METHOD AND APPARATUS FOR PREPARATION OF HOUSEHOLD WASTE BEFORE FINAL COMPOSTING

Abstract: A method and an apparatus for preparation of household waste before final composting, wherein the waste is disintegrated and compressed in a treatment shaft by forcing the waste past disintegrating knives with the aid of scissors knives arranged on a driven piston, whereby the disintegrating knives are arranged with a mutual spacing which determines the disintegrating rate and whereby the scissors knives are arranged on the piston so that they fit into said spacings.

Description: Method and apparatus for preparation of household waste before final composting The invention relates to a method of preparing household waste before final composting and an apparatus therefor, especially intended for preparation of biodegradable house¬ hold waste from blocks of flats. Known composting apparatuses do not fulfil the conditions put up when placing them inside or adjacent to dwellings. The handling of the waste does not work well, the working en¬ vironment is not good and breakdowns often occur. Composting experiments are going on in several places and the problems that remain to be solved are among others to provide an automatic apparatus which minimizes the need of manual handling of the waste. It is also important to create a good environment for the biodegradation. A special problem which exists in built-up areas which are to adopt waste sorting in order to make composting of household waste possible is the limited space. If the appara- tus shall be placed in an existing space inside a building it must possible to transport it through a door-opening and it must be possible to erect it and for it to work in said space while at the same time the conditions regarding hygiene and safety are fulfilled. In that case where an apparatus is to be built up in a separate building for serving of several houses, there is still the need of a compact apparatus which is silent and odourless. The object of the present invention is to provide a method of preparing waste for composting which makes it possible to take care of the waste substantially without any odour and to disintegrate it into a form which favours composting, and to provide a waste preparation apparatus for performing the method, adapted to be placed in connection with blocks of flats, and giving a product which without further measures can be transferred to final composting. This is achieved with the method according to the in¬ vention, according to which the waste is disintegrated and compressed in a treating shaft by forcing the waste past disintegrating knives with the aid of scissors knives arranged on a driven piston, said disintegrating knives being arranged with a mutual spacing which determines the dis¬ integration rate and said scissors knives being arranged on the piston such that they fit into said spacings. Further characteristics of the method according to the invention will be evident from claims 2 and 3. The waste preparation apparatus according to the inven¬ tion is intended for preparation of household waste before final composting and is mainly intended to be placed e.g. in connection with a block of flats, and comprises a feeding shaft, a treatment shaft connected to the feed shaft, a transport means connected to the outlet end of the treatment shaft, and a subsequent, aired intermediate storage container for the treated waste, a driven disintegration piston arranged in the working shaft, disintegrating knives, arranged with a mutual spacing over the cross section of the working shaft adjacent to its outlet end, and scissors knives on the side of piston facing the outlet end, in such a way that they can pass into and out of the spacing between the disintegrating knives arranged in the shaft. Further characteristics of the waste preparation appara¬ tus according to the invention are evident from claims 5 - 14. The waste preparation apparatus according to the present invention has a very compact construction, where the handling of the waste takes place in a closed space so nobody will get into contact with it during or after the disintegration and with a minimum of odour. Depending on the residence time in the collecting vessel, i.e. the intermediate storage con- tainer, the degradation takes place therein supported by the continuous supply of air, but the final composting is supposed to take place at another site. Further, the method and apparatus are especially well suited for automatization. The construction according to the invention results in that material will not remain in the disintegration means. In combination with suitably designed disintegration knives a very effective disintegration of the material is achieved and compost bags are not a problem either; on the contrary, by a suitable choice of compost bags the amount of litter normally required can be reduced. This in combination with a closed collecting vessel for the compost material result in a complete system which to a large extent can be automatized and give a very flexible handling of the waste. According to a preferred embodiment of the invention a transport means is air tight connected to the mechanical treatment means and with which the prepared waste is trans¬ ferred to the collecting vessel. According to a development of the apparatus according to the invention the collecting vessel is provided with means for supply of air to the collected prepared waste in order to promote aerobe degradation. Short description of the drawings Further advantages, objects and characteristics of the invention will be evident from the following detailed de¬ scription of embodiments of the invention in connection with the attached drawing, in which Fig. 1 is a schematical side view of a waste