Aquatic earthworm collection device and collection method

Abstract

To provide a collection device capable of reducing the volume of surplus sludge generated in an activated sludge treatment by utilizing the predatory behavior of aquatic earthworms, and simultaneously culturing the aquatic earthworms in the process.SOLUTION: An aquatic earthworm collection device comprises: a culture section 1 that allows aquatic earthworms present in sludge-containing water to adhere and be cultured; an egg holding section 2 that holds eggs of the aquatic earthworms and raises them as larvae; and an aquatic earthworm culture tank 3 that accommodates the culture section 1 and the egg holding section 2.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an apparatus and a method for collecting aquatic earthworms living in water containing sludge, and particularly to an efficient apparatus and method for collecting aquatic earthworms that contribute to sludge volume reduction.

Background Art

[0002] In recent years, activated sludge treatment has been widely used for treating organic wastewater with high BOD (Biochemical Oxygen Demand) and nitrogen concentration. Activated sludge treatment has the advantages of being easy to maintain and manage and having low running costs. In addition, activated sludge treatment can stably remove the raw water BOD and can always obtain good treated water quality. Therefore, activated sludge treatment is widely used for treating organic wastewater such as sewage, domestic wastewater, and industrial wastewater.

[0003] However, in activated sludge treatment, excess sludge is generated due to BOD removal. In particular, wastewater with a high BOD concentration generates a large amount of excess sludge, and the running cost associated with its disposal accounts for a high proportion of the entire treatment, and the reduction of excess sludge has become a major issue.

[0004] As a method for reducing excess sludge, for example, Patent Document 1 proposes a water treatment apparatus that can reduce excess sludge by utilizing the predation of sludge by microorganisms including Eisenia fetida. In addition, Patent Document 2 proposes a water treatment apparatus that reduces excess sludge by using a sludge treatment tank in which sludge is predated by Eisenia fetida.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Although earthworms are useful for reducing excess sludge, there is also a high demand for them mainly as feed for ornamental fish, and domestic earthworms are sold at a high price of 30,000 yen per kilogram. In addition, in Non-Patent Document 1, earthworms have high nutritional value as chicken feed and are also expected as a new protein source in modern times when there are concerns about a protein shortage on a global scale.

[0007] Thus, earthworms not only contribute to sludge volume reduction but also can convert excess sludge, which is difficult to utilize, into a protein source that can be used by humans.

[0008] Therefore, an object of the present invention is to provide a recovery device and a recovery method that can reduce the volume of excess sludge generated in activated sludge treatment by utilizing the predatory behavior of aquatic earthworms and, at the same time, cultivate aquatic earthworms in the process.

Means for Solving the Problems

[0009] In one aspect, there is provided a recovery device for aquatic earthworms, comprising a culture section for attaching and culturing aquatic earthworms present in sludge-containing water, an egg holding section for holding the eggs of the aquatic earthworms and growing them into juveniles, and an aquatic earthworm culture tank for housing the culture section and the egg holding section.

[0010] In one aspect, the culture section has a mesh structure. In one aspect, the mesh structure of the culture section has a coarser mesh at the upper part and a finer mesh at the lower part. In one aspect, the culture section is removably held in the egg holding section and can be taken out from the aquatic earthworm culture tank. In one aspect, the culture section is inclined obliquely with respect to the egg holding section. In one aspect, the egg holding part is fixed to the aquatic earthworm culture tank. In one aspect, the recovery device further includes an aeration device that generates bubbles in the sludge-containing water in the aquatic earthworm culture tank to circulate the sludge-containing water and the aquatic earthworms in the aquatic earthworm culture tank.

[0011] In one aspect, there is provided a method for recovering aquatic earthworms, which comprises introducing sludge-containing water into an aquatic earthworm culture tank, attaching the aquatic earthworms existing in the sludge-containing water to a culture part in the aquatic earthworm culture tank, culturing them, allowing the aquatic earthworms to lay eggs on the culture part, dropping the eggs onto an egg holding part and holding them on the egg holding part, circulating the grown aquatic earthworms in the aquatic earthworm culture tank by aeration, and attaching the grown aquatic earthworms to the culture part.

[0012] In one aspect, the culture part is taken out of the aquatic earthworm culture tank together with the grown aquatic earthworms.

