JP4568322B2 - Treatment method of activated surplus sludge - Google Patents

Description

The present invention, sewage treatment plants, night soil treatment plants, or relates like from various production plants to process how active excess sludge discharged by the biological treatment.

  The activated surplus sludge discharged in various wastewater treatment processes is organic surplus sludge contained in organic wastewater discharged by biological treatment. Generally, the water content is reduced by dehydration and recycled as fertilizer. Or after being reduced by incineration, landfill processing is performed as industrial waste.

  However, the activated surplus sludge has a high water content of about 80% by weight and a small solid content, so that the entire capacity increases. For this reason, the transportation cost to a processing place or the fuel cost for incineration was high. Accordingly, it has been strongly desired to reduce the processing cost by reducing the moisture content of the activated surplus sludge or to effectively use the land for disposal that is decreasing.

Examples of techniques aimed at reducing the amount of activated surplus sludge include the following.
Patent Document 1 states that excess sludge is extracted from a biological oxidation tank, transferred to a liquefaction container, adjusted to pH 8 to 14, and heated at 110 ° C. to 250 ° C. for 10 seconds to 3 hours to be decomposed by microorganisms. After being liquefied, the treated sludge is adjusted to pH 5 to 8 with a neutralizer and returned to the bio-oxidation tank for biodegradation again.

  In Patent Document 2, before surplus sludge is biologically treated, first, acid is added to sludge and the viscosity is reduced by heat treatment, and then either or both of proteolytic enzyme and cell wall degrading enzyme are hydrolyzed. It is added as an enzyme to solubilize excess sludge and then returned to the biological treatment tank for biological treatment.

In Patent Document 3, activated surplus sludge generated by biological treatment of wastewater is physically solubilized by ultrasonic treatment in an ultrasonic treatment tank to increase dispersibility and facilitate acid fermentation, and then sludge is subjected to acid fermentation. The acid fermentation is efficiently carried out in a tank to perform solubilization by biological reaction, and this solubilized processed product is returned to the activated surplus sludge processing tank through an acid fermentation processed product return line.
JP 2003-245893 A JP 2004-41925 A Japanese Patent Laid-Open No. 2004-321883

  However, although the techniques disclosed in these documents are intended for weight reduction, in addition to the fact that the process is actually complicated, the efficiency of the processing is lacking and it is difficult to reduce the processing cost. It was.

  For example, in patent document 1, after performing the process which heats excess sludge and liquefies it in the state which can be decomposed | disassembled by microorganisms, it returns to a bio-oxidation tank again and weight reduction is performed by microbial treatment. Depends on sludge biological treatment reaction. Therefore, the process of transferring excess sludge to a separate container for heat treatment is necessary and complicated, and the time required for the activation treatment by microorganisms is governed by the activity of microorganisms, so the treatment time is directly controlled. There was a problem that it was difficult.

  Also in Patent Document 2, as pre-treatment, after acid is added to excess sludge and heat treatment is performed to reduce the viscosity of the sludge, hydrolytic enzyme is added and solubilized. In addition, there is a problem that the surplus sludge must be transferred and processed.

  Patent Document 3 differs from Patent Documents 1 and 2 in that ultrasonic waves are used, but the same is that the activated surplus sludge must be transferred and treated, and there is a problem that it is complicated.

  In Patent Documents 1 to 3, sludge is reduced by dehydration after these steps, and moisture is evaporated by heating as a general method of dehydration. However, since a large amount of microorganisms remain active in the activated surplus sludge after biological treatment and contain a large amount of moisture in the cell, most of the heating energy removes the moisture in the cell. Will be consumed as latent heat. Therefore, the temperature of the activated surplus sludge is difficult to rise and the energy efficiency is very poor.

  As a result, the amount of heat required to evaporate water from the activated surplus sludge becomes larger than the amount of heat (generally 5,000 kcal / kg to 6,000 kcal / kg) of the dried sludge. Accordingly, the utilization of dried sludge is low, and it is only slightly used as a cement raw material, the incineration residue is used as a soil conditioner, or melted and used as a civil engineering or construction material. On the other hand, in the case of incineration, the transportation cost to the incineration plant is high, and if the combustion temperature at the time of incineration is low, there is a strong concern about the environmental impact due to the generation of dioxins. Fuel costs were high.

The present invention has been made based on such a problem, and the water content can be greatly reduced by destroying the microbial cells present in the activated surplus sludge and drawing out the water inside the cells to the outside. and to provide a process how active excess sludge.

