A method for the treatment of biosludge

Abstract

A method for the treatment of biosludge is disclosed, wherein the biosludge comprises cellular structures. The method may comprise mixing the biosludge (1) with at least an acid (2) to obtain a first mixture; breaking the cellular structures of the biosludge (1) in the first mixture at least partially to obtain a second mixture; and separating a solid phase (9) from the second mixture, thereby obtaining a solid product comprising the solid phase (9). The method may also comprise adding a solid component (3) to the first mixture and / or to the second mixture. A product comprising the solid phase (9) obtainable by the method and a system for the treatment of biosludge (1) are also disclosed.

Description

[0001] A METHOD FOR THE TREATMENT OF BIOSLUDGE

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a method and system for the treatment of biosludge and to a product obtainable by the method .

[0004] BACKGROUND

[0005] Pulp and paper industry waste waters typically contain wood, either in its original form or in an altered form (e . g . as lignin, starch, alcohols ) . Waste waters also contain a variety of process substances and chemicals , also either in their original form or in a form altered in some way .

[0006] The content of compounds harmful for the environment in effluent or waste water coming from plants such as pulping processes or from municipal sewage is currently quite strictly controlled for environmental reasons . Plants employ various types of solutions that are used for waste water treatment in order to ensure that the plant fulfils environmental regulations .

[0007] Most effluents of the pulp and paper industry are treated in biological waste water ( sewage ) treatment plants ( active sludge plants ) . Some of them treat also effluents from the surrounding community . Biological waste water treatment systems can be used especially for decreasing the amount of small-molecule organic substances . Biological purification uses the ability of the microorganisms to live in effluents . Microorganisms dissipate dissolved and colloidal wastes , us ing them as nutrition . Wastes are removed in part mechanically and in part by the microorganisms transforming them to carbon dioxide and water .

[0008] Waste water treatment processes typically involve a number of chemical and mechanical phases . At an early phase, fibrous primary sludge is removed from the waste water. Then the pH may be adjusted, as the most suitable pH for the biological sludge may be 7 - 7.5 and a suitable range may be 6.8 - 8. The pH may be controlled by dosing alkaline (for example, lime) or acid to the waste water before aeration depending on the pH of the incoming effluent. The nutrient concentration of the remaining waste water may also be adjusted, as the subsequent aerobic treatment using bacterial processes requires an amount of nutrients. Biological purification employs natural microbes, which use organic materials of effluents as their nutrition. Biological purification methods may involve, for example, active sludge processes, anaerobic treatment, biological filtration or an aerated pond. Typically, the bacteria present in the biological processes oxidatively degrade organic compounds present in the waste water, thus lowering its chemical oxygen demand (COD) . As oxygen is required in the process, it may be added by aeration. After the bacterial processes have operated for a sufficient time, for instance approx, three weeks, biosludge is separated from the waste water.

[0009] Sludges may be processed after thickening e.g. in a screw press or a filter belt press, either alone or in mixture with other materials, and burned e.g. in a bark boiler or in a soda recovery unit. Sludges can also be treated biologically by anaerobic digesting to provide valuable biogas or by composting, so that sludges can be utilized as a fertilizer or in landscaping. Disposal of biosludge currently poses various challenges, however. It has a foul smell and is potentially harmful to the environment, as it may contain bacteria and / or other microorganisms. It may also contain phosphorus, other nutrients, potassium, chloride, residues of chemicals, various non-process elements (NPEs) and / or heavy metals. Biosludge may retain a large amount of water, so disposal of the bi- osludge by burning often requires a supplementary fuel , even if some of the water is removed prior to burning . The large amount of water al so results in the biosludge having a gel-like consistency . This makes it challenging to handle the biosludge . On the other hand, the consistency and certain components of the biosludge tend to interfere in processes in which biosludge could be used or recycled, for example when conveyed to a soda recovery unit in admixture with black liquor .

[0010] As such, there is a need for improved methods and systems for treating biosludge .

[0011] SUMMARY

[0012] A method for the treatment of biosludge is provided, wherein the biosludge comprises cellular structures , wherein the method comprises : mixing the biosludge with at least an acid to obtain a first mixture ; breaking the cellular structures of the biosludge in the first mixture at least partially to obtain a second mixture ; and separating a solid phase from the second mixture , thereby obtaining a solid product comprising the solid phase , and adding a solid component to the first mixture and / or to the second mixture .

[0013] A product compris ing at least 30 wt . -% , or at least 40 wt . -% of dry solids derived from biosludge , and at least 10 wt . -% , or at least 20 wt . -% of a solid component is provided .

[0014] A product comprising the solid phase obtainable by the method as described herein is provided .

[0015] A system for the treatment of biosludge is provided, wherein the biosludge comprises cellular structures , the system comprising : an apparatus for breaking the cellular structures of the biosludge in a mixture of the biosludge and an acid and optional ly a solid component at least partially; means for adding a solid component to the mixture ; and a separation apparatus for separating a solid phase from the mixture to obtain a product comprising the solid phase .

