JP7804449B2 - 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.

Aerobic fermentation of sewage sludge is known as a technique for inexpensively reducing the moisture content of sewage sludge. For example, Patent Documents 1 to 3 disclose methods of mixing organic sludge with organic materials and fermenting them to improve dewatering efficiency and reduce volume.

Japanese Patent Application Publication No. 11-079873 Japanese Patent Application Laid-Open No. 2005-111374 JP 2009-274908 A

Generally, to carry out aerobic fermentation stably, it is necessary to optimize various conditions, such as the nutrients that serve as nutrient sources for the microorganisms contained in the material to be treated, as well as the moisture content, pH, and aeration rate. When aerobic fermentation is performed on sewage sludge that contains a low content of nutrients that serve as nutrient sources for microorganisms, such as digested sludge that has undergone methane fermentation during the sewage treatment process, microbial activity can become sluggish due to a lack of nutrients, and aerobic fermentation of the material may not be carried out sufficiently.

As a method for improving the aerobic fermentation state in a fermentation system where microbial activity has become sluggish, Patent Documents 1 to 3 involve adding materials rich in nutrients (hereinafter referred to as "nutrient sources" or "nutrient source materials"). However, when sewage sludge is used as the target for aerobic fermentation treatment, depending on the type of sewage sludge and the type and amount of nutrient source material added, there may be a shortage of nutrients suitable for the microorganisms contained in the sewage sludge, making it difficult to maintain good aerobic fermentation states. Therefore, in order to ensure good aerobic fermentation, it is important to design materials appropriately for each sewage sludge and material used.

In the past, material design for sewage sludge fermentation feedstocks has involved testing using actual facilities or test equipment consisting of large-capacity fermentation tanks, which required large amounts of sample material and was time-consuming. Furthermore, in recent years, sewage sludge fermentation treatment has begun to spread throughout the country, and it is recommended that sewage sludge and materials used be selected that are easily available in the local area, resulting in a wide variety of materials being used. Therefore, there was a need to select materials that are rich in nutrients necessary for microbial activity and promote microbial activity, and to design a material blend that would consistently promote aerobic fermentation.

The objective of the present invention is therefore to provide a sewage sludge fermentation raw material that can promote fermentation easily and stably without having to adjust the composition each time depending on the fermentation state.

After extensive research to solve the above-mentioned problems, the inventors discovered that the oil cake generated during vegetable oil refining contains many nutrients that promote the fermentation of sewage sludge. Furthermore, oil cake is sometimes treated with chemicals such as acids during the vegetable oil refining process, and they discovered that when the pH of the oil cake is within a specific range, the fermentation of sewage sludge is promoted. Based on these findings, the inventors discovered that adding oil cake with a specific pH range to sewage sludge in a specific blend ratio stably promotes the fermentation of sewage sludge, which is the target of fermentation, and thus completed the present invention.

That is, the present invention includes sewage sludge and oil cake,
The pH of the oil cake measured by the following method is 5 or more and 9 or less,
The present invention provides a sewage sludge fermentation raw material for aerobic fermentation treatment, which contains 10 to 130 parts by mass of the oil cake per 100 parts by mass of sewage sludge.
<pH measurement method>
A mixture of 1 part by mass of oil cake and 10 parts by mass of water is stirred for 10 minutes, and the pH of the mixture is measured at 23°C.

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 oil cake,
The present invention provides a method for treating sewage sludge, which uses the sewage sludge fermentation raw material containing 10 to 130 parts by mass of oil cake having a pH of 5 to 9 per 100 parts by mass of the sewage sludge.

According to the present invention, aerobic fermentation can be rapidly promoted and sewage sludge can be stably fermented simply by adding a specific amount of a specific material to sewage sludge. Furthermore, in industrial areas such as cement factories and sources of sewage sludge such as sewage treatment plants, it is possible to ferment large quantities of multiple types of sewage sludge, 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 oil cake 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, sewage sludge generated in sewage treatment facilities, and septic tank sludge, which can be used alone or in combination. Sewage sludge may be used as is as undigested sludge, or a self-fermented product of sewage sludge, such as digested sludge, may be used. Digested sludge generally contains fewer nutrients necessary for fermentation than undigested sludge, and therefore, the effects of the present invention are more pronounced when digested sludge is used as the target of the treatment of the present invention.
The 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 oil cake used in this invention is the residue left over after oil has been extracted from agricultural crops and other sources. Oil cake contains crude fat and crude protein, which can serve as a nutrient source for aerobic microorganisms. Therefore, it has the advantage that the organic matter present in sewage sludge is decomposed by the microorganisms, allowing aerobic fermentation to proceed steadily.

