CA2086125A1 - Method and apparatus for rf heating of heterogeneous materials - Google Patents

Abstract

Infectious medical materials are rendered harmless by heating heterogeneous medical materials (2) having wet and dry portions with a radio-frequency electric field (5). The medical materials (2) may be comminuted (4) prior to heating. The medical materials (2) are exposed to the radio-frequency electric field (5) in order to heat the medical materials. The medical materials (2) may include sorted medical or veterinary waste after heat treatment may be recycled (7).

Description

W092/00764 2 ~ 8 ~12 5 ~'Cr/US~1/04703 METHOD AND APPARATUS FOR RF HEATING
OF ~ETEROGENEOUS ~ATERIALS
BACKGROUND OF THE INVENTIOM
The pr~sent in~ntion relates generally to a method of heating haterogeneous materials and more parti~ularly to a method and apparatus for disinf~cting medical materials by expo~ing the materials to radio-frequency waves. The term medical materials encompasses medical waste, veterina~y waste, and medical products.
The problems with current medical waste handling methods, like the problems oP solid waste disposal in general, are becoming increasingly acute. Solid waste is primarily disposed of by burning or by burial in landfill. Both of the methods have severe disadvantages. Burning of solid waste liberates waste particles and fumes which contribute to acid rain and other pollution o~ the atmosphere. Burying the waste re ults in possible leaks of toXiG chemicals into the surrounding earth and contamination of ground water supplies. Although increasing amounts of solid waste are being r~cycled, which alieviates the probl~ms of incineration a~d burial, pre~ently available recycling methods do not provide a complete solution to the disposal problem.
Waste disposal is of even more urgent concern when the waste comprise~ possibly inf~ctious medical waste. Such i~f~ctious ~edical waste is a by-product of veterinary and m~dical careO For exa~ple, regulated medical waste consists of: (1) cultures and stocks of in~ectious agents and asæociated biological materialc;

(2) pathological wastes; (3) hu~an blood and blood products: (4) contaminated sharps, including needles, syringes, b].ades, scalpels, and broken gla~s; ~5) animal , ., . - . . .
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waske; (6) isolation waste, including gloves and other disposable products used in the care of patients with serious infections; and (7~ unused sharps. These wastes can generally be divided between (a) general medical waste, including cultures and stocks of infectious agents, associated biologicals, pathological waste, and human blood and blood product~;: (b) veterinary waste, including animal waste; and (c:) waste that is predominately plastic, such as the contaminated and unus~d sharps and isolation waste. The predominately plastic waste also includes ~etal as well. Hospitals typically segregate waste by types. Contaminated sharps and isolation waste, however, are of special concern as they may carry highly dang~rous pathogens ~uch as AIDS
virus or hepatitis virus. Sharps in particular have caused widespread public concern when observed washed up on beaches or in public areas.
Hospitals an other generators of medical and veterinary waste employ three ~ethods of waste handling:
(a) on-site incineration of the waste, (b~ on-site steam autoclaving of the waste followed by later shipment to a landfill for burying, and (c) collection of the waste by a licensed waste hauler with no on-site processing.
Many hospital incinerators ~ eYen those located predominately in urban areas, emit pollutants at a relatively high rate. The Environ~ental Protection Agency has identified harmful substances in the emissions of such hospital incinerators. They lnclude metals such as arsenic, cadmium and lead, organic compounds, such as ethylene, dioxins and furans, acid gases and carbon ~onoxidP as well as soot, viru5es and pathogens.
Emissisns from these incinerators may be a more significant public health hazard than improper dumping ~Steven K. Hall, "Infectious Waste ~anagement: A

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W092/0~764 2 0 8 ~ 1 2 .~ pCT/~1~91/04703 Multifaceted Problem," Pollution Engineering, 74-78 (Aug.
1989)~-Although steam autoclaving may be used tosterilize waste be oxe ~urther processing, it is expensi~e and time consuming. Heat denatures the proteins and ~icroorganisms causing protein inactivation and cell death in a short time. Temperature monitoring devices such as thermocouples, and biological indicators, such as heat resistant ~acilly3L~S~____hermophilus spores, may be used to assure effective sterilizatio~.
U.S. Patent No. 2,731,208 to Dodd teaches a staam sterilizing apparatus for dispo ing of contaminated waste which incorporates shredding the waste (~'including paper containers æuch as used sputum cups," col. 1, lines 28-29). Dodd teaches blowing steam into a container full of waste and processing only limited t~pes o~ ite~s. The Dodd system ha~ th~ disadvantage o~ depositing the shredded final ~ixture into a sewer, which would cause further environmental problems.
Whether or not the hospital ~irst autoclaves its medical wastes; includiny brok2n needles and glass, the waste is then turned over to a licen~ed waste hauler for transport to a landfill or other deposi~ory. U.S. Patent No. 3,958,936 to Knight discloses compaction o~ hospital waste for more efficient landfill disposal.
Specifically, th~ reference teaches the application of heat in the range of about 204- C. to 316- C. to hospital and other waste to ~elt tha plastic and convert it into a hard compact block for safer disposal in landfills. The waste is disinfected by the high temperatures, and sharps, such a~ needles, become embedded in the plastic where they are a reduced mechanical hazard. However, this method suffers ~rom tha disadvantage of requiring 3S relatively hiyh temperatures necessitating large energy .
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expenditures and landfill disposal. Metropolitan landfills are becoming filled, and unauthorized dumping is a problem.
A further area of concerr. is the sterilization of medical products prior to use. By medical product is meant any product which must be sterilized prior to use in health care. Thi~ is exem~pli~ied but not limited to needles, syringes, suturss, b,andages, scalpels, gloves, drapes, and other disposal itlems. Many reusable items also must be provided in ster.ile form. Widespread current sterilization methods include the use of autoclaving, ethylene oxide, and ionizing radiation such as gamma radiation. ~he heat and hu~idity o~ autoclaving are guite damaging to many diæposable metal products.
Ethylene oxide and ionizing radiation are preferred commercially in those cases~
In order to sterilize ~edical products, poisonous ethylene oxide gas may be used in a closed chamber containing the product~ to be 6teriliz~d. For effective sterilization, not only must the ethylene oxide concentration be controlled carefully, but the temperature,lhumidity, and porosity of the sterilizer load also must be carefully regulated. Ethylene oxide is relatively slow to dissipate from plastics and its use may require that medical products be stored until the ethylene oxide concentration decrease~ to a sa~e level.
Ethylene oxide also ~ust be carefully vented to the at~osphere sub~equent to the sterilization cycle in order to avoid poisoning operators o~ the sterilization apparatus.
Ionizing radiation, such as gam~a radiation, may be used to ~terilize medical products within t~eir packaging; however, it must be administered at such high doses that ~lany plastics become yellow and brittle due to .
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: -- , . :' 2 ~ 8 ~ 1 2 5 P~T/US')I/04703 the gamma rays having altered the stnlcture of the polymers of which they are made. For example, U.S.
Patent No. 3,940,325 to Hirao teaches methods for adjusting the formulas of plastics for medical syringes to avoid yellowing and cracking due to exposure to sterilizing gamma radiation. Other substances may also be damaged by exposure to ga~a radiation. Such ionizing radiation sterilizes because its hi~h energy photon~
damage and thereby inactivate the DNA of organisms such as bact~ria and viruses. As a result of the inactivation o~ the DNA, cells lose their ability to reproduce and thereby cause infeckions. On a large scale industrial basis, ionizing radiation, especially gamma radiation from cobalt 60, has been used to sterilize medical products prior to their use in patients. However, the radiation levels necessary to sterilize ~ay also damagP
the product being ~terilized.
Other meth~ds have been sugge~ted for ~terilization o~ medical products. For instance, U.S.
Patent No. 3,617,178 to Clouston teaches a method of improving sterilization efficiency by increasing hydrostatic pres~ure. Elevated hy~rostatic pressure causes sterilization resistant bacterial spores to gexminate, or begin to grow. However, it has no ef~ect on viruse~. Bacterial germi~ation, which converts the bacteria ~rom thair ~nviro~mentally resistant ~pore form, makes the bacteria more sen~itive to radiation, so that lower doses may be e~ployed. Clouston ~urther teaches optimizing the hydrostatic pressure effect by adjusting the temperature up to 80~ C. According to Clou~ton, elevated pr~ssure in heated fluid or moist gas is essential to the method. ~levated temperature alone has a negligible effect. Furthermore, the pressure, heat, or moisture tre!atment taught by Clouston is intended to -- - ' - : :
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W092/00764 P~T/US~1/0~7~
2 ~ 8 6 1 2 3 cause bacterial spores to germinate thereby rendering them more vulnerable to sterilization techniques, not to sterilize or inactivate microorganisms.
In contrast, U.S. Patent Nos. 4,620,908 to Van Duzer and 3,704,089 to Stehlik teach prefreezing injectable proteins and surgical adhesive prior to irradiation with gamma radiation from cobalt 60 for aseptic manufacture of those materials. U.S. Patent Mo.

3,602,712 to Mann discloses an apparatus for gamma irradiation and sterilization of sewage and industrial waste.
Besides ga~ma radiation, other types o~
electromagnetic radiation have been considered as potential sterilants in known systPms. Hicrow2ves are increasingly being investigated for rapid sterilization of individual msdical devices as well as shredded medical waste. Recently, an experiment showed that metallic instruments could be sterilized in only 30 seconds in a microwave oven (New Xork Times, "Science Watch ~icrowave Sterilizer is Developed, H June 20, 1989). That particular method, however, suffers from the drawback that only a few such metallic instruments can be treated at a particular ti~e. It is not particularly applicable for treatment of medical waste in ~ulk, and in particular for treatment o~ ~edical waste which has been bagged.
~ nited Kingdom Patent No. 1 406 789 to Boucher discloses a micro~ave system ~or the surface sterilization of reusable laboratory, medical, and dental instrument~ in a moist atmosphere at ~ lower temperature than those presently l~sed and in a shorter time. The system is in$ended to render aseptic reusable instruments for medical use and generates electromagnetic energy having frequencies between lO0 megahertz ~nd 23000 megahertz. Boucher emphasizes that "his invention deals - - - . . . .
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: . ' , ' . : ' ' ~092/0076~ 2 a ~ ~ 1 2 ~ PCT/~S~I/0~703 exclusiv~ly with surface sterilizatis~n" and that he "does not int~nd to cover such s~ecial cases" as "'in-depth' sterilization" (page 1, lines 58-67). Boucher teaches that only through a combinati.on of proper humidification with the thermal and nonthermal effects of microwave radiation can reproducible and satisfactory results be obtained with a wide ~ariety of species, including thermoresistant spores" (page! 1, lines 77-83). Boucher teaches the placement o~ the object to be sterilized in a gas-tight container wikh a ~ource of water vapor.
Soviet Union Patent No. 1,123,705 also discloses a method of sterilizing ~edic:al instruments for reuse by UHF tre~tment. For injection needles it discloses a ~inal temperature of 160- C. to 470 C. and for acupuncture needles it discloses a Pinal temperature of 160 C. to 270- C.
Systems are also known ~or treatment o~
disposable medical waste utilizing microwaves. This system first shred~ the waste, sprays the shredded waste with water, and passes the wet shredded waste through a microwav~ chamber designed to raise the temperature of the wet shredd~d waste to 205- C. to sterilize it. After the sterilization stap, the system compresses the sterilized shredded waste and packages it for shipment to landfills or incinerators (The Wall $treet Journal, p.
B-3, Apr. 10, 19B3). O~e potential proble~ with this system is that shredding before sterilization could release infectious particl~s to the environment and may thus spread conta~ion. Another problem is the ultimate disposal of the waste; it persists in landfills or may pollute th~ air when incinerated.
Also of interest is a ~ethod and apparatus for using miorowave frequency electroma~netic ~ields to h~at medical waste to disinfect it. I'Medical Waste Treatment - -, - : -. . . .. .
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The system includes equipment for receiving the medical waste, shredding it into particle si~es of l to l~ inch linear dimension, and applying steam to the shredded waste to increase its moisture content, as well as to inactivate certain of the mic:roorganisms thereon. The waste is then carried to a microwave treatment area where microwave energy heats the waste to 203~ C. for a l selected amount o~ time. A holding area may provide heat sealing. The wasta is then recirculated to the steaming station where steam is again applied to inactivate further microorganis~s which may etill be activ~ in the waste which is ~hredded and disinfected, disposed in a dumpster for placemant in a landfill. It may be appreciated, however, that volumetric heating cannot take place in such a microwave system that the waste has to be scattered in a relati~ely thin layer on a conveyor belt for treatment by the ~icrowave radiation as the microwave ra~iation doos not adequately penetrate the material. In addition, tha material is not enclosed so that there is no substantial transfer of moi~ture ~rom wet materials to dry materials to aid in the heating within the enclosed system.
U.S. Patent No. 3,547,577 to Lovercheck discloses a machine ~or treating garbage by shredding, compressing the shredded garbage into bri~uettes, and sterilizing the briguettec with gas. After shredding the garbage is separated into magnetic and nonmagnetic portions. The sterilization step employs ethylene gas which requires temperature control. The briquettes are maintained at a te~perature of about 54 CO
Further, microwaves are limited in their penetration and are ineffective for heatin~ when applied to large scal~, boxed medical waste of the type which ... . . . . . . . .
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~092/007~ 2 ~ ~ 6 1 2 ~ P~/U~9l/0~703 _ g _ comprises the waste disposal problem today. ~icrowaves do not heat v~ry effectively because they do not p~netrate ~ery deeply. Most of the heat is generated near the surface and quickly dissipates into the surroundings, in part because it is not well conducted into the center portions o~ t]he boxed medical waste. In contrast, radio-frequency wav,es at relatively low frequency can penetrate boxed medical waste more deeply.
It also is known in the art that thermal radiation treatment of bacterial spore~ and other pathogens may allow greatly reduced ionizing radiation dosage.to accompli~h sterilization of a given population, For instance, in "Thermoradiation Inactivation Of Naturally Occurring Bacterial Spores In Soil," M.C. Reynold~ et al., A~plied ~ic~o~io~oqv! Vol.
28, No. 3, September 1974, it is disclosed that bacterial spores may b2 inactivated by heating them with dry heat and exposing them to ionizing radiation from a cobalt 60 source allow greatly reduced treat~ent ti~es o~er the use of ~ither dry heat or radiation alone.
~ n attempt to elucidate a model for such behavior is sat forth in J.P. Brannen, ~A Kinetic ~odel For The Biological ~fects O~ Ionizing ~adiation", Sandia Laboratories, SAND74-0289 (October 1974).
Heat and radiation inactivation of bacteria are discussed at ~'Progr~ss Report Bene~icial Uses Program, Period Ending December 31, 1976~, Wast~ Management and Environmental Programs Depart~ent, Sandia Laboratories, SAND77~0426 (1977~, where it is taught that viru~es in sewage sludg may be destroyed by evaporation. ~eat inactivation may be us~d to destroy S~lmon~lla enteri~itis ser. ~onteYi-d-eo. Streptococcus bacteria may be destroyed by u~ing ionizing radiation at a dose of about 140 ki.lorads.

