JP2004305926A - Submerged membrane separation activated sludge treatment method - Google Patents

Abstract

Provided is a submerged membrane separation activated sludge treatment method capable of suppressing clogging of a filtration membrane due to a residual polymer flocculant and reducing maintenance frequency of membrane cleaning while maintaining a predetermined permeation flux in a membrane separation apparatus. I do.
SOLUTION: Sludge separation water discharged from a dehydration facility 54 is returned to a processing tank 53 in a state where supply of water to be processed to one processing tank (for example, 53) is stopped, and a membrane separation device 55 of the processing tank 53 is provided. In the membrane separation device 55 of the other treatment tanks 51 and 52, while operating while suppressing the permeation flux, the operation is performed with a predetermined permeation flux, and the treatment tanks 51 and 52 for supplying the water to be treated and the sludge separation water are separated. The processing tank 53 to be returned is changed every predetermined time.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to a submerged membrane separation activated sludge treatment method, in which water to be treated is introduced into a treatment tank to be subjected to activated sludge treatment, and the contamination contained in the activated sludge and the treated water is carried out by a membrane separation apparatus immersed and installed in the tank. The present invention relates to a technique for solid-liquid separation of an object.
[0002]
[Prior art]
BACKGROUND ART Conventionally, in industrial wastewater treatment, domestic wastewater treatment, sewage treatment, and the like, it is general to treat organic wastewater with activated sludge. As the activated sludge treatment, for example, as shown in FIG. 2, a method of immersing and installing a membrane separation device 2 in a treatment tank 1 to perform solid-liquid separation has recently become widespread. This membrane separation device 2 has a plurality of flat plate-shaped membrane cartridges 4 arranged vertically in a case 3 having an open top and bottom, and an air diffuser 5 disposed below the membrane cartridge 4. The membrane cartridge 4 has a flat membrane-like organic membrane adhered to the front and back of a filter plate.
[0003]
In the treatment tank 1, oxygen is added to the mixed liquid while circulating the mixed liquid of the water to be treated and the activated sludge containing the pollutants in the tank by the upward flow of the solid-gas-liquid mixed phase generated by the air diffused from the diffuser 5. It is dissolved and the organic matter in the polluted matter is biologically removed by the microorganism of the activated sludge. The mixed solution is supplied to the flow path between the membrane cartridges 4 by a cross-flow along the membrane surface by the upward flow to the membrane separation device 2, and the water head inside the treatment tank 1 is used as a driving force (filtration water head). In 4, the mixed solution is separated into solid and liquid, and the membrane-treated water that has passed through the filtration membrane of the membrane cartridge 4 is led out of the tank by the outlet system 6. A suction pressure can be applied to the membrane cartridge 4 by a suction pump or the like as a driving force for filtration.
[0004]
Excess sludge in the treatment tank 1 is guided to a stirring tank 8 by a sludge extraction system 7, and a flocculant is formed by stirring and mixing a flocculant. The dewatered cake discharged from the dewatering device 9 is discharged out of the system and incinerated or landfilled.
[0005]
If the polymer flocculant added in the dehydration process completely reacts with the sludge, unreacted polymer flocculant (hereinafter referred to as residual polymer flocculant) is not contained in the sludge separation water. Depending on the properties of the polymer, the reactivity with the polymer flocculant may be low, and the sludge separation water contains a large amount of the residual polymer flocculant.
[0006]
For this reason, the sludge separation water is guided to the coagulation and sedimentation treatment tank 11 in the separation water system 10, and the residual polymer coagulant is removed by a physicochemical treatment such as adding a detoxifying agent to coagulate and separate the sludge. Is returned to the treatment tank 1.
[0007]
As a prior art document of this kind, there is one described in Patent Document 1.
[0008]
[Patent Document 1] JP-A-11-57799
[Problems to be solved by the invention]
However, since the residual polymer flocculant is removed by reacting the cationic residual polymer flocculant with the anionic or inorganic flocculant in the flocculation / sedimentation treatment tank 11, the residual polymer flocculant is removed if the added amount is incorrectly adjusted. It is difficult to completely remove the polymer flocculant. When the dewatered return water containing the residual polymer flocculant flows into the treatment tank 1, a gel layer of the polymer flocculant is formed on the filtration membrane of the membrane separation device 2, and the permeation flux decreases due to clogging of the membrane. Adversely affects the maintenance of the membrane cleaning. Since the gel layer grows faster as the permeation flux in the membrane cartridge of the membrane separation device is larger, and grows slower as the permeation flux is smaller, the gel layer is grown by performing the operation with a smaller permeation flux. The frequency of maintenance of membrane cleaning can be reduced by suppressing the frequency. However, when the membrane separation device is operated with a small permeation flux, in order for the membrane separation device to exhibit a predetermined processing capacity with respect to the load given by the water to be treated flowing into the system, the membrane cartridge is required. It is necessary to increase the total membrane area of the filtration membrane in the membrane separation device by increasing the number of membranes.
