JPH09267894A - Septic tank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve reinforcement effects of a septic tank by forming corrugated ribs extending along a peripheral direction of a tank body to protrude inward the tank on at least a bottom of the tank body of the septic tank and forming continuously or continually a recess in a lengthwise direction of the rib at its top plate part. SOLUTION: Corrugated ribs 3a are integrally formed with at least a lower tank body of a tank body 10 in a combined type septic tank, and partitions for partitioning the inside of the tank body 10 into an anaerobic treatment chamber, an aerobic treatment chamber, a sedimentation chamber or the like are temporarily supported on the ribs 3a. The corrugated ribs 3a extend along a peripheral direction of the tank body and form a groove-shaped recess 5a continuously along a lengthwise direction of the rib 3a at its top plate part 4a. The recess 5a preferably is formed at an approximate center of the top plate part 4a and supports the partitions with a lower end of the partitions fitted, wherein although a depth of the recess 5a is not specifically limited, its depth is preferably 50 to 100% of a height (h) of the rib 3a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a septic tank, and more particularly to improvement of a septic tank having corrugated ribs.

[0002]

2. Description of the Related Art An anaerobic treatment tank into which sewage flows in, as a septic tank for various sewage, such as human waste discharged from a toilet or sewage discharged from a toilet, bath, kitchen, etc. Merged into an aerobic treatment tank into which anaerobic treated water flows, a precipitation tank into which aerobic treated water flows, and a disinfection tank into which the supernatant liquid separated in the precipitation tank flows There is known a septic tank or an independent septic tank which is intended for only urine and is a combination of all or part of the above-mentioned processing chambers.

In such a septic tank, in the anaerobic treatment tank (room), organic substances in wastewater are first reduced to organic acids by acid-producing bacteria, and the organic acids are converted into methane gas or carbon dioxide gas by methane bacteria. And decomposed into ammoniacal nitrogen. In the aerobic treatment tank (room), this ammonia nitrogen is oxidatively decomposed into nitrate nitrogen and nitrite nitrogen by aerobic bacteria such as nitrifying bacteria, and a part of this treated water is anaerobically treated (room). ), Nitrate nitrogen and nitrite nitrogen are decomposed into molecular nitrogen and nitrous oxide by denitrifying bacteria in the anaerobic treatment tank (room). The treated water in which the concentration of nitrate nitrogen and nitrite nitrogen is reduced in this way is separated in the settling tank (room), and the supernatant liquid is sterilized by chlorine in the disinfecting tank (room) and then used as purified water. To be released.

In such a septic tank, the tank body of the septic tank is conventionally made of fiber reinforced plastic (FRP) or the like.

[0005]

However, the septic tank formed by FRP has a problem that it is heavy and easily cracked, and a problem that the working environment at the time of manufacturing is poor and there is a problem in disposal. .

Therefore, recently, Japanese Patent Laid-Open No. 7-13707
As disclosed in Japanese Patent Publication No. 0, it has been proposed to mold a tank body of a septic tank by reaction injection molding. However, when the wall thickness of the reaction injection molded body is reduced in order to reduce the weight, there is a possibility that the strength required as a septic tank may be insufficient in a part of the tank body. In such a case, in the conventional case, for example, as shown in FIG.
In some cases, the corrugated reinforcing rib 2 as shown in FIG.

However, the conventional corrugated reinforcing rib 2 may not be able to sufficiently satisfy the mechanical strength required for the tank body of the septic tank, and the rib shape that can further improve the strength is not sufficient. Was wanted. On the other hand, in septic tanks, parts such as partition plates are installed inside, but the part that supports the partition plates is not installed in the tank body of the conventional septic tank, so work such as installation of partition plates It was complicated.

The present invention has been made in view of such an actual situation, and can further increase the reinforcing effect of the septic tank having the corrugated ribs, and moreover, the portion that temporarily holds or supports the parts such as the partition plate is inside. The purpose is to provide a septic tank formed in.

