METHOD AND ARRANGEMENT FOR PRODUCING A PEAT SUBSTITUTE FROM A FIBRE SUSPENSION

Description

[0001] The invention relates to a method for producing a peat substitute from a fiber suspension containing fibers from renewable raw materials, such as in particular a fiber suspension containing agricultural residues, such as liquid manure and / or digestate, according to the preamble of claim 1, and to a plant according to the preamble of claim 9 for carrying out the production method.

[0002] In the manufacturing process, a first solid fraction is separated from a first filtrate in at least one first solid separation step, and a second solid fraction is separated from a second filtrate of the fiber suspension in a second solid separation step following this step. Additional liquefaction can be provided between the two solid separation steps. The solid fraction obtained from this is then thermally treated in a sanitation step, for example at an elevated temperature. After this sanitation has been carried out, a peat substitute is provided that can be used as a soil improver in horticulture and / or agriculture. During the manufacturing process, an acid is also added to the fiber suspension in an acidification step in order to improve its properties or composition.The acid is added to the fiber suspension prior to the two solids separation steps in order to acidify the fiber suspension prior to solids separation and thereby dissolve precipitated salts in the fiber suspension. This dissolution of salts makes it possible, particularly when using agricultural residues as the starting material, to reduce the relatively high salt content of typically over 5 g / l to a level of maximum 1.5 g / l, suitable for a full-fledged peat substitute. At the same time, the acidification prior to the two solids separation steps enables a particularly effective recovery of other usable constituents, such as phosphate, potassium, and process water, from the filtrate resulting from the solids separation.After the acidification step, in the first solids separation step, the first solids fraction is separated from a first filtrate with the salts dissolved therein in order to subject the solids fraction, in particular the organic solids fraction, to further treatment to produce the peat substitute, and the first filtrate to further treatment to obtain additional usable materials. The solids separation is preferably carried out using a screw press, an angle press, a spiral filter, and / or another known and suitable device. Furthermore, after the first solids separation step, a washing step follows, in which the first solids fraction is mixed with rinse water to rinse out any salts still present in the solids fraction after the first solids separation step.The process chemically and biologically adapts the properties of the fibers from the fiber suspension so that they can be used in a peat-like manner. The macroscopic fibrous structure of the fibers is essentially retained, as this is necessary for use as a peat substitute.

[0003] DE10121237A1 discloses a process for improving peat substitutes usable as soil additives. In this process, a cellulose fiber-containing suspension, which contains, for example, wood fibers, is first sieved and then treated in a thickening device. Substances such as an acid are then added in a flocculating device to inhibit the growth of microorganisms contained in the suspension. This is followed by thermal treatment using a dryer, which yields the soil additive in the form of a dry substance.

[0004] EP3696142A1 describes a process for extracting phosphorus and peat-like substances from an organic material, such as agricultural waste in the form of manure or sewage sludge. In addition to acidification and two solids separation steps, at least one washing step and a thermal treatment of the phosphorus-containing material are provided.

[0005] DE102012007900A1 describes a process for reducing the nutrient content of organic waste. This process eliminates the need for a drying process after the washing process, as the liquefied gas residues remaining in the washed digestate transform into a gaseous state and evaporate after pressure relief. The resulting organic substrate can be used, for example, as a peat substitute.

[0006] DE10131347A1 shows a process for improving peat substitutes that can be used as soil additives, in which substances are added that contain acids and salts or form acids or salts in the peat substitute.

[0007] DE102011010329A1 describes the production and application of a water-storing and water-releasing organic-based composite material. The composite material contains at least one natural and / or synthetic superabsorbent polymer in the form of a hydrogel composite.

[0008] A disadvantage of the known processes for producing a peat substitute from a fiber suspension is the water consumption caused by the washing step.

[0009] The object of the invention is to avoid the disadvantages mentioned in a generic production process and to provide a full-fledged peat substitute and, in particular in the case of the use of agricultural residues as starting material, to enable the greatest possible utilization of the contained ingredients and to ensure an economical rinsing process.

[0010] This object is achieved by a manufacturing process having the features of claim 1. The first filtrate obtained in the first solids separation step is processed in a treatment process and used as rinse water in the washing step, thereby significantly reducing the overall water consumption of the process. Furthermore, the obtained solids fraction is treated in a sanitization step following the solids separation steps, for example, with steam and / or hot air, or is composted.

