JP2000210660A - Immersion type membrane filter, and production of clarified water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain bubbles from being generated on the permeation side in a filter in which a filter membrane is immersed in liquid to be treated to obtain clarified water by head pressure of the liquid to be treated by installing a clarified water storage part on the permeation side of a filter membrane and lower than an effective part of the filter membrane and installing a clarified water takeoff part in the lower part of the storage part. SOLUTION: A membrane 2 is stuck to both surfaces of a frame 4 through a clarified water flow passage material 8 to constitute a flat membrane element, and below the membrane 2, a clarified water storage part 3 is provided successively on the permeation side. A plurality of such membrane elements arranged in parallel are loaded to an element vessel 10, and a clarified water intake line 5 and a standby opening line 6 are provided successively to constitute a membrane module. The membrane module is immersed in liquid in a liquid to be treated tank 11, and by operating an intake pump 7 connected to the intake line 5, clarified water is obtained from the liquid to be treated by pressure difference encountered inside and outside the membranes 2, and the obtained clarified water is made to flow down to the storage part 3, and then discharged to outside the system by a intake pump 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a membrane filtration apparatus and a method for producing clarified water, and more particularly, to immersing a filtration membrane in water to be treated to drive the head pressure difference of the liquid to be treated. The present invention relates to a submerged membrane filtration device for taking out clear water as a force and a method for producing clear water.

[0002]

2. Description of the Related Art Conventionally, systems for water purification and wastewater treatment have been constructed and processed by using sand filtration, coagulation sedimentation, and chlorine addition as main processes. However, the sand filtration method and the coagulation sedimentation method require a large equipment area, and depending on the raw water conditions, problems such as insufficient separation cannot be achieved unless strict operation management is performed, As a technique capable of solving the disadvantage, application of a membrane separation method has been promoted. The membrane separation method can perform filtration at a higher speed than the conventional sand filtration method, has a small equipment volume, and can be combined with other processes such as the coagulation sedimentation method. There is an advantage that the sterilization treatment by such a method can be omitted or reduced.

When the membrane separation method is applied to these water purification and wastewater treatments, the water to be treated, which has been mainly used in industrial water production and the like, is pressurized by a pump or the like to perform the membrane separation treatment. The "pressurized type" has the advantage of being able to set the filtration speed widely because it can be processed at a high pressure, but has a problem in terms of cost and operation management, such as the need for pressure resistance of the apparatus. Therefore, a "immersion type" in which a membrane separation module including a membrane element and a membrane element case is immersed in water to be treated is widely used.

The immersion type membrane separation membrane module accumulates dirt substances in the water to be treated on the surface of the membrane on the side of the water to be treated. In general, a method of peeling is used. When the water to be treated is activated sludge water, aeration is performed in the water tank to be treated. Therefore, the gas-liquid multiphase flow obtained by this aeration is introduced to the membrane surface to efficiently reduce the accumulation of dirt on the membrane surface. be able to. Therefore, in the immersion type membrane separation module for wastewater treatment, Japanese Patent Application Laid-Open No. S60-150885,
As seen in, for example, -70958, application in combination with activated sludge treatment is active. Further, a method of applying a flow rate to the film surface by means such as rotating the film or generating a flow on the film surface with a pump or a stirrer can be employed. In addition, as a membrane element, a wide variety of fabric elements such as a cloth-like flat membrane type, a tubular membrane type, and a straw-like hollow fiber membrane type have been developed.

[0005] There are basically three types of methods for imparting a transmembrane pressure difference for extracting clarified water (permeated water), that is, a separation driving force in an immersion type membrane separation module. One is a method of depressurizing the permeate side of the membrane with a suction pump as exemplified in Japanese Patent Publication No. 4-70958. The other is to make the permeate side a negative pressure state by lowering the pipe on the permeate side of the membrane as compared to the membrane module as exemplified in Japanese Patent Publication No. Hei.
The same operation as that of the suction pump is obtained. As a third method, as exemplified in Japanese Patent Application Laid-Open No. 7-299490, a water level difference (water head pressure difference) is generated by immersing a membrane module in water to be treated deep. The water to be treated is placed in a pressurized state.
These methods are basically not exclusive,
There is basically no problem with using them together.

[0006]

Here, the first method has an advantage that a required processing amount can be stably obtained by adjusting and controlling the suction pressure. Requires a running cost. The second and third methods have an economical advantage in that they do not require pump power, but have the characteristic that the pressure is basically constant and it is difficult to obtain a constant throughput. are doing.

