JP2003266072A - Membrane filtration method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To keep a cleaning effect although the amount of water and a time for backward washing of a membrane module are curtailed. <P>SOLUTION: Treatment water from a raw water tank 1 is supplied to the membrane module 4 by a pressure pump 2. After a filtration process for supplying filtrate to a filtrate tank 6, the filtrate of the filtrate tank 6 is supplied to the membrane module by a backward wash pump 7. A first backward washing process for discharging backward washing wastewater from a valve 9 and a second backward washing process for discharging backward washing wastewater from a valve 10 are repeated alternately. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a membrane filtration method using a filtration membrane such as a microfiltration membrane or an ultrafiltration membrane to obtain filtered water that has passed through the filtration membrane. . 2. Description of the Related Art Membrane filtration devices are used for various industrial water treatments and wastewater treatments because of their advantages such as easy operation and stability of treated water.
Many have been introduced for water purification and other purposes. [0003] In such a membrane filtration device, filtration is performed by a filtration membrane module divided into a raw water chamber and a permeated water chamber by a microfiltration membrane or an ultrafiltration membrane. Insoluble and soluble substances in the treated water accumulate on the filter membrane surface, and the amount of filtered water (treated water) decreases. For this reason, in the membrane filtration device, the backwashing step of the filtration membrane module is performed when the pressure loss (the transmembrane pressure difference) in the filtration membrane is equal to or more than a predetermined value or when the filtration is performed for a certain period of time. As a result, the filtration capacity of the membrane filtration device is restored, and stable filtration processing can be continued. [0004] In this backwashing of the filtration membrane module, clear water such as treated water for membrane filtration is introduced into the membrane module in a direction opposite to the direction of filtration water flow, and clogging substances deposited on the surface of the filtration membrane are discharged outside the membrane module. Adopt the method of discharging. [0005] Many methods have been proposed for backwashing the membrane module for the purpose of efficiently discharging clogged substances from inside the membrane module. For example, Patent 272
No. 4673 and JP-A-8-299767,
In order to discharge clogging substances from the entire membrane module to the outside of the module, a method of alternately discharging backwash wastewater from both end faces of the membrane module has been proposed. Also, Japanese Patent Application Laid-Open
In JP-A-54789, there is proposed a backwashing method in which the supply of the water to be treated to the membrane module and the backwashing of the membrane module are performed at the same time. [0006] As described above, various backwashing methods have been proposed. In each of these methods, a clogging substance deposited on the film surface by one backwashing is proposed. The purpose of this is to discharge as much as possible out of the module. [0007] However, in these methods, the amount of water used for cleaning is increased, and the time spent for cleaning is further increased. As a result, the water recovery rate is reduced, the operation efficiency of the apparatus is reduced, and the cost of fresh water is reduced. There is a problem that increases. The present invention proposes a membrane filtration method which reduces the amount of water and time required for backwashing a membrane module and achieves a membrane module cleaning effect comparable to the conventional one. Means for Solving the Problems The inventors of the present invention have conducted various studies on backwashing of a membrane module. As a result, half of the entire membrane module is alternately backwashed so that the membrane module can be washed at a time. It was found that the same effect as the conventional backwash method of discharging the entire clogging substance was obtained, and that the amount of backwash water used at one time was sufficient for half the amount required to wash the entire membrane module. And arrived at the present invention. That is, the present invention relates to a membrane filtration method in which water to be treated is introduced into a raw water chamber of a membrane module partitioned into a raw water chamber and a permeated water chamber by a membrane, and treated water permeated through the membrane is obtained from the permeated water chamber. A pair of raw water side openings for introducing or discharging treated water are provided at both ends of the raw water chamber, and backwash water is introduced into the permeated water chamber, and any of the raw water side openings of the raw water chamber is provided. It is possible to discharge backwash wastewater from
After the filtration step for a predetermined period, one raw water side opening of the raw water chamber is opened, the other raw water side opening is closed, and backwash drainage is discharged from one raw water side opening to perform a first backwashing step. After the completion of the first backwash step, return to the filtration step, after the filtration step for a predetermined period, open the other raw water side opening of the raw water chamber, close the one opening, The backwash drainage is discharged from the other raw water side opening to perform a second backwashing step. After the second backwashing step is completed, the process returns to the filtration step, and after the filtration step, the first backwashing step is performed. And repeating the second backwashing step. As described above, according to the present invention, the first backwash for discharging backwash wastewater from one raw water side opening of the membrane module, and the backwash wastewater discharge from the other raw water side opening of the membrane module. The second backwashing is performed alternately with a filtration step interposed therebetween. As a result, although the film area that can be reliably washed by one backwashing is slightly reduced, a considerable backwashing effect can be obtained. By alternately performing two backwashing steps, the amount of water used for backwashing and the time required for backwashing are reduced by half compared to the conventional method in which the entire membrane module is washed by one backwashing operation. Can be. Accordingly, the recovery rate and operation efficiency of the entire apparatus are improved, and as a result, it is possible to reduce fresh water production costs and equipment costs of the membrane filtration apparatus. Embodiments of the present invention will be described below in detail with reference to the drawings. 