JP5105795B2 - Membrane separation tank and operation method - Google Patents

Description

  The present invention relates to a membrane separation tank and an operation method, and particularly relates to a technique for discharging deposits from a membrane separation tank.

  Conventionally, in wastewater treatment, a membrane separation tank has been employed for both aerobic treatment and anaerobic treatment. For example, what is disclosed in Patent Document 1 is to introduce organic waste into a fermentor and perform methane fermentation, and circulate fermented sludge between the fermenter and the membrane separation tank. Thus, the fermented sludge is separated into solid and liquid, and the membrane permeate is taken out of the system to maintain the SS concentration in the fermentor at or above the effective value necessary for maintaining methane fermentation.

  Then, the gas in the fermenter is aerated from a diffuser disposed below the membrane separator, and the gas-liquid mixed phase flow caused by the aerated gas acts as a sweep against the membrane surface of the membrane of the membrane separator. And excess fermentation sludge is extracted from the bottom of the fermenter.

  Further, in Patent Document 2, a diffuser is configured by providing in parallel a plurality of pipe bodies that form a ventilation path, the proximal end of the diffuser communicates with the blower, and the tip is below the membrane cartridge. Open.

Moreover, in patent document 3, while the submerged membrane separator installed in the inside of a processing tank arranges the flat plate-like membrane cartridge arrange | positioned at an up-down direction at appropriate intervals, it arrange | positions the diffuser box under the membrane cartridge. The diffuser box has an open bottom and a plurality of air discharge holes on the wall surface. The air discharge holes have a hole diameter corresponding to the distance between the membrane cartridges.
JP 2000-24661 A JP-A-9-108549 JP-A-8-267084

  As described above, the air diffusing device is disposed at a position below the membrane unit of the membrane separation device in order to assume a function of generating a scavenging flow with respect to the membrane surface of the filtration membrane. Moreover, in order to prevent obstruction | occlusion by the sludge etc. which settles in the tank bottom part of a membrane separation tank, it has arrange | positioned in the position of fixed height from the tank bottom face of a membrane separation tank.

  By the way, in wastewater treatment methods with high sludge concentration, such as methane fermentation in which organic waste is introduced into the fermenter as a raw material, the upward flow derived from aeration is less likely to occur in the lower region than the aeration device. Deposits are likely to occur at the bottom. In particular, organic waste such as garbage contains sand, shells, eggshells, etc., which are extracted from the bottom of the fermenter tank together with excess fermented sludge. It tends to stay at the bottom and become sediment. In the aerobic treatment, sludge accumulated at the bottom of the tank rots due to a shortage of DO for a long period of time, causing self-digestion and deteriorating the quality of treated water.

  The present invention solves the above-described problems, and an object thereof is to provide a membrane separation tank and an operation method capable of preventing the occurrence of harmful effects caused by the accumulation of sludge containing sand, shells, eggshells, etc. over a long period of time. And

In order to solve the above-mentioned problems, the membrane separation tank of the present invention has a membrane removal apparatus in which a membrane separation apparatus having a membrane surface cleaning apparatus is immersed in the tank, and sludge deposited on the bottom of the tank is stirred and mixed into the liquid in the tank. The apparatus is arranged on the bottom of the tank .

  The operation method of the membrane separation tank according to the present invention is that the membrane surface of the membrane separation device is washed by the membrane surface cleaning device during the membrane separation operation of the membrane separation device immersed in the tank, and the sludge is stirred to sludge in the tank, or The sludge deposited on the bottom of the tank is stirred and mixed into the liquid in the tank by a deposit removing device disposed on the bottom of the tank when the sludge is discharged to discharge the sludge in the tank.

  Further, the membrane separation operation of the membrane separation device is stopped when the sludge is stirred to stir the sludge in the tank or when the sludge is discharged to discharge the sludge in the tank.

  As described above, according to the present invention, during the membrane separation operation of the membrane separation apparatus immersed in the membrane separation tank, for example, the membrane surface cleaning fluid is diffused to stabilize the upward flow by driving the membrane surface cleaning apparatus. A gas-liquid mixed phase flow is generated, and the solid-liquid mixed phase flow acts as a scavenging flow for cleaning the membrane surface of the filtration membrane of the membrane separation device, and the liquid in the tank is separated into solid and liquid by the membrane separation device. Remove the membrane permeate from the system.

