EP3771771A1 - Simplified and efficient method for obtaining cellulose - Google Patents

Abstract

The present invention relates to a process for the production of cellulose or a mixture containing at least cellulose and at least lignocellulose from at least one aqueous substrate which is at least partially accessible to fermentation, comprising at least steps (1) to (3) and optionally (4), namely application of the aqueous substrate Substrate onto at least one sieve (step (1)), pressing the aqueous substrate onto the sieve by means of at least one pressing device with at least partial dewatering of the substrate and transferring this at least partially dewatered substrate onto and / or to the pressing device (step (2)), and removing the at least partially dehydrated substrate after performing step (2) from the pressing device used (step (3)) and optionally further dewatering of the at least partially dehydrated substrate obtained after step (3) (step (4)), step ( 4) if necessary one or more times like is repeated.

Description

The present invention relates to a method for the production of cellulose or a mixture containing at least cellulose and at least lignocellulose from at least one aqueous substrate which is at least partially accessible to fermentation, comprising at least steps (1) to (3) and optionally (4), namely application of the aqueous substrate Substrate onto at least one sieve (step (1)), pressing the aqueous substrate onto the sieve by means of at least one pressing device with at least partial dewatering of the substrate and transferring this at least partially dewatered substrate onto and / or to the pressing device (step (2)), and removing the at least partially dehydrated substrate after step (2) has been carried out from the pressing device used (step (3)) and optionally further dehydration of the at least partially dehydrated substrate obtained after step (3) (step (4)), step ( 4) possibly one or more times like is repeated.

State of the art / background

Cellulose is a chain-shaped polysaccharide, which usually has several thousand glucose units, which are linked via β-1,4-glycosidic bonds. The chains are twisted to form long, parallel arranged fibrils with a microcrystalline character. The result is the well-known fiber structure of cellulose with a solid character, which has a structured molecular structure. Lignocellulose consists of a framework made of cellulose and optionally also hemicellulose and optionally further polyoses. The framework has lignin. The lignins and other polyoses contained in the lignocellulose and their close physical bond with the cellulose give the fiber structure a particularly solid and resistant character.

Cellulose is an important raw material for paper production, for the manufacture of clothing items and can also be used as fuel for heating or as insulation material. Cellulose also serves as an important natural component of food and feed. In addition, many derivatives available from cellulose serve as starting materials for industrial applications: see above For example, xanthogenized cellulose is used for the production of viscose and, for example, methyl cellulose, cellulose acetate and cellulose nitrate are used in the construction industry, textile industry or in the chemical industry. Lignocellulose is used, for example, in the form of wood materials as a building material or fuel. Cellulose can also be broken down into glucose or oligomers of glucose by means of cellulase. These products are in turn used to manufacture other substrates such as ethanol, butyric acid, butanol, acetone, citric acid and itaconic acid.

Cellulose and also lignocellulose, in particular cellulose, are basically present in nature in large quantities, which is why there is a need for new processes for obtaining, in particular for isolating, these renewable raw materials from substrates containing biomass.

Substrates accessible for fermentation, such as raw sludge, in particular raw sludge originating from waste water, are known to the person skilled in the art. During fermentation, i.e. the anaerobic degradation of these substrates by microorganisms, methane fermentation is particularly important. In methane fermentation, methane and carbon dioxide are formed as the main end products at the end of the degradation chain by various microorganisms that live in dependence on one another. As is well known, the resulting gas mixture is also known as biogas and nowadays has a clear industrial and economic relevance, especially in the energy generation sector.

The substrates mentioned do not only consist of organic matter such as proteins, fats and water-soluble carbohydrates that are efficiently degradable during fermentation. Rather, they also contain, in particular, organic components such as cellulose and lignocellulose. The extraction of cellulose and / or lignocellulose, especially cellulose, from such substrates is made more difficult by the presence of many other organic components in such substrates: In particular, glycoproteins and glycolipids and a high concentration of organic compounds in dissolved form are to be mentioned here. The substrates used also often contain a high content of minerals. Are the substrates, especially from sewage Biologically treated raw sludge originating from raw sludge produces biomass that can be separated from the organic compounds present in dissolved form and contains in particular bacteria and other organisms as well as gel-like substances such as EPS (extracellular polymeric substances). The latter have to be separated from the cellulose fibers in the raw sludge.

