GB2413125A

GB2413125A - Reed-bed flow system

Info

Publication number: GB2413125A
Application number: GB0408379A
Authority: GB
Inventors: David Cooper
Original assignee: ARM Ltd
Current assignee: ARM Ltd
Priority date: 2004-04-15
Filing date: 2004-04-15
Publication date: 2005-10-19
Anticipated expiration: 2024-04-15
Also published as: GB2413125B; GB0408379D0

Abstract

A reed bed system comprises an inlet tank 5 fed by inlet pipe 15 and distributing waste water to reed-bed(s) 1-4 via inlet conduits 6-9. The beds are periodically flooded (tidal flow system) and allowed to drain via drain conduits 11-14 into drain tank 10 and out through outlet pipe 16. Inlet tank 5 is sectioned into an inlet chamber 20 and filling chambers 21 and (22-24). Filling chamber 21 has a connector duct 25 which is articulated 33 about one end and has a float 29 proximate the free end. In its first horizontal position duct 25 allows waste-water to flow from chamber 20 through inlet conduit 6 to reed-bed 1. Filling the reed bed causes the duct to lift (via float 29) to its second elevated position where it is retained on wheel 50 via peg 45a. In this position, further water flow through the duct is prevented. Wheel 50 is continuously rotating and will retain peg 45a for ² of a revolution. During this time, reed-bed 1 is allowed to drain. For the final revolution, peg 45a is released, allowing the duct to drop back to its horizontal position and cause the reed-bed to refill. A similar mechanism is present for filling chambers (22-24), all of which use a common wheel and are therefore filled and emptied cyclically. A similar float and conduit mechanism is present in drain tank 10 to regulate water flow out of the reed-beds.

Description

Reed-bed Flow System The present invention relates to a flow system for

reed-beds, and more particularly to a gravity flow system.

Reed beds are used for the treatment of fluid streams in sewage or waste water processing. The fluid streams are water based, but contain solid matter that is broken down by microbes in the reed bed. The reeds are used to create the optimum means for providing a source of oxygen to the microbes. Reed beds are a low cost, non- polluting and environmentally attractive option for treatment of these fluids.

Various types of reed bed system are known, and typically these are either cross-flow, where the fluid stream enters at one end or edge of the bed and leaves by an opposite edge, or down-flow in which the fluid is distributed across the top of the bed and flows down through the bed. Down-flow beds are preferable because they provide a more oxygenated, and therefore optimal, process for a given size of bed.

The difficulty with down-flow beds is that the fluid has to be supplied over the top of the bed, which requires extensive distribution pipes and multiple nozzles. Owing to the nature of the fluids, nozzles can easily become blocked. Also, flow from nozzles or pipe outlets tends to result in localised areas of high flow between regions of relatively low flow, or stagnation. To help improve the distribution sand may be used.

Unfortunately, different grades of sand are required for different fluid consistencies (i.e. different proportions or sizes of solid particles in the fluid). As the fluid streams tend to vary in consistency, it is not possible to provide sand that is suitable for all operating conditions.

Another method of operating a reed bed is to employ a tidal flow system, In which fluid enters the bed at one or more points so as to fill the bed. Once full, the supply of fluid to the bed is stopped and the bed is emptied. The emptying of the bed provides downward flow, similar to that found in down-flow beds. A problem is that hitherto these systems have required pumps and valves with electronic timers for providing and controlling the flow. These components use energy and add significantly to the installation and operating costs of the system.

It is an object of the present invention to provide a system and method for operating a reed-bed, which alleviates such problems.

According to a first aspect of the present invention there is provided a reed- bed gravity flow system comprising: an inlet tank having an inlet for receiving a fluid; at least one connector duct associated with a respective reed-bed, the connector duct having an entry at a first end for fluid from the inlet; and holding means for (i) holding a second end of the connector duct at an elevated position so as to substantially prevent flow of fluid through the connector duct from the inlet, and for (ii) releasing the second end, the connector duct being configured such that when the second end is released fluid from the inlet can flow through the connector duct to the associated reed-bed.