preparation apparatus according to the invention, Fig. 2 is a schematical cross-sectional side view of the waste preparation apparatus according to Fig. 1, and Fig. 3 shows a partial cross sectional view taken along the line III-III in Fig. 2. Detailed description of preferred embodiments. The invention will now be described in connection with the waste preparation apparatus schematically shown in the drawing, but of course alterations and modifications can be made without departing from the scope of the invention. The waste preparation apparatus according to the inven¬ tion is especially intended for placement in or adjacent to blocks of flats where the existing space normally is limited and where a minimum of odour and a low noise level are highly required. As will be evident from the following description the waste preparation apparatus according to the invention can be made very compact, so that it only takes up a surface corresponding to a pallet (80 x 120 cm) and can be moved with the aid of a conventional pallet lifter. Further, it works very silent and can be made substantially odourless. Of obvious reasons household waste is normally handled and transported in bags, which are carried to the apparatus and are thrown into it. By using bags made of paper or similar biodegradable material the amount of litter, which is necessary in composting can be reduced. The embodiment of the waste preparation apparatus accor¬ ding to the invention shown in Fig. 1 comprises a base 1, preferably made of concrete, a treatment shaft 2, shown with a dashed line in the Fig., a collecting chute 3, also shown with a dashed line, a transport tube 4 connected to the treatment shaft and a collecting container 5. A piston is working in the treatment shaft 2, the drive of which is contained in the casing 7. In dashed lines at 8 is shown how the complete piston and drive package can be withdrawn for maintenance, repair etc. A control cabinet 9 contains control circuits for the machinery. A cabinet 10 symbolizes hydraulics for the driving of the piston. A feeding chute 11 is connected to the treatment shaft. The feed shaft is closed and has a hopper opening door 12, preferably of "banking box type". Further a litter feed pocket 13 is arranged on the base in order to make possible an optimization of the compo¬ sition of the prepared waste before the final composting. In Fig. 2 a cross sectional side view of the waste preparation apparatus according to Fig. 1 is shown, with some parts removed in order to simplify the view. The bottom end of the feed shaft 11 opens into the treatment shaft 2, wherein a driven piston 14 runs, preferably a hydraulic piston. On the side facing frontwards the piston carries scissors knives 15, which preferably are bevelled, as shown in the drawing, being shorter at the top, which will be discussed further below. In a retracted position the piston leaves the treatment shaft empty underneath the feed shaft and waste thrown into the door 12 will fall down in front of the piston. Adjacent to the outlet end 16 of the treatment shaft stationary disintegrating knives 17 are arranged. Advantage¬ ously these are arranged in a vertical position and with mutual spacings 18, see Fig. 3. The waste is forced past the disintegrating knives and the disintegrated waste then passes further on to the transport tube 4 in which a screw, not shown, operates in order to transport the disintegrated waste to the collecting container 5. Advantageously a rotating means, not shown, is arranged underneath the intermediate tube 19 which connects the upper end of the transport tube with the collecting container, in order to spread out the waste evenly in the container. In the transport tube 4 and in the collecting container 5 air is supplied in order to prevent anaerobic degradation, which arrangement however is omitted from the drawing of clarity reasons. Moreover the apparatus is preferably connected to fans in order to create a sub-pressure in the apparatus. A fan can for example be controlled by the door opening movement or be driven continuously. The apparatus can also be driven on the existing ventilation. The essential thing in this context is that odour must not escape upon opening of the hopper opening door. In association with the litter container 13 a dosing piston 20 as well as a controlled piston-cylinder arrangement 21 are arranged. The amount of litter is varied depending on the composition of the waste. An operator controls this through control circuits. The composition of household waste often varies with the time of the year, which is manageable by a skilled operator. The piston 14 is arranged and controlled to move back and forth relative to the disintegrating knives 17. These are ar¬ ranged standing vertically with a mutual spacing, which determines the size of the disintegrated waste. The design of the disintegrating knives as well as the design of the piston will be described more in detail in connection with Fig. 3. A certain amount of compressing of the waste will take place at the passage past the disintegrating knives as well as during the transfer to and transport in the transport tube. Because of this compressing moisture is squeezed out of the waste. By arranging the substantially horizontal shaft somewhat sloping forwards accumulation of moisture in the back parts of the shaft, where it could cause odour and damages, is avoided. The transport screw is preferably controlled in such a way that it operates when waste is thrown into the apparatus to be disintegrated and a suitable length of time thereafter. A suitable time delay is e.g. about 10 seconds. Despite this time delay the residence time of the waste in the transport tube can become long because of the intermittent feeding of the waste