[0011] During the acidification step, the pH of the pulp suspension is advantageously adjusted to between 4 and 6, preferably between 5 and 6, which allows for particularly effective dissolution of the precipitated salts or those adhering to the fibers of the pulp suspension. This can also reduce ammonia emissions.

[0012] It is advantageous if the acid is formed by sulfuric acid during the acidification step in order to ensure safe and cost-effective availability of the acid used for the process.

[0013] In the washing step, the solid fraction is preferably mixed with 2 to 4 times the mass of rinsing water in order to ensure a sufficiently effective and at the same time economical rinsing process.

[0014] Furthermore, it is advantageous if, after the washing step, the salt-reduced second solid fraction is separated from the second filtrate, which essentially consists of the rinse water, in the second solids separation step. The solids are also separated in this second solids separation step, preferably using a screw press, an angle press, a spiral filter and / or another known and suitable device. This ensures particularly effective separation of the salts still present from the second solid fraction or from the fibers required for the production of the peat substitute, whereby the second filtrate can also be used to obtain recyclable materials. In this case, it is particularly possible to process the second filtrate so that it can subsequently be reused as rinse water.

[0015] Advantageously, the second solids separation step is followed by the sanitization step, in which the salt-reduced second solids fraction is subjected to a thermal treatment. This can kill germs and pathogens contained in the fiber suspension and denature hormones and medications.

[0016] For this purpose, the salt-reduced second solid fraction, preferably after pre-drying, is subjected to steam or hot air sanitization in the sanitization step. This allows germs and pathogens contained in the solid fraction to be killed particularly effectively.

[0017] In a preferred embodiment of the process, the fiber suspension is also subjected to pre-separation with an additional separator prior to acidification and the two solids separation steps, and optionally to pre-mixing of the pre-separated solids with water. In this way, an already pre-separated agricultural residue can be fed to the acidification and the two solids separation steps, thereby significantly reducing the transport effort until treatment by the process according to the invention.

[0018] It is advantageous if the first filtrate in the treatment process is treated using reverse osmosis. This treatment can produce treated process water from the first filtrate, which can be used, for example, as rinse water or directly discharged into the sewage system. The retentate also produced during reverse osmosis also has a relatively high potassium content, so it can also be recovered as another usable ingredient. This can further increase the utilization rate of the fiber suspension used as the starting material.

[0019] In addition, the first filtrate in the treatment process undergoes hydroxide precipitation before reverse osmosis, which can precipitate hardness-forming substances such as Ca, Mg, and / or phosphates. This also allows these constituents to be recycled, particularly the recovered phosphate salts, which can be used as phosphate fertilizer.

[0020] Advantageously, the first filtrate in the treatment process between hydroxide precipitation and reverse osmosis is post-acidified to approximately pH 5. This allows the ammonium-ammonia equilibrium to be shifted towards ammonium, which can be essentially completely separated during reverse osmosis, while ammonia can only be partially retained.

[0021] It is also advantageous to strip the first filtrate in the treatment process prior to post-acidification to remove nitrogen by-products, such as ammonium sulfate, ammonium nitrate, and / or ammonium formate, in order to obtain further usable components. During this stripping step, nitrogen compounds, particularly in the form of ammonia, are stripped from the filtrate and released in the form of an ammonium sulfate solution through an acidic gas scrubbing process with sulfuric acid.

[0022] Furthermore, the above-mentioned object is achieved by a plant for carrying out the process for producing a peat substitute from a fiber suspension in one of the embodiments described above. For this purpose, the plant comprises a first solids separation stage for carrying out the first solids separation step, a second solids separation stage for carrying out the second solids separation step, and a hygienization stage downstream of the second solids separation stage for carrying out the hygienization step. It is provided that an acidification stage with a mixing device for mixing the fiber suspension with an acid is provided upstream of the first solids separation stage.The mixing device in the acidification stage ensures that the fiber suspension is mixed as completely and relatively evenly as possible with the added acid, thus dissolving the salts contained in the starting material as completely as possible. A washing stage for carrying out the washing step is located downstream of the first solids separation stage. This means that the first solids fraction is mixed with rinse water to remove any salts still present in the solids fraction after the first solids separation step. The first solids separation stage is also connected to a treatment system for treating the filtrate.In this way, the washing step can be carried out with treated rinse water, which is at least partially obtained from the first filtrate of the first solids separation stage. This can significantly reduce the production plant's freshwater consumption.

