GB2365448A

GB2365448A - Combined sewer overflow

Info

Publication number: GB2365448A
Application number: GB0013896A
Authority: GB
Inventors: James P Carew; M Jolly
Original assignee: GALLIFORD UK Ltd
Current assignee: GALLIFORD UK Ltd
Priority date: 2000-06-07
Filing date: 2000-06-07
Publication date: 2002-02-20
Anticipated expiration: 2020-06-07
Also published as: GB2365448B; GB0013896D0

Abstract

A combined sewer overflow 10 comprising a housing 12 having an inlet 14, an outlet 16 and an overflow outlet 18, the housing 12 containing flow guide means, wherein the housing 12 is formed from corrugated metal having a corrosion resistant coating and the flow guide means are at least partially defined by a concrete structure fitted to the housing 12.

Description

<Desc/Clms Page number 1> Combined Sewer Overflow The present invention relates to a combined sewer overflow commonly referred to by the acronym CSO.

A CSO is a subterranean device which is utilised in combined sewerage systems, that is to say sewerage systems which convey both wastewater and stormwater. Under normal operating conditions the flow in a combined sewer is ultimately directed to a treatment plant. However, during and after a period of heavy rainfall the flow in a combined sewer may exceed that which can be handled by the treatment plant. In such conditions the CSO is utilised to discharge excess flow into a natural watercourse or to appropriate temporary storage means. Typically the CSO is provided with means such as screens or weirs to prevent the discharge of solid matter along with the excess flow.

According to a first aspect of the present invention there is provided a combined sewer overflow comprising a housing having an inlet, an outlet and an overflow outlet, the housing containing flow guide meanslwherein the housing is formed from corrugated metal having a corrosion resistant coating and the flow guide means are at least partially defined by a concrete structure fitted to the housing.

The use of metal reduces the wall thickness of the housing and hence reduces the outer dimensions of the housing for given internal dimensions when compared to existing combined sewer overflows having housings constructed from fibreglass, reinforced concrete or brick. The concrete structure provides ballast to the housing and further provides a base to which further internal components of the overflow may be sited. By utilising the concrete structure in this manner, the need to provide fixings on the metal housing is greatly reduced. This in turn reduces the possibility that the effectiveness of the corrosion resistant coating will be compromised by the provision of such fixings. The concrete structure may further be adapted to eliminate voids within the housing which, in use, may trap solid matter introduced via the inlet. In a preferred embodiment the housing is constructed from galvanised steel. Preferably the galvanised steel is further coated with a polymer layer.

The concrete structure may be formed in situ within the housing during production thereof, or alternatively may be pre-formed at a location remote from the housing. The concrete structure may define a weir arranged between the outlet and the overflow outlet. In an alternative embodiment the concrete structure may define a base upon which a weir arrangement can be sited. In such an embodiment the weir may be manufactured from steel and attached to the concrete base with appropriate fixings. The weir may be provided with screening means which in use, seek to prevent the communication of solid matter to the overflow outlet. Said screening means may be passive, for example a mesh screen, or alternatively, powered, for example a rotary brush extending along the length of the weir.

The housing may be provided with an access tube so as to allow the admission of maintenance personnel to the inside thereof.

According to a second aspect of the present invention there is provided a method of manufacturing a combined sewer overflow, the method comprising the steps of forming a housing from a corrugated metal having a corrosion resistant housing, said housing having an inlet, an outlet and an overflow outlet; and fitting to the housing a concrete structure at least partially defining flow guide means.

The step of forming the housing may comprises the steps of-..

winding said-corrugated metal onto a former so as to define a hollow body; and fitting a bulkhead to an open end of said body. .

In a preferred embodiment, the step of fitting the concrete structure is carried out after said bulkhead has been fitted to the body, and thereafter a further bulkhead is fitted to substantially close the body.

The step of fitting the concrete structure may involve forming the structure in situ or alternatively fitting a pre-formed structure to the body.

Embodiments of the present invention will now be described with reference to the accompanying drawings in which: Figures 1 and 2 show partially cutaway perspective views of a CSO having a mechanical screen; Figures 3 and 4 show partially cutaway perspective views of a CSO having a non mechanical screen; Figure 5 shows a plan view of the CSO of figures 3 and 4; and Figure 6 shows a cross-sectional view of the CSO of figures 3 and 4.

