Method for sludge dewatering, device and use thereof

Abstract

The invention relates to a method for sludge dewatering, comprising the steps of: measuring one or more properties of the sludge, wherein said properties are selected from: moisture content, total solids (TS), volatile solids (VS), fixed solids (FS), total suspended solids (TSS), density, pH value, electrical conductivity, chemical oxygen demand (COD), biochemical oxygen demand (BOD). The invention is characterized in that the sludge mixed with a flocculant is filled into a filter tube and, beforehand, the flocculant is determined in dependence on the measured property or properties of the sludge.

Description

[0001] Eisenführ Speiser

[0002] Hamburg, January 16, 2026

[0003] Our reference: NH 646-02WO LBI / akp / mwi / bki

[0004] Applicant / Owner: Naue GmbH & Co. KG

[0005] Official file number: New registration

[0006] Naue GmbH & Co. KG

[0007] Gewerbestraße 2, 32339 Espelkamp

[0008] Methods for sludge dewatering, apparatus and their use for this purpose

[0009] The invention relates to a method for sludge dewatering using a filter hose, a filter hose for sludge dewatering and a use of such a filter hose for sludge dewatering.

[0010] Sludge dewatering is used when water-containing sludge is unsuitable for further use or disposal, or when prior separation of the solids from the water in the sludge is advantageous for such further use or disposal.

[0011] Sludge dewatering is known to be carried out using separator devices such as screw separators, in which the sludge is dewatered under high pressure through a sieve or a developing filter cake. Such separator devices offer efficient dewatering for sludges with a specific composition, but require significant equipment and regular maintenance.

[0012] From US 2024 / 0254028 A1, it is known to dewater water-containing sludge by filling it into a filter bag made of a multi-layered fabric and dewatering it by allowing the water content of the sludge to pass through the fabric of the filter bag. Multi-layered fabrics with certain tensile strengths are described as particularly suitable, whereas so-called "non-woven" materials are unsuitable for dewatering using such a filter bag due to their rapid clogging of pores. Furthermore, due to the necessary design for sufficient long-term load-bearing capacity in such dewatering applications, they are unsuitable for long-term landfilling or hydrocarbon recovery. The multi-layered fabric bags used according to this prior art have a specific pore size.For effective sludge dewatering with such hoses, the woven hoses must possess a tensile strength appropriate to the pressure conditions to prevent rapid clogging of the fabric openings. This approach to sludge dewatering is also necessary because the filter bag is designed to be biodegradable. This biodegradability further limits its use to short-term, rapid dewatering at elevated pressure. Besides the problematic clogging of the fabric openings at insufficient pressure inside the filter bag, a reduction in mechanical strength also occurs over time. This means that after a certain dewatering period, the filter bag can no longer withstand the pressures required for effective dewatering, and failure due to rupture is imminent.To prevent this, this prior art proposes a special sewing technique for manufacturing the hose, which is particularly well-suited for woven materials and provides high seam strength to ensure sufficient mechanical strength even in the event of partial biodegradation. However, a disadvantage is that the use of this type of dewatering via a woven bag is only applicable to certain types of sludge and is highly sensitive to sludge components that unexpectedly accelerate biological degradation, potentially leading to total failure. If further use of the dried sludge beyond mere landfilling is desired, a further problem lies in efficiently managing this subsequent use of the dried sludge.For numerous applications, it is necessary to separate the dried sludge and the filter bag as carefully as possible after drying, which requires elaborate separation steps in order to be able to use the sludge for further purposes beyond mere landfilling.

[0013] A method for removing residues from a tank is known from CN 118084287. For this process, the residues are mixed with water to form a flowable mass, combined with 0.05 to 0.1% (based on the dry mass ratio) of polyaluminum chloride and polyacrylamide in a ratio of 10-30:1 as solidifying additives, and filled into a bag. The bag is made of age-resistant, woven polypropylene with a thickness of 170-180 g / m². A disadvantage of this method is the relatively long dewatering period required, up to 25 days, combined with a still significant solids content in the water exiting the bag.

[0014] A sludge drying process is known from CN111574013, in which the sludge is pumped onto a flat vibrating screen to remove large solids, subsequently the sludge is pressurized, pumped into a chemical feeding and mixing device, and then the flocculated sludge is filled into a geotextile, woven bag and dewatered therein. A disadvantage of this process is that a solids content of only 60 to 70% is achieved after up to four weeks.

[0015] From RU2741566C1, another multi-stage mechanical-biological-chemical process for sludge dewatering is known. In this process, the sludge is first fed into a slotted screen, denitrified, nitrified, biofiltered, and then temporarily stored. Subsequently, a coagulant, a flocculant, and an alkaline solution are added to the sludge, which is then heated to a temperature of 65°C and filled into bags made of a non-woven polymer material. The process is technologically very complex and energy-intensive.

[0016] The object of the invention is to propose a method for sludge dewatering, a device for sludge dewatering and a use of this device for sludge dewatering in such a way that these disadvantages arising from the prior art are at least partially overcome.

[0017] This problem is solved according to the invention by a method for sludge dewatering, comprising the steps:

[0018] a. Measuring a property of the sludge, wherein this property is selected from: moisture content, dry matter (DM), organic solids (oDM), inorganic solids (iDM), total suspended solids (TSS), density, pH value, conductivity, chemical oxygen demand (COD), biochemical oxygen demand (BOD), nitrogen concentration, in particular as total nitrogen concentration, ammonium nitrogen concentration, nitrate nitrogen concentration or nitrite nitrogen concentration, phosphorus concentration, in particular as total phosphorus concentration or concentration of soluble phosphorus components, potassium concentration, concentration of volatile organic compounds, oil content and fat content; b. Selecting a flocculant depending on the measured property of the sludge.

[0019] c. Adding the selected flocculant to the sludge,

[0020] d. Pouring the sludge containing the flocculant into a filter hose,

[0021] e. Storing the filter hose on a base for a drainage period, and

[0022] f. At least one refilling of the filter bag with sludge containing the flocculant after the drainage period has ended and storage of the filter bag on the base for a second drainage period.

[0023] According to the invention, a filter bag is used for sludge dewatering, which is filled with the sludge to be dewatered. The method according to the invention provides that a property of the sludge to be dewatered is determined by measurement before the filter bag is filled. This property can be physical, chemical, or biological. One or more properties can be determined. For example, by measuring the moisture content, dry matter content, density, or electrical conductivity, the sludge's capacity for rapid or slow dewatering can be inferred, and the dewatering period required to achieve a predetermined degree of dewatering or drying rate can be determined.Furthermore, by determining sludge properties such as pH value, electrical conductivity, chemical or biochemical oxygen demand, and the concentration of certain substances within the sludge, the rate of effective dewatering can be estimated. In particular, one or more of the measured properties can be used to determine which flocculant should be advantageously selected and what concentration of the selected flocculant can effectively support sludge dewatering by achieving flocculation within the sludge through a reaction during dewatering, thereby creating favorable conditions for effective and rapid sludge dewatering.

[0024] Basically, it should be understood that the proportion, content, or concentration of certain substances within the sludge to be dewatered is determined as a percentage by weight, and the selection of the appropriate flocculant is based on this value. The sludge properties can be measured using the following methods in particular:

[0025]

[0026] It should be understood that a measurement can optionally be carried out according to DIN standard specifications or according to the standard method SM used in the US; the deviations resulting from these measurement methods and the accuracy of the results do not affect the function and effect of the invention any more than deviations that arise within or outside such standards due to different measurement methods or measuring instruments.

