Method and system for managing sludge

Abstract

A method and a system (100) for managing dry solid concentration of sludge are disclosed. The method comprises feeding (215) an amount of the sludge, referred to as "sludge amount", into a refrigerating device (114), having rod-shaped freezing elements, by means of a pump (112), wherein the sludge amount is pumpable, freezing (220), in the refrigerating device (114), the sludge amount into frozen units, each frozen unit having the shape of a rod with a through-hole, releasing (225), from the refrigerating device (114), the frozen sludge amount at a transportation arrangement (120) by that the freezing elements are heated, wherein the feeding (215), the freezing (220), and the releasing (225) are performed in sequence and repeatedly for each sludge amount of a batch of respective sludge amounts.

Description

[0001] METHOD AND SYSTEM FOR MANAGING SLUDGE

[0002] TECHNICAL FIELD

[0003] The embodiments herein relate to the field of waste management, particularly to the processing of sludge containing water. One objective is to increase the dry solid concentration of the sludge. The methods involve feeding the sludge into a refrigerating device, freezing the sludge to obtain a frozen sludge, releasing the frozen sludge onto a transportation system, and then thawing the frozen sludge during transportation. This process leads to the separation of liquid water from the sludge. The liquid water is then conveyed to a water outlet, and the sludge is output at a sludge outlet. This technology can be applied in various industries dealing with sludge management, including wastewater treatment, food processing, and chemical industries.

[0004] BACKGROUND

[0005] The field of waste management, particularly the processing and treatment of sludge, has been an area of continuous advancement. Sludge refers to a viscous, semi-solid, or gelatinous material that is often the byproduct of various industrial processes or wastewater treatment. It typically consists of a mixture of solids, water, and, in some cases, chemicals or organic matter. Sludge can be found in a variety of applications such as sewage treatment plants, manufacturing facilities, or oil refineries. Its composition and characteristics vary depending on the source and treatment process involved.

[0006] Sludge management and disposal are crucial considerations to ensure environmental sustainability and comply with relevant regulations.

[0007] Sludge generally contains a large amount of water which can make it more challenging to manage and dispose of. In the context of wastewater treatment, there are different types of water found in sludge-related processes. These are generally categorized as:

[0008] Free Water: This is the water that can be easily separated from the sludge. It is typically the liquid portion that can be drained or filtered out.

[0009] Interstitial Water: Also known as interstitial or bound water, this water is held in the spaces between the solid particles in the sludge. The water is typically associated with physical adsorption or absorption on the surface or within the structure of the solid. It is not easily separated and may require additional processes for extraction. Capillary Water: This is the water held in the capillary spaces within the sludge particles. It is also not easily separated and may require specific techniques for removal.

[0010] Bound Water: Some water in sludge may be bound, such as chemically bound, to the solid particles. Removing this water may involve more advanced processes, and it may not be as easily separated as free water.

[0011] Free water and interstitial water are typically fairly easy to separate from the sludge, for example using various draining, pressing, filtering, centrifuging processes, etc. These processes are typically known as mechanical dewatering processes. The capillary water and chemically bound water, however, is more challenging and may involve more advanced processes for removal, which may require significant energy input or addition of chemical reagents. This not only increases operational cost but also may have associated environmental concerns.

[0012] Another approach towards handling large quantities of sludgy waste involves freezing and thawing cycles. This is based on the principle that water in media such as soil or sludge will tend to migrate towards colder regions and subsequently freeze. Upon thawing, this can result in a higher concentration of solid matter separated from the liquid part. Essentially, this process transforms the capillary and chemically bound water into free water, which can be removed using a mechanical dewatering process, such as the ones described above.

[0013] Transferring frozen sludge within a transportation system forms another key aspect for consideration. It is important to maintain effective operations while ensuring minimal loss or contamination during transfer from one point to another within the system.

