JP7804451B2 - Sewage sludge fermentation raw material and sewage sludge treatment method - Google Patents

Description

The present invention relates to a raw material for aerobic fermentation of sewage sludge and a method for treating sewage sludge.

Sewage sludge is a muddy substance containing organic matter and water, which is inevitably discharged during the sewage treatment process associated with daily activities. The amount of sewage sludge discharged is increasing as the amount of sewage treated increases, and like municipal solid waste, its disposal is becoming a problem. Attempts have been made to treat sewage sludge, for example, by incinerating the sludge and using the heat generated during the process as an energy source, but there is a need to reduce the moisture content of sewage sludge in order to make incineration more efficient.

A technique for aerobically fermenting sewage sludge is known as a cheap way to reduce the moisture content of sewage sludge. For example, Patent Document 1 discloses a technique in which peat, a type of organic soil, is added to animal manure or sewage sludge, and aerobically fermented to reduce the moisture content.

Patent Document 2 discloses a method for treating organic waste in which sediments of organic waste are stirred and fermented in a state with a predetermined void ratio. Patent Document 3 discloses a fermentation treatment device for organic materials that is provided with an air intake and suction port to ensure air circulation during aerobic fermentation, allowing the material to be fermented while being stirred.

Japanese Patent Application Publication No. 61-215284 JP 2010-284608 A JP 2012-20224 A

Generally, to achieve stable aerobic fermentation, it is necessary to optimize various conditions, such as the amount of microorganisms contained in the material to be treated, the breathability of the material, and the amount of nutrients and water that serve as nutrient sources for the microorganisms. Peat, a type of organic soil described in Patent Document 1, is used as a material to increase the amount of microorganisms and promote fermentation because the organic matter it contains makes it easy for fungi to colonize, and it contains soil bacteria, which can supply the fungi necessary for aerobic fermentation. On the other hand, peat is characterized by its high moisture content, large amounts of organic matter, and high viscosity. For this reason, when a high-moisture material such as sewage sludge is subjected to aerobic fermentation, mixing organic soil with the sewage sludge to increase the amount of microorganisms and achieve stable aerobic fermentation can result in an excessive increase in the moisture content and viscosity of the mixture, which can lead to a decrease in breathability and raise concerns that the stabilizing effect of aerobic fermentation cannot be fully achieved.

In this regard, Patent Document 1 does not consider at all the effect of deteriorating breathability caused by adding organic soil to sewage sludge, or the progress of stable aerobic fermentation.
The techniques described in Patent Documents 2 and 3 are thought to contribute to improving breathability, but both of these techniques are merely improvements on the equipment, and when the composition and properties of the sewage sludge or the material to be treated that contains the sludge change, stable aerobic fermentation may not be sufficiently achieved.

The objective of the present invention is therefore to provide a sewage sludge fermentation raw material that can suppress deterioration of the aeration properties of the material being treated when organic soil is added during aerobic fermentation of sewage sludge, thereby enabling stable aerobic fermentation.

As a result of extensive research into resolving the above-mentioned problems, the inventors discovered that when adding organic soil to the aerobic fermentation of sewage sludge, using organic soil with specific properties stably promotes the fermentation of the sewage sludge, which is the fermentation target, and thus developed the present invention.

That is, the present invention provides a method for producing a compost containing sewage sludge and organic soil,
The organic soil has a density of 1.40 g/ ^cm3 or less.
The present invention provides a sewage sludge fermentation raw material for aerobic fermentation treatment.

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 organic soil,
The sewage sludge fermentation raw material is used, wherein the density of the organic soil is 1.40 g/cm3 or ^less .
A method for treating sewage sludge is provided.

According to the present invention, aerobic fermentation can be rapidly promoted and sewage sludge can be stably fermented simply by adding specific materials to the sewage sludge. This allows for the fermentation of large quantities of multiple types of sewage sludge in industrial areas such as cement factories and sewage sludge sources such as sewage treatment plants, leading to the effective use of resources.

FIG. 1 is a cross-sectional view schematically showing one embodiment of a sealed vertical fermenter. 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.

