EP2694119A1

EP2694119A1 - Autoclave for medical waste sterilization and operation method thereof

Info

Publication number: EP2694119A1
Application number: EP12718338.2A
Authority: EP
Inventors: Mario DAMIANI
Original assignee: Ecosystem SRL
Current assignee: Ecosystem SRL
Priority date: 2011-04-07
Filing date: 2012-04-04
Publication date: 2014-02-12
Also published as: RU2013147284A; CN103547295A; WO2013050822A1; ITBA20110015A1; JP2014512909A

Abstract

The invention relates to a machine for the treatment of infectious waste in order to obtain its sterilization, and more specifically to an autoclave to be inserted in the processing cycle of medical waste, in order to disinfect and neutralize the biological agents by means of the inactivation of the pathogenic microorganisms, virus, and sporogenic bacteria contained therein. The autoclave is provided with two chambers: an internal and an external one, where high-pressure saturated steam is injected; the external chamber keeps warm the walls avoiding steam condensation and resulting leachate.

Description

AUTOCLAVE FOR MEDICAL WASTE STERILIZATION AND OPERATION

METHOD THEREOF DESCRIPTION

TECHNICAL FIELD

The present invention relates to the field of machines for the sterilization of hazardous infectious sanitary waste. Said machines, commonly called sterilization autoclaves, have the purpose of implementing disinfection and bioremediation of particularly hazardous medical waste in order to make inactive the pathogenic microorganisms, virus and sporogenic bacteria therein, thus obtaining waste which can be incorporated into the municipal solid waste that can be transported and disposed of in public landfills without any risk of contamination or infection.

More specifically, the purpose of the present invention is to obtain the inactivation of the microorganisms by means of the action of high-pressure saturated steam, by installing the sterilization autoclave into a larger plant together with other devices also intended to neutralize waste.

According to the present invention, the infectious medical waste undergoes, at the end of a more complex process, high-temperature heat treatment for a period of time necessary to ensure the inactivation of the microorganisms contained therein.

Damage is irreversible and leads to the elimination of the growth and multiplication function of the microorganisms themselves.

Furthermore, the device does not produce reject liquids, while the gaseous effluents are captured inside the plant itself in order to be processed by a suitable disinfection process, and then discharged into the environment with properties that meet the existing law concerning emissions. As it is known, hospitals, medical laboratories, as well as all other organizations related to health services produce a large amount of potentially infectious waste, such as for example bandages, syringes, cannulas, or other materials that contacted with potentially infectious patients, as well as infectious waste such as bacteria, virus, spores, etc.

Until it is delivered at the designated centers, where it may be destroyed by thermal means, said medical waste require special measures in order to prevent infection.

The sterilization process consists in reducing the bacteria content in order to guarantee a S.A.L. (Sterility Assurance Level) of at least 10^"6.

Sterilization is carried out according to the UNI 10384/94 regulation, part 1, by means of a process which includes shredding and drying, for the purposes of removing any recognizable semblance of the waste and improving the efficiency of the treatment, as well as reducing the volume and weight of the waste itself. Only potentially infectious hazardous sanitary waste can be sterilized. Sterilization of infectious sanitary waste is a viable option to simplify the handling of the waste itself.

BACKGROUND ART

A known technique to avoid the risk of contagion consists in collecting the waste in containers, which are hermetically sealed once full, and that are moved to a collection center inside the hospital building. Said containers are periodically removed by specialized companies tasked with transporting them to designated plants, where they are finally thermo-destroyed.

An additional known method consists in disinfecting medical waste by means of chemical agents, which react when they come into contact with infected waste, or irradiation with gamma rays.

The aforementioned sterilization method is obtained by placing the waste in special containers and adding a disinfectant. Once full, the containers are further placed into a microwave chamber; in this manner sterilization is obtained by the thermal and chemical action on the microorganisms. However, the container allows for a single treatment for special small size waste, and, in addition, it does not ensure the required level of prevention against infections. Furthermore, said method has an additional disadvantage resulting from the disposal of the chemicals used in the treatment.

