Sludge composting system

Abstract

To provide a sludge composting system that submerges biomass in microbial cells within a biomass production tank to form microbial biomass, mixes and stirs the formed microbial biomass with sludge and a coagulant to facilitate coagulation, and dewaters the coagulated mass in a solid-liquid separation device to compost the dewatered sludge, thereby allowing for the efficient production of 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 microbial biomass production tank 9 that submerges biomass in microbial cells to form microbial biomass; a coagulation and mixture tank 3 that mixes and stirs the microbial biomass with sludge and a coagulant to form coagulated sludge; a solid-liquid separation device 16 that subjects the coagulated sludge to solid-liquid separation operation to produce dewatered sludge; and a composting facility 21 that ferments the dewatered sludge to produce fermented sludge. This structure enables the production of the dewatered sludge with uniformly incorporated microbial cells and biomass, allowing for enhanced fermentation efficiency within the composting facility 21.SELECTED DRAWING: Figure 1

Description

Technical Field

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

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 pre-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.

[0004] Patent Document 2 discloses a technique in which organic residues (biomass) containing fibers such as livestock excrement, night soil, household 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 sludge before agglomeration are also known.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

[0006] 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.

[0007] Patent Document 1 uses not only wood waste (biomass) but also microorganisms (starter cultures) as an aid to promote fermentation, which necessitates the installation of a large mixer for mixing with 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 large amount of solid matter, 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.

[0008] Patent Document 2 describes a technique for adding organic residue (biomass) and microorganisms (bacterial cells) to methane fermentation digestate prior to the coagulation process. However, the microorganisms (bacterial cells) are added as seed sludge to improve the fermentation efficiency in the acid fermentation tank located prior to the coagulation tank, and are not added to improve the fermentation efficiency of the dewatered sludge produced after dewatering.

[0009] The present invention provides a sludge composting system in which, in the preceding step of the coagulation process, bacterial cells and biomass are supplied to a bacterial biomass generation tank to produce bacterial biomass to which bacterial cells are attached, the bacterial biomass is mixed and stirred with sludge and a coagulant to coagulate, and then dewatered in a solid-liquid separator to compost the dewatered sludge. [Means for solving the problem]

[0010] In a sludge composting system that produces fermented sludge by fermenting dewatered sludge obtained by solid-liquid separation of coagulated sludge, Plant-based By providing a microbial biomass generation tank that generates microbial biomass by immersing biomass in microbial cells, a coagulation mixing tank that generates coagulated sludge by mixing and stirring the microbial biomass with sludge and a coagulant, a solid-liquid separation device that generates dewatered sludge by separating the coagulated sludge into solid and liquid components, and a composting facility that generates fermented sludge by fermenting the dewatered sludge, it is possible to produce dewatered sludge in which microbial cells and biomass are uniformly incorporated, thereby increasing the fermentation efficiency in the composting facility. [Effects of the Invention]

[0011] This invention prevents poor sludge flocculation due to biomass floating within the flocculation tank by immersing biomass in liquid microbial cells prior to the flocculation process and supplying the generated microbial biomass to the flocculation mixing tank. The supplied biomass acts as a nucleus, improving the flocculation properties of the sludge, thus enabling the production of strongly flocculated sludge and reducing the amount of flocculant used. Furthermore, mixing and stirring the microbial biomass with the sludge in the flocculation mixing tank improves the kneading properties with the sludge, eliminating the need for a large mixer prior to the composting equipment. In addition, since microbial cells and biomass can be uniformly incorporated into the sludge, the dewatering efficiency in the solid-liquid separation process is improved, and dewatered sludge with low moisture content and improved aeration can be produced. By supplying this dewatered sludge to the composting equipment, uniform fermented sludge can be produced in a short time, reducing the frequency of turning the fermented sludge and suppressing the generation of malodorous odors. [Brief explanation of the drawing]

[0012] [Figure 1] This is a flow diagram of the sludge composting system according to the present invention. [Modes for carrying out the invention]

[0013] Figure 1 is a flow diagram of the sludge composting system according to the present invention, in which a sludge supply pipe 1 and a coagulant supply pipe 2 are connected to a coagulation mixing tank 3. The coagulation mixing tank 3 is equipped with a coagulation stirring device 4 for mixing and stirring the sludge supplied from the sludge supply pipe 1 and the coagulant (polymer coagulant, inorganic coagulant) supplied from the coagulant supply pipe 2.