[0027] The flocculant should generally be selected based on the aforementioned measurement results, with particular emphasis preferably placed on the measured values ​​for dry matter (DM), organic solids content (oDM), total suspended solids (TSS), pH value, electrical conductivity, and temperature in order to select the flocculant and its dosage (as concentration in the sludge). Depending on the intended subsequent use of the dried sludge, for example, as fertilizer, for energy recovery in a biogas plant, or for incineration, certain flocculants are suitable. An automated process for dosing sludge and flocculant into a passive sludge dewatering system (such as a geo-tube, centrifuge, etc.) is used.During sludge pumping, a process density meter can be used to determine the instantaneous sludge density as a useful indicator of the current sludge concentration. It should be noted that, due to the complexity of the sludge, fluctuations in sludge concentration are likely over time. This information can be used for the optimal (automatic) dosing of flocculant, as the flocculant dosage depends on the sludge concentration. Therefore, the type of flocculant is generally selected based on the properties of the sludge. Additionally or alternatively, the use of dried sludge can also influence the choice of flocculant, for example, because using dried sludge excludes the presence of certain components, and the flocculant must therefore not contain these components.

[0028] For example, chitosan / chitosin or tannin can be added as a suitable flocculant.Other exemplary flocculants suitable for use in the process according to the invention are: the group of synthetic polymeric flocculants such as polyacrylamide derivatives CPAM (cationic, anionic, non-ionic, amphoteric), polyacrylic acid (anionic), polystyrene sulfonates (anionic), polyvinyl alcohol (non-ionic), polyethylene oxide (non-ionic), polyethyleneimine (cationic), poly-DADMAC (cationic), poly(2-vinylimidazoline) (cationic) or the group of natural polymeric flocculants, i.e. mostly chemically modified natural polymers, such as chitosan / chitosine and chitosan-based polymers (cationic), starch-based polymers (cationic), cellulose-based polymers (anionic), dextran (non-ionic), lignin-based polymers (cationic), tannins (weakly anionic) or the group of inorganic coagulants, such as aluminum salts (aluminum sulfate).Aluminum chloride, polyaluminum chloride (PAC)) and iron salts (ferrous chloride, ferrous sulfate, polyferrous sulfate). Furthermore, starch and guar gum, for example, can be used as flocculants, particularly when components are found in the sludge that cause its biodegradation, but the concentration of these components is not so high that the flocculation effect is impaired due to excessively rapid biodegradation. Other aspects to consider when selecting a suitable flocculant include:

[0029] Depending on its charge type (anionic vs. cationic), the flocculant can be selected according to the particle type in the sludge: An anionic flocculant is used for sludge with a relevant proportion of mineral particles - e.g., sludge with high TS and low oTS).

[0030] A cationic flocculant is used for sludge containing organic particles (sludge with high oTS).

[0031] • The charge density of a polymeric flocculant can be selected based on the sludge type:

[0032] The higher the oTS content, the higher the cationic charge of the flocculant should be.

[0033] Low to medium anionic flocculants are well suited for mineral sludge (e.g., sludge with mainly mineral particles, for example from mineral processes such as mining processing),

[0034] Low anionic to low cationic flocculants are well suited for physicochemical sludge; such sludge is, for example, the result of physicochemical wastewater treatment.

[0035] Low-cationic flocculants are suitable for stabilized and primary sludge, for example from settling processes.

[0036] Cationic flocculants are suitable for mixed sludge, such as mixtures of primary and biological sludge.

[0037] Highly cationic flocculants are suitable for biological sludge, such as from biological wastewater treatment.

[0038] • The molecular weight and molecular structure are also relevant properties of the flocculant:

[0039] The higher the molecular weight of the polymeric flocculant, the larger the flocs and the more viscous the polymer solution becomes, making it more difficult to mix the sludge with the flocculant.

[0040] A linear molecular structure delivers good performance even at low doses and exhibits high viscosity.

[0041] A branched molecular structure provides excellent drainage performance at medium dosage.

[0042] A cross-linked molecular structure provides good dehydration performance at high doses. The dry matter (DM) has the following influence on the flocculant:

[0043] The higher the dry matter concentration of the sludge, the lower the flocculant consumption.

[0044] The higher the total solids (TS) concentration of the sludge, the more difficult it is to mix in a viscous flocculant solution. Linear flocculants with a lower molecular weight, as well as branched or cross-linked flocculants, should then be used.

[0045] • The proportion of organic solids (oTS) has the following influence on the flocculant:

[0046] Higher oTS content makes dewatering more difficult and requires more flocculant. Strongly cationic flocculants are recommended here. BOD, COD, nitrogen, phosphorus, etc. correlate positively with oTS. Temperature has the following influence on the flocculant:

[0047] The lower the temperature of the sludge, the more difficult it is for the polymeric flocculant to dissolve. Linear flocculants with a lower molecular weight, as well as branched or cross-linked flocculants, dissolve more easily in cold sludge.

[0048] • The conductivity has the following influence on the flocculant:

[0049] Higher conductivity means more dissolved electrolytes in the sludge and therefore fewer charged particles. Less charged flocculants with lower molecular weight and lower dosages can be used.

[0050] • The pH value has the following influence on the flocculant:

[0051] Synthetic and natural polymeric flocculants function in a wide pH range (2-12).

[0052] Strongly anionic flocculants are required for alkaline sludge (pH>9-10).

[0053] • The hydrolysis of cationic charges in cationic flocculants occurs at pH > 5.5, which can affect their performance. The best performance of cationic flocculants is expected at pH < 5.5. Inorganic flocculants have a moderate pH range (5-9) and are more pH-sensitive than organic polymeric flocculants.

[0054] Synthetic polymeric flocculants are generally superior to natural flocculants in both performance (smaller molecular weight, lower charge density, poorer water solubility) and cost. Chitosan contains numerous free amino groups along its chain structure, which are cationically charged under acidic conditions and therefore usually outperform other polysaccharide-based flocculants. Chitosan is generally more expensive than starch- or cellulose-based flocculants. Anionic polymeric flocculants, in turn, are generally considerably cheaper than cationic ones.

[0055] The selection and dosage of the flocculant are based on the results of the sludge property measurements, taking into account the relationships and specifications described above. It can also be determined with regard to the subsequent use or disposal of the dried sludge, as previously explained. In borderline cases, the selection and optimal concentration of the flocculant can be further refined by conducting empirical tests in which the sludge is treated with various flocculants to determine the most suitable one.

[0056] According to the invention, after selecting and adding the appropriate flocculant, the sludge mixed with the flocculant is filled into the filter bag through a filling opening, and the filter bag is placed on a base to carry out the dewatering process. Advantageously, the filter bag is held at ambient pressure inside – apart from hydrostatic pressure conditions due to the weight of the filled sludge – meaning that no overpressure filling of the filter bag takes place. Dewatering through the filter bag therefore occurs purely by gravity and is positively influenced by the added flocculant.At least once, and preferably several times, the filter bag is refilled after a drainage period. A drainage period can be observed between the first and second fillings that differs from subsequent drainage periods, for example, between the second and, if applicable, third fillings. This two or more refills ensure efficient use of the filter bag's drainage capacity and are particularly effective for the drainage process under ambient pressure inside the filter bag, resulting in a longer drainage time and corresponding volume reduction within the filter bag.

