Biological denitrification device and denitrification method for sewage with low carbon nitrogen ratio

Abstract

The invention discloses a biological denitrification device and a denitrification method for sewage with a low carbon-nitrogen ratio. The denitrification device comprises a raw water tank, a bioreactor and a secondary sedimentation tank which are connected in sequence, wherein the bioreactor sequentially comprises an anaerobic zone, a swing zone, an anoxic zone and an aerobic zone; the swing area is provided with four stages of reaction tanks which are arranged in a split mode, and the dissolved oxygen concentration and the hydraulic retention time of each stage of reaction tank are adjusted based on the inflow water quality. When the system disclosed by the invention is used for treating sewage with a low carbon-nitrogen ratio, an exogenous carbon source does not need to be added through a specific technological process, so that the operation cost of the system is remarkably reduced, and efficient biological phosphorus removal can be realized while the nitrogen removal efficiency is remarkably improved.

Description

Technical Field

[0001] The present invention relates to a biological nitrogen removal device for sewage with a low carbon-nitrogen ratio, and also relates to a nitrogen removal method based on the above nitrogen removal device. Background Art

[0002] Traditional biological nitrogen removal processes include A / O (Anaerobic / Oxic) process, A / A / O (Anaerobic / Anoxic / Oxic) process, Oxidation Ditch (OD) process, etc. After decades of development, the above processes have been very mature and have good nitrogen removal effects. However, the above processes generally have disadvantages such as long flow paths, large reactors, large floor areas, the need for additional carbon sources, high energy consumption, and high costs, and it is difficult to meet the increasingly strict standards.

[0003] For example, the oxidation ditch process has a simple structure and a relatively high sludge concentration to improve the treatment capacity, but it has poor adaptability to fluctuations in sewage quality and poor treatment effects under high pollution loads. At the same time, the energy consumption of the aeration system is relatively high, and the long-term operating cost is relatively large. Compared with the oxidation ditch process, the AAO process is more widely used. It connects the anaerobic, aerobic, and anoxic reaction zones in series, and has a series of advantages such as simple structure, short total hydraulic retention time, low control complexity, and not easy to cause sludge bulking, and has become one of the most widely used synchronous nitrogen and phosphorus removal processes in current urban sewage treatment plants. However, its disadvantage is the high energy consumption of the aeration reflux system. The C / N of municipal sewage is relatively low, and the lack of carbon source will lead to poor nitrogen removal effect of the AAO process, while adding an external carbon source will greatly increase the operating cost of the system. Summary of the Invention

[0004] Object of the Invention: The object of the present invention is to provide a biological nitrogen removal device for sewage with a low carbon-nitrogen ratio. Another object of the present invention is to provide a nitrogen removal method based on the above nitrogen removal device. When treating sewage with a low carbon-nitrogen ratio, the present invention realizes the need not to add an external carbon source through a specific process, thereby significantly reducing the operating cost of the system, and at the same time can achieve efficient biological phosphorus removal while significantly improving the nitrogen removal efficiency.

[0005] Technical Solution: The biological nitrogen removal device for sewage with a low carbon-nitrogen ratio described in the present invention includes a raw water tank, a biological reactor, and a secondary sedimentation tank connected in sequence; wherein, the biological reactor is an ASAO biological reactor, which sequentially includes an anaerobic zone, a swing zone, an anoxic zone, and an aerobic zone, and the total hydraulic retention time of the biological reactor is 18 h; the swing zone is provided with four reaction pools arranged separately, and the dissolved oxygen concentration and hydraulic retention time of each reaction pool are adjusted based on the influent water quality;

[0006] When the COD in the influent is 100-200 mg / L, the TP is 2-3 mg / L, and the NH4 +- When the COD is 200 - 300 mg / L, TP is 3 - 5 mg / L, NH₄-N is 20 - 30 mg / L, and TN is 25 - 30 mg / L, the volume ratio of the anaerobic zone, the swing zone (aerobic), the swing zone (anoxic), the anoxic zone, and the aerobic zone corresponding reaction tanks is 2:2:2:2:1. The hydraulic retention times of the anaerobic zone, the swing zone (aerobic), the swing zone (anoxic), the anoxic zone, and the aerobic zone are 4 h, 4 h, 4 h, 4 h, and 2 h respectively. The dissolved oxygen concentration in the two - stage aerobic reaction tanks in the swing zone shows an increasing trend 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 of each stage of the aerobic reaction tank is 2 h;

