GB2408736A

GB2408736A - Treating solid waste

Info

Publication number: GB2408736A
Application number: GB0328218A
Authority: GB
Inventors: Christopher Paul Reynell; Christopher Roy Whaley
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-12-05
Filing date: 2003-12-05
Publication date: 2005-06-08
Anticipated expiration: 2023-12-05
Also published as: GB0328218D0; GB2408736B

Abstract

A process for treating solid waste and a digestion vessel suitable for use therein. The process comprising the steps of: <SL> <LI>a) providing a solids digestion vessel 10 having an inlet side 22, outlet side 24, moving means 40 and removal means 36. The vessel containing a liquid layer 28 and a floating solids layer 30. <LI>b) transferring solid waste 25 to the vessel; <LI>c) providing a liquid digester tank (12,fig 1) containing a source of organic material undergoing anaerobic bacterial digestion to produce a fluid fraction containing active bacteria; <LI>d) transferring at least part of the fluid fraction into the vessel to create treated solid waste 55; <LI>e) transferring the liquid layer within the vessel to the liquid digester tank; <LI>f) using the moving means to move the floating solids layer from the inlet side to the outlet side of the vessel; and <LI>g) using the removal means to remove the floating solids layer in the vessel from the outlet side. </SL>

Description

- 1 - 2408736 Process and apparatus for treating solid waste The present

invention relates to a process for treating waste and a solids digestion vessel suitable for use in the process.

Abattoirs, farms, food processing plants and the like regularly produce solid organic waste which needs to be treated in order to render it suitable for discharge into the environment.

One method for treating solid waste is described in International Patent document WO 96/23054 showing a solids digestion vessel which is initially charged with a source of solid waste and then treated with a fluid fraction containing a source of active bacteria. The solid waste is left in the vessel for a period of time during which it is digested by the active bacteria and then removed as treated solid waste. During the period when the solids digestion vessel is either being charged and/or emptied, no solids are being digested and the vessel therefore has a significant down-time when it is not being used to its full potential. This process also requires the storage of solid waste which is waiting for treatment and/or treated solid waste which is waiting to be transported away.

According to the invention, there is provided a process for treating solid waste, the process comprising the steps of: a) providing at least one solids digestion vessel 4097a2 04 December 2003 - 2 - having an inlet side, outlet side, moving means and removal means, the outlet side being located on the opposite side of the vessel to the inlet side, the removal means being located on the outlet side and the solids digestion vessel containing a liquid layer and a floating solids layer floating on said liquid layer; b) transferring solid waste to the at least one solids digestion vessel at the inlet side; c) providing at least one liquid digester tank containing a source of organic material undergoing anaerobic bacterial digestion in a fluid digestion phase to produce a fluid fraction containing active bacteria; d) transferring at least part of the fluid fraction containing active bacteria into the solids digestion vessel to create treated solid waste in a solids digestion phase; e) transferring at least some of the liquid layer within the solids digestion vessel to the liquid digester tank; f) using the moving means to move at least some of the floating solids layer from the inlet side to the outlet side in the solids digestion vessel; and g) using the removal means to remove at least some of the floating solids layer in the solids digestion vessel from the outlet side.

The invention also extends to apparatus suitable for 4097a2 04 December 2003 - 3 carrying out the above process, the invention therefore provides a solids digestion vessel having an inlet side for solid waste and an outlet side on the opposite side of the solids digestion vessel to the inlet side, the solids digestion vessel containing a liquid layer and a floating solids layer floating on said liquid layer, and the vessel further comprising: a) moving means for moving the floating solids layer within the vessel from the inlet side to the outlet side and; b) removal means located adjacent the outlet side for removing at least some of said floating solids layer.

It should be understood that the term floating solids layer refers to material which is buoyant. This buoyant material does not have to be floating on the surface of the liquid layer and may be floating just beneath the surface. It should also be understood that the part of the liquid layer within the solids digestion vessel which is taken off and transferred back to the liquid digester tank may be transferred to any liquid digester tank. The term treated solid waste means solid waste which has been treated and thus rendered more acceptable for discharge to the environment.

