SND energy-saving denitrification process applied to double-path sludge backflow

Abstract

The invention relates to the technical field of sewage nitrogen and phosphorus removal treatment, and discloses an SND energy-saving nitrogen removal process applied to double-path sludge refluxing, which comprises the following steps: S1, pretreatment: wastewater sequentially passes through a mechanical grid, a water inlet well, a lifting pump, an oil separation tank, a primary sedimentation tank and an adjusting tank, large-particle suspended solids, floating oil and part of suspended solids are removed, and the water quality and the water quantity are homogenized; s2, core biochemical treatment: sequentially introducing the homogenized wastewater into an anoxic tank, a UASB (Upflow Anaerobic Sludge Blanket) reactor, an acidification tank and a four-stage aerobic tank. According to the SND energy-saving denitrification process applied to double-path sludge backflow, sludge generated by the secondary sedimentation tank is subjected to anaerobic fermentation and then flows back to the front section of the fourth-stage aerobic tank as a carbon source, the carbon source is supplemented for the aerobic tank, and no additional carbon source needs to be supplemented. Normal operation of microorganisms is ensured, sufficient microbial biomass in the aerobic tank is ensured, and efficient removal of COD (Chemical Oxygen Demand) and thorough proceeding of nitration reaction are ensured; the sludge activity is maintained, microorganisms in the aerobic tank are quickly supplemented, and the system stability is maintained.

Description

TECHNICAL FIELD

[0002] The present application relates to the technical field of sewage denitrification and phosphorus removal treatment, in particular to a SND energy-saving denitrification process applied to double-path sludge reflux. BACKGROUND

[0003] With the continuous improvement of the national requirements for the effluent quality of sewage treatment, AAO (Anaerobic-Anoxic-Oxic, anaerobic-anoxic-aerobic) process is widely used as the mainstream biochemical treatment process in municipal sewage treatment plants to achieve simultaneous nitrogen and phosphorus removal. This process is widely used in China, with a utilization rate of over 60%. In recent years, to address the problems of low C / N ratio in the influent and high energy consumption during operation, derivative processes such as "sludge double reflux-AOA" and "AAOA+MBR" have emerged, and demonstration projects with a capacity of ten thousand tons have been completed in Chongqing and Shandong, etc. The total nitrogen (TN) in the effluent can be stably below 8 mg / L, and the total phosphorus (TP) can be below 0.2 mg / L, showing good treatment effect.

[0004] However, the existing AAO and MBR coupled processes all adopt a "single-point high-proportion" sludge reflux structure, i.e. the oxygen-rich nitrated liquid in the secondary sedimentation tank or membrane tank is once refluxed to the front end of the anaerobic / anoxic zone. This structure continuously transports biomass while directly bringing high-concentration DO (3-5 mg / L -1 ) and NO3 - -N (>15 mg / L -1 ) into the environment that should be strictly anaerobic or anoxic, causing the ORP in the anaerobic section to rise, the phosphorus release of PAOs to be blocked, the carbon source in the anoxic section to be consumed extra, the denitrification to be incomplete, and the system to be forced to increase the dosage of external carbon source and chemical phosphorus removal agent; the fundamental reason is that the reflux path is short, the reflux point is single, and there is a lack of oxygen-consuming / pre-denitrification zone, which cannot reduce DO and NO3 - -N in the reflux liquid in advance, resulting in the "oxygen-carrying side effect" of sludge reflux continuously impacting the gradient environment of biological nitrogen and phosphorus removal. SUMMARY

[0005] (I) Technical problems solved In view of the deficiencies in the prior art, the present application provides a SND energy-saving denitrification process applied to double-path sludge reflux to solve the problems of ORP rising in the anaerobic section, PAOs phosphorus release being blocked, carbon source being consumed extra in the anoxic section, denitrification being incomplete, and the system being forced to increase the dosage of external carbon source and chemical phosphorus removal agent in the background art.