[0014] While using this technique can effectively separate solids from liquids in certain cases by exploiting different freezing points, it also introduces several new complexities into the process. For instance, managing thermal properties and heat exchange across different stages becomes critical. Moreover, freeze-thaw cycles may lead to structural changes in some types of waste material which could affect subsequent handling or treatment steps.

[0015] Further complications arise when considering how best to handle release points for both liquid water and processed sludge within these systems. The efficient routing and separation of different processing streams is necessary for maintaining productivity, reducing clogging issues at various outlets. Different types of sludge also exhibit varying freezing and thawing behaviors. For example, sewage sludge behaves differently from oil sludge or sludge that is contaminated with mercury or chrome, which further complicates the process.

[0016] On a more general level, there are common challenges around improving efficiency and reducing costs associated with waste management processes including those dealing with high volumes of sludgy waste materials containing substantial quantities of water.

[0017] Current solutions have sought ways around these limitations through various mechanisms; however they still fall short in terms of delivering an optimized solution that offers efficiency both in terms of energy consumption as well as operational cost while maintaining high performance levels across all stages involved in processing waste material of different types.

[0018] SUMMARY

[0019] An object may be to mitigate, or even eliminate, the abovementioned disadvantage, or other disadvantages or problems.

[0020] According to an aspect, there is provided a method for managing, such as changing, altering, amending, increasing, or the like, dry solid concentration of sludge, comprising water and solids. The method comprises feeding an amount of the sludge, referred to as "sludge amount", into a refrigerating device, and freezing, in the refrigerating device, the sludge amount. At this stage, i.e. after the freezing, the refrigerating device includes a frozen sludge amount, being the sludge amount when frozen. The method further comprises releasing, from the refrigerating device, the frozen sludge amount at a transportation arrangement, and transporting, by the transportation arrangement, the sludge amount while thawing the sludge amount. Thanks to the thawing, at least some liquid water leaves, such as through gravity, dripping, evaporation, or the like, the sludge amount, whereby an output sludge is formed, i.e. the sludge amount remaining after said at least some liquid water has left the sludge that was frozen. The output sludge has a dry solid concentration that is greater than a dry solid concentration of the sludge amount fed into the refrigerating device. Moreover, the method comprises conveying said at least some liquid water to a water outlet, and outputting, e.g. by the transportation arrangement, the output sludge at a sludge outlet of the system. Thanks to the freezing of the sludge, separation of water from the sludge amount is enhanced. Thereby, an increased dry solid concentration of the sludge can be achieved. Advantages of increased dry solid concentration of the sludge includes reduced cost from transportation, e.g. due to reduced weight and / or volume of the sludge. Furthermore, recycling of the sludge is facilitated since the output sludge can be recycled separately from the recycling of the water.

[0021] In some embodiments, the method can release the sludge batchwise at the transportation arrangement.

[0022] In some embodiments, the feeding, the freezing, and the releasing are performed in sequence and repeatedly for each sludge amount of a batch of respective sludge amounts. Accordingly, the method can include batchwise feeding, freezing and releasing of the sludge amount, e.g. at the refrigerating device.

[0023] In the embodiments herein, the batch includes a set of respective sludge amounts, wherein each respective sludge amount is associated with a respective repetition of the feeding, the freezing and the releasing.

[0024] In some embodiments, the method comprises, after the feeding of the sludge amount and before the freezing of the sludge amount stopping the feeding of the sludge amount.

[0025] In some embodiments, the method comprises feeding a flow of air at a portion of the transportation arrangement to crack the amount of frozen sludge, thereby facilitating separation of water from the sludge.

[0026] In some embodiments, the method comprises receiving the sludge at an inlet, and homogenizing the sludge. Thanks to the homogenization, viscosity of the sludge is increase, e.g. as compared to before homogenization. In this manner, the sludge can be made pumpable. Thus, facilitating handling of the sludge.

[0027] In some embodiments, the method is performed by a system comprising a container having a first module and a second module. The first module has a lower temperature than the second module. The system also comprises the refrigerating device and the transportation arrangement.

[0028] The first and second module can be separated by a separating wall, having a feed-through hole.

