Domestic sewage treatment system and method based on low-oxygen nitrification and denitrification

Abstract

The invention discloses a low-oxygen nitrification and denitrification synchronous domestic sewage treatment system and method, which are mainly driven by whole-course nitrifying bacteria to complete a nitrification process and synchronously promote the realization of a denitrification process, realize the synchronous treatment of nitrification and denitrification of domestic sewage in the same reaction device, improve the denitrification efficiency of a single tank, and improve the denitrification efficiency of the single tank. The energy consumption and the operation cost are reduced. The system mainly comprises a water inlet tank, a low-oxygen nitrification and denitrification synchronous reaction tank, a DO control unit and a mud-water separation device. The DO value in the low-oxygen nitrification and denitrification synchronous reaction tank is controlled to be not greater than 0.5 mg / L. The device has the advantages of being simple in structure, saving investment cost and operation cost and the like.

Description

Technical Field

[0001] The invention relates to a low-oxygen nitrification synchronous denitrification domestic sewage treatment system and method, belonging to the technical field of water treatment. Background Art

[0002] According to the 2021 China Water Resources Bulletin, the total water consumption in China has been rising slowly since 1997, and has remained basically flat since 2013. Among them, domestic water consumption has continued to increase, and in 2021, domestic water consumption by urban and rural residents accounted for 10.8% of the total water consumption. Domestic sewage is one of the main sources of nitrogen and phosphorus in polluted water bodies. Treating domestic sewage to meet discharge standards before discharging it into natural water bodies is an indispensable measure to protect the water environment.

[0003] The mainstream nitrogen and phosphorus removal process used in traditional urban sewage treatment plants in my country is A 2 / O (Anaerobic-Anoxic-Oxic) process: sewage and return sludge first enter the anaerobic tank (dissolved oxygen DO <0.2mg / L) to be completely mixed. After a certain period of anaerobic decomposition, the polyphosphate microorganisms (polyphosphate bacteria, etc.) in the return sludge release phosphorus. Then the sewage flows into the anoxic tank (DO ≤ 0.5mg / L). The denitrifying bacteria in the tank use the undecomposed carbon-containing organic matter in the sewage as a carbon source to reduce the nitrate nitrogen returned from the aerobic tank through the internal circulation to N2 and release it. Next, the sewage flows into the aerobic tank (DO is 2-4mg / L), and the NH4 + -N (ammonia nitrogen) undergoes nitrification to generate NO3 - -N nitrate nitrogen, while the organic matter in the water is oxidized and decomposed to provide energy for phosphorus-absorbing microorganisms. The microorganisms absorb phosphorus from the water, the phosphorus enters the cell tissue, and is enriched in the microorganisms. After sedimentation and separation, it is discharged from the system in the form of phosphorus-rich sludge.

[0004] But A 2 The A / O process has a large aeration volume, high energy consumption for sludge and nitrification liquid return (nitrification liquid return ratio is usually 200-300% to improve denitrification efficiency), and usually requires additional carbon source, so the operating cost is high. 2 The nitrogen removal effect of the / O process is affected by the mixed liquor reflow ratio, and the phosphorus removal effect is affected by the DO (dissolved oxygen) and nitrate oxygen entrained in the return sludge, so the nitrogen removal and phosphorus removal efficiency cannot be very high. Based on this, various process improvements have also emerged, such as adding carrier fillers in the aerobic zone to allow autotrophic nitrifying bacteria to adhere to the surface of the carrier to grow, in order to solve the problem of different sludge ages required for different microorganisms to maximize their functions. Or improved processes, such as inverted A 2 / O process and improved inverted A with water inlet at different points 2 / O process, or JHB process (also known as A+A 2 / O process), UCT process, etc., but the basic essence of these processes is still A 2 / O process. Summary of the invention

[0005] The present invention aims to provide a low-oxygen nitrification and synchronous denitrification domestic sewage treatment system and method, which uses full-process nitrifying bacteria as the main driving force to complete the nitrification process and simultaneously promote the denitrification process, thereby achieving simultaneous nitrification and denitrification treatment of domestic sewage in the same reaction device, improving the denitrification efficiency of a single pool while reducing energy consumption and operating costs.

