Sludge composting system

Abstract

To provide a sludge composting system that subjects coagulated sludge to solid-liquid separation operation in a solid-liquid separation device to form dewatered sludge, adds microbial cells to the dewatered sludge in the solid-liquid separation device, and then ferments the dewatered sludge, thereby producing the fermented sludge.SOLUTION: A sludge composting system ferments dewatered sludge derived from the solid-liquid separation of coagulated sludge, to produce fermented sludge. This system includes: a coagulation and mixture tank 3 that mixes and stirs sludge and a coagulant to form coagulated sludge; a solid-liquid separation device 7 that subjects the coagulated sludge to solid-liquid separation operation to produce dewatered sludge; a microbial injection part 37 that adds microbial cells to the dewatered sludge in the solid-liquid separation device 7; and a composting facility 16 that ferments the dewatered sludge to produce fermented sludge. This structure enables enhanced fermentation efficiency within the composting facility 16.SELECTED DRAWING: Figure 1

Description

Technical Field

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[0001] The present invention relates to a sludge composting system using bacteria.

Background Art

[0002] Conventionally, after mixing and stirring organic sludge such as sewage, night soil, or food production and processing wastewater with a polymer flocculant in an agglomeration mixing tank, solid-liquid separation is performed using a solid-liquid separation device such as a screw press, a centrifuge, or a belt press, and the generated dehydrated sludge is fermented to produce compost. The dehydrated sludge produced by the conventional method has a high water content and it is difficult to maintain voids, making it difficult to compost as it is. Therefore, in order to improve the fermentation efficiency, dehydrating aids (biomass) such as sawdust, straw, and rice husks are added in the early stage of the fermentation process to adjust the water content of the sludge and increase the porosity.

[0003] Patent Document 1 discloses a composting technique in which sewage sludge and tap water sludge are mixed with wood waste (biomass) such as pruning branches, bark, and large sawdust and microorganisms (seed bacteria), and then fermented and composted. Techniques for supplying biomass and bacteria to dehydrated sludge to improve fermentation efficiency are known. <00000!4> Patent Document 2 discloses a technique in which organic residues (biomass) containing fibers such as livestock excrement, night soil, food waste, and food processing residues are mixed with microorganisms (bacteria) such as lactic acid bacteria, acetic acid bacteria, and citric acid bacteria in a methane fermentation digestate, and then agglomerated and dehydrated. Techniques for supplying biomass and bacteria to the sludge before agglomeration are also known.

[0005] Further, Patent Document 3 discloses a screw press in which an aggregant supply path is provided in a screw shaft, nozzle holes are formed in screw blades wound around the screw shaft, and the aggregant supplied from the aggregant supply path is added to the sludge in the filtration chamber from the nozzle holes.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Patent No. 4947673 [Patent Document 2] Patent No. 5112793 [Patent Document 3] Japanese Patent Publication No. 2006-55819 [Overview of the project] [Problems that the invention aims to solve]

[0007] Conventionally, to promote sludge fermentation, auxiliary materials such as woody biomass are supplied to dewatered sludge to adjust the moisture content and porosity of the sludge. However, because the auxiliary materials supplied immediately before the fermentation process are not uniformly mixed with the sludge, fermentation is inefficient.

[0008] Patent Document 1 describes a method that adds not only wood waste (biomass) but also microorganisms (starter cultures) as an aid to promote fermentation. This necessitates the installation of a large mixer for mixing the starter cultures with the sludge, in addition to a hopper and conveyor for the starter cultures. Furthermore, the biomass and starter cultures are only mixed with the sludge in the mixer before the fermentation tank, making it difficult to sufficiently improve the mixing properties with the sludge. In addition, mixing the sludge and biomass results in a high solid content, making it difficult to diffuse the microorganisms (bacterial cells) into the sludge. Moreover, because the sludge is transported to the fermentation tank without uniform mixing of biomass and starter cultures, variations in fermentation rate occur, the frequency of turning in the fermentation tank increases, and problems such as the generation of foul odors and prolonged fermentation time arise.

[0009] Patent Document 2 describes a technique for adding organic residue (biomass) and microorganisms (bacterial cells) to methane fermentation digestate prior to the coagulation process, and is not a technique for supplying bacterial cells during the dehydration process.

