AU2017201681A1

AU2017201681A1 - Waste treatment system

Info

Publication number: AU2017201681A1
Application number: AU2017201681A
Authority: AU
Inventors: Noel Mancuso
Original assignee: Pioneer Waste Management Holdings Trust Pty Ltd
Current assignee: PIONEER WASTE MANAGEMENT HOLDINGS Pty Ltd
Priority date: 2009-01-27
Filing date: 2017-03-10
Publication date: 2017-05-18
Also published as: JP3160332U; AU2010200304A1; CN201644485U

Abstract

The present invention provides a putrescible organic waste treatment system including a comminution unit including a comminution means adapted to substantially comminute putrescible organic waste into a pulp slurry, the comminution unit being adapted to be 5 connected to a supply of water, and a control means adapted to control the supply of water to the comminution unit, and to control the operation of the comminution means so that waste of a predetermined physical characteristic is produced by the comminution means. The foreign matter detector is located upstream of the comminution means and is arranged to detect foreign matter fed into the comminution 10 unit. Operation of the comminution means is prevented when foreign matter is detected by the foreign matter detector.

Description

1001753424 2017201681 10 Mar 2017 1

Waste Treatment System

Field of the invention

This invention relates to a putrescible waste treatment system.

Background of the invention 5 It is well known that it is undesirable to dump putrescible waste in land fill waste sites due to the fact that, as the waste decomposes, it gives off methane gas which is harmful to the environment. Methane gas is, however, valuable if captured since it is capable of driving gas powered electricity generators, or can be burnt for heating purposes.

Many systems have been proposed for capturing the methane gas produced during 10 decomposition of putrescible waste including systems for capturing methane gas given off in land fill sites.

It would, however, be far more efficient if the putrescible waste could be treated in biodigesters rather than simply being dumped into waste sites. However, in order to be treated in a biodigester, putrescible waste needs to be separated from non-putrescible 15 waste such as plastic, metal and other non bio-degradable materials.

Separating putrescible waste from non-putrescible waste is a somewhat complex and inefficient operation, adding significantly to the cost of the methane gas produced in any biodigester. The applicant has identified that it is far more efficient for putrescible waste to be separated at source, that is, in the kitchen or food preparation area where the 20 waste is produced. This avoids the problem of downstream waste separation. The applicant has thus proposed a system where the putrescible waste is separated and comminuted at source and mixing the waste with an amount of water to thereby produce a waste pulp product which is suitable for direct feed into a bio-digester.

The applicant has filed two patent applications, PCTAU2004/001460 and PCT 25 AU2008/000685, which detail and protect aspects of the putrescible waste treatment process outlined above. 1001753424 2017201681 10 Mar 2017 2

Further development of the system has resulted in a number of innovative improvements. In particular, the developments relate to improving the usability, efficiency and/or safety of the system.

Reference to any prior art in the specification is not, and should not be taken as, an 5 acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art.

Summary of the invention I0 According to a first aspect of the invention there is provided a putrescible organic waste treatment system including: a comminution unit including a comminution means adapted to substantially comminute putrescible organic waste into a pulp slurry, the comminution unit being adapted to be connected to a supply of water; a control means adapted to control the supply of water to the comminution unit, and to control the 15 operation of the comminution means so that waste of a predetermined physical characteristic is produced by the comminution means; and a foreign matter detector located upstream of the comminution means, the foreign matter detector being arranged to detect foreign matter fed into the comminution unit, wherein operation of the comminution means is prevented when foreign matter is detected by the foreign matter 20 detector.

The foreign matter detector may be adapted to detect metal and may include an induction coil which waste material must pass by prior to being comminuted by the comminution means, and wherein the system further includes a means for detecting a change in inductance in the induction coil caused by metal passing by the coil. 25 The foreign matter detector may be adapted to detect ferromagnetic and non-ferromagnetic metals.

The induction coil may be an annular induction coil through which waste material must pass prior to being comminuted by the comminution means. 2017201681 10 Mar 2017 1001753424 3

The comminution unit may include a waste receiving passage upstream of a receiving chamber, the receiving chamber upstream from the comminution means, and the foreign matter detector may be located in or adjacent one of the waste receiving passage and receiving chamber. 5 The foreign matter detector may be located in a channel in a wall of the waste receiving chamber.

The comminution unit may be located within a housing having a top, at least one sidewall and a base, the top provided with a waste receiving mouth leading to the waste receiving passage, and the waste receiving passage may be of truncated conical form I0 having an opening leading into the receiving chamber, and the foreign matter detector may be located between the opening and the receiving chamber.