[0023] Preferably, the mixing device is formed by a stirred tank and / or a pipe with turbulence-generating means to ensure the most uniform mixing of the fiber suspension with the acid possible. Regardless of the type of mixing device, pH monitoring is advantageously provided, via which an appropriate amount of acid can be controlled or regulated.

[0024] Furthermore, the first solids separation stage and the second solids separation stage preferably each comprise a screw press, an angle press and / or a spiral filter in order to ensure reliable separation of the solids fraction.

[0025] It is also advantageous if the sanitization stage includes a steam sanitization system and / or a hot air sanitization system. Both systems ensure complete thermal treatment of the solid fraction, which in turn ensures sufficient destruction of germs and pathogens, as well as sufficient denaturation of hormones and medications, allowing the resulting peat substitute to be used in horticulture or agriculture without further treatment. Alternatively, or in addition to thermal treatment, the solid fraction can also be sanitized through composting.

[0026] In a particularly preferred embodiment, a pre-separation device for carrying out the pre-separation and preferably a pre-mixing device for carrying out pre-mixing are arranged upstream of the two solids separation stages. The pre-separation device can, for example, be formed by one or more separators located remotely from the actual treatment plant, such as in an agricultural operation. At this at least one separator, the solids fraction is separated in advance in order to reduce transport costs to the actual production plant. At this plant, the delivered solids fraction can then be mixed, if necessary, with a predetermined amount of water to form the fiber suspension to be treated or used directly as the starting material.

[0027] It is advantageous if the treatment system includes a reverse osmosis system, which, in addition to recovering purified water, can also recover other usable byproducts, such as potassium. To protect the reverse osmosis system, a microfiltration system can be installed upstream to retain solid particles. If necessary, a nanofiltration system can also be installed between this microfiltration system and the reverse osmosis system to retain fine organic matter and some of the hardness-forming ions.

[0028] Alternatively or additionally, a hydroxide precipitation device can be installed upstream of the reverse osmosis system, which can precipitate, in particular, the hardness-forming elements calcium and magnesium. Precipitation preferably takes place in a stirred tank, followed by a conventional sedimentation device, such as a settling tank, inclined clarifier, or similar. The sediment obtained can then be filtered, for example, using a chamber filter press, belt filter, and / or drum filter.

[0029] Advantageously, a post-acidification stage is arranged between the hydroxide precipitation device and the reverse osmosis device to lower the pH of the filtrate in order to shift the ammonium-ammonia equilibrium towards ammonium and thereby increase the efficiency of the reverse osmosis.

[0030] The treatment system also includes a stripping device for separating the nitrogen by-products before the post-acidification stage. During the stripping step, nitrogen compounds, particularly in the form of ammonia, are stripped from the filtrate and treated with sulfuric acid through an acidic gas scrub. This stripping, which is arranged before acidification, allows for the separation of ammonium sulfate, ammonium nitrate, and ammonium formate.

[0031] The peat substitute obtained by the production process in one of the above-mentioned embodiments advantageously has a salt content of 0.5 to 1.5 g / l, a phosphate content of 0.3 to 0.6 g / l, and a nitrogen content of 0.05 to 0.15 g / l, and further preferably a potassium content of 0.3 to 0.6 g / l. As a result, the peat substitute produced by the described production process and the described plant is sufficiently low in salt and nutrients to be used as a soil improver in horticulture and agriculture without further treatment. The nitrogen content can be adjusted by the amount of suspension and wash water added. The salt and phosphate content can also be adjusted by selecting the pH value in the acidification step. The more salt and phosphate are dissolved, the lower the pH value is generally set within the specified spectrum.

[0032] It is pointed out that all features of the subject matter according to the invention described above are interchangeable or combinable with one another, unless an exchange or combination thereof is excluded for technical reasons.

[0033] The figures illustrate an exemplary embodiment of the invention. They show: Figure 1 shows a schematic structure of a system for carrying out a method according to the invention for producing a door replacement, Figure 2 shows an alternative structure of the system for carrying out the method according to the invention, and Figure 3 shows a further, alternative structure of the system for carrying out the method according to the invention.

[0034] As from Figure 1As can be seen, in the plant 2 shown here, a fiber suspension FS serving as starting material AS, which contains fibers from renewable or plant-based raw materials, is fed into a mixing device 4 of an acidification stage 6. The fiber suspension FS preferably contains agricultural residues LR, such as liquid manure and / or fermentation residues, or consists entirely of these.

