GB2105210A

GB2105210A - Filtration apparatus

Info

Publication number: GB2105210A
Application number: GB08223594A
Authority: GB
Inventors: Phyllis Entis; Michael Peter Entis
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-08-24
Filing date: 1982-08-17
Publication date: 1983-03-23
Also published as: JPS5840120A; CA1182053A; DE3231281A1

Abstract

Filtration apparatus comprises first and second housing portions 10 and 12 which are hinged together at 14, a relatively coarse filter (32) being releasably retained on shoulder 20 of the first housing portion and a fine filter being releasably mounted between the 9 housing portions. In use suction is applied to outlet 24 to draw suspension through the filters, coarse filter (32) removing solid particles but allowing bacteria to pass through to be collected on the fine filter for subsequent processing and examination. The coarse filter is wire mesh of 4 to 15 micron pore size, the fine filter in a hydrophilic membrane of 0.1 to 1.0 microns. The apparatus is used in testing food, drugs and body fluids, the coarse filter removing particles which would interfere with the examination of the fine filter. <IMAGE>

Description

SPECIFICATION Filtration Apparatus This invention relates to filtration apparatus.

In the field of microbiology, it is necessary to conduct various tests on products such as foods, drugs and cosmetics to quantitatively and/or qualitatively assess the contamination absent or present in such products. Membrane filtration has numerous advantages as a procedure for microbiological evaluation, but cannot be used, since such products deposit particulate matter on the surface of the membrane filter during filtration. The particulate matter interferes with the enumeration of bacterial colonies on the membrane filter, since these colonies can be totally hidden by the particles. An automated enumeration system has been developed which uses a hydrophobic grid membrane filter as described in U.S.

Patent 3,929,583. In order to use this automated system for the anlysis of foods, drugs and cosmetics, necessitated designing suitable filtration apparatus which will not only eliminate the particulate matter from a suspension of the products without altering the bacterial content ofthe suspension, but which will allowforthe subsequent filtration of the clarified product through a membrane filter in order to impregnate the filter for the isolation and/or enumeration of microorganisms.

Various filtration devices have been proposed for use in the microbiological field. One example, disclosed in U.S. Patent 4,148,732, is used as a bacterial filter unit in anaesthesia and respiratory procedures but does not provide an apparatus for producing an impregnated filter suitable for an enumeration process.

Other filtration devices such as disclosed in U.S.

Patent Nos. 3,888,765 (Bolk), 2,127,397 (Freedlander), 3,954,625 (Michalski), 3,919,089 (Gonzalez), and 3,836,464 (Brookins etal), contain a filter between two housings. None of these devices would enable a preliminary filtration of a suspension with subsequent impregnation of a second filter medium for use in an enumeration procedure.

According to one aspect of the present invention we propose filtration apparatus comprising a first housing portion and a second housing portion, a first filter medium retained in the first housing portion, and means adapted to receive and releasably retain a second filter medium between the first and second housing portion.

The above apparatus enables clarifying a suspension thus rendering the suspension filterable and allow for subsequent impregnation of a second filter medium for subsequent processing. When the sec ond filter medium is a membrane filter, the dual filtration enables the production of an impregnated hydrophobic grid membrane filter.

According to another aspect of the invention filtration apparatus which comprises a first housing portion, and a second housing portion which is pivotally connected to the first housing portion, the first housing portion being divided along its length by an annular shoulder into an upper chamber and a lower chamber, the diameter of the lower chamber being greater than the diameter of the upper chamber, a small opening extending through the wall of the lower chamber immediately below the annular shoulder, the second housing portion having a rectangular upper section and a base extending therefrom, a first filter medium retained between the upper chamber and the lower chamber of the first housing portion, and a second filter medium retained between said first housing portion and said second housing portion.

Other aspects and features of the present invention are set forth in the appendent claims.

A preferred embodiment of the invention will now be described by way of example with reference to the accompanying drawings of which: Figure 1 is a perspective view of filtration apparatus according to the present invention; Figure 2 is a plan view thereof; Figure 3 is a section view along line 3-3 of Figure 1; Figure 4 is a perspective view of a first housing portion of the apparatus shown in Figure 1; Figure 5 is a perspective view of a second housing portion of the apparatus shown in Figure 1; Figure 6 is a perspective view of a press fit ring and the first filter medium.

