CA1289331C - Fluid media sterilization apparatus - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A unit for the sterilization of fluid media, for example contaminated water, the unit including a source of germicidal radiation disposed substantially centrally within a tubular structure or housing, there being provided between said source of germicidal radiation and the innermost surface of said tubular structure an annular passage constituting a flow path for the fluid media. The unit is capable of providing a lethal or "killing"
dosage of germicidal radiation, in excess of 99.99% "kill", even for very large flow rates of fluid media through the unit.

Description

~8~33.t Improvements in fluid media sterilization apparatus.
The present invention relates, in general, to improvements in a process and apparatus for the sterilization of fluid media and relates more particularly, but not exclusively, to an improved process and to an improved form of apparatus or unit for the sterilization of water. The invention also relates to an improved form of what might be termed an irradiation tube for use in such sterilization processes and apparatus or units.
Throughout the ensuing description, for ease of explanation reference will be made to an especially preferred embodiment of the present invention, invo]ving a process and apparatus for use in the sterilization of water. It should be realized however, that the process and apparatus in accordance with the present invention will be equally suited for the sterilization of other fluid media and is not intended to be restricted solely to the preferred embodiment described.
Nowadays the need for water sterilization is regarded as being critical, for a variety of reasons.
This is especially the case in less developed areas and/
or areas not blessed with adequate water storage facilities. At the present time there is a considerable need for the provision of sterilizing equipment or apparatus which will be capable of handling large volumes of fluid medi.a. Such a need has arisen, in some areas or instances, by reason of the demands for more efficient and higher productivity of the greater populations evident these days, and the increased usage of water by such larger populations. In yet other instances sterilization is made essential by virtue of the adverse effects of our modern society on ecological conditions in general.

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The prior art ~rocesse~, app~ratus and units eln~.~loyed for such purpo.ses have been found to be somewhat inappropriate, espec:ially where an eco~omical trea~.ment of substantially l~r~e volumes of ~luid is re~uired, since the resorting to or reliance upon )arge flow media pip~ h~s been found, in accordance with the prior ar~, to re~uce the eifective rate of efficiency of "kill'l o~ fungi, bactcria, viruses and~or other pollutants in the fluid ~inder consideration.
]0 qlhe mo~t comm~nly employed method o~
st:erili2ing such fluid mediA, in parti¢ular water, ;nvolves exposur~ of that m~dium to what is t~rmed a lothal dose of radiation, mor~ especially ultr~-violet radia~ion, of a so-cal].ed germicidal wavelength.
]5 Apparatus employed for such purposes serv~d to expose a flow of fluid medium to radiation from a suitable source, ~or example an ultra-violet lamp or lamps, or a sou~ce of ultra~violet radiatlon of any known type.
In this regard i.t should be realized that, ln ~cordance with acc~pted and wcll-establi~hed standards .set. down by the relevant authorities, an acceptable "kill" ra~e for bactexia is of the ord~r of 99.99~.
A "kill" rate below ~hat figure i~ not satisfactory.
~he prior art or known apparatus generally inv41ved a source o~ r~diation ( lAmp or the like) di~sDo~ed within a hollow tubul~r elc~ent and around which a flui.d medium ~o be sterili~ed ~as adapted to be passed or flowed. ~xperimontation hAe revealed that the material actually employed for m~king ~Uch a hollow tubular element can have a marked effect on the efficiency of irradiati.on, in t:erms of peroentage "kill" o~ bacteria, fun~i, etc. pres~nt. in the flui.d medium. Tubular olements constructed from fu~ed silica or quartz have been ~ound to ~xh.i.bit good transmissîbilit~ to ultra-1~89~3~

