Solids separator used in liquid flow streams, typically sewer overflows

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Introduction

The present invention relates to improvements in solids/liquid separators such as those used in separating floating bodies from a liquid in sewer overflows.

Background of the Invention

Particularly with older sewerage systems predominantly in service in Europe, Asia and North and South America, both sewage and stormwater are conveyed in the same pipe to a sewerage treatment plant. The system works well until a storm or a blockage where the combined sewage and stormwater flow exceeds the capacity of the sewerage system and excess flow is discharged to local waterways such as rivers, streams, lakes and the sea by way of overflow chambers. This causes serious environmental, health and aesthetic problems to communities in that excess water together with entrained floating sewage bodies are released into the local waterways.

In recent years various types of separators have been introduced into sewerage systems to remove objectionable floating matter from overflowing water before the water reaches local water bodies. An example of such a separator is described in German Patent Application no. 102005008743.4 also by the present applicant. In this application a screen is used to filter bodies from overflows whereby the bodies are returned to the sewer flow.

In practice there are operational problems with known separators relating to the effectiveness of the separator, its efficiency and susceptibility to blockages. The present invention aims to mitigate problems encountered with available separator systems without reliance on external power sources.

Summary of the Invention

In accordance with the invention there is provided a solids separator for use in a combined sewer overflow chamber having an inlet, a flow chamber and a main outlet whereby liquid, having solids entrained therein, flows from the inlet through the flow chamber and to the outlet, the solids separator comprising: an overflow weir over which liquid flows during large flows into a separation chamber; a filter in the separation chamber that filters solids and allows liquid to pass through to an overflow outlet; a return system containing a one-way valve, whereby the return system flushes filtered solids back to the flow chamber; and a damper spaced from the overflow weir for dampening turbulent flow entering the separation chamber from the flow chamber.

The damper is preferably a baffle wall located in the flow chamber and spaced from the weir. The baffle wall hangs downwardly from a ceiling of the flow chamber and is located higher than the weir but with the bottom of the baffle wall located lower than the top of the weir.

The baffle wall is spaced from the weir at a distance equal to or less than the size of a return outlet in the return system so as to prevent solids that could become stuck in the return system from entering the separation chamber.

The filter is preferably a curved screen wall that convexly curves outward from the top of the weir down towards the return system and terminates at a floor of a trough in the return system.

The holding means is preferably an open trough having walls and a floor that is inclined towards a return outlet at which is located the one-way valve. The holding trough preferably has one low wall for allowing filtered liquid to overflow the trough to the overflow outlet and extends the width of the filter, wherein the filter is a convex screen wall. The filter extends from a top of the weir down into the trough such that the trough holds both solids as well as filtered liquid. The trough, which is to contain the filtered liquid, is also preferably segmented along its length.

The valve is preferably a floating ball valve captured in a valve chamber. The chamber has a ceiling that is inclined upwards towards the return outlet located at an apex of the ceiling. A pointed stop on the floor of the valve chamber directs the ball sideways of the stop to one side of the chamber as the ball lowers, thereby avoiding the ball from obstructing a central opening of the return conduit.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments, incorporating all aspects of the invention, will now be described by way of example only with reference to the accompanying drawings in which:

Figures Ia to Ie are a sequence of side sectional views of a solids separator according to a first embodiment of the invention and illustrating an overflow mode of operation of the separator, where Figures Ia, Ib, Id and Ie are taken at section A-A of Figure 2 and Figure Ic is taken at section B-B of Figure 2 that is downstream of section A-A;

Figure 2 is a plan view of the solids separator taken at section C-C of Figure Ib;

Figure 3 is a sectional side view of a valve chamber of the solids separator;

Figure 4 is a sectional plan view of the valve chamber of the solids separator;

Figure 5 illustrates the solids separator of Figures Ia to Ic in a bypass mode of operation;

Figure 6 is a cross-section of a solids separator according to a second embodiment illustrating a method of increasing the flush-water volume;

Figures 7a and 7b are side elevations of perforation designs to demonstrate methods of preventing sewer solids from catching on the inclined perforations; and

Figure 8 is a longitudinal section of the separator to illustrate an alternative means of storing the increased flush-water volume.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

The drawings illustrate two similar versions of a solids separator 10 designed to remove sewage bodies, such as solids, paper, sanitary materials, litter and other visible matter from sewer system overflows. While the solids separator is discussed in terms of sewer systems, it is understood that the separator could be used to separate matter from liquid generally.