[0029] A module can be exemplified by a compartment, a portion, a section, or the like. The first module is insulated at least towards the second module.

[0030] The feeding, the freezing and the releasing can be performed in the first module, e.g. of the container.

[0031] The transporting, the outputting and the conveying can be performed in the second module, e.g. of the container.

[0032] In some embodiments, the method comprises breaking the frozen sludge into smaller pieces.

[0033] In some embodiments, the outputting of the output sludge comprises transporting the output sludge to a drying arrangement for further drying of the output sludge.

[0034] In some embodiments, the method comprises collecting water that left the sludge amount, e.g. during the transportation and thawing of the amount of frozen sludge.

[0035] In some embodiments, the method comprises outputting water that left the sludge amount, e.g. during the transportation and thawing of the amount of frozen sludge, at the water outlet.

[0036] According to another aspect, there is provided a system configured for performing examples of the method herein.

[0037] BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG. 1 shows a schematic view of a sludge processing system, in accordance with one embodiment.

[0039] FIG. 2 shows flowchart of a method for processing of sludge, in accordance with one embodiment.

[0040] Like reference numerals indicate like components.

[0041] DETAILED DESCRIPTION

[0042] As used herein, "dry solid concentration" refers to a measure of the amount of solid material in a wastewater sample, such as sludge or the like. The measure can be given by a weight percentage, or sometimes by a volume percentage.

[0043] As used herein, "sludge" refers to a mixture of water and solids, where the solid can include bound water. The sludge can further include one or more of proteins, oils, further contaminants, debris, or the like.

[0044] An object of the invention can be to provide a method for processing sludge, which includes water and solids, to increase the dry solid concentration of the sludge. A significant benefit offered by the various embodiments of the invention lie in its energy efficiency compared to conventional methods, such as hydrothermal dewatering, mechanical dewatering, or the like, used for increasing dry solid concentrations in similar materials.

[0045] Additionally, the methods according to the various embodiments described herein avoid using any chemicals typically needed when dealing with such materials. Absence of chemicals not only reduces operational costs but also minimizes potential environmental impact associated with their use and disposal.

[0046] Experiments by the inventors have demonstrated that at the end of the processing, the sludge thus obtained can have approximately 80% dry solid concentration. With conventional techniques, a final dry solid concentration can be approximately 17-23%, e.g. at the same or higher energy consumption. Thus, the embodiments herein show a four- or five-fold increase in concentration of solids compared to existing technologies. Further experiments show that it is possible, with the embodiments herein, to obtain up to 80% dry solid concentration.

[0047] Various embodiments will now be described in further detail and with reference to the drawings.

[0048] FIG. 1 shows a schematic view of a sludge processing system 100 for processing of sludge, in accordance with one embodiment.

[0049] As shown in FIG. 1, the sludge processing system 100 includes a cold module 102, as an example of the first module, and a warm module 104, as an example of the second module. The cold module 102 has an inlet 106 through which sludge is input into the system 100 and the warm module 104 has an outlet 108 through which the processed sludge is output at the end of the processing. The warm module 104 further has a water outlet 124 for outputting of water separated from the incoming sludge. The cold module 102 has a lower temperature than the warm module 104.

[0050] It should be noted that while only a single inlet 106, a singe sludge outlet 108 and a single water outlet 124 are illustrated in FIG. 1 for simplicity, there can be one or more of each of these depending on application. In some examples, there can be several inlets 106, for example, for sludge coming from different sources. The extracted water can be pumped out, through the water outlet 124, separately from the remaining solids of the sludge after processing. The sludge outlet 108 for solids and the water outlet 124 for water may be in close physical proximity, such that collection of both may be facilitated, or the outlets 108 may be spaced apart, such that the extracted water and the solids can be conveyed into different external systems. Many variations can be envisioned by those having ordinary skill in the art, depending on the particular circumstances at hand. The system 100 can comprise a container 101 having a separating wall 107, which can be insulated. The separating wall 107 can separated the cold and warm modules 102, 104 from each other. The separating wall 107 can have a through-hole (not shown), though which frozen sludge can be passed from the cold module 102 to the warm module 104.

