Sludge treatment equipment

Abstract

This disclosure describes a sludge treatment apparatus capable of efficiently reacting ozone with concentrated excess sludge. [Solution] The sludge treatment apparatus comprises a reaction tank and a stirrer configured to agitate the concentrated excess sludge and ozone in the reaction tank. The stirrer includes a rotating shaft, a drive unit configured to rotate the rotating shaft, and a first impeller mounted on the rotating shaft so as to be located inside the reaction tank. The first impeller includes a plurality of first stirring blades projecting laterally from the rotating shaft. Each of the plurality of first stirring blades includes a pair of plate-shaped first blade members. The pair of first blade members are arranged to face each other in the vertical direction and to approach each other as they move from the leading edge to the trailing edge. Each of the pair of first blade members has a plurality of first through holes that penetrate it in the blade thickness direction, arranged along the radial and circumferential directions of the rotating shaft, respectively.

Description

Technical Field

[0001] The present disclosure relates to a sludge treatment apparatus. Background Art

[0002] In recent years, technology for utilizing sewage sludge generated in sewage treatment facilities as a biomass resource has attracted attention. Sewage sludge includes primary settling sludge generated during primary sewage treatment and excess sludge generated during secondary sewage treatment. Primary settling sludge is sludge formed by precipitation of suspended solids contained in sewage. Excess sludge is sludge composed of aggregates of microorganisms propagated through decomposition of soluble organic matter.

[0003] Sewage sludge, for example, after being concentrated by a concentrator, is charged into a digestion tank and decomposed by methanogenic bacteria, thereby generating biogas. The energy of the biogas is utilized as electric power, for example, through gas power generation. On the other hand, residual sludge not decomposed by methanogenic bacteria is discarded as dewatered sludge.

[0004] In order to increase the production amount of biogas, a method of modifying recalcitrant components of sludge into easily decomposable components or solubilized components with ozone as a pretreatment before charging into a digestion tank is known. For example, Patent Document 1 discloses a method of subjecting a sludge-containing liquid to ozone treatment and alkali treatment. Prior Art Documents Patent Documents

[0005] Patent Document 1 Japanese Patent Application Laid-Open No. 2005-219043 Summary of the Invention Problem to be Solved by the Invention

[0006] However, since concentrated excess sludge tends to have high viscosity, the ozone bubbles supplied to it do not diffuse easily. As a result, the ozone sometimes floats to the surface without reacting with the concentrated excess sludge, causing it to leak out of the reaction tank. While it is possible to use a stirring device to diffuse the ozone, stirring the highly viscous concentrated excess sludge requires a relatively large amount of energy, and does not lead to effective ozone diffusion.

[0007] Therefore, this disclosure describes a sludge treatment apparatus capable of efficiently reacting ozone with concentrated excess sludge. [Means for solving the problem]

[0008] An example of a sludge treatment apparatus comprises a reaction tank configured to treat concentrated excess sludge with ozone, a liquid supply unit configured to supply concentrated excess sludge to the reaction tank, a gas supply unit configured to supply ozone to the concentrated excess sludge in the reaction tank, and a stirrer configured to agitate the concentrated excess sludge and ozone in the reaction tank. The stirrer includes a rotating shaft extending vertically within the reaction tank, a drive unit configured to rotate the rotating shaft, and a first impeller mounted on the rotating shaft so as to be located within the reaction tank. The first impeller includes a plurality of first stirring blades projecting laterally from the rotating shaft. Each of the plurality of first stirring blades includes a pair of plate-shaped first blade members. The pair of first blade members are arranged to face each other vertically and to approach each other from the leading edge to the trailing edge. Each of the pair of first blade members has a plurality of first through holes that penetrate it in the blade thickness direction, arranged along the radial and circumferential directions of the rotating shaft, respectively. [Effects of the Invention]

[0009] The sludge treatment apparatus described herein makes it possible to efficiently react ozone with concentrated excess sludge. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a schematic cross-sectional view of an example of a sludge treatment system, seen from the side. [Figure 2] Figure 2 is a cross-sectional view taken along line II-II in Figure 1. [Figure 3] Figure 3 is a perspective view showing an example of a configuration in which two impellers are combined. [Figure 4] Figure 4 is a top view of Figure 3. [Figure 5] Figure 5 is a side view of Figure 3. [Figure 6] Figure 6 is a perspective view showing an example of a single impeller. [Figure 7] Figure 7 is a cross-sectional view taken along line VII-VII in Figure 6. [Figure 8] Figure 8(a) is a top view showing an example of a wing member, and Figure 8(b) is a side view of the wing member's side end as seen from the longitudinal direction of the wing member. [Modes for carrying out the invention]

[0011] In the following descriptions, the same reference numeral will be used for identical elements or elements with the same function, and redundant explanations will be omitted. Furthermore, in this specification, when referring to the top, bottom, right, and left of a figure, the direction of the reference numeral in the figure will be used as the reference.