The putrescible organic waste treatment system may further include a water supply means connected to the comminution unit and through which water is supplied to the comminution unit so as to mix with the putrescible waste, the water supply means 15 including a variable aperture inlet valve adapted to control the flow of water into the comminution means, and a pressure sensor adapted to determine the pressure of water supplied to the comminution unit; wherein the control means may be connected to the inlet valve and the pressure sensor and is adapted to open and close the inlet valve and to vary the aperture of the inlet valve depending on the pressure of water measured by 20 the pressure sensor such that, when the inlet valve is open, a substantially constant flow rate of water is supplied to the comminution unit irrespective of the pressure of water supplied to the comminution unit so that in use a waste pulp of a predetermined physical characteristic is produced by the comminution unit.

The putrescible organic waste treatment system may further include a shredder adapted 25 to receive pre-comminuted waste and shred the waste to a pre-determined size, the shredder having an outlet for shredded waste which feeds into the comminution unit. 1001753424 2017201681 10 Mar 2017 4

The shredder may be located, in use, at an elevation above the comminution unit so that shredded waste feeds directly into the comminution unit under the influence of gravity.

The shredder may be connected to the control means such that the comminution means 5 is caused to operate automatically when shredded waste is supplied by the shredder.

The putrescible organic waste treatment system may further include a waste receiving tank connected to the comminution unit via a conduit, the tank, conduit and comminution unit including a closed system; and a level sensor located in the tank adapted to measure on a regular or constant basis the level of waste in the tank, the I0 level sensor being connected to the control means and the control means being adapted to prevent operation of the comminution means when the level of waste in the tank reaches a predetermined level.

The putrescible organic waste treatment system may further include a pump for pumping waste produced by the comminution means along a conduit to the tank, the 15 pump including a secondary comminuter adapted to further comminute waste.

The foreign matter detector may be connected to the control means, and the control means may be adapted to prevent operation of the comminution means when foreign matter is detected by the foreign matter detector.

In a second aspect the present invention provides a distributed putrescible organic 20 waste treatment system including: a plurality of waste treatment systems as described above; at least one waste receiving tank to which each waste treatment system is connected; one or more connection conduits connecting the waste treatment systems to the tank/s; and a monitoring means associated with each comminution unit for monitoring the usage of each comminution unit in order to determine the proportion of 25 total waste supplied to the tank/s that has been produced by each comminution unit in the system. 1001753424 2017201681 10 Mar 2017 5

The monitoring means may include a flow sensor for sensing water supplied to each waste treatment system over a period of time.

The monitoring means may include a means for establishing the energy consumption of each waste treatment system over a period of time. 5 The monitoring means may include a flow sensor for sensing waste flow from each waste treatment system over a period of time.

The monitoring means may be connected to the control means of each waste treatment system, the control means of each waste treatment system adapted to record and store the usage monitored by the monitoring means for later interrogation and allocation of I0 usage to each unit in the system.

Also described herein is a putrescible organic waste treatment system including: a comminution unit including a comminution means adapted to comminute putrescible waste supplied to the comminution unit; water supply means connected to the comminution means through which water is supplied to the comminution means so as to 15 mix with the putrescible waste, the water supply means including a variable aperture inlet valve adapted to control the flow of water into the comminution means, and a pressure sensor adapted to determine the pressure of water supplied to the comminution unit; and a control means to control the operation of comminution unit, the control means being connected to the inlet valve and the pressure sensor to open and 20 close the inlet valve and to vary the aperture of the inlet valve depending on the pressure of water measured by the pressure sensor so that, when the inlet valve is open, a substantially constant flow rate of water is supplied to the comminution means irrespective of the pressure of water supplied to the comminution unit so that in use a waste pulp of a predetermined physical characteristic is produced by the comminution 25 means.

Also described herein is a putrescible organic waste treatment system including: a comminution unit including a comminution means adapted to comminute putrescible waste supplied to the comminution unit; water supply means connected to the 1001753424 2017201681 10 Mar 2017 6 comminution means through which water is supplied to the comminution means so as to mix with the putrescible waste; a control means to control the operation of comminution unit; a waste receiving tank connected to the comminution means via a conduit, the tank, conduit and comminution means including a closed system; and a level sensor 5 located in the tank adapted to measure on a regular or constant basis the level of waste in the tank, the level sensor being connected to the control means which is adapted to prevent operation of the comminution means when the level of waste in the tank reaches a predetermined level.