The solids separator is adapted to manage and redirect liquid overflow from the sewerage line to a water body, such as a river, the sea, etc., while separating solids from the redirected overflow. The solids separator can be made in various forms depending on requirements for installation. For example, the solids separator may be

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incorporated inside an existing combined sewer overflow chamber by modifying the overflow chamber to include the features of the solid separator. In another embodiment the solids separator may be constructed as a module for installation alongside a combined sewer overflow chamber.

In yet another embodiment the solids separator may be constructed as a complete unit installed in the sewer line and in addition to the solids separator features includes a main chamber through which sewer and liquid ordinarily flow from an inlet to an outlet without overflowing.

In the embodiment where the solids separator is formed as a module or complete unit, the solids separator is typically formed from reinforced concrete and stainless steel. In the description that follows the solids separator is illustrated as ^λ 10' and includes generally the features described herein which, unless specified, apply to all installation forms of the solids separator described above.

As shown in Figure 2 which is a plan view of the solids separator, inlet and outlet conduits 11, 12 communicate with a main flow chamber 14 containing the liquid source for the separator 10. The inlet conduit 11 and outlet conduit 12 are typically in service or may alternatively form part of a larger unit containing the solids separator 10 and a sewer flow service. In the version illustrated, the components of separator 10 are retrofitted inside an existing combined sewer overflow chamber which includes an inlet opening 15 for inlet conduit 11 and an outlet opening 16 for outlet conduit 12.

In the first and most common mode of operation, which is shown in Figure Ia, the level of liquid 18 flowing through main chamber 14 is low and flows unobstructed through outlet opening 16 and conduit 12 towards a treatment area.

The second mode of operation is the overflow mode and occurs when the liquid level 18 in main chamber 14 begins to rise. In this mode overflowing water is redirected from the sewage flow in the main chamber 14 through to a water body.

Figure Ib illustrates liquid level 18 rising but still at a level less than the top of a weir 20 separating the main chamber 14 from a separation chamber 21. In this mode a one-way valve 22 of a solids return system closes by way of liquid flowing from main chamber 14 through a return conduit 25 and into a valve chamber 23 of the one-way valve 22 where a ball valve 24 floats upwardly and closes a return outlet 26 leading to the separation chamber 21. This prevents short-circuiting of liquid into the separation chamber in the reverse direction allowed by the one-way valve 22 as well as prevents unacceptable frequencies of discharge to a water body which is intended to only receive filtered liquid overflow.

Figure Ic illustrates the liquid level 18 in main chamber 14 rising above weir 20. Once liquid level 18 crests the top of weir 20 the liquid containing entrained bodies 19 enters separation chamber 21 and flows down a curved face of a screen wall 28 that acts as a filter in filtering bodies 19 from liquid flow. The convexly curved screen 28 is shaped so that overflow liquid is always in contact with the screen up to the maximum treatable overflow.

Screened liquid as well as unscreened liquid flows- down through the separation chamber 21 and is caught by an open liquid flush holding means in the form of a trough 30. Screen wall 28 is joined to and extends from the top of weir 20 and curves convexly downward to terminate at a floor 31 of trough 30 and at a point spaced from walls 32, 33 and 34 of trough 30. In this manner liquid flowing

into separation chamber 21 will collect in trough 30 on either side of screen 28 but floating or other solid bodies 19 collect in trough 30 on the unfiltered side of screen 28. Since the trough 30 is open and does not impinge on the screen 28, the entire area of the screen is available for filtering.