The method for treating activated surplus sludge of the present invention is to reduce the amount of activated surplus sludge contained in organic wastewater discharged by biological treatment, and the activated surplus sludge having a water content of 94% by weight or more, It includes a steam injection process in which steam is directly injected and heat treatment is performed, and the activated surplus sludge contains spore-forming microorganisms that form spores, and in the steam injection process, the spore-forming microorganisms determine the average temperature of the activated surplus sludge. The temperature is 30 ° C. lower than the spore formation temperature, and 20 kg or more of water vapor is injected into 1 m ^{3 of} activated surplus sludge.

According to the process how the active excess sludge of the present invention, the active excess sludge moisture content is more than 94 wt% state, since to perform the heat treatment elaborate Spray steam directly, activity by crowded spouted water vapor The surplus sludge can be convected to bring more activated surplus sludge and steam into contact with each other, microbial cells contained in the activated surplus sludge can be destroyed, and the moisture in the cells can be taken out. In addition, heating with water vapor causes biopolymers such as proteins and nucleic acids that have flowed out from the microbial population and the microbial cells that constitute the microbial population to thermally denature and function as a flocculant, so that the activated surplus sludge can be easily solid-liquid. Can be separated. Therefore, it is possible to easily reduce the water content while efficiently collecting the solid content of the activated surplus sludge.

  In particular, in the steam injection process, if the average temperature of the activated surplus sludge is made lower than the spore formation temperature at which the spore-forming microorganisms form spores, the formation of spores can be prevented, and the microbial cells are more effective. Can be destroyed.

Further, in the water vapor injection process, if 20 kg or more of water vapor is injected into 1 m ^{3 of} activated surplus sludge, or the water vapor pressure injected into the activated excess sludge is 9.8 N / cm ² or more. For example, activated surplus sludge and water vapor can be brought into contact with each other more effectively to destroy microbial cells.

  Furthermore, if the average temperature of the activated surplus sludge is 30 ° C. or more and 85 ° C. or less in the steam injection step, the water content can be further reduced.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, since the processing method of the activated surplus sludge which concerns on this Embodiment can be used also as a manufacturing method of solid fuel, it demonstrates together below.

  FIG. 1 shows the steps of a method for treating activated surplus sludge and a method for producing solid fuel according to an embodiment of the present invention, and FIG. 2 shows the process of activated surplus sludge according to an embodiment of the present invention. The structure of the apparatus used for the processing method and the manufacturing method of solid fuel is represented.

  In this activated surplus sludge treatment method and solid fuel production method, first, for example, organic wastewater that has been discharged after being subjected to microbial activation treatment in various factories such as sewage treatment plants, human waste treatment plants, chemical factories or food factories. W is once accumulated and stored in the biological treatment tank 1 (accumulated storage step; step S110). Inside the biological treatment tank 1, biological treatment is still in progress.

  Next, if necessary, a predetermined amount of organic waste water W is transferred from the biological treatment tank 1 to the precipitation tank 2, and solid-liquid separation is performed by precipitation separation by standing for a predetermined time (solid-liquid separation step; step S120). . Thereby, the activated surplus sludge S contained in the organic waste water W is precipitated. In addition, although precipitation here is natural precipitation, you may make it accelerate | stimulate precipitation using a suitable flocculant if needed.

  Subsequently, the activated surplus sludge S precipitated in the lower part of the settling tank 2 is transferred to the heat treatment tank 3. The water content of the activated surplus sludge S at this time is usually 90% by weight or more, and the active microorganisms account for 80% by weight or more. In addition, the moisture content of the activated surplus sludge S in this specification is calculated | required by the drying loss method. Specifically, the moisture content meter can be obtained by drying and solidifying the sample by infrared irradiation and obtaining the moisture content from the mass change due to evaporation of the contained moisture.

  The heat treatment tank 3 is not limited to this, for example, has a cylindrical shape having a capacity of about 100 t, and is intermittently or continuously transferred from the settling tank 2 in accordance with its processing capacity. The activated surplus sludge S is stored. The transfer of the activated surplus sludge S is performed, for example, in a batch system (batch system) from the upper part of the heat treatment tank 3. At the bottom of the heat treatment tank 3, an ejection pipe 4 for directly ejecting the water vapor M into the activated surplus sludge S is disposed.

  A large number of jet outlets 41 for jetting water vapor M are formed in the jet pipe 4. Further, a steam supply pipe 5 that supplies water vapor M from an external supply source such as a once-through boiler (not shown) is connected to the ejection pipe line 4 via an on-off valve 51. A liquid temperature sensor 31 is disposed inside the heat treatment tank 3, and the water vapor M to be supplied can be adjusted by adjusting the on-off valve 51 based on information from the liquid temperature sensor 31. preferable. Moreover, you may make it promote the convection of the activated surplus sludge S by providing the stirrer which is not shown in the inside of the heat processing tank 3 as needed.

