Wastewater treatment apparatus

Abstract

To provide movement of water containing solid from an aerobic treatment tank to upstream.SOLUTION: A wastewater treatment apparatus has a pretreatment tank, an aerobic treatment tank located downstream of the pretreatment tank, a partition wall dividing the pretreatment tank and the aerobic treatment tank, and a first wall and a second wall connected to the partition wall. The partition wall has a communication part that communicates the pretreatment tank and the aerobic treatment tank. The communication part forms one or both of an opening and a weir. The communication part communicates the pre-treatment tank with the aerobic treatment tank by one or both of: at least a part of the first part, which is a one-third portion including the first end on the first wall side, and at least a part of the second part, which is a one-third portion including the second end on the second wall side, of a virtual line connecting the first wall and the second wall at a standard water level height along the boundary surface between the pretreatment tank and the aerobic treatment tank, including the specified side.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This specification relates to a technology for treating wastewater.

Background Art

[0002] Conventionally, wastewater treatment devices that use microorganisms to treat wastewater have been used (wastewater treatment devices are also called septic tanks). The wastewater treatment device may include a plurality of water treatment tanks including an aerobic treatment tank that performs aerobic treatment (for example, a contact aeration tank, a carrier flow tank, or a contact filter bed tank). In the aerobic treatment tank, solids such as microorganisms can flow. In order to transfer water containing solids from the aerobic treatment tank to the upstream water treatment tank, a transfer device such as an air lift pump is provided.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, there was room for improvement in the movement of water containing solids from the aerobic treatment tank to the upstream side.

[0005] This specification discloses a technology for moving water containing solids from the aerobic treatment tank to the upstream side.

Means for Solving the Problems

[0006] The technology disclosed in this specification can be realized as the following application examples.

[0007] [Application Example 1] A wastewater treatment device, A pretreatment tank that treats water without aeration, and An aerobic treatment tank provided downstream of the pretreatment tank and having an aeration device, A partition wall that separates between the pretreatment tank and the aerobic treatment tank, A first wall and a second wall that respectively form inner side surfaces of the aerobic treatment tank in directions different from a specific side surface that is an inner side surface of the aerobic treatment tank formed by the partition wall, and the first wall and the second wall that are respectively connected to the partition wall, Comprising, The partition wall has a communication part that communicates the pretreatment tank and the aerobic treatment tank at the height of the standard water level of the aerobic treatment tank between the first wall and the second wall, The communication part forms one or both of an opening that extends from a position lower than the standard water level to a position higher than the standard water level and a weir that forms an upper end of the partition wall disposed at a position lower than the standard water level. The opening allows the movement of water between the pretreatment tank and the aerobic treatment tank at the height of the standard water level inside the opening, and the weir allows the movement of water between the pretreatment tank and the aerobic treatment tank at the height of the standard water level higher than the upper end of the partition wall, The communication part is at least a part of a first part that is 1 / 3 of the portion including the first end on the first wall side and / or at least a part of a second part that is 1 / 3 of the portion including the second end on the second wall side among virtual lines that connect the first wall and the second wall at the height of the standard water level along a boundary surface between the pretreatment tank and the aerobic treatment tank including the specific side surface, and communicates the pretreatment tank and the aerobic treatment tank, Wastewater treatment device.

[0008] The water in the aerobic treatment tank rises due to aeration by the aeration device. The water that has risen to the water surface can move along the water surface to the position of the first wall or the second wall. After that, the water can move along the first wall or the second wall to the position of the partition wall. The communication part is a virtual line that connects the first wall and the second wall at the height of the standard water level along the boundary surface between the pretreatment tank and the aerobic treatment tank, which includes a specific side surface. At least a part of the first part, which is 1 / 3 of the part including the end on the first wall side, and at least a part of the second part, which is 1 / 3 of the part including the end on the second wall side, communicate with the pretreatment tank and the aerobic treatment tank, either one or both. The water that has moved along the first wall or the second wall to the position of the partition wall can easily move to the pretreatment tank through the communication part. Thus, the above configuration can move the water containing solids from the aerobic treatment tank to the upstream pretreatment tank.

[0009] [Application Example 2] A wastewater treatment device according to Application Example 1, wherein the pretreatment tank has a filter bed for supporting anaerobic microorganisms, the pretreatment tank is configured to form a target water surface that is a water surface communicating with the upper part of the filter bed without passing through the lower part of the filter bed, the pretreatment tank is configured such that the entire target water surface communicates with the communication part. Wastewater treatment device.

[0010] According to this configuration, the solids contained in the water that has moved from the aerobic treatment tank to the pretreatment tank through the communication part can be dispersed on the target water surface of the pretreatment tank. The dispersed solids can settle on the upper part of the filter bed. Thus, the pretreatment tank can capture the solids by the filter bed.

[0011] [Application Example 3] A wastewater treatment device according to Application Example 1, wherein the pretreatment tank has a filter bed for supporting anaerobic microorganisms, the pretreatment tank is configured to form a target water surface that is a water surface communicating with the upper part of the filter bed without passing through the lower part of the filter bed, The pretreatment tank has a baffle that divides the target water surface into a closed first water surface portion continuous with the communication portion and the remaining second water surface portion. The area of the first water surface portion is 1 / 5 or more of the area of the target water surface. Wastewater treatment device.

[0012] According to this configuration, the solids contained in the water that has moved from the aerobic treatment tank to the pretreatment tank through the communication portion can be dispersed in the first water surface portion of the target water surface in the pretreatment tank. The dispersed solids can settle on the upper part of the filter bed. Since the area of the first water surface portion is 1 / 5 or more of the area of the target water surface, the possibility that the solids cannot be dispersed before settling and return to the aerobic treatment tank again is reduced compared to the case where the area of the first water surface portion is less than 1 / 5 of the area of the target water surface. Thus, the movement of solids from the aerobic treatment tank to the pretreatment tank is promoted. Also, the baffle can reduce the possibility that the solids floating on the second water surface portion move to the aerobic treatment tank through the communication portion.

[0013] [Application Example 4] The wastewater treatment device according to Application Example 2 or 3, wherein the pretreatment tank is configured such that the water flowing into the pretreatment tank from the upstream side of the pretreatment tank passes through the filter bed from bottom to top and flows into the aerobic treatment tank through the communication portion. Wastewater treatment device.

[0014] When the pretreatment tank is configured such that the water flowing into the pretreatment tank passes through the filter bed from top to bottom, a flow path (also called a baffle or a cleaning hole) connecting the region below the filter bed and the communication portion is provided in the pretreatment tank. The solids that have moved from the aerobic treatment tank to the flow path through the communication portion cannot be dispersed before settling and can return to the aerobic treatment tank again. According to the above configuration, since the flow path connecting the region below the filter bed and the communication portion can be omitted, the possibility that the solids return to the aerobic treatment tank can be reduced.

[0015] [Application Example 5] The wastewater treatment device according to any one of Application Examples 1 to 4, further comprising an outer wall forming the outer surface of the wastewater treatment device. The outer wall houses the pretreatment tank and the aerobic treatment tank, The first wall is a part of the outer wall, The communication part is at least a part of the first part and communicates the pretreatment tank and the aerobic treatment tank. Wastewater treatment device.

[0016] According to this configuration, the water that has moved along the first wall to the position of the partition wall can easily move to the pretreatment tank through the communication part.

[0017] [Application Example 6] A wastewater treatment device according to any one of Application Examples 1 to 5, The air diffuser has a plurality of discharge parts for discharging gas, The first wall is arranged at a position that does not intersect with the virtual straight line connecting the first end and the discharge part closest to the first end, The communication part is at least a part of the first part and communicates the pretreatment tank and the aerobic treatment tank. Wastewater treatment device.

[0018] According to this configuration, the water that moves due to the air diffusion by the air diffuser can appropriately move to the pretreatment tank through the communication part.

[0019] Note that the technology disclosed in this specification can be realized in various forms, for example, in the form of a wastewater treatment device, a wastewater treatment method, etc.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Mode for Carrying Out the Invention

[0021] A. First Embodiment: A1. Device Configuration: FIG. 1, FIG. 2(A), FIG. 2(B), and FIG. 3 are diagrams showing the schematic configuration of a wastewater treatment device as an embodiment. FIG. 1 shows the wastewater treatment device 800 viewed from the side, FIG. 2(A) shows the wastewater treatment device 800 viewed from below, FIG. 2(B) shows a part of the wastewater treatment device 800 viewed from below, and FIG. 3 shows the contact filter bed tank 830 and the treatment water tank 840. In these figures, the Z direction indicates the vertically upward direction, the X direction indicates the longitudinal direction (horizontal direction) of the wastewater treatment device 800, and the Y direction indicates the direction (horizontal direction) orthogonal to each of the X direction and the Z direction. Hereinafter, the X direction is also referred to as the “+X direction”, and the opposite direction of the X direction is also referred to as the “-X direction”. The same applies to the Y direction and the Z direction.

