Sludge self-backflow-based sewage enhanced nitrogen and phosphorus removal process

Abstract

The invention relates to the field of sewage treatment, in particular to a sewage enhanced nitrogen and phosphorus removal process based on sludge self-backflow, and the process uses a reaction precipitation system and comprises an anoxic tank and an aerobic tank which are separated by a partition plate. A water inlet is formed in the top of the sediment sludge hopper and communicated with the aerobic tank, and the bottom of the sediment sludge hopper is communicated with the anoxic tank through a return pipe. The aeration pipeline is positioned between the communication opening and the lower closing opening of the sedimentation mud bucket, so that a circulation loop consisting of an ascending channel, a water inlet, a sinking channel and the lower closing opening is formed in the aerobic tank. The aerobic tank is in a micro-aerobic environment, nitrification, synchronous denitrification and phosphorus accumulation reaction occur in the ascending channel, mud-water separation is completed in the sinking channel, and precipitated sludge completely flows back to the anoxic tank and the aerobic tank through a return pipe. The one-way circulation of the sewage enables the sedimentation direction to be consistent with the water flow, accelerates the sludge sedimentation, greatly shortens the retention time of the sludge in the sedimentation area, inhibits the secondary phosphorus release of the phosphorus-accumulating bacteria, and enhances the nitrogen and phosphorus removal effect of the system.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment, and in particular to a wastewater enhanced nitrogen and phosphorus removal process based on sludge self-recirculation. Background Technology

[0002] Wastewater treatment methods mainly include the activated sludge process and the biofilm process. Among these, the activated sludge process and its derivative processes (such as...) Activated sludge processes (SBR, SBR, etc.) are mainstream technologies for nitrogen and phosphorus removal in wastewater. The core of these processes lies in enriching and regulating functional microbial communities (such as nitrifying bacteria, denitrifying bacteria, and polyphosphate-accumulating bacteria) to effectively degrade organic matter in wastewater and remove nutrients such as nitrogen and phosphorus. The activated sludge process is essentially an artificially enhanced microbial purification system. It cultivates activated sludge flocs (microorganisms) with degradation capabilities through aeration in the aerobic environment of the aerobic tank. Subsequent secondary sedimentation tanks achieve sludge-water separation and sludge recirculation, thereby continuously and efficiently purifying wastewater. During this process, sludge is recirculated from the secondary sedimentation tank to the aerobic tank via sludge pumps (such as screw pumps or axial flow pumps) to maintain a stable concentration of microorganisms (activated sludge) in the aerobic tank, thus ensuring wastewater treatment effectiveness. Traditional processes generally rely on secondary sedimentation tanks for sludge-water separation and use external sludge pumps (such as screw pumps or axial flow pumps) to recirculate a portion of the settled sludge back to the aerobic tank. The recirculation ratio is typically controlled at 30%-70%. This "partial recirculation" mode has the following inherent drawbacks:

[0003] 1. Biomass loss and system instability: The solid-liquid separation efficiency of the secondary sedimentation tank is not 100%. Some activated sludge (especially nitrifying bacteria and young polyphosphate-accumulating bacteria with slightly poor settling performance) will be lost with the effluent, directly causing the loss of the core functional bacteria in the system. This makes it difficult to maintain a stable high level of sludge concentration (MLSS) in the reactor, weakening the system's resistance to shock loads.

[0004] 2. The Sludge Age Contradiction and Phosphorus Removal Bottleneck: Nitrifying bacteria require a long generation time for denitrification, necessitating a long sludge turnover period (SRT) in the system; however, traditional biological phosphorus removal relies on discharging phosphorus-rich excess sludge, objectively requiring a short SRT. This contradiction is further exacerbated in partial recirculation mode. To compensate for sludge loss and maintain biomass in the tank, the system is often forced to reduce sludge discharge, resulting in an excessively long sludge age. This increases the risk of sludge aging and secondary phosphorus release by polyphosphate-accumulating bacteria in the secondary settling tank, while also limiting the effectiveness of enhanced phosphorus removal through sludge discharge.

[0005] It is evident that "partial recirculation" essentially restricts the system's ability to maintain high biomass, reconcile sludge age discrepancies, and optimize carbon source utilization.

