JP2003300085A - U-shaped air lift pump pipe and sewage purifying tank - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an air lift pump pipe the diameters of a liquid sucking pipe and a water pumping-up pipe of which can be made smaller than those of the conventional pump pipe, in which sludge is hardly accumulated, to which sludge is hardly stuck and in which an adjustment apparatus such as an adjustment pit is not necessary. <P>SOLUTION: This air lift pump pipe 1 is constituted so that the erected water pumping-up pipe 3 having a liquid discharge port 5 in the upper part is connected in a U-shaped form to an air supplying pipe 4 having an opening 8 in the upper part. The liquid sucking pipe 2 having a liquid sucking port 10 on the top end is branched erectly from the lower side part of the pipe 3 and the height of the port 10 is made lower than that of the port 5. An inflow hindering member 14 is arranged around the port 10 for preventing scum 15 from intruding into the port 10. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sewage purification tank for treating human waste discharged from homes and other domestic wastewater (also simply referred to as sewage), and an air lift pump pipe attached to the sewage purification tank. .

[0002]

2. Description of the Related Art FIG. 11 shows an example of a conventional air lift pump pipe provided in a sewage purification tank (for example, an actual open flat 4-tube).
118199). The air lift pump pipe is used by being submerged in water and erected, and a liquid suction pipe 2 having a liquid suction port 10 in the upper part and a pumping pipe 3 having a liquid discharge port 5 in the upper part are substantially U-shaped. Of the substantially U-shaped pipes, and the lower end opening 9 of the air supply pipe 4 is slightly above the bottom of the pumping pipe side of the substantially U-shaped pipe.
Is connected so as to branch from the pumping pipe 3, and air is blown from the upper end opening 8 of the air supply pipe 4. Further, the liquid discharge port 5 above the pumping pipe 3 is provided with an adjusting mass 13 for adjusting the transfer amount, and is provided with a notch portion for returning excess water to the original tank when excessive water is pumped. In addition, in FIG. 11, a solid line arrow shows a liquid flow, and a dotted line arrow shows an air flow. Water is pumped by the air lift pump pipe as follows. When the air entering from the upper end opening 8 of the air supply pipe 4 is discharged into the pumping pipe 3 from the lower end opening (branching part) 9, the air becomes air bubbles and rises in the pumping pipe 3 together with the liquid. . In the liquid suction pipe 2 connected to the pumping pipe 3 at the bottom of the U-shaped pipe, the liquid in the tank outside the liquid suction pipe 2 is sucked from the liquid suction port 10 and pumped through the bottom of the U-shaped pipe. . At this time, the pumped water that has been pushed up reaches the adjusting mass 13 from the liquid discharge port 5. In the adjustment mass 13, excess pumped water is caused to overflow from the cutout portion, and only the necessary amount is transferred to the destination.

[0003]

However, since the air lift pump pipe is used for transferring the waste water as described above, when the operation is continued, the sludge in the waste water adheres to the inner walls of the liquid suction pipe 2 and the pumping pipe 3.・ Accumulates, and finally the sediment becomes a resistance and pumping becomes difficult. Therefore, in order not to cause a problem even if a small amount of sludge adheres to and accumulates on the inner wall of the pipe, conventionally, the liquid suction pipe 2 and the pumping pipe 3 (for example, the inner diameter of 40 mm are larger than the pipe diameter)
~ 60 mm) was used, and after pumping more water than necessary, the excess liquid was returned to the original state by an adjusting device such as an adjusting mass.

The present invention provides an air lift pump pipe in which the diameters of the liquid suction pipe and the pumping pipe can be made smaller than in the conventional case, the adhesion and accumulation of sludge is reduced, and an adjusting device such as an adjusting mass is not required. Is an issue.

[0005]

As a result of various investigations by the present inventors in order to achieve the above object, the inner walls of both the liquid suction pipe and the pumping pipe during operation are discharged from the air supply pipe and sewage. An air lift pump pipe having a structure of automatically cleaning with a gas-liquid mixed fluid in which and are mixed can be conceived, and the present invention has been completed. That is, in the air lift pump pipe of the present invention, the pumping pipe 3 which is provided upright with the liquid discharge port 5 in the upper portion and the air supply pipe 4 having the opening portion 8 in the upper portion are substantially U
It is directly connected in a V shape or is connected in a substantially U shape via connecting members (6a, 6b). At the lower part (and side part) of the pumping pipe 3, the liquid suction port 10 is provided at the upper end. The liquid suction pipe 2 has, directly or via the connecting member (6c),
The air lift pump pipe 1 is branched so as to stand up, and the height of the liquid suction port 10 of the liquid suction pipe 2 is lower than the height of the liquid discharge port 5 of the pumping pipe 3. Is.

