Note: Descriptions are shown in the official language in which they were submitted.
w o 91/16~ 2 ~ ~ 0 3 '1 ~ P~T/~S91/02451
Process and Unit for Disinfection and Sterilisation
of infectious Waste
The invention relates to a process for disinfection cr sterilisa~ion of
infectious waste, in which the waste is granulated, wetted and thermally
treated by irradiation with microwaves, and a unit for that purpose.
A unit which, as a compact disposal plant, comprises an input section
embodying a waste shredder and a microwave chamber for the he.at treatment is
known for such a process for treating infectious waste with the aid of
microwaves from German Patent Specification 35 05 570. A conveyor path which
is surrounded by a microwave-transmissive housing is provided in the
microwave chamber. A multiplicity of microwave generators which irradiate
the granulated and wetted infectious waste with microwaves until it is
sterilised is arran~ed along the conveyor path. To prevPnt the escapP of
mlcrobes and steam, the entire unit is outwardly sealPd.
.
For this process carried out with the known unit, it has been found th2t the
destruction of microorganisms and also the inactivation o; viruses necPssary
for a disinfection and, in particular, sterilisa-tion require long heat
treatment throughput times. The energy consumption for a heat treatment
carried out in this way is consequently high.
It is therPfore an object of the invention to provide a process and a unit
for disinfection and sterilisation of infectious waste which ma~es possible
a reliablP disinfection or sterilisation in a rapid and economical manner.
This object is achieved in accordance with the features of claims 1 and S,
respecti vely.
This provides a process and a unit for carrying out the prccess whicr,
shorten the heat treatmen~ for the disin;ection or slerilisation substan-
.
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tially as a result of simultaneous use of moist heat, microwaves and
eventually overpressure and at the same tlme also prevent the survival of
resistant microorganisms and viruses. The feeding-in of steam during the
charging operation already ensures a rapid and good preheating with the
introduction of moisture. The subsequent heatirg-up and holding phase makes
possible an effective attack by microwaves in the moist overpressure medium.
A substantial reduction or destruction of all microorganisms, etc. is thus
possible within a few minutes.
Preferably, the temperatures in the micro~/ave chamber are set between lOO
arc; 145C. For the purpose of as uniform as possible feeding-in of the
steam, a plurality of injection pcints can be aistributed at a distance
along the microwave chamber. A distribution of the microwa~es 2S a result of
reflection can be achieved by a metallic conveyor screw. For a continucus
waste flow, the microwave chamber can be equipped at the input si~e with a
transfer chamber and at the output side with a discharge chamber having
conveyor screws which compact the waste at the input ard output side cf the
microwave chamber to allow treatment at a pressure of at least 1,3 bar
(absolute) in the microwave chamber. To speed up the process, the treatment
can be carried out at a pr~ssure of at least 2 bar (absolute).
Other objects, features and advantages of the invention will become more
fully apparent upon consideration of the claims and the following descript-
ion.
The invention is explained in greater detail below with reference to the
exemplary embodiment shown in the attached drawings.
Fig. l shows a longitudinal section cf a unit for disin;ection
and sterilisation of in;ectious waste;
Fig. 2 shows a cross section in accordance with Figure 1.
Figures l and 2 show a unit for treating, in particular slerilising,
infectious waste, which is integrated in a container l.
For receiving infectious waste, an input section co~prises ar infeed gate
which is separated by a revolving wing into a loading compartment 2 and a
shredder hopper 3~ These both compartments can be sealed in a fluid-light
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manner by means o~ a cover. Arranged in the shredder hopper 3 is a crank 4
which precomminutes the waste and ~eeds it to a waste shredder 5 adjoining
the bottom side. The escape of microbes or steam can be prevented by means
of a sterile filter 6. Furthermore, at least one injection point 7 is let
into the shredder l1opper 3 for feeding-in steam. The hopper walls are
preferably thermally insulated, but may also be constructed as indirectly
heatable.
The waste shredder 5 comprises a cutting mechanism having two opposed cutter
sha~ts 8 and shreds the refuse material fed through the shredder hopper 3
with the aid of the crank 4.
