TWI411583B - A method for driving air diffusing device - Google Patents

Abstract

This invention relates to a method for driving air diffusing device which is disposed in an activated sludge aeration tank, and includes an air diffusing unit that supplies air to be diffusion, and an air supplying unit that supplies air to be diffusion to the air diffusing unit, wherein the air diffusing unit includes at least one of air diffusing pipes arranged substantially horizontally, and which has a plurality of air diffusing holes formed on the vertical side of the air diffusing pipe and at least one of inlet/outlet for sludge formed on the underside of the air diffusing pipe, the method including: supplying air to be diffused from the air supplying unit toward the air diffusing unit such that a pressure head &Dgr; H of each of the air diffusing pipe calculated by the following formula (I) is regulated within the range from 0.2 to 0.9 times the inner diameter of the air diffusing pipe d1, and stopping supplying the air to be diffused without opening the inside of the air diffusing pipe to atmosphere.

Description

Operating method of the diffusing device

The present invention relates to a method of operating a diffusing device used in a diffused gas in an activated sludge aeration tank.

In the past, a diffusing pipe in which a plurality of air holes are formed is disposed in an activated sludge aeration tank, and a gas for diffusing air such as air is discharged into the tank to treat the activated sludge.

In the activated sludge treatment, as the treatment progresses, the activated sludge is dried and consolidated in the diffusing pipe, and also accumulates around the diffusing holes, so that the diffusing holes are closed and the exhaust gas becomes unstable.

As a method for solving such a problem, for example, Patent Document 1 describes a method of supplying a cleaning liquid to a diffusing pipe and cleaning the inside of the diffusing pipe to remove the sludge.

Patent Document 2 describes a diffusing pipe in which a discharge port is formed in a lower portion of a diffusing pipe and a tip end is bent downward to open. Further, it is described that an air supply pipe connecting the air diffusing pipe and the blower is provided with a valve for opening the pressure in the air diffusing pipe to atmospheric pressure. Further, it is described that the supply of air from the air blower is stopped to stop the air release, and the valve is opened to open the pressure in the air diffusing pipe to the atmospheric pressure, so that the sludge in the tank flows back into the air diffusing pipe from the opening of the front end or the like. According to this method, since the sludge deposited by drying in the vicinity of the discharge port can be wetted, the humidified sludge can be caused to flow away when the air is started next time.

Patent Document 3 describes that an extension to the lower side than the diffuser is provided. The long pipe portion is provided with an opening portion in the extension pipe portion to discharge the sludge remaining in the air diffusion pipe from the opening portion. Further, it is described that the sludge is washed away by intermittently supplying water to the air diffusing pipe before the sludge is dried and enlarged.

[Advanced technical literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2004-305886

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2002-307091

[Patent Document 3] Japanese Patent No. 3322206

However, in the method described in Patent Document 1, it is necessary to provide a line for cleaning liquid for supplying a cleaning liquid to the air diffusing pipe, and a device installation cost is required.

In the method described in Patent Document 2, after the air is stopped, the valve provided in the air supply pipe is opened, and the pressure in the air pipe is lowered to the atmospheric pressure. Therefore, the sludge in the tank is not only diffused in a large amount. The inside of the trachea and a large amount flow into the air supply pipe. Specifically, the sludge also flows into the air supply pipe until it reaches a height corresponding to the liquid level of the sludge in the tank. When such a large amount of sludge flows into the air supply pipe, a large load is applied to the blower at the next start of the air blow, and a large amount of sludge adheres to the air supply pipe and is dried, and if the sludge is transported to the air pipe , there is also the problem of occluding the diffusing holes.

Further, as described in Patent Document 3, in the method of discharging sludge only from the open portion located below the diffusing pipe, it is not easy to peel the sludge firmly adhered to the periphery of the diffusing hole. Therefore, as a result, it is necessary to use a cleaning method in which water is intermittently supplied to the diffusing pipe, so that it is required to be supplied. Water equipment setup fee.

The present invention has been made in view of the above circumstances, and an object of the invention is to provide a method for operating a diffusing device that prevents an excessive load from being applied to a blower (gas supply unit) or prevents a device from being occluded. Dry consolidation of sludge from the trachea.

The inventors of the present invention have found that a plurality of diffusing holes for discharging the gas for diffusing gas are formed in the upper portion of the diffusing portion such as the diffusing pipe, and the sludge for entering and leaving the diffusing portion in the lower portion is formed in the lower portion. The above problem can be solved by repeating the supply and the stop of the gas for the diffusion of the air diffusing portion.

The present invention for solving the above problems has the following aspects.

(1) A method of operating a diffusing device, comprising: a diffusing portion disposed in an activated sludge aeration tank to discharge a gas for diffusing air; and a gas supply unit that supplies the diffusing portion to the diffusing portion In the gas gas, the air diffusing portion includes one or more air diffusing pipes arranged substantially horizontally, and a plurality of air diffusing holes are formed in a vertical upper portion of the air diffusing pipe, and one or more sludges are formed in a root portion of the air diffusing pipe. In the hole, the pressure head ΔH calculated by the following formula (I) is a value of 0.2 times to 0.9 times the inner diameter d ₁ of the diffuser pipe, and the gas supply unit is used. The gas for diffusing gas is supplied to the air diffusing portion, and the supply step of supplying the gas for diffusing gas from the gas supply portion to the air diffusing portion is repeated, and the gas for diffusing gas is stopped without opening the atmosphere in the air diffusing pipe. The stop step of the supply.

Where △H: pressure head (m)

ρ: density of activated sludge (kg/m ³ )

ρ': density of gas for diffusion (kg/m ³ )

v: ejection speed of the gas for diffusion from each of the air holes (m/sec)

C: the elution coefficient represented by the following formula (II)

g: gravitational acceleration (m/s ² )

[Number 2] C = 0.597 - 0.011m + 0.432m ² (II)

Wherein m is an opening ratio represented by the following formula (III)

Where A ₀ : area of each diffusing hole (m ² )

A _I : sectional area of the diffusing pipe (area of the inner diameter reference of the surface perpendicular to the longitudinal direction) (m ² )

d ₀ : diameter of each diffusing hole (m)

d _I : inner diameter of the diffuser (m)

(2) The method of operating a diffusing device according to (1) above, wherein the supplying step is performed for 30 minutes to 12 hours, and the stopping step is performed for 15 seconds to 600 seconds.

(3) The method of operating a diffusing device according to (2) above, wherein the inner diameter d ₁ is 10 mm to 100 mm.

