TECHNICAL FIELD The present invention relates to filters for water drainage systems, and in particular to filters for stormwater drainage systems.

BACKGROUND For environmental reasons, it is becoming increasingly necessary to filter or trap pollutants from water collected by drainage systems to prevent these pollutants from being discharged into bays, rivers, creeks, or other environmentally sensitive areas. This is particularly the case for stormwater drainage systems, in which water run-off from streets, roof areas, pathways, etc collects trash, debris, and other waste with it before it runs into a water way. In recent times the filtration and trapping of pollutants has become important, as "stormwater harvesting" has become a viable way of sustaining water resources. In some areas, government regulations now mandate that in new developments stormwater filtration must be provided. There is also often a need to filter pollution from water in industrial systems. Pollutants in stormwater fall into a number of categories. There are larger solid pollutants, known as gross pollutants, fine solid pollutants, and liquid pollutants. Solid pollutants can be further categorised by their relative density to water. Solid pollutants having a relative density of less than 1, such as twigs, closed containers, etc, are buoyant pollutants that float on the water. Solid pollutants with a relative density of between 1 and 1.5 are considered to be low density pollutants, and this includes most plastics. Solid pollutants with a relative density higher than 1.5 are considered to be high density pollutants, and this includes dense sediment. Whilst dense sediments such as clay particles are part of the environment, they are contributors to pollution. It has recently become understood that chemicals become attached to clay particles, which then cause aggregation and storage of chemicals in sediment beds. High density pollutants tend to sink faster than low density pollutants. Liquid pollutants include floating liquids having a relative density of less than 1, such as oils. Scum is also a pollutant that floats on the water and may include mixtures of liquid and fine particles. 2

Various stormwater filters are known and are in use. They are often referred to as "gross pollutant traps" or "solid pollutant filters". They are typically installed in-ground with their top exposed for access, and are connected in-line with a stormwater pipe. Prior art stormwater filters employ various methods of trapping pollutants. One method is to use filter screens to trap solid pollutants. In typical prior art systems employing filter screens, the water flows directly at the screens, which reduces the efficiency of the filter screen because when the screen becomes partially blocked it creates a high resistance to water flowing directly at it.

Typically, prior art filters employing filter screens also include a means for water to bypass the screens if they become blocked or the flow through the filter is excessive (such as in heavy storms). An example of a prior art stormwater filter with filter screens and a bypass system is disclosed in WO 98/17875 (Ecosol Pty Ltd). The bypass system in this filter is a barrier that normally directs polluted water through the filter, but allows overflow to bypass it. Another prior art arrangement uses a bypass system comprising a floating or otherwise movable boom. Bypass systems are typically necessary where filter screens are employed, but it is desirable for a stormwater filter to minimise the amount of water that bypasses the filter screens because the bypass water carries pollutants with it.

An alternative type of stormwater filter utilizes cyclonic motion about a vertical axis. One example is the Rocla CDS™ unit by Rocla Pty Ltd which utilises the energy of the inflow to create a a vortex flow regime within the screening chamber. Another example of this type of filter is sold by Humes Water Solutions under the brand Humeceptor™. A disadvantage of this latter stormwater filter is that a deep, costly excavation is required to install it and collected pollutants are deposited deep in the filter, which can be difficult to remove. Also, the capture volume of such a filter is limited.

Another disadvantage of typical prior art gross pollutant traps is that they do not efficiently capture oil or scum in the polluted water. Also, access to clean or replace the filter screens, or to remove collected solid waste, is often difficult in prior art filters due to the nature of their design. Also, the design of some prior art filters is such that collected pollutants build up and block filter access. Furthermore, some prior art filters have many components constructed from steel, which results in a relatively short service life unless they are constructed from expensive corrosion resistant steels. The present invention seeks to ameliorate at least one of the disadvantages of the prior art. SUMMARY OF INVENTION

In a first aspect, the present invention consists of an apparatus for filtering polluted water in drainage systems, comprising

a collection chamber for collecting the water, having a first end, a second end opposite the first end, and two sides between the ends;

an inlet at or near the first end for the water to enter the collection chamber; and

at least one filter screen disposed in at least one of the sides through which the water exits the collection chamber, characterised in that

a deflector is disposed at or near the second end of the collection chamber, the deflector being arranged to deflect downwardly the water flowing towards it.