[0016] BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawing, which is included to provide a further understanding of the embodiments and constitute a part of this specification, illustrate various embodiments . In the drawing :

[0018] Figure 1 illustrates a method and a system for the treatment of biosludge .

[0019] DETAILED DESCRIPTION

[0020] Disposal of biosludge may be quite challenging, because it tends to retain a large amount of water . Biosludge may in some cases also contain various components that may need to be released and possibly removed prior to disposal , for example heavy metals , such as cadmium (Cd) .

[0021] It has now been found, however, that it i s possible to treat biosludge such that the solids content of the biosludge may be increased . The product obtainable by the method may thus have a s ignificantly increased energy content and may be burnt with an improved energy efficiency . The amount , e . g . volume and total weight , of the biosludge , which may be considered a waste , can be decreased . The use of water may also become more effective . Furthermore , its heavy metal content , for example Cd content , can be reduced . The product obtainable by the method may be suitable for use e.g. as a raw material for fertilizer products and / or for soil improvement. The use of supplementary fuels or other materials during the processing or disposal of biosludge may also be reduced or even eliminated. The method may be considered to be a chemi-mechanical treatment method, as it employs both a chemical agent (an acid) and a mechanical treatment.

[0022] The description related to the method described below apply to the product and system also described below and vice versa. The description related to the product also applies to the system and vrce versa.

[0023] A method for the treatment of biosludge

[0024] A method for the treatment of biosludge (1) is provided, wherein the biosludge (1) comprises cellular structures, wherein the method comprises: mixing the biosludge (1) with at least an acid (2) to obtain a first mixture; breaking the cellular structures of the biosludge (1) in the first mixture at least partially to obtain a second mixture; and separating a solid phase (9) from the second mixture, thereby obtaining a solid product comprising the solid phase (9) , and adding a solid component (3) to the first mixture and / or to the second mixture.

[0025] The method may be suitable for removing heavy metals and / or for releasing and optionally removing water from the biosludge (1) , i.e. increasing the dry solids (DS) content of the biosludge (1) . The acid (2) may assist in the method e.g. to extract or chemically separate certain components, such as heavy metals. In combination with the breaking of the cellular structures, the acid (2) can significantly improve the removal of water and / or potentially harmful components from the biosludge (1) .

[0026] The cellular structures of the biosludge (1) may be derived from plant material and / or from the microbes employed in the biological waste water treatment process from which the biosludge (1) is obtained. When the cellular structures of the biosludge (1) are broken at least partially, i.e. at least a part of the cellular structures of the biosludge (1) are broken, intracellular water can be released. Water within (i.e. intracellular water) or otherwise bound to the cellular structures can thus be released and removed from the biosludge (1) at least partially with the present method.

[0027] The term "biosludge" may be understood as referring to sludge obtainable from biological waste water treatment, i.e. residual, semi-solid material left from a biological waste water treatment process. Biosludge (1) typically contains various organic, inorganic, and microbiological contaminants. Biosludge (1) may contain cellular structures derived from the microbes used in the biological waste water treatment.

[0028] The biosludge (1) may be obtainable from the treatment process of waste water obtainable from a pulping process, such as a chemical pulping process. Such biosludge (1) may contain cellular structures derived from the wood material used in the pulping process. The biosludge (1) may also be obtainable from municipal sewage or from any other source of biosludge (1) . The biosludge (1) may therefore contain cellular structures derived from various sources, for example cellular structures derived from plant-based materials (other than wood material) .

[0029] The separated solid phase (9) may comprise the cellular structures and the solid component (3) . The method may further comprise adding a polymer (7) to the second mixture, prior to separating the solid phase (9) from the second mixture.

[0030] The polymer (7) may be added to the second mixture between the step of breaking the cellular structures of the biosludge (1) in the first mixture and separating the solid phase (9) from the second mixture. The second mixture may be mixed after the addition of the polymer (7) and prior to separating the solid phase (9) from the second mixture. Preferably, the added polymer (7) is capable of crosslinking in the second mixture. The polymer (7) can be any polymer that is capable of crosslinking in the conditions of the second mixture. However, the mixing should be applied such that the crosslinking of the polymer (7) is not negatively affected.

[0031] The polymer (7) may comprise a cationic polymer, such as cationic polyacrylamide.

[0032] In one embodiment, the polymer (7) consists of a cationic polymer, such as cationic polyacrylamide. The polymer (7) may have a charge of at least 5 meq / g, or at least 8 meq / g, or at least 15 meq / g. The polymer (7) may have an average molar mass of at least 300 000 g / mol, or 750 000 - 2 500 000 g / mol.

[0033] The polymer (7) may be added in an amount of 0,01 - 0, 05 kg / 100 kg dry product, or 0,02 - 0, 03 kg / 100 kg dry product.