(4) The method of operating a diffusing device according to any one of the above (1), wherein the air diffusing hole has a diameter of 1.5 mm to 30 mm.

(5) A diffusing device comprising: a diffusing portion disposed in an activated sludge aeration tank to discharge a gas for diffusing gas; and a gas supply unit that supplies the gas for diffusing air to the diffusing portion, the gas The apparatus is characterized in that: 1) the air diffusing portion includes one or more air diffusing tubes arranged substantially horizontally; and 2) a plurality of air diffusing holes are formed in a vertical upper portion of the air diffusing duct, and a lower portion of the air diffusing duct is formed at a lower portion of the air diffusing duct One or more sludge inlet and outlet holes; 3) In the tube connecting the gas diffusion pipe and the gas supply pipe, the pressure in the gas diffusion pipe is kept self-active even in the stop step of stopping the supply of the gas for diffusion gas The water pressure from the water surface of the sludge aeration tank to the air vent is connected to the pressure equivalent.

(6) The air diffusing device according to (5) above, wherein a pipe is disposed in a pipe connecting the air diffusing pipe and the air pipe valve.

(7) The air diffusing device according to (6) above, wherein the valve is a three-way valve, and the three-way valve is connected to the air diffusing pipe, the air supply pipe, and the exhaust pipe.

According to the present invention, the excessive load is not applied to the blower (gas supply portion), or the newly installed equipment is not required, and the dry consolidation of the sludge toward the air diffusing tube that blocks the air diffusion hole can be prevented.

The above and other objects, features and advantages of the present invention will become more <RTIgt;

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a configuration diagram schematically showing an example of a wastewater treatment device including a gas diffusion device that is suitably used in the present invention.

The wastewater treatment apparatus 10 of this example includes an activated sludge aeration tank 12 into which activated sludge 11 as a water to be treated is introduced, and is immersed in the activated sludge aeration tank 12, and includes a membrane element for solid-liquid separation ( a membrane separation device of the membrane element 13; and a gas diffusion device 20 for discharging a gas for diffusion in the activated sludge aeration tank 12. The membrane element 13 for solid-liquid separation is configured by including a separation membrane such as a hollow fiber membrane in this example. Further, the suction mechanism 16 including the suction pipe 14 and the suction pump 15 is connected to the membrane element 13 for solid-liquid separation, and suction filtration can be performed.

The air diffusing device 20 includes a diffusing pipe (distributing portion) 21 that is disposed substantially horizontally in the vicinity of the bottom portion of the activated sludge aeration tank 12, and a gas supply portion for supplying the gas for diffusing gas to the diffusing pipe 21. twenty two. The diffuser tube is preferably disposed such that its gradient in the axial direction is within 1/50, preferably within 1/100.

The air diffusing pipe 21 of this example is constituted by a circular pipe having a circular cross section perpendicular to the longitudinal direction (hereinafter referred to as a vertical cross section), and a plurality of (up to six in the example of Fig. 1) are used for discharging. The circular diffusing holes 23 of the gas for diffusing gas are formed in a row along the longitudinal direction, and on the other hand, in the lower portion of the peripheral wall, the circular sludge inlet and outlet holes 24 for allowing the activated sludge 11 to enter and exit the diffusing pipe 21 are In this example, it is formed as one. Specifically, in the air diffusing hole 23 and the sludge inlet and outlet hole 24 of this example, the center of each hole is located at the intersection of the vertical line (the vertical line in the vertical direction) intersecting the axis of the air diffusing pipe 21 and the peripheral wall of the air diffusing pipe 21 And configured. That is, in this example, the air diffusing holes 23 are disposed such that the center of each of the air diffusing holes 23 is located at the intersection of the vertical line in the vertical direction intersecting the axis of the air diffusing pipe 21 and the peripheral wall of the air diffusing pipe 21. Further, the sludge inlet/outlet hole 24 is disposed such that the center of the sludge inlet and outlet hole 24 is located at the intersection of the vertical line in the vertical downward direction intersecting the axis of the air diffusing pipe 21 and the peripheral wall of the air diffusing pipe 21. The diffusing pipe 21 is made of, for example, a synthetic resin such as polycarbonate, polyfluorene, polyethylene, polypropylene, acrylic resin, Acrylonitrile Butadiene Styrene (ABS) resin, vinyl chloride resin or the like. Metal and so on.

Further, the lower portion of the peripheral wall here is a peripheral wall of a portion located lower than the axis of the diffusing pipe 21. When the center of the sludge inlet and outlet hole 24 is located at the lower portion of the peripheral wall At this time, the sludge inlet and outlet hole 24 is formed in the lower portion of the air diffusing pipe 21.

The sludge inlet and outlet holes are preferably formed by a line whose center is drawn from the axis of the air diffusion pipe 21 in the vertical downward direction and which is formed within a range of 45 degrees or less on the peripheral wall, more preferably within 30 degrees.

The gas supply unit 22 includes a blower 25 as a gas supply mechanism, and an air supply pipe 26 that connects the blower 25 and the air diffusing pipe 21. In this example, the air supply pipe 26 is also connected to the one end 21a of the air diffusing pipe 21 as shown in FIG. 2A, and the air for exhaust gas from the air blower 25 is supplied into the air diffusing pipe 21. The sludge inlet/outlet hole 24 of the air diffusing pipe 21 is formed in the vicinity of the other end 21b of the closed side opposite to the one end 21a of the air diffusing pipe 21 to which the air supply pipe 26 is connected. Further, in the air supply pipe 26 of this example, as shown in FIG. 1, the exhaust pipe 27 is branched to dissipate and discharge the gas for diffusion in the air supply pipe 26 to the atmosphere, and a three-way valve is provided at the branch portion. 28. Further, the gas supply unit 22 of this example includes the control device 29, and the operations of the blower 25 and the three-way valve 28 are automatically controlled by the control device 29.

According to this configuration, the air diffusing pipe of the air diffusing device of the present invention has a structure in which the pressure in the pipe is not opened to the atmosphere even when the air is stopped. For example, in FIG. 1, since the three-way valve 28 is used, if the three-way valve 28 is opened to allow the blower 25 to communicate with the exhaust pipe 27, the supply of air can be stopped without stopping the blower, and the pressure inside the pipe of the diffusing pipe can be Maintained.

Further, as shown in Figs. 2A and 2B, the number of valves may be two valves or one valve.

In the method of operating the diffusing device of the present invention, the supply step of supplying the gas for diffusing gas from the gas supply unit 22 to the diffusing pipe 21 is repeated, and the stopping is performed. The step of stopping the supply of the gas for diffusion from the gas supply unit 22.