[0006] To address the aforementioned issues, some improvements have been attempted in existing technologies, such as structurally integrating the secondary sedimentation tank and the aerobic tank, allowing the settled sludge to directly return to the aerobic tank, thus eliminating the need for an external return pump and simplifying the process. However, this integrated structure still has inherent drawbacks: since the treated water needs to overflow from the secondary sedimentation tank area, polyphosphate-accumulating bacteria are prone to secondary phosphorus release during the sludge sedimentation process of sludge-water separation—that is, releasing the phosphorus absorbed in the aerobic tank back into the water body, making it difficult to guarantee that the phosphorus content in the treated water meets the requirements.

[0007] Therefore, the existing activated sludge process, which relies on secondary sedimentation tanks and partial sludge recirculation, still has significant shortcomings in achieving complete and efficient sludge recirculation while simultaneously addressing the sludge age conflict and secondary phosphorus release issues during nitrogen and phosphorus removal. An innovative technical solution is urgently needed to address these shortcomings. Summary of the Invention

[0008] To address the aforementioned problems, this invention provides a wastewater enhanced nitrogen and phosphorus removal process. Through innovative process design, it achieves "complete" sludge recirculation and recycling within the biochemical reaction zone, thereby simultaneously realizing deep nitrogen removal, efficient phosphorus removal, and energy savings under ultra-high sludge concentration and optimal sludge age. The technical solution of the equipment of this invention is as follows:

[0009] An enhanced nitrogen and phosphorus removal process for wastewater based on sludge self-recirculation utilizes a reactive sedimentation system. This system includes an anoxic tank and an aerobic tank connected by a connecting port, separated by a partition. The aerobic tank contains a sludge hopper, and its bottom is equipped with aeration pipes with aeration ports. The sludge hopper is located opposite the partition in the aerobic tank, with an inlet at its top connecting to the aerobic tank and a converging outlet at its bottom, also connecting to the aerobic tank. The converging outlet is equipped with... A return pipe is connected to the anoxic tank; the connecting port is located on the partition plate and is close to the bottom of the aerobic tank; the sedimentation hopper has a sedimentation slope, the lower constriction is located on the opposite side of the outlet connecting the anoxic tank and the aerobic tank, the aeration pipe is located between the lower constriction and the connecting port, in the aerobic tank, an upward channel is formed between the outer side of the sedimentation slope and the partition plate, and in the sedimentation hopper, a downward channel is formed on the inner side of the sedimentation slope, the upward channel, the sedimentation hopper inlet, the downward channel and the sedimentation hopper lower constriction together form a circulation loop;

[0010] The continuous return flow through the return pipe and the continuous aeration through the aeration pipe cause the wastewater entering the aerobic tank to circulate along the circulation loop, thereby accelerating the sludge settling speed at the sedimentation slope in the sedimentation hopper and inhibiting the phosphorus release reaction. During this process, the aerobic tank is in a micro-aerobic environment, with the oxygen content in the rising channel being greater than that in the sinking channel. The wastewater undergoes nitrification, simultaneous denitrification, and polyphosphate accumulation in the rising channel. In the sinking channel, the wastewater undergoes sludge-water separation, and all the sludge is returned to the aerobic tank.

[0011] In this scheme, the sedimentation sludge hopper, serving as the secondary sedimentation tank, is vertically installed directly within the aerobic tank. The activated sludge, after solid-liquid separation in the sedimentation hopper, can directly fall back into the aerobic tank by gravity, eliminating the need for additional sludge return pipelines. This ensures the direct return of activated sludge, effectively extending its age and maintaining the sludge content in the aerobic tank. Furthermore, due to bottom aeration in the aerobic tank, the liquid rises with the aeration airflow from the aeration ports and enters the inlet of the sedimentation sludge hopper from the top of the aerobic tank. The wastewater in the aerobic tank is then... The riser channel, the sludge hopper inlet, the sinking channel, and the sludge hopper bottom outlet form a single circulation loop. Wastewater is fed into the aerobic tank from the top of the sludge hopper and fed into the aerobic tank from the bottom outlet. This effectively avoids the interference of air resistance in the aerobic tank on the sludge settling in the sludge hopper, while also ensuring that the sludge settling direction is consistent with the wastewater flow direction. This accelerates the sludge settling speed in the sludge hopper, thereby shortening the residence time of phosphorus-removing bacteria in the sedimentation tank. This effectively prevents phosphorus release from the sludge hopper and enhances the phosphorus removal effect.

