Membrane separation device, its operation method, and biological treatment device

Abstract

To provide a membrane separation device that can effectively be backwashed, and can maintain its membrane filtration capacity stable for a long period of time, an operation method therefor, and a biological treatment device.SOLUTION: A biological treatment liquid in a reaction tank 1 is fed to a primary side of a membrane separation device 5 via a pipe 2, a water feed pump 3 and a pipe 4, and is subjected to a membrane separation treatment using a membrane 5a. Concentrated water not permeating the membrane 5a flows out of the primary side of the membrane separation device 5, and is returned to the reaction tank 1 via a pipe 6. Treated water having permeated the membrane 5a flows into a treated water tank 10 via a pipe 7, a valve 8, and a pipe 9 from a secondary side of the membrane separation device 5 and is extracted via a pipe 11. In order to start backwashing of the membrane separation device 5, the valve 8 is opened, and a valve 19 is closed and a valve 16 is opened while operating the pump 3, and subsequently a back-washing pump 13 is started. When the output of the backwashing pump 13 becomes sufficiently high after a lapse of a specified period of time, the valves 8, 16 are closed, the valve 19 is opened, and subsequently backwashing of the membrane separation device 5 is started.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a membrane separation type biological treatment apparatus that biologically treats wastewater containing organic matter and obtains treated water by membrane separation.The present invention also relates to a membrane separation device suitable for this biological treatment apparatus and a method for operating the same. [Background technology]

[0002] Patent Document 1 describes a biological treatment device that produces treated water by filtering the sludge from the primary side of the membrane toward the secondary side while circulating it through a membrane outside the biological reactor. During operation, solids gradually adhere to the primary side of the membrane. Therefore, a backwash operation is performed at regular intervals, passing treated water from the secondary side toward the primary side to remove and remove the solids adhering to the primary side of the membrane. This prevents a decrease in filtration capacity due to sludge adhering to the primary membrane surface, ensuring stable production of treated water. The backwash wastewater is returned to the biological treatment tank. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-249235 Summary of the Invention [Problem to be solved by the invention]

[0004] Backwashing the membrane is best performed for a short period of time at a higher flux (permeation flux) than during filtration, in terms of the cleaning effect on the membrane surface and the recovery rate of treated water. However, when the backwash pump is started at a predetermined interval, it takes a certain amount of time (hereinafter referred to as a time lag) for the discharge flow rate to reach a predetermined value after the backwash pump starts. During this time lag, the backwash water (treated water) has a low flow rate, so it is returned to the biological reactor as backwash wastewater without having sufficient cleaning effect. This creates a problem: the return of treated water that does not contribute to backwashing reduces the membrane filtration efficiency (recovery rate of treated water).

[0005] Furthermore, if the amount of sludge adhering to the primary side of the membrane increases during the filtration cycle or if the adhering sludge is poorly permeable, the membrane permeation differential pressure will rise significantly. Therefore, if the backwash pump output is set to a fixed value, the discharge pressure required for backwashing will be higher than the actual discharge pressure of the backwash pump, and it may become impossible to achieve the desired backwash flux.

[0006] An object of the present invention is to provide a membrane separation device that can effectively backwash the membrane separation device, reduce the amount of backwash water used, and stably maintain membrane filtration performance for a long period of time, a method for operating the same, and a biological treatment device. [Means for solving the problem]

[0007] The membrane separation device of the present invention is a membrane separation device in which the water to be treated is passed through the primary side and the treated water that has permeated the membrane is extracted from the secondary side to a treated water tank, and is characterized in that the membrane separation device is equipped with a backwash pump for supplying the treated water in the treated water tank to the secondary side, and is equipped with a switching means for switching the supply destination of the backwash pump's discharge water between the secondary side and the treated water tank.

[0008] In one aspect of the present invention, after the backwash pump is started, the switching means operates to return the discharged water to the treatment tank until the output of the backwash pump reaches a reference value or until a predetermined time has elapsed, and thereafter to introduce the discharged water into the secondary side.

