A synchronous nitrification and denitrification activated sludge method O-type biochemical device and sewage treatment method

Abstract

The application discloses a kind of synchronous nitrification denitrification activated sludge process O-type biochemical device and sewage treatment method, the O-type biochemical device includes: one completely mixed O-type biochemical reactor (2);Aeration device is arranged at the bottom of the O-type biochemical reactor (2), for providing oxygen or air to mixed liquor;Stirring device (6) is arranged in the O-type biochemical reactor (2);Dissolved oxygen detection and control unit includes the dissolved oxygen on-line monitor (7) being arranged in the O-type biochemical reactor (2), and the automatic control system being signal connected with the dissolved oxygen on-line monitor (7) and aeration device;Sedimentation tank (10) is connected with the water outlet of the O-type biochemical reactor (2);Sludge return device (12).The application is for the C / N of sewage 1.8~3, to complete denitrification function, also need not additional carbon source.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment, specifically to an activated sludge O-type bioreactor that simultaneously performs nitrification and denitrification. Background Technology

[0002] The activated sludge process, a major wastewater treatment technology, has a history of over a hundred years. Based on its specific nitrogen and phosphorus removal functions, it is divided into two types: AAO (anaerobic-anoxic-aerobic) and AOA (anaerobic-aerobic-anoxic). Specific processes include three forms: plug-flow activated sludge process, oxidation ditch activated sludge process, and sequencing batch activated sludge process. Nitrogen removal functions are divided into AO (anoxic-aerobic) and OA (aerobic-anoxic) types. Plug-flow and oxidation ditch processes each involve two independent biological treatment tanks (or zones), A tank (zone) and O tank (zone). The O tank (zone) performs aerobic nitrification, while the A tank (zone) performs anoxic denitrification. Regardless of whether the A tank (zone) or the O tank (zone) comes first, it is essentially asynchronous nitrification and denitrification. Although the sequencing batch process has a single biological treatment tank (or zone) spatially, it operates in an alternating anoxic-aerobic mode through automatic control, thus also belonging to asynchronous nitrification and denitrification in terms of time.

[0003] The characteristics of asynchronous nitrification-denitrification include: ① low sludge load, hydraulic retention time (HRT) ≥ 16h, and large biological reactor volume; ② air-to-water ratio greater than 6:1, resulting in high energy consumption; ③ low utilization rate of internal carbon sources in denitrification, requiring a C / N ratio ≥ 4, often necessitating the addition of external carbon sources. This leads to high sludge production and, due to the addition of external carbon sources, high effluent COD and suboptimal effluent quality. Furthermore, the system has a long carbon footprint and generates a large amount of CO2, which is detrimental to carbon neutrality.

[0004] Currently, the wastewater treatment process for simultaneous nitrification and denitrification (SND) is typically researched and applied in practice. This involves cultivating a biofilm using various types of packing materials or carriers. A dissolved oxygen concentration gradient exists on the surface and inside the biofilm, creating an aerobic-anoxic microenvironment. The microorganisms in the biofilm then undergo simultaneous nitrification and denitrification reactions. This type of SND is a microscopic-level process. In activated sludge systems, research and application of macroscopically stable and reliable SND are relatively limited. Summary of the Invention

[0005] The main objective of this invention is to provide an activated sludge O-type bioreactor that simultaneously performs nitrification and denitrification, in order to solve at least one of the problems in the prior art.

[0006] The technical solution of the present invention is as follows:

[0007] A simultaneous nitrification and denitrification activated sludge O-type biological reactor, comprising:

[0008] A fully mixed O-type bioreactor (2) is used to contain the mixture of activated sludge and wastewater, and serves as the main site where nitrification and denitrification reactions occur simultaneously.

[0009] An aeration device is installed at the bottom of the O-type bioreactor (2) to provide oxygen or air to the mixture;

[0010] A stirring device (6) is installed inside the O-type bioreactor (2) to ensure that the mixture is in a fully mixed state.

