JP4834435B2 - Automatic cleaning method of strainer for water treatment equipment by membrane filtration - Google Patents

Description

  The present invention relates to an automatic cleaning method for a strainer used in a water treatment apparatus using membrane filtration, in which contaminants contained in raw water such as water supply, sewerage, industrial water, or wastewater treatment water are separated and removed by a filtration membrane and purified. .

  As a method for removing pollutants in the water to be treated, a water treatment method using a membrane module for filtration is well known. In the water treatment using this membrane module, as the water treatment operation continues, an adhering layer of pollutants is formed on the surface of the membrane, clogging, and fouling such as clogging of the flow path due to solid matter occurs. Filtration performance decreases. The deterioration of the membrane filtration performance due to these causes can be recovered by washing the membrane module.

  The membrane module cleaning method includes physical cleaning and chemical cleaning. Physical washing includes back pressure water washing (back washing) that reverses the membrane filtration water, flushing by water flow on the primary side of the membrane, and primary membrane by bullet flow (slag flow) formed by mixing water with air. There are air flushing on the side, air scrubbing that vibrates the membrane with air, etc., and the adhered substances are removed by physical action. On the other hand, chemical cleaning is a cleaning method that removes substances that cannot be removed by physical cleaning by decomposing or dissolving them with chemicals, and can restore the filtration capacity of the membrane to almost the initial state. However, it is desirable to reduce the number of times as much as possible from the viewpoint of cost and chemical wastewater treatment. As a method combining the physical cleaning and the chemical treatment, a cleaning method using ozone-containing water or ozone gas has recently been proposed.

  FIG. 4 shows a system diagram of an example of a conventional membrane filtration system for washing a membrane module (or membrane filtration unit) using backwash water. The system shown in FIG. 4 consists of four membrane modules. The raw water 1 that has flowed into the raw water tank (or raw water tank) 2 passes through the raw water supply valve 5 by the raw water pump 3 and is supplied to each membrane module 6 for filtration. The filtration processing operation method in this example is a full-volume filtration method (dead-end filtration method). Here, when the supply water amount of the operation pump 3 is larger than the filtration water amount, the rotation speed of the pump impeller is changed by an inverter. Drop and reduce the flow rate. Also, normally, the raw water tank is supplied with raw water from an unillustrated intake pump via an intake water supply line and stored, and a strainer is provided on the intake water supply line, and the strainer is used to store the raw water. Contaminants are removed in advance.

  The filtered treated water 10 is normally fed to a filtered water distribution reservoir (not shown) through the filtered water outlet valve 7. Since part of the treated water is used as backwash water, the water is sent to the backwash water storage tank 11 via the automatic opening / closing valve 9. The automatic open / close valve 9 controls the water level in the backwash water storage tank 11 so that it can be backwashed.

  In the backwashing process after the filtration process, the backwashing water passes through the backwashing water supply valve 14 by the backwashing pump 13, flows from the secondary side of the membrane module 6 to the primary side, and is drained from the drainage drain valve 15. The In addition, the additional washing process other than the back washing process may be performed every predetermined number of times after the back washing process. Moreover, as a washing | cleaning method, a backwashing process may not be performed.

  In the above system, the filtration membrane used is a membrane capable of removing turbid components and bacteria, and usually a microfiltration membrane (MF membrane) or an ultrafiltration membrane (UF membrane) is used. As microfiltration membranes used in waterworks, those with a nominal pore size of greater than 0.01 μm and 1 μm or less are used, and as ultrafiltration membranes, the nominal pore size is 0.01 μm or less and the molecular weight cut off is about 1000 Daltons. Is used.

  The membrane module may be in the form of a hollow fiber, spiral, tubular, flat membrane or the like. Furthermore, the filtration method of the membrane module is known to be the total filtration method (dead end filtration method) and the cross flow filtration method, and the water flow method to the filtration membrane includes an external pressure type and an internal pressure type. It has been known. Furthermore, when the raw water is injected into the primary side of the membrane, the membrane module structure is injected through a water collecting part (end cap) in the axial direction of the membrane module, and filtered water is supplied to the secondary side of the membrane. There are various systems, such as those that send to both sides or one side in the axial direction, and they are appropriately selected according to needs.

