GB2519052A

GB2519052A - Waste disposal apparatus

Info

Publication number: GB2519052A
Application number: GB1310326.2A
Authority: GB
Inventors: Peter Sage-Passant
Original assignee: Individual
Current assignee: Individual
Priority date: 2013-06-11
Filing date: 2013-06-11
Publication date: 2015-04-15
Also published as: GB201310326D0

Abstract

A waste disposal apparatus for disposing of waste materials using aerobic decomposition includes a decomposition chamber, a stirrer 18 for stirring waste materials in the chamber, a drive mechanism 30, 32 for driving the stirrer with a torque limiter for limiting the torque (52:fig 9b) delivered to the stirrer from the drive mechanism, a rotation sensor 60 for sensing rotation of the stirrer and a control device which receives a rotation signal from the rotation sensor, wherein the control device detects a blocked or obstructed condition in which rotation of the stirrer is prevented and deactivates the drive mechanism in response to the a blocked condition. The torque limiter may be a friction clutch and is intended to limit the maximum torque transmitted between the drive mechanism and the stirrer so that if the stirrer becomes jammed, excess force is not transmitted to the stirrer and damage to the drive mechanism and stirrer is prevented. The rotation sensor may include a proximity sensor and an indexing wheel. The control device may apply a de-blocking operation in response to a blocked condition and generate an alarm signal. The waste maybe domestic food waste.

Description

Waste Disposal Apparatus The present invention relates to a waste disposal apparatus and in particular but not exclusively to a waste disposal apparatus for disposing of unwanted food waste using aerobic decomposition. The invention also relates to a method of disposing of waste materials using aerobic decomposition.

Aerobic decomposition is a well-known method for disposing of unwanted food waste. It is usethi in that it diverts food waste from landfill, which is generally agreed to be expensive, environmentally unfriendly and unsustainable.

The present invention allows for the aerobic decomposition of food waste at the point of production, using microorganisms.

Machines exist that allow aerobic decomposition using microorganisms at the point of food waste production. These machines generally include a decomposition chamber having a stirrer device for stirring the waste material and a dispensing device for dispensing a working fluid containing waste-digesting enzymes onto the waste materials. The waste materials arc stirred within the decomposition chamber during the digestion process and once the waste materials have been digested and converted to liquid, the waste liquid is discharged into a sewer. There are however certain disadvantages associated with these existing machines.

It is important not to overload this type of waste disposal apparatus. If the machine is seriously overloaded this can jam the stirrer and prevent it from rotating, thereby halting the waste digestion process. The stirrer can also be jammed by the presence in the decomposition chamber of large foreign objects, such as bones, cutlery and other items.

This can result in the machine having to be manually unloaded, which is a time-consuming, unpleasant and expensive operation. A serious jam can also damage the stirrer or the drive mechanism for the stirrer.

In order to prevent damage to the stirrer and the drive mechanism, many existing waste digesters include an overload sensor that detects a jam by sensing the current supplied to the drive motor. When ajam takes place the current supply to the motor increases and this is detected. The machine is then stopped and an alarm is sounded, providing an opportunity for the jam to be dcared.

When starting the machine from rest the current supplied to the motor is normally higher during the initial start-up phase than it is subsequently when the machine is running continuously at the normal operating speed. To prevent this higher initial current from tripping the overload sensor a timed override feature is provided, which allows a higher current to be supplied for a short period, typically a few seconds. This allows the motor to get up to speed when the machine starts without tripping the overload sensor.

A problem with this arrangement is that some operators have been known to misuse the override feature while trying to clear a jam. If the machine stops due to a jam they may turn it on and off repeatedly in the hope that the higher current supplied to the motor during the override period will eventually clear the jam. However, repeated use of the override facility when the stirrer is jammed can cause damage to the motor, the drive train and the stirrer device.

