Filtration cassette and lifting device

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 and forming a filtration layer between the inlet and the outlet, and a lifting member installed to be able to move up and down within a range including a first position that opens the inlet and a second position that covers the inlet. When the lifting member is positioned in the first position, a first flow path is formed between the lifting member and the housing to guide the water to be treated to the filtration layer. When the lifting member is positioned in the second position, a second flow path is formed between the lifting member, the housing, or the lifting member and the housing to guide the water to be treated to the outside of the housing.

Description

Technical Field

[0001] The present invention relates to a filtration cassette installed in a treatment tank and a lifting device attached to the housing of the filtration cassette.

Background Art

[0002] Conventionally, in a water treatment plant, a sewage treatment plant, etc., raw water to be treated is stored in a sedimentation tank to precipitate solids, and then the raw water 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 filters raw water to be treated by flowing it upward. 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 raw water and prevent the passage of the filter medium are provided at the lower and upper openings of the housing.

[0004] Also, Patent Document 2 discloses a technique for adjusting the compression pressure of a filter medium layer by disposing a vertically movable perforated plate on a screen suspended inside a filtration tank in an upward flow type filtration device.

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 lifting member installed to be vertically movable within a range including a first position that opens the inlet and a second position that covers the inlet, wherein when the lifting member is positioned in the first position, a first flow path is formed between the lifting member and the housing for guiding the water to be treated to the filtration layer, and when the lifting member is positioned in the second position, a second flow path is formed between the lifting member, the housing, or between the lifting member and the housing for guiding the water to be treated to the outside of the housing. [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 front 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 first state of the filtration cassette 50A according to Embodiment 1 during filtration operation. [Figure 4] Figure 4 is a front view showing the second state of the filtration cassette 50A according to Embodiment 1 during the washing operation. [Figure 5] Figure 5 is a longitudinal cross-sectional view showing the second state of the filtration cassette 50A according to Embodiment 1 during the washing operation. [Figure 6]Figure 6 is a longitudinal cross-sectional view showing the second state of the filtration cassette 50A according to Embodiment 1 when the water is drained. [Figure 7] Figure 7 is a longitudinal cross-sectional view showing the first state of the filtration cassette 50B according to Embodiment 2 during filtration operation. [Figure 8] Figure 8 is a longitudinal cross-sectional view showing the second state of the filtration cassette 50B according to Embodiment 2 when the water is drained. [Figure 9] Figure 9 is a longitudinal cross-sectional view showing the third state of the filtration cassette 50B according to Embodiment 2 during the washing operation. [Figure 10] Figure 10 is a cross-sectional view of the filtration cassette 50B, showing a cross-section along the CC line in Figure 7. [Figure 11] Figure 11 is a cross-sectional view of the filtration cassette 50B, showing a cross-section along the DD line in Figure 9. [Figure 12] Figure 12 is a cross-sectional view of the housing 1B according to Embodiment 2. [Figure 13] Figure 13 is a longitudinal cross-sectional view showing the first state of the filtration cassette 50C according to Modification 1 of Embodiment 2 during filtration operation. [Figure 14] Figure 14 is a longitudinal cross-sectional view showing the third state of the filtration cassette 50C according to Modification 1 of Embodiment 2 during the washing operation. [Figure 15] Figure 15 is a cross-sectional view of the filtration cassette 50C, showing a cross-section along the EE line in Figure 14. [Figure 16] Figure 16 is a longitudinal cross-sectional view showing the second state of the filtration cassette 50D according to Modification 2 of Embodiment 2 during water drainage. [Figure 17] Figure 17 is a longitudinal cross-sectional view of the filtration cassette 50D, showing a cross-section along the FF line in Figure 16. [Modes for carrying out the invention]

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. However, such descriptions should not be construed in a limiting sense and do not limit the subject matter recited in the claims. Also, various changes, substitutions, and modifications can be made without departing from the spirit and scope of the present disclosure. Further, different embodiments can be appropriately combined.

[0011] Note that the treatment tank where the filtration cassette according to the present disclosure is to be installed may be any tank for separating solid components (suspended solids), which are the objects to be separated, from the water to be treated, and is not particularly limited. Specifically, the treatment tank may be, for example, a sedimentation tank for sedimenting and removing solid components contained in the water to be treated in sewage treatment and further performing a filtration treatment on the sedimented water to be treated. This sedimentation tank may be the sedimentation tank of the primary sedimentation basin provided on the upstream side of the reaction tank, or may be the sedimentation tank of the final sedimentation basin provided on the downstream side of the reaction tank. Also, the treatment tank may be, for example, a solid-liquid separation tank for separating, concentrating, recovering, and removing solid components contained in the water to be treated by utilizing the specific gravity difference between the liquid and the solid in industrial water treatment. Hereinafter, as an example of the treatment tank, the case where the filtration cassette of the present disclosure 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 common to each embodiment (Embodiment 1, 2) will be described. The sedimentation tank 100 is an example of a filtration device equipped with the filtration cassette according to the embodiment.

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

[0014] [Overall structure] Figure 1 shows the configuration of a sedimentation tank 100 equipped with a filtration cassette 50 according to an embodiment. Figure 1(A) is a top view of the sedimentation tank 100, Figure 1(B) is a longitudinal cross-sectional view of the sedimentation tank 100 showing a cross-section along line AA in Figure 1(A), and Figure 1(C) is a longitudinal cross-sectional view of the sedimentation tank 100 showing a cross-section along line BB in Figure 1(A). Here, the sedimentation tank 100 is configured such that the water to be treated flows in from the upstream side and flows toward the downstream side. Hereinafter, the direction in which the water to be treated flows in the sedimentation tank 100 will be referred to as the "flow direction" and denoted by the symbol L. The depth direction (i.e., the vertical direction) of the sedimentation tank 100 will be referred to as the "up and down direction" and denoted by the symbol V. The direction perpendicular to the flow direction L and the up and down direction V will be referred to as the "width direction" and denoted by the symbol H. Therefore, Figure 1(B) shows a cross-section perpendicular to the width direction H, and Figure 1(C) shows a cross-section perpendicular to the flow direction L. Furthermore, the flow direction L, vertical direction V, and width direction H will have the same meanings in the description of the filtration cassette 50 described later.

[0015] As shown in Figure 1(A), the sedimentation tank 100 includes, for example, a sedimentation tank 10 for containing the water to be treated, and a filtration cassette 50 installed in the sedimentation tank 10 for circulating and filtering the water to be treated. The sedimentation tank 100, for example, allows relatively coarse solids contained in the water to be treated that flows into the sedimentation tank 10 to settle in the sedimentation tank 10 by gravity, and then separates relatively fine solids by filtering the water to be treated with the filtration cassette 50. The water to be treated (hereinafter also referred to as "filtered water"), from which the solids have been filtered and separated by the filtration cassette 50, is discharged to, for example, a downstream facility. Specifically, if the sedimentation tank 100 is the primary sedimentation tank, the water to be treated is discharged to a reaction tank, for example, by a pump. If 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). The sterilization treatment device then sterilizes the water to be treated discharged from the final sedimentation tank, for example, and discharges the sterilized treated water into a river or the like.

