WO2005047452A1

WO2005047452A1 - Bioreactor

Info

Publication number: WO2005047452A1
Application number: PCT/GB2004/004724
Authority: WO
Inventors: Oluyinka Ogunjimi Adebayo
Original assignee: SAROKO ENERGY SYSTEMS Ltd
Current assignee: SAROKO ENERGY SYSTEMS Ltd
Priority date: 2003-11-07
Filing date: 2004-11-08
Publication date: 2005-05-26
Anticipated expiration: 2006-05-07
Also published as: GB0326062D0; GB2408702B; EP1685233A1; GB0424651D0; GB2408702A

Abstract

A bioreactor is provided for the continuous or substantially continuous anaerobic digestion of organic matter. The bioreactor is preferably a small-scale, stand alone unit (10), which is ideally suited for small-scale industrial or domestic use. The bioreactor includes a main reaction chamber (40) for the digestion of organic matter, and two anti-chambers (36, 38) arranged between an inlet (16) for organic matter and the main reaction chamber (240). The chambers are arranged so that organic matter can pass from the inlet, through the anti-chambers and into the main reaction chamber, under gravity. Additional organic matter can be introduced into the bioreactor through the inlet into the first anti-chamber, without substantially affecting the level of oxygen in the main reaction chamber, thus maintaining the efficiency of the rate of production of methane during digestion in the main chamber. The bioreactor can be coupled to a sewage outflow from a domestic dwelling.

Description

Bioreactor

The present invention relates to a bioreactor, more particularly to an anaerobic digester for continuous or substantially continuous anaerobic digestion of organic matter

Anaerobic digestion is the decomposition of organic matter in a substantially oxygen free environment. A major product of this digestion is methane, which can be used to generate heat and/or electricity or used to run an internal combustion engine, for example. Commercially, apparatus referred to as 'anaerobic digesters' or 'bioreactors' are used to create the environment for anaerobic digestion to occur and to collect or utilise the gaseous product. It is common for animal waste, effluent slurry, human waste, as well as food processing and other organic waste, to be utilized in anaerobic digesters.

In the current climate of increasing focus on renewable energy sources, as well as an increased need for recycling and a reduction of organic waste, in particular for domestic and small scale industrial purposes, anaerobic digesters have a potential to offer a valuable solution to modern requirements for waste minimisation at source and waste disposal problems, whilst taking advantage of renewable energy.

Current anaerobic digestion techniques are based on large-scale processes relying on the natural anaerobic process to generate biogases. They tend to be both capital intensive and inefficient, which has made the use of anaerobic digesters for small-scale commercial purposes economically unjustifiable in most cases.

Known anaerobic digester systems take the form of large scale sewage works, municipal organic recycling centres or large farm installations for processing waste from animal husbandry. Because of their scale, the operation of the known systems is dictated largely by atmospheric temperature, which means that known systems operate typically in a mesophilic range of temperature (0 to 40C). The rate of production of methane during anaerobic digestion increases with an increase in temperature, and is more efficient at higher temperatures. However, for most systems the cost of increasing the efficiency and maintaining the efficiency level of the rate of methane production of known digester plant outweighs the benefits of the output from the systems.

There is a need for smaller scale bioreactors, which provide better control and efficiency of methane production. However, known small-scale reactors have, to date, been rather crude, using a proportion of the generated methane to maintain the temperature within the reactor. This practice makes reactors of this kind largely unsafe for commercial use. Furthermore, the recycled methane can only be used for heating in the mesophilic range of temperature rather than at a more efficient temperature range, for example the thermophilic range (typically 40 to 60C), thus reducing the effective efficiency of the level of output of the reactors. Additionally, such small-scale reactors rely on a batch feed process, which only compounds the inefficiency of the rate of production of methane of the reactors.

It is an object of the invention to provide an improved bioreactor.

According to the broadest aspect of the invention, there is provided a bioreactor for continuous or substantially continuous anaerobic digestion of organic matter, the bio reactor havingan inlet for introducing organic matter into the bioreactor, a main reaction chamber for the organic matter, and at least one anti-chamber arranged between the inlet and main reaction chamber, in which the chambers are arranged so that organic matter can pass from the inlet, through the or each anti-chamber and into the main reaction chamber, and that additional organic matter can be introduced into the bioreactor through the inlet, without substantially affecting the level of oxygen in the main reaction chamber.