[0006] The present invention is achieved through the following technical solutions.

[0007] According to one embodiment of the present invention, on the one hand, the present invention provides a low oxygen nitrification simultaneous denitrification domestic sewage treatment system, which mainly includes a low oxygen nitrification simultaneous denitrification reaction tank and a DO control unit, and a mud-water separation device; the DO control unit can control the DO value in the low oxygen nitrification simultaneous denitrification reaction tank to no more than 0.5 mg / L.

[0008] In the above technical solution, the mud-water separation device includes an ultrafiltration membrane assembly and an outlet pool. The ultrafiltration membrane assembly is arranged in the low-oxygen nitrification simultaneous denitrification reaction pool, and the ultrafiltration membrane assembly is provided with an outlet pipe connected to the outlet pool; the outlet pipe is provided with an outlet pump.

[0009] In another technical solution, the mud-water separation device includes a sedimentation tank and a sludge return device. The sedimentation tank is connected to the hypoxic nitrification simultaneous denitrification reaction tank, and the sludge separated by sedimentation in the sedimentation tank can be returned to the hypoxic nitrification simultaneous denitrification reaction tank through the sludge return device.

[0010] As an optimized technical solution, the system also includes an anaerobic tank, the mud-water separation device includes a sedimentation tank and a sludge return device, the anaerobic tank is connected to the low-oxygen nitrification synchronous denitrification reaction tank and the sedimentation tank in sequence, and the sludge return device can return the sludge separated by sedimentation in the sedimentation tank to the anaerobic tank.

[0011] In the above technical solution, the DO control unit includes a DO control device, an aerator, and an aeration device and a DO probe arranged in the hypoxic nitrification and simultaneous denitrification reaction tank.

[0012] Based on the above domestic sewage treatment system, the present invention provides a method for treating domestic sewage by low oxygen nitrification and simultaneous denitrification, comprising:

[0013] S1, startup phase

[0014] An appropriate amount of activated sludge with nitrification performance or activated sludge containing full-process nitrifying bacteria taken from a municipal sewage treatment plant is used as an inoculum and inoculated into a hypoxic nitrification simultaneous denitrification reaction tank;

[0015] Using low-concentration domestic sewage as influent, the activated sludge in the hypoxic nitrification and denitrification reaction tank was domesticated under hypoxic conditions with a DO value of no more than 0.5 mg / L. The sludge was considered to be successfully domesticated when there was no residual ammonia nitrogen in the effluent and the denitrification efficiency was stable at more than 20%. + -N concentration is 5-25 mg / L, COD concentration is 50-150 mg / L.

[0016] Under the condition of low oxygen with DO value maintained at no more than 0.5mg / L, the influent load is gradually increased to increase the NH4 + The system is considered to be successfully started when the N concentration is increased to 40-60 mg / L, the COD concentration is increased to 200-300 mg / L, the effluent ammonia nitrogen concentration is lower than 5 mg / L and the denitrification efficiency is stabilized at more than 40%.

[0017] S2, system operation

[0018] The sewage to be treated enters a low-oxygen nitrification and simultaneous denitrification reaction tank, and the organic matter and ammonia nitrogen in the sewage to be treated are degraded in a low-oxygen environment with a DO value of no more than 0.5 mg / L; the degraded sewage is separated into mud and water by a mud-water separation device.

[0019] In the above technical solution, the residence time of the sewage to be treated in the hypoxic nitrification simultaneous denitrification tank is 6 to 16 hours.

[0020] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0021] 1) Make full use of the ability of the whole-process nitrifying bacteria to maintain high activity under low dissolved oxygen conditions to achieve the conversion of ammonia nitrogen to nitrate nitrogen under low dissolved oxygen conditions, thereby ensuring the removal effect of ammonia nitrogen in the sewage treatment process and providing nitrate nitrogen for the denitrification process. In the same reaction device, the whole-process nitrifying bacteria complete the low-oxygen nitrification and the denitrifying bacteria simultaneously complete the denitrification degradation process.