[0051] As further shown in FIG. 1, the cold module 102 can include a homogenization unit 110, a feeding device, such as pump 112 or the like, and a refrigerating device 114, such as a freezer adapted to freeze pumpable fluids into frozen units, such as rods, or the like. The frozen units can have the shape of rods with a through-hole. The functioning of these components will be described in detail below with reference to FIG. 2, but on a general level, the purpose of the homogenization unit 110 is to homogenize the incoming sludge to make it easier to pump by the pump 112 to the refrigerating device 114, where it undergoes a freezing process. The cold module 102 can further include a cutter 116, such as a threader, i.e., a shredder, or the like, for cutting the frozen sludge coming out of the refrigerating device 114 into smaller pieces, which will also be described in further detail with respect to FIG. 2. It should be noted, that in some embodiments, the cutter 116 could alternatively be placed just inside the warm module 104. The main point is to enable the frozen material to be broken down into appropriately sized pieces before the warming, or heating, process, such as thawing, starts - or has proceeded disadvantageously far - in the warm module 104.

[0052] The freezer, as an example of the refrigerating device, can include a bottom container, and a freezing compartment, housing one or more freezing elements, such as rod-shaped elements, or the like. Said one or more freezing elements can be positioned inside the freezing compartment in which sludge can be distributed, e.g. via the top of the freezing compartment. The freezing elements can be elongated, e.g. having a circular, oval, or rectangular, square, or the like, cross-sections. During freezing, the sludge from the bottom container is circulated to be distributed at the top of the freezing compartment. Frozen sludge will then build up on the freezing elements. In this manner, it can be ensured that the sludge is frozen from inside to outside, e.g. water from the sludge material closest to the freezing element is thus drawn out of the sludge and frozen at the freezing element(s). In this manner, the sludge is successively frozen into frozen units. Due to the freezing elements, a rod of frozen sludge has a through-hole at, or along, the longitudinal direction thereof, e.g. at the center as seen in a transversal cross-section of the rod. This kind of freezer can be a bulk freezer, a freezer with rod-like freezing elements, or the like. Any non-frozen sludge distributed over the freezing elements is collected in the bottom container, preferably located under the freezing compartment, and circulated back to the top of the freezing compartment. In order to release the frozen sludge, the freezing elements can be heated. A net or grid or the like can cover the bottom container such that frozen sludge can be fed out of the refrigerating device for further processing, e.g. in the warm module 104.

[0053] It is understood that, in some examples, the cold module 102 can be represented by the refrigerating device 114. Even though it can be efficient that the surroundings, e.g. the cold module, of the refrigerating device 114 is colder than the warm module 104, it is not strictly necessary. Accordingly, it is the refrigerating device 114 that is colder than the warm module 104.

[0054] The warm module 104 includes a hot air inlet 118 for letting hot air into the warm module 104 at a desired rate, in order to maintain an appropriate temperature in the warm module 104, which will be described in further detail with reference to FIG. 2. It should be noted that while the hot air inlet 118 is shown in FIG.l as being located at the top of the warm module 104, in some embodiments, it may be located close to the ground or essentially anywhere along the vertical sides of the warm module 104, as long as a desired temperature can be maintained inside the warm module 104. However, it should be noted that from a dewatering perspective, there may be certain advantages to having the hot air inlet 118 in close proximity to where the frozen sludge first enters the warm module 104, so as to obtain a rapid temperature increase of the frozen sludge coming out of the cutter 116, as this may improve the dewatering process.