through the tube, e.g. at low load when a long time passes between the events of someone throwing waste into the apparatus. The degradation of the waste is a continuous process and in order to avoid anaerobic degradation it is essential that oxygen is supplied. Suitably, this is done at several locations along the transport tube, which however is not shown in the drawing. The invention is not limited to the above described method of transportation, but instead this can also take place with e.g. an intermittently working piston which forces the waste through the transport tube. When the waste leaves the tube and falls down into the collecting container 5 it is in a compressed state. In order to disintegrate the waste and at the same time avoid that it is disposed in a pile in the container a motorized rotor or similar means is advantageously arranged adjacent to the mouth of the tube which spreads out the waste in the collect- ing container so that it falls in an airy well dispersed state therein. This is only an expedient measure and is not shown in the drawing. Moreover, air or any other oxygen carrier is supplied at the bottom of the container, whereby the composting/biodegradation continues also during the residence in the container, when awaiting transport to the place of final composting. A certain pre-composting thus takes place in the collect¬ ing container 5, but since it is impractical to arrange containers sufficiently large to allow final composting of all household waste from blocks of flats adjacent thereto, it is advantageous to use containers of a manageable size, which then on a regular basis are emptied in order to perform final composting at another site. In the embodiment shown in Fig. 2 the horizontal shaft 9 has a rectangular cross section and consists of an inner plate casing 22 moulded into the concrete base 1. Hereby possible leakage in welding seams are avoided while at the same time the construction will be very stable and may withstand the high loads appearing when the apparatus operates. A suitable compressive force is estimated to be about 10 tons, which however also is dependent of the design of the knives. The piston 14 is substantially box-shaped and thus obtains a good guidance in the shaft. The scissors knives 15 are suitably bevelled so that the edge slopes backwards/- upwards, seen in the direction of movement. Hereby a sub¬ stantially enhanced cutting effect is obtained, and even plate, which by mistake has been mixed with the waste will be effectively disintegrated. Moreover, displaced waste will end up on top of the piston and thereby contributes to the lubrication of the system. Underneath the treatment shaft 2 a collecting chute 3 runs with a screw 23 working therein for removal of waste material which unavoidably falls down during the work of the piston. In the embodiment shown the screw 23 is driven by an electric motor 24. It is essential that no waste remains in the apparatus in view of the problems of odour which would occur then. This screw is also driven during a predetermined length of time after that the piston has stopped, of the same reasons that allow the transport screw to continue to operate for a certain length of time after that the piston has stopped. In Fig. 3 a cross section taken along the line III-III in Fig. 2 is shown. The piston 14 is driven by a hydraulic cylinder 25 arranged in the casing 7. The scissors knives at the front end of the piston are arranged with a mutual spacing and in the embodiment shown the knife-edges lie on a curve with the longest knives outermost. It is also useful to arrange the knife edges on a S-shaped curve. This means that a substantially enhanced cutting effect is obtained in addition to the one achieved with the bevelled edges. The spacings between the scissors knives are so adapted that the stationary disintegrating knives at the outlet end of the treatment shaft fit into the spacings, when the piston is at its forward end-position. The piston 14 is advantageously controlled so that it performs several strokes for each "set" of waste. The piston is preferably controlled by a pressure sensor and turns when a preset pressure is achieved. A suitable method is to control the piston to perform 5 strokes with a predetermined compression force, e.g. 10 tons, for each batch. If the waste then has not passed by the disintegrating knives, the piston is controlled so that it e.g. performs another 15 strokes. If the waste still has not been forced past the disintegrating knives, the driving of the piston is automatically stopped and cleaning is called for in any suitable way. If these 20 strokes in total is not sufficient it is likely that some forbidden/non-breakable waste has been placed in the waste preparation apparatus. Examples of this can be a diaper in combination with a plastic bag, heavy duty tools etc. According to an advantageous embodiment the transport screw in the transport tube 4 and the screw working in the collecting chute are driven for another 10 seconds when the piston has been stopped. Hereby is achieved that the machinery is well emptied and the risk for odour is further reduced. Between the scissors knives cleaning means at 26 are preferably arranged, e.g. in the form of freely movable grid elements. During the forward movement of the piston the cleaning means are dragged along in the movement. During the retraction movement the movement of the cleaning means is braked or hindered before the piston arrives at its retracted end position. This can be achieved by friction, arranging of stop notches, etc. When the cleaning means are braked or stopped they clean the spacings between the scissors knives 15 from e.g. cartoon and plastic, which have a tendency of getting stuck between the knives.

