WO2021217213A1

WO2021217213A1 - Methods and systems for grit removal from waste water

Info

Publication number: WO2021217213A1
Application number: PCT/AU2021/050393
Authority: WO
Inventors: Lisa Beth LEMONT; Vincent Khee Sin HO
Original assignee: Vor Environmental Australia Pty Ltd
Priority date: 2020-05-01
Filing date: 2021-04-30
Publication date: 2021-11-04
Also published as: AU2021262229A1

Abstract

A method of modifying a vortex grit trap (10) of the type including: an influent channel (31) for receiving waste water inflow; a tank (30a) including: an upper chamber (33) in fluid communication with the influent channel (31) to receive the waste water inflow from the influent channel (31); and a lower grit well (34) in fluid communication with the upper chamber (33), the lower grit well (34) configured to receive grit suspended in the waste water inflow from the upper chamber (33); and a rotary impeller arrangement configured to create a vortex within the tank (30a); a degritted effluent channel (32) in fluid communication with the upper chamber (33) for exiting degritted water from the tank (30a); and a concentrated grit slurry effluent channel (42) in fluid communication with the lower grit well (34), the concentrated grit slurry effluent channel (42) configured for exiting concentrated grit slurry from the lower grit well (34); the method including: fitting a baffle tray (35) within the degritted effluent channel (32), the baffle tray (35) comprising a base portion (37) having an opening (38) therein and a weir portion (36) extending from a periphery (37a) of the base portion (37), wherein the baffle tray (35) is fitted to the degritted effluent channel (32) in such a manner that: the opening (38) is disposed over the upper chamber (33) of the tank (30a); the degritted water from the upper chamber (33) is directed through the opening (38) into the baffle tray (35); and the weir portion (36) obstructs direct flow of waste water from the influent channel (31) into the degritted effluent channel (32).

Description

METHODS AND SYSTEMS FOR GRIT REMOVAL FROM WASTE WATER

FIELD

[0001] The present disclosure relates to methods and systems for grit removal from waste water. The disclosure further relates to a method of modifying a vortex grit trap system.

BACKGROUND

[0002] Sewage and waste water pose public health hazards and require treatment before being deemed safe to be discharged into receiving water bodies in a natural environment (wastewater) or converted to potable water (drinking water). Sewage and waste water must be treated e.g. at a water treatment plant to remove grit, organic matter (e.g. faecal matter) and bacteria using a series of costly treatment processes. At a water treatment plant, grit removal is a pre-treatment step for removing grit from waste water before it undergoes other steps of organic matter removal and water purification.

[0003] Grit removal equipment is generally used at the inlet of a water treatment plant. This equipment captures inorganic grit present in waste water. Although grit concentrations in waste water are generally small, grit is extremely abrasive with the result that, if not captured upstream, causes significant wear, tear and loss of operational efficiency of various downstream components of the water treatment system.

[0004] Conventional grit removal equipment such as grit extractors or vortex grit traps have been used in water treatment systems to remove grit from waste water. The inventors have established that these systems have certain shortcomings which lead to inefficient removal of grit from inflowing waste water. The degritted effluent flow exiting from conventional grit removal equipment may still include an amount of uncaptured grit which may pose some of the aforementioned problems to the downstream water treatment system. In particular, accumulated grit in the water treatment system may clog pipes, and increase wear and tear of pumps and valves, thereby raising maintenance and operational costs. [0005] Therefore, it is desirable to develop and provide methods and systems which allow for effective grit removal from sewage or waste water, or at least provide a useful alternative.

[0006] Reference to any prior art in the specification is not an acknowledgement or suggestion that this prior art forms part of the common general knowledge in any jurisdiction or that this prior art could reasonably be expected to be combined with any other piece of prior art by a skilled person in the art.

SUMMARY

[0007] In accordance with a first aspect, the invention provides a method of modifying a vortex grit trap of the type including: an influent channel for receiving waste water inflow; a tank including: an upper chamber in fluid communication with the influent channel to receive the waste water inflow from the influent channel; and a lower grit well in fluid communication with the upper chamber, the lower grit well configured to receive grit suspended in the waste water inflow from the upper chamber; and a rotary impeller arrangement configured to create a vortex within the tank; a degritted effluent channel in fluid communication with the upper chamber for exiting degritted water from the tank; and a concentrated grit slurry effluent channel in fluid communication with the lower grit well, the concentrated grit slurry effluent channel configured for exiting concentrated grit slurry from the lower grit well; the method including: fitting a baffle tray within the degritted effluent channel, the baffle tray comprising a base portion having an opening therein and a weir portion extending from a periphery of the base portion, wherein the baffle tray is fitted to the degritted effluent channel in such a manner that: the opening is disposed over the upper chamber of the tank; the degritted water from the upper chamber is directed through the opening into the baffle tray; and the weir portion obstructs direct flow of waste water from the influent channel into the degritted effluent channel.

