Patent Publication Number: US-2022234933-A1

Title: Screw-type separation device, casing, wastewater treatment system, and cleaning method of screw-type separation device

Description:
FIELD 
     The present invention relates to a screw-type separation device, a casing, a wastewater treatment system, and a cleaning method of a screw-type separation device. 
     BACKGROUND 
     Conventionally, methods adopted for what is called a separation device such as a concentrator and a dehydrator include a centrifugation method, a flotation concentration method, a screen concentration dehydration method, and the like. Moreover, a screw-type separation device that conveys, squeezes, and dehydrates an object, by feeding sludge such as sewage and industrial liquid waste with high water content as an object into a cylindrical-shaped casing, and by rotating a screw provided in the casing, has been used. 
     For example, Patent Literature 1 discloses a device that conveys and squeezes sludge, by rotating a screw provided with two screw blades. In this device, a first region and a second region interposed between the two screw blades are formed inside a casing the side surface of which is provided with a sludge feeding port. In the device, sludge is squeezed, dehydrated, and conveyed in the first region, and the dehydrated sludge is discharged. Moreover, in the device, separated liquid generated by dehydration is conveyed in the second region, and the separated liquid is discharged. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: WO2015/186612 
       
    
     SUMMARY 
     Technical Problem 
     However, in such a device, sludge may not slide on the surface of the screw blade, and may rotate with the screw blade and stay on the screw blade. In such a case, it is difficult to convey the sludge to a sludge discharging port, and the discharge efficiency of sludge may be decreased. Thus, it has been desired to suppress a decrease in the discharge efficiency of an object to be dehydrated such as sludge. 
     The present invention has been made in view of the above, and an object of the present invention is to provide a screw-type separation device, a casing, a wastewater treatment system, and a cleaning method of a screw-type separation device capable of suppressing a decrease in the discharge efficiency of an object. 
     Solution to Problem 
     To solve the problem and achieve the object above, a screw type separation device in the present disclosure includes; a casing including an object discharging port provided on one end part side and discharging an object having been dehydrated, and a separated liquid discharging port provided on another end part side and discharging separated liquid having been separated from the object by dehydration; a screw shaft provided inside the casing and extending in an extending direction that is a direction from the one end part to the another end part; a first screw blade extending spirally on an outer peripheral surface of the screw shaft; and a second screw blade extending spirally on the outer peripheral surface of the screw shaft such that a predetermined gap is formed with respect to the first screw blade in the extending direction, wherein a groove is formed on an inner peripheral surface of the casing. 
     It is preferable that the groove extends in the extending direction. 
     It is preferable that in the groove, width of an inlet part that is opened on the inner peripheral surface of the casing is smaller than width of a space on a radially outer side of the inlet part 
     It is preferable that width of the groove is increased from the inlet part toward a radially outer side. 
     It is preferable that viewed from the extending direction, the groove is inclined to a rotation direction side of the screw shaft toward a radially inner side. 
     It is preferable that in the groove, an opening area of the inlet part that is opened on the inner peripheral surface of the casing in an end part at the separated liquid discharging port side is greater than an opening area of the inlet part at the object discharging port side of the end part. 
     It is preferable that the casing includes a first casing, and a second casing that is inserted into inside of the first casing and an inner peripheral surface of which is formed with the groove. 
     It is preferable that in the casing, at least a portion formed with the groove is made of resin. 
     To solve the problem and achieve the object above, a wastewater treatment system in the present disclosure includes; a solid-liquid separation tank that separates sludge from organic wastewater, and the screw-type separation device, wherein the screw-type separation device is capable of concentrating sludge discharged from the solid-liquid separation tank, and returning the separated liquid generated when the sludge is concentrated to the solid-liquid separation tank. 
     It is preferable that the screw-type separation device is provided in the solid-liquid separation tank. 
     To solve the problem and achieve the object above, a casing for a screw-type separation device in the present disclosure stores therein a screw, the screw including a screw shaft extending in an extending direction that is a direction from one end part to another end part, a first screw blade extending spirally on an outer peripheral surface of the screw shaft, and a second screw blade extending spirally on the outer peripheral surface of the screw shaft such that a predetermined gap is formed with respect to the first screw shaft in the extending direction, wherein, a groove is formed on an inner peripheral surface of the casing. 
     To solve the problem and achieve the object above, a wastewater treatment system in the present disclosure includes; a reaction tank that performs biological treatment on organic wastewater; a solid-liquid separation tank that separates sludge from the organic wastewater; and the screw-type separation device, wherein the screw-type separation device is capable of extracting sludge from the reaction tank, concentrating the extracted sludge, returning the concentrated sludge to the reaction tank, and supplying the separated liquid generated when the sludge is concentrated to the solid-liquid separation tank. 
     To solve the problem and achieve the object above, a cleaning method of the screw-type separation device in the present disclosure includes; a step of closing the object discharging port; a step of accumulating a cleaning solution in the casing and the groove, by supplying the cleaning solution into the casing while the object discharging port is closed; and a step of discharging the cleaning solution accumulated in the casing and the groove from the object discharging port, by opening the object discharging port after the step of accumulating. 
     Advantageous Effects of Invention 
     With the present invention, it is possible to suppress a decrease in the discharge efficiency of sludge. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a partial sectional view of a screw-type separation device according to the present embodiment. 
         FIG. 2  is a sectional view of the screw-type separation device according to the present embodiment. 
         FIG. 3  is a schematic diagram illustrating another example of a groove according to the present embodiment. 
         FIG. 4  is a schematic diagram illustrating the groove according to the present embodiment. 
         FIG. 5A  is a schematic diagram illustrating the groove according to the present embodiment. 
         FIG. 5B  is a schematic diagram illustrating the groove according to the present embodiment. 
         FIG. 6  is a schematic diagram for explaining an operation of the screw-type separation device according to the present embodiment. 
         FIG. 7  is a partial sectional view of a screw-type separation device according to another example of the present embodiment. 
         FIG. 8  is a schematic diagram of a screw according to the other example of the present embodiment. 
         FIG. 9  is a schematic diagram of a screw according to the other example of the present embodiment. 
         FIG. 10  is a flowchart for explaining a cleaning method of the screw-type separation device according to the present embodiment. 
         FIG. 11  is a configuration diagram illustrating a part of a wastewater treatment system according to a first example. 
         FIG. 12  is a schematic diagram illustrating a sedimentation basin for explaining a modification of the first example. 
         FIG. 13  is a configuration diagram illustrating a part of a wastewater treatment system according to a second example. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiment described below. 
     Configuration of Screw-type Separation Device  FIG. 1  is a partial sectional view of a screw-type separation device according to the present embodiment. As illustrated in  FIG. 1 , a screw-type separation device  1  according to the present embodiment includes a casing  10  provided with a first casing  30  and a second casing  32 , a screw shaft  12 , a first screw blade  14 , a second screw blade  16 , a first partition wall part  18 , a second partition wall part  20 , a cover part  22 , a feeding unit  24 , a discharge pump  26 , an inclination adjusting unit  28 , and a control unit  29 . A unit provided with the screw shaft  12 , the first screw blade  14 , and the second screw blade  16  may be, referred to as a screw  11 . The screw-type separation device  1  dehydrates a pre-object A 0  fed into the casing  10  from an object feeding port  31 A, which will be described below, and discharges an object A having been dehydrated from an object discharging port  31 B, which will be described below. Then, the screw-type separation device  1  discharges separated liquid C, which is separated from the pre-object A 0  by dehydration, from a separated liquid discharging port  31 C, which will be described below. The pre-object A 0  is sludge such as sewage and industrial liquid waste with high water content. The pre-object A 0  is an object before being dehydrated by the screw-type separation device  1 , and in the present embodiment, is sludge such as sewage and industrial liquid waste with high water content. Additionally, the pre-object A 0  is sludge added with a flocculating agent, and sludge containing flocculated solid components and moisture. In the present embodiment, for example, by using a device provided at a previous stage of the screw-type separation device  1 , the pre-object A 0  which is a solid material containing a liquid component, is generated by adding a flocculating agent and flocculating the solid component. However, the properties of the pre-object A 0  are optional, and for example, the pre-object A 0  may also be sludge not added with a flocculating agent and not flocculated. 
     Hereinafter, a direction parallel to a ground surface G, that is, a horizontal direction, is referred to as a direction X. One direction in the direction X is referred to as a direction X 1 , and the other direction in the direction X, that is, a direction opposite to the direction X 1  is referred to as a direction X 2 . Moreover, a direction orthogonal to the direction X, and a direction orthogonal to the ground surface G, that is, a vertical direction, is referred to as a direction Z. Then, one direction in the direction Z is referred to as a direction Z 1 , and the other direction in the direction Z, that is, a direction opposite to the direction Z 1 , is referred to as a direction Z 2 . The direction Z 1  is an upward direction in the vertical direction, that is, a direction away from the ground surface G. The direction Z 2  is a downward direction in the vertical direction, that is, a direction toward the ground surface G side. 