A preferred embodiment of the present invention is described below. Note that the present invention is not limited to the following embodiment.

The sewage sludge fermentation raw material of the present invention contains sewage sludge and organic soil as its ingredients. This sewage sludge fermentation raw material is suitable for use in aerobic fermentation treatment of sewage sludge.

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, and sewage sludge and septic tank sludge generated in sewage treatment facilities. These can be used alone or in combination. The 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.
The water content of the 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 water content, whether it has been digested, and the dehydration treatment method.

The sewage sludge fermentation raw material of the present invention contains organic soil. Organic soil is dark brown to black soil formed by the decomposition of plants, soil microorganisms, and other organic matter mixed with soil. The organic matter and soil components contained in the organic soil favor the growth of microorganisms. Therefore, adding organic soil to sewage sludge promotes the growth of aerobic fermentation bacteria that decompose the organic components in the sewage sludge, enabling stable aerobic fermentation of the sewage sludge. However, the properties of organic soil vary depending on the type and origin of the soil. High-density organic soil or organic soil with a high water content may make it difficult to sufficiently increase the aeration of the mixture when mixed with sewage sludge, which may offset the growth effect of the aerobic fermentation bacteria and prevent stable aerobic fermentation.
As used herein, organic soil refers to soil classified as "organic soil" in the broad soil classification in the book "Ground Material Testing Methods and Commentary" (Geotechnical Society, November 2009, pp. 53-79). Specifically, the organic soil used in the present invention includes organic soil classified under the medium classification symbol O (O), such as organic clay and organic volcanic ash soil, and highly organic soil classified under the medium classification symbol Pt, such as peat and black mud. These soils contain organic matter. Organic soil has an organic matter content of less than 20% by mass, while highly organic soil has an organic matter content of 20% by mass or more. The organic matter content can be determined by the loss on ignition, as described below.
In the following explanation, unless otherwise specified, "organic soil" will be used as a general term for these soils.

The density of the organic soil used in the present invention is preferably 1.40 g/ ^cm3 or less, more preferably 1.35 g/ ^cm3 or less, and even more preferably 1.30 g/ ^cm3 or less. The density of organic soil reflects the amount of voids within the particles of the organic soil and the amount of voids between the particles. A density within this range means that the organic soil has a sufficient amount of voids to contribute to improving breathability. When such organic soil is mixed with sewage sludge, the organic soil dispersed in the mixture forms voids, improving the breathability of the mixture. This allows for stable aerobic fermentation.
The lower limit of the density of the organic soil is determined from the viewpoint of improving breathability and promoting the growth of aerobic fermentation bacteria. From this viewpoint, the lower limit is preferably 0.80 g/cm or ^more , more preferably 1.00 g/cm or ^more , and even more preferably 1.20 g/cm or ^more .
The density of the organic soil is measured according to JIS A 1225:2009 "Test method for wet density of soil."

The inventors speculate that the reason why aerobic fermentation can proceed stably by adding organic soil satisfying a specific density to sewage sludge, as in the sewage sludge fermentation raw material of the present invention, is as follows.
Organic soil forms an aggregated structure in which multiple soil particles are bound together by polymers produced by microorganisms and other factors when the organic matter contained in the soil is decomposed. As a result, numerous voids are formed between soil particles and aggregates in organic soil. Organic soil also contains fibrous particles derived from plant remains. These fibrous particles exist in an entangled state in organic soil, creating voids within the soil. Due to these properties, when organic soil is mixed with sewage sludge, the air permeability of the mixture is improved due to the void structure. The amount of voids in organic soil is thought to be closely related to the density of the organic soil, and we believe that achieving the above-mentioned density of organic soil provides sufficient air permeability improvement. Based on the above, organic soil that meets a specific density not only promotes the growth of aerobic fermentation bacteria but also improves air permeability, thereby sufficiently stabilizing the progress of fermentation.

