NZ282429A - Sealed chamber high-frequency electromagnetic field hazardous waste steriliser - Google Patents

Description

282429 New Zealand No. 282429 International No. PCT/FR95/00278 Priority Data{a): CompNrt# Sp«*c*ton RM: Q»w: (8) .ay..^./.9.fi;...awt)r..U9.S.

Publication Oatfa: P.O. Journal Mo: (htJ.lff.

NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION Title of Invention: Method for sterilising hazardous waste, particularly hospital waste, using high frequency treatment, and device therefor Name, address and nationality of applicant(s) as in international application form: SOCIETE GENERALE POUR LES TECHNIQUES NOUVELLES SGN, of 1 Rue des Herons, Montigny-Le-Bretonneaux, 78184 ST. Quentin en Yvelines, France 282429 1 Method for sterilizing hazardous waste, particularly hospital waste using high-freauencv treatment, and device therefor The present invention has for its object a method for sterilizing hazardous waste and the device associated therewith. Said method, as will appear from its description, is 5 suitable for sterilizing liquid and/or s6lid waste presenting a certain humidity rate and particularly for sterilizing solid waste produced by hospitals, medical, dental, veterinary... surgeries or liquid waste coming from slaughterhouses. It employs a high frequency electromagnetic field.

Insofar as traditional incineration did not offer guarantees of hygiene and safety 10 with such waste, special, very expensive incinerators have been developed and numerous other techniques have been developed in parallel.

According to the prior art, numerous processes have been proposed for sterilizing such waste, and in particular: - processes by incineration (incineration with extended dwell time, IS incineration in plasma medium, magmatic process); - thermolytic processes (i.c. with pyrolysis in the absence of oxygen); - processes by sterilization/disinfection (autocluving process; process of chemical decontamination employing for example Javel water; process by ionization); - processes by micro-wave and high frequency heating.

Those employing micro-wave energy can efficiently process only finely divided matter and they therefore require prior grinding of the waste to be processed.

Furthermore, from the energetic standpoint, as the frequency of relaxation of the free water (between 1 and 100 GHz) is very different from that of the water bonded to the cellulose (close to 20 MHz), it will be understood that the yield of the micro-waves 25 cannot be optimum.

In this spirit, a method for processing hospital waste which uses, not microwaves, but high frequency, has been developed in the United States. Said method is called the STERICYCLE method, whereby the medical waste to be processed is previously packed in sealed boxes, passed in a grinder-shredder and compacted. It is 30 then introduced in thermally insulated containers made of a material permeable to the electromagnetic field which advance, for about 5 minutes, in a tunnel applicator between the electrodes of a high frequency generator. Said isothermal containers are taken in said HF tunnel to uniform temperatures of 85-l25°C and are capable of maintaining these conditions for 3 to 4 hours. However, such conditions of temperature and duration 35 cannot be exceeded in view of the material constituting said containers. 282429 Said STERICYCLE method and methods of the same type are described in particular in Applications WO-A-92 04920, WO-A-92 00764 and WO-A-92 00766.

According to the invention, for sterilizing and/or disinfecting such waste, a method is proposed which uses high frequency energy but which, in addition, 5 optimalizes this use, making it possible to obtain the expected result in record times: 3 minutes, for example. Such optimalization employs the parameter pressure.

The present invention therefore proposes a method for sterilizing liquid and/or solid hazardous waste presenting a certain rate of humidity, which includes the treatment of said waste by a high frequency electromagnetic field . In characteristic manner, said 10 treatment is carried out in a sealed chamber, the means of application of the electromagnetic field constituting all or part of said chamber.

Said method is particularly suitable for processing hospital waste which contains damp cellulose.

The choice according to the invention of high-frequency electromagnetic 15 radiation is particularly judicious. In fact: - said electromagnetic radiation brings the heating energy in homogeneous manner to the heart of the processed waste (poor heat conductors), and rapidly. (Inversely, the low heat conductivity of said waste renders the conventional heating methods by heat conduction inefficient. Such methods are generally carried out in heating screws with very long dwell times...); - said electromagnetic radiation has a frequency particularly adapted to the composition of the waste to be processed. In fact, damp cellulose presents a domain of relaxation in high frequencies. (This is why it heats less well in micro-wave); - said electromagnetic radiation has a wave-length higher than the 25 dimensions of the waste to be processed. It is therefore unnecessary, at high frequency, to grind said waste and reduce its volume to ensure homogeneous heating, in its mass. (Inversely, such a prior grinding and a small processing volume are compulsory in the case of micro-wave treatment. The use of a grinder then poses problems of bulk, excess cost and contamination of said grinder...).

