WO2000012448A1

WO2000012448A1 - Method and device for composting

Info

Publication number: WO2000012448A1
Application number: PCT/SE1999/001430
Authority: WO
Inventors: Lars Adolfsson; Jan Wallgren
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-08-28
Filing date: 1999-08-24
Publication date: 2000-03-09
Anticipated expiration: 2001-02-28
Also published as: AU5890099A; SE9802885D0; SE9802885L

Abstract

The present invention relates to a method for composting, the material undergoing composting being fed to a rotatable container (1), said material, preferably to a certain extent, constituting organic waste, that oxygen is fed to the material inside the container (1) by blowing air into the container (1), that exhaust air is discharged from the container (1), that the temperature of the material undergoing composting is supervised, that feeding of the material into the container (1) takes place in connection to one end of the container (1), and that discharge of the finally composted material takes place in connection to said one end. The invention also relates to a device for composting. The method according to the invention being characterized in that the exhaust air is dehumidified, and that the condensating water, produced by dehumidification, at least to a certain part is returned to the container (1). The device according to the present invention being characterized in that the air discharging means (17) comprises a dehumidifier (22) and means (23) for returning at least a portion of the condensating water to the interior of the container (1), said condensating water being extracted from the exhaust air.

Description

METHOD AND DEVICE FOR COMPOSTING

Technical Field of the Invention

The present invention relates to a method for composting where oxygen is fed to the material that is undergoing composting, said material preferably being organic waste, and that the temperature of the material undergoing composting is supervised. The invention also relates to a device for composting.

Prior Art

From WO 97/12031 is previously known a method and a device for composting where, in order to avoid an embarrassing smell, the air, that is fed to the material undergoing composting, is circulating in a closed system. The device according to WO 97/12031 comprises an oblong, rotatable, generally cylindrical vessel where waste is fed at one end while the composted material is discharged from the vessel at the opposite end. According to an embodiment of the device according to WO 97/12031 the air is fed via a manifold, extending along the centre axis of the cylinder, and a number of pipes projecting radially from said manifold. According to an alternative embodiment the air is fed by a manifold system arranged externally of the vessel, the manifold system being in contact with the interior of the vessel by a number of openings in the envelope surface of the vessel . The method and device according to WO 97/12031 comprise also means for supervising and controlling the conditions inside the composting vessel, e.g. the temperature, the humidity, the oxygen content in the air and the carbon dioxide content in the air.

Objects and Features of the Invention

A primary object of the present invention is to present a method and a device for composting where it is guaranteed that a complete mixing of the material undergoing composting is effected.

A further object of the invention is that the feeding of oxygen is effected in such a way that all parts of the material is subjected to composting by having the aerobic digestion propagating in a uniform way in all parts of the material undergoing composting.

Still a further object of the invention is that sanitation of the material undergoing composting is guaranteed in a satisfying way.

At least the primary object of the present invention is realised by means of a method and a device that has been allotted the features defined in the appending independent claims. Preferred embodiments of the invention are defined in the independent claims.

Brief Description of the Drawings

Below an embodiment of the present invention will be described, reference being made to the accompanying drawing, where : Figure 1 shows a schematic longitudinal section through the device according to the present invention; Figure 2 shows a section along A-A in Figure 1; and Figure 3 shows a perspective view of a mixing and screw feeding device.

Detailed Description of a Preferred Embodiment of the Invention The device according to the present invention, shown in figures 1 and 2, comprises a container 1 that is symmetrical of rotation, said container 1 being pear-shaped in the shown embodiment. Said container 1 is rotatably supported on a frame 3 in such a way that the longitudinal axis 5 of rotation of the container 1 is somewhat inclined relative to the foundation that the frame 3 rests upon, said foundation normally being horizontal. The container 1 has an axial extension in parallel with its axis 5 of rotation.

The container 1 is supported, on one hand by the frame 3, via a roll stand 7, in an intermediate portion of the container 1 and on the other hand by a coupling 9, at an end portion of the container 1, said coupling 9 being connected to a change gear mechanism 10 that is driven by a power source in the shape of a motor 11. At its end facing away from the change gear mechanism 9 the container 1 is provided with an opening 12 , through which both feeding of waste and decharge of material that has been composted takes place. Preferably, the opening 12 is provided with doors or a lid (not shown) and by such an arrangement said opening 12 may be closed when not used.

A mixing and screw feeding device 13 is provided inside the container 1, said mixing and screw feeding device 13 extending in principle along the entire axial extension of the container 1. The mixing and screw feeding device 13 is attached to the inner wall of the container 1, e.g. by welding, and consequently the mixing and screw feeding device 13, see figure 3, has an external contour that likewise is pear-shaped. A pipe 14 for the supply of air is provided inside the container 1, said pipe 14 extending axially relative to the container 1 and the centre axis of the pipe 14 coincides with the axis 5 of rotation of the container 1. The pipe 14 has one end located in connection with the opening 12 and in accordance with the shown embodiment the pipe 14 projects somewhat beyond the opening 12. A fan 15 is provided at said end of the pipe 14, said fan 15 pressing air into the pipe 14 in direction towards the interior of the container 1. In order to vary the air flow the fan 15 is preferably controlled by a rheostat . The end of the pipe 14 that faces away from the fan 15 is attached to the internal end of the container 1 that faces away from the opening 12. Along a limited portion of the pipe 14, in connection with the end of the pipe 14 that faces away from the fan 15, said pipe 14 being provided with perforations 16, through which the air that is pressed into the pipe 14 may flow out in the interior of the container 1, more precisely into the material, not shown, that is present in the container 1 and undergoing composting. Preferably, said perforations 16 are located along a portion that constitutes about 30% of the total length of the pipe 14.