[0007] When the influent COD is 200 - 300 mg / L, TP is 3 - 5 mg / L, NH₄ + - When the COD is 200 - 300 mg / L, TP is 3 - 5 mg / L, NH₄-N is 35 - 50 mg / L, and TN is 40 - 55 mg / L, the volume ratio of the anaerobic zone, the swing zone (aerobic zone), the swing zone (anoxic), the anoxic zone, and the aerobic zone corresponding reaction tanks is 2:3:1:2:1. The hydraulic retention times of the anaerobic zone, the swing zone (aerobic), the swing zone (anoxic), the anoxic zone, and the aerobic zone are 4 h, 6 h, 2 h, 4 h, and 2 h respectively. The dissolved oxygen concentration in the three - stage aerobic reaction tanks in the swing zone shows an increasing trend 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 of each stage of the aerobic reaction tank is 2 h;

[0008] When the influent COD > 300 mg / L, TP > 5 mg / L, NH₄ + - When the influent COD > 300 mg / L, TP > 5 mg / L, NH₄-N > 50 mg / L, and TN > 55 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. The hydraulic retention times of the anaerobic zone, the swing zone (aerobic), the anoxic zone, and the aerobic zone are 4 h, 8 h, 4 h, and 2 h respectively. The dissolved oxygen concentration in the four - stage aerobic reaction tanks in the swing zone shows an increasing trend 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 stage of the aerobic reaction tank is 2 h.

[0009] Among them, K2 - type biological fillers are added to at least one - stage reaction tank in the swing zone and the anoxic zone.

[0010] Among them, the dosage of the K2 - type biological filler is 15% of the volume of the reaction tank.

[0011] Among them, stirring devices and aeration devices are provided in the anaerobic zone, the swing zone, the anoxic zone and the aerobic zone.

[0012] Among them, the secondary sedimentation tank is connected to the anaerobic zone through a first sludge return pump, and the secondary sedimentation tank is connected to the last-stage reaction tank of the swing zone through a second sludge return pump. At the same time, the anaerobic zone is connected to the last-stage reaction tank of the swing zone through a bypass pump (allowing some of the nutrients at the front end to bypass the swing zone and directly enter the subsequent anoxic zone to provide COD and ammonia nitrogen for the operation of the anoxic zone), providing the anoxic mixed liquid of the anaerobic zone for the last-stage reaction tank of the swing zone and the subsequent anoxic zone.

[0013] The nitrogen removal method based on the above nitrogen removal device is specifically as follows:

[0014] (1) The water in the raw water tank enters the anaerobic zone of the ASAO bioreactor through a feed pump. At the same time, the concentrated sludge at the bottom of the secondary sedimentation tank is pumped into the anaerobic zone of the ASAO bioreactor through a first sludge return pump. The hydraulic retention time of the anaerobic zone is controlled to be 4 h, and the dissolved oxygen content in the anaerobic zone is controlled to be less than 0.2 mg / L (the anaerobic zone is not aerated, and usually the dissolved oxygen content is lower than 0.2 mg / L); the glycan-accumulating organisms and polyphosphate-accumulating organisms in the sludge are used to convert the organic matter in the sewage into an internal carbon source and complete the release of phosphate.

[0015] (2) The sewage in the anaerobic zone flows into the swing zone. The swing zone adjusts the number of aerated split reaction tanks in the swing zone and the aeration intensity therein according to the influent water quality and quantity: the overall hydraulic retention time of the swing zone is 8 h, and the total hydraulic retention time of the aerated reaction tanks is 4 - 8 h. The dissolved oxygen concentration in the aerated reaction tanks in the swing zone is controlled to be 0.8 - 2.0 mg / L by adjusting the aeration intensity.

[0016] (3) The sewage in the swing zone flows into the anoxic zone; the total hydraulic retention time of the anoxic zone is controlled to be 4 h. In the anoxic zone, anaerobic ammonium oxidation reaction is carried out using the ammonia nitrogen from the anaerobic zone bypass flow and the nitrite nitrogen from the swing zone. At the same time, in the anoxic zone, nitrite nitrogen can also be provided for anaerobic ammonium oxidizing bacteria through the short-cut denitrification process. The anaerobic ammonium oxidizing bacteria take the added K2-type biological filler as an attachment carrier and achieve enrichment thereon.

