Automatic switching sewage treatment process of air stripping reflux type anaerobic and intermittent MBR

Abstract

This invention discloses an air-lift reflux anaerobic and intermittent MBR automatic switching wastewater treatment process, relating to the field of wastewater treatment. The wastewater treatment equipment automatically switches between three wastewater treatment modes based on the wastewater volume: AO+MBR, AO and MBR in parallel, and AO+membrane SBR intermittent operation. The wastewater treatment equipment includes an anaerobic tank, an intermittent MBR tank, and a sedimentation tank connected by valves. The anaerobic tank is equipped with a basket-type screen connected to the inlet pipe. The intermittent MBR tank is equipped with MBR membrane modules and an ultrasonic level gauge. The sedimentation tank is equipped with an overflow outlet. This invention operates with low energy consumption and employs A... The O+ membrane SBR operates intermittently, automatically every hour, and is idle when there is no water. When the water volume is too large, it automatically switches to AO+MBR mode, and the sedimentation tank starts automatically. It is suitable for decentralized rural sewage treatment with large water volume fluctuations, or sewage treatment (or pretreatment) in factories without connection conditions, as well as domestic sewage treatment in scenic spots and mobile boat berths. This invention uses an air lift reflux method to realize the reflux of nitrified liquid and the reflux of settled sludge. The remaining sludge is also refluxed using an air lift reflux method to realize sludge discharge. That is, the air lift reflux method of blower replaces the return water pump and sludge discharge pump in the traditional process, saving investment and simplifying operation and management.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment, and in particular to a wastewater treatment process with automatic switching between air-lift reflux anaerobic and intermittent MBR. Background Technology

[0002] The AO+MBR combined process is a novel wastewater treatment technology developed in recent years to meet stringent emission standards. It builds upon the traditional AO process by adding a membrane reactor (MBR tank) or directly converting the original AO sedimentation tank into a membrane reactor (MBR tank), and increasing the sludge concentration in the aerobic MBR tank, thus forming the AO+MBR combined process. This improvement leverages the powerful biological nitrogen and phosphorus removal advantages of the AO anaerobic-aerobic alternating biological treatment tank, while also utilizing the high sludge load of the MBR tank and the strong solid-liquid separation characteristics of the MBR membrane, thereby achieving biological wastewater treatment that meets stringent emission standards. Compared to traditional AO+physicochemical deep treatment processes, it offers advantages such as smaller footprint, comparable investment, lower operating costs, less sludge production (including no chemical sludge), and convenient operation. In recent years, it has been widely applied in industrial wastewater treatment, scenic area wastewater treatment, livestock wastewater treatment, and decentralized rural wastewater treatment in China, achieving significant economic and environmental emission reduction benefits.

[0003] However, this AO+MBR combined process also has significant shortcomings in practical applications: it has poor adaptability to changes in water volume. When water volume fluctuates significantly, membrane flux mismatch can easily lead to wastewater overflow. For example, the theoretically designed water volume is 2m³ / h. 3 For an MBR wastewater treatment facility with a flow rate of approximately 5.56 liters per second (L / h), the flow fluctuation coefficient is required to be 2.0-2.3 according to the "Technical Specification for Membrane Biological Wastewater Treatment Engineering (HJ 2010-2011)". If the flow rate exceeds this requirement, the MBR membrane flux will be mismatched, leading to wastewater overflow. If the MBR membrane flux is further increased, the investment in membrane flux, the volume of the membrane bioreactor, and the corresponding operating costs will increase exponentially. Adding an equalization tank increases both investment and land area, inevitably leading to higher overall project investment and operating costs. This is especially true for decentralized rural wastewater and seasonal / holiday-peak domestic wastewater in scenic areas, where peak flow rates can be more than 10 times higher than normal, and this situation does not occur frequently each year. Therefore, there is an urgent need to find a high-efficiency, low-cost air-lift recirculation anaerobic intermittent MBR automatic switching wastewater treatment process to solve the above problems. Summary of the Invention

[0004] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0005] An air-lift reflux anaerobic and intermittent MBR automatic switching wastewater treatment process uses wastewater treatment equipment to automatically switch between three wastewater treatment modes according to the amount of wastewater: AO+MBR, AO and MBR in parallel, and AO+Membrane SBR intermittent operation.