Preferably, the or each anti-chamber is arranged for reducing the level of oxygen in the organic matter as the matter passes to the main reaction chamber. Preferably, the bioreactor is arranged for continuous or substantially continuous anaerobic digestion from successive loads of organic matter through the inlet.

In a preferred embodiment, the bioreactor includes first and second anti- chambers arranged so that organic matter can pass from the first anti-chamber to the second anti-chamber, before passing into the main reaction chamber.

Preferably, the anti-chambers are arranged so that the level of oxygen in the organic matter is successively reduced as the matter passes from the first anti- chamber to the second chamber and into the main reaction chamber.

Preferably, the first anti-chamber is arranged above the second anti-chamber.

Preferably, the first and second anti-chambers are arranged for passage of matter between the first and second anti-chambers under gravity.

Preferably, the first and second anti-chambers are arranged above the main reaction chamber.

Preferably, the main reaction chamber is arranged for receiving matter from the first and second anti-chambers under gravity.

Preferably, the or each anti-chamber is arranged for passage of organic matter between adjacent chambers under predetermined conditions.

Preferably, the bioreactor includes limiting means for limiting the passage of organic matter between adjacent chambers.

In a preferred embodiment, the limiting means is configured to permit matter to pass from a first of said chamber under a predetermined mass of matter present above said limiting means. In a preferred embodiment, a rotary vane is arranged between adjacent chambers. Each rotary vane may be configured to enable matter to pass between adjacent chambers under a predetermined mass of organic matter present above said rotary vane.

Preferably, the inlet includes a hatch, operable between an open position and a sealed closed position.

The bioreactor may include a solar powered energy store.

Preferably, the bioreactor includes means for heating said main reaction chamber.

In a preferred embodiment, the bioreactor includes control means for monitoring local conditions within at least one of said chambers, and may include a closed loop control system provided to automatically maintain a set process window for anaerobic digestion of waste.

The bioreactor may include means for promoting optimised conditions for anaerobic digestion to occur within organic matter introduced into the bioreactor.

Preferably, the bioreactor includes means for assisting movement of organic matter between the chambers.

In a preferred embodiment, the bioreactor is solar powered and adapted for operating continuously in the thermophilic temperature range without an auxiliary supply of energy.

Preferably, the bioreactor is adapted for collecting leachate from organic matter in the bioreactor and reintroducing said leachate into organic matter in the bioreactor. In a preferred embodiment, the bioreactor is in the form of a portable unit.

According to a further aspect of the invention, there is provided a bioreactor for continuous or substantially continuous anaerobic digestion of substantially solid organic matter, in which the bioreactor is in the form of a non-fixed portable unit.

According to a still further aspect of the invention, there is provided a solar powered bioreactor adapted for operating continuously in the thermophilic temperature range without an auxiliary supply of energy.

According to another aspect of the invention, there is a solid waste bioreactor adapted for collecting leachate from solid waste in the bioreactor and reintroducing said leachate into solid waste in the bioreactor.

The invention is advantageous in that it provides a cost effective bioreactor that can operate continuously and reliably in the thermophilic temperature range using renewable energy. A preferred embodiment of the invention is also advantageous in that the bioreactor is a portable unit. The unit may be self- contained and suitable for domestic use and small-scale industrial use, for example in restaurants and supermarkets, as well as institutions such as schools, hospitals and prisons.

Other preferred features of the invention will be readily apparent from the following description and dependent claims.

The invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic perspective view of a standalone bioreactor unit in accordance with a first preferred embodiment of the invention; Figure 2 is a schematic view of the bioreactor of Figure 1 , showing a number of the internal components;

Figure 3 is a schematic diagram showing the interrelationship between the internal components of the bioreactor shown in Figures 1 and 2;

Figure 4 is a schematic view of a rotary vane for use in the invention;

Figure 5 is a schematic representation showing a bioreactor in accordance with a second preferred embodiment of the invention in use in a domestic environment; and

Figure 6 is a more detailed schematic view of the bioreactor shown in Figure 5.