In principle, an alternative way of preventing damage to the machine would be to provide a torque sensor in the drive train. This could be used to turn off the motor if an excessive torque is sensed. Howcvcr, such a system would have to include a detection delay to avoid transient torque peaks and this could result in damage to the drive train caused by the high forces experienced during the detection d&ay. Another disadvantage of using a torque sensor is that they tend to be very expensive.

It is an object of the present invention to provide a waste disposal apparatus that mitigates one or more of the disadvantages described above.

According to one aspect of the present invention there is provided a waste disposal apparatus for disposing of waste materials using aerobic decomposition, the apparatus including a decomposition chamber, a stirrer for stirring waste materials in the decomposition chamber, a drive mechanism for driving the stirrer, a torque limiter for limiting the torque delivered to the stirrer from the drive mechanism, a rotation sensor for sensing rotation of the stirrer and a control device connected to receive a rotation signal from the rotation sensor, wherein the control device is constructed and arranged to sense a blocked condition in which rotation of the stirrer is substantially prevented and to deactivate the drive mechanism in response to sensing a blocked condition.

The provision of a torque limiter prevents damage to the stirrer device and the drive mechanism for the stirrer device by limiting the forces that can be transmitted through the system. At the same time, the rotation sensor senses rotation of the stirrer device, allowing the control device to detect a blocked condition in which rotation is prevented. The stirrer device can then be deactivated, allowing the blockage to be cleared. The system is simple and reliable, it prevents damage to the machine and is relatively inexpensive, thereby

overcoming many of the problems of the prior art.

IS The apparatus can be used for the disposal of biodegradable waste materials, for example food waste. This allows the waste materials to be disposed of easily, quickly and hygienically and avoids the environmental and economic disadvantages associated with disposing of those waste materials in landfill sites.

Advantageously, the control system is constructed and arranged to apply a dc-blocking operational control signal to the stirrer motor in response to sensing a blocked condition, and to deactivate the drive mechanism if the dc-blocking operation fails to clear the blocked condition. The dc-blocking signal may for example cause the motor to reverse for a period of time, for example 30 seconds, in an attempt to clear the blockage.

Altematively, the motor may be driven backwards and forwards one or more times.

Advantageously, the control device is operably connected to an alarm device and is configured to generate an alarm signal, for example an audible warning signal andlor a visual signal such as a flashing light, in response to sensing a blocked condition. This alerts an operator to the blocked condition so that it can be cleared.

Advantageously, the waste disposal apparatus includes a drive motor and means for sensing the load on the drive motor, wherein the control unit is configured to indicate when the load on the drive motor reaches a predetermined limit. The sensed load may for example be the electrical load on the motor, sensed by a current sensing device. This allows the control device to monitor the resistance to rotation of the stirrer device, which depends on other factors on the amount of materials in the decomposition chamber. If the load reaches or exceeds a set value the waste disposal apparatus may be locked closed to prevent more waste materials being added until the load has reduced.

Advantageously, the waste disposal apparatus includes a closure member for closing the decomposition chamber and a locking device for locking the closure member in a closed condition, the control system being constructed and arranged to lock the closure member in the closed condition when the load on the drive motor reaches a predetermined limit.

The rotation sensor preferably includes a proximity sensor and an indexing wheel configured for rotation with the stirrer device. This allows rotati on of the stirrer device to IS be monitored constantly and, if required, allows the rotation speed of the stirrer to be sensed. The proximity sensor is preferably an optical proximity sensor, although other types of sensor may alternatively be used.

The torque limiter preferably comprises a friction clutch, which is an inexpensive and highly reliable device that provides a high level of protection to the drive train and the stirrer device. Preferably, the torque limiter is adjustable to allow a service engineer to set the maximum torque evel deliverable to the stirrer device according to the expected operational conditions.

Advantageously, the waste disposal apparatus includes a load sensing device for sensing the quantity of waste materials in the decomposition chamber, the control system being constructed and arranged to lock the closure member in the closed condition in response to sensing a fully loaded condition. By locking the lid when the decomposition chamber is fully loaded, the risk of overloading and potential blocking of the chamber can be reduced or avoided. This helps to avoid the need for manually clearing a blockage. The load sensing device may for example be configured to sense the weight of waste materials in the decomposition chamber.