The container 1 is also provided with an exhaust air conduit 17, through which air is discharged from the container 1. A filter 18 is provided in the exhaust air conduit 17, the exhaust air passing through said filter 18 when being discharged from the container 1. A dehumidifier 22 is also provided in the exhaust air conduit 17 and the condensation water that is extracted from the exhaust air is, at least partly, returned to the composting process via a conduit 23 that extends between the dehumidifier 22 and the pipe 14. The exhaust air conduit 17 emerges into the free air.

As is indicated in figure 1 the container 1 is provided with two thermometers 19, 20 that measure the temperature of the material undergoing composting in the container 1. Said thermometers may be connected to an electronic control unit, from which the air supply is regulated as well as the rotation of the container as regards frequency and durability.

The Function of the Device According to the Invention The material that is fed to the container 1 via the opening 12 constitutes preferably organic waste, especially remains of food and domestic waste. The feeding of waste and the removal of composted material is symbolised by the double arrow 21. For instance litter, preferably straw, shavings, pellets or the like, is fed to the container 1 in order to achieve the desired dry matter content of the waste and also to feed carbon to said waste. In exemplifying and non- restricting purpose it may be mentioned that when about 230 kg waste is fed also about 80 litre of straw or 50 litre of pellets is fed.

Waste and carbon-containing material are fed in batches until the desired filling extent of the container 1 has been achieved, said filling period may for instance constitute three weeks (depends on the amount of waste and the volume of the container) . During the filling period a certain rotation of the container 1 takes place as well as supply of oxygen to the interior of the container 1 by pressing air into the pipe 14 by means of the fan 15. The rotation of the container 1 also imparts a rotation of the mixing and screw feeding device 13 and thereby a proper mixing of the waste and the carbon- containing material is effected. Inside the container 1 the structural design of the mixing and screw feeding device 13 guarantees on one hand that the supplied waste is fed to the area at the end of the container 1 that faces away from the opening 12 and on the other hand that all material undergoing composting in the container 1 is mixed to a uniform mixture, i.e. no portion of the material undergoing composting remains un-mixed. The rotation of the container may take place every 20^th minute and last for a period of 3-4 minutes.

The air supply brings about that the temperature of the degradation process is kept within a prescribed interval, the supplied air lowering the temperature of the degradation process. A positive pressure is created inside the container 1 when air is supplied, through the pipe 14 and the perforations 16, to the material undergoing composting inside the container 1. This means that air must be discharged from the interior of the container 1 in order to supply fresh air through the pipe 14. The discharge of air is effected through the exhaust air conduit 17, said exhaust air on one hand being filtered to avoid embarrassing smell in the environment and on the other hand being dehumidified, which results in the creation of condensating water. At least a part of said condensating water is returned to the container 1 to take part in the composting process. By this arrangement a further possibility is given to control the dry matter content of the material undergoing composting apart from the possibility that already is present by feeding of carbon-containing material. When the filling period approaches its end it is desirable to perform so-called sanitation of the material undergoing composting. Said measure aims at killing bacteria/virus, if any, that carry for instance salmonella, ebola and swine fever. The temperature in the container is allowed to rise, e.g. to 70°C, and said temperature is allowed to stay for a certain time, for instance during at least one hour. The lower sanitation temperature the longer time of treatment in order to effect sanitation.

When the filling period is terminated the composting in the container 1 is allowed to proceed during a certain time of treatment and during said period no further material, i.e. waste and carbon containing material, is fed to the container. The treatment period may for instance be equal long as the filling period, i.e. three weeks. A benefit with such an arrangement is that if two alternating containers are used, one is in the filling period while the other is in the treatment period, said periods changing continuously between the containers .

Both during the filling period and the treatment period a mixing of the material undergoing composting is effected as soon as the container rotates . As pointed out above said mixing is extremely effective when using the mixing and screw feeding device 13 according to the shown embodiment, i.e. the material undergoing composting is extremely uniform. As regards frequency and durability of the rotation of the container 1 reference is made to what has been said above during the filling period.

