Sludge grading reflux denitrification and dephosphorization process and device suitable for municipal sewage

Abstract

The present application relates to a kind of sludge grading backflow denitrification and phosphorus removal process and device suitable for municipal wastewater, comprising the following steps: active sludge and raw water are introduced into anaerobic zone one simultaneously by water inlet pipe, forming mixed liquor;The mixed liquor is lifted to anaerobic zone two using variable frequency booster pump, and further mixed reaction is carried out by stirrer;The mixed liquor treated after anaerobic zone two is introduced into transition zone, and denitrification reaction is strengthened;Make mixed liquor into aerobic zone, carry out nitrification and partial simultaneous denitrification reaction, then carry out screening treatment by cyclone screen, the heavy density sludge separated is backflowed to anaerobic zone one by pre-sedimentation backflow pipe, and the remaining sludge is transported to secondary sedimentation tank for sedimentation treatment, and part of the sludge after sedimentation treatment is backflowed to transition zone by external backflow pipe.Compared with prior art, the present application realizes the continuous gravity screening of sludge system denitrification and phosphorus removal sludge and the optimal allocation of carbon source, effectively controls sludge bulking, and improves sludge concentration and system processing efficiency.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a sludge grading and reflux process and apparatus for nitrogen and phosphorus removal suitable for urban wastewater. Background Technology

[0002] Staged sludge recirculation is primarily used to improve the density and settling properties of activated sludge, thereby enhancing wastewater treatment efficiency, reducing sludge volume, and lowering treatment costs. This process is commonly applied in activated sludge (AS) systems, using physical, chemical, or biological methods (such as selective pressure, flocculant addition, or reactor optimization) to promote the transformation of sludge particles from loose flocs to dense particles (such as aerobic granular sludge, AGS). Compared to traditional activated sludge processes, staged sludge recirculation can achieve higher sludge concentrations (10-15 g / L vs. 3-5 g / L), better settling velocities (5-10 m / h vs. 1-2 m / h), and energy savings (30-50% reduction).

[0003] The pretreatment stage of traditional sludge staged recirculation mainly includes gravity thickening, dissolved air flotation (DAF) thickening, and mechanical thickening. Recent improvements have focused on increasing efficiency, reducing energy consumption, minimizing chemical dosage, and enhancing equipment stability and automation. Gravity thickening, one of the most widely used technologies, optimizes the thickening tank structure using a "grid thickener." It utilizes slowly rotating vertical grids within the tank to agitate the sludge, promoting the release of water and gas, breaking up solid "bridging" to improve efficiency. Simultaneously, it integrates an online monitoring and automated control system to precisely control sludge inflow and outflow cycles, ensuring stable thickening results. Dissolved air flotation (DAF) addresses the thickening needs of activated sludge by improving microbubble generation technology to enhance dissolved air and release efficiency. The system optimizes the structure of the dissolved air flotation tank, using a new type of dissolved air releaser to generate finer and more uniform microbubbles. Combined with improvements to the water distribution and scum scraping systems, it achieves rapid scum separation and reduces energy consumption. In mechanical thickening, the centrifugal thickener increases processing capacity and effective volume through a cone-angle-free design. High-end models are equipped with differential speed automatic adjustment, which can adjust the speed difference in real time according to the sludge flow rate and concentration, reducing flocculant consumption and energy consumption. The screw thickener (stacked screw type) has been upgraded in terms of materials, wear-resistant coatings, and processing precision to extend equipment life. At the same time, the screw shaft design has been optimized to improve extrusion and shearing efficiency, and an integrated automation system ensures stable operation. The rotary drum thickener focuses on the filter material, pore size design, and enhanced self-cleaning function to avoid filter clogging and maintain continuous operation.

