AU713900B1 - Linear buoyancy separation device - Google Patents

Description

LINEAR BUOYANCY SEPARATION DEVICE Technical Field The present invention relates to a device for removing pollutants from a flow of liquid and, in particular, from flowing storm water in a drain.

Background Art In times of heavy rain, flooding is often controlled by use of a network of stormwater drains which convey the storm water away from flood-prone locations, such as cities, to areas where the water may be safely dissipated.

Such areas may be ocean outlets or natural wetland catchment areas, where the water is reintroduced into wetlands. A major problem is that storm water often collects various types of pollutants ranging from light particle pollutants such as dust and oil to heavy or large pollutants such as coarse sediments, paper, cardboard, bottles and pieces of wood or metal. Such pollutants are environmentally detrimental and can also cause blockage in drainage systems, which can result in flooding or physical damage to the drainage system of surrounding areas. It is therefore desirable to be able to remove, in a convenient way, at least a portion of these pollutants from the drainage system.

Many attempts have been made in the past to remove such pollutants, with varying degrees of success. For example, devices consisting of cylindrical chambers into which a stormwater drain empties have been employed. These cylindrical chambers generally cause the inflowing stormwater to circulate around the chamber in a whirlpool-like manner, encouraging heavy pollutants to drop to the bottom of the chamber and light pollutants to float to the surface of the water. An outlet then removes the 'clean' water from the chamber and allows it to rejoin the stormwater pipe. Other systems include grates, to filter the pollutants from the water. These systems have the disadvantage that the grates readily become clogged and need to be cleaned frequently. This also leads to blockages in the system which has an adverse effect on its ability to disperse water.

When designing a stormwater drain system, it is important to design the system so as to try and maintain the energy of the flowing stormwater. It is also desirable to attempt to avoid chokes or reductions in network flow capacity throughout the system, otherwise flooding is more likely to occur, particularly during sudden and heavy storms. The devices of the prior art all have the disadvantage that they significantly disrupt the flow of water through the stormwater drain system, dissipating the energy of the stormwater and decreasing the effectiveness of the system.

It is recognised that to maintain a substantially consistent flow of water, the shape and direction of the water jet should be maintained as much as possible so as to conserve the energy of the jet. If a flow of water is caused to change direction rapidly, the natural flow of the jet is disrupted and large energy losses occur. This results in reduced flow capacities at particular points in the stormwater drain system, reducing the system's efficiency and possibly causing flooding upstream. Prior art systems that cause the water to circulate or to pass through a grid system dramatically disrupt the flow of water.

It would therefore be advantageous to provide a device which can remove at least a portion of the pollutants from the water in a stormwater drain system whilst minimising the energy loss of the water flows. The device of the present invention is directed to providing an improved device for separating solid pollutants from water flows.

Summary of the Invention According to a first aspect of this invention there is provided a stormwater pipe section for use in a holding pit of a stormwater drainage system, said pipe section including at least one elongated slit extending along a length of the pipe section wherein; the pipe section is adapted to be located intermediate a pit inlet and a pit outlet; the said at least one elongated slit is adapted to enable contact between liquid passing through the pipe section and liquid in the holding pit and to enable solid pollutants to pass through said at least one elongated slit; and the width of said elongated slit being at least about 1 cm, said width being substantially uniform along said elongated slit.

oVY It is preferred that the pipe section has two opposed, substantially parallel elongated slits. The longer the slit, the greater will be the effectiveness of the pipe section in discharging solid pollutants. Accordingly, it is preferred that the elongated slits extend along a substantial length, or preferably the entire length, of the pipe section. The length of each elongated slit does not have to be equal.

It is further preferred that the pipe section includes a shallow bend or curve in the same plane as the plane defined by the two elongated slits. If the bend or curve is too great, this may cause significant disruption in the flow of the stormwater, a substantial loss of energy and a higher risk of flooding upstream.

The narrower the elongated slits, the greater will be the energy retention capability of stormwater flowing through the pipe section. However, this will reduce the amount of solid pollutants able to be removed from the stormwater.