[0012] [Configuration of sludge treatment equipment] First, the configuration of the sludge treatment device 1 will be described with reference to Figures 1 and 2. The sludge treatment device 1 comprises a liquid supply unit 10, a gas supply unit 20, a reaction tank 30, and a stirrer 40.

[0013] The liquid supply unit 10 is configured to supply a sludge-containing liquid containing concentrated excess sludge and water to the reaction tank 30, as shown in FIG. 1. The concentrated excess sludge is obtained, for example, by concentrating excess sludge obtained through secondary treatment of sewage sludge generated in sewage treatment equipment to a predetermined concentration. Examples of concentration methods include gravitational concentration and mechanical concentration. The viscosity of the concentrated excess sludge is higher than that of the excess sludge before concentration treatment. The viscosity of the concentrated excess sludge may be, for example, 10 Pa·s or more.

[0014] The gas supply unit 20 is configured to supply an ozone-containing gas to the reaction tank 30. As shown in FIG. 1 and FIG. 2, the gas supply unit 20 includes a supply source 21, a supply line 22, and a plurality of discharge nozzles 23. The supply source 21 may be configured to, for example, supply an ozone-containing gas obtained by mixing ozone with another gas (e.g., air, inert gas, etc.) to the supply line 22, or may be configured to supply only ozone to the supply line 22.

[0015] The supply source 21 may be, for example, an ozone generator (a so-called ozonizer). The supply line 22 extends to connect the supply source 21 and the plurality of discharge nozzles 23. The plurality of discharge nozzles 23 are configured to discharge the ozone-containing gas upward. As shown in FIG. 2, when viewed from above, the plurality of discharge nozzles 23 may be arranged such that the whole thereof forms a circular shape centered on a rotating shaft 42 described later.

[0016] The reaction tank 30 is configured to treat the concentrated excess sludge supplied from the liquid supply unit 10 with ozone supplied from the gas supply unit 20. The reaction tank 30 only needs to be capable of storing the concentrated excess sludge supplied from the liquid supply unit 10, and may have a cylindrical shape, for example.

[0017] The stirrer 40 is configured to stir the concentrated excess sludge and ozone in the reaction tank 30. The stirrer 40 includes a drive unit 41, a rotating shaft 42, and a plurality of impellers 100.

[0018] The drive unit 41 is configured to rotationally drive the connected rotating shaft 42. In the example of Fig. 1, the drive unit 41 rotates the rotating shaft 42 clockwise when viewed from above. The drive unit 41 may be, for example, a motor. The drive unit 41 may be disposed above the reaction tank 30. The rotating shaft 42 extends downward from the drive unit 41 along the vertical direction. As shown in Fig. 1, the upper end of the rotating shaft 42 is connected to the drive unit 41. A portion of the rotating shaft 42 other than the upper end extends along the vertical direction inside the reaction tank 30. Note that the lower end of the rotating shaft 42 does not need to be held by another member, or may be held by a bearing or the like provided on the bottom surface of the reaction tank 30.

[0019] The plurality of impellers 100 (three impellers 100A, 100B, 100C in the example of Fig. 1) are attached to the rotating shaft 42 so as to be positioned inside the reaction tank 30. Accordingly, when the rotating shaft 42 is rotationally driven by the drive unit 41, the plurality of impellers 100 rotate together with the rotating shaft 42.

[0020] The impeller 100A (first impeller) and the impeller 100B (second impeller) are attached to the lower end of the rotating shaft 42 so as to be positioned above the plurality of discharge nozzles 23, as shown in Fig. 1. The impeller 100A and the impeller 100B are positioned adjacent to each other inside the reaction tank 30. That is, the impeller 100A is located in the vicinity of the impeller 100B. The set of impellers 100A and 100B is configured to micronize ozone bubbles supplied into the reaction tank 30 from the plurality of discharge nozzles 23. Note that the impellers 100A and 100B may be attached to the rotating shaft 42 in a state where a gap is provided between the shaft member 110 (described later) of the impeller 100A and the shaft member 110 (described later) of the impeller 100B in the extending direction of the rotating shaft 42. The gap may be approximately 10 mm to 40 mm, or may be approximately 25 mm.