[0022] The wastewater treatment device 800 has an outer wall 801 that forms the outer surface of the wastewater treatment device 800. The outer wall 801 forms a space for accommodating a plurality of water treatment tanks. An inlet 804 and an outlet 805 are provided on the outer wall 801. Inside the outer wall 801, two partition walls 802 and 803 arranged in the X direction are provided. The partition walls 802 and 803 partition the internal space of the outer wall 801 perpendicular to the X direction.

[0023] The space on the -X direction side of the partition wall 802 (here, the space surrounded by the partition wall 802 and the outer wall 801) forms the impurity removal tank 810. The space between the partition walls 802 and 803 (here, the space surrounded by the partition wall 802, the partition wall 803, and the outer wall 801) forms the anaerobic filter bed tank 820.

[0024] On the +X direction side of the partition wall 803, as shown in Fig. 2(A), side wall portions 843, 842, 844 arranged in a substantially U shape when viewed from above are fixed. The space surrounded by the side wall portions 843, 842, 844 and the partition wall 803 forms the treatment water tank 840. Among the space on the +X direction side of the partition wall 803 (here, the space surrounded by the partition wall 803 and the outer wall 801), the portion outside the side wall portions 843, 842, 844 forms the contact filter bed tank 830.

[0025] Fig. 3 shows a schematic configuration of the portion forming the contact filter bed tank 830 and the treatment water tank 840 in the wastewater treatment apparatus 800 as viewed in the X direction. As shown in Fig. 2(A) and Fig. 3, the side wall portion 843 is the side wall on the +Y direction side of the treatment water tank 840, the side wall portion 842 is the side wall on the +X direction side of the treatment water tank 840, and the side wall portion 844 is the side wall on the -Y direction side of the treatment water tank 840. The configuration of the side wall portion 843 on the +Y side is the same as that of the side wall portion 844 on the -Y side. As shown in Fig. 1 and Fig. 3, the lower portions of the side wall portions 843, 842, 844 have a so-called hopper structure. The lower ends of the side wall portions 843, 842, 844 are separated from the bottom surface of the outer wall 801, forming an opening 836 that communicates the bottom of the contact filter bed tank 830 and the bottom of the treatment water tank 840. As shown in Fig. 1, the disinfection tank 850 is arranged above the treatment water tank 840.

[0026] The wastewater from the inflow port 804 (Fig. 1) flows into the impurity removal tank 810. The impurity removal tank 810 has an inflow baffle 812. The inflow baffle 812 separates impurities from the water. After the impurities are separated, the water flows into the anaerobic filter bed tank 820 through the opening 814 provided in the partition wall 802.

[0027] Inside the anaerobic filter bed tank 820, an inflow baffle 821 and a filter medium 822 for anaerobic microorganisms to adhere to are provided. The filter medium 822 may have portions of various shapes such as a plate portion and a net portion. The water flowing into the anaerobic filter bed tank 820 through the opening 814 is guided under the filter medium 822 by the inflow baffle 821. The filter medium 822 is not provided inside the inflow baffle 821 and is arranged outside the inflow baffle 821. The water guided under the filter medium 822 passes through the filter medium 822 from bottom to top. The water that has moved above the filter medium 822 flows into the contact filter bed tank 830 through the opening 824 provided in the partition wall 803.

[0028] As shown in FIG. 3, the contact filter bed tank 830 has an air diffuser 834, an aerobic filter medium 833 arranged above the air diffuser 834, and a contact material 832 arranged above the aerobic filter medium 833. The aerobic filter medium 833 and the contact material 832 are for aerobic microorganisms to adhere to. These members 834, 833, 832 are provided on the +Y direction side and the -Y direction side of the treatment water tank 840 (FIG. 2(A)), respectively. The contact material 832 and the aerobic filter medium 833 may have portions of various shapes such as a plate portion and a net portion. The contact material 832 may have, for example, a plurality of plates. The aerobic filter medium 833 may have, for example, a net-like portion.

[0029] Figure 2(B) shows the air diffuser 834 as viewed from below. In this embodiment, the air diffuser 834 is composed of a pipe. A plurality of holes 834o are provided on the bottom surface of the pipe. In the figure, the holes 834o seen through the air diffuser 834 are shown. Air is supplied to the air diffuser 834 by a blower (not shown). A large number of bubbles are discharged from the plurality of holes 834o of the air diffuser 834. The large number of bubbles move upward, pass through the inside of the aerobic filter medium 833 and the contact material 832 (Figure 3), and reach the water surface. The movement of the bubbles generates a water flow, and the water in the contact filter bed tank 830 is agitated. Also, oxygen is supplied into the water from the large number of bubbles. The aerobic microorganisms attached to the members 832 and 833 perform aerobic treatment using oxygen. Thereby, the organic matter is decomposed. Also, by the action of nitrifying bacteria contained in the aerobic microorganisms, the ammonium ions contained in the water are oxidized to generate nitrite ions and then nitrate ions (referred to as nitrification). The water treated by the contact filter bed tank 830 flows into the treatment water tank 840 through the opening 836 at the bottom of the contact filter bed tank 830.

[0030] In the treatment water tank 840 (Figure 1), the water stays temporarily. Solid substances in the water (such as sludge and suspended substances, etc.) can settle to the bottom of the treatment water tank 840. A circulation air lift pump 880 is provided in the treatment water tank 840. The suction port 882 of the circulation air lift pump 880 is arranged at the bottom of the treatment water tank 840. The discharge port 884 of the circulation air lift pump 880 is arranged in the impurity removal tank 810 (inside the inflow baffle 812 in this embodiment). The circulation air lift pump 880 transfers the water containing the solid substances settled at the bottom of the treatment water tank 840 to the impurity removal tank 810.

[0031] The water transferred by the circulation air lift pump 880 contains water containing nitrate ions (also called nitrification liquid) generated by aerobic treatment in the contact filter bed tank 830. The nitrification liquid flows into the anaerobic filter bed tank 820 through the impurity removal tank 810. In the impurity removal tank 810 and the anaerobic filter bed tank 820, nitrate ions contained in the nitrification liquid are reduced by the action of denitrifying bacteria contained in anaerobic microorganisms to generate nitrogen gas, and the generated nitrogen gas is released into the air (so-called denitrification).

[0032] The disinfection tank 850 (Fig. 1) is arranged at the upper part of the treated water tank 840. In this embodiment, the disinfection tank 850 has a discharge air lift pump 870. The suction port 872 of the discharge air lift pump 870 is arranged at the same height as the height of the standard water level LWL in the treated water tank 840. The discharge port 874 (Fig. 2(A)) of the discharge air lift pump 870 is arranged in the upstream part of the disinfection tank 850. The discharge air lift pump 870 uses the gas supplied by a blower (not shown) to transfer the water (water from which solids have been separated) near the water surface of the treated water tank 840 little by little to the disinfection tank 850. When the water level in the treated water tank 840 is higher than the standard water level LWL, the discharge air lift pump 870 sucks water from the suction port 872 and transfers the sucked water to the disinfection tank 850. When the water level in the treated water tank 840 drops to the standard water level LWL, the discharge air lift pump 870 cannot suck water from the suction port 872 and does not transfer water. Thus, the standard water level LWL is a stable water level in a state where there is no inflow of water into the wastewater treatment apparatus 800.

[0033] When a large amount of water temporarily flows into the wastewater treatment device 800 (for example, during peak inflow), the water levels in the water treatment tanks 810, 820, 830, and 840 upstream of the discharge air lift pump 870 can temporarily rise above the standard water level LWL. In this embodiment, the water level can rise up to the high water level HWL. When the water level exceeds the high water level HWL, water flows from the treatment water tank 840 to the disinfection tank 850 through an overflow opening (not shown) of the disinfection tank 850. Thus, in the normal usage state, the highest water level is the high water level HWL. The high water level HWL can be referred to as the design maximum water level. When the inflow water volume per unit time exceeds the assumed range, the water level can temporarily rise to a position higher than the high water level HWL.

[0034] During peak inflow, the water levels in the plurality of water treatment tanks 810, 820, 830, and 840 temporarily rise, thereby mitigating the increase in the outflow volume per unit time from the contact filter bed tank 830. As a result, the possibility of untreated water flowing out from the contact filter bed tank 830 can be reduced. The discharge air lift pump 870 operates as a mechanism (also referred to as a "peak cut mechanism") for mitigating the increase in the outflow volume per unit time from the contact filter bed tank 830 due to peak inflow.

[0035] The disinfection tank 850 has a chemical cylinder 854 filled with a disinfectant (for example, solid chlorine agent). In the disinfection tank 850, water is disinfected by contacting the disinfectant. The disinfected water is discharged to the outside of the wastewater treatment device 800 through the outlet 805.

