JP3659833B2 - Operation method of multi-stage submerged membrane separator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for operating a multi-stage submerged membrane separator used for sewage treatment, sludge concentration, and the like.
[0002]
[Prior art]
As a solid-liquid separator used for sewage wastewater treatment, sludge concentration, etc., there is a submerged membrane separator 1 as shown in FIGS. This membrane separation device 1 has a plate-like membrane cartridge 3 arranged in the upper part of a casing 2 and an air diffuser 4 provided in the lower part thereof. The number of units in the treatment tank 5 according to the amount of treated water. In a state where the raw water 6 is continuously introduced and diffused from the diffuser 4, the treatment target liquid 7 in the tank is filtered by the membrane cartridge 3, and the permeated water that has passed through the membrane surface is passed through the tube 8, The water is extracted to the outside of the tank through the water collecting pipe 9 and the permeated water outlet pipe 10. In order to facilitate transport and maintenance management, the casing 2 is often divided into a membrane case 2a for housing the membrane cartridge 3 and an air diffuser case 2b for housing the air diffuser 4.
[0003]
This membrane separation device 1 is capable of cross-flow filtration and membrane surface cleaning by raising a gas-liquid mixed flow generated by bubbles from the air diffuser 4 between the membrane cartridges 3 and is stable. In addition to exhibiting filtration performance, the membrane area per unit installation area (corresponding to the number of installed membrane cartridges 3) can be increased, so the capacity of the treatment tank 5 can be reduced compared to the case of using other types of membrane separation devices. It is widely accepted that it is easy to operate and maintain.
[0004]
[Problems to be solved by the invention]
However, since a plurality of membrane separation apparatuses 1 are conventionally installed in parallel at intervals, that is, in a plane, the number of membrane cartridges 3 is not necessarily large from the viewpoint of the filling efficiency in the tank, and the processing tank capacity is reduced. The advantage of being able to reduce was not fully utilized.
[0005]
For this reason, the present inventors have proposed in Japanese Patent Application No. 10-334835 that a plurality of membrane cases are stacked in multiple stages via a spacing case. Since the bubbles are more dispersed depending on the case, the film surface cleaning effect is different between the lower film case and the upper film case, and the upper film can obtain a higher cleaning effect. Since the effective membrane area is kept larger in the upper membrane cartridge having a higher cleaning effect, if the permeation flux in the upper and lower membrane cartridges is set to be the same, the substantial permeation flux limited to the effective membrane area is The lower membrane cartridge is higher, and as a result, the lower membrane cartridge may be clogged first.
[0006]
In order to eliminate the deterioration of filtration performance due to clogging, usually chemical liquid backwashing is performed periodically to send the chemical liquid to the permeate flow path of the membrane cartridge, but there is a cake layer that cannot be resolved even by chemical liquid backwashing. For example, the membrane cartridge needs to be taken out of the tank together with the membrane case and subjected to another cleaning method such as physical cleaning. At that time, since the lower membrane case can be taken out only after the upper membrane case is taken out, the upper membrane cartridge that does not impair the filtration performance must be taken out of the tank. When the cake layer is formed, it is necessary to take it out again, so it is bothersome. In order to avoid the complexity of the work, it is conceivable that the upper membrane cartridge that does not impair the filtration performance is also washed outside the tank at the same time as the lower membrane cartridge.
[0007]
An object of the present invention is to solve the above-described problems and to facilitate and efficiently perform the detachment of the membrane cartridge when the membrane surface is clogged.
[0008]
[Means for Solving the Problems]
In order to solve the above problems, the present invention arranges a plurality of rigid plate-like membrane cartridges in a membrane case having an opening at the top and bottom, with the membrane surfaces in the vertical direction, and with a certain gap between the membrane surfaces. Thus, a plurality of membrane case units are arranged in multiple stages via an interval case that forms an open space between the membrane cases, and an air diffuser is placed below the lowermost membrane case unit. When operating a multi-stage submerged membrane separator with a diffused case provided and a permeate outlet tube connected to one end on the permeate side of each arrayed membrane cartridge for each membrane case unit, By controlling the membrane differential pressure generating means for generating the membrane differential pressure through the tube, the upper membrane cartridge is operated with a larger permeation flux.
