Sewage sludge fermentation raw material and sewage sludge treatment method

Abstract

To provide a fermentation raw material capable of allowing aerobic fermentation to quickly proceed and promoting an effective use of resources, by a simple operation alone of adding a prescribed amount of a specific material to sewage sludge.SOLUTION: The sewage sludge fermentation raw material according to the present invention for use in aerobic fermentation of sludge, includes sewage sludge and coffee grounds, in which the coffee grounds are included therein in an amount of 52 pts.mass or more and 200 pts.mass or less relative to 100 pts.mass of the sewage sludge. The present invention also provides a sewage sludge processing method that uses a sewage sludge fermentation raw material including 52 pts.mass or more and 200 pts.mass or less of coffee grounds relative to 100 pts.mass of the sewage sludge.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a raw material for aerobic fermentation of sewage sludge and a method for treating sewage sludge. [Background technology]

[0002] Sewage sludge is a muddy substance containing organic matter and water, and is inevitably discharged during the process of sewage treatment associated with daily activities. The amount of sewage sludge discharged is increasing as the amount of sewage treated increases, and its disposal, like that of urban solid waste, has become a problem. To treat sewage sludge, for example, attempts have been made to incinerate the sludge and use the heat generated during the process as an energy source, but it is desirable to reduce the moisture content of sewage sludge in order to perform incineration more efficiently.

[0003] A technique for aerobic fermentation of sewage sludge is known as a technique for inexpensively reducing the moisture content of sewage sludge. For example, Patent Documents 1 and 2 and Non-Patent Document 1 disclose a method of mixing organic sludge with organic materials and fermenting the mixture in order to improve dewatering efficiency, reduce volume, etc. Patent Document 3 also discloses a technique for reducing the moisture content of sewage sludge by adding a breathability improving material and aerobic fermentation. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-079873 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-274908 [Patent Document 3] Japanese Patent Application Laid-Open No. 2005-111374 [Non-patent literature]

[0005] [Non-Patent Document 1] Fukui et al., "Study on Composting of Sludge," Journal of the Japan Society of Irrigation, Drainage and Rural Engineering, 2000, Vol. 2000, No. 205, pp. 131 Summary of the Invention [Problem to be solved by the invention]

[0006] Generally, stable aerobic fermentation requires optimization of various conditions, such as the nutrients contained in the material to be treated that serve as nutrient sources for the microorganisms, as well as the moisture content, pH, and aeration rate of the material to be treated. When aerobic fermentation is performed on sewage sludge that contains a low content of nutrients that serve as nutrient sources for the microorganisms, such as digested sludge that has undergone methane fermentation during sewage treatment, microbial activity can be sluggish due to a lack of nutrients, and aerobic fermentation of the material may not be sufficient.

[0007] As a method for improving the aerobic fermentation state of such a fermentation system in which microbial activity has become sluggish, Patent Documents 1 to 3 disclose the addition of nutrient-rich materials (hereinafter also referred to as nutrient source materials) or aeration improvers to sludge or compost raw materials. However, when sewage sludge is used as the target of aerobic fermentation treatment, depending on the type and amount of nutrient source material added, there may be a shortage of nutrients suitable for the microorganisms contained in the sewage sludge, or an excess of components that inhibit microbial activity, making it difficult to maintain a good aerobic fermentation state. In particular, when sewage sludge is treated in a large-scale continuous device such as a sealed vertical fermenter, the fermentation state differs between the raw material inlet and the outlet, making it difficult to adjust the fermentation conditions.

[0008] Furthermore, depending on the type of nutrient material added, even if it contains nutrients suitable for the microorganisms contained in sewage sludge, it may contain excessive oil or water content, which can worsen the breathability when mixed with sewage sludge, making it difficult to maintain good aerobic fermentation conditions.

[0009] As described above, when promoting aerobic fermentation of sewage sludge by adding nutrient-rich materials, it was necessary to select materials that contain nutrients suitable for the microorganisms contained in the sewage sludge and do not contain components that interfere with microbial activity or reduce breathability, and to design a material composition that would consistently promote aerobic fermentation.

