Return sludge hydrolysis enhanced denitrification system and method, and multi-mode switchable biological denitrification system and method

Abstract

The invention provides a backflow sludge hydrolysis enhanced denitrification system and method and a multi-mode switchable biological denitrification system and method, and relates to the technical field of urban sewage treatment and recycling, the backflow sludge hydrolysis enhanced denitrification system comprises a biochemical tank and a secondary sedimentation tank which are connected in sequence; the biochemical tank comprises a first biochemical grid tank, a second biochemical grid tank, a third biochemical grid tank and a fourth biochemical grid tank which are connected in sequence; a sludge return pipeline is arranged between the bottom of the secondary sedimentation tank and the first biochemical grid tank; wherein the first biochemical grid tank is a sludge hydrolysis area and is used for hydrolyzing sludge from the secondary sedimentation tank; the second biochemical cell is an anaerobic zone, is connected with a domestic sewage conveying pipeline, and is used for receiving domestic sewage and sludge from the first biochemical cell and carrying out anaerobic treatment; the third biochemical cell is an aerobic zone and is used for receiving the sewage treated by the second biochemical cell and carrying out aerobic treatment on the sewage; the fourth biochemical cell is a rear anoxic zone and is used for receiving the sewage treated by the third biochemical cell and carrying out anoxic treatment on the sewage.

Description

Technical Field

[0001] The present invention relates to the technical field of urban sewage treatment and resource utilization, and in particular to a return sludge hydrolysis enhanced denitrification system and method, and a multi-mode switchable biological denitrification system and method. Background Art

[0002] With the acceleration of urbanization, the demand for domestic sewage treatment continues to increase, and the removal of nitrogen from sewage, in particular, has become a key issue in wastewater treatment. In the current field of environmental governance, existing water treatment processes face severe challenges in the face of complex conditions such as fluctuating temperatures and significant changes in total nitrogen content. This is particularly true for water bodies with a carbon-nitrogen ratio of less than 3. The unique chemical composition of these water bodies makes it difficult for traditional water treatment methods to achieve the desired treatment results.

[0003] Among the many problems, the treatment of water bodies with low carbon-nitrogen ratios is particularly difficult. Existing water treatment processes, such as the activated sludge process and the biofilm process, often rely on the metabolism of microorganisms to remove organic matter and nitrogen from sewage. However, when the influent C / N ratio is extremely low (generally less than 3), the limited carbon source in the influent is preferentially used by denitrifying bacteria to remove nitrates (from sludge return or mixed liquor return) that are returned to the anaerobic zone, resulting in the inability of polyphosphate organisms (PAOs) to fully store internal carbon sources (such as PHB) in the anaerobic zone; at the same time, the competition for carbon sources between denitrification and phosphorus release further reduces the organic matter available for denitrification in the anoxic zone, ultimately leading to a simultaneous decrease in the denitrification and phosphorus removal efficiencies of the system.

[0004] Overall, existing water treatment technologies are unable to simultaneously meet the requirements for multiple wastewater treatment standards. On the one hand, traditional biological treatment processes are ineffective for treating wastewater with a low carbon-to-nitrogen ratio, resulting in effluent quality that fails to meet environmental standards. On the other hand, while chemical treatment methods can address some special wastewaters, they are costly and may cause secondary pollution. Therefore, to address these challenges, it is crucial to develop an efficient, cost-effective denitrification process suitable for low-carbon-to-nitrogen ratio influent. Summary of the Invention

[0005] The purpose of the present invention is to provide a return sludge hydrolysis enhanced denitrification system and method, and a multi-mode switchable biological denitrification system and method, which solves the problem that when the influent C / N ratio is low, the limited carbon source cannot completely remove the nitrate in the return flow in the anaerobic zone, resulting in the anaerobic zone being unable to fully utilize its internal carbon source storage function, thereby affecting the denitrification effect of the entire system.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The present invention provides a return sludge hydrolysis enhanced denitrification system, comprising a biochemical tank and a secondary sedimentation tank connected in sequence;

[0008] The biochemical pool includes a first biochemical cell pool, a second biochemical cell pool, a third biochemical cell pool and a fourth biochemical cell pool connected in sequence, and a sludge return pipeline is provided between the bottom of the secondary sedimentation tank and the first biochemical cell pool;

[0009] Among them, the first biochemical tank is the sludge hydrolysis area, which is used to hydrolyze the sludge from the secondary sedimentation tank;

[0010] The second biochemical cell is an anaerobic zone, which is connected to the domestic sewage delivery pipeline and is used to receive domestic sewage and sludge from the first biochemical cell and perform anaerobically treatment on the domestic sewage;

[0011] The third biochemical cell is an aerobic zone, which is used to receive the sewage treated by the second biochemical cell and perform aerobic treatment on it;

[0012] The fourth biochemical cell is a post-anoxic zone, which is used to receive the sewage treated by the third biochemical cell and perform anoxic treatment on it.

[0013] Furthermore, based on the above technical solution, the carbon-nitrogen ratio of the domestic sewage is lower than 3.

[0014] Furthermore, based on the above technical solution, a first stirrer is provided in the first biochemical cell;

[0015] And / or, the second biochemical cell is provided with a second water inlet valve and a second agitator;

[0016] And / or, a first aeration system is provided in the third biochemical cell;

[0017] And / or, a third agitator is provided in the fourth biochemical cell;

[0018] And / or, a sludge return valve is provided on the sludge return pipeline between the first biochemical cell and the secondary sedimentation tank.

[0019] The present invention also provides a method for enhanced denitrification by hydrolysis of return sludge, which is carried out using the above-mentioned system for enhanced denitrification by hydrolysis of return sludge, and comprises the following steps:

[0020] Domestic sewage enters the second biochemical cell, which is an anaerobic zone. The domestic sewage mainly undergoes anaerobic phosphorus release and organic matter hydrolysis in the second biochemical cell;

[0021] After staying in the second biochemical tank for 1.5-2 hours, the domestic sewage enters the third biochemical tank. The third biochemical tank is an aerobic zone, where the domestic sewage mainly undergoes nitrification reaction.

[0022] Domestic sewage stays in the third biochemical tank for 3-5 hours before entering the fourth biochemical tank. The fourth biochemical tank is an anoxic zone, where domestic sewage mainly undergoes endogenous denitrification.

[0023] Domestic sewage stays in the fourth biochemical cell for 4.5-8.5 hours before entering the secondary sedimentation tank. Domestic sewage settles in the secondary sedimentation tank and returns to the first biochemical cell after the sludge concentration at the bottom of the secondary sedimentation tank reaches the requirement. The first biochemical cell is the sludge hydrolysis area. The returned sludge first undergoes denitrification reaction and then hydrolysis of organic matter in the first biochemical cell. The returned sludge stays in the first biochemical cell for 1.5-2 hours before entering the second biochemical cell to provide a carbon source for anaerobic phosphorus release and hydrolysis of organic matter in the second biochemical cell.

[0024] Furthermore, based on the above technical solution, the first agitator provided in the first biochemical cell is operated continuously or intermittently, preferably intermittently, and the alternating time of the intermittent operation is set to be off for 5-23 hours / on for 0.5-1 hour;

[0025] The sum of the sludge retention time in the first biochemical cell and the total retention time of the sewage in the second, third and fourth biochemical cells is 12-16 hours;

[0026] And / or, the domestic sewage is settled in the secondary sedimentation tank for 2-4 hours.

[0027] Furthermore, based on the above technical solution, the dissolved oxygen concentration in the aerobic zone is controlled to be 0.5-4 mg / L by the first aeration system;

[0028] and / or, the sludge concentration of the return sludge is 8000-15000 mg / L,

[0029] and / or, the sludge return ratio is 50-150%,

[0030] and / or, the surface load of the secondary sedimentation tank is 0.6 to 1.5 m 3 / (m 2 ·h).

