JP3943748B2 - Cleaning method for membrane filtration equipment - Google Patents

Description

この実験の結果における従来例と、本発明の場合の膜間差圧（一定のろ過処理水を得るための膜ろ過エレメント２２の原水室２６側と処理水室２４側の差圧）の変化を図４に示す。このように、従来法では、運転２ヶ月で、膜間差圧が増大し、薬品洗浄が必要になった。一方、本発明では、薬品洗浄が必要になったのは、運転７ヶ月であった。
【００３０】
これより、本発明の装置により、膜洗浄が効果的に行われ、安定運転期間を大きく延長できることが理解される。
【００３１】
【発明の効果】
以上説明したように、本発明では、通常の逆洗を行った後に自然流下により洗浄用水を原水室に流通してろ過膜を押し出し洗浄する。このため、原水室内の圧力を低くして、原水室内に洗浄用水を流通することができ、これにより、逆洗によって剥離しかかっているろ過膜表面の汚染物質を効果的に剥離除去することができる。これによって、ろ過膜の洗浄を効果的に行え、長期間にわたってろ過を継続することができる。
【００３２】
また、ろ過の時と通水方向が逆の押し出し洗浄を行うことで、逆洗で剥離しかかった汚染物質を鱗をはがすようにして、ろ過膜面から除去することができ、十分な洗浄効果を得ることができる。
【図面の簡単な説明】
【図１】 本発明の実施形態に係る膜ろ過装置の構成を示す図である。
【図２】 内圧型中空糸膜の構成を示す図である。
【図３】 各工程における汚染物質の状態を示す図である。
【図４】 運転継続による膜間差圧の変化を示す図である。
【符号の説明】
１０ 原水貯槽、１４ 膜ろ過モジュール、１６ 原水ポンプ、１８ 原水流入室、２０ 原水排出室、２２ 膜ろ過エレメント、２４ 処理水室、２６ 原水室、３４ 洗浄用水貯留槽、４０ 逆洗ポンプ。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for cleaning a membrane filtration device including a raw water chamber and a treated water chamber partitioned by a filtration membrane, and having a membrane filtration module that removes suspended substances from raw water by permeating the filtration membrane.
[0002]
[Prior art]
Conventionally, raw materials such as river water, lake water, dam water, industrial water, etc. are used as raw water for manufacturing industrial water, clean water, pure water or ultrapure water, or in the purification process of wastewater 2. Description of the Related Art Membrane filtration devices that perform filtration treatment using filtration membranes having pores are used. This membrane filtration device includes MF (microfiltration), UF (ultrafiltration), NF (nanofiltration), etc., depending on the pore size of the membrane used. The membrane shape includes a hollow fiber membrane, a tubular membrane, a spiral membrane, and a flat membrane.
[0003]
Such a membrane filtration apparatus arrange | positions a filtration membrane in a pressure vessel, and isolate | separates the inside into a raw | natural water chamber and a treated water chamber. And raw | natural water is inject | poured into a raw | natural water chamber from a press-fit pump, and the filtered treated water which passed the filtration membrane into the treated water chamber is obtained.
[0004]
And by the filtration process, the contaminant which consists of a suspended substance filtered and isolate | separated on the filter membrane surface accumulates, and the filtration capability falls. Therefore, regular backwashing is performed to restore the filtration capacity. That is, clean water such as filtered treated water or tap water is pumped as backwash water to the treated water chamber, and the washing water is passed from the treated water chamber to the raw water chamber through the filtration membrane in the direction opposite to the raw water filtration direction. , Strips and removes contaminants accumulated on the membrane surface.
[0005]
[Problems to be solved by the invention]
In membrane filtration equipment, this backwash must be performed at a very high frequency in order to restore the capacity of the filtration membrane. However, even if such backwashing is performed, contaminants cannot be sufficiently separated from the membrane surface. As a result, the contamination of the membrane progressed rapidly, and therefore the membrane had to be cleaned with chemicals such as acid and alkali at an early stage.
[0006]
This invention is made | formed in view of the said subject, and aims at providing the membrane filtration apparatus which can wash | clean a filtration membrane more effectively.