[0010] Therefore, an object of the present invention is to provide a sewage sludge fermentation raw material that can promote fermentation easily and stably without having to adjust the composition each time depending on the fermentation state. Another object of the present invention is to provide a new method for effectively utilizing coffee grounds that are currently disposed of as industrial waste. [Means for solving the problem]

[0011] As a result of extensive research aimed at solving the above problems, the inventors discovered that coffee grounds contain many nutrients that promote the fermentation of sewage sludge, and also have a porous structure that improves the breathability of sewage sludge. Based on these findings, the inventors discovered that adding coffee grounds to sewage sludge in a specific blend ratio stably promotes the fermentation of the sewage sludge, which is the target of fermentation, and thus completed the present invention.

[0012] That is, the present invention provides a method for producing a compost containing sewage sludge and coffee grounds, The present invention provides a sewage sludge fermentation raw material for aerobic fermentation treatment, which contains 52 to 200 parts by mass of the coffee grounds per 100 parts by mass of the sewage sludge.

[0013] The present invention also provides a method for treating sewage sludge by aerobic fermentation of a sewage sludge fermentation raw material containing sewage sludge and coffee grounds, The present invention provides a method for treating sewage sludge, using the sewage sludge fermentation raw material containing 52 to 200 parts by mass of coffee grounds per 100 parts by mass of sewage sludge. [Effects of the Invention]

[0014] According to the present invention, aerobic fermentation can be rapidly promoted and sewage sludge can be stably fermented simply by adding a predetermined amount of a specific material to the sewage sludge. This allows for the fermentation of large quantities of sewage sludge with different properties in industrial areas such as cement factories and sewage treatment plants, where sewage sludge is generated, leading to the effective use of resources. Furthermore, coffee grounds, a type of local biomass that has previously been disposed of as industrial waste, can be effectively utilized. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a cross-sectional view schematically showing one embodiment of a sealed vertical fermenter. [Figure 2] FIG. 2(a) is a schematic perspective view showing the appearance and dimensions of the fermentation vessel used in the aerobic fermentation evaluation in the examples and comparative examples, and FIG. 2(b) is a cross-sectional view showing the arrangement positions of each component during temperature measurement. [Figure 3] 1 is an example of a scanning electron microscope image of coffee grounds used in the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] Preferred embodiments of the present invention will be described below, but the present invention is not limited to the following embodiments.

[0017] The sewage sludge fermentation raw material of the present invention contains sewage sludge and coffee grounds as its ingredients. This sewage sludge fermentation raw material is suitable for use in aerobic fermentation treatment of sewage sludge.

[0018] The sewage sludge used in the present invention is a waste product generated during sewage treatment and is a muddy substance containing organic matter, inorganic matter, and water. Sewage sludge is typically obtained by dewatering excess sludge discharged from activated sludge-based wastewater treatment facilities. Examples of such sewage sludge include general sewage sludge generated in sewage treatment plants, sewage sludge generated in sewage treatment facilities, and septic tank sludge, which can be used alone or in combination. Sewage sludge may be used as is as undigested sludge, or a self-fermented product of sewage sludge, such as digested sludge, may be used. Digested sludge generally contains fewer nutrients necessary for fermentation than undigested sludge, and therefore, the effects of the present invention are more pronounced when digested sludge is used as the target of the treatment of the present invention. The moisture content of sewage sludge is not particularly limited, but is, for example, about 50% by mass to 90% by mass, and preferably 50% by mass to 85% by mass. The type of sewage sludge can be selected based on at least one of its moisture content, whether it has been digested, and the dehydration treatment method.