[0036] A2. Configuration of the opening: Figs. 4(A) - 4(E) are explanatory views of the opening 824 that communicates the anaerobic filter bed tank 820 and the contact filter bed tank 830. Fig. 4(A) shows a part of the contact filter bed tank 830 viewed downward. In the figure, the part of the contact filter bed tank 830 on the +Y direction side of the treatment water tank 840 is shown.

[0037] The outer wall 801t in the figure is the wall portion on the +Y direction side of the outer wall 801. The wall forming the contact filtration tank 830 includes the partition wall 803, the outer wall 801t, and the side wall portion 843. The partition wall 803 partitions between the anaerobic filtration tank 820 and the contact filtration tank 830. The outer wall 801t and the side wall portion 843 are each connected to the partition wall 803.

[0038] The partition wall 803, the outer wall 801t, and the side wall portion 843 respectively form the inner side surfaces 803s, 801s, and 843s of the contact filtration tank 830. Hereinafter, the side surface 803s formed by the partition wall 803 is referred to as the specific side surface 803s. The specific side surface 803s is the side surface on the -X direction side of the contact filtration tank 830 and is the side surface between the outer wall 801t and the side wall portion 843. The side surface 801s is the side surface on the +Y direction side of the contact filtration tank 830, and the side surface 843s is the side surface on the -Y direction side of the contact filtration tank 830. Thus, the outer wall 801t and the side wall portion 843 respectively form side surfaces 801s and 843s in directions different from the specific side surface 803s.

[0039] Figures 4(B) and 4(C) show a part of the partition wall 803 seen from the -X direction inside the contact filtration tank 830. The opening 824 extends from the outer wall 801t in the -Y direction. The communication part 900 is the part of the partition wall 803 that forms the opening 824 (here, the U-shaped part corresponding to the edge of the opening 824). In the figure, a virtual line L is shown. The virtual line L is a virtual line that connects the outer wall 801t and the side wall portion 843 on the specific side surface 803s at the height of the standard water level LWL. The first end e1 is the end of the virtual line L on the outer wall 801t side. The second end e2 is the end of the virtual line L on the side wall portion 843 side.

[0040] In the figure, three parts L1, L2, and L3 forming the virtual line L are shown. The first part L1 is the part including the first end e1, the second part L2 is the part including the second end e2, and the third part L3 is the part between the first part L1 and the second part L2. The lengths of these parts L1 - L3 are the same as each other. That is, the parts L1 - L3 are each a part with a length of 1 / 3 of the virtual line L.

[0041] In this embodiment, a part of the virtual line L (specifically, a part of the first part L1) is located inside the opening 824. Inside the opening 824, the virtual line L is arranged on a virtual plane 824s obtained using the specific side surface 803s. As the virtual plane 824s, when the part of the opening 824 below the standard water level LWL can be closed by a plane, that plane is adopted. In this embodiment, the part of the specific side surface 803s that forms the opening 824 (here, the part surrounding the opening 824, that is, the surface of the contact filter bed tank 830 side of the communication part 900) is flat. In this case, as the virtual plane 824s, a plane that is continuous and parallel to this flat part (that is, the plane closing the opening 824) is adopted. Also, in this embodiment, the virtual line L is a straight line. The plane BP including the virtual plane 824s and the specific side surface 803s is an example of the boundary surface between the anaerobic filter bed tank 820 and the contact filter bed tank 830 (hereinafter, the plane BP is referred to as the boundary plane BP).

[0042] If the communication part 900 includes a bent part and the part of the opening 824 below the standard water level LWL cannot be closed by a plane, the virtual line L is determined as follows. That is, the shortest straight line connecting the two edges of the opening 824 at the height of the standard water level LWL (for example, the first edge eo1 and the second edge eo2 in FIG. 4(B)) is adopted as a part of the virtual line L. As the virtual plane 824s, the plane including this straight line and closing the part of the opening 824 below the standard water level LWL with the minimum area is adopted. As shown in FIG. 4(B), when one edge eo1 of the opening 824 at the height of the standard water level LWL is formed by the outer wall 801t instead of the partition wall 803, the part of the outer wall 801t at the height of the standard water level LWL that is closest to the second edge eo2 formed by the partition wall 803 is adopted as the first edge eo1 (and thus the first end e1).

[0043] The water surface WS shown in Fig. 4(C) indicates the water surface of the standard water level LWL. Among the inner part of the opening, in the part below the standard water level LWL, water is movable regardless of the usage status of the drainage treatment device 800. Hereinafter, the communication part formed by the communication part below the standard water level LWL is called the sub-standard part. In Fig. 4(C), the sub-standard part 824q of the opening 824 is hatched. In this embodiment, the shape of the sub-standard part 824q is approximately rectangular. The sub-standard part 824q is surrounded by approximately two horizontal sides (i.e., two sides approximately parallel to the water surface WS) and approximately two vertical sides. The width Wa is the horizontal size of the sub-standard part 824q, and the height Ha is the vertical size of the sub-standard part 824q. In this embodiment, the opening 824 is formed by the edge of the outer wall 801t and the partition wall 803. The width Wa of the sub-standard part 824q is the same as the distance from the outer wall 801t to the end on the -Y direction side of the sub-standard part 824q (here, the second edge eo2). Hereinafter, the opening that forms the rectangular sub-standard part is also called a corner opening. The formation method of the corner opening 824 in this embodiment may be various methods. For example, the opening 824 may be formed by cutting off the end of the partition wall 803 corresponding to the opening 824.

[0044] Thus, in this embodiment, the opening 824 is at least a part of the first part L1 and communicates the anaerobic filter bed tank 820 and the contact filter bed tank 830. The reason for this is to move water from the contact filter bed tank 830 to the upstream anaerobic filter bed tank 820. Figs. 4(D) and 4(E) show examples of the water flow in the contact filter bed tank 830. Fig. 4(D) shows a part of the partition wall 803 facing the -X direction as seen from inside the contact filter bed tank 830, similar to Fig. 4(B). Fig. 4(E) shows a part of the contact filter bed tank 830 facing downward as seen from below, similar to Fig. 4(A).

[0045] As described with reference to FIG. 3 and the like, in the contact filtration tank 830, the gas discharged from the air diffuser 834 moves upward in the water. As a result, as shown in FIG. 4(D), an upward water flow F0 is generated. The water that reaches the vicinity of the water surface WS cannot move upward beyond the water surface WS. Such water can move horizontally along the water surface WS. For example, a water flow F1 that moves toward the outer wall 801t can be generated. As shown in FIG. 4(E), the water that reaches the vicinity of the outer wall 801t cannot move outside the contact filtration tank 830 beyond the outer wall 801t. Such water can move horizontally along the outer wall 801t. For example, a water flow F2 that moves toward the partition wall 803 can be generated. Among the partition walls 803, an opening 824 is provided in the vicinity of the outer wall 801t. The water flowing along the outer wall 801t toward the partition wall 803 can easily move through the opening 824 directly into the anaerobic filtration tank 820.

[0046] As described above, the opening 824 promotes the movement of water from the contact filtration tank 830 to the anaerobic filtration tank 820. The solids in the contact filtration tank 830 can flow in the contact filtration tank 830 together with the water. The flowing solid water can move from the contact filtration tank 830 to the anaerobic filtration tank 820 by the water flows F0, F1, and F2. The opening 824 can transfer the water containing solids from the contact filtration tank 830 to the upstream anaerobic filtration tank 820.

[0047] When water flows from the contact filtration tank 830 into the anaerobic filtration tank 820 through the opening 824, approximately the same amount of another water moves from the anaerobic filtration tank 820 into the contact filtration tank 830 through the opening 824. In this way, water is exchanged between the anaerobic filtration tank 820 and the contact filtration tank 830. Note that the solids that have moved from the contact filtration tank 830 to the anaerobic filtration tank 820 through the opening 824 can settle at a position lower than the opening 824. In this way, solids can be transferred from the contact filtration tank 830 to the anaerobic filtration tank 820.

[0048] In this embodiment, during the normal operation of the wastewater treatment device 800, the circulating air-lift pump 880 transfers water from the contact filtration bed tank 830 to the impurity removal tank 810. As a result, water moves from the anaerobic filtration bed tank 820 to the contact filtration bed tank 830 through the opening 824. When wastewater is flowing into the wastewater treatment device 800, the amount of water moving from the anaerobic filtration bed tank 820 to the contact filtration bed tank 830 through the opening 824 is larger than when no wastewater is flowing into the wastewater treatment device 800. The movement of water (i.e., return) from the contact filtration bed tank 830 to the anaerobic filtration bed tank 820 is more promoted when no water is flowing into the wastewater treatment device 800.

