A method for strengthening operation of a full-process autotrophic denitrification process

Abstract

The present invention relates to an enhanced operation method of a full-process autotrophic denitrification process, and belongs to the technical field of biological treatment of nitrogen-containing wastewater. The present invention starts the full-process autotrophic denitrification process by setting a sludge internal reflow system on a membrane bioreactor, applying an electromagnetic field generating system on the internal reflow pipeline, and gradually increasing the ammonia nitrogen concentration of the influent. By regulating the magnetic field intensity and application cycle, the reflux ratio in the mixed liquid, and the dissolved oxygen concentration, the growth rate and activity of aerobic ammonia oxidizing bacteria and anaerobic ammonia oxidizing bacteria are promoted, so that the two can coexist harmoniously and efficiently, and the rapid start-up of the full-process autotrophic denitrification process is achieved, and the process operation stability is enhanced. The method to which the present invention belongs has a simple process and mild reaction conditions, and can improve the denitrification effect of the process under medium and low temperature conditions; the internal reflow of muddy water and the higher reflux ratio are conducive to the full mixing of activated sludge and sewage in the reactor, reducing the stirring power demand, reducing the reactor operation cost, and more easily forming granular sludge; the reactor is not limited by the size of the permanent magnet, has no magnetic field attenuation problem, can adjust the magnetic field intensity at any time, has a wider range of application, can be modified on the basis of the existing reactor, and is convenient for engineering application.

Description

Technical Field

[0001] The invention belongs to the technical field of biological treatment of nitrogen-containing wastewater, and specifically relates to an enhanced operation method of a full-process autotrophic denitrification process. Background Art

[0002] The completely autotrophic nitrogen removal over nitrite process (CANON process) is a new type of biological denitrification technology for sewage developed based on the theory of anaerobic ammonium oxidation. The process achieves the harmonious coexistence of aerobic ammonia oxidizing bacteria (AOB) and anaerobic ammonia oxidizing bacteria (AnAOB) in one reactor, using AOB to convert part of the ammonia nitrogen into nitrite nitrogen, and then cooperates with AnAOB to use nitrite nitrogen as an electron acceptor to oxidize the remaining ammonia nitrogen into N2, thereby achieving autotrophic denitrification of sewage. Compared with the traditional nitrification-denitrification denitrification process, this process can save a lot of aeration energy consumption and organic carbon source demand, and the residual sludge and greenhouse gas emissions are low, which has great application prospects.

[0003] However, the differences in oxygen requirements between AOB and AnAOB, as well as the reaction substrate NH4 + -N competition, resulting in the need for CANON process control to take into account the needs of both, AOB and AnAOB activities are easily inhibited. In addition, AnAOB has a long doubling time and slow growth rate, resulting in a long start-up cycle, unstable denitrification efficiency, and susceptibility to ambient temperature interference, which limits the promotion and application of the process.

[0004] The key to achieving efficient and stable autotrophic nitrogen removal in the CANON process is to regulate the growth and metabolism of the main microorganisms in the reaction process, inhibit the growth of nitrite oxidizing bacteria (NOB), and maintain high activity of AOB and AnAOB in the same reactor. Both the external magnetic field and the magnetic field of the organism itself can affect the metabolism of the organism, that is, the biomagnetic effect. Within the appropriate intensity range, the magnetic field can enhance the activity of microbial enzymes, increase the reaction rate, and promote the growth and metabolism of microorganisms. Therefore, it is possible to use magnetic fields to enhance the biological treatment process of sewage.

[0005] Chinese patent CN201510373241.5 discloses a device and method for treating low-temperature high-ammonia nitrogen wastewater using a constant magnetic field. This method symmetrically arranges two magnets on the outside of a short-range nitrification SBR reactor to form a magnetic field with a strength of 50-100mT, forming a magnetic field-ammonia oxidizing bacteria enhancement system to achieve rapid startup and stable operation of short-range nitrification.

[0006] Chinese patent CN202011611200.2 discloses a method for synchronously strengthening the cultivation of anaerobic ammonia-oxidizing bacteria and enhancing stability by coupling a nano-zero-valent iron magnetic field. Permanent magnets are set on both sides of the upflow anaerobic sludge blanket reactor, and nano-zero-valent iron particles are added to the anaerobic sludge to promote the start-up of anaerobic ammonia oxidation and enhance the stability of the anaerobic ammonia oxidation reactor.