More in general, the prior arts have a series of disadvantages; first of all there is the substantial risk of infection for the medical and hospital auxiliary staff, as well as for the personnel responsible for transporting and handling the waste.

An additional disadvantage consists in the cost of waste transport and its incineration, which is substantially higher than the costs for household waste.

The autoclaves designated for this purpose have a series of disadvantages so that it is not always possible to obtain the desired results in the waste sterilization process.

One of these disadvantages consists in the fact that when the waste is placed inside the autoclave, it builds up in the machine, so that the steam action is more effective on the waste located externally of the pile, but it is not effective for sterilization of the waste concentrated in the middle of the pile itself.

Another disadvantage is caused by the fact that the waste is heated only by the steam injected into the autoclave, which thereafter tends to condense on the colder walls of the container by causing leachate. A machine that attempts to overcome the above disadvantages is described in patent WO99/12580 A2, which describes a horizontal autoclave provided with a means for shredding the waste and its re-mixing. However, it has been found that waste shredding by means of scrapers/mixers located only inside the autoclave is not sufficient to reach the microorganisms lodged in the waste, therefore making the subsequent sterilization less effective. Furthermore, the autoclave described in said patent does not provide for the injection of the steam inside the main sterilization chamber, but it only uses the steam arising from heating of the wet component of the waste. Laboratory tests have confirmed that the steam generated from the wet component of the waste only is not enough to guarantee a good level of sterilization.

Patent WO 92/12738 describes a process for the sterilization of medical waste. Said process provides for the waste to be first introduced into a container and thereafter shredded by means of rotating blades. Said process presents the disadvantage resulting from the employed shredding method, which does not allow the fine shredding of the waste, with the result that the steam subsequently introduced is not sufficient to destroy all the microorganisms contained in the waste itself. Furthermore, the lack of a means for re-mixing and expelling the waste prevents the complete evacuation of the waste from inside the container at the end of the sterilization cycle.

BRIEF DESCRIPTION OF DRAWINGS

These and additional disadvantages are solved by the autoclave for the sterilization of medical waste of the present invention, which is described in a preferred non-limiting embodiment of further embodiments within the scope of the patent itself, with reference to the following figures: Fig. 1, a lateral cross-section view of the autoclave with counter-clockwise rotation of the screw to obtain stirring of the waste;

Fig. 2, a lateral cross-section view of the autoclave with clockwise rotation screw to promote the waste discharge;

Fig. 3, a lateral cross-section view of the autoclave with partially raised screw to allow maintenance work inside the autoclave;

Fig. 4, a cross-section plan view of the autoclave;

Fig. 5, a cross-section view of a segment of the autoclave wall;

Fig. 6, a plan view of the autoclave;

Fig. 7, a detail of the bottom support of the screw axle;

Fig. 8, an example of a medical waste sterilization plant, where the autoclave is implemented according to the provisions of the present patent. DETAILED DESCRIPTION OF THE INVENTION

The medical waste sterilization autoclave in the present invention is described hereinafter with reference to the enclosed drawings.

In particular, with reference to Figure 1, the autoclave comprises an internal sterilization chamber 1 and a cavity 4, both chambers comprising a volume inside of which high-pressure steam is injected through two distinct and separate circuits operating at two different pressures; more in particular, the steam pressure inside said sterilization chamber 1 is two bars lower than the pressure inside cavity 4 for the entire duration of the waste treatment cycle.

Steam injection into cavity 4 determines a thermal exchange into the internal sterilization chamber 1 , so as to facilitate heating of the newly introduced waste, in addition to maintaining a constant high temperature inside chamber 1 itself, and further preventing the formation of condensate and leachate as a result.

According to the present invention, shell 2 of the autoclave presents an inverted half-shell shape supported on a base 21, and comprises an internal wall 3, a cavity 4 wherein the high-pressure saturated steam flows, and an external wall 5 covered with an insulation layer 6. In order to make the shell more resistant, a number of reinforcements 27 are present inside cavity 4, which connect the internal wall 3 with the external wall 5.

