A method for low-energy nitrogen and phosphorus removal from wastewater with low CN ratio

Abstract

This invention provides a low-energy-consumption method for nitrogen and phosphorus removal from wastewater with a low C / N ratio. The wastewater first undergoes anaerobic ammonia oxidation (AMO) for nitrogen removal in the outer ring, then sequentially enters the suspended sludge zone and the inner ring for denitrification and phosphorus removal. Sludge from the secondary sedimentation tank is returned to the suspended sludge zone. Through optimized sludge return port design, the returned sludge forms a hydraulic vortex within the suspended sludge zone, achieving sludge-water mixing. Part of the treated effluent is returned to the outer ring to further enhance anaerobic ammonia oxidation for nitrogen removal. This invention maintains stable and efficient nitrogen and phosphorus removal performance even with insufficient influent carbon sources, without requiring external carbon sources. Furthermore, by optimizing the reactor, replacing traditional stirring with hydraulic mixing, replacing traditional microporous aeration discs with aeration membrane modules, and replacing the traditional anaerobic-aerobic phosphorus removal process with an anaerobic-micro-aerobic process, this invention solves the problem of nitrogen and phosphorus removal from wastewater with a low C / N ratio while maintaining low energy consumption.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, and in particular relates to a method for low-energy nitrogen and phosphorus removal from wastewater with low CN ratio. Background Technology

[0002] With the advancement of urbanization, wastewater treatment has become a key issue in environmental protection. Traditional nitrogen and phosphorus removal processes typically consist of three stages: anaerobic, anoxic, and aerobic. Anaerobic and anoxic processes require agitation to ensure sludge suspension, while aerobic processes require strong aeration to maintain sufficiently high dissolved oxygen levels, resulting in high overall energy consumption. Furthermore, traditional nitrogen and phosphorus removal processes cannot resolve the contradiction between the long sludge age required for nitrifying bacteria and the short sludge age required for phosphorus-removing bacteria. More importantly, traditional nitrogen and phosphorus removal processes often face the problem of insufficient influent carbon source, making it difficult to achieve simultaneous and efficient nitrogen and phosphorus removal. This is especially true when the influent C / N ratio is low, where insufficient carbon source significantly inhibits nitrogen and phosphorus removal performance, often requiring the addition of additional carbon source. Therefore, nitrogen and phosphorus removal from low C / N wastewater remains a significant technical challenge.

[0003] Currently, there are several designs for low C / N ratio wastewater nitrogen and phosphorus removal systems or treatment devices on the market. CN202311188351.5 (authorization number CN116924569B) designs a system for enhanced nitrogen and phosphorus removal from low C / N ratio wastewater, consisting of an influent tank, a primary SBBR reactor, a first intermediate tank, a secondary SBBR reactor, a second intermediate tank, an anaerobic ammonia oxidation phosphorus removal reactor, and an effluent tank. To achieve good phosphorus removal, both SBBR tanks in this system require maintaining dissolved oxygen levels of 2-4 mg / L, resulting in high energy consumption. CN202321017535.0 (authorization number CN220056569U) designs an improved high-efficiency nitrogen and phosphorus removal treatment device for low C / N ratio domestic wastewater, consisting of a water tank, A2 / O, MBR, MBBR, a dual nitrification liquid return system, a dual sludge return system, and a carbon source precision dosing system. This device requires additional carbon source addition to ensure effective nitrogen and phosphorus removal.

[0004] Patent application 202120295779.X discloses an integrated nitrogen and phosphorus removal wastewater treatment device. The main body is a membrane aerated bioreactor with internal flocculent sludge, coupling denitrification for phosphorus removal, partial sub-digestion, and anaerobic ammonia oxidation to achieve nitrogen and phosphorus removal. The shortcomings of this device are: denitrifying phosphorus-accumulating bacteria must undergo anaerobic phosphorus release before they can fully denitrify and accumulate phosphorus (i.e., the phosphorus removal process). Although anaerobic zones exist within the flocculent material, denitrifying bacteria are fixed in the anoxic zone of the flocculent and cannot enter the anaerobic zone to complete the anaerobic phosphorus release process. Furthermore, anaerobic ammonia oxidizing bacteria grow slowly and are sensitive to the environment; their proliferation is significantly inhibited when they coexist with denitrifying bacteria, resulting in a relatively low overall nitrogen and phosphorus removal efficiency.

