WO1995014496A1

WO1995014496A1 - An apparatus and method of waste treatment

Info

Publication number: WO1995014496A1
Application number: PCT/GB1994/002590
Authority: WO
Inventors: Robert Marshall; Peter Leslie Jones; John Lionel Driscoll
Original assignee: Robert Marshall; Peter Leslie Jones; John Lionel Driscoll
Priority date: 1993-11-27
Filing date: 1994-11-25
Publication date: 1995-06-01
Also published as: GB9324424D0; AU1193995A

Abstract

An apparatus and method of waste treatment, particularly for the treatment of medical waste which is contained in plastic containers known as sharp safes. The apparatus has an inner cavity in which the waste is placeable and means for purging the cavity with steam before applying at least one form of electromagnetic radiation to the material within the cavity. The electromagnetic radiation can be infrared radiation and/or microwave radiation. The result of the waste treatment is a block of plastic encapsulating the medical waste which has been sterilised by the treatment.

Description

"An Apparatus and Method of Waste Treatment" The present invention relates to an apparatus and method of waste treatment. There is an increasing awareness that medical waste including sharps such as needles and scalpel blades as well as the many disposable plastic items such as blood bags, catheters and sample containers need to be dealt with on the assumption that they are contaminated with HIV or hepatitis virus. So called "sharp safes", plastic boxes constructed in such a way that items can be dropped through a counter weighted opening in the top which then closes preventing any contact with the contents, are the standard method of containment. The principal method of disposal of these currently

available is incineration, in which the sharp safes containing the disposable items are collected and transported to a central industrial incinerator. Recognisable medical waste must be treated in

accordance with specific guidelines. Generally in the past such guidelines have been met by the incineration, however, due to new limits on acceptable gas emissions, such incineration is no longer an environmentally acceptable method of disposing of such waste. In the past hospitals have had their own incinerators, however, the closure of these is being forced as it is not cost effectively possible for the hospitals to meet the new gas emission regulations that are being implemented. Waste is therefore being moved to other existing incinerators for treatment. In order to move the waste from its source, eg hospitals and clinics, to the incinerators, the waste must be transported by public means, generally by road. This involves the risk of road accidents involving cargoes of waste which may include infectious and contaminated fluids, needles etc. The sharp safe containers usually remain sealed during transportation from the source of the waste until reaching the incinerator. However, an accident in transporting the containers would not prevent the waste from escaping from the containers and causing danger to others involved in the accident. There are such obvious hazards associated with storing and transporting such material both within the medical establishment and beyond that the alternative of destruction at the point of creation has been proposed as the ideal solution. A number of attempts have been made to address this problem by treating the waste at its source. The prior art includes European Patent Application No EP 454122 (Kawasaki) which discloses a processing unit into which a container of medical waste is placed, compressed and sterilised and which includes the use of microwaves in the apparatus. US 4552720 (American Sterilizer Co) discloses an autoclave with a thermoplastic liner in which medical waste is placed. WO 90/14847 (DOCG Inc) discloses a container which is heat-conductive and heat-resistant and causes self-encapsulation of the waste by melting the plastic components within the waste. All these prior art disclosures have the disadvantages of producing gas emissions which require careful monitoring and produce fumes and odour. Microwaves are best known for cooking and other heating operations in which water is the main absorbing medium. It is well understood that microwave energy will not readily heat most of the polymeric materials used in the medical industry since they are largely transparent at the wavelengths involved. It is well established practice in the medical industry to use steam for sterilisation. However, given the short process time necessary to meet the requirements of disposal of a single sharp safe load, conventional steam raising techniques would be unsatisfactory. There is also the added problem that when a sharp object, such as a medical needle, is exposed to a high voltage electric field at high frequencies it is very likely to initiate arcing. If this takes place in the presence of combustible material then a fire will ensue. It is an object of the present invention to provide an apparatus for treatment of waste at its source which does not emit gaseous fumes which require control and which is unobtrusive and easy to operate. According to a first aspect of the present invention there is provided an apparatus for waste treatment comprising a cavity in which material is placeable, means for purging the cavity with steam, and means for applying at least one form of electromagnetic

radiation, to material within the cavity. The means for applying at least one form of

