JPH11128701A - Immersion-type membrane separation apparatus and method for cleaning immersion-type membrane separation apparatus thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently wash an immersion type membrane separation apparatus with a chemical agent. SOLUTION: This apparatus is for filtering a raw liquid by decreasing the pressure in the filtered liquid side of a membrane element 1 by a suction pump 3 while the membrane element 1 whose inside is set to be the filtered liquid side being immersed in the raw liquid and the membrane surface being scrubbed by air scrubbing by an aeration means 23. In this case, a chemical agent inlet 161 and a chemical agent outlet 162 are formed in the membrane element 1 and a chemical agent tank 53 and a circulation pump 54 are connected between the inlet and the outlet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a submerged membrane separation device,
In particular, the present invention relates to an immersion type membrane separation apparatus used for purification treatment or solid-liquid separation of human waste, sewage, domestic wastewater, and industrial wastewater (hereinafter referred to as sewage), and a cleaning method thereof.

[0002]

2. Description of the Related Art Recently, a gravity separation activated sludge treatment method, which is a traditional treatment method for wastewater (microbial decomposition treatment is performed in an aeration tank, the treated wastewater is led to a sedimentation separation chamber, and activated sludge is separated by gravity separation. The membrane separation activated sludge treatment method has attracted attention as an alternative to the method of returning a part of the separated sludge to the aeration tank). In this treatment method, solid-liquid separation is performed by membrane filtration, the filtrate is taken out, and excess sludge is drawn directly from the aeration tank. The MLSS (mixed liquid suspended solids) in the aeration tank is compared with the gravity separation method. Can be significantly higher,
The aeration tank can be considerably reduced as compared with the gravity separation method, and the sedimentation separation chamber is not required, so that the entire device can be downsized and the MLSS concentration in the aeration tank can be kept high. On the other hand, there are advantages such as reduction of dehydration during the treatment of excess sludge and saving of operation energy.

In the present applicant, as a sewage treatment apparatus by a membrane separation method, "a membrane element group having an air diffuser and having a vertical passage along a membrane surface is disposed immediately above the air diffuser, A diffusing aeration tank provided with a means (suction pump) for making the membrane filtration side of the membrane element group a negative pressure ”has already been proposed (Japanese Patent Publication No. 4-70958). According to this aeration type aeration tank, the undiluted solution in the tank is swirled by the air-lift effect of the air ejected from the aeration device, and the organic matter in the sewage is adsorbed and metabolically decomposed by aerobic microorganisms in contact with air. The organic matter is reduced, aerobic microorganisms are proliferated, and the membrane surface is air-scrubbed and washed by the air blown out from the diffuser to suppress the formation of a sludge cake layer on the membrane surface while the filtrate side of the membrane element. Is reduced to generate a transmembrane pressure, and water can be separated from the activated sludge by filtration with the transmembrane pressure. In place of the means for setting the negative pressure on the membrane filtration side in the aeration type aeration tank, there is also known a method in which the transmembrane pressure of the membrane element is obtained by the natural head by the immersion depth of the membrane element.

[0004]

However, in any of the above sewage treatment apparatuses, activated sludge having a high MLSS concentration is treated, so that the activated sludge adheres to the membrane surface quickly despite air scrubbing. The formation of a bed layer is remarkable, and an early decrease in filtration flux or an early rise in operating pressure cannot be avoided. This activated sludge is an organic substance, and it is difficult to remove the cake layer by washing with water. Therefore, it has been proposed to remove the cake layer by injecting a chemical solution into the membrane element and allowing the injected chemical solution to permeate the membrane and contact the activated sludge cake layer on the outer surface of the membrane. 8-9902
5, JP-A-8-323349, JP-A-9-5202
No. 6, etc.).

