WO1992011057A1

WO1992011057A1 - Systems and methods eradicating contaminants in fluids

Info

Publication number: WO1992011057A1
Application number: PCT/US1991/009708
Authority: WO
Inventors: Ludwig Wolf, Jr.; John T. Foley; William R. Bratten; Michael Stonefield; Gary Kunz
Original assignee: Baxter International Inc.; Quadra Logic Technologies, Inc.
Priority date: 1990-12-20
Filing date: 1991-12-20
Publication date: 1992-07-09
Also published as: EP0517899A4; CA2075640C; CA2075640A1; DE69130902D1; DE69130902T2; US5868695A; JPH05505128A; JP3038445B2; AU9172391A; AU649095B2; EP0517899A1; ZA919934B; EP0517899B1; ES2130168T3

Abstract

A system (10) and method for treating a fluid carrying a contaminant to which a photoactive material has been bound include a treatment device (12) that defines a flow passage (36) with a gap (28). The system and method operate to establish a flow of fluid from the inlet (38) end of the gap (28) to the outlet end (40) of the gap (28). The system and method also channel the flow of fluid in the gap (28) in succession through one or more paths. The system and method established at least two discrete sources of radiation (30) in the flow path (36) at spaced apart locations along the direction of fluid flow. At least one of the radiation sources (30) comprises a photodiode. The system and method further include a control for operating each discrete source of radiation at a selected wavelength within the prescribed range to activate the photoactive material bound to the contaminant. Upon activation, the material eradicates the contaminant. The system and method provide extracorporeal treatment of fluids like blood to quickly and effectively eradicate infection agents at relatively high flow rates.

Description

SYSTEMS AND METHODS ERADICATING CONTAMINANTS IN FLUIDS

Field of the Invention The invention generally relates to the erad¬ ication of contaminants using photodynamic therapy. The invention also generally relates to the processing of whole blood and its components for storage and transfusion. In a more specific sense, the invention relates to the extracorporeal treatment of collected whole blood and its components with photoactive mate¬ rials to eradicate viruses and other pathogenic con¬ taminants. Background of the Invention With the coming of blood component therapy, most whole blood collected today is separated into its clinically proven components for storage and administration. The clinically proven components of whole blood include red blood cells, used to treat chronic anemia; platelet-poor plasma, from which Clot- ting Factor VHI-rich cryoprecipit te can be obtained for the treatment of hemophilia; and concentrations of platelets, used to control thrombocytopenic bleeding. It is well known that blood can carry infec- tious agents like hepatitis-B virus; the human immuno¬ deficiency (AIDS) virus; the Herpes virus; and the influenza virus. To avoid the transmission of these infectious agents during blood transfusions, donors of blood are routinely screened and also undergo serolog- ic testing to detect the presence of these agents. Still, it is difficult to always assure that these infectious agents are detected.

The use of photodynamic therapy has been suggested as a way to eradicate infectious agents from collected blood and its components prior to storage and transfusion. See Matthews et al, "Photodynamic Therapy of Viral Contaminants With Potential for Blood Bank Applications," Transfusion. 28(1), pp. 81-83 (1988) . Various extracorporeal systems have been pro- posed that use photodynamic therapy to treat blood prior to storage and transfusion. See, for example, Edelson U.S. Patents 4,613,322 and 4,684,521; Troutner et al U.S. Patent 4,708,715; Wiesehahn et al U.S. Pat¬ ent 4,727,027; Sieber U.S. Patents 4,775,625 and 4,915,683; and Judy et al U.S. Patent 4,878,891.

To date, there has been a general lack of success in economically adapting the benefits of pho¬ todynamic therapy to the demands of the blood banking industry. The extracorporeal systems proposed to date have not been able to provide acceptable levels of eradication at the relatively high flow rates required to economically process therapeutic units of blood components.

For this and other reasons, the promise of photodynamic therapy in treating the nation's banked blood supply has gone largely unfulfilled.

Summary of the Invention

The inventors have discovered that systems and methods can be provided that accommodate relative¬ ly high processing flow rates and yet achieve an ac¬ ceptably high rate of contaminant eradication through photodynamic therapy. The invention provides extracorporeal systems and methods that quickly and effectively eradicate infectious agents from fluids like blood by flowing the fluids with photoactive ma¬ terial added rapidly past a sequence of discrete radi¬ ation sources.