[0049] A3. Test tank: Using the test tank of the wastewater treatment device, a test on the return of solids and water from the contact filtration bed tank to the anaerobic filtration bed tank was conducted. FIGS. 5(A)-5(D) are diagrams showing the configuration of the test tank. Five types of wastewater treatment devices were used in the test: the wastewater treatment device 800 described with reference to FIG. 4(C) and the wastewater treatment devices 800a - 800d shown in FIGS. 5(A)-5(D). The configurations of the openings 824, 824a - 824d are different from each other among these wastewater treatment devices 800, 800a - 800d. Hereinafter, the configurations of each wastewater treatment device 800, 800a - 800d will be described.

[0050] Figs. 5(A) - 5(D) show a part of the partition walls 803a - 803d facing the -X direction as seen from inside the contact filter bed tank 830, similar to Fig. 4(C). The configurations of each of the three types of wastewater treatment devices 800a - 800c (Figs. 5(A) - 5(C)), excluding the last wastewater treatment device 800d (Fig. 5(D)), are the same as the configuration of the above - mentioned wastewater treatment device 800, except that the configurations of the openings 824a - 824c are different. For example, the configurations of the partition walls 803a - 803c in Figs. 5(A) - 5(C) are the same as the configuration of the partition wall 803 (Fig. 4(C)), except that the configurations of the openings 824a - 824c are different. These four types of wastewater treatment devices 800, 800a - 800c were prepared by modifying the CE type, which is a wastewater treatment device manufactured by Fujikleen Kogyo Co., Ltd. In the CE type, a scum baffle is provided in the anaerobic filter bed tank 820. Although not shown, the scum baffle is a member that divides the water surface in the anaerobic filter bed tank 820 into a part communicating with the opening (for example, opening 824) of the partition wall 803 and another part. This scum baffle was removed. Also, by processing the partition wall that separates the anaerobic filter bed tank 820 and the contact filter bed tank 830, the partition walls 803, 803a - 803c that form the openings 824, 824a - 824c were formed.

[0051] As will be described below, the wastewater treatment device 800d in Fig. 5(D) is configured such that the direction of water flow in the filter medium of the anaerobic filter bed tank is downward. Fig. 6(A) shows the wastewater treatment device 800d as seen from the side, similar to Fig. 1. Fig. 6(B) shows the wastewater treatment device 800d as seen from below, similar to Fig. 2(A).

[0052] The wastewater treatment device 800d has partition walls 802d, 803d. The partition wall 802d separates the debris removal tank 810 and the anaerobic filter bed tank 820d, similar to the partition wall 802 (Fig. 1). The partition wall 803d separates the anaerobic filter bed tank 820d and the contact filter bed tank 830, similar to the partition wall 803 (Fig. 1). In the anaerobic filter bed tank 820d, a filter medium 822d similar to the filter medium 822 is provided.

[0053] An opening 814d is provided in the upstream partition wall 802d. The opening 814d extends from the height between the upper end of the filter medium 822d and the standard water level LWL to a height above the high water level HWL. The inflow baffle 821 (Fig. 1) is omitted. The water flowing into the anaerobic filter bed tank 820d through the opening 814d moves to the area above the filter medium 822d. The water above the filter medium 822d passes through the filter medium 822d from top to bottom.

[0054] An opening 824d is provided in the downstream partition wall 803d. Further, an advection baffle 823d is provided in the anaerobic filter bed tank 820d. As shown in Fig. 6(A), the advection baffle 823d extends from a height below the lower end of the filter medium 822d to a height above the high water level HWL. As shown in Fig. 6(B), the advection baffle 823d forms a partial region continuous with the opening 824d. The filter medium 822d is not provided inside the advection baffle 823d and is arranged outside the advection baffle 823d. The water that has moved below the filter medium 822d is guided to the opening 824d through the inside of the advection baffle 823d. Then, the water flows into the contact filter bed tank 830 through the opening 824d.

[0055] The configuration of other parts of the wastewater treatment device 800d is the same as the corresponding parts of the wastewater treatment device 800. Among the parts of the wastewater treatment device 800d, the parts corresponding to the parts of the wastewater treatment device 800 are given the same reference numerals and the description thereof is omitted.

[0056] The virtual lines L and Ld in FIGS. 5(A) - 5(D) are virtual lines that connect the outer wall 801t and the side wall portion 843 at the height of the standard water level LWL on the boundary surfaces BPa - BPd, similar to the virtual line L (FIG. 4(C)). The virtual line L in FIGS. 5(A) - 5(C) is the same as the virtual line L in FIG. 4(C). The virtual line Ld in FIG. 5(D) is also a straight line, similar to the virtual line L. Here, the boundary surfaces BPa - BPd each include the specific side surfaces 803as - 803ds and the virtual surfaces 824as - 824ds that approximate the openings 824a - 824d. The specific side surfaces 803as - 803ds are the inner side surfaces of the contact filter bed tanks 830 and 830d formed by the partition walls 803a - 803d, similar to the specific side surfaces 803s (FIG. 4(C)). In this embodiment, the portions of the specific side surfaces 803as - 803ds that form the openings 824a - 824d are each flat. As the virtual surfaces 824as - 824ds, planes that close the openings 824a - 824d are adopted. As described above, the difference between the plurality of partition walls 803, 803a - 803c is only in the configuration of the openings 824, 824a - 824c. Therefore, the boundary surfaces BPa - BPc represent the same surface.

[0057] As shown in FIGS. 5(A) - 5(D), the shape of each of the openings 824a - 824d is a circle (hereinafter, the openings 824a - 824d are also referred to as round openings 824a - 824d). In the test tank, the inner diameter of each of the round openings 824a - 824d is 77 mm. And the centers Ca - Cd of the round openings 824a - 824d are each on the virtual lines L and Ld (the height of the centers Ca - Cd is the same as the height of the standard water level LWL respectively). In the figure, the portions below the standard of the round openings 824a - 824d, 824aq - 824dq, are hatched. The shape of each of the portions below the standard 824aq - 824dq is a semi - circle.

[0058] The first distances Da1 - Dd1 in FIGS. 5(A) - 5(D) are the distances between the centers Ca - Cd of the round openings 824a - 824d and the outer wall 801t on the boundary surfaces BPa - BPd at the height of the standard water level LWL. The second distances Da2 - Dd2 are the distances between the centers Ca - Cd of the round openings 824a - 824d and the side wall portion 843 on the boundary surfaces BPa - BPd at the height of the standard water level LWL. The distances DL, DLd are the distances between the outer wall 801t and the side wall portion 843 on the boundary surface BP at the height of the standard water level LWL. The distances DL, DLd are the same as the lengths of the virtual lines L, Ld.

[0059] The communication parts 900a - 900d in FIGS. 5(A) - 5(D) are respectively the parts that form the round openings 824a - 824d among the partition walls 803a - 803d. Here, the communication parts 900a - 900d are respectively loop - shaped parts corresponding to the edges of the round openings 824a - 824d.

[0060] Next, the details of the openings 824, 824a - 824d used in the test will be described. The square opening 824 in FIG. 4(C) is arranged at a position close to the outer wall 801t. The part of the virtual line L included in the square opening 824 is only a part of the first part L1. The measured values of each parameter are as follows. Height Ha: 50 mm Width Wa: 85 mm Distance DL: 295 mm Distance D2: 211 mm Area of the lower - than - standard part 824q: 4250 mm 2 Note that the measured values of lengths such as height, width, and distance include a measurement error of about 1 mm. The same is true for other lengths described later.

[0061] The round opening 824a in FIG. 5(A) is arranged at a position close to the outer wall 801t. The part of the virtual line L included in the round opening 824a is only a part of the first part L1. The measured values of each parameter are as follows. First distance Da1: 42 mm Second distance Da2: 253 mm Distance DL: 295 mm Area of the standard lower part 824aq: 2327 mm 2

[0062] The circular opening 824b in Fig. 5(B) is arranged at a position far from both the side wall portion 843 and the outer side wall 801t. The portion of the virtual line L included in the circular opening 824b is only a part of the second portion L2. The measured values of each parameter are as follows. First distance Db1: 146 mm Second distance Db2: 149 mm Distance DL: 295 mm Area of the standard lower part 824bq: 2327 mm 2

[0063] The circular opening 824c in Fig. 5(C) is arranged at a position close to the side wall portion 843. The portion of the virtual line L included in the circular opening 824c is only a part of the third portion L3. The measured values of each parameter are as follows. First distance Dc1: 246 mm Second distance Dc2: 48 mm Distance DL: 295 mm Area of the standard lower part 824cq: 2327 mm 2

[0064] The circular opening 824d in Fig. 5(D) is arranged at a position close to the side wall portion 843. Most of the portion of the virtual line L included in the circular opening 824d is included in the third portion Ld3. The portions Ld1, Ld2, and Ld3 are each portions of 1 / 3 of the length of the virtual line Ld. The portions Ld1, Ld2, and Ld3 respectively correspond to the above portions L1, L2, and L3. The measured values of each parameter are as follows. First distance Dd1: 246 mm Second distance Dd2: 73 mm Distance DLd: 320 mm Area of the standard lower part 824dq: 2327 mm 2 The distance DLd is slightly larger than the distance DL of other test tanks. However, the difference between the capacity of the contact filter bed tank 830 of the test tank having the opening 824d and the capacity of the contact filter bed tank 830 of the test tanks having the openings 824, 824a - 824c is not large enough to affect the comparison of test results among the plurality of openings 824, 824a - 824d.