[0006] The wastewater treatment equipment includes an anaerobic tank, an intermittent MBR tank, and a sedimentation tank connected by valves. The anaerobic tank is equipped with a basket-type screen connected to the inlet pipe. The intermittent MBR tank is equipped with an MBR membrane module and an ultrasonic level gauge. The sedimentation tank is equipped with an overflow outlet.

[0007] The wastewater treatment equipment also includes a blower, a water pump, a phosphorus removal dosing device, a pipeline system, and a PLC automatic control system. The blower is connected to the pipeline system, which includes multiple pipes and air lift return valves, aeration valves, sludge return valves, and sludge discharge valves installed on the pipes.

[0008] The intermittent MBR tank is equipped with pipes connecting aeration valves, air lift return valves, and sludge discharge valves. The MBR membrane module is connected to one end of a water pump, and the other end of the water pump is connected to an overflow outlet. The sedimentation tank is equipped with pipes connecting sludge return valves, aeration valves, and sludge discharge valves.

[0009] The PLC automatic control system is electrically connected to the fan, water pump, phosphorus removal dosing device, ultrasonic level gauge, and pipeline system.

[0010] Preferably, the anaerobic tank is a two-compartment anaerobic tank, which includes a first compartment for biological packing of wastewater and a second compartment for the biological decomposition or hydrolysis of suspended activated sludge in the wastewater.

[0011] Preferably, under normal flow conditions, the AO+MBR wastewater treatment mode is adopted, as follows: Wastewater enters the basket screen through the inlet pipe. After the basket screen removes debris, larger particles, and branches, it enters the 2-compartment anaerobic tank and the intermittent MBR tank for treatment. Then, the water pump is started to extract the qualified clean water through the MBR membrane module and enter the overflow outlet. The blower and air lift return valve are started to return the digestate in the intermittent MBR tank to the 2-compartment anaerobic tank by air lift, so as to achieve simultaneous denitrification and phosphorus removal. The remaining sludge in the intermittent MBR tank is periodically lifted into the sedimentation tank by air lift through the blower and sludge discharge valve.

[0012] Preferably, when the wastewater volume is large, a parallel AO and MBR wastewater treatment mode is adopted, as follows: Wastewater enters a basket screen through the inlet pipe. After the basket screen removes debris, larger particles of stone, and branches, it enters a two-chamber anaerobic tank and an intermittent MBR tank for treatment. Then, the water pump is started to draw qualified clean water through the MBR membrane module and enters the overflow outlet. When the wastewater volume is large and the liquid level of the entire facility, including the intermittent MBR tank, is at a high level, the valve between the intermittent MBR tank and the sedimentation tank and the phosphorus removal dosing device are opened while the MBR membrane module is draining water. The phosphorus removal agent added by the phosphorus removal dosing device is mixed with the mixed liquid in the intermittent MBR tank and enters the sedimentation tank for sedimentation. After sedimentation, the supernatant is discharged. The liquid enters the overflow outlet for discharge. The blower, aeration valve, and sludge return valve are opened to allow the sludge settled in the sedimentation tank to be returned to the intermittent MBR tank via air lifting. The phosphorus removal agent used is a conventional phosphorus removal flocculant such as polyaluminum chloride (PAC) or polyferric sulfate (PFS). The blower and air lifting return valve are started, and the digestate in the intermittent MBR tank is returned to the 2-compartment anaerobic tank by air lifting using the blower, achieving simultaneous denitrification and phosphorus removal. The remaining sludge in the intermittent MBR tank is periodically air lifted into the sedimentation tank by starting the blower and sludge discharge valve. The supernatant in the sedimentation tank flows into the anaerobic tank by gravity. At this time, the entire biological reaction system is operating in parallel with the A / O and MBR until the sewage flow rate is reduced to the normal flow rate.

