JPWO2018211795A1 - Anaerobic digestion method and apparatus for organic sludge - Google Patents

Abstract

Provided is an anaerobic digestion method and apparatus capable of achieving high-efficiency energy recovery with equipment having a smaller capacity and lower construction cost and having less trouble in maintenance and management. Organic sludge having an organic substance concentration of 4.5 to 9.0% is placed in a cylindrical digestion tank 4 having an effective depth of not less than 8 m and an inner diameter of not less than 4 m. The method is an anaerobic digestion method for organic sludge, which comprises charging the sewage so as to satisfy the following conditions and performing anaerobic digestion treatment for 12 days or more.

Description

  The present invention relates to a method and an apparatus for anaerobic digestion of organic sludge, and more particularly to an organic sludge capable of anaerobically digesting organic sludge such as sewage sludge, human waste sludge, food residue, livestock manure, and recovering energy. The present invention relates to a method and an apparatus for anaerobic digestion of anaerobic sludge.

  Sewage sludge, night soil sludge, food residue, livestock manure, other organic sludge, and waste containing them can be recovered as energy because they have a calorific value in themselves. Conventionally, energy recovery methods include dehydrating and drying organic sludge, using heat generated by incineration, and anaerobic digestion using a process that converts organic matter to methane gas by the action of microorganisms. ing. However, none of these methods has been widely used because of the high construction cost of the equipment and the high energy consumption of the equipment itself, which results in low energy recovery efficiency.

  As an example, in a conventional anaerobic digestion facility for sewage sludge, low-concentration sewage sludge is introduced into an anaerobic digestion tank to ensure a digestion period of 20 days or more. Therefore, a large-capacity digestion tank is required, and construction costs are increased. Furthermore, most of the recovered energy is consumed by the equipment itself, such as energy for heating the inside of the large-capacity digestion tank and energy for stirring required to prevent sedimentation and uniformity of sludge in the tank. Therefore, there is a problem that the rate at which the energy of the input material can be effectively used is low.

  In order to improve these problems, a method has recently been adopted in which the sludge input is concentrated to about 5% to reduce the amount thereof, thereby reducing the capacity of the digestion tank and reducing the heating heat. However, the power required for the sludge circulation for stirring and heating is rather higher than in the past, and thus has not been improved significantly. In addition, in some cases, high-temperature digestion in which the temperature in the tank is about 50 to 55 ° C. is adopted in order to reduce the size of the digestion tank by increasing the reaction rate, but compared with medium-temperature digestion (about 35 ° C.). In addition, since the amount of heat required for heating increases, the merit in energy recovery efficiency is small.

  As a method for reducing the stirring power, Japanese Patent No. 3406564 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2007-130510 (Patent Document 2) disclose a mechanism capable of storing digestion gas generated in anaerobic digestion in a tank. A method of stirring the sludge in the tank by blowing the accumulated gas into the sludge in the tank at one time is shown.

Japanese Patent No. 3406564 JP 2007-130510 A

  However, all of the methods described in Patent Literatures 1 and 2 require a large-scale structure for storing and discharging gas in a tank, which is costly. In addition, if a trouble such as blockage due to residue occurs during operation of these structures, it is difficult or impossible to recover the trouble, and the structure is often not suitable for actual operation. As described above, the conventional anaerobic digestion of organic sludge has a problem that a large-capacity facility is required, construction cost is high, energy consumption by the facility itself is large, and energy recovery efficiency is low.

  In view of the above problems, an object of the present invention is to provide an anaerobic digestion method and apparatus capable of realizing highly efficient energy recovery with equipment having a smaller capacity and lower construction cost and having less trouble in maintenance. And

  In order to achieve the above object, as a result of intensive studies by the present inventors, the relationship between the size of the digestion tank used for anaerobic digestion and the properties of the organic sludge fed into the digestion tank is controlled to an appropriate range. As a result, it has been found that an anaerobic digestion method and apparatus can be obtained which can realize high-efficiency energy recovery without requiring a stirring power and have less trouble in maintenance.

According to one aspect of the present invention, which has been completed based on the above findings, an organic sludge having an organic substance concentration of 4.5 to 9.0% is placed in a cylindrical digestion tank having an effective depth of 8 m or more and an inner diameter of 4 m or more. An anaerobic digestion method for organic sludge is provided, wherein the method is charged at a load of 3.3 to 6.6 kg-VS / m ³ · d and anaerobic digestion treatment is performed in 12 or more digestion days.