[0007]
[Means for Solving the Problems]
The present invention includes a raw water chamber and a treated water chamber partitioned by a filtration membrane, and is provided at a position higher than the upper end of the membrane filtration module, and a membrane filtration module for removing suspended substances from raw water by permeating the filtration membrane. A cleaning method for a membrane filtration device having a washing water storage tank for storing washing water, wherein the treated water obtained by the membrane filtration device is pumped to the treated water chamber by a pump, and the backwash waste water is treated as raw water Compared to the backwashing process discharged from the chamber, and after this backwashing process, the washing water in the washing water storage tank is circulated under the natural flow into the raw water chamber of the membrane filtration module and the washing water is pumped by a pump. And a washing step of washing the filtration membrane in a state where the pressure in the raw water chamber is low .
[0008]
Contaminants adhering to the surface of the filtration membrane in the filtration process are mostly peeled off from the membrane surface by backwashing, but some of them are attached to the membrane surface in a state of being peeled off. . The contaminants that are about to peel off reattach to the membrane surface when entering the filtration process again, and contaminate the membrane. In the present invention, between the normal backwashing step and the filtration step, the washing membrane is passed through the raw water chamber by natural flow using the washing means to wash the filtration membrane. Accordingly, it is possible to peel and remove contaminants made of suspended substances that are about to be peeled off from the surface of the filtration membrane by backwashing so as to be washed away by the flow of cleaning water. As a result, the filtration membrane can be washed effectively, and filtration can be continued for a long period of time.
[0009]
In the above washing step, it is better not to apply pressure as much as possible in order to avoid reattachment of contaminants to the film surface, and therefore it is better to flow the washing water under natural flow.
[0010]
In the present invention, the raw water is circulated in one direction in the raw water chamber of the membrane filtration module during filtration, and the cleaning water is circulated in the raw water chamber in the opposite direction to the raw water chamber during the cleaning by the cleaning means. Is preferred.
[0011]
Contaminants adhering to the surface of the filtration membrane tend to be scaled along the direction of raw water flow during filtration. Therefore, by circulating the cleaning water in the direction opposite to the flow direction of the raw water in the filtration, it is possible to remove the pollutants that have been peeled off from the filtration membrane surface by peeling off the scales. Cleaning can be performed.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention (hereinafter referred to as embodiments) will be described with reference to the drawings.
[0013]
Drawing 1 is a figure showing the composition of the membrane filtration device concerning an embodiment. Raw water such as river water is stored in the raw water storage tank 10. A membrane filtration module 14 is connected to the raw water storage tank 10 via a raw water pipe 12. A raw water pump 16 is provided in the middle of the raw water pipe 12, and the raw water in the raw water storage tank 10 is pumped to the membrane filtration module 14 by the raw water pump 16.
[0014]
The membrane filtration module 14 is installed vertically, and includes a lower raw water inflow chamber 18, an intermediate membrane filtration element chamber in which the membrane filtration element 22 is disposed, and an upper raw water discharge chamber 20. The membrane filtration element 22 is composed of a number of internal pressure type hollow fiber membranes 22a. As shown in FIG. 2, the hollow fiber membrane partitions the space inside the hollow fiber from the external space, and the hollow fiber The inside of the membrane 22 a constitutes a raw water chamber 26 connecting the raw water inflow chamber 18 and the raw water discharge chamber 20, and the outside of the hollow fiber membrane 22 a constitutes a treated water chamber 24.
[0015]
The raw water discharge chamber 20 of the membrane filtration module 14 is connected to the suction side of the raw water pump 16 via a circulation pipe 28. Accordingly, the raw water in the raw water storage tank 10 is supplied to the raw water inflow chamber 18 of the membrane filtration module 14 by the raw water pump 16, and passes through the raw water chamber 26 inside the hollow fiber of the membrane filtration element 22 from here through the raw water discharge chamber 20. Circulated to pump 16. Here, the filtered water that has permeated the filtration membrane from the inside of the hollow fiber of the membrane filtration element 22 reaches the treated water chamber 24.
[0016]
A treated water pipe 32 is connected to the treated water chamber 24, and the treated water pipe 32 is connected to a treated water storage tank 36 via a cleaning water storage tank 34. Therefore, the filtered water obtained by the membrane filtration module 14 is introduced into the treated water storage tank 36 through the cleaning water storage tank 34. The treated water in the treated water storage tank 36 is discharged out of the system and supplied to, for example, a subsequent pure water production facility.
[0017]
In addition, a backwash pipe 38 is connected to the treated water storage tank 36, and the backwash pipe 38 is connected to the treated water pipe 32 via a backwash pump 40. Therefore, by driving the backwash pump 40, the treated water in the treated water storage tank 36 is pumped to the treated water chamber 24 of the membrane filtration module, and the membrane filtration element 22 can be backwashed. In addition, washing water drain pipes 42 and 44 are connected to the raw water inflow chamber 18 and the raw water discharge chamber 20, and backwash drainage is discharged from here.