[0019] The sewage sludge fermentation raw material of the present invention includes coffee grounds. Coffee grounds are the residue generated when coffee beverages are extracted from the powder obtained by grinding roasted coffee beans. Coffee grounds are porous materials containing organic matter and small amounts of nitrogen, phosphorus, and potassium. Coffee grounds are typically used as livestock feed, fertilizer, and supplementary raw materials for agricultural compost, with some being disposed of as industrial waste. The present inventors have newly discovered that adding such coffee grounds to sewage sludge in a specific blend ratio can promote aerobic fermentation of the sewage sludge. Furthermore, the present inventors have discovered that, although coffee grounds can be classified as industrial waste, reusing these coffee grounds together with sewage sludge reduces the amount of waste, contributing to the effective use of resources and environmental protection.

[0020] There are no particular limitations on the variety of coffee beans used as the raw material for the coffee grounds used in the present invention, and examples include Arabica, Robusta, and Liberica. There are also no particular limitations on the brand of coffee beans, and examples include Brazil, Colombia, Tanzania, Mocha, Kilimanjaro, Mandheling, and Blue Mountain. The coffee beans used as the raw material for the coffee grounds may be one type, or a blend of multiple types.

[0021] There are no particular limitations on the method for extracting coffee from coffee beans, nor on the roasting temperature or environment. For example, roasting methods include direct flame, hot air, and semi-hot air. There are also no particular limitations on the degree of roasting of coffee beans, and examples include light, cinnamon, medium, high, city, full city, French, and Italian. The coffee brewing method does not have any particular effect on the properties of the coffee grounds.

[0022] The coffee grounds used in the present invention may be those in a moist state immediately after coffee extraction, or may be dried. Moist coffee grounds can be dried by a common method, such as forced drying using a hot air convection dryer or natural drying in the sun.

[0023] The coffee grounds used in the present invention preferably have an average particle size of 0.1 mm to 5 mm, more preferably 0.3 mm to 3 mm, and even more preferably 0.5 mm to 1 mm. Coffee grounds pulverized to an average particle size within the above range may be used. By using coffee grounds with such a small average particle size, the reactive surface area of ​​the coffee grounds increases, allowing the nutrients contained in the coffee grounds to be efficiently supplied to the sewage sludge. As a result, aerobic fermentation of the sewage sludge can be further promoted. The average particle size of the coffee grounds can be the D50 of the particle size distribution measured using various sieving test methods specified in JIS Z 8815-1995, "General Rules for Sieving Test Methods."

[0024] The individual particles constituting the coffee grounds used in the present invention are preferably porous. For example, as shown in Figure 3, each particle constituting the coffee grounds has pores of approximately several tens of micrometers throughout the particle. This increases the reactive surface area compared to other organic matter of the same particle size, allowing the contained nutrients to be efficiently supplied to the sewage sludge. Furthermore, air can easily reach the interior of the sewage sludge through the pores, improving the breathability of the fermentation raw material. As a result, aerobic fermentation can be further promoted.

[0025] The coffee grounds used in the present invention preferably have a loss on ignition of 95.0% by mass or more, more preferably 96.5% by mass or more, and even more preferably 98.0% by mass or more. The loss on ignition of coffee grounds reflects the amount of organic components contained in the coffee grounds. A loss on ignition within this range means that the coffee grounds contain a predetermined amount of organic components that serve as a nutrient source. Therefore, using coffee grounds as a sewage sludge fermentation raw material can further promote the aerobic fermentation of sewage sludge. The loss on ignition of coffee grounds is measured according to JIS R5202:2015, "Methods for Chemical Analysis of Cement."

[0026] The coffee grounds used in the present invention preferably have a solid calorific value of 4500 kcal / kg or more, and more preferably 5000 kcal / kg or more. Generally, a high solid calorific value indicates that the coffee grounds contain a large amount of organic components that are useful for the progression of aerobic fermentation. When coffee grounds have such a calorific value, aerobic fermentation can be further promoted, allowing for efficient fermentation of sewage sludge.

