CA2248588A1

CA2248588A1 - Method and facility for the processing of organic waste, and biogas plant for use in such a facility

Info

Publication number: CA2248588A1
Application number: CA002248588A
Authority: CA
Inventors: Rolf-Rudiger Jessen; Petra Rabe
Original assignee: Individual
Current assignee: Biophil Gesellschaft fur Biotechnologie Energie- und Umwelttechnik GmbH GmbH; MULLER and JESSEN GmbH
Priority date: 1996-03-15
Filing date: 1997-03-06
Publication date: 1997-09-25
Also published as: WO1997034851A1; JP2000506828A; ID17696A; EP0886631A1; IL126005A0; KR20000064595A

Abstract

The invention concerns a facility for the processing of organic waste by a combination of fermentation and composting, the installation being characterized in that it includes a biogas plant (1) for the fermentation of organic waste of simple composition, the biogas plant being connected by a pipe line (2) to a tank (3) containing the fermentation substrate and the tank (3) being connected by a pipe line (4) to a clamp-type composting plant for waste of complex composition (5) and/or to an enclosed composting plant for any contaminated organic waste of complex composition and for waste from a composting reactor (6). The invention also concerns a method of processing waste in such a facility, and a biogas plant (1) for use in the facility.

Description

CA 02248~88 1998-09-09 _ .

FILE, P!~ TI IIS AMENDED
ANSLATION

A Process and a Plant for Organic Waste Utilization, and a New Biogas Plant Specification The invention relates to a plant for the simultane-ous utilization of poorly structured and highly structured organic waste, which is capable of processing the most various waste charges and can be adjusted flexibly to the arising amounts and types of waste materials.

The invention is also directed to an appropriate utilization process and to a new biogas plant for a two-step fermentation of organic waste materials, which plant is either a component of the above plant or may also be em-ployed independently of the above-mentioned plant.

Organic waste materials arise in various forms and compositions in communities and industry and can easily be collected separately:
- organic components from domestic garbage cans;
- green cuts and other debris from trees (twigs from horticulture, parks and road planting) - uncontaminated waste timber such as construction wall planks and commercial pallets;
- waste timber from constructional demolitions as well as from aged track systems, contaminated with impreg-nating agents (e.g., tar oils and formaldehyde) and colors;
- soil contaminated with tar oils, mineral oil hydro-carbons or other organic substances;

CA 02248~88 1998-09-09 - leftovers, waste food and waste vegetables from canteen kitchens, slaughter-houses, dairies, central mar-kets and factories producing and processing foods as well as from agriculture;
- clarification sludge;
- fats, organic solvents and other organic remainders from chemistry, pharmacy and cosmetics;
- animals bodies which must be utilized.

The disposal of biologically decomposable waste ma-terials on dumps gives rise to hazards and adverse environ-mental effects and is therefore more and more restricted and/or prevented by laws and regulations, which is why they find increasing biological utilization.

The biological- methods are advantageous in that they come quite close to the decomposition processes occur-ring in nature and thus, cause the smallest changes in the material balance in nature. Lignins and humic substances are retained. The products resulting from the biological processes may be re-fed into the food cycle in various forms. Biological processes involve a lower decomposition rate than thermal processes and therefore, a larger storage or reactor volume is required in order to accomplish them.
On the other hand, the technological input is substantially lower in general, making the processing costs significantly lower than those of thermal processes.

The biological waste utilization employs two basic biotechnological operations having their specific effects and a preferred field of application:
- composting - anaerobic biomethanization (fermentation).

Above all, composting appears to be the choice when converting solid organic waste materials to humus-contain-ing soil improvers. Predominantly, composting allows decom-CA 02248~88 1998-09-09 -position of highly structured materials such as grass, wood or tree cuts which are difficult to decompose. The rotting process proceeds very slowly. With insufficient ventilation or excessive moisture, the process undergoes a complete change and the desired humus formation no longer takes place. Unpleasant odors arise. Therefore, composting re-quires considerable expense in mixing and/or compression energy for ventilation. On the other hand, the spontaneous heating of the compost in the first rotting phase results in a hygienization of the waste. A huge amount of waste heat arises which can hardly be utilized. Compost ventila-tion results in a loss of mass, particularly caused by evaporation of water but also by conversion of organic mat-ter to CO2 and water.