[0008] In an embodiment, the method further comprises at least partially removing the impeller arrangement from the grit trap or deactivating the impeller arrangement.

[0009] In an embodiment, the baffle tray is fitted with a gap defined between a base of the degritted effluent channel and the base portion of the baffle tray to increase the height of the weir portion to further obstruct direct flow of waste water from the influent channel into the degritted effluent channel.

[0010] In an embodiment, the opening in the base portion of the baffle tray is circular and has a diameter between the full width and half the width of the base portion.

[0011] In an embodiment, the method further comprises modifying the vortex grit trap to exhibit a continuous flow of the concentrated grit slurry from the lower grit well through the concentrated grit slurry effluent channel.

[0012] In an embodiment, an original pump of the vortex grit trap is either modified or replaced with a new pump such that the modified or new pump has a larger capacity than the original pump.

[0013] In an embodiment, the modified or new pump is capable of continuous operation for assisting continuous underflow of the concentrated grit slurry from the lower grit well.

[0014] In an embodiment, an original underflow pipe of the vortex grit trap is either modified or replaced with a new underflow pipe such that the modified or new underflow pipe has a larger cross-sectional area than the original underflow pipe for assisting continuous underflow of the concentrated grit slurry.

[0015] In an embodiment, slurry dewatering equipment used with the vortex grit trap is either modified or replaced with an up-scaled slurry dewatering equipment such that the modified or up-scaled slurry dewatering equipment is capable of accommodating and processing a larger volume of the concentrated grit slurry and organics in comparison to the original grit washer.

[0016] In an embodiment, the floor of the upper chamber is modified with a downward sloping portion or increased downward sloping portion towards an opening of the lower grit well to facilitate the movement of grit from the upper chamber to the lower grit well.

[0017] In accordance with a second aspect, the invention provides a modified grit trap obtained by modifying an existing vortex grit trap using the method provided by the first aspect. [0018] In accordance with a third aspect, the invention provides a grit trap for removing grit from waste water, the grit trap including: an influent channel for receiving waste water inflow; a tank including: an upper chamber in fluid communication with the influent channel to receive the waste water inflow from the influent channel; and a lower grit well in fluid communication with the upper chamber, the lower grit well configured to receive grit suspended in the water inflow from the upper chamber; a degritted effluent channel in fluid communication with the tank for exiting degritted water from the tank; a concentrated grit slurry effluent channel in fluid communication with the lower grit well, the concentrated grit slurry effluent channel for exiting concentrated grit slurry from the lower grit well; and a baffle tray provided within the degritted effluent channel, the baffle arrangement comprising a base portion having an opening therein, and a weir portion extending from a periphery of the base portion; wherein the baffle tray is located in the degritted effluent channel in such a manner that: the opening is disposed over the upper chamber; the degritted water from the upper chamber is directed through the opening into the baffle tray; and the weir portion obstructs direct flow of waste water from the influent channel into the effluent channel.

[0019] In an embodiment, the baffle tray is formed integrally with the degritted effluent channel.

[0020] In an embodiment, the baffle tray is fitted with a gap defined between a base of the degritted effluent channel and the base portion of the baffle tray to increase the height of the weir portion to further obstruct direct flow of waste water from the influent channel into the degritted effluent channel.

[0021] In an embodiment, the opening in the base portion of the baffle tray is circular and has a diameter between the full width and half the width of the base portion.

[0022] In accordance with a fourth aspect, the present invention provides a grit trap system comprising: a grit trap according to the first aspect; a pump in fluid communication with the concentrated grit slurry effluent channel, the pump for pumping concentrated grit slurry continuously out of the lower grit well through the concentrated grit effluent channel; and a grit washer for receiving the concentrated grit slurry from the concentrated grit slurry effluent channel, wherein the grit washer has a grit washer tank with a concentrated slurry outlet and an organic refuse outlet. [0023] Further aspects of the present disclosure will become apparent from the following description, given by way of example and with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Preferred embodiments of the invention are described, by way of examples only, with reference to the accompanying figures, wherein:

[0025] Fig. 1a shows a perspective schematic view of one type of related art vortex grit trap;

[0026] Fig. 1 b shows a more detailed side sectional view of the vortex grit trap of Fig. 1 (a);

[0027] Fig. 2 shows results of Computational Fluid Dynamic (CFD) modelling of a conventional vortex grit trap system;

[0028] Figs. 3a, 3b, and 3c show various views of a modified vortex grit trap, according to an embodiment of the disclosure;

[0029] Fig. 3d shows a perspective view of a baffle tray which is disposed in the effluent channel of the grit trap of Figs. 3a-c;

[0030] Fig. 4a shows an example of a modified grit trap system including the modified grit trap of Figs. 3a-c.;

[0031] Fig. 4b shows a top plan view of the modified grit trap system as shown in Fig. 4a.