[0016] The sedimentation tank 10 is an example of a treatment tank according to this disclosure, and is a horizontal flow type sedimentation tank that, for example, retains the water to be treated that flows into the sedimentation tank 10 and separates the solids contained in the water to be treated by gravity settling. The water to be treated flows into the sedimentation tank 10 from the upstream side in the flow direction L and flows downstream. The sedimentation tank 10 is formed in a substantially rectangular parallelepiped shape having a bottom 10a and side walls 10b, and the longitudinal direction of the sedimentation tank 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 tank 10, specifically from left to right in Figure 1(A). In a top view, the side walls 10b have a long rectangular shape in the flow direction L.

[0017] Furthermore, as shown in Figures 1(A) to 1(C), the sedimentation tank 100 includes, for example, a plurality of partitions that divide the inside of the sedimentation tank 10. The plurality of partitions include a plurality of partition plates 20 installed vertically and a plurality of partition plates 30 installed horizontally. The partition plates 20 and 30 divide the inside of the sedimentation tank 10 into, for example, a sedimentation section 110, a filtration section 120, a treated water flow path 130, and a washing and drainage tank 140.

[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 3). 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 that flows in from the treated water channel 130. As shown in Figure 1(B), the washing wastewater tank 140 is 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 to be treated, from which the solids have been separated by sedimentation, 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. 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 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 to 5 are schematic diagrams showing the filtration cassette 50A according to Embodiment 1. More specifically, Figure 2 is a front view showing the first state of the filtration cassette 50A according to Embodiment 1 during filtration operation, illustrating the filtration cassette 50A as viewed along the flow direction L. Figure 3 is a longitudinal cross-sectional view showing the first state of the filtration cassette 50A according to Embodiment 1 during filtration operation, illustrating a cross section of the filtration cassette 50A perpendicular to the flow direction L. Figure 4 is a front view showing the second state of the filtration cassette 50A according to Embodiment 1 during washing operation, illustrating the filtration cassette 50A as viewed along the flow direction L. Figure 5 is a longitudinal cross-sectional view showing the second state of the filtration cassette 50A according to Embodiment 1 during washing operation, illustrating a cross section 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 to 5, the filtration cassette 50A comprises, for example, a housing 1, a filter material 2, an inlet 3, an outlet 4, and a lifting device 5.

[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 Figure 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. 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 of the filtration chamber 1a will be called the "bottom wall", and the wall that defines the top of the filtration chamber 1a will be called the "top wall". As shown in Figure 2, the housing 1 has a side wall 11, an upper screen 13 formed as the top wall, and a frame body 14.

[0049] 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.

[0050] As shown in Figure 3, an inlet 3 is formed at the bottom of the housing 1 for the water to be treated to flow into the interior of the housing 1 (filtration chamber 1a). The inlet 3 is formed facing downwards to the filtration cassette 50A, for example, by opening at the lower end of the side wall 11 (i.e., the bottom surface of the housing 1). As shown in Figure 3, the inlet 3 is positioned below the filtration layer 2a that is formed inside the housing 1 (filtration chamber 1a) by the upward flow during filtration operation. The inlet 3 has a rectangular shape in plan view, for example. The inlet 3 also has an opening width larger than the communication hole 51a formed in the lifting member 51 described later, and is formed so that the water to be treated and the filter material 2 can pass through. However, the inlet 3 only needs to be able to pass through the water to be treated, and does not need to be able to pass through the filter material 2. Furthermore, the number and shape of the inlets 3 are not particularly limited; for example, multiple inlets 3 may be provided at the bottom of the housing 1, or they may have a circular shape in plan view.

[0051] In the embodiment shown in Figure 3, etc., the entire bottom of the housing 1 (the bottom surface of the filtration chamber 1a) is open as an inlet 3. However, the housing 1 may have a bottom wall that covers a part of the bottom surface of the filtration chamber 1a, excluding the inlet 3. In other words, the housing 1 may have a bottom wall in which the inlet 3 is formed, and in that case, the part of the bottom wall excluding the inlet 3 may be formed so that the water to be treated and the filter material 2 cannot pass through.

[0052] As shown in Figure 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] The frame body 14 is, for example, a component that forms the skeleton of the housing 1. The frame body 14 includes, for example, a plurality of vertical frames 14a extending in the vertical direction and a plurality of horizontal frames 14b extending in the horizontal direction. As shown in Figure 2, the vertical frames 14a are arranged along the side ends of the side walls 11 in the width direction H and extend above the side walls 11. The horizontal frames 14b extend in the width direction H and connect pairs of vertical frames 14a, 14a by being horizontally placed between the upper ends of adjacent pairs of vertical frames 14a, 14a in the width direction H. In the frame body 14, multiple gate-shaped skeletons formed by these pairs of vertical frames 14a, 14a and horizontal frames 14b are arranged at intervals in the flow direction L to reinforce the side walls 11. Note that the frame body 14 is not an essential component in the filtration cassette according to this disclosure.

[0057] As shown in Figure 3, an air cleaning pipe 602 is inserted into the 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 near the inlet 3 at the bottom of the filtration chamber 1a.

[0058] [Filter material 2] As shown in Figure 3, the housing 1 contains multiple filter media 2. The filter media 2, for example, has a form that allows it to float in the water to be treated and capture solid matter contained in the water to be treated. As the filter media 2, for example, it can be formed into a cylindrical shape from a resin material such as foamed resin and has irregularities on its surface. However, the material and shape of the filter media 2 are not particularly limited.

[0059] During filtration operation, the buoyancy acting on the filter material 2 and the upward flow 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 Figure 3. Specifically, the filtration layer 2a is located above the inlet 3 and below the outlet 4.

[0060] 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 of the water to be treated push the filter media 2 upwards and cause them to float, so as shown in Figure 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.

[0061] [Lifting device 5] As shown in Figure 2, the lifting device 5 according to Embodiment 1 includes, for example, a lifting member 51, a pair of sliding parts 52, 52, an operating part 53, and a pair of guide parts 54, 54, and is mounted on the outside of the housing 1. Specifically, the lifting device 5 is mounted, for example, on the frame body 14 of the housing 1. The lifting device 5 is configured to allow the lifting member 51 to move up and down (vertically) within a range that includes, for example, a first position P1 shown in Figures 2 and 3 and a second position P2 above the first position P1 shown in Figures 4 and 5. As a result, the lifting device 5 can switch the filtration cassette 50A between a first state in which the inlet 3 is open by positioning the lifting member 51 at the first position P1, as shown in Figures 2 and 3, and a second state in which the inlet 3 is covered by the lifting member 51 positioned at the second position P2, as shown in Figures 4 and 5.

[0062] Furthermore, the first position P1 does not necessarily have to be a position where the lifting member 51 completely opens the inlet 3. It is sufficient if the distance between the lifting member 51 and the inlet 3 is greater when the lifting member 51 is in the first position P1 (first state) than when the lifting member 51 is in the second position P2 (second state).

[0063] The lifting member 51 is, for example, a water-conducting plate formed in the shape of a plate, and is positioned below the housing 1 (filtration chamber 1a) in a state perpendicular to the vertical direction V.