Advantages of the Invention

[0013] According to the present invention, in a sludge treatment method in which surplus sludge is generated, such as the activated sludge treatment method, surplus sludge can be reduced by the predatory behavior of aquatic earthworms, the aquatic earthworms can be propagated, and furthermore, the aquatic earthworms that can be a protein source can be recovered.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing an embodiment of an aquatic earthworm recovery device. FIG. 2 is a perspective view of the aquatic earthworm recovery device shown in FIG. 1. The recovery device includes a culture unit 1 for attaching and culturing aquatic earthworms present in sludge-containing water, an egg holding unit 2 for holding eggs of aquatic earthworms and growing them into larvae, and an aquatic earthworm culture tank 3 for housing the culture unit 1 and the egg holding unit 2. Examples of sludge-containing water include organic wastewater such as sewage, domestic wastewater, and industrial wastewater.

[0016] The culture unit 1 and the egg holding unit 2 are arranged in the aquatic earthworm culture tank 3 and are immersed in the sludge-containing water. In this embodiment, a plurality of culture units 1 and a plurality of egg holding units 2 are provided. In one embodiment, a single culture unit 1 and a single egg holding unit 2 may be provided. The aquatic earthworm culture tank 3 has a sludge inlet 6 through which sludge-containing water flows in and a sludge outlet 7 through which the sludge-containing water treated in the aquatic earthworm culture tank 3 is discharged. In the aquatic earthworm culture tank 3, a flow of sludge-containing water is formed from the sludge inlet 6 toward the sludge outlet 7.

[0017] The egg holding unit 2 is arranged near the bottom 3a of the aquatic earthworm culture tank 3. The egg holding unit 2 is installed parallel to the water surface in the aquatic earthworm culture tank 3, that is, horizontally. The egg holding unit 2 is fixed to the aquatic earthworm culture tank 3. In this embodiment, the egg holding unit 2 is fixed to a pedestal 9 installed on the bottom 3a of the aquatic earthworm culture tank 3. However, the installation structure of the egg holding unit 2 is not limited to this embodiment. In one embodiment, the egg holding unit 2 may be fixed to the side surface of the aquatic earthworm culture tank 3.

[0018] The culture unit 1 is removably held by the egg holding unit 2. The culture unit 1 is inclined obliquely with respect to the egg holding unit 2 (i.e., with respect to the horizontal plane). More specifically, the culture unit 1 is removably held by the egg holding unit 2 and extends obliquely upward from the egg holding unit 2. Although not shown, in one embodiment, guide stays for supporting both sides of the culture unit 1 may be attached to the side surface of the aquatic earthworm culture tank 3.

[0019] FIG. 3 is a perspective view showing an embodiment of the culture unit 1 and the egg holding unit 2, and FIG. 4 is an enlarged view showing a part of the culture unit 1 and the egg holding unit 2 shown in FIG. 3. The egg holding unit 2 includes a culture unit holding mechanism 12 configured to removably hold the culture unit 1. As shown in FIG. 4, the culture unit holding mechanism 12 has two holding members 15 having two parallel holding surfaces 15a extending obliquely upward from the upper surface of the egg holding unit 2. These two holding members 15 are fixed to the upper surface of the egg holding unit 2. In one embodiment, instead of the two holding members 15, a single holding member 15 may have two parallel holding surfaces 15a.

[0020] There is a gap between the two holding surfaces 15a, and by inserting the lower part of the culture unit 1 into the gap between the holding surfaces 15a, the culture unit 1 is held by the culture unit holding mechanism 12. The culture unit 1 is not fixed to the culture unit holding mechanism 12 but is merely supported. Therefore, the culture unit 1 can be removed from the egg holding unit 2 by pulling the culture unit 1 upward from the culture unit holding mechanism  12. However, the specific configuration of the culture unit holding mechanism 12 is not limited to the embodiment shown in FIG. 3 as long as it can hold the culture unit 1 obliquely and removably hold the culture unit 1.

[0021] The culture section 1 and the egg holding section 2 have a mesh structure. In this embodiment, the culture section 1 and the egg holding section 2 have a sheet-shaped mesh structure. The material of the mesh structure is not particularly limited, and examples include corrosion-resistant metals or resins, or combinations thereof. For example, a wire mesh made of stainless steel can be used for the mesh structure of the culture section 1 and the egg holding section 2. The mesh size is preferably 5 to 30 meshes. When the average body length of the cultured aquatic earthworms is too large or too small, it is desirable to appropriately adjust the mesh size.

[0022] The reason why the culture section 1 is arranged obliquely is to receive the eggs of the aquatic earthworms that have fallen due to gravity from the culture section 1 by the egg holding section 2. Specifically, as shown in FIG. 5, it is desirable that the culture section 1 is inclined at an angle of 20 to 70 degrees with respect to the egg holding section 2 to drop the eggs onto the egg holding section 2.