[0011] The dissolved oxygen detection and control unit includes an online dissolved oxygen monitor (7) installed in the O-type bioreactor (2), and an automatic control system connected to the online dissolved oxygen monitor (7) and the aeration device. The automatic control system is configured to dynamically adjust the aeration rate according to the dissolved oxygen monitoring value to maintain the dissolved oxygen concentration in the O-type bioreactor (2) at a constant value. Different wastewaters correspond to different dissolved oxygen levels, with a minimum of 0.5 mg / L and a maximum of 1.8 mg / L. The system is configured to achieve symbiosis between nitrifying and denitrifying bacteria under the dissolved oxygen concentration range, and to simultaneously carry out nitrification and denitrification reactions.

[0012] A sedimentation tank (10) is connected to the outlet of the O-type bioreactor (2) for separating mud and water from the mixture from the bioreactor;

[0013] A sludge return device (12) is used to return at least a portion of the settled sludge at the bottom of the sedimentation tank (10) to the O-type bioreactor (2).

[0014] Furthermore, the dissolved oxygen detection and control unit is configured to stably maintain the dissolved oxygen concentration within the range of 0.8 mg / L to 1.0 mg / L.

[0015] The term "fully mixed" in this invention refers to the complete mixing of wastewater with the original mixed liquid in the tank after the wastewater enters the bioreactor, resulting in a uniform composition of the mixed liquid in the tank.

[0016] Furthermore, the sludge return device (12) is configured with a return ratio of 50% to 100%.

[0017] Furthermore, the hydraulic residence time (HRT) of the O-type bioreactor (2) is designed to be less than or equal to 10 hours.

[0018] Furthermore, the system is configured to treat wastewater with a carbon-to-nitrogen ratio (C / N) between 1.8 and 3.0, and to achieve total nitrogen compliance without the need for the addition of an external carbon source.

[0019] Furthermore, the aeration device is a disc-type microporous aerator (4), and the stirring device (6) is an underwater stirrer.

[0020] Another objective of this invention is to provide a method for treating wastewater by simultaneous nitrification and denitrification based on low dissolved oxygen control, comprising the following steps:

[0021] (a) System startup and sludge acclimatization phase:

[0022] Inoculated sludge was added to a completely mixed bioreactor, and the sludge concentration in the mixed liquor was controlled at 3000-6000 mg / L;

[0023] The wastewater to be treated is introduced, and aeration is carried out during or after the water intake process.

[0024] During the simmering process, the dissolved oxygen concentration in the bioreactor is stably maintained in the range of 0.8 mg / L to 1.0 mg / L by controlling the aeration rate for 40 to 50 days, so as to cultivate a special microbial community suitable for simultaneous nitrification and denitrification in a low dissolved oxygen environment.

[0025] Stop aeration, let it settle, and drain the supernatant;

[0026] (b) Formal Operation Phase:

[0027] Wastewater to be treated is continuously or intermittently introduced into the acclimatized bioreactor, and stirring is maintained to keep the mixture in a fully mixed state.

[0028] By monitoring online and automatically controlling the aeration rate, the dissolved oxygen concentration in the bioreactor is stably maintained within the range of 0.5 mg / L to 1.8 mg / L. Under the dissolved oxygen concentration conditions, the microbial community cultivated in step (a) is used to oxidize ammonia nitrogen in wastewater into nitrate nitrogen in an aerobic environment. At the same time, the nitrate nitrogen is reduced into nitrogen gas by denitrifying bacteria in an anaerobic environment formed inside the activated sludge flocs, thereby realizing the simultaneous occurrence of nitrification and denitrification reactions in a single reactor.

[0029] Further, in step (b), the dissolved oxygen concentration is stably maintained in the range of 0.8 mg / L to 1.0 mg / L.

[0030] Furthermore, in step (b), the hydraulic residence time in the bioreactor is less than or equal to 10 hours.

[0031] Furthermore, in step (b), wastewater with a carbon-to-nitrogen ratio between 1.8 and 3.0 is treated, and total nitrogen is achieved without the need for the addition of exogenous carbon.

[0032] Furthermore, the overall gas-to-water ratio in step (b) is less than 3:1.

[0033] Furthermore, in step (b), following the simultaneous reaction step, the following is also included:

[0034] The mixture is introduced into a sedimentation tank for mud-water separation to obtain supernatant and settled sludge.