The filter shown in Figures 1 to 5 comprise a first and second housing portions 10, 12, which are pivotally connected by means 14 and secured together by holding means 16. The first housing portion 10 has a central, circular opening 18 therein, and is generally cylindrical in shape, with an annular shoulder 20 approximately midway along its length. The diameter of the lower part of the first housing portion is marginally greater than the upper part and it extends into a rectangular shape as it extends downward. A small opening 26 which leads to a conduit (not shown) is provided in the side wall of the first housing portion 10.

The top of the second housing portion 12 is rectangular in profile and has a funnel shaped base 22 which terminates in a conduit 24 through which liquid is removed during filtration. The shape of the base 22 is not critical and may be varied to suit particular requirements. Indeed, it may, if desired, be omitted completely so that the filtrate would be removed directly from the second housing portion 12.

As will be seen from Figure 3 which is a crosssection on line 3-3 of Figure 1, the first housing portion 10 has a circular opening 18 on the top surface thereof and is divided into a first chamber 28 and a second chamber 30, by a first filter medium 32 secured to the walls 34 ofthe first housing portion 10. An opening 26 leads to a conduit 36 which communicates with a depression 38 in the interior side wall of the lower chamber 30 immediately below the filter medium 32.

The holding means 16 which comprises an enlarged latch 40 extending below the lower end of the first housing portion 10, is biased upwardly and has a lip 42 projecting inwardlyofthe exterior surface of the second housing portion 12 to hold the housing portions together.

The first filter medium 32 separating the first chamber 28 and the second chamber 30, is inserted and retained on a ring 52 (Figure 6), press fitted and retained in the upper end of the second chamber 30.

The ring 52 includes around its upper surface a protruding rim 54 which is received in an annular groove 56 cut into the shoulder 20 so as to hold the ring 52 in place.

Alternatively the ring 52 may be designed to retain the first filter medium 32 in place. For example, a groove could be cut in the ring 52 itself and the filter medium 32 could sit and be retained in the ring 52.

Other means may be provided for retaining the ring 52 and the filter medium 32 in place. For example, an annular inwardly extending protrusion may be included on the inner side wall of either the upper chamber28 on the lower chamber 30 upon which the ring 52 may rest.

The ring 52 is generally press fit into place and held by tension. The inherent resiliency in the material will allow its insertion and subsequent retention.

It is of course preferred that in constructing the means to holdthefirstfilter medium in place, all walls be made to slope downwardly, so asto prevent any of the filtrate becoming trapped on any ledges which will affect the results of the subsequent filtration on the second filter medium.

The first housing portion and the second housing portion may be pivotally connected by suitable means but in the illustrated embodiment the second housing portion 12 has a pair of arms 50 extending outwardly with a cylindrical pin 48 extending therebetween and marginally beyond the plane of each arm 50. The first housing portion 10 has a pair of curved flanges 51 in which is journalled the respective ends of the pin 48 which extends outwardly beyond the arm 50. A curved cover 53 extends outwardly from the first housing portion 10 and is adapted to fit over the area of the pin 48 between the flanges 51.

Thus, when latch 40 is released, the first housing portion 10 may be pivoted open as pin 48 rotates in the flanges 51 and the cover 53. Since the cover 53 does not extend as far downwardly as flanges 51, there is sufficient space therebetween to allowthe pin 48 to be removed thus separating the first and the second housing portions.

The first filter medium 32 is for preliminary filtration of the material to be filtered. It may be made of a variety of materials and generally has a porosity which comprises an absolute particle retention size of from about 4 microns to about 15 microns, preferably about 8 microns. Most microorganisms have a particle size in the range of about 0.5 microns to about 1.5 microns and accordingly, a filter medium with an absolute particle retention size of about 8 microns is suitable.

The filter medium 32 must be autoclavable as is necessary for the entire apparatus and, to effectively allow microorganisms to pass through the filter, it must be of sufficient porosity and structure to pass through large microorganisms. The pores or pas sageways in the filter should not twist; otherwise bacteria may become trapped even in large pores. A pore size of at least about 4 microns is preferred.

One example of a suitable material is a stainless steel twilled-weave dutch filter cloth which is available from many sources. This material is a dense, strong material of warp wires with regular passageways therethrough.

The vacuum applied through hole 26 and conduit 36 must be sufficient to aid in the primary filtration of the liquid passing through the first filter medium 32.

The exact parameters of the vacuum, including the amount, time and size of the vacuum are determined by experimentation. The liquid passing through the filter medium 32 will not be pulled into conduit 36 as the entrance of the conduit is recessed in depression 38.

When the ring as shown in Figures 6 is in position, it forms a small vertical channel with the depression 38.