[0057] The filter hose can be designed as described in more detail below. The filter hose can be placed on any suitable surface, preferably a water-permeable or water-absorbing surface, to ensure effective drainage of the portion of the filter hose directly resting on the surface.

[0058] In principle, the measurement process of one or more properties of the sludge to be dewatered and the selection of the flocculant can be carried out based on the measured property of the sludge by drawing on the experience of a user of the method according to the invention. However, it is preferred that the one or more properties of the sludge are entered into an electronic data processing device in which relationships between these properties—for example, in the form of concentration ranges of a substance in the sludge or the presence of certain properties as exclusion criteria—are pre-stored in relation to predetermined flocculants and their preferred concentration as a recommended value or concentration range. This can be implemented, for example, in the form of assignment tables or assignment algorithms.The electronic data processing device is designed to perform appropriate comparisons and calculations based on the measured values ​​of the sludge properties entered via an interface, in order to determine a suitable flocculant and its appropriate concentration, and to output this information to a user via appropriate interfaces.

[0059] The ideal time for a subsequent filling operation after the initial filling of the sludge to be dewatered, and for each subsequent filling operation, can be determined by measuring the decrease in the height of the filled filter bag and determining the optimal time for a further filling operation based on this decrease in height. For example, an initial height can be determined immediately after a filling operation, and the ideal height of the filter bag for a subsequent filling operation can be defined as a percentage of this initial height. This percentage of the initial height can preferably be determined based on the liquid or solids content previously measured in the sludge to be dewatered.

[0060] The advantages of the inventive use, method, and filter bag are that, on the one hand, sludge dewatering can be carried out without heating the sludge, and on the other hand, it is not necessary to fill the sludge into a bag. Instead, a filter bag, which is advantageous for rapid sludge dewatering, is used. The sludge is filled into the bag, and the sludge is dewatered through its walls. This results in rapid, energy-saving sludge dewatering, requiring less frequent and shorter refilling than dewatering in bags.

[0061] According to a first preferred embodiment, it is provided that before step d) a parameter of the filter bag is determined depending on the measured property of the sludge and in step d) the sludge mixed with the flocculant is filled into a filter bag which corresponds to the parameter thus determined, wherein the parameter of the filter bag is selected from:

[0062] - an average pore size in a wall of the filter hose, - a maximum pore size in a wall of the filter hose,

[0063] - a material from which the filter hose consists solely or partially, - a circumferential tensile strength of the filter hose,

[0064] - a burst pressure of the filter hose,

[0065] - a manufacturing technology for a wall of the filter tube, in particular selected from nonwoven fabric production, weaving, knitting, crocheting

[0066] - a connection technology for the filter hose, in particular a seam technology for sewing a filter wall sheet to the filter hose,

[0067] - a reinforcement of the filter hose,

[0068] - a diameter of the filter hose, and

[0069] - a length of the filter hose.

[0070] According to this embodiment, a parameter of the filter bag is selected depending on the previously measured property of the sludge. This selection of the filter bag parameter can be carried out either by manufacturing a filter bag suitable for the corresponding purposes of sludge dewatering of the sludge exhibiting the measured property, or by selecting such a suitable filter bag from a selection of at least two different, previously manufactured filter bags in order to provide a filter bag parameter for sludge dewatering that most closely matches the measured property.

[0071] It should be understood that the subject matter of this disclosure and the invention also encompasses the possibility of selecting a filter bag parameter instead of the previously described selection and addition of a flocculant based on the measured properties of the sludge. This is particularly relevant in cases where no flocculant is selected or added to the sludge. The selection of a filter bag parameter based on the measured properties of the sludge can thus improve the efficiency of sludge dewatering, either as an alternative to or in addition to the selection of a flocculant.The parameters to be selected for the filter hose can be directly related to the filter properties of the wall of the filter hose, for example by selecting a minimum, maximum or average size of the pores in the wall, or by selecting the diameter or length of the filter hose as a parameter, thus influencing the available wall area and pressure resistance of the filter hose.Furthermore, parameters of the filter hose can also be selected to enable conditions relevant to the filtration process, for example by selecting properties limiting the strength of the filter hose such as the circumferential tensile strength, the material of the filter hose, a reinforcement of the filter hose or a connection technology for the filter hose such as a specific seam technology, and in this way enabling a possible filling height of the filter hose, whereby filling height is understood to be the height of the filter hose lying on the substrate, i.e. the distance of the highest point of a cross-section of the filter hose from the substrate.

[0072] It is even more preferred if, in step d), a filling parameter is measured and the filling is carried out up to a predetermined value of the filling parameter, wherein the filling parameter is selected from: an absolute vertical height of the filled filter bag, a relative height ratio of the filled filter bag, determined as the ratio of the absolute height of the filled filter bag to the diameter of a circular cross-sectional area of ​​the filter bag, and an internal pressure of the filter bag.

[0073] According to this embodiment, during the filling process of the sludge to be dewatered into the filter bag, one or more filling parameters are measured and monitored, and the filling process continues until a predetermined value for the respective filling parameter is reached. This ensures, on the one hand, that a permissible load limit of the filter bag is not exceeded during the filling process and, on the other hand, can guarantee an ideal filling level of the filter bag for efficient sludge dewatering.The filling parameters to be monitored are selected in such a way that they are reliable and measurable with simple means in practical application, for example by filling the filling hose until its uppermost point reaches a certain distance from the surface on which it rests, or by predetermining a relative height to which the filter hose is filled, wherein the relative height is defined as the ratio of the distance achieved by the filling process between the highest point of the filter hose and the surface in relation to a theoretical diameter of the circular filter hose, or by measuring an internal pressure using a pressure sensor, wherein the determination of the internal pressure preferably takes place at a predetermined height of the filter hose and, consequently, pressure conditions influenced by the weight of the filled sludge can be taken into account.

[0074] It should be understood that if a parameter of the filter bag has been selected based on a property of the sludge, it is particularly preferred to then also predetermine the filling parameter depending on this selected parameter of the bag or depending on the measured property of the sludge and consequently adapt it to the correspondingly selected parameter of the filter bag in order to achieve efficient dewatering and avoid damage to the filter bag.

[0075] It is even more preferred that the filter hose has a longitudinal seam and is placed on the substrate in step e) such that the longitudinal seam is in contact with the substrate, preferably arranged at 5-7 o'clock in cross-sectional view, or - the filter hose has two longitudinal seams and is placed on the substrate such that one longitudinal seam is in contact with the substrate, preferably arranged at 5-7 o'clock in cross-sectional view, and the other longitudinal seam is arranged on the top of the filter hose, preferably arranged at 11-13 o'clock in cross-sectional view.

[0076] This further development of the invention is based on the inventors' finding that particularly efficient drainage can often be achieved with a filter bag design that does not provide high mechanical stability, especially, for example, when a nonwoven fabric is used as the filter wall and this nonwoven fabric is designed to have high permeability while simultaneously exhibiting a low tendency for the pores to become clogged. Such mechanically weak filter bags are often susceptible to damage, for example, in the form of tears along such a longitudinal seam, particularly in the area of ​​a seam that extends along the longitudinal axis of the filter bag due to its manufacture from one or two layers of material.

[0077] To enable such a filter bag design and achieve efficient sludge dewatering, it is advantageous to lay the filter bag in such a way that the seam rests on the substrate, thereby reducing the mechanical stress on the seam caused by frictional forces between the filter bag and the surface. Ideally, the seam should be positioned at approximately...