Here, a baffle member 14 is preferably provided around the liquid suction port 10 of the liquid suction pipe 2. This is to prevent the floating solid matter 15 called scum from being accumulated in the liquid suction port 10 and reducing the efficiency of liquid suction.

The inner diameter of each of the pumping pipe 3, the air supply pipe 4 and the liquid suction pipe 2 is preferably 5 to 20 m.
The range is m. This is because a small amount of air is needed to pump the required amount of wastewater. Further, it is preferable that the inner diameters of these three tubes are the same. This is because the step difference in the connecting portion is eliminated, the flow of fluid (sewage, air, or a gas-liquid mixed fluid in which these are mixed) is made smooth, and the types of pipes and connecting members forming the air lift pump pipe are not increased.

The present invention also relates to a sewage purification tank in which the above air lift pump pipe is used and which is arranged in the tank. What is preferable as such a sewage purification tank is an anaerobic treatment tank (flow rate adjustment tank) 22 having a flow rate adjusting function, an aerobic treatment tank 23, a filtration tank 24 and a disinfection tank 25 from the upstream side.
It is a septic tank. The air lift pump pipes are provided so as to stand in either one of the anaerobic treatment tank (flow rate adjusting tank) 22 having this flow rate adjusting function (flow rate adjusting tank) 22 and the filtration tank 23, or one of the tanks.

[0009]

In the conventional air lift pump pipe (FIG. 11), the branch portion 9 branching from the lower portion of the pump pipe 3 (to the air supply pipe 4) is the connecting portion between the liquid suction pipe 2 and the pump pipe 3, that is, Since it is located at a position higher than the bottom portion 12 of the substantially U-shaped pipe, the gas-liquid mixed fluid cannot enter the liquid suction pipe 2 side, and therefore the deposits and sludge adhered / accumulated on the inner wall of the pipe cannot be dropped. .

On the other hand, in the air lift pump pipe 1 (for example, FIG. 1) of the present invention, the liquid suction pipe 2 having the liquid suction port 10 at the upper end is slightly above the bottom portion 12 of the substantially U-shaped pipe (the pump pipe 3).
Since it is branched so as to rise from the side), part of the air from the air supply pipe 4 or the gas-liquid mixed fluid in which this air and sewage are mixed also goes into the liquid suction pipe 2 and Sludge that rises and adheres to the inner wall of the pipe can be dropped.

Particularly, when the air lift pump pipe 1 of the present invention is arranged in the flow rate adjusting tank (for example, the flow rate adjusting tank 22) of the wastewater purifying tank having the flow rate adjusting function, the water level in the tank is the lowest water level (L.W.L. ), A gas-liquid mixed fluid containing air bubbles and sewage violently flows up and down in the pumping pipe 3 to separate sludge adhered to the inner wall of the pipe (see FIG. 2). Further, since a part of the air from the air supply pipe 4 is pushed out also above the liquid suction pipe 2, the sludge adhering to the inner wall of the liquid suction pipe 2 may be peeled off or washed. In this way, sludge is peeled off (that is, washed) not only in the pipe of the pumping pipe 3 but also in the pipe of the liquid suction pipe 2. This is the reason why the inner diameter of the air lift pump pipe can be made smaller than before.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below with reference to the drawings. FIG. 1 is a cross-sectional view of an air lift pump pipe 1 of an example of the present invention when the liquid in the tank is at the highest water level. As shown in the figure, the air lift pump pipe 1 is formed by connecting a pumping pipe 3 having a liquid discharge port 5 at an upper portion and an air supply pipe 4 for supplying air at a bottom portion 12 to form a substantially U-shaped pipe. On the pumping pipe 3 side, the liquid suction pipe 2 branches upward at a position slightly above the bottom portion 12, and the upper end thereof is an opened liquid suction port 10. Used upright. In addition, the solid line arrow in FIG. 1 shows a liquid flow, and the dotted line arrow shows an air flow (the same applies to FIGS. 2 to 7 below).

