WO2008141375A1

WO2008141375A1 - Filter module

Info

Publication number: WO2008141375A1
Application number: PCT/AU2008/000701
Authority: WO
Inventors: Raffaele Buono
Original assignee: Buono-Net Australia Pty Ltd
Priority date: 2007-05-18
Filing date: 2008-05-19
Publication date: 2008-11-27

Abstract

A filter module comprising a plurality of non-metallic non-rigid planar elements held together in a mutually parallel spaced apart array by a plurality of spacer elements each spacer element extending between a pair of respective planar elements to thereby form a substantially rigid self supporting filter module.

Description

FILTER MODULE

FIELD OF THE INVENTION

The present invention relates to filters, and in particular to a filter module, and will be described hereinafter with reference to this application. However, it will be appreciated that the invention is not limited to this particular field of use.

BACKGROUND OF THE INVENTION

The following discussion of the prior art is provided to place the invention in an appropriate technical context and enable the advantages of it to be more fully understood. It should be appreciated, however, that any discussion of the prior art throughout the specification should not be considered as an express or implied admission that such prior art is widely known or forms part of common general knowledge in the field.

Previously known filter modules are disclosed in US Patent No.'s 5,772,870 and US 5,882,510. These modules are typically used as tower packing blocks for trickle filters, immersion trickle filters or submerged solid beds for biological treatment of wastewater or other fluids. For the biological treatment of wastewater, the modules are typically occupied by a biomass, a so-called "filter film". These modules suffer the drawback that they are relatively expensive to transport since the volume of empty space in a module can be as high as about 90%, and it will be appreciated that transporting large amounts of empty space is inefficient, costly and wasteful.

It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the abovementioned prior art, or to provide a useful alternative. SUMMARY OF THE INVENTION

According to a first aspect the present invention provides a filter module comprising a plurality of non-metallic non-rigid planar elements held together in a mutually parallel spaced apart array by a plurality of spacer elements, each said spacer element extending between a pair of respective planar elements to thereby form a substantially rigid self supporting filter body. It will be appreciated that when referring to the planar elements as "non-rigid" the planar elements should be construed as being "pliable" and "foldable" but not so soft as to slump under their own weight. In contrast, the filter module is a self-supporting substantially rigid body.

In some embodiments, the array of planar elements is "regular" in the respect that each planar element is spaced from the preceding or succeeding one by a substantially constant distance across the width of the planar elements. However, in alternative embodiments different portions of the array may have different spacings. For example the centre portion of the array may have a larger spacing between preceding/succeeding planar elements than at the periphery or edges of the array. In some embodiments the spacing is random or semi-random.

The planar elements (also referred to as filter sheets) are preferably substantially rectilinear multiperforate/ foraminous/reticulated flat plates which may be in the form of a non-rigid mesh having trapezoidal, round, or oval-shaped apertures. In one preferred embodiment the apertures are square. However, in an alternative embodiment the apertures are diamond-shaped.

The exterior surface of the planar elements preferably define a substrate which is adapted to support the growth of biological organisms thereon. For example, in preferred embodiments the planar elements comprise a roughened exterior surface which is sufficiently porous such that the planar elements have a relatively high surface area.

Whilst in preferred embodiments the planar elements are arranged in the form of a substantially regular stack, the present invention also encompasses alternative embodiments wherein the planar elements include one or more bends or curves to define an exterior shape of the filter module to suit the housing into which the filter module is to be loaded. Alternatively, the planar elements may be folded to form at least two element portions angled with respect to each other. Further embodiments are contemplated wherein a plurality of planar elements are formed into cylinders of varying diameters which may be nested within each other and spaced apart by one or more of the spacer elements. Alternatively, the planar element may be coiled. The planar elements are preferably substantially equidistantly spaced apart by the spacer elements. However, in alternative embodiments the planar elements may be non-uniformly spaced by appropriately sized spacer elements. In one embodiment the spacer elements are preferably in the form of rigid spacer tubes which comprise a multiperforate sidewall. These tubes may be in the form of a porous mesh having a relatively high surface area, wherein the mesh apertures may be trapezoidal, round or oval-shaped. However, in alternative embodiment the spacer elements are solid rods or tubes with smooth exterior surfaces. The diameter of the spacer tubes may be from about 20 to 90 mm, however about 45 mm is preferred.