Specifically, first, the three-way valve 28 is operated by the control device 29 so that the blower 25 communicates with the air diffusing pipe 21, and the exhaust pipe 27 side is closed. Then, the blower 25 is actuated, and the gas for a predetermined flow rate is supplied to the air diffusing pipe 21 through the air supply pipe 26 (supply step).

Here, as for the gas for diffusing gas, air is usually used, and oxygen or the like may be used as needed. Further, the flow rate of the gas for diffusion gas is usually set to a flow rate required for the activated sludge treatment (biological treatment), but in the case of performing the diffusion of gas in the apparatus including the membrane separation apparatus as in the wastewater treatment apparatus of this example, The flow rate of the gas for diffusion can also be determined from the viewpoint of effectively cleaning the film surface of the membrane separation device.

Then, after the supply step of supplying the gas for diffusion is completed for a predetermined period of time, the supply of the gas for diffusion to the gas diffusion pipe 21 is stopped (stop step). When the supply of the gas for diffusion is stopped, the blower 25 itself can be stopped, but the three-way valve 28 can be operated by the control device 29 to connect the blower 25 with the exhaust pipe 27, thereby making the branch portion of the air supply pipe 26 The flow path on the downstream side (the side of the diffuser pipe 21) is closed. By this, in the stop step, the supply of the gas for diffusion of the air diffusing pipe 21 is stopped, and the pressure in the air diffusing pipe 21 (in-pipe pressure) is maintained without being opened to the atmospheric pressure in the air diffusing pipe 21.

Then, after the stop step of stopping the supply of the gas for the diffusion gas reaches a predetermined time, the supply step of supplying the gas for diffusion from the gas supply unit 22 to the air diffusion pipe 21 is performed again.

In this way, the air diffusing device 20 includes a diffusing pipe 21 which is formed with a plurality of air diffusing holes 23 for discharging the gas for diffusing gas in the vertical upper portion, and the other In the lower portion, one or more sludge inlet and outlet holes 24 through which the activated sludge 11 enters and exits the gas diffusion pipe 21 are formed. According to the operation method in which the supply step and the stop step are repeated, the blower 25 is not excessively loaded or is not required to be The equipment is newly installed in the drainage treatment device, and the dry consolidation of the activated sludge 11 toward the air diffusion pipe 21 that blocks the air diffusion hole 23 can be prevented.

In other words, if the air diffusing hole 23 is provided in the upper portion of the air diffusing pipe 21 as in this example, when the self-feeding step is switched to the stopping step, the gas for diffusing gas remaining in the air diffusing pipe 21 is a specific activated sludge. 11 has a lower specific gravity, so it is discharged upward from the air vent 23 and is discharged upward. Then, the sludge inlet and outlet holes 24 are formed in the lower portion of the air diffusing pipe 21. Therefore, the activated sludge 11 flows into the air diffusing pipe 21 from the sludge inlet and outlet holes 24 in association with the discharge of the gas for the air diffusion. When the air diffusing hole 23 is formed in the upper portion of the air diffusing pipe 21 and the sludge inlet and outlet hole 24 is formed in the lower portion of the air diffusing pipe 21, even if the pressure in the pipe of the air diffusing pipe 21 is not lowered, for example, it is dispersed. The inside of the gas pipe 21 is opened to atmospheric pressure or the like, and the gas for diffusing gas in the diffusing pipe 21 is discharged, and the activated sludge 11 is filled instead. Therefore, in the stop step, the inside of the air diffusing pipe 21 is wetted by the activated sludge 11, and drying and solidification of the activated sludge 11 in the air diffusing pipe 21 can be prevented.

In the case where the air diffusing pipe 21 in which the air diffusing hole 23 and the sludge inlet and outlet hole 24 are formed is used as described above, even if the pressure in the pipe is not lowered, for example, the inside of the air diffusing pipe 21 is opened to the atmospheric pressure or the like. Since the activated sludge 11 flows into the diffusing pipe 21, it is possible to avoid the failure caused by opening the inside of the diffusing pipe 21 to atmospheric pressure.

That is, when switching to the stop step, if the three-way valve 28 is operated, When the exhaust pipe 27 is communicated with the air supply pipe 26 on the side of the air diffusing pipe 21, when the pressure in the pipe is lowered and the pressure is set to atmospheric pressure, not only the inside of the air diffusing pipe 21 but also the inside of the air supply pipe 26 becomes atmospheric pressure. As a result, the activated sludge 11 in the activated sludge aeration tank 12 not only flows into the air diffusing pipe 21 but also flows into the air supply pipe 26 in a large amount. Specifically, in FIG. 1, the activated sludge 11 flows into the air supply pipe 26 until the position indicated by the symbol L1 (the liquid level of the activated sludge 11 in the activated sludge aeration tank 12). As described above, when a large amount of the activated sludge 11 flows into the air supply pipe 26, when the gas for the diffusion gas is started to be supplied in the next supply step, the blower 25 must extrude a large amount of the activated sludge 11 from the air supply pipe 26, and thus the blower 25 Apply excess load. Further, a large amount of activated sludge 11 adheres to the air supply pipe 26 and is dried. If the dried activated sludge 11 is transported to the air diffusing pipe 21, the air diffusing hole 23 may be closed. On the other hand, when switching to the stop step, when the pressure in the tube is maintained without being lowered, even if the activated sludge 11 flows into the air supply pipe 26, it flows into the position indicated by the symbol L2 (with the air vent 23). The height of the formation position corresponds to). Therefore, when the supply of the gas for diffusion is started again in the next supply step, a large load is not applied to the blower 25, and the activated sludge 11 which is easily peeled off in the wet gas pipe 21 can be taken out from the sludge into the hole 24 or scattered. The air holes 23 are discharged to the outside of the air diffusing pipe 21.

Thus, the dry consolidation of the activated sludge 11 toward the air diffusing pipe 21 that blocks the air diffusing holes 23 can be prevented.

Here, the time for continuing the supply of the gas for diffusion, that is, the time for performing the supply step once is preferably from 30 minutes to 12 hours. If the time of one supply step is less than 30 minutes, the blower 25 is started. stop The frequency of the stop, the opening and closing frequency of the three-way valve 28 increase, and the mechanical damage of the blower 25 or the three-way valve 28 occurs early. On the other hand, when the supply step is performed for more than 12 hours, a part of the activated sludge 11 in the air diffusing pipe 21 is dried, and the air diffusing hole 23 may be closed after long-term use.

