CA1182053A

CA1182053A - Filtration apparatus

Info

Publication number: CA1182053A
Application number: CA000384506A
Authority: CA
Inventors: Phyllis Entis; Michael P Entis
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-08-24
Filing date: 1981-08-24
Publication date: 1985-02-05
Also published as: DE3231281A1; GB2105210A; JPS5840120A

Abstract

ABSTRACT OF THE DISCLOSURE
This invention relates to a new filtration apparatus which is suitable for clarifying a suspension thus rendering the suspension filterable and which allows for subsequent impregnation of a second filter medium for subsequent processing. The apparatus comprises a first and a second housing portion, a first filter medium retained in the first housing portion, and a means adapted to receive and releasably retain a second filter medium between the housing portions. None of the prior art devices provide for primary filtration of a suspension and subsequent impregnation of a second filter medium for isolation and/or emumeration of microorganisms.

Description

BACKGROIJND OF THE INVENTION
_. Field of the Invention This invention relates generally to the filtration art and more particularlyt to a new filtration apparatus.

2. Description of the Prior Art 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 particula~e matter on the surface of the membrane filter duriny filtration. The particulate matter interferes with the enumeration of bacterial colonies on the membrane filter, since these colonies can be to~ally hidden by khe particles. An automated enumeration system has been d~v~loped wh:ich uses a hydrophobic grid membrane filter as ~hown in U.S. patent 3,9~9,583 granted to Sharpe et al. For this automated system to be applied to the analysis of foods, drugs and cosmetics, it has become necessary to design a 5uitable filtration apparatus which would not only eliminate the particulate matter from a suspension of such products without altering the bacterial content of the suspension, but which would also allow for the subsequent filtration of the clariied product through a membrane filter in order to impregnate the filter for the isolation and/or enumeration of microorganisms.
Various filtration devices have been designed which have in the past, been used in ihe microbiological field.
One such example is shown in U.S. patent number 4,148,732 I

1 granted to Burrow t al April 10, 1979. This unit is used as a bacterial filter unit in anesthesia and respira-tory procedures but does not provide an apparatus for producing an impregnated filter suitable for an enumeration process.
Other devices, such as those shown in U.S. patent

3,888,765 (Bolk) 2,127,397 (Freedlander) 3~954,625 (Michalski), 3,919,089 (Gonzalez~ and 3,~36,464 (Brookins et al.), all relate to filtration devices which contain a filter between two housinys. ~one of these devices would enable a preliminary filt-10 ration of a suspension with subsequent impregnation of a secondfilter medium for use in an enumeration procedure.

~ RY OF THE INVENTION
Accordingly, it is an object of -the present invention to provide a novel filtration apparatus suitable for clarifying a su.spension thus rendering the suspension filterable and which allows for subse~uent impregnation of a second filter medium for ~3ubs~uen-t processing.
Xt is a fuxther object of the present invention to .rov:Ld~ a novel filtrcltion apparatus whiLch u.ses a membrane ~ iltex as a second filter medium.
Itis ~ still further object o the present invention to provide a novel filtration apparatus which incorporates a dual filtration therein and produces an impregnated hydrophobic grid membrane filter.
To this end, in one of its aspects, the invention provid~s a novel filtration apparatus which comprises a first housing portion and a second housiny portion, a first filter medium retained in said first housing portion, means adapted to receive and releasably retain a second filter medium between said first and second housing portions.

, 1 In another of its aspects, the invention provides a filtration apparatus which comprises a first housing portion, and a second housiny portion which is pivotally connected to said first 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 said lower chamber being greater than the diameter of the upper chamber, a small opening e~tending through the wall of said lower chamber immediately below said annular shoulder, said second housing portion having a rectangular 1~ upper section and a base extending therefrom, a first filter medium retained between said upper cham~er and said lower chamber of said first housing portion, and a second filter medium retained between said first housing portion and said second housing portion.
BRIEF DESCRIPTION OF TEIE DRAWINGS

.... _ .. ... .. .. .
FIGURE 1 is a perspective view of the novel ~iltration app~xatus of the present invention.
~ 'CGU~E 2 is a top view thereof.
FIGVRE 3 is a section vi.~w along line 3-3 oE E:iyure 1.
~ :tGU~E 4 is a perspective view of the holdings means of figure 1.
FIGU~E 5 is a perspective view o the second housing portion of figure 1.
FIGURE 6 is a perspective view of a press fit ring and the irst filter medium.
DESCRIPTION OF THE PREFERRED EMBODIMENT
. .
Reference is first made to figure 1 which shows a per-spective view of the filtration apparatus of the preferred embodiment of the present invention. The apparatus comprises a first housing portion 10 and a second housing portion 12, which are pivotall~ connected by pivotting means 14. Holding means 16 is pro~ided to secure the first housing portion 10 to the second housing portion 12.