[0034] It was found that adding a polymer (7) to the biosludge (1) as described above together with a solid component (3) gives the second mixture a suitable consistency such that the solid phase (9) comprising cellular structures may be separated from the second mixture at least partially. Without wishing to be bound by theory, it is believed that the slightly hydrophobic property of the polymer (7) contributes to obtaining a high dry content of the solid product. The solid component (3) may comprise waste material from the pulp and paper industry, such as primary sludge, bark, wood chips, or sawdust, or any mixture or combination thereof.

[0035] In one embodiment, the solid component (3) comprises essentially waste material from the pulp and paper industry, such as primary sludge, bark, wood chips, or sawdust, or any mixture or combination thereof. The solid component (3) may consist of or essentially comprise primary sludge. Throughout the specification, essentially may refer to, e.g., 99 wt . - % , or 99,5 wt.-%, or 99, 9 wt.-%.

[0036] The solid component (3) may have a particle size of at least 2 mm, or at least 3,5 mm, or at least 5 mm, or at least 7 mm, or at least 8 mm, or at least 9 mm.

[0037] The solid component (3) may have a particle size of 2 - 10 mm, or 3,5 - 10 mm, or 5 - 10 mm, or 7 - 10 mm, or 8 - 10 mm, or 9 - 10 mm.

[0038] The above particle size may refer to the length of the largest dimension of the solid component (3) . The largest dimension of the solid component may refer to the diameter of the smallest sphere in which the solid component (3) would fit. For the avoidance of doubt, the sphere refers to a fictious sphere.

[0039] It has surprisingly been found that the above particle size is optimal, as smaller particles can block filters in the separation step and larger particles do not provide an optimal consistency for separating the solid phase (9) from the second mixture.

[0040] The solid component (3) may be added in an amount of at least 20 wt.-%, or at least 30 wt.-%, or at least 40 wt.-%, wherein the wt.-% may refer to wt . - % in the mixture to which the solid component (3) is added .

[0041] The solid component (3) may be added in an amount of 20 - 80 wt.-%, or 30 - 80 wt.-%, 40 - 80 wt.-%, wherein the wt.-% may refer to wt.-% in the mixture to which the solid component (3) is added.

[0042] The solid component (3) may be added to the first mixture, or the solid component (3) may be added to the second mixture prior to separating the solid phase (9) from the second mixture. Alternatively, the solid component (3) may be added in two steps, i.e. to the first mixture and to the second mixture. The first and / or second mixture may be agitated after addition or simultaneously as the solid component (3) is added. The solid component (3) may be added simultaneously as the polymer (7) is added to the second mixture. The solid component (3) may be added simultaneously as the biosludge (1) and acid (2) is mixed to obtain the first mixture.

[0043] In one embodiment, the solid component (3) is added to the second mixture.

[0044] It has been found that adding to the biosludge (1) a solid component (3) as described above gives the second mixture a suitable consistency such that the solid phase (9) comprising cellular structures may be separated from the second mixture at least partially.

[0045] The acid (2) may, in principle, be any acid that can be mixed with the biosludge (1) , including any inorganic and organic acids and any mixtures or combinations thereof. Examples of possible inorganic acids may include hydrogen halides, such as hydrochloric acid (HC1) , and their solutions; sulphuric acid (H2SO4) ; nitric acid (HNO3) ; phosphoric acid (H3PO4) ; or any mixtures or combinations thereof. Examples of possible organic acids include carboxylic acids, such as acetic acid (CH3COOH) , citric acid, formic acid (HCOOH) , gluconic acid, lactic acid, oxalic acid, tartaric acid, or any mixtures or combinations thereof. In an embodiment, the acid (2) is an inorganic acid, such as sulphuric acid, hydrochloric acid, or nitric acid; an organic acid, such as a carboxylic acid; or any mixture or combination thereof. In an embodiment, the acid (2) is sulphuric acid, hydrochloric acid, or nitric acid, or any mixture thereof. It has been found that phosphoric acid and / or nitric acid is useful when the solid product is used as a fertilizer. The acid (2) may be, in an embodiment, understood as referring to an aqueous solution of an acid (2) , including any of the acids described above. The concentration of the aqueous solution of the acid (2) may be selected such that a desired pH and / or volume of the mixture of the acid (2) , i.e. the aqueous solution of the acid, and the biosludge (1) is achieved. A concentrated acid (2) solution, for example concentrated sulphuric acid (>98 weight-% H2SO4) , concentrated hydrochloric acid (>37 weight-% HC1) , or concentrated nitric acid (>68 weight-% HNO3) may be used, for example so as to avoid introducing large volumes of water into the mixture.

[0046] The acid (2) , such as concentrated acid (2) , may be added in an amount of at least 5 kg / 100 kg dry product or at least 10 kg / 100 kg dry product, or at least 23 kg / 100 kg dry product.