[0022] 2) The nitrification and denitrification processes are completed in the same reaction device (hypoxic nitrification and simultaneous denitrification reaction tank), which can reduce construction costs; and there is no need to reflux the nitrification liquid, which can significantly reduce energy consumption and operating costs.

[0023] 3) The entire sewage treatment process is maintained in a low oxygen state, and the aeration volume is reduced, which can further reduce energy consumption and operating costs; under low dissolved oxygen conditions, the growth rate of heterotrophic bacteria will also decrease, which can improve the utilization rate of carbon sources in the original sewage by denitrifying bacteria during the denitrification process, thereby adding less or no additional organic carbon sources. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of a low-oxygen nitrification and simultaneous denitrification domestic sewage treatment system according to one embodiment of the present invention.

[0025] Figure 2 This is a schematic diagram of a low-oxygen nitrification and simultaneous denitrification domestic sewage treatment system according to another embodiment of the present invention.

[0026] Figure 3 This is a schematic diagram of a low-oxygen nitrification and simultaneous denitrification domestic sewage treatment system according to the third embodiment of the present invention.

[0027] In the figure: 1 - water inlet tank; 2 - water inlet pump; 3 - low oxygen nitrification and simultaneous denitrification reaction tank; 4 - ultrafiltration membrane assembly; 5 - water outlet tank; 6 - water outlet pump; 8 - DO probe; 9 - DO control device; 10 - aeration device; 11 - aerator; 12 - sedimentation tank; 13 - sludge return device; 14 - anaerobic tank. DETAILED DESCRIPTION

[0028] The specific implementation manner and working process of the present invention will be further described below in conjunction with the accompanying drawings.

[0029] The terms such as up, down, left and right in this application document are based on the positional relationship shown in the drawings. If the drawings are different, the corresponding positional relationship may also change accordingly, so it cannot be understood as limiting the scope of protection.

[0030] This application provides a system for simultaneous nitrification and denitrification of municipal domestic sewage. Current domestic sewage generally has the following technical features:

[0031] NH4 + -N concentration is not more than 100 mg / L;

[0032] TN concentration is not more than 120 mg / L;

[0033] COD concentration is not more than 500mg / L;

[0034] BOD concentration is not more than 350 mg / L.

[0035] like Figure 1As shown in the figure, the hypoxia nitrification and simultaneous denitrification domestic sewage treatment system mainly includes an inlet tank 1, a hypoxia nitrification and simultaneous denitrification reaction tank 3, a DO control unit, and a sludge-water separation device. Usually in a municipal sewage treatment plant, any device in the previous process that may be connected to the hypoxia nitrification and simultaneous denitrification reaction tank 3 of the present application can be used as the inlet tank 1. Those of ordinary skill in the art can understand this and will not be elaborated herein.

[0036] The inlet tank 1 is connected to the hypoxia nitrification and simultaneous denitrification reaction tank 3 through an inlet pipeline, and a feed pump 2 is usually arranged on the inlet pipeline. The sewage to be treated is introduced into the hypoxia nitrification and simultaneous denitrification reaction tank 3. During the start-up stage, according to needs, domestic sewage with a corresponding concentration is prepared in the inlet tank 1 for acclimation and start-up.

[0037] The DO control unit includes a DO control device 9, an aerator 11, an aeration device 10 and a DO probe 8 arranged in the hypoxia nitrification and simultaneous denitrification reaction tank 3. The aeration device 10 is arranged at the bottom of the hypoxia nitrification and simultaneous denitrification reaction tank 3 and includes a plurality of aeration heads, and the aeration heads are preferably microporous aeration heads. The aeration device 10 is connected to the aerator 11 through a gas pipeline. The DO probe 8 is connected to the DO control device 9 through a data line and can transmit the DO value signal to the DO control device 9. By controlling the start and stop of the aerator 11, the DO value in the hypoxia nitrification and simultaneous denitrification reaction tank 3 is controlled to be not greater than 0.5 mg / L, that is, the hypoxia condition described in the present application. Preferably, under the hypoxia condition, the DO value is controlled to be 0 < DO ≤ 0.5 mg / L. A further preferred condition is to control the DO value to be 0.1 - 0.5 mg / L. The setting and principle of the DO control unit can be understood by those of ordinary skill in the art and will not be elaborated herein.

