WO2015161339A1

WO2015161339A1 - A filtration device for filtering polluted drainage water

Info

Publication number: WO2015161339A1
Application number: PCT/AU2015/000241
Authority: WO
Inventors: Leo Crasti
Original assignee: Aquavest Pty Limited
Priority date: 2014-04-23
Filing date: 2015-04-23
Publication date: 2015-10-29

Abstract

A filtration device for filtering polluted water, the polluted water including a first type of matter having a density higher than water and a second type of matter having a density lower than water, the filtration device comprising: a container portion for receiving an inflow of the polluted water and being arranged to allow an outflow of water at an outflow level that is sufficiently high such that in use water with matter of the second type will exit the container portion and, facilitated by gravity, at least a portion of the matter of the first type will remain in the container portion, the container portion having an aperture for backflow of water; a filtration element for filtering matter of the first type out of the water and having a receiving face for receiving the polluted water and being oriented such that in use the polluted water flows largely in a direction along at least a portion of the face of the filtration element and water that flowing through the filtration element exists the container portion; and an arrangement for directing water back into the container portion, the arrangement being configured such that at least a portion of the water that flowed out of the container portion at the outflow level flows back into the container portion via the aperture without or with a reduced volume of the particles of the second type. A method of filtering polluted water is also disclosed.

Description

A FILTRATION DEVICE FOR FILTERING POLLUTED DRAINAGE WATER

Field of the Invention The present invention broadly relates to a filtration device for filtering polluted water.

Throughout this specification the term "polluted water" is used for any water from industrial and non-industrial sources. Examples include drainage water, storm or rain water, water from dams, weirs, reservoirs, detention units, channelled water ways, trenches and the like.

Further examples include waste water, such as waste water from industrial sources including contaminated water from industrial sites, such as mining sites, contaminated water that was used for watering coal piles and any other waste water .

Background of the Invention

Urbanisation including agriculture and industrial

activities generates contaminants that can be transported by rainfall run-off into water storage systems or

receiving waters such as streams, rivers, lakes and ultimately into the oceans. Some contaminants may be toxic, others are organic that break down in time and some are nutrients.

Such anthropogenically generated contaminants degrade health and sustainability of water in the general

environment and in harvesting or re-cycling. Environmental and government regulations consequently either mandate or propose to mandate that all run-off waters be treated to remove contaminants. Though this is initially applied to new developments, stormwater filtration is also

progressively required for existing polluted water

systems, such as drainage water systems.

The contaminants include pollutants such as trash,

organics, suspended solids, nutrients (particularly nitrogen and phosphorus), hydrocarbons and heavy metals. The pollutants may be classified by their behaviour in water flowing from a rainfall event and through a drainage system to the treatment location. Buoyant materials include trash and litter, which at the time of collection have a relative density of less than that of water. In time these may absorb water and sink. Oils though mostly of a lesser density than water are emulsified or appear as scum and need to be separated from the flow by different means. Suspended solids are known as the prime carriers of nutrients and heavy metals and appear in a range of sizes and composition. Though size and density are factors in grading, time in suspension is also an important factor when reduction of turbidity is a requirement.

A portion of carrier particles have a negative surface charge that is often related to their clay content and a diameter of such particles may range from 250 micrometres 10 micrometres. Unless such particles are trapped, the device has marginal performance which cannot be relied upon. For example, an open pit will collect some sediment, but the removal rate and size range is unpredictable and unreliable.

Whilst dense sediments including clay particles are part of the environment, they are also 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. Various devices for treating stormwater are known. 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. The devices may be in-line, off-line or located at ends of pipes and may also be included in open drains as well as pipes.

Various prior art stormwater treatment devices use filter screens to trap solid pollutants. However, such known devices have the disadvantage that the filter screens are easily blocked. Bypass systems are usually necessary when filter screens are employed, but it is desirable for a stormwater treatment device to minimise an amount of water that bypasses the filter screens because the bypass water carries pollutants with it.

Other known devices rely on quiescence to allow particles time to settle and oil micro globules to coalesce and rise to the surface. Quiescence times are at least 10 minutes and up to 2 hours for smaller carrier particles. This requires the device to be of a large size and hold all the early flows, which is obviously impractical, therefore the device tends to limit the percentage of run-off treated to reduce cost.

International Patent Publication No. WO 2012/045120 and International Patent Publication No. WO/2014005175 provide improvement. In the devices disclosed therein stormwater rotates about an axis that is transversal and horizontal whereby buoyant materials are separated from solid

particles that settle below.

The present invention provides further improvement.