[0055] The warm module 104 also includes a transportation arrangement 120, such as a conveyor belt 123, a ramp 121, or the like. The transportation arrangement 120 can thus include a ramp 121 and a conveyor belt 123. The conveyor belt 123 can snake its way through the warm module 104. Thus, saving space. The warm module 104 includes a ramp 121 that transports the cut pieces of the frozen sludge from the cutter 116 onto the conveyor belt 123. As mentioned, the conveyor belt 123 is an example of the transportation arrangement. It should be noted while the conveyor belt 123 is illustrated in FIG. 1 in a vertical plane, it also extends in a horizontal plane. The geometrical configuration of the conveyor belt 123 can be determined through experimentation by those having ordinary skill in the art, but the overall goal is for the conveyor belt 123 to be sufficiently long that an optimal dewatering process can be achieved that allows the output sludge to attain the highest possible concentration of solids. It should be noted that the geometrical configuration of the conveyor belt 123 is merely one of several factors to take into account when optimizing the dewatering process, and that the dewatering process also depends on the type of sludge, the temperature in the warm module 104, the speed of the conveyor belt 123 (which affects the time the sludge spends inside the warm module 104), just to mention a few factors. Typically, the water that is expelled through the thawing process makes its way to the bottom of the warm module 104, where it may be collected, for example, in a trough 122, and then directed to the water outlet 108. The remaining dried sludge at the end of the conveyor belt 123 is output at the sludge outlet 108, as described above.

[0056] The sludge processing system 100 is scalable and can in some embodiments accommodate an input amount of sludge in various sizes. Generally, the limiting factor is the capacity of the refrigerating device 114, which in various current embodiments range from one to 120 cubic meters per 24 hours. In some embodiments, the sludge processing system 100 can be installed as a permanent installation, whereas in other embodiments it can be a mobile system, which can be accommodated inside a 40 ft container to facilitate transport, installation and deinstallation.

[0057] The operation of the sludge processing system 100 will now be described in further detail and with respect to FIG. 2, which shows a flowchart of examples of a method 200 for processing of sludge. In more detail, FIG. 2 can thus show examples of a method 200 for managing dry solid concentration of sludge.

[0058] The method 200 starts by inputting sludge through the inlet, step 205. The sludge in question possesses pumpable characteristics and exhibits a dry matter content ranging from one to ten per cent. Notably, it is essential to acknowledge that sludges with a higher dry matter content are also viable for processing. The determining factor for inclusion lies in the pumpability of the sludge, rather than the specific dry matter content.

[0059] Next, the sludge can be finely divided in the homogenization unit 110 to break up any lumps that may be included in the sludge, step 210. Typically, there is also a coarse screening before the next step to protect the equipment from any larger foreign objects that may be included in the sludge. This preventive measure enhances the operational efficiency and integrity of the equipment involved in the sludge treatment process.

[0060] The homogenized sludge is then pumped, or fed, from the homogenization unit 110 to the refrigerating device 114, by the pump 112, step 215.

[0061] Sometimes, the homogenization can be omitted, then the system 100, such as the pump 112, or the like, can feed the sludge amount into the refrigerating device 114. The feeding of the sludge into the refrigerating device can be performed batchwise, meaning that feeding of sludge can be stopped when an amount of the sludge has been fed into the refrigerating device 114. Following the homogenization process if performed, the sludge is subjected to freezing in step 220 utilizing the refrigerating device 114. This freezing operation is accomplished after the sludge has been fed into the refrigerating device 114. In certain embodiments, the refrigerating device 114 may be structured as a tower, whereby the force of gravity facilitates the movement of the sludge from the top to the bottom. It is beneficial that the freezing occurs under specific pre-established conditions, which are primarily influenced by the type of sludge being processed. Typically, the freezing of the sludge occurs within a timeframe lasting between 200 and 600 seconds. The sequential freezing of the sludge serves to enhance the ability of the water to repel the solids, thereby contributing to the overall effectiveness of the process. This can be expressed as that the sludge is frozen successively, e.g. from inside to the outside. As a result, improved separation of water from the sludge can be achieved. The successive freezing pushes water out of the sludge, thereby improving separating of water bound in the sludge. Free water in the sludge can be separated from the sludge by heating or the like.