  In one embodiment, the method for anaerobic digestion of organic sludge according to the present invention, wherein the bottom surface of the digestion tank includes a concave kettle formed at the center and a peripheral bottom surface surrounding the kiln, Is a horizontal plane, or has a tapered shape having an inclination of 30 ° or less with respect to the horizontal plane, and includes pulling out anaerobic digested organic sludge from a kamaba.

  In another embodiment of the anaerobic digestion method of organic sludge according to the present invention, a digestion tank is disposed at a lower portion of the digestion tank, and a shaft provided in the vertical direction at the center of the digestion tank is used as a central axis. The method includes providing a first rake member rotatable in the circumferential direction of the digestion tank, and rotating the first rake member forward or backward at a peripheral speed of 10 m / min or less.

  In still another embodiment of the anaerobic digestion method for organic sludge according to the present invention, the digestion tank further includes a picket fence connected to the first rake member, and the first rake member and the picket fence are provided. Including rotating in the digestion tank.

  In still another embodiment, the anaerobic digestion method for organic sludge according to the present invention is arranged near the liquid surface of the organic sludge to be charged into the digestion tank, and the periphery of the digestion tank is centered on the shaft. A second rake member rotatable in the direction, the method further comprising rotating the second rake member.

  In still another embodiment, the method for anaerobic digestion of organic sludge according to the present invention further comprises a cylindrical draft tube disposed around a shaft, and the organic sludge in the digestion tank is placed above the draft tube. Alternatively, the method further includes the downward transfer.

According to another aspect of the present invention, a digestion tank having a cylindrical shape, an effective depth of 8 m or more, and an inner diameter of 4 m or more is provided, and organic sludge having an organic substance concentration of 4.5 to 9.0% is loaded in the digestion tank with an organic substance volume load of 3. An anaerobic digester for organic sludge, which is charged so as to be 0.3 to 6.6 kg-VS / m ³ · d and is subjected to anaerobic digestion treatment in 12 or more digestion days, is provided.

  In one embodiment, the anaerobic digester for organic sludge according to the present invention includes, in one embodiment, a bottom surface of a digestion tank, which includes a concave kettle formed at a central portion, and a peripheral bottom surface surrounding the kiln. Is a horizontal plane, or has a tapered shape having an inclination of 30 ° or less with respect to the horizontal plane, and includes that a drawing pipe for drawing organic sludge is connected to the kiln.

  In another embodiment of the anaerobic digester for organic sludge according to the present invention, a digestion tank is disposed at a lower portion of the digestion tank, and a shaft provided in the center of the digestion tank in a vertical direction as a central axis. And providing a first rake member rotatable in a circumferential direction of the digestion tank.

  In still another embodiment of the anaerobic digester for organic sludge according to the present invention, the digestion tank further comprises a picket fence connected to the first rake member.

  In still another embodiment, the anaerobic digester for organic sludge according to the present invention is disposed near the liquid surface of the organic sludge to be charged into the digestion tank, and has a shaft portion as a central axis. And providing a second rake member rotatable in the direction.

  In still another embodiment, the anaerobic digester for organic sludge according to the present invention is arranged around a shaft and has a cylindrical shape for transferring organic sludge in a digestion tank to above or below a draft tube. Including further including a draft tube.

  Advantageous Effects of Invention According to the present invention, it is possible to provide an anaerobic digestion method and apparatus capable of achieving high-efficiency energy recovery with equipment having a smaller capacity and lower construction cost and having less trouble in maintenance.

It is the schematic which shows an example of the anaerobic digestion apparatus of the organic sludge which concerns on embodiment of this invention. It is the schematic which shows the 1st modification of the digestion tank with which the anaerobic digestion apparatus of the organic sludge which concerns on embodiment of this invention is provided. It is the schematic which shows the 2nd modification of the digestion tank which concerns on embodiment of this invention. It is the schematic which shows the 3rd modification of the digestion tank which concerns on embodiment of this invention. It is the schematic which shows the 4th modification of the digestion tank which concerns on embodiment of this invention. It is the schematic which shows the 5th modification of the digestion tank which concerns on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. The embodiments described below exemplify an apparatus and a method for embodying the technical idea of the present invention. The technical idea of the present invention describes the structure, arrangement, and the like of component parts as follows. It is not something specific.