The process and apparatus according as described above mean that the digestion process can be a continuous or semi-continuous process. This may be an extended batch process but in all cases the amount of solid waste that can be treated in the vessel and/or by the process is 4097a2 04 December 2003 - 4 - increased. This is because there will be reduced build up of material at the bottom of the vessel and the material floating on the surface of the liquid layer is also removed continuously which again ensures there is no build up. The process may still occasionally need to be shut down so that the vessel can be cleaned out but this will be comparatively rarely.

It is preferred that the moving means comprises a conveyor belt which moves the floating solids layer from the inlet side of the vessel to the outlet side. However, it should be understood that the moving means may also be any other means that carries out substantially the same function.

For example, this could be a single rake which moves along the surface of the contents of the vessel or a jet located just underneath the surface of the liquid layer which is directed towards the outlet side.

The conveyor belt may have projections from its surface.

The projections will make contact with the floating solids layer and thereby enhance the function of the conveyor belt as a moving means.

At least a portion of this conveyor belt may be located beneath a surface of the liquid layer. This ensures that the floating solids layer which is floating on the liquid layer beneath the conveyor belt will be entirely submerged within the liquid layer. This is advantageous as it ensures that the floating solids layer will be fully covered by the liquid layer and thus it will be more 4097a2 04 December 2003 - 5 effectively treated and digested by the active bacteria.

Preferably, the conveyor belt contains apertures such that fluid can pass through the conveyor belt. This is an advantageous feature because it ensures that any liquid coming from above the floating solids layer can percolate down through the apertures in the conveyor belt and make contact with the floating solids layer. For example, the upper portion of the conveyor belt may have some residual liquid clinging to it which may then drip down through the apertures onto the floating solids layer. This again increases the interaction of the active bacteria in the liquid layer with the floating solids layer and improves the efficiency of the process.

Preferably, the process additionally includes the step of forcing at least part of the floating solids layer down into the liquid layer using agitation means. This part of the process again maximises the exposure of the floating solids layer to the active bacteria in the liquid layer.

The agitation means may be eccentric cams that act upon the conveyor belt. This is advantageous as the eccentric cams move the conveyor belt unevenly up and down and therefore the floating solids layer located beneath the conveyor belt will be repeatedly plunged deeper into the liquid layer. This ensures that not only is the floating solids layer fully covered and submerged in the liquid layer but also that it is agitated and mixed by the uneven movement of the agitation means. This will improve 4 097a2 04 December 2003 - 6 - mixing of the contents and also means that any large aggregations within the floating solids layer may be broken down. There may also be agitation means which are separate from and do not act upon the conveyor belt.

The vessel may also include de-watering means for removing excess liquid from at least some of the treated solid waste. This ensures that the treated solid waste taken from the vessel will be lighter, less messy and generally more practical for transportation and/or storage purposes.

In addition, the excess liquid taken-off may still be only part-treated and it must therefore be returned to the liquid digestion vessel for a period of approximately 25 days for further treatment until it is more acceptable for discharge to the environment.

It is preferred that the removal means comprises a conveyor belt. A conveyor belt is an effective and economic method of removing the treated solid waste from the solids digestion vessel. The removal means may alternatively be a bucket or scoop mechanism having several buckets or scoops arranged on a continuous belt which scoop up the treated solid waste and remove it from the vessel. If the removal means is a conveyor belt, the conveyor belt may again have projections from its surface which make contact with the floating solids layer and enhance its function as a removal means.

When the removal means comprises a conveyor belt, the de watering means may also comprise at least part of the 4097a2 04 December 2003 removal means. This means that the apparatus has fewer components thereby reducing construction costs and also that the apparatus will be more compact. In this case, the de-watering means may comprise another conveyor belt located above the conveyor belt comprising the removal means or it may be a roller or several rollers which roll along the top of the treated solid waste sitting on the conveyor belt comprising the removal means. The dewatering means, will then act in conjunction with the removal means to squeeze excess water out from the treated solid waste. Alternatively, the de-watering means may be separate from the removal means.

At least some of the fluid fraction containing active bacteria may be introduced into the solids digestion vessel from above the floating solids layer. This ensures that as much of the floating solids layer as possible comes into contact with the active bacteria contained within the fluid fraction.