[0009] The method for operating a membrane separation apparatus of the present invention is a method for operating a membrane separation apparatus of the present invention, which includes a step of supplying treated water in the treatment water tank to the secondary side by the backwash pump to backwash the membrane, and is characterized in that after the backwash pump is started, the discharge water of the backwash pump is returned to the treatment water tank until the output of the backwash pump reaches a reference value or until a predetermined time has elapsed, and then the discharge water of the backwash pump is supplied to the secondary side to perform backwashing.

[0010] The biological treatment device of the present invention has a reaction tank for biologically treating wastewater containing organic matter, a membrane separation device installed outside the reaction tank for obtaining treated water by membrane filtration, a treated water tank for storing the treated water, and a backwash pump for intermittently backwashing the membrane separation device with treated water, and is characterized by having a switching means for switching the supply destination of the backwash pump's discharge water between the secondary side of the membrane separation device and the treated water tank. [Effects of the Invention]

[0011] In this invention, the backwash pump is started to circulate the treated water to the treated water tank during the filtration cycle, and after the backwash pump output becomes sufficiently high, the valve is switched to perform membrane backwash. This allows for sufficient and efficient membrane backwashing. It also reduces the amount of backwash water used, improving the recovery rate of treated water.

[0012] Furthermore, this effect can be further improved by setting the predetermined output of the backwash pump to a value that results in a predetermined backwash flux relative to the pressure inside the tubular membrane during the filtration cycle, which is determined from the pump performance curve. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a configuration diagram of a biological treatment device according to an embodiment. [Figure 2] 1 is a configuration diagram of a biological treatment device according to an embodiment. [Figure 3] 1 is a configuration diagram of a biological treatment device according to an embodiment. [Figure 4] 1 is a configuration diagram of a biological treatment device according to an embodiment. [Figure 5] 1 is a configuration diagram of a biological treatment device according to an embodiment. [Figure 6] 1 is a configuration diagram of a biological treatment device according to an embodiment. [Figure 7] 1 is a configuration diagram of a biological treatment device according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, an embodiment will be described with reference to the drawings.

[0015] FIG. 1 shows a membrane separation device according to an embodiment, where (a) shows the filtration process, (b) shows the state immediately after starting the backwash pump, and (c) shows the backwash process.

[0016] Raw water is introduced into a biological treatment reactor 1 and subjected to biological treatment. The reactor 1 is equipped with an agitator 1a.

[0017] As shown in FIG. 1(a), in the filtration process, valve 8 is opened and feed pump 3 is operated. The biological treatment liquid in reaction tank 1 is supplied to the primary side of membrane separation device 5 through pipe 2, feed pump 3, and pipe 4, and undergoes membrane separation treatment by membrane 5a. Concentrated water that does not permeate membrane 5a flows out from the primary side of membrane separation device 5 and is returned to reaction tank 1 through pipe 6. Treated water that permeates membrane 5a flows from the secondary side of membrane separation device 5 through pipe 7, valve 8, and pipe 9 into treated water tank 10, and is taken out through pipe 11. In this filtration process, backwash pump 13, which will be described later, is stopped.

[0018] In this embodiment, the treated water tank 10 and the pipe 7 are connected by pipe 12, backwash pump 13, pipes 14 and 18, valve 19, and pipe 20 so that the treated water in the treated water tank 10 backwashes the membrane 5a of the membrane separation device 5. In addition, pipe 15, valve 16, and pipe 17 are provided so that the water from pipe 14 is returned to the treated water tank 10 when the backwash pump 13 starts. During the filtration process, both valves 16 and 19 are closed.

[0019] To start backwashing of the membrane separation device 5, as shown in Figure 1(b), with valve 8 open and feedwater pump 3 operating, valve 19 is closed, valve 16 is opened, and backwash pump 13 is started. The discharge water from backwash pump 13 is returned to the treated water tank 10 through pipes 14 and 15, valve 16, and pipe 17.