[0021] Impeller 100C (the third impeller) is mounted in the middle of the rotating shaft 42 so as to be positioned above the set of impellers 100A and 100B. In other words, impeller 100C is located inside the reaction vessel 30. Impeller 100C is configured to further refine the ozone bubbles that have been refined by the set of impellers 100A and 100B.

[0022] [Details of the impeller] Here, the configuration of the impeller 100 will be explained in more detail with reference to Figures 3 to 8. The impeller 100 includes a shaft member 110 and a plurality of stirring blades 120 (a first stirring blade, a second stirring blade, and a third stirring blade).

[0023] The shaft member 110 is cylindrical, as shown in Figures 3, 4, 6, and 7. The rotating shaft 42 can be inserted into the shaft hole 111 located in the center of the shaft member 110. The shaft member 110 may be fixed to the rotating shaft 42 by fasteners (such as bolts) while the rotating shaft 42 is inserted into the shaft hole 111.

[0024] Multiple stirring blades 120 (four stirring blades 120 in the example shown in Figures 3 to 7) are attached to a shaft member 110. The multiple stirring blades 120 extend from the shaft member 110 so as to protrude laterally from the rotating shaft 42 while the shaft member 110 is fixed to the rotating shaft 42. The multiple stirring blades 120 are arranged at predetermined intervals in the circumferential direction of the rotating shaft 42 (hereinafter sometimes simply referred to as the "circumferential direction"). The multiple stirring blades 120 may be arranged at approximately equal intervals in the circumferential direction, or at different intervals in the circumferential direction. For example, if the impeller 100 includes four stirring blades 120, the four stirring blades 120 may be arranged at approximately 90° intervals.

[0025] As shown in Figure 3, the multiple stirring blades 120 of impeller 100A and the multiple stirring blades 120 of impeller 100B are offset in the circumferential direction. More specifically, when viewed from above, the multiple stirring blades 120 of impeller 100A are positioned alternately with the multiple stirring blades 120 of impeller 100B so that they are located in the space between the multiple stirring blades 120 of impeller 100B in the circumferential direction. For example, the multiple stirring blades 120 of impeller 100A and the multiple stirring blades 120 of impeller 100B may be positioned approximately 45° apart when viewed from above.

[0026] The stirring blade 120 includes a pair of blade members 130, 140 (a first blade member, a second blade member, and a third blade member). Each pair of blade members 130, 140 is plate-shaped overall. When viewed from the direction of extension of the rotation shaft 42, each pair of blade members 130, 140 is substantially rectangular in shape overall, with its radial length being greater than its circumferential length. The base ends of each pair of blade members 130, 140 on the shaft member 110 side may be fixed to the shaft member 110 by fasteners (e.g., bolts).

[0027] The pair of wing members 130 and 140 are arranged to face each other in the vertical direction (the direction in which the rotation axis 42 extends), as shown in Figures 3, 5, and 6. Each of the pair of wing members 130 and 140 includes a leading edge LE located on the front side in the rotation direction of the impeller 100 (hereinafter sometimes simply referred to as the "rotation direction") and a trailing edge TE located on the rear side in the rotation direction.

[0028] The pair of wing members 130 and 140 are arranged so that they move closer to each other as you move from the leading edge LE to the trailing edge TE. In other words, the pair of wing members 130 and 140 are arranged to form a shape resembling the Japanese character "ハ" (ha) when viewed from the radial direction of the rotation axis 42 (hereinafter sometimes simply referred to as the "radial direction").

[0029] The pair of blade members 130 and 140 extend radially outward, moving away from each other as they extend outward, as shown in Figures 3 and 5-7. That is, the pair of blade members 130 and 140 are arranged to form a shape resembling the Japanese character "ハ" (ha) when viewed from the leading edge LE or trailing edge TE. The angle θ (see Figure 7) formed by the pair of blade members 130 and 140 when viewed from the leading edge LE or trailing edge TE can vary depending on various conditions (e.g., the size of the blade members 130 and 140, the rotational speed of the impeller 100, the viscosity of the concentrated excess sludge, the supply flow rate of the concentrated excess sludge, the supply flow rate of ozone, etc.). This angle θ may be, for example, around 20° to 45° or around 30° to 35°.

