An off-line recovery cleaning method for a decentralized wastewater treatment MBR system

Abstract

The application discloses an off-line recovery cleaning method for a decentralized sewage treatment MBR system, which comprises the following steps: emptying the membrane pool of the MBR system by controlling the sludge discharge operation of the anoxic pool, the aerobic pool, the membrane pool and the reflux pool of the MBR system, soaking and cleaning the membrane assembly by using the water produced by the MBR to prepare alkaline cleaning solution / acid cleaning solution, and finally discharging the alkaline cleaning solution / acid cleaning solution into the biochemical system for consumption and recovering the system operation. The cleaning method is suitable for the recovery cleaning of the membrane of the MBR system for decentralized sewage treatment, has short cleaning time and high efficiency, the cleaning foam generated in the cleaning process will not overflow and pollute the environment, and the cleaning waste liquid will not impact the biochemical system.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and more specifically to an offline restorative cleaning method for a decentralized wastewater treatment MBR system. Background Technology

[0002] Wastewater treatment systems are generally classified into centralized and decentralized types. Centralized wastewater treatment systems are characterized by large treatment capacity, high infrastructure costs, and high operating costs, and are suitable for wastewater treatment in areas with concentrated pollution sources. However, domestic sewage from specific areas such as black and odorous water bodies, intercepted sewage, pump station forebay sewage, and rural and urban-rural fringe areas, military bases, tourist areas, detached villa areas, and airports—areas located in the suburbs or far from towns and not covered by urban municipal pipe networks—is characterized by small sewage volume, large fluctuations, dispersed sources, and numerous pollution sources, making centralized treatment unsuitable. For this type of wastewater, decentralized treatment, i.e., on-site treatment and reuse, is currently the focus of research and application. Among these, the MBR membrane treatment process has been widely used in the field of wastewater treatment, especially in decentralized wastewater treatment, due to its advantages of increased membrane flux, reduced membrane costs, and extended lifespan. However, after a period of operation, MBR membranes are susceptible to varying degrees of fouling, resulting in a decrease in membrane flux, requiring periodic restorative cleaning.

[0003] Currently, the main problems with offline restorative cleaning of membranes in decentralized wastewater treatment MBR systems are as follows:

[0004] 1. Offline recovery cleaning is difficult.

[0005] Offline restorative cleaning includes two methods: removing the membrane modules from the membrane tank and immersing them in a cleaning tank containing chemical cleaning agents (ex-situ offline restorative cleaning), or evacuating the activated sludge from the membrane tank and directly injecting chemical agents into the membrane tank to immerse the membrane modules (in-situ offline restorative cleaning). Ex-situ offline restorative cleaning has been extensively researched. Chinese patents CN206173093U and CN205386415U provide two types of mobile MBR membrane cleaning devices. These devices utilize heavy-duty trucks to transport the membrane cleaning equipment to the treatment point, and the membrane modules are hoisted from the membrane tank to the cleaning device for cleaning. This solves the problem of high risk of membrane fiber dehydration and scrapping associated with return-to-factory offline restorative cleaning. However, it also introduces problems with applicability to areas with poor road transport and cleaning conditions, such as scenic tourist areas, polluted water bodies, and pump station forebays. In summary, poor applicability, high transportation and hoisting costs, and high wastewater treatment costs are the key factors limiting the large-scale application of ex-situ offline restorative cleaning.