Further, the present inventors have obtained the following findings in the course of developing and studying a submerged membrane filtration module. In the first and second methods, that is, when the permeate side is suctioned to reduce the pressure, the air dissolved in the liquid to be treated cannot be completely dissolved as compared with the case where the pressure is not reduced. It was found that bubbles were generated on the permeation side. These bubbles are likely to stay on the permeation side, and the flow of the clarified water (permeated water) is hindered in the portion where the bubbles are stagnated, so that the effective membrane area is reduced and the flow resistance of the clarified water (permeated water) is increased, This will reduce the filtration performance.

[0008] In this case, in the first method, in order to obtain a constant flow rate, the output of the suction pump is increased, and an attempt is made to secure a constant flow rate. As a result, the permeation flux of the membrane locally increases, and the membrane becomes fouled. Also, if the suction pressure is too high, dirt is drawn into the pores of the membrane, and the recoverability by physical cleaning and chemical cleaning also decreases. Further, as a result of the basic studies performed by the present inventors, the permeation flux and the accumulation of dirt on the membrane surface show a series of changes. It has been found that the accumulation of dirt rapidly progresses, which is very undesirable. In addition, when we actually examined the operation, the generated bubbles were
It is easily drawn into the line of the suction pump, and the load on the pump is likely to fluctuate in the process. As a result, pulsation occurs, which causes a situation where suction at a constant flow rate becomes difficult.

Further, in the second method, since suction is performed by a siphon, the generation of air bubbles is fatal, and the siphon becomes ineffective during long-term operation, and continuous operation is difficult.

On the other hand, in the third method, the generation and accumulation of bubbles can be suppressed because the transmission side is not set to a negative pressure.
Since the pressure difference applied to the membrane cannot be controlled, so-called constant pressure operation is performed. In the case of constant pressure operation, when the permeation performance is high in a new state of the membrane, the permeation flux becomes high. This accelerates the accumulation of dirt on the membrane surface, as described above, and has been a factor of shortening the continuous operation period.

An object of the present invention is to provide an immersion-type membrane filtration device capable of performing continuous operation stably for a long period of time while eliminating obstacles caused by generation of bubbles on the permeation side and suppressing a decrease in permeation performance of the membrane, and a method for producing clear water. It is to be.

[0012]

SUMMARY OF THE INVENTION The present invention relates to an immersion type membrane filtration apparatus of a type in which a filtration membrane is immersed in a liquid to be treated and clear water is obtained by the head pressure of the liquid to be treated. Means for having a pipe open to the atmosphere on the permeation side, having a clarified water reservoir below the effective portion of the filtration membrane, and taking out the clarified water out of the system downstream of the clarified water reservoir. Immersion-type membrane filtration device characterized by comprising: ".

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention basically uses the third method mentioned above as a method for obtaining a driving force for separation, that is, a pressure based on a head pressure. Thus, it is not necessary to reduce the pressure on the permeation side, and it is possible to perform immersion type membrane filtration in which generation of bubbles is suppressed.

Here, a side sectional circuit diagram showing an example of an embodiment of the immersion type filtration device of the present invention is shown in FIG. 1, an external appearance of a membrane module is shown in FIG. 2, and an external appearance of a membrane element is shown in FIG. The membrane element (FIG. 3) used here is a flat membrane element in which the clarified water channel material 8 is inserted on both sides of the frame 4 and the membrane 2 is adhered with an adhesive. It is connected to the structure. Reference numerals 5 and 6 in the figure denote a pipe for clear water intake and a pipe for opening to the atmosphere. In the membrane module shown in FIG. 2, a plurality of these elements are arranged in parallel, loaded into the element container 10, and the clarified water intake pipe 5 and the atmosphere opening pipe 6 are connected.

FIG. 4 shows that this membrane module is immersed in a liquid tank 11 to be treated, and a water intake pump 7 is connected to a clarified water intake pipe 5.
FIG. As shown in FIG. 4, a water head pressure is generated by the liquid to be treated on the liquid to be treated side of the membrane, and the pressure on the permeate side is set to normal pressure by the atmosphere opening pipe 6.
A pressure difference is created across the membrane. As a result, clarified water can be obtained from the liquid to be treated, and the obtained clarified water flows down to the clarified water storage unit 3 and is stored. The stored clear water is taken out of the system by a clear water intake pump 7.