[0009]

In order to achieve the above object, a septic tank according to the present invention is provided at least at the bottom of the septic tank along the circumferential direction of the septum so as to project into the inside of the septic tank. A corrugated rib extending is formed, and a concave portion is formed in a top plate portion of the corrugated rib continuously or intermittently along the longitudinal direction of the rib.

The thickness of the corrugated rib is preferably substantially the same as the thickness of the tank body, preferably 3 to 12 mm,
More preferably 5 to 11 mm, particularly preferably 6 to 10 mm
mm. If the thickness is too thin, the moldability will be poor and the strength will be too weak.

The height of the corrugated ribs is preferably 10 to 100 mm, more preferably 15 to 90 mm, and particularly preferably 20 to 80 mm. By setting in such a range, the function as a reinforcing rib can be utilized. The width of the top plate portion of the corrugated rib is preferably 25 mm to 3
00 mm, more preferably 30 to 200 mm, particularly preferably 35 to 150 mm. By setting in such a range, the function as a reinforcing rib can be utilized.

The width of the base end portion of the corrugated rib is determined to be equal to or greater than the width of the top plate portion, and is determined from the ease of die-cutting after molding and the reinforcing effect. 10
It is set to 0 to 150%, preferably 110 to 140%. If this width is too large than the width of the top plate,
The reinforcing effect is weakened.

In the present invention, the top plate portion of the corrugated rib is formed with a recess continuously or intermittently along the longitudinal direction of the rib. The recess is preferably formed substantially in the center of the top plate portion, and the width of the recess at the top plate portion is preferably 5 to 50 mm, more preferably 6 to 40 mm.
mm, particularly preferably 7 to 35 mm. The width at the bottom of the recess is preferably 0 relative to the width at the top plate portion of the recess.
The width is preferably ˜100%, more preferably 20-80%. If the width at the bottom of the recess is too large compared to the width at the top plate, it may be difficult to perform die cutting after molding, and if it is too small, the function as a temporary presser for the partition plate, etc. I can't do it.

When such recesses are provided intermittently along the longitudinal direction of the corrugated ribs, the pitch is preferably 5 to 100 cm, more preferably 5.
5 to 50 cm, particularly preferably 6.0 to 33 cm, and the length of each recess in the longitudinal direction is preferably 5 to 50 m.
m, more preferably 6 to 40 mm, particularly preferably 7 to
35 mm. In this case, the size of the bottom of the recess is determined in consideration of the ease of die cutting.

It is particularly preferable that the tank body of the septic tank according to the present invention is formed of a reaction injection molded body of norbornene-based monomer. When the tank body of the septic tank according to the present invention is formed of a reaction injection molded body of norbornene-based monomer, the tank body of the septic tank having corrugated ribs according to the present invention can be easily integrally formed, and has a relatively large size. The tank body can be easily molded. Further, the polynorbornene-based resin can have a sufficient pressure resistance required as a septic tank by utilizing a material characteristic of low specific rigidity but high specific strength.

In the present invention, since the top plate portion of the corrugated rib is formed with the concave portion continuously or intermittently along the longitudinal direction of the rib, the rigidity of the corrugated rib is further improved, and the rib is increased. The reinforcing effect of is further improved. In addition, this recess is a partition plate of the septic tank, an air diffuser, a transfer pipe,
It can serve as a temporary support or a main support for parts such as a backwash pipe, and can improve workability of positioning work or mounting work of these parts.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a septic tank according to the present invention will be described in detail based on an embodiment shown in the drawings. First Embodiment FIG. 1 is a schematic perspective view of a main part of a corrugated rib of a tank body of a septic tank according to an embodiment of the present invention, and FIG. 2 is a schematic vertical sectional view of the septic tank.

First, the overall structure of the septic tank will be described with reference to FIG. Merger treatment septic tank 10 according to the present embodiment
0 has the tank body 10. The tank body 10 is assembled by, for example, mounting the upper tank body and the lower tank body inside the components such as the filter medium 30 and then stacking them.

