Sewage sludge fermentation raw materials and sewage sludge treatment method

Abstract

To provide a fermentation raw material capable of smoothly proceeding aerobic fermentation by simple operation of adding a specified material to a sewage sludge, fermenting a large amount of sewage sludge stably, and achieving effective utilization of resources.SOLUTION: A sewage sludge fermentation raw material involves a sewage sludge and an incineration ash excluding a coal ash with the content of the incineration ash 0.2 pt.mass or over and 8 pts.mass or under to 100 pts.mass of the sewage sludge, and is used for aerobic fermentation treatment. A processing method of a sewage sludge involves a treatment step of a sewage sludge by aerobic fermentation of a sewage sludge fermentation raw material involving a sewage sludge and an incineration ash excluding a coal ash.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to raw materials 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 sewage treatment process associated with daily life activities. The amount of sewage sludge discharged is increasing along with the increase in the amount of sewage treated, and like municipal waste, its disposal is becoming a problem. Attempts are being made to treat sewage sludge, for example, by incinerating the sludge and using the heat generated as an energy source, but to further improve the efficiency of incineration, it is desirable to reduce the water content of sewage sludge.

[0003] A known technique for inexpensively reducing the moisture content of sewage sludge is aerobic fermentation of the sludge. For example, Patent Documents 1 to 3 disclose a method of mixing organic sludge with fly ash and fermenting it in order to improve dewatering efficiency and prevent foul odors.

[0004] Furthermore, Patent Document 4 discloses a technique for reducing the moisture content of sewage sludge by adding an aeration improving agent and inducing aerobic fermentation. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 185881 / 1981 [Patent Document 2] Japanese Patent Application Publication No. 09-074899 [Patent Document 3] Japanese Patent Application Publication No. 11-228267 [Patent Document 4] Japanese Patent Publication No. 2005-111374 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Generally, to ensure stable aerobic fermentation, it is necessary to optimize various conditions, including the amount of nutrients and water that serve as food sources for microorganisms in the material being treated, as well as pH and aeration rate, in addition to the amount of aeration. When aerobic fermentation is carried out under sealed conditions to prevent environmental pollution such as foul odors, the amount of aeration tends to be insufficient, which leads to anaerobic fermentation progressing, lowering the pH of the entire fermentation system and slowing down the decomposition rate of organic matter. As a result, the aerobic fermentation treatment of the material may not be carried out sufficiently.

[0007] To maintain a good aerobic fermentation state by adjusting the overall pH of the fermentation system, which has become low due to anaerobic fermentation, to neutral or alkaline, one method involves adding alkaline substances such as alkaline compost to raw materials such as livestock manure or organic waste. However, when using sewage sludge as the target of aerobic fermentation, the buffering effect of the sewage sludge does not change the overall pH of the fermentation system much, making it difficult to adjust the pH to the desired range. In particular, when treating sewage sludge in large-scale continuous equipment such as closed vertical fermentation tanks, the fermentation state near the raw material input port differs from the fermentation state near the discharge port, making it difficult to adjust the fermentation conditions.

[0008] As described above, when promoting fermentation of sewage sludge through pH adjustment, a formulation that can stably obtain the effect of promoting aerobic fermentation is required. In this regard, the technologies described in Patent Documents 1 to 4 do not consider appropriately adjusting the fermentation conditions in the aerobic fermentation process, nor do they consider optimizing the fermentation conditions during sealing or compaction.

[0009] Therefore, the present invention aims to provide a sewage sludge fermentation raw material that can easily and stably promote fermentation without having to adjust the formulation each time according to the fermentation state. [Means for solving the problem]

[0010] As a result of intensive studies to solve the above problems, the present inventors have found that by adding incineration ash excluding coal ash to sewage sludge, the fermentation of sewage sludge as the fermentation target is stably promoted, and thus the present invention has been completed.

[0011] The present invention includes sewage sludge and incineration ash excluding coal ash, and provides a sewage sludge fermentation raw material for aerobic fermentation treatment, which contains 0.2 parts by mass or more and 8 parts by mass or less of the incineration ash with respect to 100 parts by mass of the sewage sludge.

[0012] The present invention also includes a step of subjecting a sewage sludge fermentation raw material containing sewage sludge and incineration ash excluding coal ash to aerobic fermentation to treat the sewage sludge, and provides a method for treating sewage sludge, which uses the sewage sludge fermentation raw material containing 0.2 parts by mass or more and 8 parts by mass or less of the incineration ash with respect to 100 parts by mass of the sewage sludge. [[ID=1​​​​​​​​​​​​​​​​​​​​​​​​Preferred embodiments of the present invention will be described below. Note that the present invention is not limited to the following embodiments.

[0016] The raw material for sewage sludge fermentation of the present invention includes, as its materials, sewage sludge and incineration ash excluding coal ash. This raw material for sewage sludge fermentation is preferably used for the aerobic fermentation treatment of sewage sludge.

[0017] The sewage sludge used in the present invention is a waste generated in the process of sewage treatment and is a mud-like substance containing organic substances, inorganic substances and water. Sewage sludge is typically dehydrated excess sludge discharged from a wastewater treatment facility using the activated sludge process. Examples of such sewage sludge include general sewage sludge generated at sewage treatment plants, night soil sludge generated at night soil treatment facilities, and septic tank sludge, etc., and these can be used alone or in combination. Sewage sludge may be used as undigested sludge as it is, or alternatively, a self-fermentation product of sewage sludge such as digested sludge may be used. The water content of the sewage sludge is not particularly limited. For example, it is about 50% by mass or more and 90% by mass or less, preferably 50% by mass or more and 85% by mass or less. The type of sewage sludge can be selected based on at least one of its water content, presence or absence of digestion, and dehydration treatment method.

