JP2007245064A - Washing apparatus for filtration membrane - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a washing apparatus for a filtration membrane by a chemical addition reverse washing system capable of performing a desired flow rate control by a simple constitution without performing PID control of a flow rate of reverse washing water by an inverter for a reverse washing pump. <P>SOLUTION: The washing apparatus for the filtration membrane of the chemical addition reverse washing system is provided with the filtration membrane for cleaning raw water to obtain treatment water; a reverse washing line 30 for performing reverse washing of the filtration membrane using a part of the treatment water as reverse washing water of the filtration membrane; and a chemical injection line 24 for adding the chemical to the reverse washing line 30 to perform reverse washing. The reverse washing line 30 is provided with a by-pass line 31 for the reverse washing water on a part, and an opening/closing valve 33 is provided on one of the reverse washing line 30 and the by-pass line 31 and a constant flow rate valve 32 is provided on the other. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a water treatment apparatus using membrane filtration that separates and removes contaminants contained in raw water, such as waterworks, sewerage, industrial water, or wastewater treated water, using a filtration membrane, and in particular, backwashing with added chemicals. The present invention relates to a filter membrane cleaning apparatus.

  As a method for removing pollutants in the water to be treated, a water treatment method using membrane filtration is well known. In this water treatment using membrane filtration, as the operation continues, an adhering layer of pollutants is formed on the surface of the filtration membrane, clogging, fouling such as blockage of the flow path due to solid matter, and filtration performance decreases. There is a problem to do.

  Therefore, in the operation cycle, physical cleaning or chemical cleaning is performed after the filtration process for a predetermined time to reduce fouling. Physical cleaning includes backflow cleaning (backwashing) that reverses the treated water after membrane filtration, flushing by water flow on the primary side of the membrane, and air scrubbing that vibrates the membrane with air. Has been removed. On the other hand, chemical cleaning is a method of removing substances that cannot be removed by physical cleaning by decomposing or dissolving them with chemicals. For example, water treatment using backwashing with chemicals such as sodium hypochlorite, sulfuric acid and hydrochloric acid added. A method has been proposed (see Patent Document 1).

  FIG. 3 shows a schematic system diagram of an example of a general filtration membrane cleaning method using a conventional chemical enhanced back wash (CEB) method, which is a subject of the present invention, in which sodium hypochlorite is added. An example of the washing | cleaning method which performs backwashing is shown.

  In FIG. 3, 1 is raw water, 2 is a raw water tank, 3 is a main pump, 4 is a raw water supply valve, 5 is a membrane inlet pressure gauge, 6 is a thermometer, 7 is a membrane module (or membrane filtration unit), and 8 is a membrane. Outlet pressure gauge, 9 is a flow sensor, 10 is a filtrate outlet valve, 11 is a filtrate tank inlet valve, 12 is a filtrate tank, 13 is treated water, 14 is a backwash pump, 15 is a backwash water supply valve, 16 Is a drain valve, 17 is a sodium hypochlorite tank, 18 is a sodium hypochlorite addition pump, and 19 is a sodium hypochlorite addition valve. In addition, in FIG. 3, illustration of the sodium hypochlorite addition amount control device is omitted.

  Next, a water treatment method and a cleaning method for the filtration membrane shown in FIG. 3 will be described. The raw water 1 flowing into the raw water tank 2 is supplied to the membrane module 7 by the main pump 3 via the raw water supply valve 4 and filtered (filtering step). Here, the filtration flow rate is performed by inverter-controlling the main pump 3 so that the value of the flow rate sensor 9 becomes constant. The filtered water flows into the filtrate water tank 12 through the flow rate sensor 9, the filtrate water outlet valve 10, and the filtrate water tank inlet valve 11. The filtered water exceeding the capacity in the filtered water tank 12 is passed to the next process as treated water 13. When filtration is performed for a predetermined time, backwashing is performed (backwashing step). In the backwashing process, the water in the filtrate water tank 12 (or the water in a backwash water tank (not shown) provided separately from the filtrate water tank) is supplied to the membrane module 7 by the backwash pump 14 via the backwash water supply valve 15. It is made by flowing from the secondary side to the primary side, and the water after backwashing is drained through the drain valve 16.