[0064] The lifting member 51 is configured, for example, to allow the water to be treated to pass through while preventing the filter material 2 from passing through. The lifting member 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 have an opening width smaller than the inlet 3 and penetrate the lifting member 51 in the thickness direction, and are formed so that 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 lifting member 51 is positioned at the second position P2 covering the inlet 3, the water to be treated is allowed to flow into the housing 1 (filtration chamber 1a) through the inlet 3, and the filter material 2 is prevented from flowing out to the outside of the housing 1 through the inlet 3.

[0065] The material and shape of the lifting member 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 lifting member 51 does not have to be plate-shaped.

[0066] The sliding portion 52 is, for example, a rod-shaped member that connects the lifting member 51 and the operating portion 53 and slides vertically in the direction V along the guide portion 54. The sliding portion 52 extends along the vertical direction V, with its lower end connected to the lifting member 51 and its upper end connected to the operating portion 53. In this embodiment, a pair of sliding portions 52, 52 are arranged with a gap in the width direction H. The material, shape, and number of the sliding portions 52 are not particularly limited.

[0067] The operating section 53 is a component operated by an external power source (not shown) or by an operator to raise or lower the lifting member 51, for example, from above the filtration cassette 50A. The operating section 53 is located above the housing 1 and is connected to the lifting member 51 via a pair of sliding sections 52, 52. The operating section 53 is positioned above the water surface WS of the water to be treated so that it can be operated from above or around the sedimentation tank 10. The operating section 53 is, for example, a rod-shaped component extending along the width direction H. The shape of the operating section 53 is not particularly limited.

[0068] The guide portion 54 is, for example, a cylindrical member that guides the sliding of the slide portion 52 in the vertical direction V. The guide portion 54 extends along the vertical direction V and is fixed to the housing 1. The slide portion 52 is inserted through the guide portion 54. The slide portion 52 is slidable in the vertical direction V within the guide portion 54, and the sliding of the slide portion 52 is guided by the inner wall of the guide portion 54. In this embodiment, a pair of guide portions 54, 54 are fixed to the lateral frame 14b or side wall 11 of the frame body 14 with a gap in the width direction H. The material, shape, and number of the guide portions 54 are not particularly limited. The guide portion 54 may be formed in the shape of a rail that slidably holds the slide portion 52.

[0069] [Lifting and lowering operation of Embodiment 1] The following describes the operation for raising and lowering the lifting member 51 between the first position P1 and the second position P2 in Embodiment 1.

[0070] When raising the lifting member 51 from the first position P1 to the second position P2, the lifting member 51, which is connected to the operating part 53 via the sliding part 52, is also raised by pulling up the operating part 53 of the lifting device 5 using an external power source (not shown), such as hydraulics or pneumatics. At this time, the sliding part 52 is guided upward by the guide part 54. When the lifting member 51 is positioned at the second position P2 and the inlet 3 of the housing 1 is covered from below by the lifting member 51, the second state shown in Figures 4 and 5 is achieved. In the second state, in order to prevent the lifting member 51 from descending from the first position P1 due to its own weight, the operating part 53 may be held stationary by an external power source such as hydraulics or pneumatics, or the sliding part 52 may be fixed to the guide part 54 by a fixing member such as a pin. This fixes the lifting member 51 at the second position P2.

[0071] Furthermore, by performing the reverse operation of raising the lifting member 51, the lifting member 51 can be lowered from the second position P2 to the first position P1. Specifically, for example, by pulling down the operating part 53 of the lifting device 5 using external power, the lifting member 51 can also be lowered. When the lifting member 51 is positioned at the first position P1 and the inlet 3 of the housing 1 is opened, the first state shown in Figures 2 and 3 is achieved. Alternatively, the lifting member 51 may be lowered using gravity; for example, by releasing the locking of the lifting member 51 at the second position P2 in the second state, the lifting member 51 will descend to the first position P1 by its own weight.

[0072] Furthermore, the above-mentioned lifting and lowering operations may be performed manually by an operator. For example, an operator can grasp the operating unit 53 from a work platform (not shown) installed around the sedimentation tank 10 or on the water inside the sedimentation tank 10 and perform the lifting and lowering operation of the lifting and lowering member 51. [Flow channel formation in Embodiment 1]

[0073] The following describes the flow path formed in the filtration cassette 50A in Embodiment 1.

[0074] As shown in Figure 3, in the first state, the lifting member 51 is positioned at the first position P1, thereby ensuring a predetermined separation distance between the lifting member 51 and the inlet 3, and opening the inlet 3. At this time, a first flow path F1 is formed between the lifting member 51 and the housing 1, leading to the inside of the housing 1 (filtration chamber 1a) via the inlet 3. More specifically, the first flow path F1 is formed, for example, between the lifting member 51 and the lower end of the side wall 11. That is, in the first state, for example, the gap formed between the lifting member 51 and the housing 1 functions as a first flow path F1 that guides the water to be treated to the filtration layer 2a via the inlet 3.

[0075] Furthermore, as shown in Figure 5, in the second state, the lifting member 51 is positioned at the second position P2, so that the inlet 3 is covered by the lifting member 51. At this time, the entire area of ​​the inlet 3 is covered by the lifting member 51. In the second state, for example, the lifting member 51 and the housing 1 are in contact without any gaps, so the first flow path F1 is not formed. However, in the second state, for example, the communication hole 51a of the lifting member 51 covering the inlet 3 forms a second flow path F2 that leads to the inside of the housing 1 (filtration chamber 1a) via the inlet 3. That is, in the second state, for example, the communication hole 51a formed in the lifting member 51 functions as a second flow path F2 that guides the water to be treated into the inside of the housing 1 via the inlet 3.

[0076] The second flow path F2 has a flow path width such that it allows the water to be treated to pass through but prevents the filter material 2 from passing through. Therefore, in the second state where the lifting member 51 is positioned at the second position P2, the water to be treated is allowed to flow into the housing 1 (filtration chamber 1a) and out of the housing 1 via the second flow path F2, while the filter material 2 is prevented from flowing out of the housing 1 via the outlet 4.

[0077] In contrast, the first flow path F1 has a wider flow path width than the second flow path F2. Specifically, the flow path width of the first flow path F1 is, for example, greater than the opening width of the communication hole 51a formed in the lifting member 51. The first flow path F1 has a flow path width sufficient to allow the passage of the water to be treated and the filter material 2. However, the first flow path F1 only needs to be able to allow the water to be treated to pass through and have a wider flow path width than the second flow path F2; for example, it may have a flow path width sufficient to allow the passage of the water to be treated but prevent the passage of the filter material 2.

[0078] As shown in Figure 3, in Embodiment 1, for example, the filtration operation is performed in a first state in which the lifting member 51 is positioned at a first position P1. The water to be treated reaches the inlet 3 through a first flow path F1 formed between the lifting member 51 and the housing 1, and flows into the interior of the housing 1. Since the water to be treated passes through the first flow path F1, the adhesion of solid matter contained in the water to be treated to the lifting member 51 is suppressed. In addition, since the inlet 3 is open, the adhesion of solid matter contained in the water to be treated to the bottom of the housing 1 is also suppressed.

