JP2007130587A - Membrane filtration apparatus and method for washing membrane - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane filtration apparatus in which a membrane can be washed satisfactorily even when washed with comparatively small amounts of a disinfectant and backwashing water. <P>SOLUTION: The original water side (the primary side) of the filtration membrane of the membrane filtration apparatus is washed circularly with disinfectant-remaining backwashing water, so that the filtration membrane can be washed satisfactorily even when washed with comparatively small amounts of the disinfectant and backwashing water. As a result, the operation of the membrane filtration apparatus can be continued stably and the running cost thereof can be reduced. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a membrane filtration device comprising a membrane module for purifying water such as river water and lake water, groundwater, etc. to obtain industrial water, purified water, etc., and a backwash mechanism for the membrane module. The present invention relates to a cleaning method.

  Many membrane filtration devices equipped with membrane modules (separation membrane modules) have been introduced to various industrial water treatments, wastewater treatments, water purification treatments, and the like from the advantages of easy operation and stability of treated water.

  In such a membrane filtration device, insoluble substances and the like in the water to be treated accumulate on the filtration membrane surface in the course of continuing the membrane filtration treatment, and the filtration resistance increases (clogs). For this reason, in a membrane filtration apparatus, when the pressure loss (transmembrane differential pressure) in a filtration membrane becomes more than predetermined, or when filtration is performed for a certain period of time, a back washing process of a membrane module is performed. As a result, the filtration capacity of the membrane filtration device is recovered. At this time, as the backwash water, if clarified water (membrane filtered water, etc.) to which a bactericide (oxidant) is added is used, microorganisms attached to the membrane surface are removed. It can be removed more effectively and the cleaning effect can be increased (see, for example, Patent Documents 1 and 2).

JP-A-6-238136 Japanese Patent Laid-Open No. 11-19490

  However, in the backwashing with clear water to which a bactericidal agent is added as in the methods proposed in Patent Documents 1 and 2, in the case of raw water containing a large amount of microorganisms and organic substances, a relatively large amount of bactericidal agent and backwashing are used. I need water. For this reason, an increase in the amount of disinfectant used and the amount of backwash wastewater greatly affects the operating cost including wastewater treatment.

  In addition, as a measure for reducing the amount of disinfectant used, there is a method of increasing the contact time of the disinfectant by providing a step of immersing the film in water to which the disinfectant is added after backwashing after reducing the amount of backwash water. However, a sufficient cleaning effect cannot be obtained if the immersion time is within a range that does not reduce the amount of water produced.

  The present invention is a membrane filtration apparatus and a membrane cleaning method capable of obtaining a sufficient membrane cleaning effect even with the use of a relatively small amount of a disinfectant and backwash water.

  The present invention is a membrane filtration device for filtering and purifying the water to be treated, the filtration membrane for passing the water to be treated from the raw water side to the filtered water side and performing the filtration treatment, and the filtered water filtered by the filtration membrane A sterilizing agent adding means for adding a sterilizing agent, a backwashing means for washing the filtration membrane by passing the filtered water added with the sterilizing agent from the filtrate water side to the raw water side of the filtration membrane, and the filtration membrane Circulation washing means for washing at least one part of the backwash waste water obtained on the raw water side of the filtration membrane by washing back to the raw water side of the filtration membrane.

  Further, the present invention is a membrane cleaning method in a membrane filtration apparatus including a filtration membrane for filtering and purifying the water to be treated, and a filtration step of filtering the water to be treated from the raw water side to the filtrate water side And adding a bactericidal agent to the filtered water filtered by the filtration membrane, and passing the filtered water to which the bactericidal agent has been added from the filtered water side to the raw water side to wash the filtered membrane. And a circulation washing step of washing at least one part of the backwash waste water obtained on the raw water side of the filtration membrane by washing the filtration membrane to the raw water side of the filtration membrane to wash the filtration membrane. .

  Further, in the membrane cleaning method, it is preferable to use backwash wastewater in the latter half of the backwash process as backwash wastewater used for the circulation cleaning.