In addition, at least some of the fluid fraction containing active bacteria may be introduced into the solids digestion vessel adjacent an inlet for the solid waste on the inlet side of the solids digestion vessel.

This ensures that the untreated solid waste comes into contact with the active bacteria in the fluid fraction as soon as it enters the vessel thereby maximising digestion efficiency.

It should be understood that there may be multiple inputs 4097a2 04 December 2003 8 - for the fluid fraction containing active bacteria and these may be located anywhere in the solids digestion vessel. Additionally, there may be a rotating sprinkler mechanism located at the top of the vessel and above the floating solids layer which introduces the fluid fraction into the vessel and down onto the floating solids layer.

The process may also include the step of removing at least some sunken solids from the bottom of the vessel using at least one means for removing sunken solids. This step ensures that the build up of sunken solids at the bottom of the solids digestion vessel is minimized and the vessel may therefore remain in continuous use as it does not need to be constantly emptied. It should be understood that the sunken solids may be digestible solids or indigestible solids.

It is preferred that the means for removing at least some sunken solids from the solids digestion vessel is located at or adjacent the inlet side of the vessel. The advantage of this feature is that the denser solids will sink to the bottom of the vessel as soon as they enter it and therefore the dense, sunken solids will usually be found on the bottom of the vessel at the inlet side. The means for removing at least some sunken solids is therefore ideally placed for their removal. It should however be understood that the means for removing sunken solids may be located anywhere in the solids digestion vessel.

4097a2 04 December 2003 - 9 - The means for removing at least some sunken solids may be an auger. An auger is an effective and economic way of removing dense, indigestible solids such as stones from the bottom of the vessel. However, there may instead be a conveyor belt or any other means for removal of the sunken solids.

Additionally, the process may include the step of mechanically breaking down and re-circulating at least some other sunken solids in the solids digestion vessel using a means for mechanically breaking down and recirculating. It is envisaged that other sunken, sludge- like, slightly dense solids will also eventually fall to the bottom of the vessel. The advantage of having a mechanism/means of breaking them down and re-circulating is that these sunken solids will also not be permitted to build up at the bottom of the vessel which would reduce the capacity of the vessel and therefore the efficiency of the process. This will also ensure that the process does not need to be repeatedly shut down so that the solids digestion vessel can be emptied.

It is preferred that the means for mechanically breaking down and recirculating at least some other sunken solids is located at or adjacent the outlet side of the vessel.

It is envisaged most of these other sunken solids will be slightly lighter and therefore more likely to be carried across to the outlet side of the vessel. The means for mechanically breaking down and re- circulating them will therefore be ideally placed to deal with these other 4097a2 04 December 2003 - 10 sunken solids found on the outlet side. However, it should be understood that the means for mechanically breaking down and recirculating may be located anywhere in the solids digestion vessel.

The means for mechanically breaking down and re- circulating may optionally be a chopper pump. A chopper pump is an economic and effective way of carrying out the break down and re- circulation of sunken solids. However, any alternative means having the same function may also be used. Examples may include means for vibration, grinding or chopping.

A bottom of the solids digestion vessel may also include a baffle on the interior of the vessel which is located in between the inlet side and the outlet side. This ensures that the denser solids which fall straight to the bottom of the vessel upon entry remain there for removal by one of the removing means.

The solids digestion vessel may also have at least one heater for heating the contents of the vessel. The effect of heating the contents of the vessel is that it increases the rate at which the active bacteria digest the solids thereby reducing the required residence time for the solids in the vessel.

It is preferred that at least one of the heaters is located below and adjacent the inlet side of the vessel.

The advantage of having a heater located adjacent an inlet 4097a2 04 December 2003 side of the vessel is that the solid waste is heated slightly as soon as it enters the vessel thereby ensuring that the rate of their digestion is increased or "kick- started" straight away. It should be understood that the heater/s may be located anywhere around the solids digestion vessel.

The vessel may optionally have mixing means for agitating the contents of the vessel. This ensures that all solids in the vessel come into contact with the active bacteria in the fluid fraction thereby maximizing the efficiency of the process. The mixing means may be located anywhere around the vessel.