[0005] However, when the transmembrane pressure is obtained by the natural head, the natural head acts even during the washing by injecting the chemical, and the chemical is completely injected into the membrane element due to the filtrate permeating into the membrane element. It is difficult to perform effective cleaning because it is difficult to dilute the drug solution with the permeated filtrate. However, when the transmembrane pressure is obtained by reducing the pressure on the filtrate side of the membrane element, the chemical solution is injected into the membrane element in a state where the decompression is stopped. For example, it is difficult to perform satisfactory cleaning mainly due to dilution of the chemical solution with the filtrate.

An object of the present invention is to provide a immersion type membrane separation device, in particular, a membrane element provided in a treatment tank, and a suction pump for reducing the pressure of the filtrate side connected to the membrane element. A diffuser tube is provided below the air diffuser, and air is blown out from the diffuser tube to perform air-scrubbing cleaning of the membrane surface of the membrane element while efficiently performing chemical cleaning of the membrane separation device that performs filtration by operating the suction pump. It is in.

[0007]

According to the cleaning method of the immersion type membrane separation apparatus of the present invention, a membrane element having an inner side as a filtrate is immersed in a stock solution, and the membrane surface is air-scrubbed by a diffuser. This is a method of washing a membrane separation device that filters the undiluted solution by depressurizing the filtrate side of the membrane element.A chemical solution tank is installed, the filtration under reduced pressure is interrupted, and the solution is applied to the membrane element while the membrane element is immersed in the undiluted solution. The chemical solution in the tank is circulated and circulated. One immersion type membrane separation device according to the present invention is to immerse the membrane element having the inside on the filtrate side in the undiluted solution, and to reduce the pressure on the filtrate side of the membrane element while air scrubbing the membrane surface with a diffuser. In a membrane separation device for filtering a stock solution, a chemical solution inlet and a chemical solution outlet are provided in a membrane element, and a chemical solution tank and a circulation pump are connected between the inlet and the outlet. In another immersion type membrane separation device according to the present invention, a membrane element group whose inside is a filtrate side is immersed in a stock solution, and the filtrate side of the membrane element group is depressurized while air scrubbing the membrane surface by a diffuser. In the membrane separation apparatus for filtering the undiluted solution, a chemical solution inlet is provided in each membrane element, and a filtrate collection header of the membrane element group is provided.
A switching valve is provided at the outlet of, and one outlet of the switching valve is connected to the filtrate taking-out pipe, and the chemical solution tank and the circulation pump are connected between the other outlet of the switching valve and the header for the chemical solution inlet of the membrane element group. This is a configuration characterized by the following.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1A is a plan view of an example of the flat membrane element used in the present invention.
(B) is a cross-sectional view taken along the line (b) in FIG. 1 (a), and a spacer 14 for filtrate passage (for example, a plastic net, a plastic nonwoven fabric, a tricot, etc.) is accommodated in a plastic frame 11. The periphery of the flat membranes 13 and 13 is sealed and fixed to the upper and lower surfaces of the frame body 11 with an adhesive 12 or fusion, and the frame body 11 has a filtrate outlet 15, a chemical inlet 161, and a chemical outlet 162. Is provided. An epoxy resin, a urethane resin, a hot melt resin, or the like can be used for the adhesive 12, and a thermal fusion method, an ultrasonic fusion method, or the like can be used for fusion. The flat membrane 13 is formed by laminating an ultrafiltration membrane or a microfiltration membrane on a support material such as a nonwoven fabric or a woven fabric, or a support material such as a woven fabric or a nonwoven fabric on the ultrafiltration membrane or the microfiltration membrane. Can be used. The above flat membrane element 1
The dimensions are usually 50 to 150 cm in length and 20 to 100 in width.
cm and a thickness of 3 mm to 6 mm.

The above-mentioned membrane element 1 is usually used in the form of a module having an air diffuser, and FIG.
In FIG. 2, reference numeral 2 denotes a rack having a skirt portion 21 at the lower end, and 1,...
In the rack 2, a plurality of flat membrane elements 1,... Although not shown, an air diffuser is accommodated in the skirt 21.
Reference numeral 22 denotes an air supply port for the air diffuser. The distance between the flat membrane elements 1 and 1 varies depending on the quality of raw water to be used for treatment, but is usually 5 mm to 15 mm.