The organic soil used in the present invention preferably has a moisture content of 45% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less. By using organic soil with such a moisture content, when the organic soil is mixed with sewage sludge, the viscosity and adhesiveness of the mixture are reduced and breathability is improved. As a result, aerobic fermentation can be carried out stably. The moisture content of the organic soil is preferably low, and the organic soil may be dried by methods such as natural drying or hot air drying to reduce the moisture content before use.
The lower limit of the moisture content of the organic soil is determined from the viewpoints of the viscosity and adhesiveness of the organic soil, and the cost and effort required for drying. From this viewpoint, the lower limit of the moisture content of the organic soil is preferably 0.5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more.
The moisture content of organic soil is measured according to JIS A 1203:2009 "Test method for moisture content of soil."

The present inventors speculate that the reason why aerobic fermentation proceeds stably when organic soil has a specific moisture content is as follows.
Organic soil generally contains a large amount of organic matter and fine particles, and the higher the moisture content, the greater the viscosity and adhesiveness of the organic soil. Therefore, the organic soil is difficult to disperse in sewage sludge, and the permeability improvement effect resulting from the pore structure described above is less likely to occur throughout the sewage sludge. As a result, it is believed that adding organic soil to sewage sludge does not fully improve permeability. From the above, organic soil that meets a certain density and moisture content not only has the ability to promote the growth of aerobic fermentation bacteria, but also has the permeability improvement effect, thereby sufficiently stabilizing the progress of fermentation.

The organic soil used in this invention can be used as is in a moist state immediately after collection, or it can be dried. Moist organic soil can be dried using common methods, such as forced drying in a hot air convection dryer or natural drying in the sun. The moisture content mentioned above is the value when the organic soil is mixed with sewage sludge.

The organic matter content of the organic soil used in the present invention is not particularly limited as long as the density of the organic soil is the value described above. However, from the perspective of suppressing an increase in viscosity of the mixture obtained by mixing sewage sludge and organic soil, the loss on ignition of the organic soil is preferably 50% by mass or less, and more preferably 30% by mass or less. The loss on ignition of organic soil reflects the amount of organic components contained in the organic soil. The loss on ignition of organic soil is measured according to JIS A 1226:2020, "Test method for loss on ignition of soil."

The organic soil content in the sewage sludge fermentation raw material of the present invention is preferably 2 to 15 parts by mass, more preferably 5 to 10 parts by mass, per 100 parts by mass of sewage sludge. In this case, the reference mass of sewage sludge is the mass in a wet state. By keeping the content within this range, the breathability of the mixture can be improved when mixed with sewage sludge, stabilizing the progress of fermentation.

The organic soil used in this invention is preferably Kuroboku. Kuroboku is a type of organic soil in which organic matter is mixed with soil derived from volcanic ash. Kuroboku has voids due to its aggregate structure, and the soil particles themselves are porous, giving it low density and excellent water retention, even among organic soils. Kuroboku is also found on plateaus and hilly areas, and has a relatively low moisture content compared to other organic soils. Kuroboku is easily available in density and moisture content ranges. By using Kuroboku, an organic soil with these properties, when sewage sludge is mixed with Kuroboku, the Kuroboku absorbs the moisture from the sewage sludge, efficiently reducing the viscosity and adhesiveness of the mixture and efficiently forming voids within the mixture, enabling stable aerobic fermentation. Furthermore, Kuroboku is a soil found nationwide and is relatively easily available at sewage sludge generating sources, such as sewage treatment plants, allowing for efficient fermentation of sewage sludge.

The sewage sludge fermentation raw material of the present invention may consist solely of sewage sludge and organic soil. Alternatively, it may also preferably contain, in addition to these, other materials in addition to sewage sludge and organic soil (hereinafter, these may also be simply referred to as "materials").

Examples of materials include those that promote stable aerobic fermentation when sewage sludge fermentation raw material is subjected to fermentation. Specific examples include materials that are intended to provide easily decomposable organic matter that serves as a nutrient source for microorganisms that contribute to aerobic fermentation, reduce the moisture content of sewage sludge, improve the breathability of sewage sludge fermentation raw material during fermentation, and provide a wide variety of microorganisms that contribute to aerobic fermentation.