A standalone bioreactor, in the form of a compact, self-contained anaerobic digester unit according to a first preferred embodiment of the invention is indicated at 10 in Figures 1 and 2. The unit 10 is of a size corresponding to a typical domestic skip, for example having a height of between 1.75 metres to 2 metres, a length of between 1.50 metres to 1.8 metres and a width of between 1.2 metres to .5 metres. The unit 10 is portable and is adapted for transportation on a skid, not shown. The relatively small and compact nature of the unit 10 is ideal for domestic and small-scale industrial use, for example by restaurants, grocers and supermarkets, as well as institutions such as schools and prisons.

As can be seen in Figure 1 , the upper portion of the unit 10 includes an energy store 12, incorporating a solar panel assembly 14 of generally known construction and operation, for supplying power to the unit 10. The solar panel assembly 14 consists of two parts: a solar electric power generator and a solar water heater. As will be described in more detail below, the solar panel assembly 14 is used to maintain a heated environment within the unit 10 for controlling and optimising the conditions for anaerobic digestion of organic waste matter. However, auxiliary heating sources can be used.

An inlet in the form of a spring-loaded hatch 16 is provided in a side 17 of the unit 10, whereby organic material can be introduced into the unit 10. An outlet 18 is provided in an end 19 of the unit 10 for removing waste product from the unit 10, as will be described in more detail below.

The unit 10 includes a central control unit (not shown in Figures 1 or 2, but indicated at 20 in Figure 3) having associated circuitry (not shown), for controlling the operation of the unit 10 as will be described in more detail below. A control panel 22 for the control unit 20 is provided on the side 17 of the unit 10.

A methane tank 26 is included for storing gaseous product from the anaerobic digestion process, and a water tank 28 is provided for storing water for circulation within the unit 10, as described in more detail below with reference to Figure 3. The unit 10 includes cylinders 30, 32, which are provided for storing acid and alkali respectively, for use in the digestion process. The cylinders 30, 32 can be accessed externally from the end 19 of the unit 10, as can be seen in Figure 1 , to enable a user to top up the level of acid or alkali. A linear, free piston pump 34 is also provided for circulating water stored in the tank 28.

The energy store 12, methane tank 26, water tank 28, cylinders 30, 32 and pump 34 are in operative communication with the control unit 20. The unit 10 includes a digestion system 24 for digesting organic matter, indicated in Figure 2, which is discussed in more detail below with reference to Figure 3.

Referring now to Figure 3, the unit 10 includes first, second and third chambers 36, 38, 40.

The hatch 16 is formed in a portion of the first chamber 36, so that organic waste is loaded into the digestion system 24 through the hatch 16. The hatch 16 can be opened, by pulling the hatch 16 open against the spring bias, or automatically via the control unit 20. The hatch 16 includes a seal (not illustrated) for maintaining an airtight condition within the first chamber 36 when the hatch 16 is in a closed position.

The first chamber 36 includes an inclined base wall 37, which terminates at an outlet portion 39. The base wall 37 is arranged such that organic matter introduced into the unit 10 can move under gravity towards the outlet portion 39, for example after successive loads have been introduced. The first chamber is used to stabilize and consolidate successively introduced loads of organic matter under gravity, to reduce the oxygen level in matter present in the region of the outlet portion 39.

The second chamber 38 is arranged below the first chamber 36 and is in operative communication with the outlet portion 39 of the first chamber 36 via a rotary vane 42. The vane 42 has a plurality of vane arms 44 and is generally of known construction, and is configured to allow organic matter to pass from the first chamber 36 to the second chamber 38 under gravity. In this embodiment, the vane 42 is configured to rotate if a predetermined mass of organic matter is present on an upper arm 44, to thus enable organic matter from the first chamber 36 to drop down into the second chamber 38. Alternatively, the vane 42 can be programmed or otherwise selectively caused to rotate by the control unit 20, as preferred. The rotary vane 42 is arranged between the first and second chambers 36, 38 with the arms adapted for substantially airtight contact with the walls of the first and second chambers 36, 38 when in a non-rotating position. In this embodiment, the ends of the arms 44 include sealing means, for providing the substantially airtight contact with the walls of the first and second chambers 36, 38. A preferred embodiment of a suitable sealing means is indicated at 45 in Figure 4 only.