[0078] At 6 o'clock, effective relief of mechanical forces on the seam is also achieved if the seam is located in the 5 to 7 o'clock range. If two longitudinal seams are present because the filter bag is made from two layers of material, it is advantageous if one of the two longitudinal seams rests on the substrate and the other is approximately opposite it. This arrangement also effectively avoids the excessively high stress on the seams that would occur if these seams were located laterally, thus improving the load-bearing capacity of the filter bag.

[0079] According to a further preferred embodiment, the filter bag has a local reinforcement that extends over at least a first partial section of a wall of the filter bag and does not extend over a second partial section of the wall of the filter bag, wherein the first partial section is preferably arranged in a region located laterally with respect to the cross-section of the filter bag, preferably between 2 and 5 o'clock and / or between 7 and 11 o'clock, and preferably extends over the entire axial length of the filter bag, wherein the second partial section is further preferably arranged in a region located downwards with respect to the cross-section of the filter bag, preferably between 5 and 7 o'clock.

[0080] According to this preferred embodiment, the filter hose has local reinforcement, meaning that the filter hose is reinforced partially, but not over its entire circumference. This reinforcement can preferably extend over the entire length of the filter hose, but optionally only over a portion of the total length, for example, if the filter hose has no reinforcement or full reinforcement at the ends. The local reinforcement in the lateral areas, i.e., in the areas located between the 2 and 5 o'clock or 7 and 11 o'clock positions in the cross-section, specifically reinforces those areas of the filter hose that are subjected to the greatest stress when the hose is filled with sludge and the resulting weight is applied.The local reinforcement thus makes it possible to design the filter hose in a mechanically favorable way against the occurring load, while at the same time achieving effective and efficient separation with high permeability by not providing reinforcement in less stressed areas.

[0081] In particular, the lower and upper sections of the filter hose, which are sealed by the additional covering provided by the base on which the filter hose rests, and which also exhibit a low pressure differential across the filter hose wall due to the low hydrostatic pressure in the upper section, cannot be reinforced to achieve efficient water flow in these areas. Local reinforcement can be achieved by doubling the wall thickness through the application of an additional filter wall, matching the existing filter hose wall thickness, to the inner or outer surface of the filter hose. However, reinforcements different from those used in the filter hose wall, such as industrial reinforcements, can also be employed.

[0082] It is even more preferred if the filter hose has a positioning mark indicating the top side of the filter hose that should be facing upwards in step f), wherein the positioning mark is preferably formed by a print, a seam line, or a filling opening. According to this improved design, the position in which the filter hose is laid on the base with respect to an angular orientation in cross-section can be easily identified at any time, thus ensuring that the filter hose is laid in the desired position. This is particularly important if a seam of the filter hose is to be laid in the area between 5 and 7 o'clock, or specifically at 6 o'clock, in order to mechanically relieve stress on this seam.This position marker can be formed by one or more filling openings, which in this case are preferably arranged at an angle of 180° with respect to the cross-sectional area opposite the seam connecting the filter web(s). Alternatively, the position marker can also be implemented by a printed text or marking, or a color-contrasting seam, which is present on the filter bag as a joining seam or as a purely marking seam. For example, if the filter bag is joined from two material webs by means of two longitudinal seams, one seam can serve as a position marker to ensure that the other seam is positioned as precisely as possible at approximately 6 o'clock on the substrate. This allows both seams to be located in a less stressed area of ​​the filter bag, provided they are offset from each other by approximately 180° in cross-section.

[0083] According to a further preferred embodiment, the filter bag is made of a biodegradable material. After the final filling with sludge and storage of the filter bag over a dewatering period, the dewatered sludge contained within, along with the filter bag itself, is used for a common purpose, particularly as fertilizer in agriculture. According to this embodiment, the filter bag is not made of a conventional filter material such as polyester, polyethylene, polyamide, or polypropylene, which, due to their durability, pose an environmental burden during subsequent use or disposal. Instead, a biodegradable material designed for the specific application is used.Design for a specific application means that the filter bag is made of a biodegradable material that maintains sufficient mechanical strength throughout the sludge dewatering process to withstand the hydrostatic pressure during dewatering. Examples include PLA, PBS, PBAT, thermoplastic starch, cellulose-based materials, viscose, and lyocell. For short sludge storage times in the filter bag of a few days to a few weeks, viscose, lyocell, and thermoplastic starch are preferred. For medium filtration durations of several months to a few years, PBS and PBAT are suitable. For long filtration periods of up to ten years, PLA can be used as the filter bag material.

[0084] Often, after sludge dewatering, i.e., when the filter bag is filled with dewatered sludge, loading the filter bag may be desirable. In such cases, it is further desirable that the filter bag be made of a material that retains sufficient mechanical strength after dewatering to allow for such loading. At the same time, the material from which the filter bag is made must also be biodegradable to the extent that significant biodegradation of the filter bag occurs within a period of less than five years, particularly less than two years, preferably less than one year, after sludge dewatering or, alternatively, after loading, so that it does not pose an environmental burden in the medium or long term.It is understood that this necessary design of the filter bag can include the selection of the filter bag material and material dimensions, such as the wall thickness of the filter bag wall and the fiber thickness of the fibers from which the filter bag wall is made. The filter bag material can be selected, in particular, depending on a measured property of the sludge and, if applicable, the flocculant. Consequently, a suitable biodegradability and thus the degradation rate of the filter bag are preferably a result of the selected filter bag parameter. The previously explained selection of one or more filter bag parameters based on measured sludge properties is therefore closely and advantageously related to the biodegradability of the filter bag.

[0085] Biodegradability is defined according to the invention in accordance with the principle of standard ISO 16929 or according to a marine degradation test developed by TÜV Austria Belgium. The material according to the invention must meet at least one of these two conditions, preferably both.

[0086] According to ISO 16929, a material is considered compostable if it meets three criteria. One of these criteria is defined as follows: after 84 days in controlled composting, no more than 10% by weight of the material remains in a 2 mm sieve when the material or its components are sieved. Based on this system and adapted to the needs of filter bags, the filter wall material exhibits biodegradability such that, within six months in controlled composting according to ISO 16929 under thermophilic composting conditions, no more than 50% by weight of the dry mass of the initial structural material remains in the sieve after sieving through a 2 mm sieve. Therefore, the filter wall material does not necessarily qualify as compostable according to ISO 16929. However, it may be compostable, or it may achieve the degradation of 90% by weight of particles <2 mm over a period longer than six months.The degradation test under marine conditions simulates the degradation of standardized samples under accelerated conditions in seawater. Here, too, the degree of degradation is determined by a final sieving based on the dry weight remaining in the sieve. However, the increased mobility of the material is simulated by two intermediate sievings after 4 and 8 weeks.

[0087] Both degradation tests are performed using specimens with defined dimensions. Length and width are defined, while the thickness is based on the original material, i.e., the thickness of the material in its manufactured form. For layered composites, where the material is arranged in separate, superimposed layers and bonded together, this can be the thickness of the material in each individual layer. If the original material is produced as a composite layer, such as a nonwoven fabric or as a layer woven, knitted, or otherwise bonded from two different fibers, then a sample of the material with the original thickness of the layer, made exclusively from the material under investigation, must be used for the purposes of the degradation test.Significant degradation is preferably understood to mean that within the respective period 50% or more of the initial mass is biologically degraded, whereby degradation is also understood to mean that this degraded mass fraction only consists of particles of a size that can pass through a sieve with a mesh size of 2mm.