[0013] Preferably, when the wastewater volume is small, an AO+membrane SBR intermittent operation wastewater treatment mode is adopted, as follows: Wastewater enters a basket screen through the inlet pipe. After the basket screen removes debris, larger particles of stone, and branches, it enters a two-chamber anaerobic tank and an intermittent MBR tank for treatment. Since the wastewater volume is small, the overall liquid level of the facility, including the intermittent MBR tank, is at a low level. At this time, the blower stops aeration, and the dissolved oxygen (DO) in the intermittent MBR tank gradually decreases, transitioning from an aerobic state to anoxic and anaerobic states, entering the idle period of the membrane SBR process mode. When the liquid level of the facility, including the intermittent MBR tank, rises to the design height, the blower starts aeration again. The intermittent MBR tank enters the aerobic state. When the aerobic state lasts for 2 hours, the MBR membrane module and water pump start up, and the system begins to drain water. If the water volume is still small and the liquid level in the facility drops to the set low level, the blower stops aeration again, the MBR membrane module and pump are shut down, and the system enters the idle period of the membrane SBR process mode again. This cycle repeats. When the water volume is small or there is no water inflow, the anaerobic tank and intermittent MBR tank are at a low liquid level. At this time, the intermittent MBR tank stops aeration, the sedimentation tank is in an anaerobic sedimentation state, and the mixed liquor in the tank undergoes in-situ denitrification under the action of anaerobic bacteria, denitrifying nitrate nitrogen to generate nitrogen gas, thereby removing the total nitrogen in the mixed liquor.

[0014] Preferably, depending on the terrain elevation, gravity flow or pump lifting can be used to allow sewage to enter the inlet pipe.

[0015] Preferably, the pore diameter of the basket-type grid is 10 mm.

[0016] Preferably, the HRT of the first anaerobic tank is 1-1.5h, the HRT of the second anaerobic tank is 2-2.5h, the HRT of the intermittent MBR tank is 2-4h, the DO of the first anaerobic tank is less than 0.2mg / L, the DO of the second anaerobic tank is less than or equal to 0.5mg / L, the DO of the intermittent MBR tank is 2.5-4.5mg / L, the sludge loading is 0.05-0.15 (kgBOD5 / kgMLSS.d), the SV30 of the intermittent MBR tank is 25%-60%, and the MLSS is 6-12g / L.

[0017] Beneficial effects of this invention:

[0018] 1. The wastewater treated by this invention can meet the Class A standard of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB18918-2002), namely: pH value of 6-9 mg / L, COD of 50 mg / L, total nitrogen of 15 mg / L, ammonia nitrogen of 5 mg / L, and total phosphorus of 0.5 mg / L;

[0019] 2. Low energy consumption operation: It adopts AO+Membrane SBR intermittent operation, automatically running every hour. When there is no water, it is in an idle state. When the water volume is too large, it automatically switches to AO+MBR state and the sedimentation tank starts automatically. It is suitable for rural decentralized sewage treatment with large water volume fluctuations or industrial sewage treatment (or pretreatment) without connection conditions, scenic spots and mobile boat berths, etc.

[0020] 3. This invention uses an air-lift reflux method to achieve nitrification liquid reflux and sedimented sludge reflux; the remaining sludge is discharged using an air-lift reflux method; that is, the air-lift reflux method using a blower replaces the reflux water pump and sludge discharge pump in the traditional process, saving investment and simplifying operation and management. Attached Figure Description

[0021] Figure 1 This is a side cross-sectional view of the operating liquid level and mode of the sewage treatment equipment when the water volume is appropriate.

[0022] Figure 2 This is a flowchart of a wastewater treatment system operating at an appropriate water volume.

[0023] Figure 3 This is a side cross-sectional view of the operating liquid level and mode when the size of the wastewater treatment equipment exceeds twice the water flow rate;

[0024] Figure 4 This is a flowchart for wastewater treatment equipment operating with a large volume of water.

[0025] Figure 5 This is a side cross-sectional view of the operating liquid level and mode of the sewage treatment equipment when the water volume is relatively small;

[0026] Figure 6 This is a flowchart for wastewater treatment equipment when the water volume is relatively small. Detailed Implementation

[0027] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0028] like Figures 1 to 6 As shown, an air-lift reflux anaerobic and intermittent MBR automatic switching wastewater treatment process is used. The wastewater treatment equipment automatically switches between three wastewater treatment modes according to the amount of wastewater: AO+MBR, AO and MBR in parallel, and AO+membrane SBR intermittent operation.

