Sludge volume reduction method

Abstract

To provide a sludge volume reduction method capable of suppressing precipitation of substances dissolved in sludge as the sludge temperature decreases.SOLUTION: A sludge solubilization method is a method for hydrothermally solubilizing sludge, comprising supplying at least one of water and a chelating agent to the sludge after solubilization with high-temperature high-pressure water.SELECTED DRAWING: Figure 2A

Description

[Technical Field]

[0001] The present invention relates to a method for reducing the volume of sludge. [Background technology]

[0002] A method combining hydrothermal treatment and microbial treatment is known as a method for reducing the volume of organic waste, particularly organic sludge discharged during organic wastewater treatment such as activated sludge. In this treatment method, the solid components of the organic sludge are solubilized by hydrothermal treatment. Subsequently, the liquid components of the solubilized organic sludge are subjected to microbial treatment. Patent Document 1 discloses an example of such an organic waste treatment method. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-021797 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, in hydrothermal treatment, a form is known in which the sludge is heated by blowing steam into a solubilization device containing the sludge, thereby solubilizing the sludge.

[0005] The sludge discharged from the solubilization unit and immediately after being transferred to the storage tank is at high temperatures. This sludge contains high concentrations of dissolved organic matter and metal ions. The metal ions originate from, for example, the flocculants and coagulants added during the activated sludge treatment process.

[0006] As the temperature of sludge drops, the solubility of each substance often decreases. It has also been confirmed that when oxygen dissolves in sludge that has been solubilized by contact with the outside air, metal ions dissolved in the solubilized sludge are oxidized to form insoluble substances. It is also known that the solubility of metal ions varies significantly depending on the pH. This causes dissolved metal ions to precipitate. The precipitation of dissolved metal ions means an increase in the amount of solubilized residue. In other words, this means a decrease in the solubilization rate, diminishing the effectiveness of reducing sludge, which is industrial waste.

[0007] Therefore, the present invention aims to provide a method for reducing sludge volume that can suppress the precipitation of substances dissolved in sludge due to a decrease in sludge temperature, dissolution of oxygen, and pH adjustment during treatment after solubilization. [Means for solving the problem]

[0008] The sludge solubilization method of the present invention is a sludge solubilization method for hydrothermally solubilizing sludge, in which at least one of water and a chelating agent is supplied to the sludge after solubilization with high-temperature, high-pressure water. [Effects of the Invention]

[0009] According to the present invention, a method for reducing the volume of sludge can be provided that can suppress the precipitation of substances dissolved in sludge that occurs as the temperature of the sludge decreases. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of a sludge volume reduction system according to one embodiment of the present invention. [Figure 2A] FIG. 1 is a diagram showing the behavior of molten iron. [Figure 2B] FIG. 1 is a diagram showing the behavior of molten iron. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a diagram showing the schematic configuration of a sludge volume reduction system 1 according to one embodiment of the present invention. The sludge volume reduction system 1 is a system for reducing the volume of sludge to be disposed of as industrial waste. The sludge volume reduction system 1 includes an activated sludge treatment apparatus 10 and a hydrothermal solubilization apparatus 50.

[0012] The activated sludge treatment device 10 is a device that decomposes organic matter and the like using activated sludge. The activated sludge treatment device 10 includes an adjustment tank 12, an aerobic tank line 102, and an aerobic tank 14. The adjustment tank 12 is a tank for adjusting the amount of water to be treated that is treated in the aerobic tank 14. The adjustment tank 12 stores the water to be treated. The aerobic tank 14 is a tank for decomposing organic matter contained in the water to be treated using microorganisms. The aerobic tank 14 holds a high concentration of aerobic microorganisms in the form of activated sludge. The aerobic tank line 102 is a line connected at one end to the adjustment tank 12 and at the other end to the aerobic tank 14. The water to be treated flows from the adjustment tank 12 to the aerobic tank 14 through the aerobic tank line 102.

[0013] The activated sludge treatment apparatus 10 further includes a sludge separation mechanism 20. The sludge separation mechanism 20 separates the treated liquid treated in the aerobic tank 14 into solid and liquid.