[0088] Another aspect of the invention is a geotextile filter hose for sludge dewatering, which has a filter wall made of a nonwoven fabric. This aspect of the invention is based on the understanding that while filter hoses made of regularly arranged fiber structures, such as woven, knitted, or crocheted fabrics, exhibit higher mechanical strength, allowing for a large fill volume, almost to the point of cylindrical filling, and possibly even pressure exceeding this degree of filling when used as filter hoses as described in the prior art, this does not necessarily translate into efficient dewatering of the sludge. However, the pore size distribution in such filter hoses with a regularly arranged fibers is often detrimental to achieving a high degree of purity in the water exiting during dewatering.According to the invention, it is therefore proposed to manufacture the filter bag from a nonwoven fabric. The resulting lower mechanical strength is accepted according to the invention, which means that the filter bag can often only be filled to a shallow oval cross-section and, in particular, cannot be subjected to pressure exceeding the maximum filling level. In return, a longer dewatering period is provided to achieve a comparatively very efficient dewatering process, in which even small particles are retained in the filter bag without rapid clogging of the nonwoven fabric's pores.

[0089] This is also achieved according to the invention because a nonwoven fabric not only allows radial flow, but also permits water to move circumferentially or axially within the filter wall of the filter bag. This ensures efficient use of the pores of the nonwoven fabric distributed over its entire length, circumference, and thickness.

[0090] It is further preferred if the filter wall is made of a nonwoven fabric, the edges of which are needled, sewn, welded or glued along a connection area extending axially in the longitudinal direction of the filter tube, or

[0091] - The filter wall is made of two nonwoven webs, the edges of which are needled, sewn, welded, or glued together along a first and second connection area extending axially in the longitudinal direction of the filter tube. In a filter tube made from a nonwoven fabric, the connection area of ​​the material web edges, particularly when manufactured from a single web, represents a mechanical weak point. Such a connection can be achieved by needled an overlapping area of ​​these edge regions, by sewing, or, with suitable materials, by welding or gluing.In principle, especially with filter bags made of a nonwoven fabric, it is advantageous, according to the inventors, if this connection point is located in a lower and / or upper area with respect to the cross-section when the filter bag is filled and laid down, in order to relieve this mechanical weak point through friction on the substrate and to place it in less stressed areas of the filter bag cross-section.

[0092] It is even more advantageous if the filter wall is made of a biodegradable material. Regarding the definition of biodegradability, reference is made to the preceding definition, which applies equally to the inventive aspect of the filter bag. Providing a biodegradable filter bag is particularly advantageous in connection with its design made of a nonwoven fabric, since the biodegradation of the nonwoven fabric does not directly impair the filtering performance of the filter bag. Therefore, with a filter bag made of nonwoven fabric, even if the biodegradation of the filter bag begins during the dewatering process, the separation quality remains unchanged, as would be the case, for example, with filter bags with a regular fiber arrangement.In this respect, a filter bag made of nonwoven fabric can be designed with regard to the speed of its biological degradation in such a way that biological degradation to a predetermined degree already occurs over the drainage period without adversely affecting the quality of the drainage.

[0093] The filter tube according to the invention can be further developed by an external support structure that at least partially surrounds the nonwoven fabric, which is permeable to liquids and has openings that allow the passage of larger particles than the nonwoven fabric, wherein the support structure is preferably located at least in a region at the bottom with respect to the cross-section of the filter tube, preferably in a region that is arranged at least between 2 and 10 o'clock or at least between 3 and 9 o'clock or at least between 4 and 8 o'clock.

[0094] According to this training method, the nonwoven fabric is at least partially surrounded by a support structure that provides external support. The support structure can enclose the nonwoven fabric along the entire length of the filter tube and, if necessary, also support it at the ends. The support structure can also enclose the nonwoven fabric completely. Alternatively, the support structure can only partially support the nonwoven fabric, specifically by extending only over a portion of the circumference and / or length of the nonwoven fabric, or by not being positioned at the ends.

[0095] By providing such a support structure, the nonwoven fabric is effectively braced from the outside against the internal pressure that arises during filling. This support structure provides mechanical stabilization, allowing the nonwoven fabric itself to be designed with a lower mechanical strength than would be necessary if the stresses caused by filling the fabric had to be absorbed by the nonwoven fabric itself. Consequently, the nonwoven fabric can be manufactured with a thinner wall thickness, a lower basis weight, and / or thinner fibers than in a configuration where the nonwoven fabric alone had to absorb the stresses caused by filling. This improves the filter properties, particularly with regard to the rate of sludge dewatering, and reduces the reduction in the nonwoven fabric's permeability due to pore clogging.The support structure can be, for example, a metal frame, a metal mesh, or a net made of other materials, such as a plastic mesh grid, a plastic grid, a woven rope structure, or the like. In particular, the support structure can also be designed like a tube that completely surrounds the nonwoven fabric and can be closed at the ends. The inner diameter of the support structure and its length after the ends are closed can be dimensioned such that the filter tube fits inside and, when filled with liquid sludge, presses against and is supported by the inside of the support structure. The size of the openings in the support structure can be greater than 10, 100, or 1000 times the pore size of the nonwoven fabric.

[0096] It is particularly preferred if the support structure exerts a supporting effect especially where the stresses on the nonwoven fabric are particularly high, i.e., especially in the lower circumferential region of the nonwoven fabric, which is particularly stressed by the internal pressure and the weight of the sludge inside the nonwoven fabric. The support structure can enclose less than 180° or more than 180° of the nonwoven fabric. It is particularly preferred if the support structure does not enclose and support the nonwoven fabric in an upper region at an angle of more than 60°, preferably more than 90°, and particularly more than 120°, thereby allowing the removal of the nonwoven fabric with the collected solids through the opening thus formed in the support structure.In other embodiments, the support structure can completely enclose and support the nonwoven fabric, but is designed to be opened by providing a corresponding detachable connection or pivoting of a segment of the support structure, thereby enabling the removal of the nonwoven fabric with the collected solids after sludge dewatering. These designs allow the support structure to be reused multiple times for multiple sludge dewatering processes, so that, if necessary, only the nonwoven fabric is used once for sludge dewatering as a single-use product, while the support structure remains reusable.

[0097] It is particularly preferred if the support structure comprises a grid structure, preferably a grid extending over the entire circumference of the filter bag. Such a grid structure can be made, for example, of polyester, polypropylene, aramid, polyvinyl alcohol, or a composite of two of these plastics. The grid can be formed from plastic strands laid in two different directions relative to each other and joined at the intersection points by welding or bonding to form the grid. Such a grid structure is known, for example, under the brand name Secugrid®. Preferably, the grid has an open area of ​​more than 90%, so that the contact area and resulting seal of the grid to the nonwoven fabric constitutes less than 10% of the total area of ​​the grid, thus minimizing any impairment of filtration.

[0098] It is even more preferred if the tensile strength of the nonwoven fabric of the filter wall is less than 120%, preferably less than 100%, of the maximum static stress of the nonwoven fabric when the filter bag is completely filled with water and the nonwoven fabric is not supported by the external support structure. The maximum static stress of the nonwoven fabric when the filter bag is completely filled is understood to be the stress occurring in the nonwoven fabric at the point of maximum load, typically a stress occurring in the circumferential area of ​​the nonwoven fabric located laterally to the base surface of the nonwoven fabric when filled. This stress can primarily be a tensile stress in the circumferential direction.The nonwoven fabric can be dimensioned such that its tensile strength is only slightly above or even below this maximum static stress because additional support from the supporting structure prevents the nonwoven fabric from bursting, thus making the filter bag resilient to these static and also additional dynamic stresses. Dimensioning the fabric close to the static stress point allows it to be designed in a particularly advantageous way for filter properties and sludge dewatering.

