Specific substance recovery system and specific substance recovery method

Abstract

To provide a specific substance recovery system capable of completing the recovery of a specific substance such as a rare metal from sewage flowing into a sewage treatment plant in the same sewage treatment plant, and a specific substance recovery method.SOLUTION: A specific substance recovery system includes a recovery unit 10 that recovers a fibrous substance from sewage in a sewage treatment plant, a reforming unit 20 that reforms the fibrous substance recovered by the recovery unit 10 into an adsorbent 31 that adsorbs a specific substance, an adsorption unit 30 that causes the adsorbent 31 to adsorb the specific substance present in the sewage flowing into the sewage treatment plant, and a separation unit 40 that separates the adsorbent 31 and the specific substance adsorbed by the adsorbent 31.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a specific substance recovery system and a specific substance recovery method. [Background technology]

[0002] Precious metals and rare metals (rare metals), including gold and silver, have small reserves, and their reserves and production are significantly unevenly distributed in certain countries. Despite their low production volumes, these metals have become essential in recent years for key industries such as automobiles and electronics. However, access to rare metals in particular can be restricted depending on the political situation abroad, raising concerns about the impact on domestic companies. Therefore, it is important to secure a quantitative supply. Trace amounts of rare metals flow into sewage treatment plants, and there is a need for a means to easily recover them (see Patent Document 1).

[0003] Patent Document 1 discloses a valuable resource recovery system that injects engineered powder that adsorbs valuable resources into wastewater flowing from a water source, and recovers valuable resources such as fluorine, boron, phosphorus, rare metals, and oil from the wastewater. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-69395 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the valuable resource recovery system described in Patent Document 1, the third component, which is a functional powder that adsorbs the valuable resources, needs to be procured from outside, which increases costs and labor, and the recovery of valuable resources cannot be completed within the same sewage treatment plant.

[0006] The present invention has been made in consideration of the problems inherent in the prior art, and an object of the present invention is to provide a specific substance recovery system and a specific substance recovery method that can complete the recovery of specific substances, such as rare metals, from sewage flowing into a sewage treatment plant within the same sewage treatment plant. [Means for solving the problem]

[0007] A specific substance recovery system according to one embodiment of the present invention includes a recovery section that recovers fibrous material from sewage in a sewage treatment plant, a modification section that modifies the fibrous material recovered in the recovery section into an adsorbent that adsorbs the specific substance, an adsorption section that adsorbs the specific substance present in the sewage flowing into the sewage treatment plant onto the adsorbent, and a separation section that separates the adsorbent from the specific substance adsorbed onto the adsorbent.

[0008] In addition, a specific substance recovery method according to one embodiment of the present invention includes a recovery process for recovering fibrous material from sewage in a sewage treatment plant, a modification process for modifying the fibrous material recovered in the recovery process into an adsorbent that adsorbs the specific substance, an adsorption process for adsorbing the specific substance present in the sewage flowing into the sewage treatment plant onto the adsorbent, and a separation process for separating the adsorbent from the specific substance adsorbed onto the adsorbent. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a specific substance recovery system and a specific substance recovery method that can complete the recovery of specific substances such as rare metals from sewage flowing into a sewage treatment plant within the same sewage treatment plant. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a block diagram showing the configuration of a specific substance recovery system according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram illustrating an example of an extraction unit according to the present embodiment. [Figure 3] FIG. 10 is a schematic diagram illustrating another example of an extraction unit. [Figure 4] 1 is a schematic diagram of an adsorption device that can be used in the specific substance recovery system of this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] <Specific substance recovery system> The specific substance recovery system of this embodiment includes a recovery section that recovers fibrous substances from sewage in a sewage treatment plant, a modification section that modifies the fibrous substances recovered in the recovery section into an adsorbent that adsorbs the specific substances, an adsorption section that adsorbs the specific substances present in the sewage flowing into the sewage treatment plant onto the adsorbent, and a separation section that separates the adsorbent from the specific substances adsorbed onto the adsorbent.