[0005] CN202211350282.9 (Authorization No. CN115557605B) discloses a process for simultaneous nitrogen and phosphorus removal from domestic sewage and nitrate wastewater through dual short-cut denitrification and anaerobic ammonium oxidation coupled with denitrification. The apparatus includes a domestic sewage raw water tank, an SBR reactor, and a nitrate wastewater tank. Part of the domestic sewage enters the SBR reactor, where polyphosphate-accumulating bacteria and polysaccharide-accumulating bacteria store organic matter as PHAs, while simultaneously releasing phosphorus. Subsequently, a second batch of domestic sewage and nitrate wastewater are introduced for anoxic mixing. Denitrifying bacteria utilize the secondary influent domestic sewage for short-cut denitrification to rapidly provide substrate for anaerobic ammonium oxidation. After the readily degradable organic matter is consumed, endogenous short-cut denitrification by polysaccharide-accumulating bacteria provides nitrite as substrate for anaerobic ammonium oxidation, achieving dual short-cut denitrification coupled with anaerobic ammonium oxidation for nitrogen removal. Summary of the Invention

[0006] In view of this, the present invention aims to propose a method for low-energy nitrogen and phosphorus removal in wastewater with low CN ratio, so as to achieve efficient nitrogen and phosphorus removal while reducing energy consumption.

[0007] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0008] A method for low-energy nitrogen and phosphorus removal from wastewater with low CN ratios, comprising the following steps:

[0009] S1, Device Connection

[0010] The equipment used in this method includes an inlet tank, a reactor, and a secondary sedimentation tank. The bottom of the reactor has a suspended sludge zone containing denitrifying polyphosphate-accumulating bacteria. The area above the suspended sludge zone is divided into an inner ring and an outer ring. The outer ring contains packing material loaded with anaerobic ammonia-oxidizing bacteria. The outer ring is separated from the suspended sludge zone by a support net. The inner ring contains an aeration membrane assembly on which a biofilm grows. Nitrifying bacteria grow in the inner layer of the biofilm (i.e., near the membrane surface). The bottom of the inner ring has an inlet with a Laval nozzle. The suspended sludge zone has an aeration pipe directly opposite the Laval nozzle. The inlet of the outer ring is connected to the inlet tank via a pipe, and the outlet of the inner ring is connected to the secondary sedimentation tank via a pipe. The effluent return port of the secondary sedimentation tank is connected to the inlet of the outer ring, and the sludge return port of the secondary sedimentation tank is connected to the suspended sludge zone.

[0011] S2, denitrification and phosphorus removal reaction

[0012] S21. Biological wastewater enters the inlet tank, and the wastewater is pumped from the inlet tank into the outer ring, where anaerobic ammonia oxidation denitrification is completed.

[0013] S22. Afterwards, the wastewater enters the suspended sludge zone and mixes with the sludge returned from the secondary sedimentation tank. Denitrifying polyphosphate bacteria ingest organic matter here and complete the anaerobic phosphorus release process. The sludge-water mixture in the suspended sludge zone is flushed into the inner ring through the Laval nozzle at the bottom of the inner ring, so that the denitrifying polyphosphate bacteria that have completed the anaerobic phosphorus release process can fully contact the nitrates produced in the micro-aerobic zone of the inner ring and carry out the denitrification polyphosphate process.

[0014] S23. Wastewater treated in the inner ring enters the secondary sedimentation tank. The concentrated sludge in the secondary sedimentation tank is returned to the suspended sludge zone for anaerobic phosphorus release. At the same time, the wastewater in the upper layer of the secondary sedimentation tank is returned to the outer ring.

[0015] Furthermore, the loading of anaerobic ammonia-oxidizing bacteria, calculated as lipids and phosphorus, was maintained at 300-800 nmol phosphorus / cm³. 3 If the load is too low, it will not be able to complete the effective anaerobic ammonia oxidation; if it is too high, it will lead to an increase in head loss. In the suspended sludge zone, the abundance of denitrifying polyphosphate-accumulating bacteria in the total bacterial community is maintained at 10-15%, and the abundance of nitrifying bacteria in the total bacterial community of the biofilm is maintained at 5%-10%.

[0016] Furthermore, the sludge return ratio is 100-150%, and the return sludge concentration is 6000-10000 mg / L. The sludge entering the suspended sludge zone adopts a tangential influent design to form a hydraulic vortex, achieving uniform mixing of the sludge, with a tangential flow velocity of over 2 m / s. At the same time, the hydraulic vortex replaces traditional mechanical stirring, ensuring thorough mixing of sludge and water in the outer ring sludge zone and reducing operating energy consumption.