Usually, when treating wastewater in sewage treatment plants, a rough pre-cleaning process is carried out using rakes and / or sand traps. The pre-treated wastewater is then transferred to a primary clarifier. The wastewater is slowly led through this basin, with impurities settling (sedimenting) or floating to the surface. The so-called primary sludge is obtained through the mechanical separation of these impurities. The remaining wastewater is then further purified by aerobic microorganisms, with the organic components present in the wastewater after mechanical cleaning being utilized by the aerobic microorganisms (aerobic activation system), so that finally sufficiently purified water is produced.

The microorganism population, which is constantly growing in the aerobic activation system due to the utilization of the impurities, is regularly separated off (secondary sludge, excess sludge) and mostly combined with the primary sludge.

The sludge resulting from the combination of primary sludge and secondary sludge is commonly referred to as raw sludge. It usually contains a comparatively high water content (98 to 99.5% by weight, based on the total weight of the raw sludge). The solid content is made up of the organic compounds described above as well as microorganisms originating from the secondary sludge and also usually contains a proportion of inorganic compounds. In addition to more stable compounds such as cellulose and / or lignocellulose, the organic fraction also contains easily putrefactive organic matter such as water-soluble polysaccharides, proteins and fats. This digestion produces, for example, low molecular weight fatty acids, ammonia or hydrogen sulfide.

In the next step, the raw sludge is usually subjected to controlled anaerobic digestion or fermentation in digestion towers. The easily putrefactive compounds are gradually broken down by anaerobic bacterial cultures. In a first phase, the so-called hydrolysis and acidification phase, the substances are converted by appropriate microorganisms mainly into lower fatty acids or carboxylic acids and alcohols as well as hydrogen and carbon dioxide. Acetic acid is ultimately produced via the acetogenic phase, which is then converted into methane and carbon dioxide by appropriate microorganisms (methane bacteria) in the second stage, the methane phase. In addition, the conversion of hydrogen and carbon dioxide into methane and water is effected. In addition to the main product methane, which is specifically discharged and then used as a biogas component or for general energy generation (grid feed-in), nitrogen-based compounds such as ammonia or corresponding ammonium salts are also produced in the digestion tower. The so-called digested sludge (stabilized sewage sludge) that remains after the roughly 20 to 30-day digestion process contains not only inorganic compounds, for example the inorganic ammonium salts mentioned, but also the more stable organic compounds mentioned, in particular cellulose and lignocellulose, which are not or only one in the digestion tower implemented or reduced. Often larger solid particles and agglomerates that are present in the original raw sludge are only incompletely decomposed, although they contain the anaerobically decomposable substances. The reason for this is that the attack surface for the anaerobic conversion in such agglomerates is correspondingly small.

Methods for wastewater treatment are for example from EP 1 310 461 A1 , EP 0 960 860 A1 , US 2003/192831 A1 , JP 2005-046691 A and the U.S. Patent 4,370,235 known.

Sufficient targeted separation of cellulose and / or lignocellulose, in particular cellulose, from the raw sludge or from primary sludge by mechanical methods such as sedimentation, sieving, filtration or centrifugation, however, does not succeed with the conventional methods. The raw sludge possesses extremely poor sedimentation and drainage properties and cannot be separated satisfactorily by other methods. In particular, sufficient targeted separation of cellulose and / or lignocellulose, in particular cellulose, from the raw sludge by conventional disintegration processes cannot be achieved to a sufficient extent, since the raw sludge is still in a highly viscous, viscous form even after disintegration, with the fibers contained therein and gel-like fractions, a felt-like, strongly conglomerated character of the raw sludge results, which means that the sludge is very difficult to access, if at all, for subsequent mechanical separation. Although a slight improvement is achieved through disintegration, this is usually not sufficient. The same applies to the other substrates known to the person skilled in the art which are used for methane fermentation and which also have the aforementioned fibrous and gel-like constituents. Even with substrates that are accessible for fermentation, for example grass and maize or grass and maize silage, liquid manure or biowaste, it would be of enormous advantage if an advantageous and economical form of processing would allow the usable compounds cellulose and / or lignocellulose contained therein to be achieved could be isolated.