[0012] Preferably, the bottom of the aerobic tank is provided with a sludge discharge pipe with a control valve. The opening of the sludge discharge pipe is directly opposite the lower end of the sedimentation sludge hopper. The sludge concentration in the aerobic tank is adjusted by the control valve so that the sludge concentration in the aerobic tank is between 3500-6500 mg / L.

[0013] In this scheme, the sludge discharge pipe is located near the lower inlet opening, where the sludge concentration is highest after sedimentation. At this point, the sludge discharge pipe can effectively and dynamically adjust the sludge concentration in the entire aerobic tank, ensuring that the sludge concentration in the aerobic tank is higher than 3500 mg / L, allowing the denitrification and phosphorus removal reactions in the aerobic tank to proceed normally. At the same time, it ensures that the sludge concentration in the aerobic tank does not exceed 6500 mg / L, avoiding affecting the sedimentation rate of the sludge in the sedimentation hopper and not affecting the circulation loop in the aerobic tank.

[0014] Preferably, the anoxic tank provides an anaerobic environment and introduces activated sludge and raw water. In the anoxic tank, the activated sludge is mixed with the wastewater returning from the return pipe through a stirring mechanism, and the wastewater in the anoxic tank is continuously introduced into the aerobic tank through the liquid level difference.

[0015] In this scheme, water enters the anoxic tank, providing a continuous supply of organic matter to the system. The anoxic tank provides an anaerobic environment, allowing microorganisms in the activated sludge to use the carbon source in the organic matter as an energy source to reduce nitrate nitrogen in the liquid flowing from the return pipe into nitrogen gas. The nitrogen gas is then directly discharged, achieving denitrification. Furthermore, the organic matter is converted into an internal carbon source, causing polyphosphate (Poly-P) within the cells to decompose into phosphate (…). ), to release phosphorus.

[0016] Preferably, the aerobic tank is used to provide a micro-aerobic environment with an oxygen content of 0.5-1.2 mg / L.

[0017] In this scheme, because the structure of the circulation loop can effectively reduce the residence time of sludge in the sedimentation hopper, there is no need to worry about the anaerobic phosphorus release phenomenon in the sedimentation hopper. Therefore, the oxygen content in the entire aerobic tank can be controlled in a lower range of 0.5-1.2 mg / L, thereby ensuring that each reaction can be carried out at a low load, effectively improving the nitrification rate, ensuring complete removal of ammonia nitrogen, and reducing the sludge production in the sedimentation hopper compared to traditional processes.

[0018] Preferably, the aerobic tank is used to provide a micro-aerobic environment with an oxygen content of 0.8 mg / L.

[0019] In this scheme, by controlling the oxygen content input into the aeration pipeline, the aerobic tank is kept in a micro-aerobic environment with an oxygen content of 0.8 mg / L. Under this condition, the removal rates of TN and TP in the water obtained after the denitrification and phosphorus removal process carried out by this equipment are the highest.

[0020] Preferably, the return pipe is located in the sedimentation hopper or in the aerobic tank outside the sedimentation hopper, and a high-pressure air injection pipe is connected to the return pipe.

[0021] In this scheme, a return pipe is installed in the sedimentation sludge hopper. High-pressure gas is injected into the return pipe, which generates suction in the sedimentation sludge hopper, forming an air lift effect. This generates return power for the return pipe, which can effectively accelerate the sludge flow in the initial stage of sedimentation, increase the sludge settling rate, effectively reduce the residence time of sludge in the sedimentation sludge hopper, and prevent phosphorus release in the sedimentation sludge hopper.

[0022] Preferably, the reaction precipitation system further includes a dissolved oxygen monitoring device, which is installed in the aerobic tank and / or anoxic tank to monitor the dissolved oxygen content in the aerobic tank and / or anoxic tank.

[0023] Preferably, the activated sludge contains polyphosphate-accumulating bacteria, nitrifying bacteria, and denitrifying bacteria.

[0024] Preferably, the supernatant produced by the mud-water separation in the sedimentation hopper is discharged from the overflow weir provided on the sedimentation hopper.

[0025] Since the sedimentation sludge hopper continuously settles new sludge during solid-liquid separation, in order to prevent the sludge level in the aerobic tank from becoming too high, a portion of the sludge can be periodically and quantitatively discharged through the sludge discharge pipe to ensure the stability of the sludge content in the system.

