Method and device for the wet-mechanical treatment of a substance mixture, particularly of refuse of all types

ES 2 294 562 T3

DESCRIPTION

Process and device for the mechanical wet treatment of a mixture of substances, in particular wastes of all kinds.

Disposal of urban settlement waste as well as industrial waste poses a sustainability challenge that is increasingly required by politics. After reducing the amounts of waste through waste avoidance and the introduction of independent collection of recyclables, there are still wastes that cannot be put directly into any use. As a mixture of three substances based on inert substances, organic matter and water cannot be used for the exploitation of mineral substances due to their excessive proportion of organic matter, or too large a proportion of water and / or minerals, nor at a use of biomass. Due to the excessive load of harmful substances, discharge as wastewater is also not possible.

For the disposal of these wastes, the new legal regulations require in the medium term in Germany (Waste Sedimentation Regulation) an inerting before being deposited in a landfill.

Various processes or ways of utilization are available for use. Thus, energy utilization takes place during fermentation, combustion or gasification. An important criterion for product quality in all energy utilization processes is that there is a low proportion of mineral substances or inert substances. In a different way, it is necessary to assess the optimum humidity of the product and the grain size. For fermentation there are also dry and wet fermentation processes as well as anaerobic wastewater treatment processes available.

For the utilization of the materials of the organic components, the agricultural utilization is found in the first place, which however is limited by the load of harmful substances of the material. Forms of material utilization of fiber proportions such as insulating materials, paper or pressed boards are only marginally considered here.

For inert substances there are ways of use in the construction industry or they are taken to landfill.

But only the separation of waste into fractions usable in terms of material and / or energy allows effective use. For this, the separation as a previous treatment for the actual use, should also satisfy the sustainability requirements, that is to say, take care of the resources and avoid immissions, simultaneously with economic and social compatibility.

For the treatment of waste with organic fractions, the procedures described below are currently available, which differ in terms of the content of harmful substances from organic fractions:

- Treatment of residual materials with uncharged organic fraction

Composting

Solid organic waste or sludge with the addition of structural material is treated aerobically after screening for coarse nuisance substances. By means of the biological treatment the organic substances are degraded or transformed and the water content is reduced, so that a stabilization is achieved. Through this process the availability of plants is reduced and at the same time the compatibility of the compost with the plants is increased. The nuisance substances are separated in addition to the coarse treatment, mainly from the finished compost, and dried by the composting process, by the separation of hard substances and separation by air. The separation of hard substances is usually carried out with pneumatic washing tables. Composting organic waste is associated with high exhaust air emissions and high energy consumption.

Fermentation

In anaerobic biological treatment, and especially in wet fermentation processes, inert substances (sand) are separated before fermentation. In most fermentation processes, a subsequent maceration is carried out for the biological drying of the dehydrated fermentation residue, with or without the addition of structural material, before agricultural use. The characteristic of a fermentation is the production of regenerative energy based on biogas and the reduction of exhaust air emissions compared to composting. The following technical variants of the fermentation process have been carried out on a large technical scale:

Dry fermentation in one or more stages in the case of a dry substance content of 20% 50%: From the prospectuses of the companies and the plants carried out, the Valorga dry fermentation procedures of the Valorga Firm are known, among others, France; the Dranco procedure, from Organic Waste Systems nv., Belgium; the dry fermentation Linde-BRV, Switzerland and the pro

ES 2 294 562 T3 Kompogas, from the Kompogas Firm, Switzerland. What is essential in these procedures is that the separation of inert substances is generally not carried out or only after fermentation. According to WO 98/28145 A1, Frank Rindelaub, Switzerland, a pre-separation of inert substances from a partial fraction is provided in a dry fermentation process. At the plant in La Coruña, Spain, which works according to the so-called Valorga process, a dry separation of inert substances is carried out before fermentation during mechanical treatment to protect the fermentation plant.

Wet fermentation of one and more stages in the case of a dry substance content of 5% 20%: Wet fermentation procedures are known for waste with prior separation of inert substances from company prospectuses, among others from the Linde-KCA Firms -Dresden GmbH, Dresden, Germany; MAT Müll- und Abfalltechnik GmbH, Munich, Germany; Avecon, Finland as well as the WABIO process of the Eco Tec Firm, Finland. In these processes, in addition to fermentation, the separation of inert substances is decisive, that is, the pre-treatment of the organic fraction before fermentation.