The means for removing clarified water out of the system in the present invention is not particularly limited, but a water suction pump is generally used, and a centrifugal pump, a reciprocating pump, a rotary pump, There is no particular limitation such as an air lift pump. However, in the practice of the present invention, it is preferable that the filtration can be performed without a certain amount of pulsation, and furthermore, the clarified water at a low position is often pumped. In this case, a self-contained rotary pump is preferable. When the liquid to be treated is a biological treatment tank and needs aeration, the use of an air lift pump using an aeration line can eliminate the power for water intake, which is a desirable method because the apparatus can be simplified.

The method of taking the clarified water is not particularly limited, but it is preferable to take the water at a constant flow rate from the gist of the present invention. However, if the water intake is greater than the membrane permeation immediately after the start of operation, the pump will not be able to stably absorb the clarified water because the supply to the clarified water storage unit will be insufficient. Therefore, at least a flow rate smaller than the membrane permeated water amount obtained immediately after the start of operation must be set as the water flow rate. At this time, in a situation where the water intake amount is smaller than the membrane permeate water amount, the clarified water amount in the clarified water storage unit increases with time. As a result, the clarified water accumulates toward the clarified water intake pipe 5 and the atmosphere opening pipe 6 as shown in FIG. 4, so that the head pressure difference, which is the driving force for membrane filtration, is reduced. The amount of permeated water decreases. Eventually,
An equilibrium state is reached at a height where the water intake and membrane permeate are the same. In this state, the membrane filtration is continued. However, as the filtration proceeds, the membrane is clogged with a contaminant in the liquid to be treated and the like, and the membrane permeation performance decreases, and the amount of water permeated through the membrane falls below the water intake. As a result, contrary to the above, the water level of the stored clarified water decreases and the head pressure difference increases, which increases the amount of permeated water and stabilizes the water level when the amount of water is balanced. I do. In this way, the amount of clarified water that is constantly withdrawn is replenished to the clarified water storage unit by membrane filtration, so that any type of water intake method is possible depending on the method of selecting and setting the water intake means. Quantitative filtration that was not possible becomes possible. As a result, accumulation of dirt on the membrane surface can be suppressed, and stable operation can be performed for a long period of time.

Here, regarding the setting of the water intake amount, since the initial value of the membrane permeated water amount in the water to be treated is the same as the value measured with pure water, before the membrane module is immersed in the liquid to be treated, By measuring the water permeability coefficient K, it is possible to obtain an appropriate amount Q (m3 / d) of clear water.
Generally, if the permeability of the membrane is reduced by continuous operation,
The performance is restored by performing so-called chemical cleaning, for example, by immersing the membrane element in a chemical.

The timing of chemical cleaning is generally performed when the transmission performance is reduced to about 1/10 to 1/2 times the initial transmission performance. In the case of the immersion type membrane filtration device in the present invention, when the membrane is new and has high permeation performance, the water level of the clarified water is in a high state, and when the membrane performance is reduced, the water level of the clarified water is reduced, and finally, The permeation performance at this point is 1/10 to 1/2 times the initial permeation performance because the life of the continuous operation is the time until the clarified water storage unit becomes empty and the set amount of water cannot be taken. Is more efficient.

From this, it has been found that it is preferable to set the water intake Q within a range satisfying the following equation.

Q = a × K × L × S (1/10 ≦ a ≦ 1/2) where L: lowest water depth (m) of the effective membrane portion of the membrane element K: effective membrane element before use Pure water permeation coefficient (m3 / d ・) when the membrane part is immersed in pure water at the same temperature as the liquid to be treated
1 mAq) S: film area (m) In order to obtain K at the same temperature as the liquid to be treated, correction may be made using the following equation.

K = (K at the temperature T ° C.) × (viscosity of the water at the temperature T ° C.) / (Viscosity of the water at the temperature of the liquid to be treated) It should be noted that the amount of water withdrawal set when the clarified water storage unit is empty is obtained. When it is no longer possible, the continuous operation is terminated and the membrane is washed with a chemical solution or the membrane is replaced.However, as a means for automatically recognizing this time, a water level detecting means of the clear water storage unit is provided. , By detecting that the water level has fallen below a certain value, or by providing a flow rate sensor in the clarified water intake line to detect a situation where the intake amount has fallen below the set lower limit flow rate.
It is possible to execute physical cleaning or chemical cleaning for generating an alarm or restoring the film performance.