[0009]
In order to control the membrane pressure generating means, for example, when performing suction filtration with a permeated water outlet pipe interposed with a pump device, each permeated water outlet pipe is provided with a pump device to adjust the suction pressure, Alternatively, if the flow control means provided in each permeate outlet pipe is shared by sharing the pump device, and the other end of the permeate outlet pipe is opened under atmospheric pressure and gravity filtration is performed using the water head, the open end Adjust the vertical position of.
[0010]
According to the above configuration, considering the difference in the membrane surface cleaning effect due to bubbles at the upper and lower stages, the permeation flux is increased in the upper stage membrane cartridge, thereby preventing the membrane contamination of the upper stage membrane cartridge from progressing. This can be preceded by a membrane cartridge.
Therefore, by making an appropriate difference in the permeation flux of the upper and lower membrane cartridges, the frequency of removing membrane contamination that cannot be eliminated in the tank by washing outside the tank can be reduced by multiple times of the upper membrane cartridge that can be easily detached. On the other hand, it is possible to set the lower membrane cartridge which is difficult to be detached, and to simplify the removal / removal operation of the membrane cartridge while using each membrane cartridge for a long time without impairing the filtration performance. Can do.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
In the membrane separation apparatus 11 shown in FIG. 1, a plurality of rigid plate-like membrane cartridges 13 (thickness: about 6 mm) are placed in a membrane case 12 having an opening at the top and bottom, with the membrane surface set in the vertical direction, The membrane case unit 14 is configured by arranging them at regular intervals (usually 6 to 10 mm), and the membrane case units 14 are arranged in two stages in the vertical direction and an open space is formed between the membrane cases 12. An interval case 15 is provided, and an air diffuser case 17 provided with an air diffuser 16 is provided below the lower membrane case unit 14.
[0012]
The membrane cartridge 13 is as shown in FIGS. 2 (a) and 2 (b), and a filtration membrane sheet 13B is disposed on both surfaces of a rigid filter plate 13A made of ABS resin or the like at the periphery of the membrane. The filter plate 13A is provided with a permeate flow path 13C that is bonded (or welded) and formed in the filter plate 13A, and a permeate outlet 13D that communicates between the filter plate 13A and the filter membrane sheet 13B. The filtration membrane sheet 13B is formed integrally by applying (coating) a polyolefin resin or the like to a nonwoven fabric or the like as a support.
[0013]
A slit 12A for inserting the peripheral edge of the membrane cartridge 13 is formed on the inner surface of each membrane case 12, and a circulation opening 17A for the liquid to be treated is formed in the diffuser case 17. The upper membrane case 12 and the spacing case 15 are provided with water collecting pipes 19 and 20 that communicate with the permeate outlet 13D of the membrane cartridge 13 via the tube 18, respectively. The water collecting pipe 20 is integrated with the spacing case 15, and the connection nozzle for the tube 18 is opened inside the case. Membrane retainers 21 and 22 that prevent the membrane cartridges 13 from rising are in contact with the upper ends of the membrane cartridges 13 arranged in each membrane case 12.
[0014]
Permeate discharge pipes 23 and 24 communicate with the water collection pipes 19 and 20, respectively. Each permeated water outlet pipe 23, 24 is provided with a pump device 25, 26, and the other end is opened by a treated water tank (not shown) outside the tank. The pump devices 25 and 26 can control the suction pressure by the control device 27.
28 is an air supply source such as a blower or a compressor, 29 is an air supply pipe disposed between the air supply source 28 and the diffuser 16, and 30 is a water supply means communicating with the air supply pipe 29 via a valve device 31. .
[0015]
The operation of the above configuration will be described.
In the state where the membrane separation device 11 is immersed and installed in the activated sludge mixed solution 33 of the treatment tank 32 for performing biological treatment and the raw water 34 is continuously introduced, the air supply source 28 diffuses air through the air diffuser 16, The control device 27 controls the suction pressures of the pump devices 25 and 26, and generates appropriate membrane differential pressures in the upper and lower membrane cartridges 13 through the permeate outlet tubes 23 and 24. Depending on the quality of the raw water 34, a separate air diffuser (not shown) is also diffused so as not to run out of oxygen. Further, in order to prevent the air holes of the air diffuser 16 from being blocked, the flow path is periodically switched by the valve device 31 for a predetermined time, and the cleaning water is supplied from the water supply means 30 to the air diffuser 16 through the air supply pipe 29. .