[0079] In the first state, for example, the width of the first flow path F1 is greater than the opening width of the communication hole 51a of the lifting member 51. Therefore, most of the water to be treated flows into the interior of the housing 1 through the first flow path F1, without passing through the communication hole 51a, which has a smaller opening width and higher water flow resistance than the first flow path F1. In other words, in the first state, the water to be treated preferentially passes through the first flow path F1 over the communication hole 51a of the lifting member 51.

[0080] Furthermore, since the first flow path F1 has a relatively large flow path width, for example, the adhesion of solids contained in the water to be treated to the first flow path F1 is suppressed. As mentioned above, during filtration operation, for example, the buoyancy acting on the filter material 2 and the upward flow of the water to be treated push the filter material 2 upward and cause it to float above the first flow path F1. Therefore, even if the first flow path F1 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.

[0081] As shown in Figure 5, in Embodiment 1, for example, the cleaning operation is performed in a second state in which the lifting member 51 is positioned at the second position P2. During aeration cleaning of the cleaning operation, for example, the filter material 2 flows due to the swirling flow 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 inlet 3 is covered by the lifting member 51, and the second flow path F2 formed in the lifting member 51 is impassable for the filter material 2. Therefore, the lifting member 51 prevents the filter material 2 from flowing out of the housing 1 due to the swirling flow during aeration cleaning.

[0082] Figure 6 is a vertical cross-sectional view showing the second state of the filtration cassette 50A according to Embodiment 1 during draining, and shows a cross-section perpendicular to the flow direction L of the filtration cassette 50A. As shown in Figure 6, in Embodiment 1, for example, draining of the filtration cassette 50A is performed in the second state in which the lifting member 51 is positioned at the second position P2. In the second state, for example, the communication hole 51a of the lifting member 51 covering the inlet 3 functions as a second flow path F2, so that the water to be treated inside the housing 1 flows out to the outside of the housing 1 through the second flow path F2 via the inlet 3. During draining, since the water to be treated flows out to the outside of the housing 1 via the inlet 3, 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, for example, the second flow path F2 formed in the lifting member 51 covering the inlet 3 is impassable for the filter material 2, so the lifting member 51 prevents the filter material 2 from flowing out to the outside of the housing 1. Furthermore, when the lifting member 51 is immersed in the water to be treated during the filtration operation, any solid matter adhering to the communication hole 51a is removed by the water pressure during draining.

[0083] 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 lifting member 51 at the second position P2, it is prevented that the filter material 2 will flow out of the filtration chamber 1a. When installing the filtration cassette 50, for example, the lifting member 51 may be fixed at the second position P2 by fixing the slide part 52 to the guide part 54 with a fixing member such as a pin, and then the fixing may be released when the water level in the sedimentation tank 10 (filtration section 120) rises and the filter material 2 floats, and the lifting member 51 may be lowered to the first position P1.

[0084] [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 lifting member 51 installed to be able to move up and down within a range including a first position P1 that opens the inlet 3 and a second position P2 that covers the inlet 3. Furthermore, when the lifting member 51 is positioned at the first position P1, a first flow path F1 is formed between the lifting member 51 and the housing 1 to guide the water to be treated to the filtration layer 2a, and when the lifting member 51 is positioned at the second position P2, a second flow path F2 is formed in the lifting member 51 to guide the water to be treated to the outside of the housing 1.

[0085] With the filtration cassette 50A according to Embodiment 1 configured as described above, during filtration operation, the lifting member 51 is positioned in the first position and the inlet 3 is opened, which prevents solid matter contained in the water to be treated from adhering to the bottom of the housing 1 and the lifting member 51. During cleaning operation or draining, the lifting member 51 is positioned in the second position P2 and the inlet 3 is covered, which prevents the filter material 2 from flowing out of the housing 1. As a result, solid matter contained in the water to be treated is prevented from adhering to the filtration cassette 50A, thus reducing the number of times the filtration cassette 50A needs to be cleaned. Consequently, the number of times the filtration operation needs to be stopped for cleaning is reduced, and the filtration operation can be performed continuously for a long period of time. In other words, the filtration operation of the sedimentation tank 100 can be performed more efficiently.

[0086] Furthermore, the lifting member 51 of the filtration cassette 50A according to Embodiment 1 has a communication hole 51a through which the water to be treated can pass. When the lifting member 51 is positioned at the second position P2, the communication hole 51a forms the second flow path F2. This allows the water to be treated to be discharged through the communication hole 51a while preventing the filter material 2 from flowing out by positioning the lifting member 51 at the second position P2 during draining.

[0087] [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.

[0088] Figures 7 to 9 are schematic diagrams showing the filtration cassette 50B according to Embodiment 2. More specifically, Figure 7 is a longitudinal cross-sectional view showing the first state of the filtration cassette 50B according to Embodiment 2 during filtration operation, Figure 8 is a longitudinal cross-sectional view showing the second state of the filtration cassette 50B according to Embodiment 2 during water draining, and Figure 9 is a longitudinal cross-sectional view showing the third state of the filtration cassette 50B according to Embodiment 2 during washing operation. Figures 7 to 9 show cross-sections of the filtration cassette 50B perpendicular to the flow direction L. Figure 10 is a cross-sectional view of the filtration cassette 50B showing a cross section along the CC line in Figure 7, and Figure 11 is a transverse cross-sectional view of the filtration cassette 50B showing a cross section along the DD line in Figure 9. Figures 10 and 11 show cross-sections of the filtration cassette 50B perpendicular to the vertical direction V.

[0089] As shown in Figures 7 to 11, 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 lifting device 5B.

[0090] [Cabinet 1B] Figure 12 is a cross-sectional view of the housing 1B according to Embodiment 2. In Figure 12, a cross-section perpendicular to the vertical direction V is shown. As shown in Figure 12, the side wall 11 of the housing 1B includes, for example, a pair of plate-shaped wall portions 111, 111 arranged perpendicular to the flow direction L, and a pair of plate-shaped wall portions 112, 112 arranged perpendicular to the width direction H, and is formed in a rectangular tubular shape with a horizontal cross-section. In a top view, the pair of wall portions 111, 111 extend along the width direction H, and the pair of wall portions 112, 112 extend along the flow direction L.

[0091] Furthermore, as shown in Figure 7, the housing 1B according to Embodiment 2 has, for example, a bottom wall 12. That is, a bottom wall 12 is provided at the bottom of the housing 1B. The bottom wall 12 is formed, for example, in the shape of a plate and is arranged perpendicular to the vertical direction V so as to cover a part of the bottom surface of the filtration chamber 1a, except for the inlet 3B. 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.

[0092] As shown in Figure 12, the bottom wall 12 has, for example, an inlet 3B for the water to be treated to flow into the interior of the housing 1B. The inlet 3B is formed so that, for example, the water to be treated and the filter material 2 can pass through.

[0093] More specifically, the bottom wall 12 includes, for example, a pair of wall sections 12a, 12a spaced apart in the width direction H, with an inlet 3B formed between the pair of wall sections 12a, 12a. In other words, the pair of wall sections 12a, 12a are arranged to sandwich the inlet 3B from both sides in the width direction H. As shown in Figure 12, the inlet 3B is formed, for example, in the center of the bottom of the housing 1B in the width direction H, and across the entire bottom of the housing 1B in the flow direction L (i.e., across both ends of the bottom in the flow direction L). However, the arrangement of the inlet 3B at the bottom of the housing 1B is not limited to this. For example, the bottom wall 12 may be arranged to surround the inlet 3B.