[0006] (II) Technical solutions To achieve the above-mentioned purpose, the present application provides the following technical solutions: a SND energy-saving denitrification process applied to double-path sludge reflux, comprising the following steps: S1, Pretreatment: The wastewater sequentially passes through a mechanical grid, an inlet well, a lifting pump, an oil separation tank, a first sedimentation tank, and a conditioning tank to remove large particles of suspended solids, floating oil, and part of suspended solids, and to homogenize water quality and quantity; S2, Core biochemical treatment: The homogenized wastewater is sequentially introduced into an acidification tank, a UASB reactor, an anoxic tank, and a four-stage aerobic tank for organic matter degradation, nitrification, and denitrification. A simultaneous nitrification and denitrification microenvironment is constructed in the four-stage aerobic tank, the DO concentration is controlled by gradient aeration, and the utilization efficiency of internal carbon source is strengthened. At the same time, the internal carbon source provided by sludge return supports the denitrification process, and there is no need to add additional carbon source. S3, Double reflux sludge system: S31, First reflux path: Most of the sludge settled in the second sedimentation tank is refluxed to the front end of the four-stage aerobic tank after anaerobic treatment. The refluxed sludge releases internal carbon source after anaerobic acidification, and at the same time, nitrification and denitrification reactions occur simultaneously in the gradient aeration environment of the aerobic tank, which improves the total nitrogen removal efficiency. S32, Second reflux path: Part of the sludge is refluxed to the acidification tank. The refluxed sludge is rich in organic matter, which can be used as an internal carbon source to supplement the acidification tank. The nitrate carried by the refluxed sludge undergoes partial denitrification in the facultative environment of the acidification tank, reducing the ineffective consumption of carbon source and providing sufficient carbon source for the subsequent denitrification process. S4, Advanced treatment: The supernatant of the second sedimentation tank is introduced into a biological filter through an intermediate tank for advanced purification, and finally collected in a clear water tank for discharge.

[0007] Preferably, the first reflux path is used to maintain a high concentration of microbial flora to ensure sufficient microbial quantity in the four-stage aerobic tank.

[0008] Preferably, the four-stage aerobic tank adopts a combination device of step aeration and microporous aeration disc. The front end of the first-stage aerobic tank of the four-stage aerobic tank adopts low-intensity aeration DO to adapt to the residual anaerobic microorganisms in the pretreated sludge, so as to avoid the inhibition of microbial activity caused by sudden increase of DO. The DO of the second-stage to fourth-stage aerobic tanks of the four-stage aerobic tank is gradually increased to meet the oxygen demand of nitrification reaction.

[0009] Preferably, the gradient aeration control of the four-stage aerobic tank is as follows: the DO of the first-stage aerobic tank is controlled at 0.5-1.0 mg / L to form a micro-aerobic zone to induce simultaneous nitrification and denitrification; the DO of the second-stage to fourth-stage aerobic tanks is gradually increased to 2.0-2.5 mg / L to ensure complete nitrification, and an alternating environment of "aerobic-micro-aerobic" is constructed by gradient change of DO to promote the synergistic effect of nitrifying bacteria and denitrifying bacteria.

[0010] Preferably, the sludge refluxed to the acidification tank of the second reflux path is rich in organic matter, which can be used as an internal carbon source, and at the same time, the nitrate NO3 - Partial denitrification can occur in the facultative environment of the acidification tank.

[0011] Preferably, an on-line monitor is arranged at the inlet of the clear water tank for real-time monitoring of parameters such as COD, ammonia nitrogen, TN, TP, pH, etc., and feeding the monitoring data to the control system to realize intelligent adjustment of the reflux ratio.

[0012] Preferably, the UASB reactor is used to anaerobically degrade most of the organic matter and produce biogas for energy recycling.

[0013] Preferably, after the polyphosphorus bacteria PAOs absorb excess phosphorus in the fourth-stage aerobic tank, the sludge enters the secondary sedimentation tank, and the phosphorus-rich residual sludge is discharged to the sludge tank to remove phosphorus. The double reflux sludge system forms a cycle between the fourth-stage aerobic tank and the acidification tank to optimize the phosphorus release and absorption environment of the polyphosphorus bacteria PAOs.

[0014] Preferably, the supernatant of the secondary sedimentation tank is sent to the intermediate water tank and then pumped into the biological filter for deep purification.