On the other hand, the wider the elongated strip, the greater will be the energy loss experienced by the stormwater whilst flowing through the pipe section, but the greater will be the ability to remove solid pollutants from the stormwater.

Thus, in designing the pipe section, a balance needs to be struck between energy retention and the extent of pollutant removal. Accordingly, it is preferred that the width of each elongated slit is between about 10% and 25% of the circumference of the pipe section. However, a slit width of even 1% (which equates to about 1 cm on standard pipes envisaged for this application) would be viable. The desired width is also dependent on the type of pollutants to be removed.

It is further preferred that the pipe section includes two substantially identical pipe panels, separated by the two elongated slits. The two pipe panels may be joined together by suitable connection means. Preferably, the connection means are located at the ends of each panel. The connection means may be integral with the two panels when the pipe section is made from cement or plastic). Alternatively, the pipe panels may have any other suitable connection means, such as metal braces or rings fastened to the panels.

It is possible for the pipe panels not to be joined together, in which case they will need to be held in position by securing means located within the water reservoir.

3a The pipe section is intended to be located in a stormwater holding pit where it extends between a pit inlet and a pit outlet.

According to a second aspect of this invention there is provided a stormwater holding pit, including: a pollution separation device for removing pollutants from a flow of liquid, said separation device including; a pit; a pit inlet and a pit outlet; and a pipe section located intermediate said pit inlet and said pit outlet, said pipe section including at least one elongated slit extending along a length of the pipe section said slit being adapted to enable contact between liquid passing through the pipe section and liquid in the holding pit and to enable solid pollutants to pass through said at least one elongated slit.

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The at least one elongated slit should be facing either upwards or downwards. Heavy (sinkable) pollutants will tend to migrate downwards in the pipe whilst flowing there through and, thus, where the slit is located at the bottom part of the pipe section (facing downwards) such pollutants will come into contact with stationary water contained in the pit. This causes the pollutants to slow down, so that the influence of gravity may exceed the flow inertia, and the pollutants may then pass through the slit and fall to the bottom of the pit where they are collected until removed. Light (floatable) pollutants will tend to migrate upwards in the pipe whilst flowing through and, thus, where the slit is disposed in the upper part of the pipe (facing upwards), such pollutants will come into contact with stationary water in the pit. The pollutants are thereby slowed down and then are able to pass through the slit and float to the surface of the water in the pit.

It is preferred that the pipe section has two opposed, substantially parallel elongated slits. Preferably, the elongated slits extend along a substantial length, or preferably the entire length of the pipe section. These slits should be orientated so that one faces upwards and the other faces downwards. This enables both heavy and light pollutants to be removed from the stormwater simultaneously. The preferred width of each elongated slit can be chosen as discussed above.

It is further preferred that the pipe section includes a shallow bend or curve in the same plane as the plane defined by the two elongated slits. In use, this bend should be orientated so that one or, preferably, both of the ends of the pipe section are located in the pit at a higher location than a central portion of the pipe section. This shallow bend or curve serves to smoothly deflect the stormwater in the pipe section into the pit outlet.

A short, downwardly sloping deflection plate may extend from a base of the chamber outlet so as to further assist this deflection. Preferably, the pit inlet will be vertically higher than the pit outlet.

The abovementioned bend in the pipe section helps to redirect the stormwater in a slight upward direction before it passes through the chamber outlet to an outflow pipe. Such upward directed flow of stormwater through the outlet helps to inhibit (due to gravity) heavy pollutants from passing through the R R pit outlet.

It is further preferred that stormwater entering the pit through the pit inlet will have a slight downward direction. This may be effected by having an inflow pipe located outside the pit, with a slight bend or curve.

Preferably, the pipe section is adapted to be removably installed within the chamber. Easy removal of the pipe section will facilitate cleaning of the chamber during removal of collected debris (in particular, the heavy pollutants).

In order to minimise water movement in the chamber, it is preferred that the chamber is square-shaped (or has any other suitable non-circular shape).