[0010]
The present invention solves the above-described problems, and can reduce the maintenance frequency of membrane cleaning by suppressing clogging of a filtration membrane due to a residual polymer flocculant while maintaining a predetermined permeation flux in a membrane separation device. An object of the present invention is to provide a submerged membrane separation activated sludge treatment method.
[0011]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the immersion type membrane separation activated sludge treatment method of the present invention conducts biological treatment by guiding the water to be treated to a plurality of treatment tanks, and the inside of the tank is separated by a membrane separation device immersed in each treatment tank. A immersion type membrane separation activated sludge treatment method in which the mixed liquid is subjected to solid-liquid separation to take out the membrane treatment water, and the excess sludge in each treatment tank is guided to a dehydration facility, and a coagulant is added and dewatered.
The sludge separation water discharged from the dehydration equipment is returned to the processing tank in a state in which the supply of the water to be processed to one processing tank is stopped, and the operation is performed while suppressing the permeation flux in the membrane separation device of the processing tank. In a membrane separation device of another treatment tank, the treatment tank is operated at a predetermined flux and the treatment tank for supplying the water to be treated and the treatment tank for returning the sludge separation water are changed every predetermined time.
[0012]
By the above-described configuration, the system for treating the water to be treated in the treatment tank and the system for treating the sludge separation water in the treatment tank are operated separately, so that the residual polymer flocculant is treated in the treatment tank for treating the water to be treated. There is no adverse effect such as a decrease in the permeation flux due to the gel layer derived from the above, and the duration of the normal operation performed at a predetermined permeation flux, that is, the period up to the time when backwashing is required, is lengthened. In addition, it is also possible to increase the processing capacity by setting a predetermined permeation flux in the normal operation to be large, and to reduce the capacity of the treatment tank by increasing the permeation flux and shortening the residence time in the tank. The power of the pneumatic device can be reduced.
[0013]
On the other hand, in a treatment tank for treating sludge separated water, it is possible to operate the sludge separated water in accordance with the properties of the sludge separated water while suppressing the permeation flux. Biological treatment of waste organic matter and residual polymer flocculant, foaming can be suppressed, and clogging of the filter membrane due to the residual polymer flocculant can be suppressed, and the period until backwashing becomes necessary can be extended. . The sludge separation water can be pretreated and returned to the treatment tank.
[0014]
By the way, if the operation with a short residence time in the tank is continued in the activated sludge treatment, the number of microorganisms in the activated sludge in the treatment tank decreases, and it becomes difficult to decompose metabolites generated in the biological treatment. May cause
[0015]
However, by changing the treatment tank for supplying the water to be treated and the treatment tank for returning the sludge separation water at predetermined time intervals, in each treatment tank, a predetermined permeation flux and a short residence time in the tank are used. The high load operation to be performed and the low load operation to be performed under a long residence time in the tank with suppressed permeation flux are performed alternately. By accumulating and decomposing metabolites generated in biological treatment, membrane clogging can be prevented and the frequency of backwashing can be significantly reduced. In addition, when the water to be treated is supplied to the treatment tank that has treated the sludge separation water, the residual polymer flocculant remaining in the tank can help the pollutants in the water to be treated to adhere to the activated sludge. It helps to prevent clogging.
[0016]
Therefore, the system for treating the water to be treated in the treatment tank and the system for treating the sludge separated water in the treatment tank are operated separately, and the treatment tank for returning the sludge separated water is changed at predetermined time intervals. By alternately performing high-load operation and low-load operation, membrane clogging of the filtration membrane due to residual polymer flocculant is suppressed while maintaining biological treatment capacity and solid-liquid separation capacity for the water to be treated as a whole. Cleaning maintenance frequency can be reduced.