[0027] The content of coffee grounds in the sewage sludge fermentation raw material of the present invention is preferably 52 to 200 parts by mass, more preferably 70 to 160 parts by mass, and even more preferably 90 to 120 parts by mass, per 100 parts by mass of sewage sludge. Here, the reference mass of sewage sludge is the mass in a hydrated state. By having the coffee grounds content within this range, aerobic fermentation of the sewage sludge can be easily promoted and the progress of fermentation can be stabilized at a high level. Note that a coffee grounds content of more than 200 parts by mass is undesirable because the ratio of coffee grounds to sewage sludge becomes too high, reducing the efficiency of treating the large amount of sewage sludge generated. The above content is measured in dry coffee grounds. "Dry" means that the moisture content of the coffee grounds is 10% by mass or less. The moisture content of the coffee grounds can be adjusted as appropriate, for example, by drying the coffee grounds using the method described above. Specific methods for measuring the moisture content are explained in the examples below.

[0028] The inventors speculate that the reason why aerobic fermentation proceeds efficiently when a specific amount of coffee grounds is added to the sewage sludge fermentation raw material of the present invention is as follows: Coffee beans contain nutrients suitable for the microorganisms contained in sewage sludge, such as carbohydrates, lipids, and proteins. Furthermore, coffee beans are processed during the refining process, such as by removing the seed coat and grinding, so that the nutrient-rich portions are exposed on the surface and have a large surface area. The surface area of ​​the coffee grounds obtained from such coffee beans is even larger, so when the coffee grounds are mixed with sewage sludge, the microorganisms contained in the sewage sludge can efficiently take up the nutrients contained in the coffee grounds.

[0029] When coffee beans are roasted, some of the moisture and organic components contained in the beans evaporate, creating gas-filled voids within the coffee beans. The creation of these voids makes the coffee beans porous, and the particles that make up the powder obtained by grinding the coffee beans also become porous, resulting in coffee grounds with excellent breathability. Therefore, when porous coffee grounds are mixed into a sewage sludge fermentation raw material, air can easily reach the interior of the sample through the pores in the porous material that adhere between the sludge flocs, allowing aerobic fermentation to proceed efficiently.

[0030] The sewage sludge fermentation raw material of the present invention may be composed only of sewage sludge and coffee grounds. In addition, it is also preferable that the sewage sludge fermentation raw material further contains materials other than sewage sludge and coffee grounds (hereinafter, these may also be simply referred to as "materials").

[0031] Examples of materials include those that promote stable aerobic fermentation when sewage sludge fermentation raw material is subjected to fermentation, such as those that reduce the moisture content of sewage sludge, improve the breathability of the sewage sludge fermentation raw material during fermentation, and supply a wide variety of microorganisms that contribute to aerobic fermentation.

[0032] It is preferable that the sewage sludge fermentation raw material further contains an aeration aid as a material for improving the aeration of the sewage sludge fermentation raw material and promoting aerobic fermentation of the sewage sludge. By including the aeration aid, the aeration of the sewage sludge fermentation raw material can be easily improved regardless of the state of consolidation of the sewage sludge fermentation raw material, and aerobic fermentation of the sewage sludge can be carried out stably. In particular, when aerobic fermentation is carried out using a vertical fermenter described below, for example, the sewage sludge in the fermenter can be consolidated due to the accumulation of the sewage sludge fermentation raw material, making it difficult for the aerobic fermentation of the sewage sludge to proceed. However, by including the aeration aid, it is possible to further suppress excessive consolidation while further ensuring aeration, which is advantageous in that it allows the aerobic fermentation of the sewage sludge to proceed stably and effectively.

[0033] Examples of aeration aids include organic aeration aids such as rice straw, rice husks, plants, or dried or crushed materials thereof, and inorganic aeration aids such as perlite, zeolite, diatomaceous earth, or coal ash such as fly ash. These aeration aids can be used alone or in combination. Among these, coal ash is a relatively fine particle and contains oxide components such as CaO and MgO. Therefore, using coal ash as an aeration aid is preferable because it has high dispersibility in the sewage sludge fermentation feedstock and can uniformly form flocs (agglomerates of particles), further improving breathability during aerobic fermentation.