The vacuum is drawn from the chamber 30 upwardly through the funnel channel and out through the conduit 36 and the opening 26. This effectively prevents removal of any filtrate from the chamber 30 due to the action of the vacuum.

If desired, the conduit 36 may communicate with a corresponding conduit in the ring 52 which then communicates with the second chamber 30. This structure is more difficult to assemble since it would be necessary to accurately align the conduit in the ring 52 with the conduit 36.

The second filter medium is placed on the top ofthe second housing portion 12 and receives the clarified filtrate (after passing through the first filter medium 32) which is then passed through the second filter medium with the aid of a vacuum drawn applied through conduit 24.

While the second filter medium may be of any type depending upon the intended use of the apparatus, a membrane filter, which retains microorganisms on its surface for subsequent processing, is particularly suitable. A membrane filter generally comprises a porous, non- fibrous plastics film material in which the absolute size and the uniformity of size of the pores are carefully controlled.

The membrane filter should have a pore size of about 0.1# to 1.owl and preferably from about 0.2# to about 0.7to. The preferred pore size is about 0.45 .

The membrane must be hydrophilic to allow water and various nutrients to pass therethrough and it must be capable of being sterilised without structural or functional damage. It must also be non-toxic to bacteria. The thickness of the filter is not critical, but preferably, should not exceed 0.5 mm. The apparatus is also suited for using a hydrophobic grid membrane filter (HGMF) as the second filter medium.

In the preferred embodiment of the apparatus designed for use with an HGMF, the lower part of the first housing 10 and the upper part of the second housing 12 are rectangular in profile to allow a rectangular HGMF to be secured therebetween.

However, the shape of these sections may be varied.

For example, many standard membrane filters are rounded in which case, the respective sections of the first and second housing portions will be rounded in profile. The exact shape of these sections will depend upon the nature of the second filter medium and its shape.

The entire filtration apparatus may be manufactured of any material. It is recommended that such material be autoclavable and that the entire apparatus be sterilised prior to use. Two suitable examples include a polysulphone made by Union Carbide Co. or TPX (registered Trade Mark) which is a methylpentane polymer sold by Mitsui Petrochemical Industries Ltd., of Japan.

One process employing the above described filtration apparatus will now be described by way of example. While not restricted thereto, the invention will be described with a hydrophobic grid membrane filter (HGMF) as the second filter medium.

It is essential in many industries to be able to determine whether or not microorganisms are present in raw materials, finished products and intermediates used and made in that industry, as well as by-products and effluent resulting from the industrial process, and also to be able to classify the microorganisms, if present, into their proper taxonomic categories. Many such microorganisms are not only undesirable but some are detrimental to the health of the consumer of the products and thus prohibited by government regulation.

This need exists in many industries, but it is particu larlyimportantin,forexample,thedrug industry,the food industry and the cosmetics industry. Govern ment regulations in most jurisdictions strictly control the quantity of certain microorganisms which is per mined in food, drug, cosmetic and similar products, and accurate tests must be performed at regular intervals to ensure compliance with these regulations.

Several methods exist today for detecting, count ing and identifying microorganisms present in a sample. Most methods entail depositing a portion of the sample in or upon one or more culture media which encourage the growth of the microorganisms.

Usually, a different kind of culture medium is used for each type of microorganism of interest. Once the mic roorganisms have grown on these culture media, furthertests are often required to complete their identification. This usualy requires the transfer of a portion of the growth to other culture media, in order to determine various important characteristics of the microorganisms (such as the ability to ferment certain sugars, or to grow in the presence of certain chemicals).

These methods are widely used in a number of areas including testing of foods, water and effluent for pathogenic bacteria, spoilage organisms, or bacteria indicative of poor sanitory practices, testing of pharmaceutical products, and testing of urine in the diagnosis of urinary tract infections. Other applications include, for example, the control of starter cultures used in fermentation processes (such as in cheese oryoghurt manufacture and in the production of beers and wines). United States Patent 3,929,583 (Canadian Patent and Development Limited) relates to apparatus for enumerating microorganisms and comprising a membrane filter capable of retaining microorganisms on its surface when a fluid sample is passed through it. A barrier material is imprinted on the surface of the filter which restricts the spread of colonies through its physical properties.The pattern produced defines a plurality of ordered, microbial colony-isolating cells wherein the cells are usually smaller in the area than in normal colony area.