[0015] (Three) beneficial effects Compared with the prior art, the present application provides an SND energy-saving denitrification process applied to double-path sludge reflux, which has the following beneficial effects: The present application synchronously solves the chain defects of "anaerobic environment destruction - invalid consumption of carbon source - difficulty in simultaneous standardization of total nitrogen and total phosphorus" by reconstructing the sludge reflux path, adding an oxygen-consuming / pre-denitrification zone, and introducing on-line closed-loop regulation, and realizes low-carbon and low-drug-consumption operation under high-standard effluent.

[0016] High denitrification and phosphorus removal efficiency: by refluxing part of the sludge to the acidification tank and intelligently regulating based on the TN value, precise on-demand supply of denitrification carbon source is realized, the denitrification problem caused by fluctuation of the carbon-nitrogen ratio of wastewater is solved, and the biological phosphorus removal effect is simultaneously strengthened.

[0017] Stable operation and impact resistance: the double reflux system enhances the toughness of the process chain and has strong buffering capacity for fluctuations in wastewater quality and quantity, and the effluent quality is stable.

[0018] Resource utilization and energy saving: the biogas produced in the UASB stage can be recycled, realizing energy recycling; the entire system optimizes the internal circulation, reduces the addition of external carbon source, and reduces the operation cost. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a step schematic diagram of the SND energy-saving denitrification process applied to double-path sludge reflux of the present application; Figure 2 is a flow schematic diagram of the SND energy-saving denitrification process applied to double-path sludge reflux of the present application; Figure 3 COD, TN, NH4 + -N, TP and water quantity; Figure 4 The present application is a traditional anaerobic-anoxic-aerobic (AAO) process flow diagram. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0021] Embodiment 1: Referring to the accompanying Figures 1 to 3 A SND energy-saving denitrification process applied to double-path sludge reflux, comprising the following steps: S1, pretreatment: wastewater passes through mechanical grid, water inlet well, lifting pump, oil separation tank, primary sedimentation tank and adjusting tank in sequence to remove large particle suspended solids, floating oil and part of suspended solids, and to homogenize water quality and quantity; S2, core biochemical treatment: the homogenized wastewater is introduced into acidification tank, UASB reactor, anoxic tank and four-stage aerobic tank in sequence for organic matter degradation, nitrification and denitrification reaction; S3, double-reflux sludge system: S31, first reflux path: most of the sludge settled in the secondary sedimentation tank is subjected to anaerobic treatment and then is refluxed to the front end of the four-stage aerobic tank to maintain high concentration of microorganisms and keep sludge activity; S32, second reflux path: part of the sludge is refluxed to the acidification tank, and the effluent TN value is detected in real time by an online total nitrogen (TN) monitor, and the sludge flow refluxed to the acidification tank is automatically adjusted according to the detection result; S4, advanced treatment: the supernatant of the secondary sedimentation tank is introduced into the biological filter tank through the intermediate tank for advanced purification, and finally is collected in the clear water tank for discharge.

[0022] Through the double-path sludge reflux process, the sludge in the secondary sedimentation tank is no longer simply refluxed to the anaerobic tank. Two independent sludge reflux paths are set, one path refluxes part of the sludge to a special oxygen-consuming / pre-denitrification zone, and in this zone, the DO and NO3 - -N in the reflux liquid are first reduced through specific process conditions, and the "oxygen-carrying side effect" of sludge reflux is reduced; The other path refluxes the treated sludge to the anaerobic / anoxic zone and other key treatment areas in a suitable proportion. Such design effectively avoids the high concentration of DO and NO3 -N directly enters the anaerobic / anoxic environment, guarantees the strict anaerobic conditions of the anaerobic section, enables the PAOs to release phosphorus normally, reduces the additional consumption of carbon source in the anoxic section, improves the denitrification efficiency, reduces the dependence of the system on the additional carbon source and chemical phosphorus removal agent, and reduces the impact on the gradient environment of biological denitrification and phosphorus removal.

[0023] The problem that the oxygen-rich nitrification liquid in the secondary sedimentation tank or membrane tank is once returned to the front end of the anaerobic / anoxic zone, so that the ORP in the anaerobic section is increased, the PAOs are hindered to release phosphorus, the carbon source in the anoxic section is additionally consumed, the denitrification is not complete, and the system is forced to increase the amount of additional carbon source and chemical phosphorus removal agent is solved.

