A method of preventing bulking of viscous sludge from plugging a denitrification system

Abstract

The present application relates to a method for preventing sticky sludge from expanding and blocking a denitrification system, characterized in that a plate-and-frame tank is arranged between a secondary sedimentation tank and a filter tank to intercept sticky sludge in an expanded state; the plate-and-frame filler adhering to the sticky expanded sludge is collected for air flushing and chemical micro-stimulation, growth factors generated by promoting the expansion of the sticky sludge are returned to a biochemical tank, the hydraulic retention time of the biochemical tank is shortened, the expansion of the sticky sludge is promoted, and then physical separation of the sticky sludge is performed, so that the treatment cycle of the sticky sludge expansion is reduced, and a simple, energy-saving, economical and easy-to-control water treatment process is provided for relieving the sticky sludge expansion.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a method for preventing the expansion and clogging of a denitrification system by sticky sludge. Background Technology

[0002] The activated sludge process is the most widely used biological treatment method for domestic sewage and industrial wastewater. In the activated sludge process, sewage and activated sludge enter an aeration tank together to form a mixed liquor. Aeration provides dissolved oxygen to the sewage and provides the driving force for the mixed liquor, keeping it in a state of intense agitation, improving the mixing of sludge and sewage, enhancing mass transfer, and thus promoting the metabolism of aerobic microorganisms in the activated sludge, thereby purifying the sewage.

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

[0004] Sludge bulking is a common problem in activated sludge processes, referring to the phenomenon where sludge becomes loosely structured, increases in volume, and has a higher sludge settling ratio (SV), making it difficult to settle and separate, thus affecting effluent quality. Non-filamentous bacterial bulking mainly occurs when wastewater temperature is low and sludge load is too high. At these times, bacteria adsorb large amounts of organic matter with low metabolic rates. A large amount of high-viscosity extracellular secretions accumulate, representing a high concentration of organic matter, greatly increasing surface adhesion and making it difficult to settle. Furthermore, flocculants alone are insufficient to remove this substance from the water. Old, sticky substances act as catalysts for new sticky substances, leading to increasingly severe viscous bulking. When bulked sludge enters a denitrification filter, it easily clogs or hardens the filter surface, deteriorating the denitrification effect.

[0005] Currently, most methods to solve the problem of viscous sludge bulking are to increase the sludge return ratio; increase aeration to prevent the formation of anaerobic conditions; and add nutrients to adjust the material balance in the mixed liquor. However, all of these methods will increase the operating costs of wastewater treatment plants. Summary of the Invention

[0006] 1. The purpose of this invention is to provide a process operation method for rapidly solving the problem of viscous sludge bulking. A movable plate and frame packing material is placed at the rear end of the secondary sedimentation tank. Through the adhesion and hydraulic shearing action of the plate and frame packing material, viscous bulking sludge is separated. Simultaneously, the saturated packing material is sent to an air-flushing tank for regeneration. A low-concentration bactericide is used for chemical stimulation, causing the bulking sludge to further secrete a protective liquid, which acts as a growth factor for the viscous sludge, promoting the aggregation of viscous sludge in the aeration tank and inducing viscous sludge bulking. This quickly enters the explosive phase of sludge bulking (obvious white foam is produced on the surface of the biological tank). After the viscous sludge bulking explosion, the viscous sludge is thoroughly physically separated through manual sludge discharge and plate and frame packing interception.

[0007] 2. This method can significantly shorten the conditioning cycle of non-filamentous viscous sludge bulking, while also reducing the operating costs of traditional conditioning methods.

[0008] To address the problem of sludge loss and clogging of denitrification filter beds caused by viscous sludge bulking in conventional activated sludge processes, this invention provides a method that utilizes physical interception to directly remove viscous flocs. Simultaneously, it employs chemical stimulation to promote cellular self-protection mechanisms, increasing the production of cell secretions. The secreted protective liquid acts as a growth factor for viscous sludge, promoting its bulking and thus improving the physical removal rate. The main content is: a method for preventing viscous sludge bulking and clogging of denitrification systems.