[0014] In this embodiment, bacterial cells and biomass are also added to the coagulation mixing tank 3. 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 mainly consisting of photosynthetic bacteria and lactic acid bacteria yeast. The bacterial cells are stored in liquid form and are supplied to the bacterial biomass production tank 9 via a bacterial cell supply pipe 6 connected to the bacterial cell storage tank 5. Since YM bacteria have the effect of promoting sludge fermentation and also have the effect of deodorizing organic waste, they also contribute to the odor suppression effect of the solid-liquid separation device 16 described later.

[0015] On the other hand, the biomass is porous, highly absorbent woody biomass, which is supplied from the biomass storage tank 7 to the microbial biomass production tank 9 via the biomass supply pipe 8. Specifically, woody biomass includes driftwood, thinned wood, and woody waste (bark, sawdust, and wood chips generated during lumbering, as well as demolition materials from buildings, pruned branches, and bark). Biomass has little utility value in its raw state and is usually disposed of as waste, making it excellent from the perspective of resource reuse. In addition, the biomass may also be cellulose-based fibrous materials such as bamboo, or plant-based waste such as tea residue and food scraps. Furthermore, if necessary, pretreatment such as crushing may be applied to make it a shape and properties that are easily absorbed by sludge.

[0016] The microbial cells and biomass supplied to the microbial biomass production tank 9 are mixed and stirred by the microbial biomass stirring device 10 installed in the microbial biomass production tank 9. At this time, the biomass is immersed in the microbial cells, and the microbial cells adhere to the biomass to produce microbial biomass. The biomass has many micropores and a large surface area, resulting in high adhesion efficiency of the microbial cells.

[0017] The microbial biomass generated in the microbial biomass generation tank 9 is supplied to the coagulation and mixing tank 3 via a microbial biomass supply pipe 12 from a microbial biomass supply device 11 (such as a belt-type or screw-type device) connected to the microbial biomass generation tank 9. In this embodiment, microbial biomass is supplied using a microbial biomass supply machine 13 consisting of the microbial biomass generation tank 9, the microbial biomass supply device 11, and the microbial biomass supply pipe 12. However, a pump (not shown) may also be connected to the microbial biomass generation tank 9 to supply microbial biomass. Furthermore, while liquid microbial cells and biomass are supplied to the microbial biomass generation tank 9 to generate microbial biomass, this configuration can be modified as appropriate, such as supplying powdered microbial cells together with liquid and biomass to the biomass generation tank 9.

[0018] In this embodiment, woody biomass immersed in microbial cells is supplied to the coagulation and mixing tank 3. The biomass increases in weight due to the moisture content of the microbial cells, and its hydrophilicity is improved, making it easily absorbed within the coagulation and mixing tank 3. In addition, the force of the transport flow generated when the biomass is supplied from the microbial biomass supply pipe 12 causes it to diffuse uniformly within the coagulation and mixing tank 3.

[0019] Woody biomass is porous and highly water-repellent, and when supplied alone, it floats in the coagulation and mixing tank 3, making it difficult to improve its mixing with sludge. However, in this embodiment, by using woody biomass immersed in microbial cells, it can be uniformly mixed with sludge and coagulant in the tank. This makes it possible to produce coagulated flocs in which biomass is uniformly incorporated. In addition, microbial cells that are not attached to the biomass will adhere to the sludge during transport to the coagulation and mixing tank 3 and downstream equipment.

[0020] The microbial biomass is supplied to the coagulation and mixing tank 3 via the microbial biomass supply pipe 12, and then mixed and stirred together with the sludge and coagulant in the coagulation and stirring device 4. The coagulation and stirring device 4 and the microbial biomass stirring device 10 can be anything that can mix and stir, and in this embodiment, stirring blades are used.