Although not shown in the figure, the tank body 10 is a septic tank 1.
00, a mounting hole for mounting a manhole cover, which is necessary for constructing 00, is formed in the longitudinal direction of the tank body 10.
An inflow pipe 18 for introducing sewage and a discharge pipe 20 for discharging purified water after treatment are provided at the front and rear of the tank body 10 in the longitudinal direction.

Since the septic tank 100 is a combined treatment septic tank that performs anaerobic treatment and aerobic treatment, the tank body 10
The inside of a plurality of partition plates 40, 4 along the longitudinal direction
2, 44 and the partition wall 46 form a plurality of chambers 50, 52, 54,
It is divided into 56 and 58. In the present embodiment, from the upstream side where sewage is introduced, the first anaerobic treatment chamber 50, the second anaerobic treatment chamber 52, the aerobic treatment chamber 54, the precipitation chamber 56, and the disinfection chamber 58, which are five chambers in total, are treated. The chamber is formed.

The first anaerobic treatment chamber 50 is a treatment chamber into which dirty water is introduced from the inflow pipe 18, and is separated from the adjacent second anaerobic treatment chamber 52 by a partition plate 40. Both chambers 50 and 52 are communicated with each other through a communication hole 40a formed in the upper portion of 40. This first anaerobic treatment chamber 5
An anaerobic filter bed 30 having anaerobic bacteria adhered to a filter medium such as a synthetic resin is provided at 0, and sewage flowing from the inflow pipe 18 is anaerobic when passing through the anaerobic filter bed 30. After the treatment, the second through the communication hole 40a of the partition plate 40
It will flow down to the anaerobic treatment chamber 52 by natural overflow of the weir.

The second adjacent to the first anaerobic treatment chamber 50
The anaerobic treatment chamber 52 is a second anaerobic treatment chamber 52 into which the treated water anaerobically treated in the first anaerobic treatment chamber 50 is introduced, and is a partition plate 42 from the adjacent aerobic treatment chamber 54. Although partitioned, the two chambers 52, 54 are communicated with each other by a communication hole 42a formed in an upper portion of the partition plate 42.
The second anaerobic treatment chamber 52 also includes the first anaerobic treatment chamber 50.
Similarly, an anaerobic filter bed 30 in which anaerobic bacteria adhere to a filter material such as a synthetic resin is supported and provided, and the treated water flowing from the first anaerobic treatment chamber 50 is the anaerobic filter bed 30. When passing through, the partition plate 42 is further subjected to anaerobic treatment.
Through the communication hole 42a of the weir into the aerobic treatment chamber 54 due to the natural overflow of the weir.

The aerobic treatment chamber 54 adjacent to the second anaerobic treatment chamber 52 is a treatment chamber into which the treated water anaerobically treated in the second anaerobic treatment chamber 52 is introduced, and the adjacent precipitation chamber 56. Is separated by a partition plate 44, but a slot (narrow passage) 44a formed in the lower part of the partition plate 44
The two chambers 54 and 56 communicate with each other. In the aerobic treatment chamber 54, an aerobic filter bed 30 in which aerobic bacteria adhere to a contact material such as a synthetic resin is supported, and the treated water flowing from the second anaerobic treatment chamber 52 is Aerobic filter bed 30
Is passed through the slot 44a in the lower portion of the partition plate 44 and flows into the precipitation chamber 56. In FIG. 2, reference numeral “21” is an air diffuser for promoting aerobic treatment in the aerobic treatment chamber 54, and is connected to an air supply device (not shown).

The disinfection chamber 58 adjacent to the precipitation chamber 56 is
A partition 46 separates the precipitation chamber from the precipitation chamber, and the supernatant liquid of the precipitation chamber 56 flows into the disinfection chamber 58, and after the chlorine is disinfected with the disinfectant supplied by the chemical cylinder, the discharge pipe 2
0 and discharged to the outside as purified water.

