WO2000044998A1 - Terraced fluid filter for sewerage, waste and stormwater runoff - Google Patents

Abstract

A filter arrangement (12) for separating pollution from fluid is described as comprising an array of filter elements (34, 36) arranged such that each successive filter element is forward, with respect to the flow of fluid, and below the level of the top surface of the previous filter element. Such an arrangement can be described as a stepped or terraced array of filter elements. Troughs (24a, 24b) can be located between each filter element (34, 36) so as to collect pollution that passes over a filter element and these troughs are arranged to direct the captured pollution to a holding chamber and eventually to a pollution outlet. Filtered fluid is directed to an outlet for possible further treatment. Such a filter arrangement is suitable for many uses including primary sewerage treatment which contains not only solid waste but also fine paper fibres.

Description

TERRACED FLUID FILTER FOR SEWERAGE, WASTE AND STORMWATER RUNOFF

This invention relates to an all purpose fluid filter apparatus for use in all aspects of fluid purification and in particular to a filter for capturing solid pollution before, along or at a fluid transportation, treatment or storage system.

BACKGROUND

Fluid quality degradation is a problem of growing proportions. One measure of fluid quality is the amount of solid and liquid pollution that is carried from our homes and workplaces into our sewer and at times the storm water system which eventually are received by the reservoirs that we rely on for potable water. Our rivers and ultimately the ocean are becoming a repository for solid and fluid pollution and contaminants, which lowers the quality of those very important water sources.

The problem is not restricted to sewer and storm water run off and its effect on potable water. Industrial and commercial water supplies also suffer the effects of degradation and this has made it necessary to develop methods to treat the available water, to a predetermined quality level so that industrial users can carry out day to day operations. In order to successfully achieve the required quality standards, cost effective pre and post use purification methods are necessary.

A significant amount of time and money spent by industry and water authorities has returned little more than screening and separation methods which usually involve complex and expensive filters with components which require an external source of energy to either brush or spray the captured pollutants which inherently block the filter element, which in turn requires labour intensive maintenance in order to maintain the efficiency of the filter and hence achieve the required quality standards. Until the present, there does not exist an environmentally friendly, low or nil power input, low cost, low maintenance, self -cleansing fluid purification and storage apparatus preferably having no moving parts or mechanical components.

Previous designs such as a filter element laid on an angle in line with the flow, allow incoming fluid to flow through the upward and typically vertical slope of the filter element while the captured pollutants are stopped and gravitate into a storage area. Filter elements with small perforations are typically not suitable for this type of design, as the incoming fluid cannot pass through the filter perforations rapidly enough and become easily blocked by pollutants. Larger perforations in the filter element of such an arrangement enable the full flow of the fluid to pass through but in turn allow larger pollutants to also flow through the filter apertures, which may still block the flow of fluid despite the size of the apertures in the filter element.

All the various configurations of filters to date have similar sorts of problems, the most common solution being the use of externally powered brushes or sprays to help the filter element stay free of blockages. It has long been perceived that to remove solid pollutants from fluids a mechanically operated filter with brushes and/ or sprays was essential in order to minimise the risk of blockage by a range of differently sized and shaped pollutants.

Due to the irregularity of the shape of solid pollution, an apparatus has yet to be developed which can effectively separate and store a range of pollutants such as tree branches, twigs, leaves, gravel, rock, metal filings, granulated plastic, plastic bags, paper, tissue fibres, pulp, hair, food scraps, grain, seeds and cigarette butts to name a few. Acceptable results can be achieved by using filter arrangements with moving parts and an external power source but that sort of filter is impractical for remote locations due to unavailability of power and maintenance personnel.

In particular, filtering of sewer waste water using current techniques is a costly and time consuming undertaking and it is not unusual for water authorities to prefer to address filtering at many intermediate points along the drainage system and for use of large settling tanks. However, in line grates tend to quickly block and require frequent cleaning and maintenance.

Similar considerations also apply to the treatment of polluted industrial commercial and domestic fluid supplies.