The control system may be configured to instigate an energy saving operating mode in response to sensing an unloaded condition.

Advantageously, the waste disposal apparatus includes a dosing system for automatically dosing waste material in the decomposition chamber with a working fluid. This ensures that the working fluid is applied effectively and at the correct times, and that the quantity of working fluid used is controlled to avoid wastage.

Preferably, the dosing system includes a bag-in-box supply of working fluid, in which the working fluid is contained within a flexible polymeric bag within a rigid box-like container made, for example, of cardboard. This is a very convenient way to store the working fluid and it allows the supply of working fluid to be replenished easily and quickly. Degradation of the working fluid while in storage is also reduced, since the bag of the bag-in-box container is hermetically sealed.

The dosing system preferably includes a diaphragm pump for delivering working fluid to the decomposition chamber. This allows the quantity of working fluid added to the decomposition chamber to be accurately controlled.

Advantageously, the dosing system is constructed and arranged to deliver a predetermined quantity of working fluid to the decomposition chamber each time the closure member is opened. Advantageously, the working fluid includes a blend of bacteria, free enzymes and plant extracts.

Advantageously, the decomposition chamber and optionally the closure member are made substantially or wholly of a polymeric material, optionally polyethylene. This improves the thermal insulation of the decomposition chamber, thus reducing or eliminating the need fbr cxtcrnal heating (some heat bcing gcncratcd by dccomposition of thc waste materials).

If heating is required, this can be provided using a low power heating unit, thus reducing the energy demands of the apparatus.

The use of polymeric materials considerably reduces the weight and possibly also the size of thc apparatus. It is thercibre possible to design thc apparatus as a mobile unit and it relatively easy to rclocatc the apparatus whcn required. The moulded components are also less likely to leak than traditional welded metal components, and they are easy to clean and maintain.

The decomposition chamber and optionally the closure member are preferably rotationally moulded components, this manufacturing process being particularly suitable for large components of this type as it allows large wall thicknesses to be formed, which increase the level of thermal insulation. The use of moulded polymeric components is also very cost effective as compared for example to stainless steel components.

The waste disposal apparatus may include a heater for heating the decomposition chamber.

The heater is preferably thermostatically controlled and it may for example consist of a low power heat mat that is attached to the base of the decomposition chamber.

Advantageously, the waste disposal apparatus includes a gas duct having an inlet connected to the decomposition chamber and an exterior outlet, an extractor fan for drawing gas through the duet and a filter for filtering gas drawn through the duct, the fan being constructed and arranged to operate when the closure member is in an open condition, thereby extracting gas from the decomposition chamber. This prevents odorous gases and vapours from escaping into the atmosphere when the lid is opened.

Advantageously, the waste disposal apparatus includes a water recycling system for extracting water from waste materials in the waste outlet and retuming the extracted water to the decomposition chamber. This reduces both water usage and the amount of treated waste materials discharged into the drain. Preferably, the waste disposal apparatus includes a water duct for delivering water to the decomposition chamber and a valve for controlling the flow of watcr through the duct.

According to another aspect of the invention there is provided a method of disposing of waste materials using aerobic decomposition, the method including loading waste materials into a decomposition chamber, stirring the waste materials in the decomposition chamber, limiting the torque delivered to the stirrer, sensing rotation of the stirrer and, in response to sensing a blocked condition in which rotation of the stirrer is substantially prevented, deactivating the drive mechanism.

The method preferably includes applying a dc-blocking operational control signal to the stirrcr motor in rcsponsc to scnsing a blockcd condition, and dcactivating thc drivc mcchanism if thc dc-blocking opcration fails to clcar thc blockcd condition.

Advantagcously, thc mcthod includcs gcncrating an alarm signal in rcsponsc to scnsing a blocked condition.