     The first casing  30  in the casing  10  is a tubular member that extends from one end part  30 B to another end part  30 C in an extending direction E, and in which space is formed. In the example of  FIG. 1 , the diameter of the first casing  30  at the end part  30 B side is reduced. However, the diameter of the first casing  30  may not always be reduced. For example, the first casing  30  may also be formed in a cylindrical shape such that the diameter from the end part  30 B to the end part  30 C is constant. For example, in the first casing  30 , the diameter of a part where the diameter is not reduced is about 20 cm or more to 50 cm or less. However, the size of diameter is optional. The extending direction E is an axis direction of the first casing  30 . The extending direction E is a direction from the end part  30 B side toward the end part  30 C side (direction X 2  side), and is inclined to the direction Z 1  side with respect to the direction X 2 , from the end part  30 B side toward the end part  30 C side. That is, the first casing  30  is inclined in a direction in which a center axis AX in the extending direction E moves (is placed) toward the direction Z 1  side, toward the end part  30 C (direction X 2  side). Thus, the end part  30 B of the first casing  30  is placed at the direction Z 2  side of the end part  30 C. A gradient angle θ of the first casing  30  is preferably 20 degrees or more and 90 degrees or less, and more preferably 60 degrees or more and 90 degrees or less. The gradient angle θ is a gradient angle of the center axis AX with respect to the horizontal direction X (ground surface G). 
     In the present embodiment, the first casing  30  is a member made of metal (for example, made of stainless steel). However, the material of the first casing  30  is not limited to metal, and is optional. For example, the first casing  30  may also be made of resin. 
     In the first casing  30 , the object discharging port  31 B is opened on the end part  30 B, and the separated liquid discharging port  31 C is opened on the end part  30 C. The separated liquid discharging port  31 C is an opening different from a hole through which the screw shaft  12  passes, and is provided on the direction Z 1  side of the screw shaft  12 . However, the separated liquid discharging port  31 C may not be provided on the direction Z 1  side of the screw shaft  12 . For example, the separated liquid discharging port  31 C may be provided on the direction Z 2  side of the screw shaft  12  in the end part  30 C, or may be provided on the same position as that of the screw shaft  12 , and such that the screw shaft  12  can penetrate therethrough. Moreover, the separated liquid discharging port  31 C may also be provided on the outer peripheral surface (side surface) of the casing  10  in a separated liquid conveyance section K 3 , which will be described below. The object discharging port  31 B is placed on the direction Z 2  side of the separated liquid discharging port  31 C. In the present embodiment, the screw shaft  12  can penetrate through the inside of the object discharging port  31 B. However, the screw shaft  12  may not penetrate through the object discharging port  31 B. Moreover, the object discharging port  31 B may be provided on the outer peripheral surface (side surface) of the casing  10  in an object conveyance section K 2 , which will be described below. That is, in the first casing  30 , at least the separated liquid discharging port  31 C is placed on the end part  30 C side of the object discharging port  31 B, and the object discharging port  31 B is placed on the end part  30 B side of the separated liquid discharging port  31 C. 
     In the first casing  30 , the object feeding port  31 A is opened on a middle part  30 A. The middle part  30 A is a part between the end part  30 B and the end part  30 C in the extending direction E of the first casing  30 . In other words, the middle part  30 A is a part between the object discharging port  31 B and the separated liquid discharging port  31 C in the extending direction E. The middle part  30 A is placed on the center of the first casing  30  in the extending direction E, but may be placed on any position between the end part  30 B and the end part  30 C in the extending direction E. For example, the length of the first casing  30  from the end part  30 B to the middle part  30 A in the extending direction E is preferably 30% or more and 90% or less, with respect to the total length of the first casing  30  in the extending direction E. The object feeding port  31 A is opened on the outer peripheral surface (side surface) of the first casing  30  of the middle part  30 A. 
     The second casing  32  is a tubular-shaped member to be inserted into the first casing  30 . The second casing  32  is inserted into the first casing  30  so as to be coaxial with the first casing  30 , and is fixed to the inside of the first casing  30  such that the outer peripheral surface of the second casing  32  is brought into contact with an inner peripheral surface  30   a  of the first casing  30 . The second casing  32  extends from one end part  32 B to another end part  32 C in the extending direction E. In the second casing  32 , the end part  32 B is positioned substantially the same as the end part  30 B of the first casing  30  in the extending direction E, and the end part  32 C is positioned substantially the same as the end part  30 C of the first casing  30  in the extending direction E. Because the second casing  32  is coaxial with the first casing  30 , the center axis AX also becomes the center axis of the second casing  32 . 
     In the present embodiment, the second casing  32  is a member made of resin, and for example, is manufactured by a 3D printer (three-dimensional lamination device). However, the material of the second casing  32  is optional, and for example, the second casing  32  may be made of metal (such as stainless steel). A manufacturing method of the second casing  32  is also optional. 
     In the second casing  32 , an opening part  33 A is opened on the outer peripheral surface (side surface) at a position overlapping with the object feeding port  31 A of the first casing  30 . The opening part  33 A communicates with the object feeding port  31 A. Moreover, the end part  32 B of the second casing  32  which is opened, communicates with the object discharging port  31 B of the first casing  30 . The end part  32 C of the second casing  32  which is opened, communicates with the separated liquid discharging port  31 C of the first casing  30 . In the second casing  32 , a groove  34  is formed on an inner peripheral surface  32   a . The groove  34  will be described below. 
     In this manner, in the casing  10  of the present embodiment, the first casing  30  and the second casing  32  are formed by different members. However, the casing  10  may be formed by an integral member. In either case of an integral member or a plurality of members, the casing  10  is configured such that the casing  10  extends around the center axis AX in the extending direction E, the object discharging port  31 B is provided on the end part  30 B side in the direction X 1  side, the separated liquid discharging port  31 C is provided on the end part  30 C side of the direction X 2  side, the object feeding port  31 A is provided on the middle part  30 A, and the groove  34  is formed on the inner peripheral surface  32   a . When the casing  10  is formed of an integral member, the entire casing  10  is preferably made of resin. 
     The screw shaft  12  is formed in a cylindrical shape, is provided inside the casing  10 , and extends in the extending direction E. In the casing  10 , the screw shaft  12  is provided so as to penetrate through the casing  10  in the extending direction E. That is, one end part  12 B of the screw shaft  12  is placed on the end part  30 B side of the casing  10 , and protrudes to the outside of the casing  10  from the end part  30 B of the casing  10 . Similarly, another end part  12 C of the screw shaft  12  is placed on the end part  30 C side of the casing  10 , and protrudes to the outside of the casing  10  from the end part  30 C of the casing  10 . In the screw shaft  12 , at least one of the end part  12 B and the end part  12 C is coupled to a motor, which is axially supported by a bearing (both are not illustrated). When the motor is driven by the control unit  29 , the screw shaft  12  is rotated in a rotation direction R with the extending direction E as an axial center. In the present embodiment, when viewed from the end part  12 C side, the rotation direction R is a counterclockwise direction. However, it is not limited thereto. In the present embodiment, the screw shaft  12  is a member made of metal (for example, made of stainless steel). However, the material of the screw shaft  12  is not limited to metal, and is optional. For example, the screw shaft  12  may also be made of resin. 
     The first screw blade  14  is provided as to extend spirally on the outer peripheral surface of the screw shaft  12  in the casing  10 , from one end part  14 B to another end part  14 C. The end part  14 B is a position where winding of the first screw blade  14  is started, and is an end part on the object discharging port  31 B (end part  30 B) side of the casing  10 . The end part  14 B is placed on the object discharging port  31 B (end part  30 C) side of the object feeding port  31 A (middle part  30 A). Moreover, the end part  14 C is a position where winding of the first screw blade  14  is ended, and is an end part on the separated liquid discharging port  31 C (end part  30 C) side of the casing  10 . The end part  14 C is placed on the separated liquid discharging port  31 C (end part  30 C) side of the object feeding port  31 A (middle part  30 A). The first screw blade  14  extends from the end part  14 B to the end part  14 C via a portion overlapping with the object feeding port  31 A, when viewed from the radial direction of the center axis AX. 
     The first screw blade  14  is wound in a direction opposite to the rotation direction R of the screw shaft  12  from the end part  14 C toward the end part  14 B. That is, when the rotation direction R of the screw shaft  12  is a counterclockwise direction viewed from the end part  12 C side, the first screw blade  14  is provided in what is called a Z-winding (right hand) spiral. Alternatively, when the rotation direction R of the screw shaft  12  is a clockwise direction viewed from the end part  12 C side, the first screw blade  14  is provided in what is called an S-winding (left hand) spiral. The first screw blade  14  is rotated with the rotation of the screw shaft  12 . 