1 Figure 2 is a top view of the novel Eiltration apparatus.
As seen from fiyures 1 and 2, the first housing portion 10 has a central, circular opening 18 therein, and is generally cylindrical in shape, with an annular shoulder 20 at about one-half its length, the purpose of which will be explained hereinafter~ The diameter of the lower part of the first housing portion is marginally greater than the upper part and it Pxtends 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 10 housing portion 10.
The top of the second housing portion 12 is rectangular in profile and has a funnel shaped base portion 22 which ter~in-ates in a conduit 24 which allows removal of the li~uid during the eiltration process. The particular shape of the base portion 22 is nok critical to the invention and may be varied within the scope and spirik of the present invention. It may, if desirad, bcl om:itt~d completely and the top of the second housing portion 12 would constitute the entire second houl3ing poxtion 12. ln this case, the filtrate would be removed directly from the second housing portion 12.
~ he structure of the upper housing portion 10 will now be more particularly described with ref~rence to figure 3 which is a sectional view along line 3-3 of figure 1. First housing portion 10 has a circular opening 18 on the top surface thereo~ and forms a first chamber 28 and a second cha~ber 30.
A first filter medium 32 is interposed between the first chamber 28 and the second chamber 30 and is secured to the walls 34 of the 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 filtex medium 32.

5~
1Figure 4 shows the holdiny means 16 which in this e~odiment, is sh~wn as an enlarged la~ch 40 which extends beyond the lower surface of the first housi.ng portion 10~ As seen from figure 1 and 4, the latch 40 is biased upwardly and lip 42 projects inwardly of the exterior surface of second housing portion 12 to hold the housing portions together.
The first filter medium 32 is secured across the open-ing between the first chamber 28 and the second chamber 30. Pre-fexably, the filter medium 32 is inserted and retained on a press 10fit ring 52 as shown in figure 6. The press fit ring 52 is adapted to fit and be retained in the uppermost part of the second chamber 30. In one embodiment, the ring 52 includes marginally exl:ending annular protrusion 54 about its upper sur-~ace, whi.ch pro-trusion fits into and is retained in an ann~lar groo~e 56 which is cut in the inner surface of the shoulder 20.
'l'h.is structure allows the ring 52 and the filter medium 32 to b~ h~ld in place.
Othe.r ~mbod:irnents Oe the ring 52 rnay be designed to r~in the first filter medium 32 in place. For example, a groove could be cut in the ring 52 itself and the ~ilter 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 in-wardly extending protrusion may be included on the inner side wall oE either the upper chamber 28 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 retent;on.