The method of the membrane filtration operation in the present invention is not particularly limited except that the filtration operation is performed using the head pressure difference as a driving force, but the simplest operation method is that the operation is performed without any particular operation. , Filtration is performed according to the head pressure difference. It is also possible to periodically reduce the amount of filtration or perform an intermittent operation in which the filtration is stopped. In addition, when performing such an operation, it is possible to implement by temporarily reducing the intake of the clear water or stopping the intake. Further, as shown in FIG. 5, after closing a valve 6 ′ provided in the atmosphere opening pipe 6, the clarified water is pressurized and back-flowed from the water intake line to reverse the flow from the permeation side of the membrane to the liquid to be treated. Pressure washing can also be performed. Here, the means for supplying the clarified water to the permeate side of the filtration membrane is not particularly limited, but when a pump is used as the water intake means, a pump capable of reverse flow is used. This is preferable because it is possible to perform both of the cleaning step and the back pressure cleaning means.

As the physical cleaning in the present invention, there are a method of removing dirt by shearing force by applying a flow rate to the liquid side of the film to be treated, and the above-mentioned back pressure cleaning. Examples of the chemical cleaning include a method in which a chemical liquid is brought into contact with the liquid to be treated of the membrane, and a method in which the chemical liquid is injected into the permeation side. The chemical used is not particularly limited, such as acid, alkali, and sodium hypochlorite.

The membrane used in the present invention is not particularly limited, and examples of the form include a flat membrane and a hollow fiber membrane. In particular, in the case of a flat membrane, the effect of removing dirt due to shearing force when a flow velocity is applied to the membrane surface is high, and is suitable for the present invention. Further, in the case of the hollow fiber membrane, the membrane itself easily swings in the liquid, and thus has a feature that dirt is easily removed.

Examples of the membrane structure include a homogeneous membrane, a porous membrane, and a composite membrane, but are not particularly limited. Specific examples of these membranes include a polyacrylonitrile porous membrane, a polyimide porous membrane, a polyether sulfone porous membrane, a polyphenylene sulfide sulfone porous membrane, a polytetrafluoroethylene porous membrane, a polypropylene porous membrane, and a polyethylene porous membrane. A porous membrane such as a membrane, or a composite membrane or a crosslinked silicone tube obtained by compounding a rubber-like polymer such as crosslinked silicone, polybutadiene, polyacrylonitrile butadiene, ethylene propylene rubber, or neoprene rubber as a functional layer on these porous membranes. And the like.

The pore size of the membrane is not particularly limited, but the smaller the pore size, the more difficult it is to remove bubbles, which is the object of the present invention. Therefore, the smaller the pore size, the more effective the application of the present invention. Is high. Specifically, it is particularly effective to apply the present invention to those having an equivalent pore diameter of 0.1 μm or less. Note that the equivalent pore diameter d here is:
Water is permeated in a state where the membrane is not contaminated, and d = (32 × η × L × F / ΔP) 0.5 η: viscosity of water L: film thickness F: permeation flux ΔP: transmembrane pressure is calculated. It is the value obtained by doing.

The liquid to be treated to which the present invention can be applied is not particularly limited, but care should be taken because the film may be damaged and deteriorated depending on the properties of the water to be treated. The liquid to be treated suitable for the present invention includes river water, lake and marsh water, water after coagulation treatment, biologically treated water, various wastewaters, and the like. Particularly suitable.

[0029]

The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited by this.

Example 1 A composite flat membrane (pore diameter 0.01 μm, thickness 55 μm, initial pure water permeability 1.2 m 3 / m 2 · day · 1 mAq) in which a polyester non-woven fabric was coated with a polysulfone membrane was attached to both sides of a frame. 3 attached flat membrane elements (effective membrane portion: 700 mm in length, 100 mm in width, 0.14 m in effective membrane area) as shown in FIG. 3 with inner dimensions (110 mm in width × 36 mm in depth × height) as exemplified in FIG. (710 mm), and a membrane module in which a clarified water intake pipe and an atmosphere open pipe were connected to each other was produced. An immersion type membrane filtration device having a circuit shown in FIG. 1 was prepared in which a water intake pump was attached to the clarified water intake pipe of this membrane module.
This device is installed in the upper part of the aeration range in a biological treatment tank (activated sludge concentration MLSS: 10,000 ppm) of a wastewater treatment facility.
Immerse so that the distance from the lower end of the effective part of the filtration membrane to the water surface is 2 m, and set the water intake pump to a set flow rate of 0.3 m 3 / d
(A = 0.3), and water was taken continuously.