[0007] The above applications applied magnetic fields to AOB and AnAOB respectively, and successfully achieved the enhancement of short-range nitrification and anaerobic ammonium oxidation single systems. However, the following problems still exist: (1) AnAOB and AOB will compete and interfere with each other in the CANON process, and the effect of the magnetic field on the CANON process under the mutual influence of AOB and AnAOB is unclear; (2) The magnetic field is generated by applying permanent magnets, which leads to the reactor design being limited by the size of the permanent magnets and the engineering application is restricted; (3) It is not easy to adjust the magnetic field strength of permanent magnets at any time, and the magnetic field strength is easy to decay after long-term operation, affecting the effect; (4) There is a lack of research on the effect of magnetic field on process enhancement under ambient temperature, especially under medium and low temperature conditions. Summary of the invention

[0008] In view of a series of problems existing in the above-mentioned prior art, the present invention proposes an enhanced operation method of a full-process autotrophic denitrification process, which promotes the growth rate and activity of aerobic ammonia oxidizing bacteria and anaerobic ammonia oxidizing bacteria by setting a sludge internal recirculation system on the MBR reactor, applying an electromagnetic field, regulating operating parameters, etc., so that the two can coexist harmoniously and efficiently, realize the rapid start-up of the full-process autotrophic denitrification process, and enhance the stability of process operation. Compared with the above-mentioned technology, the reactor in the present invention is not limited by the size of the permanent magnet and has better adaptability under medium and low temperature conditions.

[0009] To achieve the above object, the technical solution adopted by the present invention is:

[0010] A method for strengthening operation of a full-process autotrophic denitrification process, characterized by comprising the following steps:

[0011] (1) An MBR sewage treatment reactor is provided, the reactor includes an inlet and outlet water pump, a membrane tank, a membrane assembly, an electric stirring device and an aeration device, an internal reflux pipeline is provided outside the reactor, and an electromagnetic coil is wound around the reflux pipeline to provide a magnetic field generating system, the outlet height of the reflux pipe is provided at 1 / 4 to 1 / 3 of the height of the reactor, and the inlet is at the bottom of the reactor;

[0012] (2) The reactor is inoculated with mixed activated sludge from the aerobic tank and the secondary sedimentation tank of the municipal sewage treatment plant. The ammonia nitrogen wastewater to be treated is continuously pumped into the bottom of the MBR reactor using an inlet pump, and the wastewater is mixed with the sludge by stirring in the reactor, and the water is continuously discharged through the membrane module. The hydraulic retention time in the reactor is controlled to be 6-12h, and the dissolved oxygen concentration in the reactor is controlled to be 0.1-0.5mg / L;

[0013] (3) Turn on the reflux pump to return the mud-water mixture to the bottom of the reactor, and adjust the reflux flow rate to control the reflux ratio of the mud-water mixture (the ratio of the mud-water mixture reflux flow rate to the reactor inlet flow rate); turn on the magnetic field generating system to apply a magnetic field to the mixed liquid in the reflux pipe, so that the magnetic field strength at the center of the reflux pipe is 20-80mT. During the reactor startup and stable operation period, adjust the magnetic field strength and magnetic field application cycle to enhance the reactor operation effect.

[0014] Preferably, according to the present invention, in step (1), the magnetic field generating system is composed of an electromagnetic coil wound around a return pipe and a DC power supply controller, which can generate a stable electromagnetic field.

[0015] Preferably, according to the present invention, in step (2), the reactor inoculation sludge comes from the mixed sludge of the aerobic tank and the secondary sedimentation tank, the mixing ratio (v / v) is 2:1, and the inoculation concentration is 5000-8000 mgMLSS / L.

[0016] Preferably, according to the present invention, in step (2), during the start-up of the reactor, the ammonia nitrogen concentration of the influent water is gradually increased, and the alkalinity is controlled to be stable at 800-1000 mg / L.

[0017] Preferably according to the present invention, in step (2), the dissolved oxygen concentration in the reactor is controlled at 0.1-0.3 mg / L.

[0018] Preferably, according to the present invention, in step (3), the magnetic field strength at the center of the reflux pipe is controlled to be 40-80 mT.

[0019] Further preferably, in step (3), the central magnetic field strength in the reflux pipe is 60 mT.