[0035] At least a portion (e.g., 70%-90%) of the settled sludge is returned to the bioreactor.

[0036] Beneficial effects

[0037] Compared with the prior art, the present invention has the following advantages:

[0038] 1. Because nitrification and denitrification occur simultaneously, and nitrifying and denitrifying bacteria are interdependent, meaning an infinite number of nitrification and denitrification processes take place within the same biological reactor, almost all nitrate nitrogen can be utilized through denitrification. The nitrogen removal rate lim(1- →→1 (when n→∞), the denitrification rate is close to 100%.

[0039] 2. Because nitrification and denitrification occur simultaneously, and nitrifying and denitrifying bacteria are interdependent, the dissolved oxygen can be controlled at DO≈0.5mg / L-1.8mg / L (the dissolved oxygen of the same type of water is constant) for different water qualities, and the air-to-water ratio is ≈2.5:1, which can greatly save energy consumption.

[0040] 3. The biological reactor is a completely mixed type, with good mass transfer. For wastewater with a C / N ratio of 1.8-3, denitrification can be achieved without the need for an external carbon source. Therefore, it features high sludge loading, good microbial activity, low residual sludge, and good effluent quality.

[0041] 4. The hydraulic retention time (HRT) of the bioreactor is ≤10h, requiring a small volume, which significantly reduces the construction area and cost.

[0042] 5. The completely mixed biological reactor has a uniform sludge load, and the dissolved oxygen in the O-type biological reactor is constant, with the dissolved oxygen concentration remaining unchanged over time. Therefore, the bioreactor has a high volume utilization rate;

[0043] 6. The system has a high degree of automation. Online pollutant and material indicators monitoring instruments are installed at both the influent and effluent. Through inductive transmission system and digital-analog logic, intelligent calculation and other methods, the system can correct deviations in operation in a timely manner, maintain the ecological balance of the system, and ensure that the effluent water quality meets the standards. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the results of the activated sludge O-type bioreactor for simultaneous nitrification and denitrification according to the present invention.

[0045] 1- Metering pump; 2- Completely mixed O-type biological reactor body; 3- Blower; 4- Disc microporous aerator; 5- First mixer; 6- Second mixer; 7- DO meter; 8- Effluent weir; 9- Control valve; 10- Vertical flow sedimentation tank; 11- Sludge discharge valve; 12- Sludge return pump; 13- Sludge discharge pipe. Detailed Implementation

[0046] Example 1

[0047] See Figure 1 The present invention relates to a fully mixed O-type bioreactor, comprising a fully mixed O-type bioreactor body 2. As the main container where nitrification and denitrification reactions occur simultaneously, the reactor cross-section can be circular, square, or annular, and its internal flow pattern is fully mixed. In a specific embodiment of the present invention, a circular cross-section is used.

[0048] An aeration device, located at the bottom of the fully mixed O-type bioreactor body 2, is used to supply oxygen or air to the mixed liquid. Preferably, the aeration device is a disc-type microporous aerator 4 to provide fine, uniform bubbles. The disc-type microporous aerator 4 is externally connected to a blower 3.

[0049] A stirring device is installed inside the main body 2 of the fully mixed O-type bioreactor to ensure complete mixing of the liquid, prevent sludge sedimentation, and promote mass transfer. The stirrer is an underwater low-speed propeller. It includes at least a first stirring mixer 5 located at the bottom and a second stirring mixer 6 located at the top, and these two stirring mixers are arranged opposite each other to ensure thorough mixing of the internal fluids.

[0050] Dissolved oxygen detection and control unit, the unit includes:

[0051] Dissolved oxygen online monitoring instrument 7 is installed inside the fully mixed O-type bioreactor body 2;

[0052] An automatic control system, such as a PLC, is connected to the dissolved oxygen online monitor 7 and the aeration device, such as the blower 3.