Each sealing means 45 consists of a flexible extension attached to the end of a respective arm 44 of the rotary vane. The extensions are made from a resilient plastics material, the nature of which is sufficient to provide a sealing engagement with the walls of an adjacent chamber or other surface, in use, as will be understood by the skilled reader.

It should be noted that such sealing means may be provided on each vane in the unit 10, as well as on the distal end of the hatch 16, for example for providing an airtight or substantially airtight barrier between the exterior of the unit and the digestion system 24.

The second chamber 38 includes an inclined base wall 41 , substantially as described above with reference to the base wall 37 of the first chamber, which terminates at an outlet portion 43. The second chamber 38 is used to further consolidate and stabilise the organic matter passing from the first chamber 36, as described in more detail below.

The third chamber 40 is provided below the second chamber 38, and is in operative communication with the second chamber 38 via a further rotary vane 46 corresponding in construction and configuration to the vane 42 described above. The third chamber 40 includes an inclined base wall 45, substantially as described above with reference to the base wall 37 of the first chamber 36, which terminates at an outlet portion 47. The third chamber 36 serves as a main reaction chamber and is adapted for providing optimised conditions for anaerobic digestion to occur in organic matter, as will be described in more detail below.

The third chamber 40 is larger than the first and second chambers 36, 38 and includes a rotor 52 for agitation of organic material present in the chamber 40 in use. The rotor is in operative communication with the control unit 20, for selectively agitating material in the third chamber 40, as required or as programmed. A sensor arrangement (not shown) is provided in the third chamber 40, in operative communication with the control unit 20, for monitoring the environmental parameters within the chamber 40, such as methane production rate, temperature, humidity, pH, time, and mass of organic matter. An outlet chamber or waste vessel 48 is provided adjacent the outlet portion 47 of the third chamber 40. Although not illustrated, the outlet 16 of the unit 10 is formed in the waste vessel 48, for removal of waste product from the unit 10.

The waste vessel 48 is in operative communication with the third chamber 40 via a rotary vane 50 corresponding in construction and configuration to the vane 42 described above. Matter in the third chamber 40 moves under gravity along the inclined surface and passes to the waste vessel 48 for disposal. Although not illustrated, mechanical means can be provided for moving the matter along the inclined surface, for example after a predetermined time period, or if the sensor arrangement indicates that the rate of methane production within the third chamber 40 has fallen below a predetermined level.

A spring-loaded compactor mechanism 56 is mounted in an upper part of the waste vessel 48, which is operable via the control unit 20 for compacting waste from the digestion process.

A drip tray 58 is formed in the base of the waste vessel 48, which includes a mesh opening 59 for collecting leachate from organic material in the third chamber 40 and waste material present in the waste vessel 48, in particular after compaction of the waste. A pump 61 , operable by the control unit 20, is in communication with the drip tray 58, for pumping the collected leachate, to be sprayed through nozzles (not shown) provided in a wall of the second chamber 38. Such nozzles may also be provided in the first and/or third chambers 36, 40.

Cultures present in the leachate can thus be utilised to stimulate in the chemical reaction for methane production in the first and second chamber, and to promote increased methane production rates in the third chamber 40, for example. Water from the water tank 28 can also be sprayed via nozzles (not shown) provided in the walls of the chambers 36, 38, 40, to control the humidity in the third chamber

40, for promoting optimised conditions for anaerobic digestion, for example. The third chamber 36 is contained in a circulation tank 60, which forms part of a water circulation circuit, indicated at 62. The circulation circuit includes a closed loop pipe network 64 passing from the water tank 28, through the solar panel assembly 14, and extending into the circulation tank 60 before returning to the water tank 28. The pipe network 64 encircles the third chamber 40 in the tank 60 by a plurality of turns, for heating the third chamber 40 in use, as described in more detail below. The pump 34 is located in the pipe network 64, between the energy store 12 and the circulation tank 60, for assisting the circulation of water through the network 64.

The sensor arrangement described above forms part of a closed loop monitor circuit according to a further aspect of the invention for which the applicant reserves the right to apply for combined or independent protection. The closed loop circuit also monitors the temperature of the circulated water and the volume of stored methane. This enables the heating of the water via the solar panels or auxiliary heating source, to be controlled to an optimised temperature, to minimise power consumption from the energy store 12, as will be understood by the skilled reader.