[0020] Preferably, according to the present invention, in step (3), the reflux ratio of the mud-water mixture in the reactor is 2-6.

[0021] Further preferably, the internal reflux ratio during the reactor startup process is 4 to 6, and after the startup is successful and a stable denitrification effect is achieved, the reflux ratio is gradually reduced to 2.

[0022] Preferably, according to the present invention, in step (3), the magnetic field application cycle during the reactor startup process is 24 h / day, and after the startup is successful and a stable denitrification effect is achieved, it can be reduced to 12 h / day.

[0023] During the startup process, due to the high internal reflux ratio set in the reactor, the sludge in the reactor is circulated under the action of the magnetic field. The magnetic field enhances the growth and metabolic rates of AOB and AnAOB, and promotes the aggregation of sludge to form larger flocs, making the dissolved oxygen gradient inside the sludge obvious, which is conducive to the coexistence of aerobic ammonia oxidizing bacteria and anaerobic ammonia oxidizing bacteria, and improving their resistance to medium and low temperature conditions, thereby shortening the startup cycle of the process and improving the process operation effect.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The invention adopts the MBR process and sets an internal reflow pipeline, applies an electromagnetic field in the internal reflow system, strengthens the growth and metabolic rate of functional microorganisms in the reactor, shortens the reactor startup time, and improves the denitrification effect of the reactor under medium and low temperature conditions. The strategy is efficient, safe, and the conditions are mild; the internal reflow of mud and water and a relatively high reflow ratio are conducive to the full mixing of activated sludge and sewage in the reactor, reduce the demand for stirring power, can reduce the operating cost of the reactor, and are easier to form granular sludge; the electromagnetic field is used to replace the permanent magnet, which is convenient for adjusting the magnetic field strength, and there is no problem of magnetic field strength attenuation under long-term operation, which is more suitable for different sludge conditions; the use of the reflow pipeline to apply the electromagnetic field measure can effectively solve the problem of the magnetic field limiting the size of the reactor, can be modified on the basis of the existing reactor, and is suitable for large-scale sewage treatment plants, which is conducive to the promotion and application of the process. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the structure of the reaction system of the present invention;

[0027] Figure 2 The changes in the composition and content of extracellular polymeric substances in sludge;

[0028] Figure 3 is the structure of sludge microbial community in the reactor;

[0029] Figure 4 The denitrification effect of the reactor under different magnetic field strengths;

[0030] Description of reference numerals:

[0031] 1-MBR reactor, 2-membrane assembly, 3-agitator, 4-aeration pipe, 5-aeration pump, 6-water inlet tank, 7-water inlet pump, 8-water inlet pipe, 9-water outlet pipe, 10-water outlet pump, 11-water outlet tank, 12-internal reflux pipe, 13-reflux pump, 14-electromagnetic coil, 15-electromagnetic field control power supply. DETAILED DESCRIPTION

[0032] The present invention is further described in detail below in conjunction with specific implementation modes and accompanying drawings.

[0033] Example 1

[0034] The present invention proposes an enhanced operation method of a full-process autotrophic denitrification process, the steps of which are:

[0035] (1) A sewage treatment device is established, which is a magnetic field enhanced membrane bioreactor (MBR) 1, in which a polyvinylidene fluoride (PVDF) hollow fiber membrane module 2 is installed, and a built-in stirrer 3 ensures that the activated sludge and water are evenly mixed. An aeration pipe 4 is installed at the bottom and connected to an aeration pump 5, and the dissolved oxygen concentration in the reactor is controlled by adjusting the aeration volume. Ammonia nitrogen-containing wastewater enters the reactor from the bottom through the inlet tank 6 through the inlet pump 7 and the inlet pipe 8, and after treatment, it is discharged through the membrane module 2, the outlet pipe 9 and the outlet pump 10 and collected in the outlet tank 11. An internal reflux pipe 12 is set at 1 / 3 of the reactor height, and a reflux pump 13 is used to reflux the sludge mixed liquid in the reactor, and an electromagnetic coil 14 is installed on the reflux pipe 12, and the magnetic field strength is controlled by a DC power supply 15.

[0036] (2) Reactor inoculation with activated sludge. The inoculated sludge comes from the aerobic tank and secondary sedimentation tank of the municipal sewage treatment plant, with a mixing ratio of 2:1. The inoculated sludge concentration in the reactor is 5000 mg MLSS / L.

