GB2330367A - A combined stormwater and foul water separation and overflow tank - Google Patents

Abstract

A combined stormwater and foul water separation and overflow tank having an inlet for receipt of both stormwater and foul water, a first low level outlet for sewerage sludge in liquid form, and a second high level outlet incorporating a filter for discharging overflow water, the tank being divided into successive settlement chambers, from the inlet and first outlet to the second outlet, with lower level pressure controlled valves in the dividing walls between the chambers which allow for sludge return flow back to the first outlet only when the water levels within the overflow tank fall down to the region of the valves. When, during a storm, substantial quantities of rain water flow through a sewerage pipe 4, a chamber A of the tank 1 will start to fill up and the water can then overflow into chambers B and C together with a certain amount of the sewerage material. Baffles 8 tend to deposit solid to settle out in the chambers B and C. The overflow water is filtered at 6 before passing out from an overflow pipe 7. As the levels within the chambers A, B and C fall again the pressure decrease allows flap valves 10 to open so as to allow a return flow of sewerage sludge from chambers B and C to chamber A and ultimately to be carried away through the sewer pipe 4.

Description

"Improvements relating to Storm Water Overflow Tanks" This invention is concerned with the problem of discharge water entering a sewage pipe system under flash flood conditions. When a flash flood occurs due to continuous heavy rainfall the sewage pipeline system can be overwhelmed and it may be necessary to allow for discharge of the excess water containing diluted sewage, for example, Inte a river system. This is undesirable.

It is an object of this invention to provide means whereby an unusual flow of water into a sewage pipeline system can be discharged without, at the same time, discharging significant quantities of sewerage.

Accordingly, this invention provides a combined stormwater and foul water separation and overflow tank having an inlet for receipt of both stormwater and foul water, a first low level outlet for sewerage sludge in liquid form, and a second high level outlet incorporating a filter for discharging overflow water, the tank being divided into successive settlement chambers, from the inlet and first outlet to the second outlet, with lower level pressure controlled valves in the dividing walls between the chambers which allow for sludge return flow back to the first outlet only when the water levels within the overflow tank fall down to the region of the valves.

When such an overflow tank fills up (such as during flash flood conditions) the flow of the water mixed with sewerage through the settlement chambers results in settle ment of the sewerage to a large extent on the base of the chambers of the tank and the filter on the second high level outlet can be designed to filter out a large proportion of the sewerage particles in suspension in the water. Thus the overflow water leaving the second high level outlet will be substantially "clean".

In the preferred arrangement the valves can be flap valves which are held closed due to the pressure of the water when the water level increases in the tank but which will open with any pressure from the weight of water and sewerage when the water level falls significantly. Ideally the dividing walls between the chambers bow outwardly in the downstream direction.

It is preferred that the interconnection between adjacent chambers comprises baffles creating a flow path across a dividing wall leading from a low level on one side to a low level on the other side. This helps to achieve good settlement of the sewerage sludge.

In one arrangement of the tank the inlet and first outlet form part of an in-line sewer pathway across the base of the first settlement chamber.

A further possibility is to provide that the inlet and the low level outlet are arranged for connection into a chamber of an existing sewer passageway.

The third possibility is to provide a pump operated first outlet through the first settlement chamber.

The invention may be performed in various ways and three preferred embodiments will now be described, by way of example, with reference to the accompanying drawings, in which:- Figure 1 comprises side and end sectional views through one form of overflow tank positioned in line with a sewer pathway; Figure 2 comprises side and end sectional views through a second form of overflow tank connected to one side of a manhole forming part of a sewer pathway; and Figure 3 comprises side and end sectional views through a third form of overflow tank incorporating a pump chamber for directing sludge to an existing sewer pathway.