One aspect of the invention provides a sys- tern for treating a fluid carrying a contaminant to which a photoactive material has been bound. The sys¬ tem directs fluid through a treatment chamber in a predetermined flow path. The system establishes at least two discrete sources of radiation in the flow path at spaced apart locations along the direction of fluid flow. Each discrete source is a self-contained emitter of radiation that establishes its own zone of radiation. At least one of these discrete radiation sources comprises a photodiode. The system operates each discrete source of radiation at a selected wave¬ length within the prescribed range to activate the photoactive material bound to the contaminant.

According to another aspect of the inven¬ tion, the system operates to establish a flow of fluid through the treatment chamber in which the fluid is channelled in succession through at least two differ¬ ent flow paths.

According to this aspect of the invention, the system establishes discrete sources of radiation along both flow paths. The system places at least two of these discrete sources of radiation in the first path at spaced apart locations along the direction of fluid flow. The system also places at least two addi¬ tional discrete sources of radiation in the second path at spaced apart locations along the direction of fluid flow.

The system further includes a control ele¬ ment for operating each discrete source of radiation at a selected wavelength within a range that activates the photoactive material bound to the contaminant. Upon activation, the material eradicates the contami¬ nant.

By channeling the fluid through several dis¬ crete zones of radiation at a relatively high flow rate, the invention provides a surprisingly effective cumulative effect in terms of overall degree of con¬ taminant eradication over a relatively short period of time.

By using discrete sources of radiation, the system also offers the flexibility to meet the needs of differing processing techniques. For example, in one arrangement, the control element operates the dis¬ crete sources of radiation at substantially the same wavelength. In another arrangement, the control ele- ment operates at least two of the discrete sources of radiation at different wavelengths.

In a preferred embodiment, at least two dis¬ crete sources of radiation are positioned along oppo¬ site sides of both the first and second flow paths. In this preferred arrangement, there are at least three discrete sources of light positioned along each flow path. Two of the discrete sources are positioned at spaced apart locations along one side of the flow path in the direction of fluid flow, while the other discrete source is positioned on an opposite side of the flow path.

In a preferred embodiment, each discrete source of radiation comprises a photodiode. Each dis¬ crete source can thereby be controlled to emit a rela- tively narrow band of radiation having a relatively precise wavelength. The fluid passes rapidly through these well defined bands of radiation while being treated.

By using photodiodes as sources of radia- tion, relatively low voltages can be used. The low voltages reduce the amount of heat generated by the system, thereby preserving the viability of the fluid during treatment.

Another aspect of the invention provides a method for treating a fluid carrying a contaminant to which a photoactive material has been bound. Accord¬ ing to this aspect of the invention, fluid is conveyed through a gap while being channelled through a prede¬ termined flow path. As it transits the flow path, the fluid is exposed to at least two discrete sources of radiation that are at spaced apart locations along the direction of fluid flow. At least one, and preferably all, of the discrete sources comprises a photodiode.

In another arrangement, fluid is conveyed through a gap while being channelled within the gap in succession through two different flow paths. As it transits the first flow path, the fluid is exposed to at least two discrete sources of radiation that are at spaced apart locations along the direction of fluid flow. As it next transits the second flow path, the fluid is further exposed to at least two additional discrete sources of radiation that are also at spaced apart locations along the direction of fluid flow. Each discrete source of radiation is operated at a selected wavelength within the prescribed range to activate the photoactive material bound to the contam¬ inant as the fluid flows in succession through the two paths.

The systems and methods that embody the fea- tures of the invention are applicable for use in envi¬ ronments where sterility and biologically closed sys¬ tem integrity must be maintained during processing. The systems and methods therefore readily lend them¬ selves to blood processing applications. Other features and advantages of the inven¬ tion will be pointed out in, or will be apparent from, the drawings, specification and claims that follow.