It is preferable that the sewage sludge fermentation feedstock further contains a nutritional supplement as a material for supplying the sewage sludge fermentation feedstock with a nutrient source for the microorganisms that contribute to aerobic fermentation. Specific examples of such nutritional supplements include food sludge, waste clay, meat and bone meal, waste cooking oil, oil cake, food waste, human waste, poultry and livestock feces, and seed sludge. These can be used alone or in combination. Furthermore, as the 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) can be used.

Of these, using meat and bone meal or oil cake as a nutritional supplement is preferred because it allows the nutritional components (oils, fats, proteins, nitrogen, etc.) when mixed with sewage sludge to be easily adjusted to optimal conditions for aerobic microbial activity, further promoting aerobic fermentation of sewage sludge. Using seed sludge as a nutritional supplement is also preferred because it allows the diverse aerobic microorganisms present in the seed sludge to be sufficiently supplied to the sewage sludge fermentation raw material, further promoting aerobic fermentation of sewage sludge. In particular, using a combination of meat and bone meal, oil cake, and seed sludge as nutritional supplements is also preferred, as it allows the progress of aerobic fermentation to be easily adjusted to optimal ranges in terms of both nutrition and aerobic microbial diversity, further promoting aerobic fermentation of sewage sludge.

When the sewage sludge fermentation raw material contains a nutritional supplement, the content of the nutritional supplement in the sewage sludge fermentation raw material is preferably 5 to 60 parts by mass, more preferably 10 to 50 parts by mass, and even more preferably 15 to 30 parts by mass, per 100 parts by mass of sewage sludge. In this case, the reference masses of the sewage sludge and nutritional supplement are both measured in a hydrated state. Furthermore, when multiple types of nutritional supplements are contained, the content of the nutritional supplements is based on their total amount. Having the nutritional supplement content within this range makes it easy to easily adjust the balance of nutrients necessary for aerobic microbial activity, further promoting aerobic fermentation of the sewage sludge and stabilizing the fermentation process at a high level.

When the sewage sludge fermentation raw material contains a nutritional supplement, it is preferable to use a nutritional supplement with a solid calorific value of 3000 kcal/kg or more, more preferably 3300 kcal/kg or more, and even more preferably 3500 kcal/kg or more. This solid calorific value is the calorific value per type of nutritional supplement. Generally, a high solid calorific value indicates a high content of organic matter, which is one of the nutrients useful for the progression of aerobic fermentation. Therefore, using a nutritional supplement with such a calorific value can further promote aerobic fermentation and enable efficient fermentation of sewage sludge. Examples of nutritional supplements with such a calorific value include meat and bone meal, oil cake, and poultry and livestock manure.

The shapes of the various materials mentioned above are not particularly limited, and may be, for example, solid, granular, powder, paste, fluid, liquid, etc. The total content of the materials can be adjusted as appropriate 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 is preferably 1 part by mass to 180 parts by mass, more preferably 5 parts by mass to 100 parts by mass, and even more preferably 10 parts by mass to 60 parts by mass. In this case, the mass of the sewage sludge used as the reference is the mass in a wet state.

To ensure sufficient moisture content 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 80% 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 and 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 A 1203, "Test Method for Moisture Content of Soil." The moisture content of the sewage sludge fermentation raw material can be adjusted as needed by selecting raw materials to achieve the desired moisture content, for example, by using sewage sludge with a high moisture content and dry organic soil, or by adding water to the raw materials or sewage sludge fermentation raw material.

Sewage sludge fermentation feedstock containing such materials can be produced as a mixture or sediment by, for example, mixing or piling sewage sludge and organic soil with various other materials as needed. More specifically, examples include a method of obtaining sewage sludge fermentation feedstock by mixing sewage sludge and organic soil with various other materials as needed, or a method of obtaining sewage sludge fermentation feedstock by piling the materials in any order indoors or outdoors. Alternatively, a method of providing one of the materials in a vessel such as a fermenter, followed by providing the other materials in any order, resulting in a sediment in which the materials are alternately or randomly deposited in the vessel, and then using this sediment as is or in addition to it to form a mixture in a vessel such as a fermenter, to obtain sewage sludge fermentation feedstock.

