A biological denitrification device and method for wastewater with low carbon-to-nitrogen ratio.

Abstract

This invention discloses a biological denitrification device and method for wastewater with a low carbon-to-nitrogen ratio. The denitrification device includes a raw water tank, a bioreactor, and a secondary sedimentation tank connected in sequence. The bioreactor sequentially includes an anaerobic zone, a swaying zone, an anoxic zone, and an aerobic zone. The swaying zone has four separate reaction tanks, with the dissolved oxygen concentration and hydraulic retention time of each tank adjusted based on the influent water quality. When treating wastewater with a low carbon-to-nitrogen ratio, this system achieves the elimination of the need for external carbon sources through a specific process, significantly reducing system operating costs. Furthermore, it significantly improves denitrification efficiency while also achieving highly efficient biological phosphorus removal.

Description

Technical Field

[0001] This invention relates to a biological denitrification device for wastewater with a low carbon-to-nitrogen ratio, and also to a denitrification method based on the aforementioned denitrification device. Background Technology

[0002] Traditional biological nitrogen removal processes include the A / O (Anaerobic / Oxic) process, the A / A / O (Anaerobic / Anoxic / Oxic) process, and the oxidation ditch (OD) process. After decades of development, these processes are quite mature and have good nitrogen removal effects. However, they generally suffer from drawbacks such as long process flow, large reactors, large footprint, need for external carbon sources, high energy consumption, and high cost, making it difficult to meet increasingly stringent standards.

[0003] Oxidation ditch processes, while simple in structure and high in sludge concentration to enhance treatment capacity, suffer from poor adaptability to wastewater quality fluctuations and ineffective treatment under high pollution loads. Furthermore, their aeration systems are energy-intensive, resulting in high long-term operating costs. In contrast, the AAO (Anaerobic-Aerobic-Oxygenated) process is more widely used. This process connects anaerobic, aerobic, and anoxic reaction zones in series, offering advantages such as simple construction, short total hydraulic retention time, low control complexity, and reduced sludge bulking. It has become one of the most widely used simultaneous nitrogen and phosphorus removal processes in urban wastewater treatment plants. However, its disadvantage lies in the high energy consumption of its aeration recirculation system. The low C / N ratio in municipal wastewater and the lack of carbon sources can lead to poor nitrogen removal efficiency in AAO processes, while adding external carbon sources significantly increases system operating costs. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a biological denitrification device for wastewater with a low carbon-to-nitrogen ratio. Another purpose of this invention is to provide a denitrification method based on the above-mentioned denitrification device. When treating wastewater with a low carbon-to-nitrogen ratio, this invention achieves the elimination of the need to add an external carbon source through a specific process, thereby significantly reducing the operating cost of the system. Furthermore, it can also achieve highly efficient biological phosphorus removal while significantly improving denitrification efficiency.

[0005] Technical solution: The biological denitrification device for low C / N ratio wastewater described in this invention includes a raw water tank, a bioreactor, and a secondary sedimentation tank connected in sequence; wherein, the bioreactor is an ASAO bioreactor, which includes an anaerobic zone, a swing zone, an anoxic zone, and an aerobic zone in sequence, and the total hydraulic retention time of the bioreactor is 18 hours; the swing zone is equipped with a four-stage reaction tank, and the dissolved oxygen concentration and hydraulic retention time of each stage reaction tank are adjusted based on the influent water quality;

[0006] When the influent COD is 100–200 mg / L, TP is 2–3 mg / L, and NH4+ is... +When -N is 20-30 mg / L and TN is 25-30 mg / L, the volume ratio of the corresponding reaction tanks in the anaerobic zone, the swing zone (aerobic), the swing zone (anoxic), the anoxic zone, and the aerobic zone is 2:2:2:2:1. The hydraulic retention times in the anaerobic zone, the swing zone (aerobic), the swing zone (anoxic), the anoxic zone, and the aerobic zone are 4h, 4h, 4h, 4h, and 2h, respectively. In the swing zone, the dissolved oxygen concentration in the two-stage aerobic reaction tanks increases along the water flow direction. The dissolved oxygen concentration in the first-stage aerobic reaction tank is 0.8-1.2 mg / L, and the dissolved oxygen concentration in the second-stage aerobic reaction tank is 1.0-2.0 mg / L. The hydraulic retention time in each aerobic reaction tank is 2h.