1 to 3 are schematic diagrams of a membrane filtration device for explaining an embodiment of the present invention. FIG. 1 shows a filtration step, FIG. 2 shows a first backwashing step, and FIG. The backwash process is shown. The raw water tank 1 is a tank for storing the water to be treated, and receives and stores various kinds of water to be treated such as river water, groundwater, and drainage. A suction side of a pressure pump 2 is connected to the raw water tank 1, and a discharge side of the pressure pump 2 is connected to a membrane module 4 via a valve 3. The membrane module 4 schematically shows a so-called internal pressure type hollow fiber membrane module, and is divided into a raw water chamber 42 and a permeated water chamber 43 by an internal hollow fiber filtration membrane 41. 1 to 3, for convenience, the hollow fiber filter membrane 41 is
Although only a book is shown, in an actual module, many hollow fiber filter membranes are mounted. In addition, raw water room 4
2 is one end side of the membrane module 4 (the lower end side in the figure)
A first raw water side opening 44 and a second raw water side opening 45 at the other end (upper end side in the figure) are provided. The piping from the pressure pump 2 is It is connected to the raw water side opening 44. The permeated water chamber 43 is provided with a permeated water side opening 46, and the permeated water side opening 46 is connected to the filtered water tank 6 via the valve 5. Further, the suction side of the backwash pump 7 is connected to the filtered water tank 6, and the discharge side of the backwash pump 7 is connected to the permeated water side opening 46 of the membrane module 4 and a pipe in the middle of the valve 5. ing. A backwash drain discharge valve 9 is connected to a pipe at an intermediate portion between the raw water side opening 44 of the membrane module 4 and the valve 3. A valve 10 for washing and draining is connected. Although not shown, the valves 3, 5,
8, 9 and 10, a control device for controlling the pressurizing pump 2 and the backwashing pump 7;
Control the transition to the backwash step. FIG. 1 shows a flow at the time of the filtration step, and a thick line shows a flowchart at the time of the filtration step. In this filtration step, the valves 3 and 5 shown in white in the figure are opened, the valves 8, 9 and 10 shown in black are closed, the pressure pump 2 is operated, and the backwash pump 7 is operated.
Is in a stopped state. The water to be treated is supplied from a raw water tank 1 to a pressure pump 2
Through the valve 3 and the raw water chamber 42 of the membrane module 4
Supplied to The permeated water that has passed through the hollow fiber filtration membrane 41 of the membrane module 4 is sent from the permeated water side opening 46 of the permeated water chamber 43 to the filtered water tank 6 via the valve 5. FIG.
In, arrows indicate the flow of permeated water that has passed through the hollow fiber filtration membrane 41. If this filtration step has been performed for a certain period of time, a first backwashing step (lower backwashing) is started. FIG. 2 shows a flow in the first backwashing step. In the first backwashing step of FIG.
The pressurizing pump 2 stops, the valves 3, 5, and 10 are closed, and the valves 8 and 9 are opened. In this state, the backwashing pump 7 is started, and the filtered water is returned from the filtered water tank 6 through the valve 8 to the permeated water chamber 43 of the membrane module 4, and the hollow fiber filter membrane 41 is passed through the permeated chamber 43. The backwash water is transmitted from the side to the raw water chamber 42 side to backwash the hollow fiber filtration membrane 41. The backwash drainage is discharged from the lower end of the membrane module via the valve 9. In FIG. 2, arrows indicate the flow of backwash water. In the backwashing state of FIG. 2, all the backwash water that has passed through the hollow fiber filtration membrane 41 and flowed into the hollow fibers is discharged from the raw water side opening 44 provided at the lower end. Therefore, the hollow fiber filtration membrane 41
Inside, the flow velocity becomes higher toward the lower side of the hollow fiber. Therefore, the solid matter on the inner surface of the hollow fiber filtration membrane 41 is in a state where it is easily removed toward the lower side. Therefore, the lower part of the membrane module 4 is sufficiently cleaned, but the upper part is likely to have a part that is not sufficiently cleaned. After the first backwashing step of FIG. 2 is completed, the process returns to the filtering operation step of FIG. 1 to perform the filtering operation. Then, when a predetermined time has elapsed, a second backwashing step (upper backwashing) is started. FIG. 3 shows the flow of the second backwashing step. In the second backwashing step, the pressurizing pump 2 stops, the valves 3, 5, and 9 are closed, and the valves 8 and 10 are opened. In this state, the backwashing pump 7 is started, and the filtered water is returned from the filtered water tank 6 to the permeated water chamber 43 of the membrane module 4 via the valve 8, and the hollow fiber filter membrane 41 is passed through the permeated chamber 43. The backwash water is transmitted from the side to the raw water chamber 42 side to backwash the hollow fiber filtration membrane 41. The backwash drainage is discharged from the upper end of the membrane module via the valve 10. Note that, in FIG. 3, the arrows indicate the flow of the backwash water as in the case of FIG. In the backwashing state shown in FIG.