O~3 1 It is of course preferred that in constructing the means to hold the first filter medium in place, all walls be made to slope downwardly. This structure prevents any of the filtra~
from ~ecoming trapped on any ledges which will affect the results of the su~sequent filtration on the second filter medium.
The first hous~ng portion and the second housing portion are pivotally connected by any well known means. One embodiment of a suitable pivoting means is shown in figures 1 and 2. The second housing portion 12 has a pair of arms 50 ex-tending outwardly wi$h a cylindrical pin 48 extending therebe-tween and marginally ~eyond 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 o~ the pin 48 which extends outwardly ~eyond the arm 50. A curved cover 53 extends out-wardl~ from the first hous~ng portion lO and is adapted to fit over the area of the pin 48 between the flanges 51.
Thus, when latch 40 is relea,sed, the first housiny portlon 10 may be pivotted open as pin 48 rotakes in the ~langes 51 and the cover 53. S~nce the cover 53 does not extend 29 as far downwardly as flanges 51, t~ere is a space provided there-~etween which allows the pin 48 to he removed thus ~eparating , the first and the second housing portions. This particular structure enables the first ~ousing portion ~o be pivotted upon or if desired, separated from the second housing portion.
The first filter medium 32 is provided to provide a preliminary filtration for the material to be filtered. It may be made of a variety of materials and generally has a micron 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 area i53 o~ about 0~5 microns to about 1.5 ~lcr~ns and accordin~ly, a filter medium with an absolute ~article retention size of about 8 microns is suitable.
As stated before, filter medium 32 may be made of a variety of materials, this material not being critical to the present invention.
The filter medium 32 must be autoclavable as is necessary for the entire apparatus and, to effectively allow m~croor~anisms to pass through the filter, .it must be of sufficient porosity and structure to pass throuyh large microorganismsO The pores or passageways in the filter should not twist; otherwise, bacteria may be trapped even though the pore size is sufficiently large. 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 man~
ou.rces. This material is a dense, strong material o~ warp wires w1th r~ular passageways therethrough.
The vacuum which is introduce3d throu~h hole 2fi and corlduit 36 must be sufficient to aid in the primary filtrat~on of the liquid passing through the first filter medium 32. The exact parameters of the vacuu~, .including the amount, time and size oE the vacuum are determined by experimentation. The li~uid passin~ 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 figure 6 is put in place, it is seen that the ring 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 conauit 36 and the opening 26. This effectively prevents any of the filtrate from bein~ removed from the chamber 30 due to the action of the vacuum.

If desired, the conduit 36 ;ma~ communicate w,ith a corresponding conduit in the ring 52 which then communicates with the second chamber 30. Thi,s structure is more dif~icult to assemble since it would be necessary to accurately aliyn the conduit in the ring 52 with the conduit 36.
The second filter medium ~s placed on the top o~ the second housing portion 12 and receives the clarified filtrate which has been filtered through the ~irst filter medium 32. The clarified filtrate i5 then filtered through'the second filter medium with the aid of a vacuum drawn throu~h conduit 24.
While the second filter medium may be of any type o fi,lter depending upon the use of the apparatus, within the scope of the present invention, the apparatus is particularly suitable for use with a membrane filter which retains microorganisms on :lt~ ~urface for ~ubsequent,processing. A membrane filter ~enerally comprises a porous, non-fibrous plastic film material in whlch the abso:lute size and the uniEormity of size'of the po~ ctr~ careEIllLy controllcd.
'rhc mernbrarle ~ilter should have c~ pore size'o$ ~bout 0.l~ to 1.0~ and preferably from about 0.2~ to about 0~7~ The most preferred pore size is abou-t, 0.45,u. The membrane must be h~drophilic to allow waker and various nu-trients to pass there-through and it must be capable o~ being sterilized without structural or functional damage. It must also be non-~toxic to bacteria. The thickness of the ~ilter is not critical but, preferably, should not exceed 0.5 mm. The apparatus is also suited for usin~ a hydrophobic grid membrane filter (HGMF) as the second filter medium.

1 In the preferred embodiment of the apparatus designed for use wit:h an EIGMF, 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 within the scope of ~he invention. For example, many standard membrane ~ilters are rounded so in this case, the respective sections of the irst and second housing portions will be rounded in profile. The exact shape of these sections will depend upon the nature of the 10 second filter medium and its shape.
The entire filtration apparatus may be manufactured of any material. It is recornmended that such material be autoclavable and t:hat khe entire app~ratus be steriliæed prior to use. Two suitable examples include a polysulfone made by Union Carbide Co.
or TPX* which is a methylpentane polymer sold by Mitsui Petro chcmlcal Industries Ltd. of Japan.
Thf~ principles o~ the process using the novel filtration p~ara~us wlll now be described as illustrative only and not limiting in nature. While not restricted thereto, the invention 20 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 intermediate products used and made in that industry, as well as by-products and ef~luent resulting from the industrial process, and also to be able to classify the microoxganisms 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 product 3~ and thus prohibited by government regulation.
.~