electromagnetic radiation which may be high frequency dielectric heating is in the form of a microwave or radio wave frequency source, it may alternatively apply radiant heat in the form of infra red radiation emitters. Preferably, both high frequency dielectric radiation and infra red radiation are used. Preferably, the waste is processed in a container of plastics material. Preferably, the infra red radiation emitters are disposed in an arrangement in the curved top of the cavity. A pouch containing fluid may be incorporated into the container. Alternatively, means may be provided for injecting liquid into the cavity. According to a second aspect of the present invention there is provided a method of waste treatment

comprising placing the material in a sealed cavity, purging the interior of the cavity with steam and applying at least one form of electromagnetic radiation to the material within the cavity. The form of electromagnetic radiation applied may be high frequency dielectric heating and is generated by a microwave source or radio wave frequency source, or by a radiant component in the form of infra red radiation emitters. Preferably, both high frequency dielectric heating and infra red radiation are applied. Preferably, the waste is contained in a container of plastics material prior to placing in the cavity. Preferably, the high frequency dielectric heating is microwave radiation. Preferably, the radiant component is infra red heat. Preferably, circulation means circulate the heat within the housing. Preferably, infra red radiation is initially applied to the container to melt the top of the container. Preferably, an injection of liquid is made into the open container prior to the application of the

microwaves. Alternatively, a pouch containing fluid is incorporated in the cavity, which fluid is heated by the application of microwaves to the cavity, thereby producing steam. Preferably, the cavity is cooled after the heating before opening the cavity. Preferably, the waste is removed as an encapsulated block and processed as domestic waste or recycled for further use. According to a third aspect of the present invention there is provided a sterilising apparatus comprising a sealed cavity in which objects are placeable, means for purging the cavity for a set period of time with steam, and means for applying radiant heat to the cavity. Embodiments of the present invention will now be described by way of example, with reference to the accompanying drawings, in which: Figure 1 is a simplified cross section of an apparatus for waste treatment in accordance with the present invention; Figure 2 is a half cross section along line B-B of the apparatus of Figure 1; Figure 3 is a cross section along line C-C of the apparatus of Figure 2; Figure 4 is a section through the apparatus of Figure A along line A-A; Figure 5 is an external front elevation of the apparatus of Figure 1; Figure 6a is a detail of a bracket support of the apparatus of Figure 1; Figure 6b is a detail of a base support of the apparatus of Figure 1; Figure 7 is a top elevation of the inner vessel of the apparatus of Figure 1; Figure 8 is a front elevation of the inner vessel of the apparatus of Figure 1; Figure 9 is a front elevation of the apparatus of Figure 1 without the outer jacket; Figure 10 is a top elevation of the apparatus of Figure 1 without the outer jacket; Figure 11a is a side elevation of the fan of the apparatus of Figure 1; Figure lib is a plan of the fan of Figure 11a; Figure 12a is a side view of the microwave connector to the apparatus of Figure 1; Figure 12b is a front elevation of the microwave connector of Figure 11a; Figure 13 is a schematic diagram of the extract circuit of the apparatus of Figure 1; Figure 14a is a front elevation of the microwave guide of the apparatus of Figure 1; Figure 14b is a side elevation of the microwave guide of Figure 14a; Figure 15a is a front elevation of the 90 degree bend in the microwave wave guide of the apparatus of Figure 1; Figure 15b is a side elevation of the 90 degree bend of Figure 15a; Figure 15c is the connector apparatus 1 connecting the microwave wave guide to the microwave source of the apparatus of Figure 1; Figure 16a is a plan of the infra-red heating elements of the apparatus of Figure 1; Figure 16b is a side elevation of the infra-red heating elements of Figure 16a; Figure 17a shows the horizontal component of the inner heater of the infra-red heating elements of the apparatus of Figure 1; Figure 17b shows the attachment component of the inner heater of Figure 17a; Figure 18a shows the horizontal component of the outer heater of the infra-red heating elements of the apparatus of Figure 1; Figure 18b shows the attachment component for the outer heater of Figure 18a; Figure 19 is a perspective view of the inner heater of Figure 16a and 16b; Figure 20 is a perspective view of the outer heater of Figure 17a and 17b; Figure 21 shows the microwave choke on the door of the apparatus of Figure 1. The invention described here involves a piece of equipment that with the use of several forms of heat will sterilise and render unrecognisable contaminated medical waste, making disposal into the normal refuse system possible. The material will be made safe at or near the point of use and thereby eliminate the need to transport it whilst it is contaminated. This will mean the installation of many small self contained apparatus around a hospital, in individual wards, clinics and operating theatres as well as in the typical family practitioner and other clinics. The invention

envisages the use of three readily available services only.