[0026] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0027] 1. In this invention, the sedimentation sludge hopper, which serves as the secondary sedimentation tank, is directly and vertically installed in the aerobic tank. The activated sludge after solid-liquid separation in the sedimentation sludge hopper can fall back into the aerobic tank directly by gravity, without the need for additional sludge return pipelines. This ensures the direct return of activated sludge, effectively extends the sludge age, guarantees the sludge content in the aerobic tank, and allows the activated sludge in the aerobic tank to stably absorb phosphorus.

[0028] 2. In this invention, due to bottom aeration in the aerobic tank, the liquid in the aerobic tank rises with the aeration airflow generated by the aeration port and enters the inlet of the sedimentation sludge hopper from the top of the aerobic tank. The sewage in the aerobic tank forms a single circulation loop between the rising channel, the inlet of the sedimentation sludge hopper, the sinking channel, and the lower closing port of the sedimentation sludge hopper. The sewage is fed into the aerobic tank from the top of the sedimentation sludge hopper and fed into the aerobic tank from the lower closing port. This effectively avoids the interference of the upward air resistance in the aerobic tank on the sludge settling in the sedimentation sludge hopper, while also ensuring that the sludge settling direction is consistent with the sewage movement direction, accelerating the sludge settling speed in the sedimentation sludge hopper. This shortens the residence time of phosphorus-removing bacteria in the sedimentation tank, effectively preventing phosphorus release from the sedimentation sludge hopper and enhancing the phosphorus removal effect.

[0029] 3. The aerobic tank of the present invention can form a large loop flow pattern, which can reduce the occurrence of "dead zones" in the aerobic tank, allowing activated sludge particles to be evenly dispersed and fully reacted, effectively improving the nitrogen and phosphorus removal effect. Attached Figure Description

[0030] The accompanying drawings, as part of this invention, are provided to further illustrate the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention, but do not constitute an undue limitation thereof. Clearly, the drawings described below are merely some embodiments, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0031] In the attached diagram:

[0032] Figure 1 This is a flowchart of the present invention.

[0033] Figure 2 This is a schematic diagram of the reaction precipitation system of the present invention.

[0034] Figure 3 This is an air resistance diagram simulating bottom aeration in the aerobic tank of the present invention.

[0035] Explanation of markings in the diagram:

[0036] 1-Anoxic tank, 2-Aerobic tank, 3-Sedimentation hopper, 4-Sedimentation slope, 5-Aeration pipeline, 6-Return pipe, 7-Overflow weir, 8-Sludge discharge pipe, 9-High-pressure air injection pipe.

[0037] It should be noted that these accompanying drawings and textual descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art by referring to specific embodiments. Detailed Implementation

[0038] The technical solution of the present invention will be clearly and completely described in conjunction with the accompanying drawings and through specific implementation methods of the embodiments of the present invention.

[0039] like Figure 1 The wastewater treatment process flow diagram shown uses a reaction sedimentation system, which is as follows: Figure 2 As shown, the system includes an anoxic tank 1 and an aerobic tank 2 connected to each other. The anoxic tank 1 and aerobic tank 2 are an integral structure separated by a partition. The partition has a connecting port near the bottom of the aerobic tank 2. The aerobic tank 2 is equipped with a sedimentation hopper 3, which is located on the opposite side of the partition and has a sedimentation slope 4. The inlet of the sedimentation hopper 3 is located at the top of the sedimentation hopper and is lower than the liquid level of the aerobic tank 2. The lower end of the sedimentation hopper 3 is connected to the aerobic tank 2. A return pipe 6 connecting to the anoxic tank 1 is provided at the lower end of the sedimentation hopper 3. The bottom of the aerobic tank 2 is provided with an aeration pipe 5 and an aeration port. The lower end of the sedimentation hopper 3 is located on the opposite side of the outlet connecting the anoxic tank 1 to the aerobic tank. An upward channel is formed on the outer side of the sedimentation slope 4 and inside the aerobic tank 2, while a downward channel is formed on the inner side of the sedimentation slope 4 and inside the sedimentation sludge hopper 3. Wastewater in the aerobic tank 2 forms a circulation loop between the upward channel, the sedimentation sludge hopper inlet, the downward channel, and the lower closing point of the sedimentation sludge hopper. This accelerates the sludge settling speed at the sedimentation slope in the sedimentation sludge hopper and ensures that all sludge is returned to the aerobic tank, thereby reducing the sludge settling time in the sedimentation sludge hopper 3. The air resistance simulation results under this system are as follows: Figure 3 As shown, the arrows represent the direction of fluid movement, demonstrating that a complete circulation loop can be formed within the aerobic tank. It should be noted that in this reaction-sedimentation system, the aerobic tank only needs to provide an oxygen content of 0.5-1.2 mg / L to create the target micro-aerobic environment.