[0031] The present invention also provides a multi-mode switchable biological denitrification system, which comprises a biochemical tank and a secondary sedimentation tank connected in sequence;

[0032] The biochemical pool includes a first biochemical cell pool, a second biochemical cell pool, a third biochemical cell pool and a fourth biochemical cell pool connected in sequence, and a sludge return pipeline is provided between the bottom of the secondary sedimentation tank and the first biochemical cell pool;

[0033] According to the influent water quality, the multi-mode switchable biological denitrification system can be switched to any one of the first to third subsystems.

[0034] The first subsystem is the return sludge hydrolysis enhanced denitrification system as described above;

[0035] In the second subsystem, the first biochemical cell is an anaerobic zone, which is used to receive the domestic sewage to be treated and perform anaerobically treatment on it. The second biochemical cell is an anoxic zone, which is used to receive the sewage treated by the first biochemical cell and perform anoxic treatment on it. The third and fourth biochemical cells are both aerobic zones, and the sewage from the second biochemical cell flows through the third and fourth biochemical cells in sequence for aerobic treatment.

[0036] In the third subsystem, the first biochemical grid pool is an anaerobic zone, which is used to receive the domestic sewage to be treated and perform anaerobically treatment on it. The second biochemical grid pool is an anaerobic zone, which is used to receive the sewage treated by the first biochemical grid pool and perform anaerobically treatment on it. The third biochemical grid pool is an aerobic zone, which is used to receive the sewage treated by the second biochemical grid pool and perform aerobic treatment on it. The fourth biochemical grid pool is a post-anoxic zone, which is used to receive the sewage treated by the third biochemical grid pool and perform anoxic treatment on it.

[0037] On the basis of the above technical solution, the first biochemical cell is provided with a first water inlet valve and a first agitator;

[0038] And / or, the second biochemical cell is provided with a second water inlet valve and a second agitator;

[0039] And / or, a first aeration system is provided in the third biochemical cell;

[0040] And / or, the fourth biochemical cell is provided with a third agitator and a second aeration system;

[0041] And / or, a sludge return valve is provided on the sludge return pipeline between the first biochemical cell and the secondary sedimentation tank.

[0042] The present invention also provides a multi-mode switchable biological denitrification method, including three operating modes:

[0043] The first subsystem of the multi-mode switchable biological denitrification system is used to perform the first operation mode, and the steps are the same as those in the return sludge hydrolysis enhanced denitrification method described above;

[0044] The second operation mode is performed using the second subsystem in the multi-mode switchable biological denitrification system described above, including the following steps:

[0045] Domestic sewage enters the first biochemical cell, which is an anaerobic zone. The domestic sewage mainly undergoes anaerobic phosphorus release and organic matter hydrolysis in the first biochemical cell;

[0046] After staying in the first biochemical tank for 1.5-2 hours, the domestic sewage enters the second biochemical tank. The second biochemical tank is an anoxic zone, and the domestic sewage mainly undergoes endogenous denitrification reaction in the second biochemical tank.

[0047] After staying in the second biochemical tank for 1.5-2 hours, the domestic sewage enters the third biochemical tank. The third biochemical tank is an aerobic zone, where the domestic sewage mainly undergoes nitrification reaction.

[0048] After staying in the third biochemical tank for 3-5 hours, the domestic sewage enters the fourth biochemical tank. The fourth biochemical tank is an aerobic zone, where the domestic sewage mainly undergoes nitrification reaction.

[0049] Domestic sewage stays in the fourth biochemical tank for 4.5-8.5 hours before entering the secondary sedimentation tank, where it settles. When the sludge concentration at the bottom of the secondary sedimentation tank reaches the required level, it flows back to the first biochemical tank.

[0050] The third subsystem in the multi-mode switchable biological denitrification system described above is used to perform the third operation mode, including the following steps:

[0051] Domestic sewage enters the first biochemical cell, which is an anaerobic zone. The domestic sewage mainly undergoes anaerobic phosphorus release and organic matter hydrolysis in the first biochemical cell;

[0052] After staying in the first biochemical tank for 1.5-2 hours, the domestic sewage enters the second biochemical tank. The second biochemical tank is an anaerobic zone, where the domestic sewage mainly undergoes anaerobic phosphorus release and organic matter hydrolysis reactions.

[0053] After staying in the second biochemical tank for 1.5-2 hours, the domestic sewage enters the third biochemical tank. The third biochemical tank is an aerobic zone, where the domestic sewage mainly undergoes nitrification reaction.

[0054] Domestic sewage stays in the third biochemical tank for 3-5 hours before entering the fourth biochemical tank. The fourth biochemical tank is a post-anoxic zone, where domestic sewage mainly undergoes endogenous denitrification.

[0055] Domestic sewage stays in the fourth biochemical tank for 4.5-8.5 hours before entering the secondary sedimentation tank, where it settles. When the sludge concentration at the bottom of the secondary sedimentation tank reaches the required level, it flows back to the first biochemical tank.

[0056] When the carbon-nitrogen ratio of the influent is lower than 3, the first operating mode is adopted;

[0057] When the carbon-nitrogen ratio of the influent is above 3 and below 5, the first operation mode or the third operation mode is adopted;

[0058] When the carbon-nitrogen ratio of the influent is above 5, the first operating mode, the second operating mode or the third operating mode is adopted.

[0059] Furthermore, based on the above technical solution, in the second operation mode, the first agitator is operated continuously or intermittently, preferably intermittently, and the alternating time of the intermittent operation is set to off 0.5-1h / on 0.5-1h;

[0060] and / or, in the second operation mode, the total residence time of the sewage in the first biochemical cell pool, the second biochemical cell pool, the third biochemical cell pool, and the fourth biochemical cell pool is 12-16 hours;

[0061] And / or, in the third operation mode, the first agitator and the second agitator are operated continuously or intermittently, preferably intermittently, and the alternating time of the intermittent operation is set to be off for 0.5-1 hour / on for 0.5-1 hour;

[0062] and / or, in the third operation mode, the total residence time of the sewage in the first biochemical cell pool, the second biochemical cell pool, the third biochemical cell pool, and the fourth biochemical cell pool is 12-16 hours;

[0063] and / or, in the second operating mode or the third operating mode, the domestic sewage is allowed to settle in the secondary sedimentation tank for 2-4 hours;

[0064] and / or, controlling the dissolved oxygen concentration in the aerobic zone to 0.5-4 mg / L by the first aeration system or the second aeration system;

[0065] and / or, the sludge concentration of the return sludge is 8000-15000 mg / L;

[0066] and / or, a sludge return ratio of 50-150%;

[0067] and / or, the surface load of the secondary sedimentation tank is 0.6 to 1.5 m 3 / (m 2 ·h).

[0068] The present invention provides a return sludge hydrolysis enhanced denitrification system and method, and a multi-mode switchable biological denitrification system and method, which have the following beneficial effects:

[0069] (1) The return sludge hydrolysis enhanced denitrification system and method provided by the present invention can release organic matter through the hydrolysis of the return sludge, replenish the carbon source of the system, and save the cost of adding external carbon sources.

[0070] (2) The system and method for enhanced denitrification by hydrolysis of return sludge provided by the present invention have low sludge production and save sludge disposal costs. By hydrolyzing the return sludge, sludge production can be greatly reduced, realizing sludge resource utilization.