Summary of the Invention

The present invention provides in a first aspect a

filtration device for filtering polluted water, the polluted water including a first type of matter that has a density that is higher than that of water and a second type of matter that has a density that is lower than that of the water, the filtration device comprising:

a container portion for receiving an inflow of the polluted water and being arranged to allow an outflow of water at an outflow level that is sufficiently high such that in use water with matter of the second type will exit the container portion and, facilitated by gravity, at least a portion of the matter of the first type will remain in the container portion, the container portion having an aperture for backflow of water;

a filtration element for filtering matter of the first type out of the water and having a receiving face for receiving the polluted water, the filtration element being oriented such that in use the polluted water flows largely in a direction along at least a portion of the face of the filtration element and water that flows through the filtration element exists the container portion; and

an arrangement for directing water back into the container portion, the arrangement being configured such that at least a portion of the water that flowed out of the container portion at the outflow level flows back into the container portion via the aperture and largely without or with a reduced volume of the particles of the second type .

Throughout the specification the term "matter" is used for any type of material including particles, liquids or froth. Examples of matter of the first type include, but are not limited to, mineral, metallic or any composite particulate matter or liquid that has a density that is higher than that of water. Examples of matter of the second type include, but are not limited to, plastics, paper, wood or any composite particulate matter or liquid that has a density that is lower than that of water. The matter of the first type and the matter of the second type may include any matter that is found in typical unfiltered water .

The container portion may be a first container portion and the filtration device may comprise a second container portion. The arrangement for directing the water back into the first container portion may comprise the second container portion. The filtration device may be arranged such that the water with the particles of the second type that flows out of the first container portion flows at the outflow level and into the second container portion wherein a portion of that water, without or with a reduced volume of the matter of the second type, flows back into the first container portion via the aperture. Embodiments of the present invention have practical advantages. As the polluted water largely flows along at least a portion of the face of the filtration element, a likelihood of blockage the filtration element with

particles of the first type is reduced and a dependency of filtration properties on a velocity of the polluted water is also reduced. Further, blockage may be washed away by the flow of the water along at least a portion of the face of the filtration element. In addition, blockage of the filtration element by matter of the second type can also be reduced as at least a portion of the matter of the second type is directed out of the container portion at the outflow level.

Embodiments of the present invention may be applied to environmental flows where water flows via man-made or natural drainage systems to the receiving waters and to harvesting systems where contaminants are removed prior to the harvesting of water into tanks, dams and re-entry to aquifers. Embodiments of the present invention also have application for removing contaminants prior to subsequent processes, such desalination or waste water treatment. The container portion may comprise a water inlet and a water outlet. The water inlet and the aperture may be positioned at different wall portions and/or at different height levels of the container portion. In one example the water inlet and the aperture are positioned at opposite wall portions of the container portion and the aperture is positioned at a level that is in use lower than that of the water outlet level . The aperture may be positioned at any suitable position, but in one example is in use sufficiently low, typically below a water level in the second container portion, such that return of matter of the second type into the first container portion via the aperture is reduced. For

example, the aperture may be positioned below the water outlet. The filtering device may also comprise a deflector that is positioned adjacent the aperture and shaped to deflect water in a manner such that throughput of water from the first container portion into the second container portion through the aperture and/or throughput of matter of the second type from the second container portion back into the first container portion through the aperture is reduced . The first and second container portions may be separate container portions that may be connected by a pipe or channel or the like. However, in one specific embodiment of the present invention the first and second container portions are separated by a wall portion.

Both the water inlet and the aperture may be positioned to encourage a rotating motion of water about a substantially horizontal and transversal axis in the container portion. In one specific embodiment the filtration device is arranged such that in use the water tumbles substantially about an axis that is transversal or even substantially perpendicular to the receiving face of the filtration element. The filtration element may be oriented such that in use the flow direction of the water is largely along the face of the filtration element.

The filtration device may also comprise an oil separator for removing oil from the polluted water.

Throughout this specification the term "oil" is used for any liquid hydrocarbon material (also including emulsified hydrocarbon material) that has a density that is lower than that of water and does not dissolve in water.

The oil separator may be arranged such that oil or

particles with the oil coalesce when the polluted water passes through the oil separator. In one specific example the oil separator comprises plates for capturing the oil. At least one of the plates may be oriented such that a likelihood of return of particles including the oil is reduced. The oil separator may be positioned at any suitable location and in one embodiment of the present invention the oil separator is at least partially

positioned within the second container portion.

The filtration device may further comprise a third

container portion that is in fluidal communication with the second container portion and that may be positioned to receive the captured particles including the oil.