[0038] During start-up, an appropriate amount of activated sludge with nitrification performance taken from a municipal domestic sewage treatment plant or activated sludge containing full-range nitrifying bacteria (relative abundance can reach more than 20%) is used as an inoculum and inoculated into the hypoxia nitrification and simultaneous denitrification reaction tank 3. Usually, the sludge concentration in the reaction tank after inoculation is 1 - 4 g / L, preferably 2 - 3 g / L. These activated sludges also contain denitrifying bacteria.

[0039] The start-up stage actually includes at least two stages: the sludge acclimation stage and the strain enrichment stage.

[0040] Using low-concentration domestic sewage as the inlet water, under the hypoxia condition, that is, maintaining the DO concentration value to be not greater than 0.5 mg / L (preferably, 0.1 - 0.5 mg / L), the activated sludge in the hypoxia nitrification and simultaneous denitrification reaction tank 3 is acclimated. When there is no residual ammonia nitrogen in the effluent and the denitrification efficiency is stable above 20%, it is considered that the sludge acclimation is successful. In the low-concentration domestic sewage, NH4 +-N concentration is 5-25 mg / L, COD concentration is 50-150 mg / L. Preferably, low-concentration domestic sewage contains NH4 + -N concentration is 15-20 mg / L, COD concentration is 90-110 mg / L.

[0041] Denitrification efficiency = (TN in -TN out ) / TN in ×100%;

[0042] Among them, TN in TN out are the total nitrogen concentrations in the inlet and outlet water of hypoxic nitrification simultaneous denitrification reaction tank 3, respectively.

[0043] When the denitrification efficiency is maintained above 20%, it is considered stable, and the duration is usually more than 7 days.

[0044] The sludge acclimation stage usually takes 1 to 3 months. The acclimation time required for inoculation with activated sludge containing full-process nitrifying bacteria is shorter than that for inoculation directly with activated sludge from aeration tanks of municipal sewage treatment plants.

[0045] Then enter the bacterial enrichment stage. Gradually increase the water load to reduce the ammonia nitrogen (NH4 + -N) concentration is increased to 40-60mg / L, COD concentration is increased to 200-300mg / L, and when the effluent ammonia nitrogen concentration is lower than 5mg / L and the denitrification efficiency is stabilized at more than 40%, the strain enrichment stage is considered completed, that is, the system is successfully started. Similar to the sludge acclimation stage, when the effluent ammonia nitrogen concentration is continuously lower than 5mg / L and the denitrification efficiency is continuously maintained at more than 40%, it is considered stable. This stage usually takes 1-3 months.

[0046] At this point, the entire startup phase was successfully completed, that is, the low-oxygen nitrification and simultaneous denitrification process was successfully started.

[0047] After acclimation and successful startup in a low-oxygen environment, in addition to the complete nitrifying bacteria that can become the dominant species in the activated sludge, denitrifying bacteria can also become the dominant species. This is because the complete nitrifying bacteria and denitrifying bacteria have higher activity in a low-oxygen environment. Traditional ammonia oxidizing bacteria need to maintain the DO value above 2 mg / L. Their competitiveness for oxygen is weaker than that of heterotrophic bacteria in this low-oxygen environment, and their ammonia oxidation activity will decrease. This is because the half-saturation constant of the complete nitrifying bacteria (Comammox-Nitrospira) for oxygen is only 0.17±0.02 mgO2 / L, while that of the traditional ammonia oxidizing bacteria (AOB-Nitrosomonas / Nitrosospira) is 0.22~1.28 mgO2 / L, so the complete nitrifying bacteria have a stronger competitiveness for oxygen in a low-oxygen environment.