[0004] For example, patent CN104860487A discloses AAO This wastewater treatment method, which does not involve adding an external carbon source to remove total nitrogen, first removes large debris, then smaller impurities, distributes the wastewater, and performs biochemical treatment according to the process design. The treated mixture undergoes solid-liquid separation, with clarified water discharged to a filtration tank, sludge returned to a sludge denitrification tank and anoxic tank, and excess sludge sent to a sludge thickening tank. The effluent from the sedimentation tank flows to the filtration tank for further removal of organic matter, and the backwash water flows back to the collection tank. The filtered water is then disinfected with ultraviolet light, and the effluent is discharged into a guide channel. The sludge denitrification tank is located at the beginning of the process, allowing it to preferentially obtain carbon sources from the raw water for denitrification, which is beneficial for improving nitrogen removal efficiency. This method eliminates the adverse effects of nitrate on phosphorus release in the anaerobic tank. After anaerobic phosphorus release by microorganisms, they directly enter the aerobic environment, and the phosphorus uptake power formed under anaerobic conditions can be more fully utilized. The biochemical removal rate of TP (calculated as phosphate) can reach 63%. However, this method is complex, still requires the addition of chemical agents, and carries the risk of sludge bulking. Summary of the Invention

[0005] The purpose of this invention is to provide a sludge graded return process and apparatus for denitrification and phosphorus removal suitable for urban sewage, which can effectively control sludge expansion and improve denitrification and phosphorus removal efficiency.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] One objective of this invention is to provide a sludge staged recirculation process for nitrogen and phosphorus removal suitable for urban wastewater. Raw water is sequentially fed into a biological reaction tank and a secondary sedimentation tank. The biological reaction tank includes an anaerobic zone I, an anaerobic zone II, a transition zone, and an aerobic zone. The process specifically includes the following steps:

[0008] Activated sludge and raw water are simultaneously introduced into anaerobic zone one through the inlet pipe to form a mixed liquor. The mixed liquor is then pumped to anaerobic zone two using a variable frequency pump and further mixed by a stirrer. The mixed liquor treated in anaerobic zone two is introduced into a transition zone, where denitrification is enhanced by adjusting the aeration intensity. The mixed liquor treated in the transition zone enters the aerobic zone, where nitrification and partial simultaneous denitrification are carried out by adjusting the aeration intensity. Subsequently, it is screened by a cyclone separator. The separated heavy sludge is returned to anaerobic zone one through a pre-settling return pipe, while the remaining sludge is transported to a secondary settling tank for sedimentation treatment. A portion of the sedimented sludge is then returned to the transition zone through an external return pipe.

[0009] Preferably, the process involves continuous water flow.

[0010] Preferably, the organic loading of the first anaerobic zone is greater than 0.65 kg CODcr / m³. 3 ·d.

[0011] Preferably, the liquid level in anaerobic zone one is lower than the liquid levels in anaerobic zone two, the transition zone, and the aerobic zone.

[0012] Preferably, the free settling velocity ratio R of the returned sludge needs to be greater than 2, R=V1 / V2, where V1 is the free settling velocity of the sludge in the pre-settling return pipe; and V2 is the free settling velocity of the sludge in the external return pipe.

[0013] Preferably, the flow rate of the pre-sinking return pipe is not higher than 25% of the total flow rate of the inlet pipe.

[0014] Preferably, during the initial operation phase, all the sludge treated by the secondary sedimentation tank is returned to the transition zone through the external return pipe, and the concentration of activated sludge in the biochemical reaction tank is ultimately controlled to be above 3.5 g / L. The flow rate of the external return pipe is 75-85% of the total flow rate of the inlet pipe, and the flow rate of the pre-sedimentation return pipe is 4-6% of the total flow rate of the inlet pipe.

[0015] More preferably, the flow rate of the external return pipe is 80% of the total flow rate of the inlet pipe.

[0016] More preferably, the flow rate of the pre-sinking return pipe is 5% of the total flow rate of the inlet pipe.

[0017] Preferably, during the formal operation phase, the flow rate in the pre-sinking return pipe is gradually adjusted by regulating the flow rate of the variable frequency booster pump. Every week of operation, the flow rate in the pre-sinking return pipe is increased by 4-6% of the total flow rate in the inlet pipe until it reaches 25% of the total flow rate in the inlet pipe and then it is kept in stable operation.

[0018] More preferably, the flow rate of the pre-sinking return pipe is increased by 5% of the total flow rate of the inlet pipe.

[0019] In this invention, a stable liquid level difference can be established between the anaerobic zone and the hydrocyclone separator by means of the lifting action of the variable frequency lift pump. This liquid level difference ensures that the dense sludge settled in the hydrocyclone separator flows to the anaerobic zone by gravity. Since the lift pump is variable frequency, the liquid level in the anaerobic zone can be changed by adjusting its output flow rate. The change in the liquid level in the anaerobic zone directly controls the flow rate of the pre-settling return pipe. Given that the pre-settling return flow rate affects the concentration balance of COD and nutrients in the anaerobic zone, the optimal control of the pre-settling return flow rate can be achieved through the precise adjustment of the variable frequency lift pump, laying a suitable water quality foundation for subsequent reactions.