[0007] When the influent COD is 200–300 mg / L, TP is 3–5 mg / L, and NH4+ is... + When -N is 35-50 mg / L and TN is 40-55 mg / L, the volume ratio of the corresponding reaction tanks in the anaerobic zone, the swing zone (aerobic zone), the swing zone (anoxic zone), the anoxic zone, and the aerobic zone is 2:3:1:2:1. The hydraulic retention times in the anaerobic zone, the swing zone (aerobic zone), the swing zone (anoxic zone), the anoxic zone, and the aerobic zone are 4h, 6h, 2h, 4h, and 2h, respectively. The dissolved oxygen concentration in the three-stage aerobic reaction tanks in the swing zone increases along the water flow direction. The dissolved oxygen concentration in the first-stage aerobic reaction tank is 0.8-1.0 mg / L, the dissolved oxygen concentration in the second-stage aerobic reaction tank is 1.0-1.2 mg / L, and the dissolved oxygen concentration in the third-stage aerobic reaction tank is 1.2-2.0 mg / L. The hydraulic retention time in each aerobic reaction tank is 2h.

[0008] When the influent COD>300mg / L, TP>5mg / L, and NH4+ + When -N>50mg / L and TN>55mg / L, the volume ratio of the anaerobic zone, the swaying zone (aerobic zone), the anoxic zone, and the aerobic zone is 2:4:2:1. The hydraulic retention times of the anaerobic zone, the swaying zone (aerobic zone), the anoxic zone, and the aerobic zone are 4h, 8h, 4h, and 2h, respectively. In the swaying zone, the dissolved oxygen concentration in the four-stage aerobic reactors increases along the water flow direction. The dissolved oxygen concentration in the first-stage aerobic reactor is 0.8–1.0mg / L, the dissolved oxygen concentration in the second-stage aerobic reactor is 1.0–1.2mg / L, the dissolved oxygen concentration in the third-stage aerobic reactor is 1.2–1.5mg / L, and the dissolved oxygen concentration in the fourth-stage aerobic reactor is 1.5–2.0mg / L. The hydraulic retention time of each aerobic reactor is 2h.

[0009] K2 type biological packing material was added to at least the primary reaction tank and the anoxic zone in the swing zone.

[0010] The dosage of K2 type biological packing material is 15% of the reaction tank volume.

[0011] The anaerobic zone, swaying zone, anoxic zone, and aerobic zone are all equipped with stirring devices and aeration devices.

[0012] The secondary sedimentation tank is connected to the anaerobic zone via a first sludge return pump, and to the final stage reactor of the swing zone via a second sludge return pump. Meanwhile, the anaerobic zone is connected to the final stage reactor of the swing zone via a bypass pump (which allows some nutrients from the front end to bypass the swing zone and directly enter the subsequent anoxic zone, providing COD and ammonia nitrogen for the operation of the anoxic zone), providing the sludge-water mixture from the anaerobic zone to the final stage reactor of the swing zone and the subsequent anoxic zone.

[0013] The denitrification method based on the above-mentioned denitrification device is as follows:

[0014] (1) The water from the raw water tank enters the anaerobic zone of the ASAO bioreactor via the inlet pump. At the same time, the concentrated sludge from the bottom of the secondary sedimentation tank is pumped into the anaerobic zone of the ASAO bioreactor via the first sludge return pump. The hydraulic retention time of the anaerobic zone is controlled to be 4 hours, and the dissolved oxygen content of the anaerobic zone is controlled to be less than 0.2 mg / L (the anaerobic zone is not aerated, and the dissolved oxygen content is usually lower than 0.2 mg / L). The polysaccharide bacteria and polyphosphate bacteria in the sludge are used to convert the organic matter in the wastewater into an internal carbon source and complete the release of phosphate.

[0015] (2) Wastewater from the anaerobic zone flows into the swing zone. The swing zone adjusts the number of aeration tanks and the aeration intensity of the aeration tanks according to the influent water quality and quantity. The overall hydraulic retention time of the swing zone is 8 hours, of which the total hydraulic retention time of the aeration tanks is 4 to 8 hours. The dissolved oxygen concentration of the aeration tanks in the swing zone is controlled at 0.8 to 2.0 mg / L by adjusting the aeration intensity.

[0016] (3) Wastewater from the swing zone flows into the anoxic zone; the total hydraulic retention time in the anoxic zone is controlled to be 4 hours. In the anoxic zone, ammonia nitrogen from the anaerobic zone overflow and nitrite nitrogen from the swing zone are used for anaerobic ammonia oxidation reaction. At the same time, nitrite nitrogen can be provided to the anaerobic ammonia oxidizing bacteria through a short-cut denitrification process in the anoxic zone. The anaerobic ammonia oxidizing bacteria use the added K2 type biological packing as an attachment carrier and achieve enrichment on it.

[0017] (4) Wastewater from the anoxic zone enters the aerobic zone, where nitrification, short-cut nitrification and aerobic phosphorus uptake occur;

[0018] (5) Wastewater in the aerobic zone enters the secondary sedimentation tank through the overflow pipe, where sludge and water are separated. The supernatant is discharged through the drain pipe, and the concentrated sludge at the bottom is returned to the anaerobic zone and the end swing zone, so that the concentration of activated sludge in the bioreactor is 2500-4000 mg / L.