  Using such a heat treatment tank 3, water vapor M is directly injected into the activated surplus sludge S stored inside the heat treatment tank 3 through the outlet 41 of the ejection pipe 4, and the activated surplus sludge S. Is heat-treated (steam injection step; step S130). At that time, the moisture content of the activated surplus sludge S is set to 94% by weight or more. For example, when the moisture content of the activated surplus sludge S stored in the heat treatment tank 3 is 94% by weight or more, the steam M is injected as it is. When the water content of the activated surplus sludge S is lower than 94% by weight, for example, water is added to make the water content 94% by weight or more, and then water vapor M is injected or water vapor M is injected. The water content is preferably 94% by weight or more. This is because the activated surplus sludge S is convected by injecting the steam M to bring the activated surplus sludge S into contact with the steam M more. The water content of the activated surplus sludge S may be high, that is, it may be less than 100% by weight.

  Due to the impact of the water vapor M, the microbial cells contained in the activated surplus sludge S are destroyed, and the moisture in the cells flows out to the outside. In addition, by heating with water vapor M, biopolymers such as proteins and nucleic acids flowing out from the microbial population and microbial cells constituting the microbial population are thermally denatured, functioning as an aggregating agent, and aggregating the solid content of the activated surplus sludge S. .

  When the activated surplus sludge S contains spore-forming microorganisms that form spores, the amount of water vapor M is adjusted so that the average temperature of the activated surplus sludge S is lower than the spore formation temperature at which the spore-forming microorganisms form spores. It is preferable to adjust. This is because microbial cells are less likely to be destroyed when spores are formed. Examples of spore-forming microorganisms include bacteria belonging to the genus Bacillus.

The amount of water vapor injected into the activated surplus sludge S is preferably 20 kg or more with respect to 1 m ^{3 of} the activated surplus sludge. That is, it is preferable to inject 20 kg of water as water vapor to 1 m ^{3 of} activated surplus sludge. This is because the activated surplus sludge S and the water vapor M can be brought into contact with each other to destroy the microbial cells more effectively. The amount of water vapor may be large, but if it is too large, it becomes difficult to control the temperature of the activated surplus sludge S, and it takes time, so 90 kg or less is preferable with respect to 1 m ^{3 of} the activated surplus sludge, and if it is 40 kg or more and 50 kg or less. More preferred.

The water vapor pressure injected into the activated surplus sludge S is preferably 9.8 N / cm ² (9.8 × 10 ⁴ Pa) or more, and 24.5 N / cm ² (24.5 × 10 ⁴ Pa) or more. It is more preferable. This is because the activated surplus sludge S and the water vapor M can be brought into contact with each other to destroy the microbial cells more effectively. The water vapor pressure may be high, but if it is too high, the temperature of the activated surplus sludge S rises quickly, making it difficult to control the temperature. For example, the water pressure is set to 49 N / cm ² (49 × 10 ⁴ Pa) or less. preferable.

  The average temperature of the activated surplus sludge S is preferably 30 ° C or higher and 85 ° C or lower. Biopolymers such as proteins and nucleic acids that have flowed out from the microbial population and the microbial cells constituting the microbial population are partially heated and thermally denatured by contact with the water vapor M, so that the average temperature does not need to be increased. The average temperature of the activated surplus sludge S is 30 ° C. or more and 70 ° C. or less, more preferably 30 ° C. or more and 60 ° C. or less, and further 30 ° C. or more and 50 ° C. It is more preferable that the temperature is lower than ° C. This is because the moisture content can be further reduced.

  In addition, the heat treatment time for injecting the water vapor M into the activated surplus sludge S is preferably about several seconds to about 20 hours, for example. This is because if the water vapor M can be sufficiently brought into contact with the activated surplus sludge S, the effect can be obtained even in a short time, and there is no particular problem even if it is carried out for a long time.

  After performing this water vapor injection process, water is removed from the activated surplus sludge S to reduce the water content (moisture removal process; step S140). For example, first, the activated surplus sludge S is transferred to a belt press type dehydrating device 6a equipped with a compression filtration means and dehydrated by solid-liquid separation (dehydration step; step S141). The activated surplus sludge S is compressed and filtered by the dewatering device 6a, but if necessary, an inorganic or polymer flocculant may be added to improve the efficiency of solid-liquid separation. Further, if necessary, the activated surplus sludge S that has been subjected to the compression filtration may be transferred to a dewatering device 6b such as a roller type of an abutting contact type and further dewatered.

