JP5147267B2 - Cleaning method for membrane filtration system - Google Patents

Description

  The present invention relates to a cleaning method for a membrane filtration system including an internal pressure type hollow fiber membrane module, with respect to a filtration treatment for removing a suspension in a liquid.

Further, it is known that a flushing step is performed after a membrane breakage detection step in an external pressure type hollow fiber membrane module (Patent Document 1, paragraph [0032]). However, the external pressure type has a problem that suspended substances are easily accumulated between the hollow fiber membranes, and the suspended substances cannot be sufficiently removed by flushing.
In addition, a concentration circulation tank to which raw water containing suspended solids is supplied and a plurality of cylindrical membrane filters are arranged inside the outer cylinder, and the raw water supplied from the module inlet is Flows from the inlet end face of the membrane filter, flows through the internal space of each membrane filter, flows out from the outlet end face of each membrane filter, flows out from the module outlet, and flows from the inner peripheral surface of the membrane filter toward the outer peripheral surface. The permeated water that has permeated is separated from the raw water, and is interposed in a first piping system that communicates the concentration circulation tank and the module inlet of the membrane filter module, and the raw water And a second piping system for returning the raw water flowing out from the module outlet of the membrane filter module to the concentration circulation tank. A bypass pipe for returning a part of the raw water from the first piping system to the first piping system, and the pump and the membrane filter module in the first piping system. The bypass pipe is provided with a mixer that generates fine bubbles in the raw water by mixing air into the raw water with a higher air pressure than the water pressure at the inlet of the module. A characteristic clogging prevention device for a filtering device is known (Patent Document 2). This method has a problem that a mixer for generating fine bubbles and a compressor for supplying gas must be further provided, and the equipment becomes more expensive.

Also, a hollow fiber membrane that fills the secondary side of the hollow fiber membrane, pumps a constant gas from the primary side, and measures the amount of water extruded from the primary side to the secondary side of the hollow fiber membrane after maintaining a constant pressure There is known a module safety test method in which the safety test process is performed after the back pressure washing process after the filtration operation is completed (Patent Document 3). This method is an internal pressure type hollow fiber membrane module, and the hollow fiber membrane must be suspended in the vertical direction, so that the force applied to the hollow fiber membrane is increased and the risk of breakage is high. is there.
JP 2004-188252 A JP 2000-197884 A JP 2005-13992 A

  The subject of this invention is providing the washing | cleaning method of the membrane filtration system with the high washing | cleaning effect of a membrane.

As a result of earnest research, the hollow fiber membrane was devised by devising the flow method of the raw water that causes the inside (primary side) of the hollow fiber membrane to flow when the primary side air venting step is performed after the membrane break detection test. It has been found that suspended substances adhering to the inner surface can be effectively removed.
That is, the present invention is an internal pressure type comprising a membrane module having a hollow fiber membrane, a raw water supply means for supplying raw water to the membrane module, and a membrane breakage detecting means for detecting a membrane breakage of the hollow fiber membrane. In the washing method of the membrane filtration system, a backwashing step of the hollow fiber membrane, a membrane breakage detecting step of detecting a breakage of the hollow fiber membrane after introducing gas into the hollow fiber membrane following the backwashing step, An air venting step for allowing a liquid to flow inside the hollow fiber membrane following the membrane breakage detecting step, wherein the air venting step causes the liquid to flow from one end to the other end in the longitudinal direction of the hollow fiber membrane. It is an air venting process in which an air venting process and a second air venting process in which a liquid is allowed to flow from the other end in the longitudinal direction of the hollow fiber membrane to the one end are alternately performed.

Moreover, as one form of this invention, in the said air venting process of Claim 1, the liquid to which the chemical | medical agent was added is made to flow through the inner side of a hollow fiber membrane (Claim 2). As the chemical, an oxidizing agent such as a sodium hypochlorite solution, an inorganic acid such as hydrochloric acid or sulfuric acid, an organic acid such as citric acid, or an alkaline solution such as sodium hydroxide is used.
Moreover, as one form of this invention, in the filtration process after the said air venting process in Claim 2, the filtered water from the filtration start to predetermined time is discarded (Claim 3).

Moreover, as one aspect of the present invention, the backwashing step performed immediately before the film breakage detection step according to any one of claims 1 to 3 includes at least the following steps (1) and (2): The steps (1) and (2) are performed alternately (claim 4).
(1) A step of allowing liquid to flow from one end to the other end of the hollow fiber membrane.
(2) A step of allowing a liquid to flow from the other end to the one end on the inner side of the hollow fiber membrane.
Moreover, as one form of this invention, in the said backwashing process of Claim 4, the liquid to which the chemical | medical agent was added is made to flow through the outer side of a hollow fiber membrane (Claim 5). As the chemical, an oxidizing agent such as a sodium hypochlorite solution, an inorganic acid such as hydrochloric acid or sulfuric acid, an organic acid such as citric acid, or an alkaline solution such as sodium hydroxide is used.