Referring firstly to figures 1 and 2 there is shown a first embodiment of a CSO generally designated 10. The CSO comprises a substantially cylindrical chamber 12 having an inlet 14, a service outlet 16 and an overflow outlet 18. An access tube 20 is provided so as to allow access by, for example, maintenance personnel. The chamber 12 is constructed from corrugated steel which is galvanised, typically with a layer of zinc, so as to render it resistant to corrosion. The chamber is formed from a substantially cylindrical body 13 having substantially circular bulkheads 15,17 fitted at each end. So as to enhance the corrosion resistant properties of the chamber 12 the galvanised steel may further be coated with a polymer layer. This serves to protect the galvanised coating of the steel from damage during manufacture, transport, installation or maintenance of the CSO. The polymer coating may also be readily repaired on site without the need for specialised equipment or techniques to be employed.

Internally the chamber 12 is provided with a concrete base 22 which extends throughout the length of the chamber 12. Projecting upwardly from the base 22 is a longitudinal dividing wall 24 which extends along the length of the chamber 12. It will be noted that the inlet 14 and service outlet 16 are provided on one side of the wall 24 (the service side 40), while the overflow outlet is provided on the other side thereof (the overflow side 42). A mid portion 26 of the wall 24 is lowered so as to define a weir 28. A transverse wall 38 is provided on the service side 40 of the dividing wall 24, which transverse wall 38 has an aperture 44 which serves as the mouth of the service outlet 16.

Adjacent the weir 28 on the overflow outlet side of the wall 24 there is provided a storm screen 30. The storm screen 30 comprises a drive unit 32 and brush 34 which are located between two stays 36 extending upwardly from the concrete base 22. The stays are also connected by the use of appropriate fixings to the wall 24.

In normal use, wastewater entering the chamber 12 via the inlet 14 is directed along the service side 40 of the dividing wall 24 to the service outlet 16. In elevated flow conditions, for example during and after a period of heavy rainfall when the wastewater is augmented by a large volume of stormwater, the water level on the service side 40 rises until it reaches that of the weir 28. The excess flow then passes over the weir 28 to the overflow side 42 where upon it, is conducted via the overflow outlet 18 to either a natural watercourse or an appropriate temporary storage site. In such elevated flow conditions the storm screen 30 is operated so as to reduce the amount of solid matter which passes over the weir 28 to the overflow side 42. In use, the brush 34 is rotated by the drive unit 32 so as to maintain any solid matter present at the weir 28 on the service side 40. Typically the storm screen 30 is provided with appropriate control means which ensure that it is only operated when needed. The control means may include, for example, sensor means which sense the fluid level on the service side 40. Referring now to figures 3 to 6 there is shown a second embodiment of a CSO generally designated 50. Features common to the first embodiment shown in figures I and 2 are identified with like reference, numerals. As before the CSO comprises a chamber 52 manufactured from corrugated, galvanised steel having an inlet 14, a service outlet 16, an overflow outlet 18 and an access tube 20. The chamber 52, when viewed in plan (figure 5), has an essentially "T" shaped configuration, the chamber 52 comprising a substantially cylindrical main portion 54 and a shorter substantially cylindrical secondary portion 56 extending perpendicularly from the main portion 54. It will be noted that the inlet 14 and service outlet 16 are provided at opposing ends of the main portion 54 of the casing 52, while the overflow outlet 18 is provided in the secondary portion 56 of the casing 52.

As before the casing 52 is provided with a concrete base 22. The base 22 includes an integral wall 58 defining a weir 60. The base 22 further extends into the secondary

portion 56 of the casing 52 so as to provide a plinth for the siting of a siphon means 62 Mounted on top of the weir 60 is a mesh screen 64. The screen 64 is manufactured from steel and is inclined downwardly towards the secondary portion 56 of the casing 52. The lower edge 66 screen 64 terminates at a collection channel 68 running the length thereof, which channel 68 leads to an accumulation chamber 70. The accumulation chamber 70 is provided with an outlet tract 72 which leads to the service outlet 14 of the CSO 50. A further portion of mesh screen 74 is provided at the interface of the main and secondary portions 54, 56 of the casing 52.