[0047] The acid (2) , such as concentrated acid (2) , may be added in an amount of 5 kg / 100 kg - 23 kg / 100 kg dry product, or 10 kg / 100 - 23 kg / 100 kg dry product .

[0048] The pH of the first mixture may be adjusted to a pH of 4 or lower. The pH of the first mixture may be adjusted to a pH of 2.5 or lower, or 2 - 2.4. The pH of the second mixture may be adjusted to a pH of 4 or lower. The pH of the second mixture may be adjusted to a pH of 2.5 or lower, or 2 - 2.4. For the avoidance of doubt, the pH of both the first and second mixture may be adjusted as above or only the pH of the first mixture or the second mixture may be adjusted as above. In general, a lower pH may improve the results. For example, a lower pH may be associated with improved removal of heavy metals, such as Cd. The pH may however also be optimized such that the consumption of the acid (2) remains economical. It has been found that the above pH is optimal for drying the solid product. Without wishing to be bound by theory, it is believed that the polymer (7) creates an optimal crosslinked arrangement in the above pH.

[0049] A flocculant may be added to the mixture, to the biosludge (1) or to the acid (2) . The flocculant may in some situations improve the results.

[0050] The biosludge (1) , the acid (2) , and optionally the solid component (3) may be premixed, i.e. admixed to form a mixture prior to breaking the cellular structures of the biosludge (1) at least partially. This may be done e.g. in a suitable mixing device, for example in a mixing tank. During the premixing, the properties of the mixture, for example the volume, viscosity, and / or consistency of the mixture, may be adjusted. Alternatively, or additionally, the biosludge (1) , the acid (2) , and optionally the solid component (3) may be fed separately to the apparatus for breaking the cellular structures (4) of the biosludge (1) in the mixture at least partially, in which they are simultaneously intimately mixed. For example, the acid (2) , the biosludge (1) , and optionally the solid component (3) may be fed separately to a mixer in which the cellular structures of the biosludge (1) are subsequently broken at least partially.

[0051] Various means can be employed for breaking the cellular structures of the biosludge (1) in the mixture at least partially. For example, the biosludge (1) , acid (2) , and optionally the solid component (3) , and / or the mixture thereof may be fed to a mixer and subjected simultaneously to shear forces, thereby breaking the cellular structures of the biosludge (1) at least partially. Suitable mixers for this purpose may be e.g. a blade mixer comprising a dispersion blade, a high shear impeller, or a rotor-stator mixer. Such a mixer may also impart impact forces to the mixture .

[0052] The breaking of the cellular structures may be particularly efficient, if a high shear mixer is used. In an embodiment, the first mixture is fed to a zone of high shear forces within a high shear mixer and subjected simultaneously to the zone of high shear forces, thereby breaking the cellular structures of the biosludge (1) at least partially. Since the first mixture is fed to and subjected to the zone of the high shear forces, these forces may be exerted on substantially the entire volume of the first mixture. For example, blade mixers may produce high shear forces at the rim of the blade, but they do not form a zone of high shear forces, through which all or essentially all of the biosludge (1) , acid (2) , and optionally the solid component (3) would be forced. On the other hand, high shear mixers such as impact mixers (e.g. Atrex®-type mixers) may produce high shear forces and all or essentially all of the first mixture, due to the geometry of the mixer, is forced through the zone of high shear forces formed by the rotors. For example, at least about 90 wt.-%, or at least about 95 wt.-%, or at least about 99 wt.-% of the first mixture may pass through the zone of high shear forces.

[0053] The mixing of the biosludge (1) , the acid (2) , and optionally the solid component (3) is therefore efficient and may be faster than e.g. using a conventional mixer, i.e. the residence time in the high shear mixer may be reduced. Energy consumption may also be reduced. Furthermore, the high shear forces may efficiently break the cellular structures. Further, the particle size of the solid component (3) may be modified in the high shear mixer to obtain a suitable particle size, if the solid component (3) is added to the first mixture. This saves energy as the solid component (3) does not have to be modified separately prior to its addition.

[0054] The particle size of the solid component (3) may be modified separately by subjecting the solid component (3) to high shear forces in a high shear mixer, such as an Atrex®-type mixer, prior to adding the solid component (3) to the first mixture and / or to the second mixture. The high shear mixer for the solid component (3) may be the same or a separate high shear mixer compared to the high shear mixer for the biosludge (1) , the acid (2) , and optionally the solid component (3) .