Said electromagnetic radiation, used for processing hazardous waste according to the invention, generally has a frequency included between 1 and 300 MHz. Said frequency is advantageously included between 1 and 100 MHz. Preferably still, it is" set" on the frequency of relaxation of the water bonded to the cellulose: between 1 and 30 MHz, advantageously close to 27 Mhz.

In characteristic manner, the high frequency electromagnetic field is, according to the invention, applied in a sealed chamber (rendered tight during the processing); the 282429 means of application of said field constituting all or part of said chamber. Characteristically, said electromagnetic field is applied to waste under pressure, the pressurization thereof "directly" employing the means of application of said field and not only a container containing them. Hii" is explained hereinafter.

According to the prior art - STERICYCLE method and the like - as recalled hereinbefore, the waste is processed in a container, advantageously sealed, disposed in an applicator of the electromagnetic field. Said container is necessarily chosen to be made of a material permeable to said field, such as cardboard, plastic..! It can therefore not withstand high pressures... Consequently, said container and the waste that it contains cannot be subjected to optimal sterilization conditions. Furthermore, it will be noted that, under such conditions for carrying out sterilization, the outer walls of said container cannot be sterilized.

According to the invention, the waste is processed under conditions where the parameter pressure is mastered and used to advantage. Said waste is processed within a chamber, which includes in its structure the means of application of the electromagnetic field (which may consist of said means of application) and which is rendered tight during processing. Such tightness obtained with the field application means is, according to the invention, fundamental. It allows rise in pressure... and therefore an optimal sterilization. It will be noted that, within the sealed chamber, the outer walls of the waste or of the container which contains it, are decontaminated by thermal effect.

In summary, according to the invention, in characteristic manner, the waste processed is done so under a certain pressure, insofar as the method is carried out in a sealed chamber (pressure obtained by vaporization of the water initially contained in said waste). Said pressure is perfectly tolerated insofar as the means for application of the electromagnetic field constitute all or part of said chamber. The man skilled in the art will already have understood the interest of such an arrangement.

Advantageously, during processing within the sealed chamber, the waste is compressed mechanically. Such mechanical compression optimalizes processing.

To that end, mechanical means made of a material permeable to the field may be employed within the chamber.

According to the preferred variant of the method of the invention, the means for application of the electromagnetic field are used for compressing the waste and maintaining it compressed during processing. According to this preferred variant, said waste is mechanically compressed in the chamber, by means of the electromagnetic field applicators, then said electromagnetic field is applied to said waste thus maintained compressed. 282429 The pressure at which the waste processed according to the invention is maintained, makes it possible to take it to temperatures higher than 100°C and therefore enables said waste to be sterilized in record times. In that, the method of the invention is particularly efficient. Said method makes it possible to take materials which are 5 sparingly heat-conducting beyond 100°C - up to temperatures of the order of 180*C (temperatures which ensure optimal sterilization - for example with respect to the hepatitis C virus) - by transmitting energy directly thereto, irradiating them at frequencies close to the frequency of relaxation of the water in said Waste.

The pressures recommended for carrying out the method of the invention are 10 those included between 10^ and 3.10^ Pa (between 1 and 30 bars).

Said pressure must be greater than a minimum to lead to the expected result: the rise in temperature of the waste to be sterilized beyond 100, 150°C. However, said pressure does not need to attain too high values. It is not desired to melt the materials, simply to destroy the hazardous germs (pathogen*~ agents).

Hie pressure at which the waste is maintained during the method of sterilization of the invention, is obtained in any case by the vaporization of the water that it initially contained; vaporization inherent to the high frequency irradiation. It may also be obtained, particularly in accordance with the preferred variant of the invention set forth hereinabove, by a mechanical action: the waste treated by the magnetic field is 20 advantageously done so by being compressed (simultaneous action of said field in a sealed chamber advantageously equipped with sensors and means for regulating its internal pressure and a mechanical pressure).