[0012] In the specific substance recovery system of this embodiment, fibrous material derived from toilet paper and the like is selectively recovered from sewage in a sewage treatment plant, and the fibrous material is modified into an adsorbent that adsorbs the specific substance. The adsorbent obtained by modifying the fibrous material is then used to adsorb the specific substance present in the sewage flowing into the sewage treatment plant. Furthermore, the specific substance can be recovered by separating the adsorbent from the specific substance adsorbed to the adsorbent. In this embodiment, because the fibrous material derived from toilet paper and the like is modified into an adsorbent and used, there is no need to procure an adsorbent from outside when recovering the specific substance, and the process can be completed within the same sewage treatment plant.

[0013] The specific substances present in sewage flowing into sewage treatment plants include precious metals such as gold and silver, rare metals such as Ti, V, Mn, Co, and Ni, and harmful substances such as arsenic and organic fluorine compounds.

[0014] The specific substance recovery system of this embodiment will be described below with reference to the drawings. Fig. 1 is a block diagram showing an example of the configuration of the specific substance recovery system of this embodiment. The specific substance recovery system shown in Fig. 1 includes a primary settling tank 1, a reaction tank 2, a final settling tank 3, a gravity thickening tank 4, a mechanical thickening tank 5, a digester 6, and a dehydrator 7. The specific substance recovery system of this embodiment also includes a recovery section 10, a reforming section 20, an adsorption section 30, and a separation section 40.

[0015] The primary sedimentation tank 1 separates the wastewater (DW) flowing into the sewage treatment plant into supernatant water and sediment (sludge). The reaction tank 2 purifies the organic matter in the supernatant (sewage) separated in the primary sedimentation tank 1. The final sedimentation tank 3 separates the mixed liquid in the reaction tank 2 into treated water (TW) and excess sludge. The gravity thickener 4 thickens the raw sludge separated in the primary sedimentation tank 1 to produce gravity-thickened sludge. The mechanical thickener 5 thickens the excess sludge separated in the final sedimentation tank 3 to produce mechanically thickened sludge. The digester 6 anaerobically treats the gravity-thickened sludge and mechanically thickened sludge with anaerobic microorganisms to produce digested sludge. The dehydrator 7 separates the digested sludge containing fiber produced in the digester 6 and recovered in the separation section 40 into solid and liquid.

[0016] [Recovery Department] The recovery unit 10 selectively recovers fibrous material from sludge contained in sewage in a sewage treatment plant. Specifically, the recovery unit 10 is located between the primary settling tank 1 and the gravity thickening tank 4, and recovers fibrous material from sludge, which is the sediment separated in the primary settling tank 1. The sludge contains impurities composed primarily of easily decomposable organic matter derived from food waste, suspended solids (SS), and persistent organic matter, which is the main component of toilet paper. As described above, the fibrous material is derived mainly from toilet paper and other materials contained in the sewage in the sewage treatment plant. The recovery unit 10 separates the sludge into easily decomposable organic matter and persistent organic matter, recovers the persistent organic matter, and transfers the easily decomposable organic matter to the gravity thickening tank 4.

[0017] More specifically, as shown in Fig. 2, sludge, which is solid matter in sewage transported to a collection unit 10, is ground into fine particles in a grinder 11, and then washed away with wash water to recover predetermined fibrous materials. The recovered fibrous materials are mainly derived from toilet paper and are, for example, insoluble plant fibers with lengths of 0.1 to 30 mm. That is, the recovered fibrous materials mainly contain cellulose.

[0018] The recovery unit 10 is not particularly limited as long as it can recover fibrous materials from sludge. The recovery unit 10 may include a masher 11 that breaks down raw sludge, a separator 12 that separates hard-to-decompose organic matter and easily decomposable organic matter from the mashed prepared sludge, and a recovery device 13 that extracts hard-to-decompose organic matter from the mashed prepared sludge. The recovery unit 10 may continuously separate and recover hard-to-decompose organic matter containing predetermined fibrous materials.

[0019] 2, in this embodiment, the masher 11 is equipped with a pair of disks 11c including a rotary disk 11a and a fixed disk 11b. Raw sludge supplied through a supply pipe 14 moves from the center of the pair of disks 11c toward the outer periphery while being mashed, and is then discharged outside the pair of disks 11c.