In the present embodiment, in order to collect the sludge gravity settled in the settling chamber 56 to the bottom as much as possible, the tank bottom of the tank body 10 is formed to be inclined toward the aerobic treatment chamber 54 side. As a result, the sludge in the settling chamber 56 is deposited in the vicinity of the slot 44a which is the lower end of the partition plate 44.

In the present embodiment, the treated water in the vicinity of the slot 44a which connects the aerobic treatment chamber 54 and the precipitation chamber 56 is first treated.
Circulating means 60 is provided for returning to the anaerobic treatment chamber. The circulation means 60 is provided with an intake pipe 62 for transferring treated water.
And a circulation water meter 63 for measuring the flow rate of the reflux treatment water.
And a return pipe 64 for returning an appropriate amount of the refluxed treated water to the first anaerobic treatment chamber 50, and a surplus treated water measured as a result of being measured by the circulation water diversion meter 63, is returned to the aerobic treatment chamber 54. And a return air pipe 65 for blowing air into the water intake pipe 62 in order to exert an air lift effect.

An air pipe is connected to the lower end of the intake pipe 62, and air is blown into the intake pipe 62. As a result, since the inside of the intake pipe 62 is filled with the bubble water having a low density, a difference in specific gravity from the treated water outside the intake pipe 62 occurs, whereby the treated water can be pumped from the intake pipe 62.

Since this type of air lift pump, which is the circulation means 60, has no moving parts other than the blower for producing blown air, there is no fear of wear or failure and the use of corrosion resistant materials is easy. In the septic tank 100 of this embodiment, sewage treatment is performed as follows.

That is, when the sewage enters the first anaerobic treatment chamber 50 through the inflow pipe 18, first, in the first anaerobic treatment chamber 50, the organic substances in the sewage are converted to organic acids such as acetic acid and propionic acid by the acid-producing bacteria. The molecular weight is lowered, and the organic acid is decomposed into methane gas and carbon dioxide gas by methane bacteria. Further, ammonia nitrogen (NH ₄ ⁺ -N) is produced from organic nitrogen. This treated water naturally overflows through the communication hole 40a of the partition plate 40 and flows down into the second anaerobic treatment chamber 52, and the same anaerobic treatment as in the first anaerobic treatment chamber 50 is repeated.

The treated water in the second anaerobic treatment chamber 52 naturally overflows through the communication hole 42a of the partition plate 42 and the aerobic treatment chamber 54.
Then, the ammonia nitrogen (NH ₄ ⁺ -N) generated in the first and second anaerobic treatment chambers 50 and 52 is converted into nitric acid in the aerobic treatment chamber 54 by aerobic bacteria such as nitrifying bacteria. nitrogen (NO ₃ ^- -N) and nitrite nitrogen (N
O ₂ ^- is oxidized and decomposed to -N).

A part of the treated water is a water intake pipe 62 extending near the slot 44a and a water diversion meter 6 for circulation.
It is returned to the first anaerobic treatment chamber 50 via the 3 and the return pipe 64. In this way, when the treated water nitrified in the aerobic treatment chamber 54 is returned to the first anaerobic treatment chamber 50, the denitrifying bacteria in the first anaerobic treatment chamber 50 are treated with nitric acid contained in the reflux water. nitrogen (NO ₃ ^- -N) and nitrite nitrogen (NO ₂ ^-
By using oxygen such as -N), the organic substance introduced into the first anaerobic treatment chamber 50 is decomposed to obtain energy for survival. As a result, the decomposition of organic substances in the first anaerobic treatment chamber 50 is not limited to the anaerobic treatment, but the aerobic treatment chamber 5
Since it is also carried out by the denitrifying bacteria that act on the reflux water from No. 4, the ammonia nitrogen (N
It is possible to suppress an excessive increase in H ₄ ⁺ -N) and appropriately maintain the activity of anaerobic bacteria.