[0055] The energy intensity of the high shear forces to which the first mixture is subjected in the high shear mixer may be selected depending on various factors. The energy intensity may be such that the cellular structures in the biosludge (1) are broken to such an extent that heavy metals, water and / or other components are released and removed at least partially. The energy intensity may therefore be, for example, at least 200 kWh / m3or at least 300 kWh / m3. The energy intensity may be, for example, up to 650 kWh / m3, or in the range of about 200 to about 650 kWh / m3. The energy intensity of the high shear forces to which the solid component (3) may be subjected may be at least 300 kWh / m3, or at least 350 kWh / m3, or at least 400 kWh / m3. The energy intensity of the high shear forces to which the solid component (3) may be subjected may be 300 - 500 kWh / m3, or 350 - 500 kWh / m3, or 400 - 500 kWh / m3. These high shear forces have resulted in the optimal particle size of the solid component (3) . In an embodiment , the first mixture is subj ected to an energy intensity of 300 - 500 kWh / m3in the high shear mixer . Such an energy intensity may be well suited for breaking the cellular structures .

[0056] Any energy intensities described in this specification may be calculated on the basis of the volume occupied by the mixture fed into the high shear zone .

[0057] The residence time in the zone of high shear forces may be about 0 . 01 to 60 seconds , or longer, if desired .

[0058] The high shear mixer may be capable of operating continuously .

[0059] In an embodiment , the zone of high shear forces is formed by a mixing zone of a high shear mixer having at least one rotating rotor element .

[0060] In an embodiment , the zone of high shear forces is formed by a mixing zone of a high shear mixer having at least one static stator element and at least one rotating rotor element .

[0061] In an embodiment , the zone of high shear forces is formed by a mixing zone of a high shear mixer having at least two counter-rotating rotors .

[0062] An example of a high shear mixer may be an impact mixer, for example an impact mixer sold under the trade name Atrex® (Megatrex Oy) . Such a high shear mixer may comprise a first rotor provided with blades and a second rotor provided with blades , wherein the first and second rotor are arranged concentrically with each other and configured to rotate in opposite directions in relation to each other, and the first mixture is supplied through the rotors such that it i s repeatedly subj ected to shear forces by the effect of the blades , the effect of the blades thereby forming the zone of high shear forces and breaking the cellular structures of the biosludge ( 1 ) in the mixture at least partially . The rotor elements may be capable of rotating at a speed of about 500 - 5000 rpm. Examples of such a high shear mixer are described e.g. in WO 2013 / 072559 (page 7, line 1 - page 11, line 17 and Figures 1-4) ; or in FI 105112 B (e.g. the device described in Figs. 1 - 5 and associated paragraphs in the text, e.g. p. 5, 1. 30 to p. 8, 1. 31) .

[0063] Another type of high-shear mixer is the mixer sold under the trade name Cavitron® (Hagen & Funke GmbH) . Such a Cavitron-type high-shear mixer may comprise a dispersing unit or shock-wave reactor. In the dispersing unit or shock-wave reactor, a zone of high shear forces is induced by a rotor / stator system having passage gaps at the rotor and stator. The Cavitron-type high-shear mixer may be configured to fill the gaps arranged in a row with the first mixture such that it is centrifugally accelerated by the rotor to gaps in an adjacent row of gaps, thereby generating alternating pressure fields. Examples of possible high shear mixers are described e.g. in US3165299A and US3589363.

[0064] After breaking the cellular structures of the biosludge (1) in the mixture at least partially, and adding the solid component (3) , and optionally the polymer (7) , the solid phase (9) may be separated from the mixture, thereby obtaining a product comprising the solid phase. Thus, the solid phase (9) and a liquid phase (10) may be obtained.

[0065] The solid phase (9) may be separated using suitable means, for example a filtering device or a centrifugal device. In an embodiment, the solid phase (9) is separated using at least one of a pressure filter. The pressure filter may be a vertical pressure filter. A vertical pressure filter may have a relatively good performance for separating the solid phase. However, the pressure filter may, additionally or alternatively, be a horizontal pressure filter. The separated solid phase (9) may then be recovered. The liquid phase (10) , for example a filtrate obtainable by separating the solid phase (9) using a filter, may be recovered and / or discarded. At least a part of the heavy metals, such as Cd, derived from the biosludge (1) can thus be leached into the liquid phase (10) .

[0066] The treatment may be repeated such that the solid phase (9) obtained, not the biosludge (1) , is mixed with the acid (2) , whereafter all steps of the method disclosed herein are repeated. — Repeating the treatment may improve the result.

[0067] The liquid phase (10) may be conveyed to effluent. However, the liquid phase (10) may also be treated further. For example, it may be treated to remove metals e.g. by an electrochemical treatment or ion exchange. Such treated liquid phase (10) could be reused as process water.

[0068] The solid product, i.e. the solid phase, may be in the form of a cake after it has been separated from the liquid phase (10) .

[0069] The method may further comprise drying the product for at least 16 hours, or at least 24 hours, or at least 48 hours without breaking the product. The method may further comprise drying the product for 16 hours to 4 years, or 24 hours to 4 years, or 48 hours to 4 years without breaking the product.

[0070] Not breaking the product may mean that the obtained cake is not broken, crushed, sliced, or chopped in any way.

[0071] The drying may be performed in ambient conditions. Alternatively, additional heat may be applied to the product when drying.