  As shown in FIG. 1, an anaerobic digester for organic sludge according to an embodiment of the present invention includes a concentration adjusting device 2 for adjusting the organic matter concentration of an input raw material 1, and an input material adjusted by the concentration adjusting device 2. 1 is provided with a digestion tank 4 for anaerobic digestion.

  Organic sludge is used as the input raw material 1. As the organic sludge, for example, sewage sludge, night soil and septic tank sludge, livestock manure, food production residue, agricultural residue, biomass energy recovery residue and the like, and organic waste liquid can be used, and these can be used alone or in combination. be able to. Among these, it is preferable to use sewage sludge as the organic sludge according to the present embodiment because a pipeline network suitable for collection and transportation of organic waste is constructed.

  In the concentration adjusting equipment 2, the organic sludge as the input raw material 1 is adjusted to a sludge concentration suitable for the treatment in the digestion tank 4. As the concentration adjusting equipment 2, a concentration means for concentrating the input raw material 1 to a predetermined organic substance concentration (Volatile Solids: VS concentration) by solid-liquid separation or the like can be used. Examples of the concentration means include gravity concentration using gravity sedimentation, mechanical concentration using a screen or a filter cloth, or centrifugal separation, but the method is not limited as long as it can be concentrated. Further, at the time of concentration, a small amount of a coagulant having an addition ratio of 1% by mass or less may be added.

  On the other hand, if the input raw material 1 is, for example, a dewatered cake of organic sludge and is a raw material having a high organic matter concentration, equipment shown in FIG. 2 may be used. That is, the input raw material 1 received by the hopper 21 or the like is transferred to the concentration adjusting equipment 2, mixed with the diluent 11 in the concentration adjusting equipment 2, the organic matter concentration of the input raw material 1 is adjusted, and transferred to the digestion tank 4. is there.

  As the diluent 11, dilution water and dilution sludge can be used alone or in combination. As dilution water, tap water, well water, sewage treatment water, and the like can be used. As the diluted sludge, sewage sludge before concentration, surplus sludge, septic tank sludge, and digested sludge after digestion can be used. However, when using digested sludge, water or other low-concentration sludge is required because the concentration is high and a large amount of digested sludge must be circulated, and the apparent decomposition rate in the digestion tank decreases. It is desirable to use it together with sludge.

  In the concentration adjusting equipment 2 shown in FIGS. 1 and 2, the VS concentration of the input raw material 1 is concentrated so as to be 4.5 to 9.0% by mass. Thereby, in the anaerobic digestion treatment in the digestion tank 4 to be described later, the sludge is prevented from settling to the bottom of the digestion tank 4 to stabilize the treatment without providing agitation means or the like in the digestion tank 4 actively. And high-efficiency energy recovery can be realized.

  If the VS concentration of the input raw material 1 is too high, the viscosity of the sludge in the digestion tank 4 becomes too high, and it is difficult to perform the treatment stably. On the other hand, if the VS concentration is too low, the viscosity of the sludge in the digestion tank 4 becomes low, and the sedimentation of the sludge is likely to occur in the digestion tank 4. Therefore, it is necessary to provide a stirring means for stably proceeding the treatment. Occurs, and power for stirring the digestion tank 4 is required.

  In the present embodiment, it is more preferable to adjust the VS concentration of the raw material 1 charged into the digestion tank 4 to 5.0 to 8.5% by mass in order to minimize the power required for stirring the digestion tank 4 and the like. And still more preferably 6.0 to 8.0% by mass.

  By preliminarily adjusting the VS concentration of the input raw material 1 to the above-mentioned range by the concentration adjusting equipment 2, the sedimentation speed of the particles contained in the input raw material 1 can be reduced. The occurrence of deposition can be suppressed.

  The concentration adjusting equipment 2 may perform a process of not only increasing the organic substance concentration but also removing foreign substances from the input raw material 1 supplied to the digestion tank 4 by solid-liquid separation or the like in advance. This can reduce the amount of foreign substances charged into the digestion tank 4, thereby providing an anaerobic digester with less trouble in maintenance due to the mixing of foreign substances.