     The first screw blade  14  is formed such that a gap H is generated between an outer peripheral part  14   c  and the inner peripheral surface  32   a  of the casing  10 . That is, the outer peripheral part  14   c  of the first screw blade  14  does not come into contact with the inner peripheral surface  32   a  of the casing  10 , and is separated from the inner peripheral surface  32   a  with the gap H interposed therebetween. The gap H is a minute clearance, and has a size capable of suppressing (blocking) at least a part of the object A from passing through. Moreover, the gap H is large enough so that a liquid component such as the separated liquid C can pass through. For example, the gap H is a clearance of about 1 mm or more and 2 mm or less. 
     In the casing  10 , the second screw blade  16  extends spirally on the outer peripheral surface of the screw shaft  12  in the extending direction E. The second screw blade  16  is provided on a position shifted from the first screw blade  14  such that a predetermined gap is formed with respect to the first screw blade  14  in the extending direction E, and is wound in the same winding direction as that of the first screw blade  14 . The second screw blade  16  is also rotated with the rotation of the screw shaft  12 . The second screw blade  16  extends spirally from one end part  16 B to another end part  16 C. The end part  16 B is a position where winding of the second screw blade  16  is started, and placed between the end part  14 B of the first screw blade  14  and the object feeding port  31 A in the extending direction E. The end part  16 C is a position where winding of the second screw blade  16  is ended, and is placed between the end part  14 C of the first screw blade  14  and the object feeding port  31 A in the extending direction E. Thus, the second screw blade  16  extends from the end part  16 B to the end part  16 C via a portion overlapping with the object feeding port  31 A, viewed from the radial direction of the center axis AX. The end part  16 B and the end part  16 C of the second screw blade  16  may not placed on the positions described above. For example, the end part  16 B of the second screw blade  16  may be placed on the same position as the end part  14 B of the first screw blade  14  in the extending direction E, and the end part  16 C of the second screw blade  16  may be placed on the same position as the end part  14 C of the first screw blade  14  in the extending direction E. 
     The second screw blade  16  is formed such that the gap H is generated between an outer peripheral part  16   c  and the inner peripheral surface  32   a  of the casing  10 . That is, the outer peripheral part  16   c  of the second screw blade  16  does not come into contact with the inner peripheral surface  32   a  of the casing  10 , and is separated from the inner peripheral surface  32   a  with the gap H interposed therebetween. In the present embodiment, the first screw blade  14  and the second screw blade  16  are made of resin, and for example, manufactured by a 3D printer. However, the material of the first screw blade  14  and the second screw blade  16  is not limited to resin, and is optional. For example, the first screw blade  14  and the second screw blade  16  may also be made of metal (such as stainless steel). A manufacturing method of the first screw blade  14  and the second screw blade  16  is also optional. 
     Because the first screw blade  14  and the second screw blade  16  are provided on the positions as described above, the first screw blade  14  and the second screw blade  16  are both provided in a section from the end part  16 B to the end part  16 C of the second screw blade  16  (hereinafter, this section will be referred to as a conveyance acceleration section K 1 ). Moreover, the first screw blade  14  is provided but the second screw blade  16  is not provided in a section from the end part  16 B of the second screw blade  16  to the end part  14 B of the first screw blade  14  (hereinafter, this section will be referred to as the object conveyance section K 2 ). Furthermore, the first screw blade  14  is provided but the second screw blade  16  is not provided in a section from the end part  16 C of the second screw blade  16  to the end part  14 C of the first screw blade  14  (hereinafter, this section will be referred to as the separated liquid conveyance section K 3 ). 
     The conveyance acceleration section K 1  is a double screw section in which the first screw blade  14  and the second screw blade  16  are provided. The conveyance acceleration section K 1  is a section between the object conveyance section K 2  and the separated liquid conveyance section K 3  in the extending direction E. Viewed from the radial direction of the center axis AX, at least a part of the section of the conveyance acceleration section K 1  is set so as to overlap with the object feeding port  31 A. In other words, at least a part of the conveyance acceleration section K 1  is placed on the same position as the object feeding port  31 A in the extending direction E. The length of the conveyance acceleration section K 1  in the extending direction E is preferably 20% or more and 60% or less of the total length of the casing  10  in the extending direction. 
     In the conveyance acceleration section K 1 , a first space S 1  in which the object A is conveyed, and a second space S 2  in which the separated liquid C is conveyed are formed. The first space S 1  is formed between one surface  16   a  of the second screw blade  16  and another surface  14   b  of the first screw blade  14  that faces the one surface  16   a . The second space S 2  is formed between another surface  16   b  of the second screw blade  16  and one surface  14   a  of the first screw blade  14  that faces the other surface  16   b . In  FIG. 1 , the surface at the end part  14 B side of the first screw blade  14  is referred to as the one surface  14   a , and the surface at the end part  14 C side is referred to as the other surface  14   b . However, it is not limited thereto, and the surface at the end part  14 C side may be referred to as the one surface  14   a , and the surface at the end part  14 B side may be referred to as the other surface  14   b . Similarly, in  FIG. 1 , the surface at the end part  16 B side of the second screw blade  16  is referred to as the one surface  16   a , and the surface at the end part  16 C side is referred to as the other surface  16   b . However, it is not limited thereto, and the surface at the end part  16 C side may be referred to as the one surface  16   a , and the surface at the end part  16 B side may be referred to as the other surface  16   b.    
     The object conveyance section K 2  is a section at the end part  30 B side of the casing  10 , that is, a section at the object discharging port  31 B side, than the conveyance acceleration section K 1 . Space S 3  in the object conveyance section K 2  communicates with the object discharging port  31 B. Moreover, the space S 3  communicates with the first space S 1  in the conveyance acceleration section K 1 , and the object A flows into the space S 3  from the first space S 1 . Because the space S 3  is shielded by the first partition wall part  18 , which will be described below, the space S 3  is isolated from the second space S 2  in the conveyance acceleration section K 1  in a region other than the gap H. In the present embodiment, the object conveyance section K 2  is a single screw section in which the first screw blade  14  is provided but the second screw blade  16  is not provided. However, when the end part  14 B of the first screw blade  14  and the end part  16 B of the second screw blade  16  are provided on the same position, the object conveyance section K 2  will be a section in which neither the first screw blade  14  nor the second screw blade  16  is provided. 
     The separated liquid conveyance section K 3  is a section at the end part  30 C side of the casing  10 , that is, a section at the separated liquid discharging port  31 C side, than the conveyance acceleration section K 1 . Space S 4  in the separated liquid conveyance section K 3  communicates with the separated liquid discharging port  31 C. Moreover, the space S 4  communicates with the second space S 2  in the conveyance acceleration section K 1 , and the separated liquid C flows into the space S 4  from the second space S 2 . Because the space S 4  is shielded by the second partition wall part  20 , which will be described below, the space S 4  is isolated from the first space S 1  in the conveyance acceleration section K 1 , in a region other than the gap H. In the present embodiment, the separated liquid conveyance section K 3  is a single screw section in which the first screw blade  14  is provided but the second screw blade  16  is not provided. However, when the end part  14 B of the first screw blade  14  and the end part  16 B of the second screw blade  16  are provided on the same position, the separated liquid conveyance section K 3  will be a section in which neither the first screw blade  14  nor the second screw blade  16  is provided. 
     The groove  34  is formed on the inner peripheral surface  32   a  of the second casing  32  in the conveyance acceleration section K 1 . On the inner peripheral surface  32   a  of the second casing  32 , the groove  34  extends from an end part  34 B to an end part  34 C in the extending direction E. The end part  34 B is an end part at the object discharging port  31 B side of the groove  34 , and is placed between the object discharging port  31 B and the object feeding port  31 A in the extending direction E. Additionally, the end part  34 B is preferably provided on the same position as the end part  16 B of the second screw blade  16  in the extending direction E, that is, at a boundary between the conveyance acceleration section K 1  and the object conveyance section K 2 . Moreover, the end part  34 C is an end part at the separated liquid discharging port  31 C side of the groove  34 , and is placed between the separated liquid discharging port  31 C and the object feeding port  31 A in the extending direction E. Additionally, the end part  34 C is preferably provided at the separated liquid conveyance section K 3  side (that is, in the separated liquid conveyance section K 3 ) than the same position of the end part  16 C of the second screw blade  16  in the extending direction E (boundary between the conveyance acceleration section K 1  and the separated liquid conveyance section K 3 ). 
     In this manner, the groove  34  extends in the conveyance acceleration section K 1 , and extends into the separated liquid conveyance section K 3  at the end part  34 C side. However, the groove  34  not only extends in the conveyance acceleration section K 1  and the separated liquid conveyance section K 3 , and may be provided up to the object conveyance section K 2 . 
