JP2012157849A - Membrane separation activated sludge apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a membrane separation activated sludge apparatus, which effectively cleans a membrane and supplies oxygen, reduces power consumption and facilitates maintenance.SOLUTION: There is provided the membrane separation activated sludge apparatus wherein an air diffusion device, a membrane separation device, and water stream flowing along a membrane surface of the membrane separation device are formed in an activated sludge treatment tank. In addition, a water stream forming device for forming circulation water stream is provided in or through the activated sludge treatment tank and the air diffusion device is arranged separately from the membrane of the membrane separation device in a plan view.

Description

  The present invention relates to a membrane separation activated sludge apparatus used for treatment of sewage and factory waste water.

  Various types of activated sludge apparatuses are known. Among them, there is an activated sludge treatment tank equipped with a membrane separation device (for example, Patent Document 1). This is to separate and extract the treated water with a membrane while performing activated sludge treatment. For example, as shown in FIG. 5, the activated sludge treatment tank 1 has a membrane separation device 2 and aeration devices 3, 3 ′. The air is supplied with oxygen to the activated sludge bacteria and the membrane surface is cleaned with bubbles.

JP 2004-337787 A

Usually, the membrane is always scrubbed (diffused) from directly below the membrane, and coarse bubbles (bubble diameter 1 to 10 mm) are exclusively used to enhance the cleaning effect. Aeration is aimed at supplying oxygen to activated sludge in addition to cleaning the membrane, but the oxygen dissolution efficiency is about 10% in the case of coarse bubbles compared to 20% in the case of aeration with fine bubbles. As low as about%. Therefore, in many cases, the scrubbing required for membrane cleaning alone cannot supply the oxygen of the activated sludge, and aeration with fine bubbles is performed separately, which increases the power consumption of the blower. Usually, the power consumption of the membrane separation activated sludge method is about 0.8 kWh / m ³ , and the operation cost is very large compared to the value of the standard activated sludge method. In addition, since air bubbles are used for cleaning the membrane, the air diffuser is located directly under the membrane separator, and the maintenance must be performed after removing the membrane separator and taking it out of the tank. I didn't get that, and it took extra effort and time.

  An object of the present invention is to provide a membrane separation activated sludge apparatus that can efficiently perform membrane cleaning and oxygen supply, reduce power consumption, and can be easily maintained.

  The present invention has been made in order to solve the above-mentioned problems. By forming a water flow using mechanical force and making this a flow along the membrane surface from above the membrane separation device, there is no aeration. However, it has been found that the membrane can be washed only with a water flow.

  As a result, not only can the power consumption be reduced, but also the diffuser can be used only for the purpose of supplying oxygen to the activated sludge, so it can be moved from directly below the membrane separator to another position. Maintenance can be easily performed without removing the membrane separator.

  The present invention has been made on the basis of these findings, and in the activated sludge treatment tank, an air diffuser, a membrane separator, and a water flow that flows along the membrane surface of the membrane separator, A membrane comprising a water flow forming device for forming a circulating water flow in or through the activated sludge treatment tank, wherein the air diffuser is installed separately from the membrane of the membrane separation device in a plan view A separation activated sludge apparatus is provided.

  In the above apparatus, the inventors of the present invention preferably have a water flow rate in the membrane module of 0.1 to 1.0 m / s, and in order to generate this flow rate with low power, a turning mechanism is attached as mechanical force. We have also found that the use of a propeller-type underwater stirrer and a water pump is effective. Furthermore, it has been found that by intermittently performing aeration, the shearing force on the film surface can be increased and the cleaning effect of the film can be enhanced.

  Therefore, the present invention provides a device in which the water flow forming device is a propeller type underwater stirrer and / or a water flow pump with a swivel mechanism, and the water flow rate formed by the water flow forming device is 0.1-1 in the membrane module. The present invention also provides a device that is 0.0 m / s and a device in which the air diffuser can be intermittently operated.

  The present invention eliminates the need for an air diffuser for cleaning the membrane surface, facilitates maintenance, greatly reduces power consumption, and reduces activated sludge treatment costs.

It is side surface sectional drawing which shows schematic structure of an example of the apparatus of this invention. It is side surface sectional drawing which shows schematic structure of the experimental apparatus which investigated the membrane cleaning effect by a water flow. It is a graph which shows the result of having investigated the time-dependent change of transmembrane pressure difference by changing the flow rate of water using this experimental apparatus. It is a side view which shows schematic structure of another example of the apparatus of this invention. It is side surface sectional drawing which shows schematic structure of the conventional apparatus.