As a result, continuous filtration can be performed for 28 days before the set flow rate can be withdrawn, and the amount of clarified water obtained is 8.
It was 4 m3. After the completion of the filtration operation, the central membrane element of the three membranes was pulled up, and the appearance was observed. As a result, the entire membrane was discolored to black-brown. The pure water permeation performance was measured to be 0.35 m 3 / m 2 · day · 1 mAq.

Comparative Example 1 The same apparatus was operated in the same manner as in the example except that the pipe for opening the atmosphere to the membrane element was sealed.
Bubbles accumulated in the clarified water intake pipe, and occasionally the intake pump pulsated. Also, the amount of clarified water obtained after 28 days is
It was 8.4 m 3, which was the same as in Example 1. However, after the filtration operation was completed on the 28th, the membrane element was pulled out of three sheets and the appearance was observed. On the other hand, the lower part was severely discolored to dark brown.
When the pure water permeation performance was measured, it was found to be 0.26 m3 /
m 2 · day · 1 mAq.

[0033]

According to the present invention, there is provided an immersion type membrane filtration apparatus in which a filtration membrane is immersed in a liquid to be treated and clear water is obtained by a head pressure of the liquid to be treated, wherein the permeation side of the filtration membrane is opened to the atmosphere. A submerged water storage unit provided below the effective part of the filtration membrane, and a means for removing clarified water from the clarified water storage unit to the outside of the system. Accordingly, it has become possible to provide an immersion type membrane filtration device capable of performing continuous operation stably for a long period of time while suppressing a decrease in the permeability of the membrane.

[Brief description of the drawings]

FIG. 1 is a side sectional circuit diagram of an example of an immersion type membrane filtration device according to the present invention.

FIG. 2 is an external view of an example of a membrane module according to the present invention.

FIG. 3 is an external view of a flat membrane element according to the present invention.

FIG. 4 is a side sectional view showing an operation state of an example of an immersion type membrane filtration device according to the present invention.

FIG. 5 is a side sectional view showing an example of a submerged membrane filtration device according to the present invention in a back pressure washing state.

[Explanation of symbols]

 1: Membrane element 2: Membrane 3: Refined water storage part 4: Frame 5: Refined water intake pipe 6: Atmospheric release pipe 7: Intake pump 8: Permeate side flow path material 9: Membrane adhesion part 10: Membrane element container 11 ： Treatment tank 12 ： Air diffuser

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D006 GA02 HA42 HA93 JA18A JA20A JA53A KA13 KA44 KC03 KC07 KC16 KD11 KD17 KD24 KE03R KE05P KE06P KE12P KE24P MA01 MA03 MA06 MA22 MA31 MB02 MC22 MC23 MC30 MC63 MC68 MC62 MC62 MC68 PA02 PB04 PB08 PC64

Claims (7)

[Claims] An immersion type membrane filtration apparatus in which a filtration membrane is immersed in a liquid to be treated to obtain clarified water by a head pressure of the liquid to be treated, wherein the filtration membrane is open to the atmosphere on the permeation side of the filtration membrane. It has a pipe, and has a clarified water reservoir below the effective portion of the filtration membrane, and is provided with means for taking out clarified water out of the system downstream of the clarified water reservoir. Immersion type membrane filtration device. 2. The immersion type membrane filtration device according to claim 1, wherein the means for taking out the clarified water out of the system is a constant flow pump. 3. The immersion type membrane filtration device according to claim 2, wherein said constant flow rate pump is a self-supply type. 4. An apparatus according to claim 1, which is immersed in a liquid to be treated.
A method for producing clarified water, wherein clarified water that has passed through a filtration membrane due to a head pressure is taken out of the system from a clarified water storage unit. 5. The method according to claim 4, wherein when the water level of the clarified water storage section falls below a set value, at least one of alarm generation, physical cleaning, and chemical cleaning is performed. Method for producing clear water. 6. When the flow rate of the clarified water in the means for taking out the clarified water to the outside of the system falls below a set value lower limit value,
The method for producing clear water according to claim 4, wherein at least one of an alarm generation, a physical cleaning, and a chemical cleaning is performed. 7. The method for producing clarified water according to claim 4, wherein the amount of clarified water withdrawn Q (m3 / d) satisfies the following equation. Q = a × K × L × S (1/10 ≦ a ≦ 1/2) L: Lowest water depth (m) of the effective membrane portion of the membrane element K: Liquid to be treated on the effective membrane portion of the membrane element before use Pure water permeability coefficient (m3 / m2) when immersed in pure water at the same temperature as
• d · 1 mAq) S: membrane area (m)