       FIG. 2  is a sectional view of the screw-type separation device according to the present embodiment.  FIG. 2  is a sectional view cut along the line F-F in  FIG. 1 , and is a sectional view when the screw-type separation device  1  is viewed in the extending direction E. In below, unless otherwise specified, a circumferential direction and a radial direction are the circumferential direction and the radial direction around the center axis AX. As illustrated in  FIG. 2 , on the inner peripheral surface  32   a  of the second casing  32 , a plurality of the grooves  34  are provided in the circumferential direction. In the example in  FIG. 2 , twelve grooves  34  are provided. However, the number of the grooves  34  is not limited to twelve, and is optional. An inlet part  34   a   1  provided as an end part of each of the groove  34  on the radially inner side (a side approaching the center axis AX) is opened on the inner peripheral surface  32   a . That is, the inlet part  34   a   1  is an opening portion of the groove  34 . The width of the groove  34  is increased from the inlet part  34   a   1  to a middle part  34   a   2  on the radially outer side relative to the inlet part  34   a   1 , toward the radially outer side (a side away from the center axis AX). In this example, the width is the length in the circumferential direction. The width of the groove  34  is reduced from the middle part  34   a   2  to a bottom part  34   a   3  of the groove  34  on the radially outer side, toward the radially outer side. The width of the groove  34  is increased in a straight line manner from the inlet part  34   a   1  to the middle part  34   a   2 , toward the radially outer side. The width of the groove  34  is reduced in a curved line manner from the middle part  34   a   2  to the bottom part  34   a   3 , toward the radially outer side. In other words, viewed in the extending direction E, the groove  34  is formed in a trapezoid shape in which the width is increased toward the radially outer side, from the inlet part  34   a   1  to the middle part  34   a   2 . The groove  34  is also formed in a semicircular shape, from the middle part  34   a   2  to the bottom part  34   a   3 . However, the shape of the groove  34  is not limited to a shape in which the width is increased in a straight line manner from the inlet part  34   a   1  toward the middle part  34   a   2 , and the width is increased in a curved line manner from the middle part  34   a   2  toward the bottom part  34   a   3 . For example, the width of the groove  34  may be increased in a curved line manner in at least a part of the section from the inlet part  34   a   1  to the middle part  34   a   2 , or the width of the groove  34  may be reduced in a straight line manner in at least a part of the section from the middle part  34   a   2  to the bottom part  34   a   3 . 
     In this manner, because the width (length in the circumferential direction) of the groove  34  is increased from the inlet part  34   a   1  toward the radially outer side, the width at the inlet part  34   a   1  is smaller than the width of the space on the radially outer side of the inlet part  34   a   1 . Thus, in the groove  34 , viewed from the radial direction, the area of the inlet part  34   a   1  becomes smaller than the area of the space on the radially outer side of the inlet part  34   a   1 , and the area is increased from the inlet part  34   a   1  toward the radially outer side. 
     Viewed from the extending direction E, the groove  34  is inclined to the rotation direction R side of the screw shaft  12 , toward the radially inner side. In other words, the groove  34  is inclined to the rotation direction R side with respect to the radial direction, from the middle part  34   a   2  toward the inlet part  34   a   1 . In more other words, viewed from the extending direction E, a straight line (straight line in the radial direction) that joins the center axis AX and the middle point of the middle part  34   a   2  is called as a straight line L 1 , and a straight line that joins the middle point of the middle part  34   a   2  and the middle point of the inlet part  34   a   1  is called as a straight line L 2 . The straight line L 2  is inclined to the rotation direction R side with respect to the straight line L 1 , toward the radially inner side (middle point side of the inlet part  34   a   1 ). 
     In the groove  34 , the length in the circumferential direction of the inlet part  34   a   1  is preferably the same as the length of the gap H in the radial direction, and for example, is preferably about 1 mm or more and 2 mm or less. Moreover, the length of the groove  34  in the circumferential direction of the middle part  34   a   2  (that is, the maximum width of the groove  34 ) is preferably longer than the length of the gap H in the radial direction. 
       FIG. 3  is a schematic diagram illustrating another example of a groove according to the present embodiment. The shape of the groove  34  is not limited to a shape in which the width is increased from the inlet part  34   a   1  toward the radially outer side, as described in  FIG. 2 . For example, as illustrated in  FIG. 3 , the width of the groove  34  may also be constant in the radial direction, from the inlet part  34   a   1  to a middle part  34   a   4 , and may be increased toward the radially outer side, from the middle part  34   a   4  to the middle part  34   a   2  on the radially outer side. The width of the groove  34  may also be increased in the middle part  34   a   4 , and may be constant from the middle part  34   a   4  to the bottom part  34   a   3 . In this case also, the width of the inlet part  34   a   1  is preferably smaller than the width (maximum width) of the middle part  34   a   2  on the radially outer side of the inlet part  34   a   1 . 
       FIG. 4  is a schematic diagram illustrating the groove according to the present embodiment.  FIG. 4  illustrates the shape of the groove  34  in the vicinity of the object feeding port  31 A, when the inner peripheral surface  32   a  of the casing  10  is viewed from the center axis AX toward the radially outer side (portion illustrated by F 1  in  FIG. 1 ). As illustrated in  FIG. 4 , the groove  34  does not communicate with the object feeding port  31 A (opening part  33 A) on the inner peripheral surface  32   a . More particularly, among the grooves  34 , a groove  34 F at a position close to the object feeding port  31 A in the circumferential direction does not continue from the end part  34 B to the end part  34 C (see  FIG. 1 ) in the extending direction E, and is interrupted in the vicinity of the object feeding port  31 A. The groove  34 F is on the end part  34 B side of the object feeding port  31 A, and the groove  34 F extends from the end part  34 B to an end part  34 F 1  in the extending direction E. The end part  34 F 1  does not communicate with the object feeding port  31 A, and is placed on the end part  34 B side of the object feeding port  31 A. The groove  34 F is at the end part  34 C side of the object feeding port  31 A, the groove  34 F extends from an end part  34 F 2  to the end part  34 C in the extending direction E. The end part  34 F 2  does not communicate with the object feeding port  31 A, and is placed on the end part  34 C side of the object feeding port  31 A (opening part  33 A). 
     The groove  34 F at the end part  34 B side of the object feeding port  31 A and the groove  34 F at the end part  34 C side of the object feeding port  31 A are connected by a connection groove  36  formed on the inner peripheral surface  32   a . The connection groove  36  is formed on the periphery of a portion on the inner peripheral surface  32   a , where the object feeding port  31 A (opening part  33 A) is provided. On the inner peripheral surface  32   a , the connection groove  36  does not communicate with the object feeding port  31 A, and connects the grooves  34 F to one another by communicating with the grooves  34 F. In the present embodiment, the connection groove  36  is connected to all the grooves  34 F, and connects all the grooves  34 F to one another. In the present embodiment, viewed from the radial direction, the connection groove  36  is a ring-shaped groove formed so as to surround the object feeding port  31 A. However, the shape of the connection groove  36  is not limited to a ring shape, and is optional. By connecting the groove  34  to the connection groove  36  without connecting to the object feeding port  31 A, it is possible to cause the separated liquid C that flows through the groove  34  to flow to the separated liquid discharging port  31 C side via the connection groove  36 , while suppressing the separated liquid C that flows in the groove  34  from returning to the casing  10  from the object feeding port  31 A, as will be described below. 
       FIG. 5A  and  FIG. 5B  are each a schematic diagram illustrating the groove according to the present embodiment.  FIG. 5A  illustrates the shape of the groove  34  in the vicinity of the end part  34 C, when the inner peripheral surface  32   a  of the casing  10  is viewed from the center axis AX toward the radially outer side (portion illustrated by F 2  in  FIG. 1 ).  FIG. 5B  is a sectional view of the groove  34  in the vicinity of the end part  34 C, and is a sectional view cut along the line F 3 -F 3  in  FIG. 2 . As illustrated in  FIG. 5A , in the groove  34 , the width of the inlet part  34   a   1  of the end part  34 C (length in the circumferential direction) is greater than the width of the inlet part  34   a   1  at the end part  34 B side of the end part  34 C. Thus, in the groove  34 , the opening area of the inlet part  34   a   1  of the end part  34 C is greater than the opening area of the inlet part  34   a   1  at the end part  34 B side (object discharging port  31 B side) of the end part  34 C. More specifically, in the groove  34 , the width of the inlet part  34   a   1  is increased from a position  34 C 1  toward the end part  34 C. Moreover, as illustrated in  FIG. 5B , the depth (length in the radial direction) of the groove  34  is reduced from the position  34 C 1  toward the end part  34 C. The position  34 C 1  is a position on the end part  34 B side of the end part  34 C in the extending direction E, and is a position in the vicinity of the end part  34 C. 