[0037] (3) Ammonia nitrogen-containing wastewater is introduced from the bottom of the reactor. The influent of the reactor is artificially simulated ammonia nitrogen-containing wastewater, the main components of which include (NH4)2SO4, KH2PO4, NaHCO3, MgSO4, CaCl2 and trace elements. The reactor is started by gradually increasing the ammonia nitrogen concentration of the influent, and the ammonia nitrogen concentration of the influent is gradually increased from 70 mg / L to 200 mg / L. The NaHCO3 content in the influent is adjusted so that the alkalinity of the influent is controlled at about 800 mg / L and the pH is controlled at 6.8-7.5. By adjusting the aeration volume, the dissolved oxygen concentration in the reactor is controlled to 0.1-0.5 mg / L.

[0038] (4) Adjust the inlet pump 1 and the outlet pump 10 to control the inlet and outlet flow of the reactor, so that the hydraulic retention time of the reactor is controlled to 8 hours. Turn on the reflux pump 13 to allow the mud-water mixture in the reactor to reflux through the reflux pipeline, and adjust the flow rate to control the reflux ratio of the mixed liquid to 4.0.

[0039] (5) Turn on the electromagnetic control power supply 15 and adjust the current so that the magnetic field strength generated at the center of the electromagnetic coil 14 is 40 mT. The magnetic field application cycle is 24 hours / day. The temperature of the reactor is not controlled during operation, and the internal temperature is kept consistent with the ambient temperature (12-30°C).

[0040] (6) After the reactor inlet water concentration was increased to 200 mg / L and a stable effluent effect was achieved, the mixed liquid reflux ratio was adjusted to 2.0 and the magnetic field application period was reduced to 12 h / day.

[0041] Comparative Example 1

[0042] The system and basic operation for starting the full autotrophic denitrification process in this comparative example are the same as those in Example 1, except that no magnetic field is applied to the reactor reflux pipeline in this comparative example.

[0043] Comparative Example 2

[0044] The system and basic operation of starting the full autotrophic denitrification process in this comparative example are the same as those in Example 1, except that no magnetic field is applied to the reactor reflux pipe, a pair of permanent magnets are placed in parallel on both sides of the reactor body, and the distance between the permanent magnets is adjusted so that the magnetic field strength in the middle of the reactor is 40mT.

[0045] The denitrification effects during the start-up of the reactors of Example 1 and the comparative example were analyzed, and the results are shown in Table 1:

[0046] Table 1 Comparison of reactor treatment effects

[0047]

[0048] As can be seen from Table 1, with the increase of influent ammonia nitrogen concentration, the denitrification effects of Example 1 and the comparative example are steadily improved, and the whole autotrophic denitrification process can be successfully started. The ammonia nitrogen removal rate, total nitrogen removal rate and total nitrogen removal rate of Example 1 are significantly higher than those of the comparative example. After about 62 days of acclimatization, the ammonia nitrogen removal rate is stabilized at more than 91%, the total nitrogen removal rate reaches more than 78%, and the total nitrogen removal rate is 0.47kg / m 3 / d or more, the CANON process reached stability, about 2 weeks earlier than the system without magnetic field (Comparative Example 1). After stable operation, the total nitrogen removal rate of sewage in Example 1 was increased by 25.1% compared with that in Comparative Example 1. Under low temperature conditions in the later stage of operation (average temperature 14.1°C), Example 1 still maintained a high denitrification activity, and the total nitrogen removal rate was increased by 41.9% compared with the comparative example. Under the action of the magnetic field, Example 1 showed better low temperature resistance.

[0049] Under the action of magnetic field, the content of extracellular polymeric substances (EPS) in the activated sludge in the reactor of Example 1 was 7.9%-67.7% higher than that in the comparative example 1 of the same period ( Figure 2 The protein / polysaccharide ratio in the sludge EPS of Example 1 is relatively high, which promotes the aggregation of sludge to form large flocs, and forms a significant dissolved oxygen concentration gradient inside the flocs, which is conducive to the coexistence of anaerobic ammonia oxidizing bacteria and aerobic ammonia oxidizing bacteria, thereby improving the sewage denitrification effect of the reactor in Example 1.