[0009] The technical solution of the present invention is as follows: A plate and frame filter press and a tertiary settling tank are added between the secondary settling tank and the denitrification filter to intercept severely bulky and difficult-to-break viscous sludge-water mixtures, preventing them from entering the denitrification filter and causing blockage. After the plate and frame filter presses intercept the sludge, the biofilm-forming packing material can be sent to an air-flushing tank for demolding and regeneration. Simultaneously, a low-concentration bactericide is added to chemically stimulate the viscous sludge, promoting the production of cell secretions. These secretions, acting as growth factors that promote sludge bulking, are reintroduced into the biological treatment tank, accelerating viscous sludge growth until the plate and frame filter presses can completely intercept the viscous sludge, facilitating complete removal using physical methods. The specific method is as follows: A method for preventing the bulking and clogging of a denitrification system by sticky sludge, wherein the denitrification system comprises a biological treatment tank, a secondary sedimentation tank, a plate and frame filter tank, a tertiary sedimentation tank, a denitrification filter, and an air flushing tank connected in sequence; wherein the air flushing tank is connected to the biological treatment tank.

[0010] The mud-water mixture in the biological treatment tank enters the secondary sedimentation tank for mud-water separation. The settleable sludge is kept at a concentration of 2000-5000 mg / L in the biological treatment tank through the sludge return system and sludge discharge system, so as to maintain the normal operation of the reaction in the biological treatment tank.

[0011] Unsedimentable sludge, i.e., a viscous mud-water mixture, passes through the plate and frame filter press with the effluent. The mud-water mixture with a lower sludge density flows through the plate and frame filter press, which disrupts its aggregate structure. It can then enter the tertiary sedimentation tank and denitrification filter through the interception effect of the plate and frame packing. Flocculants (such as polyferric flocculants and / or polyaluminum flocculants) are added to increase the settling properties of the sludge, ensuring that the suspended solids entering the filter do not exceed 20 mg / L. Due to the large amount of sludge loss caused by sludge bulking, this part of the sludge can be returned to the secondary sedimentation tank to participate in the biochemical reaction.

[0012] The sludge-water mixture with high bulking viscosity will not have its structure destroyed by the hydraulic action of the water flow. Due to its high adhesion properties, it will be trapped on the plate and frame packing. Once the biofilm formation on the plate and frame packing affects the liquid flux, the packing can be unloaded and transferred to the air-flushing tank.

[0013] After the plate and frame packing material is sent to the air-flushing tank, the adhering expanded sludge is desorbed using air flushing, completing the packing material regeneration. The detached expanded sludge remains in the air-flushing tank, where a low concentration of bactericide is added to promote the secretion of extracellular secretions by the expanded sludge, acting as a promoter to accelerate the bulking of sticky sludge and promote sludge aggregation. Severely expanded sticky sludge can be completely physically separated through the interception of the plate and frame packing tank and manual scraping.

[0014] A further improvement of this invention addresses the blockage and sludge loss in denitrification systems caused by viscous sludge bulking. This is achieved by adding a plate-and-frame filter bed filled with removable plate-and-frame packing material to retain sludge with low levels of viscous bulking. Furthermore, the addition of flocculants reduces suspended solids in the influent to the denitrification filter, lowering the probability of filter bed blockage. Simultaneously, when the plate-and-frame packing material becomes saturated, it is replaced with new material. Severely viscous bulking sludge is removed by air jetting. A trace amount of bactericide stimulates the bulking sludge to produce growth factors, and the hydraulic retention time in the biological treatment tank is shortened, promoting the explosive expansion of viscous sludge. This facilitates thorough viscous sludge separation and reduces the treatment cycle for viscous sludge bulking.