[0017] Furthermore, the aeration rate of the aeration pipe is 0.1-0.3 m³. 3 air / m 3 The distance between the center of the water supply, aeration pipe, and Laval nozzle is 3-5 times the diameter of the Laval nozzle throat. The Laval nozzle ensures that the sludge-water mixture in the suspended sludge zone is drawn into the inner ring with minimal aeration, achieving thorough mixing and contact within the inner ring without mechanical stirring. This guarantees stable treatment results and reduces energy consumption.

[0018] The Laval nozzle has a hyperbolic structure, with the narrower section between the hyperbolas forming the throat.

[0019] Furthermore, oxygen is supplied to the inner ring area through an aeration membrane module, maintaining a slightly aerobic state in the inner ring liquid phase. The dissolved oxygen concentration in the inner ring liquid phase is 0.5-1.0 mg / L, the hydraulic retention time is 3-6 hours, and the effective membrane area of ​​the aeration membrane module is 30-60 m². 2 / m 3 The oxygen transfer rate of the membrane should not be less than 10 g O2 / (m 2•d). Dissolved oxygen diffuses from the aeration membrane module to the surrounding liquid phase. The oxygen concentration is highest on the membrane surface of the aeration membrane module, and the dissolved oxygen concentration in the liquid phase gradually decreases to form a micro-aerobic state. The low dissolved oxygen condition reduces operating costs; and the oxygen transfer efficiency is increased and aeration energy consumption is reduced through membrane aeration.

[0020] Furthermore, the sludge concentration in the suspended sludge zone is 3000-4000 mg / L.

[0021] Furthermore, the effluent recirculation ratio of the secondary sedimentation tank is between 30% and 50%.

[0022] Furthermore, the volume ratio of the outer ring, suspended sludge zone, and inner ring is 8:1:3.

[0023] Furthermore, the filler volume ratio is 40%-60%, and the filler particle size is 1-3 cm.

[0024] The packing material is a high specific surface area block (or granular) packing material, and the support mesh aperture is smaller than the packing particle size.

[0025] Compared with existing technologies, the method for low-energy nitrogen and phosphorus removal from wastewater with low CN ratio described in this invention has the following advantages:

[0026] (1) The method for low-energy nitrogen and phosphorus removal for wastewater with low C / N ratio described in this invention is applicable to wastewater with low C / N ratio between 1 and 3. It can achieve efficient nitrogen and phosphorus removal under influent conditions with insufficient carbon source, without the need for external carbon source, thus reducing wastewater treatment operating costs.

[0027] (2) The method for low-energy nitrogen and phosphorus removal in wastewater with low CN ratio described in this invention involves the decomposition of ammonia nitrogen and nitrite nitrogen in the influent and return water into nitrogen gas by anaerobic ammonia-oxidizing bacteria in the outer ring, thus initially achieving the removal of ammonia nitrogen and total nitrogen. The suspended sludge zone realizes the anaerobic phosphorus release process of denitrifying polyphosphate-accumulating bacteria. The inner ring is a micro-aerobic zone, which utilizes the reverse mass transfer of oxygen in the biofilm on the aeration membrane component to realize the nitrification and nitrification processes. The micro-aerobic environment of the inner ring provides more nitrate electron acceptors for denitrifying polyphosphate-accumulating bacteria, which is more conducive to the completion of the denitrification polyphosphate-accumulating process by denitrifying polyphosphate-accumulating bacteria.

[0028] (3) The method for low-energy nitrogen and phosphorus removal for low C / N wastewater described in this invention combines multiple processes such as anaerobic ammonia oxidation, aerobic nitrification, micro-aerobic denitrification and phosphorus removal. It can efficiently remove nitrogen and phosphorus in the treatment of low C / N wastewater, overcoming the limitations of existing technologies in the treatment of low C / N wastewater.

[0029] (4) The method for low-energy nitrogen and phosphorus removal in wastewater with low CN ratio described in this invention integrates multiple processes into one reactor. Through the integrated design and the distinction between the outer and inner rings, the use of multiple complex equipment in traditional wastewater treatment processes is reduced, the treatment efficiency is improved, and the maintenance cost and management complexity of the system are reduced. Attached Figure Description

[0030] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0031] Figure 1 This is a diagram of the equipment used in the low-energy-consumption nitrogen and phosphorus removal method for wastewater with low CN ratio, as described in an embodiment of the present invention.