[0050] The activated sludge in Example 1 and Comparative Example 1 at different stages was sequenced by 16S rDNA high-throughput metagenomic sequencing. The results showed that by gradually increasing the ammonia nitrogen load of the influent, the abundance of the main aerobic ammonia-oxidizing bacteria Nitrosomonas and the anaerobic ammonia-oxidizing bacteria Candidatus Brocadia in the reactor gradually increased. Compared with the comparative example, the abundance of Nitrosomonas in Example 1 under the action of the magnetic field was 21.1% higher, and the abundance of Candidatus Brocadia was 25.9% higher. The application of the magnetic field promoted the growth rate of the main functional bacteria in the whole autotrophic denitrification process and enhanced the operation effect of the process.

[0051] Compared with Example 2, the difference in denitrification effect between Example 1 and Comparative Example 2 is not obvious (as shown in Table 1). In the initial stage of operation, the denitrification effect of Comparative Example 2 is slightly higher than that of Example 1, because the magnetic field in Comparative Example 2 is applied to the reactor body, and the scope of action is wider. However, the difference between the two is not large in the later stage, indicating that the method of applying an electromagnetic field to the internal reflux system in Example 1 and the method of applying a permanent magnet to the reactor body can also achieve the enhancement of the CANON process. However, compared with the method of permanent magnet action, the method of action in Example 1 can make the reactor unaffected by the size of the permanent magnet and the attenuation of the magnetic field, the magnetic field strength is adjustable, the existing reactor can be modified, and the enhancement method is more flexible and reliable, with obvious advantages.

[0052] Example 2

[0053] The experimental system and basic operation of starting the whole autotrophic denitrification process in this embodiment 2 are the same as those in embodiment 1, except that: six reactors (R0, R1, R2) are set in this embodiment. 20 ,R 40 ,R 60 ,R 80 ,R 100 ), after successful startup under normal temperature conditions, the operating temperature is controlled at 30°C, the magnetic field strengths applied to the return pipeline are 0mT, 20mT, 40mT, 60mT, 80mT, and 100mT, respectively, and the magnetic field application cycle is 12h / day.

[0054] The denitrification effect of the reactor under different magnetic field strengths is as follows: Figure 4 As shown. When the magnetic field strength is 20-80mT, the denitrification effect of the reactor is stronger than that of the control group without magnetic field (R0), and when the magnetic field strength is 40mT and 60mT, the denitrification effect is the best, and the denitrification efficiency is increased by 18.9% and 20.2%, respectively. However, when the magnetic field strength is 100mT, the denitrification effect is inhibited, and it decreases by 1.5% compared with the zero magnetic field reactor. Therefore, the magnetic field strength of the present invention is controlled at 20-80mT, which can realize the strengthening of the whole autotrophic denitrification process, and the optimal magnetic field strength is controlled at 40-60mT.

[0055] The above is a schematic description of the invention and its implementation method, which is not restrictive. If a person skilled in the art is inspired by it and creatively designs a structure and embodiment similar to the technical solution without departing from the purpose of the invention, they should all fall within the scope of protection of this patent.

Claims

1. A method for strengthening operation of a full-process autotrophic denitrification process, characterized in that: The steps include: (1) An MBR sewage treatment reactor is set up, a sludge internal return pipeline is set up outside the reactor, an electromagnetic coil is wound on the return pipeline and connected to a DC power supply controller to form a magnetic field generating system, and the sludge internal return ratio is controlled by a return pump; (2) The reactor is inoculated with mixed activated sludge from the aerobic tank and the secondary sedimentation tank of the municipal sewage treatment plant at a mixing ratio (v / v) of 2:1, and the reflux pump is turned on to allow the sludge to flow back from the top of the reactor to the bottom, thereby starting the full autotrophic denitrification process; (3) During the sludge acclimation period, the flow rate of the reflux pump is adjusted to control the reflux ratio in the sludge to 4-6, and the magnetic field generating system is turned on to apply a weak magnetic field to the reflux sludge. The magnetic field strength at the center of the reflux pipe is controlled to be 40-80 mT by adjusting the DC power supply controller. The magnetic field application cycle is 24 h / day, and the ammonia nitrogen concentration of the influent is gradually increased, and the alkalinity is controlled to be stable at 800-1000 mg / L; (4) After the reactor was successfully started and a stable denitrification effect was achieved, the sludge recirculation ratio was reduced to 2 and the magnetic field application cycle was reduced to 12 h / day, thus achieving enhanced and stable operation of the entire autotrophic denitrification process.

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