[0020] In this invention, based on the flow regulation function of the aforementioned variable frequency booster pump, the sludge return flow rate of the pre-settling return pipe can be directly controlled by changing its flow parameters, thereby accurately controlling the concentration of the returned sludge and effectively avoiding the problems of excessively dilute (affecting reaction efficiency) or excessively concentrated (increasing system load) returned sludge concentration caused by improper return flow rate, thus ensuring the stable operation of the sludge return system.

[0021] More preferably, a sludge concentration meter is installed in the anaerobic zone to monitor the sludge concentration in the tank in real time.

[0022] In this invention, combined with the aforementioned liquid level adjustment logic, the return flow rate of heavy-density sludge can be changed by adjusting the liquid level of anaerobic zone one. When the sludge concentration in anaerobic zone one is low, the return flow rate can be increased by adjusting the liquid level to replenish heavy-density sludge; when the concentration is too high, the return flow rate is reduced, so that the sludge concentration in anaerobic zone one is stabilized in the optimal range, thereby improving the efficiency of nitrogen and phosphorus removal reaction.

[0023] More preferably, the concentration of activated sludge in the anaerobic zone is controlled at 4 g / L.

[0024] More preferably, the hydrocyclone separator pre-sedimentes the sludge in the mixed liquor, and then returns the dense sludge to the anaerobic zone with the highest raw water concentration, thereby ensuring the carbon source replenishment and biological selection of the returned sludge.

[0025] More preferably, the sludge graded return nitrogen and phosphorus removal process suitable for urban sewage sequentially sends raw water into a biological reaction tank and a secondary sedimentation tank. The biological reaction tank includes an anaerobic zone one, an anaerobic zone two, a transition zone, and an aerobic zone, and specifically includes the following steps:

[0026] This process involves continuous influent, with raw water introduced into anaerobic zone one through the influent pipe, and activated sludge simultaneously introduced through the pre-settling return pipe to form a mixed liquor. A variable frequency pump is used to lift the mixed liquor to anaerobic zone two, where it is further mixed and reacted by a stirrer. The mixed liquor treated in anaerobic zone two is then introduced into a transition zone, where denitrification is enhanced by adjusting the aeration intensity. The mixed liquor then enters the aerobic zone, where nitrification and partial simultaneous denitrification reactions occur by adjusting the aeration intensity. Subsequently, it is screened by a cyclone separator, and the separated heavy sludge is returned to anaerobic zone one through the pre-settling return pipe. The remaining sludge is transported to a secondary sedimentation tank for sedimentation treatment, and a portion of the sedimented sludge is returned to the transition zone through an external return pipe.

[0027] The second objective of this invention is to provide an apparatus for a sludge graded return process for nitrogen and phosphorus removal in urban wastewater, comprising a biological reaction tank and a secondary sedimentation tank. The biological reaction tank is arranged sequentially along the direction of raw water flow: an anaerobic zone one, an anaerobic zone two, a transition zone, and an aerobic zone. A variable frequency lift pump is installed in the anaerobic zone one, and the variable frequency lift pump is connected to the anaerobic zone two through a water distribution pipe. An agitator is installed in the anaerobic zone two. Aeration pipes are installed in both the transition zone and the aerobic zone. A hydrocyclone screen is also installed at the end of the aerobic zone. The heavy sludge outlet of the hydrocyclone screen is connected to the anaerobic zone one through a pre-settling return pipe, and the light sludge outlet of the hydrocyclone screen is connected to the secondary sedimentation tank through an output pipe. The secondary sedimentation tank is connected to the transition zone through an external return pipe.

[0028] More preferably, a stirrer is also provided in the transition zone.

[0029] Preferably, the aeration pipes in the transition zone and aerobic zone are connected to a blower, an external return pump is installed on the external return pipe, and a residual sludge discharge pipe is installed on the external return pipe downstream of the external return pump, with a residual sludge discharge valve installed on it.

[0030] More preferably, the discharge of residual sludge is controlled by a residual sludge discharge valve.