violet radiation, but such fused silica or quartz elements have been found to be subject to fouling, involving the building up or accumulation of a film on such tubular elements, thereby resultin~ in a loss of transmissibility therethrough of the radiation employed for purposes of sterilization. Of course the greater the degree of fouling of such fused silica or quartz tubular elements, then the lesser ls the transmissibility of such fouled tubes to ultra-violet radiation and, accordingly, the efficiency of operation in t~rms of percentage "kill" of bacteria, fungi, viruses etc. is reduced. In a practical sense it then became necessary to regularly arrange for cleaning of such fouled apparatus, thereby resulting in interr-uption of the procedure of sterilization.
One form of prior art ultra-violet sterilization apparatus or unit employed relied upon the use of one or more tubes or tubular elements of a material, sold under the registered trade mark "TEFLON", which is known technically as FEP (fluorinated ethylene propylene). Such material, hereinafter referred to simply as "TEFLON"* has the characteristics of being transparent to germicidal rays (for example ultra-violet radiation of the requisite wavelength) and has non-stock properties such that, to all intents and purposes, effectively no film builds up on such a tube during use, thereby minimizing fouling with its inherent problems of reduced transmissibility, etc. With such an arrangement, with a source of ultra-violet radiation located within such a tube and fluid flowing therearound, it has been found that tubes of teflon of at least .02 inches thickness will allow for the passage or trans-mission of 81% of incident ultra-violet radiation.
However, as the thickness of such tubing is increased *Trade-mark 1~8933:1 then the degree of transmissibility of radiation to the fluid has been found to drop off somewhat alarmingly.
In a more practical sense, however, tubes of a thickness of the order of .02 inches also have been found to be physically incapable of withstanding the external water pressure in any apparatus which would be responsible for even a reasonable, let alone a large, volume flow treatment rate. In order to allow such tubes to be physically capable of withstanding external water pressure w thout unwanted col]apse, it would be necessary to increase the thickness thereof, but such increase in thickness would then result in an unacceptable decrease in ultra-violet radiation transmissibility. With such arrangements, therefore, it has been found that while an acceptable degree of transmissibility of radiation can be achieved - provided of course that the tubular element was not too thick -problems were encountered in terms of constructing elements capable of withstanding external water pressure and thereby avoiding unwanted collapse. In a practical sense the thickness required for a tube of this type to be capable of withstanding the pressures associated with even a reasonable, let alone a large, volume flow of fluid media for treatment was found to give rise to a tube or tubular element which exhibited a totally inappropriate or inadequate level or degree of trans-missibility for ultra-violet radiation.
In yet an alternative embodiment in accordance with the prior art a sterilization unit is employed involving a chamber having one or more such TEFLON
tubes, with the medium to be irradiated being adapted to actually flow through such tubes. Arranged around such a tube or tubes are appropriate ultra-violet radiation . ~ ;

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- ' ' 3933~1 souroes. Again in a practical sense, however, such ~n arrangement has been found ~o be not par~icularly efficien~ in terms of its ~uffering from ~n unacceptable loss of incident radiation, or in other words radiation em~nating from ~he relevant source ~nd not incident on the T~FJ,0~ tube and hence not cCfe~tive in ste~ilization.
It is therefore ~ primary ohject of th~
prosent invention ~o develop A form o~ sterilizing unit 10 f or f lu id media ~hi ch wo~ld be capab 1 e~ of handling large volumes of f lui d media over an ex~ended period of time to meet the demand~ set upon it. Th~ invention ~lso seeks to pr~vide an improved fo~m of tubular element for use in such ~ s~.eriliz~r unit. The present invention also seeks to find A material, or p~rhap8 more correctly a ~ombination of material~, which woul~
allow for tr~nsmission of ultrl-viol~t. radiati~n over atl extended period of time wit.hou~ being subjected to an~ photochemical ohbnge causing deteriorAtion thereof or thexeto. ~he invcntion also seeks to provide an apparAtUs for treating ~]uid media, fiuch as water, by irr~diation in ~ continuous operation of a flow of material through a tubul~r ~]ement composed of mate~ial ilavin~ chemical Jnertness, non-stick properties and being not pron~ to det.erioration over extendod periods of operation. ~ n~lly the inven~lon se~ks to provide a sterilizing uni~ for ~terili?ing fluid media whi~h will run efficicntly over an oxt~nded period o~ ~ime by in effect elimin~ting the need fox frequent cleaning of operating parts o~ that unit.
The present invention seeks to overcome the problems and disadvantages associated with ~he prior art by pro~idin~ ~n arrangem~nt includlng ~
.sl~bstantially ~ntrally-arr~nged tubular ~le~ent, 3933~