Alternatively, the chamber may contain one or more baffle plates, or other suitable means, to inhibit water movement within the chamber.

According to a third aspect of this invention there is provided a method of separating solid pollutants from stormwater, said method including passing stormwater through a pipe section or a stormwater holding pit as described above.

Brief Description of the Drawings Figure 1 is a front elevation of the device according to the present invention.

Figure 2 is a cross-section of the pipe of figure 1 along the line A-A.

Figure 3 is a plan view of the device of figure 1.

Figure 4 is a schematic diagram illustrating the principle employed by the present invention.

Figure 5 is a front elevation of an alternative form of the device of the present invention.

Referring to figure 1, pollution separation device 10 includes chamber which consists of a pit dug below ground level, an inlet 21, an outlet 22 and slotted pipe 50. Inflow pipe 30 and outflow pipe 40 may be part of an existing stormwater drain network in which device 10 is conveniently installed.

Alternatively, device 10 may be installed as part of a new stormwater drain network.

The main components of the device are factory pre-fabricated and installed on site. An in situ reinforced concrete base is poured for the chamber.

Interlocking wall panels are set together to form the chamber 20 with special blocked out panel units for the inlet and outlet openings. These blocked out panel units fit the inlet and outlet pipe connections. The slotted pipe 50 which may be made of galvanised steel, is then put into place.

In the preferred embodiment, slotted pipe 50 consists of two inwardly curved shells which when secured into position, form circular slotted pipe with an upper slot 51 extending along the length of the upper surface of slotted pipe 50 and a lower slot 52 extending along the length of the lower surface of slotted pipe 50, as shown in figure 2.

Chamber 20 may be of any shape, however, in a preferred form, it will be a rectangular or square shaped box so that water contained in chamber 20 is not able to maintain any momentum due to the sharp changes in direction the water experiences in moving around the chamber.

When water enters the stormwater drain system, it will eventually reach inflow pipe 30. If the amount of water in pipe 30 is small, the water will trickle over the bottom lip of pipe 30 through lower slot 52 of pipe 50 and into chamber

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As water continues to flow, chamber 20 will begin to fill with water and pollutants until the water in the chamber reaches the level of the outflow pipe at which time the water continues its journey through the stormwater drain network. Heavy pollutants will have sunk to the bottom of chamber 20 and will remain there. A grate may be located at the outlet to prevent light and floating pollutants from entering the outflow pipe The device of the present invention is very effective in instances of low water flow, however, its main advantage becomes apparent in situations of high water flow, where many prior art devices are inadequate. In such instances, the jet of water flow may substantially or completely fill the volume of inflow pipe and will be ejected intochamber 20 with such force that it will be effectively contained within slotted pipe 50 to be conveyed through the chamber 20 to the outlet 22 and into outflow pipe 40. Because the jet of water has effectively maintained its shape, and has not experienced any dramatic changes in direction throughout its journey through the chamber 20, its energy losses are minimal, resulting in a virtually uninterrupted flow.

As the jet passes through slotted pipe 50 one of three situations may be present. In the first instance, the level of water in chamber 20 may not have reached the level of the lowermost surface of the slotted pipe 50. In this case, some of the water and pollutants in the jet will fall through slot 52 into the chamber as described above. In the second instance, the water level in chamber 20 may be about level with the axis of the slotted pipe 50. In this case, the lower portion of the fast moving water in pipe 50 will come into contact with the relatively static water in chamber 20. This will result in an exchange of momentum between the fast moving water and the static water, the effect of which will be to slow down the water in the lower portion of pipe 50. Heavy pollutants (ie. those with a specific gravity greater than water) in this region of the water will in turn be slowed down causing them, under the influence of gravity, to drop out of slotted pipe 50 through lower slot 52. In the third instance, the level of the chamber water will be above the uppermost level of the slotted pipe 50. The same exchange of momentum as described above will also occur at the interface between the water in the upper portion of pipe 50 and the chamber water, causing the water in the upper portion of the pipe to slow down.