[0010] Patent Document 3 describes a technique for spraying a coagulant from a nozzle formed on the screw blades that make up a screw press, but it does not describe or suggest spraying bacterial cells from the nozzle.

[0011] The present invention provides a sludge composting system that generates dewatered sludge with attached microorganisms by adding microbial cells during solid-liquid separation of coagulated sludge, and then ferments this dewatered sludge to stably produce fermented sludge in a short time. [Means for solving the problem]

[0012] The present invention relates to a sludge composting system that produces fermented sludge by fermenting dewatered sludge obtained by solid-liquid separation of coagulated sludge, comprising: a coagulation mixing tank that mixes and stirs sludge and a coagulant to produce coagulated sludge; a solid-liquid separation device that produces dewatered sludge by solid-liquid separation of the coagulated sludge; a microbial cell ejection unit that adds microbial cells to the dewatered sludge within the solid-liquid separation device; and a composting facility that produces fermented sludge by fermenting the dewatered sludge. The solid-liquid separation apparatus is a screw press that forms a filtration chamber with an outer cylinder stretched with a screen and a screw shaft around which screw blades are wound. A cell supply passage is provided within the screw shaft to supply cell cells from outside the screw shaft, and the cell cells are supplied from a cell ejection section having at least one ejection hole located between the pitches of the screw blades downstream of the filtration chamber. This allows for the fermentation of dewatered sludge to which microbial cells are attached, improving fermentation efficiency and enabling the stable production of fermented sludge in a short time. Furthermore, it is possible to infiltrate the dewatered sludge, which has a low amount of free water generated in the filtration chamber, with bacterial cells. Cut.

[0013] In a sludge composting system that produces fermented sludge by fermenting dewatered sludge obtained by solid-liquid separation of coagulated sludge, the system comprises: a coagulation mixing tank that mixes and stirs sludge and a coagulant to produce coagulated sludge; a solid-liquid separation device that separates the coagulated sludge into solid and liquid to produce dewatered sludge; a microbial cell ejection unit that adds microbial cells to the dewatered sludge within the solid-liquid separation device; and a composting facility that ferments the dewatered sludge to produce fermented sludge. The solid-liquid separation device is a belt press that pressurizes and dewaters sludge by sandwiching it between a pair of endless filter cloths wrapped around a number of rolls. By configuring the system to supply microbial cells from the microbial cell ejection unit just before the sludge is sandwiched between the pair of filter cloths, the dewatered sludge to which the microbial cells have adhered can be fermented, improving fermentation efficiency and enabling the stable production of fermented sludge in a short time, while also allowing the microbial cells to permeate the dewatered sludge, which has less free water generated in the filtration chamber. [Effects of the Invention]

[0014] This invention involves adding microbial cells to dewatered sludge with low free water content within a solid-liquid separation device, allowing the microbial cells to penetrate and firmly adhere to the sludge. By supplying this dewatered sludge, to which the microbial cells have firmly adhered, to a composting facility, the microbial cells promote sludge fermentation, enabling the stable production of fermented sludge in a short time. Consequently, the frequency of sludge turning and the amount of aeration required in the composting facility can be reduced, thereby reducing the labor and cost associated with fermentation. Furthermore, since the microbial cells are added in liquid form within the solid-liquid separation device, the microbial cells are not affected by surrounding environmental factors such as dust or temperature changes. In addition, the microbial cell supply channel and microbial cell ejection section have a simple structure, making them easily applicable to existing screw presses. Moreover, the microbial cells have an odor-suppressing effect, and by adding them before the dewatered sludge is discharged from the solid-liquid separation device, the sludge's characteristic odor does not adversely affect the surrounding environment. [Brief explanation of the drawing]

[0015] [Figure 1] It is a flowchart of a sludge composting system according to the present invention. [Figure 2] Similarly, it is a longitudinal sectional view of a screw press. [Figure 3] Similarly, it is a longitudinal sectional view of a main part of a screw shaft provided with a bacterial cell ejection part. [Figure 4] Similarly, it is a longitudinal sectional view of a main part of a screw shaft provided with a bacterial cell ejection part according to another embodiment. [Figure 5] Similarly, it is a longitudinal sectional view of a main part of a screw shaft provided with a bacterial cell ejection part according to another embodiment. [Figure 6] Similarly, it is a schematic side view of a belt press.