The man skilled in the art will have understood on reading this description that the waste to be processed must imperatively contain a minimum of water. In fact, said 25 waste must imperatively present dielectric losses.

This minimum (100 g of water for 10 kg of waste) has been assessed at about 1% by weight. Water is understood here to mean both "pure" water and water laden in particular with impurities, mineral salts... Hospital waste is particularly laden with urine, blood,...

This rate of I % by weight is generally widely exceeded. However, it is not impossible to have to process, by the method of the invention, waste which does not present the required rate of humidity. Such waste, before being subjected under pressure to the high frequency electromagnetic field, must be packed and/or treated to adjust its rate of humidity. To that end, it may be humidified by watering for example or by 35 packing it in a bag, of the refuse bin type, presenting a water-laden gel in an interior coating. 282429 The waste presenting the required rate of humidity may be subjected to the high frequency electromagnetic field as it is or in the compressed state. (In any case, it has been seen that it is maintained under pressure during processing).

In fact, it is not impossible to process by the method of the invention waste 5 previously compressed, previously subjected to a mechanical compression in a device other than the one in which it is subjected to the electromagnetic field.

However, it is particularly interesting to note that the method of the invention makes it possible to process waste having undergone no prior mechanical treatment (cither grinding or compacting)...

In accordance with its preferred variant (within the framework of which the means for application of the electromagnetic field are used for compressing the waste and maintaining it compressed during said treatment), said method successively employs compacting and high frequency treatment under pressure, in the same device, which is auto-sterilized upon each use. Such a compacting, in-situ, is advantageously "employed 15 as it makes it possible, on the one hand, to reduce the volume of the waste to be processed and, on the other hand, to increase its density. Said waste then presents a higher dielectric constant, this reinforcing the efficiency of the high-frequency treatment.

According to this preferred variant, waste maintained under pressure is therefore 20 treated by a high-frequency electromagnetic field, said pressure resulting from a mechanical action (compacting in situ) and from vaporization of the water that said waste contained.

The method according to the to the waste the following conditions 25 - temperature - pressure - duration of processing nvention is advantageously carried out by applying 150 to 180°C .105 to 10<> Pa (5 to 10 bars) to 3 mins.

These conditions are established, according to the invention, by subjecting said waste, in an adequate device, to a high frequency electromagnetic field. In fact, said 30 waste is subjected to a stoving in a humid environment. Such stoving is advantageously carried out at 180°C under a pressure of 10 bars, for a few minutes.

The method of the invention is particularly advantageous in that it employs a high frequency electromagnetic radiation (cf. hereinabove in the present specification) and in that it may be employed with waste which has not been mechanically treated (for 35 example waste such as in garbage bags), on the site of production thereof or in the proximity. 282429 For example, garbage bags may be directly treated according to the invention in devices of small dimensions. As a result of the method of the invention, such bags, made of plastic, filled with the waste, lead to pellets presenting a rigid gangue, which are nontoxic, non-infectious and easy to handle.

The method according to the invention is also advantageous in that it is question of a discontinuous batch method. This allows a more efficient control of the sterilization and/or disinfection by a better follow-up of the physical conditions imposed on the product treated.

Said method does not pose any particular problem in its implementation. The 10 man skilled in the art can optimalize his parameters for the treatment of a given batch. It will be noted here that the presence of metal in said batch does not constitute a major obstacle. Batches which contain up to 5% by weight of metals can be treated according to the invention.

The method has been described more particularly with refcrcncc to solid waste, 15 of the hospital waste type. The man skilled in the art will easily appreciate that it is also suitable for treating liquids such as those coming from slaughterhouses.

Said method is also advantageous in that it may be employed in a simple device, possibly of small dimensions.

Such a device, of which various variants may exist, constitutes another object of 20 the present invention.

In characteristic manner, it comprises: - means for generating a high-frequency electromagnetic field; - a sealed chamber adapted to receive the waste to be treated, said chamber comprising the means for application of said electromagnetic field and being equipped with sensors and means for regulating its internal pressure.