Adjoining the waste shredder 5 is a transfer container 9 which is used as an
intermediate store for the comminuted waste. Located at the sides o; the
transfer container 9 are filling level monitors 10 for a minimum or maximum
filling level. The shredder 5 is timed so that the filling level of the
transfer container 9 always varies between minimum and maximum. In addition,
a liquid filling-level monitor 11 which emits a warning at excessively high
liquid level is installed. From the bottom of the ~ransfer container 9, a
transfer screw 12 (Fig. 2) conveys the comminuted waste to a microwave
chamber 13. The transport screw 12 comprises a screw beam and is driven by a
geared motor whilch is controlled by the filling level monitor 10 and the
microwave chamber 13. The comminuted waste is transferred to the microwave
chamber 13 by means of the conveyor screw 12.
The microwave chamber 13 comprises a tubular or channel-shaped process
chamber 14 which is arranged between the transfer container 9 and a dis-
charging chamber 15. The connec~ion of the microwave chamber 13 on the input
and output side can be sealed in a fluid-tight manner by means of a slide or
a shutt-off valve 16, 17 in each case. Arranged at a distance from each
other along the process chamber 14 is a plurality o~ microwave generators
18. The process chamber 14 is of metallic construction or is encased with a
material which is not transmissive for microwaves and has individual cutouts
or windows for coupling in the microwave beams, which cutouts or windows are
sealed with microwave-transmissive material. The microwave generators 18 are
connected to the cutouts or windows by means of a wave guide and resonance
chamber system in a 1luid-tight and pressure-loadable manner. Preferably,
every microwave generator 18 radiates microwaves into the microwave chamber
13 via one or two cutouts which are rotated with respect to one another in
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the circumferential direction. The working frequency of the microwave
generators 18 can be appropriately chosen and in this case is 2450 MHz.
Arranged in the process chamber 14 is a conveying device 19, in this case a
conveyor screw (process screw), which preferably extends over the entire
length of the process chamber 14. This process screw 19 comprises a screw -
beam and is composed of a material which reflects the microwaves. It can be
driven by a geared motor 20, in particular in a forward-rotating manner for
filling the microwave chamber and in a forward-rotating and reverse-rotating
manner with the microwave chamber isolatecl (closed shut-off valves 16, 17)
during a chargewise operation.
A plurality of nozzles 21 arranged at a distance from each other are let
into the wall of the passage housing along the process chamber 14. These
nozzles 21 are injection points for feeding in steam and are connected for
this purpose to a steam generator 23 via a feed pipe system 22. At leasl one
nozzle 21 is located in the input region of the microwave chamber 13 and
each nozzle 21 can preferably be connected and switched off by means of its
own valve 24. The pressure settable by feeding steam intff the microwave
chamber 13 can be regulated and kept constant by means of a pressure-mainte-
nance valve 25.
The choice of the dimensions of the microwave chamber 13 is such that
charges o^ in~ectious waste of between, preferably, 200 and 400 1 can be
received.
The discharging chamber lS connected to the output side of the microwave
chamber 13 comprises a tubular passage housing 27 in which a conveyor screw
28 (discharge screw) is arranged and is driven by means of a geared motor.
Housin~ 27 and screw 28 are preferably composed of siainless steel. For a
betler mobile operation of the unit, the discharging chamber 15 is connected
to the microwave chamber 13 by means of a rotary link 29. Consequently, if
not in operation, the discharging chamber 15 can be swung upward by means of
a geared motor 30 (Fig~ 1) and if in operation, can be swung out of the
container 1 (Fig. 2). The choice of the dimensions o, the discharging
chamber 15 is such that a charge previously treated in the microwave chamber
13 can be received completely.
Fcr a heat treatment at at least 1,3 bar (absolute), preferably 2 bar
(absolute), the process chamber 14 can be formed as a pressure chamber. The
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shut-off devices 16, 17 are constructed as pressure-loadable. For a contin-
uous waste flow the transfer container conveyor screw 12 and the discharging
chamber conveyor screw 28 can compact the waste at the input and output side
of the microwave chamber 13 to shut-off the latter. For this purpose the
conveyor screws 12, 28 can run with a higher or lower speed as the process
screw 19. Alternatively, the screws 12, 28 can be provided with screw path
di~t~rencPs
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A process-control computer is provided for the electrical control. It is
located in a switch cabinet 31 and contains a program for automatic and
manual operation, i.e. for switch and sensor scanning, motor and microwave
conlrol, and moni~oring and driving display devices.