[0094] Furthermore, the bottom wall 12 has, for example, a plurality of communication holes 121 in addition to the inlet 3B. The plurality of communication holes 121 are, for example, through holes that penetrate the bottom wall 12 in the thickness direction. The communication holes 121 have, for example, an opening width smaller than the inlet 3B, and are formed so that the water to be treated can pass through but the filter material 2 cannot. Therefore, the water to be treated is allowed to flow out of the housing 1B (filtration chamber 1a) through the communication holes 121, while the filter material 2 is prevented from flowing out of the housing 1B through the communication holes 121.

[0095] For the bottom wall 12, a screen such as a perforated plate like punched metal or a mesh plate like metal mesh can be used.

[0096] [Lifting device 5B] As shown in Figure 7, the lifting device 5B according to Embodiment 2 includes, for example, a lifting member 51B disposed inside the housing 1B, a plurality of restricting parts 55 provided on the side wall 11 of the housing 1B, and a pair of expandable members 56, 56 provided on the side wall 11 of the housing 1B.

[0097] The lifting device 5B is configured to allow the lifting member 51B to move up and down (vertically) within the housing 1B within a range that includes, for example, the first position P1B shown in Figure 7 and the second position P2B shown in Figure 8, which is lower than the first position P1B. Furthermore, the lifting device 5B is configured to allow the expandable member 56 to expand and contract within a range that includes, for example, the normal state of the expandable member 56 shown in Figure 7 and the expanded state in which the expandable member 56 is expanded beyond its normal state, as shown in Figure 9. As a result, the lifting device 5B can switch the filtration cassette 50B between a first state in which the lifting member 51B is positioned at the first position P1B and the expandable member 56 is in its normal state, as shown in Figure 7; a second state in which the lifting member 51B is positioned at the second position P2B, as shown in Figure 8; and a third state in which the lifting member 51B is positioned at the first position P1B and the expandable member 56 is in the expanded state, as shown in Figure 9. As shown in Figures 7 and 9, in the first and third states, the lifting member 51B is positioned at the first position P1B, opening the inlet 3B, and as shown in Figure 8, in the second state, the inlet 3B is covered by the lifting member 51B positioned at the second position P2B.

[0098] Furthermore, the first position P1B does not necessarily have to be a position where the lifting member 51B completely opens the inlet 3B. It is sufficient if the distance between the lifting member 51B and the inlet 3B is greater when the lifting member 51B is positioned at the first position P1B (first and third states) than when the lifting member 51B is positioned at the second position P2B (second state).

[0099] The lifting member 51B is, for example, located inside the housing 1B (filtration chamber 1a) and has buoyancy relative to the water to be treated. The lifting member 51B is, for example, a floating plate formed in the shape of a plate and is located between the filtration layer 2a and the inlet 3B in a state perpendicular to the vertical direction V. More specifically, the lifting member 51B is located, for example, inside the housing 1B, below the filtration layer 2a and the air outlet 602a of the air irrigation pipe 602.

[0100] As shown in Figure 10, the lifting member 51B includes, for example, a pair of side ends 511, 511 arranged perpendicular to the flow direction L, and a pair of side ends 512, 512 arranged perpendicular to the width direction H, and is formed in a substantially rectangular shape in top view. In top view, the pair of side ends 511, 511 extend along the width direction H, and the pair of side ends 512, 512 extend along the flow direction L. Also, for example, side end 511 is in contact with the wall portion 111 of the housing 1B opposite to side end 511, and side end 512 is spaced apart from the wall portion 112 of the housing 1B opposite to side end 512.

[0101] As shown in Figure 10, the side end portion 512 of the lifting member 51B is formed, for example, in a comb-like shape. More specifically, the side end portion 512 has, for example, a plurality of recesses 513 that are recessed in the width direction H and spaced apart in the flow direction L. The recesses 513 have a rectangular cross-section and penetrate the lifting member 51B in the thickness direction (vertical direction V). However, the number and shape of the recesses 513 are not particularly limited. Also, in Embodiment 2, recesses 513 are formed on both of the pair of side end portions 512, 512, but they may be formed on only one of them.

[0102] The lifting member 51B is configured to prevent, for example, the water to be treated and the filter material 2 from passing through. In other words, the water to be treated and the filter material 2 cannot pass through the lifting member 51B.

[0103] The material of the lifting member 51B is not particularly limited, but resin materials such as foamed resin are examples. Furthermore, the shape of the lifting member 51B is not limited to a plate shape, and various shapes can be adopted.

[0104] As shown in Figure 7, the multiple restricting parts 55 are provided, for example, on the side wall 11 of the housing 1B and restrict the upward movement of the lifting member 51B by contacting it from above at the first position P1B. The restricting parts 55 are formed, for example, in the shape of a plate and are erected on the wall portion 112 of the side wall 11 in a state perpendicular to the vertical direction V.

[0105] As shown in Figure 10, for example, two restricting parts 55 are provided on each of the pair of wall sections 112, 112, and the restricting parts 55 abut against each of the pair of side ends 512, 512 of the lifting member 51B from above. However, the shape and number of restricting parts 55 are not particularly limited. Also, restricting parts 55 may be provided on each of the pair of wall sections 111, 111.

[0106] The expandable member 56 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 56 are not particularly limited. The pair of expandable members 56, 56 are each provided on the side wall 11 in a state that extends along the flow direction L, as shown in Figure 10. More specifically, the expandable member 56 is provided on each of the pair of wall portions 112, 112. As shown in Figure 7, the expandable member 56 is positioned below the regulating portion 55, for example, and is positioned opposite the side end portion 512 of the lifting member 51B located at the first position P1B.

[0107] As shown in Figure 10, for example, an air supply pipe 56a is connected to one end of the expandable member 56, and an air discharge pipe 56b is connected to the other end. The air supply pipe 56a 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 56. The air discharge pipe 56b is provided with, for example, an on / off valve 56c.

[0108] The expandable member 56 can change between, for example, a normal state as shown in Figure 7 and an expanded state that is more expanded than the normal state as shown in Figure 9. Specifically, for example, in the normal state, by closing the on-off valve 56c and supplying air to the expandable member 56 from the air supply pipe 56a, the expandable member 56 expands and changes to the expanded state. Also, for example, in the expanded state, by opening the on-off valve 56c and discharging air from the expandable member 56 to the air discharge pipe 56b, the expandable member 56 contracts and changes to the normal state. As shown in Figure 7, for example, in the first state, the lifting member 51B located at the first position P1B and the expandable member 56 in the normal state do not come into contact, and the side end 512 of the lifting member 51B and the wall portion 112 of the housing 1B are separated. Also, as shown in Figure 9, for example, in the third state, the lifting member 51B located at the first position P1B and the expandable member 56 in the expanded state are in partial contact except for the recess 513.