Composts are used for soil improvement in agricul-ture, in horticulture, for soil sanitation, recultivation of soils, and for dump covering.

The anaerobic biogas process (fermentation) is par-ticularly suitable for easily decomposable, moist waste low in structure. When using said process, the best possible utilization of the organic substance is achieved in total, which predominantly is converted to methane and only to a minor extent to carbon dioxide. Thus, DE-A1-44 46 661 de-scribes a process and a plant for anaerobic processing of waste food.

Biogas provides a valuable regenerative energy car-rier which is comparable to natural gas and suitable for the production of electric energy in a block-type thermal power plant.

Likewise, processes for biological waste utiliza-tion are known wherein composting and fermentation are com-bined. In these processes, the production of biogas is fol-lowed by composting the solid matter (e.g., HGG process, _ CA 02248~88 1998-09-09 _ _ LINDE KCA process), or composting is effected prior to and after the production of biogas (3A process) (cf., ~Arbeitskreis fur die Nutzbarmachung von Siedlungsabfallen e.V.", Volume 29, October 1994, p. 61-77).

However, these processes and plants are disadvanta-geous in that they cannot be adjusted to the various amounts of waste and varying waste charges because compost-ing and biogas production cannot be operated independently from each other and waste materials arise which must be subjected to further treatment or disposal.

Another drawback of the well-known two- or three-step processes which involve both composting and anaerobic treatment is that part of the material in the first stage is not subjected to optimum treatment:

1. If the first stage consists of an anaerobic bio-methanization, those components which are difficult to de-compose and highly structured pass this stage without a substantial decomposition effect; they require additional reactor volume, thereby making the treatment more costly.
On the other hand, they cause additional difficulties in operating the process: formation of surface mats or settling material, obstruction of complete mixing and homo-geneous conditions regarding temperature and concentration within the anaerobic reactor. Accordingly, more expensive reactor constructions, an increased input in energy and higher operating costs are required for expensive purifica-tion cycles.

2. If the first stage involves composting (aerobic), a substantial part of the easily decomposable, poorly struc-tured organic matter is decomposed to carbon dioxide and water and therefore is no longer available for the anaero-bic formation of biogas, thereby making the energetic utilization less efficient. Furthermore, a strictly aerobic CA 02248~88 1998-09-09 first stage involves a risk in that fatty acids formed at the end of the aerobic process where lack of oxygen is steadily increasing, have an unfavorable composition for methanization, e.g., an excessively high ratio of lactic acid and propionic acid which impair the subsequent metha-nization and sometimes give rise to interferences of the anaerobic process which may be as serious as a total break-down. As a consequence, there are considerable problems re-garding odor, and the amounts of biogas and its quality are reduced.

Moreover, in the first stage, a~mi~'ng materials unsuitable for the respective biological process represents a quasi-"dilution" or "contamination". Thus, having this configuration, it is not possible to employ intensively working high-performance bioreactors in the first stage.

Therefore, it was the object of the invention to provide a plant for organic waste utilization, which allows optimum and efficient processing of waste charges to be treated differently, such as leftovers, waste food and waste vegetables, e.g., from canteen kitchens, slaughter-houses, dairies, agricultural enterprises and food-produc-ing companies, fats, organic solvents and other organic re-mainders from chemistry, pharmacy and cosmetics, animal bodies to be utilized, organic components from domestic biological trash, green cuts and debris from trees, uncon-taminated and contaminated waste timber and contaminated soil in biological high-performance reactors to yield biogas, compost and liquid fertilizer. The plant should be flexibly adjustable to the amounts and charges of waste and transportable, if desired. The employed high-performance reactors should be constructed as simply as possible.

The object of the invention is attained using a plant in accordance with claims 1 through 7, wherein the waste flow for composting and biogas production is con-CA 02248~88 1998-09-09 ducted in parallel so that biogas production and composting can be employed in combination as well as independently from each other, thus ensuring efficient utilization of en-ergy and waste. A precondition for the plant of the inven-tion and the pertaining process to work properly is that the biogas plant 1 utilizes waste which is easily perish-able and nearly 100 percent decomposable. As a result, water containing mineral substances is produced, which is almost free of solid matter. This fermentation substrate is collected in tank 3.

Waste containing components that are highly struc-tured and thus, difficult to decompose is fed into the com-posting units 5 and 6 which are supplied with additional nutrients by the outflow of the biogas plant from tank 3 in order to accelerate composting.