[0024] The core of the present application is to disclose a sludge return intelligent control strategy based on real-time feedback of effluent water quality, and the sludge return of the acidification tank is innovatively set as an intermittent condition start mode instead of a traditional continuous state. Through the strategy, the system realizes efficient utilization of internal carbon source and minimization of sludge production.

[0025] By reconstructing the sludge return path, adding the oxygen-consuming / pre-denitrification zone and introducing the online closed-loop control, the chain defects of "anaerobic environment destruction - carbon source ineffective consumption - difficulty in simultaneous standard of total nitrogen and total phosphorus" are simultaneously solved, and low-carbon and low-drug consumption operation under high-standard effluent is realized.

[0026] High denitrification and phosphorus removal efficiency: by returning part of the sludge to the acidification tank and intelligently controlling based on the TN value, precise on-demand supply of denitrification carbon source is realized, the denitrification problem caused by fluctuation of carbon-nitrogen ratio of wastewater is solved, and the biological phosphorus removal effect is synergistically enhanced.

[0027] Stable operation and impact resistance: the double-return system enhances the toughness of the process chain and has strong buffering capacity for fluctuations in wastewater quality and quantity, and the effluent quality is stable.

[0028] Resource utilization and energy saving: the biogas produced in the UASB stage can be recycled, realizing energy recycling; the entire system reduces the addition of external carbon source through optimization of internal circulation, reducing the operation cost.

[0029] Intelligent control: innovatively linking the effluent quality index (TN) and internal material return (sludge return) for closed-loop control, the process operation is fine and intelligent.

[0030] This design is particularly suitable for complex composition and large load fluctuation of dairy industry wastewater, and has high application value and promotion prospect.

[0031] Specifically, the first return path is used for maintaining high-concentration microbial flora and ensuring sufficient microbial amount in the fourth-stage aerobic tank, so as to guarantee efficient removal of COD and nitrification, and convert NH4 + Into NO3- The sludge activity is maintained to quickly replenish the microorganisms in the fourth-stage aerobic tank and maintain system stability. The sludge in the sludge tank is continuously delivered to the front end of the aerobic tank at a rate of 50 m 3 / day to ensure the amount of sludge in the aerobic tank. When the TN index of the effluent is higher than 11 mg / L, the amount of sludge entering the aerobic tank is increased to 100 mg / L, and the increased sludge delivery is maintained for 1-2 days until the TN concentration of the effluent decreases and returns to the normal sludge amount.

[0032] A modular anaerobic ammonia oxidation reactor is embedded in the sludge storage tank in the first reflux path, which is used to convert the residual NH4 + -N and NO2 - -N in the sludge into N2 and H2O under anaerobic conditions by using anaerobic ammonia oxidation bacteria (such as Candidatus Brocadia), while degrading part of the refractory organic matter. The pretreated sludge is then delivered to the front end of the fourth-stage aerobic tank by a reflux pump to form a “sludge pretreatment-aerobic enhancement” synergistic treatment link.

[0033]

[0034] Technical advantages: reducing the load of the aerobic tank: the NH4 + -N content in the pretreated sludge is reduced by 60%-70%, reducing the oxygen consumption required for nitrification in the fourth-stage aerobic tank, and the energy consumption is reduced by 15%-20%.

[0035] Optimizing sludge activity: the anaerobic ammonia oxidation process can degrade part of the extracellular polymeric substance (EPS) in the sludge, release trace nutrients, and improve the activity of nitrifying bacteria (such as Nitrosomonas and Nitrobacter) in the reflux sludge, with an increase of more than 25% in the nitrification rate.

[0036] Reducing secondary pollution: trace amounts of antibiotics, surfactants, and other refractory pollutants in the sludge are synergistically degraded by anaerobic ammonia oxidation bacteria, and the COD removal rate in the subsequent aerobic tank can be increased by 8%-12%.

[0037] Implementation process: sludge tank modification: the original sludge tank is divided into a “pretreatment zone” and a “buffer zone”, the modular anaerobic ammonia oxidation reactor is installed in the pretreatment zone, and the buffer zone is used to temporarily store the treated sludge.