[0006] In-situ offline restorative cleaning avoids the aforementioned problems, but it also poses new requirements for MBR system design. Chinese patent CN110776091A discloses an in-situ offline restorative cleaning method for submerged MBR systems that has no impact on sludge activity: the system has n membrane tanks (n≥4), of which n-1 are working membrane tanks and the remaining 1 is an empty membrane tank. During in-situ offline restorative cleaning, the cleaning pump first pumps the sludge from the working membrane tank to be cleaned into the empty membrane tank, then pumps the cleaning agent from the cleaning agent tank into the working membrane tank to be cleaned. After soaking for a certain period, the reducing agent from the reducing agent tank is pumped into the working membrane tank to be cleaned. Finally, the non-toxic waste liquid is returned to the equalization tank, and the sludge from the empty membrane tank is pumped back to the cleaned working membrane tank. Essentially, it achieves the scheduling of sludge mixed liquor through the empty membrane tank, obtains cleaning water through the parallel operation of n-1 MBR systems, and disposes of cleaning waste liquid through reduction with the reducing agent. However, the minimum economic permeate output of n-1 (n≥4) MBR systems is inconsistent with the characteristics of small and fluctuating wastewater output in decentralized systems, making them difficult to apply universally. The installation of empty membrane tanks contradicts the dispersed nature of decentralized wastewater sources and the large number of pollution sources, resulting in poor economic efficiency and making widespread application difficult.

[0007] Due to the characteristics of decentralized wastewater, the following problems exist when MBR systems (especially single MBR systems) are cleaned offline in situ: (1) it is difficult to transfer the mixed liquor of activated sludge in the membrane tank; (2) it is difficult to obtain cleaning water source; (3) it is difficult to control cleaning foam, which can easily cause environmental pollution; (4) it is difficult to treat cleaning waste liquid, which can easily impact the biochemical system.

[0008] 2. Existing cleaning agents have poor cleaning effects.

[0009] MBR system membrane restoration cleaning often employs a combined "alkaline washing" and "acid washing" method. Currently, alkaline washing agents typically use 0.1%–0.3% sodium hypochlorite solution, while acid washing agents typically use 1%–3% citric acid solution. However, with increasingly stringent effluent standards, decentralized wastewater treatment MBR systems are increasingly being used for high-efficiency nitrogen and phosphorus removal wastewater treatment. Phosphorus removal is gradually shifting from primarily biological to primarily chemical methods. Chemical phosphorus removal coagulants introduce Fe... 3+ Al 3+ and PO4 3- Plasma easily deposits on the membrane surface, forming new membrane contaminants. Existing cleaning agents are ineffective against Ca2+. 2+ Mg 2+ Fe 3+ Al 3+ and PO4 3- The pollutants formed by these substances have a weak dissolving ability, resulting in poor cleaning effect. Summary of the Invention

[0010] To address the aforementioned technical problems, this invention provides an offline restorative cleaning method for decentralized wastewater treatment MBR systems.

[0011] The technical solution adopted in this invention is:

[0012] An offline restorative cleaning method for a decentralized wastewater treatment MBR system, the decentralized wastewater treatment MBR system comprising, in sequence, an anoxic tank, an aerobic tank, a membrane tank, a return tank, a clear water tank, and a sludge removal system. The membrane tank houses MBR membrane modules. Permeate from the MBR membrane modules is pumped into the return tank and the clear water tank. The return tank is connected to the anoxic tank via a return pump. The clear water tank is connected to the permeate pipe of the MBR membrane modules via a chemical cleaning pump. Each of the anoxic tank, aerobic tank, membrane tank, return tank, and clear water tank is equipped with a sludge discharge valve at its bottom. The sludge discharge valve is connected to the sludge removal system via a sludge discharge pipe and a sludge discharge pump. The clarified liquid separated by the sludge removal system is pumped back to the anoxic tank. The offline cleaning method for the decentralized wastewater treatment MBR system includes the following steps in sequence:

[0013] Step 1: Without adding any new cleaning equipment, empty the membrane tank by controlling the sludge discharge operations of the anoxic tank, aerobic tank, membrane tank, and return tank.

[0014] Step 2: Use the permeate from the MBR to prepare an alkaline washing agent to soak the membrane module in alkaline washing. The alkaline washing waste liquid is discharged to the biological treatment system for disposal.

[0015] Step 3: Use the permeate from the MBR to prepare an acid washing agent to soak the membrane modules in acid washing. The acid washing waste liquid is discharged into the biological treatment system for disposal.

[0016] Step 4: Restore system operation.