Following appropriate processing, such as optional shredding and extruding, highly structured organic waste materials, e.g., cardboard, wood and green cuts, which do not cause problems in composting, may easily be processed in a usual stack composting unit 5 to yield quality com-post. Depending on the nitrogen content of the material to be composted, which may vary, e.g., as a function of green cuts, more or less fermentation residual material from tank 3 may be supplied as nutrient source and composting accelerator via pipelines 4 and 4a.

Following appropriate pretreatment such as optional shredding and extruding, problematic materials such as con-taminated waste wood and soil, odor-loaded waste or waste exceedingly difficult to decompose, as well as highly structured waste from domestic biological trash are decon-taminated and composted in a single processing step in a closed, ventilated composting reactor 6, optionally with addition of specifically breeded, pollutant-degrading micro-organisms and fermentation residual material from CA 02248~88 1998-09-09 tank 3. Here, the more expensive composting reactor 6 is necessary in order to create uniform conditions such as moisture, ventilation, optimum temperature throughout the material, which are required for safe degradation of pol-lutants, and to ensure controlled biotechnological process operation at high decomposition rates.

Alternatively, it is also possible to use the com-posting reactor 6 for composting "clean", highly structured waste in those cases where, for instance, the plant may take just a small area due to lack of space or must be housed due to noise pollution. In this case, the composting reactor 6 is supplied with non-contaminated wood via feed line 14, with cardboard via feed line 27, and with green cuts via feed line 28.

Following homogenization in a homogenizer 16, eas-ily decomposable waste and clarification sludge are fer-mented in the biogas plant 1. The biogas plant may be of single- or multistage design, i.e., may have an upstream hydrolysis in addition to the fermentation. The biogas plant preferably includes at least one standard hydrolysis reactor and one or two biogas reactors. Also, one or more hygienization reactors or bioreactors or thermal or chemi-cal reactors where special substances such as bones, hair or feathers are pre-decomposed, may be provided upstream the hydrolysis reactor. A plant known from prior art may be used as biogas plant. However, it is particularly preferred to use the biogas plant in accordance with the present in-vention, which is described below.

The biogas formed may be transformed into electric energy and thermal energy in a block-type thermal power plant. Following an appropriate gas purification step, it may also be used directly for combustion in heating units or to drive machines or vehicles having a gas motor. Ac-cording to the requirements, the mineral-containing water CA 02248~88 1998-09-09 from tank 3 is partly fed into the composting units 5 and/or 6 or is used as liquid fertilizer in agriculture or horticulture.

Figure 1 illustrates a plant for the utilization of organic waste, which is preferred according to the inven-tion. The single plant components such as homogenizer, shredder and extruder are known from prior art and commer-cially available.

The invention is also directed to a process for the utilization of organic waste using the above-described plant in accordance with the process claims 8 through 16.
It is apparent that, according to the invention, not only biogas, liquid fertilizer and quality compost are formed but also, a plant substrate may be produced in a processing step following composting. To this end, the compost ob-tained in the composting units 5 and/or 6 is mixed in the mixer 24 with swellable organic polymers and optionally ma-terials containing loam or clay to yield a complete plant substrate. Optionally, shredded and extruded wood from the extruder 19 may be added. Preferably, crosslinked acrylic amide/acrylic acid polymerizates are added as polymers. In a particularly preferred embodiment, the plant substrate is mixed in such fashion that it consists of from 30 to 85~ by volume of cellulose- and/or lignin-containing porous fiber, from 3.5 to 30~ by volume of polymers in a pre-swelled state, from 12 to 40~ by volume of compost, and from 3 to 20~ by volume of clay. Optionally, fertilizer may already be added. This substrate may then be used in agriculture or horticulture as a water-storing substrate, especially for plantations in soils low in water.

Furthermore, the invention is directed to a new biogas plant in accordance with claim 17, by means of which a wet fermentation of waste food may be carried out in an efficient and stable manner. In addition, by using this CA 02248~88 1998-09-09 . _ ,. .

plant, not only waste food but any low-structured waste ma-terial having a content of organic dry substance of up to 25~, which also includes animal bodies, may be fermented.