[0032] Fig. 4c shows a side sectional view of the modified grit trap system shown in Fig. 4a;

[0033] Fig. 4d shows a front view of the modified grit trap system of Fig. 4a;

[0034] Fig. 4e shows a perspective view of the baffle tray and the holder of the suspension apparatus in isolation from the remainder of the modified grit system shown in Figs. 4a-4d. [0035] Fig. 5 shows results of Computational Fluid Dynamic (CFD) modelling of the grit trap of Figs. 3a-d or Figs. 4a-d.

DETAILED DESCRIPTION

[0036] Embodiments of the present disclosure provide methods and systems for removing grit from waste water.

Conventional Vortex Grit Trap

[0037] Fig. 1 a shows a perspective view of a conventional vortex grit trap 10 and Fig. 1 b shows a more detailed side sectional view of the vortex grit trap 10. The grit trap is deigned to remove inorganic grit from sewage or waste water. The grit trap 10 comprises an influent channel 11 to receive sewage or waste water, a degritted effluent channel 12 for exiting degritted water, and a concentrated grit slurry effluent channel 18 for exiting concentrated grit slurry out of the grit trap 10. The grit trap 10 further comprises a tank 10a including an upper chamber 13 and a lower grit well or hopper 14. The upper chamber 13 communicates with the tangential influent channel 11 for receiving sewage/waste water. The lower grit well 14 communicates with a transverse component of the concentrated grit slurry effluent channel 18 (referred as “grit effluent channel” hereinafter) via a vertical component of the grit effluent channel, namely grit removal pipe 16. The tank also comprises a rotary impeller arrangement comprising impeller blades 15a supported on a floor plate 15d, a drive tube 15b and a drive motor assembly 15c for rotating the drive tube 15b and impeller blades 15a.

[0038] The concentrated grit slurry can be removed from the lower grit well 14 via the vertical grit removal pipe 16 by either an air lift (e.g. using air lift supply lines 17a and 17b), a recessed impeller (not shown) or a grit pump (not shown). Some vortex grit traps may have an outlet pipe for underflow instead of the vertical grit removal pipe 16. The outlet pipe can be located outside the grit trap and connected at the base of the lower grit well 14.

[0039] When the waste water is received at the influent channel 11 , it moves into the upper chamber 13 of the tank. The waste water is generally received continuously at the influent channel 11. The conventional understanding in the field is that the operation of the rotary impeller arrangement creates a vortex of waste water within the upper chamber 13. The rotational forces created by the vortex allow the organic matter present in the waste water to remain in suspension while the heavier grit settles at the floor of the upper grit chamber 13. The rotational forces from the impeller arrangement help move the grit inwardly over the floor plate 15d of the upper chamber 13 into the lower grit well 14. The concentrated grit slurry captured in the lower grit well 14 exits via the vertical grit removal pipe 16 through the effluent channel 18. The degritted water flows continuously through the degritted tangential effluent channel 12.

[0040] In the grit trap 10 as shown in Figs. 1 a and 1 b, the effluent channel 18 is located at the top and the concentrated grit slurry is removed from the lower grit well 14 by pumping it out through the vertical grit removal pipe 16. In an alternative vortex grit trap, the effluent channel 18 may be located at the bottom and the concentrated slurry may be removed/pumped out from the sump of the lower grit well 14.

[0041] The pump (not shown in figs. 1 a and 1 b) for exiting the concentrated grit slurry from the lower grit well 14 is operated intermittently i.e. the pump is turned on for a few minutes and then closed off (e.g. using a mechanical/automatic valve) for anywhere between 15 to 60 minutes so that a body of grit can accumulate in the sump of the lower grit well.

[0042] The inventors have conducted an analysis of currently available vortex grit trap systems (similar to the one shown in Fig.1 ) and have concluded that the grit capturing performance of these systems is lower than expected. Upon further investigations and analysis, the inventors have found that certain existing grit trap systems are prone to “short circuiting”, meaning that a portion of the grit in the influent channel 11 flows directly to the degritted effluent channel 12 without settling to the base of the vortex grit system as intended.