[0017]
In addition, by separately operating the system for treating the water to be treated in the treatment tank and the system for treating the sludge separated water in the treatment tank, the solid matter is contained in the sludge separated water by saving the flocculant in the concentration and dewatering process of the dewatering equipment. Even if the residue remains, a safe treatment system that does not affect the treatment process of the water to be treated can be configured at all, so that the use of an expensive flocculant can be suppressed as much as possible.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In FIG. 1, treated water 50 is organic sewage in industrial wastewater treatment, domestic wastewater treatment, sewage treatment, etc., and the immersion type membrane separation activated sludge treatment equipment includes a plurality of treatment tanks 51, 52, 53 and a dewatering equipment 54. Consists of
[0019]
A membrane separation device 55 is immersed in each of the processing tanks 51, 52, 53. The membrane separation device 55 has a plurality of flat plate-shaped membrane cartridges 57 arranged vertically in a case 56 having an open top and bottom, and an air diffuser 58 disposed below the membrane cartridge 57. is there. The membrane cartridge 57 has a flat membrane-like organic membrane adhered to the front and back of the filter plate. The membrane cartridge 57 has a secondary side connected to the membrane water pipe 59 through a tube and a water collection pipe, and is sucked into the membrane water pipe 59. A pump 60 is provided.
[0020]
In a raw water supply pipe 61 for supplying the water 50 to be treated, raw water branch pipes 62, 63, and 64 communicate with the processing tanks 51, 52, and 53 via raw water valves 65, 66, and 67, respectively. Sludge extraction pipes 68, 69, and 70 for discharging excess sludge from the processing tanks 51, 52, and 53 communicate with each other through sludge valves 71, 72, and 73, and communicate with the dewatering facility 54. The dewatering equipment 54 is composed of a stirring tank 74 and a dewatering device 75. Separated water pipes 76 for discharging sludge separated water are connected to respective separated water branch pipes 77, 78, 79 through separated water valves 80, 81, 82, respectively. It communicates with tanks 51, 52, and 53.
[0021]
Hereinafter, the operation of the above configuration will be described.
First, the basic operation of each of the processing tanks 51, 52, 53 and the dewatering equipment 54 will be described. In each of the treatment tanks 51, 52, and 53, air is diffused from a diffuser 58 to a mixed solution of the water 50 to be treated supplied from the raw water branch pipes 62, 63, and 64 and the activated sludge retained in the tanks. By dissolving oxygen in the mixed solution while circulating the mixed solution inside the processing tanks 51, 52 and 53 by the upward flow of the solid-gas-liquid mixed phase generated by the air lift action of air, the organic matter in the polluted matter by the microorganisms of the activated sludge Is removed by biological treatment.
[0022]
The mixed solution is supplied to the membrane separation device 55 to the flow path between the membrane cartridges 57 by an upward flow in a cross flow along the membrane surface. The membrane separation device 55 operates by using a transmembrane pressure generated between the primary side and the secondary side of the membrane cartridge 57 as a driving force by the suction pressure given by the suction pump 60, and filters the mixed solution by filtering through the filtration membrane of the membrane cartridge 57. Is separated into solid and liquid, and the membrane-treated water that has passed through the filtration membrane is discharged out of the system through the membrane-treated water pipe 59.
[0023]
The permeation flux in each membrane cartridge 57 of the membrane separation device 55 increases as the transmembrane pressure increases, and decreases as the filtration resistance due to the cake layer attached to the membrane surface of the filtration membrane increases with time. Become. For this reason, during normal operation of the membrane separation device 55, the suction pressure given by the suction pump 60 is adjusted to control the transmembrane pressure difference, and the flow rate of the membrane treatment water measured by the flow meter 83 is kept constant, so that the permeate flow is maintained. The bundle is controlled to a predetermined value.
[0024]
In the present embodiment, the operation of the membrane separation device 55 is performed by forcible suction filtration using suction pressure given by the suction pump 60. As another method, the transmembrane pressure generated by the suction pressure given by the suction pump 60 is controlled within the range of the head from the water surface in each of the processing tanks 51, 52, 53 to the membrane separation device 55, and the two Gravity filtration can be performed by setting the next side to a positive pressure (a pressure higher than the atmospheric pressure).
[0025]
Excess sludge in the treatment tanks 51, 52, and 53 is led to the stirring tank 74 of the dewatering facility 54 through the sludge withdrawals 68, 69, and 70, and the flocculant is formed by stirring and mixing the flocculant. . The dewatered cake discharged from the dehydrator 75 is discharged out of the system and incinerated or landfilled.