Claims: Claims 1. A method of preparation of household waste before final composting, wherein the waste is disintegrated and compressed in a treatment shaft by forcing the waste past disintegrating knives with the aid of scissors knives arranged on a driven piston, whereby the disintegrating knives are arranged with a mutual spacing which determines the disintegrating rate and whereby the scissors knives are arranged on the piston so that they fit into said spacings. 2. A method according to claim 1, characterized in that the piston is made to perform a predetermined number of strokes at a predetermined compression force in order to force the waste through the disintegrating knives with the aid of the scissors knives and whereby the driving of the piston is so controlled that if the waste to be treated has not passed the disintegrating knives after said number of strokes the driving of the piston is stopped. 3. A method according to claim 2, characterized in that litter is dosed in an amount adapted to the actual composi- tion of the waste upon activation of the piston. 4. A waste preparation apparatus for preparation of household waste for composting intended to be placed e.g. in connection with blocks of flats, containing a feed shaft, a treatment shaft connected thereto, a transport means connected to an outlet end of the treatment shaft and a subsequent collecting container with air supply means for the prepared waste, a driven piston arranged in the treatment shaft, disintegrating knives, arranged with mutual spacings over the cross section of the treatment shaft adjacent to its outlet and, and scissors knives on the side of the piston facing the outlet end so arranged that they can pass into and out of the spacings between the disintegrating knives arranged in the shaft. 5. A waste preparation apparatus according to claim 4, characterized in that the scissors knives are designed with different lengths. 6. A waste preparation apparatus according to claim 4, characterized in that the scissors knives are longest in the middle part and in that their lengths diminishes towards the edges . 7. A waste preparation apparatus according to claim 5, characterized in that the lengths of the scissors knives are so adapted that their points lie on an S-shaped curve. 8. A waste preparation apparatus according to any of claims 4 - 7, characterized in that the scissors knives are bevelled. 9. A waste preparation apparatus according to any of claims 4 - 7, characterized by cleaning means arranged to clean the spacings between the scissors knives. 10. A waste preparation apparatus according to claim 9, characterized in that the cleaning means are movably arranged between the scissors knives so that they with the aid of e.g. stopping means, friction, at the retraction of the piston are arranged to stop before the piston reaches a retracted end position. 11. A waste preparation apparatus according to any of claims 4 - 10, characterized by a compressing chamber for waste disintegrated by the disintegrating knives arranged after the disintegrating knives. 12. A waste preparation apparatus according to claim 4, characterized in that the transport means is comprised of a transport tube having air supply means as well as a transport screw rotating in the tube. 13. A waste preparation apparatus according to claim 4, characterized in that the collecting container comprises means for air supply in the prepared waste as well as dis¬ integrating and spreading means adjacent to the opening of the transport tube in the collecting chamber. 14. A waste preparation apparatus according to any of claims 4 - 13, characterized in that a transport screw working in a collecting chute is arranged underneath the treatment shaft for feeding material that have fallen down out to the transport means.

Inventors: LINDKVIST LISS-OLA, LINDKVIST, LISS-OLA
Applicants: LINDKVIST LISS OLA, LINDKVIST, LISS-OLA
Application year: 1996
Main classification: C05F17
IPC codes: B02C18, C05F9, C05F17