Filtration cassette

Abstract

This technology enables more efficient filtration operation of treatment tanks. [Solution] The filtration cassette installed in the treatment tank comprises a housing, an inlet provided at the bottom of the housing through which the water to be treated flows in, an outlet provided in the housing through which the water to be treated flows out, a filter material housed inside the housing that forms a filtration layer between the inlet and the outlet, and a switching device that can switch the filtration cassette between a first state and a second state in which the opening width of the inlet is smaller than that of the first state.

Description

Technical Field

[0001] The present invention relates to a filtration cassette installed in a treatment tank.

Background Art

[0002] Conventionally, in water treatment plants, sewage treatment plants, etc., the water to be treated is stored in a sedimentation tank to precipitate solids, and then this water to be treated is passed upward through a filtration member installed in the sedimentation tank for filtration treatment.

[0003] In relation to this, Patent Document 1 discloses a filtration cassette installed in a sedimentation tank that circulates and filters the water to be treated by an upward flow. This filtration cassette includes a housing and a filter medium disposed within the housing, and perforated plates (water-permeable plates) that allow the passage of the water to be treated and prevent the passage of the filter medium are provided at the lower opening and the upper opening of the housing.

[0004] Further, Patent Document 2 discloses a technique for providing a water-permeable member (water-permeable plate) detachably in a filter bed having a water-permeable member (water-permeable plate) and a filter medium placed thereon.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] The technology according to the present disclosure aims to enable more efficient filtration operation of a treatment tank.

Means for Solving the Problems

[0007] To solve the above problems, the technology disclosed herein employs the following configuration. Specifically, the technology disclosed herein is a filtration cassette installed in a treatment tank for circulating and filtering water to be treated, comprising: a housing; an inlet provided at the bottom of the housing through which the water to be treated flows in; an outlet provided in the housing through which the water to be treated flows out; a filter material housed within the housing and forming a filtration layer between the inlet and the outlet; and a switching device capable of switching the filtration cassette between a first state and a second state in which the opening width of the inlet is smaller than that of the first state. [Effects of the Invention]

[0008] According to the technology disclosed herein, it becomes possible to perform the filtration operation of the treatment tank more efficiently. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 shows the configuration of a sedimentation tank 100 equipped with a filtration cassette 50 according to an embodiment. [Figure 2] Figure 2 is a longitudinal cross-sectional view showing the first state of the filtration cassette 50A according to Embodiment 1 during filtration operation. [Figure 3] Figure 3 is a longitudinal cross-sectional view showing the second state of the filtration cassette 50A according to Embodiment 1 during the washing operation. [Figure 4] Figure 4 is a longitudinal cross-sectional view showing the first state of the filtration cassette 50B according to Embodiment 2 during filtration operation. [Figure 5] Figure 5 is a longitudinal cross-sectional view showing the second state of the filtration cassette 50B according to Embodiment 2 during the washing operation. [Figure 6] Figure 6 is a longitudinal cross-sectional view showing the first state of the filtration cassette 50C according to Embodiment 3 during filtration operation. [Figure 7] Figure 7 is a longitudinal cross-sectional view showing the second state of the filtration cassette 50C according to Embodiment 3 during the washing operation. [Figure 8] Figure 8 is a cross-sectional view of the filtration cassette 50C, showing a cross-section along the CC line in Figure 6. [Figure 9]Figure 9 is a cross-sectional view of the filtration cassette 50C, showing a cross-section along the DD line in Figure 7. [Figure 10] Figure 10 is a bottom view showing the first state of the filtration cassette 50D according to Embodiment 4. [Figure 11] Figure 11 is a bottom view showing the second state of the filtration cassette 50D according to Embodiment 4. [Modes for carrying out the invention]

[0010] Embodiments of this disclosure will be described below with reference to the drawings. However, this description should not be interpreted as limiting, and will not limit the subject matter described in the claims. Furthermore, various changes, substitutions, and modifications can be made without departing from the spirit and scope of this disclosure. Different embodiments can also be combined as appropriate.

[0011] The treatment tank to which the filtration cassette described herein is installed is not particularly limited, as it is any tank for separating solid matter (suspended matter) from the water to be treated. Specifically, the treatment tank may be, for example, a sedimentation tank for sedimenting and removing solid matter contained in the water to be treated in sewage treatment, and for further filtration treatment of the water from which sediment has been removed. This sedimentation tank may be a primary sedimentation tank located upstream of the reaction tank, or a final sedimentation tank located downstream of the reaction tank. The treatment tank may also be, for example, a solid-liquid separation tank that separates, concentrates, recovers, and removes solid matter contained in the water to be treated by utilizing the difference in specific gravity between liquid and solid in industrial water treatment. Below, as an example of a treatment tank, a case in which the filtration cassette described herein is installed in a sedimentation tank in sewage treatment will be described.

[0012] [Sedimentation tank 100] First, the overall configuration of the sedimentation tank 100, which is common to each embodiment (Embodiments 1 to 4), will be described. The sedimentation tank 100 is an example of a filtration device equipped with a filtration cassette according to the embodiment.

[0013] The sedimentation tank 100, for example, as a sedimentation tank exemplified by the primary sedimentation tank or the final sedimentation tank, constitutes a part of a water treatment system that treats treated water (e.g., sewage). This water treatment system includes, for example, a primary sedimentation tank that sediment-separates solids such as contaminants (e.g., solid organic matter) contained in the treated water, a reaction tank provided on the downstream side of the primary sedimentation tank that treats the treated water by biological treatment such as the standard activated sludge method, a final sedimentation tank provided on the downstream side of the reaction tank that sediment-separates solids such as activated sludge contained in the treated water, a concentration device that concentrates the contaminants (primary sludge) sediment-separated by the primary sedimentation tank and the activated sludge (excess sludge) sediment-separated by the final sedimentation tank, and a digestion tank that biologically treats the organic components contained in the primary sludge and excess sludge supplied from the concentration device by anaerobic bacteria.

[0014] [Overall Configuration] FIG. 1 is a diagram showing the configuration of the sedimentation tank 100 provided with the filtration cassette 50 according to the embodiment. FIG. 1(A) is a top view of the sedimentation tank 100, FIG. 1(B) is a longitudinal sectional view of the sedimentation tank 100 showing a cross section along the line A-A in FIG. 1(A), and FIG. 1(C) is a longitudinal sectional view of the sedimentation tank 100 showing a cross section along the line B-B in FIG. 1(A). Here, the sedimentation tank 100 is configured such that the treated water flows in from the upstream side and flows toward the downstream side. Hereinafter, the direction in which the treated water flows in the sedimentation tank 100 is referred to as the "flow direction" and is indicated by the symbol L. Also, the depth direction (i.e., the vertical direction) of the sedimentation tank 100 is referred to as the "vertical direction" and is indicated by the symbol V. Also, the direction orthogonal to the flow direction L and the vertical direction V is referred to as the "width direction" and is indicated by the symbol H. Therefore, in FIG. 1(B), a cross section orthogonal to the width direction H is shown, and in FIG. 1(C), a cross section orthogonal to the flow direction L is shown. Note that the flow direction L, the vertical direction V, and the width direction H also mean the same directions in the description of the filtration cassette 50 described later.

[0015] As shown in Fig. 1(A), the sedimentation tank 100 includes, for example, a sedimentation basin 10 for storing the water to be treated, and a filtration cassette 50 installed in the sedimentation basin 10 for circulating and filtering the water to be treated. The sedimentation tank 100, for example, precipitates relatively coarse solids contained in the water to be treated flowing into the sedimentation basin 10 by gravity sedimentation in the sedimentation basin 10, and further separates relatively fine solids by filtering the water to be treated with the filtration cassette 50. The water to be treated from which solids have been filtered and separated by the filtration cassette 50 (hereinafter also referred to as "filtered water") is discharged to, for example, subsequent equipment. Specifically, when the sedimentation tank 100 is the first sedimentation tank, the water to be treated is discharged to the reaction tank by, for example, a pump or the like. When the sedimentation tank 100 is the final sedimentation tank, the water to be treated is discharged to, for example, a sterilization treatment device (not shown). Thereafter, the sterilization treatment device sterilizes, for example, the water to be treated discharged from the final sedimentation tank and discharges the sterilized treated water into a river or the like.

[0016] The sedimentation basin 10 is an example of the treatment tank according to the present disclosure. For example, it is a cross-flow sedimentation basin that retains the water to be treated flowing into the sedimentation basin 10 and separates the solids contained in the water to be treated by sedimenting them by gravity sedimentation. The water to be treated flows into the sedimentation basin 10 from the upstream side in the flow direction L and flows toward the downstream side. The sedimentation basin 10 is formed in a substantially rectangular parallelepiped shape having, for example, a bottom 10a and side walls 10b, and the longitudinal direction of the sedimentation basin 10 coincides with the flow direction L of the water to be treated. That is, the water to be treated flows along the longitudinal direction of the sedimentation basin 10, specifically, from the left side to the right side in Fig. 1(A). In a top view, the side wall 10b has a rectangular shape elongated in the flow direction L.

[0017] Also, as shown in Figs. 1(A) to 1(C), the sedimentation tank 100 includes, for example, a plurality of partition walls partitioning the inside of the sedimentation basin 10. The plurality of partition walls includes a plurality of vertically installed partition plates 20 and a plurality of horizontally installed partition plates 30. By the partition plates 20 and 30, for example, a sedimentation section 110, a filtration section 120, a treatment water flow path 130, and a washing and drainage tank 140 are partitioned inside the sedimentation basin 10.

[0018] In the sedimentation section 110, for example, treated water flows in, and a portion of the solids in the treated water settles by gravity. As shown in Figure 1(B), the sedimentation section 110 is, for example, the area enclosed by the bottom 10a, side walls 10b, and partition plates 20, 30 of the sedimentation tank 10. The sedimentation section 110 is formed in the flow direction L, extending from the upstream side to the downstream side of the sedimentation tank 10. As shown in Figure 1(B), the bottom 10a of the sedimentation tank 10 that constitutes the sedimentation section 110 is formed such that the depth of the sedimentation tank 10 gradually decreases as the flow direction L is directed from the upstream side to the downstream side. A solids discharge pipe 102 equipped with a solids discharge valve 101 is installed at the bottom 10a. For example, by opening the solids discharge valve 101 at all times or at predetermined intervals, the solids that have settled in the sedimentation section 110 are discharged from the sedimentation tank 10 via the solids discharge pipe 102 and supplied to downstream equipment (for example, a concentration device).