*Trade Mark 9 -1 This need exists for many industries, but it is part-icularly important for such industries as the drug industry, the food industry and the cosmetic industry. Government regulations in most jurisdictions strictly control the quantity of certain microorganisms which is permitted in food, drug~ cosmetic and similar products, and accurate tests must be performed at regular intervals to ensure compliance with these regulations.
Several methods ~xist today for detecting, c~unting and identifying microorganisms present in a sample. Most methods ~O entail depositiny 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 oP rnicroorganism of interest. Once the microorganisms have grown on these culture media, further tests are often required to complete their .identiEication. This usually requires the transfer of a port:ion of the growth to other culture media, in order to cle~.rmln~ vax.iou~ impor-tant ch~racteY:ist:.ics of the mi.crooryanisms (Kuch a~ the ability to ferment certain sugars, or to grow in the presence of certain chemicals) ~ ~hese 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 sanitary 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 or yoghurt manu:Eacture and in the production of beers and wines).
~ novel apparatus for enumerating mic.roorganisms has been developed. As discussed in United States patent number 3,929,583 granted on December 30, 1975 to Canadian Patents and Development Limiked, this apparatus comprises a membrane fi.ltsr capable of retaining microorganisms on its surface when a53 1 a fluid sarnple is passed through it. ~ barrier material is imprinted on the surface of the filter which restricts the ~pre~d 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 area than in normal colony area.
The use of the hydrophobic grid membrane filter (hereinafter referred to as HGME~) has produced a substantial advance in the field of microbiology. The regulari-ty in size, 10 shape and optical density, and the orderly arrangement of colonies as a result of the gridded pattern of barrier material of the HGM~ has permitted the replacement of manual counting with opto-~lectronic scanniny, thus saving analyst time and producing more reliable and reproducible results.
The present invention facilitates the use of the HGMF.
rl'he ~IGMF is clasped between the first housing portion lO and the ~ cond hous:Lng port:ion 12. As shown in :Eigure 2, in the preerred ~mhod:im~nt, the .lower part o the first housing portion lO and the upper part of the second housing portion 12 are rectangular, 20 thus allowing the HGMF to si~ 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 fil-ter medium 32. The HGMF acts as a "seal" or "gask~t" between the housing portions lO and 12.
A suspensiQn of the sample to be tested is prepared and then fed into opening 18. The suspension is filtered through the first filter medium 32 with the aid of the vacuum which is drawn through opening 26. Particulate matter is filtared out of the suspension and is retained on the surface of the first 30 filter medium 32, and the filtrate passes therethrough. As the 1 pore size of the filter medium 32 is sufficiently large to allow microoorganisms to pass through, the filtrate will contain all of the microorganisms present in the original sample suspension.
The filtrate then contacts the HGMF which is secured between the first housing portion 10 and the second housing portion 12. l'he filtrate is filtered through the HGMF with the aid of a vacuum drawn throuyh 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 ~IGMF is removed for ~ubsequent processing and evaluation.
A further embodimenk of the invention includes the use o~ multiple first and second filter med:ia within a single housing.
In this embodiment, the first housing portion 10 comprises a plural~ty O.e lonyitudinally extending, conti.nuous and discrete channel~ ~hroucJhout its length. Each chal-nel i5 interrupted with a discrete ~irst filter medium located across the channel at the 20 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 altern-atively, 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 pulled. In the latter case, a plurality of openings correspond-ing to the number of channels is re~uired and a vacuum must be pulled through each opening 26.

3,S~3 1 Each of the channels terminates at the juncture between the firs-t housing portion 10 and the second houslng portion ]2, and a discrete second filter medium is secured at the end of each channel~ Each discrete second f-ilter 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 ~est 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 portio~
oE ~ach channel in chamber 30. The filtrate then contacts each respective second filter mediwm and each second filter medium retains on its surface, all of the microorganisms which were ~rc~nt in the original sample suspension. Since the material ing throucJh the second filter media is waste material, it is co.llect~d in th~ common second housing portion 12.
The first housing portion 10 is then pivotted away ~rom the second housing portion 12 and the plurality of impregnated second filter media are removed for subsequent processing and evaluation.
The adva~tages of this embodiment are that a plurality of impreynated 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 sampl~s without the need for removing the second filter media after each suspension is filtered.

i Although the disclosure describes and illuskrates a preferred embodiment of the invention, it is to b~ understood that the invention is not restricted to this particular embodiment.