[0071] (3) The system and method for enhanced denitrification by hydrolysis of return sludge provided by the present invention saves energy consumption of the agitator. By controlling the intermittent start and stop of the agitator, the sludge hydrolysis effect is enhanced while saving the power consumption of the agitator.

[0072] (4) The return sludge hydrolysis-enhanced denitrification system and method provided by the present invention promotes the partial hydrolysis of the sludge to release organic matter, which is used as an electron donor for denitrification, thereby removing nitrates from the return sludge. The remaining organic matter is directly adsorbed on the surface of microorganisms or converted into an internal carbon source, which is conducive to further storage of carbon sources in the anaerobic zone. At the same time, the denitrification effect is further improved by optimizing the operating parameters of the system, including controlling the agitator. In addition, the system and method can also reduce the generation of excess sludge, effectively reducing the cost of sludge treatment.

[0073] (5) The multi-mode switchable biological denitrification system and method provided by the present invention can select different operating modes for treatment according to the actual water inlet conditions. It has high flexibility and simple switching operation. After four months of continuous operation, it has stable operation and good water output effect. It is suitable for sewage treatment plants with large changes in water quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0075] Figure 1 This is a schematic structural diagram of a return sludge hydrolysis and enhanced denitrification system provided by the present invention;

[0076] Figure 2 A schematic structural diagram of a multi-mode switchable biological denitrification system provided by the present invention;

[0077] Figure 3 This is a flow chart of three operating modes in a multi-mode switchable biological denitrification system provided by the present invention; wherein (a) is the second subsystem, (b) is the first subsystem, and (c) is the third subsystem;

[0078] icon:

[0079] 1. Biochemical pool; 1.1. First biochemical pool; 1.2. Second biochemical pool; 1.3. Third biochemical pool; 1.4. Fourth biochemical pool; 2. Second sedimentation tank. DETAILED DESCRIPTION

[0080] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. The process parameters for which specific conditions are not specified in the following examples are generally in accordance with conventional conditions.

[0081] The endpoints of the ranges and any values disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in the present invention.

[0082] According to the first aspect of the present invention, Figure 1 As shown, a return sludge hydrolysis enhanced denitrification system is provided, comprising a biochemical tank 1 and a secondary sedimentation tank 2 connected in sequence;

[0083] The biochemical pool 1 comprises a first biochemical cell pool 1.1, a second biochemical cell pool 1.2, a third biochemical cell pool 1.3 and a fourth biochemical cell pool 1.4 connected in sequence, and a sludge return pipeline is provided between the bottom of the secondary sedimentation tank 2 and the first biochemical cell pool 1.1;

[0084] Among them, the first biochemical cell 1.1 is a sludge hydrolysis zone, which is used to hydrolyze the sludge from the secondary sedimentation tank 2;

[0085] The second biochemical cell 1.2 is an anaerobic zone. The second biochemical cell 1.2 is connected to the domestic sewage pipeline and is used to receive domestic sewage and sludge from the first biochemical cell 1.1 and perform anaerobically treatment on the domestic sewage.

[0086] The third biochemical cell 1.3 is an aerobic zone, which is used to receive the sewage treated by the second biochemical cell 1.2 and perform aerobic treatment on it;

[0087] The fourth biochemical cell 1.4 is a post-anoxic zone, which is used to receive the sewage treated by the third biochemical cell 1.3 and perform anoxic treatment on it.

[0088] Specifically, the first biochemical cell serves as the sludge hydrolysis zone. The hydrolysis zone only accepts return sludge, not domestic sewage, to ensure the return sludge's initial anoxic environment. The return sludge contains a small amount of nitrate. After entering the sludge hydrolysis zone, the nitrate undergoes denitrification in the anoxic environment, generating nitrogen gas, which gradually transforms the sludge hydrolysis zone from an anoxic environment to an anaerobic environment. The activated sludge continues to react in the local anaerobic environment. After the nitrate removal is completed, it undergoes hydrolysis to release carbon sources, which exist in the system in the form of dissolved organic matter, extracellular polymers, or intracellular carbon sources. This part of the carbon source can enter the subsequent anaerobic zone with the sludge to supplement the carbon source for the biochemical system. By hydrolyzing the return sludge, the sludge is partially hydrolyzed to release organic matter, which is used as an electron donor for denitrification to remove nitrate from the return sludge. The remaining organic matter is directly adsorbed on the surface of microorganisms or converted into an internal carbon source, which is conducive to strengthening the further storage of carbon sources in the subsequent anaerobic zone. However, if domestic sewage is introduced into the first biochemical cell, the cell will be converted into an anaerobic zone. When the carbon-nitrogen ratio in the influent is less than 3, the limited carbon source in the influent will be preferentially used by denitrifying bacteria to remove nitrates flowing back into the zone, resulting in the inability of polyphosphate bacteria to fully store the internal carbon source in the anaerobic zone, ultimately affecting the denitrification effect of the system.

[0089] Furthermore, the second biochemical grid pool serves as an anaerobic zone, where microorganisms store the carbon sources of domestic sewage and the hydrolysis zone as internal carbon sources; the third biochemical grid pool serves as an aerobic zone, completing the nitrification reaction; and the fourth biochemical grid pool serves as a post-anoxic zone, completing endogenous denitrification.

[0090] In the system described in the first aspect of the present invention, the design or arrangement of the anaerobic zone, the aerobic zone and the anoxic zone refers to the design of the conventional activated sludge method in the field. The main function of the anaerobic zone is to release phosphorus and degrade some organic matter, the aerobic zone is nitrification and further degradation of organic matter, and the anoxic zone is denitrification and denitrification.

[0091] The return sludge hydrolysis enhanced denitrification system provided in the first aspect of the present invention is suitable for treating domestic sewage with any carbon-nitrogen ratio, but since the present invention specially designs a return sludge hydrolysis zone, based on the function of the sludge hydrolysis zone, the system of the first aspect of the present invention preferably treats domestic sewage with a carbon-nitrogen ratio of less than 3.

[0092] The first biochemical cell serves as a hydrolysis zone for the return sludge. This zone contains only the return sludge from the secondary sedimentation tank, without any additional sewage. To ensure uniform mixing of the return sludge in this zone, as an optional embodiment of the present invention, a first agitator is provided in the first biochemical cell.

[0093] In one embodiment of the present invention, the second biochemical cell is provided with a second water inlet valve for controlling the sewage to enter the system and a second agitator for agitating the sewage in the cell;

[0094] In one embodiment of the present invention, the third biochemical cell is provided with a first aeration system for maintaining dissolved oxygen in the cell;

[0095] In one embodiment of the present invention, the fourth biochemical cell is provided with a third agitator for uniformly mixing the sewage in the cell;

[0096] In order to control the return amount of sludge, in one embodiment of the present invention, a sludge return valve is provided on the sludge return pipeline between the first biochemical cell tank and the secondary sedimentation tank.

[0097] According to a second aspect of the present invention, a method for enhanced denitrification by hydrolysis of return sludge is provided, which is carried out using the above-mentioned system for enhanced denitrification by hydrolysis of return sludge, and comprises the following steps:

[0098] Domestic sewage enters the second biochemical cell, which is an anaerobic zone. The domestic sewage mainly undergoes anaerobic phosphorus release and organic matter hydrolysis in the second biochemical cell;

[0099] After staying in the second biochemical cell for 1.5-2 hours (such as 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours, etc.), the domestic sewage enters the third biochemical cell. The third biochemical cell is an aerobic zone, and the domestic sewage mainly undergoes nitrification reaction in the third biochemical cell.