[0030] The wing member 130 is located above the wing member 140. The wing member 130 consists of a main portion 131 including a leading edge LE and a trailing edge portion 132 including a trailing edge TE. The main portion 131 and the trailing edge portion 132 may each be flat. The inclination angle of the main portion 131 with respect to the horizontal plane is θ / 2, and may be approximately 10° to 22.5°.

[0031] The trailing edge portion 132 may be curved relative to the main portion 131 so as to approach the opposing wing member 140, as shown in Figures 3, 5 to 7, and 8(b). In other words, the trailing edge portion 132 may be inclined relative to the main portion 131 so as to approach the trailing edge portion 142 (described later) of the wing member 140 from the leading edge LE side to the trailing edge TE side. The angle φ between the main portion 131 and the trailing edge portion 132 (see Figure 8(b)) can vary depending on the various conditions described above. The angle φ may be, for example, around 150° to 170°, or around 160° to 170°.

[0032] The width L1 of the trailing edge portion 132 in the direction in which the leading edge LE and trailing edge TE are aligned (hereinafter sometimes simply referred to as the "alignment direction") may be smaller than the width L2 of the main portion 131 in the same direction. The size of the width L1 can vary depending on the various conditions described above. The width L1 may be, for example, about 1 / 4 to 1 / 2 the size of the width L2.

[0033] The wing member 140 is composed of a main portion 141 including the leading edge LE and a trailing edge portion 142 including the trailing edge TE. Since the wing member 140 has the same structure as the wing member 130, its description will be omitted.

[0034] As shown in Figures 3 to 7 and Figure 8(a), the wing members 130 and 140 are provided with a plurality of through holes 150 (a first through hole, a second through hole, and a third through hole). The plurality of through holes 150 penetrate the wing members 130 and 140 in the wing thickness direction. The plurality of through holes 150 are arranged to be aligned along the radial and circumferential directions, respectively. The shape of the through holes 150 is not particularly limited, but may be various shapes such as rectangular, polygonal, circular, cross-shaped, or star-shaped. The plurality of through holes 150 may be arranged in a grid pattern (arranged in rows vertically and horizontally) or in a staggered pattern (alternating). The plurality of through holes 150 may be distributed substantially evenly throughout the wing members 130 and 140.

[0035] The size of the through-hole 150 may vary depending on the various conditions described above. The vertical and horizontal dimensions of the through-hole 150 may be, for example, approximately 10mm x 10mm to 50mm x 50mm, or approximately 10mm x 10mm to 30mm x 30mm. When the vertical and horizontal dimensions of the through-hole 150 are 10mm x 10mm or larger, ozone bubbles tend to be made finer. When the vertical and horizontal dimensions of the through-hole 150 are 50mm x 50mm or smaller, the strength of the wing members 130 and 140 tends to be maintained. It should be noted that wing members 130 and 140 may contain through-holes 150 of different sizes and shapes.

[0036] The total opening area of ​​the multiple through holes 150 provided in the wing member 130 may be, for example, about 50% to 80% or about 70% of the total area that would be available if the through holes 150 were not formed in the wing member 130. The same applies to the wing member 140.

[0037] [Effect] As shown in the above example, the ozone bubbles supplied into the reaction tank 30 by the gas supply unit 20 are lighter than the concentrated excess sludge, and therefore move toward the rotation axis 42 by centrifugal force as the impeller 100 rotates. At this time, the ozone bubbles pass through the space between the blade members 130 and 140 and move along the surfaces of the blade members 130 and 140. As a result, a relatively large shear force acts on the ozone bubbles moving along the surfaces of the blade members 130 and 140 due to collisions with the through holes 150. Consequently, the ozone bubbles are more easily atomized, and the specific surface area of ​​ozone in the concentrated excess sludge increases. This makes it easier for ozone to dissolve in the concentrated excess sludge, which tends to have high viscosity. As a result, it becomes possible to react ozone with the concentrated excess sludge efficiently.

[0038] According to the above example, the through-holes 150 can be rectangular in shape. In this case, a larger number of through-holes 150 can be formed in the blade members 130 and 140. As a result, a greater shear force acts on the ozone bubbles. Therefore, it becomes possible to react the ozone with the concentrated excess sludge more efficiently.