[0048] The whole-process nitrifying bacteria can complete ammonia oxidation and nitrite oxidation by themselves, and the denitrifying bacteria can use the nitrate nitrogen produced by the whole-process nitrifying bacteria and the organic matter in the domestic sewage for denitrification, achieving the effect of simultaneous denitrification and organic matter removal. Other heterotrophic bacteria in the sludge can also remove organic matter in the sewage, but the degradation rate of organic matter will decrease in a low-oxygen environment, thereby improving the utilization efficiency of the original organic matter in the sewage as a denitrification carbon source, and adding less or no carbon source in the denitrification process, thereby reducing the consumption of reagents. At the same time, completing the above process in the same reactor is more efficient than A. 2 The O process can reduce the nitrification solution reflux link. This reflux ratio usually needs to be 200%-400%, thereby reducing the energy consumption of nitrification solution reflux.

[0049] The mud-water separation device uses an ultrafiltration membrane component or a sedimentation tank.

[0050] When the ultrafiltration membrane assembly 4 is used as the mud-water separation device, a water outlet pool 5 is also included. One embodiment is to set the ultrafiltration membrane assembly 4 in the low oxygen nitrification simultaneous denitrification reaction pool 3, and the ultrafiltration membrane assembly 4 is provided with a water outlet pipe connected to the water outlet pool 5. Preferably, the ultrafiltration membrane assembly 4 is arranged in the upper middle part of the low oxygen nitrification simultaneous denitrification reaction pool 3. A water outlet pump 6 is arranged on the water outlet pipe.

[0051] The sewage to be treated (municipal domestic sewage) completes the degradation of organic matter and nitrogen in the low-oxygen nitrification simultaneous denitrification reaction tank. The degraded domestic sewage is separated into mud and water through the ultrafiltration membrane component 4, and under the suction action of the effluent pump 6, the effluent after the mud and water separation enters the effluent tank 5, while the separated sludge continues to participate in the nitrification and denitrification degradation reaction in the low-oxygen nitrification simultaneous denitrification reaction tank.

[0052] In another embodiment, the mud-water separation device is a sedimentation tank 12, and in this case, a sludge return device 13 is also included. Figure 2 As shown, the sedimentation tank is connected to the hypoxic nitrification simultaneous denitrification reaction tank, so that the degraded mud-water mixture is precipitated in the sedimentation tank for mud-water separation. The sludge return device is connected between the sedimentation tank and the hypoxic nitrification simultaneous denitrification reaction tank, and can return the sludge separated by sedimentation in the sedimentation tank to the hypoxic nitrification simultaneous denitrification reaction tank to continue to participate in nitrification and denitrification degradation reactions.

[0053] The present application also provides an optimized technical solution that can further remove phosphorus. In this case, the system also includes an anaerobic tank 14, and the mud-water separation device uses a sedimentation tank and a sludge return device, such as Figure 3 The anaerobic tank is connected with the hypoxic nitrification synchronous denitrification reaction tank and the sedimentation tank in sequence, and the sludge return device can return the sludge separated from the sedimentation tank to the anaerobic tank.

[0054] In fact, the present low oxygen nitrification and denitrification domestic sewage treatment system and method can be directly used in existing municipal sewage treatment plants. 2 / O process transformation.

[0055] One implementation method is to operate the anoxic tank and the aerobic tank as a hypoxic nitrification simultaneous denitrification tank. That is, the original anoxic tank and the aerobic tank are operated as hypoxic nitrification simultaneous denitrification reaction tanks by controlling the DO value, that is, maintaining the DO value to be no more than 0.5 mg / L. The sludge inoculation, acclimatization and startup process in the hypoxic nitrification simultaneous denitrification reaction tank are as described above.

[0056] Another implementation method is to operate only the aerobic pool as a low-oxygen nitrification simultaneous denitrification pool. That is, the original aerobic pool is operated as a low-oxygen nitrification simultaneous denitrification reaction pool by controlling the DO value, that is, maintaining the DO value to be no more than 0.5 mg / L. The sludge inoculation, acclimatization and startup process in the low-oxygen nitrification simultaneous denitrification reaction pool are as described above. The original nitrification liquid return system is still retained, but the nitrification liquid return ratio will be greatly reduced. At this time, the sewage to be treated first enters the anaerobic pool.