The second and the third container portions may be

separate container portions that are connected by a pipe or channel or the like. In one specific embodiment of the present invention the second and third container portions are separated by a wall portion. The first and the second and/or the third container portion may be positioned in series.

The filtration device may also comprise a container in which portions of the filtration device are positioned and which may be used to receive and direct filtered water that exists the filtration element. Alternatively, a suitable tube, channel or the like may be used to receive and direct the filtered water.

Further, the filtration element may be a first filtration element and the filtration device may comprise a second filtration element that is arranged to receive water that exited the container portion via the first filtration element. The second filtration element may be arranged to filter particles having a diameter in the range of 100 - 80, 80 - 60, 60 - 40, 40 - 20 and 20 - 10 micrometres.

In a second aspect of the present invention there is provided a method of filtering polluted water, the

polluted water including a first type of matter that has a density that is higher than that of water and a second type of matter that has a density that is lower than that of the water, the method comprising the steps of:

directing the polluted water into a container portion;

directing in the container portion at least a portion of the polluted water along at least a portion of a receiving face of a filtration element;

filtering matter of the first type using the

filtering element such that filtered water exists the container portion via the filtering element;

allowing an outflow of water from the container portion at a level that is sufficiently high such that the water together with the matter of the second type exits the container portion at that level and gravity

facilitates that at least a portion of the matter of the first type will remain within the container portion; and redirecting at least some of the outflow of the water back into the container portion without or with only a reduced volume of the matter of the second type. The polluted water may be directed into the container such that a rotating motion of water about a substantially horizontal and transversal axis is encouraged. Further, the step of redirecting the water back into the container portion may also be performed such that a rotating motion of water about a substantially horizontal and transversal axis encouraged.

The method may further comprise separating oil from the polluted water.

In one specific embodiment the method is conducted in at least two stages. In a first stage at least a portion of the matter or the first type is collected and in a second stage at least a portion of the matter of the second type is collected. Oil may be separated from the polluted water in a third stage.

In a third aspect the present invention provides a

filtration device for filtering polluted water, the polluted water including a first type of matter that has a density that is higher than that of water and a second type of matter that has a density that is lower than that of the water, the filtration device comprising at least a first, a second and a third stage, the first stage being in fluidal communication with the second stage and the second stage being in fluidal communication with the third stage, the first stage being arranged for receiving the polluted water and collecting at least a portion of the matter of the first type,

the second stage being arranged for receiving an outflow of water with matter of the second type from the first stage and collecting at least a portion of the matter of the second type, and the third stage being arranged for collecting oil that has been separated by the filtration device .

The first stage may comprise a filtration element for filtering matter of the first type out of the water and having a receiving face for receiving the polluted water, the filtration element being oriented such that in use the polluted water flows largely along at least a portion of face of the filtration element.

The filtration device may be arranged such that at least some water is redirected from the second stage back to the first stage without or with only a reduced volume of the matter of the second type.

In a fourth aspect of the present invention there is provided an oil separator for separating oil from polluted water, the oil separator comprising:

a first coalescence element arranged for coalescence of oil in the polluted water, the first coalescence element having a receiving region for receiving the polluted water and an output region for output of the water with oil after coalescence of the oil; and a second element positioned relative to the first coalescence element such that a likelihood of a flow of oil back through the first coalescence element is reduced. The first coalescence element may comprise a plurality of coalescence plates that may be substantially vertically oriented .

The second element may comprise at least one deflector element that may comprise at least one plate, such as a coalescence plate, that in use may be inclined about a transversal and substantially horizontal axis and may be positioned to oppose a flow of the oil back to the first coalescence element.

The oil separator may also be arranged such that a return of oil with particles having a diameter of less than 60, 50, 40, 30, 20 or 10 micrometre back to the second

coalescence element is reduced.

The filtration device in accordance with the first aspect of the present invention may comprise the oil separator in accordance with the fourth aspect of the present

invention .