[0099] It is even more advantageous if the nonwoven fabric is loosely inserted into the support structure, and the support structure is designed to allow the nonwoven fabric to be removed when filled without damaging the structure. Loose insertion means that the nonwoven fabric is not permanently attached to the grid structure, i.e., not glued, welded, sewn, or otherwise bonded to it. This loose connection between the nonwoven fabric and the support structure makes it possible to remove the nonwoven fabric from the support structure after it has filled with solids and the sludge dewatering cycle for the nonwoven fabric is complete. Removal of the solids-filled nonwoven fabric from the support structure can be accomplished and facilitated by tilting, turning, or rotating the entire filter bag. If necessary, the filter bag can be moved to a storage location before the nonwoven fabric is removed from the support structure.The support structure can also be designed so that it can be opened at the end and the nonwoven fabric can be removed from the support structure in an axial direction.

[0100] In accordance with this design of the filter bag, a further aspect of the invention is the use of the filter bag in such a way that, prior to sludge dewatering, the filter bag is inserted into a support structure and, after dewatering has been completed, is removed from the support structure along with the collected solids, particularly in such a way that the support structure is not damaged in the process. According to this use, the support structure can therefore be reused multiple times, while the nonwoven fabric, which constitutes the smaller proportion of the material, is used as a disposable product.

[0101] Finally, another aspect of the invention is a method for sludge dewatering in which the nonwoven fabric is placed in a support structure before filling and the nonwoven fabric with the solids collected therein is removed from the support structure after sludge dewatering, preferably without destroying the support structure, wherein the support structure is preferably designed according to one of claims 6-9.

[0102] Another aspect of the invention is the use of a filter bag with the features described above for sludge dewatering, whereby a water-containing sludge is filled into the filter bag and the filter bag is stored on a base for a dewatering period. The use according to the invention enables particularly efficient sludge dewatering with a high degree of purity of the separated water and a simultaneously high solids concentration in the dewatered sludge.

[0103] The use can advantageously be carried out in the manner previously described as a method according to the invention.

[0104] Furthermore, in the use according to the invention, it is preferred if the filter bag is made of a biodegradable material and, after a single use for sludge dewatering, is conveyed, along with the dewatered sludge, to a downstream use or landfill. Such single-use application can therefore be carried out in an environmentally friendly manner and with high process efficiency, since the biodegradation of the filter bag eliminates the need for reprocessing in the form of emptying and cleaning the filter bag for a second use in sludge dewatering. At the same time, advantageous logistics are provided for the dried sludge, in which it can be relocated together with the filter bag and conveyed to a further use. Reference is also made to the preceding definition regarding biodegradation in this respect.The dried sludge can be preferably applied as fertilizer together with the filter bag, or it can be fed into an energy processing process, preferably in a biogas plant, where a cellulose-based filter bag such as viscose is preferably used. This application allows for efficient further use of the dried sludge together with the filter bag, thus eliminating the need for time-consuming separation of the sludge from the filter bag.

[0105] It is even more preferred if the filter hose has a longitudinal seam and the filter hose is laid on the base such that the longitudinal seam is arranged in an area between 5 and 7 o'clock or between 11 and 1 o'clock in the cross-section, or if the filter hose has a local reinforcement that extends over two circumferential sections and over the entire length of the filter hose, and the filter hose is laid on the base such that the two reinforced circumferential sections are arranged in an area between 1 and 5 o'clock and between 7 and 11 o'clock in the cross-section.

[0106] This specific arrangement of a longitudinal seam on the one hand and a reinforcement on the other hand on the filter bag, and their placement when the filter bag is stored on the base, allows for advantageous utilization of the filter bag's mechanical load-bearing capacity, particularly when it is made of nonwoven fabric and / or a biodegradable material. For specific advantages and embodiments of this type of application, reference is made to the preceding explanation of the inventive method and the inventive filter bag with the corresponding seam and reinforcement arrangement.

[0107] Finally, another aspect of the invention is a method for separating water from water-containing sludge, in which the separation is carried out by filling the water-containing sludge once or several times into a filter bag with a filter wall made of nonwoven fabric and storing the filled filter bag for a dewatering period after each filling. This type of sludge dewatering with the method according to the invention takes advantage of the favorable filter properties of a nonwoven fabric described above, particularly when the filter bag made from the nonwoven fabric consists of a biodegradable material, and compensates for the lower mechanical strength of the filter bag by means of a suitable process in which the filter bag is filled several times, even if this requires a potentially longer dewatering period.Thus, any fill quantity potentially limited by mechanical load-bearing capacity can be compensated for in this way with regard to the overall throughput of the filter bag. The separation process can preferably be carried out with a filter bag of the previously described design and can be further preferably developed with the features of the previously explained method.

[0108] Finally, a preferred aspect of the invention is a filtration device comprising a filter bag of the type described above, at least one flocculant, a feed pump with suction and pressure-side connection lines designed for conveying sludge, a metering device for adding the flocculant, and preferably further, a device for closing the end of the filter bag or closing a filling nozzle, in particular a sewing machine. This filtration device includes all the necessary means to carry out sludge dewatering decentrally, i.e., in particular where the sludge originates or where the dried sludge is to be used further.The filtration system can be loaded and transported in a standard container, thus enabling environmentally friendly sludge dewatering, as it eliminates the need for energy-intensive transport of the sludge to a separation unit or of the dried sludge to further use / landfilling. Furthermore, the filtration system allows for easy adjustment of the filtration capacity on-site by cutting and sewing the filter bag as required.

[0109] Preferred embodiments of the individual aspects of the invention are described by way of example with reference to the accompanying figures. These show:

[0110] Figure 1: a schematic process flow of the method according to the invention,

[0111] Figures 2a-d: a sequence of the inventive use of a filter bag for sludge dewatering according to the inventive method in a schematic cross-sectional view (Figs. 2a-c) and a schematic longitudinal section view (Fig. 2d) of the filter bag, Figure 3a: a half cross-sectional view of a preferred embodiment of the filter bag,

[0112] Figure 3b: a perspective view of a section of the preferred embodiment of the filter hose according to the invention, Figures 4a, b: two preferred embodiments of a method of joining one or two material webs at their edge section to form a longitudinal seam for the production of a filter hose according to the invention from one or more material webs.

[0113] Referring initially to Figure 1, in one embodiment of the method according to the invention, a property of the sludge to be dewatered is first determined in step A. This property can be, for example, a pH value, a concentration of a specific substance, a mechanical property such as viscosity, a solids content, or an average, minimum, or maximum particle size of the sludge.

[0114] In step B1, a flocculant is selected based on the determined properties of the sludge. This selection can be made, for example, by choosing a flocculant for acidic environments if the pH is less than seven, and a flocculant for alkaline environments if the pH is greater than seven. Furthermore, the flocculant can also be selected based on the concentration of specific substances within the sludge to achieve effective flocculation of substances present in high concentrations.

[0115] In step C1, the selected flocculant is then added to the sludge.

