JP2001079367A - Membrane separation method and device thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent clogging of a membrane by suppressing sticking and growth of a manganese oxide on the membrane surface. SOLUTION: When raw water containing manganese ions is fed to a membrane module 18 and is filtered through the membrane, a sodium hypochlorite solution from an oxidant tank 34 is added to the raw water flowing in a piping 16 for a specified time, then a sodium hydrogensulfite solution from a chemical tank 44 is added to the raw water for a specified time. This process is intermittently repeated, then proliferation of bacteria and sticking and growth of manganese dioxide on the surface of a filter membrane 22 are prevented and clogging of the membrane is prevented, thus a filter operation under low filtering resistance for a long period is possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a membrane separation method and an apparatus therefor, and more particularly to a membrane separation method for filtering raw water containing manganese ions through a filtration membrane and an apparatus therefor.

[0002]

2. Description of the Related Art In a membrane separation method in which raw water is filtered by a filtration membrane, suspended substances in the raw water adhere to the membrane surface by filtration or microorganisms grow, thereby increasing the filtration resistance of the membrane. Close the membrane. For this reason, the surface of the film is regularly cleaned.

[0003] However, it is difficult to remove microorganisms that have propagated on the membrane surface only by physical washing.
There is known a method of intermittently or continuously adding an oxidizing agent such as sodium hypochlorite to the raw water in the course of a filtration operation to oxidatively decompose the microorganism to prevent the membrane from being clogged. According to this method, the unreacted oxidizing agent in the treated water that has permeated the membrane acts as a disinfectant, and has an advantage that it is suitable for beverages.

[0004]

However, the above method of adding an oxidizing agent such as sodium hypochlorite to raw water is effective in preventing the growth of microorganisms on the membrane surface, According to the knowledge, a new problem has arisen. That is, raw water usually contains trace amounts of iron ions and manganese ions, and these metal ions are oxidized by the oxidizing agent, thereby precipitating as metal oxides, which are fixed to the film surface, It was found to occlude the membrane. In particular, once the manganese dioxide crystal, which is an oxide of manganese, adheres to the film surface, its catalysis promotes the oxidation of manganese, causing the crystal to become coarser, thereby accelerating the blockage of the film.

An object of the present invention is to solve the above-mentioned problems of the prior art and to minimize the fixation and growth of manganese oxide on the membrane surface even in the case where raw water containing manganese ions is subjected to membrane filtration. Another object of the present invention is to provide a membrane separation method and a device capable of preventing membrane clogging and performing a long-time filtration operation with low filtration resistance.

[0006]

A membrane separation method according to the present invention is a membrane separation method for filtering raw water containing manganese ions through a filtration membrane, wherein sodium hydrogen sulfite is intermittently added to the raw water for filtration. It is characterized by.

The membrane separation method according to the present invention is a membrane separation method for filtering raw water containing manganese ions through a filtration membrane, wherein the raw water is filtered by alternately adding an oxidizing agent and sodium bisulfite. Features.

The membrane separation apparatus according to the present invention comprises: a membrane module; raw water supply means for supplying raw water containing manganese ions to the membrane module; oxidizing agent adding means for adding an oxidizing agent to the raw water; It is characterized by comprising sodium hydrogen sulfite addition means for adding a sodium bisulfite solution to raw water, a treatment water tank for storing treated water that has passed through the membrane module, and stirring means disposed in the treatment water tank. .

[0009]

FIG. 1 is an apparatus system diagram showing an embodiment of the present invention. Raw water is introduced into the raw water tank 12 from the pipeline 10. The raw water tank 12 has a pipeline 16 provided with a pump 14.
And one end of the conduit 16 is connected to the raw water side 20 of the membrane module 18. The membrane module 18 is divided into a raw water side 20 and a permeated water side 24 by a filtration membrane 22, and the permeated water side 24 is connected to a treated water tank 28 via a pipe 26. A stirrer 30 is disposed in the treated water tank 28, and an outlet pipe 32 of the treated water is connected.

The type of the filtration membrane 22 used in the membrane module 18 is not particularly limited, and may be any of a microfiltration membrane, an ultrafiltration membrane, a nanofiltration membrane, and a reverse osmosis membrane. Further, the type of the membrane is not particularly limited, and may be any of a hollow fiber membrane, a flat membrane, and a tubular membrane.