FIG. 2 is a vertical sectional view of the air lift pump pipe 1 when the liquid in the tank is at the lowest water level. The operation of the air lift pump (which is a combination of an air lift pump pipe and a blower) in the tank 22 having a flow rate adjusting function (flow rate adjusting tank) 22 will be described with reference to FIGS. 1 and 2. In the flow rate adjusting tank 22 having the air lift pump pipe 1, the liquid suction port 10 is adjusted so that the water level in the tank varies between the highest water level and the lowest water level.
Predetermine the position of. First, the air from the blower is continuously supplied from the air supply pipe 4. When the water level is higher than the minimum water level, the liquid in the tank is pumped up and moved from the liquid discharge port 5 to a predetermined destination. At this time, the liquid in the tank that was transferred (the amount of pumped water)
When the amount of inflowing wastewater is larger than that, the difference is accumulated and the water level gradually rises, and in some cases rises to the maximum water level.

On the other hand, if the sewage does not flow into the flow rate adjusting tank 22 for a long time, the water level gradually lowers to the minimum water level, and the sewage sucked into the liquid suction port 10 almost disappears.
The pumping of the liquid in the tank is almost zero (Fig. 2). Then,
The pressure balance between the pumping pipe 3 and the liquid suction pipe 2 is lost, and the air flowing in from the air supply pipe 4 sometimes flows into the liquid suction pipe 2 to wash the liquid suction pipe 2 with air. On the pumping pipe 3 side, the gas-liquid mixed fluid having a high air bubble ratio violently moves up and down in the pumping pipe 3 (indicated by arrows with arrows at both ends) to clean the pipe inner wall. In this way, the sludge adhered to the inner wall of the liquid suction pipe 2 and the inner wall of the pumping pipe 3 is peeled off, and the accumulation of sludge can be avoided.

FIGS. 3 and 4 show an example of the air lift pump pipe of the second embodiment of the present invention, in which a hollow cylindrical baffle member 14 is provided around the liquid suction port. After a certain amount of time passes, floating solids 15 such as floating sludge lumps called scum and oil balls (oil lumps) that are oil components appear in the flow rate adjusting tank 22. The floating solid matter 15 accumulates in the vicinity of the liquid suction port 10 and reduces the liquid suction efficiency. The baffle member 14 prevents the floating solid matter from accumulating in the liquid suction port 10.

FIG. 5 shows the air lift pump pipe 1 of the third embodiment of the present invention, considering the maintainability of the baffle member 14,
The liquid suction port 10 is provided on the side wall of the baffle member 14 having a hollow cylindrical shape. This makes it easier to remove sludge and the like adhering to the baffle member 14 by cleaning. The baffle member 14 may have a hollow rectangular tube shape instead of the hollow cylinder shape.

FIG. 6 shows an air lift pump pipe according to a fourth embodiment of the present invention, which is a modification of the air lift pump pipe shown in FIG. In order to prevent the floating solid matter from entering the baffle member 14, the two opposite sides of the hollow rectangular tubular baffle member 14 are bent as shown in the figure, and one lower end is made lower than the other lower end. It is overhanging. Also, the liquid suction pipe 2 near the liquid suction port 10
Is inclined and connected so that air bubbles can easily escape when it is close to the minimum water level (L.W.L). As a result, the inside of the liquid suction pipe 2 is efficiently cleaned.

FIG. 7 is a schematic configuration diagram of a wastewater purification tank equipped with the air lift pump pipe, and FIG. 8 is a sectional view taken along the line AA of FIG. Next, the sewage purification tank of the present invention will be described with reference to these drawings.

From the upstream side, the sewage purification tank 20 has a first tank 21 for causing sedimentable solid matter in the sewage to settle under gravity, and the subsequent (upper) liquid to overflow into the next tank, and the overflowing liquid. A second tank 22 for storing and quantitatively transferring the liquid to the next tank, a third tank 23 for biologically aerobic treatment of the transferred liquid, and sludge (also referred to as floating suspended matter, SS) Is divided and divided into a fourth tank 24 for advancing the filtrate to the next tank and a fifth tank 25 for disinfecting the liquid, and these tanks are partitioned by partition walls 26, 27, 28, 29, respectively. There is. Further, the first tank 21 is a settling separation chamber 21a in which settling solid matter in wastewater is settled under gravity and a sludge concentrating chamber 21b in which settling solid matter is stored and concentrated.
It is divided into two rooms.