[0065] A4. Test Results: Figures 7(A) - 7(D) are graphs showing the test results. In this test, the respective changes over time in the concentration of solids (here, so - called suspended solid (SS)) and the concentration of lithium in the contact filter bed tank 830 were measured. For the test, the above - mentioned five types of wastewater treatment devices 800, 800a - 800d were used. In each graph, the symbols of the openings 824, 824a - 824d of the wastewater treatment devices 800, 800a - 800d are used as identifiers of the line graphs.

[0066] The test method is as follows. (Step S1) Using tap water, the wastewater treatment devices 800a, 800a - 800d are filled with water. The water levels of the water treatment tanks 810, 820, 820d, 830, 840 after filling are at the standard water level LWL. (Step S2) Close the openings 824, 824a - 824d with lids. (Step S3) Put 500 g of sludge and 2.5 g of lithium chloride into the contact filter bed tank 830. Lithium chloride is an example of a dissolved substance. (Step S4) With the circulation air - lift pump 880 stopped, the aeration of the contact filter bed tank 830 is continued for 30 minutes. Thereby, the water in the contact filter bed tank 830 is stirred. The respective concentration distributions of sludge and lithium in the contact filter bed tank 830 become approximately uniform. (Step S5) After Step S4, remove the lids of the openings 824, 824a - 824d and start the transfer of water by the circulation air - lift pump 880. The transfer amount per unit time is the same among the wastewater treatment devices 800, 800a - 800d. (Step S6) Water is sampled from the contact filtration tank 830 at each of the following elapsed times from Step S5, and the concentration of SS and the concentration of lithium in the sampled water are measured. Elapsed time = 0, 5, 10, 20, 30, 45, 60, 120 (minutes)

[0067] In the graph of Fig. 7(A), the horizontal axis indicates the elapsed time TM (unit: minute), and the vertical axis indicates the concentration C1 of SS (unit: %). The graph of Fig. 7(B) shows the concentration C1 of SS after 30 minutes of elapsed time (TM = 30 minutes). The concentration C1 of SS indicates the ratio to the concentration C1 of SS at the initial stage (TM = 0 minute) (unit: %).

[0068] In the graph of Fig. 7(C), the horizontal axis indicates the elapsed time TM (unit: minute), and the vertical axis indicates the concentration C2 of lithium (unit: %). The graph of Fig. 7(D) shows the concentration C2 of lithium after 30 minutes of elapsed time (TM = 30 minutes). The concentration C2 of lithium indicates the ratio to the concentration C2 of lithium at the initial stage (TM = 0 minute) (unit: %).

[0069] Note that in this test, the measurement of the concentration by Steps S1 - S6 was repeated three times. The concentrations C1 and C2 in each graph indicate the average of the three measurement results.

[0070] As shown in Fig. 7(A) and Fig. 7(C), for each of the openings 824, 824a - 824d, the concentrations C1 and C2 decreased with the passage of time. The reason is that the water in the contact filtration tank 830 is transferred to the impurity removal tank 810 by the circulation air lift pump 880, and the water is transferred from the contact filtration tank 830 to the anaerobic filtration tank 820 through the openings 824, 824a - 824d. Also, a difference occurred in the concentrations C1 and C2 among the openings 824, 824a - 824d. As described above, the transfer amount per unit time by the circulation air lift pump 880 is common to the openings 824, 824a - 824d. Therefore, the difference in the concentrations C1 and C2 is presumed to be due to the difference in the configuration of the openings 824, 824a - 824d.

[0071] The decreasing rates of concentrations C1 and C2 of the angular opening 824 (Fig. 4(C)) and the round opening 824a (Fig. 5(A)) (for example, the decreasing amounts of concentrations C1 and C2 after 30 minutes (Fig. 7(B), Fig. 7(C))) were faster than those of the other openings 824b - 824d. The reason is presumably that, as explained in Fig. 4(D) and Fig. 4(E), the movement of solids and water by the water flows F0, F1, and F2 (i.e., the return of solids and water through the openings 824 and 824a) is promoted.

[0072] Also, the area of the sub - standard part 824aq of the round opening 824a (2327 mm 2 ) is approximately half of the area of the sub - standard part 824q of the angular opening 824 (4250 mm 2 ). Between these openings 824 and 824a, the decreasing rates of concentrations C1 and C2 are approximately the same. Thus, various - sized openings close to the outer wall 801t can promote the return of solids and water.

[0073] The decreasing rate of concentrations C1 and C2 by the round opening 824b (Fig. 5(B)) was slower than that by the round opening 824a (Fig. 5(A)). The reason is presumably that since the round opening 824b is far from the outer wall 801t, it is difficult for the solids and water moving by the water flow F2 (Fig. 4(E)) to reach the round opening 824b.

[0074] The circular opening 824c (Fig. 5(C)) could not promote the decrease in concentrations C1 and C2 as compared with the circular opening 824a (Fig. 5(A)), despite being close to the side wall portion 843. The reason is presumed as follows. As shown in Figs. 3, 4(D), and 5(C), the side wall portion 843 has a shelf 843a. The shelf 843a protrudes from the treatment water tank 840 toward the contact filter bed tank 830 (here, in the +Y direction) when tracing the side wall portion 843 from top to bottom. Due to such a configuration of the side wall portion 843, the upward water flow F0 (Fig. 4(D)) generated by air diffusion is difficult to reach the upper part of the shelf 843a, that is, the vicinity of the side wall portion 843 at the water surface level. Different from the water flow F1 toward the outer side wall 801t (Figs. 4(D) and 4(E)), the water flow moving along the water surface toward the side wall portion 843 weakens in the vicinity of the side wall portion 843. Different from the water flow F2 moving along the outer side wall 801t (Fig. 4(E)), the water flow moving along the side wall portion 843 toward the circular opening 824c (Fig. 5(C)) weakens. As a result, the decreasing speed of concentrations C1 and C2 by the circular opening 824c close to the side wall portion 843 becomes slower than that by the circular opening 824a close to the outer side wall 801t.

[0075] The rate of decrease in concentrations C1 and C2 due to the round opening 824d (Fig. 5(D)) was slower than the rate of decrease in concentrations C1 and C2 due to the round opening 824c (Fig. 5(C)) close to the side wall portion 843, similar to the round opening 824d. The reason is presumed as follows. As shown in Fig. 6(B), the anaerobic filter bed tank 820d of the wastewater treatment device 800d has a cross-flow baffle 823d. The cross-flow baffle 823d prohibits the diffusion of water from the inside to the outside of the cross-flow baffle 823d near the water surface. Such a cross-flow baffle 823d can restrict the movement of solids and water passing through the opening 824d from the contact filter bed tank 830 to the anaerobic filter bed tank 820d. For example, the water in the cross-flow baffle 823d can push back the solids and water from the contact filter bed tank 830 to the contact filter bed tank 830. Also, after the solids move from the contact filter bed tank 830 through the opening 824d to the anaerobic filter bed tank 820d, the solids cannot move to a position far from the opening 824d (e.g., outside the cross-flow baffle 823d). Such solids can return to the contact filter bed tank 830 through the opening 824d again before settling to a position lower than the opening 824d.

[0076] On the other hand, as shown in Fig. 2(A), the anaerobic filter bed tank 820 of the wastewater treatment device 800 does not have a cross-flow baffle. The solids and water that move from the contact filter bed tank 830 to the anaerobic filter bed tank 820 through the square opening 824 can be dispersed in a region farther from the square opening 824 compared to the solids and water that move into the cross-flow baffle 823d (Fig. 6(B)). Thus, the wastewater treatment devices 800, 800a - 800c without a cross-flow baffle are more receptive to the return of solids and water passing through the openings 824, 824a - 824c compared to the wastewater treatment device 800d having the cross-flow baffle 823d. As a result, when the cross-flow baffle 823d is provided, the rate of decrease in concentrations C1 and C2 can become slower.