During the filling period and the treatment period a supply of oxygen is effected via the fan 15, the conduit 14 and the perforations 16. However, the supply of oxygen decreases continuously during the treatment period. The supply of oxygen to only a limited length of the pipe 14, more precisely to the portion of the pipe 14 that is located furthest away from the opening 12, brings about that air is supplied in the portion of the container 1 where the material undergoing composting is assembled, i.e. a highly uniform supply of air to the material undergoing composting is effected. The supply of air is important to control the composting process during the filling period, but said supply of air is even more important during the treatment period to control said composting process. As pointed out above the supply of air lowers the temperature of the composting process in the container 1 and it is important that said temperature does not become too high since in such a case the composting process declines. A temperature level above about 60°C normally prolongs the process time, i.e. the temperature in the container 1 should normally not exceed 60°C. However, in connection with the above described sanitation the temperature may exceed 60°C. It is suitable that the rotation is controlled in such a way that the container always stops in the same position after a cycle of rotation. By such an arrangement the thermometers 19, 20 will always register the temperature in a corresponding point in the material undergoing composting. The dehumidification described above of the exhaust air is continued also during the actual treatment period.

When the treatment period is terminated the composted material is discharged through the opening 12, this being effected in the embodiment described above by rotating the container 1 in opposite direction compared to the direction during the filling period. Thereby, the composted material will be discharged through the opening 12 where it is taken care of in a suitable way, for instance packed in order to be used as a soil improvement substance. The discharge of the composted material is effected without having to change the inclination of the container 1, see figure 1.

In this connection it should also be pointed out that it is extremely beneficial to be able to provide feeding of waste into the container 1, mixing of the material undergoing composting and discharging of the composted material by means of the same unit, i.e. the mixing and screw feeding device 13.

Feasible Modifications of the Invention According to the above described embodiment the container is pear-shaped and provided with a mixing and screw feeding device. Within the invention it is of course feasible to imagine other designs of the container 1 with peripheral equipment that brings about simple feeding and discharge as well as proper mixture of the material undergoing composting. According to the above described embodiment the pipe 14 of the air supply extends in principle up to the interior end of the container 1 that is opposite to the opening 12. However, it is feasible, within the scope of the invention, to imagine that the pipe 14 of the air supply terminates at a distance from said interior end. In such a case it is possible that the perforations 16 of the pipe 14 are omitted.

It is also feasible, within the scope of the invention, that the container 1 is provided with means for measuring the humidity inside the container 1. Such a measuring means may likewise be connected to an electronic control unit.

According to the above described embodiment the container 1 is equipped with two thermometers. Within the scope of the invention it is feasible to imagine that the container is equipped with several thermometers in order to supervise the temperature in different parts of the material undergoing composting.

Claims

1. Method for composting, the material undergoing composting being fed to a rotatable container (1), said material, to a certain extent, preferably constituting organic waste, that oxygen is fed to the material inside the container (1) by blowing air into the container (1) , that exhaust air is discharged from the container (1) , that the temperature of the material undergoing composting is supervised, that feeding of the material into the container (1) takes place in connection to one end of the container (1) , and that discharge of the composted material takes place in connection to said one end, c h a r a c t e r i z e d in that the exhaust air is dehumidified, and that the condensating water, produced by dehumidification, at least to a certain part is returned to the container (1) .

2. Method according to claim 1, c h a r a c t e r i z e d in that during the end phase of the period when further material is fed to the container (1) , the temperature of the material undergoing composting is raised.

3. Device for composting a material, preferably to a certain extent constituting organic waste, said device comprising a rotatable container (1) , means for feeding oxygen, in the shape of air, to the interior of the container (1) , means (17) for discharging exhaust air from the interior of the container (1), means (19, 20) for measuring the temperature of the material undergoing composting in the container (1) , said container (1) having an opening (12) , through which on one hand the material undergoing composting is fed and on the other hand the finally composted material is discharged, c h a r a c t e r i z e d in that the air discharging means (17) comprises a dehumidifier (22) and means (23) for returning at least a portion of the condensating water to the interior of the container (1) , said condensating water being extracted from the exhaust air.

4. Device according to claim 3, c h a r a c t e r i z e d in that the means for returning the condensating water constitutes a conduit (23) that extends between the dehumidifier (22) and a pipe (14) for a supply of air to the interior of the container (1) .

5. Device according to claim 3 or 4 , c h a r a c t e r i z e d in that the air supply means (17) comprises a filter (18) .

6. Device according to any of claims 3-5, c h a r a c t e r i z e d in that the container (1) has a mixing and screw feeding device (13) that is attached to the inner side of the container (1) , and that said mixing and screw feeding device (13) extends along the entire axial extension of the container (1) .

7. Device according to any of claims 3-6, c h a r a c t e r i z e d in that the supply of air is effected via a pipe (14) that runs parallel to the axis (5) of rotation of the container, and that an area of said pipe (14) has perforations (16) for said supply of air, said area being located in connection to the end of the container that faces from the opening (12) .

8. Device according to any of claims 3-6, c h a r a c t e r i z e d in that the supply of air is effected via a pipe that runs parallel to the axis (5) of rotation of the container, and that said pipe terminates at a certain distance from the interior end of the container (1) that faces away from the opening (12) .

9. Device according to any of claims 3-8, c h a r a c t e r i z e d in that the axis (5) of rotation of the container (1) is inclined relative to the horizontal plane .

10. Device according to any of claims 3-9, c h a r a c t e r i z e d in that the container (1) is pear- shaped.