[0031] Technological advancements in sludge staged recirculation processes are reflected in the exploration and application of emerging technologies, with bio-densification being a prime example. The core of this relatively new technology lies in utilizing biological selection mechanisms to screen for microbial aggregates (such as aerobic granular sludge) with superior settling performance within the activated sludge system. By installing selectors (such as rapid hydrocyclones) within the system, dense sludge, even granular sludge, with fast settling velocity, high density, and excellent nitrogen and phosphorus removal performance, is recirculated back to the reactor, while flocculent sludge with poor settling performance and rapid carbon source consumption is discharged, gradually improving the settling performance and concentration of the sludge throughout the system. Bio-densification technology not only significantly improves sludge thickening performance and reduces or even eliminates the need for chemical additives, but it can also be integrated with wastewater treatment processes to achieve unified treatment, providing a more environmentally friendly and economical new path for sludge treatment.

[0032] In this invention, anaerobic zone one and anaerobic zone two are the core functional areas, where sludge can simultaneously complete phosphorus release and denitrification processes. Due to space constraints and a high concentration of returned sludge, anaerobic zone one is dominated by raw water, maintaining a high concentration of volatile fatty acids (VFAs) in the influent. This environment provides ideal conditions for polyphosphate-accumulating organisms (PAOs): under anaerobic conditions, PAOs can use readily degradable organic matter (VFAs) in the influent as a carbon source, releasing intracellularly stored polyphosphates (in the form of orthophosphates) and converting organic matter into intracellular stored substances such as polyhydroxyalkanoates (PHBs), reserving energy for subsequent reactions. The sludge returned to anaerobic zone one is mostly dense sludge, with significantly better denitrification and phosphorus removal performance than light sludge; therefore, the system prioritizes carbon and nutrient supply to the dense sludge in this zone, not only maintaining its performance advantages but also promoting the full secretion of extracellular polymeric substances (EPS), further driving the sludge granulation process. In the transition zone, further enhanced denitrification can be achieved, reducing the total nitrogen concentration. Within the aerobic zone, polyphosphate-accumulating bacteria oxidize stored PHB under aerobic conditions to generate energy and absorb excess phosphorus from wastewater, forming polyphosphates stored within their cells. Furthermore, this zone not only facilitates nitrification through flocculent sludge but also achieves partial sludge granulation, simultaneously initiating a localized denitrification process. This design significantly reduces carbon source consumption and system operating costs. For better screening, the sludge discharged from the system originates from the secondary settling tank. From a technological perspective, this system achieves sludge age separation between heavy and light sludge.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The present invention provides a sludge graded return process for denitrification and phosphorus removal applicable to urban sewage. The biochemical reaction tank is divided into four parts: anaerobic zone one, anaerobic zone two, transition zone and aerobic zone. The aerobic zone is connected to the secondary sedimentation tank. A hydrocyclone screen is installed in the aerobic zone. The heavy sludge screened by the hydrocyclone screen is returned to the beginning of the anaerobic zone through the pre-settling return pipe. The remaining sludge enters the secondary sedimentation tank. Part of the sludge treated in the secondary sedimentation tank is returned to the transition zone through the external return pipe. The present invention can realize continuous gravity screening and carbon source optimization configuration of the sludge system through the above process design, suppress sludge bulking from the source, and enhance the denitrification and phosphorus removal function, thus solving the pain point of low treatment efficiency of the existing process.

[0035] (2) In this invention, the liquid level in the first anaerobic zone is lower than that in other zones, and there is a liquid level difference between the anaerobic zone and the hydrocyclone separator. This allows the dense sludge settled in the hydrocyclone separator to flow to the first anaerobic zone by gravity. The first anaerobic zone is equipped with a variable frequency lift pump. By adjusting the flow rate of the lift pump, the liquid level height between the first anaerobic zone and the hydrocyclone separator can be adjusted, thereby accurately controlling the sludge return flow rate of the pre-settling return pipe, so that the sludge concentration in the first anaerobic zone is stabilized in the optimal range, thereby achieving the optimized configuration of carbon sources and improving the efficiency of nitrogen and phosphorus removal reaction.

[0036] (3) In this invention, the anaerobic zone II is enhanced by a stirrer, the transition zone enhances the denitrification reaction, and the aerobic zone achieves nitrification and partial simultaneous denitrification through aeration. The functions of each zone are synergistic and complementary, further improving the efficiency of nitrogen and phosphorus removal.