Another method for wastewater treatment is also off WO 2015/011275 A1 known. However, this method requires a step with ultrasound treatment using a suitable ultrasound device. The method is therefore comparatively complex to carry out and therefore has disadvantages, in particular from an economic point of view.

There is therefore a need for an improved and, in particular, simplified process which enables the targeted separation, in particular isolation, of cellulose and / or lignocellulose, in particular cellulose, from substrates that are at least partially accessible for fermentation, such as raw sludge originating in particular from waste water or from primary sludge.

problem

It is therefore an object of the present invention to provide a method for obtaining cellulose and / or lignocellulose from at least one substrate that is at least partially accessible to fermentation, such as raw sludge originating in particular from wastewater or directly from primary sludge, in particular such a method which has advantages over the conventional methods known from the prior art. In particular, it is an object of the present invention to provide such a method which makes it possible to separate cellulose and / or lignocellulose, in particular cellulose, from substrates that are at least partially accessible for fermentation, such as raw sludge, in particular, from waste water or directly from primary sludge, wherein the method should be advantageous in particular from an economic point of view and also represents a simplification in comparison to known methods.

solution

This object is achieved by the subject matter claimed in the patent claims and the preferred embodiments of this subject matter disclosed below in the present description.

1. (1) Aufbringen des wässrigen Substrats auf wenigstens ein Sieb,
2. (2) Anpressen des wässrigen Substrats auf das Sieb mittels wenigstens einer Anpressvorrichtung unter zumindest teilweiser Entwässerung des Substrats und Übertragung dieses zumindest teilweise entwässerten Substrats auf und/oder an die Anpressvorrichtung,
3. (3) Entfernen des zumindest teilweise entwässerten Substrats enthaltend Cellulose oder einer Mischung enthaltend wenigstens Cellulose und wenigstens Lignocellulose nach der Durchführung von Schritt (2) von der eingesetzten Anpressvorrichtung, sowie
4. (4) gegebenenfalls weitere Entwässerung des nach Schritt (3) erhaltenen zumindest teilweise entwässerten Substrats enthaltend Cellulose oder einer Mischung enthaltend wenigstens Cellulose und wenigstens Lignocellulose, wobei Schritt (4) gegebenenfalls ein- oder mehrfach wiederholt wird.

The present invention therefore relates to a process for the production of cellulose or a mixture containing at least cellulose and at least lignocellulose from at least one aqueous substrate at least partially accessible to fermentation and containing cellulose or containing a mixture containing at least cellulose and at least lignocellulose comprising at least the steps (1 ) to (3) and optionally (4), namely

1. (1) applying the aqueous substrate to at least one sieve,
2. (2) pressing the aqueous substrate onto the sieve by means of at least one pressing device with at least partial dewatering of the substrate and transferring this at least partially dewatered substrate to and / or to the pressing device,
3. (3) removing the at least partially dehydrated substrate containing cellulose or a mixture containing at least cellulose and at least lignocellulose after performing step (2) from the pressing device used, and
4. (4) optionally further dehydration of the at least partially dehydrated substrate obtained after step (3) containing cellulose or a mixture containing at least cellulose and at least lignocellulose, step (4) optionally being repeated one or more times.

It has surprisingly been found that the method according to the invention enables cellulose or a mixture containing at least cellulose and at least lignocellulose to be obtained from at least one aqueous substrate that is at least partially accessible to fermentation, such as from raw sludge or in particular from primary sludge, and these compounds thus for a large number of Branches of industry and for a variety of applications.

In particular, it was surprisingly found that the method according to the invention enables cellulose or a mixture containing at least cellulose and at least lignocellulose, in particular cellulose, to be produced in high yields, for example of up to 60% by weight, based on the total solids content of the fermentation used at least partially accessible aqueous substrate and / or high degrees of purity, for example in a purity in the range from 75 to 95% by weight. From the cellulose obtained in this way, glucose or oligomers of glucose can be obtained in particular by means of cellulase, which in turn can be used - in particular by microorganisms - for the production of other substrates such as ethanol, butyric acid, butanol, acetone, citric acid and itaconic acid.