[0100] The domestic sewage stays in the third biochemical cell for 3-5 hours (such as 3.2 hours, 3.4 hours, 3.6 hours, 3.8 hours, 4.0 hours, 4.2 hours, 4.4 hours, 4.6 hours, 4.8 hours, etc.) and then enters the fourth biochemical cell. The fourth biochemical cell is an anoxic zone, and the domestic sewage mainly undergoes endogenous denitrification reaction in the fourth biochemical cell.

[0101] The domestic sewage stays in the fourth biochemical cell for 4.5-8.5h (such as 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, etc.) and then enters the secondary sedimentation tank. The domestic sewage is settled in the secondary sedimentation tank and returned to the first biochemical cell after the sludge concentration at the bottom of the secondary sedimentation tank reaches the requirement. The first biochemical cell is a sludge hydrolysis area. The returned sludge first undergoes denitrification reaction and then hydrolysis of organic matter in the first biochemical cell. The returned sludge stays in the first biochemical cell for 1.5-2h (such as 1.6h, 1.7h, 1.8h, 1.9h, etc.) and then enters the second biochemical cell to provide a carbon source for anaerobic phosphorus release and hydrolysis of organic matter in the second biochemical cell.

[0102] As an optional embodiment of the present invention, the first agitator provided in the first biochemical cell is operated continuously or intermittently, preferably intermittently, and the alternating time of the intermittent operation is set to off for 5-23 hours / on for 0.5-1 hour.

[0103] Specifically, in the first operating mode, when the agitator operates intermittently, a long period of no stirring can cause the sludge to settle, increase the local sludge concentration, enhance sludge hydrolysis, denitrification and internal carbon source storage, and combined with short-term stirring, the sludge can be mixed evenly to avoid problems such as accumulation and agglomeration.

[0104] As an optional embodiment of the present invention, the sum of the sludge retention time in the first biochemical cell and the total retention time of the sewage in the second biochemical cell, the third biochemical cell and the fourth biochemical cell is 12-16 hours.

[0105] As an optional embodiment of the present invention, the domestic sewage is settled in the secondary sedimentation tank for 2-4 hours (eg, 2.5 hours, 3 hours, 3.5 hours, etc.) to ensure the effluent quality.

[0106] As an optional embodiment of the present invention, the dissolved oxygen concentration in the aerobic zone is controlled by the first aeration system to be 0.5-4 mg / L (e.g., 1 mg / L, 2 mg / L, 2.5 mg / L, 3 mg / L, 3.5 mg / L, etc.), which should not be too high;

[0107] The sludge concentration of the return sludge is 8000-15000 mg / L (such as 9000 mg / L, 10000 mg / L, 12000 mg / L, etc.); controlling the return sludge concentration can further ensure the initial denitrification reaction in the hydrolysis tank to remove nitrates and the subsequent anaerobic decomposition of organic matter.

[0108] The sludge return ratio is 50-150% (such as 70%, 90%, 110%, 130%, etc.); the sludge return ratio of the present invention is the amount of return sludge divided by the amount of domestic sewage inlet into the biochemical pool.

[0109] The surface load of the secondary sedimentation tank is 0.6~1.5m 3 / (m 2 h), for example, 0.8 m 3 / (m 2 ·h)、1m 3 / (m 2 ·h)、1.2m 3 / (m 2 h), 1.4m 3 / (m 2 h) etc.

[0110] According to the third aspect of the present invention, Figure 2 As shown, a multi-mode switchable biological denitrification system is provided, wherein the multi-mode switchable biological denitrification system comprises a biochemical tank 1 and a secondary sedimentation tank 2 connected in sequence;

[0111] The biochemical pool 1 comprises a first biochemical cell pool 1.1, a second biochemical cell pool 1.2, a third biochemical cell pool 1.3 and a fourth biochemical cell pool 1.4 connected in sequence, and a sludge return pipeline is provided between the bottom of the secondary sedimentation tank 2 and the first biochemical cell pool 1.1;

[0112] According to the influent water quality, the multi-mode switchable biological denitrification system can be switched to any one of the first to third subsystems.

[0113] like Figure 3 As shown in (b), the first subsystem is the return sludge hydrolysis enhanced denitrification system as described above;

[0114] like Figure 3 As shown in (a), in the second subsystem, the first biochemical cell is an anaerobic zone, which is used to receive the domestic sewage to be treated and perform anaerobically treatment on it. The second biochemical cell is an anoxic zone, which is used to receive the sewage treated by the first biochemical cell and perform anoxic treatment on it. The third and fourth biochemical cells are both aerobic zones, and the sewage from the second biochemical cell flows through the third and fourth biochemical cells in sequence for aerobic treatment.

[0115] like Figure 3 As shown in (c), in the third subsystem, the first biochemical grid tank is an anaerobic zone, which is used to receive the domestic sewage to be treated and perform anaerobically treatment on it. The second biochemical grid tank is an anaerobic zone, which is used to receive the sewage treated by the first biochemical grid tank and perform anaerobically treatment on it. The third biochemical grid tank is an aerobic zone, which is used to receive the sewage treated by the second biochemical grid tank and perform aerobic treatment on it. The fourth biochemical grid tank is a post-anoxic zone, which is used to receive the sewage treated by the third biochemical grid tank and perform anoxic treatment on it.

[0116] Specifically, in the second subsystem, the first biochemical grid pool serves as an anaerobic zone, and the microorganisms store the carbon source in the influent as an internal carbon source and release phosphorus. The microorganisms store the carbon source in the influent as an internal carbon source. When the second biochemical grid pool serves as an anoxic zone, the microorganisms use the influent carbon source for denitrification; the third biochemical grid pool and the fourth biochemical grid pool serve as aerobic zones to complete the nitrification reaction.

[0117] Furthermore, in the third subsystem, the first biochemical grid pool serves as an anaerobic zone, where microorganisms store the carbon source in the influent as an internal carbon source; the second biochemical grid pool serves as an anaerobic zone, and its function is the same as that of the first biochemical grid pool; the third biochemical grid pool serves as an aerobic zone, completing the nitrification reaction; and the fourth biochemical grid pool serves as a post-anoxic zone, completing endogenous denitrification.

[0118] In the multi-mode switching system of the present invention, in order to facilitate switching between different modes, as an optional embodiment of the present invention, a first water inlet valve and a first agitator are provided in the first biochemical cell; the first water inlet valve is used to control whether the sewage to be treated enters the first biochemical cell.

[0119] The second biochemical cell is provided with a second water inlet valve and a second agitator. The second water inlet valve is used to control whether the treated sewage enters the second biochemical cell. When switching to the first subsystem, the second water inlet valve is opened and the first water inlet valve is closed. When switching to the second and third subsystems, the first water inlet valve is opened and the second water inlet valve is closed.

[0120] The third biochemical cell is provided with a first aeration system;

[0121] The fourth biochemical cell is provided with a third agitator and a second aeration system. The second aeration system is usually used when the fourth biochemical cell is used as an aerobic zone to ensure the dissolved oxygen concentration in the zone.

[0122] A sludge return valve is provided on the sludge return pipeline between the first biochemical cell pool and the secondary sedimentation tank.

[0123] According to a fourth aspect of the present invention, a multi-mode switchable biological denitrification method is provided, comprising three operating modes:

[0124] The first subsystem of the multi-mode switchable biological denitrification system is used to perform the first operation mode, and the steps are the same as those in the return sludge hydrolysis enhanced denitrification method described above;

[0125] The second operation mode is performed using the second subsystem in the multi-mode switchable biological denitrification system described above, including the following steps:

[0126] Domestic sewage enters the first biochemical cell, which is an anaerobic zone. The domestic sewage mainly undergoes anaerobic phosphorus release and organic matter hydrolysis in the first biochemical cell;

[0127] After staying in the first biochemical cell for 1.5-2 hours (such as 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours, etc.), the domestic sewage enters the second biochemical cell. The second biochemical cell is an anoxic zone, and the domestic sewage mainly undergoes endogenous denitrification reaction in the second biochemical cell.