[0029] The wastewater treatment equipment includes an anaerobic tank, an intermittent MBR tank, and a sedimentation tank connected by valves. The anaerobic tank is equipped with a basket-type screen connected to the inlet pipe. The mesh diameter of the basket-type screen is 10mm. Depending on the terrain, wastewater can be fed into the inlet pipe by gravity or pump. The intermittent MBR tank is equipped with an MBR membrane module and an ultrasonic level gauge. The sedimentation tank is equipped with an overflow outlet.

[0030] The wastewater treatment equipment also includes a blower, a water pump, a phosphorus removal dosing device, a pipeline system, and a PLC automatic control system. The blower is connected to the pipeline system, which includes multiple pipes and air lift return valves, aeration valves, sludge return valves, and sludge discharge valves installed on the pipes.

[0031] The intermittent MBR tank is equipped with pipes connecting aeration valves, air lift return valves, and sludge discharge valves. The MBR membrane module is connected to one end of a water pump, and the other end of the water pump is connected to an overflow outlet. The sedimentation tank is equipped with pipes connecting sludge return valves, aeration valves, and sludge discharge valves.

[0032] The PLC automatic control system is electrically connected to the fan, water pump, phosphorus removal dosing device, ultrasonic level gauge, and pipeline system.

[0033] The anaerobic tank adopts a two-compartment anaerobic tank, which includes a first compartment for biological filling of wastewater and a second compartment for the biological decomposition or hydrolysis of suspended activated sludge in the wastewater.

[0034] Under normal flow conditions, the AO+MBR wastewater treatment mode is adopted, as follows: Wastewater enters the basket screen through the inlet pipe. After the basket screen removes debris, larger particles, and branches, it enters the 2-compartment anaerobic tank and the intermittent MBR tank for treatment. The water pump is started to draw qualified clean water through the MBR membrane module and enters the overflow outlet. The blower and air lift return valve are started, and the digestate in the intermittent MBR tank is airlifted back to the 2-compartment anaerobic tank by the blower to achieve simultaneous denitrification and phosphorus removal. The remaining sludge in the intermittent MBR tank is periodically airlifted into the sedimentation tank by the blower and sludge discharge valve. After the sludge return valve is opened, the activated sludge in the sedimentation tank is returned to the intermittent MBR tank through the sedimentation tank air lift return pipe. After the sludge discharge valve is opened, the remaining sludge is discharged.

[0035] When the wastewater volume is large, a parallel AO (Anaerobic / Anaerobic) and MBR (Medium-terminal Bleach) wastewater treatment mode is adopted, as follows: Wastewater enters a basket screen through the inlet pipe. After the basket screen removes debris, larger particles of stone, and branches, it enters a two-chamber anaerobic tank and an intermittent MBR tank for treatment. Then, a water pump is started to extract the treated water through the MBR membrane module and discharge it into the overflow outlet. When the wastewater volume is large and the liquid levels of the entire facility, including the intermittent MBR tank, are high, the valves between the intermittent MBR tank and the sedimentation tank, as well as the phosphorus removal dosing device, are opened while the MBR membrane module discharges water. The phosphorus removal agent added by the dosing device mixes with the mixed liquor in the intermittent MBR tank and enters the sedimentation tank for sedimentation. After sedimentation, the supernatant is discharged into the overflow outlet. The blower, aeration valve, and sludge return valve are opened to allow the sludge settled in the sedimentation tank to be returned to the intermittent MBR tank via air lifting. The phosphorus removal agent used is polyaluminum chloride. Conventional phosphorus removal flocculants such as PAC or PFS are added to enhance phosphorus removal efficiency due to the reduced biological phosphorus removal efficiency caused by the direct sedimentation of some digestate in the intermittent MBR tank when the treatment volume is large. The process involves using chemical precipitation with phosphorus removal agents to strengthen the phosphorus removal effect. The blower and air lift return valve are activated, and the digestate in the intermittent MBR tank is airlifted back to the two-compartment anaerobic tank for simultaneous denitrification and phosphorus removal. The remaining sludge in the intermittent MBR tank is periodically airlifted into the sedimentation tank by the blower and sludge discharge valve. The supernatant from the sedimentation tank flows by gravity into the anaerobic tank. At this time, the entire biological reaction system operates in parallel with the MBR and A / O system until the wastewater flow rate decreases to normal. After opening the sludge return valve, the activated sludge in the sedimentation tank is returned to the intermittent MBR tank via the sedimentation tank air lift return pipe. The remaining sludge is discharged after the sludge discharge valve is opened.