  According to the above invention, at the initial stage of the air venting process, the gas introduced by the film breakage detecting process performed before the air venting process is inside the hollow fiber membrane. And the compound of the said gas and the said liquid flows through the inside of a hollow fiber membrane by flowing a liquid inside a hollow fiber membrane at an air venting process. At this time, the suspended substance adhering to the inside of the hollow fiber membrane is released by alternately switching the flow direction of the liquid. Since the air venting process was performed while the gas introduced by the membrane breakage detection process was inside the hollow fiber membrane, the inside of the hollow fiber membrane was separately cleaned without the operation of introducing air into the hollow fiber membrane. can do. The present invention is particularly effective not only when the membrane module is formed of one membrane element, but also when the membrane module is composed of a plurality of membrane elements and a plurality of the membrane elements are arranged in series. It is. This is because air tends to stay between the membrane elements. And since each membrane element can be made small, it is easy to carry, maintainability can be improved, and it is easy to construct a large-scale membrane filtration system.

Moreover, according to invention of Claim 2, the effect which liberates the suspended solid adhering to the inside of a hollow fiber membrane is improved by using the liquid which added the chemical | medical agent in an air venting process, and it is performed after an air venting process. The membrane module can be sterilized before the filtration step.
According to the invention of claim 3, when chemicals are added to the liquid that flows during the air venting process, the control means for branching the filtered water from the start of filtration to a predetermined time in the filtration process after the air process; By installing a valve and piping in the membrane filtration system and discarding the filtered water in which the chemicals are dissolved, it is possible to prevent chemicals from entering the filtered water produced by the membrane filtration system, and to supply safe filtered water. Can supply.

Further, in the invention according to any one of claims 1 to 3, in the backwashing step performed immediately before the membrane breakage detecting step, the flow direction of the liquid is switched and the pressure fluctuation is also given, so that it adheres to the hollow fiber membrane. Suspended substances can be removed more effectively.
Also, in the backwashing process, by using a liquid to which chemicals are added, the effect of releasing suspended substances adhering to the inside of the hollow fiber membrane is improved, and the membrane breakage detection capability of the membrane breakage detection process after the backwashing process To improve. This is because in the membrane breakage detection step, pressure is applied from the inside of the hollow fiber membrane, so that if the suspended material remains inside the hollow fiber membrane, the suspended material adheres to the hole in the hollow fiber membrane that has been damaged. This is because the broken hole is blocked, and it may be erroneously determined that the hollow fiber membrane is not broken.

  Below, the Example which applied the washing | cleaning method of a membrane filtration system is described concretely.

In FIG. 1, the schematic block diagram of the membrane filtration system concerning Example 1 of this invention is shown. First, the apparatus configuration will be described.
The raw water tank 8 is provided with piping connected to both ends of the pressure vessel 6. The raw water tank is provided with a valve 15 on the raw water tank side from the filtration pump 7 installed in the middle of the piping, and the filtration pump 7 and the pressure vessel 6 are connected to each other. Valves 16 and 17 are provided between both ends.

At least one membrane element 1 is provided in the pressure vessel 6. A plurality of membrane elements may be connected in series in order to increase the filtration throughput. In FIG. 2 , the arrow view of the AA cross section of a membrane element is shown. The membrane element describes only a few hollow fiber membranes for easy understanding of the figure, but actually, for example, it is a bundle of thousands of hollow fiber membranes. The membrane module is a membrane element housed in a pressure vessel 6. Both ends of the pressure vessel 6 through which raw water flows are in communication through the inside of the hollow fiber membrane. In the membrane element, the adhesive layer 4 holds both ends of the hollow fiber membrane and isolates raw water and filtered water. Filtrated water flows through the space 3 surrounded by the adhesive layers 4 at both ends of the hollow fiber membrane 2 and outside the hollow fiber membrane 3. The membrane module may be installed vertically or horizontally.

  The filtered water passes through the water collecting pipe 5 and is discharged from the membrane module. The pipes extending from the water collecting pipes 5 at both ends of the pressure vessel 6 are each provided with a valve 18 and a valve 19, and both pipes extended from the valves 18 and 19 are collected and connected to the filtrate water tank 10. A valve 22, a backwash pump 9, and a valve 21 are sequentially installed in the pipe between the aggregated portion and the filtrate water tank 10. The pipe connected to the upper space of the filtrate water tank 10 from the pipe between the valve 19 and the valve 22 is provided with a valve 20.