FIG. 3 shows an example of an immersion type membrane separation apparatus according to the present invention. In FIG. 3, reference numeral 3 denotes an open type liquid tank to be treated. A is the above-mentioned membrane module. Reference numeral 31 denotes a filtrate outlet 15 of each membrane element 1 of the membrane module A.
, A filtrate collecting pipe 32 connected to an outlet of the header 31, a suction pump 33 provided in the pipe 32, an open / close valve 34, and a filtrate storage tank 35. Reference numeral 41 denotes a stock solution supply pipe, and reference numeral 42 denotes a liquid feed pump provided in the pipe 41. 51 is a header communicating with the chemical solution inlet 161 of each membrane element 1, 52 is each membrane element 1
Header 53 communicating with the chemical solution outlet 162 of FIG.
A chemical tank inserted between 51 and 52, 54 is a circulation pump, 5
Reference numerals 5 and 55 denote on-off valves. Numeral 23 denotes an air diffuser arranged immediately below the membrane element group, which is usually attached to the membrane module. 6 is a blower connected to the air diffuser 23.

FIG. 4 shows another example of the immersion type membrane separation apparatus according to the present invention. In this immersion type membrane separation device, a switching valve 43 is connected to the outlet side of the filtrate collecting header-31,
The suction pump 33 and the filtrate storage tank 35 are connected to one outlet side 431 of the switching valve 43, and the chemical tank 53 is provided between the header 51 for the chemical inlet 161 of the membrane element group and the other outlet 432 of the switching valve 43. , Circulation pump 54, on-off valve 5
5 is connected. FIG. 5 shows an example of a membrane element used in this immersion type membrane separation apparatus. Reference numeral 161 denotes a chemical solution inlet provided on the frame 11, and reference numeral 152 denotes a common outlet for a filtrate solution chemical outlet and a chemical solution outlet.

In order to treat sewage by the above-mentioned membrane separation device, the sewage is supplied to the liquid tank 3 to be treated by the liquid feed pump 42, and the air is blown out of the air diffuser 23 by driving the blower 6, and the blown air flow The sewage in the tank is swirled and the suction pump 33 is intermittently operated to intermittently reduce the pressure on the filtrate passage side of the flat membrane element 1 so that organic matter in the sewage is adsorbed and metabolically decomposed by aerobic microorganisms under contact with air. Then, filtration is performed while reducing organic substances and growing aerobic microorganisms (activated sludge), and the filtrate is stored in a filtrate storage tank 34. The diffusion flow rate of the air diffuser 23 is set so that the swirling velocity of the wastewater in the tank due to the air diffusion is 0.01 to 2 m / s. It is difficult to satisfactorily perform adsorption and metabolic decomposition by aerobic microorganisms, and the adhesion of activated sludge particles to the membrane surface becomes remarkable.If it exceeds 2 m / s, a problem occurs in the strength of the membrane element). With the progress of the filtration process, the activated sludge adheres to the membrane surface and a cake layer is formed. In the case of a constant pressure operation at a constant operating pressure, the filtration flux decreases, and a constant flux operation with a constant permeation flux is performed. In the case of, the operating pressure increases.