An oxidizing agent adding means and a sodium hydrogen sulfite adding means are connected to the pipe line 16. That is, the oxidizing agent adding means includes an oxidizing agent tank 34 for storing a sodium hypochlorite solution, the oxidizing agent tank 34 and the pipe 16.
And a conduit 40 provided with a pump 38 in the middle thereof. The sodium hydrogen sulfite adding means connects a chemical solution tank 42 for storing a sodium bisulfite solution with the chemical solution tank 42 and the pipe 16 via an on-off valve 48 and has a pipe 50 provided with a pump 50 in the middle thereof. 52. Reference numeral 54 denotes a controller which opens and closes the on-off valves 36 and 46 and turns on the pumps 38 and 48 by a built-in timer.
N, OFF are controlled.

In the above configuration, raw water is supplied from the raw water tank 12 to the membrane module 18 by the pump 14 and filtered by the filtration membrane 22. The treated water obtained by the filtration is sent from a pipe 26 to a treated water tank 28, where it is temporarily stored, and then sent from a pipe 32 to a target location.

In this filtration step, the controller 54 controls the oxidizing agent adding means and the sodium hydrogen sulfite adding means in the cycle shown in FIG. 2 such that the time T of one cycle is executed by the following equation (1).

[0014]

[Equation 1] T = t ₁ + t ₂ + t ₃ + t ₄

In the above formula (1), t ₁ and t ₃ are time zones in which only raw water is passed, t ₂ is a time zone in which the sodium hypochlorite solution is added to the raw water, and t ₄ is a time zone in which the sodium bisulfite solution is added to the raw water. It is a time zone for addition, and the time T of one cycle is usually 20 minutes to 24 hours.

First, after the operation at the time t ₁ for passing only the raw water, the controller 54 opens the on-off valve 36 and operates the pump 38 to flow through the pipeline 16 for the time t _2. Add sodium hypochlorite solution to raw water. The addition amount is adjusted so that the concentration of sodium hypochlorite to the raw water is 1 to 20 ppm, and the time t ₂ is 1
About 30 minutes. The raw water to which the sodium hypochlorite solution has been added forms the filtration membrane 22 of the membrane module 18.
When the microorganisms reach the surface of the membrane, the microorganisms that are attached to the membrane and are about to proliferate are oxidatively decomposed and killed by the action of sodium hypochlorite. For this reason, blockage of the membrane due to propagation of microorganisms on the membrane surface can be prevented.

However, when manganese ions are contained in the raw water, the manganese ions are oxidized by the action of sodium hypochlorite to precipitate manganese dioxide as described above. This manganese dioxide adheres to the surface of the film, causing an adverse effect of closing the film. For this reason, after the addition operation of the sodium hypochlorite solution is stopped, only the raw water is passed for the time t ₃ , and then the controller 54
Off valve 46 is opened, by operating the pump 48, during the time t _4, the addition of sodium bisulfite solution to the raw water flowing through the pipe 16 by. In the above operation in which only the raw water at time t ₃ is passed, the sodium hypochlorite added in the former stage and the sodium bisulfite added in the latter stage come into contact before the filtration membrane 22 to be neutralized. Time t ₃ for this purpose.
Then, only the raw water is passed through for a few minutes, and the inside of the pipeline 16 and the raw water side 20 of the membrane module 18 are replaced with raw water not containing sodium hypochlorite.

The amount of the sodium bisulfite is ₃ to 10 ppm with respect to the raw water, and the time t ₄ is about 1 to 10 minutes. When the raw water to which the sodium bisulfite solution has been added reaches the membrane surface of the filtration membrane 22 of the membrane module 18, manganese dioxide (strictly, hydrated manganese dioxide) fixed to the membrane surface is converted to sodium bisulfite. By action, it is reduced and dissolved as in the following formula 2. Therefore, it is possible to prevent manganese dioxide from sticking to the film surface and preventing the film from being clogged due to growth.

[0019]

[Formula 2] MnO ₂ · nH ₂ O + 2NaHSO ₃ → MnSO ₄
+ Na ₂ SO ₃ + (n + 1) H ₂ O

Since the reaction product of the above formula (2) and the surplus sodium bisulfite not contributing to the reaction are water-soluble, they permeate the filtration membrane 22 and are dissolved in the treated water to be treated in the treated water tank 2.
To 8. In the treated water in the treated water tank 28, surplus sodium hypochlorite when the sodium hypochlorite is added is dissolved. Therefore, the excess sodium bisulfite is neutralized by the reaction shown in the following formula 3.

[0021]

[Formula 3] NaHSO ₃ + NaClO → NaHSO ₄ + NaCl

Therefore, if the amounts of the sodium hypochlorite solution and the sodium bisulfite solution are adjusted so that the sodium hypochlorite becomes slightly excessive, it is possible to prevent the sodium bisulfite from remaining in the treated water. Can be avoided.