Surprisingly, the fermentation process was found to reach remarkable process stability in the hydrolysis and pre-acidification step when the hydrolysis reactor (1.7) is ventilated continuously with pressurized air through the surface of the homogenized material or by devices in the interior of the reactor, i.e., the first step of the fer-mentation is not conducted in an anaerobic but in a semi-anaerobic fashion. The ventilation rate depends on the spectrum of fatty acids, which in turn depends on the ratio of the various substances in the feed, such as fats, sug-ars, starch, and proteins. The spectrum of fatty acids can be determined in preceding experiments for each material to be fed, using standard E~_ se known methods. In a preferred embodiment, the plant is therefore designed in such a man-ner that the hydrolysis reactor 1.7 is connected to a com-pressor 1.8.

In addition, the controlled feeding of air promotes stripping of the hydrogen sulfide formed so that the biogas produced in the plant has a hydrogen sulfide content below the detection limit of 10 ppm. At the same time, the bacte-rial decomposition in the hydrolysis reactor is enhanced by the controlled feeding of air.

In addition, the efficiency of the hydrolysis step can be further increased when the hydrolysis is not carried out at ambient temperature (as a rule, the plant will be in the open air both in summer and winter time) but at least at 20~C and at maximum, 40~C, i.e., under mesophilic condi-tions. To this end, and in a preferred embodiment, the hy-drolysis reactor 1.7 is equipped with a standard tempera-ture controller which regulates the temperature to at least 20~C and at maximum, 40~C. This results in increased opera-CA 02248~88 1998-09-09 _ tional safety because the major part of the micro-organisms will find their optimum within this temperature range.

In order to further improve the described process with respect to more rapid throughput and operational safety, it has proven exceedingly efficient to connect at least two settling tanks both at one and two methanization reactors, which tanks are in alternate operation, ensuring a minimum rest period of 6 hours and more preferably, 12 hours. This results in a substantially more rapid concen-tration of biomass in the process water.

Furthermore, it appeared essential with respect to process stability and efficiency, not to recycle the biomass, as described in DE 44 46 661, but biomass-contain-ing process water at a ratio relative to the amount of waste fed of preferably from 2:1 to 1:2 into the hydrolysis reactor 1.7 and optionally, the methanization reactor 1.11 for inoculation (cf., pipeline system 1.15). The biomass-containing process water may be recycled into the methani-zation reactor 1.11 at a ratio of from 1:5 to 1:10 relative to the amount of hydrolyzed material leaving the hydrolysis reactor 1.7. Thus, the expensive removal of biomass is no longer required; the process water enriched with biomass, which has accumulated in the bottom part of the respective settling tank after at least 6 hours, is simply recycled.

According to the invention, about 40-60~ of the process water is recycled, ensuring inoculation on the one hand and simultaneously, a dilution of the material in the hydrolysis reactor of about from 2:1 to 1:2 on the other hand. Said dilution which is excluded in the process de-scribed above, provides an essential advantage with respect to process stability.

Furthermore, complete mixing in the reactors 1.7, 1.11.1 and 1.11.2 is ensured, for which purpose these may CA 02248~88 1998-09-09 be equipped with mixing units, for example. Likewise, re-circulation of the reactor contents or injection of biogas is possible.

If desired and/or required by legal or other regu-lations, the hydrolysis reactor 1.7 may have an upstream hygienization tank 1.3 for hygienization, into which the crushed material is supplied from homogenizer 16 by using the pump 1.2 and then heated to, e.g., from 70 to 90~C over a half to one hour. Other hygienization units, e.g., oper-ated using ozone are also possible. Furthermore, an aerobic or semi-anaerobic working bioreactor or a thermal or chemi-cal reactor may be provided upstream, in order to digest poorly decomposable components such as bones or feathers.

Depending on the material to be fermented, the units 16, 1.3 and 1.5 may be present or not, or may be ar-ranged in a different order. For example, where grinding sludges are to be fermented, homogenization may not be nec-essary, so that the homogenization unit 16 may be aban-doned. Similarly, reservoir 1.5 and hygienizer 1.3 are not necessary in each case. In case they should be necessary, a reservoir having an integrated homogenizer is used in a preferred modification of the invention. Hygienization tank 1.3 and reservoir 1.5 may be stirred or not, depending on optimum process design as appropriate for the starting ma-terial.

In the fermentation of materials having a high min-eral content, the solids must be removed initially in the settling tank 1.13 and, if necessary, transferred to a sol-ids tank to be connected; only thereafter, the process water enriched with biomass can be recycled into the hy-drolysis and the methanization stage.

