A method for efficient denitrification and rapid control of sludge bulking in the activated sludge process of urban sewage

Abstract

A method for efficient nitrogen removal and rapid control of sludge bulking in the activated sludge process of municipal sewage, belonging to the field of water environment restoration and regeneration. Under low dissolved oxygen conditions, it realizes the efficient utilization of dissolved oxygen and the efficient removal of total nitrogen in municipal sewage, and rapidly improves the sedimentation performance of sludge. The continuous flow activated sludge process of municipal sewage is adopted, which consists of a continuous flow anoxic / aerobic activated sludge reactor and a secondary sedimentation tank. The activated sludge in the expanded state is inoculated, and the influent is simulated municipal sewage. An anoxic compartment and an aerobic compartment are set in the reactor. The dissolved oxygen in the aerobic compartment is 0 - 0.8 mg / L, which is beneficial to improving the oxygen transfer rate and saving aeration energy consumption. The sludge in the secondary sedimentation tank is refluxed to the inlet through an external reflux pump, and the nitrified liquid in the aerobic zone is refluxed to the anoxic zone through an internal reflux pump. By adding diatomite heavy medium and polyferric sulfate flocculant, the sludge bulking under low dissolved oxygen conditions is rapidly controlled, ensuring the stable operation of the continuous flow activated sludge process of municipal sewage.

Description

Technical Field

[0001] The present invention belongs to the technical field of sewage treatment, and relates to a method for efficient denitrification and rapid control of sludge bulking in the activated sludge process of urban sewage. Background Art

[0002] Biological denitrification of urban domestic sewage generally adopts the activated sludge process. Under aerobic conditions, nitrifying bacteria use oxygen to oxidize ammonia nitrogen to nitrate nitrogen; under anoxic conditions, denitrifying bacteria use carbon sources to reduce nitrate and nitrite to nitrogen gas. Under low dissolved oxygen conditions, the activated sludge process has the advantages of saving aeration energy consumption and high denitrification efficiency. Compared with the high dissolved oxygen condition, the low dissolved oxygen condition has a greater oxygen transfer rate and better energy-saving effect. Under the low dissolved oxygen condition, better simultaneous nitrification and denitrification can be achieved in the aerobic section, improving the overall denitrification effect of the system. However, under low dissolved oxygen and high load conditions, the activated sludge system is prone to sludge bulking. When the SVI value (volume occupied by 1 g of dry sludge, mL / g) of the activated sludge exceeds 150 mL / g, it indicates that the activated sludge is about to or has already been in a bulking state, and the sedimentation performance of the activated sludge deteriorates and is lost with the effluent of the secondary sedimentation tank. Severe sludge bulking will lead to the collapse of the entire sewage treatment system.

[0003] In recent years, researchers have reported a method for rapidly controlling activated sludge bulking by adding diatomite heavy medium. Diatomite has a huge specific surface area, high porosity, and strong adsorption capacity for activated sludge. The activated sludge will adsorb to the surface of diatomite, and the sedimentation performance is effectively improved. Researchers have carried out the short-term effect of diatomite on sludge bulking performance in a sequencing batch reactor, and the results show that diatomite can rapidly improve the sedimentation performance of sludge. At present, there is less research on the rapid control strategy of sludge bulking in continuous flow reactors. Moreover, the addition of diatomite alone can only improve the bulking performance of sludge in the short term. With the operation of the activated sludge process, the sedimentation performance of the sludge will gradually deteriorate. Polyferric sulfate is a commonly used chemical agent for phosphorus removal in sewage treatment, with the characteristics of high efficiency, low dosage, and non-toxicity. As a commonly used coagulant, polyferric sulfate can promote the aggregation of sludge flocs to a certain extent and improve the sedimentation performance of sludge. Summary of the Invention

[0004] The present invention can achieve energy conservation and efficient denitrification of the activated sludge process of urban sewage under low dissolved oxygen conditions, rapidly control the sludge bulking of the activated sludge, improve the removal effect of ammonia nitrogen and total nitrogen, and maintain good sludge sedimentation performance for a long time. The present invention relates to a method for efficient denitrification and rapid control of sludge bulking in the activated sludge process of urban sewage, and the steps are as follows:

[0005] (1) The continuous - flow activated sludge process for municipal sewage is adopted, which consists of a continuous - flow anoxic / aerobic activated sludge reactor and a secondary sedimentation tank. The effective volume of the continuous - flow activated sludge reactor is 54 L. The reactor is composed of 6 compartments, and the volume of each compartment is 9 L. The sludge is mixed by a mechanical stirrer, and the rotation speed of the stirring paddle is 200 r / min. The effective volume of the secondary sedimentation tank is 22 L.