Further, this way nitrate nitrogen contained in the reflux water from the aerobic treatment chamber 54 to ^{- -} (-N NO ₂₎ oxygen, such as is denitrificans (NO ₃ -N) and nitrite nitrogen As a result of being utilized, these nitrate nitrogen and nitrite nitrogen are reduced and decomposed into molecular nitrogen (N ₂ ) and nitrous oxide (N ₂ O), and the nitrate nitrogen and nitrous oxide in the aerobic treatment chamber 54 are reduced. The concentration of nitrate nitrogen will be reduced as much as possible.

In the septic tank 100 of this embodiment, since the circulation means 60 is provided, the treated water in the aerobic treatment chamber 54 can be uniformly collected to maintain the activity of anaerobic bacteria.
Nitrogen components in wastewater are removed, and each treatment chamber 50, 5
The retention time at 2, 54 can be lengthened to increase throughput.

When the treated water in which the concentration of nitrate nitrogen or nitrite nitrogen is reduced in this way passes through the slot 44a under the partition plate 44 and reaches the precipitation chamber 56, it becomes turbid in the precipitation chamber 56. The quality component is precipitated and separated, and the supernatant liquid is transferred to the disinfection chamber 58. Finally, this supernatant liquid is used in the disinfection chamber 5
After being sterilized with chlorine at 8, it is discharged to the outside through the discharge pipe 20 as purified water. A medicine cylinder 70 for disinfection is provided above the partition wall 46.

In the present embodiment, such a septic tank 100
In at least the lower tank body of the tank body 10, the corrugated rib 3a is integrally formed, and the partition plates 40 and 42 are temporarily supported at the portions. The corrugated rib 3a is a rib extending along the circumferential direction of the tank body as shown in FIG.
A groove-shaped recess 5a is continuously formed in the top plate portion 4a along the longitudinal direction of the rib 3a.

The thickness of the corrugated rib 3a depends on the tank body 10.
Is substantially the same as the thickness t ₁ , preferably 3 to 12 mm, more preferably 5 to 11 mm, and particularly preferably 6 to 10 mm. If this thickness is too thin, the moldability will be poor and the strength will be too weak.

The height h of the corrugated rib 3a is preferably 10 to 100 mm, more preferably 15 to 90 m.
m, particularly preferably 20 to 80 mm. By setting in such a range, the function as a reinforcing rib can be utilized. The width a of the top plate portion 4a of the corrugated rib 3a is
Preferably 25 mm to 300 mm, more preferably 30 mm
200 mm, particularly preferably 35 to 150 mm. By setting in such a range, the function as a reinforcing rib can be utilized.

Width c of the base end of the corrugated rib 3a
Is determined to be equal to or larger than the width a of the top plate portion 4a, and is determined from the ease of die-cutting after molding and the reinforcing effect. 100 to 300% of the width a of the top plate portion 4a, preferably 110
It is set to about 200%. If this width c is too larger than the width a of the top plate portion, the reinforcing effect will be weakened.

In this embodiment, the corrugated rib 3a is provided.
In the top plate portion 4a of the above, a recess 5a is formed continuously or intermittently along the longitudinal direction of the rib 3a. The recess 5a
Is preferably formed substantially at the center of the top plate portion 4a, and the width of the recess 5a in the top plate portion 4a is preferably 5 to 50 mm, more preferably 6 to 40 mm, and particularly preferably 7 to 35 mm. . Width d at the bottom of the recess 5a
Is preferably 0 with respect to the width b at the top plate portion of the recess 5a.
The width is preferably ˜100%, more preferably 20-80%. The width d at the bottom of the recess 5a is
If the width b at the top plate portion is too large, it may be difficult to perform die cutting after molding, and if it is too small, the partition plate or the like cannot function as a temporary retainer.