[0019] In step (1), the sludge used for inoculation is sludge from the reactor of a municipal wastewater treatment plant. The carbon source absorption rate in the anaerobic zone reaches 90% and the denitrification rate in the anoxic zone reaches 80%, which indicates that the sludge has matured.

[0020] In step (4), the hydraulic retention time in the aerobic zone is 2 hours; the dissolved oxygen content in the aerobic zone is controlled to be 2-3 mg / L.

[0021] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0022] (1) Compared with the traditional AAO process, the present invention optimizes the operating conditions of the device to achieve the domestication and enrichment of nitrifying and denitrifying bacteria and endogenous denitrifying bacteria, thereby enabling the use of endogenous carbon sources for denitrification, eliminating the need for the addition of exogenous carbon sources, and significantly reducing the operating cost and carbon emissions of the system.

[0023] (2) The operating conditions of the device of the present invention can promote the enrichment of key functional bacteria (low DO conditions are conducive to the enrichment of synchronous nitrifying and denitrifying bacteria, endogenous denitrifying bacteria, etc.), which can significantly improve the denitrification efficiency and achieve efficient biological phosphorus removal by utilizing the denitrification phosphorus removal process.

[0024] (3) During the operation of the system of the present invention, the emission of N2O can be effectively reduced to a minimum of only 1.1% of the nitrogen load of the influent, which meets the environmental protection requirements of energy conservation and emission reduction.

[0025] (4) The present invention sets up a swing zone (S) in the bioreactor, so that the entire reaction device can be adjusted to operate in different modes according to different influent water quality conditions by changing the volume and aeration intensity of the aerobic zone in the swing zone. By optimizing the volume ratio, aeration intensity and hydraulic retention time of the aerobic reaction tank in the swing zone, the overall energy consumption of the system can be effectively reduced. That is, the size of the aeration area in the swing zone can be optimized and the aeration intensity can be adjusted according to the influent conditions, thereby effectively saving aeration energy consumption and avoiding aeration waste. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the denitrification device of the present invention. Detailed Implementation

[0027] like Figure 1As shown, the biological denitrification device for low C / N ratio wastewater of the present invention includes a raw water tank 1, a bioreactor 2, and a secondary sedimentation tank 3 connected in sequence; wherein, the bioreactor 2 is an ASAO bioreactor, which includes an anaerobic zone, a swaying zone, an anoxic zone, and an aerobic zone in sequence; wherein, the anaerobic zone includes anaerobic zone 1 2.1 and anaerobic zone 2.2 connected in sequence; the swaying zone includes swaying zone 1 2.3, swaying zone 2.4, swaying zone 3 2.5, and swaying zone 3 connected in sequence. Zone 4 (2.6); the anoxic zone is sequentially connected to anoxic zone 1 (2.7) and anoxic zone 2 (2.8); the aerobic zone (2.9) is connected to the secondary sedimentation tank (3) via overflow pipe (2.14); the secondary sedimentation tank (3) is connected to anaerobic zone 1 (2.1) via the first sludge return pump (3.2), and to the swing zone 4 (2.6) via the second sludge return pump (3.1). At the same time, anaerobic zone 1 (2.1) is connected to the swing zone 4 (2.6) via the bypass sludge pump (2.13); the effluent from the secondary sedimentation tank (3) is discharged via drain pipe (3.3).

[0028] The anaerobic zone 1 (2.1), anaerobic zone 2 (2.2), swaying zone 1 (2.3), swaying zone 2 (2.4), swaying zone 3 (2.5), swaying zone 4 (2.6), anoxic zone 1 (2.7), anoxic zone 2 (2.8), and aerobic zone 2 (2.9) are all equipped with a stirring device (2.10) and an aeration disc (2.11). The biological nitrogen removal device of the present invention also includes an aeration pump (2.12), which is connected to the aeration disc (2.11) via a rotor flow meter (2.16).

[0029] K2-type biological packing material 2.15 was added to all three zones: Zone 4 (2.6), Zone 1 (2.7), and Zone 2 (2.8). The K2-type biological packing material 2.15 has 6 pores. The filling amount of K2 type biological packing material 2.15 in the swing zone 4 2.6, anoxic zone 1 2.7 and anoxic zone 2 2.8 is 15% of the reaction chamber volume.

