JPH11128699A - Filtration by separating membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a filtration treatment stable for a long period of time with saved driving power by repeating filtration and stoppage, disposing a head difference between the primary side of a separating membrane and the liquid level of backward washing water and supplying a washing liquid to backward wash the separating membrane during stoppage. SOLUTION: The outlet of piping 5 on the secondary side of the separating membrane is opened to the atmosphere on the outside of a treating vessel 1 in the state of maintaining liquid-tightness from the primary side of the separating membrane of a membrane separation mechanism section 3 and the position of the outlet of this piping 5 is set in a position lower than the water level of the liquid 2 to be treated in the treating vessel 1, more preferably in a position lower than the primary side of the separating membrane, by which the head difference is disposed between the primary side and the secondary side. The piping 5 is branched on the outside of the treating vessel 1, and the primary side of the separating membrane of the membrane separation mechanism section 3 is communicated with a backward washing tank 8 opened to the atmosphere. In addition, the liquid level of the washing liquid 9 in the backward washing tank 8 is set higher than the primary side of the separating membrane, more preferably in a position higher than the level of the liquid 2 to be treated in the treating vessel 1, by which the head difference is disposed between the primary side of the separating membrane and the liquid level of the washing liquid 9 in the backward washing tank 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a filtration method using a separation membrane.

[0002]

2. Description of the Related Art In a filtration process of purified water or wastewater,
In recent years, a membrane filtration technique of performing solid-liquid separation using a separation membrane has been used from the viewpoints of treated water quality and volume efficiency. In the membrane filtration device used, usually, the water to be treated is supplied to the membrane module through power of a pump or the like and filtration is performed.
There is a problem that running costs for operating the filter continuously are high.

Further, as disclosed in Japanese Utility Model Laid-Open No. 4-134492, a technique of performing filtration by a head difference without using mechanical power is known, but in this technique, continuous filtration is performed. On the other hand, clogging of the membrane has been a problem because no measures have been taken against clogging of the membrane.

[0004]

DISCLOSURE OF THE INVENTION The present invention has been studied in order to reduce the power required for the operation of the membrane filtration process and to obtain a filtration method capable of stably performing a long-term filtration process. In view of the foregoing, an object of the present invention is to provide a filtration method using a separation membrane capable of performing a long-term stable filtration treatment with low power consumption.

[0005]

SUMMARY OF THE INVENTION The present invention provides a filtration method using a head difference as a means for giving a pressure difference between the primary side and the secondary side of a separation membrane. A method of providing a head difference between the primary side of the separation membrane and the liquid level of the backwashing liquid to supply a washing liquid to backwash the separation membrane.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration diagram of an embodiment of the filtration method of the present invention. In FIG. 1, a processing tank 1 is provided with a membrane separation mechanism 3 and a diffuser 4 below the membrane separation mechanism, and a liquid 2 to be processed injected into the processing tank 1 passes through the membrane separation mechanism 3 to be separated into a solid and a liquid. Then, the processing liquid is discharged out of the processing tank 1 through the pipe 5, and air is bubbled from the air diffuser 4.

In the filtration method of the present invention, it is essential to provide a head difference between the primary side, which is the inlet side of the liquid to be treated, and the secondary side, which is the outlet side of the processing liquid, of the separation membrane of the membrane separation mechanism. . FIG.
In the above, the outlet of the pipe 5 on the secondary side of the separation membrane is opened to the atmosphere outside the treatment tank 1 while maintaining the liquid tightness with the primary side of the separation membrane of the membrane separation mechanism 3, and The outlet is located at a position lower than the water level of the liquid 2 to be treated in the treatment tank 1, preferably at a position lower than the primary side of the separation membrane, and a head difference is provided between the primary side and the secondary side. The pipe 5 shown in FIG. 1 is provided with a valve 6.

In FIG. 1, the pipe 5 is branched outside the processing tank 1 so that the primary side of the separation membrane of the membrane separation mechanism 3 is open to the atmosphere while keeping the primary side liquid-tight. The liquid level of the cleaning liquid 9 in the cleaning liquid tank 8 communicating with the cleaning liquid tank 8 and containing the cleaning liquid for backwashing is higher than the primary side of the separation membrane, preferably the water level of the liquid 2 to be processed in the processing tank 1. As a higher position, a water head difference is provided between the primary side of the separation membrane and the liquid level of the cleaning liquid 9 in the cleaning liquid tank 8.