[0016]
By doing so, an upward flow of the activated sludge mixed liquid 33 is generated by the air lift action of the diffused air uniformly ejected from the diffuser 16 into the diffuser case 17, and this gas-liquid mixed upward flow causes a flow opening. Since a circulating flow occurs inside and outside the apparatus through 17A, the activated sludge mixed liquid 33 in the tank is sufficiently stirred and mixed, and the contact opportunity of activated sludge / oxygen / polluted substances is increased, so that the activated sludge treatment is performed efficiently. .
[0017]
Further, while this gas-liquid mixed upward flow sequentially flows into the membrane case unit 14 (that is, the membrane case 12) arranged in two stages and passes through the gap between the membrane cartridges 13, the membrane of each membrane cartridge 13 The activated sludge mixed liquid 33 is cross-flow filtered at the surface, and the permeated water that has permeated through the filtration membrane sheet 13B and flowed into the permeated water flow path 13C is the permeated water outlet 13D, the tube 18, the water collecting pipes 19, 20, and the permeated water outlet pipe. Although it guide | induces to a treated water tank through 23 and 24, since concentration polarization is prevented by a gas-liquid mixing upward flow, and the film | membrane surface of the film | membrane cartridge 13 is wash | cleaned by the bubble of diffused air, the filtration efficiency is high.
[0018]
At that time, the membrane case unit 14 is arranged in a plurality of stages (in this case, two stages) up and down, thereby causing the gas-liquid mixed upward flow across the plurality of membrane case units 14 as described above by the diffuser 16 at the lower part of the apparatus. Therefore, the amount of diffused air per membrane cartridge 13 can be reduced. Moreover, since the apparatus installation area per sheet cartridge 13 can be reduced, a sufficient gap can be taken around the apparatus to prevent uneven flow, and local deposition of the cake layer and blockage between the films can be prevented.
[0019]
Further, since the spacing case 15 is interposed between the membrane cases 12, the bubble flow constituting the gas-liquid mixed upward flow once diffuses in the open space and then uniformly flows into the gap between the upper membrane cartridges 13. This can also prevent local deposition of the cake layer and thereby blockage between the films.
However, at this time, since the bubble flow is dispersed by the spacing case 15, the membrane surface cleaning effect in the upper membrane case 12 is higher than that in the lower membrane, so that the controller 27 controls the pump devices 25 and 26 as described above. When controlling the suction pressure, for example, the upper stage 0.8 (m ³ / m ² · day) and the lower stage 0.6 (m ³ / m ² · day) so that the permeation flux becomes larger as the upper membrane cartridge 13 increases. The membrane differential pressure generated in each stage of the membrane cartridge 13 is adjusted so that The appropriate permeation flux size at each stage varies depending on the speed of the gas-liquid mixed upflow, but usually the permeation flux of the upper membrane cartridge 13 is 130 to 200 of the permeation flux of the lower membrane cartridge 13. %, Preferably 150% or more.
[0020]
While the operation is continued, film contaminants are gradually deposited by the above-described film surface cleaning. Therefore, chemical solution back-washing is periodically performed to eliminate clogging. That is, a chemical solution such as sodium hypochlorite or oxalic acid corresponding to the type of membrane contaminant is fed into the permeate flow path of the membrane cartridge 13 through the permeate outlet tube 27.
When a cake layer that cannot be eliminated even by back washing with the chemical solution is generated, the membrane cartridge 13 is taken out of the tank together with the membrane case 12, and another washing method such as physical washing is performed. At that time, as described above, since the permeation fluxes of the upper and lower membrane cartridges 13 are different, the cake layer is deposited faster on the upper membrane cartridge 13, and the upper membrane cartridge 13 is placed in the tank. The frequency of cleaning outside is higher than the frequency of cleaning the lower membrane cartridge 13. With the permeation flux ratio as described above, although depending on the difference in the membrane surface cleaning effect due to bubbles at the upper and lower stages, the upper membrane cartridge 13 in which the membrane case 12 can be easily detached is washed two to three times. In this case, the lower membrane cartridge 13 in which the membrane case 12 is difficult to be detached is washed once. Therefore, the membrane cartridge 13 can be easily attached and detached while using the membrane cartridges 13 at the upper and lower stages for a long time as long as the filtration performance is not hindered. However, if a cake layer is deposited so that the gap between the lower membrane cartridges 13 is blocked, the bubble flow is biased, and as a result, the upper membrane cartridge 13 is blocked between the membranes. The out-of-tank cleaning frequency of the lower membrane cartridge 13 is set so as not to invite.