[0053] Traditional knowledge and common practice in this field indicate that efficient carbon oxidizers, or aerobic nitrification tanks, typically have dissolved oxygen (DO) control targets above 2.0 mg / L. This is because low DO (<1.0 mg / L) is generally considered to strongly inhibit nitrifying bacteria activity, leading to system denitrification failure. Existing aeration tanks are designed to provide a uniform aerobic environment, and their control systems (such as DO control) are typically set above 2.0 mg / L to ensure nitrification efficiency. However, this invention, through the specific structure of a "completely mixed reactor," precisely maintains a narrow low DO window, creating a unique ecological environment conducive to the symbiotic relationship between nitrifying and denitrifying bacteria, thus achieving macroscopically simultaneous nitrification and denitrification effects.

[0054] The fully mixed O-type bioreactor also includes:

[0055] A vertical flow sedimentation tank 10 is connected to the outlet of the fully mixed O-type biological reactor body 2 for mud-water separation. The outlet is an outlet weir 8 located in the upper part of the fully mixed O-type biological reactor body 2.

[0056] The sludge return device 12 is used to return a portion of the settled sludge at the bottom of the vertical flow sedimentation tank 10 to the fully mixed O-type bioreactor body 2.

[0057] This invention also includes an automatic control system, which is specially configured and programmed to overcome the conventional practice of maintaining dissolved oxygen (DO) above 2.0 mg / L. Instead, it treats DO as a process parameter that needs to be precisely stabilized within a "suboptimal nitrification level." Various existing technologies can be used to control the dissolved oxygen concentration within this range, depending on the process requirements. For example, the control system can employ various algorithms (such as fuzzy PID control or model predictive control), with the core control logic being to "stablely suppress and maintain the dissolved oxygen concentration in the reactor within a narrow range of 0.5 mg / L to 1.8 mg / L," a control logic that is diametrically opposed to that of conventional aeration tanks.

[0058] The system, through the coordinated operation of the aforementioned units, is configured to achieve symbiosis between nitrifying and denitrifying bacteria within the dissolved oxygen concentration range of 0.5-1.8 mg / L, and to simultaneously carry out nitrification and denitrification reactions.

[0059] This invention provides a wastewater treatment method with a short process, low energy consumption, no need for external carbon sources, and low sludge production. This method cultivates a special microbial community through a unique sludge acclimation stage, and achieves stable simultaneous nitrification and denitrification in a completely mixed reactor through precise control of dissolved oxygen during the formal operation phase. The method comprises two main stages:

[0060] (a) System startup and sludge acclimatization stage

[0061] This stage is crucial to the success of this invention, and its purpose is to cultivate and domesticate special nitrifying and denitrifying bacteria that can adapt to and work efficiently in low dissolved oxygen environments and have synergistic effects.

[0062] Inoculation sludge: Inoculation sludge (preferably dewatered sludge from a municipal wastewater treatment plant) is added to a completely mixed bioreactor, and the mixed liquor sludge concentration (MLSS) is controlled within the range of 3000-6000 mg / L.

[0063] Sedentary aeration cultivation: Wastewater to be treated is introduced, and sedentary aeration (i.e., no water is introduced or discharged, only aeration and stirring) is performed during or after the influent flow. During this process, the dissolved oxygen concentration in the bioreactor is stably maintained within a narrow range of 0.5 mg / L to 1.8 mg / L for 24 to 72 hours by precisely controlling the aeration rate. Examples include 0.6 mg / L, 0.7 mg / L, 0.8 mg / L, 0.9 mg / L, 1.0 mg / L, 1.1 mg / L, 1.2 mg / L, 1.3 mg / L, 1.4 mg / L, 1.5 mg / L, 1.6 mg / L, and 1.7 mg / L.

[0064] The selection of this DO range (0.5-1.8 mg / L) is an equilibrium point verified through extensive experiments. When DO is below 0.5 mg / L, the nitrification process will be inhibited; when DO is above 1.8 mg / L, oxygen or air will penetrate the sludge flocs, disrupting the internal anoxic microenvironment, and denitrification will terminate.

[0065] Sedimentation and sludge removal: Stop aeration, let it settle for 1.5-2.5 hours, and remove the supernatant and floating sludge rich in inert substances and unadapted bacteria.