[0032] Explanation of reference numerals in the attached figures:

[0033] 1. Inlet tank; 2. Inlet pump; 3. Flow meter; 4. Outer ring top cover; 5. Outer ring; 6. Support net; 7. Inner ring; 8. Suspended sludge zone; 9. Laval nozzle; 10. Aeration membrane assembly; 11. Air inlet; 12. Blower; 13. Exhaust port; 14. Effluent pump; 15. Aeration pipe; 16. Sludge return pump; 17. Effluent return pump; 18. Secondary sedimentation tank. Detailed Implementation

[0034] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] A method for low-energy nitrogen and phosphorus removal from wastewater with low CN ratios, comprising the following steps:

[0037] S1, Device Connection

[0038] like Figure 1 The equipment used in this method includes an inlet tank 1, a reactor and a secondary sedimentation tank 18. The bottom of the reactor is provided with a suspended sludge zone 8 containing denitrifying polyphosphate-accumulating bacteria. The area above the suspended sludge zone 8 is divided into an inner ring 7 and an outer ring 5. The volume ratio of the outer ring 5, the suspended sludge zone 8 and the inner ring 7 is 8:1:3.

[0039] The outer ring 5 contains packing material loaded with anaerobic ammonia-oxidizing bacteria. The loading of anaerobic ammonia-oxidizing bacteria, calculated as lipids and phosphorus, is maintained at 300-800 nmol phosphorus / cm³. 3 The outer ring 5 is separated from the suspended sludge zone 8 by a support net 6. The filler volume ratio is 40%-60%, the filler particle size is 1-3cm, and the filler is a high specific surface area block (or granular) filler. The pore size of the support net 6 is smaller than the filler particle size. The top of the outer ring is provided with an outer ring top cover 4, so that the outer ring forms a closed cavity.

[0040] The inner ring 7 is equipped with an aeration membrane module 10, on which a biofilm grows and forms. Nitrifying bacteria grow in the inner layer of the biofilm, and their abundance in the total bacterial community of the biofilm is maintained at 5%-10%. The bottom of the inner ring 7 has an inlet, and a Laval nozzle 9 is installed at the inlet. The suspended sludge zone 8 has an aeration pipe 15 directly opposite the Laval nozzle 9, with an aeration rate of 0.1-0.3 m³ / h. 3 air / m 3 The distance between the center of the aeration pipe 15 and the center of the Laval nozzle 9 is 3-5 times the throat diameter of the Laval nozzle 9. The inner ring 7 is oxygenated through the aeration membrane module 10. The liquid phase in the inner ring 7 is in a slightly aerobic state, with a dissolved oxygen concentration of 0.5-1.0 mg / L, a hydraulic retention time of 3-6 hours, and an effective membrane area of ​​30-60 m². 2 / m 3 The oxygen transfer rate of the membrane should not be less than 10 g O. 2 / (m 2 •d). The blower 12 supplies air to the aeration pipe 15 and the aeration membrane assembly 10. The connecting pipe of the blower 12 is connected to the air inlet 11 of the aeration membrane assembly 10, and the exhaust port 13 is used to discharge the gas generated during the reaction process to avoid gas accumulation affecting operation.

[0041] The inlet of the outer ring 5 is connected to the inlet tank 1 via a pipe, which is equipped with an inlet pump 2 and a flow meter 3; the outlet of the inner ring 7 is connected to the secondary sedimentation tank 18 via a pipe, which is equipped with an outlet pump 14; the outlet return port of the secondary sedimentation tank 18 is connected to the inlet of the outer ring 5, and the return pipe is equipped with an outlet return pump 17 and a flow meter 3; the sludge return port of the secondary sedimentation tank 18 is connected to the suspended sludge zone 8, and the return pipe is equipped with a sludge return pump 16 and a flow meter 3. The effluent recirculation ratio is 30%-50%, the sludge recirculation ratio is 100-150%, and the recirculated sludge concentration is 6000-10000 mg / L. The sludge entering the suspended sludge zone 8 adopts a tangential influent design to form a hydraulic vortex and achieve uniform mixing of the sludge. The tangential flow velocity is above 2 m / s. The sludge concentration in the suspended sludge zone 8 is 3000-4000 mg / L, and the abundance of denitrifying polyphosphate-accumulating bacteria in the total bacterial community in the suspended sludge zone is maintained at 10-15%.