[0030] Example 1

[0031] The denitrification method based on the above-mentioned biological denitrification device is as follows:

[0032] The influent water quality simulates municipal low C / N wastewater. The nitrogen and carbon sources in the simulated wastewater are provided by ammonium chloride and sodium acetate, respectively. The influent COD concentration is 150 mg / L, the influent ammonia nitrogen concentration is 30 mg / L, the influent TP concentration is 3 mg / L, and the influent TN concentration is 30 mg / L. In addition, 1 mL of trace element solution is added per liter of simulated wastewater.

[0033] The sludge is inoculated into the reactor of a municipal wastewater treatment plant. The sludge acclimation is considered complete when the carbon source absorption rate in the anaerobic zone reaches 90% and the intrinsic denitrification rate in the anoxic zone reaches 80%. The specific acclimation process is as follows:

[0034] The activated sludge used in this embodiment was sourced from a municipal wastewater treatment plant in Nanjing, which employs a pretreatment-oxidation ditch (OD) biological treatment process. The obtained secondary sedimentation tank sludge was first filtered through a 1.0mm stainless steel mesh screen to remove impurities, then washed three times with deionized water; subsequently, it was inoculated into the bioreactor of this invention. The simulated municipal wastewater was used as the influent, and the concentration of the inoculated sludge was approximately 4 g MLSS / L (4000 mg / L). The volume ratio of the anaerobic zone, the swing zone (aerobic), the swing zone (anoxic), the anoxic zone, and the aerobic zone was 2:2:2:2:1. The hydraulic retention times for the anaerobic zone, the swing zone (aerobic), the swing zone (anoxic), the anoxic zone, and the aerobic zone were 4 h, 4 h, 4 h, 4 h, and 2 h, respectively. The swing zone contained two stages of aerobic and oxidative ditch treatment. The dissolved oxygen concentration in the aerobic reactor increases along the water flow direction. The dissolved oxygen concentration in the first-stage aerobic reactor (swing zone 1, 2.3) is 0.8–1.2 mg / L, and the dissolved oxygen concentration in the second-stage aerobic reactor (swing zone 2, 2.4) is 1.0–2.0 mg / L. The hydraulic retention time of each aerobic reactor is 2 hours. During the above operation, the use of low-oxygen aeration conditions is conducive to the rapid and large-scale enrichment of endogenous denitrifying bacteria. When the carbon source absorption rate in the anaerobic zone reaches 90% and the endogenous denitrification rate in the anoxic zone reaches 80%, it indicates that the sludge has matured. At this time, the device operates for 33 days, and no sludge is actively discharged during this operation stage.

[0035] (1) On the 34th day of operation, active sludge discharge begins, with a normal daily discharge of 2L to 2.5L, and the sludge age is controlled at 30 days. At this time, simulated domestic sewage is fed into anaerobic zone 2.1 at a flow rate of 1L / h, and mixed with sludge returned from secondary sedimentation tank 3. The total residence time of the mixed liquid in the anaerobic zone is controlled at 4h, and the dissolved oxygen content in the anaerobic zone is kept below 0.2mg / L. Polysaccharide bacteria and polyphosphate bacteria in the sludge are used to convert organic matter in the sewage into internal carbon sources and complete the release of phosphate.

[0036] (2) The mixed liquor enters the swing zone 1 2.3 (aerobic reaction tank) and swing zone 2 2.4 (aerobic reaction tank) sequentially from anaerobic zone 2.2. The total hydraulic retention time of the mixed liquor in the aerobic reaction tanks (swing zone 1 2.3 and swing zone 2.4) is controlled to be 4h, and the dissolved oxygen content in swing zone 1 2.3 and swing zone 2.4 is controlled to be 1mg / L. Aerobic phosphorus uptake, nitrification and simultaneous nitrification-denitrification reactions occur in the aerobic reaction tank of the swing zone. At this time, the denitrification effect of the aerobic reaction tank of the swing zone is significant. The TN in the effluent of the aerobic reaction tank of the swing zone is reduced by 16.41mg / L, and the denitrification contribution rate reaches 54.7%.

[0037] (3) The mixed liquor flowing out from the second swing zone 2.4 enters the third swing zone 2.5, and then continues to enter the fourth swing zone 2.6. At this time, there is no aeration in the third swing zone 2.5 and the fourth swing zone 2.6, and the dissolved oxygen content is less than 0.5 mg / L. The total hydraulic residence time of the mixed liquor in the third swing zone 2.5 and the fourth swing zone 2.6 is 4 hours.

