JP2004237202A - Membrane separation type activated sludge treatment apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently perform aerobic treatment with activated sludge without bringing about an oxygen deficiency while keeping the washing effect of the membrane surface of a membrane separation means. <P>SOLUTION: In the membrane separation type activated sludge treatment apparatus equipped with an aerobic tank 10 for biologically and aerobically treating water to be treated by activated sludge held in the tank, the membrane separation means 14 immersed in the aerobic tank 10, an air diffusing means 18 for diffusing air from the area under the membrane separation means 14 and a suction pump 24 for discharging treated water permeated through the membrane separation means 14, an air bubble pulverizing means 30, which finely pulverizes air bubbles diffused from the air diffusing means 18 to arrive at the upper region of the membrane separation means 14 by rotary blades 32, is provided. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a membrane separation type activated sludge treatment apparatus, and more particularly to a membrane separation type activated sludge treatment apparatus in which a membrane separation means is immersed in an aerobic tank holding activated sludge.
[0002]
[Prior art]
2. Description of the Related Art A membrane separation type activated sludge treatment device is used as a device for efficiently removing organic substances, nitrogen, phosphorus, and the like in water to be treated. FIG. 4 is a side sectional view schematically showing a membrane separation type activated sludge treatment apparatus of this type. The to-be-processed water which flowed in from the to-be-processed water inflow pipe 2 is stuck in the aerobic tank 1. In the aerobic tank 1, activated sludge is previously held at a high concentration, and the membrane separation means 3 is immersed. As the membrane separation means 3, a structure having a structure in which a large number of rectangular flat membranes each having a separation membrane stretched on both sides are arranged side by side at small intervals in the horizontal direction is generally used. A diffuser 4 is provided below the membrane separator 3, and diffuses air supplied from the blower 5 toward the membrane separator 3. The membrane separation means 3 is provided with a suction pump 6 for discharging treated water permeated through the flat membrane to the outside of the apparatus in the middle of a discharge pipe 7.
[0003]
In the above configuration, the water to be treated that has flowed into the aerobic tank 1 is biologically aerobicly treated by activated sludge, and organic substances, nitrogen, phosphorus, and the like in the water to be treated are removed. In the membrane separation means 3, the membrane is separated by the suction force of the suction pump 6, and the activated sludge and the treated water are separated into solid and liquid. The treated water that has passed through the flat membrane is discharged to the outside of the apparatus through a discharge pipe 7. As a result, the activated sludge stays in the aerobic tank 1, and the activated sludge is maintained at a high concentration in the aerobic tank 1 together with the multiplication by the aerobic treatment.
[0004]
The air diffuser 4 has three purposes. The first purpose is to keep the inside of the aerobic tank 1 aerobic. Since oxygen is consumed in the biological aerobic treatment by activated sludge, oxygen is supplemented by aeration to keep the dissolved oxygen in the water to be treated in the aerobic tank 1 high. The second purpose is to clean the separation membrane of the membrane separation means 3. Activated sludge and various solids adhere and accumulate on the membrane surface of the flat membrane due to membrane separation, and if left as it is, the permeability of the separation membrane will gradually decrease, so air is diffused for the purpose of cleaning the membrane surface. Is That is, the air bubbles diffused from below the membrane separation means 3 rise by buoyancy. During the ascent process, a shearing force is applied to the film surface of the flat film, and the solid matter adhered and deposited on the film surface is peeled off. The third object is to form a circulating flow of the water to be treated in the aerobic tank 1. The upward flow of the water to be treated occurs in the membrane separation means 3 with the rising force of the diffused air bubbles, and the water to be treated is sucked from below the membrane separation means 3. The to-be-processed water pushed out above the membrane separation means 3 then goes down the flow path 8 and is sucked again from below the membrane separation means 3. In the process of circulating the water to be treated, the water to be treated and the activated sludge are sufficiently mixed and contacted, and the aerobic treatment with the activated sludge actively proceeds.