These mixing means may be mechanical stirring means or any other type of stirring means such as shaking means or a pump. However, it is thought that a mechanical stirring means will be the cheapest way of the mixing the contents of the vessel.

4097a2 04 December 2003 - 12 The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic representation of the process according to the invention; Figure 2 is a cross-section through the solids digestion vessel; Figure 3 is a cross-section through an alternative embodiment of the solids digestion vessel; and Figure 4 is a view from above the solids digestion vessel of Figure 2.

Figure 1 is a schematic diagram of a continuous digestion process which shows a solids digestion vessel 10 connected to a liquid digestion vessel 12. The solids digestion vessel 10 has an inlet 14 for the input of solid waste and an outlet 16 for take-off of treated solid waste. The solids digestion vessel 10 is connected to the liquid digestion vessel 12 via two lines, an input 18 and an output 20. These lines may be pipes, tubes or any other form of conduit.

Figure 2 shows the solids digestion vessel 10 having an inlet side 22 for solid waste 25 and an outlet side 24 on the opposite side of the solids digestion vessel 10 to the inlet side 22. The solids digestion vessel 10 contains a 4 097a2 04 December 2003 - 13 liquid layer 28 and a floating solids layer 30 floating on said liquid layer 28. The vessel 10 further comprises moving means 40 which is found at a top 23 of the vessel for moving the floating solids layer 30 within the vessel from the inlet side 22 to the outlet side 24. The vessel 10 further has removal means 36 located adjacent the outlet side 24 for removing at least some of the floating solids layer 30 as treated solid waste 55.

The liquid layer 28 in the vessel 10 contains active bacteria which act on the solid waste 25 such that when it is removed from the solids digestion vessel 10 it has become treated solid waste 55 which is more acceptable for discharge to the environment. The liquid layer 28 is made up of a fluid fraction taken off from the liquid digestion vessel 12 via the output 20.

Solid waste 25 is input into the solids digestion vessel at an inlet 26 and then remains there for a period of approximately 3-5 days where it is acted upon by the active bacteria and is then taken off as treated solid waste 55.

The vessel 10 has three different means for the removal of solids. The first of these removal means is an auger 32 located on the inlet side 22 of the vessel 10 which removes sunken solids 33 from a bottom 29 of the vessel 10 adjacent the inlet side 22. The second of these removal means is a chopper pump 34 which removes other sunken solids 33 from the bottom 29 of the vessel 10. The 4097a2 04 December 2003 - 14 chopper pump 34 is located at the bottom 29 of the vessel and adjacent the outlet side 24. It is envisaged that the sunken solids 33 removed by the chopper pump 34 will be slightly less dense, digestible sludge-like solids whereas those removed by the auger 32 will be more dense, indigestible solids which sink straight to the bottom 29 of the vessel 10 as soon as the solid waste 25 enters the vessel. The sunken solids 33 removed by the chopper pump 34 are broken down and re-circulated back into the solids digestion vessel 10 for further treatment before they can be discharged into the environment. In contrast, the sunken solids 33 removed by the auger 32 are disposed of elsewhere and require no further treatment by this process.

In addition, the vessel 10 has further removal means located at the top of the vessel 10 on the outlet side 24 which removes treated solid waste 55. These removal means consist of a conveyor belt 36 which lifts off the floating solids layer 30 from the top 23 of the vessel 10. The floating solids layer 30 makes contact with the conveyor belt 36 at the edge of the vessel 10 and is dragged up and out of the vessel 10 whilst resting on an upper surface of the conveyor belt 36. There is also a de-watering means which in this case is another conveyor belt 38 located above the first conveyor belt 36. The conveyor belt 38 presses down on the treated solid waste 55 and thereby, in conjunction with the conveyor belt 36, squeezes excess liquid from the treated solid waste 55 so that it becomes de-watered, treated solid waste 57. There are also two 4 0 97a2 04 December 2003 15 rotating brushes 54 located adjacent the conveyor belts 36 and 38 which ensure that the de-watered, treated solid waste 57 is brushed off and does not stick to the conveyor belts 36 and 38 respectively. This improves the efficiency of the removal of the dewatered, treated solid waste 57 from the solids digestion vessel 10.