[0109] [Lifting and lowering operation in Embodiment 2] The following describes the raising and lowering operation of the lifting member 51B in Embodiment 2. In Embodiment 2, the lifting and lowering operation of the lifting member 51B is performed using buoyancy and upward flow.

[0110] As shown in Figure 7, during filtration operation, the lifting member 51B is pushed up by, for example, buoyancy acting on it and the upward flow of the water to be treated, causing it to float to the first position P1B. At this time, the restricting part 55 provided on the side wall 11 contacts the lifting member 51B from above, restricting the upward movement of the lifting member 51B at the first position P1B. On the other hand, during filtration operation, the lifting member 51B is pressed against the restricting part 55 by, for example, buoyancy and the upward flow, thus restricting the downward movement of the lifting member 51B. As a result, during filtration operation, the state in which the lifting member 51B is positioned at the first position P1B is maintained.

[0111] As shown in Figure 9, during aeration cleaning in the cleaning operation, for example, the swirling flow generated inside the housing 1B of the filtration cassette 50B (filtration chamber 1a) causes the filter material 2 to flow, acting as a force to push down the lifting member 51B located at the first position P1B. In response to this, for example, a portion of the air supplied from the blower 601 is sent to the inflatable member 56 via the air supply pipe 56a, causing the inflatable member 56 to expand, so that it comes into contact with the side end 512 of the lifting member 51B at the first position P1B. As a result, as shown in Figure 9, the lifting member 51B is held between a pair of inflatable members 56, 56 from both sides in the width direction H. This restricts the downward movement of the lifting member 51B during cleaning operation, and maintains the state in which the lifting member 51B is located at the first position P1B.

[0112] As shown in Figure 8, when the water in the filter cassette 50B is drained, for example, the water pressure of the water to be treated pushes down the lifting member 51B, causing it to descend to the second position P2B and rest on the bottom wall 12 of the housing 1B. At this time, the bottom wall 12 of the housing 1B contacts the lifting member 51B from below, restricting the descent of the lifting member 51B at the second position P2B. As a result, when draining the water, the lifting member 51B remains in the second position P2B and is prevented from falling off.

[0113] Furthermore, for example, when installing the filtration cassette 50B in the sedimentation tank 10 or after draining the water from the filtration cassette 50B, there is no water inside the housing 1B, so no buoyancy acts on the lifting member 51B, and the lifting member 51B is positioned at the second position P2B by its own weight.

[0114] [Flow channel formation in Embodiment 2]

[0115] The following describes the flow path formed in the filtration cassette 50B in Embodiment 2.

[0116] As shown in Figure 7, in the first state, for example, the inlet 3B is opened by positioning the lifting member 51B at the first position P1B. Also, as shown in Figure 10, in the first state, for example, the lifting member 51B positioned at the first position P1B and the expandable member 56 in its normal state are separated, forming a first flow path F1B between the lifting member 51B and the side wall 11 of the housing 1B. More specifically, in the first state, for example, the gap formed between the side end 512 of the lifting member 51B and the expandable member 56 functions as a first flow path F1B that guides the water to be treated to the filtration layer 2a.

[0117] As shown in Figures 9 and 11, in the third state, for example, the lifting member 51B at the first position P1B and the inflatable member 56 in the expanded state are in partial contact. More specifically, for example, the inflatable member 56 is in contact with the portion of the side end 512 of the lifting member 51B excluding the recess 513. As a result, a third flow path F3B is formed between the side end 512 of the lifting member 51B and the inflatable member 56, that is, between the lifting member 51B and the side wall 11 of the housing 1B. More specifically, in the third state, for example, the recess 513 formed in the side end 512 of the lifting member 51B functions as a third flow path F3B that guides the water to be treated into the interior of the housing 1B.

[0118] Furthermore, as shown in Figure 8, in the second state, for example, the lifting member 51B is positioned at the second position P2B, so that the inlet 3B is covered by the lifting member 51B. For example, the entire area of ​​the inlet 3B is covered by the lifting member 51B. Also, in the second state, for example, the lifting member 51B is placed on the bottom wall 12 of the housing 1B, but a part of the bottom wall 12 is not covered by the lifting member 51B. Therefore, in the second state, for example, the communication hole 121 formed in the bottom wall 12 functions as a second flow path F2B that guides the water to be treated to the outside of the housing 1B.

[0119] The second flow path F2B has a flow path width such that it allows the water to be treated to pass through but prevents the filter material 2 from passing through. The first flow path F1B has a larger flow path width than the second flow path F2B and allows the water to be treated and the filter material 2 to pass through. The third flow path F3B has a smaller opening width than the first flow path F1B and allows the water to be treated to pass through but prevents the filter material 2 from passing through.

[0120] In Embodiment 2, the filtration cassette 50B is configured such that a first flow path F1B and a second flow path F2B are formed between the end of the lifting member 51B in the width direction H and the side wall 11 of the housing 1B, but the formation of the flow paths is not limited to this. For example, the filtration cassette 50B may be configured such that a first flow path F1B and a second flow path F2B are formed between the end of the lifting member 51B in the flow direction L and the side wall 11 of the housing 1B.

[0121] As shown in Figure 7, in Embodiment 2, for example, by setting the filter cassette 50B to a first state during filtration operation, a first flow path F1B is formed between the lifting member 51B and the side wall 11 of the housing 1B. The water to be treated flows into the housing 1B through, for example, the open inlet 3B and is guided to the filtration layer 2a through the first flow path F1B. Since the water to be treated flows in through the inlet 3B, the adhesion of solid matter contained in the water to be treated to the bottom of the housing 1B is suppressed.

[0122] Here, for example, since the opening width of the inlet 3B is wider than the opening width of the communication hole 121 formed in the bottom wall 12, most of the water to be treated flows into the interior of the housing 1B through the inlet 3B, without passing through the communication hole 121, which has a smaller flow path width and higher water flow resistance than the inlet 3B. In other words, in the first state, the water to be treated preferentially passes through the inlet 3B over the communication hole 121 in the bottom wall 12.

[0123] Furthermore, since the first flow path F1B has a relatively large flow path width, for example, the adhesion of solids contained in the treated water to the first flow path F1B is suppressed. Also, as described above, during filtration operation, for example, the filter material 2 floats above the first flow path F1B, so even if the first flow path F1B 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 1B is suppressed.

[0124] As shown in Figure 9, in Embodiment 2, for example, by setting the filter cassette 50B to a third state during the washing operation, a third flow path F3B is formed between the lifting member 51B and the side wall 11 of the housing 1B. Since the filter material 2 cannot pass through the third flow path F3B, the expandable member 56 prevents the filter material 2 from flowing out of the housing 1B due to the swirling flow during aeration washing.

[0125] As shown in Figure 8, in Embodiment 2, for example, when draining the water from the filter cassette 50B, the filter cassette 50B is put into a second state, causing the communication hole 121 formed in the bottom wall 12 of the housing 1B to function as a second flow path F2B. The water to be treated inside the housing 1B flows out to the outside of the housing 1B, for example, through the second flow path F2B. In the second state, for example, the inlet 3B is covered by the lifting member 51B, and the second flow path F2B formed in the bottom wall 12 of the housing 1B cannot be passed through, so the lifting member 51B prevents the filter material 2 from flowing out to the outside of the housing 1B due to the water pressure during draining. In addition, solid matter adhering to the communication hole 121 when the bottom wall 12 of the housing 1B is immersed in the water to be treated during filtration operation is removed by the water pressure during draining.