A rear wall 33 defines the rear wall of trough 30 on the unfiltered side and extends vertically upward to a height comparable to the height of weir 20. Rear wall 33 contains overflowing liquid in the separation chamber and directs the liquid towards trough 30. In times of severe overflow, liquid is allowed to flow over rear wall 33 bypassing the separation chamber 21 straight to an overflow outlet 38. A screened partition 41 mounted on top of rear wall 33 prevents transfer of large solids and other waste over rear wall 33 during bypassing overflow.

Overflow wall 32 of trough 30 is positioned opposite rear wall 33 and is a low wall that is spaced from weir 20 to form a gap 35 so as to allow filtered liquid to overflow trough 30 and flow down through gap 35 into a discharge chamber 36 from where the filtered liquid flows out of the separator 10 through overflow outlet 38 and towards a water body (not shown) capable of taking overflows.

During overflow events, such as storms or flash flooding, the violent agitation of the flow in main chamber 14 causes surface wave surges leading to uneven flow over the weir 20 and thus inefficient solids/liquids screening by screen 28. To "iron out" or dampen the wave action in overflowing liquid from the main chamber a baffle wall 40 is placed in front of the weir to provide a throttling action. The baffle wall 40 dampens turbulent surges to evenly distribute the flow along the weir and so improve the separating capacity of the curved screen.

The baffle wall 40 is mounted in the main chamber 14 to hang spaced a distance from the weir 20. The bottom of wall 40 hangs lower than the top of weir 20 such that overflowing liquid is forced through gap 46 in order to enter separation chamber 21.

Baffle wall 40 may be mounted in main chamber 14 by several ways. It may be mounted to hang from ceiling 45 of main chamber 14. Alternatively, the baffle wall may be suspended in position spaced from weir 20 in main chamber 14 by horizontal bars (not shown) extending between the bottom of baffle wall 40 and the top of weir 20 and/or between baffle wall 40 and rear wall 33. The horizontal bars would be spaced along the length of the baffle and along the lengths of the weir and/or rear wall.

In the second or overflow mode of operation, the wall 40 is partly submerged which suppresses the effect of surges in the main chamber on overflow liquid flow rates. It has been found that flow rate fluctuations can be suppressed by around 95% by using the wall 40. Thus the wall 40 is effective in improving the evenness of distribution of overflowing liquid along the crest of weir and hence the efficiency of solids/liquid separation of screen 28.

Another advantage of the partly submerged wall 40 is to act as a size restrictor in that it prevents floating sewer solids larger than the valve's return outlet 26 from entering separation chamber 21 and possibly blocking outlet 26. This is achieved by limiting the gap 46 between wall 40 and weir 20 and specifically limiting the gap 46 to a distance equal to or less than the size of the return outlet 26.

During overflow, the impact of liquid flowing down the convexly curved screen 28 into the separation chamber and onto the surface 18 of liquid therein sets up a so called

^hydraulic jump' 51 against the open face of screen wall 28. This natural phenomenon occurs when liquid flowing at super-critical velocity suddenly slows thereby setting up a violent rotary motion with high loss of energy. The shear force exerted by the falling water against the screen combined with the rotary motion of the hydraulic jump has the effect of continually cleaning the perforations in screen 28 and allowing liquid to pass through the screen while retaining bodies 19 in separation chamber 21 in a state of suspension.

When flow of liquid into separation chamber 21 slows or ceases, the surface of the liquid falls to discharge all filtered liquid out through discharge chamber 36 leaving a catchment of filtered liquid and unfiltered liquid entrained with bodies 19 in trough 30 as illustrated in Figures Ic and Id. As long as the liquid level 18 in main chamber 14 is higher than the one-way valve 22 in the return system, ball valve 24 bears against return outlet 26, which is located in the floor 31 of trough 30, preventing the liquid in trough 30 from discharging through return outlet 26.