[0026]
The sludge separation water containing the residual polymer flocculant is returned to any of the treatment tanks 51, 52, 53 through the separation water pipe 76 as dewatered return water. The amount of the sludge separation water varies depending on the properties of the water to be treated 50, but is about 2 to 10% of the water to be treated 50, for example, when the sewage is about 100 to 500 mg / L BOD.
[0027]
Hereinafter, the operation of the immersion type membrane separation activated sludge treatment facility will be described. By opening the raw water valves 65 and 66 and closing the raw water valve 67 and opening the separation water valve 82 and closing the separation water valves 80 and 81, the first and second treatment tanks 51 and 52 can be opened. The water to be treated 50 is supplied, the supply of the water to be treated 50 to the third treatment tank 53 is stopped, and the sludge separation water discharged from the dehydration equipment 54 is returned to the third treatment tank 53, and the first and second waters are returned. The supply of the sludge separation water to the processing tanks 51 and 52 is stopped.
[0028]
In this state, while operating the membrane separation device 55 of the first and second treatment tanks 51 and 52 for supplying the water to be treated 50 at a higher set value which is a predetermined permeation flux in normal operation, sludge separation water is removed. The membrane separation device 55 of the third processing tank 53 to be supplied is operated while being suppressed to a lower set value equal to or lower than a predetermined permeation flux.
[0029]
Then, the processing tanks 51 and 52 for supplying the water to be treated 50 and the processing tank 53 for returning the sludge separation water are changed every time a predetermined time elapses. The predetermined time during which the treatment tanks 51, 52, 53 are changed depends on the biological growth rate in the biological treatment tank for treating the water to be treated 50 or the biological growth rate in the biological treatment tank for sludge separation water, and the growth rate is high. In this case, the set value of the predetermined time is shortened, and when the growth rate is low, the set value of the predetermined time is increased.
[0030]
The treatment tanks 51, 52 and 53 are changed by opening and closing the raw water valves 65, 66 and 67 and the separation water valves 80, 81 and 82, and the water to be treated 50 is changed from the above-described state to the second and third treatment tanks. 52, 53, and change to a state in which the sludge separated water is supplied to the first treatment tank 51, or the water to be treated 50 is supplied to the first and third treatment tanks 51, 53, and the sludge separated water is supplied. The state is changed to the state of supplying to the second processing tank 52, and the state is sequentially changed every predetermined time.
[0031]
The timing of extracting the excess sludge through the sludge extraction 68, 69, 70 depends on the quality of the dewatered return water returned through the separation water pipe 76. For example, if the amount of pollutants in the dewatered return water is relatively large, excess sludge will be generated during the treatment of the dewatered return water. After receiving the dewatered return water, the excess sludge is extracted.
[0032]
It should be noted that the processing tanks 51, 52, and 53 can be changed by operating pumps individually instead of operating valves.
The permeation flux of the membrane separation device 55 affects the residence time of the water 50 to be treated in the treatment tanks 51, 52, and 53. The larger the permeation flux, the shorter the residence time in the tank, and the smaller the permeation flux. The residence time in the tank becomes longer. For this reason, the upper set value of the permeation flux is set by an empirical rule according to the properties of the water 50 to be treated, and the permeation flux that realizes the residence time in the tank necessary for sufficiently biologically treating the water 50 to be treated. And In addition, the lower set value of the permeate flux is set by an empirical rule according to the properties of the sludge separation water, and the residence time in the tank necessary for biologically treating the sludge separation water containing the residual polymer flocculant is realized. In addition, a permeation flux that can suppress the growth of the gel layer derived from the residual polymer flocculant is used.
[0033]
As described above, by separately operating the system for treating the water 50 to be treated in the treatment tanks 51 and 52 and the system for treating the sludge separated water in the treatment tank 53, the treatment tank 51 for treating the water 50 to be treated is separated. , 52, the water to be treated 50 can be biologically treated without adverse effects such as a decrease in the permeation flux due to the gel layer derived from the residual polymer flocculant, In other words, the period until the time when backwashing is required becomes longer. In addition, it is also possible to increase the processing capacity by setting a predetermined permeation flux in the normal operation to be large, and to shorten the residence time in the tank by increasing the permeation flux to reduce the capacity of the processing tanks 51, 52, and 53. And the power of the air diffuser 58 can be reduced.