[0057] In the above two implementations, the original anaerobic tank, secondary sedimentation tank and sludge return system are still retained, and the secondary sedimentation tank is used as a mud-water separation device. When the mud-water separation device uses a secondary sedimentation tank (sedimentation tank), it is necessary to include a sludge return system to return the separated and precipitated sludge to the system.

[0058] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. Hypoxic nitrification and simultaneous denitrification domestic sewage treatment system, characterized in that: It at least comprises a low oxygen nitrification and simultaneous denitrification reaction pool (3), a DO control unit, and a mud-water separation device; the DO control unit can control the DO value in the low oxygen nitrification and simultaneous denitrification reaction pool (3) to be no greater than 0.5 mg / L.

2. The domestic sewage treatment system according to claim 1, characterized in that: The mud-water separation device comprises an ultrafiltration membrane assembly (4) and a water outlet pool (5); the ultrafiltration membrane assembly (4) is arranged in the low-oxygen nitrification synchronous denitrification reaction pool (3), and the ultrafiltration membrane assembly (4) is provided with a water outlet pipe connected to the water outlet pool (5); and the water outlet pipe is provided with a water outlet pump (6).

3. The domestic sewage treatment system according to claim 1, characterized in that: The mud-water separation device comprises a sedimentation tank (12) and a sludge return device (13); the sedimentation tank (12) is connected to the hypoxic nitrification synchronous denitrification reaction tank (3), and the sludge separated in the sedimentation tank can be returned to the hypoxic nitrification synchronous denitrification reaction tank (3) through the sludge return device (13).

4. The domestic sewage treatment system according to claim 1, characterized in that: The system further comprises an anaerobic tank (14), the mud-water separation device comprises a sedimentation tank (12) and a sludge return device (13), the anaerobic tank is sequentially connected to the low oxygen nitrification synchronous denitrification reaction tank (3) and the sedimentation tank (12), and the sludge return device (13) can return the sludge separated in the sedimentation tank (12) to the anaerobic tank (14).

5. The domestic sewage treatment system according to claim 1, characterized in that: The DO control unit comprises a DO control device (9), an aerator (11), and an aeration device (10) and a DO probe (8) arranged in the hypoxic nitrification and simultaneous denitrification reaction tank (3).

6. A method for treating domestic sewage by low oxygen nitrification and simultaneous denitrification, using the domestic sewage treatment system as claimed in claim 1, characterized in that: The method comprises: S1, startup phase An appropriate amount of activated sludge with nitrification performance or activated sludge containing full-process nitrifying bacteria taken from a municipal sewage treatment plant is used as an inoculum and inoculated into a hypoxic nitrification and simultaneous denitrification reaction tank (3); Using low-concentration domestic sewage as influent, the activated sludge in the hypoxic nitrification simultaneous denitrification reaction tank (3) was domesticated under hypoxic conditions with a DO value maintained at no more than 0.5 mg / L. The sludge domestication was considered successful when there was no residual ammonia nitrogen in the effluent and the denitrification efficiency was stable at more than 20%. NH4 + -N concentration is 5-25mg / L, COD concentration is 50-150mg / L; Under the condition of low oxygen with DO value maintained at no more than 0.5mg / L, the influent load is increased to remove NH4 + -N concentration is increased to 40-60mg / L, COD concentration is increased to 200-300mg / L, when the effluent ammonia nitrogen concentration is lower than 5mg / L and the denitrification efficiency is stabilized at more than 40%, the system is considered to be successfully started; S2, system operation The wastewater to be treated enters a low oxygen nitrification and simultaneous denitrification reaction pool (3), and the organic matter and ammonia nitrogen in the wastewater to be treated are degraded in a low oxygen environment with a DO value of no more than 0.5 mg / L; the degraded wastewater is separated into mud and water by a mud and water separation device.

7. The method for treating domestic sewage according to claim 6, characterized in that: The residence time of the wastewater to be treated in the hypoxic nitrification simultaneous denitrification tank is 6 to 16 hours.

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