  Next, for example, the dehydrated activated surplus sludge S is dried (drying step; step S142). In the drying step, for example, the activated surplus sludge S may be left at room temperature (naturally left) without being actively heated as it is, and dried. At that time, the activated surplus sludge S may be subdivided with various cross-sections such as small particles or strings to increase the surface area per volume. If it subdivides, the contact area with air will increase and the efficiency of natural radiation will increase, which is preferable.

  Further, the activated surplus sludge S may not be left alone, but may be dried while actively circulating air. It is preferable that air is circulated positively because it can be dried more efficiently.

  Furthermore, the activated surplus sludge S may be dried using a drier such as the drum rotary drier 7 in order to bring the water content as close to “zero” as possible. Air may be forced to flow through the drum of the drum rotary dryer 7, and dry air or hot air may be used. When heating, a temperature atmosphere of 10 ° C. or higher and 120 ° C. or lower is preferable, and a temperature atmosphere of 20 ° C. or higher and 40 ° C. or lower is more preferable. Thereby, the solid fuel which concerns on this Embodiment is obtained.

  As described above, according to the present embodiment, since the steam M is directly injected into the activated surplus sludge S having a moisture content of 94% by weight or more, the heat treatment is performed. The surplus sludge S can be convected to bring more activated surplus sludge and water vapor into contact with each other, microbial cells can be destroyed, and moisture inside the cells can be taken out. In addition, when heated with water vapor, biopolymers such as proteins and nucleic acids that have flowed out from the microbial population and the microbial cells that constitute the microbial population are thermally denatured and function as a flocculant, so that the activated surplus sludge S can be easily solidified. Liquid separation can be performed. Therefore, the moisture content can be easily reduced while efficiently collecting the solid content of the activated surplus sludge S.

  Therefore, the activated surplus sludge S can be easily converted into fuel, and industrial waste can be reused as solid fuel.

  In particular, in the steam spraying step (step S130), if the average temperature of the activated surplus sludge S is made lower than the spore formation temperature at which the spore-forming microorganisms form spores, the formation of spores can be prevented, Microbial cells can be destroyed more effectively.

Further, in the water vapor injection step (step S130), if 20 kg or more of water vapor is injected into 1 m ³ of the activated surplus sludge, or the water vapor pressure injected into the activated excess sludge S is 9.8 N / cm ² or more. By doing so, the activated surplus sludge S and the water vapor M can be brought into contact with each other more effectively to destroy the microbial cells.

  Furthermore, in the steam spraying step (step S130), the average temperature of the activated surplus sludge S is 30 ° C. or more and 85 ° C. or less, more preferably 30 ° C. or more and 70 ° C. or less, further 30 ° C. or more and 60 ° C. or less, and further 30 ° C. If the temperature is lower than 50 ° C., the moisture content can be further reduced.

  Furthermore, it demonstrates concretely based on an Example.

Example 1
As described in the above embodiment, heat treatment was performed by directly injecting steam M into activated surplus sludge S having a water content of 98% by weight or more separated from the organic waste water W by precipitation. At that time, the steam M was set at a set gauge pressure of 9.8 N / cm ² , the steam amount was set to 50 kg per 1 ton of excess sludge, and the average temperature of the activated surplus sludge S was set to about 60 ° C.

  Next, the activated surplus sludge S subjected to the steam spraying step was dehydrated by a belt press type dehydrator 6a. The dehydrator 6a used has the ability to compress and filter the activated surplus sludge S introduced at 7.5 t / h and a filter cloth width of 1.5 m at a belt speed of 0.45 m / min. As a result, the activated surplus sludge S was compressed and filtered at a rate of 50 cm per minute and formed into a plate having a thickness of about 22 mm. The water content of the activated surplus sludge S immediately after the dehydration treatment was about 80% by weight. Subsequently, when the dehydrated activated surplus sludge S was naturally left in a plate shape and dried, the water content of the activated surplus sludge S decreased from 63 wt% to 68 wt% after about 6 hours, and about 40 wt%. After a lapse of time, it decreased from 20% by weight to 25% by weight.

  Further, the activated surplus sludge S dehydrated by the dewatering device 6a was transferred to a face-contact type roller-type dewatering device 6b and processed into a thin plate shape of 1 mm to 3 mm with a roller having a peripheral speed of 10 m / min. After that, when allowed to stand for about 30 minutes, the water content of the activated surplus sludge S was reduced to 15% by weight or less.

Furthermore, the activated surplus sludge S dehydrated by the dehydrator 6 b was dried for 10 minutes using the rotary drum dryer 7. The specifications of the rotary drum dryer 7 used were as follows: drum diameter φ: 0.38 m, drum length: 2.42 m, rotating drum rotation speed: 10 rpm, blowing air temperature: 25 ° C., aeration air volume: 30 (m ³ / Min). The moisture content of the activated surplus sludge S after drying was 5% by weight or less.