The invention will be more fully understood from the following description of specific embodiments of the invention by way of example only. The description is provided with reference to the accompanying drawings. Brief Description of the Drawings

Fig. 1 is a perspective view of a first embodiment of a filtration device for use in a stormwater pollutant apparatus with its lid not shown and the portions of it side cut-away;

Fig. 2 is a schematic elevation sectional view of the stormwater pollutant apparatus having the filtration device shown in Fig. 1 ; Fig. 3 is a schematic plan sectional view of the

stormwater pollutant apparatus having the filtration device shown in Fig. 1 ;

Fig. 4 is a schematic elevation sectional view of the stormwater pollutant apparatus having the filtration device as shown in Fig. 2 with arrows depicting water flow;

Fig. 5 is a schematic plan sectional view of the

stormwater pollutant apparatus having the filtration device shown in Fig. 3 with arrows depicting water flow; Fig. 6 is a perspective view of a second embodiment of a filtration device for use 15 where water is discharged to a body of water;

Fig. 7 is a perspective view of the filtration device shown in Fig. 6 with a portion of it side cut away; Fig. 8 is a cut-away perspective view of a third

embodiment of a filtration device for use in a stormwater pollutant apparatus; Fig. 9 is a cut-away perspective view of the filtration device in a stormwater pollutant apparatus of Fig. 8 with arrows depicting water flow;

Fig. 10 is a schematic elevation sectional view of the stormwater pollutant apparatus having the filtration device shown in Fig. 8 with arrows depicting water flow;

Fig. 11 is a cut-away front perspective view of a first embodiment of oil separator and arrangement for use in a stormwater pollutant apparatus;

Fig. 12 is a cut-away rear perspective view of the oil separator and arrangement as shown in Fig. 11;

Fig. 13 is a schematic of the oil migration that occurs in the oil separator shown in Fig. 11;

Fig. 14 is a perspective view of a second embodiment of oil separator for use in a stormwater 30 pollutant apparatus ;

Fig. 15 is a side schematic of the oil migration that occurs in the oil separator shown in Fig. 14;

Fig. 16 is a schematic elevation sectional view of a third embodiment of a filtration device; and

Fig 17 is a schematic plan sectional view of the

filtration device of Fig. 16.

Detailed Description of Specific Embodiments

Embodiments of the present invention relate to a

filtration device for filtering polluted water. Such polluted water may originate from any domestic or industrial sources, for example the polluted water may be industrial drainage water. The polluted water may include matter that is found in typical unfiltered drainage water. That matter may be divided into groups of first and second types of the matter. A first type of the matter has a density that is higher than that of the water and a second group of the matter has a density that is lower than that of the water. The filtration device comprising a (first) container portion that is arranged for receiving an inflow of the polluted drainage water and comprises a filtration element for filtering matter of the first type out of the water. The filtration element has a receiving face for receiving the polluted water and is oriented such that in use the polluted water flows largely along at least a portion of face of the filtration element. A water outlet is

positioned at a level that is sufficiently high such that in use water with matter of the second type will exit the container portion via the water outlet and, facilitated by gravity, at least a portion of the matter of the first type will remain in the container portion. The filtration device further comprises an arrangement for directing water back into the container portion. The arrangement is configured such that at least a portion of the water that flowed out of the container portion flows back into the container portion via an aperture and largely without or with a reduced volume of the particles of the second type.

Referring initially to Figs. 1 to 5, a stormwater

pollutant filtration apparatus 1 in accordance with a first embodiment of the present invention is now described. The apparatus 1 comprises a filtration device 3 that is disposed therein. The apparatus 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 Figs. 2 and 3, the apparatus 1 comprises a water tight, open, box shaped enclosure (main pit) 2. The enclosure 2 has a removable lid or lids (not shown) .

The enclosure 2 has an inlet 4 and an outlet 5 at opposed ends thereof. A filtration device 3 is disposed between inlet 4 and outlet 5. The filtration device 3 has a first container portion 7 and a second container portion 8.

The first container portion 7 has a first end 10, a second end 11 opposite to the first end 10, and two 15 side walls 14, 15 between ends the 10, 11. The first end 10 is located at or the near inlet 4. An entry channel 6 is disposed between first end 10 and inlet 4. Each of side walls 14, 15 has a filter screen 12 disposed in their upper portions. The second container portion 8 is downstream of the first container portion 7 and separated therefrom by a first wall 13 at second end 11. The first wall 13 has a first aperture 16 disposed 20 therein in its upper portion, and a second aperture 17 there below. The aperture 16 allows a return of water from the second container portion 8 into the first container portion 7. However, a deflector or guard member 19 guards the second aperture 17. The

deflector or guard member 19 is a material portion that is shaped such that the likelihood that beyond material can return into the first container portion 7 or water from the first container portion enters the second container portion via the aperture is reduced. In this embodiment the filtration device 3 also comprises a third container portion 9 that is downstream of the second container portion 8 and separated therefrom by a second wall 18. An oil separator 30 is at least partially disposed within the second container portion 8, and extends into the third container portion 9. A further filtration element 40 is disposed between the third container portion 9 and the outlet 5. In use stormwater 20 flows through the apparatus 1 entering from inlet 4. The entry channel 6 provides a "flow transition" so that the water 20 entering the first container portion 7, does so in smooth flow pattern. As the water 20 enters the first container portion 7, sediment (solid pollutants) having a density that is higher than that of the water will fall to the bottom of first container portion 7. When the water height in the first container portion 7 is at the level of the

filtration screens 12, water will pass through screens 12 as shown arrows S in Fig. 5, and a central portion of the flow illustrated as arrows C will tend to flow towards the first wall 13.

