WO2005051805A1

WO2005051805A1 - Underground storage tank and septic waste treatment system

Info

Publication number: WO2005051805A1
Application number: PCT/NZ2004/000309
Authority: WO
Inventors: Neville Robert Moon; Paul Collier
Original assignee: Rx Plastics Limited
Priority date: 2003-11-27
Filing date: 2004-11-29
Publication date: 2005-06-09
Also published as: NZ529820A; AU2004293359A1

Abstract

A polymeric underground storage tank (3) for holding effluent, and the like, has a spherical first wall portion (11) joined to a collar (6) surrounding an accessway with a closure (5). The collar (6) is fixed to the first wall portion (11) above an equator (33) of the first wall portion (11). An offset (41) is formed between the axis of the collar (31) and the diametrical axis of the first wall portion (30). A bulbous second wall portion (14) joins the first wall portion (11) to the collar (6) to provide an increased liquid surface area near the top of the tank (3). A septic waste treatment system includes a plurality of such underground tanks (3) with pipes transferring products between them.

Description

Underground storage tank and septic waste treatment system

TECHNICAL FIELD

The present invention relates to underground storage tanks and septic waste treatment systems incorporating same. In particular, the present invention relates to multiple tank treatment systems that are adapted for burial in the ground, the tanks being connected by pipe to other tanks of the septic system.

BACKGROUND ART

The invention has particular applicability to septic tanks for holding effluent and will be described with particular reference thereto. It will be appreciated, however, that the invention has broader applications such as underground storage of other products, particularly where connection is required between the tanks, such as in septic waste treatment systems.

Underground tanks for septic use have historically been constructed primarily of concrete, although fiberglass, and steel tanks have also been used. The tanks include an inlet for receiving raw effluent; an outlet which permits treated fluids to pass to pass out and generally, there is an access opening in the top. To install a tank, an excavation is made of suitable size and depth to place the outlet generally in the plane of the surrounding ground. A mobile crane is employed to lower the tank into the excavation.

One of the problems encountered when installing the prior art tanks in this manner is a difficulty in bringing the mobile crane to the excavation site. Installation is limited to firm, generally level ground which is able to support the heavy equipment necessary to lift and lower the tanks. Another problem with the prior art tanks has been flotation. In installations in which the level of ground water becomes high, the tanks tend to become buoyant.

Prior attempts to produce polymeric underground tanks have failed to achieve successful products. Polymeric tanks tend to be more expensive than their concrete, fiberglass, or steel counterparts unless the tanks are made very lightweight. However, prior art lightweight tanks have failed to achieve the strength required to provide a satisfactory service life prevent damage from the superimposed soil and ground water loads.

There is thus a need for a new and improved tank which overcomes the above- referenced problems and others and in particular to provide a lightweight plastic tank which is cost and strength competitive with concrete, fiberglass, steel, and other prior art tanks.

Typical multi-tank underground waste treatment systems provide a cleaner effluent than the traditional single septic tank systems. Typically, these systems use standard septic tanks to hold the waste during processing and the installation of these systems is much like the installation of a simple anaerobic single chamber septic tank. However, these conventional systems suffer from several disadvantages. For example, two or more concrete tanks may provide separate septic, aeration and clarifier chambers which are connected by the requisite pipework. Such a system requires extensive excavation and the pipework internal and external to the system must be designed to allow for uneven settlement of the tanks and must be assembled on-site by a skilled worker. The main drawback with systems using conventional reinforced concrete septic tanks is that they are very large and heavy (enclosing a low volume per unit of surface area of the wails), thus making transport and installation costly. The tank quality may often be variable, the tanks themselves are also difficult to handle, and not optimally designed to resist loads from superimposed backfill.

It is an object of the present invention to provide an improved septic waste treatment system that addresses one or more of the foregoing problems with the conventional waste treatment systems or at least to provide the public with a useful choice.