In addition, it has surprisingly been found that the method according to the invention makes it possible to use aqueous fermentation which is at least partially accessible Substrates such as raw sludge or, in particular, primary sludge without energy-intensive processing such as one at high temperatures, in particular at temperatures> 100 ° C, to be converted into a state that enables cellulose or a mixture containing at least cellulose and at least lignocellulose from this substrate such as Raw sludge, or in particular primary sludge, to obtain and isolate.

In addition, it was surprisingly found that the method according to the invention makes it possible to convert at least partially accessible aqueous substrates used for fermentation, such as raw sludge or in particular primary sludge, into a state that in turn makes it possible to cellulose without the comparatively expensive use of an ultrasonic device and thus without having to undergo an ultrasonic treatment or to obtain and isolate a mixture containing at least cellulose and at least lignocellulose from this substrate such as raw sludge or in particular primary sludge.

In particular, surprisingly, it has been shown that the solution of the problem on which the present invention is based can be achieved by combining the process parameters of steps (1) and (2) and (3), in particular by pressing according to step (2), of the process according to the invention , since after step (2) has been carried out, the at least partially dewatered substrate remains adhering to the pressing device like a roller and can be removed therefrom in a simple manner in step (3). Further dehydration and thus concentration of cellulose or cellulose / lignocellulose is possible by running through step (4) one or more times.

In particular, it was also surprisingly found in this context that in particular a large part of the many other organic constituents which are present in high concentration in dissolved form in the substrate used, such as primary sludge, are separated in a simple manner by step (2) in the context of the dewatering carried out in this way and can therefore no longer have a disruptive influence on the further process. In particular, the dissolved, colloidal and non-fibrous components of the substrate used, such as primary sludge, can thus be removed from the cellulose or cellulose / lignocellulose fibers are largely separated and these fibers are further cleaned and enriched in subsequent steps.

Detailed description

The inventive method for obtaining cellulose or a mixture containing at least cellulose and at least lignocellulose from at least one of the fermentation at least partially accessible aqueous substrate containing cellulose or containing a mixture containing at least cellulose and at least lignocellulose comprising at least steps (1) to (3) and if applicable (4),

Ultimately, all substrates known to the person skilled in the art in connection with fermentation, in particular methane fermentation, and the associated biogas production can be used as substrates at least partially accessible to fermentation. Ultimately, this includes all substrates that contain decomposable or fermentable organic compounds. Fermentation is known to refer to the anaerobic degradation of organic compounds by microorganisms, i.e. the decomposition of more complex, possibly polymeric organic compounds such as polysaccharides, fats and proteins into low molecular weight compounds such as methane, carbon dioxide and water, as well as ammonia and hydrogen sulfide. Fiber-containing materials are particularly preferably used. Such substrates include, for example, grass and maize as well as grass and maize silage, thin pulp, fodder beet, whole plant silages, green waste, stalk-like biomass, industrial fruit, liquid manure, press cake, rapeseed meal, rapeseed cake, beet leaf silage, sugar beet, liquid manure, biowaste and raw sludge from sewage and, in particular, primary sludge. The at least one substrate that is at least partially accessible to fermentation and used in the process according to the invention contains cellulose or a mixture containing at least cellulose and at least lignocellulose in at least certain amounts that can be separated therefrom, particularly preferably in a proportion of up to 70% by weight, for example in one Proportion from 20 to 60% by weight, based on the total solids content of the substrate used. Determination methods for determining the Solid content are known to the person skilled in the art. The solids content is preferably determined in accordance with EN 12880 (S2A) by determining the dry residue.

Preferably, the at least one substrate that is at least partially accessible to fermentation is selected from the group consisting of grass, maize, grass silage, maize silage, thin pulp, fodder beet, whole plant silages, green waste, stalk-like biomass, industrial fruit, liquid manure, press cake, rapeseed meal, rapeseed cake, beet leaf silage, sugar beet, Liquid manure, biowaste and raw sludge originating from waste water, in particular primary sludge, secondary sludge and / or digested sludge, and mixtures thereof, but most preferably primary sludge.

Preferably, raw sludge or primary sludge, preferably primary sludge, is used as the at least one aqueous substrate that is at least partially accessible to fermentation. The reason for this is in particular that the predominant part of cellulose or cellulose / lignocellulose is present within the primary sludge.