- Waste treatment with organic fraction with load

Most of the processes for the treatment of loaded organic fractions envisage their disposal in a landfill or in a garbage incineration plant. In accordance with the current legal situation, the stabilization of the organic fraction must be foreseen in Europe before discharge to the landfill. This pre-treatment before discharge to the landfill is achieved in mechanical-biological treatment plants through composting and fermentation processes.

If energy efficiency is sought, drying and separation of inert substances from generally humid waste and containing inert substances is required. Inert substances separation processes can be carried out mechanically wet or dry. Furthermore, for physical reasons, wet separation in which water is used as the separation medium has a higher degree of performance than dry separation in which air is the separating medium.

Mechanical processes for separating dry inert substances after biological drying are known by the dry stability process from HerHof Umwelttechnik GmbH, Solms-Niederbiel, Germany, and by the DE 196 49 901 A1 process. Devices and processes for the mechanical separation of inert substances when wet are known from the publications DE 196 23 027 C1, DE 198 44 006 A1, DE 199 24 164 A1, DE 201 12 681 U1, DE 42 43 171 C1, DE 197 29 802 C2, DE 44 36 639 A1, DE 198 46 336 A1, DE 197 45 896 A1, DE 44 15 858 A1, DE 43 12 005 A1, DE 199 23 108 A1 and DE 41 20 808 A1. In addition to these there are special processes for the treatment of port sludge and street sweeping, such as the ASRA plant in Hamburg Stellinge of the firm Kupczik Umwelttechnik GmbH Hamburg and the MoReSa process of AKW Apparate und Verfahren GMBH, Hirschau, document DE 196 17 501 C2. This publication discloses various features of independent claims 1 and 10 of the present invention.

The objective of most of the processes mentioned above is the separation of inert substances. To this end, the wastes to be separated are first shredded and mixed and finally the inert substances are removed from the total flow, often in a single treatment phase. This has repeatedly led to major problems in subsequent equipment.

By intensive shredding to defibration, for example by using a hydropaste as described in the publications DE 41 20 808 A1, DE 199 23 108 A1, DE 198 29 648 C2, DE 198 00 2242 C1, DE 196 55 101 A1, DE 100 12 530 A1, DE 39 34 478, DE 198 07 116 A1, DE 4042 226 A1, DE 4042 225 A1, DE 4406 315 C2 or an upstream cascade ball mill, as in DE documents 102 10 467 A1 and DE 41 26 330 A1, the viscosity of the suspension increases which is opposed to an effective separation. The viscosity decreases due to the disintegration of the organic matter only after the subsequent fermentation, for which undesirable sedimentation of inert substances occurs here that disturb the operation, and that in the previous separation had not been captured due to the higher previous viscosity .

Other mechanical wet separation processes with less intensity of comminution before the separation of substances - see EP 0521 685 A2 and DE 197 55 223 A1, EP 567 184 B1 carry out the separation of inert substances in a separation phase, and according to DE 197 55 223 A1, even with stirring, whereby a very imprecise separation is achieved.

In EP 0639 108 B1 an automatic block regime with corresponding performance limitations is proposed, which has also been carried out in various large-scale installations. In the absence of a controlled separation of sand by means of locks, for example in another separation phase, considerable sedimentation problems were produced in the subsequent treatment phases.

The percolation processes such as in the publications DE 198 46 336 A1, DE 196 48 731 A1, DE 199 09 353 A1, DE 199 09 328 A1 and DE 198 33 624 A1 only remove very fine inert substances that

ES 2 294 562 T3 are leached with the wash or percolation water, before or during precolation. Coarse inert substances such as stones, glass and fragments of crockery, which represent the largest proportion of inert substances in population waste, are included in the percolation, resulting in higher energy consumption and wear.

In all the aforementioned processes for the separation of inert substances, in particular in the wet fermentation processes, the protection of the plant is put first and not the improvement of the quality of the material for its later use. However, the separation of waste should not only ensure the technical and economic requirements related to the plant technique but also the optimal use of the partial fractions.

In all the aforementioned processes, the treatment of most of the organic substances is obligatorily provided, so that these can be brought directly to an anaerobic treatment or to a previous hydrolysis followed by an anaerobic treatment of the hydrolysates. However, it is not taken into account that the degree of energy efficiency of a fermentation in comparison with an incineration depends on the parameter of anaerobic degradability and the parameter of dry substances. Dry wood combustion has a higher degree of energy efficiency than dry wood fermentation. However, it is evident that the fermentation of humid organic industrial waste with a high biogas yield presents a higher degree of energy efficiency than the combustion of this humid fraction.