Some of the less than desirable features of prior and current pollution filters include:

• use of many metal parts which require anti-rusting treatment or use of expensive stainless steel elements

• moving parts to prevent or clear blockages which require maintenance and periodic replacement, and which are liable to jam, corrode and require frequent cleaning to maintain their efficiency

• spray and brush mechanisms to prevent or clear blockages which require an external power source and frequent maintenance

• use of a large area adjacent the existing fluid system for providing settling tanks which are sometimes many times wider than the drains and conduits with which they are associated

• high hydraulic head loss between the inlet and outlet resulting in low filter efficiency at low and high flow rates and great disruption to the drainage layout providing unwanted restrictions and prohibitions to the retro-fitting of such filters to existing drainage systems

• small time intervals between pollution collection are required when many small pollution filters are incorporated into the drainage system and further, existing shapes of pollutant collection sumps are often difficult to empty and clean

• different filters for different types of pollutants require large areas and volumes and have an increased potential for blockage as well as often requiring the manufacture of unique elements at greater cost than desirable

• different efficiency at different flow rates, and often the poorest efficiency occurs at both low and high flow rates • blockages caused particularly by pollution build up at the inlet and outlet of the filter apparatus and the accumulation of certain types of pollutants can be a health hazard and cause unnecessary use of overflow routes which bypass the filter apparatus

• prior arrangements also often induce a back pressure along the incoming fluid pipe during and certainly after the filter arrangement becomes inefficient and unable to filter the flow of incoming fluid carrying pollutants.

These and other problems are significantly reduced or eliminated by the invention disclosed herein.

Embodiments of the invention will now be described in some further detail with reference to and as illustrated in the accompanying figures. These embodiments are illustrative and not meant to be restrictive of the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig 1 depicts a perspective view of the filter apparatus without its removable top;

Fig 2 depicts a lateral cross-section of the perspective view of the filter apparatus of

Fig l;

Fig 3 depicts a top plan view of the filter apparatus of Fig 1; and

Fig 4 depicts a side elevation view of the filter apparatus of Fig 1.

Detailed description of the invention includes fluid and entrained pollution being carried by a pipe 10 which may emanate from a sewer main line or primary sewerage treatment facility which would otherwise, without the use of a further filter, dump its output into a river, lake or ocean outfall.

A filter apparatus 12 comprises an inlet 14 (as depicted in Fig 5) which is connected to a pipe 10 so that fluid and entrained pollution can enter an inlet chamber 16. In this embodiment, the inlet 14 is located at the bottom of the inlet chamber and the fluid and entrained pollution rises up a weir wall 18 and spreads over a filter approach surface 20 which preferably has a slope downwards relative to the vertical weir wall 18. The area of the passage formed between the side walls of the inlet chamber 16 and the top of weir wall 18 is preferably such that it is larger than the area of the inlet pipe. This has the effect of reducing the rate of flow of the fluid and entrained pollutants so that it can spread out over the approach surface rather than spraying upwards and taking a more direct path to the filter array below.

The fluid and entrained pollution preferably evenly spreads over the approach surface 20 and flows forward towards an in line array of filter elements 24. Very generally, each filter element lies transverse of the flow path and each successive filter element is arranged one below the other in a stepped or terraced array. In this embodiment, sewerage is being received by the filter arrangement and it is known that paper and tissue fibres are the pollutants most likely to cause blocking of a filter arrangement.

In this embodiment a first trough 26 is arranged to lie at or below the edge 21 of the approach surface 20, into which slow moving heavier pollutants can readily fall. The first trough 26, as is the case for other troughs that are a part of the filter arrangement, has a bottom wall which may be level but is preferably sloped to one side of the filter arrangement so that pollutants will slide or be carried with some of the fluid towards a common trough/ channel into which the pollutants are directed and then guided thereafter to a pollutant holding chamber 28. This chamber is optional, as the pollutants filtered from the main flow may be channelled directly into an outlet pipe.