The filter module according to the invention may include any number of planar elements, for example, about 2 to 50 planar elements and about 2 to 20 spacer elements between the adjacent planar elements. However, a preferred filter module is configured with 20 planar elements and 5 spacer elements between each adjacent planar element. In a preferred embodiment, the spacer elements are elongate tubes which are positioned substantially parallel to each other in the plane of the planar elements. However, in an alternative embodiment the spacer tubes may be positioned substantially perpendicularly to the plane of the planar elements. In such a case, the perpendicularly positioned spacer tubes or elements are relatively shorter, with respect to their width, than in the case of parallel positioned spacer tubes or elements.

The applicant contemplates further embodiments in which the spacer elements are in the form of a corrugated sheet, which again may be a rigid porous mesh having a relatively high surface area. The corrugated sheet may be a complete sheet spanning the width of the planar elements or only a portion of the corrugated sheet, for example a peak-trough-peak section.

Preferably the planar elements and the spacer elements are formed from thermoplastic materials allowing the spacer elements to be thermally fused with the adjacent ends of the planar elements to produce the filter module according to the invention. Preferably the planar elements are substantially coterminous and the ends of the spacer elements and planar elements are thermally fused together to produce a substantially rigid filter module of the invention.

Commercially available filters typically comprise a plurality of cylinders which are welded together to form a filter module. These cylinders typically comprise a mesh- like sidewall and are typically intentionally formed with a roughened outer surface to provide a relatively large surface area. It will be appreciated that such filter modules are typically relatively expensive to transport since the volume of empty space in a filter module can be relatively high, for example as high as 90%, and it will be appreciated that transporting such empty space is inefficient and costly. Accordingly, it would be advantageous if a filter module could be transported to its intended place of use in either a compressed form or a form which is readily easily assembled and prepared on-site, or even assembled close to its intended place of use, thereby minimising transportation costs. The present Applicant has taken an entirely different approach compared to the prior art by forming planar elements rather than filter tubes. The planar elements can be transported in a "compressed" form, i.e. in a compressed stack, spacer elements may be then interleaved between the planar elements at the destination, and the planar and spacer elements welded together (thermally fused) to form the filter module according to the invention. The skilled person will appreciate that a greater number of planar elements can be transported in a given transportation volume compared to the number of filter tubes which would occupy that volume. Therefore, the present invention enables a significant reduction in transportation costs.

It will be appreciated that when tubular spacer elements are employed in the filter module of the invention, transport of the tubular elements will still be somewhat inefficient (similarly to prior art filter modules). However, the skilled person will appreciate that relatively fewer tubular spacer elements are required in the filter module of the invention compared to prior art filters, since the planar elements themselves provide the majority of filtration, and the majority of the substrate for the growth of biological organisms. Transporting relatively fewer tubular spacer elements provides a reduction in transportation costs. Further, the Applicant contemplates other embodiments wherein the spacer element may be any spacer element that may be relatively easily sourced at the destination. However, the most cost effective arrangement for transportation purposes is a configuration of planar elements separated and spaced by corrugated spacer elements, since both the corrugated spacer elements and the planar elements will stack and occupy the minimum transportation volume compared to prior art tubular filter modules. The Applicant contemplates further embodiments in which the planar elements could be cut to size and rolled to form the tubular spacer elements, thereby obviating the need for a separately made spacer element and simultaneously minimising transportation costs. The filter module of the invention is particularly suited to applications ranging from trickling filters, aerobic and anaerobic submerged filters, air purification, water aeration and degassing and oil separation. However the skilled person will appreciate that the filter module of the invention is not limited to these applications.

The roughened surface of the planar element is particularly suited for rapid bio mass accumulation, and the very high surface area to volume ratio promotes the growth of microbial bacteria. Preferably one, two or more colonies of bacteria, of aerobic and/or anaerobic types occupy the filter module to ensure an advantageous rate of decomposition of waste or biological material in water. The combination of anaerobic and aerobic bacteria is advantageous in providing an improved cleaning effect on wastewater, as they each digest or decompose different types of waste.

Further, the filter module is preferably designed to ensure that a large amount of bacteria will grow on the planar elements within a short period of time, such as within two weeks. The bacteria are contemplated to break-down or decompose waste in water flowing through the filter module. The filter module may be positioned in the ground or in a wastewater treatment facility. The filter module may have a surface area between about 25 to 800 m²/m³. However, the surface area may be between about 90 to 100 m²/m³, 100 to 150, 150 to 200, or 200 to 300 m²/m³.