[0126] Furthermore, for example, when installing the filtration cassette 50B in the sedimentation tank 10 or after draining the filtration cassette 50B, the lifting member 51B, positioned at the second position P2B, prevents the filter material 2 from flowing out of the filtration chamber 1a due to its own weight.

[0127] [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 lifting member 51B installed to be able to move up and down within a range including a first position P1B that opens the inlet 3B and a second position P2B that covers the inlet 3B. Furthermore, when the lifting member 51B is positioned at the first position P1B, a first flow path F1B is formed between the lifting member 51B and the housing 1B to guide the water to be treated to the filtration layer 2a, and when the lifting member 51B is positioned at the second position P2B, a second flow path F2B is formed in the bottom wall 12 of the housing 1B to guide the water to be treated to the outside of the housing 1B.

[0128] With the filtration cassette 50B according to Embodiment 2 configured in this way, during filtration operation, the lifting member 51B is positioned in the first position and the inlet 3B is opened, which prevents solid matter contained in the water to be treated from adhering to the bottom of the housing 1B. During draining, the lifting member 51B is positioned in the second position P2B and the inlet 3B is covered, which prevents the filter material 2 from flowing out of the housing 1B. As a result, the adhesion of solid matter is suppressed, and the frequency of cleaning the filtration cassette 50B can be reduced. Consequently, similar to Embodiment 1, the filtration operation of the sedimentation tank 100 can be performed more efficiently.

[0129] Furthermore, the location where the second flow path F2B is formed is not limited to the bottom wall 12 of the housing 1B. The second flow path F2B can be formed in the housing 1B, and for example, a communication hole formed in the side wall 11 of the housing 1B may function as the second flow path F2B.

[0130] Furthermore, in Embodiment 2, the first position P1B is located above the second position P2B, the lifting member 51B is positioned inside the housing 1B and has buoyancy relative to the water to be treated, and the side wall 11 of the housing 1B is provided with a restricting section 55 that restricts the upward movement of the lifting member 51B at the first position P1B. When the lifting member 51B is positioned at the first position P1B, a first flow path F1B is formed between the lifting member 51B and the side wall 11 of the housing 1B. As a result, for example, during filtration operation, the lifting member 51B is held at the first position P1B by buoyancy and the restricting section 55, so that the state in which the first flow path F1B is formed can be maintained.

[0131] Furthermore, the side wall 11 of the housing 1B according to Embodiment 2 is provided with an expandable member 56 that is disposed between the lifting member 51B in a first position P1B and the expandable member 56, and which can change between a normal state and an expanded state that is more expanded than the normal state. When the lifting member 51B is in the first position P1B, the expandable member 56 is in the normal state, forming a first flow path F1B between the expandable member 56 and the lifting member 51B. When the lifting member 51B is in the first position P1B, the expandable member 56 is in the expanded state, forming a third flow path F3B between the expandable member 56 and the lifting member 51B, which has a flow path width smaller than the first flow path F1B. As a result, for example, during a washing operation, by forming a third flow path F3B with a flow path width smaller than the first flow path F1B, it is possible to prevent the filter material 2 from flowing out of the housing 1B.

[0132] Furthermore, the bottom of the housing 1B according to Embodiment 2 is provided with an inlet 3B and a bottom wall 12 that restricts the descent of the lifting member 51B located at the second position P2B. The bottom wall 12 has a communication hole 121 through which the water to be treated can pass. When the lifting member 51B is positioned at the second position P2B, the communication hole 121 in the bottom wall 12 forms a second flow path F2B. This makes it possible to form a second flow path F2B while, for example, preventing the lifting member 51B from falling off during draining.

[0133] [Modification 1 of Embodiment 2] Next, the configuration of the filtration cassette 50 according to Modification 1 of Embodiment 2 will be described. Hereinafter, the filtration cassette 50 according to Modification 1 of Embodiment 2 will also be referred to as filtration cassette 50C. In the following description of Modification 1, the differences from filtration cassette 50B will be the main focus, and the same reference numerals will be used for components similar to those in filtration cassette 50B, thus omitting detailed explanations.

[0134] Figure 13 is a longitudinal cross-sectional view showing the first state of the filtration cassette 50C according to Modification 1 of Embodiment 2 during filtration operation, and Figure 14 is a longitudinal cross-sectional view showing the third state of the filtration cassette 50C according to Modification 1 of Embodiment 2 during washing operation. Figures 13 and 14 show cross-sections of the filtration cassette 50C perpendicular to the flow direction L. Figure 15 is a transverse cross-sectional view of the filtration cassette 50C showing a cross-section along the EE line in Figure 14. Figure 15 shows a cross-section of the filtration cassette 50C perpendicular to the vertical direction V.

[0135] As shown in Figures 13 and 14, the lifting device 5C of the filter cassette 50C according to the modified example 1 of Embodiment 2 has, for example, a pair of expandable members 56C, 56C. The pair of expandable members 56C, 56C differ from the above-described pair of expandable members 56, 56 in that they are positioned below the lifting member 51B, which is positioned at the first position P1B. More specifically, the expandable member 56C is provided, for example, on the wall portion 112 of the side wall 11 that faces the side end portion 512 of the lifting member 51B, and is positioned below the lifting member 51B in the first and third states. The expandable member 56C can change between, for example, the normal state shown in Figure 13 and an expanded state that is more expanded than the normal state shown in Figures 14 and 15.

[0136] As shown in Figure 13, for example, in the first state, the lifting member 51B positioned at the first position P1B and the expandable member 56C in its normal state do not come into contact, and the lifting member 51B and the expandable member 56C are separated. As a result, in the first state, a first flow path F1C is formed between the lifting member 51B and the side wall 11 of the housing 1B. More specifically, in the first state, for example, the gap formed between the side end 512 of the lifting member 51B and the expandable member 56C functions as the first flow path F1C.

[0137] Furthermore, as shown in Figure 14, for example, in the third state, the pair of inflatable members 56C, 56C in their expanded state come into contact with the lifting member 51B located at the first position P1B from below. This restricts the downward movement of the lifting member 51B at the first position P1B. Also, as shown in Figure 15, the inflatable member 56C in its expanded state overlaps the side end 512 of the lifting member 51B from below, so that the recess 513 formed in the side end 512 is partially covered from below by the inflatable member 56C. In other words, in the third state, the recess 513 is covered from below except for a portion of it. As a result, in the third state, a third flow path F3C with a flow path width smaller than the first flow path F1C is formed between the side end 512 of the lifting member 51B and the inflatable member 56C, that is, between the lifting member 51B and the side wall 11 of the housing 1B. More specifically, in the third state, for example, the portion of the recess 513 formed in the side end 512 of the lifting member 51B that is not covered from below by the expandable member 56C functions as a third flow path F3C. The third flow path F3C has a flow path width that allows the water to be treated to pass through but prevents the filter material 2 from passing through. Therefore, by putting the filter cassette 50C into the third state during aeration washing, the expandable member 56C prevents the filter material 2 from flowing out of the housing 1B due to swirling flow.