[0018] The raw material for sewage sludge fermentation of the present invention includes incineration ash excluding coal ash (hereinafter, this is also simply referred to as "incineration ash"). Examples of such incineration ash include one or more of incineration ash of paper sludge (hereinafter, this is also referred to as "PS ash"), municipal solid waste incineration ash, woody biomass incineration ash, sewage sludge incineration ash, etc., preferably one or more of PS ash, municipal solid waste incineration ash, and woody biomass incineration ash. These can be used alone or in combination of a plurality.

[0019] These incinerated ashes typically become industrial waste or are used for purposes such as concrete improvement in civil engineering or soil improvement in agriculture. Surprisingly, the inventors have discovered a new use for such PS ash by reusing it as a component material for sewage sludge fermentation, thereby promoting efficient aerobic fermentation of sewage sludge. Furthermore, they have found that while these incinerated ashes can become industrial waste, reusing them together with sewage sludge reduces the amount of waste, contributing to the effective use of resources and environmental protection.

[0020] Paper sludge is a residue (muddy or slurry-like) obtained by concentrating and dewatering wastewater containing impurities such as short fibers and inorganic components that cannot be used as recycled paper, which is generated during the manufacturing process of recycled paper using waste paper as a raw material. PS ash is incineration ash obtained by drying and incinerating such paper sludge. Such incineration ash can be obtained as fly ash generated during incineration or as crushed material of the bottom ash. This PS ash is composed of porous particles including calcium oxide (CaO) derived from additives such as calcium carbonate contained in waste paper, various oxides such as silicon dioxide, aluminum oxide, and silicon-aluminum composite oxides, and unburned particles derived from the fibers of waste paper.

[0021] Municipal solid waste incineration ash is the ash produced when combustible waste generated in households and other places is incinerated in a waste incinerator, and both fly ash and bottom ash can be used. Municipal solid waste incineration ash is composed of porous particles that include additives such as calcium carbonate contained in paper, calcium oxide derived from slaked lime, calcium carbonate, and quicklime used in the treatment of exhaust gases in incinerators, various oxides such as silicon dioxide, aluminum oxide, and silicon-aluminum composite oxides, and unburned particles.

[0022] Woody biomass incineration ash is the ash produced when woody resources such as forest residues, sawmill residues, construction waste, and palm kernel shells are burned, and both fly ash and bottom ash can be used. Woody biomass incineration ash is composed of a particle composite that includes various oxides such as calcium oxide derived from slaked lime, calcium carbonate, and quicklime used in the exhaust gas treatment of the incinerator, as well as silicon dioxide, silicon-aluminum composite oxides, and porous particles consisting of unburned particles and silicon dioxide particles.

[0023] Sewage sludge incineration ash is the ash generated when sewage sludge is incinerated to reduce its volume and stabilize it. It contains calcium oxide derived from coagulants used in sewage sludge treatment, as well as silicon dioxide, magnesium, phosphorus, etc., and is composed of a particle composite containing porous particles.

[0024] As stated above, coal ash, which is ash produced by the combustion of coal, is excluded from the term "incinerated ash" in this specification. This is because coal ash has a lower alkali content per unit mass compared to the other incinerated ashes mentioned above, and therefore, when coal ash is used alone, it is difficult to raise the pH to create a pH environment in which aerobic fermentation of sewage sludge can proceed efficiently. This is supported by the fact that, as shown in the examples described later, the effect of promoting aerobic fermentation when the incinerated ash of the present invention is added to sewage sludge is more significant than the effect of promoting aerobic fermentation when coal ash is simply added to sewage sludge.

[0025] The incinerated ash used in this invention, regardless of its origin, preferably has an average particle size of 1 μm to 100 μm, more preferably 2 μm to 60 μm, and even more preferably 2 μm to 20 μm. By using incinerated ash with a small particle size, the reaction surface area of ​​the incinerated ash is increased, and the alkaline components in the incinerated ash, such as calcium oxide, are supplied to the sewage sludge at an appropriate alkali supply rate, thereby effectively exhibiting the pH adjustment effect in the microscopic region described later. As a result, aerobic fermentation of sewage sludge can be further promoted. The average particle size of incinerated ash can be defined as the median diameter of the volume-based particle size distribution measured by a laser diffraction particle size distribution analyzer.

[0026] The incinerated ash used in this invention, regardless of its origin, contains fine particles with a high content of free calcium oxide, and is typically an aggregate of such fine particles. More specifically, the incinerated ash is a dry powder containing calcium compounds such as CaO or Ca(OH)2.

[0027] The incinerated ash used in this invention, regardless of its origin, preferably has a free calcium oxide content of 2% or more, more preferably 5% to 20%, and even more preferably 5% to 10%, as measured by JCAS I-01:1997 "Method for Determination of Free Calcium Oxide". Having a free calcium oxide content within this range ensures an appropriate amount of alkali is supplied to the sewage sludge, effectively exhibiting the microscopic pH adjustment effect described later and further promoting aerobic fermentation of the sewage sludge. Furthermore, since the pH adjustment effect described later can be achieved by adding only a relatively small amount to the sewage sludge, the sewage sludge content in the sewage sludge fermentation raw material can be increased, allowing for efficient aerobic fermentation treatment of the sewage sludge. The free calcium oxide content measured by the above method is expressed as "mass%".