Lighter pollutants are more likely to be in this top region and as they are caused to slow down, they will tend to rise out of the pipe 50 through upper slot 51.

This situation is illustrated schematically in figure 4, where the outline of slotted pipe 50 is shown as phantom line 71. The direction of flow of the water jet in pipe 50 is shown by arrow 70. The region of static chamber water is indicated by 73. Regions 72 are the interfaces between the water in pipe and the chamber water, and it is in these regions that the abovementioned partial exchange of momentum occurs. Regions 72 have greater energy than regions 73, but less energy than region 70. The progress of pollutants in regions 72 will thus be slowed down, and the heavy pollutants will be able to sink down into chamber 20. The light pollutants will be able to float up into chamber 20. The water jet indicated by 70 will retain most of its energy and will thus maintain a substantially constant flow rate.

Figure 3 shows a plan view of the invention as shown in figure 1. Like elements are labelled accordingly. Upper slot 51 in the topmost surface of slotted pipe 50 is shown.

Figure 5 shows an alternative form of the pollution separation device In this embodiment, inflow pipe 30 begins to turn down at bend 31 slightly before inlet 21 so as to convey the jet of water in a downwards direction. At some point 53 before outlet 22, slotted pipe 50 will begin to turn upwards to direct the jet of water upwards to join outflow pipe 40. The changes in direction of travel experienced by the water jet are gradual and gentle so as not to have large energy loss of the water jet. This arrangement will increase the efficiency of the pollution separator device in removing heavy pollutants, because some heavy pollutants that have not dropped through slot 52 before passing through outlet 22 will be urged to fall back into chamber 20 due to the influence of gravity. Baffle plate 60 may be located at outlet 22 to assist in deflecting the water jet up towards outlet 22.

Preferably, chamber 20 has an access port and lid 23 through which access may be gained for regular cleaning and maintenance. Slotted pipe may be completely removed from chamber 20 to facilitate cleaning.

Alternatively, slotted pipe 50 may be hingedly supported at either of its ends so that it may be tilted up to a vertical position to clear the way to the pit instead of being completely lifted out of the pit.

The width and length of slots 51 and 52 in slotted pipe 50 may also be varied to accommodate different conditions and applications. If the slots are narrower and shorter,the jet of water will be contained more effectively and thus improve flow rate. However, fewer pollutants will be able to be removed. With wider and longer slots, more pollutants may be removed, but the water jet will not be contained as effectively, resulting in a greater disruption in flow. In this way, a suitable balance may be found between the amount of pollution separation and maintaining a constant flow rate to suit the particular circumstances of application. The width and length of the slots could be adjusted by way of sliding plates associated with pipe 50 which can be slid into position to provide a desired slot width and/or length and fixed into position by any suitable means. The sliding plates could conceivably be attached to a floating mechanism which controls the position of the plates to adjust the slot width depending upon the level of water in the pit. At full capacity, the slits will be made narrower to enable the slotted pipe to pass more water through at the expense of pollution removal. When the pit is not so full, the slits will be made wider so as to allow more pollutants to be removed from the water at the expense of flow through.

Because device 10 is relatively easy to install, total costs are low when compared to prior art devices that involve complicated and extensive framework to construct multi-chamber reinforced concrete devices with large area screen meshes.

Maintenance is also made much easier by the device of the invention.

Because of complicated structures used in prior art devices, certain sections of the chamber are not always easily accessible. Thus, cleaning of chambers is traditionally carried out using suction hoses, which is time consuming and costly. The bulk of gross materials is most effectively removed by using a claw or grab arm to lift the debris into a truck or skip bin. Because of the simple structure of the present invention, the majority of the cleaning process may be done by such a claw or grab arm. Since slotted pipe 50 can be tilted up or lifted out, chamber 20 is left open and unobstructed, allowing easy access to all parts of the chamber. Fine material and sediments can then be removed, though not necessarily at every cleanout, by suction hose.

The device of the invention is also ideal for use in industrial catchments.