[0043] Fig. 2 shows results of Computational Fluid Dynamic modelling (CFD) of an existing vortex grit trap system (similar to the one shown in Figs. 1a and 1b). This modelling shows particle/grit trajectory path lines 23 starting from the influent channel 21. As observed from this modelling, multiple grit particles (e.g. shown by lines 24) are short-circuited directly to the effluent channel 22 rather than migrating under gravity to the lower grit well 14. [0044] The inventors have developed a method and system directed to the grit capture/removal performance of a grit trap by either retrofitting an existing vortex grit trap or by designing and manufacturing a novel and upgraded grit trap.

Modifying Existing Vortex Grit Trap

[0045] Referring to Figs. 3a-d, embodiments of the present disclosure are directed to providing a baffle tray 35 within the degritted effluent channel 32 of a grit trap 30. The baffle tray 35 has a U-shaped geometry, an open end 35a, a closed end 35b, a weir portion 36, and a base portion 37.

[0046] The weir portion 36 extends vertically from the periphery 37a of the base portion 37. The weir portion 36 and the base portion 37 define the open end 35a and the closed end 35b of the baffle tray 35. It will be appreciated that the weir portion 35 does not have to be exactly vertical. In other words, the weir portion 36 may extend substantially vertically from the base portion 37, or in an upright manner such that it creates a flow barrier which is designed to prevent or at least reduce the short circuiting of grit particles from the influent to the effluent channels as per the modelling of Figure 2.

[0047] The base portion 37 has an opening 38 located toward the closed end 35b of the baffle tray 35. The opening 38 is circular, however, it is envisaged that the opening may have other shapes.

[0048] More particularly, the baffle tray 35 is provided within the path of the degritted effluent channel 32 in such a manner that the degritted water from the upper chamber 33 is directed through the opening 38 in the baffle tray 35 and into the effluent channel 32. The height of the weir portion 36 is designed such that it obstructs any direct flow of incoming waste water from the influent channel 31 into the degritted effluent channel 32. In this way, the incidence of short circuiting is reduced in the grit trap 30.

[0049] The baffle tray 35 has a width W that may be approximately similar to or slightly different than the width of the degritted effluent channel 32. This is to ensure that the baffle tray 35 can fit snugly and securely within the degritted effluent channel 32 without leaving any gaps along the edges. [0050] The existing vortex grit trap 30 can be further modified by removal of the rotatory impeller arrangement. The inventors have investigated certain existing vortex grit traps and found that the operation of rotatory impeller arrangement may create a high speed vortex in the upper chamber 33 of the tank 30a which may not allow the grit to easily settle at the base of the upper chamber 33, and may result in the grit exiting via the degritted effluent channel 32. Therefore, a relatively slow vortex is preferably required in the upper chamber 33. Since the waste water inflow through the influent channel 31 into the upper chamber 33 has a tangential trajectory, this creates a relatively slow vortex in the upper chamber 33. The rotational forces of this slow vortex may allow the separation of the grit from waste water and also may allow the grit to easily settle down on the floor of the upper chamber 33. The settled grit then slowly moves into the lower grit well 34 of the tank 30a under the effect of gravity and the vortex.

[0051] Since the modified grit trap system of the present disclosure relies on a slow vortex in the upper chamber 33, smaller-sized grit particles may also be likely to settle down at the base of the upper chamber 33. Certain existing vortex grit traps may be configured to capture on average coarse grit particles of size 200 micro-meters or above. However, the modified grit trap that is fitted with a baffle tray 35 and does not use a rotary impeller arrangement, may also capture fine grit particles of size from 100- 200 micro-meters. The slow vortex created in the modified grit trap further improves the grit capture/removal from the gritted waste water in addition to the reduced short- circuiting effect provided by the newly fitted baffle tray 35.

[0052] Therefore, it is believed that the modified grit trap system 30 of Fig. 3a may improve the grit capture/removal performance in two ways. Firstly, it reduces short- circuiting of the gritted waste water from the influent channel 31 directly into the degritted effluent channel 32, stopping or at least reducing any direct grit flow into the degritted effluent channel 32. Second, the slower vortex created in the modified grit trap 30 allows the grit particles (both coarse and fine particles) to settle down, thereby possibly further improving the grit capture/removal.

[0053] When modifying an existing grit trap, the entire rotary impeller arrangement (including impeller blades 15a, drive tube 15b, drive assembly 15c, and floor plate 15d) is generally removed. In some embodiments, only impeller blades 15a or impeller blades 15a and drive tube 15b are removed and the remaining parts of the impeller arrangement can stay in place. In other embodiments the rotary impeller arrangement is not removed.