[0021] In addition, in order to prevent the porous biomass from floating in the microbial biomass production tank 9, it is possible to supply the liquid microbial cells while overflowing them and add biomass to the overflow section, connect a biomass supply pipe 8 in the middle of the flow path of the microbial cell supply pipe 6, and add biomass using the conveyance flow of the microbial cells. Appropriate measures may be taken, such as arranging a suction member (not shown) in the microbial biomass production tank 9 and providing a circulation line for extracting the microbial biomass from below the tank and returning it upward. Similarly, in order to prevent floating in the agglomeration mixing tank 3, the microbial biomass supply pipe 12 may be connected to the lower part or the lower side surface of the agglomeration mixing tank 3.

[0022] The sludge mixed and stirred in the agglomeration mixing tank 3 becomes strong flocs (agglomerated sludge) and is supplied to the solid-liquid separation device 16 through the agglomerated sludge supply pipe 15 by the supply pump 14. A pressure gauge 23 for measuring the pressure of the agglomerated sludge supplied to the solid-liquid separation device 16 is provided in the agglomerated sludge supply pipe 15.

[0023] The solid-liquid separation device 16 can dewater the agglomerated sludge, and conventional devices such as a filter press for batch type, a belt press, a screw press, a centrifugal dehydrator, etc. for continuous type can be used.

[0024] After the agglomerated sludge supplied to the solid-liquid separation device 16 separates the filtrate, it is discharged as dehydrated sludge (dehydrated cake). The separated filtrate is discharged to the outside from the filtrate discharge pipe 19 connected to the filtrate storage tank 18.

[0025] The dehydrated sludge discharged from the solid-liquid separation device 16 is transferred to the composting facility 21 through the dehydrated sludge supply pipe 22. The composting facility 21 is a known aerobic fermentation tank having an air supply means 20 composed of a blower for supplying air into the facility. By blowing air as an oxygen source necessary for aerobic fermentation into the composting facility 21, the organic matter in the dehydrated sludge is decomposed by the action of the microbial cells which are aerobic microorganisms, and the organic matter decreases and becomes stabilized fermented sludge. At this time, although the water content decreases due to evaporation of water, the fermented sludge is matured to such an extent that it can be used as compost (fertilizer).

[0026] Furthermore, if necessary, an aeration means may be installed in front of the composting equipment 21. 20 Alternatively, a hopper with a hopper may be installed to improve the aeration of the dewatered sludge before transferring it to the composting facility 21.

[0027] 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 before the coagulation process. By adding microbial cells before the coagulation process, the microbial cells are incorporated into the coagulated flocs and then transferred to the subsequent equipment, thereby improving the mixing of the microbial cells with the sludge. As a result, dewatered sludge with uniformly incorporated microbial cells is produced, and this dewatered sludge can be fermented in the composting equipment 21, improving fermentation efficiency and enabling the stable production of fermented sludge in a short time.

[0028] At the same time, biomass is uniformly incorporated into the dewatered sludge, improving its aeration, which reduces the amount of air required when supplying air to the composting facility 21. Consequently, the overall operating time of the facility can be reduced, leading to energy savings.

[0029] In this embodiment, the liquid bacterial cells were immersed in biomass to prevent leakage of the liquid filtrate during solid-liquid separation. However, this can be modified as appropriate, for example, by spraying the liquid bacterial cells onto the biomass.

[0030] 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]

[0031] The sludge composting system of the present invention produces coagulated sludge by supplying woody biomass immersed in microbial cells to a coagulation and mixing tank, where it is mixed and stirred with sludge and a coagulant. By utilizing locally unused biomass as woody biomass, local resources can be effectively utilized. Furthermore, the generated compost can be used locally to promote local agriculture. In addition, 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]

[0032] 3 Coagulation mixing tank 9. Bacterial biomass production tank 16 Solid-liquid separator 21 Composting equipment

Claims

[Claim 1] In a sludge composting system that produces fermented sludge by fermenting dewatered sludge obtained by solid-liquid separation of coagulated sludge, A microbial biomass generation tank (9) is used to generate microbial biomass by immersing plant-based biomass in microbial cells, and a coagulation mixing tank (3) is used to generate coagulated sludge by mixing and stirring the microbial biomass together with sludge and a coagulant. A solid-liquid separation device (16) that separates coagulated sludge into solid and liquid to produce dewatered sludge, A composting facility (21) that ferments dewatered sludge to produce fermented sludge, Equipped with A sludge composting system characterized by the following features.

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