[0035] As in Figure 1As shown, the fiber suspension FS fed into the mixing device 4 as starting material AS can optionally originate from a directly upstream or locally separate pretreatment stage 8, which, for example, has a pre-separation device 10. By means of this pretreatment stage 8, the agricultural residue LR serving as starting material AS can be largely separated, in particular from a liquid component, such as liquid manure G; in order to reduce the transport effort of the agricultural residue LR to the acidification stage 6 and / or to provide the fiber suspension FS in a composition suitable for treatment by the plant 2. For this purpose, the agricultural residue LR treated by the pre-separation device 10 can also be pre-mixed with water in the pretreatment stage 8 and / or in the mixing device 4 to form a suitable suspension (not shown).

[0036] If the optional pre-treatment stage 8 is used, the slurry G separated in the pre-separation device 10 can, for example, be passed on to a slurry storage facility 12 in order to be able to subject it to its own treatment or to be spread by means of a corresponding vehicle 14.

[0037] In any case, an acid S, preferably in the form of sulfuric acid, is added to the fiber suspension FS serving as the starting material AS in the mixing device 4 of the acidification stage 6. For this purpose, the acid S can be added to the mixing device 4 via a dosing device 16, preferably automatically controlled or regulated, such as, for example, depending on a pH monitor 18 provided in the mixing device 4. The mixing device 4 can, as shown, be formed, for example, by a stirred tank. Alternatively, the acidification stage 6 can also have a pipe with turbulence-generating means (not shown) for mixing the fiber suspension FS with the acid S.

[0038] In any case, the acidification stage 6 is followed by a first solids separation stage 20, in which a first filtrate F1 is separated from a first solids fraction FF1 of the fiber suspension FS. For this purpose, the first solids separation stage 20 comprises, for example, a screw press, an angle press, and / or a spiral filter.

[0039] The first solids separation stage 20 is in turn followed by a washing stage 22, in which the first solids fraction FF1 of the fiber suspension FS obtained by the first solids separation is mixed with rinse water SW in a washing step. Preferably, the first solids fraction FF1 is mixed with 2 to 4 times the mass of rinse water SW.

[0040] The washing stage 22 is then followed by a second solids separation stage 24, in which a second filtrate F2 is separated from a second solids fraction FF2 of the salt-reduced fiber suspension FS obtained in the washing step. For this purpose, the second solids separation stage 24 also comprises, for example, a screw press, an angle press, and / or a spiral filter.

[0041] The second solids separation stage 24 is in turn followed by a hygienization stage 26, in which the second solids fraction FF2 of the fiber suspension FS obtained by the second solids separation is thermally treated in a hygienization step. For this purpose, the hygienization stage 26 comprises, for example, a steam hygienization device 28 for applying steam to the second solids fraction FF2 and / or a hot air hygienization device 30 for applying hot air to the solids fraction FF2.

[0042] After the sanitization step, a peat substitute TE is produced that can be fully used in horticulture or agriculture without further treatment. The treatment process in Plant 2 proceeds as follows: In the acidification step carried out in acidification stage 6, the fiber suspension FS serving as the starting material AS is mixed with the acid S in the mixing device 4. Using the dosing device 16 and the pH monitor 18, a pH value of the fiber suspension FS is adjusted between 4 and 6, preferably between 5 and 6. This dissolves the precipitated salts contained in the starting material AS.

[0043] In the first solids separation stage 20, these dissolved salts are largely separated from the first solids fraction FF1 with the first filtrate F1. The resulting salt-reduced fiber suspension FS is then mixed with the rinse water in the washing step performed in the washing stage 22, in which the remaining salts can also be further dissolved.

[0044] In the second solids separation stage 24, the second filtrate F2, consisting predominantly of the rinse water SW and the salts now dissolved therein, is separated from the second solids fraction FF2. The fiber suspension FS, largely freed of salt in this way, is then thermally treated at temperatures above 80 °C in the sanitization step carried out in the sanitization stage 26, killing any germs and pathogens contained therein and denaturing any hormones and medications contained therein.

[0045] As a result, the peat substitute TE provided by the process has a salt content of only 0.5 to 1.5 g / l, a phosphate content of 0.3 to 0.6 g / l, a nitrogen content of 0.05 to 0.15 g / l and a potassium content of 0.3 to 0.6 g / l after the hygienization step, which means that it can be used in horticulture or agriculture without any problems and without further treatment.