[0072] It has been found that a lower moisture content may be achieved faster in the solid product when the solid product is dried without breaking the solid product. Without wishing to be bound by theory, it is believed that the polymer (7) creates a capillary ar- rangement within the dried product and with the help of stored heat inside the dried product, moisture may escape the dried product through the capillaries.

[0073] Heating of the second mixture may improve the results, such as the dry solids content of the product obtainable and / or the removal of heavy metals, such as Cd. The second mixture may be heated to a temperature of at least 30°C, or at least 40°C, or at least 50°C before separating a solid phase (9) from the mixture. However, it is also possible to heat the second mixture to a higher temperature, for example to a temperature of at least 60°C, or at least 70°C, or up to 70°C. It is possible to heat the second mixture to a temperature of 30 - 40 °C, 40 - 50°C, or 50 - 70°C. The second mixture may be heated before or after adding the solid component (3) and optionally the polymer (7) . The second mixture may be heated after adding the solid component (3) and before adding the polymer (7) . The heating may be done e.g. using steam.

[0074] A product comprising dry solids derived from biosludge

[0075] A product comprising at least 30 wt.-%, or at least 40 wt.-% of dry solids derived from biosludge (1) , and at least 10 wt.-%, or at least 20 wt.-% of a solid component (3) is provided. The product may comprise 30 - 60 wt.-%, or 40 - 70 wt.-% of dry solids derived from biosludge (1) , and 10 - 40 wt.-%, or at least 20 - 50 wt.-% of a solid component (3) .

[0076] The product may further comprise at least 0,01 wt.-%, or at least 0,02 wt.-%, or at least 0,03 wt.-% of a polymer (7) . The product may further comprise at least 0,01 - 1 wt.-%, or 0,02 - 1 wt.-%, or 0,03 - 1 wt.-% of a polymer (7) .

[0077] The polymer (7) may comprise a cationic polymer (7) , such as cationic polyacrylamide. The polymer (7) may consist of a cationic polymer (7) , such as cationic polyacrylamide. The solid component (3) may comprise dry solids derived from waste material from the pulp and paper industry and preferably primary sludge, bark, wood chips, sawdust, or any mixture or combination thereof.

[0078] In one embodiment, the dry solids derived from waste material from the pulp and paper industry comprises essentially primary sludge, bark, wood chips, sawdust, or any mixture or combination thereof. The dry solids may consist of or comprise essentially primary sludge.

[0079] The product may comprise less than 40 wt.-%, or less than 30 wt.-%, or less than 20 wt.-%, or less than 10 wt.-% water. The product may comprise 0 - 40 wt.-%, or 0 - 30 wt.-%, or 0 - 20 wt.-%, or 0 - 10 wt . -% water .

[0080] The product may comprise less than 0,01 wt . - % , or less than 0,02 wt.-% heavy metals, and preferably less than 2 ppm, or less than 1 ppm cadmium. The product may comprise 0 - 0, 01 wt.-%, or 0 - 0,02 wt.-% heavy metals, and preferably 0 - 2 ppm, or 0 - 1 ppm cadmium.

[0081] The dry solids derived from waste material from the pulp and paper industry may have a particle size of at least 2 mm, or at least 3,5 mm, or at least 5 mm, or at least 7 mm, or at least 8 mm, or at least 9 mm. The dry solids derived from waste material from the pulp and paper industry may have a particle size of 2 - 10 mm, or 3,5 - 10 mm, or 5 - 10 mm, or 7 - 10 mm, or 8 - 10 mm, or 9 - 10 mm.

[0082] The product may be a fertilizer product, a soil conditioner, or biofuel.

[0083] The product may be incinerated. Due to the relatively high dry solids content of the product, it may be incinerated without a supplementary fuel. Some embodiments of the product may have a lower heating value greater than 6 MJ / kg, or even greater than 10 MJ / kg.

[0084] Use of the product for fertilizing or soil conditioning is also disclosed.

[0085] A product comprising the solid phase (9) obtainable by the method is provided.

[0086] A system for the treatment of biosludge

[0087] A system for the treatment of biosludge (1) is provided, wherein the biosludge (1) comprises cellular structures, the system comprising: an apparatus for breaking the cellular structures (4) of the biosludge (1) in a mixture of the biosludge (1) and an acid (2) and optionally a solid component (3) at least partially; means for adding a solid component to the mixture (5) ; and a separation apparatus (8) for separating a solid phase (9) from the mixture to obtain a product comprising the solid phase. The apparatus for breaking the cellular structures (4) of the biosludge (1) in the mixture of the biosludge (1) and the acid (2) and optionally the solid component (3) at least partially may comprise a high shear mixer.