The use of the hydrophobic grid membrane filter (hereinafter referred to as HGMF) has produced a substantial advance in the field of microbiology. The regularity in size, shape and optical density, and the orderly arrangement of colonies as a result of the gridded pattern of barrier material of the HGMF has permitted the replacement of manual counting with optoelectronic scanning, thus saving analyst time and producing more reliable and reproducible results.

The present invention facilitates the use of the HGMF. The HGMF is clasped between the first housing portion 10 and the second housing portion 12. As shown in Figure 2, in the preferred embodiment, the lower part of the first housing portion 10 and the upper part of the second housing portion 12 are rectangular, thus allowing the HGMF to sit on the upper surface of the second housing portion 12, so that when the two housing portions are clamped together the HGMF will receive the liquid which is filtered through the filter medium 32. The HGMF acts as a "seal" or "gasket" between the housing portions 10 and 12.

A suspension ofthe sample to be tested is prepared and then fed into opening 18. The suspension is fil tered through the first filter medium 32 with the aid of the vacuum which applied through opening 26. Particular matter is filtered out of the suspension and is retained on the surface of the first filter medium 32, and the filtrate passes therethrough. As the pore size of the filter medium 32 is sufficiently large to allow microorganisms to pass through, the filtrate will contain all of the microorganisms present in the original sample suspension.

The filtrate than contacts the HGMF which is secured between the first housing portion 10 and the second housing portion 12. The filtrate is filtered through the HGMF with the aid of a vacuum applied through conduit 24. The HGMF retains on its surface all of the microorganisms which were present in the original sample suspension.

The latch 40 is then unclasped by moving clip 42 outwardly. The first housing portion 10 is pivotted away from the second housing portion 12 and the impregnated HGMF is removed for subsequent processing and evaluation.

Afurtherembodimentofthe invention includes the use of multiple first and second filter media within a single housing. In this embodiment, the first housing portion 10 comprises a plurality of longitudinally extending, continuous and discrete channels throughout its length. Each channel is interrupted with a discrete first filter medium located across the channel at the axis of the annular shoulder 20.

With this structure, the conduit 36 leads directly to each of the channels below the first filter medium or alternatively, there may be provided a plurality of openings 26 and corresponding conduits 36 leading separately to each channel thus allowing a vacuum to be pulled from each channel. In the former case, only one opening 26 is required and only one vacuum is applied. In the latter case, a plurality of openings corresponding to the number of channels is required and a vacuum must be applied through each opening 26.

Each of the channels terminates at the junction between the first housing portion 10 and the second housing portion 12, and a discrete second filter medium is secured at the end of each channel. Each discrete second filter medium is of a size and is aligned such that all the material passing through the channel is filtered through the second filter medium and will not contact any of the other filter media.

This embodiment allows for the testing of a plurality of samples simultaneously. Each test suspension is fed into a separate channel at opening 18. Each suspension is filtered through the first filter media with the aid of the vacuum and the particulate matter is filtered out of the suspension and the filtrate passes therethrough into the corresponding lower portion of each channel in chamber 30. The filtrate then contacts each respective second filter medium and each second filter medium retains on its surface, all of the microorganisms which were present in the original sample suspension. Since the material passing through the second filter media is waste material it is collected in the common second housing portion 12.

The first housing portion 10 is then pivotted away from the second housing portion 12 and the plurality of impregnated second filter media are removed for subsequent processing and evaluation.

The advantages ofthis embodiment are that a plurality of impregnated second filter media are obtained simultaneously each one of which is impregnated with the microorganisms of a different suspension.

This allows for the testing of a number of samples without the need for removing the second filter media after each suspension is filtered.

Claims

1. Filtration apparatus comprising a first housing portion and a second housing portion, a first filter medium retained in the first housing portion, and means adapted to receive and releasably retain a second filter medium between the first and second housing portion.

2. Apparatus according to claim 1 wherein the first housing portion is pivotally and releasable sec ured to the second housing portion.

3. Apparatus according to claim 1 wherein the second filter medium is a membrane filter.

4. Apparatus according to claim 3 wherein the membrane filter is a hydrophobic grid membrane filter.

5. Apparatus according to any one of claims 1 to 4 wherein the first housing portion is divided along its length by an annular shoulder into an upper chamber and a lower chamber.

6. Apparatus according to claim 5 wherein the lower chamber has a marginally greater diameter than the diameter of the upper chamber.

7. Apparatus according to claim 5 or claim 6 wherein a small opening extends through the wall of the first housing portion into the lower chamber immediately below the annular shoulder.

8. Apparatus according to any one of claims 1 to 7 wherein the bottom of the first housing portion and the top of the second housing portion are both circu lar and of the same size.