[0019] The filtration section 120 filters the water to be treated, from which some of the solids have been separated by the sedimentation section 110, using a filtration cassette 50. As shown in Figures 1(A) to 1(C), the filtration section 120 is a rectangular parallelepiped region defined, for example, by the filtration cassette 50. As shown in Figure 1(B), for example, the filtration section 120 is adjacent to the upper region of the sedimentation section 110 on the downstream side in the flow direction L, and adjacent to the downstream region of the sedimentation section 110 on the upper side. The top and bottom surfaces of the filtration section 120 are open. The water to be treated flows into the filtration section 120 from the downstream region of the sedimentation section 110 by an upward flow. In addition, a partition plate 20 between the filtration section 120 and the sedimentation section 110 prevents the water to be treated from overflowing the sedimentation section 110 and flowing into the filtration section 120.

[0020] The filtration section 120 has, for example, multiple rectangular parallelepiped-shaped filtration cassettes 50 arranged in parallel. Specifically, as shown in Figure 1(A), the filtration section 120 has, for example, three filtration cassettes 50 arranged in a row with spacing in the width direction H. However, the number and shape of the filtration cassettes 50 arranged in the filtration section 120 are not particularly limited.

[0021] The filtration cassette 50 is installed in the filtration section 120, for example, immersed in the water to be treated. Between adjacent filtration cassettes 50 spaced apart in the width direction H, a sealing member 40 is provided to prevent the water to be treated flowing in from the sedimentation section 110 from leaking out through the gaps between the filtration cassettes 50 and flowing downstream (to the treated water flow path 130). The sealing member 40 is, for example, a flange-shaped member that protrudes from the side of the filtration cassette 50 and extends horizontally. The flange-shaped members of adjacent filtration cassettes 50 overlap near the water surface, sealing the gaps between the filtration cassettes 50. The water to be treated (filtered water), from which solids have been separated by the filtration cassette 50, overflows the filtration section 120 and flows into the treated water flow path 130.

[0022] Hereinafter, as will be explained in detail later, the housing 1 of the filtration cassette 50 contains a filter material 2 for filtering the water to be treated (see Figure 2). In the sedimentation tank 100, for example, under normal circumstances, the water to be treated is filtered by the filtration cassette 50, and at predetermined intervals, or when the solid-liquid separation performance of the filter material 2 deteriorates, the filtration of the water to be treated is temporarily stopped and the filter material 2 is washed. Hereinafter, in the sedimentation tank 100, the operation of filtering the water to be treated will be referred to as the "filtration operation," and the operation of washing the filter material 2 will be referred to as the "washing operation."

[0023] As shown in Figure 1(B), the sedimentation tank 100 is equipped with, for example, an aeration cleaning mechanism 60 for performing a cleaning operation. The aeration cleaning mechanism 60 includes, for example, a blower 601 for supplying air and an air cleaning pipe 602 connected to the blower 601. The air outlet of the air cleaning pipe 602 is inserted into the filter cassette 50, and the air supplied from the blower 601 is sent into the filter cassette 50 via the air cleaning pipe 602. The aeration cleaning mechanism 60 generates a swirling flow inside the filter cassette 50 by aeration, thereby agitating and cleaning the filter material 2. The treated water containing solids (hereinafter also referred to as "cleaning wastewater") generated during the cleaning operation by the aeration cleaning mechanism 60 overflows the filtration section 120 and flows into the treated water flow path 130.

[0024] The treated water channel 130 carries the treated water (filtered water and washing wastewater) that flows in from the filtration section 120. As shown in Figure 1(B), the treated water channel 130 is formed in a roughly U-shape in a top view, for example, so as to surround the filtration section 120 and the washing wastewater tank 140. More specifically, the treated water channel 130 has, for example, a pair of troughs 130a, 130a extending in the flow direction L and a trough 130b extending in the width direction H. The pair of troughs 130a, 130a are arranged adjacent to the filtration section 120 and the washing wastewater tank 140 on both sides in the width direction H (i.e., sandwiching them). The trough 130b is adjacent to the filtration section 120 on the upstream side in the flow direction L and connects the upstream ends of the pair of troughs 130a, 130a in the flow direction L. As shown in Figure 1(C), the treated water channel 130 is formed in a trough shape by, for example, the side wall 10b of the sedimentation tank 10 and the partition plates 20 and 30. The top surface of the treated water channel 130 is open, and the bottom surface is closed by the partition plate 30.

[0025] The water to be treated flows from the filtration section 120 into the treated water channel 130, and flows from the upstream side to the downstream side in the flow direction L. As shown in Figure 1(A), for example, a gate 70 is provided at the downstream end of the treated water channel 130 to open and close the downstream opening of the treated water channel 130. In addition, an outlet 150 is provided between the pair of troughs 130a, 130a and the washing drainage tank 140, for example, to discharge the washing drainage generated during the washing operation into the washing drainage tank 140. Therefore, during filtration operation, by keeping the gate 70 open, the filtered water flowing from the filtration section 120 into the treated water channel 130 flows out through the gate 70 to the downstream equipment of the sedimentation tank 100 (for example, a sterilization treatment device). At this time, a portion of the filtered water may also flow out to the washing drainage tank 140 through the outlet 150. On the other hand, during the washing operation, by keeping the gate 70 closed, the washing wastewater does not flow out of the sedimentation tank 100 but flows through the outlet 150 into the washing wastewater tank 140.

[0026] The washing wastewater tank 140 stores, for example, washing wastewater flowing in from the treated water channel 130. As shown in Figure 1(B), the washing wastewater tank 140 is, for example, adjacent to the downstream side of the filtration section 120 in the flow direction L, and adjacent to the upper side of the downstream region of the sedimentation section 110. The washing wastewater tank 140 is formed, for example, by the side wall 10b of the sedimentation tank 10 and the partition plates 20 and 30. The top surface of the washing wastewater tank 140 is open, and the bottom surface is closed by the partition plate 30.

[0027] Here, the sedimentation tank 100 includes, for example, a return mechanism 80 that returns the washing wastewater stored in the washing wastewater tank 140 to an area upstream of the filtration unit 120. The return mechanism 80 includes, for example, a pump 801 installed in the washing wastewater tank 140 and a return line 802 that transfers the discharged water from the pump 801. The return mechanism 80 returns the washing wastewater to, for example, the sedimentation unit 110 or equipment upstream of the sedimentation tank 100 (for example, an inflow channel to the sedimentation tank 100).

[0028] [Filtration operation] The filtration operation of the sedimentation tank 100 will be described below. The filtration operation is carried out with the water to be treated continuously flowing into the sedimentation section 110 and the gate 70 of the treated water flow path 130 open.

[0029] In the filtration operation, first, relatively coarse solids contained in the water to be treated that flows into the sedimentation section 110 are separated by sedimentation in the sedimentation section 110. Then, the water from which the solids have been separated flows into the filtration section 120 by upward flow. The water to be treated that flows into the filtration section 120 flows into the filtration cassette 50 and passes through the filtration cassette 50 upward by upward flow. As the water to be treated passes through the filtration cassette 50, relatively fine solids are filtered and separated.

[0030] The water to be treated (i.e., filtered water) that has passed through the filtration cassette 50 overflows the filtration section 120 and flows into the treated water channel 130. The filtered water that has flowed into the treated water channel 130 then flows out of the sedimentation tank 100 through the gate 70.

[0031] At the start of the filtration operation, the water level in the sedimentation section 110 and the water level in the filtration section 120 are approximately equal. However, as time passes, the water flow resistance of the filtration cassette 50 increases, causing the water level in the sedimentation section 110 to rise and become higher than the water level in the filtration section 120. For example, after a certain period of time has elapsed since the start of the filtration operation, or when the water level difference between the sedimentation section 110 and the filtration section 120 exceeds a predetermined level, the system switches to a washing operation.

[0032] [Washing operation] The cleaning operation of the sedimentation tank 100 will be described below. The cleaning operation includes an aeration cleaning process and a rinse cleaning process.

[0033] In the washing operation, aeration washing is performed first. In the aeration washing process, the gate 70 of the treated water flow path 130 is closed to stop the outflow of treated water from the sedimentation tank 100 to the outside. Subsequently, by stopping the outflow of treated water, the water level difference in the sedimentation tank 10 is eliminated, and the inflow of treated water into the sedimentation tank 100 is stopped.

[0034] In this state, the blower 601 of the aeration cleaning mechanism 60 is driven to send air into the filter cassette 50 via the air cleaning pipe 602, aerating the air and creating a swirling flow. The swirling flow causes the filter material 2 inside the filter cassette 50 to flow, and the filter material 2 comes into contact with each other and rubs against each other, thus cleaning the filter material 2. As a result, any solid matter that was trapped in the filter material 2 is detached from the filter material 2 and resuspended in the cleaning wastewater.

[0035] The washing wastewater generated by aeration overflows the filtration section 120 and flows into the treated water channel 130. The washing wastewater that flows into the treated water channel 130 then flows through the outlet 150 into the washing wastewater tank 140.

[0036] Furthermore, during aeration and cleaning, the treated water (cleaning wastewater) is returned by driving the pump 801 of the return mechanism 80. Specifically, the cleaning wastewater that flows into the cleaning wastewater tank 140 is sucked up by the pump 801 and returned upstream of the filtration section 120 via the return line 802.

[0037] After performing aeration cleaning for a predetermined period of time, the aeration cleaning is terminated by stopping the blower 601.

[0038] In the washing operation, a rinse wash is performed next. During the rinse wash process, the blower 601 is stopped and the gate 70 is closed, while the return mechanism 80 continues to return the treated water (washing wastewater). During the rinse wash, the treated water that flows from the sedimentation section 110 to the filtration section 120 passes through the filtration cassette 50 by upward flow and flows into the washing wastewater tank 140 via the treated water flow path 130. The treated water that flows into the washing wastewater tank 140 is returned upstream of the filtration section 120 by the pump 801. By continuing the rinse wash, the washing wastewater is flushed out by the filtered water, and the treated water after the filtration section 120 is gradually purified.