[0037] (4) The carbon source dosage of the present invention can be reduced by about 18%, the aeration energy consumption can be reduced by about 15%, and the overall operating cost can be reduced by about 14%. While ensuring the treatment effect, it effectively alleviates the cost pressure of urban sewage treatment plants and has stronger practical application value. Attached Figure Description

[0038] Figure 1 This is a process flow diagram of the present invention;

[0039] Figure 2 This is a top view of the overall device of the present invention;

[0040] Figure 3 for Figure 2 Schematic diagram of the BB section structure;

[0041] Figure 4 for Figure 2 Schematic diagram of CC section structure in

[0042] In the diagram: 1-Biological reaction tank; 1.1-Anaerobic zone one; 1.2-Anaerobic zone two; 1.3-Transition zone; 1.4-Aerobic zone; 1.5-Inlet pipe; 1.6-Variable frequency lift pump; 1.7-Agitator; 1.8-Cyclone screen; 1.9-Pre-settling return pipe; 1.10-Water distribution pipe; 1.11-Aeration pipe; 1.12-Blower;

[0043] 2-Secondary sedimentation tank; 2.1-External return pipe; 2.2-External return pump; 2.3-Excess sludge discharge valve. Detailed Implementation

[0044] This embodiment is implemented based on the technical solution of the present invention, and provides detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiment.

[0045] Unless otherwise specified, the reagents, methods, instruments, and equipment used in this invention are conventional in the art. Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0046] A sludge staged recirculation process for nitrogen and phosphorus removal suitable for urban wastewater, such as Figure 1 As shown, raw water is sequentially fed into biological reaction tank 1 and secondary sedimentation tank 2. The biological reaction tank includes anaerobic zone 1.1, anaerobic zone 2 1.2, transition zone 1.3, and aerobic zone 1.4, specifically including the following steps:

[0047] Activated sludge and raw water are simultaneously introduced into anaerobic zone 1.1 through inlet pipe 1.5 to form a mixed liquor. The mixed liquor is then pumped to anaerobic zone 2.2 using variable frequency pump 1.6 and further mixed and reacted by stirrer 1.7. The mixed liquor treated in anaerobic zone 2.2 is introduced into transition zone 1.3, where denitrification is enhanced by adjusting the aeration intensity. The mixed liquor treated in transition zone 1.3 enters aerobic zone 1.4, where nitrification and partial simultaneous denitrification reactions are carried out by adjusting the aeration intensity. Subsequently, it is screened by hydrocyclone screener 1.8, and the separated heavy sludge is returned to anaerobic zone 1.1 through pre-settling return pipe 1.9. The remaining sludge is transported to secondary sedimentation tank 2 for sedimentation treatment, and part of the sedimented sludge is returned to transition zone 1.3 through external return pipe 2.1.

[0048] During the initial operation phase, all the sludge treated by the secondary sedimentation tank 2 is returned to the transition zone 1.3 through the external return pipe 2.1, and the concentration of activated sludge in the biochemical reaction tank 1 is controlled at 3~4 g / L. The flow rate of the external return pipe 2.1 is 75-85% of the total flow rate of the inlet pipe 1.5, and the flow rate of the pre-sedimentation return pipe 1.9 is 4-6% of the total flow rate of the inlet pipe 1.5.

[0049] During the formal operation phase, the flow rate in the pre-sinking return pipe 1.9 is gradually adjusted by regulating the flow rate of the variable frequency booster pump 1.6. Every week of operation, the flow rate of the pre-sinking return pipe 1.9 is increased by 4-6% of the total flow rate of the inlet pipe 1.5 until it reaches 25% of the total flow rate of the inlet pipe 1.5 and then it is kept in stable operation.