[0039] As shown in the above example, the trailing edge 132 of the blade member 130 and the trailing edge 142 of the blade member 140 are inclined with respect to the main parts 131 and 141 such that they approach each other as they move from the leading edge LE side to the trailing edge TE side. Therefore, shear forces are more likely to act on the ozone bubbles at the trailing edges 132 and 142 just before the ozone bubbles pass through the space between the blade members 130 and 140. As a result, it becomes possible to react the ozone with the concentrated excess sludge more efficiently.

[0040] In the above example, the blade members 130 and 140 extend so that they move away from each other as they extend radially outward. Therefore, as the ozone bubbles move toward the axis of rotation due to centrifugal force and along the surfaces of the blade members 130 and 140, a larger shear force acts on the ozone bubbles due to collisions with the through holes 150. This makes it possible to react the ozone with the concentrated excess sludge more efficiently.

[0041] As shown in the above example, multiple agitators 120 can be arranged at approximately equal intervals in the circumferential direction. In this case, the size of the space between adjacent agitators 120 in the circumferential direction of the rotating shaft 42 is approximately equal when viewed from above. Therefore, compared to the case where the size of one space and another space between adjacent agitators 120 in the circumferential direction of the rotating shaft 42 differs when viewed from above, the phenomenon of ozone bubbles rising through that space is suppressed. Consequently, shear force is more easily applied to the ozone bubbles, making it possible to more uniformly refine the ozone bubbles. As a result, it becomes possible to react ozone with concentrated excess sludge more efficiently.

[0042] As shown in the above example, the multiple stirring blades 120 of impeller 100A and the multiple stirring blades 120 of impeller 100B are arranged alternately so as to be offset in the circumferential direction. Therefore, compared to the case where the agitator 40 includes impeller 100A but does not include impeller 100B, the phenomenon of ozone bubbles rising through the space between adjacent stirring blades 120 in the circumferential direction of the rotating shaft 42 is suppressed by the stirring blades 120 of impeller 100B. Consequently, shear force is more easily applied to the ozone bubbles, making it possible to more uniformly and finely atomize the ozone bubbles. As a result, it becomes possible to react ozone with concentrated excess sludge more efficiently.

[0043] In the above example, the agitator 40 includes an impeller 100C located above the set of impellers 100A and 100B. Therefore, the ozone bubbles that have been atomized in impellers 100A and 100B rise to impeller 100C and are atomized further. Thus, it becomes possible to react the ozone with the concentrated excess sludge more efficiently.

[0044] [Differentiation] The disclosures herein should be considered in all respects to be illustrative and not restrictive. Various omissions, substitutions, and modifications may be made to the above examples without departing from the claims and the gist of the claims.

[0045] (1) The agitator 40 does not have to include an impeller 100C located above the set of impellers 100A and 100B. Alternatively, the agitator 40 may further include other impellers 100 adjacent to impeller 100C.

[0046] (2) The impeller 100 attached to the lower end of the rotating shaft 42 may be one or three or more.

[0047] (3) If the agitator 40 includes multiple impellers 100, each may be configured to rotate independently.

[0048] (4) The pair of wing members 130, 140 may extend radially outward from the shaft member 110 while maintaining a substantially constant distance in the radial direction.

[0049] (5) The trailing edges 132 and 142 of the wing members 130 and 140 do not have to be curved relative to the main parts 131 and 141. That is, the trailing edges 132 and 142 may extend continuously relative to the main parts 131 and 141 such that the main parts 131 and 141 and the trailing edges 132 and 142 are located on substantially the same plane.

[0050] [Test Results] Here, we prepared the following three types of sludge treatment equipment and conducted tests to measure the gas holdup (the volume ratio of gas in a gas-liquid two-layer flow, also called the void fraction). The gas holdup is measured by the parameter ε g ,H g H0 respectively ε g : Gas hold up H g : Liquid level height when ozone gas is injected H0: Liquid level before ozone gas injection The calculation was performed using the following formula.

number

[0051] Furthermore, the sludge treatment conditions using the sludge treatment device were as follows: • Diameter of reaction vessel 30: 0.97 m • Liquid depth in reaction vessel 30: 1.063m • Impeller rotation speed: 150 rpm • Ozone gas flow rate: 102.8 L / min • SS (Suspended Solids) concentration of concentrated excess sludge: 2.5%~4.0%

[0052] (Example 1) The sludge treatment apparatus 1 described above was used. (Example 2) In each impeller 100, the same sludge treatment apparatus 1 as in Example 1 was used, except that the trailing edges 132 and 142 of the blade members 130 and 140 were not bent relative to the main parts 131 and 141. (Comparative example) The same sludge treatment apparatus 1 as in Example 1 was used, except that each impeller 100 was replaced with a concave turbine blade (a blade with a circular arc cross-section obtained by cutting a cylinder in half).