[0023] Aquatic earthworms specifically belong to either the Oligochaeta of Annelida or the Polychaeta of Annelida. Specifically, species classified into the order Tubificida are desirable, and in particular, species such as Tubifex tubifex and Limnodrilus hoffmeisteri that grow widely in the country are desirable. In this embodiment, Tubifex tubifex is used as the aquatic earthworm. Other examples of aquatic earthworms include Tubifex tubifex (Goto's Tubifex), Tubifex hattai, and Branchiura sowerbyi. Also, the body length of the aquatic earthworms used in this embodiment ranges from 1 mm to 100 mm. By making the culture section 1 and the egg holding section 2 have a mesh structure, it is possible to separately culture individuals of 1 mm or less and 100 mm or more.

[0024] In Fig. 1, the sludge-containing water flows from left to right in the aquatic earthworm culture tank 3. In order to keep the dissolved oxygen concentration in the aquatic earthworm culture tank 3 constant, an aeration device 18 is installed at the bottom 3a of the aquatic earthworm culture tank 3. The aeration device 18 is arranged at a position lower than the culture part 1 and the egg holding part 2. The aeration device 18 injects air into the sludge-containing water to form bubbles in the sludge-containing water. As shown by the arrow in Fig. 1, due to the rising of the bubbles, a circulating flow of the sludge-containing water is formed in the aquatic earthworm culture tank 3. The aeration device 18 is arranged between the egg holding parts 2 so that the bubbles formed by the aeration device 18 do not contact the eggs on the egg holding part 2.

[0025] Fig. 6 is a schematic diagram showing an embodiment of the culture part 1. The culture part 1 has a sheet-shaped mesh structure. The culture part 1 has a coarser mesh at the upper part and a finer mesh at the lower part. In other words, the closer to the bottom 3a of the aquatic earthworm culture tank 3, the finer the mesh, and the closer to the water surface, the coarser the mesh. In the embodiment shown in Fig. 6, the mesh structure of the culture part 1 has three different sizes of meshes. That is, the mesh structure of the culture part 1 has an upper part 31 with a coarse mesh, a lower part 33 with a fine mesh, and an intermediate part 32 with a mesh smaller than that of the upper part 31 and larger than that of the lower part 33. Here, the "coarse mesh" of the upper part 31 and the "fine mesh" of the lower part 33 do not mean absolutely coarse and fine meshes, but mean that the mesh of the upper part 31 is relatively coarser than that of the lower part 33.

[0026] The intermediate part 32 is located between the upper part 31 and the lower part 33. However, the mesh structure of the culture part 1 is not limited to this embodiment. In one embodiment, the mesh structure of the culture part 1 may have two different sizes of meshes, or may have four or more different sizes of meshes.

[0027] In this way, the mesh structure of the culture section 1 has meshes of different sizes, so that when aquatic earthworms are carried to the water surface by the upward current caused by aeration and sink, they can attach to the mesh section of a size that matches their body length. For example, if a small aquatic earthworm sinks to the upper part 31 of the coarse mesh, the gaps in the mesh are large compared to the body length of the aquatic earthworm, so the probability of the aquatic earthworm becoming entangled in the upper part 31 is low, and most of them are re-wound up by the upward current. On the other hand, if a large aquatic earthworm sinks to the lower part 33 of the fine mesh, the aquatic earthworm can become entangled in the lower part 33, allowing it to be active at that point.

[0028] The upward flow caused by aeration causes the aquatic earthworms to repeatedly rise and sink, so that all of the aquatic earthworms attach to the mesh sections that match their body length. As a result, the body length of the aquatic earthworms increases toward the top of the culture section 1, and decreases toward the bottom. In this way, the culture section 1 has a mesh structure with different mesh sizes, so that the aquatic earthworms attach to different sections of the culture section 1 depending on their body length and thickness.

[0029] Aquatic earthworm eggs laid in the culture section 1 fall into the egg holding section 2 due to gravity. Aquatic earthworms lay multiple egg sacs, each about 1 mm in size, so in order to receive all of the egg follicles, it is desirable that the egg holding section 2 be made of a material such as wire mesh with a fine mesh of about 25 meshes. The egg holding section 2 serves to hold the aquatic earthworm eggs and raise the young. After that, as the aquatic earthworms grow to a certain extent, they are caught in the upward current caused by aeration as they move, and are able to attach to the mesh section that matches their body length. By repeating this series of steps, the larger the aquatic earthworms, the higher they can be positioned in the culture section 1.

[0030] The culture unit 1 can be removed from the egg holding unit 2. The culture unit 1 is taken out of the earthworm culture tank 3 together with the aquatic earthworms, and only the large-sized aquatic earthworms attached to the coarser-mesh part of the culture unit 1 can be easily separated from the culture unit 1 by water flow or gravity. At this time, the aquatic earthworms attached to the finer-mesh part are difficult to be separated from the culture unit 1 because they are entangled in the mesh structure. Therefore, the small-sized aquatic earthworms can be left in the culture unit 1.