[0128] After staying in the second biochemical cell for 1.5-2 hours (such as 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours, etc.), the domestic sewage enters the third biochemical cell. The third biochemical cell is an aerobic zone, and the domestic sewage mainly undergoes nitrification reaction in the third biochemical cell.

[0129] The domestic sewage stays in the third biochemical tank for 3-5 hours (such as 3.2 hours, 3.4 hours, 3.6 hours, 3.8 hours, 4.0 hours, 4.2 hours, 4.4 hours, 4.6 hours, 4.8 hours, etc.) and then enters the fourth biochemical tank. The fourth biochemical tank is an aerobic zone, and the domestic sewage mainly undergoes nitrification reaction in the fourth biochemical tank.

[0130] The domestic sewage stays in the fourth biochemical tank for 4.5-8.5 hours (such as 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, etc.) and then enters the secondary sedimentation tank. The domestic sewage settles in the secondary sedimentation tank and returns to the first biochemical tank after the sludge concentration at the bottom of the secondary sedimentation tank reaches the requirement;

[0131] The third subsystem in the multi-mode switchable biological denitrification system described above is used to perform the third operation mode, including the following steps:

[0132] Domestic sewage enters the first biochemical cell, which is an anaerobic zone. The domestic sewage mainly undergoes anaerobic phosphorus release and organic matter hydrolysis in the first biochemical cell;

[0133] After staying in the first biochemical cell for 1.5-2 hours (such as 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours, etc.), the domestic sewage enters the second biochemical cell. The second biochemical cell is an anaerobic zone, and the domestic sewage mainly undergoes anaerobic phosphorus release and organic matter hydrolysis reactions in the second biochemical cell.

[0134] After staying in the second biochemical cell for 1.5-2 hours (such as 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours, etc.), the domestic sewage enters the third biochemical cell. The third biochemical cell is an aerobic zone, and the domestic sewage mainly undergoes nitrification reaction in the third biochemical cell.

[0135] The domestic sewage stays in the third biochemical cell for 3-5 hours (such as 3.2 hours, 3.4 hours, 3.6 hours, 3.8 hours, 4.0 hours, 4.2 hours, 4.4 hours, 4.6 hours, 4.8 hours, etc.) and then enters the fourth biochemical cell. The fourth biochemical cell is a post-anoxic zone, and the domestic sewage mainly undergoes endogenous denitrification reaction in the fourth biochemical cell.

[0136] The domestic sewage stays in the fourth biochemical tank for 4.5-8.5 hours (such as 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, etc.) and then enters the secondary sedimentation tank. The domestic sewage settles in the secondary sedimentation tank and returns to the first biochemical tank after the sludge concentration at the bottom of the secondary sedimentation tank reaches the requirement;

[0137] When the carbon-nitrogen ratio of the inlet water is lower than 3 (such as 1, 1.5, 2, 2.2, 2.4, 2.6, 2.8, etc.), the first operating mode is adopted;

[0138] When the carbon-nitrogen ratio of the inlet water is above 3 and below 5 (such as 3.2, 3.4, 3.6, 3.8, 4, 4.2, 4.44, 4.6, 4.8, etc.), the first operation mode or the third operation mode is adopted, and the third operation mode is preferably adopted;

[0139] When the carbon-nitrogen ratio of the influent is above 5 (such as 6, 7, 8, etc.), the first operating mode, the second operating mode, or the third operating mode is adopted, and the second operating mode is preferably adopted.

[0140] Specifically, in the second and third operating modes, domestic sewage enters the first biochemical cell;

[0141] In the first operating mode, domestic sewage enters the second biochemical cell.

[0142] In the second operation mode, the first agitator is operated continuously or intermittently, preferably intermittently, and the alternating time of the intermittent operation is set to off 0.5-1h / on 0.5-1h;

[0143] In the third operation mode, the first agitator and the second agitator are operated continuously or intermittently, preferably intermittently, and the alternating time of the intermittent operation is set to off for 0.5-1h / on for 0.5-1h;

[0144] In the second operation mode or the third operation mode, the total residence time of the sewage in the first biochemical cell pool, the second biochemical cell pool, the third biochemical cell pool and the fourth biochemical cell pool is 12-16 hours;

[0145] Specifically, in the second operation mode, when the agitator is operated intermittently, the sludge can be properly settled, the bottom sludge concentration is increased, and the bottom sludge hydrolysis, denitrification and phosphorus release are enhanced.

[0146] Specifically, in the third operation mode, when the agitator is operated intermittently, the sludge can be properly settled, the bottom sludge concentration is increased, and the bottom sludge hydrolysis, denitrification and internal carbon source storage are enhanced.

[0147] As an optional embodiment of the present invention, in the second operating mode or the third operating mode, the domestic sewage is settled in the secondary sedimentation tank for 2-4 hours (e.g., 2.5 hours, 3 hours, 3.5 hours, etc.);

[0148] The dissolved oxygen concentration in the aerobic zone is controlled to be 0.5-4 mg / L (e.g., 1 mg / L, 2 mg / L, 2.5 mg / L, 3 mg / L, 3.5 mg / L, etc.) by the first aeration system or the second aeration system;

[0149] The sludge concentration of the return sludge is 8000-15000 mg / L (such as 9000 mg / L, 10000 mg / L, 12000 mg / L, etc.);

[0150] The sludge return ratio is 50-150% (such as 70%, 90%, 110%, 130%, etc.);

[0151] The surface load of the secondary sedimentation tank is 0.6~1.5m 3 / (m 2 h), for example, 0.8 m 3 / (m 2 ·h)、1m 3 / (m 2 h), 1.2m 3 / (m 2 h), 1.4m 3 / (m 2 h) etc.

[0152] The multi-mode switchable biological denitrification system and method provided by the present invention can select different operating modes for treatment according to the actual water inlet conditions, with high flexibility. By controlling the agitator, aeration system and water inlet valve of each biochemical cell to place different cells in different environmental areas, switching between three different operating modes can be achieved. The switching operation is simple and is suitable for sewage treatment plants with large changes in water quality.

[0153] The present invention will be further described in detail below with reference to specific examples and comparative examples.

[0154] Example 1

[0155] In a sewage treatment plant in southern China with a daily water treatment capacity of 160,000 tons, the project requires the average values of various water quality indicators in the effluent as shown in Table 1:

[0156] Table 1

[0157]

[0158] The sewage treatment plant applied the return sludge hydrolysis enhanced denitrification system provided by the present invention and operated for 4 months. The carbon-nitrogen ratio of the sewage in the sewage treatment plant was 2.7±0.7, and was always maintained below 3. The sewage in the sewage treatment plant was treated by using the return sludge hydrolysis enhanced denitrification system provided by the present invention.

[0159] The specific indicators of the sewage treatment plant's influent and effluent quality are shown in Table 2:

[0160] Table 2

[0161]

[0162] The method for enhanced denitrification by hydrolysis of return sludge provided by the present invention specifically comprises the following steps:

[0163] In this system, the first water inlet valve in the first biochemical cell is kept closed all the time.

[0164] The second water inlet valve is opened, and the domestic sewage enters the second biochemical cell. The second agitator is turned on and operates in a continuous mode. The second biochemical cell is an anaerobic zone. The domestic sewage mainly undergoes anaerobic phosphorus release and organic matter hydrolysis reactions in the second biochemical cell. Microorganisms store the carbon source in the domestic sewage as an internal carbon source.