[0036] When the wastewater volume is small, an AO+membrane SBR intermittent operation wastewater treatment mode is adopted, as follows: Wastewater enters a basket screen through the inlet pipe. After the basket screen removes debris, larger particles of stone, and branches, it enters a two-chamber anaerobic tank and an intermittent MBR tank for treatment. Due to the small wastewater volume, the overall liquid level of the facility, including the intermittent MBR tank, is at a low level. At this time, the blower stops aeration, and the dissolved oxygen (DO) in the intermittent MBR tank gradually decreases, transitioning from an aerobic state to anoxic and anaerobic states, entering the idle period of the membrane SBR process mode. When the liquid level of the facility, including the intermittent MBR tank, rises to the design height, the blower starts aeration, and the intermittent MBR tank enters an aerobic state. When the aerobic state lasts for 2 hours, the MBR membrane... The components and pumps start, and the system begins drainage. If the influent flow remains low and the facility level drops to the set low level, the blower stops aeration again, the MBR membrane components and pumps shut down, and the system re-enters the idle period of the membrane SBR process mode. This cycle repeats automatically using PLC control. An ultrasonic level gauge is installed in the first compartment of the anaerobic tank to control the anaerobic tank water level. Because the wastewater flow rate of this equipment fluctuates significantly between morning and evening, when the flow rate is low or there is no influent, the anaerobic tank and the intermittent MBR tank are at a low level. At this time, the intermittent MBR tank stops aeration, and the sedimentation tank is in a facultative sedimentation state. The mixed liquor in the tank undergoes in-situ denitrification under the action of facultative bacteria, denitrifying nitrate nitrogen to generate nitrogen gas, thus removing total nitrogen from the mixed liquor. After opening the sludge return valve, the activated sludge in the sedimentation tank flows back to the intermittent MBR tank through the sedimentation tank airlift return pipe; after opening the sludge discharge valve, the remaining sludge is discharged.

[0037] The first anaerobic tank has a HRT of 1-1.5h, the second anaerobic tank has a HRT of 2-2.5h, and the intermittent MBR tank has a HRT of 2-4h. The DO in the first anaerobic tank is less than 0.2mg / L, the DO in the second anaerobic tank is less than or equal to 0.5mg / L, the DO in the intermittent MBR tank is 2.5-4.5mg / L, the sludge loading is 0.05-0.15 (kgBOD5 / kgMLSS.d), and the SV30 in the intermittent MBR tank is 25%-60%, and the MLSS is 6-12g / L.

[0038] The MBR membrane module of the present invention can be hollow fiber type, capillary type, spiral wound type, flat plate type, or cylindrical type, and can be purchased from the market without special requirements.

[0039] Example 1

[0040] Daily emissions 5-20m 3The main tanks and retention times for mobile berth wastewater include: anaerobic tank 1 hRT1h, anaerobic tank 2 hRT2h, intermittent MBR tank 2 hRT2h, sedimentation tank 2 hRT2h, anaerobic tank 1 DO 0.1mg / L, anaerobic tank 2 DO 0.4mg / L, intermittent MBR tank DO 2.5mg / L, and sludge loading 0.05 (kgBOD5 / kgMLSS.d). The sludge age SRT (20-30d) of the entire system is controlled by maintaining the SV30 of the intermittent MBR tank at 25% and the MLSS at 6g / L, and by using air lift to remove excess sludge.