Mode for Carrying Out the Invention

[0016] FIG. 1 is a flowchart of a sludge composting system according to the present invention, in which a sludge supply pipe 1 and a flocculant supply pipe 2 are connected to a flocculation mixing tank 3. In the flocculation mixing tank 3, a flocculation stirring device 4 for mixing and stirring the sludge supplied from the sludge supply pipe 1 and the flocculant (polymer flocculant, inorganic flocculant) supplied from the flocculant supply pipe 2 is provided. The flocculation stirring device 4 may be anything that can mix and stir, and in this embodiment, a stirring blade is used.

[0017] The sludge mixed and stirred in the flocculation mixing tank 3 becomes strong flocs (flocculated sludge), and is supplied to a solid-liquid separation device 7 through a flocculated sludge supply pipe 6 by a supply pump 5. A pressure gauge 8 for measuring the pressure of the flocculated sludge supplied to the solid-liquid separation device 7 is disposed in the flocculated sludge supply pipe 6.

[0018] The solid-liquid separation device 7 can dehydrate the flocculated sludge, and conventional devices such as a filter press in a batch type, a belt press, a screw press, and a centrifugal dehydrator in a continuous type can be used.

[0019] In this embodiment, bacterial cells are supplied to the solid-liquid separation device 7. The bacterial cells are stored in a bacterial cell storage tank 9 and supplied to the solid-liquid separation device 7 from a bacterial cell supply pipe 10 connected to the bacterial cell storage tank 9. The specific method of supplying the bacterial cells will be described in detail later.

[0020] The bacterial cells are aerobic thermophilic bacteria that are active at high temperatures in the presence of air, and any type can be used. An example of aerobic thermophilic bacteria is YM bacteria (registered trademark), which is a complex of microorganisms centered on photosynthetic bacteria and lactic acid bacteria and yeast. The bacterial cells are stored in liquid form and supplied to the solid-liquid separation device 7, which will be described later, via a bacterial cell supply pipe 10 connected to the bacterial cell storage tank 9. YM bacteria have the effect of promoting sludge fermentation and also have the effect of deodorizing organic waste, thus contributing to the odor suppression effect of the solid-liquid separation device 7.

[0021] In the solid-liquid separation device 7, the coagulated sludge supplied from the coagulated sludge supply pipe 6 is separated into solid and liquid components, and then dewatered sludge (dewatered cake) is produced. The generated dewatered sludge is supplied to the composting equipment 16 from the dewatered sludge supply pipe 13. At this time, the dewatered sludge is sent to the composting equipment 16 with microbial cells incorporated into it, so the microbial cells act as a fermentation accelerator and increase the fermentation efficiency. The separated filtrate is discharged to the outside from the filtrate discharge pipe 12 connected to the filtrate storage tank 11.

[0022] The dewatered sludge discharged from the solid-liquid separator 7 is transferred to the composting facility 16 via the dewatered sludge supply pipe 13. The composting facility 16 is a known aerobic fermentation tank having an aeration means 15 consisting of a blower that supplies air into the facility. By blowing air, which is the oxygen source necessary for aerobic fermentation, into the composting facility 16, the organic matter in the dewatered sludge is decomposed by the action of aerobic microorganisms, resulting in a reduced amount of organic matter and stabilized fermented sludge. At this time, the moisture content decreases due to evaporation, but the fermented sludge is allowed to mature to a level where it can be used as compost (fertilizer).

[0023] The composting equipment 16 is connected to a return pipe 17 for returning the generated fermented sludge. The other end of the return pipe 17 is connected to a dewatered sludge supply pipe 13, and a predetermined amount of fermented sludge is returned based on the value of a moisture content meter (not shown) installed in the composting equipment 16. By returning the fermented sludge and composting it again, it is possible to reduce the moisture content of the fermented sludge to the desired level, resulting in compost of stable quality. At this time, since microbial cells are also returned along with the sludge, the microbial cells can be reused as a fermentation accelerator.

[0024] Furthermore, if necessary, an aeration means may be installed in front of the composting equipment 16. 15 A hopper (not shown) having the following characteristics may be installed to improve the aeration of the dewatered sludge before transferring it to the composting facility 16.