[0053] (Test results) The test results showed that the gas holdup in Example 1 was 7.78%, in Example 2 it was 6.81%, and in the comparative example it was 3.65%. Therefore, it was confirmed that in Examples 1 and 2, the ozone bubbles were efficiently dispersed in the concentrated excess sludge. Furthermore, in Example 1, where the trailing edges 132 and 142 of the blade members 130 and 140 are bent relative to the main parts 131 and 141, it was confirmed that the ozone bubbles were dispersed even more efficiently than in Example 2, where this was not the case.

[0054] [Other examples] Example 1. An example of a sludge treatment apparatus comprises a reaction tank configured to treat concentrated excess sludge with ozone, a liquid supply unit configured to supply concentrated excess sludge to the reaction tank, a gas supply unit configured to supply ozone to the concentrated excess sludge in the reaction tank, and a stirrer configured to agitate the concentrated excess sludge and ozone in the reaction tank. The stirrer includes a rotating shaft extending vertically within the reaction tank, a drive unit configured to rotate the rotating shaft, and a first impeller mounted on the rotating shaft so as to be located within the reaction tank. The first impeller includes a plurality of first stirring blades projecting laterally from the rotating shaft. Each of the plurality of first stirring blades includes a pair of plate-shaped first blade members. The pair of first blade members are arranged to face each other vertically and to approach each other from the leading edge to the trailing edge. Each of the pair of first blade members has a plurality of first through holes that penetrate it in the blade thickness direction, arranged along the radial and circumferential directions of the rotating shaft, respectively. In this case, the ozone bubbles supplied into the reaction tank by the gas supply unit are lighter than the concentrated excess sludge, and therefore move toward the axis of rotation due to centrifugal force as the first impeller rotates. At this time, the ozone bubbles pass through the space between the pair of first blade members and move along the surface of the first blade members. In the apparatus of Example 1, the pair of first blade members are arranged to face each other in the vertical direction and to move closer to each other as they move from the leading edge to the trailing edge, and multiple through holes are formed in the first blade members. Therefore, a relatively large shear force acts on the ozone bubbles moving along the surface of the first blade members due to collisions with the multiple through holes. Consequently, the ozone bubbles are more easily atomized, and the specific surface area of ​​ozone in the concentrated excess sludge increases. This makes it easier for ozone to dissolve in the concentrated excess sludge, which tends to have high viscosity. As a result, it becomes possible to react ozone with the concentrated excess sludge efficiently.

[0055] Example 2. In the apparatus of Example 1, each of the pair of first blade members may include a trailing edge portion on the trailing edge side that is inclined with respect to the main portion on the leading edge side so that they move closer to each other as they move from the leading edge side to the trailing edge side. In this case, shear force is more likely to act on the ozone bubbles at the trailing edge portion just before the ozone bubbles pass through the space between the pair of first blade members. Therefore, it becomes possible to react the ozone with the concentrated excess sludge more efficiently.

[0056] Example 3. In the apparatus of Example 1 or Example 2, the pair of first blade members may extend so as they move away from each other radially outward from the axis of rotation. In this case, as the ozone bubbles move toward the axis of rotation by centrifugal force and along the surface of the first blade members, a larger shear force acts on the ozone bubbles due to collisions with multiple through holes. Therefore, it becomes possible to react the ozone with the concentrated excess sludge more efficiently.

[0057] Example 4. In any of the apparatuses of Examples 1 to 3, the agitator further includes a second impeller mounted on a rotating shaft so as to be located near the first impeller in the reaction vessel, the second impeller includes a plurality of second stirring blades projecting laterally toward the side of the rotating shaft, each of the plurality of second stirring blades being arranged alternately with the plurality of first stirring blades such that they are offset from the plurality of first stirring blades in the circumferential direction of the rotating shaft when viewed from above, and includes a pair of plate-shaped second blade members, the pair of second blade members being arranged so as to face each other in the vertical direction and approach each other from the leading edge to the trailing edge, and each of the pair of second blade members may have a plurality of second through holes that penetrate itself in the blade thickness direction, arranged along the radial direction of the rotating shaft. In this case, the first and second impellers have similar structures, and the first stirring blades and the second stirring blades are offset when viewed from above. Therefore, compared to a system where the agitator includes a first impeller but not a second impeller, the second impeller's second blade suppresses the phenomenon of ozone bubbles rising through the space between adjacent first impeller blades in the circumferential direction of the rotation axis. Consequently, shear force is more easily applied to the ozone bubbles, making it possible to more uniformly and finely atomize the ozone bubbles. As a result, it becomes possible to react ozone with concentrated excess sludge more efficiently.