Between the pipe extending from the water collecting pipe 5 at the end of the pressure vessel 6 to the valve 19, a pipe that can be opened to the atmosphere and a valve 34 are provided. Both pipes extending from the upper ends of both ends of the pressure vessel 6 are provided with valves 23 and 24, and a valve 25 is provided on a pipe obtained by integrating both pipes.
A pipe 31 and a valve 31 which are oriented upward at the end of the pressure vessel 6 and can be opened to the atmosphere are provided. Further, a pipe and a valve 32 oriented downward are provided at the opposite end of the pressure vessel 6 connected to the valve 31.

A pipe communicating with the end of the pressure vessel 6 includes a compressor 13, a pressure reducing valve 37, and a valve 33.
In order to inject the chemical into the pipe between the filtration pump 7 and the pressure vessel 6, a pipe is connected from the chemical tank 12, and the valve 26, the chemical pump 11, and the valve 27 are sequentially provided in the pipe. Furthermore, it branches from the piping between the chemical pump 11 and the valve 27, and is connected to the piping between the backwash pump 9 and the valve 22 via the valve 35.

  A valve 28 is provided in the pipe that extends from both ends of the pressure vessel 6 and branches from the pipe that is aggregated and communicates with the upper space of the waste water treatment tank 14. The inside of the waste water treatment tank 14 is divided by a net, and substances that do not pass through the net can be discharged to the outside from a pipe provided with the valve 30. The pipes are connected so that the liquid that has passed through the net flows through the pipe provided with the valve 29 and can pass through the pipe between the filtration pump 7 and the valve 15.

Further, a valve 26 is provided by branching a pipe capable of discharging filtrate from the valve between the valve 18 and the valve 20 and between the valve 19 and the valve 20.
Next, the membrane cleaning method from the filtration procedure of the membrane filtration system will be described step by step.
First, filtered water is obtained by repeating a filtration step and a backwashing step in which pressure is applied from the outside to the inside of the hollow fiber membrane 2 in a state where the inside and outside of the hollow fiber membrane are in contact with the liquid to obtain filtered water. .
More specifically, during the filtration process, the valves 15, 16, 17, 18, 19, 20 are opened, the other valves are closed, the filtration pump 7 is operated, and the whole amount of raw water is filtered through the membrane module (see FIG. 3). . The end of the filtration step is determined in advance for a predetermined duration. For example, in the case of water treatment, the filtration step is performed for several minutes to several hours.
A backwashing process is performed after a filtration process. In the backwashing process, after the filtration pump 7 is stopped, the valves 18, 19, 21, 22, 23, 24, and 25 are opened, and the other valves are closed and the backwash pump 9 is operated (see FIG. 4). .

As another aspect of the backwashing step, it is more preferable to include at least the following steps (1) and (2) and alternately perform the following steps (1) and (2) (see FIGS. 5 and 6).
(1) A step of allowing liquid to flow from one end to the other end of the hollow fiber membrane.
(2) A step of allowing a liquid to flow from the other end to the one end on the inner side of the hollow fiber membrane.

  That is, the valves 21, 22, 18, 24, and 25 are opened, the other valves are closed, the backwash pump 9 is moved, and the filtered water flows from the secondary side (outside) to the primary side (inside) of the membrane element. And then back-opening the valves 21, 22, 19, 23, 25, closing the other valves, moving the back-wash pump 9 and passing the filtered water from the secondary side (outside) of the membrane element to the primary. Repeat the backwashing operation by letting it flow to the side (inside).

Such filtration step and backwashing step are repeated to obtain filtered water.
In the process of repeating the filtration step and the backwashing step, when the membrane differential pressure in the filtration step exceeds a predetermined value (hereinafter referred to as a chemical washing membrane differential pressure value), suspended substances adhering to the hollow fiber membrane are removed. It is desirable to carry out a chemical addition backwashing step in which the chemical to be removed is added to the liquid flowing outside the hollow fiber membrane (see FIGS. 4, 5 and 6). Or it is desirable to implement the said chemical | medical agent addition backwashing process for every predetermined period. More specifically, in FIGS. 4, 5, and 6, the valve 26 is opened, the chemical pump 11 is moved, and the chemical is added to the filtered water. The chemical used depends on the chemical resistance of the hollow fiber membrane. For example, a sodium hypochlorite solution (effective chlorine concentration of 120,000 mg / L or more), an inorganic acid (47% (w / v) sulfuric acid, etc.), It is desirable to use citric acid (100,000 mg / L), alkali (20% (w / v) sodium hydroxide, etc.) and the like. The said chemical | medical agent is diluted in a flow path, for example, a sodium hypochlorite solution (effective chlorine concentration 10-1000 mg / L), an inorganic acid (sulfuric acid etc., pH 2-4), a citric acid (10-10,000 mg). / L) and alkali (sodium hydroxide, etc., pH 8-12), it is desirable to add a desired amount after considering the amount of chemical injection in advance.