[0046] Figure 2 shows an extended embodiment of Annex 2 according to Figure 1 or the manufacturing process that can be carried out therewith. In addition to the procedure described above, a treatment arrangement 32 is provided for carrying out a treatment process. In this arrangement, the first filtrate F1 produced in the first solids separation stage 20 is treated in such a way that it can be used in the washing stage 22 as rinse water SW for carrying out the washing step.

[0047] For this purpose, the treatment system 32 comprises a reverse osmosis device 34, which can be preceded by a microfiltration 36 for the retention of solid particles and optionally by a nanofiltration for the additional retention of fine organic matter (not shown). A hydroxide precipitation device 38, which comprises, for example, a stirred tank with sedimentation and sediment filtration, is connected upstream of the reverse osmosis device 34. The hydroxide precipitation device 38 serves to precipitate hardness-forming substances such as calcium and magnesium and to obtain phosphates in the form of phosphate salts.

[0048] Furthermore, the treatment system 32 can have a stripping device 40 downstream of the hydroxide precipitation device 38, by means of which nitrogen by-products in the form of ammonium sulfate solutions (ASL) can be separated. For this purpose, an acidic gas scrubbing process to expel the ammonia nitrogen can be carried out at the stripping device 40 after the stripping step by adding the acid S. Depending on the selected acid S, by-products such as ammonium sulfate, ammonium nitrate, ammonium formate, etc., can be obtained.

[0049] Furthermore, the treatment arrangement 32 has a post-acidification stage 42 upstream of the reverse osmosis device 34 for lowering the pH of the first filtrate F1 to be treated to a pH value of approximately 5. This shifts the ammonium-ammonia equilibrium towards ammonium, since this can be retained more completely in the reverse osmosis than ammonia.

[0050] The water purified by the reverse osmosis system 34 can thus be used as rinse water SW for the washing stage 22. If the available quantity of rinse water SW from the treatment system 32 is insufficient, additional fresh water FW can be used for the washing step. The reverse osmosis concentrate K also produced in the reverse osmosis system 34 can, for example, be fed together with the retained substances RS from the microfiltration system 36 to a common residue storage facility 44. The potassium-containing residue KS stored in this way can be used, for example, as potassium fertilizer.

[0051] Figure 3 shows Annex 2 with an alternative embodiment of the processing arrangement according to Figure 2 , in which the first filtrate F1 2 produced in the first solids separation stage 20, in contrast to the process according to Figure 2after the microfiltration device 36 is fed directly to the reverse osmosis device 34.

[0052] This procedure is particularly feasible if the calcium concentration of the first filtrate F1 after microfiltration 36 and, if applicable, additional nanofiltration (not shown) is sufficiently low so that no scaling or significant particle deposition is to be expected during reverse osmosis. This is particularly the case if the hardness range of the first filtrate F1 is as significantly below 50°dH as possible.

[0053] Following the reverse osmosis unit 34 is the hydroxide precipitation unit 38 for separating phosphate from the reverse osmosis concentrate, which can be used as phosphate fertilizer. Next is the stripping unit 40, where the stripping step and, if necessary, an acidic gas scrubbing process for expelling the ammonia nitrogen can take place with the addition of the acid S. Depending on the selected acid S, by-products such as ammonium sulfate, ammonium nitrate, ammonium formate, etc. can also be obtained here. Furthermore, the stripping unit 40 essentially produces potassium water KW, which can be collected in the corresponding storage unit 44 and, if necessary, fed for further treatment. The potassium water KW also produced in the stripping unit 40 can also be fed to a common residue storage unit 44 together with the retained substances RS from the microfiltration unit 36.The potassium-containing residue KS stored in this way can, for example, be used as potassium fertilizer.

[0054] The upstream reverse osmosis device 34 has the advantage in this process sequence that the purified water produced here can be used directly as rinse water SW for the washing stage 22, thus allowing significantly lower flow rates to be treated at the hydroxide precipitation device 38 and the stripping device 40. If the quantity of rinse water SW treated in this way is insufficient, additional fresh water FW can also be added to the washing stage 22 as needed.

[0055] In both manufacturing processes according to the embodiments according to the Figure 2 and 3 In addition to the low-salt peat substitute TE, several other usable solids are also obtained via the processing system 32.

[0056] It is pointed out that all elements and features of the various embodiments of the subject matter according to the invention described above are interchangeable or combinable with one another, unless an exchange or combination thereof is excluded for technical reasons.