From a functional viewpoint of each tank, the first tank 21 is a sedimentation separation tank, the second tank 22 is a flow rate adjusting tank, the third tank 23 is an aerobic treatment tank, the fourth tank 24 is a filtration tank, and the fifth tank is a fifth tank. The tank 25 can also be called a disinfection tank. The first tank 21 and the second tank 22 also have an anaerobic biodegradation function. In order to further enhance the anaerobic biodegradation function, an anaerobic filter bed tank or an anaerobic treatment tank filled with a filler (filter material, filter bed) can be used.

In the settling / separating chamber 21a, a sewage introduction pipe 43 is provided on a wall portion located at a position higher than the liquid level in the tank, and a partition wall 26 on the opposite side thereof is advected to the flow rate adjusting tank 22 (second tank). An opening 44 is provided. An opening 32 is provided in the lower part of the partition walls 30 and 31 (FIG. 8) surrounding and surrounding the sedimentation separation chamber 21a, extending from the wall surface on the sewage introduction pipe 43 side to the partition wall 26 of the advection opening 44. .

A slanted baffle plate 33 is provided near the liquid surface in the sedimentation separation chamber 21a on the sewage introduction pipe 43 side to suppress the liquid flow when sewage flows in.

After passing through the baffle plate 33, the sewage that has flowed into the sedimentation separation chamber 21a from the sewage introduction pipe 43 becomes a substantially horizontal flow and flows toward the advection opening 44. During this time, the solid matter having a sedimentation velocity higher than the horizontal flow velocity passes through the opening 32 at the lower part of the sedimentation separation chamber 21a, and the sludge concentration chamber 21
It reaches the bottom of b and accumulates.

In the sludge concentrating chamber 21b, since it is less likely to be disturbed by the liquid flow of the inflowing wastewater, the settled solid matter accumulates at a high concentration and becomes sludge. The sludge solidified gradually becomes anaerobic with the passage of time and a part becomes scum, and floats near the liquid surface above the sludge thickening chamber 21b. At this time, since the lower end of the partition wall 30 is longer than the lower end of the partition wall 31 and juts out in the horizontal direction, the floating scum causes the floating separation scum from the opening 32 below the sedimentation separation chamber 21a.
Prevent entry into 1a.

In the flow rate adjusting tank 22 (second tank), an air lift pump pipe (connecting to the blower 35) 1 for transferring the liquid in the tank to the aerobic treatment tank (third tank) 23 of the next tank is arranged, and the wastewater purifying tank It absorbs the fluctuation of the amount of sewage flowing into 20. That is, the transfer of the in-tank liquid to the next tank is an averaged transfer via the air lift pump pipe 1.

Here, if the amount of liquid transferred by the air lift pump pipe 1 is larger than the inflow amount from the advection opening 44, the liquid in the tank accumulates by the difference, and the water level goes from the lowest water level to the highest water level. In the opposite case, the water level goes from the highest water level to the lowest water level. At the lowest water level, the liquid in the tank is not pumped up by the air lift pump pipe 1, and the air is also discharged from the liquid suction port 10 (so-called idle operation).

Although not shown in the figure, a packing material such as a filter material or a contact material to which sludge and microorganisms adhere can be arranged in the flow rate adjusting tank 22, and in this case, the upper part of the packing material is placed in the atmosphere. Can be exposed to water (function of sprinkling filter).

In the aerobic treatment tank (third tank) 23, organic substances in the liquid are decomposed and removed by aerobic microorganisms. In the tank,
Usually, a microbial carrier (microorganism adhering material, contact material) suitable for retaining and growing microorganisms is filled to form a filter bed (aerobic filter bed, for microbial reaction) 34. The filter bed 34 may be a fixed bed on which a microbial carrier is fixed, or a fluidized bed that flows with a liquid. At this time, air is discharged from the blower 35 through the air diffuser 37 in order to maintain the aerobic condition.