Also described herein is a putrescible organic waste treatment system including: a I0 comminution unit including a comminution means adapted to comminute putrescible waste supplied to the comminution unit; water supply means connected to the comminution means through which water is supplied to the comminution means so as to mix with the putrescible waste; a control means to control the operation of comminution unit; a waste receiving tank connected to the comminution means via a conduit, the 15 tank, conduit and comminution means including a closed system; and a shredder adapted to receive pre-comminuted waste and shred the waste to a pre-determined size, the shredder having an outlet for shredded waste which feeds into the comminution unit.

Also described herein is a putrescible organic waste treatment system including: a 20 plurality of comminution units, each unit including a comminution means adapted to comminute putrescible waste supplied to the comminution unit; each unit including water supply means connected to the comminution means through which water is supplied to the comminution means so as to mix with the putrescible waste; each unit including a control means for controlling the comminution means and the water supply 25 means so that comminuted waste produced by the comminution means has a predetermined physical characteristic; at least one waste receiving tank to which each comminution unit is connected; one or more connection conduits connecting the comminution units to the tank/s; and a monitoring means associated with each comminution unit for monitoring the usage of each comminution unit in order to 30 determine the proportion of total waste supplied to the tank/s that has been produced by each comminution unit in the system. 1001753424 2017201681 10 Mar 2017 7

Also described herein is a putrescible organic waste treatment system including: a comminution unit including a comminution means adapted to comminute putrescible waste supplied to the comminution unit; water supply means connected to the comminution means through which water is supplied to the comminution means so as to 5 mix with the putrescible waste; a control means to control the operation of comminution unit and the water supply means such that putrescible waste of a predetermined physical characteristic is produced by the comminution means; a waste receiving tank connected to the comminution means via a conduit; and a pump located adjacent the comminution means for pumping waste produced by the comminution means along the I0 conduit to the tank, the pump including a secondary comminuter adapted to further comminute waste prior to the waste passing through the conduit. As used herein, except where the context requires otherwise, the term "comprise" and variations of the term, such as "including", "includes" and "comprised", are not intended to exclude further additives, components, integers or steps. 15 These and further features of the invention will be made apparent from the description of preferred embodiments given below by way of examples. In the description references made to the accompanying drawings, but the specific features shown in the drawings should not be construed as limiting on the invention.

Brief description of the drawings 20 Figure 1 shows a diagrammatic view of a first unit embodiment of comminution unit according to the invention;

Figure 2A shows a diagrammatic view of a second embodiment of comminution unit according to the invention;

Figure 2B provides a partial diagrammatic view of an embodiment of the foreign matter 25 detector of the second embodiment of the invention;

Figure 3 shows a diagrammatic view of a third embodiment of comminution unit according to the invention; 1001753424 2017201681 10 Mar 2017 8

Figure 4 shows a series of comminution units connected to a single receiving tank.

Detailed description of the embodiments

In the drawings various comminution units are shown, each having variations of one type or another. It will be appreciated that the drawings depict various optional features 5 of the comminution unit, and that a single comminution unit may make use of one or more of those features. In the drawings, like components have been given the same reference numerals for ease of reference.

Referring initially to figure 1, a putrescible waste treatment system 10 includes a comminution unit 12 in which putrescible waste is comminuted to a relatively small I0 particle size (typically smaller than 3mm diameter). The comminuted waste is then conveyed to a temporary storage tank 14. The comminution unit includes a comminution means 16 which is driven by a motor 18. The comminution means 16 includes a series of blades 19 which cooperate to comminute the waste material. The communition unit 12 includes a lid 20 which, when open, leads into a truncated conical 15 receiving bowl 22 which has an open bottom leading through to a receiving chamber 24 located above the comminution means 16. The waste receiving bowl 22 defines a waste receiving passage through which waste to be comminuted passes. Water is supplied to the receiving bowl 22 and the receiving chamber 24 via upper and lower water supply passages 26 and 28 respectively. Water supply is controlled via a valve 29 which is 20 described below in greater detail. The comminution unit is controlled by control means 30 which, in the present embodiment, is provided as a programmable logic controller (PLC). Alternative control means 30 could, of course, be provided, such as a microprocessor. The comminution unit 12 is connected to the tank 14 by a conduit 32 and waste pulp generated by the comminution means 16 is pumped along conduit 32 to 25 the tank 14 by means of a pump 34 provided in the conduit 32 just adjacent the comminution means. The pump 34 is also controlled by the control means 30. The control means 30 may be controlled or operated via a control panel 36, or may be remotely controlled via a wireless link 38. 1001753424 2017201681 10 Mar 2017 9