The solids digestion vessel 10 further has moving means located at the top 23 of the vessel 10. The moving means is a conveyor belt 40 which is located such that its lower surface lies beneath a surface 31 of the liquid layer 28 in the solids digestion vessel 10. In this way, the conveyor belt 40 ensures that the floating solids layer 30 which is floating on the liquid layer 28 is submerged within the liquid layer 28 and thereby provides conditions suitable for the treatment of the floating solids layer 30 by active bacteria located within the liquid layer 28 of the solids digestion vessel 10. The conveyor belt 40 has projections, which in this case are protruding fins 41 which make contact with the floating solids layer 30 and thereby move it along from the inlet side of the vessel 22 to the output side of the vessel 24. There is also a weir 42 on the output side 24 of the solids digestion vessel 10 at the top 23 adjacent the conveyor belt 36 so that when the liquid layer 28 gets too high the overflow can run out over the weir 42 thereby maintaining a substantially constant liquid level in the vessel 10. There is a further liquid take-off 27 at the bottom 29 of the vessel on the outlet side 24 adjacent the chopper pump 34.

The take-off 27 returns part of the liquid layer 28 to a 4097a2 04 December 2003 - 16 liquid digestion vessel 12. It should be noted that this may be to any liquid digestion vessel and not necessarily liquid digestion vessel 12.

The conveyor belt 40 is acted upon by two eccentric cams 44 which move the conveyor belt 40 up and down as it rotates such that the floating solids layer 30 located just beneath the conveyor belt 40 is repeatedly submerged and agitated within the liquid layer 28. This ensures that the floating solids layer 30 is fully covered by the liquid layer 28 and that all parts of the layer 30 will be acted upon by the active bacteria in the liquid layer 28 so that the floating solids layer 30 will emerge from the vessel 10 as treated solid waste 55. The eccentric cams 44 specifically act on portions 47 of the conveyor belt 40 that are in contact with the floating solids layer 30. In addition, the conveyor belt 40 contains apertures 43 so that when the belt 40 is pushed down into the liquid layer 28 the liquid may fully penetrate up through the floating solids layer 30 located beneath the belt 40 and then percolate back down through the floating solids layer 30 when the conveyor belt 40 is moved back up and out of the liquid layer 28 by the eccentric cams 44.

A fluid fraction from the liquid digestion vessel 12 containing active bacteria is input into the solids digestion vessel 10 at several locations around the vessel 10. There are two inputs 46 at the top 23 of the vessel and another 48 on the inlet side 22 near the top 23 of the vessel 10 which is adjacent the inlet 26 for the solid 4097a2 04 December 2003 - 17 waste 25. This second input 48 ensures that the solid waste 25 comes into contact with a fresh fluid fraction containing active bacteria from the liquid digestion vessel as soon as it enters the solids digestion vessel 10. The two inputs 46 at the top of the vessel are located above the conveyor belt 44. Because the conveyor belt 40 contains apertures, the fluid fraction introduced via the two inputs 46 percolates down through the floating solids layer 30 located beneath the conveyor belt 40 thereby maximizing the possibility of all parts of the floating solids layer 30 coming into contact with the active bacteria.

The bottom 29 of the solids digestion vessel 10 has a baffle 50 which is located in between the inlet side 22 and the outlet side 24 of the vessel 10 such that the inlet side 22 is substantially separated from the outlet side 24 and such that any material in the vessel passing from one side to the other must pass up and over this baffle 50. The baffle 50 comprises a raised surface on the bottom 29 of the vessel 10. The main function of this baffle 50 is to keep the heavy solids that fall straight to the bottom 29 of the vessel 10 as soon as they enter it on the inlet side 22 of the vessel 10.

The solids digestion vessel 10 further includes heaters 52 located at the bottom 29 of the vessel 10 adjacent the inlet side 22. The purpose of these heaters 52 is to increase the activity of the active bacteria in the liquid layer 28 of the solids digestion vessel 10 such that the 4097a2 04 December 2003 - 18 length of time needed to digest and process the solid waste 25 is decreased. It should be understood that there may be more than two heaters 52 in the vessel 10 and that these may be located at any position around the vessel 10.