The surface roughness may be between about 5 to 1000 Ra, Rz and Rmax. For example the roughness may be 7 to 700, 25 to 500, 100 to 300, 50 to 75, 75 to 150, 150 to 225, 225 to 300, 300 to 350, 350 to 400, and 400 to 500 Ra, Rz and Rmax (measured in μm).

According to a second aspect the present invention provides a method of forming a substantially rigid self supporting filter module comprising the steps of arranging a plurality of non-metallic non-rigid planar elements in the form of a stack, providing a plurality of spacer elements between respective pairs of planar elements and connecting said spacer elements to said planar elements.

According to a third aspect the present invention provides a filter module when prepared by the method according to the second aspect. According to a fourth aspect the present invention provides apparatus for producing non-metallic non-rigid planar elements of a filter module according to the invention, comprising: a reservoir for storing granulate material having a first melting point, the reservoir having a first inlet and a first outlet, the granulate material including a foaming additive having a second melting point, a heating and pressurising unit including a chamber having a second inlet and a second outlet, the second inlet in communication with the first outlet, a path of travel defined from the second inlet to the second outlet, the heating unit comprising heating and pressurising elements distributed along the path of travel, an extruder unit mounted downstream relative to the heating and pressurising unit at the second outlet, the extruder unit further including an extruder heating unit, the extruder defining an extruder outlet, the extruder unit generating a non-metallic non-rigid planar element, a cooling unit mounted at the extruder unit for cooling the granulate material, and a measuring and cutting device for measuring and cutting said non-metallic non-rigid planar element into a plurality of non- metallic non-rigid planar elements having a predetermined length within a specific interval.

The apparatus of the present invention may further comprise a feed screw in the path of travel, the feed screw defining a cylindrical or conical geometry. The feed screw may then constitute a conveyor for conveying the material from the inlet of the heating and pressurising unit to the output thereof. The geometrical structure of the feed screw may perform the pressurising of the material as it is conveyed along the path of travel.

According to a fifth aspect the present invention provides a method of producing non-metallic non-rigid planar elements of a filter module of the invention using apparatus as described in the fourth aspect, the method comprising the steps of: supplying the granulate material to the heating and pressurising unit from the reservoir via the second inlet, conveying the granulate material along the path of travel, heating the granulate material to an elevated temperature and pressurising the granulate material to an elevated pressure while conveying the granulate material along the path in the heating and pressurising unit, the heating and pressurising performed according to a specific heating and pressurising profile, transferring the heated and pressurised granulate material to the extruder unit, heating the granulate material within the extruder heating unit to a temperature above the first melting point and/or at or above the second melting point, extruding the non-metallic non-rigid planar element from the granulate material, the heating of the granulate material causing an expansion of the foaming additive causing the non-metallic non-rigid planar element to obtain an porous structure, cooling the extruded non-metallic non-rigid planar element by the cooling unit according to a specific cooling profile thereby stopping or halting expansion of the granulate material and/or the foaming additive and locking or fixating the porous structure of the non-metallic non-rigid planar element, and cutting the non-metallic non-rigid planar element to length using the measuring and cutting unit.

According to a sixth aspect the present invention provides a filter module when prepared by the method according to the fifth aspect.

According to one embodiment of the method according to the fifth aspect of the present invention, the non-metallic non-rigid planar element is cut into individual or discrete non-metallic non-rigid planar elements which are in a further step joined or held together in a mutually parallel spaced apart array by a plurality of spacer elements, each said spacer element extending between a pair of respective planar elements to thereby form a substantially rigid self supporting filter body. The individual or discrete non- metallic non-rigid planar elements may be joined or sealed together by means of an adhesive, by the application of heat, by integrally formed detent means, or even by a clip for releasably connecting the spacer elements and planar elements together. The step of joining or assembling the individual and discrete non-metallic non-rigid planar elements together may provide a filter module of the conventional cubic configuration or a substantially box-like configuration or may alternatively provide a contact filter module having a base surface from which the individual or discrete planar elements extend, preferably perpendicularly from the base surface. The base surface may have any relevant geometrical configuration such as a square, a rectangle, a circle, a polygonal or a rhombic configuration.