[0050] Apparatus used in the above process, such as Figure 2-4As shown, the system includes a biological reaction tank (1) and a secondary sedimentation tank (2). The biological reaction tank 1, along the direction of the raw water flow, is sequentially configured with an anaerobic zone 1.1, an anaerobic zone 2 1.2, a transition zone 1.3, and an aerobic zone 1.4. A variable frequency lift pump 1.6 is installed in the anaerobic zone 1.1, and the variable frequency lift pump 1.6 is connected to the anaerobic zone 2 1.2 via a water distribution pipe 1.10. A stirrer 1.7 is installed in the anaerobic zone 2 1.2. Aeration pipes 1.11 are installed in both the transition zone 1.3 and the aerobic zone 1.4. A cyclone screen 1.8 is also installed at the end of the aerobic zone 1.4. The heavy sludge outlet of the cyclone screen 1.8 is connected to the anaerobic zone 1.1 through the pre-settling return pipe 1.9. The light sludge outlet of the cyclone screen 1.8 is connected to the secondary sedimentation tank 2 through the output pipe. The secondary sedimentation tank 2 is connected to the transition zone 1.3 through the external return pipe 2.1.

[0051] The aeration pipes 1.11 in the transition zone 1.3 and aerobic zone 1.4 are connected to the blower 1.12. An external return pump 2.2 is installed on the external return pipe 2.1. A residual sludge discharge pipe is installed on the external return pipe 2.1 downstream of the external return pump 2.2, and a residual sludge discharge valve 2.3 is installed on it.

[0052] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0053] For urban wastewater, the first step is to inoculate with sludge, maintaining an external return flow rate of 0.8 times the influent flow rate Q without discharging excess sludge. The activated sludge concentration is then cultivated to a normal level, typically 3-4 g / L. Next, the booster pump is started, and the flow rate in the pre-settling return pipe is gradually adjusted, increasing by 5% of the influent flow rate Q each time, maintaining this operation for one week. Then, the flow rate in the pre-settling return pipe is increased by one level until it reaches 25%, at which point the operation is maintained, and changes in sludge settling performance and wastewater treatment efficiency are observed.

[0054] Implementation Case 1: Denitrification of Low-Concentration Wastewater and Optimization of Sludge Performance in Small Town Wastewater Treatment Plants

[0055] A small town wastewater treatment plant treats domestic sewage, with an average influent CODcr concentration of 120 mg / L (below 150 mg / L). Traditional processes have long faced problems of low denitrification efficiency and sludge bulking. Therefore, the process of this invention was adopted for modification, aiming to improve denitrification efficiency and sludge settling performance. In implementation, the wastewater treatment plant uses a continuous flow process including an influent pipe, anaerobic zone one, anaerobic zone two, transition zone, aerobic zone, cyclone separator, and secondary sedimentation tank. The total volume of the biological reaction tank is 2000 m³. 3 Daily water treatment capacity 5000m³ 3 / d, the influent flow rate Q is 208.3m³ / d. 3 / h; During the initial operation phase, the activated sludge concentration was controlled at 3.5 g / L through sludge inoculation, and the external return flow rate was set to 0.8 times the influent flow rate (approximately 167 m³ / h). 3 / h), start the variable frequency booster pump, and set the initial pre-settling return pipe flow rate to 5% of the influent flow rate (approximately 10.4m³). 3 / h); During operation and adjustment, the flow rate of the pre-settling return pipe should be reduced by 5% of the influent flow rate (i.e., 10.4 m³ / h) every week. 3 The rate was increased gradually, starting at 1 / h, and then adjusted to 25% (approximately 52.1 m). 3 During this period, anaerobic zone one uses a hydrocyclone separator to return denser sludge, anaerobic zone two uses a mixer to enhance mixing, the transition zone enhances denitrification, and the aerobic zone achieves nitrification and partial simultaneous denitrification through aeration. After the pre-settling return pipe flow rate reaches 25%, the system is operated stably for 2 months and relevant indicators are monitored. The results show that during operation, the organic load of anaerobic zone one should be controlled to be greater than 0.71 kg CODcr / m³. 3 •d, the flow rate of the pre-settling return pipe is less than 0.28 times the total influent flow rate of the reactor, and the free settling velocity ratio of the returned sludge is set to R=2.15. When the total nitrogen in the influent is 43 mg / L, the total nitrogen in the effluent drops to 7 mg / L, achieving a denitrification efficiency of 84%. Furthermore, the simultaneous denitrification of granular sludge in the aerobic zone reduces the external carbon source requirement by approximately 15%. The sludge settling ratio (SV30) decreases from the initial 45% to 25%, essentially eliminating the sludge bulking problem. The dense sludge returned by the cyclone separator also increases the sludge concentration in the anaerobic zone, enhancing system stability. Simultaneously, the carbon source dosage is reduced, aeration energy consumption decreases by approximately 10%, and overall operating costs decrease by approximately 12%.