[0040] Preferably, a downward-sloping air baffle is installed at the constriction point, so that the opening formed by the air baffle and the lower constriction point of the sedimentation hopper 3 faces the outlet connecting the anoxic tank 1 to the aerobic tank. This ensures that the rising gas does not affect the sludge sedimentation in the sedimentation hopper 3, while also controlling the air resistance direction of the fluid output from the constriction point to a certain extent, allowing the water and activated sludge particles in the external aerobic tank to mix thoroughly. Meanwhile, the return pipe 6 can be installed inside the sedimentation hopper 3 or in the aerobic tank 2 outside the sedimentation hopper 3. Regardless of its location, one end of the return pipe must be aligned with the lower constriction point of the sedimentation hopper 3. Figure 2The document indicates two possible arrangements for the return pipe 6. In most cases, only one set of return pipes 6 is required. It should be noted that the return pipe 6 can be powered by a pump structure, but in this embodiment, it is preferable to connect a high-pressure air injection pipe 9 in the return pipe, so that the return pipe 6 can generate return power by injecting high-pressure fluid.

[0041] The specific process includes the following steps:

[0042] S1. Wastewater pretreatment.

[0043] In this step, the wastewater first undergoes coarse filtration, including but not limited to using a screen to intercept larger suspended solids, using a grit chamber to remove denser inorganic particles (such as stones and sand) from the wastewater, and a primary sedimentation tank for the initial settling of suspended solids, thus reducing the load of the biological treatment in the sedimentation system.

[0044] S2, Anaerobic reaction: The pretreated wastewater enters the anaerobic tank of the system and is stirred with the activated sludge.

[0045] In this step, the wastewater is stirred with the activated sludge in the anoxic tank to ensure thorough mixing. This allows the denitrifying bacteria in the activated sludge to use the organic carbon source in the influent as an energy source to denitrify nitrate nitrogen (N). ) is reduced to nitrogen gas ( Furthermore, the return pipe 6, connected to the aerobic tank 2, also inputs the return liquid from the aerobic tank 2 into the anaerobic tank. This return liquid is also rich in nitrate nitrogen. In the anaerobic tank, denitrifying bacteria perform denitrification, reducing the nitrate nitrogen in the wastewater to nitrogen gas, thus achieving nitrogen removal. Simultaneously, due to the anaerobic environment, the polyphosphate-accumulating bacteria in the activated sludge cannot efficiently produce energy (ATP) through respiration as they would in an aerobic environment. They can only decompose polyphosphate (Poly-P) within their cells, releasing phosphate (…). It uses a small amount of energy and the small amount of energy generated by the release of phosphorus to convert organic carbon sources in wastewater into internal carbon sources, thus exchanging phosphorus for carbon.

[0046] S3. Micro-aerobic reaction: After stirring in the anoxic tank, the liquid is discharged from the anoxic tank 1 into the bottom of the aerobic tank 2 under the influence of the liquid level difference. The bottom of the aerobic tank 2 is equipped with an aeration pipeline 5 with a microporous aeration device. This pipeline is linked to an online dissolved oxygen monitor via a gas flow regulating valve. The aeration rate is dynamically adjusted according to the real-time dissolved oxygen concentration in the aerobic tank 2 to maintain a stable dissolved oxygen (DO) level within the range of 0.5-1.2 mg / L. The aeration supply per unit volume of wastewater is generally controlled between 0.5-2.0 Nm³ air / m³ wastewater, specifically adaptively adjusted based on the influent ammonia nitrogen load and sludge concentration.