Organic substances which are largely freed from inert substances and soluble organic substances and which can be dehydrated by simple screw presses to dry substance contents> 45% TS, have a calorific value of approx. 6000 kJ / kg, which is at the limit of an automatic combustion. If the proportion of anaerobically degradable organic matter is less than 50%, as for example in the case of material retained in bars, then from the economic point of view, energy use through thermal processes such as combustion should be preferred for this material flow or gasification, with or without prior drying, better than an anaerobic treatment by fermentation.

This problem is mentioned in the approaches of documents EP 0037 612 B1 and DE 196 00 711 A1. In the latter, the easily degradable organic matter is separated by washing the waste in an endless washing machine. The easily degradable organic matter is concentrated in the recirculating water that is taken to an anaerobic treatment. But here, too, the 2-8 hours of residence (2-6 hours are mentioned in DE 198 46 336 A1) for washing off easily degradable organic matter remain problematic. But in practical application, however, it has been seen that to obtain a high degree of dissolution of the easily degradable organic matter, an intensive washing with recirculation water is first necessary and not a long residence time, as described in the manufacturer and service provider catalog 1997/98, 9. Kassel Waste Forum, Editorial MIC Baeza, p. 12.

Increasing the residence time only exposes the waste to longer mechanical stress or dissolution. In this process, hydrolysis, a special chemical or enzymatic disintegration of the molecules catalyzed by bases or acids including water, plays a secondary role in this process, while dissolution using water as solvent is more efficient.

It is only very late that it has been recognized that sufficient hydrolysis of the organic fraction of the waste already takes place during the collection and storage of the waste until its treatment. It is not uncommon for 2-4 weeks to elapse from waste to treatment, during which time natural hydrolysis takes place. The technical application of this knowledge is not known according to the state of the art.

Faced with the aforementioned processes for waste treatment, the present invention has set itself the objective of producing fractions that are usable in terms of material and / or energy, and this avoiding as much as possible the discharge to landfills and optimizing the process of separation in terms of yield, energy consumption, wear, investment costs and flexible further treatment of the produced fractions.

To solve this objective, the method according to claim 1 is proposed as well as the device for carrying out this method according to claim 35.

In the process according to the invention, a three-substance mixture consisting of water, inert substances and organic matter is separated in a three-stage separation system into three inert substance fractions and three organic matter fractions as well as a liquid fraction which It contains dissolved substances as well as extremely fine inert substances and fine organic particles.

Depending on economic and local circumstances, inert substances are purified with recirculating water and fresh water until they can be used for use. Especially in the coarse fraction of inert substances, the use of the substance according to national legislation is questionable. This fraction can be discharged to a landfill for stabilization, either directly or after a short aging phase, or it can be treated in another subsequent treatment phase until it achieves the appropriate quality for its use. The separated organic matter fractions can be used either directly for drying, composting or fermentation.

ES 2 294 562 T3

In the process according to the invention (see Figure 1), inert substances are secreted in several stages, starting with a very high content of dry substance. Once the coarse stones (inert matter 1, Figure 1) have been separated, the coarse organic matter (organic matter 1, Figure 1) can be separated by screening, which is then duly free of stones of the corresponding screening size, and then, since it is coarse organic matter, it can be easily washed away from sand and adhering fine organic matter with small amounts of water.

The grating-retaining material-like fraction (organic matter 1) can then be squeezed out with simple pressing techniques and reduced wear to achieve high dry substance contents. This is achieved by washing off all the fine organic matter, which is very difficult to squeeze out, and due to the removal by washing of the stone structure or the inert material structure that in other cases preferably supports the pressing force. without contributing to great dehydration. To improve the dissolution of easily biodegradable organic matter, a shredding can be carried out before squeezing in order to remove juices.

This first phase is the most important phase of the entire process. Due to the high degree of squeezing of the coarse organic matter (organic matter 1), the material rich in structure is already separated in this phase of the process for energy use by incineration or gasification of the fermentable organic matter found in the pressing water. .

Carrying out the corresponding pressing can be counted in a first pressing stage using normal screw presses with a degree of dehydration of about 45% - 60% dry substance content.

In a second pressing phase this material (organic matter 1) can be squeezed to a dry substance content of 60% - 75%.