In normal use, wastewater entering the chamber 52 via the inlet 14 flows directly to the service outlet 16. In elevated flow conditions, for example during and after a period of heavy rainfall when the wastewater is augmented by a large volume of stormwater, the water level rises until it reaches that of the weir 60. Excess flow passes over the weir 60 and through mesh screen 64 before passing to the overflow outlet 18. Solid matter is prevented from passing to the overflow outlet 18 by the mesh screen 64. So as to prevent the mesh screen 64 from becoming blocked, it is angled towards the collection channel 68. During elevated flow conditions, solid matter which comes into contact with the mesh screen 64 is washed down into the collection channel 68. The solid matter is then passed via the accumulation chamber 70 to the service outlet 14.

The siphon means 62 comprises a siphon tube 76 and a priming reservoir 78 and tube 80. The siphon means 62 is operable to,enhance the flow through the overflow outlet 18 once the water level in the secondary portion 56 of the casing 52 is sufficient to prime the siphon tube 76.

As described above the CSO is, in use, installed at an underground location. Where flotation criteria are to be satisfied, the housing may be located upon a concrete plinth or foundation by appropriate fixing means, for example by straps and bolts. However the CSO may be located, backfilling and reinstatement against the corrugated housing is then carefully carried out with selected material so as to minimise the possibility of the housing being damaged.

Claims

Claims 1. A combined sewer overflow comprising a housing having an inlet, an outlet and an overflow outlet, the housing containing flow guide means, wherein the housing is formed from corrugated metal having a corrosion resistant coating and the flow guide means are at least partially defined by a concrete structure fitted to the housing.
2. A combined sewer overflow as claimed in claim 1 wherein the housing is constructed from galvanised steel.
3. A combined sewer overflow as claimed in claim 2 wherein the galvanised steel is further coated with a polymer layer.
4. A combined sewer overflow as claimed in any preceding claim wherein the concrete structure is formed in situ within the housing during production thereof
5. A combined sewer overflow as claimed in any of claims 1 to 3 wherein the concrete structure is pre formed at a location remote from the housing.
6. A combined sewer overflow as claimed in any preceding claim wherein the concrete structure defines a weir arranged between the outlet and the overflow outlet.
7. A combined sewer overflow as claimed in any of claims 1 to 5 wherein the concrete structure defines a base upon which a weir arrangement can be sited.
8. A combined sewer overflow as claimed in claim 7 and including a weir attached to said concrete base with appropriate fixings.
9. A combined sewer overflow as claimed in claim 8 wherein the weir is manufactured from steel.

<Desc/Clms Page number 7>
10. A combined sewer overflow as claimed in claims 6, 7 or 9 wherein the weir is provided with screening means which in use, seek to prevent the communication of solid matter to the overflow outlet.
11. A combined sewer overflow as claimed in claim 10 wherein said screening means are passive
12. A combined sewer overflow as claimed in claim 11 wherein said screening means comprise a mesh screen
13. A combined sewer overflow as claimed in claim 10 wherein said screening means are powered.
14. A combined sewer overflow as claimed in claim 13 wherein said screening means comprise a rotary brush extending along the length of the weir.
15. A combined sewer overflow as claimed in any preceding claim wherein the housing is provided with an access tube so as to allow the admission of maintenance personnel to the inside thereof.
16. A method of manufacturing a combined sewer overflow, the method comprising the steps of: forming a housing from a corrugated metal having a corrosion resistant housing, said housing having an inlet, an outlet and an overflow outlet; and fitting to the housing a concrete structure at least partially defining flow guide means.
17. A method as claimed in claim 16 wherein the step of forming the housing comprises the steps of: winding said corrugated metal onto a former so as to define a hollow body; and fitting a bulkhead to an open end of said body.

<Desc/Clms Page number 8>
18. A method as claimed in claim 17 wherein the step of fitting the concrete structure is carried out after said bulkhead has been fitted to the body, and thereafter a further bulkhead is fitted to substantially close the body.
19. A method as claimed in any of claims 16 to 18 wherein the step of fitting the concrete structure involves forming said concrete structure in situ
20. A method as claimed in any of claims 16 to 18 wherein the step of fitting the concrete structure involves fitting a pre-formed structure to the body.
21. A combined sewer overflow substantially as hereinbefore described with reference to or as shown in the accompanying drawings.
22. A method of manufacturing a combined sewer overflow substantially as hereinbefore described with reference to or as shown in the accompanying drawings.