[0041] By using the wastewater treatment process described in this invention, COD in wastewater can be reduced from 400-420 mg / L to 25-30 mg / L, ammonia nitrogen from 20-21 mg / L to 1-1.5 mg / L, total nitrogen from 35-40 mg / L to 3.5-4 mg / L, and total phosphorus from 3-3.5 mg / L to 0.1-0.15 mg / L, with removal rates of 97%, 98%, 90%, and 95%, respectively. The effluent quality is lower than the main indicators of the Class A standard of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB 18918-2002).

[0042] Example 2

[0043] Daily emissions 20-40m 3 Decentralized rural domestic sewage treatment: The main tanks and retention times include the first anaerobic tank (HRT 1.2h), the second anaerobic tank (HRT 2.2h), the intermittent MBR tank (HRT 2.5h), the sedimentation tank (HRT 2.5h), the first anaerobic tank (DO 0.12mg / L), the second anaerobic tank (DO 0.42mg / L), and the intermittent MBR tank (DO 3mg / L). The sludge loading is 0.12 (kgBOD5 / kgMLSS.d). By controlling the SV30 of the intermittent MBR tank to 30% and the MLSS to 8g / L, and by using air lift to remove excess sludge, the sludge age SRT of the entire system is controlled to be 20-30 days.

[0044] By using the wastewater treatment process described in this invention, COD in wastewater can be reduced from 420-440 mg / L to 30-35 mg / L, ammonia nitrogen from 21-22 mg / L to 1.5-2 mg / L, total nitrogen from 40-50 mg / L to 4-5 mg / L, and total phosphorus from 3.5-3.8 mg / L to 0.15-0.2 mg / L, with removal rates of 97%, 96%, 90%, and 92%, respectively. The effluent quality is lower than the main indicators of the Class A standard of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB 18918-2002).

[0045] Example 3

[0046] Daily emissions 40-60m 3 Livestock farm wastewater: The main tanks and retention times include the first anaerobic tank (HRT 1.3h), the second anaerobic tank (HRT 2.3h), the intermittent MBR tank (HRT 3h), the sedimentation tank (HRT 3h), the first anaerobic tank (DO 0.14mg / L), the second anaerobic tank (DO 0.44mg / L), and the intermittent MBR tank (DO 3.5mg / L). The sludge loading is 0.13 (kgBOD5 / kgMLSS.d). By controlling the SV30 of the intermittent MBR tank to 40% and the MLSS to g / L10, and by using air lift to remove excess sludge, the sludge age SRT of the entire system is controlled to be 20-30 days.

[0047] By using the wastewater treatment process described in this invention, COD in wastewater can be reduced from 440-460 mg / L to 35-40 mg / L, ammonia nitrogen from 22-23 mg / L to 2-3 mg / L, total nitrogen from 50-60 mg / L to 5-6 mg / L, and total phosphorus from 3.8-4 mg / L to 0.2-0.3 mg / L, with removal rates reaching 95%, 95%, 90%, and 91%, respectively. The effluent quality is lower than the main indicators of the Class A standard of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB 18918-2002).

[0048] Example 4

[0049] Daily emissions 60-80m³ 3 Wastewater from the plant area that does not meet the conditions for connection: The main tanks and retention times include the first anaerobic tank with a HRT of 1.4h, the second anaerobic tank with a HRT of 2.4h, the intermittent MBR tank with a HRT of 3.5h, the sedimentation tank with a HRT of 3.5h, the first anaerobic tank with a DO of 0.16mg / L, the second anaerobic tank with a DO of 0.46mg / L, the intermittent MBR tank with a DO of 4mg / L, and a sludge loading of 0.14 (kgBOD5 / kgMLSS.d). By controlling the SV30 of the intermittent MBR tank to 50% and the MLSS to 11g / L, the excess sludge is removed by air lifting, and the sludge age SRT of the entire system is controlled to be 20-30d.

[0050] By using the wastewater treatment process described in this invention, COD in wastewater can be reduced from 460-480 mg / L to 40-45 g / L, ammonia nitrogen from 23-24 mg / L to 3-4 mg / L, total nitrogen from 60-70 mg / L to 6-7 mg / L, and total phosphorus from 4-4.5 mg / L to 0.3-0.4 mg / L, with removal rates of 97%, 92%, 90%, and 90%, respectively. The effluent quality is lower than the main indicators of the Class A standard of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB 18918-2002).