[0006] (2) The inoculated sludge is the activated sludge in an expanded state in the laboratory. The inoculated volume is 20 L, the sludge concentration is 14000 mg / L, and the sludge dilution sludge volume index is 170 - 190 mL / g.

[0007] (3) The influent of the reactor is simulated municipal domestic sewage. The influent ammonia - nitrogen concentration is 50 - 70 mg / L, the nitrate - nitrogen concentration is less than 1 mg / L, the nitrite - nitrogen concentration is less than 1 mg / L, and the COD concentration is 160 - 250 mg / L. The specific influent components are: NH4 + -N (NH4Cl), 50 - 70 mg / L; COD (NaCH3COO), 160 - 250 mg / L; KH2PO4, 30 mg / L; CaCl2, 90 mg / L; MgSO4·7H2O, 140 mg / L; trace elements 1 mL / L; the component concentrations of trace elements are Na2 - EDTA, 50 g / L; FeSO4·7H2O,, 5 g / L; CoSO4·5H2O, 1.9 g / L; MnCl2·4H2O, 5.1 g / L; CuSO4·5H2O, 1.6 g / L; ZnSO4·7H2O, 5 g / L; NaMoO4·2H2O, 1.1 g / L.

[0008] (4) The temperature in the reactor is controlled at 25 °C. The 1st, 2nd, and 3rd compartments of the reactor are anoxic tanks without aeration; the 4th, 5th, and 6th compartments of the reactor are aerobic tanks, which are aerated by an air - blower, and the aeration rate is 2 L / min. The dissolved oxygen in the aerobic compartments is 0 - 0.8 mg / L. The return sludge from the secondary sedimentation tank is externally returned to the inlet by a peristaltic pump, and the flow ratio of the externally returned sludge to the influent is 1. The nitrified liquid in the 6th compartment is internally returned to the 1st compartment by a peristaltic pump, and the flow ratio of the internally returned sludge to the influent is 2. The hydraulic retention time of the reactor is controlled at 6 h.

[0009] (5) Measures for rapid control of sludge bulking: Diatomite with a particle size of 200 mesh (74 μm) is added to the reactor once, so that the diatomite concentration in the reactor is 4000 mg / L. Then, a concentrated polyferric sulfate solution is added to the 6th compartment of the reactor every day, and through external reflux, the polyferric sulfate concentration in the whole continuous - flow reactor is 125.0 mg / L.

[0010] (6) Definition of the dilution volume index of sludge. The sludge sedimentation ratio of activated sludge is closely related to the sludge concentration. To facilitate the comparison of changes in sludge sedimentation performance, take the mixed liquor of sludge in the reactor, add tap water to control the sludge concentration at 4000 mg / L, and settle it statically for 30 minutes to obtain the dilution sludge sedimentation ratio of activated sludge. Define the ratio of the dilution sludge sedimentation ratio to the sludge concentration as the sludge dilution volume index. Description of the Drawings

[0011] Figure 1 It is a diagram of the reactor device.

[0012] Figure 1 In it, 1 - influent pump; 2 - continuous - flow activated sludge reactor; 3 - secondary sedimentation tank; 4 - internal reflux pump; 5 - external reflux pump; 6 - aeration pump; 7 - heating rod; 8 - mechanical stirrer; 9 - effluent from the secondary sedimentation tank

[0013] Figure 2 It is the concentration of the three nitrogen species in the influent and effluent of the reactor.

[0014] Figure 3 It is the total nitrogen concentration in the influent and effluent of the reactor, and the removal rates of ammonia nitrogen and total nitrogen.

[0015] Figure 4 It is the dilution sludge sedimentation ratio and the sludge dilution volume index of the reactor. Detailed Implementation Modes

[0016] 1. The reactor device is as Figure 1 shown.

[0017] 2. The operation steps using the above - mentioned method are as follows:

[0018] (1) Experimental device: As Figure 1 shown, the urban sewage treatment process consists of a continuous - flow anoxic / aerobic activated sludge reactor and a secondary sedimentation tank. The effective volume of the continuous - flow activated sludge reactor is 54 L. The reactor consists of 6 compartments, and the volume of each compartment is 9 L. The sludge is mixed by a mechanical stirrer, and the rotation speed of the stirring paddle is 200 r / min. The effective volume of the secondary sedimentation tank is 22 L.