It is an advantage that a tidal flow through the reed bed can be provided by a system which relies on gravity to provide both the flow of fluid and the starting and stopping of the fluid flow. Thus pumps, valves and electronic timing devices are not required, thereby reducing energy usage, installation costs and maintenance required.

The connector duct may be articulated such that the second end is moveable relative to the first end by articulation of the duct.

In a preferred embodiment the connector duct is provided with float means for raising the second end as the level of fluid In the reed bed rises, the holding means being configured to capture the second end when the reed bed is full. The holding means ensures that the second end is held at the elevated position so that the reed bed can then be emptied.

In a preferred embodiment, the holding means comprises means for capturing the connector duct and means for releasing the connector duct at a predetermined time after capture. The holding means may be rotatably driven and provided with the means for capturing the connector duct at a first angular position of rotation and the means for releasing the connector duct at a second angular position of rotation.

Conveniently, the holding means comprises a plate mounted for rotation about an axis substantially perpendicular to the plate, and having a rim for holding a peg attached to the second end of the connector duct, the rim extending from the first angular position to the second angular position.

In embodiments of the invention, the inlet tank comprises a plurality of connector ducts each associated with a respective reed-bed. The system may be configured to provide flow of liquid to each of the reed-beds sequentially. It is an advantage that a sequential system involving more than one reed bed allows an overall substantially continuous flow of fluid to be maintained, even though the flow through each reed-bed is intermittent.

Preferably, the inlet tank comprises a plurality of chambers, each chamber being associated with a respective reed-bed and including the respective connector duct therein, whereby fluid flowing through a connector duct enters the respective chamber such that the level of fluid in the chamber rises as the respective reed-bed is filled.

Embodiments of the invention may further comprise: an outlet tank having an outlet chamber in fluid communication with a respective reed-bed; an outlet duct configured for a first end thereof to be raised by fluid entering the outlet chamber such that the fluid does not enter the first end, and having a second end for fluid outflow; and means for causing fluid to enter the first end when the liquid in the outlet chamber reaches a predetermined level, whereby the weight of fluid entering the outlet duct causes the first end of the duct to remain below the level of liquid in the outlet chamber such that fluid can flow through the outlet duct and out of the second end.

According to a second aspect of the present invention there is provided a method of operating a reed-bed system comprising at least one reed-bed, an associated inlet tank and an associated outlet tank, the inlet tank having an inlet chamber and a connector duct with a free end having a float, the outlet tank having an outlet chamber and an outlet duct with a free end that can float above the level of fluid m the outlet chamber when there is no fluid in the outlet duct, the method comprising the steps of: providing a flow of fluid to the inlet tank; holding the first end of the connector duct at above the level of fluid in the reed-bed; releasing the connector duct so that it drops to a level that allows liquid to flow from the inlet and through the connector duct so as to fill the reed-bed, the inlet chamber and the outlet chamber, thereby raising the float of the connector duct and the free end of the outlet duct; capturing the free end of the connector duct; and causing liquid to enter the first end of the outlet duct so that the weight of liquid holds the outlet duct below the level of liquid in the outlet chamber while the liquid flows out from the reed-bed through the outlet tank.

Embodiments of the invention are described below with reference to the following drawings.

Figure 1 shows a plan view of a reed-bed installation having a gravity flow system according to the present invention.

Figures 2a and 2b show plan and elevation views respectively of an inlet tank of the installation of Figure 1.

Figures 3a and 3b show end and side elevations views of a capture mechanism of the inlet tank of Figres 2a and 2b.

Figure 4 shows a plan view of an outlet tank of the installation of Figure 1.

Figure 5 is a table of graphic symbols that illustrate a sequence of steps in operating the installation of Figure 1. s

Referring to Figure 1, a reed-bed installation has four reed-beds 1, 2, 3, 4.