[0039] The rinse cleaning is terminated by stopping the pump 801 after a predetermined time has elapsed since the start of the rinse cleaning, specifically, for example, after a predetermined time has elapsed since the start of the pump 801 operation or after a predetermined time has elapsed since the blower 601 was stopped. The blower 601 may be stopped based on the water quality of the cleaning wastewater measured by a water quality sensor (not shown). For example, a turbidity meter may be installed in the return line 802, and the pump 801 may be stopped when the turbidity of the cleaning wastewater falls below a predetermined value (for example, equivalent to filtered water).

[0040] Once the rinsing is complete, the filtration operation is restarted by opening gate 70. As described above, in the sedimentation tank 100, the filtration operation is temporarily stopped and a washing operation is performed.

[0041] [Draining the water] For example, for periodic cleaning of the sedimentation tank 100 and the filter cassette 50, the treated water is drained from the sedimentation tank 10 while the filter cassette 50 is installed, thereby draining the filter cassette 50 and emptying the water to be treated from within. Alternatively, the filter cassette 50 may be drained by, for example, lifting it out of the sedimentation tank 10.

[0042] [Filtration Cassette 50] The filtration cassette 50 is installed, for example, in the sedimentation tank 10 and is configured to filter the water to be treated by passing it through it. The configuration of the filtration cassette 50 according to each embodiment will be described below.

[0043] [Embodiment 1] First, the configuration of the filtration cassette 50 according to Embodiment 1 will be described. Hereinafter, the filtration cassette 50 according to Embodiment 1 will also be referred to as the filtration cassette 50A. Figures 2 and 3 are schematic diagrams showing the filtration cassette 50A according to Embodiment 1. More specifically, Figure 2 is a longitudinal cross-sectional view showing the first state of the filtration cassette 50A according to Embodiment 1 during filtration operation, and Figure 3 is a longitudinal cross-sectional view showing the second state of the filtration cassette 50A according to Embodiment 1 during washing operation. Figures 2 and 3 show cross-sections of the filtration cassette 50A perpendicular to the flow direction L.

[0044] In the following explanation, when a component is described as "impossible to pass through" an object, it means, for example, that the object is prevented from passing through the component. Also, "opening width" or "flow channel width" refers to the size of the opening or the width of the flow channel that determines the size of an object that can pass through the opening (hole). The opening width may be, for example, a dimension corresponding to the diameter of the largest circle that can be accommodated within the contour of the opening in a plan view. For example, if the opening is circular, the diameter of the opening may be used as the opening width, and if the opening is rectangular, the width in the shorter direction of the opening may be used as the opening width or flow channel width. The flow channel width may be, for example, a dimension corresponding to the diameter of the largest circle that can be accommodated within the contour of a cross-section perpendicular to the flow channel (flow channel cross-section). For example, if the flow channel cross-section is circular, the diameter of the flow channel cross-section may be used as the flow channel width, and if the flow channel cross-section is rectangular, the width in the shorter direction of the flow channel cross-section may be used as the flow channel width.

[0045] As shown in Figures 2 and 3, the filtration cassette 50A comprises, for example, a housing 1, a filter material 2, an inlet 3, an outlet 4, a switching device 5, and a guide section 6. The filtration cassette 50A can be switched by the switching device 5 between a first state shown in Figure 2 and a second state shown in Figure 3, in which the opening width of the inlet 3 is smaller than that of the first state.

[0046] [Cabinet 1] The housing 1 is a container into which the water to be treated is supplied and filtered. The housing 1 is formed, for example, in the shape of a box with a rectangular horizontal cross-section. However, the shape of the housing 1 is not particularly limited, and for example, it may be a cylindrical shape with a circular or elliptical horizontal cross-section.

[0047] As shown in Figure 1(A), the housing 1 has, for example, a rectangular shape when viewed from above, and the filtration cassette 50A is positioned in the sedimentation tank 10 such that the orientation of any two opposing sides of the housing 1 coincides with the flow direction L of the water to be treated. However, the orientation of the filtration cassette 50A is not limited to this.

[0048] As shown in Figures 2 and 3, a filtration chamber 1a is defined inside the housing 1, which is a space through which the filter material 2 is housed and the water to be treated flows. As shown in Figure 2, during filtration operation, a filtration layer 2a is formed in the filtration chamber 1a by the filter material 2 accumulated by the upward flow (indicated by the symbol F1 in Figure 2). Hereinafter, among the walls constituting the housing 1, the wall that defines the side of the filtration chamber 1a will be called the "side wall", the wall that defines the bottom surface of the filtration chamber 1a will be called the "bottom wall", and the wall that defines the top surface of the filtration chamber 1a will be called the "top wall". As shown in Figures 2 and 3, the housing 1 has a side wall 11, a bottom wall 12, and an upper screen 13 formed as the top wall.

[0049] As shown in Figures 2 and 3, the side wall 11 is formed, for example, in a cylindrical shape extending in the vertical direction V, and is arranged to surround the side surface of the filtration chamber 1a. More specifically, the side wall 11 is formed, for example, in a rectangular tubular shape with a square horizontal cross-section. The side wall 11 is configured to prevent, for example, the passage of the water to be treated and the filter material 2.

[0050] Here, as shown in Figures 2 and 3, among the wall portions constituting the side wall 11, the wall portions that are arranged perpendicular to the horizontal direction (for example, the width direction H in this embodiment) and facing each other are designated as a pair of wall portions 11a and 11b. In Figures 2 and 3, wall portion 11a is located on the left side, and wall portion 11b is located on the right side.

[0051] As shown in Figures 2 and 3, the bottom wall 12 is formed, for example, in the shape of a plate and is positioned perpendicular to the vertical direction V at the bottom of the housing 1 (the bottom of the filtration chamber 1a). The bottom wall 12 is provided, for example, at the lower end of the side wall 11. However, the bottom wall 12 only needs to be located below the filter material 2, and may be provided in the middle of the side wall 11. The distance between the lower surface of the filtration layer 2a and the bottom wall 12 is not particularly limited, but it is preferable that it be 30% or more of the thickness (length in the vertical direction) of the filtration layer 2a.

[0052] An opening 14 is formed in the bottom wall 12, which connects the inside (filtration chamber 1a) of the housing 1 to the outside. In other words, the bottom wall 12 covers a portion of the bottom of the filtration chamber 1a, except for the opening 14. The portion of the bottom wall 12 excluding the opening 14 is formed in such a way that, for example, the water to be treated and the filter material 2 cannot pass through it.

[0053] As shown in Figures 2 and 3, the opening 14 is formed, for example, in the vertical direction V, below the filtration layer 2a formed inside the housing 1 (filtration chamber 1a) during filtration operation. The opening 14 is also formed, for example, in the horizontal direction (for example, the width direction H in this embodiment), at the corner of the bottom of the housing 1. Specifically, the opening 14 is formed, for example, at the corner on the wall portion 11a side of the side wall 11 at the bottom of the housing 1.

[0054] As shown in Figure 2, the opening 14, for example, in the first state, is opened to form an inlet 3 for the water to be treated to flow into the inside of the housing 1 (filtration chamber 1a). The opening 14 has a larger opening width than, for example, the communication hole 51a formed in the water passage section 51 described later, and is formed so that the water to be treated and the filter material 2 can pass through. Therefore, as shown in Figure 2, in the first state in which the inlet 3 is formed by the open opening 14, the water to be treated and the filter material 2 can pass through the inlet 3. However, in the first state, the inlet 3 (opening 14) only needs to be able to pass the water to be treated, and does not need to be able to pass the filter material 2. Also, the number and shape of the openings 14 are not particularly limited. For example, multiple openings 14 may be provided at the bottom of the housing 1, or they may be circular in plan view.

[0055] In the embodiments shown in Figures 2 and 3, the opening 14 is formed only in a part of the bottom of the housing 1, but for example, the entire bottom of the housing 1 (the bottom surface of the filtration chamber 1a) may be formed as the opening 14. In other words, for example, the housing 1 does not have to have a bottom wall 12.

[0056] As shown in Figures 2 and 3, the upper screen 13 is formed, for example, in the shape of a plate and is arranged perpendicular to the vertical direction V so as to cover the upper surface of the filtration chamber 1a. The upper screen 13 is provided, for example, at the upper end of the side wall 11. However, the upper screen 13 only needs to be located above the filter material 2 and may be provided in the middle of the side wall 11. It is preferable that the upper screen 13 is located below the water level of the filtration section 120 in the sedimentation tank 10.

[0057] The upper screen 13 is configured to, for example, allow the water to be treated to pass through while preventing the filter material 2 from passing through. The upper screen 13 has a plurality of communication holes formed therein, for example, as outlets 4 for the water to be treated to flow out from the inside of the housing 1 to the outside. The plurality of communication holes are, for example, through holes that penetrate the upper screen 13 in the thickness direction, and are formed so that the water to be treated can pass through but the filter material 2 cannot. In other words, the water to be treated is allowed to flow out to the outside of the housing 1 (filtration chamber 1a) through the outlets 4, while the filter material 2 is prevented from flowing out to the outside of the housing 1 through the outlets 4.

[0058] For the upper screen 13, for example, a perforated plate such as punched metal or a mesh plate such as metal mesh can be used.

[0059] Furthermore, in this embodiment, the outlet 4 is formed on the upper surface of the housing 1, but the position of the outlet 4 on the housing 1 is not limited to this. The outlet 4 only needs to be formed in a position that sandwiches the filtration layer 2a between it and the inlet 3, and may be provided on the side wall 11.

[0060] As shown in Figures 2 and 3, an air cleaning pipe 602 is inserted and positioned inside the housing 1 (filtration chamber 1a) to clean the filter material 2 by blowing air onto it during the cleaning operation. The air outlet 602a of the air cleaning pipe 602 is located below the filtration layer 2a and directly above the opening 14 in the bottom wall 12. In other words, the air outlet 602a is located near the wall portion 11a of the side wall 11 inside the housing 1.

[0061] [Filter material 2] As shown in Figures 2 and 3, the housing 1 contains a plurality of filter materials 2. The filter material 2 has, for example, the ability to float in the water to be treated and to capture solid matter contained in the water to be treated. As the filter material 2, for example, a cylindrical material made of a resin material such as foamed resin with irregularities on its surface can be used. However, the material and shape of the filter material 2 are not particularly limited.