Using the continuously operating plant according to the invention, any waste having an oTS content of 25~ at CA 02248~88 l998-09-09 maximum can be fermented in a fully automatic, operation-ally safe and efficient manner. It is a hygienically closed system. The organic substances are decomposed by 90~. The biogas produced is of high quality and contains 65-75~, preferably 70-75~ of methane.

The quality of the biogas allows purposeful utili-zation for the plant management. For example, direct ther-mal utilization, production of electric and thermal power via force-heat coupling or feeding into a local natural gas network is possible.

For controlling, each functional unit of the plant (reservoir, hydrolysis reactor, bioreactor) has a microcon-troller module controlling the process parameters by means of a dynamically adjustable program.

In Fig. 2 below, a preferred embodiment of the biogas plant 1 of the invention is illustrated. All the components of the technical plant as well as the automatic control and the pipeline system may be designed as modules, so that the processing capacity can be increased further by additional modules. According to the invention, it is pre-ferred that all units be of equal constructional type and size. Also, the plant of the invention may be accommodated in a transportable container.

CA 02248~88 1998-09-09 List of Reference Numbers Fig. 1 1 Biogas plant 12 Feed line 2 Fermentation substrate feed line 13 Feed line

3 Fermentation substrate tank 13a Separation unit for domestic biological trash

4 Feed line 14 Feed line 4a Feed line 15 Feed line 4b Feed line 16 Homogenizer

5 Stack composting unit 17 Shredder for composting highly structured organic waste 18 Shredder

6 Closed composting unit for 19 Extruder composting possibly contaminated, highly 20 Extruder structured organic waste 21 Mesh 22 Feed line

7 Feed line 23 Feed line

8 Feed line 24 Mixing unit

9 Feed line 25 Feed line 9a Unpacking unit for 26 Feed line waste food

10 Feed line 27 Feed line

11 Feed line 28 Feed line CA 02248~88 1998-09-09 List of Reference Numbers (Continued) Fiq. 2 16 Homogenizer 1.2 Pump 1.3 Hygienization unit 1.4 Pump 1.5 Reservoir or reactor for pretreatment 1.6 Pump 1.7 Hydrolysis reactor 1.8 Compressor 1.9 Effluent air filter 1.10 Pump 1.11.1 Methanization reactor 1.11.2 Methanization reactor 1.12 Pump 1.13.1 Settling tank 1.13.2 Settling tank 1.14 Pump 1.15 Process water recycling 1.16 Gas reservoir 1.17 Gas flare 1.18 Block-type thermal power plant 2 Fermentation substrate feed line ,

Claims

1. A plant for the utilization of organic waste by using a combination of fermentation and composting, characterized in that the plant includes a biogas plant (1) for the fermentation of low-structure organic waste, which is connected to a fermentation substrate tank (3) via pipeline (2), and the tank (3) is connected via pipeline (4) to a stack composting unit (5) for composting highly structured organic waste and/or a closed composting unit (6) for composting optionally contaminated highly structured organic waste as well as waste from domestic biological trash, whereby the stack composting unit (5) is connected to an upstream shredder (17) and/or an extruder (19), with the shredder (17) being connected to the feed line (10) at the inlet side, and the extruder (19) being connected to the feed lines (10) and (11) at the inlet side and the closed composting unit (6) is connected to an upstream shredder (18) and/or an extruder (20) and/or a mesh (21), with the shredder (18) being connected to feed lines (13) and/or (14) at the inlet side, the extruder (20) being connected to feed lines (25) and/or (27) at the inlet side, and the mesh (21) being connected to feed line (15) at the inlet side.

2. The plant according to claim 1, characterized in that the biogas plant (1) is connected to an up-stream homogenizer (16) which is connected to feed lines (8) and/or (9) at the inlet side.

3. The plant according to claim 1 or 2, characterized in that the stack composting unit (5) and/or the closed composting unit (6) are connected to a mixing unit (24) by means of drain line (22) and drain line (23), respectively.

4. The plant according to one of claims 1 through 3, characterized in that the feed line (26) connects extruder (19) and mixing unit (24).

5. The plant according to one of claims 1 through 4, characterized in that the biogas plant (1) is directly connected to feed line (7), the stack composting unit (5) is directly connected to feed line (12), and the closed composting unit (6) is directly connected to feed line (28).