[0038] Online monitoring linkage: NH4 + -N, NO2 - -N online monitors are installed at the outlet of the pretreatment zone. When the NH4 + -N concentration is > 5 mg / L, the HRT is automatically extended or anaerobic ammonia oxidation bacteria are supplemented to ensure that the effluent meets the standards.

[0039] Return flow control: The pretreated sludge is transported to the front end of the four-stage aerobic tank by a variable frequency return flow pump, and the return flow rate (200-300 m³ / h) is automatically adjusted according to the MLSS concentration (controlled at 3000-4000 mg / L) of the aerobic tank.

[0040] The four-stage aerobic tank adopts a combination device of stepped aeration and microporous aeration disc; the front end of the first-stage aerobic tank of the four-stage aerobic tank adopts low-intensity aeration (DO = 1.0-1.5 mg / L), which is suitable for the residual anaerobic microorganisms in the pretreated sludge and is used to avoid the inhibition of microbial activity caused by the sudden increase of DO; the aeration intensity of the second-stage to fourth-stage aerobic tanks of the four-stage aerobic tank is gradually increased (DO = 2.0-2.5 mg / L), which is used to meet the oxygen demand of the nitrification reaction.

[0041] Intelligent control of aeration flow: According to the NH4 + - concentration of the influent of the first-stage aerobic tank (usually <8 mg / L after pretreatment), the frequency of the aeration blower is automatically adjusted through the DO online monitor and the frequency converter, which can save energy by 10%-15%.=-0.05.

[0042] Optimization of sludge age (SRT): The overall SRT of the four-stage aerobic tank is controlled at 15-20 d, and the local SRT of the first-stage aerobic tank is extended to 25 d through a sludge interception device (such as a inclined plate settling tank), which strengthens the domestication and proliferation of microorganisms in the pretreated sludge and improves the impact resistance of the system.

[0043] Periodically (every 7 d), the sludge activity of each stage of the aerobic tank is detected (using the dehydrogenase activity detection method), and when the activity is <0.5 μg / (g h), the return flow rate of sludge is appropriately reduced, the SRT is extended to 22 d, and the microbial activity is restored.

[0044] Biological phase control: Functional biological fillers (such as polyurethane foam carriers with a specific surface area of 500-800 m² / m³) are added to the four-stage aerobic tank to enrich nitrifying bacteria and polyphosphate bacteria (PAOs), and after the carrier is colonized, the nitrification rate is increased by 30%, and the phosphorus uptake efficiency of PAOs is increased by 20%.

[0045] Periodically (every 10 d), the biofilm is sampled and analyzed, and when the proportion of nitrifying bacteria is <20%, nitrifying bacteria agents (such as Nitrosospira bacteria agents) are supplemented to maintain the stability of the biological phase.

[0046] The gradient environment of the four-stage aerobic tank is shown in the following table:

[0047] Install ORP online monitor in each aerobic tank to monitor gradient environment change in real time. When ORP of the first-stage aerobic tank is greater than 0 mV, automatically reduce aeration flow (by 20%) and supplement a small amount of internal carbon source (such as sodium acetate, with a dosage of 5-10 mg / L) to restore micro-aerobic denitrification environment.

[0048] When ORP of the fourth-stage aerobic tank is less than 250 mV, increase aeration flow (by 15%) to ensure aerobic environment required by PAOs to absorb phosphorus, and maintain TP removal rate at more than 95%.

[0049] Utilize micro-aerobic environment of the first-stage aerobic tank to hydrolyze refractory organic matters (such as protein and polysaccharide) in the reflux sludge into easily degradable carbon source (such as VFAs), supplement carbon source required by denitrification, and reduce dosage of external carbon source (by 30-40%).

[0050] When COD of the first-stage aerobic tank is less than 50 mg / L, supplement a small amount of methanol (with a dosage of 3-5 mg / L) through an intelligent dosing system to ensure sufficient carbon source for denitrification, and maintain TN removal rate at not less than 85%.