[0014] The sludge separation mechanism 20 includes a separation tank 22 and a separation tank line 104. The separation tank 22 is a tank for performing solid-liquid separation of the water to be treated that has been treated in the aerobic tank 14. The separation tank line 104 is a line connected at one end to the aerobic tank 14 and at the other end to the separation tank 22. The water to be treated that has been treated in the aerobic tank 14 flows from the aerobic tank 14 to the separation tank 22 through the separation tank line 104.

[0015] The sludge separation mechanism 20 further includes a treated water line 112. One end of the treated water line 112 is connected to the separation tank 22. The liquid separated in the separation tank 22 is discharged as treated water E1 from the separation tank 22 to the outside of the activated sludge treatment device 10 through the treated water line 112. Arrow 302 in Figure 1 indicates the flow of treated water E1.

[0016] The sludge separation mechanism 20 further includes a post-separation storage tank 24 and a post-separation storage tank line 114. The post-separation storage tank 24 is a tank for storing excess sludge. Excess sludge refers to solid components that have been separated into solid and liquid in the separation tank 22. The post-separation storage tank line 114 is a line connected at one end to the separation tank 22 and at the other end to the post-separation storage tank 24. The excess sludge that has been separated into solid and liquid in the separation tank 22 flows from the separation tank 22 to the post-separation storage tank 24 through the post-separation storage tank line 114. Arrow 304 in FIG. 1 indicates the flow of excess sludge.

[0017] The sludge separation mechanism 20 further includes a dehydrator 26 and a dehydrator line 116. The dehydrator 26 is a machine that dehydrates excess sludge. The dehydrator 26 may be a thickener. The dehydrator line 116 is a line connected at one end to the post-separation storage tank 24 and at the other end to the dehydrator 26. The excess sludge stored in the post-separation storage tank 24 flows from the post-separation storage tank 24 to the dehydrator 26 through the dehydrator line 116.

[0018] The sludge separation mechanism 20 further includes a post-dehydration storage tank 28 and a post-dehydration storage tank line 118. The post-dehydration storage tank 28 is a tank for storing dehydrated sludge. Dehydrated sludge refers to sludge after being dehydrated by the dehydrator 26. The post-dehydration storage tank line 118 is a line connected at one end to the dehydrator 26 and at the other end to the post-dehydration storage tank 28. The dehydrated sludge dehydrated by the dehydrator 26 flows from the dehydrator 26 to the post-dehydration storage tank 28 through the post-dehydration storage tank line 118. Arrow 306 in Figure 1 indicates the flow of dehydrated sludge.

[0019] The sludge separation mechanism 20 further includes an industrial waste line 120. One end of the industrial waste line 120 is connected to the post-dehydration storage tank 28. The dehydrated sludge stored in the post-dehydration storage tank 28 is discharged as industrial waste E2 from the post-dehydration storage tank 28 to the outside of the activated sludge treatment device 10 through the industrial waste line 120.

[0020] The sludge separation mechanism 20 further includes a desorption liquid tank 30 and a desorption liquid tank line 122. The desorption liquid tank 30 is a tank for storing liquid generated by dehydration by the dehydrator 26. The desorption liquid tank line 122 is a line connected at one end to the dehydrator 26 and at the other end to the desorption liquid tank 30. The liquid generated by dehydration by the dehydrator 26 flows from the dehydrator 26 to the desorption liquid tank 30 through the desorption liquid tank line 122.

[0021] The sludge separation mechanism 20 further includes an equalization tank line 124 and an equalization tank line pump 32. The equalization tank line 124 is a line connected at one end to the desorption liquid tank 30 and at the other end to the equalization tank 12. The liquid stored in the desorption liquid tank 30 flows to the equalization tank 12 through the equalization tank line 124. The equalization tank line pump 32 is a pump provided in the equalization tank line 124. The liquid stored in the desorption liquid tank 30 is forced to flow into the equalization tank 12 by the equalization tank line pump 32.

[0022] The hydrothermal solubilization apparatus 50 will now be described. The hydrothermal solubilization apparatus 50 includes a solubilization apparatus 52 and a solubilization apparatus line 142. The solubilization apparatus 52 is an apparatus for solubilizing the dewatered sludge produced in the sludge separation mechanism 20. The solubilization apparatus 52 can be formed of a pressure vessel. The solubilization apparatus line 142 is a line connected at one end to the post-dehydration storage tank 28 and at the other end to the solubilization apparatus 52. The dewatered sludge stored in the post-dehydration storage tank 28 flows from the post-dehydration storage tank 28 to the solubilization apparatus 52 via the solubilization apparatus line 142.