[0028] The incinerated ash used in this invention, regardless of its origin, preferably has an ignition loss of 1% or more as measured by JIS R5202:2015 "Chemical Analysis Method for Cement". The ignition loss of incinerated ash measured by the same method is realistically 35% or less, but may be 15% or less, or even 10% or less. The ignition loss of the incinerated ash reflects the amount of carbon elements derived from unburned particles contained in the ash. An ignition loss within this range means that a predetermined amount of porous unburned particles are present in the incinerated ash, and the presence of these porous particles effectively enhances the aeration improvement effect during consolidation, as described later. As a result, aerobic fermentation of sewage sludge can be further promoted. The ignition loss measured by the above method is expressed as "mass%".

[0029] Regardless of its origin, the incinerated ash preferably has a Blaine specific surface area of ​​4000 cm². 2 / g or more 16000cm 2 It is less than or equal to / g, and more preferably 8000cm². 2 / g or more 15000cm 2 The specific surface area is less than or equal to / g. The Blaine specific surface area can be measured, for example, according to JIS R5201. Having a specific surface area of ​​incinerated ash within this range allows for a moderate increase in the supply of alkali to sewage sludge due to the dissolution of CaO in the incinerated ash, while also improving the aeration of the fermentation raw materials during compaction. As a result, aerobic fermentation of sewage sludge can be promoted more efficiently.

[0030] The incinerated ash content in the sewage sludge fermentation raw material of the present invention is preferably 0.2 parts by mass to 8 parts by mass, more preferably 0.4 parts by mass to 5 parts by mass, and even more preferably 1 part by mass to 3 parts by mass, per 100 parts by mass of sewage sludge. In this case, the mass of the reference sewage sludge is the mass in a water-containing state. If multiple types of incinerated ash are included, the incinerated ash content is based on the total amount. By being within this range, aerobic fermentation of sewage sludge can be easily promoted and the progress of fermentation can be stabilized at a high level.

[0031] The inventors speculate that the reason why aerobic fermentation proceeds efficiently when incinerated ash is added to the sewage sludge fermentation raw material of the present invention in a specific amount is as follows. Incinerator ash contains free calcium oxide and becomes alkaline when it comes into contact with water. When incinerator ash is added to sewage sludge, the pH buffering effect of the sewage sludge prevents a significant increase in the overall pH of the system (a macroscopic increase in pH). However, in the microscopic environment where the incinerator ash is present (for example, the surface of the ash particles and the surrounding microscopic region), the pH is adjusted to the alkaline side. In this microscopic region where the pH has risen, it rises to a level suitable for the decomposition of organic matter by aerobic microorganisms, and as a result, aerobic fermentation is thought to proceed efficiently.

[0032] On the other hand, if the amount of incinerated ash added is less than the range described above, the supply of alkali will be insufficient, making it difficult to raise the microscopic pH of the sewage sludge to an appropriate range. Conversely, if the amount of incinerated ash added is more than the range described above, the amount of incinerated ash will be excessive compared to the amount of sewage sludge and the amount of microorganisms present, creating multiple localized areas where the pH is excessively high and aerobic activity by microorganisms cannot be adequately carried out, thus hindering aerobic fermentation. Therefore, by controlling the amount of incinerated ash within the range described above, the overall pH of the sewage sludge fermentation raw material remains almost unchanged, but microscopic areas with a pH suitable for the decomposition of organic matter are uniformly distributed and formed within the sewage sludge fermentation raw material, allowing aerobic fermentation of sewage sludge to proceed simply and efficiently.

[0033] On the other hand, incinerated ash contains porous particles, and such porous particles have excellent permeability. When incinerated ash containing porous particles is mixed with sewage sludge fermentation raw materials, air can easily penetrate to the inside of the sample through the pores of the porous particles attached between the sludge flocs, allowing aerobic fermentation to proceed efficiently. This effect is particularly pronounced when the sample is compacted, mitigating the deterioration of permeability due to the compaction of the raw materials, preventing the inhibition of aerobic fermentation, and allowing aerobic fermentation to proceed stably even in a compacted state. Compaction tends to occur in the lower region (near the discharge port) when processing fermentation raw materials in a fermentation tank, due to the weight of the accumulated raw materials.

[0034] The sewage sludge fermentation raw material of the present invention may consist only of sewage sludge and incinerated ash. In addition, it is preferable to further include other materials other than sewage sludge and incinerated ash (hereinafter also simply referred to as "materials").

[0035] Examples of materials include those that promote stable aerobic fermentation when sewage sludge fermentation raw materials are used for fermentation. Specifically, these materials include those that reduce the moisture content of sewage sludge, improve aeration during fermentation of sewage sludge fermentation raw materials, supply a wide variety of microorganisms that contribute to aerobic fermentation, and supply easily decomposable organic matter that serves as a nutrient source for microorganisms that contribute to aerobic fermentation.

[0036] To supply nutrients for microorganisms contributing to aerobic fermentation to the sewage sludge fermentation raw material, it is preferable that the sewage sludge fermentation raw material further contains nutritional supplements. Specific examples of such nutritional supplements include food sludge, waste clay, meat and bone meal, waste cooking oil, food waste, human waste, feces of poultry and livestock, and seed sludge. These can be used individually or in combination. As seed sludge, for example, commercially available agricultural compost may be used, or sludge fermented product (fermented product produced by aerobic fermentation treatment of the sewage sludge fermentation raw material of the present invention) may be used.