Alternatively, the holding chamber 28 may or may not be in fluid communication with a pollutant outlet 30 and a respective pipe 32 which communicates the pollutants to a remote location for further treatment. Such collected pollutants are sometimes referred to as screenings. If an outlet and respective pipe are not provided, filtered pollutants may be collected from the holding chamber on a periodic basis.

The filter arrangement of this embodiment is ideal for use in a sewer system at the location of a Combined Sewer Overflow (CSO) where sewer and stormwater flows in the same, typically underground, pipe and when that pipe becomes overloaded an overflow arrangement provides an outlet to open air or an ocean outflow of the surplus combined sewer fluid and pollution. Clearly, this circumstance does not occur often during a year and typically for periods measured in hours, but, when it does the consequence is untreated sewerage being released into the environment.

The purpose of the filter arrangement of this embodiment is to remove solid and the very prevalent tissue fibre pollutants from the overflow so as to reduce potential environmental damage. A filter arrangement such as that of the embodiment described herein, which has no moving parts and which does not block can be relied upon to achieve the desirable filtering of the overflow condition described above.

However, use of the embodiment or any filter based on the principle disclosed is not restricted in its use to the above circumstances. As the filter has been found to eliminate blocking, its use may extend to use as a primary filter of pollution from sewer and stormwater fluid at a primary treatment plant, it may be useful as a filter located at the output of an industrial process or complex, it may be useful as a filter located at the outflow of storm water pipe, etc.

The first of a plurality of filter elements 34 of the filter arrangement of this embodiment, comprises a strip of perforated sheet material preferably of stainless steel but it may also be comprised of metal, plastics or other suitable material. The strip is positioned laterally of the flow of incoming fluid and the entrained pollutants and is spaced from the edge of the approach surface 20 and slightly below it. The sheet may also comprise a mesh and the mesh may be formed without actually removing material from the sheet it is made of. For example, the sheet may be cut and pressed (expanded) to form a grate which comprises evenly spaced and formed apertures between the mesh structure. This type of grate is sometimes referred to as

"expanded mesh" or "one way vision" mesh.

In this embodiment, expanded mesh is preferably used in a preferred orientation. The mesh is orientated such that its upper surface presents a substantially smooth surface to the flowing water and entrained pollutants.

This particular mesh and its orientation encourages the pollutants to flow down the face of the one or more filter elements and also encourages the fluid flow direction to change direction and run below and behind the filter element.

At the highest filter element, the quantity of reverse flow fluid is small relative to the main flow, but at the lower filter elements the reverse flow fluid quantity relative to the main flow will, by the time it occurs on the lower filter elements, equalises or exceeds the quantity of fluid flowing towards the holding chamber. The size of the apertures will determine the proportion of fluid passing through the mesh.

The top surface of the filter element is preferably substantially smooth and sloped downwards. The angle of the slope may need to vary from filter arrangement to filter arrangement to suit the anticipated flow rate/s, pollutant types and fluid. In the sewerage filter arrangement depicted in this embodiment, the preferable angle is 50 degrees to the vertical.

The momentum of the fluid and entrained pollution will typically result in the fluid landing on the top surface of the filter element 34 with some of the pollutants falling short and into the first trough 26a or rolling or skimming over the top surface of the filter element 34 and beyond. Alternatively, pollutants land on the filter element 34 and the following fluid urges the pollutants to move forwards and towards the next trough 26b (or next filter element) which is arranged to lie immediately below the trailing edge of the preceding filter element 34.

The stepped filter arrangement creates an environment in which the pollutants are accelerated with respect to the fluid carrier flow so that they are more easily separated from the fluid and are directed down the slope into the holding chamber. Lighter pollutants such as paper fragments and filaments are drawn along the surface of the filter element and sometimes heavy enough then to fall into one or other of the troughs or are light enough to be propelled down the substantially smooth filter element surfaces towards and into the holding chamber while part of the fluid is projected over the trough and onto the next filter element.