Next, a film breakage detection step is performed. In addition, as for the backwashing process before performing a film | membrane breaking detection process, it is more desirable to perform the said chemical | medical agent addition.
The procedure of the film break detection process will be described below. The valves 31 and 32 are opened, the other valves are closed, and the raw water side of the membrane module is drained. After draining, the valves 18, 19, 20, 34 are opened, the other valves are closed, and after the pressure on the raw water side of the membrane module (the portion communicating with the inside of the hollow fiber membrane) is stabilized, the valve 34 is close up. Next, the valve 33 is opened and the compressor 13 is operated to pressurize the raw water side of the membrane module to a predetermined pressure set by the pressure reducing valve 37 and then close the valve 33. The pressure on the raw water side of the membrane module is continuously measured, and if this pressure falls below a predetermined threshold pressure within a predetermined time, it is determined that the membrane is broken and an alarm is issued.

As the film breakage detection step, a diffusion flow rate test may be performed instead of the pressure holding test. Specifically, the valves 18, 19, 20, 33 are opened, the pressure reducing valve 37 is set to a predetermined pressure in advance, the compressor 13 is operated, and the pressure on the raw water side of the membrane module is kept constant. The amount of water flowing out from the valve 20 within a predetermined time is measured with a flow meter (not shown).
At the end of the membrane rupture detection step, the valves 31, 34, 18, 19, 20 are opened, the other valves are closed, and the pressure in the apparatus is returned to atmospheric pressure.

A first air venting step for allowing the liquid to flow inside the hollow fiber membrane following the membrane breakage detecting step, wherein the liquid is allowed to flow from one end to the other end in the longitudinal direction of the hollow fiber membrane; Then, an air venting step is performed in which a second air venting step of allowing a liquid to flow from the other end in the longitudinal direction of the hollow fiber membrane to the one end is alternately performed.
By carrying out as described above, the suspended substances adhering to the hollow fiber membrane 2 can be removed during the air venting step.

  More specifically, as the first air venting process, the valves 15, 16, 24, and 25 are opened, and the other valves are closed, and the filtration pump 7 is operated at a high flow rate to start from one end inside the hollow fiber membrane. The raw water is passed through the other end (see FIG. 12). After a certain period of time, as the second air venting process, the valves 15, 17, 23, 25 are opened, the other valves are closed, the filtration pump 7 is moved, and water passes from the other end to the one end in the future. (See FIG. 13). By this operation, it is possible to effectively remove the turbidity that adheres to the inside of the film and cannot be removed by the normal backwashing process. Before the first air venting step, the valves 15, 16, 17, 23, 24, 25 are opened, the other valves are closed, the filtration pump 7 is moved, and both ends of the membrane module are filled with water. Good (see FIG. 11).

In addition, it is more desirable to add a sterilizing chemical to the liquid flowing inside the hollow fiber membrane during the air venting process (see FIGS. 14 and 15). As a chemical having a sterilizing effect, a sodium hypochlorite solution is desirable.
Specifically, the filtration pump 7 is operated with the valves 16, 24, 28, 29 opened and other valves closed, or with the valves 17, 23, 28, 29 opened and other valves closed. It moves for a predetermined time, maintains the flow that circulates through the waste water treatment tank 14, opens the valves 26 and 27, drives the chemical pump 11, adds chemicals to the water circulating in the apparatus, and The chemical concentration is made uniform by the flow of After injecting the necessary amount of chemical to reach the chemical concentration, the chemical pump 11 is stopped and the valves 26 and 27 are closed. Even after the chemical injection is finished, it is desirable to move the filtration pump 7 intermittently or continuously. By doing this, even if the chemical reacts with the turbidity on the membrane surface and the chemical concentration is reduced, water containing the chemical is circulated, so a local decrease in the chemical concentration can be prevented. .

  When draining the chemicals, drain the raw water side and the filtered water side sequentially. As a drainage procedure on the raw water side, the valves 15, 16, 17, 23, 24, and 28 are opened, the others are closed, and the filtration pump 7 is operated to discharge the chemical-containing water on the raw water side (see FIG. 17). Subsequently, as a drainage procedure on the filtrate side, the valves 21, 22, 18, 19, 23, 24, and 28 are opened, and the backwash pump 9 is moved with the other valves closed, and the filtrate contains a chemical on the filtrate side. Water is discharged (see FIG. 17).