[0005]
Thus, the membrane separation type activated sludge treatment apparatus can simultaneously perform the aerobic treatment with activated sludge and the solid-liquid separation in the aerobic tank 1. For this reason, compared with the conventional activated sludge treatment apparatus provided with a sedimentation basin, the sedimentation basin can be omitted, and the apparatus can be made compact and highly efficient.
[0006]
However, there are difficult problems in simultaneously achieving the three purposes of the aeration. In order to achieve the first object, it is necessary to increase the gas-liquid contact area per unit volume by minimizing the diffused air bubbles as much as possible. However, when the air bubbles are made finer, the rising force of the air bubbles decreases, and a sufficient shearing force cannot be applied to the membrane surface of the membrane separation means 3. Therefore, the effect of cleaning the film surface, which is the second object, is reduced. In addition, the formation of the circulation flow, which is the third object, becomes insufficient. Conversely, if the air bubbles diffused by giving priority to the second and third purposes are made coarse, the efficiency of dissolving oxygen in the water to be treated decreases, and the efficiency of aerobic treatment with activated sludge also decreases due to lack of oxygen. There is. Thus, there is a trade-off relationship between the first object and the second and third objects with respect to the size of the air bubbles to be diffused, and it is extremely difficult to simultaneously achieve the three objects only by air diffusion. .
[0007]
Patent Document 1 discloses a configuration in which a baffle plate is provided in the vicinity of a liquid surface of a reaction tank in order to solve the above-described problems of the related art. According to this configuration, the air bubbles that have risen in the liquid collide with the baffle plate and are dispersed along the lower surface, thereby improving the oxygen dissolving efficiency. It is also disclosed that a projection is provided on the lower surface of the baffle plate to break air bubbles, thereby improving the oxygen dissolving efficiency.
[0008]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 10-263852
[Problems to be solved by the invention]
According to the configuration described in Patent Document 1, although an improvement in oxygen dissolving efficiency of about 10% is recognized, such a static baffle plate is insufficient for further improving oxygen dissolving efficiency. It is. In particular, when the activated sludge held in the aerobic tank has a high concentration of about 10,000 mg / L, the aerobic treatment proceeds promptly, so that the water to be treated circulates in the process of circulating in the aerobic tank. There was a problem that shortage occurred and the efficiency of aerobic treatment with activated sludge also decreased.
[0010]
SUMMARY OF THE INVENTION An object of the present invention is to improve the drawbacks of the above-mentioned prior art, and to perform aerobic treatment with activated sludge efficiently without causing oxygen deficiency while maintaining the cleaning effect on the membrane surface, and a membrane separation type activated sludge treatment apparatus. Is to provide.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, a membrane separation type activated sludge treatment apparatus according to the present invention includes an aerobic tank for biologically and aerobicly treating water to be treated with activated sludge held in a tank; Membrane separation means immersed in a tank, air diffusion means for diffusing air from below the membrane separation means, and treated water discharge means for discharging treated water permeated by the membrane separation means The activated activated sludge treatment apparatus is characterized in that a bubble refining means is provided for refining air bubbles diffused from the air diffusing means and reaching the upper region of the membrane separation means by rotating blades. Further, the present invention is characterized in that, in the above configuration, the operation of the bubble miniaturization means is controlled based on the dissolved oxygen concentration of the water to be treated in the aerobic tank.
[0012]
[Action]
According to the present invention, the coarse air bubbles reaching the upper region of the membrane separation means are dynamically made finer by the rotating blades, so that the specific surface area per unit volume of the air bubbles in the upper region is remarkable. To increase. Therefore, the oxygen dissolving efficiency in the upper region is improved, and the concentration of dissolved oxygen in the water to be treated can be kept high. Therefore, even when the activated sludge held in the aerobic tank is made to have a high concentration, oxygen deficiency does not occur, and the aerobic treatment with the activated sludge can be efficiently performed while maintaining the effect of cleaning the membrane surface.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a front sectional view schematically showing a first embodiment of a membrane separation type activated sludge treatment apparatus according to the present invention, and FIG. 2 is a side sectional view thereof. The treated water flowing from the treated water inflow pipe 12 is inserted into the aerobic tank 10. In the aerobic tank 10, activated sludge is held at a high concentration in advance, and the membrane separation means 14 is immersed. The membrane separation means 14 has a structure in which a large number of rectangular flat membranes 16 having separation membranes stretched on both sides are arranged side by side in a horizontal direction at a narrow pitch. The gap between the adjacent flat membranes 16 is 4 to 10 mm, and membrane separation is performed while the water to be treated passes through the narrow gap.