In one embodiment, the spacer elements are in the form of a corrugated plate, or sections of a corrugated plate. These corrugated plate spacer elements may be produced by any means, however in one preferred embodiment the corrugated spacer elements are produced by thermoforming the non-metallic non-rigid planar elements as described above into the desired corrugated plate shape. The person skilled in the art will be well versed in the equipment and methods that would be required to thermoform corrugated plate spacer elements. The provision of corrugated spacer elements provides a further advantage in relation to the volume or space used for transportation since the corrugated spacer elements may be stacked to occupy a minimum volume.

The term "a foaming additive" is to be construed as a generic term including any material present in solid, liquid or gaseous phase which allows the granulate material to be expanded for providing the porous structure of the planar elements produced in accordance with the method according to the fifth aspect of the present invention. Furthermore, granulate material is also to be construed including any material conventionally used in the polymer or plastics industry in the extrusion technical field and may include solid granulate material or polymer material included in a semi- pasteous or liquid state dependent on the actual melting point of the polymer composition. It is further construed that any two-component polymer system, the one component constituting a component similar to the granulate material and the second component constituting a component similar to the foaming additive, which system provides as the two components are brought together, a physical and chemical reaction similar to the reaction caused by the straightforward addition of the foaming additive to the granulate material within the heating and pressurising unit is also to be contemplated part of the components used or usable in accordance with the teachings of the present invention.

The planar elements of the invention comprise an enlarged surface originating from the release of the foaming additive. The increase in surface area is contemplated to be 10 to 50%, 50% to 100% or even more compared to planar elements produced without a foaming additive. In the present context, the terms heating and pressurising unit and extruder unit respectively define two sections of an apparatus conventionally known as an extruder. In the present context, the above terms heating and pressurising unit and extruder units are used solely for the purpose of defining specific properties and functions of the respective parts or sections of the extruder. Further, it is to be understood that the term extruder unit may be considered equivalent to or identical to the part of the conventional extruder commonly known as the die head.

The large surface of the planar elements is contemplated to provide space for one, two or more colonies of bacteria, of aerobic and/or anaerobic types. The combination of aerobic and anaerobic bacteria is contemplated to ensure an advantageous rate of decomposition of waste or biological material in water. Also, the planar elements are contemplated to ensure that a large amount of bacteria will grow on the planar elements within a short period of time, such as within two weeks.

The reservoir may be constituted by a simple funnel into which a granulate material is poured automatically, semi-automatically or manually. Alternatively, the reservoir may be a tank or the like, for continuously supplying granulate material to the apparatus. The reservoir may have at least two inlets and/or outlets for refilling the reservoir and for delivering the granulate material to the apparatus. The heating and pressurising unit receives the granulate material from the reservoir and heats and pressurises the granulate material. The granulate material is heated up to but preferably not significantly beyond the melting point of the granulate material. In alternative embodiments, the granulate material may be heated above or beyond the melting point.

The granulate material preferably comprises a foaming additive that, when heated above a certain temperature, expands and thereby creates bubbles in the melted or soft granulate material. The foaming additive is chosen in combination with the granulate material such that it foams at a temperature where the granulate material is a liquid or soft mass.

The pressure to which the granulate material is pressurised is preferably within the interval 5 to 5000 bar, such as 5 to 50 bar, such as 50 to 1000 bar, such as 60 to 900 bar, such as 65 to 850 bar, such as 75 to 750 bar, such as 100 to 650 bar, such as 150 to 600 bar, such as 200 to 500 bar, such as 275 to 450 bar, such as 300 to 400 bar, such as 325 to 375 bar, such as 5 to 25 bar, such as 25 to 45 bar, such as 45 to 75 bar, such as 75 to 150 bar, such as 150 to 200 bar, such as 200 to 275 bar, such as 275 to 340 bar, such as 340 to 375 bar, such as 375 to 425 bar, such as 425 to 500 bar, such as 500 to 550 bar, such as 550 to 625 bar, such as 625 to 700 bar, such as 700 to 775 bar, such as 775 to 850 bar, such as 850 to 1000 bar, preferably around 350 bar.

The extruder heating unit provides an additional heating of the material. When the extruder heating unit heats the material, the foaming additive is contemplated to reach its foaming state and cause an expansion or creation of bubbles in the material, thereby creating a porous structure in the material.