[0066] Commissioning phase: Inlet water volume 1-3 m³ 3 The blower is controlled by an online DO meter to maintain dissolved oxygen in the biological reactor at a level of 0.5-1.8 mg / L per hour. The mixing agitator in the biological reactor is constantly running. The supernatant flows into the vertical flow sedimentation tank. The total nitrogen concentration of the effluent from the vertical flow sedimentation tank is measured. If the total nitrogen concentration does not meet the standard, the effluent is returned to the biological reactor for further denitrification. 100% of the sludge from the bottom of the vertical flow sedimentation tank is returned to the biological reactor.

[0067] The acclimatization period (40-50 days) ensures sufficient succession and adaptation of the microbial community. If the time is shorter than this, the microbial community will not be stable; if the time is longer than this, it may lead to nutrient deficiency and sludge aging.

[0068] Preferably, the dissolved oxygen detection and control unit is configured to stably maintain the dissolved oxygen concentration within a more favorable range of 0.8 mg / L to 1.0 mg / L.

[0069] (b) Formal Operation Phase

[0070] After successfully acclimating the sludge, the system entered formal operation.

[0071] Continuous operation: The wastewater to be treated is continuously or intermittently fed into the acclimatized bioreactor, and stirring is maintained to keep the mixture in a fully mixed state.

[0072] Precise DO control: The aeration rate is dynamically adjusted through an online dissolved oxygen monitor and an automatic control system to stably maintain the dissolved oxygen concentration in the reactor within the range of 0.5 mg / L to 1.8 mg / L (preferably 0.8 mg / L to 1.0 mg / L).

[0073] Simultaneous reaction: Under the above DO conditions, utilizing the special microbial community formed during the acclimation stage, ammonia nitrogen in the wastewater is oxidized to nitrate nitrogen by nitrifying bacteria in the aerobic environment outside the sludge flocs. Simultaneously, this nitrate nitrogen diffuses into the anoxic environment formed inside the sludge flocs and is reduced to nitrogen gas by denitrifying bacteria. Nitrification and denitrification occur simultaneously in the same reactor and at the same time.

[0074] Subsequent treatment: The mixed liquor after the reaction enters the sedimentation tank for sludge-water separation. The supernatant is discharged as treated effluent or reused, a portion of the settled sludge is discharged as excess sludge, and most of it (return ratio 50%-150%) is returned to the bioreactor via a sludge return pump to maintain a high biomass in the system.

[0075] Example 2: Treatment of urban domestic sewage using the apparatus of Example 1 of the present invention

[0076] Engineering Experiment:

[0077] Inlet water volume: 1.125m³ 3 / h, influent water quality: domestic sewage COD concentration 105mg / L, BOD5 concentration 55mg / L, SS concentration 48mg / L, ammonia nitrogen concentration 35mg / L, total nitrogen concentration 43mg / L. This water quality is typical of low C / N domestic sewage, with a C / N ratio of 2.44.

[0078] Bioreactor effective volume 9m 3 The water residence time (HRT) was 10 hours, and the dissolved oxygen (DO) concentration was 0.9 mg / L.

[0079] Domestic sewage enters the biological treatment unit via a metering pump, where it is aerated and activated by a blower and microporous aerator. A stirrer further mixes the liquid to ensure complete mixing. Simultaneous nitrification and denitrification occur within the integrated biological treatment unit. Dissolved oxygen is monitored online and controlled at 0.9 mg / L. Nitrifying bacteria utilize oxygen or air to degrade ammonia nitrogen, while denitrifying bacteria use the sewage's own carbon source to convert nitrate nitrogen into nitrogen gas, thus completing denitrification. After 10 hours of reaction, the mixed liquid flows through an effluent weir into a vertical flow sedimentation tank for sludge-water separation. The supernatant is the denitrified effluent, and a small portion of the settled sludge is discharged as excess sludge, while the majority (80%) is returned to the biological treatment unit via a sludge return pump.

[0080] The specific system startup steps are as follows:

[0081] Inoculation with sludge: The above-mentioned urban domestic sewage is introduced into the biological treatment unit and inoculated with dewatered sludge from the municipal sewage treatment plant. The sludge concentration is controlled at 4500 mg / L, and the mixture is aerated for 24 hours. The dissolved oxygen is controlled between 0.8 mg / L and 1.0 mg / L.