[0042] S2, denitrification and phosphorus removal reaction

[0043] 1) Wastewater first enters the inlet tank 1, which serves as the initial storage and distribution unit of the system. The inlet pump 2 is used to lift the wastewater to the reactor.

[0044] After the wastewater is pumped from the inlet tank 1 into the outer ring 5, the wastewater is converted into nitrogen gas under anaerobic conditions in the outer ring 5, thus completing the denitrification process.

[0045] 2) Subsequently, the wastewater enters the suspended sludge zone 8 and mixes with the sludge returned from the secondary sedimentation tank 18. Denitrifying polyphosphate bacteria ingest organic matter here. The suspended sludge zone 8 maintains an anaerobic environment to ensure that the denitrifying polyphosphate bacteria can fully release phosphorus anaerobically. The sludge-water mixture in the suspended sludge zone 8 is flushed into the inner ring 7 through the Laval nozzle 9 at the bottom of the inner ring 7, so that the denitrifying polyphosphate bacteria that have undergone anaerobic phosphorus release can fully contact the nitrates produced in the microaerobic zone of the inner ring 7 to carry out the denitrification polyphosphate process. The aerobic nitrifying bacteria in the inner layer of the biofilm on the membrane module complete the conversion of ammonia nitrogen to nitrite and nitrate. The oxygen supply of the membrane aeration module is controlled to keep the liquid phase in the inner ring zone in a microaerobic environment, which promotes the denitrifying polyphosphate bacteria to use the organic matter, nitrates and phosphates in the water to carry out the denitrification polyphosphate process, thereby achieving nitrogen and phosphorus removal.

[0046] The aeration membrane module 10 is a hollow fiber membrane with hydrophobic and breathable membrane fibers and nanoscale pore size, which ensures efficient oxygen transfer while preventing water from entering the inner cavity of the membrane fibers.

[0047] Specifically, the aeration membrane module 10 includes membrane fibers and a membrane frame, with the membrane fibers fixed to the membrane frame in a wavy shape. One end of the membrane module's air inlet 11 is connected to a blower 12 for oxygen supply, with an oxygen supply pressure between 10-15 kPa. The other end of the membrane module is a residual exhaust port 13, which discharges residual gas that did not enter the aqueous phase back into the air.

[0048] 3) Wastewater treated in the inner ring 7 enters the secondary settling tank 18, where sludge-water separation is completed. A portion of the settled sludge is returned to the suspended sludge zone 8 of the reactor. The sludge return inlet of the suspended sludge zone 8 is designed with tangential inlet water to create a hydraulic vortex, ensuring uniform mixing of the sludge. The secondary settling tank effluent is returned to the outer ring of the reactor to replenish nitrite, dilute the concentration of organic matter in the influent, and promote sufficient anaerobic ammonia oxidation, further improving the denitrification effect.

[0049] Example 1

[0050] A method for low-energy nitrogen and phosphorus removal from wastewater with low CN ratios includes the following steps:

[0051] 1) After the equipment connection is completed, biological wastewater with a C / N ratio of 2 enters the inlet tank 1. The water is then pumped from the inlet tank 1 into the outer ring 5 by the inlet pump 2, with an inlet pipe pressure of 0.02 MPa. The packing area is filled with polyurethane black sponge at a filling ratio of 40%, and the anaerobic ammonia-oxidizing bacteria biomass loaded on the sponge carrier is 400 nmol P / cm³. 3 (Based on lipids and phosphorus), anaerobic ammonia oxidation denitrification is completed in this area. A stainless steel support mesh 6 is installed below the packing layer to prevent the packing from settling.

[0052] 2) The wastewater then enters the suspended sludge zone 8, where it is thoroughly mixed with the sludge returned from the secondary sedimentation tank 18 (sludge return ratio 100%) by hydraulic swirling. Denitrifying polyphosphate-accumulating bacteria ingest organic matter here, completing the anaerobic phosphorus release process. The sludge-water mixture in the suspended sludge zone 8 is flushed into the inner ring zone through the Laval nozzle 9 at the bottom of the inner ring, avoiding mechanical stirring and significantly reducing energy consumption.