For ensuring that the porous structure in the material is fixed or not changed, a cooling unit is provided. The cooling unit cools the material after it exits the extruder unit which is contemplated to stop the expansion of the foaming additive. The cooling may be obtained by using water, air, any fluid or liquid. Further, the extruder unit may include a multitude of nozzles each defining a cross-section having a substantially square, round, semi-round, rectangular, oblong, triangular, semi-hyperbolic, trapeze, inverse trapeze shaped or any combinations thereof, preferably round. In the present context, the term nozzle is used for describing the outlets of the extruder. In performing the methods according to the present invention, the granulate material is supplied from the reservoir into the heating and pressurising unit. The heating and pressurising unit has an inlet through which the granulate material is supplied. The inlet may be in fluid communication with the reservoir. The granulate material is conveyed along the path of travel defined in the heating and pressurising unit while heating units heat the granulate material. The heating is performed according to a specific heating profile.

In a first instance the heating elements may emit the same amount of heat at all positions along the path of travel, i.e. the same number of watts is emitted from all elements. In a second instance the heating element or elements may emit an increasing or decreasing amount of heat along the path of travel to ensure that the temperature of the granulate material is near the melting point at the outlet of the heating and pressurising unit. In a third instance, the specific heating profile may include one or more temperature peaks along the path of travel, such as short and/or longer bursts of heat emitted from the heating elements or element. The temperature peaks may be substantially equal or in the alternative different, both in terms of amount and width/duration, further alternatively, a combination of two or more substantially equal peaks and one or more peaks different from the two.

Further, the speed of which the granulate material is conveyed along the path of travel may be controlled to ensure that the temperature of the granulate material is near or at the melting point at the outlet of the heating and pressurising unit.

The heating and pressurising unit may also increase or decrease the pressure of the granulate material as it is conveyed from the inlet to the outlet of the heating and pressurising unit. The pressure may be controlled according to a specific pressurising profile. After the material has been extruded, the extruder heating unit may provide extra heat for heating and thereby causing the foaming additive to expand and thereby create a porous structure in the material. The cooling unit cools the material to a temperature below the temperature at which the foaming additive expands, thereby fixing the porous structure.

The apparatus may include a screw conveyor defining an axis or path of travel along which the granulate material is transported. Typically, the granulate material is heated to a temperature just below its melting point and the screw conveyor compresses the granulate material as it is conveyed along the path of travel. The heating of the granulate material and the speed at which the screw conveyor conveys the granulate material are chosen in combination to ensure a desired outflow of suitably heated and expanded material is produced.

The granulate material used in the methods of the present invention is preferably HDPE. Further, the granulate material may further include an amount of PP or LDPE or a combination thereof, and/or may include PVS, NYLON, ABS or any other polymer materials.

According to the teachings of the present invention, the weight of the foaming additive may constitute 0.1% to 50%, such as 1 % to 40%, such as 5% to 35%, such as 8% to 20%, such as 9% to 12%, such as 0.1 % to 5%, such as 5% to 15%, such as 15% to 25%, such as 25% to 35%, such as 35% to 45%, such as 45% to 50%, preferably 3- 5% or 5-10% of the weight of the granulate material.

The granulate material may be heated to 140 to 300°C, dependent on the polymer material or materials in question.

Additionally, the granulate material may further include a colouring additive, such as green, black or any other colour. The screw conveyor may be a simple screw having a substantially constant profile or cross section, or it may have an increasing or decreasing cross section so that the granulate material is compressed as it passed through the conveyor. Even where the screw conveyor has a substantially constant cross section along the path of travel, the granulate material may still be compressed by the inflow of granulate material. The operation of the heating elements and/or the screw conveyor may be controlled by an external unit such as a computer. Specialised hardware and/or software can monitor the operation of the screw conveyor and/or the heating elements by receiving feedback as to processing parameters like the rotational frequency of the screw conveyor and pressure and/or temperature information from inside the apparatus.

Feedback between the apparatus and the controller can be carried via any conventional means such as cables or wires RF, IR, HF or other wireless transfer techniques.

The apparatus can be configured to produce the mesh in a variety of forms, e.g. flat sheet mesh, corrugated mesh, tubular mesh.

The width of flat sheet mesh (and corrugated mesh) is determined by the width of the extruder die, and may be sized by cutting to length. Flat sheet mesh is produced by any conventional slit die. Corrugated mesh can be prepared by any known means. It may be produced by moving the die outlet up and down relative to the flow of extruded material, or it may be made by post treating flat material, ie continuously or batchwise with heated rollers, shaped presses or other forming tools.