[0054] Figs. 3a-c show various views of a modified vortex grit trap 30, according to an embodiment of the invention. Fig. 3d shows a perspective view of the baffle tray 35, which is fitted into the grit trap 30 as shown in Figs. 3a-c.

[0055] As is evident from Fig 3a, the baffle tray 35 is fitted in the path of the degritted effluent channel 32 with the open end 35a in fluid communication with the effluent channel 32 and the opening disposed above the upper chamber 33. Also, as part of the modification, as previously noted, the rotatory impeller arrangement (not shown in this figure) is removed from the original vortex grit trap. The concentrated grit slurry collected in the lower grit well 34 is removed through a grit effluent channel 39 using a pump (not shown in Figs. 3a, 3c, and3d). The grit effluent channel 39 is shown in Fig. 3b.

[0056] Fig. 3b shows a partly schematic side view of the modified grit trap 30.

The baffle tray 35 may be installed at a “step up” from the effluent channel 32 to raise the weir portion 36 of the baffle tray 35, thereby reducing the high-flow bypass from the influent channel 31 to degritted effluent channel 32. There is shown a small elevation/step of size 0-0.05 meters between the base of the degritted effluent channel 32 and the base portion 37 of the baffle tray 35. In other embodiments, the baffle tray can be installed as high as 0.15 meters above the base of the degritted effluent channel 32. The height of the baffle tray 35 may be adjusted empirically for each installation, depending on factors such as the required pressure head of degritted water passing out through the effluent channel 32.

[0057] Fig. 3c shows a top plan view of the modified grit trap 30. The optimum width/diameter of the opening 38 can be varied from W to about W/2, where W is the approximate width of both the degritted effluent channel 32 and the baffle tray 35.

[0058] In some embodiments, the grit trap may be further modified to operate the grit effluent channel 39 to remove the concentrated grit slurry on a continuous basis instead of an intermittent basis. In an embodiment, this modification is done by adjusting the intermittent valve (or replacing the intermittent valve with a continuously operating valve) on the existing grit system underflow to change the underflow flow rate from intermittent operation (usually 5 minutes/hour in conventional vortex grit traps) to continuous operation (meaning, always open and always flowing). This adjustment may also involve increasing the diameter of the underflow pipe to accommodate a greater throughflow of gritted effluent. In alternative embodiments, this may not require any physical modification and will only require operational modification of the valve to change the underflow rate from intermittent to continuous operation. Furthermore, it will be appreciated that the continuous underflow modification is not essential and the modified grit trap can function even when the underflow of the concentrated grit slurry is kept intermittent.

[0059] Fig. 4a shows an example a modified grit trap system 40 having a modified grit trap 30 as shown in Figs. 3a-c with a concentrated grit slurry effluent channel in the form of an underflow pipe 42, a grit washer 41 , , and a suspension apparatus 43. The modified grit trap 30 has been retrofitted with the baffle tray 35, which is disposed snugly and securely within the degritted effluent channel 32.

[0060] The suspension apparatus 43 comprises a platform 43a, hanger supports 43b, and a holder 43c. The holder 43c of the suspension apparatus 43 is connected to the weir portion 36 of the baffle tray 35 (see, for example, Fig. 4e). The suspension apparatus 43 holds the baffle tray 34in place and stops the baffle tray 35 from moving under the pressure of degritted water flowing up through the opening 38 into the baffle tray 45. The platform 43a may in some cases be present in the existing vortex grit trap that is being modified, and only hanger supports 43b, and holder 43c may be required to be installed to keep the baffle tray 35 in place.

[0061] As described with reference to Figs. 1 a and 1 b, many existing vortex grit trap systems have a rotary impeller arrangement (15a, 15b, 15c, and floor plate 15d) and a grit removal pipe 16 (which may be vertical, horizontal or angled, and may be located within or outside the grit trap). In the present example of Fig. 4a, both the rotatory impeller arrangement and the vertical grit removal pipe have been removed. The underflow pipe 42 is installed in place of the vertical grit removal pipe. The underflow pipe 42 has a valve 42a that is movable between an open position and a closed position. [0062] In some embodiments, the existing underflow pipe/grit removal pipe may not be replaced or may not require any physical changes. The existing underflow pipe may be used with the modified grit trap 30. It will be appreciated that the underflow pipe may be located inside, outside, or partially inside and partially outside of the grit trap.

[0063] Most existing vortex grit traps are used with downstream slurry dewatering equipment. This may include a grit washer for undertaking a process for removing any organics and other objects that may have been captured in the concentrated grit slurry exiting from the grit trap. The grit washer equipment has a grit washer tank into which the concentrated grit slurry is fed using pipes and pumps.