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The use of cesium 137 to inactivate pathogen~ in sludge is discussed in "Sludge Or Radiation Disinfection For Beneficial Use", Applied Biology And I~otope Utilization Division 4535, "General Description Of The Sludge And Radiation Process", SAND80-2744 (Dec. 1980~, where it is disclo~ed that ce~ium-137, emitting gamma radiation may be used to inactivate pathogens in sewage sludge~ See also, "Use Of Cesium-137 To Process Sludge For Further Reduction Of Pathogens, Sludge Or Radiation Disinfection For Beneficial Use, H Disease Control Requirements For Various Sludge Uses, Applled Biology and Isotope Utilization Division 4535, SAND80-2744 (Dec.
1980), which disclo~e~ that in order to render sewage sludge sa~e, in particular for certain agricultural usages, irradiation ~ay be used as an add-on process in con~unction with ~terilization where sludge is maintained at 30 ~in. at a temperature of at least 70' C. In each of the aforementioned papers, it may be appreciated that the sludge which is being treated is substantially homogeneous in its dielectric characteristics and, thus, in its heating characteristics.
The gamma irradiation ~quipment commonly used and disclosed in this application is o~ the type disclosad in HGamma Proce sing Equipment", AECL
Industrial and Radiation Division (Jan. 19873.
The dual plate 18 megahertz plate type radio-frequency heater i~ of the type disclosed in "Di~lectric HeatingH, PSC, Inc., which, although undated, constitutes prior art to this application.
Like microwaves, radio-frequency waves are a form of electromagnetic ener~y. They also trans~er energy directly into materials r primarily by the interaction of their time-varying electric fields with molecules. Radio-fre~uency wave~ may be applied by , , ,, , .: :

-W092/00764 2 ~ ~ 612 ~ Pr/us~l/o~o3 connecting a radio-frequency alternating current to a pair o~ electrodes. Between the two electrodes an alternating radio-~requency electromagnetic ~ield having a time-varying electric field component is established.
When objects are placed between thP electrodes in the time-varying electric field, 1:he time-varying electric field partially or completely penetrates the object and heats it.
Heat is produced when the time-varying electric field accelerates ions and el~ctrons which collide with moleculesu Heat also is produced because the time-varyin~ electric field causes molecules, and particularly those with a relatively high electric dipole mom~nt, to rotate back and forth as a result of the torque placed upon them by the time-varying electric field. Mo~t large molecules, or molecules with evenly distributed charge, have relatively low or nonexistent dipole ~oments and are not very ~uch affected by the radio-frequency time-varyin~ electric ~ield. Small molecules, in particular with polar groups, have relatively large electric dipole moments and thus have relati~sly large torques exerted upon them by the time-varying alectric field. In particular, highly polar molecules, like water, experi~ce relatively large torques and as a result are rotated by the time-varying electric field, thereby transf~rring ~echanical energy to their surroundings as internal energy or heat. Lower ~requency ti~e-varying electric fields penetrate deeply and heat obj~cts ~ore evenly. Relatively high ~requency ti~e-varying electric fields do not penetrate a~ deeply, but heat mare rapidly the portions of objects they interact with.
It should be noted that a time-varying lectric field is always accompanied by a time-varying magnetic - , . . ,, ,, . :
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W092/0076~ pcr/us91/o47n3 2~86~2~ ' field, except where destructive cancellation occurs with interference patt~rns. For most materials being considered here, the principal heating mechanism arises from the electric fi~lds. These fields can cau~e both ohmic heating via induced ionic currents and dielectric heating via molecular stressing from the internal electric fields. For very moist ~aterials, the presence of the acco~panying time-varying ~agnetic ~ield can also induce eddy-currents which can also heat th~ ~aterial.
Also, some type of combined effect of magnetic fields and heat may occur. While the ensuing discussion is presented in context of an electric field ef~0ct, it should be understood that the effects o~ accompanying time-varying magnetic field are defined here for simplification as part of the electric field phenomena.
Becau~e different materials are compo~ed of different types of ~olecules with dif~ring electric dipoles, they heat at different rates when exposed to a given time-varying electric field. For example, plastics, which are formed of very large polymer molecules, are not heated by time~Yarying electric fields as rapidly as water. Hetal objects ~ay or may not be easily heated when exposed to ti~e varying electric fields either in the radio-fre~uency or microwave region. The high conductivity of the metal objects tends to short out the electric fields and rescatter them. As a consequence, there are many conditions where metal objects are di*ficult to heat, a~ exemplified by the metal liner of the interior microwave ovens. On the other hand, such ti~e-varying fields can also induce substantial rurrents which ~low on the outside o~ the metal objects. Under certain circumstances heating effects wil:l occur on the surface of the metal object which, in the case of a small needle, the heat is readily - . :
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~092/00764 2 ~ ~ 612 ~ Pcr/us~l/o~7o3 dif~used into the interior. In addition, the presence of long, thin ~etal objects in an electric ~ield causes enhancement o~ the electric fi.eld intensity near the ends of the metal objects and a diminution or shadowing of the fields nPar the middle. Thus, i~ the electric ~ield is parallel to the axis of the metal object, strong electric ~ields will exist near the ti.ps and weak electric fields will exist near the center o~ the rod or needle. Such field enhancsments can lead to arcing and pos~ible fires. In addition, the fielcl suppression or shadowing of such metal objects is also an unwanted feature if the presence of a single electric ~ield vector is relied upon in its entirety to provide the sterilization. The failure of the radio-frequency electromagnetic field to penetrate the object causing surface heating only, or the opposite failure o~ the materials to absorb thP electric field energy, causes unev~n heating of the ~edical waste. The uneven heating is exacerbated because the medical waste usually comprises mixed ~aterials which are difficult to heat effectively using radio-frequency energy due to the presence of areas of high field absorption, such as are due to ~etals and concomitant shadowing and cold spots. In addition, ~imilar but less pronounced absorption e~fects are ~ound with water ~olecules. Thus, when heterogeneous or mixed medical wastes have wet and dry portions, it ~ay be seen that only the wet portions of such material wDuld be heated.
Mixed loads such as hospital wastes were considered impossible to disinfect by radio-frequency energy because the waste contain~ a wide variety of ~at~rials, each having di~ferent dielectric pxoperties. A great concern was that the pre~ence of a su~ficient number o~ metallic sharps would lead to arcing, causing ignition o~ the acco~panying dry wastes. Another concern was that even . - . , - .
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20~125 if fire was not started, the dif~erenti 1 energy absorption of ~luid~ and ~harp~ would leave dry objects undisinfected.
In fact, other atte~pts to kill microorganisms with radio-~requency energy have been considered unsuccessful. In his 1980 review, "Effects Of Microwave Irradiation On Microorganism~", dvances in APplied Microbiology 26:129~45, Chipley cites an experiment of applying radio-freguency energy to bacteria an~ viruses which grow on tobacco. The experi~ent found no effect of the radio-frequency energy on the bacteria and viruses.
In another tudy of radio-frequency energy on contaminated liquid ~ood, th~re was no ~howing of "selective killing effect" except when ethanol was added.
In the sa~e review, Chipley cit~d numerous tests of microwaves on microorganism6 and concluded that "results of tests for viability of ~._subtilis spores also showed idsntical death curves compared with tho e obtained by conventional heat.~ On the other hand, however, ~hipley cites several references w~ich support the view that microwave irradiation has collateral thermal and nonthermal effectsO rFor example, Culkin and Fung (1975) found ~hat ~icrobial d~struction occurred at reduced te~peratures and shorter time periods when the makerial was exposed to ~icrowaves as co~pared to conYentional heating ~ethods. Wayland et al., 1977 also dsmonstrated the interdependence ~f heat and ~isrowaves effects in the StUdiQS of spores o~ B. subtilis.
U.S. Patent No. 2,114,345 to Hay~ord discloses a radio-frequency applicator with electroscopic control ~or destroying bacteria in bott~ed beer and similar products. Hayford teaches an apparatus ~or sterilizing a series of small objects. The radio-~requency ~ield must be const~ntly readjusted by the el~ctroscopic control.

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W092/00764 2 0 ~ 61~ a Pcr/ussl/o~7o3 There is no teaching or suggestion that large scale disinfection o~ heterogeneous waste could be carried out.
U.S. Patent No. 3,948,601 to Fraser et al.
teaches th~ indirect use of r;ldio~frequen~y energy in sterilizing medical and hospital equipment as w~ll as human waste. Ths re~erence teaches the use of radio-frequency energy for heating gases, particularly argon, and exciting them so that they ionize into a plasma having a temperature o:E approximately lOoD C. to 500 C. The re~erence teaches that a cool plasma at a temperature of only 25~ C. to 50- C. and v~-ry low pressure ~ay effectively ster:ilize an artirle. However, sterilization by pla~ma does not suggest the direct use of radio-~requency wav~s in sterilization since it is the chemical reactive ef~ect of the plasma which presumably performs the sterilization function rather than the direct or thermal e~ects of radio-frequency ~nergy on pathogens contained on the material. It may be appreciated that only those portions o~ the equip~ent and waste actually contacted by the plasma would be treated.
Reprocessing of the waste, and ~specially medical waste, is also vital for ssveral reasons. Even if the medical waste has been rendered harmless or innocuous by the destruction of any pathogens associated therewith, there is still the problem o~ the disposal of the bulk ~aterial including the plastics, the sharps, and fibrous material such as go~ns, diapers, and the like.
The material is relatively bulky and landfills, particularly in many urban area~, have become ~illed. In addition, older landfills ~ay leak and nonpathegenic but chemically polluting substances may leak into surrounding ground water, causing health hazards. Thus, burying the sterilized ~edi~al waste is becoming less attractive.
Further, merely burning the sterili2~d medical waste can , - : . : . -, ~ -.