[0165] After staying in the second biochemical cell for 1.8 hours, the domestic sewage enters the third biochemical cell. The first aeration system is turned on. The third biochemical cell is an aerobic zone. The aeration volume in the aerobic zone controls the DO concentration at 1.5-2 mg / L. The domestic sewage mainly undergoes nitrification reaction in the third biochemical cell.

[0166] After staying in the third biochemical cell for 3 hours, the domestic sewage enters the fourth biochemical cell. The third agitator is turned on and operates continuously. The fourth biochemical cell is a post-anoxic zone, so the second aeration system in the fourth biochemical cell remains closed. The domestic sewage mainly undergoes endogenous denitrification in the fourth biochemical cell.

[0167] Domestic sewage stays in the fourth biochemical cell for 5.7 hours before entering the secondary sedimentation tank. After settling in the secondary sedimentation tank for 4 hours, when the sludge concentration at the bottom of the secondary sedimentation tank reaches the requirement (the return sludge concentration is within 8000-15000 mg / L), the sludge return valve is opened, and the sludge at the bottom of the secondary sedimentation tank is returned to the first biochemical cell. The sludge return ratio is 80%, and the return sludge concentration is about 10000 mg / L. The first agitator is turned on and the operation mode of the first agitator is intermittent operation, which is turned off for 23 hours and turned on for 1 hour. Long-term non-stirring can cause the sludge to settle, increase the local sludge concentration, strengthen the sludge hydrolysis, denitrification and internal carbon source storage, and combine with short-term stirring to make the sludge mixed evenly to avoid accumulation and agglomeration. The first biochemical cell serves as the sludge hydrolysis zone. Only return sludge enters the hydrolysis zone, but no domestic sewage. The return sludge contains a small amount of nitrate. After entering the sludge hydrolysis zone, the nitrate undergoes denitrification reaction in an anoxic environment to generate nitrogen, which gradually changes the sludge hydrolysis zone from an anoxic environment to an anaerobic environment. The activated sludge continues to react in the local anaerobic environment. When the nitrate removal is completed, hydrolysis occurs to release carbon source, and the carbon source exists in the system in the form of dissolved organic matter, extracellular polymers or intracellular carbon source. After the return sludge stays in the first biochemical cell for 1.5 hours, this part of the carbon source can enter the second biochemical cell along with the sludge to supplement the carbon source for the anaerobic phosphorus release and organic matter hydrolysis reaction in the second biochemical cell.

[0168] Example 2

[0169] In a sewage treatment plant with a daily treatment capacity of 55 L and the same effluent standards as those in Table 1 above, due to the large variation in influent quality, three operating conditions were set to operate the multi-mode switchable biological denitrification system provided by the present invention according to the changes in the carbon-nitrogen ratio in the monitored influent. The system was operated continuously for 4 months in each operating condition. The specific influent and effluent water qualities of each operating condition are shown in Table 3:

[0170] Table 3

[0171]

[0172]

[0173] For three different working conditions, the multi-mode switchable biological denitrification method provided by the present invention is adopted, which specifically includes the following steps:

[0174] Operating condition 1: the carbon-nitrogen ratio of the influent is greater than 5. The second operating mode is preferably adopted, including the following steps:

[0175] The first water inlet valve is opened, and the second water inlet valve is closed. The domestic sewage enters the first biochemical cell. The first agitator is turned on and operates continuously. The first biochemical cell serves as an anaerobic zone. The domestic sewage mainly undergoes anaerobic phosphorus release and organic matter hydrolysis reactions in the first biochemical cell. Microorganisms store the carbon source in the influent as an internal carbon source and release phosphorus.

[0176] After staying in the first biochemical cell for 2 hours, the domestic sewage enters the second biochemical cell. The second agitator is turned on and operates continuously. The second biochemical cell is an anoxic zone, where microorganisms use the carbon source of the influent to perform endogenous denitrification on the domestic sewage.

[0177] After staying in the second biochemical cell for 2 hours, the domestic sewage enters the third biochemical cell. The first aeration system is turned on. The third biochemical cell is an aerobic zone with a DO concentration of 2-4 mg / L. The domestic sewage mainly undergoes nitrification reaction in the third biochemical cell.

[0178] After staying in the third biochemical cell for 4 hours, the domestic sewage enters the fourth biochemical cell. The third agitator and the second aeration system are turned on. The third agitator operates continuously. The fourth biochemical cell is an aerobic zone with a DO concentration of 2-4 mg / L. The domestic sewage mainly undergoes nitrification in the fourth biochemical cell.

[0179] After staying in the fourth biochemical cell for 8 hours, the domestic sewage enters the secondary sedimentation tank. After settling in the secondary sedimentation tank for 4 hours, when the sludge concentration at the bottom of the secondary sedimentation tank reaches the requirement (the return sludge concentration is within 8000-15000 mg / L), the sludge return valve is opened, the sludge return ratio is 150%, and the return sludge concentration is about 12000 mg / L. The sludge at the bottom of the secondary sedimentation tank is returned to the first biochemical cell.

[0180] Working condition 2: the carbon-nitrogen ratio of the influent is greater than 4 and less than 5. The third operating mode is preferably adopted, including the following steps:

[0181] The first water inlet valve is opened, and the second water inlet valve is closed. Domestic sewage enters the first biochemical cell. The first agitator is turned on and operates intermittently, with an on-time of 0.5h and an off-time of 0.5h. When the agitator operates intermittently, the sludge can be properly precipitated, the bottom sludge concentration can be increased, and the bottom sludge hydrolysis, denitrification and phosphorus release can be enhanced. The first biochemical cell is an anaerobic zone. Domestic sewage mainly undergoes anaerobic phosphorus release and organic matter hydrolysis reactions in the first biochemical cell. Microorganisms store the carbon source in the influent as an internal carbon source.

[0182] After staying in the first biochemical cell for 2 hours, the domestic sewage enters the second biochemical cell. The second agitator is turned on and operates continuously. The second biochemical cell is an anaerobic zone. The domestic sewage in the second biochemical cell mainly undergoes anaerobic phosphorus release and organic matter hydrolysis reactions. Microorganisms store the carbon source in the influent as an internal carbon source and release phosphorus.

[0183] After staying in the second biochemical cell for 2 hours, the domestic sewage enters the third biochemical cell. The first aeration system is turned on. The third biochemical cell is an aerobic zone with a DO concentration of 0.5-2 mg / L. The domestic sewage mainly undergoes nitrification reaction in the third biochemical cell.

[0184] After staying in the third biochemical cell for 4 hours, the domestic sewage enters the fourth biochemical cell. The third agitator is turned on and runs continuously. The second aeration system is turned off. The fourth biochemical cell is a post-anoxic zone. The domestic sewage mainly undergoes endogenous denitrification reaction in the fourth biochemical cell.

[0185] After the domestic sewage stays in the fourth biochemical cell for 8 hours, it enters the secondary sedimentation tank from the fourth biochemical cell. After the domestic sewage settles in the secondary sedimentation tank for 4 hours, when the sludge concentration at the bottom of the secondary sedimentation tank reaches the requirement (the return sludge concentration is within 8000-15000 mg / L), the sludge return valve is opened, the sludge return ratio is 150%, and the return sludge concentration is about 12000 mg / L. The sludge at the bottom of the secondary sedimentation tank is returned to the first biochemical cell.

[0186] Working condition three: the carbon-nitrogen ratio of the inlet water is less than 3, and the first operating mode is preferably adopted:

[0187] In the first subsystem, the first water inlet valve in the first biochemical cell is kept closed.