[0015] The key feature of this invention is the development of a method to prevent the bulking and clogging of denitrifying filters by sticky sludge. This method prevents sticky, bulking sludge from entering the denitrification filter, significantly alleviating the clogging problem. Furthermore, compared to traditional methods that increase the return ratio and enhance aeration, this invention reduces the content of extracellular secretions in the biological treatment tank through physical separation, thereby reducing the outbreak and treatment time of sticky sludge bulking, lowering the operating costs of the biological treatment tank, and promptly returning uncontaminated sludge to the biological treatment tank, maintaining the sludge concentration and ensuring the normal operation of the process. Attached Figure Description

[0016] Figure 1A schematic diagram of a process to prevent the bulking and clogging of a denitrification system by sticky sludge. Figure 2 For removable plate and frame packing Explanation of reference numerals in the attached figures: 1. Biological treatment tank; 2. Secondary sedimentation tank; 3. Expanded sludge-water mixture; 4. Plate and frame filter press; 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. Manual assisted sludge scraping; 15. Sludge discharge; 16. Flocculant; 17. Bactericide. Detailed Implementation

[0017] The invention will be further described below with reference to the accompanying drawings and examples: Figure 1 A schematic diagram of a process to prevent the bulking and clogging of a denitrification system by sticky sludge. Figure 2 Removable plate and frame packing A method for preventing the bulking and clogging of a denitrification system by sticky sludge is described in the following process flow: During normal operation, the sludge-water mixture in biological treatment tank 1 flows into secondary sedimentation tank 2. The settled sludge is maintained at a concentration of 2000-5000 mg / L through sludge return system I9 and sludge discharge system. However, if viscous sludge bulking occurs, resulting in high levels of extracellular secretions, the sludge cannot settle in the sedimentation tank. The floating viscous sludge-water mixture flows into plate and frame tank 4 with the effluent. Plate and frame tank 4 is filled with plate and frame-type rope-woven mesh packing material, with a mesh width of 1000-3000 mm and an aperture of 1-20 mm. The packing material is one or more of nylon, polyethylene, and polypropylene.

[0018] Because of the shear force when the water flows through the plate and frame tank 4, the sludge flocs with low viscosity and expansion will be quickly broken up when passing through the plate and frame packing. Before entering the tertiary sedimentation tank 6, 0.1-1‰ flocculant (such as iron-based and / or aluminum-based flocculants) is added by pumping to accelerate sludge sedimentation, ensuring that the suspended solids in the effluent of the tertiary sedimentation tank 6 are 1-20 mg / L. The settled sludge is re-entered into the secondary sedimentation tank through sludge return II10 for sludge circulation, maintaining the sludge concentration in the biological treatment tank.

[0019] The viscous, swollen bacterial flocs will not be broken up by the hydraulic impact when they come into contact with the plate and frame packing. Instead, they will be blocked by the plate and frame and adhere to the packing. These bacterial flocs will quickly adhere to the packing. When the water flow rate is 10%-40% lower than the normal flow rate, it is considered that the plate and frame packing is saturated with biofilm and can be sent to the air-flushing tank 11 for packing regeneration.

[0020] The regeneration air flushing intensity of air flushing tank 11 is 5 L / (m 2·s)~30 L / (m 2 The air-flushing time is 0.5-10 hours. After the packing material is regenerated, it can be reused in the plate and frame filter press 4. The severely bulky sludge 13 that has been desorbed remains in the air-flushing tank 11. By adding bactericide 17 to the air-flushing tank, the production of cell secretions is promoted. The bactericide 17 is sodium hypochlorite at a concentration of less than 5 mg / L or ozone at a concentration of less than 1 mg / L. After the bactericide treatment lasts for 2-10 hours, the secretion return liquid 12 is returned to the biological treatment tank 1, which shortens the hydraulic retention time of the biological treatment tank by 5-20%, promoting the bulking of viscous sludge into the explosive phase.

[0021] When the foam on the surface of the biological treatment tank exceeds 20 cm and stops rising, it indicates the end of the bulking phase of the viscous sludge. In addition to using the plate and frame filter press 4 for interception, a manual sludge scraper 14 is added to remove the foam from the surface of the biological treatment tank, ensuring that all the viscous bulking sludge is removed by physical methods. At the same time, the hydraulic retention time of the biological treatment tank is restored to normal levels to stop the fermentation of the viscous bulking sludge.