  On the other hand, when the activated surplus sludge S separated from the organic waste water W by precipitation was dehydrated by the dehydrator 6a without performing the steam injection step, the water content of the activated surplus sludge S was 82% by weight. It was. Further, even when the activated surplus sludge S dehydrated by the dewatering device 6a was dehydrated by the dewatering device 6b and then dried by the rotary drum dryer 7, the water content of the activated surplus sludge S was 81.5% by weight.

  That is, it was found that the moisture content of the activated surplus sludge S can be significantly reduced by performing the steam spraying step. Moreover, it turned out that after dehydrating the activated surplus sludge S, the water content can be reduced by natural drying.

(Examples 2-1 and 2-2)
The activated surplus sludge S was placed in a heat treatment tank provided with a water vapor M outlet near the bottom, and the heat treatment was performed by directly injecting the water vapor M into the activated surplus sludge S. In Example 2-1, activated surplus sludge S having a water content of 96.02% by weight before injecting water vapor M was used, the water vapor pressure was 9.8 N / cm ² , and the amount of water vapor M injected was the active surplus sludge. The average temperature of the activated surplus sludge S rose to 50 ° C. with respect to 1 m ³ . In Example 2-2, activated surplus sludge S having a water content of 98.52% by weight before injecting water vapor M is used, the water vapor pressure is 24.5 N / cm ² , and the amount of water vapor M injected is active. 86 kg of surplus sludge 1 m ^{3 was used} , and the average temperature of the activated surplus sludge S increased to 60 ° C.

  Next, the activated surplus sludge S that had been subjected to the steam spraying step was dehydrated by a screw press type dehydrator. When the moisture content of the activated surplus sludge S immediately after the dehydration treatment was examined, Example 2-1 was 81.17% by weight and Example 2-2 was 80.91% by weight.

  Then, about Example 2-1, when the dehydrated activated surplus sludge S was sun-dried at a temperature of 30 ° C. for 3 hours, the water content was reduced to 46.87% by weight. Furthermore, after pulverizing the activated surplus sludge S that had been sun-dried into Example 2-1, it was sun-dried at a temperature of 30 ° C. for 3 hours, and the water content decreased to 12.64% by weight. Moreover, about Example 2-2, when the dehydrated activated surplus sludge S was sun-dried for 4 hours at the temperature of 30 degreeC, the moisture content fell to 63.00 weight%. Next, for Example 2-2, after the sun-dried activated surplus sludge S was finely crushed and granulated, it was sun-dried at a temperature of 30 ° C. for 3 hours. As a result, the water content decreased to 13.83 wt%. Furthermore, about Example 2-2, when the dehydrated activated surplus sludge S was left to stand for 14 hours in a room with an air temperature of 28 ° C. and a humidity of 35% and dried, the water content decreased to 33.30%. The obtained results are shown in Table 1. In addition, about the activated surplus sludge S of Example 2-1 which reduced the moisture content to 12.64% by weight and the activated surplus sludge S of Example 2-2 which reduced the moisture content to 13.83% by weight, ignition was performed. When the test was conducted, it was confirmed that it easily ignites and burns.

  That is, it was found that if the steam injection step is performed, the moisture content of the activated surplus sludge S can be sufficiently reduced by natural drying, and the dried product can be used as fuel.

  Further, the activated surplus sludge S before and after the steam injection was observed with a microscope. FIG. 3A is a micrograph of the activated surplus sludge S before the steam injection, and FIG. 3B is a micrograph of the activated surplus sludge S after the steam injection. Microbial masses such as filamentous microorganisms and large microorganisms are seen before the water vapor injection in FIG. 3A, whereas the masses of microorganisms have generally disappeared after the water vapor injection in FIG. 3B. In other words, it was found that microbial cells were destroyed by steam injection. In addition, in the activated surplus sludge S after injecting water vapor in FIG. 3B, it was observed that the broken microbial cells were entangled with the proteins and nucleic acids that were denatured by heat. That is, it was found that the contents that flowed out of the microbial cells by heating were denatured and functioned as a flocculant.