1 Single phase electricity with a maximum rating of 7kW.

2 Mains water.

3 Municipal drains. Referring to the drawings, an apparatus and method of waste treatment is described. The apparatus 1 has an outer jacket 2 enclosing an inner vessel 12. The jacket has a dished lid 10. The area between the jacket 2 and the inner vessel 12 has a 50mm void which is filled in situ with foamed insulation 4. The inner vessel 12 has a 25mm thick high temperature ceramic insulation shroud 5 and is supported on ceramic support brackets 8 which are attached to the inner wall of the jacket 2. The apparatus 1 is supported on base supports 11. The jacket 2 encloses the components of the apparatus 1 forming a free standing apparatus 1 which is easily installable and which is powered using a 30 amp power supply. The inner vessel 12 encloses a cavity 3 into which the waste itself or, ideally, containers

containing the waste can be placed. The containers can be in the form of plastic sharp safes as generally used in hospitals to collect medical waste products. Once the medical waste has been placed in the sharp safe and the sharp safe shut, the safe will not need to opened again and the sharp safe is placed directly into the cavity 3 in the apparatus 1. At the base of the apparatus 1 a microwave generator 22 and an isolator 19 are situated. The isolator 19 communicates with the cavity 3 within the inner vessel 12 via a microwave wave guide 15. A water reservoir 26 and a mains water supply 28 also communicate with the inner vessel 12. Entry into the cavity 3 within the inner vessel 12 is via a door 6 (see Figures 2 and 3). The jacket 2 has an opening which is sealed with a pvc moulder piece 41 which ensures that the foam insulation 4 is maintained around the door 6. The door 6 has a choke 9 to ensure that it is microwave tight. The jacket 2 has a dished lid 10 which is formed of pressed metal of a radius of 1200mm and is fitted to the cylindrical portion of the jacket 2 using a