  During the membrane separation operation, the deposit removing air diffuser is in a stopped state, and the inside of the membrane separation tank is in a steady state in which a uniform flow circulates in a steady flow. In this steady state, sand, shells, eggshells and the like having poor fluidity are precipitated in the liquid in the tank. These precipitates having poor fluidity are generally hard and heavy, and the flow adversely affects the membrane surface of the filtration membrane. Therefore, it is preferable that the precipitate is in a precipitated state during the membrane separation operation.

  However, it is difficult to discharge these poorly flowable materials when they are deposited in layers, and particularly when sludge containing a sparingly soluble organic acid calcium salt is deposited in layers. Moreover, in anaerobic digestion, organic acid fermentation and methane fermentation occur, and in order to efficiently ferment methane fermentation of organic waste, it is important to contact the organic acid produced in organic acid fermentation with methane bacteria. However, in the steady state during the membrane separation operation, a part of the organic acid is unevenly distributed at the bottom of the tank as an organic acid calcium salt or the like. For this reason, the entire membrane separation tank is stirred from the bottom of the tank by the deposit removing device to uniformly disperse the organic acid and methane bacteria in the membrane separation tank, thereby promoting methane fermentation.

  The agitation by the deposit removing device is performed when any sludge is agitated, sludge is discharged, or when deposits at the bottom of the tank are detected by the deposit sensing means, and the deposit removing device is in a state where the operation of the membrane separator is stopped. Is driven, and, for example, pressurized air or biogas is supplied from the deposit removing device disposed on the bottom surface of the tank, and sludge accumulated on the bottom of the tank is spouted from the bottom surface of the tank to be stirred and mixed into the liquid in the tank. .

  In this way, the sludge accumulated at the bottom of the membrane separation tank is stirred and mixed into the liquid in the tank periodically or at any time, so that the accumulated sludge can be prevented from decaying in the aerobic treatment. . Moreover, it can suppress that sand etc. accumulate on a tank bottom part, and can reduce the frequency of cleaning in a tank. Furthermore, by reducing the accumulation of sludge and sand, there is no deposit around the diffuser for cleaning the membrane surface of the membrane separator, and normal aeration operation can be performed at all times. Blockage of the membrane surface of the separator can be prevented.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Although the membrane separation tank of the present invention can be used alone and can be used for both aerobic treatment and anaerobic treatment, as shown in FIG. 1, in this embodiment, human waste, septic tank sludge, The membrane separation tank 1 used in the facility for methane fermentation of organic waste such as garbage and food waste will be described as an example.

  The membrane separation tank 1 has a sealed structure and communicates with a methane fermentation tank (not shown) through a sludge circulation system 2 and a sludge return system 3. The sludge circulation system 2 is used to circulate the fermentation sludge from the methane fermentation tank to the membrane separation tank 1 and has a circulation pump, a screen, etc., and the sludge return system 3 converts the fermentation sludge from the membrane separation tank 1 into the methane fermentation tank. It is something to return.

  In the present embodiment, a membrane separation device 5 having a membrane surface cleaning air diffuser 4 as a membrane surface cleaning device is immersed in the membrane separation tank 1, and a plurality of deposit removal devices are disposed on the bottom of the tank. The deposit removing air diffuser 6 is arranged at an appropriate interval. The film surface cleaning device and the deposit removing device are not limited to the air diffuser, and a mechanical device can also be applied.

  The deposit removal air diffuser 6 is located below the film surface cleaning air diffuser 4, and the film surface cleaning air diffuser 4 uses an air diffuser having an air diffuser or the like. As the air diffuser 6, a bottom-mounted disk diffuser or the like that is less likely to block is used.