  After a predetermined number of times of the filtration step and the backwashing step are completed, the chemical is added to perform the backwashing (chemical addition backwashing step). In the case of FIG. 3, as sodium hypochlorite addition backwashing, sodium hypochlorite stored in the sodium hypochlorite tank 17 is replaced with sodium hypochlorite addition pump following backwashing with the filtered water. 18 is added to the backwash water through a sodium hypochlorite addition valve 19 and water having a predetermined residual chlorine concentration is injected into the membrane module. When the inside of the membrane module 7 is filled with residual chlorine water of a predetermined concentration, the backwash pump 14 is temporarily stopped, each valve is closed, and the membrane module 7 is immersed in the residual chlorine water for a predetermined time (chemical solution immersion step). After immersing for a predetermined time, the backwash pump is started again, and backwashing is performed with filtered water, thereby rinsing off the chlorine water in the membrane module (rinsing step).

  As described above, a cleaning method for a filtration membrane including a backwashing step, a chemical addition backwashing step, a chemical solution immersion step, and a rinsing step is referred to as a chemical addition backwashing method. In addition to the above sodium hypochlorite, sulfuric acid, hydrochloric acid, and other chemicals may be used as cleaning chemicals for fouling substances on the membrane surface. Further, as disclosed in Patent Document 1, a plurality of chemicals may be used.

  By the way, as a flow control method of the backwash water in the normal backwash process or the chemical addition backwash process, the constant flow control is conventionally performed by PID control using an inverter. The conventional control method and apparatus will be described with reference to FIG. In FIG. 2, water in a backwash water tank 22 provided separately from the filtrate water tank is passed through a membrane filtration unit 21 via a backwash line 30 having a backwash pump 22. An example in which an injection line 24 is provided is shown. In FIG. 2, 25 is a flow meter (transmitter), 26 is a flow controller (PID controller), 27 is an inverter, 28 is a controller (PLC), and 29 is a programmable operation display (POD).

  According to FIG. 2, flow control as described below is performed and flow monitoring is performed. The output of the flow meter 25 controls the pump motor in the feedback loop of the flow controller (PID controller) 26 → inverter 27 → backwash pump 23 motor. Further, the transmission output of the flow meter 25 is branched and directly input to the controller 28 to monitor whether or not an abnormal deviation has occurred with respect to the command flow rate. Further, a flow rate command value and setting parameters are transmitted from the control controller (normal PLC: programmable controller) 28 to the flow rate controller 26, and the flow rate controller 26 performs control according to this command value.

Further, the current operation value and abnormality information are transmitted from the flow rate controller 26 to the control controller 28. The flow rate controller 26 monitors the vertical deviation with respect to the set flow rate. If the deviation is exceeded, an alarm is transmitted to the controller 28, and the controller 28 notifies the deviation abnormality. Furthermore, the frequency range assumed in each set flow rate is set, and when the frequency range is out of the frequency range, the controller 28 has a function of transmitting an alarm (frequency monitoring function).
JP 2004-41935 A

  By the way, as shown in FIG. 2, the method and device for controlling the flow rate of backwash water by the inverter for backwash pump is effective and necessary when the device scale is relatively large. In the case of a large-scale device, a relatively simple device is desired in terms of the device configuration and the control method.

  In the chemical addition backwash (CEB) process, the backwash flow rate is lower than the normal backwash process (for example, about 1/2 is desirable from the viewpoint of washing with emphasis on the efficiency and safety by chemicals. ), Constant flow control is required. On the other hand, in normal backwashing, if the chemical addition backwashing (CEB) is performed at a fixed cycle each time multiple normal backwashing is performed, the increase in the differential pressure of the filtration membrane in a long-term operation is small. The need for strict flow control or adjustment may be lower than during the chemical backwash (CEB) process. Therefore, in particular, in a chemical addition backwashing filter membrane cleaning apparatus, a configuration that is easy to control by a method that does not perform PID control is desired in consideration of the above.

  The present invention has been made in view of the above points, and an object of the present invention is to achieve a desired flow rate control with a simple configuration without performing PID control on the flow rate of backwash water by an inverter for backwash pumps. Is to provide a filtration membrane cleaning apparatus by a chemical addition back-cleaning method.

  In order to solve the above-mentioned problems, the present invention performs a backwashing of a filtration membrane using a filtration membrane that purifies raw water to obtain treated water, and a part of the treated water as backwash water for the filtration membrane. In a washing apparatus for a filtration membrane of a chemical addition backwashing method comprising a backwashing line and a chemical injection line for performing chemical backwashing by adding a chemical to the backwashing line, the backwashing line includes a part of the backwashing line. A backwash water bypass line is provided, and one of the backwash line and the bypass line is provided with an on-off valve and the other is a constant flow valve.

  As an embodiment of the invention of claim 1, the inventions of claims 2 to 4 below are preferable. That is, in the filtration membrane cleaning apparatus according to claim 1, the backwash line or bypass line provided with the on-off valve is provided with a throttle member in series with the on-off valve (claim 2). Furthermore, in the filtration membrane cleaning apparatus according to claim 2, the throttle member is an orifice or a valve with a flow rate adjusting function (claim 3).