[0038] (4) Part of the mixed liquor in the swing zone 2.6 and the anaerobic zone 2.1 is mixed in the anoxic zone 2.7. At the same time, the sludge from the bottom of the secondary sedimentation tank 3 is also mixed into the anoxic zone 2.7 to ensure that the dissolved oxygen in the anoxic zone 2.7 is less than 0.2 mg / L. The anoxic zone 2.7 and the anoxic zone 2.8 use the ammonia nitrogen from the anaerobic zone 2.1 and the nitrite nitrogen in the mixed liquor to carry out the anaerobic ammonia oxidation reaction. At the same time, the anoxic zone 2.7 and the anoxic zone 2.8 can also provide nitrite nitrogen to the anaerobic ammonia oxidizing bacteria through the short-cut denitrification process. The anaerobic ammonia oxidizing bacteria use the added K2 type biological packing as the attachment carrier and achieve the enrichment of denitrification functional bacteria on it.

[0039] (5) The mixed liquor flowing out of the anoxic zone 2.8 enters the post-aerobic zone 2.9. The residence time of the mixed liquor in the aerobic zone 2.9 is controlled to be 2 hours, and the dissolved oxygen content in the aerobic zone 2.9 is controlled to be 2-3 mg / L. The mixed liquor flowing out of the aerobic zone 2.9 enters the secondary sedimentation tank 3, and sludge-water separation is carried out in the secondary sedimentation tank 3. There is no obvious floating sludge phenomenon in the secondary sedimentation tank 3. The concentration of activated sludge in the bioreactor is monitored daily, and the sludge concentration in the bioreactor is always kept at 3500-4000 mg / L through the secondary sedimentation tank reflux.

[0040] The effluent from the monitoring device contains COD and NH4. + The average effluent concentrations of -N, TN, and TP were 31.76 mg / L, 2.05 mg / L, 7.63 mg / L, and 1.84 mg / L, respectively, with average removal rates of 78.83%, 93.17%, 75.57%, and 38.67%.

[0041] The direct N2O emissions in each zone of the reactor were determined using a gas collection bag and gas chromatography. The results showed that the total N2O emissions were only 1.1 to 1.3% of the influent nitrogen load.

[0042] Example 2

[0043] The device includes a bioreactor with a working volume of 15 m³ and a secondary sedimentation tank with a working volume of 4.8 m³. The bioreactor is divided into an anaerobic zone, a swing zone, an anoxic zone, and an aerobic zone from the influent direction. Sludge is recycled from the secondary sedimentation tank to the front end of the anaerobic zone. The influent is actual municipal wastewater with an average influent COD concentration of 250 mg / L, an average influent ammonia nitrogen concentration of 45 mg / L, an average influent TN concentration of 50 mg / L, and an average influent TP concentration of 5 mg / L. The hydraulic retention time (HRT) of the domestic wastewater in the bioreactor is 18 h, and the sludge retention time (SRT) is approximately 40 days. The zones are anaerobic, swing (aerobic), swing (anoxic), and anoxic. The volume ratio of the anaerobic zone to the aerobic zone is 2:3:1:2:1. The hydraulic retention times of the anaerobic zone, the swaying zone (aerobic), the swaying zone (anoxic), the anoxic zone, and the aerobic zone are 4h, 6h, 2h, 4h, and 2h, respectively. The dissolved oxygen concentration in the three-stage aerobic reactor in the swaying zone increases along the water flow direction. The dissolved oxygen concentration in the first-stage aerobic reactor (swaying zone 1, 2.3) is 0.8–1.0 mg / L, the dissolved oxygen concentration in the second-stage aerobic reactor (swaying zone 2, 2.4) is 1.0–1.2 mg / L, and the dissolved oxygen concentration in the third-stage aerobic reactor (swaying zone 3, 2.5) is 1.2–2.0 mg / L. The hydraulic retention time of each aerobic reactor is 2h.

[0044] (1) During the operation of the device, sludge is discharged normally every day, and the sludge age is controlled at 30 days; at this time, domestic sewage is discharged at a flow rate of 1m³ / h. 3 / h of influent enters anaerobic zone 2.1 and forms a mixed liquor with the sludge returned from secondary sedimentation tank 3. The total retention time of the mixed liquor in the anaerobic zone is controlled to be 4h, and the dissolved oxygen content in the anaerobic zone is kept below 0.2mg / L. Polysaccharitrophs and polyphosphate-accumulating bacteria in the sludge are used to convert the organic matter in the wastewater into an internal carbon source and complete the release of phosphate.

[0045] (2) The mixed liquor enters the swing zone 2.3 (aerobic reaction tank), swing zone 2.4 (aerobic reaction tank), and swing zone 3.5 (aerobic reaction tank) sequentially from anaerobic zone 2.2. The total hydraulic retention time of the mixed liquor in the aerobic reaction tanks (swing zone 2.3, swing zone 2.4, and swing zone 3.5) is controlled to be 6 hours. The dissolved oxygen content in swing zone 2.3 and swing zone 2.4 is controlled to be 0.8-1.2 mg / L, and the dissolved oxygen content in swing zone 3.5 is controlled to be 1.2-2.0 mg / L. Aerobic phosphorus uptake, nitrification, and simultaneous nitrification-denitrification reactions occur in the aerobic reaction tanks of the swing zones. At this time, the denitrification effect of the aerobic reaction tanks of the swing zones is significant. The TN in the effluent of the aerobic reaction tanks of the swing zones is reduced by 20.95 mg / L, and the denitrification contribution rate reaches 41.9%.