The organic fraction (organic matter 1) can be used for energy according to the pre-treatment according to the invention, either directly or after drying, by incineration or gasification. In addition to this, organic matter 1 can be used for the use of its substance in agriculture if the corresponding limit values ​​are met. For this it is important that in addition to the removal of inert substance and the corresponding high degree of squeezing, the mesh material is subjected to batch drying. Furthermore, drying should be carried out in such a way as to achieve sanitization by means of corresponding temperature control during drying. After drying, the material should be freed from nuisance substances, according to a fine composting treatment and should be pelletized to obtain a good storage capacity, transport capacity and compatibility with plants, of the material that is going to be used later. as dry compost pellets.

Once the coarse stones (inert matter 1) and organic matter (organic matter 1) have been separated from the suspension of materials, the dry substance content of the remaining suspension has been considerably reduced. This reduction is caused by the removal of dry matter with a high dry matter content, such as stones with a dry matter content> 90% and squeezed organic matter with a dry matter content of> 45%. In addition, additional water is used for washing the inert substances and for washing the organic matter, which contributes to a further reduction of the dry substance content. Other inert substances are separated from the remaining suspension in the second and third stages of the process.

In the second stage, coarse and fine sand with a grain size of approx. 2-25 mm (inert substance 2, Figure 1). In the subsequent phase, the organic fraction can be separated by sieving by means of a fine sieve whose mesh size is greater than the size of the maximum inert substances to be separated, of approx. > 3 mm. The organic fraction (organic matter 2) separated by sieving is also washed again with water and squeezed out. The sand (inert matter 2) that is separated in this stage is removed through a sand separator, washed again with recirculating water and washed again with clear water, so that according to the use of water When fresh, either a fraction of inert matter suitable for landfill or a fraction of usable sand is obtained.

Finally, the third stage of the process follows in which now for the first time in the entire process development a pump is used.

Due to the separation of the various fractions of inert matter and organic matter, which are largely separated dry, as well as by the total amounts of recycled water or fresh water supplied, the suspension sieved at approx. 3mm has now increased so much in terms of water content that together with the dry substance content between 3-8% it is ideal for a downstream classification hydrocyclone.

The hydrocyclone overflow contains the remaining fine organic matter components that are free of fine minerals. The lower outlet of the hydrocyclone contains the segregated inert substances, but due to their degree of fineness, they are still partially contaminated with adhering organic matter. This fine mineral substance can be brought up to usable qualities (inert material 3, Figure 1), by further treatment, for example by means of a sorting spiral or fine sieving with washing. The organic fraction of the sieve overflow is subjected to a fine sieving of approx. 50-500 pm. The filter cake that forms on the fine screen (organic matter 3, Figure 1) can also be squeezed out. In addition to the total of six fractions, a recirculation water is obtained that is enriched with dissolved organic substance due to the various pressing and washing.

ES 2 294 562 T3

In this way, a large part of the fermentable organic matter has been transferred to the recirculation water, while the part rich in structure and more difficult to ferment is contained in the squeezed fraction. To reduce the viscosity of the recirculating water, it should now be conditioned by a biological process. If the recirculating water were not treated, the viscosity could increase so much that the recirculating water would no longer be usable as a separation medium for the segregation of inert matter. Anaerobic wastewater purification processes such as the solid-bed fermentation process or the submerged fermentation process with biomass retention are available for the treatment of recirculation water. In addition to this, there is the possibility of a joint fermentation of the recirculation water and the organic matter fractions by means of dry and wet fermentation processes for suspensions containing solid substances or precolation processes.

Better solubility of organic matter in recirculating water can be obtained by thermal conditioning by heating the suspension to about 70 ° C. But at the same time it should be noted that due to thermal conditioning the press water contains a higher CSB and a higher retention load of heavy metals. This effect is used with the present invention in such a way that the squeezed organic matter that does not reach the fermentation is decontaminated while the load is supplied in a controlled way to the liquid phase by means of thermal conditioning.

Contaminated organic matter is thus markedly reduced due to a high fermentable proportion of dissolved organic matter, and at the same time heavy metals are precipitated in fermentation by complexing of organic matter during fermentation. The pollutant load is then preferably found in the fermentation residue. In the case of a fermentation exclusively with recirculating water, after fermentation the organic matter is therefore the sink for harmful substances from the process.

The material use of the organic fractions is preferably used in agriculture as fertilizer and / or as a soil improvement. For this, the organic matter is either compostized in compost plants or fermented in fermentation plants and used composted or dried as well as pelletized and as loose compost discharge or in the form of fertilizer pellets. For energy use, organic matter is mechanically dehydrated as much as possible and used in gasification or incineration plants. Pretreatment using the method object of the invention is advantageous for both ways of utilization.