Each reed-bed 1, 2, 3, 4 is supplied with fluid from an inlet tank 5 via a respective mlet pipe 6, 7, 8, 9 at one end of the bed. Each reed-bed has an outlet pipe, 11, 12, 13, 14 at its other end leading to an outlet tank l O. Fluid is supplied to the inlet tank through a supply pipe 15. Fluid leaves the outlet tank 10 either by way of a drain pipe 16 or by way of a recirculation pipe 17 through which the fluid is pumped back to the inlet tank 5. The inlet tank 5 and the outlet tank 6 are provided with means that rely on gravity to provide a tidal flow of fluid through each of the reed-beds, in a manner that will be explained in more detail below.

Referring to Figure 2a, the inlet tank 5 is divided into separate chambers that include an inlet chamber 20 and first, second, third and fourth filling chambers 21, 22, 23, 24. Each filling chamber 21, 22, 23, 24, feeds a respective one of the inlet pipes 6, 7, 8, 9. Inside each filling chamber 21, 22, 23, 24, is a connector duct 25, 26, 27, 28, having an opening at a first end 37, 38, 39, 40 through a dividing wall 49 that separates the filling chambers 21, 22, 23, 24 from the mlet chamber 20, such that fluid in the inlet chamber 20 can enter the first end 37, 38, 39, 40 of the connector duct 25, 26, 27, 28. Each connector duct has an articulated section or joint 33, 34, 35, 36 near the first end. Each connector duct has a free second end 41, 42, 43, 44, close to which is mounted a float 29, 30, 31, 32. Each connector duct is further provided with a laterally extending peg 45, 46, 47, 48 at its second end 41, 42, 43, 44.

Figure 2b, shows a sectional elevation through the inlet tank 5 at the first filling chamber 21. The connector duct 25 is shown in two positions, designated 25 and 25a respectively. In one position, the connector duct shown as 25 rests horizontally near the base of the inlet tank 5. In the other position, the connector duct shown as 25a is inclined and has a bend at the articulated joint 33. In this position the connector tube 25 is supported at its free end 41a by engagement of the laterally extending peg 45a on a rim 52 of a circular plate 50 forming part of a holding means (as will be described in more detail below with reference to Figures 3a and 3b).

Referring to Figures 3a and 3b, the plate 50 of the holding means has a rim 52 extending around three-quarters of the circumference. Thus the plate has a rimmed 270-degree sector and an un-rimmed 90-degree sector. The rim 52 has first and second profiled lips 56, 58 at each end. The plate 50 can be rotated on a shaft (not shown) extending through an aperture 54 in its centre.

In use, fluid from the supply pipe 15 enters the inlet tank 5 to fill the inlet chamber 20. With the connector duct 25 in its horizontal position as shown in Figure 2b, fluid enters the filling chamber 21 and passes out through the inlet pipe 6 to the first reed-bed l (as shown in Figure 1). The level of fluid in the filDng chamber 21 and in the reed bed 1 rises. Due to buoyancy the float 29 causes the free end 41 to rise with the fluid level. As a result, the connector duct 25 bends at the artculatedJoint 33. Provided the fluid level in the inlet chamber 20 is above the free end 41 of the connector duct 25, the fluid will continue to flow through from the supply 15 to the reed-bed 1. When the level in the reed-bed 1 and filling tank 21 reaches a certain height, corresponding to the reed- bed being full, the connector duct 25 adopts the position in which it is shown as 25a in Figure 2. At this position the end 41a is at substantially the same level as that of the fluid in the inlet chamber 20 so that the flow of fluid through the connector duct 25a effectively ceases.

Throughout the process, the plate 50 is continuously rotated at a predetermined rotational speed. When the reed-bed 1 is full, rotation of the plate 50 reaches a point where the first lip 56 of the rim 52 engages the peg 45a so that the free end 41a Is captured on the rim 52 as the plate 50 continues to rotate. Thus the free end 41 of the connector duct 25 will remain at the raised position during subsequent emptying of the reed-bed 1 and emptying of the filling chamber 21.