[0034] When the sewage sludge fermentation raw material further contains an aeration aid, the content of the aeration aid in the sewage sludge fermentation raw material is preferably 5 to 50 parts by mass, more preferably 5 to 30 parts by mass, and even more preferably 5 to 15 parts by mass, per 100 parts by mass of sewage sludge. In this case, the masses of the sewage sludge and the aeration aid used as the reference are both masses in a wet state. When multiple types of aeration aids are contained, the content of the aeration aids is based on the total amount. By keeping the content of the aeration aid within this range, it is possible to ensure uniform aeration while preventing the sewage sludge fermentation raw material from becoming excessively compacted over a long period from the start to the end of fermentation, and to allow the aerobic fermentation of the sewage sludge to proceed stably and effectively.

[0035] The sewage sludge fermentation feedstock preferably further contains seed sludge as a material for supplying the sewage sludge fermentation feedstock with microorganisms that contribute to aerobic fermentation. As such seed sludge, for example, commercially available agricultural compost or a sludge fermentate (a fermented product produced by aerobic fermentation of the sewage sludge fermentation feedstock of the present invention) may be used.

[0036] When the sewage sludge fermentation feedstock further contains seed sludge, the content of the seed sludge in the sewage sludge fermentation feedstock is preferably 5 to 100 parts by mass, more preferably 20 to 80 parts by mass, and even more preferably 40 to 60 parts by mass, per 100 parts by mass of sewage sludge. Here, the reference masses of the sewage sludge and seed sludge are both measured in a wet state. By setting the seed sludge content within this range, the amount of microorganisms in the sewage sludge fermentation feedstock can be maintained at a high level over a long period from the start to the end of fermentation, allowing the aerobic fermentation of the sewage sludge to proceed stably and effectively.

[0037] The shapes of the various materials, such as the aeration aid and seed sludge, described above are not particularly limited, and may be, for example, solid, granular, powdery, paste-like, fluid, liquid, etc. The total content of the materials can be adjusted appropriately depending on the physical properties and purpose of the materials used, but the total parts by mass of the materials per 100 parts by mass of sewage sludge can be preferably 5 parts by mass or more and 150 parts by mass or less, more preferably 10 parts by mass or more and 100 parts by mass or less, and even more preferably 20 parts by mass or more and 75 parts by mass or less. In this case, the mass of the sewage sludge used as a reference is the mass in a wet state.

[0038] From the viewpoint of ensuring a sufficient amount of moisture for stable aerobic fermentation from the initial stage of fermentation, the moisture content of the entire sewage sludge fermentation raw material is preferably 30% to 70% by mass, and more preferably 40% to 60% by mass. The moisture content can be measured, for example, using a commercially available halogen moisture meter based on the difference in mass before and after drying at a heating temperature of 120°C. Alternatively, it can be measured in accordance with JIS A1203 "Testing Method for Moisture Content of Soil." The moisture content of the sewage sludge fermentation raw material can be appropriately adjusted by selecting raw materials to achieve the desired moisture content, for example, by using sewage sludge with a high moisture content and dried coffee grounds, or by adding water to the raw materials or the sewage sludge fermentation raw material.

[0039] A sewage sludge fermentation feedstock containing such materials can be produced as a mixture or sediment by, for example, mixing or heaping sewage sludge and coffee grounds with various other materials as needed. Specifically, examples include a method of obtaining the sewage sludge fermentation feedstock by mixing sewage sludge and coffee grounds with various other materials as needed, or a method of obtaining the sewage sludge fermentation feedstock as a sediment by heaping the materials in any order indoors or outdoors. Alternatively, examples include a method of supplying one of the materials to a vessel such as a fermenter, and then supplying the other materials in any order to the vessel, so that the materials are heaped alternately or randomly in the vessel, and then mixing the heap in a vessel such as a fermenter as is or in addition to the heap to obtain a mixture.

[0040] The sewage sludge fermentation raw material described above, whether in the form of a sediment or a mixture, is suitable for use in the aerobic fermentation treatment of sewage sludge. The sewage sludge fermentation raw material can be placed outdoors or indoors as is, or can be placed in a container as a sediment or a mixture and subjected to the aerobic fermentation treatment of sewage sludge.