The water circulation circuit 62 is configured to enable efficient heat exchange between the circulating water and the third chamber 40, by using thin walled conduits. Water channels may also be built into the walls of the chamber 40.

A typical operation of the unit 10 will now be described, in which successive loads of organic matter have been introduced into the unit 10 over a substantially continuous period. Thus organic matter is present in each of the chambers 36, 38 and 40.

A new load of organic matter (not shown) is introduced into the first chamber 36 by pushing open the hatch 16 and releasing the organic matter. After loading, the hatch 16 closes under action of the spring bias and is maintained airtight by the seal. Thus, a limited amount of oxygen is introduced into the first chamber 36 during each loading of the organic matter, and further oxygen in-take is at least substantially prevented, until the hatch 16 is re-opened.

In the first chamber 36, the organic matter consolidates with time as it moves towards the outlet 39 under gravity. This consolidation is further increased with the introduction of successive loads of organic matter through the hatch 16, substantially as described above, as the mass of matter in the first chamber 36 increases. This consolidation helps to stabilize the organic matter in the first chamber 36, and helps to reduce the oxygen level in the matter, in particular at the bottom of the first chamber 36. Also, oxygen present in the matter is gradually used up by aerobic bacteria breeding in the matter, in particular in the consolidated matter, at the bottom of the chamber 36. The rate of reduction in oxygen in the matter in the first chamber 36 can be increased by the use of a chemical compound with a high affinity for oxygen introduced through the hatch 16.

With successive loads of organic matter into the first chamber 36, a portion of the matter moves under gravity in the direction of the incline of the base wall 37, towards the outlet portion 39 and ultimately drops down onto an arm 44 of the rotary vane 42. The rotary vane 42 is configured to rotate under a predetermined weight of organic matter, to allow only a specific weight of matter to pass to the second chamber 38. Thus, when a predetermined mass of matter is present on the arm 44, the rotary vane 42 rotates and said matter falls from the rotated arm and into the second chamber 38.

It will be understood that the level of oxygen in the matter present at the bottom of the first chamber 36, in particular in the region adjacent the outlet portion 39, is less than the value of said matter upon first loading into the unit 10. Thus, the level of oxygen in the organic waste passing into the second chamber 38 is limited, by only allowing incremental amounts of consolidated matter from the bottom of the first chamber 36 to pass to the second chamber 38. Also, the substantially air-tight co-operation of the arms 44 with the first and second chambers 36, 38, acts to significantly reduce the flow of ambient oxygen in the first chamber 36 to the second chamber 38.

The consolidated matter falling into the second chamber 38 will fall onto or adjacent matter already present in the second chamber 38. The successive passage of matter into the second chamber 38 leads to further consolidation and progressive movement of the matter in the second chamber 38 under gravity towards the outlet portion 47. Thus, successive loads of organic matter being introduced into the unit 10, causing an incremental passage of matter from the first chamber 38, assists in the progressive movement of matter within the second chamber 38.

Bacteria breeding in the second chamber 38 gradually use up oxygen present in the matter that has moved into the second chamber 38. When a significant proportion of the oxygen in the matter in the second chamber 38 has been removed, the natural anaerobic digestion process begins. It will be understood that, if the conditions for anaerobic digestion are met in the first chamber 36, i.e. if the oxygen level in portions of the matter present in the first chamber 36 is substantially eliminated, natural anaerobic digestion of at least a portion of said matter will begin in the first chamber 36.

The rotary vane 46 between the second and third chambers 38, 40 is configured to permit organic matter to move from the second chamber 38 into the third chamber 40 in response to a predetermined mass of material present on an arm of the vane 46, substantially as described above with reference to vane 42. Therefore, it will be understood that the controlled rotation of the vane 46 and the cooperation of the vane with the walls of the chambers 38, 40 serves to effectively limit or control the amount of oxygen passing into the main reaction chamber 40.

As described above, the passage of consolidated matter between the adjacent chambers, under gravity, leads to a further consolidation and progressive movement of the matter in unit 10. Thus, matter which falls from the second chamber 38 will land on matter already present in the third chamber 40, causing further consolidation and movement towards the outlet portion 47 of the third chamber 40.