[0188] The second water inlet valve is opened, and the domestic sewage enters the second biochemical cell. The second agitator is turned on and continuously operates. The second biochemical cell is an anaerobic zone. The domestic sewage mainly undergoes anaerobic phosphorus release and organic matter hydrolysis reactions in the second biochemical cell. Microorganisms store carbon sources in the domestic sewage as internal carbon sources.

[0189] After staying in the second biochemical cell for 2 hours, the domestic sewage enters the third biochemical cell. The first aeration system is turned on. The third biochemical cell is an aerobic zone with a DO concentration of 0.5-2 mg / L. The domestic sewage mainly undergoes nitrification reaction in the third biochemical cell.

[0190] After staying in the third biochemical cell for 4 hours, the domestic sewage enters the fourth biochemical cell. The third agitator is turned on and operates continuously. The second aeration system is turned off. The fourth biochemical cell is a post-anoxic zone, so the second aeration system in the fourth biochemical cell remains closed. The domestic sewage mainly undergoes endogenous denitrification in the fourth biochemical cell.

[0191] After staying in the fourth biochemical cell for 8.5 hours, the domestic sewage enters the secondary sedimentation tank. After settling in the secondary sedimentation tank for 4 hours, when the sludge concentration at the bottom of the secondary sedimentation tank reaches the requirement (the return sludge concentration is within 8000-15000 mg / L), the sludge return valve is opened, the sludge return ratio is 150%, and the return sludge concentration is about 12000 mg / L. The sludge at the bottom of the secondary sedimentation tank is returned to the first biochemical cell. The first biochemical cell is the sludge hydrolysis area. The first agitator is turned on and runs intermittently, shutting down for 23 hours and starting for 1 hour. The return sludge first undergoes denitrification reaction and then hydrolysis reaction of organic matter in the first biochemical cell. The return sludge stays in the first biochemical cell for 2 hours and then enters the second biochemical cell to supplement the carbon source for anaerobic phosphorus release and hydrolysis reaction of organic matter in the second biochemical cell.

[0192] From the above, it can be seen that the multi-mode switchable biological denitrification system and method provided by the present invention can select different operating modes for treatment according to the actual water inlet conditions, with high flexibility. By controlling the agitator, aeration system and water inlet valve of each biochemical cell, it is possible to switch between three different operating modes. The switching operation is simple, and after four months of continuous operation, the operation is stable and the water outlet effect is good. It can be applied to sewage treatment plants with large changes in water quality.

[0193] Comparative Example 1

[0194] The influent water quality of this comparative example is exactly the same as that of Example 1. The treatment system used in this comparative example is:

[0195] The traditional AOA process includes the following steps:

[0196] Open the first water inlet valve and close the second water inlet valve.

[0197] Domestic sewage enters the first biochemical cell, and the first agitator is turned on. The first agitator is operated intermittently, off for 23 hours and on for 1 hour. The first biochemical cell is an anaerobic zone, where domestic sewage mainly undergoes anaerobic phosphorus release and organic matter hydrolysis. Microorganisms store the carbon source in the influent as an internal carbon source and release phosphorus.

[0198] After staying in the first biochemical cell for 1.5 hours, the domestic sewage enters the second biochemical cell. The second agitator is turned on and operates continuously. The second biochemical cell is an anaerobic zone, and the domestic sewage mainly undergoes anaerobic phosphorus release and organic matter hydrolysis reactions in the second biochemical cell.

[0199] After staying in the second biochemical cell for 1.8 hours, the domestic sewage enters the third biochemical cell. The first aeration system is turned on. The third biochemical cell is an aerobic zone with a DO concentration of 1.5-2 mg / L. The domestic sewage mainly undergoes nitrification reaction in the third biochemical cell.

[0200] After staying in the third biochemical cell for 3 hours, the domestic sewage enters the fourth biochemical cell. The third agitator is turned on and runs continuously. The second aeration system is turned off. The fourth biochemical cell is a post-anoxic zone. The domestic sewage mainly undergoes endogenous denitrification reaction in the fourth biochemical cell.

[0201] After domestic sewage stays in the fourth biochemical cell for 5.7 hours, it enters the secondary sedimentation tank. After the domestic sewage settles in the secondary sedimentation tank for 4 hours, when the sludge concentration at the bottom of the secondary sedimentation tank reaches the requirement (the return sludge concentration is within 8000-15000 mg / L), the sludge return valve is opened, the sludge return ratio is 80%, and the return sludge concentration is about 10000 mg / L. The sludge at the bottom of the secondary sedimentation tank is returned to the first biochemical cell.

[0202] After 4 months of operation, the inlet and outlet water quality indicators of this comparative example are shown in Table 4:

[0203] Table 4

[0204]

[0205]

[0206] From the above, it can be seen that when the carbon-nitrogen ratio of the influent is less than 3, the traditional AOA process has a poor effect on the treatment of wastewater with a low carbon-nitrogen ratio, and the total nitrogen content in the effluent is high, which makes it difficult to meet the various water quality index requirements in Table 1.

[0207] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A return sludge hydrolysis enhanced denitrification system, characterized in that: It includes a biochemical pool and a secondary sedimentation tank connected in sequence; The biochemical pool includes a first biochemical cell pool, a second biochemical cell pool, a third biochemical cell pool and a fourth biochemical cell pool connected in sequence, and a sludge return pipeline is provided between the bottom of the secondary sedimentation tank and the first biochemical cell pool; Among them, the first biochemical tank is the sludge hydrolysis area, which is used to hydrolyze the sludge from the secondary sedimentation tank; The second biochemical cell is an anaerobic zone, which is connected to the domestic sewage delivery pipeline and is used to receive domestic sewage and sludge from the first biochemical cell and perform anaerobically treatment on the domestic sewage; The third biochemical cell is an aerobic zone, which is used to receive the sewage treated by the second biochemical cell and perform aerobic treatment on it; The fourth biochemical cell is a post-anoxic zone, which is used to receive the sewage treated by the third biochemical cell and perform anoxic treatment on it.

2. The return sludge hydrolysis enhanced denitrification system according to claim 1, characterized in that: The carbon-nitrogen ratio of the domestic sewage is lower than 3.

3. The return sludge hydrolysis enhanced denitrification system according to claim 1, characterized in that: A first stirrer is provided in the first biochemical cell; And / or, the second biochemical cell is provided with a second water inlet valve and a second agitator; And / or, a first aeration system is provided in the third biochemical cell; And / or, a third agitator is provided in the fourth biochemical cell; And / or, a sludge return valve is provided on the sludge return pipeline between the first biochemical cell and the secondary sedimentation tank.

4. A method for enhanced denitrification by hydrolysis of return sludge, characterized in that: The method is carried out using the return sludge hydrolysis enhanced denitrification system according to any one of claims 1 to 3, comprising the following steps: Domestic sewage enters the second biochemical cell, which is an anaerobic zone. The domestic sewage mainly undergoes anaerobic phosphorus release and organic matter hydrolysis in the second biochemical cell; After staying in the second biochemical tank for 1.5-2 hours, the domestic sewage enters the third biochemical tank. The third biochemical tank is an aerobic zone, where the domestic sewage mainly undergoes nitrification reaction. Domestic sewage stays in the third biochemical tank for 3-5 hours before entering the fourth biochemical tank. The fourth biochemical tank is an anoxic zone, where domestic sewage mainly undergoes endogenous denitrification. Domestic sewage stays in the fourth biochemical cell for 4.5-8.5 hours before entering the secondary sedimentation tank. Domestic sewage settles in the secondary sedimentation tank and returns to the first biochemical cell after the sludge concentration at the bottom of the secondary sedimentation tank reaches the requirement. The first biochemical cell is the sludge hydrolysis area. The returned sludge first undergoes denitrification reaction and then hydrolysis of organic matter in the first biochemical cell. The returned sludge stays in the first biochemical cell for 1.5-2 hours before entering the second biochemical cell to provide a carbon source for anaerobic phosphorus release and hydrolysis of organic matter in the second biochemical cell.