     Returning to  FIG. 1 , the first partition wall part  18  is a wall-shaped member provided from the first screw blade  14  to the second screw blade  16  adjacent to the first screw blade  14  in the extending direction E. The first partition wall part  18  is provided in the second space S 2  in the conveyance acceleration section K 1 , and shields the second space S 2  from the space S 3  in the object conveyance section K 2 . Additionally, the first partition wall part  18  is provided between the object discharging port  31 B and the object feeding port  31 A, in this example, is provided on the end part  16 B of the second screw blade  16 . That is, the first partition wall part  18  is provided so as to separate the second space S 2  and the space S 3 , which means that the first partition wall part  18  is provided at a boundary between the second space S 2  and the space S 3 . 
     The second partition wall part  20  is a wall-shaped member provided from the first screw blade  14  to the second screw blade  16  adjacent to the first screw blade  14  in the extending direction E. The second partition wall part  20  is provided in the first space S 1  in the conveyance acceleration section K 1 , and shields the first space S 1  from the space S 4  in the separated liquid conveyance section K 3 . Additionally, the second partition wall part  20  is provided between the separated liquid discharging port  31 C and the object feeding port  31 A, in this example, is provided on the end part  16 C of the second screw blade  16 . That is, the second partition wall part  20  is provided so as to separate the first space S 1  and the space S 4 , which means that the second partition wall part  20  is provided at a boundary between the first space S 1  and the space S 4 . However, the second partition wall part  20  is not a necessary component. The second partition wall part  20  suppresses the separated liquid C in the space S 4  from flowing into the first space S 1 . However, even if the second partition wall part  20  is not provided, for example, the separated liquid C in the space S 4  is suppressed from flowing into the first space S 1 , by being blocked by the object A accumulated in the first space S 1 . Moreover, even if the separated liquid C is flowed into the first space S 1 , the separated liquid C may be separated from the object A in the first space S 1  again, and returned to the space S 4 . 
     The cover part  22  is provided in a region overlapping with the object feeding port  31 A, between the first screw blade  14  and the second screw blade  16  that form the second space S 2  in the conveyance acceleration section K 1 . The cover part  22  can suppress the pre-object A 0  from the object feeding port  31 A from being fed into the second space S 2 , by covering the outer periphery of the second space S 2  in a section overlapping with the object feeding port  31 A. However, the cover part  22  is not a necessary component. For example, if the object feeding port  31 A is provided on a position not overlapping with the second space S 2 , it is possible to suppress the pre-object A 0  from being fed into the second space S 2 , and thus the cover part  22  will not be required. 
     The feeding unit  24  is a device connected to the object feeding port  31 A and that controls the feeding amount of the pre-object A 0  into the casing  10 . For example, the feeding unit  24  is an opening/closing valve, and feeds the pre-object A 0  into the casing  10  by opening, and stops feeding the pre-object A 0  into the casing  10  by closing. Moreover, the feeding unit  24  can adjust the feeding amount of the pre-object A 0  by adjusting the opening degree. The feeding unit  24  controls the feeding amount of the pre-object A 0  into the casing  10 , by being controlled by the control unit  29 . However, the feeding unit  24  is not limited to the opening/closing valve, as long as the feeding unit  24  can control the feeding amount of the pre-object A 0  into the casing  10 . For example, the feeding unit  24  may also be a pump for conveying sludge. 
     The discharge pump  26  is connected to the object discharging port  31 B of the casing  10  via a discharge pipe  26 A. The discharge pipe  26 A is a pipe connected to the object discharging port  31 B. The object A from the object discharging port  31 B is introduced into the discharge pipe  26 A. The discharge pump  26  is a pump provided on the discharge pipe  26 A. When the discharge pump  26  is stopped, the object A transferred to the end part  30 B of the casing  10  is stopped. Moreover, when the discharge pump  26  is being driven, the discharge pump  26  sucks the discharge pipe  26 A. Hence, the object A in the casing  10  can be forcibly discharged from the object discharging port  31 B. The discharge pump  26  can adjust the discharge amount of the object A in the casing  10 , by being controlled by the control unit  29 . However, the discharge pump  26  is not a necessary component, and for example, the object A may be discharged by gravity, without forcibly discharging the object A by the discharge pump  26 . 
     The inclination adjusting unit  28  is fixed to the casing  10 . The inclination adjusting unit  28  changes the inclination angle θ of the casing  10 , by being controlled by the control unit  29 . However, the inclination adjusting unit  28  is not a necessary component, and the inclination angle θ may be constant. 
     The control unit  29  is a control device that controls the operation of the screw-type separation device  1 . The control unit  29  controls at least one of the rotation of the screw shaft  12  by the motor, the feeding amount of the pre-object A 0  by the feeding unit  24 , the operation of the discharge pump  26 , which is the discharge amount of the object A in the casing  10 , and the inclination angle θ by the inclination adjusting unit  28 . For example, the control unit  29  is an arithmetic device, that is, a computer including a central processing unit (CPU), and controls the operation of the screw-type separation device  1  by the calculation of the CPU. 
     Operation of Screw-Type Separation Device 
     Next, an operation of the screw-type separation device  1  configured as described above, and behavior of an object will be described.  FIG. 6  is a schematic diagram for explaining an operation of the screw-type separation device according to the present embodiment. 
     As illustrated in  FIG. 6 , the control unit  29  controls the feeding unit  24  and rotates the screw shaft  12 , by feeding the pre-object A 0  into the casing  10  from the object feeding port  31 A. Because the position of the object feeding port  31 A is overlapped with the conveyance acceleration section K 1 , the pre-object A 0  from the object feeding port  31 A is fed into the first space S 1  in the conveyance acceleration section K 1 . The pre-object A 0  fed into the first space S 1  is transferred to the object discharging port  31 B side, by gravity and by sliding on the surface of the first screw blade  14  and the second screw blade  16  in the conveyance acceleration section K 1 , while the liquid component is separated. Because the solid component of the pre-object A 0  in the first space S 1  is difficult to pass through a minute gap H, the solid component is suppressed from entering the second space S 2 . Moreover, the solid component of the pre-object A 0  in the first space S 1  is blocked from entering the space S 4 , by the second partition wall part  20  that isolates between the first space S 1  and the space S 4 . 
     The screw-type separation device  1  conveys the pre-object A 0  to the object discharging port  31 B side, by causing the pre-object A 0  to slide on the surface of the first screw blade  14  and the second screw blade  16  (hereinafter, appropriately referred to as the surface of the screw blade). However, if the pre-object A 0  does not slide on the surface of the screw blade, the pre-object A 0  rotates with the screw blade, and stays on the same position on the surface of the screw blade. Hence, it is difficult to transfer the pre-object A 0  to the object discharging port  31 B side. Alternatively, in the present embodiment, by forming the groove  34  on the inner peripheral surface  32   a  of the casing  10 , the surface roughness of the inner peripheral surface  32   a  is increased, and the friction coefficient of the inner peripheral surface  32   a  is increased. Consequently, the pre-object A 0  is made to slide easily on the surface of the screw blade, by reducing the ratio of the friction force applied to the pre-object A 0  from the surface of the screw blade with respect to the friction force applied to the pre-object A 0  from the inner peripheral surface  32   a . That is, the pre-object A 0  is made to slide easily on the surface of the screw blade, by using the inner peripheral surface  32   a  formed with the groove  34  as resistance. In this manner, by making the pre-object A 0  to slide easily on the surface of the screw blade by the groove  34 , the screw-type separation device  1  can appropriately convey the pre-object A 0  to the object discharging port  31 B side. In the screw-type separation device  1 , the friction force applied to the pre-object A 0  from the inner peripheral surface  32   a  (friction coefficient of the inner peripheral surface  32   a ) is preferably made greater than the friction force applied to the pre-object A 0  from the surface of the screw blade (friction coefficient of the surface of the screw blade). 
     The pre-object A 0  conveyed in the first space S 1  in the conveyance acceleration section K 1  flows into the space S 3  in the object conveyance section K 2  that communicates with the first space S 1 . The pre-object A 0  that has flowed into the space S 3  passes through the object discharging port  31 B as the object A from which the liquid component is separated, and is discharged to the outside of the casing  10 . The object A that has flowed into the space S 3  passes through the object discharging port  31 B by the discharge pump  26  driven by the control unit  29 , and is forcibly discharged to the outside of the casing  10 . 