[0017] Furthermore, step one includes:

[0018] 1.1) Stop the system water intake, open the sludge discharge valves at the bottom of the aerobic tank and membrane tank to connect the two tanks; turn on the reflux pump and the permeate pump to discharge the permeate to the clear water tank; continue to produce water until the liquid level in the reflux tank drops to the reflux pump protection level, then stop the reflux pump.

[0019] 1.2) Close the sludge discharge valves at the bottom of the aerobic tank and membrane tank, open the sludge discharge valve at the bottom of the return tank, and start the sludge discharge pump. The remaining activated sludge mixture in the return tank enters the desludge system via the sludge discharge pump. When the return tank is empty, close the sludge discharge valve at the bottom of the return tank. The clear liquid produced by the desludge system is pumped into the anoxic tank by the clear liquid pump.

[0020] 1.3) Open the sludge discharge valves at the bottom of the aerobic tank and membrane tank, close the inlet valve of the clear water tank, open the inlet valve of the return tank, and discharge the permeate to the return tank; continue to produce water, and when the liquid level in the return tank reaches the high level, close the inlet valve of the return tank, open the inlet valve of the clear water tank, and discharge the permeate to the clear water tank.

[0021] 1.4) When the liquid level in the membrane tank drops to 20-30 cm below the membrane fibers, stop the permeate pump and use static pressure permeate until the liquid level in the membrane tank submerges the membrane fibers.

[0022] 1.5) Close the sludge discharge valve at the bottom of the aerobic tank and turn on the sludge discharge pump. The remaining activated sludge mixture in the membrane tank enters the desludge system through the sludge discharge pump. When the membrane tank is empty, close the sludge discharge valve at the bottom of the membrane tank. The clear liquid produced by the desludge system is pumped into the anoxic tank by the clear liquid pump.

[0023] Furthermore, step two includes:

[0024] 2.1) Use a temporary pump to transfer the permeate temporarily stored in the return tank to the membrane tank, add alkaline washing agent into the membrane tank, and stop the temporary pump when the liquid level in the membrane tank submerges the top of the membrane fibers by 10-15 cm.

[0025] 2.2) Start alkaline washing and soaking, and control the soaking time to 8-12 hours. The cleaning foam generated during the alkaline washing and soaking process flows from the membrane tank into the return tank and is pumped into the desludge system for disposal through the sludge discharge pump.

[0026] 2.3) After alkaline washing, the residual chlorine load q is determined to be no greater than 0.01m. 3 At a rate of / h, a temporary pump is used to transfer the alkaline washing waste liquid in the membrane tank to the aerobic tank for disposal until the membrane tank is emptied.

[0027] q = C1·Q1 / M1;

[0028] C1 represents the residual chlorine concentration in the alkaline washing waste liquid;

[0029] M1 is the concentration of activated sludge in the aerobic tank;

[0030] Q1 is the temporary pump flow rate.

[0031] Furthermore, step three includes:

[0032] 3.1) Start the chemical cleaning pump and reverse the flow of the permeate temporarily stored in the clear water tank into the membrane tank; add the acid washing agent into the membrane tank until the liquid level in the membrane tank submerges the top of the membrane fibers by 10-15 cm, then stop the chemical cleaning pump.

[0033] 3.2) Start pickling and soaking, and control the soaking time to 8-12 hours. The cleaning foam generated during the pickling and soaking process flows from the membrane tank into the return tank and is pumped into the desludge system for disposal through the sludge discharge pump.

[0034] 3.3) After pickling is completed, use a temporary pump to transfer the pickling waste liquid from the membrane tank to the return tank, turn off the return pump, and start the system to produce water under static pressure.

[0035] 3.4) Use a temporary pump to transfer the pickling waste liquid in the return tank to the anoxic tank until the return tank is emptied. Adjust the flow rate of the temporary pump and the flow rate of the static pressure permeate to ensure that the relative COD concentration R is not greater than 0.01.

[0036] R = C2·Q1 / Q3·M1

[0037] Q1 is the temporary pump flow rate;

[0038] Q3 is the static pressure permeable flow rate;

[0039] C2 represents the COD concentration of the pickling waste liquid;

[0040] M1 represents the concentration of activated sludge in the aerobic tank.