[0019] (2) Inoculated sludge: The inoculated sludge is the activated sludge in an expanded state in the laboratory. The inoculated volume is 20 L, and the sludge concentration is 14000 mg / L.

[0020] (3) Reactor influent: Simulated urban domestic sewage is used. The influent ammonia nitrogen concentration is 50 - 70 mg / L, the nitrate nitrogen concentration is less than 1 mg / L, the nitrite nitrogen concentration is less than 1 mg / L, and the COD concentration is 160 - 250 mg / L. The specific influent components are: NH4 +-N(NH4Cl), 50 - 70 mg / L; COD(NaCH3COO), 160 - 250 mg / L; KH2PO4, 30 mg / L; CaCl2, 90 mg / L; MgSO4·7H2O, 140 mg / L; Trace elements 1 mL / L; The concentration of trace element components is Na2-EDTA, 50 g / L; FeSO4·7H2O, 5 g / L; CoSO4·5H2O, 1.9 g / L; MnCl2·4H2O, 5.1 g / L; CuSO4·5H2O, 1.6 g / L; ZnSO4·7H2O, 5 g / L; NaMoO4·2H2O, 1.1 g / L.

[0021] (4) Reactor operation parameters: The temperature inside the reactor is controlled at 25 °C. The first, second, and third compartments of the reactor are anoxic tanks without aeration; the fourth, fifth, and sixth compartments of the reactor are aerobic tanks, and aeration is carried out through an aeration pump with an aeration rate of 2 L / min, and the dissolved oxygen in the aerobic compartment is 0 - 0.8 mg / L. In the following three aerobic compartments, the activated sludge oxidizes ammonia nitrogen to nitrate nitrogen and nitrite nitrogen. Due to the low dissolved oxygen concentration, the activated sludge can also carry out simultaneous nitrification and denitrification. The return sludge from the secondary sedimentation tank is externally refluxed to the inlet through a peristaltic pump, and the flow ratio of the externally refluxed sludge to the influent is 1. The nitrified liquid in the sixth compartment is internally refluxed to the first compartment through a peristaltic pump to remove nitrate nitrogen and nitrite nitrogen in the nitrified liquid using the carbon source in the influent. The flow ratio of the internally refluxed sludge to the influent is 2, and the hydraulic retention time of the reactor is controlled at 6 h. In the previous three anoxic compartments, the activated sludge can use the nitrate nitrogen (nitrate nitrogen and nitrite nitrogen) in the internal reflux and the carbon source in the influent for denitrification and nitrogen removal.

[0022] (5) Definition of the dilution volume index of sludge. The sludge sedimentation ratio of the activated sludge is closely related to the sludge concentration. To facilitate the comparison of changes in sludge sedimentation performance, the mixed liquor of sludge in the reactor is taken, and tap water is added to control the sludge concentration at 4000 mg / L, and it is statically settled for 30 min to obtain the dilution sludge sedimentation ratio of the activated sludge. The ratio of the dilution sludge sedimentation ratio to the sludge concentration is defined as the sludge dilution volume index.

[0023] (6) Operating conditions of the reactor: The operation of the reactor is divided into two stages. Stage 1 (1 - 10 d) is the activated sludge expansion stage, where the activated sludge is in an expanded state, and the dilution sludge volume index of the sludge is 170 - 190 mL / g; from the first day to the tenth day, the sludge concentration in the reactor is 3500 - 4600 mg / L, the effluent ammonia nitrogen concentration is 6.1 - 9.7 mg / L, the ammonia nitrogen removal rate is 85.2% - 90.0%, and the total nitrogen removal rate is 74.0% - 77.6%.

[0024] Stage 2 (11 - 34d) is the rapid control stage of sludge bulking, and the sedimentation performance is significantly improved. On the 11th day, diatomite with a particle size of 200 mesh (74μm) was added to the reactor at one time, so that the diatomite concentration in the reactor was 4000 mg / L. Then, a concentrated polyferric sulfate solution was added to the 6th compartment of the reactor every day, and through external reflux, the polyferric sulfate concentration in the entire continuous flow reactor was 125.0 mg / L. On the 11th day, the diluted sludge volume index of the activated sludge decreased to 80.0 mg / L, and the sludge concentration in the reactor increased to 5600 mg / L; from the 11th day to the 34th day, the diluted sludge volume index of the activated sludge was always stably maintained below 80 mL / g. From the 21st day to the 34th day, the sludge concentration in the reactor was 5900 - 8240 mg / L, the effluent ammonia nitrogen concentration decreased to 0.1 - 2.1 mg / L, the ammonia nitrogen removal rate was 97.0% - 99.1%, and the total nitrogen removal rate was 74.4% - 82.4%. Compared with Stage 1, the sedimentation performance of the sludge in Stage 2 was significantly improved and remained stable, the effluent ammonia nitrogen concentration was significantly reduced, and the total nitrogen removal rate increased.