[0064] In a further embodiment, if the grit underflow is continuous and the pump is continuously operating to remove the concentrated grit slurry from the grit trap, then the grit washer may need to be up-sized to accommodate the higher flow load brought in by a continuous underflow of the concentrated grit slurry. In addition, the slurry may include a higher load of organics due to the continuous mode of operation and potentially the lower vortex speed which allows larger organic particles to settle with the smaller organic particles which have a similar specific gravity.

[0065] In the example of Fig. 4a, the grit washer 41 has been up-scaled. The modified grit washer 41 comprises a grit washer tank 44 (larger than the original tank of the existing vortex grit trap), pipes 45 and 46, a grit outlet 47 for removing dewatered grit into a skip/bin (not shown), and an organic outlet 48 for removing organic matter from the tank 44. The pipe 45 has a valve 45a that is movable between an open position and a closed position.

[0066] When the valve 42a is in the open position, the concentrated grit slurry can be removed from the lower grit well 34 of the modified grit trap 30 through the pipe 42 using a pump (not shown). The underflow pipe has a valve 47b that can be opened or closed as required. When the valve 45a is in the open position, the concentrated grit slurry can flow from the pipe 42, through the pipe 45, and into the tank 44.

[0067] The concentrated grit slurry undergoes a dewatering process in the tank

44, where any organic matter present in the concentrated grit slurry floats to the top and the grit particles settle at the base of the tank 44. The settled grit is removed from the base of the tank 44 via the pipe 46 using a pump (not shown), from where the settled grit exits via the grit outlet 47. The organic matter floating at the top is allowed to exit the tank 44 through the organic refuse outlet 48 and is piped into screened degritted waste water downstream of the modified grit trap system 40.

[0068] Certain existing vortex grit traps require a pump to remove concentrated grit slurry from the lower grit well. When the pump is operated, the concentrated grit slurry exits from the lower grit well into an underflow pipe. After that, the concentrated grit slurry is passed into the next installation in the water treatment plant e.g. in to slurry dewatering equipment. In further embodiments of the disclosure, when modifying an existing vortex grit trap, the size of the pump that operates the underflow (removal of concentrated grit slurry) through the underflow pipe may be replaced/modified with a larger pump (having larger volume flow rate or capacity) for handling the greater throughflow.

[0069] As noted from Figs. 1 , 3, and 4, the angle of the influent channel 31 to degritted effluent channel 32 may be different. For example, in Figs. 1a and 1b, the conventional vortex grit trap is shown to have influent and degritted effluent channels at a 90 degree angle (i.e. they are perpendicular or substantially perpendicular to each other). Flowever, the modified grit traps as show in Fig. 3a are shown to have a 180 degree angle between the influent and degritted effluent channels (i.e. they are parallel to each other). Embodiments of the present disclosure are not restricted to any specific angles between the influent channel 31 and the degritted effluent channel 32. This angle may be 90 degrees, 180 degrees, 270 degrees, 360 degrees or any other value from 0-360 degrees, with the main requirement being that both the influent and degritted effluent channels need to be substantially tangential to the upper chamber 33 so that a vortex is induced within the upper chamber 33.

[0070] Fig. 5 shows results of Computational Fluid Dynamic modelling of the modified grit traps of fig. 3a or fig. 4a. It is noted from this modelling that the grit short- circuiting from the influent channel to the degritted effluent channel is significantly reduced, at least based on the modelling. [0071] When designing the baffle tray 35 for an existing/new grit trap, the following parameters need to be suitably selected:

• Height of the weir portion 36 of the baffle tray 35. A higher weir portion 36 means less or no high-flow bypass from influent channel 31 to degritted effluent channel 32.

• Diameter of the opening 38 of the baffle tray 35 to ensure an optimum head-loss. A smaller opening 38 means higher head-loss but higher grit capture performance.

• Fraction of total flow exiting the grit trap system 30 via the degritted effluent channel 32 versus the underflow (i.e. total flow of concentrated grit slurry from the lower grit well 34).

• Elevation/step size at which baffle tray 35 is installed above the base of the degritted effluent channel 32. This may be between 0-0.15 meters. The lowest possible installation of the baffle tray 35 is for the base portion 37 of the baffle tray 35 to be set equal to the base of the degritted effluent channel 32 (i.e. a step size of zero meters).

[0072] The above mentioned parameters of the baffle tray 35 may be selected for a particular grit trap system based on CFD modelling of that specific grit trap system, and may also be empirically selected, in particular when fine-tuning. Different grit trap systems will have different baffle tray parameters.