[0020] After a predetermined time has passed and the output of backwash pump 13 has become sufficiently large, valve 8 is closed, valve 16 is closed, and valve 19 is opened while water supply pump 3 is operating, as shown in Figure 1(c). As a result, the treated water in treatment tank 10 passes through pipes 12, 14, and 18, valve 19, and pipes 20 and 7 and is supplied to the secondary side of membrane separation device 5, and by permeating membrane 5a from the secondary side to the primary side, deposits adhering to the primary side of membrane 5a are peeled off.

[0021] During this backwashing process, the water supply pump 3 is also operating, and the biological treatment liquid from the reaction tank 1 is passed through the primary side of the membrane separation device 5. Therefore, the material peeled off from the primary side of the membrane 5a flows into the reaction tank 1 through the pipe 6 together with the biological treatment liquid.

[0022] After such backwashing has been carried out for a predetermined time, the backwashing pump 13 is stopped, the valve 8 is opened, and the valve 19 is closed, as shown in FIG. 1(a), and the process returns to the filtration step.

[0023] In this embodiment, as shown in Figure 1(b), when the backwash pump 13 is started, the valve 19 is closed and the valve 16 is opened, and during the start-up period until the output of the pump 13 becomes sufficiently high, the discharge water of the pump 13 is returned to the treated water tank 10, and no backwash water is supplied to the membrane separation device 5. Therefore, during the start-up period of the backwash pump 13, backwash water at a low flow rate is not supplied to the membrane separation device 5, and treated water with little backwash effect is not returned. As a result, the wasteful use of treated water for backwashing is avoided, and the treatment efficiency (membrane filtration efficiency) is improved.

[0024] Another embodiment will be described with reference to Figures 2 to 7. This embodiment relates to a biological treatment device in which two membrane separation devices 38, 44 are arranged.

[0025] 2 shows a state in which the biologically treated liquid is passed through the first membrane separation device 38, and the resulting concentrated water is passed through the second membrane separation device 44 for filtration. In FIG. 2, the liquid to be treated is passed through the membrane separation devices 38 and 44 in the forward direction.

[0026] 2, the backwash pump 62 is stopped, and only the feedwater pump 33 is operating. Also, the valves 35, 41, 47, 53, and 58 are open, and the other valves are closed.

[0027] The biological treatment liquid in reaction tank 31 equipped with agitator 31a is supplied to the primary side of membrane separation device 38 through pipe 32, feed pump 33, pipe 34, valve 35, and pipes 36 and 37. Concentrated water that did not permeate membrane 38a is supplied from the primary side of membrane separation device 38 through pipes 39 and 40, valve 41, and pipes 42 and 43 to the primary side of membrane separation device 44. Concentrated water that did not permeate membrane 44a is returned to reaction tank 31 from the primary side of membrane separation device 44 through pipes 45 and 46, valve 47, and pipes 48 and 49.

[0028] The treated water that has permeated membrane 38a of membrane separation device 38 is introduced from the secondary side of membrane separation device 38 through pipes 51 and 52, valve 53, and pipe 54 into treated water tank 55. The treated water that has permeated membrane 44a of membrane separation device 44 is introduced from the secondary side of membrane separation device 44 through pipes 56 and 57, valve 58, and pipe 59 into treated water tank 55.

[0029] In this embodiment, in order to backwash the membrane separation device 38 with the treated water in the treated water tank 55, a pipe 61, a backwash pump 62, a valve 90, pipes 63 and 64, a valve 65, and a pipe 66 are provided, and the pipe 66 is connected to the connection point of the pipes 51 and 52.

[0030] In addition, in order to backwash the membrane separation device 44, a pipe 67 branched from the junction of the pipes 63 and 64 is connected to the junction of the pipes 56 and 57 via a valve 68 and a pipe 69.