[0041] Furthermore, step four includes: after the pickling waste liquid is treated, the reflux pump is turned on, water is introduced into the reflux tank, and the system operates normally.

[0042] Furthermore, the alkaline washing agent is prepared from sodium hypochlorite, a conversion agent, a chelating agent, a surfactant, and water; the concentration of sodium hypochlorite in the alkaline washing agent is 1000-3000 mg / L, the concentration of the conversion agent is 10-50 mg / L, the concentration of the chelating agent is 10-50 mg / L, and the concentration of the surfactant is 1-10 mg / L.

[0043] Further, the converting agent is selected from at least one of sodium hydroxide, sodium carbonate, and sodium bicarbonate; the chelating agent is selected from at least one of sodium hexametaphosphate, disodium ethylenediaminetetraacetate, and tetrasodium ethylenediaminetetraacetate; and the surfactant is selected from at least one of nonylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, and alkanolamide.

[0044] Furthermore, the pickling agent is prepared from citric acid, sulfamic acid, corrosion inhibitor, chelating agent, surfactant, and water; the concentration of citric acid in the pickling agent is 1000-3000 mg / L, the concentration of sulfamic acid is 50-100 mg / L, the concentration of corrosion inhibitor is 10-50 mg / L, the concentration of chelating agent is 10-50 mg / L, and the concentration of surfactant is 1-10 mg / L.

[0045] Furthermore, the corrosion inhibitor is selected from at least one of amines and thioureas; the chelating agent is selected from at least one of sodium tripolyphosphate and ethylenediaminetetraacetic acid; and the surfactant is selected from at least one of nonylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, and alkanolamide.

[0046] The beneficial effects of this invention are:

[0047] 1. The cleaning method of the present invention can realize in-situ offline restorative cleaning of membranes in decentralized sewage treatment MBR systems, especially single MBR systems. During the cleaning process, the cleaning foam will not overflow and will not impact the biochemical system or affect the system's recovery operation.

[0048] 2. The cleaning solution of the present invention does not require additional chemical treatment for the waste liquid generated during the cleaning process. The alkaline washing waste liquid is transferred to the aerobic tank for disposal, and the acid washing waste liquid is transferred to the anoxic tank for disposal, thereby reducing the pollution load. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the decentralized wastewater treatment MBR system of the present invention. Detailed Implementation

[0050] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0051] It should be noted that all chemical reagents used in the following examples were purchased from the market.

[0052] Example 1

[0053] See Figure 1 This embodiment provides an offline restorative cleaning method for a decentralized wastewater treatment MBR system. The decentralized wastewater treatment MBR system includes an anoxic tank 1, an aerobic tank 2, a membrane tank 3, a return tank 4, a clear water tank 5, and a sludge removal system 6 connected in sequence. The membrane tank is equipped with an MBR membrane module 7. The permeate from the MBR membrane module enters the return tank 4 and the clear water tank 5 through a permeate pump 8. The return tank 4 is connected to the anoxic tank 1 through a return pump 9. The clear water tank 5 is cleaned by a chemical cleaning pump 10. The permeate pipe is connected to the MBR membrane module 7; the bottom of the anoxic tank 1, aerobic tank 2, membrane tank 3, return tank 4 and clear water tank 5 are all equipped with sludge discharge valves. The sludge discharge valves are connected to the desludge system 7 through sludge discharge pipes and sludge discharge pump 11. The clear liquid separated by the desludge system is returned to the anoxic tank 1 through the clear liquid pump 12; an alkaline washing tank 21 and an acid washing tank 22 are set above the membrane tank 3. The alkaline washing tank 21 is connected to the membrane tank 3 through an alkaline pump and valves, and the acid washing tank 22 is connected to the membrane tank 3 through an acid pump and valves.