The tank 1 shown in Figure 1 is divided into three chambers, A, B and C, by dividing walls 2 and 3. Chamber A is in communication with a sewer pathway in the form of a pipe 4 which opens within chamber A as indicated by the dashed outline 5. At the downstream end of the tank 1, in chamber C, there is a filter chamber 6 at the top which leads to an overflow pipe 7. Baffles 8 cause liquid flowing between chambers A and B and chambers B and C to follow a path as indicated by arrows 9 so that liquid overflowing into a downstream chamber is deposited towards the base thereof, thus promoting a degree of settlement of solids suspended within the liquid.

In normal use, sewerage will flow along the pipe 4 at an accepted average rate to a sewerage plant or the like.

However, it is envisaged that the system will be linked to storm drains and that, during a storm, substantial quantities of rain water flow through the pipe 4 and the chamber A will start to fill up. If the quantity of storm water is such that the water then overflows into chambers B and C a certain amount of the sewerage material may be carried over to the secondary chambers but will tend to settle out in the settlement chambers B and C. More finely suspended solids will be trapped by the filter before the overflow water is allowed to pass out from the overflow pipe to an acceptable outlet such as into a river system. As the levels within the chambers A, B and C fall again following abatement of the storm, the relative pressures between the chambers will be such that flap valves 10 will be caused to open so as to allow a return flow of sewerage sludge from chambers B and C to chamber A and ultimately to be carried away through the sewer pipe 4. Of course, the build-up of pressure between chambers A, B and C due to the overloading with storm water will create the pressure necessary to keep the flap valves closed.

The tank 1 is supported above a concrete raft 11 and is secured thereto by hold-down straps 12. A manhole 13 provides for access to the filtered storm water outlet so that the filter can be changed or cleaned periodically.

In the modified form of tank illustrated in Figure 2, the sewer pipe is not connected in line. Instead, the tank is positioned to one side of a manhole chamber 14 of the sewerage system and filling of the tank with storm water will occur through a high level overflow pipe 15 from the chamber 14. This version operates in much the same way as that shown in Figure 1 except that as the storm water level falls within the tank 1, thus resulting in opening of the flap valves 10, sludge is returned to the sewer pipe 4 via an outlet passageway 16 which incorporates a flap valve 17 (or other form of flow control valve) which is kept closed when the storm water pressure builds up within the chamber 14.

In the arrangement shown in Figure 3, again an overflow inlet pipeline 15 from a manhole chamber of a sewer system is provided at a high level into the tank 1. At the base of the primary chamber A of the tank 1 an outlet 18 is provided through which sewerage is pumped, by a pump 19, through an outlet pipe 20 so as to be discharged back into the main sewer system. The pump (supported by a guide rail 21) starts up as soon as a flow is detected. Under storm conditions excess flow passes to the chambers B and C for eventual discharge as in the version of Figure 1).

Claims (8)

1. A combined stormwater and foul water separation and overflow tank having an inlet for receipt of both stormwater and foul water, a first low level outlet for sewerage sludge in liquid form, and a second high level outlet incorporating a filter for discharging overflow water, the tank being divided into successive settlement chambers, from the inlet and first outlet to the second outlet, with lower level pressure controlled valves in the dividing walls between the chambers which allow for sludge return flow back to the first outlet only when the water levels within the overflow tank fall down to the region of the valves.

2. A tank according to Claim 1, wherein the valves are flap valves.

3. A tank according to Claim 1 or Claim 2, wherein the dividing walls between the chambers bow outwardly in the downstream direction.

4. A tank according to any one of Claims 1 to 3, wherein the interconnection between adjacent chambers comprises baffles creating a flow path across a dividing wall leading from a low level on one side to a low level on the other side.

5. A tank according to any one of Claims 1 to 4, wherein the inlet and first outlet form part of an in-line sewer pathway across the base of the first settlement chamber.

6. A tank according to any one of Claims 1 to 4, wherein the inlet and first outlet are arranged for connection into a chamber of an existing sewer passageway.

7. A tank according to any one of Claims 1 to 4, wherein a pump-operated first outlet is provided from the first settlement chamber.

8. A combined stormwater and foul water separation and overflow tank, substantially as herein described with reference to the accompanying drawings.