The above-mentioned sewage sludge fermentation raw material, whether in the form of a sediment or a mixture, is suitable for use in aerobic fermentation treatment of sewage sludge. The sewage sludge fermentation raw material can be placed outdoors or indoors as is, or it can be stored in a container as a sediment or mixture and used to perform aerobic fermentation treatment of sewage sludge.

In more detail, the sewage sludge fermentation raw material can be aerobically fermented by piling it in a compost building or by storing it in an open or closed fermentation tank. When the sewage sludge fermentation raw material is supplied to a fermentation tank for aerobic fermentation, aerobic fermentation can be carried out stably from the early stages of fermentation over a long period of time, regardless of the presence or absence of stirring equipment in the fermentation tank or the stirring method, and the sewage sludge can be efficiently treated. From the perspective of reducing adverse effects on the surrounding environment, such as odors, when aerobic fermentation of sewage sludge in the sewage sludge fermentation raw material is carried out in a closed fermentation tank. A closed system refers to a reaction system in which the intrusion of air from the external environment and the outflow of fermentation gases generated from the fermentation tank to the outside are controlled during aerobic fermentation, 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.

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 sewage sludge can proceed stably over an extended period of time without having to change environmental conditions such as the ingredient mix or aeration volume each time depending on the fermentation state. In other words, a method for fermenting sewage sludge preferably includes a step of supplying sewage sludge, organic soil, and, if necessary, other materials to a sealed vertical fermenter in any order, or supplying a mixture containing these raw materials to a sealed vertical fermenter and aerobically fermenting the materials; and more preferably, this step is carried out in a sealed system. The sealed vertical fermenter may be equipped with stirring equipment for stirring the contents of the fermenter, so that the raw materials supplied to the fermenter can be stirred continuously or intermittently.

When aerobic fermentation is carried out in a sealed vertical fermenter, the accumulation of sewage sludge fermentation material causes the sewage sludge fermentation material in the fermenter to become compacted, making it difficult for the sewage sludge to proceed with aerobic fermentation. This degree of compaction is particularly pronounced in the lower region of the fermenter (near the discharge outlet). In this regard, the sewage sludge fermentation material of the present invention, by containing organic soil with the above-described properties, can prevent the sewage sludge fermentation material in the fermenter from becoming excessively compacted while ensuring breathability, which is advantageous in that it allows the aerobic fermentation of sewage sludge to proceed stably and effectively, whether the sewage sludge is in an unconsolidated or compacted state.

Figure 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 a mixture of sewage sludge, organic soil, and, if necessary, 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 openable or detachable 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 can treat sewage sludge by aerobic fermentation in a sealed system.

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.

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 within the tank section 20 to the outside of the tank section 20. This allows for appropriate control of the flow of air and gases inside and outside the reaction system, making it possible to more efficiently promote aerobic fermentation, particularly in a sealed system.

In the embodiment shown in FIG. 1, oxygen-containing gas F can be supplied from air circulation equipment 60 installed outside the tank section 20 to the vertically downward side of the agitator blade 51, preferably via the hollow agitator shaft 52 and the interior of the agitator blade 51. The vertically downward 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.

From the perspective of facilitating the supply of oxygen-containing gas throughout the fermentation tank and increasing the efficiency of aerobic fermentation of sewage sludge, it is preferable that oxygen-containing gas F be supplied from the vertically lower side of tank section 20, and that oxygen-containing gas F and gas be 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 fermentation tank through inlet 30, and the sewage sludge fermentation raw material is aerobically fermented in the fermentation tank for approximately two weeks, after which the fermented sewage sludge fermentation raw material is discharged from the outlet as fermented sludge.