When the apparatus is configured to produce tubular mesh, it may be cut into individual tubular elements using a cutting saw or cutting wheel. Alternatively, the tubular mesh may be cut lengthwise by means of a cutting knife converting it into a substantially planar structure. This substantially planar structure may be introduced into a heating and pressing dye and converted into a corrugated structure, which can be cut into individual corrugated plate element

In one preferred embodiment of the present invention, the extruder has two oppositely rotating extruder heads. The extruded material exits the extruder unit at outlets distributed in a circle. The distribution of the extruder outlets ensures along with the rotation of the extruder heads that the resulting structure is a tubular mesh-type structure, although in other embodiments, the extruder unit may comprise two or more parallel moving parts, two parts moving or rotating in the same direction, or parts not moving or rotating themselves. Whilst a substantially circular geometrical cross section is preferred however, the extruder outlets may define a substantially square, star-shaped, triangular, polygonal, elliptical, rectangular, truncated pyramidal, inverse truncated pyramidal, hexagonal, pentagonal configuration or any combinations thereof.

The individual mesh-structure elements may be joined together at any position to provide the desired structure.

Unless the context clearly requires otherwise, throughout the description and the claims, the words 'comprise', 'comprising', and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to". Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used herein are to be understood as modified in all instances by the term "about". The examples are not intended to limit the scope of the invention. In what follows, or where otherwise indicated, "%" will mean "weight %", "ratio" will mean "weight ratio" and "parts" will mean "weight parts". BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figures IA to C show alternative embodiments of the planar elements of the invention;

Figures 2 A and B show spacer elements in the form of a tube, wherein Figure 2 A has a mesh sidewall and Figure 2B has a closed sidewall;

Figure 3 is a perspective front view of a filter module according to the invention, showing tubular spacer elements interleaved between planar elements;

Figures 4 A to F are sectional views of alternative embodiments of the invention showing various configurations of spacer elements and planar elements;

Figures 5A to C are sectional views of alternative embodiments of the invention showing corrugated spacer elements interleaved between planar elements; and Figure 6 is perspective front view of an alternative embodiment of the invention, wherein the top planar element has been partially peeled away to show a particular configuration of spacer elements.

PREFERRED EMBODIMENT OF THE INVENTION References will now be made to the drawings wherein like reference numerals refer to like parts throughout. The present invention relates to a filter module 1 comprising a plurality of non-metallic non-rigid planar elements 2 held together in a mutually parallel spaced apart array by a plurality of spacer elements 3. Each of the spacer elements 3 extend between a pair of respective planar elements 2 to thereby form the substantially rigid self supporting filter module 1 of the invention. In the embodiments as shown in Figures 3, 4 A to 4C and 4E the planar elements 2 are non-rigid meshes which have square-shaped apertures. The exterior surfaces of the planar elements 2 define a substrate which is adapted to support the growth of biological organisms thereon and are preferably "roughened" to be sufficiently porous such that the planar elements 2 have a relatively high surface area. As the person skilled in the art would be aware a number of processing techniques may be employed to achieve this effect (discussed further below).

Whilst in the embodiments as shown in Figures 3, 4A to 4C and 4E the planar elements 2 are arranged in the form of a substantially regular stack, the Applicant contemplates alternative embodiments such as shown in Figures 4D and 4F wherein the planar elements 2 include one or more bends or curves to define an exterior shape of the filter module 1 to suit the housing into which the filter module 1 is to be loaded. For example a plurality of planar elements 3 may be formed into cylinders of varying diameters which may then be nested within each other and spaced apart by one or more of the spacer elements 3. In one preferred construction the planar elements 2 are substantially equidistantly spaced apart by the spacer elements 3. However, in alternative constructions the planar elements 2 may be non-uniformly spaced by appropriately sized spacer elements 3, as best shown in Figure 4E.

In the embodiments as shown in Figures 3 and 4 the spacer elements 3 are in the form of substantially rigid spacer tubes 4 which are formed from the same material as the planar elements 2. However, the spacer elements may be solid rods or tubes with smooth exterior surfaces. In alternative embodiments the spacer elements 3 are in the form of corrugated or zig-zagged sheets 5, which are formed from the same material as the planar elements 2. The corrugated sheet 5 may be a complete sheet spanning the width of the planar elements 2, as best shown in Figure 5 A, or only a portion of a corrugated sheet 5, for example a peak- trough-peak section as best shown in Figure 5 C. In one construction of the filter module 1 of the invention the spacer elements 3 are tubes positioned substantially parallel to each other in the plane of the planar elements 2 (see Figure 3 for example). However, in alternative embodiments the tubular spacer elements 4 may be relatively short and positioned substantially perpendicularly to the plane of the planar elements 2, as best shown in Figure 6.