  Further, in the filtration step after the air venting step (including the case where a chemical having a bactericidal effect is added), it is more desirable to discard filtered water from the start of filtration to a predetermined time (see FIG. 18).

1 is a schematic configuration diagram of a membrane filtration system according to Example 1 of the present invention. The arrow line view of the AA cross section of the membrane element in FIG. The figure which shows the flow of the substance at the time of the filtration process in Example 1 of this invention. The figure which shows the flow of the substance at the time of the backwashing process in Example 1 of this invention. The figure which shows the flow of the substance at the time of the backwashing process in Example 1 of this invention. The figure which shows the flow of the substance at the time of the backwashing process in Example 1 of this invention. The figure which shows the flow of the substance at the time of discharging | emitting a chemical | medical agent in the backwashing process which added the chemical | medical agent in Example 1 of this invention. The figure which shows the flow of the substance at the time of the film | membrane fracture | rupture detection process in Example 1 of this invention. The figure which shows the flow of the substance at the time of the film | membrane fracture | rupture detection process in Example 1 of this invention. The figure which shows the flow of the substance at the time of the film | membrane fracture | rupture detection process in Example 1 of this invention. The figure which shows the flow of the substance at the time of the air venting process in Example 1 of this invention. The figure which shows the flow of the substance at the time of the air venting process in Example 1 of this invention. The figure which shows the flow of the substance at the time of the air venting process in Example 1 of this invention. The figure which shows the flow of the substance at the time of the air venting process which added the chemical | medical agent in Example 1 of this invention. The figure which shows the flow of the substance at the time of the air venting process which added the chemical | medical agent in Example 1 of this invention. The figure which shows the flow of the substance at the time of discharging | emitting the chemical-containing water by the side of raw | natural water in the air venting process which added the chemical | medical agent in Example 1 of this invention. The figure which shows the flow of the substance at the time of discharging | emitting the chemical-containing water by the side of filtered water in the air venting process which added the chemical | medical agent in Example 1 of this invention. The figure which shows the flow of the substance at the time of discarding filtered water in the filtration process initial stage in Example 1 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Membrane element 2 Hollow fiber membrane 3 Outside of hollow fiber membrane 4 Adhesive layer 5 Water collecting pipe 6 Pressure vessel (The state where the membrane element is stored in the pressure vessel is called a membrane module)
7 Filtration pump 8 Raw water tank 9 Backwash pump 10 Filtration water tank 11 Chemical pump 12 Chemical tank 13 Compressor 14 Wastewater treatment tank (Sludge removal / neutralization / reduction treatment tank)
15 to 36 Valve 37 Pressure reducing valve

Claims (5)

Method of cleaning an internal pressure type membrane filtration system comprising a membrane module having a hollow fiber membrane, raw water supply means for supplying raw water to the membrane module, and membrane breakage detecting means for detecting membrane breakage of the hollow fiber membrane In
A back washing process of the hollow fiber membrane;
A membrane breakage detecting step for detecting a breakage of the hollow fiber membrane after introducing gas into the inside of the hollow fiber membrane following the backwashing step,
An air venting step for allowing liquid to flow inside the hollow fiber membrane following the membrane breakage detection step,
The air vent step, through a first air vent step from the longitudinal one end to flow through the liquid to the other end, the liquid to the one end in the longitudinal direction of the other end of the pre-Symbol hollow fiber membrane of the hollow fiber membrane A method for cleaning a membrane filtration system, wherein the second air venting step is an air venting step that is alternately performed. Oite the air venting step, membrane filtration system cleaning method according to claim 1, characterized in that flow through the added chemicals liquid inside the hollow fiber membrane.   The method for cleaning a membrane filtration system according to claim 2, wherein in the filtration step after the air venting step, the filtered water from the start of filtration to a predetermined time is discarded. The backwashing step performed immediately before the film breakage detection step includes at least the following steps (1) and (2), and the following steps (1) and (2) are alternately performed. The method for cleaning a membrane filtration system according to any one of 1 to 3.
(1) A step of allowing liquid to flow from one end to the other end of the hollow fiber membrane.
(2) A step of allowing a liquid to flow from the other end to the one end on the inner side of the hollow fiber membrane.   5. The membrane filtration system cleaning method according to claim 4, wherein in the backwashing step, a liquid to which a chemical is added is allowed to flow outside the hollow fiber membrane.