[0054] When the transmembrane pressure differential of the decentralized wastewater treatment MBR system in this embodiment rises to 30 kPa, offline cleaning is performed using a self-prepared cleaning agent. The offline cleaning method includes the following steps:

[0055] 1) Preparation of alkaline washing agent: Weigh 50g of 10wt% sodium hypochlorite solution, 0.5g of sodium hydroxide, 0.5g of sodium hexametaphosphate, and 0.05g of nonylphenol polyoxyethylene ether, dilute with water to 50L, and mix thoroughly for later use. In this example, the concentration of sodium hypochlorite in the alkaline washing agent is 1000mg / L, the concentration of the conversion agent is 10mg / L, the concentration of the chelating agent is 10mg / L, and the concentration of the surfactant is 1mg / L.

[0056] 2) Preparation of pickling agent: Weigh 50g citric acid, 2.5g sulfamic acid, 0.5g dicyclohexyl nitrite, 0.5g sodium tripolyphosphate, and 0.05g nonylphenol polyoxyethylene ether. Dilute with water to 50L and mix thoroughly. In this example, the concentration of citric acid in the pickling agent is 1000mg / L, the concentration of sulfamic acid is 50mg / L, the concentration of corrosion inhibitor is 10mg / L, the concentration of chelating agent is 10mg / L, and the concentration of surfactant is 1mg / L.

[0057] 3) Draining the membrane tank:

[0058] 3.1) Stop the system water intake, open the sludge discharge valves at the bottom of aerobic tank 2 and membrane tank 3 to connect the two tanks; turn on the permeate pump 8 to discharge permeate to clear water tank 5, and continue to produce water until the liquid level in return tank 4 drops to the protection level of return pump 9, then stop return pump 9.

[0059] 3.2) Close the sludge discharge valves at the bottom of aerobic tank 2 and membrane tank 3, open the sludge discharge valve at the bottom of return tank 4, and start sludge discharge pump 11. The remaining activated sludge mixture in return tank 4 enters desludge system 6 through sludge discharge pump 11 until return tank 4 is emptied. Close the sludge discharge valve at the bottom of return tank. The clear liquid produced by desludge system 6 is pumped into anoxic tank 1 by clear liquid pump 12.

[0060] 3.3) Open the sludge discharge valves at the bottom of aerobic tank 2 and membrane tank 3, close the inlet valve of clear water tank 5, open the inlet valve of return tank 4, and discharge the produced water to return tank 4; continue to produce water until return tank 4 reaches a high liquid level, then close the inlet valve of return tank 4, open the inlet valve of clear water tank 5, and discharge the produced water to clear water tank 5.

[0061] 3.4) When the liquid level in the membrane tank 3 drops to 20-30 cm below the membrane fibers, stop the permeate pump 8 and continue static pressure permeate until the liquid level in the membrane tank 3 submerges the membrane fibers.

[0062] 3.5) Close the bottom sludge discharge valve of aerobic tank 2 and turn on sludge discharge pump 11. The remaining activated sludge mixture in membrane tank 3 enters the desludge system 6 through sludge discharge pump 11. When membrane tank 3 is emptied, close the bottom sludge discharge valve of membrane tank 3. The clear liquid produced by desludge system 6 is pumped into anoxic tank 1 by clear liquid pump 12.

[0063] 4) Alkaline washing and soaking:

[0064] 4.1) Use temporary pump 9 to transfer the permeate temporarily stored in return tank 4 to membrane tank 3. Add the alkaline washing agent prepared in Example 1 into membrane tank 3 through alkaline washing tank and alkaline pump. Stop temporary pump 9 when the liquid level in membrane tank 3 submerges the top of the membrane fibers by 10-15 cm.

[0065] 4.2) Start alkaline washing and soaking, and control the soaking time to 8-12 hours. The cleaning foam generated during the alkaline washing and soaking process flows from the membrane tank 3 into the return tank 4 and is pumped into the desludge system 6 through the sludge discharge pump 11 for disposal.

[0066] 4.3) After alkaline washing, the residual chlorine concentration C1 of the alkaline washing wastewater in membrane tank 3 is measured to be 20 mg / L, and the activated sludge concentration M1 in aerobic tank 2 is measured to be 10000 mg / L. A temporary pump is used to transfer the alkaline washing wastewater from membrane tank 3 to aerobic tank 2 for disposal until membrane tank 3 is emptied. During the emptying process, the flow rate Q1 of the temporary pump is adjusted to 2 m³ / L. 3 / h, ensuring that the residual chlorine load q remains below 0.01m 3 / h.