[0077] As described above, in this embodiment, the wastewater treatment apparatuses 800 and 800a (Figs. 1, 2(A), and 5(A)) include an anaerobic filter bed tank 820, a contact filter bed tank 830 provided downstream of the anaerobic filter bed tank 820, partition walls 803 and 803a that partition between the anaerobic filter bed tank 820 and the contact filter bed tank 830, an outer wall 801t, and a side wall portion 843. The anaerobic filter bed tank 820 is an example of a pretreatment tank that treats water without aeration. The contact filter bed tank 830 has an aeration device 834. The contact filter bed tank 830 is an example of an aerobic treatment tank provided downstream of the pretreatment tank. As described with reference to Figs. 2(A) and 5(A), the outer wall 801t and the side wall portion 843 are connected to the partition walls 803 and 803a. The partition walls 803 and 803a respectively form specific side surfaces 803s and 803as that are the inner side surfaces of the contact filter bed tank 830. The outer wall 801t and the side wall portion 843 respectively form inner side surfaces 801s and 843s of the contact filter bed tank 830. As shown in Fig. 2(A), when viewing the wastewater treatment apparatuses 800 and 800a facing downward, the outer wall 801t forms a side surface 801s in a direction different from the specific side surface 803s (and thus the specific side surface 803as of the partition wall 803a) of the partition wall 803. Similarly, the side wall portion 843 forms a side surface 843s in a direction different from the specific side surface 803s (and thus the specific side surface 803as). The outer wall 801t and the side wall portion 843 are examples of a first wall and a second wall that respectively form side surfaces in directions different from the specific side surface.

[0078] Partition walls 803 and 803a (Figs. 4(C) and 5(A)) each have a communication portion 900 and 900a, respectively. The communication portions 900 and 900a each form an opening 824 and 824a, respectively. The openings 824 and 824a communicate the anaerobic filter bed tank 820 and the contact filter bed tank 830 at the standard water level LWL between the outer wall 801t and the side wall portion 843. The openings 824 and 824a extend from a position lower than the standard water level LWL to a position higher than the standard water level LWL. The openings 824 and 824a allow the movement of water between the anaerobic filter bed tank 820 and the contact filter bed tank 830 at the height of the standard water level LWL inside the openings 824 and 824a. In this embodiment, the openings 824 and 824a allow the movement of water in the standard lower portions 824q and 824aq including the portion at the height of the standard water level LWL.

[0079] The communication portions 900 and 900a (Figs. 4(C) and 5(A)) communicate the anaerobic filter bed tank 820 and the contact filter bed tank 830 at at least a part of a first portion L1 which is a 1 / 3 portion including the first end e1 on the outer wall 801t side of the virtual line L. According to this configuration, as described in Figs. 4(D) and 4(E), the water that has moved along the outer wall 801t to the positions of the partition walls 803 and 803a can easily move into the anaerobic filter bed tank 820 through the communication portion (here, the openings 824 and 824a). Thus, the above configuration can move the water containing solids from the contact filter bed tank 830 to the upstream anaerobic filter bed tank 820. Therefore, the amount of solids in the contact filter bed tank 830 can be reduced. As a result, the concentration of solids in the water transferred to the downstream side from the contact filter bed tank 830 can be reduced. For example, the concentration of solids contained in the water discharged from the wastewater treatment device can be reduced.

[0080] Also, in the contact filter bed tank 830, nitrification proceeds by aerobic treatment. When the nitrified liquid is returned to the anaerobic filter bed tank 820 through the communication portion, denitrification by anaerobic treatment in the anaerobic filter bed tank 820 proceeds. Therefore, the concentration of nitrogen (for example, any one of nitrite nitrogen concentration, nitrate nitrogen concentration, and total nitrogen concentration) contained in the water discharged from the wastewater treatment device can be reduced.

[0081] In addition, in this embodiment, the anaerobic filter bed tank 820 has a filter medium 822 for supporting anaerobic microorganisms. A member for supporting microorganisms is also called a filter bed (the filter medium 822 is an example of a filter bed). As described above, the anaerobic filter bed tank 820 does not have a member (for example, a scum baffle) that divides the water surface of the anaerobic filter bed tank 820 into a part communicating with the communication part (for example, the communication part 900) of the partition wall 803 and another part. Thus, the anaerobic filter bed tank 820 has the following configuration. FIG. 2(A) shows the target water surface WSt of the anaerobic filter bed tank 820. The target water surface WSt is a water surface that communicates with the upper part 822p of the filter medium 822 without passing through the lower part 822q (FIG. 1) of the filter medium 822. Here, the upper part 822p of the filter medium 822 is a part of the filter medium 822 that contacts the region without the filter medium 822 on the upper side of the filter medium 822, that is, the part that forms the upper end of the filter medium 822. Similarly, the lower part 822q of the filter medium 822 is a part of the filter medium 822 that contacts the region without the filter medium 822 on the lower side of the filter medium 822, that is, the part that forms the lower end of the filter medium 822. In this embodiment, the target water surface WSt is the remaining part of the water surface of the anaerobic filter bed tank 820 excluding the inner part of the inflow baffle 821. From the target water surface WSt, it is possible to reach the upper part 822p without passing through the lower part 822q. From the water surface inside the inflow baffle 821, it is impossible to reach the upper part 822p without passing through the inside of the inflow baffle 821 and the lower part 822q.

[0082] The anaerobic filter bed tank 820 forms such a target water surface WSt. And the anaerobic filter bed tank 820 is configured such that the entire target water surface WSt communicates with the communication part (for example, the communication parts 900, 900a). Therefore, the water and solids that have moved from the contact filter bed tank 830 to the anaerobic filter bed tank 820 through the communication part can be dispersed on the target water surface WSt of the anaerobic filter bed tank 820. Thus, the anaerobic filter bed tank 820 can easily receive the water and solids that move from the contact filter bed tank 830 through the communication part. In addition, the solids dispersed on the target water surface WSt can settle on the upper part 822p of the filter medium 822. Thus, the anaerobic filter bed tank 820 can capture the solids returned from the contact filter bed tank 830 by the filter medium 822.

[0083] Also, in this embodiment, the anaerobic filter bed tank 820 (Fig. 1) is configured such that water flowing into the anaerobic filter bed tank 820 from the upstream side of the anaerobic filter bed tank 820 passes through the filter medium 822 from bottom to top and flows into the contact filter bed tank 830 through the communication parts (for example, communication parts 900, 900a). If the anaerobic filter bed tank is configured such that the water flowing into the anaerobic filter bed tank passes through the filter bed from top to bottom, a flow path connecting the region below the filter bed and the communication part (for example, communication part 900d) is provided in the anaerobic filter bed tank, such as the advection baffle 823d in Fig. 6(A). As described above, such a flow path can limit the movement of solids that have moved from the contact filter bed tank to the anaerobic filter bed tank through the communication part to a position far from the communication part. And the solids that have moved from the contact filter bed tank to the anaerobic filter bed tank can return to the contact filter bed tank again. When the flowing direction of the water in the filter medium 822 is upward, a flow path such as the advection baffle 823d can be omitted, so the possibility of solids returning to the contact filter bed tank can be easily reduced.

[0084] Also, in this embodiment, the wastewater treatment devices 800, 800a include an outer wall 801 (Fig. 1) that forms the outer surface of the wastewater treatment devices 800, 800a. The outer wall 801 houses the anaerobic filter bed tank 820 and the contact filter bed tank 830. The outer side wall 801t (Figs. 4(C), 5(A)) is a part of the outer wall 801. The communication parts 900, 900a are at least a part of the first part L1 of the virtual line L and communicate the anaerobic filter bed tank 820 and the contact filter bed tank 830. According to this configuration, as shown in Fig. 4(E), the water that has moved along the outer side wall 801t to the position of the partition wall 803 can easily move into the anaerobic filter bed tank 820 through the communication part (for example, communication part 900).

[0085] Normally, the outer wall 801 does not have a part that protrudes toward the inside of the wastewater treatment device like the shelf 843a (Fig. 3). Therefore, it is preferable to arrange the communication parts 900, 900a near the outer wall 801 (for example, the first part L1) from the viewpoint of returning solids.

[0086] Also, in this embodiment, the aeration device 834 (FIG. 2(B)) has a plurality of holes 834o for discharging gas. The holes 834o are examples of discharge portions for discharging gas. The communication portions 900, 900a (FIG. 3(C), FIG. 5(A))) are at least a part of the first portion L1 and communicate the anaerobic filter bed tank 820 and the contact filter bed tank 830. The outer wall 801t (FIG. 4(D)) is different from the side wall portion 843 having the shelf 843a and is configured not to inhibit the upward water flow F0 generated by aeration from reaching the vicinity of the outer wall 801t. Such a wall configuration may be specified, for example, as follows. The first hole 834o1 of the aeration device 834 (FIG. 2(B), FIG. 3) is the hole 834o closest to the first end e1 among the plurality of holes 834o of the aeration device 834. The first virtual straight line segment SL1 is a virtual straight line segment connecting the first end e1 and the first hole 834o1. The outer wall 801t is arranged at a position that does not intersect the first virtual straight line segment SL1. Therefore, the upward water flow generated by the bubbles from the first hole 834o1 can easily reach the vicinity of the first end e1. Such an upward water flow can easily flow into an opening (for example, the opening 824) close to the outer wall 801t as described in FIGS. 4(D) and 4(E). Thus, the water moved by the aeration by the aeration device 834 can appropriately move to the anaerobic filter bed tank 820 through the communication portions 900, 900a.