The at least one substrate which is at least partially accessible to fermentation is aqueous, i.e. contains water. The at least one substrate which is at least partially accessible to fermentation is particularly preferably in the form of an aqueous mixture. It goes without saying that the substrate used according to the invention comprises at least cellulose or a mixture containing at least cellulose and at least lignocellulose, so that a corresponding extraction is possible.

The term “primary sludge” is known to the person skilled in the art. This is preferably understood to mean that sludge that is obtainable after (a) mechanical purification of wastewater in sewage treatment plants, for example by means of rakes and / or sand traps, and (b) subsequent mechanical separation of sedimented and / or surface (floated) impurities, for example by raking and / or sand traps after passing through a sedimentation.

The method according to the invention preferably does not include a step that provides for an ultrasonic treatment.

Each of steps (1) to (3) and optionally (4) is preferably carried out at a temperature <100 ° C, in particular <80 ° C or <60 ° C, most preferably <40 ° C. This preferably applies to the entire method according to the invention.

Step (1) of the method according to the invention

Step (1) of the method according to the invention provides for the aqueous substrate to be applied to at least one sieve. The sieve used can also be referred to as a filter.

The sieve used is preferably comparatively large-meshed.

When performing step (1), the pore size of the sieve or the filter is selected so that the anisotropic, elongated fibers of cellulose or a mixture containing at least cellulose and at least lignocellulose remain on the sieve or filter material, while the other particles remain like the spherical ones inorganic particles, which as a rule have particle sizes of less than 100 μm, for example less than 75 μm or less than 50 μm or less than 25 μm or less than 10 μm (measured using a microscope or wet sieving) together with the water still present or optionally added through the Pass the sieve. Corresponding sieving and filtration systems and a corresponding selection of sieves and / or filters can be easily selected by the person skilled in the art. An overview of the separation processes and separation principles that can be used can be found in the general technical literature, for example from " Technical Microbiology "by Hermann Kretzschmar, pages 265 to 286, (Parey, 1968, ISBN 3489715144 ) or the manual " Filters and Filtration Handbook "(Elsevier, Advanced Technology, 4th Edition, ISBN 185617322 ).

The sieve used in step (1) preferably has a pore diameter that is 2 mm, but is at least 0.1 mm. The sieve used in step (1) particularly preferably has a pore diameter in the range from 0.2 to 1 mm, preferably from 0.3 to 0.8 mm. The pore diameter corresponds to the mesh size of the sieve used. The mesh size is determined in accordance with DIN ISO 3310-1 (2017-11).

If the pore diameter is <0.1 mm, in particular if it has a pore diameter in the micrometer range, then undesirable clogging of the screen can occur.

The sieve used in step (1) is preferably a non-moving and non-moving sieve. Alternatively, the sieve used in step (1) can be moved, in particular a rotatable sieve is used in this case. The sieve is preferably mounted horizontally.

The screen used in step (1) is preferably a drum screen, screen belt and / or screen fabric. Corresponding sieves are also referred to as drum filters, belt filters and / or mesh filters.

Step (1) is preferably carried out under normal pressure (1 bar). Preferably, step (1) is not carried out with the application of pressure.

In accordance with step (1), the application is preferably carried out by means of a distributor device, in particular uniformly.

Step (2) of the method according to the invention

Step (2) of the method according to the invention provides for pressing the aqueous substrate onto the screen by means of at least one pressing device with at least partial dewatering of the substrate and transferring this at least partially dewatered substrate onto and / or to the pressing device. Step (2) can take place before step (3) is carried out, but it is also possible to carry out steps (2) and (3) simultaneously.

By means of step (2), a filtrate with a higher water content than the substrate can be obtained prior to performing step (2). The filtrate contains a large part of the undesirable organic compounds present in dissolved form as well as non-fibrous components. The latter get into the filtrate in particular due to the selected pore diameter of the sieve used in step (1). The at least partially dehydrated substrate, on the other hand, can surprisingly stick to the pressing device and is thus transferred to the pressing device during step (2). The essentially fibrous constituents, in particular cellulose and / or lignocellulose fibers, are thus lifted off the sieve and form the at least partially dehydrated substrate on and / or on the pressing device. In contrast, the dissolved, colloidal and particulate, non-fibrous components are separated off with the liquid (filtrate). Within the at least partially dewatered substrate, an accumulation of the cellulose and / or lignocellulose fibers to be obtained thus takes place.