  The activated sludge treatment tank, which is the main body of the apparatus of the present invention, is a tank that accommodates and works activated sludge. The shape can take various forms such as a cylindrical shape, but is usually a box shape.

  A membrane treatment apparatus is provided in the activated sludge treatment tank. The membrane separates activated sludge and treated water, and a microfiltration membrane or an ultrafiltration membrane can be applied for the pore size of the membrane. As the shape of the membrane, a flat membrane type, a hollow fiber type, a tubular type or the like can be used, and a membrane having an appropriate area is installed based on the permeation flux of the membrane and the amount of treated water. The arrangement of the membranes is usually parallel to each other so as not to disturb the water flow.

  The water flow forming device forms a water flow by mechanical force, and there is a method of installing a stirrer and a submersible pump. It is suitable because it can be uniformly stirred. On the other hand, since the water flow pump can discharge a strong water flow with directionality, it is suitable for the apparatus of the present invention. In the present invention, it has been found that this water flow is a flow along the membrane surface, and that the membrane surface can be cleaned only by the water flow.

  This was confirmed with the apparatus shown in FIG. This device consists of a single hollow fiber (average outer diameter: 1.45 mm, length: 20 cm, material: PVDF, type: UF membrane) and a tube made of transparent vinyl chloride with an upper and lower end closed (inner diameter: 8 mm). Installed inside. A valve (normally closed) was attached to the upper end of the hollow fiber, and the inside of the hollow fiber could be decompressed with a suction pump. A beaker was placed under the hollow fiber to receive treated water that passed through the hollow fiber, and its weight could be measured with a balance. On the other hand, an activated sludge tank was provided outside the system, and an activated sludge circulation line was formed by connecting pipes to the upper and lower parts of the vinyl chloride cylinder. A circulation pump and a flow rate adjusting valve were provided in the middle of the circulation line. A pressure gauge was attached to measure the pressure difference inside and outside the hollow fiber. This flow rate was obtained by dividing from the pump flow rate and the cross-sectional area of a cylinder with an inner diameter of 8 mmΦ. The flow rate in the cylinder was changed to 0.1 m / s and 0.56 m / s, membrane separation of the treated water was performed, and the change over time in the differential pressure at each flow rate was measured. The obtained results are shown in FIG. 3, and as shown in the figure, the transmembrane pressure difference is almost constant at a flow rate of 0.56 m / s, indicating that the membrane cleaning is performed well.

The flow rate of this water flow is 0.1 to 1.0 m / s, preferably 0.4 to 0.6 m / s. If it is less than 0.1 m / s, the cleaning effect of the membrane becomes insufficient, the increase in the transmembrane pressure difference and the membrane filtration flux are lowered, and the treatment capacity is lowered. On the other hand, if it exceeds 1.0 m / s, accumulation of sludge can be suppressed on the membrane surface and stable membrane filtration treatment can be performed, but it is necessary to use an excessively high power pump, resulting in an increase in power consumption.
The direction of the water flow is parallel to the membrane surface, and when the membrane is installed in the vertical direction, either upward flow or downward flow may be used, but since there is no air diffuser at the bottom of the membrane, maintenance is improved. Down flow is preferred.

It is preferable that the water outlets are uniformly distributed so that the water flows through the entire membrane.
Further, in order to smoothly form a circulating water flow in the activated sludge treatment tank, it is preferable to provide a baffle plate that partitions the inside of the tank in the vertical direction. When a diffuser for activated sludge bacteria is installed in one chamber partitioned by a baffle plate, an upward flow is formed in the chamber by the diffused bubbles. Therefore, when a membrane separation device is installed in the other chamber, a circulating water flow is formed in the tank, so that the water flow of the membrane separation device becomes a downward flow.

  In the present invention, the air diffuser is provided in a plan view, that is, separated from the membrane of the membrane separator as viewed from above. This allows maintenance such as repair and cleaning without removing the membrane separation device. This air diffuser jets bubbles to supply oxygen to activated sludge. The structure may be basically the same as that of a normal air diffuser, and a large number of air jets are provided in a manifold having a shape such as a box or a tube. The air outlet may be a fine hole, and a nozzle may be attached. The diameter of the air outlet is determined so as to form fine bubbles in order to increase the oxygen dissolution efficiency, and the diameter of the bubbles should be about 0.5 to 4 mm, particularly about 0.5 to 1.0 mm. . If the bubble diameter is too large, sufficient oxygen dissolution efficiency cannot be obtained, and if it is too small, the pressure loss of the air diffuser is high and it is difficult to perform stable operation. A bubble diameter of 0.5 to 1.0 mm is preferable because an oxygen dissolution efficiency of 30 to 40% can be obtained.

