Combined sewer overflow

Abstract

 A combined sewer overflow comprises a chamber 1 formed from a length of plastics pipe for ease of off-site manufacture. The chamber has storm and foul water inlet and outlet ports 4, 5 for connection to a drainage system. A barrier 12 and weir 17 is provided to divide the chamber into a normal flow passage 13 and an overflow passage 14. A filter 16 is provided in relation to the barrier 12 and weir 17 so that when the level of sewerage within the chamber rises above the filter, at least some solids are prevented from reaching an overflow 6.

Description

[0001] This invention relates to combined sewer overflows (CSOs) for assisting sewage networks to cope with storm water flows while retaining solids within the network.

[0002] A conventional CSO is preferably individually designed for the particular drainage network site having regard to the flow characteristics likely to be encountered by the drainage system on that site. Hence, these CSOs are typically constructed on site using traditional concrete casting techniques involving shuttering and steel reinforcement. These construction techniques are disadvantageous because they are time consuming and expensive. There are also safety issues to contend with during on-site construction, particularly when working at the bottom of a 4 metre deep excavation in poor weather conditions. Steel and pre-cast concrete alternatives have been proposed but these have been of standard sizes, making them unsuitable for bespoke applications because each potential new CSO is site specific in relation to weir length, spill flow and hydraulics.

[0003] According to the present invention, there is provided a combined sewer overflow comprising a chamber having storm and foul water inlet and outlet ports for connection to a drainage system, a filter, and overflow arranged so that when the level of sewerage within the chamber rises above a predetermined level, the filter prevents at least some solids in the sewerage from reaching the overflow, wherein the chamber is formed from a length of plastics pipe.

[0004] The chamber may be configured to comprise a passage for normal flow of the sewerage between the inlet and outlet ports, and an overflow passage separated from the normal flow passage by a barrier. The barrier is provided with a weir portion over which sewerage flows to the overflow via the overflow passage, wherein the height of the weir defines the predetermined level.

[0005] The present invention recognises that the critical functional dimensions of a CSO chamber are determined by relatively few key parameters. Specifically, the main variable relates to the overall length and height of the weir provided in the barrier, this determining the overflow characteristics of the CSO. Formation of the principal chamber from a length of plastics pipe allows easy and inexpensive manufacture of a CSO for a given site because the length of plastics pipe can be cut or formed according to the barrier and weir length which is to be fitted within the pipe to provide the overflow characteristics for that site. Embodiments of the present invention are therefore advantageous in that they provide a simpler and cheaper construction technique for bespoke CSOs. Factory production of the CSOs also allows for more effective quality control procedures. The use of large diameter pipes has the advantage that the overall weight of the CSO can be kept as low as possible.

[0006] In a preferred embodiment, the length of pipe is closed at opposite ends by end plates of plastics material. The length of plastics pipe, barrier and end plates are integrally formed from HDPE (high density polyethylene) components which are welded together. The inlet and outlet ports may be formed in opposite ones of the end plates.

[0007] It is especially advantageous to manufacture the pipe using a spiral winding technique. This facilitates production of a pipe having the desired length for the bespoke CSO.

[0008] Plastics pipes having a diameter greater than 1 metre are large enough to provide a chamber suitable for a CSO. However, plastics pipe diameters are preferably in the region of 2 to 3 metres in diameter.

[0009] According to the present invention, there is further provided a method of constructing a combined sewage overflow tank comprising: defining a tank chamber by a length of plastics pipe, providing storm and foul water inlet and outlet ports for connecting the tank chamber to a drainage system, installing a filter and overflow within the chamber, the filter and the overflow being arranged so that when the inlet and outlet ports are connected to a drainage system and the level of sewerage within the chamber rises above a predetermined level, the filter prevents at least some solids in the sewerage from reaching the overflow.

[0010] The method may include the installation of a barrier within the chamber for defining a passage for normal flow of the sewerage between the inlet and outlet ports. A weir is provided in the barrier to facilitate flow of filtered sewerage to the overflow.

[0011] The method may comprise forming the length of plastics pipe by way of a spiral winding technique.

[0012] According to the present invention, there is further provided a method of establishing a combined sewer overflow comprising: manufacturing off-site as an integral unit the combined sewer overflow including a chamber formed from a length of plastics pipe, a barrier for defining a normal flow passage and an overflow passage, a weir formed in the barrier for facilitating passage of overflow, and a filter for filtering solids in the sewerage prior to flow of overflow over the weir; transporting the integral unit to an installation site; and installing the integral unit into the ground.

[0013] The invention will now be further described by way of example with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of a combined sewerage overflow (CSO) embodying the present invention;

Figure 2a is an exploded view of the CSO of figure 1 detailing sewerage flows; and

Figure 2b is a view of a barrier, weir and filter of the embodiment of figure 2a when seen in the direction of arrow A.

[0014] Figure 1 illustrates a CSO having a chamber 1 formed from a length of spirally wound plastics pipe having a diameter in the region of 1 to 3 metres or more depending on the design criteria for the site. Plastics end plates 2, 3 are welded to opposite ends of the pipe 1, end plate 2 being shown connected to a combined sewerage and storm water inlet pipe 4 of a drainage system (not shown). The end plate 3 is shown connected to an outlet pipe 5 (of the drainage system) and overflow pipe 6. The diameter of the outlet pipe 5 may be less than that of the inlet pipe 4. The chamber 1 is provided with an opening 7 for facilitating access to the interior of the chamber for replacement or installation of a filter screen (see below). A pair of ducts 8, 9 are provided for carrying power cables to any electrical equipment which may be housed within the chamber 1. Manholes 10, 11 are provided for facilitating access to the chamber 1 as will be described in more detail below with reference to figures 2a and 2b.