[0087] On the other hand, the configuration of the side wall portion 843 is specified as follows. The second hole 834o2 of the aeration device 834 (FIG. 2(B), FIG. 3) is the hole 834o closest to the second end e2 among the plurality of holes 834o of the aeration device 834. The second virtual straight line segment SL2 is a virtual straight line segment connecting the second end e2 and the second hole 834o2. The side wall portion 843 includes a portion (for example, the shelf 843a) that intersects the second virtual straight line segment SL2. The portion that intersects the second virtual straight line segment SL2 may inhibit the upward water flow generated by the bubbles from the second hole 834o2 from approaching the vicinity of the second end e2.

[0088] B. Second Embodiment: Figures 8(A) and 8(B) are diagrams showing the schematic configuration of another embodiment of the wastewater treatment apparatus. As with FIG. 1, FIG. 8(A) shows the wastewater treatment apparatus 800e viewed from the side. As with FIG. 2(A), FIG. 8(B) shows the wastewater treatment apparatus 800e viewed from below. The difference from the embodiments of FIGS. 1 and 2(A) is only that a baffle 829 is added to the anaerobic filter bed tank 820e. The configurations of the other parts of the wastewater treatment apparatus 800e are the same as those of the corresponding parts of the wastewater treatment apparatus 800. Among the parts of the wastewater treatment apparatus 800e, the parts corresponding to the parts of the wastewater treatment apparatus 800 are given the same reference numerals and the description thereof is omitted.

[0089] As shown in FIG. 8(A), the baffle 829 extends from the height between the standard water level LWL and the filter medium 822 to a height above the standard water level LWL (here, a height above the high water level HWL). As shown in FIG. 8(B), the baffle 829 extends from the +Y-side connection part to the -Y-side connection part between the partition wall 803 and the outer wall 801. The baffle 829 divides the target water surface WSt into a closed first water surface part WSt1 continuous with the communication part 900 and the remaining second water surface part WSt2. The baffle 829 can reduce the possibility that solids (also called scum) floating on the second water surface part WSt2 move to the contact filter bed tank 830 through the opening 824.

[0090] Such a baffle 829 can limit the movement of solids and water passing through the opening 824 from the contact filter bed tank 830 to the anaerobic filter bed tank 820, similar to the advection baffle 823d in FIG. 6. Here, when the first water surface part WSt1 is wide, the solids and water that have moved to the anaerobic filter bed tank 820 through the opening 824 can diffuse to a position far from the opening 824. Thus, when the ratio of the area of the first water surface part WSt1 (referred to as the first partial area St1) to the area of the target water surface WSt (referred to as the target area St) is large, the movement of solids from the contact filter bed tank 830 to the anaerobic filter bed tank 820 through the opening 824 is promoted. The ratio of the first partial area St1 to the target area St is preferably large, for example, preferably 1 / 5 or more, particularly preferably 1 / 4 or more, and most preferably 1 / 3 or more.

[0091] C. Third Embodiment: FIG. 9 is a diagram showing another embodiment of the wastewater treatment apparatus. Similar to FIG. 4(C), FIG. 9 shows a part of the partition wall 803f as viewed in the -X direction from inside the contact filter bed tank 830. The difference between this embodiment and the embodiment of FIG. 4(C) is only that the partition wall 803f of this embodiment is the same as the upper part of the partition wall 803 of FIG. 4(C) above the opening 824 removed. The configuration of other parts of the wastewater treatment apparatus 800f is the same as the corresponding parts of the wastewater treatment apparatus 800. Among the parts of the wastewater treatment apparatus 800f, the parts corresponding to the parts of the wastewater treatment apparatus 800 are given the same reference numerals and the description thereof is omitted.

[0092] As shown in the figure, instead of the opening 824 (FIG. 4(C)), the partition wall 803f forms a weir 824f. The weir 824f is formed by the upper end 803fu of the partition wall 803f disposed at a position lower than the standard water level LWL. The weir 824f allows the movement of water between the anaerobic filter bed tank 820 and the contact filter bed tank 830 at a height of the standard water level LWL higher than the upper end 803fu of the partition wall 803f. In this embodiment, the weir 824f allows the movement of water in the open part between the standard water level LWL and the upper end 803fu. The communication part 900f is the part of the partition wall 803f that forms the weir 824f (here, the L-shaped part corresponding to the edge of the weir 824f).

[0093] The virtual line L in the figure is a virtual line that connects the outer wall 801t and the side wall portion 843 at the height of the standard water level LWL on the boundary surface BPf, similar to the virtual line L (Figure 4(C)). The virtual line L in Figure 9 is the same as the virtual line L in Figure 4(C). Here, the boundary surface BPf includes the specific side surface 803fs and the virtual surface 824fs indicating the open part of the weir 824f (i.e., the part above the upper end 803fu). The specific side surface 803fs is the inner side surface of the contact filter bed tank 830 formed by the partition wall 803f, similar to the specific side surface 803s (Figure 4(C)). As the virtual surface 824fs, when the part below the standard water level LWL in the open part of the weir 824f can be closed by a plane, that plane is adopted. In this embodiment, the part of the specific side surface 803fs that forms the weir 824f (i.e., the surface of the contact filter bed tank 830 side of the communication part 900f) is flat. In this case, as the virtual surface 824fs, a plane that is continuous and parallel to this flat part (i.e., the plane that closes the open part of the weir 824f) is adopted.

[0094] If the communication part 900f includes a bent part and the part below the standard water level LWL in the open part of the weir 824f cannot be closed by a plane, the shortest straight line connecting the two edges of the weir 824f at the height of the standard water level LWL (e.g., the first edge eo1 and the second edge eo2 in Figure 9) is adopted as part of the virtual line L. As the virtual surface 824fs, the surface with the minimum area that includes this straight line and closes the part below the standard water level LWL in the open part of the weir 824f is adopted. As shown in Figure 9, when one edge eo1 of the weir 824f at the height of the standard water level LWL is formed by the outer wall 801t instead of the partition wall 803f, the part of the outer wall 801t at the height of the standard water level LWL that is closest to the second edge eo2 formed by the partition wall 803f is adopted as the first edge eo1 (and thus the first end e1).

[0095] As described above, the difference between the partition wall 803 in FIG. 4(C) and the partition wall 803f in FIG. 9 is only that the opening 824 is replaced by the weir 824f. Therefore, the boundary surface BPf indicates the same surface as the boundary surface BP. Also, the substandard portion 824fq of the weir 824f is the same as the substandard portion 824q in FIG. 4(C).

[0096] Similar to the communication portion 900 in FIG. 4(C), the communication portion 900f is at least a part of the first portion L1 of the virtual line L and communicates the anaerobic filter bed tank 820 and the contact filter bed tank 830. Therefore, in this embodiment, similar to the embodiment in FIG. 4(C), water containing solids can be moved from the contact filter bed tank 830 to the upstream anaerobic filter bed tank 820.

[0097] D. Modification example: (1) Instead of the above configuration, the configuration of the communication portion may be various other configurations. For example, the outer wall 801t (FIG. 2(B), FIG. 3) may include a portion intersecting the first virtual straight line segment SL1. For the transfer of solids from the contact filter bed tank 830 to the anaerobic filter bed tank 820, it is preferable that the portion of the outer wall 801t intersecting the first virtual straight line segment SL1 is small.

[0098] The communication portion may communicate the anaerobic filter bed tank 820 and the contact filter bed tank 830 in the second portion L2 (FIG. 4(B)). Here, it is preferable that the portion of the side wall portion 843 (FIG. 2(B), FIG. 3) intersecting the second virtual straight line segment SL2 is small, and it is particularly preferable that the side wall portion 843 is arranged at a position where it does not intersect the second virtual straight line segment SL2.

[0099] The communication part may form one or both of the opening and the weir. The shape of the opening may be any shape such as a circle, a rectangle, an ellipse, etc. The communication part may communicate the anaerobic filter bed tank 820 and the contact filter bed tank 830 across the whole between the outer wall 801t (Fig. 4(B)) and the side wall part 843. That is, the communication part may communicate the anaerobic filter bed tank 820 and the contact filter bed tank 830 across the whole of the virtual line L. Here, the whole between the outer wall 801t and the side wall part 843 of the partition wall 803 may form a weir. In this case, unlike the specific side surface 803s (Fig. 4(C)), the specific side surface formed by the partition wall does not include a portion higher than the standard water level LWL. In such a case, as a virtual surface indicating the open part of the weir, a virtual surface obtained by extending the upper end (for example, the upper end 803fu (Fig. 9)) of the partition wall formed by the weir in the vertically upward direction may be adopted. As a virtual line connecting the outer wall 801t and the side wall part 843 at the height of the standard water level LWL, a line on such a virtual surface can be adopted.