The pressing device used in step (2) is preferably at least one roller and / or at least one stamp, preferably at least one roller, particularly preferably at least one pressure roller.

The pressing according to step (2) is preferably carried out by passing over the substrate applied to the screen in step (1) by means of the pressing device such as a roller, which results in a transfer of the at least partially dehydrated substrate with an enriched proportion of cellulose and / or lignocellulose -Fibers on and / or on the pressing device such as the roller.

The pressing device used in step (2) is particularly preferably at least one rotating roller. As a result of the rotary movement of the roller, the at least partially dewatered substrate is lifted from the screen and can be removed from the pressing device in the following step (3) for further processing.

The at least partially dehydrated substrate preferably has a solids content of at least 8% by weight, preferably of at least 10% by weight, after step (2) has been carried out. Determination methods for determining the solids content are known to the person skilled in the art. The Solids content is determined in accordance with EN 12880 (S2A) by determining the dry residue.

Step (2) is preferably carried out under normal pressure (1 bar). Preferably, step (2) is not carried out with the application of air pressure.

Step (3) of the method according to the invention

Step (3) of the method according to the invention provides for removing the at least partially dehydrated substrate containing cellulose or a mixture containing at least cellulose and at least lignocellulose after performing step (2) from the pressing device used.

Preferably, the removal according to step (3) takes place by means of at least one scraping device such as a scraper, for example. In particular when steps (2) and (3) are carried out simultaneously, the scraping device used in step (3) is preferably connected to the pressing device used in step (2) such as the roller used. For example, a sheet metal such as a metal sheet can be used as a scraping device, which is mounted on the rear side of the roller and, when the roller rotates, removes the at least partially dewatered substrate transferred to and / or to the pressing device.

The at least partially dehydrated substrate is preferably transferred to a conveyor belt and / or a screw by means of the scraper device - if necessary after having passed through step (4) one or more times, as described in more detail below.

Optional step (4) of the method according to the invention

The optional step (4) of the process according to the invention provides for further dewatering of the at least partially dehydrated substrate obtained after step (3) and containing cellulose or a mixture containing at least cellulose and at least lignocellulose.

The further dewatering according to step (4) is preferably carried out in that the at least partially dewatered substrate obtained after step (3) is applied again to the screen used in step (1) and steps (1), (2) and (3) repeated one or more times. Step (4) is preferably carried out and steps (1), (2) and (3) are repeated at least once.

The at least partially dehydrated substrate preferably has a solids content of at least 12% by weight, particularly preferably at least 14% by weight, very particularly preferably at least 16% by weight or at least 18 after the at least one simple implementation of step (4) % By weight, and most preferably at least 20% by weight. Determination methods for determining the solids content are known to the person skilled in the art. The solids content is determined in accordance with EN 12880 (S2A) by determining the dry residue.

Optional step (4a) of the method according to the invention

Optional step (4a) of the process according to the invention provides for further dewatering of the at least partially dehydrated substrate containing cellulose or a mixture containing at least cellulose and at least lignocellulose obtained after step (3) or optionally step (4).

The further dewatering according to step (4a) is preferably carried out by means of a system of at least two counter-rotating rollers, between which the at least partially dewatered substrate obtained after step (3) or after step (4) is carried out and / or moved, with step (4a) can optionally be repeated one or more times. The two rollers are pressed against each other in opposite directions. The substrate is in between. Step (4a) is preferably repeated at least once.

Optional step (5) of the method according to the invention

The optional step (5) of the method according to the invention provides for a treatment of the further dehydrated substrate obtained after step (3) or the further dehydrated substrate obtained after step (4), preferably with exclusion of air, to a temperature in the range from 20 to 70 ° C.

Step (5) serves to hydrolyze the dissolved substances contained in the remaining aqueous mixture and the dissolved, colloidal, biodegradable substances still adhering to the cellulose or cellulose / lignocellulose fibers, or this process, even with a low water content to accelerate. As a result, surprisingly, despite the comparatively low water content, rapid fermentation takes place with hydrolysis of the insoluble, non-cellulose / lignocellulose components and conversion into soluble compounds, in particular fatty acids and ammonia. By washing with a small amount of water, a very concentrated solution can be obtained from the insoluble constituents, which can be broken down very effectively and inexpensively in a granular reactor.