Further, the time for stopping the supply of the gas for diffusion, that is, the time for performing the first stop step is preferably 15 seconds to 600 seconds. When the time for performing the stop step is less than 15 seconds, there is a possibility that when the activated sludge 11 is not sufficiently flowed into the air diffusing pipe 21, the supply step is switched. On the other hand, when the time of one stop step exceeds 600 seconds, the amount of gas for diffusion in the activated sludge aeration tank 12 required for biological treatment of the activated sludge 11 may be insufficient.

Further, in the case where the activated sludge aeration tank 12 of the membrane separation apparatus is immersed as in this example, the filtration treatment of the membrane separation apparatus usually needs to be stopped when the step is stopped. Therefore, when the time for performing the stop step exceeds 600 seconds, the amount of treated water in the membrane separation device is lowered.

In the supply step, it is preferable that the pressure head ΔH calculated by the following formula (I) is the inner diameter d _{1 of the} diffusing pipe 21 when the gas for a predetermined flow rate is supplied to the air diffusing pipe 21. The discharge velocity v (m/sec) of the gas for diffusion of the gas from each of the air holes 23, the area A ₀ (m ² ) of each of the air holes, and the sectional area of the air diffusing pipe 21 are defined as a value of 0.2 to 0.9 times. (perpendicular to the longitudinal direction of the cross-sectional area of the inner diameter of reference) a ₁ (m ^2), each of the aeration holes of the inner diameter d ₀ 23 (m), diffusing pipe inner diameter d 21 of ₁ (m), is supplied to a bulk The flow rate Q (m ³ /sec) of the gas for gas diffusion of the gas pipe 21 and the number of the air holes 23 are obtained.

The following formula (I) is generally known as a formula used in flow calculation of an orifice.

Where △H: pressure head (m)

ρ: density of activated sludge (kg/m ³ )

ρ': density of gas for diffusion (kg/m ³ )

v: ejection speed of the gas for diffusion from each of the air holes (m/sec)

C: the elution coefficient represented by the following formula (II)

g: gravitational acceleration (m/s ² )

[Number 5] C = 0.597 - 0.011m + 0.432m ² (II)

Wherein m is an opening ratio represented by the following formula (III)

Where A ₀ : area of each diffusing hole (m ² )

A _I : sectional area of the diffusing pipe (area of the inner diameter reference of the surface perpendicular to the longitudinal direction) (m ² )

d ₀ : diameter of each diffusing hole (m)

d _I : inner diameter of the diffuser (m)

In addition, the air diffusing device 20 of the illustrated example includes a diffusing pipe 21, but may also include a plurality of diffusing pipes 21, and in this case, with respect to each of the diffusing pipes 21, a pressure head Δ calculated by the formula (I) is preferable. H is a value 0.2 to 0.9 times the inner diameter d ₁ of the air diffusing pipe 21. In addition, the flow rate Q of the gas for diffusing gas supplied to the one air diffusing pipe 21 is a value obtained by dividing the total flow rate of the air diffused in the activated sludge aeration tank 12 by the number of the air diffusing pipes 21. The number of the air diffusing tubes 21 can be arbitrarily set according to the shape and size of the activated sludge aeration tank 12, and when the membrane separating apparatus is included, it is arbitrarily set according to the shape, the size, the number of installations, and the like.

Further, when the gas for diffusion is air, the density ρ' of the gas for diffusion can be set to 1.2 (kg/m ³ ). Regarding the density ρ of the activated sludge 11, the value is actually measured.

Further, the discharge velocity v (m/sec) of the gas for diffusing gas from the air diffusion hole 23 is a value obtained by dividing the flow rate Q of the gas for diffusion gas supplied to the one air diffusing pipe 21 into the air diffusion pipe. The total area of the air holes 23 of 21 (the area of each air hole × the total number of air holes formed in one air pipe).

Further, in this example, the air diffusing pipe 21 is a circular pipe having a circular cross section, but is not particularly limited to the shape of a vertical cross section, and may be, for example, a polygonal shape such as an elliptical shape or a quadrangular shape. At this time, in the formula (III), m is obtained from the area A _{0 of} each of the diffusing holes 23 and the cross-sectional area A ₁ of the diffusing pipe 21, and the pressure head ΔH is calculated using the m, and the pressure head ΔH can be obtained. The value is set to a value 0.2 to 0.9 times the inner diameter d ₁ .

Further, in the formula, m is an opening ratio, and indicates a ratio of the cross-sectional area A ₁ of the diffusing pipe 21 to the area A ₀ of each of the diffusing holes 23. C is the outflow coefficient.

As described above, the pressure head ΔH calculated by the above formula (I), that is, the pressure acting on the air diffusing pipe 21 is smaller than the pressure corresponding to the inner diameter d ₁ of the air diffusing pipe 21, particularly the inner diameter d ₁ When the gas for the diffusion gas is supplied to the air diffusing pipe 21, that is, in the supply step, the activated sludge 11 flows into the air diffusing pipe 21 from the sludge inlet and outlet holes 24 in the supply step. Therefore, the activated sludge 11 is always present in the diffusing pipe 21 not only in the stop step but also in the supply step, and the inside of the diffusing pipe 21 is kept in a wet state, so that the drying of the activated sludge 11 in the diffusing pipe 21 can be further prevented. Consolidation.

Here, when the pressure head (ΔH) in the formula (I) is a value smaller than 0.2 times the inner diameter d ₁ , the amount of the air diffusing holes 23 and the diameter of the air diffusing holes 23 are supplied to the air. The amount of gas for diffusing gas of the gas pipe 21 is small. Therefore, at this time, unevenness is likely to occur in the amount of the gas for diffusion from the respective air holes 23 . Specifically, there is a tendency that the more the gas is formed in the air vent hole at the position close to the one end 21a of the air diffusing pipe 21 to which the air supply pipe 26 is connected, the more the gas for the air is discharged, and the gas is formed close to the other end 21b. The amount of the gas for diffusing gas discharged from the air holes 23 at the position is small. On the other hand, when the pressure head (ΔH) in the formula (I) is a value exceeding 0.9 times the inner diameter d ₁ , the amount of the gas for diffusing gas supplied into the diffusing pipe 21 in the supply step is large, and therefore, The amount of the activated sludge 11 present in the diffusing pipe 21 in the supply step is reduced, so that it is difficult to maintain the inside of the diffusing pipe 21 in a sufficiently wet state.