In most cases, the majority of the oxygen content is reduced to levels suitable for the on-set of natural anaerobic digestion in the third chamber 40, with the first and second chambers 36, 38 serving effectively as anti-chambers to the third, main reaction chamber 40. The control unit 20 controls the environmental conditions in the third chamber 40, to promote optimised conditions for anaerobic digestion in the organic matter. The temperature in the third chamber 40 is kept in the thermophilic range using water based heat transfer from the solar panel assembly 14, via the closed loop pipe network 64. Water passing through the solar panel assembly 14 is heated and circulated by the pump 34 to the circulation tank 62. In the circulation tank 62, the water passes through the pipe turns around the third chamber 40, thereby transferring heat to the walls of third chamber 40. However, it will be appreciated that auxiliary heat sources can also be used, such as waste hot water from an associated attached building (for example a hospital or food processing plant), or other heating means.

The pH value of the matter in the third chamber 40 is also regulated by the closed loop control sensor arrangement, to introduce acid or alkali from the cylinders 30, 32 respectively, as required.

Leachate from the drip tray 58 in the waste vessel 48 is also sprayed into the chambers 36, 38, 40, as required, thus introducing cultures of bacteria into the digesting matter. Similarly, water from the water tank 24 is introduced into the third chamber 40, as required, through the nozzles described above, to control the humidity of the digesting matter and thereby maintain an environment in which bacteria used in the digestion process can thrive. Additionally, the digesting waste in the third chamber 40 is agitated periodically, as required, by the rotor 52, dependent upon the level of power available to the unit 10, e.g. from the energy store 12, to promote a uniform digestion of the material in the third chamber 40.

It will be appreciated that the majority of the anaerobic digestion in the organic matter takes place in the third chamber 40. At the point of anaerobic digestion, methane is produced, which is collected in the methane tank 26, for use as required, for example as a fuel for operating a boiler.

The digested matter passes under gravity or by mechanical means from the third chamber 40 into the waste vessel 48, through rotary vane 50. In the waste vessel 48, the digested matter is compacted into a waste bale by the compactor mechanism 56. The waste bale can then be removed through the outlet 16, to be used as a soil conditioner or dried and burnt as an organic fuel, for example.

The arrangement of the digestion chambers 32, 34 and 36, whereby the chambers provide substantially airtight zones for the removal of oxygen from the organic matter, and whereby the rate of passage of organic matter falling through the chambers can be controlled is of particular advantage to the efficiency of the unit 10. Furthermore, the arrangement is such that it ensures that new deposits of organic material into unit 10 do not interfere with or contaminate the microbial stability of the unit 10 at the position where the main anaerobic digestion occurs, i.e. in the third chamber 40. Moreover, the control unit 20, sensor arrangement and circulation circuit 62 are utilised to create the optimised conditions for anaerobic digestion in the third chamber 40. The arrangement of the chambers 36, 38, 40 is of particular advantage in that the unit 10 is able to operate at an efficient level, with successive loads of organic material, and without having to modulate the feed rate or methane production cycle. Mechanical or driven means may be provided for movement of matter within the first, second and third chambers 36, 38, 40, towards their respective outlet portions.

It should be noted that the invention has a particularly advantageous application in the processing of domestic waste, such as domestic refuse and foul waste. A modified bioreactor according to a second preferred embodiment of the invention, for use in a domestic environment, is indicated generally at 200 in Figures 5 and 6.

As can be seen firstly from Figure 5, the unit 200 is coupled to the foul water flow path 202 from a domestic house 204, for processing human effluent from the toilets 206 of the house 204.

The unit 200 is installed in a specially prepared hole 207 in the ground, with the main body of the unit 200 partially installed below ground level, indicated at 208, so that the inlet of the bioreactor is arranged above the ground level 208. As will be described in more detail below with respect to Figure 6, the unit 200 includes outflow means, indicated at 210 in Figure 5, which connect the unit to the local sewage network for the house 204.

It should be noted that the unit 200 can easily be coupled to the fowl water flow path from any number of adjacent houses, for example one bioreactor can be installed to service a cul-de-sac, terrace or street of houses.