[0067] q = C1·Q1 / M1;

[0068] C1 represents the residual chlorine concentration in the alkaline washing waste liquid;

[0069] M1 is the concentration of activated sludge in the aerobic tank;

[0070] Q1 is the temporary pump flow rate.

[0071] 5) Acid washing and soaking:

[0072] 5.1) Start the chemical cleaning pump 10 and reverse the flow of the permeate temporarily stored in the clear water tank 5 into the membrane tank 3; add the acid washing agent prepared in Example 1 into the membrane tank 3 through the acid washing tank and acid pump until the liquid level in the membrane tank submerges the top of the membrane fibers by 10 to 15 cm, then stop the chemical cleaning pump 10.

[0073] 5.2) Start pickling and soaking, and control the soaking time to 8-12 hours. The cleaning foam generated during the pickling and soaking process flows into the return tank 4 through the membrane 3 and is pumped into the desludge system 6 through the sludge discharge pump 11 for disposal.

[0074] 5.3) After pickling is completed, use a temporary pump to transfer the pickling waste liquid in membrane tank 3 to return tank 4, turn off return pump 9, and start water intake and static pressure water production.

[0075] 5.4) When the COD concentration C2 of the pickling waste liquid is determined to be 100 mg / L and the activated sludge concentration M1 in aerobic tank 2 is 10000 mg / L, the pickling waste liquid in return tank 4 is transferred to anoxic tank 1 using a temporary pump until return tank 4 is emptied. During the emptying process, the flow rate Q1 of the temporary pump is adjusted to 2 m³ / s. 3 / h and static pressure permeate flow rate Q3 is 2m 3 / h, so that the relative COD concentration R is always below 0.01.

[0076] R = C2·Q1 / Q3·M1

[0077] Q1 is the temporary pump flow rate;

[0078] Q3 is the static pressure permeable flow rate;

[0079] C2 represents the COD concentration of the pickling waste liquid;

[0080] M1 represents the concentration of activated sludge in the aerobic tank.

[0081] 6) System recovery: After the pickling waste liquid is treated, water is introduced into the return tank 4, and the return pump 9 is turned on, and the system is running normally.

[0082] After the system had been running normally for 24 hours, the membrane flux recovery rate was measured to be 77.6%.

[0083] Example 2

[0084] Preparation of alkaline washing agent: Weigh 1500g of 10wt% sodium hypochlorite solution, 2.5g of sodium carbonate, 0.5g of disodium ethylenediaminetetraacetate, and 0.5g of alkanolamide, dilute with water to 50L, mix well and set aside.

[0085] Preparation of pickling agent: Weigh 150g citric acid solution, 5g aminosulfonic acid, 2.5g thiourea corrosion inhibitor, 0.5g ethylenediaminetetraacetic acid, and 0.5g fatty alcohol polyoxyethylene ether, dilute with water to 50L, mix well and set aside.

[0086] Using the cleaning agent prepared in Example 2, and employing the same method as in Example 1, the cleaning agent was applied to... Figure 1 The decentralized wastewater treatment MBR system shown was subjected to offline restorative cleaning. After 24 hours of normal operation, the membrane flux recovery rate was measured to be 88.2%.

[0087] Example 3

[0088] Preparation of alkaline washing agents: Alkaline and acid washing agents were prepared using the same raw material composition as in Example 3. In the alkaline washing agent of this example, the concentration of sodium hypochlorite was 1500 mg / L, the concentration of the conversion agent was 30 mg / L, the concentration of the chelating agent was 30 mg / L, and the concentration of the surfactant was 5 mg / L. In the acid washing agent of this example, the concentration of citric acid was 2000 mg / L, the concentration of sulfamic acid was 70 mg / L, the concentration of the corrosion inhibitor was 20 mg / L, the concentration of the chelating agent was 20 mg / L, and the concentration of the surfactant was 5 mg / L.