Here, the gas supply amount is set to a fixed amount by a valve or the like, but it is of course possible to instantaneously exceed the set amount in the blower start time or the valve opening and closing time.

However, when the supply of the gas is started again, the rapid flow fluctuation occurs in the air diffusing pipe to improve the cleaning effect in the air diffusing pipe.

Therefore, in order to cause a sudden flow rate fluctuation in the air diffusing pipe, the flow rate exceeding the flow rate of the formula (I) is preferably supplied to the air diffusing pipe within 10 seconds. More preferably less than 5 seconds.

Further, at this time, the diameter (inner diameter) of each of the air diffusing holes 23 is preferably set in the range of 1.5 mm to 30 mm. When it is less than 1.5 mm, there is a tendency that the diffusing holes 23 are easily closed due to foreign matter such as inclusions or solids contained in the activated sludge 11. Further, even if the self-feeding step is switched to the stop step, the gas for diffusing gas in the air diffusing pipe 21 is not discharged from the air vent 23 by the action of the surface tension, and as a result, the activated sludge 11 from the sludge inlet and outlet hole 24 is present. There is also a tendency for inflows to be insufficient. On the other hand, if it exceeds 30 mm, the air bubbles of the gas for diffusion from the air vent 23 in the supply step are coarsened, and the dissolution efficiency of the gas for diffusion is lowered, which may cause the biological treatment of the activated sludge 11 The amount of gas is insufficient, or the efficiency of activated sludge treatment is low.

Further, the shape of each of the air holes 23 is not limited to a circular shape.

Each of the air holes 23 is preferably located at the center of each hole as shown in the example. The intersection of the vertical line intersecting the axis of the diffusing pipe 21 and the peripheral wall is formed in a line. When formed in this manner, it is easy to uniformly discharge the gas for diffusion from the respective air holes 23 .

Further, when the center of each hole of the air diffusing hole 23 is located at the intersection of the vertical line and the peripheral wall intersecting the axis of the air diffusing pipe 21, the stoppage step of stopping the supply of the gas for diffusion can be performed from the sludge inlet hole. It is more preferable that the sludge flows in so that the inside of the pipe is reliably filled with sludge.

In the case where the air diffusing hole 23 is provided at a position deviated from the intersection of the vertical line and the peripheral wall which intersects the axis of the air diffusing pipe 21, the space in the air diffusing pipe 21 from the air venting hole upward is stopped even in the space for stopping the gas for diffusing gas. The sludge is not filled in the stopping step, and thus the dry sludge may adhere to the inner wall of the diffusing pipe which is in contact with the space.

Further, each of the air diffusing holes 23 is preferably formed at equal intervals in the longitudinal direction of the air diffusing pipe 21.

The sludge inlet and outlet holes 24 are not limited as long as they are formed in the lower portion of the air diffusing pipe 21, and one or more of them can be formed.

The diameter of the sludge inlet and outlet hole 24 is preferably 3 mm or more. When it is less than 3 mm, the sludge inlet/outlet hole 24 is easily closed by foreign matter such as inclusions or solid components contained in the activated sludge 11.

Further, the sludge inlet and outlet hole 24 is preferably provided at a position farthest from the connection position of the discrete gas pipe 21 and the gas supply pipe 26. In other words, in the case where the air supply pipe 26 is connected only to the one end 21a of the air diffusing pipe 21, the sludge inlet and outlet hole 24 is preferably formed at the end of the air diffusing pipe 21 on the side where the air supply pipe 26 is not connected. One end) near 21b. In general, in the diffuser tube 21, The pressure in the pipe near the connection position of the air diffusing pipe 21 and the air supply pipe 26 is the highest. Therefore, if the sludge inlet and outlet hole 24 is provided in this portion, the activated sludge 11 does not enter and exit from the sludge inlet and outlet hole 24, and it is possible to discharge the gas. gas.

Further, as shown in FIG. 2B, when the air supply pipe 26 is connected to both ends 21a and 21b of the air diffusing pipe 21, and the gas for diffusing gas is supplied from the both ends 21a and 21b to the air diffusing pipe 21, even in the case of For example, when the length of the air diffusing pipe 21 is 1 m or more, the gas for diffusing air can be uniformly discharged from the air diffusing hole 23, which is preferable. At this time, the sludge inlet and outlet hole 24 is preferably formed in the vicinity of the center portion in the longitudinal direction of the air diffusing pipe 21.

The diameter of the air diffusing hole 23 and the diameter of the sludge inlet and outlet hole 24 preferably satisfy the above-described appropriate ranges, and further, if the diameter of the sludge inlet and outlet hole 24 is formed larger than the diameter of the air diffusing hole 23, the activated sludge 11 is easy. It is more suitable to smoothly enter and exit the sludge inlet and outlet holes 24.

The inner diameter d _{1 of the} diffusing pipe 21 is preferably set in the range of 10 mm to 100 mm. When the inner diameter d _{1 is} less than 10 mm, the inside of the air diffusing pipe 21 is easily blocked by foreign matter such as inclusions or solid components present in the activated sludge 11. Further, when the inner diameter d _{1 is} less than 10 mm, the range of the flow rate of the gas for diffusion gas supplied to each of the diffusing tubes in the range of the formula (I) is reduced.

Further, the air diffusing tubes 21 can be arranged side by side in a plurality of directions. In this case, if the inner diameter d ₁ of the air diffusing duct 21 is 100 mm or less, the air diffusing tubes 21 can be closely arranged, and as a result, the air diffusing holes 23 can also be provided. Tight configuration. At this time, the activated sludge aeration tank 12 can be more uniformly dispersed in the air.

Further, when the inner diameter d ₁ is 100 mm or more, the flow rate of the gas for diffusing gas supplied to each air diffusing pipe required to satisfy the lower limit value of the formula (I) (0.2 of the inner diameter d ₁ ) is increased. .

In the above description, the air diffusing pipe 21 is exemplified as the air diffusing portion. For example, as shown in FIG. 3 and FIG. 4A and FIG. 4B, a plurality of air diffusing pipes 21 arranged in parallel may be connected to both ends of the plurality of air diffusing pipes 21. A set of header pipes 30 constitutes a diffusing portion, and each of the front tubes 30 is connected to the air supply pipe 26. At this time, the gas for diffusion gas is supplied from the air supply pipe 26 to the front pipe 30, and is supplied to each of the air diffusing pipes 21 via the front pipe 30. Further, at this time, the sludge inlet and outlet holes 24 may be formed in the lower portion of each of the diffusing tubes (FIG. 3), or may be formed in the lower portion of each of the front tubes 30 (FIGS. 4A and 4B).