The unit 200 is shown in more detail in Figure 6, from which it will be immediately apparent that the internal configuration of the unit 200 is substantially the same as the unit 10 described above, having a digestion system substantially identical to the digestion system 24 described with reference to Figure 3. In this respect, the same reference numerals have been used in Figure 6 to denote the similar or identical components described above with reference to Figure 3, albeit with the prefix "2", for example methane storage tank 226.

It should be noted that, although many of the components of the unit 200 not shown as being located inside the body of the unit 200, Figure 6 is schematic and those components are housed within the unit 200. However, the methane outlet, a user interface for the control unit 220, the acid/alkali cylinders 230, 232 and the waste outlet 248 may all be accessible from the exterior of the unit 200.

The configuration and operation of unit 200 is substantially the same as for the unit 10 described above, and therefore detailed description of the operation of unit 200 is unnecessary for the skilled reader. However, the main points of difference will now be described.

In this embodiment, the first chamber 236 is in direct communication with the house 204, in that the foul water flow path 202 is routed directly into the lower end of the first chamber 236, as can be seen in Figure 6. This enables waste matter from the house 204 to travel into the unit 200, towards the main reaction chamber 240, along the lower wall 237 of the first anti-chamber 236. All other organic refuse from the house 204 can be loaded into the unit 200 through the swing hatch 226, which in this embodiment opens inwardly.

In addition to a waste outlet 248, for removing solid matter from the until 200 after processing, the unit 200 is also directly coupled to the local sewage system by an outflow system, indicated generally at 300 in Figure 6. The outflow system 300 includes an outflow conduit 302 for waste liquid from the unit 200 to pass down into the sewage system.

A filter outlet 304 is formed in the bottom wall 245 of the third chamber 240, to the left as viewed in Figure 6, directly beneath the vane 246. As matter falls down into the third chamber 240 from the vane 246, liquid present in the matter is able to pass down though the filter 304 into a filter conduit 306. From the filter conduit, the liquid passes to a liquid powered generator 308 including a rotary vane 310. The fall of liquid from the conduit 306 causes the generator 308 to rotate, although rotation of the generator vane 310 can also be controlled by the control 220, which is in communication with the generator 308 via link 312 partially indicated in Figure 6. As the generator 308 rotates, power from the generator 308 is supplied to a UV lamp assembly 314 forming part of the a further conduit 316 for receiving and conveying liquid passing through the generator 308 to a downstream section of the outflow conduit 302, so as to transfer the liquid to the sewage network. The assembly 314 includes a UV bulb 318 for treating liquid passing down through the filter 304.

Under power from the generator 308, radiation emitted by the UV lamp assembly 314 is sufficient to treat the leachate liquid passing down from the third chamber 240 through the filter 304 into the system 300, to sterilise and render harmless the organisms in the liquid, before the liquid is transferred to the local sewage network.

With reference now to the main reaction chamber 240, it can be seen that the rotor 252 is of a different construction to the rotor 52 in Figure 3. The rotor 252 includes a number of rotor blades, which are shaped and arranged to exert a downward pressure on matter present in the chamber 240 under rotation of the rotor 252, so as to consolidate the matter. Also, during rotation, the rotor blades are configured to urge the matter towards the outlet vane 250. The rotation is preferably controlled by the control unit 220, so as to minimise energy consumption within the unit 200. The rotary speed of the rotor 252 can be set to a constant number of revolutions per day or number of days, for example 1 revolution per day. The rotation can also be incremental, for example the rotor

252 can be turned through a set number of degrees at regular intervals, for example 5 degrees after every hour. It can also be seen that the rotor 252 is also in communication with the heated water circuit, via water tank 60, so that heated water is able to circulate round the shaft of the rotor 252, so as to convey heat to the centre of the chamber 240 and also to matter present in the chamber via convection with matter in contact with the rotor 252.

Finally, it should be noted that the unit 200 includes an excess liquid conduit 350 in communication with the waste chamber 248 and extending vertically to ground level. This conduit 350 is configured for communication with an auxiliary pump for removing any excess liquid which may gather in the unit 200 during use and to prevent a back flow of liquid and waste matter back up into the system 224.