[0056] Example 2: Treatment of low-concentration mixed industrial and domestic wastewater in a medium-sized town wastewater treatment plant

[0057] A medium-sized town wastewater treatment plant treats a mixture of domestic sewage and some industrial wastewater. The influent CODcr concentration fluctuates between 100-140 mg / L, and the total nitrogen concentration is approximately 35 mg / L. Traditional processes suffer from insufficient nitrogen removal efficiency (only 60%) and poor sludge settling performance (SV30 as high as 70%). Therefore, the process optimization of this invention is adopted. In specific implementation, the wastewater treatment plant has a daily treatment capacity of 15,000 m³ / h. 3 / d, total volume of biochemical reaction tank 6000 m³ 3 The influent flow rate Q is 625 m³ / h. 3 The process, with a flow rate of [number] / h, includes anaerobic zone one, anaerobic zone two, transition zone, aerobic zone, and hydrocyclone separators. During initial operation, the sludge concentration is controlled at 4 g / L through sludge inoculation, and the external return flow rate is set to 0.8 times the influent flow rate (approximately 500 m³ / h). 3 / h), start the booster pump, with the initial pre-settling return pipe flow rate being 5% of the influent flow rate (approximately 31.3 m³ / h). 3 / h); During the operation and adjustment phase, increase the pre-sinking return pipe flow rate by 5% (approximately 31.3 m³) per week. 3 The organic load was gradually adjusted to 25% (approximately 156.3 m³ / h). During this period, high-density sludge was returned to anaerobic zone one via a hydrocyclone separator, phosphorus release and denitrification were enhanced in anaerobic zone two using a mixer, denitrification was enhanced in the transition zone, and efficient nitrification and simultaneous denitrification were achieved in the aerobic zone through flocculent and granular sludge. After three months of stable operation, monitoring indicators showed that the organic load in anaerobic zone one was controlled to be greater than 0.75 kg CODcr / m³ during operation. 3 •d, the flow rate of the pre-settling return pipe is less than 0.25 times the total influent flow rate of the reactor, and the free settling velocity ratio of the returned sludge is set to R=2.11. When the total nitrogen in the influent is 45 mg / L, the total nitrogen in the effluent drops to 6 mg / L, and the denitrification efficiency reaches 86.7%. The enhanced denitrification in the transition zone and the simultaneous denitrification in the aerobic zone are significant, and the carbon source dosage is reduced by about 20%. The sludge settling ratio (SV30) is reduced from the initial 50% to 22%, the sludge granulation degree is improved, the settling performance is excellent, the sludge bulking problem is completely solved, and the dense sludge returned by the hydrocyclone screen also increases the sludge concentration in the anaerobic zone, enhancing the system's shock resistance. In addition, the carbon source dosage is reduced by about 18%, the aeration energy consumption is reduced by about 15%, and the overall operating cost is reduced by about 14%.