Description of the Drawings Fig. 1 is a perspective view, with portions broken away, of a system for treating a fluid carrying a contaminant with the treatment chamber closed as it is in use;

Fig. 2 is a perspective view of the system shown in Fig. 1, with the treatment chamber opened to receive the irradiation section of the associated flu¬ id flow path prior to use;

Fig. 3 is a section view of the closed treatment chamber taken generally along line 3-3 in Fig. 1;

Fig. 4 is a view of the irradiation section of the fluid path in place within the treatment cham¬ ber, taken generally along line 4-4 in Fig. 3;

Fig. 5 is a schematic view of the control element that operates the discrete sources of radia¬ tion located within the treatment chamber;

Fig. 6 is a perspective view of the compo¬ nent parts of the fluid flow path associated with the system shown in Fig. 1, with the component parts dis- assembled prior to use; Fig. 7 is an enlarged view of a portion of the treatment chamber showing one arrangement of the discrete radiation sources along the irradiation sec¬ tion of the flow path; and Fig. 8 is an enlarged view of a portion of the treatment chamber showing another arrangement of the discrete radiation sources along the irradiation section of the flow path.

The invention is not limited to the details of the construction and the arrangements of parts set forth in the following description or shown in the drawings. The invention can be practiced in other em¬ bodiments and in various other ways. The terminology and phrases are used for description and should not be regarded as limiting.

Description of the Preferred Embodiments

Fig. 1 shows a system 10 for treating a flu¬ id carrying a contaminant that embodies the features of the invention. The system 10 includes a treatment device 12 that receives the fluid from a source con¬ tainer 14 and conveys the fluid after treatment to a collection container 16.

The fluid to be treated can vary. In the illustrated embodiment, the fluid comprises a compo¬ nent of whole human blood that is intended to be stored for transfusion. More specifically, the fluid consists of red blood cells suspended in plasma. Typ¬ ically, a quantity of white blood cells is also pres- ent with the red blood cells. The fluid can also in¬ clude an anticoagulant and, optionally, a storage me¬ dium for the blood component. Alternatively, the flu¬ id can consist of platelets suspended in plasma.

In the illustrated embodiment, the conta i- nant comprises a pathogenic virus typically carried in the blood. For example, the contaminant can consist of the hepatitis-B virus; the human immunodeficiency virus; the Herpes virus; or the influenza virus.

The fluid in the source container 14 in- eludes a photoactive material that has an affinity for the contaminant carried by the fluid. The photoactive material is added to the blood contained in the source container 14 after the blood is collected from a do¬ nor. The step of adding the photoactive material will be described in greater detail later.

Due to its affinity for the contaminant, the photoactive material becomes bound to the contaminant within the source container 14. The photoactive mate¬ rial is of a type that becomes active by exposure to radiation within a prescribed wavelength range. When activated by radiation, the material eradicates the contaminant.

Various types of photoactive materials can be used. In the illustrated embodiment, the photoactive compound comprises a family of light-acti¬ vated drugs derived from benzoporphyrin. These deriv¬ atives are commonly referred as BPD's. BPD's are com¬ mercially available from Quadra Logic Technologies, Inc., Vancouver B.C., Canada. BPD's, like other types of hematoporphyrin materials, have an affinity for the cell walls of many viral organisms that are carried in blood. They therefore bind or attach themselves to the biological cell wall of these organisms. When exposed to radia- tion, BPD's undergo an energy transfer process with oxygen, forming a singlet oxygen. When the singlet oxygen oxidizes, it kills the biological cells to which it has attached. BPD's are described in greater detail in Judy et al U.S. Patent 4,878,891. According to the invention, the contaminant to which the BPD's is attached is exposed to the radi¬ ation in a predetermined manner as the fluid passes through the treatment device.

As Figs. 2 and 3 best show, the treatment device 12 includes body 18 that defines a treatment chamber 20. Two platens 22 and 24 on the body 18 form the treatment chamber 20. The first platen 22 is at¬ tached on the mid-portion of the body 18. The second platen 24 is carried on a door 26 that moves on the body 18 between an opened position (as Fig. 2 shows) and a closed position (as Figs. 1 and 3 show) .

As best shown in Fig. 3, when the door 26 is in its closed position, the first and second platens 22 and 24 face each other in a spaced apart relation- ship, thereby forming the confines of the treatment chamber 20. The space between the two platens 22 and 24 forms a gap 28 of a predetermined size through which fluid traverses the chamber 20. In the illus¬ trated embodiment, the gap 28 is about 0.125 inch in width.