[0034]
On the other hand, in the treatment tank 53 for treating the sludge separation water, the operation is performed while suppressing the permeation flux, thereby suppressing the clogging of the filtration membrane due to the residual polymer flocculant to reduce the period up to the time when back washing is required. The sludge separation water can be made longer, and the residence time in the tank of the sludge separation water can be lengthened to biologically treat the organic matter and the residual polymer flocculant contained in the sludge separation water.
[0035]
By the way, when the operation in which the residence time in the tank is short is continued in the activated sludge treatment, the number of microorganisms in the activated sludge in the treatment tanks 51, 52, and 53 decreases, and it becomes difficult to decompose metabolites generated in biological treatment. May cause clogging of the membrane.
[0036]
However, by changing the processing tanks 51, 52, 53 for supplying the water to be treated 50 and the processing tanks 51, 52, 53 for returning the sludge separation water at predetermined time intervals, the processing tanks 51, 52, 53 have A high-load operation performed under a short tank residence time at a predetermined permeation flux and a low-load operation performed under a long tank residence time at a suppressed permeation flux are alternately performed, Changes in the internal environment of each of the processing tanks 51, 52, 53 acclimate various microorganisms to activated sludge and decompose metabolites generated in biological treatment, thereby preventing clogging of the membrane and significantly increasing the frequency of backwashing. Can be reduced.
[0037]
【The invention's effect】
As described above, according to the present invention, the system for treating the water to be treated in the treatment tank and the system for treating the sludge separated water in the treatment tank are operated separately, and the treatment tank for returning the sludge separated water is operated for a predetermined time. By alternately performing high-load operation and low-load operation in each treatment tank in each treatment tank, the treatment tank that treats the water to be treated has a predetermined permeation flux without being affected by the residual polymer flocculant. Normal operation can be continued for a long time to reduce the frequency of backwashing.In the treatment tank that treats sludge separation water, the sludge retention time in the tank is lengthened by reducing the permeation flux according to the properties of the sludge separation water to increase the sludge retention time. The organic matter and the residual polymer flocculant contained in the separated water are subjected to biological treatment, whereby clogging of the filtration membrane by the residual polymer flocculant can be suppressed, and the frequency of backwashing can be reduced. In addition, by alternately performing high-load operation and low-load operation in each treatment tank, it is possible to accumulate various microorganisms in activated sludge and decompose metabolites generated in biological treatment, thereby preventing membrane clogging, The frequency of backwashing can be significantly reduced. Therefore, clogging of the filtration membrane due to the residual polymer flocculant can be suppressed while maintaining the biological treatment ability and solid-liquid separation ability for the water to be treated as the entire apparatus, and the maintenance frequency of membrane cleaning can be reduced.
[Brief description of the drawings]
FIG. 1 is a flow sheet diagram showing a submerged membrane separation activated sludge treatment facility according to an embodiment of the present invention.
FIG. 2 is a flow sheet diagram showing a conventional immersion type membrane separation activated sludge treatment facility.
[Explanation of symbols]
50 treated water 51, 52, 53 treatment tank 54 dehydration equipment 55 membrane separation device 56 case 57 membrane cartridge 58 air diffuser 59 membrane treatment water pipe 60 suction pump 61 raw water supply pipes 62, 63, 64 raw water branch pipes 65, 66, 67 Raw water valves 68, 69, 70 Sludge extraction pipes 71, 72, 73 Sludge valve 74 Stirrer tank 75 Dehydrator 76 Separated water pipes 77, 78, 79 Separated water branch pipes 80, 81, 82 Separated water valves

Claims (1)

The water to be treated is guided to a plurality of treatment tanks for biological treatment, and the mixed liquid in the tanks is separated into solid and liquid by a membrane separator immersed in each treatment tank to take out the membrane treatment water, and excess sludge in each treatment tank is removed. A immersion type membrane separation activated sludge treatment method in which a coagulant is added and dewatered by leading to a dehydration facility,
The sludge separation water discharged from the dehydration equipment is returned to the processing tank in a state in which the supply of the water to be processed to one processing tank is stopped, and the operation is performed while suppressing the permeation flux in the membrane separation device of the processing tank. An immersion type membrane operated by a predetermined permeation flux in a membrane separation device of another processing tank, and a processing tank for supplying water to be treated and a processing tank for returning sludge separation water are changed every predetermined time. Separation activated sludge treatment method.

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