[0020] The separator 12 includes a rotatable cylindrical screen 12a, and the recovery device 13 includes a spiral screw blade 13a provided inside the screen 12a. The prepared sludge that has been comminuted in the masher 11 is transported by the screw blade 13a from one end of the screen 12a, which is the masher 11 side, to the other end, which is the discharge outlet 15 side. Easily decomposable organic matter such as comminuted impurities is separated and discharged through the numerous pores provided in the screen 12a, and fibrous material with predetermined properties that will serve as the raw material for the adsorbent 31 is discharged from the discharge outlet 15 and recovered.

[0021] In addition, in Fig. 2, an example has been described in which the masher 11 is arranged inside the separator 12. However, as shown in Fig. 3, the masher 11 may be arranged outside the separator 12, and the masher 11 and the separator 12 may be formed independently. Even in this configuration, by sending the prepared sludge to the separator 12 via the transfer pipe 16, it is possible to prepare and separate the prepared sludge continuously.

[0022] Furthermore, in this embodiment, an example has been described in which the recovery unit 10 is disposed between the primary sedimentation tank 1 and the gravity thickening tank 4, and fibrous materials are recovered from sludge, which is the sediment separated in the primary sedimentation tank 1. However, fibrous materials may also be recovered from sludge that has settled in at least one of the primary sedimentation tank 1 and the gravity thickening tank 4. Therefore, the recovery unit 10 does not have to be disposed between the primary sedimentation tank 1 and the gravity thickening tank 4.

[0023] [Modification section] In the modifying section 20, the fibrous material recovered in the recovery section 10 is modified into an adsorbent 31 that adsorbs a specific substance. The recovered fibrous material is mainly cellulose, and this cellulose is modified into an adsorbent 31 that adsorbs a specific substance. An example of a modifying agent for modifying the fibrous material into the adsorbent 31 is amino acid. Details of the modification in the modifying section 20 will be described later in the modification step.

[0024] The adsorbent 31 obtained in the reforming section 20 is an adsorbent that adsorbs specific substances, but it can also be a different adsorbent depending on the specific substance to be adsorbed.

[0025] The adsorbent 31 obtained as described above is preferably formed into a sheet or granules and filled into a container for use in the adsorption section 30. Alternatively, the sheet-like adsorbent 31 may be formed into a cylindrical shape for use. Details of such adsorbent 31 will be described below in connection with the adsorption section 30.

[0026] [Adsorption part] In the adsorption section 30, specific substances present in sewage flowing into the sewage treatment plant are adsorbed onto the adsorbent 31. That is, the adsorbent 31 obtained in the reforming section 20 is molded into an appropriate shape to adsorb the specific substances. In this embodiment, the adsorption section 30 is disposed between the primary sedimentation tank 1 and the reaction tank 2, and the specific substances present in the supernatant water separated in the primary sedimentation tank 1 are adsorbed onto the adsorbent 31.

[0027] The adsorption unit 30 is not particularly limited as long as it can adsorb specific substances present in sewage onto the adsorbent 31. For example, as shown in FIG. 4(a), the adsorption unit 30 may have the adsorbent 31 formed in a sheet shape. Alternatively, as shown in FIG. 4(b), the adsorption unit 30 may have the adsorbent 31 formed in a cylindrical shape. Alternatively, as shown in FIG. 4(c), the adsorption unit 30 may have the adsorbent 31 in a granular shape. In either adsorption unit 30, supernatant water from which solids have been removed as much as possible in the primary sedimentation tank 1 is supplied and passed through the adsorption unit 30, thereby efficiently adsorbing specific substances contained in the sewage onto the adsorbent 31. The residence time of the sewage in the adsorption unit 30, etc., can be set appropriately.