Further, in the above example, the gas supply unit 22 includes the air blower 25 as the air supply mechanism, but a compressor may be used instead of the air blower 25.

Further, the air supply pipe 26 of the example of Fig. 1 is provided with a three-way valve 28 at the branch portion, and instead of the three-way valve 28, as shown in Fig. 5, two opening and closing valves (two-way valves) 31, 32 are provided. At this time, in the supply step, the two-way valve 31 provided in the exhaust pipe 27 is closed, and the two-way valve 32 provided in the air supply pipe 26 on the downstream side (the air diffusing pipe 21 side) of the branch portion is opened. In the stop step, on the other hand, the two-way valve 31 provided in the exhaust pipe 27 is opened, and the two-way valve 32 provided on the downstream side of the branch portion is closed. Thereby, in the stop step, the supply of the gas for diffusion to the air diffusing pipe 21 is stopped, and the inside of the air diffusing pipe 21 is not opened to the atmospheric pressure.

Further, in the operation method of the present invention, a plurality of air diffusing portions including a diffusing portion and a gas supply portion for supplying the gas for diffusing gas to the diffusing portion may be used. Set. At this time, the supply step and the stop step switching timing may be set simultaneously between the air diffusing devices, and the timing may be shifted for each air diffusing device. In particular, in the case of an activated sludge aeration device in which a membrane separation device is impregnated, when no gas is supplied, the filtration treatment of the membrane separation device usually stops. Therefore, the timings of the switching supply step and the stopping step are shifted in advance for each air diffusing device, and when any of the air diffusing devices is at least in the supplying step, the activated sludge aeration tank is continuously diffused, thereby eliminating the need to stop the membrane separating device. Filter processing. Further, in this manner, if the gas can be continuously diffused, it is also preferable in that the activated sludge treatment can be continuously performed.

In the above example, the wastewater treatment device 10 in which the membrane separation device including the membrane element 13 for solid-liquid separation is immersed in the activated sludge aeration tank 12 has been described, but the operation method of the present invention is also described. It can be suitably used for a water treatment device that does not include a membrane separation device.

(Example 1)

Water treatment is performed in the drainage treatment apparatus of the configuration of Fig. 1 .

As the membrane element 13 for solid-liquid separation, STERAPORE SADF (trade name, manufactured by Mitsubishi Rayon. Engineering Co., Ltd., a hollow fiber membrane made of poly(vinylidene fluoride)) was used. As the activated sludge 11 to be treated with water, activated sludge having a Mixed Liquor Suspended Solids (MLSS) concentration of about 9,500 mg/L was used.

As the air diffusing pipe 21, a round pipe made of vinyl chloride resin having an inner diameter d ₁ 20 mm (0.02 m) and a length of 650 mm was used, and a diffusing hole 23 having a diameter of φ 5 mm (0.005 m) was plumbed to the diffusing pipe 21 The upper portion (the vertical line intersecting the axis of the diffusing tube) is formed at equal intervals. The gradient of the axial direction of the diffuser tube is within 1/100. In addition, in FIG. 1, six air vent holes 23 are illustrated, and five in this example 1 are formed.

The air supply pipe 26 is connected only to one end 21a of the air diffusing pipe 21, and a sludge inlet/outlet hole 24 having a diameter of 10 mm is formed in the lower portion of the peripheral wall in the vicinity of the other end 21b on the side where the air pipe 26 is not connected. Using a Roots Blower as the blower 25, the air diffusing pipe 21 is passed through the air supply pipe 26 in such a manner that the flow rate Q supplied to each air diffusing pipe is 60 L/min (1.0 × 10 ^-3 m ³ /sec). Supply gas for diffusion. Air used for the gas for diffusion is air, the density ρ' of the gas for diffusion is 1.2 kg/m ³ , the density ρ of the activated sludge 11 is 1,000 kg/m ³ , and the g acceleration g is 9.8 m/sec ² .

The in-pipe pressure head ΔH calculated by the above formula (I) is 18 mm (0.018 m), which is a value 0.9 times the inner diameter d ₁ of the diffusing pipe 21, and is preferably in the present invention. In the range.

In the apparatus, the supply step of supplying the gas for diffusion is repeated for 6 hours, and then the step of stopping the supply of the gas for diffusion is repeated for 180 seconds, and the water treatment test is performed.

After the water treatment test was continued for 30 days, the venting by the activated sludge 11 was not confirmed in the diffusing holes 23 of the 13 portions in the air diffusing pipe 21.

Although a certain amount of sludge adhered to the inner wall of the air diffusing pipe 21, the clogging caused by the activated sludge 11 was not confirmed in the sludge inlet and outlet hole 24.

Further, in the test period of 30 days, the adhesion of the activated sludge 11 to the membrane element 13 for solid-liquid separation was not confirmed, and the stabilization was continued. Membrane filtration.

(Example 2)

The water treatment test was carried out under the same conditions as in Example 1 except that the diameter of the air diffusion hole 23 was set to φ 4 mm (0.004 m), and the air diffusion holes 23 were formed in 13 places.

The in-pipe pressure head ΔH calculated by the above formula (I) is 6 mm (0.006 m), which is a value 0.3 times the inner diameter d ₁ of the diffusing pipe 21, and is preferably in the present invention. In the range.

After the water treatment test was continued for 30 days, the clogging caused by the activated sludge 11 was not observed in the air diffusing holes 23 of the 13 portions in the air diffusing pipe 21.

Although a certain amount of sludge adhered to the inner wall of the air diffusing pipe 21, the clogging caused by the activated sludge 11 was not confirmed in the sludge inlet and outlet hole 24.

In addition, in the test period of 30 days, the adhesion of the activated sludge 11 to the membrane element 13 for solid-liquid separation was not confirmed, and stable membrane filtration was continued.

(Example 3)

The water treatment test was carried out under the same conditions as in Example 1 except that the flow rate Q of the gas for diffusion gas supplied to each of the diffusing tubes was set to 50 L/min (8.3 × 10 ^-4 m ³ /sec).

The in-pipe pressure head ΔH calculated by the above formula (I) is 12 mm (0.012 m), which is 0.6 times the inner diameter d ₁ of the diffusing pipe 21, and thus is preferable in the present invention. Within the scope.