[0023] The hydrothermal solubilization apparatus 50 further includes a solubilization apparatus line pump 60 and a solubilization apparatus line valve 62. The solubilization apparatus line pump 60 is a pump provided in the solubilization apparatus line 142. The dewatered sludge stored in the post-dehydration storage tank 28 is caused to flow into the solubilization apparatus 52 by the solubilization apparatus line pump 60. The solubilization apparatus line valve 62 is a valve provided in the solubilization apparatus line 142 downstream of the solubilization apparatus line pump 60. The solubilization apparatus line valve 62 makes it possible to switch whether or not dewatered sludge flows through the solubilization apparatus line 142 and to adjust the amount of dewatered sludge flowing through the solubilization apparatus line 142.

[0024] The hydrothermal solubilization apparatus 50 further includes a steam line 150 and a steam line valve 64. The steam line 150 is a line connected at one end to the solubilization apparatus 52. Steam S is supplied to the solubilization apparatus 52 via the steam line 150. The steam line valve 64 is a valve provided on the steam line 150. The steam line valve 64 makes it possible to switch whether or not steam S flows through the steam line 150 and to adjust the amount of steam S flowing through the steam line 150.

[0025] The hydrothermal solubilization apparatus 50 further includes a post-solubilization storage tank 54, a post-solubilization storage tank line 144, and a post-solubilization storage tank line valve 66. The post-solubilization storage tank 54 may be simply referred to as a storage tank. The post-solubilization storage tank 54 is a tank for storing sludge solubilized in the solubilization apparatus 52. The post-solubilization storage tank 54 can be formed of a non-pressure vessel. The post-solubilization storage tank line 144 is a line connected at one end to the solubilization apparatus 52 and at the other end to the post-solubilization storage tank 54. The sludge solubilized in the solubilization apparatus 52 flows from the solubilization apparatus 52 to the post-solubilization storage tank 54 through the post-solubilization storage tank line 144. The post-solubilization storage tank line valve 66 is a valve provided in the post-solubilization storage tank line 144. The post-solubilization storage tank line valve 66 makes it possible to switch whether or not solubilized sludge flows through the post-solubilization storage tank line 144 and to adjust the amount of solubilized sludge flowing through the post-solubilization storage tank line 144. The post-solubilization storage tank line valve 66 can be, for example, an electric valve.

[0026] The hydrothermal solubilization apparatus 50 further includes a water and / or chelating agent supply line 148 and a water and / or chelating agent supply line pump 68. The water and / or chelating agent supply line 148 may be referred to as a supply line. The water and / or chelating agent supply line 148 is a line connected at one end to the post-solubilization storage tank 54. Water and / or chelating agent WC is supplied to the post-solubilization storage tank 54 via the water and / or chelating agent supply line 148. The water and / or chelating agent supply line pump 68 is a pump provided in the water and / or chelating agent supply line 148. The water and / or chelating agent is supplied to the post-solubilization storage tank 54 by the water and / or chelating agent supply line pump 68.

[0027] The hydrothermal solubilization apparatus 50 further includes an air line 152 and an air line pump 70. The air line 152 is a line connected at one end to the post-solubilization storage tank 54. Air A is supplied to the post-solubilization storage tank 54 via the air line 152. The air line pump 70 is a pump provided on the air line 152. Air is supplied to the post-solubilization storage tank 54 by the air line pump 70.

[0028] The hydrothermal solubilization apparatus 50 further includes a flash steam treatment section 100 and a flash steam discharge line 146. The flash steam treatment section 100 treats organic matter contained in the flash steam discharged from the post-solubilization storage tank 54. In the example shown in FIG. 1 , the flash steam treatment section 100 is the aerobic tank 14. The flash steam discharge line 146 is a line connected at one end to the post-solubilization storage tank 54 and at the other end to the flash steam treatment section 100. The flash steam discharged from the post-solubilization storage tank 54 flows from the post-solubilization storage tank 54 to the flash steam treatment section 100 through the flash steam discharge line 146. Arrow 312 in FIG. 1 indicates the flow of flash steam. Note that the flash steam discharge line 146 is always open, i.e., it is always open and not closed by a valve or the like, and is connected to the post-solubilization storage tank 54. The flash steam discharge line 146 is also equipped with a check valve or vacuum breaker valve (not shown). By installing a check valve or a vacuum breaker valve, it is possible to prevent backflow in the flash steam discharge line 146 even when the internal pressure of the post-solubilization storage tank 54 drops due to cooling or the like. Furthermore, by connecting the flash steam discharge line 146 to the post-solubilization storage tank 54 in a constantly open state, it is possible to avoid the post-solubilization storage tank 54 being designated as a pressure vessel.