With reference to Figure 1 , the length of internal sterilization chamber 1 is crossed by a screw 7 coupled with a shaft 8 operatively connected to a reduction gear and a motor M; screw 7 has two functions, namely stirring the waste when the rotation applied to shaft 8 is counter-clockwise, or promoting the waste discharge through valve 9 when the rotation applied to shaft 8 is clockwise. In order to enable the stable rotation of shaft 8, and at the same time allow the shaft itself to be easily pulled out from the internal sterilization chamber 1, an end 8a is inserted into a plain bearing fixed to a guide 25.

One or more rods 10 are attached crosswise to the shaft 8. These rods hold scrapers 1 1 at their ends, helping to remove the waste potentially deposited on internal wall 3.

In order to allow the steam circulation, the autoclave presents a number of valves; in particular valves 17 for steam penetration into the internal sterilization chamber 1, one or more valves 18 for steam penetration into the cavity 4, one or more valves 19 for discharging and draining the condensate formed inside the cavity 4, a valve 20 for venting the air contained in the internal sterilization chamber 1 when replaced by the high-pressure saturated steam, a valve 26 for discharging the steam from internal sterilization chamber 1 at the end of the process, a valve 29 for air ejection from the cavity 4 during steam injection. The autoclave also has a number of control devices for the sterilization process; and more in particular, two capacity sensors 23a and 23b for managing the volume of waste injected in the internal sterilization chamber 1, and a pressure sensor 24 located at the base of the internal sterilization chamber 1 itself.

With reference to Figure 6, one or more windows 28 are present on top of the autoclave, which allow inserting bioindicators inside the internal sterilization chamber 1.

In order to allow maintenance work inside the sterilization chamber 1, the autoclave is provided with a top opening 22 comprising a top flange 12, attached by means of pins or bolts to a second removable blind flange 13.

The waste is introduced into the internal sterilization chamber 1 through a valve 14 located on the top section of the autoclave, and connected to it by means of flange 15. On the other hand, the waste is expelled through valve 9 fixed on the bottom to the autoclave by means of flange 16. According to what is claimed, the waste sterilization process according to the present invention is carried out by means of the following steps:

1. Loading valve 14 open:

a. Discharge valve 9 is closed;

b. Scrapers 11 attached to the screw 7 by means of rods 10, rotate clockwise, so as to facilitate filling of the internal sterilization chamber 1 with the waste; c. Screw 7 is held on the shaft by means of a suitable guide 25;

d. Cavity 4 is kept under pressure by injecting steam through valves 18; e. Excess condensation present in cavity 4 is drained through discharge valve 19, placed next to bottom discharge valve 9;

f. Any air or vacuum is ejected by means of valve 20;

g. Reinforcements 27 ensure the possibility of having a minimum positive pressure from the outside towards the inside with respect to the internal sterilization chamber 1 ;

h. Filling internal sterilization chamber 1 continues until capacity sensors 23 a and 23b stop the counter-clockwise rotation of screw 7.

2. Loading valve 14 closed:

a. Internal sterilization chamber 1 is completely isolated from the outside and the treatment cycle begins;

b. Screw 7 rotates counter-clockwise by stirring the waste inside the internal sterilization chamber 1 ; c. Steam is injected through steam injection valve 17 into the internal sterilization chamber 1 , until the internal pressure measured by pressure sensor 24 reaches a predefined level; at the same time, the air inside internal sterilization chamber 1 is sent through valve 20 to a high-efficiency air filtration system before being released into the environment;

d. The pressure inside internal sterilization chamber 1 is kept to a value always below the external chamber, or cavity 4, in order to facilitate the heat exchange towards the inside, thus preventing the formation of condensation in sterilization chamber 1, and allowing the liquids in the chamber to evaporate following the same thermal cycle of the waste.

ssure reduction into the internal chamber:

a. At the end of the treatment cycle, before evacuating the material which has now been sterilized, the internal pressure must be reduced;

b. Actuation of a vacuum pump (not illustrated in the enclosed drawings) that extracts any residual steam, and completely dries the waste inside the internal sterilization chamber 1 ;

c. Pressure sensor 24 allows the pneumatic actuator opening placed on discharge valve 9.

harge of sterilization chamber:

a. Discharge valve 9 opens upon receiving the opening signal;

b. Screw 7 reverses the rotation direction;

c. Side scrapers 11 ease the movement of the waste towards the bottom;

d. Pressure sensor 24 sends the discharge complete signal to the control system; e. Discharge valve 9 closes;

f. A ticket is generated indicating the processing cycle parameters (time, weight, data related to the origin of the waste, operator);

g. The process restarts from step 1.