The treatment device 12 further includes a plurality of radiation sources (generally designated by the numeral 30) positioned along the gap 28. Fluid traversing the chamber 20 is thereby exposed to the radiation sources 30. In the illustrated embodiment, each platen 22 and 24 carries a number of radiation sources 30.

According to the invention, each radiation source 30 is "discrete," meaning that each source 30 is a self-contained emitter of radiation that estab¬ lishes its own zone of radiation. Being discrete, each source 30 also is capable of operation to emit a radiation independent of the emission of radiation by the other sources 30. In the illustrated and preferred embodiment, each radiation source 30 takes the form of a photodiode. Various types of photodiodes can be se¬ lected, depending upon the fluid to be treated and the characteristics of the photoactive material used. In the illustrated embodiment, where the treated fluid contains red blood cells, all the photodiodes use transparent substrate aluminum gallium arsenide mate¬ rial (TS AlGaAs) . Photodiodes of this type are com¬ mercially available from Hewlett-Packard Co. (Product Designation "HIMP-8150 15 Candella") .

These photodiodes emit a band of radiation at a relatively narrow viewing angle of about 4 de¬ grees. The prescribed band of radiation has a rela¬ tively precise wavelength displaying a red color hav- ing a peak wavelength of about 690 nm. Red blood cells are essentially transparent to radiation at this wavelength. The BPD's, however, are not. The BPD's absorb radiation in this wavelength to become activat¬ ed. If the fluid to be treated contains platelets, the photodiode would be selected to have a wavelength displaying a blue color having peak wave¬ length of about 425 nm. Platelets are essentially transparent to radiation at this wavelength. In the illustrated embodiment, each discrete photodiode radiation source has a minimum intensity of about 8.0 cd (at 20 mA) , a maximum intensity of about 36.0 cd (at 20 mA) , and a typical intensity of about 15.0 cd (at 20 mA) . Each photodiode operates at a low maximum forward voltage of about 2.4 V.

In the illustrated embodiment (as Fig. 4 best shows) , the discrete radiation sources 30 are arranged in banks or arrays 32 on each platen 22 and

24. As Fig. 4 shows, each bank or array 32 includes a plurality of discrete sources 30 arranged in alter- nating rows of four and five each (shown horizontally in Fig. 4) . The alternating number in each row stag¬ gers the spacing of the sources 30 between adjacent rows. In the illustrated embodiment, each array 32 includes about 90 discrete radiation sources 30.

In the illustrated arrangement (as Fig. 2 shows) , four arrays 32 are carried on the body 18 be¬ hind the first platen 22 (comprising about 360 dis¬ crete sources of radiation) . Four additional arrays 32 are carried on the door 26 behind the second platen 24. Each platen 22 and 24 is made of a clear glass or plastic material that is transparent to the radiation emitted by the sources.

In an alternative arrangement (not shown) , only one platen 22 or 24 would carry the radiation sources 30. In this arrangement, the other platen would preferably carry a surface that reflects the radiation emitted by the sources 30 back into the gap 28. For example, the surface of the other platen could be plated with gold or like highly reflective material to reflect the wavelengths of radiation de¬ scribed above.

The treatment device includes a control ele¬ ment 34 for operating each discrete radiation source 30 (see Fig. 5) . As Fig. 5 shows, the radiation sources 30 are electrically interconnected in parallel banks 31, with each bank 31 containing five sources 30 in series connection.

As Fig. 1 shows, the fluid passes through the treatment chamber 20 from the source container 14 to the collection container 16 following a predetermined flow path 36 that embodies the features of the invention. The flow path 36 includes an inlet section 38 that conveys fluid from the source contain- er 14 into the treatment chamber 20. The flow path 36 also includes an outlet section 40 that conveys fluid from the treatment chamber 20 to the collection con¬ tainer 16.

The flow path 36 further includes an inter- mediate irradiation section 42 . One end of the irra¬ diation section 42 communicates with the inlet sec¬ tion 38. Another end of the irradiation section 42 communicates with the outlet section 40.

In use (as Fig. 1 shows) , the inlet and out- let sections 38 and 40 are located outside the treat¬ ment chamber 20, while the irradiation section 42 is located within the treatment chamber 20, sandwiched between the two platens. The maximum size of the flow path 36 through the irradiation section 42 is defined by the gap 28 formed between the two platens 22 and 24.