[0082] After a day of simmering, stop aeration and let it settle for 2 hours. Then drain the supernatant and surface sludge from the bioreactor.

[0083] Commissioning phase: Inlet water volume 1.125m³ 3 The blower is controlled by an online DO meter to maintain dissolved oxygen in the biological reactor at a level of 0.9 mg / L per hour. The mixing agitator in the biological reactor is constantly on. The supernatant flows into the vertical flow sedimentation tank. The total nitrogen concentration of the effluent from the vertical flow sedimentation tank is measured. If the total nitrogen concentration does not meet the standard, the effluent is returned to the biological reactor for further denitrification. 100% of the sludge from the bottom of the vertical flow sedimentation tank is returned to the biological reactor.

[0084] Operational Phase: After 45 days of commissioning, the nitrifying and denitrifying bacteria in the bioreactor have completed their acclimatization and are now in formal operation. Inlet water flow: 1.125 m³. 3 The system maintains a constant flow rate of 10 h, with DO controlled at 0.9 mg / L, a hydraulic retention time of 10 h, a sludge return ratio of 80%, and all effluent indicators meeting standards. The system's effluent quality is as follows: COD concentration ≤ 23 mg / L, SS concentration ≤ 15 mg / L, ammonia nitrogen concentration ≤ 1 mg / L, and total nitrogen concentration ≤ 1.5-6 mg / L.

[0085] It is worth noting that the denitrifying bacteria acclimated in the O-type biological reactor are facultative bacteria. When the influent C / N ratio is greater than 4 and the carbon source is sufficient, even if the dissolved oxygen is at a level of 4-5 mg / L, it can still effectively carry out denitrification and achieve a good total nitrogen removal effect, with the total nitrogen in the effluent below 6 mg / L.

[0086] Currently, in treating domestic sewage with low C / N ratios, the common practice in this field is to control dissolved oxygen above 2.0 mg / L and add an external carbon source to ensure that total nitrogen meets the standards.

[0087] Comparative experiment: For urban domestic sewage with the same water quality, after the total nitrogen in the effluent met the standard under the above operating conditions, the aeration rate of the blower was increased to maintain the dissolved oxygen in the biological reactor at 2.5 mg / L, the sludge return ratio at 80%-100%, and the system was operated for 45 days. The effluent water quality of the system was as follows: COD concentration at 20-25 mg / L, SS concentration at 12-15 mg / L, ammonia nitrogen concentration at 1-3 mg / L, and total nitrogen concentration at 20-28 mg / L.

[0088] Therefore, for wastewater with a low C / N ratio, if dissolved oxygen is maintained at a relatively high level (DO ≥ 2.0 mg / L), carbon-oxidizing bacteria will rapidly consume the dissolved oxygen in the water due to their rapid growth rate (short generation time, approximately 20-30 minutes) and large numbers, leading to localized hypoxia. This severely inhibits the activity of nitrifying bacteria, as nitrifying bacteria grow slowly (generation time can be over 10 hours) and are at a disadvantage in the competition for oxygen. Furthermore, carbon-oxidizing bacteria consume a large amount of carbon source in the wastewater, causing denitrifying bacteria to grow slowly and be at a disadvantage in the competition for carbon source.