[0062] During filtration operation, the buoyancy acting on the filter material 2 and the upward flow F1 of the water to be treated cause multiple filter materials 2 to accumulate, forming a filtration layer 2a between the inlet 3 and outlet 4 in the filtration chamber 1a, as shown in Figures 2 and 3. Specifically, the filtration layer 2a is located above the inlet 3 and below the outlet 4.

[0063] The filtration layer 2a is constructed by filling it with multiple filter media 2, so that fine gaps are formed between the filter media 2. When the water to be treated passes through these gaps between the filter media 2 and the hollow parts of the cylindrical filter media 2, solid matter contained in the water to be treated is captured on the surface of the filter media 2. During filtration operation, the buoyancy acting on the filter media 2 and the upward flow F1 of the water to be treated push the filter media 2 upward and cause them to float. As shown in Figures 2 and 3, the filtration layer 2a is positioned offset towards the upper part of the filtration chamber 1a. At this time, the upward movement of the filter media 2 is restricted by the upper screen 13, so the filtration layer 2a accumulates on the lower surface of the upper screen 13.

[0064] [Switching device 5] The switching device 5, for example, allows the filtration cassette 50A to be switched between a first state and a second state. As shown in Figures 2 and 3, the switching device 5 according to Embodiment 1 includes, for example, a water passage section 51, a sliding mechanism 52, an air supply pipe 53, intake and exhaust pipes 54a, 54b, a switching valve 55, and a scraper 56, and is mounted on the outside of the housing 1.

[0065] The switching device 5 is configured to allow the water passage section 51 to slide horizontally (for example, in the width direction H in this embodiment) along the bottom of the housing 1, within a range that includes, for example, a first position P1 that opens the opening 14 in the bottom wall 12 as shown in Figure 2, and a second position P2 that covers the opening 14 as shown in Figure 3.

[0066] As shown in Figure 2, for example, when the water passage section 51 is positioned at the first position P1, the open opening 14 forms an inlet 3 at the bottom of the housing 1, and the filtration cassette 50A enters the first state. Also, as shown in Figure 3, for example, when the water passage section 51 is positioned at the second position P2, the communication hole 51a provided in the water passage section 51 covering the opening 14 forms an inlet 3 at the bottom of the housing 1 with a smaller opening width than in the first state, and the filtration cassette 50A enters the second state.

[0067] The water-conducting section 51 is, for example, a water-conducting plate formed in the shape of a plate, and is arranged along the bottom wall 12 of the housing 1 in a state perpendicular to the vertical direction V. For example, in the first state shown in Figure 2, the water-conducting section 51 is positioned at a first position P1 so as to overlap with the bottom wall 12 in the vertical direction V, thereby opening the opening 14, and in the second state shown in Figure 3, the water-conducting section 51 is positioned at a second position P2 so as to overlap with the opening 14 of the bottom wall 12 in the vertical direction V, thereby covering the opening 14.

[0068] Note that the first position P1 does not have to be a position in which the water passage 51 completely opens the opening 14, but rather a position in which the opening width of the inlet 3 is larger when the water passage 51 is positioned at the first position P1 (first state) than when the water passage 51 is positioned at the second position P2 (second state).

[0069] The water passage section 51 is configured, for example, to allow the passage of water to be treated while preventing the passage of the filter material 2. Specifically, the water passage section 51 has, for example, a plurality of communication holes 51a through which the water to be treated can pass. The plurality of communication holes 51a are, for example, through holes that penetrate the water passage section 51 in the thickness direction. In the second state, for example as shown in Figure 3, the opening 14 of the bottom wall 12 is covered by the water passage section 51 located at the second position P2, thereby forming an inlet 3 for the water to be treated to flow into the inside of the housing 1 (filtration chamber 1a). In detail, the inlet 3 in the second state is formed, for example, by a communication hole 51a from the plurality of communication holes 51a that overlaps the opening 14 of the bottom wall 12. In the second state, the water to be treated flows into the inside of the housing 1 through the inlet 3.

[0070] The multiple communication holes 51a are formed such that, for example, the water to be treated can pass through, but the filter material 2 cannot. Therefore, as shown in Figure 3, in the second state, where the opening 14 is covered by the water passage section 51 located at the second position P2, and the inlet 3 is formed by the communication holes 51a of the water passage section 51, the water to be treated is allowed to flow into the interior of the housing 1 (filtration chamber 1a) through the inlet 3, and the filter material 2 is prevented from flowing out of the housing 1 through the inlet 3. In addition, the multiple communication holes 51a have an opening width smaller than, for example, the opening 14 formed in the bottom wall 12. Therefore, the opening width of the inlet 3 (communication holes 51a) in the second state is smaller than the opening width of the inlet 3 (opening 14) in the first state.

[0071] The material and shape of the water passage section 51 are not particularly limited, but examples of materials include resin and metal, and examples of shapes include screens such as perforated plates and mesh plates. Furthermore, the water passage section 51 does not have to be plate-shaped.

[0072] As shown in Figures 2 and 3, the slide mechanism 52 is, for example, attached to the bottom wall 12 of the housing 1 and slides the water passage 51 along the bottom of the housing 1 within a range including a first position P1 and a second position P2. The slide mechanism 52 is, for example, an air cylinder that moves a piston (not shown) inside the cylinder tube 521 in a straight line by driving compressed air supplied into the cylinder tube 521. The slide mechanism 52 moves the water passage 51, which is connected to the piston via a rod 522, back and forth within a range including a first position P1 and a second position P2 by, for example, reciprocating the piston.

[0073] In the following description, the slide mechanism 52 is assumed to be an air cylinder, but the slide mechanism 52 is not limited to an air cylinder that reciprocates the water passage section 51 by pneumatic drive, and various mechanisms can be employed. For example, the slide mechanism 52 may be a hydraulic cylinder that reciprocates the water passage section 51 by hydraulic drive, or a linear actuator or the like that reciprocates the water passage section 51 by electric motor drive.

[0074] The air supply pipe 53 branches off from, for example, the air cleaning pipe 602 of the aeration cleaning mechanism 60, and sends a portion of the air supplied from the blower 601 to the air cleaning pipe 602 during aeration cleaning to the slide mechanism 52 via the switching valve 55 and the intake / exhaust pipes 54a and 54b. The intake / exhaust pipes 54a and 54b supply air to or exhaust air from the slide mechanism 52, for example, depending on the state of the switching valve 55. For example, the intake / exhaust pipe 54a supplies air to and exhausts air to the intake / exhaust port (not shown) on the head side of the cylinder tube 521 of the slide mechanism 52, and the intake / exhaust pipe 54b supplies air to and exhausts air to the intake / exhaust port (not shown) on the rod side of the cylinder tube 521. The switching valve 55 is, for example, a solenoid valve, and switches between supplying and exhausting air to the intake / exhaust pipes 54a and 54b.

[0075] For example, when the water passage section 51 is positioned at the first position P1 during aeration cleaning (i.e., when the filter cassette 50A is in the first state), the switching valve 55 supplies air to the slide mechanism 52 via the intake / exhaust pipe 54a and discharges air from the slide mechanism 52 via the intake / exhaust pipe 54b, thereby driving the slide mechanism 52 and moving the water passage section 51 from the first position P1 to the second position P2. This switches the filter cassette 50A from the first state to the second state.

[0076] Furthermore, for example, when the water passage section 51 is positioned at the second position P2 during aeration cleaning (i.e., when the filter cassette 50A is in the second state), the switching valve 55 supplies air to the slide mechanism 52 via the intake / exhaust pipe 54b and discharges air from the slide mechanism 52 via the intake / exhaust pipe 54a, thereby driving the slide mechanism 52 and moving the water passage section 51 from the second position P2 to the first position P1. This switches the filter cassette 50A from the second state to the first state.

[0077] The switching operation of the filtration cassette 50A may be performed automatically, for example, by control of the switching device 5 by a control device (not shown), or it may be performed manually by an operator operating the switching device 5.

[0078] The scraper 56 is formed of, for example, rubber or resin, and as shown in Figures 2 and 3, has a wedge-shaped cross-section and extends in a direction perpendicular to the sliding direction (for example, the width direction H in this embodiment) and the vertical direction V of the water passage section 51 (for example, the flow direction L in this embodiment, which is perpendicular to the plane of the paper in Figures 2 and 3). The scraper 56 is positioned in contact with the lower surface of the water passage section 51 to remove deposits such as solid matter that adhere to the lower surface of the water passage section 51 as the water passage section 51 slides to switch the state of the filter cassette 50A.

[0079] Specifically, for example, when the water passage section 51 moves from the first position P1 to the second position P2, thereby switching the filter cassette 50A from the first state to the second state, the scraper 56 moves relative to the water passage section 51 in the direction from the second position P2 to the first position P1, causing the tip of the scraper 56 to slide along the underside of the water passage section 51 and remove any deposits from the underside of the water passage section 51. Conversely, for example, when the water passage section 51 moves from the second position P2 to the first position P1, thereby switching the filter cassette 50A from the second state to the first state, the scraper 56 moves relative to the water passage section 51 in the direction from the first position P1 to the second position P2, causing the tip of the scraper 56 to slide along the underside of the water passage section 51 and remove any deposits from the underside of the water passage section 51.

[0080] [Guide section 6] As shown in Figures 2 and 3, the guide portion 6 is provided, for example, at the bottom of the housing 1 and is configured to guide the downward flow in the swirling flow (indicated by the symbol F2 in Figure 3) generated during the washing operation in the lateral direction (horizontal direction, for example, the width direction H in this embodiment). The guide portion 6 is, for example, a haunch provided at the corner of the bottom of the housing 1 and having an inclined surface 6a that slopes from the bottom wall 12 to the side wall 11. The guide portion 6 is provided, for example, at the corner opposite to the corner where the opening 14 (inlet 3) is formed at the bottom of the housing 1 in the horizontal direction (for example, the width direction H in this embodiment). In other words, the guide portion 6 is formed at the corner on the wall portion 11b side of the side wall 11 at the bottom of the housing 1.

[0081] [Filtration operation using filter cassette 50A] As shown in Figure 2, in Embodiment 1, for example, the filtration operation is performed in a first state in which the water passage section 51 is positioned at a first position P1. As described above, in the first state, the inlet 3 is formed at the bottom of the housing 1 by the opening 14 which is opened when the water passage section 51 is positioned at the first position P1. The water to be treated flows into the inside of the housing 1 through the inlet 3 formed by the opening 14.