(Examples 3-1, 3-2, 4-1, 4-2)
The activated surplus sludge S was put in a heat treatment tank provided with a water vapor M outlet near the bottom, and the heat treatment was performed by directly injecting the water vapor M into the activated surplus sludge S. In Examples 3-1 and 3-2, activated surplus sludge S having a water content of 99.62% by weight before injecting water vapor M is used, and in Examples 4-1 and 4-2, water vapor M is injected. The activated surplus sludge S having a previous water content of 99% by weight or more was used. The water vapor pressure was 9.8 N / cm ² for all, and the average temperature of the activated surplus sludge S was 40 ° C. in Example 3-1, 50 ° C. in Example 3-2, and in Example 4-1. It was carried out until 60 ° C. and 70 ° C. in Example 4-2.

  Subsequently, after leaving the activated surplus sludge S which performed the water vapor | steam injection process, it gravity-filtered with the filter cloth. In Examples 3-1 and 3-2, the standing time was 60 minutes and the filtration time was 40 minutes. In Examples 4-1 and 4-2, the standing time was 18 hours and the filtration time was 30 minutes. Immediately after filtration, the water content of the activated surplus sludge S separated on the filter cloth was examined. As a result, Example 3-1 was 95.52% by weight, Example 3-2 was 95.87% by weight, and Example. 4-1 was 94.80% by weight, and Example 4-2 was 95.31% by weight.

  Then, about each Example, the activated surplus sludge S isolate | separated by filtration was left as it was in a room | chamber and dried naturally, and the change of the moisture content was investigated. In Example 3-1, it decreased to 60.22% by weight after 24 hours and to 59.58% by weight after 48 hours, and in Example 3-2, 75.69% by weight after 24 hours and after 48 hours. Decreased to 62.06% by weight. In Example 4-1, it decreased to 87.24% by weight after 2 hours, and in Example 4-2, it decreased to 87.80% by weight after 2 hours. The obtained results are shown in Tables 2 and 3.

  In addition, as Comparative Example 3-1 with respect to Examples 3-1 and 3-2, except that heat treatment was not performed, the experiment was performed in the same manner as in Examples 3-1 and 3-2, and activated excess sludge. The moisture content of S was examined. As Comparative Examples 3-2 and 3-3, the experiment was performed in the same manner as in Examples 3-1 and 3-2 except that the activated surplus sludge S was heated by heat exchange instead of steam injection. The water content of the activated surplus sludge S was examined. At that time, in Comparative Example 3-2, heating was performed until the average temperature of the activated surplus sludge S was 40 ° C, and in Comparative Example 3-3, heating was performed until the average temperature of the activated surplus sludge S was 50 ° C. The obtained results are shown in Table 2.

  Further, as Comparative Example 4-1 with respect to Examples 4-1 and 4-2, the experiment was performed in the same manner as in Examples 4-1 and 4-2, except that heat treatment was not performed, and the activated surplus sludge was used. The moisture content of S was examined. As Comparative Example 4-2, except that it was heated until the average temperature of the activated surplus sludge S was changed to 60 ° C. by heat exchange instead of steam injection, the others were the same as in Examples 4-1 and 4-2. Experiments were conducted to examine the moisture content of the activated surplus sludge S. The obtained results are shown in Table 3.

  As shown in Tables 2 and 3, according to Examples 3-1, 3-2, 4-1, and 4-2 in which steam was blown in, Comparative Examples 3-1 and 4 without heat treatment were performed. Compared to -1, it was found that the moisture content was significantly reduced by natural drying. On the other hand, in Comparative Examples 3-2 and 4-2 heated by heat exchange, the moisture content was lower than Comparative Examples 3-1 and 4-1, which were not subjected to the heat treatment, but compared with the present example. And the degree was small. Moreover, in Comparative Example 3-2 heated by heat exchange, although the water content after 24 hours was lower than that of Comparative Example 3-1, in which heat treatment was not performed, it was high after 48 hours.

  That is, it has been found that if heat treatment is performed by injecting water vapor, microbial cells can be destroyed and moisture in the cells can be taken out, and the water content can be further reduced.

(Example 5)
Activated surplus sludge S having a moisture content of 94.10% by weight is placed in a heat treatment tank provided with a water vapor M outlet near the bottom, and steam M is directly injected into the activated surplus sludge S for heat treatment. It was. The water vapor pressure was 9.8 N / cm ² and the water vapor was blown in until the average temperature of the activated surplus sludge S reached 50 ° C. After that, it was left as it was in the room and dried naturally, and the change in water content was examined.

  As Comparative Example 5-1 with respect to Example 5, the same activated surplus sludge S as in Example 5 was naturally dried in the same manner as in Example 5 without performing the heat treatment by injecting water vapor, and the change in moisture content was examined. It was.

  As Comparative Example 5-2, the activated surplus sludge S having a moisture content of 87.17% by weight was naturally dried in the same manner as in Example 5 without performing the heat treatment by steam injection, and the change in the moisture content was examined. .