  In the membrane cleaning method, it is preferable that the residual chlorine concentration of the backwash waste water used for the circulation cleaning is in the range of 1 mg / L to 6 mg / L.

  According to the present invention, in a membrane filtration device, the use of a relatively small amount of bactericidal agent and backwash water by circulatingly washing the raw water side (primary side) of the filtration membrane using backwash waste water in which the bactericide remains. However, a sufficient membrane cleaning effect can be obtained and the operation can be continued stably. Therefore, the operating cost of the membrane filtration device can be reduced.

  Embodiments of the present invention will be described below.

  An outline of an example of a membrane filtration device according to an embodiment of the present invention is shown in FIG. The membrane filtration device 1 is a raw water tank 10, a membrane module 12, a filtered water tank 14, a sterilizing agent storage tank 16, a circulating cleaning water storage tank 18, a pressurizing pump 20 that is a circulating cleaning means, and backwashing means. A backwash pump 22 and a sterilizing agent injection pump 24 which is a sterilizing agent adding means are provided.

  More specifically, in the membrane filtration device 1 of FIG. 1, the raw water tank 10 is a tank that stores the water to be treated, and various kinds of water to be treated such as river water, groundwater, and wastewater flow in and are stored. The raw water tank 10 is connected to the suction side of the pressurization pump 20 via a valve 26, and the discharge side of the pressurization pump 20 is connected to the membrane module 12. The membrane module 12 schematically shows a so-called internal pressure hollow fiber membrane module, and is divided into a raw water chamber 30 and a filtrate (permeate) chamber 32 by an internal hollow fiber filtration membrane 28. In FIG. 1, only one hollow fiber filtration membrane 28 is shown for convenience, but in an actual membrane module, a large number of hollow fiber filtration membranes are usually mounted. Further, the raw water chamber 30 includes a first raw water side opening 34 on one end side (lower end side in FIG. 1) of the membrane module 12 and a second raw water side opening 36 on the other end side (upper end side in the figure). The piping from the pressurizing pump 20 is connected to the first raw water side opening 34. The filtrate water chamber 32 is provided with a filtrate water side opening 38, and the filtrate water side opening 38 is connected to the filtrate water tank 14 via a valve 40. Further, the suction side of the backwash pump 22 is connected to the filtered water tank 14, and the discharge side of the backwash pump 22 is connected to a pipe 42 in the middle of the filtrate water side opening 38 and the valve 40 of the membrane module 12. Connected through. Further, the discharge side of the sterilizing agent injection pump 24 is connected to the intermediate pipe between the backwash pump 22 and the valve 42 via the valve 54, and the sterilizing agent storage tank 16 is connected to the suction side of the sterilizing agent injection pump 24. Has been.

  Further, a valve 44 for discharging backwash drainage is connected to a pipe in the middle portion between the first raw water side opening 34 and the valve 26 of the membrane module 12, and the second raw water side opening 36 of the membrane module 12. Is connected to a valve 46 for discharging backwash drainage.

  Further, the circulating cleaning water storage tank 18 is connected to a pipe in the middle portion between the second raw water side opening 36 and the valve 46 of the membrane module 12 via a valve 48. Further, the circulating cleaning water storage tank 18 is connected to a pipe in an intermediate portion between the pressurizing pump 20 and the valve 26 through a valve 50. A drain valve 52 is connected to the circulating cleaning water storage tank 18. The pressurizing pump 20 may be used for filtration, and another pump may be provided for circulation (as circulation cleaning means).

  Next, the membrane cleaning method and the operation of the membrane filtration device 1 according to this embodiment will be described. The operation process of the membrane cleaning method according to the present embodiment includes a filtration process, a lower backwashing process, an upper backwashing (bactericide-containing circulating water storage) process, and a circulating cleaning process.

  In the present embodiment, in the method of purifying the treated water by filtration through a separation membrane, the backwash wastewater in which the disinfectant remains after the backwash of the separation membrane is performed using the clarified water to which the disinfectant is added. Is used to circulate and wash the primary side of the separation membrane. This is a method of effectively using a bactericide and water, thereby reducing the amount of bactericide used and the amount of drainage.