[0017] (4) The sewage in the anoxic zone enters the aerobic zone, where nitrification reaction, short-cut nitrification reaction and aerobic phosphorus uptake occur.

[0018] (5) The sewage in the aerobic zone enters the secondary sedimentation tank through an overflow pipe, where the separation of sludge and water is realized. The supernatant is discharged through a drain pipe, and the concentrated sludge at the bottom is refluxed to the anaerobic zone and the last-stage swing zone, so that the concentration of activated sludge in the bioreactor is 2500 - 4000 mg / L.

[0019] Among them, in step (1), the inoculated sludge is the sludge from the reactor of a municipal domestic sewage treatment plant. 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 domestication is mature.

[0020] Among them, in step (4), the hydraulic retention time of the aerobic zone is 2 h; 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 remarkable advantages:

[0022] (1) Compared with the traditional AAO process, by optimizing the operating conditions of the device, the present invention can achieve the domestication and enrichment of nitrifying and denitrifying bacteria and endogenous denitrifying bacteria, so as to utilize endogenous carbon source for denitrification, cancel the addition of exogenous carbon source, and greatly reduce the operating cost and carbon emission of the system;

[0023] (2) The operating conditions of the device of the present invention can promote the enrichment of key functional bacteria groups (low DO conditions are beneficial to the enrichment of simultaneous nitrification and denitrification bacteria, endogenous denitrifying bacteria, etc.). While significantly improving the denitrification efficiency, it can also achieve efficient biological phosphorus removal through the denitrifying phosphorus removal process;

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

[0025] (4) The present invention sets a swing zone (S) in the biological reactor, so that according to different influent water quality conditions, by changing the volume and aeration intensity of the aerobic zone in the swing zone, the entire reaction device can be adjusted to operate in different modes, and 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 according to the influent water situation and the aeration intensity can be adjusted, so as to effectively save aeration energy consumption and avoid aeration waste. Description of the Drawings

[0026] Figure 1 It is the structural schematic diagram of the denitrification device of the present invention. Detailed Embodiments

[0027] Such as Figure 1As shown in the figure, the biological nitrogen removal device of the present invention for low carbon-nitrogen ratio sewage includes a raw water tank 1, a biological reactor 2, and a secondary sedimentation tank 3 connected in sequence. Among them, the biological reactor 2 is an ASAO biological reactor, which successively includes an anaerobic zone, a swing zone, an anoxic zone, and an aerobic zone. Among them, the anaerobic zone includes an anaerobic zone 2.1 and an anaerobic zone 2.2 connected in sequence. The swing zone includes a swing zone 2.3, a swing zone 2.4, a swing zone 2.5, and a swing zone 2.6 connected in sequence. The anoxic zone is successively connected to an anoxic zone 2.7 and an anoxic zone 2.8. The aerobic zone 2.9 is connected to the secondary sedimentation tank 3 through an overflow pipe 2.14. The secondary sedimentation tank 3 is connected to the anaerobic zone 2.1 through a first sludge return pump 3.2, and the secondary sedimentation tank 3 is connected to the swing zone 2.6 through a second sludge return pump 3.1. At the same time, the anaerobic zone 2.1 is connected to the swing zone 2.6 through a bypass sludge pump 2.13. The effluent of the secondary sedimentation tank 3 is discharged through a drain pipe 3.3.

[0028] Stirring devices 2.10 and aeration discs 2.11 are provided in the anaerobic zone 2.1, the anaerobic zone 2.2, the swing zone 2.3, the swing zone 2.4, the swing zone 2.5, the swing zone 2.6, the anoxic zone 2.7, the anoxic zone 2.8, and the aerobic zone 2.9. The biological nitrogen removal device of the present invention further includes an aeration pump 2.12, and the aeration pump 2.12 is connected to the aeration disc 2.11 through a rotor flowmeter 2.16.

[0029] K2 type biological fillers 2.15 are added to the swing zone 2.6, the anoxic zone 2.7, and the anoxic zone 2.8. The size of the K2 type biological fillers 2.15 is 6 holes. The filling amount of the K2 type biological fillers 2.15 in the swing zone 2.6, the anoxic zone 2.7, and the anoxic zone 2.8 is 15% of the reaction chamber volume.

[0030] Example 1

[0031] The nitrogen removal method based on the above biological nitrogen removal device is specifically as follows:

[0032] The influent water quality simulates municipal low C / N sewage. The nitrogen source and carbon source 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, the influent TN concentration is 30 mg / L, and 1 mL of trace element solution is added to each liter of simulated wastewater.