preferably constructed of fused silica or quartz, having a source of ultra-violet radiation located therewithin and having water or other medium to be treated~flowing therearound. In accordance with the present invention the tubular element has what is in effect a thin sheet of fluorinated ethylene propylene or TEFLON* or the equivalent material, attached thereto in any ~nown manner.
In accordance with one aspect of the present invention, therefore, there is provided an irradiation unit for the sterilization of fluid media, said unit including: an irradiation tube constructed of a material transparent to germicidal radiation and having coated externally thereon or attached thereto a sleeve or layer of a material which is substantially -transparent to germicidal ultra-violet radiation but to whicn impurities contained in said fluid media do not stick, said tube having a source of germicidal ultra-violet radiation disposed internally and substantially centrally thereof; and a housing of a complementary shape to said tube and disposed substantially coaxially therewith, said housing being of a larger dimension than said tube, the arrangement being such that an annular space is provided between said tube and said housing, said annular space providing a flow path for said fluid media, said annular space beinq in the rana~ af from. 15 to 25 mm in width.
In accordance with a further aspect of the present invention there is provided a sterilizer unit for fluid media, said unit including: respective inlet and outlet means for fluid media to be sterilized; at least one irradiation unit connected to and extending between said inlet and outlet means, said at least o..e irradiation unit including an irradiation tuoe constructed of a material transparent to germicidal * Trade-mark ,. ~ .

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radiation and having coated externally thereon or at~ached thereto a sleeve or layer of a material which is substantially transparent to germicidal ultra-violet radiation but to which impurities contained in said fluid media do not stick, said tube having a source of germicidal ultra-violet radiation disposed internally and substantially centrally thereof; and a housing of a complementary shape to said tube and disposed substantially coaxially therewith, said housing being of a larger dimension than said tube, the arrangement being such that an annular spa e is provided between said tube and said housing, said annular space providing a flow path for said fluid media, said annular space being in the range of from 15 to 2S mm in width.
In accordance with the invention there is also provided a process for the sterilization of fluid media, using an irradiation unit and sterilizer unit as set down in the preceding paragraphs.
In order that the invention may be more clearly understood and put into practical effect there shall now be described in detail a preferred embodiment of an ir-radiation unit in accordance with the present invention, designed for use in a fluid medium sterilization unit.
The ensuing description is given by way of non-limitative example only, and is with reference to the accompanylng drawings, wherein:
FIG. 1 is a perspective view of a sterilizer unit in accordance with the present invention; and FIG. 2 is a sectional view of the unit of FIG. 1.
In accordance with the known or prior art 3~ techniques, it has been effectively universally considered that, in order to achieve a satisfactory "kill" rate of bacteria in a situation calling for an enlarged flow rate of fluid media to be sterilized, it was merely necessary to direct more "killing" or ultra-violet radiation into .

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~l2893~1 the ~c~ual tre~tment area itsel. Indeed, p~eviously emplo~ed te~hnlques generally, if not ex~l~sively, dictatcd that as desired flow rate incre~sed, then more ;ources of ultra-violet radiation should be brought in~o play or operation. In the result, it has been th- aGcep~ed pr~etice to have ~om 8 to AS many ag 200 individual ultra-violet lalnE~ in c~ ste~ilization uni.t in order to allow the ~nit to ~npe with high rates of rlow of fluid medium therethrough. This practice of co~r~se has ~ant that known units have been extremely large and bulky, not to mention excessively expen~ive.
The pre~en~ applican~ has also found, through experim~n~ion, that p~oblems will be expe~ienced with such prior art units ln guarant~eing that the fluid ~lowing thro~h the uni.t ls receiving a uniform, and more important a "killin~", dose o ~ltra-violet r~di~tion. Experimentation hA~ shown, for ex~mple, that in a multi-tubular element unit in ~ccordance with ~he hnown art ultra-violet radiatlon emanating from one Z0 lamp or source may be almost completeiy attenuated as it passes through and impinges on a n~.ighbouring lamp or ~Jource. The prior art units c~uld ~herefore be seen to l~e rJeneral~y wasteful o~ incid~nt ultra-violet radiation or energy, and also ~xtremely qu~stionahl~ jn terms o~
cnr.l~rin~ an acceptable "kill" of bacteria in the fluid be;ng treated.
Micro-or~anisms o~ ~he typ~ requirin~ "~illing"
have heen found to differ si.gnificantly in their susceptibility to u]tra-violet radiation, with ~he more resi3tant types perhaps requirin~ up to ~ix time6 the dosage of more s~sceptible species in order tv achieve an ~cep~able "ki~l". The aotual dosage~ achieved with an u~trA-violet pu~ification ch~m~er is subject to such l:actors or parame~ers as the na~ure o~ ~he hydxo-', ' ' ' 1~39;~3~