[0116] Alternatively or additionally, in step B2, depending on the previously determined sludge properties, a parameter of the filter bag used for sludge dewatering can also be selected. This parameter could, for example, be a selection of the material from which the filter bag is made. Similarly, a wall thickness of the filter bag, a pore size, or a fiber thickness of the material from which the filter bag wall is made can be selected. Furthermore, a construction method of the filter bag, such as seam techniques or locally applied reinforcements, can also be selected. In a subsequent step C2, a filter bag with this parameter can then be manufactured, or such a filter bag can be selected from a range of different, already manufactured filter bags.

[0117] In the subsequent step D, the sludge to be dewatered is filled into the filter bag. Depending on whether a flocculant was previously selected and added, and / or whether a parameter of the filter bag was previously selected, the sludge can be filled into the filter bag with the corresponding parameter along with the flocculant.

[0118] In a subsequent step E, the sludge to be dewatered is stored within the filter bag for a dewatering period. During this period, water seeps through the filter bag to the outside and can be collected for further use, cleaning, or the like. If necessary, mechanical pressure can be applied to the filter bag during this dewatering period to accelerate the dewatering process.

[0119] Steps D and E are repeated at least once, and possibly several times, by refilling the filter bag with sludge and, if necessary, flocculant after the first dewatering period. It is important to understand that the second fill volume is smaller than the first due to the amount of dewatered sludge already present in the filter bag, and this affects each subsequent fill accordingly. Similarly, the second dewatering period following this second fill may differ from the first. For example, the second dewatering period may be longer than the first due to partial clogging of the filter bag with fine particles from the previous dewatering period.Similarly, depending on the sludge composition, the second dewatering period may be shorter than the first due to the smaller amount of water-containing sludge used in the second filling process.

[0120] After the filter bag has been filled two or more times with the sludge to be dewatered and the last dewatering period has elapsed, the filter bag contains a dry mass of sludge that has been dewatered as intended. In a subsequent step F, the filter bag along with this dried sludge can then be put to further use, for example by transporting the filter bag and the sludge to another location and using it there, for example, for filling a biogas plant.

[0121] It is preferred that in step B2 a filter bag made of a biodegradable material is selected, or that in step D the sludge is filled into such a filter bag made of a biodegradable material, so that for further use in step F a separation of the dried sludge from the filter bag is not necessary.

[0122] Figure 2a shows a filter bag 10 after initial filling with the suspension of water-containing sludge. The filter bag 10 rests on a water-permeable filter layer 20 as a base. Due to the gravitational force of the filled sludge 40a, a pressure distribution is established in the filter bag 10, which is only filled until it forms a flat-oval cross-section. This pressure distribution is schematically shown as a pressure distribution 30 to the right of the filter bag. This pressure distribution 30 forces water out of the filter bag through the pores of the filter wall, occurring to a greater extent at the lower lateral surfaces and in the lower region than in the upper region of the filter bag.

[0123] The filter tube has a connection 11a at the 6 o'clock position in the cross-sectional view, formed by overlapping and sewing the nonwoven filter wall. A similarly designed connection 11b is present at the 12 o'clock position in the cross-sectional view of Fig. 2a. These connections 11a and 11b join two layers of material 10a and 10b to form a filter tube.

[0124] During the first drainage period, a filter cake 50a forms on the inner surface of the material layers 10a, b forming the filter wall, and the filter tube loses internal volume due to the water that escapes until the entire interior of the filter tube is filled with filter cake 50b, as shown in Figure 2b. The pressure 3ß' is significantly reduced. Any natural precipitation (rain) 70 occurring during the drainage period is drained off on the outside of the filter.

[0125] After this initial dewatering period, more sludge 40c to be dewatered is introduced into the filter bag, and a quantity of suspension consisting of water-containing sludge forms again within the filter bag, positioned above the filter cake 50b. This is illustrated in Figure 2c. A pressure ratio 30 is again established within the filter bag, and the water exits the filter bag through the filter cake 50a and the filter wall until completely dried sludge, in the form of a filter cake, is once again present within the filter bag. This refilling, followed by a dewatering period, can be repeated as necessary until effective dewatering through the filter wall is no longer possible or the filter bag is completely filled with filter cake 50b.

[0126] Subsequently, as shown in Figure 2d, the filter cake 50d is put to further use, for example by bulk material transport. During this transport and further use of the filter cake, it is unnecessary to remove the filter cake from the biodegradable tube; instead, the filter cake together with the filter tube can be put to further use.

[0127] Figure 3a also shows a cross-sectional view of the filter tube as in Figure 2a, but only the right half of the filter tube 110 is shown. As can be seen, the filter tube has a reinforcement 112 located at its edge within the flat oval, which is attached to the filter wall on the inside. This reinforcement 112 can, for example, consist of a doubling of the filter wall material and effectively reinforces the filter tube in the area of ​​highest stress, so that the stress can be reduced by a reinforced filter edge.

[0128] The end of the hose is sewn flat with a finishing seam. Typically, no particular stress concentrations occur there.

[0129] Figure 3b shows a perspective view of a portion of the filter hose, depicting a filling opening 213, designed as a hose or pipe flange, on the top of the filter hose at the 12 o'clock position. The filter hose is reinforced in the area of ​​this filling opening by a doubling in the form of a double patch 214a, b to prevent damage in this area that could be caused by handling during the connection of a feed hose.

[0130] Figures 4a and 4b illustrate two preferred joining techniques for the material webs from which the filter tube is manufactured. Figure 4a shows an overlap of the material webs 311a and 311b with a connection between the two overlapping material webs, schematically represented by perpendicular lines, which creates a strong joint between the material webs that can exhibit a strength of approximately 80% or more of the mechanical strength of the material web itself. This joint can preferably be made by sewing with one or more seams, or alternatively or additionally by needling with preferably closely spaced needling points.

[0131] Figure 4b shows a joining technique in which two opposing end sections of the material webs 411a, b are sewn together. This seaming technique can be readily implemented in many automated filter bag production processes and can achieve sufficient strength. As previously described, the joining point for the longitudinal connection of the material webs is preferably located in the 5-7 o'clock position and in the 11-1 o'clock position in a cross-sectional view to keep it away from areas subjected to high internal pressure and to position it in an area where the load is relieved by the substrate and the friction of the filter bag against the substrate.

Claims

Claims 1. Geotextile filter hose for sludge dewatering, characterized in that the filter hose has a filter wall made of a nonwoven fabric.

2. Filter hose according to claim 1 , characterized by the fact that the filter wall is made from a nonwoven fabric sheet, the edges of which are needled, sewn, welded or glued along a connection area extending axially in the longitudinal direction of the filter tube, or the filter wall is made from two nonwoven fabric sheets, the edges of which are needled, sewn, welded or glued together along a first and second connection area extending axially in the longitudinal direction of the filter tube.

3. Filter hose according to claim 1 or 2 characterized by the fact that the filter wall is made of a biodegradable material.

4. Filter hose according to one of claims 2-3, characterized in that the filter hose has a positioning mark which indicates the top of the filter hose, wherein the positioning mark is preferably formed by a print, a seam line or a filling opening.

5. Filter hose according to one of claims 3-4, characterized in that the filter hose has a local reinforcement which extends over at least a first partial section of a wall of the filter hose and does not extend over a second partial section of the wall of the filter hose, wherein the first partial section is preferably arranged in a region located laterally with respect to the cross-section of the filter hose, preferably between 2 and 5 o'clock and / or between 7 and 11 o'clock, and extends over the entire axial length of the filter hose. wherein the second subsection is preferably arranged in a lower area with respect to the cross-section of the filter hose, preferably between 5 and 7 o'clock.