  First, in the filtration process, the valves 26 and 40 are opened (the other valves are closed), the pressurizing pump 20 is in an operating state (the backwash pump 22 and the sterilizing agent injection pump 24 are stopped), and stored in the raw water tank 10. The treated water is fed to the raw water chamber 30 of the membrane module 12. Insoluble substances and the like in the water to be treated are captured by the filtration membrane 28, and the water to be treated passes from the raw water side to the filtered water side through the filtration membrane 28 and moves to the filtered water chamber 32. And sent to the filtered water tank 14.

  In the lower backwash process, the valves 42, 44 and 54 are opened (the other valves are closed), the backwash pump 22 and the sterilizing agent injection pump 24 are in operation (the pressurizing pump 20 is stopped), and a predetermined amount of The filtered water in which the sterilizing agent is injected is passed as backwash water from the filtered water side of the membrane 28 of the membrane module 12 to the raw water side, and the filtered membrane 28 is backwashed. The backwash wastewater (bottom backwash wastewater) obtained on the raw water side of the filtration membrane 28 generated at that time is discharged out of the system through the valve 44.

  At the initial stage of the top backwash process, the valves 42, 46 and 54 are opened (the other valves are closed), the backwash pump 22 and the sterilizing agent injection pump 24 are in operation (the pressurizing pump 20 is stopped), and a predetermined amount. Mainly the upper part of the membrane 28 of the membrane module 12 is backwashed by the filtered water into which the sterilizing agent is injected. The backwash wastewater (upper backwash wastewater) generated at this time is discharged out of the system through the valve 46. And when the top backwashing process is carried out for a certain period of time and the properties of the backwash drainage become relatively clear, the bactericide-containing circulating water storage process (top top backwashing process) that stores backwash drainage as circulating water (Late)

  During the transition to the disinfectant-containing circulating water storage process, the valve 48 is opened and 46 is closed, and the backwash waste water is stored in the circulating wash water storage tank 18.

  In the circulation cleaning process, the valves 48 and 50 are opened (the other valves are closed), the pressure pump 20 is in an operating state (the backwash pump 22 and the sterilizing agent injection pump 24 are stopped), and the backwashing in which the sterilizing agent remains is performed. Waste water (circulated water) is circulated to the raw water side (primary side) of the filtration membrane 28, and the inner surface of the filtration membrane 28 of the membrane module 12 is sterilized and washed for a certain period of time. The circulating wastewater after the end of the circulating cleaning process is discharged out of the system through the drain valve 52.

  In the membrane cleaning method according to the present embodiment, the following steps are repeated: filtration step → lower back washing step → upper back washing (disinfectant-containing circulating water storage) step → circulating washing step. By adopting a sterilization washing process by circulating washing, stable operation can be performed even if the amount of backwash water and the amount of sterilizing agent used is reduced once compared with the conventional method of repeating the filtration process and the backwashing process. . Accordingly, the recovery rate of the entire apparatus is improved, the amount of drainage is reduced, and the amount of sterilizing agent used is also reduced. As a result, the operation cost can be reduced.

  In addition, the apparatus shown to a figure shows an example of embodiment of this invention, and this invention is not limited to the form of illustration, unless the summary is exceeded. Further, all of the upper backwashing wastewater may be used for circulation cleaning, or the upper backwashing washing process → the lower removal backwashing process may be performed in order, and a part of the lower backwashing wastewater may be used for circulation washing. The order of the bottom removal backwashing step → the top removal backwashing step is preferable because air removal from the membrane module 12 is easy. Furthermore, the drainage used for circulating water should be as clear as possible, and it is preferable to use the drainage from the first half of the backwashing process.