neoprene moulding. The jacket 2 is made from 2mm thick rigidized metal and the surface is textured stainless steel. Figures 7 and 8 show the inner vessel 12 without the outer jacket 2. The inner vessel 12 is cylindrical in shape and has a rectangular door 6 which is of greater size that the short communicating tunnel 42 between the door 6 and the inner vessel 12. The door opening has a rectangular size of 280mm × 500mm and has a machine flange or choke 9. The inner vessel 12 is formed with 10mm aluminium on its top, bottom and flange. The walls of the inner vessel 12 are formed with 3mm aluminium. Figure 9 shows a front elevation of the apparatus 1 with the various components surrounding the inner vessel 12 which would in practice be contained within the jacket 2. The door 6 has a hinge 7 at the bottom of the door. Although other arrangements of door opening could be used. A thermocouple 30 is provided on one of the sides of the vessel 12. A drain 23 is provided at the base of the vessel 12. A microwave generator of 0-2kW and 2450mHz is attached to an isolator 19 which is attached to a microwave guide 15 which passes through a 90 degree bend with a tuning stob and continues on to communicate via a window 18 with the cavity 3 within the inner vessel 12. A mains water supply 28 also communicates with the inner vessel 12 and has a manually operated ball valve 29 connected to a spray nozzle. A dosing system 26 is also provided with a 50ml water reservoir and a manually operated ball valve 27. Referring to Figure 10, a heater terminal enclosure 55 is spaced off from the inner vessel 12 at the top of the vessel 12 by a silicon glass laminate (not shown). Two heaters are provided for the provision of infra-red heat to the vessel 12. The two heaters are a first inner heater 32 and an outer heater 33. The heaters 32, 33 are symmetrical about the centre 56 of the vessel 12 and are disposed 65mm below the top of the vessel 12 in the domed top. A fan 35 is disposed in the top of the vessel dome 13 (Figure 11a and lib) and has a duct formed from 1-6mm aluminium sheet. The microwave guide 15 communicates with the cavity 3 inside the inner vessel 12 via a 10mm thick PTFE microwave window 18 and the 12mm aluminivim plate of the end waveguide flange 50 is welded into the wall of the inner vessel 12 to form a tight fit . There is an extraction circuit 37 ( see Figure 13 ) with a liquid jet vacuum 24 , a filter 38 and a second pump 39 for extraction of fumes from the cavity 3 . Details of the microwave guide 15 will now be provided . A standard flange 43 is provided which is attached to the microwave generator 22 via the isolator 19 . The standard flange 43 is attached to a standard microwave wave guide 44 which via three components turns through a bend of 90 degrees . The first component 45 of the wave guide 15 has a stub tuner 46 with three tapped holes to be drilled and tapped after soldering to the wave guide 15 . The holes are along the centre of the wave guide 15 . A second standard flange 47 is used to attach the three components of the wave guide 15 to a forth straight component 48 . The straight component has a portion of reduced wave guide 49 and has a flange 50 with a dimensioned opening to suit the reduced wave guide 49 . The flange 50 is attached to the window 18 of the inner ves sel 12 . The door 6 has a flange or choke 9 which is des igned to insure that microwaves to not escape from the inner vessel 12 . The dosing system is incorporated into the apparatus 1 to purge the interior cavity 3 of the apparatus 1 with steam which prevents ignition arising from the arcing initiated by the concentration of the microwave field by the sharp points. The apparatus 1 is gas tight and microbiologically sealed such that there is no risk of leakage from the apparatus 1. The apparatus 1 has microwave and/or radiowave heating means which enable a high level of heat to be

introduced in a short time with low power consumption. The microwave energy sterilises the contents of apparatus 1 by means of dry heat. Microwaves may kill germs directly by local application of heat in the fluid in organic matter which causes them to cease to function. The microwaves are emitted from a source and travel along a waveguide and enter the cavity through a window which prevents contamination back along the microwave path from the waste or container and ensures that the container is totally sealed in use. The windows can be formed of silica, mica or other

microwave transparent material. The apparatus 1 also has infra red heating means in the form of an arrangement of heating elements disposed within the cavity 3, preferably on the inside roof surface of the cavity 3 which is dome shaped or

hemispherical. The heating elements radiate heat which uniformly heats the top surface of the waste or

container. In addition, the radiant heat may be used to collapse the container onto itself within the apparatus 1. The heating elements are metal sheet elements of 40-50kW per meter. The microwave supply is required to deliver

approximately 2 kW of power and the infra red heating elements approximately 3.5 to 4 kW and therefore the apparatus 1 can be run from a 30 Amp power supply at 240 volts. A metal tray is disposed within the apparatus 1 into which the container melts. The tray can then be ejected from the apparatus 1 containing the melted container and its contents. Vapour and air movement means are provided within the apparatus 1 in the form of a fan 35 which circulates them within the cavity 3 in order to maintain a uniform heat within the cavity 3 and to prevent volatile components from igniting. The air fan 35 is enclosed within the cavity 3 with an external motor connected to the fan 35 by a sealed shaft. The fan operation is controlled by a control system which determines the temperature in the cavity. A cooling system is also integral within the apparatus 1 to reduce the temperature within the cavity 3 and to treat the fumes, condensed vapours and: odours generated during the operation of the apparatus 1. The cooling system is required to cool the cavity of the apparatus very rapidly. A detection system used to detect the content of containers can be incorporated in the apparatus 1 and this may be achieved by measurement of weight is preferable to ascertain the moisture or fluid content of each container. If necessary extra water can be injected into the container when the container is in the cavity 3 within the apparatus. Alternatively, moisture can be injected into all containers in order to avoid measurement of the fluid content. Moisture is required within the container prior to the microwave application to ensure that there is sufficient moisture for the microwaves to operate and to avoid ignition of the non metallic products by the arcs initiated by metallic products, for example, syringe needles, within the container. The base of the apparatus 1 may also be curved so that any excess water in the cavity can be drawn down and removed from the base. A lift out floor is provided to fit into the curved base. If required a further heating means can be placed under the lift out floor of the apparatus 1. The apparatus 1 casing is formed of stainless steel material and has self cleaning material on the internal surface of the cavity thereby reducing maintenance of the apparatus. The stainless steel casing is ideal for the microwave heat within the cavity 3 and a door 6 is provided in a verticle wall of the apparatus 1 through which the waste or container are inserted into the apparatus and through which the encapsulated waste is removed. The door 6 has a choke 9 in the seal to prevent microwaves escaping from the interior of the apparatus. The door 6 may be on parallel runners and may slide open