Preferably, as the water flows through the collection chamber at least a portion of it tumbles about a substantially horizontal axis such that at the centre of the collection chamber the water near the surface flows substantially towards the second end, and the water near the bottom of the collection chamber flows substantially towards the first end.

Preferably, the deflector establishes a laminar flow state in the water in the vicinity of the deflector. Preferably, the collection chamber is elongate such that the distance between the ends of the collection chamber is greater than the distance between the sides of the collection chamber. Preferably, the deflector is at least partially submerged when the water is flowing though the apparatus.

Preferably, at least a portion of the deflector is shaped such that the distance between the front of the portion and the first end of the collection chamber increases as the portion extends towards the bottom of the collection chamber. Preferably, the deflector comprises an array of spaced apart elements, disposed parallel to the flow of the water past the deflector.

Preferably, the filter further comprises an oil separator for removing oil from the water, the oil separator being attached to or integral with the deflector. Preferably, the deflector comprises the oil separator, and the deflector comprises an array of spaced apart elements disposed parallel to the flow of the water past the deflector, and each element comprises an oil absorption material. Preferably, each element has a smooth front edge that faces the flow of the water towards the deflector.

Preferably, the inlet is a pipe, and the distance between the first and second ends of the collection chamber is at least four times the diameter of the pipe.

Preferably, the filter screen is replaceable. In one preferred embodiment, the filter screen comprises at least two modular panels.

Preferably the filter screen is made from at least one plastic material.

Preferably in one embodiment the apparatus comprises a winch system for lowering and raising the oil separator into the collection chamber.

In a second aspect, the present invention consists of an apparatus for filtering polluted water in drainage systems, comprising a collection chamber for collecting the water, having a first end, a second end opposite the first end, and an inlet at or near the first end for the water to enter the collection chamber, characterised in that an oil separator is disposed at or near the second end of the collection chamber for removing oil from the water. Preferably, the oil separator comprises an array of spaced apart elements disposed parallel to the flow of the water past the oil separator, and each element comprises an oil absorption material. Preferably, the oil separator deflects downwardly the water flowing towards it.

In a third aspect, the present invention consists of a stormwater contaminant separator and collector device for installation with stormwater pipes, said device comprising

a collection chamber for collecting water, having a first end, a second end opposite the first end, and two sides between the ends;

a stormwater inlet at or near said first end for said water to enter the collection chamber; and at least one filter screen disposed in at least one of said sides through which said water exits said collection chamber, characterised in that

a deflector structure is disposed at or near said second end of said collection chamber, at least a portion of said deflector structure being arranged to deflect downwardly water flowing towards it, and as said water flows through said collection chamber at least a portion thereof tumbles about a substantially horizontal axis such that at the centre of said collection chamber said water near the surface flows substantially towards said second end, and said water near the bottom of said collection chamber flows substantially towards said first end. Preferably, solid pollutants are substantially deposited in an area below said inlet at or near said first end, and buoyant pollutants are collected in an upper central zone of said collection chamber between said first and second ends. Preferably, an oil and scum collection zone is disposed at or near said deflector structure at said second end. In a fourth aspect, the present invention consists of a method of separating stormwater contaminants by passing polluted stormwater through a collection chamber, said method comprising imparting a tumbling motion about a substantially horizontal axis to a portion of the flow entering said collection chamber through an inlet, such that said portion of flow is directed downwardly and back towards said inlet.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 is a perspective view of a first preferred embodiment of a stormwater pollutant filter in accordance with the present invention with its lid not shown, and the top portion of its enclosure cut-away.

Figs. 2, 3 and 4 are various partial cut-away perspective views of the pollutant filter of Fig. 1.

Fig. 5 is a longitudinal sectional view through the pollutant filter of Fig. 1 showing various trapped pollutants.