When it is detected by a flow meter or a pressure gauge (not shown) that the permeation flux or the operating pressure has reached the limit value, the intermittent operation of the suction pump 33 is interrupted, the on-off valve 34 is closed, and the on-off valve 34 is opened and closed. Open the valve 55 (in the case of the membrane separation device of FIG. 4,
(The switching of the switching valve 43 is performed.) The circulation pump 54 is driven to circulate the chemical solution in the chemical solution tank 53 through a loop including the membrane element and to flow through the membrane element 1 from one end to the other end.
Even if the permeated liquid remains in the membrane element 1 at the initial stage of the distribution of the chemical, the remaining liquid can be pushed out by the inflowing chemical to distribute the chemical throughout the membrane element 1. The amount of the remaining filtrate is negligibly small compared to the total amount of the drug solution, and the inner surface of the membrane of the membrane element can be brought into contact with the drug solution at the initial concentration by the flow of the drug solution, and this drug solution is allowed to penetrate the outer surface of the membrane to allow the membrane to penetrate. The activated sludge cake layer adhering to the outer surface is swelled and deteriorated by the penetrating chemical solution, and the swelled deteriorated cake layer is peeled off and removed by air scrubbing with air from the air diffuser 23 to gradually recover the filtration flux. Let me do it. In this case, the pressure in the membrane element is higher than the depth of the undiluted solution by the height of the chemical solution tank and the pressure loss of the chemical solution flowing through the membrane element. However, since the pressure value is low (the membrane element near the chemical solution inlet of the membrane element). The differential pressure between the inside and the stock solution is almost equal to the outlet pressure of the circulating pump, but this differential pressure is 0.2 kgf / cm ² to
(0.01 kgf / cm ² ).

When the filtration flux recovers, the circulation pump 54 is stopped, the on-off valve 54 is closed, the on-off valve 34 is opened, and the intermittent operation of the suction pump 33 is restarted. It is preferable to return the filtrate to the stock solution tank 3 because the filtrate at the beginning of the re-operation contains a chemical solution. Thereafter, when the permeation flux or the operating pressure reaches the limit value, the washing according to the present invention is repeated.

The method for cleaning an immersion type membrane separation apparatus according to the present invention can also be used for an immersion type membrane separation apparatus that obtains a transmembrane pressure for filtration by a natural head. In this case, there is a mixture of the filtrate due to the natural transmembrane pressure difference in the chemical solution in the membrane element,
The mixing amount is smaller than the amount of the chemical in the chemical tank 53, and the chemical can be more efficiently washed without being affected by the amount of the filtrate. The cleaning method according to the present invention is preferably performed by an automatic operation.

In the method for cleaning an immersion type membrane separation device according to the present invention, a chemical solution is circulated from one end to the other end of the membrane element, so that cleaning can be performed more efficiently than in a case where only a chemical solution is injected into the membrane element. . This is clear from the comparison between the following example and comparative example.

【Example】

[Example] (a) and (b) of FIG.
The dimensions are 1060mm × width (width)
610 mm, the membrane has a nominal pore diameter of 0.4 μm, and an area of 1 m.
The polyolefin-based microfiltration membrane of ²
Plastic nets were used for the joints, and urethane resin was used for the adhesion between the frame and the membrane and for the seal between the frames. The membrane module was configured as shown in FIG. 2, and 15 membrane elements were stacked on a rack at an interval of 13 mm. Using the membrane separation device shown in FIG.
000-15,000 mg / liter activated sludge solution was treated. Spray flow rate is 0.5m /
Set to sec. The operation was a constant-pressure operation, and the suction pump was an intermittent operation in which one cycle consisted of driving for 8 minutes and stopping for 2 minutes. As the chemical solution, an aqueous solution of sodium hypochlorite having a concentration of 5,000 ppm was used. Filtration flux is ^{26m 3 / m 2 · day (} 1kgf / c
m ² ), the intermittent operation of the suction pump was stopped, the on-off valve was closed, the on-off valve was opened, and the circulation pump was driven to wash the membrane element. The outlet pressure of the circulation pump is 0.05k
gf / cm ² . After washing for 1 hour and restarting the suction pump, the filtration flux was 238 m ³ / m ² · day (1 kgf / c
m ² ). When the concentration of the aqueous solution of sodium hypochlorite in the chemical tank was measured, the initial concentration was maintained at 5,000 ppm, and no dilution with the filtrate was observed.