[0046] (3) The mixed liquor flowing out of the swing zone 2.5 continues to enter the swing zone 2.6. At this time, there is no aeration in the swing zone 2.6, and the dissolved oxygen content is less than 0.5 mg / L. The total hydraulic residence time of the mixed liquor in the swing zone 2.6 is 2 hours.

[0047] (4) Part of the mixed liquor in the swing zone 2.6 and the anaerobic zone 2.1 is mixed in the anoxic zone 2.7. At the same time, the sludge from the bottom of the secondary sedimentation tank 3 is also mixed into the anoxic zone 2.7 to ensure that the dissolved oxygen in the anoxic zone 2.7 is less than 0.2 mg / L. The anoxic zone 2.7 and the anoxic zone 2.8 use the ammonia nitrogen from the anaerobic zone 2.1 and the nitrite nitrogen in the mixed liquor to carry out the anaerobic ammonia oxidation reaction. At the same time, the anoxic zone 2.7 and the anoxic zone 2.8 can also provide nitrite nitrogen to the anaerobic ammonia oxidizing bacteria through the short-cut denitrification process. The anaerobic ammonia oxidizing bacteria use the added K2 type biological packing as the attachment carrier and achieve the enrichment of denitrification functional bacteria on it.

[0048] (5) The mixed liquor flowing out of the anoxic zone 2.8 enters the post-aerobic zone 2.9. The residence time of the mixed liquor in the aerobic zone 2.9 is controlled to be 2 hours, and the dissolved oxygen content in the aerobic zone 2.9 is controlled to be 2-3 mg / L. The mixed liquor flowing out of the aerobic zone 2.9 enters the secondary sedimentation tank 3, and sludge-water separation is carried out in the secondary sedimentation tank 3. There is no obvious floating sludge phenomenon in the secondary sedimentation tank 3. The concentration of activated sludge in the bioreactor is monitored daily, and the sludge concentration in the bioreactor is always kept at 3500-4000 mg / L through the secondary sedimentation tank reflux.

[0049] The effluent from the monitoring device contains COD and NH4. + The average effluent concentrations of -N, TN, and TP were 23 mg / L, 0.6 mg / L, 5.59 mg / L, and 0.46 mg / L, respectively, with average removal rates of 90.8%, 98.8%, 88.8%, and 90.8%.

[0050] The direct N2O emissions in each zone of the reactor were determined using a static chamber and gas chromatography. The results showed that the total N2O emissions were only 1.2 to 1.3% of the influent nitrogen load.

[0051] Example 3

[0052] The influent flow rate is 24000 m³ / h 3The influent to the device is actual urban sewage, with an average influent COD concentration of 320 mg / L, an average influent ammonia nitrogen concentration of 62 mg / L, an average influent TN concentration of 70 mg / L, and an average influent TP concentration of 6 mg / L. The volume ratio of the anaerobic zone, the swing zone (aerobic zone), the anoxic zone, and the aerobic zone is 2:4:2:1, and the hydraulic retention times of the anaerobic zone, the swing zone (aerobic zone), the anoxic zone, and the aerobic zone are 4 h, 8 h, 4 h, and 2 h, respectively. In the sway zone, the dissolved oxygen concentration in the four-stage aerobic reaction tanks increases along the water flow direction. The dissolved oxygen concentration in the first-stage aerobic reaction tank is 0.8–1.0 mg / L, the dissolved oxygen concentration in the second-stage aerobic reaction tank is 1.0–1.2 mg / L, the dissolved oxygen concentration in the third-stage aerobic reaction tank is 1.2–1.5 mg / L, and the dissolved oxygen concentration in the fourth-stage aerobic reaction tank is 1.5–2.0 mg / L. The hydraulic retention time of each aerobic reaction tank is 2 hours.

[0053] (1) During the operation of the equipment, sludge is discharged normally every day, and the sludge age is controlled at 30 days; at this time, domestic sewage is discharged at a flow rate of 1000m³. 3 / h of influent enters anaerobic zone 2.1 and forms a mixed liquor with the sludge returned from secondary sedimentation tank 3. The total retention time of the mixed liquor in the anaerobic zone is controlled to be 4h, and the dissolved oxygen content in the anaerobic zone is kept below 0.2mg / L. Polysaccharitrophs and polyphosphate-accumulating bacteria in the sludge are used to convert the organic matter in the wastewater into an internal carbon source and complete the release of phosphate.