[0037] Of these, using meat and bone meal as a nutritional supplement is preferable because it allows for easy adjustment of the nutritional components (oils, proteins, nitrogen, etc.) when mixed with sewage sludge to optimal conditions for the activity of aerobic microorganisms, thereby further promoting aerobic fermentation of sewage sludge. Using seed sludge as a nutritional supplement is also preferable because it supplies a sufficient amount of the diverse aerobic microorganisms present in the seed sludge to the sewage sludge fermentation raw material, further promoting aerobic fermentation of sewage sludge. In particular, from the viewpoint of easily adjusting the progress of aerobic fermentation to an optimal range from both a nutritional and aerobic microorganism diversity perspectives, it is also preferable to use a combination of meat and bone meal and seed sludge as nutritional supplements to further promote aerobic fermentation of sewage sludge.

[0038] When the sewage sludge fermentation raw material further contains nutrient aids, the content of nutrient aids in the sewage sludge fermentation raw material is preferably 5 to 60 parts by mass, more preferably 10 to 50 parts by mass, or more preferably 25 to 55 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 mass of the standard sewage sludge and nutrient aids is the mass in a water-containing state. If multiple types of nutrient aids are included, the content of nutrient aids is based on their total amount. By being within this range, it is possible to easily adjust the balance of nutrients necessary for the activity of aerobic microorganisms, thereby further promoting aerobic fermentation of sewage sludge and stabilizing the progress of fermentation at a high level.

[0039] When nutrient supplements are further included in the sewage sludge fermentation raw material, it is preferable to use nutrient supplements with a solid content 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 content calorific value is the calorific value per type of nutrient supplement. Generally, a high solid content calorific value means that it contains a large amount of organic matter, which is one of the nutrients useful for the progress of aerobic fermentation. Therefore, by using nutrient supplements with such a calorific value, aerobic fermentation can be further promoted, and the fermentation treatment of sewage sludge can be carried out efficiently. Examples of nutrient supplements with such a calorific value include meat and bone meal, and manure from poultry and livestock.

[0040] It is preferable that the sewage sludge fermentation raw material further contains an aeration aid as a material to improve the aeration of the sewage sludge fermentation raw material and promote aerobic fermentation of the sewage sludge. By including an aeration aid, the aeration of the sewage sludge fermentation raw material can be easily improved regardless of the compaction state 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 fermentation tank, for example, as described later, the sewage sludge in the fermentation tank becomes compacted due to the accumulation of the sewage sludge fermentation raw material, making it difficult for aerobic fermentation of the sewage sludge to proceed. By including an aeration aid, it is possible to further suppress excessive compaction while ensuring aeration, which is advantageous in that it is possible to carry out aerobic fermentation of sewage sludge stably and effectively.

[0041] Examples of aeration aids include organic aeration aids such as rice straw, rice husks, plants, or their dried or crushed forms, and inorganic aeration aids such as perlite, zeolite, diatomaceous earth, or coal ash such as fly ash. These can be used individually or in combination. Of these, coal ash is preferable because its relatively fine particles and the presence of oxide components such as CaO and MgO result in high dispersibility in the sewage sludge fermentation raw material, allowing for uniform formation of flocs (aggregates of particles), thereby further improving aeration during aerobic fermentation.

[0042] 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 mass of the standard sewage sludge and aeration aid shall be the mass in a water-containing state. When multiple types of aeration aids are included, the content of the aeration aids shall be based on the total amount. By maintaining this range, it is possible to ensure uniform aeration while suppressing excessive compaction of the sewage sludge fermentation material over the long period from the start to the end of fermentation, thereby enabling stable and effective aerobic fermentation of sewage sludge. This effect is particularly pronounced when the incinerated ash content in the sewage sludge fermentation material is within the aforementioned preferred range. Furthermore, while coal ash can be treated as industrial waste, similar to sewage sludge and incinerated ash, reusing coal ash together with sewage sludge offers the advantage of contributing to the effective use of resources and environmental protection.

[0043] When using coal ash as an aeration aid, the bulk density of the coal ash is preferably 0.2 g / cm³. 3 More than 1.5g / cm 3 The following applies: Bulk density can be measured, for example, according to JIS R1628. Furthermore, the Blaine specific surface area of ​​the coal ash is preferably 1000 cm². 2 / g or more 20000cm 2 It is less than / g. The Blaine specific surface area can be measured, for example, according to JIS R5201.

[0044] The shape of the various materials such as the nutritional supplements and aeration aids mentioned above is not particularly limited, and may be in solid, granular, powdery, pastey, fluid, or liquid form. 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 mass of materials per 100 parts by mass of sewage sludge is preferably 1 to 180 parts by mass, more preferably 5 to 100 parts by mass. Even more preferably it is 10 to 60 parts by mass. In this case, the mass of the sewage sludge used as a reference is the mass in a water-containing state.

[0045] From the viewpoint of ensuring a sufficient amount of moisture to stably promote aerobic fermentation from the initial stages of fermentation, the moisture content of the sewage sludge fermentation raw material is preferably 30% by mass or more and 80% by mass or less, more preferably 30% by mass or more and 70% by mass or less, and even more preferably 40% by mass or more and 60% by mass or less. 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 "Test 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 incinerated ash in a dry state, or by adding water to the raw materials or the sewage sludge fermentation raw material.