[Comparative Example] The filtration flux was 34 m ³ / m ² · day (1 kgf
/ cm ² ), the intermittent operation of the suction pump is stopped, the on-off valve is closed, the on-off valve is opened, the circulating pump is not driven, and the aqueous solution of sodium hypochlorite having a concentration of 5,000 ppm is obtained only at the head of the chemical tank. Was injected into the membrane element. After one hour, the sodium hypochlorite aqueous solution was recovered and its concentration was measured. The concentration was found to be 3,000 ppm. Furthermore, when the suction pump was restarted, the filtration flux was 120 m ³ / m ² · da
y (1 kgf / cm ² ), and the degree of recovery was less than half that of the example.

[0018]

According to the present invention, in a membrane separation apparatus for performing filtration by a membrane element while air-scrubbing and cleaning the membrane surface of the membrane element by blowing air from an air diffuser, the filtration is interrupted to remove the membrane element. When the chemical cleaning of the membrane element is performed while the membrane element is immersed in the undiluted solution, the washing efficiency can be doubled only by adding a means for flowing the chemical solution, and the wastewater can be more efficiently filtered with a stable filtration flux.

[Brief description of the drawings]

FIG. 1A is a plan view showing an example of a membrane element used in the present invention, and FIG. 1B is a cross-sectional view taken along the line B in FIG. 1A.

FIG. 2 is a drawing showing an example of a membrane module used in the present invention.

FIG. 3 is a drawing showing an example of an immersion type membrane separation device according to the present invention.

FIG. 4 is a drawing showing another example of the immersion type membrane separation device according to the present invention.

5 is a drawing showing a membrane element used in the immersion type membrane separation device of FIG.

[Explanation of symbols]

 1 Membrane Element 161 Membrane Element Chemical Inlet 162 Membrane Element Chemical Outlet 23 Diffusion Tube 31 Filtrate Collection Header-33 Suction Pump 51 Membrane Element Chemical Inlet-52 Header Membrane Element Chemical Outlet-53 Chemical Tank 54 Circulation pump

Claims (4)

[Claims] 1. A method for washing a membrane separation device in which a membrane element whose inside is a filtrate side is immersed in a stock solution, and the membrane surface is air scrubbed by a diffuser while the stock element is filtered by the membrane element. A method for cleaning an immersion-type membrane separation device, comprising installing a tank, suspending filtration, and circulating a chemical solution in a chemical solution tank through the membrane element while immersing the membrane element in the stock solution. 2. A membrane separation device for immersing a membrane element having a filtrate side on the inner side in a stock solution and filtering the stock solution by depressurizing the filtrate side of the membrane element while air scrubbing the membrane surface with a diffuser. A washing method, in which a chemical solution tank is installed, the vacuum filtration is interrupted, and the chemical solution in the chemical solution tank is circulated and circulated through the membrane element while the membrane element is immersed in the undiluted solution. Cleaning method. 3. A membrane separation apparatus in which a membrane element having an inner side as a filtrate is immersed in a stock solution, and the membrane surface is air-scrubbed by a diffuser while the filtrate side of the membrane element is depressurized to filter the stock solution. An immersion type membrane separation device, wherein a chemical solution inlet and a chemical solution outlet are provided in a membrane element, and a chemical solution tank and a circulation pump are connected between the inlet and the outlet. 4. Membrane separation in which a membrane element group having an inner side as a filtrate side is immersed in a stock solution, and the membrane side is filtered by depressurizing the filtrate side of the membrane element group while air scrubbing the membrane surface with a diffuser. In the apparatus, a chemical solution inlet is provided for each membrane element, a switching valve is provided at an outlet of a filtrate collecting header of the membrane element group, one outlet of the switching valve is connected to a filtrate extraction pipe, and the other outlet of the switching valve is provided. An immersion type membrane separation device, wherein a chemical solution tank and a circulation pump are connected between the membrane element group and a header for a chemical solution inlet of the membrane element group.