame fillers to prevent the blockage of the denitrification system and the loss of sludge caused by the viscous sludge expansion, retain the sludge with low viscous expansion, and reduce the suspended solids in the denitrification filter by adding flocculants, thereby reducing the probability of blockage of the denitrification filter bed. At the same time, when the plate-frame fillers are saturated with adhesion, new plate-frame fillers are used to replace them, and the adhered severe viscous and swollen sludge is removed by air flushing, and a trace amount of bactericide is used to stimulate the swollen sludge to produce growth factors, and the hydraulic retention time of the biochemical pool is shortened to promote the expansion of viscous sludge, which is conducive to the thorough separation of viscous sludge and the reduction of the treatment cycle of viscous sludge expansion.

[0015] The feature of the present invention is that a method for preventing sticky sludge from swelling and clogging the filter tank is developed, so that the sticky swelling sludge cannot enter the denitrification filter tank, and the phenomenon of clogging of the denitrification filter tank is significantly alleviated. At the same time, compared with the traditional method of increasing the return ratio and strengthening aeration, the present invention reduces the content of extracellular secretions in the biochemical pool by means of physical separation, reduces the outbreak and treatment time of sticky sludge swelling, reduces the operating cost of the biochemical pool, and also returns the non-deteriorated sludge to the biochemical pool in time, maintains the sludge concentration in the biochemical pool, and maintains the normal operation of the process. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1A schematic diagram of a process flow for preventing sticky sludge from bulking and clogging a denitrification system Figure 2 For removable plate frame filler Description of reference numerals: 1. Biochemical tank; 2. Secondary sedimentation tank; 3. Expanded sludge-water mixture; 4. Plate and frame tank; 5. Retainable sludge; 6. Tertiary sedimentation tank; 7. Filter tank; 8. Effluent; 9. Sludge return system I; 10. Sludge return system II; 11. Air flushing tank; 12. Secretion return liquid; 13. Severely expanded sludge; 14. Artificially assisted sludge scraping; 15. Sludge discharge; 16. Flocculant; 17. Bactericide. DETAILED DESCRIPTION

[0017] The present invention will be further described below with reference to the accompanying drawings and examples: Figure 1 Schematic diagram of a process flow for preventing sticky sludge from bulking and clogging a denitrification system Figure 2 Removable plate and frame filler A method for preventing sticky sludge from bulking and clogging a denitrification system, the operation process of which is described as follows: During normal operation of the biochemical pool 1, the mud-water mixture flows into the secondary sedimentation tank 2, and the precipitated sludge maintains the sludge concentration of the biochemical pool at 2000-5000 mg / L through the sludge return system I9 and the sludge discharge system. However, if the viscous sludge expands, resulting in high extracellular secretions of the sludge, it cannot settle in the sedimentation tank, and the floating viscous sludge-water mixture flows into the plate-frame pool 4 with the effluent, wherein the plate-frame pool 4 is filled with plate-frame rope mesh filler, the mesh width is 1000-3000 mm, and the aperture is 1-20 mm. The filler material is one or more of nylon, polyethylene, and polypropylene.

[0018] Due to the shear force when the water flows through the plate and frame tank 4, the sludge floccules with low viscosity and expansion degree will be quickly broken when passing through the plate and frame filler. Before entering the third sedimentation tank 6, 0.1-1‰ flocculant (such as iron and / or aluminum flocculants) is added by pumping to accelerate the sludge sedimentation to ensure that the suspended solids in the effluent of the third sedimentation tank 6 are 1-20 mg / L. The precipitated sludge re-enters the second sedimentation tank through the sludge return II10 for sludge circulation to maintain the sludge concentration in the biochemical tank.

[0019] The bacterial flocs with serious viscous expansion will not be broken by hydraulic impact when contacting the plate and frame filler, but will be blocked by the plate and frame and adhere to the filler. This part of the bacterial flocs will quickly adhere to the filler. When the water flow rate is 10%-40% lower than the normal flow rate, it is regarded as the plate and frame filler is saturated with biofilm and can be sent to the air flushing tank 11 for filler regeneration.

[0020] The regeneration gas intensity of the gas pool 11 is 5L / (m 2·s)~30 L / (m 2 ·s), the gas flushing time is 0.5-10h. After the filler is regenerated, it can be used again in the plate-frame tank 4. The severely expanded sludge 13 that has been desorbed is retained in the gas flushing tank 11. By adding a fungicide 17 to the gas flushing tank, the production of cell secretions is promoted. Among them, the fungicide 17 is sodium hypochlorite below 5mg / L or ozone below 1mg / L. After the fungicide treatment for 2-10 hours, the secretion return liquid 12 flows back to the biochemical tank 1, and at the same time shortens the hydraulic retention time of the biochemical tank by 5-20%, promoting the expansion of viscous sludge to enter the outbreak period.