     On the other hand, the liquid component separated from the pre-object A 0  flows into the second space S 2  from the first space S 1  through the gap H, as the separated liquid C. The liquid level of the separated liquid C in the second space S 2  is increased with an increase in the inflow amount of the separated liquid C into the second space S 2 . With an increase in the liquid level, as illustrated in a flow passage C 1  illustrated in  FIG. 6 , the separated liquid C moves spirally in the second space S 2  to the separated liquid discharging port  31 C side, and is introduced into the space S 4  in the separated liquid conveyance section K 3 . Moreover, as illustrated in a flow passage C 2  in  FIG. 6 , the separated liquid C passes through a plurality of portions of the gap H, and is introduced into the space S 4  in the separated liquid conveyance section K 3 . Furthermore, as illustrated in a flow passage C 3  in  FIG. 6 , the separated liquid C flows into the groove  34  from the gap H. The separated liquid C that has flowed into the groove  34  flows in the groove  34  toward the separated liquid discharging port  31 C side, with an increase in the liquid level in the groove  34 . The separated liquid C is then introduced into the second space S 2  and the space S 4 , from the inlet part  34   a   1  of the end part  34 C. The separated liquid C that has introduced into the space S 4  through the flow passages C 1 , C 2 , and C 3  in this manner is discharged to the outside from the separated liquid discharging port  31 C. 
     In this manner, in the present embodiment, in addition to the flow passage C 1  that passes through the second space S 2  and the flow passage C 2  that passes through the gap H, the flow passage C 3  that passes through the groove  34  is also set as a flow passage of the separated liquid C to the space S 4 . By increasing the number of flow passages of the separated liquid C in this manner, it is possible to reduce pressure loss in a flow passage of the separated liquid C in the casing  10 , and appropriately discharge the separated liquid C. In the groove  34 , for example, the width of the inlet part  34   a   1  is made small to the same extent as the gap H. Hence, it is possible to suppress the solid component of the pre-object A 0  from entering, while allowing the separated liquid C to enter. Moreover, because the groove  34  is inclined to the rotation direction R side of the screw shaft  12 , it is further possible to preferably suppress the solid component from entering from the inlet part  34   a   1 . Furthermore, in the present embodiment, at least one of the first screw blade  14 , the second screw blade  16 , and the second casing  32  is preferably made of resin. By making at least one of the above by resin, it is possible to increase the shape accuracy, design the gap H to be small, and suppress the solid component from passing through the gap H. 
     As described above, the screw-type separation device  1  according to the present embodiment includes the casing  10 , the screw shaft  12 , the first screw blade  14 , and the second screw blade  16 . In the casing  10 , the object discharging port  31 B that discharges the dehydrated object A is provided on one end part  30 B side, and the separated liquid discharging port  31 C that discharges the separated liquid C separated from the pre-object A 0  by dehydration, is provided on the other end part  30 C side. The screw shaft  12  is provided inside the casing  10 , and extends in the extending direction E that is a direction from the end part  30 B toward the other end part  30 C. The first screw blade  14  extends spirally on the outer peripheral surface of the screw shaft  12 . The second screw blade  16  extends spirally on the outer peripheral surface of the screw shaft  12  such that a predetermined gap is formed with respect to the first screw blade  14  in the extending direction E. In the casing  10 , the groove  34  is formed on the inner peripheral surface  32   a.    
     In the screw-type separation device  1  according to the present embodiment, the groove  34  is formed on the inner peripheral surface  32   a  of the casing  10 . Hence, the object A is made to slide easily on the surface of the screw blade, by reducing the ratio of the friction force applied to the object A from the surface of the screw blade, with respect to the friction force applied to the object A from the inner peripheral surface  32   a . Consequently, with the screw-type separation device  1  according to the present embodiment, it is possible to appropriately convey the object A to the object discharging port  31 B, and suppress a decrease in the discharge efficiency of the object A. Moreover, because the separated liquid C can flow through the groove  34 , the screw-type separation device  1  can increase the flow passage of the separated liquid C to the separated liquid discharging port  31 C. Thus, with the screw-type separation device  1 , it is possible to reduce the pressure loss in the flow passage of the separated liquid C in the casing  10 , and appropriately discharge the separated liquid C. 
     Moreover, the groove  34  extends in the extending direction E. By configuring the screw-type separation device  1  such that the groove  34  extends in the extending direction E, the groove  34  can be used as a flow passage of the separated liquid C to the separated liquid discharging port  31 C. Hence, it is possible to reduce the pressure loss in the flow passage of the separated liquid C in the casing  10 , and appropriately discharge the separated liquid C. 
     Furthermore, in the groove  34 , the width of the inlet part  34   a   1  that is opened on the inner peripheral surface  32   a  of the casing  10  is smaller than the width of the space (middle part  34   a   2 ) on the radially outer side of the inlet part  34   a   1 . By reducing the width of the inlet part  34   a   1  of the groove  34 , the screw-type separation device  1  can suppress the object A, which is a solid material, from entering the groove  34  and prevent blockage in the groove  34 . Moreover, by increasing the width of the space on the radially outer side of the inlet part  34   a   1 , the screw-type separation device  1  can increase the flow passage area through which the separated liquid C flows. Thus, with the screw-type separation device  1 , it is possible to appropriately discharge the separated liquid C through the groove  34 . 
     Still furthermore, the width of the groove  34  is increased from the inlet part  34   a   1  toward the radially outer side. By gradually increasing the width of the groove  34 , the screw-type separation device  1  can suppress the pressure loss in the groove  34 , and cause the separated liquid C to flow appropriately. 
     Still furthermore, viewed from the extending direction E, the groove  34  is inclined to the rotation direction R side of the screw shaft  12  toward the radially inner side. By making the groove  34  inclined to the rotation direction R side, the screw-type separation device  1  can suppress the object A, which is a solid material, from entering the groove  34 , and prevent blockage in the groove  34 . 
     Still furthermore, in the groove  34 , the opening area of the inlet part  34   a   1  in the end part  34 C at the separated liquid discharging port  31 C side is greater than the opening area of the inlet part  34   a   1  at the object discharging port  31 B side of the end part  34 C. By increasing the opening area of the end part  34 C that is an outlet of the separated liquid C that flows through the groove  34 , the screw-type separation device  1  can suppress the pressure loss and appropriately discharge the separated liquid C. 
     The casing  10  includes the first casing  30 , and the second casing  32  inserted into the inside of the first casing  30  and the inner peripheral surface  32   a  of which is formed with the groove  34 . For example, by forming the casing  10  by different members, it is possible to increase the shape accuracy of the second casing  32  formed with the groove  34 , and design the gap H to be small. Thus, with the screw-type separation device  1 , by making the gap H to be small, it is possible to preferably suppress a solid component of the pre-object A 0  from passing through the gap H, and increase the discharge efficiency of the object A and the cleaning degree of the separated liquid C. 
     In the casing  10 , at least a portion formed with the groove  34  is made of resin. By making the portion formed with the groove  34  (in the present example, the second casing  32 ) made of resin, it is possible to increase the shape accuracy, and design the gap H to be small. Moreover, by using resin, it is possible to reduce the manufacturing cost. 
     Moreover, the casing  10  according to the present embodiment is a casing for the screw-type separation device  1 , and stores the screw  11  (unit including the screw shaft  12 , the first screw blade  14 , and the second screw blade  16 ) inside. In the casing  10 , the groove  34  is formed on the inner peripheral surface  32   a . In this manner, by forming the groove  34  on the inner peripheral surface  32   a  of the casing  10  for storing the screw  11 , it is possible to suppress a decrease in the discharge efficiency of the object A. 
     Next, another example of the first partition wall part and the second partition wall part will be described. In the above description, the first partition wall part  18  and the second partition wall part  20  are provided between the first screw blade  14  and the second screw blade  16 . However, as illustrated in  FIG. 7  to  FIG. 9 , a first partition wall part  18   a  and a second partition wall part  20   a  may be formed by an end part of the first screw blade  14  and an end part of the second screw blade  16 .  FIG. 7  is a partial sectional view of a screw-type separation device according to another example of the present embodiment.  FIG. 8  and  FIG. 9  are each a schematic diagram of a screw according to the other example of the present embodiment.  FIG. 8  illustrates an end part of the first screw blade  14  and the second screw blade  16  on the object discharging port  31 B side.  FIG. 9  illustrates an end part of the first screw blade  14  and the second screw blade  16  on the separated liquid discharging port  31 C side. 
     As illustrated in  FIG. 7  and  FIG. 8 , in this example, an end part  14 Ba on the object discharging port  31 B side of the first screw blade  14  and an end part  16 Ba on the object discharging port  31 B side of the second screw blade  16  are placed on the same position in the extending direction E. Moreover, pitch of the first screw blade  14  and the second screw blade  16  (length between the surface of the first screw blade  14  and the surface of the second screw blade  16  adjacent to each other in the extending direction E) is constant at the extending direction E side (separated liquid discharging port  31 C side) of the end part  14 Ba (end part  16 Ba). However, pitch in the vicinity of the end part  14 Ba (end part  16 Ba) is reduced toward the end part  14 Ba (end part  16 Ba) side, and the end part  14 Ba and the end part  16 Ba come into contact with each other. Thus, the second space S 2  between the first screw blade  14  and the second screw blade  16  is reduced toward the end part  14 Ba (end part  16 Ba), is closed at a contact position of the end part  14 Ba and the end part  16 Ba, and is separated from the space S 3 . That is, in this example, the end part  14 Ba and the end part  16 Ba configure the first partition wall part  18   a  that separates the second space S 2  and the space S 3 . 