[0031] In this embodiment as well, valves 90 and 91 and a pipe 92 are provided for returning the discharge water of the backwash pump 62 to the treated water tank 55 when the backwash pump 62 is started.

[0032] 3 shows a state in which the membrane separation device 38 is backwashed and filtration is performed by the membrane separation device 44. In this state, the pumps 33 and 62 are operating, the valves 35, 41, 47, 58, 65, and 90 are open, and the other valves are closed.

[0033] The biological treatment liquid in the reaction tank 31 is supplied to the primary side of a membrane separation device 38 through piping 32, a feedwater pump 33, piping 34, a valve 35, and piping 36 and 37. Backwash water is supplied to the secondary side of the membrane separation device 38, as described below. The biological treatment liquid supplied to the primary side and the backwash wastewater that has permeated through the membrane 38a from the secondary side to the primary side are mixed and supplied from the primary side of the membrane separation device 38 to the primary side of the membrane separation device 44 through piping 39 and 40, a valve 41, and piping 42 and 43. The concentrated water that did not permeate the membrane 44a is returned from the primary side of the membrane separation device 44 to the reaction tank 31 through piping 45 and 46, a valve 47, and piping 48 and 49.

[0034] The treated water that has permeated the membrane 44 a of the membrane separation device 44 is introduced from the secondary side of the membrane separation device 44 through pipes 56 and 57 , a valve 58 , and a pipe 59 into a treated water tank 55 .

[0035] A portion of the treated water in the treated water tank 55 is supplied to the secondary side of the membrane separation device 38 through the pipe 61, the backwash pump 62, the pipes 63, 64, 66, 51, and the valves 90, 65, and the membrane 38a is backwashed.

[0036] 4 shows a state in which filtration is performed in the membrane separation device 38 and backwashing is performed on the membrane separation device 44. In this state, the pumps 33 and 62 are operating, the valves 35, 41, 47, 53, 68, and 90 are open, and the other valves are closed.

[0037] The biological treatment liquid in the reaction tank 31 is supplied to the primary side of the membrane separation device 38 through piping 32, feed pump 33, piping 34, valve 35, and piping 36 and 37. The concentrated water that did not permeate the membrane 38a is supplied from the primary side of the membrane separation device 38 through piping 39 and 40, valve 41, and piping 42 and 43 to the primary side of the membrane separation device 44. Backwash water is supplied to the secondary side of the membrane separation device 44 through piping 61, backwash pump 62, piping 63, 67, 69, and 56, and valves 90 and 68. The liquid from the membrane separation device 38 supplied to the primary side and the backwash wastewater that has permeated the membrane 44a from the secondary side to the primary side are mixed together and returned from the primary side of the membrane separation device 44 to the reaction tank 31 through piping 45 and 46, valve 47, and piping 48 and 49.

[0038] The treated water that has permeated the membrane 38a of the membrane separation device 38 is introduced from the secondary side of the membrane separation device 38 through pipes 51 and 52, a valve 53, and a pipe 54 into a treated water tank 55.

[0039] When starting the backwash pump 62 to perform backwashing in Figures 3 and 4, the same start-up operation as in Figure 1(a) is performed. That is, when starting the backwash pump 62, valve 90 is closed, valve 91 is opened, and the backwash pump 62 is started, and the pump discharge water is returned to the treated water tank 55. Then, after the output of the pump 62 becomes sufficiently large, valve 90 is opened, valve 91 is closed, and backwashing is performed, as shown in Figures 3 and 4. The same applies to the cases of Figures 6 and 7 described below.

[0040] In Figures 2 to 4, the biological treatment liquid is passed through the primary side of the membrane separation devices 38, 44 in the above-mentioned direction (hereinafter referred to as the forward direction), but in Figures 5 to 7, which will be explained next, the biological treatment liquid is passed through the primary side of the membrane separation devices 38, 44 in the opposite direction to the forward direction (hereinafter referred to as the reverse direction).