The oil cake used in the present invention is preferably used in an amount of 10 to 130 parts by mass, more preferably 20 to 100 parts by mass, and even more preferably 30 to 80 parts by mass, per 100 parts by mass of sewage sludge. Using 10 parts by mass or more of oil cake has the advantage of providing a sufficient amount of nutrients for active aerobic fermentation of the sewage sludge, allowing aerobic fermentation to proceed stably. Using 130 parts by mass or less of oil cake has the advantage of significantly suppressing pH changes in the entire fermentation system due to the pH buffering action of the sewage sludge, and providing a sufficient amount of nutrients for active aerobic fermentation of the sewage sludge.

The above content is measured in dried oil cake. "Dry" means that the moisture content of the oil cake is 10% by mass or less, more preferably 7.5% by mass or less, and even more preferably 5% by mass or less. The moisture content of the oil cake can be adjusted as appropriate, for example, by drying the oil cake using a common method such as forced drying in a hot air convection dryer or natural drying in the sun. The moisture content of the oil cake is measured based on the weight loss after drying at 135°C for 2 hours, in accordance with the Feed Analysis Method.

The inventors speculate that the reason why aerobic fermentation proceeds efficiently when a specific amount of oil cake with a pH within a specific range is added to the sewage sludge fermentation feedstock of the present invention is as follows: When sewage sludge is fermented by microorganisms, acidic substances are produced, which lower the pH of the sewage sludge to the acidic side. When the pH drops, the activity of the microorganisms in the sewage sludge stagnates, inhibiting fermentation. In contrast, the present invention uses a specified amount of oil cake, which has a pH similar to that of the sewage sludge (pH 5 to 9), as a nutrient source. The inventors speculate that the pH is less likely to drop due to the pH buffering effect of the sewage sludge, and the supply of nutrients promotes fermentation. If the pH of the oil cake is 5 or higher, the pH buffering effect of the sewage sludge will be significant in suppressing a decrease in the pH of the entire fermentation system, and if the pH of the oil cake is 9 or lower, there is the advantage that the pH of the entire fermentation system is maintained in a range suitable for the activity of aerobic microorganisms. Therefore, the pH of the oil cake is preferably 5 or higher and 9 or lower, more preferably 5.5 or higher and 8.0 or lower, and even more preferably 5.7 or higher and 7.0 or lower.

The pH of oil cake can be obtained by mixing 1 part by mass of the oil cake to be measured with 10 parts by mass of water, stirring the mixture for 10 minutes, and measuring the pH of the mixture at 23°C.

The oil cake can be the residue left after extracting oil from plant seeds, and examples include rapeseed oil cake, soybean oil cake, sesame oil cake, cottonseed oil cake, castor oil cake, linseed oil cake, sunflower oil cake, and safflower oil cake. These oil cakes may be used alone or in combination of two or more. Of these, it is preferable to use at least one type from the group consisting of rapeseed oil cake, soybean oil cake, sesame oil cake, and cottonseed oil cake, in order to further enhance the effects described above.

The oil cake used in the present invention preferably has an ignition loss of 90% by mass or more, and more preferably 93% by mass or more. The ignition loss of oil cake reflects the amount of organic components contained in the oil cake. Using oil cake with such an ignition loss can further promote aerobic fermentation, enabling efficient fermentation treatment of sewage sludge. The ignition loss of oil cake is measured according to JIS R5202:2015, "Methods for Chemical Analysis of Cement."

The oil cake used in the present invention preferably has a solid calorific value of 4000 kcal/kg or more, more preferably 4300 kcal/kg or more, and even more preferably 4500 kcal/kg or more. This solid calorific value is the total calorific value of all types of oil cake used as the sewage sludge fermentation feedstock. Generally, a high solid calorific value indicates that the oil cake contains a large amount of organic matter, which is one of the nutrients useful for the progression of aerobic fermentation. Therefore, by using oil cake with such a calorific value, aerobic fermentation can be further promoted, allowing for efficient fermentation of sewage sludge.

The sewage sludge fermentation raw material of the present invention may consist solely of sewage sludge and oil cake. Alternatively, it may also preferably contain, in addition to these, other materials in addition to sewage sludge and oil cake (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 reduce the moisture content of sewage sludge, improve the breathability of the sewage sludge fermentation raw material during fermentation, and provide a wide variety of microorganisms that contribute to aerobic fermentation.