Said chamber is sealed in order to obtain the desired pressure; it is sealed and equipped with sensors and means for regulating its internal pressure for maintaining and regulating said pressure. Said means advantageously consist either of valves or of means for servo-controlling the power furnished by the generator. In the case of valves, the 30 extracted gas is filtered.

Said chamber is advantageously also equipped with means for measuring its internal temperature. By knowing this parameter (temperature), the minimum duration of the treatment may be fixed (to obtain the desired effect - sterilization and/or disinfection).

When the method is carried out, said chamber is surrounded by an electromagnetic shielding in order to limit and even avoid any wave leakage. 282429 Said chamber is advantageously dismountable in order to facilitate introduction therein of the waste to be treated and evacuation of said treated waste.

It is equipped with means for generating the high-frequency electromagnetic field within it. In particular, it is connected to a high frequency generator. Such a 5 generator and the functioning thereof are familiar to the man skilled in the art.

In particular to implement the preferred variant of the method of the invention, the sealed chamber of the device of the invention advantageously .comprises means for compressing the waste and for maintaining it in the compressed state. In such a device, the irradiated waste undergoes a pressure due to the mechanical compression and to the 10 vaporization of the water that it contained. Such a device may be qualified as a sterilizing press. Such a press system makes it possible to reduce the volume of the waste and to irradiate it thereafter at constant volume, this implying a rise in pressure of said volume.

Said means for compressing the waste and for maintaining it in the compressed 15 state during treatment may consist of "added" means, disposed inside the chamber. They are, of course, made of a material permeable to the field. However, to exert the desired compression, the means for application of the electromagnetic field are advantageously used. Within the framework of this advantageous variant, the field application means may constitute the sealed chamber taken as a whole or only a part thereof. 20 Two variants of the device of the invention will be described in detail hereinafter.

According to a first variant, the device of the invention comprises a high frequency generator connected to two electrodes which constitute two opposite walls of the chamber, the other walls being made of an insulating material with low dielectric loss. According to this variant, said chamber may be of parallelepipedic or cylindrical 25 shape. For implementing the preferred variant of the method of the invention, said chamber presents at least one mobile wall. With the aid of said wall, the required mechanical pressure may be exerted on the treated waste. In fact, said waste to be treated is introduced in the chamber, it is compressed with the aid of said wall, then the high frequency electromagnetic field is applied in the chamber thus defined. According to this 30 variant of the invention, said mobile wall preferably consists of at least one of said two electrodes, connected to the high-frequency generator. According to this variant, the field application means constitute only a part of the sealed treatment chamber.

According to another variant of the invention, the sealed chamber is a monomode cavity for the propagation mode TE^q or T^Ol- Such a cavity is parallelepipedic for the 35 propagation mode TEiq, cylindrical for the propagation mode TMqi- It is supplied by a high frequency coupling system. 282429 8 For implementation of the preferred variant of the method of the invention, said cavity is equipped with a piston mobile in translation. According to this variant, the field application means constitute the sealed treatment chamber.

Whatever the variant embodiment of the device of the invention, it must 5 obviously allow introduction of the waste to be treated and evacuation of said treated waste. Said device advantageously presents walls sliding with respect to one another, at least one of them being retractable.

The waste processing chamber presents a volume adapted to that of said waste (as it is or compressed) and obviously also adapted to the output impedance of the generator. 10 The transfer of power from an electric generator towards its load is in fact optimum if the nominal output impedance of said generator is equal to that of the load which is connected thereto.

In order to optimalize this transfer of energy, the device of the invention may be equipped with an impedance matching system. Such a system, which is advantageously 15 automatic, makes it possible to process diverse loads in the same chamber, particularly very variable quantities of waste (for example 1 kg, 5 kg, in the same way as 60 kg). Such systems exist and have been described in particular by Messrs. C. MARCHAND, T. MEUNEER and M. FORGEAT in "Industrial high-frequency and micro-wave generators". Micro-wavcs and high-frequencies. International Congress at Nice. 20 October 1991. Volume 1.

However, such systems present the drawback of being expensive.

They are in no way indispensable for carrying out the method of the invention. In fact, they constitute an appreciable advantage. In their absence, the man skilled in the art is quite capable of dimensioning and adapting a device of the invention to a given load: 25 for example, a device of the invention may be calculated to be of small dimensions, installed in a hospital, and regularly processing 60-litre garbage bags filled with waste.