  As shown in FIG. 1, the organic sludge whose VS concentration has been adjusted by the concentration adjusting equipment 2 is introduced from the upper part of the digestion tank 4 through the digestion tank introduction pipe 3. The organic sludge (hereinafter, also referred to as “input sludge”) charged into the digestion tank 4 falls into a sludge layer (not shown) formed in the digestion tank 4 and is generated by air bubbles generated and floating in the sludge layer. Dispersed in layers. The input sludge dispersed in the digestion tank 4 is decomposed and gasified by microorganisms in the sludge layer. The digestion gas generated in the digestion tank 4 is collected through the digestion gas pipe 7 and used as a fuel for heating or power generation.

  The sludge in the digestion tank 4 is heated to a medium temperature of about 35 ° C., and the organic matter contained in the input sludge is anaerobically decomposed by the action of microorganisms contained in the sludge in the digestion tank 4, and water, ammonia nitrogen Is converted to carbon dioxide and methane gas. If the temperature in the digestion tank 4 is too high, the amount of heat required for heating the digestion tank 4 increases, and the merit in energy recovery efficiency is small. However, in the present embodiment, the temperature is adjusted to a high temperature region (about 50 to 55 ° C.). It is of course possible to do so.

When the organic matter volume load of the organic sludge fed into the digestion tank 4 is too high, organic matter that cannot be completely decomposed accumulates, and as a result, it may be difficult to maintain the system. If the volume load is too low, the amount of generated gas will be small, and the agitation and uniformity of the sludge in the digestion tank 4 will be insufficient, and the efficiency of decomposing organic substances may decrease. Therefore, it is preferable that the organic sludge charged into the digestion tank 4 is charged into the digestion tank 4 so that the organic substance volume load is 3.3 to 6.6 kg-VS / m ³ · d, more preferably. a ^{4.0~6.0kg-VS / m 3 · d} , more preferably from ^{4.5~5.5kg-VS / m 3 · d} .

  In the present embodiment, for example, when sewage digestion sludge is used as the organic sludge, the reaction of decomposition and gasification of organic substances is schematically represented by the following equation (1).

  By this reaction, about 50% of the organic matter in the input sludge is decomposed and gasified, so that the VS concentration of the sludge (digested sludge) in the digestion tank 4 is about 2.25 to 4.5%. When the VS concentration of the input sludge is lower than this, the viscosity of the sludge in the digestion tank 4 decreases, so that the solids in the sludge tend to settle and separate, and a stirring means for preventing the sediment is required. On the other hand, if the VS concentration of the input sludge is too high, on the other hand, the viscosity of the sludge in the digestion tank 4 will increase, and the uniformity of the sludge and the floating of air bubbles will be hindered. Digestion inhibition may occur due to the high concentration of ammonia nitrogen in the sludge.

The gas generation amount E (Nm ³ / m ³ · d) per digestion tank volume from the digestion tank 4 due to the anaerobic digestion reaction is such that the digestion gas generation amount E ₀ per organic matter in the input sludge is 0.5 Nm ³ / kg. It is clear from the past results and the experimental results of the inventors that it is about −VS. Therefore, the gas generation amount E is expressed as in equation (2).

ここで、
Ｑ：１日あたりの消化タンクへの汚泥投入量（ｍ³／ｄ）
Ｃ₀：消化タンク投入汚泥ＶＳ濃度（ｋｇ／ｍ³）
Ｖ：消化タンク有効容量（ｍ³）

here,
Q: Sludge input amount into digestion tank per day (m ³ / d)
C ₀ : VS concentration of sludge put in digestion tank (kg / m ³ )
V: Effective capacity of digestion tank (m ³ )

On the other hand, the digestion tank capacity V (m ³ ) is calculated as follows:
V = Q × T (3)
Thus, equation (2) is

と表される。
次に消化タンク投入有機物容積負荷（ｋｇ−ＶＳ／ｍ³・ｄ）をＬ_VSとすると、

It is expressed as
Next, assuming that the organic matter volume load (kg-VS / m ³ · d) input to the digestion tank is L _VS ,

であるから、式（４）は
Ｅ＝０．５×Ｌ_VS ・・・（６）
となる。

Therefore, equation (4) is given by E = 0.5 × L _VS (6)
Becomes

Input amount as organic volume loading is 3.3~6.6kg-VS / m ³ · d to digestion tank 4, setting the digesting tank capacity, equation (6) from the digesting tank 4 per volume gas generator The quantity E amounts to 1.65 to 3.3 Nm ³ / m ³ · d. If the organic substance volume load is below this range, it is not possible to obtain a sufficient amount of gas generation to disperse and mix the input sludge. is there. In addition, in the conventional anaerobic digestion method of sewage sludge, the input organic substance volume load is generally about 1 to ³ kg-VS / m ³ · d, and the amount of gas generated per digestion tank volume is at most 1.5 Nm. ³ / m ³ · d.