[0089] The above description is merely a preferred embodiment of the present invention, and therefore should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the patent and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A simultaneous nitrification and denitrification activated sludge O-type biological reactor, characterized in that, include: A fully mixed O-type bioreactor (2) is used to contain the mixture of activated sludge and wastewater, and serves as the main site where nitrification and denitrification reactions occur simultaneously. An aeration device is installed at the bottom of the O-type bioreactor (2) to provide oxygen or air to the mixture; A stirring device (6) is installed inside the O-type bioreactor (2) to ensure that the mixture is in a fully mixed state. The dissolved oxygen detection and control unit includes an online dissolved oxygen monitor (7) installed in the O-type bioreactor (2) and an automatic control system connected to the online dissolved oxygen monitor (7) and the aeration device. The automatic control system is configured to dynamically adjust the aeration rate according to the dissolved oxygen monitoring value so as to stably maintain the dissolved oxygen concentration in the O-type bioreactor (2) at a constant value. Different wastewaters correspond to different dissolved oxygen levels, with a minimum of not less than 0.5 mg / L and a maximum of not more than 1.8 mg / L. The system is configured to achieve symbiosis between nitrifying bacteria and denitrifying bacteria under the dissolved oxygen concentration conditions, and to simultaneously carry out nitrification and denitrification reactions. A sedimentation tank (10) is connected to the outlet of the O-type bioreactor (2) for separating mud and water from the mixture from the bioreactor; A sludge return device (12) is used to return at least a portion of the settled sludge at the bottom of the sedimentation tank (10) to the O-type bioreactor (2).

2. The activated sludge O-type biological reactor for simultaneous nitrification and denitrification according to claim 1, characterized in that, The dissolved oxygen detection and control unit is configured to stably maintain the dissolved oxygen concentration within the range of 0.8 mg / L to 1.0 mg / L.

3. The activated sludge O-type biological reactor for simultaneous nitrification and denitrification according to claim 1, characterized in that, The sludge return device (12) is configured to have a return ratio of 50% to 100%.

4. The activated sludge O-type biological reactor for simultaneous nitrification and denitrification according to claim 1, characterized in that, The hydraulic residence time (HRT) of the O-type bioreactor (2) is designed to be less than or equal to 10 hours.

5. The activated sludge O-type biological reactor for simultaneous nitrification and denitrification according to claim 1, characterized in that, The system is configured to treat wastewater with a carbon-to-nitrogen ratio (C / N) between 1.8 and 3.0, and to achieve total nitrogen compliance without the need for the addition of an external carbon source.

6. The activated sludge O-type biological reactor for simultaneous nitrification and denitrification according to claim 1, characterized in that, The aeration device is a disc-type microporous aerator (4), and the stirring device (6) is an underwater stirrer.

7. A method for treating wastewater through simultaneous nitrification and denitrification based on low dissolved oxygen control, comprising the following steps: (a) System startup and sludge acclimatization phase: Inoculate sludge into a completely mixed bioreactor and control the sludge concentration in the mixed liquor at 3000-6000 mg / L; The wastewater to be treated is introduced, and aeration is carried out during or after the water intake process. During the simmering process, the dissolved oxygen concentration in the bioreactor is stably maintained in the range of 0.8 mg / L to 1.0 mg / L by controlling the aeration rate for 40 to 50 days, so as to cultivate a special microbial community suitable for simultaneous nitrification and denitrification in a low dissolved oxygen environment. Stop aeration, let it settle, and drain the supernatant; (b) Formal Operation Phase: Wastewater to be treated is continuously or intermittently introduced into the acclimatized bioreactor, and stirring is maintained to keep the mixture in a fully mixed state. By monitoring online and automatically controlling the aeration rate, the dissolved oxygen concentration in the bioreactor is stably maintained within the range of 0.5 mg / L to 1.8 mg / L. Under the dissolved oxygen concentration conditions, the microbial community cultivated in step (a) is used to oxidize ammonia nitrogen in wastewater into nitrate nitrogen in an aerobic environment. At the same time, the nitrate nitrogen is reduced into nitrogen gas by denitrifying bacteria in an anaerobic environment formed inside the activated sludge flocs, thereby realizing the simultaneous occurrence of nitrification and denitrification reactions in a single reactor.

8. The method according to claim 7, characterized in that, In step (b), wastewater with a carbon-to-nitrogen ratio between 1.8 and 3.0 is treated, and total nitrogen is achieved without the need for the addition of exogenous carbon.

9. The method according to claim 7, characterized in that, The overall gas-water ratio in step (b) is less than 3:

1.

10. The method according to claim 7, characterized in that, In step (b), following the simultaneous reaction step, the following is also included: The mixture is introduced into a sedimentation tank for mud-water separation to obtain supernatant and settled sludge. At least a portion of the settled sludge is returned to the bioreactor.

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