The sludge fermentation product produced by subjecting sewage sludge fermentation raw material to aerobic fermentation can be used for purposes such as fertilizer, soil conditioner, green farmland materials such as horticultural soil, cement clinker raw material, solid fuel, etc., enabling effective resource utilization. In particular, it is preferable to mix the sludge fermentation product with raw materials such as limestone and use it as cement clinker raw material, as this increases the effective use amount of the produced sludge fermentation product and further contributes to effective resource utilization. Furthermore, this sludge fermentation product can be reused as a nutritional supplement of the present invention when preparing sewage sludge fermentation raw material, further contributing to effective resource utilization in this respect.

As is clear from the above description, the present specification discloses not only a sewage sludge fermentation raw material, but also a method for producing the sewage sludge fermentation raw material and 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 organic soil to treat the sewage sludge. The above-mentioned explanations apply appropriately to the sewage sludge and organic soil contained in the sewage sludge fermentation feedstock used in this treatment method, as well as the types and amounts of various materials contained as needed.

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 value of the solid content. In the tables, columns marked with "-" indicate non-content.

Examples 1-1 to 1-2 and Comparative Examples 1-1 to 1-3
[Preparation of sewage sludge fermentation raw material]
Sewage sludge, organic soil, and other materials shown in (1) to (5) below were mixed in the content ratios shown in Table 1 below to prepare sewage sludge fermentation raw materials with a moisture content of 64.1% to 66.8% by mass.

(1) Digested sludge: Digested sludge obtained from a sewage treatment plant (moisture content: 84.4% by mass)
(2) Kuroboku A: Kuroboku produced in Oita Prefecture (moisture content 42.2% by mass, density 1.33 g/cm ³ , loss on ignition 26.52% by mass)
(3) Kuroboku B: Kuroboku produced in Kagoshima Prefecture (moisture content: 48.7% by mass, density: 1.46 g/cm ³ )
(4) Meat and bone meal: meat and bone meal for fertilizer (moisture content 3.5% by mass, calorific value 5070kcal/kg)
(5) Oil cake: rapeseed oil cake for fertilizer (moisture content 8.0% by mass, calorific value 4590 kcal / kg)

[Aerobic fermentation test of digested sludge in a compacted state]
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 the temperature change of the sample. 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 prepared sewage sludge fermentation material was placed into each plastic beaker, and a plunger specified in JIS A 1109:2006 or JGS 1611 was dropped freely onto the top of the measurement sample 20 times from 50 mm above the top of the plastic beaker, and the sewage sludge fermentation material was compacted evenly so that the height was uniform (the height no longer changed), and the sample for the aerobic fermentation test was prepared.

Next, the plastic beaker containing each sample was 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 the temperature. These experiments were carried out for 7 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 progressed. In this example, which was carried out in a compacted state where fermentation is relatively difficult to progress, from the perspective of quickly aerobic fermentation treatment of a large amount of sewage sludge, a time required to reach the peak temperature within 40 hours was considered to be acceptable. The results are shown in Table 1 below.

Example 1-1, Comparative Example 1-1, and Comparative Example 1-2 in Table 1 show that adding Kuroboku A, which has a low density, to digested sludge significantly shortens the time required to reach the peak temperature compared to when no Kuroboku A is added or when Kuroboku B, which has a high density, is added, and also has the effect of raising the peak temperature. Furthermore, Comparative Example 1-3 and Example 1-2 show that the material added in addition to digested sludge and Kuroboku A is not limited to meat and bone meal; adding oil cake instead of meat and bone meal also has the same effect of shortening the time required to reach the peak temperature and raising the peak temperature.

[Examples 2-1 to 2-2 and Comparative Example 2-1]
The following examples and comparative examples evaluate the effect of different amounts of organic soil on aerobic fermentation. Note that Examples 2-1 to 2-2 and Comparative Example 2-1 were conducted under different experimental conditions than the above examples, so the results cannot be compared.

[Preparation of sewage sludge fermentation raw material]
Sewage sludge, organic soil, and other materials shown in (6) to (8) below were mixed in the content ratios shown in Table 2 below to prepare sewage sludge fermentation raw materials with a moisture content of 74.4% by mass to 76.6% by mass.