[0028] In the present embodiment, an example has been described in which the adsorption unit 30 is disposed between the primary sedimentation tank 1 and the reaction tank 2, and the specific substances present in the supernatant water separated in the primary sedimentation tank 1 are adsorbed onto the adsorbent 31. However, the adsorbent 31 may be brought into contact with the supernatant water in the primary sedimentation tank 1, the mixed liquid in the reaction tank 2, or the supernatant water in the final sedimentation tank 3, and the specific substances present in the sewage may be adsorbed onto the adsorbent 31. Therefore, for example, the adsorption unit 30 may be disposed between the reaction tank 2 and the final sedimentation tank 3, and the specific substances in the water treated in the reaction tank 2 may be adsorbed onto the adsorbent 31.

[0029] [Separation section] In the separation section 40, the adsorbent 31 used in the adsorption section 30 is separated from the specific substance adsorbed to the adsorbent 31. The specific substance can be separated from the adsorbent 31 by a known reduction method, thermal decomposition method, or hydrolysis method. For example, after concentrating and dehydrating the adsorbent 31, it can be reduced and dissolved in a cellulose dissolving solution such as formic acid, and the solution can be filtered to separate and recover only the specific substance, i.e., rare metal.

[0030] As described above, in the specific substance recovery system of this embodiment, specific substances in sewage can be recovered by recovering and modifying fibrous materials in sewage and using them as adsorbent 31 that adsorbs the specific substances. Moreover, there is no need to procure adsorbent 31 from outside, and the process can be completed within the same sewage treatment plant.

[0031] <Specific substance recovery method> The specific substance recovery method of this embodiment includes a recovery process for recovering fibrous material from sewage in a sewage treatment plant, a modification process for modifying the fibrous material recovered in the recovery process into an adsorbent 31 that adsorbs the specific substance, an adsorption process for adsorbing the specific substance present in the sewage flowing into the sewage treatment plant onto the adsorbent 31, and a separation process for separating the adsorbent 31 from the specific substance adsorbed onto the adsorbent 31.

[0032] The specific substance recovery method of this embodiment can be implemented using the specific substance recovery system of this embodiment. Specifically, the recovery step S1 in the specific substance recovery method of this embodiment can be implemented using the recovery unit 10 in the specific substance recovery system of this embodiment. Similarly, the modification step S2 can be implemented using the modification unit 20, the adsorption step S3 can be implemented using the adsorption unit 30, and the separation step S4 can be implemented using the separation unit 40. Furthermore, in the specific substance recovery method of this embodiment, similar to the specific substance recovery system of this embodiment, fibrous materials derived from toilet paper and the like are modified into adsorbent 31 for use. Therefore, when recovering specific substances, there is no need to procure adsorbent 31 from an external source, and the process can be completed within the sewage treatment plant. Each step is described below. It is preferable to perform the recovery step S1, modification step S2, adsorption step S3, and separation step S4 in this order.

[0033] [Recovery process (S1)] The recovery step S1 is a step of selectively recovering fibrous material from sewage in a sewage treatment plant. As described above, solids in the sewage are transferred to the recovery section 10, where they are ground into fine particles and washed away with wash water to recover predetermined fibrous material, mainly containing cellulose. Easily decomposable organic matter not recovered in the recovery step S1 is transferred to the gravity thickener tank 4. In this embodiment, sludge settled in the primary settling tank 1 is transferred to the recovery section 10 to recover fibrous material, but gravity-thickened sludge in the gravity thickener tank 4 may also be transferred to the recovery section 10.

[0034] [Reforming process (S2)] The modification step S2 is a step in which the fibrous material recovered in the recovery step S1 is modified into an adsorbent 31 capable of adsorbing specific substances. By performing the modification step S2 within a sewage treatment plant, the fibrous material recovered in the recovery step S1 can be modified without being transported outside the plant. The cellulose derivative, which serves as the adsorbent 31 obtained by modifying the fibrous material, can be obtained, for example, by reacting an amino acid with a protected amino group with the hydroxyl groups of acylated cellulose (total average degree of substitution of acyl groups: 0.9 to 2.8). The amino protecting groups are then removed, and the deprotected amino groups are reacted with a quaternary ammonium salt in the presence of a sulfur compound. The acylated cellulose can also be obtained by reacting the hydroxyl groups of cellulose with an acylating agent to acylate all of the hydroxyl groups to form triacylated cellulose, and then deacylating some of the acyl groups in the resulting triacylated cellulose (see JP 56-59801 A). Furthermore, a fibrous material containing cellulose may be modified into an adsorbent that adsorbs specific substances by treating it with concentrated sulfuric acid at high temperature (see Japanese Patent No. 5711999).