Claims

1. Method for producing a peat substitute (TE) from a fibre suspension (FS) containing fibres from renewable raw materials, such as, in particular, a fibre suspension (FS) containing agricultural residues (LR), in which a first solids fraction (FF1) is separated from a first filtrate (F1) in at least a first solids separation step and a second solids fraction (FF2) is separated from a second filtrate (F2) in a second solids separation step downstream of the first solids separation step, in a hygienisation step, the solids fraction (FF2) obtained is hygienised, and the peat substitute (TE) is provided after the hygienisation step, wherein during the method acid (S) is added to the fibre suspension (FS) in an acidification step before the two solids separation steps in order to dissolve precipitated salts, after the acidification step in the first solids separation step, the first solids fraction (FF1) is separated from the first filtrate (F1) with the salts dissolved therein, and after the first solids separation step a washing step takes place in which the first solids fraction (FF1) is mixed with rinsing water (SW) characterized in that the first filtrate (F1) created in the first solids separation step is prepared in a treatment sequence and used as rinsing water (SW) in the washing step, and the hygienisation step is carried out downstream of the solids separation steps.

2. Method according to claim 1, characterized in that a pH value of the fibre suspension (FS) of 4 to 6 is set in the acidification step and the acid (S) in the acidification step is formed by sulphuric acid.

3. Method according to claim 1 or 2, characterized in that in the washing step the first solids fraction (FF1) is mixed with 2 to 4 times its mass in rinsing water (SW).

4. Method according to any one of claims 1 to 3, characterized in that after the washing step, in the second solids separation step, the salt-reduced second solids fraction (FF2) is separated from the second filtrate (F2), which consists substantially of the rinsing water (SW), and after the second solids separation step, the hygienisation step takes place, in which the salt-reduced second solids fraction (FF2) is subjected to a thermal treatment.

5. Method according to claim 4, characterized in that the salt-reduced second solids fraction (FF2) is exposed to steam or hot air in the hygienisation step.

6. Method according to any one of claims 1 to 5, characterized in that the fibre suspension (FS) is subjected to pre-separation prior to the acidification and the two solids separation steps.

7. Method according to any one of claims 1 to 6, characterized in that the first filtrate (F1) is treated by means of reverse osmosis in the treatment sequence and is preferably treated by hydroxide precipitation to precipitate Ca, Mg and / or phosphate before the reverse osmosis.

8. Method according to claim 7, characterized in that the first filtrate (F1) is post-acidified in the treatment sequence between the hydroxide precipitation and the reverse osmosis and preferably stripped before the post-acidification to separate nitrogen byproducts.

9. Plant (2) for performing a method for producing the peat substitute (TE) from the fibre suspension (FS) according to any one of claims 1 to 8, with a first solids separation stage (20) for performing the first solids separation step, a second solids separation stage (24) for performing the second solids separation step and a hygienisation stage (26) downstream of the second solids separation stage (24) for performing the hygienisation step, wherein an acidification stage (6) for performing the acidification step with a mixing apparatus (4) for mixing the fibre suspension (FS) with the acid (S) is provided upstream of the first solids separation stage (20), and a washing stage (22) for performing the washing step is provided downstream of the first solids separation stage (20), characterized in that the first solids separation stage (20) is connected to a treatment arrangement (32) by which the first filtrate (F1) can be prepared.

10. Production plant according to claim 9, characterized in that the mixing apparatus (4) is formed by an agitator vessel and / or a tube with turbulence generating means and has a pH monitor (18).

11. Production plant according to claim 9 or 10, characterized in that the first solids separation stage (20) and the second solids separation stage (24) each have a screw press, an angle press and / or a spiral filter.

12. Production plant according to any one of claims 9 to 11, characterized in that the hygienisation stage (26) has a steam hygienisation apparatus (28) and / or a hot air hygienisation apparatus (30).

13. Production plant according to any one of claims 9 to 12, characterized in that a pre-separation apparatus (10) for performing the pre-separation is provided upstream of the two solids separation stages (20, 24).

14. Production plant according to any one of claims 9 to 13, characterized in that the treatment arrangement (32) has a reverse osmosis apparatus (34) upstream of which a hydroxide precipitation apparatus (38) is preferably provided.

15. Production plant according to any one of claims 9 to 14, characterized in that a post-acidification stage (42) for lowering the pH of the filtrate is arranged in the treatment arrangement (32) between the hydroxide precipitation apparatus (38) and the reverse osmosis apparatus (34), and a stripping apparatus (40) for separating the nitrogen byproducts is preferably arranged upstream of the post-acidification stage (42).