  The membrane separation device 5 accommodates a plurality of membrane cartridges 5b in a membrane case 5a in a vertical direction and in parallel with an appropriate gap, and a membrane surface cleaning air diffuser 4 is disposed below the membrane cartridge 5b. Yes. The membrane cartridge 5b covers the surface of the flat filter plate, and an organic membrane is arranged. The drive system can perform gravity filtration using the water head in the tank, but in this embodiment, the suction cartridge 7 is used. Suction filtration is performed.

  An aeration gas supply system 8 for supplying a gas (biogas) in the membrane separation tank 1 or the methane fermentation tank is electrically driven in the membrane surface cleaning diffuser 4 and the deposit removing diffuser 6. 9, the aeration gas supply system 8 has a blower 8a. The blower 8a can change the air volume supplied to the film surface cleaning air diffuser 4 and the air volume supplied to the deposit removing air diffuser 6 by inverter control.

  In the present embodiment, the blower 8a that is also used as the film surface cleaning diffuser 4 is connected to the deposit removing diffuser 6, but an independent compressor is connected to the deposit removing diffuser 6 and compressed. It is also possible to supply gas in the tank (biogas).

  A gas escape system 10 for releasing the gas in the tank is provided at the upper part of the membrane separation tank 1, and a sludge discharge system 11 is provided at the bottom of the tank. A deposit detection sensor 12 serving as a deposit detection means is provided at the lower part of the membrane separation tank 1, and a torque detection type level sensor, a vibration type level sensor, or the like can be used as the deposit detection sensor 12.

  The operation of the above configuration will be described. In the methane fermentation tank, fermented sludge fermented in the tank is circulated to the membrane separation tank 1 through the sludge circulation system 2 and the sludge return system 3, and the fermentation sludge is solid-liquid separated by the membrane separation apparatus 5 of the membrane separation tank 1.

  The membrane permeate passing through the membrane separation device 5 is taken out of the system to maintain the SS (methane bacteria) concentration in the methane fermentation tank at an effective value necessary for maintaining methane fermentation, for example, 3 to 7% or more.

  During the membrane separation operation of the membrane separation device 5, the aeration gas supply system 8 supplies the gas in the tank as the membrane surface cleaning aeration fluid to the membrane surface cleaning aeration device 4. The solid-gas / liquid mixed phase flow caused by the gas in the tank to be aerated is caused to act as a sweep on the membrane surface of the filtration membrane of the membrane separation device 5 to prevent the cake layer from adhering to the membrane surface.

  During the membrane separation operation, the deposit removing air diffuser 6 is in a stopped state, and the inside of the membrane separation tank 1 is in a steady state in which a uniform flow circulates in a steady flow. In this steady state, sand, shells, eggshells and the like having poor fluidity are precipitated in the liquid in the tank. These precipitates having poor fluidity are generally hard and heavy, and the flow adversely affects the membrane surface of the filtration membrane. Therefore, it is preferable that the precipitate is in a precipitated state during the membrane separation operation.

However, it is difficult to discharge these poorly flowable materials when they are deposited in layers, and particularly when sludge containing a sparingly soluble organic acid calcium salt is deposited in layers.
For this reason, the three-way switching valve 9 is used to remove deposits from the film surface cleaning air diffuser 4 by manual operation at the time of arbitrary sludge agitation, by periodic timer operation, or when the deposit detection sensor 12 is turned on. Switching to the air diffuser 6, controlling the air volume of the blower 8 a, supplying the gas in the tank to the air diffuser 6 for deposit removal by the aeration gas supply system 8 as the air diffuser fluid for deposit removal, The entire membrane separation tank 1 is stirred from the bottom of the tank by the gas in the tank aerated from the gas device 6. The deposit removing air diffuser 6 is operated with the operation of the membrane separator 5 stopped.

  In this way, the sludge deposited on the bottom of the membrane separation tank 1 is stirred and mixed into the liquid in the tank periodically or at any time, thereby preventing the decay of the accumulated sludge in the aerobic treatment. it can. Moreover, it can suppress that sand etc. accumulate on a tank bottom part, and can reduce the frequency of cleaning in a tank. Furthermore, since the accumulation of sludge and sand is reduced, there is no deposit around the aeration device 4 for cleaning the membrane surface of the membrane separation device 5, and normal aeration operation can always be performed, resulting in poor aeration. It is possible to prevent the membrane surface of the membrane separation device 5 from being blocked.