Preferably the filter module 1 includes about 12 planar elements 2 and about 6 spacer elements 3 between the adjacent planar elements 2. In one construction the diameter of the tubular spacer element 4 is preferably 42 mm and the total dimensions of the filter module 1 are 545 x 546 x 550 mm (length x width x depth). However, it will be appreciated that the total dimensions of the filter module 1 may be any size to suit the particular application. The planar elements 2 are preferably coterminous with the ends of the spacer elements 3 and planar/spacer elements are connected e.g. thermally fused, together to produce the substantially rigid filter module 1 of the invention. The skilled person will appreciate that a number of processing techniques could be employed to connect the planar/spacer elements together e.g. gluing, thermally fusing, etc.

The planar elements 2 and the spacer elements 3 are preferably formed from thermoplastics materials. As one skilled in the art would be aware, one particularly suited technique to produce these elements 2 and 3 is by the extrusion method. Plastics extruders typically comprise a reservoir for storing a granulate thermoplastics material and a heating and pressurising unit comprising a barrel housing a conveying screw. The rotating screw forces the granulate thermoplastics material forward into the barrel which is heated to the desired melt temperature of the molten plastic (usually about 200°C). The molten plastic then enters a die which is shaped and configured such that the molten plastic evenly flows from a cylindrical/annular profile to the desired shape. The shaped molten plastic is then cooled by typically quenching in water. Once the shaped solidified plastic has cooled it can be cut into desired lengths. In the present case the die is configured to produce a continuous tubular/cylindrical element having square-shaped apertures. The tubular/cylindrical element is then continuously cut/slit down its transverse length prior to quenching to produce a continuous flat sheet of no n- metallic non-rigid planar mesh which is cut to appropriate lengths to form the planar elements 2 of the invention. As one skilled in the art would be aware the tubular/cylindrical element may be quenched without cutting/slitting down its transverse length. The so- formed tubes may be cut to length and used as the spacer elements 4 of the invention. Alternatively, the continuous flat sheet of planar mesh may be thermo formed into a corrugated sheet, to form the corrugated spacer elements 5 of the invention.

One skilled in the art of plastics extrusion will appreciate that additives such as colorants and UV inhibitors (in either liquid or pellet form) are also often used and can be mixed into the granulate thermoplastics material prior to extrusion. In order to obtain a filter module 1 with the desired surface area (of about 25 to 800 m²/m³) and surface roughness (of about 5 to 1000 Ra, Rz and Rmax) at least one foaming additive may be added to the granulate thermoplastics material. Foaming additives including any material present in solid, liquid or gaseous phase which allows the granular thermoplastics material to be expanded for providing the porous structure of the planar elements 2 and optionally the spacer elements 3. Furthermore, it will be appreciated that the granular thermoplastics material is to be construed as including any material conventionally used in the polymer or plastics industry in the extrusion technical field, for example polyethylene, polypropylene, or a combination thereof, and/or may include PVS, NYLON, ABS or any other polymer materials. The foaming additive provides an increase in surface area which is contemplated to be between about 10 to 50%, 50% to 100% or even more compared to planar elements 2 produced according to traditional production methods without such foaming additives. The weight of the foaming additive may constitute anywhere from about 0.1% to about 50% of the weight of the granular thermoplastics material, depending on the relative degree of foaming required and the type and nature of foaming additive.

In use, the substantially rigid self supporting filter module 1 of the invention is formed by arranging a plurality of non- metallic non-rigid planar elements 2 in the form of a stack, providing a plurality of spacer elements 3 between respective pairs of planar elements 2 and connecting said spacer elements 3 to said planar elements 2 by thermoforming.

Although the invention has been described with reference to specific 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 filter module comprising a plurality of non-metallic non-rigid planar elements held together in a mutually parallel spaced apart array by a plurality of spacer elements each spacer element extending between a pair of respective planar elements to thereby form a substantially rigid self supporting filter module.

2. A filter module as claimed in claim 1 wherein the planar elements are substantially flat.

3. A filter module as claimed in claim 1 wherein the planar elements are curved.

4. A filter module as claimed in any one of the preceding claims wherein the planar elements are folded to form at least two element portions angled with respect to each other.