[0089] Using the cleaning agent prepared in Example 3, and employing the same method as in Example 1, the cleaning agent was applied to... Figure 1The decentralized wastewater treatment MBR system shown was cleaned offline. After 24 hours of normal operation, the membrane flux recovery rate was measured to be 80.4%.

[0090] Comparative Example 1

[0091] Commercially available alkaline and acidic cleaning solutions were used, and the same method as in Example 1 was employed to clean the surfaces. Figure 1 The decentralized wastewater treatment MBR system shown was cleaned offline. After 24 hours of normal operation, the membrane flux was measured to have recovered to 65.6%.

[0092] As can be seen from the above embodiments and comparative examples, the cleaning agent prepared in this invention is used to perform offline cleaning of the MBR system, and its cleaning effect is far superior to that of existing cleaning solutions.

[0093] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An offline restorative cleaning method for a decentralized wastewater treatment MBR system, wherein the decentralized wastewater treatment MBR system comprises, in sequence, an anoxic tank, an aerobic tank, a membrane tank, a return tank, a clear water tank, and a sludge removal system; the membrane tank is equipped with an MBR membrane module; the permeate from the MBR membrane module enters the return tank and the clear water tank via a permeate pump; the return tank is connected to the anoxic tank via a return pump; and the clear water tank is connected to the permeate pipe of the MBR membrane module via a chemical cleaning pump; sludge discharge valves are installed at the bottom of the anoxic tank, aerobic tank, membrane tank, return tank, and clear water tank; the sludge discharge valves are connected to the sludge removal system via sludge discharge pipes and sludge discharge pumps; and the clarified liquid separated by the sludge removal system is returned to the anoxic tank via a clarified liquid pump; characterized in that: The offline cleaning method for the decentralized wastewater treatment MBR system includes the following steps connected in sequence: Step 1: Without adding any new cleaning equipment, empty the membrane tank by controlling the sludge discharge operations of the anoxic tank, aerobic tank, membrane tank, and return tank. Step 2: Use the permeate from the MBR to prepare an alkaline washing agent to soak the membrane module in alkaline washing. The alkaline washing waste liquid is discharged to the biological treatment system for disposal. Step 3: Use the permeate from the MBR to prepare an acid washing agent to soak the membrane modules in acid washing. The acid washing waste liquid is discharged into the biological treatment system for disposal. Step 4: Restore system operation; Step one includes: 1.1) Stop the system water intake, open the sludge discharge valves at the bottom of the aerobic tank and the membrane tank to connect the two tanks; turn on the permeate pump to discharge permeate into the clear water tank, continue to produce water until the liquid level in the return tank drops to the protection level of the return pump, then stop the return pump. 1.2) Close the bottom sludge discharge valves of the aerobic tank and membrane tank, open the bottom sludge discharge valve of the return tank, start the sludge discharge pump, and the remaining activated sludge mixture in the return tank enters the desludge system through the sludge discharge pump until the return tank is emptied and the bottom sludge discharge valve of the return tank is closed. The clear liquid produced by the desludge system is pumped into the anoxic tank by the clear liquid pump. 1.3) Open the sludge discharge valves at the bottom of the aerobic tank and membrane tank, close the inlet valve of the clear water tank, open the inlet valve of the return tank, and discharge the permeate to the return tank; continue to produce water until the return tank reaches a high liquid level, then close the inlet valve of the return tank, open the inlet valve of the clear water tank, and discharge the permeate to the clear water tank. 1.4) When the liquid level in the membrane tank drops to 20-30 cm below the membrane fibers, stop the permeate pump and use static pressure permeate until the liquid level in the membrane tank submerges the membrane fibers. 1.5) Close the sludge discharge valve at the bottom of the aerobic tank and turn on the sludge discharge pump. The remaining activated sludge mixture in the membrane tank enters the desludge system through the sludge discharge pump. When the membrane tank is empty, close the sludge discharge valve at the bottom of the membrane tank. The clear liquid produced by the desludge system is pumped into the anoxic tank by the clear liquid pump. Step two includes: 2.1) Use a temporary pump to transfer the permeate temporarily stored in the return tank to the membrane tank, add alkaline washing agent into the membrane tank, and stop the temporary pump when the liquid level in the membrane tank submerges the top of the membrane fibers by 10-15 cm. 2.2) Start alkaline washing and soaking, and control the soaking time to 8-12 hours. The cleaning foam generated during the alkaline washing and soaking process flows from the membrane tank into the return tank and is pumped into the desludge system for disposal through the sludge discharge pump. 2.3) After alkaline washing is completed, if the residual chlorine load q is not greater than 0.01 m3 / h, use a temporary pump to transfer the alkaline washing waste liquid in the membrane tank to the aerobic tank for disposal until the membrane tank is emptied. q = C1·Q1 / M1; C1 represents the residual chlorine concentration in the alkaline washing waste liquid; M1 is the concentration of activated sludge in the aerobic tank; Q1 is the temporary pump flow rate; Step three includes: 3.1) Start the chemical cleaning pump and reverse the flow of the permeate temporarily stored in the clear water tank into the membrane tank; add the acid washing agent into the membrane tank until the liquid level in the membrane tank submerges the top of the membrane fibers by 10-15 cm, then stop the chemical cleaning pump. 3.2) Start pickling and soaking, and control the soaking time to 8-12 hours. The cleaning foam generated during the pickling and soaking process flows from the membrane tank into the return tank and is pumped into the desludge system for disposal through the sludge discharge pump. 3.3) After pickling is completed, use a temporary pump to transfer the pickling waste liquid from the membrane tank to the return tank, turn off the return pump, and start the system to produce water under static pressure. 3.4) Use a temporary pump to transfer the pickling waste liquid in the return tank to the anoxic tank until the return tank is emptied. Adjust the flow rate of the temporary pump and the flow rate of the static pressure permeate to ensure that the relative COD concentration R is not greater than 0.

