JP2014091070A - Method for processing organic waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for processing organic waste water capable of restricting the deposition and accumulation of sediment on the lower part of a membrane unit, without using a drug solution, requiring no enormous labor and cost.SOLUTION: A method for processing organic waste water produces biologically treated water using an active sludge M and a membrane separation unit 12 in a filtration tank 10. The membrane separation unit 12 includes: a membrane unit 13 including a plurality of sheet-like separation membranes; a first air diffusing unit 14 arranged at a vertically lower part thereof; and a second air diffusing unit 15 arranged at a rear part. The processing method includes the successive steps of: forward rotating the sludge for generating a gas-liquid mixed upward flow inside the membrane unit 13 and an active sludge downward flow at the periphery of the membrane unit 13 during solid-liquid separation of the active sludge; reverse rotating the sludge for generating a gas-liquid mixed upward flow at the periphery of the membrane unit 13 and an active sludge downward flow inside the membrane unit 13; and filtering the active sludge in the filtration tank 10 with a prefilter.

Description

  The present invention relates to a method for treating organic wastewater, and in particular, without using a chemical solution, and without requiring a great deal of labor and cost, it is possible to suppress adhesion and accumulation of residues particularly at the lower part of the membrane unit. The present invention relates to a method for treating organic wastewater.

Organic to obtain biologically treated water by solid-liquid separation of activated sludge by a membrane separation device installed so that organic wastewater flows into the treatment tank containing activated sludge and immersed in the activated sludge in the treatment tank Wastewater treatment methods are known (see, for example, Patent Documents 1 and 2).
The membrane separation device has a membrane unit in which a plurality of sheet-like separation membranes are arranged with a predetermined interval so that the upper and lower portions are opened, and by applying a negative pressure by suction or the like in the separation membrane, The activated sludge is subjected to solid-liquid separation, and the obtained clean separation membrane permeate is taken out of the treatment tank. In addition, a diffuser is provided in the vertically lower part of the membrane unit, and an upward flow parallel to the membrane surface (gas-liquid mixed upward flow) is generated between the separation membranes by the floating of the air supplied from the diffuser. The gas-liquid mixed upward flow separates the deposits on the surface of the separation membrane and simultaneously performs physical cleaning of the membrane surface, thereby performing solid-liquid separation of activated sludge while preventing clogging of the membrane. A downflow (activated sludge downflow) is generated in the outer periphery of the membrane separation device, and a swirling flow is formed integrally with the gas-liquid mixing upward flow.

  Organic wastewater often contains, for example, sewage and the like, fiber materials such as hair and pulp, and residue that is a solid content such as wrinkles. When these are mixed in the biological treatment tank, the residue adheres, accumulates and grows particularly at the lower part of the membrane unit, and prevents the gas-liquid mixing upward flow generated from the vertically lower part thereof. Then, the flow of sludge stagnates on the surface of some separation membranes. As a result, the membrane surface cannot be washed, and membrane pore clogging may proceed, or a sludge cake may be formed between the separation membranes. When this happens, the burden on the separation membranes that can be used increases, and a negative vicious cycle occurs in which some sludge cake and residue lump is used as a core, and further growth of sludge cake and residue is promoted. The membrane filtration performance as a whole unit is significantly reduced.

  Normally, when membrane clogging occurs, in-line cleaning is mainly performed by injecting a chemical solution such as sodium hypochlorite from the secondary side of the membrane filtrate. In in-line cleaning, sludge cake and residue mass are removed. In order to recover these, the membrane unit is taken out of the treatment tank and recovered by physical cleaning or chemical cleaning. This requires a great deal of labor and cost, and places a burden on the separation membrane, thus shortening the membrane life.

  In order to solve such problems, usually, the organic wastewater is removed from the organic wastewater by roughing the solids with a pre-filter such as a screen before flowing the organic wastewater into the treatment tank. A method is known (see, for example, Patent Document 3). Further, a method has been proposed in which the residue is adhered to the membrane unit by passing the mesh through a line for transferring activated sludge from the denitrification tank of the treatment tank to the nitrification tank (membrane separation tank) (for example, , See Patent Document 4).