[0054] (2) The mixed liquor enters the swing zone 1 (aerobic reaction tank), swing zone 2 (aerobic reaction tank), swing zone 3 (aerobic reaction tank), and swing zone 4 (aerobic reaction tank) sequentially from anaerobic zone 2.2. The total hydraulic retention time of the mixed liquor in the aerobic reaction tanks (swing zone 1 2.3, swing zone 2 2.4, swing zone 3 2.5 and swing zone 4 2.6) is controlled to be 8h. The dissolved oxygen content in swing zone 1 2.3 and swing zone 2 2.4 is controlled to be 0.8-1.2mg / L, and the dissolved oxygen content in swing zone 3 2.5 and swing zone 4 2.6 is controlled to be 1.2-2.0mg / L. Aerobic phosphorus uptake, nitrification and simultaneous nitrification-denitrification reactions occur in the aerobic reaction tanks of the swing zones. At this time, the denitrification effect of the aerobic reaction tanks of the swing zones is significant. The TN in the effluent of the aerobic reaction tanks of the swing zones is reduced by 39.83mg / L, and the denitrification contribution rate reaches 56.9%.

[0055] (3) Part of the mixed liquor in the swing zone 2.6 and the anaerobic zone 2.1 is mixed in the anoxic zone 2.7. At the same time, the sludge from the bottom of the secondary sedimentation tank 3 is also mixed into the anoxic zone 2.7 to ensure that the dissolved oxygen in the anoxic zone 2.7 is less than 0.2 mg / L. The anoxic zone 2.7 and the anoxic zone 2.8 use the ammonia nitrogen from the anaerobic zone 2.1 and the nitrite nitrogen in the mixed liquor to carry out the anaerobic ammonia oxidation reaction. At the same time, the anoxic zone 2.7 and the anoxic zone 2.8 can also provide nitrite nitrogen to the anaerobic ammonia oxidizing bacteria through the short-cut denitrification process. The anaerobic ammonia oxidizing bacteria use the added K2 type biological packing as the attachment carrier and achieve the enrichment of denitrification functional bacteria on it.

[0056] (4) The mixed liquor flowing out of the anoxic zone 2.8 enters the post-aerobic zone 2.9. The residence time of the mixed liquor in the aerobic zone 2.9 is controlled to be 2 hours, and the dissolved oxygen content in the aerobic zone 2.9 is controlled to be 2-3 mg / L. The mixed liquor flowing out of the aerobic zone 2.9 enters the secondary sedimentation tank 3, and sludge-water separation is carried out in the secondary sedimentation tank 3. There is no obvious floating sludge phenomenon in the secondary sedimentation tank 3. The concentration of activated sludge in the bioreactor is monitored daily, and the sludge concentration in the bioreactor is always 3500-4000 mg / L through the secondary sedimentation tank reflux.

[0057] The effluent from the monitoring device contains COD and NH4. + The average effluent concentrations of -N, TN, and TP were 16 mg / L, 0.17 mg / L, 5.87 mg / L, and 0.12 mg / L, respectively, with average removal rates of 95.0%, 99.7%, 91.6%, and 98.0%.

[0058] The direct N2O emissions in each zone of the reactor were determined using a static chamber and gas chromatography. The results showed that the total N2O emissions were only 1.1 to 1.3% of the influent nitrogen load.