It is preferable to operate a stirrer 30 disposed in the treated water tank 28 so that the reaction of the above formula 3 is achieved quickly. In addition, since the property of the treated water changes subtly for each time period of one cycle shown in FIG. 2, the stirrer 30 uniformizes the property of the treated water in addition to the purpose of promoting the reaction of the above formula 3. For the purpose of this, it is preferable to operate at any time. As a means for stirring the treated water in the treated water tank 28, for example, a circulation pump may be used instead of the stirrer 30.

FIGS. 3 and 4 show modifications of the time T of one cycle in the filtration step. In the example shown in FIG. 3, the time period t _{1 in} which only raw water is passed and the time period t _{2 in} which the sodium hypochlorite solution is added to raw water are repeated three times as one cycle time T. As in the case of the above, the time zone t _{3 in which} only the raw water flows, and the time zone t _{4 in} which the sodium bisulfite solution is added to the raw water. This modification is suitable when the number of microorganisms in the raw water is relatively large and the amount of manganese ions is small.

In the example shown in FIG. 4, one cycle time T
Are those constituted by the time period t ₄ when adding sodium bisulfite solution only in a time zone t ₁ and raw water passed through the raw water, the apparatus configuration is the oxidant addition means are excluded in FIG. . This modification is suitable when the filtration membrane is of a type that is not affected by the propagation of some microorganisms, or when the raw water has few microorganisms and relatively large amounts of manganese ions. Sodium bisulfite does not have the effect of oxidatively decomposing and killing microorganisms such as sodium hypochlorite, but has the effect of inhibiting the growth of microorganisms, especially aerobic microorganisms. However, in this modified example, if more sodium bisulfite than necessary is added, surplus sodium bisulfite remains in the treated water. Therefore, in order to neutralize the surplus sodium hydrogen sulfite, for example, the oxidizing agent 52 may be directly added to the treatment tank 28 in FIG.

In the description of the above embodiment, the content of one cycle in the filtration step was mainly described. However, when the filtration resistance becomes a certain value or more due to the long-time operation, a washing step is performed as necessary, in addition to the above-described filtration step, to recover the permeation flux. For the cleaning, a known method such as chemical cleaning, air cleaning, and back pressure cleaning is appropriately selected in accordance with the use condition of the membrane module.

[0027]

As described above, according to the present invention, when raw water containing manganese ions is subjected to membrane filtration, fixation and growth of manganese oxide on the surface of the membrane are minimized, whereby the membrane is blocked. There is an extraordinary effect that the filtration operation can be performed for a long time with low filtration resistance.

[Brief description of the drawings]

FIG. 1 is an apparatus system diagram showing an embodiment of the present invention.

FIG. 2 is a time chart showing the contents of one cycle in the filtration step of the present invention.

FIG. 3 is a time chart showing a modification of one cycle in the filtration step of the present invention.

FIG. 4 is a time chart showing a modification of one cycle in the filtration step of the present invention.

[Explanation of symbols]

12 Raw water tank 18 Membrane module 22 Filtration membrane 28 Treatment water tank 30 Stirrer 34 Oxidant tank 44 Chemical tank 54 Controller t ₁ Only raw water flows hours of adding sodium bisulfite solution only time slot t ₃ ...... raw water adding sodium hypochlorite solution to the time zone t ₂ ...... raw water to the time zone t ₄ ...... raw water passed through

Continued on the front page (72) Inventor Teruhiro Kitazawa 1-1-1 Uchikanda, Chiyoda-ku, Tokyo Inside Hitachi Plant Construction Co., Ltd. (72) Inventor Hiroshi Okuno 1-1-14 Uchikanda, Chiyoda-ku, Tokyo Sun F-term in Reference Plant Construction Co., Ltd. (reference) 4D006 GA03 GA05 GA06 GA07 HA01 HA21 HA41 KA33 KD24 KD30 KE11R KE28R PA01 PB02 PB24 PB27

Claims (3)

[Claims] 1. A membrane separation method for filtering raw water containing manganese ions through a filtration membrane, wherein sodium hydrogen sulfite is added intermittently to the raw water and the raw water is filtered. 2. A membrane separation method for filtering raw water containing manganese ions through a filtration membrane, wherein an oxidizing agent and sodium bisulfite are alternately added to the raw water and the raw water is filtered. 3. A membrane module, raw water supplying means for supplying raw water containing manganese ions to the membrane module, oxidizing agent adding means for adding an oxidizing agent to the raw water, and adding a sodium hydrogen sulfite solution to the raw water. A membrane separation apparatus comprising: sodium hydrogen sulfite addition means; a treatment water tank for storing treated water permeated through the membrane module; and a stirring means provided in the treatment water tank.