[0035] [Adsorption process (S3)] The adsorption step S3 is a step in which specific substances present in sewage flowing into a sewage treatment plant are adsorbed onto the adsorbent 31. That is, the adsorbent 31 obtained in the modification step S2 is formed into a sheet or granules and configured like the adsorption section 30 described in the specific substance recovery system of this embodiment, and the specific substances present in the sewage are adsorbed onto the adsorbent 31. Note that in this embodiment, the adsorption step S3 adsorbs the specific substances by bringing the supernatant water from the primary settling tank 1 into contact with the adsorbent 31 in the adsorption section 30, but the specific substances may also be adsorbed by bringing the supernatant water from the reaction tank 2 or the final settling tank 3 into contact with the treated water TW.

[0036] [Separation process (S4)] The separation step S4 is a step of separating the adsorbent 31 from the specific substance adsorbed to the adsorbent 31. That is, the specific substance (e.g., rare metal) is separated from the adsorbent 31 with the specific substance adsorbed thereto using a known reduction method, pyrolysis method, or hydrolysis method. For example, after concentration and dehydration, the adsorbent 31 can be reduced and dissolved in a cellulose dissolving solution such as formic acid, and the resulting solution can be filtered to separate and recover only the specific substance, i.e., the rare metal. The specific substance recovery method may also include a step of introducing the liquid containing the dissolved adsorbent 31 obtained in the separation step S4 into the digester tank 6 within the sewage treatment plant. The filtrate (the cellulose dissolving solution containing the adsorbent 31) after separating and recovering the specific substance can be adjusted in advance for pH and finally introduced into the digester tank 6 to compensate for the loss of digester gas production due to the recovery of fibrous materials. Performing the separation step S4 within the sewage treatment plant eliminates the need to transport the adsorbent 31 with the specific substance adsorbed thereto outside the plant for separation and treatment.

[0037] Although several embodiments have been described above, the embodiments can be modified or varied based on the above disclosure. All components of the above embodiments and all features described in the claims may be individually extracted and combined as long as they are not mutually inconsistent. [Explanation of symbols]

[0038] 1 Primary sedimentation tank 2. Reaction tank 3 Final sedimentation tank 4 Gravity thickener 5 Mechanical thickener 6 Digestion tank 7 Dehydrator 10 Collection Department 20 Modification section 30 Adsorption part 31 Adsorbent 40 Separation part S1 Recovery process S2 reforming process S3 adsorption process S4 Separation process

Claims

1. a recovery unit that recovers fibrous materials from sewage in a sewage treatment plant; a modifying unit that modifies the fibrous material recovered in the recovery unit into an adsorbent that adsorbs a specific substance; an adsorption unit that adsorbs the specific substance present in the sewage flowing into the sewage treatment plant onto the adsorbent; a separation unit that separates the adsorbent from the specific substance adsorbed to the adsorbent; Specific material recovery systems, including:

2. The specific substance recovery system according to claim 1 , wherein the specific substance is a precious metal, a rare metal, or a hazardous substance.

3. a recovery step of recovering fibrous materials from sewage in a sewage treatment plant; a modifying step of modifying the fibrous material recovered in the recovering step into an adsorbent that adsorbs a specific substance; an adsorption step of adsorbing the specific substances present in the sewage flowing into the sewage treatment plant onto the adsorbent; a separation step of separating the adsorbent from the specific substance adsorbed to the adsorbent; A method for recovering a specific substance, including:

4. The method for recovering a specific substance according to claim 3, further comprising the step of introducing the adsorbent obtained in the separation step into a digestion tank in the sewage treatment plant.

5. 5. The method for recovering a specific substance according to claim 3, wherein the specific substance is a precious metal, a rare metal, or a hazardous substance.

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