[0025] Figure 2 is a longitudinal cross-sectional view of the screw press according to the present invention. The screw press 22 has a screw shaft 25 with screw blades 31 wound around it, which is rotatably disposed inside an outer cylinder 24 on which a screen 23 is stretched around its circumference. The screw shaft 25 expands in diameter from the sludge supply side to the cake discharge side, and the filtration chamber 26 formed between the outer cylinder 24 and the screw shaft 25 decreases from the supply side to the discharge side.

[0026] A sprocket 28 is fitted onto a screw drive shaft 27 connected to the rear end of the screw shaft 25, and the sprocket 28 is linked to a screw drive device (not shown). A raw liquid supply passage 29 is provided at the starting end of the screw shaft 25, which is housed inside the outer cylinder 24, and a supply hole 30 opens on the starting end side of the filtration chamber 26. Sludge treated with a polymer flocculant is supplied from the raw liquid supply passage 29 of the screw shaft 25 through the supply hole 30 to the starting end of the filtration chamber 26, and the filtrate is separated from the screen 23 while being conveyed by the screw blades 31, thereby concentrating and dewatering the sludge.

[0027] A back pressure adjustment compressor 32 is installed at the rear end of the filtration chamber 26. The compressor 32 is connected to a sliding device (not shown), such as a cylinder, and allows adjustment of the opening degree of the cake discharge port 33 of the filtration chamber 26.

[0028] In this embodiment, a bacterial cell supply passage 34 is formed inside each shaft, extending from the free end of the screw drive shaft 27 to the downstream section of the screw shaft 25, and the insides are connected. The bacterial cell supply passage 34 communicates with a bacterial cell supply pipe 10 connected to the end of the screw drive shaft 27 and is configured to supply bacterial cells to a bacterial cell ejection section 37, which will be described later.

[0029] Figure 3 is a longitudinal cross-sectional view of the main part of a screw shaft equipped with a microbial ejection section according to the present invention. As shown in Figures 2 and 3, a known swivel joint 36 is attached to the protruding end of a bearing unit 35 of a screw drive shaft 27, which is provided at the rear end of the large diameter side of the screw shaft 25.

[0030] A cell supply pipe 10 is connected to the swivel joint 36. The cell supply pipe 10 is composed of branched pipes, and each cell supply pipe 10 is connected to a pressure reducing valve 10a, a flow meter 10b, and an on / off valve 10c from the cell supply pump 45 side. A cell supply passage 34 is connected from the swivel joint 36 to a cell reservoir 41 located on the back surface 31b of the screw blade 31 (the small diameter side of the screw shaft 25), and the cells that flow into the cell reservoir 41 are supplied to the cell ejection section 37, which will be described in detail later.

[0031] By using a branched microbial supply pipe 10, the amount of microbial cells supplied from each line can be individually adjusted. Therefore, an appropriate amount of microbial cells can be supplied to the dewatered sludge formed around each microbial cell ejection section 37.

[0032] The bacterial cell ejection section 37 is located at an intermediate position (half the blade length) on the front surface 31a (the large-diameter side of the screw shaft 25) of the screw blade 31 wound around the screw shaft 25, one pitch from the end of the blade, and is parallel to the axis of the screw shaft 25. In addition, ejection holes 38 for spraying bacterial cells are provided at several locations on the side of the bacterial cell ejection section 37. The ejection holes 38 at several locations on the side are located on the side opposite to the rotation direction of the screw shaft 25, and are configured to spray bacterial cells in the direction of sludge flow (tangential to the diameter of the screw shaft 25). By supplying from an intermediate position in the blade length, the bacterial cells are supplied from the middle of the cake thickness of the dewatered sludge, so that the bacterial cells spread throughout the sludge in a short time.

[0033] The bacterial cell ejection section 37 is formed by a rod-shaped member protruding from the front surface 31a of the screw blade 31 (the large-diameter side of the screw shaft 25). As the blade rotates, the rod-shaped member rotates, mixing the dewatered sludge formed around each bacterial cell ejection section 37 with the bacterial cells. As a result, the bacterial cells are uniformly incorporated into the dewatered sludge, eliminating the need for a separate mixer.