In particular, it is preferable that the sewage sludge fermentation raw material further contains an aeration aid as a material for improving the aeration of the sewage sludge fermentation raw material and promoting aerobic fermentation of the sewage sludge. By including an aeration aid, the aeration of the sewage sludge fermentation raw material can be easily improved regardless of the state of consolidation of the sewage sludge fermentation raw material, allowing for stable aerobic fermentation of the sewage sludge. In particular, when aerobic fermentation is performed using a vertical fermenter, as described below, for example, the sewage sludge in the fermenter can become consolidated due to the accumulation of sewage sludge fermentation raw material, making it difficult for the aerobic fermentation of the sewage sludge to proceed. However, by including an aeration aid, excessive consolidation can be further suppressed while further ensuring aeration, which is advantageous in that it allows for stable and effective aerobic fermentation of the sewage sludge to proceed.

Examples of ventilation aids include organic ventilation aids such as rice straw, rice husks, plants, and dried or crushed materials thereof, as well as inorganic ventilation aids such as perlite, zeolite, diatomaceous earth, and coal ash such as fly ash. These materials can be used alone or in combination.

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 reference masses of the sewage sludge and aeration aid are both measured in their wet state. When multiple types of aeration aids are contained, the content of the aeration aids is based on the total amount. By keeping the content within this range, it is possible to ensure uniform aeration while preventing the sewage sludge fermentation raw material from becoming excessively compacted over a long period from the start to the end of fermentation, allowing the aerobic fermentation of the sewage sludge to proceed stably and effectively.

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 90% by mass, and more preferably 40% to 85% 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 A1203 "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 dried oil cake, or by adding water to the raw materials or sewage sludge fermentation raw material.

The sewage sludge fermentation feedstock of the present invention can be produced as a mixture or sediment by, for example, mixing or heaping sewage sludge and oil cake with various materials as needed. More specifically, examples include a method of obtaining sewage sludge fermentation feedstock by mixing sewage sludge and oil cake with various materials as needed, or a method of obtaining sewage sludge fermentation feedstock as a sediment by heaping 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 heaped alternately or randomly in the vessel, and then mixing the heap as is or in addition to the heap in a vessel such as a fermenter to obtain the 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 rate each time depending on the fermentation state. In other words, a method for fermenting sewage sludge preferably includes a step of supplying sewage sludge, oil cake, 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 mixture; 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.

Figure 1 shows one embodiment of a sealed vertical fermenter suitable for use in fermenting the sewage sludge fermentation material of the present invention. The sealed vertical fermenter 10 extends vertically relative to the installation surface and has a cylindrical tank section 20 capable of containing sewage sludge, oil cake, and, if necessary, a mixture of other materials. The tank section 20 is equipped with an inlet 30 at its top, through which the mixture can be introduced into the tank section 20, and an outlet 40 at its bottom, through which the aerobically fermented sewage sludge fermentation material can be discharged from the tank section 20. Both the inlet 30 and the outlet 40 are equipped with detachable or openable lids (not shown), and the tank section 20 of the fermenter 10 can be sealed by attaching the lids 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 oil cake to treat the sewage sludge. The above-mentioned explanations apply appropriately to the sewage sludge and oil cake 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 the following examples. The scope of the present invention is not limited to these examples. To measure the pH of the oil cakes shown below, 1 part by mass of the oil cake to be measured was mixed with 10 parts by mass of water, and the mixture was stirred for 10 minutes using a magnetic stirrer (600 rpm, manufactured by Advantec Toyo Co., Ltd.). The resulting stirred solution was measured at 23°C using a pH meter (MM-60R multi-water quality meter, manufactured by DKK-TOA Corporation). The moisture content of the sewage sludge and sewage sludge fermentation raw material 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). Furthermore, the calorific values shown below indicate the calorific value of the solid content.

[Examples 1 to 4 and Comparative Examples 1 and 2]
[Preparation of sewage sludge fermentation raw material]
The sewage sludge and oil cake shown in (1) to (6) below were mixed in the content ratios shown in Table 1 below to prepare sewage sludge fermentation raw materials with moisture contents of 65.2% by mass to 66.8% by mass.

(1) Sewage sludge: digested sludge obtained from a sewage treatment plant (moisture content: 84.4% by mass)
(2) Rapeseed oil cake: Rapeseed oil extraction residue (pH 5.8, water content 8.0% by mass, loss on ignition 93.6% by mass, calorific value 4821 kcal/kg)
(3) Soybean oil cake: soybean oil extraction residue (pH 6.7, water content 6.9% by mass, loss on ignition 93.8% by mass, calorific value 4520 kcal/kg)
(4) Sesame oil cake: sesame oil extraction residue (pH 5.9, water content 1.5% by mass, loss on ignition 92.1% by mass, calorific value 5550 kcal/kg)
(5) Cottonseed oil cake: cottonseed oil extraction residue (pH 6.3, water content 6.2% by mass, loss on ignition 94.0% by mass, calorific value 4450 kcal/kg)
(6) Corn oil cake: corn oil extraction residue (pH 4.0, water content 1.4% by mass, loss on ignition 92.6% by mass, calorific value 4520 kcal/kg)

[Aerobic fermentation test]
The sewage sludge fermentation raw materials of the Examples and Comparative Examples were subjected to aerobic fermentation treatment, and the progress of the aerobic fermentation of the sewage sludge was evaluated as a change in the temperature 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 sewage sludge fermentation raw material of each Example and Comparative Example was placed in each plastic beaker to prepare the samples.