Fig. 6 is an enlarged front perspective view of the oil separator assembly of the pollutant filter of Fig. 1. Figs. 7, 8, 9 and 10 show the normal flow through the filter of Fig. 1 without bypass flow, with Figs. 7 and 8 being partial cut away views, Fig. 9 being a longitudinal sectional view, and Fig. 10 being a plan view.

Fig. 11 is a partial sectional view through the filter of Fig. 1, showing flow that includes bypass flow.

Fig. 12 is a partial sectional view through the Filter of Fig. 1, showing total bypass flow.

Fig. 13 is a perspective view of a second preferred embodiment of a stormwater pollutant filter in accordance with the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Figs. 1 to 12 show a first preferred embodiment of a stormwater pollutant filter 1 in accordance with the present invention. Filter 1 is adapted to be installed in-line with a stormwater drain to separate and collect pollutants (contaminants) from stormwater passing through it. Referring to Fig. 1 , filter 1 comprises a water tight, open, box shaped enclosure (a main pit) 2 that is divided into chambers and houses the operating components of filter 1. In use, a lid (not shown) covers enclosure 2. In Fig. 1, the "top portion" of enclosure 2 and inlet and outlet pipes 4, 5 are cut-away, to more clearly show the location of a collection chamber 7 disposed within enclosure 2. Referring to Fig. 5, polluted stormwater 19 enters filter 1 through inlet pipe 4 at one end of enclosure 2, and filtered water 20 exits through an outlet pipe 5 at the opposite end of enclosure 2. Filter 1 is usually installed in the ground, with its lid (not shown) at or near ground level and exposed for access. Inlet and outlet pipes 4, 5 are typically below ground level. Inlet pipe 4 and outlet pipe 5 are at about the same height, near the top of enclosure 2. When filter 1 is installed and there is no flow through it, there is still residual water held in enclosure 2 at a residual water level 21 at the height of the bottom (i.e. the invert) of outlet pipe 5, which in this embodiment is the same height as the bottom of inlet pipe 4. Polluted water flowing into filter 1 , through inlet pipe 4, is collected in collection chamber 7, having a first end 8 and a second end 9 opposite thereto. Inlet pipe 4 is at first end 8 of collection chamber 7, and opens through the wall of end 8 of collection chamber 7. At the opposite end 9 of collection chamber 7 there is a "deflector", namely oil separator 10. The construction and function of oil separator 10 is described below. There are no openings in the wall of end 9 for water to flow through. Collection chamber 7 has two sides (side frames) 11, between ends 8 and 9. A plurality of vertical filter screens 12 is disposed in each side 11 of collection chamber 7. The filter screens 12 are disposed below the residual water level 21 and extend to the bottom 22 of collection chamber 7, and are disposed towards end 9 of collection chamber 7.

Filter screens 12 have a large area, preferably greater than twenty times the area of inlet pipe 4. This creates a relatively slow flow velocity through screens 12, which assists in preventing blockage and reduces the stress in screens 12. This allows screen materials of a fine micron to be used to increase particle capture efficiency and reduce the size of particles that can be captured. Filter screens 12 may be constructed from various materials including stainless steel and/or plastics, depending on the water conditions, and they may have a single layer of filter material or multiple layers. In this preferred embodiment the side frames 11 are made from high density polyethylene (HDPE) and the filter screens from a suitable polyethylene.

Filter screens 12 are removable for cleaning, servicing, or to replace with a different type of filter material as conditions change or filter material technology improves. Also, different filter screens 12 may be used depending on the specific environmental needs of a particular installation, which may vary with vegetation constraints, etc. For example, in stormwater harvesting systems requiring a higher degree of filtration, finer screens 12 can be used. This ability to change screens 12 of a particular installation is an advantage over the prior art.