The irradiation section 42 is made of a ma¬ terial that is transparent to the radiation emitted by the sources. Fluid passing through the irradiation section 42 is thereby exposed to radiation.

According to the invention, the irradiation section 42 defines at least two channels (generally designated by the letter C in Fig. 4) . The channels direct fluid in different successive paths past the radiation sources. In the illustrated embodiment, the irradiation section 42 includes eighteen (18) succes¬ sive channels, which are numbered Cl to C18 according¬ ly. As Fig. 4 shows, the channels Cl to C18 are aligned in a prescribed fashion relative to the radia- tion sources 30 to achieve the benefits of the inven¬ tion.

More particularly, the channels Cl to C18 are aligned with respect to the radiation sources 30 so that, as the fluid passes through each channel, it is exposed to at least two discrete radiation sources 30. In the illustrated embodiment, the fluid is ex¬ posed to at least eighteen discrete sources of radia¬ tion as it traverses each channel. For illustration purposes, the sources 30 associated with the first channel Cl are numbered SI to S18 in Fig. 4.

The channels Cl to C18 are further aligned so that, as the fluid passes through the next succes¬ sive channel, it is exposed to different discrete sources of radiation. For example, the eighteen radi- ation sources SI to S18 in the first channel Cl are different than the radiation sources 30 associated with the next successive channel C2. In addition, there may be some overlap between sources 30 between adjacent channels. Therefore, according to the invention, as the fluid passes through the irradiation section 42, it is not repeatedly exposed to the same source of radiation. Instead, it is exposed to numerous differ¬ ent sources of radiation, each one discrete unto it- self. In the illustrated embodiment, the fluid is ul¬ timately exposed at least once to about 360 discrete sources of radiation as it traverses the irradiation section 42.

In the illustrated embodiment, the source container 14, the collection container 16, and the irradiation section 42 each takes the form of a bag (respectively 44, 46, and 48) made of a flexible inert plastic material, like plasticized medical grade poly- vinyl chloride. Each bag 44, 46, and 48 has heat sealed peripheral edges 50 to form a sealed interior area.

The irradiation section bag 48 further in¬ cludes a series of interior heat sealed regions 52 that divide the interior area into the eighteen inter- connected flow passages. The flow passage comprise the channels Cl to C18, as just described.

The irradiation section bag 48 is attached by pins 54 (see Figs. 2 and 4) to the first platen 22. With the door 26 closed, the channels Cl to C18 formed in the bag 48 direct fluid back and forth in a serpen¬ tine path past the radiation sources 30. As before described, the fluid is exposed to several discrete radiation sources 30 in each channel of this serpen¬ tine path. And, as also before described, in each successive channel, the fluid is further exposed to several more discrete radiation sources different than those encountered in the previous channel.

In the illustrated embodiment (see Fig. 6) , the inlet section 38 of the flow path 36 includes a length of flexible inert plastic tubing 56 that joins the inlet end of the irradiation section bag 48. The tubing 56 includes a conventional inline filter 58 for removing the white blood cells from the fluid prior to entering the treatment chamber 20. The filtration me- dium used (not shown) can include cotton wool, cellu¬ lose acetate, or another synthetic fiber like polyes¬ ter.

The tubing 58 terminates in a first connec¬ tion device 60. The inlet section 38 further includes a length of flexible inert plastic tubing 62 that joins the source container 14. This tubing 62 includes a second connection device 64 that mates with the first connection device 60 to join the source container 14 to the inlet end of the irradiation section bag 48.

While various known connection devices may be used, in the illustrated embodiment, the devices 60 and 64 are preferable sterile connection devices like those shown in Granzow et al U.S. Patents 4,157,723 and 4,265,280, which are incorporated herein by refer- ence.

In use, a peristaltic pump 66 (see Fig. 1) conveys fluid through the fluid path 36 at a predeter¬ mined flow rate. The flow rate of the pump 66 will of course vary according to the volume of fluid that is to be treated and the time limitations imposed. In the context of illustrated embodiment, it is desirable to be able to treat 300 ml of blood components in about 30 minutes. Therefore, a preferred flow rate is about 10 ml/min.