Figure 3 shows an alternative embodiment of a solids digestion vessel 100. The features common to both vessels and 100 which function in the same or similar way will be given the same reference numeral as in Figure 2 but increased by 100. The solids digestion vessel 100 has a conveyor belt 136 comprising the removal means at the outlet side 24 of the vessel 100 which extends right down to the bottom 29 of the vessel 100 and can also lift off sunken solid waste from the bottom 29 of the vessel 100.

In addition, the vessel 100 further includes mixing means for agitating/mixing the contents of the vessel 100. In this embodiment, the mixing means comprise mechanical stirring means 156 which are located adjacent an inlet side 22 of the vessel 100 and in between an inlet 126 for the solid waste 25 and a conveyor belt 140 comprising the moving means. In this embodiment, there is also an auger 132 for removing sunken indigestible solids from the bottom 29 of the vessel 100. The auger 132 is again located adjacent the inlet side 22 of the vessel 100 but in this case it extends further along the bottom 29 of the vessel 100 until it reaches a baffle 150 which separates the inlet side 22 and the outlet side 24 of the vessel 100. The design of the baffle 150 is different from that of the baffle 50 of figure 2 in that it extends higher in the vessel 100 and more substantially separates the two 4097a2 04 December 2003 sides 22, 24 of the vessel 100. There is also a take-off 127 at the bottom 29 of the vessel 100 for removing sludge-like solids and/or liquid from the vessel 100. The take-off/outlet 127 is located at the bottom 29 of the vessel 100 adjacent the outlet side 24 of the vessel 100 between the conveyor belt 136 and the baffle 150.

This embodiment of the vessel 100 also has a liquid input 148 located on the inlet side 22 of the vessel 100 where the fluid fraction from the liquid digestion vessel 12 is input and a liquid take- off 142 is located on the outlet side 124 of the vessel 100 beneath the conveyor belt 136 which comprises the removal means.

Figure 4 is a view from above of the solids digestion vessel 10 of figure 2. The apertures 43 can be seen between the protruding fins 41 of the conveyor belt 40.

There are also v-shaped ribs 39 on the surface of the conveyor belt 38 which comprises the de-watering means.

The invention has been described above by way of

description only and it should be understood that

modifications in detail may be made to the invention without departing from the scope of the invention as defined in the claims.

4097a2 04 December 2003 20

Claims

Claims 1. A process for treating solid waste, the process comprising: a)

providing at least one solids digestion vessel having an inlet side, outlet side, moving means and removal means, the outlet side being located on the opposite side of the vessel to the inlet side, the removal means being located on the outlet side and the solids digestion vessel containing a liquid layer and a floating solids layer floating on said liquid layer; b) transferring solid waste to the at least one solids digestion vessel at the inlet side; c) providing at least one liquid digester tank containing a source of organic material undergoing anaerobic bacterial digestion in a fluid digestion phase to produce a fluid fraction containing active bacteria; d) transferring at least part of the fluid fraction containing active bacteria into the solids digestion vessel to create treated solid waste in a solids digestion phase; e) transferring at least some of the liquid layer within the solids digestion vessel to the liquid digester tank; f) using the moving means to move at least some of the floating solids layer from the inlet side to the outlet side in the solids digestion vessel; and g) using the removal means to remove at least some of 4097a2 04 December 2003 - 21 the floating solids layer in the solids digestion vessel from the outlet side.
2. A process as claimed in any preceding claim, further comprising the step of de-watering at least some of the treated solid waste to remove excess liquid using a de- watering means.
3. A process as claimed in any preceding claim, wherein at least some of the fluid fraction containing active bacteria is introduced into the solids digestion vessel from above the floating solids layer.
4. A process as claimed in any preceding claim, wherein at least some of the fluid fraction containing active bacteria is introduced into the solids digestion vessel adjacent an inlet for the solid waste on the inlet side of the solids digestion vessel.
5. A process as claimed in any preceding claim, wherein the process further comprises the step of forcing at least part of the floating solids layer down into the liquid layer using agitation means.
6. A process as claimed in any preceding claim, wherein the process further comprises the step of removing at least some sunken solids from the bottom of the vessel using at least one means for removing sunken solids.
7. A process as claimed in Claim 6, wherein the means 4097a2 04 December 2003 for removing sunken solids from the solids digestion vessel is located at or adjacent the inlet side of the vessel.
8. A process as claimed in any preceding claim, wherein the process further comprises the step of mechanically breaking down and recirculating at least some other sunken solids in the solids digestion vessel using a means for mechanically breaking down and re-circulating at least some other sunken solids.
9. A process as claimed in Claim 8, wherein the means for mechanically breaking down and re-circulating at least some other sunken solids is located at or adjacent the outlet side of the vessel.
10. A solids digestion vessel having an inlet side for solid waste and an outlet side on the opposite side of the solids digestion vessel to the inlet side, the solids digestion vessel containing a liquid layer and a floating solids layer floating on said liquid layer, and the vessel further comprising: a) moving means for moving the floating solids layer within the vessel from the inlet side to the outlet side and; b) removal means located adjacent the outlet side for removing at least some of said floating solids layer.
11. A solids digestion vessel as claimed in Claim 10, wherein the moving means comprises a conveyor belt.