[0041] Specifically, the sewage sludge fermentation raw material can be aerobically fermented by piling it in a compost shed or by placing it in an open or closed fermenter. When the sewage sludge fermentation raw material is supplied to a fermenter for aerobic fermentation, aerobic fermentation can be carried out stably from the early stage of fermentation over a long period of time, regardless of the presence or absence of stirring equipment in the fermenter or the stirring method, and the sewage sludge can be efficiently treated. From the viewpoint of reducing adverse effects on the surrounding environment, such as odors, when the sewage sludge in the sewage sludge fermentation raw material is aerobically fermented preferably in a closed fermenter. A closed system refers to a reaction system in which the intrusion of air from the external environment and the outflow of fermentation gas generated from the fermenter to the outside during aerobic fermentation are controlled, while an open system refers to a reaction system in which the intrusion and outflow of gases such as air and gases are not controlled in any way.

[0042] In particular, the sewage sludge fermentation raw material of the present invention is suitable for fermenting sewage sludge in a sealed, vertical fermenter (hereinafter also referred to as a "sealed vertical fermenter") by aerobic fermentation in a sealed state, because the aerobic fermentation of the sewage sludge can proceed stably over a long period of time without having to change environmental conditions such as the ingredient composition and aeration rate each time depending on the fermentation state. That is, the method for fermenting sewage sludge preferably includes a step of supplying sewage sludge, coffee grounds, and, as necessary, other materials into the sealed vertical fermenter in any order, or supplying a mixture containing these raw materials into the sealed vertical fermenter and aerobic fermentation, and more preferably, this step is carried out in a sealed system. The sealed vertical fermenter may be equipped with a stirring device for stirring the contents of the fermenter, so that the raw materials supplied to the fermenter can be stirred continuously or intermittently.

[0043] When aerobic fermentation is performed in a sealed vertical fermenter, the accumulation of sewage sludge fermentation material in the fermenter causes compaction of the sewage sludge fermentation material in the fermenter, making it difficult for the sewage sludge to proceed with aerobic fermentation. This compaction is particularly pronounced in the lower region of the fermenter (near the discharge outlet). In this regard, the sewage sludge fermentation material preferably further contains an aeration aid such as coal ash, which can ensure breathability while preventing the sewage sludge fermentation material in the fermenter from becoming excessively compacted. This is advantageous in that it allows the aerobic fermentation of the sewage sludge to proceed stably and effectively, whether the sewage sludge is in a non-consolidated or consolidated state.

[0044] Fig. 1 shows one embodiment of a sealed vertical fermenter suitable for use in the fermentation treatment of sewage sludge fermentation material of the present invention. The sealed vertical fermenter 10 extends vertically relative to the installation surface and has a cylindrical tank section 20 capable of containing sewage sludge, coffee grounds, and, if necessary, a mixture of other materials. The tank section 20 is equipped with an inlet 30 at its top, through which the mixture can be introduced into the tank section 20, and an outlet 40 at its bottom, through which the aerobically fermented sewage sludge fermentation material can be discharged from the tank section 20. Both the inlet 30 and the outlet 40 are equipped with detachable or openable lid-like members (not shown), and the tank section 20 of the fermenter 10 can be sealed by attaching the lid-like members to the inlet 30 and the outlet 40. In other words, the sealed vertical fermenter 10 is capable of treating sewage sludge by aerobic fermentation in a sealed system.

[0045] From the viewpoint of further improving the efficiency of aerobic fermentation, it is preferable that the sealed vertical fermenter 10 has a thermally insulated structure, for example, by providing a thermal insulator on the outer peripheral surface of the tank section 20. It is also preferable that the sealed vertical fermenter 10 is equipped with a stirring device 50 for mixing the raw materials in the fermenter to make the state of the components and the breathability uniform. 1 includes, for example, an agitator blade 51 provided in the tank section 20, an agitator shaft 52 connected to the agitator blade 51, and a motor (not shown) provided outside the tank section 20. The agitator blade 51 is connected to the motor provided outside the tank section 20 via the agitator shaft 52 and rotates in a fixed direction using the motor as a drive source. By further providing the agitator 50, the aeration within the reaction system can be increased, further improving the aerobic fermentation efficiency of the sewage sludge fermentation raw material.