The outlet section 40 of the flow path 36 includes a length of flexible inert plastic tubing 68 that joins the outlet end of the irradiation section bag 48. The other end of the tubing 68 joins the col- lection container 16. In an alternative arrangement (not shown) , the tubing could be normally separated into two lengths, like tubings 56 and 62, each having a (preferably sterile) connection device to join the collection container 16 to the outlet end of the irra- diation section 42 prior to use.

In the illustrated embodiment (see Fig. 6) , an auxiliary container 70 holds a solution containing the photoactive material. The auxiliary container 70 also includes a length of tubing 72 that carries with a third (preferably sterile) connection device 74. In this arrangement, the source container 14 also in¬ cludes another length of tubing 76 that carries a fourth (preferably sterile) connection device 78. By joining the third and fourth connection devices 74 and 78, the photoactive material can be conveyed from the auxiliary container 70 into the source container 14 for mixing with the fluid to be treated. The joined tubings 72 and 76 form a closed, internally sterile path for introducing the photoactive materially into the source container 14. Once the photoactive materi- al has been transferred, the tubing 76 can be heat sealed closed upstream of the joined connection devic¬ es 74 and 78 (as Fig. 1 shows) , and the auxiliary con¬ tainer 70 (with joined connection devices 74 and 78) removed.

By using the sterile connection devices 60,

64, 74, and 78, the formed flow path 36 comprises a closed, internally sterile path for conveying fluid from the source container 14, through the treatment chamber 20, and into the collection container 16.

In the treatment chamber 20, the fluid is exposed to a plurality of discrete sources 30 of radi¬ ation in the manner previously described. Each dis¬ crete radiation source 30 is operated by the control element 34 at a selected wavelength within the pre¬ scribed range to activate the photoactive material bound to the contaminant as the fluid flows in succes¬ sion through the channels Cl to C18 in the irradiation section 42. The photoactive material is activated by exposure to the radiation to eradicate the contami¬ nant. The fluid containing the eradicated contaminant is collected in the container 16 for storage and sub¬ sequent transfusion.

The system 10 provides great flexibility in treating the fluid. Because each radiation source 30 is discrete, the control element 34 can be configured to operate two or more of the radiation sources at a different wavelength. Alternatively, the control ele¬ ment 34 can be configured to operate two or more of the discrete sources 30 of radiation at substantially the same wavelength.

Furthermore, the zone of radiation emitted by each discrete source 30 can be varied, as can the intensity of radiation of each source 30. In the illustrated embodiment, where each platen 22 and 24 carries a number of radiation sourc¬ es, the discrete sources 30 of radiation are posi¬ tioned along opposite sides of the gap 28 through which the fluid flows. As Fig. 7 shows, the radiation sources 30 on the platens 22 and 24 can be arranged to be diametri¬ cally opposite to each other. Fig. 7 shows four pairs of diametrically opposite sources, designated SI to S8. In this arrangement, the zones of radiation (des- ignated Zl to Z8, corresponding with their sources SI to S8) emitted by the diametrically opposite sources SI to S8 directly overlap. The amount of radiation present in the converged zone CZ between each source is thereby intensified. Fig. 8 shows an alterative arrangement. In this arrangement, the radiation sources SI to S6 on the platens do not directly face one other. Instead, the sources SI to S6 are staggered. In this arrange¬ ment, the zones of radiation Zl to Z6 emitted by the staggered sources do not directly overlap. Instead, they provide overlapping side regions ZS of intensi¬ fied radiation between each discrete source SI to S6. The following example demonstrates the ef¬ fectiveness of the system 10 that embodies the fea- tures of the invention to process fluid undergoing photoactive therapy at relatively high flow rates.

Example:

Human red blood cell concentrates (at a he- matocrit of about 55%) containing HSV-I virus were treated in accordance with the invention. Before, treatment, BPD was added at a concentration of 4 g/ml. The red blood cell concentrate with the BPD added was pumped through a multi-channel treatment chamber at a flow rate of 5 ml/min. The treatment chamber was radiated from each side by a bank of 360 LED's at a wavelength of about 690 nm. The viral load was reduced during the treatment by two orders of mag- nitude (99%) from 10 6 units/ml to 104 units/ml.

The features and advantages of the invention are set forth in the following claims.