  As described above, in the separation membrane cleaning method according to the present embodiment, at least a part of the backwash drainage used for backwashing the filtration membrane may be circulated and used for circulation cleaning, but the filtration membrane is washed. The backwash wastewater used for the circulation washing is preferably backwash wastewater in the latter half of the backwash process. In this method, the cleaning effect can be further enhanced by using relatively clean wastewater in the latter half of the backwashing process (that is, wastewater having a large amount of the disinfectant) for circulation cleaning. Here, the backwash drainage in the latter half of the backwash process is preferably backwash drainage after 1/2 of the backwash process (bottom backwash process + top backwash process). More preferably, it is a backwash drainage after / 3.

  Moreover, the residual chlorine concentration of the backwash wastewater used for the circulation cleaning is preferably 1 mg / L or more, more preferably in the range of 1 mg / L to 6 mg / L, and 2 mg / L to 5 mg / L. The range is more preferable, and the range of 2 mg / L to 4 mg / L is particularly preferable. When the residual chlorine concentration is less than 1 mg / L, the cleaning effect of the film is lowered, and when it exceeds 6 mg / L, chemical deterioration of the film may occur depending on the film material.

  As the disinfectant, chlorine-based disinfectants such as sodium hypochlorite, liquefied chlorine, chloramine, and chlorine dioxide can be used. Sodium hypochlorite and liquefied chlorine are preferably used, and hypochlorous acid. More preferably, sodium is used.

  A hollow fiber filtration membrane is used as the filtration membrane 28, and any material used for separation membranes such as polysulfone, polyvinylidene fluoride, cellulose acetate, polyethylene, polyether sulfone, ceramics can be used as the material. It is.

  The separation membrane cleaning method according to this embodiment is particularly effective when a cellulose acetate membrane is used which is relatively susceptible to biological degradation due to microorganisms contained in the raw water. When a cellulose acetate membrane is used, the amount of the bactericide used to prevent biodegradation of the membrane is usually increased to a residual chlorine concentration of 2 mg / L or more, and in some cases about 3 to 6 mg / L. In this case, since the residual chlorine concentration in the backwash wastewater becomes large, the use of this backwash wastewater increases the membrane cleaning effect and the biological deterioration prevention effect. In addition, even when using a membrane other than cellulose acetate, the amount of the bactericide is usually 1 mg / L or more as the residual chlorine concentration, and sometimes 3 to 5 mg / L in order to prevent clogging of the membrane. However, since the residual chlorine concentration in the backwash wastewater becomes larger, the use of this backwash wastewater increases the membrane cleaning effect.

  In addition, if the residual chlorine concentration in the backwash wastewater is large, it is environmentally unfavorable to discharge it to a river or the like as it is. In addition to rising, residual chlorine in the backwash waste water can be consumed.

  The residual chlorine concentration in the backwash waste water can be measured by DPD (diethyl-p-phenylenediamine) method, OT (o-tolidine) method or the like. Further, the residual chlorine concentration may be measured by manually sampling backwash wastewater or may be measured automatically.

  Various separation pore sizes can be used for the filtration membrane 28 depending on the processing application. Usually, a separation membrane having a fractional molecular weight of about several tens of thousands to a separation pore size of several μm is applied, and preferably a fractional molecular weight of 13,000. To a separation membrane with a separation pore diameter of 3 μm is applied.

  The flow rate of backwash wastewater (circulated water) is preferably in the range of 0.05 m / sec to 1 m / sec from the viewpoint of the cleaning effect.

  As the size of the circulating washing water storage tank 18, it is only necessary to store more than the minimum amount of water necessary for circulating water.

  According to the present embodiment, by circulating and washing the raw water side (primary side) of the filtration membrane using the backwash waste water in which the disinfectant remains, the amount of disinfectant used compared to the conventional backwash only method, Even if the amount of drainage is reduced, the same cleaning effect can be obtained and the operation can be continued stably. Therefore, the operating cost of the membrane filtration device can be reduced.

  The membrane filtration apparatus according to the present embodiment is used in various treatment processes such as water treatment facilities, industrial wastewater treatment facilities, industrial water treatment facilities, and the like. It can be used for the treatment of supernatant water, various process intermediate waters, various recovered waters, various waste waters and the like.

  Hereinafter, although an example and a comparative example are given and the present invention is explained more concretely in detail, the present invention is not limited to the following examples.