The liquid level in the trough on the unfiltered side of the screen is higher than the level on the filtered side. This difference in height forces liquid on the unfiltered side through the perforations of screen 28 so that this lower section of the screen also now takes part in the screening process (see Figures Ic and Id) . Accordingly, the entire screen surface is made available for screening purposes which significantly increases the capacity of the screen and so the effectiveness of the separator.

As the liquid level 18 continues to drop in the main chamber 14 to a level below one-way valve 22, as shown in Figure Ie, the valve opens permitting retained liquid in

trough 30 to flush the solids 19 through return outlet 26 into valve chamber 23 and through return conduit 25 back into the main chamber 14 where the now diminished sewage flow collects the liquid entrained with solids and carries the solids to the waste treatment area.

The floor 31 of trough 30 is inclined towards return outlet 26 forming a sloping central gutter 37, as shown in Figure Ic. Return outlet 26 is located at a lowest point of the gutter 37 so that all liquid contained in the trough flows down the central gutter and drains through the return outlet 26. As illustrated in Figure 2 return outlet 26 and one-way valve 22 are located substantially central along the length of trough 30.

In addition, the flushing action of reserved filtered liquid not only flushes bodies 19 back into the main chamber, but also flushes back through the screen perforations. This prevents the build up of small solids and also cleans the perforations in the screen wall 28.

Figure Ie illustrates ball valve 24 in the open position to allow liquid and bodies 19 to flow back down through the return system into main chamber 14.

Additionally, the section of trough 30 between overflow wall 32 and screen 28 is divided into segments by side walls 34 that are substantially the same height as the height of overflow wall 32.

Side walls 34 enhance the flushing action in the trough by ensuring that the liquid held in each segment exits the trough by way of the adjacent lower screen perforations. This action both cleans the said perforations ahd ensures a uniform release of the liquid into the unfiltered side of the trough and along the length of the screen so that

retained sewer solids are flushed from the entire length of the trough towards the valve 22.

Other variations on trough design may include ensuring that sufficient flush flows originate from both ends of the trough in order to adequately flush away sewer solids towards the central return outlet 26. One variation may include raising the height of the end transverse (side) walls 34 of the trough together with adjacent sections of overflow wall 32, so that more flush liquid is stored in these last trough segments to facilitate the flushing action.

Figure Id shows a cross-section through the one-way valve 22 with the ball 24 closing off outlet 26 during liquid overflow. Figure Ie shows the centrally located valve 22 during chamber emptying with flush liquid together with sewer solids 19 flowing into it and returning to main chamber 14 via return conduit 25. Figures 3 and 4 show further views of the valve in the closed position. The ball 24 is a floating ball captured in valve chamber 23. The chamber has a ceiling that is inclined upwards towards the central return outlet 26 located at an apex of the ceiling. The inclined ceiling guides the ball 24 toward the outlet 26 as the liquid level rises in chamber 23.

As shown in Figures Ib, Id, Ie and 3, a pointed stop or wedge 48 on the floor of the valve chamber ensures that during emptying the ball is directed sideways of the wedge to move to one side or the other of the valve housing and provide room for the passage of flush liquid and screened sewer solids 19 to the return conduit 25 and then on to main chamber 14. A stop wall 50 shown in Figures Ib, Id, Ie and 4 prevents the ball 24 from blocking return conduit 25 by keeping the ball 24 away from the return conduit.

As illustrated in Figures Ia to Ie a manhole access 44 located in ceiling 45 above separation chamber 21 allows maintenance and cleaning to be carried out. Alternatively or in combination, a manhole access (not shown) may also be located in the ceiling above main chamber 14.