[0047] In this step, after the mixture of activated sludge and wastewater enters aerobic tank 2, nitrifying bacteria come into contact with oxygen to carry out nitrification, reducing ammonia nitrogen (…). ) is converted into non-toxic nitrate nitrogen ( This process removes harmful ammonia nitrogen from the water; simultaneously, due to the limited oxygen content, denitrifying bacteria can still carry out anaerobic denitrification, proceeding concurrently with nitrification, further reducing nitrate nitrogen in the wastewater. ) is reduced to nitrogen gas ( This enhances the system's denitrification capacity. Simultaneously, polyphosphate-accumulating bacteria can perform normal aerobic respiration after contacting oxygen. At this time, polyphosphate-accumulating bacteria can oxidize and decompose the internal carbon source absorbed in the anaerobic tank, thus having enough energy to absorb phosphorus from the water in the aerobic tank 2 that far exceeds the phosphorus required for their own growth into their cells against the concentration gradient, and resynthesize it into Poly-P (polyphosphate). The phosphorus absorbed by polyphosphate-accumulating bacteria in the aerobic environment of the aerobic tank 2 far exceeds the phosphorus released in the anaerobic environment, thus effectively absorbing and removing phosphorus from the water.

[0048] S4. Sedimentation and separation: The liquid in aerobic tank 2 rises with the aeration airflow generated by the aeration port and enters the sedimentation hopper from the top of aerobic tank 2. After settling, the sludge returns to the bottom of aerobic tank 2 through the lower end of the sedimentation hopper for re-entry into the aerobic tank for circulation. The supernatant in sedimentation hopper 3 is discharged through the clear water overflow weir. Because the aerobic tank is a micro-aerobic environment, the dissolved oxygen in the wastewater is consumed in the rising channel, and then the wastewater enters the sinking channel. The oxygen content in the sinking channel is much lower than that in the rising channel.

[0049] In this step, a return pipe 6 connected to a high-pressure air injection pipe 9 is installed in the sedimentation sludge hopper 3. One end of the return pipe 6 is located at the constriction of the sedimentation sludge hopper 3, and the other end is connected to the anoxic tank 1. By installing the return pipe 6 in the sedimentation sludge hopper 3 and injecting high-pressure gas into it, the return pipe generates suction in the sedimentation sludge hopper 3, forming an air lift effect. Combined with the circulation loop, this effectively accelerates the sludge flow in the initial stage of sedimentation, increases the sludge settling rate, effectively reduces the residence time of sludge in the sedimentation sludge hopper, and prevents phosphorus release from the sludge in the sedimentation sludge hopper 3. In aerobic tank 2, the wastewater undergoes nitrification, simultaneous denitrification, and polyphosphate accumulation. The wastewater then rises to the top of aerobic tank 2 and flows into a sedimentation hopper for solid-liquid separation. The sludge, rich in polyphosphate-accumulating bacteria, sinks down the hopper and is discharged from the bottom outlet, re-entering aerobic tank 2. Meanwhile, the clear water separated from the sludge in the sedimentation hopper, having had phosphorus removed, floats to the upper clear water zone and is discharged directly through the clear water overflow weir 7. Compared to existing water treatment technologies, this process achieves better carbon and phosphorus removal.

[0050] It is important to note that a sludge discharge pipe 8 with a control valve is installed at the bottom of the aerobic tank 2, directly opposite the lower end of the sedimentation hopper 3. After the system has been operating for a period of time, the sludge concentration meter in the equipment detects that the sludge concentration in the aerobic tank has reached a set threshold and then actively opens the valve of the sludge discharge pipe 8 to discharge the sludge settled at the bottom of the aerobic tank 2. This controls the sludge concentration in the aerobic tank to remain stable at 3500-7000 mg / L. Maintaining a sludge concentration above 3500 mg / L ensures that the nitrogen and phosphorus removal reactions in the aerobic tank can proceed normally, while ensuring that the sludge concentration in the aerobic tank does not exceed 6500 mg / L to avoid affecting the sedimentation rate of the sludge in the sedimentation hopper. The optimal sludge concentration in the aerobic tank is 5000 mg / L.

[0051] Example 1:

[0052] This experiment, designed to verify the operational process and effectiveness, used a reaction sedimentation system with a treatment capacity of 10 m³ / h. The HRT (hydraulic retention time) in the anoxic zone was 3 h, and the HRT in aerobic tank 2 was 4 h. The sludge concentration (MLSS) was 6500 mg / L, and the influent water quality was controlled as follows: COD = 300 mg / L, TN = 40 mg / L. =30mg / L, TP=5mg / L.

[0053] The micro-aerobic environment (DO) in aerobic tank 2 is maintained at 0.3 mg / L by linking the online DO meter with the aeration control system.