[0034] In addition, by placing the microbial ejection section 37 downstream of the filtration chamber 26 (one pitch from the end of the screw blade 31), liquid microbial cells can be added to the dewatered sludge that has been separated from the filtrate and formed into a cake within the solid-liquid separation device 7. Since the microbial cells can be added to dewatered sludge with low free water content, the microbial cells do not leak out with the filtrate. Furthermore, because they penetrate the dewatered cake in a short time, it is possible to produce dewatered sludge with a large amount of microbial cells attached. Since this dewatered sludge containing microbial cells can be supplied to the subsequent composting equipment 16, it is possible to improve the fermentation efficiency within the equipment. As a result, the addition of microbial cells within the composting equipment 16, as in the conventional method, becomes unnecessary, and the frequency of turning the sludge within the composting equipment 16 can be reduced.

[0035] In this embodiment, four microbial ejection sections 37 are provided at each pitch of the screw blades 31, and ejection holes 38 are provided at three locations on the side of the microbial ejection sections 37. However, the number and shape of the microbial ejection sections 37 and ejection holes 38 are not specified. In addition, although the microbial ejection sections 37 are installed at a distance of one pitch from the end of the screw blades 31, the installation position is not limited to this.

[0036] Furthermore, the bacterial cell ejection section 37 may be a nozzle attached to the screw blade 31, as shown in Figure 4. The bacterial cell ejection section 37 is attached to the front surface 31a (the large-diameter side of the screw shaft 25) of the bacterial cell reservoir 41, which communicates with the bacterial cell supply passage 34 inside the screw shaft 25, and is configured to eject bacterial cells from the bacterial cell reservoir 41. Specifically, the bacterial cell ejection section 37 has an ejection hole 38 that penetrates from the back surface 31b to the front surface 31a of the screw blade 31, and is configured to supply bacterial cells from the front surface 31a of the blade to the filtration chamber 26.

[0037] Furthermore, as shown in Figure 5, a pair of fungal ejection sections 37, 37 may be provided, projecting radially from the screw shaft 25 between the pitches of the screw blades 31. In this case, a pair of channels are projected upward (or downward) from the end of a fungal supply passage 34 provided within the screw shaft 25 to form the fungal ejection sections 37, 37. An ejection hole 38 for ejecting fungal cells is provided on the side of each fungal ejection section 37. The height of the ejection hole 38 from the base end is most preferably 1 / 2 the blade height of the screw blade 31, but a preferred height is 1 / 5 to 4 / 5 of the blade height of the screw blade 31, and a more preferred height is 2 / 5 to 3 / 5.

[0038] Two ejection holes 38 for ejecting microbial cells are provided circumferentially around the microbial cell ejection section 37. The ejection direction is tangential to the diameter of the screw shaft 25, and the angle θ between the ejection directions of the microbial cells ejected from these adjacent ejection holes 38 is set to, for example, 60°. The microbial cells are supplied between the screw blades 31 and to the central region between the inner circumferential surface of the screen 23 and the outer circumferential surface of the screw shaft 25.

[0039] In this embodiment, liquid bacterial cells supplied from the bacterial cell supply passage 34 are ejected from the bacterial cell ejection section 37 toward the filtration chamber 26. However, powdered bacterial cells may also be supplied from the bacterial cell supply passage 34 using compressed air and ejected from the bacterial cell ejection section 37.

[0040] Furthermore, although a screw press 22 is used as the solid-liquid separation device 7, other known solid-liquid separation devices such as a belt press 46 or a centrifugal dewatering machine may also be used. Figure 6 is a schematic side view of the belt press 46, in which sludge is sandwiched between a pair of endless filter cloths 43 wrapped around a number of rolls 44... and dewatered under pressure. Coagulated sludge supplied from the supply side is concentrated on one of the filter cloths 43, and then pressed and dewatered between the pair of filter cloths 43, 43 to produce dewatered sludge. In this embodiment, bacterial cells are supplied just before being sandwiched between the pair of filter cloths 43, 43, so that dewatered sludge containing bacterial cells can be produced.