9. Apparatus according to any one of claims 1 to 7 wherein the bottom of the first housing portion and the top of the second housing portion are both rectangular and the same size.

10. Apparatus according to claim 8 or claim 9 wherein the second housing portion has a conduit leading from the bottom thereof.

11. Apparatus according to claim 5 wherein the first filter medium is retained in the annular shoulder.

12. Apparatus according to claim 11 wherein the first filter medium is mounted on a press fit ring having an annular peripheral protrusion on the top surface thereof and the inner surface of the annular shoulder has an annular groove therein, which is adapted to receive and retain the protrusion of the press fit ring.

13. Apparatus according to any one of claims 1 to 12 wherein the first filter medium has an absolute particle retention size of from about 4 microns to about 15 microns.

14. Apparatus according to claim 13 wherein the first filter medium has an absolute particle retention size of about 8 microns.

15. Apparatus according to claim 13 or claim 14 wherein the first filter medium is made of stainless steel mesh.

16. Apparatus according to claim 13 or claim 14 wherein the first filter medium is a twilled-weave dutch cloth filter.

17. Apparatus according to claim 13 wherein the first filter medium is a sieve type material.

18. Apparatus according to claim 12 wherein the press fit ring forms a downwardly extending channel between the press fit ring and the wall of the lower chamber, the upper part of the channel communicating with a conduit extending through the wall of the lower chamber.

19. Apparatus according to claim 4 wherein the hydrophobic grid membrane filter is retained on the top surface of the second housing portion.

20. Apparatus according to claim 11 wherein the firstfilter medium is mounted on a press fit ring which is adapted to be inserted and retained in the first housing portion at the annular shoulder.

21. Apparatus according to any one of claims 1 to 20 which is made of an autoclavable material.

22. Apparatus according to claim 21 wherein the apparatus except forthe first filter medium is made of polysulphone.

23. Filtration apparatus comprising a first housing portion which is pivotally connected to a second housing portion, the first housing portion being divided along its length by an annular shoulder into an upper chamber and a lower chamber, the diameter of the lower chamber being marginally greater than the diameter of the upper chamber, a small opening extending through the wall of the lower chamber immediately below the annular shoulder, the first housing portion having a rectangular profile at its lower and the second housing portion having a correspondingly rectangular profile at its upper end, a filter medium having an absolute particle retention size of from about 4 microns to about 15 microns mounted on the surface of a press fit ring, the ring having an annular peripheral protrusion on the top surface thereof and the inner surface of the annular shoulder having an annular groove therin which is adapted to receive and retain the protrusion of the ring therein, thereby forming a downwardly extending channel between the ring and the inner wall of the lower chamber with the small opening communicating with the upper part of the channel, and a hydrophobic grid membrane filter retained on the top surface of the second housing portion.

24. Apparatus according to claim 1 wherein said first housing portion comprises a plurality of longitudinally extending, discrete channels.

25. Apparatus according to claim 24 wherein said first filter medium comprises a plurality of discrete filters each of which is interposed in one of said channels.

26. Apparatus as claimed in claim 24wherein said second filter medium comprises a plurality of discrete filters, each of which is located at the terminal end of one of the said channels.

27. Filtration apparatus comprising a first housing portion which is connected to a second housing portion, said first housing portion being divided along its length by an annular shoulder into an upper chamber and a lower chamber, the diameter of the lower chamber being marginally greater than the diameter of the upper chamber, a plurality of longitudinally extending, discrete channels, extending along the length of said upper housing portion, at least one small opening extending through the wall of said lower chamber immediately below said annular shoulder and communicating with at least one of said channels, said first housing portion having a rectangular profile at its lower end and said second housing portion having a corresponding rectangular profile at its upper end, a plurality of filters having an absolute particle retention size of from about 4 microns to about 15 microns mounted on the surface of a press fit ring, said ring having an annular peripheral protrusion on the top surface thereof and the inner surface of said annular shoulder having an annular groove therein which is adapted to receive and retain said protrusion of said ring therein, thereby forming a downwardly extending channel between the ring and the inner wall of said lower chamber with said small opening communicating with the upper part of said channel, and a plurality of hydrophobic grid mem brane filters retained in the top surface of said second housing portion, the number and orientation of said hydrophobic grid membrane filters corresponding to the number of channels such that one hydrophobic grid membrane filter is located at the end of each channel.

28. Apparatus as claimed in claim 27 wherein said first housing portion is pivotally connected to said second housing portion.

29. Filtration apparatus constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.