[0015] Figure 2a is an exploded view of the plastics pipe showing the interior of the chamber 1. A barrier 12, of plastics material, is welded to the bottom of the chamber as well as to the end plates 2 and 3, to define a pair of flow passages. One of these flow passages 13 carries normal flow sewage (i.e. a combination of storm and foul water) from the inlet pipe 4 to the outlet pipe 5, the other being an overflow passage 14. A filter passage 15 is attached to the barrier 12 to direct sewerage into the overflow passage 14 via a filter 16 and weir 17. The filter passage 15 may be of plastics material and welded onto the barrier 12 so that as the sewerage level rises in the chamber 1, it flows into the passage 15, up through the filter 16 and over the weir 17. Figure 2b shows the filter passage 15 and filter arrangement as seen from the direction of arrow A of figure 2a. At least some of the solids in the sewerage are prevented from passing over the weir 17 by the filter 16 so that the excess flow can be directed to the overflow 6, and on to a nearby watercourse or river (not shown).

[0016] The filter 16 may be in the form of a perforated screen of plastics or metal, accessible via the access opening 7 for replacement. The filter 16 may therefore be static or alternatively mechanical. In the latter case, the mechanical filter rotates so as to urge the solids back into the normal flow passage 13. An electronic eye may be used to switch on the mechanical filter when the sewerage level reaches a predetermined level. The manholes 10 and 11 provide access to the flow passages 13 and 14 respectively for cleaning or maintenance.

[0017] As will be apparent from the embodiment described above, the CSO can be easily manufactured to accommodate the desired flow characteristics simply by selecting an appropriate pipe length for the chamber 1. Once the pipe has been cut to length, or spirally wound to the desired length, it is a relatively straight forward matter to manufacture a barrier and weir with the dimensions necessary to provide the desired overflow characteristics for the CSO. This manufacturing process can be conveniently carried out off-site, the assembled CSO being transported to the site and lowered into place and connected into the drainage system with minimal need for on-site work.

Claims

1. A combined sewer overflow comprising a chamber having storm and foul water inlet and outlet ports for connection to a drainage system, a filter, and overflow arranged so that when the level of sewerage within the chamber rises above a predetermined level, the filter prevents at least some solids in the sewerage from reaching the overflow, wherein the chamber is formed from a length of plastics pipe.

2. A combined sewer overflow according to claim 1, wherein the chamber comprises a passage for normal flow of the sewerage between the inlet and outlet ports, and an overflow passage separated from the normal flow passage by a barrier, the sewerage flowing over the barrier to the overflow via the overflow passage, wherein the height of the barrier defines the predetermined level.

3. A combined sewer overflow according to claim 2, wherein the length of pipe is closed at opposite ends by end plates of plastics material.

4. A combined sewer overflow according to claim 3, wherein the length of plastics pipe, barrier and end plates are integrally formed from HDPE (high density polyethylene) components that are welded together.

5. A combined sewer overflow according to claim 3 or claim 4, wherein the inlet and outlet ports are formed in opposite ones of the end plates.

6. A combined sewer overflow according to any one of the preceding claims, wherein the plastics pipe is a spirally wound pipe.

7. A combined sewer overflow according to any one of the preceding claims, wherein the plastics pipe has a diameter greater than 1 metre.

8. A combined sewer overflow according to any one of the preceding claims, wherein the plastics pipe has a diameter substantially in the range of 1 to 3 metres.

9. A method of constructing a combined sewage overflow tank comprising:

defining a tank chamber by a length of plastics pipe, providing storm and

foul water inlet and outlet ports for connecting the tank chamber to a drainage system, installing a filter and overflow within the chamber, the filter and the overflow being arranged so that when the inlet and outlet ports are connected to a drainage system and the level of sewerage within the chamber rises above a predetermined level, the filter prevents at least some solids in the sewerage from reaching the overflow.

10. A method according to claim 8, comprising installing a barrier within the chamber for defining a passage for normal flow of the sewerage between the inlet and outlet ports, and for defining an overflow passage separated from the normal flow passage, the height of the barrier defining the predetermined level so that when the tank is in use and the level rises above the predetermined level, filtered sewerage flows over the barrier to the overflow.

11. A method according to claim 9, comprising closing the open ends of the plastics pipe with end plates of plastics material.

12. A method according to claim 10, comprising welding the barrier and end plates to the length of plastics pipe.

13. A method according to any one of claims 8 to 11, comprising forming the length of plastics pipe by way of a spiral winding technique.

14. A method of establishing a combined sewer overflow comprising manufacturing off-site a combined sewer overflow which comprises at least the chamber, inlet and outlet ports and overflow as defined in any one of claims 1 to 7 to form an integral unit, transporting the integral unit to an installation site, and installing the integral unit into the ground.

15. A method of establishing a combined sewer overflow according to claim 13, comprising installing a filter as defined in claim 1.

Drawing