[0082] In the first state, the water passage section 51 is positioned at the first position P1 and overlaps with the bottom wall 12 of the housing 1, so the communication hole 51a of the water passage section 51 is covered by the bottom wall 12. Therefore, in the first state, the water to be treated is prevented from passing through the communication hole 51a of the water passage section 51. In this way, in the first state, the water to be treated passes through the opening 14 without passing through the communication hole 51a of the water passage section 51, so the adhesion of solid matter contained in the water to be treated to the water passage section 51 is prevented.

[0083] Furthermore, in the first state, the opening 14, which is opened as the inlet 3, has a relatively large opening width, so solid matter contained in the water to be treated passes through the inlet 3 without blocking it. As a result, the adhesion of solid matter to the bottom of the housing 1 is suppressed. In addition, as described above, during filtration operation, for example, the buoyancy acting on the filter material 2 and the upward flow F1 of the water to be treated push the filter material 2 upward and cause it to float above the inlet 3 (opening 14). Therefore, even if the inlet 3 has a flow path width sufficient to allow the filter material 2 to pass through, the outflow of the filter material 2 to the outside of the housing 1 is suppressed.

[0084] [Cleaning operation using filter cassette 50A] As shown in Figure 3, in Embodiment 1, for example, the cleaning operation is performed in a second state in which the water passage section 51 is positioned at the second position P2. As described above, in the second state, the water passage section 51 is positioned at the second position P2 so as to cover the opening 14, and the inlet 3 is formed at the bottom of the housing 1 by the communication hole 51a provided in the water passage section 51. The water to be treated flows into the interior of the housing 1 through the inlet 3 formed by the communication hole 51a.

[0085] During aeration cleaning in the cleaning operation, for example, as shown in Figure 3, the filter material 2 flows due to the swirling flow F2 generated inside the housing 1 (filtration chamber 1a) of the filter cassette 50A, and the filter material 2 spreads throughout the housing 1. However, in the second state, the opening 14 is covered by the water passage section 51, and the inlet 3 formed by the communication hole 51a of the water passage section 51 is impassable for the filter material 2. As a result, the water passage section 51 prevents the filter material 2 from flowing out of the housing 1 due to the swirling flow F2 during aeration cleaning.

[0086] Here, as shown in Figure 3, the swirling flow F2 is generated by the rising pressure of the air ejected from the air outlet 602a, so for example, an upward flow F21 is formed directly above the air outlet 602a. More specifically, the swirling flow F2 starts from the air outlet 602a and forms an upward flow F21 along one of the side walls 11a, a lateral flow F22 along the upper screen 13 toward the other side wall 11a, a downward flow F23 along the wall 11b, and a lateral flow F24 along the bottom wall 12 toward the wall 11a. In contrast, as shown in Figure 3, in the second state, the inlet 3 is formed, for example, directly below the air outlet 602a of the air cleaning pipe 602, so during aeration cleaning, an upward flow F21 is formed directly above the inlet 3. Therefore, during aeration cleaning, the filter material 2 rises due to the upward flow F21 directly above the inlet 3. In other words, the filter material 2 moves away from the inlet 3. This more reliably prevents the filter material 2 from flowing out of the housing 1 due to the swirling flow F2 during aeration cleaning.

[0087] Furthermore, as described above, for example, a guide section 6 is provided at the corner on the wall section 11b side of the bottom of the housing 1. The downward flow F23 of the swirling flow F2 descending along the wall section 11b of the side wall 11 is guided laterally by, for example, the inclined surface 6a of the guide section 6. This makes it easier for a lateral flow F24 to form along the bottom wall 12. As a result, the accumulation of solid matter such as sludge on the bottom wall 12 of the housing 1 is suppressed by the lateral flow F24.

[0088] [Water drainage using a 50A filter cassette, etc.] In Embodiment 1, for example, draining is performed in a second state in which the water passage section 51 is positioned at the second position P2. The water to be treated inside the housing 1 flows out to the outside of the housing 1 through the inlet 3 formed by the communication hole 51a of the water passage section 51.

[0089] During draining, the treated water flows out of the housing 1 through the inlet 3, and water pressure acts to push the filter material 2 inside the housing 1 towards the inlet 3. However, as described above, in the second state, the opening 14 is covered by the water passage section 51, and the inlet 3 formed by the communication hole 51a of the water passage section 51 is impassable to the filter material 2. As a result, the water passage section 51 prevents the filter material 2 from flowing out of the housing 1 during draining. Furthermore, any solid matter or other deposits that adhere to the communication hole 51a of the water passage section 51 when it is immersed in the treated water during filtration operation are removed by the water pressure during draining.

[0090] For example, when installing the filtration cassette 50A in the sedimentation tank 10 or after draining the filtration cassette 50A, there is no water inside the housing 1, so no buoyancy acts on the filter material 2, and the filter material 2 accumulates at the bottom of the housing 1. However, by positioning the water passage section 51 at the second position P2, it is prevented that the filter material 2 will flow out of the filtration chamber 1a.

[0091] [Effects and Effects of Embodiment 1] As described above, the filtration cassette 50A according to Embodiment 1 comprises a housing 1, an inlet 3 provided at the bottom of the housing 1 through which the water to be treated flows in, an outlet 4 provided in the housing 1 through which the water to be treated flows out, a filter material 2 housed inside the housing 1 and forming a filtration layer 2a between the inlet 3 and the outlet 4, and a switching device 5 that can switch the filtration cassette 50A between a first state and a second state in which the opening width of the inlet 3 is smaller than that of the first state.

[0092] With the filtration cassette 50A according to Embodiment 1 configured in this way, by setting the opening width of the inlet 3 to a relatively large first state during filtration operation, it is possible to suppress the adhesion of solid matter contained in the water to be treated to the bottom of the housing 1. By setting the opening width of the inlet 3 to a relatively small second state during cleaning operation or draining, it is possible to prevent the filter material 2 from flowing out of the housing 1 through the inlet 3. As a result, the adhesion of solid matter contained in the water to be treated to the filtration cassette 50A is suppressed, and the number of times the filtration cassette 50A needs to be cleaned can be reduced. Consequently, the number of times the filtration operation needs to be stopped for cleaning is reduced, and it becomes possible to perform the filtration operation continuously for a long period of time. In other words, it becomes possible to perform the filtration operation of the sedimentation tank 100 more efficiently.

[0093] Furthermore, in the first state, the filtration cassette 50A according to Embodiment 1 has an opening width of the inlet 3 that allows the water to be treated and the filter material 2 to pass through the inlet 3, making it easier for solids to pass through the inlet 3. This makes it possible to more effectively suppress the adhesion of solids.

[0094] Furthermore, the housing 1 of the filtration cassette 50A according to Embodiment 1 has a bottom wall 12 that covers a part of the bottom of the housing 1, except for the opening 14 that forms the inlet 3. In other words, the housing 1 has a bottom wall 12 at the bottom, and the inlet 3 is formed in a part of the bottom wall 12. As a result, by providing a bottom wall 12 at the bottom of the housing 1, the switching device 5 can be installed on the bottom wall 12. Therefore, the structure of the switching device 5 can be simplified and space-saving can be achieved.

[0095] Furthermore, in Embodiment 1, an air cleaning pipe 602 for cleaning the filter material 2 by blowing air onto it is inserted and positioned inside the housing 1, and the inlet 3 is formed directly below the air outlet 602a of the air cleaning pipe 602. As a result, an upward flow F21 is formed directly above the inlet 3 during aeration cleaning, which makes it possible to more reliably prevent the filter material 2 from flowing out of the housing 1 through the inlet 3.

[0096] Furthermore, in Embodiment 1, when air is ejected from the air cleaning pipe 602, a swirling flow F2 is generated inside the housing 1 by the air, and a guide section 6 is provided at the bottom of the housing 1 to guide the downward flow F23 of the swirling flow F2 in the lateral direction. As a result, the guide section 6 makes it easier to form a lateral flow F24 at the bottom of the housing 1, and the accumulation of solid matter at the bottom of the housing 1 can be suppressed.

[0097] Furthermore, in Embodiment 1, an opening 14 is formed at the bottom of the housing 1, and the switching device 5 includes a water passage section 51 with a communication hole 51a through which the water to be treated can pass, and a sliding mechanism 52 that slides the water passage section 51 along the bottom of the housing 1. The water passage section 51 is slidable within a range that includes a first position P1 that opens the opening 14 and a second position P2 that covers the opening 14. When the water passage section 51 is positioned at the first position P1, an inlet 3 is formed by the opened opening 14, resulting in a first state, and when the water passage section 51 is positioned at the second position P2, an inlet 3 is formed by the communication hole 51a of the water passage section 51 that covers the opening 14, resulting in a second state. With this configuration, the filtration cassette 50A according to Embodiment 1 can switch between the first state and the second state.

[0098] Furthermore, the switching device 5 according to Embodiment 1 includes a scraper 56 that is positioned in contact with the lower surface of the water passage 51 to remove any deposits on the lower surface of the water passage 51 as the water passage 51 slides. This allows for the removal of solid deposits and other deposits from the water passage 51 each time the device switches between the first and second states, thereby reducing the frequency of cleaning the water passage 51.

[0099] [Embodiment 2] Next, the configuration of the filtration cassette 50 according to Embodiment 2 will be described. Hereinafter, the filtration cassette 50 according to Embodiment 2 will also be referred to as filtration cassette 50B. In the following description of Embodiment 2, the differences from Embodiment 1 will be the main focus, and the same reference numerals will be used for components similar to those in Embodiment 1, thus omitting detailed explanations.

[0100] Figures 4 and 5 are schematic diagrams showing the filtration cassette 50B according to Embodiment 2. More specifically, Figure 4 is a longitudinal cross-sectional view showing the first state of the filtration cassette 50B according to Embodiment 2 during filtration operation, and Figure 5 is a longitudinal cross-sectional view showing the second state of the filtration cassette 50B according to Embodiment 2 during washing operation. In Figures 4 and 5, cross-sections perpendicular to the flow direction L of the filtration cassette 50B are shown.

[0101] As shown in Figures 4 and 5, the filtration cassette 50B according to Embodiment 2 comprises, for example, a housing 1B, a filter material 2, an inlet 3B, an outlet 4, and a switching device 7.