As is described in PCT AU2004/001460 (publication number W02005/039775), The control means 30 is programmed to control the water supplied to the comminution unit during comminution of the putrescible organic waste to ensure that any one or more of the following pulp characteristics are produced by the comminution unit: a defined pulp 5 density; range of pulp densities; a defined moisture content; or a range of moisture contents, flow characteristic or range of flow characteristics. The optimal density, moisture content and flow characteristics may be chosen to ensure the most efficient conduit based transportation of the pulp waste material, or for the application or use of the pulp waste material. For example, and as described further below, the pulp waste 10 material may be transported to a biogas plant for use in a digester for the production of biogas.

The tank 14 will be of appropriate size to suit the application in which the comminution unit 10 will be used, but will typically be of the order of 1,500 litres. The tank 14 includes a valve control outlet 40 which a liquid waste removal truck will connect to in order to 15 evacuate the tank 14 as and when required. The tank 14 includes a level sensor 42 located in the roof of the tank and adapted to monitor the level of waste in the tank. The level sensor 42 is preferably an ultrasonic displacement sensor of the type manufactured by Omron. Specifically, an Omron E4PA-N type sensor is considered to be suitable. That type of sensor is able to sense the level of liquids in the tank to an >0 accuracy of approximately 1 mm.

The sensor 42 is connected to the control means 30 which in turn is adapted to prevent continued operation of the comminution unit 12 when the level of waste in the tank has reached a predetermined level. Generally the control means 30 will be adapted to provide a warning when the level in the tank is approximately 75% full, and may prevent 25 further operation of the comminution unit 12 when the level in the tank is at 90% or 95% full. Preferably the wireless link 38 will send a signal to a control station to dispatch a waste removal truck to empty the tank 14 when the tank 14 is at a selected fill level.

In one embodiment the valve 29 is a proportional type valve which will be opened to a greater or lesser extent, depending on the supplied water pressure to thereby ensure 30 that water supplied through passages 26 and 28 are supplied at a substantially constant 1001753424 2017201681 10 Mar 2017 10 flow rate irrespective of the supplied water pressure. The extent of opening of the proportional valve 29 will be controlled by the control means 30 in the following manner. A pressure sensor 44 is provided in the water supply line 46 to measure the pressure in the supply line 46. Information relating to the pressure in the supply line 46 is provided 5 to the control means 30 which in turn will cause the extent of opening of proportional valve 29 to increase or decrease so that flow through the valve 29 is constant, irrespective of supplied water pressure.

It is found in practice that mains water supply can vary considerably from one location to another and indeed can vary quite considerably over the course of any day. To ensure 10 that a constant flow rate of supplied water is provided, the valve 29 is controlled to open to the extent that it is proportional to the pressure of the water supplied. The pressure sensor 44 may comprise a piezoresistive pressure sensor of the type manufactured by TeraSensor SRL of Milan, Italy. A type J2 sensor is the preferred type of sensor for this particular application. The sensor is able to read pressure in the range from 100 millibar 15 to 20 bar and provide an electronic signal to the control means 30 which is proportional to the pressure sensed by the sensor.

It would be possible to control the flow rate of water entering the comminution unit using other arrangements for water flow rate control. For example, the valve could be opened and closed depending on the actual flow rate in the passages 26 and 28. What is 20 desirable is that when water flows into the comminution unit, it flows in at a constant flow rate, and the extent of opening and closing of the valve 29 is controlled by the control means 30, depending on other operating parameters of the comminution unit 12.

The pump 34 is arranged to receive the pulp waste from the comminution unit 12 and pump that waste along conduit 32 to tank 14. Clearly, the pump 34 will need to have a 25 pumping capacity sufficient to drive the waste pulp along conduit 32 and the capacity of the pump 34 may vary, depending on the length of the conduit 32. It is important that the waste pulp does not clog the conduit 32 and thus it is important that a consistent pulp density is achieved in the comminution unit. Preferably that will mean that the pulp particles are ground or otherwise comminuted to a relatively small particle size. 30 However, it is found that often efficiency may be improved by comminuting waste in a 1001753424 2017201681 10 Mar 2017 11 two stage process. It is found that by providing the pump 34 with a secondary communition or grinding capacity a finely particularized pulp material is produced in the unit. Smooth pulp is less likely to clog the conduit 32. Accordingly, in one embodiment of the invention the pump 34 is a combination pump and communition facility. 5 A suitable pump would be that supplied by Mono Pumps, for example a Mono G60 Grifter marine sewage pump. This is a positive displacement pump. The pump includes a progressive cavity pump and tri-hammer incarcerator pump, coupled to a single motor drive. The pump has a 75mm inlet and 32mm discharge port. Flowrate is typically approximately 60 litres per minute, and the motor size is approximately 0.93kW. 10 A further advantage of providing a small particle size is that the small particles will be more efficiently processed in a biodigester, thus ensuring optimum efficiency of the biodigester and minimum dwell time in the biodigester.