  The shorter the digestion period is, the higher the organic substance volume load is. However, if the digestion period is shorter than 12 days, the amount of cells required for the reaction may not be maintained in the tank. Therefore, it is necessary to have a tank capacity that can secure digestion days of 12 days or more, more specifically, 12 to 25 days, and more preferably about 13 to 18 days.

  The digestion gas (mixed gas of carbon dioxide and methane) generated in the course of the reaction becomes bubbles and floats in the sludge layer in the digestion tank 4 and moves to the gas phase above the digestion tank 4. The mixing of the input sludge and the sludge in the digestion tank 4 is basically performed by an ascending flow accompanying the generated gas that floats. The generation of air bubbles occurs substantially uniformly throughout the sludge layer in the digestion tank 4, and the generated air bubbles float in the sludge layer.

Assuming that the effective depth of the digestion tank 4 is h1 (m) (see FIG. 1), the digested gas amount per area that is generated and floated in the sludge layer in the digestion tank and passes through the sludge liquid surface is E × h1 (Nm ³ / m ² · d), which value is determined by the digestion tank effective depth h1.

As a result of various studies from the above viewpoint, the inventors have found that if this value has a height of 13 Nm ³ / m ² · d or more, the stirring means need not be positively arranged in the digestion tank 4. It was confirmed that the sludge was sufficiently stirred by the gas generated in the digestion tank 4. That is, it was confirmed that the sludge introduced from the upper part of the digestion tank 4 was sufficiently dispersed by the generated gas by using the digestion tank 4 having a cylindrical shape and an effective depth h1 of 8 m or more.

On the other hand, when the inner diameter D1 of the digestion tank 4 is small, the ratio of the wall surface to the sludge layer cross section is high, so that the smooth floating of bubbles is hindered, and the mixing of the input sludge and the sludge in the tank becomes insufficient. I understand. According to the verification by the inventors, the diameter at which the ratio A / l of the cross-sectional area A (m ² ) to the inner circumferential length l (m) of the tank becomes 1 or more, that is, the inner diameter D1 of the digestion tank 4 (see FIG. 1) It was confirmed that the influence of the inhibition of air bubble floating due to the wall surface of the digestion tank 4 was eliminated by setting the distance to 4 m or more.

  Therefore, as the size of the digestion tank 4 to be used, it is preferable to use a cylindrical container having an effective depth h1 of 8 m or more and an inner diameter D1 of 4 m or more. The effective depth h1 of the digestion tank 4 is more preferably 10 m or more, and the inner diameter D1 is more preferably 5 m or more.

  On the other hand, if the digestion tank 4 is too large, problems such as an increase in labor and cost of maintenance and an increase in construction cost occur. Therefore, the effective depth h1 can be set to 50 m or less. Is preferably 30 m or less. Similarly, the inner diameter D1 of the digestion tank 4 can be set to 30 m or less, and more specifically, 20 m or less.

  Depending on the input sludge, foreign matter having a large particle size and a high density may be included. Therefore, the bottom surface of the digestion tank 4 includes a concave (or convex) protruding toward the lower part of the digestion tank 4 at the center and a peripheral bottom surface portion 51 surrounding the digester tank 5, It is preferable that the peripheral bottom surface portion 51 is a horizontal plane, or that the peripheral bottom surface portion 51 has a tapered shape having an angle α of 30 ° or less (see FIG. 1) with respect to the horizontal plane. Thereby, foreign substances in the digestion tank 4 and organic sludge deposited on the bottom surface can be easily collected in the kiln 5. Furthermore, it is preferable that a draw-out pipe (digestion sludge pull-out pipe) 6 for pulling out foreign matter and organic sludge to the outside of the digestion tank 4 is connected to the kiln place 5. Thereby, the foreign substances contained in the digestion tank 4 can be pulled out together with the digested sludge, and an anaerobic digester with less equipment maintenance can be provided.