Some of the fluid that passes downwards and sometime rearwards through the apertures of the filter elements runs below the apertured sheets which are also substantially planar but roughened by the mesh shape and this assists the clearance of some of the pollutants which may have partially entered the perforations. This flow below the perforated sheets assists clearance of some of the pollutants from the perforations onto the upper surface of the filter elements, where they are assisted forward along with the flow of incoming fluid and pollutants into the next trough or further into the holding chamber 28.

The next filter element 36 has the same size and orientation as element 34 and is spaced from it to form a trough opening location of similar dimensions to that of the trough opening location associated with trough 24a. Trough 24b is of similar dimensions and orientation to that of 24a.

In this embodiment the array of filter elements comprises five separate filter elements and troughs.

The filtered fluid after having passed through the apertures in the filter elements enters an outlet chamber 38 which lies below the filter elements having an outlet 40. The outlet 40 is connected to a filtered water outlet pipe 42 which carries the filtered fluid to a further treatment area or to an outfall. The pollution content of the fluid having been substantially reduced by the filter arrangement.

The rate of flow of fluid through outlet 40 is likely to be less than the flow rate into the filter apparatus, however the outlet pipe 42 is sized so that it can accommodate the maximum flow rate expected into the filter apparatus 12.

It is also possible to incorporate into the filter apparatus 12 an overflow arrangement, which may be provided by an aperture in the wall dividing the holding chamber 28 and the outlet chamber 38. The aperture may preferably begin at a height some half way up the height of the outlet pipe (not shown).

Thus if the filter element and/ or the outlet 40 and more particularly its associated pipe becomes blocked and a majority of water and pollutants flow down the filter element array into the holding chamber 28, the inflow to that chamber can rise above the bottom level of the bypass aperture and flow into the outlet pipe 42 via the outlet chamber 38.

The filter apparatus 12 may be constructed of precast concrete, cast in-situ concrete, aluminium, steel or suitable plastics material.

The troughs of the filter arrangement can be formed during the making of the apparatus or may be constructed separately and fitted and/ or placed into the receptacles formed in the apparatus for the purpose of supporting those said troughs. The troughs can also be made integral with the filter elements so that the filter element array and trough is one piece and thus is easily installed and/ or replaced.

The troughs of course will preferably have their lower wall (floor) sloping to one or other of the sides of the filter array so as to carry to one side or the other the collected pollutants. In fact it is not necessary that all of the troughs are sloped to the same side.

There are other variables in the design and construction of the filter apparatus.

The size and distribution of the apertures in the filter element can be varied to suit the flow rate and type of pollutants being filtered. Ideally, the area of the apertures needs to allow the full maximum anticipated flow rate to pass through them. The number and size of filter elements may also need to be arranged so as to provide adequate flow through capacity for various anticipated pollutant types.

Use of troughs between each filter element is optional and filter elements may thus be separated by a vertical and/ or horizontal distance but joined by a smooth transition surface so that water and entrained pollutants are directed to the next filter element in a continuous manner.

Troughs though, do provide a convenient exit point for pollutants so that successive filter elements are only required to deal with progressively less pollutants and such an arrangement is seen as being beneficial in the reduction of the likelihood of the filter elements becoming blocked.

The width of the filter apparatus and the filter elements can vary to accommodate the anticipated flow rates as well.

The slope of each of the filter elements in this embodiment is the same and the vertical and horizontal separation of them is also constant. However, by experiment, it may be found that variations of both these characteristics is necessary to accommodate differing flow rates and/ or fluid and their entrained pollutants. For example, the slope of successive filter elements may be made successfully steeper or the trough sizes may be made smaller with respect to the horizontal separation between filters.

Although it is definitely preferable to avoid moving parts, it may also be possible to arrange for one or more of the characteristics described above to be varied as required. For example, in low and high flow conditions the slope of the filter elements may be adjusted accordingly. For example, greater horizontal and/ or vertical spacing between the filter elements may be required for higher flow conditions since the higher flow is likely to leave an upper filter element and land further away from the trailing edge of the filter element.

Further analysis of the hydrostatics of the fluid movement over various angles of the filter element/ s will allow a better determination of the optimum angle or angles of the filter element for various flow rates.