[0046] Such sewage sludge fermentation raw materials can be produced, for example, by mixing or piling sewage sludge and incinerated ash with various materials as needed, as a mixture or deposit. Specifically, methods include obtaining sewage sludge fermentation raw materials by mixing sewage sludge and incinerated ash with various materials as needed, or obtaining sewage sludge fermentation raw materials as a deposit obtained by piling each material in any order indoors or outdoors. Alternatively, one method involves supplying one of the materials to a container such as a fermentation tank, then supplying the other materials to the container in any order, to create a deposit in which each material is piling alternately or randomly within the container, and then obtaining sewage sludge fermentation raw materials as a mixture obtained by mixing this deposit as is, or with other materials, within a container such as a fermentation tank.

[0047] The aforementioned sewage sludge fermentation raw materials, whether in the form of sediment or mixture, are suitable for aerobic fermentation treatment of sewage sludge. The sewage sludge fermentation raw materials can be placed outdoors or indoors as they are, or they can be contained in a container as sediment or mixture to perform aerobic fermentation treatment of sewage sludge.

[0048] In detail, the sewage sludge fermentation raw material can be piled up in a composting facility or housed in an open or closed fermentation tank to allow the sewage sludge to undergo aerobic fermentation. When the sewage sludge fermentation raw material is supplied to a fermentation tank for aerobic fermentation treatment, regardless of the presence or method of stirring equipment in the fermentation tank, stable aerobic fermentation can be carried out from the initial stages of fermentation for a long period, allowing for efficient treatment of the sewage sludge. From the viewpoint of reducing adverse effects on the surrounding environment, such as foul odors, it is preferable to perform aerobic fermentation of the sewage sludge in the sewage sludge fermentation raw material 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 gas 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.

[0049] In particular, the sewage sludge fermentation raw material of the present invention is suitable because, when fermenting sewage sludge by aerobic fermentation in a sealed vertical fermentation tank (hereinafter also referred to as a "sealed vertical fermentation tank") in a sealed state, the aerobic fermentation of sewage sludge can be carried out stably over a long period of time without having to change the composition of the components or environmental conditions such as pH each time according to the fermentation state. In other words, it is preferable that the method of fermenting sewage sludge includes a step of supplying sewage sludge and incinerated ash and materials as needed into a sealed vertical fermentation tank in any order, or supplying a mixture containing these raw materials into a sealed vertical fermentation tank and carrying out aerobic fermentation, and it is even more preferable that this step be carried out in a sealed system. The sealed vertical fermentation tank may be equipped with stirring equipment to stir the inside of the fermentation tank, and each raw material supplied into the fermentation tank may be stirred continuously or intermittently.

[0050] When aerobic fermentation is carried out in a sealed state using a closed vertical fermentation tank, the accumulation of sewage sludge fermentation raw materials causes compaction of the sewage sludge fermentation raw materials in the fermentation tank, making it difficult for aerobic fermentation of sewage sludge to proceed. This degree of compaction is particularly noticeable in the lower region of the fermentation tank (near the discharge port). In this regard, it is advantageous that the sewage sludge fermentation raw materials preferably contain an aeration aid such as coal ash, which allows for aeration while suppressing excessive compaction of the sewage sludge fermentation raw materials in the fermentation tank. This allows for stable and effective aerobic fermentation of sewage sludge whether the sewage sludge fermentation raw materials are in an uncompacted or compacted state.

[0051] Figure 1 shows an embodiment of a sealed vertical fermentation tank suitable for use in the fermentation treatment of sewage sludge fermentation raw materials of the present invention. The sealed vertical fermentation tank 10 extends vertically with respect to the installation surface and has a cylindrical tank section 20 capable of accommodating a mixture of sewage sludge, incinerated ash, and materials as needed. At the top of the tank section 20 is an inlet 30 into which the mixture can be introduced, and at the bottom of the tank section 20 is an outlet 40 into which the aerobically fermented sewage sludge fermentation raw materials can be discharged to the outside of the tank section 20. Both the inlet 30 and the outlet 40 are provided with lid-like members (not shown) that can be opened and closed or detached, and by attaching these lid-like members to the inlet 30 and the outlet 40, the tank section 20 in the fermentation tank 10 can be sealed. In other words, the sealed vertical fermentation tank 10 can treat sewage sludge by performing aerobic fermentation of sewage sludge in a sealed system.

[0052] From the viewpoint of further improving aerobic fermentation efficiency, it is preferable that the sealed vertical fermentation tank 10 has an insulating structure, for example, by arranging insulating material on the outer surface of the tank section 20. It is also preferable that the sealed vertical fermentation tank 10 is equipped with stirring equipment 50 for mixing the raw materials in the fermentation tank to make the state of the components and the air permeability uniform. The stirring equipment 50 shown in Figure 1 includes, for example, a stirring blade 51 provided inside the tank section 20, a stirring shaft 52 connected to the stirring blade 51, and a motor (not shown) provided outside the tank section 20. The stirring blade 51 is connected to the motor provided outside the tank section 20 via the stirring shaft 52 and rotates in a constant direction using the motor as a driving source. By further providing the stirring equipment 50, the permeability within the reaction system can be increased, and the aerobic fermentation efficiency of the sewage sludge fermentation raw material can be further improved.