The liquid flowing into the aerobic treatment tank 23 flows downward through the filter bed 34 in the tank. When organic matter is biodegraded in the filter bed 34, a part of it is converted to sludge, and sludge increases,
Some sludge collects at the bottom of the tank. The collected sludge can be transferred from the bottom of the tank (using an air lift pump) to the settling separation chamber 21a, but in the case of FIG. 7, the amount of sludge generated is small, so this is transferred to the next tank via the advection pipe 38. It is transferred to the filtration tank (No. 4 tank) 24. Here, the advection pipe 38
Is a tubular one with the upper end open and the lower end closed,
An advection port is provided in the middle of this pipe. The liquid that has flowed in may be allowed to flow in the filter bed of the aerobic treatment tank 23 in the upward flow, not in the downward flow.

In the filtration tank (fourth tank) 24, the sludge in the advancing liquid is filtered and the filtrate is admitted to the next tank. In order to filter and capture the sludge, a filter bed (for filtration) 40 filled with a filter medium is formed in the filter tank 24. The flow direction in the filter bed 40 is a downward flow as shown in FIG. 7.

The sludge trapped on the filter bed 40 will be clogged when it accumulates, so that it is necessary to regularly backwash it. At a predetermined time, the timer 54 operates and the blower 36 operates to send air to both the backwash pipe 53 and the air lift pump pipe (for backwash drainage return) 11 to backwash. This backwash is
It is preferable to perform it when the water level of the flow rate adjusting tank 22 is the lowest water level. The backwash drainage is returned to the first tank 21 using the air lift pump pipe 11. At this time, in order to backwash efficiently, it is preferable to return the entire amount of the liquid in the filtration tank 24 until the water level in the filtration tank 24 has dropped to the bottom. When the water level drops to the bottom, in the air lift pump pipe 11 connected at the bottom, the gas-liquid mixed fluid violently moves up and down in the pumping pipe and the liquid suction pipe, and the sludge adhering to the inner wall of the pipe is separated.

In the disinfecting tank (fifth tank) 25, Escherichia coli and bacteria are sterilized by a disinfectant. The treatment liquid after disinfection is
Discharge from the discharge port 41 to the outside of the wastewater purification tank.

The sewage purification tank 20 is provided with a manhole in the upper part of the tank so that maintenance and inspection of the inside of the tank can be easily performed, and a manhole cover 42 is attached to the manhole.

Next, an experimental example will be shown. The dimensions of the air lift pump pipe used are as shown in Fig. 9. The liquid suction pipe 2, the pumping pipe 3, and the air supply pipe 4 are all made of vinyl chloride (inner diameter 13 m
m, VP13) and vinyl chloride joints (elbows 6a, 6b, cheese 6c) were used to connect these pipes. This air lift pump pipe was arranged in the flow rate adjusting tank 22 of a 5-person tank-scale wastewater purification tank as shown in FIG. Here, the water level in the flow rate adjusting tank 22 is 1,400 mm at the highest water level and 1,200 mm at the lowest water level (that is, the water level difference between the two is 200 mm. The water level difference from the highest water level to the liquid discharge port 5 of the pumping pipe 3 is The same shall apply), and the height from the lower end of the air lift pump pipe to the bottom of the tank was 700 mm, and the height from the maximum water level to the liquid discharge port 5 of the pump pipe 3 was 200 mm.
The air supply pipe 4 was continuously supplied from the blower 35 at an air flow rate of 5 L / min, and the combined sewage was introduced from the sewage introduction pipe 43 to carry out a long-term continuous operation test.

FIG. 10 shows the relationship between the water level (H) of the flow rate adjusting tank 22 and the pumping amount (Q) of the air lift pump pipe, that is, the so-called QH characteristic. The Q-H characteristics were stable and the flow rate adjusting function was maintained at the initial value, after 2 months, and after 4 months. Further, neither accumulation nor clogging of sludge was observed in the air lift pump pipe having an inner diameter of 13 mm.