5. The method for enhanced denitrification by hydrolysis of return sludge according to claim 4, characterized in that: The first agitator provided in the first biochemical cell is operated continuously or intermittently, preferably intermittently, and the alternating time of the intermittent operation is set to be off for 5-23 hours / on for 0.5-1 hour; and / or, the sum of the sludge retention time in the first biochemical cell and the total retention time of the sewage in the second biochemical cell, the third biochemical cell and the fourth biochemical cell is 12-16 hours; And / or, the domestic sewage is settled in the secondary sedimentation tank for 2-4 hours.

6. The method for enhanced denitrification by hydrolysis of return sludge according to claim 4, characterized in that: The dissolved oxygen concentration in the aerobic zone is controlled at 0.5-4 mg / L by the first aeration system; and / or, the sludge concentration of the return sludge is 8000-15000 mg / L, and / or, the sludge return ratio is 50-150%, and / or, the surface load of the secondary sedimentation tank is 0.6 to 1.5 m 3 / (m 2 ·h).

7. A multi-mode switchable biological denitrification system, characterized in that: The multi-mode switchable biological denitrification system includes a biochemical tank and a secondary sedimentation tank connected in sequence; The biochemical pool includes a first biochemical cell pool, a second biochemical cell pool, a third biochemical cell pool and a fourth biochemical cell pool connected in sequence, and a sludge return pipeline is provided between the bottom of the secondary sedimentation tank and the first biochemical cell pool; According to the influent water quality, the multi-mode switchable biological denitrification system can be switched to any one of the first to third subsystems. The first subsystem is the return sludge hydrolysis enhanced denitrification system according to any one of claims 1 to 3; In the second subsystem, the first biochemical cell is an anaerobic zone, which is used to receive the domestic sewage to be treated and perform anaerobically treatment on it. The second biochemical cell is an anoxic zone, which is used to receive the sewage treated by the first biochemical cell and perform anoxic treatment on it. The third and fourth biochemical cells are both aerobic zones, and the sewage from the second biochemical cell flows through the third and fourth biochemical cells in sequence for aerobic treatment. In the third subsystem, the first biochemical grid pool is an anaerobic zone, which is used to receive the domestic sewage to be treated and perform anaerobically treatment on it. The second biochemical grid pool is an anaerobic zone, which is used to receive the sewage treated by the first biochemical grid pool and perform anaerobically treatment on it. The third biochemical grid pool is an aerobic zone, which is used to receive the sewage treated by the second biochemical grid pool and perform aerobic treatment on it. The fourth biochemical grid pool is a post-anoxic zone, which is used to receive the sewage treated by the third biochemical grid pool and perform anoxic treatment on it.

8. The multi-mode switchable biological denitrification system according to claim 7, characterized in that: The first biochemical cell is provided with a first water inlet valve and a first agitator; And / or, the second biochemical cell is provided with a second water inlet valve and a second agitator; And / or, a first aeration system is provided in the third biochemical cell; And / or, the fourth biochemical cell is provided with a third agitator and a second aeration system; And / or, a sludge return valve is provided on the sludge return pipeline between the first biochemical cell and the secondary sedimentation tank.

9. A multi-mode switchable biological denitrification method, characterized in that: There are three operating modes: The first subsystem of the multi-mode switchable biological denitrification system according to any one of claims 7 to 8 is used to perform a first operation mode, which is the same as the steps in the return sludge hydrolysis enhanced denitrification method according to any one of claims 4 to 6; The second subsystem in the multi-mode switchable biological denitrification system according to any one of claims 7 to 8 is used to perform a second operation mode, comprising the following steps: Domestic sewage enters the first biochemical cell, which is an anaerobic zone. The domestic sewage mainly undergoes anaerobic phosphorus release and organic matter hydrolysis in the first biochemical cell; After staying in the first biochemical tank for 1.5-2 hours, the domestic sewage enters the second biochemical tank. The second biochemical tank is an anoxic zone, and the domestic sewage mainly undergoes endogenous denitrification reaction in the second biochemical tank. After staying in the second biochemical tank for 1.5-2 hours, the domestic sewage enters the third biochemical tank. The third biochemical tank is an aerobic zone, where the domestic sewage mainly undergoes nitrification reaction. After staying in the third biochemical tank for 3-5 hours, the domestic sewage enters the fourth biochemical tank. The fourth biochemical tank is an aerobic zone, where the domestic sewage mainly undergoes nitrification reaction. Domestic sewage stays in the fourth biochemical tank for 4.5-8.5 hours before entering the secondary sedimentation tank, where it settles. When the sludge concentration at the bottom of the secondary sedimentation tank reaches the required level, it flows back to the first biochemical tank. The third subsystem in the multi-mode switchable biological denitrification system according to any one of claims 7 to 8 is used to perform a third operation mode, comprising the following steps: Domestic sewage enters the first biochemical cell, which is an anaerobic zone. The domestic sewage mainly undergoes anaerobic phosphorus release and organic matter hydrolysis in the first biochemical cell; After staying in the first biochemical tank for 1.5-2 hours, the domestic sewage enters the second biochemical tank. The second biochemical tank is an anaerobic zone, where the domestic sewage mainly undergoes anaerobic phosphorus release and organic matter hydrolysis reactions. After staying in the second biochemical tank for 1.5-2 hours, the domestic sewage enters the third biochemical tank. The third biochemical tank is an aerobic zone, where the domestic sewage mainly undergoes nitrification reaction. Domestic sewage stays in the third biochemical tank for 3-5 hours before entering the fourth biochemical tank. The fourth biochemical tank is a post-anoxic zone, where domestic sewage mainly undergoes endogenous denitrification. Domestic sewage stays in the fourth biochemical tank for 4.5-8.5 hours before entering the secondary sedimentation tank, where it settles. When the sludge concentration at the bottom of the secondary sedimentation tank reaches the required level, it flows back to the first biochemical tank. When the carbon-nitrogen ratio of the influent is lower than 3, the first operating mode is adopted; When the carbon-nitrogen ratio of the influent is above 3 and below 5, the first operation mode or the third operation mode is adopted; When the carbon-nitrogen ratio of the influent is above 5, the first operating mode, the second operating mode or the third operating mode is adopted.

10. The multi-mode switchable biological denitrification method according to claim 9, characterized in that: In the second operation mode, the first agitator is operated continuously or intermittently, preferably intermittently, and the alternating time of the intermittent operation is set to be off for 0.5-1h / on for 0.5-1h; And / or, in the third operation mode, the first agitator and the second agitator are operated continuously or intermittently, preferably intermittently, and the alternating time of the intermittent operation is set to be off for 0.5-1 hour / on for 0.5-1 hour; and / or, in the second operation mode or the third operation mode, the sum of the total residence time of the sewage in the first biochemical cell pool, the second biochemical cell pool, the third biochemical cell pool, and the fourth biochemical cell pool is 12-16 hours; and / or, in the second operating mode or the third operating mode, the domestic sewage is allowed to settle in the secondary sedimentation tank for 2-4 hours; and / or, controlling the dissolved oxygen concentration in the aerobic zone to 0.5-4 mg / L by the first aeration system or the second aeration system; and / or, the sludge concentration of the return sludge is 8000-15000 mg / L; and / or, a sludge return ratio of 50-150%; and / or, the surface load of the secondary sedimentation tank is 0.6 to 1.5 m 3 / (m 2 ·h).

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