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 8 days in a room set at 20 °C.
The progress of aerobic fermentation was evaluated based on the maximum temperature measured. A higher maximum temperature indicates a more stable aerobic fermentation of the sewage sludge. From the perspective of stable aerobic fermentation of the sewage sludge, a sample was deemed to have passed if its peak temperature was 40°C or higher and reached 40°C within 48 hours. The results are shown in Table 1 below.

As shown in Table 1, the sewage sludge fermentation feedstocks of Examples 1 to 4, in which oil cakes with a pH within a specified range were added to the sewage sludge at a specified content, had higher peak exothermic temperatures and took less time to reach 40°C compared to the comparative examples. The reason for this is that rapeseed oil cake, soybean oil cake, sesame oil cake, and cottonseed oil cake have a pH of 5.8 to 6.7, which is close to the pH of sewage sludge, so adding them to sewage sludge did not delay fermentation and the temperature rose to 40°C or higher within two days. On the other hand, the sewage sludge fermentation feedstock of Comparative Example 2, which used corn oil cake with a low pH, reached a peak temperature of 40°C, but it took 55 hours to reach 40°C. The reason for this is thought to be that corn oil cake has a low pH, and when added to the sewage sludge, the pH of the fermentation feedstock became acidic, deviating from the pH suitable for fermentation and causing a delay in fermentation.

[Examples 5 to 9 and Comparative Examples 3 and 4]
[Preparation of sewage sludge fermentation raw material]
The above-mentioned sewage sludge (1) was mixed with the above-mentioned rapeseed oil cake (2) in the content ratios shown in Table 2 below to prepare sewage sludge fermentation raw materials with moisture contents of 46.2 to 83.3% by mass.

[Aerobic fermentation test]
The degree of equilibrium in aerobic fermentation of each sewage sludge fermentation raw material was evaluated using the same methods as in Examples 1 to 4 and Comparative Examples 1 and 2. From the perspective of stably aerobic fermentation treatment of sewage sludge, a test was deemed to pass if the peak temperature was 40°C or higher and reached 40°C within 48 hours. The results are shown in Table 2 below, which also lists the results of Comparative Example 1.

As shown in Table 2, the sewage sludge fermentation raw materials of Examples 5 to 9, in which rapeseed oil cake with a pH within a specified range was added to sewage sludge at a specified content, had a higher peak temperature than the comparative examples and reached 40°C within 48 hours. This is thought to be because mixing the specified amount of rapeseed oil cake with sewage sludge provided a sufficient supply of nutrients necessary for fermentation.

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 (5)

Contains digested sludge and oil cake,
The pH of the oil cake measured by the following method is 5 or more and 9 or less,
A sewage sludge fermentation raw material for aerobic fermentation treatment, comprising 10 parts by mass or more and 130 parts by mass or less of the oil cake per 100 parts by mass of digested sludge.
<pH measurement method>
A mixture of 1 part by mass of oil cake and 10 parts by mass of water is stirred for 10 minutes, and the pH of the mixture is measured at 23°C. The sewage sludge fermentation raw material according to claim 1, wherein the oil cake is one or more selected from the group consisting of rapeseed oil cake, soybean oil cake, sesame oil cake, and cottonseed oil cake. The sewage sludge fermentation raw material according to claim 1 or 2, further comprising an aeration aid. The method comprises a step of aerobically fermenting a sewage sludge fermentation raw material containing digested sludge and oil cake to treat the digested sludge ,
A method for treating sewage sludge , comprising using the sewage sludge fermentation raw material containing 10 to 130 parts by mass of oil cake having a pH of 5 to 9, as measured by the following method , per 100 parts by mass of the digested sludge.
<pH measurement method>
A mixture of 1 part by mass of oil cake and 10 parts by mass of water is stirred for 10 minutes, and the pH of the mixture is measured at 23°C. The treatment method described in claim 4, wherein the sewage sludge fermentation raw material is aerobically fermented in a sealed, vertical fermentation tank.