Collection chamber 7 is elongate such that its length, the distance between its ends 8 and 9, is greater than its width, the distance between its sides 11. Referring to Fig. 5, the distance 28 between the ends 8, 9 of collection chamber 7 is preferably greater than four times the diameter 29 of inlet pipe 4, for reasons discussed below. A centre weir 13 is positioned between ends 8 and 9 of collection chamber 7, across the width of collection chamber 7. Two elevated spaced apart weir walls 38 extend from inlet 4 to weir 13 in the upper zone of enclosure 2. In as best seen in Fig. 10, centre weir 13 has a pointed tip 23 facing inlet pipe 4. Referring to Fig. 5, centre weir 13 extends above residual water level 21. Below centre weir 13, an opening 26 extends the width of collection chamber 7. Centre weir 13 is closer to end 8 than end 9 of collection chamber 7, and filter screens 12 extend approximately from centre weir 13 to end 9.

Centre weir 13 divides collection chamber 7 length-wise into two zones. A settling zone 30 is between end 8 and centre weir 13, and an exit zone 31 is between centre weir 13 and end 9. Opening 26 below centre weir 13 allows free fluid flow between zones 30 and 31 in the lower half of collection chamber 7. The bottom of settling zone 30 extends the width of enclosure 2, whilst the width of exit zone 31 is the distance between sides (side frames) 11.

Oil separator 10 is constructed as an array of spaced apart elements 15, each comprising a frame 17 surrounding and supporting a sheet of oil absorption material 16. Frames 17 are preferably made of HDPE, however they may be made of any suitable plastic or stainless steel. Oil absorption material 16 may for instance be OilSorb™ filtration media or some other suitable filtration media.

Frames 17 may be individually removable for servicing. Elements 15 are vertical and are aligned parallel to the sides 11 of collection chamber 7 such that they are also aligned parallel to the direction of flow of water past them. As shown in Fig. 6, a pivotal retainer 40 may be used hold frames 17 and elements 15 in place. Retainer 40 may be lockable using a movable cam lock (not shown) or the like.

Oil separator 10 is positioned at a height such that it is partially submerged when water is flowing through filter 1, and when water is at residual water level 21. Front 18 of oil separator 10 includes the front edges 56 of elements 15 and it faces inlet pipe 4. Preferably front edges 56 of elements 15 are smooth and rounded. Front 18 of oil separator 10 is sloped (angled) from a vertical plane such that the distance between front 18 and end 8 of collection chamber 7 increases as front 18 extends towards the bottom 22 of collection chamber 7. In this embodiment, each element 15 and frame 17 has a profile which is substantially "frusto-triangular", meaning it is triangular but its tip has been truncated by a plane parallel to its triangle base. The frusto-triangular profile each element has a "right angle" disposed near the top of end 9 of collection chamber 7, and its long edge (front edge 56) facing towards the bottom of end 8.

A discharge chamber 34 is formed in enclosure 2 between end 9 of collection chamber 7 and the end wall of enclosure 2 that outlet pipe 5 opens into. Two bypass channels 37 are each disposed between a side 11 of collection chamber 7 and a respective internal sidewall of enclosure 2.

When the lid (not shown) of enclosure 2 is removed, it allows for collected waste to be readily removed from collection chamber 7, and to allow oil separator 10 or its components to be easily replaced or serviced. A shut off gate (not shown) can be used to block inlet pipe 4 for servicing filter 1.

Enclosure 2 may be constructed from concrete based materials, preferably having a design service life exceeding 100 years. As previously indicated the components making up collection chamber 7 such as side frames 11, screens 12 may be made of suitable plastic material or stainless steel.

The operation of filter 1 will now be described. Figs. 7, 8, 9 and 10 show the normal flow through filter 1. Normal flow is defined as the flow condition when all of the water passing through filter 1 passes through filter screens 12. This type of flow occurs during normal rainfall rates (i.e. not heavy storms) and when filter screens 12 are not blocked.