All of the backwash water that has passed through is discharged from the raw water side opening 45 provided at the upper end. Therefore, the hollow fiber filtration membrane 41
Inside, the flow velocity is higher toward the upper side of the hollow fiber. Therefore, the solid matter on the inner surface of the hollow fiber membrane 41 is more easily removed upward. Therefore, the upper part of the membrane module 4 is sufficiently cleaned, but the lower part is likely to have a part that is not sufficiently cleaned. After the second backwashing step in FIG. 3 is completed, the process returns to the filtration operation step in FIG. 1 and the filtration operation is performed. In the present embodiment, the steps of such a filtration step → first backwash step (lower backwash) → filtration step → second backwash step (upper backwash) →... Are repeated. By such backwashing, each end of the hollow fiber filtration membrane 41 is sufficiently washed once in two backwashing steps. Therefore,
It is possible to obtain the same backwashing effect as performing the backwashing in both directions each time as in the related art. [0023] Compared with the conventional method in which the entire membrane module is washed at once, the amount of water used for backwashing and the backwashing time can be reduced to half, and stable operation can be performed. Therefore,
The recovery rate and operation efficiency of the entire apparatus are improved, and as a result, it is possible to reduce fresh water production costs and equipment costs of the membrane filtration apparatus. The apparatus shown in the drawings is an example of an embodiment of the present invention, and the present invention is not limited to the illustrated form unless it exceeds the gist. The shape of the membrane module 4 includes a hollow fiber membrane, a tubular membrane, a monolith type, a pleated type, a flat membrane, and the like. Any separation membrane that can be backwashed can be used. However, a hollow fiber membrane, a monolith type, or a tubular membrane, which is easily backwashed, is preferably used. As the material of the filtration membrane 41, any material used for the separation membrane such as polyacrylonitrile, polysulfone, polyvinylidene fluoride, polypropylene, polyethylene, cellulose acetate, ceramic, metal, etc. can be used. The separation pore diameter of the membrane may be various depending on the application of the treatment. Usually, a separation membrane having a fractionation molecular weight of about tens of thousands to several μm is applied. A separation membrane having a separation pore diameter of 000 to 3 μm is applied. The water to be treated of the present invention is not particularly limited, and may be river water, lake water, groundwater, industrial water, clean water, or the like.
Applicable to various wastewater. In the embodiment of the present invention, the separation membrane is shown as a single unit, but the present invention is also applicable to an apparatus having a separation membrane unit in which a plurality of separation membranes are arranged in parallel to form one set. is there. Although the water flow system of the membrane module 4 is shown as dead-end filtration in the embodiment, it can be applied to cross-flow filtration. For example, in the filtration process,
By opening the valve 10 and letting a part of the raw water flowing from the first raw water side opening 44 flow out of the second raw water side opening 45 and returning it to the raw water tank 1, cross flow filtration can be performed. 2 The backwashing step may be as described above. The transition from the filtration step to the backwashing step of the membrane module 4 is generally set for a long time, but any index such as an increase in the transmembrane pressure of the membrane module 4, a raw water turbidity load, and an integrated filtered water amount is set. This can also be applied to the conditions for shifting to the backwashing step. In the embodiment of the present invention, the water supply and the backwash to the membrane module 4 are illustrated as being performed by the pressurized pump. However, the water can be supplied using the head pressure or the like. Further, the backwash drainage from the membrane module 4 is shown to be discharged through communication pipes and valves installed at the lower and upper portions of the membrane module, but the drainage can be efficiently performed from the membrane module 4. Any method can be adopted as long as it is in accordance with the gist of the invention. The present invention will be described more specifically below with reference to examples and conventional examples for comparison. A conventional backwashing method (conventional example) and a backwashing method according to the present invention (example) for the purpose of obtaining clean water from river surface water using three apparatuses described in the embodiment of the present invention. , The operation stability, the recovery rate and the operation rate of the membrane module were compared. In the apparatus of the embodiment, an operation was performed in which the first and second backwashing steps shown in FIGS. 2 and 3 described in the embodiment of the present invention were alternately performed with the filtration step of FIG. 1 interposed therebetween. . That is, the operation status is filtration (FIG. 1) → first backwash (FIG. 2) → filtration (FIG. 1) → second backwash (FIG. 3) → filtration (FIG. 1) → first backwash (FIG. 2) → Filtration (Fig. 1) → Second backwash (Fig. 3) →