[0033] The sludge of the reactor of the urban domestic sewage treatment plant is inoculated in the reaction device. 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 domestication is mature. The specific domestication process is as follows:

[0034] The activated sludge used in this embodiment is sourced from a domestic sewage treatment plant in Nanjing, which adopts a pretreatment - oxidation ditch (OD) biological treatment process. The secondary sedimentation tank sludge obtained is first filtered through a stainless steel mesh sieve with a pore size of 1.0 mm to remove impurities, and then washed 3 times with deionized water; then it is inoculated into the bioreactor of the present invention; the above - simulated domestic sewage is used as the influent, and the concentration of the inoculated sludge is about 4 g MLSS / L (4000 mg / L); the volume ratio of the anaerobic zone, the swinging zone (aerobic), the swinging zone (anoxic), the anoxic zone, and the aerobic zone is 2:2:2:2:1, and the hydraulic retention times of the anaerobic zone, the swinging zone (aerobic), the swinging zone (anoxic), the anoxic zone, and the aerobic zone are 4 h, 4 h, 4 h, 4 h, and 2 h respectively. The dissolved oxygen concentration in the two - stage aerobic reaction tanks in the swinging zone shows an increasing trend along the water flow direction. The dissolved oxygen concentration in the first - stage aerobic reaction tank (swinging zone 1 2.3) is 0.8 - 1.2 mg / L, and the dissolved oxygen concentration in the second - stage aerobic reaction tank (swinging zone 2 2.4) is 1.0 - 2.0 mg / L. The hydraulic retention time of each stage of the aerobic reaction tank is 2 h; during the above operation process, low - oxygen aeration conditions are adopted to facilitate 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 marks the maturity of sludge domestication; at this time, the device has been running 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. The normal sludge discharge is 2 L - 2.5 L per day, and the sludge age is controlled at 30 days; at this time, the simulated domestic sewage enters the anaerobic zone 1 2.1 at a flow rate of 1 L / h, and forms a mixed liquid with the sludge refluxed from the secondary sedimentation tank 3 into the anaerobic zone 1 2.1. The total retention time of the mixed liquid in the anaerobic zone is controlled at 4 h, and the dissolved oxygen content in the anaerobic zone is ensured to be lower than 0.2 mg / L. The glycan - accumulating bacteria and polyphosphate - accumulating bacteria in the sludge are used to convert the organic matter in the sewage into internal carbon sources and complete the release of phosphate.

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

[0037] (3) The mixed liquid 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, it is controlled that 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 retention time of the mixed liquid in the third swing zone 2.5 and the fourth swing zone 2.6 is 4 h;

[0038] (4) Part of the mixed liquid in the fourth swing zone 2.6 and the first anaerobic zone 2.1 is mixed in the first anoxic zone 2.7. At the same time, the sludge from the bottom of the secondary sedimentation tank 3 is also mixed into the first anoxic zone 2.7 to ensure that the dissolved oxygen in the first anoxic zone 2.7 is less than 0.2 mg / L. The first anoxic zone 2.7 and the second anoxic zone 2.8 utilize the ammonia nitrogen in the first anaerobic zone 2.1 and the nitrite nitrogen in the mixed liquid for anaerobic ammonium oxidation reaction. At the same time, in the first anoxic zone 2.7 and the second anoxic zone 2.8, nitrite nitrogen can also be provided for anaerobic ammonium oxidizing bacteria through the short-cut denitrification process. The anaerobic ammonium oxidizing bacteria use the added K2 type biological filler as the attachment carrier, and the denitrification functional flora is enriched on it;

[0039] (5) The mixed liquid flowing out from the second anoxic zone 2.8 enters the post-aerobic zone 2.9. The residence time of the mixed liquid in the aerobic zone 2.9 is controlled to be 2 h, and the dissolved oxygen content in the aerobic zone 2.9 is controlled to be 2 - 3 mg / L. The mixed liquid flowing out from the aerobic zone 2.9 enters the secondary sedimentation tank 3, and solid-liquid 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 maintained at 3500 - 4000 mg / L through the return of the secondary sedimentation tank.