[0051] According to TN concentration (target value <5 mg / L) at the outlet of the fourth-stage aerobic tank, dynamically adjust sludge reflux ratio of the first reflux path (controlled at 50-80%). When the outlet TN is greater than 6 mg / L, increase the reflux ratio to 80% to increase the number of denitrifying bacteria in the first-stage aerobic tank; when the TN is less than 4 mg / L, decrease the reflux ratio to 50% to reduce sludge load.

[0052] Specifically, the sludge refluxed to the acidification tank by the second reflux path is rich in organic matter and can be used as internal carbon source, and at the same time, the nitrate NO3 - Partial denitrification can occur in the facultative environment of the acidification tank; (in the traditional process, sludge is supplied to the acidification tank continuously, and the improved process determines whether to increase sludge according to the sludge concentration in the acidification tank. When the water in the acidification tank is relatively clear, 20-35 m3 of sludge is added, and the amount of sludge entering the acidification tank is controlled by opening and closing the valve of the sludge pipe of the secondary sedimentation tank); Referring to FIG. 1, Figure 3 The sewage treatment system provided by the embodiment of the present application shows the cooperative change relationship between key water quality indexes (COD, TN, NH4 + -N, and TP) of effluent and water quantity of influent in one operation cycle (from August 1, 2025 to September 4, 2025); the horizontal coordinate of the graph is date (from August 1 to September 4), and the upper four curves from top to bottom are concentration (unit: mg / L), which respectively represent chemical oxygen demand (COD, red broken line), total nitrogen (TN, green broken line), ammonia nitrogen (NH4 +-N (purple broken line) and total phosphorus (TP, orange broken line) concentration values. According to the appendix... Figure 3 The concentration trend graph shown illustrates that increasing the sludge volume had a rapid and positive effect on organic matter removal, confirming the effectiveness of the technology. On August 16th, when the water volume and pollutant load reached their peak, the sludge volume was increased. As shown in the graph, after this operation, the COD concentration experienced a rapid and precipitous drop, indicating that supplementing the microbial community immediately enhanced the system's ability to degrade organic pollutants, effectively coping with the organic load shock. This also proves that supplementing the system with microbial communities (sludge) is a direct and effective technical means to cope with organic load shocks, providing preliminary directional inspiration for the construction of this invention. Under the current process, the concentrations of effluent quality indicators fluctuate within the standard requirements. When the TN concentration shows an upward trend and exceeds 11 mg / L, sludge addition provides a richer microbial base for nitrification and denitrification processes, strengthening the system's denitrification capacity. This operation verifies that improving system treatment capacity by regulating the microbial mass (MLSS) is a direct and efficient technical path. It is worth noting that after sludge addition, ammonia nitrogen (NH4) decreased significantly. + The concentration of -N (purple broken line) showed a brief peak. This phenomenon profoundly reveals the competitive relationship at the molecular level within the system: the newly added heterotrophic bacteria consumed dissolved oxygen and available carbon sources when degrading COD, which may have temporarily inhibited the activity of autotrophic nitrifying bacteria (increased ammonia nitrogen) and affected the electron donor supply in the denitrification process.

[0053] By increasing the amount of sludge to improve the sludge concentration in the acidification tank, the hydrolysis acidification efficiency is enhanced. This provides sufficient high-quality carbon sources (VFAs) for the subsequent anoxic denitrification process, thereby significantly improving denitrification efficiency and ultimately reducing total nitrogen in the effluent. The sludge discharge end of the secondary sedimentation tank is equipped with two sets of pipelines via branch valves. One set is directly connected to the acidification tank, and the other set is directly connected to the sludge tank. When water quality needs to be adjusted, the valve is opened, and the sludge flows directly into the acidification tank. After 15-25 minutes (preferably around 20 minutes), the valve is closed, and the remaining sludge goes directly into the sludge tank. Finally, the sludge in the sludge tank is used to supply the aerobic tank.

[0054] Specifically, the online total nitrogen (TN) monitor is installed at the inlet of the clear water tank to monitor the total nitrogen value of the effluent in real time and feed the monitoring data back to the control system to realize intelligent adjustment of the reflux ratio; The monitored TN value is compared with the set target value. If the effluent TN value is too high, it indicates that the denitrification of the system is incomplete and more carbon source needs to be added. At this time, the control system will automatically increase the sludge flow rate returned to the acidification tank.