The supply of the cleaning liquid 9 from the cleaning liquid tank 8 at the time of backwashing is performed by closing the valve 6 of the pipe 5 and opening the valve 7 provided on the supply pipe from the cleaning liquid tank 8, by the pressure generated by the head difference. In the backwashing of the separation membrane, the washing liquid 9 supplied from the washing liquid tank 8 and supplied through the pipe 5 is passed from the secondary side of the separation membrane of the membrane separation mechanism 3 to the primary side during filtration. This is done by:

[0010] The separation membrane used in the filtration method of the present invention may be any of a flat membrane, a hollow fiber membrane, a tubular membrane, a bag-like membrane and the like. Is preferably used. Further, the material of the separation membrane includes cellulose, polyolefin, polysulfone, polyvinylidene fluoride, polytetrafluoroethylene, ceramics, and the like, and the pore diameter thereof is particularly within a range used as a solid-liquid separation membrane. There is no limitation. The separation membrane is
It is used as a membrane separation mechanism in the form of a membrane module or the like as in an ordinary membrane filtration device, but the structure and form of the membrane separation mechanism are not particularly limited.

In the filtration method of the present invention, the filtration and the stop are repeated, and during each time the filtration is stopped, the water level of the water to be treated, preferably between the primary side of the separation membrane and the liquid level of the washing liquid, is changed. This is to backwash the separation membrane by supplying a washing liquid with a head difference.The larger the ratio of the stop time to the filtration time, the smaller the throughput per hour.The smaller the ratio of the stop time to the filtration time, the smaller the separation membrane. Since the clogging progresses, when the filtration time is A and the stop time is B, it is preferable that 2/3> B / A> 1/180, and more preferably 1/2> B / A> 1/120.

In backwashing, the larger the ratio of the backwashing time to the filtration time, the smaller the throughput per hour. Also, a large amount of backwashing liquid is required, and the smaller the ratio of the backwashing time to the filtration time, the smaller the separation membrane. Since it becomes difficult to remove the clogging substance attached to the filter and shorten the life of the separation membrane, when the filtration time is A and the backwashing time is C, 1/3> B / C> 1
/ 500, more preferably 1/2
> B / C> 1/360.

If the membrane filtration flux of the separation membrane at the time of back washing is too large than the membrane filtration flux at the time of filtration, a higher pressure resistance is required for the separation membrane, and the membrane filtration flow of the separation membrane at the time of back washing is required. since the flux is too small than membrane filtration flux upon filtering the effect of backwashing is reduced, when the membrane filtration flux upon filtering and F _L, the membrane filtration flux upon backwashing and F _R, 5 > F _R / F _L > 1/2
0, more preferably 3> F _R / F _L >
1/10. The membrane filtration flux is usually m ³ / m ² / d
Expressed in units of

The washing solution used for the back washing is not particularly limited as long as it does not contain turbidity, bacteria and the like.
Either a filtrate, water such as tap water, or a drug solution may be used, but when the degree of clogging is large, a drug solution is preferably used. As a chemical, it depends on the clogging substance,
Inorganic acids such as hydrochloric acid and sulfuric acid; organic acids such as oxalic acid and citric acid; alkalis; sodium hypochlorite solution; oxidizing agents such as sodium peroxocarbonate; and surfactants.

[0015]

The present invention will be described below in more detail with reference to examples.

(Example 1) A membrane module (manufactured by Mitsubishi Rayon Co., Stellapore Co., Ltd.) in which river water is used as a liquid to be treated and a separation membrane is a hollow fiber membrane is used as a membrane separation mechanism by a method having a schematic configuration shown in FIG. L), the initial head difference between the water level of the liquid to be treated in the treatment tank and the treated water outlet of the membrane module is 40 c
m, and filtration was performed for one year, with the membrane filtration flux during filtration set to 0.3 m ³ / m ² / d. The cycle of the operation / stop of the filtration is 118 minutes for the filtration and 2 minutes for the stop. During the stop time, the aeration intensity is 30 Nm ³ / m ² / hr per projected area of the separation membrane by a diffuser from below the separation membrane of the membrane module. Air bubbled.