Any publication cited in this specification is hereby incorporated by reference, however this does not constitute an admission that the document forms part of the common general knowledge in the art, in New Zealand or in any other country. The applicant reserves the right to challenge the pertinency of any publication cited herein, or to challenge the accuracy of any assertion made in a cited publication. As used herein, the word "comprises" means "includes, but is not limited to" and its derivatives have a corresponding meaning.

Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.

DISCLOSURE OF THE INVENTION

According to one aspect of the present invention there is provided an underground storage tank including:

a first wall portion which is substantially portion of a revolution of a conic section about an upright central axis;

at least one collar surrounding an accessway for allowing access into the tank, the collar being fixed to the first wall portion above an equator of the first wall portion and terminating in an opening, an axis of the collar being offset from the central axis toward an outer side of the first wall portion, and a second wall portion joining the first wall portion to the collar portion, the second wall portion being in the form of a bulbous protuberance.

The first wall portion is preferably a portion of the surface of a first sphere having an upright central diametrical axis. By a revolution of a conic section, is meant a geometric figure formed by cutting a cone with a plane and rotating the section. This definition includes a sphere and a spheroid (as well as a paraboloid and ellipsoid). As used herein, the term "equator" denotes a section perpendicular to the upright central axis which divides a surface into congruent parts

The first wall portion is preferably a portion of a first sphere, the central axis being a diametrical axis.

The bulbous protuberance allows an increased liquid surface area to be provided toward the top of the tank without a significant loss of strength and rigidity. The bulbous second wall is preferably a portion of a revolution of a conic section, most preferably a portion of the surface of a second sphere. The centre of second sphere preferably lies generally upon the upright diametrical axis of the first wall portion and the radius of the second spherical is smaller than the radius of the first sphere. The tanks are preferably one-piece polymeric tanks. Seamless one-piece polymeric tanks can be made by several methods, including blow moulding, thermoforming, and rotational moulding. Preferably the tanks are rotomoulded from polyethylene.

The collar portion reinforces the opening in the tank, receives a closure for closing the tank, and also contains and provides access to pipes and fittings connected to the tank. The collar is preferably symmetrical about the axis thereof, the axis of the collar extending parallel to the upright central axis of the first wall portion. The collar preferably includes one or more conical sections, tapering inwardly toward the opening. The offset of the collar toward the outer side of the first wall, portion advantageously allows for a reduction in length of a connector and any pipe connecting the collars of any two adjacent tanks. This arrangement also improves access since the closures may be located within a more compact area. The collar preferably has a convex outer connector-receiving face adapted to receive a connector for connection to an adjacent tank, preferably the connector-receiving face is frustoconical.

Preferably the tank further includes a ground support surface at a bottom of the first wall portion that is disposed generally in a horizontal plane. The ground support surface serves to support the tank upright upon the ground. The ground support surface is preferably provided by an annular rib integrally formed at the base of the lower hemisphere. The ground support surface need not be continuous and may be provided by a plurality of feet, or the like.

Preferably wherein a plurality of ribs in the first wall portion extend upwardly from the base of the first wall portion. The ribs strengthen the first wall portion and preferably extend circumferentially in generally upright planes from the annular rib.

The tank may further include a localised reinforcement through which^" an aperture may be cut for receiving a pipe for connection to an adjacent tank. The reinforcement is preferably formed by a localised increase in material thickness about the area which may be cut out, but optionally ribbing or other reinforcement may be provided. Preferably the reinforcement has a planar face that projects outwardly from an adjacent outer surface of the tank.

According to another aspect of the present invention a septic waste treatment system includes:

a plurality of underground storage tanks, each tank having a first wall portion which is substantially portion of a revolution of a conic section about an upright central axis; at least one collar on each tank, the collar surrounding an accessway for allowing access into the tank, the collar being fixed to the first wall portion above an equator of the first wall portion and terminating in an opening, an axis of the collar being offset from the central axis toward an outer side of the first wall portion; at least one pipe for transferring products between the tanks; closure means located at or near ground level when each tank is installed for closing the opening in the collar, and

at least one connector connecting the collars to form an assembly.

Preferably the septic waste treatment system is a modular system wherein a number of tanks may be connected to provide systems of different performance or capacity. Each tank is preferably of a type substantially as described above.