~0

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A filtration apparatus for separating and recovering microorganisms from a fluid suspension thereof containing contaminating particulate matter comprising:
(a) A first housing portion for containing the said suspension and for passing therefrom a first filtrate;
(b) A second housing portion for passing a second filtrate out of the bottom thereof, and being in fluid communication with and disposed adjacent to said first housing portion;
(c) A first filter medium contained in said first housing portion and being disposed therein such that said first filtrate must pass therethrough;
(d) A second filter medium releasably held by and contained in or adjacent to said second housing portion, and being so disposed such that it receives said first filtrate and said second filtrate must pass therethrough;
(e) Means for providing a differential pressure across both said filters; and (f) Housing attachment means for releasably securing said first housing portion to said second housing portion;
and wherein:
(i) Said first filter medium has a pore size such that said particulate material will not pass therethrough but said first filtrate containing said microorganisms and said fluid will pass therethrough, said first filter medium having pore passageways which will not trap said microorganisms therein; and (ii) Said second filter medium having a pore size such that said microorganisms will not pass therethrough but said

Claim 1 continued...

second filtrate containing said fluid will pass therethrough;
whereby said microorganisms are retained by and recovered with said second filter medium by releasing said first housing portion from said second housing portion and removing the said second filter medium therefrom.
2. A filtration apparatus as claimed in claim 1 wherein said first housing portion is pivotally secured to said second housing portion.
3. A filtration apparatus as claimed in claim 1 wherein said second filter medium is a membrane filter.
4. A filtration apparatus as claimed in claim 3 wherein said membrane filter is a hydrophobic grid membrane filter.
5. A filtration apparatus as claimed in claim 1 wherein said first housing portion is divided along its length by an annular shoulder into an upper chamber and a lower chamber.
6. A filtration apparatus as claimed in claim 5 wherein said lower chamber has a marginally greater diameter than the diameter of the upper chamber.
7. A filtration apparatus as claimed in claim 5 wherein a small opening extends through the wall of said first housing portion into said lower chamber immediately below said annular shoulder.
8. A filtration apparatus as claimed in claim 1 wherein the bottom of the first housing portion and the top of the second housing portion are both circular and of the same size.
9. A filtration apparatus as claimed in claim 1 wherein the bottom of the first housing portion and the top of the second housing portion are both rectangular and of the same size.
10. A filtration apparatus as claimed in claim 8 or 9 wherein the second housing portion has a conduit leading from the bottom thereof.
11. A filtration apparatus as claimed in claim 5 wherein said first filter medium is retained in said annular shoulder.
12. A filtration apparatus as claimed in claim 11 wherein said 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 said annular shoulder has an annular groove therein, which is adapted to receive and retain said protrusion of said press fit ring,
13. A filtration apparatus as claimed in claim 1 wherein said first filter medium has a micron porosity which has an absolute particle retention size of from about 4 microns to about 15 microns.
14. A filtration apparatus as claimed in claim 13 wherein said particle retention size is about 8 microns.
15. A filtration apparatus as claimed in claim 13 wherein said first filter medium is made of stainless steel mesh.
16. A filtration apparatus as claimed in claim 13 wherein said first filter medium is a twilled-weave dutch cloth filter.
17. A filtration apparatus as claimed in claim 13 wherein said first filter medium is a sieve type material.
18. A filtration apparatus as claimed in claim 12 wherein said press fit ring forms a downwardly extending channel between the press fit ring and the wall of said lower chamber, the upper part of said channel communicating with a conduit extending through the wall of said lower chamber.
19. A filtration apparatus as claimed in claim 4 wherein said hydrophobic grid membrane filter is retained on the top surface of said second housing portion.
20. A filtration apparatus as claimed in claim 11 wherein said first filter medium is mounted on a press fit ring which is adapted to be inserted and retained in said first housing portion at the annular shoulder.
21. A filtration apparatus as claimed in claim 1 in which at least said housings are made of an autoclavable material.
22. A filtration apparatus as claimed in claim 21 wherein the apparatus except for the first filter medium is made of polysulfone.
23. A filtration apparatus as claimed in claim l wherein said first housing portion comprises a plurality of longitudinally extending, discrete channels.
24. A filtration apparatus as claimed in claim 23 wherein said first filter medium comprises a plurality of discrete filters, each of which is interposed in one of said channels.
25. A filtration apparatus as claimed in claim 23 wherein said second filter medium comprises a plurality of discrete filters, each of which is located at the terminal end of one of said channels.
26. A filtration apparatus as claimed in claim 1 wherein said first filter medium is releasably retained in said first housing portion.
27. A filtration apparatus as claimed in claim 1 wherein said second housing portion is pivotably releasable from said housing portion.