After 30 days of continuous water treatment test, the result is that the gas pipe 21 The clogging caused by the activated sludge 11 was not observed in the air vents 23 of the five locations, and the clogging by the activated sludge 11 was not confirmed in the sludge inlet and outlet holes 24. In addition, in the test period of 30 days, the adhesion of the activated sludge 11 to the membrane element 13 for solid-liquid separation was not confirmed, and stable membrane filtration was continued.

(Example 4)

The water treatment test was carried out under the same conditions as in Example 1 except that the flow rate Q of the gas for diffusion gas supplied to each of the diffusing tubes was set to 55 L/min (9.16 × 10 ^-4 m ³ /sec).

The in-pipe pressure head ΔH calculated by the above formula (I) is 15 mm (0.015 m), which is 0.75 times the inner diameter d ₁ of the diffusing pipe 21, and is in the preferred range of the present invention. Inside.

After the water treatment test was continued for 30 days, no occlusion by the activated sludge 11 was observed in the air diffusing holes 23 of the five portions of the air diffusing pipe 21, and the activated sludge was not confirmed in the sludge inlet and outlet holes 24. 11 caused by occlusion. In addition, in the test period of 30 days, the adhesion of the activated sludge 11 to the membrane element 13 for solid-liquid separation was not confirmed, and stable membrane filtration was continued.

(Comparative Example 1)

The same conditions as in Example 1 were carried out except that a diffusing hole 23 having a diameter of φ 5 mm (0.005 m) was formed on the lower side of the peripheral wall of the diffusing pipe at five locations, and the diffusing pipe of the sludge inlet and outlet hole 24 was not formed. The water treatment test was carried out for 7 days, and as a result, occlusion was confirmed at three of the five points of the air diffusing holes 23. Moreover, the inside of the air diffusing pipe 21 confirms the solidification of the activated sludge 11 With. In addition, after the completion of the test, the adhesion of the activated sludge 11 was confirmed in the hollow fiber membrane located in the upper portion of the air diffusing hole 23 in which the clogging was confirmed.

(Comparative Example 2)

The water treatment test was carried out for 10 days under the same conditions as in Example 1 except that the gas for the gas was continuously supplied without stopping. As a result, three of the five portions of the diffusing holes 23 were confirmed to be blocked. Further, the inside of the air diffusing pipe 21 is confirmed to be fixed to the activated sludge 11. In addition, after the completion of the test, the adhesion of the activated sludge 11 was confirmed in the hollow fiber membrane located in the upper portion of the air diffusing hole 23 in which the clogging was confirmed.

(Comparative Example 3)

The water treatment test was carried out under the same conditions as in Example 1 except that the flow rate Q of the gas for diffusion gas supplied to each of the air diffusing tubes was set to 25 L/min (4.17 × 10 ^-4 m ³ /sec).

The in-pipe pressure head ΔH calculated by the above formula (I) is 3 mm (0.003 m) and is 0.15 times the inner diameter d ₁ of the diffusing pipe 21, so that it is preferable in the present invention. Out of scope.

After 15 days from the continuous completion of such a water treatment test, as a result, three of the three air diffusing holes 23 in the air diffusing pipe 21 were confirmed to be blocked. Further, the inside of the air diffusing pipe 21 is confirmed to be fixed to the activated sludge 11. In addition, after the end of the test, the adhesion of the activated sludge 11 was confirmed in the hollow fiber membrane located in the upper portion of the air diffusing hole 23 in which the clogging was confirmed.

(Comparative Example 4)

The water treatment test was carried out under the same conditions as in Example 1 except that the flow rate Q of the gas for diffusion gas supplied to each of the air diffusing tubes was 70 L/min (1.17 × 10 ^-3 m ³ /sec).

The in-pipe pressure head ΔH calculated by the above formula (I) is 24 mm (0.024 m), which is 1.2 times the inner diameter d ₁ of the diffusing pipe 21, and thus is preferable in the present invention. Out of scope.

After 15 days from the continuous completion of such a water treatment test, as a result, occlusion was confirmed in four of the five air diffusing holes 23 in the air diffusing pipe 21. Further, the inside of the air diffusing pipe 21 is confirmed to be fixed to the activated sludge 11. In addition, after the end of the test, the adhesion of the activated sludge 11 was confirmed in the hollow fiber membrane located in the upper portion of the air diffusing hole 23 in which the clogging was confirmed.

(Comparative Example 5)

Water treatment is performed in the drainage treatment apparatus of the configuration of Fig. 1 .

As the membrane element 13 for solid-liquid separation, STERAPORE SADF (trade name, manufactured by Mitsubishi Rayon. Engineering Co., Ltd., hollow fiber membrane made of polyvinylidene fluoride) was used. As the activated sludge 11 to be treated, activated sludge having an MLSS concentration of about 9,500 mg/L was used.

As the diffusing pipe 21, a round pipe made of a vinyl chloride resin having an inner diameter of d ₁ 8 mm (0.008 m) and a length of 200 mm was used, and the diffusing hole 23 having a diameter of φ 1 mm (0.001 m) was vertically bent in the diffusing pipe 21. The upper portion (the vertical line intersecting the axis of the diffusing tube) is formed at equal intervals. The gradient of the axial direction of the diffuser tube is within 1/100. In addition, six diffusing holes 23 are illustrated in FIG. 1, and five in the present example 1.

The air supply pipe 26 is connected only to one end 21a of the air diffusing pipe 21, and a sludge inlet/outlet hole 24 having a diameter of φ 3 mm is formed in the lower portion of the peripheral wall in the vicinity of the other end 21b on the side where the air supply pipe 26 is not connected. The blower 25 is a Lu type blower, and the air diffusing pipe 21 is supplied with air by the air supply pipe 26 so that the flow rate Q supplied to each air diffusing pipe is 2 L/min (3.3 × 10 ^-5 m ³ /sec). Use gas. Air used for the gas for diffusion is air, the density ρ' of the gas for diffusion is 1.2 kg/m ³ , the density ρ of the activated sludge 11 is 1,000 kg/m ³ , and the g acceleration g is 9.8 m/sec ² .

The in-pipe pressure head ΔH calculated by the above formula (I) is 12 mm (0.012 m), which is a value 1.5 times the inner diameter d ₁ of the diffusing pipe 21, and thus is in the present invention. Good range.

In the apparatus, the supply step of supplying the gas for diffusion is repeated for 6 hours, and then the stopping step of stopping the supply of the gas for diffusion is performed for 180 seconds, and the water treatment test is performed.