The further dehydrated substrate is preferably washed with water after step (5). After the water has been squeezed out (while maintaining press water), it is preferably treated with lye. After renewed washing with water and renewed squeezing of the water (while obtaining press water), cellulose or a mixture containing at least cellulose and at least lignocellulose is preferably obtained. The proportion of cellulose or cellulose / lignocellulose is high enough to process it further. The proportion of cellulose or of a mixture of cellulose and lignocellulose is preferably 75 to 95% by weight, in particular 80 to 90% by weight, in each case based on the total solids content. Further impurities can be removed by adding lye, in particular sodium hydroxide solution. The press water contains the majority of the remaining colloidal, dissolved solids. Minerals are also enriched in it, ie the minerals are depleted in the fibers. The colloidal, suspended substances can be separated by sedimentation and with a decanter be enriched. The concentrate obtained in this way can then be fermented, in particular within one day.

Optional step (6) of the method according to the invention

The optional step (6) of the method according to the invention provides for a treatment of the further dewatered substrate obtained after step (3) or the further dehydrated substrate obtained after step (4) with an alkali and can be carried out as an alternative to the optional step (5). However, step (5) can then optionally also be carried out after step (6) has been carried out. An aqueous solution of a suitable base such as NaOH can be used as the lye.

By means of the method according to the invention, not only cellulose or cellulose / lignocellulose can be obtained in high yield and high purity, but it has also been shown that the filtrate obtained after step (1) can advantageously be further processed: the liquid running through the sieve (Filtrate) can be converted into a low-solids fraction and a high-solids, fiber-poor suspension (sludge) by sedimentation and decanter. Due to the rapid treatment, the low-solids liquid contains only a few dissolved organic compounds (no additional organic compounds from fermentation from solids) and can be transferred directly to the biological treatment. In the event that, due to its special origin, the wastewater contains high proportions of dissolved organic ingredients, the wastewater can be fed through granular methane fermentation. Because of the effectiveness of these reactors, high conversion rates are obtained. The fermentable, enriched, non-fibrous particles (solid-rich suspension) can be hydrolyzed anaerobically (ie brought into solution) and the liquid converted separately into methane.

Examples and comparative examples

The following examples and comparative examples serve to illustrate the invention, but are not to be interpreted as restrictive.

1. Exemplary description of the method according to the invention

Approx. 100 liters of primary sludge (from the Radevormwald sewage treatment plant, containing approx. 2% by weight solids in accordance with EN 12880 (S2A) via determination of the dry residue) are manually applied in a layer thickness of 5-10 mm and a width of approx. 100 mm applied to the upper sieve of a screening plant. The upper sieve is made of stainless steel. The mesh size (pore diameter) is 0.4 mm. The screening plant also includes a support screen (stainless steel, mesh size 4 mm). A roller is moved over the material without additional pressure. The roller is a steel roller (approx. 200 mm wide, 120 mm in diameter, weight 17.4 kg with holes on both sides for a pulling device (pressure / cm screen width 0.87 kg / cm contact surface). On the back A sheet metal is mounted on the roller, which serves as a scraper and removed the pressed material. The sieve passage was collected in a trough (300 x 1000 mm with floor drain). The first sieve passage that sticks to the roller (approx. 20 kg), contains 10.0-11.0% by weight solids, the sieve passage 0.4-0.5% by weight solids (approx. 80 liters) The dewatered material obtained in this way is treated a second time in the same way The second treatment (approx. 19 kg used) results in 8 liters of sieve passage with 1.4-1.5% by weight of solids. The second passage of sieve, which sticks to the roller, contains 16.0-16.4% by weight % Solids.

The content of dissolved COD, ie of dissolved organic compounds relating to the sieve passages, increased only insignificantly. The COD of the centrifuge supernatant of the primary sludge and of the centrifuge supernatant of the sieve passage was examined. The chemical oxygen demand (COD) is determined in accordance with DIN 38409 H41. This is a measure of the dissolved organic oxidizable constituents in the centrifuge supernatant. The COD indicates the amount of oxygen (in mg / L), ie the amount of oxygen in mg per L des Centrifugation supernatant, which is required for the oxidation of the organic oxidizable ingredients contained in this liter.