The water inlet 4 and the aperture 16 are positioned such that the water performs a rotating motion about a

substantially horizontal axis that is transversal to a flow of the water in the first container portion 7. Using the energy in the water flow, matter having a density that is lower than that of the water, such as scum and other buoyant materials (such as plastic bottles and the like) are pushed through the first container portion 7 past the filtration screens 12 and through the first aperture 16 and into the second container portion 8. This minimises the likelihood that scum and buoyant materials 25 will block the filtration screens 12. The buoyant materials 25 are then retained in second container portion 8, and scum (oil based scum) is substantially separated from water by an oil separator 30 and retained in the third container portion 9.

Whilst the buoyant materials 25 is carried by the water through the first container portion 7 and enters the second container portion 8 through the first aperture 16, only water can return through lower aperture 17 back into the first container portion 7, as the deflector or guard member 19 provides a "non-return" arrangement for the buoyant materials 25.

The water 20 that has passed through the filter screens 12 will then travel downstream externally of the filtration device 3 in passages 27 towards the outlet 5. However prior to reaching the outlet 5, the water will pass through the further filtration element 40 to remove any fine sediment and reduce turbidity of the water. The filtration screens 12 are positioned such that an axis of the rotating motion of the water is substantially perpendicular to a receiving face of the filtration screens 12. This positioning reduces the velocity of the water through the filtration screens 12, which also reduces likelihood of blockage. Further, this orientation of the filtration screens 12 also facilitates washing out of blockages by the flow of the water. This allows the filtration screens to have a particularly fine filter material to increase particle capture efficiency and reduce the size of particles that can be captured. The filter screens 12 have a relatively large area that may be greater than twenty times the area of the inlet pipe 20. These relatively large areas also facilitate a relatively slow velocity of the flow of the water through screens 12.

The 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. The 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 25 material or multiple layers. In this embodiment the side walls 14, 15 are made from high density polyethylene (HDPE) and the filter screens from a suitable polyethylene. In one specific example the

filtration screens 12 may be three-dimensional (for example formed from a woven fabric) have apertures of the order of 100 - 400, such as 300 micrometres. Such a filtration screen having apertures of the order of 300 micrometres have been tested to capture particles having a diameter of the order of 20 micrometres with a retention rate of greater than 90% using the arrangement of an embodiment of the present invention. The filter element 40 could be any one or more organic materials in combination. Organic materials are preferred as spent element may be blended into horticultural soils where bio actions convert contaminants into bio mass and plant food. Examples of materials for the filter element 40 are Zeolite (in various grain sizes and hardness) ,

Coir (coconut husk) , Activated Carbon, Bacteria - cultured for composting use and Peat. A person skilled in the art will appreciate that in variations of the described embodiments the filtration device may have any number filter elements that may be positioned at any suitable positions. Further the aperture 16 may be one of a plurality of apertures and may not necessarily positioned below the water outlet of the first container portion, but may alternatively be positioned at another wall of the first container portion. Further, the filtration device may not necessarily comprise three container portions and may be provided in any suitable form or shape.

Referring initially to Figs 11-13, details of the oil separator 30 are now described. The oil separator 30 comprises in this particular example a plurality of

"vertically oriented" spaced apart plates 31 disposed in the second container portion 8, which are in fluidal communication to the third container portion 9 through a third aperture 32 in second wall 18. A weir 33 is disposed near aperture 32 inside container portion 33. The plates 31 may include a frame (not shown) that may be formed from HDPE, supporting "oil absorption material" such as OilSorbTM filtration element, or some other suitable material. The plate elements 31 may be

individually removable for servicing and replacement. The space between the plates 31 is a zone in which

coalescion of oil particles is promoted. In use, as water slows as it passes between the plates 31, particles 34 including oil coalesce form larger particles 36 which are absorbed by the plate elements 31. The coalesced oil migrates through the plate elements 31 and through the aperture 32 into the third container portion 9. The migration of the oil through plate elements 31 is caused by the water continuously acting on the oil separator 30 in the second collection 20 container portion 8, and because a slight pressure differential that exists between the second container portion 8 and the third container portion 9. Some water will migrate through the oil separator 30 into the third container portion 9, however, the collected oil 37 will as a result of its relative density to water being less than 1, remain on top of the water 20 so that it can be easily skimmed from the top (see Fig. 13) .