After the water treatment test was continued for 7 days, as a result, four of the three air diffusing holes 23 in the air diffusing pipe 21 were confirmed to be blocked. Further, the inside of the air diffusing pipe 21 is confirmed to be fixed to the activated sludge 11. In addition, after the end of the test, the adhesion of the activated sludge 11 was confirmed in the hollow fiber membrane located in the upper portion of the air diffusing hole 23 in which the clogging was confirmed.

[Industry use possibility]

According to the present invention, the excessive load is not applied to the blower (gas supply portion), or the newly installed equipment is not required, and the dry consolidation of the sludge toward the air diffusing tube that blocks the air diffusion hole can be prevented.

While the present invention has been described in its preferred embodiments, the present invention is not intended to limit the invention, and the present invention may be modified and modified without departing from the spirit and scope of the invention. The scope of protection is subject to the definition of the scope of the patent application.

10‧‧‧Drainage treatment unit

11‧‧‧ Activated sludge

12‧‧‧ Activated sludge aeration tank

13‧‧‧membrane components for solid-liquid separation

14‧‧‧Aspirating piping

15‧‧‧ suction pump

16‧‧‧sucking mechanism

20‧‧‧ diffusing device

21‧‧‧ diffused air pipe (distribution department)

21a‧‧‧One end of the diffuser 21

21b‧‧‧The other end of the diffuser 21

22‧‧‧Gas Supply Department

23‧‧‧Dissipating holes

24‧‧‧Sludge access hole

25‧‧‧Blowers

26‧‧‧Air supply pipe

27‧‧‧Exhaust pipe

28‧‧‧Three-way valve

29‧‧‧Control device

30‧‧‧Before

31, 32‧‧‧Opening and closing valve (two-way valve)

L1‧‧‧ position (level of activated sludge 11 in activated sludge aeration tank 12)

L2‧‧‧ position (height corresponding to the position at which the air holes 23 are formed)

FIG. 1 is a schematic configuration diagram showing an example of a wastewater treatment device.

Fig. 2A is a schematic cross-sectional view showing a longitudinal direction of a diffusing pipe provided in the wastewater treatment device of Fig. 1;

Fig. 2B is a schematic cross-sectional view showing the longitudinal direction of the diffusing pipe provided in the wastewater treatment device of the embodiment different from Fig. 1;

Fig. 3 is a perspective view showing another embodiment of the air diffusing portion.

4A is a front elevational view showing another embodiment of the air diffusing portion.

Fig. 4B is a plan view showing another form of the air diffusing portion.

Fig. 5 is a schematic configuration diagram showing another example of the wastewater treatment device.

10‧‧‧Drainage treatment unit

11‧‧‧ Activated sludge

12‧‧‧ Activated sludge aeration tank

13‧‧‧membrane components for solid-liquid separation

14‧‧‧Aspirating piping

15‧‧‧ suction pump

16‧‧‧sucking mechanism

20‧‧‧ diffusing device

21‧‧‧ diffused air pipe (distribution department)

21a‧‧‧One end of the diffuser 21

21b‧‧‧The other end of the diffuser 21

22‧‧‧Gas Supply Department

23‧‧‧Dissipating holes

24‧‧‧Sludge access hole

25‧‧‧Blowers

26‧‧‧Air supply pipe

27‧‧‧Exhaust pipe

28‧‧‧Three-way valve

29‧‧‧Control device

L1‧‧‧ position (level of activated sludge 11 in activated sludge aeration tank 12)

L2‧‧‧ position (height corresponding to the position at which the air holes 23 are formed)

Claims (7)

A method for operating a diffusing device, comprising: a diffusing portion disposed in an activated sludge aeration tank to discharge a gas for diffusing air; and a gas supply unit that supplies the diffusing gas to the diffusing portion The air diffusing portion includes one or more air diffusing tubes arranged substantially horizontally; a plurality of air diffusing holes are formed in a vertical upper portion of the air diffusing duct, and one or more sludge inlet and outlet holes are formed in a lower portion of the air diffusing duct; The pressure head ΔH calculated by the following formula (I) is a value of 0.2 times to 0.9 times the inner diameter d ₁ of the air diffusing pipe, and is supplied from the gas supply unit to the air diffusing unit. a gas supply step; a supply step of supplying the gas for diffusion to the gas diffusion unit from the gas supply unit; and a step of stopping the supply of the gas for aeration gas without opening the atmosphere in the air diffusion tube; Wherein ΔH: pressure head (m) ρ: density of activated sludge (kg/m ³ ) ρ′: density of gas for diffusion gas (kg/m ³ ) v: gas for diffusing gas from each diffusing hole Discharge rate (m/sec) C: Outflow coefficient g represented by the following formula (II): gravitational acceleration (m/s ² ) [number 2] C = 0.597 - 0.011 m + 0.432 m ² (II) where m is The aperture ratio represented by the following formula (III) Wherein A ₀ : area (m ² ) of each of the diffusing holes A _I : sectional area of the diffusing pipe (area of the inner diameter of the surface perpendicular to the longitudinal direction) (m ² )d ₀ : diameter of each diffusing hole (m ) d _I : inner diameter (m) of the diffusing pipe. The method of operating a diffusing device according to claim 1, wherein the supplying step is performed for 30 minutes to 12 hours, and the stopping step is performed for 15 seconds to 600 seconds. The method of operating a diffusing device according to claim 2, wherein the inner diameter d ₁ is 10 mm to 100 mm. As disclosed in any one of claims 1 to 3 The operation method of the gas device, wherein the above-mentioned air diffusion hole has a diameter of 1.5 mm to 30 mm. An air diffusing device includes: a diffusing portion disposed in an activated sludge aeration tank to discharge a gas for diffusing air; and a gas supply portion that supplies the gas for diffusing air to the diffusing portion, the characteristics of the diffusing device 1) the air diffusing portion includes one or more air diffusing tubes arranged substantially horizontally; 2) a plurality of air diffusing holes are formed in a vertical upper portion of the air diffusing duct, and one or more air bubbles are formed in a lower portion of the air diffusing duct 3) in the pipe connecting the diffuser pipe and the air pipe, the pressure in the air pipe is kept exposed to the self-activated sludge even in the stop step of stopping the supply of the gas for the air diffusing The water pressure from the water surface of the gas tank to the air hole is connected to the pressure corresponding to the water pressure. The air diffusing device according to claim 5, wherein a valve is disposed in the pipe of the connecting portion between the air diffusing pipe and the air supply pipe. The air diffusing device according to claim 6, wherein the valve is a three-way valve; and the three-way valve is connected to the air diffusing pipe, the air supply pipe, and the exhaust pipe.