[0018]
In this embodiment, the cleaning water storage tank 34 is arranged at a position higher than the upper end of the membrane filtration module 14, and the cleaning water storage tank 34 and the raw water discharge chamber 20 of the membrane filtration module 14 are provided with a cleaning water pipe 46. Connected with. Therefore, the filtered water in the cleaning water storage tank 34 can be supplied to the raw water discharge chamber 20 under natural flow and drained from the cleaning drain pipe 44. As a result, the treated water in the cleaning water storage tank 34 flows naturally into the raw water chamber 26 of the membrane filtration element 22.
[0019]
In the above description, a valve is omitted, but a valve is appropriately provided in each pipe, and a flow path can be appropriately selected by opening and closing the valve.
[0020]
Next, the processing operation will be described with reference to FIG. In the filtration step, the raw water pump 16 is driven to feed the raw water to the raw water inflow chamber 18 below the membrane filtration module 14. As a result, the raw water passes through the membrane filtration module 14 in the order of the raw water inflow chamber 18, the raw water chamber 26 inside the hollow fiber, and the raw water discharge chamber 20, and then circulates through the circulation pipe 28 to the suction side of the raw water pump 16. Therefore, the raw water flows upward in the raw water chamber 26. A part of the raw water in the raw water chamber 26 passes through the hollow fiber membrane 22 a of the membrane filtration element 22 and reaches the treated water chamber 24. At this time, the suspended substances in the raw water are separated by the hollow fiber membrane 22a of the membrane filtration element 22 and accumulated on the surface of the raw water chamber 26 side. Accordingly, as the filtration process continues, contaminants made of suspended substances are gradually accumulated on the surface of the membrane filtration element 22 on the raw water chamber 26 side.
[0021]
As a result, the filtration capacity of the membrane filtration module 14 decreases, and a sufficient amount of treated water cannot be obtained. Therefore, the backwash process is periodically performed. That is, the driving of the raw water pump 16 is stopped, the backwash pump 40 is driven, and the filtered water in the treated water storage tank 36 is pumped into the treated water chamber 24. As a result, the filtered water flows through the membrane filtration element 22 from the treated water chamber 24 side toward the raw water chamber 26 side, backwashing is performed, and contamination accumulated on the raw water chamber 26 side surface of the membrane filtration element 22 is stored. The material is stripped away.
[0022]
And after this backwash process, an extrusion washing process is implemented using the filtered water in the washing water storage tank 34. In this extrusion washing process, the backwash pump 40 is stopped, and the filtered water in the washing water storage tank 34 is allowed to flow naturally into the raw water chamber 26 of the membrane filtration module, that is, into the internal space of the hollow fiber membrane 22a. As a result, as shown in FIG. 3, the contaminants remaining on the raw water chamber 26 side surface inside the hollow fiber of the membrane filtration element 22 are peeled and removed. In particular, in this extrusion cleaning process, the flow of filtered water in the raw water chamber 26 is a downward flow, and is in the opposite direction to the flow of raw water in the water flow process. Therefore, the separation of contaminants attached to the surface of the membrane filtration element 22 is promoted.
[0023]
In particular, the contaminants adhering to the surface of the membrane filtration element 22 tend to be scaled along the direction of the raw water flow in the filtration step, as shown in FIG. Therefore, if the filtration process is started immediately after the back washing process, the contaminants are again pressed against the filter membrane surface, and the contaminants adhere. By providing an extrusion washing process in which the water flow direction is reversed between the backwashing process and the filtration process, it is possible to remove the contaminants that have been peeled off from the filtration membrane surface by peeling off the scales. An effect can be obtained.
[0024]
This extrusion washing process does not need to be carried out after each backwash, and is carried out after a normal backwash at a frequency of once a day to once a week depending on the properties of the raw water. That's fine.
[0025]
Furthermore, in this embodiment, in the extrusion cleaning process, the filtered water in the backwash water storage tank 34 is caused to flow down into the raw water chamber 26 under natural flow. According to such natural flow, the pressure in the raw water chamber 26 at that time can be considerably reduced as compared with the case of pumping with a pump. Therefore, the pressing force against the film surface is low, and the attached contaminants can be effectively peeled off.