[0062] The frozen sludge is then released, such as unloaded, let out, or the like, from the refrigerating device 114, preferably in batches, step 225. The releasing of the frozen sludge empties the refrigerating device 114 and puts the frozen sludge at the transportation arrangement 120.

[0063] In some examples, the feeding 215, the freezing 220, and the releasing 225 are performed in sequence and repeatedly for each sludge amount of a batch of respective sludge amounts. Accordingly, the method can include batchwise feeding, freezing and releasing of the sludge amount, e.g. at the refrigerating device 114.

[0064] Subsequently, following the freezing process, the frozen sludge can undergo breaking, such as cutting, or the like, by the cutter 116 into smaller, more manageable pieces of material, which are then evenly distributed onto the conveyor belt 123 in step 230. When frozen, the sludge can be formed as rods, cylinders, or the like. The cutting can be performed in the cold module 102, or in the warm module 104. It is nevertheless preferred that the cutting in performed in the cold module 102 in order to avoid that liquid water would need to be handled in the cold module.

[0065] The even distribution of the frozen sludge pieces is pivotal, as it facilitates the direct heat exposure provided in the subsequent step. By ensuring uniform distribution, the sludge pieces are better positioned to receive the heat treatment, such as in step 235, thereby enabling the efficient progression of the subsequent phase in the processing operation.

[0066] The conveyor belt 123 can facilitate the transportation of the frozen sludge pieces in the warm module 104 in step 233, or even into the warm module 104 from the cold module 102 through the through- hole in the separating wall. In the warm module 108, the sludge pieces are subjected to the effects of hot air at high velocity emanating from the hot air inlet 118. In some embodiments, the hot air is generated from the heat that is output by the refrigerating device 114. This rapid heating process induces the formation of cracks in the frozen pieces of sludge. In this manner, the thawing process is facilitated due to increase of contact area between air flow and sludge, e.g. in the cracks of the frozen sludge, thereby subsequent separation of water from the sludge is enhanced. The application of hot air at high velocity serves to effectively break down the frozen sludge, thereby promoting the desired phase transition of water from solid to liquid state and enabling the efficient extraction of water from the solid components. This means that the feeding 235 can provide a flow of air at a portion of the transportation arrangement 120 to crack the amount of frozen sludge.

[0067] It shall be understood that the transportation arrangement, such as the conveyor belt 123, can carry a plurality of respective sludge amount of a batch of respective sludge amounts. Each respective sludge amount corresponds to a release of frozen sludge from the refrigerating device. In general, the longer the transportation arrangement is, the greater number of batches can be carried by it.

[0068] Following the heating from the hot air inlet, the frozen pieces progress at a low speed along the conveyor belt 123 as they traverse the warm module 104 for thawing in step 240. During thawing at least some liquid water leaves, e.g. through gravity, dripping, evaporation, or the like, the sludge amount, thereby forming an output sludge. Said at least some water can includes unbound water in the sludge, where at least some of said unbound water was bound in the sludge before the successive freezing of the sludge. The temperature in the warm module 104 is typically around 40-45 degrees Celsius, but it should be noted that it may vary based on the particular composition of the sludge and that it is also correlated with the speed of the conveyor belt 123, so as to ensure an appropriate thawing time for the sludge. In general, the temperature, in the warm module, is between 0 and 50 degrees, 5 and 45 degrees, or the like. During the method, the bound water undergoes a transformation into free water, thereby completing the phase transition. In certain embodiments, the conveyor belt 123 is designed with perforations, allowing the water resulting from the thawing process to permeate through and be collected by gutters or troughs located beneath the conveyor belt. Subsequently, the water is directed out through the outlet 124 into an external container (not shown). The water contained in the external container can undergo thorough testing and analysis before it is released back to the designated recipient, ensuring that the quality and characteristics of the water meet specified standards and compliance requirements.