  The throttle member is provided for the purpose of increasing the fluid resistance in proportion to the square of the flow velocity when the flow rate increases, and suppressing the flow rate from becoming excessive by reducing the flow rate. When the pipe of the washing line or the bypass line itself has a large fluid resistance and has substantially the same function as the case where the throttle member is provided, it is not necessary to provide a special throttle member such as an orifice.

  Further, in the filtration membrane cleaning device according to any one of claims 1 to 3, a flow rate control valve is provided together with the on-off valve (claim 4). In the normal backwashing process, PID control by an inverter is not necessary, but when a certain amount of automatic flow control is required, the flow control valve controls the flow according to the degree of the differential pressure of the filtration membrane. Can do.

  According to the present invention, in a filtration membrane cleaning apparatus using a chemical addition backwashing method, a desired flow rate control can be performed with a simple configuration without performing PID control on the flow rate of backwashing water by an inverter for backwashing pumps. Become.

  An embodiment of the present invention will be described below with reference to FIG. In addition, this invention is not limited by this Example.

  FIG. 1 is a system diagram of a principal part according to an embodiment of the filtration membrane cleaning apparatus of the present invention. In FIG. 1, members having the same functions as those shown in FIG. The difference between FIG. 1 and FIG. 2 is that the backwash line 30 in FIG. 1 includes a bypass line 31 of backwash water in a part thereof, and a constant flow valve 32 is provided in the backwash line 30. In the chemical addition backwash (CEB) process, the on / off valve 33 is closed to stop the flow to the bypass line 31, and the backwash water is passed only to the backwash line 30. It is the point that it was able to pass the constant flow rate required for the.

  Further, in FIG. 1, as a more preferred embodiment, an orifice 34 as a throttle member is provided in the bypass line 31 in series with the on-off valve 33.

  In FIG. 1, the constant flow valve 32 may be provided on the bypass line 31 side, and the on-off valve 33 and the orifice 34 may be provided on the backwash line 30 side. A flow rate control valve (not shown) can be provided together with the on-off valve 33 as necessary. Further, a flow rate adjustment manual valve 35 may be provided separately to adjust the flow rate manually.

  The control of the backwash flow rate in the configuration of FIG. 1 will be described below. In normal backwashing, the on-off valve 33 is opened and backwashing water is passed through both the backwashing line 30 and the bypass line 31 in parallel, and a suitable backwashing flow rate predicted for each filtration membrane treatment system. (The flow rate is about twice that of CEB). When fluctuations are expected in the preferred flow rate, the flow rate is adjusted by the flow rate adjustment manual valve 35 as necessary, or is automatically adjusted by providing a flow rate control valve. In the chemical addition backwash (CEB) process, the on-off valve 33 is closed to stop the flow to the bypass line 31, the backwash water is passed only to the backwash line 30, and the CEB is required via the constant flow valve 32. A constant flow rate.

  According to the above, desired flow rate control can be performed with a simple configuration.

The principal part systematic figure which concerns on the Example of the washing | cleaning apparatus of the filtration membrane of this invention. The system diagram of the conventional control method and apparatus which perform PID control of the flow volume of backwash water with the inverter for backwash pumps. Schematic system diagram of an example of a general filtration membrane cleaning method by a conventional chemical addition backwashing system.

Explanation of symbols

  21: Membrane filtration unit, 22: Backwash water tank, 23: Backwash pump, 24: Chemical solution injection line, 30: Backwash line, 31: Bypass line, 32: Constant flow valve, 33: Open / close valve, 34: Orifice, 35: Flow control manual valve.

Claims (4)

A filtration membrane for purifying raw water to obtain treated water, a backwash line for backwashing the filtration membrane using a part of the treated water as backwash water for the filtration membrane, and chemicals in this backwash line In addition to the chemical addition backwashing type filtration membrane cleaning device equipped with a chemical injection line for backwashing by addition,
The backwash line is provided with a bypass line for the backwash water in a part thereof, and one of the backwash line and the bypass line is provided with an opening / closing valve and the other is a constant flow valve for filtration. Membrane cleaning device. The filtration membrane cleaning apparatus according to claim 1, wherein the backwash line or the bypass line provided with the on-off valve includes a throttle member in series with the on-off valve. 3. The filtration membrane cleaning apparatus according to claim 2, wherein the throttle member is an orifice or a valve with a flow rate adjusting function. The filtration membrane cleaning apparatus according to any one of claims 1 to 3, wherein a flow rate control valve is provided together with the on-off valve.

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