Preferably each connector has concave outer faces for abutting the convex outer connector-receiving on the collars of the tanks, most preferably the concave faces are frustoconical. The connectors act as structural members and may, for example be welded or secured by fasteners around the periphery of the abutting faces to join the tanks. The connectors are preferably one-piece seamless hollow member having walls substantially enclosing an interval volume.

A first connector for connecting three tanks is generally ring-shaped, having three tubular portions joined by three hollow joining portions, each joining portion having one of the concave faces.

A second connector for connecting two tanks includes two substantially parallel cylindrical portions joined by a longitudinal web, the concave faces being formed at opposing ends thereof.

In a first embodiment of the system the tanks include: a primary tank having an inlet for the introduction of influent into the system and holding anaerobic microorganisms; an aeration tank for holding aerobic microorganisms, the aeration tank receiving anaerobically treated influent from the primary tank; a clarification tank receiving aerobically treated influent from the aeration tank; a pump tank from which treated effluent is removed, wherein the primary tank includes two collars, a first of the collars being connected by a connector to the aeration tank, a second of the collars being connected by a connector to both the clarification tank and pump tank.

The tanks can be conveniently assembled in a modular manner to provide systems providing different treatments e.g. for receiving material from an existing septic tank for further treatment.

In a second embodiment of the system the tanks include:

a first tank having an inlet for the introduction of influent into the system;

a second tank receiving influent from the primary tank;

a third tank from which treated effluent is removed from the system, wherein

the first tank includes a collars connected by a connector to both the second tank and third tank.

In a third embodiment of the system the tanks include:

a first tank having an inlet for the introduction of influent into the system;

a second tank from which treated effluent is removed from the system, wherein the first tank includes a collar connected by a connector to the second tank.

This invention provides a multi-tank septic waste treatment system capable of being shipped and installed as a complete assembly ready for installation with a minimum of work necessary on-site. The shape of the tanks allows for efficient space utilisation, it makes a compact system, the reduction in overall size and weight of the system allowing an increased strength-to-weight ratio to be achieved. The shape of the tank as a revolution of a conic section not only strengthens the wall of the storage tank against the crushing due to hydrostatic pressure but, without requiring significantly deeper excavation, allows superimposed backfill to better anchor the tank to counter hydrostatic uplift. This also allows the tank to be constructed of polyethylene or similar materials with relatively thin walls, rather than more expensive fiberglass or metal. Moreover the disturbance necessary for excavations is minimized. It also provides a reduced possibility of being damaged, and ready access is available to the piping and fittings making it convenient to inspect and repair. Structurally, it also minimizes the weight and stress resulting from the backfill to efficiently meet or exceed industry structural standards, providing a strong and rigid construction capable of a long operating life.

BRIEF DESCRIPTION OF DRAWINGS

Further aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings in which:

Figures 1 a-1 d are a top view, bottom view, first and second side elevations respectively of a first embodiment of an underground storage of the present invention; Figure 2 is a pictorial view of a first embodiment of the septic waste treatment system of the present invention;

Figure 3a and 3b are pictorial views of a closure for the tank of Fig. 1 ;

Figure 4 is a sectional view (along line XX of Fig. 5) of the system of Fig. 2; Figure 5 is a plan view of the system of Fig. 4;

Figures 6a and 6b are pictorial views of two variations of a connector for joining two tanks in the septic waste treatment system of the present invention;

Figure 7 is a pictorial view a connector for joining three tanks in the septic waste treatment system of the present invention; Figure 8 is a pictorial view of a second embodiment of the septic waste treatment system of the present invention, and

Figure 9 is a pictorial view third embodiment of the septic waste treatment system of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

A first preferred embodiment of a polymeric tank 3 for underground storage of effluent is shown in Figs 1a-1 d. The tank 3 generally includes a lower spherical first wall portion 1 1 , a bulbous second wall portion 14 and a collar 6 seamlessly formed in one-piece. The upper end of the collar is closed by a separate closure 5.