dyn~rnic flow within the chamber and the vari~bleintc~sity o~ radiation achieved at differen~ distan~es .. . .
frolll a sour~e or lamp.
The arra~gemen~ as ill~strated includes a single t:u~ular element in accordance with the present invention, ener~11y designa~ed as ~, of fused silica or quart~, h a film of TEFI,ON 2 eoated on or af~ixed thereto in any suita~le manner. The element is so constructed as ~o be capabl~ of having dispo~ed substantlally ~entrally thereof a sourc~ of ultra-viole~ radia~ion 3. The c~verall arrang~ment may be located in a~y sui~able manner on a mounting frame 4. The tubular element 1 and associa~ed film 2 will be di3posed within a t~bing housing 5, preferably cons~ructed from highly polished ]5 staillless steel. The stainless steel construction will q~arantee an almost indefinite life for the sterili~A~ion unit. The unit in accord~nce wi~h the ~nvelltion i5 so oons~ru~ted as to allow the source 3 ~nd ~ubular elem~nt 1 to be easily removed when service ~0 i5 required, as for example when replacemen~ is c~lled ior by reason of failu~e of the radiation source.
The housing 5 includes inle~ and outlet means and 7 respe~tively, preferably having some form of cont~ol val~ing asso~i3ted there~o. In practice the inlct 6 will be conn~ed, in any known manner, to a sour~e of cont~minat~d fluid, for example w~ter to be sterili7,ed, whil~t th~ ou~let 7 will be connected, again in any k~own manner, to ~ repository or reservoir for ~reated fluid ~Cluid ready for use). P~eferably the housing 5 will also ~e provldQd with a drain or sample v~ve means ~, at or in th~ vicinity of the inlet 6, and an ai~ bleed o~ sample valve means 9 located at or in the vicinity of the ou~let 7, whor~y to allow for testing of fluid with the tubular elemen~ at those locations. In the e~pecia~ly prefer~ed embodiment illustrated the ~ .

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sterilization unit will be provided with appropriate electric circuitry and equipment to allow for operation, including an on/off switch 10, a lamp 11 or other visual and/or audio-visual means for purposes of indicating that the unit is operating (power is on) and more preferably a lamp or the like signal means 12 (either visual and/or audio) for purposes of indicating power failure or failure of the radiation source.
A tubular element in accordance with the present invention, therefore, for location within the housing 5, consists primarily of fused silica or quartz of a standard thickness. Such fused silica or quartz exhibits an eminently acceptable rate of transmission to ultra-violet radiation incident thereon from a source located therewithin. In order to effectively prevent the onset of fouling of any such quartz tubular element, in accordance with the present invention a sheath or sleeve of a suitable thickness, for example significantly less than .02 inches, of a suitable material, for example TEFLON* is affixed in any known manner thereto. In one embodiment a thickness of .003 inches of suchTEFLON* material will be shrunk onto, sprayed onto or baked onto the quartz tubular element using known techniques. The composite tubular element thus provided has been found to exhibit approximately 87% transmission rate for ultra-violet radiation i~ncident thereon. In an especially preferred embodiment a thickness of .002 inches ofT~LON* or the like material may be shrunk onto, sprayed onto and/or baked onto a quartz tubular element.
Such a configuration has been found to exhibit significantly greater than the aforementioned 87~
transmission for ultra-violet radiation incident thereon.
Such an arrangement will also be effectively proof against *~ade-mark rouling and i~s inhere~t side-ef~ects, and also has ~ ffi~ient physcal. str~n~th to withst~nd the effects of water pressure, et~. from fluid mcdium flowing therearound.
With the pre~ent ap~lieant's arrangement the housi.ng 5 and assoc.iated tubular element l pref~rably will be so constructed as to provide a so-called ~'film thickness" of the order of ~rom 15 to 25 mm (0.53 to n. 98 in~hest. In other words, the annular spa~e exi.stin~ between the outer periphery or surface of t~le tubular element l and the inner surface of the hnusing 5 is of that or~er, that sphce in fact providing a channel.for flow of media to be sterili7ed. In an cspecially preferred embodiment the ~ilm thickness will be of the order of 17 mm ~0.67 inche~. Experimentation has reveal~d that, with a film thi.cknes6 of less than ]~ m~ (0.59 inches), ~he "kill" r~te will be ~ood, but t~e flow rate achievab].e will not be acceptable. On the other hand the reverse will be the case for a film thickness great~r than 25 mm ~0.98 inches), with such ~iving a good th~orstical flow rate but an unaccep~able "kill" r~te.
Again in accord~nce wj.th th~ present invention it. has been found, expe~imentall.y, that the internal d.l amet~r of the tubular e~ ~mcnt has been found to hav~
a pronounced e~fect on th~ efficiency of the overall .sterili~ti.on unit. ~ndeed, for a unit involving one such tubui.ar ~lement, havin~ A source of ultra-viole~
radiation locatcd therewithin, with fluid to be 3n st.erilized being adapted to ~low around the tubular element in ~ny known mAnner, it has heen ~ound experim-~nt.ally that a tubul~r element havi.ng an ;.nternal di.~m~t~r of from 55 to ~5 mm (approxi.mately 2.2 tc 2.6 inc~hes) ls perhaps best suitod for aohi~ving an acceptah~e "kill" rate. Tu~ular elements o~ a larger 3.~