vertically. Locking means are provided for locking the door during use of the apparatus. In use, the medical waste products are placed in sharp safes or other containers, as per general hospital or clinic procedure. The containers are then sealed and placed in a apparatus 1. The apparatus 1 is a free standing apparatus 1 which can be placed conveniently and unobtrusively in a hospital or clinic room. The apparatus 1 is designed to run off a 30 Amp power supply and to be self cooling and controlling such that no gaseous emission control is required. The whole container is placed inside the apparatus 1 through a door which is opened by operation of a slide mechanism. Once the waste is inside the apparatus 1, the cavity 3 of the apparatus 1 is initially purged by injection of a blanket of steam. In this invention water is introduced into the sharp safe to achieve two objectives, sterilisation of the contained material and inerting of the atmosphere by the exclusion of oxygen. Two methods are proposed. In the first water is sealed within a pouch which is a moulded part of the sharp safe. When the microwave energy is switched on the water, being the principal dielectric load, draws all the power. This has the effect of boiling the water creating steam and thereby increasing the pressure leading to the rupture of the pouch. The resulting water vapour then acts as a means of transferring heat to the contents of the sharp safe as well as driving the air from the cavity 3 and establishing a low oxygen atmosphere where combustion cannot be sustained. The microwaves will also directly heat and sterilise the water containing substances such as blood and other body fluids contained within the medical items in the sharp safe. The second proposal envisages the use of intense local heat concentrated on the top of the sharp safe. This has the effect of melting a hole and causing the collapse of the lid. Once this has taken place a water nozzle fitted to the top of the cavity doses a

predetermined quantity of water on to the material in the container. The microwave is then automatically switched on, heating the water and creating steam as described above. This ensures that a sufficient amount of moisture is present for the operation of the microwaves. Arcing will occur due to the presence of metal objects in the waste, however, water and the absence of oxygen

prevents ignition from the arcing. Microwaves and infra red heat are then applied to the container in accordance with a control sequence which will sterilise the medical waste and melt the plastic products within the waste and the material of the container. The vapour and air movement means ensures that the infra red heat is uniformly distributed within the cavity. The plastic material of the container collapses

containing the medical waste into a metal tray in the base of the cavity of the apparatus 1. The cooling system is then activated to rapidly cool the cavity in order to enable the cavity to be opened and the metal tray containing the plastic encapsulation of the waste to be removed. A possible operation of the apparatus 1 would follow the following sequence. 1 The sharp safe with its contents will be placed in the apparatus 1 and the door sealed. 2 The automatic control will introduce a small quantity of steam to purge the apparatus 1 of air. 3 The infra-red emitters in the roof of the

apparatus 1 will be switched on.

4 The lid of the safe will soften, sag and develop holes.

5 After a predetermined time water will be dosed

into the container from a nozzle mounted in the roof.

6 The microwave will be switched on.

7 The infra-red emitters around the body of the

apparatus 1 will be switched on.

8 A fan circulating heated air will be switched on. 9 Sterilisation and melt down will take place

simultaneously.

10 The products of evaporation and decomposition will be drawn off by a vacuum pump.

11 Using a water cooled coil or other form of

condenser these products will be condensed and taken to a reboiler for a second heating to boiling point before they are dropped to drain. 12 After approximately 25 minutes the melt down will be complete and the microwave and the infra red will be switched off.