Example 1
Example 1 uses the membrane filtration apparatus 1 of FIG. 1 described in the embodiment of the present invention, and includes a filtration step → bottom-up backwashing step → top-up backwashing (bactericide-containing circulating water storage) step → circulation washing step → The continuous operation was repeated in the order. In Example 1, the circulating wash water is stored in all the top backwash wastewater (lower bottom backwash wastewater (25 sec) + top backwash wastewater (25 sec)) for 25 sec, that is, 1/2 or more of the backwash process. Minutes). The operating conditions of the membrane filtration device 1 were set as shown in Table 1.

Further, as the filtration membrane of the membrane filtration device 1, a cellulose acetate UF hollow fiber membrane, a molecular weight cut off of 150,000 and an effective membrane area of 3.5 m ² were used. A sodium hypochlorite aqueous solution having an effective concentration of 12% was used as the disinfectant.

(Example 2)
Circulating wash water storage was set to 15 seconds in the second half of the top backwash process (bottom backwash drainage (25 sec) + top backwash drainage (25 sec) 15 sec, that is, 7/10 of the backwash process) The subsequent continuous operation was repeated in the order of filtration step → bottom back washing step → top top back washing (bactericide-containing circulating water storage) step → circulation washing step → except for the following. Table 1 shows the operating conditions.

(Comparative Example 1)
In Comparative Example 1, the membrane filtration device 3 shown in FIG. 2 was used, and the continuous operation was repeated in the order of the filtration step → the lower backwashing step → the upper backwashing step → without implementing the circulation cleaning step. Table 1 shows the operating conditions. Compared with the membrane filtration device 1 of FIG. 1, the membrane filtration device 3 shown in FIG. 2 is a device that does not have a circulation washing line, that is, a circulation washing water storage tank 18, valves 48, 50, 52, and pipes attached to them. Device. The operating conditions of Comparative Example 1 were substantially the same as in Example 1, but the amount of disinfectant used and the amount of drainage were increased.

(Comparative Example 2)
In Comparative Example 2, the same membrane filtration device 3 as in Comparative Example 1 (FIG. 2) was used, and continuous operation was repeated in the order of filtration step → bottom back washing step → top back washing step → stationary step →. Table 1 shows the operating conditions. The operating conditions of Comparative Example 2 are the same as Example 1 in the amount of fresh water, the amount of disinfectant used, and the amount of wastewater, and instead of the circulation cleaning step, the stationary step of immersing the membrane in the backwash water for a certain time (30 sec) after backwashing Carried out.

(Comparative Example 3)
In Comparative Example 3, continuous operation was repeated using the membrane filtration device 5 shown in FIG. 3 in the order of filtration step → bottom back washing step → top top back washing step → membrane primary side washing step →. Table 1 shows the operating conditions. The operating conditions of Comparative Example 3 were the same as in Example 1 in the amount of water produced, the recovery rate, and the amount of drainage, and the membrane primary side cleaning water used was a raw water added with 5 mg / L of bactericide instead of backwashing water. The amount of fungicide used was slightly greater than in Example 1. In the membrane filtration device 5, the disinfectant can be injected into the raw water line via the valve 56.

図４に実施例１，２及び比較例１〜３の運転結果を示す。ろ過膜の膜間差圧が上昇し連続運転が不可能になるまでの期間（安定運転期間）は、実施例１：６ヶ月、実施例２：８ヶ月、比較例１：６ヶ月、比較例２：４ヶ月、比較例３：５．５ヶ月となった。

The operation results of Examples 1 and 2 and Comparative Examples 1 to 3 are shown in FIG. The period until the intermembrane differential pressure of the filtration membrane increases and the continuous operation becomes impossible (stable operation period) is as follows: Example 1: 6 months, Example 2: 8 months, Comparative example 1: 6 months, Comparative example 2: 4 months, Comparative Example 3: 5.5 months.