[0026]
In addition, because of natural flow, a rotating device such as a pump is unnecessary. The washing water storage tank 34 installed at a position higher than the upper end of the membrane filtration module 14 is sufficient for the volume of the raw water side chamber (raw water inflow chamber 18, raw water chamber 26, and raw water discharge chamber 20) of the membrane module 14. It is. Furthermore, this cleaning water storage tank 34 may be provided for one membrane filtration system, but since the timing of the extrusion cleaning process can be varied, only one tank is provided for a plurality of membrane filtration systems. Also good.
[0027]
Here, the cleaning water used in the extrusion cleaning step is not limited to the filtered water, and activated carbon treated water (when an activated carbon treatment apparatus is provided in the subsequent stage), tap water, or the like can be used. Further, the cleaning water is preferably as clean as possible, but raw water can also be used. The membrane filtration module is not limited to the internal pressure type hollow fiber, and various types of membrane filtration modules can be used. In particular, a tubular type membrane such as a hollow fiber membrane or a tubular membrane is suitable. Furthermore, the filtration method is not limited to the cross flow filtration as described above, and may be a whole amount filtration.
[0028]
【Example】
Using the apparatus having the same configuration as shown in FIG. 1, a conventional example in which only normal backwashing without an extrusion cleaning process is performed, and an apparatus of the present invention in which an extrusion cleaning process is provided after the backwashing process, A treatment experiment was conducted. The membrane module used is an internal pressure type hollow fiber membrane module. Table 1 shows the conditions at that time. Thus, in this invention, it is the same conditions except performing the extrusion washing | cleaning process once a week (once with respect to 220 backwashing) after a normal backwashing process.
[0029]
[Table 1]

Changes in the transmembrane differential pressure (the differential pressure between the raw water chamber 26 side and the treated water chamber 24 side of the membrane filtration element 22 for obtaining constant filtration treated water) in the case of the present invention and the conventional example in the result of this experiment. As shown in FIG. Thus, in the conventional method, the transmembrane pressure difference increased in 2 months of operation, and chemical cleaning became necessary. On the other hand, in the present invention, chemical cleaning was required for 7 months of operation.
[0030]
From this, it is understood that the apparatus of the present invention can effectively perform the membrane cleaning and greatly extend the stable operation period.
[0031]
【The invention's effect】
As described above, in the present invention, after performing normal backwashing, cleaning water is circulated through the raw water chamber by natural flow to push out and wash the filtration membrane. For this reason, the pressure in the raw water chamber can be lowered and the cleaning water can be circulated in the raw water chamber, whereby the contaminants on the filter membrane surface that are about to be peeled off by backwashing can be effectively peeled and removed. . As a result, the filtration membrane can be washed effectively, and filtration can be continued for a long period of time.
[0032]
In addition, by performing extrusion washing with the water flow direction reversed at the time of filtration, it is possible to remove the contaminants that have been peeled off by backwashing from the filtration membrane surface by peeling off the scales, and a sufficient washing effect Can be obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a membrane filtration device according to an embodiment of the present invention.
FIG. 2 is a view showing a configuration of an internal pressure type hollow fiber membrane.
FIG. 3 is a diagram showing the state of contaminants in each step.
FIG. 4 is a diagram showing a change in transmembrane pressure difference due to continued operation.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Raw water storage tank, 14 Membrane filtration module, 16 Raw water pump, 18 Raw water inflow chamber, 20 Raw water discharge chamber, 22 Membrane filtration element, 24 Treated water chamber, 26 Raw water chamber, 34 Washing water storage tank, 40 Backwash pump.

Claims (2)

A membrane filtration module that includes a raw water chamber and a treated water chamber partitioned by a filtration membrane, removes suspended matter from the raw water by permeating the filtration membrane, and is provided at a position higher than the upper end of the membrane filtration module. A cleaning method for a membrane filtration device having a cleaning water storage tank for storing ,
A backwashing step of pumping the treated water obtained by the membrane filtration device to the treated water chamber by a pump and discharging the backwash wastewater from the raw water chamber;
After this backwashing step, the washing water in the washing water storage tank is circulated under the natural flow into the raw water chamber of the membrane filtration module, and the pressure in the raw water chamber is lower than when the washing water is pumped by a pump. in a cleaning process for cleaning a filtration membrane,
A method for cleaning a membrane filtration device , comprising: The method of claim 1, wherein
Cleaning of a membrane filtration device characterized in that raw water is circulated in one direction into the raw water chamber of the membrane filtration module during filtration, and cleaning water is circulated through the raw water chamber in the direction opposite to that during filtration by the cleaning means during cleaning. Way .

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