     Similarly, as illustrated in  FIG. 7  and  FIG. 9 , an end part  14 Ca on the separated liquid discharging port  31 C side of the first screw blade  14  and an end part  16 Ca on the separated liquid discharging port  31 C side of the second screw blade  16  are placed on the same position in the extending direction E. Moreover, pitch of the first screw blade  14  and the second screw blade  16  is constant at a side (object discharging port  31 B side) opposite to the extending direction E of the end part  14 Ca (end part  16 Ca). However, pitch in the vicinity of the end part  14 Ca (end part  16 Ca) is reduced toward the end part  14 Ca (end part  16 Ca) side, and the end part  14 Ca and the end part  16 Ca come into contact with each other. Thus, the first space S 1  between the first screw blade  14  and the second screw blade  16  is reduced toward the end part  14 Ca (end part  16 Ca), is closed at a contact position of the end part  14 Ca and the end part  16 Ca, and is separated from the space S 4 . That is, in this example, the end part  14 Ca and the end part  16 Ca configure the second partition wall part  20   a  that separates the first space S 1  and the space S 4 . 
       FIG. 10  is a flowchart for explaining a cleaning method of the screw-type separation device according to the present embodiment. To clean the screw-type separation device  1 , the supply of the pre-object A 0  is stopped, and the object A is discharged from the discharge pump  26  as much as possible. Then, as illustrated in  FIG. 10 , the object discharging port  31 B of the screw-type separation device  1  is closed (step S 10 ; step of closing). In the present embodiment, the object discharging port  31 B is closed by stopping the discharge pump  26 . However, a method of closing the object discharging port  31 B is optional. For example, when an opening/closing valve is provided on the object discharging port  31 B, the object discharging port  31 B may be closed by closing the opening/closing valve. Moreover, the separated liquid discharging port  31 C may also be closed with the object discharging port  31 B. 
     Then, while the object discharging port  31 B is closed, cleaning solution is supplied to the casing  10  from the object feeding port  31 A (step S 12 ; step of accumulating). At step S 12 , because the object discharging port  31 B is closed, the cleaning solution is accumulated in the casing  10 . For example, the cleaning solution is water. The cleaning solution supplied to the casing  10  also enters the groove  34 , and is accumulated in the groove  34 . Additionally, because the pressure inside the casing  10  is relatively increased by the cleaning solution, even if the groove  34  is clogged with a solid component, the cleaning solution can push out the solid material and flow into the groove  34 . The screw shaft  12  may also be rotated after supplying the cleaning solution at step S 12 . By rotating the screw shaft  12 , it is possible to cause the cleaning solution to flow in the casing, and appropriately remove the solid component in the groove  34 . 
     Then, the separated liquid discharging port  31 C is opened (step S 14 ; step of discharging). Consequently, the cleaning solution accumulated in the casing  10  and the groove  34  is discharged from the separated liquid discharging port  31 C with the solid material. 
     In this manner, the cleaning method of the screw-type separation device  1  preferably includes the step of closing, the step of accumulating, and the step of discharging. At the step of closing, the object discharging port  31 B is closed. At the step of accumulating, the cleaning solution is accumulated in the casing  10  and the groove  34 , by supplying the cleaning solution into the casing  10  while the object discharging port  31 B is closed. At the step of opening, the cleaning solution accumulated in the casing  10  and the groove  34  is discharged from the object discharging port  31 B, by opening the object discharging port  31 B after the step of accumulating. In the screw-type separation device  1 , by making the shape of the groove  34  as described above, the groove  34  is hardly clogged with solid material. However, even if the groove  34  is clogged with solid material, it is possible to preferably remove the solid material from the groove  34  by cleaning in this manner. 
     First Example 
     Next, a wastewater treatment system as a first example including the screw-type separation device  1  described above will be explained.  FIG. 11  is a configuration diagram illustrating a part of a wastewater treatment system according to a first example. 
     As illustrated in  FIG. 11 , a wastewater treatment system  100  according to the first example includes a sedimentation basin  101 , a previous stage facility  102  disposed at a previous stage of the sedimentation basin  101 , a subsequent stage facility  103  disposed at a subsequent stage of the sedimentation basin  101 , an extraction pump  104 , and the screw-type separation device  1 . The sedimentation basin  101  is a solid-liquid separation tank that sediments and separates water to be treated supplied from the previous stage facility  102  into separated liquid and sludge. For example, the previous stage facility  102  is a facility that treats organic wastewater such as sewage and that includes various treatment tanks such as a reaction tank. For example, the subsequent stage facility  103  is a facility that includes an incinerator and the like, and that incinerates or disposes sludge (concentrated sludge) discharged from the screw-type separation device  1 . The extraction pump  104  is a sludge extraction unit that extracts sludge from the sedimentation basin  101  and that supplies the extracted sludge to the screw-type separation device  1 . The screw-type separation device  1  is provided above (direction away from the ground surface of) the sedimentation basin  101  in the vertical direction. 
     In the wastewater treatment system  100 , at least a part of the water to be treated discharged from the previous stage facility  102  is supplied to the sedimentation basin  101 . In the sedimentation basin  101 , the supplied water to be treated is sedimented and separated into separated liquid and sludge. The separated sludge is then extracted by the extraction pump  104  from the lower part of the sedimentation basin  101 , and is supplied to the screw-type separation device  1 . The extracted sludge is conveyed to the inside of the screw-type separation device  1  as the pre-object A 0  through the object feeding port  31 A (see  FIG. 1 ). 
     In the screw-type separation device  1 , the separated liquid C is separated similarly to the embodiment described above. The separated liquid C that has been separated is returned to the sedimentation basin  101 . The object A that has been separated (that has been dehydrated) is conveyed to the subsequent stage facility  103  as concentrated sludge, and is incinerated or disposed. In this manner, the wastewater treatment according to the first example is performed. 
     In the first example as described above, by using the screw-type separation device  1  according to the embodiment described above, the pre-object A 0  extracted from the sedimentation basin  101  is concentrated, and the separated liquid C is returned to the sedimentation basin  101 . In this manner, it is possible to improve the concentration of the object A, and significantly improve the maintainability of the sedimentation basin  101 . That is, in many cases, intermediate water is present in the sedimentation basin  101 . If such intermediate water is present, moisture is preferentially extracted over sludge (pre-object A 0 ) during the extraction of sludge (pre-object A 0 ). Thus, there is the problem that the concentration does not increase even if sludge (pre-object A 0 ) is compressed. In regard to this problem, in the first example described above, the screw-type separation device  1  is disposed at a subsequent stage of the sedimentation basin  101 . Hence, it is possible to only separate the intermediate water from the extracted sludge (pre-object A 0 ), and return the separated intermediate water to the sedimentation basin  101 . Thus, because the concentration of sludge (pre-object A 0 ) can be improved, it is possible to improve the concentration of sludge (pre-object A 0 ) even if the sedimentation basin  101  contains intermediate water as in the conventional example. In addition, because the screw-type separation device  1  described above can be manufactured at a low cost, the wastewater treatment system  100  can also be implemented at a low cost. Moreover, even if the casing  10  is clogged with sludge (pre-object A 0 ), it is possible to easily remove the clog, by reversely rotating the screw shaft  12  with respect to the rotation direction R. 
     First Modification of First Example 
     Next, a modification of the first example described above will be explained.  FIG. 12  is a schematic diagram illustrating a sedimentation basin for explaining a modification of the first example. As illustrated in  FIG. 12 , in a first modification, the screw-type separation device  1  according to one embodiment is provided on the lower part of the sedimentation basin  101 . Then, the sludge that has sedimented on the lower part of the sedimentation basin  101  is supplied as the pre-object A 0 , into the screw-type separation device  1  through the object feeding port  31 A (see  FIG. 1 ) using a sludge recovery device (not illustrated) such as a funnel. The screw-type separation device  1  then discharges the concentrated sludge (object A) to the outside, and returns the separated liquid C that has been separated to the sedimentation basin  101 , through the inside or outside by a pipe (not illustrated) and the like. The separated liquid C may also be discharged to the outside. The other configuration is the same as that of the first example described above. 
     Second Modification of First Example 
     Moreover, as a second modification, when a gravity settling tank such as the sedimentation basin  101  is provided at a previous stage of the screw-type separation device  1 , a picket fence (not illustrated), which is formed by a rod-like member disposed upright on the upper side of a rake for scraping sludge, may also be provided in the sedimentation basin  101 . By providing the picket fence, it is possible to accelerate the sedimentation of sludge, or what is called flocculation in the sedimentation basin  101 . Thus, the screw-type separation device  1  can more effectively separate the object A and the separated liquid C, and significantly improve the solid-liquid separation properties. 