4 0 97a2 04 December 2003 - 23
12. A solids digestion vessel as claimed in Claim 11, wherein the conveyor belt has projections from its surface.
13. A solids digestion vessel as claimed in Claim 11 or Claim 12, wherein at least a portion of the conveyor belt is located beneath a surface of the liquid layer.
14. A solids digestion vessel as claimed in any one of Claims 11-13, wherein the vessel is provided with agitation means for forcing at least part of the floating solids layer down into the liquid layer.
15. A solids digestion vessel as claimed in Claim 14, wherein the agitation means are eccentric cams that act upon the conveyor belt.
16. A solids digestion vessel as claimed in any one of Claims 11 to 15, wherein the conveyor belt contains apertures such that fluid can pass through the conveyor belt.
17. A solids digestion vessel as claimed in any one of Claims 10 to 16, wherein the removal means also comprises a conveyor belt.
18. A solids digestion vessel as claimed in any one of Claims 10 to 17, wherein the vessel further comprises de watering means.

4 0 97a2 04 December 2003 - 24
19. A solids digestion vessel as claimed in Claim 18, wherein when the removal means comprises a conveyor belt, the de-watering means comprises at least part of the removal means.
20. A solids digestion vessel as claimed in any one of Claims 10 to 19, wherein a bottom of the vessel includes a baffle on the interior of the vessel which is located in between the inlet side and the outlet side.
21. A solids digestion vessel as claimed in any one of Claims 10 to 20, wherein the vessel further includes means for removing at least some sunken solids from the bottom of the vessel.
22. A solids digestion vessel as claimed in Claim 21, wherein the means for removing at least some sunken solids is located at or adjacent the inlet side of the vessel.
23. A solids digestion vessel as claimed in Claim 21 or 22 wherein the means for removing at least some sunken solids is an auger.
24. A solids digestion vessel as claimed in any one of Claims 10-23, wherein the vessel further comprises means for mechanically breaking down and re-circulating at least some other sunken solids.
25. A solids digestion vessel as claimed in any one of 4097a2 04 December 2003 - 25 Claim 24, wherein the means for mechanically breaking down and re-circulating is located at or adjacent the outlet side of the vessel.
26. A solids digestion vessel as claimed in any one of Claim 24 or Claim 25, wherein the means for mechanically breaking down and re-circulating is a chopper pump.
27. A solids digestion vessel as claimed in any one of Claims 10 to 26, wherein the vessel comprises at least one heater for heating the contents of the vessel.
28. A solids digestion vessel as claimed in Claim 27, wherein at least one heater is located below and adjacent the inlet side of the vessel.
29. A solids digestion vessel as claimed in any one of Claims 10 to 28, wherein the vessel further comprises mixing means for mixing the contents of the vessel.
30. A solids digestion vessel as claimed in Claim 29, wherein the mixing means comprise mechanical stirring means.
31. A solids digestion vessel substantially as herein described with reference to or as shown in the accompanying drawings.
32. A process substantially as herein described with reference to the accompanying drawings.

4097a2 04 December 2003