size have been found to exhibit a substantially reduced "kill" rate for any acceptable fluid flow.
In accordance with the present invention a-tubular element l of the aforementioned type, or alternatively a plurality or bank of any suitable number of such tubular elements l, may be employed in an overall sterilization unit. The arrangement is such that the f1uid medium to be treated is allowed to flow around such tubular element or elements l, disposed within separate housings 5, and to be irradiated by ultra-violet radiation emanating from a source located within the or each tubular element l. Such an arrangement has been found to allow for satisfactory irradiation or sterilization of large volumes of fluid medium, when compared with the prior art arrangements, and has also been found not to be susceptible to problems such as fouling, inefficient radiation, etc., being problems all evident in the prior art arrangements.
The arrangement in accordance with the present invention has been found, in practice, to be able to easily achieve the required "kill" rate of 99.99%, even for very high flow rates of fluid medium. This result has been achieved in an extremely cost-effective manner, without having to rely on a particularly large and bulky piece of equipment or apparatus - as was necessary with the prior art - and without having to expend wasteful amounts of energy in the generation of exorbitant amounts of ultra-violet radiation.
Finally, it is to be understood that the preceding description refers merely to a preferred embodiment of the invention, and that variations and modifications will be possible thereto without departing from the spirit and scope of the invention, the ambit of which is to be determined from the following claims.

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Claims (8)

1. An irradiation unit for the sterilization of fluid media, said unit including: an irradiation tube constructed of a material transparent to germicidal radiation and having coated externally thereof or attached thereto a sleeve or layer of a material which is substantially transparent to germicidal ultra-violet radiation but to which impurities contained in said fluid media do not stick, said tube having a source of germicidal ultra-violet radiation disposed internally and substantially centrally thereof; and a housing of a complementary shape to said tube and disposed substantially coaxially therewith, said housing being of a larger dimension than said tube, the arrangement being such that an annular space is provided between said tube and said housing, said annular space providing a flow path for said fluid media, said annular space being in the range of from 15 to 25 mm in width.

2. The irradiation unit as claimed in claim 1, wherein said sleeve or layer is of fluorinated ethylene propylene and said tube is of fused silica or quartz.

3. The unit as claimed in claim 2, wherein said annular space is about 17 mm in width.

4. The unit as claimed in claim 1, wherein said irradiation tube has an internal diameter in the range of from 55 to 65 mm.

5. A sterilizer unit for fluid media, said unit including respective inlet and outlet means for fluid media to be sterilized; and at least one irradiation unit connected to and extending between said inlet and outlet mean , said at least one irradiation unit including an irradiation tube constructed of a material transparent to germicidal radiation and having coated externally thereon or attached thereto a sleeve or layer of a material which is substantially transparent to germicidal ultra-violet radiation but to which impurities contained in said fluid media do not stick, said tube having a source of germidical ultra-violet radiation disposed internally and substantially centrally thereof; and a housing of a complementary shape to said tube and disposed substantially coaxially therewith, said housing being such that an annular space is provided between said tube and said housing, said annular space providing a flow path for said fluid media, said annular space being in the range of from 15 to 25 mm in width.

6. The unit as claimed in claim 5, wherein said sleeve or layer is of fluorinated ethylene propylene and said tube is of fused silica or quartz.

7. The unit as claimed in claim 6, wherein said annular space is about 17 mm in width.

8. The unit as claimed in claim 5, wherein said irradiation tube has an internal diameter in the range of from 55 to 65 mm.