The tank 3 is elongated vertically in the direction of the central axis 30 which is an upright diametrical axis of the spherical first wall portion 1 1. The first wall portion 11 includes a lower hemisphere 32 bounded by equator 33 and integrally formed with a congruent and concentric upper hemispherical portion 34 to which the collar portion 6 and second wall portion 14 are fixed. The first wall portion 11 is a portion of the surface of a first sphere having a radius R1.

The bulbous protuberance 14 allows a larger liquid surface area to be provided toward the top than would be possible without increasing the diameter of either the spherical first wall portion 11 or of the collar 6. The bulbous second wall portion 14 is part of a spherical surface having a centre 35 lying on upright diametrical axis 30. The intersection between the first and second wall portions 11 and 14 lies in a horizontal plane 36. Although a small radius (not shown) connects the two wall portions 11 and 14, they generally intersect at an obtuse angle 37. The equator of the spherical second wall portion 14 preferably lies in plane 36. The bulbous second wall portion 14 is a portion of the surface of a second sphere having a radius R2.

The collar 6 includes frustoconical first, second and third sections 38, 39 and 40 which surround an accessway closed by the closure 5. The sections 38- 40 are coaxial with the collar axis 31 which extends parallel to the upright central axis 30 of the first wall portion 11. The conical sections 38- 40 have different cone angles and taper progressively inwardly toward the top of the collar 6. The collar 6 and first wall portion 11 are eccentric, the axes 30 and 31 separated by dimension 41 so as to offset the collar 6 toward an outer side 42 of the first wall portion 11. The collar preferably has a convex outer connector-receiving face adapted to receive a connector for connection to an adjacent tank, preferably the connector-receiving face is frustoconical.

Eight stiffening ribs 19 integrally formed in the spherical first wall portion 11 extend in vertical planes from an annular rib 20 in the base 48 (best seen in Fig. 2a). The annular rib 20 is concentric with the central axis 30 and has a bottom edge that is disposed generally in the horizontal plane. This annular edge provides a ground support surface to support the tank upright upon the ground. Reinforcements 18a, 18b are provided in the collar 6 around the areas cut out to receive the pipes (not shown) for connection to an adjacent tank. The reinforcements 18a, 18b are formed by a localised increase in material thickness, projecting outwardly from an adjacent outer surface of the tank. The reinforcements 18a, 18b include an upright planar face 43 extending tangentially to the wall of the collar 6.

The closure 5 is the only part of the tank 3 which is not integrally formed. As shown in Figs 3a and 3b, the closure 5 includes a ring 44 and a top cover 45 received therein. The flange 46 on the ring 44 is received in the mouth of the opening at the top of the collar 6.

A second preferred embodiment of a polymeric tank 1 is illustrated in Figs 3-5 (together with tanks 2 and 4 which have the features of tank 3, but different dimensions). Like numbers are used herein to refer to like components. Tank 1 is of similar construction to tank 3, but does not have the bulbous second wall portion 14 and includes two collars 6a, 6b, the axes 31a, 31b of which are both offset on opposing sides of the central diametrical axis 30 thereof. The spherical first wall portion 11 on tank 1 has a diameter substantially equal to the height of tank 3, requiring the collars 6a, 6b to be shorter than on tanks 2-4 such that the respective closures 5 are located substantially at ground level when each tank 1-4 is installed on a flat-based excavation.