[0029] The hydrothermal solubilization apparatus 50 further includes a solubilized supernatant liquid line 180, a first valve 71, a second valve 72, a third valve 73, a fourth valve 74, a fifth valve 75, and a solubilized supernatant liquid line pump 82. The solubilized supernatant liquid line 180 includes, as output lines 160, a first output line 161, a second output line 162, a third output line 163, a fourth output line 164, a fifth output line 165, and a discharge line 167. One end of each of the first output line 161, the second output line 162, the third output line 163, the fourth output line 164, and the fifth output line 165 is connected to the post-solubilization storage tank 54 at different heights. The other ends of the first outlet line 161, the second outlet line 162, the third outlet line 163, the fourth outlet line 164, and the fifth outlet line 165 are connected to one end of a discharge line 167. The other end of the discharge line 167 is connected to the adjustment tank 12. The solubilized supernatant liquid obtained by solid-liquid separation in the storage tank after solubilization flows to the adjustment tank 12 through the first outlet line 161, the second outlet line 162, the third outlet line 163, the fourth outlet line 164, or the fifth outlet line 165, and further through the solubilized supernatant liquid line 180 and the discharge line 167. Each of the first outlet line 161, the second outlet line 162, the third outlet line 163, the fourth outlet line 164, and the fifth outlet line 165 is provided with a valve. The first valve 71 is a valve provided in the first outlet line 161. The second valve 72 is a valve provided in the second outlet line 162. The third valve 73 is a valve provided in the third outlet line 163. The fourth valve 74 is a valve provided in the fourth outlet line 164. The fifth valve 75 is a valve provided in the fifth outlet line 165. The valves provided in the outlet lines enable switching whether or not the solubilized supernatant flows through the outlet lines and adjustment of the amount of solubilized supernatant flowing through the outlet lines. Depending on which valve is opened, it is possible to switch the height from which the solubilized supernatant flows out of the post-solubilization storage tank 54. The solubilized supernatant line pump 82 is a pump provided in the solubilized supernatant line 180. The solubilized supernatant is flowed into the adjustment tank 12 by the solubilized supernatant line pump 82. Arrow 324 in FIG. 1 indicates the flow of the solubilized supernatant.

[0030] The hydrothermal solubilization apparatus 50 further includes a solubilized residue discharge line 170, a residue storage line 172, a residue dehydration line 174, and a solubilized residue discharge line pump 80. The solubilized residue discharge line 170 is a line having one end connected to the post-solubilization storage tank 54 and the other end connected to a storage / dehydration branch point 201. One end of the solubilized residue discharge line 170 is preferably connected near the bottom of the post-solubilization storage tank 54. The residue storage line 172 is a line having one end connected to the storage / dehydration branch point 201 and the other end connected to the post-separation storage tank 24. The residue dehydration line 174 is a line having one end connected to the storage / dehydration branch point 201 and the other end connected to the dehydrator 26. The solubilized residue obtained by solid-liquid separation in the post-solubilization storage tank 54 flows from the post-solubilization storage tank 54 to the storage / dehydration branch point 201 via the solubilized residue discharge line 170. The solubilized residue that has flowed to the storage / dehydration branch point 201 can flow to the post-separation storage tank 24 via the residue storage line 172. The solubilized residue that has flowed to the storage / dehydration branch point 201 can flow to the dehydrator 26 via the residue dehydration line 174. As described above, the dehydrator 26 may be a concentrator. The storage / dehydration branch point 201 may be provided with a switching device (not shown) for switching whether the solubilized residue flows to the residue storage line 172 or the residue dehydration line 174, or only one of the residue storage line 172 and the residue dehydration line 174 may be provided. The solubilized residue discharge line pump 80 is a pump provided in the solubilized residue discharge line 170. The solubilized residue is caused to flow to the post-separation storage tank 24 and / or the dehydrator 26 by the solubilized residue discharge line pump 80. Arrow 322 in Figure 1 indicates the flow of the solubilized residue.