[0022] Example 1 The simulated biological treatment process showed good sludge settling in the secondary sedimentation tank during the initial operation. The sludge concentration was approximately 3500 mg / L, the operating temperature was between 25-27 ℃, and the aerobic dissolved oxygen was controlled at 2-3 mg / L. The influent was artificially prepared, using sodium acetate:glucose (1:1 ratio) as the carbon source, ammonium chloride as the nitrogen source, and potassium dihydrogen phosphate as the phosphorus source, with a COD:N:P ratio of 100:10:1. The cycle was four times daily: 5 minutes of influent, 30 minutes of anoxic conditions, 15 minutes of aerobic conditions, alternating six times, followed by 80 minutes of sedimentation and 5 minutes of effluent discharge. After 43 days of operation, the extracellular secretions were measured to be 10 times higher than at the initial inoculation, indicating improved sludge settling volume (SV). 30 >50%, SVI>400 mL / g, and a large number of clump-shaped sludge flocs were produced.

[0023] To address the bulking of viscous sludge, sludge interception was implemented. A plate and frame filter press was added at the effluent outlet, and 0.5‰ polyferric sulfate was added after the water sample passed through the press. When the flow rate through the plate and frame filter press fell below 25% of normal, the press was regenerated by air flushing. The regenerated press and frame could be reused. Ozone (0.5 mg / L) was added to the solid-liquid mixture after air flushing, and the reaction proceeded for 5 hours. The mixture was then directly returned to the biological treatment tank, with the hydraulic retention time shortened to 25 minutes of anoxic followed by 13 minutes of aerobic, alternating 5 times. After one day, the white foam on the surface of the biological treatment tank reached a height of 40 cm. The fermentation broth return was stopped, and the surface foam was manually removed. Simultaneously, all sludge trapped by the fine screen was removed, and the operating time was changed back to 4 cycles per day: 5 minutes of influent, 30 minutes of anoxic, 15 minutes of aerobic, alternating 6 times, followed by 80 minutes of sedimentation and 5 minutes of effluent discharge. After 2 days of operation, the sludge indicators returned to the inoculation state, and the surface foam in the biological treatment tank disappeared and returned to normal.

Claims

1. A method for preventing the bulking and clogging of a denitrification system by sticky sludge, the denitrification system comprising a biological treatment tank (1), a secondary sedimentation tank (2), a plate and frame filter tank (4), a tertiary sedimentation tank (6), a filter tank (7), and an air-flushing tank (11) connected in sequence, wherein the plate and frame filter tank (4) is used to retain sludge in a sticky, bulking state; characterized in that, The method includes the following steps: (1) Use plate and frame packing to intercept and collect viscous sludge until the plate and frame packing is saturated with biofilm; (2) The plate and frame packing saturated with biofilm is regenerated by air flushing, and sodium hypochlorite at 5 mg / L or ozone at a concentration of less than 1 mg / L is added. The secreted reflux liquid (12) is returned to the biological tank (1) at the same time, and the hydraulic retention time of the biological tank (1) is shortened. (3) The viscous sludge in the biological treatment tank (1) expands and enters the outbreak period, and foam is generated on the surface of the biological treatment tank (1) until the outbreak period ends; (4) Remove the surface foam of the biological treatment tank by manually scraping the sticky sludge.

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

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

4. The method according to claim 1, characterized in that: In step (2), the regeneration air flushing intensity of the air flushing tank (11) is 5 L / (㎡·s)~30 L / (㎡·s), and the air flushing time is 0.5-10 h. After the packing is regenerated, bactericide (17) is added to the air flushing tank and treated for 2-10 hours. The secreted reflux liquid (12) is returned to the biological tank (1) to shorten the hydraulic retention time of the biological tank by 5-20%.

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