[0014]
An air diffuser 18 is provided immediately below the membrane separator 14, and diffuses air supplied from the blower 20 toward the membrane separator 14. The air diffuser 18 has a structure in which a plurality of air diffusers 19 are arranged side by side at a predetermined pitch in the lateral direction, and each air diffuser 19 has a large number of air diffuser holes. Air having a relatively large bubble diameter is diffused from the air diffusion holes. A discharge pipe 22 is connected to the membrane separation means 14, and the treated water that has passed through the flat membrane 16 is discharged outside the apparatus by a suction pump 24 provided in the middle of the discharge pipe 22. In the upper region of the membrane separation means 14, there is formed a collecting part 28 which is surrounded on all sides by an inclined plate 26 and has a narrow upper opening. At the upper opening of the collecting section 28, a bubble miniaturizing means 30 having a rotating blade 32 is arranged. A flow path 34 for circulating the water to be treated is formed between the side surface of the aerobic tank 10 and the side surface of the membrane separation means 14.
In the above configuration, the water to be treated that has flowed into the aerobic tank 10 is mixed with the activated sludge maintained at a high concentration in the tank, and is biologically aerobic treated by the activated sludge, and the organic matter and nitrogen in the water to be treated are treated. , Phosphorus and the like are removed. In the membrane separation means 14, the upward flow of the water to be treated is caused by the rising force of the air bubbles diffused from the diffusion means 18, and the activated sludge and the water to be treated are sucked in a mixed state from below the membrane separation means 14. It is. In the membrane separation means 14, the membrane is separated by the suction force of the suction pump 24, and the treated water that has passed through the flat membrane 16 is discharged to the outside of the apparatus through the discharge pipe 22. As a result, the activated sludge stays in the aerobic tank 10, and the activated sludge is maintained at a high concentration in the aerobic tank 10 together with the multiplication by the aerobic treatment. Further, the oxygen supplied by the air diffusion from the air diffusion means 18 is dissolved in the water to be treated, and the inside of the aerobic tank 10 is kept aerobic. Dissolved oxygen dissolved in the water to be treated is used and consumed in biological aerobic treatment with activated sludge. The supply of oxygen by the aeration and the consumption of oxygen by the aerobic treatment are balanced so that the dissolved oxygen in the water to be treated in the aerobic tank 10 is maintained within a certain range.
[0016]
As described in the section of the prior art, the air diffusion from the air diffusion means 18 is also intended for cleaning the membrane surface of the membrane separation means 14. The size of the air bubbles to be diffused is important for effective cleaning. For this reason, each air diffuser pipe 19 is provided so that the diameter of the air bubbles to be diffused is 50 to 80% with respect to the gap (normally 4 to 10 mm) between the adjacent flat membranes 16 of the membrane separation means 14. Select the diameter of the aeration holes to be drilled. If the diameter of the air bubbles is less than the above range, the rising force of the air bubbles becomes too small, so that a sufficient shearing force cannot be applied to the film surface of the flat film 16, and the cleaning effect is reduced. In addition, the formation of a circulating flow of the water to be treated becomes insufficient. Conversely, when the diameter of the air bubbles exceeds the above range, the frictional resistance between the larger air bubbles and the membrane surface increases due to the coalescence of the air bubbles, and the air bubbles smoothly fill the gap between the flat membranes 16. It does not rise, leading to unstable driving. Such instability of the operation particularly hinders the smooth formation of the circulating flow of the water to be treated and exerts an excessive impact on the surface of the flat membrane 16 to shorten the life of the membrane.