[0100] (2) In each of the above embodiments and each modification, the first wall and the second wall that respectively form the inner side surfaces of the contact filter bed tank 830 in directions different from the specific side surface formed by the partition plate may be various other walls instead of the outer wall 801t and the side wall part 843. For example, both the first wall and the second wall may be walls different from the outer wall 801 (that is, walls arranged inside the space formed by the outer wall 801). And the partition plate may have one or both of a communication part that communicates at a first part close to the first wall and a communication part that communicates at a second part close to the second wall among the virtual lines.

[0101] (3) The baffle 829 (Fig. 8(B)) may be applied to each of the above-described embodiments (e.g., the wastewater treatment apparatuses 800, 800a - 800f) and each modification. Here, the shape of the baffle 829 when viewed downward may be any shape that divides the target water surface WSt into a closed first water surface portion WSt1 continuous with the communication portion and the remaining second water surface portion WSt2. Also, as shown in Fig. 8(A), the baffle 829 preferably extends from a position between the standard water level LWL and the filter medium 822d to a position higher than the standard water level LWL. However, like the advection baffle 823d in Fig. 6(A), the baffle 829 may extend from a position higher than the standard water level LWL to a position lower than the filter medium 822.

[0102] (4) In each of the above-described embodiments and each modification, the configuration of the aeration device may be various other configurations instead of the configuration of the aeration device 834 in Fig. 2(B). For example, the aeration device may be a porous aeration device or a membrane type aeration device. In any case, the aeration device has a plurality of portions (holes, slits, etc.) from which bubbles separate from the aeration device. Such portions are examples of discharge portions for discharging gas.

[0103] (5) The configuration of the wastewater treatment apparatus may be various other configurations instead of the above-described configuration. For example, the configuration of the wastewater treatment apparatus may be various configurations including a pretreatment tank, an aerobic treatment tank provided downstream of the pretreatment tank, a partition wall that partitions between the pretreatment tank and the aerobic treatment tank, and a first wall and a second wall respectively connected to the partition wall. Here, the first wall and the second wall respectively form inner side surfaces of the aerobic treatment tank in directions different from a specific inner side surface of the aerobic treatment tank formed by the partition wall.

[0104] Here, the pretreatment tank is not limited to an anaerobic filter bed tank (e.g., anaerobic filter bed tanks 820, 820d, 820e), and may be various water treatment tanks that treat water without aeration. For example, the pretreatment tank may be configured such that the water flowing into the pretreatment tank passes through the filter bed from top to bottom. Also, the filter bed may be omitted from the pretreatment tank. For example, the pretreatment tank may be a water treatment tank (such as an impurity removal tank, a sedimentation separation tank, etc.) that separates and stores solids.

[0105] In addition, the aerobic treatment tank provided on the downstream side of the pretreatment tank is not limited to a contact filtration bed tank (for example, the contact filtration bed tank 830), and may be various water treatment tanks having an air diffuser and performing aerobic treatment. For example, the aerobic treatment tank may be any one of a contact aeration tank, a carrier fluidization tank, and a membrane separation activated sludge tank.

[0106] In any case, the wastewater treatment device may have various water treatment tanks including a pretreatment tank and an aerobic treatment tank provided on the downstream side of the pretreatment tank. For example, the wastewater treatment device may have a flow rate adjustment tank. Further, the wastewater treatment device may be a module used in combination with other wastewater treatment devices.

[0107] The above-described embodiments and modified examples can be appropriately combined. Also, the above-described embodiments and modified examples are for facilitating the understanding of the present disclosure and do not limit the present invention. The present invention can be changed and improved without departing from its gist, and equivalents thereof are included in the present invention.

Explanation of Reference Numerals

[0108] 800, 800a - 800d... Drainage treatment device, 801... Outer wall, 801t... Outer side wall, 801s... Side surface, 802, 802d... Partition wall, 803, 803a - 803d... Partition wall, 803a - 803c... Partition wall, 803s, 803as - 803ds, 803fs... Specific side surface, 803fu... Upper end, 804... Inlet, 805... Outlet, 810... Impurity removal tank, 812... Inflow baffle, 814, 814d... Opening, 820, 820d, 820e... Anaerobic filter bed tank, 821... Inflow baffle, 822, 822d... Filter medium, 822p... Upper part, 822q... Lower part, 823d... Advection baffle, 824... Opening (corner opening), 824a - 824d... Opening (round opening), 824f... Weir, 824s, 824as - 824ds, 824fs... Virtual surface, 824q, 824aq - 824dq, 824fq... Standard lower part, 829... Baffle, 830... Contact filter bed tank, 832... Contact material, 833... Aerobic filter medium, 834... Air diffuser, 834o... Hole, 834o1... First hole, 834o2... Second hole, 836... Opening, 840... Treatment water tank, 842... Side wall part, 843... Side wall part, 843a... Shelf, 843s... Side surface, 844... Side wall part, 850... Disinfection tank, 854... Chemical agent cylinder, 870... Discharge air lift pump, 872... Suction port, 874... Discharge port, 880... Circulation air lift pump, 882... Suction port, 884... Discharge port, 900, 900a - 900d, 900f... Communication part, BP, BPa - BPd, BPf... Interface, LWL... Standard water level, HWL... High water level, WSt... Target water surface, WSt1... First water surface part, WSt2... Second water surface part, L, Ld... Virtual line, L1... First part, L2... Second part, L3... Third part, Ld1 - Ld3... Parts, e1... First end, e2... Second end, SL1... First virtual straight line segment, SL2... Second virtual straight line segment

Claims

1. A wastewater treatment apparatus comprising: a pretreatment tank that treats water without aeration; an aerobic treatment tank provided downstream of the pretreatment tank and having an aeration device; a partition wall that partitions between the pretreatment tank and the aerobic treatment tank; a first wall and a second wall that respectively form inner side surfaces of the aerobic treatment tank in directions different from a specific side surface which is an inner side surface of the aerobic treatment tank formed by the partition wall, the first wall and the second wall being respectively connected to the partition wall; and the partition wall has a communication part that communicates the pretreatment tank and the aerobic treatment tank at a height of a standard water level of the aerobic treatment tank between the first wall and the second wall; the communication part forms one or both of an opening extending from a position lower than the standard water level to a position higher than the standard water level and a weir that forms an upper end of the partition wall disposed at a position lower than the standard water level, the opening allows water movement between the pretreatment tank and the aerobic treatment tank at the height of the standard water level inside the opening, and the weir allows water movement between the pretreatment tank and the aerobic treatment tank at the height of the standard water level higher than the upper end of the partition wall; the communication part is at least a part of a first part which is 1 / 3 of a portion including a first end on the first wall side, or at least a part of a second part which is 1 / 3 of a portion including a second end on the second wall side, of a virtual line connecting the first wall and the second wall at the height of the standard water level along a boundary surface between the pretreatment tank and the aerobic treatment tank including the specific side surface, and communicates the pretreatment tank and the aerobic treatment tank; a wastewater treatment apparatus.

2. The wastewater treatment apparatus according to claim 1, wherein the pretreatment tank has a filter bed for supporting anaerobic microorganisms; the pretreatment tank is configured to form a target water surface which is a water surface that communicates with an upper part of the filter bed without passing through a lower part of the filter bed; the pretreatment tank is configured such that the entire target water surface communicates with the communication part. a wastewater treatment apparatus.

3. The wastewater treatment apparatus according to claim 1, wherein the pretreatment tank has a filter bed for supporting anaerobic microorganisms; the pretreatment tank is configured to form a target water surface which is a water surface that communicates with an upper part of the filter bed without passing through a lower part of the filter bed; The pretreatment tank has a baffle that divides the target water surface into a closed first water surface portion continuous with the communication portion and the remaining second water surface portion. The area of the first water surface portion is 1 / 5 or more of the area of the target water surface. Wastewater treatment device.

4. The wastewater treatment device according to claim 2 or 3, The pretreatment tank is configured such that water flowing into the pretreatment tank from the upstream side of the pretreatment tank passes upward through the filter bed and flows into the aerobic treatment tank through the communication portion. Wastewater treatment device.

5. The wastewater treatment device according to any one of claims 1 to 3, further comprising an outer wall forming the outer surface of the wastewater treatment device, the outer wall accommodating the pretreatment tank and the aerobic treatment tank, the first wall being a part of the outer wall, the communication portion being at least a part of the first portion and communicating the pretreatment tank and the aerobic treatment tank. Wastewater treatment device.

6. The wastewater treatment device according to any one of claims 1 to 3, the air diffuser having a plurality of discharge portions for discharging gas, the first wall being disposed at a position that does not intersect a virtual straight line connecting the first end and the discharge portion closest to the first end, the communication portion being at least a part of the first portion and communicating the pretreatment tank and the aerobic treatment tank. Wastewater treatment device.

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