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

[0041] The direct emissions of N2O in each area of the reactor are measured by using a gas collection bag and gas chromatography. The results show that the total emissions of N2O are only 1.1 - 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 water inlet direction; sludge is refluxed from the secondary sedimentation tank to the front end of the anaerobic zone; the influent of the device is actual municipal sewage, 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 domestic sewage in the bioreactor is 18 h, and the sludge retention time (SRT) is about 40 d; the volume ratio of the anaerobic zone, swing zone (aerobic zone), swing zone (anoxic), anoxic zone, and aerobic zone is 2:3:1:2:1, and the hydraulic retention times of the anaerobic zone, swing zone (aerobic), swing zone (anoxic), anoxic zone, and aerobic zone are 4 h, 6 h, 2 h, 4 h, and 2 h respectively. The dissolved oxygen concentration in the three-stage aerobic reaction tank in the swing zone shows an increasing trend along the water flow direction. The dissolved oxygen concentration in the first-stage aerobic reaction tank (swing zone 1 2.3) is 0.8 - 1.0 mg / L, the dissolved oxygen concentration in the second-stage aerobic reaction tank (swing zone 2 2.4) is 1.0 - 1.2 mg / L, and the dissolved oxygen concentration in the third-stage aerobic reaction tank (swing zone 3 2.5) is 1.2 - 2.0 mg / L. The hydraulic retention time of each stage of the aerobic reaction tank is 2 h;

[0044] (1) During the operation of the device, normal sludge discharge is carried out daily, and the sludge age is controlled at 30 days; at this time, domestic sewage is fed into anaerobic zone 1 2.1 at a flow rate of 1 m 3 / h, and forms a mixed liquid with the sludge refluxed from the secondary sedimentation tank 3 into anaerobic zone 1 2.1. The total retention time of the mixed liquid in the anaerobic zone is controlled at 4 h, and the dissolved oxygen content in the anaerobic zone is ensured to be lower than 0.2 mg / L. The glycan-accumulating organisms and polyphosphate-accumulating organisms in the sludge are used to convert the organic matter in the sewage into internal carbon sources and complete the release of phosphate;

[0045] (2) The mixed liquid sequentially enters swing zone 1 2.3 (aerobic reaction tank), swing zone 2 2.4 (aerobic reaction tank), and swing zone 3 2.5 (aerobic reaction tank) from anaerobic zone 2 2.2. The total hydraulic retention time of the mixed liquid in the aerobic reaction tank (swing zone 1 2.3, swing zone 2 2.4, and swing zone 3 2.5) is controlled at 6 h, and the dissolved oxygen content in swing zone 1 2.3 and swing zone 2 2.4 is controlled at 0.8 - 1.2 mg / L, and the dissolved oxygen content in swing zone 3 2.5 is controlled at 1.2 - 2.0 mg / L. Aerobic phosphorus uptake reaction, nitrification reaction, and simultaneous nitrification and denitrification reaction occur in the aerobic reaction tank in the swing zone. At this time, the denitrification effect of the aerobic reaction tank in the swing zone is significant. The TN in the effluent of the aerobic reaction tank in the swing zone is reduced by 20.95 mg / L, and the denitrification contribution rate reaches 41.9%;

[0046] (3) The mixed liquid flowing out of the swing zone 2.5 continues to enter the swing zone 2.6. At this time, it is controlled that there is no aeration in the swing zone 2.6, and its dissolved oxygen content is less than 0.5 mg / L. The total hydraulic retention time of the mixed liquid in the swing zone 2.6 is 2 h;

[0047] (4) Part of the mixed liquid 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 utilize the ammonia nitrogen in the anaerobic zone 2.1 and the nitrite nitrogen in the mixed liquid to carry out the anaerobic ammonium oxidation reaction. At the same time, in the anoxic zone 2.7 and the anoxic zone 2.8, the nitrite nitrogen can also be provided for the anaerobic ammonium oxidizing bacteria through the short-cut denitrification process. The anaerobic ammonium oxidizing bacteria use the added K2 type biological filler as the attachment carrier, and the denitrifying functional flora is enriched on it;

[0048] (5) The mixed liquid flowing out of the anoxic zone 2.8 enters the post-aerobic zone 2.9. The residence time of the mixed liquid in the aerobic zone 2.9 is controlled to be 2 h, and the dissolved oxygen content in the aerobic zone 2.9 is controlled to be 2 - 3 mg / L. The mixed liquid flowing out of the aerobic zone 2.9 enters the secondary sedimentation tank 3, and the mud-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 the activated sludge in the bioreactor is monitored daily, and the sludge concentration in the bioreactor is always 3500 - 4000 mg / L through the reflux of the secondary sedimentation tank.