[0055] Specifically, the UASB reactor is used for anaerobic degradation of most of the organic matter and biogas produced, forming energy recycling, and realizing energy resource utilization.

[0056] Specifically, after the polyphosphorus bacteria PAOs absorb excess phosphorus in the fourth-stage aerobic tank, the sludge enters the secondary sedimentation tank, and the phosphorus-rich residual sludge is discharged to the sludge tank, forming phosphorus removal. The double reflux sludge system forms a cycle between the fourth-stage aerobic tank and the acidification tank, cooperates to optimize the phosphorus release and absorption environment of the polyphosphorus bacteria PAOs, improves the phosphorus removal effect, and the synergistic effect of the two reflux paths creates the best conditions for the phosphorus release and absorption of the polyphosphorus bacteria, further strengthening the phosphorus removal effect.

[0057] Specifically, the supernatant of the secondary sedimentation tank enters the intermediate water tank, is sent to the biological filter tank by the lifting pump for deep purification, is used for removing residual COD, SS and trace ammonia nitrogen, and is finally collected in the clear water tank to ensure that the effluent meets the standard stably.

[0058] The traditional external reflux sludge of sewage treatment mainly enters the anaerobic tank, and specifically refers to the process schematic diagram of the traditional anaerobic-anoxic-aerobic AAO process shown in the drawing. Figure 4 As can be seen from the process schematic diagram of the traditional anaerobic-anoxic-aerobic AAO process, the principle of the traditional anaerobic-anoxic-aerobic AAO process is as follows: Anaerobic tank: Polyphosphorus bacteria (PAOs) use the influent VFAs to synthesize PHAs, and release PO4 3- at the same time; NO3 - / DO in the reflux sludge will be preferentially utilized by denitrifying bacteria, consume carbon sources and destroy the anaerobic environment, resulting in a decrease in subsequent phosphorus absorption capacity.

[0059] Anoxic tank: Denitrifying bacteria reduce NO3

[0060] Oxygen tank: Complete NH4 + -N→NO3 - -N nitrification reaction, and PAOs oxidize PHAs to absorb excess phosphorus; the terminal DO is usually controlled at 1.5-2.5 mg / L to balance the complete nitrification and the high DO of the reflux liquid.

[0061] And the optimized process adjusts the sludge reflux ratio according to the effluent, and increases the sludge reflux to the aerobic tank, which can achieve a high total nitrogen removal rate, and the minimum is reduced to below 5 mg / L; The sludge produced by the process can be reused as a carbon source, and at the same time, the stability of the process can be improved, different water quantity and water quality characteristics can be coped with, especially the occurrence of shutdown and production stoppage, and the sludge can survive for a long buffer period of up to 40 days.

[0062] Reduce sludge discharge: benthic absorption method, reduce sludge storage and discharge.

[0063] As a carbon source supply: sludge as a carbon source supply, improve biodegradability, reduce cost.

[0064] Improve process stability: domesticated sludge to achieve independent control of process operation, long mitigation period up to 40 days, minimize downtime loss.

[0065] Save electricity and achieve carbon emission reduction: use the adaptability of sludge, adopt flat peak valley operation process, jointly cope with water fluctuation and production change, in general, can realize: carbon source reduction 90%; electricity saving 8%, overall cost saving more than 200,000 yuan.

[0066] Finally, it should be noted that: the above is only the preferred embodiment of the present application, and is not intended to limit the present application, although the present application has been described in detail with reference to the foregoing embodiments, for those skilled in the art, it still can modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part of the technical features, any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application, should be included in the protection scope of the present application.