5. A filter module according to any one of the preceding claims wherein each of said planar elements is a substantially rectilinear foraminous sheet.

6. A filter module according to any one of the preceding claims wherein each of said planar elements is in the form of a mesh sheet.

7. A filter module according to any one of the preceding claims wherein each of said planar elements has apertures which are trapezoidal, round, oval, square and/or diamond shaped.

8. A filter module according to any one of the preceding claims wherein the respective planar elements are substantially co-terminous.

9. A filter module according to any one of the preceding claims wherein said spacer elements are in the form of spacer tubes.

10. A filter module according to any one of the preceding claims wherein said spacer elements comprise a foraminous sidewall.

11. A filter module according any one of the preceding claims wherein said spacer elements are produced from the same foraminous sheet material as the planar elements.

12. A filter module according to any one of the preceding claims including about 2 to 50 planar elements and about 2 to 20 spacer elements between adjacent said planar elements.

13. A filter module according to any one of the preceding claims wherein at least some of said spacer elements are elongate and lie parallel to the plane of said planar elements.

14. A filter module according to claim 13 wherein at least some of said spacer elements lie substantially parallel to each other.

15. A filter module according to any one of the preceding claims wherein said spacer elements lie substantially perpendicular to the plane of said planar elements.

16. A filter module according to any one of claims 1 to 5 wherein said spacer elements are in the form of a corrugated sheet.

17. A filter module according to any one of the preceding claims wherein said planar elements and/or said spacer elements are formed from thermoplastic material.

18. A filter module according to claim 17 wherein the ends of said spacer elements are thermally fused with the adjacent ends of said planar elements to produce a substantially rigid filter module.

19. A method of forming a substantially rigid self supporting filter module comprising the steps of arranging a plurality of no n- metallic non-rigid planar elements in the form of a stack, providing a plurality of spacer elements between respective pairs of planar elements and connecting said spacer elements to said planar elements.

20. A filter module when prepared by the method according to claim 19.

21. Apparatus for producing no n- metallic non-rigid planar elements of a filter module according to the invention comprising: a reservoir for storing granulate material having a first melting point, the said reservoir having a first inlet and a first outlet, the granulate material including a foaming additive having a second melting point, a heating and pressurising unit including a chamber having a second inlet and a second outlet, the second inlet in communication with the first outlet, a path of travel defined from the second inlet to the second outlet, the heating unit comprising heating and pressurising elements distributed along the path of travel, an extruder unit mounted downstream relative to the heating and pressurising unit at the second outlet, the extruder unit further including an extruder heating unit, the extruder defining an extruder outlet, the extruder unit generating a non-metallic non-rigid planar element, a cooling unit mounted at the extruder unit for cooling the granulate material, and a measuring and cutting device for measuring and cutting elements having a predetermined length within a specific interval.

22. Apparatus of claim 21 further comprising a feed screw in the path of travel.

23. Apparatus according to claim 22 wherein the feed screw defines a cylindrical or conical geometry.

24. Apparatus according to any one of claims 22 or 23 wherein the feed screw conveys material from the inlet of the heating and pressurising unit to the output thereof.

25. Apparatus according to any one of claims 22 to 24 wherin the feed screw pressurises the granulate material as it is conveyed along the path of travel.

26. A method of producing non-metallic non-rigid planar elements of a filter module of the invention using the apparatus according to claims 21 to 25, the method comprising the steps of: supplying the granulate material to the heating and pressurising unit from the reservoir via the second inlet, conveying the granulate material along the path of travel, heating the granulate material to an elevated temperature and pressurising the granulate material to an elevated pressure while conveying the granulate material along the path in the heating and pressurising unit, the heating and pressurising performed according to a specific heating and pressurising profile, transferring the heated and pressurised granulate material to the extruder unit, heating the granulate material within the extruder heating unit to a temperature above the first melting point and/or at or above the second melting point, extruding the non-metallic non-rigid planar element from the granulate material, the heating of the granulate material causing an expansion of the foaming additive causing the non-metallic non-rigid planar element to obtain an porous structure, cooling the extruded non-metallic non-rigid planar element by the cooling unit according to a specific cooling profile thereby stopping or halting expansion of the granulate material and/or the foaming additive and locking or fixating the porous structure of the non-metallic non-rigid planar element, and cutting the non-metallic non-rigid planar element to length using the measuring and cutting unit.