Advantageously, the method includes sensing a load on a drive motor, and indicating when the load on the drive motor reaches a predetermined limit.

Advantageously, the method includes locking a closure member for the decomposition chambcr in a closcd condition whcn thc load on thc drivc motor rcachcs a prcdctcrmincd limit.

Advantagcously, thc waste materials arc disposed of by aerobic decomposition, in which the waste materials are placed in the decomposition chamber, a working fluid that includes a blend of bacteria, free enzymes and plant extracts is applied to the waste materials, the waste materials are stirred to encourage aerobic decomposition thereof and decomposed waste materials are discharged from the chamber. The waste materials may for example be waste food products.

The method is preferably implemented using an apparatus according to any one of the

preceding statements of invention.

Certain embodiments of the invention will now be described by way of example with reference to thc accompanying drawings, in which: Figurc 1 is an isomctric vicw of a wastc disposal machinc from the right sidc; Figure 2 is an isometric view of the waste disposal machine from the left side, with the top removed; Figure 3 is an isometric view of the waste disposal machine from the right side, partially cut away to show some intemal details, including a sieve element; Figure 4 is an isometric view of the waste disposal machine from the right side, partially cut away to show some intemal details, not including a sieve element: Figure 5 is an isometric view of the waste disposal machine from the left side, partially cut away to show some internal details, including a sieve clement; Figure 6 is an isometric view of the waste disposal machine from the left side, partially cut away to show some internal dctails, not including a sicvc clcmcnt; Figures 7 and 8 are isometric views of a stirrer mechanism from the left and right sides respectively; Figure 9a is an isometric view of part of a stirrer device and Figure 9b is an exploded isometric view of a torque limiter that forms part of the stirrer device, and Figure 10 is a schematic diagram showing a control system of the waste disposal machine.

As shown in figures 1 and 2, the waste disposal apparatus 2 includes a cabinet 4 with side panels 6 and two doors 8 forming the front part of the cabinet. The top side of the cabinet is closed by an inclined top covcr 10 having a hinged lid 12.

Within the cabinet there is provided a decomposition chamber 14 having a four-sided upper part and a substantially semi-cylindrical lower part. This decomposition chamber 14 is preferably made from a polymeric material, for example polyethylene, for example by rotational moulding. A draill outlet (not shown) is providcd in the lower part of thc chamber.

Located adjaceilt the base of the decomposition chamber 14 is a semi-cylindrical sieve element 16 comprisitig a perforated wall or a mesh plate. This is usually made of thin stainless steel plate (typically with a thickness of about 0.9mm). The perforations or holes in this sieve clcmcnt 16 arc designcd to allow watcr and othcr liquids to pass through into the drain outlet, while retaining bulky waste materials in the decomposition chamber 14.

A stirrer device 18 is provided in the decomposition chamber 14 for stirring the contents of the chamber. The stirer device 18 includes a number of paddles 20 attached by aims 22 to a horizontal shaft 24. Thc shaft is mountcd for rotation in bearings 26 on opposite sides of the chamber 14. One end of the shaft 24 extends through the side of the chamber and is attached to a sprocket 28, as shown in figures 4-7. The stirrer device 18 is driven by an electric motor 30 in the lower part of the cabinet 4 via a gearbox 31 and a drive chain 32.

The hinged lid 12 serves as a closure member that may be opened to allow access to the decomposition chamber 14 or closed to seal the decomposition chamber 14. The lid 12 and the top cover 10 are preferably made from a polymeric material, for example polyethylene, preferably by rotational moulding.

The top cover 10 includes a locking device 36 (shown in figure 10), for example an electrically actuated latching bolt, for locking the lid 12 in a closed condition. Controls 40 for controlling operation of the waste disposal apparatus are provided on the front part of the cabinet above the doors 8. Concealed within the cabinet 4 behind one of the doors 8 is a compartment for receiving a container of working fluid 42, as shown in figure 10. The container 42 is preferably a bag-in-box typo, having a scaled bag of fluid supported by a surrounding box or carton and having a tap or valve 44 through which working fluid can be drawn from thc bag.