[0058] Example 5. In any of the apparatuses of Examples 1 to 4, the agitator further includes a third impeller mounted on the rotating shaft so as to be located above the first impeller and separate from the first impeller within the reaction vessel, the third impeller includes a plurality of third stirring blades projecting laterally toward the rotating shaft, each of the plurality of third stirring blades includes a pair of plate-shaped third blade members, the pair of third blade members facing each other in the vertical direction and approaching each other from the leading edge to the trailing edge, and each of the pair of third blade members may have a plurality of third through-holes that penetrate itself in the blade thickness direction, arranged along the radial direction of the rotating shaft. In this case, the ozone bubbles that are atomized in the first impeller rise and reach the third impeller where they are atomized further. This makes it possible to react the ozone with the concentrated excess sludge more efficiently.

[0059] Example 6. In the apparatus of Examples 1 to 5, the multiple first through-holes may be rectangular in shape. In this case, a larger number of first through-holes can be formed in the first blade member. As a result, a greater shear force acts on the ozone bubbles. Therefore, it becomes possible to react the ozone with the concentrated excess sludge more efficiently.

[0060] Example 7. In any of the devices in Examples 1 to 6, the multiple first agitators may be arranged at approximately equal intervals in the circumferential direction of the rotation axis. In this case, the size of the space between adjacent first agitators in the circumferential direction of the rotation axis will be approximately equal when viewed from above. Therefore, compared to the case where the size of one space and another space between adjacent first agitators in the circumferential direction of the rotation axis differs when viewed from above, the phenomenon of ozone bubbles rising through the space is suppressed. Consequently, shear force is more easily applied to the ozone bubbles, making it possible to more uniformly refine the ozone bubbles. As a result, it becomes possible to react ozone with concentrated excess sludge more efficiently.

[0061] Example 8. In any of the apparatuses in Examples 1 to 7, the viscosity of the concentrated excess sludge supplied to the reaction tank by the liquid supply unit may be 10 Pa·s or more. [Explanation of symbols]

[0062] 1...Sludge treatment device, 10...Liquid supply unit, 20...Gas supply unit, 30...Reaction tank, 40...Agitator, 41...Drive unit, 42...Rotating shaft, 100...Impeller, 100A...Impeller (First impeller), 100B...Impeller (Second impeller), 100C...Impeller (Third impeller), 120...Agitation blade (First agitation blade, Second agitation blade, Third (Agitation blade), 130... Blade member (first blade member, second blade member, third blade member), 131... Main part, 132... Trailing edge, 140... Blade member (first blade member, second blade member, third blade member), 141... Main part, 142... Trailing edge, 150... Through hole (first through hole, second through hole, third through hole), LE... Leading edge, TE... Trailing edge.

Claims

1. A reaction tank configured to treat concentrated excess sludge with ozone, A liquid supply unit configured to supply concentrated excess sludge to the reaction tank, A gas supply unit configured to supply ozone to the concentrated excess sludge in the reaction tank, The reactor comprises a stirrer configured to agitate the concentrated excess sludge and ozone in the reaction tank, The aforementioned agitator is, A rotating shaft extending vertically within the reaction vessel, A drive unit configured to rotate the aforementioned rotating shaft, It includes a first impeller mounted on the rotating shaft so as to be located inside the reaction vessel, The first impeller includes a plurality of first stirring blades projecting laterally from the rotation axis, Each of the plurality of first stirring blades includes a pair of first blade members having a plate-like shape. The pair of first wing members are arranged to face each other in the vertical direction and to move closer to each other as they move from the leading edge to the trailing edge. A sludge treatment apparatus, wherein each of the pair of first wing members has a plurality of first through holes formed therein in the wing thickness direction, arranged along the radial and circumferential directions of the rotation axis, respectively.

2. The apparatus according to claim 1, wherein each of the pair of first wing members includes a trailing edge portion on the trailing edge side that is inclined with respect to the main portion on the leading edge side so as it moves from the leading edge side towards the trailing edge side.