[0138] In addition, in the modified example 1 of Embodiment 2, the recess 513 may have a shape such that its width decreases as it moves in the direction of recession (depth direction of the recess 513), for example, like a V-groove with a triangular cross-section. By doing so, in the first state where the lifting member 51B and the expandable member 56C are separated, a larger opening width of the first flow path F1C can be secured, and in the third state where the lifting member 51B and the expandable member 56C overlap, the opening width of the third flow path F3C can be more reliably reduced.

[0139] [Modification 2 of Embodiment 2] Next, the configuration of the filtration cassette 50 according to Modification 2 of Embodiment 2 will be described. Hereinafter, the filtration cassette 50 according to Modification 2 of Embodiment 2 will also be referred to as filtration cassette 50D. In the following description of Modification 2, the differences from filtration cassette 50B will be the main focus, and the same reference numerals will be used for components similar to those in filtration cassette 50B, thus omitting detailed explanations.

[0140] Figure 16 is a longitudinal cross-sectional view showing the second state of the filtration cassette 50D according to Modification 2 of Embodiment 2 during water drainage, and shows a cross-section perpendicular to the flow direction L of the filtration cassette 50D. Figure 17 is a longitudinal cross-sectional view of the filtration cassette 50D showing a cross-section along the FF line in Figure 16, and shows a cross-section perpendicular to the width direction H of the filtration cassette 50D.

[0141] As shown in Figure 16, the bottom wall 12D of the housing 1D in the filtration cassette 50D according to Modification 2 of Embodiment 2 differs from the bottom wall 12 of the housing 1B in the filtration cassette 50B in that, for example, communication holes are not formed therein. Therefore, the bottom wall 12D in Modification 2 is configured to prevent the passage of the water to be treated and the filter material 2. In other words, the water to be treated and the filter material 2 cannot pass through the bottom wall 12D.

[0142] Furthermore, the lifting device 5D of the filter cassette 50D according to the modified example 2 of Embodiment 2 differs from the lifting device 5B of the filter cassette 50B in that it has, for example, a pair of flow path forming parts 57, 57. As shown in Figure 17, the flow path forming part 57 partially contacts the lifting member 51B located at the second position P2D, for example, thereby forming a second flow path F2D between it and the lifting member 51B.

[0143] As shown in Figure 16, the pair of flow path forming sections 57, 57 are arranged on the bottom wall 12D inside the housing 1D, for example, so as to sandwich the inlet 3B from both sides in the width direction H. The flow path forming section 57 is, for example, a block-shaped member that extends along the flow direction L. As shown in Figure 17, both ends of the flow path forming section 57 in the flow direction L are in contact with the wall portion 111 of the side wall 11. In other words, the flow path forming section 57 extends across both ends of the inside of the housing 1D (filtration chamber 1a) in the flow direction L.

[0144] As shown in Figure 17, the upper surface 571 of the flow channel forming section 57 is formed, for example, in a comb-like shape. More specifically, the upper surface 571 of the flow channel forming section 57 has, for example, a plurality of downwardly recessed recesses 572 formed at intervals in the flow direction L. The recesses 572 have, for example, a rectangular cross-section and penetrate the flow channel forming section 57 in the width direction H. However, the number and shape of the recesses 572 are not particularly limited.

[0145] As shown in Figure 17, for example, when draining the water from the filter cassette 50D, the water pressure of the water to be treated pushes down the lifting member 51B, causing it to descend to a second position P2D, where it is placed on the pair of flow path forming sections 57, 57. This puts the filter cassette 50D into a second state. As shown in Figure 17, in the second state, for example, the lifting member 51B is placed on the flow path forming section 57, causing the lifting member 51B and the flow path forming section 57 to be in partial contact. More specifically, for example, the portion of the upper surface 571 of the flow path forming section 57 excluding the recess 572 comes into contact with the lower surface of the lifting member 51B. This forms a second flow path F2D between the lifting member 51B and the bottom wall 12D of the housing 1D. More specifically, in the second state, for example, the recess 572 formed on the upper surface 571 of the flow path forming section 57 functions as a second flow path F2D that guides the water to be treated to the outside of the housing 1D. The second flow path F2D has a flow path width that, for example, allows the water to be treated to pass through but prevents the filter material 2 from passing through.

[0146] As described above, the bottom wall 12D of the filter cassette 50D according to the modified example 2 of Embodiment 2 is provided with a flow path forming portion 57 that partially contacts the lifting member 51B at the second position P2D, thereby forming a second flow path F2D between the lifting member 51B and the housing 1D. With this, for example, when draining water, the bottom wall 12D can prevent the lifting member 51B from falling off, while a second flow path F2D can be formed between the lifting member 51B and the housing 1D. [Explanation of symbols]

[0147] 1: Cabinet 11: Side wall 2: Filter material 2a: filtration layer 3: Inlet 4: Outlet 5: Lifting device 51: Lifting / lowering member 52: Sliding part 53: Operation section 54: Guide Section 55: Regulatory Department 56: Expandable member 57: Flow channel forming section 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 system includes a lifting member that is installed to be vertically movable within a range including a first position that opens the inlet and a second position that covers the inlet, When the lifting member is positioned in the first position, a first flow path is formed between the lifting member and the housing for guiding the water to be treated to the filtration layer. When the lifting member is positioned in the second position, a second flow path is formed between the lifting member, the housing, or between the lifting member and the housing, which guides the water to be treated to the outside of the housing. Filtration cassette.

2. The lifting member has a communication hole through which the water to be treated can pass. When the lifting member is positioned in the second position, the communication hole forms the second flow path. The filtration cassette described in Claim 1.

3. The first position is a position above the second position. The lifting member is arranged inside the housing and has buoyancy relative to the water to be treated. The side wall of the housing is provided with a restricting portion that restricts the upward movement of the lifting member in the first position. When the lifting member is positioned in the first position, the first flow path is formed between the lifting member and the side wall of the housing. The filtration cassette described in Claim 1.

4. The side wall of the housing is provided with an expandable member that is disposed between the lifting member in the first position and the side wall of the housing, and is capable of changing between a normal state and an expanded state that is more expanded than the normal state. When the lifting member is in the first position, the expandable member returns to its normal state, thereby forming the first flow path between the expandable member and the lifting member. When the lifting member is in the first position, the expandable member enters the expanded state, thereby forming a third flow path between the expandable member and the lifting member, the flow path width being smaller than that of the first flow path. The filtration cassette according to claim 3.

5. A lifting device installed in a treatment tank and attached to the housing of a filtration cassette that passes and filters the water to be treated, The filtration cassette 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, and a filter material housed within the housing that forms a filtration layer between the inlet and the outlet. The lifting device includes a lifting member that is installed to be able to move up and down within a range that includes a first position that opens the inlet and a second position that covers the inlet. When the lifting member is positioned in the first position, a first flow path is formed between the lifting member and the housing for guiding the water to be treated to the filtration layer. When the lifting member is positioned in the second position, a second flow path is formed between the lifting member, the housing, or between the lifting member and the housing, which guides the water to be treated to the outside of the housing. Lifting device.

Images