[0041] 5 shows the membrane separation devices 38 and 44 undergoing filtration operation with reverse water flow. In this state, the water supply pump 33 is operating, and the backwash pump 62 is stopped. Also, valves 53, 58, 72, 76, and 82 are open, and the other valves are closed.

[0042] The biological treatment liquid in the reaction tank 31 is supplied to the primary side of the membrane separation device 38 through piping 32, feed pump 33, piping 34 and 71, valve 72, and piping 73 and 39. The concentrated water that did not permeate through membrane 38a is supplied from the primary side of the membrane separation device 38 to the primary side of the membrane separation device 44 through piping 37 and 75, valve 76, and piping 77 and 45. The concentrated water that did not permeate through membrane 44a is returned to the reaction tank 31 from the primary side of the membrane separation device 44 through piping 43 and 81, valve 82, and piping 83 and 49.

[0043] The treated water that has permeated membrane 38a of membrane separation device 38 is introduced from the secondary side of membrane separation device 38 through pipes 51 and 52, valve 53, and pipe 54 into treated water tank 55. The treated water that has permeated membrane 44a of membrane separation device 44 is introduced from the secondary side of membrane separation device 44 through pipes 56 and 57, valve 58, and pipe 59 into treated water tank 55.

[0044] 6 shows a state in which the membrane separation device 38 is backwashed and filtration is performed by reverse water flow in the membrane separation device 44. In this state, the pumps 33 and 62 are operating, the valves 58, 65, 72, 76, 82, and 90 are open, and the other valves are closed.

[0045] The biological treatment liquid in the reaction tank 31 is supplied to the primary side of the membrane separation device 38 through piping 32, feedwater pump 33, piping 34, 71, valve 72, and piping 73, 39. Backwash water is supplied to the secondary side of the membrane separation device 38 through piping 61, backwash pump 62, piping 63, 64, 66, 51, and valves 90, 65. The biological treatment liquid supplied to the primary side and the backwash wastewater that has permeated through the membrane 38a from the secondary side to the primary side are mixed and supplied from the primary side of the membrane separation device 38 to the primary side of the membrane separation device 44 through piping 37, 75, valve 76, and piping 77, 45. The concentrated water that did not permeate the membrane 44a is returned from the primary side of the membrane separation device 44 to the reaction tank 31 through piping 43, 81, valve 82, and piping 83, 49.

[0046] The treated water that has permeated the membrane 44 a of the membrane separation device 44 is introduced from the secondary side of the membrane separation device 44 through pipes 56 and 57 , a valve 58 , and a pipe 59 into a treated water tank 55 .

[0047] 7 shows a state in which filtration is performed in the membrane separation device 38 and backwashing is performed on the membrane separation device 44. In this state, the pumps 33 and 62 are operating, the valves 53, 68, 72, 76, 82, and 90 are open, and the other valves are closed.

[0048] The biological treatment liquid in the reaction tank 31 is supplied to the primary side of the membrane separation device 38 through piping 32, feed pump 33, piping 34, 71, valve 72, and piping 73, 39. The concentrated water that did not permeate the membrane 38a is supplied from the primary side of the membrane separation device 38 through piping 37, 75, valve 76, and piping 77, 45 to the primary side of the membrane separation device 44. Backwash water is supplied to the secondary side of the membrane separation device 44 through piping 61, backwash pump 62, piping 63, 67, 69, 56, and valves 90, 68. The liquid from the membrane separation device 38 supplied to the primary side and the backwash wastewater that has permeated the membrane 44a from the secondary side to the primary side are mixed together and returned from the primary side of the membrane separation device 44 to the reaction tank 31 through piping 43, 81, valve 82, and piping 83, 49.

[0049] The treated water that has permeated the membrane 38a of the membrane separation device 38 is introduced from the secondary side of the membrane separation device 38 through pipes 51 and 52, a valve 53, and a pipe 54 into a treated water tank 55.