Figure 5 illustrates a third mode of operation when liquid overflow entering the separator 10 is so large that it floods the separator. The liquid level 18 rises above weir 20 and exceeds the capacity of the separation chamber. In order to drain this large overflow as quickly as possible and avoid surcharging upstream of inlet conduit 11, an amount of liquid entrained with bodies 19 is allowed to bypass separation chamber 21 and flow over rear wall 33, down through bypass passage 42 and directly through to overflow outlet 38.

In these extreme circumstances larger items of waste and other solids are retained in separator chamber 21 by a screen partition 41 mounted on top of rear wall 33 although smaller items may not be separated from the overflow liquid before entering the overflow outlet. This third mode may occur simultaneously with the second overflow mode but the duration of the third mode is relatively short compared to that of the second overflow mode .

In another embodiment, shown in Figure 6 the screen perforations 50 are limited to the lower portion of the screen 51 with the rear wall 52 also reduced in height to a level just above the top row of the said perforations. In this embodiment, all the falling liquid 53 is flowing at super-critical velocity and passes down the screen surface 51 to plunge below the lower water surface 54 against the said screen, shearing away any attached sewer solids 56 and so keeping the said perforations 50 free of matter. The energy of the plunging liquid 53 finally

dissipates in a hydraulic jump 55 that maintains the retained sewer solids 56 in suspension thus preventing them from settling.

The lowered rear wall 52 limits the depth of liquid 59 in the separation chamber 21 to that which the plunging liquid 53 can penetrate to keep the perforations 50 free of sewer solids 56. When rare overflows greater than the screen capacity occur, the excess flow passes over the lowered rear wall 52 and is discharged from the separator. By this means blockage of the said perforations is prevented even during such excessive overflows.

Because the screen curvature in the vicinity of the said perforations is still slightly inclined to the vertical, a further measure to reduce the possibility of perforation blockage, as will be seen in Figures 7a and 7b, is to set the lower edge 57 of the perforations 50 vertically behind the upper edge 58 so that vertically falling solids 56 will not catch on the former. This is accomplished by either bending back the lower edge 57, as shown in Figure 7a or by bevelling it, as shown in Figure 7b.

To further enhance solids flushing, a flush tank 60 may be incorporated behind the curved screen 51 and above the trough 30, as shown in Figure 6. To fill the flush tank 60, the crest 61 of screen 51 meets the vertical wall 20 horizontally so that overflowing liquid 53 separates from screen 21 at weir crest 61, allowing a portion of liquid to pass through rows of perforations 62 in the weir crest

61 while sewer solids 56 are carried over the perforations

62 with liquid 53 and so do not obstruct them. Liquid falls into flush tank 60 where it collects during an overflow event.

Small one-way ball valves 63 are used to prevent liquid from flowing into trough 30 until the main ball valve 22

has opened and the water level in the latter has consequently fallen. The one-way ball valves 63 then open releasing the stored liquid from flush tank 60 to aid in the flushing of sewer solids through ball valve 22 and back to sewer chamber 14.

In a further variation of the above principle, shown in figure 8, collection channels 64 run beneath the said rows of perforations and lead the collected liquid 67 to tanks 65, 66 located at either end of the separator.

The present separator provides significant advantages over known separators of liquids and solids. The advantages include a more efficient use of the separating mechanism and namely the filtering screens. An effective catchment and a reserve of filtered liquid assist in the self- cleaning of the separator and the flushing of waste materials back into the main liquid flow without the need of an external power source. The separator is furthermore extremely efficient when it matters most, namely during large and violent overflows when the efficiency of known separators is likely to drop. With the present separator a baffle wall strategically positioned before the inlet into the separation chamber dampens and regulates flows into the separation chamber.

On the whole, the solids separator provides a more reliable and effective means for controlling and regulating the discharge of excess liquid and the containment of waste entrained within the liquid. This in turn leads to a safer, cleaner and certainly a healthier environment .

It will be understood to persons skilled in the art of the invention that many modifications may be ¹ made without departing from the spirit and scope of the invention.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.