Patent Publication Number: US-2013228527-A1

Title: Filter for polluted water

Description:
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. 
     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  1   a  in accordance with the present invention. Filter  1   a  is similar to filter  1  described above, except that is has a deeper enclosure (i.e. a deeper main pit)  2   a,  and therefore a deeper collection chamber  7   a  and discharge chamber  34   a.  In this embodiment, each side  11 , is made of two modular frame panels  11   a  abutted end to end. Each panel  11   a  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  2   a  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  7   a  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  7   a , establishes this beneficial tumbling flow. 
     Whilst the above described embodiments depict filters  1  and  1   a  having enclosures  2  and  2   a  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”.