[0046] The sealed vertical fermenter 10 also preferably includes an air circulation system 60 for supplying oxygen-containing gases such as air and oxygen into the fermenter, and an exhaust port 70 for exhausting gases from the tank section 20 to the outside of the tank section 20. This allows for appropriate control of the circulation of air and gases inside and outside the reaction system, thereby promoting aerobic fermentation more efficiently, particularly in a sealed system.

[0047] 1, oxygen-containing gas F can be supplied from air circulation equipment 60 provided outside the tank section 20 to the vertically lower side of the agitator blade 51, preferably via the hollow agitator shaft 52 and the interior of the agitator blade 51. The vertically lower side of the agitator blade 51 is also preferably provided with a plurality of gas circulation holes (not shown) through which the oxygen-containing gas F can flow. The oxygen-containing gas present in the tank section 20 and the gas generated by aerobic fermentation are exhausted from the top of the tank section 20 via exhaust port 70 as exhaust air.

[0048] From the viewpoint of facilitating the supply of oxygen-containing gas to the entire fermenter and increasing the efficiency of aerobic fermentation of sewage sludge, it is preferable that oxygen-containing gas F is supplied from the vertically lower side of tank section 20, and that oxygen-containing gas F and gas are exhausted from the vertically upper side of tank section 20. The sewage sludge fermentation raw material is continuously or intermittently introduced into tank section 20 of the fermenter through inlet 30, and the sewage sludge fermentation raw material is aerobically fermented in the fermenter for about two weeks, after which the fermented sewage sludge fermentation raw material is discharged from the outlet as fermented sludge.

[0049] The sludge fermentation product produced by subjecting sewage sludge fermentation raw material to aerobic fermentation can be used for purposes such as fertilizer, soil improvement material, green farmland materials such as horticultural soil, cement clinker raw material, solid fuel, etc., enabling effective utilization of resources. In particular, it is preferable to mix the sludge fermentation product with raw materials such as limestone and use it as a cement clinker raw material, as this increases the effective use amount of the produced sludge fermentation product and further contributes to effective utilization of resources. Furthermore, this sludge fermentation product can be reused as a material to supply the microorganism of the present invention when preparing sewage sludge fermentation raw material, which also contributes to effective utilization of resources.

[0050] Furthermore, the present invention utilizes coffee grounds, which would otherwise become industrial waste, as one of the fermentation raw materials, which is advantageous in that it promotes the effective use of coffee grounds and reduces the environmental burden.

[0051] As is clear from the above explanation, the present specification discloses not only a sewage sludge fermentation raw material but also a method for treating sewage sludge using the sewage sludge fermentation raw material. The method for treating sewage sludge comprises a step of aerobically fermenting a sewage sludge fermentation feedstock containing sewage sludge and coffee grounds to treat the sewage sludge. The above-mentioned explanations apply as appropriate to the types and amounts of sewage sludge and coffee grounds contained in the sewage sludge fermentation feedstock used in this treatment method, as well as the types and amounts of aeration aids and seed sludge contained as needed. [Example]

[0052] The present invention will be described in more detail below with reference to examples. The scope of the present invention is not limited to these examples. The moisture content of the raw materials shown below was measured using a halogen moisture meter (HM1105 manufactured by AS ONE Corporation) and calculated from the mass difference when dried at a heating temperature of 120°C. The calorific values ​​shown below indicate the calorific values ​​of the solid content. In the tables, the column marked with "-" indicates that the material is not contained.