     Second Example 
     Next, a wastewater treatment system as a second example including the screw-type separation device  1  according to one embodiment described above will be explained.  FIG. 13  is a configuration diagram illustrating a part of a wastewater treatment system according to the second example. 
     As illustrated in  FIG. 13 , a wastewater treatment system  200  according to the second example includes a reaction tank  201 , a previous stage facility  202  disposed at a previous stage of the reaction tank  201 , a sedimentation basin  204  disposed at a subsequent stage of the reaction tank  201 , extraction pumps  203   a  and  203   b , and the screw-type separation device  1 . The screw-type separation device  1  is provided above (direction away from the ground surface) the reaction tank  201  and the sedimentation basin  204  in the vertical direction. 
     For example, the reaction tank  201  is configured by a plurality of biological reaction tanks. For example, the biological reaction tanks that configure the reaction tank  201  are various biological reaction tanks such as an anaerobic tank, an oxygen-free tank, and an aerobic tank. For example, the previous stage facility  202  is a facility including a sand basin, an inclined plate sedimentation basin, or the like, that treats organic wastewater such as sewage. The extraction pump  203   a  is a sludge extraction unit that extracts sludge such as activated sludge from the reaction tank  201 , and that supplies the extracted sludge to the screw-type separation device  1  as the pre-object A 0 . Similarly, the extraction pump  203   b  is a sludge extraction unit that extracts sludge from the reaction tank  201 , and that supplies the extracted sludge to the sedimentation basin  204  in a subsequent stage. The sedimentation basin  204  is a solid-liquid separation tank that sediments and separates the water to be treated and the separated liquid C each supplied from the reaction tank  201  and the screw-type separation device  1 , to the separated liquid C and sludge (object A). 
     In the wastewater treatment system  200  according to the second example, at least a part of the water to be treated discharged from the previous stage facility  202  is supplied to the reaction tank  201 . In the reaction tank  201 , biological treatment such as nitrification and denitrification is performed on the water to be treated. The activated sludge in the reaction tank  201  is extracted by the extraction pumps  203   a  and  203   b . The sludge extracted by the extraction pump  203   a  is supplied to the screw-type separation device  1  as the pre-object A 0 , and is conveyed to the inside through the object feeding port  31 A (see  FIG. 1 ). 
     In the screw-type separation device  1 , the conveyed sludge (pre-object A 0 ) is concentrated, and the separated liquid C is separated. The separated liquid C that has been separated is supplied to the sedimentation basin  204  in a subsequent stage. The sludge and water to be treated extracted from the reaction tank  201  by the extraction pump  203   b  is supplied to the sedimentation basin  204 . In the sedimentation basin  204 , similar to the first example, solid-liquid separation treatment is performed by gravitational sedimentation. In this manner, the wastewater treatment according to the second example is performed. 
     In the second example described above, by using the screw-type separation device  1 , sludge (pre-object A 0 ) is extracted from the reaction tank  201 , compressed and concentrated, and the compressed and concentrated sludge (object A) is returned to the reaction tank  201 . Moreover, the separated liquid C is supplied to the sedimentation basin  204  serving as the solid-liquid separation tank. Consequently, it is possible to solve the following problems. 
     That is, conventionally, electric power used for operating a return pump (not illustrated) for returning sludge (object A) to the reaction tank  201  from the sedimentation basin  204  has been extremely large. However, with the second example, the sludge (object A) compressed and concentrated using the screw-type separation device  1  can be returned to the reaction tank  201 . Hence, it is possible to significantly reduce electric power required for returning the sludge (object A). Moreover, by using the screw-type separation device  1 , it is possible to sufficiently perform solid-liquid separation. Consequently, because the frequency of sludge extraction from the sedimentation basin  204  can be reduced, it is possible to reduce power consumption of the wastewater treatment system  200  and save energy. 
     Moreover, conventionally, when a separation film is provided in the reaction tank  201 , there has been problems such as the initial cost and burden required for maintaining the facility are increased. However, by implementing the screw-type separation device  1  at a low cost instead of a separation film, it is possible to reduce the initial cost. Moreover, because the screw-type separation device  1  can be maintained easily, it is possible to reduce the burden of maintenance, and reduce the maintenance cost. 
     Furthermore, with the second example, mixed liquor suspended solids (MLSS) in the reaction tank  201  can be increased. Hence, it is possible to reduce the load in the sedimentation basin  204 , and reduce the power consumption of the extraction pumps  203   a  and  203   b  used for extracting sludge from the reaction tank  201 . Consequently, it is possible to save energy in the wastewater treatment system  200 . 
     Still furthermore, in each example, sludge (pre-object A 0 ) to be fed into the screw-type separation device  1  may not be sludge added with a flocculating agent. That is, a flocculating agent may not be added to the sludge in the sedimentation basin  101 , and a flocculating agent may not be added to the sludge in the reaction tank  201 . Because the screw-type separation device  1  can also separate sludge by gravity, it is also possible to suppress a decrease in separation efficiency of sludge not containing a flocculating agent. 
     The embodiment of the present invention has been described in detail. However, the present invention is not limited to the embodiment described above, and various modifications may be made based on the technical idea of the present invention. Moreover, the components described above include components that can be easily assumed by those skilled in the art, components that are substantially the same, and components within a so-called range of equivalents. Furthermore, the components described above can be appropriately combined. Still furthermore, various omissions, substitutions, or changes of the components may be made without departing from the spirit of the embodiment described above. For example, the numerical values given in the embodiment described above are merely examples, and different numerical values may be used as necessary. 
     In the embodiment described above, the screw shaft  12  is formed in a cylindrical shape. However, the shape of the screw shaft  12  is not limited thereto. For example, the screw shaft  12  may be formed in what is called an enlarged diameter shape in which the diameter of the screw shaft  12  is gradually increased from the end part  30 C to the end part  30 B side of the casing  10 . 
     Moreover, in the embodiment described above, the solid-liquid separation device that separates sludge into solid matter and moisture is used as an example. However, the embodiment described above is not limited to separate sludge into solid and liquid, and may be applicable to various methods of separating solid and liquid. 
     Moreover, in the embodiment described above, the position of the separated liquid discharging port  31 C may be changed in various ways. 
     Furthermore, in the embodiment described above, the separated liquid C is transferred through the gap H. However, for example, the separated liquid C may also be transferred by additionally providing a filtration unit formed in a mesh-like shape or that has a large number of minute holes on at least a part of the first screw blade  14  and the second screw blade  16 . 
     Still furthermore, the screw-type separation device  1  according to the embodiment described above may also be used as a pre-concentrator for a dehydrator, a simple concentrator for private use, a confluence improvement screen, and the like. 
     In the first example in one embodiment described above, sludge extracted by the extraction pump  104  is sludge sedimented in the sedimentation basin  101 . However, sludge is not limited to the sedimented sludge. For example, floating sludge tends to generate in the sedimentation basin  101  during summer and the like. The floating sludge may be extracted by the extraction pump  104  and supplied to the screw-type separation device  1 . 
     In the first example described above, the screw-type separation device  1  according to one embodiment is combined with the sedimentation basin  101 . However, the form is not limited thereto. More specifically, for example, a filtration concentration device may also be combined with the screw-type separation device  1 . In this case, the screw-type separation device  1  described above can be mounted on a bottom part of a line that extracts sludge in a filtration concentration device or a bottom part of a filtration concentration device. In this example, the filtration concentration device is intermittently operated. Hence, the concentrated sludge is temporarily accumulated in the filtration concentration device, and sludge is extracted from the lower part. Thus, supernatant liquid accumulated above the sludge is extracted with the concentrated sludge, when the sludge is temporarily accumulated. Consequently, the same problem as that in the first example described above is present. However, by using the screw-type separation device  1  according to the one embodiment, it is possible to separate the supernatant liquid (supernatant water) during the extraction of sludge, and stably increase the concentration of the concentrated sludge. 
     The embodiment, examples, and modifications of the present invention have been described. However, the embodiment is not limited to the content of the embodiments and the like. Moreover, the components described above include components that can be easily assumed by those skilled in the art, components that are substantially the same, and components within a so-called range of equivalents. Furthermore, the components described above can be appropriately combined. Still furthermore, various omissions, substitutions, and changes of the components may be made without departing from the spirit of the embodiment or the like described above. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  screw-type separation device 
               10  casing 
               12  screw shaft 
               14  first screw blade 
               16  second screw blade 
               18  first partition wall part 
               20  second partition wall part 
               30  first casing 
               30 B,  30 C end part 
               31 A object feeding port 
               31 B object discharging port 
               31 C separated liquid discharging port 
               32  second casing 
               32   a  inner peripheral surface 
               34  groove 
               34   a   1  inlet part 
             K 1  conveyance acceleration section 
             K 2  object conveyance section 
             K 3  separated liquid conveyance section 
             S 1  first space 
             S 2  second space 
             S 3 , S 4  space