Referring to Fig. 9 in particular, polluted water 19 entering collection chamber 7 through inlet pipe 4 flows along its surface, through opening 26 below centre weir 13, towards end 9 of collection chamber 7. As the flow approaches end 9, oil separator 10 deflects the flow downwards towards bottom 22 of collection chamber 7. As water 19 nears bottom 22 it then flows back towards end 8. As it approaches end 8, water 19 flows up again and merges with the incoming flow from inlet pipe 4. In this manner, water 19 tumbles (swirls) about an approximately horizontal axis 42, as indicated by flow arrows 57. As this tumbling flow occurs, water 19 is drawn off from the tumbling flow and exits collection chamber 7 through filter screens 12 at the same rate as the inflow through inlet pipe 4. Filtered water 20 that has passed through filter screens 12 then flows into discharge chamber 34, as indicated by flow arrows 58 and 59 in Figs 7, 8 and 10. Referring to Fig. 5, as polluted water 19 enters collection chamber 7 through inlet pipe 4, the dissipation of energy causes high density pollutants 44 to immediately drop out and settle in settling zone 30 of collection chamber 7, near end 8, below inlet pipe 4. The remaining pollutants are initially carried with water 19 as it goes through its tumbling motion. The centrifugal action of the tumbling motion also deposits low density pollutants 45 in settling zone 30 and at the bottom 22 of collection chamber 7. In this manner, the tumbling motion deposits various pollutants to designated capture areas.

The shape and construction of oil separator 10, with assistance from the elongate construction of collection chamber 7, establishes this beneficial tumbling flow. Sloping front 18 of oil separator 10, and its construction as an array of spaced apart elements 15, smoothly deflects the flow downwards to establish the tumbling flow with a minimum of turbulence (i.e.

substantially laminar flow). Distance 28 between ends 8 and 9 of collection chamber 7 being greater than four times diameter 29 of inlet pipe 4 is beneficial in establishing the tumbling flow. Whilst front 18 of oil separator 10 is "substantially flat", in other not shown

embodiments it may have various other shapes to deflect the flow. For example the front 18 may have a concave shape.

The smooth front edges 56 of elements 15 of oil separator 10 and its spaced apart construction establishes a laminar flow state in the vicinity of oil separator 10, by dissipating the energy of the flow in a controlled manner, such that water 19 in the spaces between elements 15 is largely stagnant at its surface. This causes oil and scum type pollutants in water 19 to coalesce in the gaps between elements 15. The oil and scum is then attracted to and absorbed by oil absorption material 16, which retains these pollutants until absorption material 16 is replaced, by replacing individual elements 15 or the whole of oil separator 10. As with filter screens 12, elements 15 can be changed to use different types of absorption materials 16. The area in the vicinity of oil separator 10 where oil and scum collects is an oil and scum collection zone 49, as shown in Fig. 5. Due to the tumbling flow, state in collection chamber 7, the polluted water is largely flowing across the surface of filter screens 12, with a portion of this flow being drawn off out of the tumbling flow to exit through filter screens 12. This improves the efficiency of filter screens 12 compared with prior art arrangements in which the water flows directly at screens, because the flow through filter screens 12 is relatively slow and smooth (less turbulence), and larger particles are deflected off screens 12, so they do not clog screens 12, to eventually be deposited in settling zone 30. Filter screens 12 may be sized, as an example, to trap particles down to sizes of 25 microns. Another reason that water flowing across the surface of screens 12 improves efficiency, is that particles sizes less than the aperture size of screens 12 can still be captured. The water flowing across the surface of filter screens 12, due to the tumbling flow, also washes pollutants off filter screens 12 such that the screens 12 are self-cleaning.

Some fine particles of pollutant will pass through filter screens 12. However, a proportion of these pollutants will settle to bottom 22 outside of collection chamber 7 due to the slow flow velocity through screens 12, Pollutants collected in the bottom 22 can be removed when filter 1 is serviced.

Referring to Fig. 5, centre weir 13 collects buoyant pollutants 46 that float on the surface of water 19 in an upper central zone 48 between centre weir 13 and oil separator 10. These buoyant pollutants 46 are washed through opening 26 in centre weir 13 and then become trapped.