[0073] It will be further appreciated that the total inflow of the waste water (and grit concentration in the inflow waste water) passing through the modified/retrofitted grit trap will remain the same as passing through the existing grit trap before modification/retrofitting. However, the amount of concentrated grit slurry captured in the lower grit well 34 may be greater for the retrofitted/modified grit trap 30 in comparison to the amount of concentrated grit slurry captured by the existing grit trap 10 before retrofitting.

[0074] Furthermore, upon retrofitting, the characteristics of the underflow also change. When underflow in the existing grit trap 10 operates intermittently, the grit underflow is highly concentrated with grit. This is because, during off-operation, grit accumulates and concentrates in the lower grit well 34 for a period of time (e.g. approximately 45 minutes to a few hours) and then, during the on-operation (e.g. over a 5 minute period), it is very quickly flushed out of the lower grit well 34. In contrast, if the grit trap is retrofitted to capture more grit, as described in embodiments of the present disclosure, the total captured grit load in the underflow pipe increases. In a typical example, the grit capture may be of the order of 1.5 to 3 times more than the grit captured by the grit trap before retrofitting. This means that the grit load in the underflow will be 1.5 to 3 times higher than before. Therefore, a continuous underflow of the modified grit trap system 40 is more suitable/preferred over operating it in intermittent mode.

[0075] When modifying existing grit traps that already have an underflow pipe (i.e. the original underflow pipe), the original underflow pipe may be replaced with a new underflow pipe having a larger cross-sectional area than the original underflow pipe. Replacing the original underflow pipe with a new underflow pipe having a larger cross sectional area may assist with removing concentrated grit slurry from the lower grit well 34, especially when the modified grit trap system 40 is operated with continuous underflow of concentrated grit slurry from the lower grit well 34.

[0076] To further assist with grit settling in the lower grit well 34 from the upper chamber 33, a portion of the upper chamber 33 may be modified to include a downward sloping portion 33a (see Fig. 3a) or, if the upper chamber 33 already includes a sloping portion 33a, increasing the angle of the sloping portion 33a. This sloping portion 33a slopes towards the lower grit well 34, which facilitates the movement of grit from the upper chamber 33 to the lower grit well 34.

[0077] The above embodiments of the present disclosure may provide a solution for improving grit capture performance of the existing vortex traps by retrofitting/modifying them. These modifications are made based on bespoke system needs. There is generally no need to modify shape and size of the existing influent or effluent channels which can be costly or impractical in particular in the case of materials such as preformed concrete. [0078] Although the above methods of modifying existing grit traps 10 describe totally removing the rotary impeller arrangement or only removing parts of the rotary impeller arrangement, it is also envisaged that the entire rotary impeller arrangement may be left in place within the grit trap when modifying the grit trap 10 as described above. In this case, when operating the modified grit trap 30, the rotary impeller arrangement is not operated or is disabled such that a high vortex is not generated in the upper chamber 33 of the modified grit trap 30.

New Grit Trap with an Integrated Baffle Tray

[0079] Further embodiments of the disclosure relate to designing and manufacturing a new custom made grit trap system from scratch. This is an upgraded grit trap that is designed to have an in-built baffle tray (similar to the baffle tray 35) and it does not comprise any rotatory impeller arrangement or associated apparatus. The in built baffle tray may be an integral component of the upgraded grit trap. Furthermore, the influent and effluent channels are designed to have specific shape and size that permit a tangential trajectory of the inflow and outflow through the influent channel and degritted effluent channel, respectively to generate a vortex. This upgraded grit trap system does not require a rotatory impeller arrangement.

[0080] The upgraded grit trap may also have a suitable pump that is sufficient for removing concentrated grit slurry via the underflow pipe. The underflow may be continuous or intermittent. The upgraded grit trap may also have a large-sized grit washer that is sufficient to accommodate a large amount of grit slurry including inorganics if the grit effluent channel is continuously operated.

[0081] As used herein the terms “include” and "comprise" (and variations of those terms, such as “including”, “includes”, "comprising", "comprises", "comprised" and the like) are intended to be inclusive and are not intended to exclude further features, components, integers or steps.

[0082] It will be understood that the embodiments disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the embodiments.