JP-A-7-275668 Japanese Patent No. 3937620 JP 2012-585 A JP 7-299494 A

  However, in the method of Patent Document 3, since the residue includes fibrous materials such as hair and short fibers, it is difficult to completely remove the residue with a prefilter such as a screen. In particular, the short fibers can be entangled with each other in the processing tank or the lower part of the membrane separation device, and can become a core for forming a residue lump. Although a method of removing with a very fine prefilter is also conceivable, since clogging is fast, frequent and high-strength maintenance is required, and turbid components removed by the prefilter increase. The amount of waste may increase, which is not realistic. In addition, the method of Patent Document 4 is effective in suppressing the adhesion and accumulation of residue on the membrane unit, but requires frequent maintenance, and the short fibers cannot be sufficiently removed. was there. In this case, as in the above-mentioned Patent Document 3, short fibers can be removed by adopting a very fine prefilter, but since activated sludge is also included, the progress of clogging is faster, more frequent and higher. Not only does maintenance of strength become necessary, but also power consumption increases.

  Therefore, the present invention provides an organic wastewater treatment method that can suppress the adhesion and accumulation of residues particularly at the lower part of the membrane unit without using chemicals and without requiring much labor and cost. The task is to do.

  The present inventors perform a step of generating a gas-liquid mixed upward flow in the outer peripheral portion of the membrane unit as a cleaning step of the membrane unit, and generating an activated sludge downward flow in the membrane unit, and after the step, The present invention is completed by finding that the above-mentioned problems can be solved by filtering at least part of the activated sludge with a prefilter having a mesh width that allows the microorganisms in the activated sludge to pass through and returning the filtered activated sludge. It came to.

That is, this invention is the following (1)-(5).
(1) The biologically treated water is obtained by solid-liquid separation of the activated sludge by a membrane separator installed so that the organic waste water flows into the filtration tank containing the activated sludge and is immersed in the activated sludge in the filtration tank. An organic wastewater treatment method for obtaining
The membrane separation device is configured such that a plurality of sheet-like separation membranes are arranged such that their membrane surfaces are parallel to each other in the vertical direction and the membrane surfaces are parallel to each other with a predetermined gap therebetween. A membrane unit in which a gap between the membranes opens at least upward and downward, a first air diffusion unit disposed in a vertically lower portion of the membrane unit, and a second disposed in a side portion of the membrane unit With a diffuser unit,
During the solid-liquid separation of the activated sludge, by supplying gas to the first aeration unit, a gas-liquid mixed upward flow for advancing the activated sludge from below to above inside the membrane unit, and the membrane A sludge forward swirling step for generating an activated sludge descending flow for advancing the activated sludge from above to below on the outer periphery of the unit;
After the sludge forward swirl step, gas is supplied to the second aeration unit to generate a gas-liquid mixed upward flow at the outer periphery of the membrane unit and an activated sludge downflow inside the membrane unit. Sludge reverse swirl process,
After the sludge reverse turning step, taking out at least a part of the activated sludge in the filtration tank, filtering it with a prefilter having a mesh width of 0.1 to 10 mm, and returning the filtered activated sludge to the filtration tank; ,
An organic wastewater treatment method characterized by comprising:
(2) The treatment of organic waste water according to (1), wherein the second air diffusion unit is disposed at a position lateral to the membrane unit and perpendicular to the membrane surface of the separation membrane. Method.
(3) The organic wastewater treatment method according to (1) or (2), wherein solid sludge separation of the activated sludge is stopped during the sludge reverse turning process.
(4) The first air diffuser unit and the second air diffuser unit are connected to the same gas supply device, and the supply destination of the gas supplied from the gas supply device is switched by a valve. The method for treating organic waste water according to any one of (1) to (3), wherein a sludge forward turning process and a sludge reverse turning process are switched.
(5) The organic material according to any one of (1) to (4), wherein the sludge reverse swirl step is performed at a frequency of once or more a week and for 1 minute or more per time. Of waste water.