6. The plant according to one of claims 1 through 5, characterized in that it contains a biogas plant (1) for the two-step fermentation of organic waste materials having a content of organic dry substance of 25% at maximum, which comprises a hydrolysis reactor (1.7) for hydrolyzing and pre-acidifying the organic material, followed by one, preferably two methanization reactors (1.11) for thermophilic fermentation of the hydrolyzed and pre-acidified material, whereby the hydrolysis reactor (1.7) can be ventilated using pressurized air, the methanization reactor (1.11) is followed by two settling tanks (1.13.1, 1.13.2) connected in parallel for concentrating the generated biomass in the process water, which are operated alternately, and the settling tanks (1.13.1, 1.13.2) are connected via pump (1.14) and via pipeline (1.15) for process water recycling to the hydrolysis reactor (1.7) and optionally to the methanization reactor (1.11).

7. A process for the utilization of organic waste using a combined composting and fermentation process, characterized in that by using a plant according to claims 1 through 6, low-structure and liquid organic waste is fermented in a biogas plant (1), the remaining fermentation substrate as a nutrient source is fed from tank (3) via pipeline (4a) into a stack composting unit (5) which is used for composting highly structured organic waste, and/or via pipeline (4b) into a closed composting unit (6) which is used for composting optionally contaminated highly structured organic waste as well as waste from domestic biological trash, thus effecting complete decomposition of the organic waste to yield biogas, liquid fertilizer and compost, the compost subsequently being conveyed optionally via feed lines (22) and (23) into a mixing unit (24) where additional material and optionally via feed line (26) shredded and extruded wood from the extruder (19) are added, so that a plant substrate is obtained.

8. The process according to claim 7, characterized in that said low-structure and liquid organic waste materials to be fermented in the biogas plant (1) are leftovers, waste food, waste fruits and vegetables, animal bodies, fats, waste water, clarification sludges, and waste from chemistry, pharmacy and cosmetics.

9. The process according to claim 7, characterized in that said highly structured organic waste materials to be composted in the stack composting unit (5) or in the closed stack composting unit (6) are non-contaminated waste materials such as wood, wood chips, cardboard and green cuts.

10. The process according to claim 7, characterized in that said contaminated, highly structured organic waste materials to be composted in the closed composting unit (6) are problematic waste materials such as contaminated soils, contaminated waste wood, and odor-loaded waste materials.

11. The process according to claim 7, characterized in that swellable organic polymers and optionally materials containing loam or clay are fed into the mixing unit (24) as additional materials.

12. The process according to claims 7 and 8, characterized in that the biogas plant (1) is fed with said low-structure and liquid organic waste materials from chemistry, pharmacy and cosmetics via feed line (7), said leftovers, waste fruits and vegetables as well as animal bodies via feed line (8), and the waste food optionally unpacked in unit 9a via feed line (9), with leftovers, waste fruits and vegetables as well as animal bodies optionally being homogenized in the homogenizer (16) prior to feeding into biogas plant (1).

13. The process according to claims 7 and 9, characterized in that the stack composting unit (5) is fed with wood via feed line (10), with cardboard via feed line (11), and with green cuts via feed line (12), in which process the wood is optionally shredded in the shredder (17) and/or extruded in the extruder (19) prior to being fed into the stack composting unit (5) and likewise, the cardboard is optionally extruded in the extruder (19) prior to being fed into the stack composting unit (5).

14. The process according to claims 7 and 10, characterized in that the closed composting unit (6) is fed with highly structured domestic biological trash via feed line (13), optionally subsequent to classifying, sorting and separating in unit 13a, contaminated wood via feed line (14), and problem waste including contaminated soil via feed line (15), in which process the contaminated wood is optionally shredded in the shredder (18) and/or extruded in the extruder (20) prior to being fed into the closed composting unit (6), and the problem waste is passed through a mesh (21) prior to being fed into the closed composting unit (6).

15. The process according to claims 7 and 9, characterized in that the closed composting unit (6) is fed with not-contaminated waste, with wood being fed via feed line (14), cardboard via feed line (27), and green cuts via feed line (28), in which process the wood is optionally shredded in the shredder (18) and/or extruded in the extruder (20) prior to being fed into the unit (6), and likewise, the cardboard is optionally extruded in the extruder (20) prior to being fed into the unit (6).