Claims

1. A method of modifying a vortex grit trap of the type including: an influent channel for receiving waste water inflow; a tank including: an upper chamber in fluid communication with the influent channel to receive the waste water inflow from the influent channel; and a lower grit well in fluid communication with the upper chamber, the lower grit well configured to receive grit suspended in the waste water inflow from the upper chamber; and a rotary impeller arrangement configured to create a vortex within the tank; a degritted effluent channel in fluid communication with the upper chamber for exiting degritted water from the tank; and a concentrated grit slurry effluent channel in fluid communication with the lower grit well, the concentrated grit slurry effluent channel configured for exiting concentrated grit slurry from the lower grit well; the method including: fitting a baffle tray within the degritted effluent channel, the baffle tray comprising a base portion having an opening therein and a weir portion extending from a periphery of the base portion, wherein the baffle tray is fitted to the degritted effluent channel in such a manner that: the opening is disposed over the upper chamber of the tank; the degritted water from the upper chamber is directed through the opening into the baffle tray, and; the weir portion obstructs direct flow of waste water from the influent channel into the degritted effluent channel.

2. The method of claim 1 , wherein the method further comprises at least partially removing the impeller arrangement from the grit trap or deactivating the impeller arrangement.

3. The method of claim 1 or 2, wherein the baffle tray is fitted with a gap defined between a base of the degritted effluent channel and the base portion of the baffle tray to increase the height of the weir portion to further obstruct direct flow of waste water from the influent channel into the degritted effluent channel.

4. The method of any one of the preceding claims, wherein the opening in the base portion of the baffle tray is substantially circular and has a diameter between the full width and half the width of the base portion.

5. The method of any one of the preceding claims, wherein the method further comprises modifying the vortex grit trap to exhibit a continuous flow of the concentrated grit slurry from the lower grit well through the concentrated grit slurry effluent channel.

6. The method of any one of the preceding claims, wherein an original pump of the vortex grit trap is either modified or replaced with a new pump such that the modified or new pump has a larger capacity than the original pump.

7. The method of claim 6, wherein the modified or new pump is capable of continuous operation for assisting continuous underflow of the concentrated grit slurry from the lower grit well.

8. The method of any one of the preceding claims, wherein an original underflow pipe of the vortex grit trap is either modified or replaced with a new underflow pipe such that the modified or new underflow pipe has a larger cross-sectional area than the original underflow pipe for assisting continuous underflow of the concentrated grit slurry.

9. The method of any one of the preceding claims, wherein slurry dewatering equipment used with the vortex grit trap is either modified or replaced with modified or up-scaled slurry dewatering equipment such that the modified or up-scaled slurry dewatering equipment is capable of accommodating and processing a larger volume of the concentrated grit slurry and organics in comparison to the original slurry dewatering equipment.

10. The method of any one of the preceding claims, wherein the floor of the upper chamber is modified to with a downward sloping portion or increased downward sloping portion towards an opening of the lower grit well to facilitate the movement of grit from the upper chamber to the lower grit well.

11. A modified grit trap obtained by modifying an existing vortex grit trap using the method of any one of the preceding claims.

12. A grit trap for removing grit from waste water, the grit trap including: an influent channel for receiving waste water inflow; a tank including: an upper chamber in fluid communication with the influent channel to receive the waste water inflow from the influent channel, and a lower grit well in fluid communication with the upper chamber, the lower grit well configured to receive grit suspended in the waste water inflow from the upper chamber, a degritted effluent channel in fluid communication with the tank for exiting degritted water from the tank; a concentrated grit slurry effluent channel in fluid communication with the lower grit well, for exiting concentrated grit slurry from the lower grit well; a baffle tray provided within the degritted effluent channel, the baffle arrangement comprising a base portion having an opening therein, and a weir portion extending from a periphery of the base portion; wherein the baffle tray is located in the degritted effluent channel in such a manner that: the opening is disposed over the upper chamber; the degritted water from the upper chamber is directed through the opening into the baffle tray; and the weir portion obstructs direct flow of waste water from the influent channel into the effluent channel.

13. The grit trap of claim 12, wherein the baffle tray is formed integrally with the degritted effluent channel.

14. The grit trap of claim 12 or 13, wherein the baffle tray is fitted with a gap defined between a base of the degritted effluent channel and the base portion of the baffle tray to increase the height of the weir portion to further obstruct direct flow of waste water from the influent channel into the degritted effluent channel.

15. The grit trap of any one of claims 12 to 14, wherein the opening in the base portion of the baffle tray is circular and has a diameter between the full width and half the width of the base portion.

16. A grit trap system comprising: a grit trap according to any one of claims 12 to 15; a pump in fluid communication with the concentrated grit slurry effluent channel, for pumping concentrated grit slurry continuously out of the lower grit well through the concentrated grit slurry effluent channel; and a grit washer for receiving the concentrated grit slurry from the concentrated grit slurry effluent channel, wherein the grit washer has a grit washer tank with a concentrated slurry outlet and an organic refuse outlet.