The process object of the invention can be used advantageously in combination with all existing mechanical-biological and thermal processes as well as with dry and wet fermentation processes, precolation processes, hydrolysis processes, composting processes, aerobic and anaerobic processes. wastewater purification, membrane separation procedures for purifying recirculation water, drying procedures, pelletizing procedures as well as combustion procedures, with or without prior drying. Even retrofitting existing plants is also advantageous. Due to national regulations, the sale of compost from some composting facilities for material use is no longer guaranteed due to the loading of harmful substances in the compost or its discharge to a landfill. By means of a subsequent equipment with the process object of the invention, the content of harmful substances of the organic matter fractions can be reduced and at the same time it is possible to use energy as biomass by separating the inert substances and the use of compost for drying. of organic fractions.

Inert fractions 1, 2 and 3 should preferably be used as materials in the construction industry. For inert fractions 1 and 2 there is application of the material in most material mixtures. The inert fraction 1 does not always meet the quality for material use, for example in population waste and without any subsequent treatment and therefore it has to be discharged in a landfill. Since heavy substances have relatively low biological activity, these heavy substances meet most of the national criteria for landfilling of biologically stabilized waste. In certain cases, a subsequent stabilization can be carried out.

Many organic wastes with a high content of easily biodegradable organic matter often cannot be treated with anaerobic wastewater treatment procedures for biogas production without prior treatment, due to their load of heavy materials and coarse organic substances. With the process according to the invention, it is possible to carry out the universally necessary pretreatment for all currently known organic industrial wastes, from the pomace through contents in the belly of ruminants to the liquor. Mixing can generally be dispensed with in order to avoid sedimentation in the fermentation facilities.

The present invention therefore represents a universal process for pre-treatment that allows flexible further treatment, adapted to local circumstances, regardless of the load of harmful substances contained in the waste. The intensity of treatment depends on economic and local circumstances and can be modular in structure. It should be possible to adapt the installation technique to the future quality requirements of the fractions for reuse and disposal as well as the adaptation to future environmental legislation by means of a simple extension or transformation of the installation technique.

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Furthermore, the facility technique should be able to be used for the largest possible number of wastes, in the sense of decentralized waste management. The present method and the present device are therefore suitable for treating, among other things, population waste, biological waste, organic industrial waste, liquor, street sweeping, contaminated soils and waste from municipal and industrial wastewater treatment.

The method and the implementation of the method by means of the device according to the invention are schematically represented in the following drawings:

Figure 1 shows in a diagram the variation that the composition of a mixture of substances undergoes in the different stages of the process or steps of the process.

Figure 2 shows a process development scheme in combination with the device necessary for the implementation.

Regarding the stages of the process represented in Figure 1, reference is made to the explanation that appears above.

Figure 2 explains the implementation of the process by way of example by means of the device represented schematically.

In the first place, the mixture of substances 1 to be treated is crumbled and slightly defibrated, with which a better possibility of segregation is achieved, since due to the slight dissolution of the fiber materials the viscosity of the water of the fiber is not unnecessarily increased. recirculation. In certain cases, it is also possible to dispense with the fine comminution of the substance mixtures before entering the device of the invention, since the device is prepared for a piece size of up to approximately 120 mm.

Subsequently, the substance mixture 1 is conveyed to a mixer 4 by means of a metering conveyor 2, preferably a screw conveyor. In doing so, the mixture of substances in the screw conveyor is already moistened with recirculation water, and at the outlet to the mixer it is washed with recirculation water 5, 6 to avoid clogging.

The moistened substance mixture 3 passes into the mixer, which is driven from below by a stirrer 7. The agitator revolutions and the content of dry substance in the mixer are adjusted by means of the recirculation water supply as a function of the current consumption of the agitator and the viscosity of the recirculation water, so that light substances are incorporated and run off together with the entire suspension through a lower outlet of the mixer by means of a conveyor 9 and are optimized in the subsequent separation steps. The incorporation of the light substances is favored due to the pre-wetting by means of the dosing screw 2 and by the formation of thrombi in the mixer, which can be adjusted by means of a current divider.