Claims

We Claim:

1. A system for treating a fluid carrying a contaminant to which a photoactive material has been bound, the material being activated by exposure to radiation within a prescribed wavelength range to eradicate the contaminant, the system comprising means for establishing a flow gap having an inlet end and an outlet end, means for establishing a flow of fluid from the inlet end of the gap to the outlet end of the gap, means for channeling the fluid within the gap in a predetermined flow path, means for establishing at least two discrete sources of radiation in the flow path at spaced apart locations along the direction of fluid flow, at least one of the discrete sources of radiation comprising a photodiode, and means for operating each discrete source of radiation at a selected wavelength within the pre¬ scribed range to activate the photoactive material bound to the contaminant.

2. A system according to claim 1 wherein at least two of the discrete sources of radiation are operated at a different wavelength.

3. A system according to claim 1 wherein at least two of the discrete sources of radiation are operated at substantially the same wavelength.

4. A system according to claim 1 wherein each discrete source of radiation comprises a photodiode.

5. A system according to claim 1 wherein the at least two discrete sources of light are positioned along opposite sides of the first flow path.

6. A system according to claim 1 wherein there are at least three discrete sources of light positioned along the flow path, two of the discrete sources being positioned at spaced apart locations along one side of the flow path in the direction of fluid flow and one of the discrete sourc¬ es being positioned on an opposite side of the flow path.

7. A system for treating a fluid carrying a contaminant to which a photoactive material has been bound, the material being activated by exposure to radiation within a prescribed wavelength range to eradicate the contaminant, the system comprising means for establishing a gap having an inlet end and an outlet end, means for establishing a flow of fluid from the inlet end of the gap to the outlet end of the gap, means for channeling the fluid within the gap in succession through at least two different flow paths, means for establishing at least two discrete sources of radiation in the first path at spaced apart locations along the direction of fluid flow, means for establishing at least two addi¬ tional discrete sources of radiation in the second path at spaced apart locations along the direction of fluid flow, and means for operating each discrete source of radiation at a selected wavelength within the pre¬ scribed range to activate the photoactive material bound to the contaminant.

8. A system according to claim 7 wherein at least two of the discrete sources of radiation are operated at a different wavelength.

9. A system according to claim 7 wherein at least two of the discrete sources of radiation are operated at substantially the same wavelength.

10. A system according to claim 7 wherein at least one of the discrete source of radiation comprises a photodiode.

11. A system according to claim 7 wherein every discrete source of radiation comprises a photodiode.

12. A system according to claim 7 wherein the at least two discrete sources of light are positioned along opposite sides of the first flow path.

13. A system according to claim 7 wherein the at least two additional discrete sources of light are positioned along opposite sides of the second flow path.

14. A system according to claim 7 wherein there are at least three discrete sources of light positioned along at least one of the first and second flow paths, two of the discrete sources being positioned at spaced apart locations along one side of the flow path in the direction of fluid flow and one of the discrete sources being posi¬ tioned on an opposite side of the flow path.

15. A method for treating a fluid carrying a contaminant to which a photoactive material has been bound, the material being activated by exposure to radiation within a prescribed wavelength range to eradicate the contaminant, the method comprising the steps of conveying the fluid through a gap while channeling the fluid within the gap through a predetermined flow path, exposing the fluid, as it transits the flow path, to at least two discrete sources of radiation that are at spaced apart locations along the direction of fluid flow, at least one of the discrete sources comprising a photodiode, operating each discrete source of radiation at a selected wavelength within the prescribed range to activate the photoactive material bound to the con¬ taminant as the fluid flows through the paths.

16. A method for treating a fluid carrying a contaminant to which a photoactive material has been bound, the material being activated by exposure to radiation within a prescribed wavelength range to eradicate the contaminant, the method comprising the steps of conveying the fluid through a gap while channeling the fluid within the gap in succession through at least two different flow paths, exposing the fluid, as it transits the first flow path, to at least two discrete sources of radia¬ tion that are at spaced apart locations along the di¬ rection of fluid flow, exposing the fluid, as it transits the sec- ond flow path, to at least two additional discrete sources of radiation that are at spaced apart loca¬ tions along the direction of fluid flow, and operating each discrete source of radiation at a selected wavelength within the prescribed range to activate the photoactive material bound to the con¬ taminant as the fluid flows in succession through the two paths.