  In order to sufficiently promote the mixing of the organic sludge in the digestion tank 4 with the digestion gas generated in the digestion tank 4 and to efficiently collect foreign substances and organic sludge in the kamaba 5, the inner diameter D2 of the kamaba is determined by: It is preferable that the inner diameter D1 of the digestion tank 4 is about 1/10 to 1/5, and the effective depth h2 of the kamaba is 1 to 2 m. As a result, highly efficient energy recovery can be realized with smaller capacity and lower construction cost equipment, and an anaerobic digestion method and apparatus with less trouble in maintenance can be provided.

  As shown in FIG. 3, the digestion tank 4 is a first rake member 9 </ b> A rotatable in the circumferential direction of the digestion tank 4 around a shaft 8 provided in the center of the digestion tank 4 in a vertical direction as a central axis. It is preferable to provide The first rake member 9 </ b> A is provided below the digestion tank 4, more specifically, near the bottom surface of the digestion tank 4. The lower end of the shaft 8 is accommodated in the kiln place 5. A motor 81 for applying rotational power to the shaft 8 is connected to the upper end of the shaft 8.

  The first rake member 9A is connected to a shaft 8 disposed at the center of the digestion tank 4, extends in the radial direction of the digestion tank 4, and is rotatable about the shaft 8 as a center axis. And one or more rake plates 9b connected to the rake plate 9b. The rake plate 9b is attached to the bottom of the digestion tank 4 at an angle at which foreign matter or organic sludge is swept toward the center by forward rotation, for example, at an angle of 10 to 45 ° with respect to the rake arm 9a, and clearance with the bottom is provided. Is set to be 20 mm or less. By providing the first rake member 9A, when the input raw material 1 in which high-density particles and large-sized residue are mixed as organic sludge is charged and foreign matter is deposited on the bottom of the digestion tank 4, foreign matter is removed. To be easily discharged to the outside of the digestion tank 4 together with the organic sludge.

  The rotation speed of the first rake member 9A is preferably 10 m / min or less, more preferably 5 m / min or less, and still more preferably 3 m / min or less. In the conventional method, the inside of the digestion tank 4 is strongly agitated, including the prevention of the sedimentation of the sludge particles themselves, so that the accumulation of foreign substances on the bottom of the digestion tank 4 has been suppressed. In the present invention, there is basically no need to dispose the stirring means in the digestion tank 4 since the sludge particles do not settle. However, when the raw material is likely to generate sediment on the bottom of the digestion tank 4 due to the properties of the sludge, the first rake member 9A is rotated in the forward direction to scrape foreign substances into the kamaba 5 and reduce the organic matter. It can be easily discharged to the outside of the digestion tank 4 together with the activated sludge. As a result, it is possible to suppress the occurrence of troubles such as clogging due to residue and the like during operation, and it is possible to provide an anaerobic digestion method and apparatus with less trouble in maintenance. According to the embodiment of the present invention, by rotating first rake member 9A at a low peripheral speed of 10 m / min or less, a liquid flow is generated in digestion tank 4 with less power than conventional stirring means. Can be done.

  If there is no need to discharge foreign matter and the VS concentration of the sludge in the digestion tank 4 becomes too low for some reason, the operation is performed in reverse rotation to prevent the sludge in the digestion tank 4 from being reduced in concentration. It is possible.

  The rotation direction of the first rake member 9A can be controlled by a control device (not shown) or manually. As for the timing of switching between forward rotation and reverse rotation, for example, when throwing sludge from the upper part of the digestion tank 4, the first rake member 9A is rotated in the reverse rotation, Is caused. After the input sludge is input, after the processing state in the digestion tank 4 is stabilized, the first rake member 9A is switched to rotate in the forward rotation. Accordingly, the processing can be stably performed, and the accumulation of foreign substances in the digestion tank 4 on the bottom of the digestion tank 4 can be effectively suppressed.

  As shown in FIG. 3, the digestion tank 4 can further include a picket fence 10 connected above the first rake member 9A, and the first rake member 9A and the picket fence 10 are connected in the digestion tank. It is preferable to rotate simultaneously.