The depth of the recess 5a is not particularly limited, but is preferably 50 to 100% of the height h of the rib 3a. If this depth is too shallow, the function of reinforcing the ribs 3a is small, and if it is too deep, there is a risk of protruding outside the tank body and becoming an obstacle. In this embodiment, the tank body 10 is made of a polynorbornene-based resin obtained by a reaction injection molding method (RIM). In particular, those composed of a ring-opened polymer of a norbornene-based monomer modified with an elastomer are preferable.

Examples of the elastomer include polybutadiene, styrene-butadiene copolymer (SBR), styrene-butadiene-styrene block copolymer (SB).
S), polyisoprene, styrene-isoprene-styrene block copolymer (SIS), ethylene-propylene-diene terpolymer (EPT) and the like.

The mixing ratio of the elastomer is 1 to 20 parts by weight, preferably 2 to 15 parts by weight, based on 100 parts by weight of the norbornene-based monomer. When the blending ratio of the elastomer is low, the flexibility decreases. Conversely, if the proportion of the elastomer is too large, the glass transition temperature decreases and the strength decreases, which is not preferable.

The monomer is a cycloolefin having a norbornene ring such as dicyclopentadiene, dihydrodicyclopentadiene, tetracyclododecene and tricyclopentadiene. The metathesis catalyst is not particularly limited as long as it is a known metathesis catalyst for bulk polymerization of norbornene-based monomers such as organic ammonium molybdates such as tungsten hexachloride, tridodecyl ammonium molybdate, and tri (tridecyl) ammonium molybdate. However, organic ammonium molybdate is particularly preferred.

Examples of the activator (cocatalyst) include alkylaluminum halides such as ethylaluminum dichloride and diethylaluminum chloride, alkoxyalkylaluminum halides thereof, and organic tin compounds. As a preparation for reaction injection molding, a reaction injection molding material containing a norbornene-based monomer, a metathesis catalyst, and an activator as a main component is a liquid comprising a norbornene-based monomer and a metathesis catalyst, and the norbornene-based monomer and the activator are used. Separately into two stable liquids and separate liquids. At the time of reaction injection molding, the two liquids are mixed, and then the mixed liquid is poured into a cavity of a mold and subjected to bulk polymerization in the cavity to obtain a tank body 10.

The mold used for the reaction injection molding is not necessarily an expensive mold having high rigidity, and is not limited to a metal mold, and a resin mold or a simple mold can be used. This is because the reaction injection molding of the norbornene-based resin can be performed at a relatively low temperature and a low pressure using a low-viscosity reaction liquid. The inside of the mold is sealed with an inert gas, and the components used for the polymerization reaction are stored under an inert gas atmosphere such as nitrogen gas.
And it is preferable to operate.

The mold temperature is preferably 10 to 150.
C., more preferably 30 to 120.degree. C., still more preferably 50 to 100.degree. Mold pressure is usually 0.1-1
It is in the range of 00 kg / cm ² . The polymerization time may be appropriately selected, but is usually from 30 seconds to 2 hours after the completion of the injection of the reaction solution.
It is 0 minutes, preferably 5 minutes or less.

Since the tank body 10 according to this embodiment is made of the polynorbornene resin obtained by the reaction injection molding method, the rib 3a can be easily integrally molded, and the relatively large tank body 10 can be easily manufactured. It can be molded. Further, the polynorbornene-based resin can have a sufficient pressure resistance required as a septic tank by utilizing a material characteristic of low specific rigidity but high specific strength.

In this embodiment, the corrugated rib 3a is used.
Since a recess 5a is continuously formed in the top plate portion 4a of the rib 3a along the longitudinal direction of the rib 3a, the corrugated rib 3 is formed.
The rigidity of a is further improved, the reinforcing effect of the ribs is further improved, and as a result, the strength of the tank body is improved. For example, by providing the recess 5a shown in FIG. 1, the second moment of area of the rib 3a in the x direction (corresponding to bending rigidity) is reduced by the recess 5a.
Compared to the rib 2 shown in FIG. 4 under the same conditions, except that a is not provided, it is improved by about 15% or more. Further, the second moment of area in the y direction is improved by 20% or more in the case shown in FIG. 1 as compared with the rib shown in FIG.