Turning now to figure 2A of the drawings, a similar comminution unit is shown to that of figure 1, and components already described will not be described again. The 15 comminution unit 12 shown in figure 2 includes a foreign matter detector 50 which is located upstream of the comminution means. More specifically, and in the present embodiment, the foreign matter detector 50 is located between the receiving bowl 22 and the receiving chamber 24.

The foreign matter detector in this embodiment includes a metal detector 52 which 20 includes an annular induction coil 54 linked to an oscillator. As will be appreciated, all matter to be comminuted by the comminution means 16 passes through the centre of the annular induction coil 54. If metal passes into the receiving chamber 24 through the centre of the coil 54 this will change the inductance of the coil 54 and that change in inductance will be detected and will cause the control means 30 to prevent further 25 operation of the comminution means 16. By using an induction coil both ferromagnetic and non-ferromagnetic objects (such as stainless steel cutlery or other implements) can be detected. 1001753424 2017201681 10 Mar 2017 12

Figure 2B provides a partial diagrammatic view of the foreign matter detector 50 shown in figure 2A. As can be seen, in this particular embodiment the wall 25 of the receiving chamber 24 is shaped to create a channel 53 which accommodates the induction coil 54. The induction coil 54 is located in the channel 53 and sealed in place using a 5 sealant 57 which does not substantially impact the operation of the induction coil 54, for example a silicone based sealant. By locating the induction coil 54 in the channel 53 the internal surface of the receiving chamber 24 is substantially planar and does not block or impede the flow of waste through the receiving chamber 24.

It will be appreciated that the metal detector 52 operates in the manner of a 10 conventional metal detector. Different coil and sensor arrangements are possible, and a pulse induction (PI) arrangement is considered to be particularly suitable for the present application. However, by having the coil of the metal detector extend around the passage through which waste material must pass provides an accurate device for assessing where the metal is inadvertently included in the waste stream. When metal is 15 detected, an error message will appear on the display screen 56 and/or be otherwise communicated (e.g. by audible alert) and the control means 32 will cease operation of the comminution means 16. The control means 32 may cease operation of the comminution means 16 passively (e.g. by cutting power to the comminution means 16) or, if required, may actively cease operation by applying a brake to the comminution >0 means 16. This enables an operator to manually locate the metal item in the receiving chamber 24 and remove the metal item before that item can damage or jam the comminution means 16, which would require a maintenance call to the operator of the unit.

Other types of foreign matter detectors are also envisaged. For example, it is important 25 that certain liquids such as antiseptics and high strength detergents do not pass into the tank 40 since such liquids could interfere with the biodigestion process. Thus, a chemical sensor able to detect such substances could be included in the receiving chamber 24 and be similarly linked to the control means 30. Likewise, a sensor able to detect the presence of plastics or other non biodegradable material in the chamber 24 30 could be employed in conjunction with the detectors discussed above. 1001753424 2017201681 10 Mar 2017 13

The comminution unit shown in figure 3 of the drawings further includes a shredder 60, located above the comminution unit 12 and having a downward passage 62 which feeds into the receiving bowl 22 of the comminution unit 12. The shredder includes a pair of motor device rotating shredder blades 64 and has a receiving hopper 66 into which 5 material to be processed is introduced into the shredder. The shredder 60 serves as a pre-comminution unit. The shredder 60 will be sized and configured depending on the type of waste intended to be passed through the shredder on its way to the comminution unit 12. It is envisaged that a shredder 60 will be employed for large bulk operation such as, for example food processing plants or the like where considerable I0 volumes of large sized waste material needs to be processed. The purpose of the shredder therefore, is to cut the incoming material down to a much smaller particle size, say between 5 and 10mm diameter, so that when waste material passes into the comminution unit 12 the comminution unit 12 is able to quickly process the material and mix the material during processing with an optimal volume of water so that a waste pulp 15 material is produced having a consistent physical characteristic.