Claims

1. A bioreactor for continuous or substantially continuous anaerobic digestion of organic matter, the bioreactor having: an inlet for introducing organic matter into the bioreactor, a main reaction chamber for the organic matter, and at least one anti-chamber arranged between the inlet and main reaction chamber, in which the chambers are arranged so that organic matter can pass from the inlet, through the or each anti-chamber and into the main reaction chamber, and that additional organic matter can be introduced into the bioreactor through the inlet, without substantially affecting the level of oxygen in the main reaction chamber.

2. A bioreactor as claimed in claim 1 , in which the or each anti-chamber is arranged for reducing the level of oxygen in the organic matter as the matter passes to the main reaction chamber.

3. A bioreactor as claimed in claim 1 or 2, in which the bioreactor is arranged for continuous or substantially continuous anaerobic digestion from successive loads of organic matter through the inlet.

4. A bioreactor as claimed in any of claims 1 to 3, in which the bioreactor includes first and second anti-chambers arranged so that organic matter can pass from the first anti-chamber to the second anti-chamber, before passing into the main reaction chamber.

5. A bioreactor as claimed in claim 4, in which the anti-chambers are arranged so that the level of oxygen in the organic matter is successively reduced as the matter passes from the first anti-chamber to the second chamber and into the main reaction chamber.

6. A bioreactor as claimed in claims 4 or 5, in which the first anti-chamber is arranged above the second anti-chamber.

7. A bioreactor as claimed in any of claims 4 to 6, in which the first and second anti-chambers are arranged for passage of matter between the first and second anti-chambers under gravity.

8. A bioreactor as claimed in any of claims 4 to 7, in which the first and second anti-chambers are arranged above the main reaction chamber.

9. A bioreactor as claimed in claims 4 to 8, in which the main reaction chamber is arranged for receiving matter from the first and second anti-chambers under gravity.

10. A bioreactor as claimed in any preceding claim, in which the or each anti- chamber is arranged for passage of organic matter between adjacent chambers under predetermined conditions.

11. A bioreactor as claimed in any of preceding claim, in which the bioreactor includes limiting means for limiting the passage of organic matter between adjacent chambers.

12. A bioreactor as claimed in claim 9, in which the limiting means is configured to permit matter to pass from a first of said chamber under a predetermined mass of matter present above said limiting means.

13. A bioreactor as claimed in any preceding claim, in which a rotary vane is arranged between adjacent chambers.

14. A bioreactor as claimed in claim 13, in which each rotary vane is configured to enable matter to pass between adjacent chambers under a predetermined mass of organic matter present above said rotary vane.

15. A bioreactor as claimed in any preceding claim, in which the inlet includes a hatch, operable between an open position and a sealed closed position.

16. A bioreactor as claimed in any preceding claim, in which the bioreactor includes a solar powered energy store.

17. A bioreactor as claimed in any preceding claim, in which the bioreactor includes means for heating said main reaction chamber.

18. A bioreactor as claimed in any preceding claim, in which the bioreactor includes control means for monitoring local conditions within at least one of said chambers.

19. A bioreactor as claimed in claim 18, in which a closed loop control system is provided to automatically maintain a set process window for anaerobic digestion of waste.

20. A bioreactor as claimed in any preceding claim, in which the bioreactor includes means for promoting optimised conditions for anaerobic digestion to occur within organic matter introduced into the bioreactor.

21. A bioreactor as claimed in any preceding claim, in which the bioreactor includes means for assisting movement of organic matter between the chambers.

22. A bioreactor as claimed in any preceding claim, the bioreactor being solar powered and adapted for operating continuously in the thermophilic temperature range without an auxiliary supply of energy.

23. A bioreactor as claimed in any preceding claim, the bioreactor being adapted for collecting leachate from organic matter in the bioreactor and reintroducing said leachate into organic matter in the bioreactor.

24. A bioreactor as claimed in any preceding claim, in which the bioreactor is in the form of a portable unit.

25. A bioreactor for continuous or substantially continuous anaerobic digestion of substantially solid organic matter, in which the bioreactor is in the form of a non-fixed portable unit.

26. A solar powered bioreactor adapted for operating continuously in the thermophilic temperature range without an auxiliary supply of energy.

27. A solid waste bioreactor adapted for collecting leachate from solid waste in the bioreactor and reintroducing said leachate into solid waste in the bioreactor.

28. A bioreactor substantially as herein described and as illustrated in Figures 1 and 2, Figure 3, Figure 5 or Figure 6.