As Comparative Example 5-3, after the heat treatment was performed by directly injecting water vapor M into the activated surplus sludge S in the same manner as in Example 5 for the same activated surplus sludge S as in Comparative Example 5-2, Then, it was naturally dried and the change in water content was examined. As Comparative Example 5-4, the same activated surplus sludge S as Comparative Example 5-2 was subjected to heat treatment by directly spraying water vapor M on the surface, and then naturally dried in the same manner as in Example 5 to obtain a moisture content. We examined changes. In Comparative Examples 5-3 and 5-4, the water vapor pressure was 9.8 N / cm ² and the average temperature of the activated surplus sludge S was heated to 50 ° C.

Further, as Comparative Example 5-5, an experiment was performed in the same manner as Comparative Example 5-3 except that the steam M was blown in for a longer time than Comparative Example 5-3, and the change in moisture content was examined. . As Comparative Example 5-6, an experiment was performed in the same manner as Comparative Example 5-4 except that the surface of the water vapor M was sprayed for a longer time than Comparative Example 5-4, and the change in the moisture content was examined. . In Comparative Examples 5-5 and 5-6, the water vapor pressure was 9.8 N / cm ² and the average temperature of the activated surplus sludge S was heated to 60 ° C. Table 4 shows the obtained results. In Table 4, the numerical values described in the column immediately after the treatment are the moisture content immediately after the heat treatment and before natural drying in Example 5 and Comparative Examples 5-3 to 5-6, and Comparative Examples 5-1 and 5 -2 is the moisture content before natural drying.

  As shown in Table 4, according to Example 5 in which water vapor M was blown into activated surplus sludge S having a moisture content of 94% by weight or more, compared to Comparative Example 5-1 in which no heat treatment was performed, It was found that the moisture content was significantly reduced by natural drying. On the other hand, in Comparative Examples 5-3 and 5-5 in which water vapor M was sprayed into the activated surplus sludge S having a moisture content of less than 94 weight percent, the decrease in the moisture content was small and no comparison was performed. Even when compared with Example 5-2, the effect of injecting water vapor M was not observed. Moreover, also in Comparative Examples 5-4 and 5-6 in which water vapor M was sprayed on the activated surplus sludge S having a water content of less than 94 weight percent, the decrease in the water content was also small.

  This is because, if the water content of the activated surplus sludge S is low, even if the steam M is injected into the activated surplus sludge S, stirring and convection due to the injection of the steam M do not occur sufficiently, and the microbial cells can be sufficiently destroyed. This seems to be because there was not. That is, it was found that the moisture content of the activated surplus sludge S when the steam M was sprayed was preferably 94% by weight or more.

(Examples 6-1 to 6-4)
As Example 6-1, activated surplus sludge S having a water content of 98.61 wt% was placed in a heat treatment tank provided with a water vapor M outlet near the bottom, and the water vapor M was directly put into the activated surplus sludge S. The heat treatment was carried out by spraying. The water vapor pressure was 24.5 N / cm ² , the amount of water vapor M injected was 21 kg with respect to 1 m ^{3 of} activated surplus sludge, and the average temperature of the activated surplus sludge S was increased to 30 ° C.

Subsequently, the activated surplus sludge S that had been subjected to the steam spraying step was dehydrated by a belt press type dehydrator to form a dehydrated cake having a thickness of about 8 mm. When the moisture content of the activated surplus sludge S immediately after the dehydration treatment was examined, it was 78.20% by weight. The total weight of the activated surplus sludge S immediately after the dehydration treatment was 1400 kg, and the weight per 1 m ^{3 of} the activated surplus sludge was 18.7 kg. Subsequently, when the dehydrated activated surplus sludge S was sun-dried for 5 hours in a well-ventilated environment at a temperature of 18.6 ° C. to 23.5 ° C. and a humidity of 38% to 64%, the moisture content was 59.01% by weight. It dropped to. Furthermore, when the activated surplus sludge S that had been sun-dried was naturally dried indoors, it decreased to 52.04% by weight after 24 hours from the start of indoor drying, and to 15.89% by weight after 72 hours. The results obtained are shown in Table 5.

As Comparative Example 6-1 with respect to Example 6-1, the experiment was performed in the same manner as Example 6-1 except that steam injection was not performed. The water content of the activated surplus sludge S immediately after the dehydration treatment was 80.30% by weight, the total weight of the activated surplus sludge S immediately after the dehydration treatment was 3000 kg, and the weight per 1 m ^{3 of} the activated surplus sludge was 40 kg. The moisture content after sun-drying was 68.64% by weight, the moisture content after 24 hours from the start of indoor drying was 69.99% by weight, and the moisture content after 72 hours was 36.67% by weight. The obtained results are shown in Table 5 together.