[0053] Furthermore, it is preferable that the sealed vertical fermentation tank 10 is equipped with an air circulation system 60 for supplying oxygen-containing gases such as air and oxygen into the fermentation tank, and an exhaust port 70 for exhausting the gas inside the tank section 20 to the outside of the tank section 20. This allows for appropriate control of the flow of air and gas inside and outside the reaction system, and promotes aerobic fermentation more efficiently, especially in a sealed system.

[0054] In the configuration shown in Figure 1, the oxygen-containing gas F is supplied from an air circulation system 60 located outside the tank 20, preferably through the interiors of the hollow stirring shaft 52 and the stirring blade 51, to the vertically downward side of the stirring blade 51. It is also preferable that the vertically downward side of the stirring blade 51 is provided with multiple gas circulation holes (not shown) through which the oxygen-containing gas F can flow. The oxygen-containing gas present in the tank 20 and the gas produced by aerobic fermentation are exhausted as exhaust air from the top of the tank 20 through the exhaust port 70.

[0055] From the viewpoint of facilitating the supply of oxygen-containing gas throughout the fermentation tank and improving the aerobic fermentation efficiency of sewage sludge, it is preferable that the oxygen-containing gas F is supplied from the vertically downward side of the tank section 20, and that the oxygen-containing gas F and the gas are exhausted from the vertically upward side of the tank section 20. The sewage sludge fermentation raw material is continuously or intermittently introduced into the tank section 20 of the fermentation tank from the inlet 30, and the sewage sludge fermentation raw material is aerobically fermented in the fermentation tank for about two weeks, after which the fermented sewage sludge fermentation raw material is discharged from the discharge port as sludge fermented product.

[0056] The sludge fermented product produced by subjecting sewage sludge fermentation raw materials to aerobic fermentation can be used for purposes such as fertilizer, soil conditioner, green and agricultural land materials such as horticultural soil, cement clinker raw material, and solid fuel, enabling the effective use of resources. In particular, it is preferable to mix the sludge fermented product with raw materials such as limestone and use it as a cement clinker raw material, as this increases the effective use of the produced sludge fermented product and further contributes to the effective use of resources. Furthermore, this sludge fermented product can also be reused as a nutritional supplement in the preparation of sewage sludge fermentation raw materials according to the present invention, which also contributes to the effective use of resources.

[0057] Furthermore, since this invention utilizes incinerated ash, which can become industrial waste, as one of the raw materials for fermentation, it is advantageous in that it promotes the effective utilization of incinerated ash and reduces the environmental burden.

[0058] As is clear from the above description, this specification discloses not only raw materials for fermenting sewage sludge, but also a method for producing raw materials for fermenting sewage sludge, and a method for treating sewage sludge using raw materials for fermenting sewage sludge. The sewage sludge treatment method comprises a step of treating the sewage sludge by aerobic fermentation of a sewage sludge fermentation raw material containing sewage sludge and incinerated ash excluding coal ash. The above explanation applies appropriately to the types and amounts of sewage sludge and incinerated ash contained in the sewage sludge fermentation raw material used in this treatment method, as well as the nutrients and aeration aids included as needed. [Examples]

[0059] 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 calculated from the mass difference when dried at a heating temperature of 120°C using a halogen moisture meter (HM1105, manufactured by AS ONE Corporation). The calorific value shown below represents the calorific value of the solids. In the table, a column marked with "-" indicates that the material is not present. Furthermore, the average particle diameter shown below represents the median diameter of the particle size distribution measured using a laser diffraction particle size distribution analyzer (SALD2200, manufactured by Shimadzu Corporation). The following brain specific surface area is a value measured according to JIS R5201.

[0060] [Examples 1-1 to 1-2 and Comparative Examples 1-1 to 1-3] [Preparation of Sewage Sludge Fermentation Raw Material] The sewage sludge, PS ash, and seed sludge as a nutrient aid shown in the following (1) to (3) were mixed at the respective content ratios shown in Table 1 below to prepare a sewage sludge fermentation raw material with a water content of 61.5% to 65.6% by mass.

[0061] (1) Sewage sludge: Undigested sludge obtained from a sewage treatment plant (water content 84.36% by mass) (2) PS ash: Incineration ash of paper sludge (water content 0% by mass, free calcium oxide content 6.2% by mass, loss on ignition 1.9% by mass, average particle diameter 2.2 μm, brain specific surface area 14060 cm 2 / g) (3) Seed sludge: Commercially available agricultural compost (water content 28% by mass) [[ID=二十]]

[0062] [[ID=二十一]] [[ID=二十二]][Aerobic Fermentation Test] [[ID=二十三]] [[ID=二十四]]The sewage sludge fermentation raw materials of the examples and comparative examples were subjected to aerobic fermentation treatment, and the progress of aerobic fermentation of the sewage sludge was evaluated as the temperature change of the sample. As the fermentation container, a 500 mL poly beaker and a simple heat insulating container covering the side and bottom of the beaker were used. Their arrangement positions and dimensions were as shown in Fig. 2(a). The sewage sludge fermentation raw materials of each example and comparative example were placed in the poly beaker at about 400 mL each to prepare samples. [[ID=二十五]] [[ID=二十六]]

[0063] [[ID=二十七]] [[ID=二十八]]Among the samples contained in the poly beaker, the samples for aerobic fermentation treatment in the unconsolidated state were used as they were contained in the poly beaker. For the samples for aerobic fermentation treatment in the consolidated state, a tamping rod specified in JIS A1109:2006 or JGS 1611 was freely dropped 20 times from 50 mm above the upper end of the poly beaker onto the upper surface of the measurement sample to uniformly compact the sewage sludge fermentation raw material so that the height was uniform (the state where the height did not change). [[ID=二十九]] [[ID=三十]]