[0017]
However, the size of the air bubbles during the aeration is not suitable for the purpose of dissolving the oxygen supplemented by the aeration into the water to be treated and increasing the dissolved oxygen in the water to be treated. Therefore, in the present embodiment, the air bubbles reaching the upper region of the membrane separation means 14 are reduced by the bubble reduction means 30 by playing the role of cleaning the membrane surface and forming a circulating flow of the water to be treated. That is, the air bubbles that have reached the upper region of the membrane separation means 14 repeat the coalescence of the air bubbles in the process of passing through the gap between the flat membranes 16 and become coarser than in the case of air diffusion, and the oxygen dissolving efficiency is low. It is in. The coarse air bubbles are guided to the upper opening by the inclined plate 26 of the collecting part 28. The rotating blades 32 of the bubble miniaturizing means 30 are arranged in the upper opening, and the air bubbles passing through the upper opening are dynamically reduced by rotating the rotating blades 32. Such a rotating blade 32 is convenient because the number of rotations thereof can be changed to adjust the level of fineness of the air bubbles. It is sufficient that the rotary blade 32 has a stirring function. However, it is more preferable to use a structure that also functions as an axial pump, because it is useful for forming a circulating flow of the water to be treated.
[0018]
The air bubbles refined by the rotating blades 32 have a significantly increased specific surface area per unit volume. Therefore, the oxygen dissolving efficiency is improved, and the concentration of dissolved oxygen in the water to be treated can be kept high. Moreover, since the microbubble air bubbles have a small buoyancy, they are less likely to separate from the water to be treated and dissipate upward. For this reason, the contact time with the water to be treated increases, and the oxygen dissolving efficiency improves. In addition to the air bubbles being finer, the rotating blades 32 disintegrate loosely the activated sludge mixed with the water to be treated and increase the activity of the activated sludge.
[0019]
The water to be treated whose dissolved oxygen concentration has increased in the upper region of the membrane separation means 14 descends along the flow path 34 along the circulating flow, and is again sucked in from below the membrane separation means 14 and circulated. The aerobic treatment with the activated sludge continuously proceeds in all regions in the process of circulating the water to be treated, and the aerobic treatment also proceeds at the stage where the water to be treated descends in the flow path 34. The dissolved oxygen in the water to be treated is consumed as the aerobic treatment proceeds, and the concentration of dissolved oxygen in the water to be treated gradually decreases toward the downstream side of the flow path 34. However, in this embodiment, the concentration of dissolved oxygen in the water to be treated is sufficiently high in the upper region, so that there is no shortage of oxygen in the middle of the flow path 34, and the aerobic treatment with activated sludge is stably maintained. can do.
[0020]
In addition, when the load of the organic matter and nitrogen flowing into the aerobic tank 10 is small, the amount of oxygen consumed in the aerobic treatment is also reduced almost in proportion. In such a case, it is assumed that the amount of dissolved oxygen necessary for the aerobic treatment can be sufficiently covered only by the air diffuser 18. Therefore, in this embodiment, a sensor 36 for detecting the dissolved oxygen concentration of the water to be treated is provided downstream of the flow path 34. The detection value of the sensor 36 is transmitted to the controller 38, and the controller 38 controls the operation of the bubble miniaturization means 30 based on the dissolved oxygen concentration of the water to be treated transmitted from the sensor 36. That is, when the concentration of dissolved oxygen in the water to be treated is equal to or higher than the set value, the operation of the bubble refining means 30 is stopped, and only when the dissolved oxygen concentration is less than the set value, the bubble refining means 30 is operated. At this time, the set value is preferably set to 1 to 2 ppm. By performing such control, useless operation of the bubble miniaturization means 30 can be eliminated, and energy can be saved.