Each of the other filling chambers 22, 23, 24 is also provided with a corresponding plate 50 as shown in Figures 3a and 3b. During the filling of the first reed-bed 1 (see Figure l), the free ends 42, 43, 44 of the connector ducts 26, 27, 28 in the other filling chambers 22, 23, 24 (as shown in Figure 2a) are held in the raised position by the respective pegs 46, 47, 48 on the rims 52 of the corresponding plates 50. However, the rim 52 on each plate is disposed at 90 degrees relative to the rim In the next chamber. This means that just as the peg 45 on the connector duct 25 in the first filling chamber 21 is being captured by the corresponding plate 50, the peg on the connector duct 26 in the second filling chamber 22 is released at the second lip 58 of the rim 52 of its corresponding plate 50. The second filling chamber is empty when this occurs, so that the connector duct 26 drops to its horizontal position in the second filling chamber 22 and fluid can flow through from the inlet chamber 20 to commence filling of the second reed-bed 2.

While the second reed-bed 2 is filling, the first reed-bed 1 can be emptied.

This could occur by simply allowing the first reed-bed l to dram naturally. However, in such an arrangement the filling rate must be significantly faster than the emptying rate (otherwise the reed-bed would never fill). To increase the filling rate, the outlet tank 6 is provided with an emptying system, as will be described below.

Referring to Figure 4, the outlet tank 10 is divided into four outlet chambers 61, 62, 63, 64, each of which can be supplied with fluid from a respective reed-bed 1, 2, 3, 4 as shown in Figure 1, by way of an associated outlet pipe 11, 12, 13, 14. Each chamber is provided with an outlet duct 65, 66, 67, 68 having a free first end 69, 70, 71, 72 and a fixed second end 73, 74, 75, 76. The fixed second ends open into a common chamber 82 from which fluid can flow out through the outlet 16.

Considering, for example, Just one duct 65, the first end 69 is configured to float on fluid in the outlet chamber 61 when the outlet duct 65 is empty such that fluid does not enter the outlet duct 65 through the first end 69. However, when the outlet chamber 61 is almost full, the outlet duct 65 reaches a height limit, which may, for example be a lid on the outlet tank 10. At the height limit the first end 69 is prevented from rising further as the level of fluid in the outlet chamber 69 continues to rise. The first end 69 is configured such that fluid can then enter the duct 65 through the first end 69. The weight of fluid in the duct 65 causes it to drop below the fluid surface so that fluid can then flow through the duct 65, the second end 73, and the common chamber 82 to the outlet 16.

The other ducts 66, 67, 68 operate in the same manner. As the ducts operate in response to the level of fluid in each of the outlet chambers 61, 62, 63, 64, which itself is determined by the level of fluid in each of the reed-beds 1, 2, 3, 4, supplied from the inlet tank 5, no timing device is required.

The operation of a tidal flow system in a four reed-bed installation is shown schematically in Figure 5. The procedure commences at step 1 with all four reed-beds empty. The inlet connector duct of reed-bed number 1 Is released and drops to the bottom of its filling chamber. Fluid in the inlet chamber then starts to flow through the inlet connector duct at step 2 so that the level of fluid in the filling chamber and in the reed- bed number 1 starts to rise. At the same time the level of fluid in the outlet chamber of reed-bed number 1 starts to rise so that the associated outlet duct starts to rise. This continues through step 3 as the fluid level in reed-bed number 1 rises. At step 4, reed-bed number 1 is full and the inlet connector duct is captured at the top of the filling chamber by the holding means. At substantially the same time the outlet duct reaches its height limit and fluid starts to enter the outlet duct. Also, at substantially the same time the inlet connector duct associated with reed-bed number 2 is released to start the filling of reed-bed number 2.

At step 5 the entry of fluid into the outlet duct causes it to drop below the fluid level in the outlet chamber so that fluid starts to flow to the outlet and the reed-bed number 1 starts to empty. At step 6 the filling process for reed-bed number 2, and the emptying of reed-bed number 1 continue, until at step 7 reed-bed number 1 Is empty and reed-bed number 2 is full.