Referring now to Figures 14 and 15, an oil separator in accordance with an alternative embodiment of the present invention is now described. Similar to the oil separator 30, oil separator 30a comprises a plurality of "vertically oriented" plate elements 31 disposed in the second

container portion 8, which are in fluid communication to the third container portion 9 through an aperture 32a in second wall 18. The aperture 32a is much larger than aperture 32 of the above-described arrangement. A

plurality of angled plate elements 35 extend from the plate elements 31 in the vicinity of aperture 32a.

In use, oil separator 30a results in water slowing as it passes between plate elements 31 and particles including oil 34 coalesce and form larger particles 36 which are absorbed by the plate elements 31. The coalesced oil migrates through plate elements 31, through aperture 32a and the angled plate elements 35 into the third container portion 9. The angled plate elements 35 allow particles including the oil to further coalesce and rise into the adjoining third container portion 9 above water 20a that also enters the third container portion 9. The relative height and arrangement of angled plate elements s 35 causes a variation of the "water level" in the third container portion 9, which reduces backflow of trapped oil/scum. In both arrangements of oil separators 30 and 30a, it should be understood that means (not shown) can be

provided to monitor levels of collected oil/scum in the third container portion 9 and means (not shown) for automated removal of oil/scum from third container portion 9, could be employed.

Referring now back to Figs. 6 and 7, a second embodiment of the filtration device is now described. Filtration device 3a can be used without an enclosure (pit) or filtration element 40. In this arrangement polluted water to be discharged to a body of water enters the filtration device 3a at inlet 4a. The filtration device 3a functions in manner that is similar to that of the filtration device 3 illustrated above with reference to Figs. 1 to 5. Matter that has a density that is higher than that of the water, such as sediment (solid particles) settles in first container portion 7, matter that has a density that is lower than that of the water (buoyant materials) collect in the second container portion 8, and oil collects in the third container portion 9. In Fig. 7 oil separator 30 in container portion 8 is shown. Plates ("oil racks") of the oil separator are attached to an end wall of the second container portion 8. A second wall separates container portions 8 and 9, but has been omitted for ease of reference. Water that exits the screens 12 in this embodiment is discharged directly to the body of water that surrounds the filtration device. Referring now to Figures 8 to 10, a third embodiment of a stormwater apparatus lb with filtration device 3b and outer container (main pit) 2b is now illustrated. The function of the filtration device 3b is similar to that of the above-described filtration devices and like components and flow arrows are referenced similarly to the earlier described embodiment. However, in this embodiment outer container 2b that houses the filtration device 3b is long and narrow, but can be more shallow. As such the apparatus 1 does in this case not require deep excavation to be installed. Furthermore, the use of elongate container portions in series and in a narrow configuration of the above-described third embodiment slows the flow allowing sediments to settle and avoids "churning". The container portions, namely first container portion 7, second container portion 8 and third container portion 9, can be varied in relative size to suit catchment area contaminant loads. Catchments vary, some have high

sediments loads, whilst others have high oil and scum load. Another advantage of embodiments of the present invention is that buoyant materials are moved into second container portion 8, which allows time for certain buoyant litter to wet thereby increasing in density and sink with minimal churning and reduced dissolution. The flow rates into the third container portion 9 are also further reduced thereby creating quiescence and aggregation of micro particles of oil.

The filtration device 3a as shown in Figs 6 and 7 can be installed in tanks and end of pipe applications without an "enclosure", reducing installation and service costs.

Referring now to Figs. 16 and 17, a filtration device in accordance with a third embodiment of the present invention is described. Filtration device 103 is disposed between an inlet 4 and outlet 5. In this embodiment there are three container portions, namely a first container portion 107, second container portion 108 and third container portion 109. These container portions 107, 108, 109 are disposed within separate modular units 137, 138 and 139, respectively, which can be fitted together using male connectors 104 and female connectors 105. External walls 102 of the modular units 137, 138 and 139 provide the equivalent of the enclosure 2 in 20 of the apparatus described with reference to Fig. 2. The filtration device functions in a similar fashion to the above-described embodiments of the present invention. However unlike in the above described embodiments no walls exists between the container portions, but rather male/female connectors 104 and 105 create connection zones 106a and 106b through which polluted water can travel.