[0058] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A sludge fractionation reflux denitrification and dephosphorization process suitable for municipal sewage, characterized in that, The raw water is sequentially sent into a biochemical reaction tank (1) and a secondary sedimentation tank (2), the biochemical reaction tank comprises an anaerobic zone one (1.1), an anaerobic zone two (1.2), a transition zone (1.3) and an aerobic zone (1.4), and specifically comprises the following steps: The activated sludge and the raw water are synchronously introduced into the anaerobic zone one (1.1) through the water inlet pipe (1.5) to form a mixed liquid; the mixed liquid is lifted to the anaerobic zone two (1.2) by the variable frequency lifting pump (1.6) and is further mixed by the stirrer (1.7); the mixed liquid treated by the anaerobic zone two (1.2) is introduced into the transition zone (1.3) to strengthen the denitrification reaction by adjusting the aeration intensity; the mixed liquid treated by the transition zone (1.3) enters the aerobic zone (1.4) to perform the nitrification and partial simultaneous denitrification by adjusting the aeration intensity, and then is screened by the cyclone screen (1.8); the heavy density sludge separated out is returned to the anaerobic zone one (1.1) through the pre-sedimentation return pipe (1.9), and the remaining sludge is transported to the secondary sedimentation tank (2) to perform the sedimentation treatment, and part of the sludge treated by the sedimentation is returned to the transition zone (1.3) through the external return pipe (2.1); The liquid level of the anaerobic zone one (1.1) is lower than that of the anaerobic zone two (1.2), the transition zone (1.3) and the aerobic zone (1.4); With the lifting effect of the variable frequency lifting pump (1.6), a stable liquid level difference is constructed between the anaerobic zone one (1.1) and the cyclone screen (1.8), which ensures that the heavy density sludge precipitated in the cyclone screen (1.8) flows to the anaerobic zone one (1.1) by gravity; since the lifting pump is variable frequency, the liquid level of the anaerobic zone one (1.1) is changed by adjusting the output flow of the lifting pump, and the liquid level change of the anaerobic zone one (1.1) directly controls the flow of the pre-sedimentation return pipe (1.9) to control the concentration of the return sludge; In the initial operation stage, the sludge treated by the secondary sedimentation tank (2) is returned to the transition zone (1.3) through the external return pipe (2.1), and finally the concentration of the activated sludge in the biochemical reaction tank (1) is controlled to be greater than 3.5 g / L; In the formal operation stage, the flow of the pre-sedimentation return pipe (1.9) is gradually adjusted by adjusting the flow of the variable frequency lifting pump (1.6), and the flow of the pre-sedimentation return pipe (1.9) is increased by 4-6% of the total flow of the water inlet pipe (1.5) every week until the flow of the pre-sedimentation return pipe (1.9) reaches 25% of the total flow of the water inlet pipe (1.5) and remains stable.

2. The sludge fractionation and return-flow denitrification and dephosphorization process for municipal wastewater according to claim 1, characterized in that, The organic load of the anaerobic zone (1.1) is greater than 0.65 kg CODcr / m 3 d.

3. The sludge fractionation and return-flow denitrification and dephosphorization process for municipal wastewater according to claim 1, characterized in that, The free settling velocity ratio R of the return sludge needs to be greater than 2, R=V1 / V2, wherein V1 is the free settling velocity of the sludge in the pre-sedimentation return pipe (1.9), and V2 is the free settling velocity of the sludge in the external return pipe (2.1).

4. The sludge fractionation reflux denitrification and dephosphorization process for municipal wastewater according to claim 1, characterized in that, In the initial operation stage, the flow of the external return pipe (2.1) is 75-85% of the total flow of the water inlet pipe (1.5), and the flow of the pre-sedimentation return pipe (1.9) is 4-6% of the total flow of the water inlet pipe (1.5).

5. The sludge fractionation and return-flow denitrification and dephosphorization process for municipal wastewater according to claim 1, characterized in that, The device for the process comprises a biochemical reaction tank (1) and a secondary sedimentation tank (2), the biochemical reaction tank (1) is sequentially provided with an anaerobic zone one (1.1), an anaerobic zone two (1.2), a transition zone (1.3) and an aerobic zone (1.4) along the direction of raw water flow, wherein the anaerobic zone one (1.1) is provided with a variable frequency booster pump (1.6), the variable frequency booster pump (1.6) is connected with the anaerobic zone two (1.2) through a water distribution pipe (1.10), the anaerobic zone two (1.2) is provided with a stirrer (1.7), the transition zone (1.3) and the aerobic zone (1.4) are both provided with an aeration pipe (1.11), the aerobic zone (1.4) is further provided with a cyclone screen classifier (1.8) at the end, the heavy density sludge outlet of the cyclone screen classifier (1.8) is connected with the anaerobic zone one (1.1) through a pre-sedimentation backflow pipe (1.9), the light density sludge outlet of the cyclone screen classifier (1.8) is connected with the secondary sedimentation tank (2) through an output pipe, and the secondary sedimentation tank (2) is connected with the transition zone (1.3) through an external backflow pipe (2.1).

6. The sludge fractionation return activated sludge process for municipal wastewater of claim 5, wherein, The aeration pipe (1.11) in the transition zone (1.3) and the aerobic zone (1.4) is connected with a blower (1.12), the external backflow pipe (2.1) is provided with an external backflow pump (2.2), and a residual sludge discharge pipe is arranged at the downstream position of the external backflow pump (2.2) on the external backflow pipe (2.1), and a residual sludge discharge valve (2.3) is arranged on the residual sludge discharge pipe.

Images