The mode o~ operation of the unit described above and the process which can
be carried out with it to treat infectious waste is described below.
The infectious waste, which is stored, for example, in a collection con-
tainer 33 is filled into the loading compartment 2. An additional lifting
and tipping device 32 may be provided for lifting the collection container
33. As a result or actuating the crank 4, the waste is fed to the waste
shrP~der 5 while being precomminuted. The granulated waste then falls into
the transfer container 9. The f~illing level monitoring system regulates the
comminution operation by switching off if the filling level monitor 10 is
reached. The amount of granulated waste corresponding to a chosen charge is
conveyed out of the transfer container 9 by means of the conveyor screw 12
and is moved into the microwave chamber ~3 by means of the forward-rotating
process screw 19. With the beginning of the input of the waste into the
microwave chamber 13, the feeding-in of steam is started. The injection of
the s~eam results in a moistening and preheating of the waste to about 50 to
100C during a filling operation.
For 2 continuous waste fiow the preheatPd waste is slowly moved through the
proc-,, chamber 14 heating the waste by at least temporarily simultaneous
exposure to steam and irradiation with microwaves and keeping there for a
minimum time.
For a continuous waste flow at a pressure of at least 1,3 bar tabsolute) in
the process chamber 14 the conveyor screws 12, 28 compact the waste at the
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input and output side of the process chamber 14 while preheating of the
waste using steam and microwaves takes place as described above.
For a chargewise waste flow at a pressure of at least 1,3 bar (absolute),
preferably 2 bar (absolute), in the process chamber 1~ formed as a pressure
chamber the shut-off valve 16 of the microwave chamber 13 on the input side
is first opened and the shut-off valve 17 on the output side is prefPrably
closed. The infectious waste is filled into the loading compartmen~ 2,
comminuted and moved into the pressure chamber. With the beginnung of the
input of the waste into the pressure chamber the feeding-in of steam is
started. The injection of the stearn results in a moistening and preheating
of the waste to about 50 to 100C during a filling operation of about 3 to
10 minutes for charges between 200 and 400 l.
Once the microwave chamber 13 has been filled with comminuted waste, the
shut-off valve 16 on the input side and the one on the output side are
closed. Consequently, the microwave chamber 13 is isolated from the transfer
container 9 and the discharging chamber 15. The further steam iniection with
preferably saturated steam results in the build up of a pressure which is
kept constant by means of the pressure-maintenance valve 25. The saturated
steam from the steam generator 23 has a working pressure of up to 6 bar,
i.e. a woirking temperature-of 165C.
Additionally, microwave beams are coupled into the microwave chamber 13.
During the microwave treatment the process screw 19 rotates ~orwards and
backwards in order to prevent reflection back-radiation onto the microwave
generators 18. Once the chosen pressure of at least 1,3 bar (absolute) has
been reached in the microwave chamber 13, the steam exposure is switched
off. The desired treatment temperature of over 100C, preferably 130 to
145C, can be regulated by means of a microwave radiation. This temperaturP
is maintained for a certain minimum time in order to ensure the destruction
of the microorganisms etc. Then the shut-off valve 17 is opened and the
charge of treated waste is emptied into the discharging chamber 15.
The shut-o~f valve 17 of the microwave chamber 13 on the output side isclosed again in order to prevent a fresh contamination of the already
treated waste. In the discharging chamber 15 the waste is able to cool
further and when the subsequent charge is transferred from the microwave
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chamber 13, it is ejected as disinfected or s-terilised waste for removal by
transporcation.
Although the invention has been described in connection with what is
presently considered to be the most pract;ical and pre~erred embodiment, it
is to be understood that the invention is not limited to the disclosed
embodiment, but rather is intended to cover various modifications and
equivalent arrangements included within the spirit and scope of the appended
claims.
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