  The amount of diffused air is determined from the amount of oxygen required for activated sludge.

  Further, it is preferable to change the flow rate instead of a constant flow from the viewpoint of the cleaning effect, and this effect can be obtained by making the generation of water flow by aeration or mechanical stirring an intermittent flow. The intermittent flow mechanism can be controlled by an airline solenoid valve timer. However, a separate air storage chamber is provided in the airline, and the discharge port of the air storage chamber opens at a certain pressure or higher. This can be realized easily. The opening interval is about 1 to 30 times / minute, preferably about 5 to 15 times / minute. When the opening interval is too small, the cleaning effect of the film is insufficient, and sludge accumulates on the film surface, so that clogging of the film proceeds.

  In addition, the activated sludge treatment tank is appropriately provided with a dissolved oxygen concentration meter, a pH meter, a thermometer, and the like.

  A schematic configuration of a membrane separation activated sludge apparatus according to an embodiment of the present invention is shown in FIG.

  The activated sludge treatment tank 1 of this device is box-shaped, and a membrane separation device 2, an air diffuser 3 and a water flow forming device 4 are installed therein.

  The membrane separation device 2 is a device in which a large number of hollow fiber type membranes are arranged vertically, and the upper and lower ends are connected to a water collecting part, and a filtrate can be obtained by a suction pump. In many cases, the pore diameter of the membrane is in the range of about 0.01 to 1 μm, and particularly in the range of 0.02 to 0.5 μm, a clear treated water quality is obtained and an economical permeate flux is obtained. Often used in

  A water pump was used as the water flow forming device 4. The water flow pump 4 is attached outside the activated sludge apparatus tank 1 and connected to the bottom of the activated sludge apparatus tank 1 while a drawing pipe is provided on the upper surface of the membrane separation apparatus 2. . This pipe is branched into multi-tubes on the way, and a large number of nozzles are arranged uniformly so that the entire membrane can be washed with water vertically downwardly.

The air diffuser 3 has a flat plate or straight pipe shape, and the surface is made of rubber, a metal plate, a ceramic sintered body, or the like, and a large number of pores for releasing bubbles are formed. The bubbles released from the pores have a diameter of about 1.5 mm immediately above the diffuser surface. Each straight pipe is connected by a connecting pipe and connected to the blower 5 outside the tank.
The activated sludge tank is provided with a baffle plate 6 that vertically partitions between the membrane separation device 2 and the air diffuser 3, and is partitioned into two chambers so that a circulating water flow can be smoothly formed between the two chambers.

FIG. 4 shows a schematic configuration of a membrane separation activated sludge apparatus which is another embodiment of the present invention.
This apparatus is the same as that of Example 1 except that a propeller type underwater stirrer with a turning mechanism is used for the water flow forming device 4.

  The water flow formed by this stirrer forms a swirl flow in the activated sludge treatment tank and is attached to the lower part of the side surface of the treatment tank 1 opposite to the membrane separation device so as to be a downward flow in the membrane installation section. . With this equipment configuration, the downward flow velocity on the membrane surface was able to be 0.4 m / s at the maximum. Moreover, in this apparatus, the aeration was intermittently implemented by providing a pressure valve in the air supply part of the aeration apparatus.

The results of comparing the power for treating 1 m ³ of sewage when the water flow pump of Example 1 is used, when the propeller stirrer of Example 2 is used, and when performing conventional aeration cleaning are shown. Table 1 shows.

  According to the present invention, the maintenance of the activated sludge treatment apparatus can be facilitated, and the electric power used for the apparatus can be greatly reduced, so that it can be widely used in membrane separation activated sludge treatment equipment.

DESCRIPTION OF SYMBOLS 1 Activated sludge processing tank 2 Osmotic membrane separator 3, 3 'Air diffuser 4 Water flow forming device 5, 5' Blower 6 Baffle plate

Claims (4)

  In the activated sludge treatment tank, an air diffuser, a membrane separator, and a water flow that flows along the membrane surface of the membrane separator are formed, and a circulating water stream is formed in or through the activated sludge treatment tank. A membrane separation activated sludge apparatus comprising a water flow forming device, wherein the air diffuser is installed separately from a membrane of the membrane separation device in a plan view.   The membrane separation activated sludge apparatus according to claim 1, wherein the water flow forming device is a propeller type submerged stirrer and / or a water flow pump with a turning mechanism.   The membrane separation activated sludge device according to claim 1 or 2, wherein a flow rate of water formed by the water flow forming device is 0.1 to 1.0 m / s in the membrane module.   The membrane separation activated sludge apparatus according to any one of claims 1 to 3, wherein the air diffuser is capable of intermittent operation.

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