It may also be possible to use a unitary piece of filter element material which has a profile in cross section which is of a stepped shaped. For example, a sloped first perforated portion may be followed by a solid vertical portion which is then followed by a further sloped perforated portion followed by yet a further solid vertical portion. Such an array of filter surfaces will provide for some but not all of the preferable features of the invention.

It will be appreciated that various other configurations of filter arrays is possible using the principles disclosed herein.

For example, a single inlet pipe may be arranged to supply a single inlet chamber which has two opposed weir walls which lead to separate filter element arrays as described previously. In regard to the trailing edge of a filter element, it may be preferable to arrange for a suitable planar sheet to be placed along and below the underside of the trailing edge.

Such an arrangement will assist the spreading and positioning of the fluid and entrained pollution onto the next lower filter element.

Furthermore, so as to facilitate access for cleaning and maintenance to the filter apparatus, a removable top may be utilised since the location of the filter apparatus may well be below the ground surface so as to provide for access for cleaning and maintenance.

It will be appreciated by those skilled in the art, the invention is not restricted to its use or particular application described which relates to the filtering of sewer fluid and contaminants whereas it may also be useful in separating pollutants from industrial waste fluid. Nor is it restricted to the feature of the preferred embodiment described herein.

It will be appreciated that various modifications can be made without departing from the principles of the invention, therefore, the invention should be understood to include all such modifications within its scope.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A filter apparatus for separating pollution from a fluid entrained with pollution comprising: an inlet; an outlet lower than said inlet; a plurality of filter elements located intermediate said inlet and said outlet, a first one of said filter elements located so as to receive fluid entrained with pollution which has entered said inlet wherein each of said filter elements are sloped so as to allow said fluid and pollutants to flow downwards over said elements and further arranged so that the upper surface of each successive filter element is located below the upper surface of the preceding filter element and such that each of said filter elements allows fluid to pass through to said outlet.

2. A filter apparatus according to claim 1 wherein said filter elements are sloped at an angle between 40 to 60 degrees to the vertical.

3. A filter apparatus according to claim 1 further comprising a collection chamber and second outlet located downstream of said plurality of filter elements.

4. A filter apparatus according to claim 3 wherein said filter elements are separated from each other both vertically and horizontally and an open trough located between said filter elements, arranged for collecting pollutants and directing said pollutants into said collection chamber and expulsion from said filter apparatus through said second outlet.

5. A filter apparatus according to claim 1 wherein a said filter element comprises a substantially smooth top surfaced sheet having a rectangular shape with the longitudinal axis of said sheet lying transverse of said fluid flow and having an array of apertures allowing for the passage of fluid through said filter element for expulsion through said outlet and sized to restrict passage of a predetermined size of pollutant therethrough.

6. A filter apparatus according to claim 1 further comprising a bypass channel which provides fluid communications between said holding chamber and said outlet for allowing fluid and entrained pollution to flow to said outlet when fluid and entrained pollution ceases to flow from said second outlet.

7. A filter apparatus according to claim 1 further comprising a fluid and pollution spreading means located below at least one of said filter elements for distributing said fluid and pollution across an adjacent lower filter element.

8. A filter apparatus according to claim 1 further comprising a weir located between said inlet and said plurality of filter elements.

9. A filter apparatus according to claim 8 further comprising a filter approach surface located along the top surface of said weir for distributing said fluid and entrained pollution to a first of said plurality of filter elements.

10. A filter apparatus according to claim 1 wherein said filter element comprises expanded mesh orientated so as to present a substantially smooth surface to the flow of fluid and entrained pollutants.

11. A method of filtering fluid entrained with pollution comprising the steps of a) directing said fluid entrained with pollution through an inlet of a filter apparatus and over an array of filter elements arranged such that successive filter elements forward and below the level of the top surface of the previous filter element each receive in turn some portion of said fluid entrained with pollution, b) directing fluid passing through said filter elements to an outlet of said filter apparatus, and directing pollution that does not pass through said filter elements to a holding chamber and then to a respective outlet from said filter apparatus.