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

[0050] The direct emissions of N2O in each area of the reactor are measured by using a static chamber and gas chromatography. The results show that the total emissions of N2O are only 1.2 - 1.3% of the influent nitrogen load.

[0051] Example 3

[0052] The influent flow rate is 24000 m 3 / d, the influent water of 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), the anoxic zone, and the aerobic zone are 4 h, 8 h, 4 h, and 2 h respectively. The dissolved oxygen concentration in the four-stage aerobic reaction tank in the swing zone shows an increasing trend 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 stage of the aerobic reaction tank is 2 h;

[0053] (1) During the operation of the device, normal sludge discharge is carried out daily, and the sludge age is controlled at 30 days; at this time, domestic sewage is fed into anaerobic zone 2.1 at a flow rate of 1000 m 3 / h, and forms a mixed solution with the sludge refluxed from the secondary sedimentation tank 3 into anaerobic zone 2.1. The total retention time of the mixed solution in the anaerobic zone is controlled at 4 h, and the dissolved oxygen content in the anaerobic zone is ensured to be lower than 0.2 mg / L. The glycan-accumulating organisms and polyphosphate-accumulating organisms in the sludge are used to convert the organic matter in the sewage into an internal carbon source and complete the release of phosphate;

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

[0055] (3) Part of the mixed liquor in the swinging four - zone 2.6 and the anaerobic first - zone 2.1 is mixed in the anoxic first - zone 2.7. At the same time, the sludge from the bottom of the secondary sedimentation tank 3 is also mixed into the anoxic first - zone 2.7, ensuring that the dissolved oxygen in the anoxic first - zone 2.7 is less than 0.2 mg / L. The anoxic first - zone 2.7 and the anoxic second - zone 2.8 utilize the ammonia nitrogen in the anaerobic first - zone 2.1 and the nitrite nitrogen in the mixed liquor for the anaerobic ammonium oxidation reaction. At the same time, in the anoxic first - zone 2.7 and the anoxic second - zone 2.8, nitrite nitrogen can also be provided for the anaerobic ammonium - oxidizing bacteria through the shortcut denitrification process. The anaerobic ammonium - oxidizing bacteria use the added K2 - type biological packing as the attachment carrier, and the denitrifying functional flora is enriched on it;

[0056] (4) The mixed liquor flowing out of the anoxic second - 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 h, 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 solid - liquid separation is carried out in the secondary sedimentation tank 3, and 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 maintained at 3500 - 4000 mg / L through the return of the secondary sedimentation tank.

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

[0058] The direct emissions of N2O in each area of the reactor are measured by using a static chamber and gas chromatography. The results show that the total emissions of N2O are only 1.1 - 1.3% of the influent nitrogen load.

Claims

1. A biological denitrification device for low carbon-nitrogen ratio sewage, characterized by: It comprises a raw water tank (1), a bioreactor (2) and a secondary sedimentation tank (3) which are connected in sequence; wherein the bioreactor (2) comprises an anaerobic zone, a swing zone, an anoxic zone and an aerobic zone in sequence; the swing zone is provided with a four-stage split reaction tank, and the dissolved oxygen concentration and hydraulic retention time of each stage of the reaction tank are adjusted based on the influent water quality.