[0031] The sludge volume reduction system 1 may further include a control unit (not shown). The control unit can control the opening and closing of the valves and the operation of the pumps described above.

[0032] A sludge solubilization method that supplies at least one of water and a chelating agent is described below. This sludge solubilization method can be implemented, for example, by the sludge volume reduction system 1 described above. In the sludge solubilization method of this embodiment, at least one of water and a chelating agent is supplied to sludge after solubilization with high-temperature, high-pressure water. The sludge solubilization method may further include, for example, a cooling step for cooling the solubilized sludge, and a chelating agent or the like may be supplied to the sludge cooled in the cooling step. This allows for dilution and / or formation of a soluble chelating compound before the solubility of organic matter and metal components decreases or their precipitation occurs due to factors such as a temperature drop in the solubilized sludge, oxygen dissolution, and pH adjustment during post-solubilization treatment, thereby effectively and simply suppressing their precipitation. This in turn prevents a decrease in the solubilization rate and the industrial waste reduction effect.

[0033] The hydrothermal solubilization apparatus 50 includes a water and / or chelating agent supply line 148 for supplying at least one of water and a chelating agent to the storage tank. The sludge solubilized in the solubilization apparatus 52, which is in a high-temperature, high-pressure state exceeding 100°C, is passed through the post-solubilization storage tank line 144 from the solubilization apparatus 52 to the post-solubilization storage tank 54, which is open to the atmosphere. The sludge in the post-solubilization storage tank 54 is instantaneously cooled to 100°C with the generation of flash steam. This process is referred to as the cooling process. In the sludge solubilization method of this embodiment, at least one of water and a chelating agent is supplied to the sludge that has undergone the cooling process via the chelating agent supply line 148. This suppresses the precipitation of organic matter and metal ions from the solubilized supernatant due to a temperature drop. Consequently, the solubilization rate immediately after hydrothermal treatment can be maintained even after cooling.

[0034] Regarding water supply, when hydrothermal solubilizing organic sludge, (1) the higher the sludge concentration, i.e., the lower the moisture content, the lower the solubilization rate (SS reduction rate) tends to be. However, if the sludge is diluted in advance to increase the moisture content, (2) not only does it require more energy to heat the sludge to the specified temperature per unit of SS component input, (3) it requires a larger reactor, and (4) it takes longer to cool after treatment, resulting in trade-offs. Therefore, the hydrothermal solubilization process is performed for a certain period of time when the sludge has a low moisture content (e.g., dehydrated sludge with a moisture content of approximately 70–90%). After the cooling process, water is injected from outside the system or is released to the atmosphere and then added for dilution. This (1) increases the sludge solubilization rate, or in other words, the industrial waste volume reduction rate, (2) minimizes the energy required to heat the sludge to the specified temperature per unit of SS component input, (3) minimizes the need for a larger reactor, and (4) shortens the cooling time.

[0035] The above (1) sludge solubilization rate, in other words, industrial waste volume reduction rate, was verified through a simple experiment. The outline of the experiment is as follows: 1. to 5. 1. 150g of dewatered sludge from the activated sludge process at a certain food factory was solubilized by holding it at 180°C for 1 hour without dilution. Two samples were prepared under the same conditions. The moisture content of the dewatered sludge was 86.5% (i.e., the SS concentration was 135,000mg / kg, and the amount of SS in the 150g of dewatered sludge used for the test was 20,250mg). 2. After the treatment, as soon as the temperature dropped below 100°C, the equipment, i.e., the pressure vessel, was opened to the atmosphere. 3. One of the two samples was not diluted, but was transferred as a whole (150 g) to a plastic container, stored, and allowed to cool naturally (solubilized sludge A). 4. To the other sample, 300 g of pure water preheated to approximately 90°C was added. This resulted in a three-fold dilution, bringing the total weight to 450 g. The sample was then stored in a plastic container and allowed to cool (solubilized sludge B). This sample simulated the condition of solubilized sludge at 180°C when room-temperature water was injected into it. 5. The SS and TOC of the supernatant were analyzed for the solubilized liquid (solubilized sludge A) that was not diluted after solubilization treatment and the liquid that was diluted three times (solubilized sludge B) corresponding to the embodiment of the present application.