  When Examples 1 and 2 were compared with Comparative Example 1, the stable operation period of Example 1 was the same as that of Comparative Example 1, and the stable operation period of Example 2 was greater than that of Comparative Example 1. Compared with Comparative Example 1, Examples 1 and 2 were less effective in reducing the operating cost because the amount of sterilizing agent used and the amount of drainage were smaller.

  When Examples 1 and 2 were compared with Comparative Example 2, the stable operation period of Examples 1 and 2 was longer than that of Comparative Example 2. From this result, it was confirmed that the washing effect was improved and the stable operation period could be extended while keeping the amount of fresh water, the amount of disinfectant used, and the amount of waste water as in Comparative Example 2.

  When Examples 1 and 2 were compared with Comparative Example 3, the stable operation period of Examples 1 and 2 was longer than that of Comparative Example 3. From this result, it was confirmed that under the same amount of water production, recovery rate, and amount of drainage, it was possible to improve the cleaning effect and extend the stable operation period compared to the case where a bactericidal agent was added to the raw water as circulating cleaning water. . It was also confirmed that the amount of fungicide used could be reduced slightly.

  In comparison between Example 1 and Example 2, the stable operation period was longer in Example 2 in which only the drainage in the latter half of the top backwash process was used for circulation cleaning. From this, it was confirmed that the cleaning effect can be further enhanced by using only the relatively clear waste water in the latter half of the backwashing process as the circulating wash water.

It is the schematic which shows an example of a structure of the membrane filtration apparatus which concerns on embodiment of this invention. It is the schematic which shows the structure of the membrane filtration apparatus used by the comparative examples 1 and 2 of this invention. It is the schematic which shows the structure of the membrane filtration apparatus used by the comparative example 3 of this invention. It is a figure which shows the driving | running result of the membrane filtration apparatus in the Example and comparative example of this invention.

Explanation of symbols

1, 3, 5 Membrane filtration device, 10 Raw water tank, 12 Membrane module, 14 Filtration water tank, 16 Disinfectant storage tank, 18 Circulating wash water storage tank, 20 Pressure pump, 22 Backwash pump, 24 Disinfectant injection pump, 26, 40, 42, 44, 46, 48, 50, 54, 56 Valve, 28 Filtration membrane, 30 Raw water chamber, 32 Filtration water chamber, 34 First raw water side opening, 36 Second raw water side opening, 38 Filtration water side Opening, 52 drain valve.

Claims (4)

A membrane filtration device for filtering and purifying treated water,
A filtration membrane for passing the treated water from the raw water side to the filtered water side for filtration treatment,
A bactericidal agent addition means for adding a bactericidal agent to the filtered water filtered by the filtration membrane;
Backwashing means for passing the filtered water to which the sterilizing agent has been added from the filtrate water side of the filtration membrane to the raw water side and washing the filtration membrane;
Circulating and washing means for washing the filtration membrane by circulating at least a part of the backwash waste water obtained on the raw water side of the filtration membrane to the raw water side of the filtration membrane by backwashing the filtration membrane;
A membrane filtration apparatus comprising: A method for cleaning a membrane in a membrane filtration device comprising a filtration membrane for filtering and purifying treated water,
A filtration step in which the water to be treated is filtered from the raw water side to the filtered water side;
A backwashing step of adding a bactericidal agent to the filtered water filtered by the filtration membrane, and allowing the filtered water to which the bactericidal agent is added to flow from the filtered water side of the filtration membrane to the raw water side to wash the filtration membrane; ,
A circulating washing step of washing the filtration membrane by circulating at least a part of the backwash drainage obtained on the raw water side of the filtration membrane to the raw water side of the filtration membrane by backwashing the filtration membrane;
A method for cleaning a film, comprising: A method for cleaning a membrane according to claim 2,
A method for cleaning a membrane, comprising using backwash wastewater in the latter half of the backwash process as backwash wastewater used for the circulation cleaning. A method for cleaning a membrane according to claim 2 or 3,
A method for cleaning a membrane, wherein the residual chlorine concentration of the backwash wastewater used for the circulation cleaning is in the range of 1 mg / L to 6 mg / L.

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