1. 1. Siebdurchgang: 1260 mg/l
2. 2. Siebdurchgang: 2780 mg/l

The following COD values were determined:
Primary sludge centrifuge supernatant: 1100 mg / l

1. 1st sieve pass: 1260 mg / l
2. 2nd sieve pass: 2780 mg / l

The sieve passage can therefore be transferred to the biology after sedimentation without additional pollution. The sieve passage contained very few fibrous materials that can be removed by simple sieving if necessary.

Treatment with small amounts of sodium hydroxide allows high concentrations of dissolved organic compounds to be extracted from the sieve passage (4 g NaOH / kg in the case of the second sieve passage, COD value of dissolved organic substances: 21,000 mg / l). The higher the determined COD value, the more organic compounds can be efficiently separated from cellulose to be recovered or the mixture to be recovered containing at least cellulose and at least lignocellulose by the method according to the invention, whereby cellulose or cellulose / lignocellulose is efficiently recovered in a simplified process becomes.

Claims (15)

A process for the production of cellulose or a mixture containing at least cellulose and at least lignocellulose from at least one of the fermentation at least partially accessible aqueous substrate containing cellulose or containing a mixture containing at least cellulose and at least lignocellulose comprising at least steps (1) to (3) and optionally (4), namely (1) applying the aqueous substrate to at least one sieve, (2) pressing the aqueous substrate onto the sieve by means of at least one pressing device with at least partial dewatering of the substrate and transferring this at least partially dewatered substrate onto and / or to the pressing device, (3) removing the at least partially dehydrated substrate after performing step (2) from the pressing device used, and (4) optionally further dehydration of the at least partially dehydrated substrate obtained after step (3), step (4) optionally being repeated one or more times. The method according to claim 1, characterized in that the sieve used in step (1) has a pore diameter which is ≤ 2 mm, but is at least 0.1 mm. The method according to claim 1 or 2, characterized in that the sieve used in step (1) has a pore diameter in the range from 0.2 to 1 mm, preferably from 0.4 to 0.8 mm. The method according to one of the preceding claims, characterized in that the screen used in step (1) is a drum screen, screen belt and / or screen fabric. The method according to one of the preceding claims, characterized in that the pressing device used in step (2) is at least one roller and / or at least one punch, preferably at least one roller. The method according to one of the preceding claims, characterized in that the pressing device used in step (2) is at least one rotating roller. The method according to any one of the preceding claims, characterized in that the at least partially dehydrated substrate has a solids content of at least 8% by weight, preferably of at least 10% by weight, after performing step (2). The method according to one of the preceding claims, characterized in that the removal according to step (3) is carried out by means of at least one scraping device. The method according to one of the preceding claims, characterized in that the further dewatering according to step (4) takes place in that the at least partially dewatered substrate obtained after step (3) is applied again to the sieve used in step (1) and the steps (1), (2) and (3) are repeated one or more times. The method according to claim 9, characterized in that the at least partially dehydrated substrate after the at least simple implementation of step (4) has a solids content of at least 12% by weight, particularly preferably of at least 14% by weight, very particularly preferably of at least 16 wt% or at least 18 wt%, and most preferably at least 20 wt%. The method according to one of the preceding claims, characterized in that it also comprises a further step (4a) after step (3) has been carried out or, if appropriate, after step (4) has been carried out at least once, namely
(4a) further dewatering of the substrate by means of a system of at least two counter-rotating rollers, between which the substrate is passed. The method according to any one of the preceding claims, characterized in that it also comprises a further step (5) after performing step (3) or optionally step (4), namely
(5) Treating the further dehydrated substrate obtained after step (3) or optionally after step (4), preferably with exclusion of air, at a temperature in the range from 20 to 70.degree. The method according to any one of claims 1 to 11, characterized in that it also comprises a further step (6) after performing step (3) or optionally step (4), namely
(6) Treating the further dehydrated substrate obtained after step (3) or optionally after step (4) with an alkali. The method according to any one of the preceding claims, characterized in that the method does not include a step that provides ultrasonic treatment. The method according to one of the preceding claims, characterized in that raw sludge or primary sludge, preferably primary sludge, derived from waste water is used as the at least one substrate which is at least partially accessible to fermentation.