Further, as shown in FIG. 2, the recess 5a can serve as a temporary support or a main support for the partition plates 40, 42 of the septic tank, and work for positioning or mounting the partition plates 40, 42. It is possible to improve the sex. Second Embodiment FIG. 3 is a schematic perspective view of a main part of a corrugated rib according to another embodiment of the present invention.

In this embodiment, as shown in FIG. 3, a recess 5b is formed in the top plate portion 4b of the corrugated rib 3b.
A septic tank is constructed in the same manner as in the first embodiment except that the hole is formed into a hole shape and the rib 3b is intermittently formed along the longitudinal direction. Descriptions of overlapping parts will be omitted, and only different parts will be described.

In this embodiment, the arrangement pitch p of the recesses 5b is set.
Is preferably 5 to 100 cm, more preferably 5.
5 to 50 cm, particularly preferably 6.0 to 33 cm, and the length e of each recess 5b in the longitudinal direction is preferably 5 to 50 cm.
It is 50 mm, more preferably 6 to 40 mm, particularly preferably 7 to 35 mm. In this case, the size of the bottom of the recess 5b is determined in consideration of the ease of die cutting. The depth of the recess 5b is similar to that of the embodiment shown in FIG.

Also in the septic tank according to the present embodiment, since the top plate portion 4b of the corrugated rib 3b is formed with the recesses 5b which are intermittent along the longitudinal direction of the rib 3b,
The rigidity of the corrugated rib 3b is further improved, the reinforcing effect of the rib is further improved, and as a result, the strength of the tank body is improved.

Further, the recess 5b can serve as a temporary support or a permanent support for the partition plates 40 and 42 of the septic tank shown in FIG. 2, and improve the workability of positioning or mounting the partition plates 40 and 42. Can be made. However, in order to temporarily support the partition plates 40 and 42, it is necessary to provide a convex portion that fits into the concave portion 5b at the bottom of the partition plates 40 and 42.

The present invention is not limited to the above-described embodiment, but can be variously modified within the scope of the present invention. For example, in the above embodiment, the recesses 5a, 5 provided in the top plate portions 4a, 4b of the corrugated ribs.
Although the partition plates 40 and 42 are temporarily supported on b, the other parts of the septic tank may be temporarily supported or permanently pressed.

[0055]

As described above, according to the septic tank of the present invention, the top plate portion of the corrugated rib is formed with the concave portion continuously or intermittently along the longitudinal direction of the rib. Therefore, the rigidity of the corrugated rib is further improved, and the reinforcing effect of the rib is further improved.

Further, this recess can serve as a temporary support or a permanent support for parts such as a partition plate of the septic tank, an air diffuser, a transfer pipe, and a backwash pipe, and work for positioning or mounting these parts. It is possible to improve the sex.

[Brief description of drawings]

FIG. 1 is a schematic perspective view of a main part of a corrugated rib of a tank body of a septic tank according to an embodiment of the present invention.

FIG. 2 is a schematic vertical sectional view of a septic tank.

FIG. 3 is a schematic perspective view of a main part of a corrugated rib according to another embodiment of the present invention.

FIG. 4 is a schematic perspective view of a main part of a corrugated rib of a septic tank according to a conventional example.

[Explanation of symbols]

 3a, 3b ... Corrugated ribs 4a, 4b ... Top plate portions 5a, 5b ... Recesses 10 ... Tank body 100 ... Septic tank

Claims (1)

[Claims] 1. A corrugated rib extending along the circumferential direction of the tank is formed at least at the bottom of the tank of the septic tank so as to project into the tank, and a top plate portion of the corrugated rib is formed. In the septic tank, concave portions are formed continuously or intermittently along the longitudinal direction of the rib.