[0025] The composite dosing strategy of diatomite and polyferric sulfate proposed in this application can quickly control sludge bulking and maintain good sludge sedimentation performance in the long term. The internal mechanism is as follows: after adding diatomite, the expanded activated sludge will adsorb onto the diatomite to form denser aggregates; when polyferric sulfate is added to the reactor every day, polyferric sulfate will generate positively charged iron ions, and these positively charged ions will neutralize the surface negatively charged sludge to "destabilize" it; in addition, the high molecular polymer iron salt will also form a large number of polynuclear complexes and iron hydroxide colloids, which can cause the activated sludge and diatomite to collide, adsorb, and destroy the stable suspension state of the activated sludge under the action of forces such as van der Waals force, colloidal attraction, and Brownian motion, gradually coagulating into large particles and forming dense flocs, which helps to improve the sedimentation performance of the sludge.

[0026] (7) Based on the above principles, other forms of changes and variations can also be made. These changes and variations are still within the protection scope of the present invention.

Claims

1. A method for efficient nitrogen removal and rapid control of sludge bulking in the activated sludge process of urban sewage, characterized in that include: 1) The continuous flow activated sludge process of urban sewage is adopted, which is composed of a continuous flow anoxic / aerobic activated sludge reactor and a secondary sedimentation tank; the effective volume of the continuous flow activated sludge reactor is 54L; the reactor is composed of 6 cells, each of which has a volume of 9L, and the sludge is mixed by a mechanical stirrer, and the stirring paddle speed is 200r / min; 2) The inoculated sludge is the activated sludge in the expanded state in the laboratory, with an inoculation volume of 20L, a sludge concentration of 14000mg / L, and a diluted sludge volume index of 170-190mL / g; 3) The reactor influent is simulated urban domestic sewage, with an influent ammonia nitrogen concentration of 50-70 mg / L, a nitrate nitrogen concentration of less than 1 mg / L, a nitrous acid concentration of less than 1 mg / L, and a COD concentration of 160-250 mg / L; 4) The temperature in the reactor is controlled at 25°C; the first, second and third compartments of the reactor are anoxic tanks without aeration; the fourth, fifth and sixth compartments of the reactor are aerobic tanks, which are aerated by an aeration pump with an aeration rate of 2L / min, and the dissolved oxygen in the aerobic compartment is 0-0.8mg / L; the return sludge from the secondary sedimentation tank is returned to the water inlet by a peristaltic pump, and the flow ratio of the return sludge to the inlet is 1; The nitrification liquid in the sixth compartment is refluxed into the first compartment through a peristaltic pump. The flow ratio of the internal reflux sludge to the influent is 2, and the hydraulic retention time of the reactor is controlled to be 6 hours. 5) Rapid control measures for sludge bulking: Add diatomaceous earth with a particle size of 200 mesh (74 μm) into the reactor at one time to make the diatomaceous earth concentration in the reactor 4000 mg / L; then, add concentrated polyferric sulfate solution to the 6th compartment of the reactor every day, and make the polyferric sulfate concentration in the entire continuous flow reactor 125.0 mg / L through external reflux.

2. A method for efficient denitrification and rapid control of sludge bulking in an activated sludge process for urban sewage according to claim 1, characterized in that: The influent water is artificially prepared water, and the component concentrations are NH4 + -N (NH4Cl), 50 - 70 mg / L; COD (NaCH3COO), 160 - 250 mg / L; KH2PO4, 30 mg / L; CaCl2, 90 mg / L; MgSO4·7H2O, 140 mg / L; trace elements 1 mL / L; the component concentrations of trace elements are Na2-EDTA, 50 g / L; FeSO4·7H2O, 5 g / L; CoSO4·5H2O, 1.9 g / L; MnCl2·4H2O, 5.1 g / L; CuSO4·5H2O, 1.6 g / L; ZnSO4·7H2O, 5 g / L; NaMoO4·2H2O, 1.1 g / L.

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