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W092/007~ ~cr/us9l/o47n3 2 ~8 ~2~ - 16 -pollute the atmosphere and cause acid rain. Current reprocPssing technology ~hould be employed to process the sterilized medical waste for effective utilization and proper disposal. What is needed is a method ~or sterilizing the medical waste and destroying the pathogens thereon and disposing of the sterilized waste in a manner which is harmless to health care workers, waste handlers, and the public at large.
1 A serie~ sf inv~tigations has been undertaken a~ to sterilization, especially for food. This has resulted in patents or inventions wherein the material to be tr~ated is housed in a microwave transparent container such that the material can be h~ated at vapor pressures which coexist with temperatures of 120~ C. These include Gray U.S. Patent No. 3,494,723; Nakagawa U.S. Patent No.

4,80R,782; Stenstron U.S. Patent No. 4,808,783; Landy U.S. Patent No. 3,215,539; Utosomi U.S. Patent No.
3,885,915; and Fritz U.S. Patent No. 4,775,770. All of th~se pat~nts disclo~e heating homogeneous ~akerial in soms form of pouch or pressure container where the material, typically ~ood, i~ homogeneous. They do not address th~ special problem considered bere where the material is heterogeneous and contains ~harps, moist materials and dry ~aterials.

SUM~ARY OF THE INVENTION

Tha present invention provides a ~ethod and apparatus for heating hetarogeneous and in particular proces~ing medical materials such as ~edical and veterinary waste and ~edical products which disinfects : the materials by heating them with radio~frequency energy. The invention disinf~cts containerized bulk medical waste by heating it with a radio-frequency ' ~ ' - . ~
'~ ' ' ~ , : . ' WV9~/00764 % 0 3 ~ :L 2 ~ PCr/US'~1/04703 electric field. The medical waste is heterogeneous, that is, it comprises wet and dry materials such as dr~ssings, diapers, tissue and the like and material such as plastic gloves, plastic syringes and the like. The medical waste also contains metal containing sharps as such hypodermic needles, suturing needles, sc:alpels and the like. The waste is exposed to a radio-frequency electric field having a fr~quency of in the range of 500 kilohertz to 600 megahertz, preferably from about 10 megahertz to about 100 megahertz. The lower frequencies of operation are preferred to assure good depth of penetration of the electric fi~lds into the ~ore moist ~aterial. If microwave ~requencies are used (above 900 ~z), the depth of penetration is often less than a few c~ntimeters. The depth of penetration is decreased by increasing the moisture content.
While not wishing to be bound by any particular ~heory, it is noted that the time-varying electric field heats the water on the wet portions and boils off a portion of it. The evaporated water or water vapor apparently travels by convection and diffusion throughout the container containing the medical waste and may condense on the cooler, dry portions b~cause, other than the metal-containing sharps, dry material has not been heated substantially by the time-varying electric field.
It is believ~d ~hat the condensation of ~oisture on the formerly dry material gives up heat of vaporization and ther~by transfers heat to the previously dry material.
It is believed that this trans~er o~ moisture makes the materials relatively homogeneous with respect to wat~r cont~nt. This permits all of the material to be rapidly heated volumetrically by the field. The condensed moisture Oll or in the previously dry material can now absorb energy from the electric field. This generates ..
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heat within or on the previously dry material which is now rapidly heated by the field. In one embodiment of the invention, the bags of medical waste are confined within pressure vessels within the electric field and the medical waste is rapidly heated above 90 C.
One step of the pressure-vessel method comprises heating the medical materials with radio-frequency energy, possibly within one or more bags housed within a closed container, to raise the internal temperature to about gon C. In another embodiment, the temperature may be raised to 100- C. The pre6sure within ths bags, if used, increases to a point where the bags will burst thereby interconnecting the fluids among the bags within the container to permit vapor ransfer from one bag to another. The heating ~ay then continue to 120' C.
The vapor-containing version of this invention is suitable to treat a wide variety of wet and dry conglomerations of per~eable ~aterial which must be raised to temperatures below or close to that of the vaporization point of water. The use of radio-~requency heating in such a container creates volumetric heating and reduce~ the time reguirsments associated with autoclaving. The invention also is useful for the treatment of certain nonuniform ~oisture content co~modities which are highly per~eable, such as breakfast cereals, tobacco, and whole grains, which are hi~hly permeable to gas flow and at the sa~e time often re~uire heating treatments to disinfects the produce, to kill ins~ct in~estations and to equalize the ~oisture contents.
In another embodiment, to impl~ent the vapor-containing version of the process, the materials to be treated ~ay be collected and eventu~lly placed in a plastic bag capable of withstanding temperatures, for .::

- . : . . .
:: . ' : , . . '.' - - . . . ~ ., ~ . .. : . .: : , W092/00764 2 0 ~ ~12 5 Pr/u5(~l/o~7o3 about 15 minutes, of just above the vaporization point of water which, in this case ~or sea-level atmospheric pressure, would be just above 100 c. When the bags are filled, these are sealed and placed in a fiberboard box container. An additional vapor seal such as a fiber reinforced plastic sheet, plastic sheet or cylinder may be applied over a number of boxes which can then be placed on a pallet ~or ease of transport through the RF
heating facility. The additional vapor seal con~ines material up to 15 psig or more.
Thus, by selecting this type of spscific packaging, several of the r~quirement~ for the successful vapor-containment, disinfection process are realized.
First of all, a vapor impermeable barri~r is placed around the material. Secondly, the heat capacity of the vapor barrier is small since the wall thickness of the plastic material is quite thin. Thirdly, th~rmal transfer outside the treatment material is inhibited by the use of the fiberboard box. Such fiberboard boxes are relatively good thermal insulators, owing to the air-sack-like spacing betwe~n ~he inner and outer portions of the fiberbox ~aterial. Finally, the outer plastic or fiberglas~ reinforced pla~tic vapor seal prevents inti~ate con~act between the combu~tible fiberboard or portions of the ~edical waste with outside air.
One of the embodiments of the invention additionally ~ompri~es the step of trans~erring heated ~edical waste to a heat-soaking area which maintains the elevated temperature for about 45 minutes. The temp~ratura is maintained in an energy e~fective and cost efficient fashion in order to provide extra assurance that all pathogens are destroyed by the heat.
One advantage of the above-mentioned pressure :............ ~ :. . . . .

: . . , ~ - .~ , . . : .
.':~ . , ~ -., : . , .
. . .

W~92/007~ 2~ PCT/US~1/047 - 2~ -vessel which retains vapors up to temperatures of at least 120- C. is obtaining su:E~icient utilizatiDn of the radio-frequency energy by not allowing the water vapor to escape. Thus, energy losses which might o~cur in a nonpressurized container due to the need ko vaporize the water are avoided.
In some versions, the walls of the cavity or belt are heated to a temperature that is compArable to the temperature of the materiill being proces6ed. As a consequence, in the GaSe of the invention at hand, little or no energy is transferred out of the items to be heated. The purpo~e of minimizing thi~ transfer is that i~ the surface is too hot, the material beco~es sticky and gummy and thereby eventually clogs the mechanics o~
the system. On the other hand, i~ the wall ~aterial is significantly lower than that o~ the material being processed, energy is lost ~rom the m~terial being processed. In the ca~e of wet or moist material where a high energy absorption occurs/ this may not be a significant pro~lQm, but it can be significant in the case of very dry ~aterials. These have little dielectric absorbing ability and thereforæ have little capability to simultaneously heat them~elves and the adjacent walls.
To overcome this, a preferred embodiment of the inve~tion employs the use o~ peripheral guard heaters along the walls such that the wall temper ture assumes approxi~ately the same te~perature as that of the ~aterial being processed. Alternatively, insulated wall materials ~ay be used which have low thermal c~nductivity and heat capacity, ~hereby the heated gases from the material being processed can easily heat ~he wall so that they can be heated such that the wall temperature can i~mediately rise to ~he temperature of the material being process~d.

. . ~ : -.: . . : : . . ~ . . .................. ~ . . . .
~, .: . ... :

~092/007~4 2a~6~2~ PCT/VS~1/047~3 However, it may be advantageous in certain situations not to treat the material or waste in a pressure resistant container, but rather the material can be exposed in an unpressurized container to the radio-frequency energy such that the temperature of the material or ~edical waste is :Eirst heated to about 90~ C. Further heating to at least 120 C. substantially evaporates all of the water contained in the medical waste. Hence in another embodiment of this invention, to avoid possible underheating e:efect~ associated with shadowing through the presence of metallic objects in the waste, the material in the container can be tu~bled such that all portions of the ~aterial are expo~ed to all three vector orientation~ o~ the electric field.
The tumbling proce6s also en6ures exposure of all the material to the el~ctric fields to take advantage of collateral the~mal and nonthermal effects which may exist at a~out 90- C. and may allo~ complete sterilization to be accomplished without a significant degree of vaporization~
Another e~bodiment o~ the invention also comprises steps o~ ~urther procassing the medical waste by presorting the ~aterial into recyclable plastic or refuse deriv~d fuel, comminuting or shredding both types of materials, repackaging and shipping to co~mercial users.
In a still furth~r embodiment o~ the invention, the medical material, specifically comprising medical and veterinary waste, is received for processing. The waste is then co~minut~d or shredded to an average linear particle dimension oP 1 to 2 inches. If the waste i5 particu'larly dry when it is packed in a container for.
processing, water or foam may be added to the waste. The foam specifically comprises a surfactant such as a .~
- . .. .

- ~ . - .
: .
.
.
. ~ . .

WO9~/0076~ PCr/US~1/0~71 2 ~S~ 2 5 - 2~ ~
detergent mixad with wat~r. The shredding reduce~ the partiele size and reduces the ~ield intensitie~ in any metal materials in the particles in order to reduce the likelihood or intensity o~ arcing wh~n the shredded material is e~posed to the radio-frequency radiation.
The container also may be lined with w~tted cardboard to increa~e its RF absorption.
In mo~t cases, water need not be added to the matexial as the material contains up to ten per cent water by w~ight. Thus, when l:he material is h~ated by the radio-freguency field, water ~rom the wet material is vaporized, transported to the dry ~aterial where it conden~es, and couples with the radio-~requency radiation to heat the dry material. In the event that water is to be added, it may be added to the container in several ways. First, it ~ay be sprayed on in the form of a misting strea~ or may be simply be u~ed to soak the shredded ~aterialO If large amounts o~ water, how~ver, 2~
are used, the radio-frequency energy may be substantially reflected away from the interior of the container causing the processing time to increase or requiring that higher power equipment be used to obtain reasonabl~ heating ti~es. In order to reduce the amount of reflection, the water ~ay be addad in the for~ of ~oa~ which i5 volume filling, but which has a relatiYely low average - dielectric constant. In experiments which we have perfor~ed, foam havin~ a diele~tric constant of about 1 to 10, r~ther than 80, has been employed, causing only about 10% of the input power at 12 ~egahertz to be re~lected, ràther than about 90% of the input power, a~
happens with volumes of liquid water. The foa~ also provides a ~uenching medium for reducing tha likelihood o~ ~ires within the container.
The container =ay be compri~ed o~ epoxy . ~ I

:
- .

.. .. :. ~ . . . :
.. ,. . . ,: . .