[0053] In the inner ring, the aeration membrane module 10 is located in the center of the inner ring and is fixed to the membrane frame in a wavy shape. The air inlet 11 at the lower end of the membrane module is connected to the blower 12 through a pipe, and air diffuses outward through the inner cavity of the membrane fibers to supply oxygen to the reactor; the exhaust port 13 at the upper end of the membrane module is connected to the tail gas discharge pipe to discharge the residual gas in the membrane cavity, which is controlled by a regulating valve. Flow meters 3 are also installed on each pipeline, and the air inlet 11 is connected to the regulating valve.

[0054] Specifically, in this embodiment, the hydraulic retention time ratio of the outer ring 5, the suspended sludge zone 8, and the inner ring 7 is 8:1:3, and the effluent recirculation ratio of the secondary sedimentation tank is 30%. The aeration membrane module 10 is equipped with a modified PVDF hollow fiber membrane module, with an effective membrane module area of ​​50 m². 2 / m 3 The dissolved oxygen in the inner ring area is controlled at around 0.5 mg / L.

[0055] Under the conditions of sludge return ratio r=100%, C / N=2, C / P=40, and DO=0.5-1.0 mg / L, its nitrogen and phosphorus removal efficiency is as follows: NH4 + -N removal rate 96%, TN removal rate 95%, TP removal rate 78%, total energy consumption reaches 490 kWh / m³ 3 .

[0056] Comparative Example 1: Traditional A 2 / O process

[0057] This comparative example uses the traditional A 2 The / O process (anaerobic-anoxic-aerobic process) treats wastewater with a low C / N ratio. The system configuration includes an anaerobic tank, an anoxic tank, and an aerobic tank.

[0058] Under low C / N wastewater conditions, due to insufficient carbon sources, the competition for carbon sources between denitrifying bacteria and polyphosphate-accumulating bacteria intensifies, and the denitrification and polyphosphate-accumulating processes cannot proceed simultaneously and efficiently, resulting in limited nitrogen and phosphorus removal efficiency.

[0059] Meanwhile, in the aerobic zone of wastewater treatment, maintaining nitrification requires high-intensity aeration, leading to a significant increase in energy consumption. Furthermore, to achieve effective nitrogen removal, additional external carbon sources are often required, thus increasing operating costs. Although mixed liquor recirculation can partially supplement the required carbon source, this practice increases system complexity and brings inconvenience to operation and management.

[0060] Meanwhile, in wastewater treatment systems, there is a significant conflict in the sludge age requirements of nitrifying bacteria and polyphosphate-accumulating bacteria. Nitrifying bacteria require a longer sludge age to maintain their activity and effectively carry out nitrification; while polyphosphate-accumulating bacteria require a shorter sludge age to inhibit phosphorus release and improve phosphorus removal efficiency. This conflict in requirements makes it difficult for the two microorganisms to coexist in the same system, resulting in a lack of synergistic balance in system functions and thus limiting overall treatment efficiency.

[0061] Specifically, traditional A 2 In the / O process, DO in the anaerobic zone is ≤0.1 mg / L, DO in the anoxic zone is 0.2-0.5 mg / L, and DO in the aerobic zone is 2-4 mg / L. The sludge return ratio is 100%, and the mixed liquor return ratio is 200%. Under the same influent conditions as in Example 1, A 2 The nitrogen and phosphorus removal efficiency of the / O process is as follows: NH4 + -N removal rate 75%, TN removal rate 65%, TP removal rate 63%, total energy consumption reaches 712 kWh / m³ 3 Compared to Example 1, its NH4 + The removal rates of -N, TN, and TP were 21.9%, 31.6%, and 19.2% lower, respectively, and the total energy consumption was 31% higher.

[0062] Therefore, compared to this embodiment, A 2 The O system suffers from problems such as lengthy processes, high energy consumption, and weak resistance to shock loads.

[0063] Comparative Example 2: Operation under hypoxic conditions in the inner ring area

[0064] This comparative example was maintained in an anoxic state (DO=0.2-0.5 mg / L) by adjusting the dissolved oxygen in the inner ring zone, while the other conditions remained the same as in the example.

[0065] The MABR tank maintains a strictly anoxic environment, and denitrifying polyphosphate-accumulating bacteria (DPAOs) use nitrate nitrogen as an electron acceptor to simultaneously remove nitrogen and phosphorus.

[0066] The limitations of a low dissolved oxygen environment on system performance are mainly reflected in the inhibition of the nitrification process. Insufficient DO concentration leads to limited activity of nitrifying bacteria, while NH4+... + -N-nitrate nitrogen (NO2) - / NO3 - The conversion efficiency of DPAOs is significantly reduced. This result directly leads to insufficient supply of electron acceptors required for DPAOs to denitrify and remove phosphorus, thus limiting their metabolic efficiency.