The working fluid includes a blend of bacteria, free enzymes and plant extracts, which are effective to promote aerobic decomposition of the waste materials including food waste, IS oils and greases, and which help to eliminate odours.

The stirrer device 18 comprises part of a stirrer mechanism 48, which is shown in detail in figures 7, 8, 9a and 9b. The stirrer mechanism 48 includes the stirrer device 18 and a drive mechanism 50 for the stirrer device 18, which includes the motor 30, the gearbox 31 and the drive chain 32. Rotary drive is transmitted from the motor 30 to the stirrer device 18 through the gearbox 31, the drive chain 32 and the sprocket 28. The drive sprocket 28 is attached to a drive end 24a of the drive shaft 24 via a torque limiter 52, the components of which are shown in figure 9b.

The torque limiter 52 includes a drive collar 54 that is fixed to the shaft 24 with a drive key, two friction plates 56 located on opposite sides of the sprocket 28, a first washer 58 that is configured to rotate with the collar 54, a tensioning spring 60, a second washer 62 that is configured to rotate with the collar 54 and a tensioning collar 64 that is bolted to the drive collar 54 with tensioning bolts 66. The friction plates 56 are pressed against the sides of the sprocket 28 by the tensioning collar 64 and the compressed tensioning spring 60 so that rotary drive is transmitted from the sprocket 28 to the collar 54 and the shaft 24 via the friction plates 56 and the washers 58, 62. The maximum torque that can be transmitted is detemiined by the coefficient of friction between the sprocket 28 and the friction plates 56 and the force applied by the compressed tensioning spring 60, and this maximum torque can be adjusted by turning the tensioning bolts 66.

The torque limiter 52 limits the maximum torque that can be transmitted between the drive mechanism 50 and the stirrer device 18. If the stirrer device 18 becomes jammed by objects in the decomposition chamber so that it cannot rotate, the torque limiter 52 will prevent excessive forces from being transmitted to the stirrer device 18 by allowing the sprocket 28 to rotate relative to the shaft 24 when the torque reaches the limit set by the torque limiter 52. This prevents damage to the drive mechanism 50 and the stirrer device 18.

A rotation sensor 68 is provided for sensing rotation of the stirrer shaft 24. In this embodiment the rotation sensor 68 comprises an optical proximity sensor 70 and an index wheel 72 that is attached to the undriven end 24b of the stirrer shaft 24, opposite the drive end 24a. The index wheel 72 has a set of raised crenellations around its circumference, IS which are sensed by the optical proximity sensor 70 as the index wheel 72 rotates. The proximity sensor thus generates an alternating binary signal as the index wheel 72 rotates, the frequency of this alternating binary signal being related to the rotational speed of the index wheel 72 and the shaft 24.

The operational parts and the control system of the waste disposal apparatus are shown schematically in figure 10.

A plurality of spray nozzles 74a, 74b are located within the decomposition chamber 14.

Some of these nozzles 74a are desiicd to spray waste materials within the chamber 14 with water, which is supplied to the nozzles 74a through water supply lines 76. The flow of water to the nozzles 74a is controlled by a solenoid valve 78, which is activated by a central control unit 80. The central control unit 80 is linked to a lid switch 82 that senses when the lid 12 is closed, and only activates the valve 78 to supply water to the decomposition chamber 14 when the lid is closed. The central control unit 80 is also connected to a timer 84 that measures the time for which the valve 78 is open to control the amount of water supplied to the chamber 14.

Water can be supplied to the chamber either from an external water supply 86 or from a waste water recycling system 88. The waste water recycling system 88 is connected to the drain outlet 90 of the decomposition chamber 14 and includes a separator 92 that separates some of the water from the decomposed waste materials flowing from the chamber 14.