[0064] [[ID=三十一]] Next, the poly 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 poly beaker. A data logger was connected to the thermocouple, and the samples were subjected to aerobic fermentation while the temperature could be continuously measured. These experiments were carried out in a room set at 20°C for 17 or 21 days. The progress of aerobic fermentation was evaluated by the number of days required to reach the peak temperature, which was defined as the highest temperature measured. A shorter number of days to reach the peak temperature compared to the experimental start temperature (20°C) indicates that the aerobic fermentation of the sewage sludge is progressing rapidly and efficiently. The results are shown in Table 1 below. In the table, the column indicated by "17<" shows that no peak temperature was observed during either the 17-day or 21-day measurement period.

[0065] [Table 1]

[0066] As shown in Table 1, the sewage sludge fermentation raw materials in Examples 1-1 to 1-3, which contain sewage sludge and PS ash, and have a PS ash content within a predetermined range, show that the number of days required to reach the peak temperature is shorter compared to each comparative example. Therefore, the sewage sludge fermentation raw materials in the examples can stably and quickly and efficiently promote aerobic fermentation of sewage sludge through the simple operation of adding specific materials to sewage sludge.

[0067] Furthermore, in the case of the sewage sludge fermentation raw materials in Comparative Examples 1-1 to 1-2 that were in a compacted state, the temperature of the fermentation raw material was maintained at approximately the same level as the experimental start temperature (20°C) during the observation period, and no clear peak temperature was observed. Therefore, it can be seen that aerobic fermentation does not proceed in the sewage sludge fermentation raw materials having the composition of Comparative Examples 1-1 to 1-2 when in a compacted state.

[0068] [Examples 2-1 to 2-3 and Comparative Examples 2-1 to 2-3] The following examples and comparative examples evaluate the effects of the presence or absence of nutritional supplements and aeration aids on aerobic fermentation. Note that the experimental conditions for Examples 2-1 to 2-3 and Comparative Examples 2-1 to 2-3 differ from those for Examples 1-1 to 1-2 and Comparative Examples 1-1 to 1-3 described above, so a direct comparison of the results is not possible.

[0069] In addition to the materials (1) to (3) used in Examples 1-1 to 1-2, a nutrient supplement ((4) meat and bone meal) and an aeration supplement ((5) coal ash) were mixed in the proportions shown in Table 2 below to prepare a sewage sludge fermentation raw material with a water content of 61.0% to 68.2% by mass. This fermentation raw material was subjected to an aerobic fermentation test in the same manner as in Example 1-1. The results are shown in Table 2 below. In the table, the column indicated by "17<" indicates that no peak temperature was observed during either the 17-day or 21-day measurement period.

[0070] (4) Meat and bone meal: Meat and bone meal for fertilizer (moisture content 0.7% by mass, calorific value 3600kcal / kg) (5) Coal ash: Coal ash collected from the company's own coal-fired power plant (manufactured by Ube Industries, Ltd., moisture content 0% by mass)

[0071] [Table 2]

[0072] As shown in Table 2, the sewage sludge fermentation raw materials of Examples 2-1 to 2-3, which contain sewage sludge and PS ash, with the PS ash content within a predetermined range, and further include nutrient aids and aeration aids, show that the number of days required to reach the peak temperature is shorter compared to the comparative example. Therefore, the sewage sludge fermentation raw materials of the examples can stably and quickly and efficiently promote aerobic fermentation of sewage sludge through the simple operation of adding specific materials to sewage sludge. In particular, Example 2-2, in which the PS ash content was set to a more favorable range, showed that the number of days required to reach the peak temperature was further shortened, regardless of whether the sludge was in an unconsolidated or consolidated state, and that the aerobic fermentation of the sewage sludge proceeded even more efficiently, when combined with coal ash.

[0073] Furthermore, in the case of the sewage sludge fermentation raw materials in the compacted state of Comparative Example 2-1 and the sewage sludge fermentation raw materials of Comparative Example 2-2, the temperature of the fermentation raw materials remained at the same level as the experimental start temperature (20°C) during the observation period, and no clear peak temperature was observed. Therefore, it can be concluded that aerobic fermentation did not proceed in the sewage sludge fermentation raw materials having the compositions of Comparative Examples 2-1 and 2-2.

[0074] Furthermore, as shown in Comparative Example 2-2, aerobic fermentation did not proceed in the sewage sludge fermentation material to which only coal ash was added, whereas aerobic fermentation was significantly promoted in the sewage sludge fermentation material of Example 2-2, to which a small amount of incinerated ash was added compared to coal ash. From this, it can be seen that there is a clear difference in the effect of incinerated ash and coal ash on promoting aerobic fermentation.

[0075] [Examples 3-1 to 3-5 and Comparative Example 3-1] The following examples and comparative examples evaluate the effect of different types of incinerated ash on aerobic fermentation. Note that the experimental conditions for Examples 3-1 to 3-5 and Comparative Example 3-1 differ from those of the above-mentioned examples, therefore, a direct comparison of the results is not possible.