[0051] Example 5

[0052] Daily emissions 80-100m 3 Wastewater from the scenic area: The main tanks and retention times include the first anaerobic tank (HRT 1.5h), the second anaerobic tank (HRT 2.5h), the intermittent MBR tank (HRT 4h), the sedimentation tank (HRT 4h), the first anaerobic tank (DO 0.18mg / L), the second anaerobic tank (DO 0.48mg / L), and the intermittent MBR tank (DO 4.5mg / L). The sludge loading is 0.15 (kgBOD5 / kgMLSS.d). By controlling the SV30 of the intermittent MBR tank to 60% and the MLSS to 12g / L, and by using air lift to remove excess sludge, the sludge age SRT of the entire system is controlled to be 20-30 days.

[0053] By using the wastewater treatment process described in this invention, COD in wastewater can be reduced from 480-500 mg / L to 45-50 mg / L, ammonia nitrogen from 24-25 mg / L to 4-5 mg / L, total nitrogen from 70-75 mg / L to 7-8 mg / L, and total phosphorus from 4.5-5 mg / L to 0.4-0.5 mg / L, with removal rates reaching 95%, 90%, 90%, and 90%, respectively. The effluent quality is lower than the main indicators of the Class A standard of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB 18918-2002).

[0054] As is known from common technical knowledge, this invention can be implemented through other embodiments that do not depart from its spirit or essential characteristics. Therefore, the disclosed embodiments described above are merely illustrative in all respects and are not the only ones. All modifications within the scope of this invention or its equivalents are included in this invention.