It is envisaged that waste material having a density of approximately 1.15 tonne per cubic metre will be produced by the comminution unit 12. Clearly, by controlling the volume of water mixed with the waste during the processing the density of the waste material may be optimised, depending on the consistency of waste pulp that the 20 biodigestion process requires.

Clearly the form of the shredder 60 may vary, and a large volume hopper may be located above the shredding unit 60 in order that material to be passed through the comminution unit may be contained to ensure continuous supply of waste for processing by the shredder 60 in the comminution unit 12. Various safety controls are 25 built into the system in order to ensure that the shredder only operates when it is safe to do so. The safety components may, for example, include a hopper door mechanism linked to the PLC controller 30 which will cause the PLC controller 30 to shut the shredder down whenever the hopper door is open.

It is envisaged that with a shredder as described with reference to figure 3, a 30 comminution unit 12 could be configured to run virtually continuously, provided an 1001753424 2017201681 10 Mar 2017 14 adequate supply of waste material can be supplied to the shredder. As mentioned above, a system which includes a shredder and a comminution unit is intended for use in high waste volume applications, such as might apply for a supermarket for when considerable food processing is done, and unsold food is discarded. 5 It is desirable that the pulped waste and water mix is produced at the location where the waste is generated, and is then piped to an on-site storage tank where it will await collection by means of a waste removal tanker. The tanker will then supply the waste material to a biodigester. It will be appreciated that because the unit processes only biodegradable waste, and the waste that is produced is mixed with an optimal volume of 10 water, no processing of waste is required at the biodigester. This considerably reduces the amount of putrescible waste being directed to landfill, and also converts what would otherwise be environmentally damaging waste into a valuable feedstock for a biodigester.

Figure 4 shows a multi-comminution unit arrangement in which comminution units 12 15 are connected to a main water supply 46 via connection lines 46 . Each comminution unit 12 is connected to a common waste conduit 32 which leads to a receiving tank 14. The comminution units 12 each have a control means 30 for control of that unit. Located in each connection line 46 is a flow monitor 49 which is adapted to monitor the flow of water passing into the comminution unit 12. The flow of water is recorded so that each 20 time the tank 14 is emptied it will be possible to accurately assess what proportion of the total pulp in the tank 14 has been produced by each comminution unit. Calculating the usage by each unit 12 will be important in applications where pulp collection is paid for by the users of the individual comminution units on a user pays basis. Thus, particularly heavy users will pay more than those users who use their unit infrequently 25 so that the overall cost of waste collection is fairly shared between the respective users.

It is envisaged that the individual control units will be linked to a central controller which will be adapted to allocate the proportion of use in the manner outlined above on regular basis, such as for each pump out, or on a monthly basis. 2017201681 10 Mar 2017 1001753424 15

An alternative arrangement would be to monitor and record the power consumption of the individual comminution units 12. As a further addition or alternative, the flow of comminuted waste from each comminution unit 12 could also be measured, thereby providing a further metric for assessing the contribution of each unit 12 to the total 5 volume of waste.

It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

Claims

1. A putrescible organic waste treatment system including: a comminution unit including a comminution means adapted to substantially comminute putrescible organic waste into a pulp slurry, the comminution unit being adapted to be connected to a supply of water; a control means adapted to control the supply of water to the comminution unit, and to control the operation of the comminution means so that waste of a predetermined physical characteristic is produced by the comminution means; and a foreign matter detector located upstream of the comminution means, the foreign matter detector being arranged to detect foreign matter fed into the comminution unit, wherein operation of the comminution means is prevented when foreign matter is detected by the foreign matter detector.

2. A putrescible organic waste treatment system according to claim 1, wherein the foreign matter detector is adapted to detect metal and includes an induction coil which waste material must pass by prior to being comminuted by the comminution means, and wherein the system further includes a means for detecting a change in inductance in the induction coil caused by metal passing by the coil.

3. A putrescible organic waste treatment system according to claim 2, wherein the foreign matter detector is adapted to detect ferromagnetic and non-ferromagnetic metals.

4. A putrescible organic waste treatment system according to claim 3, wherein the induction coil is an annular induction coil through which waste material must pass prior to being comminuted by the comminution means.

5. A putrescible organic waste treatment system according to claim 4, wherein the comminution unit includes a waste receiving passage upstream of a receiving chamber, the receiving chamber upstream from the comminution means, and wherein the foreign matter detector is located in or adjacent one of the waste receiving passage and receiving chamber.