3. The apparatus according to claim 1, wherein the pair of first wing members extend so as to move away from each other radially outward from the axis of rotation.

4. The apparatus according to claim 2, wherein the pair of first wing members extend so as to move away from each other radially outward from the axis of rotation.

5. The agitator further includes a second impeller mounted on the rotating shaft so as to be located in the vicinity of the first impeller within the reaction vessel, The second impeller includes a plurality of second stirring blades projecting laterally from the rotation axis, Each of the aforementioned plurality of second stirring blades is, When viewed from above, the plurality of first stirring blades are offset from the plurality of first stirring blades in the circumferential direction of the rotation axis, and are arranged alternately with respect to the plurality of first stirring blades. It includes a pair of second wing members that are plate-shaped, The pair of second wing members are arranged to face each other in the vertical direction and to move closer to each other as they move from the leading edge to the trailing edge. The apparatus according to claim 1, wherein each of the pair of second wing members has a plurality of second through holes that penetrate it in the wing thickness direction, arranged along the radial direction of the rotation axis.

6. The agitator further includes a second impeller mounted on the rotating shaft so as to be located in the vicinity of the first impeller within the reaction vessel, The second impeller includes a plurality of second stirring blades projecting laterally from the rotation axis, Each of the aforementioned plurality of second stirring blades is, When viewed from above, the plurality of first stirring blades are offset from the plurality of first stirring blades in the circumferential direction of the rotation axis, and are arranged alternately with respect to the plurality of first stirring blades. It includes a pair of second wing members that are plate-shaped, The pair of second wing members are arranged to face each other in the vertical direction and to move closer to each other as they move from the leading edge to the trailing edge. The apparatus according to claim 2, wherein each of the pair of second wing members has a plurality of second through holes that penetrate it in the wing thickness direction, arranged along the radial direction of the rotation axis.

7. The agitator further includes a second impeller mounted on the rotating shaft so as to be located in the vicinity of the first impeller within the reaction vessel, The second impeller includes a plurality of second stirring blades projecting laterally from the rotation axis, Each of the aforementioned plurality of second stirring blades is, When viewed from above, the plurality of first stirring blades are offset from the plurality of first stirring blades in the circumferential direction of the rotation axis, and are arranged alternately with respect to the plurality of first stirring blades. It includes a pair of second wing members that are plate-shaped, The pair of second wing members are arranged to face each other in the vertical direction and to move closer to each other as they move from the leading edge to the trailing edge. The apparatus according to claim 3, wherein each of the pair of second wing members has a plurality of second through holes that penetrate it in the wing thickness direction, arranged along the radial direction of the rotation axis.

8. The agitator further includes a second impeller mounted on the rotating shaft so as to be located in the vicinity of the first impeller within the reaction vessel, The second impeller includes a plurality of second stirring blades projecting laterally from the rotation axis, Each of the aforementioned plurality of second stirring blades is, When viewed from above, the plurality of first stirring blades are offset from the plurality of first stirring blades in the circumferential direction of the rotation axis, and are arranged alternately with respect to the plurality of first stirring blades. It includes a pair of second wing members that are plate-shaped, The pair of second wing members are arranged to face each other in the vertical direction and to move closer to each other as they move from the leading edge to the trailing edge. The apparatus according to claim 4, wherein each of the pair of second wing members has a plurality of second through holes that penetrate it in the wing thickness direction, arranged along the radial direction of the rotation axis.

9. The agitator further includes a third impeller mounted on the rotating shaft so as to be located above the first impeller and separate from the first impeller within the reaction vessel, The third impeller includes a plurality of third stirring blades projecting laterally from the rotation axis, Each of the plurality of third stirring blades includes a pair of plate-shaped third blade members, The pair of third wing members are arranged to face each other in the vertical direction and to move closer to each other as they move from the leading edge to the trailing edge. The apparatus according to any one of claims 1 to 8, wherein each of the pair of third wing members has a plurality of third through holes that penetrate it in the wing thickness direction, arranged along the radial direction of the rotation axis.

10. The apparatus according to claim 1, wherein the plurality of first through holes are rectangular in shape.

11. The apparatus according to claim 1, wherein the plurality of first stirring blades are arranged at substantially equal intervals in the circumferential direction of the rotation axis.

12. The apparatus according to claim 1, wherein the viscosity of the concentrated excess sludge supplied to the reaction tank by the liquid supply unit is 10 Pa·s or more.

Images