  As shown in Table 5, it was found that if the heat treatment by steam injection is performed, the moisture content can be reduced even if the average temperature of the activated surplus sludge S is not as high as 30 ° C.

  In addition, as Example 6-2, the activated surplus sludge S that was subjected to the steam spraying process in the same manner as in Example 6-1 was manually squeezed and dehydrated to form a dehydrated cake with a thickness of about 2 mm to 3 mm. It was left to dry in the room for 24 hours. The water content of the activated surplus sludge S immediately after dehydration was 72.50% by weight, and the water content after 24 hours was 16.86% by weight.

Example 6-3 is the same as Example 6-1 except that the time for injecting water vapor M is shortened and the amount of water vapor M injected is 19 kg with respect to 1 m ³ of activated surplus sludge. The experiment was conducted. The average temperature of the activated surplus sludge S increased to 29 ° C. The water content of the activated surplus sludge S immediately after dehydration was 77.61% by weight, and the water content after 24 hours was 55.31% by weight.

Example 6-4 is the same as Example 6-1 except that the time for injecting water vapor M is shortened and the amount of water vapor M injected is 9.5 kg with respect to 1 m ³ of activated surplus sludge. The experiment was conducted. The average temperature of the activated surplus sludge S increased to 25 ° C. The water content of the activated surplus sludge S immediately after dehydration was 80.58% by weight, and the water content after 24 hours was 60.87% by weight. The obtained results are shown in Table 6.

As shown in Table 6, in Example 6-2, the water content was significantly reduced as compared with Examples 6-3 and 6-4. Moreover, about Example 6-2 and Example 6-3, the activated surplus sludge S after water vapor | steam injection was observed with the microscope. 4A is a photomicrograph of activated surplus sludge S of Example 6-2, and FIG. 4B is a photomicrograph of activated surplus sludge S of Example 6-3. In FIG. 4B, it can be seen that a mass of microorganisms such as filamentous microorganisms and large microorganisms is still seen, whereas in FIG. That is, it was found that higher effects can be obtained if the amount of water vapor M injected is 20 kg or more with respect to 1 m ³ of the activated surplus sludge.

  The present invention has been described with reference to the embodiment. However, the present invention is not limited to the above embodiment, and various modifications can be made. For example, the method for treating activated surplus sludge and the method for producing solid fuel of the present invention may not include all the steps described in the above embodiment, and may include other steps. For example, in the moisture removal process, only one of the dehydration process and the drying process may be performed. Further, the dehydration step may be performed by filtration or the like without using the above-described dehydration apparatus.

  It can be used for the treatment of activated surplus sludge discharged from various factories. The solid fuel of the present invention can be used as a carbon neutral boiler fuel. Therefore, unlike fossil fuels such as heavy oil and city gas, it becomes a new fuel that does not worry about the emission of global warming gas.

It is a flowchart showing the process of the processing method of the activated surplus sludge and the manufacturing method of solid fuel which concern on one embodiment of this invention. It is a block diagram of the apparatus used in the processing method of the activated surplus sludge which concerns on one embodiment of this invention, and the manufacturing method of solid fuel. It is a microscope picture showing the state of activated surplus sludge before water vapor injection. It is a microscope picture showing the state of activated surplus sludge after water vapor injection. It is a microscope picture showing the state of activated surplus sludge which inject | poured 21 kg of water vapor | steam with respect to 1 m ³ of activated surplus sludge. Is a microscope photograph showing the state of the active excess sludge yelling Spray water vapor 19kg for the active excess sludge 1 m ^3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Biological treatment tank, 2 ... Precipitation tank, 3 ... Heat processing tank, 31 ... Liquid temperature sensor, 4 ... Jet pipe, 41 ... Spout, 5 ... Steam supply pipe, 51 ... Open / close valve, 6a, 6b ... Dehydration 7: Drum rotary dryer, W: Organic waste water, S: Activated surplus sludge, M: Water vapor

Claims (1)

A method for treating activated surplus sludge that reduces the amount of activated surplus sludge contained in organic wastewater discharged by biological treatment,
Including a steam injecting step of performing heat treatment by directly injecting steam into activated surplus sludge having a moisture content of 94% by weight or more,
The activated surplus sludge contains spore-forming microorganisms that form spores,
In the steam spraying step, the average temperature of the activated surplus sludge is set to 30 ° C. which is lower than the spore formation temperature at which the spore-forming microorganisms form spores, and 20 kg or more of steam is spouted into 1 m ^{3 of the} surplus activated sludge. A method for treating activated surplus sludge.