1^to stage

From the mixer 4 the suspension 8 passes to the conveyor 9. The conveyor is designed as a screw conveyor with a minimum diameter of about 300 mm and a helical pitch of approx. 150 mm. The auger trough is designed as a U trough and has a free section above the auger of approx. 150 mm. The screw conveyor 9 is flanged at the bottom of the mixer 4 so that heavy substances can slide into the screw conveyor at an angle of about 45 °. The suspension is driven by means of the hydraulic pressure of the mixer to the bottom current and through a counter-current classifier 10 reaches a screening screw 16. Before reaching the countercurrent classifier 10, the suspension passes along the auger 9, the heavy substances not being drawn into the countercurrent classifier 10 but are evacuated through the slowly rotating auger 9. Since the sinking heavy substances are still loaded with adhered and retained organic matter, the auger 9 is washed in the zone of the countercurrent classifier 10 with recirculation water 11 from the second stage. The heavy substances transported by the screw conveyor 9 beyond the zone of the countercurrent sorter 10 are now washed again with the recirculation water 12 from the third stage. In the area above the suspension level in the screw 9, the heavy substances are rinsed with purified recirculation water or with fresh water 13, and from the system they are discharged as the first inert fraction 15 to a container or to another delivery point.

By means of the cascade washing system described above, where clean washing water is always used after the washing process, a reduced consumption of purified recirculation water or fresh water is achieved and higher qualities of residual substance are achieved.

The light substances 14 discharged through the countercurrent sorter 10 are screened with an auger screen 16 with a gap width of approx. 30 mm. To avoid floating layers, the suspension with the light substances is led to the endless sieve 16 through a section of closed pipe. In this way, the substances are forced into the area of ​​the auger fins of the auger screen 16 below the liquid level, transported and screened. To improve the sieve performance, recirculating water 18 is added to wash the auger sieve 16. At the rear of the auger sieve, light substances are pre-pressed 22.1

ES 2 294 562 T3 before the light substances 22.1 are delivered to a washing press 19. In the washing press the light substances are washed with fresh water 20 or with purified recirculation water and dehydrated to high degrees of dehydration of up to 60% of the dry substance content, and are discharged into a container such as press cake or first organic fraction 22, or are delivered to a corresponding conveyor system.

The screened suspension 17 and the pressing water 21 are led without pumping into a settling tank 23.

2^to stage

In the second stage of the separation process the suspension 17,21 reaches a settling basin 21 which is constructed as a sand classifier. The heavy substances descend to the discharge auger 24 while the light substances 27 reach a gap screening auger 29 through an overflow. In the screening screw, the light substances are washed with recirculation water 30 from the 3rd stage, with fresh water 31 or with purified recirculation water, and dehydrated to 45% of the dry substance. The second fraction of dehydrated organic matter 32 is discharged into a container or delivered to a corresponding conveyor system.

The heavy substances secreted in the discharge screw 24 are first cleaned by means of a cascade washing system, first with recirculation water 25 and then with purified recirculation water or with fresh water 28 removing light substances, they are washed and discharged as second inert matter fraction 28 to a dewatering container or subsequent conveyor system.

The sieved suspension 33 with a grain size less than 3 mm is led into a filter container 34.

3rd stage

A pumpable suspension 51 is conveyed from the filtering container of the second stage, either by means of a centrifugal pump 55 as circulating water for washing, or it is delivered to a hydrocyclone 36 by another centrifugal pump 35. The suspension 37.1 discharged through the dip tube of the hydrocyclone still contains siftable organic fiber materials and particles which are screened by means of a vibrating screen 53 in two stages, first for approx. 200 pm and then for approx. 50 pm. To improve the quality of the screening, the screen can be washed. The screen cake 44 which has been statically pre-dewatered to a content of about 20% dry substance is dehydrated again by means of an endless screw press 45 to approx. 40% of dry substance, and it is discharged as press cake or third fraction of organic matter 49. The pressing water 46 passes into a collecting tank 47 and is then returned to the sieve 43 by means of a pump 48. The sieved suspension 50 passes by gravity into a filtering container 52.

The heavy fraction 37.2 from the hydrocyclone bottom stream is further scrubbed by means of a sorting spiral 38. Due to the special flow conditions to be set in the sorting spiral 38, recirculation water 58 is added. The purified heavy fraction is led to a soaking bath with sand discharge 39, while the heavy fraction 42 polluted with organic matter is returned to the hydrocyclone through the filtering container 34 of the second stage. The wash water 41 is also led to the filter tank 34 of the second stage. The remaining heavy fraction is dehydrated by means of an endless screw 39, after washing with fresh water 37.3 and segregated as a third fraction of inert matter 40.

The excess water is led through an overflow from the third stage filter container 52 as waste water 53 to a recirculation water purification system, which cleans the recirculation water so that it can be reused again as separation and wash water.

If necessary, the entire system can be heated by means of a heat exchanger 56.