[0102] [Cabinet 1B] As shown in Figures 4 and 5, the housing 1B according to Embodiment 2 differs from the housing 1 described above, for example, in that it does not have a bottom wall 12, and the lower end of the side wall 11 is open. As a result, in Embodiment 2, for example, the entire bottom of the housing 1B (the bottom surface of the filtration chamber 1a) is formed as an opening 14B. The opening 14B has a larger opening width than, for example, the communication hole 71a formed in the water passage section 71 described later, and is formed so that the water to be treated and the filter material 2 can pass through. Note that the housing 1B may have a bottom wall at its bottom, and the opening 14B may be formed in the bottom wall.

[0103] [Switching device 7] As shown in Figures 4 and 5, the switching device 7 according to Embodiment 2 has, for example, a water passage section 71 that can be folded in a bellows-like manner. The switching device 7 is configured to change the water passage section 71 between a state in which the water passage section 71 is folded to open the opening 14B of the housing 1B (hereinafter referred to as the folded state), as shown in Figure 4, and a state in which the water passage section 71 is extended beyond the folded state to cover the opening 14B (hereinafter referred to as the extended state), as shown in Figure 5.

[0104] As shown in Figure 4, for example, when the water passage section 71 is folded, the opening 14B creates an inlet 3B at the bottom of the housing 1B, and the filtration cassette 50B enters a first state. Also, as shown in Figure 5, for example, when the water passage section 71 is extended, the communication hole 71a provided in the water passage section 71 that covers the opening 14B creates an inlet 3B at the bottom of the housing 1B with a smaller opening width than in the first state, and the filtration cassette 50B enters a second state.

[0105] As shown in Figures 4 and 5, the water passage section 71 is, for example, a water passage plate (screen) that can be folded in an accordion shape and is disposed in the opening 14B of the housing 1B. The water passage section 71 is formed by, for example, a plurality of panels 711 that are bendably connected via a hinge section 712. As a result, the water passage section 71 can be expanded and contracted in the horizontal direction (for example, the width direction H in this embodiment) by folding and unfolding in an accordion shape at the hinge section 712, for example. More specifically, the water passage section 71 can change between a folded state in which it opens the opening 14B by folding, and an extended state in which it extends beyond the folded state to cover the opening 14B.

[0106] Furthermore, the folded state does not necessarily mean that the water passage section 71 completely opens the opening 14B; it is sufficient that the opening width of the inlet 3B is larger when the water passage section 71 is folded (first state) than when the water passage section 71 is extended (second state). Also, the extended state does not necessarily mean that the water passage section 71 is completely unfolded; it is sufficient that the water passage section 71 extends beyond the folded state and covers the opening 14B.

[0107] The water passage section 71 is configured, for example, to allow the passage of water to be treated while preventing the passage of the filter material 2. Specifically, the water passage section 71 has, for example, a plurality of communication holes 71a through which the water to be treated can pass. The plurality of communication holes 71a are, for example, through holes that penetrate the water passage section 71 in the thickness direction. As shown in Figure 5, for example, in the second state, the opening 14B of the housing 1B is covered by the extended water passage section 71, thereby forming an inlet 3B for the water to be treated to flow into the inside of the housing 1B (filtration chamber 1a). In the second state, the water to be treated flows into the inside of the housing 1B, for example, through the inlet 3B and the opening 14B.

[0108] The multiple communication holes 71a are formed such that, for example, the water to be treated can pass through, but the filter material 2 cannot. Therefore, as shown in Figure 5, in the second state, where the opening 14B is covered by the extended water passage section 71 and the inlet 3B is formed by the communication holes 71a of the water passage section 71, the water to be treated is allowed to flow into the interior of the housing 1B (filtration chamber 1a) through the inlet 3B, and the filter material 2 is prevented from flowing out of the housing 1B through the inlet 3B. In addition, the multiple communication holes 71a have an opening width smaller than the opening 14B of the housing 1B. Therefore, the opening width of the inlet 3B in the second state is smaller than the opening width of the inlet 3B in the first state.

[0109] The material and shape of the water-conducting section 71 are not particularly limited, but examples of materials include resin and metal, and examples of shapes include screens such as perforated plates and mesh plates. Furthermore, the water-conducting section 71 does not have to be plate-shaped. The water-conducting section 71 may be, for example, a fibrous net or mesh.

[0110] The switching device 7 may have, for example, a drive device (not shown) for changing the state of the water passage section 71 between a folded state and an extended state. As the drive device, for example, an air cylinder, a hydraulic cylinder, a linear actuator, etc., may be used.

[0111] [Filtration operation using filter cassette 50B] As shown in Figure 4, in Embodiment 2, for example, the filtration operation is performed in a first state in which the water passage section 71 is folded. As described above, in the first state, the inlet 3B is formed at the bottom of the housing 1B by the opening 14B that is opened when the water passage section 71 is folded. The water to be treated flows into the inside of the housing 1B through the inlet 3B formed by the opening 14B.

[0112] In the first state, the water passage section 71 is folded, which prevents the water to be treated from passing through the communication hole 71a of the water passage section 71. Thus, in the first state, the water to be treated passes through the opening 14B without passing through the communication hole 71a of the water passage section 71, which prevents solid matter contained in the water to be treated from adhering to the water passage section 71.

[0113] Furthermore, in the first state, the opening 14B, which is opened as the inlet 3B, has a relatively large opening width, so solid matter contained in the water to be treated passes through the inlet 3B without blocking it. As a result, adhesion of solid matter to the bottom of the housing 1B is also suppressed.

[0114] [Cleaning operation using filter cassette 50B] As shown in Figure 5, in Embodiment 2, for example, the cleaning operation is performed in a second state in which the water passage section 71 is extended. As described above, in the second state, the water passage section 71 is extended to cover the opening 14B, and the inlet 3B is formed at the bottom of the housing 1B by the communication hole 71a provided in the water passage section 71. The water to be treated flows into the interior of the housing 1B through the inlet 3B formed by the communication hole 71a.

[0115] In the second state, the opening 14B is covered by the water passage section 71, and the inlet 3B formed by the communication hole 71a of the water passage section 71 is inaccessible to the filter material 2. As a result, the water passage section 71 prevents the filter material 2 from flowing out of the housing 1B due to the swirling flow F2 during aeration cleaning in the cleaning operation.

[0116] [Water drainage using filter cassette 50B, etc.] In Embodiment 2, for example, draining the water and installing the filtration cassette 50B are performed in a second state in which the water passage section 71 is extended. During draining, the water to be treated inside the housing 1B flows out to the outside of the housing 1B through the inlet 3B formed by the communication hole 71a of the water passage section 71.

[0117] As described above, in the second state, the opening 14B is covered by the water passage section 71, and the inlet 3B formed by the communication hole 71a of the water passage section 71 is inaccessible to the filter material 2. As a result, the water passage section 71 prevents the filter material 2 from flowing out of the housing 1B during draining, after draining, and when installing the filter cassette 50B.

[0118] [Effects and Effects of Embodiment 2] As described above, the filtration cassette 50B according to Embodiment 2 comprises a housing 1B, an inlet 3B provided at the bottom of the housing 1B through which the water to be treated flows in, an outlet 4 provided in the housing 1B through which the water to be treated flows out, a filter material 2 housed inside the housing 1B and forming a filtration layer 2a between the inlet 3B and the outlet 4, and a switching device 7 that can switch the filtration cassette 50B between a first state and a second state in which the opening width of the inlet 3B is smaller than that of the first state.

[0119] With the filtration cassette 50B according to Embodiment 2 configured in this way, similar to the filtration cassette 50A according to Embodiment 1, the adhesion of solid matter contained in the treated water to the filtration cassette 50B can be suppressed. As a result, the number of times the filtration cassette 50B needs to be cleaned can be reduced, and the filtration operation of the sedimentation tank 100 can be performed more efficiently.

[0120] Furthermore, in Embodiment 2, an opening 14B is formed at the bottom of the housing 1B, and the switching device 7 has a bellows-like foldable water passage section 71 disposed in the opening 14B, and a communication hole 71a is formed in the water passage section 71 through which the water to be treated can pass. The water passage section 71 can change between a folded state in which it opens the opening 14B and an extended state in which it extends beyond the folded state to cover the opening 14B. When the water passage section 71 is in the folded state, the inlet 3B is formed by the opened opening 14B, and the filtration cassette 50B enters the first state. When the water passage section 71 is in the extended state, the inlet 3B is formed by the communication hole 71a of the water passage section 71 that covers the opening 14B, and the filtration cassette 50B enters the second state. With this configuration, the filtration cassette 50B according to Embodiment 2 can switch between the first state and the second state.

[0121] [Embodiment 3] Next, the configuration of the filtration cassette 50 according to Embodiment 3 will be described. Hereinafter, the filtration cassette 50 according to Embodiment 3 will also be referred to as the filtration cassette 50C. In the following description of Embodiment 3, the differences from Embodiment 1 will be the main focus, and the same reference numerals will be used for components similar to those in Embodiment 1, thus omitting detailed explanations.

[0122] Figures 6 and 7 are schematic diagrams showing the filtration cassette 50C according to Embodiment 3. More specifically, Figure 6 is a longitudinal cross-sectional view showing the first state of the filtration cassette 50C according to Embodiment 3 during filtration operation, and Figure 7 is a longitudinal cross-sectional view showing the second state of the filtration cassette 50C according to Embodiment 3 during washing operation. Figures 6 and 7 show cross-sections of the filtration cassette 50C perpendicular to the flow direction L. Figure 8 is a cross-sectional view of the filtration cassette 50C showing a cross-section along the CC line in Figure 6, and Figure 9 is a transverse cross-sectional view of the filtration cassette 50C showing a cross-section along the DD line in Figure 7. Figures 8 and 9 show cross-sections of the filtration cassette 50C perpendicular to the vertical direction V.

[0123] As shown in Figures 6 and 7, the filtration cassette 50C according to Embodiment 3 comprises, for example, a housing 1C, a filter material 2, an inlet 3C, an outlet 4, and a switching device 8.

[0124] [Cabinet 1C] As shown in Figures 6 and 7, the housing 1C according to Embodiment 3 has, for example, a bottom wall 12C. The bottom wall 12C is formed, for example, in the shape of a plate and is arranged perpendicular to the vertical direction V. The bottom wall 12C is provided, for example, at the lower end of the side wall 11. However, the bottom wall 12C only needs to be located below the filter material 2, and may be provided in the middle of the side wall 11.