In addition, about the washing | cleaning method of a film | membrane, a filtration system, etc., it describes in the following nonpatent literature 1.
Supervised by the Department of Health and Welfare, Department of Water Supply, Water Environment Division, “Membrane Filtration Method Q & A”, Water Supply Process Association, February 28, 1995, p. 114-115 and p. 142-143

  As described above, in a conventional water treatment apparatus using membrane filtration, a strainer is disposed on the intake water supply line, and impurities in the raw water are removed in advance by the strainer. It must be cleaned at appropriate intervals so that the strainer function can be maintained. However, the strainer cleaning method has the following problems.

  Conventionally, since the strainer cleaning is performed by the water intake pump, the pressure and flow rate necessary and sufficient for the strainer cleaning cannot be obtained, the cleaning power is poor, and there is a problem that the strainer deteriorates in function at an early stage. In addition, to compensate for this poor cleaning power, some strainers have a device that scrapes the inner mesh surface of the strainer with a steel wire brush, scraper, etc., but the wire brush or mesh breaks down in long-term use. There is a problem of entering the element and causing damage to the membrane element.

  The present invention has been made in view of the above points, and an object of the present invention is to enable automatic cleaning of a strainer using raw water having better cleaning ability than the conventional one, and thus a water treatment apparatus by membrane filtration. The purpose is to improve the filtration performance.

To attain the above object, the present invention is raw water flows through the membrane module having a filtration membrane by the raw water pump from the raw water tank, a water treatment apparatus for obtaining purified processing to filtered water by the filtration membrane In the method for automatically washing a strainer in a water treatment apparatus provided with a strainer for removing contaminants in the previous stage of the purification treatment, a strainer is disposed between the raw water pump and the membrane module, and the secondary side water of the strainer the scan trainer outlet valve provided between the outlet and the membrane module, and a washing drain line to the aperture and washing water discharge valve means of the strainer is provided, before or after the raw water pump membrane filtration process under operating conditions With the strainer outlet valve closed, the cleaning drain valve is opened and raw water is passed from the primary side of the strainer at least at the prescribed pump pressure required for strainer cleaning. By sending a detergent drain from the washing water discharge line, characterized in that flushing clean the strainer Te (claim 1).

Further , in the automatic cleaning method for a strainer for a water treatment device by membrane filtration according to claim 1, the raw water flow rate control at the time of strainer cleaning is based on PID control or PI control by an inverter of the raw water pump ( Claim 2 ).

Furthermore , in the automatic cleaning method for a strainer for a water treatment device by membrane filtration according to claim 1 or 2 , the throttle means is an orifice (claim 3 ).

For reference, the strainer automatic cleaning method can also be performed as follows. That is, a water treatment device for obtaining raw water by flowing raw water from a raw water tank to a membrane module having a filtration membrane with a raw water pump, and purifying the membrane with the filtration membrane (membrane filtration). In an automatic strainer cleaning method in a water treatment apparatus equipped with a strainer for removing contaminants, a strainer is disposed between the raw water pump and the membrane module, and the secondary water outlet of the strainer and the membrane module are disposed between the raw water pump and the membrane module. Is provided with an on-off valve (strainer outlet valve) and an on-off valve (washing drainage valve) and a throttle means in the strainer washing drainage line, before or after the membrane filtration step under the operating condition of the raw water pump, With the strainer outlet valve closed, open the flush drain valve and allow raw water to flow from the secondary side of the strainer at least at the specified pump pressure required for strainer cleaning. By sending a detergent drain from the wash drain line you backwashing strainer.

For further reference, the strainer automatic cleaning method can also be performed as follows. That is, a water treatment device for obtaining raw water by flowing raw water from a raw water tank to a membrane module having a filtration membrane with a raw water pump, and purifying the membrane with the filtration membrane (membrane filtration). In the automatic strainer cleaning method in the water treatment apparatus equipped with a strainer for removing contaminants, a strainer is disposed on the intake water supply line for supplying raw water from the intake pump to the raw water tank, and the secondary water outlet of the strainer is provided. An open / close valve (strainer outlet valve) is provided between the raw water tank and the open / close valve (cleaning drain valve) and a throttle means in the strainer's cleaning / drainage line, and further on the raw water tank and the intake / water supply line. Connecting a point between the strainer and the intake pump, providing a raw water recirculation line having a dedicated strainer cleaning pump, stopping the intake pump, and connecting the strainer outlet valve In this state, the washing drain valve is opened, the strainer washing dedicated pump is operated, and the water in the raw water tank is transferred from the primary side or the secondary side of the strainer to the washing drain line through the raw water return line. wash the strainer flows through.