[0069] Upon completion of the transportation and thawing steps, the output sludge, aka dried sludge, is discharged through the sludge outlet 108, in step 250. At this stage, the dried sludge is ready to be gathered for subsequent handling and processing, thus representing the culmination of the entire process. The output of the dried sludge through the outlet 108 signifies the successful completion of the treatment and drying cycle, making it available for further utilization or disposal as per specific operational requirements. As an example, the output sludge can be transported to a drying arrangement for further drying of the output sludge, if desired.

[0070] In step 245, the water that left the sludge amount, e.g. during the transportation and thawing of the amount of frozen sludge can be collected, e.g. by the collecting device 122, such as a trough, or the like.

[0071] Overall, the examples of the method herein achieve improved separation of water from sludge thanks to the at the sludge is frozen and thawed in a controlled manner. E.g. the cold module ensures stable and controlled conditions before and during freezing, and the warm module ensures stable and controlled conditions during the thawing of the frozen sludge.

Claims

CLAIMS1. A method for managing dry solid concentration of sludge, comprising water and solids, wherein the method comprises: feeding (215) an amount of the sludge, referred to as "sludge amount", into a refrigerating device (114), having rod-shaped freezing elements, by means of a pump (112), wherein the sludge amount is pumpable, freezing (220), in the refrigerating device (114), the sludge amount into frozen units, each frozen unit having the shape of a rod with a through-hole, releasing (225), from the refrigerating device (114), the frozen sludge amount at a transportation arrangement (120) by that the freezing elements are heated, wherein the feeding (215), the freezing (220), and the releasing (225) are performed in sequence and repeatedly for each sludge amount of a batch of respective sludge amounts, transporting (233), by the transportation arrangement (120), the sludge amount while thawing (240) the sludge amount, whereby at least some liquid water leaves the sludge amount, whereby an output sludge is formed, wherein the output sludge has a dry solid concentration that is greater than a dry solid concentration of the sludge amount fed into the refrigerating device (114), outputting (250) the output sludge at a sludge outlet (108), and conveying (260) said at least some liquid water to a water outlet (124).

2. The method according to claim 1, wherein the method comprises, after the feeding (215) of the sludge amount and before the freezing (220) of the sludge amount: stopping (217) the feeding (215) of the sludge amount.

3. The method according to any one of the preceding claims, wherein the method comprises: feeding (235) a flow of air at a portion of the transportation arrangement (120) to crack the frozen sludge amount, thereby facilitating separation of water from the sludge amount.

4. The method according to any one of the preceding claims, wherein the method comprises: receiving (205) the sludge amount at an inlet (106), and homogenizing (210) the sludge amount.

5. The method according to any one of the preceding claims, wherein the method comprises breaking (230) the frozen sludge amount into smaller pieces.

6. The method according to any one of the preceding claims, wherein the method comprises collecting (245) water that left the sludge amount.

7. The method according to any one of the preceding claims, wherein the method comprises outputting (265) water that left the sludge amount at the water outlet (124).

8. A system (100) comprising: a pump (112) for feeding an amount of the sludge, referred to as "sludge amount", into a refrigerating device (114), having rod-shaped freezing elements, wherein the sludge amount is pumpable, and the refrigerating device (114) configured for freezing the sludge amount into frozen units, each frozen unit having the shape of a rod with a through-hole, wherein the refrigerating device (114) is configured for releasing, from the refrigerating device (114), the frozen sludge amount at a transportation arrangement (120) by that the freezing elements are heated, wherein the system (100) is configured to perform the feeding, the freezing, and the releasing in sequence and repeatedly for each sludge amount of a batch of respective sludge amounts, wherein the system (100) comprises the transportation arrangement (120) configured for transporting the sludge amount while thawing the sludge amount, whereby at least some liquid water leaves the sludge amount, whereby an output sludge is formed, wherein the output sludge has a dry solid concentration that is greater than a dry solid concentration of the sludge amount fed into the refrigerating device (114), a sludge outlet (108) for outputting the output sludge, and a water outlet (124) for conveying said at least some liquid water to external systems.

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