[0050] By alternately passing water in the forward direction shown in Figures 2 to 4 and passing water in the reverse direction shown in Figures 5 to 7, deposits adhering to the vicinity of the inlets of the membrane separation devices 38, 44 can be removed by switching the water passing direction.

[0051] That is, when water is passed in the forward direction, sludge, precipitated inorganic matter, membrane peelings, and the like adhere to the vicinity of the inlet on the pipe 37 side of membrane separation device 38 and the vicinity of the inlet on the pipe 43 side of membrane separation device 44. When the forward water flow is switched to the reverse water flow, the deposits that adhered to the vicinity of the inlet on the pipe 37 side of membrane separation device 38 during the forward water flow flow out from pipe 37 to pipe 75, and the deposits that adhered to the vicinity of the inlet on the pipe 43 side of membrane separation device 44 flow out from pipe 43 to pipe 81.

[0052] When water is flowing in the reverse direction, deposits that have adhered near the inlet on the pipe 39 side of the membrane separation device 38 and near the inlet on the pipe 45 side of the membrane separation device 44 also flow out to the pipe 40 side and the pipe 46 side, respectively, when water is switched to flow in the forward direction.

[0053] By reversing the direction of sludge flow through the membrane module every 1 to 8 hours, it is possible to prevent blockage of the flow path due to deposits and maintain stable filtration performance.

[0054] The biological treatment tank, membrane separation device, and suitable operating conditions for use in the present invention will be described below.

[0055] <Biological treatment tank> The biological treatment tank may be either aerobic or anaerobic, but anaerobic treatment is preferred when using an external tubular membrane. In this case, the sludge concentration in the tank is 3,000 to 50,000 mg / L, preferably 8,000 to 40,000 mg / L, and particularly 20,000 to 30,000 mg / L, which allows for high-load treatment and does not impair membrane filtration performance. The temperature is 25 to 40°C or 45 to 60°C, preferably 30 to 38°C or 50 to 58°C. The pH in the tank is 6.5 to 8.0, preferably 6.8 to 7.4. If necessary, the pH is adjusted by adding an alkaline agent such as NaOH or NaHCO3 or an acid agent such as HCl to the sludge circulation line to the external membrane (the return pipe 49 from the membrane to the anaerobic reaction tank).

[0056] <Membrane separation equipment> An internal pressure type tubular membrane is suitable as the membrane separation device.

[0057] The internal pressure type tubular membrane is preferably a membrane module in which multiple tubulars (e.g., 100 to 1000 tubulars) with an inner diameter (diameter) of 3 to 10 mm are packed inside, and sludge flows through the inside of each tubular. The permeated water seeps out of the tubulars, and the permeated water that seeps out from each tubular is collected and discharged from the membrane module as treated water. The pore size of the membrane is preferably 0.01 to 1 μm, particularly 0.03 to 0.1 μm.

[0058] Pressure sensors are attached to the sludge inlet and outlet pipes of the tubular membrane, and the intermediate value is used as the primary pressure of the tubular membrane to measure the pressure inside the membrane, while the secondary pressure is measured with a pressure sensor attached to the piping on the permeate side.

[0059] <Membrane filtration and backwash water flow patterns> In the membrane filtration step, the sludge from the biological treatment tank is preferably passed through the tubular filter at a flow rate of 0.5 to 2 m / sec, more preferably 0.8 to 1.5 m / sec. The flux during filtration is preferably 0.1 to 0.8 m / d, more preferably 0.2 to 0.5 m / d.

[0060] In the backwashing step, it is preferable to perform backwashing with treated water for 5 to 30 seconds at a flux of 4 to 10 m / d for 10 to 60 minutes of filtration. It is preferable to operate in a manner in which such membrane filtration step and backwashing step are repeated alternately.

[0061] <Start-up operation of backwash pump> When starting the backwash pump, it is preferable to start the backwash pump in a manner that circulates the treated water in the treatment water tank during the filtration process, 10 seconds to 5 minutes, preferably 1 to 5 minutes, before moving on to the backwash process, and after the output of the backwash pump has increased to a specified value, to start backwashing by switching the valve.