Polluted water shown by arrow D carrying buoyant material may pass from the first container portion 107 through to zone 106a to urge the buoyant materials 25 into second container portion 108. A water return zone 117 is

provided. Whilst buoyant materials 25 carried by 30 water through the first container portion 107 enter the second container portion 108 through zone 106a, water can only return through return zone 117 back into first container portionl07 thereby providing a "non-return" arrangement for buoyant materials 25.

In this embodiment, an oil separator 30 is disposed at through zone 106b between container portions 108 and 109. Water can return through return zone 117b from the third container portion 109 back into second container portion 108. In this embodiment, return zones 117 and 117b can be created by guards/flaps 118 as shown in Fig 16. However, it should be understood that in not shown embodiments a conduit or other return means could be employed to create return zones 117 and 117b.

A fourth modular unit 110 contains filtration element 40 to remove any fine sediment and reduce turbidity of the water before it returns to the outlet 5.

Using the energy in the water flow, scum and buoyant materials (such as plastic bottles and the like) 25 are pushed through the first container portion 107, past screens 12 and through zone 106 and into the second container portion 108. This minimises the likelihood that scum and buoyant materials 25 will block the screens 12. Buoyant materials 25 are then retained in the second container portion 108, and scum (oil based scum) is substantially separated from the water by oil separator 30 15 and retained in the third container portion 109.

Water 20 that has passed through the filter screens 12 will then travel downstream externally thereof in the passages 127 towards the outlet 5. However prior to reaching the outlet 5, the water will pass through the filtration element 40.

One of the advantages of an embodiment of the present invention is the collection of different pollutants namely, solid, buoyant and oil/scum materials in separate container portions, making the emptying, maintenance, and repair of the filtration apparatus far easier than the prior art. Oil can be removed mechanically from the third container portion, either manually or automatically using sensors and pumps. Another advantage is that upward extensions (turrets) can be added to each container portions. A further advantage is that dry sump

arrangements are easier to apply, due to shallow depth. Weep holes or drainage lines can be added below discharge pipe inverts.

The multi chamber in-line arrangement in accordance with embodiments of the present invention also advantageously operates at a high efficiency at very low flows. Drainage systems are not required to be sealed and often have trickle flows from ground water, leaks and condensation. These trickle in-flows also cause trickle out flows which can be highly charged with dissolved chemicals. The low trickle flows induce a gradual movement of water to second and third container portions in which contaminates are trapped and settle away from "churning effects" of

subsequent flows.

The devices and methods in accordance with embodiment of the present invention have various further advantages. Because blockage of the filter elements can be reduced or avoided, a larger flow of drainage water can be treated and consequently only a smaller portion of untreated water (or no untreated water) may be allowed to pass. In

embodiments of the present invention the container

portions are separate portions or are separable, which has advantages compared with known cartridge-type arrangements in which trash and litter (and other buoyant materials) usually need to be removed prior to entering the devices as there is usually no provision for retaining of the same. Such cartridge-type arrangements may rely on the inclusion of pit baskets upstream which are difficult to service and cannot be installed where kerb entry units are used or where a system is installed in an existing drainage system. The devices in accordance with embodiment of the present invention have a one-way chamber built-in that may trap all manner of material. Further, the devices in accordance with embodiments of the present invention allow water treatment to be separated from water storage, facilitate access for service and maintenance, and allow a shallow and narrow design that reduces installation cost and space .

Whilst the above described embodiments are directed to stormwater systems, the invention is also applicable to other drainage applications.

It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

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.

Although the invention has been described with reference to particular examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

Claims

Claims :

1. A filtration device for filtering polluted water, the polluted water including a first type of matter that has a density that is higher than that of water and a second type of matter that has a density that is lower than that of the water, the filtration device comprising:

an arrangement for directing water back into the container portion, the arrangement being configured such that at least a portion of the water that flowed out of the container portion at the outflow level flows back into the container portion via the aperture and largely without or with a reduced volume of the particles of the second type.

2. The device of claim 1 wherein the container portion is a first container portion and the filtration device comprises a second container portion.

3. The device of claim 2 wherein the arrangement for directing the water back into the first container portion comprises the second container portion.

4. The device of claim 2 or 3 wherein the filtration device is arranged such that the water with the particles of the second type that flows out of the first container portion flows at the outflow level and into the second container portion, and wherein a portion of that water, without or with a reduced volume of the matter of the second type, flows back into the first container portion via the aperture.

5. The device of any one of the preceding claims wherein the aperture is positioned at a level that is in use lower than that of the water outlet level.

6. The device of any one of the preceding claims wherein the aperture is in use sufficiently low such that return of matter of the second type into the first container portion via the aperture is reduced.