W092/00764 2 0 ~ 612 ~ PCr/US91/04703 fiberglass and is seal~d, and may either have a pressurated seal or nonpressurated seal. With the nonpressurated seal, the contai~er will vent moisture at 100 C. With a pressurated seal, the container may be pressurized to about 15 lbs. per square inch above ambient or more, allowing the medical material therein to be haated to 120 C. or ~ore, causing disinfection of the material within a short time.
1 Before the medical materials are heated, they may also be compacted to allow ~ore ~terial to be heated at any one time and to cause the dielectric material, including the foam and insulating material in the medical waste, to be driven into more in~imate contact with any metal therein, ~ausing a reduction in the likelihood of arcing and fires in the ~edical material when it is heated. Reduction in fires is also achieved in this alternative method by the use of the sealed containers composed o~ the fire resi~tant plastic, which limits the amount of oxygen within the container, to prevent fires from spreading if arching cau~as partial combustion of the contents.
In a still further alternative embodiment, the radio-frequency ~-reatment chamber may be a pressurized radio-fxequency treat~ent eha~ber which can receive relatively low strangth plastic container~ who~e interior pre~sure may be equilibrated to the pressure within the pres~uri%ed radio-~requency cha~ber. The ~edical materials then have the radio-~requency energy applied to them to heat them to approximately 120- C. so that the materials are rapidly di~infected by heating due to the ~pplied radio-frequency energy, and possibly also due t~
the direct electric field e~fects of the radio--freguency energy on the microorganisms, including YirUses bacteria, and b~cterial spores therein.

. . . . .

. .
: .
. . ' ~ .
, W092t00~64 PC~/VS91/0470~
20s6~2~
- 2~ -Therefore, in view of the foregoing, it is a primary object of the present invention to render harmless or disinfect medical materials by heating them with radio-frequency waves. A further object or aspect of the invention is to di~pose of disinfected medical and veterinary waste in an enviro~mentally safe manner.
Ad~itional objects, advantages, and novel features of the invention will be set forth in part in the description which follows, and in part wil:l become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a f`low diagram of the steps involved in rendering containarized ~edical wa~te innocuous by heat treatment with radio-frequency electromagnetic fields;
FIGS. 2A, 2B, 2C and 2D are schematic representations of radio-frequency treatment units and radio-frequency energy ~ource~ which ~ay be used in the iradio-~requency disinfecti~n of infectious medical waste;
FIG. 3 is a schematic view of a system for continuously disinfecting bagged and containerized medical waste by using radio-~requency energy:
FIG. 4 is a section of a radio-frsquency reactor of FIG. 3, showing the electric field vector lines and equipotential lines generated within the radio-frequency treatment unit;
FIG. 5 is ~n isometric view of the radio-frequency treatment unit of FIG. 3 and a conveyor associated th~rewith showing details of the orientation of the conveyor with respect to an exciter plate within the reactor and the radio-frequency treatment unit;

, ~ .. .:
.

:
. : ~

W0~2/0076~ 2 0 ~ 6 1 2 ~ P~/U~9~/047~3 FIGS. 6A, 6B and 6C are plan and front side elevational views of a diff~rent type of radio-~requency treatment unit which can be used without the excit~r plate, the top and bottom of the shielded cavity serving as termination points for the electric fields, theraby simplifying the cavity design and permitting operation at higher freguencies.
FIGS. 7A, 7B and 7C are graphs of a normalized frequency power density in a single-end dri~en radio-frequency treatment unit and a radio-~re~uency treatment unit driven at opposite ends by radio-~requency energy having two different ~requencie6 to provide uni~orm average power throughout a major portion o~ the treating cha~ber of the unit:
FIG. 8 is a schematic view o~ a semicontinuous waste disinfecti~n system employing the radio-frequency treatment unit illuetrated in FIGS. 6A, 6B a~d 6C, FIG. 9 is a ~low diagram showing the steps of waste disinfection carried out by the apparatu~ o~ the present invention:
FIG. 10 is an elevational view, shown partly in ~ection, of a pre sure vessel ~or holding medical waste for placement inside the radio-frequency reactor of the apparatus of the present invention;
FIGS. llA and llB show side and end elevational views of the pres ure vessel of FIG. 10 and the mounting and driving apparatu~ there~or;
FIG. 12 i~ a diagrammatic view of the vapor treatment system a~sociated with the apparatus shown in ~IGS. 3 and 8; and FIG. 13 is a diagrammatic represantation o~ an alternative vapor treatme~t syste~ employing condensation and waste treat~ent;
FI~ 14 is sectional view of another container for receiYing medical material to be disinfect~d;

, ~ ..

,: . .

W09~/0076~ P~T/US91/~7s'~

2 o~ ~?~ - 2fi -FIG. 15 is a block diagram of another radio-frequency treat~ent system embodying ~or disinfecting medical materials; and FIG. 16 is a flow diagram o~ the steps of treating medical materials o~ the system shown in FIG.
15; and FIG. 17 is a sectional view o~ a pressurized radio-fre~uency treatment apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODI~ENTS

The method of the instant invention is illustrated in the flow diagram o~ FIG. l and consists o~
gathering medical waste from a waste source in a step 2 and placin~ the waste in a thermally insulated vapor sealed container, which may consist o~ a plastic bag, in a step 3. In a step 4, the vapor sealed con~ainer may be placed inside a box and the box loaded on a pallet. The box and pallet are then sealed in a vapor seal comprising a shrink-fit plastic or thQ like to prevent the escape o~
moisture from the container during proces~ing. The vapor sealed containers are placed in a radio-~requency field applicator in a ~tep 5 and a radio-frequency power source energizes the applicator to heat the ~aterial for a sufficient time to evaporate some of the water ther~in, transfer the resulting water vapor to dry portions o~ the material where it condenses and wete providing additional absorption and thereby heats the entire volume o~ medical waste in a step 6. After heating of the medical waste is completed and the waste is disinfected by heat inactivation of the microorganisms thereon the disinfecte~ ~edical waste may be converted to a . . . : . .
:
.
- -,~ -- :: ' : : .
- : ~: , . ~ - .. .

~0~2/00764 ~ 2 ~ Pcr/us~l/0~703 refuse-derived fuel or may be transferred to a landfill in a step 7~
Referring now to the drawings and especially to FIG. 3, an apparatus 10 for continuous waste treatment is generally shown in FIG. 3 and include~ a radio-frequency treatment unit 12 and a waste transport system or conveyor 14 for feeding bayged and/or boxed heterogeneous medical waste 16 to the radio~fr~quency treatment unit 12. A source of radio-~requency energy 18 is connected to the radio-frequency treatment unit 12 to energize it and an effluent handling system 22 is connected to the radio-frequency treat~ent unit 12 to treat gases and vapors evolved during the heating of the bagged and boxed medical waste ~6~ Also a ~ource 20 of inert sweep gas, such as nitrogen, i8 connected to the radio-frequency treatment unit 12 for driving oxyg~n thexe~rom to ~void combu~tion of the medical wa~te being heated~
The radio-~requency treatment unit 12 includes an applicator or reactor 34 providing a r~action chamber to which radio-frequ2ncy energy is applied. The design of the applicator 34 to produce the re~uired electric field and exposure time is of intere~t. Such applicators may be divided into three ba6ic groups- (1) TEM parallel plate applicators where the wavelength of the excitation freguency is large or ~o~parable to the dimensions of the reactor 34; (2) TE or TM controlled mode applicators where the dimen~ions of the reactor 34 are comparable to or several times the wav~length of the excitation frequency; and multi~mode TE and TN applicators where the maxi~um di~ension of the reactor 34 is typically 4 or more times t.he wavelength of the excitation ~r~quency.
Typically wi.th the ~ulti-mode TE or TM applicators, the modes are not controlled such that a number of peaks and nulls of the! electric field exist within the heating unit, such as exists typically in a micr~wave ovenO

~:'; ' " ~ , . , , ' '' - ~ ' ~ ' :
- ~ ' ~ - ', ' - ' - . ~ . ., :
.

W092~00764 PCT/~'S9l/0~7~3 FIGS. 2A, 2B, 2C and 2D illustrate the transition from a parallel plate TEM applicator 34 to a controlled limited mode TE or TM applicator. FIG. 2A
shows a reactor 34 ~ormed o~ two parallel plates 66 and 70 with the material 16 plac:ed between the upper ~nd lower plates 66 and 70, respectively. Voltage is applied between the upper and lower plate by means of a tuning coil which is driven from the RF source 18. As long as the wavelength o~ the applied voltage is large compared to the dimensions of the applicator 34, and the box 16 is well within the extended portions of the metal pla~es 66, 70, a uni~or~ field can be applied.
The applicator shown in FIG. 2A is an example of the TEM applicator and is limited to the lower frequencies, and because the dielectric absorption is roughly proportional to the "nth" power of the frequency (where n ranges ~rom 0.3 ko 1.0 for ~reguancies below about 300 ~Hz) and the s~uare of the el~ctric field strength, sub~tantially higher electric field strengths for lower frequencies are required to cause the same heating effect as ~iqht be expected for higher frequency operation. Higher frequency operation is possible in a controlled mode heating cavity 34 such a~ ~hown in ~IG.
2D, which is an exa~ple o~ th~ controlled mode TE or TM
applicator. The transition of the xeactor 34 from the e~bodiment of FIG. 2A to that shown in FIG. 2D is illustrated in FIGS. 2B and 2C. The parallel plates 66, 70 shown in FI 2A are re~onatad with the thin wire s2ri~s inductance 67. ~owever, by reducing the value of ~his inductance, higher ~requency resonances are possible. Neverthele~s, there is an upper limit to the ~requency at which this resonance can be ~ade to occur if just a single thin wire solenoidal inductor is employed.
~o increase the re~onant ~requency, straps 69 on the sides of t:he two parallel plate~ 66, 70 can be employed - .

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W09~/007~ 2 0 8 612 ~ PCr/US')1/0~703 as shown in FI~S. 2B and 2C, with power applied by way of a launching coil or turn 67. Eventually this arrangement is transfo~med into the controlled mode ~E or '~M
applicator as shown in FIG. ZD. The controlled mode TE
or TM applicator 34 is defineld where l/2 wavelenyth is comparable to one of the largler dimensions of the box.
This limits the number of per~issible modes and allows controlled and uniform heating. In the case of a microwave oven, th~ dimensionls are in the order of 6 to 8 half wavelengths. Thie results in uncontrallad modes and nonuniform heating.
In another embodiment, as may best be se~n in FIG. 3, the waste transport sy6tem 14 also includes a conveyor motor 24 which drives an input conveyor drum 26.
An output idler conveyor drum 2 also compris~s a portion of the conveyor 14 and a conveyor belt 30 engages both the input driven drum 26 and the output idler drum 280 A portion 32 of the conveyor belt 30 extends through the radio-frequency treat~ent unit 12 for carrying the containerized ~edical w28te 16 therethrough for treatment.
The radio-frequency treatment unit 12 comprises a radio ~requency cha~ber 34 having a radio freguency chamber inlet opening 36 and a radio-frequency chamber outlet opening 38. The radio frequency treatment unit 12 has a l~ngth of 18 meters, a width of 4.5 meters and a height o~ 3 meters. The radio-frequency chamber 34 comprises a bottom wall 40, a top wall 4~, an inlet wall 44, an outlet wall 46, a first side wall 48, and a second side wall 50. Each o~ the ~ha~ber walls is constructed of highly conducting material such as copper or aluminum. Typically 6 millimeter aluminum can be used, which allows the chamber walls to be self-supporting, Also 3 millimeter thick copper could be used in conjunction with additional physical support. The ' '' ' . ~ ' ' ' .
, - ~' ' ' ,, ..

WO~2/007fi~ PCr/US9l/0~7Q~
2 ~ 2 ~

radio-~requency treatment unit 12 also includes an inlet tunnel 52 connected to the inlet wall 44 at the inlet opening 36. The inlet tunnel 52 has a rectangular cross section and is dimensioned to act as a wave guide below cutoff to prevent the radiation of electromagnetic fields from the interior of the radio-frequency chamber 34 to the environment while allowing the containerized medical waste 16 to be carried freely into the radio-frequ~ncy chamber 34 by the conveyor belt 30. Likewise, a wave guide below cutoff forms an OlltpUt tunnel 54 from the outlet 38 at the outlet wall 46 to carry containerized disinfected medical waste 16 out o~ the vicinity of the radio-fre~uency treating chamber 34 without allowing radio-frequency energy from the radio-frequency treating chamber 34 to leak into the ~urroundings~
In order to energize a radio-~requency electromagnetic field and, in particular, the time-varying electric ~ield component thereo~, within the radio-frequency treating rha~ber 34, the radio-frequency energy generator 1~ is pro~ided and includes a radio-frequency current generator 56 connected to a coaxial cable 58 ~or ~eeding power therethrough. A
matching network 60 receives the radio-frequency ~nergy from the coaxial cable 5~ to which it is connected. A
second coaxial cable 62 is also connected to the matching network 60 to carry the radio-frequency power tharefrom.
That coaxial cable has a center lead 64 which penetrate~
the top wall 42 o~ t~e radio-frequency cha~ber 34 and is connect2d to a vertically ~ovable ~ubstantiaIly rectangular conductive exciter plate 66. Th outer conductor is connected to the top wall 42 and grounded.
The exciter plate 66 is ~uspended by a plurality of nonconductive ropes 68, preferably nylon or orlon, from the top wall 42 of the radio-frequency chamber 34. This allows the e!xciter electrode 66 to be moved with respect .