Industrial liquids spilled into stormwater draining systems are often of different density to water, and can thus be separated from the water by this device. The chamber can hold moderate amounts of such spillages and can assist in cleanups as well as help to identify the factory responsible for the spillage where the factory is at a factory stormwater discharge point.

Furthermore, due to the simplicity of design and the absence of grates in the device of the invention, blockages caused by large or long objects such as fence palings are much less likely than in prior art systems.

It will be appreciated that variations and additions are possible within the general inventive concept of the disclosure.

Claims (17)

1. A stormwater pipe section for use in a holding pit of a stormwater drainage system, said pipe section including at least one elongated slit extending along a length of the pipe section wherein; the pipe section is adapted to be located intermediate a pit inlet and a pit outlet; the said at least one elongated slit is adapted to enable contact between liquid passing through the pipe section and liquid in the holding pit and to enable solid pollutants to pass through said at least one elongated slit; and the width of said elongated slit being at least about 1 cm, said width being substantially uniform along said elongated slit.

2. A pipe section according to claim 1 wherein the pipe section has two opposed, substantially parallel elongated slits extending along a length of the pipe section.

3. A pipe section according to claim 1 or claim 2 wherein said elongated slit or slits extends along substantially the entire length of said pipe section.

4. A pipe section according to any one of claims 1 to 3 wherein the width of said elongated slit or slits is between about 10% and 25% of the circumference of the pipe section. A pipe section according to any one of claims 2 to 4 wherein the pipe section has a bend along a portion of its length in a plane defined by the two elongated slits.

6. A pipe section according to any one of claims 2 to 5 wherein said pipe section consists of two substantially identical pipe panels separated by the two elongated slits.

7. A pollution separation device for removing pollutants from a flow of liquid, said separation device including; a pit; a pit inlet and a pit outlet; and a pipe section located intermediate said pit inlet and said pit outlet, said pipe section including at least one elongated slit extending along a length of the pipe section, said slit being adapted to enable contact between liquid passing through the pipe section and liquid in the holding pit and to enable solid pollutants to pass through said at least one elongated slit.

8. A pollution separation device according to claim 7 wherein said pipe section has two opposed, substantially parallel elongated slits extending along a length of the pipe section.

9. A pollution separation device according to claim 7 or claim 8 wherein the width of said elongated slit or slits is at least about 1cm, said width being substantially uniform along said elongated slit. A pollution separation device according to any one of claims 7 to 9 wherein the width of said elongated slit or slits is between about 10% and of the circumference of the pipe section.

11. A pollution separation device according to any one of claims 8 to wherein said pipe section has a bend along a portion of its length in a plane defined by the two elongated slits.

12. A pollution separation device according to claim 11 wherein an outer portion of the bend faces downwardly.

13. A pollution separation device according to any one of claims 7 to 12 wherein said pit inlet is vertically higher than said pit outlet.

14. A pollution separation device according to claim 13 wherein an inflow pipe directing liquid into said pit has a slight curvature to direct said liquid into I .said pit in a slightly downwards direction. "3 V A pollution separation device according to any one of claims 7 to 14 wherein a horizontal cross-section of said pit is substantially square-shaped.

16. A pollution separation device according to any one of claims 7 to wherein said pipe section is removably installed in said pit.

17. A method of separating solid pollutants from a liquid, said method including the step of passing said liquid through a pollution separation device according to any one of claims 7 to 16.

18. A stormwater pipe section substantially as hereinbefore described with reference to the accompanying figures 2, 3 and 4.

19. A pollution separation device substantially as hereinbefore described with reference to the accompanying figures 1 to A method of separating solid pollutants from a liquid substantially as hereinbefore described with reference to the accompanying figures. DATED this 221d day of April, 1999. RAY PARSELL WATERMARK PATENT TRADEMARK ATTORNEYS UNIT 1, THE VILLAGE RIVERSIDE CORPORATE PARK

39-117 DELHI ROAD NORTH RYDE NSW 2113 AUSTRALIA PJM:MP:ES DOC 23 AU6365198.WPC UAC /C