Claims

1. An autoclave for the sterilization of medical waste and operation method thereof, comprising an internal sterilization chamber (1), said internal sterilization chamber (1) being contained inside a vertical shell (2), said vertical shell (2) consisting of a first internal wall (3), a cavity (4), and an external wall (5), said external wall (5) being covered with an insulation layer (6), a vertical screw (7) crossing lengthwise the autoclave, scrapers (11) fixed to the axle of said vertical screw (7) by means of pins or bolts, characterized in that high-pressure saturated steam is injected inside the internal sterilization chamber (1) and inside the cavity (4) through two separate circuits operating at different pressures.

2. Autoclave according to claim 1, characterized in that inside said cavity (4), steam is always maintained at a pressure of two bars higher than the steam injected into the internal sterilization chamber (1) during the waste treatment cycle and hence during both the loading and discharge steps of the waste itself.

3. Autoclave according to the preceding claims, characterized in that the internal sterilization chamber (1) is lengthwise crossed by a screw (7), said screw (7) being coupled with a shaft (8), said shaft (8) being programmed to rotate counter-clockwise when the waste is to be stirred inside the internal sterilization chamber (1) during the sterilization process, and clockwise when the waste is to be discharged through a discharge valve (9) at the end of the treatment cycle.

4. Autoclave according to one or more of the preceding claims, characterized in that a flange (12) is present on the top section of the autoclave, said flange (12) being coupled with a second blind flange (13)by means of pins or bolts, both flanges (12) and (13) being of suitable size to allow the vertical extraction of the screw (7) and of the scrapers (1 1), and a waste loading valve (14) coupled with the autoclave by means of an additional flange (15).

5. Autoclave according to one or more of the preceding claims, characterized in that a flange (16) is present on the bottom of the internal sterilization chamber (1), said flange (16) being coupled with a waste discharge valve (9).

6. Autoclave according to one or more of the preceding claims, characterized in that the high-pressure saturated steam is injected into the internal sterilization chamber (1) through valves (17a and 17b) and into said cavity (4) through one or more valves (18) through separate circuits operating at different pressures and temperatures.

7. Autoclave according to one or more of the preceding claims, characterized in that said cavity (4) presents a bottom valve (19) for air venting and condensation draining, and a top valve (20) for ejecting the air present inside the sterilization chamber (1) during the injection step of the high-pressure saturated steam.

8. Method for the sterilization of medical waste by means of the autoclave of claim 1, comprising the following steps:

- Opening loading valve (14);

- Closing discharge valve (9);

- Clockwise rotation of screw (7);

- Injecting steam into cavity (4) through valve (18) and potentially draining excess condensation through discharge valve (19) located on the bottom section next to discharge valve (9);

- Venting the air inside cavity (4) through valve (20);

- Introducing the waste into internal sterilization chamber (1) until complete filling as signaled by capacity sensors (23a) and (23b);

Stopping the counter-clockwise rotation of screw (7);

- Closing loading valve (14);

Counter-clockwise rotation of screw (7) to stir the waste inside the sterilization chamber (1);

- Injecting steam into the sterilization chamber (1) through valve (17) until reaching the operating pressure as detected by pressure sensor (24), simultaneously opening valve (20) to vent the air present in said internal sterilization chamber (1) by means of a high-efficiency air-filtration system before being released into the environment;

- During the entire sterilization cycle the pressure in the internal sterilization chamber (1) is maintained at a level of 2 bar lower than the internal pressure in cavity (4);

- Reducing the pressure in internal chamber (1) at the end of the cycle;

- Actuating a vacuum pump to extract the steam from the internal sterilization chamber (1);

- Opening discharge valve (9);

- Reversing the rotation direction of screw (7) and waste discharge;

- Closing discharge valve (9).