In the present invention, when cleaning the membrane unit, gas is supplied to the second air diffuser unit disposed on the side of the membrane unit, and the gas-liquid mixed upward flow is supplied to the outer periphery of the membrane unit. By performing a sludge reverse swirl process in which an activated sludge descending flow is generated inside the membrane unit, the accumulated residue formed at the lower part of the membrane unit can be peeled off from the membrane unit. Further, after the sludge reverse swirl step, at least a part of the activated sludge in the filtration tank is taken out, filtered with a prefilter having a mesh width that allows the microorganisms in the activated sludge to pass through, and the filtered activated sludge is returned to the filtration tank. By further performing the process, the residue separated in the sludge reverse swirl process can be discharged out of the tank before reattaching to the lower part of the membrane unit in the subsequent sludge forward swirl process. Residues such as short fibers that are difficult to remove with a prefilter as they are grow to some extent under the membrane unit by the sludge forward swirl process and become a lump lump, so they can be removed by passing through the prefilter.
Therefore, according to the present invention, there is provided a method for treating organic waste water that can suppress adhesion and accumulation of residues particularly at the lower part of the membrane unit without using chemicals and without requiring a great amount of labor and cost. Can be provided.

It is the schematic explaining an example of the waste water treatment apparatus for enforcing the processing method of organic waste water. It is a schematic perspective view which shows two adjacent membrane elements in a membrane unit. It is the schematic which looked at the filtration tank of the waste water treatment equipment of the present invention from the side. It is a figure for demonstrating the gas-liquid mixing upward flow and activated sludge downward flow in a sludge forward turning process. It is a figure for demonstrating the gas-liquid mixing upward flow and activated sludge downward flow in a sludge reverse turning process.

Hereinafter, the present invention will be described in more detail.
FIG. 1 is a schematic diagram illustrating an example of a wastewater treatment apparatus for carrying out an organic wastewater treatment method. Organic wastewater is wastewater containing organic matter, and includes, for example, sewage, rural wastewater, and organic industrial wastewater. The organic waste water may be diluted with water.

  In FIG. 1, the wastewater treatment apparatus 1 has a biological treatment tank 20 containing activated sludge M and a filtration tank 10, and a membrane separation device 12 is immersed in the activated sludge M in the filtration tank 10. The membrane separation device 12 includes a membrane unit 13, a first air diffusion unit 14 disposed below the membrane unit 13 in the vertical direction (hereinafter referred to as “vertical lower portion”), and a side portion of the membrane unit 13. The second air diffuser unit 15 is different from the first air diffuser unit 14 disposed in the area. The biological treatment tank 20 includes a prefilter 21 having a mesh width that allows the microorganisms in the activated sludge M to permeate, and the activated sludge M fed to the filtration tank 10 is filtered by the prefilter 21.

  The membrane unit 13 has a plurality of sheet-like separation membranes arranged in parallel so that the membrane surfaces are parallel to each other in the vertical direction and the membrane surfaces are parallel to each other with a predetermined interval. As shown in FIG. 2, for example, a sheet-like separation membrane 132 is disposed on both front and back surfaces of a frame 133 formed of resin, metal, or the like, and communicates with an internal space surrounded by the separation membrane 132 and the frame 133. A plurality of membrane elements 131 having a structure in which a water outlet 134 is provided at the upper part of the frame 133 is arranged, and a gap (intermembrane space) Z between the membrane elements 131 is arranged so as to open at least upward and downward. Yes.

  The first air diffusion unit 14 only needs to have a function of generating air bubbles in the activated sludge. For example, an air diffusion tube having a predetermined hole in a resin or metal pipe, or a cylindrical support tube A fine bubble diffusing tube that generates a fine bubble from the fine slit by supplying an air to the gap between the cylindrical support tube and the elastic member is suitably used. As shown in FIGS. 1 and 3, the first air diffusion unit 14 is disposed in the vertically lower part of the membrane unit 13. If the pressure loss of the first air diffuser unit 14 is too high, power consumption increases, leading to loss of energy savings and economy. Therefore, it is preferable that the pressure loss is low. On the other hand, the air diffused by the first air diffuser unit 14 not only cleans the membrane surface as described above, but also supplies oxygen necessary for microorganisms in the activated sludge M to oxidize and decompose organic wastewater. Therefore, those having high oxygen dissolution efficiency such as fine bubbles are also preferable, and it is preferable that they are appropriately determined depending on the characteristics of the organic waste water and the membrane separation device.