[0067] Meanwhile, under strict hypoxic conditions, excessively low DO levels inhibit the aerobic polyphosphate accumulation process of polyphosphate-accumulating bacteria, thereby suppressing the overall phosphorus removal performance, indicating an imbalance in the synergy between denitrification and phosphorus removal pathways under low DO conditions.

[0068] Specifically, compared to the example, this comparative example adjusted the dissolved oxygen from a slightly aerobic state (DO=0.5-1.0 mg / L) to an anoxic state (DO=0.2-0.5 mg / L), with an influent water quality of C / N=2. Under these conditions, the reactor achieved a total nitrogen (TN) removal rate of 85% and a total phosphorus (TP) removal rate of 53%, indicating that the polyphosphate accumulation function of DPAOs was not fully activated.

[0069] Therefore, compared to this embodiment, the synergistic effect of nitrification and denitrification in nitrogen and phosphorus removal is suppressed under strict anoxic conditions, making it impossible to achieve efficient and simultaneous removal of nitrogen and phosphorus.

[0070] Comparative Example 3: The volume ratios of the outer ring, suspended sludge zone, and inner ring are different.

[0071] This comparative example adjusts the volume ratio of the outer ring, suspended sludge zone, and inner ring to 1:1:3, while keeping the other conditions the same as the example.

[0072] The hydraulic retention time of outer ring 5 is significantly shortened. Anaerobic ammonia oxidizing bacteria are autotrophic, with slow proliferation and metabolism. If the hydraulic retention time of outer ring 5 is too short, it will hinder the anaerobic ammonia oxidizing bacteria from converting NH4+ in the water. + -N and NO2 — N is promptly converted into N2, achieving effective denitrification.

[0073] Specifically, compared to the example, this comparative example adjusts the volume ratio of the outer ring, suspended sludge zone, and inner ring from 8:1:3 to 1:1:3, while maintaining the same influent water quality. Under these conditions, the process achieves ammonia nitrogen removal of 68%, total nitrogen (TN) removal of 64%, and total phosphorus (TP) removal of 75%. Both ammonia nitrogen and TN removal rates are significantly lower than in the example, but the TP removal rate remains unchanged. This change in volume ratio severely inhibits the anaerobic ammonia oxidation denitrification process in the outer ring 5, but because the ratio of the suspended sludge zone to the inner ring remains unchanged, it does not affect the nitrogen and phosphorus removal efficiency of the MABR.

[0074] Comparative Example 4: Different sludge return ratios

[0075] This comparative example adjusts the sludge return ratio from 100% in the example to 50%, while keeping the other conditions the same as in the example.

[0076] On the one hand, a reduced sludge return ratio leads to insufficient anaerobic phosphorus release by denitrifying polyphosphate (PPP) bacteria, decreasing the amount of available carbon source (poly-β-hydroxybutyrate) for PPP denitrification in the inner ring microaerobic zone, thus resulting in decreased TP removal efficiency. On the other hand, a reduced sludge return ratio also causes PPP to carry NO3 back to the inner ring MABR tank. - The decrease in -N content also affects the denitrification and polyphosphate accumulation process in the inner ring. However, the decrease in sludge return ratio does not affect the nitrifying bacteria on the inner ring aeration membrane module, so the decrease in ammonia nitrogen and total nitrogen removal rates is relatively small, while the decrease in TP removal rate is significant.

[0077] Specifically, compared to the previous example, the sludge return ratio was adjusted from 100% to 50%, while the influent water quality remained exactly the same. Under these conditions, the process achieved a 90% removal rate for ammonia nitrogen, an 85% removal rate for total nitrogen (TN), and a 62% removal rate for total phosphorus (TP).

[0078] This invention achieves a balance between efficient nitrogen and phosphorus removal and energy consumption through structural innovation and process optimization. Through the synergistic effect of the outer and inner rings, it achieves efficient treatment of low C / N wastewater.