Referring to Fig. 2, a first embodiment of the septic waste treatment system of the present invention combines anaerobic and aerobic treatment and includes the four underground liquid storage tanks 1-4, each of which has a wall section 11 which is spherical. Pipes and fittings 7 pass through each collar 6, 6a, 6b for transferring the contents between the tanks 1 -4. Connectors 8 joins the offset collars 6 and 6b (of tanks 1 and 2 respectively) and connector 9 joins the three offset collars 6 and 6a (of tanks 1 , 3 and 4 respectively) to form an assembly. The connectors 8, 9 engage with the upper sections 38 of the collars 6, 6a, 6b, generally at an outermost position thereon. This geometry allows relatively short connectors 8, 9 to join two or three tanks respectively. It also reduces the length of any pipe connecting the collars of any two adjacent tanks and improves access, since the closures 5 may be located within a more compact area. This mechanical design assures structural integrity, tightness, and shape, and is thus able to resist high static and dynamic loads, and resist uneven settlement of the tanks. Also, this allows the system to be delivered completely finished ready to be installed in an excavation on- site requiring only the supply lines to be attached. Figs 4 and 5 illustrate the construction and operation of the system in further detail. Primary tank 1 has an inlet 9 for the introduction of influent into the system and holds anaerobic microorganisms. The aeration tank 2 holds aerobic microorganisms, and receives the anaerobically treated influent from the primary tank 1 via pipe 7a. The clarification tank 3 is connected to the aeration tank 2 by pipe 7b and to the primary tank 1 by a sludge return line 7c. Treated waste is passed through pipe 7d from the clarification tank 3 to the pump tank 4 tank, from which it is intermittently pumped via outlet 10 for irrigation or discharge to a drain or the like.

As seen in Figs. 6a, 6b and 7, the connectors 8 and 9 have two or three concave faces 16 respectively for abutting the frustoconical sections 38 for connecting two or three tanks respectively. The connectors 8, 9 act as structural members and may be welded around the periphery of the faces 16 to join the tanks, transferring structural loads for added strength and rigidity. The connectors 8, 9 also serve to protect the pipes connected between the tanks during backfilling.

The first connector 8 is a one-piece seamless hollow member which is oval in cross- section. Fig. 6b illustrates an alternative connector 8a for joining two tanks. Connector 8a includes two substantially parallel cylindrical portions 50, 51 joined by a longitudinal web 52, the concave faces 16 being formed at opposing ends thereof.

The second connector 9 for connecting three tanks is generally ring-shaped and is also is a one-piece seamless hollow member. Three tubular portions 54, 55 and 56 are joined by three hollow joining portions 57, 58 and 59. Each joining portion 57-59 has one of the concave faces 16. When joining the collars of two tanks the tubular portions 54, 55 and 56 extend generally radially from the centres of the collars. The ring-shape of connector 9 allows backfill to be inserted through the central aperture to fill the space between the three tanks when they are buried. Figs 8 and 9 illustrate the manner in which the tanks may be assembled in a modular manner to provide systems for differing levels of treatment. Fig. 8 shows a second embodiment of the system comprising a two-stage system, with a septic tank or primary tank 1 for anaerobic digestion, a clarification tank 3 and a pump tank 4 all fixed together by connector 9. Fig. 9 illustrates a third embodiment of the system comprising a single stage septic tank or primary tank 1 fixed by connector 8a to a pump chamber 4.

In the use of the system, the tanks 1-4 are manufactured, assembled to form the treatment system which is then delivered complete and ready for immediate use e.g. in the form shown in Fig. 1. A hole is excavated which is large enough to accommodate the system which is then lowered into the hole. Then the ground is backfilled so that only closures 5 are visible at ground level. The system is not fragile and may be handled with the same degree of care required for conventional polyethene tanks. All of the parts which might wear out or fail due to corrosion over a period of years are readily accessible within the collar 6. The use of closure 5 makes it possible to provide access when a major job of repair is required, even permitting a worker to enter if the tank is large enough. Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof.

Claims

WHAT WE CLAIM IS:

1. An underground storage tank including a first wall portion which is substantially portion of a revolution of a conic section about an upright central axis; at least one collar surrounding an accessway for allowing access into the tank, the collar being fixed to the first wall portion above an equator of the first wall portion and terminating in an opening, an axis of the collar being offset from the central axis toward an outer side of the first wall portion, and a second wall portion joining the first wall portion to the collar portion, the second wall portion being in the form of a bulbous protuberance.

2. The tank of claim 1 wherein the first wall portion which is a portion of the surface of a first sphere having an upright central diametrical axis.

3. The tank of claim 1 or claim 2 wherein the bulbous second wall portion is a portion of the surface of a second sphere.