13 The "pancake" will be cooled and removed and

placed in the normal commercial waste system. The waste is then unrecognisable as medical waste and has been sterilised such that it can now be treated like domestic waste and safely transported by public routes. It is an aim of the apparatus 1 that no emissions that cannot be readily disposed of are generated by the apparatus 1. The plastic encapsulations can be left as blocks or shredded to further destroy any recognisable objects or left as blocks. It is envisaged in the future to recycle the material of the blocks for further use. As a secondary use of the apparatus 1, the apparatus 1 can be used as a sterilizing apparatus 1 for surgical tools and apparatus. Apparatus and tools can be placed on a tray in the cavity of the apparatus 1 and the cavity purged with steam as previously described with the waste. The cavity must be maintained at a

temperature above 98°c for 15 minutes or for a

corresponding time at a lower temperature. Infra red radiation can then be applied to remove the moisture from the apparatus and tools and the cooling means operated to reduce the temperature of the cavity prior to opening. This has the advantage that a sterilizing apparatus 1 can be unobtrusively available in a hospital or a doctor or dentist's surgery. Modifications and improvements can be incorporated without departing from the scope of the present

invention.

Claims

CLAIMS 1 . An apparatus for waste treatment comprising a

cavity in which material is placeable , means for purging the cavity with steam, and means for applying at least one form of electromagnetic radiation, to material within the cavity . 2 . An apparatus as claimed in Claim 1 , wherein the means for applying at least one form of

electromagnetic radiation applies high frequency dielectric heating and is in the form of a microwave or radio wave frequency source . 3 . An apparatus as claimed in Claim 1 , wherein the means for applying at least one form of

electromagnetic radiation applies radiant heat and is in the form of infra red radiation emitters . 4 . An apparatus as claimed in Claim 1 , wherein the means for applying at least one form of

electromagnetic radiation applies both high frequency dielectric radiation and infra red radiation . 5 . An apparatus as claimed in any one of the

preceding claims , wherein the waste is processed in a container of plastics material . 6 . An apparatus as claimed in Claim 2 or Claim 3 , wherein a plurality of infra red radiation

emitters are disposed in an arrangement in the curved top of the cavity. 7 . An apparatus as claimed in any one of the preceding claims, wherein a pouch containing fluid is incorporated into the container. 8. An apparatus as claimed in any one of Claims 1 to 6, wherein means are provided for injecting liquid into the cavity. 9. A method of waste treatment comprising placing the material in a sealed cavity, purging the interior of the cavity with steam and applying at least one form of electromagnetic radiation to the material within the cavity. 10. A method of waste treatment as claimed in Claim 9, wherein the form of electromagnetic radiation applied is high frequency dielectric heating and is generated by a microwave source or radio wave frequency source. 11. A method of waste treatment as claimed in Claim 9, wherein the form of electromagnetic radiation is infra red radiation emitted from a radiant

component. 12. A method of waste treatment as claimed in Claim 9, wherein the form of electromagnetic radiation is high frequency dielectric heating and infra red radiation. 13. A method of waste treatment as claimed in any one of Claims 9 to 12, wherein the waste is contained in a container of plastics material prior to placing in the cavity. 14. A method of waste treatment as claimed in Claims 10 and 12, wherein the high frequency dielectric heating is microwave radiation. 15. A method of waste treatment as claimed in any one of Claims 9 to 14, wherein circulation means circulate the heat within the housing. 16. A method of waste treatment as claimed in any one of Claims 9 to 15, wherein infra red radiation is initially applied to the container to melt the top of the container. 17. A method of waste treatment as claimed in Claim 16, wherein an injection of liquid is made into the open container prior to the application of the microwave. 18. A method of waste treatment as claimed in anyone of Claims 9 to 16, wherein a pouch containing fluid is incorporated in the cavity, which fluid is heated by the application of microwaves to the cavity, thereby producing steam. 19. A method of waste treatment as claimed in any one of Claims 9 to 18, wherein the cavity is cooled after the heating before opening the cavity. 20. A method of waste treatment as claimed in any one of Claims 9 to 19, wherein the waste is removed as an encapsulated block and processed as domestic waste or recycled for further use. 21. A sterilising apparatus comprising a sealed cavity in which objects are placeable, means for purging the cavity for a set period of time with steam, and means for applying radiant heat to the cavity.