Once again, the interest of the invention is emphasized, in that it makes it possible to process waste in-situ, without prior grinding, virtually as it is produced. The problem of decontamination of the grinder is thus overcome. Similarly, with compacting 30 in-situ, the problem of decontamination of a compactor used upstream, in accordance with the prior art methods is dispensed with.

According to the invention, the waste contaminates only the chamber which, by carrying out the method, is auto-sterilized.

The interest of the method and device of the invention follows obviously from 35 the above description. 282429 9 : — ■ The waste decontaminated in accordance with the invention may subsequently be handled and processed without problem. In particular, it may be ground and incinerated by conventional incineration.

Three Figures accompany the present description.

Figure 1 schematically shows in perspective the preferred variant of the device of the invention for carrying out the claimed method of sterilizing hazardous waste.

Figures 2 and 3 schematically show in perspective two other variants of said device.

Figure 1 shows a cylindrical press (references 1 + 2 •+ 3) within which 10 contaminated waste may be processed according to the invention. Said waste is introduced for treatment in the scaled chamber 6, defined by the clcctrodes 1, 2 and the vertical wall 3. (Electrode 2 is retracted for introduction of said waste).

Electrode 1, called hot electrode, is immobile, while earth electrode 2 is mobile in translation and may thus perform the role of piston. Thanks to it, the volume of the 15 chamber 6 and the density of the waste to be processed may be adjusted before the high frequencies are applied.

The vertical wall 3 is made of an (electrically) insulating material with low dielectric loss. It is raised to recover the processed waste.

Said electrodes 1 and 2 are connected to a high frequency generator 4 controlled 20 by a quartz at, for example 27.12 MHz. The electromagnetic circuit is, in addition, equipped with an automatic impedance matching system 5 which makes it possible to optimalize the transfer of energy between the generator 4 and the press 1 + 2 + 3.

A grid is arranged around such a press, acting as electromagnetic shielding in order to avoid any wave leakage.

A press of this type was used for carrying out the method claimed, particularly under the conditions of the Example given hereinafter by way of example.

Within the framework of this variant of the invention, the means for application of the electromagnetic field (electrodes 1 and 2) constitute a part of the sealed treatment chamber (1 + 2 + 3 = 6).

Figures 2 and 3 show other devices of the invention, in principle of larger dimensions, which function in monomode.

Figure 2 shows a parallelepipedic monomode cavity 10 for the propagation mode TEiq. Dimensioned at 27.12 MHz, it presents the following dimensions: 4 m x 3 m x 1.5 m. It is advantageously equipped with a mobile piston 12. It is supplied by the high 35 frequency coupling system 11, connected to the high-frequency generator 4'. The 282429 electromagnetic circuit advantageously comprises an automatic impedancc matching system 5'.

Said high-frequency coupling system 11 consists of a coaxial cable with antenna, said antenna advantageously being retracted when the waste to be treated is loaded in the 5 wave guide (the mobile piston 12 also being retracted), then entered in said wave guide for carrying out the method of sterilization.

Figure 3 shows a cylindrical monomode cavity 20 for propagation mode TMoi-Dimensioned at 27.12 MHz, it presents the following dimensions: height: 4 m 10 diameter of the bases: 2 m It is advantagoeusly equipped with a mobile piston 22. It is supplied by a high-frequency coupling system 21, connected to the high-frequency generator 4". The electromagnetic system advantageously comprises an automatic impedance matching system 5".

The high-frequency coupling system 21 consists of a coaxial cable with antenna, said antenna advantageously being retracted when the waste to be treated is loaded in the wave guide (the mobile piston 22 also being retracted), then entered in the latter for carrying out the method of sterilization.

In order to recover the waste processed in the devices according to Figures 2 and 20 3, the parallelepipedic or cylindrical sleeve is advantageously slid, the bases remaining fixed.

Within the framework of its other variants of the invention, the means for application of the electromagnetic field (the wave guide) constitute the sealed treatment chamber.

The following example will illustrate the implementation of the method of the invention, in a device of the type as shown in Figure 1. However, it will be noted that the device employed presents a parallelepipedic (and not cylindrical) chamber.