[0054] After the system has been running stably for 30 days, the water quality was measured as follows:

[0055] COD≤30mg / L;

[0056] TN≤6mg / L (removal rate≥85%)

[0057] ≤1mg / L;

[0058] TP≤0.5mg / L (removal rate≥90%)

[0059] Electricity consumption per ton of water: 0.23 kWh.

[0060] Comparative Example 1:

[0061] This comparative example uses traditional equipment and traditional methods. The wastewater treatment process was used, with the influent quality being the same as in Example 1. The system was also operated after 30 days of stabilization. The effluent quality was measured and compared with that of Example 1. The comparison table is as follows:

[0062]

[0063] The table above clearly shows that the process of this invention has higher nitrogen and phosphorus removal efficiency, with a TN removal rate of ≥85% and a TP removal rate of ≥90%. At the same time, since there is no need to set up a sludge return pump, the system's power consumption per ton of water is ≤0.25 kWh, which is significantly energy-saving compared to existing processes. The sludge production rate is reduced by 20%-30% compared to traditional processes. The high sludge concentration and micro-oxygen control enhance system stability and resistance to shock loads. The integrated system structure saves more than 30% of the floor space.

[0064] To obtain the optimal micro-oxygen control range, the following experiments were conducted:

[0065] Experimental Example 1:

[0066] In this experimental example, under the equipment and influent conditions of Example 1, the DO in aerobic tank 2 was adjusted to 0.3 mg / L. After 7 days of stable operation, the effluent TN was measured to be 15.2 mg / L and the effluent TP was measured to be 1.2 mg / L, indicating low simultaneous nitrification and denitrification efficiency in the entire aerobic tank 2.

[0067] Experimental Example 2:

[0068] This experimental example is the same as Experiment 1. Under the equipment and influent conditions of Example 1, the DO in aerobic tank 2 was adjusted to 0.5 mg / L. After 7 days of stable operation, the effluent TN was measured to be 8.5 mg / L and the effluent TP was measured to be 0.8 mg / L. The simultaneous nitrification and denitrification efficiency in the entire aerobic tank 2 was moderate.

[0069] Experiment Example 3:

[0070] This experimental example is the same as Experiment 1. Under the equipment and influent conditions of Example 1, the DO in aerobic tank 2 was adjusted to 0.8 mg / L. After 7 days of stable operation, the effluent TN was measured to be 5.8 mg / L and the effluent TP was measured to be 0.4 mg / L, indicating high simultaneous nitrification and denitrification efficiency throughout aerobic tank 2.

[0071] Experiment Example 4:

[0072] This experimental example is the same as Experiment 1. Under the same equipment and influent conditions as in Example 1, the DO in aerobic tank 2 was adjusted to 1.2 mg / L. After 7 days of stable operation, the effluent TN was measured to be 7.2 mg / L and the effluent TP was measured to be 0.6 mg / L. The simultaneous nitrification and denitrification efficiency in the entire aerobic tank 2 was moderate.

[0073] Experiment Example 5:

[0074] This experimental example is the same as Experiment 1. Under the equipment and influent conditions of Example 1, the DO in aerobic tank 2 was adjusted to 1.5 mg / L. After 7 days of stable operation, the effluent TN was measured to be 12.1 mg / L and the effluent TP was measured to be 1.0 mg / L. The simultaneous nitrification and denitrification efficiency in the entire aerobic tank 2 was low.

[0075] Experimental Example 6:

[0076] This experimental example is the same as Experiment 1. Under the equipment and influent conditions of Example 1, the DO in aerobic tank 2 was adjusted to 2.0 mg / L. After 7 days of stable operation, the effluent TN was measured to be 18.5 mg / L and the effluent TP was measured to be 1.5 mg / L. The simultaneous nitrification and denitrification efficiency in the entire aerobic tank 2 was almost zero.

[0077] The data from all the experimental cases were statistically analyzed, resulting in the following table:

[0078]

[0079] Since the influent TN=40mg / L and TP=5mg / L, the above experimental examples and tables clearly show that when the oxygen content in aerobic tank 2 is kept at DO=0.5~1.2mg / L through the aeration pipeline, the water treatment effect is the best, the TN removal rate can reach more than 79%, and the TP removal rate can reach more than 84%. The optimal DO is 0.8mg / L, the TN removal rate can reach 85%, and the TP removal rate can reach 92%.