[0041] Generally, sludge contains soil bacteria useful for fermentation, but this alone is insufficient to improve fermentation efficiency. Therefore, in this embodiment, microbial cells are supplied to the solid-liquid separator 7. By adding microbial cells to the solid-liquid separator 7, the dewatered sludge containing the microbial cells can be supplied to the composting equipment 16, thereby increasing the fermentation efficiency in the composting equipment 16 and enabling the stable production of fermented sludge in a short time. Furthermore, by adding microbial cells to the dewatered sludge, which has been compressed in the solid-liquid separator 7 and has a low free water content, the microbial cells penetrate into the sludge and adhere firmly to it, eliminating the need to mix and stir the sludge with the microbial cells.

[0042] In this embodiment, dewatered sludge is returned from the return pipe 17 to the dewatered sludge supply pipe 13 in order to adjust the moisture content of the fermented sludge. However, the return pipe 17 may be omitted, and instead, biomass acting as a dewatering aid may be supplied to improve the dewatering properties of the sludge. In that case, as shown in Figure 1, the biomass is supplied to the coagulation and mixing tank 3 and mixed and stirred together with the sludge and coagulant.

[0043] Examples of biomass include driftwood, thinned timber, wood waste (bark, sawdust, and wood chips generated during lumbering, as well as demolition materials from buildings, pruned branches, and bark), cellulosic fibrous materials such as bamboo, and plant-based waste such as tea residue and food scraps. Such biomass has little practical value in its original state and is usually disposed of as waste, making it excellent from the perspective of resource reuse.

[0044] The present invention is not limited to the embodiments described in detail above. Modifications can be made as appropriate without departing from the spirit of the invention. [Industrial applicability]

[0045] The sludge composting system of the present invention is a technology that promotes sludge fermentation by adding microbial cells to a solid-liquid separation device to produce dewatered sludge to which the microbial cells have adhered, and then fermenting this dewatered sludge. This technology can be applied not only to screw presses but also to all solid-liquid separation devices such as belt presses and filter presses. Because the present invention enables the stable production of fermented sludge (compost) in a short time, the number of days required for composting can be shortened. Furthermore, compost derived from sewage is quite beneficial as compost because it is rich in nutrients and minerals, mainly nitrogen and phosphorus, which are necessary for plant growth. [Explanation of symbols]

[0046] 3 Coagulation mixing tank 7 Solid-liquid separator 16 Composting equipment 22 Screw Press 23 screens 24 Outer cylinder 25 Screw shaft 26 Filtration Chamber 31 Screw blades 34 Bacterial body supply channel 37 Fungal cell spouting part 38 Blowhole

Claims

1. In a sludge composting system that produces fermented sludge by fermenting dewatered sludge obtained by solid-liquid separation of coagulated sludge, A coagulation mixing tank (3) mixes and stirs sludge and a coagulant to produce coagulated sludge, A solid-liquid separation device (7) that separates coagulated sludge into solid and liquid to produce dewatered sludge, A microbial cell ejection unit (37) for adding microbial cells to dewatered sludge within the solid-liquid separation device (7), A composting facility (16) that ferments dewatered sludge to produce fermented sludge, Equipped with, The solid-liquid separation device (7) is a screw press (22) that forms a filtration chamber (26) with an outer cylinder (24) stretched with a screen (23) and a screw shaft (25) around which screw blades (31) are wound. A cell supply passage (34) is provided within the screw shaft (25) to supply cell cells from outside the screw shaft (25), and the cell cells are supplied from the cell ejection section (37) which has at least one ejection hole (38) located between the pitches of the screw blades (31) located downstream of the filtration chamber (26). A sludge composting system characterized by the following features.

2. A sludge composting system that produces fermented sludge by fermenting dewatered sludge obtained by solid-liquid separation of flocculated sludge, A coagulation mixing tank (3) mixes and stirs sludge and a coagulant to produce coagulated sludge, A solid-liquid separation device (7) that separates coagulated sludge into solid and liquid to produce dewatered sludge, A microbial cell ejection unit (37) for adding microbial cells to dewatered sludge within the solid-liquid separation device (7), A composting facility (16) that ferments dewatered sludge to produce fermented sludge, Equipped with, The solid-liquid separation device (7) is a belt press (46) that pressurizes and dewaters sludge by sandwiching it between a pair of upper and lower endless filter cloths (43, 43) wound around a number of rolls (44...). The configuration is such that bacterial cells are supplied from the bacterial cell ejection section (37) just before the sludge is trapped between the pair of filter cloths (43, 43). A sludge composting system characterized by the following features.

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