4. The tank of claim 3 wherein the centre of the bulbous second wall portion lies generally upon the upright central axis of the first wall portion and the radius of the bulbous second wall portion is smaller than the radius of the first sphere.

5. The tank of any one of the preceding claims wherein each collar is symmetrical about the axis thereof, the axis of the collar extending parallel to the upright central axis of the first wall portion.

6. The tank of claim 4 wherein each collar includes one or more conical sections, tapering inwardly toward the opening.

7. The tank of any one of the preceding claims wherein each collar has a convex outer connector-receiving face adapted to receive a connector for connection to an adjacent tank.

8. The tank of any one of the preceding claims wherein the tank further includes a ground support surface at a bottom of the first wall portion that is disposed generally in a horizontal plane.

9. The tank of claim 8 wherein the ground support surface is provided by an annular rib formed at the base of the first wall portion.

10. The tank of any one of the preceding claims wherein a plurality of ribs in the first wall portion extend upwardly from the base of the first wall portion.

11. The tank of claim 10 wherein the ribs extend circumferentially in generally upright planes.

12. The tank of any one of the preceding claims wherein the tank further includes a localised reinforcement through which an aperture may be cut for receiving a pipe for connection to an adjacent tank.

13. The tank of claim 12 wherein the reinforcement is formed by a localised increase in material thickness about the area which may be cut out.

14. The tank of claim 13 wherein the reinforcement has a planar face that projects outwardly from an adjacent outer surface of the tank.

15. A septic waste treatment system including: a plurality of underground storage tanks, each tank having a first wall portion which is substantially portion of a revolution of a conic section about an upright central axis; at least one collar on each tank, the collar surrounding an accessway for allowing access into the tank, the collar being fixed to the first wall portion above an equator of the first wall portion and terminating in an opening, an axis of the collar being offset from the central axis toward an outer side of the first wall portion; at least one pipe for transferring products between the tanks; closure means located at or near ground level when each tank is installed for closing the opening in the collar, and at least one connector connecting the collars to form an assembly.

16. The septic waste treatment system of claim 15 wherein each of said tanks is an underground storage tanks as claimed in any one of claims 1 to 13.

17. The system of claim 15 or claim 16 wherein one of the connectors has concave faces for abutting the convex outer connector-receiving on the collars of the tanks

18. The system of claim 17 wherein the concave faces are frustoconical.

19. The system of any one of claims 15-18 wherein one of the connectors is a one- piece seamless hollow member having walls substantially enclosing an interval volume.

20. The system of claim 18 or claim 19 wherein one of the connectors for connecting three tanks is generally ring-shaped, having three tubular portions joined by three hollow joining portions, each joining portion having one of the concave faces.

21. The system of claim 18 or claim 19 wherein one of the connectors for connecting two tanks includes two substantially parallel cylindrical portions joined by a longitudinal web, the concave faces being formed at opposing ends thereof.

22. The system of any one of claims 15-18, the tanks including: a primary tank having an inlet for the introduction of influent into the system and holding anaerobic microorganisms; an aeration tank for holding aerobic microorganisms, the aeration tank receiving anaerobically treated influent from the primary tank; a clarification tank receiving aerobically treated influent from the aeration tank; a pump tank from which treated effluent is removed, wherein the primary tank includes two collars, a first of the collars being connected by a connector to the aeration tank, a second of the collars being connected by a connector to both the clarification tank and pump tank.

23. The system of any one of claims 15-18, the tanks including:

a first tank having an inlet for the introduction of influent into the system; a second tank receiving influent from the primary tank; a third tank from which treated effluent is removed from the system, wherein

24. The system of any one of claims 15-18, the tanks including:

a first tank having an inlet for the introduction of influent into the system;

a second tank from which treated effluent is removed from the system, wherein

the first tank includes a collar connected by a connector to the second tank.

25. A one-piece polymeric tank for underground storage substantially as hereinbefore described and as illustrated in the accompanying drawings.

26. A septic waste treatment system substantially as hereinbefore described and as illustrated in the accompanying drawings.