[0125] An opening 14C is formed in the bottom wall 12C, which connects the inside (filtration chamber 1a) of the housing 1C to the outside. The opening 14C is formed, for example, at the corner of the bottom of the housing 1C in the width direction H. Specifically, the opening 14C is formed, for example, at the corner on the wall portion 11a side of the side wall 11 at the bottom of the housing 1C. Also, as shown in Figures 8 and 9, the opening 14C is formed over the entire bottom of the housing 1C in the flow direction L (i.e., across both ends of the bottom in the flow direction L). Therefore, the bottom wall 12C is spaced apart from the wall portion 11a of the side wall 11 in the width direction H, and the opening 14C is formed by the gap between the bottom wall 12C and the wall portion 11a. However, the arrangement of the opening 14C at the bottom of the housing 1C is not limited to this. For example, the bottom wall may be arranged to surround the opening 14C.

[0126] Here, as shown in Figures 8 and 9, of the opening edges 141 that constitute the contour of the opening 14C, one edge (in this embodiment, for example, the wall portion 11a side) in the horizontal direction (for example, the width direction H) is designated as the first edge portion 141a, and the other edge (in this embodiment, for example, the wall portion 11b side) is designated as the second edge portion 141b. The first edge portion 141a is formed, for example, by the wall portion 11a of the side wall 11, and the second edge portion 141b is formed, for example, by the side end of the bottom wall 12C that faces the wall portion 11a. As shown in Figures 8 and 9, the first edge portion 141a is provided with an expandable member 81, which will be described later.

[0127] As shown in Figures 8 and 9, the second edge portion 141b facing the expandable member 81 is formed, for example, in a comb-like shape. More specifically, the second edge portion 141b has, for example, a plurality of recesses 142 that are recessed in the width direction H and spaced apart in the flow direction L. The recesses 142 have a rectangular cross-section and penetrate the bottom wall 12C in the thickness direction (vertical direction V). The recesses 142 are included in the opening 14C, for example, and constitute a part of the opening 14C. The number and shape of the recesses 142 are not particularly limited.

[0128] [Switching device 8] As shown in Figures 8 and 9, the switching device 8 according to Embodiment 3 includes, for example, an expandable member 81, an air supply pipe 82, an air discharge pipe 83, and an on / off valve 84. The switching device 8 is configured to change the expandable member 81 between, for example, the normal state shown in Figures 6 and 8, and a state that is more expanded than the normal state shown in Figures 7 and 9 (hereinafter referred to as the extended state).

[0129] When the expandable member 81 returns to its normal state, the expandable member 81 and the second edge 141b of the opening 14C separate, and the filter cassette 50C enters a first state. When the expandable member 81 expands, the expandable member 81 and the second edge 141b of the opening 14 come into partial contact, and the filter cassette 50C enters a second state.

[0130] The expandable member 81 is a cylindrical body formed to be expandable and contractible by an elastic material such as a membrane (elastic film). However, the material and shape of the expandable member 81 are not particularly limited. As shown in Figures 8 and 9, the expandable member 81 is disposed in the opening 14C of the housing 1C, for example, extending along the flow direction L. More specifically, the expandable member 81 is attached to the wall portion 11a of the side wall 11 so as to follow the first edge portion 141a of the opening 14C. As a result, the expandable member 81 is positioned opposite the second edge portion 141b where the recess 142 is formed.

[0131] As shown in Figures 8 and 9, for example, an air supply pipe 82 is connected to one end of the expandable member 81, and an air discharge pipe 83 is connected to the other end. The air supply pipe 82 branches off from, for example, the air cleaning pipe 602 of the aeration cleaning mechanism 60, and supplies a portion of the air supplied from the blower 601 to the air cleaning pipe 602 during aeration cleaning to the expandable member 81. The air discharge pipe 83 is provided with, for example, an on / off valve 84.

[0132] The expandable member 81 can change between, for example, the normal state shown in Figures 6 and 8 and the expanded state which is more expanded than the normal state shown in Figures 7 and 9. Specifically, for example, in the normal state, by closing the on-off valve 84 and supplying air to the expandable member 81 from the air supply pipe 82, the expandable member 81 expands and changes to the expanded state. Also, for example, in the expanded state, by opening the on-off valve 84 and discharging air from the expandable member 81 to the air discharge pipe 83, the expandable member 81 contracts and changes back to the normal state.

[0133] As shown in Figure 8, for example, when the expandable member 81 is in its normal state, the expandable member 81 and the second edge 141b of the opening 14C are separated (not in contact), and as shown in Figure 9, for example, when the expandable member 81 is in an expanded state, the expandable member 81 and the second edge 141b of the opening 14C are in partial contact except for the recess 142.

[0134] [Inlet 3C] As shown in Figures 8 and 9, in Embodiment 3, for example, an inlet 3C is formed at the bottom of the housing 1C by the expandable member 81 of the switching device 8 and the opening edge 141 of the opening 14C. More specifically, for example, the region A1 (the region shown as a dot pattern in Figures 8 and 9) surrounded by the expandable member 81 and the opening edge 141 forms the inlet 3C.

[0135] As shown in Figure 8, in the first state, the expandable member 81 in its normal state and the second edge 141b of the opening 14C are separated, so that the gap between the expandable member 81 and the second edge 141b, including the recess 142, becomes region A1, forming the inlet 3C.

[0136] As shown in Figure 9, in the second state, the expanded expandable member 81 and the second edge 141b of the opening 14C are in partial contact except for the recess 142, so that the recess 142 becomes region A1 and forms the inlet 3C. Therefore, in the second state, the expanded expandable member 81 disposed in the opening 14C is in an expanded state, so that the inlet 3C becomes narrower compared to the first state. As a result, the filtration cassette 50C is configured such that the opening width of the inlet 3C in the second state is smaller than the opening width of the inlet 3C in the first state.

[0137] In the first state, the inlet 3C has an opening width such that, for example, the water to be treated and the filter material 2 can pass through, and in the second state, the inlet 3C has an opening width such that, for example, the water to be treated can pass through but the filter material 2 cannot. However, in the first state, it is sufficient that the inlet 3C can pass through, but it is not necessary that the filter material 2 can pass through.

[0138] [Filtration operation using filter cassette 50C] As shown in Figure 6, in Embodiment 3, for example, the filtration operation is performed in a first state where the expandable member 81 is in its normal state. In the first state, since the inlet 3C has a relatively large opening width, solid matter contained in the water to be treated passes through the inlet 3C without blocking it. Therefore, the adhesion of solid matter to the bottom of the housing 1C is suppressed.

[0139] [Cleaning operation using filter cassette 50C] As shown in Figure 7, in Embodiment 3, for example, the cleaning operation is performed in a second state in which the expandable member 81 is in an expanded state. In the second state, the inlet 3C is narrowed by the expanded expandable member 81, so that the filter material 2 cannot pass through the inlet 3C. As a result, the expandable member 81 prevents the filter material 2 from flowing out of the housing 1C due to the swirling flow F2 during aeration cleaning of the cleaning operation.

[0140] [Water drainage using filter cassette 50C, etc.] In Embodiment 3, for example, draining the water and installing the filter cassette 50C are performed in a second state in which the expandable member 81 is in an expanded state. During draining, the water to be treated inside the housing 1C flows out to the outside of the housing 1C through the inlet 3C. As described above, in the second state, the filter material 2 cannot pass through the inlet 3C. As a result, the expandable member 81 prevents the filter material 2 from flowing out to the outside of the housing 1C during draining, after draining, and when installing the filter cassette 50C.

[0141] [Effects and Effects of Embodiment 3] As described above, the filtration cassette 50C according to Embodiment 3 comprises a housing 1C, an inlet 3C provided at the bottom of the housing 1C through which the water to be treated flows in, an outlet 4 provided in the housing 1C through which the water to be treated flows out, a filter material 2 housed inside the housing 1C and forming a filtration layer 2a between the inlet 3C and the outlet 4, and a switching device 8 that can switch the filtration cassette 50C between a first state and a second state in which the opening width of the inlet 3C is smaller than that of the first state.

[0142] With the filtration cassette 50C according to Embodiment 3 configured in this way, similar to the filtration cassette 50A according to Embodiment 1, the adhesion of solid matter contained in the treated water to the filtration cassette 50C can be suppressed. As a result, the number of times the filtration cassette 50C needs to be cleaned can be reduced, and the filtration operation of the sedimentation tank 100 can be performed more efficiently.

[0143] Furthermore, in Embodiment 3, an opening 14C is formed at the bottom of the housing 1C, and the switching device 8 has an expandable member 81 disposed in the opening 14C, and the expandable member 81 can change between a normal state and an expanded state that is more expanded than the normal state. Also in Embodiment 3, an inlet 3C is formed by the expandable member 81 and the opening edge 141 of the opening 14C, and when the expandable member 81 is in the normal state the filtration cassette 50C enters the first state, and when the expandable member 81 enters the expanded state the filtration cassette 50C enters the second state. With this configuration, the filtration cassette 50C according to Embodiment 3 can switch between the first state and the second state.

[0144] The expandable member 81 does not necessarily have to be positioned opposite the second edge 141b where the recess 142 is formed. For example, the expandable member 81 may be positioned in the opening 14C such that it does not cover the recess 142 in the normal state, but covers a part of the recess 142 from above or below when expanded. In this case, in the first state, the inlet 3C is formed by the gap between the expandable member 81 and the second edge 141b, including the recess 142, and in the second state, the inlet 3C is formed by the portion of the recess 142 that is not covered by the expanded expandable member 81 in the expanded state. Therefore, in the second state, the inlet 3C is narrower compared to the first state.

[0145] [Embodiment 4] Next, the configuration of the filtration cassette 50 according to Embodiment 4 will be described. Hereinafter, the filtration cassette 50 according to Embodiment 4 will also be referred to as the filtration cassette 50D. In the following description of Embodiment 4, the differences from Embodiment 1 will be the main focus, and the same reference numerals will be used for components similar to those in Embodiment 1, thus omitting detailed explanations.

[0146] Figures 10 and 11 are schematic diagrams showing the filtration cassette 50D according to Embodiment 4. More specifically, Figure 10 is a bottom view showing the first state of the filtration cassette 50D according to Embodiment 4, and Figure 11 is a bottom view showing the second state of the filtration cassette 50D according to Embodiment 4.