7. The device of any one of the preceding claims comprising a deflector that is positioned adjacent the aperture and shaped to deflect water in a manner such that throughput of water from the first container portion into the second container portion through the aperture and/or throughput of matter of the second type from the second container portion back into the first container portion through the aperture is reduced.

8. The device of any one of the preceding claims comprising a water inlet and wherein both the water inlet and the aperture are positioned to encourage a rotating motion of water about a substantially horizontal and transversal axis.

9. The device of claim 8 wherein the filtration device is arranged such that in use the water tumbles

substantially about an axis that is transversal to the receiving face of the filtration element.

10. The device of claim 9 wherein the filtration element is oriented such that in use the flow direction of the water is largely along the face of the filtration element.

11. The device of any one of the preceding claims comprising an oil separator for removing oil from the polluted water.

12. The device of claim 11 wherein the oil separator is arranged such that oil or particles with the oil coalesce when the polluted water passes through the oil separator.

13. The device of claim 11 or 12 wherein the oil

separator comprises plates for capturing the oil and wherein at least one of the plates is oriented such that a likelihood of return of particles including the oil is reduced.

14. The device of claim 2 or any one of claims 3 to 13 when dependent on claim 2 wherein the oil separator is at least partially positioned within the second container portion and wherein the filtration device further

comprises a third container portion that is in fluidal communication with the second container portion and that is positioned to receive the captured particles including the oil.

15. The device of any one of the preceding claims wherein the filtration element is a first filtration element and the filtration device comprises a second filtration element that is arranged to receive water that exited the container portion via the first filtration element.

16. A method of filtering polluted water, the polluted water including a first type of matter that has a density that is higher than that of water and a second type of matter that has a density that is lower than that of the water, the method comprising the steps of:

directing the polluted water into a container portion;

filtering matter of the first type using the

allowing an outflow of water from the container portion at a level that is sufficiently high such that the water together with the matter of the second type exits the container portion at that level and gravity facilitates that at least a portion of the matter of the first type will remain within the container portion; and redirecting at least some of the outflow of the water back into the container portion without or with only a reduced volume of the matter of the second type.

17. The method of claim 16 wherein the polluted water is directed into the container such that a rotating motion of water about a substantially horizontal and transversal axis is encouraged.

18. The method of claim 16 or 17 wherein the step of redirecting the water back into the container portion is performed such that a rotating motion of water about a substantially horizontal and transversal axis is

encouraged .

19. The method of any one of claims 16 to 18 further comprising separating oil from the polluted water.

20. The method of any one of claims 16 to 19 wherein the method is conducted in at least two stages and wherein in a first stage at least a portion of the matter or the first type is collected and in a second stage at least a portion of the matter of the second type is collected.

21. The method of claim 20 wherein oil is separated from the polluted water in a third stage.

22. A filtration device for filtering polluted water, the polluted water including a first type of matter that has a density that is higher than that of water and a second type of matter that has a density that is lower than that of the water, the filtration device comprising at least a first, a second and a third stage, the first stage being in fluidal communication with the second stage and the second stage being in fluidal communication with the third stage, the first stage being arranged for receiving the polluted water and collecting at least a portion of the matter of the first type, the second stage being arranged for receiving an outflow of water with matter of the second type from the first stage and collecting at least a portion of the matter of the second type, and the third stage being arranged for collecting oil that has been separated by the filtration device.

23. The device of claim 22 wherein the first stage comprises a filtration element for filtering matter of the first type out of the water and having a receiving face for receiving the polluted water, the filtration element being oriented such that in use the polluted water flows largely along at least a portion of face of the filtration element.

24. The device of claim 22 or 23 wherein the filtration device is arranged such that at least some water is redirected from the second stage back to the first stage without or with only a reduced volume of the matter of the second type.

25. An oil separator for separating oil from polluted water, the oil separator comprising:

a first coalescence element arranged for coalescence of oil in the polluted water, the first coalescence element having a receiving region for receiving the polluted water and an output region for output of the water with oil after coalescence of the oil; and

a second element positioned relative to the first coalescence element such that a likelihood of a flow of oil back through the first coalescence element is reduced.

26. The oil separator of claim 25 wherein the first coalescence element comprises a plurality of coalescence plates that are substantially vertically oriented.

27. The oil separator of claim 25 or 26 comprising at least one deflector element that in use is positioned to oppose a flow of the oil back to the first coalescence element .

28. The device of any one of claims 1 to 15 comprising the oil separator of any one of claims 25 to 27.