  The picket fence 10 is a device used for dispersing the digestion gas generated by anaerobic digestion in the digestion tank 4 in the digestion tank 4. In addition to the lattice shape shown in FIG. May be comb-shaped such that the rods are arranged at intervals along the longitudinal direction of the rake arm 9a. By attaching the picket fence 10 corresponding to the entire height or a part of the sludge in the digestion tank 4 to the rake arm 9a, it is possible to make the floating of the air bubbles in the sludge layer smooth and promote the mixing state in the sludge layer.

  Depending on the properties and concentration of the input sludge, air bubbles floating on the liquid surface may not easily burst, and may gradually accumulate on the liquid surface and dry and solidify. In such a case, as shown in FIG. 4, it is arranged near the liquid surface of the organic sludge to be charged into the digestion tank 4 and is rotatable in the circumferential direction of the digestion tank 4 around the shaft 8 as a central axis. It is preferable to further include a second rake member 9B, and to rotate the second rake member 9B in the forward or reverse direction.

  By installing the second rake member 9B near the liquid surface and scraping the sludge with air bubbles attached to the liquid surface, solidification and accumulation of the liquid surface can be prevented. In addition, the direction in which the sludge is scraped by the rake plate 9b of the second rake member 9B disposed near the liquid surface is opposite to the direction in which the sludge is scraped by the rake plate 9b of the first rake member 9A. Sludge in the entire digestion tank 4 can be slowly circulated, and a more favorable mixed state can be maintained.

  As shown in FIG. 5, a cylindrical draft tube 12 further disposed around the shaft portion 8 is further provided, and the organic sludge in the digestion tank 4 is transferred above or below the draft tube so that the inside of the tank is reduced. It is also possible to promote sludge circulation. The central axis of the draft tube 12 is the same as that of the first and second rake members 9A and 9B, and the diameter of the draft tube 12 can be about 1/10 to 1/5 of the tank inner diameter D1. A stirring blade 13 is arranged inside the draft tube 12. Sludge can be transported in the vertical direction by winding the sludge into the draft tube 12.

  As shown in FIG. 6, when heating the digestion tank 4, the lower part of the digestion tank 4 (about １ ／ to １ ／ of the height of the digestion tank 4) is covered with a heating device 16. A configuration in which hot water or the like is supplied into the heating device 16 via the pipe 14 and discharged from the pipe 15 may be adopted.

  ADVANTAGE OF THE INVENTION According to the anaerobic digestion method and the anaerobic digestion apparatus of the organic sludge which concern on embodiment of this invention, the downsizing of a digestion tank drastically is implement | achieved compared with the past, and at the same time cost reduction can be achieved. In addition, the energy consumption of the equipment can be reduced as compared with the conventional case, and the epoch-making improvement of the energy recovery efficiency can be realized. Organic sludge, which is a raw material, is a carbon-neutral raw material and has a low utilization rate as energy at present. Therefore, the widespread adoption of the present invention will result in tight energy supply and demand and reduction of greenhouse gas emissions. It is thought that it can greatly contribute to problem solving.

  Hereinafter, Examples of the present invention are shown together with Comparative Examples, but these Examples are provided for better understanding of the present invention and its advantages, and are not intended to limit the invention. In the description of the present invention, “%” means “% by mass” unless otherwise specified.

  Anaerobic digestion treatment was performed using the digestion tank 4 shown in FIG. Table 1 shows the specifications of the digestion tank used. Mixed raw sludge (gravity concentrated sludge) from a sewage treatment plant was used as organic sludge. The properties are shown in Table 2.

  The sludge concentrated by the concentration screen after adding a polymer flocculant to the raw material sludge was used as sludge fed into the digestion tank. The coagulant injection rate was set to 0.5% (relative to TS), and the concentrated sludge (the sludge fed into the digestion tank) was set so that the TS concentration was about 8%. Table 3 shows the operation conditions of the digestion tank.

Under these conditions, a continuous digestion operation for one year or more was performed. Table 4 shows the operation results. As shown in Table 4, no pH decrease due to accumulation of organic acids in digested sludge and poor digestion due to ammonia inhibition were not observed throughout the period, and good sludge decomposition (VS decomposition rate: 53%) and generation of digestive gas ( Gas generation rate: 520 Nm ³ / t-VS).