[0036] The undiluted sample (solubilized sludge A) had a supernatant TOC of 29,000 mg / L and a SS concentration of 77,000 mg / L (11,550 mg of SS per 150 g), resulting in a 43% SS reduction. On the other hand, the 3-fold diluted sample (solubilized sludge B) had a supernatant TOC of 9,700 mg / L (29,100 mg / L before dilution), a SS concentration of 22,000 mg / L (9,900 mg of SS per 450 g), resulting in a 51% SS reduction. As shown above, the 3-fold diluted sample after solubilization showed higher dissolved organic matter concentrations and SS reduction rates than the undiluted sample. This means that the 3-fold diluted sample after solubilization suppressed the precipitation of dissolved substances from the sludge. In addition, the dewatered sludge was diluted three times with pure water before solubilization, then held at 180°C for one hour and allowed to cool naturally (solubilized sludge C). The supernatant TOC after solubilization, SS after solubilization, and SS reduction rate were the same as those of the sample diluted three times after solubilization (solubilized sludge B).

[0037] Next, we will explain the results of the experimental verification of the supply of chelating agents. The experiment is outlined in 1. to 3. below. 1. Sludge from the activated sludge treatment process at a certain food factory was hydrothermally treated and removed from the pressure vessel test device. After that, it was immediately filtered through 5A filter paper, and the filtrate was divided into four bottles of 40 mL each. 2. 10 mL of each of the following was added to the four bottles: (1) pure water (no chelating agent added), (2) 180 mM chelating agent (EDTA: ethylenediaminetetraacetic acid) aqueous solution, (3) 180 mM chelating agent (citric acid) aqueous solution, and (4) 180 mM chelating agent (HEDP: 1-hydroxyethane-1,1-diphosphonic acid) aqueous solution. The solutions from 3.2, i.e., a 1.25-fold dilution of the solubilized stock solution and a 50-fold dilution of that solution, were sealed and left at room temperature, and iron less than 0.2 μm in size was monitored as a dissolved iron indicator. Note that iron less than 0.2 μm in size was quantified by ICP after filtering the sample through a 0.2 μm syringe filter.

[0038] Figures 2A and 2B show the behavior of dissolved iron. Figure 2A shows the behavior of dissolved iron in the solubilized stock solution, and Figure 2B shows the behavior of dissolved iron in the pure 50-fold diluted solution. The horizontal axis of Figures 2A and 2B represents the time elapsed since dilution, T [h], and the vertical axis of Figures 2A and 2B represents the iron concentration C [mgFe / L] below 0.2 μm. (1) to (4) in Figures 2A and 2B correspond to (1) to (4) described in Section 2. In (1) pure water, i.e., no chelating agent added, the iron concentration significantly decreased over time in both the solubilized stock solution (see Figure 2A) and its 50-fold diluted solution (see Figure 2B). In contrast, in (2) to (4) with the addition of chelating agents, the decrease in iron concentration was suppressed ideally. In other words, in (2) to (4), the precipitation of dissolved substances in the sludge was suppressed.

[0039] Although the present invention has been described above as an embodiment, it is not limited to the above-described embodiment, and various changes, modifications, and combinations are possible.

[0040] [Contribution to the United Nations-led Sustainable Development Goals (SDGs)] This disclosure includes matters that contribute to achieving Goal 6 of the SDGs (Sustainable Development Goals): "Clean water and sanitation" and Goal 7: "Affordable and clean energy." [Explanation of symbols]

[0041] 1 Sludge volume reduction system 10. Activated sludge treatment equipment 12 Adjustment tank 14 Aerobic tank 20 Sludge separation mechanism 22 Separation tank 24 Post-separation storage tank 26 Dehydrator 28 Storage tank after dehydration 30 Desorption tank 50 Hydrothermal solubilization equipment 52 Solubilizer 54 Post-solubilization storage tank 100 Flash steam treatment section

Claims

1. A sludge solubilization method for hydrothermally solubilizing sludge, comprising: After solubilization with high-temperature, high-pressure water, A sludge solubilization method in which at least one of water and a chelating agent is supplied.

2. The method further comprises a cooling step of cooling the solubilized sludge, The chelating agent is supplied to the sludge cooled in the cooling step. The sludge solubilization method according to claim 1.

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