According to the invention, by a throttle means provided in the washing water discharge line of the raw water pump and the strainer are secured pressure and flow required for cleaning the strainer, automatic strainer with raw water better than cleaning capability conventional Cleaning is possible. Thereby, the improvement of the filtration performance of the water treatment apparatus by membrane filtration can be aimed at.

Embodiments of the present invention will be described below with reference to the drawings . Figure 1 is a schematic system diagram showing a main part of the embodiment using the raw water pump of the present invention, FIG. 2 is a schematic system diagram showing an essential part of a form status with strainer cleaning dedicated pump as a reference example, FIG. 3 is a diagram (a diagram) showing a control procedure for performing strainer cleaning after the membrane filtration step in the embodiment of FIG. 1 and a diagram (b diagram) showing a control procedure for performing strainer cleaning before the membrane filtration step. . The present invention is not limited to this embodiment. 1 to 3, the same functional members are denoted by the same reference numerals.

  First, the embodiment of FIG. 1 will be described. In FIG. 1, 23 is a raw water pump, 24 is an inverter, 25 is a strainer, 25a is a primary and secondary partition in the strainer, 26 is a membrane module, 31 is an on-off valve (strainer outlet valve), 32 is an on-off valve ( Washing drain valve) 33 is an orifice as a throttle means. In addition, the raw | natural water tank which is abbreviate | omitting illustration in FIG.

  The control procedure for performing strainer cleaning according to the embodiment of FIG. 1 is as shown in FIG. 3, and the control procedure for performing strainer cleaning after the membrane filtration step is shown in FIG. The control procedure is shown in FIG. That is, before or after the membrane filtration step under the operating state of the raw water pump 23, with the strainer outlet valve 31 closed, the cleaning drain valve 32 is opened, and at least at a predetermined pump pressure required for strainer cleaning, The raw water is passed from the primary side of the strainer 25 to the cleaning drainage line to flush the strainer. In FIG. 1, the strainer can be backwashed by passing raw water from the secondary side of the strainer 25 to the washing drainage line.

  The details of FIG. 3 will be further described below in the case of the flushing cleaning. The upper diagram in FIG. 3A shows the state of normal filtration operation, and the raw water pump 23 is operated at a frequency for constant flow filtration by inverter control. Normally, it is operated by PID control or PI control by flow rate feedback. In this state, the on-off valve (cleaning drain valve) 32 is in a closed state.

  The lower part of FIG. 3A shows the state of the strainer cleaning operation, and after closing the on-off valve (strainer outlet valve) 31, the cleaning drain valve 32 is opened. In this case, the raw water pump 23 is changed to the frequency for washing the strainer without stopping. In this case, the flow rate control for the strainer cleaning is a constant flow rate control by PID, PI control or a fixed operation amount (MV fixed value). After continuing the above strainer cleaning for a predetermined set time, the raw water pump 23 is stopped and the cleaning drain valve 32 is closed. The stopping and closing are preferably performed at the same time, thereby preventing air contamination. After confirming the stop and closing, the process proceeds to the next step, for example, a backwash step.

  Next, a control procedure for performing strainer cleaning before the membrane filtration step of FIG. The upper part of FIG. 3B shows the state of the strainer cleaning operation, the raw water pump 23 is activated, and the cleaning drain valve 32 is opened. The raw water pump 23 has a frequency for strainer cleaning (in this case also, the flow rate is constant flow rate control by PID, PI control or MV fixed value). After the above strainer cleaning is continued for a predetermined set time, the process proceeds to the normal filtration operation at the lower stage of FIG.