[0088] In an embodiment, the high shear mixer comprises a first rotor provided with blades and a second rotor provided with blades, wherein the first and second rotor are arranged concentrically with each other and configured to rotate in opposite directions in relation to each other, so that the biosludge (1) and the acid (2) and optionally the solid component (3) , or the mixture thereof are repeatedly subjected to shear forces by the effect of the blades, the effect of the blades thereby breaking the cellular structures of the biosludge (1) in the mixture of the biosludge (1) and the acid (2) and optionally the solid component (3) at least partially. Such a high shear mixer is thus configured to form the zone of high shear forces by the effect of the blades.

[0089] In an embodiment, the high shear mixer is a Cavitron-type mixer or an Atrex-type mixer.

[0090] The separation apparatus (8) may be, for example, a centrifugal apparatus, or a filter. In an embodiment, the separation apparatus (8) is a pressure filter, such as a vertical pressure filter or a horizontal pressure filter.

[0091] The apparatus for breaking the cellular structures (4) of the biosludge (1) in a mixture of the biosludge (1) , an acid (2) , and optionally a solid component (3) at least partially may be configured to intimately mix the biosludge (1) and acid (2) fed or injected therein separately. The mixing may be done simultaneously as the breaking of the cellular structures. However, alternatively or additionally, the system may comprise a mixing device for mixing the biosludge (1) with at least an acid (2) and optionally a solid component (3) to obtain the mixture prior to breaking the cellular structures. The mixing device may be suitable for premixing the biosludge (1) with the acid (2) and optionally the solid component (3) to obtain the mixture prior to conveying the mixture to the apparatus for breaking the cellular structures (4) of the biosludge (1) in the mixture of the biosludge (1) and the acid (2) at least partially.

[0092] The system may further comprise means for adding a polymer (6) to the mixture.

[0093] The system may further comprise a storage vessel, such as a buffer tank, for storing the mixture after breaking the cellular structures at least partially .

[0094] The system may, in an embodiment, further comprise at least one of: a mixing device for mixing the biosludge (1) with at least an acid (2) to obtain the mixture; a heater and / or a dryer for increasing the dry solids content of the product, such as a thermal dryer.

[0095] The system may further comprise a high shear mixer, such as an Atrex-type mixer, for modifying the particle size of the solid component (3) . For the avoidance of doubt, the high shear mixer for modifying the particle size of a solid component (3) may be the same or different from the apparatus for breaking the cellular structures (4) of the biosludge (1) .

[0096] EXAMPLES

[0097] Example 1

[0098] The following example illustrates a process for making a product comprising dry solids derived from biosludge.

[0099] Primary sludge was ground in an Atrex® (CD500G45) mixer and subjected to an energy intensity of 286 kWh / m3. The pH of biosludge was adjusted to 2 and the pH adjusted biosludge was ground in an Atrex® (CD500G45) mixer and subjected to an energy intensity of 406 kWh / m3.

[0100] 65 kg of the primary sludge was mixed with 35 kg of the biosludge and the temperature was adjusted to 70°C.

[0101] 3,7 g of a polymer was added.

[0102] 40 kg of the primary sludge / biosludge / polymer mixture was added to a vertical pressure filter (Outotec Larox FP 0.9) having a feed chamber of 40 mm in diameter, a feed of 7,5 minutes and 15 bar, a compression of 5 minutes and 15 bar, and an airdrying of 1 minutes and 6 bar.

[0103] 37 kg of filtrate was removed during the pressure filtration and a 3 kg cake of solids was obtained. The 3 kg cake had a dry content of 40 wt.-%. The pressure filter was opened.

[0104] The cake was dried indoors in ambient conditions for 96h.

[0105] Example 2

[0106] The following example illustrates a process for making a product comprising dry solids derived from biosludge.

[0107] Primary sludge was ground in an Atrex® (CD500G45) mixer and subjected to an energy intensity of 215 kWh / m3. The pH of biosludge was adjusted to 2 and the pH adjusted biosludge was ground in an Atrex® (CD500G45) mixer and subjected to an energy intensity of 406 kWh / m3.

[0108] 65 kg of primary sludge was mixed with 35 kg of biosludge and the temperature was adjusted to 70°C.

[0109] 3,7 g of a polymer was added.

[0110] 58,22 kg of the primary sludge / biosludge / polymer mixture was added to a vertical pressure filter (Outotec Larox FP 0.9) having a feed chamber of 2x40 mm in diameter, a feed of 30 minutes and 6 bar, a compression of 35 minutes and 10 bar, and an airdrying of 1 minutes and 6 bar.

[0111] 52 kg of filtrate was removed during the pressure filtration and a 6.22 kg cake of solids was obtained. The 6.22 kg cake had a dry content of 40 wt.-%. The pressure filter was opened.

[0112] The cake was dried indoors in ambient conditions for 96h.