[0021]
As described above, in the membrane separation type activated sludge treatment apparatus according to the present embodiment, the diffuser 18 diffuses relatively large air bubbles to clean the membrane surface of the membrane separator 14 and to treat the water to be treated. Stabilizes the formation of a circulating flow. Further, since the coarse air bubbles reaching the upper region of the membrane separation means 14 are forcibly miniaturized by the rotating blades 32, the dissolved oxygen concentration in the water to be treated can be kept high. Therefore, even when the activated sludge held in the aerobic tank 10 is made to have a high concentration, oxygen deficiency does not occur, and the aerobic treatment with the activated sludge can be efficiently performed while maintaining the cleaning effect on the membrane surface. . Furthermore, since the operation of the bubble refining means 30 is controlled based on the dissolved oxygen concentration of the water to be treated in the aerobic tank 10, the bubble refining means is controlled when the load of the organic matter or nitrogen of the water to be treated is small. 30 can be eliminated, and energy saving can be achieved.
[0022]
FIG. 3 is a front sectional view schematically showing a second embodiment of the membrane separation type activated sludge treatment apparatus according to the present invention. In the figure, elements denoted by the same reference numerals as those in FIG. 1 have the same functions as those in FIG. In the present embodiment, a rotating shaft 42 is supported in a region above the membrane separation means 14 so as to cross the aerobic tank 10, and a plurality of bubble cutting blades 44 are provided on the rotating shaft 42. The bubble refiner 40 refines the air bubbles by rotating the rotary blade composed of the rotating shaft 42 and the bubble cutting blade 44 at a predetermined number of revolutions. In FIG. 3, when the membrane separation means 14 is long and continuous in the direction perpendicular to the paper, a plurality of the bubble miniaturization means 40 are arranged in parallel in the direction perpendicular to the paper. According to the bubble refining means 40 according to the second embodiment, all the air bubbles reaching the upper region of the membrane separation means 14 are finely reduced without requiring a special structure for collecting the air bubbles. be able to.
[0023]
【The invention's effect】
According to the present invention, since the coarse air bubbles reaching the upper region of the membrane separation means are forcibly reduced by the rotating blades, the specific surface area per unit volume of the air bubbles in the upper region is increased. I do. Therefore, the oxygen dissolving efficiency in the upper region is improved, and the concentration of dissolved oxygen in the water to be treated can be increased. Therefore, even when the activated sludge held in the aerobic tank is made to have a high concentration, oxygen deficiency does not occur, and the aerobic treatment with the activated sludge is efficiently performed while maintaining the cleaning effect of the membrane surface of the membrane separation means. be able to.
[Brief description of the drawings]
FIG. 1 is a front sectional view schematically showing a first embodiment of the present invention.
FIG. 2 is a side sectional view schematically showing the first embodiment of the present invention.
FIG. 3 is a front sectional view schematically showing a second embodiment of the present invention.
FIG. 4 is a side sectional view schematically showing a membrane separation type activated sludge treatment apparatus according to a conventional technique.
[Explanation of symbols]
10 ... aerobic tank, 12 ... inflow pipe, 14 ... membrane separation means, 16 ... flat membrane, 18 ... diffuser means, 19 ... diffuser pipe, 20 ... blower , 22 ... discharge pipe, 24 ... suction pump, 26 ... inclined plate, 30 ... bubble miniaturization means, 32 ... rotating blades, 34 ... flow path, 36 ... sensor , 38... Controller, 40... Bubble miniaturization means, 42... Rotating shaft 44... Bubble cutting blades.

Claims (2)

An aerobic tank for biologically aerobic treatment of the water to be treated with activated sludge held in the tank, a membrane separation means immersed in the aerobic tank, and air diffused from below the membrane separation means. In a membrane separation type activated sludge treatment apparatus provided with a diffuser means for performing treatment and a treated water discharge means for discharging treated water permeated by the membrane separation means. A membrane separation type activated sludge treatment apparatus characterized in that a bubble refining means is provided for refining air bubbles having reached a region by a rotating blade. The activated sludge treatment device according to claim 1, wherein the operation of the bubble refining means is controlled based on the dissolved oxygen concentration of the water to be treated in the aerobic tank.

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