Claims

1. A denitrification method for a biological denitrification device used in wastewater with a low carbon-to-nitrogen ratio, characterized in that: The biological denitrification device includes a raw water tank (1), a bioreactor (2), and a secondary sedimentation tank (3) connected in sequence; wherein, the bioreactor (2) includes an anaerobic zone, a swing zone, an anoxic zone, and an aerobic zone in sequence; the swing zone is equipped with a four-stage reaction tank; the secondary sedimentation tank (3) is connected to the anaerobic zone through a first sludge return pump (3.2), and the secondary sedimentation tank (3) is connected to the final stage reaction tank of the swing zone through a second sludge return pump (3.1), while the anaerobic zone is connected to the final stage reaction tank of the swing zone through a bypass pump (2.13); The denitrification method based on the above-mentioned biological denitrification device includes the following steps: (1) The water in the raw water tank enters the anaerobic zone of the bioreactor through the inlet pump. At the same time, the concentrated sludge at the bottom of the secondary sedimentation tank is pumped into the anaerobic zone of the bioreactor through the first sludge return pump. The hydraulic retention time of the anaerobic zone is controlled to be 4 h, and the dissolved oxygen content of the anaerobic zone is controlled to be less than 0.2 mg / L. (2) Wastewater from the anaerobic zone flows into the swing zone. The dissolved oxygen concentration and hydraulic retention time of each stage of the reaction tank in the swing zone are adjusted based on the influent water quality. Specifically, when the COD in the influent is 100~200 mg / L, TP is 2~3 mg / L, and NH4+ is... + When -N is 20~30mg / L and TN is 25~30mg / L, the first two stages of the four-stage reaction tanks in the swing zone are set as aerobic tanks, and the last two stages are set as anoxic tanks. The dissolved oxygen concentration in the two aerobic reaction tanks increases along the water flow direction. The dissolved oxygen concentration in the first aerobic reaction tank is 0.8~1.2mg / L, and the dissolved oxygen concentration in the last aerobic reaction tank is 1.0~2.0mg / L. The hydraulic retention time of each aerobic reaction tank is 2h. When the influent COD is 200~300 mg / L, TP is 3~5 mg / L, and NH4+ is... + When -N is 35~50 mg / L and TN is 40~55 mg / L, the first three reaction tanks in the four-stage split reaction tank of the swing zone are set as aerobic tanks, and the last reaction tank is set as anoxic tank. The dissolved oxygen concentration in the three aerobic reaction tanks increases along the water flow direction. The dissolved oxygen concentration in the first aerobic reaction tank is 0.8~1.0 mg / L, the dissolved oxygen concentration in the second aerobic reaction tank is 1.0~1.2 mg / L, and the dissolved oxygen concentration in the third aerobic reaction tank is 1.2~2.0 mg / L. The hydraulic retention time of each aerobic reaction tank is 2 hours. When the influent COD > 300 mg / L, TP > 5 mg / L, NH4 + When -N>50mg / L and TN>55mg / L, all four reaction tanks in the four-stage split reaction tank of the swing zone are set as aerobic tanks. The dissolved oxygen concentration of the four aerobic reaction tanks increases along the water flow direction. The dissolved oxygen concentration of the first aerobic reaction tank is 0.8~1.0mg / L, the dissolved oxygen concentration of the second aerobic reaction tank is 1.0~1.2mg / L, the dissolved oxygen concentration of the third aerobic reaction tank is 1.2~1.5mg / L, and the dissolved oxygen concentration of the fourth aerobic reaction tank is 1.5~2.0mg / L. The hydraulic retention time of each aerobic reaction tank is 2h. (3) Wastewater from the swing zone flows into the anoxic zone; the total hydraulic retention time in the anoxic zone is controlled to be 4 hours; in the anoxic zone, ammonia nitrogen from the anaerobic zone overflow and nitrite nitrogen from the swing zone are used for anaerobic ammonia oxidation reaction, and nitrite nitrogen is also provided to the anaerobic ammonia oxidizing bacteria through a short-cut denitrification process in the anoxic zone. (4) Wastewater from the anoxic zone enters the aerobic zone, where nitrification, short-cut nitrification and aerobic phosphorus uptake occur; (5) Wastewater in the aerobic zone enters the secondary sedimentation tank through the overflow pipe, where mud and water are separated. The supernatant is discharged through the drain pipe, and the concentrated sludge at the bottom is returned to the anaerobic zone and the end swing zone.

2. The denitrification method for a biological denitrification device for low C / N ratio wastewater according to claim 1, characterized in that: K2 type biological packing material (2.15) was added to at least the primary reaction tank and the anoxic zone in the swing zone.

3. The denitrification method for a biological denitrification device for low C / N ratio wastewater according to claim 2, characterized in that: The dosage of K2 type biological packing is 15% of the reaction tank volume.

4. The denitrification method for a biological denitrification device for low C / N ratio wastewater according to claim 1, characterized in that: The anaerobic zone, swaying zone, anoxic zone and aerobic zone are all equipped with a stirring device (2.10) and an aeration device (2.11).

5. The denitrification method for a biological denitrification device for low C / N ratio wastewater according to claim 1, characterized in that: In step (1), the sludge used for inoculation is sludge from the reactor of an urban sewage treatment plant. The carbon source absorption rate in the anaerobic zone reaches 90% and the denitrification rate in the anoxic zone reaches 80%, which indicates that the sludge has matured.

6. The denitrification method for a biological denitrification device for low C / N ratio wastewater according to claim 1, characterized in that: In step (4), the hydraulic retention time in the aerobic zone is 2 hours; the dissolved oxygen content in the aerobic zone (2.9) is controlled to be 2~3 mg / L.

7. The denitrification method for a biological denitrification device for low C / N ratio wastewater according to claim 1, characterized in that: In step (5), the concentrated sludge at the bottom of the secondary sedimentation tank is returned to the anaerobic zone and the end swing zone, so that the concentration of activated sludge in the bioreactor is 2500~4000 mg / L.

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