The remaining waste materials flow through an outlet pipe 94 to a drain.

The other nozzles 74b are designed to spray waste materials in the chamber 14 with a working fluid that includes a blend of bacteria, free enzymes and plant extracts. This working fluid is drawn from the fluid container 42 and is supplied to the nozzles 74b by a diaphragm pump 96 via a fluid supply line 98. The pump 96 is connected to the central control unit 80, which controls its operation. The pump 96 is activated only when the lid 12 is opened and then only for a predetermined period of time determined by the timer 84, in order to control the amount of fluid supplied to the decomposition chamber 14.

The central control unit 80 also controls operation of the motor 30 that drives the stirrer 18, and activates the stirrer only when the lid 12 is closed, as sensed by the lid switch 82.

IS Electrical power is supplied to the motor 30 via an electrical inverter 100 and the load on the motor 30 as it drives the stirrer 18 is detected by a current sensing relay 102. The load on the motor depends on the amount of waste materials in the decomposition chamber 14, and when the chamber is loaded to its maximum capacity the relay 102 activates the latching bolt 36 to lock the lid 12 closed. The lid remains locked until some of the waste materials in the chamber have been digested and the load on the motor has fallen. The latching bolt 36 is then released, allowing the lid to be opened so that more waste materials can be loaded into the chamber.

The central control unit 80 is also connected to receive signals from the rotation sensor 68 via a signal conditioner 112. This central control unit 80 is thus able to sense the rotational speed of the stirrer device 18 and can detect whether it is rotating or has become jammed, for example by foreign objects in the decomposition chamber 14. If the stirrer device 18 has stopped rotating, or if its rotational speed has fallen below a predetermined level indicating that the stirrer has become jammed, this is detected by the central control unit 80.

Upon detecting a blockage or obstruction in the decomposition chamber 14, the central control unit 80 first attempts to release the blockage by reversing the rotation direction of the stirrer device 18 one or more times. If a sustained blocked condition is sensed that cannot be freed by reversing the stirrer device 14, for example a blocked condition that persists for a period exceeding a set time such as 30 seconds, the control unit 80 shuts down the motor 30, releases the latching bolt 36 and generates an alarm signal via a sounder 104 so that the blockage can be cleared manually.

The central control unit 80 is operably connected to an extractor fan 106, which is connected via a duct (not shown) to the decomposition chamber 14 and is arranged to extract air from the chamber and discharge it through a carbon filter (not shown).

Operation of the fan 106 is controlled by the lid switch 82, so that the fan is activated whenever the lid 12 is opened. This creates a partial vacuum in the decomposition chamber 14, causing ambient air to flow into the chamber and preventing odorous gases and vapours from escaping into the atmosphere.

The central control unit 80 is also operably connected to a thermostatically controlled hcatcr 108 for heating the wastc materials in thc decomposition chamber 14 to an idcal temperature for aerobic decomposition (typically about 43C). The heater 108 may for example consist of a low energy heater mat that is mounted against a wall or the base of the decomposition chamber 14.

In use, waste material, for example food waste, is tipped into the decomposition chamber 14 and the lid 12 is then closed. Closing of the lid 12 is sensed by the lid switch 82, whereupon the waste material in the chamber 14 is sprayed with water and working fluid through the nozzles 74a, 74b. The motor 30 is activated to operate the stirrer device 18 and if necessary the heater 108 is turned on to heat the waste materials to the ideal decomposition temperature.

If the lid 12 is opened while the machine is in operation, the motor 30 is shut down to deactivate the stirrer device 18 and the extractor fan 106 is turned on to prevent odours escaping into the atmosphere. Additional waste materials may then be added to the chamber 14. After the waste materials have been added, the lid 12 is closed whereupon the motor 30 is reactivated and the fan 106 is deactivated. The waste material is again sprayed with water and working fluid through the nozzles 74a, 74b.

The resistance to rotation of the stirrer device 18 is sensed by the current sensing relay 102.