01. R=C2·Q1 / Q3·M1 Q1 is the temporary pump flow rate; Q3 is the static pressure permeable flow rate; C2 represents the COD concentration of the pickling waste liquid; M1 represents the concentration of activated sludge in the aerobic tank.

2. The offline restorative cleaning method according to claim 1, characterized in that, Step four includes: After the pickling waste liquid is treated, the reflux pump is turned on, water is introduced into the reflux tank, and the system operates normally.

3. The offline restorative cleaning method according to claim 1, characterized in that, The alkaline washing agent is prepared from sodium hypochlorite, a conversion agent, a chelating agent, a surfactant, and water; the concentration of sodium hypochlorite in the alkaline washing agent is 1000-3000 mg / L, the concentration of the conversion agent is 10-50 mg / L, the concentration of the chelating agent is 10-50 mg / L, and the concentration of the surfactant is 1-10 mg / L.

4. The offline restorative cleaning method according to claim 3, characterized in that, The conversion agent is selected from at least one of sodium hydroxide, sodium carbonate, and sodium bicarbonate; the chelating agent is selected from at least one of sodium hexametaphosphate, disodium ethylenediaminetetraacetate, and tetrasodium ethylenediaminetetraacetate; and the surfactant is selected from at least one of nonylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, and alkanolamide.

5. The offline restorative cleaning method according to claim 1, characterized in that, The pickling agent is prepared from citric acid, sulfamic acid, corrosion inhibitor, chelating agent, surfactant and water; the concentration of citric acid in the pickling agent is 1000-3000 mg / L, the concentration of sulfamic acid is 50-100 mg / L, the concentration of corrosion inhibitor is 10-50 mg / L, the concentration of chelating agent is 10-50 mg / L and the concentration of surfactant is 1-10 mg / L.

6. The offline restorative cleaning method according to claim 5, characterized in that, The corrosion inhibitor is selected from at least one of amines and thioureas; the chelating agent is selected from at least one of sodium tripolyphosphate and ethylenediaminetetraacetic acid; and the surfactant is selected from at least one of nonylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, and alkanolamide.

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