[0076] Instead of the materials (1) and (3) to (5) described above, the material (2) described above, along with the sewage sludge, incinerated ash, and seed sludge as a nutrient aid shown in (6) to (10) below, were mixed in the proportions shown in Table 3 below to prepare a sewage sludge fermentation raw material with a water content of 75.6% to 76.3% by mass. In this example, no aeration aid was included. Aerobic fermentation tests were conducted in the same manner as in Example 1-1, except that the fermentation raw material was tested only in an uncompacted state. The results are shown in Table 3 below. In Table 3, a higher peak temperature indicates that aerobic fermentation is progressing more favorably.

[0077] (6) Sewage sludge A: Undigested sludge obtained from sewage treatment plant A (moisture content 83.70% by mass) (7) Municipal solid waste incineration ash A: Municipal solid waste incineration ash generated in a fluidized bed incinerator of municipality A (moisture content 0% by mass, free calcium oxide content 9.5% by mass, loss on ignition 14.7% by mass, average particle size 54.2 μm, Blaine specific surface area 9120 cm²2 / g) (8) Municipal solid waste incineration ash B: Municipal solid waste incineration ash generated in a stoker-type incinerator of municipality B (moisture content 0% by mass, free calcium oxide content 7.2% by mass, loss on ignition 11.6% by mass, average particle size 79.4 μm, Blaine specific surface area 5680 cm² 2 / g) (9) Woody biomass incineration ash: Incineration ash generated at woody biomass-fired power generation facilities (produced at domestic woody biomass power plants, moisture content 0.1% by mass, free calcium oxide content 3.7% by mass, loss on ignition 7.2% by mass, average particle size 43.3 μm, Blaine specific surface area 4570 cm² 2 / g) (10) Type A sludge: Commercial agricultural compost product A (moisture content 62.3% by mass)

[0078] [Table 3]

[0079] As shown in Table 3, the sewage sludge fermentation raw materials of Examples 3-1 to 3-5, which contain sewage sludge and various incineration ashes, and have an incineration ash content within a predetermined range, show that the number of days required to reach the peak temperature is shorter and the peak temperature is higher compared to Comparative Example 3-1. Therefore, the sewage sludge fermentation raw materials of the examples can stably and quickly and efficiently promote aerobic fermentation of sewage sludge through the simple operation of adding specific materials to sewage sludge.

[0080] From the above, it can be concluded that the sewage sludge fermentation raw material of the example allows for stable, early, and efficient aerobic fermentation of sewage sludge through a simple operation of adding specific materials to sewage sludge. Furthermore, since the sewage sludge fermentation raw material of the example can promote aerobic fermentation by containing only a relatively small amount of incinerated ash, it is possible to increase the proportion of sewage sludge in the sewage sludge fermentation raw material and ferment a large amount of sewage sludge, leading to the effective utilization of resources.

Claims

1. It includes sewage sludge and incinerated ash excluding coal ash. The incinerated ash is contained in an amount of 0.2 parts by mass or more and 3 parts by mass or less per 100 parts by mass of the sewage sludge. The aforementioned incinerated ash is one or more types selected from the group consisting of paper sludge incinerated ash, municipal solid waste incinerated ash, and woody biomass incinerated ash. A sewage sludge fermentation raw material for aerobic fermentation treatment, wherein the free calcium oxide content of the incinerated ash is 2% by mass or more and 20% by mass or less.

2. A sewage sludge fermentation raw material according to claim 1, further comprising a nutritional supplement.

3. The sewage sludge fermentation raw material according to claim 2, wherein the nutritional supplement is contained in an amount of 5 to 60 parts by mass per 100 parts by mass of the sewage sludge.

4. A sewage sludge fermentation raw material according to any one of claims 1 to 3, further comprising an aeration aid.

5. The sewage sludge fermentation raw material according to claim 4, wherein the aeration aid is contained in an amount of 5 to 50 parts by mass per 100 parts by mass of the sewage sludge.

6. The sewage sludge fermentation raw material according to any one of claims 1 to 5, wherein the incinerated ash is municipal solid waste incinerated ash.

7. The sewage sludge fermentation raw material according to any one of claims 1 to 6, wherein the use of the sludge fermented product obtained by aerobic fermentation of the sewage sludge fermentation raw material is solid fuel.

8. The process includes a step of treating sewage sludge by aerobic fermentation of a sewage sludge fermentation raw material containing sewage sludge and incinerated ash excluding coal ash, The aforementioned incinerated ash is one or more types selected from the group consisting of paper sludge incinerated ash, municipal solid waste incinerated ash, and woody biomass incinerated ash. The free calcium oxide content of the incinerated ash is 2% by mass or more and 20% by mass or less. A method for treating sewage sludge, comprising using the sewage sludge fermentation raw material containing 0.2 parts by mass or more and 3 parts by mass or less of the incinerated ash per 100 parts by mass of the sewage sludge.

9. Using the sewage sludge fermentation raw material which further contains a nutrient aid and an aeration aid, The above-mentioned sewage sludge contains 5 to 60 parts by mass of the above-mentioned nutritional supplement with respect to 100 parts by mass of the above-mentioned sewage sludge. The treatment method according to claim 8, wherein the aeration aid is present in an amount of 5 to 50 parts by mass per 100 parts by mass of sewage sludge.

10. The processing method according to claim 8 or 9, wherein the sewage sludge fermentation raw material is aerobically fermented in a sealed, vertical fermentation tank.

11. The treatment method according to any one of claims 8 to 10, wherein the sludge ferment product obtained by aerobic fermentation of the aforementioned sewage sludge fermentation raw material is used as solid fuel.

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