. . : . : :
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: . ' ' : . :' :~ ' `: :. :

W092/00764 2 ~ ~ ~ 1 2 ~ P~T/US91/04703 to the containerized medical waste 16 to provide a spatially uni~orm, time-varying electric field to heat the containerized medical waste 16 relatively unifor~ly.
A three millimeter thick copper bottom plate 70, which is substantially flush with a palr of bottom plates 72 and 74 of the inlet and outlet wave guide below cutc~f~
tunnels 52 and 54, respectively, comprises the bottGm plate of what is in essenc:e a biplate configural:ion reactor. Typically, the bottom plate 73, as well as the walls 42, 44, 46, 48, 40, and 50 of the radio~frequency chamber 34, are maintained at ground pot~ntial while the exciter plate 66 i~ excited by the radio-frequency energy fed through the coaxial cable 62~
It is particularly i~portant in the practice of the present i~vention that the excitar plate 66 be movable, as this allows adjustment oX the relatively uni~orm portion of the electric ~ield within the radio-frequ~ncy chamber 34. This is important because the size of the containers containing the c:ontainerized medical waste 16 may vary ~rom time to time. It is important that when the containers are traveling through the center portion of the radio-frequency heaking chamber 25 34, they be subjected to a ~ubstantially spatially uniform time-varying electric field so that the contents thereo~ are uniformly heated.
In the case of the parallel plate exciter, the dimensions o~ ~he box 16 compared with the dimensions of tha electrode 66 ar~ i~portant in order to assure reasonably uniform electric ~iel~ and resultant heating effects. To dete~mine the relationship between the box dimensions and the size of the electrode exciter, the data in FIG. 4 were developed. This shows equi-potential lines (horizontal) coupled with the displacement current lines (near-vertical) for a limited extent exciter electrode 66 centrally located in a large conducting :
.

w~92/no76~ PCTtUS~ 47Q3 ~8 ~ 12~ - 32 -box. The relative electric field at any location can be developed by determining the dimensions of a square at any location and a similar s~lare in the u~i~orm region (far right) and dividing the ~aximum dimensions o~ this uniform field squar~ by a sim:ilar dimension of the square at the desired location.
It can be seen there:Eore, if the guard distance, that is the distance from the edge of the box to the downward projection of the edge of the electrode, is equal to the height of the electrode/ that very little field distortion occurs and that thP ~lectric ~ield in the region to the right oP this point is rea~onably uniform. Further studies show that if khe edge of the box is moved farther to the left/ field distortion occurs such that the electric field is signi~icantly less near the ground plan~ and therefore the material o~ the box would experience a significantly lower heating rate.
Guard distance~ which are equal to about one-fourth or less than the hai~ht o~ the exciter electrode are relatively unsatisfactory.
on the other hand, it i~ se~n that as the height of the box i8 increased, the ~ield distortion near the edge o~ the electrode is such a~ to contribute exces~
field intensitie~, particularly where the height o~ the box is 75% of that of the e~citer electrode and the guard distance i~ equal ko one-guarter of the electrode height.
Data taken from thi~ plot are summarlzed in Table 1. It may be seen that guard distances a~ little as one-fourth the height o~ the elec~rode ~re acceptable but, on the othar hand/ the maxi~um h~ight of ~he box probably should preferably be no more than 67% of the height o~ the exciter elec:trode. The reason ~or this is that as the box enters ~rom the left going into the right, it encoUntQrS i.ncreasingly high levels o~ electric ~ield nea~ the edge of the electrode. As a consequence, excess ... , , . .. : .

W092/00764 2 0 ~ 612 ~ PCT/US91/04703 field intensity can occur there which can lead to potential graAients and arcing pheno~ena. To ensure against such effect~ as well as over or under heating, the normalized heating rate tluring entry wear the top edge of the box should not vi~ry more than 1.5 to 1.0 for the parallel plate type of heatar shown in FIG. 3. Where the bulk of the water is not evaporated but rather repositioned, heating ratios of 2.0 to 1.0 can be tolerated~ Where the bulk oiE the water is evaporated and heating is contained beyond 1:he vaporization point, the heating rate variation should be less than 1O5 to 1Ø

TABLE l. HEATING POTENTIAL (E2~ NORMALIZED TO
~HE HEATING POTENTIAL IN THE UNIFORM FIELD
REGION ~S A FUNCTION OF T~E BOX HEIGHT
RELATIVE TO THE HEIGHT OF THE ELEC~RODE
AND FOR R~LATIYE GUARD LEN~THS:.

Dimensions RelativeNormalized Heating to ElectrOdrL~5i9h~l_h Potential~ ~E2L

25 Box Guard Top ofBotto~ of Top of Box Height Length Box. Box Duxing Entry 0.5 0.5 0.92 0.96 1~0 0.5 0.25 0.92 0.8B 1.0 0.6~ 0.5 1.25 0.96 1.21 0.67 0.25 1.1~ 0~8~ 1.21 0.75 0.5 1.44 0.96 1~8 0.75 0.25 1.2 0.8~ 1.8 In the present embodiment, in particular for the type of reactor shown in FIG. 3, a 12 megahertz radio-freguency currsnt generates a 12 megahertz .
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W092/007S~ PCT/US9~/047~
2~8~12~
radio-frequency electric field within the radio-frequency chamber 34 to heat the ~edical waste 1~ within the hospital waste containers. I1: may be appreciated that the hospital or medical waste may comprise a wide variety of waste having many dif~erenl: dielectric constants. For instance, the sharps will include metals in which collected displacement currents will be induc2d by the time-varying electric ~ield. Very moi6t materials will also be included, as well as ~ite dry materials such as gloves and the like. In particular, the moist materials couple well with the radio-frequency field due to the fact that ~he dipole ~oments o~ the water molecules cause the water molecules to h~ve a torque exerted thereon by the electric field when it is unaligned with the dipole moments. This causes the molecules to be moved, in particular rotated by the field. The water ~olecules then transfer disordered kinetic energy to the materials upon which they are in contact, causing them to be heated.
When the ~edical waste 16 is first p~aced in the radio-frequency chamber 34, the wet portion~ of the medical waste 16 are rapidly heated by the radio-~requency energy, causing water vapor to be evolved therefrom. The water vapor is dispersed by convection and diffusion throughout the bags of hospital waste and condenses on th~ dry wa~te therein, due to the fact that the dry wa~te has been relatively unheated until it comes in contact with water. The condensation of tha water vapor on the cooler ~aterial transfers heat thereto by giving up heat of vaporization. More i~portantly, however, the condensed vapor wets the formerly dry material whe.reby the water is volumetrically heated by the time-va~ying electric ~ield, there~y generating thermal energy in the previously dry waste and causing the waste within the container to be subs~antially - :
: . . : -: - ' , ' - ~ ' ' . ~ , ' , . :

WV92/00764 PC~/US91/04703 2~12~

uniformly ~olum~trically heated. Since the ~requ~ncy of the time-va~ying electric fi~Ld is selected to b~ 12 megahertz, or, in the alternal:ive 64 megahertæ, the electric field penetrates wel:L into t~pical waste bags, and the entire volume of ~edical waste within the bags is substantially uniformly heated once the water is dispersed, allowing the waste tn be rapidly heat~,d. Once a minimum temperature of about 90 C. is reached, virtually all pathogenic organisms are all destroyed by the heat, and th~ waste is disinfected.
In the present e~bodiment for a plate-type radio frequency treatme~t apparatu6 with a guard l~ngth of no less than 1/4 the height of the container 17 and a container height no more than 3/4 of the electrode height and for the treatment of shredded material, it has been found that the electric field strength needed to achieve a particular heating rate, is defined as: .
E = ~ 1 m . ~t Eq. 1 V ~
where E is the electric field strength, f is equal to the frequency in ~egahertz, k is the mas~ o~ heterogeneous material to be treat~d, in pounds per hour and t is the tempexatur~ rise in degrees Fahre~heit and in ranges from 0.3 to lØ It has al~o been ~ound that the radio-frequency power ne~ded to h~at a given quantity material as provided by equation 2, where PR~ is the power, k2 equals from 1 x 10-4 to 2 x 10 4, m is the rate of ~ass processing in pounds of the material per hour and ~t: is the temperaturs rise o~ the heterogeneous material.
PR~ - k2 m ~ t Eq. 2 The AC power which must be applied in order to process a W092/0076~ PCT/US~1/047.~3 c~a~2~

given mass rate per hour at a give temper~ture rise, is defined in equation thxee where P~C is the AC power, k3 is a constant ranging from 2 x 10 4 to 6 x 10 4, m is the number of pounds of ~aterial per hour to be processed and ~ t is the templerature rise in degrees Fahrenheit.

PAC = k3 m At Eq. 3 In one embodiment of the invention, as ~hown in FIG. 3, the exit tunnel 54 is lined with electric resistance heaters 80, which are ~eans Por heat soaking the medical waste, if a further margin of safety is desired. As the containerized medical waste 16 passes through the exit tunnel 54, the electrical resistance heaters 80 transfer sufficient heat energy via radiation to prevent heat loss from the waste boxes 17. This heat is not sufficient to r~ise the temperature of boxes 17 further, but it i5 only sufficient to ~aintain the temperature of the boxes 17 at the ~xit. As a result, the exit tunnel 54 in combination with a similar tunnel 54a of much longer length will provide a ~eans ~or heat soaking the ~edical wastes 16 over the appropriate period of time. This can be done with a relatively low power consumption in order to hold the ~edical waste 16 at the dasired t~mperature ~or up to approximately 45 minutes.
In addition, such a heating tunnel in combination with the RF source heating nethod provides a mean~ to heat the m~dical waste in a controlled ~anner such that c~bustion does not occur and the plastic does not melt or partially pyrolyze. It would, o~ course, be difficult, if not impossible, ~o use such electric resistance heaters or other infrared radiative heaters solely to heat bulky materials li.ke the hospital waste from ambient temperature due to the fact that infrared heaters provide -:~ ~ .- , ,~
- , . .

W092/00764 2 ~ 8 ~ ~ 2 5 PCT/U~l/04703 e sentially sur~ace and not volumetric heating. That is, in accordance with the present invention, the waste i5 first heated volumetrically to the desired temperature and held at that temperaturQ by surface heating. I~ the surface is maintained at the clesired temperakure, the interior cannot c401.
Doors may be providecl at the distal ends of the inlet wave guide below cutoff 52 and the outlet wave guide below cutoff 54 as well as the heat soak entrance and exit to trap gase~ generated by the heating within the unit. These gases might, like the contents of the medical waste containers 16, be combustible. As a result, the inert gas systQm 20 flood~ the radio-~requency heating chamber 34 as well as the inlet tunnel 52 and the outlet tunnel 54 with nitrogsn. The flow is a counter flow in the inlet tunnel 52 keeping oxygen out of the system in order to prevent fires. The nitrcgen flush also provides other important ~eatures to the invention.
Since the injection point ~or the nitrogen flush i~ near the inlet tunnel 52l or actually on it, t~e relatively coQl nitrogen enters the radio-frequency treating area at approximately the same temperature as the waste 16.
Nitrogen is carried in the sa~e dîrection as the waste 16 and is heated thereby by conduction, radiation and convection from the heated ~edical waste 16. As a result, an effective tsmperature ramp is provided from the inlet portion of the radio-frequency heating cha~ber 34 to the outlet portion by the flawing of the gas in combination with the gradual heating. Due to the fa~t that the gas flows in the direction in which the temperature is increasing, refluxiny of any vapors released from the containerized medical waste 16 is preventad to the cooler input hospital waste by the directed flow of the nitrogen gas and thus prevents condensation on the cooler ~xterior of the con~ainer~, . . .
'`,' . ~ ~ .