Claims

1. A SND energy-saving denitrification process applied to double-path sludge reflux, characterized in that, The method comprises the following steps: S1, pretreatment: the wastewater is sequentially subjected to a mechanical grid, a water inlet well, a lifting pump, an oil separation tank, a first sedimentation tank and a regulating tank to remove large particle suspended solids, floating oil and part of suspended solids and to homogenize water quality and quantity; S2, core biochemical treatment: the homogenized wastewater is sequentially introduced into an acidification tank, a UASB reactor, an anoxic tank and a four-stage aerobic tank for organic matter degradation, nitrification and denitrification; a simultaneous nitrification and denitrification microenvironment is constructed in the four-stage aerobic tank, the DO concentration is controlled through gradient aeration, and the utilization efficiency of internal carbon source is strengthened; meanwhile, the internal carbon source provided by sludge backflow supports the denitrification process, and no additional carbon source needs to be added; S3, double backflow sludge system: S31, first backflow path: used for backflowing most of the sludge settled in the secondary sedimentation tank to the front end of the four-stage aerobic tank after anaerobic treatment; The backflow sludge releases internal carbon source through anaerobic acidification, and the nitrification and denitrification reactions occur simultaneously in the gradient aeration environment of the aerobic tank, thereby improving the total nitrogen removal efficiency; S32, second backflow path: used for backflowing part of the sludge to the acidification tank; The backflow sludge is rich in organic matter and serves as an internal carbon source for the acidification tank; the nitrate carried by the backflow sludge undergoes partial denitrification in the facultative environment of the acidification tank, thereby reducing the ineffective consumption of carbon source and reserving sufficient carbon source for the subsequent denitrification process; S4, advanced treatment: the supernatant of the secondary sedimentation tank is introduced into a biological filter tank through an intermediate water tank for advanced purification, and finally collected in a clear water tank for discharge in accordance with the standard.

2. The SND energy-saving denitrification process applied to double-path sludge return according to claim 1, characterized in that: The first backflow path is used to maintain a high concentration of microbial flora and ensure sufficient microbial amount in the four-stage aerobic tank.

3. The SND energy-saving denitrification process applied to double-path sludge return according to claim 2, characterized in that: The four-stage aerobic tank adopts a combination device of step aeration and microporous aeration disc; the front end of the first-stage aerobic tank of the four-stage aerobic tank adopts low-intensity aeration DO to adapt to the residual anaerobic microorganisms in the pretreated sludge, so as to avoid the inhibition of microbial activity caused by the sudden increase of DO; the DO of the second-stage to fourth-stage aerobic tanks of the four-stage aerobic tank is gradually increased, so as to meet the oxygen demand of the nitrification reaction; through step aeration, gradient degradation is formed, so as to increase the residence time and realize the gradient degradation of the wastewater concentration, thereby realizing microbial domestication.

4. The SND energy-saving denitrification process applied to double-path sludge return according to claim 3, characterized in that: Four-stage aerobic tank gradient aeration regulation: the DO of the first-stage aerobic tank is controlled at 0.5-1.0 mg / L to form a micro-oxygen zone to induce simultaneous nitrification and denitrification; the DO of the second-stage to fourth-stage aerobic tanks is gradually increased to 2.0-2.5 mg / L to ensure complete nitrification; through the gradient change of DO, an alternating environment of "aerobic-micro-oxygen" is constructed to promote the synergistic effect of nitrifying bacteria and denitrifying bacteria.

5. The SND energy saving denitrification process applied to double path sludge return according to claim 1, characterized in that: An online monitoring instrument is arranged at the inlet of the clear water tank to monitor parameters such as COD, ammonia nitrogen, TN, TP and pH in real time, and the monitoring data are fed back to the control system to realize intelligent adjustment of the backflow ratio.

6. The SND energy saving denitrification process applied to double path sludge return according to claim 1, characterized in that: The UASB reactor is used to anaerobically degrade most of the organic matter and produce biogas to form energy recycling.

7. The SND energy saving denitrification process applied to double path sludge return according to claim 1, characterized in that: After the PAOs excessively absorb phosphorus in the four-stage aerobic tank, the PAOs enter the secondary sedimentation tank with the sludge, and the phosphorus-rich residual sludge is discharged to a sludge tank to remove phosphorus; The double backflow sludge system forms a cycle between the four-stage aerobic tank and the acidification tank to optimize the phosphorus release and absorption environment of the PAOs.

8. The SND energy saving denitrification process applied to double path sludge return according to claim 1, characterized in that: The supernatant of the secondary sedimentation tank is pumped into the intermediate water tank and then into the biological filter tank for further purification.

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