Further, for 30 seconds during the stop time in each cycle, an aqueous sodium hypochlorite solution having a concentration of 1 mg / liter was used as a washing solution, and the membrane filtration flux was set to 0.1 m ³ / m ² / m ² .
Backwashing was performed as d. The initial head difference between the water level of the liquid to be treated in the treatment tank and the liquid level of the cleaning liquid in the cleaning liquid tank is 20c.
m. At this time, B / A (A: filtration time, B: stop time) = 2 minutes / 118 minutes = 0.017, C / A (A: filtration time, C: backwashing time) = 0.5 minutes / 118 Min = 0.0
05, F _R / F _L (F _L : membrane filtration flux at the time of filtration, F _R : membrane filtration flux at the time of back washing) = 0.1 m ³ / m ² /d/0.3 m ³ /
m was ^{2 /d=0.333.} One year after filtration, the head difference required to maintain the initial membrane filtration flux in filtration is 46
cm, which was almost the same as the initial value, and the head difference required for maintaining the initial membrane filtration flux in the backwash was 25 cm, and the separation membrane was not clogged even after one year of filtration.

(Comparative Example 1) In Example 1, the filtration was continuously performed for one year without stopping the filtration during the filtration. The head difference required to maintain the initial membrane filtration flux in filtration one year after filtration is 200 cm or more,
After backwashing one year later, the head difference required to maintain the initial membrane filtration flux in the backwash was 200 cm or more, and the separation membrane was significantly clogged.

(Comparative Example 2) In Example 1, the cycle of filtration operation / stop was 118 minutes for filtration and 2 minutes for stop, and the backwash time during the stop time in each cycle was changed to 10 seconds to perform backwash. went. The initial head difference between the level of the liquid to be treated in the treatment tank and the level of the cleaning liquid in the cleaning liquid tank was set to 20 cm. At this time, B / A = 2 minutes / 118 minutes = 0.017, C / A
= 0.167 min / 118 min = 0.001, F _R / F _L =
0.1 m ³ / m ² /d/0.3 m ³ / m ² /d=0.333
Met. One year after filtration, the head difference required to maintain the initial membrane filtration flux in filtration is 75 cm, and the head difference required to maintain the initial membrane filtration flux in backwash is 38 c.
m, and one year after filtration, the separation membrane was clogged.

(Comparative Example 3) In Example 1, the cycle for starting and stopping the filtration was changed to 199 minutes for filtration, 1 minute to stop, and the backwashing time during the stop time in each cycle was changed to 10 seconds. Backwashing was performed by changing the membrane filtration flux of the aqueous solution of sodium hypochlorite having a concentration of 1 liter to 0.01 m ³ / m ² / d. The initial head difference between the liquid level of the liquid to be treated in the treatment tank and the liquid level of the cleaning liquid in the cleaning liquid tank was set to 5 cm. At this time, B / A = 1 minute / 199 minutes = 0.005, C / A
= 0.167 min / 199 min = 0.0008, F _R / F _L =
0.01 m ³ / m ² /d/0.3 m ³ / m ² /d=0.03
It was 3. One year after filtration, the head difference required to maintain the initial membrane filtration flux in the filtration is 178 cm, and the head difference required to maintain the initial membrane filtration flux in the backwash is 2
It became 3 cm, and one year after the filtration, the separation membrane was clogged.

[0021]

The filtration method of the present invention saves power by performing filtration and backwashing using a pressure generated due to a head difference, and prolongs the backwash by performing backwash during a predetermined stop time in the filtration operation. This enables a stable filtration treatment with a separation membrane.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of a filtration method of the present invention.

[Description of Signs] 1 Processing tank 2 Liquid to be processed 3 Membrane separation mechanism 4 Aeration tube 5 Piping 6 Valve 7 Valve 8 Cleaning liquid tank 9 Cleaning liquid

Claims (6)

[Claims] 1. A filtration method using a head difference as a means for giving a pressure difference between a primary side and a secondary side of a separation membrane,
Separation membrane characterized by repeating filtration and stop, providing a head difference between the primary side of the separation membrane and the liquid level of the backwash liquid during the stop time, supplying the wash liquid and backwashing the separation membrane. Filtration method. 2. The filtration method using a separation membrane according to claim 1, wherein one of a filtrate, water, and a chemical solution is used as the washing liquid. 3. The method according to claim 1, wherein when the filtration time is A and the stop time is B, 2/3> B / A> 1/180. 4. The method according to claim 2, wherein when the filtration time is A and the backwash time is C, 1/3> C / A> 1/500. 5. When the membrane filtration flux upon filtering F _L, the membrane filtration flux upon backwashing was set to _{F R, 5> F R /} F L> 1/20 a is claim 2, claim A filtration method using the separation membrane according to claim 3 or 4. 6. The filtration method using a separation membrane according to claim 2, wherein a hollow fiber membrane is used as the separation membrane.