Claims

CLAIMS1. A method for the treatment of biosludge (1) , wherein the biosludge (1) comprises cellular structures, wherein the method comprises: mixing the biosludge (1) with at least an acid (2) to obtain a first mixture; breaking the cellular structures of the biosludge (1) in the first mixture at least partially to obtain a second mixture; and separating a solid phase (9) from the second mixture, thereby obtaining a solid product comprising the solid phase (9) , and adding a solid component (3) to the first mixture and / or to the second mixture.

2. The method according to claim 1, wherein the method further comprises adding a polymer (7) to the second mixture, prior to separating the solid phase (9) from the second mixture.

3. The method according to claim 2, wherein the polymer (7) comprises a cationic polymer, such as cationic polyacrylamide.

4. The method according to any of claims 2 or 3, wherein the polymer (7) is added in an amount of 0,01 - 0, 05 kg / 100 kg dry product, or 0,02 - 0, 03 kg / 100 kg dry product.

5. The method according to any preceding claims, wherein the solid component (3) comprises waste material from the pulp and paper industry, such as primary sludge, bark, wood chips, or sawdust, or any mixture or combination thereof.

6. The method according to any preceding claims, wherein the solid component (3) has a particlesize of at least 2 mm, or at least 3,5 mm, or at least 5 mm, or at least 7 mm, or at least 8 mm, or at least 9 mm.

7. The method according to any preceding claims, wherein the solid component (3) is added in an amount of at least 20 wt.-%, or at least 30 wt.-%, or at least 40 wt.-%.

8. The method according to any preceding claims, wherein the acid (2) is an inorganic acid, such as sulphuric acid, hydrochloric acid, or nitric acid; an organic acid, such as a carboxylic acid; or any mixture or combination thereof.

9. The method according to any preceding claims, wherein the first mixture is fed to a zone of high shear forces within a high shear mixer and subjected simultaneously to the zone of high shear forces, thereby breaking the cellular structures of the biosludge (1) at least partially.

10. The method according to claim 9, wherein the first mixture is subjected to an energy intensity of at least 300 kWh / m3, or at most 500 kWh / m3, or 300 - 500 kWh / m3in the high shear mixer.

11. The method according to any preceding claims, wherein the solid phase (9) is separated using a pressure filter, such as a vertical pressure filter.

12. The method according to any preceding claims, wherein the pH of the first mixture is adjusted to a pH of 5 or lower, or 4 or lower, or to a pH of 2.5 or lower, or to a pH of 2 to 2.4 and / or wherein the pH of the second mixture is adjusted to apH of 5 or lower, or 4 or lower, or to a pH of 2.5 or lower, or to a pH of 2 to 2.4.

13. The method according to any preceding claims, wherein the method further comprises heating the second mixture to a temperature of at least 40°C, or at least 50°C, or at least 60°C before separating a solid phase (9) from the mixture.

14. The method according to any preceding claims, wherein the method further comprises drying the product for at least 24 hours, or at least 48 hours, or at least 72 hours without breaking the product .

15. A product comprising at least 30 wt.-%, or at least 40 wt.-% of dry solids derived from biosludge (1) , and at least 10 wt.-%, or at least 20 wt.-% of a solid component (3) .

16. The product according to claim 15, wherein the product further comprises at least 0,01 wt.-%, or at least 0,02 wt.-%, or at least 0,03 wt.-% of a polymer ( 7 ) .

17. The product according to claim 16, wherein the polymer (7) comprises a cationic polymer, such as cationic polyacrylamide.

18. The product according to any of claims 15 to 17, wherein the solid component (3) comprises dry solids derived from waste material from the pulp and paper industry, and preferably primary sludge, bark, wood chips, sawdust, or any mixture or combination thereof .

19. The product according to any of claims 15 to 18, wherein the product comprises less than 40 wt . - % , or less than 30 wt.-%, or less than 20 wt.-%, or less than 10 wt.-% water.

20. The product according to any of claims 15 to 19, wherein the solid component (3) has a particle size of at least 2 mm, or at least 3,5 mm, or at least 5 mm, or at least 7 mm, or at least 8 mm, or at least 9 mm.

21. The product according to any of claims 15 to 20, wherein the product is a fertilizer product, a soil conditioner, or biofuel.

22. A product comprising the solid phase (9) obtainable by the method according to any of claims 1 to 14.

23. A system for the treatment of biosludge (1) , wherein the biosludge (1) comprises cellular structures, the system comprising: an apparatus for breaking the cellular structures (4) of the biosludge (1) in a mixture of the biosludge (1) and an acid (2) and optionally a solid component (3) at least partially; means for adding a solid component to the mixture (5) ; and a separation apparatus (8) for separating a solid phase (9) from the mixture to obtain a product comprising the solid phase (9) .

24. The system according to claim 23, wherein the apparatus for breaking the cellular structures (4) of the biosludge (1) in the mixture of the biosludge (1) and the acid (2) and optionally a solid component (3) at least partially comprises a high shear mixer.

25. The system according to claim 23 or 24, wherein the separation apparatus (8) is a pressure filter, such as a vertical pressure filter.

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