[0080] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A wastewater enhanced nitrogen and phosphorus removal process based on sludge self-recirculation, using a reactive sedimentation system, wherein the reactive sedimentation system includes an anoxic tank and an aerobic tank connected by a communication port, the anoxic tank and the aerobic tank being separated by a partition, the aerobic tank being equipped with a sludge hopper, and the bottom of the aerobic tank being provided with aeration pipes with aeration ports, characterized in that, The sedimentation hopper is located on the opposite side of the partition in the aerobic tank, with an inlet at the top connecting to the aerobic tank and a constriction at the bottom connecting to the aerobic tank. A return pipe connecting to the anoxic tank is located at the constriction. The connection port is located on the partition and is close to the bottom of the aerobic tank. The sedimentation hopper has a sedimentation slope. The constriction is located on the opposite side of the outlet connecting the anoxic tank to the aerobic tank. An aeration pipe is located between the constriction and the connection port. In the aerobic tank, an upward channel is formed between the outer side of the sedimentation slope and the partition. In the sedimentation hopper, a downward channel is formed on the inner side of the sedimentation slope. The upward channel, the sedimentation hopper inlet, the downward channel, and the sedimentation hopper constriction together form a circulation loop. The continuous return flow through the return pipe and the continuous aeration through the aeration pipe cause the wastewater entering the aerobic tank to circulate along the circulation loop, thereby accelerating the sludge settling speed at the sedimentation slope in the sedimentation hopper and inhibiting the phosphorus release reaction. During this process, the aerobic tank is in a micro-aerobic environment, with the oxygen content in the rising channel being greater than that in the sinking channel. The wastewater undergoes nitrification, simultaneous denitrification, and polyphosphate accumulation in the rising channel. In the sinking channel, the wastewater undergoes sludge-water separation, and all the sludge is returned to the aerobic tank.

2. The wastewater enhanced nitrogen and phosphorus removal process based on sludge self-recirculation according to claim 1, characterized in that, The bottom of the aerobic tank is equipped with a sludge discharge pipe with a control valve. The opening of the sludge discharge pipe is directly opposite the lower end of the sedimentation sludge hopper. The sludge concentration in the aerobic tank is adjusted by the control valve to keep the sludge concentration in the aerobic tank between 3500-6500 mg / L.

3. The wastewater enhanced nitrogen and phosphorus removal process based on sludge self-recirculation according to claim 1, characterized in that, The anoxic tank provides an anaerobic environment and introduces activated sludge and raw water. In the anoxic tank, the activated sludge is mixed with the wastewater returning from the return pipe through a stirring mechanism. After phosphorus release and denitrification reactions, the wastewater in the anoxic tank is continuously introduced into the aerobic tank through the liquid level difference.

4. A wastewater enhanced nitrogen and phosphorus removal process based on sludge self-recirculation according to claim 1 or 2, characterized in that, The aerobic pool is used to provide a micro-oxygen environment with an oxygen content of 0.5-1.2 mg / L.

5. The wastewater enhanced nitrogen and phosphorus removal process based on sludge self-recirculation according to claim 4, characterized in that, The aerobic pool is used to provide a micro-oxygen environment with an oxygen content of 0.8 mg / L.

6. The wastewater enhanced nitrogen and phosphorus removal process based on sludge self-recirculation according to claim 1, characterized in that, The return pipe is installed in the sedimentation hopper or in the aerobic tank outside the sedimentation hopper, and a high-pressure air injection pipe is connected to the return pipe.

7. The wastewater enhanced nitrogen and phosphorus removal process based on sludge self-recirculation according to claim 4, characterized in that, The reaction precipitation system also includes a dissolved oxygen monitoring device, which is installed in the aerobic tank and / or anoxic tank to monitor the dissolved oxygen content in the aerobic tank and / or anoxic tank.

8. The wastewater enhanced nitrogen and phosphorus removal process based on sludge self-recirculation according to claim 3, characterized in that, The activated sludge contains polyphosphate-accumulating bacteria, nitrifying bacteria, and denitrifying bacteria.

9. The wastewater enhanced nitrogen and phosphorus removal process based on sludge self-recirculation according to claim 5, characterized in that, The supernatant produced by the mud-water separation in the sedimentation hopper is discharged from the overflow weir set on the sedimentation hopper.

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