[0021] When the foam on the surface of the biochemical pool is higher than 20cm and no longer increases, it indicates that the outbreak period of viscous sludge expansion has ended. In addition to using the plate-frame pool 4 for interception, an artificial auxiliary sludge scraper 14 is added to remove the foam on the surface of the biochemical pool to ensure that all viscous expanded sludge is removed by physical methods. At the same time, the hydraulic retention time of the biochemical pool is restored to a normal level to stop the fermentation of viscous expanded sludge.

[0022] Example 1 The biochemical pool treatment process was simulated. At the beginning of operation, the sludge sedimentation in the secondary sedimentation tank was good. The sludge concentration during the operation of the biochemical pool was about 3500 mg / L, the operating temperature was between 25-27 ℃, the aerobic dissolved oxygen was controlled at 2-3 mg / L, the influent was artificially distributed water, with sodium acetate: glucose = 1:1 as the carbon source, ammonium chloride as the nitrogen source, potassium dihydrogen phosphate as the phosphorus source, COD:N:P=100:10:1, 4 cycles per day, 5 minutes of water inlet, 30 minutes of anoxic, 15 minutes of aerobic, 6 alternations, 80 minutes of sedimentation, and 5 minutes of drainage. When it was running for 43 days, it was measured that the extracellular secretions were 10 times that of the extracellular secretions at the beginning of inoculation, and the sludge sedimentation SV 30 >50%, SVI>400 mL / g, and a large number of lumpy sludge flocs were produced.

[0023] For the viscous sludge expansion, sludge interception is performed, and plate and frame fillers are added at the outlet. After the water sample passes through the plate and frame fillers, 0.5‰ of polyferric sulfate is added. When the flow through the plate and frame is lower than 25% of the normal flow, the plate and frame fillers are gas-blasted and regenerated. The regenerated plate and frame can continue to be used. 0.5mg / L of ozone is added to the solid-liquid mixture after gas blasting for 5h, and then the mixture is directly returned to the biochemical pool. At the same time, the hydraulic retention time is shortened to 25 minutes of anoxic and 13 minutes of aerobic, alternating 5 times. One day later, the white foam on the surface of the biochemical pool rose to 40cm high, the fermentation liquid was stopped, the surface foam was removed manually, and all the sludge intercepted by the fine grid was removed, and the operation time was changed back to 4 cycles per day, 5 minutes of water inlet, 30 minutes of anoxic, 15 minutes of aerobic, alternating 6 times, 80 minutes of sedimentation, and 5 minutes of drainage. After 2 days of operation, the sludge index returned to the inoculation state, and the foam on the surface of the biochemical pool was eliminated and returned to normal.

Claims

1. A method for preventing viscous sludge from swelling and clogging a denitrification system, the denitrification system comprising a biochemical tank (1), a secondary sedimentation tank (2), a plate-frame tank (4), a tertiary sedimentation tank (6), a filter tank (7) and an air flushing tank (11) connected in sequence, the plate-frame tank (4) being used to intercept viscous swollen sludge; characterized in that: The method comprises the following steps: (1) Use plate and frame fillers to intercept and collect sticky sludge until the plate and frame fillers are saturated with biofilm; (2) regenerating the plate-and-frame filler saturated with biofilm by air flushing, adding a chemical bactericide, secreting a reflux liquid (12) to flow back to the biochemical pool (1), and shortening the hydraulic retention time of the biochemical pool (1); (3) The viscous sludge in the biochemical pool (1) expands and enters the outbreak period until the outbreak period ends; (4) Physical separation of sticky sludge.

2. The method according to claim 1, characterized in that: The plate-frame pool (4) is filled with a plate-frame rope mesh filler, the mesh width is 1000-3000 mm, the pore size is 1-20 mm, and the filler material is one or more of nylon, polyethylene, and polypropylene.

3. The method according to claim 1, characterized in that: In step (1), when the water flow rate is lower than 10%-40% of the normal flow rate, the plate and frame filler is sent to the air flushing tank (11) for filler regeneration.

4. The method according to claim 1, characterized in that: In step (2), the regeneration gas intensity of the gas flushing pool (11) is 5L / (m 2 ·s)~30 L / (m 2 ·s), the air flushing time is 0.5-10h. After the filler is regenerated, a fungicide 17 is added to the air flushing pool for 2-10 hours. The secreted reflux liquid (12) flows back to the biochemical pool (1), shortening the hydraulic retention time of the biochemical pool by 5-20%.

5. The method according to claim 4, characterized in that: The bactericide is sodium hypochlorite with a concentration less than 5 mg / L or ozone with a concentration less than 1 mg / L.

6. The method according to claim 1, characterized in that: In step (3), foam is generated on the surface of the biochemical pool (1).

7. The method according to claim 1, characterized in that: Step (4) removes the surface foam of the biochemical pool by artificially assisted scraping.

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