  Similar to the first air diffuser unit 14, the second air diffuser unit 15 only needs to have a function of generating air bubbles in the activated sludge. The second air diffusion unit 15 is for generating a gas-liquid mixed upward flow in the outer peripheral portion of the membrane unit 13 and an activated sludge downward flow in the membrane unit 13, that is, in the intermembrane space Z. A coarse bubble diffusing tube that generates a coarse bubble with a small pressure loss and about 5 to 50 mm is preferable. Further, as shown in FIGS. 1 and 3, it is preferable that the membrane unit 13 is disposed perpendicular to the membrane surface of the membrane element 131 (separation membrane 132) at a side position. As a result, the activated sludge descending flow generated in the intermembrane space Z becomes more uniform, and the effect of removing the residue lump accumulated at the lower part of the membrane unit 13 is increased.

  The first air diffuser unit 14 and the second air diffuser unit 15 are connected to the same gas supply device 31, and the supply destination of the gas supplied from the gas supply device 31 is switched by the valves V1 and V2. Air is released from each air diffuser unit.

Next, the process of processing organic wastewater using the wastewater treatment apparatus 1 of the present invention will be specifically described.
As shown in FIG. 1, the organic wastewater flows into the biological treatment tank 20 through the pipe P5 and the prefilter 21 and is mixed with the activated sludge M. Here, by flowing the organic wastewater into the biological treatment tank through the prefilter 21, it is preferable because a large solid content such as residue contained in the organic wastewater can be roughly removed by the prefilter 21. It is not necessary to intervene. The activated sludge M in the biological treatment tank 20 is sent to the filtration tank 10 through the pipe P4 and returned to the biological treatment tank 20 through the pipe P3 by the pump 33. The filtration tank 10 contains activated sludge with a solid content of 5 to 20 g / L, for example. The inflowing organic wastewater is subjected to biological treatment such as denitrification and oxidative decomposition in the process of contacting the activated sludge M accommodated in the biological treatment tank 20 and the filtration tank 10. For example, the biological treatment tank 20 functions as a denitrification tank when the biological treatment tank 20 does not perform aeration, and functions as an aerobic tank when aeration is performed. When functioning as an aerobic tank, the biological treatment tank 20 and the filtration tank 10 are combined into one treatment tank, and the pipe P3 for circulating and returning sludge may be omitted.

  During the solid-liquid separation of the activated sludge M, gas is supplied from the gas supply device 31 to the first aeration unit 14. The gas is usually air. This gas supply is performed by opening the valve V1 provided in the pipe P1 between the gas supply device 31 and the first air diffusion unit 14 so that the gas supply device 31 and the second air diffusion unit 15 are connected to each other. It is performed by closing the valve V2 provided in the pipe P2 between them. As the gas is diffused from the first aeration unit 14, as shown in FIG. 4, the gas-liquid mixed upward flow F <b> 1 for advancing the activated sludge from the lower side to the upper side inside the membrane unit 13, and the membrane An activated sludge descending flow F2 for advancing the activated sludge from above to below is generated on the outer peripheral portion of the unit 13, and the activated sludge M turns between the inside and the outer peripheral portion of the membrane unit 13 (forward turning). ). This process is called a sludge forward turning process in the present invention.

  In the sludge forward turning process, the amount of air diffused from the first air diffuser unit 14 may be appropriately selected according to the size of the filtration tank 10 and the amount of activated sludge M. For example, 5 to 20 NL / min. / EL ("NL / min / EL" indicates "normal liter per minute per element"), and according to such conditions, the activated sludge M between the inside and the outer periphery of the membrane unit 13 is included. A difference in density occurs and the forward turning occurs.

  The solid-liquid separation of the activated sludge M is carried out by subjecting the activated sludge M to membrane filtration by applying a negative pressure to the secondary side of the separation membrane 132 by a suction means 34 such as a suction pump or a water head difference. The clean separation membrane permeate W obtained by the above is taken out from the treated water outlet 134 of the membrane element 131, gathered in the water collection section 32, and discharged outside the filtration tank 10.