(6) Undigested sludge: Undigested sludge obtained from a sewage treatment plant (moisture content: 83.7% by mass)
(7) Kuroboku A: Kuroboku produced in Oita Prefecture (moisture content 42.2% by mass, density 1.33 g/cm ³ , loss on ignition 26.52% by mass)
(8) Seed sludge: Commercially available agricultural compost (moisture content 62.3% by mass)

[Aerobic fermentation test of undigested sludge in an unconsolidated state]
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 arrangement 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 the plastic beaker to serve as a sample for the aerobic fermentation test. In Examples 2-1 to 2-2 and Comparative Example 2-1, the fermentation state was evaluated in an unconsolidated state; therefore, unlike the above-mentioned Examples, compression with a poker was not performed, and the aerobic fermentation test was performed in the state directly placed in the plastic beaker.

The plastic beaker containing each sample was 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 the temperature. These experiments were carried out for 7 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 progressed. In this example, which was carried out in an unconsolidated state where fermentation is relatively easy to proceed, from the perspective of quickly aerobic fermentation treatment of a large amount of sewage sludge, a time required to reach the peak temperature within 24 hours was considered to be acceptable. The results are shown in Table 2 below.

From Comparative Example 2-1, Example 2-1, and Example 2-2 in Table 2, it can be seen that adding Kuroboku A to undigested sludge at any addition amount shortens the time required to reach peak temperature, just as with digested sludge.

From the above, it can be seen that the sewage sludge fermentation raw material of the present embodiment can shorten the time required to reach the peak temperature by simply adding organic soil with a density of 1.40 g/cm3 or ^less to the sewage sludge, regardless of the type of sewage sludge or the compaction state of the fermentation raw material, and can stably carry out aerobic fermentation of the sewage sludge.

10 Sealed vertical fermentation tank 20 Tank section 30 Inlet 40 Outlet 51 Mixing blade 52 Mixing shaft 60 Air circulation equipment 70 Exhaust port

Claims (7)

The method comprises the steps of:
The organic soil has a density of 1.40 g/cm ³ or less and a moisture content of 45% by mass or less ,
The organic soil is classified as an "organic soil" in the major classification and classified as an intermediate classification symbol [O (O)] in "Methods and Commentary on Ground Material Testing" (Geotechnical Society of Japan, November 2009, pp. 53-79),
The sewage sludge fermentation raw material contains the organic soil in an amount of 2 to 15 parts by mass per 100 parts by mass of sewage sludge . 2. The sewage sludge fermentation raw material according to claim 1 , wherein the organic soil is black soil. The sewage sludge fermentation raw material according to claim 1 or 2 , further comprising a nutritional supplement. The sewage sludge fermentation raw material according to claim 3 , wherein the nutritional supplement is contained in an amount of 5 parts by mass to 60 parts by mass based on 100 parts by mass of the sewage sludge. The method comprises a step of treating the sewage sludge by aerobic fermentation of a sewage sludge fermentation raw material containing sewage sludge and organic soil having a density of 1.40 g/cm3 or ^less and a moisture content of 45 mass% or less ,
A method for treating sewage sludge, comprising mixing 100 parts by mass of the sewage sludge with a sewage sludge fermentation raw material containing 2 parts by mass or more and 15 parts by mass or less of the organic soil, and treating the mixture,
The method for treating sewage sludge, wherein the organic soil is classified as an "organic soil" in the major classification and classified as an organic soil with the intermediate classification symbol O in "Methods and Commentary on Ground Material Testing" (Geotechnical Society of Japan, published November 2009, pages 53-79) . The sewage sludge fermentation raw material further contains a nutritional supplement,
The method for treating sewage sludge according to claim 5 , wherein the sewage sludge contains 5 to 60 parts by mass of a nutritional supplement per 100 parts by mass of the sewage sludge. 7. The method for treating sewage sludge according to claim 5 or 6 , wherein the sewage sludge fermentation raw material is aerobically fermented in a sealed, vertical fermenter.