.
- .

.

:

W092/00764 P~T/V~1/0470~
~Q~2~ 38 -which could i~hibit volume~ric heating. The nitrogen ga~
al50 operates as a sweep gas and carri.es ef~luents out through an ~ffluent exit port 8~ which comprises a portion of the inert g2s system 20. Ths effluent exit port 82 is connected to a blower 84 which i5 connected to the effluent treatment system 22.
The effluent treatment system 22, as may best be seen in FIG. 12, processes the! effluents evolved in the heating of the in~ectious medi.cal waste. These ef~luents essantially consist of skeam, air and inert gases, such as the nitrogen eweep gas, as well a~ som~ hydrocarbons generated during heating o~ the waste and pvssibly pathogens that ~ight have b~en released during the waste processing. Under normal conditions, though, all o~ the pathogens would be inactiv~ted or destroyed by the radio-fre~uency heating. The effluent exits through the duct from the radio-fr~quency heating chamb~r.34 and passes a hydrocarbon sen~or 92 connected to the duct 82 for determining whether hydrocarbon~ are pra~ent. If hydrocarbons are presant in exces~ of a predetermined value, an air in~ction sy~tem 94 injects air into the efflu~nt gas strea~ so that a combustible mixture of air and hydrocarbons, as well a inert ga~es, is ~2d to a vapor preheater 96. Tha vapor preheater i5 a heat exchanger fed with exhaust gases fro~ downstream ~quipment. A hydrocarbon sen60r 98 i~ connected to a condenser duct lO0 adaptad to rec~ive an inlet ~rom the condenser. The gases are then fed through a duct 102 to a ca~alytic oxidation system 104 which may be purch~ed from ~llied ~ignal UOP or other commercial suppliers.
The catalytic oxidation system r~ceives fuel such as propane or natural gas, if needed, via a fuel delivery line lOS. The catalytic oxidizer alæo includes a catalyst, such as Torvex catalyst available from Englehart, for the oxidation of hydrocarbons into carbon : . ' ' , - ' . ~ . ' - . : ~ ' ~
. - . .
: . ..

WO9~/00764 2 0 8 612 5 Pcr/us~l/oq~o3 ~ 39 - .
dioxide and water. The oxidizable components are oxidized ~y contact with the catalytic oxidizer and resulting hot combustion products are fed through a combustion output line 108 to a blower 110 which directs the hot combustion products through a hot gas output line 112 into the heat exchanger 96 to con~erve heat energy by trans~orming heat from the ho1: combustion products before they are vented to the envirollment to the ef~luent gases in the input duct. The combustion products are then vented through khe outp~t duc1: 100 to the enYironment.
The hydrocarbon sensor 98 will signal an alarm if unburnt hydrocarbons are pas~ing through the output duct 100, causing a syste~ shutdown to allow correction or alteration of the syste~ parameters to e~ure complete combustion of all co~bu~tible e~fluents. The combustion of the combustible e~fluents also destroys any pathogens which may be trapped therein and which had remained active b~fore combustion.
In an alternative ~y~tem, the radio-~requen~y chamber 3~, as may best be seen in FIG. 13, is co~nected to an effluent output line 111 having electrical re6istance heatinq elements 113 wrapped thereabout to maintain a high te~perature o~ the output ~f~luent, ~hereby preventing any heavy fractions from condensing within the duct 111 and also disinfecting the effluents.
Thermal insulation 114 is also ~ound about the heating elements 113 to prevent axc~6~ive hQat 108s from the electrical he ting el~men~s and al~o to prev~nt condensation of heavy fractions within the duct 11~. An air cooled vapor cosling system ~1~, which in the alternative ~ay be water cooled, causes condensation of heavy fractions which may then be passed by a duct 18 to a demister 120. ~he demister 120 separates any remaining gas ~lowing through th~ duct 118 into a gaseous ~raction which is ~ed on a gas line 122, and a liquid fraction fed : ' ' , '' ' ~

wo s2/on764 Pcr/ussl/0~7n~

2 o ~ 2 ~) via a liquid lin~ 124. A carbon adsorbent system 126 receives the gas from the line 122 and vents any inert gases left over through a line 128 which is connected to a venting blower 130. The venting blower 130 feeds the remaining inert cleaned gases through an output duct 132 to the environment. Similarly, the liquids are fed via the duct 124 to a liquid adsorbent system 134 which is filled with a commercially ava~ilable adsorb~nt material for water cleaning, such as Fi.ltrasorb from Calgon. As an added precaution, clean water is then fed vi~ duct 136 to a pump 138 which passes the clean water through a pipe 140 to a sterilizer 142 which heats the water to 90 C.
Por sterilization. The sterilized water is fsd via a duct 144 to a receiving container 146 which receives and stores it. The sterilized water may then be disposed o~
in an appropriate ~anner.
As may best ~e seen in FIG. 8, ~n alternative semicontinuous waste system 200 is shown therein, utilizing the radio-frequency system shown in FIG. 6.
The semicontinuous waste disinfection system 200 includes a radio-~requency waste treater 202 and a waste transport system 204. ~ radio-frequency energy generator 206 is coupled to the radio-~requency waste treating reactor 34. In operation, the radio-frequency energy generator 206, which includes a control ~ystem 208 connected via a cable 210 to a radio-fre~uency power source 212, generates radio-frequency energy i~ response to control signals ~rom the control 208 and ~eeds the xadio-~requency energy via a cable 214 to a matching network 216. The matching network 216 has a power delivery cable 218 connected to it which has an inner conductor 220 terminating at a field exciter 222 of a loop type or other suitable type. A dielectric plug 224 terminates an end of an insulating jacket 226 of the coaxial cable and mates with an upper wall 203 of the .. ... . . . . . . .

- . : . . . : ~ . . .

W092/00764 2 ~ ~ S 12 5 PCT/U$91/04703 radio-frequency waste treating reactor 34. The radio-~requency waste treating reactor 202 also includes a bottom wall 232, an inlet wall 234, an outlet wall 236, and a pair side walls, one o~ which is shown as a first side wall 238. Coupled to the treatment chamber is an inlet wave guide below cutoff tunnel 240 which is substantially rectangular in ~-ross section, connected at an inlet 242 to the reactor 34. The reactor 34 also includes an outlet 244 formed in the wall 236 to which is conducted an outlet tunn~l 248 which comprises a radio-freguency wave guide be:Low cutoff. The system may also include an inert gas source as well as an ef~luent handling system a~ shown in ~IG. 3, although for simplicity such are not shown in FIG. 8.
The conveyor system or waste transport system 204 includes an electric motor 250 controlled by signals carried on a cable 252 ~rom the control 208.: The motor 250 tlrives an input dru~ 252 of ths conv~yor syst~m which in turn drive a conveyor belt 254. An output drum 25 also engages the belt 254 in a convantional fashion.
Pressure vessels 260 of the type which may be~t be seen in FIGS. 10, llA, and llB, are carried by the conveyor belt 254 through the inlet tunnel 240 into the radio-frequency reackor 34. The pressure vessels 260 are substantially cylindrical in shape and include an inlet 262 ter~inating in a flang~ a~ embly 264 which receives a closure cap 266. The closure cap 265 ~eats against an o-ring or gasket 268 for a ga~ tight seal therewith. The o-ring 268 is also trapped against the flange 2~4. The cap 266 is held in compressive engagement with the 0-ring by a plurality of bolts 270. The pressure Yessel 260 includes a wall 272 whi~h ~ay either be completely transparent to radio-frequency radiation, or be deliberately absorbent to heat the wall by the radio-frequency energy such that the wall temperature ~ , - ~ . -- ., .:'-, - . : , : . . . ' : :
,, . ~ : ~ .: : -W092/00764 PCT/US91/Oq7 2 ~ 2~ ~ 4~ _ approximates that of the material being heated.
Alternatively, the interior portion of the wall of the container may be thermally insulating to achieve the same purpose. The pressure vessel 260 is preferably made using fiberglass r~inforced his~h temperature epoxies or equivalent plastic material to withstand the ~emperatures and pressures ne~ded for disinfection. A plurality of waste bags 276 are held in the interior 278 of the pressure vessel 260 for heating by the radio-frequency energy as was set forth above.
A plurality of thermocouple openings 280 are provided in an upper portion of the vessel so that, if desired, temperature readings may be made of the interior of the vessel 260 to as~ure a minimum o~ 9O~ C. A pair of pressure relief valv~s 282 are also included. The pres~ure relief valves are rated at about 15 psi, that is, they remain closed until the internal pressure of the vessel 260 exceeds the external pressure by 15 pounds per square inch. This allows vapor to be contained even if the medical waste 16 is heated above lOOC., the boiling point of water at atmospheric pressure. It also allows the waste or medical materials to be heated to 120' C.
without vaporizing ~ost of the water within the bags.
The release valves 282 are provided in order to protect the operators of the system from overpressure within the pressure vessels 260. ~hould it be necessary to inject additional water into the pressure vessel 260, a water injection port 288 i~ provided in th~ wall of the vessel. A rupture disk 290 is also pro~ided in the vessel 260 to prevent exc~sive buildup of pressure in the event of failure of th2 pressure release valves 282.
An optional disinfected waste port 292 is provided as an aid for pushing m~dical waste fro~ the pr~ssure vessel ~60 following disinfection with the radio~requency energy.

.. . . . . . .
, . . :. , , .. , . , ,:........ , .. . :

, ' . ': ., -. . : ` ' ' ~: ' ,"` ~', ` , ' W092/0076~ PCT/~'S~l/04703 - 2~12~
-- ~3 --The pressure vesRel 260 al~o includes gear cog~
300 arranged around the neck 262 of the inlet of the pressure ve~sel 260. When the pressure vessel 250 is transported into the radio-fret~uency heating chamber 34, the drive gear box 304 and mounting assembly 301 are normally below the bottom surface 232 of the reactor 34.
To rotate the vessel, the drive gear 304 and the mounting assembly 301 are raised so that the drive gear 304 engages the cog 300 to rotate the pressure vessel so that all bagged medical waste within the pressure vessel 260 is exposed to all three time-varying vectors oP the electromagnetic field to ~urther ensure complete electric field exposure and uniform heating.
In an alternative embodim0nt the pressure relief valves can be set to relieve the pressure at nearly atmospheric levels. The pressure ves~el thus can be used both as a waste bag container for transportation through the system and to contain vapors for vapor transfer for condensation on dry ~aterials.
In the event that the heating is to be taken above the vaporlzation point at atmospheric pressure, then it is important that the large pressure vessel also be rotated to sliminate the p~ssibility of shaded areas, as previously discussed. Thus, by this ~ethod, all parts of the waste material are e~posed to substantial levels of electric fields with a resultant possibility of achieving lower te~perature disin~ection by th@ combined or collateral effects of temparature and electric fields. In practice, the material in the temperature vessel first is heated to the vaporization point of water as in the case for the system shown in FIG. 3. The dry, relatively poorly absorbing ~aterial receives water vapor from the moist ~edi~al material and thereby becomes more absorbing to realize an almost equal temperature rise of the wet and dry medical material within the bags. At . ~

~ .. - ., . , . .~ .

- -. : . ,: ~ : .
.,. : , . . : . : ~ :
. . . .
- - : :: . . , . :
,- . . . .