[0036]

The air lift pump pipe of the present invention has a simple structure and is unlikely to cause sludge to adhere or accumulate on the inner wall of the pipe. In addition, the tube diameter can be made smaller than in the past, and an adjusting device such as an adjusting mass is not required. It is also free from troublesome work such as removing adhered substances in maintenance. If the inner diameter of the air lift pump pipe is in the range of 5 mm or more and 20 mm or less,
It is economical because less material is used, and the area occupied by the air lift pump pipe in plan view can be reduced. Further, since the pumping capacity is low and the amount of air to be sent is sufficient, the power consumption of the blower can be reduced. According to the sewage purification tank having the flow rate adjusting function using the air lift pump pipe of the present invention, sewage having a large flow rate fluctuation can be averaged and advected, so that stable sewage treatment can be performed.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of an air lift pump pipe according to a first example of the present invention when a liquid in a tank is at a maximum water level. Solid arrows in the figure indicate liquid flow, and dotted arrows indicate air flow.

FIG. 2 is a vertical cross-sectional view when the liquid in the tank is at the lowest water level.

FIG. 3 is a vertical cross-sectional view of the air lift pump pipe of the second embodiment of the present invention (in which a baffle member is formed around the liquid suction port) when the liquid in the tank is at the highest water level.

FIG. 4 is a vertical cross-sectional view when the liquid in the tank is at the lowest water level.

FIG. 5 is a longitudinal sectional view of the air lift pump pipe of the third example of the present invention when the liquid in the tank is at the maximum water level.

FIG. 6 is a vertical cross-sectional view of the air lift pump pipe according to the fourth example of the present invention when the liquid in the tank is at the lowest water level.

FIG. 7 is a schematic configuration diagram of an example of a sewage purification tank according to the present invention.

8 is a sectional view taken along the line AA of FIG.

FIG. 9 is a front view of an air lift pump pipe used in a test.

FIG. 10 is a graph (Q-H characteristic) in which a pumped water amount Q and a water level H are plotted.

FIG. 11 is a vertical cross-sectional view of a conventional air lift pump pipe.

[Explanation of symbols]

1: Air lift pump pipe 2: Liquid suction pipe 3: Pumping pipe 4: Air supply pipe 5: Liquid discharge port (of pumping pipe) 6a, 6b, 6c: Connection member 8: Upper end opening 9 of air supply pipe 9: Air supply Lower end opening of pipe (branch part) 10: Liquid suction port 11: Air lift pump pipe (for backwash drainage return) 12: Bottom 13: Adjustment mass 14: Barrier member (cylindrical) 15: Scum (floating solid 20) Sewage purification tank 21: First tank 21a: Sedimentation separation chamber 21b: Sludge concentration chamber 22: Second tank (flow rate adjustment tank) 23: Third tank (aerobic treatment tank) 24: Fourth tank (filtration tank) ) 25: Fifth tank (disinfection tank) 26: Partition wall 27: Partition wall 28: Partition wall 29: Partition wall 30: Partition wall 31: Partition wall 32: Opening 33: Baffle plate 34: Filter bed 35: Blower 36 : Blower 37: Air diffuser 38: Advection tube 40: Filter bed 41: Outlet port 42: Down hole cover 43: sewage inlet pipe 44: advection opening 53: backwash tube 54: timer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroshi Yamashita             1250 Shimoeren, Shimodate City, Ibaraki Prefecture Stock Association             Hitachi House Tech Yuki factory F-term (reference) 4D027 AB06 AB07 AB12 AB14

Claims (5)

[Claims] 1. A pumping pipe having a liquid discharge port in the upper portion and an air supply pipe having an opening portion in the upper portion are directly connected in a substantially U shape or are connected in a substantially U shape via a connecting member. In the lower part of the pumping pipe, a liquid suction pipe having a liquid suction port at the upper end is branched directly or through a connecting member so as to rise, and the liquid suction port of the liquid suction pipe is The position is an air lift pump pipe formed at a position lower than the position of the liquid discharge port of the pumping pipe. 2. The air lift pump pipe according to claim 1, further comprising a baffle member formed at the liquid suction port of the liquid suction pipe. 3. The air lift pump pipe according to claim 1, wherein the pumping pipe, the air supply pipe and the liquid suction pipe each have an inner diameter of 5 mm or more and 20 mm or less. 4. A sewage purification tank comprising the air lift pump pipe according to claim 1. 5. A sewage purification tank comprising an anaerobic treatment tank having a flow rate adjusting function, an aerobic treatment tank, a filtration tank and a disinfection tank from the upstream side, wherein at least one of the anaerobic treatment tank and the filtration tank is claimed. A sewage purification tank equipped with the air lift pump pipe according to any one of Items 1 to 3.