[0147] As shown in Figures 10 and 11, the filtration cassette 50D according to Embodiment 4 comprises, for example, a housing 1D, an inlet 3D, and a switching device 9. The filtration cassette 50D also comprises a filter material 2 and an outlet 4, but these are the same as those in the embodiments described above and are therefore not shown.

[0148] [Cabinet 1D] As shown in Figures 10 and 11, the housing 1D according to Embodiment 4 does not have a bottom wall 12, for example, and the lower end of the side wall 11 is open. As a result, in Embodiment 4, for example, the entire bottom of the housing 1D (the bottom surface of the filtration chamber 1a) is formed as an opening 14D. Note that the housing 1D may have a bottom wall, and the opening 14D may be formed in the bottom wall.

[0149] [Switching device 9] As shown in Figures 10 and 11, the switching device 9 according to Embodiment 4 includes, for example, a frame body 91, an expandable member 92, an air supply pipe 93, an air discharge pipe 94, and an on / off valve 95.

[0150] The frame body 91 is, for example, a metal structure and is installed in the opening 14D of the housing 1D. The frame body 91 is formed, for example, by combining multiple rod members, and has an outer frame 911 and an inner frame 912.

[0151] The outer frame 911 is formed, for example, in a rectangular shape in a plan view. The outer frame 911 is fitted into the opening 14D, for example, along the side wall 11 of the housing 1. The inner frame 912 is provided, for example, inside the outer frame 911. The inner frame 912 has, for example, a plurality of horizontal members 912a that extend in the width direction H and are arranged at predetermined intervals in the flow direction L, and a plurality of vertical members 912b that extend in a direction perpendicular to the horizontal members 912a (i.e., the flow direction L) and are arranged at predetermined intervals in the width direction H. The vertical members 912b are intermittent between the horizontal members 912a and between the horizontal members 912a and the outer frame 911.

[0152] The expandable member 92 is a cylindrical body formed to be expandable and contractible by an elastic material such as a membrane (elastic film). However, the material and shape of the expandable member 92 are not particularly limited. As shown in Figures 10 and 11, the expandable member 92 is arranged in a meandering manner in the horizontal plane so as to overlap in the vertical direction V (the direction perpendicular to the plane of the paper in Figures 10 and 11) with the region enclosed by the frame body 91 within the opening 14D. More specifically, the expandable member 92 meansders so as to extend in the width direction H within the opening 14D and overlap with the intermittent portions of the vertical members 912b of the frame body 91. As a result, the frame body 91 and the expandable member 92 are arranged to overlap in a grid-like manner.

[0153] As shown in Figures 10 and 11, for example, an air supply pipe 93 is connected to one end of the expandable member 92, and an air discharge pipe 94 is connected to the other end. The air supply pipe 93 branches off from, for example, the air cleaning pipe 602 of the aeration cleaning mechanism 60, and supplies a portion of the air supplied from the blower 601 to the air cleaning pipe 602 during aeration cleaning to the expandable member 92. The air discharge pipe 94 is provided with, for example, an on / off valve 95.

[0154] The expandable member 92 can change between, for example, the normal state shown in Figure 10 and the expanded state which is more expanded than the normal state shown in Figure 11. Specifically, for example, in the normal state, by closing the on-off valve 95 and supplying air to the expandable member 92 from the air supply pipe 93, the expandable member 92 expands and changes to the expanded state. Also, for example, in the expanded state, by opening the on-off valve 95 and discharging air from the expandable member 92 to the air discharge pipe 94, the expandable member 92 contracts and changes back to the normal state.

[0155] [Inlet 3D] As shown in Figures 10 and 11, in Embodiment 4, for example, the frame body 91 and the expandable member 92 of the switching device 9 form an inlet 3D within the opening 14D at the bottom of the housing 1. More specifically, for example, a mesh-like region surrounded by the frame body 91 and the expandable member 92 overlapping in a grid pattern within the opening 14D forms the inlet 3D. In Figures 10 and 11, the inlet 3D is shown as a dot pattern.

[0156] As shown in Figures 10 and 11, in the second state, the expandable member 92 is in an expanded state, which narrows the inlet 3D compared to the first state when the expandable member 92 is in its normal state. As a result, the filtration cassette 50D is configured such that the opening width of the inlet 3D in the second state is smaller than the opening width of the inlet 3D in the first state.

[0157] In the first state, the inlet 3D has an opening width such that, for example, the water to be treated and the filter material 2 can pass through, and in the second state, the inlet 3D has an opening width such that, for example, the water to be treated can pass through but the filter material 2 cannot. However, in the first state, it is sufficient that the inlet 3D can pass through, but it is not necessary that the filter material 2 can pass through.

[0158] [Filtration operation using filter cassette 50D] In Embodiment 4, for example, the filtration operation is performed in a first state where the expandable member 92 is in its normal state. In the first state, since the inlet 3D has a relatively large opening width, solid matter contained in the water to be treated passes through the inlet 3D without blocking it. As a result, the adhesion of solid matter to the bottom of the housing 1D is suppressed.

[0159] [Cleaning operation using filter cassette 50D] In Embodiment 4, for example, the cleaning operation is performed in a second state in which the expandable member 92 is in an expanded state. In the second state, the inlet 3D is narrowed by the expanded expandable member 92, so that the filter material 2 cannot pass through the inlet 3D. As a result, the expandable member 92 prevents the filter material 2 from flowing out of the housing 1D due to the swirling flow F2 during aeration cleaning of the cleaning operation.

[0160] [Water drainage using filter cassette 50D, etc.] In Embodiment 4, for example, draining the water and installing the filter cassette 50D are performed in a second state in which the expandable member 92 is in an expanded state. During draining, the water to be treated inside the housing 1D flows out to the outside of the housing 1 through the inlet 3D. As described above, in the second state, the filter material 2 cannot pass through the inlet 3D. As a result, the expandable member 92 prevents the filter material 2 from flowing out to the outside of the housing 1D during draining, after draining, and when installing the filter cassette 50D.

[0161] [Effects and Effects of Embodiment 4] As described above, the filtration cassette 50D according to Embodiment 4 comprises a housing 1D, an inlet 3D provided at the bottom of the housing 1D through which the water to be treated flows in, an outlet 4 provided in the housing 1D through which the water to be treated flows out, a filter material 2 housed inside the housing 1D and forming a filtration layer 2a between the inlet 3D and the outlet 4, and a switching device 9 that can switch the filtration cassette 50D between a first state and a second state in which the opening width of the inlet 3D is smaller than that of the first state.

[0162] With the filtration cassette 50D according to Embodiment 4 configured in this way, similar to the filtration cassette 50A according to Embodiment 1, the adhesion of solids contained in the water to be treated to the filtration cassette 50D can be suppressed. As a result, the number of times the filtration cassette 50D is cleaned can be reduced, and the filtration operation of the sedimentation tank 100 can be performed more efficiently.

[0163] In Embodiment 4, an opening 14D is formed at the bottom of the housing 1D, and the switching device 9 includes a frame body 91 mounted on the opening 14D, and an expandable member 92 tube installed so as to overlap with the area surrounded by the frame body 91, which can change between a normal state and an expanded state that is more expanded than the normal state. In Embodiment 4, an inlet 3D is formed by the frame body 91 and the expandable member 92, and the filtration cassette 50D enters a first state when the expandable member 92 is in a normal state, and enters a second state when the expandable member 92 is in an expanded state. With this configuration, the filtration cassette 50D according to Embodiment 4 can switch between a first state and a second state.

[0164] The various embodiments and variations described above may be combined as appropriate.

[0165] (Note) This disclosure includes the following aspects: [Aspect 1] A filtration cassette installed in a treatment tank, through which water to be treated is passed and filtered, The casing and An inlet is provided at the bottom of the housing, into which the water to be treated flows, The housing is provided with an outlet through which the treated water flows out, A filter material housed within the aforementioned housing, which forms a filter layer between the inlet and the outlet, The filter cassette is equipped with a switching device that can switch between a first state and a second state in which the opening width of the inlet is smaller than that of the first state. Filtration cassette. [Aspect 2] In the first state, the opening width of the inlet is formed to such an extent that the water to be treated and the filter material can pass through the inlet. A filtration cassette as described in Embodiment 1. [Aspect 3] The housing has a bottom wall at the bottom, The inlet is formed in a part of the bottom wall, A filtration cassette according to embodiment 1 or 2. [Aspect 4] An air cleaning pipe is inserted and positioned inside the housing to clean the filter material by blowing air onto it. The inlet is formed directly below the air outlet of the air cleaning pipe. A filtration cassette as described in any of embodiments 1 to 3. [Aspect 5] When air is ejected from the air cleaning pipe, a swirling flow is generated inside the housing by the air. The bottom of the housing is provided with a guide section that directs the downward flow in the swirling flow in the lateral direction. A filtration cassette as described in Embodiment 4. [Explanation of Symbols]

[0166] 1: Cabinet 12: Bottom wall 14: Opening 2: Filter material 2a: filtration layer 3: Inlet 4: Outlet 5: Switching device 6: Guide Section 7: Switching device 8: Switching device 9: Switching device 10: Sedimentation tank (an example of a treatment tank) 50: Filtration cassette 100: Sedimentation tank (an example of a filtration system)

Claims

1. A filtration cassette installed in a treatment tank, through which water to be treated is passed and filtered, The casing and An inlet is provided at the bottom of the housing, into which the water to be treated flows, The housing is provided with an outlet through which the treated water flows out, A filter material housed within the aforementioned housing, which forms a filter layer between the inlet and the outlet, The filter cassette is equipped with a switching device that can switch between a first state and a second state in which the opening width of the inlet is smaller than that of the first state. Filtration cassette.

2. In the first state, the opening width of the inlet is formed such that the water to be treated and the filter material can pass through the inlet. The filtration cassette described in Claim 1.

3. The housing has a bottom wall at the bottom, The inlet is formed in a part of the bottom wall, The filtration cassette described in Claim 1.

4. An air cleaning pipe is inserted and positioned inside the housing to clean the filter material by blowing air onto it. The inlet is formed directly below the air outlet of the air cleaning pipe. The filtration cassette described in Claim 1.

5. When air is ejected from the air cleaning pipe, a swirling flow is generated inside the housing by the air. The bottom of the housing is provided with a guide section that directs the downward flow in the swirling flow in the lateral direction. The filtration cassette according to claim 4.

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