W092/007~ PC~/~S91/0~71~3 2~8~2~
this point a minimum temperature in the bags of 90 C.
may be realized. Then the bags and the boxes are removed through the exit tunnel and heat soaking arrangement as previously described ~or the '30 C. or mora heat soaking system, except that the heat soaking temperature in this case of 100" C. ~ay be pre~erred.
Alternatively, it may be desirable to further heat the material at atmospheric pressure to temperatures of about 100 C. or 120- C. This ma~ b~ done by ~urther application of the time varying electric fields such that the matarial is dehydrated nearly completely and a minimum temperature o~ 100 C. or 120 ~. is realized through dielectric heating.
In many cases, especially i~ pressurization at near atmospheric levels is employed and if haating beyond the vaporization temperature of the dry ~edical material is required, the total energy or "dose~ applied to the medical waste ~ust be controlled. Energy should be suf~ici~nt to accompli~h the de6ired ~inal temperature with some additional sa~ety ~argin. This may result in some of the medical material bsing overheated beyond the desired final temperature of approximately 120~ C.
However, too little energy can result in underheating some portions of the ~edical ~aterial and too much energy can result in excessive energy consumption along with partial or complete pyrolysi~ of the medical waste.
Excessive waste also g~nerates noxious gases and thereby burdens the effluent treatment system.
To ~itigate thefie probl~ms, as shown in FIG. 8 sensors 237a and 238b are used to determine the moisture content andfor the presence o~ ~harps. Previously the ~aterial may have been weighed and the weight data 35 supplied to the control unit 208 via a cable 239. The control unit 208 then program~ the exposure level and controls thi:; via the electric field sensor 234 and the - ~ --- . - - - - - . - . . .
~. :~ . . , - . : :

, . . . ' . , - - - : . . . : . ' ' ' . ~
. . - : . . : . ., . :
., ,. , . , ,, :.... ' . ' ., .:

- :
, .

WO9~/nO764 2 0 ~ 612 5 PCr/~S91/04703 - ~5 duration of the exposure by sequentially activating the belt 254 via a line 252 and a motor 250. A s2nsor 237d remotely monitors the temp~rature of the material in the vessel 260 by monitoring the infrared or longer wavelength electromagnetic emissions ~rom the material being heated. The s~nsor ~37e monitors the gaseous effluent so as to limit exces,sive pyrolysis~
Additional wall insu:lation and/or wall heating may also be employed to suppr,ess heat losses due to convection and diffusion. This is especially desirable if heating above the vaporization temperatur~ is needed.
Additional wall and panel in6ulation 241 along with a wall and a panel heater 343 may be employed. The wall and panel heater 343 is also controlled by the control system 208.
For those case6 where heating above the ~aporization point of water is employed, it is especially important that the chamber be filled with an inert gas such as nitrogen. The ~eans ~or the injecting the nitrogen in and keeping the oxygen out ar~ described for the system shown in FIG. 3. For the semicontinuous system shown în FIG. 8, less care is needed in controlling the direction of s~eep gasas. However, if a . con~inuous version of FIG. 8 is e~ployed, the dir~ction of sweep gases should be from the cooler material to the hotter material as discus~ed in the embodiment shown in FIG. 3.
The pres~ure ves~el may then be carried, a~ter treatment by the radio-~requency energy, to the outlet tunnel 248 wh~re electrical resistance heaters 306 provide heat soaking to the pressure vessel 260, holding it at the d~sired temperature for a specified period of time in order to pro~ide extra assurance o~ the destruction of pathogens in the infectious ~adical waste.
Details of a radio-~requency feed structure for , - ~ , , ~- -- : . . . ~
: , - , . , -: , . . - , . , W0~2/00764 PCT/~ /047r~

2 ~ 8 ~ 6 -the cavity resonator 32 ~ay best be seen in PIG5. 6A, 6B
and 6C. The cavity resonator 32 may in an alternative embodiment be ~ed ~rom opposite sides by loop-type exciters 310 and 312. The loop exciter 310 is driven at a frequency of 40.68 megahert~ while the loop exciter 312 is driven at twice that frequency, B1.36 megahertz. It may be appreciated that this arrangement allows a highly uniform average power to be present within the cavity.
As may best be ~een in FIG. 7A, a cavity having standing waves induced therein at the lowest mode, has an average power density with a peak at the center of the cavity.
If the cavity is driven at a frequency of 81.3S megahertz a pair of power peaks occur, as ~ay be ~een in FIG. 7B.
The continued effect of the two feeds o~ the twin feed cavity ~hown in FIGS. 6A through 6C is shown in FIG. 7~
with the power density curve Por a relative a~plitude for power of 0.864 at the ~undamental 40.68 megahertz frequency and a relative a~plitude o~ 0.48 at the first octave or 81~36 ~egahertz ~requency, thereby providing a highly uniform power across three quarters of the distance across tha cavity as shown in FIG. 7C. This further provides unifo~m heating for the medical waste 15 2 5 within the cavity.
A detailed flow chart of the process steps carried out by the apparatus and ~ethod of the present invention is shown in FIG. 9. In ~tep 400, the medical waste is received at a receiving bay and transferred to a belt conveyor in st~p 402. Optionally, in step 404, the medical waste 16 ~ay be appropriately identified by bar ~oding or any other identification method and may be sorted according to waste into lightweight boxes in step 406, heavy and liquid waste boxes in step 408, sharps containers i.n step 410 and possibly cardboard in step 412. optionally, the ~edical waste may be repacked in processing containars such as additional boxes of .
.
:
. .
.. . .

, .. . : . . .

WOg2/007~4 2 a3 ~l2 ~ PCT/~S91/~703 - ~7 -corrugated material in step 414 and then is further transferred by conveyor to a radio-frQquency heating system in step 416. The ~edic:al waste may be restacked and optional temperature validlation procadures may be carried out in step 418.
The medical waste is then segregated in step 420. Disinfected sharps conta~iners are fed to a shredder for sharps containers in step 422. Other material is fed to a shredder for general waste in step 424. The waste may be optionally separated in step 426.
Preliminary to the use of the present invention, medical waste arrives at a processing and recycling ~acility. Pr~ferably the material is shipped in sealed containers, usually sealed plastic bags. The plastic of the bags does not signifi~antly absorb the radio-frequency energy with which the medical waste 16 is traated. This means of shipping medical materials 16 is known in the art and has the advantage that the medical waste 16 does not inf~ct or contaminate its handlers in transit.
The containers remain in the heating chamber and receive radio-frequency waves for a su~ficient time to raise the temperature of the medical materials to approxi~ately 85' C. to 125- C. It will be recognized by those skilled in the art th~t te~peratures as high as 170 C. may be e~ployed without adversely affecting the material to be disinfected. In ~he disclosed e~bodiment, the ~edical waste 16 is moved through the radio-~re~uency treat~ent unit 12. The total dose of radio-frequency energy to which the medical waste l6 is exposed during its dwell time in the unit 12 is planned to provide sufficient disinfection.
Preferably, a medical material disinection facility using the present invention is validated to assure the adequacy of the disinfection process.

- : : , . . . - . . . :

, WO~/0076~ PC~/US~I/(t~71~
~o~6~2~

Validation may be per~ormed when each facility is constructed and at intervals during its operation.
Validation may consist o~ placing heat detecting devices such as thermocouples, re~istance temperature detectors, or the like, and/or known amounts o~ particular microorganisms which arQ resistant to heat into a container load of ~edical materials. Su~fici~nt radio-frequency energy is applied to raiæe th~
temperature of a load to about 85~ C. to 1~5 C. I~
t~ermocouples are used, they should all record at least 85 C. indicating that all portions of the load have been heated to at least 85- C. and that there are no cold spots where microorgani~s might ~urvive~ After the entire cycle is complete, the ~icroorganism samples are removed from the container and cultured by being given nutrients and other appropriate conditions ~or growth in order to determlne whether any have survived.the radio-freguency energy treat~ent. A typical heat resistant microorgani~m which ~ay be used in validation of the process is Bacil~s stearothe~mo~hilus. If more than one in ten thou~and of any microorganism survives the exposure to radio-~requ~ncy energy, the exposure ~ust be increased and another container tested, and the previously te~ted container ~ust be retreated with radio-frequency energy. On retest, a t~mperature of 92 C. may be tried. If that is nst adequate, further retests at 94- C., 96- C., and 98- C. ~ay be undertaken until the necessary kill rate i5 obtained.
The containers are held in the radio-fre~uency chamber and e~posed to radio-~requency waves for a sufficient ti~e to raise the temp~rature of the medical materials to at least approximately 85- C. It will be recognized ~y those s~illed in the art that temperatures as high as 170 C. will not adversely affect the process. P:referably, the exposure ti~e to . .

- - ~.

W092/00764 2 0 8 ~ 1 2 5 P~/US~l/0~703 _ ,~9 _ radio-frequency waves will vary depending upon the radio-fr~quency power and the weight of material in order to elevate the temperature o~ the ~dical materials to 85 C. to 125~ C. and hold that temperature for up to 45 minutes as an extra ~argin of sa~ety, assuring an even higher kill rate. ~owever, the optimal exposure time to the radio-frequency waves and the field strength of the electromagnetic field of the time-varying field for a particular facility will vary and may be determined as described above.
In a still further e~bodi~ent, the load may consist of 18 inch by 18 inch boxes loaded with polyethylene bags filled with hospital waste containing approximately 5 to la percent water by w~ight. In a further embodiment the load may consist of 18H x 18"
boxes loaded with polyethylene bags filled with shredded hospital waste. Inside each such box an envelope containing test strips load~d with 1 x 106 spores of Bacillus subtilis, var. ~iqer. ~ay be employed.
Thermocouple temperature probes al80 may he plac~d within and around the boxes.
Another embodiment of the invention consists of starting with mPdical or veterinary waste that has been presorted into containers o~ plastic and general medical waste, respectively. High grade plastics are employed in medical products and can be shredded and molded into a variety o~ other products. This waste is subjected to radio-fregusn~y energy and the containers of waste are moved to a shredder for the plastics. For example, an electrically power~d shredd~r having a pneumatic ram assist with a negative pres~ure canopy can shred the m~dical waste to ~mall particles. Such a shr~dder may be 35 purchased from Shredding Systems, Inc. o~ Wilsonville, oregon, and is identified as a ~odel Dual 1000 E. The negative pressure air canopy re~oves odors and particles ' ' '-'' ' ' :

, : :
' .: ' ' - ' : : , . . . - , , , ~:

W09~/007~ pcrl/us(~l/o~7o3 8 6 ~2r~ - 50 -entering the surrounding air and c~ntaminating theatmosphere. The odorous air is then scrubbed and particulates removed by impact filters or electromagnetic precipitators. The containers or medical waste bags are opened and the disinfected plastic is placed in the shredder and shredded to particles of about one-quarter to one-half inch mean linear dimension. The disinfected shredded plastic is tran~ferred to 55 gallon drums for shipment to plastic recyclers.
Likewise, the containers o~ disinfected general medical wa~te may be placed in a general medical waste shredder. After the containa~rs are opened, the di~infected general medical wa~te is placed in the shredder and shredded to particles have a mean linear dimension of one-quarter to one-half inch. The disin~ected waste i~ placed in further containers containing a ~ixture of paper, plastic, and metal, which can be used as ~uel. Pofisible users include ce~ent kilns which burn fuel to create te~peratures of about 130- C.
or more and which ~ight otherwise employ high sulfur coal. BeGause the general medical waste is low in sulfur, its use a~ ~uel will not generate sulfur co~pounds which ~ight be released into the atmosphere and contribute to acid ràin.
It is believed that part of the superior ef~ectiveness of the radio-frequency he~ting ~ethod disclosed herein i8 due to the fact that radio-freguency electromagnetic ~nergy penetrates large boxes and volumetrically heat~ the contents thereof very efficiently. However, this factor alone is not believed to account entirely ~or the difference obser~ed. Ik is further believeA thak the e~ficacious results of the instant process may be due to the fact that bacteria and viruses have a much high~r water content than ~ost of the mixed medical waste. As a r~sult, the ralatively high .
~: . ' : . -., , . , - :
. . , ~ .