  In the normal filtration operation at the lower stage of FIG. 3B, the raw water pump 23 is changed to a frequency for filtration flow rate (PID control) without stopping. Further, after opening the strainer outlet valve 31, the washing drain valve 32 is closed and the normal filtration operation is started as it is.

  In the embodiment shown in FIG. 1 and FIG. 3, it is preferable to select a raw water pump 23 that meets the flow rate and pressure specifications of both membrane filtration and strainer cleaning. Necessary cleaning pressure can be obtained by appropriately designing the diameter and orifice of the strainer drain. The required strainer washing pressure is usually about 0.2 to 0.3 MPa, but the membrane filtration pressure is about 20 to 80 kPa. It is also possible to use a throttle adjusting valve without using an orifice as the throttle means.

  According to the said embodiment, there exists an effect which a collection rate improves as a membrane filtration system by wash | cleaning a strainer using raw | natural water. In addition, the raw water pump can be shared with the strainer cleaning. Furthermore, since the strainer cleaning is performed continuously with the membrane filtration operation, the pump start / stop frequency can be reduced, and the pump life can be extended.

Next, FIG. 2 will be described. FIG. 2 is a reference example using a strainer cleaning pump; 22 is a raw water tank, 25 is a strainer, 30 is a water intake / feed line, 32 is an on-off valve (cleaning drain valve), 33 is an orifice, and 34 is an on-off valve ( Strainer outlet valve), 36 and 37 are check valves, 40 is a water intake pump, 41 is a strainer cleaning dedicated pump, and 50 is a raw water recirculation line. Depending on the type of strainer, the raw water reflux line indicated by 50a is used instead of the raw water reflux line indicated by 50a.

According to the reference example shown in FIG. 2, the intake pump 40 is stopped, the strainer outlet valve 34 is closed, the cleaning drain valve 32 is opened, the strainer cleaning dedicated pump 41 is operated, and the inside of the raw water tank 32 is operated. The strainer 25 can be washed by passing the water through the raw water reflux line 50 (or 50a) from the primary side or the secondary side of the strainer 25 to the washing drainage line. The strainer cleaning dedicated pump 41 is selected based on the necessary cleaning pressure and flow rate of the strainer 25.

By reference example of FIG. 2, by cleaning the strainer with raw water, as membrane filtration system, the recovery rate can be improved.

The typical systematic diagram which shows the principal part of embodiment using the raw | natural water pump of this invention. Schematic system diagram showing an essential part of a form status with strainer cleaning dedicated pump as a reference example. In the embodiment of FIG. 1, the figure (a figure) which shows the control procedure which performs strainer washing | cleaning after a membrane filtration process, and the figure (b figure) which shows the control procedure which performs strainer washing | cleaning before a membrane filtration process. The system system | strain diagram of an example of the conventional membrane filtration system which wash | cleans a membrane module using backwash water.

2 3: raw water pump, 24: inverter, 25: Strainer, 25a: partition, 26: membrane module, 31: on-off valve (strainer outlet valve), 32: on-off valve (wash drain valve), 33: orifice or.

Claims (3)

Flows through the membrane module having a filtration membrane by the raw water pump from the raw water tank raw water, the a water treatment apparatus for obtaining purified processing to filtered water by filtration membranes, for contaminant removal in front of the purification process In the automatic strainer cleaning method in a water treatment apparatus equipped with a strainer,
Wherein arranged a strainer between the raw water pump and the membrane module, the scan trainer outlet valve between the secondary side water outlet and the membrane module of the strainer is provided, and detergent drain line washing water discharge valve of the strainer And squeezing means,
Under the operating condition of the raw water pump, before or after the membrane filtration step, with the strainer outlet valve closed, the cleaning drain valve is opened, and at least a predetermined pump pressure required for strainer cleaning, the strainer primary A method for automatically washing a strainer for a water treatment apparatus by membrane filtration, wherein raw water is passed from the side and the washing wastewater is sent from a washing drainage line to flush the strainer. The automatic cleaning method according to claim 1, wherein the raw water flow rate control at the time of strainer cleaning is based on PID control or PI control by an inverter of the raw water pump. 3. The automatic cleaning method according to claim 1 , wherein the throttling means is an orifice.

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