[0053] [Examples 1 to 4 and Comparative Examples 1 to 5] [Preparation of sewage sludge fermentation raw material] The sewage sludge and coffee grounds shown in (1) and (2) below were mixed in the proportions shown in Table 1 below to prepare sewage sludge fermentation raw materials with moisture contents of 37.9% to 84.4% by mass.

[0054] (1) Sewage sludge: Digested sludge obtained from a sewage treatment plant (moisture content: 84.4% by mass) (2) Coffee grounds: sun-dried powder of coffee extraction residue (moisture content 6.9% by mass, loss on ignition 98.5% by mass, solid calorific value 5325 kcal / kg, average particle size 0.64 mm)

[0055] [Aerobic fermentation test] The sewage sludge fermentation raw materials of the Examples and Comparative Examples were subjected to aerobic fermentation treatment, and the progress of the aerobic fermentation of the sewage sludge was evaluated as a change in the sample temperature. A 500 mL plastic beaker and a simple insulated container covering the sides and bottom of the beaker were used as fermentation vessels. The positions and dimensions of these were as shown in Figure 2(a). Approximately 400 mL of the sewage sludge fermentation raw material of each Example and Comparative Example was placed in each plastic beaker to prepare the samples.

[0056] Next, the plastic beakers containing each sample were placed in an insulated container as shown in Figure 2(b), and a T-type thermocouple (manufactured by Chino Corporation) was inserted into the center of the sample inside the plastic beaker. A data logger was connected to the thermocouple, and the sample was subjected to aerobic fermentation while continuously measuring its temperature. These experiments were carried out for 8 days in a room set at 20°C. The degree of progress of aerobic fermentation was evaluated based on the peak temperature, which was the highest temperature measured, and the time required to reach the peak temperature. The higher the peak temperature and the shorter the time required to reach the peak temperature from the starting temperature (20°C), the faster and more efficiently the aerobic fermentation of the sewage sludge is progressing. From the perspective of quickly aerobic fermenting large amounts of sewage sludge, a peak temperature of 30°C or higher and a time required to reach the peak temperature within 96 hours (within 4 days) was considered to be acceptable. The results are shown in Table 1 below. In the table, the column marked with "*" indicates that no exothermic peak was observed during the measurement period.

[0057] [Table 1]

[0058] As shown in Table 1, the sewage sludge fermentation raw materials of Examples 1 to 4, which contain sewage sludge and coffee grounds and have a coffee grounds content within a predetermined range, have higher peak temperatures and shorter times to reach the peak temperature compared to the comparative examples. This is thought to be because mixing a predetermined amount of coffee grounds with the sewage sludge provides a sufficient supply of nutrients necessary for fermentation and improves the breathability of the fermentation raw material. As described above, the sewage sludge fermentation raw material of the Examples allows for stable, efficient aerobic fermentation of sewage sludge in a short period of time, simply by adding a predetermined amount of specific materials to the sewage sludge. [Explanation of symbols]

[0059] 10. Closed vertical fermentation tank 20 Tank section 30 Inlet 40 Outlet 51 Mixing blade 52 Agitator shaft 60 Air circulation equipment 70 exhaust port

Claims

1. sewage sludge and coffee grounds, The sewage sludge fermentation raw material for aerobic fermentation treatment contains the coffee grounds in an amount of 90 parts by mass or more and 200 parts by mass or less per 100 parts by mass of the sewage sludge.

2. The sewage sludge fermentation feedstock of claim 1, further comprising an aeration aid.

3. The method comprises a step of aerobically fermenting a sewage sludge fermentation raw material containing sewage sludge and coffee grounds to treat the sewage sludge, A method for treating sewage sludge, comprising using the sewage sludge fermentation raw material containing 90 parts by mass or more and 200 parts by mass or less of the coffee grounds per 100 parts by mass of the sewage sludge.

4. The treatment method according to claim 3, wherein the sewage sludge fermentation raw material further contains an aeration aid.

5. 5. The method according to claim 3, wherein the sewage sludge fermentation raw material is aerobically fermented in a sealed, vertical fermenter.

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