[0021]
Note that the difference in the permeation flux of the upper and lower membrane cartridges 13 extends the membrane life of the lower membrane cartridge 13, that is, the usable period without fear of the filtration membrane sheet 13B being broken, from the upper one. Therefore, it is advantageous in terms of time and effort to replace with a new membrane cartridge.
In FIG. 3, the permeated water outlet pipe 23 is provided with a pump device 25, and the permeated water outlet pipe 23 is communicated with the permeated water outlet pipe 23 via the flow rate adjusting valves 35, 36 to adjust the flow rate. By adjusting the flow rate of the permeated water led out through the permeated water outlet pipes 23 and 24 by the valves 35 and 36, the permeate flux of the upper membrane cartridge 13 is made larger than that of the lower membrane cartridge 13. A damper may be arranged in place of the flow rate adjusting valves 35 and 36.
[0022]
FIG. 4 shows an apparatus configuration in which the other ends of the permeate outlet pipes 23 and 24 are opened under atmospheric pressure, and gravity filtration is performed using a water head at a position corresponding to the open ends 23a and 24a. The permeation flux of the upper membrane cartridge 13 is made larger than that of the lower membrane cartridge 13 by adjusting the vertical positions of the open ends 23a and 24a.
[0023]
Furthermore, it is possible to make a difference between the permeation fluxes of the upper and lower membrane cartridges by arranging separate membrane cartridges having different permeation fluxes under the same membrane differential pressure condition in the upper and lower stages.
[0024]
【The invention's effect】
As described above, according to the present invention, when operating a multi-stage submerged membrane separation apparatus in which a plurality of membrane case units in which a plurality of membrane cartridges are arranged are arranged in multiple stages, the permeation flux is increased as the upper membrane cartridge is operated. By increasing the size, the membrane contamination of the upper membrane cartridge proceeds before the lower membrane cartridge. As a result, the operation of taking the membrane cartridge out of the tank and cleaning it can be set to one time for the lower membrane cartridge, which is difficult to be detached, with respect to the upper membrane cartridge, which is easy to be detached. It is possible to simplify the operation while using the cartridge for a long time as long as the filtration performance is not hindered.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing a multi-stage stacked immersion type membrane separation apparatus to which an operation method according to a first embodiment of the present invention is applied.
FIG. 2 is an explanatory view showing a configuration of a membrane cartridge arranged in the multi-stage submerged membrane separation apparatus.
FIG. 3 is an explanatory view showing a multi-stage stacked immersion type membrane separation apparatus to which an operation method according to a second embodiment of the present invention is applied.
FIG. 4 is an explanatory view showing a multi-stage stacked immersion type membrane separation apparatus to which an operation method according to a third embodiment of the present invention is applied.
FIG. 5 is a perspective view of a conventional membrane separation apparatus.
FIG. 6 is an explanatory view showing a state in which the membrane separation apparatus is immersed in the treatment tank.
[Explanation of symbols]
12 Membrane case
13 Membrane cartridge
14 Membrane case unit
15 spacing case
16 Air diffuser
17 Aeration case
23,24 Permeate outlet pipe
23A, 24A Open end (Membrane pressure generation means)
25,26 Pump device (Measuring means for differential pressure)
35,36 Flow control valve (Means for generating differential pressure)

Claims (1)

A membrane case unit is configured by arranging a plurality of rigid plate-like membrane cartridges with a fixed gap between the membrane surfaces in a vertical direction inside the membrane case having upper and lower openings. Membrane case units are arranged in multiple stages through gap cases that form an open space between the membrane cases, and a diffuser case with a diffuser is provided below the lowermost membrane case unit. When operating a multi-stage submerged membrane separation apparatus provided with a permeate outlet pipe communicating at one end on the permeate side of each membrane cartridge arranged, a membrane differential pressure that causes a membrane differential pressure through each permeate outlet pipe An operation method of a multi-stage stacked immersion type membrane separation apparatus, wherein the upper membrane cartridge is operated with a larger permeation flux by controlling the generating means.

Images