The high-frequency generator used is controlled by a quartz at 27.12 MHz. It restores a power of 1.2 kW. It is mounted in series with an automatic impedance 30 matching system at 50 Q.

The electrodes are rectangular, of dimensions: 7.5 cm x 15 cm. The other two walls of the chamber are made of a composite material (glass fibers + silicone). Said electrodes and walls constitute a gas-tight chamber. 1 litre of waste, constituted by : - one latex glove - a damp cellulosic substrate (diaper) 282429 - a bottle of serum - five stainless steel needles - two cardboard packingsis treated in said chamber according to the invention. The mass of said waste contains about 100 g water. It is positioned in the sealed chamber, then compressed by manually descending the upper electrode. The waste thus compacted presents a volume of about 0.51, for a height of about 5 cm.

The high-frequency electromagnetic field of 1.2 kW is applied for 3 mins. Within i the waste thus processed, the temperature attains 180°C. The object of sterilization of said waste is thus attained. 282429 ® J#~IZ

Claims (13)

1. WHAT WE CLAIM IS;
2. PIT ATT.iCft
3. \Aao "*"V;1. Method for sterilizing liquid and/or solid hazardous waste Ipfooonting a|eeftain mumidity rate, particularly hospital waste, said method including the treatment of said;5 waste by a high-frequency electromagnetic field, and being characterized in that said waste is treated 'n a chamber rendered tight during said treatment, the means of application of s?id electromagnetic field constituting all or part of said chamber.;2. Methou according to Claim 1, characterized in that said waste is compressed mechanically during said treatment.;10 3. Method according to one of Claims 1 or 2, characterized in that it comprises, in said sealed chamber:;- the mechanical compression of the waste by means in particular of the means for application of the electromagnetic field;;- subjecting said waste, maintained compressed, to the action of the 15 electromagnetic field.;
4. 4. Method according to any one of Claims 1 to 3, characterized in that said electromagnetic field has a frequency included between 1 and 300 MHz, advantageously close to 27 Mhz.;
5. 5. Method according to any one of Claims 1 to 4, characterized in that said waste is 20 treated at a pressure included between 10^ and 3.10^ Pa (1 and 30 bars).;
6. 6. Method according to any one of Claims 1 to 5, characterized in that said waste, before being subjected to said electromagnetic field in said chamber:;- have been packed and/or pre-treated in order to adjust itsjhumidity rate and/or;25 - have been mechanically compressed.;
7. 7. Method according to any one of Claims 1 to 6, characterized in that said waste is treated for 10 to 3 minutes, at a temperature included between 150°C and 180°C and at a pressure included between 5.10^ and 10^ Pa (5 and 10 bars).;
8. 8. Device for carrying out the method according to any one of Claims 1 to 7, 30 characterized in that it comprises :;- means for generating a high-frequency electromagnetic field ;;- a sealed chamber adapted to receive the waste to be treated, said chamber comprising the means for application of said electromagnetic field and being equipped withjsensors and means for regulating its internal pressure.;j*r
9. 9. Device according to Claim 8, characterized in that said sealed chamber is equipped with means for compressing the waste and maintaining it in the compressed state during treatment. 5
10. 10. Device according to one of Claims 8 or 9, characterized in that the means for application of the electromagnetic field are used for compressing said waste and maintaining it in the compressed state during the 10 treatment during treatment. 282429
11. 11. Device according to one of Claims 8 to 10, characterized in that it comprises a high-frequency generator connected to two electrodes which constitute 15 two opposite walls of said chamber, the other walls being made of an insulating material with low dielectric loss; at least one of said two electrodes advantageously being mobile in translation. 20
12. 12. Device according to any one of Claims 8 to 10, characterized in that said chamber is a chamber adapted to the frequency of the.electromagnetic field to function in monomode (TE10 or TMqi), advantageously equipped with a piston mobile in translation. 25
13. 13. Device according to any one of Claims 8 to 12, characterized in that it comprises an impedance matching system. 30 SOClfiTfi GfiNfiRALE POUR LES TECHNIQUES NOUVELLES SGN By its Attorney DON HOPKINS & ASSOCIATES 35 Per: end of claims