Although gas generation rate per digesting tank volume was 1.5Nm ³ / m ³ · about d at maximum in the conventional method, it was confirmed that the significantly increased and 2.3Nm ³ / m ³ · d in this method . The power density of the rake member was 1 W / m ³ or less, which was equal to or less than that of a conventional digestion tank stirrer. From these results, it was shown that the present invention can reduce the construction cost by reducing the capacity of the digestion tank, and increase the effective available energy by reducing the energy consumption in the digestion facility. In addition, there was no obstruction of the digestive gas tube or accumulation of scum due to extreme foaming throughout the period.

  After the operation was completed, the entire amount of sludge in the digestion tank was pulled out and the inside was confirmed.As a result, no accumulation of sludge or foreign matter on the bottom was observed, and the entire inside of the digestion tank was effectively functioning without forming a dead space. It was confirmed that.

1. Input material (organic sludge)
2 ... Concentration adjustment equipment 3 ... Digestion tank input pipe 4 ... Digestion tank 5 ... Kamaba 6 ... Digestion sludge extraction pipe 7 ... Digestion gas pipe 8 ... Shaft 9A ... First rake member 9B ... Second rake member 9a ... Rake arm 9b Rake plate 10 Picket fence 11 Diluent 12 Draft tube 13 Stirrer blade 21 Hopper 51 Peripheral bottom surface

Claims (10)

Effective depth 8m or more cylindrical, in more digesting tank inner diameter 4m, organic volume organics concentration from 4.5 to 9.0% of organic sludge load 3.3~6.6kg-VS / m ³ · d An anaerobic digestion method for organic sludge, which comprises charging the mixture in such a manner as to achieve an anaerobic digestion treatment in 12 days or more.   The bottom surface of the digestion tank includes a concave kettle formed at the center and a peripheral bottom surface surrounding the kiln, and the peripheral bottom surface is a horizontal plane, or 30 ° or less with respect to a horizontal plane. The method for anaerobic digestion of organic sludge according to claim 1, which has a tapered shape having an inclination, and comprises extracting the organic sludge after anaerobic digestion from the kiln. The digestion tank is
A first rake member disposed at a lower portion of the digestion tank and rotatable in a circumferential direction of the digestion tank around a shaft provided in a vertical direction at a central portion of the digestion tank;
The method for anaerobic digestion of organic sludge according to claim 1 or 2, comprising rotating the first rake member forward or backward at a peripheral speed of 10 m / min or less. The digestion tank is
A picket fence connected to the first rake member,
4. The method of anaerobic digestion of organic sludge according to claim 3, comprising rotating the first rake member and the picket fence in the digestion tank. A second rake member disposed near the liquid level of the organic sludge to be charged into the digestion tank and rotatable in the circumferential direction of the digestion tank around the shaft as a central axis,
The method for anaerobic digestion of organic sludge according to claim 3 or 4, comprising rotating the second rake member. A digestion tank having a cylindrical shape and an effective depth of at least 8 m and an inner diameter of at least 4 m is provided, and organic sludge having an organic substance concentration of 4.5 to 9.0% is loaded in the digestion tank with an organic substance volume load of 3.3 to 6.6 kg-VS. / M ³ · d, and an anaerobic digester for organic sludge, characterized in that it is subjected to anaerobic digestion in 12 days or more.   The bottom surface of the digestion tank includes a concave kettle formed at the center and a peripheral bottom surface surrounding the kiln, and the peripheral bottom surface is a horizontal plane, or 30 ° or less with respect to a horizontal plane. The anaerobic digester for organic sludge according to claim 6, which has a tapered shape with an inclination, and includes a drawing pipe for drawing out the organic sludge to the kiln. The digestion tank is
A first rake member disposed at a lower portion of the digestion tank and rotatable in a circumferential direction of the digestion tank around a shaft provided vertically in a central portion of the digestion tank. The anaerobic digester for organic sludge according to 6 or 7. The digestion tank is
The organic sludge anaerobic digester according to claim 8, further comprising a picket fence connected to the first rake member.   A second rake member disposed near a liquid surface of the organic sludge to be charged into the digestion tank and rotatable in a circumferential direction of the digestion tank around the shaft as a central axis. The anaerobic digester for organic sludge according to 8 or 9.

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