When the chamber is niH, the relay fires the latching bolt 36 to lock the lid 12 and prevent further materials being added to the chamber. As the waste is digested, it falls through the mesh plate 16 into the base of the decomposition chamber 14 from where it flows through the drain outlet 90 into a drainage system. If required, some water can be extracted from the waste fluids by the separator 92 and recycled into the chamber through the water nozzles 74a. When the load in the chamber has fallen below a predetermined level, which is preferably about 80% of the maximum capacity of the chamber, the latching bolt is released so that additional waste material can be added to the chamber. If a blockage preventing rotation of the stirrer device 18 is detected, this is resolved by the procedures described above.

Claims

CLAIMS1. A waste disposal apparatus for disposing of waste materials using aerobic decomposition, the apparatus including a decomposition chamber, a stirrer for stirring waste materials in the decomposition chamber, a drive mechanism for driving the stirrer, a torque limiter for limiting the torque delivered to the stirrer from the drive mechanism, a rotation sensor for sensing rotation of the stirrer and a control device connected to receive a rotation signal from the rotation sensor, wherein the control device is constructed and arranged to sense a blocked condition in which rotation of the stirrer is substantially prevented and to deactivate the drive mechanism in response to sensing a blocked condition.
2. A waste disposal apparatus according to claim 1, wherein the control system is constructed and arranged to apply a dc-blocking operational control signal to the stirrer motor in response to sensing a blocked condition, and to deactivate the drive mechanism if the dc-blocking operation fails to clear the blocked condition.
3. A waste disposal apparatus according to claim 1 or claim 2, wherein the control devicc is operably connected to an alarm device and is configured to generate an alarm signal in response to sensing a blocked condition.
4. A waste disposal apparatus according to any one of the preceding daims, including a drive motor and means for sensing the load on the drive motor, wherein the control unit is configured to indicate when the load on the drive motor reaches a predetermined limit.
5. A waste disposal apparatus according to claim 5, including a closure member for closing the decomposition chamber and a locking device for locking the closure member in a closed condition, the control system being constructed and arranged to lock the closure member in the closed condition when the load on the drive motor reaches a predetermined limit.
6. A waste disposal apparatus according to any one of the preceding claims, wherein the rotation sensor includes a proximity sensor and an indexing wheel configured for rotation with the stirrer device.
7. A waste disposal apparatus according to any one of the preceding claims, wherein the torque limiter comprises a friction clutch.
8. A method of disposing of waste materials using aerobic decomposition, the method including loading waste materials into a decomposition chamber, stirring the waste materials in the decomposition chamber, limiting the torque delivered to the stirrer, sensing rotation of the stirrer and, in response to sensing a blocked condition in which rotation of the stirrer is substantially prevented, deactivating the drive mechanism.
9. A method according to claim 8, including applying a dc-blocking operational control signal to the stirrer motor in response to sensing a blocked condition, and deactivating the drive mechanism if the dc-blocking operation fails to clear the blocked condition.
10. A method according to claim 8 or claim 9, including generating an alarm sial in response to sensing a blocked condition.
11. A method according to any one of claims 8 to 10, including sensing a load on a drive motor, and indicating when the load on the drive motor reaches a predetermined limit.
12. A method according to claim II, including locking a closure member for the decomposition chamber in a closed condition when the load on the drive motor reaches a predetermined limit.
13. A method according to any one of claims 8 to 12, wherein the waste materials are disposed of by aerobic decomposition, in which the waste materials are placed in the decomposition chamber, a working fluid that includes a blend of bacteria, free enzymes and plant extracts is applied to the waste materials, the waste materials are stirred to encourage aerobic decomposition thereof and decomposed waste materials are discharged from the chamber.
14. A method according to any one of claims 8 to 13, in which the waste materials are waste food products.
15. A method according to any one of claims 8 to 14, wherein the method is implemented using an apparatus according to any one of claims 1 to 7.