6. Filter hose according to one of the preceding claims, characterized by an external support structure that at least partially surrounds the nonwoven fabric, which is permeable to liquids, and has openings that allow larger particles to pass through than the nonwoven fabric, wherein the support structure is preferably located at least in a region below the cross-section of the filter hose, preferably in a region that is arranged at least between 2 and 10 o'clock or at least between 3 and 9 o'clock or at least between 4 and 8 o'clock.

7. Filter hose according to claim 6, characterized in that the support structure comprises a grid structure, preferably a grid extending over the entire circumference of the filter tube or formed by such a grid.

8. Filter hose according to claim 6 or 7, characterized in that the tensile strength of the nonwoven fabric of the filter wall is less than 120%, preferably less than 100%, of the maximum static stress of the nonwoven fabric when the filter tube is completely filled with water and the nonwoven fabric is not supported by the external support structure.

9. Filter hose according to one of claims 6 to 8, characterized in that the nonwoven fabric is loosely inserted into the support structure and the support structure is designed to allow the nonwoven fabric to be removed from it in a filled state without destroying the support structure.

10. Use of a filter bag according to one of claims 1-9 for sludge dewatering, in that a water-containing sludge is filled into the filter bag and the filter bag is stored on a base for a dewatering period.

11. Use according to claim 10, characterized in that the sludge dewatering is carried out according to a method according to one of claims 16, 20-24.

12. Use according to claim 10 or 11, characterized in that the filter bag is made of a biodegradable material and, after a single use for sludge dewatering, is supplied together with the dewatered sludge to a downstream use or landfill.

13. Use according to any one of the preceding claims 10-12, characterized by the fact that the dried sludge is applied as fertilizer together with the filter hose, or the dried sludge together with the filter bag is fed to an energy processing process, preferably in a biogas plant, wherein preferably a cellulose-based filter bag such as viscose is used.

14. Use according to any one of claims 10-13, characterized in that the filter hose has a longitudinal seam and the filter hose is laid on the base in such a way that the longitudinal seam is arranged in a cross-section in an area between 5 and 7 o'clock or between 11 and 1 o'clock.

15. Use according to any one of claims 10-14, characterized in that the filter hose has a local reinforcement which extends over two circumferential part areas and over the entire length of the filter hose and the filter hose is laid on the base such that the two circumferential part areas are arranged in a cross-sectional area between 1 and 5 o'clock and between 7 and 11 o'clock.

16. Use according to one of claims 10-15, characterized in that the nonwoven fabric is placed in a support structure before filling and the nonwoven fabric with the solids collected therein is removed from the support structure after sludge dewatering, preferably without destroying the support structure. wherein the support structure is preferably designed according to one of claims 6-9.

17. Filtration device comprising - a filter hose according to any one of the preceding claims 1-9, - at least one flocculant, - a pump with suction and pressure side connection lines, designed for pumping sludge - a dosing device for adding the flocculant, - preferably also a device for closing the end of the filter tube or closing a filling nozzle, in particular a sewing machine.

18. Method for separating liquid, in particular water, from a liquid-containing sludge, characterized in that the separation is carried out by filling the liquid-containing sludge into a filter bag with a filter wall made of nonwoven fabric once or several times and storing the filled filter bag for a dewatering period after each filling.

19. Sludge dewatering process, comprising the following steps: a. Measuring one or more properties of the sludge, wherein these properties are selected from: - Moisture content, - Dry matter (DM), - Organic solids (oTS), - Inorganic solids (iTS), - Total suspended solids (TSS), - Density, - pH value, electrical conductivity, chemical oxygen demand (COD), biochemical oxygen demand (BOD), Nitrogen concentration, especially as total nitrogen concentration, ammonium nitrogen concentration, nitrate nitrogen concentration, or nitrite nitrogen concentration. Phosphorus concentration, in particular as total phosphorus concentration or concentration of soluble phosphorus components, Potassium concentration Concentration of volatile organic compounds, Oil content, and Fat content b. Selecting a flocculant depending on the measured properties of the sludge, c. Adding the selected flocculant to the sludge, d. Pouring the sludge containing the flocculant into a filter hose, e. Storing the filter hose on a base for a drainage period, and f. At least one refilling of the filter bag with sludge containing the flocculant after the drainage period has ended and storage of the filter bag on the base for a second drainage period.

20. Method according to claim 19, comprising the steps: characterized in that, prior to step d), a parameter of the filter bag is determined depending on the measured property of the sludge, and in step d), the sludge mixed with the flocculant is filled into a filter bag corresponding to the parameter thus determined, wherein the parameter of the filter bag is selected from: an average size of the pores in a wall of the filter hose, a maximum size of the pores in a wall of the filter hose, a material from which the filter hose consists solely or partially, a circumferential tensile strength of the filter hose, a burst pressure of the filter hose, a manufacturing technology for a wall of the filter bag, in particular selected from nonwoven fabric production, weaving, knitting, knitting; a joining technology for the filter bag, in particular a seam technology for sewing a filter wall panel to the filter bag; a reinforcement of the filter bag; a diameter of the filter hose, and a length of the filter hose.

21. Method according to any one of the preceding claims 19-20, characterized in that in step d) a filling parameter is measured and the filling is carried out up to a predetermined value of the filling parameter, wherein the filling parameter is selected from: an absolute vertical height of the filled filter hose, a relative height ratio of the filled filter hose, determined as the ratio of the absolute height of the filled filter hose to the diameter of a circular cross-sectional area of ​​the filter hose, an internal pressure of the filter hose.

22. Method according to any one of the preceding claims 19-21, characterized by the fact that The filter hose has a longitudinal seam and in step e) is placed on the substrate such that the longitudinal seam is in contact with the substrate, preferably arranged at 5-7 o'clock in cross-sectional view, or the filter hose has two longitudinal seams and is placed on the substrate such that one longitudinal seam is in contact with the substrate, preferably arranged at 5-7 o'clock in cross-sectional view, and the other longitudinal seam is arranged on the top of the filter hose, preferably arranged at 11-13 o'clock in cross-sectional view.23.Method according to one of the preceding claims 18-22, characterized in that the filter hose has a local reinforcement which extends over at least a first partial section of a wall of the filter hose and does not extend over a second partial section of the wall of the filter hose, wherein the first partial section is preferably arranged in a region located laterally with respect to the cross-section of the filter hose, preferably between 2 and 5 o'clock and / or between 7 and 11 o'clock, and preferably extends over the entire axial length of the filter hose. wherein the second subsection is preferably arranged in a lower area with respect to the cross-section of the filter hose, preferably between 5 and 7 o'clock.

24. Method according to any one of the preceding claims 19-23, characterized in that the filter hose has a positioning mark which indicates the top of the filter hose which should be on top in step f), wherein the positioning mark is preferably formed by a print, a seam line or a filling opening.

25. Method according to any one of the preceding claims 18-24, characterized in that the filter bag is made of a biodegradable material and, after the final filling with sludge and storage of the filter bag over a dewatering period, the dewatered sludge contained therein, together with the filter bag, is used for a common purpose, in particular as fertilizer in agriculture.

26. Method according to any one of the preceding claims 18-24, characterized in that the nonwoven fabric is placed in a support structure before filling and the nonwoven fabric with the solids collected therein is removed from the support structure after sludge dewatering, preferably without destroying the support structure, wherein the support structure is preferably designed according to one of claims 6-9.

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