Steps were repeated. In the conventional apparatus, an operation was carried out in which the backwashing step described with reference to FIGS. 2 and 3 was continued after the completion of the filtering step of FIG. 1 described in the embodiment of the invention. The operating conditions are as follows: filtration (FIG. 1) → first backwash (FIG. 2) → second backwash (FIG. 3) → filtration (FIG. 1) → first backwash (FIG. 2) → second backwash (FIG. 3) ) → filtration (FIG. 1). The filtration membranes of both devices were made of cellulose acetate,
A product having a UF hollow fiber membrane, a molecular weight cut off of 150,000, and an effective membrane area of 5 m was used. The operating conditions for both devices were set as shown in Table 1. [Table 1] As shown in Table 1, the operating conditions of the conventional example are 2
Conditions. That is, in the first conventional example, the first backwashing and the second backwashing time are set to be the same as the conditions of the embodiment, and in the second conventional example, the first backwashing and the second backwashing are performed so that the recovery rate is the same as that of the embodiment.
The time for the backwash and the second backwash was halved. FIG. 4 shows the operation results. Example, Conventional Example 1
In both cases, no increase in the transmembrane pressure of the membrane module and the like were observed during the operation period of about 6 months, and stable operation was maintained. On the other hand, it was confirmed that the operation according to the example had a higher water recovery rate and the ratio of the filtration time to the operation time, and was effective in reducing the running cost. Next, when the example and the conventional example 2 are compared, in the conventional example 2, an increase in the transmembrane pressure of the membrane module was recognized from the beginning of the operation, and continuous operation was not performed in the operation period of about 3 months. Until it became possible, the blocking of the membrane module had progressed. From these results, according to the embodiment, the water recovery rate was reduced by the conventional example 2.
It has been confirmed that the backwashing effect can be increased and the stable operation period can be extended while maintaining the same condition. According to the present invention, the amount of water used for backwashing and the amount of backwashing can be reduced as compared with the conventional method in which the whole membrane module is washed at once by continuously performing two types of backwashing. By reducing the washing time to half, the same backwash effect is obtained, and the operation can be continued stably. Accordingly, the recovery rate and operation efficiency of the entire apparatus are improved, and as a result, it is possible to reduce fresh water production costs and equipment costs of the membrane filtration apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration of a membrane filtration device according to an embodiment, showing a filtration step. FIG. 2 is a schematic configuration of a membrane filtration device according to an embodiment, showing a first backwashing step. FIG. 3 is a schematic configuration of a membrane filtration device according to an embodiment, showing a second backwashing step. FIG. 4 is a diagram showing a change state of a transmembrane pressure with a lapse of operation time. [Description of Signs] 1 Raw water tank, 2 Pressurizing pump, 3, 5, 8, 9, 10
Valve, 4 membrane module, 6 filtered water tank, 7 backwash pump.

Continuation of front page    F term (reference) 4D006 GA06 GA07 HA02 KA61 KC03                       KE24Q MA01 MA02 MA03                       MA04 MC02 MC03 MC18 MC22                       MC23 MC29 MC39 MC62 PB04                       PB05 PB08

Claims (1)

Claims: 1. A membrane filter for introducing treated water into a raw water chamber of a membrane module partitioned by a membrane into a raw water chamber and a permeated water chamber, and obtaining treated water that has passed through the membrane from the permeated water chamber. A method, wherein a pair of raw water side openings for introducing or discharging treated water is provided at both ends of the raw water chamber, and backwash water is introduced into the permeated water chamber, and the raw water side opening of the raw water chamber is provided. It is possible to discharge the backwash wastewater from any of the following. After the filtration step for a predetermined period of time, one raw water side opening of the raw water chamber is opened, the other raw water side opening is closed, and one raw water The first backwashing step is performed by discharging the backwash wastewater from the side opening. After the first backwashing step is completed, the process returns to the filtration step. After the filtration step is completed for a predetermined period, the other of the raw water chamber is removed. Open the raw water side opening, close the one opening, and open the other raw water side opening. The second backwashing step is performed by discharging the backwash wastewater. After the second backwashing step is completed, the process returns to the filtration step. With the filtration step interposed, the first backwashing step and the second backwashing step are performed. A membrane filtration method characterized by repeating.