The sequence continues through steps 8 to 13 for the filling and emptying of reed-beds numbers 2 and 3 and for the filling of reed-bed number 4. At steps 14 to 16 reed-bed number 4 is emptied and reed-bed number 1 is filled. The situation at step 16 is identical to that at step 5 and so the sequence continues indefinitely by repeating steps 6 to 16 until stopped.

It will be appreciated that the above description relates to a four-bed installation, but the same principles may be applied to an installation having any number of reed-beds.

Claims

1. A reed-bed gravity flow system comprising: an inlet tank having an inlet for receiving a fluid; at least one connector duct associated with a respective reed-bed, the connector duct having an entry at a first end for fluid from the inlet; and holding means for (i) holding a second end of the connector duct at an elevated position so as to substantially prevent flow of fluid through the connector duct from the inlet, and for (ii) releasing the second end, the connector duct being configured such that when the second end is released fluid from the inlet can flow through the connector duct to the associated reed-bed.

2. A system according to claim 1 wherein the connector duct is articulated such that the second end is moveable relative to the first end by articulation of the duct.

3. A system according to claim I or claim 2 wherein the connector duct Is provided with float means for raising the second end as the level of fluid in the reed bed rises, the holding means being configured to capture the second end when the reed bed is full, thereby ensuring that the second end is held at the elevated position so that the reed bed can then be emptied.

4. A system according to any preceding claim wherein the holding means comprises means for capturing the connector duct and means for releasing the connector duct at a predetermined time after capture.

5. A system according to claim 4, wherein the holding means is rotatably driven and provided with the means for capturing the connector duct at a first angular position of rotation and the means for releasing the connector duct at a second angular position of rotation.

6. A system according to claim 5 where n the holding means comprises a plate mounted for rotation about an axis substantially perpendicular to the plate, and having a rim for holding a peg attached to the second end of the connector duct, the rim extending from the first angular position to the second angular position.

7. A system according to any preceding claim wherein the inlet tank comprises a plurality of connector ducts each associated with a respective reed-bed.

8. A system according to claim 7 configured to provide flow of liquid to each of the reed-beds sequentially.

9. A system according to claim 7 or claim 8 wherein the inlet tank comprises a plurality of chambers, each chamber being associated with a respective reed-bed and including the respective connector duct therein, whereby fluid flowing through a connector duct enters the respective chamber such that the level of fluid in the chamber rises as the respective reed-bed is filled.

to. A system according to any preceding claim further comprising: an outlet tank having an outlet chamber in fluid communication with a respective reed-bed; an outlet duct configured for a first end thereof to be raised by fluid entering the outlet chamber such that the fluid does not enter the first end, and having a second end for fluid outflow; and means for causing fluid to enter the first end when the liquid in the outlet chamber reaches a predetermined level, whereby the weight of fluid entering the outlet duct causes the first end of the duct to remain below the level of liquid in the outlet chamber such that fluid can flow through the outlet duct and out of the second end.

l 1. A method of operating a reed-bed system comprising at least one reedbed, an associated inlet tank and an associated outlet tank, the inlet tank having an inlet chamber and a connector duct with a free end and a float, the outlet tank having an outlet chamber and an outlet duct with a free end that can float above the level of fluid in the outlet chamber when there is no fluid in the outlet duct, the method comprising the steps of: providing a flow of fluid to the inlet tank; holding the first end of the connector duct at above the level of fluid in the reed-bed; releasing the connector duct so that it drops to a level that allows liquid to flow from the inlet and through the connector duct so as to fill the reed-bed, the inlet chamber and the outlet chamber, thereby raising the float of the connector duct and the free end of the outlet duct; capturing the free end of the connector duct; and causing liquid to enter the first end of the outlet duct so that the weight of liquid holds the outlet duct below the level of liquid in the outlet chamber while the liquid flows out from the reed-bed through the outlet tank.