[0062] The specified output of the backwash pump is preferably determined by measuring the pressure inside the tubular membrane during membrane filtration during trial operation of the biological treatment device, taking into account the membrane's water flow pressure, and then determining the output that will result in a specified backwash flux from the pump's performance curve (the calibration relationship between the discharge pressure and discharge flow rate at each pump output). For example, if the pressure inside the tubular membrane during membrane filtration is P1 and the membrane's water flow pressure is P2, the specified output is set by determining from the pump's performance curve the output that will result in a discharge flow rate corresponding to the specified backwash flux at discharge pressure P1 + P2. Note that the specified output can also be set from the discharge rate during trial operation or actual backwashing.

[0063] In the above embodiment, the backwash pumps 13, 62 are controlled to be ON / OFF, but the water supply pumps 3, 33 are always ON, so even when the membrane is in one stage and the process shifts from the membrane filtration process to the backwash process, the circulating sludge continues, and internal pressure is applied to the primary side of the membrane, just as during membrane filtration.

[0064] When multiple membrane modules are used, the modules may be arranged in series, in parallel, or both. However, when arranged in series, it is preferable to configure the modules so that, when the sludge flow direction is reversed, the sludge in the connecting piping between the modules is returned to the anaerobic reaction tank without passing through the modules, as in the embodiments of Figures 2 to 7 described above, in order to prevent the accumulation of coarse solid particles between the modules.

[0065] The retention time in the treatment tank is preferably 0.5 to 8 hours, particularly 1 to 4 hours, in order to prevent contamination of the backwash water due to the proliferation of microorganisms in the treatment tank.

[0066] By performing backwashing under these conditions, backwashing can be performed more effectively in a membrane separation type biological treatment device using an internal pressure type tubular membrane installed outside the tank, and the membrane filtration performance can be maintained stably for a long period of time. [Explanation of symbols]

[0067] 1,31 Biological treatment tank 3,33 Water supply pump 5,38,44 Membrane separation equipment 13,62 Backwash pump

Claims

1. A membrane separation device in which water to be treated is passed through a primary side, and treated water that has permeated the membrane is taken out to a treated water tank from a secondary side, A membrane separation apparatus equipped with a backwash pump for supplying treated water in a treatment tank to the secondary side, A switching means is provided for switching the supply destination of the discharge water of the backwash pump from a supply mode in which the discharge water is supplied to the treatment water tank without being supplied to the secondary side to a supply mode in which the discharge water is supplied to the secondary side, A membrane separation apparatus characterized in that the switching means operates to return the discharged water to the treatment water tank after the backwash pump is started until the output of the backwash pump reaches a reference value, and thereafter to introduce the discharged water into the secondary side.

2. 2. The method for operating a membrane separation apparatus according to claim 1, further comprising the step of supplying treated water in the treated water tank to the secondary side by the backwash pump to backwash the membrane, A method for operating a membrane separation apparatus, characterized in that after starting the backwash pump, the discharge water of the backwash pump is returned to the treatment water tank until the output of the backwash pump reaches a reference value, and then the discharge water of the backwash pump is supplied to the secondary side to perform backwashing.

3. A biological treatment device having a reaction tank for biologically treating wastewater containing organic matter, a membrane separation device installed outside the reaction tank for obtaining treated water by membrane filtration, a treated water tank for storing the treated water, and a backwash pump for intermittently backwashing the membrane separation device with the treated water, A switching means is provided for switching the supply destination of the discharge water of the backwash pump from a supply mode in which the discharge water is supplied to the treated water tank without being supplied to the secondary side of the membrane separation device to a supply mode in which the discharge water is supplied to the secondary side, This biological treatment device is characterized in that the switching means operates to return the discharged water to the treatment tank after the backwash pump is started until the output of the backwash pump reaches a standard value, and thereafter to introduce the discharged water into the secondary side.

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