  Further, when the excess sludge is discharged, the three-way switching valve 9 is operated manually, and the aeration gas supply system 8 supplies the gas in the tank to the deposit removing diffuser 6 as the deposit removing diffused fluid. The liquid in the tank is discharged from the sludge discharge system 11 while stirring the entire membrane separation tank 1 from the bottom of the tank with the gas in the tank aerated from the diffuser 6 for removing deposits.

  In the methane fermentation tank and the membrane separation tank 1, organic acid fermentation and methane fermentation occur as anaerobic digestion. In order to efficiently ferment methane fermentation of organic waste, organic acids and methane bacteria produced in organic acid fermentation are used. Contact with is important. However, in the steady state during the membrane separation operation, a part of the organic acid is unevenly distributed at the bottom of the tank as an organic acid calcium salt or the like.

  For this reason, the three-way switching valve 9 is operated by manual operation at the time of arbitrary sludge agitation or by periodic timer operation, and the gas in the tank is removed by the aeration gas supply system 8 as an aeration fluid for deposit removal. The entire membrane separation tank 1 is stirred from the bottom of the tank by the gas in the tank supplied to the air diffuser 6 and aerated from the deposit removing air diffuser 6. By this stirring, sludge containing organic acid calcium salt and the like deposited on the bottom of the tank and methane bacteria are uniformly dispersed inside the membrane separation tank 1 to promote methane fermentation.

  Thus, in the operation of the membrane separation tank 1 in methane fermentation, a steady state and an agitated state are intentionally formed inside the membrane separation tank 1, and in the steady state, a flow that has an adverse effect such as damage to the membrane surface of the filtration membrane. Precipitates with poor properties, and in a stirred state, sludge containing organic acid calcium salt and the like at the bottom of the tank and methane bacteria are uniformly dispersed, thereby realizing membrane surface protection of the membrane separation device 5 and promotion of methane fermentation. .

  As other embodiment of this invention, as shown in FIG. 3, it is also possible to employ | adopt the stirring blade 20 for a deposit removal apparatus. The stirring blade 20 is disposed in the vicinity of the bottom of the tank, and may have a continuous shape or a discontinuous and single shape. The stirring blade 20 is rotationally driven by a motor 21 disposed outside the tank.

Schematic diagram showing the membrane separation operation of the membrane separation tank in the embodiment of the present invention Schematic showing the stirring of the membrane separation tank in the same embodiment The schematic diagram which shows the membrane separation tank in other embodiment of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Membrane separation tank 2 Sludge circulation system 3 Sludge return system 4 Aeration device for membrane surface cleaning 5 Membrane separation device 5a Membrane case 5b Membrane cartridge 6 Aeration device for deposit removal 7 Suction pump 8 Aeration gas supply system 8a Blower 9 Three-way Switch valve 10 Gas escape system 11 Sludge discharge system 12 Deposit detection sensor 20 Stirring blade 21 Motor

Claims (4)

A membrane separation tank characterized in that a deposit removal apparatus for immersing a membrane separation apparatus having a membrane surface cleaning apparatus in a tank and stirring and mixing sludge deposited on the bottom of the tank into the liquid in the tank is disposed on the bottom surface of the tank. 2. The membrane separation tank according to claim 1, further comprising a deposit sensing means, wherein the deposit sensing means detects the deposit at the bottom of the tank and drives the deposit removing device. During membrane separation operation of the membrane separator immersed in the tank, the membrane surface of the membrane separator is cleaned by the membrane surface cleaning device, stirring the sludge in the tank, or when discharging the sludge discharging the sludge in the tank A method for operating a membrane separation tank, wherein the sludge deposited on the bottom of the tank is stirred and mixed into the liquid in the tank by a deposit removing device disposed on the bottom. The method for operating a membrane separation tank according to claim 3, wherein the membrane separation operation of the membrane separation apparatus is stopped at the time of sludge stirring for stirring the sludge in the tank or at the time of sludge discharge for discharging the sludge in the tank.

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