When this sludge forward swirl process is performed, a residue lump may be formed and accumulated in the lower part of the membrane unit 13. Therefore, in the present invention, a sludge reverse turning process is performed in order to remove the residue lump.
In the sludge reverse swirl process, first, gas is supplied from the gas supply device 31 to the second aeration unit 15 disposed on the side portion of the membrane unit 13. The gas is usually air. The gas supply is performed by closing the valve V1 provided in the pipe P1 between the gas supply device 31 and the first air diffusion unit 14 so that the gas supply device 31 and the second air diffusion unit 15 are connected. The operation is performed by opening the valve V2 provided in the intermediate pipe P2. As the gas diffuses from the second air diffuser unit 15, as shown in FIG. 5, the gas-liquid mixed upward flow F <b> 3 is present at the outer periphery of the membrane unit 13, and the activated sludge descends within the membrane unit 13. The flow F4 is generated, and the activated sludge turns between the inside and the outer periphery of the membrane unit 13 in the direction opposite to the forward turning (reverse turning).

  In the sludge reverse turning process, the amount of gas diffused from the second aeration unit 15 may be appropriately selected according to the size of the filtration tank 10, the arrangement of the membrane separation device 12, the amount of activated sludge M, and the like. It is preferable that the air volume is equal to or greater than that in the sludge forward turning process. According to such conditions, the density difference of the activated sludge M is generated between the inside and the outer peripheral portion of the membrane unit 13, and the reverse rotation occurs.

  The installation position of the second air diffuser unit 15 is not particularly limited as long as it is a side part of the membrane unit 13 and the sludge is swirled in a reverse direction. It is good to provide in the position near the same height as the 1st air diffusion unit 14.

By performing the sludge reverse turning process, the accumulated lump formed at the lower part of the membrane unit 13 can be peeled off from the membrane unit 13.
In addition, when performing a sludge reverse turning process, it is preferable to stop the membrane filtration of the activated sludge by a separation membrane. During the sludge reverse turning process, gas diffusion from the first air diffusion unit 14 is stopped, so that bubbles do not come into contact with the membrane surface, and if membrane filtration is performed, the progress of membrane clogging becomes severe. It is.

  In the above, the first air diffuser unit 14 and the second air diffuser unit 15 are connected to the same gas supply device 31, and the supply destination of the gas supplied from the gas supply device is set by the valves V1 and V2. By switching, the sludge forward turning process and the sludge reverse turning process are switched. According to such a configuration, it is not necessary to use a separate gas supply device in each step, so that the method of the present invention can be implemented at low cost.

The sludge reverse turning process is preferably performed at a frequency of once or more a week, preferably 2 to 7 times a week, and 1 minute or more, preferably 5 minutes or more per time. By performing the membrane cleaning at a frequency of once or more per week for one minute or more, adhesion and accumulation of residue on the lower part of the membrane unit 13 can be further suppressed.
In addition, after a sludge reverse turning process is complete | finished, a sludge forward turning process can be performed continuously.

  Next, in the method of the present invention, after the sludge reverse swirl step, at least a part of the activated sludge M in the filtration tank 10 is taken out, filtered through a prefilter 21 having a mesh width that allows the microorganisms in the activated sludge M to pass through, and filtered. A step of returning the activated sludge M to the biological treatment tank 20 is performed.

  At this time, the gas diffused from the first air diffuser unit 14 and the second air diffuser unit 15 may be stopped, or only the air diffused from the first air diffuser unit 14 may be performed. However, it is preferable to stop the air diffuser from the first air diffuser unit 14 and only the air diffuser from the second air diffuser unit 15. Thus, the sediment mass can be efficiently removed by the pre-filter 21 while preventing the sediment mass from re-adhering to the lower part of the membrane unit and preventing sediment sedimentation. Moreover, you may respond by changing the exit to P3 'using the line of the piping P3 which circulates and returns sludge from a filtration tank to a biological treatment tank. Thereby, it can be implemented at low cost without adding to the circulation line necessary for biological treatment.