[0079] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for low-energy nitrogen and phosphorus removal from wastewater with low CN ratio, characterized in that: The method includes the following steps: S1, Device Connection The equipment used in this method includes an inlet tank, a reactor, and a secondary sedimentation tank. The bottom of the reactor has a suspended sludge zone containing denitrifying polyphosphate-accumulating bacteria. The area above the suspended sludge zone is divided into an inner ring and an outer ring. The outer ring contains packing material loaded with anaerobic ammonia-oxidizing bacteria. The outer ring is separated from the suspended sludge zone by a support net. The inner ring contains an aeration membrane assembly on which a biofilm grows, with nitrifying bacteria growing in the inner layer of the biofilm. The bottom of the inner ring has an inlet with a Laval nozzle. The suspended sludge zone has an aeration pipe directly opposite the Laval nozzle. The inlet of the outer ring is connected to the inlet tank via a pipe. The effluent from the inner ring is connected to the secondary sedimentation tank via a pipe. The effluent return port of the secondary sedimentation tank is connected to the inlet of the outer ring. The sludge return port of the secondary sedimentation tank is connected to the suspended sludge zone. S2, Denitrification and Phosphorus Removal Reactions S21. Biological wastewater enters the inlet tank, and the wastewater is pumped from the inlet tank into the outer ring, where anaerobic ammonia oxidation denitrification is completed. S22. Afterwards, the wastewater enters the suspended sludge zone and mixes with the sludge returned from the secondary sedimentation tank. Denitrifying polyphosphate bacteria ingest organic matter here and complete the anaerobic phosphorus release process. The sludge-water mixture in the suspended sludge zone is flushed into the inner ring through the Laval nozzle at the bottom of the inner ring, so that the denitrifying polyphosphate bacteria that have completed the anaerobic phosphorus release process can fully contact the nitrates produced in the micro-aerobic zone of the inner ring and carry out the denitrification polyphosphate process. S23. Wastewater treated in the inner ring enters the secondary sedimentation tank. The concentrated sludge in the secondary sedimentation tank is returned to the suspended sludge zone for anaerobic phosphorus release. At the same time, the wastewater in the upper layer of the secondary sedimentation tank is returned to the outer ring.

2. The method for low-energy nitrogen and phosphorus removal from wastewater with low CN ratio according to claim 1, characterized in that: The loading of anaerobic ammonia-oxidizing bacteria, expressed as lipids and phosphorus, was maintained at 300-800 nmol phosphorus / cm³. 3 In the suspended sludge zone, the abundance of denitrifying polyphosphate-accumulating bacteria in the total bacterial community remained at 10-15%, and the abundance of nitrifying bacteria in the total bacterial community of the biofilm remained at 5%-10%.

3. The method for low-energy nitrogen and phosphorus removal from wastewater with low CN ratio according to claim 1, characterized in that: The sludge return ratio is 100-150%, the return sludge concentration is 6000-10000 mg / L, and the sludge entering the suspended sludge zone adopts a tangential influent design with a tangential flow velocity of 2 m / s or more.

4. The method for low-energy nitrogen and phosphorus removal from wastewater with low CN ratio according to claim 1, characterized in that: The aeration rate of the aeration pipe is 0.1-0.3m. 3 air / m 3 The distance between the center of the water aeration pipe and the center of the Laval nozzle is 3-5 times the diameter of the Laval nozzle throat.

5. The method for low-energy nitrogen and phosphorus removal from wastewater with low CN ratio according to claim 1, characterized in that: The inner ring area is oxygenated through an aeration membrane module, maintaining a slightly aerobic state in the liquid phase. The dissolved oxygen concentration in the inner ring liquid phase is 0.5-1.0 mg / L, the hydraulic retention time is 3-6 hours, and the effective membrane area of ​​the aeration membrane module is 30-60 m². 2 / m 3 The oxygen transfer rate of the membrane should not be less than 10 g O2 / (m 2 •d).

6. The method for low-energy nitrogen and phosphorus removal from wastewater with low CN ratio according to claim 1, characterized in that: The sludge concentration in the suspended sludge zone is 3000-4000 mg / L.

7. The method for low-energy nitrogen and phosphorus removal from wastewater with low CN ratio according to claim 1, characterized in that: The effluent recirculation ratio of the secondary sedimentation tank is between 30% and 50%.

8. The method for low-energy nitrogen and phosphorus removal from wastewater with low CN ratio according to claim 1, characterized in that: The volume ratio of the outer ring, suspended sludge zone, and inner ring is 8:1:

3.

9. The method for low-energy nitrogen and phosphorus removal from wastewater with low CN ratio according to claim 1, characterized in that: The filler volume ratio is 40%-60%, and the filler particle size is 1-3cm.

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