W092/00764 PCr/US91/04703 2a~6l2~

- 5~ -dielectric constant of the bacteria and viruses ef~iciently couples the electromagnetic or time-varying electromagnetic field energy to the water, causing rapid heating of the microorganisms and subsequent inactivation or destruction thereof. Substances with high dielectric constants selectively absorb radio-frequency energy.
Therefore, radio~frequency energy may heat the bacteria and viruses to a lethal temperature be~ore the surrounding waste reachefi what is generally considered a lethal temperature.
Individually, the box~s ware placed in a two-plate 40XW radio-frequency heating chamber. The radio-frequency was 18 megahertz, although in the preferred e~bodiment a frequency o~ 12 megahertz is used. The following parameters were used:
Plate RV = 13XVDC
Plate A~ps = O.5 Amps (No Load) to 0.8 A~ps (Loaded) Grid Amps = 0.4 - 0.6 Amps Electrode Height = 9.75" ~Approximately 1~ above box) Time = 57 Minutes Temperature = 108 C. (maximum internal) At the end of the run, the load was allowed to cool. The boxes and individual bags were opened and the spore strips were removed and cultured according to standard techniques. For one run, of thirteen strips, four showed no growth at all. ~or the nine viable strips, the D-value, or ~mount o~ ti~e needed to kill 90%
of a test dose/ was calculated. For RF, at a maximum temperature of 108C, the D-value ~as approximately 9 minutes.
As a control, a dry heat test vessel was used to determine the D-values for Ba~ illus~mmsmubtilis, var. ni~er .

- , , - ~ :

.- ~ .

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WO9~/0~76~ PC~/US91/0~7 2 ~8 ~2 ~ - 52 -pore strips at 149 C., 160~ C., and 179n C. These D-values were graphed and ext.rapolated to 108 C. At a temperature of 108 C. the D~value for the dry heat 5 process was 20 minutes. Therefore, at a temperature of 108 C. the D-value of 9 minut:es ~or the RF treatment was less than half of the dry heat value. This is evidence that XF heating is markedly more efficient than is the dry heat process, in that it yields a comparable microbial kill rate in signi~i.cantly shorter time.
At 121 C., the D-value for the RF heating process was 0.31 minutes. A c:ontrol test of dry heat yielded no kill at this time at any temperature. At 121 C., RF was markedly ~ore effective than the dry heat process.
In a still further alternative embodiment of the present invention, an apparatus 600 for trea~ment of medical materials, the apparatus 600 as may best be seen in FIG. 15, comprises a comminuter 602 for receiving the waste material 16 fro~ a source of wasta. ~he comminuter receives the waste 16 and transfers it to a water station 604 where water may be added to broken up waste. A
radio-~requency treatment apparatus 608, which may either be of the parallel plate type or re~onant cavity type, as 25 disclo~ed hereinabove, receives the wa~te and heats it to a temperature between 85 C and 125-C to disin~ect the waste. The trea~ed waste then leaves the radio~frequency tr~atment apparatus.
In further detail, as shown in FIG. 16, the waste is received in a ~tep 620, the waste is then sent to thP comminuter 602 wherein step 622 it is broken into an average particle size of approxi~ately 1 to 2 inches linaar di~ension. The c~mminuter 602 may comprise a shredder of the type previously disclosed. The w~ste is then examined t9 deter~ine whether water needs to be f added in a step 624. If water is to be addedl the waste I

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, - . , W092/0076~ 2 0 ~ 61 2 ~ pcr/us~l/o~7n3 s further exami~ed in a step 626 to determine whether it is desirable to add an aqueous foam, such as a sur~actant and water. In the event that foam needs to be added, it is added in a step 628 in water station 604. If ~oam need not be added, water is added in a step 630. The material having the additional wat~r either in ~he form of foam or pure water, is then examined to determine whether the waste is dense enough. Likewise, waste which is not too dry which is adequately wetted is al~o examined.
The waste 16 then is placed in a closed container 635, as shown in FIG. 14, having a body 635a and a top 635b fitt~d to the body 635a which may be comprised of an epoxy ~illed with ~iberglass which closed container may either be able to ~aintain pressure slightly above atmospheric or up to 15 pounds per square inch above atmospheric pressure. The oontainer i~ then placed in the radio-frequency treatment apparatus which may either be a parallel plate type or resonant cavity in which should be excited between 100 and ~OO ~egahertz.
If the waste container 635 is not rated at a pressure of 15 pounds per square inch above atmo~pheric pressure, the radio-frequency treatment apparatus itself may be pressurized so that the waste may be adequately heated therein. When the electric field is appli~d to the waste 16 by the radio-fre~uency treatment apparatus S08 in the step 638 waste 16 having water thereon or therein is rapidly heated liberating vapor which travels to portions o~ the waste which do not have water thereon. The water vapor then condenses on the dry portions of the waste 16, having be~n confi~ed in proximity with the drier waste ~y the clo~ed container. The water vapor transfers its heat of vaporization to the previously dry waste and increases its radio-frequency absorption. The waste is then additionally heated by transf~r of energy from the - . ' - :, ' :, ~ ~, .

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W0~0076~ r/~'~9l/0~703 2 0~ 2 ~ - 5~ -radio-fregue~cy electric field which heats the condensed water within or on the previously dry waste. In the event that the container 635 is can withstand a pre~sure over atmospheric, the waste may be heated to above 100C.
preferably to 100 C. to 125~C. If the radio-frequency treatment apparatus and container are only able to maintain the wa~te 16 at atmospheric pressure, the waste will be heated to from about 90C. to about 100C.
One of tha advantages of the instant process is that when the waste 16 is comminuted, dielectric materials in the wa te 16 are brought into close contact with the metal-containing portions of the waste thereby reducing the likelihood sf arcing. In addition, arcing is reduced by the addition of the ~oam or water which woul~ tend to quench the arc and in addition prevent combustible materials in the waste from burning should arcing occur when the radio-frequency electric field is applied. The closed container 635 also helps to prevent unwanted combustion of the waste 16 while it is being heated by the radio-frequency electric field ~ince the amount of oxygen within the container is limited and would be rapidly used when combustion starts. The rontainer itself, being made of a combination of epoxy and fiberglass, can withstand temperatures of up to 400-F~ be~ore being damaged by the heat. Thus, the container is substantially combustion resistant.
In order to render the process ~ore ef~icient, the aqueous foam may ~e added in the step 628 which provideæ an ahsorbing dielectric in contact with metal portions of the comminuted waste to prevent combustion due to arcing but which reflscts relatively little radio~frequency energy directed into the waste. This is due to the fact that such a foam aqueous dielectric t~pically has a dielectric constant of 2 which would result in a reflection of only about 10% of th power ,',' ~ ~ ' .

W092/0076~ 2 ~ P~T/U~91/04703 directed at the waste 16. While liquid water, having a dielectric constant of 80 would rsflect almost 90% of the radio-frequency power fed to comminuted waste.
An alternative embod:iment of the pressurized version of the invention is shown in FIG. 18. A
radio frequency treatment apparatus 700 ha~ing a pressurized or pressur~-con~ining radio-frequency chamber 702 is used for processing containers 704 containing medi~al materials. An entrance conveyor 706 and an exit conveyor 708 are used to load and unload containers 704.
A roller-type conveyor 710 or the like i5 used to transport the waste containing containers 704 through the chamber 702. The conveyors 710 may rely on gravity for propulsion or may be driven by an electric motor or the like. An entrance door 730 and an exit door 734 are open2d to permit movement o~ containers 704 through the chamber 702. The apparatus 700 may be u~ed ~or either batch or continuous processing of medical waste. For continuous processing, the entrance door 730 is first opened to pass a container 7~4 into an entrance area 738, the entrance door 730 is closed. The door 732 is then opened to let the container 704 en~er the chamber 702. A
similar ~ethod is used with the doors 734 and 736 to remove processed containers 704. ~he double door method will ~inimize loss of pressure ~rom the chamber 702 during loading and unloading. A plurality of effluent withdra~al lines 742 are used to remove the effluents from the entrance and exit areas 738 and 740, by intermittently activa~ing senæors 744.
Radio-frequency energy is applied to the cha~ber 702 using a power source 712, an optional matching network 714, a coaxial cabl~ 716, an insulator 718 and an applicator 720.
Th~e pressure inside the chamber 702 is maintainad at a predetermined value ranging from about ... . .
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W092/00764 PC~/~'S91/0~7n~
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one to about seventy pounds per square inch above atmospheric pressur~ using an adjustable pressure relief valv~ 722. Effluents passing through the pressure valv~
are treated using ef~luent trleatment system 726. The chamber 702 may be swept with nonoxidizing gas, using an external source 728 or using the steam generated from evaporating of the moisture p:resent in the medical materials. The pre~sure insi~e the chamber 702 is set using the pressure relief valve 722 to achieve the desired sterilization tempera-ture of 100 C. to 150 C.
inside containers 704.
The chamber 702 wallc are heated to the desired sterilization temperature or to a slightly higher value using guard heaters 746, and is insulat~d with thermal insulation 748.
The chamber 702 is fabricated using good conductors of radio-frequency energy such as:copper, copper-cladded ste~l or aluminum. The chamber can have a 2 squar~, rectangular or circular cross section. Circular cylindrical chambers are more economical to contain the above atmospheric pressure. As an alternate, a rectangular or square cross section cha~ber can be positioned within a circular cylindrical pressure vessel. Portions of the cha~ber 702 ~ay be filled with impermeable low loss dielectrio 75G to reduce the amount free aix space.
In addition to medical materials, including medical waste, other heterogeneous materials may be heated using the process and apparatus disclosed herein.
For instance, it is ~ay be desirable to rQmove certain hydrocarbons from tar sands by heating. By the use of the present invention, tar sands may be placed in a container, ~;uch as container 17, which may either have a pressure seal or may be partially vented to collect hydrocarbons boiling from the tar sands. The tar sands, ' , : : ~
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W092/~076~1 2 ~ ~ ~ 1 2 ~ P~l/US91/~470~

when subjected to the radio-frequency electric field, in particular having a frequency between 10 and 100 m~gahertz but will have portions having relatively large amounts of water or wet portions heated first. The water therein will be converted to water vapor, which under pressure will diffuse and convect to drier portions of the tar sands where it will condense, transferring its heat of vaporization to the drier tar sand~ and thereby heating them. once condensed, the water will r~main at the point of condensation cont:inuin~ to absorb ener~y from the radio-frequ~ncy electric field and heating the tar sands. Once heating has been completed the tar sands may be removed Prom the containers. Thus, the invention disclosed herein i~ not only directed to disinfecting medical materials, but is directed in general directed to the heating o~ heterogeneous ~aterials having wet portions and dry portions by using radio-~requency time-varying electric fields to disperse water vapor throughout the material to absorb the radio-~requency eneryy being used to heat the ~aterial.
The ~oregoing descriptions o~ the preferred embodiments of the pre~ent invention have been presented Por purposes of illustration and de~cription. They are not intended to ba exhaustive or to limit the invention to the precise forme disclosad, and obviously many other modifications and variations are pos~ible in light o~ the aforemention~d teaching~. ThQ e~bodiments were chosen and described to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to utili2e best the invention in its various embodiments and with various modifications as are suited to the particular use 35 Contempla~ed. . .

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Claims (6)

WHAT IS CLAIMED IS:

1. A method of heating heterogeneous material, comprising the steps of:
confining a quantity of heterogeneous material comprising wet portions and dry portions in a closed treatment container;
exposing the treatment container to a time-varying electric field to evaporate water from the wet portions of the heterogeneous material, transporting the resulting water vapor by convection and diffusion to dry portions of the heterogeneous material, condensing some of said water vapor on cooler dry portions to wet the cooler portions, heating the wetted cooler portions by the persisting time-varying electric field until all portions of the heterogeneous material are substantially uniformly heated by the time-varying electric field; and removing the material from the container.

2. A method of heating heterogeneous material according to claim 1, wherein the treatment container confines the evaporated water at substantially greater than ambient pressure whereby the water is heated above 100° C. to allow the heterogeneous material to be heated above 100° C.

3. A method of heating heterogeneous material according to claim 1, wherein the frequency of the time-varying electric field is less than the frequency of microwaves.

4. A method of heating heterogeneous material according to claim 1, further comprising the step of adding water to the heterogeneous material to increase the energy transfer from the radio-frequency electric field to the heterogenous material.

5. A method of heating heterogeneous material according to claim 1, wherein the time-varying electric field has a frequency of about 500 kilohertz to about 600 megahertz.

6. A method of heating heterogeneous material with radio-frequency energy, comprising applying a time varying electric field to said heterogeneous material, said time varying electric field having a magnitude equal to the frequency of the field in megahertz divided by ten and exponentiated by a factor ranging from 0.3 to 1.0 to yield a frequency factor which is multiplied by the number of pounds per hour of material to be treated, multiplied by the temperature rise in the material.