[0031] The culture unit 1 with the remaining attached aquatic earthworms is put back into the aquatic earthworm culture tank 3 and held by the egg holding unit 2. As the small-sized aquatic earthworms grow, they move to the coarser-mesh part of the culture unit 1 as described above. The large-sized aquatic earthworms that have moved to the coarser-mesh part are taken out of the aquatic earthworm culture tank 3 together with the culture unit 1 and separated from the culture unit 1 as described above. In this way, only the large-sized aquatic earthworms can be separated and recovered from the culture unit 1, and the small-sized aquatic earthworms can be left in the culture unit 1, so that the aquatic earthworms can be continuously cultured.

[0032] Hereinafter, experimental examples using the recovery device will be shown. An aquatic earthworm culture tank 3 with a width of 30 cm, a depth of 18 cm, and a height of 24 cm was prepared. Three-stage wire meshes with meshes of 5, 10, and 20 meshes were each cut to a height of 6 cm and a width of 20 cm and combined so that the mesh became coarser toward the water surface. The size of the opening holes of the mesh was 4 mm square for 5 meshes, 1.8 mm square for 10 meshes, and 0.9 mm square for 20 meshes. The above opening holes are square meshes, but are not limited thereto. In this experimental example, white worms were used as the aquatic earthworms.

[0033] When 10 ml of white worms with a body length of about 20 to 30 mm were put into the aquatic earthworm culture tank 3, most of them adhered to the mesh parts of 5 and 10 meshes, and hardly adhered to the mesh part of 20 meshes. From this, it was shown that for the white worms with a body length of 20 to 30 mm used in the experiment, the mesh size of 5 or 10 meshes was optimal, and the attachment position of the culture unit 1 could be controlled according to the body length of the aquatic earthworms.

[0034] The above-described embodiments are described for the purpose of enabling a person having ordinary knowledge in the technical field to which the present invention pertains to practice the present invention. Various modifications of the above embodiments can be naturally made by those skilled in the art, and the technical idea of the present invention can also be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but is construed in the broadest scope in accordance with the technical idea defined by the claims.

Explanation of Reference Numerals

[0035] 1 Culture section 2 Egg holding section 3 Aquatic earthworm culture tank 6 Sludge inlet 7 Sludge outlet 9 Pedestal 12 Culture section holding mechanism 15 Holding member 15a Holding surface 18 Aeration device 31 Upper portion 32 Middle portion 33 Lower portion

Claims

1. A culture section for attaching and culturing aquatic earthworms present in sludge-containing water, An egg holding section for holding eggs of the aquatic earthworms and growing them into larvae, An aquatic earthworm culture tank for housing the culture section and the egg holding section, A recovery device for aquatic earthworms, characterized by comprising the above.

2. In the above Claim 1, The culture section has a mesh structure. A recovery device for aquatic earthworms, characterized by this.

3. In the above Claim 2, The mesh structure of the culture section has a coarser mesh at the upper part and a finer mesh at the lower part. A recovery device for aquatic earthworms, characterized by this.

4. In the above Claim 1, The culture section is removably held by the egg holding section, and the culture section can be taken out from the aquatic earthworm culture tank. A recovery device for aquatic earthworms, characterized by this.

5. In the above Claim 1, The culture section is inclined obliquely with respect to the egg holding section. A recovery device for aquatic earthworms, characterized by this.

6. In the above Claim 1, The egg holding section is fixed to the aquatic earthworm culture tank. A recovery device for aquatic earthworms, characterized by this.

7. In the above Claim 1, The recovery device for aquatic earthworms further comprises an aeration device for generating bubbles in the sludge-containing water in the aquatic earthworm culture tank and circulating the sludge-containing water and the aquatic earthworms in the aquatic earthworm culture tank.

8. Introduce sludge-containing water into an aquatic earthworm culture tank, Attach and culture the aquatic earthworms present in the sludge-containing water to a culture section in the aquatic earthworm culture tank, Let the aquatic earthworms lay eggs on the culture section, let the eggs fall onto an egg holding section, and hold them on the egg holding section, Circulate the grown aquatic earthworms in the aquatic earthworm culture tank by aeration, A method for recovering aquatic earthworms, characterized by attaching the grown aquatic earthworms to the culture section.

9. In the above Claim 8, A method for recovering aquatic earthworms, characterized by taking out the culture section from the aquatic earthworm culture tank together with the grown aquatic earthworms.

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