Claims

1. A wastewater treatment process with automatic switching between air-lift reflux anaerobic and intermittent MBR, characterized in that, The wastewater treatment equipment automatically switches between three wastewater treatment modes based on the amount of wastewater: AO+MBR, AO and MBR in parallel, and AO+Membrane SBR in intermittent operation. The wastewater treatment equipment includes an anaerobic tank, an intermittent MBR tank, and a sedimentation tank connected by valves. The anaerobic tank is equipped with a basket-type screen connected to the inlet pipe. The intermittent MBR tank is equipped with an MBR membrane module and an ultrasonic level gauge. The sedimentation tank is equipped with an overflow outlet. The wastewater treatment equipment also includes a blower, a water pump, a phosphorus removal dosing device, a pipeline system, and a PLC automatic control system. The blower is connected to the pipeline system, which includes multiple pipes and air lift return valves, aeration valves, sludge return valves, and sludge discharge valves installed on the pipes. The intermittent MBR tank is equipped with pipes connecting aeration valves, air lift return valves, and sludge discharge valves. The MBR membrane module is connected to one end of a water pump, and the other end of the water pump is connected to an overflow outlet. The sedimentation tank is equipped with pipes connecting sludge return valves, aeration valves, and sludge discharge valves. The PLC automatic control system is electrically connected to the fan, water pump, phosphorus removal dosing device, ultrasonic level gauge and pipeline system. The anaerobic tank adopts a two-compartment anaerobic tank, which includes a first compartment anaerobic tank for biological filling of wastewater and a second compartment anaerobic tank for biological decomposition or hydrolysis of suspended activated sludge in wastewater. Under normal flow conditions, the AO+MBR wastewater treatment mode is used, as follows: Wastewater enters the basket screen through the inlet pipe. After the basket screen removes debris, larger stones, and branches, it enters the 2-compartment anaerobic tank and the intermittent MBR tank for treatment. Then, the water pump is started to extract the qualified clean water through the MBR membrane module and enter the overflow outlet. The blower and air lift return valve are started to return the digestate in the intermittent MBR tank to the 2-compartment anaerobic tank by air lift, so as to achieve simultaneous denitrification and phosphorus removal. The remaining sludge in the intermittent MBR tank is periodically airlifted into the sedimentation tank by the blower and sludge discharge valve. When the wastewater volume is large, a parallel AO (Anaerobic / Anaerobic) and MBR (Mechanical Bioreactor) wastewater treatment mode is adopted, as follows: Wastewater enters a basket screen through the inlet pipe. After the basket screen removes debris, larger particles of stone, and branches, it enters a two-chamber anaerobic tank and an intermittent MBR tank for treatment. Then, the water pump is started to draw qualified clean water through the MBR membrane module and discharge it into the overflow outlet. When the wastewater volume is large and the liquid level of the entire facility, including the intermittent MBR tank, is at a high level, the valve between the intermittent MBR tank and the sedimentation tank and the phosphorus removal dosing device are opened simultaneously with the water pump discharge from the MBR membrane module. The phosphorus removal agent added by the phosphorus removal dosing device is mixed with the mixed liquor in the intermittent MBR tank and then enters the sedimentation tank for sedimentation. The supernatant is discharged into the overflow outlet. The blower, aeration valve, and sludge return valve are opened to allow the sludge settled in the sedimentation tank to be returned to the intermittent MBR tank by airlift. The phosphorus removal agent used is polyaluminum chloride (PAC) or polyferric sulfate (PFS). The blower and airlift return valve are started, and the digestate in the intermittent MBR tank is returned to the 2-compartment anaerobic tank by airlift using the blower to achieve simultaneous denitrification and phosphorus removal. The remaining sludge in the intermittent MBR tank is periodically airlifted into the sedimentation tank by starting the blower and sludge discharge valve. The supernatant in the sedimentation tank flows into the anaerobic tank by gravity. At this time, the entire biological reaction system is operating in parallel with the MBR and the A / O system until the sewage flow rate is reduced to the normal flow rate. When the wastewater volume is small, the AO+Membrane SBR intermittent operation wastewater treatment mode is adopted, as follows: Wastewater enters the basket screen through the inlet pipe. After the basket screen removes debris, larger particles of stone, and branches, it enters the 2-chamber anaerobic tank and the intermittent MBR tank for treatment. Due to the small wastewater volume, the overall liquid level of the facility, including the intermittent MBR tank, is at a low level. At this time, the blower stops aeration, and the dissolved oxygen (DO) in the intermittent MBR tank gradually decreases, transitioning from an aerobic state to anoxic and anaerobic states, entering the idle period of the membrane SBR process mode. When the liquid level of the facility, including the intermittent MBR tank, rises to the design height, the blower starts aeration again, and the intermittent operation resumes. When the MBR tank enters the aerobic state, and the aerobic state lasts for 2 hours, the MBR membrane module and water pump start up, and the system begins to drain water. If the water volume is still small and the liquid level in the facility drops to the set low level, the blower stops aeration again, the MBR membrane module and pump are shut down, and the system enters the idle period of the membrane SBR process mode again. This cycle repeats. When the water volume is small or there is no water inflow, the anaerobic tank and intermittent MBR tank are at a low liquid level. At this time, the intermittent MBR tank stops aeration, the sedimentation tank is in an anaerobic sedimentation state, and the mixed liquor in the tank undergoes in-situ denitrification under the action of anaerobic bacteria, denitrifying nitrate nitrogen to generate nitrogen gas, thereby removing the total nitrogen in the mixed liquor.

2. The wastewater treatment process with automatic switching between air-lift reflux anaerobic and intermittent MBR as described in claim 1, characterized in that: The basket-style grille has a pore diameter of 10 mm.

3. The wastewater treatment process with automatic switching between air-lift reflux anaerobic and intermittent MBR as described in claim 1, characterized in that: The first anaerobic tank has a HRT of 1-1.5h, the second anaerobic tank has a HRT of 2-2.5h, the intermittent MBR tank has a HRT of 2-4h, the first anaerobic tank has a DO of less than 0.2mg / L, the second anaerobic tank has a DO of less than or equal to 0.5mg / L, the intermittent MBR tank has a DO of 2.5-4.5mg / L, the sludge loading is 0.05-0.15 (kgBOD5 / kgMLSS.d), the intermittent MBR tank has an SV30 of 25%-60%, and an MLSS of 6-12g / L.

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