Fig. 11 shows the flow through filter 1 when the flow rate through inlet pipe 4 is near its maximum, such as during a heavy storm. In this case some of the flow bypasses filter screens 12. In this condition, the water level in collection chamber 7 rises such that some of the water passes over weir walls 38, indicated by flow arrows 60, directly into bypass channels 37, before exiting filter 1 through discharge chamber 34 and outlet pipe 5. Even though some flow bypasses filter screens 12 under these conditions, the design of filter 1 minimises this bypass flow, which minimises the amount of polluted water 19 that is not filtered. In particular, the relatively slow, smooth flow through filter screens 12 continues such that they still operate efficiently in these conditions. Fig. 12 shows the flow through filter 1 when filter screens 12 are completely blocked. In this condition, all flow is over weir walls 38, through bypass channel 37 and into discharge chamber 34, as indicated by flow arrows 60, 61 ^' . The design of filter 1 is such that pollutants collected in collection chamber 7 do not escape during this flow condition. The location of weir walls 38, centre weir 13, and inlet pipe 4 creates a substantially laminar flow condition between inlet pipe 4 and bypass weirs 38 during total bypass flow such that the water below the bottom of inlet pipe 4 is substantially stagnant, which does not stir up pollutants 44, 45 deposited in collection chamber 7. In the abovementioned embodiment, oil separator 10 is integral with the "deflector", such that oil separator 10 is also the deflector of filter 1. However, in other not shown embodiments of the invention, oil separator 10 can be replaced with a dedicated "deflector structure" to establish the tumble flow without necessarily collecting oil. In this case, the deflector may have a similar construction to oil separator 10 except with plates replacing absorption material 16 in elements 15. Furthermore, a dedicated deflector may be constructed as other than spaced apart elements. For example, it may be a full surface facing the incoming flow to deflect it downwards. Also, the front of a dedicated deflector may have various shapes. For example, it may have a flat sloping face like front 18 of oil separator 10, or it may have a concaved surface facing the flow towards it. Also, in other not shown embodiments of the invention, the oil separator may be a separate component that is attached to a deflector, or otherwise positioned nearby.

In other not shown embodiments of the invention, various sensors may be added to filter 1 to indicate that servicing is, or may soon be, required. For example, a sensor may be added to oil separator 10 to monitor the volume of oil captured to signal that oil absorption material 16 needs to be changed. Such a sensor may detect the oil concentration in the oil absorption material 16. Other sensors may be added to, for example, detect the level of sediments captured or the amount of buoyant pollutants captured. Also, blockage of filter screens 12 may be detected by monitoring pressure differential across screens 12. The information collected by these sensors may be transmitted wirelessly for remote monitoring, and they may be powered by a solar panel with battery storage. Fig. 13 shows a second embodiment of a stormwater pollutant filter la in accordance with the present invention. Filter la is similar to filter 1 described above, except that is has a deeper enclosure (i.e. a deeper main pit) 2a, and therefore a deeper collection chamber 7a and discharge chamber 34a. In this embodiment, each side 1 1, is made of two modular frame panels 11a abutted end to end. Each panel 11a has plurality of filter screens 12 similar to filter 1 of the first embodiment. Like the first embodiment it has a centre weir 13 and weir walls 38 and an oil separator. In this second embodiment as enclosure 2a is quite deep, a winch mechanism 70 is used to lower and raise oil separator 10 for the purposes of servicing and replacement. In use oil separator 10 is disposed at location 71. In use, a similar tumbling action and flow arrangement occurs through collection chamber 7a of filter 1 a of this second embodiment as does in collection chamber 7 of filter 1. The shape and construction of oil separator 10, with assistance from the elongate construction of collection chamber 7a, establishes this beneficial tumbling flow. Whilst the above described embodiments depict filters 1 and la having enclosures 2 and 2a that are substantially rectangular in shape, it should be understood that in other embodiments the shape of the enclosure may vary. For example, the shape of the enclosure may be substantially cylindrical, similar to that of the Humeceptor™ prior art filter or any other shape that can be readily made as pre-cast concrete component, including cubic or elliptical.

Whilst the above described embodiments are directed to stormwater systems, the invention is also applicable to other drainage applications. Also, filters in accordance with the present invention may be constructed from other than concrete, or be adapted to be above ground rather than placed in the ground.

The terms "comprising" and "including" (and their grammatical variations) as used herein are used in an inclusive sense and not in the exclusive sense of "consisting only of.