  The prefilter 21 is preferably one that permeates most of the microorganisms in the activated sludge M and captures most of the residue mass, specifically, a prefilter having a mesh width of 0.1 to 10 mm is preferable. More preferably, it is a prefilter having a mesh width of 0.5 to 5 mm, and most preferably 1 to 3 mm. By using the prefilter 21 having such a mesh width, the target residue lump can be efficiently removed and the loss of microorganisms necessary for biological treatment can be suppressed while suppressing the clogging of the prefilter. it can. As the shape, for example, various screens such as bar screens, mesh screens, drum-type screens and the like, which are used for removing sediment from sewage by a normal membrane separation activated sludge method, and an auto strainer are preferably used. The

The activated sludge M is filtered by the pre-filter 21 and returned to the biological treatment tank 20, whereby the residue separated in the sludge reverse swirl process is reattached to the lower part of the membrane unit 13 in the subsequent sludge forward swirl process. It can be discharged out of the filtration tank 10 before, and the outflow of activated sludge can be suppressed. Residues that are difficult to remove with the prefilter 21 as they are, such as short fibers, have grown to some extent in the lower part of the membrane unit 13 by the sludge forward swirl process, and thus can be removed by passing through the prefilter 21.
Note that the entire activated sludge M taken out from the filtration tank 10 may be filtered by the prefilter 21.

By the treatment method of the present invention, a gas-liquid mixed upward flow is generated at the outer periphery of the membrane unit, and a swirl flow that generates an activated sludge downflow is generated inside the membrane unit. The accumulated residue can be peeled from the membrane unit.
Therefore, it is possible to provide an organic wastewater treatment method that can suppress adhesion and accumulation of residue particularly under the membrane unit without using a chemical solution and without requiring a great deal of labor and cost. .

DESCRIPTION OF SYMBOLS 1 Waste water treatment apparatus 10 Filtration tank 12 Membrane separation apparatus 13 Membrane unit 14 1st air diffuser unit 15 2nd air diffuser unit 20 Biological treatment tank 21 Prefilter 31 Gas supply apparatus 32 Water collecting part 33 Pump 34 Suction means 131 Membrane Element 132 Separation membrane 133 Frame 134 Treatment water outlet P1, P2, P3, P3 ', P4, P5 Piping V1, V2 Valve M Activated sludge W Separation membrane permeate Z Gap

Claims (5)

Organic to obtain biologically treated water by solid-liquid separation of the activated sludge by a membrane separator installed so that the organic waste water flows into the filtration tank containing the activated sludge and is immersed in the activated sludge in the filtration tank A method for treating effluent,
The membrane separation device is configured such that a plurality of sheet-like separation membranes are arranged such that their membrane surfaces are parallel to each other in the vertical direction and the membrane surfaces are parallel to each other with a predetermined gap therebetween. A membrane unit in which a gap between the membranes opens at least upward and downward, a first air diffusion unit disposed in a vertically lower portion of the membrane unit, and a second disposed in a side portion of the membrane unit With a diffuser unit,
During the solid-liquid separation of the activated sludge, by supplying gas to the first aeration unit, a gas-liquid mixed upward flow for advancing the activated sludge from below to above inside the membrane unit, and the membrane A sludge forward swirling step for generating an activated sludge descending flow for advancing the activated sludge from above to below on the outer periphery of the unit;
After the sludge forward swirl step, gas is supplied to the second aeration unit to generate a gas-liquid mixed upward flow at the outer periphery of the membrane unit and an activated sludge downflow inside the membrane unit. Sludge reverse swirl process,
After the sludge reverse turning step, taking out at least a part of the activated sludge in the filtration tank, filtering it with a prefilter having a mesh width of 0.1 to 10 mm, and returning the filtered activated sludge to the filtration tank; ,
An organic wastewater treatment method characterized by comprising:   The method for treating organic waste water according to claim 1, wherein the second air diffusion unit is disposed perpendicular to the membrane surface of the separation membrane at a position lateral to the membrane unit.   The organic wastewater treatment method according to claim 1 or 2, wherein solid sludge separation of the activated sludge is stopped during the sludge reverse turning process.   The first aeration unit and the second aeration unit are connected to the same gas supply device, and the supply destination of the gas supplied from the gas supply device is switched by a valve, whereby the sludge forward swirl The method for treating organic waste water according to any one of claims 1 to 3, wherein a process and a sludge reverse turning process are switched.   The treatment of organic waste water according to any one of claims 1 to 4, wherein the sludge reverse swirl step is performed at a frequency of once or more a week and for 1 minute or more per time. Method.

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