2. The biological denitrification device for low carbon-nitrogen ratio sewage according to claim 1, characterized in that: 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 of the influent is 100-200 mg / L, TP is 2-3 mg / L, NH4 + -N is 20-30 mg / L, TN is 25-30 mg / L, the first two reaction pools in the four-stage split reaction pool in the swing zone are set as aerobic pools, and the last two reaction pools are set as anoxic pools. The dissolved oxygen concentration of the two aerobic reaction pools increases along the water flow direction. The dissolved oxygen concentration of the first aerobic reaction pool is 0.8-1.2 mg / L, and the dissolved oxygen concentration of the last aerobic reaction pool is 1.0-2.0 mg / L. The hydraulic retention time of each aerobic reaction pool is 2 hours. When the COD of the influent is 200-300 mg / L, TP is 3-5 mg / L, NH4 + -N is 35-50mg / L, TN is 40-55mg / L, the first three reaction pools in the four-stage split reaction pool in the swing zone are set as aerobic pools, and the last reaction pool is set as anoxic pool. The dissolved oxygen concentration of the three-stage aerobic reaction pool increases along the water flow direction. The dissolved oxygen concentration of the first-stage aerobic reaction pool is 0.8-1.0mg / L, the dissolved oxygen concentration of the second-stage aerobic reaction pool is 1.0-1.2mg / L, and the dissolved oxygen concentration of the third-stage aerobic reaction pool is 1.2-2.0mg / L. The hydraulic retention time of each aerobic reaction pool is 2h; When COD>300mg / L, TP>5mg / L, NH4 + -N>50mg / L, TN>55mg / L, the four reaction pools in the four-level split reaction pools in the swing zone are all set as aerobic pools, and the dissolved oxygen concentration of the four aerobic reaction pools increases along the water flow direction. The dissolved oxygen concentration of the first aerobic reaction pool is 0.8-1.0mg / L, the dissolved oxygen concentration of the second aerobic reaction pool is 1.0-1.2mg / L, the dissolved oxygen concentration of the third aerobic reaction pool is 1.2-1.5mg / L, and the dissolved oxygen concentration of the fourth aerobic reaction pool is 1.5-2.0mg / L. The hydraulic retention time of each aerobic reaction pool is 2h.

3. The biological denitrification device for low carbon-nitrogen ratio sewage according to claim 1, characterized in that: K2 type biological filler (2.15) is added to at least one primary reaction tank in the swing zone and the anoxic zone.

4. The biological denitrification device for low carbon-nitrogen ratio sewage according to claim 3, characterized in that: The dosage of K2 type biological filler is 15% of the reaction tank volume.

5. The biological denitrification device for low carbon-nitrogen ratio sewage according to claim 1, characterized in that: The anaerobic zone, the swaying zone, the anoxic zone and the aerobic zone are all provided with a stirring device (2.10) and an aeration device (2.11).

6. The biological denitrification device for low carbon-nitrogen ratio sewage according to claim 1, characterized in that: The secondary sedimentation tank (3) is connected to the anaerobic zone via a first sludge return pump (3.2), the secondary sedimentation tank (3) is connected to the final reaction tank of the swing zone via a second sludge return pump (3.1), and the anaerobic zone is connected to the final reaction tank of the swing zone via an overrunning pump (2.13).

7. The denitrification method based on the denitrification device according to claim 1, characterized in that: The steps include: (1) The water in the raw water tank enters the anaerobic zone of the bioreactor through the water inlet pump, and 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 hours, and the dissolved oxygen content in the anaerobic zone is controlled to be less than 0.2 mg / L; (2) The sewage from the anaerobic zone flows into the swing zone. The number of aeration split reaction tanks in the swing zone and the aeration intensity therein are adjusted according to the influent water quality and water volume: the hydraulic retention time of the swing zone as a whole is 8 hours, of which the total hydraulic retention time of the aeration reaction tank is 4 to 8 hours. By adjusting the aeration intensity, the dissolved oxygen concentration of the aeration reaction tank in the swing zone is controlled at 0.8 to 2.0 mg / L; (3) The sewage in the swing zone flows into the anoxic zone; the total hydraulic retention time in the anoxic zone is controlled to be 4 hours; (4) The sewage in the anoxic zone enters the aerobic zone, where nitrification and short-range nitrification reactions occur and aerobic phosphorus absorption occurs; (5) The sewage in the aerobic zone enters the secondary sedimentation tank through the overflow pipe, where the mud and water are separated. The supernatant is discharged through the drain pipe, and the concentrated sludge at the bottom flows back to the anaerobic zone and the terminal swing zone.

8. The denitrification method of the denitrification device according to claim 7, characterized in that: In step (1), the inoculated sludge is the sludge from the reactor of the urban domestic sewage plant. The carbon source absorption rate in the anaerobic zone reaches 90% and the endogenous denitrification rate in the anoxic zone reaches 80%, indicating that the sludge is mature.

9. The denitrification method of the denitrification device according to claim 7, characterized in that: In step (4), the hydraulic retention time of the aerobic zone is 2 hours; and the dissolved oxygen content of the aerobic zone (2.9) is controlled to be 2 to 3 mg / L.

10. The denitrification method of the denitrification device according to claim 7, 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 terminal swing zone, so that the concentration of the activated sludge in the bioreactor is 2500-4000 mg / L.

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